Spoof Surface Plasmon Polaritons Waveguide Research Articles

A microwave permittivity sensor on a Mach–Zehnder Interferometer of: Spoof surface plasmon polariton waveguides

A microwave Mach–Zehnder Interferometer (MZI) sensor for the permittivity characterization of liquids is presented in this paper. Two spoof surface plasmon polariton (SSPP) waveguide transmission lines (TLs) composed of compact spiral units is utilized in a differential architecture. Loading a dielectric material on the sensing arm induces a phase difference between the two arms, leading to periodic interference dips on the transmission curve. The spectral positions and magnitudes of these dips change with different dielectric materials. Due to the nonlinear dispersion characteristics of the SSPP TL, the proposed SSPP-based MZI sensor achieves improved sensitivity compared with microstrip-based MZI sensor. To validate the sensor’s performance, six different oil samples and a set of adulterated oils were measured, incorporating a polydimethylsiloxane (PDMS) channel on the sensing arm. The variations in the spectral position and magnitude of the interference dip centered at 3.2 GHz are employed to determine the dielectric constants and loss tangents of the tested oils. The sensitivity in measuring the dielectric constant is 3.61 %. The maximum errors for measuring the dielectric constant and the loss tangent are 4.3 % and 6.7 %, respectively. Compared to other sensors for liquid oil detection, the proposed sensor provides a relatively high sensitivity while maintaining a low liquid volume, making it a promising candidate for permittivity measurements of liquid analytes and solid materials with similar dielectric constants.

Spoof surface plasmon Polaritons dual beam scanning antenna for 5G application

Dual beam scanning (DBS) antenna exited by two different spoof surface plasmon polaritons (SSPPs) transmission lines is proposed in this paper. The antenna is constructed by placing three rows of circular patches on both sides of two different planar SSPPs waveguide. These patches convert the SSPP guided waves into radiating waves. This simple single-layer antenna is characterized by dual without need to use switches or other complex configurations. It is designed to support application of several 5G sub-6 GHz bands (3.5 (n78) GHz, 3.7 (n77) GHz, and 4.5 (n79) GHz). The proposed antenna realizes the dual beam scanning by controlling the dispersion properties and field confinement along two different SSPPs transmission lines, based on different propagation constant. Numerical simulations are carried out by CST Microwave Studio and Ansys HFSS. These numerical simulations are verified by experimental results over the operating frequency band from 1 GHz to 6 GHz.

Reconfigurable terahertz stretchable spoof surface plasmon polariton waveguide for filter applications

In this paper, a reconfigurable terahertz spoof surface plasmon polariton (SPP) waveguide is proposed on a stretchable polydimethylsiloxane (PDMS) substrate. The SPP unit incorporates a folded stub and a conventional V-shaped SPP groove, enhancing the equivalent capacitance and consequently reducing the cutoff frequency. The cutoff frequency of the proposed SPP unit can be tuned from 285 to 390 GHz with stretchable factors of 1 ∼ 1.2, thereby achieving a reconfigurable operating frequency. The horizontal dimension of the proposed SPP waveguide can be tuned from 6.36 mm to 7.12 mm. Moreover, the SPP waveguide can generate transmission continuous phase shifts of −30°, −60°, −90°, and −120° with stretchable factors of 1.05, 1.1, 1.15, and 1.2, respectively, in the 150–190 GHz band. Applying the characteristic mode theory, a split ring resonator (SRR) functions as the equivalent magnetic dipole, which remains unaffected by stretchable deformation. When loaded with four SRR cells, the proposed SPP waveguide generates a tunable passband with a fixed notched frequency at 193 GHz. Another stretchable SPP resonator serves as the equivalent electric dipole, operating from 284 GHz to 256 GHz in 1∼1.2 stretchable states. By loading three SPP resonators, the SPP waveguide can achieve a passband for the initial state, and a tunable stopband is introduced under 1.1 and 1.2 stretchable states. The proposed stretchable method provides a promising solution for planar terahertz components and systems with reconfigurable functions.

