Resonant Modes Research Articles

Dual-Band SIW Antenna with High Frequency Ratio for UAV Detection Applications

A dual-frequency antenna based on substrate integrated waveguide (SIW) for unmanned aerial vehicle (UAV) applications is proposed, which provides a new idea for the design of multi-frequency antennas by stimulating multiple high-order modes. A group of fan-shaped patches are added to the circular slots on both sides of the dumbbell slots to form modified dumbbell slots. Two resonant modes are excited by this slot structure, and a dual-frequency response is achieved. Different opening angles and offset angles of fan-shaped patches can cause the deviation of the dual-frequency response bands. Therefore, the antenna working frequency band can be freely designed within a certain frequency band, which improves the flexibility of antenna design. The designed antenna is analyzed theoretically and optimized by simulation. Finally, the antenna was manufactured, and the experimental results were basically consistent with the simulation optimization results. The antenna worked in the X-band and the Ku-band, and the relative working bandwidth of the two bands was 6.06% (9.6–10.2 GHz) and 1.41% (14.06–14.26 GHz), respectively. The maximum gain of simulation in low frequency and high frequency operating bands is 5.9dBi and 6.13dBi, respectively.

A microwave sensing system combination of interdigital structure (IDS)-based microstrip line and RF circuits for extracting complex permittivity of liquid samples

In this manuscript, a microwave sensing system for extracting complex permittivity of binary aqueous solutions based on a modified microstrip line with interdigital structure (IDS) etched is proposed. The passive resonance unit and active circuits constitute the microwave sensing system. The passive resonance unit is evolved from conventional microstrip line with the characteristic impedance of 50Ω, then the IDS is etched on the top surface of passive resonance unit to enhance the confinement of electrical field. The modified passive sensor can produce two resonant modes, i.e., odd-mode 1 and odd-mode 2, the electrical fields of these two modes are both concentrating at IDS, and odd-mode 1 with higher density of electrical field is adopted to retrieve complex permittivity of liquid samples. Except for the passive sensor, the sensing system consists of power divider, low noise amplifier (LNA), isolator, orthogonal hybrid coupler, phase shifter, mixer, and low-pass filter (LPF). The proposed microwave sensing system has two output DC voltages, i.e., channel-I and channel-Q. The mathematical relationship between complex permittivity and resonant frequency shift can be transformed into the relation between complex permittivity and two DC voltages by the proposed microwave sensing system, which is beneficial to discard the use of VNA. The two output voltages of microwave sensing system will be changed according to the injections of liquid samples with different complex permittivity, then the mathematical models can be established by summarizing the rule between complex permittivity and DC voltages. Finally, the established mathematical models can be adopted to predict the binary aqueous solutions with unknown complex permittivity. In measurement, the proposed microwave sensing system has the average sensitivities of about 2.478 mV/εr′ and 1.418 mV/εr′ for channel-I and channel-Q, respectively, which are several times higher than other reported ones. Low-cost, high sensitivity, convenient measurement, and easy fabrication are the merits for the proposed sensing system, and it is a good template in the region of detecting liquid samples.

Enhanced Second-Harmonic Generation in Thin-Film Lithium Niobate Circular Bragg Nanocavity.

Second-order nonlinearity gives rise to many distinctive physical phenomena, e.g., second-harmonic generation, which play an important role in fundamental science and various applications. Lithium niobate, one of the most widely used nonlinear crystals, exhibits strong second-order nonlinear effects and electro-optic properties. However, its moderate refractive index and etching sidewall angle limit its capability in confining light into nanoscales, thereby restricting its application in nanophotonics. Here, we exploit nanocavities formed by second-order circular Bragg gratings, which support resonant anapole modes, to achieve a 42 000-fold enhanced second-harmonic generation in thin-film lithium niobate. The nanocavity exhibits a record-high normalized conversion efficiency of 1.21 × 10-2 cm2/GW under the pump intensity of 1.9 MW/cm2. Besides, we also show s- and p-polarization-independent second-harmonic generation in elliptical Bragg nanocavities. This work could inspire the study of nonlinear optics at the nanoscale on thin-film lithium niobate, as well as other novel photonic platforms.

