Spoof Surface Plasmon Research Articles

Compact wideband filter with wide stopband using transition-free spoof surface plasmon polaritons

In this article, a newly spoof surface plasmon polaritons (SSPPs) is proposed and used to design a compact wideband bandpass filter (BPF). Different from the traditional SSPP unit cell with one-shaped structure, the unit cell of the proposed SSPPs consists of an H-shaped slotline and a bilateral T-shaped slotline. Benefiting from the hybrid structure, no transition portion is needed for impedance matching in the design of the microwave filter, which highly reduces the horizontal size of the SSPPs-based filter. The transition structure of microstrip to slotline provides a capacitance with a highpass frequency response, which enables the realization of a passband by cooperating with the natural lowpass property of SSPPs. Also, the upper and lower cutoff frequencies of the proposed filter can be adjusted independently by the key parameters. Besides, a wide upper stopband can be obtained by properly designing the SSPPs unit cell and the microstrip to slotline structure. Finally, a well-designed BPF operated at 1.3–6.2 GHz and its upper stopband rejection reaching 20 GHz is fabricated and measured. The test results are in good agreement with the simulations, which verifies the feasibility of the proposed structure and design method.

Leaky wave antenna with backfire to endfire beam-scanning capability based on even mode spoof surface plasmon polaritons

In this paper, a leaky wave antenna (LWA) based on even mode excited spoof surface plasmon polaritons (SSPPs) is proposed. The LWA can radiate beams from backfire to endfire as the frequency increases. The proposed LWA is asymmetrically modulated by the method of sinusoidal modulation of the reactance surface at two sides of the SSPP structure, which brings a phase difference between two sides of the antenna. The phase difference produces the field component that radiates the beam in the backfire or endfire direction. In this way, the full-angle beam scanning is realized. Moreover, to reduce the open-stop band effect, an improved LWA with multiperiod modulation and asymmetric units is proposed. The simulated results indicate that the radiation beam steers from backfire to endfire. A prototype of the proposed LWAs is fabricated and measured. The measured results agree well with the simulated ones.

Spoof Surface Plasmon Polariton Based on Stepped Grooves and Its Application in Compact Low-Pass Filter Design

Spoof Surface Plasmon Polariton Based on Stepped Grooves and Its Application in Compact Low-Pass Filter Design

Spoof Surface Plasmon Polariton-Based Continuously Tunable Cutoff Frequency Filter

Spoof Surface Plasmon Polariton-Based Continuously Tunable Cutoff Frequency Filter

Electromagnetic Spatiotemporal Differentiation Meta‐Devices

AbstractSpatiotemporal optical computing devices that can perform mathematical operations in both spatial and temporal domains can provide unprecedented measures to build efficient and real‐time information processing systems. It is particularly important to realize the comprehensive functions in a compact design for better integration with electronic components. In this work, an analog spatiotemporal differentiator in microwaves based on an asymmetrical metasurface that has a phase singularity in the spatiotemporal domain is experimentally demonstrated. It is shown that this structure can give rise to a spatiotemporal transfer function required by an ideal first‐order differentiator in both spatial and temporal domains by tailoring the unidirectional excitation of spoof surface plasmon polaritons (SSPPs). The spatial edge detection is performed utilizing a metallic slit, and the temporal differentiation capability of the device is examined by Gaussian‐like temporal pulses of different widths. It is further confirmed that the differentiator demonstrated here can detect sharp changes in spatiotemporal pulses even with intricate profiles and theoretically estimated the resolution limits of the spatial and temporal edge detection. It is also shown that the pulse input after passing the spatiotemporal differentiator implemented here could carry a transverse orbital angular momentum (OAM) with a fractal topology charge.

Compact balanced filter with high common mode suppression using hybrid microstrip and slotline spoof surface plasmon polaritons

Compact balanced filter with high common mode suppression using hybrid microstrip and slotline spoof surface plasmon polaritons

A semi-analytical method for characterization of fractal spoof surface plasmon polaritons with a transfer matrix and bloch theory

In this paper, a semi-analytical approach is introduced to analyze a spoof plasmonic structure, with an arbitrary geometry. This approach is based on a combination of techniques that employ a full-wave simulator and the Bloch theorem. By applying periodic boundary conditions, the real and imaginary parts of the equation obtained from the equivalent network have been calculated. To show the accuracy and validity of this proposed approach, a complementary Minkowski fractal SSPP unit cell has been designed and analyzed, and this has been used in a surface plasmonic transmission line. The results of our proposed method have been compared to measured results, and the simulated and measured results showed that the SSPP transmission line possesses high performance, from 1.45 to 5 GHz.

