• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.15 no.1
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• pp.46-52
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• 2019

This work proposes a noncontact ultrasonic transducer for detecting wall-thinning of containment liner plates of nuclear power plants by measuring their thickness without physical contact. Because the containment liner plate is designed to prevent atmospheric leakage of radioactive substances under severe nuclear accident, its wall-thinning inspection is important for safety of nuclear power plants. Wall-thinning investigation of containment liner plates have been carried out by measuring their thickness with contact-type ultrasonic thickness gauge by inspectors and needs a lot of time and cost. As an alternative, an electromagnetic acoustic transducer measuring precisely thickness of containment liner plates without any physical contact or couplant was suggested in this research. A transducer generating and measuring shear ultrasonic waves in thickness direction was designed and wave field produced by the transducer was analyzed to verify the design. The working performance of the suggested transducer was tested with carbon steel plate specimens with various thicknesses. The test result shows that the proposed transducer can measure thickness of the specimens precisely without any couplant and implies that swift scanning of wall-thinning of containment liner plates will be possible with the proposed transducer.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.8
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• pp.771-776
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• 2012

A technique is presented that uses a circular waveguide for the measurement of the bulk shear(S-wave) velocities of unconsolidated, saturated media, with particular application to near surface soils. The technique requires the measurement of the attenuation characteristics of the fumdamental T(0,1) mode that propagates along an embedded pipe, from which the acoustic properties of the surrounding medium are inferred. From the dispersion curve analysis, the feasibility of using T(0,1) mode which is non-dispersive and have constant attenuation over all frequency range is discussed. The principles behind the technique are discussed and the results of an experimental laboratory validation are presented. The experimental data are best fitted for the different depths of wetted sand and the shear velocities as a function of depths are formulated using power law curves.

• Journal of Electrical Engineering and Technology
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• v.6 no.1
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• pp.111-118
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• 2011

In recent years, various types of partial discharge (PD) methods such as capacitive, inductive, electromagnetic, and acoustic coupling techniques have been developed for diagnosing rotating machines. An electromagnetic (EM) probe, which is an inductively coupled type of sensor, is required for detecting corona and internal discharges during off-line tests. In this study, a new technique for enhancing the measurement sensitivities for corona and internal discharge based on an EM inductive position sensor is proposed. An EM probe that winds wires around horseshoe-shaped and cylindershaped ferrites as helices is designed and optimized for the implementation of off-line PD monitoring of the stator winding of a rotating machine. The measurement system based on this design is implemented, and it is verified from the results of the experiment performed in this study that the probe provides similar performance as existing commercial products.

• The Journal of the Acoustical Society of Korea
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• v.14 no.5
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• pp.11-19
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• 1995

The Interaction between tire and road is responsible for the excited vibration of the tire, and It is also important for the sound radiation. In this paper. measurement of tire structural vibration noise from a chassis dynamometer using Spatial Transformation of Sound Field(STSF) technique is studied. STSF involving a scan that uses an array of transducers over a planar surface close to the source is under investigation. From cross spectra measurement during the scan, a principal component representing the sound field is extracted. Any power descriptor of the near field can then be investigated by means of near-field acoustic holography, while the distant field can be determined by application of Helmholtz integral equation. The results of the measurement were used to obtain the radiation sound pattern from the center line of the tire, and to locate the radiation sound generating regions in the vicinity of the tire.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.332-339
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• 2007

As the economy has grown and the main industry in Korea has been changed from secondary industry to tertiary industry, the importance of indoor environment has been a matter of common concern, in which one of the main concerns is to improve the indoor acoustic conditions. However, even though this is required more than before, there are no measures to protect the human being from the noise of electric home appliances. This is owing to the absence of the data about sound power level of electric home appliances. So, we investigate the sound power level of them and analyze the acoustical characteristics of each one. First, we tried to investigate the sound power measurement method of each electric home appliance. After it we test the sound power level of them. From the survey, we can know that the vacuum cleaner is the most noisy electric home appliance, and the refrigerator is the least noisy one. The noise of a range hood is distributed over a wide range frequency. Lastly, we intented to propose the proper method measuring sound power level on each electric home appliance.

