Resonant Behavior Research Articles

Tuning d-Orbital Electronic Structure via Au-Intercalated Two-Dimensional Fe3GeTe2 to Increase Surface Plasmon Activity.

While extensive research has been dedicated to plasmon tuning within non-noble metals, prior investigations primarily concentrated on markedly augmenting the inherently low concentration of free carriers in materials with minimal consideration given to the influence of electron orbitals on surface plasmons. Here, we achieve successful intercalation of Au atoms into the layered structure of Fe3GeTe2 (FGT), thereby exerting control over the orbital electronic states or structure of FGT. This intervention not only amplifies the charge density and electron mobility but also mitigates the loss associated with interband transitions, resulting in increased two-dimensional FGT surface plasmon activity. As a consequence, Au-intercalated FGT detects crystal violet molecules as a surface-enhanced Raman scattering substrate, and the detection lines are 3 orders of magnitude higher than before Au intercalation. Our work provides insight for further studies on plasmon effects and the relation between surface plasmon resonance behavior and electronic structures.

Synthesis and characterization of PANI-CZF nanocomposites for enhanced electromagnetic interference shielding

The Zn0.5Cu0.5Fe2O4 nano ferrites were prepared by the solution combustion method using aloe vera gel. The polyaniline-Zn0.5Cu0.5Fe2O4 nano ferrite composites were prepared by Ex-situ polymerization method with different weight percentage ratio. The prepared samples were examined by X-Ray diffraction, SEM, EDAX, BET, TEM, VSM and Impedance analyser to investigate their structural, morphological, elemental analysis, average pore size and the porosity, magnetic, and dielectric properties, respectively. The cubic spinel structure was confirmed by X-ray diffraction patterns. Addition of PANI to zinc-copper nano ferrite exhibits shift in crystalline peaks towards larger angle. The existence of spherical and clumped particles was revealed by SEM examination. The retentivity and coercivity are determined and the magnetic moment values were decreases with increase in PANI to the ferrite nanocomposites. The ac conductivity constant at lower frequency and there is a sudden increase and decrease in its value as a function of frequency shows resonance behaviour. The CZF-1 (CZF 30%) composite shows highest ac conductivity and dielectric constant. The electromagnetic shielding interference studies were conducted for S-band frequency. The CZF-1 (CZF 30%) nano composite shows highest shielding effectiveness as compared to other composite in the frequency range 2 to 3 GHz. The experimental result showed that these materials are used for applications in electromagnetic interference shielding.

Stochastic resonance in 2D materials based memristors

Stochastic resonance is an essential phenomenon in neurobiology, it is connected to the constructive role of noise in the signals that take place in neuronal tissues, facilitating information communication, memory, etc. Memristive devices are known to be the cornerstone of hardware neuromorphic applications since they correctly mimic biological synapses in many different facets, such as short/long-term plasticity, spike-timing-dependent plasticity, pair-pulse facilitation, etc. Different types of neural networks can be built with circuit architectures based on memristive devices (mostly spiking neural networks and artificial neural networks). In this context, stochastic resonance is a critical issue to analyze in the memristive devices that will allow the fabrication of neuromorphic circuits. We do so here with h-BN based memristive devices from different perspectives. It is found that the devices we have fabricated and measured clearly show stochastic resonance behaviour. Consequently, neuromorphic applications can be developed to account for this effect, that describes a key issue in neurobiology with strong computational implications.