Topology and curvature effects in the photonics of ring – split ring – cuboid transitions

Topological transitions in various materials are actively being studied, including topological quantum phase transitions, going beyond the Landau theory and the concept of the order parameter. Here we propose the concept of a transition between two structures with different topology using the example of the transition between a flat dielectric ring and a split ring and its further unbending into a rectangular Fabry-Pérot resonator. Experimentally and theoretically, we discovered the lifting of the degeneracy of the CW-CCW photonic modes of the ring and the formation of two families: topological, which acquire an additional phase π, equal to the Berry phase in a thin Möbius strip, and ordinary ones, which do not acquire an additional phase. Topological modes arise due to the gradual “cutting” of one antinode of the field by a gap into two antinodes as the angular size of the gap increases from zero to one degree. Thus, using a topological Fabry-Pérot resonator with variable curvature and fixed length, resonant modes with an arbitrary non-integer number of waves are realized and a new generation of resonators is created with the prospect of unique classical and quantum applications.

An exact analytical solution for coupled vibration analysis of a piezoelectric resonator

Abstract Piezoelectric resonators are widely used as the active components in devices such as sensors, actuators, communication filters, and micro/nano-electro-mechanical systems (MEMS / NEMS). Due to the piezoelectric effect, Poisson’s ratio, and its finite dimension, the thickness and lateral vibration modes in a piezoelectric resonator are inevitably coupled. In this paper, an exact analytical model for coupled vibration analysis of a piezoceramic disk is developed based on a new superstition method. The free vibrations are decomposed into thickness and lateral directions in a new form of Fourier-Bessel series and then they are superimposed to satisfy the boundary conditions. To verify the validity of the analytical model proposed here, numerical simulations are performed using COMSOL Multiphysics. An excellent agreement is observed. This analytical model can be applied to the design and optimization of piezoelectric devices.

Broadband multiple resonant metasurface for mixture surface-enhanced infrared absorption based on polarization-sensitive folded nanoantennas

Multiple resonant metasurfaces for mixture component detection by surface-enhanced infrared absorption in a broadband spectrum region are still highly desirable. This paper presents a polarization-sensitive multi-resonant broadband metasurface in the mid-infrared (MIR) region based on an odd symmetric folded antenna array. Six major resonant modes are effectively excited in 6–15 μm covering the absorption peak of multiple gases and biomolecules. In addition, the calculation indicates the maximum electric field intensity enhancement reaches 3607 and the average electric enhancement factors are dominantly amplified to a maximum of 75.08. The excited multiple hotspots provide more spatial overlap with analytes and would be beneficial for label-free detection. Moreover, owing to the contributions of the intrinsic phonons and polaritons in the ENZ material, the spectroscopy features are relatively stable when changing the geometry parameters and the incident angles, allowing more fabrication tolerance and experiment flexibility. Furthermore, the multiple resonant metasurface is also effectively enabled under orthogonal circular polarizations. Finally, the sensing abilities of the designed metasurface for polyethylene terephthalate and isopropanol molecules have been computationally validated. These results indicate the potential for nanophotonic detection and mixture spectroscopy analysis.

Evaluation of highly sensitive vibration states of nanomechanical resonators in liquid using a convolutional neural network

Nanomechanical resonators can detect various small physical quantities with high sensitivity using changes in resonant properties. However, viscous damping in liquids significantly reduces the measurement sensitivity. This study proposes convolutional neural network (CNN) vibration spectrum analysis to evaluate the highly sensitive vibration states of nanomechanical resonators, which are useful for in-liquid measurements. This research was carried out through the measurement of acetone concentration. First, we compared the concentration classification ability between the proposed and conventional methods and determined that the proposed method of analyzing vibration spectral changes using the CNN model can provide higher measurement sensitivity than the conventional measurement method of observing resonance properties changes and comparing the values for each measurement condition. This result shows that CNN-based spectral analysis is effective for the vibration spectra of in-liquid measurements. Next, gradient-weighted class activation mapping (Grad-CAM) was applied to verify which frequency bands are important for concentration classification in CNN model decision-making. The vibration states in these frequency bands were analyzed in terms of oscillation modes. This analysis revealed significant oscillation modes of the nanomechanical resonator in the liquid environment. Notably, in addition to the resonance states utilized in the conventional method, several other oscillation modes were found to be significant for measurements. This finding suggests that these oscillation modes may be highly sensitive for measurements in liquid environments. Among these oscillation modes, the mode with very small amplitude is highly promising for achieving unprecedented levels of sensitivity in sensing technologies.

Experimental Demonstration of High-Efficiency Harmonic Generation in Photonic Moiré Superlattice Microcavities.

