Spoof Surface Plasmon Research Articles

A Wideband High-Gain Endfire Antenna Based on Spoof Surface Plasmon Polaritons

A novel endfire antenna based on spoof surface plasmon polaritons (SSPPs) is proposed in this letter. The main radiator of the antenna is excited by the SSPP waveguide, due to the high transmission performance of the SSPP waveguide, which is realized by etching a series of periodic corrugated grooves on the metal strip. The gradient corrugated grooves are used as the transition to transform the quasi-TEM mode in the microstrip line to the SSPP mode and get maximum impedance matching. In the bottom layer of the proposed antenna, to improve the front-to-back ratio of the endfire antenna, an extended U-shaped metal plane is positioned to act as the reflector of the antenna. Three printed metal strips are designed as the directors of the endfire antenna and improve the directivity. A prototype of the endfire antenna was fabricated and measured in this letter. The simulation and measurement results demonstrate that the gain of the antenna is about 9.1 dBi at the designed frequency 7 GHz, the fractional bandwidth of the antenna is up to 31%. The endfire antenna, which is implemented on a single layer dielectric substrate has the advantages of high efficiency, good directivity, high gain, wide band, easy fabrication, and compact size.

Spoof Surface Plasmon Polaritons Developed From Coplanar Waveguides in Microwave Frequencies

In this article, a new spoof surface plasmon polariton (SSPP) waveguide developed from traditional coplanar waveguide (CPW) is proposed. The asymptotic frequency of the SSPP unit cell can be easily manipulated by changing the meander groove dimensions of the SSPPs. A simple and efficient mode-conversion structure with gradient groove lengths is designed on the CPW’s ground to match the momentum of CPW to the proposed SSPPs smoothly. The designed SSPP waveguide has a good low-pass filtering property with cut-off frequency at 10.4 GHz. On this basis, another improved SSPP waveguide based on conventional grounded CPW (GCPW) is constructed, where a defected ground structure (DGS) is employed on the bottom layer of the circuit. Compared with the above work, this design has a lower cut-off frequency (8.9 GHz) and stronger field confinement. In order to validate the propagation performance, both SSPP waveguides are fabricated and measured. The measurements show that the GCPW based SSPP waveguide can effectively reduce the cut-off frequency. Such results are of great significance to the miniaturizations of plasmonic devices in microwave regime.

A customizable linearly polarized transmission line based on microstrip spoof surface plasmon polaritons with tilted grooves

In this paper, an ultrathin linearly polarized transmission line (TL) based on tilted microstrip spoof surface plasmon polaritons (SSPPs) is proposed. The proposed structure of the TL consists of an ultrathin corrugated metallic strip with periodic tilted groove arrays and metallic ground. Compared with the reported traditional SSPPs, the proposed SSPPs structures with tilted grooves can support the SSPPs wave with a larger propagation constant, which means a stronger field confinement in the microstrip SSPPs structure and effectively lower the dimension in transverse direction of the TL. Besides, the simulation demonstrates that the wave confinement performance can be well maintained when the grooves tilt from 0 to 60°, and the electric field vectors of the tilted grooves undergo a rotation correspondingly, resulting in a flexible polarization. Therefore, the polarization of different angles can be easily realized when the proposed SSPPs is employed as radiating or feeding structure. To verify characteristic of the proposed structure at microwave frequencies, we simulate, fabricate and measure a back-to-back transition sample with 45°-titled grooves. Both simulations and measured results have clearly validated the good characteristic of the proposed designs.

Design and verification of a broadband highly-efficient plasmonic circulator* *Project supported by the Six-Talent-Peaks Project in Jiangsu Province of China (Grant No. XYDXX-072) and the National Natural Science Foundation of China (Grant No. 61372048).

Circulators play a significant role in radar and microwave communication systems. This paper proposes a broadband and highly efficient plasmonic circulator, which consists of spoof surface plasmon polaritons (SSPPs) waveguides and ferrite disks to support non-reciprocal mode coupling. The simulated performance of symmetrically designed circulator shows that it has an insertion loss of roughly 0.5 dB while the isolation and return loss is more than 12 dB in the frequency range of 6.0 GHz–10.0 GHz (relative bandwidth of 50%). Equivalent circuit model has been proposed to explain the operating mechanism of the plasmonic circulator. The equivalent circuit model, numerical simulations, and experimental results are consistent with each other, which demonstrates the good performance of the proposed plasmonic circulator.

