Automatically Adaptive Ventilated Metamaterial Absorber for Environment with Varying Noises

Abstract

thickness, health and environment issues, fire resistance, moisture resistance, and durability issues. [1][2][3][4] In the past two decades, varieties of artificial structures, collectively called "acoustic metamaterials," have been designed to manipulate sound waves beyond natural limits. [5][6][7][8][9][10][11][12][13] For example, low-frequency (<500 Hz) sound waves have strong penetration ability, long propagation distance, and low attenuation coefficient, hence it is still a great challenge to deal with low-frequency noises. [1,3,4,14] In the last decade, diverse sound-absorbing metamaterials in subwavelength scales have been designed, which generally increase the density of states at targeted low-frequencies in the metamaterials in order to enhance the dissipation of sound energy. [15][16][17][18][19][20][21][22][23][24][25] However, for most acoustic metamaterials, their targeted frequencies and operating functions can hardly be adjusted after being fabricated. It is hence an intrinsic barrier for their applications in scenarios where the frequencies of noise can change over time.To overcome this stringent barrier, tunable acoustic metamaterial absorbers have been proposed and investigated in recent years. [26,27] Some tunable mechanisms, mainly employing the mechanical deformations, piezoelectric, and/or magnetic effects, have been presented. [28][29][30][31][32][33] However, they generally require rigid backings to impede sound transmissions, which forbid the transmission of fluids, such as air and water. The absorption of a ventilated acoustic metamaterial composed of subwavelength scatters is usually much smaller compared with its reflection. It is a challenge to break the limit and finally achieve a tunable absorber with simultaneously good absorption and ventilation at low frequencies. [33] Besides, their intricate mechanical, electronic, and magnetic structures are inconvenient and may be unstable for daily applications. [34,35] Moreover, previously designed adjustable metamaterial absorbers could not automatically perceive incident sound to realize intelligent adjustment and absorption. [21,[36][37][38][39][40][41][42][43] A simpler, more adjustable, and more automatic scheme is eagerly needed.Here, we demonstrate an automatically adaptive ventilated metamaterial absorber (AAVMA) for low-frequency sound that can achieve high-efficiency (>90%) absorption for onesided incidence with frequency varying in the working range. The ventilated absorber can automatically monitor the environmental noise and intelligently adjust the sound absorption An automatically adaptive metamaterial sound absorber is designed, which can absorb tunable low-frequency (<500 Hz) sounds under ventilated conditions by designing a feedback circuit to actively detect the noise signals and adjust the sliders on the reconfigurable absorbers. The automatically adaptive ventilated absorber provides an intelligent route to adapt for different low frequencies, through adjusting the sound absorption units directly in accordance with the...

Development of Adjustable Parallel Helmholtz Acoustic Metamaterial for Broad Low-Frequency Sound Absorption Band

“…The sound absorption effect of APH-AM was realized by the resonance effect of the resonators with the same parameters and the coupling effect among the resonators with the different parameters [ 45 , 46 , 47 , 48 ], which could be judged from the distribution of acoustic pressure at the resonance frequencies obtained in acoustic finite element simulation models for the two APH-AM samples with normal incidence, as shown in the Figure 12 . The whole 3D structural model, the whole gridded model and the gridded model of APH-AM were shown in the Figure 12 a–c respectively, which were constructed similarly with the finite element simulation model for the double resonators in the Figure 2 .…”

Subwavelength Broadband Perfect Absorption for Unidimensional Open‐Duct Problems

“…In the unidimensional (1D) reflection problem (either with a rigid boundary [36][37][38] or a soft boundary [39] ), perfect absorption can be realized at a given frequency by using a single resonator. In the opposite, the maximum absorption coefficient that can be achieved with either a single monopolar or a dipolar type resonator is α max = 1/2 in the 1D transmission problem [25,[40][41][42] ; to yield perfect absorption, at least two coupled resonators are necessary, because both types of resonances at the same frequency are required to suppress the reflection and the transmission simultaneously. [40,43] Note that, by using two resonators of the same type, the distance between them in the wave direction should be properly chosen to produce the other type of resonance.…”