A Simple and Low-Cost Measurement System for the Complex Permittivity Characterization of Materials

A microwave planar resonant sensor, its equivalent circuit, and the driving electronics for the measurement of the complex permittivity in compact areas of the material under test are presented. Compared to transmission or reflection sensors, the adoption of a scalar two-port measurement procedure reduces the cost of the system and improves its robustness. The measuring system requires only the calculation of two parameters, namely, the resonant frequency and the 3 dB bandwidth, thus achieving a substantial reduction of cost and computation time. Such a sensor can be adopted in moisture measurement systems, and its low cost is such as to allow its use even in a disposable manner.