Multiple Resonant Peaks Research Articles

A square-framed ME composite with inherent multiple resonant peaks for broadband magnetoelectric response

A square-framed ME composite with inherent multiple resonant peaks for broadband magnetoelectric response

Magnetic properties and high frequency characteristics of isotropic FeCoZr thin films with stripe domains

Magnetic properties and high frequency characteristics of (Fe70.6Co29.4)100−xZrx (x = 4.0 − 18.2 at.%) thin films have been investigated. The saturation magnetization 4πM s decreases continuously from 21.7 kGs for x = 4.0 at.% to 12.2 kGs for x = 18.2 at.% and it is consistent with the decreasing of Fe-Co composition. It is found that the films show nearly isotropic magnetic behavior in the film plane for the Zr content ranging from 7.2 to 18.2 at.%. These films exhibit a weak perpendicular magnetic anisotropy with coercivity values of 24–67 Oe. Meanwhile, the in-plane isotropic FeCoZr films show a good high frequency response of permeability. In particular, the film with x = 7.2 at.% shows a resonance frequency of 2.8 GHz along the direction perpendicular to the stripe domain axis. The permeability spectra of the thin films with higher Zr content display multiple resonance peaks, which may be due to the perpendicular magnetic anisotropy induced by the stress.

Transformative Heterointerface Evolution and Plasmonic Tuning of Anisotropic Trimetallic Nanoparticles.

Multicomponent nanoparticles that incorporate multiple nanocrystal domains into a single particle represent an important class of material with highly tailorable structures and properties. The controlled synthesis of multicomponent NPs with 3 or more components in the desired structure, particularly anisotropic structure, and property is, however, challenging. Here, we developed a polymer and galvanic replacement reaction-based transformative heterointerface evolution (THE) method to form and tune gold-copper-silver multimetallic anisotropic nanoparticles (MAPs) with well-defined configurations, including structural order, particle and junction geometry, giving rise to extraordinarily high tunability in the structural design, synthesis and optical property of trimetallic plasmonic nanoantenna structures. MAPs can easily, flexibly integrate multiple surface plasmon resonance (SPR) peaks and incorporate various plasmonic field localization and enhancement within one structure. Importantly, a heteronanojunction in these MAPs can be finely controlled and hence tune the SPR properties of these structures, widely covering UV, visible and near-infrared range. The development of the THE method and new findings in synthesis and property tuning of multicomponent nanostructures pave ways to the fabrication of highly tailored multicomponent nanohybrids and realization of their applications in optics, energy, catalysis and biotechnology.

Thickness dependence of the magnetic anisotropy and dynamic magnetic response of ferromagnetic NiFe films

We investigate the thickness dependence of the magnetic anisotropy and dynamic magnetic response of ferromagnetic NiFe films. We go beyond quasi-static measurements and focus on the dynamic magnetic response by considering three complementary techniques: the ferromagnetic resonance, magnetoimpedance and magnetic permeability measurements. We verify remarkable modifications in the magnetic anisotropy, i.e. the well-known behavior of in-plane uniaxial magnetic anisotropy systems gives place to a complex magnetic behavior as the thickness increases, and splits the films in two groups according to the magnetic properties. We identify magnetoimpedance and magnetic permeability curves with multiple resonance peaks, as well as the evolution of the ferromagnetic resonance absorption spectra, as fingerprints of strong changes of the magnetic properties associated to the vanishing of the in-plane magnetic anisotropy and to the emergence of non-homogeneous magnetization configuration, local anisotropies and out-of-plane anisotropy contribution arisen as a consequence of the non-uniformities of the stress stored in the film as the thickness is increased and/or to the columnar growth of the film. We interpret the experimental results in terms of the structural and morphological properties, quasi-static magnetic behavior, magnetic domain structure and different mechanisms governing the magnetization dynamics at distinct frequency ranges.

High frequency magnetic properties of multistriped patterned FeCoBSi thin films

Abstract A series of multistripe patterned FeCoBSi thin films were fabricated by DC magnetron sputtering and traditional lithography lift-off technology. A broadened band spectrum was observed attributable to the existence of multiple resonances in accordance with a predictive LLG model. It is assumed that separate resonances are ascribed to the shape anisotropy induced by the different widths of magnetic stripes. Meanwhile, the broadened resonance band, due to the superpositioning of multiple resonance peaks, may pave the way for future applications as wide-band microwave EMI absorbers.

多共振峰圆形光栅滤波器

多共振峰圆形光栅滤波器

Broadband noise attenuation using a variable locally reacting impedance.

