The vaporization rate of water was significantly enhanced by a magnetic field in air and in an oxygen atmosphere. The enhancement was largest around the positions with large magnetic field gradients. It was shown that the flow of water vapor was influenced by the magnetic force. All the experimental results obtained in this experiment were consistently explained by considering the generation of gas convection above the water surface by the magnetic force.

View full abstract

The effects of a magnetic field on the germination of plants were studied. When a 10 T magnetic field was applied, a cucumber shoot that germinated in the horizontal bore of a superconducting magnet leaned in the direction of the magnetic field center. In contrast, the root grew in the direction opposite to the field center. The observed result seems to have occurred as follows: the cucumber recognized the direction of the resultant force of gravity and the magnetic force as the direction of gravity, the shoot and the root then grew along the line of the resultant force, according to their taxis. The results of analysis of the experimental data supported this idea qualitatively. These observations offer us important knowledge about the effect of magnetic fields on living bodies. They also suggest the possibility of applying magnetic fields in other areas of research.

View full abstract

It was found that wind can be induced by heating in a magnetic field gradient. The effect was explained in terms of the following mechanism. When the temperature of air increases, its susceptibility decrease because of the paramagnetic property of oxygen gas. In this case, the magnetic force, which is proportional to the susceptibility, decreases. The change in the magnetic force produces an effective force acting on the air, and wind is induced. We have observed the phenomenon experimentally by using a heating system placed in a superconducting magnet.

View full abstract

This paper reports our observations of concentrated heavy corrosion patterns of a steel cylinder, and the relationship between the corrosion pattern and a gradient magnetic field near the steel. A uniform static magnetic field up to 3 T was applied to the steel in our experiment. The steel was positioned in the center of a chamber filled with purified water, which in turn was placed in the center of the bore of a superconducting magnet. The steel itself produced a surrounding magnetic field, so that dissolved oxygen was attracted to the upper and the lower part of the steel by the magnetic force. As a result, these two parts were corroded badly, while lateral parts were not corroded. Our work suggests that the areas of corrosion of a steel can be specified by analysis of the spatial distribution of a magnetic field.

View full abstract

Substances adhering to the inner walls of a boiler and piping were magnetically removed and recovered by applying controlled magnetic field with the aid of magnets attached to the outside of the piping while the boiler was in operation. The compositions, product phases, magnetic characteristics, and so on of the substances adhering to the piping were measured by using fluorescent X-ray spectrographic analysis, X-ray diffraction, and a vibrating samples magnetometer. As a result, it was found that the major constituent of the substances was Fe₃O₄, with which compounds of substances such as Zn, Cu, and Si has coagulated. Comparison of the cases in which a magnet was and was not used explicitly revealed that the amount of substances removed increased 4 times 2 months later in the former case. In a test conducted during the period from December to April, in which a magnetic remover and recoverer were installed on a boiler on site, the results showed almost the same tendency as those seen in the laboratory experiment.

View full abstract

A variable-temperature scanning Hall probe microscope was developed for imaging a microscopic magnetic field distribution. The microscope probes the surface of magnetic materials with a micro-Hall probe, whose active area is 0.6-2.0 μm². The microscope‘s operating temperature range is between room temperature and liquid He temperature. The results of observing magnetic images of a thermally demagnetized permanent Sr-ferrite magnet at room temperature and a high-temperature superconducting NdBa₂Cu₃O_y thin film at 77 K are presented.

View full abstract

We developed a near-field magnetic noise mapping system by using a shielded-loop type coil array. High-resolution (0.1 mm) two-dimensional magnetic field vector detection was realized. We demonstrated a noise map of the loop antenna, microstrip line, and printed circuit board of a personal computer.

View full abstract

Eddy-current testing (ECT) is a powerful and useful technique for detecting cracks and flaws in uniform conductive plates and pipes. We investigated the diagnostics of printed circuit boards (PCBs) as a new application of ECT. Recent high-density PCBs require a new cost-effective testing system for the production phase. ECT is an interesting approach for inspection of as-made printed wirings, because it uses non-contact testing, low stress, conductive testing, and fast scanning. This paper describes the detection characteristics for some flaws in printed wirings. We experimentally examined the use of ECT for inspecting disconnections, chipping defects, and imperfections in the thickness of printed wirings. The results confirm than the ECT approach is attractive and effective for PCB diagnostics.

