Acoustic transducers
Piezoelectric materials (in crystal form) are also used as sensor transducers, since they have the ability to generated and transmit acoustic waves. The resonance frequency of these acoustic waves depends on physical properties of piezoelectric materials and these physical properties change, when antibodies are coated or when antigens bind to these antibodies (since this leads to increase in mass). These are affinity biosensors and there are two classes of acoustic transducer;
(i) bulk wave (BW) devices. which transmit an acoustic wave from one crystal face to another and
(ii) surface acoustic wave (SAW) devices, which transmit an acoustic wave along a single crystal face from one location to another. The operation of these devices is gas phase is well established. This technology is available for many years and is cheap.