Near-resonant Frequency Research Articles

Long-Term Converse Magnetoelectric Response of Actuated 1-3 Multiferroic Composite Structures

Multiferroic composite materials operating under the principle of strain mediation across the interfaces separating different material boundaries address many limitations of single-phase magnetoelectric materials. Although significant research has been conducted to explore their responses relating to the topography and directionality of material polarization and magnetic loading, there remain unanswered questions regarding the long-term performance of these multiferroic structures. In this study, a multiferroic composite structure consisting of an inner Terfenol-D magnetostrictive cylinder and an outer lead zirconate titanate (PZT) piezoelectric cylinder was investigated. The composite was loaded over a 45-day period with an AC electric field (20 kV/m) at a near-resonant frequency (32.5 kHz) and a simultaneously applied DC magnetic field of 500 Oe. The long-term magnetoelectric and thermal responses were continuously monitored, and an extensive micrographic analysis of pretest and post-test states was performed using scanning electron microscopy (SEM). The extended characterization revealed a significant degradation of ≈30–50% of the magnetoelectric response, whereas SEM micrographs indicated a reduction in the bonding interface quality. The increase in temperature at the onset of loading was associated with the induced oscillatory piezoelectric strain and accounted for 28% of the strain energy loss over nearly one hour.

IMPROVEMENT POTENTIAL FOR SOUND INSULATION OF SINGLE- AND MULTILAYER WALL PANELS

Relevance: Acoustic comfort in residential, public and industrial buildings. Existing types of wall panels often do not provide the required noise control.Purpose: Investigation of the improvement potential for sound insulation of single- and multi-layer wall panels having finitegeometric dimensions with diffuse sound lowering. Design/methodology/approach: Consideration of the sound propagation through the wall panel based on the theory of selfcoordination of wave fields developed by the Prof. Sedov‟s scientific school.Research findings: Analytical equations for calculating the limiting sound insulation of the wall panels determined by the inertial sound propagation. The improvement potential for sound insulation of single- and multi-layer wall panels having finite dimensions. Comparison of theoretical and xperimental results. It is shown that single- and multi-layer wall panels of finite geometric dimensions have improvement potential for sound insulation, which is determined by the ratio between their own and limiting sound insulation.Practical implications: Wall panel design must take into account the improvement potential for sound insulation. The sound insulation of wall panels is improved without increasing their mass and thickness. This is of great importance for design solutions for wall panels of civil and industrial buildings.Originality/value: The proposed method shows good agreement between experimental data and theoretical calculations. The improvement potential for sound insulation at the frequency level locates near the resonant frequencies, namely: near-boundary frequency of the full spatial resonance for single-layer wall panels; near-resonant frequency of the mass-elasticity-mass panels and near-boundary frequency of the full spatial resonance for multilayer wall panels and panel linings, respectively.

Slow-fast dynamics in the truss core sandwich plate under excitations with high and low frequencies

In this manuscript, slow-fast motions in a two degrees of freedom model under slow parametric and fast external excitations are analyzed using analytical and numerical methods. By expressing the state variables as the sums of slowly varying average and fast oscillations, the averaged equations which govern the slow dynamics for different magnitudes of external amplitude are obtained. For the averaged equations, analyzation about the equilibria and the corresponding stability shows that, the averaged slow manifolds constitute a pitchfork structure. Meanwhile, the harmonic balancing method is used to compute the slowly varying envelopes of the fast oscillations. On the other hand, bifurcation diagrams of the fast sub-system show structures in accordance with the pitchfork obtained from averaged equations as well as the amplitude curves computed by harmonic balancing method. Two forms of relative location between the folds of cycle on the handle and pitchfork bifurcation point are presented. Based on these, concerning on the slow-fast flow, two patterns of transition behavior between the handle and the upper (lower) branch of pitchfork namely “pitchfork/pitchfork” and “fold/pitchfork” types are analyzed, which indicate the dynamic buckling behaviors. Particularly, discussion about the influence of external excitation shows that, for case of near-resonant external frequency, increasing the amplitude of external excitation will change the local structures as well as the quantitative properties of the pitchfork, but holistic form of pitchfork type is a topological invariant.

