• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.2
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• pp.148-156
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• 2016

The paper deals with improvement of a piezoelectric ultrasonic transducer for measuring both pipe thickness and flow velocity. The transducer structure is based on the conventional transducers for measuring flow velocity by obliquely transmitting ultrasonic waves to the flow direction. The transducer invented earlier for measuring flow velocity and pipe thickness had an advantage of including only one piezoelectric disc, but for the thickness measurement the ultrasonic wave had to be reflected twice in a wedge material to be transmitted vertically to a pipe, and thus the wave signal was too weak. The transducer has been improved to transmit waves for thickness measurement vertically to a pipe without any prior reflection by electrically connecting two piezoelectric discs, one for flow velocity and the other for pipe thickness measurement. By comparing the measured results of specimen thickness with the improved transducer and conventional transducers, the accuracies of the improved one have been evaluated in the pipe thickness measurements.

• The Journal of Korean Physical Therapy
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• v.22 no.5
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• pp.49-56
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• 2010

Purpose: The aim of this study was to evaluate a possible role for cranial artery velocity in cervicogenic headache. Methods: We studied 13 patients with cervicogenic headaches (M=9, F=4, age=$24.50{\pm}3.50\;y$) these were compared to 20 normal subjects (M=10, F=10, age=$23.30{\pm}2.90\;y$). Cervicogenic headache patients were divided into two groups (a myofascial relaxation group, a placebo group). Pain levels were measured using a visual analog scale (VAS). Transcranial Doppler (TCD) ultrasound recordings were used to measure blood flow velocity in the cranial artery. Results: Cervicogenic headache patients exhibited a significantly lower blood flow velocity in the middle cerebral artery. The patients who received an intervention had a significantly higher blood flow velocity in the left middle cerebral artery, right vertebral artery and basilar artery. Compared to the placebo group, the myofascial relaxation group exhibited a significantly decreased level of pain. Conclusion: Cervicogenic headache is pain referred to the head from a source in the cervical spine. Manual therapy affect to cervical spine and soft tissue as well as the passage of these vessels and nerves to recover because it is thought to be able to help.

• Journal of Power System Engineering
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• v.17 no.4
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• pp.72-78
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• 2013

Compacted graphite iron 340 was carried out the heat treatment from 873 to 1,273 K. Compacted graphite iron 340 was evaluated relationship between the sound velocity, the attenuation coefficient and the tensile strength. The obtained results are as following. The signal strength of C scan images were weak according to increasing of heat treatment temperature and time. The amplitude of A scan and B scan was also low. This can be cause that the graphite was grown into the type of vermicular, and the many of grain boundary with ultrasound scattering were increase. The sound velocity was depend upon the heat treatment temperature and time, the attenuation coefficient had nothing to do with the temperature and time. The higher the heat treatment temperature, the tensile strength and the sound velocity were decreased. However, the tensile strength was proportional to the sound velocity. The higher tensile strength, the faster the sound velocity.

• International Journal of Advanced Culture Technology
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• v.10 no.3
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• pp.339-345
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• 2022

In this paper, the effect of porosity on the acoustic phase velocity of the 3D printed Kelvin closed-cell structure was investigated using the spectral phase analysis. Since Kelvin cells bring about the large amount of scattering, acoustic pulses in ultrasonic measurements undergoes a distortion of waveforms due to the dispersion effect. In order to take account on the dispersion, mathematical expressions for calculating the phase velocity of longitudinal waves propagating normal to the plane of the Kelvin structure are suggested by introducing a complex wave number based on Fourier transform. 3D Kelvin structure composed of identical unit-cells, a polyhedron of 14 faces with 6 quadrilateral and 8 hexagonal faces, was developed and fabricated by 3D CAD and 3D printer to represent the micro-structure of porous materials such as aluminum foam and cancellous bone. Total nine samples of 3D Kelvin structure with different porosity were made by changing the thickness of polyhedron. Ultrasonic pulse of 1MHz center frequency was applied to the Kelvin structures for the measurement of the phase velocity of ultrasound using the TOF(time-of-flight) and the phase spectral method. From the experimental results, it was found that the acoustic phase velocity decreased linearly with the porosity.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.11
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• pp.2322-2327
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• 2002

The corrosion degradation characteristics of the 12Cr alloy steel, which is widely used in fossil power plants as a turbine blade material, are evaluated nondestructively by use of the backward radiated Rayleigh surface wave. In order to evaluate corrosion degradation characteristics, we constructed automated system for the backward radiation, and the frequency dependency of the Rayleigh surface wave is investigated indirectly by measuring the angular dependency of the backward radiation of the incident ultrasonic wave in the specimens. The velocity of the surface wave decrease as the increase of the aging time in the backward radiation profile, which seems to result from the increase of the effective degrading layer thickness. And, amplitude of the surface wave increase as the aging time, which seems to result from the increase of the intergranular corrosion. The result observed in this study demonstrates high potential of the backward radiated ultrasound as a tool for the nondestructive evaluation of the corrosion degradation characteristics of the aged materials.

