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Sensors and Actuators A 151 (2009) 145–153

Contents lists available at ScienceDirect

Sensors and Actuators A: Physical

journa l homepage: www.e lsev ier .com/ locate /sna

esign and characterization of a microwire fluxgate magnetometer

. Andòa, S. Baglioa,∗, A.R. Bulsarab, C. Trigonaa

Dipartimento di Ingegneria Elettrica, Elettronica e dei Sistemi, University of Catania, V. le A. Doria 6, 95125 Catania, ItalySpace and Naval Warfare Systems Center, Code 71730, 49590 Lassing Road, San Diego, CA 92152-6147, USA

r t i c l e i n f o

rticle history:eceived 16 March 2008eceived in revised form 15 December 2008ccepted 16 February 2009vailable online 5 March 2009

a b s t r a c t

This paper deals with the characterization of fluxgate magnetometers that adopt a FeSiB microwire asmagnetic core. The proposed device has a number of peculiarities that make this sensor very interesting.In fact this magnetometer affords the detection of weak magnetic targets with a very high spatial res-olution and low power consumption. The readout strategy is based on the use of the “Residence TimesDifference”; the DC magnetic field information is derived from the temporal positions of the output

eywords:TD-fluxgateagnetometer

eSiB microwireicrowire fluxgate magnetometer

waveform spikes. In the paper an accurate device characterization is performed with particular regardsto sensor resolution, sensitivity and power consumption; moreover, some comparisons between the FeSiBmicrowire fluxgate and a “ribbon” Magnetic Alloy FR4-fluxgate, previously developed by the authors, arepresented. Finally exhaustive experimental characterization results demonstrate the possibility to usethe microwire fluxgate as a low power system (with high spatial resolution) operating with a sinusoidalbias current of 5 mApp.

. Introduction

Fluxgate magnetometers have always been of interest for theeasurement of very low static magnetic fields. The main advan-

ages of fluxgate magnetometers are high precision, good resolutionas low as a few pT with an appropriate observation period) andow noise floor, moreover, current technological solutions allowor low cost and small size implementations. Applications of theuxgate exist in many different areas such as military, geophysical,ecurity, automotive, bio-systems, with the target magnetic fieldanging from large to very small (10 nT to 1 pT) values. Additionalxamples, of typical and emerging applications, can be found ineference [1,2]. The magnetometer affords an innovative system tonalyze rock properties and measure the fall-out of particles (fol-owing a volcanic eruption), adopting the magnetic properties ofhe geophysical materials [3]. Fluxgate magnetometers, moreover,an be used to analyze traffic flow and also for biomedical appli-ations, e.g. magnetic bead detection for immuno-assays as well ashe detection of spotted magnetic beads for innovative DNA analy-

is [4]. The conventional readout strategy of these magnetometerss via “second harmonic”, i.e., detection of the output voltage in aual cylindrical core architecture [5]. Residence Times Differenceluxgates, with a time domain readout strategy, has several distin-

∗ Corresponding author. Tel.: +39 0957382325.E-mail address: salvatore.baglio@diees.unict.it (S. Baglio).

924-4247/$ – see front matter © 2009 Elsevier B.V. All rights reserved.oi:10.1016/j.sna.2009.02.029

© 2009 Elsevier B.V. All rights reserved.

guishing features such as a simple sensor structure, intrinsic digitalform of the output signal and a power consumption decrement withan increasing sensitivity demand.

The target magnetic field information is based on the conversionof voltage output signal into time domain signal.

In previous work, theoretical models and experimental setupsbased on the Residence Times Difference (RTD) readout have beenpresented; in particular, the fundamentals of the RTD readout strat-egy, its advantages, and fluxgate architectures have been discussedin [6]. The main advantage of this readout strategy is the conversionbetween the magnetic field information (in the amplitude domain),and the time domain, with high performance in terms of reliabilityand efficiency of signal processing. Recently, innovative technolo-gies and new materials open to novel routes to realize miniaturizeddevices via either MEMS or printed circuit board technologies thatadopt either a thick or a thin permalloy film core [7]; other realiza-tions have been made by using a high permeability microwire witha standard two coil architecture [8].

