Symmetric Resonator Research Articles

Design of a triple band notched polarization independent compact FSS at UWB frequency range

The design of a compact triple band notched Frequency Selective surface (FSS) at Ultra-Wide-Band (UWB) frequency range is presented. To make the proposed FSS polarization insensitive, on the upper part of the substrate a single metallic square loop (SL) and four identical rotational symmetric square split ring resonators (SSRR1) are placed, whereas at the bottom part another four identical rotational symmetric SSRR loops (SSRR2) are printed. Here each SSRR is rotated in 90°clockwise direction over a single layered FR4 substrate. Triple band notches are obtained at WiMAX and Satellite communication downlink C-band (3.3-4.2 GHz), WLAN (5.1-5.9 GHz) and Satellite communication X-band (7.2-8.4 GHz) for both TE and TM polarizations. Angular stability is achieved until 70° and attenuation of more than 25 dB is observed at resonance. The passband is obtained at 4.37 and 6.22 GHz. The proposed structure separates the closely spaced frequency bands by a ratio of 1.44 and 1.39 at the stop band and 1.42 at the pass band. The dimensions of the proposed FSS unit cell are 0.13λ0 × 0.13λ0 × 0.020 λ0, where λ0 represents the free space wavelength at the lowest resonance frequency. Good agreement between modeled and measured results is obtained.

Coding DGS resonator sensor for ultra-high Q-factor dielectric thickness detection

In this paper, a high Q-factor-based defective ground structure (DGS) etched microwave resonator is demonstrated to identify the unknown thickness of non-destructive monolayer dielectric material. The proposed structure consists of coupled sharp-edged split-square resonator (CS-SSR), a high-impedance microstrip line, and symmetrically coded DGS optimized by adaptive genetic algorithm (AGA), which is evaluated through simulation and experiment assessment. AGA is applied to obtain ultra-high quality factor (Q-factor) using a robust calculation model with rapid convergence speed. The high Q-factor leads to high sensitivity, better accuracy, and enhanced resolution of the microwave sensor. Furthermore, the comparison of the results between the codeless, asymmetrical, and symmetrical DGS resonator illustrates that the symmetrical coding DGS resonator with higher sensitivity and better performance for dielectric material thickness detection sensors.

Charge and spin transport through a normal lead coupled to an s -wave superconductor and a Majorana zero mode

Zero-bias charge conductance peak (ZBCCP) is a significant symbol of Majorana zero modes (MZMs). The proximity effect of $s$-wave superconductor is usually demanded in the fabrication of MZMs. So in transport experiments, the system is inevitably coupled to the $s$-wave superconductor. Here we study how the ZBCCP is affected by coupling of the $s$-wave superconductor. The results show that the ZBCCP could be changed into a zero-bias valley due to the coupling of $s$-wave superconductor, although the conductance at the zero bias still keeps a quantized value $2{e}^{2}/h$. So it does not mean no MZM exists when no ZBCCP is experimentally observed. In addition, the spin transport is investigated. Four reflection processes (the normal reflection, spin-flip reflection, normal Andreev reflection, and equal-spin Andreev reflection) usually occur. The reflection coefficients are strongly dependent on the spin direction of the incident electron, and they may be symmetrical or Fano resonance shapes. But the spin conductance always shows a zero-bias peak with the height $e/2\ensuremath{\pi}$ regardless of the direction of the spin bias and the coupling strength of the $s$-wave superconductor. So measuring spin transport properties could be a more reliable method to judge the existence of MZMs.

PT -symmetric Helmholtz resonator dipoles for sound directivity

Parity-time ($\mathcal{PT}$)-symmetric or, more generally, non-Hermitian systems have opened a new area for unconventional management of waves, with significant applications, especially in optics. However, fewer proposals are found in acoustics, possibly due to the lack of a simple mechanism for coherent gain. In this paper, we propose a composite non-Hermitian system in acoustics consisting of assemblies of $\mathcal{PT}$-symmetric Helmholtz resonator (HR) dipoles. Like meta-atoms are used as building elements in metamaterials, we propose $\mathcal{PT}$-symmetric dipoles to design non-Hermitian systems intended to engineer complicated directivity fields. We theoretically analyze, numerically confirm, and experimentally show the symmetry breaking in a two-dimensional space of non-Hermitian dipoles consisting of a pair of Helmholtz resonators with different levels of gain and loss. In particular, we explore, as an application, a metastructure to concentrate the sound pressure inside the circular array formed by $\mathcal{PT}$-symmetric dipoles. The proposed HR dipoles may be a convenient composite element for smart control of sound.

