Co/Pt multilayers were prepared on mica substrates with an Au or Pt layer as an underlayer. Surface probe microscope measurements revealed that the surface of Au underlayers is rather rough and that their surface morphology drastically changes with an increase in thickness. On the other hand, the surface of Pt underlayers was relatively smooth, irrespective of the thickness. The surface morphology of the Co/Pt multilayers was almost the same as that of the underlayers. Co/Pt multilayers as well as Au and Pt underlayers were textured with the (111) plane parallel to the film plane. The perpendicular magnetic anisotropy (PMA) became larger with enhancement of the (111) orientation, and the coercivity of Co/Pt multilayers on Pt underlayers increased with increasing PMA. On the other hand, the coercivity of Co/Pt multilayers on Au underlayers seems to depend on the surface roughness rather than the PMA.

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Superlattice structures and interlayer coupling between Co layers in Co/Ir superlattices were investigated. Co/Ir(001) superlattices were grown by means of an MBE system. X-ray diffraction patterns show that the superlattices have good coherency, good periodicity and low interdiffusion between Co and Ir layers. The easy axis of magnetization of the superlattices was parallel to <110> in the plane. Ir-thickness-dependent interlayer coupling was observed even at an Ir thickness of 5Å, and showed unperiodical oscillation. This anomalous oscillation could be considered as the result of multiperiodicity of the interlayer coupling in the Co/Ir(001) superlattice.

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The shielding effectiveness of an alternating magnetic field was studied experimentally and analytically by comparing shields made of grain-oriented silicon steel sheets with shields made of non-oriented silicon steel. Magnetic shielding in alternating fields became complex owing to anisotropic-frequency-dependent permeability and eddy currents. Shields with <100> axes cross-stacked showed higher shielding effectiveness and isotropic distribution. The analytical results obtained by 3-D FEM showed some discrepancies with the experimental results.

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Non-oriented 3% silicon steel sheets were cold-rolled to a thickness of 0.1 mm, and annealed in an argon atmosphere. Their magnetic properties varied according to the cooling conditions. Two directions of easy magnetization in samples were observed when they were annealed at a low cooling rate. A sample with two strong easy directions was also obtained through two step cooling: in the first step, the annealing temperature was 900°C, and the holding time was 1.5 hours, and in the second step, the annealing temperature was 500°C and the holding time was 5 hours. The magnetic induction at 800 A/m was 1.64 T in the rolling direction and 1.62 T perpendicular to the rolling direction, respectively.

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Fe-based amorphous alloys containing Al or Ti as impurities become surface-crystallized during casting, with a resultant deterioration in their soft magnetic properties. This phenomenon is known to be caused by compressive stress induced by surface crystallization, but there have been few systematic investigations of this compressive stress. In the present study, the compressive stress was found to range from 1 to 15 MPa, and is proportional to the ratio of the surface crystalline layer thickness to the ribbon thickness. The deterioration of the core losses has been evaluated. This result shows that the deterioration is mainly caused by the compressive stress induced by the surface crystalline layer.

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This paper described the application of an Fe-based nanocrystalline ribbons to a noise filter in the 1 MHz ∼ 1 GHz frequency range. A 10-μm-thick Fe_76.2Cu_1.0Nb_2.0Si_14.9B_5.9 amorphous ribbon was converted into an Fe-based nanocrystalline ribbon by annealing at 500°C∼ 600°C for 10 min. This ribbon exhibited high permeability and high impedance characteristics. It was confirmed that an Fe-based nanocrystalline ribbon noise filter with a 1/18th that of a conventional filter (ferrite core) exhibited the same noise attenuation.

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(CoFeB) -(SiO₂) amorphous magnetic films for magnetic cores of micro-magnetic power devices were deposited on glass substrates by a synchronous dual-rf magnetron sputtering method. The relation between the magnetic properties and resistivities of the films and core losses was investigated. Highly electrically resistive soft magnetic Co_66.6Fe_7.4B₂₆-SiO₂ films with low core losses in the high-frequency range were obtained by reducing the hysteresis losses. The films exhibited an anisotropy field of 40 Oe , a permeability of 200 and a saturation magnetization of 7.3 kG. The core loss of the films for a coercivity of 0.20 Oe and a resisitivity of 2200 μΩ cm was less than 1 J/m³ at 1 MHz, B_m = 0.1 T, as good as that of Co-based ultra-thin soft magnetic amorphous ribbons.

