By using sub-wavelength resonators, metamaterial absorber shows great potential in many scientific and technical applications due to its perfect absorption characteristics. For most practical applications, the absorption bandwidth is one of the most important performance metrics. In this paper, we demonstrate the design of an ultra-broadband infrared absorber based on metasurface. Compared with the prior work [Opt. Express22(S7), A1713-A1724 (2014)], the proposed absorber shows more than twice the absorption bandwidth. The simulated total absorption exceeds 90% from 7.8 to 12.1 um and the full width at half maximum is 50% (from 7.5 to 12.5 μm), which is achieved by using a single layer of metasurface. Further study demonstrates that the absorption bandwidth can be greatly expanded by using two layers of metasurface, i.e. dual-layered absorber. The total absorption of the dual-layered absorber exceeds 80% from 5.2 to 13.7 um and the full width at half maximum is 95% (from 5.1 to 14.1 μm), much greater than those previously reported for infrared spectrum. The absorption decreases with fluctuations as the incident angle increases but remains quasi-constant up to relatively large angles.

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Tungsten carbide (WC) hard metals are universally used in industrial fields owing to their superior properties, and the machining accuracy of WC products is playing an important role in their service performance. However, how to achieve a balance between high accuracy and processing cost according to different applications is a key engineering issue. Thus, it is necessary to reveal the material removal characteristics of such difficult-to-cut hard metals. In this article, ultra-precision grinding characteristics of WC-Ni hard metals were investigated based on the wafer rotation grinding method using #120, #600, #2000, and #12000 diamond cup wheels as coarse, semi-finished, fine, and finish grinding wheels, respectively. A polished sample was taken for comparison. The optical surface profilers, scanning electron microscope, and atomic force microscope were employed for checking surface topographies, surface morphology, and cutting depth. An ultra-smooth and defect-free WC-Ni surface with less than 2 nm Ra and the average cutting depth of about 10 nm can be obtained using a #2000 diamond wheel, which can replace polishing and satisfy the requirements of most high-performance applications. This study provides useful observations for ultra-precision manufacturing of hard metal products.