Multifunctional broadband bidirectional electromagnetic modulation using asymmetrically biased metasurface

Abstract

This paper presents a method of utilizing asymmetrically controlled PIN diodes to design a multifunctional active broadband metasurface with tunable reflectance, transmittance, and absorptance, thereby enabling bidirectional radar cross-section (RCS) control. The metasurface comprises an ABA tri-layer structure with PIN diodes asymmetrically biased in the top and bottom layers, acting as variable impedance elements. An equivalent circuit model (ECM) guides the design to achieve a broad operational bandwidth of 6−14 GHz (~80% fractional bandwidth). By varying the direct current (DC) bias voltage from 0.4 V to 0.6 V, the metasurface supports three operational modes: near-perfect reflection (>95% reflectance), near-perfect absorption (>90% absorptance), and partial transmission, with RCS reductions up to 15 dB for forward and backward incident electromagnetic waves. The fabricated array, controlled by DC biased voltage, demonstrates switchable characteristics across these modes, validated through full-wave simulations and measurements. Compared to conventional tunable metasurfaces, the proposed design offers broader bandwidth and enhanced tunability, making it ideal for electromagnetic shielding, stealth technology, and adaptive wireless systems.

Graphical abstract

Keywords

Bidirectional / broadband / PIN diodes / radar cross section (RCS) / tunable metasurface

1 Introduction

Metasurfaces have garnered increasing attention for their ability to manipulate electromagnetic (EM) wave propagation [1−3]. As a result, they have facilitated a wide variety of functional devices, including antennas [4−6], polarization converters [7−11], vortex beam generators [12, 13], absorbers [14−19], among others [20]. In addition to these applications, metasurfaces have emerged as effective solutions for reducing radar cross section (RCS) by absorbing or redirecting incident energy, while simultaneously preserving desirable functionalities for communication and sensing systems [21−26]. Nevertheless, these metasurfaces are predominantly passive, resulting in fixed functionalities and limited adaptability.

To overcome the limitations of passive metasurfaces with fixed functionalities, active metasurfaces incorporating tunable components have been proposed, offering dynamic and real-time control over EM wave propagation. This reconfigurability enables these structures to adapt to varying operational environments and meet mission-specific requirements, thereby addressing the growing demand for multifunctional and broadband stealth applications [27−38]. A variety of tunable mechanisms have been explored in recent years. For instance, metasurfaces with intensity-dependent characteristics have shown potential for responsive surface-wave suppression [39]. An ultrawideband and flexible metamaterial absorber based on a lossy stepped-impedance resonator has been demonstrated, in which the integration of voltage-controlled PIN diodes enables tunable absorption intensity while maintaining broadband performance [40]. Polarization-insensitive designs further enhance robustness under diverse operating conditions [41]. Advanced modulation methods adjust orthogonal polarization components via circularly polarized basis vectors for broadband control, while embedding pairs of PIN diodes in resonators allows independent dual-channel amplitude switching with minimal phase variation, simplifying control and boosting capacity [42]. Recent studies have demonstrated metasurfaces capable of switching among reflection, transmission, and absorption by integrating PIN diodes or other active elements [43−45]. These works achieve tri-functional control through discrete state transitions; however, they are generally restricted to unidirectional regulation and lack the flexible, independent bidirectional tunability required for broader applications.

In this work, a multifunctional broadband bidirectional metasurface embedded with asymmetrically arranged PIN diodes is proposed. By applying different direct current (DC) biasing schemes, the metasurface exhibits dynamic and reversible control over bidirectional RCS performance. The design leverages the active switching characteristics of PIN diodes to enable real-time tuning of EM response, thereby achieving simultaneous absorption control from both sides of the structure. This approach offers a compact and efficient solution that integrates broadband absorption, directional control, and dynamic tunability within a unified metasurface platform.

