Maria A. Rzepecka

Permittivity Measurements at Microwave Frequencies Using Lumped Elements

A simple frequency-domain method for measurement of the dielectric properties of materials is described. Theoretical analysis of the frequency dependence of the reflection coefficient of a shunt lumped capacitor located at the end of a transmission line and filled with a very small amount of the dielectric (typically a few microliters) is given. Analysis and calculations of the overall uncertainty in permittivity measurements, as well as experimental results for some normal alcohols, are presented and limitation of the method discussed.

A Lumped Capacitance Method for the Measurement of the Permittivity and Conductivity in the Frequency and Time Domain-A Further Analysis

Further discussion of a lumped capacitance method for measurement of the permittivity and conductivity of materials in the radio and microwave frequency ranges is presented. The analysis of the method applicable in both frequency and time domains is given for materials having low frequency conductivity or Debye dispersion.

A Cavity Perturbation Method for Routine Permittivity Measurement

ABSTRACTA novel method of permittivity measurement by a cavity perturbation technique at microwave frequencies is suggested. The method employs a frequency counter for the determination of a cavity Q factor instead of a rather sophisticated circuitry previously used.The principle of operation, uncertainty analysis and measurement set up are described. The structure of the resonator and the sample holder permit continuous control and monitoring of a sample temperature. The method was verified experimentally by measuring a few substances of known permittivities. Dielectric properties of several foodstuffs measured using this method are reported.Both the analysis and the experiment showed that the accuracy of the method is comparable with that of the most accurate methods employing frequency markers while the measurement procedure is simpler and the equipment needed is usually easily available.

Permittivity of Some Dairy Products at 2450 MHzAmendments to the U.S. Department of Health, Education, and Welfare Microwave Oven Performance Standard*

ABSTRACTThe permittivity of several dairy products was measured using a cavity perturbation method at a frequency of 2450 MHz in the temperature range from —10°C to 7O°C and in the moisture content range typical for these products. Materials examined were non fat milk powder, whey powder and commercial butter. The experimental results were compared with theoretical predictions derived from the mixture theory.

A Microwave Open-Ended Cavity as a Void Fraction Monitor for Organic Coolants

A novel application of an open-ended microwave cavity in the field of on-line nuclear instrumentation, specifically to the determination of the void fraction in organic coolants used for cooling nuclear reactors, is presented. The sensor consists of a section of circular waveguide inserted in series with the piping system transporting the coolant. For the selected frequency of operation, the sensor section forms a resonant cavity whose resonant frequency, being a measure of the void fraction, can be automatically and continuously monitored by an electronic system.

Monitoring of Concrete Curing Process by Microwave Terminal Measurements

The feasibility of applying microwave techniques for nondestructive testing of concrete strength during the curing process is investigated in terms of the dielectric permittivity variations during the process. The experimental data show that the interrelation between permittivity and strength of concrete can be established.

Modified Infinite Sample Method for Routine Permittivity Measurements at Microwave Frequencies

A modified infinite sample method for routine permittivity measurements of granular or powder as well as liquid materials is described. The method permits continuous monitoring of the temperature, moisture content, and density of the test sample. Analytical and graphical solutions, which lead to the material permittivity from experimental data and measurement uncertainty, are presented. The method is particularly valuable when a large number of samples must be tested as a function of temperature, moisture content, and density, or when a continuous monitoring of the permittivity is required during irradiation by microwave power.

High-Frequency Monitoring of Residual and Bound Water in Nonconductive Fluids

This paper presents a novel application of open-ended microwave cavities for monitoring residual water content or bound water content in nonconductive fluids transported in circular pipes. The sensor consists of a section of a circular waveguide lined with a solid dielectric inserted in series with the piping system transporting the test fluid. At the selected frequency of operation, the end waveguides formed by the piping system operate below cutoff, while the sensor forms a resonant cavity. The resonant frequency of the cavity, which is a measure of the water content in the test fluid, is monitored automatically by an electronic system.

A Waveguide Applicator for Irradiation of Samples At Controlled Temperature

abstractA new waveguide applicator for irradiation & small samples of aqueous solutions with microwave energy under controlled temperature has been developed. The principle of operation, the electrical and thermal designs of the applicator as well as the experimental results for a WR284 waveguide applicator operating at a frequency of 2.45 GHz are presented.