Low-frequency Vibrational Excitations Research Articles

Researching low frequency vibration of automobile-robot

Automobile-robot (self-driving automobile) is being researched and developed vigorously. When the automobile-robot is moving on the road surface, the low frequency vibration excitation not only influences the ride comfort of the automobile-robot but also strongly affects the durability of the vehicle’s structures. To research the automobile-robot’s vibration in the low frequency region, a dynamic model of the vehicle is established to calculate the vibration equations in the time region. Based on the theory of the Laplace transfer function, the automobile-robot’s vibration equations in the time region are transformed and converted to the vibration equations in the frequency region. Then, the effect of the design parameters and operation parameters on the characteristic of the automobile-robot’s acceleration-frequency is simulated and analyzed to evaluate the ride comfort as well as the durability of the automobile-robot’s structures in the frequency region. The research results show that the design parameters of the stiffness, mass, and road wavelength remarkably affect the characteristic of the automobile-robot’s acceleration-frequency. To reduce the resonant amplitude of the acceleration-frequency in the vertical and pitching direction of the automobile-robot, the stiffness parameters of the automobile-robot's and tires should be reduced while the mass of the automobile-robot’s body should be increased. Additionally, the road’s roughness also needs to be decreased or the road’s quality needs to be enhanced to reduce the resonant amplitude of the automobile-robot’s acceleration-frequency.

Temperature sensing and energy harvesting with A MEMS parametric coupling device under low frequency vibrations

The frequency-based self-powered sensor has an important place in the era of the Internet of Things. In existing reports, the resonator is used either as an energy harvester or a sensor, yet it cannot undertake both demands simultaneously in a single structure. A parametric coupling device (abbreviated as PCD), capable of both temperature sensing and energy harvesting, is proposed with a common wings-inspired structure. Under one low frequency vibration excitation, the vibration energy can be potentially converted to electric energy, while the output frequency is observed to have a linear relationship with the temperature. The wings-inspired structure is comprised of three parts bonded in series, two side beams for collecting vibration energy one of them synchronously for temperature sensing, and a middle flexible beam for achieving parametric coupling. Once the heat is applied to the sensing one, the internal thermal stress is generated in the beam, while the reaction force acts on the anchor end of the beam to create compressive stress, for which the stiffness is decreased to cause frequency shifts and turn the working frequency domain. The parametric coupling is designed to improve the PCD performance, which is supported by theoretical analysis and experimental verification. With a manufactured MEMS PCD prototype, under a harmonic vibration excitation, when the temperature varies from 35.85 °C to 48.35 °C, both frequency shifts for sensing and working frequency domain for harvesting are 13.7 Hz which is 3.5 times larger than those of a non-parametric coupling device (abbreviated as NPCD). The sensing sensitivity of PCD is measured as 2.91 times higher than that of NPCD under a harmonic vibration excitation, while that of PCD is analyzed as 1.69 times higher than that of NPCD under a random one. Theoretical analysis shows the maximum temperature detection range is from 33.32 °C to 84.07 °C and can be further enlarged from 33.32 °C to 108.54 °C by adjusting the length of the sensing beam. The proposed PCD has the potential to be applied to temperature compensation systems or to maintain the operating environments of sensing nodes in self-powered wireless sensing networks (WSN).

Analytical and numerical modeling of nonlinear lamb wave interaction with a breathing crack with low-frequency modulation

To characterize fatigue crack, an analytical calculation and finite element (FE) simulation of Lamb wave propagating through the region of a breathing crack in a two-dimensional(2D) isotropic plate were studied. Contact surface boundary conditions between the two surfaces of the vertical crack were considered to study contact acoustic nonlinearity (CAN) from the breathing contact crack in conjunction with the modal decomposition method, Fourier transform, and variational principle-based algorithm. Reflection and transmission coefficients in the fundamental frequency and second harmonic frequency were calculated and analyzed quantitatively. Different ratios of incident wave amplitude to crack width were studied to calculate CAN results related to micro-crack width. In addition, a low-frequency (LF) vibration(10 Hz) excitation was introduced to perturb the free surface vertical crack to close, and an interrogating Lamb wave(1 MHz) was used to study crack-related CAN in different conditions for interpreting the modulation mechanism. The contact boundary conditions between two surfaces of vertical crack were set which were dynamically changed due to the low frequency modulation. The clapping effects when the crack closed due to the modulation of the contact boundary conditions between the crack surfaces were studied and analyzed to get the quantitative correlation between CAN and LF modulation. The results obtained from the analytical model were compared with those from the FE simulation, showing good consistency. Knowledge of these effects is essential to correctly gauge the severity of surface cracks in the plate, which can be spotlighted in its application to quantitative evaluation of micro fatigue cracks in structural health monitoring(SHM).

