Jinsong Gao

A novel wideband, low-profile and second-order miniaturized band-pass frequency selective surfaces

A novel wideband, low-profile and second-order miniaturized band-pass frequency selective surface (FSS) made of metallic mesh and its complementary structures with skewed arrays of modified triples is presented in this paper. Compared with traditional second-order bandpass FSSs obtained using λ/4 apart from one another, the novel FSS with an overall thickness of λ/18 is composed of three metallic layers (the outside and middle layers are complementary) separated by two electric thin dielectric substrates. This arrangement can shorten the inter-element spacing and increase the bandwidth, while the up and bottom metallic layers can constitute a symmetric biplanar FSS and thus realize ability of maximally flat second-order bandpass response. The novel FSS has a −3 dB bandwidth about 8.2 GHz (6.9 -15.1 GHz) and a fractional bandwidth exceeds 75%. Moreover, such an FSS has the merits of stable performance for incident angles within 50° and different polarizations. The principles of operation along with guidelines for the design of the proposed FSS, the simulated results by vector modal matching method, and the experimental values of the fabricated prototype are also presented and discussed.

Infrared transparent frequency selective surface based on metallic meshes

This paper presents an infrared transparent frequency selective surface (ITFSS) based on metallic meshes. In this ITFSS structure, periodic cross-slot units are integrated on square metallic meshes empowered by coating and UV-lithography. A matching condition is proposed to avoid the distortion of units. Experimental results show that this ITFSS possesses a good transmittance of 80% in the infrared band of 3–5 μm, and also a stable band-pass behavior at the resonance frequency of 36.4 GHz with transmittance of −0.56 dB. Theoretical simulations about the ITFSS diffractive characteristics and frequency responses are also investigated. The novel ITFSS will attract renewed interest and be exploited for applications in various fields.

Floquet Topological Insulator in the BHZ Model with the Polarized Optical Field

Topological phase of newly found matter has aroused wide interests, especially related with the external periodical modulating. With the help of the Floquet theory, we investigate the possibility of externally manipulating the topological property in a HgTe/CdTe quantum well system with the polarized optical field. We give the phase diagram, showing that by modulating the parameters of the polarized optical field, especially the phase, the topological phase transition can be realized in the QW and lead to the so-called Floquet topological insulator. When the optical field is weak, the driven QSH state of QW is robust with the optical field. However, when the optical field is relatively larger, the group velocity of edge states and the gap between the bulk states exhibit certain oscillations. The implications of our results are discussed.

A dual-band flexible frequency selective surface with miniaturized elements and maximally flat (Butterworth) response

A dual-band flexible frequency selective surface (FSS) with miniaturized elements and maximally flat (Butterworth) response is presented in this paper. It is composed of three metallic layers, which are fabricated on thin flexible polyimide substrates and bonded together using thin bonding films. The overall thickness of the proposed structure is only about 0.3 mm, making it an attractive choice for conformal FSS applications. All the three layers can constitute a miniaturized-element FSS (MEFSS) and produce the first pass-band with miniaturization property, while the up and bottom layers can constitute a symmetric biplanar FSS and produce the second pass-band with maximally flat (Butterworth) response. The two pass-bands are independent and there is a wide band spacing up to 30 GHz between them. The principles of operation, the simulated results by using the vector modal matching method, and the experimental values of the fabricated prototype are also presented and discussed.

Negative refraction by a planar Ag/SiO2 multilayer at ultraviolet wavelength to the limit of silver

For planar structured hyperbolic metamaterial, the shortest wavelength achievable for negative refraction is often limited by dielectric layers, which are usually wide band gap semiconductors that absorb light strongly at wavelength shorter than their absorption edge. Here we proposed that using SiO2 may break such limitation based on effective medium theory. Through calculation and simulation we demonstrated broad angle negative refraction by a planar Ag/SiO2 layered structure at wavelength down to 326 nm. Its imaging and focusing abilities were also presented. The lower limit of wavelength here is defined by the property of silver, whose permittivity turns positive below 324 nm.

A novel broadband bi-mode active frequency selective surface

A novel broadband bi-mode active frequency selective surface (AFSS) is presented in this paper. The proposed structure is composed of a periodic array of convoluted square patches and Jerusalem Crosses. According to simulation results, the frequency response of AFSS definitely exhibits a mode switch feature between band-pass and band-stop modes when the diodes stay in ON and OFF states. In order to apply a uniform bias to each PIN diode, an ingenious biasing network based on the extension of Wheatstone bridge is adopted in prototype AFSS. The test results are in good agreement with the simulation results. A further physical mechanism of the bi-mode AFSS is shown by contrasting the distribution of electric field on the AFSS patterns for the two working states.

A novel 2nd-order bandpass MFSS filter with miniaturized structure

In order to effectively obtain a miniaturized structure and good filtering properties, we propose a novel 2nd-order bandpass metamaterial frequency selective surface (MFSS) filter which contains two capacitive layers and one inductive layer, where there are multi-loop metallic patches as shunt capacitor C and planar wire grids as series inductor L respectively. Unlike the traditional operation way—the tuned elements used in resonant surface approximately equal to one wavelength in circumference and the structure thickness with a spacing of a quarter wavelength apart, by changing the value of L and C and matching multilayer dielectric to adjust the LC coupling resonance and the resonance impedance respectively, the proposed MFSS filter can achieves a miniatured structure with ideal bandpass properties. Measurement results of the fabricated prototype of the bandpass filter (BPF) indicate that the dimension of the tuned element on resonant surface is approximately 0.025 wavelength, i.e., 0.025λ. At the same ...

Closely packed dense frequency selective surface

In order to realize wideband filtering properties of frequency selective surface (FSS), FSS of closely packed elements is presented. The Y loop elements are chosen as the graphics elements. Based on the spectral domain method, the frequency response is analyzed for different incident angles and polarizations. The result of the numerical analysis shows that the dense FSS has wide passband with better independence of angle and polarization.

Achieving dynamic switchable filter based on a transmutable metasurface using SMA

We propose a switchable filter composed of transmutable array using shape memory alloys (SMA). It could exhibit a temperature induced morphology change spontaneously like the biological excitability, acting as a shutter that allows the incident energy to be selectively transmitted or reflected with in excess of 12dB isolation at the certain frequencies for both polarizations. Equivalent circuit models describe the operational principle qualitatively and the switching effect is underpinned by the full-wave analysis. A further physical mechanism is shown by contrasting the distributions of electric field and surface current on the surface at the same frequency for the two working modes. The experimental results consist with the theoretical simulations, indicating that the metasurface could serve as one innovative solution for manipulating the electromagnetic waves and enlighten the next generation of advanced electromagnetic materials with more freedom in the processes of design and manufacturing.

The tunable property of complementary frequency selective surface with rotationally symmetric element

In this paper, the tunable property of two complementary frequency selective surface (CFSS)designs is presented. The unit cell of each design comprises of rotationally symmetric element. CFSS is a double layer structure with a patch array and an aperture array separated by a thin substrate. Simulation results prove that the resonant frequency of the two CFSSs could be tuned by rotating the patch elements. Such tunable property is explained by the electromagnetic interaction between the two complementary layers. Experimental results showed that both CFSS have good angular stability and their resonance could be tuned. Such tunable property provides a promising solution to the active FSS design.