Dr. Lei Wang Profile

Dr. Lei Wang

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Proceedings Article | 19 April 2007 Paper

Lamb wave propagation in composite laminates using a higher-order plate theory

Lei Wang, F. Yuan

Proceedings Volume 6531, 65310I (2007) https://doi.org/10.1117/12.716499

KEYWORDS: Wave plates, Composites, Dispersion, Wave propagation, Phase velocity, Structural health monitoring, Matrices, Nondestructive evaluation, Damage detection, Anisotropy

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A new consistent higher-order plate theory is developed for composites with the aim of accurately and efficiently modeling multiple higher-order Lamb waves over a higher frequency range. The dispersion relations based on this theory that can be analytically determined comprise five symmetric and six anti-symmetric wave modes. Computational procedures for phase and group velocities are discussed. Meanwhile, characteristic wave curves including velocity, slowness, and wave curves are introduced to investigate the dispersive and anisotropic behavior of Lamb wave propagation in composites. From numerical results of Lamb waves in both lamina and symmetric laminate, it shows that the higher-order plate theory not only gives good agreement with three-dimensional (3-D) elasticity theory over a wide high frequency range, but also provides a more robust method than 3-D elasticity theory. This study demonstrates a feasibility of using the proposed theory for realizing near real-time Structural Health Monitoring for composites at a higher frequency range.

Proceedings Article | 10 April 2007 Paper

Energy harvesting by magnetostrictive material (MsM) for powering wireless sensors in SHM

Lei Wang, F G. Yuan

Proceedings Volume 6529, 652941 (2007) https://doi.org/10.1117/12.716506

KEYWORDS: Sensors, Energy harvesting, Sensor networks, Diodes, Magnetism, Magnetostrictive materials, Structural health monitoring, Prototyping, Ferroelectric materials, Electromechanical design

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A new class of vibrational energy harvester based on Magnetostrictive material (MsM) Metglas 2605SC is deigned, developed, and tested in building practical energy harvesting wireless sensor networks. Compared to piezoelectric material, Metglas 2605SC offers advantages including ultra-high energy conversion efficiency, high power density, longer life cycles without depolarization issue, and flexibility to operate in strong ambient vibrations. To enhance the energy conversion efficiency and shrink the size of the harvester, Metglas is annealed in the direction normal to the axial strain direction without the need of electromagnet for applying bias (static) magnetic field. To seamlessly integrate with a newly developed wireless sensor at NC State¹, a prototype design for the MsM harvester is proposed. An analytical model is developed for the harvesting using an equivalent electromechanical circuit. The model resulting in achievable output performances of the harvester powering a resistive load and charging a capacitive energy storage device, respectively, is quantitatively derived. An energy harvesting module, which powers a wireless sensor, stores excess energy in an ultracapacitor is designed on a printed circuit board (PCB) with dimension 25mm x 35mm. The main functionalities of the circuit include a voltage quadrupler, a 3F ultracapacitor, and a smart regulator. The output DC voltage from the PCB can be adjusted within 2.0~5.5V. In experiments, the maximum output power and power density on the resistor can reach 200 &mgr;W and 900 &mgr;W/cm³, respectively. For a working prototype, the average power and power density during charging the ultracapacitor can achieve 576 &mgr;W and 606 &mgr;W/cm³ respectively, which are much higher than those of most piezo-based harvesters.

Proceedings Article | 11 April 2006 Paper

Experimental study of Lamb wave propagation in composite laminates

Lei Wang, F. Yuan

Proceedings Volume 6174, 617442 (2006) https://doi.org/10.1117/12.677936

KEYWORDS: Composites, Wave propagation, Dispersion, Actuators, Sensors, Phase velocity, Wavelet transforms, Structural health monitoring, Wave plates, Ferroelectric materials

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This paper focuses on the existence of higher-order Lamb wave modes that can be observed from piezoelectric sensors by the excitation of ultrasonic frequencies from piezoelectric actuators. Using three-dimensional (3-D) elasticity theory, the exact dispersion relations governed by transcendental equations are numerically solved for an infinite number of possible wave modes. For symmetric laminates, a robust method by imposing boundary conditions on mid-plane and top surface is developed to separate wave modes. Then both phase and group velocity dispersions of Lamb waves in composites are obtained. Meanwhile three characteristic wave curves including velocity, slowness, and wave curves are introduced to analyze the angular dependency of Lamb wave propagation at a given frequency. In the experiments, two surface-mounted piezoelectric actuators are operated corporately to excite either symmetric or anti-symmetric wave modes with narrow banded excitation signals, and a Gabor wavelet transform is used to extract group velocities from arrival times of Lamb wave received by a piezoelectric sensor. In comparison with the results from the theory and experiment, it is confirmed that the higher-order Lamb waves can be excited from piezoelectric actuators and the measured group velocities agree well with those from 3-D elasticity theory.

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