This paper presents our design, working modes and induced ME voltage behavior of a self-powered magnetoelectric sensor for micro-Tesla magnetic-fields based on Fe80Co2078Si12B10/PZT lam-i
Trang 1Contents lists available atScienceDirect Sensors and Actuators A: Physical
j o u r n a l h o m e p a g e :w w w e l s e v i e r c o m / l o c a t e / s n a
Magnetoelectric sensor for microtesla magnetic-fields based
on (Fe 80 Co 20 ) 78 Si 12 B 10 /PZT laminates
D.T Huong Giang∗, N.H Duc
Laboratory for Nano Magnetic Materials and Devices, Faculty of Engineering Physics and Nanotechnology, College of Technology,
Vietnam National University, Hanoi, E3 Building, 144 Xuan Thuy Road, Cau Giay, Hanoi, Vietnam
a r t i c l e i n f o
Article history:
Received 23 May 2008
Received in revised form 1 December 2008
Accepted 1 December 2008
Available online 11 December 2008
Keywords:
Magnetic sensor
Magnetoelectric
Magnetostrictive
Piezoelectric
Multiferroics
a b s t r a c t The magnetoelectric sensor based on (Fe80Co20)78Si12B10/PZT laminates is designed, fabricated and char-acterized for determining dc and ac magnetic-field strengths as well as field orientations At low dc
magnetic-fields, a ME-voltage response (dVME/dH) as high as 2 mV/Oe is achieved The linear relation
VME(hac) with a slope of dVME/dhacof 17 mV/Oe shows a great ability to self-powered detecting low ac
magnetic-fields The field orientation can be detected by using the sinusoidal dependence of the mag-netoelectric voltage The sensor is promising not only for microtesla magnetic-field sensing but also for magnetic biosensor applications
© 2008 Elsevier B.V All rights reserved
1 Introduction
Traditional Hall and magnetoresistive effect based
magnetic-field sensors always need to provide for the power supply, which
raises some deficiencies In this context, self-powered
magnetic-field sensors transferring directly magnetic energy into electrical
signal are of great interest Such sensors can be realized thanks
to the magnetoelectric (ME) effect, which is observed in
multi-ferroics and/or ferromagnetic-ferroelectric composites (hereafter
denoted as ME materials) In these materials, an electric
polariza-tion P can respond to an applied magnetic-field H, or conversely
a magnetization M can respond to an applied electric field
E In applied dc magnetic-fields, a ME sample undergoes
pol-ing that creates an electric field E =˛EH, where˛E denotes the
magnetoelectric voltage coefficient As a results, a ME-voltage
VME= tE (=˛E tH) appears between the surface of the sample
with thickness t Large magnetoelectric voltage coefficients ˛E
(=dE/dH = VME/hact) offer potential device applications as highly
sensitive magnetic-field sensors, microwave filters, transformers,
gyrators, etc.[1]
As regards the high magnetoelectric voltage coefficients,
multi-ferroic composites using magnetostrictive ferrites and rare earth –
transition intermetallic compounds have been studied intensively
∗ Corresponding author Tel.: +84 4 754 9332; fax: +84 4 754 7460.
E-mail address:giangdth@vnu.edu.vn (D.T.H Giang).
from the beginning of this century[2–8] In particular, the design, operation principles and characteristics of this new ME sensor were
also reported The value of magnetic-field responsibility dVME/dH as
high as 0.06 mV/Oe, 56 mV/Oe and 13 mV/Oe were achieved for ME-composite based magnetic-field sensors using the magnetostrictive
Ni0.5Zn0.5Fe2O4ferrite[2], Terfenol-D laminate[6]and Terfecohan thin film[7], respectively In addition, the ME-sensors can apply to determine the strength of ac magnetic-field In this case, Dong et
al.[8]have developed a promising generation of extremely low fre-quency magnetic-field sensors to achieve sensitivities of 10−7T and below in the mHz frequency range
This paper presents our design, working modes and induced
ME voltage behavior of a self-powered magnetoelectric sensor for micro-Tesla magnetic-fields based on (Fe80Co20)78Si12B10/PZT lam-inates We will show that our sensor can be applied to measure the strength of both dc and ac magnetic-fields as well as magnetic-field orientation
2 Sensor construction
The ME composite under investigation is formed by using self-fabricated melt spinning 5 mm-wide and 30m-thick magne-tostrictive (Fe80Co20)78Si12B10ribbon sheets magnetized along the longitudinal (or length) direction and an out-of-plane poled
piezo-electric PZT plate (APCC-855) with thickness tPZT= 200m supplied
by the American Piezoceramics Inc The optimum design for the ME composite based magnetic-field sensor is realized with the configu-ration using two magnetostrictive 450◦C-annealed FeCoBSi ribbon 0924-4247/$ – see front matter © 2008 Elsevier B.V All rights reserved.
