Magnetic circuit

About: Magnetic circuit is a research topic. Over the lifetime, 15707 publications have been published within this topic receiving 118099 citations.

Eddy-current and hysteresis effects in rotating machines

Abstract: Hysteresis in the magnetic circuit of a rotating machine is represented by an approximate method which neglects harmonics and enables the hysteresis motor to be analysed by the equivalent Kron primitive machine. The method is extended to hysteresis and eddy-current effects in hysteresis, induction and synchronous machines; steady-state equivalent circuits are derived for the hysteresis motor and induction machine.

Electromagnetic actuator and optical disk apparatus incorporating the same

Abstract: In an electro-magnetic actuator, a pair of magnetic circuits are separately arranged in a tracking direction and a carriage is located between the magnetic circuits and is movably supported or guide rails extending along the tracking direction. On the carriage, a lens holder for holding an objective lens is movably suspended and focusing coils are fixed on side surfaces of the lens holder. A tracking coil is fixed in the carriage and is extended in the magnetic circuit. Focusing permanent magnets of the magnetic circuits are so extended along the tracking direction as to produce, focusing magnetic fluxes penetrating the focusing coil and leakage magnetic fluxes penetrating the tracking coil. A focus drive force is generated by an interaction between a current supplied to the focusing coil and the focusing magnetic fluxes and a biasing track drive force is generated by an interaction between a current supplied to the tracking coil and the leakage magnetic fluxes.

Two related types of parametric transformers

Abstract: The paper describes the two types of parametric transformers referred to as the "chain type" and "cross-winding type". They are related in the sense that they have identical magnetic circuits, but they differ in their windings arrangement. These transformers utilize the principle of parametric oscillations to develop an output voltage and transfer energy from the input circuit to the output circuit without direct mutual coupling. The two types belong to two different categories in which the MMF's of the input and output circuits act either at right angle to one another (orthogonal) or along the same line (co-linear) in the common regions. The operation of each type is described by two simultaneous nonlinear differential equations and the magnetization characteristics which relate the MMF's and fluxes in the input and output sides of the transformer. The experimental results on a small unit show that the cross-winding type is more efficient and has a higher output to weight ratio than the chain type.

Distributed Multilevel Current Models for Design Analysis of Electromagnetic Actuators

Abstract: This paper presents a generalized source modeling method, referred here as distributed multilevel current (DMC) models, utilizing equivalent magnetizing currents as local point sources to describe material effects of commonly used magnetic components. Unlike existing numerical methods, which solve for the magnetic fields from Maxwell's equations and boundary conditions, the DMC-based method develops closed-form solutions to the magnetic field and force problems, while allowing tradeoffs between computational speed and accuracy using a multilevel structure to discretize geometry and minimize modeling errors in the neighborhood around the point sources. Typical DMC models for volume and surface current elements, permanent magnets, electromagnets, iron plate, and induced eddy currents are derived and validated by comparing their magnetic fields and forces with known (analytical, numerical, and/or experimental) solutions. Results of benchmark comparison demonstrate that the DMC methods reduce the computation time of magnetic fields and forces by several orders as compared to exact solutions numerically integrated from the Biot–Savart law and Lorentz force equation and finite-element analysis. The DMC models were experimentally applied to identify the EM coil position and PM magnetization of a commercial PM linear synchronous motor validating their effects on its torque ripple.

A Single-chip Squid Magnetometer

Abstract: THIS PAPER WILL DISCUSS the design and test of a superconducting quantum interference device (SQUID) magnetometer integrated on a single chip. This technique can be used in the construction of a multichannel magnetometer array that could serve as an image sensor in medical and other similar areas. The chip with a pickup coil, sensor, and feedback circuit, fabricated with niobium superconducting thin film on a Si substrate, and is operated at 4.2’K. Conventional RF and dc SQUID magnetometers use analogfeedback circuits, such as lock-in-amplifiers, making integration difficult’. A digital feedback loop using room-temperature electronics, has been tested’. Unlike other types, however, the present design combines a digital feedback circuit on the chip. This circuit must be able to function as a counter and a D/A converter. Its fabrication conventionally requires a large-scale Josephson logic circuit. However, in our chip the feedback circuit was integrated by introducing a circuit t o store magnetic flux quanta in a super-conducting loop, requiring only one write gate. The magnetometer requires only an ac bias and t o produce a digital output, without supplementary circuitry at room temperature: Figure 1. The output pulse can be processed by a digital processor or can, alternatively, be applied to a display instrument through a counter for directly monitoring input magnetic field waveforms. Figure 2 illustrates the circuit. A figure-eight pickup coil transmits the magnetic flux t o be measured t o the sensor through a pair of 20-turn integrated coils. The sensor is an interferometer having two Josephson junctions and two inductors, and has an asymmetric threshold curve; Figure 3a. The interferometer switches from a zero-voltage state to a finite-voltage state of lmV, when the bias current crosses the threshold curve. It is ac-biased and produces a pulse sequence. A positive or negative pulse is generated, depending on whether the input is positive or negative; Figure 3b. It is operative as a comparator by counting the number of positive ( N t ) and negative (N-) pulses. The difference (N’ N-) indicates whether the input is positive or negative; Figure 3c. The digital feedback circuit was fabricated using a superconducting storage loop and an interferometer as a write gate; Figure 2 . The write gate receives a pulse sequence and writes a positive or negative flux quantum to the storage loop when a pulse arrives. The threshold curve of the write gate affords operating-point crossing of the threshold curves twice, as shown by the dashed lines in Figure 4a. The two junctions, J1 and Jz,