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Chapter 1 INTRODUCTION

1.1 What are Biological Tissues?

1.1.1 Classification of Animal Tissues

1.1.2 Classification of Plant Tissues

1.2 What are Microwaves?

1.3 Sources of Microwaves

1.3.1 ‘O’ type Tubes

1.3.2 ‘M’ type Tubes

1.4 Microwave Measurement Techniques

1.4.1 Frequency Domain Measurements

1.4.2 Time Domain Measurements

1.5 Survey of Literature on Dielectric

Behavior of Biological Tissues

1.6 Genesis of the Present Investigation

Electrical properties of biological tissues and their interaction

with electromagnetic waves have attracted the attention of researchers

working in the field of medicine and electromagnetics. Extensive

research has been done in radio frequency (RF) fields and is still going

on, since its results have direct impact on human life. In this modern

world, where the microwaves are extensively utilized for

communication, the study of the dielectric properties of tissues at

microwave frequencies is of special interest. In order to understand

the interaction of electromagnetic field with biological tissue, it is

important to know its complex permittivity (Staebell, et.al., 1990).

Recently, microwave imaging (Larsen, et. al., 1985) has emerged as

another field of great potentiality. The knowledge of the dielectric

properties of various biological tissues at microwave frequencies is of

much significance in deriving useful information in this kind of

imaging.

When microwaves are directed towards a material, part of the

energy is reflected, part is transmitted through the surface and of this

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latter quantity, part of it is absorbed. The proportions of power which

fall into three categories that have been defined as the dielectric

properties. The fundamental electrical property through which the

interactions are described is the complex relative permittivity of the

material ( ). Mathematically expressed as ' ''* j , where ' =

dielectric constant and '' = dielectric loss factor.

The absolute permittivity of a vacuum, , is determined by

using the relation Co μo = 1, where Co = speed of light (3x108 m/

s.), μo = magnetic permeability (1.26 x 10-6H/m.) and = absolute

permittivity of a vacuum (8.854 x 10-12 F/m).

Dielectric spectra of biological cells and tissues typically show

three kinds of dielectric dispersion in different frequency regions: -

dispersion (<10 kHz), β-dispersion (10 kHz to100 MHz) and γ-

dispersion (> 1 GHz) according to Schwan’s classification. The -

dispersion is due to the orientation of water molecules. The β -

dispersion is well interpreted in terms of interfacial polarization.

Several possible mechanisms responsible for the γ -dispersion have

been proposed.

An accurate measurement of dielectric properties of biological

substances is essential for both fundamental studies and biomedical

application. The main aim the present study is to measure the

dielectric parameters of some biological tissues at microwave

frequencies, such as permittivity, conductivity, loss tangent,

attenuation factor and penetration depth of electromagnetic field. This

information finds useful for the electrical measurement of the

moisture content, dielectric heating in the agricultural industry and

food is processing industry of those materials. Also in numerical

simulation of cells, microwave imaging, microwave hyperthermia,

calculation of specific absorption rate (SAR) determination and

medical applications.

The Roberts von-Hippel shorted waveguide line method is

employed for its characterization. This method is well-accepted as it

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provides best results and requires only small amount of sample in the

rectangular waveguide shape.

1.1 What are Biological Tissues?

A living system includes different types of tissues in which

various physico-chemical processes proceeds under different biological

conditions to keep an organism in a living condition. A tissue can be

defined as a group of similar or dissimilar cells that perform a

common function and have a common origin. All these tissues are

composed of cellular elements and their derivatives. The cell is the

smallest unit of life in our bodies for example, brain cells, skin cells,

liver cells, stomach cells, etc and so on. All of these cells have

exclusive functions and features and all have some identifiable

similarities. All cells have a 'skin', called the plasma membrane,

protecting it from the outer environment. The cell membrane

regulates the movement of water, nutrients and wastes into and out of

the cell. Inside of the cell membrane are the working parts of the cell.

At the center of the cell is the cell nucleus.

Fig. 1.1 Animal cell Fig. 1.2 Plant cell

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1.1.1 Classification of Animal Tissues

Body tissues can be classified in to four types according to their

function and structure they are epithelial tissues, connective tissues,

muscle tissues and nerve tissues (Fig1.3). Again on the basis of

molecular composition, tissues can be classified as soft tissues and

hard tissues. A soft tissue contains a large quantity of water and

inorganic material in traces (example muscle tissue), while in a hard

tissue inorganic content is high and the presence of water is relatively

low (example bone tissue).

Fig. 1.3 Classification of animal tissue.

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a). Epithelial Tissue

The cells of epithelial tissue pack firmly together and form

continuous sheets that serve as linings in different parts of the body.

Epithelial tissue serves as membranes lining organs and helping to

keep the body's organs separate, in place and protected. Examples of

epithelial tissue are the outer layer of the skin, in the mouth and

stomach, and the tissue surrounding the body's organs.

b). Connective Tissue

There are several types of connective tissue in the body.

Generally, connective tissue gives support and structure to the body.

Most types of connective tissue have fibrous strands of the protein

collagen that add strength to connective tissue. Few examples of

connective tissue include the inner layers of skin, tendons, ligaments,

cartilage, bone and fat tissue. In addition to these more identifiable

forms of connective tissue, blood is also considered a form of

connective tissue.

c). Muscle Tissue

Muscle tissues are a specialized tissue that can contract.

Muscle tissue contains the specific proteins actin and myosin that

slide past one another and allow movement. Examples of muscle

tissue are contained in the muscles all over your body.

d). Nerve Tissue

Nerve tissue contains two types of cells: neurons and glial cells.

Nerve tissue has the capability to generate and conduct electrical

signals in the body. These electrical communications are managed by

nerve tissue in the brain and transmitted down the spinal cord to the

body.

The different types of animal tissues present indifferent parts of

human body are shown in fig 1.4.

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Fig. 1.4 Different types of tissues

1.1.2 Classification of Plant Tissues

The classification of plant tissues are basically meristematic and

permanent tissues and their sub classification are as given in (Fig1.5).

a) Meristematic Tissues

Meristematic tissues are cells or group of cells that have the

aptitude to divide. These tissues in a plant consist of little, densely

packed cells that can keep dividing to form new cells (Fig.1.6).

Meristems provide to permanent tissues

Types of Meristems

Sub classification of meristem are made 1)Based on origin:(Primary,

Secondary) and 2)Based on position:(Apical, Intercalary and Lateral)

meristems.

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Fig. 1.5 Classification of plant tissue.

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a ) Meristematic Tissues

Apical meristem

structure

Intercalary

Meristems structure

Lateral Meristems

structure

b) Permanent Tissues

Simple Tissue Complex Tissue Secretory Tissue

Stomata Closed/Open

Parenchyma

Chlorenchyma

Xylem

Phloem

Secretory Tissues

Sclerenchyma Collenchyma

Fig.1.6 Different types of tissues in plants

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Primary Meristems

A primary meristem arises in the tissue of the embryo and

continues to exist in the plant organ in which it rose. The primary

meristem is found at the tips of stems or roots is called the apical

meristem which is responsible for increase in length as it gives rise to

the first or primary permanent tissues.

Secondary Meristems

In flowering plants, meristems develop from cells that suspend

their ability to divide, and resume this activity later. Such meristems

are known as secondary meristems. These cells give rise to permanent

secondary tissues.

Apical Meristems

Apical meristems are located at the apices or tips (Fig1.6) at root

and shoot tips and are directly involved in their elongation They create

derivatives which form primary growth.

The protoderm which forms the outer dermal layer of tissues,

The ground meristem which forms the cortical cells and

The procambium which forms the vascular tissue.

In shoots, plants protect their meristems with young leaves and by

forming dormant reserve meristems (i.e., buds), that protect their

apical meristems with a root cap.

Intercalary Meristems

It occurs between mature tissues sections in the vicinity of the

nodes or leaf attachment (Fig.1.6).

Common in grasses (occur at bases of nodes)

Helps regenerate parts removed (by lawnmowers, herbivores

etc.)

Lateral Meristems

Lateral meristem is responsible for a) Vascular meristem-

internal growth in girth which involves secondary tissues (xylem and

phloem). In the fasicular region the cambial cells which split toward

the center form xylem tissue and towards the outside phloem tissue.

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Interfasicular indicate the cambium between the 'fasciles of xylem &

phloem and b) Cork cambium- outside girth growth beyond the

phloem area. They form the characteristic corky film as well as an

internal layer (Fig. 1.6).

b). Permanent Tissues

The cells of permanent tissues don’t have the capability to

divide. These cells are already differentiated in different tissue types

and are now specialized to perform specific functions. They are

subdivided into three groups, viz, simple tissues, complex tissues and

secretory tissues. Permanent tissues in plants are simple tissues,

complex tissues and secretory tissues.

1. Simple Tissues

If a group of cells are more or less the same, then it is known as a

Simple tissue. Simple tissues are listed as fallows

Epidermis

Parenchyma

Chlorenchyma

Collenchyma

Sclerenchyma

Epidermis

The epidermis is the outmost cellular layer which covers the whole

plant structure, i.e. it covers roots, stem, leaves, flowers & fruit. It is

composed of a single layer of alive cells, although there are exceptions.

Epidermis is typically closely packed, without intercellular spaces or

chloroplasts. The outer walls, which are exposed to the atmosphere

and generally thickened, and may be covered by a waxy, waterproof

cuticle which are made up of cutin. Separately from the normal

epidermal cells there are as well stomata in the epidermis of leaves

and stem.

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A stoma (Fig. 1.6) is a opening or a pore which is bounded by two

bean shaped cells called guard cells. The guard cells vary from normal

epidermal cells in that they have chloroplasts and the cell walls are

thickening unevenly the outer wall is lean and the inner wall (nearest

the opening) is thick. The thin-walled epidermal cells of roots give rise

to root hairs. Hair- like outgrowth may also be found in the epidermis

of leaves and stems.

Parenchyma

Parenchyma (Fig1.6) is the most common plant tissue. It is relatively

unspecialized and makes up a substantial part of the volume of a

herbaceous plant and of the leaves, flowers and the fruits of woody

plants. The thin-walled parenchyma cells have large vacuoles and

distinct intercellular spaces.

Specialized Parenchyma

Chlorenchyma- Photosynthetic cells have high density of

chloroplasts (Fig. 1.6)

Aerenchyma- Prominent intercellular spaces that improve gas

exchange capacity of the tissue, provide maximum support with a

minimum metabolic requirement

Transfer cells- Specialized for short distance transfer of solutes

between cells, have secondary cell walls, they are inner extensions of

wall that increase surface area.