2 Design and analysis

2.1 Structure design

A tunable metasurface with an ABA-stacked configuration is proposed. As shown in Fig. 1(a), the structure consists of two active layers (A₁ and A₂) that symmetrically sandwich a passive metallic mesh layer (B layer). To achieve dynamic tunability, PIN diodes are integrated into the gaps of cross-shaped metallic patches within both A₁ and A₂ layers, as illustrated in Fig. 1(b), enabling voltage-controlled modulation of the EM response. The intermediate B layer, depicted in Fig. 1(c), is composed of three open resonant rings of varying sizes, each embedded with lumped resistors to enhance broadband absorption through tailored ohmic loss. All patterned structures are fabricated on FR-4 dielectric substrates with a relative permittivity of 4.3 and a loss tangent of 0.025. When an EM wave impinges on the forward (−z) or backward (+z) direction, the absorptance A(ω) can be calculated by the reflectance R(ω) and transmittance T(ω) as follows:

(1)A\left(\omega \right)=1-R\left(\omega \right)-T\left(\omega \right).

The reflectance and transmittance are related to the S-parameter as R(ω) = |S₁₁(ω)|², T(ω) = |S₂₁(ω)|².

2.2 Operating principle

The conceptual design of a tunable bidirectional metasurface for independent control of reflection, transmission, and absorption is illustrated in Fig. 2. Two tunable A layers are established to achieve bidirectional tunability of the EM wave radiated from the forward (−z) and backward (+z) directions. PIN diodes, functioning as rheostats, are employed to enable the active adjustable function. The resistance of the PIN diode can be dynamically tuned via the applied bias voltage. Since only the variable resistance under forward bias is exploited in the design, each PIN diode can be reasonably modeled as a bias-dependent resistor R_D for simplicity. In this regime, the resistor primarily acts as a perturbation to the overall EM system, enabling controllable modulation within the designed tunable range. Based on the biased state of the PIN diodes in the top and bottom tunable layers, the proposed metasurface features three implementation schematics. In Fig. 2, V_D1 represents the voltage in the top tunable layer, and V_D2 represents the voltage in the bottom tunable layer.

1) Function 1 (V_D2 = 0.7 V, V_D1: 0−0.7 V): When EM waves are incident from the forward (−z) direction, the metasurface functions as a reflective tunable surface. By varying V_D1, tunable absorption is achieved, as shown in Fig. 2(a).

2) Function 2 (V_D2 = 0.7 V, V_D1: 0−0.7 V): When EM waves are incident from the backward (+z) direction, the structure behaves as a near-perfect reflector regardless of the V_D1 bias. This behavior is shown in Fig. 2(b).

3) Function 3 (V_D2 = 0 V, V_D1: 0−0.7 V & V_D1 and V_D2: 0−0.7 V): When V_D2 is fixed at 0 V and V_D1 varies, or both V_D1 and V_D2 vary synchronously, the metasurface enables simultaneous tunability of reflectance and transmittance. This enables dynamic control of absorptance, as shown in Fig. 2(c).

4) Function 4 (V_D2 = 0 V, V_D1: 0−0.7 V): When EM waves are incident from the backward (+z) direction, tunable absorption is achieved by regulating the transmitted wave, as shown in Fig. 2(d).

2.3 Design scheme based on ECM

Fig. 3 illustrates the ECM of the proposed ABA-structured tunable metasurface. Two tunable layers are employed to achieve bidirectional tunability under forward (−z) and backward (+z) incidences, where PIN diodes provide resistance tuning. The inductance L_x mainly originates from the elongated current paths along the patterned metallic interconnections connecting the PIN diodes, while the resistance R_D and the capacitance C_s represent the effective tunable resistance and junction capacitance of the PIN diodes under different biasing voltages, respectively. The equivalent impedances of the top and bottom tunable layers are denoted by Z₁ and Z₃, respectively. The middle resistive sheet, introduced to enhance absorption performance, is modeled by Z₂, which is represented using multiple parallel RLC branches to capture broadband absorption behavior arising from distributed loss and multiple resonant mechanisms. The dielectric and air layers between the tunable layers and the resistive sheet are modeled as transmission-line sections with equivalent impedances Z_d0, Z_d1, and Z_d2.