Integration of coupling resonator as port-isolator and MMLC-Minkowiski fractal loop for Wi-Max rejection in 4-port compact UWB MIMO antenna

This paper presents a 4-port compact UWB MIMO antenna. It has 45 tilted offset feed for better impedance matching and connected to cornered cut-out quad-radiators. Radially symmetric resonators are provided for impedance matching and isolation improvements. A miniaturized magnetic LC (MMLC) Minkowiski fractal loop acts as a magnetic shield between electric walls of feed and resonator for Wi-max band rejection. The contra-rotational symmetry of resonator and rotationally asymmetric strips in ground enhances isolation. To validate, a prototype antenna is fabricated and measured which shows good agreements. The proposed antenna has a compact dimension 31 mm × 31 mm, operates from 2.27 to 11.7 GHz and reject bands at 3.0–4.2 GHz. The average gain is > 4 dBi with ECC < 0.16 in the operating band. An equivalent circuit topology is also modelled which validates the design. The multi-port antenna system can be used for microwave imaging, RF-sensing and radar applications.

Strain sensing based on resonant states in 2D dielectric photonic quasicrystals.

This paper reports the numerical and experimental study of the strain sensing effect of bidimensional quasiperiodic structures made with dielectric cylinders. Structures of around 100 cylinders arranged following a Penrose quasiperiodic disposition were simulated, built and measured, in different states of deformation. The selected quasiperiodic structure contains a symmetric decagonal ring resonator that shows two states in its photonic band gap. The frequency of these states varies linearly in opposite directions as the structure is axially deformed, becoming an interesting sensing principle that can be exploited to build optical strain gauges. As a proof of concept, centimeter-scale glass cylinder (εr=4.5) structures were fabricated and their transmission spectra were measured in the microwave range. The same structures were simulated using finite integration time domain showing a good agreement with the measurements. The sensitivity of the prototype built was 12.4 kHz/µε, very linear in a wide range. Therefore, we conclude that the states in the gap of the resonator rings of 2D quasicrystals can find an interesting application in optical strain gauge construction.

Extremely high Q-factor terahertz metasurface using reconstructive coherent mode resonance.

High Q-factor resonance has a pivotal role in wide applications for manipulating electromagnetic waves. However, high Q-factor resonance, especially in the terahertz (THz) regime, has been a challenge faced by plasmonic metamaterials due to the inherent ohmic and radiation losses. Here, we theoretically present a unique metasurface scheme to produce extremely high Q-factor Fano resonance of the reconstructive coherent mode in the THz regime. The THz metasurface is composed of periodically arranged vertical symmetric split ring resonators (SRRs), which can produce perfect reconstructive coherent coupling effect in the sense that dipole radiation is destructively suppressed. Under the polarized electric field perpendicular to SRR gap, the surface currents are out of phase for an individual SRR, leading to the cancellation of net dipole moment. The reconstructive coherent mode resonance can occur between each SRR and its neighboring SRRs, accompanied by destructive interference of the scattered fields of each SRR. This is due to the coupling between the localized resonance of individual particles and the Rayleigh anomaly of the array. The proposed metasurface can significantly suppress far-field radiation and perform an extremely high Q-factor beyond 104 level with large modulation depth in the THz region, which pushes the advancement of THz high Q-factor resonance. The extremely high Q-factor of reconstructive coherent mode is tunable by adjusting the geometry parameters. The design strategy is useful to develop ultra-sensitive sensors, narrow-band filters and strong interaction of field-matter in the THz regime.

Sensing and Induced Transparency with a Synthetic Anti-PT Symmetric Optical Resonator.

Synthetic dimensions and anti-parity-time (anti-PT) symmetry have been recently proposed and experimentally demonstrated in a single optical resonator. Here, we present the effect of the rotation-induced frequency shift in a synthetic anti-PT symmetric resonator, which enables the realization of a directional rotation sensor with improved sensitivity at an exceptional point (EP) and transparency assisted optical nonreciprocity (TAON) in the symmetry-broken region. The orthogonal rotation of this system results in the direction-independent frequency shift and maintenance of the EP condition even with rotation. Tunable transparency at the EP can thus be fulfilled. Hopefully, the proposed mechanisms will contribute to the development of high-precision rotation sensors and all-optical isolators and make the study of the synthetic anti-PT symmetric EP with rotation possible.

