Digital Emulation of Dielectric Relaxation Functions for Capacitive Sensors of Non-Destructive Dielectric Spectrometry

Abstract

This paper addresses a problem of reference means for the adjusting, calibrating and testing of nondestructive dielectric spectrometers employing one-side access capacitive sensors. Due to specific features of these sensors caused by non-homogeneous electric exciting fields, the application of the conventional reference means, particularly the artificial ones, is not always possible. We propose to solve the problem by digital emulation of dielectric relaxation functions for capacitive sensors. A digital emulator is developed for one-side access capacitive sensors with active guarding for the spectrometers, working according to a two-port network measuring model. The test results are provided for digital emulation of the responses of the capacitive sensor system to sinusoidal excitations, corresponding to complex dielectric permittivity described by the Debye relaxation function, with varying of the real part of dielectric permittivity from 1 to 100, over a frequency band from 10 Hz to 0.33 MHz.

The Impact of Atmospheric Parameters on the Dielectric Permittivity Values of SikaBlock®-M150 and Other Rigid Polyurethane Foams Measured with a Capacitive One-Side Access Sensor

“…Stray-immune capacitance measurements were made, using active guarding of the sensing electrode to increase the sensitivity and accuracy of measurements. The spectrometer consists of three main blocks: a multi-frequency excitation generator, a capacitive sensor system (CSS) of a one-side access type, and a multi-frequency response signal-processing unit [ 14 ], Figure 1 .…”

“…By suppressing the electric field between the driven electrode and the sensing electrode outside the working surface of the sensor, the solution, proposed for CSS in [ 11 ], prevented any impact of stray capacitances on the output signal and ensured that the current through the sensing electrode was proportional to the capacitance between the driven electrode and the sensing electrode. This capacitance was denoted as the sensing capacitance C 0 when the CCS was in air; when the test object was put on the capacitive sensor without a gap, the sensing capacitance C 0 was multiplied by the complex dielectric permittivity of the test object—the sample [ 14 ].…”

“…[ 7 , 8 ]. The method had wider application with developing capacitive one-side access (COSA) sensors [ 11 , 12 , 13 , 14 , 15 ]. They allow NDE by applying the sensor to one side of the testing object, without making test samples.…”

Polytetrafluoroethylene Films in Rigid Polyurethane Foams’ Dielectric Permittivity Measurements with a One-Side Access Capacitive Sensor

“…Permittivity was measured with an innovative, experimental dielectric spectrometer equipped with a capacitive sensor of OSA type [ 21 ]. Stray-immune capacitance measurements were carried out by using active guarding of the sensing electrode to increase the sensitivity and accuracy of the measurements.…”

“…The following test objects were investigated: (1) single samples of PUR foams and monolithic polyurethane, diameter D = 45 mm, thickness h = 20–25 mm, Figure 1 , and (2) complex samples “A single PUR foams’ sample + PTFE film”. The true dielectric permittivity spectra ε t were measured on single samples, when calibration of the spectrometer was made before the measurement series, with regard to the measurement value, delivered by the OSA sensor in air [ 21 ].…”