In the equivalent circuit model, the effective impedance of each layer is represented as follows:

(2)Z_1=Z_3=R_{\mathrm{D}}+{\displaystyle \frac{1}{\mathrm{j}\omega C_{\mathrm{s}}}}+L_x,

(3)\begin{array}{rl}{Z}_2=& \left(R_1+\mathrm{j}\omega L_1+\frac{1}{\mathrm{j}\omega C_1}\right)\parallel \left(R_2+\mathrm{j}\omega L_2+\frac{1}{\mathrm{j}\omega C_2}\right)\parallel \\ & \left(R_3+\mathrm{j}\omega L_3+\frac{1}{\mathrm{j}\omega C_3}\right).\end{array}

According to transmission-line theory, the dielectric substrate and the air spacer are modeled as transmission-line sections. The characteristic impedance is derived under the assumptions of normal incidence and quasi-TEM dominant-mode propagation. Specifically, the substrate is assumed to be electrically thin within the operating frequency range, such that higher-order modes and spatial dispersion effects can be neglected. Accordingly, the characteristic impedance of the dielectric substrate can be expressed as

(4)Z_{\mathrm{d}i}=\mathrm{j}{Z}_0\sqrt{{\displaystyle \frac{1}{{\epsilon }_{\mathrm{r}i}}}}\tan \left({\displaystyle \frac{2\pi f}{c}}\sqrt{{\epsilon }_{\mathrm{r}i}{d}_i}\right),\left(i=0,1,2\right).

Therefore, the equivalent impedance of the proposed metasurface can be expressed as

(5)Z_{\mathrm{R}\mathrm{e}}=Z_1\parallel Z_{\mathrm{d}0}||Z_{\mathrm{d}1}\parallel Z_2\parallel Z_{\mathrm{d}2}\parallel Z_{\mathrm{d}1}\parallel Z_{\mathrm{d}0}\parallel Z_3.

The reflection and transmission coefficients of the metasurface can be calculated as follows:

(6)\left|S_{11}\right|=20\lg \left|{\displaystyle \frac{Z_{\mathrm{R}\mathrm{e}}-Z_0}{Z_{\mathrm{R}\mathrm{e}}+Z_0}}\right|,

(7)\left|S_{21}\right|=20\lg \left|{\displaystyle \frac{2Z_{\mathrm{R}\mathrm{e}}}{Z_{\mathrm{R}\mathrm{e}}+Z_0}}\right|,

where Z₀ represents the wave impedance of free space, ε_ri represents the dielectric constant of the dielectric substrate of the i-th layer, and d_i is the thickness of the dielectric substrate of the i-th layer.

The ECM exhibits three implementation schemes based on the bias states of the PIN diodes in the tunable layers 1 and 2. Figure 4 shows the calculated S-parameters using the Advanced Design System (ADS) software. Figures 4(a)−(c) shows the S-parameters when the PIN diode in tunable layer 2 is ON. As R_D1 increases within 5−15 GHz, |S₁₁| decreases from −3 dB to below −10 dB, while |S₂₁| gradually increases and |S₂₂| remains unchanged, exhibiting near-total reflection. In Figs. 4(d)−(f), where the PIN diode in tunable layer 2 is OFF, |S₁₁| initially decreases within 7−15 GHz but increases when R_D1 exceeds 1142 Ω, while |S₂₁| increases with R_D1. |S₂₂| also increases with its −10 dB bandwidth narrowing. However, near 11 GHz, |S₂₂| remains smaller than −10 dB regardless of R_D1, enabling dynamic tuning of reflectance and transmittance for forward/backward EM waves. Figures 4(g) and (h) depicts the S-parameters when both tunable layers are in the same bias condition. The tunable performance is similar to when the PIN diode in tunable layer 2 is switched OFF, as shown in Figs. 4(d) and (e). Due to the reciprocal ECM, |S₂₁| and |S₁₂| display identical tunable properties.

3 Results and discussion

3.1 R_D2 = 2 Ω, R_D1 changes from 75.5 Ω to 1 MΩ.

Figures 5(a)−(f) exhibit the simulated absorptance, reflectance, and transmittance in the forward and backward directions when PIN diodes in the A₂ layer are all in the ON state, and the R_D1 of the PIN diodes in the A₁ layer changes from 75.5 Ω to 1 MΩ. Within the frequency range of 6−14 GHz, when the EM wave is incident from the forward direction, |S₁₁| decreases as R_D1 increases, and inversely, |S₂₁| increases as R_D1 increases, resulting in tunable absorption performance, and the absorbance spectrum remains relatively stable within the frequency range. When the EM wave is incident from the backward direction, as R_D1 increases, reflectance changes slightly, fluctuating from −1 dB to −1.5 dB. Transmittance is the same as the EM wave incident from forward directions due to the reciprocity of the metasurface. Thus, the calculated absorptance decreases from 0.4 to 0.1 with increased R_D1. In this case, the equivalent impedance of the A₂ layer is minimal, and the resonance in the A₂ layer is suppressed by electric shorting. The tunability of absorbance is primarily achieved by adjusting reflectance. When the PIN diode is in the ON state, the metasurface performs as a nearly perfect reflector, and the dielectric loss mainly causes the absorptance since FR-4 is used in the design. A 20 × 20 array is simulated to analyze the RCS tunable performance, and its RCS is compared with a same-size metal plate.

