Acoustic wave devices have been in commercial use for more than 60 years. The telecommunications industry is the largest consumer, accounting for ~3 billion acoustic wave filters annually, primarily in mobile cell phones and base stations.
These are typically surface acoustic wave (SAW) devices, and act as bandpass filters in both the radio frequency and intermediate frequency sections of the transceiver electronics. Several of the emerging applications for acoustic wave devices as sensors may eventually equal the demand of the telecommunications market.
These include automotive applications (torque and tire pressure sensors), medical applications (chemical sensors), and industrial and commercial applications (vapor, humidity, temperature, and mass sensors). Acoustic wave sensors are competitively priced, inherently rugged, very sensitive, and intrinsically reliable. Some are also capable of being passively and wirelessly interrogated (no sensor power source required).
Acoustic wave sensors are extremely versatile devices that are just beginning to realize their commercial potential.
They are competitively priced, inherently rugged, very sensitive, and intrinsically reliable, and can be interrogated passively and wirelessly.
Wireless sensors are beneficial when monitoring parameters on moving objects, such as tire pressure on cars or torque on shafts.
Sensors that require no operating power are highly desirable for remote monitoring of chemical vapors, moisture, and temperature.
Other applications include measuring force, acceleration, shock, angular rate, viscosity, displacement, and flow, in addition to film characterization. The sensors also have an acoustoelectric sensitivity, allowing the detection of pH levels, ionic contaminants, and electric fields.
Surface acoustic wave sensors have proved to be the most sensitive in general as a result of their larger energy density on the surface. For liquid sensing, a special class of shear-horizontal surface acoustic wave sensors called Love wave sensors proved to be the most sensitive. Much work is continuing in developing these sensors for future applications.
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