Combined Thickness and Permittivity Measurement of Thin Layers with Open-Ended Coaxial Probes

Abstract

This paper presents a method to simultaneously determine the thickness and permittivity of thin layers from multi-frequency reflection coefficient measurements using an open-ended coaxial probe. This is achieved by exploiting that the probe becomes radiating at frequencies higher than the probe’s typical operating range. Permittivity information is extracted from measurements in the typical frequency range, whereas thickness information is obtained from high frequency measurements by exploiting resonances that occur when the radiated waves are reflected at the layer boundary. A finite element model of the measurement set-up is made in COMSOL MultiphysicsTM, and a matrix of simulations spanning the relevant layer thicknesses and permittivity range is generated. The measured permittivity spectra of unknown samples are compared to the simulation matrix to estimate layer thickness and permittivity. The method is verified by measurements of water–ethanol mixtures. An application example where the water fraction and layer thickness of a gas hydrate deposition layer is estimated from permittivity measurements in a multiphase flow loop is also presented.

Noncontact monitoring of thin hydrate layers with microwave cavity resonator

“…Permittivity measurement as a fast and accurate tool makes it a potentially real-time monitoring technique for layer thickness and component ratio evaluation in closed systems. 10 Open-ended coaxial probes mounted nonintrusively can measure permittivity in a small aperture close to the wall, 11 but the terminal of probes must penetrate the pipe wall and contact the measured media. Microwave resonators obtain more sensitive sensing because of their high Q-factor, [12][13][14] and resonator type sensors have been used in interface detection.…”

Study on the Formation and Disassociation Process of Hydrate in Porous Media by Permittivity Dispersion Measurement

“…it is meaningful to study the formation process of hydrate crystals [13], [14]. For the formation of gas hydrates in emulsions gives rise to a change in the bulk permittivity, the dielectric spectroscopy obtained with open-end probe was found to be a potential technique for the detection of gas hydrates in emulsified systems [15], [16], e.g.…”

Combined Thickness and Permittivity Measurement of Thin Layers with Open-Ended Coaxial Probes

“…In these cases, the probe will sense an effective permittivity that depends on the thickness of the dielectric layer and the permittivity of both the dielectric layer and the backing material. The objective of this paper, which is an extension of a conference paper [11], is to present a methodology for obtaining both layer permittivity and layer thickness of relatively thin dielectric layers from measurements with open-ended coaxial probes. The focus is on liquid layers and deposits that grow directly on the probe, such that good contact between the probe and the material under test is achieved.…”