piezoelectric microphone

Devices that use an un-powered microphone: usually a cheap dynamic or piezoelectric microphone.

They range from the very low impedance of ribbon microphones (can be less than one ohm) to the very large impedance of piezoelectric microphones which are measured in megohms.

Many modern engines are equipped with a knock sensor (a small piezoelectric microphone), which sends a signal to the engine control unit, which in turn retards the ignition timing when detonation is detected.

Detection of pressure variations in the form of sound is the most common sensor application, e.g. piezoelectric microphones (sound waves bend the piezoelectric material, creating a changing voltage) and piezoelectric pickups for acoustic-electric guitars.

The company made its major breakthrough with the development of a piezoelectric microphone whose electric adaptation was precisely tailored to the vacuum tube amplifiers commonly used at the time; the company revised and improved it several times over the years.

The television show Ghost Hunters International recently made a trip to Chavin and the Lanzón and recorded odd heartbeat-like sounds coming from the stone on a piezoelectric microphone and had odd experiences with other equipment that could not be explained.

The ceramic EIA Class 2 dielectrics used in high-K capacitors ("Z5U" and "X7R") are piezoelectric and directly transform mechanical vibration into a voltage in exactly the same way as a ceramic or piezoelectric microphone.