Frequency Vibration Measurement Research Articles

Fiber bragg grating accelerometer based on asymmetric shaped flexible hinge structure

To achieve real-time health monitoring in civil engineering, a FBG acceleration sensor with asymmetric shaped flexible hinge structure is proposed. Combined with the theoretical analysis, the expressions of resonance frequency and sensitivity are deduced, and the effects of the structural parameters of the sensor on the resonance frequency and sensitivity are analyzed and simulated. Based on the optimization results, a fiber Bragg grating acceleration sensor was designed and fabricated. The amplitude-frequency response, linear sensitivity response, and lateral anti-interference ability were tested experimentally. The experimental data shows a sensor resonance frequency of 350 Hz, a sensitivity of 90.96 pm/g, and a linear correlation of 99.59%. These results closely align with the theoretical predictions of a resonance frequency of 344 Hz, and a sensitivity of 98 pm/g, confirming the accuracy of the sensor's theoretical analysis.The transverse interference immunity of the sensor is 3.7%, and an operating frequency band of 10–250 Hz. It indicates that the sensor is promising for medium and low frequency vibration measurement.

Structural vibration frequency monitoring based on event camera

Compared with traditional cameras, event cameras (ECs) have the significant advantages of high temporal resolution, low data redundancy, and microsecond delay, which are beneficial in structural monitoring to extract the dense response of structures in both spatial and temporal dimensions. In this paper, the vibration frequency detection method based on ECs is studied. This study investigates vibration frequency detection methods based on ECs, and proposes two algorithms for vibration frequency detection based on event streams: marker tracking and event count. Experimental verification is conducted through forced vibration experiments. The results indicate that the event count method achieves high-precision measurement of vibration frequencies in the range of 10–190 Hz for different vibration scales, with a maximum relative error of 1% and an average relative error of 0.673%. The marker tracking method demonstrates a maximum relative error of 1.43% and an average relative error of 0.575% in frequency measurement for large-amplitude vibrations. However, as the amplitude decreases, the frequency measurement error increases. When the amplitude is less than 3 pixels, the frequency measurement error exceeds 30%, rendering the measurement results unreliable. This research provides technical support for high-precision structural vibration frequency monitoring and further expands the application of ECs in structural monitoring.

Time-varying vibration characteristics and surface topography of thin-walled cylinders during machining operations

Machining thin-walled cylindrical workpieces is frequently subjected to vibration due to their low rigidity, resulting in complicated surface topography. This paper investigates the vibration characteristics of thin-walled cylinder turning as well as its effect on the machined surface topography comprehensively by means of numerical simulations and experimental measurements. It is seen that the circumferential shell mode of vibration exhibits higher sensitivity to the variation of the wall thickness than the axial beam mode. The features of the vibration characteristics as well as the machined surface textures of thin-walled workpieces are shifting in a cutting pass. The underlying physical mechanism behind this phenomenon was interpreted. By extracting the critical vibration frequency and surface waviness measurement along the cutting path, a hybrid physics and data-driven surface topography was reconstructed, which showed consistency with the real surface topography. The formulated correlation between the vibration characteristics and the surface topography contributes to a holistic understanding of dynamic behaviors of thin-walled cylinder machining, and a tool that utilizes vibration to produce functional microstructures on cylindrical surfaces.

PMFSE: a video phase-based micro-vibration measurement algorithm for bridge cables in complex background

