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Abstract
Metasurfaces have shown extraordinary capability in individually manipulating various electromagnetic (EM) properties, including polarization, phase, and amplitude. However, it is still a challenge to manipulate these EM properties in one metasurface simultaneously. In this paper, a programmable multifunctional metasurface (PMFMS) is demonstrated with polarization, phase, and amplitude manipulation abilities. By controlling tunable coding states and changing the direction of incident waves, the PMFMS can operate as a transmission cross-polarization converter, spatial wave manipulator, and low-RCS radome. Besides, the PMFMS possesses an ultra-wideband property, which can operate from 6.5 to 10.2 GHz with 44.3% relative bandwidth. More importantly, multiple functionalities can also be achieved in reflection operating mode by reassembling the PMFMS. As a proof of concept, the PMFMS is fabricated and experimentally verified. Measured results are in good agreement with simulated results. Benefiting from multifunctional EM manipulations in an ultra-wideband, such a design can be applied in wireless communication systems, radar detection, and EM stealth platform.
© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Metasurfaces, as periodic or quasi-periodic planar artificial materials, have the extraordinary capability to manipulate electromagnetic (EM) waves. Compared with three-dimensional metamaterials [1–6], metasurfaces possess the characteristics of low profile, reduced mass, simplified fabrication, and accessible design. In the past decades, metasurfaces have been extensively investigated in scientific research and engineering applications [7–14].
As substantial research progress, coding metasurface provides a novel strategy to manipulate EM wave digitally [15]. From then on, a connection between EM metasurfaces and information coding theories is built. The design, optimization, and application of coding metasurfaces have drawn much attention [16–20]. Various novel EM functionalities are realized through designing coding metasurfaces. With the deepening of research, scholars are no longer satisfied with designing several independent metasurfaces to achieve multiple functionalities. Various EM functionalities are attempted to be integrated with one metasurface, and multifunctional metasurfaces attract more and more attention. Although multifunctional integration inevitably leads to greater design difficulties, multifunctional metasurfaces possess a wide range of application values and are urgently required in miniaturized systems [21–29]. For example, by changing the polarization and direction of incident waves, a passive multifunctional metasurface for simultaneous reflection and transmission phase coding in the same band is demonstrated [24]. Besides, multiple functionalities in several different operating bands can also be integrated with one fixed metasurface [26,27].
Evolved from passive multifunctional metasurfaces, active multifunctional metasurfaces are employed with tunable devices to implement real-time electronic manipulation among diverse functionalities [30–43]. On the one hand, different functionalities of one kind of EM property can be electronically switched. For example, programmable reflection-transmission metasurfaces for phase manipulation are presented to realize arbitrary reflection or transmission phase coding [36–38]. For polarization manipulation, an active multifunctional metasurface with switchable functionalities between polarization conversion and polarization separator is presented [39]. On the other hand, active multifunctional metasurfaces show great superiority in simultaneously manipulating different EM properties, including polarization, phase, and amplitude. In [40], under the illumination of different polarized incident waves, an active multifunctional metasurface for reflection phase and amplitude manipulations in two separate bands is demonstrated. In the open literature, more programmable metasurfaces are demonstrated to manipulate phase and polarization simultaneously. For instance, an all-in-one integrated multifunctional metasurface using reflected polarization conversion meta-atom is proposed to implement signal processing, polarization conversion, beam manipulation, and near-field sensing [41]. Based on manipulating reflection phase and polarization, multi-band and dual-polarized reconfigurable metasurfaces for multifunctional applications are manifested in [42] and [43], respectively.
Although existing active multifunctional metasurfaces can manipulate one or two different EM properties, it is still a challenge to simultaneously manipulate three important EM properties, including polarization, phase, and amplitude (Table 1). Furthermore, attainable multiple functionalities are usually limited to one or several divided bands, and few previous studies can integrate multifarious functionalities in a shared ultra-wideband.
Table 1. Comparison of state-of-the-art active multifunctional metasurfaces in the literature
In this paper, we propose an ultra-wideband programmable multifunctional metasurface (PMFMS), which can manipulate EM wave polarization, phase, and amplitude, by controlling tunable coding states and changing the direction of incident waves. Owing to its diverse EM manipulation capabilities, the PMFMS can operate as a transmission cross-polarization converter, spatial wave manipulator, and low-RCS radome. It should be noted that the proposed functionalities can also be achieved in reflection operating mode by reassembling the PMFMS. To the best of our knowledge, ultra-wideband manipulations of polarization, phase, and amplitude in one programmable metasurface are presented for the first time.
