Wireless Communications with Programmable Metasurface: New Paradigms, Opportunities, and Challenges on Transceiver Design

Programmable metasurfaces have shown exceptional potentials in wireless communications due to their capability to manipulate electromagnetic (EM) waves dynamically and flexibly. However, the large-scale application and flexible deployment of programmable metasurfaces still face challenges of high communication capacity requirements and stringent energy constraints. Here, we report an ambient-energy-driven space-time-coding metasurface to address these issues. On one hand, the metasurface can achieve efficient space-frequency-division multiplexing manipulations by dynamically controlling multiple frequencies and the spatial propagation directions of reflection EM waves. On the other hand, the shared-aperture ambient solar energy harvesting capability and low power consumption characteristic of the metasurface enable it to be self-powered without relying on any external power supply. To demonstrate these remarkable features, a four-channel wireless communication system prototype is built using the programmable metasurface. Experimental results confirm that four distinct images can be transmitted to four user terminals simultaneously, independently, and in real time with remarkably low energy consumption per bit. Such innovative metasurface provides a simple and effective approach for integrating ambient energy harvesting, multi-dimensional microwave manipulation, and direct information modulation on a single physical platform, which will advance the wireless communications in cost-effectiveness, enhanced capacity, energy efficiency, and environmental friendliness.

Over the past two decades, an extensive research effort has been devoted to elastic metamaterials, structured artificial materials at subwavelength scales, for elastic wave manipulations in solids. Due to the extreme values of material parameters, negative and/or positive, they achieved, the applications can range from wave and/or vibration attenuations, wave guiding and imaging, enhanced sensing, to invisible cloaking. However, conventional passive metamaterials have limitations, i.e. they can only be operated in narrow frequency regions and their functions are usually locked into space or with minor tunabilities once fabricated, lacking real time reconfigurabilities. Those limitations strongly hinder them from practical usages. With the rapid development of smart materials and structures, more and more intelligent elements are being introduced into wave propagation, vibration and sound control systems. The piezoelectric shunting technique is one well known method that receives considerable attention. In this dissertation, by leveraging the circuit control concept, both analog and digital, we propose some circuit controlled active/adaptive/hybrid/programmable metamaterials and metasurfaces for unprecedent elastic wave manipulations. Analytical, numerically and experimentally approaches are combined throughout the dissertation to illustrate design concepts, characterize wave propagation properties, and valid the designs. Specifically, active elastic metamaterials with tunable stiffness in local resonators are first designed for tunable wave and/or vibration mitigations. We then extend this concept to achieve super broadband wave attenuations with frequency-dependent stiffness elements. By introducing the variable stiffness elements to the host medium, a hybrid metamaterial is developed for switched ON/OFF wave propagations and broadband negative refractions. Based on a developed approximate transformation method, an active metamaterial is designed and placed on a plate to achieve spatially varying effective mass densities for broadband elastic trajectory control. Finally, a programmable metasurface with ultrathin-thickness is demonstrated for broadband, real-time and multifunctional wavefront manipulations in a plate. The active, adaptive, hybrid, and programmable elastic metamaterials and/or metasurfaces are still in their infant stages. The examples presented in the dissertation are transformable to different length and time scales and could serve as efficient and powerful tools in exploring some unconventional wave phenomenon in solid structures, i.e. by using concepts in quantum mechanics, where passive approaches are significantly limited. The designs could also immediately open new possibilities in elastic wave control devices including, but not limited to structural health monitoring, stealth technology, active noise control, as well as medical instrumentation and imaging.

Programmable metasurfaces show great application potential in many fields, so studying their radar cross-section reduction (RCSR) characteristics is very important. Metasurfaces based on polarization conversion and artificial magnetic conductors are widely used for RCSR, but they cannot scan beams. Programmable metasurfaces can dynamically steer beams in-band and reduce RCS by changing the phase of electromagnetic waves. But to meet practical needs, they must be stealthy both in-band and out-of-band. This paper presents a low-profile self-stealth programmable metasurface. Self-stealth describes the capability of the metasurface to achieve in-band and out-of-band RCSR through its intrinsic design, without requiring additional structures such as radomes or absorbing materials. The design principle is to achieve out-of-band RCS reduction without increasing the profile height or adding extra radio frequency components. The meta-atom has a positive-intrinsic-negative (PIN) diode to control the in-band ( f 0 ) x -polarization phase. Switching the PIN diode states gives 1-bit phase modulation. The in-band y -polarization uses a bridge design. Changing the size can get 1-bit phase, and the x - and y -polarizations can be adjusted separately. Also, the top layer has 4 cross-shaped dumbbells and 4 branch structures for out-of-band high ( fh 1 ) and low ( fl 1 ) frequencies. The middle layer has four 45° rotated cross-shaped dumbbells and 4 branch structures for out-of-band high ( fh 2 ) and low ( fl 2 ) frequencies. So, the meta-atom can modulate phase across 5 frequency bands ( fl 2 < fl 1 < f 0 < fh 2 < fh 1 ). The profile height is 0.065λ of the in-band center frequency, which is more conducive to conformal design. A 12 × 12 prototype was made. Simulation and measurement show that the metasurface reduces RCS in 5 bands and its in-band radiation can be used in communication transmission mode, which is good for programmable metasurface technology development.

