Recent works demonstrated the abilities of magneto rheological elastomers (MREs) for mechanical to electrical energy conversion. This class of materials consists of composites composed of a soft elastic matrix filled by ferromagnetic particles. In this work we focus primarily on anisotropic MREs featuring particles that are non-homogenously dispersed in the matrix but form of chains of particles. Such anisotropic MRE are good candidates for energy conversion and harvesting purpose because of the coupling between high magnetization of the soft ferromagnetic particles and low elastic modulus of the matrix; thus, the anisotropic MREs can convert a mechanical cyclic deformation into electric signal. In the framework of magnifying the conversion capabilities of such materials, this study reports the investigation of different filling factors of particles, submitted to various magnetic excitations and amplitudes of mechanical deformation. The multiscale analysis provided by this work, from local effect to global characterization, shows that optimal conditions depend on intrinsic material parameters (e.g. filling factor) as well as external conditions (mainly bias magnetic flux density and applied mechanical solicitation).

For biomedical applications, smart materials that are used as sensors or actuators have to match some criteria, especially bio-compatibility and softness. Smart polymers are candidates that fulfill these two criteria. A sensitivity to compression is created by adding magnetic particles to a compressible foam polymer. A foam-based composite is fabricated for its small Poisson’s ratio, which enables significant compression, up to 50%. This large compression induces a change in its magnetic properties, which can be detected using coils. By setting the sensing coils as a compact array of 3 × 3, the sensor successfully detected and localized an applied deformation.

This study reports the development of a magneto-rheological foam, which consists in a porous matrix filled by ferromagnetic particles. The porous matrix of such a composite being easily deformable, large magnetic properties changes are expected. The measurements of the magnetic properties of such a magneto-rheological foam submitted to a compressive strain are reported. Main aspect of the magnetic properties is the low field magnetic permeability as the function of the compression and filling factor. Then, larger field magnetization measurement allowed to investigate the saturation field as a function of the filling factor. Because of the large amount of pores in the material, the magnetic relative permeability, µ _r , is quite small ( µ _r ∼ 1). However, these materials can be easily deformed over a large range of strain providing important relative variation of the magnetic properties under mechanical solicitation. The composite magnetic permeability is increasing under compression for all the considered filling factors. A model is then developed to understand the variation of the permeability with the strain. Hence, from a simple concept consisting of taking advantage of high deformation of foams, the present study demonstrates the interest of such a highly compressible while cheap composite for obtaining a large magneto-rheological effect.