Abstract
The Luneburg lens is a spherically symmetrical gradient refractive index (GRIN) device with unique imaging properties. Its wide field-of-view (FoV) and minimal aberration have lead it to be successfully applied in microwave antennas. However, only limited realizations have been demonstrated in acoustics. Previously proposed acoustic Luneburg lenses are mostly limited to inherently two-dimensional designs at frequencies from 1 kHz to 7 kHz. In this paper, we apply a new design method for scalable and self-supporting metamaterials to demonstrate Luneburg lenses for airborne sound and ultrasonic waves. Two Luneburg lenses are fabricated: a 2.5D ultrasonic version for 40 kHz and a 3D version for 8 kHz sound. Imaging performance of the ultrasonic version is experimentally demonstrated.
Highlights
The Luneberg lens[1] is a representative gradient refractive index (GRIN) lens that offers a variety of unique wave controlling properties: first, a Luneberg lens bends a plane wave to a focal spot on the opposite spherical surface of the lens, which is a very attractive feature in imaging since the lens maps the direction information directly to the spatial locations of the focuses
To demonstrate our design method, here we present two acoustic GRIN lenses designed with the above-mentioned unit cell structures and CAD tool
A number of potential applications are enabled by ultrasound lenses such as the Luneburg lens described above
Summary
The Luneberg lens[1] is a representative GRIN lens that offers a variety of unique wave controlling properties: first, a Luneberg lens bends a plane wave to a focal spot on the opposite spherical surface of the lens, which is a very attractive feature in imaging since the lens maps the direction information directly to the spatial locations of the focuses. Previous realizations of acoustic Luneburg lenses are limited to inherently two-dimensional designs and audible frequency range (1 kHz to 7 kHz)[14,15]. It remains challenging to design a true three-dimensional acoustic Luneburg lens, for the airborne ultrasonic frequency range. The proposed ultrasonic Luneburg lens can be potentially useful for enhancing the sensing performance of existing pulse-echo-based airborne ultrasonic sensors and imaging systems (e.g. shaping the radiation pattern, extending the sensing range), and the audible version may be used for improving the radiation pattern for speaker systems. We expect many other three-dimensional GRIN devices can be conveniently realized with similar methods for better control of airborne acoustic waves
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