2. Metasurface design
A conceptual illustration of the proposed PMFMS is depicted in Fig. 1(a). Depending on tunable 1-bit coding states and the direction of incident waves, the PMFMS can realize polarization (F1), phase (F2), and amplitude (F3) manipulations in transmission operating mode. When all programmable meta-atoms are provided with the same bias voltages, the PMFMS works as a polarization converter to implement cross-polarization transmission for the y-polarized incident wave along + z-axis direction. Moreover, each programmable meta-atom can be independently controlled for a 1-bit transmission phase shift. Real-time spatial wave manipulation can be implemented by changing the phase coding states of PMFMS. At the same time, for the y-polarized incident wave along -z-axis direction, the PMFMS works as an analog circuit absorber to effectively weaken the reflection amplitude.
Fig. 1. The sketch of the proposed PMFMS and its functionalities. (a) Conceptual illustration of multiple functionalities. (b) Geometry of absorber layer. R1 = 70 Ω, R2 = 100 Ω, R3 = 100 Ω, and R4 = 15 Ω. (c) Geometry of PPC layer. (d) Perspective view of meta-atom. (e) Detailed structure of meta-atom. Geometrical parameters are provided as h = 2.5 mm, l1 = 11.5 mm, l2 = 10.8 mm, l3 = 9.7 mm, l4 = 9.5 mm, p = 12 mm, w1 = 8.5 mm, w2 = 8.5 mm, w3 = 6.6 mm, w4 = 1.7 mm, r1 = 1 mm, r2 = 0.3 mm, r3 = 0.2 mm, d1 = 1.0 mm, d2 = 0.4 mm, d3 = 0.2 mm. (f) Equivalent series circuits of PIN diode in ON and OFF states. Ron = 1 Ω, L = 450 pH, Roff = 10 Ω, and C = 0.086 pF. (g) The distribution of induced current with or without T-shaped bias structure. (h) Partial magnification of T-shaped bias structure.
The structural design of programmable meta-atom is the key to achieving multifunctional operation. The meta-atom consists of two functional layers (Layer I and Layer II) separated by an air layer, as shown in Fig. 1(d). F4B substrates (ɛr = 2.55, tanδ=0.0009, h1 = 2.0 mm) are utilized in two functional layers. The top and bottom metal coatings with 0.035 mm thickness are engraved on substrates. One functional layer (Layer I) serves as an absorber, and the other functional layer (Layer II) realizes programmable polarization conversion (PPC).
Resistor-embedded metal strips, substrate, and metal grating make up an absorber layer (Layer I), as shown in Fig. 1(b). The metal grating and strips are all along y-axis direction. Under the illumination of y-polarized incident wave along -z-axis direction, the resistor-embedded metal strips dissipate EM wave energy, and the metal grating serves as a ground (GND). Due to the selective polarization permeability of metal grating and strips, the x-polarized wave can transmit through the absorber layer along + z and -z-axis directions.
As depicted in Fig. 1(c), the PPC layer (Layer II) comprises a square patch embedded with two PIN diodes (SMP1340-040LF), substrate, and metal grating along x-axis direction. The tunable meta-atom can be electronically switched between two operating states. State-1) PIN 1 is ON, and PIN 2 is OFF; State-2) PIN 1 is OFF, and PIN 2 is ON. Diodes in ON and OFF states are modeled as different series circuits, as exhibited in Fig. 1(f). Hence, the square patch embedded with two inverted diodes is equivalent to an anisotropic structure to realize programmable polarization conversion. The metal grating of the PPC layer works as the biasing lines and GND for diodes. Herein, a grating-based T-shaped bias structure is proposed to ensure separate control of all meta-atom. Two inductors (10 nH) are employed in the T-shaped structure to achieve radio frequency (RF) and direct current (DC) circuit isolation. Figure 1(g) suggests that the added grating-based T-shaped bias structure does not affect RF current distribution at 9 GHz.
3. Principles for multifunctional manipulations
This section studies the principles of multifunctional EM manipulations through theoretical calculation and numerical simulation. Multiple interference scattering processes, polarization decomposition theory, and equivalent circuit model are performed to illustrate the underlying principle of polarization, phase, and amplitude manipulations, respectively.
