FBG应变挠度法标定及过程仿真

介绍了一种基于挠度分析的等强度悬臂梁FBG传感器应变标定测试方法和装置,研究了FBG传感器应变传递过程中的相关参量的仿真分析方法,精确测量了应变传递过程中的相关参量,并且针对不同载荷下的等强度悬臂梁的表面应变和挠度进行了理论分析和仿真。同时解析了挠度与梁表面应变、FBG传感器应变的关系,给出了标定后FBG传感器的应变灵敏度,并对挠度法测量FBG传感器的标定结果进行了不确定度评定。当包含因子k=2时,FBG传感器应变灵敏度的相对扩展不确定度＜0.5％,能够满足高精度的应变测试要求,为高精度FBG传感器的应变标定提供了技术支持。     

Design and analysis of an integrated optical sensor for scanning force microscopies

In this paper, a novel probe for displacement sensing will be introduced. It is based on a conventional GaAs cantilever, integrated with a Bragg grating as a photo-elastic strain sensor. The deflection of the cantilever is measured directly from the intensity modulation of the reflected light. The principle of the experimental setup and the sensor, as well as the theoretical investigation of the force and displacement sensitivity of the probe, is presented. Finite-element method simulations were performed to get the optimum sensor design. Transfer matrix method simulation of the waveguide grating have been described in detail. In order to enhance the sensitivity, different types of grating structures are discussed. Using this new design, it should be possible to achieve sensitivities, defined as the fractional change in detected optical power per unit displacement of the cantilever, as high as 10/sup -4/ /spl Aring//sup -1/ of cantilever deflection.     

3D finite element analysis of electrostatic deflection of commercial and FIB-modified cantilevers for electric and Kelvin force microscopy: I. Triangular shaped cantilevers with symmetric pyramidal tips

The investigation of the nanoscale distribution of electrostatic forces on material surfaces is of paramount importance for the development of nanotechnology, since these confined forces govern many physical processes on which a large number of technological applications are based. For instance, electric force microscopy (EFM) and micro-electro-mechanical-systems (MEMS) are technologies based on an electrostatic interaction between a cantilever and a specimen. In the present work we report on a 3D finite element analysis of the electrostatic deflection of cantilevers for electric and Kelvin force microscopy. A commercial triangular shaped cantilever with a symmetric pyramidal tip was modelled. In addition, the cantilever was modified by a focused ion beam (FIB) in order to reduce its parasitic electrostatic force, and its behaviour was studied by computation analysis. 3D modelling of the electrostatic deflection was realized by using a multiphysics finite element analysis software and it was applied to the real geometry of the cantilevers and probes obtained by using basic CAD tools. The results of the modelling are in good agreement with experimental data.     

绳锯线弓角静态测量方法的研究

金刚石绳锯在切割圆弧板材时,受到进给方向的阻力,形成"线弓角",使板材中部产生"过切",严重时导致材料报废.为解决这一问题,提出了线弓角的概念,从理论上提出了一种基于悬臂式力传感器的绳锯线弓角的静态测量方法,通过轴力传感器输出的电压值计算出线弓角度.试验在自行设计和搭建的绳锯线弓角测量平台上进行,用钢丝绳模拟串珠绳产生线弓角,并进行导轮受力与线弓角关系的静态测量试验分析,以验证该方法测量线弓角的可行性.试验结果表明:在一定范围内,串珠绳初始张紧力越大,线弓角的计算值越接近理论值.因此,采用所提出的测量方法,当装有轴力传感器的导轮处在刚好与钢丝绳接触的状态下,选择合适的初始张紧力,可以测得较准确的角度值.     