Studies on electromagnetic properties of lithium based ferrimagnetic spinel oxides prepared with different additives and microwave sintering

Soft ferrimagnetic spinel lithium based oxides were prepared with additives like V2O5 and Na2SiO3 and sintered with the efficient microwave sintering technique. Tetravalent metal ions substituents like Mn+4, Ti+4 were used to enhance the important properties like D. C. resistivity, saturation magnetization, permeability, hysteresis and dielectric behavior. The ferrites were sintered at different sintering temperatures viz., 900, 950 and 1000 °C for 10 min by microwave technique and by conventional technique at 1050 °C for 4h. X-ray diffraction (XRD) studied the structural behavior which confirmed the spinel characteristics, Scanning electron microscopy (SEM) and EDAX revealed the microstructural and elemental compositions respectively of the ferrites. The use of additives and the microwave sintering significantly influencing the microstructural behavior and subsequently on the electromagnetic properties could be observed. Studies of initial permeability and initial permeability loss found to remain nearly constant with change in frequency until at certain frequency they showed resonance behavior. The resonance frequency’s dependence on the microstructures of the ferrites could be observed. Temperature dependence behavior of the dielectric parameters and the B-H loop traced from torroidal samples of the ferrites were studied.

Broadband stripline Lenz lens achieves 11 × NMR signal enhancement

A Lenz lens is an electrically passive conductive element that, when placed in a time-varying magnetic field, acts as a magnetic flux concentrator or a magnetic lens. In the realm of nuclear magnetic resonance (NMR), Lenz lenses have been exploited as electrically passive metallic radiofrequency interposers placed between a sample and a tuned or untuned NMR detector in order to focus the B1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${B}_1$$\\end{document}-field of the detector onto a smaller sample space. Here we explore a novel embodiment of the Lenz lens, which acts as a non-resonant stripline interposer, i.e., the B1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${B}_1$$\\end{document}-field acts along the longitudinal volume of a sample container, such as a capillary or other microfluidic channel that is coincident with the axis of the stripline. The almost vanishing self-resonance of the stripline Lenz lens, at frequencies relevant for NMR, leads to a desirable B1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${B}_1$$\\end{document}-field amplitude that is nearly perfectly uniform across the sample and hence lacking a characteristic sinusoidal modal shape. The action of Lenz’ law ensures that no stray B1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${B}_1$$\\end{document}-field is found outside of the stripline’s active volume. Because the stripline Lenz lens does not rely on its own geometry to achieve resonance, its frequency response is thus widely broadband for field enhancements up to a factor of 11, with only the external driving resonator properties governing the overall resonant behaviour. We explore the use of the stripline Lenz lens with a sub-nanolitre sample volume, readily detecting 4 isotopes with resonances ranging from 125.76 to 500 MHz. The concept holds potential for the NMR study of thin films, small biological samples, as well as the in situ study of battery materials.

Eigenmodes of 1-kink skyrmions in cylindrical magnetic discs

The stability and resonance spectra associated with a domain wall skyrmion embedded within a Néel skyrmion, forming a 1-kink skyrmion, has been studied using micromagnetic simulations. We show that the 1-kink skyrmion is stable over a wide range of fields at moderate strengths of the Dzyaloshinskii-Moriya interaction. By exciting these structures with a broadband magnetic field excitation, we find complex resonance behavior deviating from that of a pure Néel skyrmion. For out-of-plane excitations, the 1-kink skyrmion demonstrates an additional mode relative to that of the Néel skyrmion at reduced amplitude. These consist of low frequency and high frequency modes associated with both a breathing mode and an oscillation of the embedded domain wall skyrmion. Following an in-plane excitation, both Néel and 1-kink skyrmions exhibit a counterclockwise rotational mode with similar frequencies, as well as a higher frequency mode associated with the interaction of the structure with the ferromagnetic background state. These results may help pave the way for exploration of more complex spin structures for magnetic-based microwave devices.