Experimental modal analysis of nonlinear systems by using response-controlled stepped-sine testing

Although the identification and analysis of structures with a localized nonlinearity, either weak or strong, is within reach, identification of multiple nonlinearities coexisting at different locations is still a challenge, especially if these nonlinearities are strong. In such cases, identifying each nonlinearity separately requires a tedious work or may not be possible at all in some cases. In this paper, an approach for experimental modal analysis of nonlinear systems by using Response-Controlled stepped-sine Testing (RCT) is proposed. The proposed approach is applicable to systems with several nonlinearities at various different locations, provided that modes are well separated and no internal resonances occur. Step-sine testing carried out by keeping the displacement amplitude of the driving point constant yields quasi-linear frequency response functions directly, from which the modal parameters can be identified as functions of modal amplitude of the mode of concern, by employing standard linear modal analysis tools. These identified modal parameters can then be used in calculating near-resonant frequency response curves, including the unstable branch if there is any, for various untested harmonic forcing cases. The proposed RCT approach makes it also possible to extract nonlinear normal modes experimentally without using sophisticated control algorithms, directly from the identified modal constants, and also to obtain near-resonant frequency response curves experimentally for untested constant-amplitude harmonic forcing cases by extracting isocurves of constant-amplitude forcing from the measured Harmonic Force Surface (HFS), a new concept proposed in this paper. The key feature of the HFS is its ability to extract unstable branches together with turning points of constant-force frequency response curves directly from experiment, accurately. The method is validated with numerical and experimental case studies. The numerical example consists of a 5 DOF lumped system with strong several conservative nonlinear elements. Experimental case studies consist of a cantilever beam supported at its free-end by two metal strips which create strong stiffening nonlinearity, and a real missile structure which exhibit moderate damping nonlinearity mostly due to several bolted joints on the structure.

Extraordinary transmission through a narrow slit

We revisit the problem of extraordinary transmission of acoustic (electromagnetic) waves through a slit in a rigid (perfectly conducting) wall. We use matched asymptotic expansions to study the pertinent limit where the slit width is small compared to the wall thickness, the latter being commensurate with the wavelength. Our analysis focuses on near-resonance frequencies, furnishing elementary formulae for the field enhancement, transmission efficiency, and deviations of the resonances from the Fabry–Pérot frequencies of the slit. We find that the apertures’ near fields play a dominant role, in contrast with the prevalent approximate theory of Takakura (2001). Our theory agrees remarkably well with numerical solutions and electromagnetic experiments (Suckling et al., 2004), thus providing a paradigm for analysing a wide range of wave propagation problems involving small holes and slits.

Atom Manipulations by Enhanced Quadrupole Interaction

We develop a theory that leads to the explanation of the atom manipulations due to active quadrupole interaction of twisted light with atoms at near-resonance frequencies. We demonstrate that the total mechanical effects of active quadrupole interaction on atoms just gives a rotational motion in the case of the configuration of a two counter-propagating beams. Typical parameters are assumed to determine both dissipative and quadrupole forces to obtain the trajectories for an atom.

ИДЕНТИФИКАЦИЯ ПАРАМЕТРОВ МЕХАНИЧЕСКОЙ СИСТЕМЫ ВИБРАЦИОННОГО ЭЛЕКТРОМАГНИТНОГО АКТИВАТОРА ПО ГРАНИЧНЫМ ОКОЛОРЕЗОНАНСНЫМ ЧАСТОТАМ

Актуальность исследования обусловлена тем, что вибрационные электромагнитные активаторы являются эффективными устройствами для перемешивания суспензий, эмульсий, приготовления буровых растворов, разжижения высоковязких нефтепродуктов. Якорь специальной конструкции представляет собой гидравлический вентиль. При вибрации якоря на частотах, близких к резонансной частоте, в обрабатываемой жидкой среде создаются глубоко затопленные струи, которые при относительно невысоком энергопотреблении вибрационного электромагнитного активатора обеспечивают высокую эффективность перемешивания жидкой среды и снижение вязкости нефтепродуктов на достаточно продолжительном интервале времени. Резонансная частота механической системы зависит от жесткости пружины, массы якоря-активатора, присоединенной массы колеблющейся с якорем жидкой среды и от коэффициента вязкого трения, определяющего отведение энергии из колеблющейся механической системы. При изменении реологических свойств обрабатываемой жидкой среды изменяются как параметры механической колебательной системы, так и вид амплитудно-частотных характеристик вибрационного электромагнитного активатора. Способ организации мониторинга изменения реологических свойств обрабатываемой вибрационным электромагнитным активатором жидкой среды на основе прямых измерений, например с помощью вискозиметров, пригоден только для лабораторных условий и не годится для промышленного внедрения. По мнению авторов, более перспективным является подход, основанный на решении обратной математической задачи, когда, анализируя вид амплитудно-частотных характеристик вибрационного электромагнитного активатора, в частности граничные околорезонансные частоты, можно получить достоверные оценки параметров механической колебательной системы вибрационного электромагнитного активатора. Эти оценки удобно применять для организации как косвенного мониторинга изменения реологических свойств обрабатываемой жидкости в процессе работы вибрационного электромагнитного активатора, так и для усовершенствования структуры системы автоматического управления вибрационным электромагнитным активатором. Цель исследования заключается в разработке метода идентификации параметров механической системы вибрационного электромагнитного активатора на основе анализа граничных околорезонансных частот и определении границ применимости метода в сильно нагруженных колебательных механических системах. Методы: обыкновенные дифференциальные уравнения, преобразование Лапласа, передаточные функции, амплитудно-частотные характеристики, алгебраические уравнения. Результаты. Получены аналитические выражения, связывающие граничные околорезонансные частоты с параметрами механической колебательной системы, на основе которых составляются системы алгебраических уравнений. Показаны границы применимости метода в сильно нагруженных колебательных механических системах.

