**5. Conclusions**

This study proposed a damage identification method of incorporating topology optimization with the visualization of ultrasonic wave propagation. The distribution of the damage parameter in a design domain was estimated by reproducing the ultrasonic maximum amplitude map of the target data. The proposed method was verified by applying it to numerical and experimental examples with known damage. The conclusions are summarized below:


Damage identification in simple and ideal model cases was demonstrated as the first attempt. In our future research, potential of the proposed method will be explored in general cases such as oblique incident to an embedded crack.

**Author Contributions:** Conceptualization, K.R. and S.Y.; methodology, K.R., S.Y., and H.N.; software, K.R.; validation, K.R., S.Y., and N.T.; formal analysis, K.R.; investigation, K.R., S.Y., and N.T.; resources, S.Y.; data curation, K.R.; writing—original draft preparation, K.R.; writing—review and editing, S.Y., H.N., and N.T.; visualization, K.R.; supervision, S.Y.; project administration, S.Y. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.
