Adjacent Resonators Research Articles

Five-pole wideband quasi-reflectionless interdigital BPF with second harmonic suppression

Abstract In this paper, a 5-pole quasi-reflectionless (QR) interdigital BPF with a wide range of non-reflecting signals is proposed, offering good impedance matching. Two absorptive T-shaped stubs are placed at the input and output ports of the interdigital BPF. The absorptive stubs are optimised to obtain the reflection as low as possible for a wide range. Additionally, we shift the adjacent resonators of the interdigital BPF up and down to improve overall performance. The design follows a specific procedure in order to investigate factors affecting the performance. Firstly, the convetional interdigtial bandpass filter is designed relying on the coupling matrix method. Next, we study the conversion of the stopband filter into an absorptive stub. The input impedance of the stub plays a vital role in determining the reflection bandwidth, so it is optimised as well. Meanwhile, the interdigital BPF and one abosrptive stub are combined, where the bandwidth of reflectionless becomes wider compared to the conventional interdigital BPF. Another absorptive stub is added into the other port of the BPF to make the proposed filter symmetric. Different orders of the interdigital PBF are analysed, where the fifth order has the best response. The proposed filter is fabricated and tested, and an FR4 substrate with a thickness of 1.5 mm and a dielectric constant of 4.5 is utilized. The simulation and measurement results agree well. The realised S11 is less than -10dB from 0.72GHz to 4.1GHz (i.e., -10dB reflectionless bandwidth 3.38GHz), while the realised S11 is less than -3dB from 0.42GHz to 6GHz (i.e., -3dB reflectionless bandwidth 5.58GHz). The S21 response is good for the transmission band. Finally, some slots are etched out from the gorund to reduce the influence of the second harmonic response.

Excitation and manipulation of super cavity solitons in multi-stable passive Kerr resonators

We report on the theoretical analysis as well as the numerical simulations about the nonlinear dynamics of cavity solitons in a passive Kerr resonator operating in the multistable regime under the condition of a sufficiently strong pump. In this regime, the adjacent tilted cavity resonances might overlap, thus leading to the co-existence of combinatory states of temporal cavity solitons and the extended modulation instability patterns. The cavity in the regime of multistablity may sustain distinct families of cavity solitons, vividly termed as super cavity solitons with much higher intensity and broader spectra if compared with those in the conventional bi-stable regime. The description of such complex cavity dynamics in the multstable regime requires either the infinite-dimensional Ikeda map, or the derived mean-field coupled Lugiato-Lefever equations by involving multiple contributing cavity resonances. With the latter model, we revealed the existence of different orders of super cavity solitons, whose stationary solutions were obtained by using the Newton-Raphson algorithm. Along this line, with the continuation calculation, we have plotted the Hopf / saddle-node bifurcation curves, thus identifying the existing map of the stable and breathing (super) cavity solitons. With this defined parameter space, we have proposed an efficient method to excite and switch the super cavity solitons by adding an appropriate intensity (or phase) perturbation on the pump. Such deterministic cavity soliton manipulation technique is demonstrated to underpin the multi-level coding, which may enable the large capacity all-optical buffering based on the passive fiber ring cavities.

DFT insights into the basicity of some cyclic allenes

ABSTRACT The proton affinity (PA) and gas phase basicity values of previously reported cyclic allene series are investigated using high-level quantum chemical calculations. Some of the studied structures possessed more than one protonation site. All protonation types were explored for each structure and the compounds with PA value more than ≈1030 kJ mol−1 were considered superbasic structures. Cyclic allene's basicity strength was affected by ring size, adjacent heteroatom's presence and resonance existence in protonated form.

P-wave resonances in the exponential cosine screened Coulomb potential* *This work was supported by the National Natural Science Foundation of China (Grant No. 12174147) and the Chinese Scholarship Council (Grant Nos. 202108210152 and 202006175016).

We perform benchmark calculations of the p-wave resonances in the exponentially cosine screened Coulomb potential using the uniform complex-scaling generalized pseudo-spectral method. The present results show significant improvement in calculation accuracy compared to previous predictions and correct the misidentification of resonance electron configuration in previous works. It is found that the resonance states approximately follow an n 2-scaling law which is similar to the bound counterparts. The birth of a new resonance would distort the trajectory of an adjacent higher-lying resonance.

