|Title:||High-frequency and endoscopic ultrasonic transducers based on PMN-PT and PIN-PMN-PT single crystals|
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Applied Physics|
|Pages:||xvii, 125 leaves : ill. ; 30 cm.|
|Abstract:||Relaxor-based ferroelectric -oriented single crystals Pb(Mg₁/₃Nb₂/₃)O₃ PbTiO₃ (PMN-PT) and Pb(In₁/₂Nb₁/₂)O₃-Pb(Mg₁/₃Nb₂/₃)O₃-PbTiO₃ (PIN-PMN-PT) exhibit excellent piezoelectric properties. These single crystals have large piezoelectric coefficients (i.e. d₃₃>1000 pC/N), high electromechanical coupling factors (kt>55%) and low dielectric loss (<1%). In this dissertation, endoscopic and high-frequency ultrasonic intravascular transducers with very good performance were fabricated using PMN-0.28PT single crystals. A novel mechanical dimpling technique was implemented in high-frequency focused transducer fabrication using PMN-PT single crystal. In addition, the properties of new ternary PIN-PMN-PT single crystal were investigated and this crystal was used to fabricate high-frequency ultrasonic transducer. Furthermore, the fabrication and characteristics of ultrasonic transducer with PIN-PMN-PT single crystal / epoxy 1-3 composites based on the dice-and-fill method were carried out. The main achievements of this thesis are as follows: 1. Ultrasonic imaging catheters with good performance were fabricated based on PMN-0.28PT single crystal. The center frequencies of the transducers are about 10 and 30 MHz, which are suitable for endoscopic and intravascular imaging applications, respectively. 2. High-frequency (~30 and ~80 MHz) focused ultrasonic transducers were fabricated using a PMN-0.28PT single crystal by a mechanical dimpling technique. The dimpled single crystal was used as an active element in the focused transducer. Compared with a plane transducer, the focused transducer fabricated with a dimpled active element exhibits much broader bandwidth and higher sensitivity. 3. The complete set of constants for 0.27Pb(In₁/₂Nb₁/₂)O₃-0.45Pb(Mg₁/₃Nb₂/₃)O₃-0.28PbTiO₃ (0.27PIN-0.45PMN-0.28PT) single crystal was determined by the -poled domain engineered system with 4mm symmetry. There are a total of 11 independent physical constants describing the elastic-piezo-dielectric matrices for this EDED tetragonal symmetry including six elastic constants (sEij , sDij , cEij , cDij , ij = 11, 12, 13, 33, 44, 66), three piezoelectric constants(emi , dmi , gmi , hmi , mi = 15, 31, 33), and two dielectric constants (εTmn , εSmn , βTmn , βSmn , mn = 11, 33). The complete set of elastic, piezoelectric and dielectric constants are important for transducer design, components optimization, performance investigation and simulation analysis for prototype preparation. 4. Ferroelectric domain structure and evolution, as well as phase transition of -oriented PIN-PMN-PT single crystal have been studied through temperature and frequency-dependent relative permittivity measurements. 5. A high-frequency (~60 MHz) ultrasonic transducer with a -oriented PIN-PMN-PT single crystal as an active element has been fabricated and characterized. The -6 dB bandwidth of the transducer is 73 % and the insertion loss at its center frequency is 20 dB. 6. Single element broad-band and high-temperature ultrasonic transducer using a PIN-PMN-PT single crystal / epoxy 1-3 composite was fabricated and characterized as a function of temperature.|
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