Enhanced Properties of 3-MHz Sliver-Mode Vibrators for Cardiac Probes With Alternating Current Poling for Pb(Mg1/3Nb2/3)O3-PbTiO3 Single Crystals.

We investigated the effects of alternating current poling (ACP) on the piezoelectric and dielectric properties of 3-MHz sliver mode (L13 mm × W0.10-0.25 mm × T0.48 mm) vibrators fashioned from Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 (PMN-0.30PT) single crystal (SC) plate manufactured using the continuous-feeding Bridgman (CF-BM) method for cardiac probes. The ACP SC plate (L13 mm × W24 mm × T0.48 mm) exhibited ultrahigh dielectric permittivity ( εT33/ε0 ) and piezoelectric coefficient ( d33 ) of 9690 and 2920 pC/N, respectively. After array dicing, the SC slivers with widths of 0.10, 0.15, 0.20, and 0.25 mm were obtained, and their average εT33/ε0 values decreased from the SC plate εT33/ε0 by 45% (5330), 29% (6880), 19% (7840), and 15% (8240), respectively, possibly because of heat and mechanical damage during the dicing. A combination of the ACP and a postdicing direct current poling (ACP-DCP) recovered their εT33/ε0 values to 6050, 7080, 8140, and 8540, respectively. The sliver mode electromechanical coupling factors ( k'33 ) were confirmed to exceed 93% after the ACP-DCP process, which were more than 4% higher than those of DCP-DCP SC slivers. The measured impedance spectra indicated that the SC slivers with 0.10-0.20 mm in width showed no spurious mode vibration near the fundamental k'33 mode. We conclude that the ACP-DCP SC slivers maintained more enhanced piezoelectric and dielectric properties than the DCP-DCP samples. These results will have important implications for the commercial application of ACP technology to medical imaging ultrasound probes.

A Review on Alternating Current Poling for Perovskite Relaxor-PbTiO3 Single Crystals.

With the great success on verifying its effectiveness on relaxor-PbTiO3 (PT) single crystals (SCs), alternating current poling (ACP) has been taking a center as a new domain engineering method in the last few years. Compared with the conventional direct current poling (DCP), ACP enables enhanced piezoelectric and dielectric properties. In this article, research progress in ACP and perspectives are introduced. Initially, optimized conditions of ACP for relaxor-PT SCs and unsolved issues on polycrystalline ceramics and spurious modes are reviewed. Second, the ferroelectric domain size dependence of piezoelectricity associated with ACP is discussed. We hypothesize that a tradeoff between domain and domain wall contributions exists for high piezoelectricity, suggesting an optimum 109° domain wall size, which is presumably dependent on compositions, crystallographic symmetries, and domain configurations. Finally, crystals synthesized by a solid-state crystal growth (SSCG) method are briefly introduced due to their unprecedented piezoelectricity obtained by ACP ( d33  âˆ¼ 5500 pC/N). We hope that this work helps to grasp the current status of ACP and to guide future tasks to be studied.

A Review of Lead Perovskite Piezoelectric Single Crystals and Their Medical Transducers Application.

Piezoelectric materials have been developed since early 1900s and many research had been conducted on the composition and process to obtain higher piezoelectric constants ( d33 ). Within composition research, lead perovskite relaxor piezoelectric single crystals (SCs) of Pb(Mg1/3Nb2/3)O3-lead titanate PbTiO3 type have been actively studied since 1990s because of their outstanding pC/N compared with those of the conventional Pb(Zr,Ti)O3 ceramics. A major driving force of these SC research has been promoted by mass production of ultrasound transducers and array probes for medical diagnostic systems since early 2000s. However, higher d33 material and process research for these ultrasound devices are almost saturated. In this review article, we present a brief overview of the history, current situation, and future perspective of piezoelectric SCs. The authors believe that the main research in the next century is high d33 SCs with a high composition uniformity and low-energy SC growth methods, such as solid-state SC growth, low-loss SC transducer manufacturing technique, and improved poling process. This is a big technical challenge for all the scientists; however, the relatively large market of medical ultrasound has been expanded year by year, and we hope that the community is motivated to solve such technical problems in the near future.

