유한요소해석 및 방사음장해석에 의한 판형 웨이브가이드 센서의 방사 빔 조향 해석 및 실험적 검증

박상진,주영상,김회웅,박창규 한국비파괴검사학회 2022 한국비파괴검사학회지 Vol.42 No.6

A plate-type waveguide (WG) sensor is a remote ultrasonic inspection device developed for severe environments such as high temperature and high radioactivity. A WG sensor uses the ability of long-distance propagation of Ao-mode Lamb wave and phenomenon of leaky Lamb wave. In addition, it can steer the radiation beam based on the phase velocity dispersion characteristics of the Ao-mode Lamb wave. Particularly, the beam steering technique is an electrical steering method that can change the radiation angle depending on the excitation frequency without the physical movement of the sensor. In this study, we analyze the steering characteristics of the radiation beam radiated from the WG sensor using finite element analysis and Rayleigh-Sommerfeld integral (RSI) analysis. Two dimensional simulations for the Ao-mode Lamb wave propagation and radiation with three types of excitation frequencies are performed, and simulation results of the radiation beam profile are experimentally demonstrated using the measured underwater results. The radiation angle of the radiation beam profiles obtained from the constructed two analysis models corresponds well with that of the measurement results, and the radiation characteristics such as near-field distance are validated to change with a change in the radiation angle depending on the excitation frequency. 판형 웨이브가이드 센서는 고온, 고방사능과 같은 가혹한 환경에서 초음파 트랜스듀서에 어떠한 물리적 손상이나 성능 저하없이 검사할 수 있는 원격 초음파 검사 센서이다. 개발한 웨이브가이드 센서는 웨이가이드 판을 따라 전파하는 Ao-모드 판파의 장거리 전파 성능과 누설 판파 현상을 이용하며, Ao-모드 판파의 위상속도 분산특성을 기반으로 초음파 방사 빔을 조향할 수 있다. 특히 방사 빔 조향 기능은 센서의 기계적 구동없이 전기적으로 가진주파수를 조정하는 것만으로 방사 빔의 방출 각도를 바꿀 수 있다. 본 논문에서는 유한요소해석 및 RSI(Rayleigh-Sommerfeld Integral) 방사 빔 해석 모델을 구축하여 웨이브가이드 센서의 방사 빔 조향 특성을 분석하였다. 세 가지 가진 주파수 변화와 함께 Ao-모드 판파의 전파 및 방사현상에 대한 2차원 시뮬레이션을 수행하였고, 방사 빔 프로파일 시뮬레이션 결과를 수중에서 측정된 방사 빔 프로파일과 비교하여 해석결과를 검증하였다. 구축한 두 모델로부터 얻은 방사 빔 프로파일의 방사각은 실험에서 측정한 결과와 잘 일치하였으며 가진 주파수 변화에 따라 방사 각도도 변화하지만 근거리음장 거리와 같은 방사 특성도 같이 변화한다는 사실을 확인하였다.

판재의 초음파 비선형 특성평가를 위한 Lamb Wave 기법

이태훈(Taehun Lee),김정석(Chung Seok Kim),장경영(Kyung-Young Jhang) 한국비파괴검사학회 2010 한국비파괴검사학회지 Vol.30 No.5

