Spoof Surface Plasmon Research Articles

Resolved terahertz spectroscopy of tiny molecules employing tunable spoof plasmons in an otto prism configuration

Sensitive detection of terahertz fingerprint absorption spectrum for tiny molecules is essential for bioanalysis. However, it is extremely challenging for traditional terahertz spectroscopy measurement because of the weak spectral response caused by the large mismatch between terahertz wavelengths and biomolecular dimensions. Here, we proposed a wideband-tunable metal plasmonic terahertz biosensor to detect tiny biomolecules, employing attenuated total reflection in an Otto prism configuration and tightly confined spoof surface plasmons on the grooved metal surface. Benefitting from the plasmonic electric field enhancement, such a biosensor is able to identify the molecular terahertz fingerprints. As a proof of concept, a hypothetical molecule modeled by the Lorentz model with two vibrational modes is used as the sensing analytes. Simulation results show that the absorption of two vibrational modes of analytes can be selectively enhanced up to ten times by plasmonic resonance, and their fingerprints can be resolved by sweeping incident angle in a wide waveband. Our work provides an effective approach for the highly sensitive identification of molecular fingerprints in fields of biochemical sensing for tiny analytes.

Research on Spoof Surface Plasmon Polaritons (SPPs) at Microwave Frequencies: a Bibliometric Review

Research on Spoof Surface Plasmon Polaritons (SPPs) at Microwave Frequencies: a Bibliometric Review

Design and Analysis of a Compact Frequency Beam-Scanning Antenna Based on Composite FHMSIW/SSPP Waveguide

In this letter, a novel compact frequency beam-scanning antenna (FBSA) using composite waveguide based on folded half-mode substrate integrated waveguide (FHMSIW) and spoof surface plasmon polaritons (SSPP) is proposed. The novel composite FHMSIW/SSPP waveguide with compact size and high field-confinement is initiated by embedding dual SSPP structures into the FHMSIW. Its transmission characteristic has flexible features from both the FHMSIW and SSPP. To excite the radiation mode from the composite slow-wave waveguide, a simple single-sided sinusoidal modulation method is designed and used. In this way, the common open stop-band problem around broadside is effectively eliminated, and the beam-scanning range of the antenna can be flexibly designed without changing the modulation structure. The presented scanning antenna owns a compact size and a simple feeding network. The experimental results indicate that the proposed FBSA can achieve continuous beam scanning from backward to forward in a wide scanning range of 60° within a bandwidth of 7.7–10.1 GHz. The stable unidirectional radiation patterns and appropriate gains are also realized in the entire operating frequency band.

Ultrawide-Angle and High-Scanning-Rate Leaky Wave Antenna Based on Spoof Surface Plasmon Polaritons

An ultrawide-angle frequency beam scanning leaky-wave antenna (LWA) with a high scanning rate based on spoof surface plasmon polaritons (SSPPs) waveguide is proposed in this communication. A row of elliptical patches is placed periodically near the SSPPs waveguide, which can shift the fundamental mode of SSPPs waveguide to the fast-wave region and radiate electromagnetic (EM) waves. The simulated results show that the proposed LWA achieves an ultrawide scanning angle range of 172° over a narrow operation bandwidth of 9.8–12.28 GHz, which implies a high scanning rate. The simulated average gain of the proposed LWA is 10.13 dBi and its average total efficiency is 75.35%. The proposed LWA is fabricated and measured. The measured scanning angle range is 167° in the frequency band of 9.9–12.25 GHz, and the measured average gain is 9.73 dBi. Good agreements between the simulated and measured results are obtained, validating the proposed design.

An Endfire Controllable-Filtering Antenna Based on Spoof Surface Plasmon Polaritons

In this letter, a planar endfire filtering antenna with a controllable passband and a high gain based on spoof surface plasmon polaritons (SSPPs) is proposed. Its radiating part consists of three pairs of sector-shaped patches and I-shaped directors which are linked with the end of SSPPs feeding line. As demonstrated, the filtering performance of the proposed antenna can be easily adjusted by changing the size of all the branches with metal vias, round-shaped, and π-shaped resonators. A prototype operating in 8–9 GHz is fabricated and tested to verify the design, which reveals an average gain of 8.6 dBi, an out-of-band suppression level of more than 12 dB, and a profile of 0.014–λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . Good agreement is achieved between the simulated and measured results. Simple and controllable design methods and good performance indicate its significance in modern communication systems.

