# Smart Patch for Structural Health Monitoring of Composite Repair
## 4 Conclusions  
This paper developed a smart repair patch using the diagnostic film embedded into the patch using an edge cut-out method. This film has been verified to perform well under extreme environmental and operational conditions. Electro-mechanical impedance results showed that embedded lead zirconate titanate transducers' bonding qualities were good after manufacturing. For damage detection and localization, the damage index correlation coefficient and delay-and-sum algorithm based on the active sensing technique were used. In addition, blue contact gel was used to bond the repair patch and host structure together for easier removing the patch and inserting KAPTON(r) films to create artificial delamination. Furthermore, the A\({}_{0}\) mode at 50 kHz was not applicable due to the overlap between the crosstalk and the first wave packet of measured signals.  
According to the damage index results, the use of a smart repair patch can detect the artificial delamination and surface-mounted artificial damage at 250 kHz using both three and four lead zirconate titanate transducers. Furthermore, the smart repair patch can locate the delamination using three lead zirconate titanate transducers and surface-mounted artificial damage using four lead zirconate titanate transducers accurately. Since the resin film was replaced by blue contact gel for simulating the bonding and caused the inconsistency and uncertainty between the baseline and current signals due to removing the patch and inserting delamination, so the delay-and-sum results were not accurate when using four lead zirconate titanate transducers for the S\({}_{0}\) mode at 250 kHz. However, the use of resin film will keep the composite repair structure consistent and it can be confirmed that using four transducers will locate the delamination accurately using the delay-and-sum algorithm for actual composite repair. Therefore, the smart repair patch embedded with the developed diagnostic film and lead zirconate titanate transducers can be used to detect and locate bonding defects of repaired composite structures based on Structural Health Monitoring techniques.  
Experimental work, analysis and preparation of the manuscript, T.F.; supervision of the research and preparation of the manuscript, M.H.F.A. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding. [PERSON]'s scholarship is supported by the Aviation Industry Corporation of China, Ltd. (AVIC).  
Not applicable.  
Figure 10: Detection of surface-mounted artificial damage on the bottom of the host structure using (**a**) three PZT transducers and (**b**) four PZT transducers, and localization using (**c**) three PZT transducers and (**d**) four PZT transducers at 250 kHz for the position 2 (where the “\(\Circarrow\)” is the position for real damage and the “\(\times\)” is the position for predicted damage).  
Data Availability Statement: Not applicable.  
Acknowledgments: The first author wishes to acknowledge the funding from the Aviation Industry Corporation of China, Ltd. (AVIC), AVIC General Huanan Aircraft Industry Co., Ltd. and the China Scholarship Council (No. [2017] 5082).