Detection of Presence and Posture of Vehicle Occupants Using a Capacitance Sensing Mat

Capacitance sensing is the technology that detects the presence of nearby objects by measuring the change in capacitance. A change in capacitance is triggered either by a change in dielectric constant, area of overlap or distance of separation between the electrodes of the capacitor. It is a technology that finds wide use in applications such as touch screens, proximity sensing etc. Drawing motivation from such applications, this paper investigates how capacitive sensing can be employed to detect the presence and posture of occupants inside vehicles. Compared to existing solutions, the proposed approach is low-cost, easy to deploy and highly efficient. The sensing system consists of a capacitance-sensing mat that is embedded with copper foils and an associated sensing circuitry. Inside the mat the foils are arranged in rows and columns to form several touch-nodes across the surface of the mat. The system segregates row and column capacitances from each other and computes their tensor product to generate grayscale capacitance-sensing images. The images are real-time pictorial representation of the capacitance of each touch-node. When the mat is placed on a vehicle seat and an occupant sits on it, there will be a change in the capacitance of those touch-nodes that are in contact with the occupant’s body. The resultant sensing image reflects this change and the presence of the occupant is detected. In addition, through closer observation of the image and pattern analysis, it is possible to identify the sitting posture of the occupant in the seat - whether he or she is leaning backward, forward or sideways. The sensing system is implemented and tested on a vehicle seat. The results of the experiment and its analyses are presented in this paper.