Programmable metasurface antenna based information mapping scheme that approaches efficiency limit
Metasurfaces are two-dimensional artificial structures specifically engineered to achieve flexible manipulations of electromagnetic waves. By tailoring the geometry, size, and arrangement of meta-atoms, the metasurfaces can control various wave parameters, including amplitude, phase, and polarization, to achieve precise wavefront shaping and manipulations. The great capabilities of metasurfaces have found important applications in imaging, sensing, telecommunications, and photonic information processing.
Digital coding and programmable metasurfaces were proposed and realized in 2014 [Cui et al., Light: Science & Applications 3, e218, 2014]. The programable metasurface is composed of meta-atoms integrated with dynamic controllable components and can be used for versatile and real-time wave manipulations in a reprogrammable way. The programmable metasurface in radio environment has led to the concept of reconfigurable intelligent surface [Tang et al., IEEE Transactions on Wireless Communications 20, 421, 2021], which can be employed to improve wireless communication quality by using in-situ beamforming to scatter the waves toward desired target directions.
In 2019, we proposed another direction for metasurface-assisted communication networks, in which the programmable metasurface was used to construct new-architecture transmitter [Cui et al. Research 2019, 2584509, 2019]. The programmable metasurface based transmitter enables both information generation and transmission simultaneously, eliminating the need for complicated information modulation components such as I/Q channels. In this transmitter, the information is directly generated by the encoding states of the metasurface itself, and is retrieved by measuring the scattered electromagnetic fields. The established communication strategies using the programmable metasurface transmitters include direct beamforming, time-domain frequency-shift keying, space-frequency multiplexing, 256-state quadrature amplitude modulation, light-to-microwave transmission, and full-characteristics modulated space-time metasurface antennas. Despite these advances, the current schemes faced a key challenge of low information mapping efficiency, which greatly diminishes data transmission speeds in the programmable metasurface-based communication links. Information mapping efficiency is defined as the ratio of the amount of information that can be extracted by the receiver to the amount of information supplied by the programmable metasurface in a unit of switching time. Ideally, this efficiency would be unity; however, no reported scheme has yet approached this limit, either theoretically or in practical implementation.
In this study, we propose a generalized theoretical model and construct a prototype of the programmable metasurface antenna to show the possibility of approaching the information mapping limit. The schematic of the working mechanism of the proposed programmable metasurface antenna-based transmitter is shown in Fig. 1. Specifically, for a one-dimensional, 1-bit phase-modulated programmable metasurface antenna consisting of p columns, we establish that when p is an odd prime (e.g. p = 3, 5, 7…) and the measurement direction corresponds to the first spatial harmonic of the metasurface, nearly all programmable patterns, with only one exception, can be mapped to the far-field region in a bijective manner, featuring the C2p symmetry in the produced constellation diagram. The proposed scheme achieves information mapping efficiency that approaches unity.
Figs. 2a-c illustrate the prototype of the proposed programmable metasurface antenna and the experimental setup. The central five columns of the programmable metasurface antenna serve as radiators, while the outer four columns are configured as dummy elements to establish uniform boundary conditions. By applying different bias voltages to the PIN diodes in each column, the effective length of the feeding line will be changed, resulting in a 180° phase shift in the radiated wave. The designed 1-bit programmable metasurface antenna can generate a total of 25 = 32 distinct coding states. To synthesize the constellation diagram in the direction of the 1st harmonic, multiple far-field measurements were performed for each encoding pattern. The harmonic field responses produced by each encoding pattern were measured by 1000 times, with the input power supplied to the programmable metasurface antenna varying from 0.0125 mw to 0.05 mw, as shown in Figs. 2d-f. Overall, the experimentally retrieved constellation diagrams exhibit great agreement with the theoretically predicted results shown in Fig. 1. Our findings are generally applicable over a wide spectral range and are expected to lay the groundwork for future programmable metasurface enabled high-speed RF-chain-free wireless networks.

Figure 1. Conceptual illustration of the information mapping model enabled by the programmable metasurface antenna. A 1-bit phase-modulated programmable metasurface antenna is employed, where the number of the operating columns is an odd prime (e.g. p = 5). In the information mapping process, the bit string is modulated by the microcontroller unit (MCU), and 2p-1 encoding states can be distinctly mapped to the first harmonic direction to form a constellation diagram with C2p symmetry.

Figure 2. The prototype, experimental setup, and retrieved constellation diagrams of the programmable metasurface antenna. a, The measurement setup of the programmable metasurface antenna in a microwave anechoic chamber. b-c, The photographs of the programmable metasurface antenna and the integrated controlling unit. d-f, Experimentally retrieved constellation diagrams at the direction of the 1st harmonic, with the input power of 0.0125 mw (d), 0.025 mw (e), and 0.05 mw (f), respectively.
Tie Jun Cui
Professor, Southeast University
Tie Jun Cui is the academician of Chinese Academy of Sciences and the Chief Professor of Southeast University, Nanjing, China. He authored or co-authored five books and published over 700 peer-review journal papers, which have been cited by more than 74000 times (H-index 131, Google Scholar). He proposed the concepts of digital coding metamaterials and programmable metamaterials, and realized their first experimental demonstrations. He further established a new system of metamaterials: information metamaterial, and devoted to pushing its applications and connections to information science and technology. Dr. Cui received the National Natural Science Awards of China in 2014 and 2018, respectively; Highly Cited Researcher (Clarivate Analytics) from 2019 to 2023, Frontiers of Science Award in the First International Congress of Basic Science in 2023; National Teaching Achievement Award in 2023; Tan Kah Kee Information Science Award in 2024; IEEE Communications Society Marconi Prize in 2024, and so on. Dr. Cui is an IEEE Fellow.
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