Similar ideas related to the time domain analysis can be foundin [9–11].

The common problems (magnetic noise increasing, power con-sumption due to large bias current, low sensitivity) are correlatedwith the miniaturization process. In practice an optimal RTD-

fluxgate requires high sensitivity, low resolution, low noise floor,and an optimal geometric design (focused on the target magneticfield distribution). The microwire fluxgate magnetometer is analternative solution based on the high permeability propertiesof 100 �m magnetic microwire. The main features that charac-

146 B. Andò et al. / Sensors and Actuators A 151 (2009) 145–153

al pic

tmatcFmbc

flt

moootis

Fo

Fig. 1. (a) RTD-fluxgate sensor structure; (b) typic

erize this magnetic material are sharp hysteresis, anisotropy,agnetostriction and material composition. The “wire-core”

rchitecture presents interesting features especially in terms ofhe (small) core dimension, coil density, high quality magneticoupling, high spatial resolution performance and high flexibility.urthermore, several of this advantages can be used to developiniaturized RTD-fluxgate magnetometer custom process-

ased with the possibility to adopt magnetic micro/nanowireore.

In this paper, the experimental characterization of the microwireuxgate magnetometer is presented, with an extensive analysis inerms of sensitivity, resolution, and power consumption.

In the experimental section a comparison between the proposedicrowire-magnetometer and the FR4-fluxgate, previously devel-

ped by the authors, is presented. In the final section, the results

f our experimental characterization demonstrate the suitabilityf the microwire-based design as a low power system; moreover,he characterization of the spatial resolution demonstrates the abil-ty of this device to sense very weak and localized magneto-staticignals.

ig. 2. (a) Relation between the positive and the negative stable states of the dynamic magnf the DC target signal on the potential function.

k-up coil output signal for a sinusoidal excitation.

2. The RTD-fluxgate magnetometer: working principle

In this section, an overview of the RTD-fluxgate magnetometeris presented, with more details reported in [12,13]. A RTD-fluxgatemagnetometer is based on the two coils architecture; this includes aprimary coil (excitation coil), a secondary coil (detection coil), withan amorphous ferromagnetic core having a hysteretic input–outputcharacteristic. When a time-periodic bias current Ie is forced inthe primary coil, a time-periodic magnetic field He parallel to thegeometry of the core will be generated (Fig. 1).

The dynamical response of a fluxgate magnetometer ferromag-netic core is derived from a bistable potential energy function,U(x). The double-well potential energy function is strictly corre-lated to the micromagnetic phenomena and is, typically, obtainedby approximating the collective motion of the core domain wall

within a mean-field framework; the dynamics are expressed viathe potential [14]:

U(x) = x2

2− 1

cln cosh[c(x + He(t) + Hx)] (1)

etization reported in the hysteresis loop and the potential function; (b) consequence

B. Andò et al. / Sensors and Actua

Ft

wefipUapro

�

ig. 3. Residence Times Difference working principle: (a) bias signal compared withhe coercive field Hc; (b) magnetization; (c) fluxgate output voltage signal.

here x(t) is the normalized magnetization, He is the sinusoidalxcitation magnetic field and Hx represents the target DC magneticeld; c (inversely proportional to the temperature) is a nonlineararameter which controls the topology of the potential function(x): the system becomes monostable for c < 1 corresponding ton increase in the core temperature over the Curie point. Then, theartial derivative of the double-well potential energy function with

espect to the magnetization x represents the dynamical behaviourf the (normalized) magnetization x(t) in the ferromagnetic core:

dx

dt= −x + tanh

[x + He(t) + Hx

K

]≡ −∂U(x, t)

∂x(2)

Fig. 4. Correlation between the double-well potential energy fun

tors A 151 (2009) 145–153 147

where � is the system time-constant, and K = 1/c the temperaturedependent control parameter. Fig. 2a shows a qualitative relationbetween the potential energy function U(x) and the hysteresis loop:the two saturation states of the core hysteresis loop correspond tothe two stable states of the potential function U(x). In the absence oftarget magnetic field, the hysteresis loop and the potential functionare symmetric, however the presence of an external DC target signalHx leads to a skewing of the hysteresis loop (Fig. 2b).

