Resonant Mode Coupling Research Articles

3-DOF ultrasonic elliptical vibration tool holder based on coupled resonance modes for manufacturing micro-groove

This paper reports the innovative design of three degrees of freedom ultrasonic elliptical vibration tool holder (3-DOF UEVTH) based on coupled resonance modes. The purpose of the 3-DOF UEVTH was to fabricate a unique microgroove (μ-groove) pattern compared to traditional cutting (TC). The 3-DOF UEVTH consisted of three key components: a prismatic horn, a backed mass, and a full set of three sandwiched piezo actuators. Modal analysis was applied to determine the 3-DOF UEVTH final dimension. The 3-DOF UEVTH operated in a natural frequency of approximately 24 kHz, which was verified by both simulations and experimental assessments. The 3-DOF UEVTH produced an amplitude on the micro-scale at a resonance frequency of approximately 0.42, 0.5, and 0.6 μm for x-, y- and z-axis directions, respectively. The transient analysis was performed to estimate the 3D-elliptical trajectory, and the device feasibility was examined during microgrooving (μ-grooving) on AISI 1045 material. An excellent topography was obtained using this innovative design.

The Simulation of Resonant Mode and Effective Electromechanical Coupling Coefficient of Lithium Niobate Crystal with Different Orientations

At present, the proportion and role of thin film bulk acoustic wave (FBAR) filters in mobile communication products are becoming more and more obvious due to its higher work frequency and smaller size. As a commonly used piezoelectric material, aluminum nitride (AlN) limits the bandwidth of the FBAR filter because of its small electromechanical coupling coefficient (kt 2) of ~6.5%. On contrast, lithium niobate (LiNbO3, LN) crystals with some certain specific orientations have much better acoustic properties, making this type of material the promising candidate for FBAR applications. In this work, the acoustic resonant mode in LN crystal is analyzed by FEM simulations. In order to obtain the optimal orientations with good longitudinal wave property, Euler angle (EA) method is used to simulate the resonant modes and calculate the corresponding kt 2 of different orientations. Besides, the correctness of EA method has been demonstrated in this work by comparing the displacement change under electrostatic field with the traditional matrix transformation operation depending on the piezoelectric effect. The simulations show that the 43°Y-cut LiNbO3 has a high kt 2 and a pure longitudinal wave vibration mode simultaneously, making this orientation the most proper candidate for FBAR filters application with large bandwidth.

Switchable Metasurface With Broadband and Highly Efficient Electromagnetic Functionality

Electromagnetic metasurface is a kind of artificial electromagnetic structure, which can control the transmission, reflection, polarization and beam of electromagnetic wave within sub-wavelength thickness. Efficiency, bandwidth and dynamic control are very important in the application of metasurface. The bandwidth of electromagnetic transparency can be broadened by interlayer coupling of local resonance modes of the stacked layers. In this paper, we propose that the electromagnetic wave could be switched on or off in a broadband frequency range by metasurface which consists of three layers of metal microstructures with PIN diodes. When the diodes are biased with forward voltage, the switching diodes are in the on state, and the slab reflects electromagnetic wave completely, just like a perfect metal. When the diodes are biased with backward voltage, the switching diodes are equivalent to a capacitor, and all the electromagnetic wave energy passes through the sample. The simulation results show that the transmissivity is less than 1% when the sample is loaded with forward voltage in the frequency range of 8-12GHz, while the transmittance is more than 96% when the sample is loaded with reverse bias. We have fabricated the corresponding samples and measured the reflection and transmission in the waveguide. The measurements verify the properties of broadband highly efficient electromagnetic transparency and perfect reflection.

Solving locomotive wheel polygonisation by reducing variable frequency drive interharmonics

Severe vibrations and an increase in structural component fatigue failures have been observed on a freight locomotive class operating in South Africa. The cause of the severe vibration was linked to polygonal wheel wear dominated by the 20th order. This locomotive is powered by an alternating current traction system, which is controlled by a variable frequency drive. The variable frequency drive generates interharmonics that produce torque pulsations in the torque output from the motors. Interharmonics are determined by the alternating current supply frequency ([Formula: see text]) and the fundamental frequency ([Formula: see text]) of the variable frequency drive. The interference of the torque pulsations with a coupled resonance mode is reaffirmed as the root cause of the polygonal wheel wear. An experimental investigation of this phenomenon was performed by means of on-track testing. It was found that the [Formula: see text] interharmonic excited the coupled resonance mode at approximately 42 km/h, which fixes the 20th-order polygon on the wheel. Two approaches that may eliminate the polygonal wheel wear were introduced and discussed. It was found that the forced excitation of the coupled mode by the [Formula: see text] interharmonic could be avoided by postponing the speed where the alternating current traction motor's pulse mode changed.

