Post on 12-Aug-2020
International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:14 No:05 59
147504-1405-2828-IJMME-IJENS © October 2014 IJENS I J E N S
Development of Low Cost Microwave Detection
System for Salinity and Sugar Detection E.M. Cheng*
,1, M. Fareq
2, Shahriman A. B.
1, Mohd Afendi
1, Zulkarnay Z.
1, S. F. Khor
2, Liyana Z.
3,
Nashrul Fazli M. N.1, W. H. Tan
1, N. S. M. Noorpi
2, N. M. Mukhtar
2 and M. Othman
2
1School of Mechatronic Engineering, Universiti Malaysia Perlis, UniMAP, 02600 Arau, Perlis, Malaysia
emcheng@unimap.edu.my*
shahriman@unimap.edu.my
afendirojan@unimap.edu.my
zulkarnay@unimap.edu.my
nashrul@unimap.edu.my
whtan@unimap.edu.my 2School of Electrical System Engineering, Universiti Malaysia Perlis, UniMAP, 02600 Arau, Perlis, Malaysia
mfareq@unimap.edu.my
sfkhor@unimap.edu.my
nursabrina@unimap.edu.my
nurhakimah@unimap.edu.my
mardianaliza@unimap.edu.my 3School of Computer and Communication Engineering, Universiti Malaysia Perlis, UniMAP, 02600 Arau, Perlis,
Malaysia
liyanazahid@yahoo.com
*Corresponding author:E.M. Cheng
Abstract— This work is proposed to develop a low cost
measurement system to check the salinity and sugar content of
food. A Mini-Circuits ZX95-2800+ voltage controlled oscillator
(VCO), Mini-Circuits ZGDC10-362HP+ high power directional
coupler, Mini Circuits PWR-6GHS+ USB Smart power sensor
and open-ended coaxial probe made of semi-rigid coaxial cable
RG402/U are used. The main idea for this work is based on
electromagnetic reflection due to the impedance mismatch. In
order to verify efficiency and accuracy of this developed
detection system, comparison with measured result from P-series
network analyzer (PNA) is conducted. The measured reflection
coefficient from developed system was discussed among Agilent
85052D High-Temperature probe, RG405/U and RG402/U open-
ended coaxial probe.
Index Term— Salinity; Sugar; open-ended coaxial probe,
reflection coefficient; microwave detection system
1. INTRODUCTION
Sodium chloride is one type of salt, with molecular
formula as NaCl. Salt is a vital to supply essential component
for the human body [1], e.g. salt help to maintain osmosis
equilibrium in cells to maintain and is used to transmit
information in our nerves and muscles. Salt is also added to
food usually for purpose of seasoning, preservatives and
texture aid. However, excessive intake of salt for long term
will lead to high blood pressure, stroke, edema, kidney failure
and cardiovascular diseases. According to the United States
Department of Health and Human Services, a man should
consume not more than 3750-5750 mg of salt (1500-2300 mg)
per day depending on age. In addition, the nutrition labels of
salt on food packing which is administered by Food Standards
Agency [2] regulate the level of salt intake by human body.
Although the Food Standards Agency has regulated the
quantity of the salt mandatory in the food industry with act,
some industry runner may ignore the act by applying
excessive salt to enhance flavor of their food product for the
sake of sales.
Sugar usually refers to all carbohydrates of the general
formula Cn(H2O)n in a chemical term. Sugar composed of
carbon, hydrogen and oxygen. Sucrose is the most common
sugar which is a crystalline tabletop and industrial sweetener
used in foods and beverages. Apart from salt, sugar is also a
flavor-enhancer. Sugar used to interacts with molecules of
protein or starch during baking and cooking process.
Excessive sugar intake can cause drowsiness, decreased
activity, hyperactivity, anxiety, difficulty concentrating, and
crankiness. Hence, American Heart Association advised that
30g of daily sugar intake for women and a man should not
consume more than 45g. For diabetic patient, advised amount
of sugar intake is 20g per day for women patient and 30g per
day for men patient [3]. Hence, a low cost and efficient
method is proposed in this work as liquid compound
chromatography to monitor the salt and sugar intake by a
person or applied by food industry.
