Low-frequency Mechanical Vibrations Research Articles

Liver Magnetic Resonance Elastography: Focus on Methodology, Technique, and Feasibility.

Magnetic resonance elastography (MRE) is an imaging technique that combines low-frequency mechanical vibrations with magnetic resonance imaging to create visual maps and quantify liver parenchyma stiffness. As in recent years, diffuse liver diseases have become highly prevalent worldwide and could lead to a chronic condition with different stages of fibrosis. There is a strong necessity for a non-invasive, highly accurate, and standardised quantitative assessment to evaluate and manage patients with different stages of fibrosis from diagnosis to follow-up, as the actual reference standard for the diagnosis and staging of liver fibrosis is biopsy, an invasive method with possible peri-procedural complications and sampling errors. MRE could quantitatively evaluate liver stiffness, as it is a rapid and repeatable method with high specificity and sensitivity. MRE is based on the propagation of mechanical shear waves through the liver tissue that are directly proportional to the organ's stiffness, expressed in kilopascals (kPa). To obtain a valid assessment of the real hepatic stiffness values, it is mandatory to obtain a high-quality examination. To understand the pearls and pitfalls of MRE, in this review, we describe our experience after one year of performing MRE from indications and patient preparation to acquisition, quality control, and image analysis.

Identification of pressure pulsation spectrum in a hydraulic system with a vibrating proportional valve

In this paper, attention was focused on identifying the components of the amplitude-frequency spectrum of pressure pulsations in a hydraulic system in which an external low-frequency mechanical vibration was subjected to a proportional hydraulic directional control valve. It was observed that an operating machine or device equipped with hydraulic valves is a source of mechanical vibrations with a wide frequency spectrum. The influence of these vibrations on the pressure pulsation spectrum was analyzed, identifying the components resulting from the forcing of the directional control valve spool. In addition, it was noted that the pressure pulsation spectrum includes components resulting from the pulsation of the displacement pump output feeding the hydraulic system. A description of these spectrum components was also made and, using the solution superposition method, the components of the pressure pulsation spectrum over a wide frequency range were identified.

Polyvinyl alcohol-based economical triboelectric nanogenerator for self-powered energy harvesting applications

Triboelectric nanogenerators (TENGs) have emerged as a promising alternative for powering small-scale electronics without relying on traditional power sources, and play an important role in the development of the internet of things (IoTs). Herein, a low-cost, flexible polyvinyl alcohol (PVA)-based TENG (PVA-TENG) is reported to harvest low-frequency mechanical vibrations and convert them into electricity. PVA thin film is prepared by a simple solution casting technique and utilized to serve as the tribopositive material, polypropylene film as tribonegative, and aluminum foil as electrodes of the device. The dielectric-dielectric model is implemented with an arch structure for the effective working of the PVA-TENG. The device showed promising electrical output by generating significant open-circuit voltage, short-circuit current, and power . Also, PVA-TENG is subjected to a stability test by operating the device continuously for 5000 cycles. The result shows that, the device is mechanically durable and electrically stable. Further, the as-fabricated PVA-TENG is demonstrated to show feasible applications, such as charging two commercial capacitors with capacitances 1.1 and 4.7 μF and powering green light-emitting diodes. The stored energy in the 4.7 μF capacitor is utilized to power a digital watch and humidity and temperature sensor without the aid of an external battery. Thus, the PVA-TENG facilitates ease of fabrication, robustness, and cost-effective strategy in the field of energy harvesting for powering lower-grid electronics by demonstrating their potential as a sustainable energy source.

Effect of low frequency vibration-assisted shielded metal arc welding on the properties of mild steel

Vibration-assisted welding (VAW) has emerged to be a feasible alternative to thermal and post-weld vibration treatments for arc welds in order to minimize stress concentrations and distortions thereby improving mechanical characteristics. Limited research is available considering low frequency vibration. The main objective is to develop an experimental setup to analyze the properties of welded connections made with shielded metal arc welding (SMAW) using low-frequency mechanical vibrations. Mild steel (MS) plates with dimensions of 100 mm by 50 mm and thickness of 5 mm are considered in this study. Heat inputs of 80 Amps, 100 Amps and 120 Amps were taken into consideration as input current. Vibration was varied between 0 and 100 Hz at every 20 Hz interval to study the Hardness, Tensile Strength and Impact Strength of welded joints. Microstructure of welded MS plates has been analyzed using SEM analysis. Experimental results revealed improved mechanical properties due to the application of low-frequency vibrations that may tend to increase the welding speed thus reducing time and enabling stronger, durable and reliable welded joints. A fine grain structure is seen for Low-frequency vibration-assisted welded butt joints implying improved mechanical properties due to excitation of weld pool.