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In our previous study of Fe-Al-O high-resistivity granular films, we proposed a microscopic shape anisotropy model and successfully explained the behavior of the uniaxial anisotropy of the films. To confirm the validity of this model, the relations between the anisotropy fields and the stiffness constants of the films were investigated by domain observation. Fe-Al-O stripe samples with widths of 50 μm and 10 μm and thickness of 0.3 μm were prepared. Their uniaxial anisotropy fields were adjusted in the range from 0.5 to 162.5 Oe, and the easy axes were set perpendicular to the stripe direction. All the domains of these samples are of a flux closure type. From the observed domain periods, the domain wall energy and stiffness constants were calculated. It was found that the exchange stiffness constants along the hard axis were smaller than those along the easy axis and much smaller than that of the pure Fe. This result supports the proposed microscopic shape anisotropy model, and furthermore, implies that the films have a great advantage as thin-film cores in downsized elements such as recording heads and inductors.

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The high -frequency electrical properties of high -resistivity nanocrystalline magnetic films were investigated. Fe(Co-Fe)-Hf-O films had a nanostructure consisting of fine-grain bcc Fe(Co-Fe) and amorphous phase Fe-Hf-O. To clarify the high-frequency electrical properties of the nanocrystalline films, we measured their high-frequency resistivities. The electrical resistivities of Fe (Co-Fe)-Hf-O films were nearly constant up to 100 MHz.

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Laminated film structures composed of exchange-biased and nonmagnetic layers are proposed. Their anisotropy fields can be easily controlled by changing the thickness of the soft magnetic layer. In an anti-parallel-bias laminated film, a stable single-domain-like structure can be formed. The permeability exhibits a maximum value when the demagnetizing field in a patterned film is equal to the exchange-biasing one in a parallel-bias laminated film.

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Preparation of writing-head cores by the electroless plating method was investigated. Electroless CoFeB plating has poor selectivity of deposition onto a patterned surface; that is, film deposition occurred not only on the catalytic surface but also on the photoresist, which had no catalyst. To improve the selectivity of electroless CoFeB plating, the effects of agitation and additives were investigated. Deposition onto the photoresist was decreased by agitation, but was still observed. Some organic additives were found to inhibit deposition onto the photoresist, and CoFeB plating from a bath including that additive had good selectivity. By combining of these two methods, it may be possible to obtain coherent deposition onto the patterned surface of a writing-head core.

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The magnetic properties of electroplated CoNiFe films were investigated. Anomalous codeposition (suppression of Ni deposition) was observed in the CoNiFe electroplating process. Co₇₄Ni₁₇Fe₉ films showed high saturation magnetization (1.8 T), low coercivity (< 1.0 Oe), and low magnetostriction (+4 × 10^-6). The coercivity of CoNiFe films was decreased by addition of trimethylamine-borane (TMAB) to the bath, because this decreased their grain size. Co₇₄Ni₂₁Fe₅ films with lower magnetostriction (+1 × 10^-6) and low coercivity (< 1.0 Oe) were obtained by addition of TMAB to the bath. The resistivity and coercivity was unchanged after annealing at 300°C. The corrosion rates of CoNiFe films and TMAB-CoNiFe in a saturated NaCl solution were also investigated.

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Electrodeposited CoNiFe soft magnetic films with high B_s were investigated for use as head core materials. It was found that a film consisting of an fcc phase structure with low Fe content has low magnetostriction of +2∼+6 × 10^-6. When the film composition was fixed at Co₆₂Ni₁₂Fe₂₆, the operating conditions for obtaining soft magnetic properties were optimized It was found that soft magnetic thin films composed of fine crystals 10-15 nm in diameter were obtained in conditions of low pH (< 3.0) and low current density (< 40 mAcm^-2). In these operating conditions, a current efficiency of less than 80% with hydrogen evolution during the CoNiFe deposition was confirmed to be one of key factors for obtaining soft magnetic CoNiFe films with a suitably high B_s value. A typical Co₆₂Ni₁₂Fe₂₆ film had the following properties. B_s=2.0 T, H_c=1.7 Oe, and λ_s=+4.9×10^-6.