The cable serves as the primary structural component in cable-stayed bridges, suspension bridges, and other cable-supported bridge designs. Accurate measurement of cable tension holds paramount importance for ensuring the overall safety and stability of bridge structures. Cable tension can be inferred from the vibration frequency, making precise measurement of cable vibration frequency of utmost practical significance. Presently, video-based methodologies, such as phase-based vibration extraction, present notable advantages in terms of speed, efficiency, and non-contact capabilities over conventional acceleration sensor approaches. However, these methods face challenges in accurately discerning the micro-vibration of cables in complex background interference. To address this problem, a phase magnification-based feature signal extraction (PMFSE) algorithm is proposed, which is suitable for detecting small vibration in complex background. The overall idea is to combine the small vibration enhancement method in spatial domain with the signal separation method in time domain. Specifically, in the spatial domain, edge phase information is amplified through phase amplitude weighting and phase enhancement techniques to mitigate non-edge noise. In time domain, cable signals are extracted based on distinguishing features between the cable signal and noise signal. The efficacy of PMFSE is evaluated in various outdoor experiments. Compared with the state-of-the-art methods, PMFSE exhibits substantial improvements on the cable micro-vibration frequency measurement in complex background.

Phase-Based Bridge Cable Vibration Frequency Measurement in Complex Background

Phase-Based Bridge Cable Vibration Frequency Measurement in Complex Background

High-sensitivity dual-FBG acceleration sensor for low frequency vibration measurement

High-sensitivity dual-FBG acceleration sensor for low frequency vibration measurement

Integrated heterodyne laser Doppler vibrometer based on stress-optic frequency shift in silicon nitride

We demonstrate a compact heterodyne Laser Doppler Vibrometer (LDV) based on the realization of optical frequency shift in the silicon nitride photonic integration platform (TriPleX). We theoretically study, and experimentally evaluate two different photonic integrated optical frequency shifters (OFSs), utilizing serrodyne and single-sideband (SSB) modulation. Both OFSs employ stress-optic modulators (SOMs) based on the non-resonant piezoelectrical actuation of lead zirconate titanate (PZT) thin-films, deposited on top of the silicon nitride waveguides with a wafer-scale process. To improve the modulation bandwidth of the SOMs we investigate a novel configuration of the electrodes used for the actuation, where both electrodes are placed on top of the PZT layer. Using this top-top electrode configuration we report frequency shift of 100 kHz and 2.5 MHz, and suppression ratio of the unwanted sidebands of 22.1 dB and 39 dB, using the serrodyne and the SSB OFS, respectively. The best performing SOM structure induces 0.25π peak-to-peak sinusoidal phase-shift with 156 mW power dissipation at 2.5 MHz. We use the SSB-OFS in our compact LDV system to demonstrate vibration measurements in the kHz regime. The system comprises a dual-polarization coherent detector built in the PolyBoard platform, utilizing hybrid integration of InP photodiodes (PDs). High quality LDV performance with measurement of vibration frequencies up to several hundreds of kHz and displacement resolution of 10 pm are supported with our system.

Highly sensitive vibration frequency sensing utilising serial in-line Mach-Zehnder interferometer

A serial in-line Mach-Zehnder interferometer (ILMZI) based on a hybrid of micro-bottle structures and fibre taper structures is demonstrated for vibration frequency sensing applications. The proposed structure shows an improved vibration sensing sensitivity and accurate vibration frequency measurement. The sensing performance was demonstrated using the proposed structure mounted on a cantilever beam. The vibration frequency interrogation was based on Fast Fourier Transform (FFT) spectral peak detection. Compared to the conventional single ILMZI structure, the proposed device offers relatively much wider detection range of up to 224 Hz based on the specific experiment setup. This structure allows superior sensing performance for ILMZI, thus making it more practical to be accepted in many industrial sensing applications.

