Wide Air Gap Research Articles

Filter Influence on Rotor Losses in Coreless Axial Flux Permanent Magnet Machines

This paper investigates the eddy current losses induced in the rotor of coreless Axial-Flux machines. The calculation of eddy currents in the magnets requires the simulation of the inverter and the filter to obtain the harmonic content of the stator currents and FEM analysis of the magnets in the rotor. Due to the low inductance in coreless machines, the induced eddy current losses in the rotor remain lower than in traditional slotted machines. If only machine losses are considered, filters in DC/AC converters are not required in machines with wide airgaps as time harmonic losses in the rotor are very low. The harmonic content both from simulations and experimental results of a DC/AC converter are used to calculate the eddy currents in the rotor magnets. The properties of coreless machine topologies are investigated and some simplifications are proposed for time efficient 3D-FEM analysis. The time varying magnetic field can be considered constant over the magnets when the pole is divided in several magnets. The simplified FEM method to calculate eddy current losses is applicable to coreless machines with poles split into several magnets, although the conclusions are applicable to all coreless and slotless motors and generators.

Energy simulations of a transparent‐insulated office façade retrofit in London, UK

PurposeTransparent insulation materials (TIMs) have been developed for application to building facades to reduce heating energy demands of a building. The purpose of this research is to investigate the feasibility of TI‐applications for high‐rise and low‐rise office buildings in London, UK, to reduce heating energy demands in winter and reduce overheating problems in summer.Design/methodology/approachThe energy performance of these office building models was simulated using an energy simulation package, Environmental Systems Performance‐research (ESP‐r), for a full calendar year. The simulations were initially performed for the buildings with conventional wall elements, prior to those with TI‐systems (TI‐walls and TI‐glazing) used to replace the conventional wall elements. Surface temperatures of the conventional wall elements and TI‐systems, air temperature inside the 20 mm wide air gaps in the TI‐wall, dry‐bulb zone temperature and energy demands required for the office zones were predicted.FindingsPeak temperatures of between 50 and 70°C were predicted for the internal surface of the TI‐systems, which clearly demonstrated the large effect of absorption of solar energy flux by the brick wall mass with an absorptivity of 90 percent behind the TIM layer. In the office zones, the magnitude of temperature swings during daytime was reduced, as demonstrated by a 10 to 12 h delay in heat transmission from the external façade to the office zones. Such reduction indicates the overheating problems could be reduced potentially by TI‐applications.Originality/valueThis research presents the scale and scope of design optimisation of TI‐systems with ESP‐r simulations, which is a critical process prior to applications to real buildings.

Wide Air Gap and Large-Scale Bearingless Segment Motor With Six Stator Elements

In recent years, the demand for high purity spinning processes has been growing in certain industry branches, such as the semiconductor, biotechnological, pharmaceutical, and chemical industry. Therefore, the cleanness specifications have been tightened, and hermetically sealed process chambers are preferred. This paper presents an advantageous solution for such an application featuring a large scale, wide air gap, and a high accelerating bearingless segment motor. Bearingless slice motors allow complete magnetic levitation in combination with a very compact and economic design. The disc-shaped rotor holds permanent magnets generating magnetic flux in the air gap. Hence, three degrees of freedom are passively stabilized by reluctance forces. Thus, only the radial rotor position and the rotor angle have to be controlled actively. The announced bearingless segment motor is a subtype of the bearingless slice motor, featuring separate independent stator elements. This leads to a reduction of stator iron, cost, and weight and, in addition, leaves space for sensors and electronics enabling a very compact system design.

The improvement of a simple theoretical model for the prediction of the sound insulation of double leaf walls

This paper presents a revised theory for predicting the sound insulation of double leaf cavity walls that removes an approximation, which is usually made when deriving the sound insulation of a double leaf cavity wall above the critical frequencies of the wall leaves due to the airborne transmission across the wall cavity. This revised theory is also used as a correction below the critical frequencies of the wall leaves instead of a correction due to Sewell [(1970). J. Sound Vib. 12, 21-32]. It is found necessary to include the "stud" borne transmission of the window frames when modeling wide air gap double glazed windows. A minimum value of stud transmission is introduced for use with resilient connections such as steel studs. Empirical equations are derived for predicting the effective sound absorption coefficient of wall cavities without sound absorbing material. The theory is compared with experimental results for double glazed windows and gypsum plasterboard cavity walls with and without sound absorbing material in their cavities. The overall mean, standard deviation, maximum, and minimum of the differences between experiment and theory are -0.6 dB, 3.1 dB, 10.9 dB at 1250 Hz, and -14.9 dB at 160 Hz, respectively.

1231 並列永久磁石型ハイブリッド磁気軸受の開発と応用(磁気浮上・磁気軸受の制御(1))

Hybrid magnetic bearing is recognized as an efficient one even with wide airgap and is suitable for such application. Previously sub-pole type IPM hybrid magnetic bearing has been proposed. However the sub-pole produces bias flux and cannot produce control force. To overcome this problem, two new types of hybrid magnetic bearings are proposed which have permanent magnet within the stator core. This paper introduces structure and principle of the proposed magnetic bearings. The geometric parameters of these new type mechanisms are optimized by FEM analysis. The experimental setups are made based on these analytical results. The fundamental characteristics are measured and compared with the estimate bearing performances. The results show stable levitation and good rotated levitation.

