A Point-Focus PVDF Transducer for Lamb Wave Measurements

2002 ◽  
Vol 18 (1) ◽  
pp. 29-33
Author(s):  
Yung-Chun Lee ◽  
Yi Fan Tein ◽  
Yu Yi Chao
Keyword(s):  
Lamb Wave ◽  
Acoustic Waves ◽  
Lamb Waves ◽  
Experimental Testing ◽  
Spherical Shape ◽  
Wave Dispersion ◽  
Dispersion Curves ◽  
Pvdf Film ◽  
Wave Measurements ◽  
Metal Plates

ABSTRACTThis paper reports the development of a point-focused PVDF transducer with a large aperture surface and its application on measuring Lamb wave dispersion curves. The point-focused transducer is constructed by forcing a piezoelectric PVDF film into a concave spherical shape. The acoustic waves radiated from the PVDF film are then focused into a point without using any acoustic lens. Similar to its line-focused counterpart, the point-focused transducer is capable of measuring dispersion curves of lamb waves provided its aperture angle is large enough. To verify this, experimental testing is carried out on several thin metal plates and good measurement results are observed. Future improvements and applications on the transducer will be addressed.

Structural Health Monitoring of Plate Structures Using Lamb Wave Methods

2011 ◽  
Vol 368-373 ◽  
pp. 2417-2420
Author(s):  
Nai Zhi Zhao ◽  
Chang Tie Huang ◽  
Xin Chen
Keyword(s):  
Lamb Wave ◽  
Lamb Waves ◽  
Experimental Testing ◽  
Excitation Frequency ◽  
Diagnostic Technique ◽  
Frequency Dispersion ◽  
Dispersion Curves ◽  
Test Configuration ◽  
Wave Measurements ◽  
Test Variability

In this paper，waveform is used to excite Lamb waves in the test plates during experimental testing. The optimal excitation frequency will depend on the test configuration. In order to select an excitation frequency, dispersion curves are first created to show what frequency range is best suited for Lamb wave excitation. According to dispersion curves were created for the aluminum test plates and it was concluded that a frequency below 1 MHz will be used in order to only excite the fundamental and modes. Experiments are performed on the aluminum test plates described. Experimental testing is first performed on undamaged plates in order to determine the path-to-path and test-to-test variability in Lamb wave measurements in the absence of damage. The admittance data is analyzed in order to determine if any of the PZT transducers need to be replaced because of poor bonding or mechanical failure. The sensor diagnostic technique is applied to each plate and used to ensure proper consistency between PZT transducers

scholarly journals Fully Noncontact Wave Propagation Imaging in an Immersed Metallic Plate with a Crack

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Jung-Ryul Lee ◽  
Jae-Kyeong Jang ◽  
Cheol-Won Kong
Keyword(s):  
Wave Propagation ◽  
Lamb Wave ◽  
Continuous Wave ◽  
Imaging System ◽  
Lamb Waves ◽  
Laser Doppler Vibrometer ◽  
Wave Dispersion ◽  
Wave Mode ◽  
Dispersion Curves ◽  
Guided Wave

This study presents a noncontact sensing technique with ultrasonic wave propagation imaging algorithm, for damage visualization of liquid-immersed structures. An aluminum plate specimen (400 mm × 400 mm × 3 mm) with a 12 mm slit was immersed in water and in glycerin. A 532 nm Q-switched continuous wave laser is used at an energy level of 1.2 mJ to scan an area of 100 mm × 100 mm. A laser Doppler vibrometer is used as a noncontact ultrasonic sensor, which measures guided wave displacement at a fixed point. The tests are performed with two different cases of specimen: without water and filled with water and with glycerin. Lamb wave dispersion curves for the respective cases are calculated, to investigate the velocity-frequency relationship of each wave mode. Experimental propagation velocities of Lamb waves for different cases are compared with the theoretical dispersion curves. This study shows that the dispersion and attenuation of the Lamb wave is affected by the surrounding liquid, and the comparative experimental results are presented to verify it. In addition, it is demonstrated that the developed fully noncontact ultrasonic propagation imaging system is capable of damage sizing in submerged structures.

Determination of Vibration Source Locations in Laminated Composite Plates Using Lamb Wave Analysis

2010 ◽  
Vol 123-125 ◽  
pp. 899-902
Author(s):  
Chao Du ◽  
Qing Qing Ni ◽  
Toshiaki Natsuki
Keyword(s):  
Lamb Wave ◽  
Guided Waves ◽  
Lamb Waves ◽  
Laminated Composite ◽  
Composite Plates ◽  
Wave Dispersion ◽  
Laminated Plates ◽  
Vibration Source ◽  
Arrival Times ◽  
Wave Velocities

Signals propagate on plate-like structures as ultrasonic guided waves, and analysis of Lamb waves has been widely used for on-line monitoring. In this study, the wave velocities of symmetric and anti-symmetric modes in various directions of propagation were investigated. Since the wave velocities of these two modes are different, it is possible to compute the difference in their arrival times when these waves propagated the distance from the vibration source to sensor. This paper presents an evaluation formulation of wave velocity and describes a generalized algorithm for locating a vibration source on a thin, laminated plate. With the different velocities of two modes based on Lamb wave dispersion, the method uses two sensors to locate the source on a semi-infinite interval of a plate. The experimental procedure supporting this method employs pencil lead breaks to simulate vibration sources on quasi-isotropic and unidirectional laminated plates. The transient signals generated in this way are transformed using a wavelet transform. The vibration source locations are then detected by utilizing the distinct wave velocities and arrival times of the symmetric and anti-symmetric wave modes. The method is an effective technique for identifying impact locations on plate-like structures.