Terahertz Sensor Study Based on Spoof Surface Plasmon Polaritons

The spoof surface plasmon polaritons (SSPPs) structure can be used as a sensor in THz region for the biosensing. The accuracy of resonance and amplitude for sensor is very important for biosensing. The momentum matching of SSPPs determines the resonance position and the gap distance determines the amplitude. For the biomolecular sensing, the sample is positioned between the prism base and the SSPPs structure. The momentum matching condition at the current study does not consider the effect of sample refractive index and the resonance position has a significant error. Here the correction is made to the momentum matching condition which considers the effect of the sample refractive index. A comparative study of surface plasmon resonance (SPR) sensing performance based on frequency and angle variations shows that the sensing sensitivity for frequency region is superior to that of angle region; in the meanwhile, as an application of biosensors, we have detected different types of brain lesions in the frequency range. Furthermore, the reflection amplitude is related to gap size between the prism and SSPPs. The relationship of gap size and reflection amplitude is studied. By using the relationship between gap size and reflection amplitude, the amplitudes at different frequencies or incident angles for different refractivities have the same reflection dips compared to the other published results. The simulation is performed and the results proved the theory.

Spectrally and Spatially Selective Emitters Using Polymer Hybrid Spoof Plasmonics.

Optimized thermal emitters using optical resonances have been attracting increased attention for diverse applications, such as infrared (IR) sensing, thermal imaging, gas sensing, thermophotovoltaics, thermal camouflage, and radiative cooling. Depending on the applications, the recently developed IR devices have been tailored to achieve not only spectrally engineered emission but also spatially resolved emission using various nanometallic structures, metamaterials, and multistacking layers, which accompany high structural complexity and prohibitive production cost. Herein, this article presents a simple and affordable approach to obtain spatially and spectrally selective hybrid thermal emitters (HTEs) based on spoof surface plasmons of microscaled Ag grooves manifested in encapsulation polymer layers. Theoretical analyses found that the polymer hybrid plasmonics allows diverse emission tuning within the long-wave IR (LWIR; 8-14 μm) region as follows: (1) spatially selective emission peaks only exist in the interface of Ag grooves and IR-transparent layers and (2) near-unity spectrally selective emission is obtained by refining inherent emissivity of a thin IR-opaque layer. Also, parametric studies computationally optimized the structural parameters for spatially and spectrally selective HTEs. Using the optimized parameters, the authors fabricated two HTEs and demonstrated the intriguing emission features in terms of infrared data encoding/decoding and radiative cooling, respectively. These successful demonstrations open up the applicability of HTEs for tailoring IR emission in a spatially and spectrally selective manner.

Wide-Angle Frequency Beam Scanning Antenna Based on the Higher-Order Modes of Spoof Surface Plasmon Polariton

A wide-angle frequency beam scanning antenna based on spoof surface plasmon polaritons (SSPPs) is proposed for planar-integrated communication circuits. The SSPP-based antenna is constructed by hole arrays etched on the standard $50~\Omega $ coplanar waveguide, which can achieve ultrawide bandwidth and wide-angle beam scanning from backward direction to forward direction as the frequency changes. The radiation mechanisms of the SSPP-based antenna are based on the higher-order modes of the structure, which have been analyzed by the dispersion curves and electric field distributions. The overall width of the proposed SSPP-based antenna is only $0.95\lambda _{0}$ (with $\lambda _{0}$ being the wavelength of the lowest working frequency). The simulated results show that the proposed frequency beam scanning antenna achieves a wide scanning angle of 129° over a frequency range from 11.7 to 50 GHz (for $\vert S_{11}\vert dB) with an average gain level of 12.38 dBi. The good agreements between the simulated and measured results validate the proposed design.

Conformal Propagation and Near-Omnidirectional Radiation With Surface Plasmonic Clothing

Wireless technologies are essential components of wearable devices for applications ranging from connected healthcare to human–machine interfaces. Their performance, however, is hindered by the human body, which obstructs the propagation of wireless signals over a wide range of directions. Here, we demonstrate conformal propagation and near-omnidirectional radiation of wireless signals near the body using clothing integrated with spoof surface plasmonic (SSP) structures. These structures, fabricated entirely from conductive textiles, induce wireless signals emitted by nearby antennas to propagate around the body as surface waves and radiate as propagating waves in directions otherwise obstructed by the body. We describe the procedure for designing textile-based spoof surface plasmon waveguides, radiating elements, and impedance matching sections for operation in the 2.4–2.5 GHz industrial, scientific, and medical (ISM) band. Using a tissue phantom model of the human torso, we experimentally demonstrate 2.62 greater angular coverage by a dipole placed near the body compared to without the clothing.

