Based on the perspective of wide scanning range and ultra-broad bandwidth, Luneburg lens is highly anticipated as an outstanding option for multibeam radiations. However, owing to the lack of low-loss continuously varying permittivity materials, the practical application of Luneburg lens is far below expected proportion. In this paper, an ultra-wideband planar Luneburg lens is proposed. Due to the novel design of all dielectric lightweight radially symmetric periodic gradient metamaterial, the presented lens is able to yield highly directional emission with side lobes all below -8dB and achromatic sub-diffraction focusing with full width at half maximum (FWHM) about 0.4λ from 4GHz to 22GHz. The prototype of the lens is manufactured by computer-numerical controlled machining. Measured data of near field and far field agree well with that of the simulated one, verifying the effectiveness of the proposed design methodology. The superiority of the presented approach to design Luneburg lens is demonstrated. Therefore, the PLL owns the advantages of lightweight, compact structure, low profile, ultra-broadband function, high resolution and fabrication convenience, which has a great potential to be practically deployed.
Conformal transformation method has been extensively applied to control propagation of electromagnetic waves and acoustics waves due to the form-invariant property of Maxwell equations and acoustic equations. However, conformal transformation method’s application in elastic waves is rarely reported due to the governing equation of elastic waves don’t have form invariant property. In this paper, through igniting evanescent waves at the interface of conformally mapped Mikaelian lens with hyperbolic secant refractive index profile, conformal transformation method is successfully used to achieve highly efficient (above 75%) broadband (30kHz -80kHz) achromatic high-resolution flexural wave focusing in thin plate with full width at half maximum (FWHM) around 0.2λ. The proposed Mikaelian lens is designed by linking refractive index with the thickness in plates. Simulated results agree well with theoretical prediction. This high performance for flexural wave focusing could be used for energy harvesting and medical imaging.
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