Fatigue crack growth driven by electric fields in piezoelectric ceramics and its governing fracture parameters

Fatigue crack growth test for piezoelectric ceramics was performed under cyclic electric loading. Double cantilever beam specimen, which was made of two different piezoelectric ceramics, with a through notch was used. The specimens were, varying the amplitude and the mean value, subjected to various cyclic electric fields. It was found that crack growth behavior is greatly dependent on the amplitude and mean value of cyclic electric field and materials. Crack growth rate decreased as electric field increased and finally stopped. Crack growths under the positive, the negative and the shifted electric field were very slow compared to that under fully reversed electric field. However, threshold for the crack propagation did not depend greatly on materials. Then, as possible governing fracture parameters, CED and electric displacement intensity factor were chosen based on the results of electromechanical finite element analysis within linear framework and their closed form equations were also obtained considering the influences of electric boundary conditions inside the notch. Finally, the parameters were correlated with crack growth rate measured experimentally by employing Paris law type equation.     

Liquid crystal infiltrated photonic crystal fibers for electric field intensity measurements

The application of nematic liquid crystal infiltrated photonic crystal fiber as a sensor for electric field intensity measurement is demonstrated. The device is based on an intrinsic sensing mechanism for electric fields. The sensor probe, which consists of a 1 cm infiltrated section of photonic crystal fiber with a lateral size of ～125 μm, is very compact with small size and weight. A simple all-fiber design for the sensor is employed in an intensity based measurement scheme. The transmitted and reflected power of the infiltrated photonic crystal fiber is shown to have a linear response with the applied electric field. The sensor is operated in the telecommunication window at 1550 nm. The temperature dependence of the device at this operating wavelength is also experimentally studied and discussed. These structures can be used to accurately measure electric field intensity and can be used for the fabrication of all-fiber sensors for high electric field environments as both an in-line and reflective type point sensor.     

Symmetrical PolyMUMPs-Based Piezoresistive Microcantilever Sensors With On-Chip Temperature Compensation for Microfluidics Applications

Microelectromechanical systems (MEMS)-based cantilever beam sensors for microfluidics applications with on-chip temperature sensors for temperature drift compensation were developed. The stress induced on gold surface with polysilicon piezoresistive sensing is demonstrated. In principle, adsorption of biochemical species on a functionalized surface of the microfabricated cantilever will cause surface stress and, consequently, cantilever bending. The sensing mechanism relies on the piezoresistive properties of the doped polysilicon wire encapsulated in the beam. The beam is constructed through multiusers MEMS Process (PolyMUMPs) foundry with postprocessing silicon etching. Bending analysis is performed so that the beam tip deflection can be predicted. The piezoresistor designs on the beams were varied, within certain constraints, so that the sensitivity of the sensing technique could be measured by external read-out circuit. The mass detection of 0.0058-0.0110 g is measured by the beam resistor series as a balanced Wheatstone bridge configuration. The voltage output of the bridge is directly proportional to the amount of bending in the MEMS cantilever. The temperature dependency and sensor performance have been characterized in experiments. Compensation by resisters on the substrate significantly reduces the temperature dependence.     

微型大气电场监测装置的设计与实现

针对户外场磨式地面电场仪存在的输入阻抗高、感应电流信号弱、易受外界电磁波干扰、功耗大且无市电供电等问题,设计一种光伏发电加蓄电池储能供电的低功耗大气电场监测装置.为减小系统功耗,提高测量精度,设计微型低速双定子差分式电场传感器,传感器感应到的两路微弱电流信号经过T型反馈网络实现I/U变换.通过减法器和4 Hz低通滤波器...     

Lorentz force actuation of a heated atomic force microscope cantilever

We report Lorentz force-induced actuation of a silicon microcantilever having an integrated resistive heater. Oscillating current through the cantilever interacts with the magnetic field around a NdFeB permanent magnet and induces a Lorentz force that deflects the cantilever. The same current induces cantilever heating. With AC currents as low as 0.2 mA, the cantilever can be oscillated as much as 80 nm at resonance with a DC temperature rise of less than 5 °C. By comparison, the AC temperature variation leads to a thermomechanical oscillation that is about 1000 times smaller than the Lorentz deflection at the cantilever resonance. The cantilever position in the nonuniform magnetic field affects the Lorentz force-induced deflection, with the magnetic field parallel to the cantilever having the largest effect on cantilever actuation. We demonstrate how the cantilever actuation can be used for imaging, and for measuring the local material softening temperature by sensing the contact resonance shift.     

