Ferromagnetic microwires enabled multifunctional composite materials

The last two decades have witnessed increasing international interest in ferromagnetic microwires research. Recent attention has turned to the development of innovative materials and composites derived from these microwires, such as microwire polymer composites. Through incorporating an extremely small concentration of microwires (10(-2) vol.%), the resultant composite exhibits a multitude of functionalities which are desirable for a range of technological applications. This article aims to provide a comprehensive review of current microwire composites research, from processing to structural and property evaluations with a focus on the multi-functionalities presented in these microwire composites. Starting with an introduction to multifunctional composites and the theories pertinent to the multiple functionalities of microwire composites, a detailed description of fabrication methods of microwire composites is given with a comparison of different processing techniques. Two fundamental effects, namely, giant magnetoimpedance (GMI) and giant stress-impedance (GSI) of microwire composites, are discussed in relation to monolithic microwires. Microwave tunable properties in the presence of a dc magnetic field, stress or temperature field are presented and analysed in depth. The ferromagnetic wire composites have also been shown to possess metamaterial characteristics and microwave absorption capability. A detailed discussion of the influence of composite architecture, such as local properties of microwires and topology of wire arrangements, on the performance of resultant composites, provides useful insights for an effective design of smart composites for specific engineering applications, such as structural health monitoring, stress sensing, invisible cloaking, microwave absorption and biomedical applications. (C) 2012 Elsevier Ltd. All rights reserved.