Magnetoelectric and magnetomechanical interactions in compliant composite materials

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Conventional magnetoelectric (ME) composite materials comprise layers of piezoelectric ceramic or single-crystal materials and ferromagnetic metals or alloys. The efficiency of ME interaction is the highest when the modulation frequency of the external magnetic field coincides with eigenfrequencies of mechanical oscillations in the composite structure due to resonance enhancement of deformations in the piezoelectric layer. Since the constitutive solid-state materials have large elastic constants, the corresponding resonance frequencies are also high (typically in the range betwen 1 kHz and 300 kHz). However, for some applications, e.g. for low-frequency magnetic field sensing or vibration energy harvesting, it would be advantageous to have the mechanical resonance frequency of the composite structure much lower, e.g. in the frequency range below 100 Hz. At the present state of technology, compliant (flexible) polymer materials are promising candidates for realization of flexible ME composites. In general, polymer based smart materials are very interesting for MEMS and microfluidic applications because of the advantages of mechanical flexibility, lower fabrication cost and faster processing over silicon based devices. The purpose of this project is to develop enhanced ME layered composite materials, preferably completely made of compliant (flexible) polymers, and to investigate in detail their ME properties. To optimize ME composite materials, the relevant properties of constitutive materials must be investigated as well. Magnetoactive elastomers (MAEs) will be used as magnetostrictive component. These magnetoactive elastomers comprise micrometer-sized magnetic particles (e.g. iron) dispersed in a soft elastomer (e.g. polydimethylsiloxane, PDMS) matrix. Magnetostrictive properties of MAEs will be investigated in the broad temperature range between -60°C and +60°C and they will be related to the increase of the dynamic shear modulus in external magnetic fields, known as magnetorheological or field-stiffening effect. The Wiedemann effect in MAEs will be investigated as a specific manifestation of magnetostriction. MAE layers must be further combined with compliant (flexible) PE materials to form ME composite materials. Different possibilities of implementing PE layers will be explored. In particular, it is envisaged to investigate PDMS-based micro-structured ferroelectric structures, polyvinylidene fluoride (PVDF) and piezo fibre based sandwich composites. Temperature dependencies of ME interaction efficiency in fabricated composite structures will be determined experimentally. These temperature characteristics must be explained from temperature dependencies of constitutive materials. The achieved progress in understanding of ME and magnetomechanical phenomena in developed soft composite materials could open the way for new applications in smart structures.