Figure 1: Piezoelectric pressure transducers.
The piezoelectric pressure transducer, a measuring precision instrument, mainly works with the piezoelectric effect that is the use of electrical components and other machinery to convert the pressure to be measured into electricity, and then carries out the relevant measurement. Piezoelectric pressure transducers include pressure transmitters and sensors.
Piezoelectric transducers cannot be used in static measurements because the charge imposed by an external force could be preserved only when the circuit has an infinite input resistance. But that's not true in actual situations. Therefore, they are only used in dynamic measurements.
Piezoelectric materials in the transducers are mainly ADP (ammonium dihydrogen phosphate), Rochelle salt, and quartz. Among them, quartz is a natural crystal on which the piezoelectric effect was discovered. Within the specified limits, piezoelectricity will always exist. But if the temperature is higher or lower than the specified range, it will disappear completely.
Figure 2: Piezoelectric effect.
When the stress changes, the electric field varies little, and we use other piezoelectric crystals to replace the quartz. Rochelle salt is of a high piezoelectric coefficient and sensitivity, but it could only be used in indoor places of low humidity and temperature.
ADP is an artificial crystal used in extremely high humidity and temperature environment, with wide applications. As technology is developing, piezoelectric effects have also influenced polycrystals. For instance, they are applied in piezoelectric ceramics, niobium magnesium piezoelectric ceramics, niobate piezoelectric ceramics, and barium titanate piezoelectric ceramics.
Transducers based on piezoelectric effects are electromechanical type and self-electric type. Their sensitive elements are made of piezoelectric materials that will form charges on the surface when there is an external force. These charges will be converted into an output proportioned with the external force through the charge amplifier, amplification of the measurement circuit, and an impedance transformation.
Piezoelectric transducers are applied in the measurement of forces and non-electrical quantities converting into forces, such as acceleration and pressure. The pros are light mass, reliability, simple structure, high signal-to-noise ratio, high sensitivity, and wide signal spectrum. On the other hand, some voltage materials requiring a series of anti-humidity measures. And the poor response to the output current needs the charge amplifier or high-input impedance circuit to make the device work efficiently.
Figure 3: A charge amplifier.
Piezoelectric pressure transducers are used in an extensive range of fields such as acoustical engineering, biomedical science, and engineering mechanics. The transducers can measure combustion pressure in engines in the military. Besides, they can measure the chamber pressure variation of the gun and the shock wave pressure on the muzzle at the moment of firing.
Figure 4: Piezoelectric pressure transducers for aircraft applications.
They can measure both extremely low and high pressure. Because of the long service life, light mass, small volume, and simple structure, they involve far more than these fields. They are also applied in the measurement of impact and vibration on buildings, bridges, vehicles, and planes. Especially in the fields of aerospace and aviation, piezoelectric transducers have played a special role.