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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