• The Journal of the Acoustical Society of Korea
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• v.37 no.4
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• pp.174-180
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• 2018

In this study, the propagation characteristics of Lamb waves in anisotropic silicon wafers of (100) and (111) direction were investigated by PVDF (Polyvinylidene Fluoride) line-focused transducer. The modified V(f,z) method was used because the Lamb waves are dispersive. For confirming the anisotropy, a line-focused transducer was used and the silicon wafer was rotated 180 degrees at intervals of 1 degree. As a result, $A_0$ and $S_0$ modes were observed. The speed of $S_0$ mode according to propagation direction showed anisotropy which is associated with the crystal structure, and the speed of $A_0$ mode was isotropic. The result is consistent with the crystal structure of silicon and the mechanism of vibration of each Lamb wave modes.

• The Journal of the Acoustical Society of Korea
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• v.19 no.5
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• pp.41-45
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• 2000

The effective elastic constants of a single-crystal superlattice film have been determined by two methods based on the velocities of surface acoustic waves (SAW). One method uses formulas to calculate the effective elastic constants of a superlattice from the known elastic constants of the constituent layers. The calculated effective elastic constants are tested by comparing the corresponding SAW velocities calculated for thin-film/substrate systems with the corresponding SAW velocities measured by line-focus acoustic microscopy (LFAM). The other method determines the effective elastic constants of the superlattices by inverting the SAW velocity dispersion data measured by LFAM. The results of both methods applied to a TiN/NbN superlattice film are in good agreement.

• The Journal of the Acoustical Society of Korea
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• v.22 no.3
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• pp.202-207
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• 2003

For medical ultrasonic transducer, phase-weighting method has been used for controlling focal length with electric circuit at each vibrating element. However, the electric circuit is complex as the number of vibrating elements is increased. In this paper, we fabricated line-focus transducer with a bimorph-type piezoelectric actuator. The polyvinylidene fluoride (PVDF) piezoelectric type polymer film is used for transmitting and receiving of ultrasonic signal. Using this transducer, focal length of the transducer can be controlled mechanically by changing voltage of the actuator. It is confirmed that focal length of the transducer can be controlled in range of 1095 to radius of curvature.

• Journal of the Korean Society for Nondestructive Testing
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• v.13 no.2
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• pp.40-47
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• 1993

Composites composed of a precipitation harden 2124 alloy matrix reinforced by SiC whiskers, which are fabricated by powder metallugy, are suscepttible to fatigue damage due to the pile-up of moving dislocation and the microcrack initiation along SiC-Al interfaces, especially at the external surfaces of a body. The initial process, such as pile-up of dislocation or microcrack, that corresponds to the stage I during fatigue failure process are too small to be detected and characterized by conventional ultrasonic technique. This paper describes the applicability of an acoustic microscope with Line-Focus-Beam(LFB) lens of 225MHz to evaluate fatigue damage of SiC whiskers reinforced Al alloy. The specimens which were 6.6mm thick, 13mm wide, and 105mm long in the gage section were fatigued in tension-tension under load control. The velocity of leaky surface and leaky pseudosurface acoustic waves are obtained by FFT analysis technique from V(z) curve which is a record of output of piezoelectric transducer. These results are discussed with the change of number of fatigue cycles. The result obtained by acoustic microscope is compared with that by ultrasonic technique generated at 5MHz with conventional surface wave transducers.

• Sijohaknonchong
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• v.30
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• pp.53-90
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• 2009

This study discusses the aspects of Korean-American Sjjo writers' consciousness of sijo and its significance, focusing primarily on the Sijo-Anthologies of Korean-American authors, "The Moon of the Desert" (1989), "The Dandelion of the Desert" (1994), and The Stars of the Desert" (1996) published by the Sijo Society of America. For this purpose, I thoroughly examined "Notes of Writing Sijo' attached to the authors' works and some other sijos added at the end of the paper. They started writing sijos quite early. Sijo has been recognized as a typical traditional genre of literature, and even foreigners came to write them in English. The following is the summary of the view on sijo propounded by Korean-American authors. Firstly, they follow traditional view on the theory of sijo in terms of its nature and utility, and at the same time they emphasize the utility of katharsis through self expressions. Secondly, their recognition of the value of sijo boils down to its formal patterns. Lastly, they develop the idea of national literature through their significance of writing sijos. They think that they can contribute to the development of national literature as well as the expression of patriotism through writing sijos. Therefore, they recognize themselves as spreaders of Korean culture to the local residents, and as the main stream enhancing the status of Korean culture through the competition with other nations.

• Sijohaknonchong
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• v.43
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• pp.149-175
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• 2015

There have been few researches about Christian imagination reflected in modern sijo. The purpose of this study was to provide basic information helpful to deeply understand Christian literature and clarify the history of Christian sijo literature. For this purpose, the study focused on pieces of sijo written by Seon Jeong-ju and Jang Sun-ha both of whom put out lots of sijo based on Christian imagination. The two poets are common in that they were born in the Japanese colonial period and started their career as a poet at an almost same time. First of all, how a sijo writer, Seon Jeong-ju applied Christian imagination to his pieces of sijo can be summarized as follows. As a poet and paster, Seon Jeong-ju wrote and published 6 volumes of sijo collection. His pieces of sijo were all written based on Christian imagination. Many of the pieces contain Christianity-related stories that were poetically represented through paradoxical imagination. Among pieces of sijo written by Seon Jeong-ju, some reveal enthusiasm for seeking after truth that he kept in mind as a clergyman and others, the poet's strong belief in the Resurrection. Next, Christian imagination that another sijo writer Jang Sun-ha reflected in his works can be briefed as follows. The poet published a sijo collection of his own in 2010. As one of the best representatives of the modern sijo circles, he is a veteran poet who is still creating pieces of sijo. Since he became a Christian in 1996, he has released more than 200 pieces of Christianity-based sijo including those contained in his sijo collection, "Introduction to Love Studies". Most of the Christian poets quoted words from the Bible or borrowed episodes described in the Book. In those poets, he uses imagination that is allusive to the confession of his faith and, in some cases implies his own views of eschatology. In conclusion, both Seon Jeong-ju and Jang Sun-ha wrote and published lots of sijo works on the basis of Christianity, and each of them built up his own world of Christian sijo. In many of the two poet's pieces of sijo, critical doctrines of Christianity and their desperate devotion to that religion are found. Both of them made remarkable poetic achievements, so they deserve being recognized as second to none in the history of Christian sijo literature.