## 1 Introduction
[15] used the explicit finite difference method to study the propagation characteristics such as reflection, transmission, and attenuation of AE signals in a straight shaft, a stepped shaft, and a stepped shaft with a tool withdrawal groove. The results were verified by experiments. [PERSON] et al. [16] analyzed the influence of the stiffeners on the lamb wave via finite element simulation and obtained the lamb wave energy factor curve while studying the impact source location in the stiffened panel of the spacecraft's sealed bulkhead. However, the structure normally used was attached with multiple stiffeners, and research on the propagation characteristics of acoustic emission signals at a stiffener structure is scarce. [PERSON] et al. [17] investigated the propagation characteristics of the AE wave in a fluid-loaded pipeline and the influence of pipeline auxiliary structures such as weld, tee, and flange on defect location. The results show that these structures could affect the AE signal in different degrees and then affect the fault location accuracy. [PERSON] et al. [18] proposed a leak location method for the pipeline based on a modal AE time-frequency analysis to solve the problem of large location errors caused by dispersion during AE wave propagation, which could effectively suppress the dispersion of leakage-induced AE signals. It can be seen from the literature that many explorations on the propagation characteristics and related applications of AE signals in cylindrical structures have been carried out. However, there is little literature that reported the effect of a stiffened cylindrical shell on the propagation process of an AE signal. The propagation of AE signals in the plate with a stiffener has been studied. [PERSON] et al. [19,20] developed a simplified explanatory model for the scattering of guided plate waves at normal incidence upon an integral stiffener based on approximate guided wave theories. The guided wave propagation characteristics of plate stiffeners and its influence on the performance of acoustic source location were examined by experiments and simulations. It was demonstrated that operating in the frequency range of a high plate wave stiffener transmission could improve the reliability of the source location in a plate. [PERSON] et al. [21] shed light on the interaction of guided waves with discontinuities composed of sharp reductions in plate height and demonstrated a novel method for calculating scattering coefficients exploiting the principle of reciprocity in elastodynamics. It shows that the analytical solution provided results that coincide with those of the numerical model, which proves the effectiveness of the proposed method. [PERSON] et al. [22] simulated the modal conversion phenomenon of a hypervelocity impact AE signal at a ring-stiffened plate. [PERSON] et al. [23] experimentally analyzed the effects of the manned spacecraft with a stiffened panel on AE signals caused by a hypervelocity impact in wave mode, frequency domain, and time domain. The results implied that the stiffened panel had filtering effects on high frequency components of the signal. [PERSON] et al. [24] calculated the scattering coefficients of lamb wave modes from geometric discontinuities using an analytical method called complex mode expansion with vector projection (CMEP). The obtained experimental results agrees with the global analytical predictions. [PERSON] et al. [25] studied the effects of integral stiffeners with different geometries upon vertically incident Lamb waves. Experiments and simulations showed that stiffeners acted similar to comb filters on lamb waves of different frequencies. [PERSON] et al. [26] compared the differences in the leakage AE signals before and after passing the stiffeners in both the time domain and the frequency domain. The filtering characteristics of different frequency bands was obtained according to the proposed stiffener-passing coefficient, and the accuracy of leakage location could be improved by selecting the proper filtering frequency.