Surface array electrode is provided with high performance to improve the stimulation selectivity and controllability. Both element size and spacing on the array electrode are the key factors to affect activated area and depth. Considering the surface array electrode for hand rehabilitation,the forearm model with the concentric cylindrical layers was established in this paper. Then the finite element method ( FEM) was used to simulate the extracellular potential of the motor nerve in the forearm with the catholic direct current stimulation. Moreover,the activation function of the nerve fiber was used to evaluate the effect of external excitation on the activity of the axon. The array electrodes with different element size and pattern were investigated,while both the peak value and half width of the activation function were used to assess the stimulation performance. The simulation results showed that the activated area of the target tissue increased 169. 36 mm2 when the element size increased from 12 mm to 14 mm and the element spacing decreased from 6 mm to 2 mm,making stimulation selectivity poor. In contrast,the activated area of the target tissue decreased at least 89. 52 mm ,if all large elements were separated by small elements on the array electrode,which could improve the stimulation selectivity performance. There fore,the FEM simulation lays a foundation for the optimization of the surface array electrode.%表面阵列电极在改进刺激选择性和控制能力方面具有优越性能,而触点大小和间距是对刺激范围和深度影响最大的因素.针对手功能康复需求,在建立前臂同心圆柱层次模型的基础上,利用有限元仿真得到直流阴极表面电刺激下前臂组织内神经纤维的胞外电势分布,采用神经纤维激励函数表征外加电场对神经轴突电活动的影响.通过仿真研究不同触点尺寸和排列方式的阵列电极设计,采用激励函数峰值和半宽度评价刺激效果.结果表明,当阵列电极触点尺寸由12mm增大到14 mm,间距由6 mm减小到2 mm时,被激活的靶组织区域面积增大了169.36 mm2,使得刺激选择性变差；而大小触点交叉排列的结构设计能使激活的靶组织区域面积减小至少89.52mm2,有助于提高刺激选择性能,从而为表面阵列电极的优化设计提供理论指导.
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