Improved catalyst utilization at the ORR electrode in PEM fuel cells is of critical importance for improving power and energy output. Functionalized, aligned carbon nanotube architectures provide a robust platform for improved catalytic utilization for the reduction of oxygen molecules, report Gordon Wallace, Jun Chen, and co-workers.
We propose a method to suppress the scattering based on an ultrathin metasurface in a broad frequency band. The designed metasurface is composed of two kinds of units with different geometries and reflection phases, which provide destructive interference in most of reflected directions, suppressing the main lobe and side lobes significantly of the scattering pattern. The resonance frequencies of two units are elaborately designed to broaden the frequency band. Full-wave numerical simulation results show that a large bandwidth of 1.74 GHz is achieved using the proposed metasurface with the thickness 1 mm, which suppresses the scattering by at least 10 dB. The proposed metasurface may find wide applications in a series areas.
We propose switchable zero-index metamaterials (ZIMs) implemented by split ring resonators (SRRs) loaded with positive-intrinsic-negative (PIN) diode switching elements. We demonstrate that ZIMs can be achieved at around 10 GHz when the PIN diode is switched off. When the PIN diode is switched on, however, the designed metamaterials have impedance matching to the free space, which is useful to reduce the reflections at the interface of two media. The switchable ZIMs are suitable for a wide variety of applications like the beam forming and directive radiation. Experimental results validate the switching ability of the proposed ZIMs.
Here, we present an ultralight multilayered graphene-based metasurface for suppressing specular reflection. With the help of a joint optimization method, dual low-reflection mechanisms including absorption and random diffusion are realized within the same structure, resulting in a remarkable decrease in the backward reflected energy in an ultrabroadband range of 7.5 to 43 GHz (a relative bandwidth of 140.6%). Experiments demonstrate that our design with a thickness of approximately 3.27 mm can maintain excellent antireflection performance over a wide angle range of 0 to 45° for both TE and TM waves. Additionally, as a result of adopting low-density substrates (polyethylene terephthalate and polymethylacrylimide foam) and multilayered graphene films, the proposed metasurface shows the advantage of ultralight weight, thus opening an avenue for a number of engineering applications such as electromagnetic shielding, information security, and electromagnetic compatibility technology. In addition, owing to the natural characteristics (corrosion resistance, bending resistance, etc.) of multilayered graphene films, the proposed metasurface shows enormous potential in some particular application scenarios with harsh conditions.
A broadband and broad-angle low-scattering metasurface is designed, fabricated, and characterized. Based on the optimization algorithm and far-field scattering pattern analysis, we propose a rapid and efficient method to design metasurfaces, which avoids the large amount of time-consuming electromagnetic simulations. Full-wave simulation and measurement results show that the proposed metasurface is insensitive to the polarization of incident waves, and presents good scattering-reduction properties for oblique incident waves.
Based on the dispersion relation, surface plasmon polaritons (SPPs) or spoof SPPs are always propagating surface waves when the operating frequency is below the asymptotic limit - the surface plasma frequency. Here we propose a method to control the rejections of spoof SPPs using metamaterial particles. By introducing electrically resonant metamaterials near an ultrathin corrugated metallic strip - the spoof SPP waveguide - to produce tight coupling and mismatch of surface impedance, we show that the SPP modes are rejected near the resonant frequencies within the propagating band. Through the modulation of scaling factor of metamaterial particles, we can manipulate the rejections of SPP modes from narrowband to broadband. Both simulation and experiment results verify the tunability of SPP rejections, which have important applications in filtering SPP waves in plasmonic circuits and systems.
We propose a compact combined system which supports compound spoof surface resonances due to the coupling between spoof surface plasmon polaritons (SPPs) and localized surface plasmons (LSPs). The system is composed of ultrathin metallic spiral structures for discrete LSP resonances and an ultrathin corrugated metallic strip to guide continuous SPP modes. We demonstrate both theoretically and experimentally that the LSP resonances can be efficiently excited and captured by the SPP waveguide, while the SPP transmissions can be judiciously controlled by the LSP structures. The spoof SPP-LSP combined system may find potential applications in sensing and integrated photonic circuitry in the microwave and terahertz frequencies.
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