Non-contact Vital Sign Detection Based On Doppler Radar

Vital signs can be non-contactly detected by microwave Doppler radar. Doppler Effect occurs in electromagnetic reflected wave when radiating to a subject with cardiopulmonary activities, as a result, cardiopulmonary information can be extracted from the reflected wave by signal processing. Vital sign detection based on Doppler radar has the advantages of non-contact and through-clothing, meeting the requirements of daily healthcare, high risk population monitoring, medical diagnosis, disaster relief and security.Research subjects on bio-radar are mainly related to sensor systems and signal processing. Sensor research tries to enhance the signal quality and reduce the noise by improving the structure and integrated process of antennas and transceivers. Signal processing research aims to extract precise parameters of vital signs from the radar signal by certain algorithms. Considering both family usages and medical applications, there’re still several issues on bio-radar vital sign detection currently, for example:Signal-noise ratio and anti-interference capability of the radar system need to be improved; Cardiopulmonary information should be reconstructed linearly; Real-time radar signal processing is required in long-term monitoring; Time-domain cardiopulmonary information is difficult to distinguish from strong clutters. Focus on these issues, the main work and achievement of this dissertation could be presented as follows:(1) Analysis about configuration, signal chain and noise principle of Doppler bio-radar. The justification of Doppler radar working mode, frequency and transceiver structure were made for real applications of vital sign detection; Several parameters of the radar transceiver chain were researched, providing design choices for remote sensing of vital signs in meters’range; Relationships between subject distance, displacement and radar’s signal-to-noise ratio were measured by experiments; The actual noise sources were further located according to the radar’s noise model. All these methods and results could provide universal meanings for bio-radar design.(2) Development of Doppler radar sensors. The designing works included microstrip antennas, microwave transceivers, analog signal processing and data acquiring circuits, demodulation methods and calibration algorithms. The following steps were taken for reconstructing micro-motion of human subject:24bit ADC was employed with oversampling accumulation to provide both large dynamic range and high resolution; Calibrating algorithms based on central estimation were performed to dissociate subject’s DC information from systemic and environmental DC offset; Quadrature demodulation method was applied to realize linear reconstruction. The performance of the radar sensors were proved by experiments, which can meet the need of vital sign detection.(3) Research on real-time detection of cardiopulmonary activities. This research focused on real-time, low power and low cost software/hardware for the need of daily health monitoring, especially continuous monitoring. Short Time Fourier Transform (STFT), which just requires short duration of radar signal, was used in real-time calculation. Frequency spectrum interpolation was then performed to improve the resolution of heart and respiratory rate. The experimental results indicated that, with this method, there was7seconds delay,96%accuracy for heart rate measurement, and there was22seconds delay, nearly100%accuracy for respiratory rate measurement.(4) Research on precise extraction of physiological parameters. This research focused on improving the estimation precision of cardiopulmonary parameters, and analyzing time-domain cardiopulmonary information, for the need of medical monitoring. In the extraction algorithms, continuous wavelet transform and ensemble empirical mode decomposition (EEMD) were employed, while the heart rate, respiratory rate and heart rate variability (HRV) were estimated. The experimental results proved that, the accuracy of heart and respiratory rate measurement could nearly reach100%, and the HRV measurement based on time-domain information also provide valuable performance to non-contact medical detection.(5) System implementation of vital sign detection based on Doppler radar. Several radar systems were built for usages of scientific experiments, domestical and clinical monitoring, with the design focuses on real-time, precision, portability and integration, respectively. Efforts were taken for actual applications in Doppler radar system design, including:Miniaturization and lightweight for higher portability, even for wearable usage; Lower power dissipation for longer battery life; Using generic wireless interface for connecting with mobile devices, cloud computing platform and social medical services.