Stability of antenna support belts

Introduction. The article deals with the issues of stability of compressed belts of lattice construction, as systems in the form of continuous rods consisting of panel elements. Currently, the estimated length of compressed elements is established by design standards for calculating stability without taking into account variability due to the influence of numerous random and systemic factors. This approach does not encourage the improvement of design solutions, the quality of their execution and the control of the structure. And most importantly, it does not allow to realize the reserves of the bearing capacity of structures laid down by the norms. The purpose of this study is to identify and substantiate the reserves of the bearing capacity of antenna supports of a lattice structure according to the criterion of stability of compressed belts.Materials and methods. It is shown that the values of the calculated length coefficient are set by norms with a margin, due, in particular, to ensuring the reliability of structural systems of compressible elements. It is proposed to consider the estimated length of compressed elements as a random variable. The problem of probabilistic estimation of the free (calculated) length of a centrally compressed element as a parameter of the critical force of loss of stability is solved. The possible normative and calculated values of the calculated length coefficient are given, ensuring the reliability of the calculation of compressed antenna support belts, adopted in the current design standards. To assess the variability of stability indicators, the task is to conduct experimental studies, in particular, with the measurement of vibration frequencies of full-scale structures. By controlling the variability indicators of the calculated length coefficient, it is possible to regulate not only reliability, but also the load-bearing capacity reserves provided for by design standards.Conclusions. The proposed approach to the calculation of stability allows to control the calculated values of the calculated length coefficient by controlling statistical variability (coefficient of variation). If there are available methods for measuring indicators, the approach described in the article to calculating compressed elements for stability can be an effective means and tool for improving design solutions, the quality of their execution and control of the structure.

Event-Based Vibration Frequency Measurement With Laser-Assisted Illumination Based on Mixture Gaussian Distribution

Event-Based Vibration Frequency Measurement With Laser-Assisted Illumination Based on Mixture Gaussian Distribution

An environmentally robust design of a high-speed pendulum-type laser vibrometer using an advanced position-sensitive detector for vibration frequency monitoring of tower-like structures

Vibration monitoring of tower-like structures is a major challenge in vibration-based structural health monitoring, which is commonly expensive and time-consuming. In this paper, a novel vibration frequency measurement system based on a classical pendulum and advanced optical instruments that provides rapid, high-precision vibration measurements is developed. This system is integrated by a laser-based pendulum with an ultrafast interface position detector to form a table-top vibrometer that can precisely monitor structural vibration frequencies. In which, the position of the laser beam spot on the position-sensitive detector produces a voltage signal that is continuously recorded as the pendulum oscillates around its equilibrium position. By a comparative study of vibration frequencies between shaking table tests on the proposed system and simulations, it can be concluded that the proposed measurement system is independent of friction on the rotation shaft and other resistances; this makes the system environmentally robust over the long-term use, and thus reduces significantly maintenance and labor costs, especially in the case of tower-like structures where the measurement point is difficult to human access.

A Ring-Shaped Curved Deformable Self-Powered Vibration Sensor Applied in Drilling Conditions

Because of their low flexibility, traditional vibration sensors cannot perform arbitrary bending adjustments when facing curved surfaces and other complex working conditions during the drilling process; therefore, this research proposes a ring-shaped vibration sensor (RSV−TENG) that can deform freely in the bending direction, and which can be used in working conditions where the inner bending angle of the drill pipe changes greatly. Test results show that the vibration frequency measurement range is from 4 Hz to 16 Hz, with a measurement error less than 4%, the vibration amplitude measurement range is less than 20 mm, with a measurement error less than 5%, the output voltage and current signal are 120 V and 60 nA, respectively, when three RSV−TENGs are connected in parallel, and the maximum output power is 6 × 10−7 W when the external resistance is 106 Ω. Compared with traditional downhole sensors, this sensor has self-powered and self-sensing functions, eliminating the shortcomings of battery and cable power supply; in addition, this sensor can be installed in the drill pipe space with different curvature radii, so it is more suited to complex and changeable downhole working conditions.

A high-sensitivity FBG accelerometer and application for flow monitoring in oil wells

In this study, a cantilever beam-based fibre Bragg grating (FBG) accelerometer is presented. Two fibre supports are arranged at both ends of a cantilever beam; therefore, the FBG can be stretched longitudinally by both displacement and rotation of the free end. The principle of this sensor is analysed by the elasticity theory approach and the accuracy of the theoretical model is verified by the ANSYS modal simulation. Furthermore, the influence of key structural parameters on the sensor characteristics is analysed by Mathematica for structural optimisation. Hence, the accelerometer exhibits a resonant frequency of approximately 76 Hz, an average sensitivity of 59.3 dB re pm/g for a 1–60 Hz flat response interval and a cross-sensitivity of less than –24.43 dB (<6.1 %), which is capable of low frequency and precision vibration measurements. Finally, a flow-monitoring test is presented and the results show that it is feasible to use FBG accelerometers for flow monitoring in oil wells.

