Effect Of Slots Research Articles

Air-Gap Flux Density Characteristics of Salient Pole Synchronous Permanent-Magnet Machines

The detailed knowledge of the field distribution in the air gap is of main importance for predicting and optimizing the performance of electric machines. In this paper, the air-gap flux density of a salient pole permanent-magnet (PM) synchronous machines is determined and investigated using a new analytical model. The stator slotting and rotor saliency effect, and also the air-gap MMF harmonics are considered. Different no-load and under load simulations are performed to show the permeance effect (rotor saliency and stator slotting) on the air-gap flux density characteristics of this type of machine. The simulations results show that as results of the permeance harmonics additional harmonics are induced on the air-gap flux density and these harmonics are very sensitive on the rotor pole shape parameters. Furthermore, the time domain analysis shows also that the permeance harmonics leads to the fluctuation of the resulting air-gap flux density harmonics with the time.

Experimental Study on Air Entrainment in Slot Die Coating of High-Viscosity, Shear-Thinning Fluids

The effects of slot die geometry, substrate geometry, and fluid properties on air entrainment in coatings have been extensively investigated by several researchers in the past. However, no studies exist to explain the bubble breakup mechanisms during slot die coating of highly viscous, shear- thinning solutions. An experimental study is performed to understand the bubble breakup mechanisms and the qualitative impact of geometric conditions and viscosity of the coating solution on the sizes of the air bubbles. Blackstrap molasses and dilute blackstrap molasses are used as the primary test solutions in this study. Two bubble breakup mechanisms were identified based on the shape of the sawteeth formed prior to air entrainment. In addition, smaller slot and coating gaps and high viscosity solutions were found to produce smaller bubble sizes. For example, reducing slot gap by 41% resulted in a 58% reduction in the effective bubble diameter. It was also found that as the dynamic contact angle approaches 180° with increasing velocity, the behavior follows that of the interface formation model.

Suppression of thrust fluctuation of doubly-fed linear motor

Because the mover and stator of a doubly-fed linear motor are both equipped with three-phase windings, the motor enables contactless energy to be transferred from the stator to the mover. Thus, when a doubly-fed linear motor is used in the linear driving system of trains, neither an overhead line nor a third rail is needed. However, the doubly-fed motor will lead to more severe thrust fluctuation than the unilateral motors. In order to overcome this shortcoming, the thrust fluctuation of the doubly-fed motor should be analyzed. In this paper, an expression for motor thrust is derived. It points out that the slot effect caused by the slotted structure is the main reason for the increase of thrust fluctuation. The method of adopting unequal pole pitch and unequal slot numbers per pole per phase of stator and mover, is proposed to weaken the slot effect when designing the motor slot parameters. Three different motor models are simulated by ANSOFT. The proposed method results in a motor thrust fluctuation coefficient of 8.4%, compared to 49.4% for the conventional method. Therefore, the motor’s thrust fluctuation is effectively suppressed by the proposed method.

A Method to Segregate Detent Force Components in Permanent-Magnet Flux-Switching Linear Machines

Detent force in permanent-magnet (PM) linear machines is caused by both end effect and slot effect. Segregation of the detent force into its end-effect and slot-effect components is helpful to better analysis and design. For conventional PM linear machines, the end-effect component of detent force can be easily calculated in a related slotless linear machine model, where the slot effect is eliminated. However, the slotless model is not applicable to permanent-magnet flux-switching (PMFS) linear machines, where the magnets and core teeth are set together on either a same stator or a same mover. This is because the PMFS machines cannot work at all without the teeth or slots. Therefore, a new method for segregating the detent force in the PMFS linear machines is proposed in this paper. Since a linear machine can be considered as a part of a particular rotary machine with large radius, and furthermore, cogging torque in the PM rotary machine is caused by the slot effect only, thereby the slot-effect component of the detent force in the PMFS linear machine can be calculated from the cogging torque in a related rotary machine, while the residual of the detent force is the end-effect component. Both finite element analysis (FEA) and experimental results show that the proposed method works well for the PMFS linear machines.

