Low-frequency Vibration Research Articles

Sequential addition of cations increases photoluminescence quantum yield of metal nanoclusters near unity

Photoluminescence is one of the most intriguing properties of metal nanoclusters derived from their molecular-like electronic structure, however, achieving high photoluminescence quantum yield (PLQY) of metal core-dictated fluorescence remains a formidable challenge. Here, we report efficient suppression of the total structural vibrations and rotations, and management of the pathways and rates of the electron transfer dynamics to boost a near-unity absolute PLQY, by decorating progressive addition of cations. Specifically, with the sequential addition of Zn2+, Ag+, and Tb3+ into the 3-mercaptopropionic acids capped Au nanoclusters (NCs), the low-frequency vibration of the metal core progressively decreases from 144.0, 55.2 to 40.0 cm−1, and the coupling strength of electrons-high-frequency vibration related to surface motifs gradually diminishes from 40.2, 30.5 to 14.4 meV. Moreover, introducing cation additives significantly reduces electron transfer time from 40, 27 to 12 ps in the pathway from staple motifs to the metal core. This benefits from the shrinkage of the total structure that speeds up the shell-core electron transition, and in particular, the Tb3+ provides a hopping platform for the excited electrons as their intrinsic ladder-like energy level structure. As a result, it allows a remarkable enhancement in PLQY, from 51.2%, 83.4%, up to 99.5%.

Research on design and control method of active vibration isolation system based on piezoelectric Stewart platform.

Space payloads in orbit are vulnerable to small vibrations from satellite platforms, which can degrade their performance. Traditional methods typically involve installing a passive vibration isolation system between the platform and the payload. However, such systems are usually effective only for high-frequency, large-amplitude vibrations and perform poorly in isolating low-frequency vibrations and resonances below 10Hz. To address this limitation, this paper proposes an active vibration isolation system using a 6-degrees-of-freedom Stewart platform driven by piezoelectric actuators. First, the characteristics of the Stewart platform are analyzed and modeled, with the deformation displacement of each leg calculated through decoupling, allowing for high-precision servo control. Next, given the inherent hysteretic nonlinearity of piezoelectric ceramics, which significantly affects positioning accuracy, the hysteresis mechanism of the actuators is analyzed, and a phenomenological mathematical model based on Bouc-Wen operators is established. A Modified particle swarm optimization (MPSO) method is proposed for identifying the model's nonlinear parameters, significantly enhancing the optimization efficiency. Finally, feedforward inverse compensation and feedback linearization methods are introduced. Experimental results verify that the designed active-passive vibration isolation system greatly improves both the positioning accuracy of the piezoelectric actuators and the active vibration isolation performance of the platform.

Ultra broadband low-frequency vibration and pulse mitigation of electromagnetic induction-based metastructure

Ultra broadband low-frequency vibration and pulse mitigation of electromagnetic induction-based metastructure

Experimental study on long-term fatigue behavior of piezoelectric energy harvesters under high and Low-Frequency vibration excitation

Experimental study on long-term fatigue behavior of piezoelectric energy harvesters under high and Low-Frequency vibration excitation

A low-frequency vibration energy harvester based on a quasi-zero stiffness mechanism and magnetic repulsion

ABSTRACT This work proposes a piezoelectric energy harvester with magnetic repulsion and a quasi-zero stiffness mechanism to achieve self-powered functionality for microelectronic devices in low-frequency vibration environments (MR-QZS-PEH).The relationship between the stress and strain of the piezoelectric sheet is obtained according to the elastic theory of materials and the modal simulation of the piezoelectric sheet is conducted under different excitation frequencies. A series of experiments validate the impact of introducing nonlinear magnetic repulsive force into the quasi-zero stiffness mechanism on the efficiency of the device. The results show that the MR-QZS-PEH achieves the maximum voltage of 36.58 V when the mass block is 78.3 g and the spring wire diameter is 0.6 mm under 5.00 Hz excitation frequency and 40 mm displacement amplitude. The prototype achieves a maximum output power of 115 mW when the external resistance is 11kΩ. The MR-QZS-PEH can supply power 81 LEDs and the temperature and humidity sensor, demonstrating it can meet the power needs of microelectronic devices, which provides new ideas and methods for powering microelectronic devices in a vibration environment.