Synthesis of nonlinear frequency responses with experimentally extracted nonlinear modes

Determining frequency response curves is a common task in the vibration analysis of nonlinear systems. Measuring nonlinear frequency responses is often challenging and time consuming due to, e.g., coexisting stable or unstable vibration responses and structure-exciter-interaction. The aim of the current paper is to develop a method for the synthesis of nonlinear frequency responses near an isolated resonance, based on data that can be easily and automatically obtained experimentally. The proposed purely experimental approach relies on (a) a standard linear modal analysis carried out at low vibration levels and (b) a phase-controlled tracking of the backbone curve of the considered forced resonance. From (b), the natural frequency and vibrational deflection shape are directly obtained as a function of the vibration level. Moreover, a damping measure can be extracted by power considerations or from the linear modal analysis. In accordance with the single nonlinear mode assumption, the near-resonant frequency response can then be synthesized using this data. The method is applied to a benchmark structure consisting of a cantilevered beam attached to a leaf spring undergoing large deflections. The results are compared with direct measurements of the frequency response. The proposed approach is fast, robust and provides a good estimate for the frequency response. It is also found that direct frequency response measurement is less robust due to bifurcations and using a sine sweep excitation with a conventional force controller leads to underestimation of maximum vibration response.

Concept study of a novel energy harvesting-enabled tuned mass-damper-inerter (EH-TMDI) device for vibration control of harmonically-excited structures

A novel dynamic vibration absorber (DVA) configuration is introduced for simultaneous vibration suppression and energy harvesting from oscillations typically exhibited by large-scale low-frequency engineering structures and structural components. The proposed configuration, termed energy harvesting-enabled tuned mass-damper-inerter (EH-TMDI) comprises a mass grounded via an in-series electromagnetic motor (energy harvester)-inerter layout, and attached to the primary structure through linear spring and damper in parallel connection. The governing equations of motion are derived and solved in the frequency domain, for the case of harmonically-excited primary structures, here modelled as damped single-degree- of-freedom (SDOF) systems. Comprehensive parametric analyses proved that by varying the mass amplification property of the grounded inerter, and by adjusting the stiffness and the damping coefficients using simple optimum tuning formulae, enhanced vibration suppression (in terms of primary structure peak displacement) and energy harvesting (in terms of relative velocity at the terminals of the energy harvester) may be achieved concurrently and at nearresonance frequencies, for a fixed attached mass. Hence, the proposed EH-TMDI allows for relaxing the trade-off between vibration control and energy harvesting purposes, and renders a dual-objective optimisation a practically-feasible, reliable task.

Bragg reflector acoustic impedance RLC model

The simplified RLC model of Bragg reflector impedance was developed and presented in this work. The model allows the straightforward integration of the reflector’s electrical behavior into the most of modern CAD systems as a part of complex devices and enables the precise evaluation of the output characteristics in a relatively wide nearresonant frequency range. This is especially important in the modelling of RF systems composed of thin film bulk acoustic resonators. The model verification was given including the analysis of the total impedance frequency dependence in wide and narrow frequency ranges, the model agreement examination for different number of layers and using various materials. The evaluation of agreement error for different frequency bands presented which allowed one to determine the limits of applicability of RLC model. An important advantage of proposed solution is the decreasing of calculation time and improving of optimization efficiency of complex RF circuits with a large number of resonators. References 10, figures 6, tables 2.

