Changqing Gu

Multi-channel composite spoof surface plasmon polaritons propagating along periodically corrugated metallic thin films

In this work, we demonstrate that composite spoof surface plasmon polaritons can be excited by coplanar waveguide, which are composed of two different spoof surface plasmon polaritons (SSPPs) modes propagating along a periodically corrugated metallic thin film simultaneously. These two SSPPs correspond to the dominant modes of one-dimensional (1D) periodical hole and groove arrays separately. We have designed and simulated a planar composite plasmonic waveguide in the microwave frequencies, and the simulation results show that the composite plasmonic waveguide can achieve multi-channel signal transmission with good propagation performance. The proposed planar composite plasmonic metamaterial can find potential applications in developing surface wave devices in integrated plasmonic circuits and multi-channel signal transmission systems in the microwave and terahertz frequencies.

A Novel Absorber With Tunable Bandwidth Based on Graphene

A design of absorber using two-dimensional (2-D) periodic arrays of double-square split loops and resistive strips printed on grounded dielectric substrate is investigated in this letter. Unlike the traditional structure, graphene sheets are proposed for thin absorbing structures at microwave frequencies. The analysis of absorption properties is based on the dynamic model of graphene, which takes into account the surface impedance of graphene layer. Both narrowband and broadband tunable absorbers can be demonstrated with the same structure by tuning the conductivity of graphene. Furthermore, the equivalent circuit method (ECM) is used to introduce the working principles of the proposed absorber. In addition, the absorber shows relatively stable performance with different oblique incidence angles.

Multi-band localized spoof plasmons with texturing closed surfaces

We demonstrate that periodically textured closed surface with multiple groove depths can support multi-band spoof localized surface plasmons (LSPs). It is interesting to note that the spoof LSPs in each band resemble those generated by the textured closed surface of the same periodicity with the corresponding single groove depth. In this way, it paves the way for the generation and design of multi-band spoof LSPs. Moreover, multiple resonance band structures and devices, such as resonator, oscillator, and other band-notched structures in the microwave and terahertz regimes can be realized.

Localized spoof plasmons in closed textured cavities

Localized spoof plasmons arising with textured closed surfaces have been theoretically studied and experimentally verified, which resemble the localized surface plasmons (LSPs) in the optical regime. In this work, we go one step further and demonstrate that part of the resonance modes in closed textured cavities pertain to spoof localized surface plasmons (spoof-LSPs) modes. We show the existence of spoof LSPs in periodically textured perfect electric conductor circular cavities and make an analogy between these spoof LSPs and the real LSPs in closed metallic cavities with the Drude model in the optical regime. Also, a metamaterial approach is presented to capture the resonant features of these modes.

Tunable band-notched coplanar waveguide based on localized spoof surface plasmons

This Letter proposes a simple band-notched coplanar waveguide (BNCPW), which consists of a coplanar waveguide (CPW) and an ultra-thin periodic corrugated metallic strip that supports spoof surface plasmon polaritons (SSPPs) with defect units on the back of the substrate. By introducing a defect unit or multiple defect units into the strip, a narrow stopband or multiple narrow stopbands would be generated flexibly and conveniently. The band-notch function is based on the idea that a defect mode, which exists in the bandgap between the fundamental and the first higher mode of the SSPPs, can be introduced to form a stopband. Thus, the SSPPs field is localized around the defect units, which is another form of localized spoof surface plasmons (LSSPs). By properly tuning the dimensions of each defect unit, the absorption level and center frequency of the stopband could be adjusted independently. We offer theoretical analysis and experimental results to validate our idea and design. In this framework, a variety of band-notched devices and antennas in the microwave and terahertz (THz) frequencies can be easily designed without additional band-stop filters.

