In this work, an electromechanical metasurface is designed for wave controlling of multi-mode guided waves in plate, including shear horizontal wave, symmetrical mode and anti-symmetrical mode of Lamb waves. The metasurface is constructed by staggered arrangement of in-plane polarized and out-of-plane polarized piezoelectric patches, which are connected with shunting circuits. The transmitted phase of different guided wave modes can be changed individually in 0~2π range by adjusting the negative capacitances of the shunting circuits without changing the structure geometry. By coding transmitted phase along the metasurface, multi-function including tunable focusing and tunable anomalous refraction of guided waves can be achieved by wave front control. Furthermore, by modulating each mode wave simultaneously, the incident mixed guided wave can be separated after transmitting through the metasurface and specific wave mode can be further extracted.
The effective damage detection does not only require the location of damage but also the size. When a point or circular damage expands in size under stress state, it becomes thin and elongated to transform into a thin rectangular or elliptical slot. The methods introduced in this research use piezoelectric transducers (led zirconate titanate, PZT) to excite and sense the Lamb waves in composite laminate, which are highly sensitive to transverse cracks. The PZT transducers are arranged as a network of cells, and damage is estimated inside each cell separately. The Gabor wavelet-based continuous wavelet transformation (CWT) is used to process the complicated damage-scattered signals. The concept of centroid is used to locate the damage in two stages: the first stage locates the damaged subcell, and then the damage is accurately located in two-stage detection inside the damaged subcell. Based on accurately estimated location, the damage size is calculated using cubic spline curve (CSC) and elliptical parametric (EP) methods. These methods utilize the same arrangement of transducers, and the same data processing technique at all detection stages. The results indicate that EP method could quantify the damage size with more accuracy than the CSC method..
Piezoelectric materials provide a flexible way to control effective material properties in both space and time domain. In this work, the band structures of guided waves in a periodically piezoelectric composite plate with a mirror plane in thickness direction are studied by using the supercell plane wave expansion method. The symmetric and anti-symmetric Lamb modes are uncoupled and can be separated because of the symmetry of geometry and material properties. The guided waves including symmetric Lamb modes, anti-symmetric Lamb modes and shear horizontal modes are calculated, respectively. Results show that the band structure for each mode can be changed drastically by the position and material properties of the scatterers. Moreover, the material properties modulated by periodical piecewise structure in both space and time domain are discussed to investigate one-way wave propagation in such spatiotemporal phononic crystal waveguides theoretically. After the calculation by using finite element method, the displacement fields are conducted by two-dimensional Fourier transform to obtain numerical dispersion curves, which shows excellent agreement with theoretical results. This work provides a powerful tool to analyze the guided waves with complex modes in piezoelectric phononic crystal plate, and it has extensive potential applications in engineering structure design for modulating wave propagation.
In recent years, Non-Hermitian physics has drawn considerable attention. Bender and Boettcher suggested that the parity(P) and time(T) symmetries can be responsible for purely real spectra of non-Hermitian operators[1]. Then, it was further developed and extended to optics and acoustics[2, 3]. The PT symmetric system experience PT phase transition at critical point. This kind of PT symmetric system can be used to design single mode lasers, coherent perfect absorb, isolators and invisible sensor. However, it is difficult to apply the PT symmetric system in elastic waves because of its multi-modes and the balance of the loss and gain. In addition, the gain materials are hard to be found in nature. In this work, we first use the mass-spring model to exhibit the PT symmetric system’s characteristics. Then we expand PT symmetric system to continuous model, and analyze a PT symmetric beam structure. We use piezoelectric patches based on active shunted circuit to control the critical point of PT symmetric beam successfully. Results show that this work is useful and has potential to be developed as non-disturbance sensors for nondestructive examination method based on guided waves.
In this paper, the wavelet transform is applied to the time- frequency analysis of the flexural waves in beams for crack detection. Here, a cantilever beam with edge cracks is used for a model to analyze the wave information after it is loaded an impact hammer on its free end. The flexural waves propagating in beams are dispersive and can be measured directly by using electrical-resistance strain gauges during the dynamic process. According to the data about one-crack and two-crack beams, we utilize the Morlet wavelet transform to decompose the flexural waves into each frequency component in time domain. The experimental results illustrate that the crack position can be detected exactly by means of the signal of mid-frequency flexural wave extracted by wavelet transform. The method is also suitable for determining the existence and location of multi-crack in a beam.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.