DIFFERENTIAL CAPACITIVE METHOD FOR MEASURING THE COMPLEX DIELECTRIC PERMITTIVITY OF GEOMATERIALS AND CONCRETE COMPOSITES

Authors

S.N. Verzunov Institute of Mechanical Engineering, Automation and Geomechanics of the National Academy of Sciences of the Kyrgyz Republic

Keywords:

dielectric permittivity, dielectric loss tangent, admittance, capacitive sensor, planar comb sensor, semi-cylindrical sensor, synchronous quadrature detection, geomaterials, concrete composites

Abstract

The article considers the methodological and circuit-design foundations for building a laboratory bench intended to implement an experimental method for measuring the complex dielectric permittivity of geomaterials and concrete composites in the frequency range of 100 Hz–10 kHz. A differential “measuring–reference” approach is proposed, in which the informative signal is extracted as an imbalance signal followed by synchronous quadrature detection and digital balancing of the reference channel. Two variants of capacitive sensors are studied for samples of different geometry: a planar comb sensor for disk-shaped samples and a semi-cylindrical sensor for cylindrical cores. For the planar sensor, a technologically reproducible geometry is substantiated, simplifying fabrication and matching the sensing element parameters with the characteristics of the analog-to-digital path. It is shown that, in the low-frequency region, the measurement result is substantially affected by air gaps at the sensor–sample boundary, parasitic capacitances to ground, surface leakage currents, and amplitude-phase mismatch of the channels. Engineering estimates of sensor capacitance, reactance and measurement signal levels are presented and used to select gain factors, ADC range and digital processing parameters. The obtained results can serve as a basis for further experimental verification, numerical modeling of the electric field and development of specialized measurement modules for intelligent geotechnical monitoring systems.

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