Perfect Absorption in a Disordered Medium with Programmable Meta-Atom Inclusions

Achieving the very special condition of perfect absorption (PA) in a complex scattering enclosure promises to enable a wealth of applications in secure communication, precision sensing, wireless power transfer, analog signal processing, and random lasing. Consequently, a lot of recent research effort is dedicated to proposing wave-front shaping protocols to implement coherent PA in complex scattering environments with tunable localized absorption as well as a tunable excitation frequency. Here, the conceptually different route of solely tweaking the randomness of the complex scattering environment in order to achieve PA is proposed. An experimental proof-of-concept in the microwave domain is provided where the randomness of a 3D chaotic cavity is tuned with programmable meta-atom inclusions. The achievability and extreme sensitivity of the PA condition are systematically investigated. The presented technique can impose a PA condition at over hundred distinct frequencies within a small frequency band, enabling the proposal and experimental demonstration of a concrete practical application: receiver-powered secure wireless communication in a complex scattering enclosure. The presented fundamentally new perspective on PA applies to all types of wave phenomena; the experimental results foreshadow the large potential of this novel tool for minute wave control in sensing, communication, and energy transfer.