- Email: [email protected]
DC magnetic sensor applications
Materials and Design 92 (2016) 906–910
Contents lists available at ScienceDirect
Materials and Design journal homepage: www.elsevier.com/locate/matdes
Characterization of Metglas/poly(vinylidene fluoride)/Metglas magnetoelectric laminates for AC/DC magnetic sensor applications S. Reis a,b,1, M.P. Silva a,1, N. Castro a,b, V. Correia a,b, P. Martins a,⁎, A. Lasheras c, J. Gutierrez c, J.M. Barandiarán c,d, J.G. Rocha b, S. Lanceros-Mendez a,e a
Centro/Departamento de Física, Universidade do Minho, 4710-057 Braga, Portugal Centro Algoritmi, Universidade do Minho, 4800-058 Guimarães, Portugal Departamento de Electricidad y Electrónica, Facultad de Ciencia y Tecnología, Universidad del País Vasco (UPV/EHU), P.O. Box 644, 48080 Bilbao, (Spain) d BCMaterials, Ibaizabal Bidea Bdng 500, Parque Científico y Tecnológico de Bizkaia, 48160, Derio, Spain e BCMaterials, Parque Científico y Tecnológico de Bizkaia, 48160-Derio, Spain b c
a r t i c l e
i n f o
Article history: Received 28 October 2015 Received in revised form 9 December 2015 Accepted 14 December 2015 Available online 17 December 2015 Keywords: Magnetoelectric Magnetic sensor AC/DC Linearity Sensitivity Resolution Accuracy Hysteresis
a b s t r a c t Polymer-based magnetoelectric materials show increasing interest for a large number of applications and, in particular, for the development of magnetic sensors. Nevertheless, relevant parameters such as sensitivity, accuracy, linearity, hysteresis and resolution have been vaguely or never discussed. This work reports on those parameters on a Metglas/poly(vinylidene fluoride)/Metglas magnetoelectric laminate. The sensitivity and resolution determined for the DC (30 mV·Oe−1 and 8 μOe) and AC magnetic field sensor (992 mV·Oe−1 and 0.3 μOe) are favorably comparable with the most sensitive polymer-based ME sensors. Further, the correlation coefficient, linearity and accuracy values are 0.995, 95.9% and 99.4% for the DC magnetic field sensor and 0.9998, 99.4% and 99.2% for the AC magnetic field sensor. Therefore, the magnetoelectric materials reported in the present study can be used for innovative AC/DC magnetic field sensors. © 2015 Elsevier Ltd. All rights reserved.
1. Introduction The magnetoelectric (ME) effect is defined as the variation of the electric polarization in the presence of an applied magnetic field (direct ME effect) or as the variation of the magnetization in the presence of an applied electric field (converse ME effect) [1–3]. This effect is present in materials through different principles: by the coupling of magnetic moments and electric dipoles in single-phase multiferroic materials [4] or by the elastic coupling between piezoelectric and magnetostrictive phases in composites [2,5–9]. Nevertheless, single-phase ME materials are not suitable for technological applications due to their low ME response (≈1–20 mV·cm−1·Oe−1), which typically appears at low temperatures (≈10 K) [6]. Among composite structures, laminated ME composites, comprising bonded piezoelectric and magnetostrictive layers, are the ones with the highest ME response, thus being the most suitable materials for technological applications [6,10,11]. The piezoelectric element in such composite structures can be ceramic or polymeric [6,12]. Despite the
⁎ Corresponding author. E-mail address: pmartins@fisica.uminho.pt (P. Martins). 1 Equal contribution.
http://dx.doi.org/10.1016/j.matdes.2015.12.086 0264-1275/© 2015 Elsevier Ltd. All rights reserved.
highest ME response found in ceramic ME composites, their low electrical resistivity, high dielectric losses, fragility and fatigue [6,13,14] are the main drawbacks that impair their widespread applicability [6]. Polymerbased ME materials do not reveal the aforementioned drawbacks of ceramic composites, emerging as an appropriate solution for applications due to their high ME coupling, easy fabrication, large scale production ability, low-temperature processing into a variety of forms and, in some cases, biocompatibility [6,15]. The ME coefficients found in polymerbased ME laminates as well as the broad range of the magnetic fields at which they respond, allow a large range of applications, in particular in the fields of magnetic sensors and actuators [6,16–18]. Due to the limitations found in some of the conventional magnetic field sensors, including low operational temperatures and high operational power [6,19], self-powered polymer-based ME sensors are of increasing interest and applicability [6,20,21]. On the other hand, vital characteristics of sensors which will determine their applicability, such as sensitivity, linearity, hysteresis, accuracy and resolution [22–25], have never been (or just partially addressed) for ME materials [26–28]. Once, these parameters are properly reported, ME based magnetic field sensors will show application potential in compasses, navigation, location, magnetic anomaly detection and in the medical/biological field [6,19,29], among others.
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Fig. 1. Right, ME measurement system with coils generating the HDC and HAC magnetic fields. Left, schematic representation of the ME laminated sample (below) and its corresponding image (above).
