Electric ceramics is an information-functional ceramic material that can convert mechanical energy and electrical energy into each other. Piezoelectric effect. In addition to piezoelectricity, piezoelectric ceramics also have dielectric properties and elasticity. They have been widely used in medical imaging and sound. Sensors, acoustic transducers, ultrasonic motors, etc. Piezoelectric ceramics are made by the relative stress of the internal positive and negative charge centers under the action of mechanical stress, which causes the opposite ends of the material to have oppositely bound trapped charges, ie piezoelectric effect, and has sensitive characteristics. Ceramics are mainly used in the manufacture of ultrasonic transducers, hydroacoustic transducers, electroacoustic transducers, ceramic filters, ceramic transformers, ceramic discriminators, high voltage generators, infrared detectors, surface acoustic wave devices, electro-optic devices, In addition to being used in high-tech fields, it is used to serve people in daily life and to create a better life for people.
Piezoelectric ceramic micro-displacement compensator is a key component of laser positioning system. It utilizes the piezoelectric conversion characteristics of piezoelectric ceramics and adjusts the laser cavity length by adjusting the voltage to ensure the positioning accuracy of the laser. It is widely used in aviation, aerospace and shipbuilding. Navigation systems in other fields. "Piezoelectric micro-displacement compensator" is a national defense engineering supporting project undertaken by Tianjin University. The project uses modified lead titanate binary piezoelectric material to improve the piezoelectric properties of this type of porcelain and develop a new high. Performance piezoelectric ceramics and form mass production. The micro-displacement compensator developed by the project can completely replace imported products, and its profit can reach 200~300%. It can be widely used in navigation systems of aviation, aerospace and ships, and has high economic and social benefits.
The main applications of piezoelectric effect: 1) force-sensitive sensors: measurable force, pressure acceleration, etc.; 2) vibration shock sensors: seismographs, machinery, bridges and buildings; 3) ultrasonic sensors: sonar systems. 4) Piezoelectric microphone. 5) Ignition device: lighter, gas stove igniter, projectile detonation.
Piezoelectric ceramic sheet with piezoelectric effect: If pressure is applied to the piezoelectric ceramic, it will produce a potential difference called a positive piezoelectric effect. On the contrary, when a voltage is applied, a mechanical stress is generated, which is called an inverse piezoelectric effect. If the pressure is a high frequency vibration, then a high frequency current is produced. When a high-frequency electric signal is applied to the piezoelectric ceramic, a high-frequency sound signal, that is, mechanical vibration is generated. This is what we usually call ultrasonic signals. That is to say, piezoelectric ceramics have the function of conversion and inverse conversion between mechanical energy and electrical energy.
Later, barium titanate (BaTiO3), a piezoelectric ceramic sheet, was introduced into ultrasonic transducer applications, mainly for fish finder; recently, there was a titanate, lead zirconate system (PbTiO3PbZrO3), which has electromechanical Conversion efficiency and stability (including temperature characteristics) are far superior to existing materials. It greatly expands the range of applications of piezoelectric ceramics. When comparing other piezoelectric materials, it has the following advantages:
High electromechanical conversion efficiency; good machinability; different material compositions can achieve a wide range of characteristics (high degree of freedom design); high stability; suitable for mass production, economical. As a pioneer in the piezoelectric ceramic industry, it offers a wide range of piezoelectric applications.
Many naturally occurring crystals (such as quartz, tourmaline, and sodium potassium tartrate) exhibit piezoelectric effects, and these have been used as electromechanical transducers for many years. In order to exhibit a piezoelectric effect, the structure should have no center of symmetry, and the stress (stretching or compressing) applied to the crystal will change the separation between the positive and negative charge positions in the single crystal cell, resulting in crystals. Net polarization at the surface.
In practice this effect is actually linear, ie the polarization of the piezoelectric ceramic sheet varies directly with the applied stress and, depending on the direction, such that the compressive and tensile stresses will generate an electric field and thus produce a voltage of opposite polarity. It is also mutual, so if the piezoelectric ceramic crystal is exposed to an electric field, it will undergo elastic strain, causing its length to increase or decrease depending on the field polarity.
The factory mainly uses p-51 material to process various types of piezoelectric ceramic wafers. p-51 has the characteristics of high sensitivity and good time stability. It is mainly used in underwater acoustic transducers, piezoelectric ceramic sensors, accelerometers, Pressure gauges, buzzers, etc.
Piezoelectric ceramic sheet production process is as follows: ingredients - mixing and grinding - pre-burning - secondary grinding - granulation - molding - plastic molding - sintering into porcelain - shape processing - by electrode - High voltage polarization - aging test.
