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What do cell phones, diesel fuel injectors, acoustic guitar pickups, grill igniters, ultrasonic transducers, vibration sensors, certain printers, and musical greeting cards all have in common? Besides being electronic devices, all of these applications utilize piezoelectricity in some way. Let’s explore how piezoelectricity works and look at some applications and examples of piezoelectric materials in day to day life.

How Does Piezoelectric Material Work?

Dating all the way back to and the groundbreaking work of brothers Pierre and Jacques Curie, the piezoelectric effect refers to the ability of specific materials — such as quartz, tourmaline, topaz and Rochelle salt — to produce an electric charge when subjected to mechanical stress. The term “piezo” can even trace its roots back to ancient Greek, where its meanings relate to actions of pushing, squeezing and pressing.

No piezoelectric effect explanation would be complete without a brief discussion of what piezoelectric devices are as well. Today, thanks to the additional development of manmade piezo materials — including piezoelectric ceramics — the applications of piezoelectricity in electronic devices are growing at an exciting pace.

How Does the Piezoelectric Effect Work With Sensors and Motors?

To begin with, there’s probably no more popular application of the piezoelectric effect than as a high voltage power source in electric cigarette lighters and gas grills. In these cases, a hammer strikes a piece of piezo material, which then produces enough current to create a spark that ignites the flammable gas in its presence. However, in other applications like sensors, the hammer as an exciter of the piezo material is typically replaced by other forms of energy like sound waves — including ultrasound.

When they’re put to work in sensors, piezo materials can detect even some of the most minute disturbances and anomalies, which makes them ideal devices in industrial nondestructive testing and medical imaging.

In other instances, piezoelectric motors can perform highly precise and repeatable movements. This ability makes them excellent devices for the precision movements of sensitive optical devices like telescopes and microscopes.

What are the Advantages and Disadvantages of Piezoelectricity?

Compared to other electronic components, piezoelectric devices have several advantages, as well as some disadvantages.

Their advantages include the following aspects:

• No external power source required: Thanks to their ability to produce a voltage when acted upon by a force, piezo materials require no external power source.
• Easy installation: With small dimensions, they’re a great fit and easily installed in high-density electronic devices.
• Responsiveness to high-frequencies: Compared to other devices, piezo materials have a substantially higher frequency response — which makes them wonderfully responsive in even the most demanding situations.
• Highly flexible materials: Most piezo materials can be constructed in a wide variety of shapes and sizes, so they’re highly useful across various applications and fields.

Piezo materials also display the following limitations or disadvantages:

• Small amount of electric charge: Though they’re self-generating, piezo materials produce fairly small electric charges, which means a high impedance cable is required to connect them to an electrical interface.
• Environmental conditions affect performance: Piezo materials are affected by temperature and changes in humidity. Plus, while in the static condition, they can’t measure output.
• Output is relatively low: While some piezo materials produce more output than others, they’re all relatively low. For their use to be optimized, an external circuit will often be required.

What are Common Uses for Piezoelectricity 

What are the Uses of Piezoelectric Actuators in Industrial Applications?

The industrial sector often employs piezoelectric sensors for a variety of uses. Some common, everyday uses include:

Engine Knock Sensors — Engine manufacturers are constantly facing challenges related to the control of engine parameters. Under the wrong circumstances, gasoline engines are susceptible to an undesirable phenomenon known as detonation. When detonation occurs, the air/fuel charge explodes instead of burning smoothly thereby damaging the engine. Historically, this is why most manufacturers designed engines with conservative operational margins at the expense of efficiency — it was to avoid this notorious problem.

With the development of better control systems, the relevant engine parameters may be adjusted in real-time to maximize efficiency and power. If detonation begins to occur, piezoelectric knock sensors can be employed to sense the detonation before it becomes problematic. This gives control systems time to make the required adjustments.

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Pressure Sensors — In nearly any application requiring the measurement of dynamic pressure changes, using piezoelectric pressure sensors yields more reliable results than using conventional electromechanical pressure sensors. This is because piezoelectric devices have a high frequency response and signal conversion without requiring any bellows, diaphragm, or any type of mechanical linkage in conjunction with a strain gage or displacement sensor.

