Run Yu’s research while affiliated with Nanjing University of Aeronautics & Astronautics and other places

... Our use of conformal mappings for mechanical metamaterials is distinct from their extensive use for optical metamaterials. Transformation optics often relies on conformal mappings to achieve practical effective material parameters [20,21,22,23] (similarly for transformation acoustics [24,25,26,27]). However, transformation optics and acoustics typically apply in the non-dispersive setting [28], requiring sub-wavelength unit cells. ...

Reference:

Conformally Graded Metamaterials for Elastic Wave Guidance

... 13 Recent advances in research involving techniques to characterize and design metamaterials, particularly sonic crystals, coupled with the concept of a radial density gradient proposed by Boyles, 13 have facilitated the realization of numerous acoustic Luneburg lenses (ALL) over the past decade. The inaugural successful realization of an ALL was presented by Kim. 14 followed by various studies focusing on airborne sound waves [15][16][17][18][19][20][21][22][23][24] or waves propagating through a liquid medium, such as water. [25][26][27] Additionally, the realization of Luneburg lenses considering the propagation of elastic waves in a solid medium have also been explored in different works. ...

Reference:

Towards an optimal design of acoustic Luneburg lenses

... In general, the acoustic model of the phenomenon under consideration, the acoustic model of the scatterer (isotropic, anisotropic, relation between longitudinal and shear speed of sounds [25][26][27][28][29][30][31], etc.), and how the result obtained can be correctly applied to describe the acoustic jet phenomenon are not clear from the article under discussion. It seems that the authors of the article do not deeply understand the difference between the nature of electromagnetic and acoustic waves. ...

Reference:

Comment on Mahariq et al. Investigation and Analysis of Acoustojets by Spectral Element Method. Mathematics 2022, 10, 3145

... The inaugural successful realization of an ALL was presented by Kim. 14 followed by various studies focusing on airborne sound waves [15][16][17][18][19][20][21][22][23][24] or waves propagating through a liquid medium, such as water. [25][26][27] Additionally, the realization of Luneburg lenses considering the propagation of elastic waves in a solid medium have also been explored in different works. [28][29][30] A thorough review of ALL applications and their physical underpinnings has been provided by Zhao et al. 31 In the context of sound wave propagation, achieving the radial density gradient necessary to obtain the Luneburg refractive index involves introducing radial subwavelength discontinuities within the material. ...

Reference:

Towards an optimal design of acoustic Luneburg lenses

... Moreover, various ALL-based wave manipulation capabilities were achieved such as wave focusing [31,32], guiding [33,34], retroreflection [35], collimation [36], generation of ultra-long wave jets [37], simultaneous broadband control of multiple wave modes [38], etc. In addition, the excellent wave manipulation performance of ALL was proven to be useful for various fields such as wireless communications, transmission, and sensing [39]. In recent years, although multiple review papers have been published on metamaterial and phononic crystals for manipulating acoustic and elastic waves [36,40], no review paper focuses on ALL to the best of our knowledge. ...

Reference:

A review of acoustic Luneburg lens: Physics and applications