Body Capacitance and Resistance

The AT-cut quartz resonator can be modeled mechanically as a body containing mass, compliance, and resistance. Figurel-a) shows the mechanical vibration motion depicting the vibration of the quartz resonator. An electrical network called an equivalent electrical circuit consisting of inductive, capacitive and resistive components can represent this mechanical model. Figure... 

As shown in the previous section, the mechanical properties of a quartz crystal close to resonance frequency can be expressed by means of a motional impedance. To complete the equivalent circuit of a quartz crystal, the capacitance, Co, must be added in parallel to the motional impedance. It results in the Butterworth-Van Dyke (BVD) equivalent circuit of a quartz crystal, as shown again in Fig. 8 for an unloaded quartz crystal [32]. In this notation common in electronic Hterature, Is is the dynamic inductance and is imder-stood here as a representation of the oscillating mass of the quartz crystal. Cs is the dynamic capacitance and reflects the elasticity of the oscillating body. Rs is the dynamic resistance and returns friction of the quartz slice as well as all kinds of acoustic damping. 

Here, L is the dynamic inductance, a measure of the oscillating mass of die quartz, and Cs is the dynamic capacitance or series capacitance, a measure of the elasticity of the oscillating body [9], The resistance of the RLC circuit is related to the quality factor Q (the width of the resonance), the dissipation D [10], and the full width at half maximum f of the resonance by the relationship ... 

Bioimpedance measurements were conducted with a BIS device (SFB7, ImpediMed, Pinkeba, Australia) covering a frequency range of 5 kHz to 1 MHz. This device has an impedance accuracy of 1% and a phase resolution of 0.1° using adhesive electrodes. To ensure rehable measurements, the body position was not altered and electrode sites were cleaned before attaching the electrodes. For this trial, the whole-body and hand-to-hand bioimpedance is analyzed. Extracellular resistance intracellular resistance (i ,) and capacitive effects CJ are calculated using the Cole model [6]. 

Body fluids such as sweat, urine or tears can give information about the health state of a patient and are therefore collected and analysed in medicine. Fluids or humidity in general can be measured by two distinct physical principles either by resistive or capacitive sensors. 

Full film conditions in the cam-follower contact can easily be checked by a measurement of the Ohmic resistance or the capacitance of the film. For this, the follower plate is insulated by a 5 mm. perspex layer. In addition, the follower is insulated from the test rig mass by the hydrostatic bearing, and at the load cell and the guide blocks of the follower body. 

The seriousness of the physiological effects of current passing through the body is directly related to the current s magnitude and duration and to the path that the current takes through the body. The magnitude of the current is related to the voltage across the body and to the body s impedance. Impedance, rather than pure resistance, must be used because the body contains capacitive reactance at power frequencies. 

Consider a metal electrode consisting of a silver wire placed inside the body, with a solution of silver ions between the wire and ECF, supporting the reaction Ag" + e <— Ag. This is an example of an electrode of the first kind, which is defined as a metal electrode directly immersed into an electrolyte of ions of the metal s salt. As the concentration of silver ions [Ag" ] decreases, the resistance of the interface increases. At very low silver ion concentrations, the Faradaic impedance Zfaradaic becomes very large, and the interface model shown in Fig. 3(a) reduces to a solution resistance in series with the capacitance C. Such an electrode is an ideally polarizable electrode. At very high silver concentrations, the Faradaic impedance approaches zero and the interface model of Fig. 3(a) reduces to a solution resistance in series with the Faradaic impedance Zfaradaic. which is approximated by the solution resistance only. Such an electrode is an ideally nonpolarizable electrode. 

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