RF AND MICROWAVE DIELECTRIC PROPERTIES OF STORED-GRAIN INSECTS AND THEIR IMPLICATIONS FOR POTENTIAL INSECT CONTROL

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 23C, andpermittivities of homogenized samples of the same species were measured from 0.2 to 20 GHz at temperatures from 10 to70C with an open-ended coaxial-line probe and network analyzer. Sample densities for the coaxial-line probemeasurements were determined from the X-band measurements with a linear relationship between the cube root of thedielectric constant and sample bulk density determined from permittivity measurements on bulk samples of the adultinsects in a waveguide sample holder taken with the short-circuited line technique. Since linearity of the cube root of thedielectric constant with bulk density is consistent with the Landau & Lifshitz, Looyenga dielectric mixture equation, thisequation was used to calculate estimated dielectric constants and loss factors of the insects from measured permittivitiesand volume fractions determined from measured bulk density and adult insect density determined by air-comparisonpycnometer measurements. Estimated dielectric constants and loss factors of the insects are presented graphically fortemperatures from 10 to 70C, and tabulated data are provided for range information and comparative purposes.