Distance Detection to a Human Body via a Sensing Technique Based on Changes of Antenna Characteristics

We investigated a proximity sensor technique based on changes of an antenna's characteristics when objects such as human bodies are near the antenna. Conventionally, the difference of the return loss (DRL) has been the detection metric used for this method to detect the presence of a human body. Although the ability to detect both the presence and the distance to the body is desirable, the DRL is difficult to use for distance detection. Here, we consider a new detection metric for distance detection: the distance of the complex reflection coefficient (DRC). Finite-difference time-domain analyses and measurements were conducted to demonstrate the validity of this metric for distance detection.