Patent ID: 7888615

Claim:
A flat detector comprising: a first flat member and a second flat member both made of a nonmagnetic nonmetal, the first flat member and the second flat member being disposed to face each other with a space therebetween for transporting a medium, the medium having a shape of sheet; a first conductive wiring that generates an alternating magnetic field, the first conductive wiring being disposed on a surface of the first flat member facing toward the second flat member; a first layer made of a nonmagnetic metal and disposed at least on a surface of the first flat member opposite to the surface on which the first conductive wiring is disposed; a second conductive wiring that detects a signal generated by magnetization reversal of a magnetic material contained in the medium, the magnetization reversal being caused by the alternating magnetic field generated by the first conductive wiring, the second conductive wiring being disposed on a surface of the second flat member facing toward the first flat member; and a second layer made of a nonmagnetic metal and disposed at least on a surface of the second flat member opposite to the surface on which the second conductive wiring is disposed, wherein a thickness of the first flat member is set so that a strength of the alternating magnetic field at a contact surface of the first flat member and the first layer is 1 gauss or smaller.