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

We investigated a sensing 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 used as the detection indicator for this method. However, not only the presence of a human body but also the distance to the body must be detected to enable a wider range of sensor applications, and the DRL cannot be used for distance detection. Therefore, in this paper, we consider a new detection indicator–the distance of the complex reflection coefficient–that enables distance detection. Finite-difference time-domain analyses were performed to demonstrate the validity of this indicator for distance detection.