Design of a 35 GHz gyrotron

The conceptual design of a 35 GHz gyrotron has been developed consistently with the complex formulation of the electric field longitudinal distribution in the resonant cavity. Some models of magnetron injection guns able to produce laminar beams have been investigated leading to the design of an electron gun capable of generating a current of 5 A with a perpendicular velocity dispersion of 0.5%. The device includes three magnetic systems producting flat axial magnetic induction profiles of 1.05 kG, 13.2 kG and 0.65 kG in the cathode, cavity and collector regions, respectively. The gyrotron has been designed for pulsed operation in the TE₀₂₁ mode. Under the soft self-excitation condition, the maximum attainable efficiency is 40% with an output power of 100 kW. An analysis of the collector thermal behaviour has been carried out as well as a study of the thermophysical properties of the alumina window to be used.     

Design optimization of double-acting hybrid magnetic thrust bearings with control integration using multi-objective evolutionary algorithms

Integration of the geometric and control designs in conjunction with the optimization is the current trend in mechatronic products. In the present work, an optimal design methodology of double-acting hybrid active magnetic thrust bearings has been proposed. Double-acting actuators and controller are optimized as a unified system. Conventionally, in control of rotors in the axial direction using double-acting magnetic bearings, two identical bearings are used. However, in the present design two different bearing geometries with different operating parameters have been considered. Minimization of the powerloss, the weight, the control input and dynamic performance indices and maximization of the load capacity have been considered as objectives. The design considers the 10 geometric, two electrical, and two control design parameters. The constraints are classified into three categories, namely the geometric, electrical, and control constraints. Real coded genetic algorithm has been implemented to carry out the constrained multi-objective optimization of the present problem. The convergence and Pareto-front spaces are studied by using different populations of sizes run for different generations. Some of the convergence criterions have been observed for actuator–controller systems. Designs which are nearest to the utopia point in Pareto-front fronts are compared. Air gaps, bias currents, and lengths of permanent magnets are observed to be consistently different for individual actuators of the double-acting bearing. Performance parameters of double-acting actuators and the controller of the magnetic bearing for different choices have been presented.     

Design and evaluation of an active electromechanical wheel suspension system

This paper presents an electromechanical wheel suspension, where the upper arm of the suspension has been provided with an electric levelling and a damper actuator, both are allowed to work in a fully active mode. A control structure for the proposed suspension is described. The complex design task involving the control of the electric damper and its machine parameters is tackled by genetic optimisation. During this process, these parameters are optimised to keep the power dissipation of the electric damper as low as possible, while maintaining acceptable comfort and road-holding capabilities. The results of the evaluations carried out demonstrate that the proposed suspension can easily adopt its control parameters to obtain a better compromise of performance than that offered by passive suspensions. If the vehicle is to maintain acceptable performance during severe driving conditions, the damper has to be unrealistically large. However, if the electric damper is combined with a hydraulic damper, the size of the electric damper is significantly reduced. In addition, the design of the electric damper with the suggested control structure, including how it regenerates energy, is discussed.     

Simulation and experimental investigation of a multi-pole multi-layer magnetorheological brake with superimposed magnetic fields

This paper presents comprehensive investigations on a new multi-pole multi-layer magnetorheological (MR) brake. This unique design features MR working gaps set between two-layer individual coils. Independent current supply was proposed to generate more flexible braking torque and lower power consumption. In this article, an exploded-view drawing of the proposed MR brake was presented, and theoretical analyses of the braking torque and temperature characteristic were conducted. Then, finite element analysis was performed to verify the effect of the magnetic field superposition. A prototype MR brake was fabricated and tested to evaluate the magnetic field superposition, preliminary dynamic behavior, temperature and the performance of individual input current. The results show that the magnetic field superposition has much influence on the braking torque, and individual current supply results in different power consumption and torque ranges. Moreover, the dynamic response performance of this brake is less affected by the slip speed. Furthermore, the maximum steady-state slip power of the proposed brake is about 160 W, and the greater the slip power is, the faster the temperature increases. The results also have verified the correctness of the structure and magnetic circuit design.     

Evaluation of Electrorheological Fluid Dampers for Applications at 3-T MRI Environment

This paper evaluates the use of electrorheological fluids (ERFs) within a magnetic resonance imaging (MRI) environment. ERF is a semiactive variable impedance material, which could be used as an alternative type of resistive force/torque generation or in combination with other actuators as a damper/clutch to modulate the output force/torque of the actuator. In this paper, an ERF damper/brake is introduced and its magnetic resonance (MR) compatibility is examined at a 3-T MR imaging environment by measuring the output performance of the damper and the SNR of the MRI images. The experimental results showed that damper's resistive force generation while positioned within the MRI is almost the same as that in normal operation. The signal-to-noise investigation was performed both with a phantom and human. The results indicated that the ERF damper did not affect the MRI images when it was operated over 30 cm away from the MRI's RF coil. We hope that the synthesis and tables presented in this paper can facilitate the choice of ERF brake actuation principle to various applications in an MR environment.     

