PMNT Single Crystal Surface Acoustic Wave And Lamb Wave Propagation Characteristics And Laser Ultrasonic Measurement

Compared with the traditional piezoelectric materials, the relaxor ferroelectric single crystal which exhibits more superior piezoelectric properties and electromechanical properties has received the widespread attention in recent years. With the deepening of the research and ascension of single crystal preparation, Pb(Mg1/3Nb2/3)O3-xPbTiO3(PMN-PT) has been more and more widely used in transducer, sensors and other electronic devices. PMN-0.29 PT, near phase boundary, has a good piezoelectric performance and stability, it may be the main material of surface acoustic wave devices and lamb wave devices. Laser ultrasonic technology is mainly used in nondestructive testing at present, laser surface acoustic wave technology is more mature. In recent years, low order modes laser generation lamb wave has attracted more and more attention in related fields, great progress has been made in the nondestructive testing of thin layer materials.This dissertation mainly studies surface acoustic wave and lamb wave propagation characteristics of the Z-cut [001]c poled PMN-0.29 PT single crystal, and the innovative application of laser ultrasonic technology is used to test PMN-0.29 PT single crystal that is along different direction surface acoustic wave and the zero order mode of lamb wave.First of all, using resonance resonance-ultrasonic method to measure the [001]c poled PMN-0.29 PT single crystal’s full matrix parameters, as the basis of the theoretical calculation in follow-up study, the piezoelectric constant d33=1580pC/N and the electromechanical coupling coefficient k33 reaches 90% in single crystal samples.Using the Christoffel equation of piezoelectric materials, combine with the property of the surface acoustic wave and boundary conditions that its propagation satisfies to, the numerical calculation on metallic and nonmetallic surface along different direction of propagation of PMN-0.29 PT single crystal surface acoustic wave phase velocity, and using the relationship between the phase velocity changing with angle can get the electromechanical coupling coefficient and flow angle and the relationship between the surface acoustic wave propagation direction. Surface acoustic wave phase velocity meet 4mm symmetry, and when θ=45° propagation speed has a minimum value v=860 m/s. Setting up laser ultrasonic experiment system based on the reflection principle, the Z-cut [001]c poled PMN-0.29 PT single crystal surface acoustic wave were measured, in θ=15°, surface acoustic wave phase velocity v=1563m/s, consistent with the theoretical calculation value.Using the Christoffel equation and coordinate transformation, to calculate the relationship between zero order symmetric mode(S0) and antisymmetric mode(A0) lamb wave phase velocity propagating along different directions of PMN-0.29 PT single crystal and product of acoustic frequency and the thickness of the sample(f·d). With the increase of transmission angle, the velocity of lamb waves increase, in θ=45°, lamb wave phase velocity has a maximum value v=1984m/s. Setting up based on the interference principle of laser ultrasonic experiment system, measure the propagation of the lamb wave phase velocity of Z-cut [001]c poled PMN-0.29 PT single crystal along different directions. The center of the laser excitation of lamb wave frequency is 2-3 MHz, in θ = 45°, lamb wave phase velocity v=2160m/s.