Alfredo Gomes Neto

This paper presents a reconfigurable frequency-selective surface (FSS) featuring switchable reflection and transmission characteristics based on a complementary-inspired four-arm star geometry. The design process begins with the independent analysis of a slot element and its complementary patch counterpart, which are subsequently integrated on a single-layer substrate. To enable electrical reconfigurability, the patch element is modified by adding a switching point to integrate a PIN diode along with bias lines for feeding. The electromagnetic response is evaluated across three diode operational states: off (reverse bias), on (forward bias), and threshold bias. For TE polarization, the structure exhibits a singlepassband response near 3.75 GHz in the reverse-biased state and a dual-passband response near 2.1 GHz and 6.9 GHz in the forwardbiased state, with a stopband between the two passbands. At the threshold voltage, the reconfigurable complementary FSS provides an attenuated-transmission state, enabling control of the transmitted signal level. These operating modes allow the same surface to switch between transmission, rejection, and attenuation, which is useful for adaptive filtering, interference mitigation, and signallevel control in intelligent 5G-Advanced communication network applications.

This paper presents the design and experimental validation of a compact, single-layer, triple-band Frequency Selective Surface (FSS) based on triple square loops. The proposed structure targets resonant frequencies at 1.56 GHz, 2.45 GHz, and 3.50 GHz, corresponding to the GPS L1, Wi-Fi, and 5G bands, respectively. An equivalent circuit model (ECM) was developed to guide the initial parametric design, reducing reliance on computationally intensive full-wave simulations. The structure was optimized using HFSS and fabricated on a low-cost FR-4 substrate. Simulated and measured results show good agreement, with three well-defined stop bands exhibiting low insertion loss and stable resonant frequencies. Experimental measurements under oblique incidence up to 45° confirm the angular stability of the design for both TE and TM polarizations. Compared to prior works, the proposed FSS offers simpler geometry, lower fabrication complexity, closely spaced resonances with minimal frequency shift under angular variation, and low pass-band insertion losses. These features make the proposed FSS a strong candidate for compact and low-profile solutions in GPS, Wi-Fi, and 5G systems requiring multiband electromagnetic filtering.

The growing demand for lightweight, flexible, and efficient materials for electromagnetic interference (EMI) shielding has driven the development of conductive polymer composites (CPCs) as sustainable and reliable alternatives. These materials are essential for protecting communication systems, electronic components, and ensuring the efficient operation of expanding 5G networks. This study presents the development and characterization of PLA/MWCNT and TPU/MWCNT composites, fabricated by melt mixing and compression molding with different loadings of multi‐walled carbon nanotubes (MWCNTs). Rheological analyses indicated that the dispersion of MWCNTs begins at around 3%, with a more pronounced effect in PLA. In particular, PLA/MWCNT composites with 12% filler, where the nanotubes are effectively dispersed, exhibited electrical conductivity on the order of 10 ⁻³ S/cm. On the other hand, although TPU/MWCNT composites also showed an increase in conductivity with the addition of MWCNT, they did not reach the same order of magnitude (10 ⁻³ S/cm), even at 12% filler content. This result may be associated with a less efficient dispersion of MWCNT within the TPU matrix. Electromagnetic shielding effectiveness (EMI SE) increased with MWCNT content, exceeding 60 dB in PLA and reaching up to 50 dB in TPU. Anechoic chamber tests with a 3D‐printed PLA/MWCNT (12%) box confirmed attenuations above 40 dB at 5.9 GHz and between 10 and 15 dB at 3.5 GHz, SEM analyses confirmed the rheological and electrical results, indicating a more homogeneous dispersion of nanotubes in the PLA/MWCNT composites than in the TPU/MWCNT ones. The results highlight PLA/MWCNT as a promising material for EMI shielding in electronics, 5G networks, and aerospace applications.

This paper introduces a novel ultrathin frequency selective surface (FSS) based on interconnected logarithmic spiral geometries. The structure is fabricated on a flexible polyimide substrate with a thickness of 0.05 mm, a relative permittivity of 4.3, and a low-loss tangent of 0.004. The unit cell design follows a pursuit curve forming a logarithmic spiral, with four spirals symmetrically connected at the center. Our proposed FSS exhibits stopband resonances at 3.5 GHz and 9.2 GHz, with bandwidths of 680 MHz and 1.8 GHz, respectively. Owing to the ultrathin substrate, the overall thickness is just 0.05 mm (0.0005λ₀, where λ₀ is the wavelength at the lower resonance). Simulated results show excellent agreement with experimental measurements, confirming the accuracy of the design. Moreover, the FSS demonstrates polarization independence, angular stability up to 45° for both vertical and horizontal polarizations, and maintains performance under bending, highlighting its mechanical and electromagnetic robustness.

