关键词: 颗粒状农产品, 介电特性, 测量, 微波频段

Abstract: Dielectric properties are of important value in the application of microwave hot processing of agricultural products. A scheme for measuring the dielectric properties of agricultural products based on uncelebrated coaxial transmission reflection method and modified general effective medium formula (MGEM) was proposed, in which the granular agricultural products were taken as the research object. Dielectric property data of rapeseeds, coarse cereals and grass seeds in the microwave frequency band were measured. Relevant key issues were then analyzed and discussed. These results demonstrated that the measurement scheme could be used to measure the dielectric properties of particulate agricultural products at high frequency, and the dielectric properties of granular agricultural products under the room temperature were related with microwave frequency and water (oil) content. Such relationship met the corresponding relational equation. Given the microwave frequency 2.45 GHz for civil use and the water content M∈(2%,25%), the dielectric constant was between 3.5 and 9, and the loss factor was between 0.1 and 2. This study provided a reference method for  measurement of dielectric properties of granular agricultural products, and the basis for the design of microwave drying and nondestructive testing devices for agricultural products. The technological method was suitable to measurement and analysis of dielectric properties of other small granular substances.

Key words: granular agricultural products, dielectric property, measurement, microwave frequency band