Double-wavelength nanolaser based on strong coupling of localized and propagating surface plasmon

We theoretically demonstrate a kind of plasmon coupled cavity to achieve a nanolaser with high intensity and low threshold. The plasmon cavity is composed of the gold film substrate and gold disk array, which supports two strong coupled resonance modes (i.e. surface plasmon polariton (SPP) and localized surface plasmon (LSP)). Compared with the nanolaser with the LSP resonance structure, the scattering cross-section of the LSP-SPP coupled laser is 80 times higher. The coupled cavity nanolaser with different wavelengths can be excited with different plasmon resonance modes by selecting the appropriate gain medium. In addition, a compact tunable dual-wavelength laser can be developed using this coupled structure.

Resonant mode coupling in hybrid all-dielectric metamaterial

We present a theoretical study of resonant mode coupling in hybrid all-dielectric metamaterial consisting of inner cylinder and outer hollow cylinder. The resonant mode coupling of these two resonators is comprehensively analyzed by tracking the transmission spectrum variations and electromagnetic field distributions at resonance frequencies. It is found that the electromagnetic properties of the hybrid metamaterial are fully determined by the interaction of the resonant modes. Moreover, we achieve the mechanical tunability of the metamaterial based on the coupling of the magnetic resonances and show that the transmission of our metamaterial can be continuously modulated from −1.51 dB to −21.81 dB. The simulation results are well produced by a coupled oscillator model, providing a valuable insight into the coupling mechanism of our system.

Bifurcation diagram and dynamic response of a MEMS resonator with a 1:3 internal resonance

The dynamic response of a nonlinear resonator in the presence of resonant mode coupling is studied experimentally and theoretically. For the case of a clamped-clamped beam resonator in the presence of a 1:3 internal resonance, we show that at the onset of internal resonance, steady state oscillations cannot be sustained. At higher drive levels, stable oscillations can be maintained but the resonator amplitude undergoes amplitude modulated responses. We use these dynamic responses to build a bifurcation diagram that can be described remarkably well with a simple model consisting of a Duffing resonator coupled to a linear one.

Broadband Absorption Tailoring of SiO2/Cu/ITO Arrays Based on Hybrid Coupled Resonance Mode.

Sub-wavelength artificial photonic structures can be introduced to tailor and modulate the spectrum of materials, thus expanding the optical applications of these materials. On the basis of SiO2/Cu/ITO arrays, a hybrid coupled resonance (HCR) mechanism, including the epsilon-near-zero (ENZ) mode of ITO, local surface plasmon resonance (LSPR) mode and the microstructural gap resonance (GR) mode, was proposed and researched by systematically regulating the array period and layer thickness. The optical absorptions of the arrays were simulated under different conditions by the finite-difference time-domain (FDTD) method. ITO films were prepared and characterized to verify the existence of ENZ mode and Mie theory was used to describe the LSPR mode. The cross-sectional electric field distribution was analyzed while SiO2/Cu/ITO multilayers were also fabricated, of which absorption was measured and calculated by Macleod simulation to prove the existence of GR and LSPR mode. Finally, the broad-band tailoring of optical absorption peaks from 673 nm to 1873 nm with the intensities from 1.8 to 0.41 was realized, which expands the applications of ITO-based plasmonic metamaterials in the near infrared (NIR) region.

Bifunctional resonance effects of classical electromagnetically induced transparency and Fano response using a terahertz metamaterial resonator.

A terahertz metamaterial resonator consisting of two rectangular strips embedded in a closed-ring resonator is designed and investigated in this paper that can simultaneously generate the classical electromagnetically induced transparency effect and two Fano resonance modes. The formation of the transparent window and the Fano dips can be attributed to the coupling of the localized resonance modes between the closed-ring resonator and the two embedded rectangular strips. The effect of embedded rectangular strip sizes on the transmitted performance is discussed, and it is found that the resonant performance of the transparent window and Fano effect depends mainly on the length of the rectangular strips in the longitudinal direction. Based on this, two different device applications related to the embedded rectangular strips are discussed. The metamaterial proposed here could open up new avenues toward the control of terahertz waves in many technology-related areas.

