Relaxor ferroelectric single crystals of Pb(Zn113Nb213)03 (PZN), Pb(Mg113Nb3)O3 (PMN) and their solid solutions with normal ferroelectric PbTiO3 (PT) were investigated for ultrasonic transducer applications. Crystals offer adjustable properties not only by compositional tailoring but also by domain state engineering associated with different crystallographic orientation, which is not achievable in polycrystalline materials. Longitudinal coupling coefficients (k33) as high as 94 % and dielectric constants (K3T) in the range of 3500-6000 were achieved with low dielectric loss (<1%) using <001> oriented rhombohedral crystals of(l -x)PZN-xPT and (l-y)PMN-yPT, where xO. I and y>0. 4. The performance gains associated with these ultra-high coupling coefficients and range of dielectric constants are evident in relation to broader bandwidth and electrical impedance matching. Specifically, rhombohedral crystals offer the possibility of extremely broad bandwidth devices for transducer arrays and tetragonal crystals for single element transducers. Transducer simulation was performed using the KLM model. The pulse/echo response simulated a 124% bandwidth subdiced array element with a center frequency of 10 MHz. An optimized array design of the same geometry constructed of PZT 5H displays a 87% bandwidth.
Recent developments in piezoelectric materials include submicron grain size ceramics and single crystals. Pb(Zr,Ti)03 (PZT) ceramics with submicron grain sizes ( 0.5 tim) have been produced with properties comparable to conventional, coarse grained ( 3 to 5 rim) ceramics. The fine grain ceramics exhibit improved machinability over conventional materials. Ultrasonic transducer arrays with post widths less than 15 im have been fabricated as well as thin plates with thicknesses as low as 10 jtm. The yields and performance of such operations are expected to be much greater with fine grain ceramic than with conventional material.The single crystal piezoelectrics developed offer field induced strain an order of magnitude higher than what can be achieved in piezoelectric ceramic actuators (> 1 %). Furthermore, the strain electric field hysteresis and dielectric losses are very low for these materials and electromechanical coupling factors (k33) are greater than 90%. Applications which may benefit from the recent developments include smart materials and structures and MEMS. Pb(Zri,Ti)O3 (PZT) ceramics have been the mainstay for transducer and actuator applications. Compositionally, PZT ceramics lie near the morphotropic phase boundary (MPB) between the tetragonal and rhombohedral phases, as shown in Figure 1. MPB compositions exhibit anomalously high dielectric and piezoelectric properties as a result of enhanced polarizability arising from the coupling between two equivalent energy states, i.e. the tetragonal and rhombohedral phases, allowing optimum domain reorientation during the poling process. 56 SPIE Vol. 3241 • 0277-786X/97/$1O.OO Downloaded From: http://proceedings.spiedigitallibrary.org/ on 05/14/2015 Terms of Use: http://spiedl.org/terms
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.