It has a high electromechanical coupling coefficient, especially the transverse electromechanical coupling coefficient k31 and the longitudinal electromechanical coupling coefficient k33 of piezo ceramics. The loss of heat leads to a decrease in transmission efficiency. Therefore, the material is required to have good thermal stability, and it is also required to have a mechanical quality factor Qm which is indicative of the loss of material resonance. Qm is more suitable in the range of 500-1000. Good frequency stability and time stability ensure stable operation in a changing environment for a long time.It is necessary to avoid changes in the piezoelectric ceramics transducer constant of the material due to mechanical fatigue, and to withstand high AC electric fields and sufficient mechanical strength.
Design of piezoelectric ceramic transformer
If the material used in the transformer has been determined, and the load impedance Rl and the boost ratio GRL at load and the operating frequency of the transformer are both given at the design time, the geometry of the transformer can be calculated as follows. First, whether is using half-mode or full-mode resonance, the operating frequency of the transformer depends on the speed of sound of the piezo ceramic material and the full length of the ceramic sheet. After the material is selected, the length of the piezo ceramic can be determined. In addition, when designing the length of a piezoelectric ceramic transformer, the influence of the maximum working field strength of the material should also be considered. Because, beyond this field strength, the performance of the transformer will drop, and even severe depolarization or fracture will occur. According to experience, the safe field strength is about 100V/mm. Since the size of the ultrasound piezoelectric ceramic transformer has a great influence on the output voltage in the actual design process, the operating frequency and voltage output of the transformer should be considered, and the mechanical strength of the transformer when operating at the resonant frequency should also be considered.
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