分布式光纤传感技术在管道泄漏检测中的应用

分布式光纤传感技术由于能够获得被测物理场沿空间和时间上的连续分布信息,非常适合用于长距离管道泄漏检测。介绍了分布式光纤传感技术在管道泄漏检测中的应用情况和面临的问题,对该技术在管道泄漏检测中的应用前景进行了展望。     

基于SoPC的双频激光回馈位移测量系统设计

介绍了一种基于SoPC的双频激光回馈位移测量系统的实现方法。该系统利用双频激光回馈理论和数字细分电路,对两路正交的光回馈信号采用五细分和四细分电路相结合进行细分处理,解决了单偏振光测量位移分辨率不高的问题。实验证明了本系统的可行性,精度达到了0.791 nm,是一种应用很好的位移测量系统。     

A parallel fuzzy-controlled flexible manipulator using optical tip feedback

Investigation and development of a fuzzy-controlled highly non-linear two-axis manipulator with a single-flexible link using a novel patented optical tip displacement feedback is described. The controller comprises a parallel fuzzy supervisor that is used to alter the derivative term of a linear classical PD controller, which is updated in relation to the measured tip error and error rate.Implementation of the supervisory fuzzy controller is described using both serial and parallel operation on transputers.The design of the fuzzy rules was made with a modified closed-loop phase-plane method. The design approach results in a controller implementation that uses only 14 rules and is suitable for cheaper CPU-constrained and memory-challenged embedded processors.The benefits introduced by this procedure include a method to decide where and when the action takes effect in the controller and a greatly reduced rule base. The parallel operation achieved rise times of 0.033 s and settling times of 0.064 s for a payload of 0.7 kg considerably better than other workers did.An 128% increase in payload, 73.5% faster settling time and a reduction of steady-state error of over 50% were achieved using fuzzy control over its classical counterpart.     

High-gain observer approach to disturbance attenuation using measurement feedback

A procedure is developed for disturbance attenuation in a linear system via the use of measurement feedback. A high-gain observer is used to recover the disturbance attenuation properties asymptotically, which can be achieved using full state feedback. It is thus shown that the problem of disturbance attenuation via measurement feedback can be decomposed into two problems of disturbance attenuation via state feedback. These problems of disturbance via state feedback can then be solved using existing methods based on the algebraic Riccati equation.     

基于光纤传感的表面纳米修饰技术实验研究

针对光纤传感和纳米技术的广泛应用,分析了光纤表面纳米修饰技术的原理与过程.依据光纤表面纳米修饰技术的原理,对实验光纤进行了表面修饰的实验研究,并设计搭建了光纤表面修饰后的光测量的系统,进行了光谱测试.经过测试,表面纳米修饰后普通的光纤转变为敏感光纤,进一步扩大光纤传感技术的应用范围.     

Flow rate-insensitive microparticle separation and filtration using a microchannel with arc-shaped groove arrays

Inertial microfluidics can separate microparticles in a continuous and high-throughput manner, and is very promising for a wide range of industrial, biomedical and clinical applications. However, most of the proposed inertial microfluidic devices only work effectively at a limited and narrow flow rate range because the performance of inertial particle focusing and separation is normally very sensitive to the flow rate (Reynolds number). In this work, an innovative particle separation method is proposed and developed by taking advantage of the secondary flow and particle inertial lift force in a straight channel (AR = 0.2) with arc-shaped groove arrays patterned on the channel top surface. Through the simulation results achieved, it can be found that a secondary flow is induced within the cross section of the microchannel and guides different-size particles to the corresponding equilibrium positions. On the other hand, the effects of the particle size, flow rate and particle concentration on particle focusing and separation quality were experimentally investigated. In the experiments, the performance of particle focusing, however, was found relatively insensitive to the variation of flow rate. According to this, a separation of 4.8 and 13 µm particle suspensions was designed and successfully achieved in the proposed microchannel, and the results show that a qualified particle separation can be achieved at a wide range of flow rate. This flow rate-insensitive microfluidic separation (filtration) method is able to potentially serve as a reliable biosample preparation processing step for downstream bioassays.     