Design of the Wilkinson power divider with multi harmonic suppression

Abstract A Wilkinson power divider (PD), which can suppress the second, third, and fourth harmonics is proposed. The PD is implemented based on an asymmetric meta-structure. The meta-structure is constructed be combing defect ground structure (DGS) and spoof surface plasmon polariton (SSPP). It can not only realize the impedance conversion function in the operating frequency band, but also realize the suppression of the second, third, and fourth harmonics. The simulation and measurement results show that this structure can achieve −32 dB suppression for the second harmonic, −31 dB suppression for the third harmonic, and −28 dB suppression for the fourth harmonic respectively.

Broadside radiation antenna based on tightly coupled spoof surface plasmon polaritons

A spoof surface plasmon polariton (SSPP) is a hybrid mode of a surface wave in the air and electron oscillation within artificial electromagnetic (EM) media, with the dispersion curve lying below the light line, giving rise to many unique EM properties. In this paper, we investigate the EM properties of tightly coupled SSPP (TC-SSPP) modes and propose a slender broadside antenna based on the TC-SSPP. With the comb structure (CS), dispersion properties of different SSPP modes are firstly analyzed under plane wave illumination, and then we introduce a modified SSPP structure, the broadside-coupled (BC)-CS, to excite and guide TC-SSPP modes. Since TC-SSPP modes can be confined tightly around the slender BC-CS, EM waves can be manipulated within a much more compact space, which is favorable for miniaturization, compactness and the light weight of microwave devices. To demonstrate this, we propose a slender broadside radiation antenna based on the TC-SSPP, using a probe as the feed and a finite-length BC-CS as the radiator. Due to near-field magnetic coupling, the SSPP wave can be excited on the BC-CS. By varying the geometric parameters, the antenna can radiate in the broadside direction. A prototype was designed, fabricated and measured. Both the simulated and measured results verify our design.

Spoof Surface Plasmon Polariton Based Frequency Scanning Antennas

Frequency scanning antennas realized by loading the radiating elements on both sides of the microstrip, asymmetrically corrugated spoof surface plasmon polariton (SSPP), and symmetrically corrugated SSPP transmission lines are discussed in this paper. Both traveling and standing wave antennas are considered and performance in terms of S-parameters, radiation pattern, scan range, and gain is reported. Additionally, the crosstalk between two transmission lines is observed in all cases. Based on the analysis, it was proved that the crosstalk was minimum in the case of symmetrically corrugated SSPP transmission lines. The proven advantages of the SSPP lines find better signal integrity, high gain, and wide-angle scan frequency scanning antennas.

Wideband Vertically Polarized Planar Endfire Antenna Based on Spoof Surface Plasmon Polaritons

A novel wideband vertically polarized planar end-fire antenna based on the first and the second high-order modes of Spoof Surface Plasmon Polaritons (SSPPs) is proposed in this letter. A double-sided SSPP transmission line (TL) is used to produce vertically polarized radiation. By replacing the uniform stub in the conventional SSPP cells with a step-impedance-resonator (SIR) shaped stub, the bandgap between the first and the second high-order modes is eliminated. The double-sided SIR-shaped SSPP cells are tilted to make the maximum radiation point in the end-fire direction. Dielectric covers perforated with air vias are added to the top and bottom surfaces of the SSPP TL to generate end-fire radiation and enhance antenna gain. A grounded coplanar waveguide to double-sided parallel-strip line transition is designed to feed the radiator. A prototype of the proposed antenna has been fabricated and measured. The proposed antenna achieves a fractional bandwidth of 91.6% from 12.9 GHz to 34.6 GHz and a peak gain of 17.3 dBi.

Continuously Beam-Scanning Leaky-Wave Antenna Based on Impedance-Matched Spoof Surface Plasmon Polaritons

A leaky-wave antenna (LWA) based on impedance-matched spoof surface plasmon polaritons (SSPPs) is proposed in this paper. Periodic perturbations in the form of impedance stepping SSPPs is introduced to break the stable transmission condition of SSPPs, resulting in the energy radiation and the angle of the main radiation beam changes from backward to forward quadrant as the frequency changes. Open-stop band (OSB) existing in normal periodic LWA is suppressed by properly designing the matched structure between the impedance stepping SSPPs. A prototype of the proposed LWA is simulated, fabricated, and measured. The measured results are in reasonable agreement with the simulated results. Simulated and measured results indicate that the proposed LWA operates with a continuous beam scanning range in each upper and lower half-space, as well as an average gain level of 9.86 dBi. The proposed antenna can be easily integrated and is promising in planar wireless communication systems.

Ultra-Compact Low-Pass Spoof Surface Plasmon Polariton Filter Based on Interdigital Structure.