A Method on Vibration Positioning of Φ-OTDR System Based on Compressed Sensing

To improve the accuracy of vibration location information of the Φ-OTDR system, a method of optical fiber sensing signal processing based on Compressed Sensing (CS) is proposed in this paper. First, a sensing matrix is constructed by sparse array and observation array, and the mathematical modeling of CS is established. Then the reconstruction algorithm is designed to complete the accurate reconstruction of the vibration signal with a small number of sampling values. Second, the time domain signal composed of all scattered light at the vibration source is analyzed to complete the measurement of vibration frequency. Finally, a heterodyne Phi-OTDR system is built, using PZT to simulate the vibration source. And 36 scattered light information is continuously collected at the frequency of 100 Hz and 500 Hz. The experimental verification of the CS method in this paper is carried out, besides, the signal-to-noise ratio (SNR) is compared with the traditional difference method, Empirical Mode Decomposition (EMD) method, and Variational Mode Decomposition (VMD) method. The experimental results show that the SNR of this method is improved to 40.41 dB and 30.62 dB, the optimal spatial resolution is 9m, and the maximum relative error of frequency measurement is 8.1%. Compared with the results of traditional I/Q demodulation, the frequency information obtained by the two methods is consistent, and there is no obvious deviation from the actual frequency of PZT. While improving the SNR of the system, this method can greatly simplify the signal processing process and improve the positioning accuracy of the system, which has a certain practical application value in the fields of infrastructure monitoring, resource exploration, and vibration detection.

Proposal of Inspection Method for Shrinkage Cavities in Spheroidal Graphite Cast Iron by Electromagnetic Force Vibration Using Differential Vibration Measurement

Spheroidal graphite cast iron is often used for machine parts that require high strength. A shrinkage cavity may be generated inside the cast iron during the manufacturing process. If there is a shrinkage cavity in the cast iron, the strength of the cast iron is significantly reduced. In this article, a non-destructive testing method for detection of shrinkage cavity inside the cast iron by constant frequency vibration measurement using electromagnetic force excitation at low frequency is proposed. In this method, the electromagnetic force vibration is generated inside the cast iron from the static magnetic field by a permanent magnet and the eddy current by an alternating exciting coil. Then, the vibration is measured by an accelerometer that is in contact with the surface of the cast iron material. If there is a shrinkage cavity inside the cast iron, since the vibration intensity is changed, the shrinkage cavity is estimated by the vibration measurement. In this method, the shrinkage cavities inside cast iron can be inspected at high speed with an inexpensive device. In this article, the electromagnetic force vibration is calculated using the 3-D nonlinear electromagnetic finite element method (FEM) analysis. The displacement due to vibration in the cast iron is calculated by the 3-D displacement FEM analysis. The phenomenon of electromagnetic force excitation is clarified using these FEM analysis methods. Then, the effectiveness of the proposed inspection method is investigated by comparing the results of the verification experiment and analysis.

Measurement of vibration frequencies of ties in masonry arches by means of a robotic total station

Measurement of vibration frequencies of ties in masonry arches by means of a robotic total station

Phase-Based Vibration Frequency Measurement From Videos Recorded by Unstable Cameras

Cameras can be used as non-contact sensors to measure target vibration conveniently. Recently, spatial phase-based methods have been developed to detect small vibrations with robustness to imaging noise. To deal with videos recorded by unstable cameras, this paper proposes a novel phase-based method, which focuses on separating camera motions from target vibrations in the spatial domain and the temporal domain. The proposed method first builds a spatial representation based on adjacent-frame phase differences, which can maintain the optical flow continuity and subsequently lead to the removal of linear camera motions in the spatial domain. Then, the temporal vibration waveforms, which may still contain distortions caused by unstable camera and noise, are extracted. To restore the target vibration, singular spectrum analysis is further incorporated for characterizing target vibrations and attenuating the distortions. The proposed method is evaluated in various laboratory and outdoor experiments. Compared with the state-of-the-art methods, the proposed method demonstrates substantial improvements on the vibration frequency measurement in the presence of camera motions.