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Globus' model was used to investigate the domain structures of MnZn ferrites. The model assumes that the energy losses during a cycle in the expression of the hysteresis loop have two origins: the continuous pinning of the domain wall and the formation and destruction of a fraction of the wall surface. In the case of MnZn ferrites, the pinning force is proved to be negligible, and the wall energy derived from this model shares a temperature dependence with hysteresis losses. Although Globus' model postulates that a grain includes only one domain wall, our experimental results for samples with various average grain diameters indicate that at room temperature, grains with an average diameter of more than 8 μm would include more than two unit cells in which one domain wall moves. At higher temperatures, the difference in cell sizes becomes smaller as the magnetocrystalline energy K₁ approaches zero.

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We examined the effect of added MoO₃ on the initial permeability and other material characteristics of Mn-Zn ferrites in order to develop ferrites with high permeability. In recent years, Mn-Zn ferrites with high initial permeabilities of more than 24400 have been developed. Ferrites with these high initial permeabilities are used to miniaturize ferrite cores for communication pulse transformers.
We studied the effect of added MoO₃ on the initial permeability and investigated the relationship between the size of added MoO₃ particles and the physical properties of the ferrites.

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A new type of magnetic field sensor based on creation of the Faraday effect by rotation magnetization of YIG single crystals is described. The influences of both the Cotton-Mouton effect and cubic anisotropies on the sensor characteristics are also discussed. The linearity error of the sensor output was very small in external magnetic fields ranging of 0.02-200 Oe. The temperature dependence of the sensor output was obtained with an accuracy of ± 1 % between 20 °C and 120 °C.

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Photographic devices utilizing the pyroelectric effect have already been put to practical use. A wide-range photosensor (WRP) is a detector system using the pyromagnetic effect of a low-Curie-temperature magnetic film (LMF) with 1 μm. thickness. When light is directed onto the WRP, the latter absorbs its energy, which causes a magnetization change in the WRP. This change can be read out by a magnetoresistance element and converted into a voltage. The WRP emits a pulse in response to light with a wide range of wavelengths, from visible to invisible, and its peak value depends on the light intensity. Therefore, the WRP can be used in a radio meter and magnetic light remote control, as well as for magnetic infrared communication. This paper describes the preparation of the LMF, Hie construction of the WRP, and the light response characteristics.

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Amorphous FeCoSiB films with high saturation magnetostriction and excellent soft magnetic properties were studied to determine their strain sensitivity. The films were subjected to strain by bending of their substrates, which caused a change in the magnetic anisotropy of films via magnetoelastic coupling. The films exhibited a figure of merit F ≡ (θμ/θε)/μ (change in film permeability μ per unit of strain ε) of 1.2 × 10⁵, which is comparable to that of amorphous ribbons. To study the use of the magnetostrictive films as strain sensor elements, we prepared meander-patterned films by means of the photolithography and ion milling processes. The impedance change in the patterned films when strain was applied was measured in the frequency range from 1 MHz to 1 GHz. Reflecting the large value of F, the high-frequency impedance of the films was changed considerably: a change in impedance of 46% was observed at 100 MHz when a strain of 300 × 10^-6 was applied. It is also demonstrated that, by using the strain-dependent impedance, a small strain of 1 × 10^-7 can be detected by means of the film pattern.

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Many torque sensors are contact types or use specially processed shafts. However, such sensors suffer from various problems such as frictional wear, cost, and installation. This paper describes a sensor that detects the torque of non-special processed shafts by means of the inverse magnetostrictive effect, and shows the effectiveness of demagnetization and the possibility of non-contact measurement in low-carbon steel shafts. The output of the sensor was increased 2.37 times, and the hysteresis of the output was reduced to 1/14 by demagnetization.