Surface Adsorption and Air Damping Behavior of β‐Ga2O3 Nanomechanical Resonators

AbstractBeta gallium oxide (β‐Ga2O3) has emerged as a highly promising semiconductor material with an ultrawide bandgap ranging from 4.5 to 4.9 eV for future applications in power electronics, optoelectronics, as well as gas and ultraviolet (UV) radiation sensors. Here, surface adsorption and air damping behavior of doubly clamped β‐Ga2O3 nanomechanical resonators are probed and systemically studied by measuring the resonance characteristics under different gas and pressure conditions. High responsivities of resonance to pressure are obtained by heating the devices up to 300 °C to induce an accelerated adsorption–desorption process. The initial surface conditions of the β‐Ga2O3 thin film play important roles in affecting the resonant behavior. UV ozone treatment proves effective in altering the initial surface conditions of β‐Ga2O3 nanosheets by eliminating physisorbed contaminants and filling oxygen vacancy defects residing on the surface, resulting in a consequential and discernible modification of the resonance behavior of β‐Ga2O3 nanomechanical resonators. The surface adsorption and desorption processes in β‐Ga2O3 demonstrate clear reversibility by exposing the UV treated β‐Ga2O3 to air. This study attains first‐hand information on how the surface conditions of β‐Ga2O3 affect its mechanical properties, and helps guide future development of transducers via β‐Ga2O3 nanoelectromechanical systems (NEMS) for pressure sensing applications, especially in harsh environments.

Modeling and Analysis of a Thermo-Electro-Magneto-Viscoelastic Actuator

This study examines the dynamics of a smart actuator known as a thermo-electro-magneto-viscoelastic plate. This type of actuator is made of an electro-magneto-active polymer filled with suitably added fillers, which enhance its performance. An energy-based dynamic model is derived to analyze the behavior of the actuator, taking into account thermal, electrical, and mechanical factors. The study uses a well-known Euler–Lagrange equation to develop the governing dynamic equation of the actuator. In addition, the stability, periodicity, and resonant behavior of the actuator are evaluated through time-evolution diagrams, Poincaré plots, and phase portraits. The results indicate that the nonlinear behavior of the actuator changes when subjected to different modes of actuation such as DC and AC. Increasing particle reinforcement and reducing temperature change strengthens the polymer and depletes the level of deformation. The intensity of oscillation also decreases, and the excitation frequency increases as the temperature change reduces and the volume fraction increases. Lastly, this study provides important insights into the design of modern actuators, which have numerous potential applications in both engineering and medical industries.

Thermo-electro-mechanical effects on nonlinear dynamics of smart dielectric elastomer minimum energy structures

Minimum energy structures made up of smart electro-active polymers (SEAPs) have attracted significant attention in the field of soft robotics and actuators due to their exceptional property of undergoing large deformations when subjected to electric fields. In general, temperature also plays a crucial role in modeling of SEAPs because it affects the mechanical, electrical, and thermal properties of the polymer. These properties, in turn, determine the performance of smart polymer-based devices. Motivated by these ongoing advancements, this study investigates the effects of temperature on the nonlinear dynamic behavior of a smart dielectric elastomer-based minimum energy structure (SDEMES) actuator. The governing dynamic equation of the actuator is derived using the standard Euler–Lagrange’s equation. Through the utilization of time-evolution diagrams, Poincaré plots, and phase portraits, the study comprehensively evaluates the effects of temperature on the stability, periodicity, and resonant behavior of the actuator. The results highlight the significant influence of temperature on the stiffness of the elastomer within the SDEMES actuator, directly impacting its actuation performance. The frequency response of the actuator demonstrates a distinct increase in resonant frequency as the temperature rises. These findings shed light on the crucial role of temperature in shaping the stiffness and nonlinear dynamic behavior of smart dielectric elastomer minimum energy structures.

Improvement of signal propagation in the optoelectronic artificial spiking neuron by vibrational resonance.

Experimental evidence of vibrational resonance (VR) in the optoelectronic artificial spiking neuron based on a single photon avalanche diode and a vertical cavity laser driven by two periodic signals with low and high frequencies is reported. It is shown that a very weak subthreshold low-frequency (LF) periodic signal can be greatly amplified by the additional high-frequency (HF) signal. The phenomenon shows up as a nonmonotonic resonant dependence of the LF response on the amplitude of the HF signal. Simultaneously, a strong resonant rise of the signal-to-noise ratio is also observed. In addition, for the characterization of VR an area under the first LF period in the probability density function of interspike intervals for the LF signal and the maximal amplitude in this area were used, both of which also demonstrate a resonant behavior depending on the amplitude of the HF signal.