Measurement of micro-harmonic vibration frequency from the modulated self-mixed interferometric signal using dynamic time warping method

The vibration frequency is one of the key factors that contains vital information about the subjects/machines and offers major analytical support. The contactless measurement of vibration frequency is the crucial requirement of many industrial, scientific, and biomedical applications like predictive maintenance, non-destructive testing, and reverse engineering, chest vibration, etc. The paper presents a self-mixed optical feedback interferometry (SM-OFI) sensor to measure the vibration frequency of the micro-harmonic vibrating surface. The method employs a Dynamic Time Warping algorithm (DTW) to compute the Euclidian distance between the locally generated reference signal and the SM interferometric signal obtained from a vibrating target. The method is tested experimentally on a customized SM-OFI emitting a wavelength of 650 nm under weak feedback conditions. The proposed method was able to measure the unknown frequency with 98% accuracy in all sets of experiments. The method also exhibits an R-squared value of 0.99 with a relative error of less than unity. The comprehensive analysis of the experimental results concludes that the proposed method provides an accurate and precise vibration frequency measurement scheme for the low bandwidth range. This low bandwidth range measurement promises a non-contact measurement in industries and biomedical applications during the COVID-19 scenario.

Double-spring-piece structured triboelectric sensor for broadband vibration monitoring and warning

For modern alarm detection technologies, the vibration sensor is one of the most widely applied sensing technologies. It is of great significance for developing the sensing field to achieve the broadband monitoring of mechanical vibration by using triboelectric sensors (TES). In this work, a novel double-spring-piece structured triboelectric sensor (DS-TES) is proposed for broadband vibration monitoring and warning. The sensor adopts double three-rib longitudinal spring pieces to form an internal spring-mass-damping system, which has high stability. The physical model of the electric field system is established and analyzed by combining the dynamic model. The experimental results show that the DS-TES can achieve vibration frequency measurement in the range of 0–200 Hz with high linearity, and the error rate is less than 0.015%. The signal-to-noise ratio (SNR) of most output signals can be maintained at approximately 40 dB after signal processing. Moreover, the SNR of DS-TES can be maintained above 18 dB within the range of 70° tilt angle. Finally, the applications of DS-TES in broadband vibration real-time monitoring and grading warning are demonstrated. The present results indicate that the DS-TES holds promising potentials in acting as a warning of natural disasters or structural health monitoring systems.

Performance Evaluation of Vibrational Measurements through mmWave Automotive Radars

Thanks to the availability of a significant amount of inexpensive commercial Frequency Modulated Continuous Wave Radar sensors, designed primarily for the automotive domain, it is interesting to understand if they can be used in alternative applications. It is well known that with a radar system it is possible to identify the micro-Doppler feature of a target, to detect the nature of the target itself (what the target is) or how it is vibrating. In fact, thanks to their high transmission frequency, large bandwidth and very short chirp signals, radars designed for automotive applications are able to provide sub-millimeter resolution and a large detection bandwidth, to the point that it is here proposed to exploit them in the vibrational analysis of a target. The aim is to evaluate what information on the vibrations can be extracted, and what are the performance obtainable. In the present work, the use of a commercial Frequency Modulated Continuous Wave radar is described, and the performances achieved in terms of displacement and vibration frequency measurement of the target are compared with the measurement results obtained through a laser vibrometer, considered as the reference instrument. The attained experimental results show that the radar under test and the reference laser vibrometer achieve comparable outcomes, even in a cluttered scenario.