An ultra-compact low-pass spoof surface plasmon polariton (SSPP) filter based on an interdigital structure (IS) is designed. Simulated dispersion curves show that adding the interdigital structure in an SSPP unit effectively reduces its asymptotic frequency compared with traditional and T-shaped SSPP geometries, and the unit dimensions can be conversely reduced. Based on that, three IS-based SSPP units are, respectively, designed with different maximum intrinsic frequencies and similar asymptotic frequencies to constitute the matching and waveguide sections of the proposed filter, and the unit number in the waveguide section is adjusted to improve the out-of-band suppression. Simulation results illustrate the efficient transmission in the 0~5.66 GHz passband, excellent out-of-band suppression (over 24 dB) in the 5.95~12 GHz stopband and ultra-shape roll-off at 5.74 GHz of the proposed filter. Measurement results on a fabricated prototype validate the design, with a measured cut-off frequency of 5.53 GHz and an ultra-compact geometry of 0.5 × 0.16 λ02.

Theoretical limit and framework of dynamic modulation in spoof surface plasmon polariton interconnects.

Spoof-surface-plasmon-polariton (SSPP) interconnects are potential candidates for next-generation interconnects to satisfy the growing demand for high-speed, large-volume data transfer in chip-to-chip and inter-chip communication networks. As in any interconnect, the viability and efficiency of the modulation technique employed will play a crucial role in the effective utilization of SSPP interconnects. In light of the lack of a comprehensive platform for the performance analysis of SSPP signal modulation, this work presents a theoretical framework that contributes to the following: 1) predictions of the maximum attainable modulation speed, limited by geometric dispersion in SSPP waveguide, 2) quantification of the fundamental trade-off relation between modulation speed and energy-efficiency for an arbitrary design of SSPP structure, 3) extension of the analysis over a broad category of SSPP modulation technique. In conjunction, a novel SSPP signal modulation technique is introduced, involving controlled alteration of the resonant condition of the SSPP interconnect using a variable resistor. Analyzing a sample SSPP waveguide with a 7 GHz cut-off frequency, the study identifies a potential ∼28% change in its transmission-band by varying the implanted resistor from 5kΩ to 5Ω, a range of values practically attainable with gate-controlled, state-of-the-art submicron scale field-effect transistors. The assertions of the theoretical model have been independently validated by finite-element method based numerical simulations, which show that the underlying concept can be utilized to realize the digital modulation scheme of the amplitude shift keying. For a millimeter-scale SSPP channel having 2.75 GHz transmission bandwidth, up to 300 Mbps modulation speed with nominal power loss is achieved in a standard, thermal-noise limited communication system. By scaling the interconnect to micrometer dimensions, the speed can be augmented up to 10 Gbps for data transfer over 100 mm distance with ≥80% energy efficiency. Essentially, the presented theory is the first of its kind that provides the foundational design guideline for designing and optimizing diverse range of SSPP modulators.

Ultra-Thin Flexible Uniplanar Antenna Based on SSPP for B5G Radio Stripe Network

In this letter, a flexible and ultra-thin uniplanar endfire antenna employing spoof surface plasmon polariton (SSPP) is proposed. The single-metal layered groundless structure is an inherent advantage of the SSPP. At the SSPP transmission line's end, a metallic strip is added asymmetrically for wideband radiation, resulting in an observed tilting of the main lobe in the azimuthal plane. Three C-shaped directors are used to enhance the directivity. The proposed antenna is fabricated and measured over flat and curved surfaces of brick wall and wood with two different radii. The proposed antenna has a low profile of 0.0017λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> and a small volume of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$0.0058{\lambda }_0^3$</tex-math></inline-formula> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the free-space wavelength at the center frequency of the operating bandwidth. The antenna has an impedance bandwidth of 33.7% with a peak gain of 8.5 dBi. Measurements indicate no significant degradation in the proposed antenna's performance in different scenarios. Due to features like flexibility, ultrathin profile, very low volume, tilted beam with high gain, and wideband operation, the proposed antenna is highly suitable for beyond fifth-generation (B5G) radio stripe applications.

Wideband High-Gain Filtering Vivaldi Antenna Design Based on MS and Herringbone SSPP Structure

This paper presents a wideband high gain filtering Vivaldi antenna design that utilizes metasurface (MS) and spoof surface plasmon polariton (SSPP) metamaterial for gain enhancement and filtering performance, respectively. The design includes a set of slits etched on the external edges of the antenna to reduce diffraction current, the SSPP structure with inherent dispersion characteristic etched in the slot-line to inhibit RFI, and a novel ‘Φ’-shaped MS unit cell for wideband gain enhancement. These functional metamaterials jointly contribute to optimized performances, and the proposed prototype shows immunity to RFI above 27 GHz and high gain performance over the wide frequency range from 15 GHz to 27 GHz. For demonstration, the protype is fabricated and measured. Measured results agree well with simulated ones.

