求翻译：基于微波段二维树枝状左手材料的设计思想，设计了太赫兹波段三维左手材料结构单元模型。结构单元具有结构简单、较容易制备等特点。采用金属Drude模型，运用等效媒质理论，仿真模拟了结构单元的电磁响应特性，计算了结构单元的有关电磁参数，结果表明折射率在太赫兹波段1.17-1.38THz之间为负值。并通过模拟负折射验证了其左手特性，研究结果为采用自上而下的方法制备三维太赫兹波段左手材料指出了途径。是什么意思？

Microwave-based design of two-dimensional dendritic left-handed materials, designing Terahertz-band model for three dimensional material structures on the left hand. Structural unit has a simple structure, easy preparation, and other characteristics. Using metal Drude model, using equivalent medium theory, simulation of structural unit electromagnetic response characteristics, calculation for electromagnetic parameters of structural units, results indicate that between the refractive index in the Terahertz band 1.17-1.38THz is negative. And validates its analog negative refraction characteristics on the left hand, and research results in a top down approach was used three dimensional Terahertz-band left-handed materials have identified ways of preparation.