Collenchyma

Collenchyma (Fig. 1.6) tissues are mainly found under the

epidermis in young stems in the large veins of leaves. The cells are

composed of living, elongated cells running parallel to the length of

organs that it is found in. Collenchyma cells have thick cellulose cell

walls which thickened at the corners. Intercellular air spaces are

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absent or very small. The cells contain living protoplasm and they

sometimes contain chloroplasts.

Sclerenchyma

Mature sclerenchyma (Fig. 1.6) cells are dead and have

secondary cell walls thickened with cellulose and usually impregnated

with lignin. In contrast to collenchyma, which is pliable, sclerenchyma

is elastic. The cell cavity or lumen is very small or it may disappear

completely. There are two types of sclerenchyma cells, namely

sclereids and fibres.

Sclereids: The cells are irregular in shape. The cell walls are

thick, hard and lignified which makes the lumen very small. Simple

pits (canals) are found in the thickened cell walls and link adjacent

cells. Sclereids are commonly found in fruit and seeds.

Fibres: The cells are needle-shaped with pointed tips, thick

walls and rather small lumen. Secondary cell walls, impregnated with,

are formed. Simple pits are also present. Fibres are abundant in the

vascular tissue of angiosperms, i.e. flowering plants.

2. Complex tissue

If, however, the tissue is composed of a number of different cells, then

it is known as a complex tissue. Complex tissues are listed as fallows

Xylem

Phloem

Xylem

Xylem (Fig1.6) is a complex tissue composed of xylem vessels,

xylem tracheids, xylem fibres and xylem parenchyma.

Xylem vessels: Xylem vessels comprise a vertical chain of

lengthened, dead cells known as vessel elements. The cells are

arranged end to end and the cross-walls dissolve completely or have

simple or complex perforation plates between successive cells. The

secondary walls of vessels are impregnated with lignin and are

thickened unevenly. The walls of the vessels may be thickened in

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different ways, e.g. annular, spiral and pitted thickening may be

observed.

Xylem tracheids: A tracheids is an elongated cell, the contents

of which are non-living. The cell walls are thickened, impregnated with

lignin and the lumen is smaller. As in the case of vessels, there is a

differentiation between annular, spiral and pitted tracheids again

caused by the type of thickening of the secondary walls. Tracheids

have no perforation plates.

Xylem fibres & Xylem parenchyma: Bear a strong

resemblance to normal fibres and parenchyma. Xylem fibres are

sometimes separated by thin cross walls and the walls of xylem

parenchyma are sometimes thicker than those of normal parenchyma.

Phloem

Phloem is a complex tissue composed of sieve tubes, companion

cells, phloem fibres and phloem parenchyma

Sieve Tubes: A sieve tube, like xylem vessels, is a series of cells

(sieve elements) joined end to end. The cross walls between successive

cells (sieve elements) become perforated forming sieve plates. The cell

walls are thin. Although the cell contents are living, the nucleus

disintegrates and disappears. The lumen is filled with a slimy sap

which is composed mainly of protein.

Companion Cells: Companion Cells are specialized parenchyma

cells which always appear with the sieve tube element. They are also

elongated, thin-walled and there is a distinct nucleus in the cytoplasm

of the companion cell. Companion cells are linked with the sieve tubes

by small canals filled with cytoplasm, which are smaller than pits.

Phloem Fibres: These cells are elongated tapering cells, found

particular in the stem. They have thickened walls.

Phloem Parenchyma: Phloem Parenchyma is living and has

thin cell walls. These cells form the packing tissue between all the

other types of cells.

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3. Secretary Tissues

Transfer cells occur in areas of high solute transport, such as

secretary tissues (Fig.1.6), which release substances that are

produced within the protoplasm and are moved outside, i.e., nectar

cells, mucilage in sundews, and resins.

1.2 What are Microwaves?

‘Microwaves’ is a descriptive term used to identify

electromagnetic waves in the frequency spectrum ranging

approximately from 1GHz to 30 GHz This corresponds to the

wavelengths from 30 cm to 1 cm. Sometimes higher frequencies (above

30 GHz and up to 600 GHz) are also called ‘microwaves’. These waves

present several interesting and unusual features not found in other

portions of the electromagnetic frequency spectrum (Fig.1.7). These

features make ‘microwave’ uniquely suitable for several useful

applications. Microwave region in the electromagnetic spectrum is

subdivided in to various bands which are given in (Table1.1) since the

lower frequency part of the radio spectrum is getting crowded, there is

a trend to use more and more of microwave region (and beyond) for

various different services.

Study and research in microwave has not only been an

interesting and challenging academic endeavour, it has led to several

useful applications in communications, in radar, in physical research,

in medicine and industrial measurements and also for heating and

drying of agricultural and food products.

In the medical field microwave devices are used for a multiplicity

of therapeutic purposes together with the selective heating of tumors

as an adjunct to chemotherapy treatment (microwave hyperthermia).

Gandhi, O.P. (1982) and Gandhi, O.M (1990), are reported the tissue

heating called hyperthermia can be useful in the therapeutic

treatment of hurt tissue and cancerous tumors.

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Fig. 1.7 Electromagnetic frequency spectrum

Table1.1 Microwave frequency band designation

Ionizing

Ionization is a process by which electrons are exposed from

atoms and molecules. This process can create molecular changes that

can lead to hurt in biological tissue, including effects on DNA, the

genetic material. Examples of ionizing radiation are X-rays and

gamma rays.

Band Designations Band Frequency Range

p 230 MHz - 1 GHz L 1 -2 GHz

S 2-4 GHz

C 4-8 GHz

X 8 -12.5 GHz

Ku 12.5 -18 GHz

K 18 -26.5 GHz

Ka 26.5 -40 GHz

Q 33 - 50 GHz

U 40- 60 GHz

V 50 -75 GHz

E 60 -90 GHz

W 75 -110 GHz

F 90 -140 GHz

D 110-170 GHz

G 140 -220 GHz

Y

170 -260 GHz

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Non-Ionizing

The photon energies of radio frequency electromagnetic waves

are not great enough energy to cause the ionization of atoms and

molecules. Examples of Non-ionizing radiation are radio frequency

energy radiation visible light, infrared radiation and other forms of

electromagnetic radiation with relatively low frequencies.

1.3 Sources of Microwaves

Generation of microwaves can be done using vacuum tubes. The

classification of microwave tubes are of two types they are

i). Microwave linear-beam tubes (also known as ‘O’ type tubes) and

ii).Microwave crossed tubes (also known as ‘M’ type tubes)

The generation of microwaves can also be done using semiconductor

devices.

1.3.1 Microwave Linear-Beam Tubes (also known as ‘O’ type

tubes)

Classification of ‘O’ type tubes is as shown in (Fig. 1.8).

Conventional vacuum tubes, such as triodes, tetrodes, pentodes are

still used as signal success of low output power at low microwave

frequencies. The most important microwave tubes at present are the

linear beam tubes. The paramount ‘O’ type tube is the two cavity

klystron (Fig.1.9) and it is followed by the reflex klystron (Fig.1.10).

Fig.1.8 Classification of ‘O’ type tubes

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The helix travelling waveguide tube (TWT), the coupled cavity

TWT, the forward wave amplifier (FWA) and backward wave amplifier

and oscillator (BWA & BWO) are also O-type tubes, but they have non-

resonant period structures for electron interactions. The Twystron is a

hybrid amplifier that uses the combination of klystron and TWT

components.

Fig.1.9 Schematic diagram of two cavity klystron amplifier

Fig.1.10 Schematic diagram of reflex klystron

1.3.2 Microwave Crossed Tubes (also known as ‘M’ type tubes)

Classification of ‘M’ type tubes is as shown in (Fig. 1.11). Cross

field tubes derive their name from the fact that the D.C. electric field &

the D.C. magnetic field are upright to each other. The Principal tube

in this type, called M- type is the magnetron (Fig1.12). The magnetron

was invented by (Hull, 1921) Magnetron provides microwave

oscillations of very high peak power. Generally, the magnetron

operates with efficiency around 60 to 65% (Saltiel and Datta, 1999).

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There are three types of magnetrons they are (a) Negative resistance,

(b) Cyclotron & (c) Cavity or travelling wave type.

Fig.1.11 Classification of M- type tubes

Fig.1.12 Π- Mode of magnetron

Solid state microwave devices

The classification of Solid state microwave devices and one

example for it is considered as Gunn diode oscillator circuit (Fig.1.13).

Gunn diode oscillator circuits comprise of a resonant cavity, an

arrangement for coupling diode to the cavity, a circuit for biasing the

diode and a mechanism to couple the RF power from the cavity to the

external circuit or a load. A variety of circuits has been suggested for

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performing these functions. Two commonly used circuits use a coaxial

and a rectangular waveguide cavity.

Fig.1.13 Classification of solid state microwave devices

Fig.1.14 Gunn oscillator circuit using co axial cavity

1.4 Microwave Measurement Techniques

The dielectric properties measurement involves the

measurements of the complex relative permittivity (εr) of the materials.

It can be measured in frequency & Time domains

1.4.1. Frequency-Domain Measurements.

The frequency dependent behavior of the material has been

studied by frequency-domain measurements with a sophisticated

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instrument such as broadband network analyzers. It covers a wide

frequency ranges. Measurement of dielectric properties involves

measurements of the complex relative permittivity (εr) of the materials.

A complex dielectric permittivity consists of a real part and an

imaginary part. The real part of the complex permittivity, also known

as dielectric constant is a measure of the amount of energy from an

external electrical field stored in the material. The imaginary part is

zero for lossless materials and is also known as loss factor. It is a

measure of the amount of energy loss from the material due to an

external electric field. The term tanδ is known as loss tangent and it

represents the ratio of the imaginary part to the real part of the

complex permittivity. The loss tangent is also called by terms such as

tangent loss, dissipation factor or loss factor.

Generally, measurement techniques can be categorized into

reflection or transmission measurements by resonant or non-resonant

systems, with open or closed structures for measuring the dielectric

property of the material (Kraszewski, 1980).

Open structure techniques include free space transmission

measurements and open-ended coaxial line measurements.

Closed structures method can be divided into waveguide and coaxial

line transmission measurements and short-circuited waveguide or

coaxial line reflection measurements (Nelson, 1999).

Resonant cavity structures can be closed resonant cavity or

open resonant structures. In the case of open resonant structures, the

measurements can be done as two-port device for transmission

measurement or as one port device for reflection measurements

(Nelson, 1999).

There are many techniques developed for measuring the

complex permittivity and each technique is limited to specific

frequencies, materials, applications etc. by its own constraint. Some of

the technique which is listed in Table 1.2.