Performance Optimization of Ultralow-Frequency Electromagnetic Energy Harvester Driven by Eccentric mass

Driven by an eccentric mass through a two-layered cantilevered plectrum, the electromagnetic energy harvester (EEH) can convert low-frequency mechanical vibrations into continuous uni-directional rotation. To optimize the performance of the EEH, electromagnetic analysis of the EEH was conducted. Three-phase winding permanent magnet (PM) topology was employed, and combinations of different coils and magnet pole numbers were designed. Then, the finite element method (FEM) was applied to analyze the influence of the combinations of the coils and pole numbers as well as the PM dimensions on the three-phase induced voltage. Prototypes with different configurations were fabricated and the analysis effectiveness was confirmed. Furthermore, different types of stator yokes were designed to enhance the magnetic field. Compared to the original prototype, the output voltage of the optimal prototype increased by 0.5 V with the same rotation speed, and the harmonic components were sufficiently low. Then, experiments with excitation by linear reciprocating motions and swing motions were conducted. Under different exciting conditions, the optimal prototype can also induce the highest voltage amplitude. With an increase in the weight of the eccentric mass, a long duration can be reached that lasts up to 12 s. In summary, the proposed optimization can achieve a high-efficiency and high-power density EEH.

Axisymmetrical resonance modes in an electrowetting optical lens.

Electrowetting-based adaptive optics are of great interest for applications ranging from confocal microscopy to LIDAR, but the impact of low-frequency mechanical vibration on these devices remains to be studied. We present a simple theoretical model for predicting the resonance modes induced on the liquid interface in conjunction with a numerical simulation. We experimentally confirm the resonance frequencies by contact angle modulation. They are found to be in excellent agreement with the roots of the zero-order Bessel functions of the first kind. Next, we experimentally verify that external axial vibration of an electrowetting lens filled with density mismatched liquids ( = 250 kg/m3) will exhibit observable Bessel modes on the liquid-liquid interface. An electrowetting lens filled with density matched liquids ( = 4 kg/m3) is robust to external axial vibration and is shown to be useful in mitigating the effect of vibrations in an optical system.

Stable 671-nm external cavity diode laser with output power exceeding 150 mW suitable for laser cooling of lithium atoms.

We report the design and performance of a Littrow-type 671-nm external cavity diode laser (ECDL) that delivers output power greater than 150 mW and features enhanced passive stability. The main body of the ECDL is constructed using titanium to minimize temperature related frequency drifts. The laser diode is mounted in a cylindrical mount that allows vertical adjustments while maintaining thermal contact with the temperature stabilized baseplate. The wavelength tuning is achieved by horizontal displacement of the diffraction grating about an optimal pivot point. The compact design increases the robustness and passive stability of the ECDL and the stiff but lightweight diffraction grating-arm reduces the susceptibility to low-frequency mechanical vibrations. The linewidth of the ECDL is ∼360 kHz. We use the 671-nm ECDL, without any additional power amplification, for laser cooling and trapping of lithium atoms in a magneto-optical trap. This simple, low-cost ECDL design using off-the-shelf laser diodes without anti-reflection coating can also be adapted to other wavelengths.