Sonar Equipment — Depth sounders and sonar equipment rely extensively on piezoelectric sensors to transmit and receive ultrasonic “pings” in the 50-200kHz range. Besides having an ideal frequency response for such applications, piezoelectric transducers have a high power density that enables large amounts of acoustic power to be transmitted from a small package. For instance, a transducer that is only 4” (100 mm) in diameter may be capable of handling power output greater than 500 watts.

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What are the Uses of Piezoelectric Sensors in Medical Applications?

While piezoelectric sensors are highly valuable to the industrial sector, the industry also makes use of piezoelectric actuators for a variety of applications:

Diesel Fuel Injectors — In the last decade, regulations on emissions from diesel engines have become increasingly stringent. Additionally, customers continue to demand quieter engines with improved power and torque curves. In order to meet these stringent demands for compliance and performance, engine manufacturers have resorted to using precisely timed and metered injections of fuel during the combustion process.

As incredible as this may sound, a single fuel injector may switch fuel flow with pressures exceeding 26,000 psi ( bar) on and off several times in rapid succession during a single power stroke. Such precise control of high-pressure fluid is made possible by using piezoelectric actuators controlling small valves within fuel injectors.

Fast Response Solenoids — Some processes require quick and precise mechanical actuation that is difficult, if not impossible, to achieve with electromagnetic solenoids. While speed may not always be a concern, power consumption or compactness of size is a top priority. In such cases, piezoelectric actuators are often able to fill the niche as they provide fast response and low power consumption in small packages, compared to electromagnetic solenoids.

Optical Adjustment — Some optics need to be adjusted or modulated with a wide frequency response and with a minimum number of moving parts. Piezoelectric actuators are often employed in such applications where they provide fast and accurate control over a long service life:

– The angle of a mirror or diffraction grating may need to be precisely varied according to an electrical input. Such applications are often encountered in optical or physics experiments.

– Earth-based telescope arrays are subject to atmospheric distortion, and spacecraft optics are subject to movement and vibration. In such cases, optics may need to be adjusted (shaped or contoured) in real-time by means of a control system. This will compensate for aberrations that would otherwise impede image resolution.

– Some fiber optic converters rely on piezoelectric actuators to modulate the output of a laser.

Ultrasonic Cleaning — Piezoelectric actuators are also used for ultrasonic cleaning applications. To perform ultrasonic cleaning, objects are immersed in a solvent (water, alcohol, acetone, etc.). A piezoelectric transducer then agitates the solvent. Many objects with inaccessible surfaces can be cleaned using this methodology.

Ultrasonic Welding — Many plastics can be joined together using a process known as ultrasonic welding. This type of process requires ultrasonic waves to be transmitted to a focused area where they can cause pieces of plastic to fuse together. Frequently, piezoelectric actuators are used to accomplish this task.

Piezoelectric Motors — One advantage of using piezoelectric materials is that their characteristics are precise and predictable. Thus, expansion and contraction of a piezoelectric actuator can be precisely controlled as long as the supply voltage is controlled. Some motor designs take advantage of this fact by using piezoelectric elements to move a rotor or linear element in precise increments. Precision on the order of nanometers can be achieved with some piezo motor designs. Piezo motors work at a wide range of frequencies but typically work best in a low frequency range.

In addition to their inherent precision, piezoelectric motors can be used in environments with strong magnetic fields or cryogenic temperatures — environments where conventional motors are unlikely to work. These unique challenges are present in NMRI machines, particle accelerators, and other similar environments.

Stack Actuators — Multiple piezoelectric elements may be stacked to multiply the displacement achieved for a given voltage. These types of devices are known as stack actuators, and they are employed in a variety of specialty applications. Compared to conventional electromagnetic actuators, stack actuators have the following unique advantages:

• They can function at cryogenic temperatures or in environments with strong magnetic fields.
• They can produce a large amount of force in a small package
• They can respond almost instantly to input with high rates of acceleration.
• They can achieve extremely high degrees of precision.
• They only consume power when work is actually being performed.

These actuators find their uses in proportioning valves, electrical relays, optical modulation, vibration dampening, and other applications requiring fast or precise control of movement.

Stripe Actuators — Two strips of piezoelectric material may be sandwiched together in a configuration that is similar to a bimetallic strip. In this configuration, the electric input causes one strip to expand while the other strip simultaneously contracts, causing a deflection.

