Transducers are devices that convert one form of energy into another, such as the transfer of mechanical input to electrical output and vice versa. Piezoelectric transducers are transducers that can convert any form of pressure or mechanical stress into electrical energy and also translate that electrical signal into physical movement. To begin this discussion of piezo transducers, we must first understand the components of such a product. The term piezo or piezoelectric refers to electricity caused by physical pressure. Piezo transducers, which are commonly refered to as PZT transducers, are able to measure these physical energies and convert them to a proportional form of electrical energies or electrical signals. In the same sense, those electrical signals can then be utilized to generate more mechanical energy. Piezoelectric transducers can have two roles: to sense mechanical changes and convert them to electrical energy (sensor), or to receive an electrical signal and translate it into physical displacement (actuator).
A piezo transducer can be described as a combination of a piezoelectric sensor and a piezoelectric actuator, sometimes called a piezoelectric transmitter. A piezoelectric sensor senses mechanical changes in the outside world and translates them into an electrical signal which can be used to measure those changes. In the same sense, a piezoelectric actuator can convert the electrical signal into mechanical energy or physical movement. When assembled, a piezoelectric transducer can be designed to perform either or both roles as the sensor and actuator, depending on how the transducer is constructed. A piezoelectric sensor will receive information about a mechanical force and convert that physical input to a proportional electrical output. The other half of the transducer, the piezo actuator, can then use that electrical output to perform the necessary physical adjustments. Sometimes two piezoelectric transducers are used, with one acting as the sensor and one acting as the transducer, while other assemblies just utilize one piezo transducer to perform both functions. All in all, the piezoelectric transducer converts mechanical changes into an electrical signal, then can use that signal to generate displacement. The movements are typically fine and small; however, piezoelectric transducers are extremely accurate and precise.
Advantages and Disadvantages
Piezoelectric materials are extremely volatile in the sense that they have no restrictions on the shape in which they are manufactured. This gives piezoelectric transducers a significantly broader range of potential applications compared to other types of transducers. Their ability to self-generate voltage also eliminates the need for an external power source. Some applications take advantage of this property of PZT transducers and use it to harvest energy from mechanical impacts. Piezoelectric transducers can effectively operate at very low voltages and relatively high temperatures (up to their Curie point), further increasing their range of applications.
Despite their volatility, piezoelectric transducers do have shortcomings, one of which is high impedance. Since their resistance to current is high, piezoelectric transducers often generate very low voltages or outputs. This causes these devices to become reliant on amplifiers, which in some instances can induce electrical error.
Piezoelectric transducers are used to convert mechanical energy, normally acoustic, into electrical energy (this is the opposite of actuators – see Actuators for more). One of piezoelectric materials’ most useful properties is their responsiveness to change. This enables PZT transducers to be used in studies of explosions, in various accelerometer applications, and in other applications where fast shape changing in required.
One iconic use of transducers was during World War I, where Canadian scientist Robert Boyle used quartz to make a sonar device for the British forces to detect submarines and ships. Piezo transducers were also utilized in landline phones to trigger an audible ring when an incoming call signal was received.
Piezoelectric transducers are widely used across industrial, aerospace, automotive, commercial, and medical industries for many applications. In industrial settings, piezo transducers can be used to measure and adjust for changes in pressure, acceleration, flow, and liquid levels. In the example of flow rate, piezoelectric transducers will generate waves to measure the frequency of the liquid. Flow can be automatically adjusted by the piezo transducer to reach and monitor the defined flow rate. The adjustment of flow and liquid levels with piezoelectric transducers is commonly seen in engine, fuel, and motor functions for aerospace and automotive applications. Parking aids, lane assist, and automatic braking features all utilize piezoelectric transducers to sense the obstacle and make physical adjustments to avoid it.
Commercially, transducers can also be found extensively in musical products including microphones, keyboards, electrical guitar, etc. For example, sound production utilizes piezoelectric transducers to pick up electrical signals from microphones and amplify the sound. Many everyday consumer products also utilize piezo transducers, such as key fobs, microwaves, watches, alarms, and PIN pads. They are the function behind automatic sliding doors – a person activating the sensor (sensor) will trigger the door to open (actuator).
The medical industry is rapidly evolving everyday with the aid of piezoelectricity. Piezoelectric transducers are used in many machines and equipment to dose medication or even perform surgery. For example, piezo transducers can be used to sense and break up kidney stones. Piezoelectricity is an undeniably beneficial resource, and the applications for piezoelectric transducers is limitless.
Piezoelectric transducers also have an innate ability to vibrate at a very fast rate which is particularly useful in ultrasonic applications, various cleaning products as well as medical and surgical tools. Ultrasound cleaning utilizing piezoelectric transducers functions by rapidly vibrating when operating at the appropriate ultrasonic frequencies. With a piezo transducer in cleaning fluid, the rapid expansion and contraction from the vibrations exerts enough force to clean. This method of using extra force from vibrations is commonly seen in dentistry, jewelers, and electricians. See Ultrasonic Transducers for more.
In certain cases where cabled power sources or battery power is either extremely expensive or unviable, piezoelectric transducer provide the perfect solution. They can generate energy from ambient sources, a solution commonly used in energy-light systems. Piezo transducers are also used in conjunction with sensors and very low power machines (such as wristwatches) as they can effectively operate on just milliwatts of energy.
The ambient energy capabilities of piezoelectric transducers are best utilized when power needs are periodic and close to the harvester’s resonance frequency. If the ambient energy is constant, the problem of electron loss occurs, which causes the harvester to slowly lose energy output over time.
An example of an energy harvesting application is found in applications that generate energy by walking. By embedding piezoelectric transducers into the sole of the shoe, pressure applied from walking is converted into electrical charge that can be used to charge small appliances like old cell phones or smartwatches. The same principle applies for larger industrial applications such as trains. Piezo transducers embedded in the train tracks can convert the mechanical energy from the train’s pressure or acceleration into an electrical charge to power other devices. Another excellent example of piezo transducer energy harvesting can be seen in charging devices for internet of things, or physical internet sensors that exchange data with other sensors. These piezoelectric sensors receive ultrasonic signals in the air through vibrations. This mechanical energy is converted into an electrical signal which charges the device through energy transmission.