When the target field exceeds the positive and negative coer-cive fields (Hc and −Hc), the magnetization x evolves between itsstable saturation states. Under this hypothesis the device operatesas a static hysteretic nonlinearity (e.g. a Schmitt Trigger), with avery small time-constant; the target magnetic field Hx is appliedin the same direction as the excitation field He, a secondary coil isused as the pick-up coil, and the output voltage derived from thislatter coil is representative of the target magnetic field. The work-ing principle of the RTD-fluxgate is based on the exploitation ofthe information carried by the time position of spikes in the outputvoltage signal. The time intervals, T+ and T− (Fig. 3), identified bytwo successive peaks, represent the times spent by the core mag-netization in the two (stable) steady states. These time intervalsare called Residence Times. The Residence Time Difference is thequantity RTD = T+ − T−. The RTD is zero in absence of the externalDC magnetic field (Hx = 0) and it is non-zero for a non-zero targetsignal. The evaluation of the RTD information is based on the anal-ysis of the voltage signal vout, detected by the secondary coil: thisvoltage is proportional to the first derivative of the magnetizationand, typically, it appears as a sequence of sharp pulses. The esti-mation of the relative peak position leads to the evaluation of theRTD. In Fig. 3 a typical output voltage time evolution is shown tobetter explain the above readout strategy, while Fig. 4 shows thesynergy between the double-well potential energy function and the

Residence Times Difference readout.

A lot of effort have been previously paid for the developmentof “ribbon core” FR4-fluxgates [15]. The relationship between theRTD, the external magnetic field, and the sensitivity together withthe experimental setup have been presented, while a complete

ction and the Residence Times Difference readout strategy.

148 B. Andò et al. / Sensors and Actuators A 151 (2009) 145–153

it

3

aaCetotcrfi3

f

ogy while the table in Fig. 6b reports the constructive parametersof the magnetometer.

Fig. 5. Microwire fluxgate: input–output characteristic @ 80 Hz 40 mApp.

nvestigation of the optimal geometry to minimize the demagne-izing effect is discussed in [16].

. The microwire fluxgate magnetometer

The microwire fluxgate magnetometer is based on 100 �m FeSiBmorphous ferromagnetic core material. The ferromagnetic coresre produced by rapidly cooling alloys comprised of 80% Fe, Ni oro, and 20% P, Si, Al, C, B to obtain the desired magnetic prop-rties [17]. In particular, the FeSiB microwire is obtained usinghe in-water quenching technique with a typical diameter rangef 80–160 �m and cylindrical structure. Typically, the solidifica-ion process induces two magnetic domain regions: (1) an innerore, easy axis parallel to the wire axis, and (2) an outer shell withadial easy axis [17,18]. The internal stress induced by the solidi-cation process can be reduced through an annealing process at

50–400 ◦C.

The simplified realization steps can, then, be summarized asollows:

Fig. 6. (a) Microwire fluxgate magnetometer

Fig. 7. Characterization set-up.

• 100 �m diameter wire-coils (primary and secondary coils) arewound around a plastic structure (4 mm).

• A cylindrical glass-support (∼0.6 mm external radius and∼100 �m internal radius) is used to contain the 100 �m FeSiBfluxgate core.

The cylindrical glass-support is fixed to the center of the solenoidand the magnetic core is centered with respect to the cylindricalplastic support.

The experimental characterization of the magnetic behaviourof the microwire, adopted as core for our fluxgates, has been per-formed. Two coils have been used, to apply the magnetic field andto pick-up the derivative of the magnetic flux, respectively. In Fig. 5the integral of the output voltage (which is an estimation of the coremagnetization) is reported on the y axis vs. the applied magneticfield (estimated from the current driven into the coil).

Fig. 6a shows an RTD-fluxgate prototype in micro-wire technol-

The microwire fluxgate magnetometer shows interesting phys-ical characteristics in terms of magnetic and electric performance,mechanical flexibility, and high spatial resolution.

. (b) Microwire fluxgate characteristics.