There are many methods are reported to be liquid
compound chromatography. The estimation of compound in
liquid with High-Performance Liquid Chromatography
(HPLC) by means of Ultraviolet-Visible (UV-VIS) has been
widely investigated over the recent years [4]–[7]. As electric
properties of liquid depend on their composition, it is obvious
that the parameters either polar moment, ionic conductivity,
optical resonance or etc significantly inspired researchers to
explore in liquid compound analysis.
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2. LITERATURE REVIEW
The earliest reports of compound analyzer were published
since twentieth century. Moisture content in grain was
determined by the concept of permittivity measurement based
on DC electrical resistance. It was reported by Knipper on
year 1953 [8]. The first moisture meter was invented in the
former Union of Soviet Socialist Republics (U.S.S.R.) for
barley and wheat moisture measurement. Dunlap and
Makower (1945) [9] measured the dielectric properties of
carrots from 18 kHz to 5 MHz and reported that the dielectric
constant and conductivity of carrots are relatively depend on
moisture content, frequency, temperature, density, and particle
size.
In addition, Kundra et al. (1992) [10] studied effects of
dissolved salts in milk on dielectric properties. The salinity
and frequency effect on the dielectric constant was proved by
the Gadani et al. (2006) [11]. Their work indicated that
dielectric constant decreases when concentration of saline
water increase from 5000 to 35000ppm (parts per million).
Meanwhile, loss factor of saline water decreases when
frequency increases.
A salinometer is developed by Thomas M. Dauphi et al.
(1983) [12] based on a direct determination of the
conductivity ratio of sample to standard seawater in dual cell.
Then, a research was conducted to measure the complex
dielectric constant of pure and sea water using satellite [13].
3. Methods and Materials
3.1 Sample Preparation
In this work, the samples were prepared in liquid state.
During the sample preparation, pure NaCl and sugar are
dissolved into distilled water separately to have several
solutions with different percentage of amount of salt and
sugar. In order to ensure the complete dissolution in water, the
sample must be prepared in advance before measurement is
conducted.
3.2 System Development /Assembly
Figure 1 illustrate the developed low cost detection system for sugar and salt content in water by assembling microwave source, directional coupler, power sensor and open-ended coaxial probe. The microwave source of this developed system is Mini-Circuits ZX95-2800-S+ Voltage Controlled Oscillator (VCO) as shown in Figure 2. According to its datasheet, desired frequency of microwave signal will be generated based on the requirement of user. However, RF
Fig. 1. Overview of the developed detection System
Output of VCO is connected to input port of ZGDC10-
362HP+ high power directional coupler as shown in Figure 3.
Output port of directional coupler will be connected to probes,
i.e. Agilent 85052D High-Temperature probe, RG405/U or
RG402/U semi-rigid coaxial probe. An only coupling port is
connected to PWR-6GHS+ USB Smart power sensor (Figure
4). The coupling output will receive coupled reflected power
depending on coupling coefficient of directional coupler.
Directional coupler is mainly is used to obtain the power level
of reflected signal without interrupting the main power flow in
the system.
PWR-SEN-6G+ USB power sensor are connected to
coupling port of directional coupler. The coupled reflected
signal will be converted by power sensor to be electrical
power and its reading will be displayed on the GUI
Measurement Application Software built-in (Figure 2) using
laptop.
3.3 Reflection measurement
A precautious measure during reflection and dielectric
measurement must be conducted before reading was taken
(Figure 5), i.e. any air bubble must be avoided at aperture of
the probe. The air bubble will cause unfavorable reading
obtained.
Fig. 2. Mini-Circuits ZX95-2800-S+ Voltage Controlled Oscillator
Voltage
controlled
oscillator
Directional
Coupler
USB Power
Sensor
Directional
Coupler
USB Power
Sensor
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There were 2 types of probe used in this work, i.e. Agilent
85052D High-Temperature dielectric probe and fabricated
open-ended coaxial probes made of RG402/U and RG405/U
semi-rigid open-ended coaxial cable, respectively. For Agilent
Fig. 5. Reading is displayed in GUI Measurement Application Software
Fig. 3. Mini-Circuits ZGDC10-362HP+ high power directional coupler
Fig. 4. Mini Circuits PWR-6GHS+ USB Smart power sensor
Fig. 6. Agilent 85052D High-Temperature dielectric probe.
