Spoof SPP Research Articles

A novel beam-steering device based on spoof surface plasmon polaritons

In this paper, an ultra-compact T-shaped component is proposed in order to achieve a spoof surface plasmon polariton (SSPPs) dual-functional device with beam steering and multiple band-rejection filtering functions. The newly introduced T-shaped component provides an excellent multiple band-rejection filter response when combined with the SSPP transmission line (TL), and can be regarded as an excellent alternative to metamaterial particles to conceive multi-band rejection of spoof SPP waves. Multi-band rejection filters are designed by introducing different intervals among the symmetric T-shaped components. Furthermore, we designed a compact SSPP beam-steering device integrated with a multiple band-rejection filtering function. The multiple band-rejection integrated beam-steering device can also be realized by incorporating different intervals among the T-shaped components, as mentioned in the case of linear filters. Integration of the SSPP beam-steering device and band-rejection filter offers compact areas and controllable passband features, which broadens the application range of SSPPs. In conclusion, the proposed T-shaped component is an outstanding addition toward the advancement of highly efficient ultra-compact dual-functional plasmonic devices.

Generation of dual-band rejection filtering function in two frequency bands developed by spoof surface plasmon polaritons

In this paper, we propose the generation of dual-band rejection filters based on the interaction between spoof surface plasmon polaritons transmission line and -type resonator cells. By selecting a suitable value of spacing inside them, the -type resonator cells generate excellent dual-band band rejection filter on combining with spoof SPP transmission line in lower frequency band. A simple parametric calculation based on varying the value of spacing inside -type resonator cells, has been performed for the conversion of dual-band band rejection filter from lower frequency band to higher frequency band. Greater value of spacing results in larger LC coupling which deteriorate filtering performance by leaving us with dual-band rejection filtering function in lower frequency band. By choosing smaller value of spacing converts it into dual-band rejection filtering function in upper frequency band because of significant reduction in LC coupling, and hence leading to much improved broadband filtering performance. In short, the formation of dual-band rejection filter in lower frequency band and its conversion into dual-band rejection filter in upper frequency band can be fully controlled by just adjusting the value of vertical width inside -type resonator cells. The simulation results demonstrate the outstanding performance of the proposed filters and can play a crucial role in developing integrated plasmonic circuits at microwave and terahertz frequencies.

A novel plasmonic waveguide for extraordinary field enhancement of spoof surface plasmon polaritons with low-loss feature

In this paper, a novel spoof surface plasmon polaritons (SSPPs) waveguide based on I-shaped grooves has been presented in order to achieve extraordinary field enhancement of spoof SPPs at deep subwavelength scale. These I-shaped grooves are basically the transformed version of rectangular grooves incorporated by conventional spoof SPP waveguide, made up by virtue of lateral extension on either ends of these grooves. This approach which consists of addressing the grooves shape transformation proves very fruitful to accommodate higher capacitance and therefore leading to ultrahigh field confinement of spoof SPPs by lowering resonance frequency. Compared with plasmonic waveguide with T-shaped grooves which occupies the highest confinement of spoof SPPs than the previously reported different grooves shapes [Journal of Applied Physics 122, 123301 (2017)], the extension of lower ends of the grooves facilitates us with ultra-strong field confinement of spoof SPPs with low-loss feature. The proposed spoof SPP waveguide is more compact and a low cost structure exhibiting a strong response for spoof SPPs than the T-shaped spoof SPP waveguide. As a comparison, SPP-TL with T-shaped grooves results have been presented along with newly proposed SPP-TL with I-shaped grooves. Simulation results show that highly confined spoof SPPs can be generated by embedding I-shaped grooves in spoof SPP transmission line as compared to the spoof SPP TL with T-shaped grooves. Furthermore, a parametric study is presented to show its influence on the confinement. The proposed waveguide can be helpful in developing various integrated plasmonic circuits and systems at microwave frequencies.

Multiband modulated spoof SPP transmission based on a combined structure

We propose a combined structure that can freely control the transmission of spoof surface plasmon polarizations in the terahertz region. The combined structure is composed of a corrugated metallic strip and a textured closed surface with defect units. The spoof surface plasmon polarizations with different frequencies can be effectively trapped by the defect units with different scales in the localized spoof plasmonic structure. The designer structures provide the enhanced ability to modulate the spoof surface plasmon polarizations transmitted in the waveguide, which may provide potential applications in optical switching and sensing in the terahertz region.