Design of substrate integrated plasmonicwaveguide bandpass filter with T-shaped spoof surface plasmon polaritons

ABSTRACT A novel substrate integrated plasmonic waveguide (SIPW) filter with T-shaped slot line spoof surface plasmon polaritons (SSPPs) is proposed in this paper. By etching the SSPPs array between the two rows of the metal vias of the substrate integrated waveguide (SIW) structure, the SIPW bandpass filter can independently adjust the low cutoff frequency by changing the SIW geometric parameters and the high cutoff frequency by changing the SSPP geometric parameters, respectively. Comparing with the traditional SIPW filter with signal layer or double layers linear slot line SSPPs, the proposed SIPW filter with T-shaped SSPPs has smaller circuit size thanks to the better electromagnetic field confinement ability of the T-shaped SSPPs. The dispersion properties of the SIW unit and the T-shaped SSPPs are discussed and the parameters effect on filter’s performance are numerically investigated. A bandpass SIPW filter with T-shaped SSPPs is designed and fabricated with the proposed design method. The measurement results show that its passband is at 5.6–7.3 GHz with the return loss higher than 10 dB and the maximal insertion loss 1.8 dB. Also, its out-of-band spurious rejection is higher than 40 dB at the bandwidth 8.1–14.8 GHz. The agreements between the simulated results and measured results demonstrate the effectiveness of the proposed SIPW filter with T-shaped SSPPs.

A Tunable Graphene Filtering Attenuator Based on Effective Spoof Surface Plasmon Polariton Waveguide

In this article, to reduce the operating frequency and the size of the spoof surface plasmon polariton (SSPP) attenuator and introduce the filtering function into the graphene attenuator, we propose a tunable graphene filtering attenuator, namely the graphene-based effective SSPP (ESSPP) attenuator. It consists of an ESSPP waveguide and a graphene sandwich structure (GSS). The effect of GSS on the attenuation and dimensions of the ESSPP waveguide on the passband are analyzed in detail, and the closed form of the attenuation is proposed. Finally, five prototypes of the graphene filtering attenuator are fabricated and measured. The experimental results show that not only the attenuation of this attenuator can be tuned but also that the upper and lower cutoff frequencies can be adjusted independently, which means that this filtering attenuator demonstrates expected filtering and attenuation performance.

Terahertz Spoof Surface Plasmonic Logic Gates.

SummaryLogic gates are important components in integrated photonic circuitry. Here, a series of logic gates to achieve fundamental logic operations based on linear interference in spoof surface plasmon polariton waveguides are demonstrated at terahertz frequencies. A metasurface-based plasmonic source is adopted to couple free-space terahertz radiation into surface waves, followed by a funnel-shaped metasurface to efficiently couple the surface waves to the waveguides built on a domino structure. A single Mach-Zehnder waveguide interferometer can work as logic gates for four logic functions: AND, NOT, OR, and XOR. By cascading two such interferometers, NAND and NOR operations can also be achieved. Experimental investigations are supported by numerical simulations, and good agreement is obtained. The logic gates have compact sizes and high intensity contrasts for the output “1” and “0” states. More complicated functions can be envisioned and will be of great value for future terahertz integrated computing.

Spoof surface plasmon analysis based on Marcatili’s method

Motivated by surface plasmon polariton waveguides in the optical regime, spoof surface plasmon (SSP) waveguides have received a lot of attention in terahertz and millimeter wave frequencies. Most research on these kinds of waveguides is numerical. However, some limited analytical work can be seen in the literature. In this paper, one type of SSP waveguide that is composed of a rectangular corrugation with finite lateral width on the ground is considered, and an analytical method, which is inspired by Marcatili’s method, is proposed in order to calculate the dispersion curve of the first mode. The results of this analytical method and a numerical commercial eigenmode solver are compared. The accuracy of this method by varying different geometrical parameters is shown. Finally, it is shown that this method works well in predicting the electromagnetic fields of the first mode.

A Compact Wideband Filter Based on Spoof Surface Plasmon Polaritons With a Wide Upper Rejection Band

In this letter, spoof surface plasmon polaritons (SSPPs) are developed in a slotted half-mode substrate integrated waveguide (HMSIW) to realize a bandpass propagation feature instead of a traditional low-pass one. We investigate the dispersion properties to analyze the performance of an SSPP unit cell. Parametric sweepings are further performed to reveal the direct relationships between geometry and cut-off frequencies. We design a compact transition by etching gradient slots on a tapered microstrip-to-HMSIW transition. Then, we finally design an SSPP bandpass filter (BPF) with both wide passband and upper rejection band. The measured 3-dB relative bandwidth is 59.25% ranging from 4.24 to 7.81 GHz. The measured upper rejection band can reach up to 16 GHz with a rejection level better than -31.6 dB. The total size of the filter is only $2.69\lambda _{g} \times 0.42\lambda _{g}$ . This work can provide a new concept to design novel wideband and ultra-wideband (UWB) microwave filters. Significant potential applications of the strategy of developing SSPPs in HMSIW can be found in microwave versatile planar circuits and devices.

