An optically transparent metamaterial structure with broadband microwave absorptivity is proposed. A specifically designed optically transparent metasurfaces was designed to control the microwave absorption though properly modifying the impedance and resonance peaks of the meta-atom. Within a wide incident angle of ±60o, the proposed structure displays high absorptivity greater than 90% in the region of 33.7-44.7GHz for TE polarization. For TM polarization, the absorptivity in the region of 11.8-37.2GHz is greater than 90%. The perfect consistency between experimental results and simulation results demonstrates that the proposal has practical application of multispectral stealth technology.
In recent years, the research on radar and infrared compatible stealth has attracted much attention. In this paper, metamaterials are designed by means of theoretical calculation and modeling simulation. The entire structure consists of an infrared shielding layer (IRSL), a radar absorbing layer (RAL) and a backplane. The simulation results show that when the angle between the incident microwave and the normal of the metamaterial is in the range of 0-40°, the average absorption rate of the structure in the 7-27 GHz band is relatively stable and reaches more than 90%. In the infrared band, the emissivity of the structure is lower than 0.28 and 0.32 at 3-5 μm and 8-14 μm, respectively. In addition, through the rational design of structure and materials, the metamaterial not only achieves dual stealth functions of low infrared emission and broad microwave absorption, but also has high transparency and flexibility, providing a new method for the study of multi-band stealth materials.
KEYWORDS: Digital holography, Holograms, 3D image reconstruction, Particles, Image quality, Charge-coupled devices, Digital recording, CCD cameras, Digital imaging, Diffraction
In this paper, we propose a new reconstruction method for the synthetic aperture on-axis digital hologram with seams, and then evaluate it thoroughly. This method combines the principles of synthetic aperture and phase retrieval. It is applied to the experiment of the particle field detection. In the experiment, the pictures depict the particle is not only clearly visible at the normal region but also at the seams. With error analysis in reconstruction, method of correcting stitching errors improves accuracy furtherly. Therefore, the method proposed in this paper can effectively restrain the influence on the reconstructed image due to the loss of information at the seams and can achieve high-quality reconstructed image from the seamed stitching synthetic aperture on-axis digital hologram. It can be widely used in the diagnostic domain with high resolution and large visual field.
In the photographic process with Charge Coupled Device (CCD), the image sampling of CCD is important. Due to the previous incorrect mathematical descriptions of the sampling, a correct mathematical equation is given by analyzing the CCD image acquisition process. Comparing the previous and the given one, shortcomings of the previous are pointed out. Then, a detailed spectrum analysis of the image sampling is carried out which illustrates the influence of various parameters of CCD on image acquisition. The mathematical analysis can optimize the choice of the parameters of CCD in practical applications.
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