Transducer use
The devices that have been described are predominantly used as sensors, because with a few exceptions, their efficiency of conversion is very low and to achieve transducer use requires the electrical signals to be amplified. The piezoelectric device used for pressure sensing is also a useful transducer, and can be used in either direction. Transducer use of piezoelectric crystals is mainly confined to the conversion between pressure waves in a liquid or gas and electrical AC signals, and this use is described in detail in Chapter 5. The conversion of energy from an electrical form into stress can be achieved by the magnetically cored solenoid, as illustrated in Figure 1.20. A current flowing in the coil creates a magnetic field, and the core will move so as to make the magnetic flux path as short as possible. The amount of force can be large, so that stress can be exerted (causing strain) on a solid material. If the core of the solenoid is mechanically connected to a diaphragm, then the force exerted by the core can be used to apply pressure to a gas or a liquid. In general, though, there are few applications for electronic transducers for strain or pressure and the predominant use of devices in this class is as sensors.