A performance evaluation of an automotive magnetorheological brake design with a sliding mode controller

The aim of this work is to develop a magnetorheological brake (MRB) system that has performance advantages over the conventional hydraulic brake system. The proposed brake system consists of rotating disks immersed in a MR fluid and enclosed in an electromagnet, which the yield stress of the fluid varies as a function of the magnetic field applied by the electromagnet. The controllable yield stress causes friction on the rotating disk surfaces, thus generating a retarding brake torque. The braking torque can be precisely controlled by changing the current applied to the electromagnet. In this paper, an optimum MRB design with two rotating disks is proposed based on a design optimization procedure using simulated annealing combined with finite element simulations involving magnetostatic, fluid flow and heat transfer analysis. The performance of the MRB in a vehicle was studied using a quarter vehicle model. A sliding mode controller was designed for an optimal wheel slip control, and the control simulation results show fast anti-lock braking.     

Control and experimental study of 6-DOF vibration isolation platform with magnetorheological damper

Vibration is an inevitable excitation in the operation of the mechanical system, which reduces its reliability and service life. Therefore, a heavy-duty 6-DOF semi-active vibration isolation system (VIS) with magnetorheological (MR) damper was proposed in this paper. Firstly, A MR damper with large output force of 27 kN was designed. The properties test results showed that the dynamic range (the adjustable multiple of damping force) of the damper is as high as 15, which has excellent dynamic performance. And a Bouc-Wen model which can accurately describe the mechanical behavior of the MR damper was established. Secondly, the prototype of the MR 6-DOF vibration isolation platform (VIP) with cubic structure was developed. Thirdly, a on-off semi-active control strategy was proposed for the MR 6-DOF VIP. The numerical simulation results showed that the semi-active VIS can effectively isolate vibration in the working frequency domain. Finally, the vibration experiment on shaking table was carried out. The test results showed that the designed heavy-duty MR 6-DOF semi-active VIP can control the load's attitude in real-time according to the system state. Compared with the current of 0 A, the vibration isolation effect of the on-off control is improved by 63.27% in the resonance region. The MR 6-DOF VIP can effectively reduce the vibration transmitted to the isolated system through the platform.     

Diagnose von Dämpferstabbrüchen in Synchronmaschinen

This paper attempts to complete the existing diagnosis systems of synchronous machines. In order to avoid break downs caused by broken damper bars, a method to diagnose such failures is presented. The main idea of the method is the separation of voltages of the field winding induced according to their polarity. So, the difference of the pole voltages can be determined. This voltage difference is triggered off by the magnetic field disturbance caused by the missing damper bar. The main field in a symmetrical built machine disappears in the difference voltage. The broken damper bar location is fixed to the rotor and also to the field winding. Moreover, the voltage difference depends on the position of the missing damper bar as well as on the distribution of the field winding. In the case of a distributed winding, the damper bars under the edges of each pole can be detected exactly. The theoretical ideas are presented and checked by measurements in a model machine.     

Theoretical Analysis of the Operation of the Field-Displacement Ferrite Isolator

A theoretical analysis of the resistance-sheet isolator is carried out, and numerical solutions are obtained for the forward and reverse propagation constants of the distorted dominant mode in a rectangular waveguide containing a transversely magnetized thick ferrite slab displaced slightly from the side wall. The microwave electric field patterns within the waveguide are plotted for several values of the physical design parameters of the isolator for which experimental performance data have been reported. Field patterns are used to describe the principles of the isolator and to select the optimum values of slab thickness, internal dc magnetic field, ferrite magnetization, and location of the slab in the waveguide for the idealized isolator. Evidence is presented to show that it is necessary to use a comparatively thick ferrite slab located in a very small usable range of distances from the side wall. The appropriate value of internal dc magnetic field is simply related to the magnetization of the ferrite and to the frequency. It has not been necessary to take into account the perturbing effects of the resistance card or matching techniques in order to explain the basic design principles.     

