Showing papers on "Cantilever published in 2021"

An experimental validation of a new shape optimization technique for piezoelectric harvesting cantilever beams

Abstract: The piezoelectric energy harvester efficiency depends on optimizing the cantilever geometry and tuning its natural frequency with vibration source frequency. Moreover, the effect of harvester parameters on natural frequency is vital in tuning the resonance frequency. So, a COMSOL Multi-physics finite element analysis, Eigen frequency study and analytical analysis using MATLAB were constructed to calculate the resonance frequencies and to analyze the harvester parameters effect. Five harvester different shapes, namely, the T-shaped, rectangular, L-shaped, variable width, and triangular cantilevers were optimized using the genetic algorithm. The simulation of the five shapes was implemented using COMSOL. The results indicated that the T- shaped cantilever produced the largest power. Due to its high power and inclusive shape, the T-shaped cantilever with variable width was optimized using the COMSOL optimization module (BOBYQA). Linking genetic algorithm and COMSOL optimization module has highly improved the output power. The COMSOL results were validated using an experimental setup of piezoelectric cantilevers. The experimental setup was employed to calculate the voltage of the base excited harvester with very low excitation frequencies from 0.5 to 10 Hz. Also, the experimental setup investigated the effect of the tip mass, length of the cantilever, and piezoelectric material volume on the output voltage.

Vibration Mode Analysis for a Suspension Bridge by Using Low-Frequency Cantilever-Based FBG Accelerometer Array

Abstract: In this article, we present a vibration measurement system based on low-frequency cantilever-based fiber Bragg grating accelerometers (CFAs) for a suspension bridge. Each accelerometer has an end-loaded cantilever beam, specifically tailored to achieve a uniform sensitivity for a frequency range of 0–4 Hz, a suitable detection range for the vibration analysis. In the field test, seven CFAs were installed at specific positions along the deck of a 110-m-long suspension bridge for synchronous multipoint vibration measurements. The reflection spectra of the CFA array were recorded and processed using the pseudo-high-resolution scheme to improve the signal quality and measurement accuracy. Three natural vibration frequencies: 1.15, 1.54, and 3.17 Hz have been identified from the measurement. Following that, the acquired time-domain signals were processed by a digital bandpass filter to retrieve the waveform at each natural frequency to determine the corresponding mode shapes. The results are in agreement with the phase difference between the frequency domain signal for each natural frequency. This investigation has shown the feasibility of the proposed measurement system for determining the mode shapes and dynamic frequency analysis of a suspension bridge. It is a potential method for structural health monitoring for other similar civil structures.

Nonlinear Vibrations of Rotating Pretwisted Composite Blade Reinforced by Functionally Graded Graphene Platelets Under Combined Aerodynamic Load and Air Flow in Tip Clearance

Abstract: The primary resonance and nonlinear vibrations of the functionally graded graphene platelet (FGGP)-reinforced rotating pretwisted composite blade under combined the external and multiple parametric excitations are investigated with three different distribution patterns The FGGP-reinforced rotating pretwisted composite blade is simplified to the rotating pretwisted composite cantilever plate reinforced by the functionally graded graphene platelet It is novel to simplify the leakage of the airflow in the tip clearance to the non-uniform axial excitation The rotating speed of the steady state adding a small periodic perturbation is considered The aerodynamic load subjecting to the surface of the plate is simulated as the transverse excitation Utilizing the first-order shear deformation theory, von Karman nonlinear geometric relationship, Lagrange equation and mode functions satisfying the boundary conditions, three-degree-of-freedom nonlinear ordinary differential equations of motion are derived for the FGGP-reinforced rotating pretwisted composite cantilever plate under combined the external and multiple parametric excitations The primary resonance and nonlinear dynamic behaviors of the FGGP-reinforced rotating pretwisted composite cantilever plate are analyzed by Runge–Kutta method The amplitude–frequency response curves, force–frequency response curves, bifurcation diagrams, maximum Lyapunov exponent, phase portraits, waveforms and Poincare map are obtained to investigate the nonlinear dynamic responses of the FGGP-reinforced rotating pretwisted composite cantilever plate under combined the external and multiple parametric excitations

