Piezoelectricity is electric polarization produced by mechanical strain in certain crystals, the polarization being proportional to the amount of strain and changing sign with it. The reverse is also true: an electrical polarization induces a mechanical strain in piezoelectric crystals.
Practical use of the piezoelectric property of quartz was made in 1916 by French physicist Paul Langevin, who developed an ultrasonic sending and receiving system. A piezoelectric quartz crystal was set into oscillation by an electrical signal, and the high-frequency mechanical vibration was transmitted through water to a reflecting body. A second quartz crystal received the reflected vibratory energy (ultrasound) and, from the time of lapse between sending and receiving, the distance from the source to the reflecting body could be calculated. This major application of piezoelectricity was the forerunner of modern-day sonar.
In the strictest sense, crystals are the only materials that can demonstrate piezoelectric properties. Quartz, Rochelle salts and tourmaline were the earliest-known highly polar natural piezoelectric crystals. In common usage, however, the term piezoelectric is now used to characterize certain ceramic and polymer materials. These ceramics and polymers do not exhibit piezoelectric properties in their natural state, but rather only after the temporary application of a strong electric field. The process of making polycrystalline ceramics and polymers piezoelectric is called “poling” and is analogous to the magnetizing of a permanent magnet.
Ceramic and Polymer Materials
Available types of piezoelectric ceramics include: barium titanate, lead zirconate titanate (PZT), lead metaniobate, bismuth titanates, sodium potassium niobate and lead titanate. Currently, the most important piezoelectric ceramic materials are based on mixed-oxide crystal systems consisting of lead zirconate and lead titanate, known as PZT. Most of the piezoceramic materials in use are from the PZT family because of their excellent piezoelectric parameters, thermal stability and dielectric properties.
PZT materials are available in a variety of compositions that are optimized for different applications. Commercially used piezoceramics include:
• barium titanate (BaTiO3), the first piezoelectric ceramic discovered
• lead titanate (PbTiO3)
• lead zirconate titanate (Pb[ZrxTi1−x]O3, 0<x<1), more commonly known as PZT and the most common piezoelectric ceramic in use today
• potassium niobate (KNbO3)
• lithium niobate (LiNbO3)
• lithium tantalate (LiTaO3)
• lead metaniobate
• lead magnesium niobate-lead titanate
• bismuth titanate
A leading alternative to PZT is polyvinylidene difluoride ( PVDF), a highly non-reactive and pure thermoplastic fluoropolymer. PVDF is a specialty plastic material and is generally used in applications requiring the highest purity; strength; resistance to solvents, acids, bases and heat; and low smoke generation during a fire event.
Ceramic/polymer composites are newer piezoelectric materials. Piezoelectric ceramics/polymer composite material can provide a combination of desirable material properties that cannot be obtained in single-phase materials.
Piezoelectric ceramics are becoming more widely accepted for two reasons: their high piezoelectric activity/high permissivity; and the ease of fabricating the materials into a variety of sizes and shapes, including sheets a few mils thick to large rings, cylinders, bars, and plates. Such ceramic elements can be further combined to produce even larger structures (e.g., wedge-shaped bars assembled to make a large ring, shaped plates to form a sphere, or rings stacked to make a long cylinder).
Due to an increase in industry automation, along with a consumer taste for sophisticated gadgets and emerging home automation markets, the use of piezoelectric devices has risen substantially. Applications have also surged, including medical electronics, ultrasonics and sensors. The emerging markets are in computer-related areas, such as micro-actuators for hard disks and piezoelectric transformers for laptops. Military use has been declining, while industrial and consumer-related applications continue to grow.
New applications are emerging for piezoelectric devices, including actuators, ultrasonic motors, sensor arrays for structural health monitoring, transformers and micro-energy harvesting devices, which are an alternative to batteries in microwatt devices. Other new applications include high-resolution ultrasonic medical imaging, computer disk drives, and accelerometers in mobile phones and notebooks.
Unlike other piezo devices, commercialization of piezoelectric-operated actuators and motors is likely to proceed in those markets where the specific advantages of high torque, high precision and lack of magnetic interference are particularly useful. When the costs can be lowered to competitive levels, and remaining technical problems such as frictional wear can be solved, piezoelectric motors may also become candidates in areas such as automotive accessories, where very high volume markets are possible. The sidebar details some of the applications currently existing in the military, automotive, commercial, medical and consumer markets.
Piezoelectric Ceramic Use in Sonar
Sound navigation and ranging (sonar) is a technique that uses sound propagation (primarily underwater) to navigate, communicate or detect other vessels. There are two kinds of sonar: active and passive. The term “sonar” is also used for the equipment used to generate and receive the sound.
Sonar may be used as a means of acoustic location. Acoustic location in air was used before radar. Sonar may also be used in air for robot navigation, while SODAR (upward-looking in-air sonar) is used for atmospheric investigations.
