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History, Trends, and Applications of Piezoelectric Ceramics

Piezoelectric ceramics is a generic term for ferroelectric ceramics that are made by high-temperature sintering and the solid-phase reaction of oxide mix (zirconium oxide, lead oxide, titanium oxide, etc.) and are made to have piezoelectric effect by DC high voltage polarization treatment, which is a functional ceramic material that can convert mechanical and electrical energy to each other.

Due to the good mechanical properties and stable piezoelectric properties, piezoelectric ceramics, as an important force, heat, electricity, and light-sensitive functional materials, have been widely used in sensors, ultrasonic transducers, micro-displacers, and other electronic components.

With the continuous research and improvement of material processes, as well as the rapid development of electronics, information, aerospace, and other high-tech fields, the production technology and application development of piezoelectric ceramics as a new material containing high intelligence is a hot topic of concern.

Electroceramics Piezoelectric ceramics are a class of electronic ceramic materials with piezoelectric properties. The main difference from typical piezoelectric quartz crystals that do not contain ferroelectric components is that the crystalline phases that make up their main components are all grains with ferroelectric properties.

Since ceramics are polycrystalline aggregates with randomly oriented grains, the spontaneous polarization vectors of the individual ferroelectric grains in them are also chaotically oriented. In order for the ceramic to exhibit macroscopic piezoelectric properties, it must be polarized under a strong DC electric field after the piezoelectric ceramic has been fired and an electrode on the end face, so that the original chaotic orientation of the respective spontaneous polarization vector is optimally oriented in the direction of the electric field. The piezoelectric ceramic has a certain piezoelectric nature.

Applications of Piezoelectric Ceramics

Since the birth of the first ceramic-type piezoelectric material, barium titanate, in 1942, applications as piezoelectric ceramics have spread to all aspects of people’s lives. The application of piezoelectric materials as a link of electromechanical coupling can be roughly divided into two major areas: the application in terms of piezoelectric ceramic frequency control devices represented by piezoelectric resonators and the application as a quasi-static conversion of mechanical and electrical energy.

Piezoelectric Oscillators and Piezoelectric Ceramic Frequency Control Devices

The polarized piezoelectric ceramics, i.e., piezoelectric oscillator, has an intrinsic vibration frequency determined by its size, and stable electrical oscillation can be obtained by using the intrinsic vibration frequency of the piezoelectric oscillator and piezoelectric effect. When the frequency of the applied voltage is the same as the intrinsic vibration frequency of the piezoelectric oscillator will cause resonance, the amplitude increases greatly. This process of an alternating electric field through the inverse piezoelectric effect to produce strain, and strain through the positive piezoelectric effect to produce current, to achieve the maximum mutual conversion of electrical energy and mechanical energy. Using this feature of piezoelectric oscillators, various filters, resonators, and other devices can be manufactured.

These devices have low cost, small size, no moisture absorption, long life, good frequency stability, equivalent quality factor than the LC filter, the applicable frequency range, high precision, especially used in multi-way communication, amplitude modulation reception and a variety of radio communication and measurement instruments can improve the anti-interference ability. So now has replaced a significant part of the electromagnetic oscillator and filter, and this trend is still developing.

Piezoelectric Transformer

The piezoelectric transformer is prepared by using the mutual conversion of electrical and mechanical energy of the piezoelectric effect and consists of two parts, the input and the output, whose polarization directions are perpendicular to each other. The input end is polarized along the thickness direction and vibrates longitudinally after applying an alternating voltage, and the output end will have a high voltage output due to the inverse piezoelectric effect.

The piezoelectric ceramic transformer is a new type of solid-state electronic device, compared with the traditional electromagnetic transformer has the advantages of simple structure, small volume, lightweight, large voltage ratio, good stability, no electromagnetic interference and noise, high efficiency, high energy density, high safety, no winding, non-combustible, no leakage phenomenon and electromagnetic radiation pollution.

The working mode of the piezoelectric ceramic transformer can be divided into the following categories: Rosen type piezoelectric ceramic transformer, thickness vibration mode piezoelectric ceramic transformer, radial vibration mode piezoelectric ceramic transformer, etc.

In recent years, there are some piezoelectric transformers with better performance, such as third-order vibration mode Rosen-type piezoelectric ceramic transformers for both inputs and high-power multilayer piezoelectric ceramic transformers. At present, piezoelectric ceramic transformers are mainly used in AC-DC, DC-DC, and other power devices and high-voltage generation devices, such as cold cathode tubes in liquid crystal displays, neon tubes, laser tubes, and small X-ray tubes, high-voltage electrostatic spraying, high-voltage electrostatic flocking and radar display tube drive.