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Table 1.2 Different measuring techniques

Open Closed

Transmission

Nonresonant Free Space Waveguide

Resonant Two-Port Cavity

Reflection

Nonresonant

Open

Ended

Coax

Short

Circuited

Waveguide

Resonant One-Port Cavity

1.4.2 Time-Domain Measurements

Time domain reflectometry (TDR) is an important technique for the

measurement of the complex permittivity of materials over a wide

band. (Fig. 1.15) shows the basic concept of TDR. A step-like pulse

produced by a pulse generator propagates through the coaxial line

and is reflected from the sample section placed at the end of the line.

The reflected pulse also propagates through the same line. The

difference between the reflected and the incident pulses recorded in

the time domain contains the information on the dielectric properties

of the sample.

Fig 1.15 Block diagram of the TDR system

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Time-domain methods have some advantages over frequency-

domain methods. Since the dielectric response is recorded in the time

domain, one measurement covers a wide frequency range, sometimes

over two decades. Moreover, this method can measure the complex

permittivity not only in the microwave frequency range but also in the

radio frequency range. The instrumentation set up is quite simple and

is less expensive than that used in frequency- domain methods.

Because of these advantages, time-domain methods have long been

used by several laboratories to investigate the dielectric properties of

materials.

The TDR technique was first applied to the field of dielectric

studies by (Fellner-Feldegg, 1969). Independently, (Bagozzi, et.al.

1969) determined the dielectric relaxation time in Debye binary liquids

using a time-domain method. (Nicolson and Ross, 1970) presented a

new time-domain method based on reflected and transmitted pulses to

determine the complex permittivity and permeability of a material over

a broad range of microwave frequencies. The earlier TDR systems were

composed of sampling oscilloscopes with bandwidths up to 12.4 GHz

or 18 GHz, pulse generators with 35-45 ps rise times, signal averages

with A/D converters, and data acquisition systems.

The software improvements in TDR have been remarkable. The

basic theory of TDR has been dramatically changed during the last ten

years. Earlier TDR theory had some limitation when measuring the

complex permittivity in the frequency region higher than 1 GHz.

However, (Cole and his coworkers, 1989) improved the measurement

of complex permittivity up to 10 GHz by the introduction of the total

reflection method using linear transmission theory.

Recent developments in high speed sampling techniques and

digital processing brought a new generation in the sampling

oscilloscope (HP54 120T). This oscilloscope made it possible to

measure the time-domain signal with a time resolution of 0.25 ps with

sufficient stability.

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1.5 Survey of Literature on Dielectric Behaviour of Biological

Tissues

Hermann (1871) reported that the DC resistance of muscle

varies by a factor of 4 to 9 with orientation in freshly excised tissue,

but this anisotropy slowly disappears after death.

Galler (1913) reported the first true AC measurements on a

tissue (frog skin) and found that resistance at 1 KHz is appreciably

smaller that at DC.

Gildemeister (1919) observed the current peak that occurs when

skin is exposed to a voltage step and interpreted this as arising from a

resistance that increase with time.

Debye (1929) the earlier concept of permittivity measurements

was based on dc electrical resistance to determine grain moisture

content.

Sapengo (1930) measured the impedance of muscle at different

frequencies up to 1MHz. He noted a strong dispersion centered near

20KHz.At low frequencies the transversal impedance was found to be

twice as large as the longitudinal impedance, but at high frequencies

this difference disappeared.

Dunlap and Makower (1945) have measured dielectric

properties for carrots in the frequency rang 18 kHz to 5 MHz and

reported that higher frequencies were most suitable for moisture

determinations in food products

Works et. al. (1945) have developed a new method for measuring

the dielectric properties of insulating materials in the 100- to 1000-

megacycle range. They also obtained a greater sensitivity and

accuracy when compared to other methods operative in this frequency

range.

Brown et al. (1947) unevenness in thawing was also reported.

Values obtained for peaches, pears, beef steak, and beef fat showed

that loss factors decreased as frequency increased or as temperature

decreased.

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Shaw and Galvin (1949) dielectric properties of potato, carrot,

apple, and peach tissue were measured at frequencies form 1 to 40

MHz. Their measurements showed a general region of dispersion

between 100 kHz and 20 MHz and provided some useful data on the

temperature dependence of conductivity in fruits and vegetables.

Knipper (1953) reported that the first moisture meter was

designed and developed in the former U.S.S.R. for wheat and barley

moisture measurement.

Schwan and Kay (1956) employed alternating current (A.C) to

measure the specific resistance of dog tissue. The results obtained by

the two methods differ by a factor of three to four, the later giving the

highest values.

Schwan (1957) has obtained a great deal of information on

membrane structure by studying electrical properties. Measurement

carried out on suspensions of the bacterium, Escherichia Coli showed

the existence of low conductance surface membrane of thickness

varying from 40 to 100A. The dielectric constant of suspension falls

from several tens of thousands to the free water value as the

frequency increases from few Hz to MHz. This was accompanied by

two dispersion regions, the -region occurring below 10 KHz and -

region between 1MHz to10 MHz.

Sharpe (1960) has described a graphical method for measuring

the real and imaginary parts of the dielectric constant of materials at

microwave frequencies. TEM arrangement leads to an entirely

graphical solution in which the complex dielectric constant can be

read from a Smith chart overlay.

Bell and Rupprechet (1961) have described measuring dielectric

losses at microwave frequencies in materials with a large dielectric

constant. By observing a dielectric resonance in a sufficiently large

sample, the loss tangent of the material can be obtained. Results on

SrTiO, single crystals at 20 kMc are presented.

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Burger and Van Dongen (1961) they reported that the four

electrode method. It has several advantages over the Schwan and Kay

method Further, they investigated anisotropy of the muscle tissues of

rabbit and human upper legs.

Schwan, et. al. (1962) have reported the data on dielectric

properties of suspension of spherical colloidal particles over the

frequency range from 20Hz to several hundred KHz.

Sedunov and Frank (1963) a review article was published by in

which they discussed the existing work on electrical properties such

as dielectric constant and conductivity of living matter.

Kasvand (1963) has described the comments made by J. A.

Knudson on iterative procedure for the method of measuring the

dielectric constant and the corresponding losses of a material at

microwave frequencies by means of the perturbation method.

Muser (1964) studied the temperature dependence of dielectric

constants. An outline of the principle theories of dielectric behaviour

of gases and solids was discussed. The frequency dependence of

dielectric losses and the effect of crystal imperfections on dielectric

constant were summarized.

Schwan (1965) presented the data on electrical properties of

bound water.

Loor and Meijboom (1966) the dielectric properties of raw

potato, potato starch, and milk were measured at microwave

frequencies from 1.2 to 18 GHz.

Pauly and Schwan (1966) have studied dielectric properties and

ion mobility In erythrocytes and measured the impedance of

erythrocytes of man, cattle, sheep, dog, cat, rabbit, and chicken in the

range from 0.5 to 250 Mc. The electrical conductivity of the red cell

interior was calculated between 70 and 100 Mc. The dielectric

constant of the red cell interior is 50 at 250 Mc, varies but small with

species, and can readily be accounted for by the cells' hemoglobin

content.

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Bussey (1967) has discussed and referenced the methods for

radio and microwave measurements of dielectric and magnetic

properties of the materials.

Geddes and Baker (1967) presented a comprehensive summary

of the low-frequency conductivity of various muscle tissues.

Andrew et. al. (1967) determined the dielectric constant and

dielectric loss of human cortical bone in the frequency range from

1KHz to 100 KHz and the amount of water absorbed have been

measured explicitly as a function of humidity.

Pace et al (1968) measured dielectric properties of raw potato in

the frequency range 300 to 3000 MHz and reported dielectric

properties dropped appreciably with increasing frequency

Pace et al. (1968) have studied the potential for microwave

finish drying of potato chips in the frequency range 1.0 to 3.0 GHz

and reported that the energy absorption increased at higher moisture

contents.

Van Dyke et.al. (1969) the dielectric properties of reconstituted

ground beef were measured at 0.915 GHz. to study the influence of

moisture, ash, and fat contents. Moisture contents below 20% showed

little variation in dielectric loss. Dielectric loss factor increased sharply

with an increase in moisture from 20 to 45% and then more slowly at

higher moisture. Dielectric loss factors were also found to increase

with ash content and to decrease with fat content

Schwan and Lawrence (1969) carried out the work on

alternating current field induced forces and their biological

implications.

Auth et. al. (1969) reported light diffraction from spatially

periodic temperature variations in a transparent solid. Local

microwave heating at the antinodes of a standing wave diffracts light;

thus a determination of dielectric constant by measurement of the

microwave phase velocity is possible.

27

Watkins and Brown (1969) a program has been written for

calculating complex permittivity of lossy dielectric materials using

Roberts-von Hippel method.

Nygren and Martinson (1970) have described a computer-

program description numerical method for calculation of complex

dielectric permittivity it is possible to obtain high-precision results

without using Von Hippel tables.

Rodriguez-Vidal and Martin (1970) have described a computer-

program contribution to numerical methods for calculation of complex

dielectric permittivities by the von Hippel-Roberts’s method, using two

samples of the same material and different size.

Thompson and Zachariah (1971) the dielectric properties of

apples at frequencies of 300 to 900 MHz were found to vary with

maturity, dropping appreciably in the process of aging.

Cole (1972) suggested that the envelope surrounding the

interior of the cell fibers contains a polarization element. The envelope

was an early concept of a membrane.

Gupta (1974) has described a new method of measuring

complex dielectric constants at microwave frequencies by introducing

a resonant circuit comprised of the experimental sample within a

waveguide. By this method ε’ and tanδ was measured for the material

viniplast, tranperent plastic, sital , ceramic and rutile. Compared

these data with other methods reported by Kabin (1958) and Petrov et.

al.(1958) are well agreed.

Nelson and Stetson (1974) have presented data on the

frequency dependence of the dielectric constant and dielectric loss

factor of insects and grain, and use of such information is discussed

in relation to RF treatment of infested products to control insects.

Nelson et. al. (1974) have described briefly principles underlying

the short-circuited-waveguide measurement method and a general

computer program for precisely calculating dielectric properties of

materials from such measurements.

28

Nelson et. al. (1974) described a computer program description

to compute the dielectric properties from short-circuited waveguide

measurements on high- or low-loss materials.

Ohlsson et al. (1974) measurements of various meats and fish,

including raw beef, pork, beef and pork fat, codfish, and herring, were

made at radio frequencies from 10 to100 MHz. They found large

differences in the dielectric properties of frozen and unfrozen samples

and significant differences between samples with fibers oriented

perpendicular or parallel to the field, i.e., anisotropic behavior.

Lin (1974) studied dielectric properties of fresh mammalian

tissues over a range of frequencies from 0.1 to 12 GHz.