View full abstract

This paper presents the methods for calculating the inductance of a conductor in an LSI package that includes micro-strip lines.
The first method, for calculation the mutual inductance and external self-inductance, is based on Neumann's formula and the internal self-inductance is calculated by Maxwell's law. In this method, the micro-strip line is simulated by supposing that the mirror image conductor is based to the surface of the plane.
The second method is based on Poisson's equation by the finite element method.
The magnetic flux passing through the plane is decreased from 77% to 0.2% by the magnetic shield effect on the model when the frequency is increased from 1 MHz to lGHz.
The inductance of the specimen is calculated by the two methods and measured. The difference between the values given by the two calculation methods is less than 2.4%, and the difference between the calculated value and measured value is less than 15.5% in the frequency range 0.1 MHz to 1 GHz.

View full abstract

This paper discusses measurement of the impedance of thin-film inductors up to the GHz frequency range. We made thin-film inductors based on the silicon process, and investigated a technique for measuring their high-frequency impedance by means of a waferprobe. A waferprobe with precise dimensions permits impedance matching between the inductor and the measurement instrument. We improved the reading of the measurement data and measured the inductance of thin-film inductors accurately up to the GHz frequency range.

View full abstract

This paper deals with the properties of micromagnetic films for planar inductors with a magnetic core, and with a production process that does not damage the magnetic properties. Micro-rectangular-multilayer (CoFe)_x (SiB)_1-x/SiO₂ (x=0.82-0.90) films 300μm wide and 2 mm long were prepared by an RF-magnetron sputtering method. The frequency dependence of the complex permeability (μ' and μ'') of films was measured by using the parallel line method. The inverse loss tangent (1/tan δ) values of multilayer films were calculated from the value of μ'/μ'' at 400 MHz. The values of μ' × (1/tan δ) of multilayer films increased to a maximum of 6500 at x=0.86. Planar inductors with a multilayer film core were fabricated by using an RF sputtering method and a lift-off technique. The highest value of the maximum value of the quality factor (Q_max) of inductors is obtained by using a multilayer film of x=0.86. The present results emphasize that a higher value of μ' × (1/tan δ) and a higher flatness of the insulation layer under the magnetic core are important factors for increasing the quality factor of micro-planar devices with a magnetic core.

View full abstract

We propose a contactless power transmission system (CLPS) using new meander-type coils. The main feature of meander-type coil is their effectiveness for stabilizing the amount of the tramsmitted power against the load displacement and electromagnetic noise emission. When the pitch of the transmitter coil corresponds to the receiver shape, the maximum transmitting power was obtained. A new exciting system was realized by means of an easy circuit. The circuit always fixes the relative positions between the transmitter and receiver coils. The system is able to ensure the optional distribution of flux. Therefore, the receiver position can be determined and the pitch of the transmitter coil can be set.

View full abstract

The chipsize dependence of the magnetic characteristics of thin-film reactors using nanocrystalline Fe (Co-Fe)-Hf-O magnetic films with a high resistivity is discussed by using the finite element method in which a linear magnetization of the thin-film is asssumed. The inductance of the reactors is proportional to the 3rd power of the reactor-size W. The loss-equivalent resistances of the film and the coil-conductor are proportional to the 4th and 2nd powers of W, respectively. The iron loss of the reactors is very small, and show a high value of the quality factor at a high frequency region.

View full abstract

This paper deals with the design, based on the finite element method, of a high-frequency induction coil shape used in an electromagnetic heating device. In the case of gas heating, the center of a pan placed on the device can be effectively heated. In the case of heating with a conventional exciting coil, the heating condition is not uniform. Therefore, we improved the exciting coil shape for uniform heating by means of three-dimensional eddy current analysis under the thin plate approximation and by conducting an experiment.

View full abstract

We developed a composite metal-backed single-layered electromagnetic wave absorber of (spinel-type Ni-Zn-ferrite, SiO₂) composite materials, which operates in the frequency region from 1 to 4 GHz. A composite ferrite with a suitable thickness has the higher absorption frequency range than a Ni-Zn ferrite absorber, and the center absorption frequency can be changed by changing the mixing ratio. There are a few changes in the absorption band due to the change in the thickness in the composite ferrite.