85052D High-Temperature dielectric probe as shown in
Figure 6, it is an high accuracy of dielectric probe which is
product of Agilent Technologies. High-Temperature dielectric
probe with glass-filled has radii a = 0.33 mm and b = 1.5 mm.
The further detail of specification can be referred to technical
report [14].
(a)
(b)
Fig. 7. (a) RG402/U and RG405/U semi-rigid open-ended coaxial probe and (b) its configuration
For the open-ended coaxial probe made of RG402/U with
PTFE-filled, the outer radii of the inner conductor, a is 0.455
mm. Meanwhile, inner radii of the outer conductor, b is 1.49
mm. In addition, RG405/U with PTFE-filled has a = 0.255
mm and b = 0.838 mm. Both RG405/U and RG402/U were
connected to 3.5 mm SMA male connector, which has length
of 3 mm with a’ = 0.65 mm and b’ = 2.05 mm to fabricate
semi-rigid coaxial probes for reflection measurement. The
configuration of RG4055/U and RG402/U semi rigid coaxial
sensor/probe are illustrated in Figure 7.
4. RESULTS AND DISCUSSIONS
4.1 Salinity measurement
Figure 8 and 9 illustrated results of dielectric measurement using Agilent 85052D High-Temperature probe in conjunction with P-series Network Analyzer (PNA). Figure 4 indicates that the dielectric constant of all saline with different percentage of salt content in solution decreases when frequency increase from 200MHz to 20GHz. The delay of response to the change of applied field causes friction and heat. The dissipation of heat energy is described by loss factor. The dissolved salts are presented in positive and negative ions and oscillate in accordance to the time varying electric field. Polarization occurs in such a way to store energy. When the
frequency increases, the saline water molecules lose the
response to applied field at high frequency as illustrated by
Figure 9. As a result, energy storage declined and the
rotational losses increased. At these frequencies the mass of
the ions prevents them from responding to the variation of
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electric field. This measured result is proved by the Debye
theory and also described by Hallikainen et al. (1985) [15].
Fig. 8. The variation of dielectric constant with frequency
Fig. 9. The variation of loss factor with frequency for different percentage of salt in solution
Figure 9 show that loss factor of saline water decreases when
frequency increases. The loss factor decreases steeply from
1GHz to 4GHz and then tends to be constant beyond 4 GHz.
According to the Debye-Falkenhagen theory [16], the
variation of loss factor with respect to frequency can be
explained as it is due to the frequency dependence of the ionic
conductivity in an electrolyte solution, e.g. solution contain
ionic substance. At high frequency, the ionic conductivity of
electrolyte solution declines due to dynamic effect of
relaxation of an ions atmosphere on the motion of an ion. The
ionic atmosphere lags causes ion moving in an electrolyte
solution to experience retarding force. In other words, ion
atmosphere cannot reach the motion of an ion immediately
when it moves through the liquid with a velocity produced by
external electric field which led to a dissymmetry in the
direction of the ion motion. This dissymmetry of charge
density causes a retardation force on the moving ion and hence
decreases its mobility. The central ion oscillates in the
oscillating electric field and the ion atmosphere has less time
to reach full relaxation. As a result, it can be noticed that
dielectric constant and loss factor decrease when frequency
increases.
For the issue of variation of both dielectric constant and
loss factor with percentage of salt in water, it can be observed
that dielectric constant decreases when percentage of salt
(concentration) increases. In contrary, loss factor increases
with percentage of salt. The more concentrated the solution,
the closer these both positive and negative ions. It leads to the
greater retardation force, thus the greater the resistance
experienced by the ion. Therefore, it causes the decrement of
dielectric constant and increment of loss factor when
percentage of salt content in water increases as illustrated in
Figure 10 and 11. For the lower frequency, i.e. 1.40 GHz, it
shows higher dielectric constant and loss factor comparing
with other higher frequencies. It is consistent with the Figure 4
and 5. The dielectric constant, loss factor and reflection
coefficient remain constant beyond 25% of salt content in
solution. It is due to the attainment of state of saturation
occurred in solution. Therefore, the discussion about the
results for salt content in solution beyond 25% was omitted.
