Active acoustic resonators with reconfigurable resonance frequency, absorption, and bandwidth

Acoustic resonators play a key role in the development of subwavelength-sized technologies capable of interacting with airborne audible sound, from its emission and absorption to its manipulation and processing. Specifically, artificial acoustic media made from an ensemble of subwavelength resonators, namely, acoustic metamaterials and metasurfaces, have enabled sound manipulation possibilities well beyond what is typically achievable using natural materials. Yet, the transition of such concepts from physics-driven explorations to practical applications has been drastically hindered by the major difficulty in controlling the resonance frequency, absorption level, and bandwidth of these resonators, making acoustic metamaterials often too narrowband, or sensitive to disorder and absorption losses. Here, we demonstrate the relevance of active electroacoustic resonators to address such limitations. We propose a feedback control scheme for loudspeakers (used as acoustic scatterers), which involves passband current control based on real-time sensing and processing of the pressure signal by field-programmable gate-array technologies. We demonstrate externally reconfigurable subwavelength acoustic resonators with independently tunable levels of absorption (including near-zero and near-one), bandwidth, and resonance frequency. We believe that this work demonstrates a viable route to overcome the current limitations of metamaterials and enable their practical applications.