James C. Lin (1975) measured the complex dielectric constant

of fresh mammalian brain tissues in the frequency range of 2.25 to

3.95 GHz.

Takashima and Minikate (1975) studied the dielectric behavior

of biological macromolecules.

Foster et. al. (1976) have reported the data on electrical

resistivity of cytoplasm.

Schwan and Foster (1977) have reviewed the dielectric

permittivity and conductivity data for muscle, skin and liver tissues

over the frequency range of 0.1-10 GHz. The conductivity of muscle

increases quadratically with frequency above I GHz, suggesting a

Debye relaxation for tissue water centered at 20 GHz at room

temperature is same as for bulk water.

Athri and Mookerjee (1979) studied Actinomycin D and DNA

binding by the measurement of dielectric constant in the frequency

region of 600 Hz – 100 KHz at varying polymers to drug ratios and

temperatures.

Kwork et al (1979) have resented data on the dielectric behavior

of a few agricultural materials obtained by time-domain reflectometry

(TDR) measurements.

29

Settle et. al. (1980) have Reported the whole body impedance,

while assessing the material value of the whole body and its

components.

Joines, et al (1980) have suggested that the differences in

electrical properties of neoplastic and normal tissues should be

considered in choosing an optimum frequency for radiofrequency

hyperthermia treatment.

Pierre and Schwan (1980) obtained data on dielectric

permittivity and conductivity of human erythrocytes which exhibit

consecutive dispersions in the frequency range from 0.1 to 250 MHz.

Kenneth R. Foster, et al (1980) have shown that the microwave

dielectric relaxation process in the muscle fibers measured between

10 MHz and 17GHz is due to dipolar relaxation of the tissues water,

which shows a characteristic relaxation frequency equal to that of

pure water, ranging from 9 GHz (1degree c) to 25 GHz.(37degree c).

Stuchly and Stuchly (1980) the effect of moisture content on the

dielectric properties of granular solids was reported at 9.4 GHz over a

wide range of temperature and moisture contents. Temperature

dependence was not seen for dried solids but increased dramatically

at higher moisture contents. Many other researchers have reported

similar behavior as a function of moisture.

Burdette et. al. (1980) have described theoretically and

experimentally A novel probe technique for the determination of

dielectric ptoperties of semisolid materials and living tissues in situ.

This method, based on an antenna modeling theorem offers unique

advantages over conventional dielectric measurement technique.

Measurements of standard liquid dielectric and in vivo tissue data are

presented.

Josephlink et. al. (1980) reported the data on variation of the

low frequency dielectric constants of some anisotropic crystals.

Brady et. al. (1981) have measured the permittivities of bovine

muscle, artery, kidney, and liver are measured at 37°C in vitro at 2.0,

3.0, and 4.0 GHz, using a coaxial-line reflection technique and an

30

automatic network analyzer. The data obtained were compared with

those published for similar animal tissues are well agreed.

Euler and klilian (1981) measured the dielectric constant of

some pressed powders.

Pfutzner (1981) reported the possibility of making low frequency

impedance measurement, using raster electrodes in the case of

muscle and blood samples.

Schwan (1981) carried out investigations on electrical properties

of cells. He pointed out some unsolved problems in the field of

biological dielectrics with reference to cell suspensions and biological

soft tissue.

Stoy, et al (1982) have reported a summary data of dielectric

properties of mammalian tissues from 0.1 to 100 MHz.

Grimness (1982) has investigated the change in the electrical

characteristics of the skin owing to the psychogalvanic reflex. The

effect of conductive film formation on the inside of the sweat-duct

walls is discussed and emphasized.

Ping Liu et.al. (1982) have studied electromagnetic

hyperthermia, it is necessary to simulate human biological materials

in microwave frequencies. The precise measurement of the dielectric

constant and conductivity of the simulated materials for frequencies 8

and 10 G.Hz. was made.

Bridgeset.al. (1982) have measured the dielectric constants and

loss tangents of KRS-5 and KRS-6 thallium halide mixed crystals at

95 GHz.using both the shorted waveguide (SWG) reflection method

and the Fabry-Perot (F-P) transmission method on samples filling

standard WR-10 waveguide.

Plonsey and Barr (1982) analyzes the four-electrode method in

terms of the six conductivities used to describe, separately,

intracellular and interstitial space. The four-electrode technique is a

useful method for measuring the resistivity of an isotropic mono

domain. The technique has also been used with anisotropic mono

domains.

31

Gopal Krishna et.al.(1983a,1983b) have studied the dielectric

behavior of of yeast cells of different physiological conditions through

dielectrophoresis.

Pitzer (1983) has calculated the dielectric constant of H2O at

very high temperatures and densities. The dielectric constant is

needed in connection with studies of electrolytes such as NaCl/H20 at

very high temperature.

Epstein and Foster (1983) reported the dielectric permittivity

and conductivity of freshly excised dog skeletal muscle at frequencies

between 20Hz and 1 MHz when tissue samples oriented either parallel

or perpendicular to the applied electric field.

Schwan (1983) accounted the role of biophysics in the

interaction of electromagnetic energy with cells and membranes.

Grimnes (1983) has discussed briefly about the determination of

skin surface electrode impedance. A measuring technique was also

described with which it is possible to measure two skin surface

electrodes simultaneously, but individually at the same frequency.

Cheung and Neyzari (1984) have reviewed external heating

techniques for delivery of localized hyperthermia in patients. The

merits and demerits of electromagnetic versus ultrasound heating

techniques are compared as a conclusion to this review.

Pethig (1984) has reviewed the dielectric properties of

mammalian tissues for the frequency range 1Hz to 10 GHz. The

dielectric properties of amino acids, proteins, biological electrolytes,

cell membranes, tissue-bound water, of normal and cancerous

tissues, clinical aspects such as the hyperthermic treatment of cancer

and the stimulation of bone healing also discussed.

Chaudary, et al (1984) have made dielectric measurements on

normal and malignant human breast tissues between 3 MHz and

3GHz at 25oc. They observed the values of relative dielectric constant

of malignant tissues were considerably higher than those of normal

tissues, particularly at frequencies below 100 MHz.

32

Schwan (1984) presented a survey of research on the linear

electrical and acoustic properties of biological materials including

cells, tissues and biopolymers. He discussed the dielectric properties

of tissues and cells in the frequency range of DC to 20GHz; the

mechanisms responsible for major dielectric relaxation effects

observed such as counter ion relation, Maxwell-Wagner charging of

membrane interfaces.

Tran et al. (1984) have tabulated the dielectric properties of

selected vegetables and fruits at a frequency range 0.1 to 10 GHz.

Schwan (1985a, 1985b) summarized the electrical properties of

biological cells and tissues at extremely low frequencies and discussed

the mechanisms responsible for such properties and pointed out the

most possible sites for EM field interactions.

Schwan (1985) first reported the alpha dispersion in a tissue

(non oriented frog skeletal muscle), which appeared as a 30-fold

increase in permittivity with a centre relaxation frequency of about

100Hz. In measurements on single fibers of the frog skeletal muscle

using a vaseline gap technique,

Bur (1985) made studies on dielectric properties of polymers at

microwave frequencies.

Jonscher (1985) presented the data on universal dielectric

dispersion in low mobility solids.

Karolkar et. al. (1985) have measured of dielectric permittivity

and conductivity and relaxation time of various high loss tissues from

freshly sacrificed animals. The measurement is made at 9.4 GHz by

the ‘infinite sample’ technique. A more complex system consisting of

skin-fat-muscle combination is also studied.

Mohammed Nurul Afsar et. al.(1986) have presented a review on

dielectric properties of a materials measuring technique in the

frequency range 7 MHz to 1500 GHz approximately covers 15 years of

development

Smith et al. (1986) have presented the bulk electrical properties

of an implanted VX-2 carcinoma in rabbit liver tissue were measured

33

in the range 1 kHz to 13 MHz, together with those of normal rabbit

liver tissue. In the lower end of the frequency range, the conductivity

of the tumor tissue was 6 to 7.5 times higher and its permittivity was

2 to 5 times lower than that of the normal tissue. The increased

conductivity of the tumor tissue is believed to arise from the existence

of widespread necrosis in the tumor nodules.

Bonincontro, et al (1987) have studied the hydration properties

of DNA – lysine gels by dielectric measurements at 10GHz as a

function of temperature.

Nelson (1987) was outlined a procedure for determining the

dielectric properties of solid materials of known densities from the

dielectric properties of pulverized samples measured at a few different

bulk densities. Properties for the solid are obtained by extrapolation of

functions of the dielectric constant and loss factor that are linearly

related to the bulk density of the air–particle mixture.

Basharat Ali and Adeel Ahmad(1988) reported a comparative

study on dielectric behaviour of different tissues of the animal Ox by

determining their dielectric constant and dielectric loss from the

measurement of capacitance and the dissipation factor at 1KHz

frequency. Investigations were made on dispersion of dielectric

constant and conductivity of skeletal muscle,(for fresh and dry

samples, with the fiber orientations parallel and perpendicular to the

applied alternating electric field) and brain, liver, kidney of the animal

Ox, is studied in the frequency range from 100Hz to 1MHz. Further,

the dielectric properties of skeletal muscle tissue with respect to its

water content and time of the tissue in the applied alternating electric

field for fresh and dry samples, at 1KHz frequency with the fiber

orientations parallel and perpendicular to the applied electric field

have been studied.

Schwan (1988) discussed the unusual dielectric properties of

biological cells and summarized the possible mechanisms responsible

for the dielectric relaxation processes. Further he described the

fundamentals of electro-rotation techniques, which is an additional

34

valuable technique to determine dielectric properties of biological cells,

and discussed the comparative advantages and disadvantages of

dielectric spectroscopy and electro rotation.

Pethig (1988) reviewed various studies of the electrical and

dielectric properties of proteins of low hydration content in order to

indicate that transport processes provide a major contribution to the

effects that have been observed.

Hawkes and Pethig (1988) made dielectric measurements on

lysozyme compressed powers as a function of hydration and of the PH

at which the samples were lyophilized, and found that the dielectric

dispersion (the α – dispersion) which appears in the frequency range

from 10-4 Hz to 100 KHz for lysozyme of hydration ranging from 2 to

20 wt % water, is related to the state of ionization of acidic and basic

groups in the protein structure.

Watters and Brodwin (1988) have assembled an instrument to

measure complex permittivity at microwave frequencies in an efficient,

inexpensive manner. It bridges the gap between traditional, tedious

methods of characterization and expensive vector network analyzer

techniques. A microcomputer is used to control the operation of a

scalar network analyzer. Measurements of the magnitude of the

reflection and transmission coefficients are automatically made as a

function of frequency and temperature over a range of 2-18 GHz.

