Reconfigurable intelligent surfaces (RISs) are a kind of programmable structure that could be used to control the regulation of electromagnetic waves by modifying the electric and magnetic properties of a surface. They propose a novel method for boosting the effectiveness of wireless communications systems—rather than adjusting to the propagation environment, they modify it.
The combination of metallic resonators with digital equipment like PIN diodes and varactor diodes has propelled RIS research forward to a new level. With sub-wavelength resolution, RISs can now alter electromagnetic waves.
When used in combination with a field-programmable gate array, these RISs can be dynamically switched between varieties of functionalities in live time by just modifying the coding sequences.
Even then, there are problems with these diode-based RISs. First, the working principle of PIN/varactor diodes limits the degree of freedom of reconfiguration in the unit element scale: most are binary, and only a few can reach four.
Since a single diode's normal power consumption is in the hundreds of milliwatts range, sustaining functionality necessitates a constant power source.
Large-scale and long-term applications are hampered by such energy usage, which necessitates trade-offs between both the size or number of unit elements and the total RIS size.
An international research team has constructed a mechanical RIS with a high degree of reconfiguring freedom, cheap cost, and reduced energy consumption. The RIS runs at microwave frequencies and determines the rotation angle of each meta-atom using a reliable control approach. The study was published in the journal Advanced Photonics.
The RIS is made up of a 20 × 20 supercell that covers an area of 870 mm × 870 mm. A stepping motor, a set of transmission gears, and a 4 × 4 array of meta-atoms make up each supercell.
To accomplish the appropriate phase control, each meta-atom can be dynamically rotated. This reconfigurable feature enables a persistent and arbitrary phase control pattern with great efficiency and constant amplitude across the complete RIS.
By altering the RIS's operation in real-time across a number of capabilities, the researchers demonstrate effective and flexible control of the impinging wavefront. They show that the quasi-continuous phase tunability enhances wavefront controllability tremendously.
Modules and meta-atoms, capable of being mechanically reprogrammed, can be connected or disconnected in a variety of ways. Furthermore, the system maintains specified operation without requiring power, providing a new energy-saving and environmentally responsible option.
This RIS promises to achieve multidimensional manipulation of electromagnetic waves by incorporating different gear sets and different meta-atoms, which may bring RIS-related research to the next level.
Weili Zhang, Study Senior Author and Professor, Engineering, Oklahoma State University
Xu, Q., et al. (2022) Mechanically reprogrammable Pancharatnam–Berry metasurface for microwaves. Advanced Photonics . doi.org/10.1117/1.AP.4.1.016002.