Terahertz binary computing in a coupled toroidal metasurface

The applications of terahertz metamaterials are being actively explored in recent times for applications in high-speed communication devices, miniature photonic circuits, and bio-chemical devices because of their wide advantages. The toroidal resonance, a new type of metasurface resonance, has been examined with great interest to utilize its properties in terahertz metasurface applications. This study reports a proof of concept design of a toroidal metasurface that experimentally demonstrates binary computing operations in the terahertz frequency regime. The analog computing of binary operations is achieved by the passive tuning of distance between the split ring resonators comprising the meta-molecule. The amplitude modulation is utilized as a method of determining the Boolean logic outputs of the system. The proposed metasurface could be further optimized for high amplitude modulations and active logic gate operations using tunable materials including graphene and ITO. The proposed metasurface consists of three split-ring resonators, and the near-field coupling between the adjacent resonators dictates the Boolean operations. A multipole analysis of the scattered powers of terahertz radiation determines the toroidal excitation in the metasurface. The proposed metasurfaces experimentally define AND Boolean logic operation at 0.89 terahertz, and OR Boolean logic operation at 0.97 terahertz. Numerical simulations support the experimentally obtained results. Additionally, we numerically report the excitation of NAND operation at 0.87 THz. Such toroidal analog computing metasurfaces could find applications in digitized terahertz circuits and integrated photonic devices.

Machine learning approach for automated data analysis in tilted FBGs

This paper presents the development of an approach for automatic estimation of the regression coefficients as a function of the refractive index (RI) in Tilted Fiber Bragg Gratings (TFBGs) based on their optical spectral characteristics. The methodology is based on machine learning approach, where different samples are analyzed in various test conditions to obtain a dataset for the training of a kNN regression algorithm. In this case, the spectral characteristics related to the wavelength spacing between adjacent cladding mode resonances, number of valleys and amplitude of the normalized spectra are correlated with the linear regression algorithm for RI estimation using the machine learning approach. The analysis are performed as a function of the wavelength shift and optical power, considering two regions on the transmitted spectrum and the envelope of the curve. Furthermore, the number of valleys and the area of the envelope curve are also analyzed as a function of the refractive index, which result in six analyzed features. The Principal Components Analysis (PCA) is used to reduce the number of features to two principal components. The results of the proposed algorithm are obtained with different trained and untrained samples, which indicates a root mean squared error (RMSE) of around 0.003RIU for the trained samples and 0.008 RIU for the untrained ones. Therefore, the results indicate the usefulness of the proposed approach, which can be used to enhance the reproducibility of large set of TFBG sensors in practical applications.

Tunable chiral bound states in a dimer chain of coupled resonators

We study an excitation hopping on a one-dimensional (1D) dimer chain of coupled resonators with the alternate on-site photon energies, which interacts with a two-level emitter (TLE) by a coupling point or two adjacent coupling points. In the single-excitation subspace, this system not only possesses two energy bands with propagating states, but also possesses photonic bound states. The number of bound states depends on the coupling forms between the TLE and the dimer chain. It is found that when the TLE is locally coupled to one resonator of the dimer chain, the bound-state that has mirror reflection symmetry. When the TLE is nonlocally coupled to two adjacent resonators, three bound states with preferred direction arise due to the mirror symmetry breaking. By using chirality to measure the asymmetry, it is found that the chirality of these bound states can be tuned by changing the energy differences of single photon in the adjacent resonators, the coupling strengths and the transition energy of the TLE.

Coupled Micromachined Magnetic Resonators for Microwave Signal Processing.

In this paper, the theory, micromachining technology, and experimental results of the coupling of integrated magnetic film-based resonators for microwave signal filtering are presented. This is an extended contribution to the field of magnetostatic wave coupled resonators, including details about the technological results, circuit theory, and perspective applications for tunable integrated coupled magnetic resonators. An analytical approach using the magnetostatic wave approximation is used to derive the coupling coefficient between adjacent resonators coupled by the electromagnetic field decaying outside the resonators. Then, micromachining employing hot phosphoric acid etching is presented to manufacture integrated coupled resonators. Finally, circuit modeling and experimental results obtained using the ferromagnetic resonance technique are discussed.

