Standardized measurements of interaction forces in autostable superconducting magnetic bearings

Passive magnetic bearings involving superconductors combined with permanent magnets have great potential for future utilization in systems that are exceptionally critical concerning friction and wear. In the field of power systems, possible applications of these superconducting magnetic bearings include flywheels and cold machines such as generators, motors and cold compressors. Present bearing designs are based on the high-temperature superconductor YBa₂Cu₃O₇. In order to investigate the capabilities of these materials and to establish an optimized bearing design, we have built a system that allows precise and reproducible measurements of interaction forces between permanent magnets and superconductors. Different sizes and geometries and various configurations can be accommodated. Our intention is to contribute to a standardization of the experimental technique.     

A platform for analysis and control design: Emulation of energy storage flywheels on a rotor-AMB test rig

Energy storage flywheels supported on active magnetic bearings (AMBs) have attracted much attention both in the academia and in the industry due to their many advantageous features, such as short charging time, high specific energy, no pollution and long life span. Feedback control is essential in the operation of such AMB support systems. However, actual AMB suspended energy storage flywheels are not widely available for research on feedback control design. To provide an economic and effective platform for the study of AMB supported energy storage flywheels, including research on the design of their feedback controllers, we propose in this paper to emulate the operation of such flywheels on a rotor-AMB test rig we recently constructed. Specifically, the two AMBs located at the two ends of the rotor are used as supporting bearings, while the other two located at the rotor mid span and quarter span are used to emulate the generator negative stiffness and gyroscopic effects on the rotor dynamics caused by the flywheel disk. Simulation and experimental results are presented to show the effectiveness of the proposed emulation method.     

AC losses in type-II superconductors induced by nonuniform fluctuations of external magnetic field

Magnetic field fluctuations are inevitable in practical applications of superconductors and it is often necessary to estimate the ac losses these fluctuations induce. If the fluctuation wavelength is greater than the size of a superconductor, known estimates for an alternating uniform external magnetic field can be employed. The authors consider the opposite case and analyze, using a model critical-state problem, penetration of spatially nonuniform fluctuations into type-II superconductors. Numerical simulation is based on a variational formulation of the Bean model. The analytical solutions, found in a weak penetration limit, are used to evaluate ac losses for two types of fluctuations: the running and standing waves. It is shown that for spatially nonuniform fluctuations the losses are better characterized by the fluctuation penetration depth than by the fluctuation amplitude. The results can be used to estimate the ac losses in flywheels, electric motors, magnetic shields, etc.     

Superconductors come in from the cold

The author briefly discusses the discovery of superconductivity in 1911 and the two major breakthroughs in 1966 and 1986 in this field. In 1966 a stable composite conductor of Ni-Ti strands embedded in a Cu strip was developed. A superconducting magnet was made from this material. In 1986 superconductors that maintained superconductivity up to 90 K, cooled by liquid N₂, were discovered. The author goes on to briefly discuss the various research projects around the world, involved in high temperature superconductors     

A new method for improving the dynamics of superconducting magnetic bearings

This paper describes a new method for improving the dynamics of passive type superconducting magnetic bearings (SMBs). The SMBs are composed of two kinds of superconductors and a permanent magnet. The superconductors of the SMBs were field-cooled in the experiments. After the field-cooling, impulse responses were performed for various horizontal displacements. Then, changes in stiffness and damping coefficient of the SMBs were investigated. From the experimental results, it is found that the stiffness and the damping coefficient are affected by the maximum displacements and by use of sintered superconductors, respectively. The stiffness and the damping coefficient are also evaluated by using frequency responses. Then, the results by frequency responses are compared with those by impulse responses. As a result, it is found that we can control bearing stiffness by changing horizontal displacements and damping coefficient by using sintered superconductors.     

Flux trapping in a ring-shaped YBCO bulk by pulsed fieldmagnetization

A pulsed magnetic field can be applied using small coils to generate a strong magnetic field for the magnetization of the high-Tc superconductors (HTS) to be used as quasi-permanent magnets in flywheels and motors. The dynamic electromagnetic behavior of two melt-processed ring-shaped Y-Ba-Cu-O bulks using the pulsed field magnetization (PFM) process has been experimentally investigated and analyzed. The flux trapped in the bulk by PFM process was compared to the flux trapped by field cooling process. Both cases then have been analyzed with a numerical model based on the finite-element method (FEM). The power-law model was utilized to relate the electric field to the current density inside the superconductor. The dependence of the critical current density on the magnetic field density was taken into account. Measured and calculated results are compared and discussed     

Lighter fuel-the gas turbine comes of age

Some profound changes are overcoming the technology of electricity generation. A combination of environmental, economic and technical factors is increasingly leading generators to favour the adoption of gas-turbine-based plant. The author discusses the reasons for the increased use of gas turbines and discusses their operating principles. The use of turbine exhaust gases for steam generation of direct heating (cogeneration plants) is also discussed as is the application of gas turbines to base load and gasification plants. Future prospects are mentioned     

New electronics for payment

Plastic cards are now commonplace in many countries as an adjunct to cash in transactions. The author discusses how far they will go to replacing cash and cheques. The author discusses coin handling and coin operated equipment and new coin recognition principles. The increase in the number of automatic teller machines, automation of cheque handling, and the increase in cards and card systems, particularly for EFTPOS, are also described. The author discusses smart cards and gives examples of the use of prepayment cards     