Domain structures and dielectric properties resulting from tweed precursors of relaxor ferroelectric solid-solution single-crystal 24Pb(In1/2Nb1/2)O3-46Pb (Mg1/3Nb2/3)O3-30PbTio3.

The domain structures of poled and depoled lead-based relaxor ferroelectric solid-solution single-crystal 24Pb(In(1/2)Nb(1/2))O(3)-46Pb (Mg(1/3)Nb(2/3))O(3)-30PbTio(3) are studied by polarized light microscopy, piezoresponse force microscopy (PFM), scanning electron microscopy (SEM), and dielectric spectroscopy. The domain structures in the nonergodic relaxor state are found by PFM to consist of tweed structures resulting from random fields from the competition between ferroelectric and antiferroelectric distortion, and planar defects found by SEM are treated as dislocations associated with strain accommodation, resulting in superior piezoelectric properties. This domain structure is found to be connected with hierarchical domain structures.

Low acoustic attenuation silicone rubber lens for medical ultrasonic array probe.

Effects of heavy density (rho = 9.2 x 10(3) kg/m(3)) Yb(2)O(3) fine dopant (16 nm in diameter) on the acoustic properties of a high-temperature-vulcanization (HTV) silicone rubber have been investigated, to develop a new acoustic lens material with a low acoustic attenuation (alpha) for the medical array probe application. The HTV silicone rubber has advantages in that it shows a lower alpha than that of a room-temperature-vulcanization (RTV) silicone rubber and it can be mixed by applying shear stress, using roll-milling equipment. Roll-milling time dependence of the HTV silicone rubber indicates that the alpha is closely affected by the dispersion of nanopowders in the rubber matrix. The 8 vol% Yb(2)O(3)-doped HTV silicone rubber mixed for 30 min showed the lowest alpha of 0.73 dB/mm MHz with an acoustic impedance [AI = sound speed (c) x density (rho)] of 1.43 x 10(6) kg/m(2)s at 37 degrees C. Moreover, simulation results reveal that a 5 MHz linear probe using the HTV silicone rubber doped with Yb(2)O(3) powder showed relative sensitivity around 2.6 to 3.0 dB higher than a probe using RTV silicone rubber doped with Yb(2)O(3) powder or SiO2-doped conventional silicone rubber for the ultrasonic medical application.

Effects of fine metal oxide particle dopant on the acoustic properties of silicone rubber lens for medical array probe.

The effects of fine metal oxide particles, particularly those of high-density elements (7.7 to 9.7 x 10(3) kg/m3), on the acoustic properties of silicone rubber have been investigated in order to develop an acoustic lens with a low acoustic attenuation. Silicone rubber doped with Yb2O3 powder having nanoparticle size of 16 nm showed a lower acoustic attenuation than silicone rubber doped with powders of CeO2, Bi2O3, Lu2O3 and HfO2. The silicone rubber doped with Yb2O3 powder showed a sound speed of 0.88 km/s, an acoustic impedance of 1.35 x 10(6) kg/m2s, an acoustic attenuation of 0.93 dB/mmMHz, and a Shore A hardness of 55 at 37 degrees C. Although typical silicone rubber doped with SiO2 (2.6 x 10(3) kg/m3) shows a sound speed of about 1.00 km/s, heavy metal oxide particles decreased the sound velocities to lower than 0.93 km/s. Therefore, an acoustic lens of silicone rubber doped with Yb2O3 powder provides increased sensitivity because it realizes a thinner acoustic lens than is conventionally used due to its low sound speed. Moreover, it has an advantage in that a focus point is not changed when the acoustic lens is pressed to a human body due to its reasonable hardness.

Pressure dependence of piezoelectric properties of a Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) binary system single crystal near a morphotropic phase boundary.