3.1 F1: transmission polarization manipulation
We first analyze the single PPC layer as a basis for exploring the multilayered meta-atom. When the x-polarized excitation wave (E2x) illuminates to a single PPC layer, the equivalent anisotropic structure decomposes the E2x into y-polarized transmission wave (T1y), x-polarized reflection wave (R2x), and y-polarized reflection wave (R2y), as shown in Fig. 2(a). Through numerical simulation with periodic boundary conditions, the amplitudes of each component are depicted in Fig. 2(e). With a large proportion of reflection components, the cross-polarization transmission efficiency of a single PPC layer is relatively low.
Fig. 2. Principle analysis for multifunctional manipulation. (a) Conceptual illustration of a single PPC layer operation. (b) Schematic illustration of multiple interference scattering processes in a resonant cavity. (c) Co-polarization reflection component. (d) Cross-polarization transmission component. (e) Simulated results of single PPC layer. (f) A comparison between theoretical calculation and numerical simulation. (g) Cross-polarization transmission amplitudes of different bias lines. (h) Switchable transmission phase. (i) Equivalent circuit model of absorber layer. (j) The comparison between ECM calculation and numerical simulation of absorber layer.
In order to design a high-efficiency meta-atom, an absorber layer is combined with the PPC layer to form a resonant cavity. In this way, the metal gratings of the absorber and PPC layers do not just serve as GND and bias lines. More importantly, metal gratings of two functional layers are orthogonal to each other and form a Fabry-Pérot-like resonant cavity [44]. Multiple interference scattering processes in the resonant cavity can illustrate the underlying operating principle of high-efficiency cross-polarization transmission in an ultra-wideband, as shown in Fig. 2(b). We use transfer matrixes to calculate the multiple interference scattering processes.
Suppose the x-polarized excitation wave (E2x) illuminating to the proposed meta-atom along -z-axis direction, as shown in Fig. 2(b). After the E2x first penetrates through the absorber layer, the initial EM component in the air layer can be expressed as:
For simplicity and without loss of generality, we use $E_{}^{air,i}$ to represent the EM wave component in the air layer of i-th interference process (i = 1, 2, 3…). The $E_{}^{air,i}$ will be divided into two components. One component transmits through the PPC layer along -z-axis direction, and the other component is reflected by the PPC layer along + z-axis direction. The transmission component in port 1 can be written as:
Then, the reflection component is divided into two parts by absorber layer. One part penetrates through the absorber layer along + z-axis direction in port 2:
The other part is reflected again by absorber layer along -z-axis direction:
Finally, after i-th interference process, the total reflection component in port 2 is expressed as:
The total transmission component in port 1 is expressed as:
Due to the selective polarization permeability of metal gratings, the transmission component is only $T_{1y}^i$, and the reflection component is only $R_{2x}^i$. When the air layer is determined at an appropriate height, the multiple interferences of $T_{1y}^i$ and $R_{2x}^i$ are enhanced and reduced, respectively. Transfer matrixes obtained through numerical simulations are substituted into the above equations, and visible amplitude superposition processes are shown in Fig. 2(c) and Fig. 2(d). Apparently, the initial values of ∑$R_{2x}^i$ and ∑$T_{1y}^i$ are identical to R2x and T1y in Fig. 2(e), which suggests that a single PPC layer is equivalent to the initial state of the multiple interference scattering processes. After approximate sixth coupling, the meta-atom demonstrates a stable and high-efficiency cross-polarization transmission performance. The results of the theoretical calculation are in good agreement with the numerical simulation in HFSS, as shown in Fig. 2(f). The bandwidth with cross-polarization transmission amplitude above 80% is from 6.5 GHz to 10.2 GHz, and the relative bandwidth reaches 44.3%. One conclusion can be drawn: the resonant cavity is a key to realize high-efficiency cross-polarization transmission.
3.2 F2: transmission phase manipulation
For a phase programmable metasurface, all meta-atoms are controlled using different bias lines, as shown in Fig. 1(h). Thanks to the excellent isolation between RF and DC structures, the cross-polarization transmission amplitudes of different bias lines are perfectly coincident, as demonstrated in Fig. 2(g).
By changing the bias voltages of diodes, the 1-bit transmission phase can be manipulated dynamically between State-1 and State-2 within the operating band of high-efficiency cross-polarization transmission, as illustrated in Fig. 2(h). Due to the equivalent anisotropic structures in State-1 and State-2 mirrored symmetrically, the amplitude responses are the same in State-1 and State-2. The detailed phase manipulation principle can be revealed by using polarization decomposition theory, as depicted in Fig. S1 (Supplement 1).
