Stacked piezoelectric ceramics

Stacked piezoelectric ceramics are also known as piezoelectric actuators, piezoelectric actuators, piezoelectric actuators, etc. Stacked piezoelectric ceramics are formed by stacking and bonding piezoelectric ceramic substrates through a co firing process (the thickness of a single-layer piezoelectric ceramic substrate is about 100 μ m). The piezoelectric ceramics prepared by this process can withstand high pressure and stiffness, but have limited tensile strength.

Stacked piezoelectric ceramics consist of a large number of ceramic flakes. Its structural feature is that the power supply electrode is designed on both sides of the ceramic sheet, and the entire cross-sectional area of the ceramic can participate in the actuation, with a large output and good performance, and there is no local electric field deformation, making it less prone to point stress. Figure 2.1 shows a piezoelectric ceramic formed by stacking PZT (lead zirconate titanate) ceramics, with multiple layers of ceramic flakes connected to form a multi-layer capacitor structure. After applying voltage to the ceramic, the piezoelectric ceramic will undergo elongation movement in the Z-axis direction (the maximum typical elongation is 0.1% -0.2% of the ceramic length). The output is sent to the external mechanical structure through the upper and lower end faces.

Figure 2.1

The maximum displacement of the inverse piezoelectric effect in piezoelectric ceramics depends on the applied electric field strength and the magnetization saturation of the ceramic material. The breakdown voltage of ceramics limits the maximum electric field strength. Corresponding to the use of single-layer ceramic substrates with different thicknesses, the field strength values can correspond to different voltage values. For thinner sheets, the maximum voltage will decrease. The thickness of ceramic flakes composed of stacked piezoelectric ceramics is generally 100 μ m, and the typical operating voltage is 150V.

Classification of stacked piezoelectric ceramics

Stacked piezoelectric ceramics are divided into two types: low voltage and high voltage, and the production processes for these two types of ceramics are completely different:

The voltage range for low-voltage piezoelectric ceramics is 0-150V. The ceramic layer and the internal metal electrode layer are stacked together before high-temperature sintering, and then subjected to high-temperature sintering. The internal electrode is a very thin metal film (with a thickness of about 1 μ m). This process of making ceramics is commonly referred to as the 'single piece co firing process'.

The voltage range for high-voltage piezoelectric ceramics is 0-500V or 1000V, and they are fully sintered and made into PZT plates/sheets before stacking. The insertion electrode is made of a separate thin metal foil. The entire structure is fixed together with a special high-quality adhesive. Therefore, high-pressure stacked ceramics are not a single piece of ceramic, but a composite material.

Precautions for the use of stacked piezoelectric ceramics

Due to the fact that stacked piezoelectric ceramics are formed by laminating and bonding piezoelectric ceramic thin sheets through a co firing process, this process characteristic makes their compressive strength much greater than their tensile strength. When ceramics are dynamically applied, due to the acceleration of the ceramic material itself, compressive and tensile forces are generated simultaneously. To avoid damaging piezoelectric ceramics, a preloading force can be applied to protect the ceramics. Generally, the magnitude of the preloading force is one tenth of the maximum load.

It is recommended to use actuators with preloading force in the following situations:

The tensile force will act on the actuator

Dynamic application

Shear force (force perpendicular to the direction of motion) acting on the actuator

Piezoelectric ceramics cannot withstand shear, lateral, and torsional forces. The force loaded on the ceramic moving end should be applied as much as possible to the center of the ceramic movement direction. The surroundings of ceramics should be kept as free from clamping as possible.