Thus, this works focus on the determination of such characteristics on an optimized polymer-based ME laminate composed of Fe64Co17Si7B12 (Metglas) and poly(vinylidene fluoride), PVDF. Such selection is related with the highest sensitivity and lowest noise of Metglas among all magnetostrictive phases [21,30], as well as its high magnetic permeability and piezomagnetic coefficient [31]. PVDF is selected as piezoelectric component due to its highest piezoelectric coefficient among polymers, stability, flexibility, large electrical resistivity, low dielectric losses and for the possibility of being processed in different shapes at low processing temperatures [15]. Additionally, PVDF/Metglas composites exhibit the highest ME response among polymer-based ME materials, being in this way the best composite for the present study [6].
2. Methods Polymer-based ME laminates were produced by gluing two equal amorphous magnetostrictive ribbons of Metglas with a Devcon 5 min epoxy (0.7 GPa Young Modulus) to both sides of a commercial poled β-PVDF film (Measurement Specialties, USA) in a magnetostrictive–piezoelectric–magnetostrictive(MPM) configuration, following the optimized conditions presented in previous studies [32–34]. The magnetostrictive ribbons (30 mm × 2 mm × 25 μm) were magnetized along the longitudinal direction (magnetostrictive coefficient λ = 25 ppm) and the piezoelectric layer (30 mm × 3 mm × 52 μm) was poled along the thickness direction (piezoelectric coefficient d33 = −33 pC·N−1). The voltage induced in the PVDF layer was measured with a lock-inamplifier (Stanford Research SR844).
Samples were measured in a system composed by two Helmholtz coils (Fig. 1), one generating the DC magnetic field (HDC) in the range 0 to 20 Oe, and another generating the AC magnetic field (HAC) in the range 0 to 0.2 Oe. ME measurements were performed by applying simultaneously a HDC magnetic field ranging from 0 to 20 Oe and a superimposed HAC field up to 0.2 Oe. The ME voltage response of the laminate was measured with a SR830 DSP lock-in amplifier. In order to determine the resonance frequency of the composite, HDC and HAC values were maintained constant (4.75 Oe and 0.1 Oe, respectively) and the frequency was changed from 20 kHz to 100 kHz. The DC magnetic field sensor characterization was performed by keeping constant HAC and frequency at 0.1 Oe and 48 kHz, respectively. On the other hand, the AC magnetic field sensor characterization was carried out by keeping constant HDC and frequency at 4.75 Oe and 48 kHz, respectively. The linearity of the sensor was determined through the correlation coefficient r2 and by the maximum deviation from the linear fit. The sensitivity was determined through the ratio between the minimum voltage variation divided by the DC magnetic field at the minimum voltage variation. The resolution of the sensor was obtained by the smallest variation of the output signal and the accuracy by calculating the largest deviation of three measurements with increasing magnetic field. Finally, the hysteresis was measured by calculating the largest deviation of cyclic measurements with increasing and decreasing magnetic fields. The accuracy was studied by increasing the DC magnetic field from 0.2 Oe–0.7 Oe three times and hysteresis by making three increasing and decreasing cycles between 0.2 Oe and 0.7 Oe. Linearity, hysteresis and accuracy of a sensor are typically expressed as a percentage of the Full-Scale Output (FSO), i.e., the ratio of the
Fig. 2. Magnetoelectric voltage response (V) as a function of: (a) frequency and (b) DC magnetic field.
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S. Reis et al. / Materials and Design 92 (2016) 906–910
Fig. 3. DC magnetic field sensor characterization: (a) linearity, (b) resolution and sensitivity (c) accuracy and (d) hysteresis.
maximum output deviation (Δ) divided by the full-scale output, specified as a percentage (Eq. (1)) [35–37].
%FSO ¼
Δ 100% FSO
ð1Þ
The full-scale output is 86.7 mV and 200 mV for the DC and AC characterizations at resonance (48 kHz) and 2 mV for the AC characterization at non-resonance (95 kHz) frequencies.
3. Results and discussion Fig. 2 shows the ME voltage response of the Metglas/PVDF/Metglas composite. Fig. 2 shows that the highest ME voltage response is obtained at a resonance frequency of 48 kHz (Fig. 2(a)). When the laminated composite operates in the resonance mode, the ME coupling is largely enhanced, generating a ME voltage output nearly two orders of magnitude higher than for non-resonant conditions [38]. Further, the ME voltage increases with increasing applied HDC magnetic field until 4.75 Oe
Fig. 4. AC magnetic field sensor characterization at the resonance frequency (48 kHz): (a) linearity, sensitivity and resolution; (b) accuracy/hysteresis. AC magnetic field sensor characterization at non-resonance frequencies (95 kHz): (c) linearity, sensitivity and resolution; (d) accuracy/hysteresis.
