Instrumentation considerations for complex impedance measurements

The extension of complex impedance measurements and associated analytic techniques to the study of biologic systems is discussed. Because of the highly conductive nature of animal tissue, special care must be taken in instrumentation design to achieve useful data. A recently fabricated system for use in the frequency range from 5 Hz to 700 kHz is presented. At higher frequencies, the finite output capacitance of the current source (approximately 3 pf) and the finite input capacitance of the voltage sensing system (approximately 6 pf) cause unacceptable phase errors.<>