Dielectric relaxation step response

Bioimmittance is frequency dependent. In dielectric or electrolytic models there is a choice between a step (relaxational) and sinusoidal (single-frequency) waveform excitation. As long as the step response waveform is exponential and linear conditions prevail, the information gathered is the same. At high voltage and current levels, the system is nonlinear, and models and parameters must be chosen with care. Results obtained with one variable cannot necessarily be recalculated to other forms. In some cases, one single pulse may be the best waveform because it limits heat and sample destruction. 

The dielectric relaxation techniques can be sub-divided into two groups step response or continuous wave methods,... 

The phenomenological theory of the dielectric relaxation behaviour of linear systems is well-established [1-5]. The fundamental relationship joining the frequency-dependent complex permittivity c(cu) measured at frequency / = (ofln and the transient step-response function t) is the Fourier transform relationship... 

We now turn to the discussion of the so-called Debye model that allows one to account for the relaxation processes with a finite t in the expressions for the electric displacement and the dielectric permittivity. To obtain the explicit dependencies, one should know the step response function which is generally unknown. Debye assumed that, once a constant external electric field is applied, the equilibrium state of an isotropic dielectric is achieved through an exponential relaxation, i.e.. 

DC Transient-Current Method. In this method a step voltage is applied to the sample and the current response is measured by a fast-response electrometer. For the single- relaxation-time model, the current response would be given by equation (7-9). In recent years this method has been of renewed interest because with the advent of modem computing methods, it is possible to Fourier-transform the response in the time domain to obtain the frequency response. Several Fourier-transform dielectric spectrometers have been designed. We may note the one of historical significance due to Johnson et al.15, as well as modem commercial instruments.16 The method has the great... 

Fig. 25.6 shows the curves of logxo as a function of frequency (g>) for some typical materials. Contrary to the plots of non-protonic materials, steps are observed between <7 and according to the presence of well-defined relaxations. This shows that the monotonic universal dielectric response is an oversimplification. In the case of CSHSO4 at room... 

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