Development of an eddy-current-type magnetic floor hinge

A magnetic floor hinge is suggested to use a magnetic damping characteristic obtained by the eddy-current effect. It has a superior advantages compared to the conventional hydraulic floor hinge. First, there exists no wear in the magnetic damper since the disk rotates between the magnets without contact. Second, the deviation of the damping torque is very small in varying seasons due to the low temperature dependence of the conductivity of the disk to which the magnetic damping torque is proportional. The analytical models obtained for the damping torque and the recovering torque are experimentally investigated. The cost optimal design is carried out using the analytical models while satisfying the performance requirements. The analytical results are compared with experimental results. Finally, a prototype of the magnetic floor hinge is built.     

Torque ripple minimization for variable reluctance motors

The design of current waveforms that minimize torque ripples in variable reluctance (VR) motors is addressed. The general problem of torque ripple reduction has been investigated by several researchers using various nonlinear models. The results have been design methods that require exhaustive measurements of motor characteristics. The approach presented here assumes magnetic linearity to derive an efficient ripple-reducing excitation that is much easier to calculate. A nonlinear optimal design problem is developed and then converted to a linear representation by a simple transformation. The transformed linear optimization problem is straightforwardly solved by standard numerical methods, and yields the optimal current waveform characteristics in the new variable. Finally, the optimal current waveform is found by applying an inverse transformation. The analytical result presented in this paper is supplemented by a design example that also addresses the performance tradeoff resulting from ignoring magnetic saturation to achieve simplifications in design.     

Measurement of thoracic current flow in pigs for the study of defibrillation and cardioversion

Although defibrillation has been in clinical use for more than 50 years, the complete current flow distribution inside the body during a defibrillation procedure has never been directly measured. This is due to the lack of appropriate imaging technology to noninvasively monitor the current flow inside the body. The current density imaging (CDI) technique, using a magnetic resonance (MR) imager, provides a new approach to this problem [Scott et al. (1991)]. CDI measures the local magnetic field generated by the current and calculates the current density by computing its curl. In this study, CDI was used to measure current density at all points within a postmortem pig torso during an electrical current application through defibrillation electrodes. Furthermore, current flow information was visualized along the chest wall and within the chest cavity using streamline analysis. As expected, some of the highest current densities were observed in the chest wall. However, current density distribution varied significantly from one region to another, possibly reflecting underlying heterogeneous tissue conductivity and anisotropy. Moreover, the current flow analysis revealed many complex and unexpected current flow patterns that have never been observed before. This study has, for the first time, noninvasively measured the volume current measurement inside the pig torso.     

A linear motor damper for vibration control of steel structures

A hybrid mass damper based on the linear motor principle is developed to suppress structural vibration. We will call it a linear motor damper in this paper. This paper deals with the design, analysis, and manufacture of the linear motor damper. It consists of the NdFeB permanent magnets, a coil-wrapped nonmagnetic hollow rectangular structure, an iron core, mechanical springs, and so on. It is designed to be able to move the auxiliary mass of 1500 kg, up to ±250 mm stroke. A series of performance tests for the linear mass damper with H_∞ robust controller are carried out on a steel frame structure. Through performance tests, it is confirmed that the developed hybrid mass damper has reliable feasibility as a control device for structural control. In addition, the linear motor damper is more economical than both hydraulic and electric motor driving mass damper with respect to simple structure and low maintenance cost.     

Improvement in Superconducting Properties of MgB2 Superconductors by Nanoscale Carbon-Based Compound Doping

MgB2 is a relatively new superconductor; it has attracted great interest from superconductor researchers all over the world. Thorough investigations have been carried out to study the material fabrication, as well as to study the material and superconducting properties from a fundamental physics point of view. The University of Wollongong has played a very active role in this research and a leading role in the research on high critical current density and high critical magnetic fields. Our recent research on the improvement of critical current density and the upper critical magnetic field by carbon-based compound doping is reviewed in this paper.     

Improvement in Superconducting Properties of MgB_2 Superconductors by Nanoscale Carbon-Based Compound Doping

MgB2 is a relatively new superconductor; it has attracted great interest from superconductor researchers all over the world. Thorough investigations have been carried out to study the material fabrication, as well as to study the material and superconducting properties from a fundamental physics point of view. The University of Wollongong has played a very active role in this research and a leading role in the research on high critical current density and high critical magnetic fields. Our recent research on the improvement of critical current density and the upper critical magnetic field by carbon-based compound doping is reviewed in this paper.     