Development and Canned Pump Application of Wide-Gap Magnetic Bearings

Maglev pump is widely requested for artificial heart or chemical industries. Hybrid magnetic bearing is recognized as high efficient one even with wide airgap and suitable for such applications. This paper proposes two types of hybrid magnetic bearings for canned maglev pump. One is the standard (STD) type and another is the internal permanent magnet (IPM) type. Both types are analyzed using the finite element package and designed. Then the experimental setups are made and their fundamental characteristics are explained. The results show stable levitation and promising characteristics for the practical use.

Fourier transform infrared analysis of long-range surface polaritons excited by the end-fire method

The cut-off effect in slightly asymmetric systems prevents the wider practical usage of long-range surface polaritons (LRSP). Due to asymmetry caused by the presence of even a few nanometers wide air gap, the LRSP mode disappears. We propose a solution to this problem by using an effective medium approach. The basic idea is to compensate for the air gap induced asymmetry by introducing an additional layer into the system. That allows us to shift the cut-off to values sufficient for experimental observation of LRSP. Fourier transform infrared spectra of end-fire coupled LRSP in the GaAs/Au/GaAs multilayer system were measured in the (800–3000) cm−1 range. Various geometric and polarization sensitive effects of the infrared system capable of influencing the LRSP coupling are discussed. A pronounced increase in the p-polarized light transmission at long-wavelengths is explained as an increase in the propagation distance L of LRSP. A fairly good fit between experimental and calculated curves was achieved at long wavelengths.

Surface micromachined optical low-cost all-air-gap filters based on stress-optimized Si3N4 layers

A new surface micromachining approach based on a multiple Si3N4- and silicon-layer stack is presented. The fabrication process is implemented by plasma-enhanced chemical vapour deposition of stress-optimized films, reactive ion etching using SF6/CHF3/Ar, wet chemical etching of the sacrificial silicon layers by KOH and critical point drying. Using this approach, the fabrication of an optical all-air-gap vertical-cavity Fabry–Pérot filter is demonstrated. The surface micromachined filter consists of two DBR mirrors, each having five 590 nm thick Si3N4 membranes separated by 390 nm wide air gaps. The distance between the mirrors (cavity) is 710 nm. The optical characterization and a white light interferometer measurement document the accuracy of the layer positioning and the performance of this low-cost approach. The filter shows the designed filter dip at 1490 nm, the full width at half maximum (FWHM) of the filter is 1.5 nm and the insertion loss is just 1.3 dB. The process is compatible with a variety of materials, e.g. III–V compounds, silicon, as well as organic materials, facilitating a huge application spectrum for sensors.

ワイドギャップ磁気軸受の開発と磁気浮上ポンプへの応用(オーガナイズドセッション,ライフサポートにおける工学技術)

Maglev pump is widely requested for artificial heart or chemical pumps. In such applications wide magnetic gap is preferable for easy manufacturing. Hybrid magnetic bearing is recognized as high efficiency with wide airgap and is suitable for such applications. This paper proposed two types of hybrid magnetic bearing for maglev pump. The analysis and design of these experimantal setup are introduced and compared their characteristics.

Thick and thermally isolated Si microheaters for microfabricated preconcentrators

Thick thermally isolated microheaters in Si are fabricated using high aspect ratio etching technology. These thick microheaters a with large surface area provide the large adsorbent capacity needed for high sensitivity microfabricated preconcentrators in a microgas chromatography system. In addition, air gaps around the microheaters provide good thermal isolation to lower the power consumption. A 520 μm thick Si microheater with good thermal isolation has been made and its back side is anodically bonded to a pyrex glass substrate. To provide good thermal isolation, a 500 μm wide air gap around the microheater, thin poly-Si interconnects on top of dielectric membrane, and air gap isolation from the bottom glass substrate are used. Microheaters with a 500 μm air gap can be heated up 50% faster to a temperature of 270 °C compared to those with a 100 μm air gap, while the power consumption is 25% less and there is a larger temperature difference between the microheater and the bonding area. Operating the microheater in a vacuum results in lower power consumption. At 250 °C, 35% less power is needed at 1.2 Torr compared to atmospheric pressure. The power consumption is further reduced by minimizing the contact area with the heater support substrate. Up to 34% power reduction has been demonstrated by placing heaters on a thin membrane or etching trenches in the supporting substrate. These thick thermally isolated Si microheaters can provide good power efficiency, large adsorbent capacity, and high mechanical strength for microfabricated preconcentrators.