Stability Analysis of a Cantilever Structure using ANSYS and MATLAB

Abstract: The objective is to study the behavior of gallery in a concert hall under forced vibration (Man Induced Vibration) without damping to avoid deformations in the structure leading to potential damage. In order to execute this, it is vital to further find the (first three, in this case) natural frequencies and natural mode shapes of the cantilever corresponding to deformations of the beam in the x-y-plane in order to determine the stresses acting within the structure. The natural frequency of the Gallery of two proposed designs is then determined followed by finding the best design based on their natural frequencies by comparing with exact natural frequencies of a uniform cantilever beam to find the Transient Response for the given load at the tip of the Cantilever Beam. This technique has also been applied to shock wave theories that are applied underground using ultrasonic sensors to determine cracks within underground pipelines to avoid any leakage.

Piezoelectric Energy Harvesting From a Magnetically Coupled Vibrational Source

Abstract: This article presents a new magnetically coupled method to efficiently transfer vibrational energy from a source to a piezoelectric energy harvester. This method enables energy harvesting from vibration sources to which direct physical contact is not feasible or not preferred. The proposed harvester uses the piezoelectric cantilever in combination with two permanent magnets; one attached to the free end of the cantilever while the other magnet is firmly attached to the vibrational source facing the magnet on the cantilever. These magnets are kept in repulsive mode. As the source oscillates, the attached magnet follows the movement of the source. Due to this, the magnet on the cantilever gets perturbed and follows the movement of the source, bending the cantilever cyclically and generating a voltage output. This proposed arrangement not only (a) helps to scavenge energy without directly fitting the piezoelectric element and associated wiring on the vibrating source but also (b) provides more flexibility to adjust the resonant frequency, by varying the air gap between the magnets, (c) gives higher bandwidth compared to the conventional piezoelectric harvesters, ensuring less effect due to small mismatch between the frequency of the source and resonant frequency of the harvester. This is automatically achieved due to the nonlinearity of the system, introduced by the magnets. Prototypes of the proposed harvester and an equivalent conventional harvester are developed and tested. Results proved the functionality of the proposed harvester and showed superior performance in terms of gain, bandwidth, and charging time of a storage capacitor.

Ultrahigh Sensitivity Fiber-Optic Fabry–Perot Interferometric Acoustic Sensor Based on Silicon Cantilever

Abstract: Detection of weak acoustic signals is of great significance. To achieve ultrahigh sensitivity acoustic detection, a silicon cantilever-based fiber-optic acoustic sensor (FOAS) formed by a Fabry–Perot interferometric structure is proposed in this work. Theoretical analysis and finite element analysis are used to assist the sensor design. The cantilever is fabricated by the microelectro-mechanical system (MEMS) processing technology on a silicon-on-insulator (SOI) wafer. A white light interference (WLI) demodulation system based on an amplified spontaneous emission (ASE) source is used to demodulate the cavity length of the sensor. The acoustic pressure sensitivity of the sensor was measured to be $1.753~\mu \text{m}$ /Pa at a frequency of 1 kHz and $28.75~\mu \text{m}$ /Pa at the resonance frequency of the cantilever. Experimental results indicated that the minimum detectable pressure (MDP) level of the fabricated sensor was $0.21~\mu $ Pa/Hz1/2 at 1 kHz, which is the lowest reported value. The silicon-based FOAS proposed in this article demonstrates its ability to detect ultraweak acoustic signals due to its extremely high sensitivity.

Bioinspired PDMS-graphene cantilever flow sensors using 3D printing and replica moulding

