Slot Combinations Research Articles

Dual-band patch antenna for mobile satellite systems

The launch of new mobile satellite communication links for telephone and data applications demands development of small, low-profile, low-cost antennas. A single-layer, multi-band microstrip patch antenna is described, which operates over the frequency ranges of the Iridium and Globalstar satellite communication systems, 1.6 and 2.5 GHz. The antenna excites the TM10 and TM30 resonant modes which can operate with either dual linear polarisation or either hand of circular polarisation. The unwanted TM20 mode is suppressed using a combination of slots cut into the patch and by shaping the corners of the patch. Frequency band separations can be varied significantly from 1.3 to 2.5 × the lower frequency. Data for designing the patch dimensions is presented. The return loss, impedance characteristics and radiation patterns are presented for a practical design.

A stress calculation model for the 3D borehole slotter

A stress calculation model is proposed for a new stress measurement device called the 3D borehole slotter. This instrument allows the calculation of the 3D in situ stress tensor in a single borehole without the need for a drill on the site at the time of the measurement and without bonding strain gauges at the borehole wall . The 3D borehole slotter requires cutting half moon shaped slots with different orientations at a borehole wall using a small diamond impregnated blade and monitoring the strains which are relieved normal to the slot. This paper shows that combining six slots cut on the borehole wall with one to three slots cut parallel to the borehole axis and five to three cut with a 45° angle, allows the calculation of the in situ stress tensor. The optimal slot combination is determined and 3D finite element analyses are used to evaluate the degree of stress relief normal to the slot at the strain sensor location and also to estimate the strains induced parallel to the slot by this local stress relief. The results obtained from these analyses are then used directly in the stress calculation model.

Support of low delay data services in GSM

The authors examine a potential method for supporting UMTS low delay data (LDD) services in a GSM system, using a combination of slot interleaving and ARQ. The parameters of the UMTS LDD service to be accommodated are: delay < 30 ms and BER < 10-6.

Causes and characteristics of the electromagnetic vibration of a squirrel cage induction motor under load

Three-phase squirrel cage induction motors (IM) have been used in all types of industry, because of their robustness and simplicity of structure, low cost, and ease of maintenance. Due to the resultant air gap flux wave, an IM produces electromagnetic vibration and noise more or less regardless of the slot combination. Recently, reduction of electromagnetic vibration and noise has become important from the standpoint of environmental improvement. Vibration caused by an IM at no-load has been studied for many years and its basic factors have been analyzed. However, electromagnetic vibration under load has not been analyzed sufficiently. Since vibration under load conditions is affected by load and installation, analysis of this vibration is a rather difficult task. But study of the electromagnetic vibration of the motor itself under load is basically the most important item. This paper clarifies, theoretically and experimentally, the causes and characteristics of the electromagnetic vibration of an IM under load conditions. First, general equations are derived for the dominant electromagnetic force waves that produce electromagnetic vibration. Causes and vibration modes are clearly classified and a theoretical analysis provides a basic concept for electromagnetic vibrations. Second, electromagnetic vibrations for various loads are measured taking the effect of natural frequency of the motor into consideration. The measured data are classified and analyzed in detail, based on the proposed theory. © Scripta Technica, Inc. Electr Eng Jpn, 120(4): 81–89, 1997

Effects of slot combination on acoustic noise from induction motors

The electromagnetic force due to slot combination has a strong influence on acoustic noise from induction motors. When both the vibration mode and natural frequency of the stator correspond to those of the electromagnetic force, the stator causes a resonance which results in a loud noise. Therefore, it is necessary to estimate accurately the electromagnetic force before acoustic noise can be reduced. The force is calculated numerically by a combination of transient magnetic field FEM analysis and harmonic analysis by using a Fourier series expansion. The moving of the rotor and eddy currents are also taken into account in the FEM method. The acoustic noise from three types of motors is measured to verify the developed method. The simulated frequency and space harmonic order of the electromagnetic force are in good agreement with the measured frequency and vibration mode.

