blogPiezoelectric ceramics

Piezoelectric ceramic

Piezoelectric ceramic is 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 crystal phases that make up the main component are ferroelectric crystal grains. Since the ceramic is a polycrystalline aggregate in which crystal grains are randomly oriented, the spontaneous polarization vector of each of the ferroelectric crystal grains is also chaotically oriented. In order for the ceramic to exhibit macroscopic piezoelectric characteristics, it is necessary to burn the piezoelectric ceramic. After being coated on the end face, it is subjected to a polarization treatment under a strong DC electric field, so that the original polarization orientations of the respective polarization vectors are preferentially oriented in the direction of the electric field. After the polarization treatment of the piezoelectric ceramic, in the electric field After cancellation, it will retain a certain degree of macroscopic residual polarization, so that the ceramic has a certain piezoelectric properties. [1]

1.Development History of piezoelectric ceramic

In 1880, the Curie brothers first discovered the piezoelectric effect of tourmaline and began the history of piezoelectric science.

In 1881, the Curie Brothers experiment verified the inverse piezoelectric effect, giving quartz the same positive and negative piezoelectric constants.

In 1894, Voigt pointed out that the crystals of only twenty point groups without a symmetry center may have a piezoelectric effect, and quartz is a representative of piezoelectric crystals, and it has been applied.

In World War I, Curie’s successor, Lang Zhiwan, first made use of the piezoelectric effect of quartz to create an underwater ultrasonic probe that was used to probe submarines and opened a chapter in the history of piezoelectric applications.

In World War II, BaTiO3 ceramics were discovered, and piezoelectric materials and their applications made epoch-making progress.

In 1946, the Institute of Insulation of the Massachusetts Institute of Technology discovered that applying a DC high-voltage electric field to a barium titanate ferroelectric ceramic so that its spontaneous polarization is preferentially oriented in the direction of the electric field and that after the removal of the electric field, it can maintain a certain residual polarization, making it With the piezoelectric effect, piezoelectric ceramic have been born since then.

In 1947, Roberts of the United States applied high voltage on BaTiO3 ceramics for polarization treatment to obtain the piezoelectricity of piezoelectric ceramic. Subsequently, Japan actively developed ultrasonic transducers, high-frequency transducers, and pressure sensors using BaTiO3 piezoelectric ceramic. Applications of various piezoelectric devices, such as filters, resonators, etc., have continued until the mid-1950s.

In 1955, the United States B.Jaffe et al. found that PZT piezoelectric ceramic are superior to BaTiO3 piezoelectricity, which has greatly promoted the application of piezoelectric devices. Some applications that are difficult to use in the BaTiO3 era, especially piezoelectric ceramic filters and resonators, have been rapidly put into practical use with the advent of PZT. SAW filters, delay lines, and oscillators have been used. The device was also materialized in the late 1970s.

2.The mainly Manufacturing process of piezoelectric ceramic ( by He-shuai Ltd company)

The flow diagrams are as follows: Batching–mixed grinding–pre-burning–secondary grinding–granulation–forming–rowing–sintering into porcelain–shape processing–by electrode–high voltage polarization –Aging test. [3]

1. Ingredients: Before material treatment, remove impurities and then weigh various raw materials according to the formula proportion. Note that a small amount of additives should be placed in the middle of an aniseed material.

2, mixed grinding: The purpose is to mix and grind a variety of raw materials for pre-burning to complete the solid-phase reaction preparation conditions. Generally dry grinding or wet grinding method. Small batches can be dry-milled, and large-volume batches can be ball milled or jet milled with high efficiency.

3.Pre-burning: The purpose is to conduct solid-phase reaction of raw materials at high temperatures to synthesize piezoelectric ceramic. This process is very important. Will directly affect the sintering conditions and the final product performance.

4., the second fine grinding: The purpose is to pre-fired piezoelectric ceramic powder and then finely mixed and ground, for the uniformity of the performance of porcelain to lay the foundation.

5., granulation: The purpose is to make the powder form a high density of good flow particles. The method can be performed manually but is less efficient, and an efficient method is spray granulation. This process is to add adhesives.