Active sonar uses a sound transmitter and a receiver. The transmitter creates a pulse of sound, often called a “ping,” and then listens for reflections (echoes) of the pulse. This pulse of sound is generally created electronically using a sonar projector consisting of a signal generator, power amplifier and electro-acoustic transducer/array, possibly with a beam former. Active sonar is also used to measure distance through water between two sonar transducers or a combination of a hydrophone (underwater acoustic microphone) and projector (underwater acoustic speaker). When used with multiple transducers/hydrophones/projectors, active sonar can calculate the relative positions of static and moving objects in water.
Passive sonar listens without transmitting. It is often employed in military settings, although it can be used in scientific applications (e.g., detecting fish for presence/absence studies in various aquatic environments). In its broadest usage, this term can encompass virtually any analytical technique involving remotely generated sound, though it is usually restricted to techniques applied in an aquatic environment. Passive sonar systems can be used in:
• Warfare: Anti-submarine warfare, torpedoes, mines, mine countermeasures, submarines, aircraft, underwater communications, ocean surveillance, underwater security, hand-held sonar, intercept sonar
• Civil applications: Fisheries, echo sounding, net location, ship velocity measurement, remotely operated and unmanned undersea vehicle location
• Scientific applications: Biomass estimation, wave measurement, water velocity measurement, bottom type assessment, bottom topography measurement, sub-bottom profiling, synthetic aperture sonar, parametric sonar
• Sonobuoy (a combination of sonar and buoy) is a relatively small (typically 4.88 in./124 mm in diameter and 36 in./910 mm long) expendable sonar system that is dropped/ejected from aircraft or ships conducting anti-submarine warfare or underwater acoustic research
The success of piezoelectricity in sonar applications has created intense development interest in piezoelectric devices. Over the next few decades, new piezoelectric materials and applications will be explored and developed.
Commercial and Civilian Market Expands
The piezoelectric device market sector is actually comprised of a number of sectors with distinctly different characteristics. The sectors of most significance are:
• high production volume consisting of generic piezoelectric devices such as actuators, motors, sensors, accelerators, transducers for ultrasonic medical imaging and non-destructive testing acoustic devices; Langevin actuators for ultrasonic welding and cleaning; ceramic resonators; and miscellaneous types of devices designed for special applications, such as transformers, vibration and noise cancellation in structures limited to different grades of piezoelectric crystals, ceramics such as PZT, PVDF and composites
• sonar for military and civil use
• niche applications such as energy harvesting, where piezoelectric devices such as generators offer a unique competitive advantage
Piezo-devices also include ultrasonic motors (USMs), which offer a high potential for miniaturization. These actuators produce no magnetic field since the excitation is quasi-electrostatic. Through their specific advantages compared to conventional electro-magnetic motors, USMs fill a gap in certain actuator applications. A key advantage of USMs over electromagnetic motors is their compactness (i.e., their high stall torque-mass ratio and high torque at low rotational speed), often making speed-reducing gears superfluous. In addition, with no voltage applied, an inherent holding torque is present due to the frictional driving mechanism. It is worth mentioning that their compactness and the high-frequency electrical excitation make quick responses possible.
Global Industry Structure
The global piezoelectric ceramic, polymer ceramic and polymer composite devices industry is characterized by about 60 producers and suppliers of these elements and hundreds of piezoelectric device producers. For over a decade, the largest users had been the military for applications such as sonar, sonobuoys and hydrophones. However, commercial and consumer applications have now taken the lead.
Over the next several years, significant growth opportunities should arise for piezoelectric actuators in the biomedical, semiconductor, data storage, aerospace and automation arenas. A well-organized piezoelectric motor business with coordinated, integrated organizations in key regions of the world, a diversified but synergistic product offering, technical expertise in key piezoelectric technologies, and the ability to provide value-added piezoelectric solutions is particularly well-positioned to exert a significant influence in the industry and achieve robust growth. This industry segment contains many relatively small companies, as well as piezoelectric-focused organizations within some very large companies; in such a situation, a company that provides global piezoelectric solutions across multiple, key market segments is in a superior competitive position in the marketplace.
Ever since nanotechnology and biotechnology began being well funded by industry and governments, the interest in piezo-motion technology has risen steadily. The need for nano-imprinting, scanning microscopy, microlithography and automated alignment has opened new market areas in piezo-driven nanopositioning technology, parallel metrology, parallel kinematics, active trajectory control, and covers new control algorithm for vibration suppression and tracking error elimination and their benefits for the users.
Companies targeting the customer base largely include academic institutes, government and research laboratories focused on nanofabrication, fiber and integrated optics, photonics, semiconductors, data storage, microscopy and metrology, where nanometer level positioning is of prime importance. Many companies are also OEM customer oriented. Apart from this, they are looking to work with conglomerates focused on optical fiber laying. In the future, companies enjoying strong partnerships with government agencies and academic institutions that can provide advanced, customized and cost-effective solutions to geographical locations—and those that can reach out to customers more effectively and address their requirements precisely—will have the greater advantage.
Japan is a world leader in mass-
produced, low-voltage piezoelectric ceramic materials. Its large, stable piezoelectric ceramic industry is aimed at standardized mass production elements, such as resonators and filters (ceramic and SAW), buzzers, audio transducers and alarms. Excellent technology and superior production techniques allow the Japanese to produce these high-volume elements at very low prices.
