Like all TorqSense sensors, the RWT420 units depend for their operation on surface acoustic wave (SAW) transducers. These transducers comprise two thin metal electrodes, in the form of interlocking “fingers,” on a piezoelectric substrate such as quartz. When an RF signal of the correct frequency is applied to the transducer, surface acoustic waves are set up, and the transducer behaves as a resonant circuit. If the substrate is deformed, however, the resonant frequency changes. For more information, visit www.sensors.co.uk.