Metamaterials have shown great potential for controlling acoustic waves and structural dynamics. Although various types of metamaterials have been developed, simultaneous control of low-frequency sound in air and vibration in solids is less investigated. This paper presents hybrid acousto-elastic metamaterials that enable simultaneous control of low-frequency sound in air and vibration in solids. For the first time, this novel metamaterial adds a compound of membrane and silicone rubber to cladding. The membrane moves the resonance frequency to a low frequency, and the silicone rubber makes the cladding layer rigid enough to support the mass. Bandgap, sound transmission loss (STL), and vibration transmission loss (VTL) were calculated by using the finite element method. Combining modal vibration mode and sound intensity streamline, the mechanisms of vibration isolation and noise reduction were analyzed and then verified through the equivalent mass–spring model. This novel metamaterial combines acoustic metamaterials and mechanical metamaterials to achieve the collaborative control of elastic waves and acoustic waves. At the same time, the peak frequencies of both STL and VTL are lower than those of the traditional metamaterials of the same size, which provides a theoretical basis and method guidance for the next step of collaborative control research of mechanical metamaterials and acoustic metamaterials. It has potential application value in the field of low-frequency vibration and noise control engineering.
Localized resonance phononic crystals (LRPCs) are increasingly attracting scientists’ attention in the field of low-frequency noise reduction because of the excellent subwavelength band gap characteristics in the low-frequency band. However, the LRPCs have always had the disadvantage that the noise reduction band is too narrow. In this paper, in order to solve this problem, LRPCs based on double-layer plates with cavity structures are designed. First, the energy bands of phononic crystals plate with different thicknesses were calculated by the finite element method (FEM). At the same time, the mechanism of band gap generation was analyzed in combination with the modalities. Additionally, the influence of structure on the sound transmission loss (STL) of the phononic crystals plate and the phononic crystals cavity plates were analyzed, which indicates that the phononic crystals cavity plates have notable characteristics and advantages. Moreover, this study reveals a unique ”cavity cave” pattern in the STL diagram for the phononic crystals cavity plates, and it was analyzed. Finally, the influence of structural factors on the band structure and STL of phononic crystals cavity plates are summarized, and the theoretical basis and method guidance for the study of phononic crystals cavity plates are provided. New ideas are also provided for the future design and research of phononic crystals plate along with potential applications in low-frequency noise reduction.
The various types of metamaterials only have a sound transmission loss (STL) peak at the resonant frequency but are still constrained by the law of mass sound insulation at other frequencies. In this paper, a low-frequency and wideband resonant metamaterial plate with a front radial membrane was designed in order to improve the noise reduction band. Bandgap and STL were calculated by using the finite element method. Studies have shown that in the range of 1 Hz–100 Hz for new metamaterials, the frequency band with STL greater than 30 dB accounts for 75%, and the noise reduction starting frequency is 11 Hz. The mechanisms were investigated by a comprehensive analysis of mode shapes and sound intensity streamlines and then verified by the negative effective density and equivalent mass–spring model. The mechanism analysis shows that there is a wide bridge coupling bandgap between the respective bandgaps of the plate and the membrane. This novel metamaterial not only guarantees the low-frequency and wideband acoustic performance but also alleviates the problem of instability of the noise reduction performance of the membrane material after long-term use, providing a potential application in low-frequency and wideband noise control.
This study investigates a dual-cavity resonant composite sound-absorbing structure based on a micro-perforated plate. Using the COMSOL impedance tube model, the effects of various structural parameters on sound absorption and sound insulation performances are analyzed. Results show that the aperture of the micro-perforated plate has the greatest influence on the sound absorption coefficient; the smaller the aperture, the greater is this coefficient. The thickness of the resonance plate has the most significant influence on the sound insulation and resonance frequency; the greater the thickness, the wider the frequency domain in which sound insulation is obtained. In addition, the effect of filling the structural cavity with porous foam ceramics has been studied, and it has been found that the porosity and thickness of the porous material have a significant effect on the sound absorption coefficient and sound insulation, while the pore size exhibits a limited influence.
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