View full abstract

Magnetic polymer compounds containing carbonyl-iron particles surface-treated with a silane coupling agent were used to fabricate electromagnetic wave absorbers for the quasi-microwave band (1−3 GHz). The coupling treatment changed the surface property of the particles from hydrophilic to lipophilic, and simultaneously decreased the electrical conductivity on the surface of the particles. These polymer compounds can thus contain a large volume (up to 59 vol%) of the particles, and as a result show high permeability and permittivity (7 and 45, respectively, at 2 GHz) without generating much conductivity. These magnetic and electrical conditions—high permeability and permittivity with low conductivity—result in a wave absorber that is thinner (about 2 mm thick) than a conventional spinel-type ferrite absorber (about 7 mm thick).

View full abstract

Automatic magnetic measurement for bar specimens of soft magnetic materials was studied by means of the yoke method. A new magnetizing apparatus was designed to reduce to zero the difference between the magnetic flux densities induced in the center and the end search coil, in order to correct the self-demagnetization. This method allows accurate, magnetic measurements to be made for bar specimens of magnetic pure iron, as well as for the conventional ring specimens. On the other hand, a quicker measurement speed of the hysteresis loop and a larger sectional area shows an increase in the apparent coercive force due to the phenomenon of the delay of magnetization in this measurement method.

View full abstract

One of the merits of permanent magnetic gears is that they can be product compactly. However, they have the demerit that the gear can not control the magnetic force between the driving wheel (pinion) and the driven wheel (gear) while maintaining a constant gap. This report describes the design and testing of electromagnetic gears and discusses the performance characteristics of an output-efficiency test.
The test showed that the current intensity to the magnetic pole I_c is larger and the output P₀ is higher. With a constant gap, the I_c is smaller and the transmitted efficiency η' is higher. One of the reasons for this is the magnitude of the magnetic flux density of the gap between pinion and gear. The value of η' is increased by decreasing the thrust load in accordance with the electromagnetic attractive force.

View full abstract

This paper presents a moving magnetic-flux-type sensor with shading coils for non-destructive testing (NDT). Generally, an eddy current is used to detect cracks and defects on the front surface of an object in NDT. However, it is much more difficult to detect them on the back surface of an object, because of the skin effect of the eddy current We have therefore developed a new sensor that uses the moving magnetic field generated by shading coils to detect cracks and defects on the back surface of an object. In this paper, experimental results are given and discussed to confirm the effectiveness of our new sensor.

View full abstract

Magnetic properties of electrical steel sheets are usually measured by using a single-sheet tester or Epstein‘s tester. The permeability is measured as a scalar value, that is, the relationship between the magnetic flux density B and the magnetic field intensity H in only the rolling direction, and the measured value represents an average for the specimens. However, it is well known that the local distributions of B and H are not uniform in a grain-oriented silicon steel sheet. The reasons for this are closely related to not only the magnetic properties, but also the local loss distributions. Thus it is necessary to measure the local B and H as vector variables and to estimate the local iron losses with those vector relations in constructed cores. In this paper, the relationship between the grain form and the local iron loss distribution is investigated in detail by using a grain-oriented 3% silicon steel sheet without insulator coating.

View full abstract

The thickness of the non-magnetic stainless steel overlay-clad of a simulated nuclear reactor pressure vessel (RPV) wall was nondestructively measured by a magnetic method. A part of the wall steel was magnetized with a two-pole magnetic yoke through the overlay-clad, and the magnetic field distribution on the surface of the overlay-clad was measured in the vicinity of one of the poles. The overlay-clad thickness was then determined from the center value and the half-width of the pattern of the measured magnetic field distribution. The thickness can be determined irrespective of the magnetic state of the steels used in the vessel.

View full abstract

A new method is proposed for estimating the depth and inclination angle of a crack in concrete. Amorphous powders were packed into a crack and excited by means of an alternating magnetic field. The exciting field was created by an E-form ferrite core with a pick-up coil centered between the two exciting coils.
The pick-up coil measured the magnitude and phase of the magnetic flux caused by the crack packed with amorphous powders. To model the crack, acrylic pipes of various lengths were prepared and packed with amorphous powders. The experimental results show that the inclination angle were clearly recognized, and the length of the crack was determined to be 30 mm.

