基于球壳内壁反射的球形换能器自易校准方法

基于球形换能器发射的脉冲球面声波及其在同心球壳内壁的反射,应用机电互易定理,导出了在球面波发射回波声场中,用于校准球形换能器的互易常数.以此为基础,提出一种使用封闭球壳反射器的自易校准方法,通过一次测量即可得到球形换能器的5个基本电声参数.进一步,将自易法校准所得的电压灵敏度换算成平面波声场中定义的标准灵敏度,给出了换...     

Development and application of ferrite materials for low temperature co-fired ceramic technology

Development and application of ferrite materials for low temperature co-fired ceramic(LTCC)technology are discussed,specifically addressing several typical ferrite materials such as M-type barium ferrite,NiCuZn ferrite,YIG ferrite,and lithium ferrite.In order to permit co-firing with a silver internal electrode in LTCC process,the sintering temperature of ferrite materials should be less than 950°C.These ferrite materials are research focuses and are applied in many ways in electronics.     

Directional Design of Materials Based on Multi-Objective Optimization: A Case Study of Two-Dimensional Thermoelectric SnSe

The directional design of functional materials with multi-objective constraints is a big challenge,in which performance and stability are determined by a complicated interconnection of different physical factors.We apply multi-objective optimization,based on the Pareto Efficiency and Particle-Swarm Optimization methods,to design new functional materials directionally.As a demonstration,we achieve the thermoelectric design of 2D SnSe materials via the above methods.We identify several novel metastable 2D SnSe structures with simultaneously lower free energy and better thermoelectric performance in their experimentally reported monolayer structures.We hope that the results of our work on the multi-objective Pareto Optimization method will represent a step forward in the integrative design of future multi-objective and multi-functional materials.     

微波低温制备Mg2Si0.4Sn0.6-yBiy热电材料的传输机理

德拜弛豫理论表明, 在频率为2.45 GHz的外加交变电磁场的作用下, 微波对极性分子的极化过程约为10^-10 s, 因此利用微波固相反应可以在短时低温条件下制备出纳米粉体材料. 本文以MgH₂代替Mg粉, 利用微波固相反应在低温下制备了Mg₂Si_0.4Sn_0.6-yBi_y (0 ≤y ≤q 0.03)固溶体, 并结合单带抛物线计算模型对其热电传输机理进行了分析. 研究结果表明: 利用该工艺可以有效抑制Mg的挥发和MgO 的生成, 在400 ℃保温15 min内即可完成MgH₂与Si粉和Sn粉的固相反应, 获得片层间距为100 nm的超细化学计量比产物; 杂质Bi的引入可以有效增加载流子浓度, 并引起晶格畸变, 在晶格畸变和样品特有的纳米片层结构的协同作用下, 声子得到有效散射, 样品具有最低的热导率1.36 W·m^-1·K^-1. 较低的有效掺杂率和复杂的能带结构具有降低能带态密度有效质量和减小载流子弛豫时间的双刃效应, 使得本征激发提前, 在600 K样品取得最大ZT值为0.66.     

超构材料中的光学量子自旋霍尔效应

电子的量子自旋霍尔效应的发现推进了当今凝聚态物理学的发展,它是一种电子自旋依赖的具有量子行为的输运效应.近年来,大量的理论和实验研究表明,描述电磁波场运动规律的麦克斯韦方程组内禀了光的量子自旋霍尔效应,存在于界面的倏逝波表现出强烈的自旋与动量关联性.得益于新兴的光学材料:超构材料(metamaterials)的发展,不仅能够任意设定光学参数,同时也能引入很多复杂的自旋-轨道耦合机理,让我们能够更加清晰地了解和验证其中的物理机理.本文对超构材料中量子自旋霍尔效应做了简要的介绍,内容主要包括真空中光的量子自旋霍尔效应的物理本质、电单负和磁单负超构材料能带反转导致的不同拓扑相的界面态、拓扑电路系统中光量子自旋霍尔效应等.