# A Comprehensive Review of Multiband Electromagnetic Metasurface Structures for Absorption and Wave Manipulation Applications

Abhishek Arya, Mohsen Koohestani, Thomas Schlinquer, Richard Perdriau

► To cite this version:

Abhishek Arya, Mohsen Koohestani, Thomas Schlinquer, Richard Perdriau. A Comprehensive Review of Multiband Electromagnetic Metasurface Structures for Absorption and Wave Manipulation Applications. IEEE Access, 2025, pp.1-1. 10.1109/ACCESS.2025.3648281. [hal-05445826](https://hal.science/hal-05445826v1)

HAL Id: hal-05445826

https://hal.science/hal-05445826v1

Submitted on 10 Jan 2026

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
Received 3 December 2025, accepted 17 December 2025, date of publication 24 December 2025, date of current version 7 January 2026.

Digital Object Identifier 10.1109/ACCESS.2025.3648281

TOPICAL REVIEW

# A Comprehensive Review of Multiband Electromagnetic Metasurface Structures for Absorption and Wave Manipulation Applications

ABHISHEK ARYA<sup>D 1,2</sup>, (Graduate Student Member, IEEE),
MOHSEN KOOHESTANI<sup>D 1,3</sup>, (Senior Member, IEEE),
THOMAS SCHLINQUER<sup>1,4</sup>, (Senior Member, IEEE),
AND RICHARD PERDRIAU<sup>D 1,3</sup>, (Senior Member, IEEE)

<sup>1</sup>École Supérieure d'Electronique de l'Ouest (ESEO), 49107 Angers, France

<sup>2</sup>Institut National des Sciences Appliquées, University of Rennes, 35708 Rennes, France

<sup>3</sup>Institut d'Electronique et des Technologies du numéRique (IETR), 35042 Rennes, France

<sup>4</sup>ICB, Université Bourgogne Europe, 21000 Dijon, France

Corresponding author: Abhishek Arya (abhishek.arya@eseo.fr)

This work was supported by the Regional Angers Loire Metropole (ALM): PRECOCE Project: Protection contre les Rayonnements Electromagnétiques et COllecte de l'énergie du Corps humain et des ondes Electromagnétiques.

**ABSTRACT** Multiband metasurfaces have attracted significant attention as compact and multi-functional platforms for electromagnetic (EM) absorption and wave manipulation. This paper reviews recent advances in multiband absorbers, frequency selective surfaces (FSS), and polarization converters, emphasizing their operating principles, structural configurations, and performance trade-offs. Particular attention is given to the dimensional and resonator aspects of metasurfaces, highlighting how unit-cell geometry, periodicity, and resonant structures directly influence 1) absorption efficiency, angular stability, and operating frequency in absorbers, and 2) spectral selectivity, bandwidth control, and miniaturization in FSS, and 3) conversion efficiency, bandwidth, and polarization purity in polarization converters. These interdependent parameters provide key guidelines for designing compact yet high-performance metasurfaces across different functionalities. Multiband absorbers exploit impedance matching and multi-resonant unit-cell to achieve near-unity absorption across multiple frequency bands, with applications in stealth, electromagnetic interference (EMI) suppression, and RF energy harvesting. FSS structures integrate nested or hybrid resonators within subwavelength cells to deliver high selectivity, angular stability, and miniaturized filtering for communication and radar systems. Polarization converters extend metasurface functionality by enabling linear-to-linear and linear-to-circular transformations within ultra-thin platforms, addressing the growing demand for polarization-agile devices in modern wireless and sensing applications. By identifying limitations and opportunities, this review underscores the role of multiband metasurfaces as enabling technologies for next-generation EM systems.

**INDEX TERMS** Metasurfaces, multiband absorption, RF energy harvesting, wave manipulation, polarization conversion, reconfigurable metasurfaces, electromagnetic control, multiband FSS.

## I. INTRODUCTION

In the era of compact, multi-functional, and adaptive electromagnetic (EM) devices, metasurfaces have emerged

The associate editor coordinating the review of this manuscript and approving it for publication was Guido Lombardi <sup>D</sup>.

as a groundbreaking class of engineered structures. These planar arrays of subwavelength resonant elements, known as meta-atoms, are designed to impart abrupt spatial variations in EM properties, enabling unprecedented control over wavefront propagation, phase, amplitude, polarization, and absorption characteristics [1], [2], [3], [4]. Unlike their
three-dimensional metamaterial counterparts, metasurfaces offer significant advantages in terms of thickness, weight, fabrication simplicity, and compatibility with existing planar technologies, making them ideal for applications in modern wireless communication, sensing, stealth, and energy harvesting systems [5], [6], [7].

Among the broad spectrum of metasurface configurations, multiband metasurfaces represent a crucial advancement, addressing the limitations of conventional single-band designs by facilitating simultaneous or selective operation across multiple frequency bands [8], [9]. These structures eliminate the need for stacking or integrating multiple single-band components, thereby reducing system complexity and physical footprint while expanding spectral utility. The ability to manipulate EM waves at multiple frequencies is especially vital for multi-standard communication systems, frequency-diverse radar, dual-band sensing, and stealth technologies that require adaptive response under variable spectral demands [10].

One of the most prominent applications of multiband metasurfaces is in absorption [11], [12]. By engineering multiple resonant modes within the same metasurface structure typically through a combination of carefully shaped metallic patterns, dielectric substrates, and impedance matching layers, it becomes possible to achieve near-unity absorption at multiple discrete frequencies. This is typically accomplished by satisfying the critical condition of impedance matching with free space, wherein the real parts of the effective permittivity and permeability are equal, and their imaginary parts are tuned to maximize energy dissipation [13]. Modern multiband absorbers have demonstrated impressive performance, achieving > 90% absorption at multiple frequencies while maintaining angular and polarization stability [14], [15], [16].

Another key capability of metasurfaces lies in wave manipulation, particularly polarization conversion. A particularly relevant subset of metasurfaces for wave manipulation includes frequency selective surfaces (FSS), structures [17], [18], [19] which have long been employed for filtering and controlling EM waves through periodic resonant structures. FSS-based metasurfaces enhance these capabilities by incorporating subwavelength engineering, enabling precise control over transmission, reflection, and polarization conversion at multiple frequencies [5], [20]. Asymmetric metasurface unit-cell are engineered to transform the polarization state of incident EM waves with high efficiency. Polarization converting metasurfaces (PCMs) exploit geometry-induced birefringence and resonant mode coupling to reflect or transmit cross-polarized waves while suppressing co-polarized components [21]. For effective polarization conversion, state-of-the-art metasurfaces achieve cross-polarized reflection coefficients greater than -3 dB and co-polarized reflection below -10 dB, even under oblique incidence and dual-frequency operation [22], [23], [24]. Such devices are instrumental in communication systems that rely

on polarization diversity, as well as in stealth applications where depolarization is used to reduce radar cross-section.

Recent developments have further enhanced metasurface capabilities by integrating programmable, reconfigurable, and switchable functionalities. Using tunable materials like VO₂ or phase-change materials, and integrating active components such as PIN diodes, liquid crystals, or microelectromechanical systems (MEMS), researchers have demonstrated metasurfaces capable of dynamic frequency tuning, real-time polarization switching, and mode shifting between absorption and reflection [10], [25], [26].

Nevertheless, the transition from theoretical synthesis to real-world deployment introduces challenges. Fabrication feasibility, cost of high-resolution patterning, environmental stability, and scalability for large-area applications remain significant hurdles [28]. Moreover, the performance trade-offs between multi-band operation, broadband functionality, and structural robustness require careful design optimization, especially for conformal and space-constrained systems.

This review offers a comprehensive analysis of the current landscape of multiband EM metasurface structures designed for absorption and wave manipulation. We systematically categorize the most recent advances in metasurface design based on their structural geometry, resonance mechanisms, operational principles, and functional targets. The review highlights key performance indicators such as absorption efficiency, phase control, polarization purity, angular stability, and integration complexity. Special emphasis is placed on the design methodologies, including geometric tuning, resonant mode hybridization, surface impedance engineering, and advanced synthesis models that underpin high-efficiency multiband operation. Moreover, this review includes a brief discussion on how absorptive and reflective metasurfaces naturally extend to the electromagnetic operational paradigms of reconfigurable intelligent surfaces (RIS) and emerging holographic surfaces. To sum up, a focused review on multiband metasurfaces is both timely and necessary, as their unique capabilities enable broader and more practical applications compared to other metasurface categories.

## II. CLASSIFICATION OF MULTIBAND METASURFACES

Multiband metasurfaces can be broadly classified into three main categories based on their EM functionality absorbers, FSS, and polarization converters. While the focus of this review is on the fundamental design principles of multiband metasurface unit-cells, their practical significance extends far beyond a narrow application space. The ability to engineer a single, sub-wavelength structure to resonate at multiple discrete frequencies is a cornerstone for the development of highly integrated and multifunctional EM systems. This capability is paramount for modern technology, where real estate is at a premium and multi-standard operation is mandatory. A key application is in RF energy harvesting, where multiband metasurfaces are indispensable for efficiently capturing
ambient energy from a spectrum of common sources, such as Wi-Fi, 4G/5G, and FM broadcast signals simultaneously, thereby significantly increasing the total harvested power for powering low-energy IoT sensors. Furthermore, a single multiband metasurface can enable a compact smartphone antenna to seamlessly cover numerous communication bands, GPS, and Wi-Fi frequencies. In satellite communications or radar systems, such structures can facilitate simultaneous sensing and communication or multi-band radar absorption within a single, lightweight aperture. Thus, the pursuit of sophisticated multiband unit-cell is not an isolated endeavor but a critical enabler for advancing next-generation wireless communication, energy harvesting, aerospace systems, and sensing platforms by consolidating multiple functionalities into a single, efficient, and miniaturized device.

## A. PASSIVE AND ACTIVE (RECONFIGURABLE) METASURFACES

Before classifying metasurfaces in terms of EM behavior, a clear distinction between passive and reconfigurable metasurfaces is essential for understanding the practical limits of dynamic multiband operation. Passive metasurfaces operate purely through geometry-defined resonances, where fixed electric, magnetic, and bianisotropic susceptibilities ($\chi_e, \chi_m, \chi_{em}$) produce stable phase and amplitude responses with minimal loss. Their dispersion characteristics are highly predictable and robust, but their EM behavior is permanently locked after fabrication, preventing real-time adaptation to frequency drift, environmental variations, or changing illumination conditions [30].

Reconfigurable metasurfaces, in contrast, introduce external control parameters through tunable components or active materials such as VO₂, MEMS, or voltage-controlled dielectrics. These elements render the effective surface impedance

$$Z_s(\omega, u) = R(u) + j\omega L_{\text{eff}}(u) + \frac{1}{j\omega C_{\text{eff}}(u)},$$

a function of a tuning variable $u$, enabling dynamic modulation across multiple resonances. However, achieving true and stable multiband reconfigurability introduces several tightly coupled challenges [31]. Phase-change materials such as VO₂ provide large refractive-index contrast ($\Delta n \approx 1-2$) but suffer from Drude-like free-carrier absorption during the insulator-metal transition, significantly increasing ohmic losses across microwave, terahertz, and infrared bands. As higher-order modes exhibit stronger loss sensitivity, the effective quality factor $Q_{\text{eff}}$ degrades disproportionately, reducing modulation depth, phase fidelity, and overall tuning efficiency.

Furthermore, multiband metasurfaces rely on spatially overlapping resonant modes that are not strictly orthogonal integrating varactors or tunable dielectrics perturbs multiple eigenmodes simultaneously, leading to cross-resonance coupling, nonlinear tuning trajectories, mode hybridization, and unintended spectral shifts that undermine independent

multiband control [32]. The situation is further compounded by biasing-network parasitics and scaling constraints: dense bias lines introduce parasitic inductance $L_p$ and shunt capacitance $C_s$, producing distortive impedances

$$Z_{\text{parasitic}} = j\omega L_p + \frac{1}{j\omega C_s},$$

that accumulate across large apertures, degrading phase accuracy, amplitude uniformity, and beam-steering resolution. Finally, although MEMS-based tuning provides low-loss reconfiguration, it suffers from hysteresis, drift, displacement-dependent stiffness variation, mechanical fatigue, and finite actuation speed all of which induce long-term resonance instability, especially in higher-order, tightly spaced resonances.

Additional constraints in large-area and flexible platforms include:

* Scalability and fabrication tolerances: Accumulated variations in metal line width, dielectric thickness, and material uniformity introduce spatial phase errors

$$\Delta\phi(x, y) \approx \frac{2\pi}{\lambda}\Delta h_{\text{eff}}(x, y),$$

leading to resonance misalignment, degraded gain, and reduced beamforming efficiency.

* Near-field inter-element coupling: Bias-dependent mutual admittance

$$Y_{mn}(u) = Y'_{mn} + jY''_{mn}(u),$$

causes dynamic mode hybridization, resonance drift, and invalidates the assumption of independently operating unit-cells, requiring full-aperture co-simulation.

* Mechanical deformation in flexible platforms: Bending or stretching modifies resonator geometry and dielectric spacing, detuning higher-order modes, shifting resonant frequencies, and reducing spectral coherence.

* Thermal and power-distribution effects: Localized heating from VO₂ switching or bias networks produces spatial permittivity gradients, inducing unintended phase shifts and causing long-term degradation in tuning accuracy and spectral stability.

## B. MULTIBAND METASURFACE ABSORBERS (MSA)

Metasurface-based RF absorbers are essential components in modern EM systems, engineered to suppress unwanted radio frequency signals by efficiently absorbing and dissipating EM energy [33], [34]. Unlike conventional reflective surfaces that scatter RF waves and cause interference these advanced absorbers eliminate noise at the source by transforming disruptive signals into harmless heat. Remarkably, this dissipated energy can be harvested and recycled into usable electrical power, turning EM pollution into a valuable energy resource [35], [36]. This capability is crucial for ensuring high-performance operation in radar systems, wireless communication, stealth technology, and EM compatibility testing. In an era defined by escalating signal density and
sensitivity, metasurface RF absorbers emerge as powerful enablers of clarity, efficiency, and reliability in complex electronic environments.

### 1) MSA OPERATING PRINCIPLE

The functionality of perfect MSA is illustrated in Fig. 1, where there is neither reflection nor transmission for incident EM waves. In metasurface structures, the incident EM power absorbed within the material is dissipated either as ohmic loss, arising from resistive heating due to surface currents in the metallic parts, or as dielectric loss, caused by polarization relaxation in the substrate governed by its loss tangent. Together, these mechanisms convert the absorbed EM energy into heat within the structure. When the metasurface is backed by a perfect electric conductor (PEC) [13], [37], [38], [39], the transmission is inherently zero, and the absorption A is given by:

$$A(\omega) = 1 - |\Gamma(\omega)|^2$$

where Γ is the reflection coefficient.

<figure><img src="image_2.png" /><figcaption>FIGURE 1. The functionality of a perfect MSA.</figcaption></figure>

To derive the reflection, the system's input impedance is analyzed. Consider a metasurface layer with surface impedance Zs, separated from the PEC by a dielectric spacer of thickness d and relative permittivity εr. The total input impedance Zin seen by the incident wave is:

$$Z_{in} = Z_{s} + jZ_{0} \tan(kd)$$

where Z0 ≈ 377 Ω is the free-space impedance, and

$$k = \beta = \frac{2\pi\sqrt{\varepsilon_r}}{\lambda_0}$$

represents the propagation constant inside the dielectric spacer.

