Dielectrics property verification

Verification of dielectric properties, limited to power frequency voltage withstand or HV test on power as well as control and protective circuits. 

The switching memory effect is a reflection of the fact that the electric displacement, being the function of both the applied field and the material s properties, needs some finite time to adjust to the value of the electric field. The widely accepted model of the instantaneous relationship between the electric displacement and the electric field in the NLC is invalid when the characteristic times of the director dynamics are close to the relaxation times for molecular permanent dipoles. This time scale is typically in the submillisecond range which is of great interest for modem fast-switching devices. The electric displacement (as well as the dielectric torque density) becomes a function of the static dielectric properties of the NLC, the present and past electric field, and the present and past director. We discussed the recently proposed theory and experimental verification of the phenomenon [11]. The model in Ref [11] should be applicable to dynamic reorientation of other LC phases in the appropriate range of times/frequencies. In the case of ferroelectric LCs, the theory should be supplemented by the consideration of spontaneous electric polarization. A similar approach should be also... 

The measurements of physical properties can be categorized as direct or indirect. In the former are included measurements of stress relaxation, creep compliance, and dielectric relaxation. In these experiments an excitation is applied which induces a direct change of mechanical parameters, and a response is observed as a result of this change. In these direct e q>eriments the contribution from stress concentrations is inevitable. The indirect mefhod may entail the measurement of fluctuations. For example, NMR spin-lattice relaxation time (Ti) is a fluctuation quantity. No change is induced in the mechanical properties during the indirect measurement this analysis is therefore free from the stress concentrations. If the information from direct measurement is equivalent to that from indirect measurement, we can estimate the former through the measurement of the latter without the influence of the stress concentrations. The equivalence of these two measurements is guaranteed by the "fluctuation-dissipation theorem" (1,2). In the next section we will try an experimental verification of the theorem for fresh fiber san les. 

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