Built-up structural steel sections as seismic metamaterials for surface wave attenuation with low frequency wide bandgap in layered soil medium

The purpose of this work is to investigate the propagation of surface waves through periodically arranged built-up steel section (resonator) in single and multiple layered soil medium (substrate) and to study the feasibility of surface waves attenuation by finite element technique. Two types of simple and small geometric size built-up sections are taken into consideration. Due to occurrence of local resonance between resonator and surface waves propagating on the surface of semi-infinite substrate, low frequency wide bandgaps are reported. Generation of local resonance is mainly governed by (i) impedance mismatch between the resonator and substrate (ii) coupling of longitudinal resonance modes of resonator with surface waves propagating on the surface of semi-infinite substrate. To have a more general and realistic study, surface wave propagation in single and six-layered soil medium is considered and the bandgaps are compared. Furthermore, with the variation in geometrical configuration of built-up section and change in material properties (soil profile), bandgap width and location changes. In the case of a layered soil medium, a relative bandwidth greater than 1.5 for both types of resonator is achieved. This implies that the proposed built-up sections are capable of attenuating surface waves in an extremely low frequency range. The position and width of bandgaps are further validated through finite unit cell based frequency response and time transient analyses. The findings substantiate the infinite unit cell model proposed here with the conclusion of more than 50% reduction in surface wave amplitude. The feasibility study manifests that the built-up structural steel sections can be applied as resonant barriers for mitigating seismic waves to protect important civil infrastructures from earthquake hazards.

Reshaping the Second-Order Polar Response of Hybrid Metal-Dielectric Nanodimers.

We combine the field confinement of plasmonics with the flexibility of multiple Mie resonances by bottom-up assembly of hybrid metal-dielectric nanodimers. We investigate the electromagnetic coupling between nanoparticles in heterodimers consisting of gold and barium titanate (BaTiO3 or BTO) nanoparticles through nonlinear second-harmonic spectroscopy and polarimetry. The overlap of the localized surface plasmon resonant dipole mode of the gold nanoparticle with the dipole and higher-order Mie resonant modes in the BTO nanoparticle lead to the formation of hybridized modes in the visible spectral range. We employ the pick-and-place technique to construct the hybrid nanodimers with controlled diameters by positioning the nanoparticles of different types next to each other under a scanning electron microscope. Through linear scattering spectroscopy, we observe the formation of hybrid modes in the nanodimers. We show that the modes can be directly accessed by measuring the dependence of the second-harmonic generation (SHG) signal on the polarization and wavelength of the pump. We reveal both experimentally and theoretically that the hybridization of plasmonic and Mie-resonant modes leads to a strong reshaping of the SHG polarization dependence in the nanodimers, which depends on the pump wavelength. We compare the SHG signal of each hybrid nanodimer with the SHG signal of single BTO nanoparticles to estimate the enhancement factor due to the resonant mode coupling within the nanodimers. We report up to 2 orders of magnitude for the SHG signal enhancement compared with isolated BTO nanoparticles.

On-chip hybrid demultiplexer for mode and coarse wavelength division multiplexing

We propose a hybrid demultiplexer for mode and coarse wavelength division multiplexing on silicon-on-insulator (SOI) nanowires and photonic crystal (PhC) slab. First, a V-shape waveguide–cavity–waveguide filter based on PhC slab is presented. Coupling of resonant modes is introduced to the filter to suppress the crosstalk caused by connection with nanowires. Then, we cascade and optimize the filter to compose a coarse wavelength division demultiplexer. After that, a hybrid demultiplexer is constructed by combining the coarse wavelength division demultiplexer on PhC slab and mode division demultiplexer on SOI nanowires. The parameters of the hybrid demultiplexer are calculated using three-dimensional finite-difference time-domain (3D-FDTD) method. The numerical results show that the fundamental transverse electric ( $$\hbox {TE}_0$$ ) modes and the first-order TE ( $$\hbox {TE}_1$$ ) modes of 1530 nm and 1550 nm can be demultiplexed. The insertion loss is smaller than 2.0 dB, and the channel crosstalk is less than − 25 dB. The hybrid demultiplexer can be applied in a system that using mode and coarse wavelength division multiplexing simultaneously.

Strong coupling between magnetic plasmons and surface plasmons in a black phosphorus-spacer-metallic grating hybrid system.