Multilevel Fast Adaptive Cross-Approximation Algorithm With Characteristic Basis Functions

This paper presents a multilevel fast adaptive crossapproximation (MLFACA) algorithm for accelerated iterative solution of the method of moments (MoM) matrix equation for electrically large targets. The MLFACA compresses the impedance submatrices between well-separated blocks into products of sparse matrices, constructed with the aid of the fast adaptive cross-sampling (FACS) scheme and the butterfly algorithm. As a result, the MLFACA can reduce both the computational time and the storage of the MoM to O(N log2N), where N is the number of the Rao-Wilton-Glisson (RWG) basis functions in the analyzed target. Meanwhile, the MLFACA maintains the adaptive and kernel-independent properties. Furthermore, the characteristic basis function method (CBFM) is employed to decrease the size of the outer matrices of the MLFACA to further reduce the storage and iteration time. Numerical results are presented to demonstrate the advantages of the proposed method, including a successful solution of a scattering problem involving 10 861 668 RWG basis functions.

High-efficiency transition between rectangular waveguide and domino plasmonic waveguide

In this work, we propose an optimized transition structure to realize smooth and high efficiency conversion from the guided wave supported by a conventional rectangular waveguide (CRW) to the domino plasmon polaritons (DPPs) supported by a domino plasmonic waveguide (DPW) and vice versa in the X-band (8.2GHz∼12.4GHz). This transition structure consists of two tapered CRWs connected by a gradient domino array with optimized gradient heights and lateral widths. Experimental results of the S-parameters show excellent agreement with the simulations and the optimization scheme can be readily extended to other bands. Furthermore, a domino plasmonic power divider is implemented to demonstrate the application of the transition structure in the integration of conventional microwave circuits with plasmonic devices.

Dual-band trapping of spoof surface plasmon polaritons and negative group velocity realization through microstrip line with gradient holes

In this letter, dual-band trapping of spoof surface plasmon polaritons (SSPPs) is realized by a simple surface plasmon waveguide (SPW), which takes the form of a microstrip line with periodic holes. A tapered microstrip line with periodic gradient holes is built for efficient mode conversion between the quasi-transverse electromagnetic waves in the common microstrip line and the SSPPs on the SPW. It is interesting to note that negative group velocity can be clearly observed on the first high-order mode of such SPW due to the strong coupling between the corrugated microstrip line and ground. A curved SPW of the same form is also investigated for testing its field confinement and circuitry function. Measurement results agree quite well with the simulation ones, which indicate this SPW can find potential applications in plasmonic integrated circuits at microwave and terahertz frequencies.

Smooth bridge between guided waves and spoof surface plasmon polaritons

In this work, we build a smooth bridge between a coaxial waveguide and a plasmonic waveguide with subwavelength periodically cylindrical radial grooves, to realize high-efficiency mode conversion between conventional guided waves and spoof surface plasmon polaritons in broadband. This bridge consists of a flaring coaxial waveguide connected with a metal cylindrical wire corrugated with subwavelength gradient radial grooves. Experimental results of the transmission and reflection coefficients show excellent agreement with the numerical simulations. The proposed scheme can be extended readily to other bands and the bridge structure can find potential applications in the integration of conventional microwave or terahertz devices with plasmonic circuits.

Analysis of Electromagnetic Scattering from PEC Targets using Improved Fast Dipole Method

In this article, an improved fast dipole method (IFDM) is proposed to enhance the accuracy of the conventional fast dipole method (FDM). Through expanding the terms R α and RR in the formulation of the equivalent dipole-moment method (EDM) using a simple Taylors series, the improved FDM can represent the interaction between two dipoles as an aggregation-translation-disaggregation form more accurately than the conventional FDM. Furthermore, the complexity of matrix-vector products (MVPs) between the far-group pair, such as block i and block j, also can be reduced from O(N i N j ) to O(Ni + Nj ), where Ni and Nj are the numbers of dipoles in block i and block j, respectively. For a prescribed and relatively high accuracy, the new method leads to a significant decrease in computational effort. Numerical results about the electromagnetic scattering from perfect electric conducting (PEC) targets are given to demonstrate the merits of the IFDM.