Piezoelectric fans and their application In electronics cooling

Piezoelectric fans seem to represent an example of research and development that has culminated in a product that is deceptively simple. Although piezoelectric technology is capable of producing rotary motion, the fans operate quite differently from rotary fans, as they generate airflow with vibrating cantilevers instead of spinning blades.

Piezoelectric, as derived from Greek root words, means pressure and electricity. There are certain substances, both naturally occurring and man-made, which will produce an electric charge from a change in dimension and vice-versa. Such a device is known as a piezoelectric transducer (PZT), which is the prime mover of a piezoelectric fan. When electric power, such as AC voltage at 60 Hz is applied, it causes the PZT to flex back and forth, also at 60 Hz.



The magnitude of this motion is very tiny, so to amplify it, a flexible shim or cantilever, such as a sheet of Mylar, is attached and tuned to resonate at the electrical input frequency. Since piezoelectric fans must vibrate, they must use a pulsating or alternating current (AC) power source. Standard 120 V, 60 Hz electricity, just as it is delivered from the power company, is ideal for this application, since it requires no conversion.

[If direct current (DC), such as in battery-operated devices, is the power source, then an inverter circuit must be employed to produce an AC output. An inverter may be embodied in a small circuit board and is commercially available with frequency ranges from 50 to 450Hz.]

Driving the fan at resonance minimizes the power consumption of the fan while providing maximum tip deflection. The cantilever is tuned to resonate at a particular frequency by adjusting its length or thickness. The PZT itself also has a resonant frequency, so the simplistic concept of adjusting only the cantilever dimensions to suit any frequency may still not yield optimum performance. (Conceivably, tuning the electrical input frequency to match existing cantilever dimensions may work, though with the same caveat, that the resonant frequencies of all the components must match, within reason.

Applications for piezoelectric fans are just in their infancy and could really thrive through the imagination of designers. This article, which originally appeared in the April 2011 issue of Qpedia (published by Advanced Thermal Solutions, Inc. and used with permission here) explores the principles, construction, implementation, and installation of piezoelectric fans.

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