Multifrequency Sensing of Large-Sized Dielectric Boards

摘要

After introducing some possibilities and related problems of microwave moisture measurements, a non-destructive testing method of large-sized dielectric boards is shown, which is based on a microwave free-space /double transmission/reflection type two-parameter complex vector measurement. Using this basic idea, a 5.8 GHz monitoring system was developed (see Figure 1), which is used for moisture content measurement and quality forecast of particleboards continuously, before mechanical testing would be accomplished. recalling some basic equations, the calculation of Kasa's circles, dry wood basic weight, complex permittivity values, absolute moisture content and mechanical properties of composite boards, also are shown. Low cost MMICs, self-designed microstrip antennas and passive detector/backscatterers are used in the instrumentation for the realization of the concept.