Trang 2Fig 1 Schematic illustrations of a ME sensor prototype based on the magnetostrictive/piezoelectric composite operating in the longitudinal–transversal (L–T) mode (left)
and the definition for the angle ϕ between the (longitudinal) applied magnetic-fields and (transverse) poled electrical polarization direction of the multiferroic FeCoBSi/PZT composite used in present sensor design (with double ribbon sheets on each outer side) (right).
sheets bonded on both two sides of PZT plate (Fig 1, left) Presently,
the FeCoBSi ribbon is known as a soft magnetostrictive material
with the (saturation) magnetostriction s∼ 70 × 10−6 and
(par-allel) magnetostrictive susceptibility= d /dH ∼ 1.5 × 10−6Oe−1.
Thanks to mechanically coupling between these components, when
the magnetostrictive layers are strained under applied in-plane
(and/or out-of-plane) magnetic-fields, the PZT plate will undergo a
forced strain In this case, the ME-voltage VME is induced across
the thickness of the piezoelectric plate Practically, the VME is
measured directly as a response of the ME composite to an ac
magnetic-field hac(=h0sin(2f0t)) in a dc bias field H (see alsoFig 1,
right)
Shown inFig 2are photographs of the ME based sensor
pro-totype Here, the coil generating the alternating field hac (called
as ac field coil) is directly wrapped around the ME composite
with dimension of 5× 6 mm (Fig 2a) For this construction, the
ac magnetic-field is always aligned in the PZT plane, i.e always
perpendicular to the (poled) electrical polarization In this
exper-imental setup, an electrical polarization is induced by a weak ac
magnetic-field hacoscillating at resonant frequency of 5 kHz in the
presence of a dc bias field H provided by an electromagnet A lock-in
amplifier (7265 DSP) is used to generate a controllable input
cur-rent to the ac field coil and to measure the output voltage (VME)
induced across the PZT layer
Fig 3 Sensor response as a function of bias magnetic-fields.
3 Sensor operations
The fabricated sensor can operate in a (dc and ac) magnetic-field strength sensing mode as well as magnetic-magnetic-field orientation sensing one To determine the strength of the dc magnetic-field, the sensor is simply used in the configuration of the dc
magnetic-Fig 2 Sensor construction: FeCoBSi/PZT laminate (a), internal structure of magnetic sensor where the coil generating an ac field directly wrapps around the ME laminates
Trang 3fields aligned parallel to the ac magnetic-field (i.e forϕ = 90◦) In
this case, the dc magnetic-field strength dependence of the
ME-voltage of the sensor measured in hac= 4 Oe is presented inFig 3
It can be seen from this figure that the signal increases in a near
linear manner with increasing H over the range 0 < H < 100 Oe and
gradually approaches to the maximum value of about 220 mV,
cor-responding to a value of the magnetoelectric voltage coefficient
˛E= 2050 mV/cm Oe With further increase of the field, the VME
decreases gradually and falls to zero when the field increases up to
350 mT This observation can be understood in term of the strong
relation between ME voltage and the magnetostrictive
susceptibil-ity (d /dH) of the magnetic ribbon, VME∼ d/dH[5] The vanishing of
VMEcan be attributed to the magnetostriction saturation tendency
at high field (d /dH = 0)[7] For low magnetic-field sensing
applica-tions, it is worth noting that the sensor exhibits an extremely high
voltage response (dVME/dH) of about 2 mV/Oe This result is rather
promising for micro-Tesla magnetic-field sensors, in particular, for
magnetic biosensors, where only a sensitivity of about 2V/Oe
is achieved by using traditional Hall and magnetoresistive effects
[9,10]
Fig 4 Demonstration of ability of the ME sensor to detect low ac magnetic-fields
in the bias magnetic-field of 65 Oe measured in the case of ϕ = 90 ◦
Fig 5 The V(ϕ) dependence of the sensors measured in different magnetic-field values (left) and the data plotted as a function of effective in-plane magnetic-field component
H = Hsinϕ and compared to the those (straight line) measured for ϕ = 90◦ as given in Fig 3
Trang 4Fig 4illustrates the induced ME-voltage as a function of hacin
the bias field H = 65 Oe measured in the configuration ofϕ = 90◦.