Piezoelectric buzzer
1. Peripheral support mode - Fix the outer edge of the buzzer piece in the resonant cavity. Generally, there is no feedback buzzer, and the buzzer must match the resonant cavity frequency to have a higher sound pressure output. And a push signal is generated by the external oscillating circuit to make the buzzer sound.
2. Node support mode - The buzzer piece is fixed in a ring structure of the same size as the diameter of the ceramic piece. If the resonant cavity is well designed and matched with the correct frequency feedback buzzer and positive feedback circuit, it will generate a large sound pressure and the correct frequency.
Development History
In 1880, the Curie brothers first discovered the piezoelectric effect of tourmaline and began the history of piezoelectrics.
In 1881, the Curie brothers experiment verified the inverse piezoelectric effect and gave the same positive and negative piezoelectric constants for quartz.
In 1894, Voigt pointed out that crystals of only twenty point groups without symmetry centers are likely to have a piezoelectric effect. Quartz is a representative of piezoelectric crystals, and it has been applied.
In the First World War, Curie's heir, Lang Zhiwan, first used the piezoelectric effect of quartz to make an underwater ultrasonic detector for detecting submarines, thus uncovering the chapter on the history of piezoelectric applications.
BaTiO3 ceramics were discovered in the Second World War, and piezoelectric materials and their applications have made epoch-making progress.
In 1946, the Institute of Insulation of the Massachusetts Institute of Technology found that a DC high-voltage electric field was applied to the barium titanate ferroelectric ceramics, so that the spontaneous polarization was preferentially oriented along the direction of the electric field, and the residual polarization was maintained after the electric field was removed. With the piezoelectric effect, piezoelectric ceramics were born.
In 1947, Roberts applied high voltage on BaTiO3 ceramics to obtain the voltage of piezoelectric ceramics. Subsequently, Japan actively developed ultrasonic transducers, high-frequency transducers and pressure sensors using BaTiO3 piezoelectric ceramics. Applications of various piezoelectric devices such as filters, resonators, etc., have been conducted until the mid-1950s.
In 1955, B. Jaffe et al. found that PZT piezoelectric ceramics, which are superior in piezoelectricity to BaTiO3, have greatly advanced the application of piezoelectric devices. Some applications that are difficult to be practical in the BaTiO3 era, especially piezoelectric ceramic filters and resonators, have been rapidly put into practical use with the advent of PZT, and SAW filters, delay lines, and oscillators have been applied. The device was also implemented in the late 1970s.
Piezoelectric ceramic properties
Piezoelectric ceramics have sensitive characteristics and can convert extremely weak mechanical vibration into electrical signals, which can be used in sonar systems, weather detection, telemetry environmental protection, household appliances, etc. The sensitivity of the piezoelectric ceramic to external forces makes it possible to sense the disturbance of the air by the flying insects flapping their wings more than ten meters. It can be used to make piezoelectric seismographs, which can accurately measure the earthquake intensity and indicate the direction and distance of the earthquake. This cannot but be said to be a great achievement of piezoelectric ceramics.
Piezoelectric ceramics produce small deformation variables under the action of an electric field, up to a fraction of a millionth of their own size. Don't underestimate the slight change, the precise control mechanism based on this principle--piezoelectric actuator, for Precision instrumentation and mechanical control, microelectronics, bioengineering, etc. are all great news.
Frequency control devices such as resonators and filters are the key devices that determine the performance of communication devices. Piezoelectric ceramics have obvious advantages in this respect. It has good frequency stability, high precision and wide applicable frequency range, and is small in size, non-hygroscopic, and long in life. Especially in multi-channel communication equipment, it can improve the anti-interference, so that the previous electromagnetic equipment can not be expected to face it. The fate of substitution.
Piezoelectric ceramic application
1. Sound Converter Sound Converter is one of the most common applications. Piezoelectric ceramics can be used as sound transducers for pickups, microphones, earphones, buzzers, ultrasonic depth detectors, sonar, and ultrasonic flaw detectors. For example, a buzzer on a children's toy is a current that vibrates through the inverse piezoelectric effect of the piezoelectric ceramic, and emits a sound that can be heard by the human ear. Piezoelectric ceramics can generate vibrations of different frequencies through the control of electronic circuits, thereby emitting various sounds. For example, an electronic music greeting card converts an AC audio signal into a sound signal through an inverse piezoelectric effect.
2, ultrasonic transducer is suitable for ultrasonic welding equipment and ultrasonic cleaning equipment, mainly using high-power emission type piezoelectric ceramics, ultrasonic transducer is a device that can convert high-frequency electrical energy into mechanical energy, ultrasonic transducer As an energy conversion device, its function is to convert the input electrical power into mechanical power (ie, ultrasonic waves) and then pass it out, while it consumes a small amount of power itself.
