Metamaterials, recognized as advanced artificial materials endowed with distinctive properties, have found diverse applications in everyday life, military endeavors, and scientific research. Starting from monolayer metamaterials, multilayer ones are increasingly researched, especially in the field of electromagnetic wave absorption. In this article, we propose a multilayer metamaterial-absorber (MA) structure comprising two resonant layers crafted with copper and FR-4 dielectric. The presented multilayer MA structure exhibited an absorption greater than 90% in a frequency range from 4.84 to 5.02 GHz, with two maximum absorption peaks at 4.89 and 4.97 GHz. The bandwidth of the multilayer MA surpassed that of the individual single-layer MAs, with extension fractions reaching 360% and 257%, respectively. Through the simulation and calculation, the field distribution and equivalent circuit model elucidated that both individual magnetic resonances and their interplay contribute significantly to the absorption behavior of the multilayer MA. The absorption of the proposed multilayer MA structure was also investigated for the oblique incidence in the transverse electric (TE) and transverse magnetic (TM) modes. In the TE mode, the absorption intensity of two maximum peaks was maintained at over 93% up to an incident angle of 40 degrees and dropped to below 80% at an incident angle of 60 degrees. In the TM mode, the absorption was more stable and not significantly affected by the incident angle, ranging from 0 to 60 degrees. An absorption greater than 97% was observed when the incident angle increased from 0 to 60 degrees in the TM mode. Additionally, the approach in our work was further demonstrated by adding more resonant layers, making 3- and 4-layer structures. The results indicated that the absorption bandwidths of the 3- and 4-layer structures increased by 16% and 33%, respectively, compared to the bilayer structure. Furthermore, we analyzed the thermal distribution within the MA to understand the dissipation of absorbed electromagnetic energy. This research offers valuable insight into the augmented MA through a multilayer structure, presenting the implications for microwave applications like electromagnetic shielding, as well as in the design of MAs for terahertz devices and technologies, including emission and thermal imaging. These findings contribute to the advancement of knowledge in enhancing the absorption capabilities across various frequency ranges, expanding the potential applications of metamaterials.

In this study, we present a novel surface-enhanced Raman scattering (SERS) substrate based on porous silicon microcavities (PSiMCs) decorated with silver nanoparticles (AgNPs) for ultra-sensitive molecule detection. This substrate utilizes a dual enhancement mechanism: the localized surface plasmon resonance (LSPR) of AgNPs and the optical resonance of the PSiMC structure, which together create intense electromagnetic hot spots and prolong photon–molecule interactions. The porous architecture provides a large surface area for uniform nanoparticle distribution and efficient analyte adsorption. The AgNP/PSiMC substrate demonstrates an impressive detection limit of 1.0 × 10⁻¹³ M for rhodamine101 and 1.0 × 10⁻¹⁰ M for methyl parathion, outperforming many previously reported SERS platforms. Furthermore, the substrate exhibits excellent signal uniformity (RSD ≈ 6.14%) and long-term stability, retaining over 50% signal intensity after 28 days. These results underscore the potential of AgNP/PSiMCs as highly efficient, reproducible, and scalable SERS platforms for trace-level chemical and environmental sensing applications.

In this work, we investigated the correlation between interfacial parameters with anti-icing performance in terms of adhesive strength. Samples with different morphologies and surface energies ranging from superhydrophilic to superhydrophobic were evaluated in relationship with contact angle, contact angle hysteresis, water – glass work of adhesion and ice-glass work of adhesion. Superhydrophobic surfaces with well-textured nanopillars were fabricated via dry etching process following by low-energy chemical compound coating. In addition, flat quartz substrates with low wetting states achieved through UVO expose method were also examined. The results demonstrated the relationship between interfacial parameters and anti-icing performance with important considerations on surface coating material and wetting state. This insight should lead to an understanding of icing phenomena and the design of icephobic surfaces.

This study uses a hybrid concept to propose an optimal textured surface morphology for enhancing water condensation. The natural phenomenon-inspired morphology, which combined different degrees of wettability presented on the surface, documented their advantage in water harvesting compared to untreated surfaces. These superiorities might be explained by the appropriate combination of nucleation and water-driven ability facilitated by the superhydrophobic surrounding area. The uniform condensed droplets are effectively agglomerated to achieve the critical size. The best combination was found on a superhydrophobic-hydrophilic hybrid sample that improved water collection efficiency by up to 50% compared to bare Al. Condensation performance also illustrated an interesting tendency that revealed the great contribution of wettability on hydrophilic dots and the water-driven ability of the high-hydrophobicity area. The results were supported by a theoretical model which predicts the critical volume of a single droplet before it has departed from the surface. The findings reveal a good level of agreement between theory and real-time measurement, demonstrating the potential of combinations of hybrid samples to induce water collection efficiency.

In this work, we demonstrated a tunable metamaterial perfect absorber (MPA) with broadband absorption by tuning the different states of flexible sandwiched structures (graphene conductive ink/rubber/metallic layers). The broadband absorption spectrum was tuned mechanically by changing the concave-up/down states of flexible hemispherical unit-cells. When the unit-cell was concave-up, our proposed MPAs played as a broadband absorber with a fractal bandwidth (FBW) of 107% (since an absorption over 90% ranges from 5.28 to 17.6 GHz) at the normal incidence; at the same time, this broadband absorption feature could remain well at large incident angles up to 40 deg. and regardless of polarization of the incoming electromagnetic waves. In the case of the concave-down state, a narrow FBW of only 6.8% was noticed. These results could promote great application potential, such as regarding advanced stealth devices, advances in the biomedical and the communication fields, and more.

This work investigates the design and performance of a bilayer graphene metamaterial absorber operating in the GHz region. We initially analyzed a single-layer metamaterial absorber composed of a conductive ink graphene structure on a FR-4 dielectric substrate backed by a continuous copper sheet. Subsequently, a second graphene-FR4 layer of identical dimensions was added to create a bilayer structure. While the number of absorption peaks increased, they remained isolated, failing to achieve the desired broadband effect. To overcome this limitation, we explored graphene layers with varying surface resistances. Our findings demonstrate that the bilayer graphene metamaterial absorber achieves an absorption exceeding 90% with a remarkable bandwidth of 9.1 GHz, spanning frequencies from 6.21 GHz to 15.31 GHz. This significant bandwidth expansion is attributed to the synergistic interactions and contributions between the graphene and metal layers within the structure. To gain a deeper understanding of the underlying absorption mechanism, we investigated the surface current distribution, the impact of conductivity, and the individual contributions of each layer. Additionally, we examined the influences of both incident angle and polarization angle on the absorption performance of the proposed bilayer MA. These comprehensive analyses provide valuable insights into the mechanisms responsible for the enhanced absorption observed in multilayer metamaterial structures. Our work holds relevance and might be useful to develop electromagnetic wave shielding technologies and devices operating in the GHz frequency range.