Polydimethylsiloxane-based capacitive motion sensor and its read-out circuit

A capacitive motion sensor that can detect human walking and motions up to a certain distance was designed using polydimethylsiloxane (PDMS) as the primary sensor material. A read-out circuit was designed to detect capacitive coupling with the sensor material caused by the motion in the surrounding. The read-out circuit consists of sensing, filtering, and amplifying stages. A high-pass filter was used to avoid DC components, and to eliminate adverse impacts of 50Hz noise in the sensing signal, a sixth-order low-pass filter consisting of active Sallen–Key and passive RC filters was utilized. The signals obtained from the complete read-out circuit revealed that the sensor system could accurately detect human movements up to 2 m away. Also, different signal patterns were obtained from the output of the sensor system for various human motions.