Electric field is introduced as an actively tunable element. Several types of electrical voltage driven membrane-based acoustic metamaterials have been constructed and experimentally investigated. As a start, Au-coated circular plastic disk that fixed on the center of membrane is employed as one electrode, and a rigid fishnet-like metal frame placed in front of membrane as the second electrode. The frame is almost acoustically invisible so as to minimize its scattering effects.

By introducing AC voltage that could generate an additional harmonic force, the membrane’s vibration could then be significantly suppressed or enhanced, through which a phase sensitive and actively tunable muffler/amplifier has been demonstrated. With DC voltage, an anti-restoring force appears that could provid...[ Read more ]

Electric field is introduced as an actively tunable element. Several types of electrical voltage driven membrane-based acoustic metamaterials have been constructed and experimentally investigated. As a start, Au-coated circular plastic disk that fixed on the center of membrane is employed as one electrode, and a rigid fishnet-like metal frame placed in front of membrane as the second electrode. The frame is almost acoustically invisible so as to minimize its scattering effects.

By introducing AC voltage that could generate an additional harmonic force, the membrane’s vibration could then be significantly suppressed or enhanced, through which a phase sensitive and actively tunable muffler/amplifier has been demonstrated. With DC voltage, an anti-restoring force appears that could provide extra effective elastic modulus. It could lower the 1st eigen-frequency by up to 70 Hz and tuned the phase shift of transmitted wave as well. Functionalities such as phase modulation and acoustic switch with on/off ratio up to 21.3 dB are demonstrated.

Another idea was using a ring structure electrode to change the effective radius of the membrane which will lead the whole series of eigen-mode shift to higher region. Based on this, two total absorption structures with tunable capability have been studied. One is a membrane backed with a rigid wall and sealed air in between to generate a hybrid resonance mode. The frequency of the absorption peak can be shifted within certain range. The other one is a double layer of decorated membrane resonators structure with different parameters for each layer. A switch from total absorption to total reflection has been shown.