Open Magnetic Circuit Research Articles

Offset thermostability of the TFS-3 magnetometric sensors

Miniature fluxgate sensors with an open magnetic circuit having a simple and robust design were elaborated. Two kinds of magnetic materials were used as the sensitive elements of the sensors: Vacoperm 100 (Vacuumschmelze-Hanau, Germany) and amorphous Co68.25Fe4.5Si12.25B15 material (Institute of Technical Physics, Iasi, Romania). In the work the temperature dependence of the developed sensors offset was studied. Special technological procedures were used to reduce the effect of temperature variations. Using a good protection of the sensor against the thermal agents (to avoid condense), a good thermostability of the sensor offset was obtained. The temperature drift of the sensor offset has been calculated of 0.031 and 0.02 nT °C−1 respectively over the whole temperature range −75 to +25°C. The employed amorphous material Co68.25Fe4.5Si12.25B15 results are very useful as a magnetic sensing element for fluxgate sensors.

Calculation Method of Starting Characteristics of Single Phase Linear Actuator with Open Magnetic Circuit.

Calculation Method of Starting Characteristics of Single Phase Linear Actuator with Open Magnetic Circuit.

NUMERICAL CALCULATION OF DEMAGNETIZING FACTOR FOR PERMANENT MAGNET

Recently, rare earth magnets with high coercive force such as Nd‐Fe‐B magnets have been developed. When the magnetic characteristic (M‐H curve) of such a strong magnet is measured, the conventional closed magnetic circuit method using an electromagnet cannot be applicable due to the magnetic saturation of the yoke. Therefore, the open magnetic circuit method has been proposed in which high magnetic fields are generated by using a superconducting or a pulsed magnet. In this method, the correction for demagnetizing field is required. The correction can be done using the demagnetizing factor which is a function of the shape and M‐H curve. The conventional studies take into account only the shape.

Linear Drive Systems and their Related Technologies. Magnetless Voice Coil Motor and the Driving Characteristics.

A magnetless voice coil motor (MLVCM) is generally composed of a closed magnetic circuit stator core (laminated electical steels), two exciting coils on the core and a metal ring mover, without pernament magnets and leading wires connected with the mover. A driving force F is both an electromagnetic force between a mover current J2 and a gap flux density BG, which are induced by an exciting current J1, and a reluctance force due to J2. The driving force F is proportional to J12/g, where g is a gap length, and almost independent of mover position under a constant J1 and above a lower cutoff angular velocity ωJ1, of an induced current. ωJ1 becomes lower with the lower electric resistance of a mover and the lower reluctance of a magnetic circuit (stator core), and consequently a MLVCM with a closed magnetic circuit generates a higher driving force than that with an open magnetic circuit. The higher permeability and the lower iron loss of a magnetic circuit core increase a mover current J2 and a gap flux density BG, and then a driving force becomes greater. A voltage applied to the exciting coil increases proportionally to the distance between an exciting coil and a mover under a constant J1.

A Technique for Measuring Thin-Film Inductors Driven at High Flux Densities

This paper discusses the basic properties of thin-film inductors driven at high flux densities. We made inner-coil-type thin-film inductors, each with either a closed or an open magnetic circuit, and developed a technique for measuring the impedance of the inductors at high flux densities. We used this technique to reduce the multiple voltage reflections between amplifier and inductor. The impedance of the magnetic thin-film inductors varied according to the magnetic field intensity, because of flux saturation.

Magnetic Hysteresis and Demagnetizing-Field Correction for Rare Earth Magnet Materials

The standard method for measuring magnetization, using a closed magnetic circuit, cannot be applied to rare earth magnet materials with very high coercivity. Hence in this paper we examine an open magnetic circuit method in a steady high magnetic field, in which correction for the demagnetizing field is important. We measured hysteresis curves for some commercial rare earth magnet materials by using cylindrical samples with various dimension ratios. The correction for the demagnetizing field gives a reasonable result for bonded magnets, whereas even the intrinsic coercivity seems to depend on the sample shape in the case of sintered magnets. Therefore, it is necessary to reconsider the correction for the demagnetizing field as well as the standard specifications of rare earth magnet materials.

薄膜インダクタの大振幅励磁特性の計測

This paper discusses the basic properties of thinfilm inductors driven at high flux densities. We made inner-coil-type thin-film inductors, each with either a closed magnetic circuit or an open magnetic circuit, and developed a technique for measuring the impedance of the inductors at high flux densities. To do this, we used this technique to reduce the voltage multiple reflection between the amplifier and the inductor. The impedance of the magnetic thin-film inductors varied according to the magnetic field intensity, because of flux saturation.

