| 摘要 |
PURPOSE: To obtain a magnetic material detecting device which does not require any permanent magnet for magnetizing a magnetic material nor expensive complicated magnetic shield for external magnetic fields. CONSTITUTION: A detecting device is provided with a sensor 1 which has a magnetic circuits 2 and 3 and at least two coils 4 and 5 and operates in accordance with the core saturation principle. A magnetic material to be detected by this detecting device is, for example, the magnetic ink of a bank note 11. Each magnetic circuit is composed at least of one air gap 2 and a ferromagnetic core 3. The magnetic material is positioned in the air gap 2. The sensor 1 measures the effective relative permeability μr' of the magnetic circuits. A generator 6 supplies a periodic exciting current i(t) which changes with time to the coils 4 and 5. The output voltage u (t) of the sensor 1 is inputted to a device 8 constituted of a cascade circuit composed of a band-pass amplifier 9 which detects higher harmonics and a voltmeter 10. This detector does not require any permanent magnet nor magnetic shield and can perform measurement quietly. |
