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Purpose: The purpose of this study is to develop a magnetic resonance imaging (MRI)-safe iron-free electrical actuator for MR-guided surgical interventions. Design/methodology/approach: The paper deals with the design of an MRI compatible electrical actuator. Three-dimensional electromagnetic and thermal analytical models have been developed to design the actuator. These models have been validated through 3D finite element (FE) computations. The analytical models have been inserted in an optimization procedure that uses genetic algorithms to find the optimal parameters of the actuator. Findings: The analytical models are very fast and precise compared to the FE models. The computation time is 0.1 s for the electromagnetic analytical model and 3 min for the FE one. The optimized actuator does not perturb imaging sequence even if supplied with a current 10 times higher than its rated one. Indeed, the actuator's magnetic field generated in the imaging area does not exceed 1 ppm of the B0 field generated by the MRI scanner. The actuator can perform up to 25 biopsy cycles without any risk to the actuator or the patient since he maximum temperature rise of the actuator is about 20°C. The actuator is compact and lightweight compared to its pneumatic counterpart. Originality/value: The MRI compatible actuator uses the B0 field generated by scanner as inductor. The design procedure uses magneto-thermal coupled models that can be adapted to the design of a variety actuation systems working in MRI environment. [ABSTRACT FROM AUTHOR]

Purpose: In eddy current nondestructive testing, ferrite-cored probes are usually used to detect and locate defects such as cracks and corrosion in conductive materials. However, the generic analytical model for evaluating corrosion in layered conductor using ferrite-cored probe has not yet been developed. The purpose of this paper is to propose and verify the analytical model of an E-cored probe for evaluating corrosion in layered conductive materials. Design/methodology/approach: A cylindrical coordinate system is adopted and the solution domain is truncated in the radial direction. The magnetic vector potential of each region excited by a filamentary coil is derived first, and then the expansion coefficients of the solution are obtained by matching the boundary and interface conditions between the regions and the subregions. Finally the closed-form expression of the impedance of the multi-turn coil is derived by using the truncated region eigenfunction expansion (TREE) method, and the impedance calculation is carried out in Mathematica. In the frequency range of 100 Hz to 10 kHz, the impedance changes of the E-cored coil and air-cored coil due to the layered conductor containing corrosion are calculated, respectively, and the influences of corrosion on the coil impedance change are investigated. Findings: An analytical model for the detection and evaluating of corrosion in layered conductive materials using E-cored probe is proposed. The model can quickly and accurately calculate the impedance change of E-cored coil due to corrosion in layered conductor. The correctness of the analytical model is verified by finite element method and experiments. Originality/value: An accurate theoretical model of E-cored probe for evaluating corrosion of multilayer conductor is presented. The analytical model can be used to detect the inhomogeneity of layered conductor, design ferrite-cored probe or directly evaluate the corrosion defects of layered conductors. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to propose an analytical model with consideration of the permeability of soft-magnetic materials, which can predict the magnetic field distribution more accurately and facilitate the initial design and parameter optimization of the machine. Design/methodology/approach: This paper proposes an analytical model of stator yokeless radial flux dual rotor permanent magnet synchronous machine (SYRFDR-PMSM) with the consideration of magnetic saturation of soft-magnetic material. The analytical model of SYRFDR-PMSM is divided into seven regions along the radial direction according to the different excitation source and magnetic medium, and the iron permeability in each region is considered based on the Maxwell–Fourier method and Cauchy's product theorem. The magnetic vector potential of each region is obtained by the Laplace's or Poisson's equation, and the magnetic field solution is determined using the boundary conditions of adjacent regions. Findings: The inner and outer air-gap flux density, flux linkage, output torque, etc., of SYRFDR-PMSM are predicted by analytical model, resulting in good agreement with that of finite element model. Additionally, the SYRFDR-PMSM prototype is manufactured and the correctness of analytical model is further verified by experiments on no-load back electromotive force and current–torque curve. Reasonable design of the slot opening width and pole arc coefficient can improve the average output torque and reduce output torque ripple. Research limitations/implications: The analytical model proposed in this paper assumes that the permeability of soft-magnetic material is a fixed value. However, the actual iron's permeability varies nonlinearly; thus, the prediction results of the analytical model will have some deviations from the actual machine. Originality/value: The main contribution of this paper is to propose an accurate magnetic field analytical model of SYRFDR-PMSM. It takes into account the permeability of soft-magnetic material and slot opening, which can quickly and accurately predict the electromagnetic performance of SYRFDR-PMSM. It can provide assistance for the initial design and optimization of SYRFDR-PMSM. [ABSTRACT FROM AUTHOR]