AD698在RVDT传感器测量中的应用

简要介绍了AD698的工作原理,对AD698在RVDT传感器测量中的具体应用进行了研究。根据传感器使用要求,进行了详细的参数分析和电路设计。设计从电源、信号滤波、输入输出范围、信号传输连接各方面采取了提高测量准确性的可靠性措施,最终达到了理想的效果。     

Refrigeration for superconductors

Temperatures in the range of 0.05 to 80 K are required for most applications of superconductors. Refrigeration powers range from fractions of a watt for many electronic applications to kilowatts for some large magnet and power applications. This paper reviews the various types of refrigeration methods currently available to meet the needs of various applications of superconductors. The methods covered include mainly the gas cycles, which are divided into the recuperative types (steady flow), such as the Joule-Thomson, Brayton, and Claude cycles, and the regenerative types (oscillating flow), such as Stirling, Gifford-McMahon, and pulse tube cycles. Methods for reaching millikelvin temperatures are briefly mentioned as well. The operating principles of the various methods are described, and the advantages and disadvantages of each are given to help the user understand which approach may work best for a particular application. All cryogenic refrigeration methods have a common set of problems that have hindered many applications of superconductors. These problems and recent developments to overcome some of these problems are discussed.     

A hybrid-type superconducting magnetic bearing system withnonlinear control

In this paper, a hybrid-type superconducting magnetic bearing (SMB) system with nonlinear control is discussed. The hybrid-type SMB system consists of passive-type SMBs, active-type magnetic bearings (AMBs), a rotor, and sensors. The rotor position is controlled by nonlinear controller with no-bias currents. Because the controller does not need bias currents applied to the electromagnets, the energy losses are considered to be less than other magnetic bearing systems. The displacements of the rotor are suppressed by both the SMBs and the AMBs. The superconductors of the SMBs were field-cooled. Compliance for the bearings, displacements of the rotating rotor, and energy losses for the system were investigated. The results show that the hybrid-type SMB system with nonlinear control has good performances in these evaluations     

"通信原理"课程教学改革探索

针对我院省重点专业“电子信息工程”的必修主干专业基础课程。“通信原理”教学中存在的不利于培养和提高学生分析问题、解决问题的能力的因素，从课程的教学内容、教学手段等方面论述了课程改革的基本构想，并对课程的实践环节——设计性实验的改革进行了探讨。     

DECT-beyond CT2

Within Europe there are two standards for digital cordless telephony: CT2 and DECT (Digital European Cordless Telephony). The author traces the origins of both standards and compares their features, services and facilities. The author then looks at DECT in more detail discussing the service principles, network access and protocol architecture. The author then discusses the complementary roles of CT2 and DECT     

Customer and supplier: is the balance tilting?

The doctrine that `the customer rules' is firmly enshrined in every company in today's developed economies. But there are signs that the balance of advantage is shifting back towards the suppliers of goods. The author discusses the influence of large manufacturers on society and economics since the industrial revolution. In particular the author discusses the demands of customers and competition between manufacturers. In recent times a new definition of competitive advantage emerged in a world of falling prices where supply outstripped demand. But this circumstance is beginning to change. As the world climbed out of recession in 1994, commodity prices soared. There is direct evidence that, as a result, companies are starting to question the principles of lean, mean, low-inventory manufacturing. The author then discusses the means of achieving competitive advantage as this new era dawns, emphasising the importance of information as a commodity     

Putting the human being back into engineering [education]

The author suggests that the main crisis facing engineering education and the engineering industry is a crisis of professionalism. He outlines four principles of professionalism, discusses the goal of education, and examines excellence in industry     

Tools for measuring software reliability

The author discusses a measure of software reliability and various models for characterizing it, the result of 15 years of theoretical research and experimental application, which are moving into practice and starting to pay off. These tools let developers quantify reliability, give them ways to predict how reliability will vary as testing progresses, and help them use that information to decide when to release software. He examines the distinction between failures and faults and how these affect reliability. He compares execution-time models with calendar-time models, which are less effective, and discusses the choice of execution-time models. The author then describes a generic, step-by-step procedure to guide software reliability engineers in using the reliability models     

结构设计中流体静压轴承史塔芬方程的几种应用

介绍史塔芬方程的推导及其在结构设计中流体静压轴承的几种应用情况。     

直接数字频率合成器的设计及FPGA实现

直接数字频率合成器(DDS)通常使用查表的方法实现相位和幅值的转换，文章介绍了一种基于CORDIC算法的DDS。CORDIC算法在三角函数合成上有着广泛的用途，作者从DDS的一般结构和CORDIC算法的基本原理出发．深入探讨了基于CORDIC算法的DDS各部件的结构和FPGA实现。     

High temperature superconductivity applied to electric motors

The application of high temperature superconductors to electric motors is discussed. Both the advantages and limitations of using superconductors in motors are reviewed. A synchronous motor with a high-temperature superconductor field winding for pump and fan drive applications is described and some of its unique features are identified. A 10000-hp superconducting motor design and its advantages in terms of improved efficiency and reduced size are described. The performance requirements for the superconducting wire necessary for motor applications are considered, and the progress being made toward realizing these requirements is assessed