Figures 5(g) and (h) show the RCS response in the forward and backward directions when the bottom layer is in the ON state and the PIN diodes in the top layer change. In the forward direction, the metasurface exhibits RCS tunability performance, and the RCS reduction is up to 15 dB. While in the backward direction, the RCS value remains close to the metal plate due to the metasurface’s near-reflective behavior.

3.2 R_D2 = 1 MΩ, R_D1 changes from 75.5 Ω to 1 MΩ.

Figures 6(a)−(f) exhibit the simulated absorptance, reflectance, and transmittance in the forward and backward directions when PIN diodes in the A₂ layer are all in the OFF state and the R_D1 in the A₁ layer changes from 75.5 Ω to 1 MΩ. Within the frequency range of 6−14 GHz, when the EM wave is incident from the forward direction, the reflectance decreases as R_D1 increases, and inversely, the transmittance increases as R_D1 increases. Transmittance shows a linearly increasing trend with a relatively stable transmission spectrum. The absorptance initially increases as R_D1 increases and reaches a maximum when R_D1 = 467 Ω, then decreases as R_D1 continues to increase. When the EM wave is incident from the backward direction, the reflectance fluctuates below −10 dB with little change as R_D1 changes. Transmittance is the same as the EM wave incident from forward directions due to the reciprocity of the metasurface. As R_D1 increases, the absorptance exhibits a linear decreasing trend, reducing from near-perfect absorption to 0.5, while the absorptance spectrum remains stable. In this biased situation, the equivalent impedance of the A₂ layer is substantial and can be comparable to an open circuit, both the forward and backward directions exhibit excellent absorptance tunability.

Figures 6(g) and (h) show the RCS response when the PIN diodes in the A₂ layer are in the OFF state and the PIN diodes in the A₁ layer are biased. In the −z direction, RCS tunability is evident, and the RCS reduction can be up to 15 dB. In the +z direction, slight tunability occurs with RCS values below 0 dBsm due to |S₁₁| < −10 dB, demonstrating substantial RCS reduction.

3.3 R_D1 and R_D2 change simultaneously.

Figures 7(a)−(c) illustrate the simulated absorptance, reflectance, and transmittance in both forward and backward directions as R_D1 and R_D2 in the A₁ and A₂ layers simultaneously decrease from 75.5 Ω to 1 MΩ. The variation spectra of reflectance, transmittance, and absorptance are quite similar to the variation performance observed in the second implementation scenario when the EM wave is incident from the forward direction. Figure 7(d) illustrates the RCS characteristics when both layers are biased identically. The metasurface shows significant RCS tunability, with variations in reflectance, transmittance, and absorptance resembling those in the second forward incident scenario, resulting in similar RCS tuning performance.

To explain this phenomenon, the A₁ and A₂ layers can be modeled as a parallel circuit. When the bottom-layer PIN diodes are in the ON state, increasing the R_D1 of A₁ has little effect, as A₂ dominates the system impedance, denoted as Z₃ in Fig. 2. Conversely, when the A₂-layer diodes are in the OFF state, the A₁ layer dominates the system response, with the equivalent impedance represented as Z₁. When both layers are adjusted simultaneously, the overall impedance approaches half that of either layer (Z₁ ≈ Z₃), and the control trend of case 3 aligns with that of case 3.2. Notably, the CST simulated results largely match the ADS simulations in the three implementation schematics mentioned above, although some differences caused by the coupling effect among resonant patterns have been omitted in the ECM analysis.

To visualize the RCS tunability of the metasurface, we analyzed the RCS distribution at 10 GHz under normal incidence, as shown in Fig. 8. When the PIN diodes in the A₂ layer are in the ON state, the RCS in the forward direction decreases with increasing R_D1, while in the backward direction, it remains large and stable. In the OFF state, the RCS in the forward direction also decreases with R_D1, but in the backward direction, it remains small and stable. The RCS decreases in both directions when the PIN diodes in both layers change simultaneously. (Since the structures are identical, only the forward direction is simulated.) These results confirm that the metasurface dynamically controls reflection and transmission, enabling adaptive stealth and anti-stealth performance.

