Why use an alternating current to measure the impedance of a biological tissue?
Essentially for two reasons: Biological tissue is an ionic conductor: it is known that electrical conduction in a material occurs through charge carriers, which may be electrons, such as is the case for metals, free ions in suspension in solutions, as is the case for biological tissues. If a direct current is passed through an ionized solution, the well-known phenomenon of polarization occurs, i.e. very rapidly at the level of each electrode a double layer of ions is deposited which acts as an insulator and prevents the current from passing. Therefore, a direct current cannot be used to measure the resistance of such a conductor. Because it is a heterogeneous conductor: i.e. it is composed of both resistive elements and non-capacitive elements diversely associated.