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A method was investigated for measuring the value of B·dB/dx, which determines the magnetic force exerted on paramagnetic or diamagnetic substances. For this purpose, the change in the surface shape of fluids under inhomogeneous fields due to a phenomenon called the Moses effect, was used. When the space between two electrodes is filled with an electric conductive solution whose shape changes with the fields, the effective cross-section of the solution changes. As a result, the resistance between the electrodes also changes. The surface slope angle of an MnCl₂ solution was estimated for a wide range of B·dB/dx values, and the relationship between the B·dB/dx values and the resistance was calculated. Experimentally, we observed the resistance change expected according to the calculation. A system using two non-miscible liquids with different conductivities was also proposed for the detection of lower field gradients.

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In order to detect a minor reverse-side crack on a thick steel plate, it is necessary to develop a magnetic sensor with high sensitivity and stability. We developed a new rotational magnetic flux sensor with a differential search coil which consists of two three-axis search coils. A new crack estimation parameter is also presented. The experimental results show that the sensor can clearly detect miner reverse-side cracks. The new parameter was obviously affected by the properties of cracks such as the existing surface, inclination angle, and depth.

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This paper presents a moving-magnetic-field-type sensor with shading coils for detecting of cracks and defects on the back surface of an object. Numerical analysis by 2D-FEM improved the performance of the moving-magnetic-field-type sensor, and identification of cracks and defects was carried out by using an adaptive-network-based fuzzy inference system.

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The temperature properties of layered thin film magneto-impedance (MI) elements composed of FeCoSiB/Cu/FeCoSiB were investigated for use in a magnetic sensor that remains stable under temperature change. The properties of the layered thin film MI elements as deposited were changed by increasing the temperature or by establishing a temperature cycle of 25 °C-100 °C. When these MI elements were annealed under a magnetic field at the most suitable temperature, which was 150 °C lower than the curie tempaerature of the magnetic film, the change in the MI properties due to the temperature increase or the temperature cycle was decreased. In particular, the change in inductance due to the temperature increase was small when the Fe₄Co₇₄Si₈B₁₄ zero magnetostriction magnetic film was used in the layered thin film MI element.

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A sensitive twisting stress-impedance effect in a CoSiB amorphous wire (λ= -3 × 10^-6, 20 μm diameter, 10 mm length) is presented. The impedance in the wire changes by more than 50% for a twisting angle of ± 180°(1/2 turn). The impedance change occurs with the skin effect in the wire, and its twisting characteristic depends on the wire current frequency. The mechanisms of the twisting stress-impedance effect is analyzed, taking account of BH hysteresis loops in the wire’s circumferential flux path and a magnetization rotation model.

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This paper presents a new proximity sensing method for metals that uses a C-MOS IC MI sensor circuit with an amorphous wire head 30 μm in diameter and 1-2 mm in length with a coil. A sharp pulse field with a rise time of a few nano seconds is generated from the amorphous wire by a coil current and the wire axis, and induces a field with an eddy current at the surface of a metal specimen. The new metal sensor with a micro-size head and quick response is expected to be useful for non-destructive testing (NDT) of micro region in metals.

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The magneto-impedance (MI) characteristics of etched zero-amorphous wires with a diameter of 4.5-16 μm are investigated in comparision with those of amorphous wires with a diameter of 30 μm. The MI ratio decreased with decreasing diameter, while the magnetizing frequency at each maximum MI ratio and the starting frequency for the skin effect increased. The BH characteristics of the wires changed markedly with decreasing diameter owing to the increase in magnetic anisotropy along the wire axis, and a large Barkhausen flux jump was observed in thinner wires with a diameter of less than 10 μm . An MI sensor with a C-MOS multivibrator was constructed, containing a pair of micro-sized MI heads 0.7 mm in length.

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A low power consumption C-MOS MI sensor using auto bias and the pulse feedback technique is presented. The power consumption of the auto bias circuit, which is based on the asymmetrical MI effect of the amorphous wire, is less than 1 mW. On the other hand, the power consumption of conventional bias circuits that generate dc magnetic fields is more than 10 mW. The pulse feedback technique is useful for reducing the power consumption of the negative feedback circuit. The technique is achieved by switching of a current that flows through feedback coils. The linearity of field detection for the auto bias and pulse feedback C-MOS MI sensor is 0.2%/FS for ± 0.7 Oe. The power consumption of the whole circuit is about 12 mW for dc 0.5 Oe detection.