A novel insight into energy conservation and efficiency enhancement in wastewater treatment process: Low-frequency mechanical vibration induced

One important way to break the bottleneck of energy conservation and consumption reduction in sewage treatment process is to attenuate the mass transfer resistance, which is thought as one of key factors to determine the efficiency of activated sludge treatment system. Thus, in this study, two independent Anacrobic/Oxic reactors were operated under low dissolved oxygen (DO) condition to evaluate the effects of low-frequency mechanical vibrations on the removal efficiency of pollutants. Results indicate that 40 Hz low-frequency mechanical vibration could greatly strengthen the efficiency of pollutants removal. Microelectrode-mass transfer efficiency test platform revealed that 40 Hz low-frequency mechanical vibration could increase the oxygen transfer coefficient from gas to liquid by approximately 145.19 %, and oxygen diffusion coefficient from liquid to solid by 75.2 %. Fractal dimension of flocs, particle size and zeta potential analyses jointly suggested that low-frequency mechanical vibrations treatment can form more adsorption points and mass transfer channels to enhance mass transfer efficiency of oxygen in floc. In addition, low-frequency mechanical vibrations treatment further stimulated the biological activities associated with nitrogen metabolism (i.e., specific metabolism rate, metabolism enzyme activities), but slightly alerted the overall microbial community. The findings in this study suggest that low-frequency mechanical vibrations could effectively accelerate the pollutants removal under low-DO condition by enhancing oxygen transfer coefficient and stimulating the associated biological activities. Collectively, this study provides a new technical strategy for efficiency enhancement and energy conservation in the global sewage treatment industry.

Performance coefficient and determination of the output parameters of a three-phase two-stroke electromagnetic vibrometer

Determination of the optimal parameters of a three-phase two-stroke electromagnetic vibrometer of low-frequency mechanical vibrations based on a theoretical-chain model has been considered. Dependences of output power and performance coefficient are obtained to ensure effective vibration impact on heavy objects. The results obtained can be used in the optimal design of the vibrator design. Keywords: electromagnetic vibration; efficiency; circuittheoretic model; output power; vibration exciter.

SWAVE 2.0 Imaging of Placental Elasticity and Viscosity: Potential Biomarkers for Placenta-Mediated Disease Detection.

Pregnancy complications such as pre-eclampsia (PE) and intrauterine growth restriction (IUGR) are associated with structural and functional changes in the placenta. Different elastography techniques with an ability to assess the mechanical properties of tissue can identify and monitor the pathological state of the placenta. Currently available elastography techniques have been used with promising results to detect placenta abnormalities; however, limitations include inadequate measurement depth and safety concerns from high negative pressure pulses. Previously, we described a shear wave absolute vibro-elastography (SWAVE) method by applying external low-frequency mechanical vibrations to generate shear waves and studied 61 post-delivery clinically normal placentas to explore the feasibility of SWAVE for placental assessment and establish a measurement baseline. This next phase of the study, namely, SWAVE 2.0, improves the previous system and elasticity reconstruction by incorporating a multi-frequency acquisition system and using a 3-D local frequency estimation (LFE) method. Compared with its 2-D counterpart, the proposed system using 3-D LFE was found to reduce the bias and variance in elasticity measurements in tissue-mimicking phantoms. In the aim of investigating the potential of improved SWAVE 2.0 measurements to identify placental abnormalities, we studied 46 post-delivery placentas, including 26 diseased (16 IUGR and 10 PE) and 20 normal control placentas. By use of a 3.33-MHz motorized curved-array transducer, multi-frequency (80,100 and 120 Hz) elasticity measures were obtained with 3-D LFE, and both IUGR (15.30 ± 2.96 kPa, p=3.35e-5) and PE (12.33 ± 4.88 kPa, p=0.017) placentas were found to be significantly stiffer compared with the control placentas (8.32 ± 3.67 kPa). A linear discriminant analysis (LDA) classifier was able to classify between healthy and diseased placentas with a sensitivity, specificity and accuracy of 87%, 78% and 83% and an area under the receiver operating curve of 0.90 (95% confidence interval: 0.8-0.99). Further, the pregnancy outcome in terms of neonatal intensive care unit admission was predicted with a sensitivity, specificity and accuracy of 70%, 71%, 71%, respectively, and area under the receiver operating curve of 0.78 (confidence interval: 0.62-0.93). A viscoelastic characterization of placentas using a fractional rheological model revealed that the viscosity measures in terms of viscosity parameter n were significantly higher in IUGR (2.3 ± 0.21) and PE (2.11 ± 0.52) placentas than in normal placentas (1.45 ± 0.65). This work illustrates the potential relevance of elasticity and viscosity imaging using SWAVE 2.0 as a non-invasive technology for detection of placental abnormalities and the prediction of pregnancy outcomes.

