Seat Occupancy Detection Using Capacitive Sensing Technology

Capacitive sensor technology has proven to be a reliable and robust measurement technology which is suitable for various sensing applications in the very demanding automotive environment. In this paper we present the design of a novel capacitive sensor for seat occupancy detection for next generation smart airbag systems. It is intended to provide information about the position of an occupant on the seat as well as dynamic changes thereof during an incident. This leads to the requirement of high sensitivity paired with a high measurement rate. In order to cope with these requirements a high frequency measurement principle is introduced. With higher frequencies and high signal strengths, the electromagnetic emissions of such a system may become a concern. Therefore, techniques for the reduction of such emission have to be applied.

A prototype sensor system for seat occupancy detection has been realized. The sensor makes use of a versatile interface implemented in a 0.25 μm Complementary Metal Oxide Semiconductor (CMOS) technology which is capable of measuring the displacement current between several transmitter electrodes and one common receiver electrode. In-phase and Quadrature-phase (I/Q) demodulation is used in order to provide both amplitude and phase shift information (e.g. due to conductive coupling).