Noise-less hybrid nanogenerator based on flexible WPU and siloxene composite for self-powered portable and wearable electronics

The rapid growth of portable and wearable electronics demands innovative battery solutions that are both sustainable and eco-friendly. Biomechanical energy-harvesting technology is a promising approach for operating wearable electronic devices without battery dependence. In this study, a novel noise-less hybrid nanogenerator (NLHN) was developed using 3D-printed elastic resin springs and burr-shaped water-based polyurethane (water-based PU: WPU)@Siloxene nanocomposite to effectively harvest low-frequency biomechanical energy from various human movements without generating any physical noise. By rationally integrating electromagnetic generators with triboelectric nanogenerators in a sliding mode and two contact modes, the proposed NLHN exhibited excellent output performance under random low-frequency and wide-range vibrational excitations. The WPU@Siloxene was first introduced as a highly flexible positive triboelectric layer and a noise suppressor during the sliding mode operation, while elastic resin springs significantly improved the energy harvesting performance thereby suppressing the physical noise during contact-separation. The NLHN exhibited an optimal output power of 101 mW at 6 Hz and 1.5 g acceleration. Moreover, the NLHN suppressed operating noise to only 41 dB during operation and maintained a stable output performance after 50,000 cycles. The NLHN was demonstrated to function as a continuous power source for powering portable and wearable electronics, such as smart bracelets and smartphones as well as battery-free wearable ECG monitoring systems. Conclusively, the proposed NLHN has substantial potential for silent biomechanical energy harvesting as a sustainable and eco-friendly power source for portable electronics and wearable healthcare sensing devices.

Oxygen diffusion in glassy propylene carbonate: Energetics and spatial correlation of jump rates

Quenching of phenanthrene phosphorescence by molecular oxygen was used as a tool to determine the distribution function of the activation free energy of oxygen jumps in glassy propylene carbonate. The distribution width is shown to increase linearly with temperature within the range from 135 to 156 K. The dispersion of the activation free energy is caused by the spatial fluctuations of the activation entropy of oxygen jumps but not the energy barriers; the spatial dispersion of energy barriers is found to be zero. A characteristic length of the spatial correlation of the activation entropy is about 1.3 nm. The apparent activation energy linearly correlates with the macroscopic high-frequency shear modulus. The jump rates of oxygen molecules lie in the range of Johari-Goldstein relaxation rates. We suggest that an oxygen molecule overcomes the barrier between two neighboring interstitial sites due to low-frequency localized vibrational excitations of string-like groups of host molecules which draw the oxygen molecule in the motion.

Design and Experimental Investigation of an Ultra-Low Frequency, Low-Intensity, and Multidirectional Piezoelectric Energy Harvester with Liquid as the Energy-Capture Medium

Traditional piezoelectric vibration energy harvesters (PVEHs) usually adopt a rigid energy-capture structure, which can achieve efficient energy harvesting in single-directional, high-frequency, and high-intensity vibration environments. However, efficient harvesting with the use of low-frequency, low-intensity, and multidirectional vibration energy remains a challenge for existing harvesters. To tackle this problem, we proposed a PVEH with liquid as the energy-capture medium. Our previous research verified that this set up can show a good energy harvesting performance under low-frequency, low-intensity, and horizontal multidirectional vibration excitation. In this paper, we further studied the possibility of vertical multidirectional energy harvesting using this device, as well as the influence of several important parameters (rope margin, liquid level height, and floating block shape) on the output performance. The results showed that the proposed PVEH can realize energy harvesting in three-dimensional space and that the output characteristic is adjustable.