4 Experimental verification

A prototype of a 20 × 20 array was fabricated using printed circuit board (PCB) technology to experimentally verify the design procedure, as shown in Fig. 9. The fabrication of the tunable top and bottom layers is performed by patterning the metallic structure on the 1 mm thick FR-4 substrate and welding four PIN diodes (SMP1321-079) into the gap. Two Murata LQP03 inductors are embedded in series in the biasing network to achieve isolation and protect the biasing lines from EM waves, as shown in Fig. 9(a).

To provide a biasing voltage, two vertical biasing lines are printed along the sides of the prototype. All the cathodes of the diodes in a row are connected to a bias line on the right through small horizontal bias lines. Similarly, the anodes are connected to the vertical bias line on the left through smaller bias lines. The absorptive layer between the tunable top and bottom layers comprises three split square rings of different dimensions, with four resistors etched into the gap of each ring. The metallic pattern is fabricated on one side of the 0.5 mm FR-4 substrate, as shown in Fig. 9 (b). Figure 9(c) illustrates the measurement setup, where two horn antennas, covering frequency ranges from 2 to 18 GHz, are connected to a Vector Network Analyzer (ROHDE & SCHWARZ). One horn antenna transmits EM waves, while the other receives the reflected or transmitted EM waves. A voltage source is connected to the prototype to provide the bias voltage.

The prototype is measured using the free space method. The reflection and transmission coefficients can be adjusted by tuning the bias voltage. When the A₂ layer remains in the ON state, and the voltage of the A₁ layer changes from 0.4 V to 0.6 V, the response in both forward and backward directions is shown in Fig. 10. When the A₂ layer is in the OFF state, the voltage of the A₁ layer changes from 0.4 V to 0.6 V, the response in both forward and backward directions is illustrated in Fig. 11. Figure 12 presents the response when the voltage of both the A₁ and A₂ layers changes from 0.4 V to 0.6 V, revealing some differences compared to the simulated results.

The frequency offsets between simulation and measurement can be mainly attributed to diode parasitic and fabrication tolerance. In practice, small variations in key geometric parameters, such as spacer thickness, dielectric layer thickness, and dimensions associated with lumped-element loading. Moreover, ideal PIN diode models are adopted in the simulations, where parasitic inductance and capacitance are neglected, and the simulated bias conditions do not exactly match the experimental ones. In addition, the simulations assume an infinite periodic structure, whereas the measurements are performed on a finite-sized array with unavoidable parasitic effects from soldering and biasing networks. Despite these nonideal factors, the measured results show reasonable agreement with the simulated responses, confirming the broadband and dynamically tunable reflection–transmission behavior of the proposed metasurface.

Table 1 compares the performance of the proposed work with previously reported tunable metasurfaces. Referencs [39–42] reported broadband A–T or A–R type tunable metasurfaces that allow continuous adjustment of absorptance, reflectance, or transmittance; however, these designs are limited to two-mode tunability and cannot simultaneously integrate all three EM propagation channels. Although Refs. [43–45] achieved A–R–T tri-functional tunability, their operation was restricted to a single incident direction, which limits their applicability in bidirectional scenarios.

By contrast, the proposed FSR enables bidirectional and independent tunability of absorption, reflection, and transmission over a broad frequency range of 6.0−14.0 GHz (80.0% fractional bandwidth). Meanwhile, it maintains a subwavelength unit-cell periodicity of 0.18λ₀ and a moderate electrical thickness of 0.12λ₀, evaluated at the corresponding operating frequencies. This demonstrates that the proposed design achieves a favorable balance among broadband performance, multifunctional tunability, and compact physical dimensions compared with previously reported A–R and A–R–T metasurfaces.

