RESONANT-CAVITY PERTURBATION - SOME NEW APPLICATIONS OF AN OLD MEASURING TECHNIQUE

Microwave resonators have been used as sensors for determining materia l properties of dielectric objects, including permittivity, density, m oisture content, and mass, from measurements of frequency shift and ch ange in cavity transmission characteristics when a small dielectric ob ject is inserted into a microwave resonant cavity. Fundamental princip les of the shape- and size-independent measurements are discussed, and experimental results for moisture content and mass measurement of ind ividual soybeans, peanuts and grain kernels, as well as for mass deter minations on irregularly shaped objects of common plastic materials ar e presented. Measurements are fast, nondestructive, contactless, and h ave the potential for continuous operation.