Design of high gain Vivaldi antenna with a compound optical lens inspired by metamaterials

A kind of compound optical lens (COL) inspired by metamaterials whose unit cell is a closed symmetric S-type resonator (CSSR) is designed to enhance the gain and directivity of the antipodal Vivaldi antenna (AVA). COL, composed of a plano-convex lens and a double-convex lens, can generate a very narrow beam with a half-power beamwidth of 11.2° at 12 GHz. Traditional metamaterial lenses can only convert spherical waves into plane waves. Although the gain will increase, the beamwidth of the antenna is still very wide. COL can focus the plane wave transformed from the spherical wave, which makes the radiation beam extremely narrow. The proposed antenna has a −10 dB impedance bandwidth of 169.2% (1.0-12.0 GHz) and a −3 dB gain bandwidth of 133.3% (2.0-10.0 GHz) and a maximum gain enhancement of 5 dBi. The experimental results of the antennas agree with the simulation results. The proposed antenna is eventually a suitable candidate for wireless communications and radar applications.

Static and dynamic actuations of clamped-clamped V-shaped micro-resonators under electrostatic forces

This work presents detailed static and dynamic analysis of electrostatically actuated in-plane micro-electro-mechanical V-shaped micro-beam resonators. An analytical model is presented, based on the Euler Bernoulli beam theory, which accounts for the nonlinear electrostatic forces and the mid-plane stretching. The model is utilized to simulate the static and eigenvalue problems of the beam under various DC actuation scenarios. The model is validated by comparing with a finite element model and with experimental data. The experiments are based on in-plane silicon devices. The micro-beams are sandwiched between four electrodes (four ports) with uniform airgap for various electrostatic actuation options. These electrodes not only offer various electrostatic actuation options, but also allow the detection of the three lowest symmetric and anti-symmetric resonance frequencies. Results are presented for several case studies of micro-beams resonators of various geometrical parameters and airgap dimensions. With various actuation options and different V-shaped configurations, the structure may show only pull-in instability, the snap-through buckling, or both instabilities together. The results enable careful characterization of the snap-through buckling with the ability of increasing the static deflection range before pull-in. Also, the results can be promising for the realization of different wide–range tunable micro-resonator and for various vibration modes. These results can be useful in micro-scale applications that can be beneficial for designing structures with low power consumption, high sensitivity, and wide tuning range.

Symmetric and Antisymmetric Multipole Mode-based Fano Resonances in Split Theta-shaped Nanocavities

Split theta-shaped nanocavities composed of an elliptical disk embedded in a nonconcentric split ring are theoretically investigated by the finite-difference time-domain method. Symmetric and antisymmetric mode-based Fano resonances are both formed, due to the interference between the bright mode of the cavity and two types of multipole modes of the split ring, and experience different changes through adjusting the degree of symmetry breaking via an asymmetry of the ring width and displacement of the disk. As the cavity remains symmetrical with respect to the axis of the split ring, only the symmetric Fano resonances are observed. Further breaking the cavity symmetry, the antisymmetric Fano resonances appear and increase, while symmetric ones decrease. When the overall degree of symmetry breaking becomes larger due to an increasing offset of the disk relative to the asymmetric ring, this change trend becomes more complicated, and some Fano resonances are suppressed or enhanced again. Our work demonstrates that the proposed cavities with tunable Fano line shape could be used as platforms for multiwavelength biochemical sensors and enhanced spectroscopies.

Modelling of symmetrical quadrature optical ring resonator with four different topologies and performance analysis using machine learning approach

Abstract The communication network based on the optical system requires more precise and efficient devices and equipment. Optical ring resonator is a versatile device used as a filter, delay line, add/drop multiplexer, switch, sensor and analyzer etc. We modelled the new symmetrical quadrature optical ring resonator (SQORR) and proposed four different topologies architecture for the multiple optical ring resonator. The performance of the proposed symmetrical quadrature optical ring resonator is assessed using regression based machine learning (ML) approach utilizing an Artificial neural network (ANN) with various checks are done to validate the approximations like error histogram, time series response, error autocorrelation, input-error correlation and mean-square-error (MSE). The best validation performance is 8.8486e-9 stopped at 103 for rhombus topology, 8.347e-9 stopped at 242 epochs, 8.8486e-9 stopped at 311 epochs for horizontal topology and 5.8012e-09 stopped at 373 epochs for square topology. The significance of the work is to increase FSR (free spectral range) by adding rings and wide FSR achieved 299.79 THz (maximum) and throughput of 0.027 W/m for rhombus topology and other performance parameters of the optical ring resonator using symmetrical rings. Such structure is small in the size and easy to fabricate. Even by the same number of rings using different topologies structure, we can vary the performance parameters as per the different applications.

