US Patent 7612558 Bill discrimination device and sensor for same

The sensor portion of the bill discrimination device has a variable inductance portion whose inductance changes depending on thickness of the bill and the magnetic ink amount, and an output signal generator for generating an output signal depending on the inductance of the variable inductance portion. The variable inductance portion includes a contact member which may have magnetostrictive behavior, and a coil portion disposed about the perimeter thereof. The contact member is positioned so as to be subjected to pressing force of a spring via an auxiliary roller. When the pressing force received from the spring changes depending on the thickness of a currency bill, the magnetic permeability of the contact member will change and the inductance of the variable inductance portion will change. At the same time, the inductance of the variable inductance portion will also change depending on the magnetic charge of the currency bill.