Deeper Confinement of Electromagnetic Waves Beyond Spoof Surface Plasmon Polaritons

The physics of spoof surface plasmon polaritons (SSPPs) is widely studied for their intrinsic confinement of electromagnetic wave, leading to the useful applications of device miniaturization and signal integrity. As another imitation of surface plasmon polaritons (SPPs) in microwave, effective SPPs (ESPPs) are excited inside the waveguide based on structural dispersion. Without using lossy plasmonic materials, slow wave property is achieved inside the waveguide for the interface confinement. In this work, for further enhancing the field confinement of SSPPs, the waveguide dispersion method is utilized on the structure of SSPPs. In this way, the techniques of ESPPs and SSPPs are feasibly combined for the first time, coining the name of “effective SSPPs (ESSPPs).” The dispersion relation of the ESSPPs is analyzed theoretically and numerically with the obvious field confinement. The structural dispersion makes the wavelength of ESSPPs reach 1/18 of the wavelength of SSPPs, which has potential applications for device miniaturization and signal integrity. Finally, two prototypes of the ESSPPs waveguide are fabricated on the substrate integrated waveguide (SIW) platform. The experimental results of the prototypes verify the stronger field confinement, indicating new possibilities to slow down the wave propagation with controllable confinement.

Electromagnetic metamaterials—from effective media to field programmable systems

Electromagnetic metamaterials are periodic or nonperiodic artificial structures comprising basic elements in subwavelength scales. They can be used to control electromagnetic waves by designing the basic elements and their spatial arrangements. Metamaterial has been a research hotspot in physical and information sciences. In this review, I present the history and main progresses achieved in metamaterial studies conducted in the State Key Laboratory of Millimeter Waves at Southeast University, which were performed in three stages. In the first stage, we improved the developments in effective-medium metamaterials. In particular, we proposed a general theory to accurately describe the effective permittivity and permeability of metamaterials. Based on the general theory, we designed and realized a three-dimensional (3D) wideband ground-plane invisibility cloak, free-space electrostatic invisibility cloak, electromagnetic black hole, electromagnetic illusions, and radially anisotropic zero-index metamaterial for omni-directional radiations and nearly perfect power combinations of source arrays. Moreover, we undertook significant efforts in engineering applications of microwave metamaterials, such as broadband and low-loss 3D transformation-optic lens for wide-angle scanning, 3D planar gradient-index lens for high-gain radiations, and random metasurfaces to reduce radar cross sections. In the second stage, we opened up a new direction of plasmonic metamaterials from the viewpoint of microwave transmission lines. We proposed an ultrathin, narrow, and flexible corrugated metallic strip to guide spoof surface plasmon polaritons (SPPs) with small bending and radiation losses, based on which we designed and realized a series of passive SPP devices (such as power divider, coupler, filter, and resonator), active SPP devices (such as amplifier and duplexer) and SPP antennas in the microwave bands. We demonstrated a significant feature of the ultrathin SPP transmission line in overcoming challenges of signal integrity existing in the traditional integrated devices and circuits. We built up a full-SPP wireless communication system with unique properties to remotely transmit two movies in two deep-subwavelength-distance channels exhibiting excellent performance. In the third stage, we established a new area of metamaterial-information metamaterial. We proposed to describe the metamaterial using digital coding from the information science viewpoint, which directly resulted in a new kind of metamaterial-digital coding metamaterial. We theoretically and experimentally illustrated that the digital coding metamaterials comprising digital units can be controlled using different coding sequences to achieve different functions. When the digital state of the coding unit was controlled using a field programmable gate array (FPGA), we realized a field programmable metamaterial that can manipulate electromagnetic waves in real time and generate numerous different functions using a single piece of hardware. The digital coding metamaterial provides a platform to establish a digital space on the physical space and enriches the methodology and theory of metamaterials. We proposed measuring the information capacity of metamaterials using Shannon entropy and presented the convolution and addition theorems on metamaterial platforms, which can be used to simultaneously control the physical properties and digital information. Based on information metamaterials, we established new-architecture microwave imaging systems, wireless communication systems, and other intelligent information systems.