Abstract: Flow sensors found in animals often feature soft and slender structures (e.g. fish neuromasts, insect hairs, mammalian stereociliary bundles, etc.) that bend in response to the slightest flow disturbances in their surroundings and heighten the animal's vigilance with respect to prey and/or predators. However, fabrication of bioinspired flow sensors that mimic the material properties (e.g. low elastic modulus) and geometries (e.g. high-aspect ratio structures) of their biological counterparts remains a challenge. In this work, we develop a facile and low-cost method of fabricating high-aspect ratio (HAR) cantilever flow sensors inspired by the mechanotransductory flow sensing principles found in nature. The proposed workflow entails high-resolution 3D printing to fabricate the master mould, replica moulding to create HAR polydimethylsiloxane (PDMS) cantilevers (thickness = 0.5 - 1 mm, width = 3 mm, aspect ratio = 20) with microfluidic channel (150 µm wide × 90 µm deep) imprints, and finally graphene nanoplatelet ink drop-casting into the microfluidic channels to create a piezoresistive strain gauge near the cantilever's fixed end. The piezoresistive flow sensors were tested in controlled airflow (0 - 9 m/s) inside a wind tunnel where they displayed high sensitivities of up to 5.8 kΩ/ms-1, low hysteresis (11% of full-scale deflection), and good repeatability. The sensor output showed a second order dependence on airflow velocity and agreed well with analytical and finite element model predictions. Further, the sensor was also excited inside a water tank using an oscillating dipole where it was able to sense oscillatory flow velocities as low as 16 - 30 µm/s at an excitation frequency of 15 Hz. The methods presented in this work can enable facile and rapid prototyping of flexible HAR structures that can find applications as functional biomimetic flow sensors and/or physical models which can be used to explain biological phenomena.

Large colloidal probes for atomic force microscopy: Fabrication and calibration issues

Abstract: Atomic force microscopy (AFM) is a powerful tool to investigate interaction forces at the micro and nanoscale. Cantilever stiffness, dimensions and geometry of the tip can be chosen according to the requirements of the specific application, in terms of spatial resolution and force sensitivity. Colloidal probes (CPs), obtained by attaching a spherical particle to a tipless (TL) cantilever, offer several advantages for accurate force measurements: tunable and well-characterisable radius; higher averaging capabilities (at the expense of spatial resolution) and sensitivity to weak interactions; a well-defined interaction geometry (sphere on flat), which allows accurate and reliable data fitting by means of analytical models. The dynamics of standard AFM probes has been widely investigated, and protocols have been developed for the calibration of the cantilever spring constant. Nevertheless, the dynamics of CPs, and in particular of large CPs, with radius well above 10 μm and mass comparable, or larger, than the cantilever mass, is at present still poorly characterized. Here we describe the fabrication and calibration of (large) CPs. We describe and discuss the peculiar dynamical behaviour of CPs, and present an alternative protocol for the accurate calibration of the spring constant.

A Compact Cantilever-Type Ultrasonic Motor With Nanometer Resolution: Design and Performance Evaluation

Abstract: A cantilever ultrasonic motor with nanometer resolution is designed, fabricated, and tested in this article. Two orthogonal first bending vibration modes are used to form elliptical movements on driving tip to move slider. The structure of this motor is depicted, and its geometric dimensions are determined by modal analysis. The total size of this motor is 30 × 30 × 34.2 mm along the X- , Y-, and Z -direction. The working principle of the proposed motor is illustrated, and the motion characteristics of the driving tip are studied by transient analysis. A prototype of this motor is manufactured to investigate its vibration performances and mechanical characteristics. The tested results denote that this motor generates an output speed of 344.35 mm/s when the frequency and voltage are 22.7 kHz and 200 Vp-p, respectively. The maximum output force is tested as about 8 N under the voltage and preload of 100 Vp-p and 50 N, respectively. Furthermore, the proposed ultrasonic motor obtains a high displacement resolution of 48 nm under the resonant working state.

Flutter and Limit Cycle Oscillations of Cantilevered Plate in Supersonic Flow

Abstract: Research interest is growing for theoretical models of highly deflected structures in aeroelastic settings. Presented here is a model of a cantilevered plate subjected to axial supersonic flow to d...

Vibration control of cantilever beam using poling tuned piezoelectric actuator

Abstract: This paper presents active vibration control of smart cantilever beam using poling tuned piezoelectric actuator. The vibrating response of piezo-laminated cantilever beam is modeled using a lumped ...

Single frequency vertical piezoresponse force microscopy

Abstract: Piezoresponse force microscopy (PFM) uses a cantilever arm to track the electromechanical motion of the electric dipole moment to visualize the ferroelectric domain structure, which provides an important insight into the physics of switchable electric polarization—especially for memory devices and integrated microelectronics. Here, I provide a tutorial on single frequency vertical PFM, the most basic mode of PFM. I will start with the basic components of atomic force microscopy (AFM), including tip, cantilever, X–Y stage, Z actuator, and lock-in amplifier. Contact mode AFM will be briefly explained and discussed, where you can find two modes: constant deflection and constant height modes. Single-frequency vertical PFM splits the frequency domain of tip vibration into low and high frequencies and uses a low-pass filter to nullify any motion caused by topography (constant deflection). In contrast, the lock-in amplifier will pinpoint the vibration induced by the vertical piezoelectric strain along the sample’s surface normal (constant height). This tutorial will provide an overall and detailed step by step instruction to conduct PFM imaging and piezoresponse hysteresis loop measurement using atomic force microscopy and a lock-in amplifier and teach how to interpret the PFM images and the piezoresponse hysteresis loops for various applications.

