Siemens has developed an airbag sensor that can detect an accident by sound and deploy airbags up to twice as fast as ever before. The Crash Impact Sound Sensor (CISS) uses the structure-bourn sound waves created when the chassis of a vehicle deforms on impact and, based on their characteristics, determines the severity of the crash and whether the airbags should be deployed. The sensor will go into series production in 2007.
Until now different sensors were used to detect crashes and to deploy airbags in the vehicle. While sensors in the bumper recognize the deformation caused by an accident, pressure sensors in the b-pillar of the car measure the intensity of a side impact. The b-pillar is the connection between the floor and the roof in the middle of the occupant cell. In addition, acceleration sensors use the braking force and the vehicle vibration that results to determine the strength of the crash. The sensor can detect acoustic vibrations of up to 400 hertz.
While the previous sensors needed 30 milliseconds from impact to airbag deployment, CISS - which was developed by the automobile experts at Siemens VDO - only needs half that time depending on the type of crash. The trick is that in addition to the vibrations in the lower range, it also processes frequencies as high as 16 kilohertz. This allows it to detect not only inaudible oscillations, which propagate more quickly than deeper vibrations. The sensor does this by taking advantage of the characteristics of plastic deformation. When metal bends, structure-borne sound is generated as a result of a displacement in the atomic structure that varies according to the intensity and speed of the deformation. In just 15 milliseconds the sensor effectively "hears" the intensity of the accident, determines the precise nature of the accident with the aid of the acquired acceleration signals and deploys the airbags and safety belt restraints.
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