View full abstract

We developed a non-destructive evaluation system consisting of (1) a SQUID integrated with a gradiometer and (2) a cryostat. Since the cryostat contains a thin vacuum space in order to provide high spatial resolution and reduce background noise, the system was used in an unshielded environment. It was found that the system could defect a change in magnetization due to applied stress in SUS304. Simulated subsurface flaws in an aluminum plate were also detected, using an eddy current technique. These results confirmed that the system has high sensitivity and spatial resolution.

View full abstract

This paper describes the calculated characteristics of a cylindrical linear induction motor (CLIM) for linear elevators. The magnetic flux density and starting thrust are analyzed by space harmonic analysis. The conclusions are as follows: (1) the equivalent pole pitch that influenced the characteristics of the CLIM is 73 mm; (2) the calculated value of the magnetic flux density obtained by space harmonic analysis agreed approximately with the measured value; (3) the characteristics of the starting thrust, calculated by space harmonic analysis, agreed with the measured characteristics with an error of less than 10 percent.

View full abstract

High-speed and high-precision hydraulic valves are required in industry. The authors have developed a linear servo valve (LSV) with a linear dc motor (LDM). This paper describes methods for designing the magnetic circuit, and for optimizing the mechanical time constant, of a moving-magnet-type LDM. The following results were obtained:
(1) The expression for the mechanical time constant of the LDM is derived by using the permeance analysis method. The proposed stucture of the LDM, which has a minimum mechanical time constant, is obtained by using the permeance analysis method and the finite element method (FEM).
(2) The static thrust of the LDM is calculated also by the permeance analysis method and the FEM. The calculated values of the thrust constant are 61.3 N/A and 62.8 N/A, respectively. The measured value of the thrust constant is 60.7 N/A.
(3) The measured and calculated values of the mechanical time constant obtained by the permeance analysis method, and the values calculated by the FEM, are 1.7 ms, 1.6 ms, and 1.5 ms, respectively.

View full abstract

The thrust of a linear DC motor (LDM) depends on the magnetic characteristics of the magnetic material used for the yokes. It is thus necessary to clarify the relation of this material and the thrusts in order to design LDMs easily. This paper considers the relation for a thin (under 40-mm-thick) LDM with a long stroke (105 mm) on the basis of measurements. The results of the measurements were as followings; (1) the maximum magnetic flux density shows a tendency to be saturated at 10 kA/m in the five measured magnetic materials, (2) the thrust constant was saturated, and (3) the saturated value of the thrust constant of LDMs is proportional to the maximum magnetic flux density of the magnetic material used for the center yoke.

View full abstract

The main advantages of giant magnetostrictive materials (GMM) are their large magnetostriction (2000 ppm), their low Young's modulus (30 GPa), and the fact that they are softer than ordinary metals. Therefore, giant magnetostrictive material is suitable for use in the sound source of an ocean acoustic tomography system that requires low frequency, high power, small size, and a wideband vibrator. Several years ago, the development of a giant magnetostrictive vibrator was reported [H. Wakiwaka et al.: J. Magn. Soc. Jpn., 16, 389 (1992)]. Giant magnetostrictive material was used for the actuator, even though the cost of the material is high. The material gives the actuator a much higher power density than other actuator's.
This paper describes a method for calculating the limitation of the maximum output of the giant magnetostrictive vibrator, using the material properties and measurement data of the vibrator.

View full abstract

The X-Y LIM, which is capable of two-dimensional drive, was combined with the technologies of magnetic and air levitation, as advocated by the authors. In this way, X-Y LIM magnetic levitation and switching systems were developed that are capable of non-contact transport of a magnetic levitation bogie-truck, as well as continuous switching. Various characteristics of the system are reported with the aim of using the system as a clean method of both in-process and inter-process transport. With respect to the switching performance of the system, this paper (1) confirms that the system is able to switch the bogie-truck in an arbitrary direction, (2) examines the switching characteristics of the bogie-truck, on the basis of testing and analysis, and (3) considers the control conditions necessary for the bogie-truck to perform a 90-degree switch, based on the switching characteristics.

View full abstract

This paper describes how the launch velocity of a solenoid-type electromagnetic launcher (EML) was simulated by combining the finite element method (FEM) with electric circuit and equation of motion, in order to improve the launch velocity of a projectile. The system constitution, the specifications of the projectile and solenoid coil, and the magnetizing curve of the carbon steel projectile are introduced, and methods for calculating the exciting current and launch velocity are derived. The inductance and the exciting current of the solenoid coil, the thrust, and the launch velocity of the projectile are simulated. The simulation results for the dependence of the exciting current and the launch velocity on the time, and the dependence of the launch velocity on the settled position are shown, and compared with the measured values. The calculation errors of the exciting current and the launch velocity with respect to the measured results are 3%, and 5%, respectively. These results confirm the feasibility of the simulation method.