Bifurcated waveguide fed broadwall slots radiating through a baffle

A recent innovation in the development of slotted-waveguide array antennas has shown that for a rectangular waveguide radiating into a ‘half-space’ through slots located in the broadwall, polarisation selectivity can be achieved by even or odd mode excitation of a suitable combination of longitudinal and transverse slots in an axially bifurcated form of the waveguide. In practice, however, the external region of the guide is seldom a true half-space, particularly in the case of linear arrays, which are often modified by a short section of parallel plate waveguide to provide some degree of polarisation purification and/or spatial filtering. An analysis of this geometry is described here, in which the presence of the parallel plate region has been accommodated within a moment method model of a polarisation agile slot arrangement by employing an ‘imaged’ Green function to represent the parallel plate enclosure. It is also shown that particular care in identifying suitable basis functions is required in the case of the T-shaped element of the polarisation agile slot pattern which straddles the waveguide bifurcation.

Simple linear microstrip array

A new printed array antenna fed by a microstrip transmission line is introduced. The structure is a combination of slot and patch antennas. The array provides a microstrip implementation of a leaky-wave antenna that is simple to design and inexpensive to fabricate.

Scour Protection at Bridge Piers

The objective of this study is to review existing methods and propose alternative or additional devices for scour protection around bridge piers. Engineering methods used in dealing with pier‐scour problems include placing coarse riprap around the foundations. An inverted filter layer is normally placed beneath the riprap to overcome leaching problems. Practical difficulties in laying the filter according to specifications, especially in deep water, often cause failure of the riprap layer. The study examines the effect of using a slot in the pier, or a collar around it, as devices for controlling the depth of scour. Experiments conducted in clear‐water conditions show that the use of a slot alone (with a width equal to one‐fourth of the pier diameter) can reduce equilibrium scour depth by as much as 20%. A combination of slot and collar can further reduce the scour depth. These devices may be useful as additional or alternative devices for scour protection.

Non-Inclined Edge-Slot in Bifurcated Rectangular Waveguide

A parasitically excited resonant slot in the side-wall of a bifurcated rectangular waveguide is examined for the case where both the radiating and the parasitic elements of the slot combination are transverse to the waveguide axis. The theoretical predictions demonstrate that the slot behaves as a series element, and the computed results are shown to compare favorably with experiment.

Experimental study on the electromagnetic vibration caused by the slot combination of a squirrel-cage induction motor.

Experimental study on the electromagnetic vibration caused by the slot combination of a squirrel-cage induction motor.

THE CHARACTERISTIC PERFORMANCE OF INDUCTION MOTORS WITH ECCENTRICITY

ABSTRACT A new method to predict the flux density distribution in an induction machine with nonuniform air gap is described. The method employs an approximate electromagnetic model suitable for efficient computer calculations. Effects of slotting, winding arrangement, saturation, and slot combinations are considered in the model. From the nonuniform distribution of magnetic flux density, the variation of unbalanced magnetic pull, average output torque, and cogging torque with eccentricity Is calculated. Comparison between computed and measured results shows good agreement which proves the validity of this technique to be employed for any type of induction machine of known design data.

Radiating elements for hemispherically scanned arrays

The problem of obtaining hemispherical coverage using an electronically steered antenna beam is considered. Radiating elements consisting of combinations of slots, parasitic dipoles, and surface wave structures were investigated for this application. Both planar and cylindrical supporting structures were used. It was found that such elements showed enhanced radiation near the horizon in both the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</tex> -plane and the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</tex> -plane. Patterns were measured on an eight-element linear array of slots covered by a surface wave structure. When the beam was scanned electronically to endfire, the pattern was enhanced by several dB over that obtained from the array without the surface wave structure.

Effect of load on the tangential-force pulsations and harmonic torques of squirrel-cage induction motors

A method is given for the determination, on load, of the influence of slot combination on the tangential force pulsations and harmonic tooth-ripple components of torque that arise in induction motors. The method of conformal transformation and a surface integral method are used to obtain the tangential force acting on any stator or rotor tooth for any rotor position. The tangential force pulsations and the harmonic tooth-ripple torques are computed, for a given stator slot number and for a range of rotor slot numbers. Conclusions are drawn about the choice of slot combination.

Effect of load on the flux pulsations and radial-force pulsations of induction motor teeth

The analysis of the influence of slot combination on the flux and force pulsations of induction-motor teeth on load is achieved using conformal transformation. For a given stator slot number, the total airgap field is evaluated for a range of rotor slot numbers and the instantaneous flux entering any tooth is determined. Using a surface integral method, the radial components of force on stator and rotor teeth for any rotor position are also evaluated. Conclusions are drawn about the choice of slot combination.

