New Tetrapolar Method for Complex Bioimpedance Measurement: Theoretical Analysis and Circuit Realization

This paper describes the theory and practical implementation of a new tetrapolar (four-electrode) method for measuring complex bioimpedance of local tissue. The new tetrapolar method adopts three independent voltages V_IN+, V_IN-, V_R respectively from the two voltage electrodes and the sample resistor R, which is connected in serial with one of the two current electrodes. Theoretical analysis shows that the real part Z_real and imaginary part Z_imag of the complex impedance between two voltage electrodes can be acquired from the modular ratios (|V_IN+ |/|V_R|), (|V_IN-|/|V_R|) and phase differences (thetas_IN+ - thetas_R), (thetas _IN- - thetas_R) through simple calculation. Realization of this method, based on the newest generation of highly integrated electronic components for directly generating relevant amplitude ratios and phase differences, is simple. Compared with the conventional tetrapolar method, the new tetrapolar method shows its advantage of simplicity in circuit realization, enables complete microprocessor control of localized bioimpedance measurements, and may liberate the traditional bioimpedance measuring system from the complexity of electronics