Piezo Electric Sensor

Piezo Electric sensor

A piezoelectric sensor/element is a device that uses the piezoelectric effect, it is basically a device which converts voltage to vibration and vibration to voltage. It normally comes in handy to measure knock (knock  sensor) or vibration (vibration sensor). 
Now a days it is also used extensively in power generation projects e.g. Foot Step Power Generation.

This is a 27mm piezoelement.