Active noise control using a distributed mode flat panel loudspeaker

A flat panel distributed mode loudspeaker (DML) has many advantages over traditional cone speakers in terms of its weight, size, and durability. However, its frequency response is uneven and complex, thus bringing its suitability for active noise control (ANC) under question. This paper presents experimental results demonstrating the effective use of panel DML speakers in an ANC application. Both feedback and feedforward control techniques are considered. Effective feedback control with a flat panel speaker could open up a whole range of new noise control applications and has many advantages over feedforward control. The paper develops a new control algorithm to attenuate tonal noise of a known frequency by feedback control. However, due to the uneven response of the speakers, feedback control is found to be only moderately effective even for this narrow-band application. Feedforward control proves to be most capable for the flat panel speaker. Using feedforward control, the sound pressure level can be significantly reduced in close proximity to an error microphone. The paper demonstrates an interesting application of the flat panel in which the panel is placed in the path of sound and effectively used to block sound transmission using feedforward control. This is a new approach to active noise control enabled by the use of flat panels and can be used to prevent sound from entering into an enclosure in the first place rather than the traditional approach of attempting to cancel sound after it enters the enclosure.     

GSW 型高压带电显示器校验装置的研制

高压带电显示器是用来检测、反映电力系统一次设备带电与否的一种电气设备,广泛安装于变电站内各个进线和出线间隔,用于警示运行和检修人员,能够防止设备电气误操作和保障人身安全。针对生产工作中高压带电显示器缺陷多发、缺少有效校验工具的实际难题,介绍了一种专门用于校验GSW型高压带电显示器的装置,并就该装置的研制背景、结构原理和现场应用进行了详细的阐述,展示了其良好的使用效果和优越的推广价值。     

双层平板探测的双能成像检测系统

本文提出一种使用双层平板探测器单次曝光获取X射线双能图像,并实现双能减影的成像检测方法.介绍了单层平板、双层平板探测器结构以及双层平板探测成像系统工作原理.仿真分析不同、相同管电压在不同滤过下X射线的能谱变化,进一步通过试验分别探究使用kVp切换,双层平板方案时胸部体模双能成像特性.研究发现kVp切换、双层平板方案采集...     

散布式磁致伸缩平板扬声器研制

为了改善现有单个超磁致伸缩驱动器平板扬声器输出功率及音色方面的不足,提出了基于超磁致伸缩驱动器(GMA)的散布式多点配置平板扬声器设计.研究了用于新型散布式多点配置平板扬声器的音频驱动器的设计,分析了超磁致伸缩平板扬声器多点配置原理,并讨论了音板材料的选择,最后利用专业测试软件对研制的散布式多点配置磁致伸缩扬声器进行了性能测试.结果显示,与单点驱动扬声器相比较,该扬声器音显而易见提高,音质得到了进一步的改善.     

键盘接口技术在某显控设备中的应用

提出了一种利用键盘接口采集按键、开关输入的方案.该方案介绍了键盘的工作原理及与工控机通信的方法,给出了某显控设备中显控键盘的构成原理框图以及软硬件实现方法.     

Traceability of DC high voltage measurements using the Josephson voltage standard

This paper introduces a new methodology for obtaining high voltage DC measurements traceability to the International System of Units (SI) at the Egyptian National Institute for Standards (NIS). The traceability has been achieved via the NIS automated 10 V DC Josephson Voltage Standard (JVS). A 100 kV DC voltage divider with a nominal voltage ratio of 10,000:1 is being used with its display in parallel with a high sensitive digital voltmeter. The traceability has been realized by calibrating this digital voltmeter via the JVS system and then it has been used to calibrate the divider display readings. Moreover, the divider ratio has been accurately calibrated using a traceable calibrator source on its high voltage side and the calibrated digital voltmeter on its low voltage side. Accurate and traceable high voltage values have been obtained associated with their expanded uncertainties. Highly improved uncertainties have been achieved using this new calibration technique.     

