Abstract
In this paper, a gradient index acoustic metamaterial is proposed based on the concept of the optical modified generalized Luneburg lens (MGLL). With the MGLL, double-foci and high energy density between the two foci can be achieved, which enables the realization of an ultra-long acoustic jet between the two foci. This capability of the MGLL is theoretically and numerically demonstrated with an acoustic metamaterial lens. Numerical simulation results show that based on this design, ultra-long acoustic jets with a jet length of up to 30 λ can be achieved, covering both the near field and far field.
Highlights
An acoustic jet is an acoustic focal field with a subwavelength full width at half maximum (FWHM) while maintaining a long propagation distance, which has potential applications in structural health monitoring,1 medical imaging,2 and energy harvesting.3–5 With the development of acoustic metamaterials for the control and manipulation of the propagation of acoustic waves in recent years,6–8 using acoustic metamaterials to generate the acoustic jet has attracted much attention
In this paper, a gradient index acoustic metamaterial is proposed based on the concept of the optical modified generalized Luneburg lens (MGLL)
Numerical simulation results show that based on this design, ultra-long acoustic jets with a jet length of up to 30 k can be achieved, covering both the near field and far field
Summary
An acoustic jet is an acoustic focal field with a subwavelength full width at half maximum (FWHM) while maintaining a long propagation distance, which has potential applications in structural health monitoring, medical imaging, and energy harvesting. With the development of acoustic metamaterials for the control and manipulation of the propagation of acoustic waves in recent years, using acoustic metamaterials to generate the acoustic jet has attracted much attention. Lu et al designed a gradient index (GRIN) acoustic metamaterial generalized Luneburg lens (GLL), which can achieve a super long working distance up to 17k.13. The variation of the refractive index of the lens is achieved by varying the filling ratio of the lattice unit cells, which allows for tailoring the velocity of the acoustic wave propagation in the structure. With this method, the graded change of the refractive index can be obtained in a broadband frequency range
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