A Flexible Magnetoelectric Transducer Based on FeCuNbSiB/poly (vinylidene fluoride) (PVDF) Laminate Composites for Wearable Magnetic Sensors

Abstract

In recent years, flexible wearable equipment has attracted more and more attentions, and has made great development. Wearable electronics are expected to be one of the most active research areas in the next decades. There are more and more studies about flexible wearable sensors [1] and some of them have been used in life. However, there are few studies on flexible wearable magnetic sensors. Magnetic sensors [2] are useful and influential for human life, and kinds of sensors have been utilized in practice. To date, the new magnetic field detecting technologies with more excellent performance has been still the focused issues and trends. Magnetoelectric (ME) composite sensor was proposed as a candidate for the next-generation magnetic field sensors, due to its high sensitivity, compact size and room-temperature operation. Among the ME composites, laminate composites display the highest ME response, particularly those fabricated with magnetostrictive alloys and piezoceramic materials. However, piezoelectric ceramics have low electrical resistivity, high dielectric losses and are expensive, dense and brittle, which can lead to fatigue and failure, hindering their incorporation into technological applications. The piezoelectric polymer-based ME laminates [3] have several advantages over the ceramic based ones. They are easily fabricated by conventional low-temperature processing into a variety of forms, such as thin sheets or moulded shapes, and exhibit improved mechanical properties. The nanocrystalline FeCuNbSiB was elected as magnetostrictive material owing to its large piezomagnetic coefficient at low magnetic fields, high mechanical quality factor and large interface stress-strain coupling effect. For sensor applications, the optimization of the element responsible for the coupling between magnetostrictive and piezoelectric components plays a crucial role. However, coupling between the different phases is not the only parameter that requires optimization prior to their incorporation into technological applications: characteristics such as size, structure and relative geometry of the components may allow tailoring the applicability of ME composite materials. Furthermore, there is an increasing interest in fabricating smaller devices mainly in communication systems and wearable devices, which reduces the cost and improves the functionality [4]. For these reasons, it is essential to study the influence of the size on the ME coupling properties of the laminate composite. On the other hand, it is necessary to study its bending performance as the flexible ME transducer for better application for wearable magnetic sensors. In this paper, a series of flexible ME transducers based on nanocrystalline alloy (FeCuNbSiB)/poly (vinylidene fluoride) (PVDF) laminate composites for wearable magnetic sensors were fabricated. The effects of the composites size, geometry and structure on the ME coupling properties were investigated. Just as shown in Fig. 1, it is concluded that the ME voltage coefficient increases with decreasing transversal size aspect ratio (TAR) (from 3 to 1), reaching a maximum ME voltage coefficient of 203 V/cm Oe. The ME laminate composites with lowest longitudinal size aspect ratio (LAR) resulted in better ME voltage coefficient when compared with higher LAR. By investigating the ME coupling properties under different angles, it is also found that the optimal resonant ME voltage will decrease with the bending angle (θ) increases, getting the minimum of 11.56 V/cm Oe when θ = 50°, which is shown in Fig. 2. The effects of thickness and fatigue properties for the ME coupling properties also were investigated. All these results provide an experimental basis for posterior research and practical application, which is very useful for science and advanced applications.