As a conceptual paper, it is a very interesting paper, as the basic concepts, forward tendencies, and challenges are well presented. However, the absence of practical RIS examples, even if only with numerical results, makes the paper less attractive....

A review on planar printed structures that are based on Matryoshka-like geometries is presented. These structures use the well-known principle of Matryoshka dolls that are successively nested inside each other. The well-known advantages of the planar printed technology and of the meandered nested Matryoshka geometries are combined to generate miniaturized, multi-resonance, and/or wideband configurations. Both metal and complementary slot structures are considered. Closed and open configurations were analyzed. The working principles were explored in order to obtain physical insight into their behavior. Low-cost and single-layer applications as frequency-selective surfaces, filters, antennas, and sensors, in the microwave frequency region, were reviewed. Potential future research perspectives and new applications are then discussed.

The paper's main idea is interesting, but its presentation could be improved. Following are some suggestions: 1) In Fig. 12, adding an isometric view could help to visualize the antenna. Furthermore, “G” and “S” dimensions could be better depicted. ...

A review on planar printed structures that are based on Matryoshka-like geometries is presented. These structures use the well-known principle of Matryoshka dolls that are successively nested inside each other. The well-known advantages of the planar printed technology and of the meandered nested Matryoshka geometries are combined to generate miniaturized, multi-resonance and/or wideband configurations. Both metal and complementary slot structures are considered. Closed and open configurations are analyzed. The working principles are explored do get physical insight of their behavior. Low cost and single layer applications as frequency selective surfaces, filters, antennas, and sensors, in the microwave frequency region, are reviewed. Potential future research perspectives and new applications are discussed.

In this paper, a compact matryoshka DGS using dielectric resonator (DR) is proposed. Despite the use of dielectric resonators to obtain band-stop frequency response not being a new idea, the proposed compact matryoshka DGS is an original contribution, since only recently the matryoshka geometry was used in DGS applications. Furthermore, a numerical analysis of the positioning of the DR is presented, which makes it possible to determine the region of the DGS for which the minimum resonant frequency is reached, and the resonant frequency range that can be obtained. To the best of the authors’ knowledge, this numerical analysis is an unpublished result, even more so, for the matryoshka DGS. The matryoshka geometry was described, including initial design equations. To verify the expected characteristics (miniaturization, selectivity, and resonant frequency tunability), two compact matryoshka DGSs (DGS1 and DGS2) were designed using a high permittivity ceramic (MCT-115) as DR. The obtained numerical and experimental results showed good agreement, and the initial design equations proved to be applicable, which allows new dimensions to be determined for other resonant frequencies, according to the application requirements. Resonant frequencies ranging from the maximum value to 33% (DGS1) and 27% (DGS2) were achieved, depending on the DR position. Considering λ ₀ the wavelength in free space, corresponding to the resonant frequency, DGS1 and DGS2 achieved an occupied area of 0.04λ ₀ ×0.04λ ₀ , and 0.05λ ₀ ×0.05λ ₀ , respectively, a good miniaturization. The proposed compact matryoshka DGS may be especially attractive for applications that require a very selective band-stop frequency response. If a wider band-stop is required, the proposed DGS can be cascaded.

This paper describes the development of a double-sided band-pass frequency selective surface based on Matryoshka geometry, preserving features such as miniaturization, multiband operation and stability of polarization and angle of incidence. Unlike cascaded FSSs, the proposal uses only one layer of substrate, with Matryoshka geometry on one side and a square mesh on the other, reducing volume and simplifying manufacturing by avoiding spacers. The double-sided FSS allows the frequency response to be adjusted using the geometry of the opposite face, which in this work is a square loop. With an attenuation of -10 dB, the proposed configuration offers a free band from 3.48 GHz to 9.06 GHz, compared to the original configuration, which ranged from 5.88 GHz to 7.43 GHz, with only 1.55 GHz free. Initial design equations are presented which facilitate the creation of FSSs for other frequencies and applications. An FSS has been designed, fabricated, and characterized, with good agreement between numerical and experimental results. The resonant frequency remains practically constant for different incidence angles, from 0º to 60º, confirming the angular stability.