Jeongdong Woo

P2O-7 Design and Construction of an Acoustic Horn for High Power Ultrasonic Transducers

Typical high power transducers consist of a piezoelectric or magnetostrictive element of transduction and a solid acoustic horn that acts as a vibration amplifier. In order to obtain high power capacity, the acoustic horn needs to be optimized to match the active element. In this study, we did optimal design of an acoustic horn for a high power magnetostrictive transducer and constructed a sample prototype of the horn to verify the validity of the design. For the design, we derived the theoretical output power of a horn as a function of its dimensions, and determined the optimal dimensions to achieve the maximum power through finite element analyses with ANSYSreg. The analytical method could quite quickly determine the horn length while the finite element method could refine the planar dimensions of the structure. The transducer had the resonant frequency of 19.3 kHz and had the maximum sound pressure level of 199 dB with an omni-directional radiation pattern in water. The analysis method developed in this study is so general that it can be applied to the design of acoustic horns for high power transducers of various operating frequencies and transduction materials

Ultrasonic 2D matrix array transducer for volumetric imaging in real time

Matrix array transducers have been developed in this work for cardiac imaging in real-time and 3D. The matrix array transducers have 4,096 (64×64) active elements made of the piezoelectric single crystals, PMN-PT, within 1 inch square. Two different matrix array structures have been developed: (1) fabrication of whole 64×64 elements as a single unit on a PMN-PT plate with a conductive backing, and (2) assembly of eight 64×8 element modules to compose 64×64 channels. Optimal structures of the two matrix array transducer types have been determined through finite element analysis to have their center frequency at 3.5 MHz and fractional frequency bandwidth over 60%. In the single unit structure, it was very difficult to achieve good enough uniformity over the whole 4,096 elements, which was likely to cause serious difficulty in production of the transducer. The acoustic module assembly technique was developed to resolve the problem. In case some elements showed big deviation in performance due to mistakes in fabrication, that particular module containing the bad elements could be easily replaced with a good one. However, the module assembly method necessitated more complicated fabrication processes. Fabricated prototypes of the transducers satisfied the design specifications very well.

Ultrasonic two-dimensional array transducer of the single-unit type with a conductive backing of the 1–3 piezocomposite structure

A two-dimensional (2D) array transducer has been developed in this work using a new conductive backing. The 2D array transducer was designed to comprise 4,096 channels operating at the center frequency of 3.4 MHz with a fractional bandwidth over 50%. The 2D array transducer designed in this work is different from other matrix transducers in that all the active channels were installed on a single piezoelectric crystal plate as a whole unit by using the new conductive backing. The new conductive backing has a structure similar to that of 1–3 piezocomposite materials. Based on the design, an experimental prototype of the 2D array transducer was fabricated and characterized. The prototype showed good agreement with the design and excellent sensitivity uniformity over the entire channels. These results confirmed the applicability of the new conductive backing to 2D array transducers.

Development of an SH-SAW sensor for detection of DNA immobilization and hybridization

We have developed SH (shear horizontal) surface acoustic wave (SAW) sensors for detection of the immobilization and hybrdization of DNA (deoxyribonucleic acid) on the gold coated delay line of transverse SAW devices. The experiments of DNA immobilization and hybridization were performed with 15-mer oligonucleotides (probe and complementary target DNA). The sensor consists of twin SAW delay line oscillators (sensing channel and reference channel) operating at 100 MHz fabricated on 36° rotated Y-cut X-propagation LiTaO3 piezoelectric single crystals. The relative change in the frequency of the two oscillators was monitored to detect the immobilization of probe DNA with thiol group on the Au coated delay line and the hybridization between target DNA and immobilized probe DNA in a pH 7.4 PBS (phosphate buffered saline) solution. The measurement results showed a good response of the sensor to the mass loading effects of the DNA immobilization and hybridization with the sensitivity up to 1.5 ng/ml/Hz.

Mechanical wobbling high intensity focused ultrasound (HIFU) transducer for volumetric ultrasound guided treatment of uterine fibroids

Uterine fibroids are noncancerous growths that develop in or just outside a womans uterus. For treatment of these, high intensity focused ultrasound (HIFU) surgery is gaining more and more popularity. Presently, two representative types of HIFU treatment are used: magnetic resonance guided and ultrasound (US) guided HIFU treatment depending on the method to monitor the treatment. This work is about the development of a new transducer for a more versatile US guided HIFU system to treat uterine fibroids. Normally, HIFU treatment of the uterine fibroids has been carried out with an extracorporeal transducer mounted on abdomen. Use of the extracorporeal transducer requires the US to be delivered through an external surface of a human body, which causes unnecessary exposure of interstitial cells to the high intensity US. In order to resolve the problem, the HIFU needs to be insonated into only the tumors. For that purpose, the HIFU transducer incorporating both a treatment module and a US imaging module should be small enough to be inserted into vagina while providing enough acoustic power to heat the uterine fibroid tumors.

2D array transducer with a conductive backing

A new conductive backing has been developed to improve transducer performance and manufacturability. For fabrication, conductive pillars were molded in a polymeric matrix through a process similar to that for the fabrication of 1-3 piezocomposites. The best combination of pillar and backing materials was selected from experiments to achieve the maximum acoustic performance (high impedance and attenuation) and channel uniformity. The 2D array transducer with 4096 channels built had a 3.5MHz center frequency and an over 60% fractional bandwidth. Every single channel of the prototype satisfied the target specifications and the standard deviation over the entire channels was within 0.81dB.

Design and Fabrication of a 2D Array Ultrasonic Transducer

In this paper, a channel 2D array ultrasonic transducer with piezoelectric single crystals was designed, fabricated, and evaluated. Structure of the transducer was chosen to facilitate the electric connection on the planar array, and then components were fabricated in accordance with the structure. Detailed structure of the transducer was designed through finite element analyses. In order to improve the performance of the transducer, the crosstalk between adjacent elements was reduced through the control of kerf width and material, and the target frequency bandwidth was achieved through optimal design of the thickness of the single crystal and matching layers. After fabricating a prototype of the transducer according to the design and measuring its characteristics, the results were compared with those of finite element analyses to evaluate the performance of the developed transducer.

Design and Fabrication of 2D Array Ultrasonic Transducers with a Conductive Backer

In this paper, 2D array transducers using a conductive backer similar to 1-3 composites have been designed, fabricated, and evaluated. The conductive backer was based on well known manufacturing process of 1-3 composites with affordable ingredients. The 2D array transducer had 4,096 elements designed to have 3.5 MHz center frequency and a fractional bandwidth over 60 %. Fabricated prototype of the transducer satisfied the specifications in the center frequency and bandwidth. Performance over the entire elements was so uniform that the standard deviation was less than 0.81 dB. Thus applicability of the conductive backer proposed in this work to 2D array transducers was verified.