A piezo switch is an electrical

switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...

based on the

piezoelectric effect Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied mechanical stress. The word '' ...

. The

charge Charge or charged may refer to: Arts, entertainment, and media Films * '' Charge, Zero Emissions/Maximum Speed'', a 2011 documentary Music * ''Charge'' (David Ford album) * ''Charge'' (Machel Montano album) * ''Charge!!'', an album by The Aqu ...

generated by the piezoelectric element in the switch is typically used to turn on an integrated

semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...

device such as a

field effect transistor The field-effect transistor (FET) is a type of transistor that uses an electric field to control the flow of current in a semiconductor. FETs (JFETs or MOSFETs) are devices with three terminals: ''source'', ''gate'', and ''drain''. FETs contro ...

(FET), causing the switch assembly's output to be active, or "on".DiscoverCircuits
/ref> When the FET is on, current can flow through it as with a conventional metal contact-based

. After the voltage pulse is dissipated in the gate resistor, the FET turns back "off", its normal high impedance state. The

is the generation of electric charge when certain materials are under stress. In the case of piezo

es, the force could be compressive

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...

that causes the (typically disc-shaped) piezo element to bend very slightly like a

drumhead A drumhead or drum skin is a membrane stretched over one or both of the open ends of a drum. The drumhead is struck with sticks, mallets, or hands, so that it vibrates and the sound resonates through the drum. Additionally outside of percu ...

. Thus piezo switches produce a single, brief "on"

pulse In medicine, a pulse represents the tactile arterial palpation of the cardiac cycle (heartbeat) by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed near the surface of the body, such as at the n ...

. This pulse can vary with the amount of pressure which is applied, since higher pressures generate higher voltages which take longer to dissipate. A capacitor may be used to store the charge to lengthen the

time constant In physics and engineering, the time constant, usually denoted by the Greek letter (tau), is the parameter characterizing the response to a step input of a first-order, linear time-invariant (LTI) system.Concretely, a first-order LTI system is a s ...

of the gate circuit and therefore the width of the pulse. With additional circuitry this pulse can be extended further or used to change the state of an output from steady "Off" to steady "On" by toggling a flip-flop.
Piezo switches have some interesting advantages over their conventional mechanical counterparts. One is that there are no moving parts, just the small deformation on the front plate and the piezo element (typically a few micrometers). This means the lifetime of such a switch can be ensured to be tens of millions of operations, since there is no wear involved. Another advantage is that they may easily be completely sealed from the environment and thus made weatherproof. They are often constructed with stainless steel housings such that they are resistant to damage by

vandals The Vandals were a Germanic people who first inhabited what is now southern Poland. They established Vandal kingdoms on the Iberian Peninsula, Mediterranean islands, and North Africa in the fifth century. The Vandals migrated to the area betw ...

or heavy use.

References

{{Switches Switches

See also

References