In Figure 12, it is shown that reflection coefficient, |Г|
increase with frequency for all percentage of salt content in
solution. It can be explained by the dielectric properties of
electrolytic solution. Dielectric properties which are function
of frequency determine electrical impedance of solution.
The decrement of dielectric constant and loss factor due
to the increment of frequency as shown in Figure 8 and 9
cause the increment of reflection coefficient with frequency as
shown in Figure 13. This behavior can be explained by
equations [17]:
T
T
CZj
CZj
00
00
1
1
(1)
where
fT CCjC 0)"'( (2)
)(38.2 00 abC
(3)
where is angular velocity, Z0 is characteristic impedance of
coaxial line i.e. 50Ω, 0 is permittivity in free space, C0 =
capacitance of air, and Cf is capacitance of fringing field in
coaxial line. b and a is radius of external and internal
conductor of coaxial probe, respectively as shown in Figure
7(b). Since Cf can be ignored in the first approximation [18],
Eq. (1) can be simplified as
)()"'(38.21
)()"'(38.21
000
000
abjZj
abjZj
(4)
When the coaxial line contact with solution, mismatch
impedance is occurred, and hence causes reflection on the
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aperture of coaxial probe. Meanwhile, when the impedance of solution approaches characteristic impedance of coaxial line,
Fig. 10. The variation of dielectric constant, ε’ with percentage of salt content in water for different frequency
Fig. 11. The variation of loss factor, ε” with percentage of salt content in water for different frequency
Fig. 12. The variation of magnitude of reflection coefficient, |Г| with frequency for different percentage of salt content in water
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Fig. 13. The variation of reflection coefficient with percentage of salt in solution for different frequency using PNA in conjunction with Agilent 85052D High-
Temperature dielectric probe
mismatch impedance declined. It leads to the decrement of
reflection coefficient as shown in Figure 15. Figure 13
illustrates that measured magnitude of reflection coefficient
using the developed system over percentage of salt in water
for 1.40GHz, 1.70GHz, 2.10GHz, 2.60GHz, and 2.80GHz.
Meanwhile, the magnitude of reflection coefficient shown in
Figure 13 exhibit anomalous trendline. They show skewed
quadratic trendline. The reflection coefficient will increase as
percentage of salt content in solution exceeds 8%. It is
attributed to the increment of mismatch impedance as
impedance of solution discrepant from characteristic
impedance gradually when percentage of salt increases. As a
result, the anomalous of trendline can be seen. Another
explanation of this anomalous behavior is due to multiple
reflections in the coaxial line [19]. In other words, the
standing wave that occurred in coaxial line causes the
oscillation of magnitude of reflection coefficient. It can be
seen that the developed system has considerably high of
accuracy as PNA in reflection measurement for frequencies of
1.40GHz, 1.70GHz, 2.10GHz, 2.60GHz, and 2.80GHz.
Agilent 85052D High-Temperature probe was used to conduct
the reflection measurement as shown in Figure 12 and Figure
13.
Figure 14 illustrate the comparisons of magnitude of
reflection coefficient for frequency 1.40GHz, 1.70GHz,
2.10GHz, 2.60GHz, and 2.80GHz. Trendlines shown in Figure
14(a)-(c) have anomalous behavior which is similar to Figure
10 and Figure 11 for all type of probes. When frequency is
extended to 2.60 GHz and 2.80 GHz as shown in Figure
14(d)-(e), the magnitudes of reflection coefficient decreases
when percentage of salt content vary from approximately 1%
to 10%. When percentage of salt in solution exceeds 10%, the
magnitude of reflection coefficient tends to become constant
for all type of probes. In addition, Agilent 85052D High-
Temperature dielectric probe exhibit the lowest of reflection
coefficient among the probe. It is probably due to its dielectric
filler of glass that present between inner and outer conductor
which has complex permittivity of 5.4-j0.0108, since PTFE
(Polytetrafluoroethylene) that presented in RG402/U and
RG405/U has complex permittivity of 2.05-j0.0005. The
larger value of complex permittivity causes the smaller value
of magnitude of reflection coefficient as described by Eq. (4). Although RG402/U and RG405/U use same dielectric filler
and they have similar aspect ratio, (a
b ), however, aperture of
RG402/U has longer radius than RG405/U. Hence, reflection
coefficient of RG402/U is always greater than RG405/U. It
can be described by Eq. (4) where increment of (b - a) term
will lead to increment of reflection coefficient too.
