Multifunctional magneto-polymer matrix composites for electromagnetic interference suppression, sensors and actuators

Abstract

Multi-functional fiber reinforced composites with magnetic properties offer great potential for enabling new applications in a diverse range of industry sectors, such as aerospace, automotive, biomedical, and civil infrastructures. By incorporating magnetic properties into existing fiber reinforced polymer composites (FRPC), it is possible to enhance their magnetic permeability and tailor their responses to external electrostatic, magnetostatic or electromagnetic fields. With improved magnetic permeability, these new multi-functional composites offer new solutions in waveform conditioning, structural health monitoring, integrated sensors, lightweight motors and actuators, and electromagnetic interference shielding. In these applications, the additional magnetic functionalities can be optimized to improve mass efficiency, environmental durability, affordable maintenance and safety. Herein we present a critical review of fiber-reinforced magneto-polymer matrix composites regarding material selection, microstructural design, functional mechanisms, manufacturing processes, recent innovative applications, challenges and future opportunities. Throughout, a specific focus is placed on the fundamental material properties and composite architectures required to achieve desired functions and meet overall multi-functional design objectives.

Introduction

Recently there has been a rapid growth in the design and manufacturing of so-called multi-functional material systems [1] and smart structures [2] where sensors, actuators, communication or computer processing capabilities are incorporated into existing structural designs. These multifunctional systems provide functionalities beyond the passive load bearing capacity of the original structure, ideally without adding volume and/or mass. The research has been prompted by the advances in and miniaturization of consumer electronics, the growth of the so-called Internet of Things (IoT) and a general push toward improved system functionality at similar or reduced volume and mass. In this context, the use of soft magnetic composites (SMCs) in structural applications is highly desirable. However, a number of fundamental material issues exist which limit their application, including:

• Reduced material strength when compared with unmodified polymer matrices.

• Increased mass due to the inclusion of magnetic materials with higher densities.

• Degraded environmental durability and corrosion resistance associated with the commonly used magnetic materials.

Common routes to bestow additional functionality such as electrical and thermal conductivity [3], [4] to fiber composites include adding fillers into the polymer matrices and engineering new fibers with these functionalities. New powder metallurgy techniques now make it possible to produce micron- and nano-scale magnetic particles. Mixing these particulate fillers with a binder or incorporating them into the polymer matrix of a fiber-reinforced composite are being used to produce SMCs [5] with superior magnetic properties. Such SMCs offer improved efficiencies, reduced losses and adaptable manufacturing routes when compared with bulk or laminated magnetic material alternatives and are thus appearing in many emerging electromagnetic conversion devices such as motors, transformers and sensor [6]. Similarly, the design and application of electromagnetic interference (EMI) suppression [7], [8], [9], [10], [11], field controlled actuation [12], [13], [14], [15], antenna designs [16], [17], [18], [19], [20], [21], magnetic field sensors [22], [23] and sensors for structural health monitoring (e.g. damage detection [24], [25] and monitoring of load [26] and stress/strain [27], [28], [29], [30], [31], [32]) are also benefiting. New temperature sensor concepts are also emerging due to unique characteristics offered by distributed magnetic phases in polymer composites [22], [33], [34]. Composites with magnetic phase volume fractions below approximately 50 vol% are often called magneto composites, magneto-dielectrics or magneto polymer composites (MPCs) and fiber reinforced magneto polymer composites (FR-MPCs).

Numerous recent reviews exist that focus on various applications of MPCs and FR-MPCs including for morphing structures [35], biomedical applications [36], [37], EMI suppression [9], energy conversion devices [38] and structural vibration control [39]. Other reviews also focus on fundamental physical mechanisms, material states and composite designs that underpin the application of this material class, including magnetostriction [40], magnetoelectric coupling [41], magnetic nano-particulates [42], [43] and ferromagnetic microwave interactions [44]. Structural aspects and examples of MPCs exist in broader reviews of multi-functional composites [1], [4], however consideration of a structural fiber phase specifically for load bearing applications of FR-MPCs exists only in one review to date [45] which focuses on ferrite magnetic inclusions (specifically barium, cobalt and strontium ferrite) and the processing of associated MPC’s.

The use of load bearing fibers with magnetic particles in the matrix or fiber-shaped magnetic materials to produce FR-MPCs offers the ability to improve composite strength and fatigue resistance in an array of applications. Promising routes for improving material functionality and performance include optimization of the magnetic phase architectures through shaping and sizing of the magnetic fillers, patterning of magnetic fillers and distribution of magnetic fibers by additive manufacturing (AM) processes. Furthermore, as with traditional fiber reinforced polymer composites (FRPC) [46], the interfaces between polymer matrix and the magnetic phase (or matrix and fiber as with FRPCs) is important to the mechanical performance of FR-MPCs.

The intent of this article is to critically review the current state-of-the-art of FR-MPCs, including recent advances, challenges, and future opportunities, specifically with regard to their application in EMI mitigation, sensors and actuation. A particular focus will be on the underpinning functional mechanisms and structural ramifications of the included magnetic phase, with a summary of the discussed functional mechanisms as they relate to targeted FR-MPC applications provided in Fig. 1.