Negative group delay SSPP mode based on coupled periodic cells

To realize negative group delay (NGD) of spoof surface plasmon polaritons (SSPPs), two coupling strips are introduced within the U-shaped cell for SSPP waveguide. Furthermore, two such cells are coupled to form a double-structured NGD unit. At lower frequencies, the constructed unit can implement both TE and TM modes with the NGD feature, and the maximum NGD values of – 0.42 ns for TE mode is achieved at 1.83 GHz. Since the TM mode is alongside the stopband, a wide NGD band of 2.01–3.25 GHz is yielded, with a small NGD value. However, as this unit is applied to SSPP waveguides to compensate for positive delays, the measured NGD maximum is 2.81 ns at 1.93 GHz and 9.65 ns at 2.42 GHz, due to the influence of waveguide structure on the NGD unit. The proposed unit structure exhibits promising applications in delay equalization and dispersion compensation for microwave system.

Power-modulated reconfigurable nonlinear plasmonic devices without DC power supply and feed circuit

High-power electromagnetic (EM) waves can directly modulate the parameters of nonlinear varactor diodes through the rectification and Kerr effects without relying on external sources. Based on this principle, we propose a power-modulated reconfigurable nonlinear device based on spoof surface plasmon polariton (SSPP) waveguide loaded by varactor diodes, without applying DC power supply or feed circuit. Increasing the input power level reduces the effective capacitance of the varactor diode, leading to a blueshift in the cutoff frequency of the SSPP waveguide. This feature can be employed to realize the switching on/off of the input signal depending on the signal power. On the other hand, the transmission state of a low-power signal can be controlled by inputting another independent high-power EM wave simultaneously. Increasing the power of the control wave will enable the low-power signal within a wider bandwidth switched from off to on states. Experimental results are presented to show the excellent performance of the power-modulated reconfigurable SSPP device. This method can reduce the system complexity and provide inspiration for reconfigurable all-passive multifunctional devices and systems.

Fabrication and characterization of delay lines with spoof surface plasmon polariton waveguide coupled with C-shaped metamaterials for microwave integrated circuits

Abstract Here, we proposed two delay lines consisting of spoof Surface Plasmon Polariton (sSPP) waveguides and C-shaped metamaterials (C-MMs). The delay lines, namely OFF and ON devices, were designed and fabricated. On the OFF device, an sSPP waveguide is capacitively coupled to the C-MMs via an air gap on a high-resistivity silicon substrate. On the ON device, a connection is established between the C-MMs and the sSPP waveguide by metal connectors. The difference in the electrical properties in the coupling between the C-MMs and the sSPP waveguide creates a large phase contrast between the ON and OFF delay lines. The structural design was performed using a numerical calculation based on a commercial finite element solver. We successfully fabricated and characterized delay lines with phase differences equal to tens of degrees between the ON and OFF devices in the target frequency range of 2-6 GHz, while maintaining the original transmittance properties. The promising applications of the delay lines are a phase shifter or modulator when integrating with suitable switches.

Compact Muti-Frequency Band-Pass Filters Based on High-Order Mode of Folded Line Spoof Surface Plasmon Polaritons Waveguide

Compact Muti-Frequency Band-Pass Filters Based on High-Order Mode of Folded Line Spoof Surface Plasmon Polaritons Waveguide

Terahertz plasmonic functional devices enabled by multimode interference

Terahertz integrated devices have attracted great attention due to their potential applications in communication systems. Although some functional devices based on terahertz spoof surface plasmon polariton (SPP) waveguides have been studied, multimode waveguides and multimode interference mechanism have rarely been explored. This work investigates several key functional plasmonic devices based on multi-SPP mode interference in the terahertz regime. The feasibility of multimode transmission on terahertz plasmonic waveguides and control of the propagation modes by varying the waveguide parameters are first investigated. Then, the interference mechanism between two or more propagation modes and the self-imaging principle are applied to plasmonic waveguides. Finally, a series of terahertz plasmonic functional devices such as a coupler, wavelength diplexers, and cascaded devices are proposed and simulated by exploring different interference lengths, frequencies, and cascades via the self-imaging principle. These devices have good performance in transmission response, crosstalk, bandwidth, and footprint, and are expected to play an important role in the development of terahertz on-chip communication systems.

