Active control of elastic metamaterials consisting of symmetric double Helmholtz resonator cavities

Wave invisibility has quite special meaning on marine vehicles under water, which encourages people to search effective methods for a long history. Initiated by this point, we propose a new class of active elastic metamaterials and a cloaking design consisting of double Helmholtz cavities. By changing external voltage with different piezoelectric diaphragm stiffness, this structure shows a controllable effective bulk modulus in which a negative value appears over a wide frequency range. This configuration with double active cavities provides better tunable abilities to achieve the effective bulk modulus than that with a single cavity. In order to design a multilayered cloak and a non-blind cloak, the coupling of the adjacent cavity cells is considered and the control strategy for the periodic cavities with active Helmholtz resonators is developed. The parameters of the multilayered acoustic cloak can be obtained by the coordinate transformation method and the corresponding effective medium theory. This action can be implemented by the active control on each unit cell to drive the distribution of effective bulk modulus. These characteristics with a tunable effective bulk modulus at a very wide frequency range are significant to control elastic wave propagation.