Center Frequency and Bandwidth Reconfigurable Spoof Surface Plasmonic Metamaterial Band-Pass Filter

In this study, we report a design concept to obtain center frequency and bandwidth reconfigurable spoof surface plasmon polaritons (SSPP) band-pass filter using T-shaped spoof SPP resonator. The design, analysis, and implementation of the proposed filter have been given with detailed mathematical analysis. Tuning has been performed using varactor diode which is introduced at different positons in the T-shaped resonator. Since spoof SPP has high field confinement and enhancement, hence it offers low crosstalk and mutual coupling as compared with conventional microstrip which is desirable to make low-loss system. The filter has been fabricated using a 1.52-mm-thick microwave laminate and characterization has been done using Keysight Field-Fox analyzer N9918A. The fabricated filter has a reconfigurable center frequency from 4.2 to 4.4GHz with insertion loss ~4.2 dB and bandwidth reconfigurable from 4.12 to 4.52GHz with ~3.8 dB insertion loss in the tuning range. The proposed reconfigurable band-pass filter will pave an important role in the designing and developing of the flexible plasmonic circuits and systems.

Spoof Surface Plasmon Polaritons Based Reconfigurable Band-Pass Filter

This letter reports the design and analysis of the bandwidth (BW) reconfigurable band-pass filter using spoof surface plasmon polaritons at THz/microwave frequency. The designed filter consists of a spoof SPP T-shape resonator in which tuning has been introduced using variable capacitor device (having a cutoff frequency in THz regimes). Even and odd mode analysis has been carried out for a better understanding of the phenomenon. The proposed concept of variable bandwidth at a THz frequency in the SSPP structure has been demonstrated through Co-EM simulation. For the experimental validation of the proposed approach, the filter has been designed at microwave frequency, developed on a 60 mil (1.52 mm) thick microwave laminate, and characterized using a Keysight Field-Fox analyzer N9918A . In THz and microwave frequency regime, the designed filter has 3-dB BW reconfigurability of 20 GHz (0.41–0.43 THz) and 300 MHz (100–400 MHz) with the insertion loss of ~3 dB and ~1.7 dB–3.2 dB, respectively. The proposed reconfigurable bandpass filter will have an important role in the design and development of plasmonic circuits and systems.

Spoof Surface Plasmon Polariton-Based Reconfigurable Band-Pass Filter Using Planar Ring Resonator

In this paper, we report the design, analysis, and development of spoof surface plasmon polariton (SSPP)-based reconfigurable band-pass filter using a planar ring resonator. A transition from quasi-transverse electromagnetic (QTEM) mode of microstrip to SSPP mode was implemented which has been subsequently used to develop a reconfigurable band-pass filter. Trapezoidal shape periodically corrugated metallic grooves etched on the planar metallic surface have been used in the implementation of this transition. In the designed transition, impedance and mode matching between QTEM mode and SSPP mode have been achieved using gradient grooves. The developed transition has been used in the characterization of a ring resonator corrugated with the periodical array of the trapezoidal shape grooves. This SSPP ring resonator shows multiple passbands at different frequencies within the specified frequency range. Varactor diodes have been incorporated in the SSPP ring resonator to obtain tunable passband. Three types of varactor-tuned circuits have been experimentally implemented and characterized using SMV2019-079LF diode package. These circuits will pave the path for development of other front-end circuit elements using the concept of spoof SPP.

Concept, Theory, Design, and Applications of Spoof Surface Plasmon Polaritons at Microwave Frequencies

AbstractSurface plasmon polaritons (SPPs) are highly localized surface waves that exist on the interface of two media with opposite permittivities at optical frequencies. To produce spoof SPPs at microwave or terahertz frequencies, plasmonic metamaterials have been proposed by making subwavelength structures on a metal surface. Spoof SPPs inherit the properties of natural SPPs, including dispersion characteristics, field confinement, and subwavelength resolution, and therefore are highly expected to offer new solutions for advanced circuits and systems with high integration, compact size, and excellent performance. In this article, the development of spoof SPPs in recent years is reviewed, focusing primarily on the basic concept, theory, design method, and applications in microwave engineering. First, the concept and theory of SPPs and spoof SPPs are introduced, along with development from bulky waveguides to ultrathin transmission lines (TLs) and the unique merits of this new type of TL. Then, the design method is studied, including the feeding strategy of spoof SPP TLs and the realization of reconfigurable spoof SPPs. Recent progress on the engineering realization of plasmonic circuits is also demonstrated, including passive SPP circuits, active SPP devices, and SPP antennas. Finally, the future directions and potential applications of microwave spoof SPPs are discussed.

A Circularly Polarized Frequency Beam-Scanning Antenna Fed by a Microstrip Spoof SPP Transmission Line

In this letter, a planar frequency beam-scanning antenna with a circularly polarized (CP) radiation property is proposed. The beam scans along the narrow side and in lateral plane of the antenna. The antenna consists of two layers: Eight periodic symmetrical patches are presented on the top layer as radiation elements to generate CP beam, while microstrip spoof surface plasmon polariton transmission line is used as the feeding line, which improves the beam scanning range. The antenna has been fabricated and measured to verify the theory analysis. Measured results indicate that the main beam scans from –5° to +37° in a lateral plane within the operating frequency band from 12 to 16.5 GHz, of which an excellent CP characteristic is also realized. The peak gain of the antenna is about 9.5 dBi over the whole band.

