Wideband and noncontact characterization of the complex permittivity of liquids

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Abstract
The noncontact evaluation and characterization of liquids, especially chemically active reagents, is a problem for many industries, and currently there is no method available to characterize such liquid samples. In this paper, we present the results of the noncontact measurement and characterization of liquids and powders using a free‐space system. It is already established that the characterization of solids and nonuniform samples is possible using the spot‐focused free‐space measurement system from 5 to 110 GHz. Since the measured 3 dB spot size of the focused beam is 4.37 cm×3.2 cm at 9.1 GHz, only small samples are required, and the inaccuracies in free‐space measurement due to diffraction were minimized for samples of three times the spot size. The far‐field focusing ability of the horn‐lens antennas is helpful in designing a simple and noncontact wideband measurement system for the characterization of liquids. This noncontact method has the advantage of characterizing samples in high‐ and low‐temperature environments, which should find wide applications in industry forin situmaterial characterization. This method is readily applicable to monitoring the curing of polymers and gels, as well as thick‐film coating characterization in the wet state. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30: 75–79, 2001.

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