Study On The Cut Directions Of The Single Modd Transducer Slices Of PMN-PT Crystal

PMN-PT crystal is the abbreviation of PMN-x PT crystal,where x represents the content of PT.PMN-PT crystals have higher piezoelectric coefficient and electromechanical coupling coefficient than traditional ceramic materials,and the dielectric loss is small,so it has a good application prospect in piezoelectric transducer.However,simply replacing the traditional piezoelectric ceramic with a single crystal material can’t greatly improve the performance of the transducer as expected.It is necessary to design the transducer with respect to the characteristic of the anisotropy of the crystal.A transducer of a piezoelectric crystal has to satisfy a specific acoustic pattern at work.In particular,the sound wave excited by piezoelectric effects is preferably only one mode-pure longitudinal mode or pure shear mode.For transducers that excite a quasi-longitudinal mode,the direction of the particle’s vibration should be basically the same as the normal direction of the crystal,even if there is a deviation,it can’t be more than a few degrees.For transducers that excite a quasi-shear mode,the vibrating direction of the particle is essentially in the plane of the crystal,even if there is a deviation,it can’t be more than a few degrees.If at the same time exciting the two patterns of wave,the electromechanical coupling coefficient of one mode is required to be large,while the other mode is as close as possible to zero.Based on the principle,the single mode cutting direction of PMN-PT crystal was studied by numerical calculation.By solving the Christoffel equation considering the piezoelectric effect in three cases of coordinate rotation around the X,Y,and Z axes,the acoustic wave pattern is calculated and the direction of a single mode cutting is determined.The results of this paper are as follows:For the PMN-PT crystals(x=0.33)of rhombohedral phase,only Z-cut is the suitable cut for transducer.For Z-cut,the single mode is a pure longitudinal mode and the electromechanical coupling coefficient is 0.469,as well as the wave speed is 5217.5m/s.When the rotating X-cut is studied,it is found that the piezoelectric effect of the crystal excite two acoustic modes for X-cut,X-60 ° cut and X-120 ° cut.However,the one with a smaller electromechanical coupling coefficient is not close to zero.So they are not suitable cut for transducer.X-30 ° cut and X-90 ° cut are equivalent.An acoustic mode k value of 0.05 is close to zero,and another polarization mode with a larger k value deviates from the plane 14°.So it isn’t an available cutting.When rotating Y cut is studied,it is found that an acoustic mode of k value was close to zero and the other one is large when the angle is between 170 ° to 172 °.However,the direction of the polarization is too far from the ideal direction,all of them are unavailable cutting.For the tetragonal PMN-PT crystal(x=0.30,0.33,0.38,0.42),there are only three available cuts,X-cut,Y-cut and Z-cut.For X-cut,PMN-0.42 PT crystal has the largest electromechanical coupling coefficient,which is 0.80,and the single mode is a pure shear one,and the wave velocity is 1976 m/s.For Y-cut,the electric coupling coefficient of the PMN-0.42 PT crystal is the same as that of X-cut,which is the largest and it is a pure shear mode.The wave velocity is 3153 m/s.For Z-cut,the electric coupling coefficient of the PMN-0.33 PT crystal is the largest,which is 0.63,and it is a pure longitudinal mode.The wave velocity is 3153 m/s.The results of this study provide theoretical guidance for the application of PMN-PT crystals in piezoelectric transducers.