Do you understand piezoelectric ceramic history?
Piezoelectric ceramics are electric ceramic materials that have piezoelectric characteristics. These ceramics differ from typical piezoelectric quartz crystals because the crystal phases are ferroelectric crystal grains. The crystals are the main component of the piezoelectric ceramic
A Piezoelectric Ceramic is a polycrystalline aggregation of randomly oriented crystal grains. Each of the ferroelectric crystal grains having unconstrained consolidated vectors. The piezoelectric ceramic is burned to ensure that the ceramic gains the ability to manifest macroscopic piezoelectric properties.
Then, the end face of the ceramic is coated. The ceramic then undergoes polarization treatment under the influence of a strong DC electric field.
The power of the strong DC electric field alters the polarization orientation of the polarization vectors. It makes them preferentially oriented in the direction of the electric field.
Then the ceramic maintains a degree of macroscopic residual polarization, hence, the ceramic has certain piezoelectric properties.
History of the Development of Piezoelectric Ceramics.
The piezoelectric effect of tourmaline was discovered by the Curie brothers in 1880. It marked the beginning of the history of piezoelectric science. The Curie brothers carried out an experiment n 1881, to verify the inverse piezoelectric effect. The results show that quartz had the same positive and negative piezoelectric constants.
In 1894, Voigt disclosed that crystals without a symmetric centre and with only twenty point groups may have a piezoelectric effect. Also, quartz’s a good representative of piezoelectric crystals.
During World War I, Curie’s successor Lang Zhiwan used the piezoelectric effect of quartz to create an underwater ultrasonic probe. They are commonly used in probing submarines. This paved a way for piezoelectric applications.
During World War II recorded the discovery of BaTiO3 ceramics, as well as the progress of piezoelectric materials and their applications. 1946 brought about the discovery of the piezoelectric ceramics.
The Institute of Insulation of the Massachusetts Institute of Technology made a discovery. The application of a high DC voltage electric field to a barium titanate ferroelectric ceramic ensures a preferentially oriented spontaneous polarization. Also, it results in the removal of the field, it maintains a residual polarization. This piezoelectric effect brought about the piezoelectric ceramics.
1947, the piezoelectricity of piezoelectric ceramics was obtained through the application of high voltage on BaTiO3 ceramics. This brought about the active development of ultrasonic transducers. High- frequency transducers and pressure sensors using BaTiO3 piezoelectric ceramics appeared in Japan. Also the application of various piezoelectric devices such as filters, resonators etc, remain relevant till the mid-1950s.
1955, brought about the discovery by United States B.Jaffe et al. that PZT piezoelectric ceramics were superior to BaTiO3 piezoelectricity. The devices that had difficulty applying the BaTiO3 piezoelectricity especially the piezoelectric ceramic filters and resonators, switched the application to PZT.
The process of Manufacturing Piezoelectric ceramics.
The process of manufacturing piezoelectric ceramics are as follows:
sintering into porcelain shape,
processing by electrode-high voltage polarization
and ageing test.
1. Batching: Remove all impurities from the raw materials.
Weigh them according to the formula proportions.
A little amount of additives should be placed in the middle of an aniseed material.
2. Mixed grinding: Thoroughly grind and mix a variety of raw materials for pre-burning.
This is to complete the solid phase reaction preparation conditions.
Dry grinding or wet grinding method can be used.
For efficiency, small batches can be dry milled while batches with large volume can be ball milled or jet milled.
3.Pre-burning: Here, a solid phase reaction of raw materials at high temperature synthesizes piezoelectric ceramics. This ensures proper sintering conditions and final product performance.
4. Fine grinding: This is to ensure uniformity of the performance of porcelain. The piezoelectric ceramic powder is pre-fired and then finely mixed and ground.
5. Granulation: this ensures a high density of good flow particles. Adhesives are added at this point. Spray granulation is more efficient than manual granulation.
6.Forming: This means pressing the pelletized materials the required form.
7.Rowing: This is to remove the binder/ adhesive that was initially added during granulation.
8. Sintering into porcelain: This means sealing into shape and sintering at high temperature.
9. Shape Processing: This is to grind the finished product to the desired size.
10. Electrode: Here the ceramic surfaces is set on a conductive electrode. Methods such as silver layer infiltration, chemical deposition or vacuum coating are used.
11.High Voltage Polarization: This is the directional arrangement of the electric field of the ceramic, creating a piezoelectric performance.
12.Ageing Test: This is done to check the stability of the ceramic and see if it meets performance requirements.
Piezoelectric ceramics have properties influenced by the polarization treatment of ferroelectric ceramics. When they are placed under a direct current electric field it gives them a piezoelectric effect. The polarization electric field is 3 ~ 5kV/mm, temperature 100 ~ 150 °C, time 5 ~ 20min. These are the three main factors that affect the polarization effect.
Piezoelectric ceramics such as lead zirconate titanate ceramics have their mechanical coupling coefficient as high as 0.313 ~ 0.694.