3D printed three-dimensional elastic metamaterial with surface resonant units for low-frequency vibration isolation

ABSTRACT This study leverages the high manufacturing freedom of 3D printing technology to design a new type of three-dimensional elastic metamaterial with surface resonant units. This metamaterial uses chiral connecting rods and mass blocks on the surface to generate local resonance effects, achieving omnidirectional vibration isolation effects with both low frequency and wide bandwidth, and also has a certain load-bearing capacity. The mechanisms of local resonance bandgap generation are illustrated from the band structure and vibration modes at the edge frequency of the bandgap. The influence of structural geometric parameters and material properties on the bandgap is systematically investigated via finite element method. The transmission characteristics of the metamaterial are obtained through simulation and experiment, and the bandgap areas achieved from two methodologies match each other well. Through static compression tests, the compressive abilities of metamaterials with different frame thicknesses are studied, providing theoretical guidance and data support for engineering applications of balancing vibration isolation and load-bearing.

On low-frequency vibration suppression characteristics of corrugated metamaterial beams

On low-frequency vibration suppression characteristics of corrugated metamaterial beams

Numerical Investigation of Ultra-Wide Low-Frequency Wave Attenuation Using Seismic Metamaterials with Auxetic Slender Strips

Seismic metamaterials are an emerging vibration-damping technology, yet concentrating the bandgap in the low-frequency range remains challenging due to the constraints imposed by lattice size. In this study, we numerically investigated seismic metamaterials connected by auxetic (negative Poisson’s ratio) slender strips, which exhibit an exceptionally wide low-frequency band gap for vibration isolation. Using a finite element method, we first performed a comparative analysis of several representative seismic metamaterial configurations. The results showed that the auxetic thin strip-connected steel column structure demonstrated outstanding performance, with the first complete band gap starting at 1.61 Hz, ending at 80.40 Hz, spanning a width of 78.79 Hz, and achieving a relative bandwidth of 192.15%. Notably, while most existing designs feature lattice constants in the ten-meter range (with the smallest around two meters), our proposed structure achieves these results with a lattice constant of only one meter. We further analyzed the transmission characteristics of the steel column structure, both with and without concrete filling. Interestingly, significant vibration attenuation, approaching 70 dB, was observed below the first complete band gap (approximately 0.22–1.17 Hz), even without the use of concrete. By comparing the flexural wave band gap with the transmission spectrum, we attributed this attenuation primarily to the presence of the band gap, a phenomenon often overlooked in previous studies. This attenuation at lower frequencies highlights the potential for effectively reducing low-frequency vibration energy. To further enhance the attenuation, the number of periods in the propagation direction can be increased. Additionally, we systematically explored the influence of geometric parameters on the first complete band gap. We found that optimal results were achieved with a slender strip length of 0.05 m, its width between 0.05 and 0.1 m, and a steel structure width of 0.1 m. Our findings underscore the critical role of auxetic thin strips in achieving broadband low-frequency vibration isolation. The approach presented in this study, along with the discovery of low-frequency flexural wave band gaps, provides valuable insights for seismic engineering and other applications requiring effective vibration reduction strategies.

Experimental Investigation and Modeling of Surface Roughness in BTA Deep Hole Drilling with Vibration Assisted.

