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29. Impedance Measurement Using a Resonance Circuit for Detecting Steel Bars and Cables Inside Pliable Plastic Conduit Tubes Buried in Concrete Walls and Slabs.

Author

Yamazaki, K., Ishikawa, K., Haga, A., Muramatsu, K., Kobayashi, K., and Sasaki, H.

Subjects
STEEL bars, ELECTRIC impedance, NONDESTRUCTIVE testing, PARALLEL resonant circuits, ELECTRIC inductance, CONCRETE walls, CONCRETE slabs
Abstract

In order to detect steel bars and power cables inside pliable plastic conduit tubes buried in concrete walls and slabs during the renovation of old buildings, we have developed a new nondestructive inspection (NDI) system. This system, which enables high precision detection and easy handling at low cost, works by measuring the impedance due to the inductance change of a solenoid coil which exposes the test material to a magnetic field. In this system, the solenoid coil is connected to a compensating capacitor with a series-resonant circuit to reduce the impedance and multiply the impedance change by increasing the quality factor, Q, i.e., the ratio of the inductive reactance, ωL, to the coil resistance, R, which contributes to improving the signal-to-noise ratio for detection. This paper describes the validity of the design method of this NDI system. Firstly, the fractional deviation of inductance, δ, the inductance changes between with and without a steel bar and power cables were analyzed. The deviations due to the eddy currents and magnetization induced in the steel bars and power cables were computed through 3-D magnetic field analysis taking eddy currents at 5, 40 and 800 kHz into account. Secondly, the rates of change of impedance (RCIs) and phase angles were measured with the impedance meter of the newly developed NDI system. This system was designed so that the value of Q became roughly 200 and the resonance frequencies became about 5, 40 and 800 kHz. For steel bars, the predicted RCIs, which were calculated from the computed δs multiplied by the designed Q factor, roughly matched those measured. In case of power cables, the tendency of predicted RCIs were roughly in accord with those measured. The validity of the design method's detecting system was verified. In addition, the analysis and measurement proved that this NDI system can distinguish steel bars from power cables by the polarity of the phase angle. [ABSTRACT FROM AUTHOR]

Published
2010
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31. 3-D eddy current analysis in moving conductor of permanent magnet type of retarder using moving...

Author

Muramatsu, K. and Takahashi, N.

Subjects
*EDDY currents (Electric), *PERMANENT magnet motors, *BRAKE systems
Abstract

Focuses on a three-dimensional direct current steady state eddy current analysis of a permanent magnet type of retarder or braking system that rotates at high speed. Use of a moving coordinate system; Fundamental equations; Computed braking torque and its comparison with a measured one.

Published
1999
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33. Numerical and experimental investigations of current...

Author

Takahashi, N. and Muramatsu, K.

Subjects
*FINITE element method, *SUPERCONDUCTORS, *ALTERNATING currents
Abstract

Investigates the effect of the configuration of the joint between an alternating current (ac) superconducting cable and a normal conducting plate on the current distribution and the joule loss by using the three dimensional finite element method. Explanation about the analyzed joints between the superconducting cables; Method of analysis; Factors affecting current distribution and joule loss; Experimental details.

Published
1996
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