Passive control of low-frequency duct noise remains a technical challenge. Traditional noise control devices are either overly bulky or too narrowband. A broadband attenuation mechanism inspired by the mammalian cochlea is presented in this theoretical study. It consists of a parallel arrangement of an array of multiple beams or stretched strips backed by a cavity. The structure vibrates strongly in response to the broadband incident noise and hence creates substantial reflection. If both the media in the cavity and the duct are air, the mass-like load from the fluid in the cavity suppresses the response of the structure and thus lowers the transmission loss. If helium, or some other gas with lower density than air in the duct, fills the cavity, the mass-like reactance of the cavity is reduced and the silencing performance is improved. Then such a silencer can achieve a satisfactory attenuation performance at low frequency range. Multiple adjacent resonant peaks are found in the transmission loss curve and such a silencer has superiority in size and acoustic performance over expansion chamber and duct lining.

Packaged Optical Add-Drop Filter Based on an Optical Microfiber Coupler and a Microsphere

In this letter, a packaged add-drop filter composed of a silica microsphere resonator with a diameter of $80~\mu \text{m}$ and an optical microfiber coupler with a waist diameter of 1 $\mu \text{m}$ is investigated. A one-step fabrication process using UV curable epoxy is shown to stabilize the coupling between the microsphere and the microfiber coupler, which is used for the add and drop ports. The packaged microsphere-microfiber coupler device has a high $Q$ -factor of $1\times 10^{7}$ in the add–drop filter configuration. This device has excellent features, such as improved ease of fabrication, multiple resonant peaks, and high mechanical stability.

Broadband vibration control of a structure by using a magnetorheological elastomer-based tuned dynamic absorber

A passive dynamic vibration absorber (DVA) is a mass-spring system that suppresses the vibration of a structure at a particular frequency. The DVA is especially effective when its excitation frequency is close to its tuned frequency. Fixing the physical properties of the DVA limits the application to a narrowband, harmonically excited vibration problem. A frequency-tunable DVA that can modulate its stiffness provides adaptability to the vibration control device against non-stationary disturbances. In this paper, we suggest a broadband frequency-tunable DVA whose natural frequency can be extended to more than 300% of the base value by using magnetorheological elastomers. We first conducted a magnetic field analysis by using a finite element method, through which the formation of a strong magnetic field within the core was observed. By taking full advantage of the frequency adjustability of the proposed DVA, we evaluated the real-time vibration control performance for an acoustically excited plate having multiple resonant peaks. The results show that the vibration of the structure can be effectively reduced with an improved performance by using a DVA instead of a passive absorber.

A broadband frequency-tunable dynamic absorber for the vibration control of structures

A passive-type dynamic vibration absorber (DVA) is basically a mass-spring system that suppresses the vibration of a structure at a particular frequency. Since the natural frequency of the DVA is usually tuned to a frequency of particular excitation, the DVA is especially effective when the excitation frequency is close to the natural frequency of the structure. Fixing the physical properties of the DVA limits the application to a narrowband, harmonically excited vibration problem. A frequency-tunable DVA that can modulate its stiffness provides adaptability to the vibration control device against non-stationary disturbances. In this paper, we suggest a broadband frequency-tunable DVA whose natural frequency can be extended by 300% to the nominal value using the magnetorheological elastomers (MREs). The frequency adjustability of the proposed absorber is first shown. The real-time vibration control performance of the frequency-tunable absorber for an acoustically excited plate having multiple resonant peaks is then evaluated. Investigations show that the vibration of the structure can be effectively reduced with an improved performance by the DVA in comparison to the conventional passive- type absorber.

The Radioelectric effect in doped superlattices under the influence of confined phonon

The Radioelectric effect in doped superlattices under the influence of confined phonon has been theoretically studied. The analytical expression for the Radioelectric field is obtained by quantum kinetic equation method. The theoretical expression shows that the Radioelectric field in doped superlattices depends on the frequencies and amplitudes of the laser and the linearly polarized electromagnetic wave, the period of the superlattices and especially the quantum number m characterizing the phonon confinement. Numerical calculation is also applied for GaAs:Si/GaAs:Be doped superlattices. It is found that the Radioelectric field is different from that in the normal bulk semiconductor as well as two-dimensional systems in case of unconfined phonon and in case of confined phonon when the contribution of confined potential of doped superlattices and confined phonon is remarkable. The Radioelectric field has multiple resonance peaks and increases as the increasing of quantum number m.

Optical properties of local surface plasmon resonance in Ag/ITO sliced nanosphere by the discrete dipole approximation

Optical properties of localized surface plasmon resonances (LSPR) of Ag/ITO sliced nanosphere have been studied using discrete dipole approximation and plasmon hybridization theory. It is found that different morphologies of sliced nanosphere can induce distinctive features in the extinction spectra. In the meanwhile, gap distances and refractive index of the surrounding medium could modulate the plasmon hybridization and the LSPR shifting. At large separation, the shift of LSPR peaks for the nanosphere sliced in halves consisting of ITO and Ag is small and insensitive to the gap distance in the weak coupling, whereas smaller separation exhibits a distinct red shift. Additionally, multiple resonance peaks are excited for the nanosphere sliced in quarters consisting of ITO and Ag. In this situation, electric field is mainly distributed in the gap region of sliced nanosphere and the central point. These results indicate that different morphologies of sliced nanosphere could create abundant tunable LSPR modes, which provides potential for multiplex optical sensing.