B. Andò et al. / Sensors and Actua

FTTo

sp

gs

has been defined as

ig. 8. (a) Time response of the RTD signal in “zero field” working conditions. (b)ime averaged RTD over 1 s. (c) Averaged RTD computed over the observation time.he above graphs refer to a microwire fluxgate magnetometer driven by a currentf 20 mApp @ 80 Hz.

The mechanical flexibility property can be exploited for mea-

urement systems where the core is bent to form a closed magneticath that focuses on a small dimension target [11].

The wire core architecture is based on a long straight coil thatenerates a magnetic field concentrated in the center of a longolenoid; this geometry induces a large magnetic coupling that

Fig. 9. The mean square operator JiRTD for microwire fluxgate prototy

tors A 151 (2009) 145–153 149

greatly helps to reduce power consumption. The RTD expressionand the sensitivity for a sinusoidal bias signal can be easily com-puted from the following equations [19]:

RTD = 2ω

[arcsin

(Hc + Hx

He

)− arcsin

(Hc − Hx

He

)](3)

S = ∂

∂Hx�RT = 2

ω

[1/He√

1 − (Hc + Hx/He)2+ 1/He√

1 − (Hc − Hx/He)2

]

(4)

where Hc is the coercive field, Hx is the external target field andHe is the excitation magnetic field. In the next section experimen-tal results on the microwire fluxgate performance (sensitivity, RTDevolution, resolution) are reported with also some comparisonswith our (previously realized [19]) FR4-fluxgate.

4. Experimental results

The results of our characterization of the microwire fluxgatemagnetometer are presented in this section. The device perfor-mances, sensitivity and resolution have been estimated in differentoperating conditions. Our results are, then, compared with the onesobtained in the characterization of the FR4-fluxgate presented in[19].

The RTD-fluxgate characterization set-up is based on a cylindri-cal solenoid used to generate the target magnetic field, a three layerMetglas® [20] magnetic shield, and a conditioning circuit (Fig. 7)with a LabVIEW® routine to process the output RTD.

A complete characterization of the microwire device has beenperformed to define the operative conditions, in particular thedevice performance has been considered for a bias signal havingfrequency between 10 and 100 Hz and amplitude between 1 and50 mApp. These operative conditions are important in order to high-light the differences between RTD-fluxgate and the classical secondharmonic fluxgate magnetometer [1] which, typically, operates athigher frequencies and higher amplitudes of the bias signal.

Fig. 8c shows the evolution of Averaged RTD (RTD) obtained inthe observation time, at Hx = 0 A/m; as expected, the device con-verges to a steady state value (the offset shown is removed aftercalibration). The original raw RTD signal and its average with a fixedwindow of 1 s (1 s-RTD) are also shown in Fig. 8a and b, respectivelyfor the sake of completeness.

In order to evaluate the RTD fluctuations, a mean square operator

JRTDi = std(RTD

qi ) (5)

where std is the standard deviation operator, i stands for theobservation time and q counts the events on which the standard

pe operated by 10 mApp @ 40 Hz (a), and 20 mApp @ 80 Hz (b).

150 B. Andò et al. / Sensors and Actuators A 151 (2009) 145–153

Fig. 10. Sensitivity as a function of the observation time for the microwire fluxgate magnetometer (a) @ 40 Hz, 10 mApp of bias current and (b) @ 80 Hz, 20 mApp of biascurrent.

F magne

df

b

t(

@at1a

md

ig. 11. Resolution as a function of the observation time for the microwire fluxgate

eviation is estimated. Fig. 9 shows the mean square operator (5)or two operating conditions.

Fig. 10 shows the microwire fluxgate sensitivity in a small neigh-ourhood of Hx = 0.

By dividing the mean square operator J by the sensitivity ofhe device, an estimation of the device resolution can be obtainedFig. 11).

From the previous results, in case of a bias current of 20 mApp

80 Hz with an observation time of 30 s, a device sensitivity (insmall neighborhood of Hx = 0) of 0.03 �s/nT and a device resolu-

ion of 0.3 nT have been estimated. In the case of a bias current of

0 mApp @ 40 Hz a microwire fluxgate sensitivity of 0.1275 �s/nTnd a resolution of 0.6 nT have been estimated.

