1 Department of Electrical Engineering, Technical University of Denmark2 Electromagnetic Systems, Department of Electrical Engineering, Technical University of Denmark
This work investigates how to design microwave systems for vital signs detection (VSD) and monitoring (i.e. of respiration and heartbeat signals). Typical system types include ultrawideband (UWB) and continuous wave (CW) radars. Due to its ease of implementation and potential for a low-power low-cost system, emphasis is on the CW type of VSD radars. The signal theory governing both homodyne and heterodyne CW VSD architectures is thoroughly examined. Throughout the discussion it is shown, how heterodyne systems using a low intermediate frequency (IF) can overcome some of the commonly encountered problems with homodyne systems, i.e. channel mismatches and DC offsets resulting from hardware imperfections. To verify the theory, a new VSD radar system called the DTU-VISDAM (VItalSigns Detection And Monitoring) has been designed and build. The system together with the implemented signal processing methods is presented and real measurements verifies its operation. At the moment of writing, VISDAM consists of two heterodyne radar units operating at X-band with IF frequency at 1 kHz. A small scale test is performed with VISDAM showing its capabilities to track the heart rate of a person in various different scenarios, i.e. lying on a bed and sitting straight up. Multi-unit measurements are carried out to remove random body movements not associated with the vital signs from the subjects being monitored. In the pursuit of an even more compact solution, the work on a fully integrated SiGe:C VSD radar front-end was initiated. With financial support from the Danish fund H. C. Ørsteds Fonden, the IC was fabricated in the SG25H3 SiGe:C BiCMOS technology from Innovations for High Performance microelectronics (IHP) GmbH in Germany. The radar transceiver has been measured and altough some adjustments could be of benefit, it is assessed that the radar chip can contribute to a full VSD system. Time did not allow for this latter system implementation of the IC.