Effects of mechanical vibration on the heat transfer performance of shell-and-tube latent heat thermal storage units during charging process

• The melting process of LHTS unit based on tubular heat exchanger under vibration condition is investigated. • Low frequency mechanical vibration can enhance heat transfer performance. • Mechanical vibration can significantly decrease melting time for all vibration amplitudes. • The inclination angle of vibration axis has a certain effect on heat transfer, and there is an optimal value at θ = 30°. Mechanical vibrations are unavoidable in thermal systems at certain times, but they do not only have a bad effect. This paper presents the first pioneering study of the effect of vibration on the heat transfer performance of a horizontal tubular heat exchanger. Through numerical simulation methods, by applying mechanical vibrations of different vibration frequencies and vibration amplitudes, the heat transfer enhancement effect of phase change material (PCM) under vibrational conditions are fully revealed. The results show that, under lower vibration frequencies (ω = 10 ∼ 20 Hz), which can significantly promote the mixing of melted PCM and melting heat transfer rate during charging processes. However, this heat transfer enhancement begins to weaken in the range of medium to high vibration frequencies. For all amplitudes, the heat transfer enhancement is markedly stronger than that of frequency, which is linked directly to the magnitude of the amplitude value. Furthermore, the effect on heat transfer enhancement has been discussed when there is an inclination of the vibration axis to the direction of gravity. When the inclination angle is varied from 0° to 90°, the contribution to heat transfer enhancement is greatest at θ = 30°, which is optimal inclination angle. This paper could fill the knowledge gap regarding the thermal performance of heat exchangers with different geometries under mechanical vibration and provide some guidance for future practical applications.

Clustering Characterization of Acoustic Emission Signals Belonging to Twinning and Dislocation Slip during Plastic Deformation of Polycrystalline Sn.

Results of acoustic emission (AE) measurements, carried out during plastic deformation of polycrystalline Sn samples, are analyzed by the adaptive sequential k-means method. The acoustic avalanches, originating from different sources, are separated on the basis of their spectral properties, that is, sorted into clusters, presented both on the so-called feature space (energy-median frequency plot) and on the power spectral density (PSD) curves. We found that one cluster in every measurement belongs to background vibrations, while the remaining ones are clearly attributed to twinning as well as dislocation slips at −30 °C and 25 °C, respectively. Interestingly, fingerprints of the well-known “ringing” of AE signals are present in different weights on the PSD curves. The energy and size distributions of the avalanches, corresponding to twinning and dislocation slips, show a bit different power-law exponents from those obtained earlier by fitting all AE signals without cluster separation. The maximum-likelihood estimation of the avalanche energy () and size () exponents provide (at −30 °C) and (at 25 °C), as well as (at −30 °C) and (at 25 °C). The clustering analysis provides not only a manner to eliminate the background noise, but the characteristic avalanche shapes are also different for the two mechanisms, as it is visible on the PSD curves. Thus, we have illustrated that this clustering analysis is very useful in discriminating between different AE sources and can provide more realistic estimates, for example, for the characteristic exponents as compared to the classical hit-based approach where the exponents reflect an average value, containing hits from the low-frequency mechanical vibrations of the test machine, too.

Optical Sensor, Based on an Accelerometer, for Low-Frequency Mechanical Vibrations.

This article documents the design, manufacture, and testing of a silicon inertial optical sensor for low-frequency (lower than 2 kHz) applications. Three accelerometer designs optimized by parameterization using Finite Element Analysis were considered. The accelerometers were manufactured and the one with the highest performance at low frequency was chosen for testing, which was attached to a steel package. The feasibility of using probes, based on micro-machined sensing elements, to measure mechanical vibrations with high resolution was also studied. The detection is performed with an air interferometer, eliminating the need for electric signals that are susceptible to electromagnetic interference and large temperature variations. From the fabrication technology using only a silicon wafer with both sides etched, the frequency response of the sensor, temperature operation (higher than 85 °C) and with a resolution of 17.5 nm, it was concluded that is achievable and feasible to design and manufacture an optical vibration sensor for potential harsh environments with a low cost.

