Acoustic metamaterials with piezoelectric resonant structures

A resonant structure of a hard-core coated by piezoelectric composite materials is proposed as an acoustic metamaterial (AM), in which a negative effective mass density and elastic modulus are simultaneously achieved. The double negativity, appearing within a certain range of the filling ratio, is numerically demonstrated by the switch of the electrical boundary from open to closed. The bandwidth of the negative effective elastic modulus is sensitive to the piezoelectric constant e(33). The multi-unit AM offers the advantages of broadening the double-negativity domain and of reducing the primary frequency, while the cut-up frequency remains the same as that of the single-unit cell AM.