The reflection coefficient is then:

$$\Gamma = \frac{Z_{in} - Z_{0}}{Z_{in} + Z_{0}}$$

Substituting into the absorption equation yields:

$$A = 1 - \left| \frac{Z_{in} - Z_{0}}{Z_{in} + Z_{0}} \right|^{2}$$

Perfect absorption occurs when:

$$Z_{in} = Z_{0} \Rightarrow \Gamma = 0 \Rightarrow A = 1$$

This impedance matching condition ensures that no wave is reflected and all incident energy is dissipated.

The metasurface is typically designed as an array of resonant elements (e.g., patches, rings, or lossy inclusions) modeled by a parallel RLC circuit:

$$Z_{s}(\omega) = \frac{1}{\frac{1}{R} + j\omega C - \frac{j}{\omega L}}$$

Here, R captures resistive/dielectric loss, L and C depend on geometry and coupling. At resonance:

$$\omega_{0} = \frac{1}{\sqrt{LC}}, \quad Q = \frac{1}{R} \sqrt{\frac{L}{C}}$$

where Q is the quality factor. To enable multiband or broadband absorption, multiple resonators with different Lᵢ, Cᵢ can be embedded:

$$Z_{s}(\omega) = \sum_{i=1}^{N} \frac{1}{\frac{1}{R_{i}} + j\omega C_{i} - \frac{j}{\omega L_{i}}}$$

By tailoring unit-cell geometry, material parameters, and spacer thickness, designers can achieve controlled absorption across specific or multiple frequency bands. This principle underpins compact, efficient absorbers for electromagnetic interference (EMI) shielding, stealth technology, wireless energy harvesting, and sensing applications [11], [40], [41].

### 2) DESIGN METHODOLOGY FOR MSA UNIT-CELL

The absorption mechanism of MSAs is governed by the resonant behavior of their meta-atoms. To achieve perfect absorption within specific operating bands and size constraints, a clear strategy is needed to tune geometrical parameters, such as patch geometry and substrate properties, which define the effective inductance, capacitance, and loss of each resonance. Simultaneously, modal independence in closely-spaced bands must be preserved by controlling inter-resonator coupling through techniques like orthogonal current paths or multilayer stacking.

The maximum achievable absorption is fundamentally limited by the intrinsic losses of the resonant unit cells. One way to enhance absorption is to introduce additional internal losses, for example through resistive materials or tailored impedance-matching techniques [42]. An alternative strategy focuses instead on engineering the external coupling between the resonator and the incident wave [43]. Under this approach, critical coupling occurs when the external radiation leakage rate equals the internal dissipation rate, resulting in zero reflection at the resonant frequency. Depending on the relative magnitudes of these two rates, the resonator operates in either the overcoupled region (external leakage dominant, associated with a 0° reflection-phase response) or the undercoupled region (internal loss dominant, associated with a 180° reflection-phase response).
In [7], that methodology was applied to convert a simple, highly reflective unit cell into a perfect absorber for normally incident waves. Perfect absorption was achieved by modifying the external coupling through the introduction of rectangular slits in the metallic patch. The evolution of the coupling regime, overcoupled, undercoupled, or critically coupled, was monitored on the Smith chart to guide the design toward the critical-coupling condition.

### 3) DESIGN EXAMPLES BASED ON MULTIBAND MSA

The MSA proposed in [44] is a single-layer, planar periodic structure designed to achieve high-efficiency EM absorption at four discrete frequency bands, i.e., 1.7, 2.4, 3.8, and 5.3 GHz. It was reported that each unit-cell consists of two distinct categories of metallic resonators fabricated on an F4B dielectric substrate with a thickness of 0.76 mm, a relative permittivity of 2.2. As illustrated in Fig. 2a. Positive patches are connected via metal arms and chip inductors, while negative patches are grounded through metallic vias, forming asymmetric but electromagnetically balanced resonant structures. The resonant modes are excited

by the geometrically tuned distribution of surface currents localized across specific conductive elements.

The first two resonant modes arise from capacitive coupling across a subwavelength gap between the positive and negative patches, enabling strong electric dipolar resonances. A third resonance is introduced by a continuous metallic arm connecting adjacent cells, inducing a looped current path that supports a higher-order mode. A fourth mode is excited via the addition of a trapezoidal patch, which enhances mutual coupling and increases the resonance strength by modifying the local current density and effective surface reactance.

Simulated results show reflection coefficients $|S_{11}|$ below -14 dB in all four bands, indicating absorptivity > 96% Fig. 2b. The metasurface maintains stable absorptive performance for incidence angles and is polarization-insensitive due to symmetric electric and magnetic field interactions within each unit-cell. The reported surface current distributions confirm distinct resonant paths corresponding to each frequency band, validating the independent excitation of multiband responses.

The structure [44] is implemented as a 6 × 6 array measuring 180 mm × 190 mm, with standard 0.035 mm copper cladding. No multilayer stacking or active elements are used, and the metasurface relies solely on passive resonance phenomena, enhancing fabrication simplicity and scalability. The angular and polarization robustness, combined with discrete multiband response and high absorptivity, positions this design as a practical reference for multiband passive EM wave absorbers in RF shielding, radar stealth, and energy confinement systems.

A multiband MSA based on a periodic array of five asymmetrically nested splitting resonators (SRRs) designed to achieve polarization-dependent absorption across multiple Wi-Fi frequency bands is presented in [45]. Each unit-cell measures 28.3 mm × 28.3 mm and is fabricated on a 3 mm thick F4B substrate. As illustrated in Fig. 3a. They are laterally displaced along the y-axis, creating asymmetric capacitive coupling and breaking concentric symmetry, which introduces multiple resonant modes under both TE and TM polarizations.

Under TE polarization, the metasurface exhibits high absorption at 2.4, 5.2, and 5.8 GHz with simulated absorptivity values of 0.99, 0.98, and 0.98, respectively. TM polarization activates additional modes at 5.3, 4.6, 6.5, and 6.8 GHz, resulting from altered mutual inductance and redistributed surface current density. Each SRR behaves as a localized LC resonator, and the combined structure forms a coupled resonator array with tunable impedance characteristics. The use of a 377 Ω resistive termination ensures impedance matching with free space, enabling efficient energy dissipation through thin-film resistors embedded within the metasurface.

Simulated angular response shown in Fig. 3b confirms strong stability, maintaining over 90% absorptivity up to 40° for TE and up to 60° for TM incidence. The reported

<figure><img src="image_3.png" /><figcaption>FIGURE 2. (a) Structure of the proposed absorber [44]. (b) Simulated results of absorptivity.</figcaption></figure>
<figure><img src="image_4.png" /><figcaption>**FIGURE 3.** (a) Schematic of the proposed SRRs absorber unit-cell [45]. (b) Simulated absorptivity and reflectivity curves of the SRRs absorber.</figcaption></figure>

power loss density plots reveal spatially selective energy dissipation at the ring corresponding to each operating frequency, verifying distinct current-mode excitation. The metasurface also supports polarization-tunable control, with some bands attenuated or enhanced depending on incident wave orientation, an uncommon feature among passive absorbers.

A 5 × 5 array 141.5 mm × 141.5 mm was fabricated and experimentally validated under anechoic conditions. Measurements closely matched simulations, confirming the metasurface's multiband performance, polarization selectivity, and structural integrity. However, a limitation of this work [45] is the design's reliance on discrete resistive terminations may limit its scalability for integration into continuous or flexible surfaces, and its absorption performance in off-axis polarization conditions beyond 60° remains uncharacterized. Nonetheless, the design exemplifies how structural asymmetry, capacitive tuning, and mutual coupling can be exploited to realize compact, reconfigurable metasurfaces for adaptive absorption applications such as stealth, spectrum filtering, and polarization-diverse energy harvesting.

A compact, sextuple-band EM absorber based on a single-layer metasurface fabricated on a low-cost 1mm thick FR4 substrate is presented in [46]. The unit-cell measures 10 mm × 10 mm, and the absorber operates across six frequency bands ranging from 3.55 to 21.97 GHz,

covering S-, C-, X-, Ku-, and K-bands. The design integrates four resonant geometries, an outer square ring (Design 1), a circular split ring with an inner square (Design 2), a round-holed square ring (Design 3), and a central #-shaped metallic improver (Design 4), each contributing selectively to different resonant peaks.

The structure achieves near-unity simulated response, shown in Fig. 4b confirms absorptivity at all six bands with maximum peaks reaching 99.96% at 5.15 GHz and 94.45% at 21.97 GHz. Experimental results from a 20 × 20 element prototype demonstrate good agreement with simulations, confirming absorptivity above 90% across all bands. The fourfold geometric symmetry ensures polarization insensitivity, while full-wave simulations confirm angle stability up to moderate oblique incidences for both TE and TM modes.

<figure><img src="image_5.png" /><figcaption>**FIGURE 4.** (a) Design steps of the sextuple-band absorber [46]. (b) Absorptivity of the proposed absorber simulated by HFSS.</figcaption></figure>

A notable technical feature is the progressive geometry combination strategy, where each element is added step-by-step to incrementally build and enhance new absorption peaks. The reported field distribution analysis shows strong, localized electric and current densities concentrated at different geometric segments corresponding to each resonance, validating the role of mutual coupling and multimode excitation in peak formation.
This work [46] offers a structurally simple, low-cost, and broadband absorber with a small footprint and ultra-thin profile. Its modular geometry, high absorption efficiency, and manufacturability make it a strong candidate for practical applications such as radar cross-section (RCS) reduction, EMI shielding, and spectrum-selective surfaces. It serves as a benchmark for ultra-thin, multi-peak MSAs using passive geometry-driven optimization.

A triple-band, polarization-insensitive MSA optimized for high-efficiency EM energy harvesting at 2.45, 4.0, and 5.8 GHz is presented in [47]. As illustrated in Fig. 5a, the metasurface is fabricated on a low-loss Rogers RT6006 substrate ($ε_r = 6.45$, $tan δ = 0.0027$) with a thickness of 2 mm. The unit-cell measures 33.5 mm × 33.5 mm and integrates a central cross-shaped resonator with an outer square ring, forming a compact and centrally symmetric design that enables stable absorption under arbitrary polarization without additional complexity.

<figure><img src="image_6.png" /><figcaption>FIGURE 5. (a) Configuration of the proposed metasurface unit-cell with 3D view and resistance distribution on the metal substrate [47]. (b) Triple band structure. (c) Collection efficiency of metasurfaces.</figcaption></figure>

The working mechanism is rooted in multi-resonant mode excitation through structural coupling. The inner cross resonator behaves as a fundamental electric dipole, inducing a strong electric resonance at 2.45 GHz. The outer square ring, equipped with split gaps at its corners, introduces higher-order resonances by enhancing the distributed capacitance and increasing the surface current path length. This combination supports three distinct LC resonant modes, each governed by the interplay between inductive currents along the metal traces and capacitive coupling across gaps and vias. Triple band structure shown in Fig. 5b. The optimized distribution of EM fields at each band ensures energy is strongly confined and dissipated into the matched resistive loads.

Simulated reflection coefficients response shown in Fig. 5c confirms $S_{11}$ values below -25 dB at all three frequencies, corresponding to absorptivity values of 99.2%, 99.4%, and 98.8%, respectively. The metasurface maintains its absorption performance across wide angular ranges, preserving over 90% absorptivity for oblique incidence up to 60° under both TE and TM polarization. The reported surface current distributions further reveal clear modal separation. The first mode is confined to the cross-arm region, while the second and third are predominantly associated with the outer ring structure, validating the resonator configuration and functional role of each geometric feature.

Importantly, the structure uses only two vertical vias per unit-cell, each connected to a standard 50 Ω resistive load. This minimalistic configuration facilitates centralized current collection while preserving impedance matching to free space, thereby enhancing energy dissipation without increasing fabrication complexity. The central symmetry of the design ensures equivalent current induction under orthogonal field components, reinforcing its polarization insensitivity.

Experimental validation is performed on an 8 × 8 metasurface array. The measured absorptivity closely aligns with simulated results across all bands. The structure demonstrates high-efficiency absorption even under low power inputs and across varying incident angles, showcasing robustness against environmental and alignment variability. A critical factor for real-world applications such as ambient RF energy harvesting, stealth technology, and EM shielding.

This work [47] exemplifies an elegant integration of structural resonance engineering, mode separation, and impedance matching to realize a highly efficient, compact, and polarization-insensitive multiband absorber. The design sets a strong precedent for practical, low-profile metasurfaces that maintain absorptive performance under diverse operating conditions without requiring active tuning or multilayer complexity.

The study in [48] presents a highly efficient, compact MSA designed for multiband EM energy harvesting. As illustrated in Fig. 6a the structure employs a 10 mm × 10 mm unit-cell fabricated on a Rogers RT5880 substrate ($ε_r = 2.2$,
<figure><img src="image_7.png" /><figcaption>FIGURE 6. (a) Schematic structure unit-cell front-view and unit-cell back-view [48]. (b) Absorption & reflection of the proposed unit-cell with resistive loads at four distinct resonance frequencies.</figcaption></figure>

$\tan \delta = 0.0009$, thickness 1.575 mm) and incorporates an SRR combined with two outer strip lines and two inner split strip lines. This configuration, enhanced by 45° tilted SRR geometry, is tailored to excite multiple distinct resonant modes, enabling quad-band absorption centered at 3.7, 6.3, 9.9, and 14.2 GHz.

The structure achieves near-unity absorptivity, with simulation results absorption rates of 99.96%, 99.87%, 99.88%, and 99.87% at the respective resonant frequencies showing in Fig. 6b. Each resonance is attributed to a specific geometric element. The outer SRR dominates at 3.7 GHz, while subsequent bands are governed by field interactions within the inner and corner strip lines. The reported field analysis confirms strong electric, magnetic, and surface current confinement localized to the relevant resonators, with anti-parallel current flow enhancing effective power dissipation into the integrated 50 Ω resistive loads.

The absorber demonstrates robust polarization insensitivity, as confirmed by consistent absorption under varying polarization angles. Angular stability is maintained for incident angles up to 45°, with only minor absorption degradation observed at 60° and 75°. This wide-angle performance makes the design particularly well-suited for ambient EM environments.

The metasurface functions on a multi-resonant LC principle, where each resonator layer introduces a separate resonant mode. These modes are efficiently excited via capacitive gaps and inductive paths shaped by the metallic topology.

Experimental validation was conducted using a fabricated 3 × 3 array tested in an anechoic chamber. Measured reflection coefficients closely match simulations, and the EM energy harvesting efficiency (E-HE) exceeds 95% at all resonances under normal incidence. The structure also performs reliably across various resistive loading conditions, maintaining >85% E-HE with load values up to 100 Ω.

Despite its excellent performance, the design [48] exhibits modest efficiency degradation beyond 60° oblique incidence, indicating a potential limitation in extreme-angle deployment scenarios. The overall structure achieves an excellent trade-off between compactness, functionality, and real-world deployability.

This work [48] exemplifies how thoughtful geometric layering, impedance matching, and loss engineering can be synergistically applied to create polarization-independent, multiband, wide-angle MSA with near-perfect absorption, advancing the frontier of practical energy harvesting.

To sum up, Table 1 provides a comparative assessment of reported multiband MSA, highlighting their resonant topologies, substrate characteristics, unit-cell dimensions, operating frequency bands, absorption efficiency, and stability under oblique incidence. The performance of these absorbers is fundamentally governed by the excitation of multiple resonant modes and the extent of impedance matching with free space. Compact single-layer realizations, such as the ELC-based absorber [35] and planar quad- and sextuple-band absorbers [44], [46], [47] employ distributed LC resonances supported by symmetric surface current distributions to achieve polarization-insensitive absorption in a structurally simple form. However, such configurations are generally restricted to a limited number of discrete bands since each resonant inclusion contributes primarily one or two dominant modes.

