Acoustic imaging with metamaterial Luneburg lenses
Controlling and focusing acoustic waves is a crucial component of fields such as ultrasonic sensing and speaker system design. Luneburg lenses, spherically symmetrical gradient refractive index (GRIN) devices with unique imaging properties, are usually applied to electromagnetic waves but were recently developed for acoustic waves. Luneburg lenses focus incoming wavefronts to focal points opposite their incoming direction with wider operating bandwidth than diffractive devices, which would help improve control of sound waves for various applications. Unfortunately, early versions have been limited to 2D devices with narrow acoustic range in audible frequencies. There exists a need for new ways of designing and manufacturing acoustic Luneburg lenses.
Duke inventors have developed a powerful new way of designing and manufacturing acoustic Luneburg lenses. With a new CAD tool, the inventors are able to design metamaterial unit cube cells that can be tweaked and arranged into 3D Luneburg lens structures for target frequencies. These structures are easily manufactured using 3D printing. As proof-of-concept, the inventors were able to design and fabricate two acoustic Luneburg lenses: a 2.5D ultrasonic version for 40 kHz and a 3D version for 8 kHz sound, both showing excellent agreement with simulations.
Acoustic Luneburg lenses could be applied to other fields such as wireless power transmission, acoustic levitation, non-destructive testing, medical imaging, and more.
- CAD tool capable of designing lenses for wider range of audible and ultrasonic frequencies
- Modular cubic unit cell design allows for simple manufacturing and scaling
- Acoustic wave focusing reduces computational complexity of signal processing
- Minimal spherical aberration
- Wide field of view