## 6 Conclusions  
This paper proposes an AECTF method that solves the problem of large-scale accurate and fast localization of impact sources in a high-stiffened panel. The influence of the stiffeners on the Lamb wave is studied. The impact location test is carried out in a fan-ring shaped stiffened panel of sealed bulkhead of manned spacecraft with stiffeners height of 22 mm and the locating was carried out. The results show:  
1. The stiffener has almost no influence on the Lamb wave velocity, and the average wave velocity in each direction can be used as the impact locating wave velocity. When the Lamb wave passes through the same number of stiffeners, the amplitude of the first wave trough is basically the same. The more stiffeners the signal passes through, the more obvious the attenuation of the first wave trough is, and the same applies to the first wave crest.
2. The stiffener has a comb-filter effect on the S0 mode Lamb wave, and the number of passbands, the bandwidth and fluctuation of filter are related to the through-sti  
Figure 17: The distribution of absolute errors using the fixed parameters: (**a**) fixed threshold amplification factor; (**b**) fixed threshold.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Different Processing Methods** & \begin{tabular}{c} **Average Absolute** \\ **Error (mm)** \\ \end{tabular} & \
\begin{tabular}{c} **Average Relative** \\ **Error** \\ \end{tabular} &
\begin{tabular}{c} **Error Standard** \\ **Deviation (mm)** \\ \end{tabular} \\ \hline Without filtering & 25.4 & 3.10\% & 38.2 \\ With 0–100 kHz filtering & 28.6 & 3.49\% & 29.7 \\ With 100–200 kHz filtering & 7.0 & 0.86\% & 3.5 \\ With 200–300 kHz filtering & 19.9 & 2.43\% & 18.8 \\ Fixed threshold amplification factor & 17.5 & 2.13\% & 23.1 \\ with 100–200 kHz filtering & 27.8 & 3.39\% & 41.0 \\ Fixed threshold with 100–200 kHz filtering & 27.8 & 3.49\% & 41.0 \\ \hline \hline \end{tabular}
\end{table}
Table 5: The comparison of locating errors under different processing methods.  
the number of stiffeners is two, there is a clear pass band in the 70-170 kHz band, the pass band bandwidth is narrow, below 100 kHz. When the number of stiffeners is 3, the energy factor changes gently, and a wide pass band exists when the frequency is lower than 250 kHz. Comprehensive energy factor and frequency characteristics, the energy of the 100-200 kHz band signal is relatively high, and the time domain resolution is high, which is suitable for locating.
3. The AECTF method proposed in this paper has high locating accuracy and stability. When the signal is not filtered, the average locating errors of 84.4% impact points are less than 30 mm. Selecting the appropriate frequency band to filter the impact signals can further improve the locating results. The locating result is optimal when using 100-200 kHz band filtering. The maximum absolute error of 32 points is 16.3 mm, the average absolute error is 7.0 mm, the average relative error is 0.86% and the error standard deviation is 3.5 mm. There are large error points in the locating results of fixed threshold amplification factor and fixed threshold. By comparing the calculated arrival time and the actual arrival time of the signals, it is known that if the threshold is too small, it will be intercepted by noise. If the threshold is too large, the threshold will skip the S0 mode head. The AECTF method can adaptively acquire the arrival time of the S0 mode.  
[PERSON] and [PERSON] established the finite element model and performed the simulation; [PERSON], [PERSON], [PERSON] and [PERSON] designed the experiments; [PERSON], [PERSON] and [PERSON] performed the experiment; [PERSON], [PERSON] and [PERSON] analyzed the data. All authors reviewed the manuscript.  
This research was funded by National Key R&D Program of China (No. 2018 YFF0212201), Natural Science Foundation of Tianjin (No. 17)CYBJC19300) and State Key Laboratory of Precision Measurement Technology and Instrument Fund (Pilab-1706).  
The authors declare no conflict of interest.