Symmetrically structured epsilon negative metamaterial for antenna gain enhancement

An epsilon negative metamaterial (MTM) is presented in this article that bears a symmetrical structure and shows a transmission coefficient (S21) resonance at 2.78 GHz. The proposed MTM unit cell comprises an outer square ring with horizontally oriented splits, connected along the vertical axis to a circular inner ring featuring vertically oriented splits, forming an interconnected structure. The electrical dimension of the MTM cell is 0.08λ × 0.084λ, and here wavelength, λ is determined at 2.4 GHz. The MTM shows negative permittivity, near zero permeability as well as refractive index. The electric field, Magnetic field, and current distribution have been analyzed to realize resonance behavior. The compactness of the MTM is identified through an effective medium ratio (EMR) of 12.2. Moreover, an equivalent circuit is modeled and Advanced Design Systems (ADS) is utilized to confirm its performance. The prototype of the metamaterial is developed and a measured result is taken that exhibits a well-matching with the simulation result. Application of this metamaterial is checked through designing and developing an antenna and MTM is used as a superstrate over the antenna. Both the simulation and measured results reveal that as a superstrate, MTM helps to increase the antenna gain by more than 100% with less effect on the bandwidth. Thus, this new metamaterial can be a good candidate as an antenna element for increasing performance. Moreover, the proposed antenna-MTM system can be utilized for wireless power transmission as it provides an adequate gain in a compact 3D structure.

Beat phenomena of oscillating readouts.

To demonstrate slowly varying, erroneous magnetic field gradients for oscillating readouts due to the mechanically resonant behavior of gradient systems. Projections of a static phantom were acquired using a one-dimensional (1D) EPI sequence with varying EPI frequencies ranging from 1121 to 1580 Hz on clinical 3T systems (30 mT/m, 200 T/m/s). Phase due to static B0 inhomogeneities was eliminated by a complex division of two separate scans with different polarities of the EPI readout. The temporal evolution of phase was evaluated and related to the mechanical resonances of the gradient systems derived from the gradient modulation transfer function. Additionally, the impact of temporally varying mechanical resonance effects on EPI was evaluated using an echo-planar spectroscopic imaging sequence. A beat phenomenon resulting in a slowly varying phase was observed. Its temporal frequency was given by the difference between the EPI frequency and the mechanical resonance frequency of the activated gradient axis. The maximum erroneous, oscillating phase during phase encoding was ±0.5 rad for an EPI frequency of 1281 Hz. Echo-planar spectroscopic imaging images showed the resulting time-dependent stretching/compression of the FOV. Oscillating readouts such as those used in EPI can result in low-frequency, erroneous phase contributions, which are explained by the beat phenomenon. Therefore, EPI phase-correction approaches may need to include beat effects for accurate image reconstruction.

Experimental investigation of an Autler-Townes resonator with flow

The acoustic behavior of a double annular resonator with flow is studied as a special case to illustrate the possibilities, but also the difficulties, offered by flow on the acoustic performance of metamaterials. Compared with the associated single resonator, the double resonator exhibits – in the lossless case – a transmission peak near the resonant frequency. This peak is associated with an evanescent out-of-phase coupling between the two resonators and is known in literature as “Autler-Townes splitting”. In measurements with a double resonator, this peak is strongly attenuated by viscous effects, to such an extent that it almost disappears. When a flow is added, even a very small one, a gain is created and the peak reappears close to the resonator frequency. As the average flow velocity increases, this gain can become sufficiently large for a whistling to appear.

