• 비파괴검사학회지
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• 제26권1호
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• pp.7-11
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• 2006

기계부품의 세라믹 코팅 층은 사용 중 그 표면특성이 변하므로 잔류수명 예측과 신뢰성 확보를 위해 비파괴적으로 세라믹 코팅 층의 특성을 평가하는 것은 매우 중요하다. 이를 위해 본 인구는 AISI 1045 강과 오스테나이트 스테인리스 304 강 모재위에 매우 얇은 TiN 세라믹 층을 코팅한 시편에 내하여 누설 레일리(Rayleigh) 표면파를 이용한 TiN 코팅부재의 특성평가를 시도하였다. 후방복사 측정기법으로 코팅 층 내의 표면파의 전파특성이 평가되었고 표면 거칠기, 코팅 층 두께, 마모조긴 둥이 다양한 시편들에 대해 후방복사 프로파일이 측정되었다. 후방복사 프로파일의 정점각과 크기는 시편의 조건들에 따라 민감하게 변하였고, 정점각의 증가는 코팅 층 접합 강도의 저하로 설명되었다. 결과들은 후방복사 기법을 이용한 표면파의 분산성 평가가 코팅 층의 특성 평가에 매우 유용함을 보여주었다.

• 한국생산제조학회지
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• 제19권2호
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• pp.198-203
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• 2010

In this paper, study on the mode characteristics analysis of the SH-EMAT (shear horizontal, electromagnetic acoustic transducer) waves for evaluating the thickness reduction in plates such as corrosion and friction is presented. Noncontact methods for ultrasonic wave generation and detection have been a great concern and highly demanded due to their capability of wave generation and reception on surface of high temperature or on rough surface. Mode identification of the SH-EMAT wave is carried out in an aluminum plate with thinning defects using time frequency analysis method such as wavelet transform, compared with theoretically calculated group velocity dispersion curve. The changes of various wave features such as the amplitude and the time-of-flight have been observed and the correlations with the thickness reduction have been investigated. Firstly, experiments have been conducted to confirm that it is possible to selectively generate and receive specific desired SH modes. These modes have then been analyzed to select the parameters that are sensitive to the thickness change. The results show that the mode cutoff and the time-of-flight changes are feasible as key parameters to evaluate the thickness reduction.

• 비파괴검사학회지
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• 제34권4호
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• pp.290-298
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• 2014

초음파 두께 측정 방법은 초음파가 표면에서 되돌아오는 시간을 측정하여 두께를 측정하는 비파괴검사 방법이다. 이때 초음파 진행 시간은 펄스의 최대값을 이용하여 측정하기 때문에, 물체의 두께가 얇을 경우 펄스 신호가 서로 중첩이 되어 기존의 초음파 방법으로 측정하기 어렵다는 단점이 있다. 이러한 단점을 보완하기 위해 본 논문에서는 파워켑스트럼과 최소분산켑스트럼을 사용하여 두께를 측정하는 방법을 제안하고자 한다. 켑스트럼 신호 처리는 초음파 신호를 임펄스 트레인과 전달함수(초음파 펄스 신호)로 분리하기 때문에 표면에서 돌아오는 초음파 신호의 시간을 임펄스 트레인의 주기로 정확하게 측정할 수 있다. 제안된 방법을 검증하기 위하여 다양한 두께를 가진 철, 아크릴 시편에 대해 실험을 수행하였다. 두께가 얇은 시편에 대해서는 펄스가 중첩이 되기 때문에 기존방법으로 측정이 어려움을 알 수 있었다. 하지만 제안된 방법인 켑스트럼 초음파 신호 처리를 적용한 결과 임펄스 신호로 분리하기 때문에 두께를 정확히 측정함을 알 수 있었다.

• The Journal of Advanced Prosthodontics
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• 제5권3호
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• pp.341-350
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• 2013

PURPOSE. To evaluate adherence of human gingival fibroblasts (HGFs) to transmucosal abutment of dental implant with different surface conditions with time and to investigate the roles of focal adhesion linker proteins (FALPs) involved in HGFs adhesion to abutment surfaces. MATERIALS AND METHODS. Morphologies of cultured HGFs on titanium and ceramic discs with different surface were observed by scanning electron microscopy. Biocompatibility and focal adhesion were evaluated by ultrasonic wave application and cell viability assay. FALPs expression levels were assessed by RT-PCR and western blot. RESULTS. There seemed to be little difference in biocompatibility and adhesion strength of HGFs depending on the surface conditions and materials. In all experimental groups, the number of cells remaining on the disc surface after ultrasonic wave application increased more than 2 times at 3 days after seeding compared to 1-day cultured cells and this continued until 7 days of culture. FALPs expression levels, especially of vinculin and paxillin, also increased in 5-day cultured cells compared to 1-day cultured fibroblasts on the disc surface. CONCLUSION. These results might suggest that the strength of adhesion of fibroblasts to transmucosal abutment surfaces increases with time and it seemed to be related to expressions of FALPs.