Zero-bias-field microwave dynamic magnetic properties in trapezoidal ferromagnetic stripe

Dynamic magnetization response of the axially magnetized ferromagnetic stripe with trapezoidal cross section has been studied. The stripe with beveled edges exhibits multiple resonant peaks modes under an in-plane microwave excitation compared with the single resonant of vertical edge surfaces. The complexity of the observed response is attributed to the spatially nonuniform equilibrium spin distribution at the stripe edges. Micromagnetic simulations identify spin waves as spatially localized mode at the modified edges. This one is also described by effective pinning boundary conditions taking into account finite-size effects, which is related to the exchange interaction, surface anisotropy and dipole–dipole interaction. These results provide detailed insights into the nonlinear spin dynamics of microstructures influenced by the edge properties.

Resonance transmission of one-dimensional quantum walk with phase defects

In this paper, the resonance transmission of discrete time quantum walk is studied when it walks on one-dimensional lattice in which two-phase defects or a piece of phase defects exists. The quasi energy of discrete time quantum walk has a unique dispersion relation with the momentum, from which we first discuss the wave velocity direction versus the values of momentum, and distinguish the incident wave and the reflected wave. The gap between two energy bands depends on the parameters of coincident operator, so the phase defects, which break down the translation invariance of quantum walk on uniform lattices, can be regarded as an analogue of quantum potential. Then we use the condition of energy conversion at the boundary points to obtain the transmission rate and discuss its variation with the incident momentum for different strengths and widths of defects in detail. The multiple resonant peaks are observed due to the enhanced interference effect. Different resonant behaviors are shown when the strength of defect is less or greater than /2, correspondingly the resonances occur in a wide region of incident momentum or the sharp resonant peaks appear at discrete values of momentum. Under the condition of strong defect strength, i.e., approaching to , the qualitative relation between the number of resonant peaks and the widths of defect region is given. The number of resonant peaks is 2(N-1) when the two phase defects are located at N sites symmetric about the origin, while the number is 2N when a piece of phase defects is located at -N to N sites. In the case of a piece of phase defects, we also present the phase diagram in parameter space of (k, ) to show the discrete time of quantum walk propagating or tunneling through the defect region. In terms of this phase diagram, the variations of transmission rate with the incident momentum are reasonably explained. One special phenomenon is that the quantum walk is almost totally reflected in the tunneling case except for =/2 and k being slightly off -/2. Moreover, this behavior seems little affecting the defect strength, just similar to a classical particle. As a result of this research, we hope to deepen the insight of the quantum walk and provide methods to control the spreading of quantum walk through artificial defects.

The hierarchical three-dimensional cobalt superstructure: Controllable synthesis, electromagnetic properties and microwave absorption

A close-packed hexagonal (HCP)-cobalt superstructure was synthesized on a large scale through a simple, yet low-cost liquid reduction method. The cobalt superstructure was assembled by nanoflakes with strong shape anisotropy. The permittivity (εr=ε′-jε″) and permeability (μr=μ′-jμ″) of cobalt superstructure were also studied as a function of frequency in microwave range of 1–18GHz. It is demonstrated that permittivity displays remarkable multiple dielectric resonance peaks. Multiple magnetic resonances were also exhibited for permeability, which were discussed based on the LLG equation and exchange resonance mode. Multiple dielectric and magnetic resonances were beneficial to widen microwave absorption bandwidth. The calculated reflection loss (RL) indicated that the cobalt superstructure had potential application as a promising candidate for microwave absorption. The reflection loss was attributed to two main reasons, one is the destructive interference, which was related to the thickness of the absorbent layer, and the other one was multiple microwave reflection due to the structure assembled by nanoflakes.

Active vibration suppression of membrane structures and evaluation with a non-contact laser excitation vibration test

To realize a vibration suppression of flexible structures like a membrane, our research focuses on introducing smart structures technology into the membrane structure. In this study, the membrane structure is composed of a vibration control system using a flexible Polyvinylidene fluoride (PVDF) film as an actuator. A non-contact vibration test system, which uses a high power Nd: YAG pulse laser for producing an ideal impulse excitation and laser Doppler vibrometers for measuring the response on the membrane, is employed to evaluate the vibration characteristics of the smart membrane structure. To confirm the effectiveness of the proposed method, using a flexible PVDF actuator installed on the membrane structure, control experiments with H ∞ control for reducing single mode and multiple modes vibration are conducted. In the results of the control experiments for single mode vibration suppression, a corresponding resonance peak is reduced by around 20 dB. In case of multiple modes vibration suppression, the first and second resonance peaks are reduced by 14 dB and 24 dB, respectively. This study demonstrates that the present control method using a flexible piezoelectric element and a non-contact vibration test system effectively suppress and evaluate the vibration responses of smart membrane structures.