We propose a black phosphorus-spacer-metallic grating hybrid system to investigate the strong coupling between black phosphorus surface plasmons (BPSP) and magnetic plasmons (MP) at far-infrared frequencies. We theoretically and numerically illustrate interactions between the BPSP mode and MP mode in the coupling regime, which leads to a prominent Rabi splitting and the formation of multiple hybrid modes. Since the mechanisms of the two resonance modes are completely different, the fields in the system can be selectively localized in the spacer layer or metallic slits by regulating the coupling between such modes. Due to the strong anisotropic in-plane properties of black phosphorus (BP), the coupling between BPSP and MP modes in both armchair and zigzag directions is quite different. This work offers a new paradigm to enhance the light-matter interaction through the coupling of multiple resonance modes, and the proposed device will provide potential applications in constructing easy-to-fabricate BP-based plasmonic devices.

Design of Dual-Band Plasmon-Induced Transparent Effect Based on Composite Structure of Closed-Ring and Square Patch

We propose a dual-band transparent window terahertz metamaterial consisting of a closed-ring resonator and a square patch. This structure can achieve two transparent windows with transmission intensity of more than 90%. The formation of the two windows can be attributed to the coupling of the localized resonance modes between the closed-ring and square patch. The influence of the geometrical dimensions of the closed-ring resonator and the square patch on the transmitted spectrum is also discussed; it is found that the change of sizes can strongly affect the frequencies of the two transparent windows. This novel terahertz metamaterial may open up new avenues toward the control of terahertz waves in many technology-related areas.

Subwavelength and quasi-perfect underwater sound absorber for multiple and broad frequency bands.

A structure for an underwater sound absorber with subwavelength thickness and a quasi-perfect absorption property at multiple frequency bands is reported. This absorber consists of a viscoelastic coating layer embedded with periodically distributed plate scatterers (PSs). The embedded PSs cannot only slow sound waves in the coating, leading to a down-shifted resonance frequency where the absorption is maximized, but also introduce multiple local bending modes and local longitudinal modes in the coating. Via proper selection of the parameters of the PSs and the PS array, multiple local resonance modes of different types in a coating unit can be excited, resulting in quasi-perfect absorption of incident sound at multiple frequencies whose wavelengths are much longer than the thickness of the coating layer. For example, absorption (89%) of underwater sound at 462.9 Hz is achieved by such a layer with a thickness of 6 cm, which is 1.9% of the wavelength of the incident sound. Broadband quasi-perfect absorption can also be realized by coupling of those multiple local resonant modes. This quasi-perfect absorption property can also be observed for sound waves with different incident angles, because a large number of local intrinsic modes could still be excited.

Bimetallic Network with Hetero‐interfacial Plasmons

AbstractFabrication of bimetallic networks consisting of periodically arranged gold nanoparticles (AuNPs) embedded with a grid of silver nanowires, where solution‐processing materials or techniques are involved in all of the fabrication procedures, is reported. Annealing of the colloidal gold nanoparticles and the photoreduction of the silver ions in the mixture solution of AgNO3 and polyvinyl pyrrolidone in water are the main processes. The key to this fabrication is that the AuNP array is used as the mask for the photoreduction of silver ions into nanowires, where the silver nanowires are thus located between the AuNPs. Two sets of dipolar and quadrupolar plasmons, as well as their respectively coupled resonance modes, are observed in the measurements and specified using theoretical analysis. Thus, the bimetallic photonic structures not only show enhanced and extended resonance spectrum due to the overlap of multiple localized surface plasmons but also induce plasmonic hetero‐interfacial interaction between the closely adjacent AuNPs and silver nanowires.

The Delta Scuti star 38 Eri from the ground and from space

We present and discuss the pulsational characteristics of the Delta Scuti star 38 Eri from photometric data obtained at two widely spaced epochs, partly from the ground (1998) and partly from space (MOST, 2011). We found 18 frequencies resolving the discrepancy among the previously published frequencies. Some of the frequencies appeared with different relative amplitudes at two epochs, however, we carried out investigation for amplitude variability for only the MOST data. Amplitude variability was found for one of three frequencies that satisfy the necessary frequency criteria for linear-combination or resonant-mode coupling. Checking the criteria of beating and resonant-mode coupling we excluded them as possible reason for amplitude variability. The two recently developed methods of rotational-splitting and sequence-search were applied to find regular spacings based only on frequencies. Doublets or incomplete multiplets with l=1, 2 and 3 were found in the rotational splitting search. In the sequence search method we identified four sequences. The averaged spacing, probably a combination of the large separation and the rotational frequency, is 1.724+/-0.092 d-1. Using the spacing and the scaling relation $\bar\rho = [0.0394, 0.0554]$ gcm$^{-3}$ was derived. The shift of the sequences proved to be the integer multiple of the rotational splitting spacing. Using the precise MOST frequencies and multi-colour photometry in a hybrid way, we identified four modes with l=1, two modes with l=2, two modes with l=3, and two modes as l=0 radial modes.