The piezoelectric properties of a Pb[(Mg(1/3)Nb(2/3))(0.68)]Ti(0.32)O(3) binary system single crystal poled along the [001] direction in the rhombohedral phase were investigated under pressures up to 400 MPa at 25 °C. For the transverse electromechanical property, the difference Δf between the resonance f(r) and antiresonance frequencies f(a), the Δf/f(r) and the electromechanical coupling coefficient k(31) value in the k(31) mode with hydrostatic pressure (p) became smaller because of the increase in f(r) and the almost constant f(a) with p. The k(31) value decreased by 16% at 400 MPa. On the other hand, for the longitudinal electromechanical property, the Δf, the Δf/f(r) and the k(33) value in the k(33) mode with p remained almost constant because of the almost constant f(r) and f(a) with p. The changes in the values of the elastic compliances s(11)(E) and s(33)(E) with p were found to be large from the changes in f(r) and f(a) with p. s(11)(E) and s(33)(E) at 400 MPa were estimated to be 35.4 and 75.1 × 10(-12) m(2) N(-1), respectively. A mechanical quality factor Q almost constant with p in the k(33) mode in contrast to the large decrease in Q in the k(31) mode with p in the pressure range up to 200 MPa was observed. A k(33) value almost constant with p is considered, on the basis of the engineered domain concept, to be due to the stable domain configuration responsible for the longitudinal k(33) mode. Furthermore, the superior piezoelectric properties of the rhombohedral [001] single crystal in the vicinity of the morphotropic phase boundary composition were recently pointed out to come from the large shear piezoelectric constant d(15) of their single domain property. The hydrostatic pressure cannot influence the piezoelectric properties from the viewpoint of the contribution of the large shear mode d(15), since the uniform pressure introduces no shearing stresses. Consequently, the k(33) value measured for the k(33) mode remained almost constant with p in the measured pressure range.

Piezoelectric ceramics with high dielectric constants for ultrasonic medical transducers.

Complex system ceramics Pb(Sc(1/2)Nb(1/2))O3-Pb(Mg(1/3)Nb(2/3))O3-Pb(Ni(1/2)Nb(1/2))O3-(Pb0.965,Sr0.035) (Zr,Ti)O3 (PSN-PMN-PNN-PSZT abbreviated PSMNZT) have been synthesized by the conventional technique, and dielectric and piezoelectric properties of the ceramics have been investigated for ultrasonic medical transducers. High capacitances of the transducers are desired in order to match the electrical impedance between the transducers and the coaxial cable in array probes. Although piezoelectric ceramics that have high dielectric constants (epsilon33t/epsilon0 > 5000, k'33 < 70%) are produced in many foundries, the dielectric constants are insufficient. However, we have reported that low molecular mass B-site ions in the lead-perovskite structures are important in realizing better dielectric and piezoelectric properties. We focused on the complex system ceramics PSMNZT that consists of light B-site elements. The maximum dielectric constant, epsilon33T/epsilon0 = 7, 200, was confirmed in the ceramics, where k'33 = 69%, d33 = 940 pC/N, and T(c) = 135 degrees C were obtained. Moreover, pulse-echo characteristics were simulated using the Mason model. The PSMNZT ceramic probe showed echo amplitude about 5.5 dB higher than that of the conventional PZT ceramic probe (PZT-5H type). In this paper, the electrical properties of the PSMNZT ceramics and the simulation results for pulse-echo characteristics of the phased-array probes are introduced.

Present and future of piezoelectric single crystals and the importance of B-site cations for high piezoelectric response.

High quality piezoelectric single crystals, such as Pb(Zn(1/3)Nb(2/3))O3-PbTiO3 (PZNT) and Pb(Mg(1/3)Nb(2/3))O3-PbTiO3 (PMNT), have been investigated, and, because their piezoelectric properties are greatly superior to those of Pb(Zr(1-x)Ti(x))O3 (PZT) ceramics, they have been used for certain transducer applications since the late 1990s. The present situation for these relaxor-PT (lead titanate) single crystals is summarized. In this review, some possible high Tc > 200 degrees C single crystals are also introduced. Single crystals of Pb(In(1/2)Nb(1/2))O3-PbTiO3 (PINT) binary system and Pb(Mg(1/3)Nb(2/3))O3-Pb(Sc(1/2)Nb(1/2))O3-PbTiO3 (PSMNT) tertiary system have been synthesized, and their electrical properties are reported. In addition, a novel guiding principle for discovering excellent piezoelectric materials, namely the presence of low molecular mass B-site ions that can enter the lead-perovskite Pb(B'B'')O3 structure, is introduced.