希土類磁石のヒステリシスと反磁界補正

The standard method for measuring magnetization, using a closed magnetic circuit, cannot be applied to rare earth magnet materials with very high coercivity. Hence in this paper we examine an open magnetic circuit method in a steady high magnetic field, in which correction for the demagnetizing field is important. We measured hysteresis curves for some commercial rare earth magnet materials by using cylindrical samples with various dimension ratios. The correction for the demagnetizing field gives a reasonable result for bonded magnets, whereas even the intrinsic coercivity seems to depend on the sample shape in the case of sintered magnets. Therefore, it is necessary to reconsider the correction for the demagnetizing field as well as the standard specifications of rare earth magnet materials.

European intercomparison of measurements on permanent magnets

The results of a European intercomparison of measurements on permanent magnetic materials are reported. The intercomparison consists of two parts, i.e., measurements on cylindrical specimens of AlNiCo and NdFeB in a closed magnetic circuit; and measurements on spherical specimens of NdFeB in an open magnetic circuit using vibrating sample or SQUID magnetometers. Together with the other specimens, nickel reference specimens are circulated for calibration purposes. The results of the intercomparisons are complex, but in general the agreement obtained is quite good. A comparison of the two parts shows in H/sub c/, H/sub cB/ and (BH)/sub max/ are considerable, which can be interpreted in the light of the aging of the NdFeB spherical specimens due to the preparation process. >

Thin Film Inductor with Multilayer Magnetic Core

In this work, thin film microinductors were investigated from the standpoint of increasing the quality factor (Q) and inductance (L). To obtain a high Q, it is important to use a magnetic core with a small iron loss at high frequencies. Thin film microinductors were prepared using multilayered CoNbZr/AlN film. The optimum conditions for a high Q were investigated by changing the size of the magnetic core and the structure of the multilayer film and exciting coil. The Q and L values increased with decreasing thickness of individual magnetic layers and with increasing intermediate layer thickness. The demagnetization of the inductor open magnetic circuit was decreased by using a multilayer magnetic core. The stray capacitance between coil and magnetic core is dominant in these thin film inductors. It was found that multilayer magnetic core is useful for increasing the Q and L values of thin film inductors at high frequencies. An experimental inductor in which iron and copper losses were reduced through the use of a multilayer core and thick coil had an L=120 nH and Q=18 at 50 MHz, and measured 0.5 mm × 2.5 mm × 35 ?m.

Demagnetization effect in strip-line cavity measurements

Stripline resonant cavities are useful for measuring the effective high-frequency permeability of small samples of high-permeability thin-film materials. However, in such an open magnetic circuit device, the effect of sample demagnetization can seriously degrade measurement accuracy unless it is recognized and corrected. Measurements with accuracy degraded by sample demagnetization are readily identified using the demagnetization effect map that is given. Approximate correction of these measurements can be accomplished by using the demagnetization correction equation and estimated demagnetization factor for the stripline resonant cavity configuration that is shown. The accuracy of this demagnetization correction is limited by the use of the approximate demagnetization factor.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

多層薄膜磁心を用いた高周波薄膜インダクタ

In this paper, thin film micro inductor was investigated from the stand point of increased quality factor (Q) and inductance (L). To obtain a high Q, it is important to use a magnetic core in which iron loss is small in high frequency. The thin micro film inductor was prepared using multi-layered CoNbZr/ AIN film. The best condition for high Q was investigated by changing the size of magnetic core and structure of multilayer and exciting coil. The Q and L are increased with decreasing thickness of one magnetic layer and increasing one interlayer. The demagnetization of open magnetic circuit of inductor is decreased by using multi-layered magnetic core. The stray capacitance between coil and magnetic core is dominant in these thin film inductors. It was found that multi-layered magnetic core is useful to increase the Q value and L of thin film inductors in high frequency. The experimental inductor in which iron and copper loss are decreased by multi-layered core and thick coil shows L= 120 nH, Q= 18 at 50 MHz in its size of 0.5 mm×2.5 mm×35μm

Analysis of the magnetic fields in magnetostrictive rare earth-iron transducers

The magnetic problems encountered in the design of underwater transducers based on magnetorestrictive rare earth/iron alloys are using the finite element package FLUX2D. Dynamic magnetic circuit design is studied using the concept of an open magnetic circuit. Eddy-current computations show that this effect can be accurately taken into account by an analytical method. The presence of leakage flux due to the low permeability of the magnetorestrictive alloy is fully revealed with finite-element computations and is expressed by low magnetic coupling factors. The results of a systematic study of this coefficient and of the coil quality factor are presented. Different solutions for the magnetic bias using permanent magnets are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Anisotropy of magnetic properties in thin electrical sheets

Magnetic properties of thin electrical sheets of AN1 and AN3 types are described. Data on anisotropy of the coercive force determined from Epstein tests and from coercivemeter measurement (in an open magnetic circuit) anisotropy of magnetic induction in DC and AC magnetization conditions are presented. Anisotropy of core losses and degree of Goss texturing are also reported.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Horn speaker with reduced magnetic flux leakage

By adding a secondary magnetic piece with a partially open magnetic circuit to the front surface of a yoke connected to a primary magnetic piece, the magnetic flux leakage from the main magnetic piece is reduced on one hand and the magnetic flux extending across a magnetic gap is intensified through formation of a favorable magnetic field. This horn speaker is particularly useful in a ship where a horn speaker as an alarm is often required to be placed near magnetically sensitive equipment such as a compass.