Piezoelectric Relays — Piezoelectric elements may be implemented to actuate electromechanical relays or switches. For these applications, either stripe actuators or stack actuators may be used to open and close electrical contacts. Such devices are maintenance-free and last through many cycles without noticeable wear. As an additional benefit, using piezoelectric actuators to operate electrical contacts enables fast and precise control in small packages that are either difficult or impossible to achieve with electromagnetic relays.

What are the Uses of Piezoelectric Sensors in Medical Applications?

Take a look at how the medical field also implements piezoelectric sensors for a variety of day-to-day applications:

Ultrasound Imaging — Piezoelectric transducers are often used in medical ultrasound equipment. Advances in equipment over the decades have enabled improved monitoring of pregnancies and facilitated minimally invasive surgical procedures.

Ultrasonic Procedures — Some non-invasive medical procedures rely on the use of focused ultrasonic waves to break up kidney stones or destroy malignant tissue. Additionally, the advent of the harmonic scalpel has enabled surgeons to simultaneously incise and coagulate tissue during a surgical procedure without the need for cauterization. This leads to less tissue damage, less blood loss, and faster healing times.

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What are the Uses of Piezoelectric Actuators in Consumer Electronics?

What about consumer electronics and technology that is sold in stores throughout the country? Unknown to many consumers, piezoelectric actuators are used in electronics everywhere:

Piezoelectric Printers — Generally speaking, there are two main types of printers that use piezoelectric actuators:

– a dot-matrix printer —  In a piezoelectric dot matrix printer, piezoelectric actuators in the printer head move needle-like pins that “poke” through a strip of ink tape (similar to a typewriter) against a piece of paper in various patterns to form characters. For most applications, the use of dot-matrix printers has been superseded by other technologies. However, a dot-matrix printer is the only printer technology capable of generating duplicate and triplicate carbon-copy printouts.

– inkjet printer — In a piezoelectric inkjet printer, piezoelectric actuators in the printer head act on small diaphragms or otherwise change the geometry of an inkwell so that ink droplets are forced out of an orifice onto paper. This is one of the dominant technologies in the printer market to date.

Piezoelectric Speakers — Piezoelectric speakers are featured in virtually every application that needs to efficiently produce sound from a small electronic gadget. These types of speakers are usually inexpensive and require little power to produce relatively large sound volumes. Thus, piezoelectric speakers are often found in devices such as the following:

• Cell phones
• Ear buds
• Sound-producing toys
• Musical greeting cards
• Musical balloons

Piezoelectric Buzzers — Piezoelectric buzzers are similar to piezoelectric speakers, but they are usually designed with lower fidelity to produce a louder volume over a narrower frequency range. Buzzers are used in a seemingly endless array of electronic devices, including:

Piezoelectric Humidifiers — Many cool mist humidifiers use a piezoelectric transducer to transmit ultrasonic sound energy into a pool of water. The ultrasonic vibrations cause fine water droplets to break away and atomize from the surface of the pool where they become entrained in an air stream and enter the desired space.

Electronic Toothbrushes — Linear piezoelectric actuators are implemented to vibrate the bristles in some electronic toothbrushes.

Piezoelectric Materials for Musical Applications

Aside from technological and industrial applications, piezoelectricity also benefits the arts. There are a variety of musical applications that use piezoelectricity:

Instrument Pickups — Many acoustic-electric stringed instruments utilize piezoelectric pickups to convert acoustic vibrations to electric signals. Typically, a strip of piezoelectric material is placed between the instrument body and a structure that supports the strings. For instance, an acoustic-electric guitar usually houses its piezoelectric strip beneath the bridge and within the saddle. As the strings vibrate, the strip is agitated to generate an electric signal. Electric pickups on violins, violas, and cellos use the same concept, but the piezoelectric pickup may be clamped to the bridge or integrated within the bridge — instead of being located between the bridge and the instrument body.

Microphones — Some microphones (such as contact microphones for percussion instruments) use piezoelectric materials to convert sound vibrations to an electrical output. These microphones generally possess high output impedances that must be matched when designing their respective pre-amplifiers.

