Lien-Wen Chen

Acoustic energy harvesting using resonant cavity of a sonic crystal

This paper presents the development of an acoustic energy harvester using the sonic crystal and the piezoelectric material. A point defect is created by removing a rod from a perfect sonic crystal. The point defect in the sonic crystal acts as a resonant cavity, and the acoustic waves at the resonant frequency of the cavity can be localized in the cavity. The power generation from acoustic energy is based on the effect of the wave localization in the cavity of the sonic crystal and the direct piezoelectric effect of the piezoelectric material.

Vibration damage detection of a Timoshenko beam by spatial wavelet based approach

Abstract This paper presents a technique for structure damage detection based on spatial wavelet analysis. The wavelet transform is used to analyze the mode shape of a Timoshenko beam. First, the mode shapes of the Timoshenko beam containing a transverse crack are obtained. The crack is represented as a rotational spring. Then these spatially distributed signals are analyzed by wavelet transformation. It is observed that distributions of the wavelet coefficients can identify the crack position of Timoshenko beam by showing a peak at the position of the crack. It is also demonstrated that the crack position can be detected by this method even though the crack is very small. Assumed measurement errors are added to the mode shape for evaluating the effect of measurement errors on the capability of detecting crack position. The moving average method is used to process the data with assumed measurement errors. The crack positions can also be identified when there exist assumed measurement errors.

Thermal postbuckling behaviors of laminated composite plates with temperature-dependent properties

Abstract The thermal buckling behavior of composite laminated plates subjected to a uniform temperature field is investigated by the finite element method. Temperature-dependent elastic and thermal properties are considered. The stiffness and geometry matrices are derived based on the principle of minimum potential energy. The assumed displacement state over the middle surface of the plate element is expressed as the product of one-dimensional, first-order Hermitian polynomials. An iterative method is employed to determine the thermal buckling load. It is shown by numerical results that the influence of temperature-dependent mechanical properties on the thermal buckling behavior is significant.

DYNAMIC STABILITY ANALYSIS AND CONTROL OF A COMPOSITE BEAM WITH PIEZOELECTRIC LAYERS

A slender laminated composite beam with piezoelectric layers subjected to axial periodic compressive loads is considered. The dynamic stability behaviors of the laminated composite beam are investigated. The top and bottom piezoelectric layers act as actuators. The beam is restrained at both ends, and the piezoelectric actuators induce in-plane stresses affecting the dynamic behavior of the beam. The stress stiffening effects on the dynamic stability of the beam with piezoelectric layers are examined. While the top piezoelectric layer acts as an actuator, the bottom layer works as a sensor. A simple negative velocity feedback control algorithm that couples the direct and converse piezoelectric effects is employed to actively control the dynamic response of the beam through a closed control loop. The influence of the feedback control gain on the response of the beam is evaluated.

Acoustic energy harvesting by piezoelectric curved beams in the cavity of a sonic crystal

Acoustic energy harvesting by piezoelectric curved beams in the cavity of a sonic crystal is investigated. A resonant cavity of the sonic crystal is used to localize the acoustic wave as the acoustic waves are incident into the sonic crystal at the resonant frequency. The piezoelectric curved beam is placed in the resonant cavity and vibrated by the acoustic wave. The energy harvesting can be achieved as the acoustic waves are incident at the resonant frequency. A model for energy harvesting of the piezoelectric curved beam is also developed to predict the output voltage and power of the energy harvesting. The experimental results are compared with the theoretical.

The tunable acoustic band gaps of two-dimensional phononic crystals with a dielectric elastomer cylindrical actuator

By calculating the transmission coefficients by finite-element software, the study of the tunable acoustic band gap for two-dimensional (2D) phononic crystals composed of a square array of hollow cylinders in an air background is considered. The inclusions are a dielectric elastomer cylindrical actuator, which is made of a hollow cylinder sandwiched between two compliant electrodes. By applying a voltage between the compliant electrodes, the radial strain of the silicone-made actuator is investigated. The acoustic band gaps are changed due to the radial strain of the dielectric elastomer. The frequency range of the dielectric elastomer composite can be extended by increasing the applied voltage. A tunable acoustic band gap of the phononic crystal is realized via the unique character of dielectric elastomer. The calculations also demonstrate that there exists a local stop band within the pass band. With a local stop band gap, 2D phononic crystals may thus serve as an acoustic filter or switch.

Vibration and damping analysis of a three-layered composite annular plate with a viscoelastic mid-layer

The natural frequencies and modal loss factors of the three-layered annular plate with a viscoelastic core layer and two polar orthotropic laminated face layers are considered. The discrete layer annular finite element is employed to derive the equations of motion for the three-layered annular plate. The viscoelastic material in the central layer is assumed to be incompressible, and the extensional and shear moduli are described by the complex quantities. Complex eigenvalued problems are then solved, and the frequencies and modal loss factors of the composite plate are extracted. The results of the symmetric and non-symmetric composite annular plates are both presented. The effects of material properties, radius to thickness ratio, stacking sequences and thickness of face layers, and thickness of the viscoelastic core layer are discussed.

Tunable photonic-crystal waveguide Mach–Zehnder interferometer achieved by nematic liquid-crystal phase modulation

Photonic crystals (PCs) have many potential applications because of their ability to control light-wave propagation and because PC-based waveguides may be integrated into optical interferometers. We propose a novel tunable PC waveguide Mach-Zehnder interferometer based on nematic liquid crystals and investigate its interference properties numerically by using the finite-difference time-domain method. We can change the refractive indices of liquid crystals by rotating the directors of the liquid crystals. Then we can control the phase of light propagation in a PC waveguide Mach-Zehnder interferometer. The interference mechanism is a change in the refractive indices of liquid-crystal waveguides. The novel interferometer can be used either as an optically controlled on-off switch or as an amplitude modulator in optical circuits.

Thermal postbuckling analysis of laminated composite plates by the finite element method

Abstract The thermal postbuckling behavior of composite laminated plates subjected to a nonuniform temperature field is investigated by the finite element method. Based on the principle of minimum potential energy, the nonlinear stiffness matrix and geometry matrix are derived. The assumed displacement state over the middle surface of the plate element is expressed as a product of one-dimensional, first-order Hermitian polynomials. An iterative method is employed to determine the thermal postbuckling load. The results of the computations reveal that the thermal postbuckling behavior of composite laminated plates is influenced by lamination angle, plate aspect ratio, modulus ratio and the number of layers.

Elastic wave band gaps of one-dimensional phononic crystals with functionally graded materials

The propagation of elastic waves in one-dimensional (1D) phononic crystals (PCs) with functionally graded materials (FGMs) is studied using the spectral finite elements and transfer matrix methods. FGMs typically treat the graded interlayer as a system of discrete layers, and the material properties are varied according to a well-known rule, such as the power law. The 1D PCs are composed of both FGMs and isotropic materials, and their band gaps can be changed with different FGM compositions and geometry parameters. By selecting the appropriate parameters, the desired filters can be designed.