**3. The application of the coding metasurface in RC**

Since information can be encoded as OAM states that span a much larger space than threestate OAM, the proposed configuration may provide an effective way to generate vortex waves for wireless communication applications, which will greatly promote the study and application of vortex wave. Comparing to the published work, which only can generate one OAM modal, the proposed reflective metasurface is likely to double the information rate.

**Figure 9.** Phase distribution of E-filed on the observation plane at z-axis direction with mode *l* = 1 (a) at 18 GHz, (b) at 30 GHz and (c) at 42 GHz and corresponding magnitude distribution with mode *l* = 1 (d) at 18 GHz, (e) at 30 GHz, and

**Figure 8.** Configuration of the designed vortex metasurface with mode (a) *l* = 1 (b) *l* = 2 (c) *l* = 3 (d) *l* = 4 panel present the metallic patterns of the top layer. The phase of the reflection coefficient versus the length of the arrow-shaped

metasurface from 18 to 42 GHz. Reprinted with permission from Ref. [8]; Copyright 2018 IEEE.

26 Metamaterials and Metasurfaces

(f) at 42 GHz. Reprinted with permission from Ref. [8]; Copyright 2018 IEEE.

In general, the RC is rectangular and uses mode stirring or mode tuning technology to change the boundary conditions of the electromagnetic field so as to produce a statistically uniform field. To overcome the size and maintenance problems of the stirrers, it is proposed the use of diffusion metasurface in the RC to enhance the scattering. Such metasurface is much smaller than a stirrer [9]. According to the concept of coding metasurface, the designed 1-bit random coding metasurface (by employing the genetic algorithm) can provide an optimized distribution of unit cells to get a uniform backscattering (see **Figure 11**).

**Figure 11.** The 1-bit random coding diffusion metasurface distributions and simulated surface current distribution and near-field pattern under normal incidence. Reprinted with permission from Ref. [9]; Copyright 2018 Scientific Reports.

scalability of these coding metasurfaces to frequencies in the range of THz or optical is possible, allowing for the controllability of reflection, and scattering of EM waves in these fre-

Coding Metasurfaces and Applications http://dx.doi.org/10.5772/intechopen.78417 29

The authors are grateful to National Natural Science Foundation of China (61,501,227, 61,071,019), Postdoctoral Science Foundation of China (2015M581789), 56YAH17032 of NUAA, Jiangsu Innovation Program for Graduate Education (KYLX16–0370), Fundamental Research Funds for the Central Universities (NJ20160011), MINECO-Spain (TEC2016–75650-R), Generalitat de Catalunya (2017SGR-1159) and FEDER funds. Hengyi Sun acknowledges the

and Ferran Martin<sup>2</sup>

China Scholarship Council (CSC) for Grant 201,706,830,064.

, Zhuo Li<sup>1</sup>

1 Key Laboratory of Radar Imaging and Microwave Photonics, Ministry of Education, College of Electronic and Information Engineering, Nanjing University of Aeronautics and

2 CIMITEC, Departament d'Enginyeria Electrònica, Universitat Autònoma de Barcelona,

[1] Yu N, Genevet P, Kats MA, Aieta F, Tetienne JP, Capasso F, Gaburro Z. Light propagation with phase discontinuities: Generalized laws of reflection and refraction. Science.

[2] Della Giovampaola C, Engheta N. Digital metamaterials. Nature Materials. 2014;**13**:1115.

[3] Moccia M, Liu S, Wu RY, et al. Coding metasurfaces for diffuse scattering: Scaling Laws, bounds, and suboptimal design. Advanced Optical Materials. 2017;**5**(19). DOI: 10.1002/

\*Address all correspondence to: sunhy1123@nuaa.edu.cn

2011;**334**:333-337. DOI: 10.1126/science.1210713

quency domains [11].

**Acknowledgements**

**Conflict of interest**

**Author details**

Barcelona, Spain

**References**

There is no conflict of interest.

Hengyi Sun1,2\*, Changqing Gu<sup>1</sup>

Astronautics, Nanjing, China

DOI: 10.1038/nmat4082

adom.201700455

**Figure 12.** The standard deviations for the field uniformity of the test zone, which loaded the rotatable 1-bit random coding diffusion metasurface in the RC, and the purple lines are the tolerance requirements for the standard deviation of [10]. (a) the x-component, (b) the y-component, (c) the z-component, and (d) the combined of xyz components. Reprinted with permission from Ref. [9]; Copyright 2018 Scientific Reports.

When loaded the metasurface to the RC, it can act as a tuner. By setting the number of metasurface steps to 12, the standard deviation of the field is the one shown in **Figure 12**.

The results indicated that the rotatable 1-bit random coding diffusion metasurface can act as a tuner in the RC and it is of great interest as it shows that the metasurface on the wall increases the test zone available by avoiding the stirrer.
