Heartbeat detection in a microwave monitor using an adaptive least squares lattice filter

A portable low-energy microwave device has been developed to monitor remotely a human hear rate in a hazardous environment. The chest wall is illuminated with a microwave signal. Heartbeat information is encoded in the microwave returns through Doppler shifts of the microwave signal caused by movement in the chest due to the heart beating. In order to gain insight into the development of a heartbeat-detection algorithm, autoregressive modeling of the microwave returns was performed. The results of this analysis showed that the heartbeat signal can be reasonably modeled as the output of a fourth-order all-pole filter excited by a train of impulses of varying weights. The analysis also indicated that the likelihood variable has a predictable pattern during one heartbeat. It is concluded that this approach can be used to detect heartbeat