In contrast, absorbers employing multilayer or nested resonators, such as the porous multilayer [8], trigeminal resonator [14], and hepta-band metasurface [9], utilize multiple current paths and strong capacitive couplings to excite higher-order responses, thereby extending the absorption spectrum to five or more discrete bands. These approaches can deliver efficiencies approaching unity but at the cost of increased thickness, modal overlap, and reduced angular robustness. Functional enhancements are also evident, the polarization-controlled design in [45] achieves mode-selective absorption through anisotropic coupling, while absorbers in [41], [47], and [48], integrate energy-harvesting functionality and demonstrate stable operation in 5G/6G frequency regimes with polarization-insensitive and wide-angle characteristics. Designs incorporating resistive elements or vertical vias [45], [48] further enhance impedance matching across multiple frequencies and preserve absorption under oblique incidence,
<table><caption>TABLE 1. Comparison of multiband metasurface absorbers reported in literature.</caption><thead><tr><th>Ref.</th><th>Topology</th><th>Substrate</th><th>Unit-cell (mm)</th><th>Bands (GHz)</th><th>Absorption</th><th>Angular Stability</th><th>Pol. Sensitivity</th></tr></thead><tbody><tr><td>[8]</td><td>Multiparous square-layer</td><td>FR4 multilayer, ε<sub>r</sub>=4.4, h=1.6 mm</td><td>25 x 25</td><td>Nine bands (5–8.9)</td><td>Peaks ≈99.9%</td><td>Stable at moderate angles</td><td>insensitive</td></tr><tr><td>[9]</td><td>Four symmetric resonators (square, cross, ring, split-ring)</td><td>FR4, ε<sub>r</sub>=4.3, h=1.0 mm</td><td>15.7 x 15.7</td><td>Seven (2.8–19.5)</td><td>Peaks ≈99.8%</td><td>Stable to ~45°</td><td>insensitive</td></tr><tr><td>[14]</td><td>Trigeminal top metal resonator</td><td>FR4 multilayer, ε<sub>r</sub>=4.3, h=1.6 mm</td><td>17 x 17</td><td>Five bands (5.9–20.59)</td><td>Peaks ≈99.8%</td><td>Low-freq stable high-freq sensitive at large angles</td><td>insensitive</td></tr><tr><td>[33]</td><td>Electric LC (ELC) resonator</td><td>FR4, ε<sub>r</sub>=4.3, h=1.5 mm</td><td>16 x 16</td><td>2.45, 5.2</td><td>Peaks ≈97%</td><td>Stable up to 60°</td><td>insensitive</td></tr><tr><td>[39]</td><td>Dual elliptical resonators with enclosed circular ring &amp; metallic strip</td><td>FR4, ε<sub>r</sub>=4.3, h=1.5 mm</td><td>5.8 x 5.8</td><td>28.0, 33.0, 38.0</td><td>Peaks ≈99%</td><td>Stable up to 30° (TE) Stable up to 60° (TM)</td><td>insensitive</td></tr><tr><td>[42]</td><td>Two-patch asymmetric resonators + vias</td><td>F4B, ε<sub>r</sub>=2.2, h=0.76 mm</td><td>≈30 x 31.7</td><td>1.7, 2.4, 3.8, 5.3</td><td>Peaks ≈96%</td><td>Stable at moderate angles</td><td>Insensitive</td></tr><tr><td>[43]</td><td>Coupled SRR + resistive loads</td><td>F4B, ε<sub>r</sub>=2.2, h=3.0 mm</td><td>28.3 x 28.3</td><td>TE: 2.4, 5.2, 5.8<br>TM: 4.6, 5.3, 6.5, 6.8</td><td>99%, 98%, 98%</td><td>TE>90% to 40°<br>TM>90% to 60°</td><td>Tunable</td></tr><tr><td>[44]</td><td>Modular multi-geometry (rings, SRR, #)</td><td>FR4, ε<sub>r</sub>=4.4, h=1.0 mm</td><td>10 x 10</td><td>Six bands (3.55–21.97)</td><td>Peaks ≈99.9%</td><td>Stable at moderate angles</td><td>Insensitive</td></tr><tr><td>[45]</td><td>Central cross + ring + resistive vias</td><td>RT6006, ε<sub>r</sub>=6.45, h=2.0 mm</td><td>33.5 x 33.5</td><td>2.45, 4.0, 5.8</td><td>99.2%, 99.4%, 98.8%</td><td>>90% to 60°</td><td>Insensitive</td></tr><tr><td>[46]</td><td>Tilted SRR + strips + 50Ω loads</td><td>RT5880, ε<sub>r</sub>=2.2, h=1.575 mm</td><td>10 x 10</td><td>3.7, 6.3, 9.9, 14.2</td><td>Peaks ≈99.9%</td><td>Stable to ~45°; degraded 60–75°</td><td>Insensitive</td></tr></tbody></table>

but they impose fabrication challenges due to component integration and scalability concerns. Note that the study in [49], is not included in the present literature review because we were unable to reproduce the key results reported therein under comparable conditions.

Overall, the survey underscores a recurring trade-off, multilayer and resistively loaded absorbers provide extended spectral richness and near-unity absorption at the expense of profile thickness and manufacturing complexity, while single-layer designs offer compactness, robustness, and polarization insensitivity but are spectrally constrained. The outstanding challenge, therefore, remains the realization of low-profile absorbers that simultaneously combine multiband operation, wide angular tolerance, and polarization-independent performance, which may be achieved through hybrid geometries and broadband impedance-engineering strategies.

### C. MULTIBAND FREQUENCY SELECTIVE SURFACE (FSS)

They are a pivotal class of engineered, subwavelength metasurfaces designed to perform spatial filtering at microwave and optical frequencies. By imparting frequency-dependent transmission or reflection characteristics to incident EM waves, FSSs enable precise control over amplitude, phase, and polarization facilitating advanced wavefront shaping and spectral filtering. Typically realized as periodic arrays of metallic or dielectric elements printed on thin substrates, their functionality stems from resonance-driven surface current interactions and EM coupling [17], [18]. Multiband FSSs extend this concept by integrating multiple resonant elements such as split-ring resonators, apertures, or interdigital capacitors within compact unit-cells, enabling operation across several discrete frequency bands [50]. This makes them indispensable in modern high-frequency applications, including 5G, WiMAX, WLAN, radar, and satellite systems. New line achieving optimal performance requires a delicate trade-off between low profile, angular and polarization

stability, high out-of-band rejection, and multi-resonant behavior. These demands are met through geometric and material innovations such as modifying element shapes, tailoring substrate properties, and tuning inter-element spacing and reactive loading. As wave manipulation becomes increasingly central to communication, sensing, and stealth technologies, multiband FSSs continue to emerge as compact, high-efficiency solutions for multi-functional EM platforms.

#### 1) FSS OPERATING PRINCIPLE

Metasurface-based FSSs are two-dimensional periodic arrays of subwavelength resonant elements engineered to provide frequency-selective control of EM wave propagation. [51]. The functionality of FSS illustrated in Fig. 7. They function as spatial spectral filters by manipulating surface-induced resonances, facilitating frequency-dependent transmission, reflection, or absorption. The interaction mechanism is

<figure><img src="image_8.png" /><figcaption>FIGURE 7. The functionality of an FSS [17].</figcaption></figure>
governed by the boundary conditions imposed by Maxwell's equations on the engineered impedance profile of the surface.

A FSS can be modeled as an infinitesimally thin periodic sheet characterized by a surface admittance $Y_s(\omega)$, placed in free space with intrinsic impedance $\eta_0 \approx 377 \, \Omega$. For a normally incident plane wave, the tangential fields satisfy two boundary conditions [52], [53]:

* Continuity of the tangential electric field:

$$E_i + E_r = E_t,$$

* A discontinuity in the tangential magnetic field equal to the induced surface current $J_s = Y_s E_t$:

$$\frac{E_i - E_r}{\eta_0} - \frac{E_t}{\eta_0} = Y_s E_t.$$

Defining the reflection and transmission coefficients as $\Gamma = E_r/E_i$ and $T = E_t/E_i$, the above relations yield

$$\Gamma(\omega) = -\frac{\eta_0 Y_s(\omega)}{2 + \eta_0 Y_s(\omega)}, \quad T(\omega) = \frac{2}{2 + \eta_0 Y_s(\omega)}.$$

These expressions indicate, that when $\eta_0 Y_s \to 0$, the FSS is nearly transparent ($T \to 1$, $\Gamma \to 0$, passband), while for $|\eta_0 Y_s| \gg 2$, transmission is suppressed ($T \to 0$, $|\Gamma| \to 1$, stopband). The frequency dependence of $Y_s(\omega)$ therefore governs the spectral features of the FSS.

Each resonant inclusion in the unit-cell can be represented by a parallel RLC admittance,

$$Y_i(\omega) = \frac{1}{R_i} + j\omega C_i - \frac{j}{\omega L_i},$$

with a resonance at $\omega_{0,i} = 1/\sqrt{L_i C_i}$. For a unit-cell with multiple inclusions, the total admittance is

$$Y_s(\omega) = \sum_{i=1}^{N} Y_i(\omega) + Y_{bg}(\omega),$$

where $Y_{bg}(\omega)$ accounts for background effects such as substrate loading.

This formulation directly explains the origin of multiband FSS behavior each resonant inclusion contributes a distinct resonance, and their superposition produces multiple transmission dips (stopbands) or windows (passbands) [54]. Independent resonances result in well-separated frequency bands, while coupled resonators may hybridize to generate additional or shifted bands. Thus, by embedding multiple resonant elements such as concentric rings, nested slots, or multilayer inclusions compact multiband FSS structures can be realized.

Finally, to prevent the onset of higher-order Floquet modes and maintain the thin-sheet approximation, the lattice period must satisfy the subwavelength condition

$$a < \frac{\lambda_{\min}}{2},$$

where $\lambda_{\min}$ is the minimum free-space wavelength of operation. Deep spectral notches and sharp resonance peaks signify effective resonant filtering. Achieving this performance

requires careful optimization, including tailoring dielectric substrate parameters (permittivity $\epsilon_r$, loss tangent), precise engineering of the unit-cell topology, and ensuring robustness against variations in incident angle and polarization.

## 2) DESIGN EXAMPLES BASED ON FSS

An innovative multiband FSS design based on an aperture-type interdigital structure is introduced in [55], offering a compact, low-profile, and tunable solution for antenna gain enhancement across multiple communication bands. This work develops a bandpass-filter-based FSS unit-cell capable of controlling three resonant frequencies 1.8, 3.7, and 5.2 GHz corresponding to LTE, WiMAX, and WLAN bands, respectively.

The core innovation lies in the capacitive-loaded transmission line, integrated with an interdigital structure at the aperture level. This configuration induces a slow-wave effect, enabling a drastic reduction in physical size from $\lambda/2$ to $\lambda/8$ at the fundamental frequency. This miniaturization is achieved by tailoring the effective electrical length of the unit-cell, which is influenced by the localized capacitance and impedance of the transmission line. The proposed unit-cell illustrated in Fig. 8a measures 11.53 mm × 10.77 mm, fabricated on an FR-4 substrate ($\epsilon_r = 4.4$, $\tan \delta = 0.025$, $h = 1.6$ mm), and arranged into an 8 × 8 array (92.3 mm × 86.2 mm) to serve as a director behind dipole antennas.

From a physical standpoint, the multiband behavior is realized by combining two techniques:

1) Interdigital capacitive loading: By tuning the number, width ($W_3$, $W_5$), and length ($L_5$) of interdigital fingers, the effective capacitance ($C_i$) is adjusted, shifting the second and third resonant frequencies.

2) Step-impedance transmission line: The use of stepped sections with impedance values $Z_1$ and $Z_2$ allows additional tuning of the harmonic resonances by modifying the impedance ratio $K = Z_2/Z_1$. A higher $K$ leads to resonance frequency separation, while a lower $K$ compresses them.

Simulated S-parameters as shown in Fig. 8b reveal excellent transmission characteristics with low insertion losses (2.1 dB at 1.8 GHz, 1.36 dB at 3.7 GHz, and 1.21 dB at 5.2 GHz) and strong return loss suppression (7.4 dB to 23 dB). The reported electric field (E-field), magnetic field (H-field), and current density distributions confirm that each band exhibits spatially distinct field localization validating the decoupled nature of the resonances and the effectiveness of field confinement via structural tuning.

The FSS unit-cell [55] is polarization-insensitive along the x-axis excitation and demonstrates clear control over harmonic resonances. However, under y-polarized excitation, control over harmonic frequencies deteriorates, indicating an anisotropic field response that must be considered during deployment.

While the proposed design excels in gain improvement and compactness, a minor limitation is the directional anisotropy
<figure><img src="image_9.png" /><figcaption>FIGURE 8. (a) Proposed FSS unit-cell: front view and back view [55]. (b) Simulated transmission $|S_{21}|$ and reflection $|S_{11}|$ responses of the FSS.</figcaption></figure>

introduced by the aperture-based geometry, which could affect performance in environments with complex incident wave directions. Furthermore, the structure's tuning is passive dynamic reconfigurability (e.g., tunable varactors) is not addressed. Overall, this work [55] presents a structurally efficient and highly functional FSS director for multiband applications. By synergistically combining aperture inter-digital capacitive loading with stepped-impedance filtering, it delivers precise frequency control, reduced size, and enhanced antenna gain making it well-suited for low-profile

antenna systems, radome integration, and compact multiband wireless communication platforms.

A compact, multilayer FSS structure functioning as a passive gain director for wireless antenna systems is proposed in [56]. The design exploits dual-layer configuration, interdigital coplanar waveguide (ICPW) loading, and step-impedance transmission line theory to realize a miniaturized triple-band passband FSS operating at 1.8, 3.7, and 5.2 GHz, covering LTE, WiMAX, and WLAN communication standards.

The FSS unit-cell, which is illustrated in Fig. 9a measuring only 10.93 mm × 11.48 mm (approximately λ/15 at 1.8 GHz), is engineered using subwavelength resonant techniques. The top layer features a capacitive interdigital ICPW section that controls slow-wave propagation and tailors the dispersion characteristics. This section introduces artificially increased per-unit-length capacitance, which, when combined with miniaturized inductive line segments, leads to an effective reduction in electrical wavelength enabling size compression and resonance tuning without compromising transmission performance.

The bottom layer, symmetrically aligned with the top, consists of a square loop resonator embedded with a double meander line structure. The meander acts as a lumped inductive path, while the loop introduces coupling capacitance and establishes standing-wave current patterns at higher-order harmonics. The combination results in a hybrid multi-resonator topology that supports multiple independently tunable passbands. The first-order mode (1.8 GHz) arises primarily from the ICPW-based slow-wave path and square loop perimeter current. The second-order mode (3.7 GHz) is most sensitive to variations in interdigital parameters (e.g., $L_{13}$, $W_{12}$, number of fingers), showing frequency shift characteristics up to 10% for small geometry changes. The third-order mode (5.2 GHz) is governed by current folding and increased inductive storage in the meander section, leading to higher-order resonance and capacitive decoupling.

Full-wave EM simulations shown in Fig. 9b confirm transmission peaks with low insertion losses (1.4-2.2 dB across bands) and return loss better than -10 dB across the entire operational range. The reported surface current density and E-field distribution maps show clear modal separation, with localized high-density energy zones corresponding to the resonant element responsible for each band. This spatial decoupling validates the claim of low modal interference and confirms successful multiband isolation within a tightly packed unit.

