Design Of Microwave Moisture Content Instrument

In many industry and agriculture production process, certain materials moisture contents have important influence to the product performance quality and the production efficiency. In some situation, request on-line and nondestructive measurement, then realize the on-line closed-loop control to the entire production technological process, which propose higher requirement for the moisture content measurement method. Using the microwave technology for the material moisture content measurement, can achieve the on-line real-time accurate measurement, also has good reliability and strong antijamming ability , and is insensitive to the color, the structure and so on the influence of the material, may examine the interior moisture content of the material , the measurement result has the representation, therefore has the broad application prospect.Microwave is one kind of high frequency electromagnetic wave,and the matter's absorption and reflection performance to it is mainly decided by matter's permittivity. In microwave frequency, the water permittivity is much bigger than any other solid materials, when the microwave through the matter contained water, the microwave energy loss caused by the moisture content is remarkable, and measuring the power attenuation, the phase change, the resonance frequency and so on the permittivity correlation physical quantity, might measure the moisture content of the material, this namely for microwave moisture content measurement principle.This article introduced the microwave moisture content measurement theory, method, experiment(using transmission weaken law), and microwave device; researched and compared the characteristic of kinds of nowaday microwave simulation softwares, and the simulation design with Ansoft corporation HFSS 3D electromagnetic field simulation software to partial microwave devices , including waveguide type varible attenuator, optimum H funnel-shaped antenna, optimum pyramid funnel-shaped antenna, has been carried on, and achieved certain target, which was a new attempt applying the microwave simulation technology in the instruction practice.According to the microwave rectified output signal characteristic, designed and completed the corresponding moisture content detection system. Signal processing electric circuit including chose frequency amplifier, rectification filter circuit, and made its output adapts the A/D transformation scope; MCU system realized data acquisition, data processing and through MAX7219 demonstration function with the AT89C52 MCU; the software design using the KeilC language was completed under the keil uVision2 integrated environment, from these realizes the intelligent moisture content meter design.