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.

A wideband and compact Quasi-Yagi antenna based on spoof surface plasmon polaritons

In this paper, a novel wideband end-fire antenna, based on a spoof surface plasmon polaritons (SSPP) transmission line, is proposed. Periodically modulated corrugated metal strips are used as a transmission line for quasi-TEM conversion in the microstrip line to the state of SSPP and the best impedance matching. Due to the strong confinement of the field in the SSPP waveguide and its high transmission performance, it has been used as a transmission line. The antenna consists of SSPP waveguides for the transmission line, a metal plate on the ground as the reflector of the antenna, a metal strip director, and two half-rings to realize the radiation, reaching a wide bandwidth in the range of 4.1 to 8.1 GHz. The simulation results show that this antenna achieves a gain of 6.5 dBi, a bandwidth of 65%, and an efficiency of 97% across a wide operating frequency band, from 4.1 to 8.1 GHz. The proposed end-fire antenna has been fabricated, and the measured results agree well with the simulated results. The end-fire antenna implemented on a dielectric layer also has the advantages of high efficiency, good directivity, high gain, a wide bandwidth, easy fabrication, and a compact size.

A Flexible Amplitude Equalizing Filter Based on Spoof Surface Plasmon Polaritons

In this article, an amplitude equalizing spoof surface plasmon polaritons (AESSPPs) filter deposited on flexible substrate is proposed for the first time. This new hybrid device can realize both the characteristics of amplitude equalization and interference filtering when embedding into a wideband communication system, which brings the compensation process of gain fluctuation back to the microwave front end instead of traditional complex algorithm in digital chip. It is mainly composed of equalizing thin layer and spoof surface plasmon polaritons (SSPPs) waveguide. The equalizing thin layer is realized by ITO (Indium Tin Oxide) and periodically sputtered along the propagation path of SSPPs waveguide to dissipate EM energy at different frequencies. In order to better reveal the nature property of equalization and filtering, an equivalent circuit of AESSPPs unit cell is proposed and analyzed theoretically. The equalizing value and bandwidth can be regulated independently by surface impedance of ITO thin layer and the structural parameter of SSPPs, respectively. Finally, we fabricated and measured three AESSPPs filter prototypes with different critical parameters. All the theory, simulation and measurement results are proved to have achieved the artificial dominated equalizing curve with different equalizing value and bandwidth, which validate that the proposed filter demonstrates the desired flexibility, equalization and filtering capabilities simultaneously.

A Compact Axial-Mode Helical Antenna Based on Spoof Surface Plasmon Polaritons

A compact axial-mode helical antenna (AMHA) is presented based on spoof surface plasmon polaritons (SSPPs). The proposed antenna consists of an SSPP waveguide, a matching metal strip, and a reflective metal ground. To achieve miniaturization and good circular polarization (CP) performance, an SSPP waveguide formed by a periodically slotted metal strip wound around a uniform foam cylinder surface is designed as the radiation part of AMHA. Compared with the traditional AMHA using metallic strip line, the SSPP AMHA can reduce the length of metal strip by 20%, while the physical aperture, height, and volume are reduced by 36%, 20%, and 49%, respectively. Experimental results demonstrate that the antenna has good radiation performance in the operation frequency from 3.3 to 4.7 GHz with a gain of 9.6 dBic at the central frequency. In addition, the size of the proposed SSPP AMHA can be further significant reduced if the foam rod in the center of helix is replaced by a high-permittivity dielectric rod. The proposed SSPP AMHA has the advantages of compact size and good CP radiation performance, which may find potential applications in radar and wireless communication systems.

