We have developed a film-type proximity sensor by applying a new duplex silver-ink printing technique to a film substrate. The sensor is a capacitance type, with two electrodes sandwiching the film. By changing the electrode size, the electric lines of force can be extended spatially. If the sensor is approached, a part of the electric lines of force is obstructed by human bodies. This results in a decrease in capacitance, and therefore, it works as a proximity sensor. Because this sensor is very thin and lightweight, it can be easily attached to multiple locations such as the back of a table, chair, or bed, without being found. In this study, we placed it behind a Japanese tatami, and could successfully detect periodic breathing of human lying on it without contacting the body. Such an imperceptible sensor could contribute to ease examinees' discomfort during their health condition monitoring or medical check.