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This paper reports a nondestructive evaluation (NDE) method using amorphous wire MI sensors to determine the plastic deformation of steel samples. The distributions of the flux density on the surfaces of steel samples were measured. The flux density at the Lüders band was found to be clearly higher than that in non-deformed parts of the sample. The profile of contour lines for flux intensity is similar to the profile of Lüders lines. The magnetic signal from the Lüders band can be detected up to d (lift-off) = 50 mm, even for a sample covered with coating. The flux distribution for longitudinal direction of the sample was calculated, on the assumption that the magnetic poles are localized in the Lüders bands. The calculation results agree with the experimental data.

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We propose a selective excitation system of contactless power transmission for moving loads. The system detects the location of a coil relative to transmitter and receiver, only then the transmitter is located under the receiver. And can start excitation. In this way, the system can help solve the problems of contactless power transmission systems.

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We propose a design for a contactless power station system using meander-type coils. The coils have a pitch-interval parameter that gives the maximum induced voltage. The pitch-interval is an important parameter in coil design. The calculated result for the optimum pitch-interval provided us with a guidry principle in meander-type coil design.

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A new cutting method using a pulsed magnetic field has been studied Apiece of single-crystal silicon is wound with a secondary coil, and is placed in a primary coil. When a current flows in the primary coil, the secondary coil shrinks in the radial direction. We succeeded in cutting the piece of single-crystal silicon using that stress. The smaller the electric resistance of the coil, the larger the stress. The cross-section of a silicon crystal cut by thus method has small radiant steps.

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Current-feedback magnetic multivibrators are highly efficient and reliable. However, these circuits have no ability to protect themselves from overloading, and the oscillation frequency changes with the load current. We previously proposed an improved multivibrator with overload protection and frequency compensation. In this paper, the condition for cessation of oscillation and that for fixed frequency of oscillation are derived by using our model of bipolar junction transistors. This model takes account of power dissipation, because the common-emitter static forward current transfer ratio and the junction voltages depend on the junction temperature.

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This paper describes the equivalent circuit analysis of a noise-reduction transformer. The optimum design and quantitative analysis of noise-reduction transformers have not yet been clarified. To determine a method for realizing the optimum design of noise-reduction transformers, we discuss the noise attenuation characteristics of the noise-reduction transformer on the basis of both experiments and equivalent circuit analysis, taking account of the frequency characteristics of the circuit parameters. We also discuss the dependence of the noise attenuation on the variety of the load.

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In a previous paper, we proposed a bridge-connected magnetic circuit with parallel output winding made up with a toroidal core with a rectangular B-H loop, a U-form core with low permeability, and two diodes. The value of the magnetic saturation flux of the toroidal core apparently decreases when the value of the dc current flowing in the U-form core winding increases, maintaining the rectangular B-H loop. In this paper, we present a new ferro-resonant circuit constructed by using the bridge-connected magnetic circuit with parallel output winding. The amplitude of the output voltage of the ferro-resonant circuit can be easily controlled by adjusting the dc current of U-form core.

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In a previous paper, we proposed a reactor circuit comprising a combination of reactors, single-phase transformers, and resistances. The reactor circuit can remove the 5th-harmonic voltages from its three-phase output voltage. In this paper, we present a new bridge-type three-phase transformer using a three-leg core and a E-form core. Both the line and phase voltages of the three-phase voltage source are applied to the transformer windings. The 5th-harmonic component of the output voltage decreases, because the 5th-harmonic component due to the line voltage and that due to the phase voltage cancel each other out. We describe the operating principle of the bridge-type transformer and its application to a removable 5th-harmonic voltage transformer.

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By using an orthogonal-core-type variable inductor and capacitor, we will realize a simple, reliable, and high-quality voltage regulator. However, the nonlinear magnetization characteristic of the orthogonal core causes harmonics in the output current. Last year, in order to reduce the harmonic current of the variable inductor, we proposed an orthogonal core with wedge gaps. A trial three-phase 100 kVA variable inductor demonstrates that the variable inductor can be put to practical use in a 6.6-kV ac distribution system. For wide Appl.ication, it is necessary to establish a design method for the orthogonal core. This paper presents a method of calculating the characteristics an orthogonal core with wedge gaps.

