Quartz crystals as remote sensors for tire pressure

The problem with tire pressure measurements is how to provide the sensor in the tire with energy. Current measurement systems use an active sensor with either a battery or a bulky energy transmission. Quartz resonators attached to an antenna perform better, because they can operate passively giving an echo to a stimulus. Strain influences the otherwise extremely stable natural frequency of a quartz crystal which is therefore ideally suited for pressure measurements. As the natural frequency lies in the Megahertz range, stimulation and response can be transmitted by a pair of small antennas. The result is a small, lightweight sensor with excellent accuracy and resolution which is very reliable and principally maintenance-free