Broadband nonreciprocal linear acoustics through a non-local active metamaterial

Abstract

The ability to create linear systems that manifest broadband nonreciprocal wave propagation would provide for exquisite control over acoustic signals for electronic filtering in communication and noise control. Acoustic nonreciprocity has predominately been achieved by approaches that introduce nonlinear interaction, mean-flow biasing, smart skins, and spatio-temporal parametric modulation into the system. Each approach suffers from at least one of the following drawbacks: the introduction of modulation tones, narrow band filtering, and the interruption of mean flow in fluid acoustics. We now show that an acoustic media that is nonlocal and active provides a new means to break reciprocity in a linear fashion without these deleterious effects. We realize this media using a distributed network of interlaced subwavelength sensor-actuator pairs with unidirectional signal transport. We exploit this new design space to create media with non-even dispersion relations and highly nonreciprocal behavior over a broad range of frequencies. MAIN TEXT

Frozen sound: An ultra-low frequency and ultra-broadband non-reciprocal acoustic absorber

“…Another attractive aspect of the system studied here is its non-reciprocal behavior. Nowadays, systems with non-reciprocity are increasingly explored 57 , 62 , as they offer a new facet for the design of innovative devices 63 – 70 . A weakness of the device considered here is that it is not easy to implement for real-life applications, as it requires imposing a steep temperature gradient along a porous material.…”

Watching Death in the Gerbil Cochlea Using Optical Coherence Tomography

“…Could motion of the OT extracellular fluid space result in a radial RL motion whose phase is important for cochlear amplification? It is generally established that the motion difference between the RL and TM, which causes the OHC stereocilia to deflect, needs to occur with a particular phase relationship to the BM motion so that OHC somatic motility pushes the BM in the direction of BM velocity, such that this motion then opposes viscous losses and results in cochlear amplification (Gummer et al, 1996;Sasmal et al, 2020;Wang et al, 2016). Achieving the correct phase relationship has been attributed to a TM resonance that causes a lag in the radial phase of the TM, starting at about ½-octave below the best frequency (Gummer et al, 1996;Lukashkin et al, 2010;Sasmal and Grosh, 2019).…”