An Investiagtion On Sound Absorption Performance Of Perforated Plate And Its Derived Structures

In the process of transformation and upgrading of China’s manufacturing industry,noise control is a common key problem.How to effectively control large sound waves using small-scale materials or structures is one of the most important and fundamental scientific issues in noise control.Porous materials and resonant acoustic structures are two common ways for noise reduction.Porous materials can effectively absorb sound waves when its thickness is a quarter of the wavelength,and a large thickness is required for low frequency sound absorption.Among them,the most famous one is so called microperforated plate(MPP)proposed by Maa.The hole diameter of MPP is less than 1mm,which brings large manufacturing cost,especially for low frequency sound absorption,a large cavity is necessary.In this thesis,based on easily available perforated plate,a resonant acoustic structure consisting of multiple perforated plates arranged in parallel is proposed,which has excellent low-frequency and wide-band sound absorption performance.Furthermore,several derived structures are proposed to extend the sound absorption bandwidth,and the experimental results are in good agreement with theoretical predictions.This work enriches the application of parallel coupling theory and provides new ideas for lowfrequency noise control in a restricted scale.The main research contents and innovations of this paper are as follows:(1)A resonance absorber consisting of multiple perforated plates in parallel(PPAs)is proposed,and the genetic algorithm is used to find structural optimal parameters.The sub-perforated plates with large-aperture and low perforation rate have low acoustic resistance.Through the coupling effect between the perforated plates,PPAs has matchable acoustic resistance and multi-zero acoustic reactance,and achieve multiresonances peaks in a wide frequency range.Compared to a well-known MPP,at low frequencies,when they have similar sound absorption,the thickness of PPAs is about50%-70% of that of MPP.(2)A perforated plate resonance structure with variable cross section(PPSA)is composed of holes with different apertures in the same axis.Compared with single perforated plate,PPSA obtains increased increased sound resistance and mass,and is more suitable for low frequency sound absorption.A parallel variable cross-section perforated plate structure(PPSAs)is formed by inserting a rigid plate into the back cavity.Compared to a single PPSA,PPSAs has an improved absorption bandwidth of 49% due to the introduction of an additional resonance.(3)A combined perforated plate and porous material structure(PPCS)can improve low frequency sound absorption for a porous layer with the same thickness.By filling the cavity behind the perforated plate with a porous material layer,PPCS can obtain a moderately increased acoustic resistance and a slowly varying acoustic reactance close to0 in the low frequencies.The proposed PPCS behaves as a two-resonance absorption and has a similar absorption as a parallel micro-perforated plate at the same scale.PPCS achieves an effective absorption bandwidth of more than two octaves and is a subwavelength absorption structure.(4)PPR-PSAM consists of a parallel perforated plate resonant structure(PPR)and a porous material layer(PSAM).PPR is a parallel absorber with an L-shaped air cavity,providing multi-resonance at low frequencies;PSAM is a tandem structure of "porous material + air",its weak resistance helps to obtain relatively matched acoustic resistance at higher frequencies.Under the combined effect of Helmholtz resonance of perforated plate and the viscous effect of porous layer,PPR-PSAM can achieve five resonance peaks,and its effective absorption bandwidth is about two octaves.(5)A combined perforated plate and shunt loudspeaker structure(SLPP)with the same cavity is proposed.SLPP is characterized by a low perforation rate perforated plate and a shunt loudspeaker sharing the same cavity.Under the action of the perforated plate and the shunt loudspeaker,SLPP can achieve three resonances sound absorption.As a passive structure,SLPP can effectively improve the low frequency sound absorption of perforated plate.