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Using Piezoelectricity in Other Applications

Do you have an application that wasn’t listed on the list? Are you wondering if you can use piezoelectricity? The following uses of piezoelectricity represent other options for your industry:

Piezoelectric Ignitors — This is, perhaps, the most well-known and ubiquitous use of piezoelectricity. In a piezoelectric igniter, a button or trigger is used to cock and release a spring-loaded hammer, and the hammer is used to strike a rod shaped piezoelectric ceramic. The sudden mechanical shock to the piezoelectric ceramic produces a rapid rise in voltage that is high enough to jump a sizeable spark gap and ignite fuel. Piezoelectric igniters are commonly used for butane lighters, gas grills, gas stoves, blowtorches, and improvised potato cannons.

Electricity Generation — Some applications require the harvesting of energy from pressure changes, vibrations, or mechanical impulses. The harvesting of energy is possible by using piezoelectric materials to convert deflections or displacements into electrical energy that can either be used or stored for later use.

Microelectronic Mechanical Systems (MEMS) — MEMS devices have become more commonplace as more integrated capabilities are required in smaller packages, such as cell phones, tablet computers, etc. The advantage of MEMS devices is that gyroscopes, accelerometers, and inertial measuring devices can be integrated into chip-sized packages. In order to accomplish such a feat, piezoelectric actuators and sensors are often used.

Tennis Racquets — A somewhat unusual application for piezoelectricity integrates piezoelectric fibers into the throat of a tennis racquet along with a microcontroller in the handle. When the tennis player strikes the ball, the racquet frame deflects and generates an electric output that is boosted, reversed, and fed back into the fibers. This is an attempt to cause destructive interference and dampen structural vibration.

Using Piezoelectricity in Defense Applications

If you’re a part of the defense industry, you can use piezoelectricity for a variety of applications:

Micro Robotics — In the field of small robotics, small power-efficient mechanical actuators and sensors are needed. With the use of piezoelectric actuators, building something as small as a robotic fly that can crawl and fly is technically feasible. In fact, a new field of robotic technology known as Micro Air Vehicles aims to build small drones the size of insects or birds that fly using flapping wings. They control surfaces just as birds and insects do. These types of feats in miniaturization are possible, in part, by using piezoelectric actuators.

Course-changing Bullets — Recently, DARPA invented a .50-caliber bullet that can change course in mid-flight. As absurd as this innovation may sound to some readers, the bullet uses an optical sensor that is mounted on its nose in conjunction with a control system and moveable tail fins to steer itself toward a laser-illuminated target. Although DARPA has not revealed much about their Extreme Accuracy Tasked Ordinance (EXACTO) bullet, the most likely means of manipulating the tail fins probably involves piezoelectric actuators.

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What are the challenges in sourcing reliable piezoelectric materials?

Sourcing reliable piezoelectric materials can be challenging due to the variability in their properties when sourced from different manufacturers. Additionally, the difficulty in ensuring consistent quality and performance across batches complicates the selection process. APC International is a top producer of high quality piezo products. Our processing capabilities include: designing, machining, pressing, firing, custom electroding, poling and testing piezoelectric ceramics and devices. We also have our ISO certification. 

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If you wish to explore the world of using piezoelectricity or learn more about what APC International can offer, take a look at our product and service offerings. Contact our team with any questions or visit our knowledge center today.

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Piezoelectricity & Wearable Technology 

A Closer Look at Piezoelectric Crystal

Introduction

Piezoelectric crystals are a class of crystalline materials capable of inducing changes in charge distribution and generating electric field responses through mechanical stress. The unique properties of this material make it useful in many fields, especially in sensor technology and energy conversion. The core feature is that piezoelectric crystals deform or redistribute charge when mechanical stress or an electric field is applied, enabling efficient conversion between electrical and mechanical energy. With the advancement of technology, the application fields of piezoelectric crystals are expanding. From smart materials to energy recovery technologies, their innovative potential leads to new opportunities and solutions for industry. An in-depth understanding of the properties and applications of piezoelectric crystals is therefore essential for understanding the direction of modern technology.

What Is a Piezoelectric Crystal?

A piezoelectric crystal is a non-centrosymmetric crystal. When subjected to mechanical force, it deforms, causing the relative displacement of charged plasma points. This results in positive and negative bound charges appearing on the crystal surface. When the external force is removed, the crystal returns to its uncharged state. This phenomenon is known as the piezoelectric effect.

