In the high speed sliding electrical contact with large current, the temperature of contact area rises quickly under the coupling action of the friction heating, the Joule heating and electric arc heating. The rising temperature seriously affects the conductivity of the components and the yield strength of materials, as well affects the contact state and lead to damage, so as to shorten the service life of the contact elements. Therefore, there is vital significance to measure the temperature accurately and investigate the temperature effect on damage of rail surface. Aiming at the problem of components damage in high speed sliding electrical contact, the transient heat effect on the contact surface was explored and its influence and regularity on the sliding components damage was obtained. A kind of real-time temperature measurement method on rail surface of high speed sliding electrical contact is proposed. Under the condition of 2.5 kA current load, based on the principle of infrared radiation non-contact temperature sensor was used to measure the rail temperature. The dynamic distribution of temperature field was obtained through the simulation analysis, further, the connection between temperature changes and the rail surface damage morphology, the damage volume was analyzed and established. Finally, the method to reduce rail damage and improve the life of components by changing the temperature field was discussed.
The thermal protection materials for aircraft are usually assembled on the substrate surface by means of adhesion agent. It is very necessary to evaluate the interface bonding quality which has great influence on heat preservation performance. At present, there is still no relatively satisfactory and reliable method for defect detection of cohesive coating. Planar array electrical capacitance tomography (ECT) is a suitable non-invasive imaging technique when there is only limited access to the targeted object. This research aims to investigate the feasibility of using planar array electrical capacitive tomography for bondline defect detection. In this paper, a planar array ECT system is developed consist of a planar array sensor of 12 electrodes, a capacitance acquisition system and image reconstruction software. The sensor development, simulation of sensitivity map, practical application and imaging reconstruction are discussed. A series of specimens of thermal protection material with man-made defects are tested by the proposed planar array ECT system. The experimental results show that the defect in cohesive coating can be effectively detected and the minimum size can be detected is 10mm×10mm.
In this paper, a new signal processing method based on Kalman filter is presented for self-mixing displacement sensor. Based on the approximate linearized model of a LD, the robust Kalman filter is designed for an estimation of system parameters and target displacement. The proposed signal processing algorithm increases the resolution well beyond half-wavelength, without any external optical components, preliminary separate measurements, or target surface preparation. Simulation analysis and experiments have been done to illustrate the validity and the effectiveness of the method. These results show that the displacement estimation is good with little noise and the estimated accuracy of about λ/20 is achievable.
It has been established that under certain conditions a tightly focused laser beam can trap microscopic particles in the size range from tens of nanometers to tens of micrometers. This technique is commonly referred to as optical tweezers and is widely used in many biological applications. The optical forces and torques applied by the trapping beam to the particle result from the transfer of momentum and angular momentum from the trapping beam to the particle. In recent years there has been an explosive development of interest in the measurement of forces and torques at the microscopic level, such as within living cells, as well as of the properties of fluids and suspensions on this scale, using optically trapped particles as probes. Here we present a novel method for a simple, accurate, simultaneous measurement of the rotation speed of an optical trapped birefringent particle, and the optical torque acting on it, by measuring the change in angular momentum of the light from passing through the particle. This method does not depend on the size or shape of the particle or the laser beam geometry, nor does it depend on the properties of the surrounding medium, and provides a mean to accurately measure the viscosity of interest on a microscopic scale.
A nanometer range displacement measurement system is presented where a reciprocal interferometer is employed whose configuration is similar to Michelson interferometer. Although the reciprocal interferometer is very simple and insensitive to environmental perturbations, we concluded that the spectrum analysis techniques could also be used to process the interference fringes and increase the measurement precision of reciprocal interferometry. Fast-Fourier transform and filter are used to eliminate the noises in fringes. The reconstructed fringes are very clear, which location can be measured accurately. Theoretical analysis is presented. Experimentally, the displacement of a nanopositioner-driven target was measured by using a reciprocal interferometer, a CCD camera, picture card and computer. The system has demonstrated a minimum resolution is 1.5 nm when the number of sample point is 512.