Subdomain Model for Predicting Magnetic Field in Slotted Surface Mounted Permanent-Magnet Machines With Rotor Eccentricity

An analytical subdomain model for the prediction of open-circuit magnetic field in slotted surface-mounted permanent-magnet machines is developed in this paper, which considers the effect of rotor eccentricity. The magnetic field domain is divided into three types of simple and regular subdomains, viz. magnet, air gap, and stator slots. The analytical solution is derived by solving the field governing equations in each subdomain and applying the boundary conditions to the interfaces between these subdomains. The perturbation method is used to describe the effect of rotor eccentricity. The model accurately accounts for the effect of stator slots, the mutual influence between slots, and rotor eccentricity. The analytical model is validated by the corresponding finite-element results. The results show that the proposed subdomain model up to the first-order perturbation can accurately predict the open-circuit magnetic field in slotted surface-mounted permanent-magnet machines with rotor eccentricity.

A comparative study of c‐shaped, e‐shaped, and u‐slotted patch antennas

AbstractA class of popular linearly polarized slotted antennas are compared with respect to their RF mechanism, radiation mechanism, impedance matching, and cross polarization characteristics for wireless communication frequency band 1.9–2.4 GHz.It is found that C‐shaped and double C‐shaped patch antennas, even though miniaturized, suffer from narrow bandwidth and high cross polarization level, due to its orientation of slot. U‐slotted and E‐shaped patch antennas show high bandwidth with minor penalty in size and cross polarization level. In order to understand the effect of slot on the radiation in these antennas, a novel strategy of looking at the near‐field of these antennas has been presented. These near‐field plots are analyzed to explain certain far‐field radiation characteristics in these antennas such as‐ cross‐pol level. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1746–1757, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26894

Analytical Modeling of the Open-Circuit Magnetic Field in Axial Flux Permanent-Magnet Machines With Semi-Closed Slots

This paper presents a multi-slice analytical model for prediction of the open-circuit magnetic field in slotted semi-closed permanent-magnet axial flux synchronous machines. The technique is based on 2-D exact solution of the Maxwell's equations using the separation of variables method. The magnetic field expressions are developed in slots regions, slot opening regions, magnetic air gap regions, and permanent magnet regions leading to an exact calculation of the slot effects on the air gap magnetic field. The model is established considering that ferromagnetic parts are infinitely permeable, and end effects at inner and outer radii are neglected. The open circuit machine's global quantities (electromotive force and cogging torque) are then deduced from the local magnetic field expressions. Finally, the accuracy of the presented analytical model is validated by comparing its results to corresponding finite-element analyses for two different axial flux machines.

Performance of Orbitrap Mass Analyzer at Various Space Charge and Non-Ideal Field Conditions: Simulation Approach

The orbital trap mass analyzer provides a number of unique analytical features along with inevitable limitations as an electrostatic instrument operating in high space charge regimes resulting in systematic measured frequency errors as an effect of stored ion clouds on the trap field and each other effect of non-ideal machining the trap electrodes, effect of injection slot, effect of real versus theoretical trap dimensions, etc. This paper deals with determining the influence of the space charge effect and imperfection of the electrostatic field on the motion of ion ensembles in the orbital trap. We examine effects of theoretically modeled non-harmonicity of the electrostatic potential and the number of confined ions on stability of coherent ion motion in the trap that determines the frequency shifts of axial ion oscillation. Three different Orbitrap geometries were considered: geometry close to preproduction Orbitrap, close to standard Orbitrap, close to high field Orbitrap. Frequency shifts for m/z = 500 and for charge state +23 of cytochrome c isotopic cluster particles with 10(4)-6*10(6) elemental charges in the trap were considered. Refined spectra were calculated using the filter diagonalization method proposed by Mandelshtam et al. and applied to mass spectrometry by O'Connor and Aizikov.

An evaluation of inductances of a salient pole synchronous machine under different axial eccentricity conditions

SUMMARY Different radial eccentricities in salient pole machine are well documented in previous studies. In reality, the most probable case is the rotor eccentricity, which is not uniform down the axial length. This article determines a precise model of salient pole synchronous machine for general axial eccentricity condition. Proposed model allows calculating salient pole machine inductances with different static, dynamic, and mixed axial eccentricities in a unified technique. By taking into account machine geometry, slots effects, and type of winding connection, this model is able to consider most of the important features of a salient pole machine. A variant of modified winding unction approach has been used to calculate the inductances under axial eccentricity conditions. The effects of several rotor asymmetries on the inductances are shown, and the inductances are evaluated. The evaluated inductances are compared with those obtained from experiments. There is a good agreement between the simulated and the experimental inductances profiles. Copyright © 2012 John Wiley & Sons, Ltd.

Optimal Design of a Permanent Magnet Linear Synchronous Motor With Low Cogging Force

In this paper, a technique for reducing the cogging force in slotted permanent magnet linear synchronous motors (PMLSMs) is presented. A two-step minimization process that depends on the slotting and end effects is proposed. Taguchi's parameter method, coupled with 2-D and 3-D finite element analysis (FEA), is employed to minimize the cogging force.

