Application of Open-Ended Coaxial Sensor to Determine Oil Palm Fruit Ripeness

This thesis presents a critical study on the use of an open-ended coaxial sensor for the determination of both complex permittivity and moisture content of oil palm fruits of various degrees of fruit ripeness at ()125±oC. The sensor was studied based on the calculation of reflection coefficient using an integral admittance approach and finite element method (FEM). In this work, the computation of reflection coefficient of the oil palm fruits was realized using MATLAB and FEMLAB GUI software for the admittance approach and finite element method (FEM), respectively. The results were compared with the measured reflection coefficient using the open-ended coaxial sensor in conjunction with a HP8720B vector network analyzer (VNA). The sensor operating between 1 GHz and 5 GHz was fabricated from a 4.1 mm outer diameter sub-miniature A type (SMA) coaxial tub contact panel. The measuring end of the sensor was calibrated by a transmission line procedure. The integral admittance formulation was simplified into a series expression. The local truncation errors of the series approximation were critically analyzed. The two-dimensional FEM was used to solve the rotationally symmetric region of the open-ended coaxial line. The FEM results are closed to the measurements data than calculated admittance formulation. The maximum absolute errors of FEM and measurement results for magnitude and phase reflection coefficient are less than 0.02 and 0.1 rad, respectively, compared with 0.05 and 0.2 rad of admittance formulation and measurement results, respectively. However, the results were in good agreement that the minimum thickness of a sample under test is 2 mm. An inverse solution based on two admittance models (lumped-parameter admittance and integral admittance formulations) has been utilized to derive complex permittivity from measured reflection coefficient. The lumped-parameter admittance or closed form capacitance model is simpler in the calculation than integral admittance model. Unfortunately, it is not accurate for high operating frequencies (>5 GHz). However, the permittivity results from both models agree with measured data using HP 85070B coaxial probe and publish values (Cole-Cole model) ranging 1 GHz to 5 GHz. A calibration equation has been developed based on the relationship between the measured moisture content obtained by the oven drying method and the phase of the reflection coefficient of the sensor. The moisture content predicted by the sensor was in good agreement with those obtained using the standard oven drying method with its absolute error within 5 % moisture content, when tested on 145 different fruits samples. A model detailing two dielectric relaxation process parameters was proposed in order to represent the permittivity of oil palm mesocarp based on measured data using HP 85070B coaxial probe from 0.13 GHz to 20 GHz. The model successfully estimated the complex permittivity for various ripeness stages of oil palm mesocarp as a function of frequency, moisture and ionic conductivity, as well as the bulk density. A dielectric measurement software has been developed to control and acquire data from the VNA using Agilent VEE. The software is also used to calibrate measurement at the aperture plane of sensor and to calculate the complex permittivity from the measured reflection coefficient between 1 GHz and 5 GHz

Development of a New Technique for Measurement of Dielectric Properties of Oil Palm Fruits

The thesis describes the development of a low cost open-ended coaxial sensor for the determination of both complex permittivity and moisture content of the oil palm fruits of various degree of fruit ripeness. The sensor operating between 2 GHz and 4 GHz was fabricated from an inexpensive 4.1 mm outer diameter SMA coaxial stub contact panel and suitable for single fruit measurement. A theoretical analysis has been carried out to establish the optimum operating frequency based on the relation ship between the admittance and frequency of the sensor. The propagation of electromagnetic wave is assumed to be transverse electromagnetic (TEM) mode. The measurement system consists of the sensor and a PC-controlled vector network analyzer (VNA). A dielectric measurement software has been developed to control and acquire data from the VNA using Agilent VEE. The software is also used to calculate the complex permittivity from the measured reflection coefficient at each 201 frequency points between 2 GHz and 4 GHz. The permittivity values were then fitted to a dielectric mixture model to obtain the values of moisture content of oil palm fruits. The actual moisture content were found by standard oven drying method. A calibration equation relating the measured and predicted moisture content has been established based on more than 80 fruit samples. The equation was found to be accurate within 5.2 ± 0.4 % when tested on 69 different fruit samples. The values of moisture content obtained from the calibration equation were used in the mixture model to improve accuracy in the determination of the complex permittivity of the oil palm fruits. The sensitivities of the sensor in the measurement of the dielectric constant and loss factor of the oil palm fruits with respect to changes in moisture content were typically 0.82 and 0.05, respectively. The sensor can be used to monitor fruit ripeness based on the measurement of the magnitude of reflection coefficient alone. Fruits are considered to reach ripeness stage once the magnitude of the reflection coefficient is greater than 0.85 at optimum operating frequency 2.6 GHz

Materials Characterization Using Microwave Waveguide System

This chapter reviews the application and characterization of material that uses the microwave waveguide systems. For macroscopic characterization, three properties of the material are often tested: complex permittivity, complex permeability and conductivity. Based on the experimental setup and sub-principle of measurements, microwave measurement techniques can be categorized into either resonant technique or nonresonant technique. In this chapter, calibration procedures for non-resonant technique are described. The aperture of open-ended coaxial waveguide has been calibrated using Open-Short-Load procedures. On the other hand, the apertures of rectangular waveguides have been calibrated by using Short-Offset-Offset Short procedures and Through-Reflect-Line calibration kits. Besides, the extraction process of complex permittivity and complex permeability of the material which use the waveguide systems is discussed. For one-port measurement, direct and inverse solutions have been utilized to derive complex permittivity and complex permeability from measured reflection coefficient. For two-port measurement, in general, the material filled in the waveguide has been conventional practice to measure the reflection coefficient and the transmission coefficient by using Nicholson-Ross-Weir (NRW) routines and convert these measurements to relative permittivity, εr and relative permeability, μr. In addition, this chapter also presents the calculation of dielectric properties based on the difference in the phase shifts for the measured transmission coefficients between the air and the material

