Surface acoustic wave

Surface acoustic wave

A surface acoustic wave (SAW) is an acoustic wave traveling along the surface of a material having some elasticity, with an amplitude that typically decays exponentially with the depth of the substrate. This kind of wave is commonly used in devices called "SAW devices" in electronics circuits. SAW devices are employed as filters, oscillators and transformers based on the transduction of acoustic waves. The transduction from electric energy to mechanical energy (in the form of SAWs) is accomplished by the use of piezoelectric materials.

Discovered in 1885 by Lord Rayleigh who reported the surface acoustic wave mode of propagation and in his classic paper predicted the properties of these waves [Lord Rayleigh "On Waves Propagated along the Plane Surface of an Elastic Solid", [http://plms.oxfordjournals.org/cgi/reprint/s1-17/1/4 "Proc. London Math. Soc. s1-17 (1885), p. 4-11"] ] . Named for their discoverer, Rayleigh waves have a longitudinal and a vertical shear component that can couple with a medium in contact with the device’s surface. This coupling strongly affects the amplitude and velocity of the wave allowing SAW sensors to directly sense mass and mechanical properties.

Electronic devices employing the SAW normally utilize one or more interdigital transducers (IDTs) to convert acoustic wave to electrical signal and vice versa utilizing the piezoelectric effect of certain materials (quartz, lithium niobate, lithium tantalate, lanthanum gallium silicate, etc). These devices are fabricated utilizing photolithography, the process used in the manufacture of silicon integrated circuits.

SAW filters are often used in the mobile telephones and provide significant advantages in performance, cost, and size over other filter technologies such as quartz crystals (bulk wave) , LC filters, and waveguide filters.

Significant research has been done in the last 20 years in the area of surface acoustic wave sensorsfact|date=March 2008. Sensor applications include all areas of sensing (such as chemical, optical, thermal, pressure, acceleration, torque and biological). SAW sensors have seen limited commercial success to date but are commonly commercially available for some applications such as touchscreen displays.

In seismology surface acoustic waves travelling along the Earth's surface play an important role, since they can be the most destructive type of seismic wave produced by earthquakesFact|date=July 2007.

ee also

* Phonon
* Linear elasticity

External links and references

* [http://www3.sympatico.ca/colin.kydd.campbell/ SAW Filter] - understanding SAW devices
* [http://www.sensorsmag.com/articles/1000/68/main.shtml SAW Sensor]

References


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