Dynamic Control of Full-Space Electromagnetic Waves Using Highly Integrated Multifunctional Coding Metasurfaces

Metasurfaces which by definition are two-dimensional analogs of metamaterials that can manipulate electromagnetic (EM) waves in unprecedented ways. They can be engineered to control various properties of EM waves such as their phase, amplitude, polarization, and direction which make them valuable in imaging, sensing and communication systems. Despite their significant advantages the current metasurfaces face some limitations specially in their ability to independently control transmitted and reflected waves across the full space which restricts their versatility and functionality. This limitation becomes particularly problematic in advanced applications such as beamforming and wireless communication where dynamic control of wave propagation in multiple directions is essential. Furthermore, many existing metasurfaces are passive, meaning their functionalities are fixed once fabricated, and they cannot adapt to changing environmental conditions or requirements. The integration of active elements, such as PIN diodes, into metasurfaces has been proposed as a solution to enable dynamic control, but implementing this without increasing the complexity and size of the system remains a challenge. In response to these challenges, researchers led by Professor Long Li at Xidian University developed a new type of coding metasurface capable of providing independent control of transmission and reflection for different polarizations across the full space. The study aimed to design a multifunctional metasurface that could dynamically switch between various operational modes, including beam deflection, beam focusing, and vortex beam generation. By integrating active elements and employing advanced coding strategies, the researchers sought to overcome the existing limitations and expand the potential applications of metasurfaces in wireless communication and other fields. The researchers tried to validate the metasurface’s multifunctional capabilities, including vortex beam generation, dual-beam deflection, and beam focusing. They placed the metasurface prototype which is 312 mm × 312 mm in an anechoic chamber for far-field measurements. The authors used linear-polarized (LP) feed source to illuminate the metasurface and the transmitted and reflected waves were measured.  The managed to successfully generate vortex beams with different orbital angular momentum (OAM) modes. The researchers also demonstrated that the reflected x-polarized wave produced a vortex beam with OAM mode l = +1, while the reflected y-polarized wave generated a vortex beam with OAM mode l = −1. These results were confirmed through both numerical simulations and experimental measurements, which showed good agreement which indicated the metasurface’s capability to control complex wavefronts effectively. Moreover, they tested the ability of the metasurface’s to perform dual-beam deflection and beam focusing and observed that the transmitted x-polarized wave to deflect into two symmetrical beams at angles of approximately ±25° while the transmitted y-polarized wave was focused at a specific point in space. The authors’ findings were consistent with their theoretical predictions and numerical simulations which validated the metasurface’s multifunctional performance. Furthermore, the researchers performed studies to demonstrate the metasurface’s dynamic switching capabilities between different transmission and reflection states so they integrated PIN diodes into the metasurface which allowed them to switch between different operational modes in real-time. When they applied different voltage biases to the PIN diodes the researchers were able to successfully control the TR states of the x/y polarizations independently. They showed that when the PIN diodes were in the “ON” state, the transmitted x- and y-polarized waves were deflected at angles of 0° and 10°, respectively. On the other hand, when the PIN diodes were in the “OFF” state, the reflected x- and y-polarized waves were deflected at angles of 165° and 195°, respectively. Their findings confirmed the metasurface’s ability to switch between different TR states dynamically and provided a level of control that is essential for advanced applications in wireless communication.

The research team performed further experiments to evaluate the capability of the metasurface beam-scan and involved shifting the feed source along the x-axis and were able to scan the transmitted and reflected beams over a range of angles by simply varying the feed position which demonstrates the versatility of the metasurface and its capability to direct electromagnetic waves. An important implication of the research work of Professor Long Li and colleagues is its potential impact advancing wireless communication systems and with the reported ability to dynamically switch between different transmission and reflection states and to control beam direction and shape, the proposed metasurface can be considered as an excellent candidate for next-generation communication networks. For example, with increasing demand for high-capacity, high-speed and reliable communication links in 5G and future 6G networks, the new metasurface technology can be used to optimize signal directionality, reduce interference, and enhance overall system efficiency. Moreover, the metasurface’s capability to generate vortex beams with different OAM modes could be used in target detection, microwave imaging, and secure communication. OAM-based communication can allow multiplexing of multiple data streams onto a single carrier wave which increases data transmission capacity and showcase the new technology for high-bandwidth communication systems. In addition to the use in communication, the authors’ findings can be used in radar systems, remote sensing, and wireless power transfer because the demonstrated ability to precisely control beam focusing and deflection can improve the accuracy and efficiency of radar systems and also the capability to manipulate electromagnetic waves in full space can enhance the performance of wireless power transfer systems. In conclusion, the work of Professor Long Li and team in metasurface technologies opens up new possibilities for a wide range of applications specially in wireless communication.