The design of high efficiency flat pad aerostatic bearings using laminar restrictions

The design of flat pad aerostatic bearings is examined to determine the best inlet arrangement to achieve high load capacity. The paper shows that like all other forms of aerostatic bearings, the optimum selection of supply to inlet pressure (K_g) and the optimum position of inlet devices can be achieved. The paper demonstrates a relatively new type of inlet geometry — the capillary inlet slot. Both single thrust pad and opposed flat pad bearings arrangements are examined. A theoretical analysis of the flat pad arrangements has been developed using a finite difference approach previously adopted for the analysis of externally pressurized journal bearing arrangements¹.     

平板探测器坏像素校正方法研究

讨论X射线系统中平板探测器的坏像素产生原因并归纳分类。研究坏像素的探测、校正矩阵的生成和对坏像素的校正方法。通过仿真模型对所提出的校正算法进行了验证,通过比较重建图像的信噪比对该算法的效果进行了评估。研究结果表明,平板探测器的制造缺陷等固有噪声源将在重建图像中被增强,并表现为大量的条纹和环形伪影;通过校正,重建图像中的上述伪影明显减少,图像质量得到改善,且系统的低对比度探测能力也得到相应提高。     

The compaction of powder metallurgy bars using high voltage electrical discharges

A new compaction process for the production of high density powder metallurgy (P/M) bars is suggested using a high voltage electrical discharge followed by rotary swaging. This paper gives practical details concerning the production of P/M bars from iron powder by electrical discharge, and endeavours to describe the mechanism of density increase. Experimental results for determining the effect of various parameters are presented.     

Accurate stigmating of a high voltage electron microscope

To reach the 0·2 nm point-to-point resolution possible with some high voltage electron microscopes, the astigmatism of the objective lens must be compensated to within 5 nm. Due to a number of factors the resolution of the image seen on the viewing screen of the high voltage microscope is, however, quite poor and does not permit compensation of such accuracy. We describe a technique for evaluating and correcting the astigmatism that starts from a recorded micrograph of a thin amorphous specimen. The astigmatism is determined from the optical diffraction pattern using a variation of the Thon method. This variation avoids any direct measurement of the radii of the contrast transfer zones, and is extremely rapid and convenient. Adjusting the stigmator coil currents, calibrated in terms of their stigmating power, for zero astigmatism completes the correction in less than 10 min after the recording of the micrograph.     

Exact piezothermoelastic solution of simply-supported orthotropic flat panel in cylindrical bending

Exact piezothermoelastic solution is presented for infinitely long, simply-supported, orthotropic, piezoelectric, flat panel in cylindrical bending under pressure, thermal and electrostatic excitation. The displacements, electric potential and temperature are expanded in Fourier series to satisfy the boundary conditions at the longitudinal edges. The governing equations reduce to ordinary differential equations with constant coefficients. The six constants in their general solution for each Fourier component are obtained from the boundary conditions at the lateral surfaces. The solution of the inverse problem of inferring the applied temperature from the measured electrical potential difference between the lateral surfaces of the panel is also presented. Results are presented for sinusoidal thermal and electrostatic loadings and the effect of width to thickness ratio has been investigated.     

LED显示屏相机采集影像渐晕的修正

为了克服相机影像渐晕在LED显示屏逐点一致化校正过程中带来的不均匀性缺陷,从相机影像发生渐晕时的灰度分布规律出发,提出了一种基于图像平滑滤波算法的修正方法。介绍了CCD对LED显示屏进行数据采集和成像的原理;在分析其成像稳定性的基础上,描述了空域平滑滤波的原理,并选取模板对CCD采集得到的LED像素亮度空间分布做邻域平均平滑处理,得到了代表相机影像渐晕分布的曲面。最后,介绍了利用该曲面实现影像复原的算法。实验结果表明:经过对相机影像渐晕修正以后,可以使LED显示屏的显示均匀性偏差由12.9%缩小到0.73%,克服了修正前LED显示屏中心暗、四周亮的缺陷,达到了理想的校正效果。     

Experimental study of natural convection heat transfer from a nonuniformly heated flat plate simulating PV panel

Journal of Mechanical Science and Technology - In view of the characteristic of Photovoltaic (PV) conversion, an experimental study has been conducted to investigate the natural convection heat...     