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Table 1 Metglas/poly(vinylidene fluoride)/Metglas magnetic field sensor parameters. Parameter
Sensitivitya (mV·Oe−1) Linearity (r2/FSO%) Accuracy (% FSO) Resolution (μ Oe) Hysteresis (FSO%) a
DC magnetic field sensor
AC magnetic field sensor
This work
Literature
This work Resonance
Our work Non-resonance
Literature
30 0.995/ 95.9 99.4 8 1.22
≈10 ref. [26] –
992 0.9998/ 99.43 99.2 0.3 –
40 0.998/ 98.6 97.7 1 –
10 ref. [27] –
– 70 ref. [28] –
– 10 ref. [27] –
(minimum voltage variation)/(DC magnetic field at the minimum voltage variation)
when a maximum ME voltage of 100 mV is reached (Fig. 2(b)). A maximum ME coefficient (α33 — determined from Eq. (2)) of 190 V·cm−1·Oe−1 is obtained for such DC magnetic field; α 33 ¼
ΔV t H AC
ð2Þ
where ΔV, t and HAC are the induced ME voltage, the thickness of the piezoelectric PVDF layer and the AC magnetic field, respectively. This behavior is related with the increase of the piezomagnetic coefficient until the optimum DC magnetic field is reached. With further increase of the DC magnetic field, a decrease of the induced voltage is observed, resulting from the saturation of the magnetostrictive response [39–41]. Linearity, sensitivity, resolution and accuracy tests were performed by increasing HDC in order to validate the use of the Metglas/PVDF/ Metglas as a DC magnetic field sensor (Fig. 3). Tests were performed under a 0.1 Oe AC magnetic field. The linearity of the response was obtained in the 0–3 Oe DC magnetic field range (Fig. 3(a)). After a magnetic field of 3 Oe, the ME response starts to reach saturation, which results in a loss of linearity. Resolution and sensitivity (Fig. 3(b)), accuracy (Fig. 3(c)) and hysteresis (Fig. 3(d)) were determined at low DC magnetic fields (0.2 Oe–0.7 Oe) since for such small DC magnetic fields, the electromagnetic noise will have more influence on the data, thus ensuring that the sensor will be tested in the worst possible conditions for low field signal detection. From Fig. 3a a correlation coefficient r2 of 0.995 and a linearity value of 95.9% FSO are obtained. The accuracy, hysteresis, sensitivity and resolution are 99.4% FSO, 1.2% FSO, 30 mV·Oe−1 and 8 μOe, respectively. The observed ME hysteresis (Fig. 3(d)) is related with the magnetic hysteresis of the Metglas alloy, that is more pronounced in the vicinity of the maximum permeability ≈0.55 Oe [42]. Further, the behavior of the ME composite as AC magnetic field sensor was evaluated and characterized at resonance (Fig. 4(a) and (b)) and non-resonance frequencies (Fig. 4(c) and (d)) with an applied DC field of 4.7 Oe. From the linear fit of the data presented in Fig. 4(a) a correlation coefficient r2 of 0.9998 and a linearity of 99.4% FSO is obtained for the AC magnetic field sensor working at the resonance frequency of 48 kHz. Additionally, the accuracy (Fig. 4(b)), sensitivity and resolution of the sensor are 97.9% FSO, 992 mV·Oe−1 and 300 NOE, respectively. At the non-resonance frequency of 95 kHz, r2, linearity, accuracy, sensitivity and resolution are 0.998, 98.6%, 2.3%, 40 mV·Oe−1, 1 μ Oe, respectively. Further, both for resonance and non-resonance conditions no hysteresis is detected (Fig. 4(b) and (d), respectively). The DC and AC ME sensor parameters are summarized in Table 1. The sensitivity and resolution values are compared with the highsensitivity polymer-based ME materials reported in the literature. Table 1 shows that the parameter values obtained for the AC/DC magnetic field sensor reported in this study are favorably comparable with the best ones reported in the literature in terms of DC sensitivity and AC accuracy. Further, the full characterization of the sensor main parameters is provided.
In this way, the suitability of the developed laminated polymerbased ME composite for magnetic field sensor applications is demonstrated [6]. 4. Conclusions A Metglas/poly(vinylidene fluoride)/Metglas ME laminate composite has been developed in order to validate its use as AC/DC magnetic field sensors. Sensitivity and resolution values are 30 mV·Oe−1 and 8 μOe for the DC magnetic field sensor and 992 mV·Oe−1 and 0.3 μOe for the AC magnetic field sensor. Such values are positively comparable with the ones reported in the most recent and sensitive polymer-based ME sensors. Additionally, the correlation coefficient, linearity and accuracy values for the DC (0.995, 95.9% and 99.4%) and AC (0.9998, 99.4% and 99.2%) magnetic field, demonstrating the applicability of polymerbased ME materials as innovative AC/DC magnetic field sensors, is reported. Acknowledgments and funding The authors thank the FCT – Fundação para a Ciência e Tecnologia – for the financial support under project PTDC/EEI-SII/5582/2014. P.M., V.C., S.R. and M.S. acknowledges support from FCT (SFRH/BPD/96227/ 2013, SFRH/BPD/97739/2013, SFRH/BDE/406 51542/2011 and SFRH/ BD/70303/2010 grants respectively). This work was also supported by Avel-electrónica Lda, Trofa, Portugal. A. Lasheras wants to thank the Basque Government for FPI grant. The authors thank the financial support from the Basque Government Industry Department under Project Actimat, (ELKARTEK Program). References [1] W. Eerenstein, N.D. Mathur, J.F. Scott, Multiferroic and magnetoelectric materials, Nature 442 (2006) 759–765. [2] G. Srinivasan, Magnetoelectric composites, Annu. Rev. Mater. Res. 40 (2010) 153–178. [3] K.P. Jayachandran, J.M. Guedes, H.C. Rodrigues, A generic homogenization model for magnetoelectric multiferroics, J. Intell. Mater. Syst. Struct. 