Ultra-broadband sound absorption characteristics in underwater ultra-thin metamaterial with three layer bubbles

The interest of this article is to obtain the underwater broadband sound absorption characteristics by filling three layers of bubbles in Polydimethylsiloxane polymer (PDMS). In this underwater ultra-thin metamaterial, three-layer bubbles are arranged from small to large with the same radius center. The finite element analysis (FEA) method and transfer matrix (TM) method have good consistency in calculating the sound absorption coefficient of this metamaterial. The results reveals that sub-wavelength metamaterial properties can be achieved below 6.4 MHz. Bubble coupling critical viscosity, waning coupling between layers, waveform transformation, and increasing scattering (reflection) waves all affect broadband sound absorption characteristics. The position and size of three bubbles are discussed, and design summary could be potentially in underwater ultrasound filter devices and medical ultrasound field.