The piezoelectric crystal has a polar axis with a potential difference at both ends, known as piezoelectricity. The amount of charge produced by a force applied to a crystal is directly proportional to the magnitude of the external force. Conversely, if an electric field is applied to the crystal, the crystal will be mechanically deformed in a certain direction; when the applied electric field is withdrawn, the deformation disappears. This phenomenon is called the inverse piezoelectric effect, also known as the electrostriction effect.

Crystal (α-quartz) is a well-known piezoelectric crystal. Common piezoelectric crystals include sphalerite, calcite, tourmaline, red zincite, GaAs, barium titanate and its derived structural crystals, KH2PO4, NaKC4H4O6-4H2O (rosette salt), and table sugar.

Fig. 1 Natural Quartz Crystals

Crystal Structure Characteristics of Piezoelectric Crystals

Piezoelectric crystals usually have a non-centrosymmetric crystal structure. Common piezoelectric materials such as quartz (SiO₂), barium titanate (BaTiO₃), and PZT ceramics (lead zirconium titanate) fall into this category.

In a non-centrosymmetric crystal structure, the electric dipoles (i.e., the centers of charge) do not cancel each other out so that the entire crystal exhibits a net electric dipole moment. The electric dipoles (consisting of positive and negative charge centers) inside a piezoelectric crystal are usually randomly distributed in the natural state and do not exhibit macroscopic polarization. Through a polarization treatment (heating above the Curie temperature, applying a strong electric field, and then cooling), the electric dipoles can be rearranged in the presence of an applied electric field to align them in the direction of the electric field, thus giving the material a permanently polarized state.

Fig. 2 Crystal Structure of Quartz (SiO2)

Principles of Piezoelectric Phenomena

When mechanical stress is applied to a piezoelectric crystal (e.g., compression or stretching), small displacements of the electric dipoles inside the crystal result in a redistribution of the charge centers, generating a charge on the surface of the crystal. This charge distribution produces a potential difference that can be measured and expressed as a piezoelectric voltage. This process of charge generation by pressure is the positive piezoelectric effect.

Accordingly, when an electric field is applied to a piezoelectric crystal, the electric dipoles inside the crystal rearrange or rotate in response to the electric field, resulting in mechanical deformation of the crystal. This deformation can drive mechanical motion, such as in a piezoelectric actuator. This phenomenon is called the inverse piezoelectric effect.

Fig. 3 Piezoelectric Effect

It is mainly caused by the rearrangement of electric dipoles and the coupling of stress and electric field. The rearrangement of the electric dipoles occurs mainly above the Curie temperature when the crystal structure of the piezoelectric material allows the electric dipoles to rotate freely. When an electric field is applied, the electric dipoles are aligned along the direction of the electric field. Upon cooling, the alignment direction of the electric dipoles is fixed, causing the material to exhibit macroscopic polarization. The coupling effect of stress and the electric field is manifested in that when mechanical stress is applied, the crystal structure undergoes minor changes, and the relative positions of the electric dipoles are altered, leading to the redistribution of the charge centers and the generation of electric charges; when an electric field is applied, the rearrangement of the electric dipoles leads to the deformation of the crystal structure and the generation of mechanical strains.

Polarization of Piezoelectric Crystals

What is Polarization?

The polarization of piezoelectric crystals is aligning the electric dipoles in a piezoelectric material in a specific direction by applying a strong electric field. This process gives the material the ability to acquire the piezoelectric effect and maximize its piezoelectric properties.

Fig. 4 Ceramic Polarization

Steps of Polarization Treatment

1. Preparation of materials: Piezoelectric materials (e.g. barium titanate, PZT ceramics, etc.) are prepared to the desired shape and size.

2. Heating: Heat the material above its Curie temperature. Curie temperature is the temperature at which the material changes from a ferroelectric phase to a cis-electric phase. At this temperature, the electric dipoles within the material are in a randomly oriented state.

3. Applied electric field: A strong electric field (usually a few thousand volts per millimeter) is applied to the material at a high temperature. This electric field causes the electric dipoles inside the material to rearrange and align themselves in the direction of the electric field.

4. Cooling: The material is cooled below the Curie temperature while maintaining the electric field. During the cooling process, the electric dipoles remain aligned along the direction of the electric field, resulting in a permanently polarized state of the material.

5. Removal of the electric field: After the material is cooled to room temperature, the external electric field can be removed, at which point the material has acquired permanent piezoelectric properties.