The last step of the experimental characterization of theicrowire device is represented by the transduction diagram repro-

ucing the behaviour of the target field Hx as a function of the

Fig. 12. The transduction diagram of the microwire fluxgate, using an observation

tometer (a) @ 40 Hz, 10 mApp bias current and (b) @ 80 Hz, 20 mApp of bias current.

time-based quantities. The models adopted for the calibration curveare discussed in [6–13]. Fig. 12 shows the results obtained for thetwo driving signals considered: 10 mApp at 40 Hz and 20 mApp at80 Hz, with an observation window of 30 s. No offset compensationhas been made in these graphs. The maximal distance betweenthe measures and the linear interpolating method has been esti-mated as: 0.54 �s @ 40 Hz 10 mApp and 0.41 @ 80 Hz 20 mApp. Theresults emphasize the possibility of adopting this magnetometer,with the 100 �m FeSiB core, for detection of weak DC magneticfields.

The performance of the system have been compared to the

FR4-fluxgate magnetometer (the “F3” prototype in [19]). Fig. 13shows the performance comparison between microwire core andMetglas® foil core FR4-fluxgate magnetometer.

The results emphasize the advantages of the microwire fluxgatein terms of resolution, due both to the lower level of the magnetic

window of 30 s. (a) @ 40 Hz, 10 mApp bias current and (b) @ 80 Hz, 20 mApp.

B. Andò et al. / Sensors and Actua

Fig. 13. Wire core vs. FR4-fluxgate technology: sensitivity and resolution.

Fig. 14. Perming effect and “reset” for the FR4-fluxgate. The reset signal is applied at startuand demonstrates the ability of.

Fig. 15. (a) Sensitivity and (b) resolution as function of the observation time for microwir

tors A 151 (2009) 145–153 151

noise due to the materials adopted for the core, and to the betterelectromagnetic coupling due to the intrinsic device architecture.In terms of sensitivity, a better performance is observed for theFR4 magnetometer, for which a value of S = 0.77 �s/nT has beenderived in [19] while, for the microwire fluxgate, a sensitivity ofS = 0.028 �s/nT is obtained from Fig. 12.

4.1. Optimal device performance vs. power consumption

The nearly uniform magnetic field generated by the microwirefluxgate and the large coil winding density give the magnetome-ter its high performance in terms of power consumption. In fact,while the lowest bias current for the FR4-fluxgate prototype is10 mApp (this value is strictly correlated with the planar coil archi-

tecture and high distance between the coils) here we have veryacceptable behaviours with the bias current as low as 1 mApp, there-fore reducing further the power demand. Several are the limitingeffects against the low power operation in fluxgate magnetome-ter, in particular the perming effect appears as an offset shift after

p and after the magnetic shock. The output shown is in “zero target field” conditions

e fluxgate magnetometer operated by 5 mApp @ 40–80 Hz, and 1 mApp @ 40–80 Hz;.

152 B. Andò et al. / Sensors and Actuators A 151 (2009) 145–153

olutio

asirstsmtip(iloi

dapaiflbtlpob[lt8

4

tctpptrfc

dne

Fig. 16. (a) Experimental set-up adopted for the spatial res

magnetic shock. The material hysteresis shape does not changeignificantly but the applied field required may be higher than thenitial full-scale range. This problem can be removed by periodicallyegenerating the magnetic core via the amplification of the drivingignal for a very short period. The consequence of this procedure iso work outside the region of maximum sensitivity but it is a “onehot” procedure to be time by time performed to “regenerate” theagnetic properties of the core. Some experimental results related

o this procedure for recovering from magnetic shock are reportedn the following Fig. 14 with reference to the FR4-fluxgate: the out-ut RTD is shown in a zero field condition both before (a) and afterb) the application of large magnetic shock (400 �T). A large offsets observed as a consequence of the magnetic shock, the use of aarge “reset” bias field application brings the fluxgate back to itsriginal offset. No significant offset alterations have been observedn the case of microwire fluxgate.

