Abstract
With the advance of the research on acoustic metamaterials, the limits of passive metamaterials have been observed, which prompts the studies concerning actively tunable metamaterials with adjustable characteristic frequency bands. In this work, we present a tunable acoustic metamaterial with double-negativity composed of periodical membranes and side holes, in which the double-negativity pass band can be controlled by an external direct-current voltage. The tension and stiffness of the periodically arranged membranes are actively controlled by electromagnets producing additional stresses, and thus, the transmission and phase velocity of the metamaterial can be adjusted by the driving voltage of the electromagnets. It is demonstrated that a tiny direct-current voltage of 6V can arise a shift of double-negativity pass band by 40% bandwidth, which exhibits that it is an easily controlled and highly tunable acoustic metamaterial, and furthermore, the metamaterial marginally causes electromagnetic interference to the surroundings.
Highlights
Acoustic metamaterials are extensively studied owing to unprecedented characteristics, which exhibit application potentials in various fields[1,2,3,4,5,6]
Piezoelectric materials, which can convert an electric signal into an acoustic vibration, were adopted to create actively tunable acoustic metamaterials
According to Bloch theory and plasma model[28,38,39], a membrane is considered to be an acoustic reactance X MA =/S2, where S =πa[2] and mM are the area and mass of the membrane, respectively. kM is the effective stiffness of the membrane equal to 8πFτ, where Fτ is the tension in the meXffHeemActb=ivrea(nlωeenρ. g0A/tπhs)iod(fle/trhh2eo)lsaeirdceeatnhhoebleee,fsfieencectnliuvadesianacngotauhcseotiaucdsrtdeiicstiiisomtnapanelcdleeananngctdehrZienHadAcu t=acneRdcHebA, y+rethsjXpeeHacAct,oiwvueshltyei.crreraaRdnHidAatli=oarneρ380t.chA0ekcr2ca/o(dr2iduπis)naagnntddo the impedance relations at the positions of the scatterers, the input impedance and transmission coefficient of the metamaterial can be obtained by successively using the impedance transfer equation[13,39]
Summary
Acoustic metamaterials are extensively studied owing to unprecedented characteristics, which exhibit application potentials in various fields[1,2,3,4,5,6]. An tunable acoustic metafluid was created based on a piezoelectric transducer driven by the signals controlled by a sensor detecting the acoustic waves incident on the metamaterial, which was a feedback system realizing an adjustable effective mass density, modulus and transmission[22]. We design a tunable acoustic metamaterial with double-negativity on the basis of a passive metamaterial composed of periodically arranged side holes and ordinary elastic membranes[28,29]. By changing the DC voltage supplied to the electromagnets, the double-negativity pass band (DPB) and the phase velocity in the metamaterial are controlled and adjusted. Via the electromagnets converting an external electric voltage into stiffness variation in the elastic membranes, this metamaterial can be and conveniently controlled and adjusted to a great extent merely with a low-voltage DC source. The adjusting of the metamaterial requires no special equipment and no treating on the membranes, and the presented mechanism for controlling a metamaterial is available in various membrane-based metamaterials
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