A. Lasheras

Optimization of the Magnetoelectric Response of Poly(vinylidene fluoride)/Epoxy/Vitrovac Laminates

The effect of the bonding layer type and piezoelectric layer thickness on the magnetoelectric (ME) response of layered poly(vinylidene fluoride) (PVDF)/epoxy/Vitrovac composites is reported. Three distinct epoxy types were tested, commercially known as M-Bond, Devcon, and Stycast. The main differences among them are their different mechanical characteristics, in particular the value of the Young modulus, and the coupling with the polymer and Vitrovac (Fe39Ni39Mo4Si6B12) layers of the laminate. The laminated composites prepared with M-Bond epoxy exhibit the highest ME coupling. Experimental results also show that the ME response increases with increasing PVDF thickness, the highest ME response of 53 V·cm(-1)·Oe(-1) being obtained for a 110 μm thick PVDF/M-Bond epoxy/Vitrovac laminate. The behavior of the ME laminates with increasing temperatures up to 90 °C shows a decrease of more than 80% in the ME response of the laminate, explained by the deteriorated coupling between the different layers. A two-dimensional numerical model of the ME laminate composite based on the finite element method was used to evaluate the experimental results. A comparison between numerical and experimental data allows us to select the appropriate epoxy and to optimize the piezoelectric PVDF layer width to maximize the induced magnetoelectric voltage. The obtained results show the critical role of the bonding layer and piezoelectric layer thickness in the ME performance of laminate composites.

Energy harvesting device based on a metallic glass/PVDF magnetoelectric laminated composite

A flexible, low-cost energy-harvesting device based on the magnetoelectric (ME) effect was designed using Fe64Co17Si7B12 as amorphous magnetostrictive ribbons and polyvinylidene fluoride (PVDF) as the piezoelectric element. A 3 cm-long sandwich-type laminated composite was fabricated by gluing the ribbons to the PVDF with an epoxy resin. A voltage multiplier circuit was designed to produce enough voltage to charge a battery. The power output and power density obtained were 6.4 μW and 1.5 mW cm−3, respectively, at optimum load resistance and measured at the magnetomechanical resonance of the laminate. The effect of the length of the ME laminate on power output was also studied: the power output exhibited decays proportionally with the length of the ME laminate. Nevertheless, good performance was obtained for a 0.5 cm-long device working at 337 KHz within the low radio frequency (LRF) range.

Sensor applications of soft magnetic materials based on magneto-impedance, magneto-elastic resonance and magneto-electricity.

The outstanding properties of selected soft magnetic materials make them successful candidates for building high performance sensors. In this paper we present our recent work regarding different sensing technologies based on the coupling of the magnetic properties of soft magnetic materials with their electric or elastic properties. In first place we report the influence on the magneto-impedance response of the thickness of Permalloy films in multilayer-sandwiched structures. An impedance change of 270% was found in the best conditions upon the application of magnetic field, with a low field sensitivity of 140%/Oe. Second, the magneto-elastic resonance of amorphous ribbons is used to demonstrate the possibility of sensitively measuring the viscosity of fluids, aimed to develop an on-line and real-time sensor capable of assessing the state of degradation of lubricant oils in machinery. A novel analysis method is shown to sensitively reveal the changes of the damping parameter of the magnetoelastic oscillations at the resonance as a function of the oil viscosity. Finally, the properties and performance of magneto-electric laminated composites of amorphous magnetic ribbons and piezoelectric polymer films are investigated, demonstrating magnetic field detection capabilities below 2.7 nT.

Electronic optimization for an energy harvesting system based on magnetoelectric Metglas/poly(vinylidene fluoride)/Metglas composites

Harvesting magnetic energy from the environment is becoming increasingly attractive for being a renewable and inexhaustible power source, ubiquitous and accessible in remote locations. In particular, magnetic harvesting with polymer-based magnetoelectric (ME) materials meet the industry demands of being flexible, showing large area potential, lightweight and biocompatibility. In order to get the best energy harvesting process, the extraction circuit needs to be optimized in order to be useful for powering devices. This paper discusses the design and performance of five interface circuits, a full-wave bridge rectifier, two Cockcroft–Walton voltage multipliers (with 1 and 2 stages) and two Dickson voltage multipliers (with 2 and 3 stages), for the energy harvesting from a Fe61.6Co16.4Si10.8B11.2 (Metglas)/polyvinylidene fluoride/Metglas ME composite. Maximum power and power density values of 12 μW and 0.9 mW cm−3 were obtained, respectively, with the Dickson voltage multiplier with two stages, for a load resistance of 180 kΩ, at 7 Oe DC magnetic field and a 54.5 kHz resonance frequency. Such performance is useful for microdevice applications in hard-to-reach locations and for traditional devices such as electric windows, door locking, and tire pressure monitoring.

Optimized anisotropic magnetoelectric response of Fe61.6Co16.4Si10.8B11.2/PVDF/Fe61.6Co16.4Si10.8B11.2 laminates for AC/DC magnetic field sensing

The authors thank the FCT- Fundacao para a Ciencia e Tecnologia- for financial support under project PTDC/EEI-SII/5582/2014. P.M., S.R. and M.S. acknowledges also support from FCT (SFRH/BPD/96227/2013, SFRH/BDE/406 51542/2011 and SFRH/BD/70303/2010 grants respectively). This work was also supported by Avel-electronica Lda, Trofa, Portugal. J.G., A.L. and S.L.M. thank financial support from the Basque Government Industry Department under the ELKARTEK Program. SLM also thanks the Diputacion de Bizkaia for financial support under the Bizkaia Talent program.

