Capacitive Probe Array Measurements and Limitations

This paper reviews the use of electrostatic capacitive probes for detections and evaluations of dielectric material properties and flaws. Interest in using both inductive and capacitive arrays for proximity sensing, surface feature characterization, material properties evaluation, and flaw detecting has increased steadily since the mid-1980’s [1–7]. Two other papers [6,7] in this proceedings also discuss the present state of the art, particularly with regard to the measurement of lossy dielectrics (complex permittivity). In traditional dielectrometry measurements (as well as in eddy-current measurements of material properties evaluation) varying the probe frequency has long been used as a tool for extracting information about dispersion and loss mechanisms. Use of a spatially periodic array probe interrogates the material, or flaw, with a field that penetrates into the sample to a degree determined by the periodicity. This controllable penetration phenomenon (artificial-skin effect or zoom effect) has been successfully exploited by Melcher, Zaretsky [5], and Goldfine [6] in what they call imposed w-k magnetometry and dielectrometry, using interdigital probes of different periodicities. Details are given in these proceedings. Gammell’s paper [7] gives a progress report on complex permittivity measurements using probes of more conventional type.