Active Acoustic Resonators with Reconfigurable Resonance Frequency, Absorption, and Bandwidth

Abstract

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.

A brief review of metamaterials for opening low-frequency band gaps

“…With the increase in the pressure, the structural stiffness of the gasbags augments accordingly. Due to the dependence of the center frequency on the structure stiffness of the resonator, the center frequency of the band gap can be tuned easily by varying the pressure [95] . Furthermore, the stiffness can also be tuned by changing the temperature for the resonator made of the shape memory alloy, as shown in Fig.…”

Ultrabroadband sound control with deep-subwavelength plasmacoustic metalayers

“…This vexing bottleneck may be avoided by breaking passivity and using active control schemes 12 . Applied to subwavelength acoustic resonators, active approaches have led to solutions with increased reconfigurability and bandwidth 13 – 17 . Unfortunately, such advances have remained relatively limited by inherent energy and stability constraints related to the inertia of the transducers used to implement them.…”

Broadband Nonreciprocal Acoustic Scattering Using a Loudspeaker with Asymmetric Feedback

“…Active control/tuning of acoustic transducers or acoustic media is another possible way to achieve nonreciprocal propagation [7,[15][16][17][18][19][20]. In particular, the idea of using systems made with moving coil loudspeakers controlled by an active feedback or by an electric shunt [21] has already been used for the design of acoustic metamaterials such as PT-symmetric systems [22], reconfigurable acoustic resonators [23], or systems achieving perfect transmission through disorder [24].…”