Improving the Magnetoelectric Response of Laminates Containing High Temperature Piezopolymers

High magnetoelectric (ME) coefficients at room temperature have been found when 2-2 type laminates (one magnetostrictive, the other piezoelectric) made of iron-based Metglas alloys and PVDF piezoelectric polymer are used. Searching for a good ME response of such laminate composites when used at high temperatures, we have modified both constituents: first, by using magnetostrictive Metglas 2826 MB (with λs ≈ 11 ppm) in the ribbon form thermally treated at high temperature, in order to get internal stress-relief conditions. The main consequence of such thermal treatment has been to achieve a piezomagnetic coefficient of d33=1.5×10-6/Oe, higher than the measured one in the as-cast state for this alloy. As piezoelectric constituent, we have used a new class of high temperature piezopolymer: a series of nitrile containing polyimide copolymers were fabricated with a mixture of two aromatic diamines, namely 1,3-Bis-2-cyano-3-(3-aminophenoxy)phenoxybenzene (diamine 2CN) and 1,3-Bis(3-aminophenoxy)benzene (diamine 0CN). Those diamines were in 30/70, 40/60, and 50/50 proportions within the 0CN/2CN mixture. We have measured room temperature ME coefficients up to 0.37 V/cm.Oe, being this value directly correlated to the remnant polarization of each copolyimide.

Metallic Glass/PVDF Magnetoelectric Laminates for Resonant Sensors and Actuators: A Review

Among magnetoelectric (ME) heterostructures, ME laminates of the type Metglas-like/PVDF (magnetostrictive+piezoelectric constituents) have shown the highest induced ME voltages, usually detected at the magnetoelastic resonance of the magnetostrictive constituent. This ME coupling happens because of the high cross-correlation coupling between magnetostrictive and piezoelectric material, and is usually associated with a promising application scenario for sensors or actuators. In this work we detail the basis of the operation of such devices, as well as some arising questions (as size effects) concerning their best performance. Also, some examples of their use as very sensitive magnetic fields sensors or innovative energy harvesting devices will be reviewed. At the end, the challenges, future perspectives and technical difficulties that will determine the success of ME composites for sensor applications are discussed.

Synthesis and characterization of novel piezoelectric nitrile copolyimide films for high temperature sensor applications

A series of amorphous polyimides and copolyimides that contained nitrile were obtained by a two-step procedure. The first step consisted of a polycondensation reaction of 4,4’-oxydiphtalic anhydride (ODPA) with one or two aromatic diamines, namely 1,3-Bis-2-cyano-3-(3-aminophenoxy)phenoxybenzene (diamine 2CN) and 1,3-Bis(3-aminophenoxy)benzene (diamine 0CN). In the second step, a thermal cyclodehydration converted each poly(amic acid) or copoly(amic acid) into their corresponding polyimide films. The piezoelectric response was improved after corona poling of the films. A maximum d33 modulus value of 16 pC N−1 was obtained for the polymide with two cyano groups (poly 2CN). The polarization also showed time and thermal stability up to 160 °C. Additionally, the thermal stability of the amorphous polyimides, (β-CN)APB/ODPA, was studied by determining the glass transition temperature (T g ) and thermal decomposition through differential scanning calorimetry (DSC) and thermogravimetric analysis (TG), respectively. The high piezoelectric response (1–16 pC N−1), T g (160–180 °C) and degradation temperature (315–450 °C) make such polyamides excellent candidates for use as high temperature sensors.

Improving the Performance of High Temperature Piezopolymers for Magnetoelectric Applications

Piezoelectricity in amorphous polymers is mainly due to the orientation polarization of the molecular dipoles. Aromatic polyimides are high-performance polymeric materials possessing large molecular dipoles. We already reported good magnetoelectric performance of laminate composites with Vitrovac 4040® as magnetostrictive component and the 2,6(b-CN)APB/ODPA (poli 2,6) polyimide as the piezoelectric. Although the piezoelectric response of this polyimide is good, its mechanical properties can be improved. To combine the best mechanical and piezoelectric response in the same polymer, copolyimides have been synthesized by reaction of the 4,4-oxydiphtalic anhydride (ODPA) with a mixture of 1,3-Bis-2-cyano-3-(3-aminophenoxy) phenoxybenzene (diamine 2CN) and 1,3-Bis (3-aminophenoxy) benzene (diamine 0CN). We present the piezoelectric, mechanical and ME performance of laminate composites of these copolyimides.

Quantification of size effects in the magnetoelectric response of metallic glass/PVDF laminates

Metallic glass/polyvinylidene fluoride three-layered magnetoelectric laminated composites have been studied. Size effects in the magnetoelectric response arisen both from the reduction of the length of the laminate and from the increase of the operating frequency have been quantified for the lengths ranging from 3 cm down to 0.5 cm. It has been concluded that the decrease in this magnetoelectric response arises mainly from the demagnetizing effects, with reductions of 86% for the longest laminate that increase up to 99% for the shortest one. From these values, an intrinsic magnetoelectric coefficient of 325 V/cm Oe has been obtained.