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A planar parametric transfonner previously proposed by the authors has various desirable features, including voltage regulation, overload protection, and noise rejection. The dimensions of the center leg and the narrow paths near the slots influence the performance characteristics of the transformer. In this paper, the relation between the input and output voltage of the transformer is analyzed for various magnetic saturation curves of the magnetic paths.

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We present the magnetic characteristics of a compressed amorphous powder core developed in our laboratory and a boost converter using this core. The powder core has a higher saturated flux density and lower power dissipation than a conventional ferrite core. A boost converter using this powder core is highy efficient and very small.

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For biomagnetic measurements, it is important to understand the characteristics such as frequency dependence, fluctuation, and source of environmental low-frequency magnetic field noises. Biomagnetic signals, especially magnetoencephalogram and magnetocardiogram signals, always exist in the frequency range below several ten Hz. These signals are very weak in comparison with those of environmental magnetic noises. Such noises at low frequency are generated mainly by the transmitting and return currents of streetcars, movements of automobiles and elevators in geomagnetism, and vibrations of magnetically shielded rooms. In this paper, magnetic noise due to the movement of an object composed of magnetic materials is investigated by using a newly developed method of analysis. That combines the finite element method and an analytical method of calculating the magnetic fields produced by the magnetization in the object. The proposed method is verified by a basic experiment using simple steel boxes.

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We measured 3-D magnetoencephalograms(MEGs) of the magnetic fields evoked by somatosensory, auditory, and mixed stimulation of a human brain. The mixed stimulation consisted of auditory stimulation (AEF) and somatosensory stimulation (SEF). 3-D MEG measurement was carried out by using a 3-D second-order gradiometer with 39 channels, which can simultaneously detect magnetic field components perpendicular and tangential to the scalp.
In order to estimate source localization in a human brain by using frequency information, a short-term spectrua of these measured data were calculated by using an autoregressive (AR) model, and a time change in the power spectrum was analyzed (time-frequency analysis). It was found that time-frequency analysis is a useful method for estimating multiple sources overlapping in time.

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We carried out 3D vector measurement of magneto-cardiograms (MCGs) of normal subjects and subjects with myocardial infarction (MI) or premature ventricular contraction (PVC), using a 3D second-order gradiometer connected to 39-channel SQUIDs, which can detect the magnetic field components perpendicular to the chest wall (Bz) and tangential to the chest wall (Bx, By) simultaneously. We used principal component analysis in order to compare the frequency characteristics in the MCG waveforms of MI, PVC, and normal subjects. The results showed that the frequencies in the MCG waveforms of MI and PVC subjects were dominated by lower frequencies (less than 10 Hz) than in normal MCGs, and that the score proportion characteristic of Bx was different from those characteristic of Bz and By.

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We developed a multi-channel high-resolution SQUID magnetometer for measuring biomagnetic fields produced by small animals. Using this system, we measured magnetocardiograms (MCGs) of rats. The specifications of our system are as follows: pick-up coils 5 mm in diameter located on a 7.5-mm grid, a 15-mm gradiometer base-line, a one-turn pick-up coil, and a distance of 5 mm between the pick-up coil and the outside surface of the dewar. The field sensitivity was 1 OO-fT/√ Hz in the white-noise frequency. Five adult rats, ranging in weight from 0.2 to 0.4 kg, were used in the study. The rats were anesthetized intraperitoneally with nembutal (40 mg / 1 kg). The number of magnetocardiogram signals averaged 2000, with the QRS wave as the trigger. The topographies of P-waves, QRS-waves and T-waves of MCG were analyzed. We concluded that the system used in this study is useful for physiological studies of small animals.