The surface roughness of hole machining greatly influences the mechanical properties of parts, such as early fatigue failure and corrosion resistance. The boring and trepanning association (BTA) deep hole drilling with axial vibration assistance is a compound machining process of the tool cutting and the guide block extrusion. At the same time, the surface of the hole wall is also ironed by the axial large amplitude and low-frequency vibration of the guide block. The surface-forming mechanism is very complicated, making it difficult to obtain an effective theoretical analytical model of the surface roughness of the hole wall through kinematic analysis. In order to achieve accurate prediction of the surface quality of the hole wall, the chip-breaking mechanism and the hole wall formation mode of BTA deep hole vibration drilling were analyzed. The influence of drilling spindle speed, feed, amplitude, and vibration frequency on the surface roughness of the hole wall during BTA deep hole vibration drilling was illustrated by a single-factor experiment. A four-factor and three-level test scheme was designed by using the Box-Behnken design (BBD) experimental design method. A surface roughness prediction model for hole wall machining was established based on the response surface methodology. The accuracy of the prediction model was analyzed through ANOVA, and the complex correlation coefficient of the model was 0.9948, indicating that the prediction model can better reflect the mapping relationship between vibration drilling parameters and surface roughness. After optimization analysis and experimental verification, the obtained vibration drilling parameters can achieve smaller surface roughness. The error between the predicted value of the model and the experimental measurement value is 8.65%. The established prediction model is reliable and can accurately predict the surface roughness of the hole wall of BTA deep hole axial vibration drilling, providing a theoretical basis for the surface quality control of the machining hole wall. It can be applied to process optimization in practical production.

Planar Two-Dimensional Vibration Isolator Based on Compliant Mechanisms

In practical engineering applications, the vibration is often generated in various directions and can be harmful to the engineering equipment. Thus, it is necessary to develop vibration isolators that can reduce vibration in multiple directions. In this paper, we propose a planar two-dimensional vibration isolator based on compliant mechanisms. The proposed mechanism consists of two negative stiffness-compliant modules and two positive stiffness-compliant modules, which leads to the quasi-zero stiffness (QZS) property in the mechanism. The dynamic model is established by using the third-order Taylor expansion and the harmonic balance method. Based on the dynamic model, the influence of different parameters on the displacement transmissibility is discussed, including damping ratio, system stiffness, and excitation amplitude. Finally, we conducted the vibration isolation experiments and obtained the displacement transmissibility of the isolator. The results verify that the proposed isolator has good isolation performance for low-frequency vibration.

MATHEMATICAL MODELING OF OPERATIONAL RELIABILITY OF GROUND-BASED NAVIGATION SYSTEMS

The theoretical justification for improving the effectiveness of vibration isolation for navigation equipment by reducing the natural frequency of the elastic suspension through the use of an additional electromagnetic loading system on the moving part is presented. An overview of the main elements of primary sensors and vibration protection systems for reproducing vibrations is provided. It is emphasized that vibration isolation of navigation equipment in the low-frequency disturbance range, typical for terrestrial carriers, is a crucial component in preventing emergency situations on airborne and marine vessels. A detailed calculation scheme for a vibration test stand using vertically installed flat springs is presented. Relationships between the natural frequency of the suspension and the system parameters are determined. One method for reducing the natural frequency of an elastic suspension on flat springs is analyzed. The calculation scheme for the suspension with vertically installed elastic springs is outlined. The stability conditions of the linear system, which depend on the amplitude of oscillations, are analytically investigated. It is emphasized that there is no translational movement of the suspension other than the chosen one. It is proposed to consider the calculation scheme of the suspension in the absence of dry friction. The structural component of the magnetic system is analyzed. The system of dispersive fluxes and their concentration in the air gap is outlined. An analysis of the compensatory nonlinearity of the stiffness characteristic of elastic elements is carried out. The reduction of distortions in the shape of the moving oscillations of the moving platform in the horizontal plane is analyzed. Stiffness characteristics of the suspension with a magnet for several actual values of kkk and δ\deltaδ are provided. Experimental calculations demonstrate that this vibration isolation system for navigation equipment leads to a significant reduction in the natural frequency of the suspension, ensuring its operational reliability and maximum prevention of low-frequency horizontal vibrations.

Molecular Hydride Superconductor BiH4 with Tc up to 91 K at 170 GPa.