3.3 F3: amplitude manipulation
Working as an important part of resonant cavity, the absorber layer can not only improve cross-polarization transmission efficiency but also be utilized to weaken the reflection amplitude of the incident wave. Under the illumination of y-polarized incident wave along -z-axis direction, the resistor-embedded metal strips dissipate EM wave energy. To coincide with the operating band of cross-polarization transmission, the geometrical parameter of the absorber layer is elaborately determined, which is presented in Supplement 1, Fig. S2.
First of all, an equivalent circuit model (ECM) is constructed to analyze the operation mechanism of absorber, as shown in Fig. 2(i). The metal grating of the absorber serves as a GND. Resistor-embedded metal strips can be equivalent to a series RLC circuits. The dielectric substrate is equivalent to an admittance $- j{Y_0}\cot {\beta _2}h$. The input admittance (Yin) and input impedance (Zin) of the equivalent circuit can be written by the following formulas:
Then, a part of equivalent circuit parameters in ECM are analyzed. Due to the metal strips being parallel to each other, the equivalent capacitance C1 is relatively tiny. The initial values of L1 and C1 have been studied in [45]. C2 represents a capacitor formed between metal strips and metal grating.
Finally, the proposed ECM is constructed in the advanced design system (ADS). The fitting module is used to obtain the other circuit parameters. As a result, the ECM calculation is conducted using the following values: C1 = 0.02 pF, R1 = 285 Ω, L1 = 11.5 nH, and C2 = 0.11 pF. Figure 2(j) shows a good agreement between the theoretical calculation and numerical simulation. The bandwidth for at least 5-dB reflection amplitude reduction is 6.5-10.3 GHz, and the relative bandwidth reaches 45.2%.
4. Operation in reflection mode
According to the principle of polarization manipulation mentioned above, the Fabry-Pérot-like resonant cavity is the key to achieve high-efficiency cross-polarization transmission. Hence, we predict that when the resonant cavity is moved to the other side of the PPC layer, the PMFMS can also work in reflection mode.
Due to the absorber layer and PPC layer being separated by an air layer, the absorber layer can be rotated 180° along x-axis, as shown in Fig. 3(b). In this way, the metal grating of the absorber layer works as a GND for y-polarized transmission wave, and a Fabry-Pérot-like resonant cavity is formed behind the PPC layer, as plotted in Fig. 3(c). Multiple interference scattering processes can also illustrate the reflection-mode operation principle. Under the illumination of x-polarized excitation wave (E2x), T1y penetrating through the PPC layer is totally reflected by the metal grating of the absorber layer. Then, the reflected T1y is decomposed by the PPC layer. After multiple interference scattering processes, the interferences of cross-polarization component ($R_{2y}^i$) and co-polarization component ($R_{2x}^i$) are enhanced and reduced, respectively. Figure 3(d) and Fig. 3(e) depict the calculated amplitude superposition processes. The initial values of ∑$R_{2y}^i$ and ∑$R_{2x}^i$ are identical to R2y and R2x in Fig. 2(e), which suggests that a single PPC layer is equivalent to the initial state of the multiple reflected interference processes. After the approximate fifth coupling, the meta-atom demonstrates a stable and high-efficiency cross-polarization reflection performance. Based on the similar operation principle of transmission mode, polarization, phase, and amplitude manipulations can also be achieved in reflection mode, as shown in Fig. 3(f). Besides, according to the cross-polarization reflection principle, polarization and phase can be manipulated for both x- and y-polarized incident waves.
Fig. 3. The meta-atom operating in reflection mode. (a) The transmission meta-atom. (b) The reflection meta-atom. (c) Schematic illustration of reflected multiple interference scattering processes. (d) Visible amplitude superposition processes of co-polarization reflection component. (e) Visible amplitude superposition processes of cross-polarization reflection component. (f) Conceptual illustration of multiple functionalities in reflection mode.
All in all, the air layer possesses three functions. 1) The air layer is an important part of resonant cavity. 2) The air layer provides space for welding the PIN diodes and inductors. 3) The air layer is for the convenience of changing the position of the absorbing layer for reassembling the metasurface to reflection operation.
5. Multifunctional application and experimental verification
In this section, a PMFMS composed of 16 × 16 proposed meta-atoms is presented. The PMFMS working as a polarization converter, programmable spatial wave manipulator, and low-RCS radome is verified by simulation and experiment. By changing the assembly position of the absorber layer, the PMFMS operating in reflection mode is also verified by measurement.
The full-wave simulation is carried out in the CST microwave studio. When all meta-atoms are switched in State-1 (or State-2), the PMFMS can operate as a transmission cross-polarization converter. Figure 4(a) and Fig. 4(b) show that the proposed PMFMS converts the y-polarized incident wave into x-polarized transmission wave with high transmissivity.