6. Forming: The purpose is to press the pelletized material into the required preformed blank.

7., the row of plastic: The purpose is to remove the binder added during the granulation from the blank.

8. Sintering into Porcelain: The blank is sealed and sintered into porcelain at a high temperature. This link is quite important.

9., shape processing: grinding the finished product to the desired finished product size.

10, is the electrode: On the required ceramic surface is set on the conductive electrode. The general method is silver layer infiltration, chemical deposition and vacuum coating.

11, the high voltage polarizes: Makes the electric field inside the ceramic directional arrangement, thus causes the ceramic to have the piezoelectric performance.

12, aging test: After the stability of ceramic performance, test each index to see whether it meets the expected performance requirements.

Piezoelectric ceramic are characterized by the polarization treatment of ferroelectric ceramics under a direct current electric field, giving them a piezoelectric effect. The general polarization electric field is 3 ~ 5kV/mm, temperature 100 ~ 150 °C, time 5 ~ 20min. These three are the main factors that affect the polarization effect. Better piezoelectric ceramic, such as lead zirconate titanate ceramics, its mechanical coupling coefficient can be as high as 0.313 ~ 0.694.

3.THE PHYSICAL MECHANISM OF PIEZOELECTRIC CHARACTERISTICS

Polarized piezoceramics have bound charges at both ends, so that a free charge from the outside is adsorbed on the surface of the electrode. When an external pressure F is applied to the ceramic sheet, discharge occurs at both ends of the sheet. Instead, charging will cause charging. The phenomenon in which this mechanical effect is converted into an electric effect is a positive piezoelectric effect.

In addition, piezoelectric ceramic have the property of spontaneous polarization, and spontaneous polarization can be converted under the action of an external electric field. Therefore, when an external electric field is applied to a piezoelectric dielectric, a change occurs as shown in the figure, and the piezoelectric ceramic is deformed. However, the reason why the piezoelectric ceramic is deformed is that when the same external electric field as the spontaneous polarization is applied, it corresponds to the enhancement of the polarization strength. The increase in the polarization strength causes the piezoelectric ceramic sheet to elongate in the direction of polarization. In contrast, if a reverse electric field is applied, the ceramic sheet is shortened in the polarization direction. This phenomenon of conversion into a mechanical effect due to electrical effects is an inverse piezoelectric effect.

4.PIEZOELECTRIC CERAMIC OTHER FEATURES

Piezoelectric ceramic have sensitive properties that can convert extremely weak mechanical vibrations into electrical signals and can be used in sonar systems, meteorological detection, telemetry environmental protection, and household appliances. The sensitivity of piezoelectric ceramic to external forces makes it possible to sense even more than a dozen meters of flying insects’ flapping wings disturbing the air. Using it to make piezoelectric seismographs can accurately measure seismic intensity and indicate the orientation and distance of the earthquake. This can not be said that is a great merit of piezoelectric ceramic.

Piezoelectric ceramic produce a small amount of deformation under the action of an electric field, up to no more than one ten-millionth of its own size. Don’t underestimate this tiny change. The precise control mechanism based on this principle, the piezoelectric actuator, is The control of precision instruments and machinery, microelectronics, and bioengineering are all good news.

Resonators, filters, and other frequency control devices are key devices that determine the performance of communication devices. Piezoelectric ceramic have obvious advantages in this regard. It has good frequency stability, high accuracy and a wide range of applicable frequencies. It is small in size, does not absorb moisture, and has a long service life. It can improve the anti-interference performance especially in multi-channel communication equipments, making it impossible for conventional electromagnetic equipment to be faced with. Alternative fate.

