Measuring Theory And Method For Acoustic Characteristics Of Guided Wave In Piezoelectric Thin Layer

Piezoelectric materials have been widely used in industry and people's life. With the great development of electronic industry and nanotechnology, piezoelectric materials are becoming smaller and thinner. By now, sensors, resonators and filters that made by piezoelectric thin layer or film have been adopted on a grand scale. The acoustic characteristic of piezoelectric material will be influenced by boundary conditions when its scale becomes smaller. No effective methods have been adopted to analyze the acoustic characteristic of piezoelectric thin layer. In this thesis, some theoretical and experimental researches on the P5H piezoelectric ceramic have been done. This work is the basis of researching the acoustic characteristics of piezoelectric thin film and will help to design guided wave devices using P5H piezoelectric ceramic thin layer.In order to get the dielectric constants, elastic stiffness constants and piezoelectric stress coefficients of P5H ceramic, dielectric test, ultrasonic test and resonance test have been done firstly. Only the free and clamped dielectric constants in the direction of x axis and z axis need to be measured because piezoelectric ceramics have great symmetry. In ultrasonic test, the phase velocities of longitudinal and shear waves were measured along the x axis and z axis. Then, resonance tests of k 31 vibrator, k 33 vibrator and k t vibrator were done. After deducing the other constants, all the dielectric constants, elastic stiffness constants and piezoelectric stress coefficients are determined.The dispersion equations of lamb waves and SH waves have been deduced by partial wave method, then the dispersion curves can be calculated by computer programs. For the lamb wave dispersion curves, the same kind of high order modes'directions of change will exchange between each other. For the SH waves, with the increase of frequency, the phase velocity will become smaller until it reach the velocity of bulk shear wave.Finally, three transducers are used to excite lamb wave in the P5H piezoelectric ceramic thin layer according to the Snell's law, and the center frequencies are 1 MHz, 2.25 MHz and 10 MHz. By measuring leaky lamb waves, dispersion curves of lamb waves can be determined. For symmetric modes S1 and S 2, anti-symmetric modes A1 and A2 , experimental results shows perfect agreement with the theoretical calculation. For the high order modes, some mismatches appear between experimental results and theoretical calculation, but they share the same changing tendency.