Fig. 4. The PMFMS works as a transmission cross-polarization converter, spatial wave manipulator, and low-RCS radome. (a) High-efficiency plane wave transmission. (b) The y-polarized incident wave is converted into x-polarized wave. (c) The spherical wave is focused by PMFMS at 0°. (d) Steerable beam scanning at 30°. (e) A simulated 3D scattering pattern without resistor-embedded metal strips. (f) A simulated 3D scattering pattern with resistor-embedded metal strips.
By separately controlling the 1-bit phase state of meta-atoms, the PMFMS can be used as a real-time programmable spatial wave manipulator. According to coding metasurface theory, dynamically changing the phase distribution can realize diverse functionalities, including beam scanning, beam shaping, vortex electromagnetic wave generation, etc. Herein, the beam scanning functionality is demonstrated for simplicity. Predesigned beam scanning directions are at 0° and 30°. Required phase distributions are calculated by using antenna array theory, as shown in Supplement 1, Fig. S5. The PMFMS is fed by a horn antenna. Through full-wave simulation, Fig. 4(c) and Fig. 4(d) demonstrate that spherical waves radiated by the horn antenna are converted into a plane wave in predefined directions.
Under the illumination of the y-polarized detection wave along -z-axis direction, the PMFMS can be used as a low-RCS radome. As an essential ingredient of the Fabry-Pérot-like resonant cavity, the y-direction metal grating of the absorber layer performs as a metal plane for y-polarized detection wave, as shown in Fig. 4(e). After loading the resistor-embedded metal strips, the reflection amplitude decreases obviously, as depicted in Fig. 4(f). Hence, the operation mechanism of the low-RCS radome is based on the resistor-embedded metal strips of absorber layer. It is worthwhile to point out that due to the selective polarization permeability of metal strips, the resistor-embedded metal strips do not generate any effect on the transmission performance.
To validate our design, a 16 × 16 PMFMS is fabricated and assembled, as shown in Fig. 5(a) and Fig. 5(b). The bias lines are connected to 32 8-pin connectors placed at the edges of the PPC layer. Several nylon screws control the height of the air layer. Fabricated PMFMS communicates with a 16 × 16 field-programmable gate array (FPGA) through 32 flat cables. Transmission measurement system (Fig. 5(c)), reflection measurement system (Fig. 5(d)), and far-field measurement system (Fig. 5(e)) are utilized to verify multiple functionalities in an anechoic chamber. A 10-dBi standard horn antenna is used as a feeding source in the far-field measurement. Meanwhile, the polarization of receive antenna and feeding antenna are orthogonal to receive cross-polarization transmission EM waves. During the reflected amplitude measurement, the minimum incidence angles of two mechanical arms are 10°. Hence, we use the oblique incidence of 10° to approximate the vertical illumination. The time-domain gate technique is applied to filter out multipath interference signals in experiment.
Fig. 5. Experimental verification in an anechoic chamber. (a) Photograph of the fabricated PMFMS. (b) The assembled sample. (c) Transmission measurement system (d) Reflection measurement system (e) Far-field measurement system. (f) The simulated and measured cross-polarization transmission amplitude. (g) The simulated and measured beam scanning at 0°, 30°, and 60°. (h) The simulated and measured amplitude manipulation. (i) The simulated and measured cross-polarization amplitude in reflection mode.
When the PMFMS operates as a transmission cross-polarization converter (F1), Fig. 5(f) shows that the measured cross-polarization transmission amplitude keeps above 0.8 in the ultra-wideband. As a programmable spatial wave manipulator (F2), the PMFMS realizes real-time beam scanning in prescribed directions (0°, 30°, and 60°). The measured scanning loss of 30° is only 0.9 dB, as depicted in Fig. 5(g). Moreover, the beam can scan to 60° with high directivity. As a low-RCS radome (F3), the PMFMS possesses an excellent absorption effect, as demonstrated in Fig. 5(h). When the absorber layer is reassembled to the other side of the PPC layer, the PMFMS operates in reflection mode and achieves cross-polarization reflection. The simulated and measured cross-polarization reflection amplitude are plotted in Fig. 5(i). Due to processing, assembly, and experiment errors, the inconsistency between the measured and simulated results is within the allowable range. The multiple functionalities of the proposed PMFMS are demonstrated experimentally.
