Yi Lung Then

Precise Moisture Monitoring for Various Soil Types Using Handheld Microwave-Sensor Meter

A handheld microwave reflectometer-sensor system is developed to operate from 1.35 to 1.95 GHz and used to measure volumetric and gravimetric moisture content in various types of soils from 0% to 45%. A small monopole driver from coaxial line is buried into the soil, and its reflected voltage is measured and correlated with corresponding soil moisture content obtained from oven dying method. The measured reflected voltage is dependent on the nonlinear change of dielectric properties of the soil with the moisture content.

ENHANCED FIVE-PORT RING CIRCUIT REFLECTOMETER FOR SYNTHETIC BREAST TISSUE DIELECTRIC DETERMINATION

In this study,a Six-port Reflectometer (SPR) with dielectric probe sensor is used to predict relative dielectric,er of normal and tumorous breast tissue in frequency range from 2.34GHz to 3.0GHz. Other than that,a superstrate with an exterior copper layer is overlaid on the surface of a primitive Five-port Ring Circuit (FPRC),which is also a denominated,enhanced superstrate FPRC. It is the main component of the SPR and is presented in this paper as well. The enhanced superstrate FPRC is capable of improving its operating bandwidth by 26% and shifting the operating centre frequency to a lower value without increasing circuit physical size. The detailed design and characteristics of the FPRC are described here. In addition,the enhanced superstrate FPRC is integrated into the SPR for one-port reflection coefficient measurement. The measurement using the SPR is benchmarked with Agilent’s E5071C Vector Network Analyzer (VNA) for one-port reflection coefficient. Maximum absolute mean error of the linear magnitude and phase measurements are recorded to be 0.03 and 5.50°,respectively. In addition,maximum absolute error of the predicted dielectric and loss factor are 1.77 and 0.61,respectively.

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.

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.

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.

Evaluation of the Equivalent Lumped Element Parameters of Modified Microstrip Ring Resonator

Microstrip ring resonator (MRR) sensor was modeled by simple equivalent lumped element circuits in free space based on simulation data obtained from Microwave Office (AWR) simulator and comparison was made with the measurements using the E5071C Network Analyzer. The calculated reflection coefficient, |G| and complex input impedance Zin using lumped element model were compared with the measurements results. Both results showed well agreement with a little discrepancy, basically due to imperfect soldering. The MRR was designed to have operating frequencies between 0.5 GHz and 4.5 GHz. The maximum surrounding of magnetic field, Hϕ is within 15 A/m in free space.