In pursuit of high-Tc hydride superconductors, the molecular hydrides have attracted less attention because the hydrogen quasimolecules are usually inactive for superconductivity. Here, we report on the successful synthesis of a novel bismuth hydride superconductor C2/c-BiH4 at pressures around 170-180 GPa. Its structure comprises bismuth atoms and elongated hydrogen molecules with a H-H bond length of 0.81 Å at 170 GPa, characterizing it as a typical molecular hydride. Transport measurements revealed the occurrence of superconductivity with Tc up to 91 K at 170 GPa, as evidenced by a sharp drop of resistivity to zero and a characteristic downward shift of Tc under magnetic fields. Calculations by density functional theory elucidate that both midfrequency H-derived phonons and low-frequency vibrations from Bi atoms are important for the strong electron-phonon coupling in BiH4, differentiating it from most high-Tc superconducting hydrides. Our work not only places C2/c-BiH4 among the molecular hydride superconductors with the highest Tc but also offers new directions for designing and synthesizing more high-Tc hydride superconductors.

Design of nonlinear rubber vibration isolators with low resonant frequency and high load bearing capacity

Designing a rubber vibration isolator to simultaneously meet the requirements on both low-frequency vibration isolation and high load carrying capacity has always been a major challenge. To tackle this problem, in this paper, a design strategy capable of effectively balancing these two effects to guide the design of such isolators is proposed. The rubber isolator static and dynamic behavior prediction models suitable for engineering applications are first established, where Yeoh model is adopted for rubber strong nonlinear feature prediction. Experiments are carried out to determine the material constants in Yeoh model and dynamic-to-static ratio of the rubber material. Combing with Multi-Objective Genetic Algorithm, a design strategy is proposed. The conducted experiments demonstrate that based on the proposed numerical model and design procedure, rubber isolators with enough load bearing capability and low-frequency vibration isolation performance can be successfully designed.

Low-frequency vibration monitoring system measuring the fringe shift by using linear Fresnel zone plates for shiny surfaces

This paper presents a vibration monitoring system that measures the fringe shift from the Fresnel diffraction pattern for noncontact measurement of translational and angular vibrations. Conventional vibration systems have some major limitations in practical applications. For example, a laser Doppler vibrometer (LDV) fails to accurately measure large-amplitude vibrations of a mirrored object undergoing dynamic tilts or rotations. Additionally, achieving the accuracy required for micro/nanomeasurement in precision machines when measuring low-frequency vibrations (LFV) remains a significant challenge. In this study, the vibration measurement system utilizes a linear Fresnel zone plate with parallel strip lines to create the diffraction pattern. Surface vibrations cause shifts in these lines, and the resulting fringe pattern on the vibrating surface carries information about the local vibrational amplitude and frequency. To achieve this, the linear vibration and displacement of the object are accurately verified using a linear motion platform and a rotation stage, with accuracies of approximately 20 nm and 0.002°, respectively. Rotational vibration measurements utilize tracking beam deflection through the image fringe shift measurement method, while out-of-plane displacement is determined both from this method and from changes in the period density of diffraction patterns, which depend on the position of the patterns and the local spatial frequency. A CCD camera captures sequences of images of the deflected fringes due to vibrating object. The system can detect linear vibrations with frequencies above 251.91 µHz and has a displacement uncertainty of approximately 5.8 µm, achieving an angular resolution of 37.67 µrad. Compared to conventional LDV vibrometers and eddy current sensors, the proposed method offers an effective and accurate technique for measuring LFVs of shiny surfaces. Furthermore, it provides a significantly extended measurement range for both translation and rotational angles of objects in engineering applications.

Multi-Objective Topology Optimization of Thin-Plate Structures Based on the Stiffener Size and Layout

To address the limitations of existing optimization methods that focus on single objectives or neglect stiffener features, a multi-objective topology optimization (MOTO) method is proposed based on the stiffener size and layout. By constraining the initial structural performance parameters, the optimal stiffener height is determined through size optimization. Based on the stiffener height, single-objective topology optimization is used to achieve the best material distribution. The stiffener width is treated as a design variable, while MOTO is performed on the load point displacement, first natural frequency, and mass, thereby yielding an optimal stiffener width and performance. Finally, a multi-dimensional analysis of the stiffener height, width, and dynamic and static characteristics of the stiffened thin-plate structure is conducted. The results indicate that the optimized stiffener layout is considerably improved. Compared to the initial structure, the maximum and average displacements of the load point are reduced by 23.26% and 8.62%, respectively. The first natural frequency increases by 3.81%, while the maximum resonance amplitude and overall structural mass decrease by 39.97% and 1.99%, respectively. The results indicate that the optimized structure achieves a lightweight design while maintaining better stiffness and low-frequency vibration resistance. The feasibility and effectiveness of the proposed method are validated.

