Complex Permittivity Data Research Articles

Broad-band simultaneous measurement of the complex permittivity tensor for uniaxial materials using a coaxial discontinuity

A technique is presented for simultaneously measuring the complex values of the permittivity tensor of uniaxial materials. A gap in a coaxial line is filled with the material under test. Complex elements of the permittivity tensor are computed from measurements of the S-parameters (S/sub 11/ and S/sub 21/) made on the gap taking into account higher order modes excited at the discontinuity. The authors demonstrate that this problem is reduced to two systems, each containing three equations with three unknowns. Computer time is therefore reasonable without affecting accuracy. Measured complex permittivity data from 45 MHz to 18 GHz are presented. Good agreement between calculated and generally accepted values is obtained. >

Generalization of the Böttcher relation to time-dependent fields in the case of isotropic dielectrics

The static Böttcher relation, deduced from a physical electrostatic cavity model, is generalized for time-dependent fields. Its application is tested with the complex permittivity data for toluene, di-n-butylether, chlorobenzene, acetonitrile and water. Comparison and discussion have been made with the classical Cale-Cole representation.

Soft mode behaviour of a room temperature ferroelectric liquid crystal

Abstract The complex dielectric permittivity was studied in the frequency region 100 Hz ÷ 100 kHz in the vicinity of the SA→ SC* phase transition temperature Tc = 32°C for benzoic acid 4-octyloxy 4–|(2-methyl butyloxy) carbonyl | phenylester. The d.c. electric field of the intensity E = 4 kV/cm was used to unwind the helicoidal structure in S C* phase, therefore the contribution to ϵ from the Goldstone mode was eliminated. It was found that at 100 Hz the temperature dependence of the soft node contribution had the form of the Curie-Weiss law in both SA and SC* phases. At higher frequencies the maximum of ϵ at TC is lowered and at frequencies 10 ÷ 40 kHz a minimum appears. This behaviour was explained by the temperature dependence of the soft mode relaxation frequency fS which was evaluated by fitting the complex permittivity data to the Debye relaxation formula. It was established that fS depended linearly on temperature in SA as well as in SC* phases with a minimum of 1 kHz at TC.

The dielectric spectrum of water in the microwave and near-millimetre wavelength region

A combined analysis of complex permittivity data from the literature is presented for H 2O from 10 to 40° C. Included are numerous microwave data measured by spot frequency methods and recent far-infrared data determined by dispersive Fourier transform spectroscopy. The complex dielectric spectrum of water between 5 × 10 8 and 5 × 10 11 Hz can be well described by a relaxation process with a discrete relaxation time.

Refractive index measurements in liquids within the frequency region 50 to 600 GHz; complex permittivity of C6H5Cl, CH3Cl and CH2Cl2

For a complete specification of molecular processes involved in rotational dynamics it is necessary to have both the absorption spectra and their dispersive counterparts for frequencies ranging from static to infrared. The authors describe an extension of their experimental set-up for measuring the absorption coefficient alpha over the frequency range 50-600 GHz to measure also the refractive index n. They are now thus able to bridge the gap in complex permittivity data between the microwave and the far-infrared domains. Refractive index is measured using the polarising Martin Puplett interferometer in monochromatic mode of operation, with accuracies of better than 1% over all the covered frequency range. Results of calibration measurements with liquid chlorobenzene (C6H5Cl) and sample absorption-dispersion data for two other liquids, chloromethane (CH3Cl) and dichloromethane (CH2Cl2), are also presented.