Capacitive ones utilize the change in capacitance between two pieces of metal to correspond to the pressure value,
Piezoresistive ones utilize the change in resistance value to correspond to the pressure value.
The main piezoelectric materials used in piezoelectric sensors include quartz, sodium potassium tartrate and dihydrogen phosphate. Quartz (silicon dioxide) is a natural crystal in which the piezoelectric effect is found. Within a certain temperature range, the piezoelectric properties are always present, but after the temperature exceeds this range, the piezoelectric properties disappear completely (this high temperature is the so-called "Curie point"). Because of the small change in the electric field with the change in stress (i.e., the piezoelectric coefficient is relatively low), quartz is gradually being replaced by other piezoelectric crystals. Potassium sodium tartrate, on the other hand, has a large piezoelectric sensitivity and coefficient of piezoelectricity, but it can only be used in environments with low room temperature and humidity. Dihydrogen phosphate is a man-made crystal that can withstand high temperatures and fairly high humidity, so
it has been widely used.
Piezoelectric sensors are mainly used in the measurement of acceleration, pressure and force. Piezoelectric acceleration sensor is a commonly used accelerometer. It has excellent features such as simple structure, small size, light weight and long service life. Piezoelectric acceleration sensors have been widely used in vibration and shock measurements in airplanes, automobiles, ships, bridges and buildings, especially in aviation and astronautics where they have a special place. Piezoelectric sensors can also be used to measure combustion pressure measurements and vacuum measurements inside engines. It can also be used in the military industry, for example, it is used to measure the instantaneous change in the chamber pressure of the gun bullet in the chamber and the muzzle of the shock wave pressure. It can be used to measure both large and small pressures.
Piezoelectric sensors are also widely used in biomedical measurements, for example, ventricular catheterized microphones are made from piezoelectric sensors, because measuring dynamic pressure is so common.