Adeel Ahmad et.al.(1989) have studied the dielectric constants

of fast and slow muscle tissues as a function of orientation, water

content and time of applied electric field.

Rama Rao (1989) has made a detailed investigation on dielectric

behavior of derivatives of animal integument such as horn, hoof and

hair.

Schwan (1989) has described the principles and relevant

physics for pearl chain formation, cell rotation and certain field

“coupling” considerations which are relevant for understanding of

dielectric behavior of biological cells through biological cell

dielectrophoresis.

35

Gopal Krishna et.al.(1988a,1988b,1988c, 1989a,1989b) have

studied the dielectric behavior of erythrocytes belonging yo human

and animals of different locomotions.

Foster and Schwan (1989) published a detailed critical review

on dielectric properties of tissues and biological materials. In this

review, historical survey on electrical properties of biological material

is made.

Ghannouchi and Bosisio (1989) presented a nondestructive

broad-band permittivity measurement method using an automatic six-

port reflectometer. The impedance sensor is an open-ended coaxial

line terminated by a semi-infinite medium. This method is useful to

measure relatively high-loss dielectric liquids and provides a precision

comparable to other methods.

Bur et.al. (1989) have described an optical system for measuring

the response of suspended particles to imposed non-uniform electric

fields in the frequency range1Hz to 4 MHz. They reported that such

dielectrophoretic measurements could provide details of the dielectric

and surface charge properties of animate and inanimate particles.

Annapurna and Adeel Ahmad (1989) reported the data on

dielectric constants of marine molluscan shells.

Reiner Zorn, et al (1990) have studied dielectric properties of

synthetic glycolipids in mixiture with water at 9.4GHz. The dielectric

data show that in the H11 phase the binding of water is stronger than

in the Lß phase.

Davey et al (1990) has developed substitution and spread sheet

methods for analyzing dielectric spectra of biological systems.

Kraszewski et al (1990) have determined the moisture content in

individual corn kernels with a cavity resonating at 3.2 GHz.

Mishra et al (1990) have evaluated the drawback of lumped

parameter model shows errors above 1 GHz. They described a new

method using a probe consisting of coaxial transmission line with an

open-circuit end placed against the sample. Probes of 2.99 or 3.6 mm

used. This model is more accurate than the lumped-parameter model,

36

and is better suited for calibration of the automated network analyzer

(ANA).

Roggen (1990) was discussed the development of dielectric

measurement technology before and after the founding of the

dielectrics and electrical insulation society (DEIS), with the main

emphasis on measurement of permittivity and related matters in the

lower range of frequencies.

Fidanboylu et. al. (1990) have presented a new time-domain

approach for determining the complex permittivity of materials using

stripline geometry. The technique is straightforward and avoids

solving integral equations.

Ranjit singh et.al. (1990) have presented an expression for the

dielectric constant in terms of resonant frequency of arbitrary shaped

microstrip antenna. Dielectric constants measured by the present

method are in good agreement with the manufacturer specified values

taking into account the tolerance specified by them. The uncertainty

analysis for the measurement of dielectric constant has also been

done.

Nozaki and Bose (1990) have presented some TDR applications

for complex permittivity measurements for a liquid crystal from 100

kHz to 1 GHz, an ionic micro emulsion at frequencies between 30 MHz

and 20 GHz, and a strong polar liquid in the frequency range from 1

GHz to 25 GHz.

Kraszewski et.al. (1990) have measured the change in resonant

frequency, and the Q factor of the cavity, when measured with and

without single corn kernels of various shapes and dimensions using

rectangular waveguide resonator operating in the H105 mode at 3.2

GHz .

Nelson(1991) presented briefly historical interest in dielectric

properties of agricultural products and definitions of dielectric terms,

reviewed briefly techniques for measurement of dielectric properties

and presented graphical data on the dielectric properties of products

are that illustrate the dependence of these properties on moisture

37

content, frequency, temperature, and density, presented models for

estimating the dielectric properties of grain and soybeans as functions

of moisture content, frequency, temperature, and bulk density.

Finally, applications of the dielectric properties of agricultural

products are described that include radio-frequency (RF) and

microwave heating for seed treatment, improvement of nutritional and

keeping qualities of some products, and controlling insects in grain.

Watanable et. al. (1991) have made an attempt to correlate the

passive electrical properties of the lens tissue with its structure and

measured ac admittances for isolated frog lenses, lens nuclei, and

homogenate of cortical fiber cells, over the frequency range 102 - 5

X108 Hz. The whole lenses molded into discoid shape show a

characteristic "two-step" dielectric dispersion with a huge permittivity

increment of the order of 105 at 1 kHz. Data were analyzed using an

owed ellipsoidal-shells model which has been developed by taking into

account fiber orientation inside the lens tissue.

Yan-Zhen Wei and Sridhar (1991) have described an

experimental technique and associated analysis for the measurement

of the dielectric constants of liquids at microwave frequencies using

an open-ended coax probe. The technique is applicable to liquid and

liquid like (e.g., biological) samples, having dielectric constants

comparable to water, at frequencies up to 20 GHz and possibly as

high as 40 GHz.

Kraszewski A.W. (1991) reviewed the Problems concerning the

development of microwave equipment and determination of moisture

content of water content in materials at microwave radiation has

several advantages over other electrical methods applying lower

frequencies. Trends of further development of the instrumentation and

research concepts are considered.

Ganchev, et al (1992) described an open-ended rectangular

waveguide technique for dielectric measurement of lossy dielectric at

microwave frequencies.

38

Yan-zhen and Sridhar (1992) have developed a broad band Coax

technique for the measurement of dielectric properties of biological

substances up to 20GHz.

Kudra et al. (1992) investigated the effects of dissolved salts on

dielectric loss in milk and also investigated in chemical simulation

studies, which showed that predictions of milk dielectric loss factor

based on conductivities implied by ash contents needed to be

corrected for binding and non-binding interactions of milk salts.

Xu et al. (1992) have studied a new kind of coaxial probe for

measurement of microwave permittivity-open-ended elliptical aperture

from theoretical and experimental view points. Calculated results are

discussed and compared with experimental values. Both theory and

experiment show that open-ended elliptical coaxial probes can be

successfully used in wideband dielectric constant measurements with

the advantage of increased sensitivity, especially at low frequencies.

Grosse and Schwan (1992) have found membrane potentials

induced by external alternating fields are usually derived assuming

that the membrane is insulating, that the cell has not surface

conductance and the potentials are everywhere solutions of the

Laplace equation. This customary approach is reexamined taking into

account membrane conductance, surface admittance, and space

charge effects.

Nelson (1992) was discussed the dependence of the dielectric

properties of materials on other variables as it relates to agricultural

products. Reviewed briefly measurement techniques for determining

dielectric properties of such materials and presented graphical data to

illustrate the dependence of dielectric properties of some products on

frequency, temperature, moisture content, and density. Also discussed

several agricultural applications in which dielectric properties

information is useful.

Nelson et.al. (1992) have determined he moisture contents of

single corn and peanut kernels, single in-shell pecan nuts and pecan

kernel halves by measurement of the impedance of a small parallel

39

plate capacitor with the nut or kernel between and in contact with the

plates at two frequencies between 1 and 5 MHz

Kent et al. (1993) studied the effect of solid content variation

during milk products processing using a newly developed on-line

microwave based sensor.

Iglesiaset.al.(1993) have studied the proximity of the solutions of

the transcendental equation tanh Z / Z = c on the complex plane

arising in the finding of the complex dielectric permittivity with the

short circuited line method.

Nelson (1994) reviewed the methods of measuring the dielectric

properties of granular and powdered or pulverized materials at

microwave frequencies and the factors affecting the dielectric

properties of materials, such as frequency, moisture content,

temperature, and bulk density.

Bakhtiar et.al.(1994) have presented numerical and

experimental results of a microwave noncontact, nondestructive

detection and evaluation of disbands and thickness variations in

stratified composite media.

Bakhtiar et al (1994) have studied radiation from an open-ended

coaxial transmission line into an N-layer dielectric medium in

application to nondestructive evaluation of materials. The admittance

expressions for exact cases of two layer dielectric composite with

generally lossy dielectric properties, and a two layer composite backed

by a conducting sheet are presented and inspected openly.

Nelson (1994) reviewed the methods of measuring the dielectric

properties of granular and powdered or pulverized materials at

microwave frequencies and the factors affecting the dielectric

properties of materials, such as frequency, moisture content,

temperature, and bulk density.

Kraszewski and Nelson (1994) explained microwave resonant

cavities can be used as sensors for rapidly determining the mass of a

perturbing object without need for contact between the object and the

measuring system. Authors have discussed the basic principles of the

40

shape-independent measurements and presented experimental results

for some plastics.

Kraszewski and Nelson (1994) have presented principles relating

to the use of a microwave resonant cavity for determining

simultaneously the mass and moisture content of individual soybean

seeds. Measurement of the resonant frequency shift & change in the

transmission characteristics of the cavity when the soybean seed is

inserted provides essential information for calculating the mass of

water in the seed and the dry matter mass, from which the moist

mass of the seed and its moisture content can be calculated.

Ryynanen (1995) several potential applications including

interaction mechanisms for heating have been reported.

Mudgett (1995) reported the dielectric constant and loss of

meats and vegetables at temperatures above and below the freezing

point. They found large differences in the properties of frozen and

unfrozen samples.

Thawed portions of processed samples also showed “runaway”

heating effects, resulting from selective energy absorption by unfrozen

fluids.

Ghanchev et al (1995) have studied the application of open-

ended coaxial sensors for dielectric measurement of finite thickness

composite sheets. They have presented expressions for calculation of

the complex aperture admittance for two geometries. These

expressions are used to estimate the dielectric constant of infinite

half-space as well as finite thickness slabs.

Bringhurst, and lskander (1995) have devised a method for

measuring the dielectric properties of thin samples using an open-

ended coaxial probe. This method consists of modeling the probe n

sample backed by a perfect conductor using FDTD numerical

methods. Experimental data from both 2.5 mm thick ZrO2 with 8 mol

% Y2O3 and 5 mm Teflon have verified the accuracy of this method.

Keem and Holmes (1995) explained simple approximate

expressions for effective permittivity may be used only for covering

41

materials of low to moderate permittivity. For materials of higher

permittivity more rigorous (and hence more computationally involved)

solutions such as the one presented here are required. Experimentally

determined values of effective permittivity for various standard organic

liquids were also presented for comparison.

Fratta and Santamarina (1996) have presented the development

of a waveguide device and the corresponding processing methodology

to study wave propagation in particulate materials. They reviewed

fundamentals of signal processing and followed by a discussion of

design considerations including boundary effects and geometric

dispersion.

