Response characteristics capacitive conductivity

The frequency response of various chemical constituents of nerve membrane was studied. Biological membranes in general consist of lipids and proteins. Firstly, impedance characteristics of artificial lipid bilayer membranes are examined using lecithin-hexadecane preparations. It was observed that the capacitance of plain lipid membranes was independent of frequency between 100 Hz and 20 KHz. Moreover, application of external voltages has no effect up to 200 mV. Secondly, membrane capacitance and conductance of nerve axon were investigated. There are three components in nerve membranes, i.e., conductance, capaci-... 

The dependence of protein and solvent dynamics on hydration fits well into the above three-stage picture for some, but not all, properties. For dynamic properties that do not fit well, analysis on a case-by-case basis within the framework of the time-average picture can be informative. For example, consider protonic conduction, measured by the megahertz frequency dielectric response for partially hydrated powders of lysozyme. The capacitance grows explosively above a hydration level of 0.15 A, in a way characteristic of a phase transition (Section HI, A). The hydration dependence of thermodynamic properties shows, however. 

The frequency K = 1 at which the current distribution influences the impedance response is shown in Figure 13.7 with k/Co as a parameter. As demonstrated in Example 13.2, the influence of high-frequency geometry-induced time-constant dispersion can be avoided for reactions that do not involve adsorbed intermediates by conducting experiments below the characteristic frequency given in equation (13.57). The characteristic frequency can be well within the range of experimental measurements. The value k/Cq = 10 cm/s, for example, can be obtained for a capacitance Co = 10 (corresponding to the value expected for the dou-... 

In order to interpret the eleetromechanical results, the performance of IPMCs is often reported alongside of a variety of characteristics such as tire capacitance of the actuator, current during the operation cycle, charge accumulated by the time of maximum displacement/blocking force, conductivity of the electrodes, viscoelasticity of the materials, etc. Finding out how all these parameters relate to the electromechanical response of IPMCs is a subject of ongoing research in the field of electroactive polymers. 

From the separate lines of Eqs. 13-12 and 13-13 real and imaginary components of impedance at first (fundamental), second, third, and fourth harmonics can be calculated from the known voltage signal parameters and measured frequency-dependent current. The values for the Aaracteristic total capacitance C V ) and conductance G(f,j.) of the circuit can be computed. Comparison of the experimental and calculated frequency-dependent data for each harmonic serves as a diagnostic criterion that the system can indeed be represented by a simple parallel G C combination. Poor fit between the experimental and the calculated frequency-dependent impedance or current functions implies that a more complicated kinetic mechanism is responsible for the measured impedance characteristics. 

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