Abstract:

The contact free conductivity measurement is a noninvasive method to find electrical characteristics of tissue that can be used e.g. for monitoring. The system consists of an excitation coil and two sensing coils coupled together as a gradiometer. The excitation coil is driven by an alternating current. Due to this alternating magnetic field eddy currents are generated in the tissue that create a secondary magnetic field. Because of the geometrical arrangement, the induced voltage of the secondary field in the upper and the lower coil is different. The presented sensor can be used e.g. for detection of ischemic areas, monitoring wound healing or detection of hematoma beneath the skull. To demonstrate this sensor, two measurements are carried out to detect post mortem changes in a pig liver. The known characteristics from literature can be reproduced using a noncontact method. For this purpose frequencies between 50 kHz and 400 kHz are used. At a frequency of 350 kHz a phase shift of 0.3 degrees is observed post mortem after 2 to 4 hours corresponding to a conductivity change of approximately 0.4 S/m.