Feldman Yu (1996) has discussed the advantages and

disadvantages of time domain dielectric permittivity measurements.

Nelson et. al.(1996) have measured the dielectric permittivities

of bulk samples of adult rice weevils over the frequency range from 0.2

to 20 GHz at temperatures from 100 to 65 0C with an open-ended

coaxial-line probe, network analyzer, and a sample temperature

control assembly designed for the measurements

Keam and Holdem (1997) have presented a conical-tip probe for

the measurement of permittivity which retains many of the advantages

of the normal plane probe including simplicity of sample preparation

and moderate sample volume requirement, but which is mechanically

better suited than monopole probes for the measurement of a wide

range of biological materials since it does not support free moisture

regions resulting from cell rupture.

Martinsen et al (1997) have studied blister-skin and warts,

possible sources of “pure” stratum corneum without sweat ducts. The

reason of the study was to assess whether the DC electrical

conductance measured on human skin is totally subjugated by the

sweat ducts, or is also appreciably contributed to by the stratum

corneum itself. By means of galvanic skin response (GSR)

measurements, these tissues were found to be unreliable as sources of

"pure" stratum corneum.

42

Bringhurstet.al. (1997) have designed a metallized-ceramic

probe for high-temperature broadband dielectric properties

measurements. The probe has been used to make complex dielectric

properties measurements over the frequency band from 500 MHz to 3

GHz, and up to temperatures as high as 100 0 C. They have presented

results illustrating the use of this probe for broadband, high-

temperature, dielectric properties measurements of thin samples and

substrates. They have made measurements on thin (0.6 mm) alumina

and sapphire samples for temperatures up to 800°C. This

measurement method has important applications in the on-line

characterization of semiconductor wafers.

Deshpande et al (1997) have presented a simple waveguide

measurement technique to determine the complex dielectric constant

of a dielectric material. The dielectric sample is pushed into a short

circuited rectangular waveguide.

Martinsen et. al. (1997) have investigated some electrical

properties of human hair in order to determine whether a significant

DC electrical conductance is present in keratinized tissues. The DC

conductance was found to be considerable and highly dependent on

the moisture level in the hair fibers. At high moisture levels, the

conductance was found to be nearly frequency independent below 1

kHz.

Blackham and Pollard (1997), have presented an enhanced

model for an open-ended coaxial probe used for making permittivity

measurements. A permittivity measurement system consisting of the

network analyzer & coaxial probe a is described including details of

the error correction and curve fitting techniques

Nelson et.al (1997) have measured the dielectric permittivities of

bulk samples of adult rice weevils over the frequency range from 0.2

GHz to 20 GHz at temperatures from 100 C to 650 C with an open-

ended coaxial-line probe, network analyzer, and a sample temperature

control assembly designed for the measurements. Estimated dielectric

constants and loss factors of the insects from averages of seven

43

different measurement sequences are presented graphically for

temperatures from 150 C to 650 C.

Venkatesh and Raghavan (1998) described an overview of

different dielectric properties measuring techniques.

Keem and Holdem (1998) have presented an expression for the

input admittance of a coaxially driven cylindrical cavity. They have

also presented a comparison between the theory and measurements

which shows that the model is capable of yielding a high level of

accuracy.

Lai (1998) summarized the results of experiments carried out in

their laboratory on the effects of Radio frequency radiation (RFR)

exposure on the nervous system of the rat.

Gabriel et.al.(1998) have reported the summary of the basic

theory underlying microwave dielectric heating and collates the

dielectric data for a wide range of organic solvents which are

commonly used in microwave syntheses. Also reported the relaxation

times of solvents decrease as the temperature of the solvent is

increased at different microwave frequencies.

Martinsen et.al. (1998) have investigated the electrical

properties of microporous membranes in 1mm KCl solution in the

frequency range 1 MHz to 1 KHz, using a four-electrode measuring

cell. An α- dispersion centered around 0.1 Hz was detected and this

was assumed to be caused by counterion relaxation effects in the

pores of the membrane.

Martinsen and Grimnes (1998) have demonstrated a low

frequency susceptance measurements carried out in the right manner

provide information about stratum corneum hydration with the same

precision as multi frequency measurements .

Hagness et. al. (1998) reported 2-D FDTD modeling of a novel

pulsed confocal microwave system for detecting breast cancer. The

system exploits breast-tissue physical properties unique to the

microwave spectrum, namely, the translucent nature of normal breast

44

tissues (without lesions) and the high dielectric contrast between

malignant tumors and the surrounding normal breast tissues.

Trabelsi (1998) has presented a new approach in which both

bulk density and moisture content are determined directly from

measured microwave dielectric properties. They have proposed a

simple relationship between bulk density and the dielectric properties

is identified, and a new density-independent function for moisture

content prediction, exclusively dependent on the dielectric properties

of the material under test (ε’ and ε’’ ).

Nelson and Kraszewski (1998) have developed a resonant cavity

measurement technique for the rapid determination of the proportions

of coal and rock dust in powdered mixtures. The ratio of the resonant

frequency shift & the change in the transmission factor when mixed

coal and limestone samples are inserted into the void provides a

means for estimating the percentage of coal in the mixture

comparatively independent of the bulk density of the mixture.

Slima et. al. (1998) have determined the moisture of hard red

winter wheat with uncertainty less than 0.5% moisture, at the 95%

confidence level, in the moisture range from 10% to 19% at grain

temperatures between -10 C and 420 C, independent of the grain bulk

density & explained the calibration process.

Trabelsi et al (1998) have proposed a new method for

simultaneous and independent on-line determination of bulk density

and moisture content in particulate materials by measurements of the

relative complex permittivity. Presented results obtained from

measurements on wheat over broad ranges of microwave frequencies,

temperatures, densities, and moisture contents.

Lawrenceet.al. (1998) have presented a system for measuring

the dielectric properties of cereal grains from 1 to 350 MHz with a

coaxial sample holder.

Swatek and Ciric (1998) have reported the inner structure of a

heterogeneous two-dimensional object interacting with an external

electromagnetic field is completely accounted for by a pair of surface

45

operators that yield the field components tangent to the outer surface

exclusively in terms of a single unknown current density distributed

on that same surface.

Awayda et al (1999) have found that the apical plasma

membrane exhibited several populations of audio frequency dielectric

relaxation processes centered at 30, 103, 2364, and 6604 Hz, with

mean capacitive increments of 0.72, 1.00, 0.88, and 0.29 µF/cm2,

respectively, that gave rise to dc capacitances of 1.95 6 0.06 µF/cm2 in

49 tissues.

Hagness et al (1999) have presented the methodology and initial

results of three-dimensional (3-D) finite-difference time-domain

(FDTD) simulations. They also presented the reflection, radiation, and

scattering properties of the electromagnetic pulse radiated by the

antenna element within a homogeneous, layered half-space model of

the human breast and the polarization and frequency response

characteristics of generic tumor shapes.

Bois et al (1999) have discussed the two-port completely-filled

waveguide (transmission line) technique is a robust measurement

approach which is well suited for solid dielectric materials. They

described a modification to this measurement technique utilizing two

dielectric plugs which are used to house the granular or the liquid

dielectric material. Using this technique they measured the dielectric

properties of cement powder, corn oil, antifreeze solution and tap

water, constituting low- and high-loss dielectric materials (granular

and liquid).

Bois et al (1999) have calculated the dielectric properties of an

infinite-half space of a material from the measured reflection

properties referenced to the waveguide aperture. This calculation

relies on a theoretical and numerical derivation of the reflection

coefficient likewise referenced to the waveguide aperture.

Miura et al. (1999) have analyzed three relaxation processes in a

frequency range from 1 MHz to 10 GHz, the low, intermediate, and

high processes in the dielectric relaxation measurement of lung tissue.

46

Nelson et al. (1999 & 2001) have presented a brief review on the

electrical properties of cereal grains and their use in sensing moisture

content of grain and seed.

Bartley et al. (1999) have trained an Artificial Neural Network

(ANN) to determine the dielectric properties of materials from reflection

coefficient measurements of an open-ended coaxial probe.

Zhao et al. (2000) used radio frequency (RF) heating to

pasteurize surimi seafood’s as well as alfalfa and radish seeds to

investigate the effectiveness of capacitive (RF) dielectric heating. They

reported that the packaged food depended on the material’s dielectric

properties relationship with the frequency and temperature.

Trabelsi et al (2000) have proposed two methods to solve the

phase-shift ambiguity problem encountered in free-space dielectric

properties measurements. They are based on the selection of the

appropriate material thickness and needs the use of measurements at

two frequencies.

Munrot et al (2001) have aimed to produce microwave phantoms

for testing a microwave technique for treating esophageal

malignancies. They described the apparatus setup developed specially

for this purpose. Their experimental set-up provides the required

dielectric information over a frequency range of 0.8 to 2.5 GHz.

Tsakanyan et al (2001) have measured the dielectric properties

of fresh cuts animal organs and tissues such as tissue samples

(muscle, fat) and animal organs (liver, kidney, spleen, brain, lung,

testes, and udder) at 2.45 GHz by the Wei-Sridhar technique.

Stevens et al (2001) have shown the results of the modeling of

an open ended coaxial probe on a thin layer. To perform

measurements on a multilayered structure, it is important to know in

how far the lower layers are detected by the probe. A numerical

method was used based on a full-wave solution for an open ended

coaxial probe.

Trabelsi et al (2001) have presented a dielectric method for

determining bulk density of granular materials from measurement of

47

their dielectric properties at microwave frequencies. A complex-plane

representation of the dielectric properties, normalized to bulk density,

is used to generate calibration equations at 7 GHz for cereal grain and

seed over wide ranges of moisture content and temperature.

Nelson (2001) was measured the permittivities of pulverized

samples of coal and limestone over a range of bulk densities at 11.7

GHz and 200 C. The measured values were used, along with particle

densities, determined by pycnometer measurements, and the Landau

& Lifshitz, Looyenga (LLL) dielectric mixture equation to determine the

solid material permittivities.

Fukunaga et al (2002) have been evaluated mobile phone safety

by the specific absorption rate (SAR). Authors have measured the time

dependence of the dielectric properties of glycol-based dielectric

liquids, and evaluated their effects on SAR. The experimental results

suggest that relative permittivities decrease with time and that

conductivities remain nearly constant. Specific absorption ratio,

however, was not affected significantly by the change in dielectric

properties.

Fukunaga et al (2002) have measured the time dependence of

permittivities and conductivities of tissue-equivalent dielectric liquids

made of deionised water and polyhydric alcohol, and discussed its

influence on specific absorption rate values. The results suggest that

permittivities decreased with time due to evaporation of water. The

specific absorption rate, however, was not affected significantly by the

change of permittivity.