S1-State Decay Dynamics of Benzenediols (Catechol, Resorcinol, and Hydroquinone) and Their 1:1 Water Clusters.

The S1-state decaying rates of the three different benzenediols, catechol, resorcinol, and hydroquinone, and their 1:1 water clusters have been state-specifically measured using the picosecond time-resolved parent ion transients obtained by the pump (excitation) and probe (ionization) scheme. The S1 lifetime of catechol is found to be short, giving τ ∼ 5.9 ps at the zero-point level. This is ascribed to the H-atom detachment from the free OH moiety of the molecule. Consistent with a previous report (J. Phys. Chem. Lett. 2013, 4, 3819-3823), the S1 lifetime gets lengthened with low-frequency vibrational mode excitations, giving τ ∼ 9.0 ps for the 116 cm-1 band. The S1 lifetimes at the additional vibronic modes of catechol are newly measured, showing the nonnegligible mode-dependent fluctuations of the tunneling rate. When catechol is complexed with water, the S1 lifetime is enormously increased to τ ∼ 1.80 ns at the zero-point level while it shows an unusual dip at the intermolecular stretching mode excitation (τ ∼ 1.03 ns at 146 cm-1). Otherwise, it is shortened monotonically with increasing the internal energy, giving τ ∼ 0.67 ns for the 856 cm-1 band. Two different asymmetric or symmetric conformers of resorcinol give the respective S1 lifetimes of 4.5 or 6.3 ns at their zero-point levels according to the estimation from our transients taken within the temporal window of 0-2.7 ns. When resorcinol is 1:1 complexed with H2O, the S1 decaying rate is slightly accelerated for both conformers. The S1 lifetimes of trans and cis forms of hydroquinone are measured to be more or less same, giving τ ∼ 2.8 ns at the zero-point level. When H2O is complexed with hydroquinone, the S1 decaying process is facilitated for both conformers, slightly more efficiently for the cis conformer.

Theoretical Study of Proton Tunneling in the Imidazole–Imidazolium Complex

Proton tunneling in the hydrogen-bonded imidazole–imidazolium complex ion has been studied theoretically. Ab initio CASSCF/6-311++G(d,p) calculations concerning geometry optimization and vibrational frequencies have been carried out for equilibrium and transition state structures of the system. Two-dimensional double-well model potentials were constructed on the basis of ab initio results and used to analyze the proton dynamics in the hydrogen bond and the influence of the excitation of low-frequency hydrogen-bond vibrations on the proton tunneling splittings. The energy of tunneling-split vibrational sublevels of the high-frequency tunneling mode have been calculated for its ground and first excited vibrational state for the series of excitations of the coupled low-frequency intramolecular hydrogen-bond modes. The promoting and suppressing effect of the low-frequency modes on the proton splittings was shown in the ground and first excited vibrational state of the tunneling mode. The vibrational sublevels form the two separate semicontinuous bands between which the absorption transitions may occur. This mechanism explains the experimentally observed splitting and doublet-component broadening of the high-frequency N–H stretching infrared (IR) absorption band.

Prediction of the driver’s head acceleration and vibration isolation performance of the seating suspension system using the time and frequency domain modeling

