Functional Reliability Modeling of AFSS Under Thermal Loading

The reliability of active frequency selective surfaces (AFSS) under complex operational environments has become increasingly critical, with diode failure caused by solder joint fatigue cracking being a key factor leading to degradation of wave transmission performance. This paper addresses the structurefunction coupled degradation mechanism of AFSS subjected to thermal cycling loads and proposes a multi-scale reliability modeling approach. First, a thermo-mechanical coupled finite element model considering component power dissipation boundary conditions is developed to compute the plastic strain response of solder joints under typical temperature cycles. Based on fatigue life models, the temporal sequence discontinuity pattern of functional failure chains is predicted. Subsequently, electromagnetic simulations analyze the evolution of wave transmission characteristics under different failure chain states, revealing a dynamic mapping relationship among thermal cycling excitation, solder joint damage, diode failure, and electromagnetic performance degradation. Results indicate that the functional failure chains of AFSS fail sequentially at 901, 1045, and 1072 cycles. As the number of failed chains increases, wave transmission performance deteriorates significantly, evidenced by reduced passband transmission coefficients, shifted resonance points, and increased in-band fluctuations, ultimately approaching a bandstop state with complete disconnection. Notably, in the X-band, wave transmission exhibits high sensitivity to structural damage. Using the transmission rate variation ratio at 10.1GHz resonance frequency as a key degradation indicator, with a failure threshold set at 60%, the task lifetime of AFSS is determined to be 901 cycles. The proposed modeling framework systematically reveals the multi-scale evolution mechanism of AFSS functional degradation, providing a theoretical basis and engineering support for reliability prediction and optimal design of active electromagnetic structures in complex environments.