Non-contact measurement of the electrical impedance of biological tissue

The measurement of the impedance of biological tissue is a non-invasive method to find new data of diagnostic relevance. A change in the impedance for example can give a prediction of the healing process of wounds or of skin irritations [1]. The traditional way is to apply the current and measure the voltage with electrodes. This leads to stray capacitance between the electrodes as well as between the ground and patient at frequencies above 500 kHz. In the present report two sensitive systems are presented using computer simulations which can detect conductivity gradients. The systems are built up with two coils. In the first simulation the excitation coil is designed as a gradient coil to excite a magnetic field and a rectangular coil to measure. In the second simulation a rectangular coil is used as an exciting coil and a gradiometer coil is used to measure. The tissue block is divided into two halves with different conductivities. The sensors give no signal with A homogeneous tissue block. In presence of a conductivity gradient, the systems are sensitive. The main difference of the two systems is the geometrical arrangement of the eddy currents.