| Vibration and noise control of building and engineering structures is a hot topic of concerning civil engineering,especially for low-frequency,broadband and high-efficiency vibration and noise control of planar and miniaturized engineering structures.Acoustic metasurfaces achieve the purpose of "efficient control of large wavelength elastic waves in small size structures" and have important applications in low frequency vibration damping and vibration isolation,focusing imaging and energy capture.In order to realize the non-contact active control of acoustic metasurfaces,this paper introduces magnetorheological elastomer into the acoustic metasurface,and investigates the flexural wave transmission characteristics and the magnetic control characteristics of vibration energy harvesting in the magnetorheological elastomer metasurfaces.The main research contents are as follows:(1)The magneto-controlled properties of anomalous transmission of flexural wave in a magnetorheological elastomeric metasurface are investigated.The acoustic metasurface with magnetorheological elastomer material as the mass unit is proposed using the generalized Snell’s law.First,a finite element model of flexural wave transmission in the unit of magnetorheological elastomer metasurfaces is established based on the flexural wave propagation theory in acoustic metasurface and the constitutive relation of magnetorheological elastomer,and the relationship between the applied magnetic field strength and the flexural wave transmittance and phase in the metasurfaces is obtained,which provides a basis for the study of flexural wave tunable transmission characteristics.Subsequently,a magnetorheological elastomer metasurface structure constructed by multiple metasurfaces units is established,and the magneto-controlled characteristics of anomalous refraction,focusing and selfflexural wave beams are realized by modulating the external magnetic field,respectively.The results show that when the magnetic field applied to the metasurface units is of a predetermined strength value,the metasurface can achieve anomalous refraction of flexural wave in the frequency range of 5200-6600 Hz,the tunable focal point and self-flexural beam phenomena at different frequencies.(2)A double-layer magnetorheological elastomer metasurface is designed to reveal the magnetic control relationship of asymmetric transmission of flexural wave.A double-layer magnetorheological elastomer metasurface is constructed with magnetorheological elastomer cells,the asymmetric refraction and asymmetric focusing of flexural wave can be achieved in the metasurface structure by varying the magnetic field strength:i.e.,the incident flexural wave is allowed to be transmitted from the positive direction,while the transmission is prohibited in the negative direction.The results show that asymmetric refraction of flexural wave can be achieved in the frequency range of 5400-6200 Hz when the magnetic field of the unit is chosen as the selected value.Meanwhile,the magnetic field distribution of the metasurface can be adjusted to produce asymmetric focusing of the incident flexural wave at 6000 Hz and the maximum intensity of the focusing point is given.(3)The magneto-controlled characteristics of flexural wave transmission and energy harvesting of T-type magnetorheological elastomer metasurfaces are revealed,and the wide-band design of output voltage and power under different magnetic fields is realized.Based on the unit model of T-type magnetorheological elastomer metasurface,the magnetic field strength and geometric parameters required to realize flexural wave transmission and energy harvesting are obtained.Combined with the piezoelectric effect,the flexural wave energy harvesting characteristics of the T-type magneto-rheological elastomer metasurfaces are analyzed to obtain the output voltage,output power and load resistance under different magnetic fields.The results show that when a specific magnetic field is applied,the flexural wave at 6000 Hz can produce anomalous refraction and beam focusing phenomenon;by collecting the vibration energy at the focal point,the efficient energy conversion in a certain bandwidth frequency can be achieved.In this paper,three magnetorheological elastomeric metasurfaces are proposed,and the elastic wave propagation and modulation methods in magnetorheological elastomeric metasurfaces are investigated.This paper analyzes the modulation of elastic waves in magnetorheological metasurfaces and realizes the anomalous transmission,asymmetric transmission and vibration energy harvesting in magnetorheological elastomer metasurfaces.The research results provide new ideas for the active control of elastic waves in intelligent acoustic metasurfaces under magnetic field environments and new technical solutions for vibration and noise reduction of structures. |
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