25 (2014) 1243–1255. [4] G. Lawes, G. Srinivasan, Introduction to magnetoelectric coupling and multiferroic films, J. Phys. D. Appl. Phys. 44 (2011) (243001-). [5] C.-wW. Nan, M.I. Bichurin, S. Dong, D. Viehland, G. Srinivasan, Multiferroic magnetoelectric composites: Historical perspective, status, and future directions, J. Appl. Phys. 103 (2008) (031101-). [6] P. Martins, S. Lanceros-Méndez, Polymer-based magnetoelectric materials, Adv. Funct. Mater. 23 (2013) 3371–3385. [7] J. Ma, J. Hu, Z. Li, C.-W. Nan, Recent progress in multiferroic magnetoelectric composites: from bulk to thin films, Adv. Mater. 23 (2011) 1062–1087 (Deerfield Beach, Fla). [8] Y.Z. Wang, Influences of imperfect interface on effective magnetoelectric properties in multiferroic composites with elliptical fibers, Smart Mater. Struct. 24 (2015). [9] A. Bakkali, L. Azrar, A.A. Ali, Micromechanical modeling of magnetoelectroelastic composite materials with multicoated inclusions and functionally graded interphases, J. Intell. Mater. Syst. Struct. 24 (2013) 1754–1769. [10] S. Priya, R. Islam, S. Dong, D. Viehland, Recent advancements in magnetoelectric particulate and laminate composites, J. Electroceram. 19 (2007) 149–166. [11] G. Yu, H. Zhang, Surface effect on the magnetoelectric response of magnetoelectric layered composite with nanoscale thickness, Smart Mater. Struct. 24 (2015).
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[12] M. Rawat, K.L. Yadav, Dielectric, ferroelectric and magnetoelectric response in Ba0.92 (Bi0.5Na0.5)0.08TiO3–Ni 0.65Zn0.35Fe2O4 composite ceramics. Smart Mater. Struct. 23 (2014). [13] S. Jiansirisomboon, K. Songsiri, A. Watcharapasorn, T. Tunkasiri, Mechanical properties and crack growth behavior in poled ferroelectric PMN–PZT ceramics, Curr. Appl. Phys. 6 (2006) 299–302. [14] K.J. Loh, D. Chang, Zinc oxide nanoparticle-polymeric thin films for dynamic strain sensing, J. Mater. Sci. 46 (2011) 228–237. [15] P. Martins, A.C. Lopesa, S. Lanceros-Mendez, Electroactive phases of poly(vinylidene fluoride): determination, processing and applications, Prog. Polym. Sci. 39 (2014) 683–706. [16] M. Alnassar, A. Alfadhel, Y.P. Ivanov, J. Kosel, Magnetoelectric polymer nanocomposite for flexible electronics, J. Appl. Phys. 117 (2015). [17] S. Ju, S.H. Chae, Y. Choi, S. Lee, H.W. Lee, C.H. Ji, A low frequency vibration energy harvester using magnetoelectric laminate composite, Smart Mater. Struct. 22 (2013). [18] S.D. Moss, J.E. McLeod, S.C. Galea, Wideband vibro-impacting vibration energy harvesting using magnetoelectric transduction, J. Intell. Mater. Syst. Struct. 24 (2013) 1313–1323. [19] J. Lenz, A.S. Edelstein, Magnetic sensors and their applications, IEEE Sensors J. 6 (2006) 631–649. [20] Y. Zhao, C. Lu, Note: self-biased magnetic field sensor using end-bonding magnetoelectric heterostructure, Rev. Sci. Instrum. 86 (2015) 036101. [21] H. Zhang, C. Lu, C. Xu, Y. Xiao, J. Gui, C. Lin, et al., Improved magnetoelectric effect in magnetostrictive/piezoelectric composite with flux concentration effect for sensitive magnetic sensor, AIP Adv. 5 (2015) 047114. [22] R. Boll, K.J. Overshott, Sensors, Wiley, Magnetic Sensors, 2008. [23] F. Chen, Y. Jiang, L. Jiang, 3 × 3 coupler based interferometric magnetic field sensor using a TbDyFe rod, Appl. Opt. 54 (2015) 2085–2090. [24] T. Liu, Y. Chen, Q. Han, X. Lu, Magnetic Field sensor based on U-bent single-mode fiber and magnetic fluid, IEEE Photonics J. 6 (2014). [25] A. Chiolerio, I. Ferrante, A. Ricci, S. Marasso, P. Tiberto, G. Canavese, et al., Toward mechano-spintronics: nanostructured magnetic multilayers for the realization of microcantilever sensors featuring wireless actuation for liquid environments, J. Intell. Mater. Syst. Struct. 24 (2013) 2189–2196. [26] C.S. Park, D. Avirovik, S. Bressers, S. Priya, Low-frequency nanotesla sensitivity in Metglas/piezoelectric/carbon fiber/piezoelectric composites with active tip mass, Appl. Phys. Lett. 98 (2011). [27] Y.K. Fetisov, D.A. Burdin, D.V. Chashin, N.A. Ekonomov, High-sensitivity wideband magnetic field sensor using nonlinear resonance magnetoelectric effect, IEEE Sensors J. 14 (2014) 2252–2256.