A key strength of the design [56] is its analytical tractability, the authors provide not only full-wave validation but also a parametric sweep of key geometric features, demonstrating the independent tunability of each passband. This modular frequency control offers design flexibility critical for multiband or reconfigurable antenna platforms. However, the structure does exhibit polarization sensitivity due to
<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /><figcaption>FIGURE 9. (a) Schematic structure FSS unit-cell front-view and unit-cell Back-view [56]. (b) Simulated $|S_{21}|$ and $|S_{11}|$ response of the proposed FSS.</figcaption></figure>

its CPW alignment, with optimized transmission observed only under X-polarized excitation. Y-polarized waves exhibit resonance suppression and shifted harmonic behavior, limiting the applicability in circular or dual-polarized systems unless modified. Moreover, while the structure is physically compact and cost-effective (FR4 substrate, low-complexity etching), it remains a passive and static system. Future extensions could explore varactor-loaded or MEMS-based tunability for dynamic spectrum adaptation or integration with intelligent metasurfaces for beam steering. In conclusion, the proposed [56] FSS director represents a highly engineered, multilayer EMI that unites slow-wave ICPW effects, loop-meander hybrid resonance, and stepped-impedance filtering

to deliver a low-profile, high-gain, multiband enhancement surface. Its compact footprint, analytical transparency, and gain-boosting performance position it as a strong candidate for embedded antenna applications in MIMO, 5G base station enclosures, and integrated wireless nodes.

A mechanically flexible, miniaturized FSS structure capable of dual-band operation at 2.4, and 5.5 GHz, specifically optimized for conformal applications, is presented in [57]. The key innovation lies in its via-integrated 3D current path and the use of a single metal-layer construction, enabling a compact EM footprint with robust frequency stability under curvature.

The proposed unit-cell shown in Fig. 10a combines two distinct resonant geometries- a C-shaped dipole (C-dipole) and a meandered end-loaded L-dipole, both realized on a planar FR4 substrate and connected by vertical vias. The

<figure><img src="image_12.png" /></figure>

<figure><img src="image_13.png" /><figcaption>FIGURE 10. (a) Schematic structure FSS unit-cell front-view and unit-cell Back-view [57]. (b) Simulated $|S_{21}|$ response of the proposed FSS under normal incidence.</figcaption></figure>
unit-cell size of the proposed FSS is P = 9 mm for Design A and P = 6.5 mm for Design B. The C-dipole governs the fundamental resonance at 2.4 GHz through distributed planar inductance and capacitance. The L-dipole, utilizing meander segments with vertical and horizontal turns, introduces inductive elongation and capacitive coupling to produce the higher-order stopband at 5.5 GHz.

The full-wave HFSS simulations shown in Fig. 10b validated by Q3D capacitance extraction, exhibit high agreement (≤ 2% deviation), confirming the dual-mode behavior and modal separation. Under normal incidence, both designs demonstrate strong rejection in the stopbands, with Design A exhibiting –10 dB bandwidths of 28.7% (2.4 GHz) and 11.9% (5.5 GHz). Both TE and TM polarization studies up to 85° incidence angle confirm excellent angular and polarization stability, a critical performance metric for curved and conformal surfaces.

The structure's fabrication simplicity (single copper layer + standard vias) and passive behavior eliminate the need for multilayer stacking, embedded components, or active tuning, making it ideal for real-world implementations in wearable electronics, smart EM skins, and curved radar stealth surfaces. This work [57] demonstrates a structurally innovative, electrically compact dual-band FSS that maintains frequency and angular stability under mechanical deformation. The vertically coupled resonator design and independent modal tuning strategy provide a robust and scalable solution for future-generation flexible and conformal EM platforms.

A compact and polarization-insensitive penta-band FSS that achieves highly stable bandstop performance under oblique incidence up to ±54° is introduced in [58]. The design employs a dual-sided metallic pattern on a single FR4 substrate, integrating multiple resonators to independently control five distinct stopbands spanning PCS, WiFi, CBRS, lower WLAN, and X-band satellite communication frequencies.

The FSS unit-cell shown in Fig. 11a measures only $0.1\lambda \times 0.1\lambda$ (where $\lambda$ is the free-space wavelength at the lowest resonance, 1.88 GHz), enabling efficient array tiling with minimal inter-cell spacing. The top surface incorporates a convoluted loop and a meandered crossed dipole, while the bottom layer includes three concentric square loops, two of which are meandered to extend the effective current path without increasing physical dimensions. This layered configuration enables close spectral spacing while maintaining spatial decoupling, significantly reducing mutual coupling between the resonators. Furthermore, strategic corner modifications on the outer loops enhance isolation between adjacent bands, optimizing passband transparency.

The multiband stopband behavior is explained via full-wave surface current mapping and equivalent circuit modeling. At each resonant frequencies (1.88, 2.5, 3.65, 5.44, and 7.58 GHz), the reported surface current traces follow continuous half-wavelength loops with maxima near the path center and nulls at the ends indicative of standing-

<figure><img src="image_14.png" /><figcaption>FIGURE 11. (a) Schematic structure FSS unit-cell front-view and unit-cell Back-view [58]. (b) Measured $|S_{21}|$ response of the proposed FSS under normal incidence.</figcaption></figure>

wave resonance. These resonance modes are individually supported by separate structural elements, ensuring minimal spectral overlap and high modal purity. The use of meandered arms increases the electrical length of the resonators, allowing lower resonant frequencies without enlarging the footprint.

A prototype consisting of an 11 × 11 unit-cell array was fabricated on a standard 1.6 mm FR4 substrate. The design was experimentally validated using a free-space setup with horn antennas and a PNA-L 5235A vector network analyzer. The measurement setup was carefully configured to ensure far-field excitation and wide-angle coverage using multiple waveguide horn antennas. The measured $|S_{21}|$ characteristics as shown in Fig. 11b under both TE and TM polarizations showed excellent agreement with simulation, verifying the structure's spectral integrity and angular stability. Minor deviations in ripple and bandwidth under high-angle incidence were attributed to finite array dimensions and minor alignment imperfections during rotation.

Compared with previously reported multiband FSS structures, the proposed design [58] offers the highest number of independent stopbands (i.e. five) with superior angular stability, polarization insensitivity, and miniaturization. While most existing designs rely on single-layer metallization and are limited to dual- or triple-band responses, the dual-sided approach employed here increases resonator capacity without expanding the footprint or violating PCB thickness
constraints. This makes the structure highly suitable for integrated shielding, filtering, and spatial filtering in compact wireless and satellite communication systems.

A highly selective, multilayer tri-band FSS that leverages complementary resonator geometry and hybrid EM coupling to achieve steep band transitions, wide passbands, and exceptional spectral control is presented in [59]. The proposed design addresses longstanding challenges in multiband FSS design, including modal interference, limited selectivity, and angular degradation, by synthesizing a vertically stacked structure with gridded-double convoluted loops (G-DCL) and their EM complements.

The structure consists of three metallic layers as shown in Fig. 12a etched onto Rogers RO4350B substrates ($\epsilon_r$ = 3.66, tan $\delta$ = 0.0037), separated by PMI foam ($\epsilon_r$ = 1.08). The middle layer integrates the G-DCL resonators comprising a square loop, grid arms, and a circular ring while the top and bottom layers host their complementary slot structures, forming a dual-mode bandpass surface. This arrangement enables simultaneous electric and magnetic dipole coupling, giving rise to third-order filter characteristics as shown in Fig. 12b with multiple transmission poles and zeros.

<figure><img src="image_15.png" /></figure>

<figure><img src="image_16.png" /><figcaption>FIGURE 12. (a) Design of the tri-band FSS element topology showing the 3D perspective view, G-DCL elements, and their complementary counterparts [59]. (b) Frequency response curve of the tri-band FSS.</figcaption></figure>

Three distinct passbands are realized at:

* 3.79 GHz (BW = 2 GHz, 52.8% fractional bandwidth),

* 8.34 GHz (BW = 1.14 GHz, 13.7%),

* 12.52 GHz (BW = 2.46 GHz, 19.7%).

These bands correspond to controlled excitation of distinct current modes the grid structure dominates low-frequency resonance, the square loop governs the mid-band, and the circular ring contributes to high-frequency transmission. Each resonator's contribution is confirmed via full-wave surface current and field density analysis, which show spatially localized, decoupled resonant behavior critical for spectral isolation and wideband coexistence. The structure introduces multiple transmission zeros (e.g., at 6.62, 9.18, 10.0, and 15.1 GHz), which sharply suppress out-of-band leakage and deliver steep roll-offs traits typically absent in conventional metasurfaces.

Simulation results from HFSS are validated experimentally verified through far-field transmission measurements on a fabricated 40 × 40 FSS array (304 mm × 304 mm). The physical implementation uses 0.035 mm copper layers and 5 mm foam spacers to control interlayer coupling. Measured S-parameters show high transmission (>-3 dB) in all passbands and excellent correspondence with simulation. The design exhibits minimal frequency drift under oblique incidence up to 50° for both TE and TM polarizations highlighting robust angular stability.

What sets this work [59] apart is its high-order band-pass behavior within a fully passive, low-profile layout (0.092$\lambda_0$ total thickness) and its deep miniaturization (unit-cell ~ 0.096$\lambda_0$). By harnessing complementary geometries, the authors overcome the classical trade-off between bandwidth and selectivity, achieving both with no need for lumped elements or active tuning. Moreover, the circuit-based design methodology provides a scalable pathway for resonance extension and reconfigurability. In the context of multiband metasurface research, this design [59] exemplifies a next-generation passive EM surface with finely engineered modal behavior, low loss, strong spectral selectivity, and structural simplicity. It offers a compelling platform for high-performance stealth radomes, EM-transparent enclosures, RF filtering layers, and reconfigurable communication apertures.

To summarize, Table 2 provides a comparative assessment of reported multiband FSS, highlighting their resonant topologies, unit-cell dimensions, operating bands, angular stability, and polarization behavior. The spectral behavior of these structures is governed primarily by the excitation of subwavelength resonant modes and the degree of coupling between inductive and capacitive elements within the surface. Compact single-layer realizations, such as the nested loop design in [19] and the capacitive patch with Jerusalem cross in [54] achieve dual- or triple-band filtering responses within a unit-cell size of less than 0.15$\lambda_0$. These designs are attractive for low-profile integration but exhibit limited angular stability and polarization robustness because the
<table><caption>TABLE 2. Comparison of reported multiband frequency selective surfaces.</caption><thead><tr><th>Ref.</th><th>Topology</th><th>Substrate</th><th>Unit-cell (mm)</th><th>Bands (GHz)</th><th>Key performance</th><th>Angular / Pol. notes</th></tr></thead><tbody><tr><td>[19]</td><td>Dual-square loop (Nested squares)</td><td>Rogers RO6010, ε<sub>r</sub>=10.2, h=0.635 mm</td><td>19.75 × 19.75</td><td>Stopband: ~0.868<br>Passband: ~2.4</td><td>IL 11.5 dB</td><td>Normal incidence</td></tr><tr><td>[51]</td><td>Dual-layer circular patches connected by vias</td><td>Rogers RT5880, ε<sub>r</sub>=2.2, h=0.254 mm</td><td>4.3 × 4.3</td><td>Stopband: ~2</td><td>RL&gt;10 dB, BW: 1.28 GHz</td><td>Stable up to 84° for both TE &amp; TM modes; Dual-polarized</td></tr><tr><td>[52]</td><td>Capacitive patches with curled Jerusalem cross</td><td>F4B-M, ε<sub>r</sub>=2.65, h=0.45 mm</td><td>2.3 × 2.3</td><td>Passband: ~ 19.42, 42.78</td><td>IL 0.34/0.24 dB, BW: 4.34, 8.54 GHz</td><td>Stable up to 60° for both TE &amp; TM modes; Polarization-insensitive</td></tr><tr><td>[53]</td><td>Aperture-type interdigital bandpass</td><td>FR4, ε<sub>r</sub>=4.4, h=1.6 mm</td><td>11.53 × 10.77</td><td>1.8, 3.7, 5.2</td><td>IL 2.1/1.36/1.21 dB</td><td>x-axis insensitive, y-axis anisotropic</td></tr><tr><td>[54]</td><td>Dual-layer ICPW + meandered loop</td><td>FR4, ε<sub>r</sub>=4.4, h=1.6 mm</td><td>10.93 × 11.48</td><td>1.8, 3.7, 5.2</td><td>IL 1.4-2.2 dB; RL&gt;10 dB</td><td>Polarization-sensitive (x-axis); Bidirectional pattern</td></tr><tr><td>[55]</td><td>C-dipole + meandered L-dipole</td><td>FR4, ε<sub>r</sub>=4.4, h=0.4,1.6 mm</td><td>9 × 9 / 6.5 × 6.5</td><td>2.4, 5.5 (stop)</td><td>BW 28.7%/11.9%</td><td>Excellent up to 85° (TE/TM)</td></tr><tr><td>[56]</td><td>Dual-layer crossed dipole &amp; concentric meandered loops</td><td>FR4, ε<sub>r</sub>=4.4, h=1.6 mm</td><td>≈16 × 16</td><td>1.88, 2.5, 3.65, 5.44, 7.58</td><td>>25 dB rejection at all bands; Passband IL &gt; -3 dB</td><td>Stable to ±54°; polarization-insensitive</td></tr><tr><td>[57]</td><td>Multilayer G-DCL + slots</td><td>RO4350B, ε<sub>r</sub>=3.66, h=0.168,0.508 mm</td><td>~7.6 × 7.6</td><td>Passband: 3.79, 8.34, 12.52</td><td>RL&gt;10 dB, BW: 2, 1.14, 2.46 GHz</td><td>Minimal drift up to 50°</td></tr></tbody></table>

resonance relies heavily on anisotropic capacitive loading. More advanced interdigital and coplanar waveguide-based geometries [55], [56] introduce slow-wave effects that elongate current paths, thereby miniaturizing the unit-cell to nearly λ/8 while providing precise control of harmonic resonances. However, these approaches typically confine their polarization conversion performance to one axis, restricting their suitability for dual-polarized systems.

Multilayer and complementary designs demonstrate a clear step forward in both spectral selectivity and angular resilience. The dual-layer circular patch FSS with vias in [53] and the dual-layer concentric dipole configuration in [58] enhance mode separation and deliver sharper roll-off with stopband rejections exceeding 25 dB, while maintaining spectral stability up to 70°-80° incidence. Similarly, the multilayer slot-loaded structure in [59] leverages vertical coupling and EM complementarity to achieve five well-defined transmission bands with high rejection levels, although at the expense of profile thickness and fabrication complexity. Flexible and conformal FSSs [57] address a different challenge, maintaining frequency response when mounted on curved surfaces by incorporating meandered dipoles and vertical via connections, thereby expanding applicability to wearable and conformal EM platforms.

Overall, the survey underscores a recurring trade-off, compact single-layer FSSs are easy to integrate and structurally simple but limited in multiband selectivity and polarization insensitivity, whereas multilayer and hybrid designs achieve superior filtering performance and angular stability at the expense of profile thickness and manufacturing complexity. The outstanding challenge, therefore, is to engineer low-profile FSSs that combine multi-band operation, polarization independence, and wide-angle stability, a goal that may be realized by hybrid miniaturized resonators integrated with broadband phase-compensation and tunable materials.

## D. MULTIBAND METASURFACE POLARIZATION CONVERTER (MMPC)

The rapid evolution of modern EM systems spanning wireless communication, radar sensing, and imaging demands

compact high-performance components capable of dynamic and multi-functional wave control. Among the essential aspects of EM wave manipulation, polarization control plays a pivotal role in enhancing signal integrity, channel capacity and device functionality [60], [61], [62], [63]. Conventional polarization control devices are often constrained by bulky structures, narrowband operation and limited adaptability, making them unsuitable for today's frequency-diverse and space-constrained platforms [24]. In response, multiband metasurface polarization converters have emerged as a promising class of planar devices that combine polarization transformation with frequency-selective behavior across multiple operating bands. By engineering subwavelength unit-cell with tailored anisotropy, chirality or geometric phase response, these metasurfaces enable precise polarization conversion such as linear-to-circular or orthogonal linear rotation at multiple discrete frequencies within a single ultra-thin layer [64], [65], [66], [67], [68], [69], [70].

