Perfect sound absorption of Helmholtz resonators with embedded channels in petal shape

Abstract

The acoustic metamaterial in the form of a petal-shaped channel embedded Helmholtz resonator (P-CEHR) is proposed for perfect sound absorption. According to theoretical predictions, numerical simulations, and experiments, the P-CEHR achieves perfect low-frequency (e.g., 200 Hz) sound absorption across a deep subwavelength thickness (e.g., 1/34 of the corresponding acoustic wavelength). Compared with the circular-shaped channel embedded Helmholtz resonator, the sound absorption peak and bandwidth of P-CEHR are significantly improved (e.g., increased by 20.9% and 60.0%, respectively) under fixed overall dimensions. Physically, the introduction of the petal shape changes the fluid dynamic characteristics of the channel, resulting in the periodic distribution of particle velocity along the circumferential direction and the expansion of the area of the viscous boundary layer. By adjusting the morphology of the embedded channel, the tortuosity ratio and the relative static flow resistance of the channel can be regulated appropriately, so that the resonator can meet the acoustic impedance matching condition and achieve excellent sound absorption performance. This work provides a method for improving the performance of acoustic absorption metamaterials with built-in air channels and has guiding significance for the control of low-frequency noise.

Sustainable Perforated Acoustic Wooden Panels Designed Using Third-Degree-of-Freedom Bezier Curves with Broadband Sound Absorption Coefficients

“…The typical formula for acoustic surface impedance calculation is (1) [ 4 ]: where z n −1 is the surface impedance of the previous layer (typically porous, calculated in an example from the methods described in [ 4 ]), is the angular frequency, and r m is the flow resistivity in the holes (2): where is the air density (typically 1.21 kg/m 3 ), is the perforation rate, is the kinematic viscosity (typically 1.84 × 10 −5 ), a is the radius of the holes, and t is the base plate depth. Finally, the equation for m —the mass of the air inside the holes—is written as follows (3): where is the aperture correction dependent on the final hole shape [ 23 , 24 , 25 ]. These equations can be used for the regular type of perforation on plain plates, while they are impossible to use for 3D perforated panels with irregular shapes.…”

Low-frequency sound-absorbing metamaterial based on a series-parallel arrangement structure

“…3,4 Researchers have recently proposed metamaterial structures with low-frequency acoustic insulation properties. [5][6][7][8] In 2000, Liu first proposed the concept of acoustic metamaterials and designed an acoustic metamaterial with a negative energy density to achieve low-frequency sound insulation. 9 In 2006, Feng et al proposed a one-dimensional Helmholtz resonance cavity acoustic metamaterial with a negative equivalent elastic modulus when the acoustic wave frequency was close to the resonant frequency of the structure, thus achieving structural sound absorption.…”

Study on the acoustic performance of bending metasurface with ultra-thin broadband quasi-perfect sound absorption

“…Therefore, the emergence of acoustic metamaterials with small size control large wavelengths brings new directions for low frequency broadband noise control [7][8][9][10]. In 2000, Liu [11] first proposed local resonant acoustic metamaterials and then a large number of acoustic metamaterials with negative mass density, negative bulk modulus and dual negative characteristics have studied [12][13][14][15]. These acoustic metamaterial have a subwavelength characteristic in thickness, which can achieve perfect sound absorption at low frequencies.…”