Fukunaga et. al. (2002) have measured the time dependence of

the relative permittivities and conductivities of glycol-based dielectric

liquids, and discussed their influence on SAR. The experimental

results suggest that relative permittivities decreased with time and

conductivities were almost constant. SAR, however, was not affected

significantly by the change in relative permittivities.

Du et al (2002) have shown that the dielectric spectrum does

not vary in shape with temperature and moisture content, but that

48

there is a shift in amplitude and frequency. A dielectric model for

biological tissue was adopted for the cellulose-structured pressboard.

The master curve was established by fitting the data to the model.

They measured curves that show similar trends as reported in the

literature. In addition, new quantitative analysis was presented for oil-

free pressboard.

Liewei Sha et al (2002) have presented a review of the dielectric

properties of normal and malignant breast tissues for radio through

microwave frequencies, as well as a brief outline of the experiment

methods and the mechanisms that explain the difference in the

dielectric properties of normal and malignant breast tissue. This

information provides a basis for the growth of diagnostic techniques

for breast cancer.

Trabelsi et al. (2002) discussed a universal character of

permittivity based calibration function for moisture determination in

granular materials such as cereal grains and seed is tested through

measurement at microwave frequencies on the material of different

stricter and composition using free space measurement arrangements.

Bartley et al (2002) have performed a dimensional analysis on a

generalized open-ended coaxial-line probe. Applying the Buckingham

π theorem revealed that the admittance of the probe/dielectric

interface, scaled by the frequency, is a function of a single

dimensionless variable.

Nelson and Bartley (2002) have presented data for a

homogenized macaroni and cheese sample, ground whole wheat flour,

and apple juice, show the diverse frequency- and temperature-

dependent behavior of food materials and illustrate the necessity for

permittivity measurements when reliable dielectric properties data are

required. They used an open-ended coaxial-line probe was used with

sample temperature control equipment designed for use with the

probe to measure permittivities of some liquid, semisolid, and

pulverized food materials as a function of frequency and temperature.

49

Nelson et al (2002) have described the importance of cereal

grain moisture content in determining time of harvest and in

preserving grain quality. Described a new moisture calibration

function based on complex-plane plots of the density-normalized

dielectric constant and loss factor.

Fukunaga et al (2003) have measured the change of dielectric

properties with time and with temperature of tissue-equivalent liquids

recommended in the standard documents. The conductivity decreased

with increasing temperature in any glycol-type specimen. The

permittivity was nearly constant. With the evaporation of water, the

permittivity decreased, even though the conductivities remained

constant.

Fukunaga, et al (2003) have measured the change of dielectric

properties with time and with temperature of tissue-equivalent liquids

recommended in the standard documents, and evaluated their effects

on SAR. Experimental outcome proves that dielectric properties are

exaggerated by environmental conditions, and that it is inevitably

necessary to adjust the dielectric properties regularly, through the

addition of ingredients.

Hagl et.al. (2003) have used open-ended coaxial probes to

determine the dielectric properties of freshly excised normal and

diseased breast tissue specimens.

Trabelsi and Nelson (2003) were used a free-space transmission

technique in which the main sources of errors were minimized to

determine the dielectric properties of three major commodities wheat,

shelled corn and soybeans. They have tabulated the permittivity

values of wheat, shelled corn and soybeans in the frequency range 5

to 15 GHz.

Gregory et al (2004) have developed new tissue-equivalent

liquids for specific absorption rate (SAR) measurements in compliance

with international standards. They are more physically stable, less

toxic and have lower temperature coefficients than existing published

50

liquids. They have measured their dielectric properties traceably and

they have been evaluated in a National SAR-Testing Laboratory (CRL)

Nelson (2004) was presented dielectric spectral data from

different articles related to dielectric properties of agricultural

products are of interest for sensing moisture content through its

correlation with the dielectric properties of cereal grain and oilseed

crops, because of their influence on the dielectric heating of products

at microwave or lower radiofrequencies, and because of potential use

of for sensing quality factors other than moisture content and

discussed the potential for further dielectric spectroscopy applications

in agriculture.

Trabelsi and Nelson (2004) have investigated and compared

Near-field microwave measurements of the dielectric properties of

wheat and soybeans with a pair of single-patch microstrip antennas to

those taken in the far field with a pair of focused-beam horn lens

antennas.

Bartley Jr et al (2004) have developed a systematic approach for

modeling permittivity measurement probes. The technique was used

to model a commercially available probe. This model was functionally

equivalent to the provided model developed with traditional

electromagnetic techniques. The approach utilizes the results of a

dimensional analysis and a genetic algorithm to find an appropriate

model for a probe.

Nelson (2004) was discussed the permittivities, or dielectric

properties, of granular or powdered solid materials are important,

some dependable relationship between the bulk density and the

permittivity of the air-particle mixture.

Gawali et al (2005) have measured the values of dielectric

constant, loss, relaxation time and conductivity of pulverized samples

of mungbean for different packing densities at 9.84 GHz at different

temperatures. They observed that there is a fair agreement in the

values of dielectric parameters for pulverized form and bulk form

correlation formula by Landu-Lifshitz-Loyanga and Bottcher.

51

Gawali et al (2005) have studied the Dielectric behaviour of

chickpea at 10.7GHz of X-Band microwave frequency and at different

temperatures (20-50°c). The effect of packing density and

temperature on dielectric parameters was assessed. The results

showed cohesion in the particles of chickpea powder under

investigation.

Popovic, et al. (2005) have been designed a hermetic stainless-

steel open-ended coaxial probes for precision dielectric spectroscopy of

biological tissue, such as breast tissue, over the 0.5-20-GHz frequency

range.

Semenov et al (2005) have studied imaging performance of the

Newton and the multiplicative regularized contrast source inversion

(MR-CSI) methods in 2 dimension geometry and gradient and MR-CSI

methods in 3 dimension geometry using high-contrast, medium-size

phantoms, and biological objects.

Fukunaga et al (2005) have evolved mobile telecommunication

equipment by the specific absorption rate (SAR) measurement. They

have been developed a new odor-free, stable tissue-equivalent liquids

for SAR tests. They also provided permittivity matrix charts of tissue

equivalent liquids for mobile phones and walkie-talkies. The new

tissue-equivalent liquids do not affect the phantom shell made of fiber

reinforced resin, and do not smell. The twin type tissue-equivalent

liquids must be useful for SAR tests.

Kandala et al. (2005) have presented a portable electrical

instrument that measures complex impedance of parallel plate

capacitor with a sample of peanut kernels between its plates.

Nelson (2005) was discussed the relationships between the

permittivities of powdered or granular solid materials and their bulk

densities. Linear interaction between functions of the permittivity and

bulk density is recognized that are useful in determining permittivity

of solids from measurements of the permittivity of crushed samples.

Author presented the results of testing linear extrapolation techniques

52

and dielectric mixture equations on pulverized coal, limestone,

plastics, and granular wheat and flour.

Nelson (2005) were measured the dielectric properties for tissue

samples cut from nine fresh fruits and vegetables such as (apple,

avocado, banana, cantaloupe, carrot, cucumber, grape, orange, and

potato) over the frequency range from 10 MHz to 1.8 GHz and over the

temperature range from 5 to 650 C.

Buff et al (2006) have developed a dielectric composite with

permittivity ranging from 8 to 75 with selectable conductive and

dielectric losses. The composite consists of gelatin, high fructose corn

syrup (HFCS), NaCl, and water, and can be used to model soils,

loams, and sands in the frequency range 200-MHz to 20-GHz.

Developed a single-term Cole–Cole dispersion equation with frequency

independent parameters being functions of component

concentrations.

Helloran et al. (2006) have described two analytical techniques

for the modeling of Ultra Wideband signals in biomedical tissue. They

are the planar technique and the Finite Difference Time Domain

technique. Both techniques predict the response of each layer to the

UWB input signal, with the FDTD technique predicts more subtle

phenomena such as multiple reflections, albeit at a high

computational cost.

Wagmuller et al. (2006) have presented a galvanical coupling as

a promising approach for wireless intra-body communication between

sensors. The human body is characterized as a transmission medium

for electrical current by means of measurements and numerical

simulations.

Lonappan et.al. (2006) presented a quality evaluation of human

semen at microwave frequencies using the measurements made at

different intervals of time by cavity perturbation technique in the S-

band of microwave spectrum. Semen samples were also examined in

the microscopic as well as macroscopic level in clinical laboratory. It is

observed that conductivity of semen depends upon the motility of

53

sperm and it increases as time elapses, which finds applications in

forensic medicine.

Ocera et al. (2006) have presented a novel technique for the

measurement of the complex permittivity of materials that overcomes

many limitations of the conventional measurement methods. The

calculated permittivities have been compared with those obtained with

a resonant and transmission method and with data from literature,

resulting in a very good agreement for both εr and tanδ.

Hanafey (2006), was studied the dielectric properties of the total

serum proteins of the exposed mice were studied as an hint of the

effect of the electric field on the molecular structure of the serum

proteins. The molecular arrangement of the total serum proteins were

studied through measuring their dielectric relaxation and the electric

conductivity in the frequency range 0.1 – 5 MHz at 4 ± 0.5 ºC. They

were also measured absorption spectra of the extracted proteins in the

wavelength range 200 – 600 nm. They showed in their results that the

electric field lowered the permittivity value of the serum proteins and

increased its conductivity.

Gregory and Clarke (2006) discussed the requirements for

dielectric measurements on polar liquids lie largely in two areas. a)

There is scientific interest in revealing the structure of and

interactions between the molecules this can be studied through

dielectric spectroscopy. b) Polar liquids are widely used as dielectric

reference and tissue equivalent materials for biomedical studies and

for mobile telecommunications, health and safety related

measurements.

Bowler(2006) was reviewed the theories for calculating complex

permittivity of composites with layered filler particles, and

experimental observations of dielectric relaxation in composites

formed by dispersing tungsten-coated glass bubbles in paraffin wax

are shown.

Winters et al. (2006) have proposed an algorithm for estimating

patient-specific, frequency dependent average dielectric properties

54

from scattered Ultrawideband (UWB) microwave signals. They have

tested the performance of the algorithm on data simulated using

anatomically realistic 2-D numerical breast phantoms.

Lonappan et al. (2006) have reported a comprehensive study of

the dielectric properties of human breast milk at microwave

frequencies. Measurements were made in S band frequencies using

cavity perturbation technique.

Trabelsi et al. (2006) have built and tested a low-cost microwave

moisture sensor for granular materials operating at a single frequency

of 5.8 GHz. The sensor principle is based on measurement of the two

components of the relative complex permittivity. From these

measurements they have calculated a density and material

independent calibration function.