Tunable multiple plasmon resonances and local field enhancement of nanocrescent/nanoring structure**Project supported by the National Natural Science Foundation of China (Grant Nos. 61275153 and 61320106014), the Natural Science Foundation of Zhejiang Province, China (Grant No. LY12A04002), the Natural Science Foundation of Ningbo City, China (Grant Nos. 2010D10018 and 2012A610107), and the K. C. Wong Magna Foundation of Ningbo University, China.

According to the plasmon hybridization theory, the plasmon resonance characteristics of the gold nanocrescent/nanoring (NCNR) structure are systematically investigated by the finite element method. It is found that the extinction spectra of NCNR structure exhibit multiple plasmon resonance peaks, which could be attributed to the result of the plasmon couplings between the multipolar plasmon modes of nanocrescent and the dipolar, quadrupolar, hexapolar, octupolar, decapolar plasmon modes of nanoring. By changing the geometric parameters, the intense and separate multiple plasmon resonance peaks are obtained and can be tuned in a wide wavelength range. It is further found that the plasmon coupling induces giant multipole electric field enhancements around the tips of the nanocrescent. The tunable and intense multiple plasmon resonances of NCNR structure may provide effective applications in multiplex biological sensing.

Negative differential resistance in boron nitride graphene heterostructures: physical mechanisms and size scaling analysis.

Hexagonal boron nitride (hBN) is drawing increasing attention as an insulator and substrate material to develop next generation graphene-based electronic devices. In this paper, we investigate the quantum transport in heterostructures consisting of a few atomic layers thick hBN film sandwiched between graphene nanoribbon electrodes. We show a gate-controllable vertical transistor exhibiting strong negative differential resistance (NDR) effect with multiple resonant peaks, which stay pronounced for various device dimensions. We find two distinct mechanisms that are responsible for NDR, depending on the gate and applied biases, in the same device. The origin of first mechanism is a Fabry-Pérot like interference and that of the second mechanism is an in-plane wave vector matching when the Dirac points of the electrodes align. The hBN layers can induce an asymmetry in the current-voltage characteristics which can be further modulated by an applied bias. We find that the electron-phonon scattering suppresses the first mechanism whereas the second mechanism remains relatively unaffected. We also show that the NDR features are tunable by varying device dimensions. The NDR feature with multiple resonant peaks, combined with ultrafast tunneling speed provides prospect for the graphene-hBN-graphene heterostructure in the high-performance electronics.

Features of Local Electric Field Excitation in Asymmetric Nanocross Illuminated by Ultrafast Laser Pulse

Features of the asymmetric nanocross including extinction spectrum, local electric field intensity, and temporal response of the local electric field under ultrashort laser illumination are investigated in this paper. It is found that, due to the simultaneous excitation of local electric fields in the arms that are perpendicular and parallel to the laser polarization direction of the asymmetric nanocross, extinction spectrum exhibits multiple resonant peaks and the position of the peaks can be tuned by changing the lengths of the arms. Simulation results disclose that there is a strong connection between optical response of the parallel and perpendicular arms. Moreover, temporal response of electric field in arms of the asymmetric nanocross shows that oscillations in the parallel arms start earlier than that of the perpendicular arms, and they are in phase when one of the parallel arms resonantly excited, which further reflects the relationship between the parallel and perpendicular arms. Therefore, we demonstrate that the perpendicular arm excitation is attributed to that of the nonresonant parallel arm in the asymmetric structure which cannot keep the overall electric neutrality of the nanostructure, and thus, perpendicular arms are activated to maintain this balance.

A broadband terahertz absorber using multi-layer stacked bars

We present the simulation, implementation, and measurement of a broadband terahertz (THz) metamaterial absorber. By stacking 12 metallic bars of varying lengths on three polyimide layers with equal spacing, a broadband absorption spectrum is formed through merging multiple successive resonance peaks. The measured total absorption exceeds 95% from 0.81 to 1.32 THz at the normal incidence and the full width at half maximum is 64% (from 0.76 to 1.48 THz). The absorption decreases with fluctuations as the incident angle increases but remains above 62% even at the incident angle of 40°. The physical explanation to the absorption mechanism is presented and verified by a 9-bar example, which exhibits narrower absorption bandwidth. It is also experimentally demonstrated that the proposed structure is robust against misalignment of each metallic layer.