Principle of Polarization Processing

When the material is above the Curie temperature, the piezoelectric material is in the cis-phase, and the electric dipoles are free to rotate and rearrange. At this time to strengthen the electric field so that the electric dipole along the direction of the electric field alignment, the formation of a unified polarization direction. After the desired polarization direction is reached, the temperature is lowered to allow cooling. The cooling process fixes the alignment of the dipoles so that they remain polarized in the absence of an external electric field.

Importance of Polarization Treatment

Polarization treatment is critical to the performance of piezoelectric materials. Unpolarized materials do not exhibit significant piezoelectric effects, and the piezoelectric properties (e.g., piezoelectric coefficient) of polarized materials are greatly improved, enabling them to efficiently convert mechanical and electrical energy. It is through polarization that piezoelectric materials can achieve their superior performance in applications such as sensors, actuators, and electronic components.

Common Piezoelectric Materials and Their Applications

1. Quartz

Quartz is a widely used natural piezoelectric crystal, because of its stability and high performance in many fields. Its chemical composition for the hexagonal crystal system of silicon dioxide (SiO2), the appearance of the general colorless transparent crystal. The low coefficient of thermal expansion (ordinary quartz has a coefficient of thermal expansion of about 0.5*10^-6/°C) and high-quality factor (quartz has a quality factor of about 115*) allow quartz to excel in high-frequency oscillators and filters even with relatively low piezoelectric coefficients. Quartz has excellent chemical and mechanical stability and maintains its piezoelectric properties over a wide temperature range.

Quartz crystals are usually prepared both naturally mined and synthetically synthesized. As a natural mineral, quartz crystals are relatively easy and inexpensive to obtain. Synthetic quartz can often be used to meet high purity and specific size requirements. The cutting and processing of quartz crystals can be precisely controlled to ensure optimum performance in the application. Different cutting directions affect the piezoelectric properties of quartz, such as AT cut and BT cut.

Quartz crystal oscillators are used in electronic devices such as quartz watches, computers, and cellular phones to provide accurate time references. Filters made of quartz crystals can be used in wireless communication devices to ensure the quality and stability of signal transmission. Quartz crystals are also used in pressure sensors, accelerometers, and microphones to convert mechanical vibrations into electrical signals in a wide range of industrial automation, aerospace, and audio equipment.

Applications for quartz in surface acoustic wave (SAW) devices include SAW filters and SAW sensors for signal processing and environmental monitoring. In optical equipment, quartz crystals are used to make optical modulators, prisms, and lenses. In ultrasound equipment, quartz crystal ultrasonic transducers are used for medical diagnostics and industrial testing. In the field of metrology and test equipment, quartz crystals are used as standard frequency sources in frequency meters and signal generators. Quartz has an indispensable position in modern technology and industry due to its high stability, high precision, and low cost.

Fig. 5 Quartz Crystal Filters

2 Barium Titanate

Barium titanate (BaTiO3), normally colorless or white crystals, has a chalcogenide structure (with different crystalline phases at different temperatures, such as tetragonal, cubic, and hexagonal). The piezoelectric properties of barium titanate originate from the crystalline phase transition and symmetry breaking in its chalcogenide structure due to temperature changes. Barium titanate maintains its piezoelectric properties over a wide range of temperatures, making it suitable for use in a variety of environmental conditions.

The high piezoelectric constants of barium titanate (d31 is about -80 x 10^-12 C/N, while d33 is about 190 x 10^-12 C/N) give it excellent performance in many applications. The high dielectric constant of barium titanate gives it a high capacitance in capacitor applications. At room temperature, its natural dielectric constant is about .

In electronic devices, barium titanate is used in the manufacture of multilayer ceramic capacitors (MLCCs), which have high capacitance and small size and are widely used in smartphones, computers, and household appliances. In the field of sensors, barium titanate is used in the manufacture of pressure sensors and acceleration sensors, which are used in industrial automation, medical equipment, and automotive electronics.

Barium titanate is also used in the manufacture of piezoelectric actuators, which produce mechanical deformation under voltage and are used in precision positioning systems, microelectromechanical systems (MEMS), and optical alignment. Ultrasonic transducers are another important application for barium titanate, which is widely used in medical ultrasonic diagnostics, industrial non-destructive testing, and ultrasonic cleaning equipment.