[28] J.G. Tao, Y.Y. Jia, H. Wu, J.G. Yang, Low-frequency nanotesla resolution of magnetic field detection in Metglas/magnetostrictive/piezoelectric laminates, Adv. Mater. Res. (2014) 695–699. [29] S. Taghvaeeyan, R. Rajamani, Magnetic sensor-based large distance position estimation with disturbance compensation, IEEE Sensors J. 15 (2015) 4249–4258. [30] J. Jin, S.G. Lu, C. Chanthad, Q. Zhang, M.A. Haque, Q. Wang, Multiferroic polymer composites with greatly enhanced magnetoelectric effect under a low magnetic bias, Adv. Mater. 23 (2011) 3853–3858. [31] J. Zhai, S. Dong, Z. Xing, J. Li, D. Viehland, Giant magnetoelectric effect in Metglas/ polyvinylidene-fluoride laminates, Appl. Phys. Lett. 89 (2006) 083507. [32] M. Silva, S. Reis, C.S. Lehmann, P. Martins, S. Lanceros-Mendez, A. Lasheras, et al., Optimization of the magnetoelectric response of poly(vinylidene fluoride)/epoxy/ vitrovac laminates, ACS Appl. Mater. Interfaces 5 (2013) 10912–10919. [33] A. Lasheras, J. Gutiérrez, S. Reis, D. Sousa, M. Silva, P. Martins, et al., Energy harvesting device based on a metallic glass/PVDF magnetoelectric laminated composite, Smart Mater. Struct. 24 (2015). [34] M.P. Silva, P. Martins, A. Lasheras, J. Gutiérrez, J.M. Barandiarán, S. Lanceros-Mendez, Size effects on the magnetoelectric response on PVDF/Vitrovac 4040 laminate composites, J. Magn. Magn. Mater. 377 (2015) 29–33. [35] G. Singh, O. Guyon, P. Baudoz, N. Jovanovich, F. Martinache, T. Kudo, et al., Lyotbased low order wavefront sensor: implementation on the Subaru coronagraphic extreme adaptive optics system and its laboratory performance, Proc. SPIE Int. Soc. Opt. Eng. 9148 (2014) 1–9. [36] J.K. Spong, V.S. Speriosu, R.E. Fontana Jr., M.M. Dovek, T.L. Hylton, Giant magnetoresistive spin valve bridge sensor, IEEE Trans. Magn. 32 (1996) 366–371. [37] A.A. Kumar, Fundamentals of Digital Circuits, Prentice-Hall of India Pvt. Limited, 2003. [38] M. Guo, S. Dong, A resonance-bending mode magnetoelectric-coupling equivalent circuit, IEEE Trans. Ultrason. Ferroelectr. Freq. Control 56 (2009) 2578–2586. [39] X.W. Dong, B. Wang, K.F. Wang, J.G. Wan, J.M. Liu, Ultra-sensitive detection of magnetic field and its direction using bilayer PVDF/Metglas laminate, Sensors Actuators A Phys. 153 (2009) 64–68. [40] Y.S. Koo, K.M. Song, N. Hur, J.H. Jung, T.H. Jang, H.J. Lee, et al., Strain-induced magnetoelectric coupling in BaTiO3/Fe3O4 core/shell nanoparticles, Appl. Phys. Lett. 94 (2009). [41] Y.X. Zheng, Q.Q. Cao, C.L. Zhang, H.C. Xuan, L.Y. Wang, D.H. Wang, et al., Study of uniaxial magnetism and enhanced magnetostriction in magnetic-annealed polycrystalline CoFe 2O4, J. Appl. Phys. 110 (2011). [42] Z. Turgut, H. Kosai, T. Bixel, J. Scofield, S.L. Semiatin, J. Horwath, Hysteresis loss analysis of soft magnetic materials under direct current bias conditions, J. Appl. Phys. 117 (2015).
Contents lists available at ScienceDirect
Materials and Design journal homepage: www.elsevier.com/locate/matdes
Characterization of Metglas/poly(vinylidene fluoride)/Metglas magnetoelectric laminates for AC/DC magnetic sensor applications S. Reis a,b,1, M.P. Silva a,1, N. Castro a,b, V. Correia a,b, P. Martins a,⁎, A. Lasheras c, J. Gutierrez c, J.M. Barandiarán c,d, J.G. Rocha b, S. Lanceros-Mendez a,e a
Centro/Departamento de Física, Universidade do Minho, 4710-057 Braga, Portugal Centro Algoritmi, Universidade do Minho, 4800-058 Guimarães, Portugal Departamento de Electricidad y Electrónica, Facultad de Ciencia y Tecnología, Universidad del País Vasco (UPV/EHU), P.O. Box 644, 48080 Bilbao, (Spain) d BCMaterials, Ibaizabal Bidea Bdng 500, Parque Científico y Tecnológico de Bizkaia, 48160, Derio, Spain e BCMaterials, Parque Científico y Tecnológico de Bizkaia, 48160-Derio, Spain b c
a r t i c l e
i n f o
Article history: Received 28 October 2015 Received in revised form 9 December 2015 Accepted 14 December 2015 Available online 17 December 2015 Keywords: Magnetoelectric Magnetic sensor AC/DC Linearity Sensitivity Resolution Accuracy Hysteresis
a b s t r a c t Polymer-based magnetoelectric materials show increasing interest for a large number of applications and, in particular, for the development of magnetic sensors. Nevertheless, relevant parameters such as sensitivity, accuracy, linearity, hysteresis and resolution have been vaguely or never discussed. This work reports on those parameters on a Metglas/poly(vinylidene fluoride)/Metglas magnetoelectric laminate. The sensitivity and resolution determined for the DC (30 mV·Oe−1 and 8 μOe) and AC magnetic field sensor (992 mV·Oe−1 and 0.3 μOe) are favorably comparable with the most sensitive polymer-based ME sensors. Further, the correlation coefficient, linearity and accuracy values are 0.995, 95.9% and 99.4% for the DC magnetic field sensor and 0.9998, 99.4% and 99.2% for the AC magnetic field sensor. Therefore, the magnetoelectric materials reported in the present study can be used for innovative AC/DC magnetic field sensors. © 2015 Elsevier Ltd. All rights reserved.
