IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 57, NO. 1, JANUARY 2008 19 PCB Fluxgate Magnetometers With a Residence Times Difference Readout Strategy: The Effects of Noise Bruno Andò, Salvatore Baglio, Vincenzo Sacco, Adi R. Bulsara, and Visarath In Abstract—Residence times difference (RTD) fluxgates are very simple magnetic sensors that have low onboard power require- ments and an intrinsic digital (i.e., event based) form of the readout signal. These features make this class of devices competitive with the traditional second-harmonic fluxgate, which usually requires a higher power budget. Moreover, these detectors are characterized by high sensitivity and a suitably low resolution and noise floor when compared to the devices that are already on the market. Our work on RTD fluxgates has been widely presented in previous pa- pers. In this paper, an overview of this work, which deals with the development of models, prototypes, and readout electronics and the effects of electric and magnetic noise, is presented, together with some noticeable forward steps regarding the characterization of the prototype, which is developed in the standard printed circuit board (PCB) technology, and with a preliminary discussion on possible solutions to improve the performance of the device with an emphasis on the resolution. Index Terms—Fluxgate magnetometer, high sensitivity, low power, resolution, uncertainty. I. I NTRODUCTION F LUXGATE magnetometers have found application in fields such as space, geophysical exploration and map- ping, nondestructive testing, and assorted military applications [1]–[3]. Traditional second-harmonic fluxgate magnetometers suffer from the constraints of a high power budget or a large dimension (e.g., a large number of windings, a high cross- sectional core area, a high driving current) to assure an accept- able device sensitivity [4], particularly when the device size is reduced. Although these constraints, particularly the rapid increase of the magnetic noise floor with device dimensions, are at odds with the emerging needs of miniaturized devices, examples of suitable miniaturized fluxgates are available in the literature [5]–[8]. As an example, the printed circuit board (PCB) pro- totype presented in [5] shows a peak-to-peak noise level of 0.8 nT and a noise power density of 200 pT/ √ Hz at 1 Hz. The fundamentals of residence times difference (RTD) flux- gate magnetometers have been presented in [9] and [10]. As deeply evidenced, a very simple sensor structure, very low Manuscript received September 22. 2006; revised May 31, 2007. B. Andò, S. Baglio, and V. Sacco are with the Dipartimento di Ingegneria Elettrica, Elettronica e dei Sistemi, University of Catania, 95125 Catania, Italy (e-mail: bruno.ando@diees.unict.it). A. R. Bulsara and V. In are with the Space and Naval Warfare Systems Center, San Diego, CA 92152-6147 USA. Digital Object Identifier 10.1109/TIM.2007.908275 Fig. 1. Single-core RTD-based sensor design. onboard power requirements, and the intrinsic digital form of the readout signal are the main advantages of this strategy over the conventional (i.e., second harmonic) fluxgates, which require large excitation signals to improve the quality of the output signals. In this paper, a brief review of both methodological aspects and technological issues is presented, with the main effort dedicated to the characterization of a RTD fluxgate prototype developed in the traditional PCB technology. Criteria for im- proving the device performances and the innovative readout strategy are also presented. II. BRIEF REVIEW OF THE MINIATURIZED RTD FLUXGATE The readout scheme of an RTD fluxgate is given in Fig. 1 for the sake of convenience [9], [10]. The device uses a primary coil to produce the excitation field H e and a detection coil furnishing the output (voltage) signal of the magnetometer V out . The target field H x is applied in the same direction of H e . The magnetic core should, ideally, admit a sharp hysteretic loop that dominates the device dynamic [11]. Under the effect of the driving field, the core magnetization switches between its saturation states and the switching mech- anism can be described via the bistable dynamics that govern a 0018-9456/$25.00 © 2008 IEEE