4.2 Sugar content detection
Figure 15 shows the variation of measured dielectric
constant using PNA in conjunction with Agilent 85052D
High-Temperature dielectric probe for different percentages of
sugar content in water over frequency range from 200MHz to
20GHz. Overall, the dielectric constant of different percentage
of sugar in water decreases when the frequency increases from
200MHz to 20GHz. In Figure 15, the sample with 5% of sugar
content in water indicate the highest value of dielectric
constant, whereas sample with 70%-75% of sugar content in
water indicate the lower value of dielectric constant. The
amount of free water molecule presented in the water is the
key to determine the dielectric properties. When the
percentage of added sugar in water is low, less free water
molecule is bound with molecule of sugar. Free water
molecule, H2O becomes dominator in solution. As a results,
5% of sugar content in solution show the highest dielectric
constant, as which water has considerably high of dielectric
constant. Free water molecule is barely to find in high
percentage of sugar content in water or solution, for instance
80% sample. Hence, it can be seen that dielectric constant
increase when percentage of sugar content in water decreases.
Sugar molecules which are relatively large, uncharged, and
non-polar can inhibit orientation polarization by the
electromagnetic energy [20-21]. Therefore, the increment of
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(a)
(b)
(c)
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(d)
(e)
Fig. 14. Comparison of reflection coefficient over percentage of salt in solution using developed reflection measurement setup for frequency (a) 1.40 GHz, (b)
1.70 GHz, (c) 2.10 GHz, (d) 2.60 GHz, and (e) 2.80 GHz
Fig. 15. The variation of measured dielectric constant, ε’ with frequency
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Fig. 16. The variation of measured loss factor, ε” with frequency
sugar content will decline the dielectric constant. Since the
molecule of sugar is relatively large, hence the moment inertia
is greater if compare with molecule of water. The reorientation
due to change of electromagnetic polarity is inhibited at low
frequency due to moment inertia. Hence, the dielectric
constant is relatively low at high percentage.
On the other hand, loss factor decreases when frequency
increases. It can be observed in Figure 16. It is due to the
inability of sugar molecule to store charge at high frequency.
This fact attribute to low dielectric constant at high frequency.
When dielectric constant is low, the molecules are not able to
store energy. Hence, the dissipation of energy may dissipate
through conduction loss [22]. The rapid change of
electromagnetic polarity at high frequency is asynchronous
with frequency of charge oscillation and molecule
reorientation. It causes the still state is presented at high
frequency. Hence, the variation of loss factors at higher
frequency seem level off due to insignificant friction and
retardation encountered by sugar and water molecules
presented in solution. In addition, the difference between
molecule of sugar and salt in term of their relaxation
frequency [23] causes contrast behavior of loss factor.
Figure 17 shows the variation of dielectric constant of solution for different percentage of sugar in water measured
by using PNA for 1.38GHz, 1.69GHz, 2.08GHz, 2.58GHz,
and 2.77GHz. Figure 17 is clearly indicates that the dielectric
constant decreases with increment in percentage of sugar
content in water. Water has a relatively high dielectric
constant [24] as any traces of moisture trapped or absorb will
dramatically alter the desired dielectric properties. Hence, the
presences of moisture content in sugar solution will vary the
dielectric constant. For high moisture content, the free water
molecule increases and sugars are dissolved. It leads to higher
conductivity.
Figure 18 shows the measured dielectric loss against
percentage of sugar in water. Figure 18 indicates that the
dielectric loss increases when percentage of sugar in water
increases. Meanwhile, dielectric loss decreases beyond 50%
Fig. 17. Measured Dielectric Constant vs. Percentage of sugar in water for frequency 1.40GHz, 1.70GHz, 2.10GHz, 2.60GHz, and 2.80GHz
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Fig. 18. Dielectric loss vs. percentage of sugar in water for 1.40GHz, 1.70GHz, 2.10GHz, 2.60GHz, and 2.80GHz
of sugar content in water. It might be due to the absence of
free water molecule in solution as the solution attains state of
saturation beyond 50% of sugar in water. Molecules of sugar
might have greater inertia than the water molecule. In the
saturation state, free water molecule is not presented and the
molecule of sugar is excessive. The inertia of sugar molecule
may retard the oscillation of ion and hence, decrease the
dielectric loss.