Biological sensor based on a lateral electric field-excited resonator

This paper describes a biological sensor based on a lateral electric field-excited resonator using an X-cut lithium niobate plate. Its potential was shown through the example of biological interaction between bacterial cells and specific bacteriophages. The detection was based on the analysis of the measured real and imaginary parts of electrical impedance for a resonator loaded by the biological suspension under study. It has been shown that the sensor is sensitive to specific interactions between bacterial cells and specific bacteriophages in a pure state as well as in the presence of extraneous microflora. The degree of electrical impedance variation resulting from the biological interaction depends on the numbers of phage particles and bacteria cells. The sensor may be used not only for the qualitative analysis of bacteria but also for their quantitative detection.     

Voltage response and field reconstruction for a miniature fieldprobe in a spatially nonuniform electric field

A miniature E-field probe employing a 0.6-mm linear dipole antenna has been developed. The authors describe an analytical study of the probe's response to a spatially varying electric field. On the basis of the Nyquist sampling theorem, the spatial sampling frequency at which an electric field should be measured for good reconstruction is established. Using antenna theory, the voltage response of the probe is found in terms of the antenna's transmitting current and the measured electric field. This relationship is used to reconstruct the electric field from a set of discrete voltage responses. A method-of-moments program has been developed to determine numerically the voltage response of the antenna structure to a spatially varying electric field. Numerical results, which allow for the testing of certain theoretical findings important for analyzing measurement data, are presented. Although developed for only one-dimensional fields, the methodology can be applied to general three-dimensional fields     

Trace detection of peroxides using a microcantilever detector

A microcantilever sensor is reported for the trace detection of peroxide vapors. The sensor features a self-assembled monolayer that undergoes chain polymerization in the presence of peroxide radicals, causing a deflection of the cantilever. The generation of radicals using a heated filament, and the resulting surface polymerization reaction, is based on initiated Chemical Vapor Deposition chemistry. The sensor was successfully demonstrated with hydrogen peroxide and exhibited inherent reversibility and a selective, self-amplified response. Air and water were tested as interferents. This trace peroxide detector has industrial applications and addresses an aviation security need for the reliable detection of homemade explosives.     

Tensile elongation measurement device with in-plane bimorph actuation mechanism

This paper describes the development of a bimorph-actuated twin-probe device utilized for uniaxial tensile test to measure tensile elongation of a film specimen. The device consists of two sets of microscale cantilever probes with piezoresistive sensor to detect the position of two gauge marks on a specimen, and multiple pairs of bimorph actuators to produce in-plane motion for scanning those marks. By Joule's heating, the bimorph actuators connecting two cantilever probes are able to move along the tensile direction. When those probes climb the gauge marks having convex line structure, the sensor signals originating from the piezoresistive effect are output by the cantilever's deflection. The elongation of a tensile specimen can be calculated from the moving velocity of cantilever probes and the time difference between two sensor signals. The performance of the device produced through conventional micromachining technologies was investigated. Elongation of single-crystal silicon (SCS) film specimen was measured during uniaxial tensile loading. The mean Young's modulus of 165.1 GPa which was measured by using the device was in good agreement with the analytical value. The proposed bimorph-actuated twin-probe device would be useful for measuring elongation of a film specimen during the tensile test.     

Numerical determination of electric field forces and capacitance of pressure condenser microphone

Nonuniform deflection of a pressure condenser microphone membrane causes nonlinearities of a relationship between peak deflection of the membrane and the induced voltage. This paper describes how the numerical analysis carried out with the finite element method can help in more accurate determination of this nonlinearity. The dependence of the inverse capacitance (proportional to the induced voltage) on the deflection can be well approximated with the third-order polynomial and the electric field force with the second-order polynomial. There is a major influence of the nonlinearity of the inverse capacitance compared to the nonlinearity of the overall force on the microphone's overall nonlinearity. The deflection profile of the analyzed microphone's membrane is deduced from the values for a 1" microphone.     

