• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.1
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• pp.1-8
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• 2002

The high frequency ultrasonic transducers using polyvinyliden fluoride(PVDF) and polyvinylidene fluoride trifluorethyylene(P(VDF-TrFE)) were developed. The characteristics of fabricated high frequency ultrasonic transducer such as beam diameter, high frequency ultrasonic detection field and amplitude of the first pulse echo signal from the test target in the water were analyzed. The high frequency ultrasonic detection field was affected by the length of coaxial cable between high frequency transducer and ultrasonic pulser/receiver. As the size of the test target increased, the high frequency detection field decreased and the amplitude of a reflection signal increased. The peak amplitude of the first pulse echo signal of P(VDF-TrFE) transducer was higher than that of PVDF transducer. The high frequency ultrasonic detection field of PVDF transducer was wider than that of P(VDF-TrFE) transducer. With C-scan testing, the developed high frequency ultrasonic transducer could detect the 30 to $100{\mu}m$ of hydrogen induced crack of steel specimen by C-scan testing.

• The Journal of the Acoustical Society of Korea
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• v.40 no.5
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• pp.530-536
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• 2021

Recently, due to the development of deep learning, end-to-end speech recognition, which directly maps graphemes to speech signals, shows good performance. Especially, among the end-to-end models, conformer shows the best performance. However end-to-end models only focuses on the probability of which grapheme will appear at the time. The decoding process uses a greedy search or beam search. This decoding method is easily affected by the final probability output by the model. In addition, the end-to-end models cannot use external pronunciation and language information due to structual problem. Therefore, in this paper conformer with lexicon transducer is proposed. We compare phoneme-based model with lexicon transducer and grapheme-based model with beam search. Test set is consist of words that do not appear in training data. The grapheme-based conformer with beam search shows 3.8 % of CER. The phoneme-based conformer with lexicon transducer shows 3.4 % of CER.

• The Journal of the Acoustical Society of Korea
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• v.41 no.3
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• pp.278-286
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• 2022

In this study, a 33-mode Free-Flooded Ring (FFR) transducer was designed to apply piezoelectric single crystal PIN-PMN-PT, which has high piezoelectric constants and electromechanical coupling coefficient. To ensure low-frequency high transmitting sensitivity characteristics with a small size of FFR transducer, the commercial FFR transducer based on piezoelectric ceramics was compared. To develop the FFR transducer with broadband characteristics, a piezoelectric segmented ring structure inserted with inactive elements was applied. The oil-filled structure was applied to minimize the change of acoustic characteristics of the ring transducer. It was verified that the transmitting voltage response, underwater impedance, and beam pattern matched the finite element numerical simulation results well through an acoustic test. The difference in the transmitting voltage response between the measured and the simulated results is about 1.3 dB in cavity mode and about 0.3 dB in radial mode. The fabricated FFR transducer had a higher transmitting voltage response compared to the commercial transducer, but the diameter was reduced by about 17 %. From this study, it was confirmed that the feasibility of a single crystal-applied FFR transducer with compact size and high-power characteristics. The effectiveness of the performance prediction by simulation was also confirmed.

• The Journal of the Acoustical Society of Korea
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• v.31 no.7
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• pp.480-486
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• 2012

In the design of electro acoustic transducer, power factor improvement circuit is more required rather than impedance matching if the driving power amplifier has little inner resistance. Many research results have been focused on the power matching circuit designing for transferring maximum power in the wideband. There are few results in the designing study on the power factor improvement for the wide band electro acoustic transducer. In this paper, we propose a new design method on the power factor improvement for the wide band electro acoustic transducer. The proposed method consists of two steps, the chebyschev matching method and the constrained optimization, respectively.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.35 no.3
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• pp.312-322
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• 1999