This capability is especially vital for next-generation systems including multiband 5G and 6G antennas, dual and tri-band radar platforms, multispectral sensors and polarimetric imaging systems, where the ability to manipulate polarization at different frequencies in a compact and efficient form factor is critical [71], [72], [73]. Beyond their functional versatility, multiband metasurface converters offer several advantages including low-profile integration, wide angular stability and compatibility with reconfigurable or tunable materials.

### 1) WORKING PRINCIPLE OF MMPC

Multiband metasurface polarization converters manipulate the polarization state of incident EM waves by engineering anisotropic meta-atoms that introduce controlled amplitude and phase differences between orthogonal electric field components across multiple frequency bands. The functionality of MMPC illustrated in Fig. 13

Consider an incident wave with electric field components along orthogonal x and y axes, expressed as

$$E_{\text{in}} = E_{x}\hat{x} + E_{y}\hat{y}. \qquad (1)$$
<figure><img src="image_17.png" /><figcaption>FIGURE 13. Functionality of the MMPC [74].</figcaption></figure>

Upon interaction with the metasurface, each component experiences frequency-dependent transmission coefficients $T_x(\omega) = |T_x(\omega)|e^{j\phi_x(\omega)}$ and $T_y(\omega) = |T_y(\omega)|e^{j\phi_y(\omega)}$, yielding

$$ \mathbf{E}_{\text{out}} = |T_x(\omega)|E_x e^{j\phi_x(\omega)}\hat{x} + |T_y(\omega)|E_y e^{j\phi_y(\omega)}\hat{y}. \quad (2) $$

The polarization conversion is governed primarily by the relative phase difference

$$ \Delta\phi(\omega) = \phi_x(\omega) - \phi_y(\omega), \quad (3) $$

and the amplitude ratio

$$ R(\omega) = \frac{|T_x(\omega)|}{|T_y(\omega)|}. \quad (4) $$

For a linearly polarized incident wave (e.g., $E_x = E_0$, $E_y = 0$), polarization rotation by 90° is achieved if the metasurface imposes

$$ R(\omega) = 1, \quad \Delta\phi(\omega) = \pi, \quad (5) $$

resulting in an orthogonal linear polarization state at the output.

Conversion from linear to circular polarization requires

$$ R(\omega) = 1, \quad \Delta\phi(\omega) = \pm\frac{\pi}{2}. \quad (6) $$

In this scenario, the output electric field becomes

$$ \mathbf{E}_{\text{out}} = E_0 |T_x(\omega)| (\hat{x} \pm j\hat{y}), \quad (7) $$

representing right-hand circular polarization (RHC P) for $+\frac{\pi}{2}$ and left-hand circular polarization (LHC P) for $-\frac{\pi}{2}$.

For a circularly polarized incident wave,

$$ \mathbf{E}_{\text{in}} = \frac{E_0}{\sqrt{2}} (\hat{x} \pm j\hat{y}), \quad (8) $$

the metasurface can convert it to linear polarization by inducing anisotropic transmission such that

$$ |T_x| \neq |T_y| \quad \text{and/or} \quad \Delta\phi \neq \pm\frac{\pi}{2}. \quad (9) $$

The output then becomes elliptically or linearly polarized depending on these parameters [73].

To achieve multiband polarization conversion, the metasurface unit-cell is engineered to support multiple resonances at

frequencies $\omega_i$, resulting in transmission coefficients modeled as

$$ T_{x,y}(\omega) = \sum_{i=1}^{n} \frac{A_{x,y,i}}{j(\omega - \omega_i) + \gamma_i}, \quad (10) $$

where $A_{x,y,i}$, $\omega_i$, and $\gamma_i$ denote resonance strength, resonant frequency, and damping factor, respectively. This multi-resonant behavior enables independent control of phase difference $\Delta\phi(\omega)$ and amplitude ratio $R(\omega)$ at each band, facilitating polarization conversion over multiple frequencies within a compact metasurface platform.

## 2) DESIGN EXAMPLES BASED ON MMPC

Ghosh et al. proposed a compact multi-functional metasurface reflector that enables simultaneous multiband linear-to-linear (LP-to-LP) and linear-to-circular (LP-to-CP) polarization conversion in a low-profile reflective structure [75]. The metasurface design shown in Fig. 14a is based on a SRR loaded cross-dipole pattern, printed on a Rogers RO4003 substrate ($\epsilon_r = 3.55$, thickness = 2.7 mm) and backed by a metallic ground plane. A thin air gap is introduced beneath the substrate to enhance resonance control and phase tuning without increasing structural bulk.

Each unit-cell of the metasurface measures 11 mm × 11 mm, approximately $\lambda/5.5$ at the lowest operational band (~5.35 GHz), enabling compact array

<figure><img src="image_18.png" /><figcaption>FIGURE 14. (a) Schematic structure MMPC unit-cell front-view and unit-cell Side-view [75]. (b) Measured $|S_{11}|$ response of the proposed MMPC under normal incidence.</figcaption></figure>
formation and high spatial resolution in polarization manipulation.

The structure achieves:

* Tri-band LP-to-LP conversion at 5.47-5.68 GHz, 7.86-8.84 GHz, and 14.68-16.83 GHz.

* Quad-band LP-to-CP conversion at 5.30-5.41 GHz, 5.77-7.58 GHz, 9.27-13.91 GHz, and 17.53-19.59 GHz.

The working principle relies on anisotropic current distribution and asymmetric reflection phase response. LP-to-CP conversion is achieved when the co- and cross-polarized reflected components have equal magnitude and a ±90° phase difference. The SRR loading induces structural asymmetry, while the air gap alters the cavity's effective electrical length, enabling fine-tuning of the phase response. LP-to-LP conversion, on the other hand, results from dominant cross-polarized reflection with a 180° phase shift relative to the co-polarized component. The measured |S11| characteristics shown in Fig. 14b.

To reveal the underlying physics, the authors employ characteristic mode analysis (CMA), showing that specific orthogonal eigenmodes (e.g., M1 and M2 at ~5.35 GHz) are responsible for circular polarization. These modes are spatially orthogonal and resonantly excited with the required phase difference. For LP-to-LP conversion, in-phase symmetric modes dominate the response along one axis.

A 16 × 16 prototype metasurface was fabricated and tested. The structure [75] demonstrates a high polarization conversion ratio (PCR ≈ 1) in LP-to-LP bands and excellent circular polarization (axial ratio AR < 3 dB) in the CP bands. Experimental results closely match HFSS simulations, confirming the metasurface's high-efficiency multiband polarization transformation. Additionally, the metasurface's duality-enabled unit-cell is mirrored in a checkerboard phase-gradient configuration to suppress monostatic reflections and achieve RCS reduction. This architecture reduces RCS by more than 10 dB over 5.85-5.95 GHz, 9.2-10.3 GHz, and 16.6-18.5 GHz, demonstrating multifunctionality beyond polarization transformation.

This work [75] represents a structurally elegant and electromagnetically sophisticated metasurface that delivers broadband and multiband LP-to-CP and LP-to-LP polarization conversion with minimal thickness. The combined use of SRR asymmetry, characteristic mode control, circuit modeling, and experimental validation sets a benchmark for passive multi-functional metasurface design. Its integration of polarization control and stealth capability makes it an excellent candidate for next-generation radar systems, conformal communication platforms, and reconfigurable reflectors.

Dutta et al. present a planar, passive metasurface polarization converter capable of eight-band operation achieving four LP-to-LP and four LP-to-CP conversions through a novel integration of two tailored resonator geometries [76]. The metasurface comprises a periodic array of composite unit-cell

measuring 11 mm × 11 mm, fabricated on an FR4 substrate ($ε_r$ = 4.4, thickness = 3.2 mm) and backed by a metallic ground plane as shown in Fig. 15a. Each unit-cell integrates two cascaded resonators, a meandered square ring (Reso. II) and a diagonal split arrowhead strip (Reso. I). Their interplay enables discrete resonant excitation and mutual hybridization, yielding multiple polarization-converting bands within the C, X, and Ku bands.

The metasurface achieves four LP-to-LP conversions at 4.3, 7.2, 12.3, and 15.15 GHz, and four LP-to-CP conversions at 4.0, 4.75–5.95, 8.35–8.8, and 14.35–14.6 GHz. The measured |S11| characteristics shown in Fig. 15b. The polarization transformation is enabled by selective excitation of resonant electric and magnetic surface modes, combined with careful tuning of the co- and cross-polarized reflection phase difference. For LP-to-LP conversion, the structure satisfies the condition where the co-polarized reflection is suppressed and the cross-polarized reflection dominates with a 180° phase difference. For LP-to-CP conversion, both reflection components are equal in magnitude with a ±90° phase offset, resulting in AR below 3 dB across the defined frequency bands.

<figure><img src="image_19.png" /><figcaption>FIGURE 15. (a) Schematic structure MMPC unit-cell front-view [76]. (b) Measured |S11| response of the proposed MMPC under normal incidence.</figcaption></figure>
The physical mechanism behind these conversions is modeled using a 4-port scattering matrix framework. Polarization rotation occurs when incident waves decomposed along the ±45° axes experience differential phase shifts. An analytical model was developed to express the resulting reflected E-field:

$$ \vec{E}_r = (\hat{\alpha}R_{\alpha\alpha}E_\alpha e^{i\phi_{\alpha\alpha}} - \hat{\beta}R_{\beta\beta}E_\beta e^{i\phi_{\beta\beta}})e^{ikz} $$

where $\phi_{\alpha\alpha} - \phi_{\beta\beta} = \pi$ satisfies LP-to-LP, and $\phi_{\alpha\alpha} - \phi_{\beta\beta} = \pm \frac{\pi}{2}$ satisfies LP-to-CP conversion.

The reported surface current analysis confirms the excitation of parallel in-phase currents at 4.3 and 15.15 GHz (electric dipole modes), and anti-parallel loop currents at 7.2 and 12.3 GHz (magnetic resonance), establishing the LP-to-LP behavior. For LP-to-CP bands, orthogonal surface current components are observed with proper phase separation, producing circularly polarized reflection. The combination of Reso. I and Reso. II enables distinct control over field symmetry and resonant path length, allowing precise tuning of frequency-specific polarization modes. Reso. I governs higher bands through electric field confinement in the arrowhead geometry, while Reso. II supports lower-band magnetic response through increased inductive loading. Their hybrid coupling produces additional modes such as the 12.3 GHz LP-to-LP band. Parametric optimization of resonator dimensions (e.g., $a_1$, $a_2$, and $w_2$) ensures high polarization conversion ratios (PCR > 95%) and modal separation.

A 10 × 10 prototype array (110 mm × 110 mm) was fabricated and tested. Experimental results exhibit excellent correlation with full-wave simulations. The structure maintains stable polarization conversion under TE and TM incidence up to 15°, and sensitivity analysis shows tolerance to fabrication variations and dielectric fluctuation.

In summary, this metasurface [76] showcases a deeply engineered dual-resonator architecture that achieves robust, multi-band LP and CP conversion through hybrid electric and magnetic resonant modes. Its passive, single-layer construction, compact footprint, and strong experimental validation make it highly applicable to modern RF systems, including adaptive antennas, RCS-reducing skins, and polarization-agile communication platforms.

The paper in [77] presents a compact reflective metasurface designed to achieve multi-band polarization conversion across the X-band, Ku-band, and K-band, targeting advanced 6G satellite communication systems. The metasurface unit-cell shown in Fig. 16a measures 3.6 mm × 3.6 mm and is fabricated on a Rogers RO3003 substrate ($\epsilon_r = 3.0$, $\tan \delta = 0.001$, thickness = 1.52 mm). The top layer consists of two asymmetrically slotted SRR and a −45° slotted diagonal metallic stripe, while a solid copper ground plane forms the bottom layer.

The metasurface supports dual-mode polarization control, achieving LP-to-LP in three Ku-band sub-bands: 12.16-12.81 GHz, 15.28-15.66 GHz, and 17.94-18.73 GHz, and LP-to-CP conversion in four frequency bands: LHCP

<figure><img src="image_20.png" /><figcaption>FIGURE 16. (a) Schematic structure-the unit-cell front view side view and UV-axis [77]. (b) Measured $|S_{11}|$ response of the proposed unit-cell.</figcaption></figure>

at 10.90-11.90 GHz (X-band) and 15.84-17.63 GHz (Ku-band), and RHCP at 13.12-15.08 GHz (Ku-band) and 19.11-21.0 GHz (K-band). Each mode demonstrates > 90% PCR or AR < 3 dB, confirming high conversion efficiency.

The operational mechanism relies on modal excitation and precise surface current manipulation. The outer SRR (Ring 1) with a single slot and the inner SRR (Ring 2) with two slots induce magnetic resonances through circulating currents in their loops and capacitive coupling at the gaps. At LP-to-LP resonances, such as at 12.48 GHz, the dominant $E_u$ eigenmode arises due to currents on Ring 1 forming an anti-parallel path with the ground plane, producing a 180° phase shift and orthogonal polarization rotation. The slotted diagonal stripe acts as a symmetry-breaking element for LP-to-CP operation, enabling excitation of orthogonal current components with ±90° phase difference between $E_u$ and $E_v$. For example, at 18.32 GHz, strong anti-parallel currents aligned with the stripe produce quadrature phase-separated modes, resulting in pure RHCP.

The measured $|S_{11}|$ characteristics shown in Fig. 16b. Modal excitations at 12.46 GHz, 15.39 GHz, and 18.25 GHz correspond to distinct field distributions: $E_u$-dominant modes at 12.46 GHz and 18.25 GHz (linked to Ring 1 and stripe), and an $E_v$-dominant mode at 15.39 GHz (linked to Ring 2). These modes are tuned through slot geometry and inter-resonator coupling, enabling non-adjacent frequency bands for orthogonal polarizations crucial for Satcom signal isolation.
Simulations demonstrate angular stability up to 45° incidence for both TE and TM modes, with PCR > 90% [77]. Experimental validation on a 32 × 25 cell prototype (224 mm × 175 mm) confirms LP-to-LP conversion at 12.48, 15.46, and 18.32 GHz, and CP operation with AR < 3 dB and ellipticity ±1 across all CP bands. Measured results closely match simulations, with minor frequency deviations < 0.5% due to fabrication tolerances.

CP bandwidths (1–1.96 GHz) could be expanded for ultra-wideband Satcom, reconfigurability is absent, and thermal/mechanical stability for space environments is not addressed. This work [77] presents a well-optimized, multi-band reflective metasurface that leverages modal engineering and geometrical asymmetry for high-efficiency polarization manipulation. Its compactness, spectral versatility, and angular robustness make it highly suitable for next-generation 6G satellite communication platforms.

The paper [78] presents a compact reconfigurable metasurface polarization converter capable of six distinct polarization transformation functions over multiple frequency bands by exploiting the combined effects of a butterfly-shaped metallic resonator and PIN diode-controlled reconfigurability. The unit-cell shown in Fig. 17a, measures 8.7 × 8.7 mm² and features two orthogonal arc-shaped metallic arms (Arcₓ and Arcᵧ), rotated by 90° and connected at a central junction. This geometry supports both dipole-like and loop-like current paths, enabling multiple resonant modes across the microwave spectrum.

