Non-destructive permittivity measurement of solid materials

An open-coaxial probe suitable for measuring the permittivity of solid materials has been designed and tested. The peculiar structure of the probe allows an easy and firm contact with the surface of the material under measurement, resulting in highly reliable and reproducible dielectric measurements. The permittivity measurement is absolute, as the calibration procedure - based on a genetic algorithm - does not require the use of dielectric standards. The measurement system - including the probe, a network analyser, and the numerical code to determine the permittivity from reflection measurements - have been tested on solid materials of known properties, and used for determining the dielectric characteristics of several types of wood.