Experimental demonstration of a three-dimensional acoustic hyperlens for super-resolution imaging

Abstract

Acoustic hyperlenses have recently attracted much attention for promising applications in various fields. Yet the experimental realization of an acoustic hyperlens working in a real three-dimensional (3D) world is still lacking. Here, we theoretically propose and experimentally demonstrate a 3D acoustic hyperlens capable of producing super-resolution imaging for broadband airborne sound. A simple nonresonant metamaterial is designed as a practical implementation that simultaneously ensures tessellation of the curved surface and deep-subwavelength resolution. We analyze the dispersion relationship of the designed metamaterial that converts the evanescent waves into radially propagating modes based on positive extreme anisotropy. The effectiveness of our mechanism is demonstrated both numerically and experimentally via the production of 3D magnifying super-resolution imaging of small objects containing subwavelength patterns within a broad frequency range. We envision the realization of a 3D acoustic hyperlens to offer possibilities for the design of acoustic super-resolution imaging devices and their application in diverse scenarios ranging from medical ultrasound imaging to noninvasive evaluation.

Review of foundational concepts and emerging directions in metamaterial research: design, phenomena, and applications

“…2), like the electromagnetic lens, is used for subwavelength imaging beyond the diffraction limit. Near-field superlenses 63,64,153 amplify evanescent waves while far-field hyperlenses 154,155 convert evanescent waves to propagating waves. Other far-field lenses that do not use high anisotropy have also been designed.…”

“…Near-field superlenses [134,135,152] amplify evanescent waves while far-field hyperlenses [153,154] convert evanescent waves to propagating waves. Other far-field lenses that do not use high anisotropy have also been designed [155,156].…”

Far-field ultrasonic imaging using hyperlenses

“…Hence, a mechanism to achieve super resolution along with magnification capability is of much practical interest. Such ‘super resolution with magnification’ concept was demonstrated in optical 16 – 20 and acoustic 21 – 26 domains with ‘hyperlenses’ that convert evanescent waves into propagating ones, thus carrying information to the far-field. Although the term ‘hyperlens’ was originally used for an ideal indefinite medium having hyperbolic dispersion 27 , it is also applicable for lenses with elliptical dispersion, as long as the dispersion is flat for a large range of wavevectors 28 .…”

Far-field subwavelength imaging by harnessing the single-mode resonance and sparsity

“…The anisotropic metamaterial device named as 'magnifying hyperlens' was fabricated to magnify subwavelength objects by gradually converting evanescent components into propagating waves [3][4][5][6][7], resulting super-resolution imaging directly measured by a probing sensor. The scattering of evanescent waves can also be used to unravel the subwavelength world [8][9][10], in which how to realize a high efficient conversion of evanescent waves into propagating waves is quite critical.…”