<figure><img src="image_21.png" /><figcaption>FIGURE 17. (a) Schematic structure of metasurface Unit-cell front-view [78]. (b) Simulated $|S_{11}|$ response of the proposed unit-cell reflection coefficient for PIN ON and PIN OFF states.</figcaption></figure>

The working principle is governed by the phase difference $\Delta\phi$ between orthogonal reflection coefficients $R_{xx}$ and $R_{yy}$. For LP-to-LP conversion, $\Delta\phi \approx 180°$ is achieved, producing linear Polarization (LP) to cross-Linear Polarization (XLP) by suppressing co-polarized reflection via strong inter-arm coupling. For LP→CP, $\Delta\phi \approx 90°$ with $|R_{xx}| \approx |R_{yy}|$ is realized, generating either LHCP or RHCP depending on the sign of the phase shift.

PIN diodes integrated at the arm junction dynamically alter the inter-arm coupling network. In the given Fig. 17b the simulated response of the proposed unit-cell is shown for the PIN ON and PIN OFF states. In the ON state (low impedance), the diodes short the junction, increasing magnetic and electric coupling between orthogonal arms. This enhances cross-polarized reflection, broadens bandwidths, and suppresses certain co-polarized modes. In the OFF state (high impedance), the diodes isolate the arcs, introducing additional capacitances that shift resonant frequencies and allow the excitation of different mode sets.

The metasurface's multi-band behavior arises from the excitation of distinct modal currents along different arm lengths and coupling paths. Shorter arcs resonate at higher-order modes in the Ku-band (14-17 GHz), while the longer current loops dominate lower-frequency resonances in the X-band (~7-9 GHz). The ON state produces LP→XLP conversion in 7.3-8.9 GHz and 19.4-24.9 GHz, and LP→LHCP in 9.8-17.4 GHz. The OFF state supports LP→XLP in 8.9-13.2 GHz and LP→RHCP in 7.6-8.3 GHz and 14.7-16.8 GHz. Experimental measurements confirm high PCR > 90% for LP-to-LP functions and AR < 3 dB for CP functions across targeted bands, with frequency deviations <0.5% due to fabrication tolerances. The design achieves six polarization functions without increasing structural complexity, surpassing prior works limited to 2-5 bands. However, ON-state diode losses ($R_s \approx 7.8 \ \Omega$) slightly reduce efficiency, and the lack of angular stability characterization leaves performance under oblique incidence uncertain. High-frequency Ku/K-band operation also remains experimentally unverified due to measurement limitations.

This work [78] demonstrates a highly compact, reconfigurable, multi-modal metasurface whose resonant behavior is actively tailored through controlled current coupling. By combining geometric multi-resonance with PIN-diode tuning, it achieves unprecedented multifunctionality for polarization manipulation, making it a strong candidate for adaptive communication, stealth, and sensing platforms in dynamic RF environments.

Li et al. [79] propose a low-profile tri-functional metasurface that unifies cross-polarization conversion (CPC), LP-to-CP, and absorption within a compact unit-cell, achieving wideband and multiband responses across microwave and millimeter-wave regimes. The unit-cell shown in Fig. 18a is composed of a circular SRR enclosed by four L-shaped metallic arms, fabricated on a 1.6 mm FR-4 substrate ($\epsilon_r = 4.3$, $\tan\delta = 0.02$) with a lattice period of 5.5 mm. The hybridization of the SRR and orthogonal dipole arms
<figure><img src="image_22.png" /><figcaption>FIGURE 18. (a) Schematic structure of metasurface unit-cell front-view [79]. (b) Simulated $|S_{11}|$ response of the proposed unit-cell reflection coefficient.</figcaption></figure>

produces multiple EM modes (magnetic dipole resonance from the SRR, electric dipole resonance from the L-strips, and hybridized modes at higher frequencies).

The working principle of the metasurface is governed by modal phase manipulation of reflection coefficients. For CPC, the SRR supports loop currents that induce a $\pi$ phase shift ($\Delta\phi = 180^\circ$) between co- and cross-polarized reflection coefficients, yielding a PCR above 90% across 12.76-24.86 GHz. In CP operation, the orthogonal L-shaped strips excite degenerate eigenmodes ($E_u, E_v$) with nearly equal amplitude and quadrature phase difference ($\Delta\phi \approx \pm 90^\circ$). This produces dual-band CP conversion with AR < 3 dB across 11.5-12.3 GHz and 25.88-29.65 GHz, enabling both left- and right-handed circular polarization depending on phase orientation.

At higher frequencies, capacitive coupling between metallic strips and the ground plane excites localized surface currents, leading to resistive dissipation and strong absorption. A peak absorptivity of nearly 96% is achieved at 31.18 GHz.

The simulated $|S_{11}|$ characteristics shown in Fig. 18b. Surface current analysis confirms the modal mechanisms. (i) SRR anti-parallel currents induce CPC, (ii) orthogonal strip currents with $\pm 90^\circ$ phase enable CP, and (iii) edge-localized currents at higher frequencies yield absorption.

Experimental validation on a 60 × 60 array (330 × 330 mm²) demonstrated PCR > 90%, AR < 3 dB, and absorption > 90%, consistent with simulation. Angular stability was observed up to 20° for CPC, 40° for CP, and 30° for absorption.

With its ultrathin profile ($0.016\lambda_0$), multi-functionality, and passive operation, this [79] design demonstrates how structural hybridization of SRRs and L-strips can consolidate multiband polarization manipulation and absorption in a single metasurface, paving the way for practical applications in stealth technology, spectral filtering, and reconfigurable communication systems.

To summarize, Table 3 provides a comparative assessment of reported MMPCs, focusing on their unit-cell geometries, operational frequency bands, conversion types, and polarization conversion efficiency. The fundamental operation of these converters relies on inducing anisotropy or controlled symmetry-breaking within the resonator geometry to generate a prescribed phase delay between orthogonal electric field components, thereby enabling LP-to-LP and LP-to-CP transformations across multiple frequency bands. Early ultrathin metasheets [64], [65], [66], [67], [68] established the feasibility of achieving dual and triple-band polarization conversion using compact resonators that excite multiple eigenmodes within a single unit-cell. These structures achieved high PCR but remained limited in angular stability, as phase orthogonality degraded rapidly with oblique incidence.

The next stage of development emphasized broadband and multi-functional capability. The X-band multi-functional converter and the reflective metasurface in [73], [75] extended polarization transformation to wide frequency ranges, with additionally supporting simultaneous LP-to-LP and LP-to-CP conversion. More complex hybrid designs [76] pushed the state of the art further by combining electric and magnetic dipole resonances to achieve up to eight distinct conversion bands across C-, X-, and Ku-bands. While this approach demonstrated remarkable spectral multiplicity, the strong modal coupling increased fabrication sensitivity and constrained robustness. Compact approaches such as the slotted-SRR design in [77] improved efficiency in Ku- and K-bands, achieving PCR values above 90% and AR below 3 dB, which are particularly relevant for satellite and 6G systems.

Recent works [78], [79] highlight a transition toward reconfigurable and multi-functional platforms. The reconfigurable metasurface in [78] enabled tunable and multi-functional conversion by embedding active elements, while the tri-functional metasurface in [79] combined polarization conversion with absorption capability, underscoring the growing emphasis on multifunctionality for stealth and adaptive communication systems.

Taken together, Table 3 demonstrates the steady evolution of MMPCs from simple ultrathin metasheets offering limited bands, through broadband and hybrid designs with extended functionality, to the emerging class of reconfigurable and
<table><caption>TABLE 3. Comparison of reported multiband metasurface polarization converters.</caption><thead><tr><th>Ref.</th><th>Topology</th><th>Substrate</th><th>Unit-cell (mm)</th><th>Bands / Type</th><th>Key Metrics</th><th>Angular notes</th></tr></thead><tbody><tr><td>[62]</td><td>Square ring with 5 diagonal patches</td><td>FRA, ε<sub>r</sub>=4.3, h=0.3 mm</td><td>7.2 x 7.2</td><td>Triple LP→CP (X, Ka, Ka)</td><td>PCR&gt;90%; AR&lt;3 dB</td><td>Stable ±25°</td></tr><tr><td>[63]</td><td>Two oppositely faced quarter rings</td><td>FR4, ε<sub>r</sub>=4.1, h=1.6 mm</td><td>11 x 11</td><td>Dual LP→CP (Reflective)</td><td>PCR≈1; AR&lt;3 dB</td><td>Stable up to 30°</td></tr><tr><td>[64]</td><td>Square ring + diagonal split circular ring</td><td>FR4, ε<sub>r</sub>=4.4, h=0.3 mm</td><td>5.2 x 5.2</td><td>Dual LP→CP (Ku, Ka)</td><td>PCR&gt;90%; AR&lt;3 dB</td><td>Stable ±45° (Ku), ±30° (Ka)</td></tr><tr><td>[66]</td><td>Square ring + diagonal split circular ring</td><td>FR4, ε<sub>r</sub>=4.4, h=0.3 mm</td><td>5.2 x 5.2</td><td>Dual LP→CP (Ku, Ka)</td><td>PCR&gt;90%; AR&lt;3 dB</td><td>Stable small angles</td></tr><tr><td>[71]</td><td>Two-corner-cut square patch</td><td>FR4, ε<sub>r</sub>=4.3, h=1.6 mm</td><td>6.92 x 6.92</td><td>CPC (8–12 GHz) Dual LP→CP</td><td>PCR&gt;90%; AR&lt;3 dB</td><td>stable up to 45°/30°</td></tr><tr><td>[73]</td><td>SRR cross-dipole + air gap</td><td>RO4003, ε<sub>r</sub>=3.55, h=2.7 mm</td><td>11 x 11</td><td>Tri LP→LP; Quad LP→CP</td><td>PCR≈1; AR&lt;3 dB; RCS&gt;10 dB</td><td>Stable at wide angle</td></tr><tr><td>[74]</td><td>Meander + arrowhead</td><td>FR4, ε<sub>r</sub>=4.4, h=3.2 mm</td><td>11 x 11</td><td>4 LP→LP; 4 LP→CP</td><td>PCR≈1; AR&lt;3 dB</td><td>Stable small angles</td></tr><tr><td>[75]</td><td>Dual-slotted SRRs + stripe</td><td>RO3003, ε<sub>r</sub>=3.0, h=1.52 mm</td><td>3.6 x 3.6</td><td>Multi LP→CP + LLP</td><td>PCR&gt;90%; AR&lt;3 dB</td><td>Stable to 45°</td></tr><tr><td>[76]</td><td>Butterfly arcs + PIN diodes</td><td>FR4, ε<sub>r</sub>=4.4, h=2.7 mm</td><td>8.7 x 8.7</td><td>6 functions</td><td>PCR&gt;90%; AR&lt;3 dB</td><td>Reconfigurable; diode losses</td></tr><tr><td>[77]</td><td>SRR + L-arms</td><td>FR4, ε<sub>r</sub>=4.4, h=1.6 mm</td><td>5.5 x 5.5</td><td>1 CPC; 2 LP→CP; Absorp @31.18 GHz</td><td>PCR&gt;90%; AR&lt;3 dB; Abs≈96%</td><td>CPC~20°, CP~40°, Abs~30°</td></tr></tbody></table>

multi-functional platforms. Despite these advances, the majority of designs remain passive and restricted to near-normal incidence, as the phase balance necessary for polarization conversion deteriorates under oblique angles. The outstanding challenge, therefore, is to realize wide-angle, reconfigurable MMPCs that integrate tunable materials such as VO₂, graphene, or liquid crystals with active or programmable elements, thereby enabling adaptive polarization manipulation across multiple frequency bands for next-generation wireless, radar, and stealth technologies.

## E. FROM ABSORPTIVE AND REFLECTIVE METASURFACES TO RIS AND HOLOGRAPHIC SURFACES

The EM principles governing absorptive and reflective metasurfaces naturally extend to the operational paradigms of RISs and emerging holographic surfaces, enabling a unified physical framework for next-generation 6G communication, sensing, and wireless power transfer (WPT) systems. In absorptive metasurfaces, engineered loss mechanisms achieved through surface-impedance matching, critical coupling of resonant modes, or resistively/nonlinearly loaded meta-atoms enable controlled suppression of reflections and mitigation of undesired interference [79], [80], [81].

Reflective metasurfaces, in contrast, manipulate the spatial distribution of the surface impedance

$$Z_s(x, y) = R(x, y) + jX(x, y)$$

and generate prescribed phase profiles:

$$\phi(x, y) = \arg\{\Gamma(x, y)\}, \\ \Gamma(x, y) = \frac{Z_s(x, y) - \eta_0}{Z_s(x, y) + \eta_0},$$

for dynamic beam steering, polarization transformation, or wavefront reshaping. These behaviors arise from tailored electric, magnetic, and magnetoelectric surface susceptibilities, which define how meta-atoms redistribute radiative and

reactive power through resonance-induced modal interactions [82], [83]. Together, these mechanisms form the core physical foundations upon which RIS, holographic MIMO panels, and large-aperture wave-manipulation platforms are constructed.

In contemporary RIS implementations, a programmable reflective metasurface modifies the propagation channel by reconfiguring the amplitude and phase response of each unit-cell. Traditional RIS approaches minimize loss to maximize received signal power, functioning as nearly ideal re-radiating reflectors. However, insights from absorptive metasurfaces are increasingly influential. By integrating controllable resistive or nonlinear components, a RIS can selectively absorb incident fields to perform interference cancellation, multi-user isolation, and physical-layer security enhancement. Hybrid absorptive reflective RIS architectures offer spatially varying energy management capabilities, enabling more expressive channel shaping than phase-only or fully reflective surfaces. Such hybrid designs allow the RIS to suppress unwanted multipath components while simultaneously enhancing desired signal directions [83], [84].

Holographic surfaces characterized by densely sampled apertures and continuous-wave equivalent holographic modulation also rely fundamentally on metasurface absorption and reflection theory [85]. High-resolution holographic beam synthesis demands precise phase and amplitude control at subwavelength scales. Reflective-phase engineering dictates how interference fringes are constructed across the aperture, while strategically introduced absorption suppresses parasitic Floquet modes, grating lobes, and unwanted radiation channels. Through coordinated control of radiative (scattering) and non-radiative (absorptive) pathways, holographic surfaces achieve advanced functionalities such as multi-beam generation, spatial multiplexing, near-field focusing, and self-interference minimization capabilities essential for holographic MIMO arrays in 6G transceivers.
The EM principles described above directly relate to recent developments in programmable reflective architectures. Zhang et al. [86] propose a cooperative zero-energy double-RIS system for wireless power transfer, where each RIS tile operates as a passive, energy-autonomous wave manipulator. Their formulation employs a reflection-operator model equivalent to the impedance-controlled response of metasurfaces, with phase-shift matrices jointly optimized with access point (AP) transmit precoders to minimize power consumption under nonlinear harvesting constraints. The double-bounce propagation path introduced between two RIS layers demonstrates that the effectiveness of system-level optimization fundamentally depends on accurate control of the underlying surface impedance a design capability central to multiband absorbers. Thus, metasurface designs form a physical-layer benchmark against which frequency-selective power-routing or energy-focusing double-RIS systems may be evaluated.

Jalali et al. [87] introduce shape-adaptive reconfigurable holographic surfaces (RHS), wherein the aperture itself is dynamically reconfigured using binary activation matrices. While the RHS framework is optimized for real-time beam shaping and spatial multiplexing, its functionality is rooted in the same subwavelength field-synthesis principles that govern metasurface resonance engineering. Geometric deformation or aperture segmentation alters the distributed inductance and capacitance, inducing shifts in eigenfrequencies and modal distributions identical in nature to those observed in multiband metasurface unit-cell. By establishing these theoretical parallels, static or quasi-static multiband platforms represent foundational EM structures from which adaptive holographic beamformers evolve.