1. Introduction The magnetoelectric (ME) effect is defined as the variation of the electric polarization in the presence of an applied magnetic field (direct ME effect) or as the variation of the magnetization in the presence of an applied electric field (converse ME effect) [1–3]. This effect is present in materials through different principles: by the coupling of magnetic moments and electric dipoles in single-phase multiferroic materials [4] or by the elastic coupling between piezoelectric and magnetostrictive phases in composites [2,5–9]. Nevertheless, single-phase ME materials are not suitable for technological applications due to their low ME response (≈1–20 mV·cm−1·Oe−1), which typically appears at low temperatures (≈10 K) [6]. Among composite structures, laminated ME composites, comprising bonded piezoelectric and magnetostrictive layers, are the ones with the highest ME response, thus being the most suitable materials for technological applications [6,10,11]. The piezoelectric element in such composite structures can be ceramic or polymeric [6,12]. Despite the
⁎ Corresponding author. E-mail address: pmartins@fisica.uminho.pt (P. Martins). 1 Equal contribution.
http://dx.doi.org/10.1016/j.matdes.2015.12.086 0264-1275/© 2015 Elsevier Ltd. All rights reserved.
highest ME response found in ceramic ME composites, their low electrical resistivity, high dielectric losses, fragility and fatigue [6,13,14] are the main drawbacks that impair their widespread applicability [6]. Polymerbased ME materials do not reveal the aforementioned drawbacks of ceramic composites, emerging as an appropriate solution for applications due to their high ME coupling, easy fabrication, large scale production ability, low-temperature processing into a variety of forms and, in some cases, biocompatibility [6,15]. The ME coefficients found in polymerbased ME laminates as well as the broad range of the magnetic fields at which they respond, allow a large range of applications, in particular in the fields of magnetic sensors and actuators [6,16–18]. Due to the limitations found in some of the conventional magnetic field sensors, including low operational temperatures and high operational power [6,19], self-powered polymer-based ME sensors are of increasing interest and applicability [6,20,21]. On the other hand, vital characteristics of sensors which will determine their applicability, such as sensitivity, linearity, hysteresis, accuracy and resolution [22–25], have never been (or just partially addressed) for ME materials [26–28]. Once, these parameters are properly reported, ME based magnetic field sensors will show application potential in compasses, navigation, location, magnetic anomaly detection and in the medical/biological field [6,19,29], among others.
S. Reis et al. / Materials and Design 92 (2016) 906–910
907
Fig. 1. Right, ME measurement system with coils generating the HDC and HAC magnetic fields. Left, schematic representation of the ME laminated sample (below) and its corresponding image (above).
Thus, this works focus on the determination of such characteristics on an optimized polymer-based ME laminate composed of Fe64Co17Si7B12 (Metglas) and poly(vinylidene fluoride), PVDF. Such selection is related with the highest sensitivity and lowest noise of Metglas among all magnetostrictive phases [21,30], as well as its high magnetic permeability and piezomagnetic coefficient [31]. PVDF is selected as piezoelectric component due to its highest piezoelectric coefficient among polymers, stability, flexibility, large electrical resistivity, low dielectric losses and for the possibility of being processed in different shapes at low processing temperatures [15]. Additionally, PVDF/Metglas composites exhibit the highest ME response among polymer-based ME materials, being in this way the best composite for the present study [6].
2. Methods Polymer-based ME laminates were produced by gluing two equal amorphous magnetostrictive ribbons of Metglas with a Devcon 5 min epoxy (0.7 GPa Young Modulus) to both sides of a commercial poled β-PVDF film (Measurement Specialties, USA) in a magnetostrictive–piezoelectric–magnetostrictive(MPM) configuration, following the optimized conditions presented in previous studies [32–34]. The magnetostrictive ribbons (30 mm × 2 mm × 25 μm) were magnetized along the longitudinal direction (magnetostrictive coefficient λ = 25 ppm) and the piezoelectric layer (30 mm × 3 mm × 52 μm) was poled along the thickness direction (piezoelectric coefficient d33 = −33 pC·N−1). The voltage induced in the PVDF layer was measured with a lock-inamplifier (Stanford Research SR844).