5 Conclusion

A bidirectional tunable metasurface based on an equivalent circuit model has been proposed, enabling broadband and flexible control of EM waves incident from both forward and backward directions. The key component of this design is an ABA tri-layer structure with asymmetrically controlled, loaded PIN diodes, which allows dynamic tuning of attenuation levels. The reflection and transmission performance of a prototype has been measured. Across a 6−14 GHz bandwidth (~80% fractional bandwidth), the proposed metasurface has achieved tunable reflection (>95%), absorption (>90%), and radar cross-section reduction (up to 15 dB) by adjusting PIN diode bias voltages, thereby enabling seamless switching between near-perfect reflectivity and absorption. This high performance and dynamic tunability have surpassed those of conventional metasurfaces, making the design highly suitable for electromagnetic shielding, stealth, and adaptive wireless applications.

References

[1] N. Yu,P. Genevet,M. a Kats,F. Aieta,J. -P. Tetienne,F. Capasso,Z. Gaburro, Light propagation with phase reflection and refraction, Science 334(6054), 333 (2011)

[2] C. Pfeiffer and A. Grbic , Metamaterial Huygens’ surfaces: Tailoring wave fronts with reflectionless sheets, Phys. Rev. Lett. 110(19), 197401 (2013)

[3] S. J. Li , Z. Y. Li , G. S. Huang , X. B. Liu , R. Q. Li , and X. Y. Cao , Digital coding transmissive metasurface for multi-OAM-beam, Front. Phys. (Beijing) 17(6), 62501 (2022)

[4] X. Jiang , C. Xue , J. Yan , R. Li , T. Li , and X. Gao , An ultrathin, dual-band, and dual-polarized metalens antenna based on double-resonant Huygens’ metasurface, IEEE Antennas Wirel. Propag. Lett. 23(5), 1473 (2024)

[5] S. Y. Yin , J. L. Li , Y. M. Zhang , and Q. C. Ye , Fan-shaped multibeam metasurface lens antenna for high crossover levels and stable radiation gain, IEEE Antennas Wirel. Propag. Lett. 23(6), 1809 (2024)

[6] W. Kang , C. Zhou , and W. Wu , Respiration monitoring of all occupants in a vehicle using time-division multiplexing FMCW radar based on metasurface technology, IEEE Trans. Microw. Theory Tech. 72(8), 4960 (2024)

[7] R. M. H. Bilal , E. Perret , S. Genovesi , G. Manara , and F. Costa , Simplified fabrication of frequency selective surface-based microwave and millimeter-wave devices using fiber laser technology, Opt. Laser Technol. 192, 113360 (2025)

[8] H. Jing , Y. Gao , J. Kang , L. Zhao , L. Chen , J. Duan , Z. Qu , J. Wang , and B. Zhang , Bifunctional integrated metamaterial of water-based broadband absorption and polarization conversion, Opt. Laser Technol. 177, 111174 (2024)

[9] Y. Zhang , Y. Zhou , Z. Lei , J. Zhou , P. Kuang , Y. Liu , C. Xian , G. Li , G. Wen , and Y. Huang , Reconfigurable beam deflector and polarization converter using optomechanical metasurface, IEEE Trans. Antenn. Propag. 73(2), 998 (2025)

[10] G. Deng , Y. Zhu , Q. Zhang , J. Yang , Y. Li , and Z. Yin , Reconfigurable dual-functional reflective polarization converter based on liquid crystal terahertz metasurfaces, IEEE Trans. Antenn. Propag. 73(6), 4164 (2025)

[11] H. He , H. Yang , Z. Xie , and X. Yuan , Dynamic polarization rotation and vector field steering based on phase change metasurface, Front. Phys. (Beijing) 18(1), 12303 (2023)

[12] S. Wang , H. Guo , B. Chen , X. Hu , W. Zhu , J. Wu , C. Zhang , K. Fan , H. Wang , B. Jin , J. Chen , and P. Wu , Electrically active terahertz liquid-crystal metasurface for polarization vortex beam switching, Laser Photonics Rev. 18(7), 2301301 (2024)

[13] X. Pan , Y. Deng , Z. Cai , Z. Chen , Y. Ding , Z. Zheng , and F. Ding , Three-channel wavefront shaping using non-interleaved spin-multiplexed plasmonic metasurfaces, Adv. Sci. (Weinh.) 12(17), 2413138 (2025)

[14] N. Ullah , M. S. Islam , A. Hoque , P. Kirawanich , S. Alamri , H. Alsaif , and M. T. Islam , Compact dual-band metamaterial absorber: enhancing electromagnetic energy harvesting with polarization-insensitive and wide-angle capabilities, Opt. Laser Technol. 175, 110829 (2024)

