| 摘要 |
PROBLEM TO BE SOLVED: To improve detection precision in a metal state detector. SOLUTION: The metal state detector has: a first oscillation circuit 2 causing phase shift in oscillation waves according to a change in the inductance of a first detection coil L1; a second oscillation circuit 3 causing phase shift in oscillation waves according to a change in the inductance of a second detection coil L2; and a detection circuit 4 for detecting the phase shift in the oscillation waves outputted from the first oscillation circuit 2 and that in the oscillation waves outputted from the second oscillation circuit 3 to obtain a difference between them. The first and second detection coils L1, L2 have: a core for composing a closed magnetic circuit with the surface of a specimen to limit detection regions and detection directions on the surface of the specimen; and a coil wound around the core. The first and second detection coils L1, L2 are arranged to cross each other in a plan view in overlapping detection regions to detect a change in permeability in directions crossing each other. The first and second oscillation circuit 2, 3 are driven alternately to avoid interference. COPYRIGHT: (C)2009,JPO&INPIT
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