CONTACTLESS MASS DETERMINATION OF ARBITRARILY-SHAPED DIELECTRIC OBJECTS

Microwave resonant cavities have been studied as possible sensors for rapid determination of the mass or weight of perturbing dielectric obj ects of given permittivity and density, but of arbitrary shape, insert ed into the cavity. Tracking the coordinates of the peak of the resona nt curve with and without the object, i.e. measuring shift of resonant frequency and change in the cavity Q-factor, provides information tha t together with a calibration equation is sufficient for the object ma ss or weight determination. During the calibration procedure, the para meters of the empty cavity, as well as the permittivity and the specif ic gravity of the object material must be known. The measurement techn ique does not, in principle, require any contact between the object an d the measuring system, and measurements can be rapid and reasonably a ccurate. Basic principles of the shape-independent measurements are pr esented, and experimental results are given for common plastic objects of irregular shapes measured in resonant cavities operating at 640 MH z and 1.7, 2.5 and 3.2 GHz.