Integrated photonic microcavities have demonstrated powerful enhancement of nonlinear effects, but they face a challenge in achieving critical coupling for sufficient use of incident pump power. In this work, we first experimentally demonstrate that highly efficient third-harmonic generation (THG) and detectable second-harmonic generation (SHG) can be produced from high-Q photonic moiré superlattice microcavities, where a critical coupling condition can be achieved via selecting a magic angle. Furthermore, at the magic angle of 13.17°, critical coupling is satisfied, resulting in a normalized THG conversion efficiency of 136%/W2 at a relatively low peak pump power of 6.8 MW/cm2, which is 3 orders of magnitude higher than the best results reported previously. Our work shows the power of photonic moiré superlattices in enhancing nonlinear optical performances through flexible and feasible engineering resonant modes, which can be applied in integrated frequency conversion and generation of quantum light sources.

Improved performance of temperature sensors based on the one-dimensional topological photonic crystals comprising hyperbolic metamaterials

This paper seeks to progress the field of topological photonic crystals (TPC) as a promising tool in face of construction flaws. In particular, the structure can be used as a novel temperature sensor. In this regard, the considered TPC structure comprising two different PC designs named PC1 and PC2. PC1 is designed from a stack of multilayers containing Silicon (Si) and Silicon dioxide (SiO2), while layers of SiO2 and composite layer named hyperbolic metamaterial (HMM) are considered in designing PC2. The HMM layer is engineered using subwavelength layers of Si and Bismuth Germinate, or BGO (Bi4Ge3O12\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{Bi}}_{4}{\ ext{Ge}}_{3}{\ ext{O}}_{12}$$\\end{document}). The mainstay of our suggested temperature sensor is mainly based on the emergence of some resonant modes inside the transmittance spectrum that provide the stability in the presence of the geometrical changes. Meanwhile, our theoretical framework has been introduced in the vicinity of transfer matrix method (TMM), effective medium theory (EMT) and the thermo-optic characteristics of the considered materials. The numerical findings have extensively introduced the role of some topological parameters such as layers’ thicknesses, filling ratio through HMM layers and the periodicity of HMM on the stability or the topological features of the introduced sensor. Meanwhile, the numerical results reveal that the considered design provides some topological edge states (TESs) of a promising robustness and stability against certain disturbances or geometrical changes in the constituent materials. In addition, our sensing tool offers a relatively high sensitivity of 0.27 nm/°C.

Phonon-Induced Spectral Line Broadening in Dye-Doped Glass in Terms of Resonant Vibrational Modes: Tetra-tert-Butylterrylene in Polyisobutylene

Phonon-Induced Spectral Line Broadening in Dye-Doped Glass in Terms of Resonant Vibrational Modes: Tetra-tert-Butylterrylene in Polyisobutylene

Giant Kerr nonlinearity of terahertz waves mediated by stimulated phonon polaritons in a microcavity chip

Optical Kerr effect, in which input light intensity linearly alters the refractive index, has enabled the generation of optical solitons, supercontinuum spectra, and frequency combs, playing vital roles in the on-chip devices, fiber communications, and quantum manipulations. Especially, terahertz Kerr effect, featuring fascinating prospects in future high-rate computing, artificial intelligence, and cloud-based technologies, encounters a great challenge due to the rather low power density and feeble Kerr response. Here, we demonstrate a giant terahertz frequency Kerr nonlinearity mediated by stimulated phonon polaritons. Under the influences of the giant Kerr nonlinearity, the power-dependent refractive index change would result in a frequency shift in the microcavity, which was experimentally demonstrated via the measurement of the resonant mode of a chip-scale lithium niobate Fabry-Pérot microcavity. Attributed to the existence of stimulated phonon polaritons, the nonlinear coefficient extracted from the frequency shifts is orders of magnitude larger than that of visible and infrared light, which is also theoretically demonstrated by nonlinear Huang equations. This work opens an avenue for many rich and fruitful terahertz Kerr effect based physical, chemical, and biological systems that have terahertz fingerprints.

