Editing Piezoelectricity (section)

===High voltage and power sources===

Direct piezoelectricity of some substances, like quartz, can generate [[potential difference]]s of thousands of volts.
* The best-known application is the electric [[Lighter|cigarette lighter]]: pressing the button causes a spring-loaded hammer to hit a piezoelectric crystal, producing a sufficiently high-voltage [[electric current]] that flows across a small [[spark gap]], thus heating and igniting the gas. The portable sparkers used to ignite [[gas stove]]s work the same way, and many types of gas burners now have built-in piezo-based ignition systems.
* A similar idea is being researched by [[DARPA]] in the United States in a project called [[energy harvesting]], which includes an attempt to power battlefield equipment by piezoelectric generators embedded in [[soldier]]s' boots. However, these energy harvesting sources by association affect the body. DARPA's effort to harness 1–2&nbsp;watts from continuous shoe impact while walking were abandoned due to the impracticality and the discomfort from the additional energy expended by a person wearing the shoes. Other energy harvesting ideas include [[Crowd Farm]], harvesting the energy from human movements in train stations or other public places<ref>{{cite web | url = http://www.treehugger.com/files/2006/08/japan_ticket_gates.php | title = Japan: Producing Electricity from Train Station Ticket Gates | last = Richard | first = Michael Graham | website = TreeHugger | publisher = Discovery Communications, LLC | date = 2006-08-04 | url-status = live | archive-url = https://web.archive.org/web/20070709200844/http://www.treehugger.com/files/2006/08/japan_ticket_gates.php | archive-date = 2007-07-09 }}</ref><ref>{{cite web | url = http://web.mit.edu/newsoffice/2007/crowdfarm-0725.html | title = MIT duo sees people-powered "Crowd Farm" | last = Wright | first = Sarah H. | date = 2007-07-25 | website = MIT news | publisher = [[Massachusetts Institute of Technology]] | url-status = live | archive-url = https://web.archive.org/web/20070912201419/http://web.mit.edu/newsoffice/2007/crowdfarm-0725.html | archive-date = 2007-09-12 }}</ref> and converting a dance floor to generate electricity.<ref>{{cite web | url = https://abcnews.go.com/International/story?id=5358214&page=1 | title = How to Save the World One Dance at a Time | last = Kannampilly | first = Ammu | work = ABC News | date = 2008-07-11 | url-status = live | archive-url = https://web.archive.org/web/20101031010929/https://abcnews.go.com/International/story?id=5358214&page=1 | archive-date = 2010-10-31 }}</ref> Vibrations from industrial machinery can also be harvested by piezoelectric materials to charge batteries for backup supplies or to power low-power microprocessors and wireless radios.<ref>{{cite journal|url=http://www.linear.com/docs/29984 |title=True Grid Independence: Robust Energy Harvesting System for Wireless Sensors Uses Piezoelectric Energy Harvesting Power Supply and Li-Poly Batteries with Shunt Charger |last=Barbehenn |first=George H. |page=36 |date=October 2010 |journal=Journal of Analog Innovation}}</ref><ref>{{cite journal |last1=Bahl |first1=Shashi |last2=Nagar |first2=Himanshu |last3=Singh |first3=Inderpreet |last4=Sehgal |first4=Shankar |title=Smart materials types, properties and applications: A review |journal=Materials Today: Proceedings |date=2020 |volume=28 |pages=1302–1306 |doi=10.1016/j.matpr.2020.04.505 }}</ref>
* A piezoelectric [[transformer]] is a type of AC voltage multiplier. Unlike a conventional transformer, which uses magnetic coupling between input and output, the piezoelectric transformer uses [[acoustic coupling]]. An input voltage is applied across a short length of a bar of piezoceramic material such as [[Lead zirconate titanate|PZT]], creating an alternating stress in the bar by the inverse piezoelectric effect and causing the whole bar to vibrate. The vibration frequency is chosen to be the [[resonance|resonant]] frequency of the block, typically in the 100&nbsp;[[kilohertz]] to 1&nbsp;megahertz range. A higher output voltage is then generated across another section of the bar by the piezoelectric effect. Step-up ratios of more than 1,000:1 have been demonstrated.{{Citation needed|date=May 2013}} An extra feature of this transformer is that, by operating it above its resonant frequency, it can be made to appear as an [[inductor|inductive]] load, which is useful in circuits that require a controlled soft start.<ref>{{cite web | url = http://www.eetimes.com/electronics-news/4197064/Piezoelectric-Technology-A-Primer | archive-url = https://web.archive.org/web/20101006002651/http://www.eetimes.com/electronics-news/4197064/Piezoelectric-Technology-A-Primer | archive-date = 2010-10-06 | title = Piezoelectric Technology: A Primer | last = Phillips | first = James R. | date = 2000-08-10 | website = eeProductCenter | publisher = TechInsights }}</ref> These devices can be used in DC–AC inverters to drive [[cold cathode fluorescent lamp]]s. Piezo transformers are some of the most compact high voltage sources.