Nelson (2006) was presented a brief historical perspective on

dielectric properties of agricultural products, including their use for

quick measurement of moisture content in grain and in considering

potential dielectric heating applications. Common principles are

discussed as they relate to dielectric properties of materials and

energy absorption from RF and microwave electric fields. They

described the measurement principles and techniques for determining

the dielectric properties of agricultural materials and the principles

are discussed for the use of microwave dielectric properties for sensing

moisture content in grain, and relationships between dielectric

properties of granular and powdered materials and their bulk

densities.

Nelson et. al. (2006) have measured permittivities of tissue

samples from 38 melons at 25 °C over the frequency range from 10

MHz to 1.8 GHz along with refractometer determinations of soluble

solids content and moisture content and tissue density.

Trabelsi and Nelson (2006) have determined the dielectric

properties of wheat, corn, and soybeans by measuring the scattering

transmission coefficient S21 in free space at frequencies between 2 and

13 GHz. Authors have investigated the variations of the dielectric

55

properties with frequency and physical properties such as bulk

density, moisture content, and temperature. Both dielectric constant

and the loss factor decreased with frequency & increased linearly with

bulk density, moisture content, and temperature

Shunsuke Kobayashi et al. (2006), have reported the

experimental results of the electro-optical (EO) effects and the

dielectric spectroscopy including the dielectric relaxation times and

the dielectric strengths of nematic liquid crystal, doped with the metal

nanoparticles of Pd alone and Ag–Pd composite and discusses how the

observed dielectric relaxation frequency or dielectric relaxation time

depend on the concentration of the impurity added nanoparticles and

also their electrical and dielectric properties. The phenomena of the

FM/AM LCDs may be attributed to the dielectric dispersion of a

heterogeneous dielectric medium known as the Maxwell–Wagner

effect.

Ann P o’ Rourke, et al (2007) have characterized the dielectric

properties of in-vivo and ex-vivo normal, malignant and cirrhotic

human liver tissues from 0.5 to 20 GHz using a precision open ended

co-axial probe. The results of this study indicate that statistically

significant differences exist in the dielectric properties of ex-vivo

normal and malignant liver tissue, as well as in-vivo and ex-vivo

normal liver tissues at 915 MHz and 2.45GHz.

Zasreow et al (2007) have investigated the absorption of short

microwave pulses in anatomically realistic numerical breast phantoms

in an effort to formally evaluate the safety of UWB microwave breast

cancer detection technology operating in the 1–11 GHz range.

Franchitto et al. (2007) have presented the experimental

methodology used to characterize RAM based on conducting polymer

called polyaniline at X-band (8 to 12 GHz) frequencies. The correlation

between the considerable loss tangent of the material and its

reflectivity (return loss) suggests its application for aeronautical

purposes.

56

Martinsen et al. (2007) have measured simultaneously the

electrical bioimpedance of different skin layers provide a promising

method for the detection of a fake finger in biometric fingerprint

systems. Therefore a live finger detection mechanism will be a critical

part of any fingerprint system used in safety applications.

Nicolas and Burais (2007) have analyzed some of the difficulties

of bio-electromagnitics while solving discrete problems. These

difficulties come from both the electrical characterization method and

the computation method. In order to obtain the reliable results in bio-

electromagnetics, the accuracy of the measurement and

computational methods are must.

Lazebnik et.al.(2007) have reported the results of our large-scale

multi-institutional study characterizing the ultrawideband microwave

dielectric properties of normal breast tissue samples in the frequency

range of 0.5–20 GHz. For the development of phantoms with accurate

dielectric properties the Cole-Cole models were reported here.

Chung (2007) A practical problem in the reflection method for

dielectric constant measurement is the difficulty to ensure the sample

is placed exactly at the waveguide flange. It is verified with

measurement on Teflon of 0.5-mm thickness and the measured

dielectric constant of Teflon shows excellent agreement of both ε’ and

ε’’ with published data.

Barauskas et. al. (2007) have developed the finite element

nonlinear computational model for the simulation of the

radiofrequency ablation processes and taking into account coupled

electrical and thermal phenomena. Authors have performed tests on

physical characteristics of the thermal effect in ex vivo liver tissue and

results compared with the reported values.

Faktorová (2007) has measured the dielectric properties on

biological materials like pig fat, cow butter, olive oil and sunflower.

Von-Hhippel short circuited method At X band frequencies was

described

57

Sihvola (2007) discussed some interesting observations about

the peculiarities of the dipole response of spherical scatters of negative

permittivity.

Plug et.al. (2007) have developed an experimental tool with

which reproducible data for both the capillary pressure and the

complex dielectric constant are measured. Hysteresis was found for

both the dielectric constant and the capillary pressure. The

imbibitions dielectric values are higher than the drainage values. Low

frequency data is necessary for a enhanced analysis of the dielectric

measurements.

Trabelsi and Nelson (2007) have the studied of the dielectric

response of nonequilibrated moisture in wheat reveals a first phase of

sharp decrease in both the dielectric constant and loss factor, followed

by a plateau reflecting the final stage of the binding of water. Authors

were expected that the water molecules are loosely bound to the

constituents of wheat kernels in the beginning and then reach a

tighter level of binding when they reach the equilibrium stage. The

same observation is made through the analysis of the Cole-Cole

diagram.

Nelson et al. (2007) The permittivity data for watermelons over a

range of melon maturities at frequencies from 10 MHz to 1.8 GHz at

24 °C showed that dielectric constants and loss factors of internal

tissues decreased regularly with increasing frequency, showing the

dominance of ionic conduction at lower frequencies and dipolar losses

at the higher frequencies.

Trabelsi et. al. (2007) have measured dielectric properties of

albumen and yolk of eggs were measured at 240 C over the frequency

range from 10 MHz to 1800 MHz to monitor quality changes during a

5-week storage period at 150 C. Authors have presented variations of

the measured dielectric properties of albumen and yolk with

frequency, moisture content, and quality indicators.

Kuropatkina et al. (2007) reported the heterogeneous dielectrics

with conductive components have enhanced permittivity and

58

conductivity. The increase in the permittivity and conductivity as a

function of the ratios of the dielectric phase parameters is predicted

within the Skanavi model.

Irastorza et al (2008) have analyzed the estimation of the

dielectric properties of layered lossy structure using open ended

coaxial probes technique. They generalized the theoretical and

empirical exponential approximations of the relaxation process for

two, three and four-layers structures. Measurements are made in the

frequency range 100MHz. to 1GHz.

Guo et al. (2008) have determined the dielectric properties of

chickpea flour samples using an open-ended coaxial-line probe with

an impedance analyzer over the frequency range from 10 to 1800 MHz

moisture contents from 7.9% to 20.9% wb, and temperatures from 20

to 900 C. Their result shoes that the dielectric constant and loss factor

of chickpea samples decreased monotonically with increases in

frequency at all temperatures and moisture levels. Ionic conduction

was the leading factor influencing the dielectric loss at lower

frequencies in comparatively high moisture samples. Dielectric

constant and loss factor improved with increases in moisture content

and temperature. The rate of increase was larger at higher

temperature and moisture levels than at lesser temperature and

moisture levels.

Nelson et al. (2008) have made measurement of permittivities of

honeydew melons and watermelons, grown to provide a range of

maturities, were measured with an open-ended coaxial-line probe and

impedance analyzer at frequencies from 10 MHz to 1.8 GHz.

Measurements on fresh apples were also made over a ten-week

storage period.

Trabelsi et al (2008) have built a low-cost microwave sensor for

rapid and nondestructive sensing of bulk density and moisture

content in granular and particulate materials. The sensor operates at

5.8 GHz. Three permittivity-based algorithms were used to determine

59

simultaneously bulk density and moisture content from dielectric

properties measurement.

Scheller et al. (2008) have presented a new physical model for

describing heterogeneous dielectric mixtures in the terahertz

frequency range, which overcomes drawbacks of established models.

The theory is established by highly accurate data on polymeric

compounds.

Kavitha Arunachalam et. al. (2008), presented a novel

deformable reflector microwave tomography technique for noninvasive

characterization of the breast tissue. Computational possibility of the

proposed technique to image heterogeneous dielectric tissue property

is evaluated using simplified 2-D breast models.

Peyman (2009) aimed to explain structural and compositional

factors that affect the dielectric properties of biological tissues, in

particular the process of ageing.

Guhr et al (2009) presented a new tool to assess viscoelastic and

dielectric properties of biological samples are presented.

Faktorova (2009) have measured and calculated the dielectric

properties of biological tissues in the frequency band 4,5 GHz-6 GHz.

Sanjeev kumar et al.(2009) have measured the dielectric

properties of some fresh root and tuber vegetables at microwave

frequencies.

Sanjeev kumar et al. (2010) have developed a MATLAB

programs to compute the dielectric parameters such as dielectric

constant, loss, loss tangent, conductivity, penetration depth and

attenuation factor.

1.6 Genesis of the Present Investigation

A living body is made up of a complex structure of biological

tissues with very dissimilar electric properties. These properties are, to

a great extent, responsible for the interaction of electromagnetic fluids

with molecules and biological supermolecular structures.

Measurements of tissue dielectric properties are important because it

provides information necessary for calculating power absorption by

60

biological tissues. The proper knowledge of the dielectric properties of

the biological systems is essential either to determine safe levels for

personnel exposure to electromagnetic radiation or to effectively

employ electromagnetic radiation in beneficial biomedical application.

The measurement of the dielectric properties and emissivity properties

of biological tissues would play a significant role in any well founded

effort containing tissues interaction with electromagnetic energy.

Accurate measurements of dielectric properties of biological

substances are essential for both fundamental studies and biomedical

applications, such as microwave hyperthermia. Electrical properties

of biological materials and their interaction with electromagnetic

waves have attracted the attention of researchers working in the field

of medicine and electromagnetics.

It is well recognized that microwave energy can be effectively

used in the treatment of many diseases. Studies indicate that

microwaves have tremendous potential especially in the diagnostic

and therapeutical medical applications. From the knowledge of

dielectric constant, tissue properties can be characterized in the

microwave frequency range.

As it is known, dielectric constant is the parameter which

characterizes the ability of the tissue to store electrical charges

compared to free space, and the conductivity is simply a measure of

the ability to transport charges with the field. These two parameters

solely characterize the electrical characteristics of matter.

These exists mainly three distinct relaxation mechanisms in the

frequency regions of α, ß and γ for the biological tissues. Survey of

literature reveals that extensive information is available on dielectric

behavior of soft tissues in α and ß dispersion regions. But much

attention is not paid to study the dielectric behavior of soft biological

tissues in the region of microwave frequencies. In view of this,

microwave propagation properties of some vegetables at microwave

frequencies have been studied.