Surface Acoustic Wave (SAW) Technology

SAW devices are widely used to filter and condition electronic signals in cellular phones and other consumer electronics, with over 4 billion devices produced worldwide for communications applications alone. Prices of many of these chips to OEM phone manufacturers, in high volume, are less than $0.15 each.

A SAW device consists of a polished piezoelectric substrate, on which interdigitated metal electrode structures have been produced using standard photolithographic processes. The interdigitated electrodes are connected in sets to bus bars, forming transducer(s). When the SAW is used as a wireless device, an antenna connected to the bus bars allows a radio frequency (RF) signal to be applied to the transducer, producing voltages that alternate with time on groups of electrodes. The time-varying difference in voltage between adjacent electrodes produces alternating strains in the underlying piezoelectric, transducing the electromagnetic RF signal into a mechanical disturbance on the substrate, known as a surface acoustic wave. This wave propagates outward on the surface of the substrate, and in general is either reflected back to the launching transducer or is received by another transducer. In either configuration, the resulting surface wave is transduced back into another RF signal, which is sent through an antenna back to a receiver that can read the sensor response. Since any environmental property that interacts with the wave can affect wave propagation characteristics that can be measured, the device is useful as a sensor.

While SAW sensor devices are somewhat more complex than simple SAW devices, and hence are somewhat more expensive to produce, the manufacturing infrastructure exists to drive down costs with increasing volumes, provided the devices are developed to utilize standard manufacturing processes. This makes SAW sensors a cost-effective enabling solution for distributed wireless sensing for a wide range of applications.