Clearly, the VME is linearly proportional to hac and exhibits the
value of dVME/dhac= 17 mV/Oe The value of the ME voltage varies
depending on the magnetic biases and frequencies The inspection
of this result, however, reveals an ability to detect low ac
magnetic-field strength In this case, the sensor is actually self-powered, and
provides direct conversion of ac magnetic-field into an electrical
signal
The sensor response is sensitive not only to the strength of
magnetic-fields but also to their orientation Shown inFig 5(left)
are plots of the ME voltage as a function of angleϕ between external
dc magnetic-field and thickness direction (seeFig 1, right)
mea-sured at several bias magnetic-fields of H = 80, 140, 200 and 500 Oe.
It is seen from this figure that although the VME(ϕ) exhibits
dif-ferent variation tendencies, but for all cases the ME signal varies
periodically with ϕ The VME(ϕ) is perfectly characterized by a
sinus behavior for H = 80 Oe (and/or magnetic-field strengths below
maximum appeared inFig 3) It changes to a trapezoid-, M- and
well-sharp in H = 150, 200 and 500 Oe, respectively These complex
VME(ϕ) peak inflection, however, can be described well in terms
of the effective in-plane magnetic-field component Heff= Hsinϕ
Indeed, the obtained VME(ϕ) data can be transferred into the plot
of VME(Hsinϕ) and presented inFig 5(right) Clearly, it reproduces
well the experimental data (solid line), which already reported in
Fig 3for magnetic-fields aligned in plane of the ribbon (i.e for
ϕ = 90◦) The periodical variation of the output signal with respect
toϕ opens the ability to use this sensor for detecting the orientation
of the external magnetic-field For this purpose, we prefer to apply
the results obtained in bias magnetic-fields less than 80 Oe, where
the sinus behavior was found
4 Conclusions
In summary, a magnetoelectric sensor based on (Fe80Co20)78
Si12B10/PZT laminates has been designed, fabricated and
char-acterized The sensor can operate to determine the dc and ac
magnetic-field strength as well as to sense the field orientation
The results have shown that at low dc fields, a ME-voltage response
(dVME/dH) as high as 2 mV/Oe is achieved Besides, a linear
rela-tion between the induced ME-voltage and ac magnetic-fields is
observed It reveals the ability of the sensor for self-powered
detect-ing low ac magnetic-fields In addition, by usdetect-ing a charge amplifier,
this magnetoelectric sensor can also be fully self-powered for
dc magnetic-field detection, i.e without any requirements of ac
magnetic-fields to modulating the signals Finally, the sensor
response is sensitive not only to the field strength but also to the
field orientation In this case the field orientation can be detected by
using the sinus behavior of the VME(ϕ) This sensor is promising not
only for microtesla magnetic-field sensing but also for magnetic biosensor applications For a real biosensor application to detect magnetic labels, this sensor is required to diminish in micrometer-size However, the project is still in progress
Acknowledgements
This work was supported by the Fundamental Research Program
of Vietnam under the Project 410.406 and the Vietnam National University, Hanoi under the project QC 07.07
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Biographies
D.T Huong Giang received her BSc degree in Materials Science from College of
Sci-ence, Vietnam National University Hanoi in 2001 and PhD degree in Physics from the Rouen University, France in 2005 Her research interests include magnetostric-tive, magnetoresistance and magnetoelectric materials, multiferroics, sensors and devices In 2006, she joined the Faculty of Engineering Physics and Nanotechnol-ogy at the College of TechnolNanotechnol-ogy, Vietnam National University Hanoi, where she is currently an assistant professor.
N.H Duc joined the Cryogenic Laboratory, University of Hanoi as researcher after
his graduation from the group in 1980 He obtained his doctor degree in the same group in 1988 He has received the French Habilitation in Physics at the Joseph Fourier University of Grenoble in 1997 and became a full professor of the Col-lege of Technology, Vietnam National University, Hanoi in 2004 In the period passed he extended his research on various aspects of magnetism, such as: 4f–3d exchange interactions; giant magnetovolume, magnetostrictive, magnetoresistive and magnetocaloric effects; magnetic phase transition; magnetic nanostructures; multiferroics; MERAM and biochips.