Experimental Investigation on the Effects of a Large Recirculating Area on the Performance of an Effusion Cooled Combustor Liner

An experimental analysis of a realistic engine cooling scheme was performed on a test article replicating a slot injection and an effusion array with a central large dilution hole. A test section consists of a rectangular cross-section duct with a flat plate comprised of 270 effusion holes arranged in 29 staggered rows (D = 1.65 mm, Sx/D = 7.6, Sy/D = 6, L/D = 5.5, α = 30 deg) and a dilution hole (D = 18.75 mm) located at the 14th row. Both effusion and dilution holes are fed by a channel replicating a combustor annulus, which allows to control of cold gas side cross-flow parameters, especially in terms of Reynolds number of both annulus and effusion holes. Upstream the first row, a 6 mm high slot ensures the protection of the very first region of the liner. In order to simulate the combustor flowpath, a backward facing step was installed upstream the slot to generate a large recirculating area. Adiabatic effectiveness, heat transfer coefficient and net heat flux reduction were evaluated and compared with non- recirculating experiments. Measurements were performed by means of a steady-state Thermochromic liquid crystals (TLC) technique with a thin Inconel heating foil for the heat transfer measurements. A data reduction procedure based on a finite element approach has been developed to take into account the non uniform heat generation and conduction due to the large amount of holes. Experiments were carried out considering the combined effects of slot, effusion and dilution holes. Three different effusion blowing ratios (BR = 3-5-7) are investigated, keeping constant the slot flow parameters (BR = 1.3). Results highlight that the presence of the step leads to a general reduction of effectiveness while does not have effects on the heat transfer coefficient.

Does popularity decide rankings or do rankings decide popularity? An investigation of ranking mechanism design

We analyze the music charts of an online digital music distributor that displays real time and weekly rankings on its website, and study how ranking policy should be set to maximize the value of its online music ranking service. The existing mechanism considers only streaming and download volumes, while the new ranking mechanism reflects more accurate preferences for popularity, pricing policy, and the slot effect based on the exponential decay of attention. The new ranking model is designed to verify correlations with two kinds of service volumes for popularity, pricing policy, and the slot effect. Slot mechanism design is analyzed in an heuristic way. Our analysis shows that music content sellers maximize benefits by assigning their own music items to the highest-ranking slot, which provides visibility. Also sellers can strategically design the slot size to influence the popularity of music items. Music content buyers gain indirect benefits by getting segmented ranking slots and reducing search costs. Empirical analysis illustrates the features of the online music industry and validates hypotheses constructed around the new ranking model. The results show that the new ranking mechanism is more effective.

Localized Field Enhancements in Guided and Defect Modes of a Periodic Slot Waveguide

We present a periodic slot waveguide for achieving enhanced light-matter interaction that provides significant localized field and power density enhancements over traditional slot waveguides. The basic structure is based on a slot waveguide with 1-D periodic holes. The slot effect provides strong field enhancement and subwavelength confinement, and the periodicity of the structure is exploited to locally magnify or “pinch” the electric field distribution, resulting in additional enhancements. Characteristics of the modes presented by this structure are examined by finite-difference time-domain (FDTD) modeling. Distinct optical gradients and localized enhancements, which are up to 4-5 times greater than comparable slot waveguides, can be achieved. Potential application of the periodic slot waveguide structure to fields, including optical manipulation, sensing, and nonlinear or active material integration, is discussed.

An improvement of defected ground structure lowpass/bandpass filters using H-slot resonators and coupling matrix method

A novel compact wideband high-rejection lowpass filter (LPF) using H-DGS is presented. The proposed filter has neither open stub nor cascaded high-low impedance elements. It consists of two coupled H-slots in the ground plane along with a compensated line. The effect of the new slot on the filter performance is examined. The comparison with the conventional filters shows that the proposed one guarantees a large rejected-band of 20dB from 2.5 to 16 GHz. Experimental measurements by means of HP8719D network analyzer agree well with simulated results which are carried out by Microwave Office. Based on H-DGS LPF Structure, a novel bandpass filter (BPF) will be is designed and tested verified by using both J-inverter and coupling matrix methods.

