Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/1998
Publication Date: N/A
Interpretive Summary: Insects that infest grain in storage account for vast economic losses. Many physical and biological methods for controlling such insects have been studied because of potential health hazards of pesticides, but treatment with chemical pesticides is still essential for protection of grain from stored-grain insects. Treatment of infested grain by high frequency and microwave dielectric heating can be effective, but the costs have been too high for practicability. New interest in controlling stored-grain insects with higher frequency microwave energy than has previously been explored has indicated the need for information on the dielectric properties of the insects at these higher frequencies. The relative values of the dielectric properties of the grain and the insects are important in determining the possibility for selective heating of the insects. Therefore, these properties of adult insects of the rice weevil, red flour beetle, sawtoothed grain beetle, and lesser grain borer were measured at frequencies from 200 MHZ to 20 GHz Earlier studies showed that frequencies between 10 to 100 MHZ were much more effective than frequencies up to 12 GHz in controlling the insects in infested grain. The new data indicate that no advantage, compared to the lower frequencies, can be expected for microwave frequencies up to 20 GHz. However, the new data will be helpful to those who continue to explore the possibilities for insect control with microwave energy.
Technical Abstract: The permittivities of bulk samples of adult insects of the rice weevil, red flour beetle, sawtoothed grain beetle, and lesser grain borer were measured at single frequencies of 9.4 and 11.7 GHz in X-band waveguide at about 23 deg C, and permittivities of homogenized samples of the same species were measured from 0.2 to 20 GHz at temperatures from 10 to 70 deg C with an open-ended coaxial-line probe and network analyzer. Sample densities for the coaxial-line probe measurements were determined from the X-band measurements with a linear relationship between the cube root of the dielectric constant and sample bulk density determined from permittivity measurements on bulk rice weevil samples in a waveguide sample holder taken with the short-circuited line technique. Since linearity of the cube root of the dielectric constant with bulk density is consistent with the Landau & Lifshitz, Looyenga dielectric mixture equation, this equation was used to ocalculate estimated dielectric constants and loss factors of the insects from measured permittivities and volume fractions determined from measured bulk density and adult insect density determined by air-comparison pycnometer measurements. Estimated dielectric constants and loss factors of the insects are presented graphically for temperatures from 10 to 70 deg C, and tabulated data are provided for range information and comparative purposes.