Three-dimensional-simulation of arc motion between arc runners including the influence of ferromagnetic material

The behavior of the moving electric arc in low-voltage switching devices is determined by the complex interactions of magnetic forces, current flow, gas flow, heat conduction, and radiation. In this paper three-dimensional simulations of arc motion between parallel arc runners are presented, which consider all these interactions. These simulations are carried out with a computational fluid dynamics (CFD) finite volume code. Based on earlier simulations by Frank Karetta the magnetic field, expressed as vector potential formulation, is now treated by the same type of general transport equations as the other processes, which allows the direct implementation into the CFD package used. This enables one to include the effect of ferromagnetic material in the arc chamber, such as ferromagnetic flux concentrators or steel splitter plates. Typical simulation examples are presented for different design details.     

Stability Analysis and Practical Design Procedure of Time Delayed Control Systems With Communication Disturbance Observer

In a research field of network-based control systems (NBCSs), the time delay problem is one of the most significant issues. Efficient stabilization methods of time delayed control systems enable NBCSs to be flexibly applied to many kinds of situations. A novel time delay compensation method based on the concept of network disturbance (ND) and communication disturbance observer (CDOB) has been proposed. The compensation method has the same effectiveness as that of the Smith predictor. In addition, since the method is simple and does not need time delay model or time delay measurement, it can be easily implemented to various applications. However, the design method has not been concerned so far. This paper therefore presents stability analysis and studies a practical design procedure of the time delayed control systems with CDOB. At first, the concept of ND is introduced and the validity of the time delay compensation method is described. Then an analysis about the effects of parameters in control systems on stability is conducted. Characteristics of the effects of parameters on stability come out. Then we study a practical design procedure of the time delayed control systems. The validity of the design procedure is validated by experimental results. In the experiment, we also verify the performance of the system in the case of time-varying delay. Finally, comparative study of the method to the Smith predictor is presented.      

Double actuation architectures for rendering variable impedance in compliant robots: A review

Novel compliant actuation systems have been developed in recent years for a variety of possible advantages, such as establishing a safe human–robot interaction, increasing energy efficiency, reducing the effects of impacts and even for the development of neuro-inspired robotic platforms to be used in human motor control studies.In this rapidly growing and transversal research field, systems involving more than one active element (typically motors) for each actuated degree of freedom are being investigated to allow separate position and impedance regulations. Considering the wide range of applications and the large number of different arrangements deriving from the combination of two active elements and passive elastic components, several actuation architectures have been devised.This paper reviews state-of-the-art rotary variable impedance units incorporating two separate motors. Existing devices are grouped in three main categories. A critical and comparative analysis of the most relevant features is carried out, also based on most representative prototypes. Recently proposed methodologies and evaluation criteria for design optimization are illustrated and perspectives on potential applications of double actuation systems are presented.     

Pulse motor with high-temperature superconducting levitation

A simple but stable noncontact high T_c superconducting levitation system with a vertical shaft has been presented. The system consists of a superconductor and permanent magnets. In the system, only a high T_c superconductor supports the lower end of the shaft, and the other end is supported by two ordinary permanent magnets. Since the restoring force is small with respect to the radial direction, the system becomes unstable when the force acts in the radial direction, so it is difficult to drive the shaft by electromagnetic forces when using motors. A driving system using electromagnets has been presented, in which the balanced forces act on two opposite sides of the disc-type rotor in the axial direction. Since the system has no unbalanced force from an analytical point of view, the rotor will be able to rotate without control. In the system, however, since there is eccentricity between the center of rotation and the magnetic center, vibrations are generated. This study also presents an optimal control method for the vibrations. To validate the proposed system and the control method experimental tests have been carried out     

MR flow measurement using RF phase gradients in receiver coilarrays

Radio frequency (RF) phase gradients in the receiver coil field pattern can encode flow velocity information in magnetic resonance (MR) images in the form of phase variations. These phase variations are not readily observed in MR images because they are relatively small compared to phase variations caused by static magnetic field (B₀) inhomogeneities, susceptibility variations, and other sources. However, the phase contributions from these other sources are independent of the receiver coil. Therefore, the RF phase gradient encoded flow information can be recovered by subtracting images obtained simultaneously using arrays of independent receiver coils and a multiple channel receiver. This flow velocity information can be extracted retrospectively from standard imaging sequences, including flow-compensated sequences. No additional time is required for the flow study as the flow measurements are made using sequences chosen for optimal imaging, and the images from each coil are obtained simultaneously. Initial results indicate that sufficient sensitivity is obtained to make flow measurements in the range of velocities commonly found in the carotid arteries and other major vessels. In principle, the method works with only two receiver coils. However, additional elements provide additional phase measurements that can be used to increase accuracy, remove ambiguities in flow direction or velocity calculations, and increase the region over which velocity measurements can be accurately made