Programmable metasurfaces (PMs) are consisted of reconfigurable digital elements, and electromagnetic properties of the PMs can be manipulated by configuring digital states of these elements. This paper proposes to synthesize multiple beams, sum and difference beams based on a PM. Theoretical calculations validate the functions of the presented PM.

Metasurfaces have been extensively studied for generating electromagnetic waves carrying orbital angular momentum (OAM). In particular, programmable metasurfaces enable real‐time switching between multiple OAM modes in a digital manner. However, the current programmable metasurfaces are mostly based on reflective mode, which suffer from low efficiency as well as serious feed blockage. In this paper, a transmissive programmable metasurface is presented for the highly efficient generation of multimode convergent OAM beams. The proposed transmissive metasurface is composed of electronically reconfigurable units with 1‐bit phase resolution (0/π), which are obtained by integrating two PIN diodes in the radiating layer for current direction modulation. Through the antisymmetry configuration of the two PIN diodes, nearly uniform transmission magnitudes but inversed phase states in a wide band can be obtained. The simulation results show that the proposed reconfigurable unit can achieve good 1‐bit phase tuning, with minimum insertion loss of 0.2 dB and 2 dB transmission bandwidth of more than 10%. Through the dynamic modulation of the quantized code distributions on the metasurface, programmable multimode OAM beams can thus be constructed. Both simulated and measured results verify the effectiveness of the proposed design.

Digital coding and programmable metasurfaces stand out as promising candidates in future wireless communications due to their low costs and fast‐action reprogrammable capability. However, 2 significant obstacles, namely integration and power consumption, must be addressed before large‐scale engineering application of the programmable metasurface. This work proposes an easy‐integration and energy‐saving meta‐system and demonstrates its application in wireless communications. The meta‐system features a hybrid architecture and consists of a programmable feed array and a metasurface lens. The feed array comprises 3 subarrays, in which active elements are doped with passive elements and interconnected configurations are used to efficiently reduce the number of active elements by one‐third. The meta‐lens acts as a passive phase shifter to enhance the beamforming performance, further reducing the number of active elements. Moreover, the meta‐system can switch between different modes to achieve various functions. In particular, the maximum power consumption of the meta‐system is only 54 mW, which can be considered nearly passive. A wireless communication experiment is presented, where the meta‐system simultaneously serves as the direct digital modulator and the transmitting antenna. Owing to the low cost, high integration, and nearly passive and programmable features, the meta‐system has remarkable potential for future applications in wireless communications.

Programmable metasurfaces present significant capabilities in manipulating electromagnetic waves, making them a promising candidate for simultaneous wireless information and power transfer (SWIPT), which has the potential to enable sustainable wireless communication in complex electromagnetic environments. However, challenges remain in terms of maximum power transmission distance and stable phase manipulation with high-power scattered waves. Additionally, waveform limitations restrict average scattered power and rectifier conversion efficiency, affecting data transmission rates and energy transmission distance. Here we show an amplifying programmable metasurface (APM) and a joint modulation method to address these challenges. The APM mitigates the peak-to-average power ratio and improves maximum power, phase response stability, average output power, and rectifier conversion efficiency. Through experimental validation, we demonstrate the feasibility of the SWIPT system, showcasing simultaneous LED array powering and movie video transmission. This innovative SWIPT system holds promise for diverse applications, including 6 G wireless communications, IoT, implanted devices, and cognitive radio networks.