Piezoelectric Transducer

A piezoelectric transducer is the use of the piezoelectric effect and inverse piezoelectric effect of piezoelectric ceramics to achieve the mutual conversion of electrical energy and acoustic energy. The piezoelectric ultrasonic transducer is one of them, which is a hydroacoustic device that transmits and receives ultrasonic waves underwater. The piezoelectric transducer in the water under the action of sound waves, the transducer ends will be induced charge, which is the acoustic receiver; if the piezoelectric ceramic sheet on the application of an alternating electric field, the ceramic sheet will sometimes become thinner and sometimes thicker, while generating vibration, the emission of sound waves, which is the ultrasonic transmitter.

A piezoelectric transducer is also widely used in industry as underwater navigation, ocean exploration, precision measurement, ultrasonic cleaning, solid flaw detection and medical imaging, ultrasonic diagnosis, ultrasonic disease treatment, etc. Another area of application of piezoelectric ultrasonic transducers today is telemetry and remote control systems, and specific examples of their applications include piezoelectric ceramic buzzers, piezoelectric igniters, ultrasonic microscopes, etc.

Piezoelectric Ultrasonic Motor

The piezoelectric ultrasonic motor is a new type of micro motor that uses the inverse piezoelectric effect of piezoelectric ceramics to generate ultrasonic vibration, amplifies the micro deformation of materials through resonance, and drives by the friction between the vibrating part and the moving part, without the usual electromagnetic coil.

Compared with the traditional electromagnetic motor, it has the characteristics of low cost, simple structure, small size, high power density, good low-speed performance (can achieve low-speed operation without deceleration mechanism), large torque and braking torque, fast response, high control accuracy, no magnetic field and electric field, no electromagnetic interference and electromagnetic noise, etc.

Piezoelectric Composites

In order to play a role in hydrophone applications, piezoelectric composites were gradually developed in the 1970s. A piezoelectric composite is a functional composite material with a piezoelectric effect composed of a piezoelectric ceramic phase and a polymer phase according to a certain connection method.

Due to the addition of the flexible polymer phase, the density, acoustic impedance, and dielectric constant of piezoelectric composites are reduced, while the superior value and electromechanical coupling coefficient of composites are increased, overcoming the disadvantages of the brittleness of simple piezoelectric ceramics and high cost of piezoelectric polymers. In addition to their use as hydrophones, piezoelectric composites are also used in industrial, medical, and communication applications. After more than 40 years of continuous research on piezoelectric composites, its application research has made considerable progress, but its complete theory has not yet been established, and its application development has yet to be fully explored. Currently, research on piezoelectric composites is mainly focused on developing connection types, improving molding processes, and preparing multifunctional devices.

Due to its own characteristics and performance advantages, the piezoelectric ultrasonic motor is widely used in precision instruments, aerospace, automatic control, office automation, micromechanical systems, micro-assembly, precision positioning, and other fields. At present, Japan is in a leading position in this field, and has been using piezoelectric ultrasonic motors for automatic focusing of cameras and camcorders, and has formed a large-scale series of products.

Nano Piezoelectric Ceramics

With the rapid development of nanotechnology in recent years, nano-ceramics have gradually attracted attention. Nanopowders are shaped and sintered to form dense and homogeneous bulk nanoceramics, which have greatly improved the toughness, strength, and superplasticity of materials, overcoming many shortcomings of engineering ceramics and having important effects on the mechanical, electrical, thermal, magnetic, optical, and other properties of materials.

By selecting the material composition system and modifying it with nanoscale particles, whiskers, wafer fibers, etc., we can obtain nano-piezoelectric ceramic materials with both high performance and low-temperature sintering. By controlling the growth of nanograins, quantum-limited effects and exotic ferroelectrics can be obtained to improve the electromechanical conversion and thermal release performance of piezoelectric pyrolytic materials. In recent years, various types of piezoelectric transformers, piezoelectric actuators, high-power ultrasonic welding technology, piezoelectric vibratory feeders, new ultrasonic CVD processes, and high-power ultrasonic engineering matched with nuclear power plants are all applications of nanoceramics in piezoelectricity.

