• Journal of the Korean Society for Nondestructive Testing
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• v.18 no.3
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• pp.163-171
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• 1998

Near/far field length and directivity of transducers were investigated for the improvement and evaluation of the detectability of flaws in a disc. The reference block is fabricated for the disc of stage 6 in Yonggwang unit 1. The near/far field and directivity of an ultrasonic transducer with the center frequency of 5MHz were calculated for the inspection of the disc. These values showed good agreements with the experimental results. In the system composed of a wedge and a disc, those are evaluated theoretically and experimentally for the specimen with the artificial flaws of the size 2mm and 4mm and an ultrasonic transducer with the center frequency 5MHz and diameter 0.5inch. The detectability of keyway-flaw and detectable region for inspection were evaluated by using both tangential $45^{\circ}$ and $90^{\circ}$ transducers located at the distance of 53mm and 75mm from the disc hub, respectively.

• The KIPS Transactions:PartB
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• v.14B no.6
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• pp.407-412
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• 2007

The performance of ultrasonic testing systems for industrial or medical purpose largely depends on the performance of ultrasonic transducers. Generally, the information about an ultrasonic transducer performance characteristics are expressed by the ultrasonic R/F signal back from a reflector and its frequency characteristics in the data sheet provided by manufacturers. In case of focused ultrasonic transducers, the two pieces of information can, however, hardly assure that the focused ultrasonic transducer would produce well-focused C-scan images. Therefore, we propose the measured size of focal spot and the reconstructed shape of effective focal zone in the focused sound field as novel measures for the performance evaluation of the focused ultrasonic transducers. The process of getting the both measures of the transducers is conducted by the implemented software including sound field scanning and virtual 3D reconstruction functions which requires the echo of a point reflector. The proposed method could, otherwise impossible in the existing method, effectively and simply distinguish superior ones among many transducers made in the same specification and be also used to detect the performance degradation due to the aging of the transducers. Eventually, the quality of performance of the ultrasonic testing systems for industrial or medical purpose is secured.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.1
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• pp.20-26
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• 2005

Ultrasonic guided waves have been widely employed for long range inspection of structures such as plates, rods and pipes. There are numerous modes with different wave velocities, and the appropriate mode selection is one of key techniques in the application of guided waves. In the present work, phase tuning by an array transducer was applied to generate ultrasonic guided waves. For this purpose, 8-channel ultrasonic pulser/receiver and their controller which enables sequential activation of each channels with given time delay were developed. Eight transducers were fabricated in order to generate guided waves by using an array transducer. The selective tuning of wave mode can be achieved by changing the interval between elements of an array transducer.

• Journal of the Korean Society for Nondestructive Testing
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• v.14 no.2
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• pp.83-89
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• 1994

It is important for an ultrasonic testing to know the sound pressure field and the directivity of ultrasonic waves propagating in a solid. The directivity of ultrasonic wave is closely related to the sensitivity, the scanning pitch, the arrangement of angle probe, and the defect kind in ultrasonic testing. This paper describes on the directivity measurement of ultrasonic wave using ultrasonic wave visualization method. The directivity of the shear wave emitted from the angle probes were constant during propagation. The difference of directivity was existed between 2MHz and 4MHz angle probes. The centers of directivity were located backward from the incident poing and inside of the angle probe and were not changed during the wave propagation.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.5
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• pp.536-542
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• 2011

Dissimilar metal welds in nuclear power plant are known as very susceptible to PWSCC flaws, and periodically inspected by the qualified inspector and qualified procedure during in-service inspection period. According to field survey data, the majority of their DMWs are located on tapered nozzle or adjacent to a tapered component. These types of configurations restrict examination access and also limit examination volume coverage. Additionally, circumferential scan for axially oriented flaw is very difficult to detect located on tapered surface because the transducer can't receive flaw response from reflector for miss-orientation. To overcome this miss-orientation, it is necessary adapt skewed ultrasonic transducer accomodate tapered surface. The skewed refracted longitudinal ultrasonic transducer designed by modeling and manufactured from the modelling result for axial flaw detection. Experimental results showed that the skewed refracted longitudinal ultrasonic transducer get higher flaw response than non-skewed refracted longitudinal ultrasonic transducer.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.579-580
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• 2014

In this research, modeling and analysis of an ultrasonic transducer composed of single crystal piezoelectric material(PMN-28PT) are conducted with FEM in reference with that composed of piezoelectric ceramic(PZT-4). Acoustic performances of the ultrasonic transducer are compared with magnitude, phase of impedance and trasmitting voltage response according to the type of piezoelectric materials.

• Journal of Conservation Science
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• v.31 no.3
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• pp.267-278
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• 2015

In this study, the elastomer cover, a new contact material, was developed to establish the customized ultrasonic measurement considering surface irregularities of stone cultural heritages. The cover exhibits high elastic force and wear resistance because it has tensile strength of 17MPa and elongation of 625%. In addition, as a result of comparative experiments for the seven types according to transducers and contact materials including the elastomer cover, rock surface irregularities significantly affect attenuation of ultrasonic velocity. The phenomenon was more noticeable in the chiseling finish and indirect transmission measurement rather than the dabbed finish and direct transmission measurement. However, the Type F using the exponential transducer and elastomer cover showed stable P-wave velocity and high amplitude regardless of the surface irregularities. This because the elastomer cover sufficiently sticks to surface irregularities and removes pores between a transducer and a rock specimen. Therefore, the Type F should be used for the ultrasonic measurement of stone cultural heritages with surface irregularities.

• Journal of Conservation Science
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• v.25 no.3
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• pp.233-244
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• 2009

This study was focused on the transducer and suitable contact material for stone cultural heritage, and the correlation of direct-indirect method in rock types for scientific development and quantitative evaluation technique of the ultrasonic measurements. As a result, it was identified the transducer (UTREXTX(RX)54kHz) and contact material (rubber clay) of the type 3 were appropriate for the ultrasonic measurements of stone cultural heritage. The direct-indirect correction factors of type 3 were calculated 1.50 for granite, 1.38 for gabbro, 1.58 for quartz diorite, respectively. This result is the first study for improvement in reliability for the ultrasonic measurements, and it will contribute to establishment of the ultrasonic survey method for stone cultural heritage. Also, complementary studies considering the surface irregularity of rocks and various contact materials will carry out, and the database about correlation of direct-indirect in rock types will establish.

• The Journal of the Acoustical Society of Korea
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• v.21 no.8
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• pp.744-756
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• 2002

The transient acoustic fields formed by a 3.5 ㎒ curved linear array transducer which is commonly used in ultrasonic medical imaging system for diagnosis of abdomen are systematically analyzed to obtain new design parameters for the better acoustic image. In the analysis with an assumption of radiating waveform, element size, radius of curvature, amplitude apodization are considered as parameters giving constitutive relations with the fields. As simulation results, appropriate new parameters with the reduced curvature and elevation aperture and the apodization of Hamming window, which make an improved acoustic beam with lower side lobe levels than a conventional typical transducer, are obtained.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.4
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• pp.294-299
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• 1999

In this paper, the calibration system for contact transducer has been developed to improve the reliability of the inspection result of ultrasonic testing on rotors. This system consists of signal processing parts: (oscilloscope, spectrum analyzer, pulser/receiver), standard block, and user interface program. Signal processing for the calibration system was performed quickly with high accuracy. The developed system has been applied to a practical calibration of probe using the non-destructive testing on rotors, and demonstrated high sensitivity and precision.