Characterization of Hydrogen-Bonded Liquid Crystal Materials in the Millimeter-Wave Region

A novel liquid crystal (LC) materials consisting of hydrogen bonding are investigated in the millimeter-wave (MMW) frequency region of electromagnetic wave spectra. Relative permittivity (or refractive index) and loss tangent (or absorption coefficient) are evaluated using a rectangular waveguide test cell and are compared with those values of conventional LC materials. The most unusual result is that the refractive index anisotropy increases significantly in the MMW region comparing with that for visible light, which is contrary to what is observed in the conventional LC materials. Although the anisotropy, which determines the tunability of LC devices, is not so large in this stage, the loss tangent is as small as, or better than, those of the excellent conventional-type LC materials synthesized for the microwave applications. We find out a potential of the hydrogen-bonded LCs as one of the best classes of LC materials for MMW application.