Long-time exposure to low-frequency vibration will negatively impact human health.A rapid biodynamic system modeling method has been proposed to study the human body’s response to the low-frequency vibration excitation in the whole vehicle environment. The sensitivity of design parameters of the seating suspension system to the vibration isolation performance will be studied. The dynamic model consists of a lumped parameter mass-spring-dashpot model of seven degrees of freedom (7DOF) and used for the prediction of the head acceleration in the time domain and peak transmissibility ratio in the frequency domain under a sinusoidal wave excitation and random road profile excitations of different road classes and vehicle speeds. A calculation formula has been established to predict the seat effective amplitude transmissibility (SEAT) from the transmissibility ratios and frequency weighting function of the ISO 8606, while the transmissibility ratios can be calculated from the frequency response analysis of the seven degrees of freedom system dynamic equations. The simulation results in the frequency domain have been verified by those in the time domain for the linear system assumption. The change trends of the driver’s head acceleration, SEAT value, and peak transmissibility ratio from the driver’s head to the seat base with respect to the stiffness and damping coefficients of the seat and cushion have been compared with and verified by one another.It is proved that in the vehicle system, individually, reducing the individual stiffness and damping coefficients of the seat structure, reducing the individual seat cushion stiffness, and increasing the individual seat cushion damping coefficient one by one will be able to reduce the driver’s head acceleration, peak transmissibility ratio, and SEAT value from the head to seat base, and improve the ride comfort. Simultaneously reducing the stiffness and damping coefficients of the seat and cushion will be able to reduce the driver’s head acceleration, peak transmissibility ratio, and SEAT value from the head to seat base and improve the ride comfort. The reduction effect of the driver’s head acceleration is more substantial under the Class E road profile of a large profile roughness than that under the other road classes.

Collective excitations in α-helical protein structures interacting with the water environment

ABSTRACT Low-frequency vibrational excitations of protein macromolecules in the terahertz frequency region are suggested to contribute to many biological processes such as enzymatic catalysis, intra-protein energy/charge transport, recognition, and allostery. To explain high effectiveness of these processes, two possible mechanisms of the long-lived excitation were proposed by H. Fröhlich and A.S. Davydov, which relate to either vibrational modes or solitary waves, respectively. In this paper, we developed a quantum dynamic model of vibrational excitation in α-helical proteins interacting with the aqueous environment. In the model, we distinguished three coupled subsystems, i.e., (i) a chain of hydrogen-bonded peptide groups (PGs), interacting with (ii) the subsystem of the side-chain residuals which in turn interact with (iii) the environment, surrounding water responsible for dissipation and fluctuation in the system. It was shown that the equation of motion for phonon variables of the PG chain can be transformed to nonlinear Schrodinger equation which admits bifurcation into the solution corresponding to the weak-damped vibrational modes (Fröhlich-type regime) and Davydov solitons. A bifurcation parameter is derived through the strength of phonon–phonon interaction between the side-chains and hydration-shell water molecules. As shown, the energy of these excited states is pumped through the interaction of the side-chains with fluctuating water environment of the proteins. The suggested mechanism of the collective vibrational mode excitation is discussed in connection with the recent experiments on the long-lived collective protein excitations in the terahertz frequency region and vibrational energy transport pathways in proteins.

Anharmonicities in the temperature-dependent bending rigidity of BC3 monolayer

The present work investigated the temperature-dependent thermodynamic and structural characteristics of graphene-like monolayer boron carbide (g-BC3) using classical molecular dynamics simulations. Herein, we mainly focused on the temperature dependence of mean square displacement of thermally stimulated ripples and bending rigidity of g-BC3. We observed that at high temperatures, the specific heat capacity at constant volume exhibits a significant increase beyond the limit of Dulong-Petit value due to the presence of anharmonicity in the g-BC3. Besides, the linear thermal expansion coefficient is found to be negative owing to the excitation of low-frequency bending vibrations in the out-of-plane orientation. Studies reveal that the out-of-plane of height fluctuations and bending rigidity are fully dependent on temperature and are described using the continuum theory of membranes. Moreover, the study on the height fluctuation and correlation shows variation from the estimation of the harmonic theory of membranes as a consequence of the anharmonic features of g-BC3. We believe that our study will provide a notable contribution to numerous applications of g-BC3 including nanoelectromechanical (NEMS) devices to become a reality.

On the issue of inertial excitation of diagnostic low-frequency vibrations in pipelines of housing and communal services

The article discusses and analyzes issues related to the diagnosis of the technical condition of pipelines for housing and communal services. The main attention is paid to the inertial excitation of diagnostic low-frequency vibrations in the pipeline wall using the developed device. The results of experimental studies are presented.

