Thickness Dependent Characteristics of High Permittivity PMN-0.32PT Single Crystal for High Frequency Medical Imaging Applications
The dielectric, piezoelectric, and acoustic properties of PMN-0.32PT (Pb(Mg(1/3)Nb(2/3)) O(3)-PbTiO(3)) single crystals were investigated as a function of sample thickness ranging from 120 to 30 μm in order to enlighten the origin of property degradation of crystals for high frequency ultrasound applications. Electromechanical coupling factor(k(t) ), clamped and free dielectric constants decreased but sound velocity increased with decreasing crystal thickness. Particularly, repoling of the PMN-PT crystals would bring about a noteworthy enhancement in electromechanical and dielectric properties, which urges the importance of PMN-PT as a promising piezoelectric material for high frequency ultrasound transducers.
High Frequency PMN-PT 1-3 Composite Transducer for Ultrasonic Imaging Application
Development of PMN-PT single crystal/epoxy 1-3 composites for high-frequency ultrasonic transducers application is presented. The composite was fabricated by using a DRIE dry etching process with a 45% volume fraction of PMN-PT. A 35 MHz ultrasound flat transducer was fabricated with the composite, which was found to have an effective electromechanical coupling coefficient of 0.81, an insertion loss of 18 db, and a -6 dB bandwidth as high as 100%. Tungsten wire phantom image shows that the transducer had an axial resolution of 30 μm, which was in good agreement with the theoretical expectation. The initial results showed that the PMN-PT/epoxy 1-3 composite has many attractive properties over conventional piezoelectric materials for medical imaging applications.
The PNR to Relaxor Transition in PSN with nearest neighbor Pb-O divacancies
In previous work, molecular dynamics simulations based on a first-principles-derived effective Hamiltonian for (PSN), with nearest-neighbor Pb-O divacancy pairs, was used to calculate vs. T, phase diagrams for PSN with: ideal rock-salt type chemical order; nanoscale chemical short-range order; and random chemical disorder. Here, we show that the phase diagrams should include additional regions in which a glassy relaxor-phase (or state) is predicted. With respect to phase diagram topology, these results strongly support the analogy between relaxors and magnetic spin-glass-systems.
