Two Ideal Components Equivalent Circuits

We will now discuss the simplest equivalent circuits mimicking the immittance found in tissue measurements. In this section, the R-C components are considered ideal that is, frequency independent and linear. Immittance values are examined with sine waves, relaxation times with step functions. A sine wave excitation results in a sine wave response. A square wave excitation results in a single exponential response with a simple R-C combination. 

The two-component model with one resistor and one capacitor is a one-port network and is the simplest and most important model because every measurement on a specific frequency is reduced to such a circuit. The results are given as complex immittance values with two figures corresponding to the two components one resistor and one capacitor. Inductive properties and corresponding resonance phenomena are possibilities that are found, for example, in membranes, but here we limit the treatment to capacitive systems. 

Y has a direct relationship with a parallel G-C circuit, the real part Y is G, and the imaginary part Y is B = wC. 

The parallel values are measured directly because it is proportionality between admittance 

Y and measured i. v is the independent reference sine wave, with zero phase shift per definition, and therefore here designated as a scalar  

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