Terahertz Broadband Low‐Reflection Metasurface by Controlling Phase Distributions

Abstract

Recently, reflectionless or low‐reflection surfaces made of subwavelength structures have been of broad interest in practical engineering. Here, a single‐layer terahertz metasurface is proposed to produce ultralow reflections across a broad‐frequency spectrum and wide incidence angles by controlling the reflection phases of subwavelength structures. To enable full control of the phase range in a continuous band, a combination of two different subwavelength elements are employed, both of which exhibit weak interactions with the incident terahertz waves, thereby showing high local reflectivities near the operating frequency. An optimization method is utilized to determine the array pattern with the minimum overall reflections under the illumination of plane waves. Both numerical simulations and experimental results demonstrate ultralow reflections of terahertz waves by the metasurface over a broad frequency band and wide incidence angles. By using the proposed metasurface, the far‐field scattering patterns of metallic objects can be efficiently controlled, which opens up a new route for low‐reflection surface designs in the terahertz spectrum.

Random-phase metasurfaces at optical wavelengths

“…The performance of the metasurface is by design angle insensitive, and by utilizing four-fold symmetric unit cells one also achieves a polarization insensitive response. It should be noted that the best performance with respect to reflection reduction in a spectrally broad window is not a fully random-phase metasurface, as employment of optimisation routines suggests a certain correlation between neighbouring unit cells252627. In relation to radar cross section reduction, we also note earlier work utilizing a random positioning of π -phase different elements which results in a chessboard-like surface3031, and related (though different) work on the subject of cloaking by scattering cancellation32.…”

“…Moreover, we foresee the application of random-phase metasurfaces as high-quality reference structures for dark-field microscopy, hereby avoiding the usage of rather ill-defined scatterers, like dust particles42. In a different area of application, we envision that the low-reflection and diffusion of light from random-phase metasurfaces might stimulate interest within the field of camouflage technology, with stealth technology being one example for the low-frequency regime252627. Furthermore, the possibility to impose different statistics on the complex scattered light for linearly polarised and unpolarised light (or, alternatively, for two orthogonal polarizations) renders such metasurfaces interesting for security applications.…”

“…The common denominator of all these applications is the well-defined reflection coefficient that is implemented on the metasurface by proper positioning and dimensioning of the nanobricks, hereby leading to, one might say, a deterministic response in the sense that no random variables enter the design of the metasurface. In contrast, recent work2526272829 on reducing the radar cross section in the giga- and tera-hertz regimes, particularly relevant for stealth technology, has proposed reflectarrays featuring a (quasi-)random distribution of reflection phases, which will result in destructive interference of the scattered light, thus leading to a diffusion of light into a speckle-like far-field pattern and an overall low reflection. The performance of the metasurface is by design angle insensitive, and by utilizing four-fold symmetric unit cells one also achieves a polarization insensitive response.…”

Prediction of electromagnetic scattering from metasurfaces

“…Metasurface has been widely studied for manipulating electromagnetic (EM) waves [1][2][3][4][5][6][7][8]. In particular, some metasurface have been used to control the scattering of incident EM waves [6][7][8].…”

Ultra-broadband Reflective Metamaterial with RCS Reduction based on Polarization Convertor, Information Entropy Theory and Genetic Optimization Algorithm

“…In designs, the coding sequences of “0” and “1” elements are introduced to control the scattering fields. On these bases, various functionalities such as anomalous reflection, polarization conversion, scattering beam diffusion can be applied to obtain the low MRCS24252627282930. Importantly, metamaterials or metasurfaces could manipulate the polarization of EM waves with asymmetric transmission or reflection.…”