A single electron transistor on an atomic force microscope probe

We report fabrication as well as proof-of-concept experiments of a noninvasive sensor of weak nanoscale electric fields. The sensor is a single electron transistor (SET) placed at the tip of a noncontact atomic force microscope (AFM). This is a general technology to make any nanometer-sized lithography pattern at edges or tips of a cantilever. The height control of the AFM allows the SET to hover a few nanometers above the substrate, improving both the electric field sensitivity and lateral resolution of the electrometer. Our AFM-SET sensor is prepared by a scalable technology. It means that the probe can be routinely fabricated and replaced, if broken.     

Deformation of ionic polymer gel films in electric fields

Deformation of ionic polymer gel films in electrolyte solutions was studied under the influence of electric fields. The ionic polymer gel films used were poly(vinyl alcohol)-poly(sodium acrylate) composite gel films with a thickness of the order of submillimetres. The vibration of gel films in a.c. electric fields, has been observed for the first time. It was suggested that the vibration behaviour was based on a differential swelling. The vibration of the ionic gel films was roughly analysed as a mechanical bending of a uniform cantilever beam by sinusoidally varying forces.     

3D finite element analysis of electrostatic deflection and shielding of commercial and FIB-modified cantilevers for electric and Kelvin force microscopy: II. Rectangular shaped cantilevers with asymmetric pyramidal tips

This paper deals with an application of 3D finite element analysis to the electrostatic interaction between (i) a commercial rectangular shaped cantilever (with an integrated anisotropic pyramidal tip) and a conductive sample, when a voltage difference is applied between them, and (ii) a focused ion beam (FIB) modified cantilever in order to realize a probe with reduced parasitic electrostatic force. The 3D modelling of their electrostatic deflection was realized by using multiphysics finite element analysis software and applied to the real geometry of the cantilevers and probes as used in conventional electric and Kelvin force microscopy to evaluate the contribution of the various part of a cantilever to the total force, and derive practical criteria to optimize the probe performances. We report also on the simulation of electrostatic shielding of nanometric features, in order to quantitatively evaluate an alternative way of reducing the systematic error caused by the cantilever-to-sample capacitive coupling. Finally, a quantitative comparison between the performances of rectangular and triangular cantilevers (part I of this work) is reported.     

Electromechanical analysis of piezoelectric bimorph actuator in static state considering the nonlinearity at high electric field

This article contains electromechanical analysis of a piezoelectric bimorph actuator at high electric field by incorporating second-order constitutive equations of piezoelectric material. Tip deflection, block force, block moment, block load, output strain energy, output energy density, input electrical energy, and energy efficiency are analytically derived for the actuator at high electric field. The analysis shows that output energy and energy density increase more rapidly at high electric field, compared to the prediction by the linear model. The analysis shows energy efficiency depends on electric field. Some analytical results are validated with the published experimental results.     

Determination of the flexural strength and elastic modulus of ice from in situ cantilever-beam tests

From the theory of cantilever beams on an elastic foundation, it is shown that the strength index and modulus index of ice can be determined from measurements of either the failure load or the tip deflection, or both, of in situ cantilever beams tested over a wide enough range of ratio of beam length to beam thickness. Four methods are proposed, two of which do not require the measurement of beam deflection during beam loading, an often difficult task to perform with sufficient reliability, especially in the field. The methods have been applied to available field and laboratory data. The initial results show reasonably consistent estimates of the strength index but a large variation in the predicted values of the modulus index. One preferred method is suggested but its validity and reliability need to be further evaluated by analyzing a sufficient number of field and laboratory tests.     

Design and optimization of a low-frequency electric field sensorusing Pockels effect

The present paper proposes an optical device for measuring low-frequency (50-60 Hz) high electric fields (0-200 kV.cm^-1) using a LiNbO₃ crystal as sensing medium without any contacting electrode. Thus, a good galvanic insulation of material and person is obtained. An experimental setup is developed in the laboratory by using the electro-optical effect or Pockels effect, and several measurements are realized. Simulations are performed with the finite element method (FEM) to optimize the sensing medium of the device. Experimental and simulation results are presented and discussed. The sensor induces a weak disturbance of the local electric field to be measured. The sensibility of the sensor is about 4 μA/(kV.cm^-1 )