Optimization of Desired Multiple Resonant Modes of Compliant Parallel Mechanism Using Specific Frequency Range and Targeted Ratios

In this paper, a dynamic optimization method capable of optimizing the dynamic responses of a compliant parallel mechanism (CPM), in terms of its multiple primary resonant modes, is presented. A novel two-term objective function is formulated based on the specific frequency range and targeted ratios. The first term of the function is used to optimize the first resonant mode of the CPM, within a specific frequency range. The obtained frequency value of the first mode is used in the second term to define the remaining resonant modes to be optimized in terms of targeted ratios. Using the proposed objective function, the resonant modes of a CPM can be customized for a specific purpose, overcoming the limitations of existing methods. A 6-degree-of-freedom (DoF) CPM with decoupled motion is synthesized, monolithically prototyped, and investigated experimentally to demonstrate the effectiveness of the proposed function. The experimental results showed that the objective function is capable of optimizing the six resonant modes within the desired frequency range and the targeted ratios. The highest deviation between the experimental results and the predictions among the six resonant modes is found to be 9.42%, while the highest deviation in the compliances is 10.77%. The ranges of motions are found to be 10.0 mm in the translations, and 10.8° in the rotations.

Raman enhancement via double optical resonances in all-dielectric photonic crystal slabs

All-dielectric photonic structures are an important class of substrates in surface-enhanced Raman spectroscopy (SERS), utilizing optical resonant modes to significantly enhance the electromagnetic field and amplify the Raman signals. In this study, we demonstrate the double-resonance approach to realize significant Raman enhancement using all-dielectric photonic crystal (PhC) slab. The double-resonance condition is satisfied by designing optical resonant modes in photonic bands to match frequencies of both excitation laser and Raman signals. By the fabricated PhC slab, the significant enhancement for the Raman signal of silicon is demonstrated. The enhanced Raman signals exhibit a uniform distribution on the PhC slab. The method of Raman enhancement via double optical resonances can advance the field of all-dielectric SERS and holds potential for future SERS applications.

Superscattering engineering through combined resonant modes

Abstract A sub-wavelength particle with a total scattering cross section that exceeds the single channel limit is referred to as a superscatterer, which can provide ability to control light in nanoscale. A variety of superscatter structures have been suggested, most of them are typically constructed with strong forward scattering but minor backscattering. This unusual behavior can be attributed to the superposition of resonant modes in adjacent angular momentum channels. We reveal the mechanism of super backscattering for subwavelength column, which can be formed by recombining non-adjacent resonant modes, as confirmed by our numerical analysis.

Magnetization dynamics in single and trilayer nanowires

We have studied the magnetization dynamics of single Py(t) (t= 20 nm, 50 nm) and trilayer [Py(50)/Pd(tPd)/Py(20)] nanowire arrays fabricated over large areas using deep ultraviolet lithography technique. The dynamic properties are sensitive to the field orientation and magnetic film thicknesses. A single resonant mode corresponding to the excitations at the bulk part of the wire is detected in all the single-layer nanowire arrays. Furthermore, the spacer layer thickness influenced the dynamic properties in trilayer samples due to the different coupling mechanisms. A single resonant mode is observed intPd= 2 nm trilayer nanowires with a sharp frequency jump from 13 GHz to 15 GHz across the reversal regime. This indicates the exchange coupling and the coherence in magnetization precession in the ferromagnetic layers. On the other hand, wires with 10 nm-spacer display two well-resolved modes separated by ∼3 GHz with a gradual change in frequency across the reversal regime from-26mT to-46mT, indicating the presence of long-range dipolar interactions instead of exchange coupling. The spacer layer of the proposed spin-valve-type structure can be tailored for desired microwave splitters or combiners.

Two-Dimensional Exciton Oriented Diffusion via Periodic Potentials.

Excitonic devices operate based on excitons, which can be excited by photons as well as emitting photons and serve as a medium for photon-carrier conversion. Excitonic devices are expected to combine the advantages of both the high response rate of photonic devices and the high integration of electronic devices simultaneously. However, because of the neutral feature, exciton transport is generally achieved via diffusion rather than using electric fields, and the efficient control of exciton flux directionality has always been difficult. In this work, a precisely designed one-dimensional periodic nanostructure (1DPS) is used to introduce periodic strain field along with resonant mode to the WS2 monolayer, achieving exciton oriented diffusion with a 7.6-fold exciton diffusion coefficient enhancement relative to that of intrinsic, while enhancing the excitonic emission intensity by a factor of 10 and reducing exciton saturation threshold power by 2 orders of magnitude. Based on the analysis of the density functional theory (DFT) and the finite-element method (FEM), we attribute the anisotropy of exciton diffusion to exciton funneling induced by periodic potentials, which do not require excessive potential height difference for an efficient oriented diffusion. As a result of resonant emission, the exciton diffusion is dragged into the nonlinear regime owing to the high exciton density close to saturation, which improves the exciton diffusion coefficient and diffusion anisotropy more appreciably.

