https://www.sciencedaily.com/releases/2021/12/211208090119.htm

Most current drowsiness detection systems use an exterior, forward-looking camera to monitor lane position or sudden, exaggerated corrections. Others use an interior camera to check a driver's face or eyes for signs of nodding off. Camera-based systems, while useful, have drawbacks. For example, an exterior camera could be blocked by mud, and an interior camera could be less effective at night. Scientists have previously explored using piezoelectric sensors -- self-powered materials that accumulate an electrical charge in response to pressure -- for monitoring a driver's posture, which changes when a person falls asleep, has a sudden health emergency or is intoxicated. However, existing piezoelectric sensors cannot withstand high temperatures, a requirement for electrical and electronic equipment in vehicles. Toshimi Nagase and colleagues wanted to develop flexible, heat-resistant piezoelectric sheet sensors that could be embedded in a vehicle's seat to monitor the driver's posture.

The researchers prepared zinc oxide-based films directly on a polyimide surface and then screen-printed a silver paste on both sides to obtain a piezoelectric sheet. They connected a coaxial cable to detect changes in electrical charge with pressure and then folded the sheet in half around the cable. The sensor sheet resisted heating up to 250 F, with no changes in its properties. After showing that the sensor could discriminate changes in mechanical load, the team placed a sensor in the back of a chair. By detecting a seated person's slight body movements, the sensor allowed the researchers to calculate the person's respiration and pulse rates. Two other sensors attached to the seat of a chair could sense when a person leaned left or right with their upper body, which could indicate drowsiness.