Si/SiO_2周期性多层膜反射特性的FDTD数值模拟

Si/SiO2周期性多层膜是一种电介质型频率选择表面,它与金属型频率选择表面相比具有较小的吸收损耗。从介质波导理论出发,可以分析电介质型频率选择表面的反射与透射机理。与均匀介质层相比,介电常数呈周期变化的电介质层可能会激发出满足相位匹配条件k0sinθ=βg的导波模,从而在介质板的上表面与下表面辐射出与导波模具有相同波数的平面波。介质层上再辐射的平面波与上表面直接产生的反射波叠加便形成了总的反射场。当两种波相位相同时,就会增强总反射,否则反射将会减弱,并且透射波也会有相同的规律。采用周期结构时域有限差分方法可对一种Si/SiO2周期性多层膜的反射特性进行数值模拟,并计算出波长在1~100 mm微波波段的反射系数。计算结果表明,当入射角为45°时,入射波长在5,9,20 mm处具有很高的反射系数(均达到0.88以上)。因此,通过调整相关参数可以获得所需的频率选择表面。

Numerical Simulation to Reflection Performance of Si/SiO2 Periodic Multi- Layer Film Using FDTD Method

Si/SiO_2 periodic multi-layer film is a kind of dielectric frequency selective surface(DFSS),which has lower absorption loss than metallic frequency selective surface(MFSS).Based on the theory of guided wave,reflection and transmission mechanism of DFSS was analyzed.Compared with the layer that have uniform dielectric constant,periodic dielectric layer could excite guided wave mode that can satisfy the phase-match condition k_0sinθ=βg.Therefore,some plane wave,which has the same wave numbers as guided wave,radiate on the top and bottom of the layer.Reradiated plane wave above the layer adds to the reflected plane wave generated directly at the top surface of the layer to give the total reflected field.When both waves are the same in phase,strong reflections take place,otherwise,reflection become weak,and the same as for transmission.It is to use periodic structure finite difference time domain method to simulate reflection performance of Si/SiO_2 multi-film structure numerically.In 1～100 mm microwave waveband,reflection coefficients was computed.Computations show that,when incident angle is 45°,reflection coefficients reached over 0.88 at 5,9 and 20 mm.Therefore,any required DFSS can be obtained by tuning some parameters.