Homma KYOJI (本間 恭二)

A prospect system is offered to detect the plant vermin (e.g. larva of lamellicom beetle) living in the soil without digging up the soil by using a C-band microwave sensor (mean frequency: 5GHz). The characteristic of the prospect system is required to detect explicitly the behavior of vermin moving underground in the vicinity of the surface. The prospective characteristic, however, is limited by the magnitude of microwave attenuation (attenuation constant α) traveling in the soil which is depended on water contents of the soil. First of all, relation of microwave attenuation and water contents of the soil is measured for "Akadama" soil and "Kanuma" soil with uniform grain size, which are fundamentally used in gardening. Detectable critical transmission depth of soil for each water contents is confirmed as the result of the experiment. α was detected quantitatively varying the magnitude of vibration amplitude of mini-speaker (frequency: 1Hz, displacement: 0.1mm, 0.2mm, diameter of diaphragm: 25mm) embedded in the water content controlled soil (volume water contents: 0.3g/cm^3). In this case, detectable critical transmission depths of soil were 105mm, 125mm for the displacement amplitude 0.1mm, 0.2mm. The real movement of the larva of lamellicom beetle (head around width: 4mm, body length: 25mm) embedded in the soil was measured using the system. Critical transmission depths of the soil were 200mm and 100mm for the case of α: 0.1Np/cm and α: 0.2Np/cm. It was confirmed that the system is able to detect the vermin, if the moisture content of the soil is small.