Microelectronic pill
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Transcript of Microelectronic pill
Microelectronic Pill Introduction
1. INTRODUCTION
We are familiar with a wide range of sensors in the field of electronics. They
are used widely in the various experiments and research activities too. This microelectronic
pill is such a sensor with a number of channels and is called as a multichannel sensor. As the
name implies this sensor is a pill. That is it is meant to go inside the body and to study the
internal conditions.
Earlier it was when transistor was invented, that radiometry capsules were first put into
use. These capsules made use of simple circuits for studying the gastrointestinal tract. Some of
the reasons that prevented their use was their size and their limitation of not to transmit through
more than a single channel. They had poor reliability and sensitivity. The lifespan of the sensors
were also too short. This paved the way for the implementation of single channel telemetry
capsules and they were later developed to overcome the demerits of the large size of laboratory
type sensors.
The semiconductor technologies also helped in the formation and thus finally the
presently seen microelectronic pill was developed. These pills are now used for taking remote
biomedical measurements in researches and diagnosis. The sensors make use of the micro
technology to serve the purpose. The main intention of using the pill is to perform an internal
study and recognize or detect the abnormalities and the diseases in the gastrointestinal tract. In
this GI (Gastro Intestinal) tract we cannot use the old endoscope as the access is restricted. A
number of parameters can be possibly measured by these pills and they include conductivity, pH
temperature and the amount of dissolved oxygen in the gastrointestinal tract.
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Microelectronic Pill Introduction
Figure 1: Microelectronic Pill
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Microelectronic Pill Block Diagram
2. BLOCK DIAGRAM
The design of the microelectronic pill is in the form of a capsule. The encasing it
has is biocompatible. Inside this are multi- channel (four channels) sensors and a control
chip. It also comprises of a radio transmitter and two silver oxide cells. The four sensors
are mounted on the two silicon chips. In addition to it, there are a control chip, one access
channel and a radio transmitter. The four sensors commonly used are a temperature
sensor, pH ISFET sensor, a dual electrode conductivity sensor and a three electrode
electrochemical oxygen sensor. Among these the temperature sensor, the pH ISFET
sensor and the dual electrode conductivity sensor are fabricated on the first chip. The
three electrode electrochemical cell oxygen sensor will be on chip 2. The second chip
also consists of a NiCr resistance thermometer which is optional.
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Microelectronic Pill Block Diagram
Figure 2: Block diagram
Microelectronic pill consists of 4 sensors (2) which are mounted on two silicon chips (Chip 1
& 2), a control chip (5), a radio transmitter (STD- type1-7, type2-crystal type-10), silver
oxide batteries (8), 1-access channel, 3-capsule, 4- rubber ring, 6-PCB chip carrier.
The microelectronic pill consists of a machined biocompatible (non-cytotoxic),
chemically resistant polyether-terketone (PEEK) capsule and a PCB chip carrier acting
as a common platform for attachment of sensors, ASIC, transmitter & batteries. The
fabricated sensors were each attached by wire bonding to a custom made chip carrier
made from a 10pin, 0.5pitch polymide ribbon connector. The connector in turn was
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Microelectronic Pill Block Diagram
connected to an industrial STD, flat cable plug (FCP) socket attached to the PCB
carrier chip of the microelectronic pill, to facilitate the rapid replacement off the
sensors when required. The PCB chip carrier was made from 2 STD. 1.6 mm-thick
fiber glass boards attached back to back epoxy resin which maximized the distance
between the 2 sensor chips. The sensor chips are connected to both sides of the PCB by
separate FCP sockets, with sensor chip 1 facing the top face, with the sensor chip 2
facing down. Thus, the oxygen sensor on chip 2 had to be connected to the top face by
three 200nm copper leads soldered onto the board. The transmitter was integrated in
the PCB which also incorporated the power supply rails, the connection points to the
sensors, as well as the transmitter & the ASIC & the supporting slots for the capsule in
which the carrier is located.