Noncontact energy transfer system using immittance converter

AbstractNoncontact energy transfer systems are widely used in industrial material handling systems. This paper proposes a new noncontact energy transfer system using a tuned pickup coil and an immitance converter inductively coupled to a parallel transmission line excited by a high‐frequency constant‐current source.In a noncontact energy transfer system which supplies continuous energy to movers by electromagnetic induction, the efficiency is low owing to low excitation impedance because of the wide air gap of the magnetic core in the pickup coil. The excitation impedance can be increased by the resonance with a capacitor connected parallel to the pickup coil. The resonant pickup coil works as a high‐frequency constant‐current source for the load. We propose using an immittance converter to transform the high‐frequency constant‐current source into a high‐frequency constant‐voltage source. Then, the high‐frequency constant‐voltage source is rectified into a constant‐voltage dc source, and supplies power to an inverter for motor driving.In this paper, the configuration of this new noncontact energy transfer system and its characteristics are described. The experimental results and simulation waveforms are also described. © 2001 Scripta Technica, Electr Eng Jpn, 136(4): 58–64, 2001

Non-Contact Energy Transfer System Using Immittance Converter

Non-Contact Energy Transfer Systems are widely used in industrial material handling systems. This paper proposes a new Non-Contact Energy Transfer System using a tuned pick-up coil and an Immittance converter inductively coupled to a parallel transmission line excited by a high frequency constant current source.In a Non-Contact Energy Transfer System which supplies continuous energy to movers by electromagnetic induction, the efficiency is low owing to low excitation impedance because of the wide air gap of the magnetic core in the pick-up coil. The excitation impedance can be increased by the resonance with a capacitor connected parallel to the pick-up coil. The resonant pick-up coil works as a high frequency constant current source for the load. We propose using an Immittance converter to transform the high frequency constant current source into a high frequency constant voltage source. Then, the high frequency constant voltage source is rectified into a constant voltage DC source, and supplies power to an inverter for motor driving.In this paper, the configuration of this new Non-Contact Energy Transfer System and its characteristics are described. The experimental results and simulation waveforms are also described.

Electro-nanomechanically wavelength-tunable integrated-optical Bragg reflectors

Electro-nanomechanical wavelength-tuning of integrated-optical (IO) Bragg reflectors is demonstrated at visible wave-lengths. Micromachined bridges or membranes are spanned over the waveguide as ‘effective-refractive-index shifting elements’ E in the region of a surface relief grating on the waveguide. Electrostatic forces cause elastic deflections of the elements E and, consequently, changes in the width of a typically 100–200 nm wide air gap between the element E and the waveguide. Thus the effective-refractive-index changes required for device operation are induced. The IO nanomechanical devices are fabricated with silicon technology; no electro-optic materials are required. The devices have response times of μs to ms. Potential applications as wavelength-tunable filters seem feasible.

Laser beam welding of austenitic/ferritic dissimilar steel joints using nickel based filler wire

Laser beam welding of austenitic/ferritic dissimilar steel joints using a nickel based filler wire has been investigated. The feasibility of using the process to join these dissimilar steels was evaluated. Microstructural characterisation was performed using both optical and electron microscopy. The influence of the processing parameters, principally air gap width and beam alignment, on the microstructure, composition, and properties of the welds has been determined. In order to obtain a fully austenitic weld metal microstructure, an air gap 0·2 mm in width with a suitable wire feedrate is recommended, which avoids the unnecessary extra heat input and problems in controlling weld quality associated with a wider air gap. However, in some applications, the size of the air gap can be used to control the alloying effect of the filler wire and consequently to obtain the desired weld metal composition. Laser beam alignment plays an important role in processing. It can be aligned to a maximum of 0·25 mm on the stainless steel side without producing a significant change in the weld metal composition. However, beam alignment on the Cr–Mo steel side should not be used if martensite formation in the weld metals is to be avoided. Laser beam welding with nickel based filler wire shows potential for producing austenitic/ferritic dissimilar steel joints.MST/1731

Laser beam welding of austenitic/ferritic dissimilar steel joints using nickel based filler wire

Laser beam welding of austenitic/ferritic dissimilar steel joints using a nickel based filler wire has been investigated. The feasibility of using the process to join these dissimilar steels was evaluated. Microstructural characterisation was performed using both optical and electron microscopy. The influence of the processing parameters, principally air gap width and beam alignment, on the microstructure, composition, and properties of the welds has been determined. In order to obtain a fully austenitic weld metal microstructure, an air gap 0·2 mm in width with a suitable wire feedrate is recommended, which avoids the unnecessary extra heat input and problems in controlling weld quality associated with a wider air gap. However, in some applications, the size of the air gap can be used to control the alloying effect of the filler wire and consequently to obtain the desired weld metal composition. Laser beam alignment plays an important role in processing. It can be aligned to a maximum of 0·25 mm on the stainless steel side without producing a significant change in the weld metal composition. However, beam alignment on the Cr–Mo steel side should not be used if martensite formation in the weld metals is to be avoided. Laser beam welding with nickel based filler wire shows potential for producing austenitic/ferritic dissimilar steel joints.MST/1731

Circumferential Waves in a Gapped Cylinder

Experimental evidence establishing the existence of circumferential waves in a thin-walled air-filled cylinder with a finite discontinuity in the shell is presented. The discontinuity is a 0.062-in.-wide air gap extending the length of the cylinder and the full thickness of the shell. Evidence establishing that the principle portion of the circumferential wave travels within the shell and is reflected at the air gap is presented. [Work done under contract with the U. S. Office of Naval Research.]