Calorimeter for measuring ac magnetic losses in small samplesa)

A calorimeter has been developed to measure the total core loss in small samples of magnetic materials which are not suited to conventional measurement techniques. The method is similar to the helium boil-off calorimeter used in some cases to measure ac losses in superconductors. Power losses in the sample are determined by measuring the rate of boiling of a fluid in which the sample is immersed. The sample is in open magnetic circuit. Uncertainty of the method is estimated at 3%.

Reproducing characteristics of perpendicular magnetic head

Perpendicular magnetic recording with a single pole head has capabilities to record and reproduce the signals at extremely high density above 200 kMRPI. To investigate the reproducing performance of a single pole head, the amplitude, the frequency spectrum and the noise of reproduced voltage have been measured and compared with those of a ring head. A Single pole head, works at the almost intrinsic permeability of the main pole film irrespective of the open magnetic circuit. The amplitude per unit inductance of reproduced voltage was increased by using a main pole film having high initial permeability and saturation induction, and became comparable to that of the ring head even at low density. The modulation noise and the other noises in perpendicular recording are very low as compared with those of a longitudinal recording. The good SN ratio has been gained with a single pole head having very narrow track width of 6.5 μm.

Thickness dependence of magnetic properties in rapidly quenched 6.5 percent silicon iron thin ribbons

Ribbons of 6.5% Si-Fe alloy were prepared with a rapid quenching single roller method. The thickness was 10 to 90μm. After annealing these samples at 1100°C for one hour in pure hydrogen, the grain structure was observed using a 25 kV-SEM. Mechanical properties were measured with a tensile testing machine. Magnetic properties were measured using an open magnetic circuit apparatus. Thickness dependence of these results were examined. The grain size became abruptly larger with increasing thickness and reached 1.8 mm in diameter at a 90 μm thickness. The tensile strength was about 65 kg/mm2for ribbon with a 60 μm thickness. The coercive force measured at a maximum applied field of 10 Oe decreased with increasing thickness and was 0.27 Oe at a thickness of 90 μm. The coercive force was reduced to 0.24 Oe by a double heat tretment. Initial and maximum permeabilities increased with increasing thickness. The former was 700 and the latter 18000 at a 90 μm thickness. The core loss was much lower than for grain oriented 3% silicon iron steel. It was less than one third the value for the steel when measured at frequencies above 1 kHz.

Improvement of mechanical workability and constancy of permeability of Fe-Ni-Si alloy by splat cooling technique

Iron-rich alloy ribbons containing about 15 wt % nickel and 12 wt % silicon, which have been called Senperm, were prepared in the crystalline state using a single roller quenching method. The ribbons were remarkably flexible and had a silver-white lustre. They were not oxidized even if they were left in the air for a few months. They could not be bent 180° the minimum winding diameter was 6 mm. The magnetic properties were measured with an open magnetic circuit apparatus and an LCR-meter. The magnetic properties of the as-prepared ribbons were: initial permeability μi=500 and the range of constant permeability Hi=0.25 Oe for SP-No.1; μi=250 and Hi=1.4 Oe for SP-No.2. After annealing at 900°C for a few hours in a vacumm, the ribbons became more flexible and could be bent 180° easily. The minimum winding diameter decreased to 1.2 mm. The magnetic properties were improved noticeably and were: μi=350, Hi=0.6 Oe for SP-No.1 and μi=50, Hi=2.7 Oe for SP-No.2. It was also confirmed that μi was nearly constant up to 50 kHz. The grain strucrure was observed using a 25 kV scanning electron microscope.

Unconventional electrical machine for circulating molten metal

The paper deals with the application of an unconventional electrical machine for circulating molten aluminium in reverberatory furnaces. Its design is based on the classical jumping-ring principle, and it incorporates some hitherto less known aspects of open magnetic circuits and of the concepts of flux spreading. Results of trials using a prototype machine are given, and the metallurgical and other benefits which accrue from its use are discussed. To maintain the electromagnetic integrity of this machine at liquid-metal temperature (> 700°C), a study of its thermal behaviour is made using a mathematical model. This model is subsequently verified by experimental observations. Proposals are made for the future use of some unconventional electrical machines in an aluminium remelt plant.