The ASIC was attached with double-sided Cu conducting tape prior to wire
bonding to the power supply rails, the sensor inputs & the transmitter (a process which
entailed the connection of 64 bonding pads). The unit was powered by 2 STD. 1.55V
SR44 Silver oxide (Ag2O) cells with a capacity of 175mAh. The batteries were
connected & attached to a custom made 3-pin, 1.27mm pitch plug by electrical epoxy.
The connection on the matching socket on the PCB carrier provided a three point
power supply to the circuit comprising a negative supply rail (1.55V).
The capsule was machined as two separate screw-fitting compartments. The
PCB chip carrier was attached to the front section of the capsule (fig 2). The sensor chips
were exposed to the ambient environment through access ports & were sealed by 2 stainless
steel clamps incorporating a 0.8 µm thick sheet of Viton fluoroelastometer seal. A 3mm
diameter access channel in center of each of the steel clamps (incl. the seal), exposed in
sensing regions of the chips. The rear section of the capsule is attached to the front section
by a 13mm screw connection incorporating a Viton rubber O-ring. The seals rendered the
capsule water proof, as well as making it easy to maintain (e.g. during sensor & battery
replacement). The complete prototype was 16*55mm & weighs 13.5g including the
batteries.
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Microelectronic Pill Basic Components
3. BASIC COMPONENTS
1. Sensors
Figure 3: Sensors
There are basically 4 sensors mounted on two chips- Chip 1 & chip 2. On chip 1
(shown in fig 2 a), c), e)), temperature sensor silicon diode (4), pH ISFET sensor (1) and
dual electrode conductivity sensor (3) are fabricated. Chip 2 comprises of three electrode
electrochemical cell oxygen sensor (2) and optional Ni Cr resistance thermometer (5).
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Microelectronic Pill Basic Components
i. Sensor chip 1
An array consisting of both temperature sensor & pH sensor platforms were cut from
the wafer and attached onto 100-µm- thick glass cover slip cured on a hot plate. The plate
acts as a temporary carrier to assist handling of the device during level 1 of lithography when
the electric connection tracks, electrode bonding pads are defined. Bonding pads provide
electrical contact to the external electronic circuit.
Lithography was the first fundamentally new printing technology since the invention
of relief printing in the fifteenth century. It is a mechanical Plano graphic process in which
the printing and non-printing areas of the plate are all at the same level, as opposed to
intaglio and relief processes in which the design is cut into the printing block. Lithography is
based on the chemical repellence of oil and water. Designs are drawn or painted with greasy
ink or crayons on specially prepared limestone. The stone is moistened with water, which the
stone accepts in areas not covered by the crayon. Oily ink, applied with a roller, adheres only
to the drawing and is repelled by the wet parts of the stone. Pressing paper against the inked
drawing then makes the print.
Lithography was invented by Alois Senefelder in Germany in 1798 and, within
twenty years, appeared in England and the United States. Almost immediately, attempts were
made to print pictures in color. Multiple stones were used; one for each color, and the print
went through the press as many times as there were stones. The problem for the printers was
keeping the image in register, making sure that the print would be lined up exactly each time
it went through the press so that each color would be in the correct position and the
overlaying colors would merge correctly.
Early colored lithographs used one or two colors to tint the entire plate and create a
water color-like tone to the image. This atmospheric effect was primarily used for landscape
or topographical illustrations. For more detailed coloration, artists continued to rely on hand
coloring over the lithograph. Once tinted lithographs were well established, it was only a
small step to extend the range of color by the use of multiple tint blocks printed in
succession. Generally, these early chromolithographs were simple prints with flat areas of
color, printed side-by-side.