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Pulsed electromagnetic fields (PEMFs) has been clinically used for treatment of fractures. However, the mechanisms for their anabolic effects have not been yet clarified. To investigate the underlying cellular mechanisms, we measured the ALPase (alkaline phosphatase) activity, the protein content, the collagen contents, and the non-collagen contents of mouse osteoblast-Iike cells, MC3T3-E1. The cells were placed at the center of a coil and exposed to train-pulsed magnetic fields at 15 Hz with a biphasic sinusoidal wave form at 230 μsec. The intensities of the magnetic fields were 100 mT. Stimulation continued for 3 days at 20 min per day. The results were (1) the ALPase activity was not affected by pulsed electromagnetic stimulation, (2) the protein content after 7 days was significantly higher than in the control, and (3) the collagen content increased and the non-collagen decreased in comparison with the control.
These data suggest that the pulsed magnetic stimulation may activate differentiation and matrix development in osteoblasts.

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The generation and detection efficiencies of magnetoelastic waves in partially-annealed-after-drawn amorphous FeSiB wires are studied as functions of axial and circumferential bias fields applied to the annealed portions. Larger hysteresis and robustness with respect to the bias field in wires with shorter annealed portions indicate that efficient and stable generation and detection of magnetoelastic waves without bias fields can be realized in partially annealed wires.

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This paper describes the influence of ac magnetostriction measurement on the vertical vibration, friction, and bend of a sample. Mechanical disturbances of the sample cause errors in the measurement, since the ac magnetostriction amplitude is less than 1 μm. To obtain an accurate measurement, the error caused by the disturbances is calculated. By taking accurate measurements, a plate on the sample decreases the bend, even when compressive stress is applied to the sample in the measurement direction.

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This paper presents a method for estimating the depth and inclination angle of a crack in concrete. Amorphous magnetic powders were packed into a crack and magnetized with an E-form ferrite core with a pick-up coil centered between the two exciting coils. To model the crack, acrylic parallelograms of various lengths and widths were prepared and packed with amorphous magnetic powders. The magnitude and phase of the magnetic flux caused by the crack packed with amorphous magnetic powders were measured. The experimental results show that the inclination angle could be clearly recognized, and the depth of the crack was determined to be 30 mm. The magnetic flux through the pick-up coil was analyzed by the Integration Element Method. The calculated values of the magnetic flux agreed approximately with the measured values.

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In order to establish a nondestructive method of estimating residual strains induced in structural components for buildings, the magnetization properties of stress-imposed SS400 steel were measured, using a tensile tester equipped with a single sheet tester. In the elastic region, the permeability increases with increasing tensile stress and reaches a peak at the beginning of the plastic deformation, whereas the coercive force decreases with increasing stress. In the plastic region, as the applied stress increases, the permeability decreases, while the coercive force increases. Monotonic decrease and increase as functions of the tensile strain are observed in the permeability and the coercive force, respectively. These findings suggest that changes in the permeability and the coercive force with strains can be used for nondestructive estimation of deterioration of structural materials.

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This paper proposes a new system for multi-frequency testing of conducting plates. Precise crack imaging was achieved by the use of spectrograms obtained from an eddy-current probe multi-frequency response and application of a neural network. Results showing very good sensitivity to small cracks in INCONEL600 specimens are presented

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A method of visualizing two dimensional magnetic flux density has been presented. This method is realized through the use of an integrated search coils; that is, m arrayed search coils with n small coils serially connected are arranged with a Δθ pitch in the r-θ plane. The output voltage of these coils is used to reconstruct the objective flux distribution numerically. This is based on the projection method, which is used in the computed tomography (CT). At first, the basic principle is explained for a unit coil composed of n coils, and a scheme for reconstructing the flux distribution by means of Fourier transformation is shown. To confirm this method, a simple examination was performed experimentally, and the resolution of the reconstructed distribution was tested by using two filter functions.

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In waste water treatment processes, a large pool for sedimentation is used for solid-liquid separation after biological treatment. As a substitute for this pool, we are developing a magnetic separator that has a rotating disk with Nd-Fe-B permanent magnets. Activated sludge flocs are magnetized by magnetic seeding using ferromagnetic fine particles. This paper describes a method of predicting the separation characteristics, based on calculation of the particle trajectory. As the flow-out ratio is very sensitive to the particle size, the calculation takes account of the particle diameter distribution. However the calculated results for the flow-out ratio are much higher than the experimental results. The reason is that the calculation is based on the particle diameter measurement which is not suitable for evaluating the condition of particle cohesion. Our next task is to develop a method of measuring particle diameters like that used in the magnetic separator.

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