Eigenstates of soft-mode vibrational excitations in thin-film metallic glasses

The vibrational excitations in ${\mathrm{Cu}}_{50}{\mathrm{Zr}}_{50}$ thin-film metallic glasses are investigated using molecular dynamics simulations. A strong density layering parallel to surfaces is formed in the glassy thin films. This layering behavior results in a layerlike arrangement of soft regions through films. The vibrational excitations in the periodic soft layers are proved to be harmonic and in analog y with the simple one-dimensional lattice vibration. A low-frequency and optical-like phonon mode features the soft-mode excitations. The soft-mode excitations enhance the vibrational density of states in the low-frequency side, depending on the softness of layers. Our results provide direct evidence supporting the low-frequency and nonacoustic vibrational excitations of soft domains in glasses.

Enhancement of damage identification in composite structures with self-heating based vibrothermography

The self-heating vibrothermography non-destructive testing method is a promising approach for testing polymeric composite structures with a single-side access or inability of application of external heating sources for thermal excitation. The method is based on excitation of low-frequency mechanical vibrations with multiple resonant frequencies, which allows for local heating of a tested structure, and based on a captured thermal response, identification of structural damage. Although the method is quite sensitive for damage, the resulting damage signatures in thermograms are often blurred or invisible due to the measurement noise and non-uniform temperature evolution on the surface of a tested structure. In this paper, the authors examine various post-processing techniques applied for infrared thermograms in order to enhance damage detectability in polymeric composite structures. Three types of methods were examined: methods based on statistical features, a new method based on trend estimation of the temperature profiles, and a method based on similarity maps. The results of the processing reveal visible enhancement of the damage detectability using the proposed methods, which allow detecting and identifying more damage signatures compared to single raw thermograms.

Коллективные возбуждения в альфа-спиральной молекуле белка

Continuous energy supply, a necessary condition for life, excites a state far from thermodynamic equilibrium, in particular coherent electric polar vibrations depending on water ordering in the cell. The collective, low-frequency vibrational excitations in protein macromolecules in the terahertz frequency region are suggested to orchestrate many protein processes such as enzymatic activity, electron/energy transport, conformation transitions and others. The most significant type of excitations is long-lived coherent vibronic modes and waves which are either spreading over large protein subdomains or being localised states. Two possible mechanisms of the formation of collective dynamic modes in the form of Frohlich collective mode and Davydov soliton were previously suggested. We developed a unified quantum-mechanics approach to describe conditions of the formation of Frohlich vibronic state and Davidov soliton in alphahelical protein molecules interacting with the environment. We distinguish three subsystems in the model, i.e., (i) oscillating peptide groups (PGs), interacting with (ii) the subsystem of side residuals of proteins, which in turn interacts with the environment (surrounding water), which is responsible for dissipation and fluctuation processes and modelled by a system of harmonic oscillators. It was shown that the equation of motion for dynamic variables of PG chain (phonon variables) can be transformed to the nonlinear Schrodinger equation for order parameters, which determines energy “pumping” due to protein interaction with a reservoir. Solution of the order parameter equation was shown to admit bifurcation into the solution corresponding to the formation of weak damped collective vibronic mode with growing amplitude. It was also shown that the solution corresponding to Davydov soliton can exist at certain boundary conditions in this bifurcation region. The suggested mechanism of emergent of macroscopic dissipative structures in the form of collective vibronic modes in proteins is discussed in connection with recent experimental data on long-lived collective protein excitation in the terahertz frequency region

Evidence of Ultrafast Charge Transfer Driven by Coherent Lattice Vibrations.

We report evidence that intermolecular vibrations coherently drive charge transfer between the sites of a material on ultrafast time scales. Following a nonresonant stimulated Raman pump pulse that excites the organic material quinhydrone, we observe the initial appearance of oscillations due to intermolecular lattice vibrations and then the delayed appearance of a higher-frequency oscillation that we assign to a totally symmetric intramolecular vibration. We use the coherent dynamics of the transient reflectivity signal to propose that coherence transfer drives excitation of this intramolecular vibration. Furthermore, we conclude that the dynamical frequency shift of the intramolecular vibration reports the formation of a quasi-stable charge-separated state on ultrafast time scales. We calculate model dynamics using the extended Hubbard Hamiltonian to explain coherence transfer due to vibrationally driven charge transfer. These results demonstrate that the coherent excitation of low-frequency vibrations can drive charge transfer in the solid state and control material properties.