Increasingly ornate designs and dozens of bright, often gaudy, colors characterized
chromolithography in the second half of the nineteenth century. Overprinting and the use of
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Microelectronic Pill Basic Components
silver and gold inks widened the range of color and design. Still a relatively expensive
process, chromolithography was used for large-scale folio works and illuminated gift books
that often attempted to reproduce the handwork of manuscripts of the Middle Ages. The
steam-driven printing press and the wider availability of inexpensive paper stock lowered
production costs and made chromolithography more affordable. By the 1880s, the process
was widely used for magazines and advertising. At the same time, however, photographic
processes were being developed that would replace lithography by the beginning of
the twentieth century.
Chip 1 is divided into two- LHS unit having the temperature sensor silicon diode,
while RHS unit comprises the pH ISFET sensor.
DT-670-SD Silicon Diode Features
Figure 4: DT-670-SD
It measures the body core temperature.
Also compensates with the temperature induced signal changes in other sensors.
It also identifies local changes associated with tissue inflammation & ulcers.
ISFET
Figure 5: ISFET
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Microelectronic Pill Basic Components
Ion Selective Field Effect Transistor ISFET; this type of electrode contains a
transistor coated with a chemically sensitive material to measure pH in solution and
moist surfaces. As the potential at the chemically active surface changes with the pH,
the current induced through the transistor varies. A temperature diode simultaneously
monitors the temperature at the sensing surface. The pH meter to a temperature
compensated pH reading correlates the change in current and temperature.
This device has an affinity for hydrogen ions, which is the basis for the
determination of the pH. The surface of the sensitive area of the sensor contains
hydroxyl groups that are bound to an oxide layer. At low pH values hydrogen ions in
the sample will bind to these hydroxyl groups resulting in a positively charged surface.
In alkaline environments hydrogen ions are abstracted from the hydroxyl groups,
leading to a negatively charged surface.
Thus, each pH change has a certain influence on the surface charge. On its turn,
this attracts or repulses the electrons flowing between two electrodes in the
semiconductor device. The electronics compensates the voltage in order to keep the
current between the two electrodes at its set point. In this way this potential change is
related to the pH.
Attachment of a polymer membrane on the ISFET introduces the possibility to
go beyond the measurement of pH toward other ions. In this plastic layer certain
chemicals (ionophores), which can recognize and bind the desired ion, are put in. Now,
complex formations of the ionophore and the ion introduce a charge. The potential
change is a measure for the ion concentration. Typically, these sensors can be used in a
concentration range between app. 10.5 up to 1 mol/l.
ii. Sensor chip 2
The Level 1 pattern (electric tracks, bonding pads, and electrodes) was defined in
0.9µm UV3 resist by electron beam lithography. A layer of 200nm gold (including an
adhesion layer of 15nm titanium and 15nm palladium) was deposited by thermal
evaporation. The fabrication process was repeated.
Oxygen sensor detection principle
Most portable or survey instruments used for workplace evaluation of oxygen
concentrations make use of "fuel cell" type oxygen sensors. "Fuel cell" oxygen sensors
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Microelectronic Pill Basic Components
consist of a diffusion barrier, a sensing electrode (cathode) made of a noble metal such
as gold or platinum, and a working electrode made of a base metal such as lead or zinc
immersed in a basic electrolyte (such as a solution of potassium hydroxide).
Oxygen diffusing into the sensor is reduced to hydroxyl ions at the cathode:
O2 + 2H2O + 4e- OH –
Hydroxyl ions in turn oxidize the lead (or zinc) anode:
2Pb + 4OH 2PbO + 2H2O + 4e –
This yields an overall cell reaction of:
2Pb + O2 2PbO
Fuel cell oxygen sensors are current generators. The amount of current
generated is proportional to the amount of oxygen consumed (Faraday's Law). Oxygen
reading instruments simply monitor the current output of the sensor.
An important consideration is that fuel cell oxygen sensors are used up over
time. In the cell reaction above, when all available surface area of the lead (Pb) anode
has been converted to lead oxide (PbO), electrochemical activity ceases, current output
falls to zero, and the sensor must be rebuilt or replaced. Fuel cell sensors are designed
to last no more than one to two years. Even when installed in an instrument which is
never turned on, oxygen sensors which are exposed to atmosphere which contains
oxygen are generating current, and being used up.