• Journal of Power System Engineering
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• v.17 no.2
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• pp.56-62
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• 2013

A technique is presented that uses a circular waveguide for the measurement of the bulk shear (S-wave) velocities of unconsolidated, saturated media, with particular application to near surface soils. The technique requires the measurement of the attenuation characteristics of the fundamental torsional mode that propagate along an embedded pipe, from which the acoustic properties of the surrounding medium are inferred. From the dispersion curve analysis, the feasibility of using fundamental torsional mode which is non-dispersive and have constant attenuation over all frequency range is discussed. The principles behind the technique are discussed and the results of an experimental laboratory validation are presented. The experimental data are best fitted for the different depths of wetted sand and the shear velocities are evaluated as a function of depths. Also the characteristics of the reflected signal from the defects are examined and the reflection coefficients are calculated for identifying the relation between defect sizes and the magnitude of the reflected signal.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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• v.7 no.1
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• pp.56-60
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• 1996

The vocal efficiency(VE) can be calculated as the ratio of acoustic power to aerodynamic power. It relates to the vocal intensity, air Sow rate and subglottic pressure. In this study, we treated 20 cases of vocal polyps and 10 cases of vocal nodules by way of laryngo-microsurgery or laser laryngo-microsurgery. The VE was measured preoperatively and postoperatively in all cases. The results showed that there was a significant improvement of VE postoperatively than that of preoperative measurement(p＜0.01) in vocal Polyp group. However, there was no significant difference(p＞0.05) in vocal nodule group. Through comparing the results, we obtained the conclusion : The laryngo-microsurgery is the reliable method of management for the vocal polyps, but f3r the vocal nodules, the laryngo-microsurgery should be selected after other more conservative approaches fail to produce the desired results.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.5 no.2
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• pp.83-89
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• 1996

The objective of this study is to find experimentally the characteristics of the noise generated by the impinging jet on the normal plate, and also to compare the noise characteristics of the impinging jet with those of the free jet. The experiment is performed for the measurement of the noise specturm, the noise power, and the directivity for the free and impinging jets. From the experiment. it is found that the power of noises generated by the free jet as well as the impinging jet is proportional to the eighth power of the jet velocity through the circular converging nozzle, and that the noise power of the impinging jet is 15dB as high as one of the free jet when the plate distance is about within one to three times the nozzle diameter at the pressure ratio 1.39. The sound pressure level of the impinging jet depends upon the jet pressure and the plate distance. The plate distance with the maximum overall sound pressure level is increased with the jet pressure. The directivities with 1/3 octave band frequency for both the free jet and the impinging jet are greatly influenced by the convection effect.

• The Journal of the Acoustical Society of Korea
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• v.28 no.8
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• pp.732-739
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• 2009

Flow phantom with stenosis was manufactured using an auto-injector to obtain angiostenotic flow information and quality assurance (QA) for ultrasound diagnostic instrumentation. Effectiveness of manufactured flow phantom with stenosis was investigated with power Doppler that was known to have diagnostic efficiency for angiostenosis. The flow phantom with stenosis was manufactured to 70% stenosis with 8 mm and 2.4 mm silicon tube, and silicone tube was covered with gelatin that has acoustic characteristics similar to soft tissue. When the linear transducer was used for measurement, the estimated diameter of normal vessel was measured lower than that of normal value, and the estimated diameter of stenosed vessel was measured higher than that of normal value. The measured parameters were not affected except for the radical conditions such as gain of 60%, PRF of 3000 Hz, use of maximal filter or angle. In addition, when the convex transducer was used for measurement, measurement parameters were affected by gain, PRF, filter, and angle. Therefore it is expected that flow phantom with stenosis manufactured with an auto-injector will be utilized effectively for QA of angiostenotic diagnosis.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.1
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• pp.54-62
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• 2013

In this study, a wireless and non-power SAW (surface acoustic wave) temperature sensor was developed. The single inter-digital transducer (IDT) of SAW temperature sensor of which resonance frequency is 434 MHz was fabricated on $128^{\circ}$ rot-X $LiNbO_3$ piezoelectric substrate by semiconductor processing technology. To find optimal acoustic reflector for SAW temperature sensor, various kinds of acoustic reflectors were fabricated and their reflection characteristics were analyzed. The IDT type acoustic reflector showed better reflection characteristic than other reflectors. The wireless temperature sensing system consisting of SAW temperature sensor with dipole antenna and a microprocessor based control circuit with dipole antenna for transmitting signal to activate the SAW temperature sensor and receiving the signal from SAW temperature sensor was developed. The result with wireless SAW temperature sensing system showed that the frequency of SAW temperature sensor was linearly decreased with the increase of temperature in the range of 40 to $80^{\circ}C$ and the developed wireless SAW temperature sensing system showed the excellent performance with the coefficient of determination of 0.99.