Transmissive programmable metasurface can offer notable benefits for the precise agile manipulation of electromagnetic (EM) waves, which is a promising candidate for radar detection, wireless communications, and spectral imaging. However, most previous studies typically face the challenge of narrow bandwidth and are constrained by relatively simple and single functionality. Here, an ultra‐wideband (UWB) transmissive programmable metasurface is proposed to conduct agile multifunctional EM modulation. The meta‐atom is designed with a butterfly‐shaped configuration and manipulated using two pin diodes, demonstrating high‐efficiency transmission with low insertion loss less than 1 dB and stable phase difference of 180° from 15.77 to 28.59 GHz, ranging from Ku to Ka‐band with a fractional bandwidth up to 57.7%. The transmissive programmable metasurface is further constructed, and its effectiveness for multifunctional EM modulation is verified both numerically and experimentally, which can conduct different functionalities, including near‐field holographic imaging at lower‐frequency Ku‐band and far‐field high‐purity orbital angular momentum (OAM) generation at higher‐frequency Ka‐band. The proposed strategy may enrich the functionalities of programmable metasurfaces, as well as open a new pathway toward UWB multifunctional applications.

Amplitude‐phase programmable metasurfaces (APPMs) have attracted significant attention in recent years for their real‐time control of electromagnetic (EM) waves. However, existing APPMs often face challenges such as low energy efficiency, limited amplitude‐tuning range, and low phase‐modulation resolution. Additionally, achieving high‐precision amplitude and phase modulations simultaneously requires complex control circuits, thereby increasing the system cost and complexity. To address these challenges, an amplifying APPM (AAPPM) is proposed that achieves independent wide‐range amplitude tuning and high‐precision phase control through a novel and simplified architecture. Specifically, the designed AAPPM is embedded with gain‐tunable amplifiers, achieving over 5 dB EM‐energy amplification and ≈30 dB dynamic amplitude‐tuning range. Meanwhile, the AAPPM provides the 1‐bit phase modulations by controlling the states of integrated PIN diodes. With the introduction of time‐coding techniques, it can further achieve wide‐range and high‐precision phase controls of harmonics. To demonstrate its capability, a 6×6 AAPPM prototype is designed, simulated, and measured. The results indicate that AAPPM can achieve EM energy amplification, wide‐range dynamic amplitude control, and high‐precision phase modulation. By implementing various time‐coding strategies, the AAPPM facilitates flexible harmonic beam manipulations. With these distinctive features, the AAPPM shows great potential in wireless communication and radar systems.

With the gradual improvement of the future wireless communication technology, the demand for high information capacity and reliable links in communication systems is also ever-increasing. Programmable topological plasmonic metasurfaces, consisting of artificially engineered structures with robust propagation pathways control, have emerged as a revolutionary technology for stable microwave and on-chip communication systems. Programmable topological plasmonic metasurfaces offer unprecedented flexibility and adaptability in managing multiple communication channels as the propagation paths can be easily reconfigured to meet specific communication requirements. Here, we have experimentally demonstrated the ability to dynamically manipulate electromagnetic waves along eight distinct topological pathways for a multichannel direct communication system. The simulation results of topological plasmonic metasurfaces with different coding schemes have showcased their excellent performance in multichannel wavefront control. Experimental results have consistently aligned with the simulation findings, validating the effectiveness of multichannel topological routes. Furthermore, an eight-channel direct communication system based on a programmable topological plasmonic metasurface is designed and implemented to transmit different information. The proposed multichannel communication system based on a programmable topological plasmonic metasurface opens up new possibilities for high-capacity, efficient, and adaptive communication systems, which hold great potential in transformative applications in areas such as 6G, Internet of Things, and beyond.

Reconfigurable intelligent surfaces (RIS) have attracted significant interest as an enabling technology for future sixth-generation (6G) wireless communication networks. Programmable metasurfaces are a relatively low-cost and lowcomplexity architecture for realizing dynamic RIS arrays. This paper presents the design and simulation of a 128 element programmable metasurface antenna in a reflectarray configuration operating at 6 GHz with direct phase and frequency modulating capability for index modulation. This metasurface is a functional demonstration prototype and tile building block for larger RIS arrays. Specifically, we present full-wave simulation results of a meta-atom with 2-bit quantized phase shifts with an average reflection amplitude loss of 0.34 dB over all coding states. To the best of our knowledge, our 2-bit meta-atom design achieves lower reflection amplitude loss at the design frequency and is electrically thinner than existing designs. Additionally, we present full-wave simulation results of our 128 element RIS finite array performing beam steering and phase modulation.

