Last Updated on May 18, 2023 by You Ling
1、Why it is necessary to test the performance of piezoelectric ceramics
Piezoelectric ceramics are complex synthetic materials. The unique properties of piezoelectric ceramics determine their importance in various projects. However, different projects have different requirements for piezoelectric ceramics, such as high impedance or high sensitivity. Therefore, we test the performance of piezoelectric ceramics according to the project requirements to ensure that the produced ceramics meet our needs.
2、Common performance parameters of piezoelectric ceramics
Piezoelectric constant: The piezoelectric constant is a parameter that measures the strength of the piezoelectric effect in a material, which directly relates to the sensitivity of the piezoelectric output.
Elastic constant: The elastic constant and stiffness of piezoelectric materials determine the natural frequency and dynamic characteristics of piezoelectric devices.
Dielectric constant: For piezoelectric components of a certain shape and size, the inherent capacitance is related to the dielectric constant, which in turn affects the lower frequency limit of piezoelectric sensors.
Mechanical coupling coefficient: In the piezoelectric effect, this value is equal to the square root of the ratio of output energy (such as electrical energy) to input energy (such as mechanical energy); it is an important parameter for measuring the mechanical and electrical energy conversion efficiency of piezoelectric materials.
Resistance: The insulation resistance of piezoelectric materials will reduce charge leakage, thereby improving the low-frequency characteristics of piezoelectric sensors.
Curie point: The temperature at which piezoelectric materials begin to lose their piezoelectric properties is called the Curie point.
Mechanical quality factor: The ratio of mechanical energy stored in a piezoelectric resonator during one oscillation cycle to the mechanical energy lost.
3、Methods for testing the performance of piezoelectric ceramics
Testing the Curie temperature
When the temperature is above the Curie temperature (Tc), piezoelectric ceramics are in the paraelectric phase, and spontaneous polarization and piezoelectricity disappear. At the Curie temperature, many physical properties of piezoelectric ceramic materials, such as capacitance rate, heat capacity, and linear expansion coefficient, will undergo abrupt changes. Therefore, determining the temperature corresponding to this abrupt change can determine the Curie temperature of piezoelectric ceramic materials.
Testing the longitudinal piezoelectric strain constant d33 (static)
In the absence of an external electric field, satisfying the electrical short-circuit condition
Testing the strong field dielectric performance
The free relative permittivity and dielectric loss tangent of piezoelectric ceramic materials are related to temperature, humidity, frequency of alternating electric field, field strength, and applied voltage time. The strong field dielectric performance refers to the dielectric performance under a strong alternating electric field, generally referring to the free relative permittivity and dielectric loss tangent.
Testing the pyroelectric coefficient
The pyroelectric coefficient of piezoelectric ceramic materials is measured using the charge integration method. This method measures the change of residual polarization with temperature by measuring the pyroelectric charge accumulated on the capacitor.
Cylindrical longitudinal length expansion vibration mode
In the longitudinal length expansion vibration mode, the excitation electric field is parallel to the direction of propagation of the elastic wave, and the elastic stiffness (or compliance) constant is related to the electromechanical coupling effect.
Disk thickness expansion vibration mode
Under electrical short-circuit conditions, the frequency of free vibration of the whole electrode piezoelectric sample disk thickness expansion vibration mode is calculated according to the tanx = x/kt2 formula. Kt – thickness expansion vibration electromechanical coupling coefficient, X – numerical value of normalized frequency
Shear vibration mode of rectangular thickness
In the thickness shear vibration mode, the sample is polarized in the 1-direction, and an excitation electric field is applied in the 3-direction. This generates shear forces on the 1,3 surfaces as shown in Figure a, causing shear deformation on the 1,3 surfaces as shown in Figure b. When the electric field reverses, the 1,3 surfaces experience reverse shear deformation as shown in Figure c. Under the excitation of an alternating electric field, the sample produces shear vibrations with particle displacement in the 1-direction, and the wave propagation direction is along the 3-direction, making the shear wave a transverse wave.