Oxygen sensors are also influenced by the temperature of the atmosphere they
are being used to measure. The warmer the atmosphere, the faster the electrochemical
reaction. For this reason oxygen sensors usually include a temperature compensating
load resistor to hold current output steady in the case of fluctuating temperature.
(Microprocessor based instrument designs usually provide additional signal correction
in software to further improve accuracy.) Another limiting factor is cold. The freezing
temperature of electrolyte mixtures commonly used in oxygen sensors tends to be
about 5oF (-20oC). Once the electrolyte has frozen solid, electrical output falls to zero,
and readings may no longer be obtained. There are two basic variations on the fuel cell
oxygen sensor design. These variations have to do with the mechanism by which
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Microelectronic Pill Basic Components
oxygen is allowed to diffuse into the sensor. Dalton's Law states that the total pressure
exerted by a mixture of gases is equal to the sum of the partial pressures of the various
gases. The partial pressure for oxygen is the fraction of the total pressure due to
oxygen. Partial atmospheric pressure oxygen sensors rely on the partial pressure (or pO
2) of oxygen to drive molecules through the diffusion barrier into the sensor. As long as
the pO 2 remains constant, current output may be used to indicate oxygen
concentration. On the other hand, shifts in barometric pressure, altitude, or other
conditions which have an effect on atmospheric pressure will have a strong effect on
pO 2 sensor readings. To illustrate the effects of pressure on pO 2 sensors, consider a
sensor located at sea level where atmospheric pressure equals 14.7 PSI (pounds per
square inch). Now consider that same sensor at an elevation of 10,000 feet. Although at
both elevations the air contains 20.9 percent oxygen, at 10,000 feet the atmospheric
pressure is only 10.2 PSI! Since there is less force driving oxygen molecules through
the diffusion barrier into the sensor, the current output is significantly lower.
"Capillary pore" oxygen sensor designs include a narrow diameter tube through
which oxygen diffuses into the sensor. Oxygen is drawn into the sensor by capillary
action in much the same way that water or fluid is drawn up into the fibers of a paper
towel. While capillary pore sensors are not influenced by changes in pressure, care
must be taken that the sensor design includes a moisture barrier in order to prevent the
pore from being plugged with water or other fluids.
Figure 6: Capillary pore type oxygen sensor
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Microelectronic Pill Basic Components
Effects of contaminants on oxygen sensors
Oxygen sensors may be affected by prolonged exposure to "acid" gases such as
carbon dioxide. Most oxygen sensors are not recommended for continuous use in
atmospheres which contain more than 25% CO 2.
Substance-specific electrochemical sensors
One of the most useful detection techniques for toxic contaminants is the use of
substance-specific electrochemical sensors installed in compact, field portable survey
instruments. Substance-specific electrochemical sensors consist of a diffusion barrier which
is porous to gas but nonporous to liquid, reservoir of acid electrolyte (usually sulphuric or
phosphoric acid), sensing electrode, counter electrode, and (in three electrode designs) a
third reference electrode. Gas diffusing into the sensor reacts at the surface of the sensing
electrode. The sensing electrode is made to catalyze a specific reaction. Dependent on the
sensor and the gas being measured, gas diffusing into the sensor is either oxidized or reduced
at the surface of the sensing electrode. This reaction causes the potential of the sensing
electrode to rise or fall with respect to the counter electrode. The current generated is
proportional to the amount of reactant gas present.
This two electrode detection principle presupposes that the potential of the
counter electrode remains constant. In reality, the surface reactions at each electrode causes
them to polarize, and significantly limits the concentrations of reactant gas they can be used
to measure. In three electrode designs it is the difference between the sensing and reference
electrode which is what is actually measured. Since the reference electrode is shielded from
any reaction, it maintains a constant potential which provides a true point of comparison.