Single-beam leaky-wave antenna with wide scanning angle and high scanning rate based on spoof surface plasmon polariton

We propose a single-beam leaky-wave antenna (LWA) with a wide-scanning angle and a high-scanning rate based on spoof surface plasmon polariton (SSPP) in this paper. The SSPP transmission line (TL) is etched with periodically arranged circular patches, which converts the slow-wave mode into the fast-wave region for radiation. The proposed LWA is designed, fabricated, and tested. The simulated results imply that the proposed LWA not only achieves a high radiation efficiency of about 81.4%, and a high scanning rate of 12.12, but also has a large scanning angle of 176° over a narrow operation bandwidth of 8.3–9.6 GHz (for |S 11| < –10 dB). In addition, the simulated average gain of the LWA can reach as high as 10.9 dBi. The measured scanning angle range is 175° in the operation band of 8.2–9.6 GHz, and the measured average gain is 10.6 dBi. The experimental results are consistent with the simulation, validating its performance. An antenna with high radiation efficiency, wide scanning angle range, and high scanning rate has great potential for application in radar and wireless communication systems.

A Broad Dual-Band Bandpass Filter Design Based on Double-Layered Spoof Surface Plasmon Polaritons

In this work, a broad dual-band bandpass filter is designed by applying double-layered spoof surface plasmon polaritons (DLSSPPs) as the main transmission line (MTL) and loading combined-stub dual-mode resonators (CSDMRs) onto the MTL with certain spaces. Each CSDMR consists of an open stub and a short stub that are connected in parallel. Efficient mode conversion between the quasi-transverse electromagnetic waves in the microstrip line and the spoof surface plasmon polaritons (SSPPs) on the double-layered surface plasmon waveguide is realized using gradient double-layered metal gratings and via the sector structure impedance matching technique. A parametric study of the CSDMR demonstrates that center frequencies and bandwidths can be controlled by varying the stub lengths and widths of the CSDMRs. A second-order dual-band filter is designed and fabricated, and simulated and experimental S-parameters agree well. A lower loss of the passband is achieved compared with the filters that apply single-layered SSPPs. The space between two CSDMRs is shortened because of the slow-wave effect of the DLSSPPs. The lowpass performance of the DLSSPPs exhibits good rejection from the cutoff frequency above.

Embroidered Spoof Surface Plasmon Polariton Transmission Line for Wireless Body Sensor Network

A wearable Spoof Surface Plasmon Polariton Transmission Line (SSPP TL) operating at 2.45 GHz designed for embroidery production and on-body communication is proposed. The SSPP TL supports both even and odd modes launched by near field coupling with a dipole antenna perpendicular and parallel to the TL, respectively. First, the experimental dispersion curves and transmission for the even and odd modes are favourably compared to simulations. Then, experimental transmission for each mode is compared with the Line-Of-Sight (LOS) transmission between two parallel-oriented antennas. At 2.45 GHz, a transmission enhancement of 16 dB is measured for the even mode and it reaches up to 37 dB for the odd mode. A transmission enhancement of 30 dB is also measured at 2.45 GHz between two antennas with orthogonal orientations. Performances of the SSPP TL for Wireless Body Sensor Network are evaluated. Transmission is sustained for the SSPP TL under curvature and right angle bending. Transmission measured when both an arm and a copper plate obstacle between antennas were surrounded by the curved SSPP TL is compared with the obstructed LOS transmission. Measurements show a transmission enhancement up to 22 and 25 dB for the even and odd modes, respectively.

Highly Efficient Dual-Beam Frequency Scanning Based on SSPPs With Parasitic Patch Array

A leaky-wave antenna (LWA) realizes radiation of travelling wave along guiding structures. Periodic modulation is an effective approach to turn non-radiating modes into radiating modes. A high-efficient LWA based on spoof surface plasmon polaritons (SSPPs) loaded with parasitic patch array is proposed. Sinusoidal modulation is used for the radiation of SSPPs, while parasitic array mitigates the open stopband (OSB) effect. A prototype is fabricated and measured. The measured and simulated results agree well with each other. Such design shows wide angle coverage of 83° from backward to forward and stable gain distribution of about 12 dB within the whole operating band.

Unequal Bandpass Filtering Power Divider Based on Hybrid HMSIW-SSPP Modes

This letter presents a novel unequal bandpass filtering power divider based on hybrid-mode of half mode substrate integrated waveguide (HMSIW) and spoof surface plasmon polaritons (SSPPs). Bandpass response is achieved by combining the transmission properties of HMSIW and SSPPs simultaneously. The operating bandwidth can be designed in a wide range by simply optimizing the dimensions of HMSIW and SSPPs. In addition, defected ground structures (DGSs) are etched on the bottom of the substrate to improve out-of-band suppression. The power division ratio of the proposed unequal power divider is finally optimized to 1:3. The measured results agree with the simulated one. Such design provides a stable power division within wide frequency range from 6.5 to 9.5 GHz.

