Wideband and noncontact characterization of the complex permittivity of liquids

The noncontact evaluation and characterization of liquids, especially chemi cally active reagents, is a problem for many industries, and currently ther e 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 establishe d that the characterization of solids and nonuniform samples is possible us ing the spot-focused free-space measurement system from 5 to 110 GHz. Since the measurement 3 dB spot size of the focused beam is 4.37 cm X 3.2 cm at 9.1 GHz, only small samples are required, and the inaccuracies in free-spac e 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 fo r 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 for in situ material characteriz ation. This method is readily applicable to monitoring the curing of polyme rs and gels, as well as thick-film coating characterization in the wet stat e. (C) John Wiley & Sons, Inc.