Submitted to: Institute of Electrical and Electronics Engineers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/1997
Publication Date: N/A
Interpretive Summary: As a result of concern for environmental quality and public health, certain fumigants and insecticides that have been used in the past to control stored-grain insects are no longer available. Therefore, new methods must be investigated for the potential development of alternative insect control techniques. One such method, explored a few decades ago, has gained renewed interest because of advancing microwave technology. A fundamental requisite to the consideration of stored-grain insect control by the application of microwave energy is information on the dielectric properties (electrical characteristics) of the insects and the grains that they infest. Data are available on the microwave dielectric properties of grains, but such information on insects is not available at microwave frequencies above 12 GHz. Therefore, a relatively new technique has been adapted for the measurement of the microwave dielectric properties of a common stored-grain insect, the rice weevil. The purpose of this report is to describe the equipment built to obtain these measurements at different temperatures between 10 and 65 degrees C, the techniques used for sample bulk density correction, and the presentation of new data on the microwave dielectric properties of these insects at frequencies between 200 MHz and 20 GHz. These measurements provide data useful in the modeling of microwave energy absorption of insects in grain for analyses to assess the potential for insect control methods by microwave power applications.
Technical Abstract: The dielectric permittivities of bulk samples of adult rice weevils were measured over the frequency range from 0.2 to 20 GHz at temperatures from 10 to 65 C with an open-ended coaxial-line probe, network analyzer, and a sample temperature control assembly designed for the measurements. Repeated measurements were highly variable, because mean sample bulk densities did not accurately reflect effective densities of the bulk rice weevil samples in the small volume of sample sensed by the coaxial-line probe. Density corrections based on earlier permittivity measurements on bulk rice weevil samples at 9.4 GHz, at known sample densities, removed much of the variability. The corrections utilized the linear relationship between the cube root of the dielectric constant and bulk density, which permitted estimates of the weevil body permittivities to be obtained with the Landau & Lifshitz, Looyenga equation for dielectric mixtures. Estimated dielectric constants and loss factors of the insects from averages of eight different measurement sequences are presented graphically for temperatures from 15 to 65 C.