Wenyu Li

In this paper, two kinds of periodic nondiffractive beams along arbitrary trajectories, including non-accelerating and self-acceleration types, are generated by 3D-printed all-dielectric metasurfaces. The first step is to produce continuous non-accelerating and self-acceleration beams, i.e. Bessel beam and Bessel-like beams. By an appropriate modification of the conical ray pattern of the standard Bessel beams, self-accelerating Bessel-like beams can be realized. In the second step, by removing some expanding phase equivalent circles in a periodic fashion and binary modulating of the phase masks, the central main lobe of continuous beams can be modified into pulsating ones. In the third step, we construct real physical models based on the derived theories. All phase coverage can be achieved by changing the height of the proposed cube element. Therefore, the final phase distribution can be mapped to height information of each unit cell. For demonstration, several proof-of-principle metasurfaces are printed and measured, two of which are used to generate Bessel beams along different straight directions, and two of which are used to produce Bessel-like beams along C-shaped and S-shaped trajectories. In all cases, during propagation, the intensity peak alternately switches its position between the main lobe and the outing rings. Meanwhile, the measured trajectories are highly consistent with the predefined ones. The proposed metasurfaces are expected to be utilized in numerous applications like secure communication.

In this paper, a low-profile, double-layer absorber with ultra-broadband absorption and large-angle stability is proposed. In order to improve the angular stability, the square ring with concave–convex deformation is designed. It can expand the current path to realize the miniaturization of the absorber, which decreases the influence of oblique incident on absorption. The equivalent circuit model provides detailed resonance and admittance analysis, showing the existence of three resonances working together to achieve broadband absorption. The simulated results illustrate that the designed unit can achieve above 80% absorption within 2.09–18.1 GHz. The angular stability is up to 50° under TE/TM polarization with a period of 0.07 λ_L (the wavelength of the lowest operating frequency). The 300 mm × 300 mm prototype absorbers were fabricated for demonstration, with a total thickness of 0.096 λ_L. The measurement results are consistent with the simulated results, which shows that the designed absorber unit can achieve ultra-broadband and large-angle absorption. The performance of devices can be widely applied in infrared detection, radiation refrigeration, and stealth technology.