## 2 Study Organization and Search Processing Method  
This study has been carried out as a systematic literature review based on the original guidelines as proposed by [PERSON] [36]. The work aims to highlight the positive impact that the thermal IR imaging technology can have on HRI application, facilitating and enhancing this interaction by recognizing the human affective state. For this purpose, the research questions (RQ) addressed by this study were:  
* RQ1. What is the broad social impact of a facilitated HRI? Or Why is facilitated HRI important? * RQ2. What are the scientific bases for thermal IR imaging as an affective state recognition technique? * RQ3. What are the limitations of current research? * RQ4. Has thermal IR imaging already been addressed in the HRI field? One of the goals of this study was to make this review as inclusive and practical as possible. Therefore, the databases searched were both Scopus and Google Scholar. All the papers published in conferences and journals between 2000 and 2020 were considered. Papers published from the year 2000 were considered, since the word \"Affective Computing\" was coined by [PERSON] that year [6], and \"Affective Computing\" started to be applied in the HRI field. For each research question, a search process was applied. Concerning RQ1, the search was based on the words \"facilitate\" and \"human-robot Interaction\". In the Scopus database, the survey was set up by searching for those words within the following fields: article title, abstract, and keywords. The basic search generated 441 results. In the Scholar database, on the other hand, the advanced search can be performed either by searching (i) the entire text or (ii) the title only. Therefore, the search was based on \"facilitate human-robot interaction\" within the entire text. A total of 360 results were obtained from the Scholar survey. The review papers and all the papers that did not refer to a user study or that did not relate to HRI were excluded, which reduced the considered pool to 155 papers. Within those papers, 130 were related to Scopus research, and 105 were from Scholar with an overlap of 80 papers. The manual review process was adopted for the final exclusion; the papers' abstracts were scanned, and all the papers that did not report experimental applications of human interaction were discarded. A total of 18 papers were discussed in the review concerning these keywords. Among those papers, 13 papers resulted from both Scopus and Scholar research, while 5 were from Scholar only. With respect to RQ2 and RQ3, the searched keywords were \"thermal imaging\" OR \"IR imaging\" OR \"thermography\" AND \"emotion recognition\" OR \"Affective Computing\" OR \"emotion\". In the Scopus database, those keywords were surveyed in fields such as article title, abstract, and keywords. Whereas in Scholar, the advanced survey was carried out by searching for \"thermal imaging\" OR \"IR imaging\" OR \"thermography\" with at least one of these words: \"Affective Computing\" OR \"emotion\", and the field searched was the entire text. The search generated 115 results in Scopus and 163 in Scholar with an overlap of 95 papers. The results were scanned through a manual review procedure focusedon the papers' abstracts, which aimed to identify whether the considered works reported on thermal IR imaging for human emotion recognition. Papers not related to it were excluded. The resulting papers were analyzed and grouped based on their experimental applications, strengths and limitations were indicated, and 46 were reported in the present work. Among those papers, 40 papers resulted from both Scopus and Scholar research, while 6 were from Scholar only. Finally, as for the RQ4, the keywords \"thermal imaging\" OR \"IR imaging\" OR \"thermography\" AND \"human-robot interaction\" were searched. The fields checked and the procedure performed were the same reported in the previous RQs. The basic search generated 13 results in Scopus and 388 in Scholar.