Multiscale Modeling of Charge Transport in Organic Semiconductors: Assessing the Validity of the Harmonic Approximation for Low-Frequency Vibrations

Multiscale Modeling of Charge Transport in Organic Semiconductors: Assessing the Validity of the Harmonic Approximation for Low-Frequency Vibrations

Smoke Precipitation by Exposure to Dual-Frequency Ultrasonic Oscillations

The analysis conducted herein has shown that the efficiency of smoke precipitation can be improved by additionally making smoke particles interact with ultrasonic (US) oscillations. Because the efficiency of US coagulation lowers when small particles assemble into agglomerates, the authors of this work have suggested studying how smoke particles interact with complex sound fields. The fields are formed by at least two US transducers which work at a similar frequency or on frequencies with small deviations. To form these fields, high-efficiency bending wave ultrasonic transducers have been developed and suggested. It has been shown that a complex ultrasonic field significantly enhances smoke precipitation. The field in question was constructed by simultaneously emitting 22 kHz US oscillations with a sound pressure level no lower than 140 dB at a distance of 1 m. The difference in US oscillations’ frequencies was no more than 300 Hz. Due to the effect of multi-frequency ultrasonic oscillations induced in the experimental smoke chamber, it was possible to provide a transmissivity value of 0.8 at a distance of 1 m from the transducers and 0.9 at a distance of 2 m. Thus, the uniform visibility improvement and complete suppression of incoming smoke was achieved. At the same time, the dual-frequency effect does not require an increase in ultrasonic energy for smoke due to the agglomeration of small particles under the influence of high-frequency ultrasonic vibrations and the further aggregation of the formed agglomerates by creating conditions for the additional rotational movement of the agglomerates due to low-frequency vibrations.

Image Motion Blur Mechanism-Based Measurement Method for Low-Frequency Vibration Amplitude and Direction

Image Motion Blur Mechanism-Based Measurement Method for Low-Frequency Vibration Amplitude and Direction

A tri-functional integrated hybrid energy harvester for the efficient collection of low-frequency environmental vibrational energy

Abstract To address the power supply challenges of Internet of Things (IoT) devices, this study proposes a novel tri-functional integrated hybrid energy harvester (TF-HEH) for efficiently capturing low-frequency environmental vibrations. The TF-HEH integrates triboelectric, electromagnetic, and piezoelectric mechanisms within a compact, 60 g cylindrical structure. Optimized for a 40 mm magnet length, the proposed TF-HEH exhibited high efficiency in converting vibrations into electricity, with peak outputs of 13 μW (pipe wall triboelectric generator), 17 μW (pipe cap triboelectric generator), 51.2 μW (piezoelectric nanogenerators), and 12.3 mW (electromagnetic generator) under a swing input with a 0.5 Hz frequency and 30° amplitude. The lightweight and portable design renders the device suitable for self-powered sensor operation in IoT applications.

Absorption and Excited-State Coherences of Cryogenically Cold Retinal Protonated Schiff Base in Vacuo.

Retinal protonated Schiff base (RPSB), found in its all-trans conformer in Bacteriorhodopsin, undergoes barrier-controlled isomerization upon photoabsorption through polyene chain torsion. The effects of the protein environment on the active vibrations during photoabsorption and their redistribution are still not understood. This paper reports on femtosecond time-resolved action-absorption measurements of cryogenically cooled gas-phase all-trans RPSB, which exhibit two coherent vibrational oscillations, 167(14) cm and 117(1) cm , of the first excited state with dephasing times of ps. The absence of the high-frequency vibration in solution and the low-frequency vibration in the protein indicates that these vibrations are sensitive to environments. An action-absorption spectrum of cryogenically cold all-trans RPSB, reveals a cm active vibration when using a hole-burning technique and 1500 cm C=C stretching modes.