[15] S. M. A. Haque , M. Ahmed , A. Alqahtani , M. T. Islam , I. Hossain , and M. Samsuzzaman , Split ring resonator based multiband metamaterial absorber for liquid oil detection sensing applications, Opt. Laser Technol. 181, 111984 (2025)

[16] J. Ge , C. Zhang , Y. Zhang , H. Li , J. Wang , R. Jiang , K. Chen , H. Dong , and L. Zhang , Transparent bilayer ITO metasurface with bidirectional and coherently controlled microwave absorption, Adv. Opt. Mater. 11(21), 2301268 (2023)

[17] Z. Qin , C. Li , M. Yan , Y. Li , H. Wang , J. Wang , and H. Ma , Polarization- and angle-insensitive frequency-tunable metasurface absorber with multi-tailoring modes, Opt. Express 33(12), 26565 (2025)

[18] M. Hu , N. Zhang , G. Shan , J. Gao , J. Liu , and R. K. Y. Li , Two-dimensional materials: Emerging toolkit for construction of ultrathin high-efficiency microwave shield and absorber, Front. Phys. (Beijing) 13(4), 138113 (2018)

[19] Y. Zhu , Y. Liu , R. Dong , T. Li , Y. Zhao , X. Wang , and Y. Li , Composite sound-absorbing metamaterials via multiple resonance coupling and quality factor modulation, Front. Phys. (Beijing) 20(5), 054203 (2025)

[20] Z. Y. Shen , H. L. Yang , X. Liu , X. J. Huang , T. Y. Xiang , J. Wu , and W. Chen , Electromagnetically induced transparency in novel dual-band metamaterial excited by toroidal dipolar response, Front. Phys. (Beijing) 15(1), 12601 (2020)

[21] S. Wu,Y. Zhang,Y. Hu,G. Wang,Z. Liu,J. Zhang,X. Ji, A hybrid mechanism metasurface based on absorption and phase cancellation for ultra-wideband RCS reduction, Adv. Theory Simul. 8(1), 2400643 (2025)

[22] Y. Ma , W. Wu , Y. Yan , S. Wang , W. Yuan , J. Huang , and N. Yuan , Broadband RCS reduction metasurface with a reconfigurable high-selectivity transmission band, IEEE Trans. Microw. Theory Tech. 72(2), 878 (2024)

[23] M. F. El-Sewedy,M. A. Abdalla, A monostatic and bistatic RCS reduction using artificial magnetic conductor metasurface, IEEE Trans. Antenn. Propag. 71(2), 1988 (2023)

[24] Y. Liu , Y. Jia , W. Zhang , and F. Li , Wideband RCS reduction of a slot array antenna using a hybrid metasurface, IEEE Trans. Antenn. Propag. 68(5), 3644 (2020)

[25] J. Zhang , Y. Liu , Y. Jia , and R. Zhang , High-gain Fabry-Pérot antenna with reconfigurable scattering patterns based on varactor diodes, IEEE Trans. Antenn. Propag. 70(2), 922 (2022)

[26] H. Gao , X. Huang , X. Ma , X. Li , L. Guo , and H. Yang , An ultra-wideband coding polarizer for beam control and RCS reduction, Front. Phys. (Beijing) 18(4), 42301 (2023)

[27] M. K. Emara , D. Kundu , K. Macdonell , L. M. Rufail , and S. Gupta , Coupled resonator-based metasurface reflector with enhanced magnitude and phase coverage, IEEE Trans. Antenn. Propag. 72(1), 901 (2024)

[28] Y. Fan , D. Li , H. Ma , J. Xing , Y. Gu , L. K. Ang , and E. P. Li , Ultrawideband dual-polarized frequency-selective absorber with tunable reflective notch, IEEE Trans. Antenn. Propag. 71(3), 2855 (2023)

[29] M. Guo , Y. Zheng , Q. Chen , L. Ding , D. Sang , F. Yuan , T. Guo , and Y. Fu , Analysis and design of a high-transmittance performance for varactor-tunable frequency-selective surface, IEEE Trans. Antenn. Propag. 69(8), 4623 (2021)

[30] M. Saikia , K. V. Srivastava , and S. A. Ramakrishna , Frequency-shifted reflection of electromagnetic waves using a time-modulated active tunable frequency-selective surface, IEEE Trans. Antenn. Propag. 68(4), 2937 (2020)