Programmable surface plasmonic neural networks for microwave detection and processing

A range of alternative approaches to traditional digital hardware have been explored for the implementation of artificial neural networks, including optical neural networks and diffractive deep neural networks. Spoof surface plasmon polariton waveguides, which operate at microwave and terahertz frequencies, can offer low crosstalk, low radiation loss and easy integration, and are of potential use in the development of an alternative technology for artificial neural networks. Here, we report a programmable surface plasmonic neural network that is based on a spoof surface plasmon polariton platform and can detect and process microwaves. The approach uses a parallel coupled spoof surface plasmon polariton cell integrated with varactors. The weight coefficients of the cell can be adjusted by tuning the voltages of the varactors, and the activation function of the neural network can be programmed by detecting the input intensity and feeding back the threshold to an amplifier. We show that a two-layer fully connected surface plasmonic neural network consisting of four input cells and four output cells can perform a vector classification task. The surface plasmonic neural network can also be used to create a wireless communication system to decode and recover images. In addition, we show that partially connected surface plasmonic neural networks can classify handwritten digits with high accuracy. A spoof surface plasmon polariton platform can be used to create a surface plasmonic neural network with programmable weights and activation functions.

Ka-band beam-scanning leaky-wave antenna fed by reconfigurable spoof surface plasmon polaritons.

A leaky-wave antenna (LWA) based on reconfigurable spoof surface plasmon polaritons (SSPP) is proposed for beam scanning in the Ka band, which consists of a reconfigurable SSPP waveguide and a periodic array of metal rectangular split rings. Both numerical simulations and experimental measurements show that the reconfigurable SSPP-fed LWA has good performance in the frequency range from 25 to 30 GHz. Specifically, as the bias voltage changes from 0 to 15 V, we can achieve the maximum sweep range of 24° at a single frequency and 59° at multiple frequency points, respectively. Owing to the wide-angle beam-steering feature, as well as the field confinement and wavelength compression properties derived from the SSPP architecture, the proposed SSPP-fed LWA possesses great potential applications in the compact and miniaturized devices and systems of the Ka band.

Multifunctional Terahertz Spoof Plasmonic Devices

AbstractThe next‐generation wireless communications and intrachip and interchip communications require high‐speed terahertz (THz) interconnects. The interconnects based on spoof surface plasmon polaritons (SSPPs) provide a possible route to achieve this goal. Recently, some THz plasmonic devices are explored, but they suffer from bulk sizes and/or single function. Herein, planar multifunctional THz plasmonic devices based on the interaction between SSPPs and spoof localized surface plasmon (SLSPs) including the functions of pass‐through transmission, multifrequency resonances, and phase shift are proposed and experimentally demonstrated. The pass‐through transmission can be realized on the SSPP waveguide by increasing the loss of the coupled SLSP resonator; the multifrequency resonances are obtained by placing the SU‐8 films with different thicknesses on the SLSP resonator due to its high sensitivity; and the phase shift can be achieved by integrating the SU‐8 film on the SSPP waveguide due to the flexible dispersion behaviors of SSPPs. The proposed multifunctional THz plasmonic devices hold great promise for the THz on‐chip integrations, wireless communications, and sensing systems.

Reconfigurable broad-band rejection filter based on spoof surface plasmon polaritons

In this paper, we describe a new approach for constructing a broad-band tunable rejection filter based on reconfigurable spoof surface plasmon polaritons (SSPP) whose center frequency can be tuned by altering the capacitance of a varactor diode. The filter structure is composed of SSPP waveguide with double split-rings. We have analyzed and discussed the dispersion characteristics of the filter unit structure and S-parameters of the filter. The filter’s rejection band can be tuned in real-time within the frequency range of 6.4 GHz–10.2 GHz, the rejection strength can reach a positive effect, and the transmission loss in the passband can also be less than 2 dB. When a varactor diode was loaded with the same capacitance, the filter produced one rejection band, and when the varactor diode was loaded with two sets of capacitances, the filter produced two rejection bands. From the results, the filter expands microwave communication possibilities. Furthermore, SSPP structures deliver better field confinement and more substantial field augmentation than standard approaches (microstrip filters), which is beneficial for many communication system applications.