Some characteristics of magnetic field patterns in air-gaps with double-sided slotting

The conductance of air-gaps with double-sided slotting is generally considered with the assumption that the flux lines are radially directed only. Calculations allowing for the two-dimensional nature of air-gap fields, however, show a different situation with regard to the effect of slotting, especially at the higher harmonic orders. Calculated curves and tables are presented to illustrate the correlation between these two ways of approach for two slot combinations under excitation by a single coil, and also to establish the way in which the harmonics vary with changing rotor position.

Comments on "Single-Winding Single-Phase Inductor Alternator"

By using an approximate summation process it has been demonstrated that the optimum ratio of rotor to stator slot combination is 1 1/2 for a single-phase inductor alternator. An elegant and rigorous mathematical proof for this optimum ratio is presented here.

Flux sensing and control of static AC drives by the use of flux coils

Application of air gap flux sensing coils to the control of static AC induction motor drives is discussed. Optimum flux coil configurations are developed for the most frequently used slot combinations. Practical results are presented which verify the validity of the design approach. Application of flux signals to the control of practical static AC drives is included with emphasis placed on state-of-the-art techniques.

Skin Friction Reduction by Injection Through Combinations of Slots and Porous Sections

TT'LUID injection for thermal protection and skin -F friction reduction on flight vehicles has received considerably study. Energy conservation has now elevated the importance of skin friction reduction. The information available for supersonic speeds is limited, but it indicates drag reductions large enough to be interesting from a systems viewpoint. The competing configurations are the porous wall and the tangential slot, but there have been few studies when a direct comparison of the two schemes was made at the same nominal conditions. Further, combinations of the two schemes might be expected to be beneficial as a result of synergistic interactions. This report presents the results of a comparative study of slot injection, porous wall injection through a short strip and combinations of the two at freestream conditions of Mach 2.9, stagnation pressure of 6.9 N/m (100 psia) and total temperature of 290K. A flat plate, solid wall configuration was also studied as a reference point. The principal data obtained were: 1) schlieren photographs; 2) wall pressure; 3) Mach number profiles; and 4) wall shear measured with a floating element balance. Wall shear was also inferred from Preston Tube measurements.

Certain Design Aspects of Single-Winding Three-Phase Inductor Alternators

Based on mathematical analysis, this paper points out that restrictions in stator/rotor slot combinations for optimum output of a conventional inductor alternator are not applicable for one with a single winding for both dc excitation and output. Design considerations for the latter are discussed, and it is demonstrated that its performance is superior to a conventional double-winding inductor alternator in all aspects. Test results on a number of experimental machines fully support the theory.

Polyphase Induction Motor Noise and Its Control

A plethora of sources have arisen over the years that have made noise control desirable and mandatory. The growing national concern of “the environment” has culminated in many studies in the acoustical arena dealing with noise-related hearing loss, worker inefficiency, and many other physiological and psychological areas. The result of this noise awareness has been to effectuate a wealth of noise limitations. These range from federal, state, and local municipal ordinances to those found in the specifications of the motor buyer. The motor manufacturer has not been immune from this onslaught of noise restrictions. Whether the motivating agent is to meet a specification or simply remain competitive, the motor supplier has had to suddenly add a third dimension to motor design. Where previously only electrical and mechanical parameters were considered, sonance properties must now also be deliberated. In this paper, the gravitation towards the quiet motor will be presented. Of all the possible motor noise sources, only two have been found to have a major impact on the motor's airborne noise level, these being air movement (fan and ventilation passages) and magnetic (slot combination) in nature. While abatement of the former is possible by source, enclosure and/or acoustical treatment, magnetic noise is controllable solely through source diminishment. In summary, motor noise sources are enumerated, distinction as to whether peculiar to high- or low-speed machinery is explained, and means of abatement are discussed. Both calculations and test data are also presented to verify the assertions made. Finally, it is suggested that reforms necessary to reduce motor airborne noise levels were not as debilitating as first imagined. Some related areas of further investigation are delineated at the conclusion of the paper.