Characteristic frequency and dynamic resistance testing using transmission line method
The transmission line method is used to test the characteristic frequency and dynamic resistance of the cylindrical longitudinal length expansion vibration mode, disk thickness expansion vibration mode, and rectangular thickness shear vibration mode as specified.
4、Tools for testing the performance of piezoelectric ceramics
Piezoelectric material testing equipment: ZJ-3 Precision D33 Tester, ZJ-4 Wide Range Precision D33 Tester, ZJ-5 Multilayer Piezoelectric Tester, ZJ-6 Multifunctional Parameter Piezoelectric Tester, GDPT-900A High-Temperature Piezoelectric Testing System, JKZC-YDZK03A High Precision Piezoelectric Impedance Analyzer, YDH-1 Piezoelectric Charge Tester, YDB-03 Piezoelectric Ceramic Surface Voltage Tester
Piezoelectric material sample preparation equipment: PZT-JH10/4 Piezoelectric Ceramic Polarization Device, PZT-JH20/1 Powder Polarization Device, PZT-JH30/3 Piezoelectric Ceramic and Film Integrated Polarization Device, ZJ-D33-YP15 Press Machine
Dielectric material testing equipment: GWJDN-600 4-channel High-Temperature Dielectric Tester, GWJDN-1000 4-channel High-Temperature Dielectric Tester
Ferroelectric material testing equipment: ZT-4A Ferroelectric Tester, FE-5000 Variable Temperature Ferroelectric Testing System, ECM-150 Electrocaloric Effect Testing System, DCD-100 Energy Storage Dielectric Charge Discharge Testing System
5、He-Shuai company’s standardized testing process for piezoelectric ceramics
A qualified piezoelectric ceramic product must undergo a rigorous testing process. Only such a standardized testing process can guarantee product quality. Finally, we provide a product test report.
Step 1:
Physical properties: appearance, specifications, surface finish of electrodes, internal voids in ceramics, edge breakage, scratches, etc.
Step 2:
Electrical testing: free relative permittivity, dielectric loss, electromechanical coupling system, frequency constants, piezoelectric strain constants, etc.
Step 3:
Reliability performance: acid and alkali resistance, corrosion resistance, oxidation resistance, aging resistance, etc.
Sometimes we provide additional testing items based on customer requirements:
Dielectric performance testing: dielectric constant, dielectric loss, capacitance C, DC bias characteristics, loss D, capacitance-frequency thermal properties, capacitance-time thermal properties, equivalent circuit thermal properties ESR, impedance-frequency characteristics, temperature thermal properties TCC
Piezoelectric performance testing: electromechanical coupling coefficient and quality factor, quasi-static piezoelectric constant, dynamic piezoelectric constant, piezoelectric ceramic equivalent circuit parameters, piezoelectric temperature spectrum, piezoelectric ceramic characteristic frequency
Ferroelectric performance testing: breakdown voltage, remanent polarization strength, hysteresis loop, coercive field strength
Resistance testing: leakage current, thermistor, pyroelectric coefficient, varistor, thermo-stimulated depolarization current, photoresistor, Seebeck coefficient, resistance-temperature characteristics, square resistance, volt-ampere characteristics, resistivity, Hall effect, gas-sensitive resistance
Reliability verification: HBVT high-acceleration endurance test, HAST high-acceleration aging test, HTAL high-acceleration life test, electrically-induced fatigue test
Chemical composition analysis: elemental content, oxide content
6、Conclusion
Testing the performance of piezoelectric ceramics is essential for ensuring that the material meets the specific requirements of various applications. Different projects may demand distinct properties such as high impedance or high sensitivity, which is why it is crucial to test piezoelectric ceramics according to the project’s requirements. This helps guarantee that the produced piezoelectric ceramics meet the desired standards.
Various performance parameters, testing methods, and tools are employed to assess the properties of piezoelectric ceramics. A standardized testing process is necessary to ensure product quality, and a product test report is typically provided upon completion of the testing process.
In some cases, additional testing items may be required based on customer specifications. These may include dielectric performance testing, piezoelectric performance testing, ferroelectric performance testing, resistance testing, and reliability verification. Ultimately, comprehensive testing ensures that piezoelectric ceramics are suitable for their intended application and can deliver the performance required for success.
