Magnetoelectric and magnetomechanical interactions in compliant composite materials

传统的磁电（ME）复合材料包括压电陶瓷或单晶材料和铁磁金属或合金的层。当外部磁场的调制频率与复合结构中的机械振荡的本征频率一致时，由于压电层中的变形的共振增强，ME相互作用的效率是最高的。由于构成固态材料具有大的弹性常数，因此相应的共振频率也很高（通常在1 kHz和300 kHz之间的范围内）。然而，对于某些应用，例如对于低频磁场感测或振动能量收集，有利的是使复合结构的机械共振频率低得多，例如在低于100 Hz的频率范围内。在目前的技术状态下，顺应性（柔性）聚合物材料是实现柔性ME复合材料的有前途的候选者。通常，基于聚合物的智能材料对于MEMS和微流体应用是非常有趣的，因为其具有机械柔性、较低的制造成本和比基于硅的器件更快的加工的优点。该项目的目的是开发增强的ME层状复合材料，最好完全由顺应性（柔性）聚合物制成，并详细研究其ME性能。为了优化ME复合材料，还必须研究本构材料的相关性能。 磁致伸缩组件将使用磁活性弹性体（MAE）。这些磁致活性弹性体包括分散在软弹性体（例如聚二甲基硅氧烷，PDMS）基质中的微米尺寸的磁性颗粒（例如铁）。MAE的磁致伸缩特性将在-60 ° C和+60 ° C之间的宽温度范围内进行研究，它们将与外部磁场中动态剪切模量的增加有关，称为磁流变或场硬化效应。MAES中的维德曼效应将作为磁致伸缩的具体表现进行研究。MAE层必须进一步与顺应性（柔性）PE材料组合以形成ME复合材料。将探讨实现PE层的不同可能性。特别是，它是设想调查PDMS为基础的微结构铁电结构，聚偏氟乙烯（PVDF）和压电纤维为基础的夹层复合材料。将通过实验确定制造的复合材料结构中ME相互作用效率的温度依赖性。这些温度特性必须从本构材料的温度依赖性来解释。在理解ME和磁力学现象方面取得的进展，可以为智能结构的新应用开辟道路。

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.