Trends in Piezoelectric Ceramics

Lead-free piezoelectric ceramics, also known as environmentally coordinated piezoelectric ceramics, require ceramic materials that do not produce substances that may be harmful to the environment during preparation, use, and disposal in order to avoid harm to human health and reduce environmental pollution. However, currently used piezoelectric ceramic materials are mainly PZT-based materials, whose piezoelectric properties are greatly superior to other piezoelectric ceramic materials, and the electrical properties of the materials can be adjusted by doping modification and process control to meet the needs of various applications.

In the current industrial applications of various lead-containing piezoelectric ceramic materials, the content of lead oxide accounts for more than 60% of the total mass of the materials, and the hazards caused to the human body and the environment during the manufacturing, processing, storage, transportation, use and waste disposal of these materials are self-evident, so lead-free environmentally friendly piezoelectric ceramic materials are an important direction and hot topic for research and development in recent years.

At present, the research on lead-free piezoelectric materials has mainly gone through the research process from barium titanate-based, sodium bismuth titanate-based, bismuth laminate structure, niobate-based, and tungsten bronze structure lead-free piezoelectric ceramics, among which niobate-based lead-free piezoelectric ceramics are the most promising lead-free piezoelectric materials. Although the development and research of lead-free piezoelectric ceramics have made great progress, it is not possible for lead-free piezoelectric ceramics to completely replace lead-based piezoelectric ceramics, and the research and development of lead-free piezoelectric ceramics will still be a long way to go.

Main Applications of Piezoelectric Ceramics

Sound converters are one of the most common applications. Like pickups, microphones, headphones, buzzers, ultrasonic depth finders, sonar, ultrasonic flaw detectors for materials, etc. can use piezoelectric ceramics as sound converters. Such as children’s toys on the buzzer are the current through the piezoelectric ceramic inverse piezoelectric effect to produce vibration, and emit the human ear can hear the sound. Piezoelectric ceramics can produce different frequencies of vibration through the control of electronic circuits, thus emitting a variety of different sounds. For example, an electronic music greeting card is through the inverse piezoelectric effect of the AC audio signal into a sound signal.

Piezoelectric detonator Since the First World War, the British invented the tank, and for the first time in France in the Somme battle and seriously injured the German army, the tank in many battles. However, in the 1960s and 1970s, the tank lost its former glory due to the invention of anti-tank weapons. The armor-piercing rounds fired from the anti-tank guns would immediately explode when they touched the tanks, blowing them to pieces. This is because the warhead is equipped with piezoelectric ceramics, which can transform the strong mechanical force when touching into an instant high voltage, the outbreak of sparks, and detonate the explosive.

Piezoelectric lighter gas stove with a new type of electronic lighter is the use of piezoelectric ceramics made. Just use your finger to press the lighter button, the lighter on the piezoelectric ceramic can generate high voltage, the formation of electric sparks and ignite the gas, can be used for a long time. So piezoelectric lighter is not only easy to use, safe and reliable, and long life, such as titanium lead piezoelectric ceramics made of lead lighter can be used more than 1 million times.

Nuclear goggles nuclear testers with transparent piezoelectric ceramics made of goggles, when the nuclear explosion generated light radiation to a dangerous level, the piezoelectric ceramics in the goggles will turn it into transient high-voltage electricity, in 1/1000 s, can reduce the light intensity to only 1/10000, when the dangerous light disappears and can return to the original state. This goggle structure is simple, only a few dozen grams, mounted on the nuclear protective helmet is very convenient to carry.

Ultrasonic transducer Suitable for use in ultrasonic welding equipment and ultrasonic cleaning equipment, mainly using high-power emission type piezoelectric ceramic production, an ultrasonic transducer is a device that can convert high-frequency electrical energy into mechanical energy, the ultrasonic transducer is an energy conversion device, its function is to convert the input electrical power into mechanical power (i.e., ultrasonic) and then pass out, while it consumes very little part of its own power.

Sonar In naval warfare, the most difficult to deal with is the submarine, which can dive under the sea for a long time and sneak into ports and ships unnoticed, making the enemy a big headache. How to find the enemy submarine? Not my eyes, not by radar, because electromagnetic waves in seawater will be sharply attenuated, can not effectively transmit the signal, detection of submarines rely on the sonar —— underwater ears. The piezoelectric ceramic is the material for manufacturing sonar, it emits ultrasonic waves, which will be reflected back when it meets the submarine, and after being received and processed, it can measure the enemy submarine’s position, distance, etc.