Extending metasurface principles to RIS and holographic platforms enables simultaneous wireless information and power transfer (SWIPT), ambient RF harvesting, and energy recycling. Reflective metasurfaces can direct RF power to receivers or rectennas, while absorptive surfaces convert intercepted energy into heat or DC via embedded rectifiers. Dynamic reconfiguration allows a single surface to switch between communication (phase-dominant reflection), interference suppression (directional absorption), and energy harvesting (impedance-matched absorption), with aperture partitioning supporting concurrent modes aligning with 6G visions of intelligent, self-sustaining EM environments [83].

The close link between absorptive/reflective metasurface physics and RIS/holographic implementations emphasizes the importance of modal coupling, impedance engineering, and reactive power management across large apertures. These factors govern phase resolution, beam quality, and trade-offs in energy efficiency, bandwidth, and spectral agility, highlighting metasurfaces as foundational physical-layer enablers for programmable, energy-aware, and holographically controlled wireless systems.

### III. CONCLUSION

This review has provided a consolidated framework for understanding multiband metasurfaces, with emphasis on three pivotal categories absorbers, FSS, and polarization converters. Multiband absorbers exploit multi-resonant elements, impedance tailoring, and geometry-driven hybridization to achieve near-unity absorption across several frequency bands with polarization and angular stability. FSS structures, on the other hand, enable compact and highly selective spectral filtering by embedding multiple resonators within subwavelength unit-cell, offering a pathway toward miniaturized and high-efficiency spatial filters. Finally, multiband polarization converters extend the frontier of wave manipulation by enabling simultaneous LP-to-LP and LP-to-CP conversions within planar platforms, paving the way for multi-functional, ultra-thin EM modules.

Looking ahead, multiband absorbers demand further innovation to overcome trade-offs between absorption efficiency and angular stability. The incorporation of reconfigurable materials, active elements, or hybrid passive-active architectures can expand functionality toward tunable and adaptive EM shields, with particular relevance to energy harvesting and stealth technologies. For multiband FSS, future opportunities lie in achieving extreme miniaturization, wideband angular robustness, and polarization-independent operation, while exploring flexible and conformal implementations for integration into wearable, satellite, and high-frequency 5G/6G platforms. Similarly, multiband polarization converters hold untapped potential in combining high conversion efficiency with real-time tunability, enabling adaptive polarization control in massive MIMO, radar imaging, and secure wireless systems.

Despite their demonstrated promise, several practical bottlenecks must be addressed for real-world deployment. Fabrication tolerances in subwavelength features, scalability to limited or large-area implementations, and integration with complex antenna architectures present significant challenges. At higher frequencies, particularly in the millimeter-wave and sub-THz regimes, conductor and dielectric losses, thermal stability, and packaging constraints remain critical hurdles that must be mitigated through advances in low-loss materials, precision manufacturing, and robust integration strategies. Continued progress in material engineering, design methodologies, and system-level integration will ensure that multiband metasurfaces remain at the forefront of EM innovation in the coming decade.

### REFERENCES

[1] N. Yu and F. Capasso, "Flat optics with designer metasurfaces," *Nature Mater.*, vol. 13, no. 2, pp. 139-150, Feb. 2014.

[2] C. L. Holloway, E. F. Kuester, J. A. Gordon, J. O'Hara, J. Booth, and D. R. Smith, "An overview of the theory and applications of metasurfaces: The two-dimensional equivalents of metamaterials," *IEEE Antennas Propag. Mag.*, vol. 54, no. 2, pp. 10-35, Apr. 2012.

[3] T. J. Cui et al., "Roadmap on electromagnetic metamaterials and metasurfaces," *J. Phys., Photon.*, vol. 6, no. 3, Jul. 2024, Art. no. 032502.
[4] M. Kang, L. Chen, S. Qin, L. Ma, A. Rui, and S. Li, "Bifunctional electromagnetic manipulation of surface waves using metasurfaces under one circularly polarized incidence," *Photonics*, vol. 12, no. 1, p. 91, Jan. 2025.

[5] H.-T. Chen, A. J. Taylor, and N. Yu, "A review of metasurfaces: Physics and applications," *Rep. Prog. Phys.*, vol. 79, no. 7, Jul. 2016, Art. no. 076401.

[6] Z. Rahimian Omam, H. Taghvaee, A. Araghi, M. Garcia-Fernandez, G. Alvarez-Narciandi, G. C. Alexandropoulos, O. Yurduseven, and M. Khalily, "Holographic metasurfaces enabling wave computing for 6G: Status overview, challenges, and future research trends," 2025, arXiv:2501.05173.

[7] M. Koohestani and A. Ghaneizadeh, "An metasurface patch antenna for uhf rfid applications," *Sci. Rep.*, vol. 11, no. 1, p. 857, 2021.

[8] C. M. Tran, H. Van Pham, H. T. Nguyen, T. T. Nguyen, L. D. Vu, and T. H. Do, "Creating multiband and broadband band metamaterial absorber by multiporous square layer structure," *Plasmonics*, vol. 14, no. 6, pp. 1587-1592, Dec. 2019.

[9] M. Kurt, G. Ozturk, and M. Ertugrul, "Hepta-band ultra-thin metasurface absorber for S-, C-, X-, Ku-, and K-band applications," *Arabian J. Sci. Eng.*, vol. 50, no. 21, pp. 17813-17826, Nov. 2025.

[10] A. M. Shaltout, V. M. Shalaev, and M. L. Brongersma, "Spatiotemporal light control with active metasurfaces," *Science*, vol. 364, no. 6441, p. 3100, May 2019.

[11] C. M. Watts, X. Liu, and W. J. Padilla, "Metamaterial electromagnetic wave absorbers," *Adv. Mater.*, vol. 24, no. 23, pp. OP98-OP120, Jun. 2012.

[12] B. Kamal, U. Ali, J. Chen, and S. Ullah, "Applications of metamaterials and metasurfaces," in *Metamaterials*, A. Kuznetsov, Ed., London, U.K.: IntechOpen, 2022, ch. 1.

[13] Q. Zhou, W. Ma, T. Wu, Y. Li, Q. Qiu, J. Duan, J. Li, L. Jiang, W. Zhou, Y. Gao, J. Huang, and Z. Huang, "Metasurface terahertz perfect absorber with strong multi-frequency selectivity," *ACS Omega*, vol. 7, no. 41, pp. 36712-36727, Oct. 2022.

[14] H. Wu, S. Ji, J. Zhao, C. Jiang, and H. Dai, "Design and analysis of a five-band polarization-insensitive metamaterial absorber," *Int. J. Antennas Propag.*, vol. 2020, pp. 1-12, Dec. 2020.

[15] T. C. Do, B. X. Khuyen, B. Son Tung, N. N. Viet, D. T. Ha, V. T. H. Hanh, X. P. Do, D. Khanh Tung, H. A. Nguyen, and V. Dinh Lam, "Wide-angle electromagnetic wave absorption via multilayer metamaterial structures," *Phys. Scripta*, vol. 100, no. 2, Feb. 2025, Art. no. 025538.

[16] M. Ciabattoni, Z. Hayran, and F. Monticone, "Observation of broadband super-absorption of electromagnetic waves through space-time symmetry breaking," *Sci. Adv.*, vol. 11, no. 3, Jan. 2025.

[17] X. Chen, J. Tan, L. Kang, F. Tang, M. Zhao, and N. Kato, "Frequency selective surface toward 6G communication systems: A contemporary survey," *IEEE Commun. Surv. Tut.*, vol. 26, no. 3, pp. 1635-1675, 3rd Quart., 2024.

[18] R. Anwar, L. Mao, and H. Ning, "Frequency selective surfaces: A review," *Appl. Sci.*, vol. 8, no. 9, p. 1689, Sep. 2018.

[19] M. Koohestani, R. Perdriau, M. Ramdani, and J. Carlsson, "Frequency selective surfaces for electromagnetic shielding of pocket-sized transceivers," *IEEE Trans. Electromagn. Compat.*, vol. 62, no. 6, pp. 2785-2792, Dec. 2020.

[20] J. Hu, S. Bandyopadhyay, Y.-H. Liu, and L.-Y. Shao, "A review on metasurface: From principle to smart metadevices," *Frontiers Phys.*, vol. 8, Jan. 2021.

[21] L. Zhao, Y. Fang, and Z. Wang, "Dual-band polarization conversion metasurface with low profile and wide angular stability," *IEEE Antennas Wireless Propag. Lett.*, vol. 23, no. 2, pp. 1349-1353, Feb. 2024.

[22] H. Yang, S. C. Wang, P. Li, Y. He, and Y. J. Zhang, "A broadband multifunctional reconfigurable polarization conversion metasurface," *IEEE Trans. Antennas Propag.*, vol. 71, no. 7, pp. 5759-5767, Jul. 2023.

[23] L. Zhang, C. Gao, H. Guo, H. Zhang, Z. Zhao, and T. Liu, "Efficient polarization conversion metasurface for scattered beam control and RCS reduction," *Sci. Rep.*, vol. 14, no. 1, p. 26260, Nov. 2024.

[24] H. Z. Khan, J. Zafar, A. Jabbar, J. U. R. Kazim, M. U. Rehman, M. A. Imran, and Q. H. Abbasi, "Advancements in metasurfaces for polarization control: A comprehensive survey," *Next Res.*, vol. 2, no. 3, Sep. 2025, Art. no. 100407.

[25] J. Zhao, R. Zhang, S. Cao, M. Zhuang, and Z. Song, "Broadband terahertz holography using isotropic VO2 metasurfaces," *Sci. Rep.*, vol. 15, no. 1, Jan. 2025.

[26] Z. Wang, Y. Ma, M. Li, L. Wu, T. Guo, Y. Zheng, Q. Chen, and Y. Fu, "A thermal-switchable metamaterial absorber based on the phase-change material of vanadium dioxide," *Nanomaterials*, vol. 12, no. 17, p. 3000, Aug. 2022.

[27] G. Gradoni and M. D. Renzo, "Smart surface radio environments," *Rev. Electromagn.*, vol. 1, pp. 1-42, Jan. 2022.

[28] C. Pfeiffer and A. Grbic, "Metamaterial Huygens' surfaces: Tailoring wave fronts with reflectionless sheets," *Phys. Rev. Lett.*, vol. 110, no. 19, May 2013, Art. no. 197401.

[29] I.-P. Hong, "Reviews based on the reconfigurable intelligent surface technical issues," *Electronics*, vol. 12, no. 21, p. 4489, Nov. 2023.

[30] Y. Saifullah, Y. He, A. Boag, G.-M. Yang, and F. Xu, "Recent progress in reconfigurable and intelligent metasurfaces: A comprehensive review of tuning mechanisms, hardware designs, and applications," *Adv. Sci.*, vol. 9, no. 33, Nov. 2022, Art. no. 2203747.

[31] A. Magbool, V. Kumar, Q. Wu, M. Di Renzo, and M. F. Flanagan, "A survey on integrated sensing and communication with intelligent metasurfaces: Trends, challenges, and opportunities," *IEEE Open J. Commun. Soc.*, vol. 6, pp. 7270-7318, 2025.

[32] Z. Zhang, H. Shi, L. Wang, J. Chen, X. Chen, J. Yi, A. Zhang, and H. Liu, "Recent advances in reconfigurable metasurfaces: Principle and applications," *Nanomaterials*, vol. 13, no. 3, p. 534, Jan. 2023.

[33] Priyanka, A. Yadav, A. Pradeep, H. B. Baskey, and P. S. Alegaonkar, "Electromagnetic materials: Shield, meta-surface absorber, and cloak," in *Electromagnetic Field—From Atomic Level to Engineering Applications*, C. Wang, Ed., Rijeka, Croatia: IntechOpen, 2025, ch. 6.

[34] A. Pitilakis, D. Tyrovolas, P.-V. Mekikis, S. A. Tegos, A. Papadopoulos, A. Tsioliaridou, O. Tsilipakos, D. Manessis, S. Ioannidis, N. V. Kantartzis, I. F. Akyildiz, and C. K. Liaskos, "On the mobility effect in UAV-mounted absorbing metasurfaces: A theoretical and experimental study," *IEEE Access*, vol. 11, pp. 79777-79792, 2023.

[35] C. Fowler, S. Silva, G. Thapa, and J. Zhou, "High efficiency ambient RF energy harvesting by a metamaterial perfect absorber," *Opt. Mater. Exp.*, vol. 12, no. 3, pp. 1242-1250, Mar. 2022.

[36] A. Ghaneizadeh, P. Gavrillidis, M. Joodaki, and G. C. Alexandropoulos, "Metasurface energy harvesters: State-of-the-art designs and their potential for energy sustainable reconfigurable intelligent surfaces," *IEEE Access*, vol. 12, pp. 160464-160494, 2024.

[37] P.-Y. Chen, M. Farhat, Z. Ye, M. Amin, H. Bagci, and D. Erricolo, "Artificial surfaces and media for electromagnetic absorption and interference shielding," in *Recent Topics in Electromagnetic Compatibility*, A. Kishk, Ed., Rijeka, Croatia: IntechOpen, 2021, ch. 9.

[38] F. Costa, S. Genovesi, A. Monorchio, and G. Manara, "A circuit-based model for the interpretation of perfect metamaterial absorbers," *IEEE Trans. Antennas Propag.*, vol. 61, no. 3, pp. 1201-1209, Mar. 2013.

[39] F. Costa, A. Monorchio, and G. Manara, "Analysis and design of ultra thin electromagnetic absorbers comprising resistively loaded high impedance surfaces," *IEEE Trans. Antennas Propag.*, vol. 58, no. 5, pp. 1551-1558, May 2010.

[40] B.-X. Wang, C. Xu, G. Duan, W. Xu, and F. Pi, "Review of broadband metamaterial absorbers: From principles, design strategies, and tunable properties to functional applications," *Adv. Funct. Mater.*, vol. 33, no. 14, Apr. 2023, Art. no. 2213818.

[41] F. Younis, O. Khan, M. J. Ahmad, M. J. Qasim, H. Luo, and S. Wang, "A highly efficient triple band metasurface enabled absorber for 5G/6G millimeter wave applications," *Sci. Rep.*, vol. 15, no. 1, Aug. 2025.

[42] Y. Kato, S. Morita, H. Shiomi, and A. Sanada, "Ultrathin perfect absorbers for normal incident waves using dirac cone metasurfaces with critical external coupling," *IEEE Microw. Wireless Compon. Lett.*, vol. 30, no. 4, pp. 383-386, Apr. 2020.

[43] H. A. Haus, *Waves and Fields in Optoelectronics*. Upper Saddle River, NJ, USA: Prentice-Hall, 1984.

[44] Z.-J. He, L.-L. Qiu, P. Zhang, Y. Liu, S. Huang, and L. Deng, "A high-efficiency rectifying metasurface with four operating bands," *IEEE Antennas Wireless Propag. Lett.*, vol. 22, pp. 2387-2391, 2023.

[45] Y. Wei, J. Duan, H. Jing, Z. Lyu, J. Hao, Z. Qu, J. Wang, and B. Zhang, "A multiband, polarization-controlled metasurface absorber for electromagnetic energy harvesting and wireless power transfer," *IEEE Trans. Microw. Theory Techn.*, vol. 70, no. 5, pp. 2861-2871, May 2022.

