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Bioimpedance measurements are a non-invasive method to determine thecomposition of organic tissue. For measuring the complex bioimpedance betweentwo electrodes, an alternating current with a constant amplitude is injectedinto the tissue. The developed voltage drop is used to calculate the real andimaginary part of the impedance under test. Measurements in the past indicatedthat it could be possible that the beating of the heart has an effect on themeasured phase shift of the impedance under test. In this work a hardwaresystem is developed, capable of measuring changes of the bioimpedance phaseshift with high resolution. Two different measurement methods are used. Thefirst method is an analog circuit, which has been developed in a previousproject. The other method uses the integrated circuit AFE4300 (TexasInstruments) [1]. The results of both methods are transmitted with amicrocontroller (Xmega256A3BU from Atmel Corp.) via the USB interface to a hostPC. On the host PC the visualization of the measurements and the control of theembedded system is achieved with a developed LabView program. The work includesthe development of the hardware and software, as well as a comparison of theaccuracy of the two measurement methods. The result of a verification of thesystems is that both measurement methods have an effective resolution of about0.3{\deg}.

Design, Development and Comparison of two Different Measurements Devices for Time-Resolved Determination of Phase Shifts of Bioimpedances