Bifunctional spoof surface plasmon polariton meta-coupler using anisotropic transmissive metasurface

Abstract Tailoring the wavefronts of spoof surface plasmon polaritons (SSPPs) at will, especially with multifunctional integration, is of great importance in near-field photonics. However, conventional SSPP devices suffer from the issues of bulk configurations, limited functionalities, and single operating modes, which are unfavorable for electromagnetic (EM) integration. Here, a novel scheme is proposed to design bifunctional SSPP meta-devices based on the polarization dependent property via satisfying the comprehensive phase distributions and multi-mode momentum matching in a transmission geometry. As proof of the concept, we experimentally demonstrate a bifunctional SSPP meta-device in the microwave regime that can convert incident x- and y-polarized waves to transverse magnetic (TM)-mode SSPP Bessel beams and transverse electric (TE)-mode SSPP focusing beams, respectively. Our findings open a door to achieve near-field manipulation of SSPPs with multi-function and multi-mode integration, which can stimulate the applications of SSPP functional devices, such as near-field sensing, imaging, and on-chip photonics.

Design of a Differential Spoof Surface Plasmon Sensor for Dielectric Sensing and Defect Detection

A new design of a highly confined Spoof Surface Plasmon (SSP) line splitter-based differential phase sensor is presented for the THz frequency region. The position, orientation and shape of the stem cells are properly optimized to realize highly confined, compact SSP design. The designed differential splitter facilitates the relative phase difference between the transmission coefficient phase corresponding to the reference arm and the test arm. The dispersion characteristic i.e, asymptotic frequency response of stem shaped unit cell founds to be quite improved over its conventional counterpart. The incorporated splitter shaped topology provides a symmetric differential sensing environment in both THz and MW region. The proposed sensor facilitates quite high sensitivity due to its improved electric field confinement than that of the microstrip counterpart. The obtained phase difference changes with a relative change in the effective dielectric constant of the test sample at a specified frequency. The design is then scaled accordingly, and the prototype is fabricated to validate its defect detection performance in the microwave (MW) frequency region. In the present scenario, FR-4 samples (with thickness 0.8 mm, 1.6 mm) having two different defect profiles are considered for experimental validation. It is found that the developed sensor can produce substantial phase difference even for the small presence of the defect. In the present case, the measured average phase differences corresponding to the FR-4 sample having 1 mm void distributed uniformly with an interspacing of 1.25 mm, are 74.02° and 92.35° and 2.5 mm spacing between the same void gives phase difference of 31.18° and 40.26° for 0.8 mm and 1.6 mm sample thickness, respectively over the frequency range of 8–12 GHz.

Spoof surface plasmon polariton developed in a rectangular waveguide with a controllable band-pass feature for millimeter-wave applications

Spoof surface plasmon polaritons (SSPPs) are developed in a rectangular waveguide (RWG) to realize a controllable band-pass propagation feature for millimeter-wave applications. The proposed SSPP structure consisting of a single row of corrugated metallic blocks, is embedded inside the closed structure of an RWG. The dispersion property of the RWG-based SSPP (RWG-SSPP) has tunable lower and upper cut-off frequencies, and a band-pass filter with flexible bandwidth has been designed using an RWG-SSPP structure. The proposed band-pass filter is based on an RWG-SSPP with an all-metal structure, which is of great potential for millimeter-wave applications due to small losses.

Characteristics of high-contrast gratings based spoof surface plasmon polaritons and the application in microwave all-dielectric metamaterial absorbers

High-contrast gratings (HCGs) based spoof surface plasmon polaritons (SSPPs), as a new kind of SSPPs, have been proposed recently. Here, we study their particular mechanism and characteristics by comparing them with traditional metal-type SSPPs. The different fundamental dielectric resonator modes decided by the height–length ratio R of the dielectric element are found to be the key factor of the mechanism, leading to new characteristics and providing more working modes. In low R mode, HCG-based SSPPs can work under deep-subwavelength thickness and can be easily excited by free space wave and, thus, are considered to be applied to all-dielectric metamaterial absorbers (ADMMAs). Simulations and analysis confirm the microwave absorption effect of HCG-based SSPPs as a new mechanism of ADMMAs. Based on this, a carbon black based ADMMA is designed and the simulation and experimental results verify the important role of HCG-based SSPPs in broadband absorption. It is expected that this work can give rise to further and wider studies on the characteristics and applications of HCG-based SSPPs.

Surface Plasmon Polariton Leaky-Wave Antennas With Wideband Arbitrary Multibeam Radiation

A simple method to synthesize multibeam radiation patterns with modulated linear spoof surface plasmon polariton (SSPP) leaky-wave antennas (LWAs) is proposed. We analytically proved that, for this specific type of LWA, the superposition of modulated antenna shapes can lead to a direct superposition in its radiation pattern. To validate this method, several simulations are performed, and two antennas are fabricated and tested. These results show that various types of radiation pattern, e.g., single-beam, dual-beam, or multibeam at various directions, can be achieved with little need for design efforts. The proposed antennas have features of the highly diverse radiation pattern, high gain (up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 14.6$ </tex-math></inline-formula> dBi, measured), wideband, large frequency scanning capability ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 120$ </tex-math></inline-formula> ° with ignorable open stopband effect at broadside), and have very simple structures that are easy to design and fabricate.