Samples were measured in a system composed by two Helmholtz coils (Fig. 1), one generating the DC magnetic field (HDC) in the range 0 to 20 Oe, and another generating the AC magnetic field (HAC) in the range 0 to 0.2 Oe. ME measurements were performed by applying simultaneously a HDC magnetic field ranging from 0 to 20 Oe and a superimposed HAC field up to 0.2 Oe. The ME voltage response of the laminate was measured with a SR830 DSP lock-in amplifier. In order to determine the resonance frequency of the composite, HDC and HAC values were maintained constant (4.75 Oe and 0.1 Oe, respectively) and the frequency was changed from 20 kHz to 100 kHz. The DC magnetic field sensor characterization was performed by keeping constant HAC and frequency at 0.1 Oe and 48 kHz, respectively. On the other hand, the AC magnetic field sensor characterization was carried out by keeping constant HDC and frequency at 4.75 Oe and 48 kHz, respectively. The linearity of the sensor was determined through the correlation coefficient r2 and by the maximum deviation from the linear fit. The sensitivity was determined through the ratio between the minimum voltage variation divided by the DC magnetic field at the minimum voltage variation. The resolution of the sensor was obtained by the smallest variation of the output signal and the accuracy by calculating the largest deviation of three measurements with increasing magnetic field. Finally, the hysteresis was measured by calculating the largest deviation of cyclic measurements with increasing and decreasing magnetic fields. The accuracy was studied by increasing the DC magnetic field from 0.2 Oe–0.7 Oe three times and hysteresis by making three increasing and decreasing cycles between 0.2 Oe and 0.7 Oe. Linearity, hysteresis and accuracy of a sensor are typically expressed as a percentage of the Full-Scale Output (FSO), i.e., the ratio of the
Fig. 2. Magnetoelectric voltage response (V) as a function of: (a) frequency and (b) DC magnetic field.
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Fig. 3. DC magnetic field sensor characterization: (a) linearity, (b) resolution and sensitivity (c) accuracy and (d) hysteresis.
maximum output deviation (Δ) divided by the full-scale output, specified as a percentage (Eq. (1)) [35–37].
%FSO ¼
Δ 100% FSO
ð1Þ
The full-scale output is 86.7 mV and 200 mV for the DC and AC characterizations at resonance (48 kHz) and 2 mV for the AC characterization at non-resonance (95 kHz) frequencies.
3. Results and discussion Fig. 2 shows the ME voltage response of the Metglas/PVDF/Metglas composite. Fig. 2 shows that the highest ME voltage response is obtained at a resonance frequency of 48 kHz (Fig. 2(a)). When the laminated composite operates in the resonance mode, the ME coupling is largely enhanced, generating a ME voltage output nearly two orders of magnitude higher than for non-resonant conditions [38]. Further, the ME voltage increases with increasing applied HDC magnetic field until 4.75 Oe
Fig. 4. AC magnetic field sensor characterization at the resonance frequency (48 kHz): (a) linearity, sensitivity and resolution; (b) accuracy/hysteresis. AC magnetic field sensor characterization at non-resonance frequencies (95 kHz): (c) linearity, sensitivity and resolution; (d) accuracy/hysteresis.
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Table 1 Metglas/poly(vinylidene fluoride)/Metglas magnetic field sensor parameters. Parameter
Sensitivitya (mV·Oe−1) Linearity (r2/FSO%) Accuracy (% FSO) Resolution (μ Oe) Hysteresis (FSO%) a
DC magnetic field sensor
AC magnetic field sensor
This work
Literature
This work Resonance
Our work Non-resonance
Literature
30 0.995/ 95.9 99.4 8 1.22
≈10 ref. [26] –
992 0.9998/ 99.43 99.2 0.3 –
40 0.998/ 98.6 97.7 1 –
10 ref. [27] –
– 70 ref. [28] –
– 10 ref. [27] –
(minimum voltage variation)/(DC magnetic field at the minimum voltage variation)
when a maximum ME voltage of 100 mV is reached (Fig. 2(b)). A maximum ME coefficient (α33 — determined from Eq. (2)) of 190 V·cm−1·Oe−1 is obtained for such DC magnetic field; α 33 ¼
ΔV t H AC
ð2Þ
where ΔV, t and HAC are the induced ME voltage, the thickness of the piezoelectric PVDF layer and the AC magnetic field, respectively. This behavior is related with the increase of the piezomagnetic coefficient until the optimum DC magnetic field is reached. With further increase of the DC magnetic field, a decrease of the induced voltage is observed, resulting from the saturation of the magnetostrictive response [39–41]. Linearity, sensitivity, resolution and accuracy tests were performed by increasing HDC in order to validate the use of the Metglas/PVDF/ Metglas as a DC magnetic field sensor (Fig. 3). Tests were performed under a 0.1 Oe AC magnetic field. The linearity of the response was obtained in the 0–3 Oe DC magnetic field range (Fig. 3(a)). After a magnetic field of 3 Oe, the ME response starts to reach saturation, which results in a loss of linearity. Resolution and sensitivity (Fig. 3(b)), accuracy (Fig. 3(c)) and hysteresis (Fig. 3(d)) were determined at low DC magnetic fields (0.2 Oe–0.7 Oe) since for such small DC magnetic