Barium titanate is also used in piezoelectric filters and resonators in wireless communication systems to ensure signal clarity and transmission quality. In addition, the piezoelectric properties of barium titanate are used to develop piezoelectric energy harvesting devices that convert mechanical vibration or kinetic energy from the environment into electrical energy to power low-power devices.

Barium titanate also has applications in electroacoustic converters such as speakers and microphones, converting electrical signals into sound waves or vice versa. Its applications in medical devices include piezoelectric-driven medical instruments such as micropumps and precision drug delivery systems. Because of its high piezoelectric constant and good stability, barium titanate plays an important role in modern electronics, communications, medical, and industrial automation.

Fig. 6 Multilayer Ceramic Capacitors

3 Lead Zirconate Titanate (PZT)

Lead Zirconate Titanate (PZT) is a very important and widely used piezoelectric ceramic material. The chemical formula is Pb(ZrₓTi₁₋ₓ)O₃, and the structure of PZT can be varied at different Zr/Ti ratios, including the chalcocite-type structure. PZT undergoes phase transitions (e.g., from tetragonal to cubic phases) at different temperatures, and these transitions affect its piezoelectric properties.

In ultrasonic devices, PZT is used to make transducers for medical ultrasound diagnostics, industrial non-destructive testing, and underwater sonar systems. The sensor field utilizes the piezoelectric effect of PZT to make pressure sensors and acceleration sensors for applications in industrial automation, medical devices, automotive safety systems, and seismic monitoring.

PZT piezoelectric actuators produce mechanical deformations under the action of an electric field and are used for precision positioning, optical adjustments, and fine-motion control in printing devices and microscopes. In addition, PZT materials are used as piezoelectric filters and resonators in wireless communication systems to ensure signal clarity and transmission quality.

In energy harvesting, PZT converts mechanical energy or vibrational energy in the environment into electrical energy to feed wireless sensor networks and wearable devices. PZT is also used to make speakers and microphones that convert electrical signals into sound waves or vice versa. Its high piezoelectric constant and high electromechanical coupling coefficient make it play an important role in the fields of modern electronics, communications, medicine, and industrial automation.

Fig. 7 Lead Zirconate Titanate Piezoelectric Ceramic Sheet

4 Zinc Oxide (ZnO)

Zinc oxide has a hexagonal wurtzite structure, which is a non-centrosymmetric structure that gives it piezoelectric properties. The Zn²⁺ and O²- ions in the hexagonal wurtzite structure generate an electric dipole moment under stress, resulting in a piezoelectric effect. This material has a high piezoelectric constant and a good electro-mechanical coupling coefficient.

Zinc oxide (ZnO) as a piezoelectric crystal has many applications in several fields due to its high piezoelectric constant, high sensitivity, and good chemical stability. In the field of sensors, ZnO is used to make gas sensors and pressure sensors, which are widely used in industrial automation and consumer electronics.

In actuators, zinc oxide is used in microelectromechanical systems (MEMS) actuators and acoustic devices for precision positioning and high-fidelity audio output. The piezoelectric properties of zinc oxide are also used for energy harvesting, through nanogenerators and piezoelectric energy harvesters that convert mechanical energy into electrical energy to power low-power devices.

In addition, zinc oxide is used as a transparent electrode material in optoelectronic devices, light-emitting diodes (LEDs), and photodetectors to improve photoelectric conversion efficiency. Zinc oxide nanomaterials are also used in biosensors to detect biomolecular and cellular activities, which are widely used in medical diagnostics and biological research. Its excellent piezoelectric, optoelectronic, and chemical properties make zinc oxide valuable in modern electronics, communications, medical, and industrial automation applications.

Fig. 8 Zinc Oxide Varistors

5 Lithium Niobate (LiNbO₃)

Lithium Niobate (LiNbO₃) is an important piezoelectric crystal material, which is widely used in many high-tech fields because of its excellent piezoelectric, electro-optical, non-linear optical and acoustic-optical properties. Lithium niobate has a tetragonal crystal system of chalcogenide structure, the non-central symmetry of this structure gives it piezoelectric and electro-optical properties, and the relative displacement of lithium ions and niobium ions in the lattice under stress produces the shift of positive and negative charge centers.