Tactile Low Frequency Vibration in Dementia Management: A Scoping Review.

The prevalence of dementia is increasing with the ever-growing population of older adults. Non-pharmacological, music-based interventions, including sensory stimulation, were reported by the Lancet Commission in 2020 to be the first-choice approach for managing the behavioural and psychological symptoms of dementia. Low frequency sinusoidal vibration interventions, related to music interventions through their core characteristics, may offer relief for these symptoms. Despite increasing attention on the effectiveness of auditory music interventions and music therapy for managing dementia, this has not included low frequency vibration. This scoping review, following the JBI methodology guidelines, was conducted to investigate participants’ responses to both sound and mechanical vibration, the characteristics of the delivered interventions, methodological challenges, and the specifics of the research experiments reported. An extensive search was conducted in BMC, CINAHL, Cochrane Central Register of Controlled Trials, EMBASE, ERIC, MEDLINE (OvidSP), Pedro, ProQuest Central, PsycINFO, Scopus, and Web of Science. Current Controlled Trials, Clinical Trials, and Google Scholar were also searched as well as a hand search in relevant journals. Studies on adults with all types of dementia, investigating tactile low frequency sound or mechanical vibration in any context were considered. Data from eight full-length studies (three RCTs, two quasi-experimental, two case reports, and one qualitative) were extracted using the data extraction table developed by the authors and were included in the analysis and critical appraisal. Issues in quality related to, for example, control groups and blinding. Few studies addressed participants’ subjective responses to the interventions. Reporting on the intervention characteristics was unclear. It appeared more frequent sessions led to better outcomes and home-based interventions potentially addressing the issue of access and feasibility. Future research should include neuroimaging to measure and confirm the hypothesised mechanism of cerebral coherence. Standardised reporting of intervention characteristics is also needed to ensure replicability of the experiments. Higher quality research is needed to investigate the impact and effect of low frequency vibration for the symptoms of dementia and compare outcomes in meta-syntheses.

Multi-body modelling and ride comfort analysis of a seated occupant under whole-body vibration

Seated occupants of any on/off-road vehicle are continuously exposed to undue low-frequency mechanical whole-body vibration (WBV) owing to the vibration conveyed from seat and backrest because occupants need to compromise with comfort and safety, leading to several musculoskeletal disorders and injuries in the body. Pain in the lumbar region is one of the most common problems that develop because of force transmitted from the backrest. Thus, consideration of backrest is highly essential while developing a biomechanical model for ride comfort analysis. For this purpose, a 20 degrees-of-freedom (dofs) biomechanical model has been proposed with a backrest to analyse cross-coupled segmental transmissibility. The interconnection between different segments of mass and backrest are modelled using eight linearized (direct as well as cross-coupled) stiffness and damping parameters. Biomechanical model parameters are estimated and optimized through a multi-objective firefly algorithm by minimizing the sum of squares error difference between analytical results and experimental segmental transmissibility published in the literature. Subsequently, ride comfort analysis is performed by integrating the proposed model with 7-dofs passenger car model. For different body segments, simulated results are obtained in terms of vertical accelerations and compared with ride comfort standards as per ISO 2631-1:1997. Additionally, a sensitivity analysis (±20% variation in mass, stiffness and damping) is performed to enhance the ride comfort of the occupant. The findings suggest that designers must focus on the pelvis, lower and upper back regions to improve the ride comfort of the occupants. The concepts and ideas outlined in this article are directly applicable in making human dummies, car suspension and seat design in the industry.

Three Frequency Up-Converting Piezoelectric Energy Harvesters Caused by Internal Resonance Mechanism: A Narrative Review.