The Physical Mechanism of Piezoelectric Characteristics
There are two bound charges on the polarized piezoceramics that cause the surface of an electrode to absorb a free charge. Both ends of the ceramic sheets discharge once it experiences external pressure (F). The piezoelectric effect is the phenomenon where mechanical effects on the ceramics turn into an electric signal. Another property common to the piezoceramic is spontaneous polarization.
When a piezoelectric dielectric passes through an external electric field, it will undergo some changes. However, when the electric signal for polarization strength equals the electric signal for spontaneous polarization. Nevertheless, there will be deformity of the piezoceramic.
Typically, the piezoceramic will stretch in the direction of the polarization strength as it increases. Meanwhile, the application of a reverse electric cause the ceramic sheet to reduce in the direction of polarization.
Other Features of the Piezoelectric Ceramics
The piezoelectric ceramic has numerous applications due to its ability to turn weak mechanical vibrations into an electrical signal. Some of its applications include;
• Use in household appliances.
• Use in sonar systems
• Telemetry environmental protection
• Meteorological detection
• Its high sensitivity allows it to detect external forces like a couple of insects flapping their wings.
• It is also useful in the accurate detection and reading of seismic intensity, direction and distance to an earthquake.
Small deformation of roughly one ten-millionth of the piezoelectric ceramic size forms under the influence of an electric field. The small change plays a crucial role in the precise control mechanism of a piezoelectric actuator. Other applications based on the precise control mechanism include;
• Precision equipment and machinery
• Frequency devices
• Bioengineering devices
Advantages of Piezoelectric Ceramics
1. It is small in size
2. It has good frequency stability
3. IT can accommodate a variety of frequencies and it is very accurate
4. It possesses a long service life.
5. It is a great tool for dealing with anti-interference in multi-channel communication equipment.
A Practical example of Piezoelectric Ceramic
Examining a bicycle damping control controller, it is difficult to a smooth effect on the general shock absorber. Hence, the need for the ACX damping controller made up piezoelectric materials. As a result, it is able to supply variable damping functions. Using a sensor, the movement of the impact piston is monitored at a rate of 50 times per second.
Most times moving on uneven ground will cause the piston to move fast resulting in rapid impact. In such a situation, it is crucial to activating the shock absorber. But, in a flat or smooth road surface, a weak shock absorber will do as there will be the minimum impact. The breakdown below helps to illustrate the role of the piezoelectric ceramic.
Piezoelectric ceramic – vector conversion material force
Electricity – force power conversion (i.e piezoelectric ignition, weighing sensor, and brake)
Actuator – Force – Deformation – Vibration – Acoustic – Electroacoustic – Ultrasound – Displacement – Detection of electricity – force – piezoelectric transformer and many more.
Although the piezoelectric ceramic material is fairly new, it is quite widespread. The evidence of its growing popularity can be found in high technology applications. However, the raw materials for making a piezoelectric ceramic is lead and other toxic materials. Nevertheless, there are plans to develop a lead-free piezoelectric ceramic as well a low-temperature piezoelectric ceramic.
The main Applications
This is one of the most common applications. The sound transducers feature in the following;
- Ultrasonic depth detectors
- Material ultrasonic flaw detectors can be used as piezoelectric transducers.
A typical example is a buzzer on a child’s toy. It’s current generates vibrations through the inverse piezoelectric effect of piezoelectric ceramic. It also emits a sound that humans can hear.
Piezoelectric ceramics are controlled by electronic circuits, generating vibrations at different frequencies, emitting a variety of different sounds. For example, an electronic music greeting card converts AC audio electrical signals into sound signals through the inverse piezoelectric effect.
Since the invention of Tanks by the British in the First World War. They were first used in the battle of Somme in France. The tanks have played major roles in many battles. However, in the 1960s and 1970s, the invention of anti-tank weapons ended the glorious reign of tanks.
The anti-tank gun fires an armour-piercing bomb, which when in contact with the tank, explodes, crushing the tank. This is because the bullet head is equipped with piezoelectric ceramics. It can transform the powerful mechanical force at the time of collision into an instantaneous high voltage. The effects spark and detonates explosives.
A new type of electronic lighter used on gas stoves is made of piezoelectric ceramics. On pressing the ignition button, the piezoelectric ceramic on the lighter generates a high voltage. The voltage produces an electric spark and igniting the gas, which can be used for a long time.
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.
Nuclear testers wear goggles made of transparent piezoelectric ceramics to prevent temporary blindness. During testing, the optical radiation generated by the nuclear explosion reaches dangerous levels.
However, the piezoelectric ceramic in the goggles turns it into an instantaneous 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 system basically works to detect dramatic and fast changes in light. When that happens, a circuit is broken triggering the goggles to quickly turn opaque. Once the light has returned to normal the goggles will turn translucent again.
This kind of goggles has a simple structure, weighing a few dozens of grams. It is very convenient to carry it on a nuclear-protective eye-protection helmet.
These are suitable for ultrasonic welding equipment and ultrasonic cleaning equipment. Mainly made of high-power emissive piezoelectric ceramics. Ultrasonic transducers convert high-frequency electrical energy into mechanical energy.
The function of the device is to convert the input electric power into mechanical power (ie, ultrasonic waves). After, transfer it out while itself consuming a small part of the power.