A robust actively-tunable perfect sound absorber

Abstract

Perfect sound absorption (PSA), producing an absorption coefficient of 1, can be achieved based upon the coherent interaction of acoustic waves, while it can merely be achieved within a narrow frequency-band due to critical impedance matching conditions. Here, we theoretically and experimentally study self-modulation and active-tunability in PSA created on account of a membrane-covered cavity. It is observed that due to the nonlinearity of the membrane, the frequency of PSA increases with the intensities of input acoustic waves, exhibiting a self-modulation property. Furthermore, we design an apparatus to control the elasticity of the membrane via four electromagnets, and thus, the PSA frequency can be freely and effectively adjusted by changing the direct-current driving voltage of the electromagnets. Despite the critical impedance matching conditions, the absorption coefficient achieved in our system holds at 1 when the PSA frequency is freely changed, which exhibits strong robustness in active-tunability.

A low-frequency multiple-band sound insulator without blocking ventilation along a pipe

“…Additionally, attaching an extra mass on a membrane changed the resonance frequencies and vibration modes, which enhanced the sound attenuation [14][15][16][17] . Thus, membrane-type and plate-type structures were used to block sound in open space 14,16 and in pipes [18][19][20][21][22][23][24] , and they exhibited potentials of application in HVAC (Heating, Ventilating and Air Conditioning) systems.…”

“…Additionally, attaching an extra mass on a membrane changed the resonance frequencies and vibration modes, which enhanced the sound attenuation [14][15][16][17] . Thus, membrane-type and plate-type structures were used to block sound in open space 14,16 and in pipes [18][19][20][21][22][23][24] , and they exhibited potentials of application in HVAC (Heating, Ventilating and Air Conditioning) systems.Although large sound attenuation was achieved, sound insulators with sealed structures were unavailable in a practical HVAC system because they completely block the air flow along the pipe. Thus, insulators with open structures were studied, which obstructed acoustic waves and did not block ventilation.…”

Controlling the Spatiotemporal Response of Transient Reverberating Sound

“…The hardware ingredient of a programmable acoustic room is the programmable acoustic metasurface. A way to implement the latter is via acoustic meta-atoms with tunable scattering properties, such as magnetic-fieldcontrolled elastomers [30], tunable membranes [31][32][33], geometrically tunable resonators [34][35][36][37][38], or electrolysiscontrolled microbubble arrays for ultrasound [39]. The interested reader is referred to Refs.…”

Bistable sound insulator with an abrupt stiffness shift using magnetic-coupled dielectric elastomer actuator

“…Meanwhile, compared with other membrane sound insulators controlled by magnets which mainly use conventional silicone rubber [28][29][30], the sound insulator proposed above has the advantage of voltage-regulation. And it also has a more flexible tunability of acoustic performance than a sound insulator based on piezoactuator (PZT) which has a relatively small deformation [31,32].…”