Estimation of dielectric constant for various standard materials using microstrip ring resonator

Microstrip ring resonator (MRR) is known for dielectric constant determination and many studies used Teflon as a standard sample. However, there are many other materials available which able to perform better or equivalence as the Teflon in calibrating certain dielectric constant measurement. This paper presents simulation of the MRR to investigate frequency shift of materials for dielectric constant estimation using the CST STUDIO SUITE 2016 software. The MRR was designed on RT/Duroid®5880 substrate (εr = 2.2, tanδ = 0.0004) with 50 Ω matching impedance where microstrip width, substrate thickness and ring mean radius were 4.893, 1.575 and 14 mm, respectively to resonate at 2.65340 GHz. Teflon, Polyimide, Isola FR408, Arlon AD250, Arlon AD270 and Gil GML1032 were alternately selected to be placed on top of the MRR as a standard sample to obtain the frequency shift. The frequency shifts for the above materials were 2.56932, 2.46149, 2.44680, 2.53748, 2.52007 and 2.48608 GHz, correspondingly. The differences in frequency shift were used in NetBeans IDE 8.1 algorithm of Java for dielectric constant calculation. The results indicated that Polyimide and Arlon AD250 had the lowest and highest mean percentage error of 0.83536 and 1.76505 %, respectively. Hence, Polyimide might as well be the most suitable candidate as a standard sample in MRR technique for dielectric constant measurement

Precision permittivity measurement for low-loss thin planar materials using large coaxial probe from 1 to 400 MHz

This paper focuses on the non-destructive dielectric measurement for low-loss planar materials with a thickness of less than 3 mm using a large coaxial probe with an outer diameter of 48 mm. The aperture probe calibration procedure required only to make a measurement of the half-space air and three offset shorts. The reflection coefficient for the thin material is measured using a Keysight E5071C network analyzer from 0.3 MHz to 650 MHz and then converted to a relative dielectric constant and tangent loss via closed form capacitance model and lift-off calibration process. Measurement error of dielectric constant, Δεr is less than 2.5 % from 1 MHz to 400 MHz and the resolution of loss tangent, tan δ measurement is capable of achieving 3×10-3

Simple calibration and dielectric measurement technique for thin material using coaxial probe

This paper focuses on the nondestructive dielectric measurement for thin dielectric material using open-ended coaxial probe. The probe calibration procedure requires only a measurement of a half-space air and three open standard kits. The measured reflection coefficient for thin sample, which is backed by metal plate, is taken with a vector network analyzer up to 7 GHz and the reflection coefficient is converted to relative dielectric constant and tangent loss via closed form capacitance model and simple calibration process

Optimum design of a microstrip ring resonator sensor for determination the moisture content in oil palm fruits and seeds

Oil palm fresh fruit bunch (OPFFB) is the main export product of the oil palm industry. A good oil palm is between 17 to 18 weeks of age with full fruitless maturity. An automated detection system should be implemented to determine the OPFFB’s maturity and expedite the harvesting process. Various automated detection methods have been proposed for conventional method replacement. In a preliminary study, a new oil palm fruit sensor was proposed for detecting the maturity of OPFFB, and a microstrip ring resonator was designed for determining the moisture content in oil palm fruit. The coaxial feeder of the microstrip ring was a Sub-Miniature A (SMA) stub contact panel with outer and inner conductors of 4.1 mm and 1.3 mm, respectively. The measurement system consisted of a sensor and a PC controlled network analyzer. This system was tested successfully on seeds and fruits of oil palm with various degrees of maturity. The microstrip ring resonator operated between 2.2 and 3 GHz and required low frequency that enabled the electromagnetic field in the first half of the ring resonator to be transferred to the second half and subsequently cause the collinearity of the maximum field points in the feed lines and resonator

Physical and Chemical Characterization of Rice Using Microwave and Laboratory Methods

Two main species of cultivated rice in the world are Oryza sativa (Asian rice) and Oryza glaberrima (African rice). The Oryza sativa species, which is grown worldwide, is far more widely utilized compared with the Oryza glaberrima species, which is grown in West Africa. Recently, the annual rice production has reached almost 480 million tonnes, and this demand is expected to rise to 550 million tonnes in 2035. Thus, this increases the need to characterize and maintain the quality of rice and hence to determine the price of rice appropriately. Obviously, modern technologies that can provide fast and accurate measurement are essential in the large-scale industrial rice processing. In this chapter, several technologies and instruments used for rice processing are reviewed. The principle of the measurement for each technology is briefly described. The strength of this chapter is to introduce the application of microwave technology during rice processing, such as rice dying process, rice moisture detection, broken rice measurement and rice insect control. The pros and cons of the microwave method will be discussed in detail. Hence, some standard test laboratory for monitoring of carbohydrate, protein, fat and trace elements content is also described in this chapter

Development of Compact P-Band Vector Reflectometer

A compact and low cost portable vector reflectometer is designed for a reliable measurement of reflection coefficient, S11. This reflectometer focuses on return loss measurement of frequency ranges from 450 MHz to 550 MHz. The detection of magnitude and phase is based on the utilization of surface mount Analog Devices AD8302 gain/phase detector. The data acquisition is controlled by using Arduino-Nano 3.0 microcontroller, with the use of two analog to digital converter (ADC) and a digital to analog converter (DAC). One port (Open, short and matched load) calibration technique is used to eliminate systematic errors prior to data acquisition. The evaluation of the reflectometer is done by comparing the result of the measurement to that of vector network analyzer