Kok Yeow You

THE USE OF DIELECTRIC MIXTURE EQUATIONS TO ANALYZE THE DIELECTRIC PROPERTIES OF A MIXTURE OF RUBBER TIRE DUST AND RICE HUSKS IN A MICROWAVE ABSORBER

A change in the relative proportions of a mixture of rubber tire dust and rice husks will cause a change in the mixtures electrical permittivity and its ability to absorb electromagnetic energy. An open- ended coaxial probe was used in conjunction with three dielectric mixture equations (the Kraszewski equation, the Landau equation and the Lichtenecker equation) to obtain the dielectric properties of a mixture of rubber tire dust and rice husks (RTDRH) over the frequency range of 7GHz to 13GHz. Lichteneckers equation for dielectrics proved to be a useful practical formulation for determining the efiective permittivity of homogeneous dielectric mixtures. The efiectiveness of these dielectric mixture equations in determining the efiective permittivity of RTDRH was investigated in this study. A newly developed mixture equation was derived based on these dielectric

A Small and Slim Coaxial Probe for Single Rice Grain Moisture Sensing

A moisture detection of single rice grains using a slim and small open-ended coaxial probe is presented. The coaxial probe is suitable for the nondestructive measurement of moisture values in the rice grains ranging from from 9.5% to 26%. Empirical polynomial models are developed to predict the gravimetric moisture content of rice based on measured reflection coefficients using a vector network analyzer. The relationship between the reflection coefficient and relative permittivity were also created using a regression method and expressed in a polynomial model, whose model coefficients were obtained by fitting the data from Finite Element-based simulation. Besides, the designed single rice grain sample holder and experimental set-up were shown. The measurement of single rice grains in this study is more precise compared to the measurement in conventional bulk rice grains, as the random air gap present in the bulk rice grains is excluded.

Determination of Moisture Content in Mortar at Near Relaxation Frequency 17 GHz

Determination of Moisture Content in Mortar at Near Relaxation Frequency 17 GHz The knowledge of moisture content in cement based material is important especially for the safety in field work. In this paper, a non-destructive and contactless free space method is used for measurement of moisture content in cement based materials (mortar) at microwave frequencies. The measurement system consists of a 17 GHz dielectric resonator oscillator (DRO) as a microwave source, a Power Meter as the detector, and a pair of lens horn antennas to transmit and receive the microwave signal. An empirical formula of moisture content was obtained by using a relationship between attenuation and moisture content. This model is best for prediction of moisture content greater than 2% with percentage mean error of 3%.

Amplitude-only measurements of a dual open ended coaxial sensor system for determination of complex permittivity of materials

This paper describes a novel permittivity measurement technique using dual open ended coaxial sensors. The magnitudes of the re∞ection coe-cient from two open ended coaxial sensors were used to determine complex re∞ection coe-cients and permittivity of a sample under test.

Improved Formulation for Admittance of Thin and Short Monopole Driving From Coaxial Line Into Dissipative Media

An improved formulation of the admittance equation for small and thin monopole is presented where the coefficient of the capacitive correction term can be calculated directly from the values of the inner and outer radius of the coaxial line. The results were found to agree well with measurements and the finite element method (FEM). Some rules, features, and limitations of the improved formula are also discussed.

Non-destructive dielectric measurements and calibration for thin materials using waveguide-coaxial adaptors

Abstract This paper focuses on the calibration of apertures for rectangular waveguides using open-short-load (OSL) standards and transmission-line (TL) approaches. The reflection coefficients that were measured using both calibration techniques were compared with the coefficients acquired using the thru-reflect-line (TRL) method. In this study, analogous relationships between the results of OSL calibration and TL calibration were identified. In the OSL calibration method, the theoretical, open-standard values are calculated from quasi-static integral models. The proposed TL calibration procedure is a simple, rapid, broadband approach, and its results were validated by using the OSL calibration method and by comparing the results with the calculated integral admittance. The quasi-static integral models were used to convert the measured reflection coefficients to relative permittivities for the infinite samples and the thin, finite samples

Modeling of Coaxial Slot Waveguides Using Analytical and Numerical Approaches: Revisited

Our reviews of analytical methods and numerical methods for coaxial slot waveguides are presented. The theories, background, and physical principles related to frequency-domain electromagnetic equations for coaxial waveguides are reassessed. Comparisons of the accuracies of various types of admittance and impedance equations and numerical simulations are made, and the fringing field at the aperture sensor, which is represented by the lumped capacitance circuit, is evaluated. The accuracy and limitations of the analytical equations are explained in detail. The reasons for the replacement of analytical methods by numerical methods are outlined.

Soil moisture dielectric measurement using microwave sensor system

A microwave sensor system has been developed to operate from 2.2 GHz to 4.4 GHz and used to determine the change of soil dielectric constant with various values of gravimetric moisture content from 0% to 26%. Soil samples are placed on a microstrip ring resonator (MRR) sensor and the respective incident and reflected voltages are measured and converted into magnitude of return loss, |S11|. The calculated return loss, |S11| is then correlated with corresponding soil moisture content obtained from oven drying method and also the soil permittivity obtained from commercial dielectric probe with vector network analyzer.

Study of Dual Open Ended Coaxial Sensor System for Calculation of Phase Using Two Magnitudes

A dual open ended coaxial sensor system to determine complex permittivity was studied in detail. This paper focuses on determination of a reflection coefficient phase from two magnitudes using modified capacitance model from 300 kHz to 8 GHz. The phase information can then be used for calculation of the samples complex permittivity. Factors such as range and limitation of the model, samples permittivity, operating frequency, and size of sensor were investigated. Sensitivity of calculated phase with respect to small changes in measured magnitude was carried out.

Compact microstrip S-Band 90° hybrid coupler

A compact microstrip S-Band 90° hybrid coupler is designed and tested. The proposed coupler has a pass-band width of 1.9 GHz and approximately twice wider bandwidth than conventional coupler at the operating center frequency of 2 GHz. The size reduction of 40% is achieved from the conventional design model with the arrangement of open stubs.