In this article, a high-performance energy selective surface (ESS) is proposed based on a double-resonance concept, which has a nonlinear transmission response for high-power electromagnetic protection. With well-designed grid and cross patterns as well as properly chosen p-i-n diodes, bandpass and band-stop resonances are excited by the ESS at the same frequency under low and high incident power levels, respectively, resulting in low insertion loss (IL) and high shielding effectiveness (SE) of the ESS. Two samples of single-layer and double-layer ESSs operating at 3 GHz are designed to demonstrate the double-resonance concept. By utilizing a double-layer structure, a second-order band-stop resonance is produced to achieve a broader bandwidth with high SE in comparison with the single-layer ESS. Equivalent circuit models are employed to explain how the double resonances are produced and a wide bandwidth of high SE is obtained. Field circuit cosimulation is conducted to estimate the nonlinear performance of the ESS designs. Moreover, the ESS designs are measured in a rectangular waveguide setup. Good agreement is observed between the simulation and measurement. Simulated and measured results demonstrate that low IL less than 1 dB and high SE larger than 24 dB can be obtained under low and high incident power levels, respectively.

In this work, we propose an ultra-wideband and wide-angle optically transparent flexible metamaterial absorber (MMA), consisting of a multilayered structure with a transparent polyvinyl chloride layer and a periodic indium-tin-oxide patch array attached to a polyethylene terephthalate film layer. The absorptivity of the proposed MMA reaches above 90% from 5.61 to 29.17 GHz whether it is flat or even bent with 60º thanks to the flexibility of the materials. Excellent agreement between the measured and simulated results verify our design. The proposed MMA holds great promise in applications for flexible devices that require optical transparency, ultra-wideband and wide angle stealth.

In this article, we propose an ultra-compact microwave sensor based on an effective localized surface plasmon (ELSP) resonance for complex permittivity measurement of aqueous ethanol solution. The sensitivity of the sensor is dramatically enhanced thanks to the strong electromagnetic (EM) field coupling and enhancement of the ELSP in a deep-subwavelength scale. An equivalent circuit model of the sensor is established for analyzing the sensing mechanism, and the complex permittivity of the aqueous ethanol solution under test is extracted from the S-parameter through an empirical model. For demonstration, we successfully predict the complex permittivity of aqueous ethanol solution with an ethanol concentration of 0%-90% through simulations and experiments. This ELSP-based sensor features an ultra-compact size of 0.008λ ₀ ² and high sensitivity of 0.57% and can find many applications (liquid permittivity measurement, liquid testing, and so on) in highly integrated systems.

In this paper, we propose an ultrathin optically transparent metamaterial absorber (OTMMA) for broadband microwave invisibility of solar panels. The OTMMA is a multi-layered structure consists of a continuous indium tin oxide (ITO) film layer, a polymethyl methacrylate substrate layer, and an ITO film layer etched with periodic square split resonance rings. Under normal incidence, the OTMMA exhibits more than 90% absorptivity from 7.82 to 17.15 GHz with arbitrary polarization. At oblique incidence, the absorptivity of the OTMMA reaches over 75% for transverse electric polarization when the incident angle is not more than 50°, whereas it is over 80% for transverse magnetic polarization with an incident angle not greater than 75°. An OTMMA sample with a thickness of λ ₀/11 is fabricated and attached to the surface of a 300 × 300 mm² solar panel for measurement. Excellent agreement between the simulated and measured absorptivity verify our design, showing that the OTMMA can achieve 93%–99% absorption of electromagnetic waves in the whole X-band while ensuring the efficient light transmittance of the solar panels.

In this article, we present a novel ultracompact plasmonic bandpass filter (BPF) based on a recently proposed concept of effective localized surface plasmons (ELSPs). By virtue of the insensitiveness of the ELSPs resonator's dipolar mode resonance frequency to the variations of its cross-sectional area and shape, we can significantly miniaturize the occupied area of the filter. Moreover, the unloaded quality factor of the ELSPs resonator can be flexibly tuned and adjusted to be much larger than that of conventional microstrip and substrate integrated waveguide (SIW) resonators. For demonstration, we design and implement two Sub-6G BPFs centered at 3.3 and 3.4 GHz with the size of only 0.006 and 0.021λ ₀ ² . The measured in-band insertion loss (IL) and fractional bandwidth are 0.8 dB and 5.6% for the third-order BPF, and 0.7 dB and 5.9% for the fourth-order BPF, respectively. Excellent agreements between the measured and simulated results verify our design. The proposed ELSPs BPFs pave the way to realize ultracompact and high-performance functional devices for fifth-generation (5G) applications.