With this arrangement the change in potential of the sensing electrode is due solely to the
concentration of the reactant gas.
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Microelectronic Pill Basic Components
Figure 7: Three electrode electrochemical sensor
The oxidation of carbon monoxide in an electrochemical sensor provides a
good example of the detection mechanism.
Carbon monoxide is oxidized at the sensing electrode:
CO + H2O CO2 + 2H+ + 2e –
The counter electrode acts to balance out the reaction at the sensing electrode by reducing
oxygen present in the air to water:
1/2 O2 + 2H+ + 2e- H 2O
Similar reactions allow for the electrochemical detection of a variety of reactant
gases including hydrogen sulphide, sulphur dioxide, chlorine, hydrogen cyanide, nitrogen
dioxide, hydrogen, ethylene oxide, phosphine and ozone. A bias voltage is sometimes
applied to the counter electrode to help drive the detection reaction for a specific
contaminant. Biased sensor designs allow for the detection of a number of less
electrochemically active gases such as hydrogen chloride and nitric oxide. Several other
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Microelectronic Pill Basic Components
contaminants (such as ammonia) are detectable by means of other less straight forward
detection reactions.
Electrochemical sensors are stable, long lasting, require very little power and
are capable of resolution (depending on the sensor and contaminant being measured) in
many cases to 0.1ppm. The chief limitation of electrochemical sensors is the effects of
interfering contaminants on toxic gas readings. Most substance-specific electrochemical
sensors have been carefully designed to minimize the effects of common interfering gases.
Substance-specific sensors are designed to respond only to the gases they are supposed to
measure. The higher the specificity of the sensor the less likely the sensor will be affected by
exposure to other gases which may be incidentally present. For instance, a substance-specific
carbon monoxide sensor is deliberately designed not to respond to other gases which may be
present at the same time, such as hydrogen sulphide or methane.
Even though care has been taken to reduce cross-sensitivity, some interfering
gases may still have an effect on toxic sensor readings. In some cases the interfering effect
may be "positive" and result in readings which are higher than actual. In some cases the
interference may be negative and produce readings which are lower than actual.
Electrochemical sensor designs may include a selective external filter designed to remove
interfering gases which would otherwise have an effect on the sensing electrode. The size
and composition of the filter are determined by the type and expected concentration of the
interfering contaminants being removed.
2. Control Chip
ASIC (Application-Specific Integrated Circuit) is the control chip that connects
together the external components of the micro system.
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Microelectronic Pill Basic Components
Figure 8: Interfacing of ASIC with external components of the system
Application-Specific Integrated Circuit (ASIC)
An integrated circuit designed to perform a particular function by defining the
interconnection of a set of basic circuit building blocks drawn from a library provided by the
circuit manufacturer.
ASIC is a novel mixed signal design that contains an analog signal conditioning
module operating the sensors, 10-bit ADC & DAC converters & a digital data processing
module. An RC relaxation oscillator (OSC) provides the clock signal.
The analog module is based on the AMS (Automated Manifest System), which
offer a lot of power saving scheme (sleep mode) & a compact IC design. The temperature
circuitry biased the diode at constant current, so that a change in temperature would result in
corresponding change in diode voltage. The pH ISFET sensor was biased as a simple source
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Microelectronic Pill Basic Components
& drain follower at constant current with D-S voltage changing with threshold voltage & pH.
Conductivity circuit operated at direct current measuring the resistance across the electrode
pair as an inverse function of solution conductivity. An incorporated potentiostat operated
the amperometric oxygen sensor with a 10-bit DAC controlling the working electrode
potential with respect to reference. The analog signals were sequenced through a MUX prior
to being digitized by the ADC. The bandwidth for each channel was limited by the sampling
interval of 0.2ms.
