A high accuracy Bioimpedance Measurement System (BMS) for time resolved measurements

Bioimpedance analysis is a vital tool in both biomedical engineering and life science. Bioimpedance measurements are based on the injection of small well-known alternating currents via surface electrodes and by the measurement of the resultant surface voltages. Since the bioimpedance of an object under test is closely related to the structure and the properties of the investigated object, it can be used for various physiological applications like blood flow or body composition estimations. Furthermore, bioimpedance measurements are acknowledged for being non-invasive and painless with no known hazards. This research presents a Field Programmable Gate Array (FPGA) based high accuracy broadband Bioimpedance Measurement System (BMS) for time resolved bioimpedance measurements. The sys-tem is able to measure magnitude and phase of complex impedances under test in a frequency range of about 10 kHz to 500 kHz with excitation currents from 10 µA to 5 mA. The overall measurement un-certainties stay below 1 % for the impedance magnitude and below 0.5° for the phase in most measurement ranges. Furthermore, the described system has a sample rate of up to 3840 impedance spectra per second with an effective resolution down to 23 mΩ. In addition, this research introduces a novel multi-modal vital-parameter Analog Front End (AFE) add-on for the BMS. This setup is able to measure accurately and simultaneously bioimpedance, a single channel Electrocardiography (ECG), three Photoplethysmography (PPG) signals, the pressure in both ears, as well as the heart sounds. Further-more, the system complies in principle with the IEC60601-1 safety requirements. Moreover, ECG, PPG, Heart sounds and pressure measurements have a temporal resolution of about 1 ms.