All-Textile Compact Ultra-Wideband Microstrip Antenna with Full Ground Plane for WBAN Applications

A novel low-profile all-textile microstrip antenna for ultra-wideband (UWB) applications in wireless body area networks (WBANs) is presented. The antenna incorporates flexible materials such as felt and conductive fabrics which provide optimal wearing comfort and durability. The use of a single dielectric substrate layer facilitates the integration process. The antenna also features a full background plane that minimizes the back radiation towards the human body. Multiple branches are designed in a compact area to generate adjacent resonances, and their combination achieves broadband characteristics across the 4.83–9.57 GHz frequency band. The antenna has a miniaturized size of 60 mm × 60 mm, which is 1.6λg × 1.6λg (where λg represents the guided wavelength at the center frequency), and it has a high realized gain of up to 10 dBi. The fully grounded structure also ensures good isolation between the antenna and the human body, thereby alleviating concerns regarding safety and radiation degradation in WBAN context. Simulation results indicate that the antenna maintains high performance levels during various bending tests. Given its favourable properties like ultra-wide bandwidth, compact size, low profile, high flexibility, and low specific absorption rate (SAR), the proposed design could find broad application prospects in high-speed WBAN systems.

Transmission line bandpass filters with multiple attenuation poles and small number of resonators

This article considers an alternative way to generate attenuation poles (AP) in bandpass filter (BPF) with parallel type resonators and admittance inverters. It consists in using special transmission line resonators, in which one or two antiresonant frequencies ωp1, ωp2 are placed next to the main resonant frequency ω0. These frequencies ωp1, ωp2 are the poles of the input admittance Y(jω). Four new resonators are synthesized in the article. Two resonators generate one AP, and other two resonators generate two APs located near the passband of the BPFs. If we use mixed couplings between proposed adjacent resonators in BPF, then the total number of APs will become quite large. This is because each mixed coupling adds one AP. N-order BPF without cross coupling can has (3 N – 1) APs. The increased number of APs improves the BPF selectivity, including the one-sided one. With APs, the filter can provide increased attenuation in certain frequency bands and effectively suppress unwanted signals. A microstrip second order BPF with center frequency f0 = 1 GHz and bandwidth BW = 70 MHz, which has five APs, is designed. It is compared with third order BPFs with two APs.

The impact of contact and contactless interactions between the meta-atoms on terahertz bound states in the continuum

The excitation and manipulation of symmetry-protected bound states in the continuum (SP-BIC) is significantly valuable for metasurface-based biosensors. The interactions between adjacent meta-atoms determine the fundamental properties of SP-BIC; however, this topic has not been profoundly explored. In this work, we experimentally and numerically investigate the effects of contactless and contact interactions between adjacent dual-gap split-ring resonators (DSRRs) on the SP-BIC. We demonstrate that there is only one SP-BIC at 0.9 THz when the incident radiation polarization is parallel to the gap in both contactless and contact coupling conditions. When the polarization is vertical to the gap, the individual SP-BIC shifts the frequency to 0.8 THz under contactless coupling. Under contact coupling, the SP-BIC degrades to be an electromagnetically induced transparency (EIT) windows at 0.8 THz. We calculated a 3.6 ps group delay of slow light for EIT. Numerical simulations indicate that the combination of one magnetic dipole (MD) in the inner arm and another electric dipole in the outer arm of DSRR results in quasi-BIC at 0.9 THz and 0.8 THz under contactless coupling. Under contact coupling conditions, the formation of quasi-BIC at 0.9 THz is similar to contactless coupling. However, two MDs of opposite polarity results in the EIT windows at 0.8 THz. Our results reveal excitation and manipulation of terahertz SP-BIC via contactless and contact coupling, which is significant for the innovation of terahertz biosensors.

Shaping the spectral correlation of bi-photon quantum frequency combs by multi-frequency excitation of an SOI integrated nonlinear resonator.

We reveal the generation of a broadband (> 1.9 THz) bi-photon quantum frequency comb (QFC) in a silicon-on-insulator (SOI) Fabry-Pérot micro-cavity and the control of its spectral correlation properties. Correlated photon pairs are generated through three spontaneous four-wave mixing (SFWM) processes by using a co-polarized bi-chromatic coherent input with power P1 and P2 on adjacent resonances of the nonlinear cavity. Adjusting the spectral power ratio r = P1/(P1 + P2) allows control over the influence of each process leading to an enhancement of the overall photon pair generation rate (PGR) μ(r) by a maximal factor of μ(r = 0.5)/μ(r = 0) ≈ 1.5, compared to the overall PGR provided by a single-pump configuration with the same power budget. We demonstrate that the efficiency aND of the non-degenerate excitation SFWM process (NDP) doubles the efficiency a1 ≈ a2 of the degenerate excitation SFWM processes (DP), showing a good agreement with the provided model.

