The 7BB series from Murata are piezoelectric diaphragms. This piezoelectric diaphragms is a piezoelectric ceramic disks adhered to a metal plates of brass. These disphragms are typically used in clocks, calculators, digital camera and various alarms. They can be used as knock sensors or very small audio transducers.
This piezo element is 20mm in diameter and has a height of 0.2mm.
