Thermal micro energy harvesting by thermomagnetic film actuation

本课题研究了一种利用热能在微尺度上产生电能的新方法--“热磁薄膜热微能采集”。它扩展了KIT的一个先驱项目，其中已经开发了热磁发电机(TMG)，达到了活性材料的平均功率密度118兆瓦·厘米-3和卡诺效率的5%。这些规格已经在一厘米及以下的长度范围内与最好的热电发电机竞争。目前的项目解决了TMG的主要特点：(1)将可用温度范围扩大到30-100°C，(2)增加了电力，(3)提高了热力学效率。由于微型化TMG的性能与所用热磁薄膜的功能特性密切相关，这一联合建议将KIT的微系统工程能力与IFW的热磁材料科学的互补能力结合在一起。为了优化TMG特性(1)-(3)，将通过改变组成和有序度来定制Ni-Mn基Heusler和Ga基薄膜的热磁性能(转变温度、磁化强度随温度变化、Dm/dt、磁滞)。TMG的设计将通过改善传热、增强磁场梯度以及调节机械共振来优化。特别是，为了改善换热，将应用微机械薄膜，其中包含由铜填充的沟槽。TMG特性的标度特性将通过实验和集总单元模型进行研究。基于单个TMG的最佳比例，将开发TMG的一维和二维阵列的分布式系统，以使总功率符合物联网和工业4.0的实际需求。

This project on “Thermal micro energy harvesting by thermomagnetic film actuation” investigates a novel approach to generate electrical energy from thermal energy on the miniature scale. It expands a precursor project at KIT, in which thermomagnetic generators (TMGs) have been developed, reaching average power densities of the active material of 118 mW cm-3 and 5% of Carnot efficiency. These specifications already compete with the best thermoelectric generators at the length scale of a centimetre and below. The current project addresses the key characteristics of a TMG: (1) Expansion of the usable temperature range to 30–100°C, (2) increase of electrical power, and (3) improvement of thermodynamic efficiency. As the performance of miniaturized TMGs is intimately connected with the functional properties of the thermomagnetic films used, this joint proposal brings together the complementary competence on microsystem engineering of KIT and thermomagnetic materials science of IFW.For optimization of TMG characteristics (1)-(3), the thermomagnetic properties of Ni-Mn-based Heusler and Ga-based films (transition temperatures, temperature-dependent change of magnetization, dM/dT, hysteresis) will be tailored by varying composition and degree of order. The design of the TMGs will be optimized by improving heat transfer, enhancing magnetic field gradient, as well as tuning mechanical resonance. In particular, for the improvement of heat transfer micromachined films will be applied, containing trenches filled by Cu. The scaling properties of TMG characteristics will be investigated experimentally, as well as by lumped element modelling. Based on the optimum scaling of a single TMG, distributed systems of 1D and 2D arrays of TMGs will be developed in order to bring the total power in line with the practical needs of IoT and industry4.0.