Acoustic lens can help generate longer and cleaner sound jets
Acoustic lens can help generate longer and cleaner sound jets lead image
Acoustic jets are extremely narrow acoustic fields – sound waves – that can travel over a long distance relative to the wavelength without losing shape. The ability to better generate these sound beams may help improve a variety of medical and industrial applications, such as those involving ultrasonic and sonar devices.
Wu et al. created a 3D-printed mesoscale acoustic generalized Luneburg lens based on a cylindrical metamaterial, and an isotropic lens for comparison. The generalized Luneburg lens, with its multi-layered gradient refractive index (GRIN) distribution structure, was able to generate an acoustic jet longer than 17 times the wavelength of the soundwave, twice as long as what the isotropic lens was able to do.
The GRIN-structured Luneburg lens did not show any obvious sidelobes, which are spurious distributions in the wave intensity and a common side effect of lens-generated acoustic jets. The GRIN-generated jets also had better acoustic impedance matching than those generated by the isotropic lens.
“The method we used in this work provides great design flexibility and versatile applicability in acoustic imaging and sonar devices. Metamaterials are redefining ‘lenses’ in a way that natural materials cannot,” said author Chunyao Lu.
Using a microphone and a loudspeaker generating a 20 kHz sound wave, they experimentally verified the capability of the GRIN structured lens, as predicted by their theoretical calculation and numerical modeling with ray tracing.
Next, the authors plan to investigate underwater ultrasonic 3D lenses and the optimization of refractive index distribution.
“We are hopeful that imaging using the ‘perfect lens’ is going to revolutionize traditional acoustics in the next decade,” said Lu.
Source: “GRIN metamaterial generalized Luneburg lens for ultra-long acoustic jet,” by Chunyao Lu, Run Yu, Qiujun Ma, Kangyu Wang, Jing Wang, and Dawei Wu, Applied Physics Letters (2021). The article can be accessed at https://doi.org/10.1063/5.0044436 .