음향 비선형성은 재료 물성의 미세한 변화에 민감하기 때문에, 이를 측정하는 비선형 초음파 기술은 재료의 열화나 피로를 평가할 수 있는 기법으로 연구되어 왔다. 하지만 벌크파를 이용하는 일반적인 비선형 초음파 기법은 얇은 판재에 적용하는 것에는 여러 한계가 있다. 이와 같은 경우에는 비선형 Lamb 파의 사용을 생각할 수 있지만, Lamb 파는 벌크파와 매우 다른 전파 특성을 가지고 있어 그 비선형 특성에 대한 별도의 연구를 필요로 한다. 이를 위해 본 연구에서는 Lamb 파에서 비선형성에 의해 전파하면서 누적 성장할 수 있는 2차 고조파 모드의 발생 조건을 분석하였으며, 그 결과 네 가지 조건, 즉 (1) phase matching, (2) non-zero power flux, (3) group velocity matching, (4) non-zero out-of-plane displacement 를 제시하였다. 그리고 제시된 조건으로 알루미늄 판재에 대책 실험한 결과 이론 예측과 동일하게 전파 거리에 따라 2차 고조파 성분의 크기와 비선형 파라미터가 증가하였고, Al6061-T6 과 Al1100-H14에서 측정된 상대적인 비선형 파라미터의 비율이 이론적인 비율과 근접함을 보였다. Since the acoustic nonlinearity is sensitive to the minute variation of material properties, the nonlinear ultrasonic technique(NUT) has been considered as a promising method to evaluate the material degradation or fatigue. However, there are certain limitations to apply the conventional NUT using the bulk wave to thin plates. In case of plates, the use of Lamb wave can be considered, however, the propagation characteristics of Lamb wave are completely different with the bulk wave, and thus the separate study for the nonlinearity of Lamb wave is required. For this work, this paper analyzed first the conditions of mode pair suitable for the practical application as well as for the cumulative propagation of quadratic harmonic frequency and summarized the result in for conditions; (1) phase matching, (2) non-zero power flux, (3) group velocity matching, and (4) non-zero out-of-plane displacement. Experimental results in aluminum plates showed that the amplitude of the secondary Lamb wave and nonlinear parameter growed up with increasing propagation distance at the mode pair satisfying the above all conditions and that the ration of nonlinear parameters measured in Al6061-T6 and Al1100-H15 was closed to the ratio of the absolute nonlinear parameters.

Effective time-frequency characterization of Lamb wave dispersion in plate-like structures with non-reflecting boundaries

Zijian Wang,Pizhong Qiao,Binkai Shi 국제구조공학회 2018 Smart Structures and Systems, An International Jou Vol.21 No.2

Research on Lamb wave-based damage identification in plate-like structures depends on precise knowledge of dispersive wave velocity. However, boundary reflections with the same frequency of interest and greater amplitude contaminate direct waves and thus compromise measurement of Lamb wave dispersion in different materials. In this study, non-reflecting boundaries were proposed in both numerical and experimental cases to facilitate time-frequency characterization of Lamb wave dispersion. First, the Lamb wave equations in isotropic and laminated materials were analytically solved. Second, the non-reflecting boundaries were used as a series of frames with gradually increased damping coefficients in finite element models to absorb waves at boundaries while avoiding wave reflections due to abrupt property changes of each frame. Third, damping clay was sealed at plate edges to reduce the boundary reflection in experimental test. Finally, the direct waves were subjected to the slant-stack and short-time Fourier transformations to calculate the dispersion curves of phase and group velocities, respectively. Both the numerical and experimental results suggest that the boundary reflections are effectively alleviated, and the dispersion curves generated by the time-frequency analysis are consistent with the analytical solutions, demonstrating that the combination of non-reflecting boundary and time-frequency analysis is a feasible and reliable scheme for characterizing Lamb wave dispersion in plate-like structures.

Lamb wave-based blood coagulation test

Nam, Jeonghun,Choi, Hyunjoo,Kim, Jae Young,Jang, Woongsik,Lim, Chae Seung Elsevier 2018 Sensors and actuators. B Chemical Vol.263 No.-

