A Tunable Magnetic Bias Circuit With Zero Static Power Consumption

Quasi-static magnetic fields can be used to modulate the magnetic and electrical properties of many magnetic materials, thereby enabling the operation of various magnetic devices, such as multiferroic magnetic field sensors and ferro/ferrimagnetic magneto-static wave filters. We present a magnetic circuit designed to produce a tunable dc magnetic bias field and detail its operating principle. The magnitude of the bias field can be electrically tuned to achieve a desired magnetic field; when not being switched, the achieved field is maintained with zero static power consumption. The magnetic circuit comprises two distinct types of permanent magnets: an NdFeB magnet with relatively high coercivity and an AlNiCo V magnet with relatively low coercivity combined with a tuning coil for adjusting its magnetization. Soft magnetic yoke pieces link the permanent magnets and also define an air gap. Pulses of current through the coil will adjust the remanence of the AlNiCo magnet, thereby changing the flux and field in the air gap. A magnetic bias circuit with a compact volume of 0.27 cm³ has been constructed, providing an adjustable dc magnetic field with a tuning range of 3.7 to 288.5 mT within a 1 mm air gap.