射频能量收集印刷天线仿真模型中长丝机织物结构简化方法及有效性

A structure simplification method and its validity of filament-woven fabrics in the screen-printed antenna simulation model for RF energy harvesting

获得仿真精确度高且计算成本低的仿真模型是高效设计织物基丝网印刷射频能量收集天线的基础。本文构建了长丝机织物天线基底的几种不同简化结构特征的仿真模型,采用HFSS仿真软件模拟了织物仿真模型与电磁波的相互作用,且以孔隙率和粗糙度为变量参数化分析了具有不同仿真结构基底的天线性能差异,并实际制备了几种不同简化结构基底的天线。结果表明:通过对比反射率和透射率发现,细观交织结构可以等效为具有孔洞和/或凹凸结构模型,均匀结构模型基底的天线辐射性能、增益及效率都显著偏高。进一步以射频能量收集为场景的模型有效性及验证结果表明,仿真模拟结果与实际测试结果吻合良好,且不同简化结构基底的天线性能也无显著性差异。在超高频范围内,不同简化结构基底的天线最大传输距离达220 cm,在1 m处的单位面积接收信号强度在8.442 mW/cm^(2)以上,天线输出电压和能量转换效率可分别达135 mV、60%。因此,为节约计算成本,就孔隙率不超过30%且粗糙度在5.39μm以下的长丝平纹机织物基底,在丝网印刷超高频射频能量收集天线仿真模拟中可将其等效为均匀介质模型。

Radio frequency energy harvesting(RFEH)technology has been applied widely in the development of wearable electronic power supply systems because of its eco-friendly and highly efficient characteristics.In the RFEH system,the receiving antenna collects electromagnetic waves through electromagnetic coupling technology.Obviously,the receiving antenna plays a crucial role in the energy harvesting efficiency of the RFEH system.Generally,the antenna performance can be optimized by simulation and measurement.In the simulation of screen-printed fabric-based antenna for RFEH,the establishment of a precise structure model of the substrate fabric is the basis for the simulation analysis.However,in order to save the calculation cost,most studies ignore the interwoven structural characteristics of the fabric in establishing a simulation model,which leads to a big difference between the simulation and measurement results.To guide the actual product design and engineering application evaluation through the simulation of fabric-based antennas,it is necessary to establish a fabric-based antenna model with high simulation accuracy and low calculation cost.To obtain the structural model of screen-printed woven fabric-based antenna for RFEH with high accuracy and low calculation cost,this study constructed six different simplified structural models of filament woven fabrics firstly,including interwoven meso-structure,hole combining concave-convex structure,hole structure,plane concave-convex structure,curved concave-convex structure,and uniform structure.The interaction mechanism between the woven fabric and the electromagnetic wave was simulated.Based on this,the antenna performance with different simulated structural substrates was analyzed parametrically with porosity and roughness as variables.And then,several antennas with different simplified structural substrates were prepared to verify the feasibility of the simplified structural model of the substrate in the design of the antenna for RFEH.The results show that the interwoven meso-structure can be equivalent to a model with holes and/or a concave-convex structure model by comparing the reflectivity and transmittance.And the antenna radiation performance,gain,and efficiency with the uniform substrate structural model are significantly high.In addition,the structure model with a rough surface has a more significant effect on the antenna performance than the non-rough surface structure model.Furthermore,the model prediction and measured results of the antenna RFEH performance in the ultra-high frequency(UHF)range were compared.It is found that there is no significant difference between the two,and there is no significant difference among different simplified structure models.The maximum transmission distance of the antenna reaches 220 cm,and the received signal strength indication(RSSI)of unit area at 1 m distance exceeds 8.442 mW/cm^(2).The output voltage and power conversion efficiency of the antenna are up to 135 mV and 60%,respectively.Consequently,in order to save the calculation cost,the filament plain woven fabric substrate with a porosity of less than 30%and a roughness of less than 5.39μm can be equivalent to a uniform medium model in the simulation of screen-printed antenna for RFEH in the ultra-high frequency range.An effective simulation method for woven fabric-based printed antenna for radio frequency energy harvesting in the ultra-high frequency range with high accuracy and low computational cost is provided by simplifying the fabric structure of holes and surface texture features.This method of model simplification has certain reference meanings for the model simplification of the antenna with complex structure applied to other fields.Furthermore,this high-precision simulation model contributes to predicting the performance of the fabric-based antenna and optimizing the design of the fabric-based antenna,so that fabric-based RFEH antennas can be applied to more extensive fields.