Enhanced nonlinear crack-wave interactions for structural damage detection based on guided ultrasonic waves

The paper presents a new damage-detection method based on nonlinear crack-wave interaction. Low-frequency vibration excitation is introduced to perturb damage, and high-frequency interrogating wave is used to detect damage-related nonlinearities. However, in contrast to other crack-wave interaction approaches, localised wave packets are used for high-frequency excitation. The synchronisation of the low-frequency vibration with the interrogating high-frequency wave packets is a key element of the proposed method. Numerical simulations and simple experimental tests in cracked aluminium beams are performed to demonstrate the method. The results show that the proposed method can detect and localise damage-related and intrinsic nonlinearities, allowing for reliable damage detection. The method does not require baseline measurements representing an undamaged condition, and it is not sensitive to temperature variations. Copyright © 2016 John Wiley & Sons, Ltd.

Understanding the atomic dynamics and thermodynamics of glasses: Status and outlook

The heat capacity of glasses at temperatures of about ~10K for a long time was considered to be anomalously higher than that of the corresponding crystals. The related excess of the low-energy vibrational states, the so-called ‘boson’ peak, was similarly considered to be anomaly distinguishing glasses from crystals and related to their disordered state. Recent results reveal that (i) the difference in the discussed properties occurs not because the glass is structurally disordered, but because it (usually) has lower density than that of the corresponding crystal, (ii) the heat capacity of glasses and crystals with the same densities is quite similar, and (iii) the boson peak is the glassy counterpart of the van Hove singularity of the corresponding crystal. We analyze the generality of the new results and discuss the compatibility of the suggested interpretation of the boson peak with available experimental data. Analyzing the relation of the new results to various theoretical models, we discuss a possible experimental approach to explore further the nature of the low-frequency vibrational excitations in glasses.

Investigations of heme distortion, low-frequency vibrational excitations, and electron transfer in cytochrome c

Cytochrome (cyt) c is an important electron transfer protein. The ruffling deformation of its heme cofactor has been suggested to relate to its electron transfer rate. However, there is no direct experimental evidence demonstrating this correlation. In this work, we studied Pseudomonas aeruginosa cytochrome c551 and its F7A mutant. These two proteins, although similar in their X-ray crystal structure, display a significant difference in their heme out-of-plane deformations, mainly along the ruffling coordinate. Resonance Raman and vibrational coherence measurements also indicate significant differences in ruffling-sensitive modes, particularly the low-frequency γa mode found between ∼50-60 cm(-1). This supports previous assignments of γa as having a large ruffling content. Measurement of the photoreduction kinetics finds an order of magnitude decrease of the photoreduction cross-section in the F7A mutant, which has nearly twice the ruffling deformation as the WT. Additional measurements on cytochrome c demonstrate that heme ruffling is correlated exponentially with the electron transfer rates and suggest that ruffling could play an important role in redox control. A major relaxation of heme ruffling in cytochrome c, upon binding to the mitochondrial membrane, is discussed in this context.

Impact Damage Detection in Composite Chiral Sandwich Panels

This paper demonstrates impact damage detection in a composite sandwich panel. The panel is built from a chiral honeycomb and two composite skins. Chiral structures are a subset of auxetic solids exhibiting counterintuitive deformation mechanism and rotative but not reflective symmetry. Damage detection is performed using nonlinear acoustics,involves combined vibro-acoustic interaction of high-frequency ultrasonic wave and low-frequency vibration excitation. High-and low-frequency excitations are introduced to the panel using a low-profile piezoceramic transducer and an electromagnetic shaker, respectively. Vibro-acoustic modulated responses are measured using laser vibrometry. The methods used for impact damage detection clearly reveal de-bonding in the composite panel. The high-frequency weak ultrasonic wave is also modulated by the low-frequency strong vibration wave when nonlinear acoustics is used for damage detection. As a result frequency sidebands can be observed around the main acoustic harmonic in the spectrum of the ultrasonic signal.