Low frequency mechanical vibrations are ubiquitous in practical environments, and how to efficiently harvest them with piezoelectric materials remains a challenge. Frequency up-conversion strategies—up-converting low frequency vibrations to high frequency self-oscillations—can improve the power density of piezoelectric materials. This paper mainly introduces a kind of frequency which up-converts piezoelectric energy harvesters based on an internal resonance mechanism, compared with the other mechanisms caused by mechanical impact, mechanical plucking, etc.; the internal resonance-based harvesters can up-convert the frequency under a condition of lower excitation level, less energy loss, and less wideband operation bandwidth. Benefits to practical vibrations also exist in these multi-degree-of-freedom nonlinear dynamic systems. Moreover, the value of the frequency up-conversion factor based on the 1:2:6 internal resonance mechanism can reach as much as six so far, which is also a quite a high frequency up-conversion value.

Исследование способа интенсификации экстрагирования замороженного плодово-ягодного сырья в аппарате с вибрационной тарелкой

Introduction. Products containing natural extracts are in great demand. However, poor production technologies make them too expensive to satisfy consumer demand. As a result, a variety of intensification methods have been developed to increase the economic efficiency of extraction, e.g. low-frequency mechanical vibrations. However, frozen raw materials have to be processed at low temperatures, which makes the method less efficient. The research objective was to intensify the extraction process from frozen berries in a vibration tray device by increasing the temperature of the system of interacting phases.
 Study objects and methods. The research involved frozen cranberries and blueberries. They grow everywhere in Western Siberia and are rich vitamins and minerals. The berries were subjected to slow freezing at –18°C, which destroyed the cell structure and increased the processing efficiency. The study was carried out in a lab device with a vibrating tray. All parameters were measured by standard methods.
 Results and discussion. The extraction device was equipped with a jacket into which a coolant was fed, i.e. water with a temperature of 55°C. A preliminary series of experiments revealed two negative aspects associated with the supply of coolant into the jacket. First, the surface layer started to thaw, which reduced the efficiency of grinding. Second, the processing time increased. A new method was developed to solve these problems: the coolant was supplied at the end of the grinding. The time of the coolant supply depended on the type of raw materials. The processes that occurred within the device depended on two factors: the frequency of vibrations of the tray and the diameter of the holes in the tray. These factors could be adjusted to intensify the process, but they increased the power costs and energy consumption. A series of experiments determined the optimal values of these parameters. A mathematical analysis revealed regression equations, i.e. how the destruction time and power costs affected the main parameters. The established optimal process parameters made it possible to determine the minimal time of the destruction process: for cranberries – 2.5 min, for blueberries – 1.5 min. The minimal power consumption was 17.8 watts for cranberries and 11.7 watts for blueberries.
 Conclusion. The research increased the economic efficiency of the technological process of natural extraction, which can reduce the cost of the finished product and increase its availability. The values of the process parameters can be used to design new similar devices and serve as practical recommendations for berry extraction in vibration tray devices.

Ion transport through layered hydrogels for low-frequency energy harvesting toward self-powered chemical systems

Stress-induced ion transport through three-layered hydrogels with different stiffnesses and ion selectivities enabled the efficient conversion of low-frequency mechanical vibrations into electricity.

Optimization of the process of obtaining extracts in the field of low-frequency mechanical vibrations

Optimization of the process of obtaining extracts in the field of low-frequency mechanical vibrations

Adaptive impedance matching for power management circuit for a piezoelectric energy harvester on the bridge

A piezoelectric impact cantilever in the bridge and a self-powered low power management circuit with stable output voltage matched with a mechanical model are presented in this paper. Based on the piezoelectric effect, the low-frequency mechanical vibration is converted into high-frequency electrical signal oscillation. The generated voltage preserves into the low-power constant-voltage power management circuit, which can effectively store electric energy. The equivalent circuit model of vibration for a piezoelectric impact cantilever is obtained. The key of energy management circuit is to improve energy storage efficiency. When impedance matching is achieved, the efficiency is maximum. Since the equivalent impedance of piezoelectric material is different in the impact process and natural vibration process, this paper uses the delay link and D-trigger to form the peak detection circuit, which can distinguish two vibration processes. So different duty cycles are generated to control the buck-boost circuit to achieve adaptive impedance matching. It can be found that the efficiency reached more than 80 %. Compared with the traditional energy management circuit, the efficiency is increased by 18 %.