6. Conclusion
In summary, we demonstrated an ultra-wideband PMFMS with polarization, phase, and amplitude manipulation abilities. A thorough analysis, including theoretical calculation and numerical simulation, is carried out to explore the multifunctional working mechanism. Multiple interference scattering processes, polarization decomposition theory, and equivalent circuit model are performed to illustrate the underlying principle of polarization, phase, and amplitude manipulations, respectively. The full-wave simulation suggests that by dynamically switching coding states, changing the direction of incident waves, and reassembling two functional layers, the PMFMS can operate in both transmission and reflection modes as a cross-polarization converter, spatial wave manipulator, and low-RCS radome. As a proof of concept, the PMFMS is fabricated and experimentally verified in an anechoic chamber. The measured results are in good agreement with theoretical analysis and simulated results. Compared with other multifunctional metasurfaces, the proposed PMFMS possesses more diverse functionalities and a wider operating band, which can be utilized in wireless communication systems, radar detection, and EM stealth platform.
Funding
Natural Science Basic Research Program of Shaanxi Province (2020022, 20210110, 20220104, 2022JM-319, 2022JQ-685); National Natural Science Foundation of China (62171460, 62371466).
Disclosures
The authors declare that there are no conflicts of interest related to this article.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
Supplemental document
See Supplement 1 for supporting content.
References
1. H.N.S. Krishnamoorthy, G. Adamo, J. Yin, V. Savinov, N. I. Zheludev, and C. Soci, “Infrared dielectric metamaterials from high refractive index chalcogenides,” Nat. Commun. 11(1), 1692 (2020). [CrossRef]
2. X. Fang, J. Wen, L. Cheng, D. Yu, H. Zhang, and P. Gumbsch, “Programmable gear-based mechanical metamaterials,” Nat. Mater. 21(8), 869–876 (2022). [CrossRef]
3. M. Sakovsky, J. Negele, and J. Costantine, “Electromagnetic reconfiguration using stretchable mechanical metamaterials,” Adv. Sci. 10(6), 2203376 (2023). [CrossRef]
4. H. Lin, Y. Wu, J. Xiong, R. Zhou, Q. Li, and R. Tang, “Dual-polarized bidirectional three-dimensional metamaterial absorber with transmission windows,” Opt. Express 29(25), 40770–40780 (2021). [CrossRef]
5. N. Han, J. Liu, Y. Gao, K. Zhou, and S. Liu, “Topologically protected and highly localized surface waves in gyro-electromagnetic metamaterials,” Ann. Phys. 532(8), 2000022 (2020). [CrossRef]
6. D. Han, L. Zhang, and X. Chen, “Mechanical modulation of multifunctional responses in three-dimensional terahertz metamaterials,” Opt. Express 29(21), 32853–32864 (2021). [CrossRef]
7. H. F. Ma, G. Z. Wang, G. S. Kong, and T. J. Cui, “Broadband circular and linear polarization conversions realized by thin birefringent reflective metasurfaces,” Opt. Mater. Express 4(8), 1717–1724 (2014). [CrossRef]
8. H. Lv, Z. Yang, H. Xu, L. Wang, and R. Wu, “An electrical switch-driven flexible electromagnetic absorber,” Adv. Funct. Mater. 30(4), 1907251 (2020). [CrossRef]
9. Y. Li, Z. Liu, H. Zhang, P. Tang, B. Wu, and G. Liu, “Ultra-broadband perfect absorber utilizing refractory materials in metal-insulator composite multilayer stacks,” Opt. Express 27(8), 11809–11818 (2019). [CrossRef]
10. H. Yang, T. Li, L. Xu, X. Cao, L. Jidi, Z. Guo, P. Li, and J. Gao, “Low in-band-RCS antennas based on anisotropic metasurface using a novel integration method,” IEEE Trans. Antennas Propagat. 69(3), 1239–1248 (2021). [CrossRef]
11. Z. Sun, J. Zhi, Y. Chen, B. Xu, Z. Qiu, X. Wang, and X. Yu, “A complex amplitude control method of metasurface based on full phase modulation,” Results Phys. 47, 106382 (2023). [CrossRef]
