Frequency Domain Optimization of Homogeneous Anechoic Multi-Layers ‎Using ‎Genetic Programming‎

Sound-absorbing coatings are of great importance in noise control, thus to make them technically and economically effective, their design optimization is a necessity. Multi-layered homogeneous linings, intended to provide a certain level of absorption, have recently been of much interest among the anechoic coatings. In the present work, first, a mathematical model, called Transfer Matrix Method (TMM) is introduced and validated to properly predict the acoustic response of cavity-less multi-layers. Next, a two-loop optimization technique aimed at maximizing the mean value of echo reduction and minimizing the layers’ total thickness is developed. The outer loop (GP) focuses on the number and order of the layers, while the inner (ICA) is dedicated to the thickness modification of each layer. Finally, results are demonstrated for some specific cases, where promising solutions are found for different constraints and conditions. As an example, comparing a homogeneous coating invented by the GP-ICA (#Generation 50 of Section 5.3) with a typical cavity-included coating used for sound absorption shows that the thickness of this new coating is reduced by nearly two-thirds (from 50 mm to 18 mm), while the first hit of the 20 dB band of Echo Reduction (ER) has reduced by 65 % (from 20 kHz to 7 kHz), and almost did not fall from this level until the end of the frequency domain of interest (40 kHz). That’s while the conventional coating frequency response dropped soon after hitting the 20 dB threshold.