In order to evaluate the power performance of the microwireevice, a complete characterization in terms of frequency rangend bias current amplitude has been performed. Fig. 15 shows theerformance of the microwire fluxgate in terms of its resolutionnd sensitivity close to the zero target signal condition. The exper-mental results demonstrate the possibility of using the microwireuxgate as a very low power system; in fact the bias current cane reduced to ∼1 mApp and one still observes proper device opera-ion. However, this latter operating condition results in a large noiseevel caused by a minimal electro-magnetic coupling between therimary and secondary coils, as observed in Fig. 15b. In the presencef the weak (comparable to the deterministic switching threshold)ias signal, the switching events become largely noise-dominated13]. Hence, even if a bias current value of 1 mApp represents theimit for the driving signal, an optimal operating conditions inerms of overall performances has been identified at 5 mApp @0 Hz.

.2. “Punctual” magnetic field sensing characterization

The wire core architecture represents a solution to detect “punc-ual” magnetic fields, i.e. very small targets having dimensionsomparable with the wire diameter. Fig. 16b shows the output ofhe microwire fluxgate (�RTD: difference between the actual out-ut and the “no signal” status) when a grid of points is defined on alane with a spacing of 35 mm (the generic corner n, m correspondso the spatial positions of a small permanent magnet used as theeference source); the magnetometer is placed at a fixed distancerom the plane (100 mm) containing the target and aligned with the

enter point.

The results reported in Fig. 16b emphasize the ability of theevice to discern among the different positions of the source sig-al with the largest output signal obtained for the center point, asxpected.

n characterization; (b) the RTD as a function of the points.

5. Conclusions

Our studies characterize the microwire fluxgate design in termsof sensitivity, noise level, power consumption, spatial resolution;a comparison to the FR4 magnetometer previously developed bythe authors [19] has also been developed. The performance of ourdevice @ 80 Hz 20 mApp and 30 s of observation time can be sum-marized as: sensitivity of about 0.03 �s/nT, resolution of 0.3 nT anda noise level of 0.01 �s. By comparison, the FR4-fluxgate, previouslydeveloped by the authors, has a sensitivity of about 0.77 �s/nT, res-olution of 1.1 nT and a noise level of 0.75 �s. We thus note theadvantages of the FR4 prototype in terms of sensitivity, counter-balanced by high performance (in terms of resolution) of microwirefluxgate magnetometer. Moreover the experimental results demon-strate the possibility of adopting the microwire device in a lowpower system involving a very-low bias current; actually, for thedevice considered the optimal set-up, in terms of electro-magneticcoupling and power consumption, is a bias signal of 5 mApp @ 80 Hz.The comparison between both technological approaches (FR4 andmicrowire fluxgates) shows the possibility of using the FeSiB corefor applications involving a low-resolution number (i.e. better per-formance) and very low (∼100 �m) target fields. Moreover, the highspatial resolution sensing performance makes the microwire devicesuitable for a large set of applications.

References

[1] P. Ripka, Magnetic Sensors and Magnetometers, Artech House, Boston, 2001.[2] F. Kaluza, A. Gruger, H. Gruger, New and future applications of fluxgate sensors,

Sens. Actuators A 106 (2003) 48–51.[3] B. Andò, S. Baglio, N. Pitrone, C. Trigona, A.R. Bulsara, V. In, M. Coltelli, S. Scollo,

A novel measurement strategy for volcanic ash fall-out estimation based onRTD Fluxgate magnetometers, in: Proceeding of IEEE I2MTC 2008, Victoria, BC,Canada, May, 2008.

[4] B. Andò, A. Ascia, S. Baglio, A.R. Bulsara, C. Trigona, V. In, RTD Fluxgate perfor-mance for application in magnetic label-based bioassay: preliminary results,in: Proceeding of IEEE–EMBC, New York, NY, USA, September, 2006.

[5] P. Ripka, Review of fluxgate sensors, Sens. Actuators A 33 (3) (1992) 129–141.

[6] B. Andò, A. Bulsara, S. Baglio, V. Sacco, Effects of driving mode and optimal mate-rial selection on a residence times difference based fluxgate magnetometer,IEEE Trans. Instrum. Meas. 54 (4) (2005) 1366–1373.

[7] B. Andò, S. Baglio, V. Caruso, V. Sacco, A. Bulsara, Multilayer based technology tobuild RTD fluxgate magnetometer, IFSA, Sens. Transducers Mag. 65 (3) (2006)509–514.