Arbitrary Polarization Syntheses Based on Spin‐Momentum Locking in Spoof Surface Plasmon Polaritons

AbstractSpin‐momentum locking is universal and an inherent property of evanescent electromagnetic (EM) waves, which transfers the spinning or handedness of electromagnetic waves onto their propagation direction. This motivates an approach to investigate the polarization‐controlled directional transmission or emission. Here, the spin‐momentum locking is demonstrated in spoof surface plasmon polariton (SSPP) waveguides, and momentum‐controlled radiation is further realized in SSPP‐patch antennas. The study shows that the circular polarization of the SSPP‐patch antennas originates from the spin‐momentum locking in the SSPP waveguides and hence is determined by the propagation direction of the SSPP modes. Two examples are presented to achieve ±45° dual‐polarizations and vertical/horizontal dual‐polarizations by combining the SSPP‐patch antenna with hybrid couplers. Finally, a straightforward method is proposed for synthesizing the polarization emitted by the SSPP‐patch antenna, allowing access to arbitrary polarization states on the Poincare sphere. The SSPP‐patch antenna is polarization responsive, shedding light on chiral sensors, Stokes polarimetry, and polarization measurement. Hence, the spin‐momentum locking and the related momentum‐controlled radiations provide additional freedom to regulate the EM waves by engineering the helicity in the SSPP waveguide.

Wide-Angle Spoof Surface Plasmon Polariton Leaky-Wave Antenna Exploiting Prefractal Structures With Backfire to Nearly Endfire Scanning

This letter presents a single-layer, wide-angle, low-cost frequency beam scanning leaky-wave antenna (LWA) based on spoof surface plasmon polaritons (SSPPs). Here, two rows of Sierpinski prefractal parasitic patches are placed near an ultrathin planar SSPP waveguide, which can achieve continuous backfire to nearly endfire beam scanning with increasing frequency. The overall width of the proposed antenna is only 0.75 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _{\text{0}}$</tex-math></inline-formula> (with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _{\text{0}}$</tex-math></inline-formula> being the wavelength of the lowest operating frequency). This SSPP LWA provides high-performance backfire and broadside radiations due to applying prefractal units. Simulated results show that the proposed SSPP LWA achieves a wide scanning range from −90 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> to +58 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> within the frequency range of 3–8 GHz. The average gain and radiation efficiency of the antenna are 10.9 dBi and 88%, respectively. An antenna prototype is fabricated and measured. The measured results agree reasonably well with the simulated ones.

A Mach–Zehnder Interferometer Refractive Index Sensor on a Spoof Surface Plasmon Polariton Waveguide

In this paper, we experimentally and numerically confirm a planar Mach–Zehnder interferometer (MZI) device for sensing dielectric samples based on a spoof surface plasmon polariton (SSPP) waveguide. The MZI system is constructed using two different ultrathin transmission lines with distinct dispersion units supporting SSPPs. After SSPPs propagate a certain propagation distance, a resonant dip is formed at a specific frequency due to destructive interference, whose displacement enables the SSPP to be modulated by one of the MZI arms loaded with dielectric samples. We investigate how the variations in the permittivity and thickness of dielectric samples affect the sensibility. Through an error analysis between the experimental measurements and numerical calculations, it is demonstrated that the plasmonic sensor based on the MZI has a high precision. The proposed technique is compact and robust and paves a versatile route toward the chip-scale functional devices in microwave circuits.

Active Control of Electromagnetically Induced Transparency Analogy in Spoof Surface Plasmon Polariton Waveguide

Metamaterial analogues of electromagnetically induced transparency (EIT) enable a unique avenue to endow a coupled resonator system with quantum interference behavior, exhibiting remarkable properties in slow-wave and highly sensitive sensing. In particular, tunable and ultracompact-chip-integrated EIT-like effects reveal fantastic application prospects in plasmonic circuits and networks. Here, we demonstrate an electrically tuned on-chip EIT analogue by means of dynamic EIT modules side-coupled to ultrathin corrugated metallic strips supporting spoof surface plasmon polaritons (SSPPs). By embedding PIN diodes into the subradiant mode, on-to-off control of the destructive coupling between the radiative and subradiant modes results in dynamic chip-scale EIT-like behavior under the change of the bias voltage, allowing for an electrically tunable group delay of the surface waves. The physical mechanism of the active modulation is elucidated with the coupled mode theory. In addition, the cascaded capacity performed by installing multiple EIT modules with an interval of equivalent wavelength are also characterized on a planar plasmonic waveguide. The proposed system will pave a versatile route toward dynamic control in chip-scale functional devices.