[31] Z. Xue , S. Zhong , and Y. Ma , Graphene-FSS hybrid absorptive structure with amplitude/frequency dual-modulated passband, IEEE Antennas Wirel. Propag. Lett. 20(9), 1711 (2021)

[32] S. C. Bakshi , D. Mitra , and F. L. Teixeira , Multifunctional frequency selective rasorber with dual mode and continuous tunability, IEEE Trans. Antenn. Propag. 69(9), 5704 (2021)

[33] K. Payne , K. Xu , J. H. Choi , and J. K. Lee , Multiphysics analysis of plasma-based tunable absorber for high-power microwave applications, IEEE Trans. Antenn. Propag. 69(11), 7624 (2021)

[34] M. L. Hakim , M. T. Islam , and T. Alam , Ultra-miniaturized conformal polarization insensitive and incident angle stable FSS for n257 Band 5G EMI shielding applications, IEEE Trans. Antenn. Propag. 72(10), 7905 (2024)

[35] A. Pitilakis,O. Tsilipakos,F. Liu,K. M. Kossifos,A. C. Tasolamprou,D. H. Kwon,M. S. Mirmoosa,D. Manessis,N. V. Kantartzis,C. Liaskos,M. A. Antoniades,J. Georgiou,C. M. Soukoulis,M. Kafesaki,S. A. Tretyakov, A multi-functional reconfigurable metasurface: Electromagnetic design accounting for fabrication aspects, IEEE Trans. Antenn. Propag. 69(3), 1440 (2021)

[36] Z. Ning,M. Li,D. Ding,X. Ai,J. Liu,C. F. Wang, A step-by-step design methodology for broadband tunable microwave metasurface absorbers using theory of characteristic modes, IEEE Open J. Antennas Propag. 5(4), 899 (2024)

[37] J. Xing , D. Li , Y. Fan , L. Zhang , and E. P. Li , Tunable coherent perfect absorption based on varactor-embedded metamaterial absorber, IEEE Trans. Antenn. Propag. 72(4), 3461 (2024)

[38] Y. Li,J. Lin,H. Guo,W. Sun,S. Xiao,L. Zhou, A tunable metasurface with switchable functionalities: From perfect transparency to perfect absorption, Adv. Opt. Mater. 8(6), 1901548 (2020)

[39] Z. Luo , X. Shan , X. Ren , K. Wu , Y. Chen , L. Hong , H. F. Ma , Q. Cheng , and T. J. Cui , Active metasurface absorber for intensity- dependent surface-wave shielding, IEEE Trans. Antenn. Propag. 71(7), 5795 (2023)

[40] H. Xia , L. Deng , S. Huang , Z. X. Liu , L. L. Qiu , and L. Zhu , Ultra-wideband flexible and intensity-tunable metamaterial absorber based on lossy stepped impedance resonator, IEEE Trans. Antenn. Propag. 72(11), 8554 (2024)

[41] B. Zhao , C. Huang , J. Yang , J. Song , C. Guan , and X. Luo , Broadband polarization-insensitive tunable absorber using active frequency selective surface, IEEE Antennas Wirel. Propag. Lett. 19(6), 982 (2020)

[42] Z. Chu , X. Cai , J. Yang , T. Li , H. Sun , F. Wu , R. Zhu , T. Liu , Y. Han , and J. Wang , Full-polarization reconfigurable metasurface for broadband and versatile modulation of electromagnetic waves, Photon. Res. 12(12), 2812 (2024)

[43] X. Song , W. Yang , K. Qu , X. Bai , K. Chen , Y. Feng , and W. Zhu , Switchable metasurface for nearly perfect reflection, transmission, and absorption using PIN diodes, Opt. Express 29(18), 29320 (2021)

[44] S. Ye , C. Huang , J. He , H. Shao , M. Li , J. Dong , and An amplitude-modulated metadevice with switchable reflection , Transmission, and Absorption, Nanomaterials (Basel) 12(23), 4227 (2022)

[45] A. de Lustrac , B. Ratni , G. P. Piau , Y. Duval , and S. N. Burokur , Tri-state metasurface-based electromagnetic screen with switchable reflection, transmission, and absorption functionalities, ACS Appl. Electron. Mater. 3(3), 1184 (2021)

RIGHTS & PERMISSIONS

Higher Education Press