4.1 PRINCIPLE

Looking first at a new type of bicycle damping controller, the general shock absorber is difficult to achieve a smooth effect, and this ACX damping controller, through the use of piezoelectric materials, provides a continuously variable damping function for the first time. A sensor monitors the movement of the impact piston at a rate of 50 times per second. If the piston is moving fast, it is generally due to rapid impact caused by running on uneven ground. At this time, the maximum shock absorption function needs to be activated; if the piston movement is slow, then It means that the road surface is flat and you only need to use a weaker shock absorption function. To sum up, the complaint is: piezoelectric ceramic is the vector conversion material force —>; electricity —>; force 1 power conversion, typical applications: piezoelectric ignition, weighing sensor 1 power conversion: brake, Actuator–>; Force —> Deformation —> Vibration — Acoustic —> Electroacoustic —> Ultrasound and other deformation —> Displacement –> Detection of electricity ->; force ->;; electricity, piezoelectric transformers, etc. ~ It can be said that although piezoelectric ceramic is a new material, it is rather civilian. It is used for high technology, but more is to serve people in life and create a better life. The main raw materials of piezoelectric ceramic include lead and other toxic substances. In the next stage, lead-free piezoelectric ceramics and low-temperature piezoelectric ceramic will be the development direction.

5.The main applications

5.1. Sound Converter Sound Converter is one of the most common applications. Sound transducers such as pickups, microphones, headphones, buzzers, ultrasonic depth detectors, sonar, and material ultrasonic flaw detectors can be used as piezoelectric transducers. For example, a buzzer on a child’s toy is a current that generates vibrations through the inverse piezoelectric effect of a piezoelectric ceramic, and emits a sound that human ears can hear. Piezoelectric ceramic are controlled by electronic circuits and can generate vibrations at different frequencies, thereby emitting a variety of different sounds. For example, an electronic music greeting card converts AC audio electrical signals into sound signals through inverse piezoelectric effect.

5.2. Piezo detonators Since the British invented the tanks in the First World War and used them for the first time in the battle of the Somme in France, the tanks have played a role in many battles. However, in the 1960s and 1970s, due to the invention of anti-tank weapons, tanks lost their former glory. The armor-piercing bomb that was fired by the anti-tank gun contacted the tank and immediately exploded, crushing the tank. This is because the bullet head is equipped with piezoelectric ceramic, which can transform the powerful mechanical force at the time of collision into an instantaneous high voltage, which sparks and detonates explosives.

5.3. Piezoelectric lighter A new type of electronic lighter used on gas stoves is made of piezoelectric ceramic. As long as you use your finger to press the ignition button, the piezoelectric ceramic on the lighter can generate 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 easy to use, safe and reliable, but also has a long service life. For example, a lighter made of lead-titanium lead-acid piezoelectric ceramic can be used more than 1 million times. [2]

5.4. Nuclear goggles After the nuclear tester wears goggles made of transparent piezoelectric ceramic, the piezoelectric ceramic in the goggles turns it into an instantaneous high voltage when the optical radiation generated by the nuclear explosion reaches dangerous levels. Electricity, in 1/1000 s, can reduce the light intensity to only 1/10000, and when the dangerous light disappears, it can return to its original state. This kind of goggles has a simple structure, only a few dozens of grams, and it is very convenient to carry it on a nuclear-protective eye-protection helmet.

5.5. Ultrasonic transducers are suitable for ultrasonic welding equipment and ultrasonic cleaning equipment. They are mainly made of high-power emissive piezoelectric ceramic. Ultrasonic transducers are devices that convert high-frequency electric energy into mechanical energy. As an energy conversion device, the function of the device is to convert the input electric power into mechanical power (ie, ultrasonic waves) and then transfer it out while itself consuming a small part of the power.

5.6. Sonar In the naval battles, the most difficult to deal with is the submarine. It can submarine under the sea for a long time, and it can sneak attacks on the port and ships without knowing it. This can make the enemy wreak havoc. How to find enemy submarines? You can’t rely on your eyes. You can’t use radar. Because electromagnetic waves will attenuate rapidly in seawater and cannot transmit signals effectively. The detection of submarines depends on sonar—-underwater ears. Piezoelectric ceramic are the materials used to make sonars. They emit ultrasonic waves and are reflected back on submarines. After being processed, they can measure the position and distance of enemy submarines. [3]

Common application

1: Application of positive piezoelectric effect

2: Piezoelectric Ceramic Buzzer | Loudspeaker

3: Piezoelectric pickups

4: Piezoelectric transformer

5: Piezoelectric igniter