Development of a green synthesized silver nanoparticle-based antioxidant capacity method using carob extract

The measurement of total antioxidant capacity (TAC) indicating the cooperative action of all antioxidants in a complex sample is an important analytical challenge. A novel green silver nanoparticle-based antioxidant capacity (GSNP-AC) method using carob extract was designed for TAC measurement. Green synthesis of nanoparticles has various advantages such as environmentally friendliness, reliability, sustainability and fast production. In the presence of silver seeds formed with carob extract, Ag+ is reduced to spherical silver nanoparticles (SNPs) with antioxidants, resulting in enlarged particles with a symmetric surface plasmon resonance (SPR) absorption band at 434 nm. The SPR of SNPs allowed quantification of antioxidants (i.e., increase in SPR absorbance being correlated to antioxidant concentration), and the GSNP-AC method gave a linear response over a wide concentration range of antioxidants. The molar absorptivity and LOD for trolox were 11700 L mol−1 cm−1 and 0.31 µM, respectively. The proposed method was validated in terms of concentration-dependent linear response, additivity of absorbances, precision and accuracy. The results obtained with the proposed method for standard antioxidants, synthetic mixtures and real sample extracts were correlated with those of the traditional CUPRAC method. This green synthesized silver nanoparticle-based TAC method showed simple, rapid, cost-effective, and eco-friendly superiorities over similar other nanoparticle-based assays.

Characterization of Dielectric Substrates Using Dual Band Microwave Sensor

In this work, a compact, inexpensive, and efficient dual band microwave sensor is proposed. The sensor is based on two Complementary Symmetric Split-Ring Resonators (CSSRRs) and possesses a high $Q$ factor and wide sensing range. These CSSRRs are coupled electrically with two inductive patches to the Microstrip Transmission Line (MTL). This combination provides two dual bands, first at 5.35 GHz with a notch depth of -55.20 dB and second at 7.99 GHz with a notch depth of -22.54 dB. The sensor works in transmission mode and senses shift in frequency. Some commonly available dielectric substrates with relative permittivity ranges between 1 and 12 are considered Material Under Test (MUT), and detailed sensitivity analysis is being performed for each band. The dual band sensor is fabricated on a low-cost, widely available FR4 substrate and measured by CEYEAR AV3672D vector network analyzer. Additionally, the least square curve fitting method is used to develop a mathematical model for the measured results. An excellent agreement is observed between simulated, measured, and formulated results.

High sensitivity refractive index sensor in long-range surface plasmon resonance based on side polished optical fiber

A side-polished single mode optical fiber based on conventional long-range surface plasmon resonance (cLRSPR) sensor and symmetrical long-range surface plasmon resonance (sLRSPR) sensor was proposed and experimentally demonstrated. The proposed structure of cLRSPR is composed of optical fiber/dielectric buffer layer (DBL)/Ag film while for sLRSPR is consisted of optical fiber/DBL/Ag film/DBL. Magnesium fluoride, MgF2 with 50 nm thickness is used as DBL layer that lies beneath of Ag film in cLRSPR and covering both sides of Ag film in sLRSPR. 40 nm thickness of Ag layer is used with 5 mm length of sensing region. The result suggested that the sensing performance in terms of sensitivity of the cLRSPR sensor was better compared to sLRSPR and previous works of conventional surface plasmon resonance (cSPR) as it achieves as high as 2812.5 nm/RIU at 0.01 interval of refractive index with refractive index (RI) range of 1.33–1.34. The larger the sensitivity value indicates the better the performance of the SPR sensor. This design is expected to play an important role on chemical sensing and biological sensing as it displays higher penetration depth.

Interfering Tunneling Paths through Magnetic Molecules on Superconductors: Asymmetries of Kondo and Yu-Shiba-Rusinov Resonances.

Magnetic adsorbates on superconductors induce a Kondo resonance outside and Yu-Shiba-Rusinov (YSR) bound states inside the superconducting energy gap. When probed by scanning tunneling spectroscopy, the associated differential-conductance spectra frequently exhibit characteristic bias-voltage asymmetries. Here, we observe correlated variations of Kondo and YSR asymmetries across an Fe-porphyrin molecule adsorbed on Pb(111). We show that both asymmetries originate in interfering tunneling paths via a spin-carrying orbital and the highest occupied molecular orbital (HOMO). Strong evidence for this model comes from nodal planes of the HOMO, where tunneling reveals symmetric Kondo and YSR resonances. Our results establish an important mechanism for the asymmetries of Kondo and YSR line shapes.

