Introduction

A step change in our noise mitigation strategies is required in order to meet the environmental targets or regulations defined for a number of sectors of activity affecting people through noise exposure, such as air / ground transportation, building ventilation systems and wind energy production. Besides being a hindrance to our daily life, noise emission is also a competitive issue, i.e. for better passenger comfort in air / ground transportation, and for quieter domestic appliances and systems in our homes and working places. While much progress has been accomplished in the past decades in this respect, the constant growth in air and ground traffic, the desired increase of the share of wind energy production, etc., require very substantial reductions that cannot be achieved with current solutions.

Hence, new technologies have been emerging, based on radically new concepts for flow and acoustic control, such as micro-electro-mechanical devices (MEMs), meta-materials, porous treatment of airframe surfaces, airfoil leading-edge or trailing-edge serrations, micro-jets, plasma actuation, … Today the convergence of the technological progress in the domains of 3D printing process and functional materials leads to imminent technological breakthrough which will impact profoundly on the development of tomorrow’s structures, including mechanical systems and acoustic treatments. Some of these new ideas appear nowadays promising, however still largely as the result of extensive trial-and-error tests.