Microwave-Based Remote Bio-Sensing behind Walls

In this paper a novel method for microwave based remote sensing of vital signs behind walls is presented. The method is based on temporal spatial analysis of back scattered microwave signals. The use of non-optical electromagnetic radiation enables monitoring from larger distances and behind objects in contrast to similar concepts in optics. Further, such use of non-optical radiation omits the need for direct line of sight between the monitoring system and the target and enables monitoring through walls or other barriers. Micro-vibrations due to breathing and heart pulsation affect the reflection of microwaves and cause the self-interference random patterns (i.e. speckle patterns) to vary in time and space. By using this approach, the temporal change of the speckle patterns due to changes in vital signs can be tracked behind walls. In this paper we present a system in WiFi frequencies band consisting of two radio-frequency (RF) transmitters and either one or three RF receivers to detect single or multiple breathing or non-breathing human subjects, behind different type of walls. The results showed that the system was able to distinguish between breathing states, to determine the vibration frequency of heartbeats, and to distinguish between subjects' vital signs in few cases. In low SNR cases statistical analysis was applied to extract breathing and heartbeats frequencies, by a sweep of 20 different transmitted signals in sequence. This is the first step towards real time remote detection of human vital signs using RF speckle patterns.