Search results for "Lever"
showing 10 items of 191 documents
Changes in surface stress at the liquid/solid interface measured with a microcantilever
2000
Abstract The bending of microfabricated silicon nitride cantilevers was used to determine surface stress changes at solid–liquid interfaces. The radius of curvature of the bent cantilever is directly proportional to changes in the differential surface stress between its opposite sides. To demonstrate the possibilities and limitations of the technique, cantilevers coated on both sides with gold and densely packed monolayers of different thiols were put in a constant flow of aqueous electrolyte solution and the deflection was measured using a optical lever technique. Changes in the surface stress for the different thiol monolayers due to specific proton adsorption are presented. Possible appl…
Effects of temperature and pressure on microcantilever resonance response.
2003
Abstract The variation in resonance response of microcantilevers was investigated as a function of pressure (10 −2 –10 6 Pa) and temperature (290–390 K) in atmospheres of helium (He) and dry nitrogen (N 2 ). Our results for a silicon cantilever under vacuum show that the frequency varies in direct proportion to the temperature. The linear response is explained by the decrease in Young's modulus with increasing the temperature. However, when the cantilever is bimaterial, the response is nonlinear due to differential thermal expansion. Resonance response as a function of pressure shows three different regions, which correspond to molecular flow regime, transition regime, and viscous regime. …
Comparison among different rainfall energy harvesting structures
2018
In this paper, an experimental comparison between different rainfall harvesting devices through the study of the electrical rectifying circuit is proposed. In more detail, three harvesting structures are considered: the cantilever, the bridge and the floating circle. Different waveforms were acquired and discussed. The processed data were compared in order to suggest the best choice for the rectifying circuit, from the simplest one to that most frequently endorsed in the technical literature.
Construction sequence analysis of long-span cable-stayed bridges
2018
Abstract In cantilever construction of long-span cable-stayed bridges the stressing sequence of stays is fundamental for establishing the final configuration of the bridge. The structural behaviour of these bridges is usually evaluated through a forward staged construction analysis, in which the values of the prestressing forces to be applied to stays are the main unknowns. A unified procedure for determining the initial cable forces and for analyzing the entire sequence is presented here, considering the geometric nonlinearity of stays through the Dischinger equivalent elastic modulus. The target is the simultaneous determination of the initial cable forces with the simulation of the const…
Monitoring the chemical changes in Pd induced by hydrogen absorption using microcantilevers.
2003
Abstract The reactivity of the palladium shaped as a microcantilever is investigated as a function of the hydrogen stoichiometry. A small cell holding the microcantilever is designed to monitor the deflection and the flexural resonance response from high vacuum to a hydrogen gas pressure of several bars. The measurements show that the Young's modulus is accurate if the cantilever is thick enough to be described by a continuum mechanics approach. The orientation distribution function of the palladium grains determined by X-ray diffraction enables to correlate Young's modulus measured using microcantilevers with the elastic constant tensor issued from the literature. The surface stress induce…
Determining cantilever stiffness from thermal noise
2013
We critically discuss the extraction of intrinsic cantilever properties, namely eigenfrequency fn, quality factor Qn and specifically the stiffness kn of the nth cantilever oscillation mode from thermal noise by an analysis of the power spectral density of displacement fluctuations of the cantilever in contact with a thermal bath. The practical applicability of this approach is demonstrated for several cantilevers with eigenfrequencies ranging from 50 kHz to 2 MHz. As such an analysis requires a sophisticated spectral analysis, we introduce a new method to determine kn from a spectral analysis of the demodulated oscillation signal of the excited cantilever that can be performed in the frequ…
Boundary elements analysis of adhesively bonded piezoelectric active repair
2009
Abstract This paper presents the analysis of active piezoelectric patches for cracked structures by the boundary element method. A two-dimensional boundary integral formulation based on the multidomain technique is used to model cracks and to assemble the multi-layered piezoelectric patches to the host damaged structures. The fracture mechanics behavior of the repaired structures is analyzed for both perfect and imperfect interface between patches and host beams. The imperfect interface, representing the adhesive between two different layers, is modeled by using a “spring model” that involves linear relationships between the interface tractions, in normal and tangential directions, and the …
Shear Effects in Elastic Nanobeams
2020
Small-scale, shear deformable nanobeams, subjected to quasi-static loads, are analyzed by a nonlocal (integral) elasticity model with the main goal to evaluate the influence of shear deformation on size effects. To this aim a warping parametric model is considered in order to obtain a continuous family of shear deformable beam models which span from the Euler-Bernoulli to the Thimoshenko beam model, passing from the Reddy model. The strain difference based nonlocal elasticity theory is applied under the hypotheses of small displacements and isotropic material. The results, obtained by analysing a cantilever nonlocal nanobeam, indicate that shear deformation has a considerable influence upon…
Measurement of Mechanical Properties of Cantilever Shaped Materials
2008
Microcantilevers were first introduced as imaging probes in Atomic Force Microscopy (AFM) due to their extremely high sensitivity in measuring surface forces. The versatility of these probes, however, allows the sensing and measurement of a host of mechanical properties of various materials. Sensor parameters such as resonance frequency, quality factor, amplitude of vibration and bending due to a differential stress can all be simultaneously determined for a cantilever. When measuring the mechanical properties of materials, identifying and discerning the most influential parameters responsible for the observed changes in the cantilever response are important. We will, therefore, discuss the…
Detection of gas trace of hydrofluoric acid using microcantilever
2004
Abstract Microcantilevers have been used as a gas sensor in order to detect Hydrofluoric acid (HF) in the concentration range of 0.26–13 ppm. Silicon derived elements (Si 3 N 4 , SiO x ) were chosen to serve as chemical sensitive layer. Cantilever deflection and frequency shift were analyzed and compared as a function of the flow rate and the concentration of the HF molecules. The stoichiometry and roughness of the sensitive layer were found to be of major importance. Results show that the most appropriate signal at the lowest concentration ( x surface by HF. The frequency shift that is mainly governed by the loss in cantilever mass can be used at higher concentration.