Electric alternating/sinusoidal

When the applied constant potential is superimposed by an alternating (sinusoidal) potential signal of small magnitude (Eq. (3.40)), the certain periodic variations in current density and surface concentrations arise (see Eqs. (3.41)-(3.45)). It is possible to derive expressions for impedance from these equations assuming that the electric properties of the electrode can be represented by the resistance and capacitance in series. Then, the real and imaginary parts of the faradaic impedance are respectively ... 

Fourier transformation — In common with many other technologies, electrochemical instruments nowadays produce data in the form of a time series - a large array of numbers equally spaced in time. As an alternative to inspecting the data - usually electric current in electrochemical applications - in its raw time-series form, an alternative is to determine the amplitudes of the sinusoidal frequencies present in the signal. Fourier transformation is the procedure by which the time series is analyzed into its component frequencies. This task is delegated to a computer, usually through a fast Fourier transform or FFT program. 

Optically linear media are characterized by a linear response of the medium (i.e. the charged particles therein) to the electric field. We consider an alternating electric field at position r which varies sinusoidally with time according to (8),... 

The experimental glass transition is, therefore, associated with a relaxing property - the enthalpy. The enthalpy/specific heat modes, in principle, couple to all phenomena which occur in the glass transition region. Enthalpy relaxation can be studied by applying a sinusoidal temperature pulse, much like an alternating electric field, which is applied to study dielectric relaxation. The specific heat is therefore treated as a frequency (of thermal field) dependent property. The traditional adiabatic technique cannot be applied because the time required for heat diffusion across the sample has to be short compared to the measurement time and the former is determined by the thermal diffusivity, which is low for most solids and is of the order of 10 cm s. ... 

The electrical displacement also varies in a sinusoidal fashion but is not necessarily in phase with the electrical field. The relationship between these quantities is obtained by solving equation (4.5.10). When the alternating field is initially applied to the system, there are some transients which describe the initial relaxation. The solution to the differential equation presented here ignores the initial effects, and considers only the properties of the system at a steady state. Under such circumstances any fluctuation in the system occurs at the same frequency as that of the perturbing field E. 

While in lumped-circuit methods the dielectric response is measured in the frequency domain, following the ajpplication of a sinusoidal alternating electrical field, for frequencies below 10 Hz it is advantageous to cany out the measurements in the time domain because it is less time consuming. The polarization or depolarization current following the application of a step-like electrical field is measured as a function of time. 

Electrical conductivity cell. Impedance is a measure of the total opposition to the flow of a sinusoidal alternating current in a circuit containing resistance, inductance, and capacitance. Inductance and capacitance together are called the reactive part of the circuit. The changes in impedance that occur in a microbial culture can be measured by placing two metal electrodes into the culture medium and introducing an alternating potential into the circuit. 

In EA experiments, the electric field in the polymer layer, arising fi-om the application of a sinusoidal voltage of the form V = V dc + cos(wt), consists of the superposition of a direct current (DC) component (Fq) and an alternating current (AC) component (Fac) ... 

A great deal of information on the electrical properties of the interface can be obtained if the measurements are performed in alternating fields. In such a case, an effect of the frequency of the sinusoidal external field on the velocity of motion (the dielectrophoretic velocity) can be observed. The relaxations observed can be interpreted in terms of the different contributions to the polarization of the particle and its double layer. 

Dielectric phase angle n. The angular difference in phase between the alternating voltage (usually sinusoidal) applied to a dielectric and the resulting current. The angle is often symbolized by 9, the cosine of which is the power factor. Ku CC, Liepins R (1987) Electrical properties of polymers. Hanser Publishers, New York. 

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