Through the Wall Detection of Heartbeat and Breathing Using SFCW Radar

Detection of human presence behind concrete wall and/or debris is a critical in rescue and security applications. Apart from physical movement, human heartbeat and breathing detection at a stand-off distance requires careful design of radar system components, especially at the RF-front end level. Heartbeat detection especially becomes important for rescue operations after an earthquake or landslide where victims are trapped and unable to move or respond to rescuers. In such disasters, remote detection systems based on acoustics and/or infrared imaging usually has limited penetration depth than electromagnetic waves at UHF band. These systems operate close to debris or wall surface where antenna coupling to the structure adversely affects system performance and transmit-receive antenna isolation. Since heartbeat and breathing possess a few Hz frequency components, zero-IF receiver structure is used. However, DC leakage and low-frequency noise inherit to electronic components must be carefully filtered out at analog and digital domains. In this study, we present step-frequency continuous wave radar for detection of such low frequency components with high accuracy. Radar architecture and Doppler filters differ from earlier designs in terms of system sensitivity and selectivity for multiple targets and ghost echo signals. As opposed to single frequency architectures, proposed system can perform Fast Fourier Transform (FFT) on multiple, swept frequencies where background subtraction and frequency domain filtering operations can be correlated to each other for higher detection probability.