Buford Randall Jean

A microwave frequency sensor for non-invasive blood-glucose measurement

A microwave sensor having features useful for the noninvasive determination of blood glucose levels is described. The sensor output is an amplitude only measurement of the standing wave versus frequency sampled at a fixed point on an open-terminated spiral-shaped microstrip line. Test subjects press their thumb against the line and apply contact pressure sufficient to fall within a narrow pressure range. Data are reported for test subjects whose blood glucose is independently measured using a commercial glucometer.

Soil Moisture Information And Thermal Microwave Emission

This paper presents theoretical and experimental results that demonstrate the depth to which soil moisture can be directly measured using microwave radiometers. The experimental results also document the effect of uniform surface roughness on the response of thermal microwave emission to soil moisture. Experimental measurements were executed in July 1980 at the Texas A&M University Research Farm near College Station, TX. Thermal microwave emission measurements were made at 1.4, 4.9, and 10.7 GHz at both vertical and horizontal polarization at off nadir angles from 0 to 50°. It has been demonstrated that passive microwave measurements at frequencies down to 1.4 GHz can only measure soil moisture directly to very shallow soil depths, approximately 2 cm. This is due to the fact that the soil moisture dependence of the transmission coefficient across the air-soil interface predominates over the soil moisture dependence of the total energy originating within the soil volume. It also has been demonstrated that the combination of low incident angle and measurement frequency in the C-band range does not minimize the effect of surface roughness for passive microwave measurements. This result is significant in view of the fact that this combination of frequency and incident angle has been described as the optimum combination for minimizing the effect of surface roughness on the response of radar-backscatter measurements to soil moisture.

A Multiple Beam Synthetic Aperture Radar Design Concept for Geoscience Applications

The multiple beam synthetic aperture radar (SAR) has been presented as a superior alternative to conventional side-looking SAR designs for mapping earth resources from space. The multiple beam approach provides wide swath coverage at nearly constant incident angle while conserving peak power. These desirable system characteristics, however, are realized at the expense of additional signal processing. A design example illustrates the attributes of the multiple beam SAR in comparison to a conventional side-looking system. A novel beam formation processing architecture is shown which can provide simultaneous range compression while forming the beams. A configuration for the image formation processor is proposed and analyzed in terms of an analog implementation which can perform Doppler compression at speeds faster than real time. These implementation schemes indicate that on-board processing for the multiple beam SAR is possible.

Antenna Effects in Depolarization Measurements

The depolarization of electromagnetic energy scattered from natural terrain has been of interest to experimenters and theoreticians for many years. However, the reported measurements have not agreed with theoreticaly predicted results. Boresight axial ratio has commonly been used as a figure of merit to describe the polarization isolation properties of the measurement system antennas. Since depolarization measurements from terrain involve extended targets which fill the full antenna beam, boresight axial ratio is often an inadequate measure of antenna polarization purity. This paper describes antenna isolation characteristics which impact the quality of the depolarized measurements. Representative calculations demonstrate the effects of nonideal antenna systems on the observed measurements. A criterion for antenna specification is given which will provide high-quality cross-polarized measurements.

Volumetric Effects in Cross-Polarized Airborne Radar Data

In recent years the detection of soil moisture using remote sensing technology has become of interest to investigators and a variety of state and federal government agencies. The parameter of interest is important in agricultural, meteorological, biological, and hydrological applications. The use of active microwave devices has shown to provide capability for remote measurement from space. Problems do exist however, in isolating moisture information from the effects of other parameters such as roughness and vegetation. Of special concern is the suppression of the roughness effects in the radar return. This paper presents an analysis of airborne cross-polarized radar measurements of agricultural scenes. The relative responses of the system to moisture and surface roughness are presented and compared to predicted responses using radar backscatter models. It is shown that the depolarized model predictions are sensitive to soil moisture, but are much less sensitive to surface roughness effects.

A Microwave Sensor for Steam Quality

In this paper, a microwave-based in-line sensor for steam quality is described, and test results are reported. The sensor employs a novel high-pressure process seal that minimizes mismatch effects when water condenses on its inner surface.

Process composition monitoring at microwave frequencies: a waveguide cutoff method and calibration procedure

A versatile and robust microwave instrument for measuring the composition of various mixtures of known constituents is presented. Measurement is achieved by examining the propagation cutoff characteristics of a section of waveguide that is typically comprised of a section of process piping that is filled with the material under test. A calibration method that is simple to implement for industrial applications is presented and described in detail. Data from several successful commercialized applications are included. The microwave cutoff method offers significant advantages over more traditional microwave-measurement techniques.

Artificial Neural Network Analysis of Microwave Spectrometry on Pulp Stock: Determination of Consistency and Conductivity

A method for calibrating a microwave sensor is described. The method utilizes an artificial neural network trained to infer the consistency and conductivity of pulp stock slurry from the measured output spectrum of a microwave instrument. The method is both efficient and robust for extracting the multiple parameter information from the microwave signal output

A low cost ultra-wideband pulse transceiver

A low cost pulse transceiver has been developed for measuring the electrical properties of materials. The transceiver generates an ultra wide band (UWB) pulse as well as samples the received pulse. The pulse generator has been designed using a silicon-germanium (SiGe) analog comparator which is a possible alternative to step recovery diodes. The pulse is received by an extended time sampling circuit. The sampling circuit presented is an alternative design that does not require the use of a broadband balun.

A tunable UWB pulse transceiver for microwave applied metrology applications

An ultra-wide band pulse transceiver has been developed using integrated circuits which demonstrates a tunable 10dB bandwidth from 1.4 GHz to 3.3 GHz. The transceiver has a synchronous receiver which demodulates and extends the pulse in time using Equivalent Time Sampling (ETS) techniques. Equivalent time sampling has been shown to accurately reconstruct the RF pulse with an ETS factor up to 1.5 million. The RF front-end mixer has a 9dB of conversion loss with a 1dB compression point at -1dBm.