Polarization meta-converter for dynamic polarization states shifting with broadband characteristic

Independently switchable dual-passband frequency-selective surface design based on characteristic mode analysis

High-order bandpass filtering responses are highly desirable for frequency-selective surfaces (FSSs) in narrowband antenna/radar systems. In this paper, the design process of a reconfigurable dual-band FSS with second-order response is presented. Initially, the basic dumbbell-shaped resonator used in this design is theoretically investigated using the characteristic mode analysis (CMA) method to study the relation between geometric design parameters and the excited orthogonal resonance modes in different frequency bands. Then, an additional CMA process was performed on a unit cell with four such patch resonators arranged with 90-degree rotation between adjacent ones. This detailed analysis leads to a polarization-independent FSS design with a high-order dual-band response. Two of these composite resonators are combined back-to-back through coupling apertures on the middle layer. Finally, PIN diodes are loaded on separate layers to realize independent pass-band switching. The loading place of the PIN diodes is carefully chosen based on electromagnetic field analysis. A prototype was also fabricated and experimentally tested. Experimental results show that this FSS has two independently switchable passbands centered at 3 GHz and 4.8 GHz.

Deep neural network training method based on vectorgraphs for designing of metamaterial broadband polarization converters

In this work, we proposed a method of extracting feature parameters for deep neural network prediction based on the vectorgraph storage format, which can be applied to the design of electromagnetic metamaterials with sandwich structures. Compared to current methods of manually extracting feature parameters, this method can automatically and precisely extract the feature parameters of arbitrary two-dimensional surface patterns of the sandwich structure. The position and size of surface patterns can be freely defined, and the surface patterns can be easily scaled, rotated, translated, or transformed in other ways. Compared to the pixel graph feature extraction method, this method can adapt to very complex surface pattern design in a more efficient way. And the response band can be easily shifted by scaling the designed surface pattern. To illustrate and verify the method, a 7-layer deep neural network was built to design a metamaterial broadband polarization converter. Prototype samples were fabricated and tested to verify the accuracy of the prediction results. In general, the method is potentially applicable to the design of different kinds of sandwich-structure metamaterials, with different functions and in different frequency bands.

Tailorable Switching of Transmission Modes between Waveguide and Spoof Surface Plasmon Polariton for Flexible and Dynamic Control of Phase Shift

Programmable metamaterials are suitable for their dynamic and real-time control capabilities of electromagnetic (EM) functions in radars and antenna communications, but it remains a challenge to achieve dynamic modulation of arbitrary transmission phase with high transmission efficiency. Here, we propose a paradigm to tailor transmission phase shift in real time by switching modes between waveguide and SSPP based on the voltage-driven PIN diodes. Step-like phase shift is achieved by the "ON" and "OFF" states of PIN diodes, while continuous phase regulation is by the characteristic of the nonlinear region between those two states. As validations, three systems with programmable functionalities are implemented, including the multibeam generator, the dual-beam scanner, and the active phased-array antenna. The experimental results are consistent with simulation, which verify the feasibility of the proposed approach. Our work offers an alternative route for transmission full-phase modulation and provides unprecedented potential for high-gain, real-time, and multidimensional EM capabilities in applications such as active phased array radars, self-adaption radomes, smart beam shaping.

Highly efficient and tunable terahertz polarization converter based on double subwavelength metallic gratings infiltrated with liquid crystal

In this work, a tunable cross-polarized transmission structure at the terahertz frequency was demonstrated, and the polarization state during modulation was investigated. The proposed structure can significantly enhance the polarization conversion performance of nematic liquid crystals by leveraging the formation of a Fabry-Perot-like resonant cavity that consists of two metal gratings. As a result, the incident waves are continuously reflected in the liquid crystal layer to complete the accumulation of polarization angle changes. From the experimental results acquired, it was concluded that the insertion loss of the cross-polarization transmission was less than 3 dB and the extinction ratio was larger than 28 dB in the frequency range of 388-426 GHz. Our work provides useful insights for improving the efficiency of cross-polarization conversion by enhancing the resonance process in a Fabry-Perot-like resonant cavity and, thus, significantly extending the equivalent optical path.

Tailoring transmission window in a dynamic way with a multi-degree-of-freedom

With the rapid development of wireless technology, the revolution of tailoring transmission window in dynamic way for the next generation communication systems is urgently required. However, the degree-of-freedom for switching transmission spectra of an effective medium still needs further investigation. Here, we propose a paradigm of solving this difficult academic issue via the method of bias-voltage-driven. Leveraging PIN diodes and varactor diodes into the predesigned positions of plasmonic meta-structures, the macro-control of transmission windows switch and the detailed dispersion manipulation can be separately achieved by synergy modulation of feed networks. Both the numerical simulations and experimental verifications are conducted to support the effectiveness of the proposed method. Significantly, the proposed paradigm presents great potential for applications in intelligent radome, adaptive communication systems, and other EM scenarios with multi-degree-of-freedom.