Research On Multi-target Vital Signs Monitoring Radar In Vehicles Based On Metasurface Tag

With the outbreak of COVID-19,people hope to provide timely and effective feedback on the human body status through real-time monitoring of vital signs indicators to respond to unexpected situations.However,the contact monitoring devices commonly used at present have certain constraints on some occasions because of the cable ties,so the use of radar for noncontact vital signs monitoring has become a breakthrough point.Meanwhile,the development of new energy and smart vehicles requires real-time monitoring of in-vehicle passengers’ vital signs,and thus in-vehicle non-contact vital sign monitoring has attracted much attention.However,due to the strong multipath and high clutter monitoring environment in the vehicle and the close distance between passengers in the vehicle is difficult to distinguish,the multi-target vital sign monitoring for in-vehicle scenarios is still to be studied.In this paper,we propose an in-vehicle multi-target vital sign monitoring radar system based on metasurface tags to address the above problems.The system scheme combines metasurface tags with a time-diversity method based on FMCW signals to monitor and separate vital sign information of multiple targets in the rear seats of a vehicle under a single beam while maintaining low system complexity and limited computational complexity of signal processing.The main work of this paper is as follows:1)A polarization-converted retro-reflective metasurface is proposed,which cleverly combines a dual-polarization microstrip patch antenna unit with high isolation and low crosspolarization with a phase gradient metasurface,to realize metasurfaces that can simultaneously polarization conversion and-30° retro-reflection;2)A new polarization-converted filter-type retro-reflective metasurface tag with simultaneous polarization conversion,spatial filtering,and retro-reflective characteristics are realized by cascading the metasurface with the designed substrate integrated frequencyselective surface with single-sided high roll-off characteristics,and the enhancement of the target vital sign characteristics by the metasurface tag is experimentally verified;3)A multi-target vital sign monitoring radar scheme combining the polarization diversity and spatial diversity characteristics of the metasurface tag with the FMCW radar is proposed for in-vehicle multi-target vital sign monitoring,which converts the frequency diversity characteristics into temporal diversity characteristics to achieve the differentiation between adjacent multi-targets and between targets and the environment.Finally,the feasibility of the scheme is verified through the validation experiments on two adjacent targets in the rear seats of a single beam in a strong multipath and high clutter vehicle environment,and the average error rate of the validation experiments is only 2.4%.