12. S. J. Li, B. W. Han, Z. Y. Li, X. B. Liu, G. S. Huang, R. Q. Li, and X. Y. Cao, “Transmissive coding metasurface with dual-circularly polarized multi-beam,” Opt. Express 30(15), 26362–26376 (2022). [CrossRef]
13. K. Huang, H. Liu, G. Si, Q. Wang, J. Lin, and J. Teng, “Photon-nanosieve for ultrabroadband and large-angle-of-view holograms,” Laser Photonics Rev. 11(3), 1700025 (2017). [CrossRef]
14. G. Zheng, G. Liu, M. G. Kenney, Z. P. Li, A. He, S. Li, Z. Ren, and Q. Deng, “Ultracompact high-efficiency polarising beam splitter based on silicon nanobrick arrays,” Opt. Express 24(6), 6749–6757 (2016). [CrossRef]
15. T. J. Cui, M. Q. Qi, X. Wan, J. Zhao, and Q. Cheng, “Coding metamaterials, digital metamaterials and programmable metamaterials,” Light: Sci. Appl. 3(10), e218 (2014). [CrossRef]
16. X. Liu, S. Li, C. He, Z. Li, G. Huang, and X. Cao, “Multiple orbital angular momentum beams with high-purity of transmission-coding metasurface,” Adv. Theory Simul. 6(4), 2200842 (2023). [CrossRef]
17. H. Yang, X. Cao, F. Yang, J. Gao, S. Xu, M. Li, X. Chen, Y. Zhao, and Y. Zheng, “A programmable metasurface with dynamic polarization, scattering and focusing control,” Sci. Rep. 6(1), 35692 (2016). [CrossRef]
18. K. Chen, Y. Feng, F. Monticone, J. Zhao, B. Zhu, T. Jiang, L. Zhang, Y. Kim, X. Ding, S. Zhang, A. Alù, and C. W. Qiu, “A reconfigurable active Huygens’ metalens,” Adv. Mater. 29(17), 1606422 (2017). [CrossRef]
19. S. Li, Z. Li, X. Liu, C. He, G. Huang, R. Li, and X. Cao, “Transmissive digital coding metasurfaces for polarization-dependent dual-mode quad orbital angular momentum beams,” ACS Appl. Mater. Interfaces 15(19), 23690–23700 (2023). [CrossRef]
20. H. Zhao, Y. Shuang, M. Wei, T. J. Cui, P. D. Hougne, and L. Li, “Metasurface-assisted massive backscatter wireless communication with commodity Wi-Fi signals,” Nat. Commun. 11(1), 3926 (2020). [CrossRef]
21. Y. Jing, Y. Li, J. Zhang, J. Wang, M. Feng, H. Ma, and S. Qu, “Full-space-manipulated multifunctional coding metasurface based on “Fabry-Pérot-like” cavity,” Opt. Express 27(15), 21520–21531 (2019). [CrossRef]
22. J. Li and C. Zhou, “Multifunctional reflective dielectric metasurface in the terahertz region,” Opt. Express 28(15), 22679–22689 (2020). [CrossRef]
23. W. Tang, M. Chen, J. Dai, Y. Zeng, X. Zhao, S. Jin, Q. Cheng, and T. Cui, “Wireless communications with programmable metasurface: new paradigms, opportunities, and challenges on transceiver design,” IEEE Wirel. Commun. 27(2), 180–187 (2020). [CrossRef]
24. L. Zhang, R. Wu, G. Bai, H. Wu, Q. Ma, X. Chen, and T. Cui, “Transmission-reflection-integrated multifunctional coding metasurface for full-space controls of electromagnetic waves,” Adv. Funct. Mater. 28(33), 1802205 (2018). [CrossRef]
25. X. He, L. Deng, Y. Yang, and B. Feng, “Multifunctional ultrathin reflective metasurface via polarization-decoupled phase for arbitrary circularly or elliptically polarized waves,” Opt. Express 29(8), 12736–12749 (2021). [CrossRef]
26. J. Chen, W. Li, Y. Zhang, W. Ma, W. Tang, and T. Cui, “Absorption-transmission-type multifunctional coding metasurface,” J. Phys. D: Appl. Phys. 55(40), 405003 (2022). [CrossRef]
27. Q. Lv, C. Jin, B. Zhang, and Z. Shen, “Hybrid absorptive-diffusive frequency selective radome,” IEEE Trans. Antennas Propag. 69(6), 3312–3321 (2021). [CrossRef]
28. Z. Li, R. Yang, J. Wang, Y. Zhao, J. Tian, and W. Zhang, “Multifunctional metasurface for broadband absorption, linear and circular polarization conversions,” Opt. Mater. Express 11(10), 3507–3519 (2021). [CrossRef]