Detection and Location of Defects in Non-Metallic Composites Pipeline Based on Multi-Resonant Spoof Surface Plasmon Polaritons

Detection and Location of Defects in Non-Metallic Composites Pipeline Based on Multi-Resonant Spoof Surface Plasmon Polaritons

Nonmagnetic Spoof Plasmonic Isolator Based on Parametric Amplification

AbstractDriven by the miniaturization of integrated electronics, research on spoof plasmonic circuits has recently aroused widespread interest. On the other hand, nonreciprocal devices, such as isolators and circulators, are key components of integrated electronic systems. However, bulky magnets required to realize isolation and circulation prevent the application of traditional nonreciprocal technologies to integrated systems. Here, parametric amplification is explored to achieve magnetic‐free plasmonic isolation, and an ultrathin reconfigurable spoof plasmonic isolator is realized experimentally. In this isolation system, the forward signal amplified by a spoof plasmonic parametric amplifier is coupled to a second linear plasmonic waveguide via a spoof localized surface plasmon resonator, whereas the transmission from the inverse direction is prohibited, giving rise to a measured isolation ratio of up to 20 dB. By tuning the nonlinear phase‐matching condition through external bias voltage, multifrequency isolation of spoof surface plasmon polariton (SSPP) signals is also realized experimentally. This work demonstrates the possibility of producing miniaturized and low‐cost nonreciprocal SSPP devices, holding great promise for applications in nonmagnetic information processing and radar detection.

Spoof Localized Surface Plasmon Enhanced Isolation and Circulation

AbstractA miniaturized spoof plasmonic isolator comprising a deep‐subwavelength spoof localized surface plasmon (SLSP) resonator coupled with an ultrathin spoof surface plasmon polariton waveguide is proposed and experimentally demonstrated. The SLSP resonator coated with a magneto‐optical material can enhance the isolation property, allowing for multifrequency isolation, which can be dynamically controlled by changing the biased magnetic field intensity. This design scheme is extended to realize a four‐port circulator that allows one‐way transmission in opposite directions in two separate frequency bands. The proposed isolation and circulation devices have potential for nonreciprocal applications in microwave communication systems.

Dual‐Beam Leaky‐Wave Radiations with Independent Controls of Amplitude, Angle, and Polarization Based on SSPP Waveguide

New dual‐beam leaky‐wave radiations based on spoof surface plasmon polariton (SSPP) waveguide, in which the amplitude, radiation, angle and polarization of each beam can be designed independently, is proposed. The proposed SSPP waveguide is made of a corrugated metallic strip with bilateral 45°‐tilted grooves, whose surface impedance is flexibly designed by changing the depth of grooves. To realize dual‐beam leaky‐wave radiations, the surface impedance of SSPP waveguide is modulated periodically based on the superposition theory of aperture fields. By simply adjusting the modulation factors, modulation periods, and initial phase differences of the modulated surface impedance, the amplitude, radiation angle, and polarization of each beam can be further controlled independently as well. The results have been validated by both numerical simulations and experimental measurements, which show good agreement with the theoretical predictions.

Wideband compact phase shifter based on hybrid half-mode substrate integrated waveguide and spoof surface plasmon polariton

This paper proposes a wideband compact equal-length phase shifter based on the hybrid half-mode substrate integrated waveguide (HMSIW) and spoof surface plasmon polariton (SSPP) concept for the first time. The HMSIW transmission lines (TLs) with different widths result in different propagation constants. The difference of propagation constants between two HMSIW TLs with two different widths decreases as the frequency increases. Therefore, a wideband phase shifter cannot be designed by using this technique. In this paper, a series of half-butterfly grooves are etched on the top conductor layer of the HMSIW TL to compensate the phase shift. The combination of the SSPP and HMSIW structures provides a higher degree of freedom to keep the propagation constants difference constantly. Accordingly, a wideband response can be achieved by properly tuning the structure. Here, the dispersion characteristic of the butterfly-shaped HMSIW-SSPP can be adjusted by changing the width of the HMSIW and the radius and angle of the half-butterfly grooves. Moreover, the HMSIW-SSPP structure with half-butterfly grooves reduces both longitudinal and transverse dimensions of the proposed circuit. It has more slow-wave effects than the traditional counterpart with rectangular grooves. To validate the concept, a phase shifter is designed and fabricated on a single-layer substrate at the center frequency of 5.8 GHz covering WLAN. The simulated and measured results are in good agreement. The measured results show that the phase shifter has a fractional bandwidth of 31.7% with a phase error of , an insertion of dB, and a return loss of higher than 13.8 dB. Also, the size of the proposed phase shifter is .