3. Piezoelectric lighter A new type of electronic lighter used on gas stoves is made of piezoelectric ceramics. As long as the ignition button is pressed with a finger, the piezoelectric ceramic on the lighter can generate a high voltage, form an electric spark and ignite the gas, which can be used for a long time. Therefore, the piezoelectric lighter is not only convenient to use, safe and reliable, but also has a long service life. For example, a lighter made of a lead titanate piezoelectric ceramic can be used for more than one million times.
4. After the nuclear tester with anti-nuclear goggles carries the goggles made of transparent piezoelectric ceramics, when the optical radiation generated by the nuclear explosion reaches a dangerous level, the piezoelectric ceramic in the goggles turns it into a transient high voltage. Electricity, in 1/1000 s, can reduce the light intensity to only 1/10000. When the dangerous light disappears, it can return to its original state. The goggles are simple in structure and only a few tens of grams in weight. They are easy to carry on the anti-nuclear eye protection helmet.
5, piezoelectric detonator Since the British World War I invented the tank in the First World War, and the first use in the French Somme River battle and hit the German army, the tank in the battles to show their talents. However, in the 1960s and 1970s, due to the invention of anti-tank weapons, the tank lost its former glory. The warhead is equipped with piezoelectric ceramics, which can transform the powerful mechanical force at the time of collision into an instantaneous high voltage, and sparks to explode the explosive.
6, sonar In the naval battle, the most difficult to deal with is the submarine, it can snorkel under the sea for a long time, God unconsciously sneak attack on the port, the ship, so that the enemy is a big headache. How to find enemy submarines? It is not possible to use the radar, because the electromagnetic waves will be attenuated sharply in the sea water, and the signal cannot be transmitted effectively. The submarine is detected by the sonar ------ underwater ear. Piezoelectric ceramics are materials for making sonar. They emit ultrasonic waves, which are reflected back by the submarine. After being received and processed, the position and distance of the enemy submarine can be measured.
Today, the range of piezoelectric ceramic products is not only widely used in medical and industrial fields, but also penetrates into every corner of people's daily life. Its application areas mainly involve the following five aspects:
First, the frequency control device. In recent years, there have been ceramic resonators, ceramic filters, tuning tuning fork filters, mechanical filters, ceramic discriminators, traps and delay lines. Among them, the output of ceramic resonators and ceramic filters has accounted for more than 65% of China's piezoelectric ceramic products, which is quite remarkable. In particular, ceramic resonators are characterized by high stability, no adjustment, small size and low cost. Typical applications are: televisions, camcorders, computers, CD-ROM drives, automotive electronics, VCDs, telephones, copiers, speech synthesizers, remote controls and toys.
Second, piezoelectric ultrasonic transducers. Piezoelectric ultrasonic transducers are acoustic devices that transmit and receive ultrasonic waves and are widely used in water and air media. The role of radar in underwater acoustic communication, known as sonar, is an essential sensor for all types of ships. In the industry, ultrasonic transducers have been used for ultrasonic cleaning, ultrasonic precision machining, ultrasonic humidification, phacoemulsification, ultrasonic seed treatment, ultrasonic flaw detection and ultrasonic diagnosis. Today, another broad application area for piezoelectric ultrasonic transducers is telemetry, remote control systems, and alarm systems.
Third, the piezoelectric sounder. Typical products of piezoelectric sounders are piezoelectric buzzers and piezoelectric transmitters, receivers, watches, calculators, electronic alarm clocks, small alarm bells, and ringing of telephones and mobile phones. Buzzer with transistor oscillating circuit and DC power supply can make continuous sound, buzzer with switching circuit can make intermittent sound, underwater microphone and speaker belonging to sound transducer can also be used to drive or seduce Fish school.
Fourth, piezoelectric devices for measurement and control. Piezoelectric devices for measurement and control mainly include pressure, acceleration, angular velocity sensors, as well as ultrasonic sounding, ultrasonic thickness measurement, ultrasonic flow measurement, and ultrasonic diagnosis.
Fifth, piezoelectric igniters and piezoelectric transformers. Mass production of piezoelectric igniters began in 1965, and has been developed more rapidly in the past 20 years. At present, almost all gas stoves, bathroom gas boilers, gas room heaters, gas water heaters and cigarette lighters use piezoelectric igniters. Piezoelectric transformer has the advantages of simple structure, small size, high transformation ratio, high electromechanical conversion efficiency, no electromagnetic interference and safety, etc., so it is used for electrostatic smoke remover, negative ion generator, electrostatic coating equipment, electrostatic copier, electric field treatment. Instrument and LCD backlight.
Cardiovascular therapeutic instrument probes.