scholarly journals Calculation of Wave Dispersion Curves in Multilayered Composite-Metal Plates

2014 ◽  
Vol 2014 ◽  
pp. 1-6 ◽  
Author(s):  
Ameneh Maghsoodi ◽  
Abdolreza Ohadi ◽  
Mojtaba Sadighi
Keyword(s):  
Transfer Matrix ◽  
Equations Of Motion ◽  
Wave Dispersion ◽  
Dispersion Curves ◽  
Metal Plate ◽  
Material Symmetry ◽  
Major Purpose ◽  
Characteristic Equations ◽  
Multilayered Composite ◽  
Metal Plates

The major purpose of this paper is the development of wave dispersion curves calculation in multilayered composite-metal plates. At first, equations of motion and characteristic equations for the free waves on a single-layered orthotropic plate are presented. Since direction of wave propagation in composite materials is effective on equations of motion and dispersion curves, two different cases are considered: propagation of wave along an axis of material symmetry and along off-axes of material symmetry. Then, presented equations are extended for a multilayered orthotropic composite-metal plate using the transfer matrix method in which a global transfer matrix may be extracted which relates stresses and displacements on the top layer to those on the bottom one. By satisfying appropriate boundary conditions on the outer boundaries, wave characteristic equations and then dispersion curves are obtained. Moreover, presented equations may be applied to other materials such as monoclinic, transversely isotropic, cubic, and isotropic materials. To verify the solution procedure, a number of numerical illustrations for a single-layered orthotropic and double-layered orthotropic-metal are presented.

Laser Induced Lamb Wave Generation for Structural Health Monitoring of Carbon Fiber Reinforced Polymers

2015 ◽  
Author(s):  
Ron Sebastian ◽  
Benjamin Kelkel ◽  
Martin Gurka ◽  
Tobias Traub ◽  
Johannes L’huillier
Keyword(s):  
Carbon Fiber ◽  
Health Monitoring ◽  
Lamb Wave ◽  
Acoustic Waves ◽  
Lamb Waves ◽  
Piezoelectric Transducers ◽  
Signal Generation ◽  
Fiber Reinforced Polymers ◽  
Carbon Fiber Reinforced Polymers ◽  
Reinforced Polymers

In this paper we present an innovative concept for the excitation of guided acoustic waves (lamb waves) in carbon fiber reinforced polymers (CFRP). The idea is to add this external signal generation to a passive structural health monitoring system (SHM), using the now active system for nondestructive testing (NDT). The whole system consists of piezoelectric sensors, embedded in the polymer matrix of the monitored component, the external laser in combination with a scanning device for spatial resolved generation of acoustic waves and a signal processing unit for data analysis. Using laser excitation for lamb wave generation helps to overcome several dis-advantages compared to the use of piezoelectric transducers only: The flexibility in repositioning of the excitation area allows for easy compensation of the strong signal attenuation of CFRP with a minimum number of piezoelectric transducers. The variation of laser wavelength in the range of 1024 to 3500 nm in combination with variation in intensity allows for a selective coupling of the acoustic waves either into the matrix or in the C fibers. Using piezoelectric transducers for detection only, omits the need for a large number of high-voltage amplifiers for signal generation. In this contribution we present first results of a systematic investigation of the effective generation of lamb waves in CFRP. In addition to the variation of the wavelength of the laser, the intensity was varied too. A potentially damaging influence of the laser radiation on the CFRP material was investigated.

Dispersion in Nonlinear Plates: Amplitude Dependent Lamb Waves

2016 ◽  
Author(s):  
Pawel Packo ◽  
Michael J. Leamy
Keyword(s):  
Lamb Wave ◽  
Lamb Waves ◽  
Wave Dispersion ◽  
Inner Product ◽  
Solvability Conditions ◽  
Higher Harmonic Generation ◽  
Wave Technique ◽  
Lamb Wave Propagation ◽  
Higher Order Dispersion ◽  
Adjoint Solutions

This paper presents results from a perturbation-based analysis approach, and accompanying numerical validation, for calculating amplitude-dependent Lamb wave dispersion in nonlinear plates. Nonlinearities considered include those arising from geometric and material nonlinearities. Using a Lindstedt-Poincaré perturbation analysis, nonlinear dispersion relationships are presented in closed form using the partial wave technique. Solvability conditions, based on an operator formalism accompanied by inner product projections against adjoint solutions, yield higher-order dispersion approximations capturing amplitude-dependent Lamb wave propagation. Numerical simulations using a cellular automata approach verify the predicted dispersion shifts for an example nonlinear plate. The analysis and identification of amplitude-dependent, nonlinear Lamb wave dispersion complements recent research focusing on higher harmonic generation and internally resonant waves, which require precise frequency-wavenumber matching, including at large amplitudes.

Lamb Wave-Based Damage Location Detection Method of Composite Plate

2011 ◽  
Vol 301-303 ◽  
pp. 1260-1266
Author(s):  
Li Shao Zhang ◽  
Huan Guo Chen ◽  
Jian Min Li ◽  
Li Tian
Keyword(s):  
Group Velocity ◽  
Lamb Wave ◽  
Composite Laminates ◽  
Composite Plate ◽  
Velocity Dispersion ◽  
Lamb Waves ◽  
Group Velocity Dispersion ◽  
Dispersion Curves ◽  
Damage Location ◽  
The Difference

To understand more about Lamb waves on composite laminates damage detection features, the Lamb wave group velocity dispersion curves are calculated and plotted by using dichotomy method in MATLAB. The signal parameters are chosen according to Group velocity dispersion curves. The dynamic response signals of the composite plate are obtained by finite element method. Damage location is calculated by the actual group velocity of Lamb wave and time of flight of the difference signal before and after damage.

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