Resonances in the Hulthén potential: benchmark calculations, critical behaviors, and interference effects

We perform benchmark calculations of resonance states in the Hulthén potential by employing the uniform complex-scaling generalized pseudospectral method. Complex resonance energies for states with the lowest four orbital angular momenta are reported for a wide range of screening parameters where their positions lie above the threshold. Our results are in good agreement with previous J-matrix predictions, but differ significantly from the complex-scaling calculations based on oscillator basis set. By tracing the resonance poles via bound-resonance transition as the screening parameter increases, we successfully identify the electronic configurations of the numerically obtained resonances. The asymptotic laws for resonance position and width near the critical transition region are extracted, and their connections with the bound-state asymptotic law and Wigner threshold law, respectively, are disclosed. We further find that the birth of a new resonance will distort the trajectories of adjacent higher-lying resonances, while even if two resonances are exactly degenerate in real energy position, they can still be treated as near-isolated resonances provided their widths are significantly different in magnitude.

Symmetric and asymmetric Fano resonances in a broken axial symmetry metasurface of split ring resonators

In the paper, a metasurface is investigated, the unit cell of which consists of two resonators. We show that the breaking of the axial symmetry of the unit cell in such a structure leads to the appearance of two Fano resonances instead of one that is characteristic of the symmetric unit cell. The two resonances are different, one of which is symmetric and the other is asymmetric. This is confirmed by calculating the phases of currents in the adjacent resonators. Modeling results are confirmed by experimental investigation of the metasurface spectrum in a microwave frequency range showing two resonances measured experimentally. A detailed study of the currents flowing in the adjacent resonators of the unit cell demonstrates that currents at the Fano resonance dips flow either in phase or in antiphase with respect to the external electric field, whereas in peaks this difference is π/2. This confirms the interference nature of the Fano effect.

A single‐layered balanced filtering crossover with high selectivity based on square patch resonator

AbstractA new design of single‐layered balanced filtering crossover with high selectivity based on square patch resonator is proposed. Originated from the degenerate modes, that is, TM12 and TM21 on square patch resonators, the feasibility of intrinsic common‐mode (CM) suppression and channel isolation is conceived. For demonstration, a first‐order balanced crossover prototype is designed. Afterwards, to enhance selectivity, a square patch resonator is subtly divided into two identical parts and then introduced into the prototype. Hence, a balanced filtering crossover with a fifth‐order Chebyshev response is formed. Furthermore, stubs are deployed between adjacent patch resonators to introduce mixed couplings. Thus, two controllable transmission zeros are obtained, and better out‐of‐band suppression is achieved. Ultimately, the proposed crossover is fabricated and measured. High performance in terms of differential‐mode filtering response, in‐band CM suppression and channel isolation demonstrates the feasibility of the proposed method.

A single layer and very close band spacing frequency selective surface with enhanced isolation

An ultrathin and very closely located dual-band frequency selective surface (FSS) with enhanced isolation is proposed in this letter. The unit cell consists of two typical concentric hexagon rings, with several stubs loaded on each side of the inner ring. Through the stub-loaded configuration, the mutual coupling of adjacent resonators is highly decoupled and a very close band spacing FSS with better isolation can be achieved, and the ratio of the two operating bands can be as low as 1.06. Additionally, due to the independent resonant frequencies, the band ratio can be set over a wide range, from 1.06–2.43. Furthermore, the corresponding equivalent circuit model (ECM) is developed and analyzed for better comprehension of the underlying mechanisms of the proposed FSS. The validity of the design is then checked with a prototype, and the measured results show good agreement with the simulated ones.