The digital data processing module conditioned the digitized signals through
the use of a serial bit stream data compression algorithm, which decided when transmission
was required by comparing the most recent sample with the previous one. This minimizes
the transmission length & particularly effective when the measuring environment is at
quiescent, a condition encountered in many applications. The entire design is based on low
power consumption & immunity from noise interference. The digital module is clocked at 32
kHz & employed in sleep mode to conserve power from analog module.
3. Radio Transmitter
It’s assembled prior to integration in the capsule using discrete surface mount
components on a single-sided PCB. The footprint of the standard transmitter measured
8*5*3mm including the integrated coil (magnetic) antenna. It’s designed to operate at a
transmission freq. of 40.01MHz at 20˚C generating a signal of 10kHz band width. A
second crystal stabilized transmitter was also used. This unit is similar to the free
running STD transmitter, having a transmission frequency limited to 20.08MHz at
20˚C, due to crystal used. Pills incorporating the STD transmitter are Type 1, where as
the pills having crystal stabilized unit is Type 2. The transmission range was measured
as being 1m & the modulation scheme FSK (Frequency Shift Keying), with a data rate
of 1kb/s.
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Microelectronic Pill Performance
4. PERFORMANCE
Figure 9: a) Temperature Channel Performance, b) pH channel performance
1. Temperature Channel Performance
The linear sensitivity was measured over a temperature range from 0˚C to 70˚C
& found to be 15.4 mV/˚C. This amplified signal response was from the analog circuit,
which was later implemented in the ASIC. The sensor (fig a), once integrated in the
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Microelectronic Pill Performance
pill, gave a linear regression of 11.9 bits/˚C , with a resolution limited by the noise
band of 0.4˚C (Fig b). The diode was forward biased with a constant current (15 µA)
with the n-channel clamped to the ground, while p-channel was floating. Since the bias
current supply circuit was clamped to the negative V rail, any change in the supply
voltage potential would cause the temporary channel to drift. Thus, it was seen that o/p
signal changed by 1.45mV change in supply expressed in mV, corresponding to a drift
of – 41.7mV/h in the pill from a supply voltage change of –14.5mV/h.
2. pH Channel Performance
The linear performance from pH 1 to 13 corresponded to sensitivity of –
41.7mV/pH unit at 23˚C. The pH ISFET sensor operated in a constant current mode
(15 µA), with drain voltage clamped to positive supply rail & the source voltage
floating with the gate potential. The Ag/AgCl reference electrode, representing the
potential in which the floating gate was referred to, was connected to ground. The
sensor performance, once integrated in the pill (fig b), corresponded to 14.85 bits/pH
which give a resolution of 0.07pH/data point. The sensor exhibits a larger responsivity
in alkaline solutions. The sensor life time of 20h was limited by Ag/AgCl reference
electrode made from electroplated silver. The ph sensor exhibited a signal drift of –
6mV/h (0.14pH), of which –2.5mV/h was estimated to be due to the dissolution of
AgCl from the reference electrode. The temperature sensitivity of the pH sensor was
measured as 16.8mV/˚c. The changing of the pH of the solution at 40˚c from pH 6.8 to
2.3 and 11.6 demonstrated that the two channels were completely independent of each
other and there was no signal interference from the temperature channel (fig b).
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Microelectronic Pill Advantages
5. ADVANTAGES
It is being beneficially used for disease detection & abnormalities in human body.
Therefore it is also called as MAGIC PILL FOR HEALTH CARE.
Adaptable for use in corrosive & quiescent environment.
It can be used in industries in evaluation of water quality, Pollution Detection,
fermentation process control & inspection of pipelines.
Micro Electronic Pill utilizes a PROGRAMMABLE STANDBY MODE, So power
consumption is very less.
It has very small size, hence it is very easy for practical usage.
High sensitivity, Good reliability & Life times.
Very long life of the cells (40 hours), Less Power, Current & Voltage requirement
(12.1mW, 3.9mA, 3.1 V).
Less transmission length & hence has zero noise interference.