Theoretical study on the downshift of class II Bragg resonance

In this paper, a new solution for class II Bragg resonance was derived based on the multiple-scale expansion method. The proposed solution can accurately predict the reflection coefficient and effectively characterize the downshift behavior of the Bragg resonance. Subsequently, a formula that quantifies the magnitude of the wave resonance frequency is proposed. The formula's predictive ability of the frequency downshift is demonstrated through comparisons against existing analytical and numerical solutions. Furthermore, investigation of the interactions between the waves and ripples reveals the underlying mechanism of the downshift behavior, highlighting the significant influence of wave re-reflection by the doubly sinusoidal ripples. Particularly, the process where waves are initially reflected by one of the ripple components and subsequently re-interacts with their conjugates results in the downward shift from the Bragg resonance condition. Moreover, the study of the effect of ripple length on Bragg resonance demonstrated that the downshift magnitude increases up to a certain limit as the ripple length tends to infinity, and this limit is substantially affected by the ripple amplitudes. In addition, the effects of the two ripple components are examined, which reveals the existence of a threshold ratio of the second wavenumber (larger) to the first ripple wavenumber (smaller) for a specific water depth. When the ratio is smaller than the threshold value, the downshift behavior of Bragg resonance is primarily influenced by the second ripple component. Conversely, as the ratio exceeds this value, the downshift behavior is dominated by the first ripple component.

On the frequency and damping of resonances in electrical networks: a discrete state-space approach using bounce Diagrams

The paper presents a novel method to compute resonances in a power system network using a discrete state-space approach based on bounce diagrams. The approach models the distributed parameter line as a lattice diagram, considering the refection/transmission of traveling waves. This model is then represented as a discrete-time linear time-invariant system, enabling the computation of resonances in the network. Two applications are demonstrated: fault location and load placement to improve damping in black start scenario. The method is particularly useful to understand and control resonances in electric grids. Theoretical analysis and numerical examples illustrate the behavior of resonances as resistive loads are connected along the transmission line, providing insights for fault location and load allocation strategies.

A DODECAGON SLOTTED CIRCULAR TWO-ELEMENT SUB-6 GHZ FLEXIBLE ANTENNA FOR WEARABLE APPLICATIONS USING MODAL ANALYSIS

The sub-6 GHz 5G band has opened doors for a seamless and high-data-rate communication system connecting multiple devices. Multiple-input/multiple-output (MIMO) antennas are the backbone of such reliable communication systems with enhanced channel capacity. In this paper, a flexible two-element antenna is proposed for wearable applications. The dodecagon-slotted modified circular patch antenna with a defective ground structure gives isolation of 18 dB over the bandwidth. The antenna exhibits a gain of 3.38 dBi at the operating frequency of 4.8 GHz. A characteristic mode analysis was performed to investigate the resonance behavior of the antenna. Furthermore, specific absorption rate analysis was performed and found to be 0.790/0.314 W/kg for 1/10 g of tissue at 4.8 GHz. The MIMO diversity metrics exhibited an envelope correlation coefficient < 0.001, total active reflection coefficient < -10 dB, diversity gain ≈ 10, mean effective gain < -3 dB, channel capacity loss < 0.40 bps/Hz, and multiplexing efficiency < 0 over the operating frequency band.

DUAL-BAND BANDSTOP FILTERS BASED ON ULTRA THIN FREQUENCY SELECTIVE SURFACES

In this paper, we present designs for terahertz filters with two independent stopbands based on periodic metallic resonant structures patterned on the dielectric substrate. Two simple and thin structures are proposed to realize required characteristics for single-polarized and dual polarized filter designs. To realize single polarized one, a unit cell of the proposed periodic structure consists of two sets rectangular shape conducting metal patches patterned on the top of the dielectric substrate, and the dual-band response is due the lattice resonances observed in the unit cell. To realize dual polarized filter design, a modified unit cell is considered with additional patches on the bottom of the dielectric substrate. The patches on the bottom layer are the same ones as on the top layer but orthogonally oriented. For this case, polarization-independent frequency response can be obtained after geometric optimization of the unit cell because the top and the bottom layers resonantly interact with only the TE or TM incident plane wave to minimize cross coupling effects between the layers. In order to intensively understand the transmission performance of the proposed filters, a large number of simulations using integral equation method are performed based on the different values for permittivity, period of the unit cell, dielectric thickness, and geometric dimensions. The electric field distributions are analyzed to understand the mechanism of the resonance behavior.

