HIFU Bowl Transducer

HIFU Bowl Transducer

The characteristics of piezoelectric ceramics after polarization. Polarization is also an important basic knowledge point in chemistry. The following is mainly about polarization. I hope this well-organized article can provide some basic help to friends in need.

　　 The so-called polarization is to apply a strong direct current electric field to the piezoelectric ceramic to make the electric domains in the ceramic oriented along the direction of the electric field. It is also called artificial polarization treatment or single-domain treatment.

1. Polarization principle

　　 The polarization mechanism of piezoelectric ceramics depends on its internal structure. Piezoelectric ceramics are made of small crystal grains randomly “embedded”. Each small crystal grain can be regarded as a small single crystal, in which atoms (ions) are arranged regularly (periodically), forming Lattice, the lattice is composed of repeating units-unit cells. The crystal lattice direction of the crystal grain and the crystal grain are not necessarily the same, as a whole, it is still chaotic and irregular. In order to make the piezoelectric ceramics in the lowest state of energy (electrostatic energy and elastic energy), there will be several small areas in the crystal grains. The spontaneous polarization of the unit cell in each small area has the same direction, but the spontaneous polarization between adjacent areas The direction is different. The area where the spontaneous polarization direction is the same is called electric domain, and the whole ceramic includes many electric domains.　　

　　 2. Artificial polarization

　　 Add a high enough DC electric field to the piezoelectric ceramic and keep it for a certain temperature and time to force its domain to turn, or force its spontaneous polarization to make a directional arrangement. Before polarization, there are many domains with different spontaneous polarization directions in each crystal grain. The polarization intensity in the ceramic is zero. During the polarization treatment, the crystal grains can form a single domain, and the spontaneous polarization should follow the external field as much as possible.

　　 direction arrangement. After the polarization treatment, the external electric field is zero. Due to the internal restoring force (such as the release of internal stress caused by polarization, etc.), the spontaneous polarization of each crystal grain can only be oriented to a certain extent in the direction of the original external electric field. The polarization intensity is no longer zero. This polarization intensity is called the residual polarization intensity.