View full abstract

This paper considers the generation of noise in a linear induction motor (LIM) used in a linear motor car. Frequency analysis of the electromagnetic vibration established that the noise in the LIM was generated mainly by the electromagnetic attractive force between the primary member and the reaction plate (RP) and that also by high-frequency flux due to the input current supplied from a VVVF inverter.

View full abstract

Methods for digitizing braille have been developed, because braille typed on paper deteriorates easily. This paper proposes a handy type of tactile display with a low-input-power linear electromagnetic solenoid (LES) used for a data terminal. The LES allows the data terminal to display many dots. The characteristics of a cylindrical LES were calculated by using the FEM analysis method. As found to be a result, the retention thrust and attractive thrust were 2.7 and 0.51 newtons, respectively. The attractive thrust/input ratio was thus found to be 391 millinewtons/watt.

View full abstract

This paper presents two kinds of drive units whose rotation axes are parallel to the exciting outer magnetic field. One is a hard-material-type that uses permanent magnets and silicon steel sheets to obtain the radial components of the field strength, and the other is a soft-material-type that uses the vibration of an amorphous ribbon to induce a rotational force. These drive units were developed to improve the freedom of movement of sensing devices. By combining the developed units with conventional ones, it will be possible to control the movement of devices freely by means of the outer magnetic field. In this paper, the basic characteristics of the drive units and their applicability are discussed.

View full abstract

A small flying element was constructed with hard magnetic films as wings and a soft magnetic wire as a body. The element is free from power supply cables and guides, and can fly within an alternating magnetic field. To elucidate a design guideline for the elements, theoretical analysis of the flapping motion of wings was carried out by developing and solving motion equations for the wings of the element. The theoretical results coincide very well with the experimental results, suggesting that the motion equations developed here are effective for expressing the actual motion of wings.

View full abstract

Switched reluctance motors have various desirable features, including simple construction, high reliability, and low cost. However, they have not yet been thoroughly analyzed, and an optimum design has not yet been realized. The present paper describes one method for calculating the static characteristics of a switched reluctance motor with six stator poles, four rotor poles, and three phases. For the calculation, we must obtain the variation of the inductance of a stator winding, because the inductance depends on the rotor position. Finite element method analysis is used to estimate the inductance. On the basis of the inductance-rotor position curves, we can calculate the static characteristics. We also discuss the dependence of the static characteristics on the arc width of both the rotor and the stator poles.

View full abstract

This paper describes a linear dc motor (LDM) with an exciting circuit that uses Reed switches to simplify the exciting circuit (R-LDM). The Reed switches are connected to both sides of the exciting coils, thus simplifying the structure of the exciting circuit The switches are changed by switching magnets arranged on the mover. The characteristics of the manufactured LDM are as follows:
1. To use the magnetic fluxes of the magnets effectively, an LDM with an odd number of poles is more suitable than one with an even number of poles.
2. The measured thrust constant is 2.13 N.
3. The value of the pole pitch which minimizes pulsating coefficient of the static thrust is 32 mm for the coil pitch of 40 mm and then pulsating coefficient of the static thrust is 4.6% at the maximum. It is clear that the pole pitch of the manufactured R-LDM may be given fittingly.

View full abstract

This paper deals with the static thrust characteristics of a cylindrical moving-magnet-type linear oscillatory actuator (LOA). The influences of the LOA size on the static thrust are investigated. The conclusions are as follows: (1) the maximum static thrust of the LOA occurs at x=2.5mm (the thrust constant is 3 N/A); (2) the thrust values calculated by the finite element method (FEM) show good agreement with the measured results, and the error is within 4 percent; and (3) the thrust of the LOA is mainly produced in the mover at the center and at two sides; and (4) the simulation of the static thrust by FEM, only adjusting either the outer diameter of the LOA to within the range from 8 to 16 mm or the diameter of permanent magnet from 3 to 8 mm, shows that the specifications of the prototype LOA are reasonable.

View full abstract