Miniature fluxgate sensors with symmetrical closed core elements on both sides of the planar coils were manufactured using standard microtechnology. The new sensors have shown substantial improvement over the standard single-sided micro.-fluxgate sensors: for the same field range the sensor noise was reduced 10-times to 20 nT rms (20 mHz … 10 Hz) and the perming suppressed below 5 μT, for field shocks of 6 mT. The maximum sensitivity for sinewave excitation was 32 V/μT for 1 MHz frequency and 200 mA p-p excitation current amplitude. Pulse shape of the excitation current allows use of high current peaks to suppress perming, while the rms value is low. Using a 20% duty factor squarewave excitation with 180 mA p-p amplitude, the sensitivity was twice that of the sinewave excitation, while the chip temperature dropped from 80°C to 40°C.
