IEEE SENSORS JOURNAL, VOL. 7, NO. 2, FEBRUARY 2007 179 Low-Power Printed Circuit Board Fluxgate Sensor Jan Kubík, Lukᡠs Pavel, Pavel Ripka, Member, IEEE, and Petr Kaˇ spar Abstract—A new printed circuit board flat fluxgate sensor with integrated coils and amorphous alloy core was developed and its excitation parameters optimized for low-power consumption. The power consumption achieved with 10 kHz, 300 mA p-p pulse exci- tation with duty cycle 12.5% was only 3.9 mW, which is three times lower than that for sinewave B excitation. The sensor sensitivity reached 94 V/T. The required excitation bridge supply voltage was only 0.47 V. The low-cost low-power sensor has a temperature offset stability of 120 nT in the 20 to 70 C temperature range and 0.17%/ C open-loop sensitivity tempco due to the use of a new core embedding technique. The perming error due to 10 mT field shock was suppressed below 1.2 T. The short-time offset stability was 38 nT within 3 h. Thus the developed sensor is more precise and less energy consuming than a periodically flipped anisotropic magnetoresistance (AMR) sensor. The achieved parameters are sufficient for compass with 0.1 error. Index Terms—Fluxgate sensor, low power, printed circuit board (PCB). I. INTRODUCTION C LASSICAL fluxgates with wire wound coils are expensive and bulky. Recent efforts to minimize production costs and decrease the sensor size resulted in use of printed circuit board (PCB) technology [1], [2] or planar microtechnology [3]. All above-mentioned sensors use electroplating or electrode- position of core material. The quality (permeability, coercive force) of such materials does not meet the qualities of soft rapidly quenched tapes of amorphous alloys. The wet-etched amorphous alloy core was used to create a new type of PCB fluxgate sensor [4]. The miniaturized fluxgate sensors require a new type of low- power excitation, as classical excitation tuning cannot be used due to the high resistance of the excitation coil and thus low Q-factor of the excitation tank circuit. Excitation by short pulses to reduce the power consumption was already used for fluxgate sensor with flat coils [5]. First experience with pulse excitation of PCB fluxgate was described in [6]. The principal limitation of flat coil design compared to three-dimensional winding is poor magnetic coupling between the flat coils and the core. Manuscript received March 13, 2006. This work was supported by CTU, Na- tional Research Council, Prague, Czech Republic, under Grant 102/05/H032 and by the Ministry of Education, Youth and Sports of the Czech Republic re- search program under MSM6840770015. The associate editor coordinating the review of this paper and approving it for publication was Dr. Usha Varshney. J. Kubik waswith the Department of Measurement, Faculty of Electrical Engi- neering, Czech Technical University, CZ-16627 Praha 6, Czech Republic Tech- nicka 2. He is now with Tyndall National Institute, Cork, Ireland (e-mail: jan.ku- bikj@centrum.cz; jan.kubik@tyndall.ie). L. Pavel, P. Ripka, and P. Kaˇ spar are with the Department of Measurement, Faculty of Electrical Engineering, Czech Technical University, CZ-16627 Praha 6, Czech Republic Technicka 2 (e-mail: pavell@email.cz; ripka@fel.cvut.cz; kaspar@fel.cvut.cz) Digital Object Identifier 10.1109/JSEN.2006.886998 Fig. 1. Vitrovac 6025X racetrack core B-H loop measured at 10 kHz [6]. The proposed pulse-excited flat fluxgate sensor is intended for use in battery-operated precise navigation devices. The sensor is able to measure geomagnetic field with power consumption lower than 5 mW. II. MANUFACTURING PROCESS The process consists of separate core preparation and then core embedding into the prepared PCB. At first, the racetrack- shaped core was etched from 25 m thick Vitrovac 6025 X amorphous alloy sheet. The racetrack core shape was chosen for its high suppression of crossfields and improved sensitivity in longitudinal direction compared to the ringcore shape. The core is 30 mm long and 8 mm wide, and the racetrack width is 1.8 mm. The core’s B-H loop measured at 10 kHz excitation current showed a coercive force of 6 A/m and saturation flux density of 0.54 T (Fig. 1). Further measurements on the core samples indi- cated that the initial permeability ( ) was 26 000, maximum permeability was 72 000, and maximum differential perme- ability 150 000. The standard four-layer PCB manufacturing technology was used to prepare a sensor frame: three layers of 0.2-mm-thick DURAVER-E-Cu laminate and two layers of 0.065-mm-thick Prepreg solid-state adhesive in between the PCB layers were used. The core-shaped hole was milled into the inner layer of PCB laminate, and the etched core was inserted into this hole before bonding the layers together. Using this design minimizes the transfer of thermal expansion of PCB to the core material [4]. The coils are formed of copper routes on the outer layers of PCB and electroplated through-holes (vias). The sensor has four sections of windings (Fig. 2) to be used as excitation (two round sections, 2 15 turns, dc resistance 0.43 ), and pickup coils (two straight sections, 2 27 turns, dc resistance 0.64 ). The excitation coils are connected serially, thus totally 30 turns of excitation winding were used. The pickup coils are connected antiserially, forming 27 turns of pickup coil. 1530-437X/$20.00 © 2006 IEEE