Purpose – Pulse width modulated (PWM) inverters are widely used to feed induction motors for variable speed applications. The use of PWM power supplies induces additional magnetic losses in the magnetic circuit of the electrical machine. The aim of this paper is to present a novel analytical approach to account for these losses. Design/methodology/approach – The methodology proposed here consists in identifying the analytical method with a static Preisach hysteresis model. The Preisach model was validated by comparing it with measurements obtained from an Epstein frame. Then, the results obtained with this approach were compared with a basic analytical method that is widely used. Findings – The authors' model provides a fast way for estimating the minor loop iron losses introduced by static convertors. They compared the proposed model with another analytical model (J. Lavers model) for different wave forms. One can observe that the J. Lavers model overestimates the iron losses introduced by the non-centred minor loops. Originality/value – In this paper, an improved analytical model is presented which estimates the non-centred minor loop iron losses. In order to do a precise estimation of the iron loss introduced by the minor loops, the authors' model takes into account the position and the size of the minor loop. The proposed model is identified from a static Preisach model. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to investigate the impact of different mathematical formulations of the problem of optimal design of electrical machines on the results obtained using a local optimization solver. The aim is to investigate the efficiency and reliability of standard local solvers when handling different mathematical formulations. This could provide guidelines for designers in practical engineering applications. Design/methodology/approach – The paper proposes six equivalent mathematical formulations of the optimal design problem of a slotless permanent-magnet electric rotating machine. The authors investigate the impact of these different mathematical formulations on the results obtained using a local optimization solver which is well-known in the engineering community: MatLab's fmincon function. The paper first computationally compares the six proposed formulations with a fixed value for the number of pole pairs p, that gives continuous optimization problems, then discusses some results when p is free on three mixed-integer formulations. Findings – The paper shows that, even though the considered formulations are mathematically equivalent, their numerical performances are different when an optimization solver, such as the one proposed by MatLab in fmincon, is used. Thus, the designer must take care about the formulation of the design problem in order to make more efficient the use of these kind of algorithms. Originality/value – In the context of engineering applications, one usually resorts to well known and easy to use optimization solvers. The same optimization problem can be often formulated in different ways. Furthermore, the formal description of optimization problems has an impact on the applicability and efficiency of the corresponding solution methods. This is usually not taken into account when optimization solvers are exploited. The originality of this paper is in building on the theory of reformulations in mathematical optimization to investigate and highlight the impact of formulation differences. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to evaluate the cogging torque in a surface-mounted permanent magnet (SPM) machine with both uniformly and non-uniformly segmented stator cores and to find out the optimal solution of stator core segmenting. Design/methodology/approach – The cogging torque with segmented stators is synthesized from a single slot model, and analytical prediction is given to analyze the cogging torque with both uniformly and non-uniformly segmented stators. Finite element method (FEM) is used to figure out the electromagnetic field and validate the analytical prediction. Moreover, models with various shapes and positions of connecting tongues between the stator core segments are explored to achieve the optimal design. Findings – The cogging torque is found to be greatly related to the number of segments and the electrical angle between adjacent additional air gaps caused by the tolerance of stator segments. Different shapes of the connecting tongues are tested and proved to be of great importance to the flux density, both radial and tangential, and therefore affect the cogging torque. Finally, position of the connecting tongues is perceived to have little influence on the performance of machine. Practical/implications – By utilizing analytical prediction and FEM calculation, the optimal solution is discussed to minimize the cogging torque in the SPM machine from the perspective of the stator core segmentation. Originality/value – This paper establishes formula of cogging torque with segmented stators and predicts the variation of cogging torque with analytical method. Besides, different combinations of segments are compared and measures to reduce the cogging torque produced by the segmentation are proposed. [ABSTRACT FROM AUTHOR]

Purpose This paper aims to propose an analytical model for the harmonic content no-load magnetic fields and Back electric motive force (EMF) in double-sided TORUS-type non-slotted axial flux permanent magnet (TORUS-NS AFPM) machines with surface-mounted magnets considering the winding distribution and iron saturation effects.Design/methodology/approach First, a procedure to calculate the winding distribution with a rectangular cross-section is proposed. The magnetic field distribution and magnetic motive force (MMF) drop due to saturation in iron cores are then exactly extracted in a 2-D analytical model. The consequent influence on air-gap magnetic field and Back EMF are also calculated using a new iterative algorithm. The results are compared with those of the conventional analytical model without saturation, 2-D finite element analysis (FEA) and an experiment on a fabricated prototype machine.Findings Unlike the conventional method, the new method yields the no-load magnetic field distributions in air-gap and iron cores and Back EMF very exactly such that the results well match to those of the FEA and experiment.Originality/value Unlike the conventional winding factor, the winding distribution is considered here along the both axial and circumferential directions, which improves the accuracy level of results for non-slotted structures with relatively large air-gaps. The magnetic field distribution and MMF drop-in iron parts are also calculated as the basis for exact recalculation of air-gap magnetic field and Back EMF. Because of small computational burden beside superior accuracy, the proposed model can be treated as an accurate and fast substitute for FEA to be used during the design procedure or for predicting the other performance characteristics of TORUS-NS AFPM machines. [ABSTRACT FROM AUTHOR]