Study of A designed and experimental multi-beam antennas based on Spoof Surface Plasmon Polaritors structure

The new type of artificial electromagnetic two-dimensional surface consists of an array of subwavelength unit structures arranged according to the periodicity of the dispersion curve. It has a significant role in regulating electromagnetic waves, and it has become one of the hot topics in the field of information. In this paper, the Spoof Surface Plasmon Polaritons (SSPPs) are regulated and applied to the wireless millimeter-wave base station communication. It has the characteristics of low profile, low cost, high isolation, broadband, and high gain. As a proof of concept, the antenna array is designed, simulated, processed and measured. The dual-beam adaptive antenna based on SSPPs at 10 GHz. The experimental results are in good agreement with numerical simulations. The proposed antenna has promising applications on planar wireless communication devices, such as multi-beam antennas, beam-scanning antennas, and wave controllers.

Broadband and High-Efficiency Excitation of Spoof Surface Plasmon Polaritons Through Rectangular Waveguide

Spoof surface plasmon polaritons (SPPs) are highly localized surface waves that can be supported on metal surfaces with subwavelength decorations. Mode matching and momentum matching have been investigated so as to efficiently excite the spoof SPPs through conventional planar waveguides (WGs) such as the microstrip (MS) line and the co-planar waveguide (CPW). In this work, a smooth and wideband bridge between the conventional rectangular waveguide and the plasmonic waveguide of spoof SPPs has been proposed and experimentally demonstrated. High efficiency is achieved in both simulation and experiment in a wide frequency range from 12 to 18 GHz. The high-efficiency and broadband excitation of spoof SPPs through rectangular waveguide has great potentials in microwave, millimeter-wave and terahertz circuits and systems.

A New Self-Packaged Substrate Integrated Air-Filled Spoof Surface Plasmon Polaritons Line With Inherent Low Loss and Deep Upper Frequency Suppression

In this article, a novel self-packaged substrate integrated air-filled spoof surface plasmon polaritons line (SPSIAF-SSPPL) with advantages of inherent low loss, low radiation, and deep upper frequency suppression is presented. This novel transmission line is based on the substrate integrated suspended line (SISL) technology and the spoof surface plasmon polaritons (SSPP) line of bow-tie cells. Parameter adjustments of bow-tie cells are corresponded to changes of the SSPP line cut-off frequency. In this article, an SSPP line and an SPSIAF-SSPPL structure with about 9.7-GHz cut-off frequency are designed, simulated, and fabricated. Simulated and measured results indicate that the loss and the near-field radiation of SPSIAF-SSPPL are greatly reduced compared with the SSPP line with identical parameters of bow-tie cells. Moreover, the proposed structure also shows a good performance on the suppression of the upper frequency. The measured stopband is extended from 10 to 15 GHz with the suppression level above 20 dB.

A Flexible High-Selectivity Single-Layer Coplanar Waveguide Bandpass Filter Using Interdigital Spoof Surface Plasmon Polaritons of Bow-Tie Cells

In this article, a flexible high-selectivity single-layer coplanar waveguide (CPW) bandpass filter using interdigital spoof surface plasmon polaritons (SSPP) of bow-tie cells is proposed, simulated, and fabricated. The low and high cut-off frequency can be adjusted independently, which is one of the characteristics of the presented bandpass filter. The SSPP of bow-tie cells is used to adjust the high cut-off frequency, while the interdigital coupling structure of the SSPP is designed to adjust the lower one. The proposed filter also has advantages of single-layer structure and high selectivity. Simulated results of the proposed filter show a theoretical 3-dB bandwidth from 2.28 to 5.12 GHz (about 76.8%) with high selectivity ( $\vert S_{11}\vert dB and −0.4 dB $> \vert S_{21}\vert > -1.1$ dB in the passband), and measured results agree well with simulated ones. Since the filter in this article is designed based on the flexible printed circuit (FPC) board, the circuit can be tested in bent, folded, and even twisted states, and these measured results are all basically consistent with the test result of the flat state circuit. This characteristic can greatly reduce the size of the filter and increase the flexibility of the circuit application.

Detection of Defects in Non-Metallic Composite Material Based on Electronically Controlled Spoof Surface Plasmon Polaritons

A novel sensor based on electronically controlled spoof surface plasmon polaritons (SSPPs) is proposed to detect internal defects in non-metallic composites. The designed sensor is flexible and can be wrapped around the materials under test (MUT), therefore, compared with non-flexible sensors, it has a great advantage in detecting curved MUT. Moreover, traditional microwave sensors have to scan the MUT by the way of mechanical moving which consumes much time. For improving the detection speed, the electronic control scheme is adopted to control the sensing area of designed sensor, so as to replace mechanical moving. The detection is based on monitoring change in resonance frequency of the designed sensor which is caused by the defects. The sensor has the advantages of high sensitivity, fast detection speed and it is very convenient to detect curved MUT.