<P><B>Abstract</B></P> <P>Blood coagulation tests are a critical part in diagnosis of patients with bleeding disorders and cardiovascular diseases. However, most conventional blood coagulation tests require large and expensive instruments and skilled personnel. Here, we present a simple and low-cost approach to evaluate blood coagulation using Lamb wave-based device. To assess coagulation, we monitored the acoustic streaming of 5 μm fluorescent particles suspended in citrated plasma. Using a Lamb wave, citrated blood plasma and coagulation reagents can be mixed in a few seconds and the viscosity of the droplet increases due to blood coagulation. Then, the acoustic streaming of particles eventually stops, at which the “coagulation time” is defined. As a preliminary test, coagulation time was reduced with increasing calcium concentration from 0 to 25 mM. Prothrombin time results from the Lamb wave-based device were validated by comparing with those of commercial instruments with the correlation coefficient (R<SUP>2</SUP>) as 0.9432. Using the Lamb wave for blood coagulation test, the temperature can be controlled as 37 °C simultaneously by modulating experimental conditions. Our device enables lithography-free, simple and low-cost measurement of blood coagulation, which can be applied to clinical settings and developing countries.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Using a Lamb wave device, acoustic streaming of fluorescent particles suspended in citrated plasma is induced in a droplet. </LI> <LI> The viscosity of the sample droplet increases due to blood coagulation, so that the acoustic streaming velocity decreases. </LI> <LI> The acoustic streaming of particles finally stops at the “coagulation time (CT)”. </LI> <LI> With increasing calcium concentration, CT decreases drastically due to improved blood coagulation. </LI> <LI> Prothrombin time measured by the Lamb wave device was highly correlated with that of commercial instrument. </LI> </UL> </P>

Effective time-frequency characterization of Lamb wave dispersion in plate-like structures with non-reflecting boundaries

Wang, Zijian,Qiao, Pizhong,Shi, Binkai Techno-Press 2018 Smart Structures and Systems, An International Jou Vol.21 No.2

Research on Lamb wave-based damage identification in plate-like structures depends on precise knowledge of dispersive wave velocity. However, boundary reflections with the same frequency of interest and greater amplitude contaminate direct waves and thus compromise measurement of Lamb wave dispersion in different materials. In this study, non-reflecting boundaries were proposed in both numerical and experimental cases to facilitate time-frequency characterization of Lamb wave dispersion. First, the Lamb wave equations in isotropic and laminated materials were analytically solved. Second, the non-reflecting boundaries were used as a series of frames with gradually increased damping coefficients in finite element models to absorb waves at boundaries while avoiding wave reflections due to abrupt property changes of each frame. Third, damping clay was sealed at plate edges to reduce the boundary reflection in experimental test. Finally, the direct waves were subjected to the slant-stack and short-time Fourier transformations to calculate the dispersion curves of phase and group velocities, respectively. Both the numerical and experimental results suggest that the boundary reflections are effectively alleviated, and the dispersion curves generated by the time-frequency analysis are consistent with the analytical solutions, demonstrating that the combination of non-reflecting boundary and time-frequency analysis is a feasible and reliable scheme for characterizing Lamb wave dispersion in plate-like structures.

구조물 건전성 모니터링을 위한 Lamb파 모드 구별법

전용주(Yongju Jun),박일욱(Ilwook Park),이우식(Usik Lee) Korean Society for Precision Engineering 2012 한국정밀공학회지 Vol.29 No.8

Lamb waves have received a great attention in the structural health monitoring (SHM) societies because they can propagate over relatively large distances in wave guides such as thin plates and shells. The time-of-flights of Lamb waves can be used to detect damages in a wave guide. However, due to the inherent dispersive and multi-mode characteristics of Lamb waves, one must decompose the Lamb wave modes into the symmetric and anti-symmetric modes for SHM applications. Thus, this paper proposes a decomposition method for the two-mode Lamb waves based on two rules: the group velocity ratio rule and the mode amplitude ratio rule. The group velocity ratio rule means that the ratio of the group velocities of fundamental symmetric and antisymmetric modes is constant, while the mode amplitude ratio rule means that the magnitude of the fundamental symmetric modes of all measured response signals should be always larger than those of the anti-symmetric mode once the input signal is applied so that the magnitude of fundamental symmetric mode of excited Lamb-wave is larger than that of anti-symmetric mode, and vice versa. The proposed method is verified through the experiments ducted for an aluminum plate specimen.

