Acoustic metamaterial with negative mass density in water

A two-dimensional (2D) acoustic metamaterial (AM) with negative effective mass density in water is designed by periodically arranging hollow tube "meta-atoms." Experimental and simulated results demonstrate that transmission dips accompanied with inverse phases are presented in the transmission spectra of the 2D AM at the ultrasonic frequency band. Effective parameters extracted from the experimental measured transmission and reflection coefficients of the 2D AM show that the effective mass density and refractive index are negative near the dip frequency range of 35.31-35.94 kHz. The simulation also shows the negative response in the 2D AM. Due to the excellent properties, the 2D AM is appealing for the potential applications in areas such as subwavelength imaging, ultrasonic cloaking in water, and so on.