Low cost inductor current sensing for power converters using feedback compensation

One of the key components in the current mode control of power converters is the sensing of inductor current. Traditional low cost implementation is to add a sensing resistor in series with the inductor to sense the inductor current. This will reduce the overall efficiency of the power converter. An alternative is to apply a current transformer to the inductor to sense its current. This however will significantly increase the cost of power converters. One low cost implementation is to add a resistor–capacitor network in parallel with the inductor so that the inductor current can be derived from the capacitor voltage. The problem of this implementation is that the capacitor voltage is very sensitive to temperature variations. In this paper, a simple feedback loop is applied to the sensed capacitor voltage based on the steady state duty ratio of power converters such that the sensed inductor current will be independent of temperature variations. The sensing element with feedback compensation can be applied to inductors fitted to power converters such as buck converters and boost converters. Although experimental studies based on a buck converter were carried out to illustrate the correctness of the new sensing technique, the proposed technique is applicable to other converter topologies.     

光学遥感舰船目标识别方法

提出一种基于粗糙集理论和分层判别回归技术的光学遥感舰船目标识别方法。该方法首先提出新的光学遥感舰船识别特征———面积比编码,并与四类特征组合作为备选特征;然后基于粗糙集理论按同可区分度来计算各备选特征的重要性权值,自动选择出对正确识别贡献较大的特征组合;最后根据分层判别回归原理生成分类判决树来识别光学遥感舰船目标。实验结果表明,本文方法在识别精度和速度方面优于最近邻和支持向量机方法,且通用可行。     

Flow velocity measurement in microchannels using temperature-dependent fluorescent dye

The size of microfluidic channels prevents the use of conventional methods for flow velocity measurement. This paper presents and evaluates a method of flow velocity measurement using a temperature dependent fluorescent dye and a microheater. The microheater applied a heat pulse to the dye flowing in a glass capillary, resulting in a plug of fluid of lower fluorescent intensity. By tracking this low intensity region, the velocity of the heat pulse travelling with the flow was determined and used to calculate average flow velocity using correlations. The method was verified by measuring a range of flow velocities in two different sized glass capillaries.     

Implementation of a high-accuracy phase unwrapping algorithm using parallel-hybrid programming approach for displacement sensing using self-mixing interferometry

The Journal of Supercomputing - Phase unwrapping is an integral part of multiple algorithms with diverse applications. Detailed phase unwrapping is also necessary for achieving high-accuracy metric...     

Validation of optical remote sensing measurement strategies applied to industrial gas emissions

In May 2004 a field campaign was conducted at a power plant in Spain, aiming to validate the use of a miniaturized, fibre‐optic, ultraviolet, differential optical absorption spectrometer (mini‐DOAS) for sulfur dioxide (SO₂) flux quantification. Emissions were determined by integrating the total number of molecules in a vertical cross‐section of the gas plume, and multiplying them by the wind component at plume height. Calculated wind data were compared with balloon soundings. Plume height, computed from a tomographic reconstruction of the plume, was compared with stereo‐photogrammetric methods and a plume rise model. Finally, SO₂ fluxes were compared to emissions reported by the power station. Although the meteorological conditions during the field campaign were adverse, with large fluctuations in wind speed and wind direction, the optical measurements performed proved to be practically feasible and compared well with the techniques used for validation. SO₂ fluxes derived by the mini‐DOAS were within 7% of those reported by the power station.     

Head–disk spacing measurement based on Michelson interferometry using white light illumination

Head–disk spacing of hard disk drives was measured based on Michelson interferometry using white light illumination. This method utilizes the phase comparison of two interference fringe patterns formed respectively on the inner surface of a glass disk and the air bearing surface of a slider through the glass disk. To suppress interference noise and to further enhance measurement accuracy, low coherent white light was adopted as an illuminating source to replace high coherent laser. A high sensitive CCD digital camera was used to compensate for the attenuation of the brightness and contrast of the interference fringe pattern in the white light-based Michelson interferometer. The captured images and the measured results indicate that the application of white light illumination effectively improves the interference fringe pattern, and the measurement error of extracting the ridgeline can be consequently reduced five times in comparison with a laser. Spacing resolution (=λ/2w) was enhanced to 0.68 nm/pixel in our experiment, closely approaching the extreme spacing resolution (at the largest fringe interval w _max) of 0.64 nm/pixel. Indirect and direct methods for determining fringe interval were proposed, and the latter provides higher accuracy. Head–disk spacing was measured at different spacing resolutions of 2.61 and 0.68 nm/pixel to clarify the effect of fringe interval on measurement accuracy. The results show that tested spacing at larger fringe interval achieves not only better agreement with the calculated example, but also better deviation tolerance characteristics. Based on the advantages, measurement of 10 nm spacing was realized with high accuracy and good repeatability.     

