Full metadata record
DC FieldValueLanguage
dc.contributorDepartment of Applied Physicsen_US
dc.contributor.advisorDai, Jiyan (AP)en_US
dc.creatorWong, Chi Man-
dc.identifier.urihttps://theses.lib.polyu.edu.hk/handle/200/11815-
dc.languageEnglishen_US
dc.publisherHong Kong Polytechnic Universityen_US
dc.rightsAll rights reserveden_US
dc.titleStudy of high-frequency ultrasound transducers for advanced biomedical imagingen_US
dcterms.abstractUltrasound imaging is one of the main medical diagnostic tools for clinical use due to its non-radioactive and harmless nature. In recent decades, medical ultrasound technologies are being widely developed for not only improving the image quality in convectional clinical use but also applying on new aspects such as clinical therapeutic and preclinical pathology or physiology research applications. New designs of transducer are desired to accomplish those application, and the performance improvement of those assistance material is also required. In this study, analysis is conducted on the synergistic effect of preclinical biomedical imaging through the usage of the high resolution clinical imaging technique. Therefore, high frequency ultrasound transducers accompanied by high performance, such as high spatial resolution and sensitivity, is investigated due to its finer detail with higher spatial frequency in the imaging targets, such as small mammalian and human tissues. Meanwhile, development of fabrication process and fabrication of advanced acoustic materials aiming at improving transducer's performance are also carried out.en_US
dcterms.abstractMatching layer is a critical component that determines the performance of piezoelectric-based ultrasound transducers. For most piezoelectric materials, their acoustic impedances are significantly higher than human tissues and organs (around 1.6 MRayl), so a tunable matching layer with a high acoustic impedance is required for optimizing the acoustic wave transmission. In this thesis work, a high compression fabrication method is invented, with which the acoustic impedance of alumina-epoxy composite matching layer can be tuned from 6.50 to 9.47 MRayl by controlling the applied compression pressure and ratio of alumina to epoxy. This enhancement of acoustic impedance is attributed to the increased acoustic longitudinal velocity when alumina content reaches a critical value causing coalitions and domination of the acoustic wave propagation in the matching layer. Furthermore, the attenuation of this newly developed matching layer is only -10 dB/mm at 40 MHz. The very high acoustic impedance value and very low attenuation make this matching material superior than all reported matching materials, and therefore, can enhance the performance of the ultrasound transducers, especially for medical imaging applications at high to ultra-high frequency regime.en_US
dcterms.abstractIn vivo ultrasound imaging with phase array transducers is of great importance for both clinical application and biomedical research. In this work, relaxor ferroelectric PMN- 0.28PT single crystal with very high piezoelectric constant (d33≥2000 pC/N) and a higher electromechanical coupling factor (k33~0.92), was used to develop high-frequency phase array transducers. A 128-element 20-MHz phased-array ultrasound transducer was successfully fabricated with optimized performance of an average ~84% bandwidth at -6 dB and insertion loss of -43 dB. The axial and lateral resolutions of this transducer were determined to be 40.5 µm and 121.5 µm, respectively. With this transducer and Verasonics image platform, in-situ images of a fisheye and in-vivo laboratory mice's cardiac images were acquired, demonstrating successful application of our developed high-frequency phase array transducer for biomedical research of small animals.en_US
dcterms.abstractCranial ultrasound is limited at infant and temple brain imaging because the rest parts of skull bone are too thick for penetrating. A new 2D annular array transducer idea based on the structure of Fresnel annular array is raised, designed and developed, aiming at transcranial brain imaging and stimulating through the pterion. The simulation result shows a pair of separated sectors in a modified structure produces an on-axis focal point at 34 mm with maximum 20 kPa pressure. The focal spot size is 12 mm length along axial direction and 0.045 mm width along lateral direction. The developed PZT 2D annular array transducer contents total 48 elements distributed in 8 sectors is also measured. The represented elements along the sector show a 16.10 MHz average center frequency and a -6 dB bandwidth around 80%. By further using an electrical signal control, a 3D conical shape image may be obtained. More work needs to be done to include more elements and develop new imaging method.en_US
dcterms.extentxviii, 162 pages : color illustrationsen_US
dcterms.isPartOfPolyU Electronic Thesesen_US
dcterms.issued2022en_US
dcterms.educationalLevelPh.D.en_US
dcterms.educationalLevelAll Doctorateen_US
dcterms.LCSHDiagnostic ultrasonic imagingen_US
dcterms.LCSHTransducers, Biomedicalen_US
dcterms.LCSHUltrasonic transducersen_US
dcterms.LCSHHong Kong Polytechnic University -- Dissertationsen_US
dcterms.accessRightsopen accessen_US

Files in This Item:
File Description SizeFormat 
6302.pdfFor All Users13.52 MBAdobe PDFView/Open


Copyright Undertaking

As a bona fide Library user, I declare that:

  1. I will abide by the rules and legal ordinances governing copyright regarding the use of the Database.
  2. I will use the Database for the purpose of my research or private study only and not for circulation or further reproduction or any other purpose.
  3. I agree to indemnify and hold the University harmless from and against any loss, damage, cost, liability or expenses arising from copyright infringement or unauthorized usage.

By downloading any item(s) listed above, you acknowledge that you have read and understood the copyright undertaking as stated above, and agree to be bound by all of its terms.

Show simple item record

Please use this identifier to cite or link to this item: https://theses.lib.polyu.edu.hk/handle/200/11815