Scaling down the supply voltage (Vdd) below the transistors threshold voltage (Vth) has become a very popular technique in designing Ultra-Low-Power circuits whose demand has dramatically increased in the last few years. Designing these kinds of circuit is still a challenge, especially when the latest advanced process technologies are employed. The well-known design methodology used in the typical super-threshold domain (Vdd>Vth) cannot be applied to the design of a sub-threshold circuit due to the different transistor current-voltage relationships that hold when Vdd

This paper provides an original closed-form analytical model of frequency-pulling phenomenon in unlocked-driven nonlinear oscillators. The formulas are more general and accurate in estimating the spectral components and degree of phase perturbation of the unlocked driven oscillator under weak as well as strong injection signal level. The accuracy and superiority of the proposed analytical model in predicting injection locking of oscillators in strong injection signal level over prior literature have been established analytically and experimentally. [ABSTRACT FROM AUTHOR]

Purpose: In this work, a method to design a slotless permanent magnet machine (SPMM) based on the joint use of an analytical model and deterministic global optimization algorithms is addressed. The purpose of this study is to propose to include torque ripples as an extra constraint in the optimization phase involving de facto the study of a semi-infinite optimization problem. Design/methodology/approach: Based on the use of a well-known analytical model describing the electromagnetic behavior of an SPMM, this analytical model has been supplemented by the calculus of the dynamic torque and its ripples to carry out a more accurate optimized sizing method of such an electromechanical converter. As a consequence, the calculated torque depends on a continuous variable, namely, the rotor angular position, resulting in the definition of a semi-infinite optimization problem. The way to solve this kind of semi-infinite problem by discretizing the rotor angular position by using a deterministic global optimization solver, that is to say COUENNE, via the AMPL modeling language is addressed. Findings: In this study, the proposed approach is validated on some numerical tests based on the minimization of the magnet volume. Efficient global optimal solutions with torque ripples about 5% (instead of 30%) can be so obtained. Research limitations/implications: The analytical model does not use results from the solution of two-dimensional field equations. A strong assumption is put forward to approximate the distribution of the magnetic flux density in the air gap of the SPMM. Originality/value: The problem to design an SPMM can be efficiently formulated as a semi-infinite global optimization problem. This kind of optimization problems are hard to solve because they involve an infinity of constraints (coming from a constraint on the torque ripple). The authors show in this paper that by using analytical models, a discretization method and a deterministic global optimization code COUENNE, this problem is efficiently tackled. Some numerical results show that the deterministic global solution of the design can be reached even if the step of discretization is small. [ABSTRACT FROM AUTHOR]

Purpose – To derive an analytical model for a dc-ac-dc parallel resonant converter operating in lagging power factor mode based on the steady-state operation conditions and considering the effects of a high-frequency transformer. Design/methodology/approach – A range of published works relevant to dc-ac-dc converters and their control methods based on pulse-width-modulation technique are evaluated and their limitations in output measurement of higher output voltage converters are indicated. The circuit diagram of the converter is described and the general mathematical model of the system is obtained by deriving and combining the mathematical models of the different converter blocks existing in the system. The derived mathematical model is used to study the steady-state and transient performance of the converter. The deriving procedure of the analytical model for a parallel resonant converter is extensively given and the analytical model obtained is verified by simulation results achieved using MATLAB/SIMULINK and the program written by the authors. Findings – The paper suggests an analytical model for dc-ac-dc parallel resonant converters. The model can be used in the output voltage estimation of a converter in terms of its phase-shift angle and the dc-link voltage. Research limitations/implications – The resources in the library of the authors' university and also the English resources relative to dc-ac-dc converters reachable through the internet were researched. Practical implications – The analytical model suggested can be used in estimating the output voltage of the converters used in high-voltage applications or where there are difficulties in employing sensors in measurement of the output voltage due to high price or implementation problems. Originality/value – The originality of the paper is to present an analytical model for dc-ac-dc parallel resonant converters. Using this model makes it possible to estimate the output voltage of the converter using the dc-link voltage and the phase-shift angle. The proposed model provides researchers to regulate the output voltage of the converters using feed-forward control technique. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to evaluate and minimize the losses of alternating current (AC) in the winding of electrical machines. AC winding losses are frequently disregarded at low frequencies, but they become a significant concern at high frequencies. This is the situation where applications require a high speed. The most significant applications in this category are electrical propulsion and drive systems. Design/methodology/approach: An analytical model is used to predict the AC losses in the winding of electrical machines. The process involves dividing the slot into separate layers and then calculating the AC loss factor for each layer. The model aims to calculate AC losses for two different winding arrangements involving circular conductors. This application focuses on the stator winding of a permanent magnet synchronous motor that is specifically designed for electric vehicles. The model is integrated into an optimization process that makes use of the genetic algorithm method to minimize AC losses resulting from the arrangement of conductors within the slot. Findings: This study and its findings demonstrate that the arrangement of the conductors within the slot has a comparable effect on the AC losses in the winding as the machine's geometric and physical properties. The effectiveness of electrical machines depends heavily on optimizing the arrangement of conductors in the slot to minimize AC winding losses. Originality/value: The proposed strategy seeks to minimize AC winding losses in high-speed electric machines by providing a cost-effective and precise solution to improve energy efficiency. [ABSTRACT FROM AUTHOR]

