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


October 3, 2014


Steffen Kaufmann and Ankit Malhotra


Institute of Medical Engineering, University of Lübeck, Lübeck, Germany, Laboratory for Medical Electronics, Lübeck University of Applied Sciences, Lübeck, Germany


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.


Steffen Kaufmann and Ankit Malhotra

Steffen Kaufmann was born in Hann. Münden, Germany in 1984. He holds a Dipl.-Ing. (FH) degree in electrical engineering and a Master of Engineering (M. Eng.) degree in Information Engineering. From 2005 to 2009, he worked at the Garz and Fricke GmbH as a hardware and software developer for embedded systems. Afterwards, he worked for the Hamburg University of Applied Sciences in the laboratory for multimedia systems on 3d-visualizations. Since 2010, he is working as a research associate at the campus Lübeck on bioimpedance measurements and Electrical Impedance Tomography (EIT). He is an expert in the field of analog and digital electronics and signal processing. Currently he is working on Magnetic Particle Imaging (MPI) at the institute of medical engineering at the University of Lübeck.

Ankit Malhotra was born in Delhi, India in 1987. He holds a Bachelor of Honors (B. Tech. hon.) degree in Biomedical Engineering from the Rajasthan Technical University, India and a Master of Science (M. Sc.) degree in Biomedical Sciences from the University of Lübeck, Germany. Since 2013, he is working as a scientific research assistant at the Laboratory for Medical Electronics (LME) at the Lübeck University of Applied Sciences. His research focus is on bioimpedance measurements and arterial stiffness diagnosis techniques. Since childhood, he is passionate about biology and the advancement of biomedical engineering. His major skills are a blended of human biology, medical electronics and signal processing. Whereas he has special expertise in deducting and processing of physiological signals like ECG, PPG, EMG and Heart sounds.