Piezoceramic transducers in technical applications are part of a specific system environment, including the electrical circuitry and connected mechanical parts.
The specific designs of functional units depend on the application. They can be highly complex and require interdisciplinary work.
Technical application areas of piezoceramic transducers are here classified as actuator, sensor, generator, transformer or acoustic transducer. The basic principles of these, here called functional units, are explained on the present web site.
Actuators
Piezoceramic actuators convert electrical signals (voltage, charge) into controlled mechanical displacement. Even small changes of voltage generate small displacements, thus allowing for positioning with nanometer resolution. Primarily, the temperature and the stability of electronics define the accuracy, not the piezo transducer itself. The magnitude of displacement depends on external mechanical forces. When the displacement is blocked, a characteristic force will develop, which is called the blocking force. Piezoceramic actuators are used for precise positioning tasks of lightweight and heavy components. Short raise time and high acceleration meet the requirements of variable valve control, for example of fuel injectors in combustion engines. Other application of interest are based on miniaturized piezo motors and pumps.
Sensors
As sensor, piezoelectric devices convert external mechanical quantities (force, pressure) into electrical signals and transmit them to the control unit. Depending on design, two sensor types are known, axial and bending type sensors. Basically, piezoelectric sensors are suitable for dynamic measurement tasks. Under static load, the separated charges compensate with time and the measurable charge or voltage disappear. Within limits, the allowed measurement frequencies can be adjusted by the device design and circuit layout. Piezoelectric sensors are used to measure force, pressure, and acceleration. Knock sensor for engine control are a well-known example.
Generators
A piezoelectric generator converts external mechanical forces into electrical energy. Optimum designed generators deliver electrical output voltages proportional to the mechanical stress. Piezoelectric generators allow for the generation of very high voltages, for example used in gas lighters and gas ignitors. An alternative application is harvesting of electrical energy from vibrations of the surrounding (energy harvesting). The achievable power output is relatively small and is in the range of 100 µW – 1 mW. Realistic applications are seen in decentralized power supply of low power sensors.
Transformer
Piezoelectric transformer convert an alternating (AC) input voltage into an AC output voltage. The transformation ratio is defined by the device design. Energy transfer through the transformer takes place by piezoelectric induced mechanical vibrations. Piezoelectric transformer are an alternative approach to electromagnetic transformers, characterized by compact design, high efficiency, high electrical insolation resistance between input and output electrodes, as well as no magnetic stray fields. Power up 50 W can be transformed. Accuracy of the output voltage under load and changes of temperature are problems to be solved by design of the device and the lay out of the electrical circuit.
Sound transducer
Piezoelectric transducer are able to transform alternating (AC) electrical signals into propagating mechanical waves, e.g. sound waves or ultrasound waves. These waves are used to measure distances in various media (air, water, other), flow velocity, and filling levels. Ultrasound waves are also used to clean surfaces, to evaporate liquids, to support machining of complex shaped materials, to heat-sealing of plastics and in medical diagnostics. Because the piezoelectric effect is invers, piezoelectric transducers are able to excite and receive acoustic waves. Both functions can be used in combination. Often transducers are optimized for one of the two tasks. The piezoceramic element is the core component of a sound converter system. It works in combination with other passive components (membrane, housing, acoustic matching layer, preload element, amplitude transformer). Depending on application, specific electric circuitries are used.