Nonlinear vibration analysis of a cantilever beam with multiple breathing edge cracks

Abstract: The nonlinear vibration analysis of cracked structures could be a suitable indicator for diagnosing defects. When breathing cracks appear on the beam, its behavior can be modeled as a bilinear oscillator. In this paper, the nonlinear vibration behavior of a cantilever beam with multiple breathing cracks is investigated. For this purpose, the multi-cracked beam’s stiffness is calculated by introducing the effective length for the local stiffness reduction in the vicinity of cracks. Furthermore, owing to the importance of the damping variation in a cracked beam, its exact value is evaluated through theoretical expressions. A continuous polynomial function with the Weierstrass approximation is exploited to simulate the bilinear behavior of breathing cracks. By performing nonlinear analysis using the perturbation technique, the cracked beam’s dynamic behavior is studied. Moreover, the sensitivity of the response to the crack parameters in the primary resonance of the structure is analyzed. Finally, the sensitivity of the beam’s nonlinear response to the different number of breathing cracks and various crack depths is investigated. It is shown that the beam with a higher number of cracks or deeper ones has obvious softening behavior, and hence a more significant jumping can appear in the response.

Full-Field Bridge Deflection Monitoring with Off-Axis Digital Image Correlation

Abstract: Video deflectometer based on using off-axis digital image correlation (DIC) has emerged as a robust non-contact optical tool for deflection measurements of bridges. In practice, a video deflectometer often needs to measure the deflections at multiple positions of the bridge. The existing 2D-DIC-based measurement methods usually use a laser rangefinder to measure the distance from each point to the camera to obtain the scale factor for the point. It is only suitable for the deflection measurements of a few points since manually measuring distances for a large number of points is time consuming and impractical. In this paper, a novel method for full-field bridge deflection measurement based on off-axis DIC is proposed. Because the bridge is usually a slender structure and the region of interest on the bridge is often a narrow band, the new approach can determine the scale factors of all the points of interest with a spatial straight-line fitting scheme. Moreover, the proposed technique employs reliability-guided processing and a fast initial parameter estimation strategy for real-time and accurate image-matching analysis. An indoor cantilever beam experiment verified the accuracy of the proposed approach, and a field test of a high-speed railway bridge demonstrated the robustness and practicability of the technique.

A Measurement Platform for Label-Free Detection of Biomolecules Based on a Novel Optical BioMEMS Sensor

Abstract: In this article, a novel optical Bio-microelectromechanical system (MEMS) sensing platform is proposed based on a tunable laser and its lasing wavelength to detect the biomolecules and measure their quantities. The present biosensor consists of a BioMEMS cantilever and a proposed external cavity tunable laser. While the target samples (i.e., DNA, mRNA, or protein) are exposed to the cantilever surface, target-analyte bindings are happened. This can induce a surface stress on the MEMS cantilever and results in its bending due to the surface stress difference in each side of the cantilever. Thus, the gap size between the laser cavity and the gain medium is changed which can be measured by the wavelength variations of the proposed tunable laser source. Consequently, by analyzing the output response, one can detect the amount of target biomolecules in the sample and assign a level of contamination, infection, or bioparticles, caused by the specific disease. Various parameters of the proposed device are designed by numerical and analytical approaches. Furthermore, functional characteristics of the present BioMEMS sensor are obtained as follows: mechanical sensitivity of $1.8~\mu \text{m}$ /Nm−1, optical sensitivity of 422 nm/RIU, Q-factor of 610, and resonant frequency of 6.43 kHz. The obtained functional characteristics of the proposed device show that the present optical BioMEMS sensor can be appealing for highly sensitive diagnoses of various types of diseases and their progress level.