In this paper, we propose a tool for the design of 4H-polytype Silicon Carbide Junction Barrier Schottky, JBS, diodes, which are promising devices for their low on-state resistance and their high blocking voltage. Our tool calculates the width of the channel region in terms of the geometrical and physical parameters and of the doping concentration in order that the device shows forward electrical characteristics similar to that of Schottky Barrier Diode. Their operating principle is defined by the control of the flow of electron carriers through a potential barrier, which is located in the n-type region under the Schottky metal contact surrounded by the p + -type regions. Indeed, if the electric fields of the p + -n junctions extend for the whole channel region under equilibrium conditions, the height of the induced potential barrier can be higher than that of the conventional Schottky built-in potential and can affect the electrical characteristics of the device, for example increasing the turn-on voltage. Although they have been firstly developed in Silicon technology, 4H-SiC JBS diodes are easier to fabricate because the electric fields of 4H-SiC p–n junctions have a wider space charge region for the same values of the doping concentrations with respect to Si JBS devices, resulting in a more relaxed design constrain of the channel geometry. Our analytical model can calculate the potential barrier height as function of the geometrical and physical parameters of the device and can evaluate the maximum channel width for which the potential barrier is higher than Schottky built-in voltage. The analytical results are compared through numerical simulations obtained from ATLAS Silvaco software. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a novel MAC (media access control) protocol named CSMA/CP for a metropolitan area network for the next generation Internet, which is an OPS (optical packet switch) network that all-optically and directly transfers IP packets over a WDM (wavelength division multiplexing) ring network. The proposed protocol uses the concepts of CSMA (carrier sense multiple access) and CP (carrier preemption) to all-optically transfer the IP packets of the nodes in the WDM ring networks. This paper studies the length effect of FDL (fiber delay line) in each node to support variable packet transmission, and develops an analytical model to analyze and simulate the packet delay and throughput. [Copyright &y& Elsevier]

Abstract: This paper deals with the analytical computation of the magnetic field distribution in a wholly superconducting reluctance motor. The rotor is made with high temperature superconductor bulks which nearly present a diamagnetic behavior under zero-field cooling. The stator consists of superconducting armature windings fed by AC currents of high amplitude. The superconducting stator winding can generate a high rotating magnetic field without the need of ferromagnetic material in the rotor. The electromagnetic torque is obtained by the interaction between the rotating magnetic field created by the superconducting stator windings and the variable reluctance due to the superconducting bulks. The proposed analytical method is based on the resolution of Laplace's equation (by the separation of variables method) for each sub-domain, i.e. rotor shaft, holes between superconducting bulks and air-gap. The global solution is obtained using boundary and continuity conditions. Magnetic field distribution and electromagnetic torque obtained by the analytical method are compared with those obtained from finite element analyses. [Copyright &y& Elsevier]

Abstract: This paper presents a detailed study of the generation of traveling waves in finite-length beams. The method used is the mode superposition. It consists in exciting, with two actuators, two standing waves space shifted of a quarter wavelength and time shifted of a quarter period. Thanks to an analytical model giving the general solution of the flexural wave, we define the ideal conditions ensuring the best quality of this wave across the beam. Then, through an optimization process, we get the excitation parameters, actuator positions and driving frequency, that allow to approach at most these conditions. [ABSTRACT FROM AUTHOR]

We develop an accurate analytical expression for the propagation delay of submicrometer CMOS inverters that takes into account the short-circuit current, the input-output coupling capacitance, and the carrier velocity saturation effects, of increasing importance in submicrometer CMOS technologies. The model is based on the nth-power-law MOSFET model and computes the delay from the charge delivered to the gate. Comparison with HSPICE level 50 simulations and other previously published models for a 0.18-μm and a 0.35-μm process technologies show significant improvements over previous models. [ABSTRACT FROM AUTHOR]