Spoof surface plasmon polaritons based notch filter for ultra-wideband microwave waveguide

Spoof surface plasmon polaritons based notch filter for ultra-wideband microwave waveguide is proposed. Owing to subwavelength confinement, such a filter has advantage in the structure size without sacrificing the performance. The spoof SPP based notch is introduced to suppress the WLAN and satellite communication interference simultaneously. Both the cutoff frequency and the notch frequency are sensitive to the structure parameters, and the cut-off frequency can reach 20GHz. An adiabatic transition relying on gradient hole-size and flaring ground is designed to effectively couple energy into spoof SPP waveguide. The result shows its cut-off frequency of 17.4GHz with the insertion loss better than 3dB during the whole pass-band, while having more than 20dB rejections at 5.36GHz and 9.32GHz with 10dB fractional bandwidth 1.07% and 0.74% respectively to avoid the existing WLAN and satellite communication signals. Due to planar structures proposed here, it is easy to integrate in the microwave integrated systems, which can play an important role in the microwave communication circuit and system.

K-dispersion engineering of spoof surface plasmon polaritons for beam steering.

In this paper, we propose to achieve beam steering by k-dispersion engineering of spoof surface plasmon polaritons (spoof SPP) at microwave frequencies. The planar plasmonic metamaterials (PPMs) are employed to couple and guide spoof SPP. High-efficiency transmission based on spoof SPP coupling is realized via matching the wave-vectors of the spoof SPP and the space wave. The transmission phase can be modulated by k-dispersion engineering of the spoof SPP with great freedom. Due to the independent phase shift produced by the spoof SPP on the PPMs, the phase gradient achieved by using the PPMs as the sub-unit cells can be altered by changing the repetition period of the sub-unit cells. Two phase gradient materials (PGMs) are achieved by using nine different PPMs as the sub-unit cells with the repetition period q = 4mm and 4.5mm. Both the simulated and measured results demonstrated the excellent performances of the PGMs on high efficiency, wideband, tunable beam steering.

Quasi-three-dimensional post-array for propagation and focusing of a terahertz spoof surface plasmon polariton

This paper presents a quasi-three-dimensional post-array designed to propagate a terahertz spoof surface plasmon polariton (terahertz spoof SPP) with confinement. A transmission line making use of a terahertz spoof SPP is a promising device in the terahertz wave band, and there are many previous reports of two-dimensional structures. Three-dimensional structures provide sophisticated designs for transmission lines propagating a terahertz spoof SPP. Eigenmode analysis is used to derive a dispersion diagram for one post with boundary conditions extracted from the full model. The propagation frequency of the terahertz spoof SPP increases with lower heights or smaller diameters, and that remains virtually unchanged for post-spacing and thickness of a substrate. The analysis of the full model confirms the confinement of a terahertz spoof SPP vertically on the post-array. The magnitude of the electric field is strong around the top and bottom and weak at approximately one-third height. The terahertz spoof SPP is confined in the space around the post-array as well as a substrate, while it is confined only on substrates in conventional two-dimensional structures. The designed post-array can control the three-dimensional focusing of a terahertz spoof SPP in an arbitrary volume of space.

Electron-beam induced terahertz radiation from graded metallic grating.

We have numerically analyzed, based on a simplified particle-in-cell finite-difference time-domain (PIC-FDTD) method, an electron-beam (e-beam) induced terahertz (THz) radiation from metallic grating structures with graded depths (graded grating). Upon exciting with e-beam, directional THz radiations with wide-band spectrum containing several sharp peaks are obtained only from the one of the edge of the grating, which cannot be expected from the conventional theory of Smith-Purcell radiation. It was clarified that each modes originate from different locations on the graded grating reflecting different dispersion characteristics of spoof surface plasmon polariton (spoof SPP) at each locations, and they can propagate toward only the shallower groove as a surface wave due to the cutoff at each locations, and all of these modes eventually emitted from the one of the edge of the graded grating. These directional radiations can be directed toward either backward or forward by making the groove depth deeper or shallower. The lowest and the highest frequency of the radiation can be chosen by appropriately designing the deepest and the shallowest groove depths, respectively. These unique radiations cannot be obtained from the uniformly grooved grating. Our findings may open the way for a development of novel THz radiation source based on the spoof SPP on the wide variety of metallic grating structures or metasurfaces.

Controlling extraordinary transmission characteristics of metal hole arrays with spoof surface plasmons

We experimentally controlled the spectral characteristics of the extraordinary transmissions observed in metal hole arrays by analogy with spoof surface plasmon-polaritons (spoof SPPs). We constructed doubly periodic metal hole arrays. The larger and smaller periodic holes are for inducing extraordinary transmissions and modifying the spoof SPPs’ characteristics, respectively. Introducing the smaller holes that surround the larger hole arrays can modify the dispersion curve of the surface waves excited on a structured metal surface analogous to the spoof SPP model, and consequently, the extraordinary transmission peak will show a redshift.