H. Kikuchi

Motion capture system of magnetic markers using three-axial magnetic field sensor

We have developed a magnetic motion capture system consisting of up to two magnetic markers (Nd-Fe-B magnet) and four three-axial sensors. The position and orientation of the magnetic markers (dipole) are detected by measuring the magnetic field of markers. Position accuracy of one marker is about 3 mm when a marker is located 150 mm from a sensor, position accuracy of two markers is about 20 mm when the markers are located 150 mm from sensors. The most common error source is crosstalk between the cores of three-axial sensors.

Relationship between mechanical and magnetic properties in cold rolled low carbon steel

Structure-sensitive properties of minor hysteresis loops have been compared with Vickers hardness and ductile-brittle transition temperature (DBTT) obtained by Charpy impact test for cold rolled low carbon steel. Minor loops were measured with increasing magnetic field amplitude, step by step, and were analyzed in connection with the rolling reduction. We found that minor-loop coefficients deduced from relations between minor-loop parameters increase with increasing rolling reduction and have a simple relationship with both mechanical properties, Vickers hardness, and DBTT. We also found that these coefficients have a linear relation with coercive force obtained by the major loop. The present analysis method using minor loops is highly effective for nondestructive evaluation of ductile-brittle transition, in terms of the high sensitivity to lattice defects as well as low measurement field.

A high frequency carrier-type magnetic field sensor using carrier suppressing circuit

A highly sensitive high frequency carrier-type magnetic field sensor based on the giant magnetoimpedance effect has been developed. It has been combined with a high frequency carrier suppressing circuit to reduce carrier phase noise dramatically. Highly sensitive magnetic field resolution of 8.8/spl times/10/sup -7/ Oe (8.8/spl times/10/sup -11/ T) was demonstrated.

In situ magnetic measurements under neutron radiation in Fe metal and low carbon steel

Magnetic minor hysteresis loops of low carbon steel and Fe metal have been measured during neutron radiation at 563K in a 50MW nuclear reactor. For investigation of nucleation mechanism of copper precipitates and dislocation loops during neutron radiation, special attention was paid to minor-loop coefficients, which are deduced from simple relations between minor-loop parameters and are very sensitive to lattice defects such as dislocations, copper precipitates, and grain boundaries. We found that with increasing neutron fluence, the minor-loop coefficients of low carbon steel sharply increase and show a maximum at the fluence of 1×1019cm−2, followed by a slow decrease. The appearance of the maximum suggests the presence of two mechanisms of internal stress; while copper precipitates and dislocation loops in the matrix make the internal stress increase, those grown in the vicinity of dislocations compensate the internal stress of dislocations so as to minimize the elastic energy. On the other hand, the mi...

Effect of Microstructure Changes on Barkhausen Noise Properties and Hysteresis Loop in Cold Rolled Low Carbon Steel

Low carbon steel specimens cold rolled at ratios of 0-40% have been examined comprehensively by means of magnetic Barkhausen noise (MBN) method and a physical parameter obtained from a hysteresis loop, and their microstructures were studied by a transmission electron microscope. The behaviors of MBN and coercive force with reduction ratio were discussed in relation to microstructure changes. The MBN energy rises rapidly with cold rolling below 10% reduction, and saturates at higher reduction ratio. The peak in averaged rms voltage exhibited the same behavior as that of the MBN energy, whereas the coercive force and the magnetizing current when the averaged rms showed a peak increased monotonically with increasing reduction ratio. These phenomena are attributed to the combined effects of cell texture and dislocation density.

Micro Magnetic Thin - Film Sensor Using LC Resonance

This paper reports the performance of a new micro magnetic thin-film magnetic field sensor which makes use of LC resonance of the sensor element as well as the impedance change due to the permeability change of the magnetic film. A large impedance change of 105% was achieved at a carrier frequency of 100 MHz. The large change was realized when the LC resonance frequency of the sensor element was lower than the frequency at which the eddy-current losses increased.

Low-field magnetic characterization of ferromagnets using a minor-loop scaling law

A scaling power law relating hysteresis loss and remanence in minor hysteresis loops is proposed for the low-field magnetic characterization of ferromagnetic materials. We demonstrate that the law holds true for very low to an intermediate level of magnetization, associated with a universal exponent of ≈1.35, irrespective of types of ferromagnets and temperature, unlike the Steinmetz law with limited applicability. The coefficient in the scaling law shows almost the same behavior as coercivity and can be used for the evaluation of the magnetic quality of materials for which the Steinmetz law cannot be applied and/or low measurement field is necessary.

Effects of easy axis direction on the magnetoimpedance properties of thin films with uniaxial anisotropy

In this paper, we investigate the effects of easy axis direction against magnetoimpedance elements on stepped impedance properties. The angle between the easy axis and the element width is changed from 0° to 90°, and we examine the resulting impedance profiles. The magnetic field at which impedance is highest shifts to a lower field with increasing easy axis angles, which can be explained by a bias susceptibility theory. On the other hand, stepped impedance changes appear for the elements with an easy axis angle in the range of 35°–75°. We confirmed the stepped impedance property through our observations that those impedance jumps occur at transitional points of domain structure between single and multi domains by domain observations. The area where the impedance shows relatively low value and the element has multiple domains becomes narrower with increasing easy axis angles, which can be explained qualitatively on the basis of a simplified domain structure model.

Evaluation of Embrittlement in Isochronal Aged Fe-Cr Alloys by Magnetic Hysteresis Loop Technique

Fe-Cr alloys with different Cr contents were prepared by an arc melting technique. The alloys were isochronally aged in the range from 400 ℃ to 900 ℃ with 50 ℃ steps with a holding time of 100 hours. The ageing produced embrittlement in the alloys due to either the formation of a Cr-rich α’ phase or a σ phase at high temperatures. Magnetic Hysteresis Loop (MHL) and Micro-Vickers hardness were measured at each step to correlate the magnetic and mechanical properties. Coercivity and hardness of the alloys were increased and remanence decreased up to 500-550 ℃ due to formation of a Cr-rich α’ phase. Beyond 500-550 ℃ range, the coercivity and hardness decreased and remanence increased due to the coarsening or dissolution of the Cr-rich α’ phase. In the Fe-48% Cr alloy, formation of the σ phase at 700 ℃ reduced the maximum induction of the alloy significantly.

Feasibility Study of Application of MFL to Monitoring of Wall Thinning Under Reinforcing Plates in Nuclear Power Plants

This paper discusses a feasibility of magnetic flux leakage (MFL) method for estimation of wall thinning on pipes under reinforcing plates in nuclear power plants. The layered steel plates having a slit on its underlayer were prepared and the estimation of slit size by MFL method was examined. A single magnetic yoke is fixed on a layered specimen, and then a magnetic field sensor scans the leakage flux between the yoke legs for condition monitoring. The single magnetic yoke with a field sensor fixed at the center of the yoke is also scanned over layered specimens. It is clarified that estimation of the size of slit fabricated on underlayer of the layered specimen using profile of leakage field is possible: this indicates monitoring conditions of wall thinning to be occurred under reinforcing plates will be possible by MFL methods. Additionally, the effect of an air gap between yoke and first layer and a gap between first and under layer were also investigated experimentally.