• Smart Structures and Systems
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• v.24 no.4
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• pp.435-446
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• 2019

The existing piezoelectric spherical transducers with fixed prescribed dynamic characteristics limit their application in scenarios with multi-frequency or frequency variation requirement. To address this issue, this work proposes an improved design of piezoelectric spherical transducers using the resistance tuning method. Two piezoceramic shells are the functional elements with one for actuation and the other for tuning through the variation of load resistance. The theoretical model of the proposed design is given based on our previous work. The effects of the resistance, the middle surface radius and the thickness of the epoxy adhesive layer on the dynamic characteristics of the transducer are explored by numerical analysis. The numerical results show that the multi-frequency characteristics of the transducer can be obtained by tuning the resistance, and its electromechanical coupling coefficient can be optimized by a matching resistance. The proposed design and derived theoretical solution are validated by comparing with the literature given special examples as well as an experimental study. The present study demonstrates the feasibility of using the proposed design to realize the multi-frequency characteristics, which is helpful to improve the performance of piezoelectric spherical transducers used in underwater acoustic detection, hydrophones, and the spherical smart aggregate (SSA) used in civil structural health monitoring, enhancing their operation at the multiple working frequencies to meet different application requirements.

• Proceedings of the Acoustical Society of Korea Conference
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• 1993.06a
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• pp.165-168
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• 1993

• The Journal of the Acoustical Society of Korea
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• v.12 no.4
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• pp.78-85
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• 1993

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.3
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• pp.383-390
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• 2018

Piezoelectric micro-machined ultrasonic transducers for highly directional speaker need DC bias voltage. Most existing power amplifiers are not suitable for use in highly directional transducers because they are based on AC. In addition, since the piezoelectric micro-machined ultrasonic transducer has a large capacitive reactance, the power efficiency of the power amplifier is very low. Thus this paper proposes a new high efficiency power amplifier with DC bias voltage. In addition, by designing a matching circuit to compensate the capacitive reactance of the micro-machined ultrasonic transducer, the power efficiency of the power amplifier increases. The operating characteristics of the proposed power amplifier was verified by an experimental prototype. The proposed power amplifier is expected to be widely used in designing and implementing other related power amplifiers.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1995.05a
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• pp.1-4
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• 1995

The most of conventional ultrasonic transducers are constructed to generate either longitudinal or shear waves, but not both of them. We investigated the mechanism of dual mode transducers that generates both of the longitudinal and shear waves simultaneously with a single PZT element. The study has been aimed to find the desired cut by the examining the piezoelectric properties. Theory predicts that a mixed P/S mode transducer can be constructed using a related Z-cut of a PZT ceramics. We studied the performance of a PZT element as a function of its rotation angle so that its efficiency is optimized to excite the two waves equally strongly. The results are verified by checking the impedance variation of the element with Finite Element Methods, and chocking the wave form by pulse-echo test simulation. Based upon the theory a rotated Z-cut was prepared and a transducer were fabricated. Validity of the theory calculation is verified through the

• Journal of Sensor Science and Technology
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• v.21 no.6
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• pp.408-412
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• 2012

An in-line dispersive delay line (DDL) demands low and controllable reflectivity of the reflectors, especially if the surface acoustic wave (SAW) propagates all the way along the reflecting structure. The metal reflectors are usually too strong and introduce too much attenuation in such a device. The proposed solution of this problem is to spatially separate the acoustic channels for different frequencies with the help of Fan-shaped Transducers (FIDT) and to use narrow open metal reflectors to reduce reflectivity. Special arrangement of FIDT is performed to use 180-deg. reflection of the SAW. Narrow open metal strips with a metallisation ratio of the order of 20% are used as reflectors with small and controllable reflectivity. Reflectivity of such strips is estimated both theoretically and experimentally. Experimental performance of the proposed DDL is presented.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.3
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• pp.239-245
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• 2007

A torsional guided wave mode in a tubular structure has many advantages in obtaining a higher sensitivity and lower attenuation for a defect, because it shows no dispersion characteristics and no radial displacement for a tubular structure. Many attempts have been made to excite and receive torsional guided waves by conventional piezoelectric transducers, but only a few examples are used during a practical field inspection. In this study, an array of electromagnetic acoustic transducers (EMATs) were for an excitation and reception of the torsional guided waves in a pipe was designed and fabricated. The signal patterns were analyzed based on various beam path length. The feasibility of detecting the defects was investigated through a series of experiments with artificial notches on a pipe.

• The Journal of the Acoustical Society of Korea
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• v.21 no.1
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• pp.56-61
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• 2002

In piezoelectric ultrasonic linear array transducers widely used for diagnosis, the cross talk caused by the structural cross-coupling between adjacent elements inside the transducer affects the probe performance in a significant manner. In this study, we constructed a finite element model of a piezoelectric ultrasonic transducer, and analyzed its cross talk level with respect to the shape of and materials inside the kerf, The results of this work can be utilized in optimal design of the transducers for medical diagonosis and treatment as well as W applications.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.333-334
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• 2004

The central aspect of the research into virtual acoustic imaging for multiple listeners involves a detailed study of the relative orientation of both sources and listeners. It is vital in any multiple listener system to first establish the conditioning of the potential geometrical arrangements of transducers and listeners. In this paper, this made clear the important link between the conditioning of the electro-acoustic transfer function matrix between transducers and ears and the design of inverse filters for crosstalk cancellation. This work has been undertaken by using simple free field models of the electro-acoustic transfer functions. Therefore, optimal transducer arrangements have been identified and these have been proved by time domain solutions.

• Proceedings of the Korea Concrete Institute Conference
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• 1990.04a
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• pp.35-38
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• 1990

Depths of the vertical cracks in the concrete were determined by the time of flight of the ultrasonic waves. The ultrasonic waves are diffracted at the crack tip, and the arrival time of ultrasonic waves are dependent on the crack depth and speration distance between transmitting and receiving ultrasonic transducers. The vertical cracks with 0.2-2mm width and 10-100mm depth were examined by multi-layered ultrasonic transducers. It was found that the time of flight of ultrasonic waves were proportional to the depth of vertical cracks. The depth of vertical cracks in the range of 20-100mm depth could be determined by the transient time of the diffracted ultrasonic waves