What are SAW Resonators?

Jo Dunaway

Surface acoustic wave (SAW) resonators are coupled with a variety of filters in surface wave frequency control chip technology and used in a wide array of electronics devices. These SAW filters must meet all industry standards for use in cellular phones, global positioning systems, digital satellite receivers and keyless entry remote controls, to name a few. SAW resonators have been used in applications as diverse as wireless point of sale terminals, wireless tire pressure monitoring devices and microwave digital radios. They have been used as biomarkers in detecting disease markers and can even sniff out the presence of plastic explosives remotely.

SAW resonators may reduce the amount of E. coli from infecting people through undercooked food.
SAW resonators may reduce the amount of E. coli from infecting people through undercooked food.

A surface acoustic wave is a mechanical wave motion traveling along the surface of a solid material, and it has both a vertical shear and longitudinal component that is capable of coupling with any media in contact with that same surface. Amplitude and velocity are born into the wave of this coupling, which makes SAW resonators then capable of sensing both mechanical and mass properties. This gives the SAW resonator the capability of high-frequencies beyond the conventional ceramic and crystal resonators on the market.

SAW resonators may be able to be used as an early detection device for ovarian cancer.
SAW resonators may be able to be used as an early detection device for ovarian cancer.

Upon a piezoelectric substrate such as quartz are placed metal electrodes transducers as receivers that can then receive an electrical signal and convert it to an acoustic wave, then take the acoustic wave and convert it back to an electric signal. This feedback loop creates a long delay because acoustic waves are slow, and these delays make them useful in many devices, such as pulse compression radar and bandpass filters for radios. SAW resonators are used so widely that there are millions of them made in countries around the world every day.

New developments have been studied for further use of SAW resonators as wireless temperature measurement sensors in harsh and isolated environmental conditions. They need no batteries and require little periodic calibration and little maintenance. These resonators can receive and transmit wirelessly, so they can sense without invasion of high-powered switchgear and smart grid applications of all kinds.

Another possible avenue for the use of SAW resonators is in the development of wireless food probes to replace the wired food probes found in many commercial food ovens. This could reduce the amount of salmonella, E. coli and clostridium pathogens from infecting people through undercooked food. Without the wiring necessary for these wired probes, a SAW resonator could be read and powered by an interrogation antenna from embedded electronics.

Perhaps the most interesting discovery is that SAW resonators can possibly smell disease markers for ovarian cancer and be used as an early testing device for a form of cancer that is a silent killer and that had no early warning test available as of 2011. It already has been established that SAW resonators can sniff out plastic explosives and trinitrotoluene (TNT). These qualities can make them immensely helpful for robotics to be used by bomb squads in unfamiliar and dangerous situations. They can thus be used in the service of saving lives on two very difficult-to-solve fronts.

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