Remote sensing technique for near-surface wind by optical images of rough water surface

The study of a new remote-sensing technique for the investigation of near-surface wind fields is an important oceanographic problem. This article is focused on a new method of recording wind fields by the analysis of optical images of sea surface and range–time–intensity images (RTI images) of the sea surface. An RTI image constructed from optical profiles of the sea surface is an optical analogue of a side-looking radar image of the sea surface but has a higher spatial resolution and some possibility for remote sensing of sea roughness. It is possible to form RTI images with a range from some tens of metres to tens of kilometres, depending on the spatial resolution needed. A set of original optical devices for recoding RTI images using linear arrays of CCD-photodiodes was created. An analytical model of sea surface radiance for visible light was developed taking into account the polarization of light and shadowing of surface waves for grazing view geometry. The principle of remote sensing of near-surface winds by its manifestations on a waved surface under grazing angles based on a comparison of measured and modelled surface radiance is discussed. Investigations of near-surface wind field features in internal reservoirs and various regions of the seas during the last few years have been conducted by optical systems. The structure of near-surface wind fields, eddies, wind fronts, and katabatic wind flows for ranges from hundreds of metres to some tens of kilometres was recorded and analysed. Derived data of optical monitoring of water surfaces may serve for future investigations of near-surface wind features.     

Heat transfer in microchannel devices using DSMC

The heat transfer characteristics of supersonic flows in microchannels is studied using direct simulation Monte Carlo (DSMC) method. The velocity components and the spatial coordinates of the simulated particles are calculated and recorded by using a variable-hard-sphere (VHS) collision model. The effects of Knudsen number (Kn) on the heat transfer of the microchannel flows are examined. The results show that the magnitude of the temperature jump at the wall increases with increasing Kn. The heat transfer to the isothermal wall is found to increase significantly with Kn. The possible causes for the increase of wall heat transfer are discussed     

A novel technique for measuring pico-scale flow rate of a liquid solution using a microchannel

As micrototal analysis system (μ-TAS) becoming more extensively used, techniques for fabricating microchannels, microactuators, and measuring systems are becoming increasingly important. This study describes a novel method for fabricating a closed microchannel that can be used to measure the pico-scale flow rate of a liquid solution with an accuracy of better than 1 pL/s. The flow rate of 9 pL/s is calculated from the measurements. Without any high temperature or high-voltage processing, the microchannel can be integrated in the complementary metal–oxide–semiconductor (CMOS) microfluidic system and the fabricating process involves only some standard CMOS processes and common materials. The batch fabrication of a single integrated circuit (IC) chip is essential to reaching the goal of a system in one chip.     

折叠反馈补偿技术的铂电阻温漂修正方法

由于铂电阻自身存在的非线性会给测量带来误差.采用折线形式的反馈电路,将铂电阻以4线制的方法接入到测试电路中.设计的温度传感器可以大幅提高测量精度.经实验测试,在0~100℃范围内,其非线性误差在0.04%以内,最大输出电压误差在0.002 V以内.此类温度传感器具有高可靠、高精度、低成本等特点,非常适用于对温度测量有着苛刻要求的工业环境中.     

Reaching condition for variable-structure output feedback controller using a search technique

The aim of this paper is to establish the reaching condition for a variable-structure output feedback controller based on Genetic Algorithms (GA). The design of the variable-structure controller using output feedback provides a technique to compute matrix parameters and guarantees the reaching conditions for a general class of linear systems. A combination of both a modified control law and a simple search technique based on the GA approach is proposed to obtain a good dynamic response. The proposed method is computationally simple and tractable, and guarantees a sliding motion along the switching surface. The efficacy of the theoretical results is illustrated by considering a linearized model of an aircraft control problem.     

基于BOTDA的分布式光纤温度传感测量实验研究

为了进一步提高布里渊光时域分析(BOTDA)的测温精度,基于BOTDA的原理,构建了温度传感测量系统。测温实验发现,测温光纤的保护层厚度影响了其测温的精度;裸纤直接测温的精度较高,但也易受外界影响,且易断,故改进光纤的保护层可以提高其测温精度。提出一种将导热硅脂涂敷在光纤上进行测温试验的方法,提高了温度测量的准确性。