Inductively coupled wideband transceiver for bioimpedance spectroscopy (IBIS)

Most measurement devices for bioimpedance spectroscopy are coupled to the measured object (tissue) via electrodes. At frequencies >500kHz they suffer from artifacts due to stray capacitances between electrode leads as well as between ground and object. The non-invasive measurement of the brain conductivity is hardly possible with surface electrodes. These disadvantages can be obviated by inductive coupling. Aim of this work was the development of a wideband transceiver. In order to define its specifications a feasibility study has been carried out with a simulation model for two different coil systems above a homogeneous conducting plate. According to simulation results both systems render possible to resolve conductivity changes down to 10^-3 (Ωm)^-1 at 50 kHz. The sensitivity increases with the square of the frequency. The receiver electronics must then resolve voltages > = 1 μV at an excitation current of 1 A. We have realized a transceiver which matches these specifications with a S/N-ratio of 22 dB at 1 μV. The frequency range is 50 kHz-5 MHz.