• Journal of the Korean Wood Science and Technology
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• v.33 no.5 s.133
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• pp.21-28
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• 2005

For the proper conservation of wooden cultural properties, non-destructive evaluation (NDE) method, which can be used to quantitatively evaluate the internal state of wood members, are needed. In this study, an ultrasonic CT system composed of portable devices was attempted, and the capacity of this system was verified by reconstructing the CT images for two phantoms and two artificially defected specimens. Results from this study showed that the sizes of detected defects were enlarged and the shapes were distorted on the CT images. Also, the positions were shifted somewhat toward the surface of specimen, which is regarded due to the anisotropic property of wood. Compared to the filtered back-projection method, SIRT (simultaneous iterative reconstruction technique) method was determined to be more efficient as the algorithm of image reconstruction for wood. A new ultrasonic CT system is thought to be used as a NDE method for wood. However wood characteristics and wave diffraction within wood made it difficult to accurately evaluate the size, shape and position of defects. To improve the quality of CT image of wood, more research including the relationship between wood and ultrasound is needed, and wood properties should be taken into consideration on the image reconstruction algorithm.

• The Journal of the Acoustical Society of Korea
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• v.29 no.4
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• pp.251-257
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• 2010

This paper deals with the attenuation and dispersion of ultrasound in bubbly liquids. Bubble clouds in liquid are formed by a variety of mechanisms, leading to different bubble sizes and spectra. Our aim is to investigate how bubble sizes and spectra affect the attenuation and dispersion characteristics of bubbly liquids. Especially, we highlight the attenuation and dispersion behaviors of nano-bubbles, which have not been reported elsewhere. Computations show that the attenuation and dispersion characteristics of bubbly liquids depend heavily on the quality factors of constituent bubbles. The present study is expected to facilitate in-depth understanding of sound propagation in bubbly liquids.

• Proceedings of the KIEE Conference
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• 1988.07a
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• pp.705-708
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• 1988

Ultrasound Doppler Diagnostic System utilizes the Doppler effect for measurement of blood velocity. The sign of the Doppler frequency shift represents blood flow direction. Pulsed Doppler System uses Phase detector and zerocrossing method to produce simultaneous independent audio and velocity signals for forward and reverse blood flow direction in the time domain, had been fabricated. But time-domain analyzing such as audio evaluation and zerocrossing detection for instantaneous and mean frequency measurement doesn't, provide both an accurate and quantitative result. Therefore, it is necessary to adopt frequency domain technique to improve system performance. In this paper, we describe a unit which is composed of Pulsed Doppler System and real-time spectrum analyzer (installed TMS 32010 DSP Chip). This unit shows time-dependent spectrum variation and mean velocity of blood Signal.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.69-74
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• 2001

It is well known that an air bubble trapped in water emits light at its collapse robustly with a proper forcing amplitude of ultrasound. Instability mechanism which causes deviation from sphericity of bubble wall was investigated theoretically. The rapid change of the bubble wall velocity which is both dependent on the forcing amplitude, was found to be a major factor of instability of the interface. The Rayleigh-Taylor instability which occurs when rapid acceleration is directed from the lighter towards the heavier fluid is found to be not related to the instability of the sonoluminescing gas bubble. A good agreement between the calculation results and experimental data is found.

• Proceedings of the KOSOMBE Conference
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• v.1992 no.11
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• pp.43-46
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• 1992

$\underline{In\;vitro}$ velocity measurements were made using both the pulsed Doppler ultrasound (PDU) machine and laser Doppler anemometer (LDA) system in order to investigate the flow characteristics near the aortic bifurcation. Velocities measured from the PDU machine was in good agreement with those from the LDA. The flow in the daughter branches was three-dimensional with a secondary flow. The oscillating wall shear stress with this secondary fluid motion is well correlated with the localization of the atherosclerosis.