Lithium niobate has high piezoelectric constants and electromechanical coupling coefficients, making it excellent for many applications. As a piezoelectric crystal, lithium niobate (LiNbO₃) has a wide range of applications in several fields due to its excellent piezoelectric, electro-optical, acousto-optical, and non-linear optical properties.

Lithium niobate fabricates electro-optical modulators and waveguide devices in optical devices, which are widely used in optical communications and integrated optics. In acousto-optic devices, lithium niobate is used in acousto-optic modulators and acousto-optic delay lines, which are used to modulate and process light beams and radio frequency signals.

In the field of sensors, lithium niobate accelerometers, and pressure sensors are widely used in aerospace, automotive safety systems, seismic monitoring, and industrial automation. Piezoelectric filters and resonators made of lithium niobate are used in wireless communication systems to select and control frequencies, ensuring signal clarity and transmission quality.

In laser devices, the nonlinear optical properties of lithium niobate are used in the manufacture of frequency multipliers and optical parametric oscillators to enable modulation of the laser frequency and adjustment of the wavelength. In addition, lithium niobate has important applications in the medical and biotechnology fields, such as in medical ultrasound devices and biosensors that provide high-precision ultrasound imaging and biomolecular detection.

Its high piezoelectric constant, excellent electro-optical effect, and chemical stability make lithium niobate valuable for modern electronics, communications, optics, medical and industrial automation applications.

Fig. 9 Crystal Structure of Lithium Niobate

6 Lithium Tantalate (LiTaO₃)

Lithium Tantalate (LiTaO₃) is an important piezoelectric crystal material, which is widely used in many high-tech fields because of its excellent piezoelectric, electro-optical, acousto-optical, and non-linear optical properties. Lithium tantalate has a calcite structure with a tripartite crystal system, and this non-centrosymmetric structure gives it piezoelectric, electro-optical, and nonlinear optical properties. Lithium tantalate has a high piezoelectric constant and electromechanical coupling coefficient, which can effectively convert mechanical energy into electrical energy or vice versa.

As a piezoelectric crystal, lithium tantalate (LiTaO₃) has a wide range of applications in several fields due to its excellent piezoelectric, electro-optical, acousto-optical, and non-linear optical properties.

In optical devices, LiTaO₃ is used to manufacture electro-optical modulators and optical waveguide devices, which are widely used in optical communications and integrated optics. In acousto-optic devices, lithium tantalate is used in acousto-optic modulators and acousto-optic delay lines, which are used to modulate and process light beams and radio frequency signals.

For sensor applications, lithium tantalate-based accelerometers and pressure sensors are prevalent in aerospace, automotive safety systems, seismic monitoring, and industrial automation. Its piezoelectric filters and resonators are essential in wireless communication systems to select and control frequencies, thereby ensuring signal clarity and transmission quality.

The nonlinear optical properties of lithium tantalate are crucial in laser devices, particularly in the manufacturing of frequency multipliers and optical parametric oscillators. These devices enable modulation of the laser frequency and adjustment of the wavelength. Additionally, lithium tantalate finds significant use in the medical and biotechnology sectors, such as in medical ultrasound devices and biosensors that offer high-precision ultrasound imaging and biomolecular detection.

Its robust piezoelectric constant, superior electro-optical effect, and excellent chemical stability make lithium tantalate indispensable for modern electronics, communications, optics, medical, and industrial automation applications.

Fig. 10 Lithium Tantalate Crystal

7 Conclusion

Piezoelectric crystals have the function of interconverting mechanical and electrical energy due to their special microstructure. The discovery and application of piezoelectric crystals such as quartz, lithium niobate, and lithium tantalate have not only profoundly influenced the direction of modern scientific and technological progress, but also demonstrated the great potential of materials science in solving real-world problems.

With the increasing demand for new material properties, further innovations in piezoelectric crystal technology will continue to push the boundaries of human technology and bring more innovation and progress to our society. Stanford Advanced Materials (SAM) is at the forefront of providing high-quality piezoelectric materials to meet these growing technological needs.

References:

[1] Nogueira A E F ,Campos B V R ,Nascimento D C P J , et al.Piezoelectric temperature acoustic sensor of LiNbO3 crystal fibers operating at radio frequencies[J].Journal of Crystal Growth,,-.

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