Liquid crystal mediated active nano-plasmonic based on the formation of hybrid plasmonic-photonic modes

The present study aims to demonstrate how active hybrid nano-plasmonic modes become excited due to the coupling of localized plasmonic resonance and Fabry-Perot (FP) optical modes. The proposed structure includes an integration of a micro-cavity filled with liquid crystals with high anisotropy and a layer of gold nanoislands (NIs). The optical absorption of NI is controllably discretized to the narrow-width modes, called “hybrid modes (HM),” due to the interplay between FP and plasmonic modes. HM could demonstrate a strongly intensified and diminished absorption, compared to the absorption of the bare gold layer. Based on the active plasmonic experiments, the HM boosted the figure of merit related to activation capability up to 40 times and subsequently experienced impressive spectral shifts, leading to very wavelength-selective changes. The theoretical simulation of the HM is provided to suggest relevant insights into the experimental results.

Oscillation Mode Variability in Evolved Compact Pulsators from Kepler Photometry. I. The Hot B Subdwarf Star KIC 3527751

Abstract We present the first results of an ensemble and systematic survey of oscillation mode variability in pulsating hot B subdwarf (sdB) and white dwarf stars observed with the original Kepler mission. The satellite provides uninterrupted high-quality photometric data with a time baseline that can reach up to 4 yr collected on pulsating stars. This is a unique opportunity to characterize long-term behaviors of oscillation modes. A mode modulation in amplitude and frequency can be independently inferred by its fine structure in the Fourier spectrum, from the sLSP, or with prewhitening methods applied to various parts of the light curve. We apply all these techniques to the sdB star KIC 3527751, a long-period-dominated hybrid pulsator. We find that all the detected modes with sufficiently large amplitudes to be thoroughly studied show amplitude and/or frequency variations. Components of three identified quintuplets around 92, 114, and 253 μHz show signatures that can be linked to nonlinear interactions according to the resonant mode coupling theory. This interpretation is further supported by the fact that many oscillation modes are found to have amplitudes and frequencies showing correlated or anticorrelated variations, a behavior that can be linked to the amplitude equation formalism, where nonlinear frequency corrections are determined by their amplitude variations. Our results suggest that oscillation modes varying with diverse patterns are a very common phenomenon in pulsating sdB stars. Close structures around main frequencies therefore need to be carefully interpreted in light of this finding to secure a robust identification of real eigenfrequencies, which is crucial for seismic modeling. The various modulation patterns uncovered should encourage further developments in the field of nonlinear stellar oscillation theory. It also raises a warning to any long-term project aiming at measuring the rate of period change of pulsations caused by stellar evolution, or at discovering stellar (planetary) companions around pulsating stars using timing methods, as both require very stable pulsation modes.

Spectral Control of Near-Field Thermal Radiation With Periodic Cross Resonance Metasurfaces

Near-field thermal spectra can be engineered using periodic cross resonance metasurfaces. Structures consisting of single crosses, double crosses, and multiple crosses are proposed to control the spectral heat flux from narrow band to broadband with the Fabry-Perot-cavity-like effect and the interaction between the emitter and receiver. Radiation peaks originating from the cross structures split into two adjacent peaks in the near-field, due to the separate contributions of s- and p-polariton modes. Their frequency can be manipulated by adjusting the length of the crosses. Multiple radiation peaks can be generated by double crosses, and due to the strong coupling of resonance modes, multiple crosses can yield a broadband thermal spectrum ranging from 100-180 THz, with the total heat flux two orders of magnitude above the blackbody limit. The inherent physical mechanisms are illustrated by analyzing the energy transmission coefficients of the cross structures. The features of the radiation peaks and spectra are robust to the change of the gap distance or the temperature, which is advantageous for both the experimental design and fabrication of thermal radiation devices.