Spin-to-charge conversion via dual-mode ferromagnetic resonance in Ta/NiFe/FeMn/CoFeB multilayer

The precise engineering of microwave absorption frequencies is of paramount importance in the advancement of spintronic-based RF devices. In the pursuit of this objective, magnetic thin films demonstrate unrivaled efficacy in enabling external modulation of their microwave responses in a reconfigurable manner. Here, we demonstrate dual-frequency ferromagnetic resonance modes and corresponding spin-to-charge conversion efficiency in thin film structures comprising Ta/NiFe/FeMn/CoFeB multilayer. A systematic thickness variation of the NiFe layer (i.e., 4–20 nm) has been undertaken to elucidate the impact on both static and dynamic properties across the multilayer structure. The presence of two distinct magnetic layers manifests in the emergence of two-step magnetic hysteresis loops, which are incorporated with unique resonant modes. The separation between the resonant fields shows tunable properties with excitation frequencies, thereby offering a wide range of reconfigurable operating parameters. The effective damping parameter has shown a decrement with increasing thickness of the NiFe layers. The effective spin mixing conductance for the NiFe layer was found to be 7.4 ± 0.6 nm−2. The spin-to-charge conversion within these structures has been demonstrated through measurements of the inverse spin Hall effect. Systematic thickness variation revealed that the prominent voltage drop was observed in the NiFe layer compared to the CoFeB layer. Considering the opposite spin Hall angles of Ta and FeMn layer, the direction of the spin flow and spin-to-charge conversion efficiency are summarized.

New limit on dark photon kinetic mixing in the 0.2–1.2 μeV mass range from the Dark E-field Radio experiment

We report new limits on the kinetic mixing strength of the dark photon spanning the mass range 0.21−1.24 μeV corresponding to a frequency span of 50–300 MHz. The Dark E-field Radio experiment is a wideband search for dark photon dark matter. In this paper we detail changes in calibration and upgrades since our proof-of-concept pilot run. Our detector employs a wide-bandwidth E-field antenna moved to multiple positions in a shielded room, a low noise amplifier, wideband analog-to-digital converter, followed by a 224-point fast Fourier transform. An optimal filter searches for signals with Q≈106. In nine days of integration, this system is capable of detecting dark photon signals corresponding to a kinetic mixing strength ε several orders of magnitude lower than previous limits. We find a 95% exclusion limit on ε over this mass range between 6×10−15 and 6×10−13, tracking the complex resonant mode structure in the shielded room. Published by the American Physical Society 2024

High-k2eff AlSc0.095N-based two-dimensional coupled mode resonators with transducer design toward 5G application

This paper presents the two-dimensional coupled mode resonators (TCMRs) based on 9.5 % scandium-doped aluminum nitride (AlScN) films. We report the design, fabrication, and characterization of 770 nm-thick AlSc0.095N TCMRs, which utilize the e31 and e33 piezoelectric coefficients to jointly excite the coupled mode with high electromechanical coupling coefficient (k2eff). The TCMRs with different electrical boundary conditions (TCMR-I and TCMR-II) are proposed, and the dependence of the resonant mode on the electrode period was studied. The effect of electrode duty factor (DF) on the resonator performance was explored, and both TCMR-Ⅰ and TCMR-II with DF = 0.5 exhibit the maximum k2eff value. Through measured characterization and simulation analysis, the effect of interdigitated transducer (IDT) thickness on resonator performance was studied. In addition, the equivalent electrical parameters of the prepared resonator were extracted using the MBVD equivalent circuit model. The Qs values of TCMR-Ⅰ and TCMR-II fabricated in this paper can reach 1134 and 165, and the k2eff values can reach 3.5 % and 7.86 %, respectively.

Statistics of Lyapunov exponent in random Fibonacci multilayer

Abstract We numerically investigated the localization properties of band-gap and band-edge modes in a one-dimensional random Fibonacci optical multilayer. The statistics of the Lyapunov Exponent (LE) reveal distinct behaviors of localization effects for band-edge and band-gap modes as a function of disorder strength. In particular, a deviation from the single parameter scaling theory (SPST) of localization was observed within a frequency window corresponding to the band-gap of an ordered Fibonacci multilayer. To provide a physical explanation for the violation of SPST, a close correlation between the frequency distribution of the resonant modes in the band-gap and the variance of the LE has been found. The spatial distribution of resonant modes has been reported and discussed. Finally, the dynamics of the gap closing of the two main band-gaps as a function of the disorder strength has been analyzed.