[46] X. Yang, X. Zhang, Z. Ding, and Z. Zhang, "Compact and ultra-thin absorber based on metasurface for multi-band energy absorption," *Optik*, vol. 273, Feb. 2023, Art. no. 170478.
[47] H. Zhang, Y. Li, W. Hu, Q. Lu, B. Zhang, and L. Y. Yang, "Polarization-insensitive electromagnetic metamaterial design for multi-band energy harvesting," *IEEE Access*, vol. 11, pp. 143956-143963, 2023.

[48] N. Ullah, M. S. Islam, A. Hoque, A. Alzamil, M. S. Soliman, and M. T. Islam, "Design and development of a compact, wide-angle metamaterial electromagnetic energy harvester with multiband functionality and polarization-insensitive features," *Sci. Rep.*, vol. 14, no. 1, p. 19000, Aug. 2024.

[49] N. Ullah, M. Shabiul Islam, A. Hoque, W. H. Yong, M. S. Soliman, and M. T. Islam, "A compact-sized four-band metamaterial-based perfect absorber for electromagnetic energy harvesting applications," *Opt. Laser Technol.*, vol. 168, Jan. 2024, Art. no. 109836.

[50] H. Maheswaran, G. N. Alsath Mohammed, G. Govindarajan, M. Kanagasabai, K. Savarimuthu, S. K. Palaniswamy, S. Kumar, B. Goyal, and M. I. Hussein, "Active multifunctional frequency selective surfaces: An insight into design, behavior analysis, and applications," *IEEE Access*, vol. 13, pp. 125993-126011, 2025.

[51] W. Afzal, M. Z. Baig, A. Ebrahimi, M. R. Robel, M. T. A. Rana, and W. Rowe, "Frequency selective surfaces: Design, analysis, and applications," *Telecom*, vol. 5, no. 4, pp. 1102-1128, Nov. 2024.

[52] K. Achouri and O. J. F. Martin, "Angular scattering properties of metasurfaces," *IEEE Trans. Antennas Propag.*, vol. 68, no. 1, pp. 432-442, Jan. 2020.

[53] T. Li, D. Li, P. Qin, Y. Fan, Y. Gu, P. Zuo, W. E. I. Sha, and E. Li, "A novel miniaturized strong-coupled FSS structure with excellent angular stability," *IEEE Trans. Electromagn. Compat.*, vol. 63, no. 1, pp. 38-45, Feb. 2021.

[54] Z. Li, X. Weng, X. Yi, K. Li, W. Duan, and M. Bi, "A broadband second-order bandpass frequency selective surface for microwave and millimeter wave application," *Sci. Rep.*, vol. 14, no. 1, p. 12040, May 2024.

[55] P. Chomtong, P. Krachodnok, K. Bandudej, and P. Akkaraekthalin, "A multiband FSS director using aperture interdigital structure for wireless communication systems," *IEEE Access*, vol. 10, pp. 11206-11219, 2022.

[56] P. Chomtong, N. Somjit, P. Krachodnok, C. Mahathanajatuphat, S. Tawatchai, and P. Akkaraekthalin, "A miniaturized multiband FSS director using double layer with ICPW technique structure for wireless communication systems," *IEEE Access*, vol. 11, pp. 81527-81544, 2023.

[57] P.-S. Wei, C.-N. Chiu, C.-C. Chou, and T.-L. Wu, "Miniaturized dual-band FSS suitable for curved surface application," *IEEE Antennas Wireless Propag. Lett.*, vol. 19, pp. 2265-2269, 2020.

[58] A. Ghosh, M. Kumar, S. N. Islam, and S. Das, "Design and analysis of a compact penta-band polarization-insensitive bandstop frequency selective surface," *IEEE Antennas Wireless Propag. Lett.*, vol. 19, pp. 59-63, 2020.

[59] Z. Li, X. Weng, X. Yi, K. Li, W. Duan, and M. Bi, "Design and analysis of a complementary structure-based high selectivity tri-band frequency selective surface," *Sci. Rep.*, vol. 14, no. 1, p. 9415, Apr. 2024.

[60] A. Bansal and W. Whittow, "Structural morphing metasurface for electromagnetic beam manipulation," 2024, arXiv:2408.11231.

[61] C. Dietlein, A. Luukanen, Z. Popovi, and E. Grossman, "A W-band polarization converter and isolator," *IEEE Trans. Antennas Propag.*, vol. 55, no. 6, pp. 1804-1809, Jun. 2007.

[62] A. K. Fahad, C. Ruan, R. Nazir, and B. Hassan, "Transmissive polarizer metasurfaces: From microwave to optical regimes," *Nanomaterials*, vol. 12, no. 10, p. 1705, May 2022.

[63] Z.-L. Deng, J. Deng, X. Zhuang, S. Wang, K. Li, Y. Wang, Y. Chi, X. Ye, J. Xu, G. P. Wang, R. Zhao, X. Wang, Y. Cao, X. Cheng, G. Li, and X. Li, "Diatomic metasurface for vectorial holography," *Nano Lett.*, vol. 18, no. 5, pp. 2885-2892, May 2018.

[64] A. Fahad, C. Ruan, T. H. Haq, S. Ullah, and K. Chen, "Triple-wide-band ultra-thin metasheet for transmission polarization conversion," *Sci. Rep.*, vol. 10, no. 1, p. 8810, Jun. 2020.

[65] L. Nama, Nilotpal, S. Bhattacharyya, and P. K. Jain, "A metasurface-based, ultrathin, dual-band, linear-to-circular, reflective polarization converter: Easing uplinking and downlinking for wireless communication," *IEEE Antennas Propag. Mag.*, vol. 63, no. 4, pp. 100-110, Aug. 2021.

[66] A. K. Fahad, C. Ruan, R. Nazir, M. R. Saleem, T. U. Haq, S. Ullah, and W. He, "Ultra-thin metasheet for dual-wide-band linear to circular polarization conversion with wide-angle performance," *IEEE Access*, vol. 8, pp. 163244-163254, 2020.

[67] A. K. Fahad, C. Ruan, and K. Chen, "A wideband terahertz transmissive polarization manipulator based on metasurfaces," *Electronics*, vol. 8, no. 10, p. 1068, Sep. 2019.

[68] A. K. Fahad, C. Ruan, R. Nazir, T. U. Haq, and W. He, "Dual-band ultrathin meta-array for polarization conversion in Ku/Ka-band with broadband transmission," *IEEE Antennas Wireless Propag. Lett.*, vol. 19, pp. 856-860, 2020.

[69] F. Ding, R. Deshpande, C. Meng, and S. I. Bozhevolnyi, "Metasurface-enabled broadband beam splitters integrated with quarter-wave plate functionality," *Nanoscale*, vol. 12, no. 26, pp. 14106-14111, 2020.

[70] F. Ding, B. Chang, Q. Wei, L. Huang, X. Guan, and S. I. Bozhevolnyi, "Versatile polarization generation and manipulation using dielectric metasurfaces," *Laser Photon. Rev.*, vol. 14, no. 11, Nov. 2020, Art. no. 2000116.

[71] H. Taghvaee, M. Khalily, G. Gradoni, and R. Tafazolli, "An overview of electromagnetic illusions: Empowering smart environments with reconfigurable metasurfaces," 2024, arXiv:2404.12089.

[72] V. G. Ataloglou, S. Taravati, and G. V. Eleftheriades, "Metasurfaces: Physics and applications in wireless communications," *Nat. Sci. Rev.*, vol. 10, no. 8, p. 164, Jun. 2023.

[73] T. K. T. Nguyen, T. M. Nguyen, H. Q. Nguyen, T. N. Cao, D. T. Le, X. K. Bui, S. T. Bui, C. L. Truong, D. L. Vu, and T. Q. H. Nguyen, "Simple design of efficient broadband multifunctional polarization converter for X-band applications," *Sci. Rep.*, vol. 11, no. 1, p. 2032, Jan. 2021.

[74] P. Naseri, G. Goussetis, N. J. G. Fonseca, and S. V. Hum, "Synthesis of multi-band reflective polarizing metasurfaces using a generative adversarial network," *Sci. Rep.*, vol. 12, no. 1, p. 17006, Oct. 2022.

[75] S. Ghosh, J. Ghosh, M. Santoshkumar Singh, and A. Sarkhel, "A low-profile multifunctional metasurface reflector for multiband polarization transformation," *IEEE Trans. Circuits Syst. II, Exp. Briefs*, vol. 70, no. 1, pp. 76-80, Jan. 2023.

[76] R. Dutta, J. Ghosh, Z. Yang, and X. Zhang, "Multi-band multifunctional metasurface-based reflective polarization converter for linear and circular polarizations," *IEEE Access*, vol. 9, pp. 152738-152748, 2021.

[77] H. Z. Khan, A. Jabbar, J. U. R. Kazim, J. Zafar, M. Ur-Rehman, M. A. Imran, and Q. H. Abbasi, "Reflective metasurface for multi-band polarization conversion for satellite applications in 6G networks," *IEEE Open J. Antennas Propag.*, vol. 6, pp. 332-343, 2025.

[78] Q. Guo, F. Hao, M. Qu, J. Su, and Z. Li, "Multiband multifunctional polarization converter based on reconfigurable metasurface," *IEEE Antennas Wireless Propag. Lett.*, vol. 23, pp. 1241-1245, 2024.

[79] V. Singh, S. Bhattacharyya, and R. Agrahari, "A low-profile tri-functional metasurface toward polarization conversions and absorption," *IEEE Antennas Wireless Propag. Lett.*, vol. 23, pp. 2593-2597, 2024.

[80] I. Alamzadeh, G. C. Alexandropoulos, N. Shlezinger, and M. F. Imani, "A reconfigurable intelligent surface with integrated sensing capability," *Sci. Rep.*, vol. 11, no. 1, p. 20737, Oct. 2021.

[81] M. D. Renzo, M. Debbah, D.-T. Phan-Huy, A. Zappone, M.-S. Alouini, C. Yuen, V. Sciancalepore, G. C. Alexandropoulos, J. Hoydis, H. Gacanin, J. D. Rosny, A. Bounceur, G. Lerosey, and M. Fink, "Smart radio environments empowered by reconfigurable AI meta-surfaces: An idea whose time has come," *EURASIP J. Wireless Commun. Netw.*, vol. 2019, no. 1, pp. 1-20, Dec. 2019.

[82] Q. Hu, H. Yang, X. Zeng, Y. Rao, and X. Y. Zhang, "Methodology and design of absorptive filtering reconfigurable intelligent surfaces," *IEEE Trans. Antennas Propag.*, vol. 72, no. 6, pp. 5301-5306, Jun. 2024.

[83] M. Di Renzo, A. Zappone, M. Debbah, M.-S. Alouini, C. Yuen, J. de Rosny, and S. Tretyakov, "Smart radio environments empowered by reconfigurable intelligent surfaces: How it works, state of research, and the road ahead," *IEEE J. Sel. Areas Commun.*, vol. 38, no. 11, pp. 2450-2525, Nov. 2020.

[84] M. Iqbal, T. Ashraf, M. Zubair, S. M. Jameel, M. Jazib, and J.-Y. Pan, "A comprehensive survey on reconfigurable intelligent surfaces (RIS) and STAR-RIS for next-generation wireless networks," *Discover Appl. Sci.*, vol. 7, no. 11, p. 1253, Oct. 2025.

[85] A. T. Joy, A. Tishchenko, H. Taghvaee, P. Botham, F. Burton, M. Khalily, and R. Tafazolli, "From reconfigurable intelligent surfaces to holographic MIMO surfaces and back," in *Proc. 18th Eur. Conf. Antennas Propag. (EuCAP)*, Mar. 2024, pp. 1-5.

[86] L. Zhang, Y. Zhou, and L. Hao, "Power minimization for wireless power transfer systems with cooperative zero-energy double-RIS," *IEEE Trans. Veh. Technol.*, vol. 74, no. 9, pp. 14854-14859, Sep. 2025.

[87] J. Jalali, M. Darabi, and R. C. de Lamare, "Shape adaptive reconfigurable holographic surfaces," 2025, arXiv:2503.21542.
<figure><img src="image_23.png" /></figure>

**ABHISHEK ARYA** (Graduate Student Member, IEEE) received the B.Tech. degree in electrical and electronics engineering from the Maharaja Agrasen Institute of Technology, Delhi, India, in 2017, and the M.Tech. degree in microwave electronics science from the Department of Electronic Science, University of Delhi, India, in 2021. He is currently pursuing the Ph.D. degree with INSA, IETR, University of Rennes, France.

He is also a Research Assistant with the Faculty of Electronic Engineering, ESEO, Angers, France. His doctoral research focuses on shielding human body from EMR and harvesting RF- and body-generated (thermal and biomechanical) energy and metasurface-based wave manipulation & absorption. Previously, he was a Research Scientist with the SAMEER, Ministry of Electronics and Information Technology, India. He was a RF System Engineer with Eiwave Digitech Pvt. Ltd., where he contributed to several projects for the Defence Research and Development Organisation (DRDO), India. His research interests include wave propagation, antennas, metasurfaces, radar technologies, RF front-end design, EMC, biomedical engineering, and co-simulation methodologies.

<figure><img src="image_24.png" /></figure>

**THOMAS SCHLINQUER** (Senior Member, IEEE) received the Engineering degree in mechatronics and robotics from ENSMM, Besançon, and the Ph.D. degree in topology optimization applied to piezoelectric structures using the SIMP approach from the Femto-ST Institute, Besançon. He began his career as a Teacher in applied mechatronics with Elisa Aerospace, Saint-Quentin, and then switched to an Associate Professor with ESEO, Dijon, where he is currently

the Head of the industry 4.0 major and in charge of mechatronic courses from applied robotic to 3D printing. His research interests include applied mechatronics, with a wide scope of applications, such as embedded design for medical and multi-physics modeling of technological systems.

<figure><img src="image_25.png" /></figure>

**MOHSEN KOOHESTANI** (Senior Member, IEEE) received the joint Ph.D. degree (Hons.) in electromagnetics from the École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland, and the Universidade de Lisboa (ULISBOA), Lisbon, Portugal, in 2014, and the Higher Doctorate (H.D.R.) degree from the Université de Rennes, Rennes, France, in 2023.

From 2014 to 2018, he was a Senior Research Fellow with the Institut d'Électronique et des Technologies du numérique (IETR), Université de Rennes 1. Since 2018, he has been an Associate Professor with the École Supérieure d'Électronique de l'Ouest (ESEO), Angers, France, where he was promoted to a Full Professor, in 2024. He is currently an Associate Researcher with IETR, UMR CNRS 6164. He has authored over 100 peer-reviewed scientific papers. His main research interests include domain of antennas, microwaves, EMC, and biomedical engineering.

Prof. Koohestani is an Official Member of AFNOR, the IEC standardization working group (WG2 and WG9), and in the SC47A French Subcommittee on the EMC for integrated circuits.

<figure><img src="image_26.png" /></figure>

**RICHARD PERDRIAU** (Senior Member, IEEE) was born in Angers, France, in 1971. He received the Engineering degree in electronics and computer science from ESEO, Angers, in 1992, the Ph.D. degree in applied sciences from the Université Catholique de Louvain, Louvain-la-Neuve, Belgium, in 2004, and the Habilitation à Diriger des Recherches (Accreditation) degree from the Université de Rennes 1, France, in 2012.

From 1992 to 2012, he was Assistant Professor and then an Associate Professor with ESEO, in the fields of microelectronics and embedded systems. In 2013, he was promoted to a Full Professor. His research interests include EMC of integrated circuits, mixed-signal hardware description languages, and integrated circuit design. He is an active member of IEC SC47A. He served as the Vice-Chair and the Technical Program Co-Chair for EMC Europe 2017. Moreover, he is the Technical Program Chair of EMC Europe 2025. He is the current Secretary of the IEEE France Section.

<figure><img src="image_27.png" /></figure>