European companies are trying to maintain the second position in the world market, close to China. China, Taiwan, Korea and the rest of the world are targeting low-cost, high-volume devices like resonators, buzzers, speakers used in mobile phones, ultrasonic motors used in digital cameras, and transformers and hard disks as used in laptops.
North America, like Europe, enjoys a unique position in research related to PZT, PVDF and composite applications. Most U.S. companies are engaged in manufacturing high-technology, high-value piezoelectric devices like sonar, nano-positioning motion control devices, transformers, accelerometers, energy harvesting devices, sensors and switches.
Markets for piezoelectric ceramics, polymers and ceramic/polymer composites have been expanding. Growth in the piezoelectric devices market continues to be driven by increasing demand in camera phones for autofocus mechanisms, piezo-transformers, data storage, semiconductors, microelectronics production, precision mechanics, life science and medical technology, optics and more. Sonar for military and civil uses and other applications constitute an established market.
The global market for traditional piezoelectric devices is quite mature in applications. However, the global market for new piezoelectric devices will see a robust two-digit growth rate in next five years.
The global market for piezoelectric devices using ceramics, PVDF and ceramic/polymer composites topped $20 billion in 2012 and is expected to reach $38.4 billion by 2017, as shown in Table 1. Among the devices, piezoelectric actuators and motors have the highest growth rates because of their applications in information technology, robotics, biomedical engineering, automotive, ecology, and energy engineering.
Among the current applications, the largest share goes to equipment for semiconductor manufacturing and testing, lab equipment, sensors, and accelerators, with 39% of the market. The next biggest segment is piezo devices used in mobile phones, digital cameras, laptops and other consumer electronic equipment, where piezo devices used include six categories of devices: ultrasonic motors, piezo transformers, resonators, acoustic devices, sensors (primarily SAW sensors), and piezo generators, with a market share of 32%. This is followed by medical transducers, mini-grippers, dentist tools, ultrasonic non-destructive testing, vibration testing, welding and cleaning, telecommunication, traffic control, piezo print heads, gas ignitions, and diesel injectors, with a 22% share. Sonar for military and civil use constitutes the final segment, with 9% of the market.
Among the 11 product-type market segments in 2012, actuators have the largest share of the market with 31%, followed by ultrasonic motors with 14%; sonar with 9%; transducers with 8%; piezo sensors and accelerators with 7%; acoustic devices with 6%; and smaller shares for Langevin actuators, piezo transformers, resonators and other miscellaneous types.
New devices such as piezoelectric generators will see the highest growth rate, estimated to be 24.5% annually from 2012 to 2017. This category is followed by ceramic resonators (17.9%) and miscellaneous applications (acousto-optic modulators in telecommunication engineering, 16.5%; vibrators, 16.2%; diesel/gasoline injectors, 15.9%; and dentistry surgery tools, 14%).
Traditional devices will also see growth, including acoustic devices (14.2%), actuators (13.5%), Langevin actuators for welding and cleaning (13.2%), sonar (6.7%), transducers (14.8%), gas igniters (7.9%), and piezo printing heads (10.7%).
In 2012, Japan had the highest market share of 25%, followed by Europe with 23%, China with 22%, North America with 12%, Korea with 11%, and the rest of the world with 7%. By 2017, China is projected to occupy the top position ahead of Japan, with a 25% share of the global market.
Editor’s note: This article is based on a recent IRAP market research study entitled “Piezoelectric Ceramics, Polymers and Ceramic/Polymer Composite Devices-Types, Materials, Applications, New Developments, Industry Structure and Global Markets.” Contact IRAP for details.
Piezoelectric Ceramic/Ceramic Composite Applications
- Sonar, hydrophones, sonobuoys, depth sounders, targets, fuse devices, SAW devices, sub bottom profiling, ringers
- Ultrasonic cleaners, welders, degreasers, touch sensors and probes; thickness gauging; flaw detection; seismic and integrated sensors; level indicators; pyroelectric detectors; ultrasonic drilling; vibrators and vibration measurements; geophones; delay lines; TV and radio resonators; airplane beacon locators; ignition systems; impact, humidity, pressure and position sensors; relays; ink printing; alarm systems; structural health monitoring; straingauges; smart materials for aircraft wings; precision mechanics; HVDC building control systems; noise and vibration damping; non-destructive testing
- Ultrasonic cataract removal, bubble detectors, therapy, and transducers; insulin pumps; fetal heart detectors; flow meters; disposable patient monitors; ultrasonic imaging; vaporizers
- Knock sensors, wheel balances, radio filters, seat belt buzzers, air flow, airbag sensors, fuel atomization, tire pressure indicators, spark ignition, audible alarms, keyless door entry, interior light movement
- Humidifiers, gas grill igniters, telephones, tread wear indicators, smoke detectors, microwave ovens, jewelry cleaners, phonograph cartridges, speakers, cigarette lighters, lighting security, musical instruments, ultrasonic sewing, squiggle motors for camera phones, electronic shock absorbers for skis, robots and toys, microphones, headphones, beepers in watches and other electronics
- Micro-actuators for hard disks, transformers for notebooks, semiconductor equipment, micro- and nano-lithography, data storage components, print heads