Metasurfaces have shown unparalleled controllability of electromagnetic (EM) waves. However, most of the metasurfaces need external spatial feeding sources, which renders practical implementation quite challenging. Here, a low-profile programmable metasurface with 0.05λ0 thickness driven by guided waves is proposed to achieve dynamic control of both amplitude and phase simultaneously. The metasurface is fed by a guided wave traveling in a substrate-integrated waveguide, avoiding external spatial sources and complex power divider networks. By manipulating the state of the p-i-n diodes embedded in each meta-atom, the proposed metasurface enables 1-bit amplitude switching between radiating and nonradiating states, as well as a 1-bit phase switching between 0° and 180°. As a proof of concept, two advanced functionalities, namely, low sidelobe-level beam scanning and Airy beam generation, are experimentally demonstrated with a single platform operating in the far- and near-field respectively. Such complex-amplitude, programmable, and low-profile metasurfaces can overcome integration limitations of traditional metasurfaces, and open up new avenues for more accurate and advanced EM wave control within an unprecedented degree of freedom.

Terahertz modulation technology based on programmable metasurfaces can respond in real time to external signals or environmental changes, enabling flexible and adaptive control of terahertz waves. This technology demonstrates significant potential and importance across various fields, including communication, imaging, scientific research, security monitoring, and industrial applications. This paper proposes a terahertz programmable metasurface based on solid-state plasma, utilizing solid-state plasma devices to achieve dynamic control of properties such as the amplitude and phase of terahertz waves. Compared to traditional silicon-based devices, GaAs/AlGaAs heterostructures enhance both the forward current and solid-state plasma concentration of the metasurface devices by two orders of magnitude, with carrier concentrations exceeding 1019 cm-3. Additionally, we designed a solid-state plasma metasurface containing 12×12 supercells, achieving dynamic modulation of terahertz waves in the elevation direction through different coding schemes. Furthermore, this paper explores the stealth control mechanism of solid-state plasma metasurfaces, achieving effective cloaking of detection targets through specific phase compensation.

In this paper, we propose the utilization of a programmable metasurface for flexibly manipulating ambient Wi-Fi signals. First, we propose a new and efficient optimization algorithm CWGS (Complex Weighted Gerchberg-Saxton), which is based on an electromagnetic scattering model of the metasurface. The proposed algorithm quickly redesigns the complex amplitude distribution of the Wi-Fi field bounced off the programmable metasurface to enhance the Wi-Fi signals at desired locations significantly. Second, we fabricated a large-scale programmable metasurface that operates at the 2.4 GHz frequency band. We conducted several experiments using the fabricated metasurface to verify the proposed optimization algorithm’s feasibility and effectiveness. Both the theoretical and experimental results show that the programmable metasurface can dynamically boost Wi-Fi signals at multiple locations. Besides, we experimentally verified that using the developed strategy could improve the Wi-Fi signals by 23.5 dB. The results of our work improve the usability and practicality of the programmable metasurface in real-world applications and pave the way for wireless communications, future smart homes, and other applications.

Programmable metasurfaces incorporating with tunable materials or components are emerging as an attractive option to realize reconfigurable manipulations of electromagnetic (EM) behaviors in real-time. Many efforts have been devoted to the realization of active EM manipulations of the metasurface and significant progress has been achieved, showing their unprecedented ability to arbitrarily manipulate wavefronts in dynamic functions. However, most of the existing multi-beam metasurfaces are based on passive building blocks, only possessing one or a few functions, which cannot provide tunable and independent multi-beam control, thus limiting their further uses in wireless communications. Hence, a 1-bit coding metasurface with high-efficiency, programmable, and independent multi-beam control is proposed in this paper, providing dynamic EM responses with real-time reconfigurability, and controlled by external digital circuits through direct current (DC) bias networks. Specifically, the meta-atom loaded with PIN diodes is employed to achieve independently tunable phase characteristics, thus complex EM functions can be manipulated by redistributing the spatial phases of the metasurface. Symmetric/asymmetric independent dual- and multi-beam manipulations are analyzed theoretically and simulated by EM software. Then as an experimental verification, a metasurface consisting of 14 × 14 meta-atoms is fabricated and tested in a standard microwave anechoic chamber, and the measured results accord well with the simulations. The proposed metasurface has promising ability to generate the arbitrary and independent multi-beams, which may largely enhance the information capacity of the metasurfaces, offering untapped potentials in wireless communication systems.