Analogy of polarization-independent, multi-band and tunable electromagnetically induced transparency with high sensitivity based on simple circular ring resonators and vanadium dioxide film

An analogy of polarization-independent, multi-band and tunable electromagnetically induced transparency (EIT) effect is proposed based on simple combination of circular ring resonators and vanadium dioxide film. The EIT-like effect is generated by bright-bright coupling resulting from adjacent ring resonators. High sensitivity up to 1.60 THz/RIU to the environmental refractive index is achieved utilizing the transparency peak. Accompanying with the EIT-like effect, the multi-band slow light phenomenon is obtained around the transparency windows. In addition, by inducing the insulator-metallic transition of the vanadium dioxide layer, the EIT-like curves can be actively manipulated while the multiple modulation is realized without refabricating the structure. Particularly, due to structural symmetry, the EIT-like windows keep unchanged and maintain noticeable with various polarization angles. The proposed structure has potential applications such as terahertz sensors, slow-light devices and modulators.

Novel Synthesis Method for Reconfigurable Filtering Phase Shifter With Frequency-Dependent Coupling Using Optimization Technique

A novel optimization technique is proposed for reconfigurable filtering phase shifter with frequency-dependent coupling in this brief. It incorporates both the coupling matrix entries and the circuit elements into optimization process. With the proposed technique, it can not only obtain desired insertion phase at the center frequency, align the phase slope between different phase states to be same, but also maintain satisfactory return loss in the passband and have multiple transmission zeros in the stopband. The proposed method well suits the reconfiguration application scenario where frequency-dependent coupling is adopted between adjacent resonators. To validate the proposed idea, a microstrip prototype is fabricated and measured. Experimental results show that the operating center frequency can be tuned from 0.6 GHz to 0.71GHz, with a continuously tunable phase shifting range of larger than 175° at each frequency state.

Analytical study of Bragg resonances by a finite periodic array of congruent trapezoidal bars or trenches on a sloping seabed

For water waves propagating over a finite periodic array of congruent trapezoidal bars on a sloping seabed or trenches dug on a sloping seabed, an analytical solution in terms of Taylor series to the modified mild-slope equation (MMSE) is constructed. Based on the analytical solution, influences of various topographic parameters (e.g., the slope of seabed, bar/trench number, bar height or trench depth, and bar/trench width) on the peak value, peak phase and zero reflection of Bragg resonances are investigated. Especially, starting from the original definition of Bragg resonances, a modified Bragg's law for characterizing the excitation condition of the nth order Bragg resonance is derived, which shows that the excitation of Bragg resonances depends entirely on the average phase velocity of the water wave within the bar/trench field. When the influence of the bar/trench field on the average phase velocity is quite small, the modified Bragg's law degenerates into the traditional Bragg’s law borrowed from X-ray crystallography, which also reflects the essential difference between the water wave as a mechanical wave and the non-mechanical X-ray wave. In addition, for N bars/trenches on a flat seabed, there are at least N−1 zero reflections between any two adjacent Bragg resonance peaks. When the bars are very low or the trenches are very shallow, the phase of the N−1 zero reflections in those zero reflections is exactly the position of the N−1 zero points of the Chebyshev polynomial of the second kind, UN−1(cosk0d), where k0 is the wavenumber on the flat seabed and d is the bar/trench spacing. However, once a sloping seabed is added, all these N−1 zero reflections disappear possibly due to the destruction of the symmetry of the background bar/trench field. Finally, regardless of the number of bars/trenches, when the bar/trench width varies, the peak value of the nth order Bragg resonance oscillates periodically, leading to n local maxima. A comparative study shows that these characteristics are consistent with the band structure shown in the Bloch periodic gap map (PGM).

A Novel HTS Ultra-Narrowband Bandpass Filter Using Hairpin Meander-Line Resonator With Gradient Line-Width

A six-pole high-temperature superconducting ultra-narrowband bandpass filter (BPF) using microstrip hairpin meander-line resonators is proposed in this article. The hairpin resonators are meandered first to enclose the whole electromagnetic field in the structure, aiming to greatly reduce the coupling between two adjacent resonators. To further decrease the coupling, the line-width of the meander-line resonators are gradually increased from the inner turn to the outside turn. An ultra-narrowband BPF with center frequency of 845.1 MHz and the equal-ripple bandwidth of 0.17% is designed, fabricated, and measured. Measured minimum in-band insertion loss is 0.55 dB and the measured in-band return loss is better than 14.5 dB. The measured results are in good agreement with the simulated ones.