Water in Fuel Sloshing for Aircraft Fuel Tanks

Water is an unavoidable contaminant in aircraft fuel tanks. During an aircraft manoeuvre, fuel and water will slosh. The sloshing of two liquids (two-liquid sloshing) gives rise to a number of interesting phenomena which single-liquid sloshing does not experience. These include internal waves at the liquid-liquid interface and interaction between the motions of the two liquids. This paper investigated the ability of three commercial Computational Fluid Dynamics (CFD) modelling packages to accurately predict the pressures imparted on the tank walls of a rectangular tank when excited at near-resonant frequency while containing two liquids; water and fuel. A sloshing test rig was set-up to provide both qualitative (visual images) and quantitative (pressure data) results for comparison with the CFD calculations. The CFD calculations correlated well with the experimental results qualitatively and quantitatively. Snapshots of the sloshing show that CFD is able to model the wave modes reasonably well; and the pressure data show that CFD is able to simulate the pressure them were postulated.

Modified self-Kerr-nonlinearity in a four-levelN-type atomic system

The self-Kerr-nonlinearity of a four-level N-type atomic system is studied both experimentally and theoretically. The self-Kerr-nonlinear coefficient n{sub 2} of the probe beam is greatly enhanced near atomic resonance, and can be dramatically modified by changing the switching laser power. With an increasing switching laser power, the slope of the Kerr nonlinear coefficient n{sub 2} around the atomic resonance changes from negative to positive, and the value of n{sub 2} varies from {approx}-4 x 10{sup -6} to 4 x 10{sup -6} cm{sup 2}/W at certain near-resonant probe frequency detunings. Such controllable Kerr nonlinearity can find applications in optoelectronic devices, such as all-optical switching and logic gates.

Forward scattering at low acoustical frequencies from schools of swim bladder fish

Low frequency acoustic scattering from swim bladder fish is dominated by the bladder resonance response. At near-resonance frequencies in dense schools of these fish, acoustical interactions between the fish can cause the ensemble scattering behavior to become highly complex. A school scattering model [J. Acoust. Soc. Am. 99(1), 196 (1996)] has previously been developed to incorporate both multiple scattering effects between neighboring fish, and coherent interactions of their individual scattered fields, in order to realistically describe the collective back scattering behavior of fish schools. In this present work, the school scattering model has been extended to investigate the properties of the acoustic field scattered in the forward direction. In this region, the scattered field and the incident field must be added coherently to obtain the total field. As in the case of back scattering, the field displays marked frequency dependent affects, which are caused by different combinations of the packing de...

Carrier-envelope phase dependence of the duration of generated solitons for few-cycle rectangular laser pulses propagation

We investigate the nonlinear propagation of few-cycle rectangular laser pulses on resonant intersubband transitions in semiconductor quantum wells using an iterative predictor–corrector finite-difference time-domain method. An initial 2π rectangular pulse will split into Sommerfeld–Brillouin precursors and a self-induced transparency soliton during the course of propagation. The duration of generated soliton depends on the carrier-envelope phase of the incident pulse. In our case, not only the near-resonant frequency components but also the low frequency components could contribute to the generation of the soliton pulse when the condition of multi-photon resonance is satisfied. The phase-sensitive property of the solitons results from the phase-dependent distribution of high and low frequency sidebands of few-cycle rectangular pulses.

Low-frequency acoustical interactions and scattering from schools of swim bladder fish.

Low-frequency acoustic scattering from swim bladder fish is dominated by the bladder resonance response. Dense schools of these fish frequently consist of individuals of similar size, arranging themselves about one fish length apart. At near-resonance frequencies, acoustical interactions between the fish can cause the ensemble behavior of the school to become highly complex. Multiple scattering between neighboring fish affects the wave field of each individual. Additionally, since the wavelength at resonance is generally many times the fish spacing, the scattered fields interact coherently. Both features must also be incorporated to realistically describe scattering from fish schools. An effective methodology is available through the application of self-consistent multiple scattering techniques. The mathematical formalism used is based upon the solution of sets of coupled differential equations and incorporates a verified swim bladder scattering kernel for an individual fish. All orders of multiple scattering interactions between the fish are included, and the aggregate scattering field is calculated by coherent summation. Application to groups of closely spaced fish indicates significant deviations from the returns expected when incoherent scattering is dominant. The approach promotes an improved understanding of the ensemble physical properties of, as well as backscattering from, schools of swim bladder fish.

