• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.6
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• pp.773-777
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• 2011

Conventional ultrasonic thickness measurement is to be considered as the assumption that the ultrasonic velocity is known. In actual applications the velocity is often not well known and access is often limited to one side. This paper aims at determining the ultrasonic velocity and thickness of plates with parallel or wedged surfaces using contact measurements made on one surface only. For wedged plates the thickness at one point and the wedge angle are determined. Equations are used for determining the ultrasonic velocity, thickness and wedge angle of the plate based on the times-of-flight measured by two contact transducers coupled to one surface. The time-of-flight of the obliquely reflected longitudinal wave echo was measured as a function of the separation between the two transducers. In addition, a simulation was made for comparing the experimental data and a FEM image. Experiments and simulations were performed on flat and wedged plates of aluminium materials; the calculated results for the unknown quantities are generally agreed with them to some degree.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.5
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• pp.416-420
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• 2008

In EMAT field, spiral RF coils are much more widely used when compared with solenoid coils. In the field of the magnetostrictive strip transducers for long range ultrasonic testing of cylindrical structures, however, solenoid coils has been used. This seems to be attributed to the difficulty in fabricating low frequency (i.e., large size) spiral coils. In this paper, we describe a method for fabricating spiral coil magnetostrictive strip guided wave transducers from FFC (flexible flat cable). It is demonstrated through a comparison experiment that the spiral coil transducer has much superior performance (sensitivity, SNR, and guided wave direction control capability) than the previous transducer with solenoid coils.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1658-1660
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• 2000

Simple signs were usually exchanged as the means of underwater communications. As people recently, need more informations for underwater activities, necessities of underwater communication systems exchanging hunman voice are increased. The purpose of this paper is understanding the ordinary characteristics of underwater communication and investigating the necessary conditions for a good underwater communication system by making a basic communication module. The experiment is achieved by applying AM (Amplitude Modulation) which is mainly used for the underwater communication systems and using common ultrasonic transducers. Ultrasonic transducers usually have narrow bandwidth for transducing electrical energy to mechanical energy. For improvement of sound reconstruction, transducers need more bandwidth which covers voice's frequency range, and goof linearity characteristics in this frequency range. As underwater transmissions have many factors to distort signals. Amplitude Modulation is not a proper way for underwater communications. Using digital signal by sampling human voice should be a good way for this systems, because digital communication simplify transmitting signals.

• Electrical & Electronic Materials
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• v.8 no.5
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• pp.572-579
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• 1995

Most of conventional ultrasonic transducers are constructed to generate either longitudinal or shear waves, but not both of them. We investigate the mechanism of dual mode transducers that generate both of the longitudinal and shear waves simultaneously with single PZT element. The study is aimed to find the optimally desired cut by examining the anisotropic piezoelectric properties. Theory predicts that a mixed P/S mode transducer can be constructed using a rotated Z-cut of PZT piezoelectric ceramics. We study the performance of a PZT element as a function of its rotation angle so that its efficiency is optimized to excite the two waves as much as equally strong. The results are verified by the waveform in pulse-echo computer simulation and experiments. When the transducer is subjected to impedance analysis, it shows two thickness mode resonances, each of which being a mixed P/S thickness mode. By examining wave speeds on E transmitter delay line receiver setup, it is confirmed that the transducer can transmit and detect both longitudinal and shear wave simultaneously.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.3
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• pp.199-206
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• 2015

This paper deals with the vibration characteristics of stacked transducers composed of piezoelectric discs, which are main elements of ultrasonic sensors or actuators. The stacked transducers were devised in the sense of natural frequencies. Two- or three-layer transducers were fabricated with piezoelectric discs of different diameters. The natural frequencies were determined by the finite element analysis and they were verified by comparing them with experimental results. It appeared that the natural frequencies of the stacked piezoelectric transducers include the natural frequencies of the constituent piezoelectric discs and the natural frequencies caused by stacking. Based on these results, it would be possible to predict the vibration characteristics of the stacked piezoelectric transducers in a design process.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.373-376
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• 2002

Most previous studies using ultrasound for osteoporosis diagnosis have employed ultrasound in a frequency range of 0.2-1 MHz. In this study, acoustic properties of the 12 defatted bovine cancellous bone specimens were investigated in vitro. Speed of sound (SOS) and broadband ultrasonic attenuation (BUA) were measured using three matched pairs of transducers with the center frequencies of 1, 2.25, and 3.5 MHz, respectively, in order to cover a broad frequency range of 0.5-2 MHz. The relative orientation between ultrasonic beam and bone specimens was the mediolateral (ML) direction of the bovine tibia. SOS showed significant linear positive correlations with apparent density for all three pairs of transducers of 1 MHz, 2.25 MHz, and 3.5 MHz, respectively. BUA showed relatively weak correlations with apparent density for the pairs of transducers of 1 MHz and 2.25 MHz. Furthermore, in the measurement with the pair of 3.5 MHz transducers, BUA was independent of apparent density. SOS and BUA were only weakly correlated with each other. The linear combination of SOS and BUA showed significant correlations with apparent density. These results suggest that the frequency range up to 1.5 MHz may be also useful in the osteoporosis diagnosis.

• 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.

• 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 Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.733-735
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• 2014

The paper deals with the energy transmission ratio of the elastic waves obliquely transmitting through a plate and a pipe. The incidence angle corresponding to the maximum transmission was determined theoretically and considered in the design of ultrasonic transducers for flow velocimetry. Experimentally-obtained transmission ratios were compared with and confirmed the theoretically-calculated results.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.1
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• pp.47-52
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• 2011

It is well known that stiffness of composites depends on layup sequence of CFRP(carbon fiber reinforced plastics) laminates because the layup of composite laminates influences their properties. Ultrasonic NDE of composite laminates is often based on the backwall echoes of the sample. A pair of such transducers was mounted in a holder in a nose-to-nose fashion to be used as a scanning probe on composites. Miniature potted angle beam transducers were used (Rayleigh waves in steel) on solid laminates of composites. Experiments were performed to understand the behavior of the transducers and the nature of the waves generated in the composite (mode, wave speed, angle of refraction). C-scan images of flaws and impact damage were then produced by combining the pitch-catch probe with a portable manual scanner known as the Generic Scanner ("GenScan"). The pitch-catch signal was found to be more sensitive than normal incidence backwall echo of longitudinal wave to fiber orientation of the CFRP composites, including low level porosity, ply waviness, and cracks. Therefore, it is found that the experimentally Rayleigh wave variation of pitch-catch ultrasonic signal was consistent with numerical results and one-side ultrasonic measurement might be very useful to detect the defects.