## 2 Research Methodology
### Review Protocol Development
#### 2.2.2 Search Process  
The target databases for our search process are shown in Table 2. Therefore, we have used different keywords in these databases. The employed time filter is \"_2007-2023_\". The achieved results with the AND operator may not confirm the relevance of the research context. Consequently, the OR operator has been used. It allows us to obtain relatively moresound and concrete search results. Nevertheless, the OR operator generates an enormous number of results. The scanning of this enormous amount of data is a daunting task. Therefore, two additional filters have been employed. These filters are \"content type = article\", and \"subject area = Engineering\".  
Figure 2 elaborates various steps in the search process. Different search terms were used in the target databases. Consequently, we analyzed approximately 10,282 search results. In the next step, 7136 research studies were filtered out by observing their _Title_. Similarly, 1451 research articles were filtered out by observing their _Abstracts_. Then, we performed a general study of 1695 articles. During this general study, the coherency among different sections as well as the formulated research questions (RQ1 to RQ4) were checked. Based on our general study, we discarded 1268 articles that did not meet the selection and rejection criterion. As a result, 427 articles were selected for a comprehensive evaluation. Based on the comprehensive evaluation (termed as the \"detailed study\" in Figure 2), we were able to filter 381 articles. In the last step, 46 research articles were finalized.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Serial No.**} & \multirow{2}{*}{**Search Terms**} & \multirow{2}{*}{**Operator**} & \multicolumn{6}{c}{**No. of Search Results**} \\ \cline{3-10}  & & & **IEEE** & **Springer** & **Elsevier** & **SAGE** & **Wiley** & **MDPI** & \begin{tabular}{c} **Taylor and** \\ **Francis** \\ \end{tabular} \\ \hline \multirow{2}{*}{1} & \multirow{2}{*}{\begin{tabular}{c} 'Bridges’ ‘SHM’ ’WSN’ \\ \end{tabular} } & AND & 34 & 252 & 171 & 52 & 38 & 96 & 27 \\ \cline{2-10}  & & OR & 43,730 & 44,663 & 53,187 & 2446 & 34,669 & 91,732 & 31,689 \\ \hline \multirow{2}{*}{2} & \multirow{2}{*}{\begin{tabular}{c} '[PERSON] ‘SHM’ energy \\ harvesting’ \\ \end{tabular} } & AND & 8 & 40 & 276 & 26 & 47 & 133 & 38 \\ \cline{2-10}  & & OR & 43,014 & 8251 & 63,791 & 218 & 32,487 & 94,200 & 43,969 \\ \hline \multirow{2}{*}{3} & \multirow{2}{*}{\begin{tabular}{c} '[PERSON] ‘solar’ \\ \end{tabular} } & AND & 172 & 2143 & 95 & 109 & 6071 & 8687 & 4269 \\ \cline{2-10}  & & OR & 99,245 & 56,065 & 32,451 & 2557 & 74,032 & 158,234 & 61,236 \\ \hline \multirow{2}{*}{4} & \multirow{2}{*}{\begin{tabular}{c} '[PERSON] ‘wind’ \\ \end{tabular} } & AND & 271 & 6508 & 137 & 426 & 6995 & 11,103 & 3719 \\ \cline{2-10}  & & OR & 98,198 & 74,122 & 42,910 & 3594 & 68,996 & 161,536 & 63,476 \\ \hline \multirow{2}{*}{5} & \multirow{2}{*}{\begin{tabular}{c} '[PERSON] ‘thermal’ \\ vibration’ \end{tabular} } & AND & 573 & 10,768 & 78 & 457 & 7315 & 23,598 & 4279 \\ \cline{2-10}  & & OR & 97,877 & 148,310 & 73,401 & 6251 & 53,679 & 279,510 & 47,296 \\ \hline \multirow{2}{*}{6} & \multirow{2}{*}{\begin{tabular}{c} 'Bridges’ ‘RF’ \\ \end{tabular} } & AND & 276 & 2300 & 127 & 78 & 4428 & 4403 & 3145 \\ \cline{2-10}  & & OR & 88,981 & 62,249 & 36,512 & 2.523 & 31,984 & 279,510 & 32,459 \\ \hline \multirow{2}{*}{7} & \multirow{2}{*}{\
\begin{tabular}{c} 'Bridges’ ’ PZT vibration’ \\ \end{tabular} } & AND & 8 & 365 & 294 & 60 & 2754 & 13 & 2911 \\ \cline{2-10}  & & OR & 21,148 & 13,233 & 11,036 & 860 & 21,398 & 84,993 & 18,398 \\ \hline \multirow{2}{*}{8} & \multirow{2}{*}{
\begin{tabular}{c} 'Bridges’ Electromagnetic \\ vibration’ \\ \end{tabular} } & AND & 33 & 1282 & 108 & 119 & 4189 & 113 & 4287 \\ \hline \hline \end{tabular}
\end{table}
Table 2: A quantitative summary of the search process.  
Figure 2: The flow of the employed search process.