Damage detection on two-dimensional structure based on active Lamb waves

Peng, Ge,Yuan, Shen Fang,Xu, Xin Techno-Press 2006 Smart Structures and Systems, An International Jou Vol.2 No.2

This paper deals with damage detection using active Lamb waves. The wavelet transform and empirical mode decomposition methods are discussed for measuring the Lamb wave's arrival time of the group velocity. An experimental system to diagnose the damage in the composite plate is developed. A method to optimize this system is also given for practical applications of active Lamb waves, which involve optimal arrangement of the piezoelectric elements to produce single mode Lamb waves. In the paper, the single mode Lamb wave means that there exists no overlapping among different Lamb wave modes and the original Lamb wave signal with the boundary reflection signals. Based on this optimized PZT arrangement method, five damage localizations on different plates are completed and the results using wavelet transform and empirical mode decomposition methods are compared.

Lamb 탄성파를 이용한 평판 결함탐지 : 수치해석 Numerical Analysis

박경조,김정엽 여수대학교 1999 論文集 Vol.14 No.2

The interaction of individual Lamb waves with a variety of defects simulated by notches has been investigated using finite-element analysis. It has been shown that a two-dimensional(2-D) Fourier transform method may be used to qualify Lamb wave interactions with defects. The results have shown that the sensitivity of individual Lamb waves to particular notches is dependent on the frequency-thickness product, the mode type(symmetric or antisymmetric), the mode order, and the geometry of the notch. Also the results have shown that the transmission ratios of Lamb waves across defects are highly frequency dependent, particularly at higher frequency-thickness.

Lamb wave-based damage imaging method for damage detection of rectangular composite plates

Qiao, Pizhong,Fan, Wei Techno-Press 2014 Structural monitoring and maintenance Vol.1 No.4

A relatively low frequency Lamb wave-based damage identification method called damage imaging method for rectangular composite plate is presented. A damage index (DI) is generated from the delay matrix of the Lamb wave response signals, and it is used to indicate the location and approximate area of the damage. The viability of this method is demonstrated by analyzing the numerical and experimental Lamb wave response signals from rectangular composite plates. The technique only requires the response signals from the plate after damage, and it is capable of performing near real time damage identification. This study sheds some light on the application of Lamb wave-based damage detection algorithm for plate-type structures by using the relatively low frequency (e.g., in the neighborhood of 100 kHz, more suitable for the best capability of the existing fiber optic sensor interrogator system with the sampling frequency of 500 kHz) Lamb wave response and a reference-free damage detection technique.

램파 혼합 기법을 이용한 알루미늄 합금의 부식 결함 검출에 대한 실험 연구

최희웅(Heeung Choi),이재선(Jaesun Lee),조윤호(Younho Cho) 대한기계학회 2016 大韓機械學會論文集A Vol.40 No.11

본 연구에서는 비선형 체적파 혼합 기법의 선행연구를 토대로 램파 기법에 적용하여 램파 혼합기법에 대한 연구를 수행하였다. 램파 혼합 기법의 타당성을 증명하기 위해 결함이 없는 시편과 부식에 의해 발생된 표면 결함이 있는 시편에 대해 실험을 진행하였다. 실험 대조군으로는 램파의 지배적인 면내변위와 면외변위를 가지는 모드 및 주파수로 선정하였다. 그 결과 램파 혼합 기법으로도 결함 검출이 가능하였고, 기존의 램파 기법의 경향성과 유사하게 나타났다. 그리고 이론과 동일한 지배적인 변위와 모드가 발생된 것을 확인 할 수 있었다. 그러나 결함 검출 성능은 측정 방법 및 단순 모드 선정에 따라 결정되는 것이 아니라 변위 비율에 따라 결정된다. In this study, the Lamb wave mixing technique, which is basised on advanced research on the nonlinear bulk wave mixing technique, is applied for corrosion detection. To demonstrate the validity of the Lamb wave mixing technique, an experiment was performed with normal and corroded specimens. Comparison group in an experimentation are selected to mode and frequency with dominant in-plane displacement and out-of-plane displacement of Lamb waves. The results showed that the Lamb wave mixing technique can monitor corrosion defects, and it has a trend similar to that of the conventional Lamb wave technique. It was confirmed that the dominant displacement and mode matching the theory were generated. Flaw detectability is determined depending on displacement ratio instead of using the measurement method and mode selection.