The magnitude of reflection coefficient in Figure 19 was
measured by using high temperature dielectric probe. The
highest magnitude of reflection coefficient can be found at
1.40GHz when percentage of sugar in water increases. This
trend is followed by 2.80GHz, 1.70 GHz, 2.60 GHz, and lastly
at 2.10GHz. At frequency 2.10GHz, 2.60GHz, and 2.80GHz
show obvious fall in magnitude of reflection coefficient from
5% to 50% of sugar in water. Reflection coefficient increases
from 50% to 80% of sugar content in solution. At frequency
1.40 GHz and 1.70GHz, decrement of reflection coefficient
occur from 5% to 60% of sugar in water. Beyond 60% of
sugar in water, dielectric loss increase with sugar
concentration up to 80% of sugar in solution. The similar
trendline can be found as in Figure 13 and the explanation is similar as encountered in salinity measurement where it is
associated with degree of mismatch impedance.
Figure 20(a) shows the magnitude of reflection coefficient
against percentage of sugar content in water for 3 different
probes at 1.40GHz by using portable microwave detection
system. The trendline shown in Figure 20(a) is similar as
Figure 14(a). However, the detectable range of sugar content
is wider than salinity measurement. Figure 14(a) and Figure
20(a) exhibit quadratic trendline. The turning point for salinity
measurement occurred at 5 percent in saline water, while
sugar content measurement occurred at 60% in sugar solution.
The molecular weight of sugar and salt probably is the factor
which causes the different in term of the turning point. On the
other hand, it can be noticed that the salt attain the saturation
state at lower percentage of salinity at approximately 5
percent. It might attribute to lower solubility of salt [25] than
sugar. Meanwhile, sugar attains saturation at greater
percentage than salt. It can be justified from Figure 20(a)-(e)
Fig. 19: Magnitude of reflection coefficient vs. percentage of sugar in water for Portable Microwave Detection system measured by using high temperature
probe
0
2
4
6
8
10
12
14
16
18
20
0 20 40 60 80
Die
lect
ric
loss
, ɛ''
Percentage of sugar in water(%)
1.40GHz
1.70GHz
2.10GHz
2.60GHz
2.80GHz
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(a)
(b)
(c)
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(d)
(e)
Fig. 20. Magnitude of reflection coefficient vs. percentage of sugar in water at frequency (a)1.40 GHz, (b) 1.70 GHz, (c) 2.10 GHz, (d) 2.60 GHz and (e) 2.80
GHz which measured by using portable microwave detection system with RG 402 coaxial probe, RG405 coaxial probe and Agilent 85052D high temperature
probe
if compared with Figure 14(a)-(e). The variation of magnitude
of reflection coefficient with percentage of solvent is
consistent for all type of sensors over the exhibited frequency
range.
5. Conclusion
A low cost microwave detection system which consists of
main microwave components, i.e. VCO, directional coupler
and RG402/U as well as RG405/U semi rigid coaxial probe
for salt and sugar content in solution. These components are
assembled for percentage of salt and sugar in solution. On the
other hand, PNA in conjunction with Agilent 85052D High-
Temperature probe are used to measure the dielectric constant
and loss factor of solution with different percentage of salt
(salinity) and sugar content (sweetness). The reflection
measurements were then conducted using these probes for
reflection coefficient and comparison was conducted in terms
of its performance in salinity and sugar content detection in
solution via reflection coefficient. It can be noticed that
RG405 has better agreement with Agilent 850520 High
Temperature Probe in measuring reflection coefficient for all
selected frequency in salinity measurement. Meanwhile,
RG405 performed consistently with High Temperature Probe.
The variation of reflection coefficient over percentage of sugar
content in solution is maintained at certain accuracy. RG402
performed inconsistently in sugar content detection comparing
with RG405.
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