基于无功调压的高压电抗器优化配置研究

针对高压电抗器的优化配置问题,提出了一种依据层次分析法构建的以电压指标为主、综合考虑网损指标和无功动作指标的高抗优化配置指标体系,并在改进层次分析法和熵权系数法的基础上建立了一种综合赋权方法,通过该指标体系对高抗优化配置备选方案进行了评价打分,得到了高抗最佳配置方案。研究结果表明,该模型得到的最佳方案能有效改善高抗配置地点的母线电压,并可以提升电网的整体性能。     

Preliminary study on the tribology of an organic-molecule-coated touch panel display surface

The use of touch panel displays has been increasing due to the popularity of tablet PCs and smart phones. In order to protect the touch panel surface from scratches, contaminants from fingerprints and skin oils and so on, anti-contamination coating is necessary.One of the ways to protect the surface is to cover it with a thin and dense organic molecular layer. At the present time, the primary requirement for the coating is fingerprint-resistance or easy removal of contaminants. An adsorbed molecular layer of PFPE-derivatives is currently used for this purpose, in order to reduce the surface energy of the surface. Since the current major concern of panel makers is anti-fingerprint performance, degradation of the molecular layer by both tribological and environmental conditions is a major issue for the development of the coatings.Given the current priorities, however, tribological research into such subjects as the touch feeling of the panel and the friction characteristic has not been conducted. The touch feeling and its relation to the operation are very important but very difficult to study because it is very hard to express the touch feeling numerically. As a preliminary study, several different coated surfaces were prepared and their friction coefficients were measured by rubbing with a finger or a steel or glass ball to clarify the tribological characteristics of the surface.An Si wafer and a glass plate were used in this study as models of the solid substrate of a display. They were coated with an adsorbed organic molecular layer of two PFPE-derivatives with different molecular structures named Type-F and Type-D or several reference molecular layers, such as OTS-SAM and FDTE-SAM. In addition to the tribological data, degradation by UV irradiation was also examined to compare the performance. The results are discussed from the tribological and chemical points of view.     

A self-sensing technology of active magnetic bearings using a phase modulation algorithm based on a high frequency voltage injection method

Conventional AMB(active magnetic bearings) systems consist of electromagnetic coils, position sensors, power amplifiers and a feedback controller. This hardware configuration can lead to a structural complexity, problems of space limitations for the installation, and position control difficulties due to the non-collocation of actuators and sensors. In this paper, a self-sensing mechanism is proposed to resolve such limitations of the general AMB system. The proposed self-sensing scheme uses a phase difference of the injected current of two opposite electromagnetic actuators while an object is levitating between the actuators. The relationship between the phase difference of injected currents and the position of a levitated object was theoretically derived and linearized. In order to realize the proposed self-sensing scheme, a signal processing algorithm was developed. The frequency response of the estimator was measured to verify the performance of the proposed self-sensing scheme. In addition, a magnetic levitation and a disturbance rejection response were experimentally obtained to verify the feasibility of the proposed self-sensing mechanism. Experimental results showed that the developed self-sensing technique has similar performance as a practical gap sensor.     

Quantitative tensile-tilting stages for the high voltage electron microscope.

This paper describes a soft and a hard tensile stage for the high voltage electron microscope. Both stages can be combined with a top entry double tilting stage. The devices are driven by thermal expansion elements operating against water cooled parts. The drive mechanism shows smooth action with a relatively low response time and good long-time stability. The stages are equipped with strain gauge bridges for force and elongation measurements. The soft stage has a maximum load of 13 g, and a hard one reaches 1.5 kg.