• 한국음향학회지
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• 제22권3호
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• pp.208-216
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• 2003

의료 진단용으로 널리 사용되는 1차원 배열형 압전 초음파 변환기는 소자들간의 음향 간섭에 의해 성능이 저하된다. 본 연구에서는 기존의 커프로 효과를 볼 수 없는 변환기 표면을 따라 전파하는 음파로 인한 간섭을 감소하기 위해 음향 벽 설치를 제안하고, 유한 요소 해석법을 이용하여 convex 1차원 배열형 압전 초음파 변환기에 설치한 음향 벽의 형상. 크기 및 재질에 따른 음향 간섭 수준을 분석하였다. 시뮬레이션 결과는 소자들간의 음향 간섭을 최소화하는 초음파 변환기의 최적화 설계를 위해 매우 유용한 정보로 사용될 것으로 기대된다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 추계학술대회 논문집 Vol.18
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• pp.232-233
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• 2005

In this paper, disk-type ultrasonic motor using a combination of radial and bending vibration modes is newly designed and fabricated. The characteristics of the test motor are also measured. By means of travelingelastic wave induced at the surface of circumference of the elastic disk, a steel bar in contact with the surface of circumference of elastic disk bonded onto the piezoelectric ceramic disks is driven inboth directions by changing the sine and cosine voltage inputs. The stator of the motor is composed of two sheets of piezoelectric ceramic disk to bond onto both surfaces of a elastic disk, respectively. As the results, the diameter of elastic body is increased, the resonant frequency is decreased. The resonant frequency of the stator is about 92 kHz, which is composed with piezoelectric ceramic disks of 28 mm in diameter and 2 mm in thickness, and an elastic body of 32 mm in diameter and 2 mm in thickness. A driving voltage of 20 Vpp produces 200 rpm with a torque of 1Nm and an efficiency of about 10 %.

• 비파괴검사학회지
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• 제22권2호
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• pp.149-154
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• 2002

실제 사용 온도 보다 높은 $630^{\circ}C$에서 열처리 시간을 변수로 하여 최대 1000 시간 동안 등온 열처리를 통해 2.25Cr-1Mo 강의 경년열화재를 제작하고 열화에 따른 미세조직과 기계적 특성 변화에 대한 초음파 비파괴평가 법으로 표면 특성평가에 우수한 표면 SH파를 적용하였다. 열화에 따른 초음파의 감쇠와 전파시간 및 웨이블렛을 이용한 음속과 감쇠계수의 주파수 의존성평가를 수행한 결과 열화가 진행됨에 따라서 탄화물은 점차 조대화되고 경도는 감소하였다. 감쇠계수는 열화시간이 증가함에 따라서 증가하였고 전파시간 역시 열화의 초기단계에 급격히 증가했다. 초음파의 감쇠와 경도와는 좋은 상관관계를 나타내어 감쇠계수는 경년열화 평가에 중요한 파라미터임을 알 수 있었다.

• 한국생산제조학회지
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• 제6권1호
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• pp.27-33
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• 1997

A neural network approach has been developed to determine the depth of a surface breaking crack in a steel plate from ultrasonic backscattering data. The network is trained by the use of feedforward three-layered network together with a back-scattering algorithm for error correction. The signal used for crack insonification is a mode converted 70$^{\circ}$transverse wave. A numerical analysis of back scattered field is carried out based on elastic wave theory, by the use of the boundary element method. The numerical data are calibrated by comparison with experimental data. The numerical analysis provides synthetic data for the training of the network. The training data have been calculated for cracks with specified increments of the crack depth. The performance of the network has been tested on other synthetic data and experimental data which are different from the training data.

• 한국가시화정보학회지
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• 제20권3호
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• pp.19-26
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• 2022

In droplet microfluidics, precise droplet manipulation is required in numerous applications. This study presents ultrasonic surface acoustic wave (USAW)-based microfluidic device for label-free droplet separation based on size. The proposed device is composed of a slanted-finger interdigital transducer on a piezoelectric substrate and a polydimethylsiloxane microchannel placed on the substrate. The microchannel is aligned in the cross-type configuration where the USAWs propagate in a perpendicular direction to the flow in the microchannel. When droplets are exposed to an acoustic field, they experience the USAW-induced acoustic radiation force (ARF), whose magnitude varies depending on the droplet size. We modeled the USAW-induced ARF based on ray acoustics and conducted a series of experiments to separate different-sized droplets. We found that the experimental results were in good agreement with the theoretical estimation. We believe that the proposed method will serve as a promising tool for size-based droplet separation in a label-free manner.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 학술대회 논문집 정보 및 제어부문
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• pp.273-275
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• 2005

Active thermography is being used since several years for remote non-destructive testing. It provides thermal images for remote detection and imaging of damages. Also, it is based on propagation and reflection of thermal waves which are launched from the surface into the inspected component by absorption of modulated radiation. For energy deposition, it use external heat sources (e.g., halogen lamp or convective heating) or internal heat generation (e.g., microwaves, eddy current, or elastic wave). Among the external heat sources, the ultrasound is generally used for energy deposition because of defect selective heating up. The heat source generating a thermal wave is provided by the defect itself due to the attenuation of amplitude modulated ultrasound. A defect causes locally enhanced losses and consequently selective heating up. Therefore amplitude modulation of the injected ultrasonic wave turns a defect into a thermal wave transmitter whose signal is detected at the surface by thermal infrared camera. This way ultrasound thermography(UT) allows for selective defect detection which enhances the probability of defect detection in the presence of complicated intact structures. In this paper the applicability of UT for fast defect detection is described. Examples are presented showing the detection of defects in PCB material. Measurements were performed on various kinds of typical defects in PCB materials (both Cu metal and non-metal epoxy). The obtained thermal image reveals area of defect in row of thick epoxy material and PCB.