Optimising flat-walled multi-layered anechoic linings using evolutionary algorithms

Previous investigations indicated that a flat-walled, multi-layered anechoic lining system, with an overall thickness slightly less than a quarter of a wavelength, could be used to achieve a required cut-off frequency. However, the work proved to be tedious and time consuming because of the numerous trial-and-error measurements involved. On the other hand, the successful application of a method of calculating the overall acoustic impedance of multi-layered absorbing systems has indicated that the design of multi-layered absorbing systems can be carried out on a desktop computer. In the present work, a MATLAB genetic and evolutionary algorithm toolbox is implemented as the optimiser to aid and speed up the design process. The optimisation results indicate that a three-layered lining system can achieve results comparable with quality wedge-type anechoic linings with overall thickness slightly less than a sixth of a wavelength at the 100 Hz cut-off frequency.