Dielectric spectroscopy of a thin surface layer by differential time-domain reflectometry using a coplanar waveguide circuit line probe

Dielectric spectroscopy is a powerful method for measuring the relaxation properties of various materials, especially soft materials. Among these soft materials, living systems and artificial multilayer films have layered structures with a thickness on the order of nano- to micrometers. To measure the dielectric spectra of such a thin layer, the measurement probe for dielectric spectroscopy requires the structure to possess a low measurement depth that is comparable to the thickness of the thin layer. For this purpose, we developed a probe for measuring the dielectric spectra of material surfaces of various depths using differential time-domain reflectometry. The developed probes consist of coplanar waveguide circuits of 280 µm to 1 mm line width, which allows for the measurement of the dielectric spectra of the material surface layer with thicknesses in the range of 450 µm to 1.2 mm. The proposed structure of the measurement probe enables the dielectric spectroscopy of a thinner material surface layer by reducing the width and pitch of the coplanar waveguide circuit lines. (paper)