A Low-Cost In Situ Monitoring System for the Measurement of Losses in Resonant Cavities.

Resonant cavities can be used as tools for the measurement of material parameters. Usually a material sample is placed inside and a network analyzer is connected to the cavity and measures their S-parameters from which the resonance parameters are extracted. The cost of such laboratory equipment is high (usually multiple tens of thousand dollars) and its shape factor is large, which limits its usefulness for in-situ applications. And especially if one is only interested in the electrical losses of the material under test, the measurement of S-parameters is superfluous. We will show that it is sufficient to determine the wave attenuation by measuring the integral power loss over a broad bandwidth. Only a low-cost noise generator and a power detector diode is needed for this method. With our inexpensive setup (below $10), we were able to determine e.g. the dielectric losses of water at microwave frequency in close agreement with the literature.