Answers to some common questions about piezoelectric ceramics

1)I want to apply a layer of paint on my piezoelectric ceramic,this will reduce its displacement.

Answer: Any additional material parallel to the piezoelectric ceramic will increase the load of the piezoelectric ceramic, thereby reducing its performance. However, in most cases, the stiffness of the outer garment will be lower than the stiffness of piezoelectric ceramics, so the effect is small (<5%).

2) Can I use oil to cool the piezoelectric ceramics?

Answer: Yes. For some applications, the heat generated by the piezoelectric ceramic itself (self-heating) is significant and can be cooled by air flow or oil flow. The cooling oil must be clean dielectric oil (insulating oil), because any impurities may cause electrochemical reactions, which eventually lead to damage and failure of the piezoelectric ceramic. Also note that for a piezoelectric ceramic with a larger cross-section, the thermal gradient between its surface and inside may be large, so maintaining an acceptable surface temperature may not be sufficient.

3) Is it possible to apply torque to piezoelectric ceramics?

Answer: It is not recommended to apply torque to the piezoelectric ceramics. When is applying a pre-tightening force to the piezoelectric ceramic through the nut, it must be ensured that the pre-tightening torque is not transmitted to the piezoelectric ceramic. A shear force greater than 1 MPa may cause fracture of the adhesive layer between piezoelectric ceramics.

4) How much preload can I apply to the piezoelectric ceramic?

Answer: We recommend that piezoelectric ceramics work under a preload of 0~80MPa. The design of the preload force must ensure that the preload force is within this range under any conditions. The normal value is 10~20MPa.

5) Can I apply negative pressure to the piezoelectric ceramic stack?

Answer: Yes. The displacement of the piezoelectric ceramic under quasi-static can be increased by applying a certain negative pressure. However, in order to avoid the risk of depolarization of the piezoelectric ceramics, the electric field should be limited, at room temperature and no load, the negative pressure must not exceed -0.7kV/mm for N51 and N57 materials, and -0.25kV/ for N59 materials mm, N46 material is -1.5kV/mm. In the case of high temperature and high load, these recommended values must be reduced.

1) I can't measure the resonance frequency value in the parameter table of the piezoelectric ceramic bending sheet. What is the reason?

Answer: The resonant frequency listed in the parameters is defined without additional mass (cantilever). In the state without any clamping, the first resonance frequency will be higher, so the clamping force has an effect on the resonance frequency. Similarly, adding a load (such as a lens, etc.) to the top of the piezoelectric ceramic bending piece will lower the first resonance frequency.

2) How to deal with the internal electrodes of the multilayer piezoelectric ceramic exposed?

Answer: For multilayer piezoelectric ceramics, if the internal electrodes are exposed, you need to reduce the applied voltage Vmax to avoid arcing. The exposed area must be coated. For safety, please replace with new piezoelectric ceramics.

1) No output is mentioned in the piezoelectric shears. What is its output?

Answer: For stock piezoelectric hemisphere shears, due to its high rigidity, it is very difficult to measure its output. This is the reason we did not mention in the parameter table. The force can be estimated by multiplying the free displacement and the stiffness. The stiffness value can be obtained by S55E, and the value of S55E is 4.3e-11m^2/N.

2) Can piezoelectric ceramic shears be used at high frequencies?

Answer: Due to its high stiffness and high resonance frequency, piezo cylinder pipe

shears can be used for fast operation (fast response). However, continuous high-frequency use may cause problems. This is because its nonlinearity means high loss (higher than d33 ceramic), so the piezoelectric ceramic itself will generate heat. Usually, working at 2kHz for a few minutes is not a problem. If higher frequencies or longer durations are required, the applied operating voltage must be reduced, otherwise the piezoelectric ceramic will slowly depolarize (loss of polarization).

3) What is the recommended preload for piezoelectric ceramic shears?

Answer: The usual d33 piezoelectric ceramic stack needs to be pre-tensioned when is used at high frequency, because the inertial force will become significant and generate tensile stress inside the piezoelectric ceramic. For shear-type piezoelectric ceramics, its inertial force is a shearing force, so the effect of axial preload is limited. But in some cases, in order to improve the rigidity (by compressing the glue layer/gluing line) or to avoid bending (if the center of gravity is far from the fixed end), the axial preload is very beneficial.

4)What is the maximum axial load that can be applied on the piezoelectric ceramic shearing disc?

Answer: Piezoelectric ceramic shears are usually tested under a pressure of 3.5MPa. Piezoelectric ceramics can withstand higher compressive forces (>50MPa), but in actual use, we recommend that the axial load of the piezoelectric ceramic shears does not exceed 5MPa. This is because small defects on the contact surface can also lead to concentration of stress, thereby destroying the piezoelectric ceramic. If high pressure is required, we recommend using a higher flatness contact surface (including the contact surface between the piezoelectric shear plate surface and the structure).

5)What is the maximum shear load that can be applied to the piezoelectric ceramic shear ?

Answer: This piezoelectric sphere transducer can withstand very high loads. In fact, the interface between the pzt ceramic and the substrate determines the maximum shear load.

If the motion is transmitted by friction, the maximum load will depend on the pressure at the contact surface and the coefficient of static friction. For example, 2MPa pressure × 0.2 friction coefficient = 0.4MPa, for a 5×5mm shear sheet, its maximum shear load is about 10N. If epoxy bonding is used, the maximum shear load will depend on the strength of the epoxy used. Generally, epoxy resin can be safely used under a shear stress of 5 MPa, and it can be used on a 5×5 mm shear sheet. Its maximum shear load is about 125N.