Computational Algorithms for Induction-Motor Equivalent Circuit Parameter Determination—Part I: Resistances and Leakage Reactances

This paper deals with methods and algorithms for the estimation of induction-motor equivalent circuit parameters starting from the geometrical and electrical data generally available after an electromagnetic design. The main aim of this paper is to help the readers pass from the theoretical analysis to the numerical code suitable to be included in its own design software. For this reason, the step-by-step algorithms are included in this paper. Some of the methods are based on well-known approaches while the other ones are original. For the latter ones, a complete discussion of the theoretical analysis is reported and discussed. The first part deals with the stator- and rotor-resistance computations and the determination of the leakage inductances based on an original flux classification. Finally, the skewing slot effects on the machine parameters are provided. The comparison between computed and measured values confirms the accuracy of the proposed computational algorithms.

Ferrofluid flow in the annular gap of a multipole rotating magnetic field

A solution is obtained for the ferrohydrodynamic problem of ferrofluid flow in the annular gap between two coaxial cylinders under the influence of the magnetic field generated by a multipole stator winding. The solution is applicable to small values of the applied magnetic field amplitude, takes into account the spatial harmonics produced by the multipole stator winding, and includes the effect of spin viscosity. The special case for which the internal diameter goes to zero, corresponding to the cylindrical “spin-up flow” geometry, is also obtained. Results show that for zero spin viscosity (η'=0), no flow is predicted for any number of poles in the winding. In the case of nonzero spin viscosity, for a two-pole stator winding (m = 1) the solution predicts counter-rotating flow with respect to the magnetic field close to the inner cylinder and co-rotating flow with respect to the magnetic field near the outer cylinder, in agreement with previously reported experimental observations. For stator windings with larger number of poles (m>1), the solution predicts co-rotation of fluid and field in the annular gap. Using a four-pole stator winding (m=2), experimental measurements show that a ferrofluid co-rotates with the magnetic field in both the cylindrical and annular cases, with qualitative agreement between the theory with nonzero spin viscosity and the experiments. Non-idealities in the stator winding distribution, e.g., due to slot effects, are considered through linear superposition of higher order harmonics, again predicting zero flow in the absence of spin viscosity and counter-rotating flow with respect to the magnetic field close to the inner cylinder wall only for the case where the fundamental harmonic (m=1) is dominant.

Modification of Radiation Patterns of First Harmonic Mode of Slot Dipole for Dual-Frequency Operation

The effect of parasitic slots on the radiation patterns of the first harmonic mode of a coplanar waveguide-fed slot dipole antenna is presented. By adding four parasitic slots, two on each of the two arms of the slot dipole, the radiation patterns of the first harmonic mode of the slot dipole can be modified to be similar to those of its fundamental mode, while the performance of the fundamental mode is retained. Therefore, the antenna would operate as a dual-band operator with similar radiation patterns. Details of the design and measured and simulated results are presented and discussed.

Broadband, high gain slot loaded square microstrip array antenna

A novel two-element right angle slot loaded square microstrip array antenna (TESMAA) is presented for 52.18% of bandwidth and 11.22 dB of gain. The effect of different slots placed in the ground plane is studied for enhancing the bandwidth and gain. It is found that when bow-tie slot is placed in the ground plane of TESMAA the antenna gives maximum 95.54% of bandwidth and 15.92 dB of gain without affecting the nature of broad side radiation characteristics. The design concepts of antennas are described and experimental results are discussed. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26110

Bending efficiency analysis of horizontal single- and multiple-slot waveguide microrings

The bending efficiencies of three-dimensional (3D) horizontal single- and multiple-slot waveguide microrings are analyzed using the effective index and modified transfer matrix methods. The effects of waveguide parameters, low-index material, high-index material, asymmetric structure, and asymmetric slots on the bending loss are studied. The results show that the bending efficiency can be enhanced by applying asymmetric structures and asymmetric slots. In addition, it is demonstrated that the bending loss increases with the increase of the number of slots. However, by using proper thicknesses for different high-index layers of the horizontal multiple-slot waveguide, it is possible that the horizontal multiple-slot waveguide can provide a lower bending loss than the single-slot one.

The Shielding Effectiveness of a Narrow Slot Exposed to a Nearby Dipole Source and a Plane Wave

This paper presents the shielding effectiveness (SE) characteristics of a metallic wall with a narrow slot when exposed to a nearby dipole source or a plane wave. In order to characterize the dipole source SE, a radiation field, including the near field from the dipole source, is calculated. The results show that the dipole source SE depends on the source and field points. This SE is different from the plane wave SE in that it fluctuates with the position of the dipole source; the fluctuation period is about 0.5λ.