fields, the electromagnetic noise will have more influence on the data, thus ensuring that the sensor will be tested in the worst possible conditions for low field signal detection. From Fig. 3a a correlation coefficient r2 of 0.995 and a linearity value of 95.9% FSO are obtained. The accuracy, hysteresis, sensitivity and resolution are 99.4% FSO, 1.2% FSO, 30 mV·Oe−1 and 8 μOe, respectively. The observed ME hysteresis (Fig. 3(d)) is related with the magnetic hysteresis of the Metglas alloy, that is more pronounced in the vicinity of the maximum permeability ≈0.55 Oe [42]. Further, the behavior of the ME composite as AC magnetic field sensor was evaluated and characterized at resonance (Fig. 4(a) and (b)) and non-resonance frequencies (Fig. 4(c) and (d)) with an applied DC field of 4.7 Oe. From the linear fit of the data presented in Fig. 4(a) a correlation coefficient r2 of 0.9998 and a linearity of 99.4% FSO is obtained for the AC magnetic field sensor working at the resonance frequency of 48 kHz. Additionally, the accuracy (Fig. 4(b)), sensitivity and resolution of the sensor are 97.9% FSO, 992 mV·Oe−1 and 300 NOE, respectively. At the non-resonance frequency of 95 kHz, r2, linearity, accuracy, sensitivity and resolution are 0.998, 98.6%, 2.3%, 40 mV·Oe−1, 1 μ Oe, respectively. Further, both for resonance and non-resonance conditions no hysteresis is detected (Fig. 4(b) and (d), respectively). The DC and AC ME sensor parameters are summarized in Table 1. The sensitivity and resolution values are compared with the highsensitivity polymer-based ME materials reported in the literature. Table 1 shows that the parameter values obtained for the AC/DC magnetic field sensor reported in this study are favorably comparable with the best ones reported in the literature in terms of DC sensitivity and AC accuracy. Further, the full characterization of the sensor main parameters is provided.
In this way, the suitability of the developed laminated polymerbased ME composite for magnetic field sensor applications is demonstrated [6]. 4. Conclusions A Metglas/poly(vinylidene fluoride)/Metglas ME laminate composite has been developed in order to validate its use as AC/DC magnetic field sensors. Sensitivity and resolution values are 30 mV·Oe−1 and 8 μOe for the DC magnetic field sensor and 992 mV·Oe−1 and 0.3 μOe for the AC magnetic field sensor. Such values are positively comparable with the ones reported in the most recent and sensitive polymer-based ME sensors. Additionally, the correlation coefficient, linearity and accuracy values for the DC (0.995, 95.9% and 99.4%) and AC (0.9998, 99.4% and 99.2%) magnetic field, demonstrating the applicability of polymerbased ME materials as innovative AC/DC magnetic field sensors, is reported. Acknowledgments and funding The authors thank the FCT – Fundação para a Ciência e Tecnologia – for the financial support under project PTDC/EEI-SII/5582/2014. P.M., V.C., S.R. and M.S. acknowledges support from FCT (SFRH/BPD/96227/ 2013, SFRH/BPD/97739/2013, SFRH/BDE/406 51542/2011 and SFRH/ BD/70303/2010 grants respectively). This work was also supported by Avel-electrónica Lda, Trofa, Portugal. A. Lasheras wants to thank the Basque Government for FPI grant. The authors thank the financial support from the Basque Government Industry Department under Project Actimat, (ELKARTEK Program). References [1] W. Eerenstein, N.D. Mathur, J.F. Scott, Multiferroic and magnetoelectric materials, Nature 442 (2006) 759–765. [2] G. Srinivasan, Magnetoelectric composites, Annu. Rev. Mater. Res. 40 (2010) 153–178. [3] K.P. Jayachandran, J.M. Guedes, H.C. Rodrigues, A generic homogenization model for magnetoelectric multiferroics, J. Intell. Mater. Syst. Struct. 25 (2014) 1243–1255. [4] G. Lawes, G. Srinivasan, Introduction to magnetoelectric coupling and multiferroic films, J. Phys. D. Appl. Phys. 44 (2011) (243001-). [5] C.-wW. Nan, M.I. Bichurin, S. Dong, D. Viehland, G. Srinivasan, Multiferroic magnetoelectric composites: Historical perspective, status, and future directions, J. Appl. Phys. 103 (2008) (031101-). [6] P. Martins, S. Lanceros-Méndez, Polymer-based magnetoelectric materials, Adv. Funct. Mater. 23 (2013) 3371–3385. [7] J. Ma, J. Hu, Z. Li, C.-W. Nan, Recent progress in multiferroic magnetoelectric composites: from bulk to thin films, Adv. Mater. 23 (2011) 1062–1087 (Deerfield Beach, Fla). [8] Y.Z. Wang, Influences of imperfect interface on effective magnetoelectric properties in multiferroic composites with elliptical fibers, Smart Mater. Struct. 24 (2015). [9] A. Bakkali, L. Azrar, A.A. Ali, Micromechanical modeling of magnetoelectroelastic composite materials with multicoated inclusions and functionally graded interphases, J. Intell. Mater. Syst. Struct. 24 (2013) 1754–1769. [10] S. Priya, R. Islam, S. Dong, D. Viehland, Recent advancements in magnetoelectric particulate and laminate composites, J. Electroceram. 19 (2007) 149–166. [11] G. Yu, H. Zhang, Surface effect on the magnetoelectric response of magnetoelectric layered composite with nanoscale thickness, Smart Mater. Struct. 24 (2015).
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