29. Y. Guo, S. Zhang, M. Pu, Q. He, J. Jin, M. Xu, Y. Zhang, P. Gao, and X. Luo, “Spin-decoupled metasurface for simultaneous detection of spin and orbital angular momenta via momentum transformation,” Light: Sci. Appl. 10(1), 63 (2021). [CrossRef]
30. Z. Li, C. Jiang, K. Wang, M. Liu, C. Li, C. Tian, H. Zhang, and Y. Zhang, “Active manipulation of Dirac semimetals supported chiral coding metasurfaces for multifunctional applications in terahertz region,” Results Phys. 46, 106323 (2023). [CrossRef]
31. H. Wang, H. Ma, M. Chen, S. Sun, and T. Cui, “A reconfigurable multifunctional metasurface for full-space control of electromagnetic waves,” Adv. Funct. Mater. 31(25), 2100275 (2021). [CrossRef]
32. J. Liao, S. Guo, L. Yuan, C. Ji, C. Huang, and X. Luo, “Independent manipulation of reflection amplitude and phase by a single-layer reconfigurable metasurface,” Adv. Opt. Mater. 10(4), 2101551 (2022). [CrossRef]
33. Y. She, C. Ji, C. Huang, Z. Zhang, J. Liao, J. Wang, and X. Luo, “Intelligent reconfigurable metasurface for self-adaptively electromagnetic functionality switching,” Photonics Res. 10(3), 769–776 (2022). [CrossRef]
34. Z. Qin, Y. Li, H. Wang, C. Li, C. Liu, Z. Zhu, Q. Yuan, J. Wang, and S. Qu, “Transmission reflection integrated programmable metasurface for real-time beam control and high efficiency transmission polarization conversion,” Ann. Phys. 535(1), 2200368 (2023). [CrossRef]
35. R. Phon, M. Lee, C. Lor, and S. Lim, “Multifunctional reflective metasurface to independently and simultaneously control amplitude and phase with frequency tunability,” Adv. Opt. Mater. 11, 2202943 (2023). [CrossRef]
36. L. Bao, Q. Ma, R. Wu, X. Fu, J. Wu, and T Cui, “Programmable reflection-transmission shared-aperture metasurface for real-time control of electromagnetic waves in full space,” Adv. Sci. 8(15), 2100149 (2021). [CrossRef]
37. Q. Hu, J. Zhao, K. Chen, K. Qu, W. Yang, J. Zhao, T. Jiang, and Y. Feng, “An intelligent programmable omni-metasurface,” Laser Photonics Rev. 16(6), 2100718 (2022). [CrossRef]
38. H. Yu, P. Li, J. Su, Z. Li, S. Xu, and F. Yang, “Reconfigurable bidirectional beam-steering aperture with transmitarray, reflectarray, and transmit-reflect-array modes switching,” IEEE Trans. Antennas Propag. 71(1), 581–595 (2023). [CrossRef]
39. Y. Li, Q. Cao, and Y. Wang, “Li Y, Cao Q, Wang Y. A wideband multifunctional multilayer switchable linear polarization metasurface,” Antennas Wirel. Propag. Lett. 17(7), 1314–1318 (2018). [CrossRef]
40. Y. Saifullah, G. Yang, Y. Lee, and F. Xu, “Multifunctional programmable metasurface for flexible control of EM wave scattering and absorption,” IEEE MTT-S International Wireless Symposium. 1, 1–3 (2020). [CrossRef]
41. B. Liu, J. Du, X. Jiang, Y. Li, S. Wong, Q. Cheng, T. Cui, and Q. Zhang, “All-In-One integrated multifunctional broadband metasurface for analogue signal processing, polarization conversion, beam manipulation, and near-Field Sensing,” Adv. Opt. Mater. 10(20), 2201217 (2022). [CrossRef]
42. C. Huang, C. Zhang, J. Yang, B. Sun, B. Zhao, and X. Luo, “Reconfigurable metasurface for multifunctional control of electromagnetic waves,” Adv. Opt. Mater. 5(22), 1700485 (2017). [CrossRef]
43. M. Wang, D. Liao, J. Dai, and C. Chan, “Dual-polarized reconfigurable metasurface for multifunctional control of electromagnetic waves,” IEEE Trans. Antennas Propag. 70(6), 4539–4548 (2022). [CrossRef]
44. N. K. Grady, J. E. Heyes, D. R. Chowdhury, Y. Zeng, M. T. Reiten, A. K. Azad, A. J. Taylor, D.A. R. Dalvit, and H. Chen, “Terahertz metamaterials for linear polarization conversion and anomalous refraction,” Science 340(6138), 1304–1307 (2013). [CrossRef]
45. R. J. Langley and E. A. Parker, “Equivalent circuit model for arrays of square loops,” Electron. Lett. 18(7), 294–296 (1982). [CrossRef]