Photonic Neural Networks Based on Integrated Silicon Microresonators

Recent progress in artificial intelligence (AI) has boosted the computational possibilities in fields in which standard computers are not able to perform adequately. The AI paradigm is to emulate human intelligence and therefore breaks the familiar architecture on which digital computers are based. In particular, neuromorphic computing, artificial neural networks (ANNs), and deep learning models mimic how the brain computes. There are many applications for large networks of interconnected neurons whose synapses are individually strengthened or weakened during the learning phase. In this respect, photonics is a suitable platform for implementing ANN hardware owing to its speed, low power dissipation, and multi-wavelength opportunities. One photonic device that could serve as an optical neuron is the optical microring resonator. Indeed, microring resonators exhibit a nonlinear response and the capability for optical energy storage, which can be used to implement fading memory. In addition, their characteristic resonant behavior makes them extremely sensitive to input wavelengths, which promotes wavelength division multiplexing (WDM) applications and enables their use as WDM-based synapses (weight banks) in the linear regime. Remarkably, using silicon photonics, photonic integrated circuits can be fabricated in volume and with integrated electronics onboard. For these reasons, here, we describe the physics of silicon microring resonators and arrays of microring resonators for application in neuromorphic computing. We describe different types of ANNs, from feedforward networks to photonic extreme learning machines, and reservoir computing. In addition, we discuss hybrid systems in which silicon microresonators are coupled with other active materials. This review introduces the basics and discusses the most recent developments in the field.

Resonance behavior for a fractional underdamped bistable system with multiplicative and additive noise driven by one high-frequency and one low-frequency periodic signal

Resonance behavior for a fractional underdamped bistable system with multiplicative and additive noise driven by one high-frequency and one low-frequency periodic signal

Spatiotemporal Dynamics of Neuroinflammation Relate to Behavioral Recovery in Rats with Spinal Cord Injury.

The degree and dynamic progression of neuroinflammation after traumatic spinal cord injuries (SCI) are crucial determinants of the severity of injury and potential for recovery. We used Positron Emission Tomography (PET) to monitor neuroinflammation longitudinally, correlating it with Chemical Exchange Saturation Transfer (CEST) Magnetic Resonance Imaging (MRI) and behavior in contusion-injured rats. These studies help validate CEST metrics and confirm how imaging may be used to evaluate the efficacy of therapies and understand their mechanisms of action. 12 SCI and 4 sham surgery rats were subjected to CEST MRI and PET-Translocator Protein (TSPO) scans for 8weeks following injury. Z-spectra from the SCI were analyzed using a 5-Lorentzian pool model for fitting. Weekly motor and somatosensory behavior were correlated with imaging metrics, which were validated through post-mortem histological and immuo-staining using ionized calcium-binding adaptor protein-1 (iba-1, microglia) and glial fibrillary acidic protein (GFAP, astrocytes). PET-TSPO showed widespread inflammation and post-mortem histology confirmed the presence of activated microglia. Changes in CEST and nuclear Overhauser Effect (NOE) peaks at 3.5ppm and -1.6ppm respectively were largest within the first week after injury and more pronounced in rostral versus caudal segments. These temporal indices of neuroinflammation corresponded to the recovery of locomotor behaviors and somatic sensation in rats with moderate contusion injury. The results confirm that CEST MRI metrics are sensitive indices of states of neuroinflammation within injured spinal cords. The detection of dynamic spatiotemporal features of neuroinflammation progression underscores the importance of considering their timings and locations for neuroprotective and anti-inflammatory therapies. The availability of noninvasive MRI indices of neuroinflammation may facilitate clinical trials aimed at treatments that promote recovery after SCI.