Silver-gelatine metal-dielectric composites made from developed X-ray films

The artificial dielectric properties of developed silver-gelatine X-ray film have been evaluated at microwave frequencies. The density of the silver particles in the thin films on the surface of the plastic substrate determines the real and imaginary parts of the complex permittivity. The resulting metamaterial was evaluated between 5 and 20 GHz using the split-post dielectric resonator technique. The real part of the relative permittivity of silver-gelatine mixtures varies in the range 4-170 depending on the concentration of silver. The dielectric loss tangent for such materials is in the range 0.06-0.25 and is largest for the highest permittivity samples.Jerzy Krupka, Janusz Parka, Przemyłsaw Łoś, John G. Hartnett, and Karolina Naguszewsk

Dielectric Properties of Compounds Creating Dual-Frequency Nematic Liquid Crystals

In this paper we report how dielectric spectroscopy can help in creating of dual-frequency nematic liquid crystals. Dual-frequency nematic liquid crystals is new class of liquid crystal materials. Such mixture is usually formed by a combination of many components (even more than 10), which can be split into two groups: molecules having large transverse dipole moment and molecules with a large longitudinal dipole moment. The behavior of a base (parent) mixture, functional admixtures and final dual-frequency nematic liquid crystals mixture is investigated by dielectric spectroscopy in wide frequency (100 Hz-10 MHz) and temperature ranges. This allows us to find out why the dual-frequency liquid crystal has an important feature: positive and negative dielectric anisotropy at different frequencies. We present parameters of molecular motions around short (S-mode) and long (L-mode) molecular axes observed in investigated materials and discuss how the creation of final dual-frequency nematic liquid crystals mixture can modify molecular relaxations