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Microelectronic Pill Other Applications
6. OTHER APPLICATIONS
The generic nature of microelectronic pill makes it adaptable for use in
corrosive environments related to environmental & industrial applications, such as the
evaluation of water quality, pollution detection, fermentation process control & inspection of
the pipelines. The integration of radiation sensors & the application of indirect imaging
technologies such as ultrasound & impedance tomography, will improve the detection of tissue
abnormalities & radiation treatment associated with cancer & chronic inflammation.
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Microelectronic Pill Limitations
7. LIMITATIONS
It cannot perform ultrasound & impedance tomography.
Cannot detect radiation abnormalities.
Cannot perform radiation treatment associated with cancer & chronic inflammation.
Micro Electronic Pills are expensive & are not available in many countries.
Still its size is not digestible to small babies.
Further research is being carried out to remove its draw backs.
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Microelectronic Pill Conclusion
8. CONCLUSION
We have therefore described about the multichannel sensor, which has been
implemented in remote biomedical using micro technology, the microelectronic pills, which is
designed to perform real time measurements in the GI tract providing the best in vitro wireless
transmitter, multi channel recordings of analytical parameters.
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Microelectronic Pill Future Developments
9. FUTURE DEVELOPMENTS
Further developments focus on the photo pattern able gel electrolyte and
oxygen and cation selective membranes. Also in the future, these measurements will be used
to perform physiological analysis of the GI tract. For e.g., Temperature sensors can be used to
measure the body core temperature, also locate any changes corresponding to ulcers or tissue
inflammation; pH sensors may be used for determination of presence of pathological
conditions associated with abnormal ph levels etc.
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Microelectronic Pill Future Challenges
10. FUTURE CHALLENGES
In the future, one objective would be to produce a device, analogous to a micro
total analysis system (µTAS) or lab on a chip sensor which is not only capable of collecting
& processing data, but which can transmit it from a remote location. The overall concept
would be to produce an array of sensor devices distributed throughout the body or
environment, capable of transmitting high-quality information in real time.
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Microelectronic Pill References
11. REFERENCES
http://www.lib.udel.edu/ud/spec/exhibits/color/lithogr.htm
http://www.lakeshore.comp/temp/sen/sd670_po.html
http://www.globalspec.com/specification/spechpal?
name=IonSelectiveElectrodes&comp=309
http://www.sentron.nl/nieuw/index.php?id=86
http://www.biosystems.com/appnotes/howoxyge.htm
http://computing_dictionary.thefreedictionary.com/applicatio_specific%20integrated
%20circuit
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CONTENTS
Page No
1. Introduction 1
2. Block Diagram 3
3. Basic Components 6
4. Performance 17
5. Advantages 19
6. Other Applications 20
7. Limitations 21
8. Conclusion 22
9. Future Developments 23
10. Future Challenges 24
11. References 25
ABSTRACT
The invention of transistor enabled the first use of radiometry capsules, which
used simple circuits for the internal study of the gastro-intestinal (GI) tract. They couldn't
be used as they could transmit only from a single channel and also due to the size of the
components. They also suffered from poor reliability, low sensitivity and short lifetimes
of the devices. This led to the application of single-channel telemetry capsules for the
detection of disease and abnormalities in the GI tract where restricted area prevented the
use of traditional endoscopy.
They were later modified as they had the disadvantage of using laboratory type
sensors such as the glass pH electrodes, resistance thermometers, etc. They were also of
very large size. The later modification is similar to the above instrument but is smaller in
size due to the application of existing semiconductor fabrication technologies. These
technologies led to the formation of "MICROELECTRONIC PILL".
Microelectronic pill is basically a multichannel sensor used for remote biomedical
measurements using micro technology. This is used for the real-time measurement
parameters such as temperature, pH, conductivity and dissolved oxygen. The sensors are
fabricated using electron beam and photolithographic pattern integration and were
controlled by an application specific integrated circuit (ASIC).