A ultrasonic transduce with a single acoustic matching layer has been designed as an attempt to increase the bandwidth of underwater transducer. The wideband resonance condition was accomplished by attaching a single matching layer on the front face of a ceramic resonator composed of a piezoelectric bar, a taper part and a head part. A modified Mason's model was used for the performance analysis and the design of transducers, and the constructed transducers were tested experimentally and numerically by changing the impedance and thickness of the matching layer in the water tank.The obtained results are summarized as follows:1. Measured resonant and antiresonant frequencies of the piezoelectric transducer with no matching layer in air were 24.7 kHz and 25.6 kHz, respectively. 2. Two resonant frequencies of the piezoelectric transducer with a single matching layer were 21.7 kHx and 26.9 kHz, respectively, in air and 21.4 kHz and 22.7 kHz, respectively, with a water load.3. Two distinct resonance peaks in the transmitting voltage response(TVR) of the developed transducer were observed at 22.0 kHz and 25.8 kHz, respectively, with center frequency of 24.0 kHz. The values of TVR at these frequencies were 130.1 dB re $1 \muPa$/V at 22.0 kHz and 128.5 dB re $1 \muPa$/V at 25.8 kHz, respectively.Reasonable agreement between the experimental results and the numerical values was achieved.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.4 s.175
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• pp.972-981
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• 2000

The phased array transducer has two distinct advantages. One is rapid scanning comparing with the conventional mechanical or manual scanning system. Therefore, output image is represented in real-time. The other is the dynamic focusing and the dynamic steering of ultrasonic beam. Only the delay times that are controlled electrically are used to focus and to steer beam without any lenses or wedges. In this study, the profile of the ultrasonic beam for the phased array transducer has been simulated in the Huygens principle with varying the inter-element spacing of the linear phased array transducer. From the result of this study, it was found that the ultrasonic beam spread wider as the inter-element spacing was decreased. However, the focusing effect was improved, even when the number of the element was not big. In addition, there was grating lobes that are constructed when the inter-element spacing is more than half wavelength. However, this grating lobe has lower amplitude than the main lobe.

• Smart Structures and Systems
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• v.1 no.1
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• pp.47-61
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• 2005

A ring-shaped lead zirconate titanate (PZT) piezoceramic sensor has been integrated with the Langevin-type piezoceramic driver of an ultrasonic wire-bonding transducer to form a smart transducer for in-situ measurement of three essential bonding parameters: namely, impact force, ultrasonic amplitude and bond time. This sensor has an inner diameter, an outer diameter and a thickness of 12.7 mm, 5.1 mm and 0.6 mm, respectively. It has a specifically designed electrode pattern on the two major surfaces perpendicular to its thickness along which polarization is induced. The process-test results have indicated that the sensor not only is sensitive to excessive impact forces exerted on the devices to be bonded but also can track changes in the ultrasonic amplitude proficiently during bonding. Good correlation between the sensor outputs and the bond quality has been established. This smart transducer has good potential to be used in automatic process-control systems for ultrasonic wire bonding.

• The Journal of the Acoustical Society of Korea
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• v.22 no.3
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• pp.208-216
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• 2003

In one dimensional linear array type piezoelectric ultrasonic transducers widely used for medical diagnosis, the acoustic cross talk caused by the structural acoustic coupling between the adjacent piezoelectric elements reduces significantly their performance. In the study, we have proposed an acoustic wall to reduce the acoustic cross talk by wave propagation through the surface the transducer which can not be prevented by conventional kerf and have analyzed using a finite element method the acoustic cross talk level with respect to the shape, size and materials of the acoustic wall mounted on a convex one dimensional piezoelectric ultrasonic transducer. We expect that the simulated results provide us with a valuable information to make an optimized design of the way type ultrasonic transducer minimizing the acoustic cross talk level.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.26 no.6
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• pp.252-257
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• 2016

Dust-collecting behavior of tonpilz transducer was simulated with finite-element-method (FEM) software. In order to optimize the performance of tonpilz transducer, the shape factors including the thickness of head mass, the diameter of tail mass and the depth of bolt were analyzed as variables. As a vibrating energy source, the piezoelectric materials was also tested with PZT-4 and two kinds of piezoelectric single crystals. The output power of the transducer was maximized with the shape factors and then the behavior of the dust-collection was demonstrated with the multi-physics software, COMSOL.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.12
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• pp.967-975
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• 2013

In the design of underwater electro acoustic transducer, power factor improvement circuit is more required rather than impedance matching if the driving power amplifier has little inner resistance. Many research results have been focused on the power matching circuit designing for transferring maximum power in the wideband. There are few results in the designing study on the power factor improvement for the wide band underwater electro acoustic transducer. In this paper, we set up a new design method on the power factor improvement for the wide band electro acoustic transducer, and confirm its feasibility by the experiments.