Deep neural network based design of sub wavelength acoustic absorbers for low frequency sound absorption

Abstract

Audible sound/noise with frequency less than 500 Hz is considered as the low frequency sound. The absorption of low frequency noise is necessary due to its detrimental (psychological and physiological) effects on human beings. Conventional newlinesound absorbers such as foam, fibre, cloth, etc. need to be bulky for low frequency sound newlineabsorption else these waves, with larger wavelengths, pass through absorbers without newlineany absorption. Hence the challenge is to create such low frequency absorbers with newlineminimum thickness without compromising the absorption bandwidth. Resonant absorbers newlinesuch as Helmholtz resonator (HR) and microperforated panel (MPP) are suitable option for this purpose. Thus, initially, the absorption characteristics of sound absorbers newlineconsisting of microperforated panel and Helmholtz resonator with inserted neck (HRIN) newlineare theoretically and experimentally investigated. The absorption characteristics of series newlineand parallel arrangements of MPP and multiple HRINs are theoretically modelled using newlineelectro-acoustic analogy. Most importantly, it is observed that the parallel arrangement newlineof MPP and multiple HRINs considerably reduced thickness of the absorber. To forecast the optimum geometric parameters of the acoustic absorber, inverse design using deep newlineneural network (IDDN) is proposed. Using this, a quasi-perfect low-frequency acoustic newlineabsorber with minimum thickness and broadband characteristics is deduced. Importantly, newlineit is demonstrated that the proposed absorber, comprising four parallel HRINs and a newlinemicroperforated panel, absorbed more than 90% sound in the frequency band of 347 630 newlineHz. However, there is a requirement to develop absorbers that has applicability in newlinefrequencies much lower than this range without increasing the total thickness of the newlineabsorber. newlineIn this context, a new hybrid acoustic configuration consisting of MPP and Helmholtz newlineresonator with inserted curvy neck (HRICN) is presented. The proposed absorber is a newlineparallel-conjunction of MPP and four HRICNs (MHRICN).