Metamaterials and artificial materials with effective properties that may be controlled to a large degree have been at the basis of exciting schemes for wave manipulation and are particularly well suited to hide an object from electromagnetic waves. To realize practical invisibility cloaks, transformation electromagnetics (TE) methods and scattering cancellation techniques are currently the most popular approaches. Simplified versions of these proposals have been implemented and examined in recent years.
Sensing an incoming signal is typically associated with absorbing a portion of its energy, inherently perturbing the measurement and creating reflections and shadows. Here, in contrast, Prof. Andrea Alù and students Romain Fleury and Dimitrios Sounas demonstrate a non-invasive, shadow-free, invisible sensor for airborne sound waves at audible frequencies, which fully absorbs the impinging signal, without at the same time perturbing its own measurement or creating a shadow.