Accelerometers utilising MEMS technology and their design considerations for automotive restraint systems

Automotive crash sensing provides unique challenges to accelerometer manufacturers using MEMS technology. To fulfil the rigid firing requirements of a timely airbag deployment, the entire signal chain of the restraint system has to be considered and accounted for in the sensor design and the restraint system algorithm. Until recently, the effects of signals containing high frequency content (>2000 Hz) were ignored in the automotive applications mainly because these did not serve any useful purpose and were quite often heavily filtered by the mechanical or electronic filters. This resulted in very limited data available to the restraint system designer to recommend appropriate sensor signal conditioning design attributes to the sensor manufacturer. With the advent of sensors utilising MEMS technologies proliferating into the vehicle environment and due to their inherent advantage of superior stiffness to mass ratio these devices can respond to such high frequencies and the signal conditioning circuitry needs to account for this high frequency content present in the automotive environment. This paper describes the adaptation of the MEMS device (accelerometer) to the restraint system to cope with the automotive environment, including crash and misuse test conditions. Also, specific recommendation is made in the sensor signal conditioning chain to improve robustness. MEMS process technologies are summarised and the choice of these technologies reflect the performance/cost of the sensor in the restraint system. Restraint system designers have to understand these MEMS process technologies and their implications on the overall restraint system in order to successfully integrate the appropriate MEMS processing technology for automotive safety application.