Uncertainty in multiple penetration depth fringing electric field sensor measurements

Measurement of multilayer material properties with fringing electric field dielectrometry sensors requires the processing of terminal admittance data from multiple electrode pairs. The choice of the algorithmic approach for data analysis is critical because of a high sensitivity to small measurement uncertainties. While individual channel uncertainties are usually within a reasonable instrumentation range, measurement of properties of multiple material layers fails unless special techniques are used to prevent numerical instabilities. This paper demonstrates the mechanism of uncertainty in a successive stair-step property estimation in which the estimates of one layer´s properties are used to estimate the subsequent layer´s properties. Three-wavelength measurements of dielectric permittivity and conductivity illustrate the problem in two-layer experimental setups. Limitations of the stair-step approach and possible future improvements are discussed.