springs, tines, strings, bowls,
what is a piezo disk?
Piezo crystal generates a voltage when deformed or bent. It is commonly used as a thin piezoelectric ceramic round glued to a thin brass or alloy metal disc. This center disc is positively charged while the brass disc is negatively charged. The voltage can be measured across those parts and then amplified to produce sound.
The reverse is also true. Send an amplified signal to a piezoelectric crystal and it will produce tones.
A contact microphone is a small flat piezo disk/element that translates physical surface vibrations into voltage. The piezo discs are a layer of crystal in the center of a thin brass disk. When there is a vibration on a surface of an object, the disc bends slightly which generates a (small) electrical signal.
Contact microphones in practice…