Two-dimensional mechanically resonating fiber optic scanning display system

A microdisplay system based on an optical fiber driven by a 2-D piezoelectric actuator is presented. An optical fiber is extended from the free end of a 2-D piezoelectric actuator free length 4.3 mm. A field programmable gate array FPGA drives the actuator using a triangular waveform to deflect the optical fiber in orthogonal directions. The FPGA also controls a LED light source, and the light is coupled into a chemi- cally tapered single-mode fiber SMF-28, core diameter 10 m .A t a preset pairing of near-resonance frequencies horizontal 22 Hz, vertical 5070 Hz, the deflected optical fiber in combination with controlled light produces an output image with an approximate dimension of 0.1 0.1 mm 2 , and a potential resolution of 400 lines per scan. This work details the design and fabrication of the microdisplay system. The me- chanical and optical design for the microresonating scanner is dis- cussed. In addition, the mechanical and optical performance and the resulting output of the 2-D scanner is presented. © 2010 Society of Photo-

Diffraction of monochromatic waves on a metallic cylinder with longitudinal slots

The projection matching method is applied to the calculation of a circular cylindrical slot line with one and two slots. The diffraction problem is studied at near-resonance frequencies.

Seated whole body vibrations with high-magnitude accelerations—relative roles of inertia and muscle forces

Reliable computation of spinal loads and trunk stability under whole body vibrations with high acceleration contents requires accurate estimation of trunk muscle activities that are often overlooked in existing biodynamic models. A finite element model of the spine that accounts for nonlinear load- and direction-dependent properties of lumbar segments, complex geometry and musculature of the spine, and dynamic characteristics of the trunk was used in our iterative kinematics-driven approach to predict trunk biodynamics in measured vehicle's seat vibrations with shock contents of about 4 g (g: gravity acceleration of 9.8 m/s 2) at frequencies of about 4 and 20 Hz. Muscle forces, spinal loads and trunk stability were evaluated for two lumbar postures (erect and flexed) with and without coactivity in abdominal muscles. Estimated peak spinal loads were substantially larger under 4 Hz excitation frequency as compared to 20 Hz with the contribution of muscle forces exceeding that of inertial forces. Flattening of the lumbar lordosis from an erect to a flexed posture and antagonistic coactivity in abdominal muscles, both noticeably increased forces on the spine while substantially improving trunk stability. Our predictions clearly demonstrated the significant role of muscles in trunk biodynamics and associated risk of back injuries. High-magnitude accelerations in seat vibration, especially at near-resonant frequency, expose the vertebral column to large forces and high risk of injury by significantly increasing muscle activities in response to equilibrium and stability demands.

Coherent lattice vibrations in superconductors

A recent analysis has shown that the pair wavefunction within the BCS theory may be represented in real-space as a spherical electronic orbital (on the scale of the coherence length ξ 0 ) coupled to a standing-wave lattice vibration with wavevector 2 k F and a near-resonant phonon frequency. The present paper extends this picture to a coherent pattern of phonon standing-waves on the macroscopic scale, with electrons forming Bloch waves and an energy gap much like those in the classic band theory of crystals. These parallel planes form a diffractive waveguide permitting electron waves to traveling parallel to the planes, corresponding to lossless supercurrent. A similar picture may be extended to unconventional superconductors such as the cuprates, with an array of standing spin waves rather than phonons. Such coherent lattice vibrations should be universal indicators of the superconducting state, and should be observable below T c using X-ray and neutron diffraction techniques. Further implications of this picture are discussed.

Compression of Laser Radiation in Plasmas Using Electromagnetic Cascading

Compressing high-power laser beams in plasmas via generation of a coherent cascade of electromagnetic sidebands is described. The technique requires two copropagating beams detuned by a near-resonant frequency Omega approximately < omega(p). The ponderomotive force of the laser beat wave drives an electron plasma wave which modifies the refractive index of plasma so as to produce a periodic phase modulation of the laser field with the beat period tau(b) = 2pi/Omega. A train of chirped laser beat notes (each of duration tau(b)) is thus created. The group velocity dispersion of radiation in plasma can then compress each beat note to a few-laser-cycle duration. As a result, a train of sharp electromagnetic spikes separated in time by tau(b) is formed. Depending on the plasma and laser parameters, chirping and compression can be implemented either concurrently in the same plasma or sequentially in different plasmas.