Fano-Kondo resonance versus Kondo plateau in an Aharonov-Bohm ring with an embedded quantum dot

We theoretically examine the transport through an Aharonov-Bohm ring with an embedded quantum dot (QD), the so-called QD interferometer, to address two controversial issues regarding the shape of the Coulomb peaks and measurement of the transmission phase shift through a QD. We extend a previous model [B. R. Bulka and P. Stefanski, Phys. Rev. Lett. 86, 5128 (2001); W. Hofstetter, J. Konig, and H. Schoeller, ibid. 87, 156803 (2001)] to consider multiple conduction channels in two external leads, L and R. We introduce a parameter p_{\alpha} (|p_{\alpha}| \le 1) to characterize a connection between the two arms of the ring through lead \alpha (=L, R), which is the overlap integral between the conduction modes coupled to the two arms. First, we study the shape of a conductance peak as a function of energy level in the QD, in the absence of electron-electron interaction U. We show an asymmetric Fano resonance for |p_{L,R}| = 1 in the case of single conduction channel in the leads and an almost symmetric Breit-Wigner resonance for |p_{L,R}| < 0.5 in the case of multiple channels. Second, the Kondo effect is taken into account by the Bethe ansatz exact solution in the presence of U. We precisely evaluate the conductance at temperature T=0 and show a crossover from an asymmetric Fano-Kondo resonance to the Kondo plateau with changing p_{L,R}. Our model is also applicable to the multi-terminal geometry of the QD interferometer. We discuss the measurement of the transmission phase shift through the QD in a three-terminal geometry by a "double-slit experiment." We derive an analytical expression for the relation between the measured value and the intrinsic value of the phase shift.

Perfect Absorption in Mirror-Symmetric Acoustic Metascreens

Mirror-symmetric acoustic metascreens producing perfect absorption independently of the incidence side are theoretically and experimentally reported in this work. The mirror-symmetric resonant building blocks of the metascreen support symmetric and antisymmetric resonances that can be tuned to be at the same frequency (degenerate resonances). The geometry of the building blocks is optimized to critically couple both the symmetric and the antisymmetric resonances at the same frequency allowing perfect absorption of sound from both sides of the metascreen. A hybrid analytical model based on the transfer matrix method and the modal decomposition of the exterior acoustic field is developed to analyze the scattering properties of the metascreen. The resulting geometry is 3D printed and experimentally tested in an impedance tube. Experimental results agree well with the theoretical predictions proving the efficiency of these metascreens for the perfect absorption of sound in the ventilation problems.

Hierarchical Construction of Higher-Order Exceptional Points.

The realization of higher-order exceptional points (HOEPs) can lead to orders of magnitude enhancement in light-matter interactions beyond the current fundamental limits. Unfortunately, implementing HOEPs in the existing schemes is a rather difficult task, due to the complexity and sensitivity to fabrication imperfections. Here we introduce a hierarchical approach for engineering photonic structures having HOEPs that are easier to build and more resilient to experimental uncertainties. We demonstrate our technique by an example that involves parity-time symmetric optical microring resonators with chiral coupling among the internal optical modes of each resonator. Interestingly, we find that the uniform coupling profile is not required to achieve HOEPs in this system-a feature that implies the emergence of HOEPs from disorder and provides resilience against some fabrication errors. Our results are confirmed by using full-wave simulations based on Maxwell's equation in realistic optical material systems.

Symmetric and antisymmetric multipole electric-magnetic fano resonances in elliptic disk- nonconcentric split ring plasmonic nanostructures

A plasmonic nanostructure composed of a displaced elliptical disk in a nonconcentric split ring is proposed and investigated theoretically by the finite difference time domain method. The simulated scattering spectra and electric field distributions reveal that multiple Fano resonances can be formed due to the destructive interference of the longitudinal dipole mode of the disk and multiple multipole magnetic modes of the split ring. It is also found that the spectral position of each Fano dip is insensitive to the offset caused by moving the disk in either direction, but the depth varies to a different extent. When the disk moves parallel to the split, it is very suitable for the generation and evolution of the symmetric Fano resonance, particularly the structural symmetry of the split ring is further broken. As the disk moves perpendicular and closer to the split, the depth of each antisymmetric Fano resonance increases, while the appeared symmetric ones weaken. Such a nanostructure may be used as a potential platform for spectral line shaping and multiwavelength bio-chemical sensing.