[8] B. Ando, A. Ascia, S. Baglio, A.R. Bulsara, V. In, N. Pitrone, C. Trigona, Resi-dence times difference fluxgate magnetometers for magnetic biosensing, in:J.A.C. Bland, A. Ionescu (Eds.), Biomagnetism and Magnetic Biosystems Basedon Molecular Recognition Processes, American Institute of Physics, USA, 2008,ISBN 978-0-7354-0547-9.

[9] P.D. Dimitripoulos, et al., Boosting the performance of miniature fluxgates withnovel signal extraction techniques, Sens. Actuators A 90 (2001) 56–72.

[10] J.-B. Kammerer, et al., A two-axis magnetometer using a single magnetic tunneljunction, IEEE Sens. J. 4 (2004 June) 313–321.

[11] G. Malinowski, et al., Fluxgate like 2D magnetometer based on a single magnetictunnel junction, Eur. Phys. J.-Appl. Phys. 30 (2005) 113–116.

Actua

[

[

[

[

[

[

[

[

[

B

Bi1Ee2mf

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14] H. Eugene Stanley, Introduction to Phase Transitions and Critical Phenomena,Oxford University Press, New York, 1971.

15] B. Andò, S. Baglio, A.R. Bulsara, V. In, V. Sacco, PCB fluxgate magnetometers witha residence times difference (RTD) readout Strategy: the effects of noise, IEEETrans. Instrum. Meas. 57 (1) (2008) 19–24.

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iographies

runo Andò received his M.S. degree in electronic engineering and the Ph.D. degreen electrical engineering from the University of Catania, Catania, Italy, in 1994 and

999, respectively. From 1999 to 2001, he was a Researcher with the Electrical andlectronic Measurement Group, Dipartimento di Ingegneria Elettrica, Elettronicadei Sistemi, University of Catania, where he became an Assistant Professor in

002. His main research interests are sensors design and optimization, advancedethodologies and smart transducers for bioapplications, sensing architectures

or impaired people, smart materials, nonlinear techniques for signal processing,

tors A 151 (2009) 145–153 153

with particular interest in stochastic resonance and dithering applications, anddistributed measurement systems. He is the coauthor of several scientific paperspresented at international conferences and published in international journals andbooks.

Salvatore Baglio received the “Laurea” and Ph.D. degrees from the University of Cata-nia, Catania, Italy, in 1990 and 1994, respectively. Since 1996, he has been with theDipartimento di Ingegneria Elettrica Elettronica e dei Sistemi, University of Cata-nia, where he is currently Associate Professor of electronic instrumentations andmeasurements. He teaches courses in “measurement theory and electronic instru-mentations,” and “integrated sensors and transducers.” Dr. Baglio is a senior memberIEEE and has served as an Associate Editor for the IEEE Transaction on Circuitsand Systems and a Distinguished Lecturer for the IEEE Circuits and Systems Soci-ety. He is author of more than 200 scientific publications. His research interests aremainly focused on measurement methodologies, smart sensors, microsensors andmicrosystems.

Carlo Trigona was born in Siracusa (Italy) in December 18th 1981. He received hisM.S. in Automation Engineering and Control of Complex System from University ofCatania, Catania, Italy in 2006. Since then he worked, as contract research engineer, atthe Dipartimento di Ingegneria Elettrica Elettronica e dei Sistemi (DIEES) of the sameUniversity where he is now Ph.D. student in Electronic, Automation Engineering andControl of Complex Systems (XXII cycle).He is author of several scientific papers. Hisresearch interests include microsystems and microsensors, fluxgate magnetometers,analog and digital electronic circuit designs.

Adi R. Bulsara received his Ph.D. degree in physics from the University of Texas,

Austin, in 1978. He is currently a Senior Researcher with the U.S. Navy’s Space andNaval Warfare Systems Center, San Diego, CA, where he heads a group that specializesin applications of nonlinear dynamics. He is the author of more than 100 articlesin the physics literature. His primary research interests include the physics of noisynonlinear dynamic systems, with a preference for applications. Dr. Bulsara is a Fellowof the American Physical Society.