Principle and Material Classification of Ultrasonic Piezoelectric Ceramic Transducer

The principle of the piezoelectric effect of an ultrasonic piezoelectric ceramic sheet is that if pressure is applied to a piezoelectric material, it will generate a potential difference (called the positive piezoelectric effect), and if a voltage is applied, it will generate mechanical stress (called the inverse piezoelectric effect piezoceramic elements ring ). If the pressure is high-frequency vibration, high-frequency current will be generated. When a high-frequency electrical signal is applied to a piezoelectric ceramic, a high-frequency acoustic signal (mechanical vibration) is generated, which is what we usually call an ultrasonic signal. In other words, piezoelectric ceramics have the function of conversion and inverse conversion between mechanical energy and electrical energy. This mutual relationship is very interesting.

It is divided into piezoelectric ceramics crystals and ultrasonic piezoceramic elements. Piezoelectric crystals usually refer to piezoelectric single crystals, and piezoelectric ceramics usually refer to piezoelectric polycrystals. Piezoelectric ceramics are a type of polycrystals that are formed by mixing, molding, and sintering high-temperature raw materials with the necessary components, as well as irregular fine particles obtained by solid-phase reaction and sintering between particles. Piezo ceramic plates with piezoelectric properties are called piezoelectric ceramics, which are actually ferroelectric piezoceramics. The grains of this piezoceramic have ferroelectric domains. The ferroelectric domains are composed of 180 domains with anti-parallel spontaneous polarization directions and 90 domains with perpendicular spontaneous polarization directions. Under the condition of artificial polarization (application of enhanced DC electric field), these domains are perfectly aligned in the direction of the external electric field, and the remaining polarization strength is maintained after the external electric field is removed, so they have macroscopic piezoelectric characteristics. For example, barium titanate Bt, lead zirconate titanate PZT, modified lead zirconate titanate, lead metaniobate, lithium lead niobate barium pbln, modified lead titanate pt, and the like. The successful development of this PZT material has promoted the improvement and enhancement of the performance of various piezoelectric devices of acoustic ultrasonic transducers and piezoelectric sensors.

The piezoelectric effect of the ultrasonic piezoelectric ceramic sheet means that the structure of some single piezocrystal materials has asymmetric characteristics. When these PZT materials are subjected to applied stress and strain, changes (deformation) in the internal lattice structure will destroy the originality of the electric neutrality. The macroscopic state generates a polarized electric field (polarization), and the generated electric field (polarization intensity) is proportional to the magnitude of the strain. This phenomenon is called the positive piezoelectric effect, which was discovered by the Curie brothers in 1880. Later, in 1881, it was further discovered that this single crystal material also has a reverse piezoelectric effect. When a material with positive piezoelectric effect is subjected to an external electric field, stress and strain will be generated, and the strain is proportional to the magnitude of the external electric field. Piezoelectric effect is a feature of crystal structure, which is related to the asymmetry of the crystal structure, and the magnitude and nature of the piezoelectric effect is related to the direction of the applied stress or electric field relative to the crystal axis. There are a variety of single PZT high power piezo ceramic crystal materials with piezoelectric effects, such as natural quartz (SiO 2) crystals and artificial single crystal materials, such as lithium sulfate (Li2SO4), lithium niobate (LiNbO3), and the like.