Triple-Beam Leaky-Wave Antenna Based on Spoof Surface Plasmon Polaritons With Hybrid Periodic Modulation

In this letter, a triple-beam leaky wave antenna (LWA) based on modulated spoof surface plasmon polaritons (SSPPs) transmission line (TL) with hybrid period is presented. The one side of SSPPs TL is modulated sinusoidally with period of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> 1, and another side is modulated with composite period of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> 2 and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> 3. The analysis of dispersion curves indicates that the modulated periods at each side of the TL is independent and hence the radiation beams can be controlled independently by adjusting the modulation periods. In this design, the LWA radiates three beams simultaneously. From 7.8 to 9.1GHz, the gain difference of beams is lower than 3-dB. which have cover range from 49º to 149º. To validate the performance of the designed LWA, a prototype is fabricated and measured. The measured results are in good agreement with the simulated ones.

Localized Spoof Surface Plasmon Skyrmions Excited by Guided Waves

AbstractRecently, skyrmions are constructed in the system of localized spoof surface plasmons (LSSPs), showing topological robustness and near‐equidistant multi‐resonant response. Guided wave excitation of the LSSP skyrmions plays an elementary role in large‐scale planar integration and construction of complex networks. However, it is not investigated. In this study, the LSSP skyrmions are excited by guided waves supported by two kinds of widely used transmission lines, microstrip line and coplanar waveguide. Space‐coiling meta‐structures with different shapes that support LSSP skyrmions are etched on the ground planes as defected ground structures (DGSs). All structures including resonator, transmission line, input and output ports are in one plane. The structures are fabricated on printed circuit boards (PCBs) and the near‐equidistant multi‐resonant spectra of the LSSP skyrmions are measured. Moreover, to reduce the material loss, the structure is made on MgB2 superconducting film, and the quality factor (Q‐factor) is increased by seven times compared to the corresponding mode on PCB. This study paves the way for the massive planar integration of the LSSP skyrmions and the construction of complex networks with the LSSP skyrmions, and provides an idea for developing metasurfaces with low material loss in the microwave and terahertz bands.

Low-loss high-confinement terahertz guided-wave propagation along a subwavelength gap between double-dielectric-ridge-integrated gratings

Dielectric grating-based spoof surface plasmonic (SSP) structures are among the recent low-loss and subwavelength field-concentrating solutions for realizing high-density terahertz (THz) and sub-THz integrated circuits. In this paper, we report on a novel waveguide structure capable of supporting highly confined SSP mode while exhibiting much lower propagation loss compared to other similar SSP structures. The proposed structure is composed of two perfectly aligned identical silica ridges placed on the inner faces of the metallic plates of a parallel plate waveguide with a proper plate distancing in order to leave an empty gap region between the ridges. Each of the ridges embodies a periodic arrangement of high-resistivity silicon blocks with the same height as their own, although with smaller widths compared to their width. By performing modal analysis on the 2D and 3D structures of the proposed waveguide, its propagation properties are studied. It is observed that if the gap region is properly designed, a waveguiding structure with a subwavelength cross-sectional size around λ0/3×λ0/3, where λ0 is the free-space wavelength at the maximum frequency of operation, capable of providing a high degree of field confinement over a wide frequency bandwidth of nearly two octaves and with a very low propagation loss factor compared to similar SSP structures is achieved. Moreover, the performance of the proposed waveguide for implementing a 90° waveguide bend of the radius λ0/3, and for obtaining a spectroscopy-based refractive-index sensor is addressed. The results of our assessments suggest that the proposed waveguide can bring the state-of-the-art SSP designs yet another step closer to realizing ideal waveguiding structures for various applications in THz and sub-THz regimes.

Spoof surface plasmon polaritons of complementary periodic units with negative group velocity effect

AbstractPeriodically patterned conductor surfaces can transmit electromagnetic modes similar to surface plasmon polaritons, which are called spoof surface plasmon polaritons (SSPPs). In this paper, noncoplanar dentate complementary structure units are proposed. In this case, the fundamental SSPP is split into two modes, of which the mode in the high‐frequency side exhibits negative group velocity (NGV) near the cutoff frequency. The dispersion characteristics of NGV modes can be controlled by manipulating the symmetry of the complementary structure. It is confirmed that the actual transmission wave in the SSPP waveguide is the superposition result of the two split‐mode wave components.