This paper investigates the dynamic and vibration energy harvesting behaviors of defect phononic crystal beams in thermal environments. Variations in the first bandgap and the defect band for flexural waves are discussed with different geometric parameters of the defect cell and structural temperatures by using the supercell technique for infinite defect phononic crystal beams. Transmission characters of defect models with a finite length are studied, considering the influence of thermal loads, and the performance of the defect based energy harvesting is discussed as well. Predicted results indicate that temperature increments reduce the frequency ranges of bandgap and defect band due to the softening effect of thermal load on the phononic crystal beam, and the performance in defect based energy harvesting is obviously depressed with temperature rise. Defect cells with a higher content of the soft component are beneficial for generating defect modes which have relatively stable frequencies in thermal environments. However, higher levels of open-circuit voltage and output power of harvested energy are more likely to be generated with defect cells which have a higher content of the hard component.

Flexural wave manipulation and energy harvesting characteristics of a defect phononic crystal beam with thermal effects

A locally resonant elastic metamaterial based on coupled vibration of internal liquid and coating layer

As an effective means to manipulate elastic wave energy, the defect mode of phononic crystals (PCs) has recently been employed to implement vibration energy harvesting by localizing waves within certain areas at defect frequencies. Prior research has indicated that the thermal environment affects the defect behavior and energy harvesting of single defects. However, the dynamic characteristics of multi-defect phononic crystals have not yet been discussed. This paper presents an investigation of the coupling behavior and energy harvesting of double defects in heated PC beams. The frequencies and mode shapes of defect modes are studied for different defect pairs within the first bandgap. Results indicate that the difference in the single-defect frequency between the two defects plays a dominant role in determining the intensity of the defect interaction which splits the defect modes. Meanwhile, the influence of the energy distribution around the defects on the coupling behavior becomes prominent when the two defects are quite close to each other. These two factors could cause degeneration of the defect modes. As an external factor, thermal load could enhance the defect coupling intensity, and may reactivate the degenerated defect modes. This effect would increase as the initial defect interaction gets stronger. For vibration energy harvesting, temperature rise may lead to a significant reduction in defect-based harvested energy, even though the number of defect-induced resonance peaks could be increased in the thermal environment. The thermosensitivity of harvesting performance varies greatly for different combinations of defects. Thermal effects should be considered in the design of defect-based harvesters.

Defect coupling behavior and flexural wave energy harvesting of phononic crystal beams with double defects in thermal environments

The unique characteristics like periodic and locally resonant behaviors of acoustic metamaterials result in an anomalous response to the wave propagation and exhibit complete elastic wave bandgaps. However, these unusual properties arise from the geometry of the artificially designed metastructure and can be significantly affected under the exposure of the thermal environment. In this paper, we present a thermally tunable two-dimensional acoustic metamaterial with a hexagonal lattice. The numerical results demonstrated that by adjusting the externally applied temperature to the structure and imposing several different load conditions like thermal deformation and thermal stress, a tunable effective mass density of the metamaterial could be obtained. The proposed concept further extends the ongoing research in the field of tunable acoustic metamaterials.

Thermal tuning of negative effective mass density in a two-dimensional acoustic metamaterial with hexagonal lattice

A study on dynamical characteristics of a ternary locally resonant phononic crystal (PC) plate (i.e., hard scatterer with soft coating periodically disperse in stiff host matrix) is carried out in this paper. The effect of thermal deformation on the structure stiffness, which plays an important role in the PC’s dynamical characteristics, is considered. Results show that both the start and the stop frequency of bandgap shift to higher range with the thermal deformation. In particular, the characteristics of band structure change suddenly at critical buckling temperature. The effect of thermal deformation could be utilized for tuning of phononic band structures, which can promote their design and further applications.

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The Lamb wave bandgap variation of a locally resonant phononic crystal subjected to thermal deformation

In this study, the numerical investigation of thermal effect on band gap dynamical characteristic for a two-dimensional binary structure composed of aluminum plate periodically filled with nitrile rubber cylinder is presented. Initially, the band gap of the binary structure variation trend with increasing temperature is studied by taking the softening effect of thermal stress into account. A breakthrough is made which found the band gap being narrower and shifting to lower frequency in thermal environment. The complete band gap which in higher frequency is more sensitive to temperature that it disappears with temperature increasing. Then some new transformed models are created by changing the height of nitrile rubber cylinder from 1mm to 7mm. Simulations show that transformed model can produce a wider band gap (either flexure or complete band gap). A proper forbidden gap of elastic wave can be utilized in thermal environment although both flexure and complete band gaps become narrower with temperature. Be...

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Xian Wang

Papers

The band gap variation of a two dimensional binary locally resonant structure in thermal environment