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state-of-the-art in terms of various types of self-powered wearable IoT sensors, their functionalities, and
their diverse applications across different fields. The primary focus is to explore the capabilities and
potential of these sensors in enabling seamless interaction between humans and machines. The review
concludes by summarizing the key findings and discussing their implications in the field of self-powered
wearable IoT sensors as human-machine interfaces. Furthermore, the study addresses their limitations and
offers recommendations for future research.

Mainly, but not limited to, multiple electronic databases, including Web of Science and Scopus, were used
to conduct a comprehensive literature search. The following keywords were used: “self-powered”, “wearable
sensor”, “Internet of Things (IoT)”, and “human-machine interface”. The search string in Web of Science
consisted of the following: [“self-powered” OR “wearable sensor” AND “Internet of Things (IoT)” AND
“human-machine interface”] with the limitation of (“English language” AND “article”) AND (Publication
Year: 2020-2023). Similarly, the search string in Scopus included: TITLE-ABS-KEY[“self-powered” OR
“wearable sensor” OR “Internet of Things (IoT)” OR “human-machine interface”] AND {LIMIT-
TO[LANGUAGE, “English”] AND LIMIT-TO[DOCTYPE, “ar”] AND [LIMIT-TO(PUBYEAR, 2020-
2023)]}. Additionally, there was a search and screening for English articles published between 2010-2020
using a similar search strategy. Web of Science and Scopus databases were selected for the literature search
due to their comprehensive coverage of scholarly articles across various disciplines [63-66] . These databases are
widely recognized for their extensive indexing and inclusion of high-quality scientific literature [67-71] . By
using both Web of Science and Scopus, we aimed to ensure a comprehensive retrieval of relevant articles.
Only articles published in English were included to ensure accessibility and readability. Articles directly
related to the themes of “self-powered”, “wearable sensor”, “Internet of Things (IoT)”, and “human-
machine interface” were considered for inclusion. We focused on articles published between 2020 and 2023
to capture recent developments and up-to-date research. In addition to these criteria, we also excluded
duplicate articles and conducted a careful screening of titles and abstracts to assess their alignment with the
inclusion criteria. Full-text articles were then retrieved and further evaluated based on the defined criteria.

Literature selection
As illustrated in Supplementary Figure 1, an initial retrieval of 8,096 articles was conducted. These articles
underwent a screening process based on their titles and abstracts, resulting in the exclusion of irrelevant
articles [72,73] . The full texts of the remaining 305 articles were reviewed in detail to ensure compliance with
the inclusion criteria. Articles that were not relevant or did not provide relevant information on self-
powered wearable IoT sensors and human-machine interfaces were excluded. A final set of 225 articles was
included in the review.

The evaluation process involved reading and excluding articles of low relevance or significance. Only
articles aligned with the research content were considered. Relevant information from the selected articles
was carefully extracted and organized for subsequent analysis. The data extraction primarily focused on key
elements, including technology, applications, advantages, challenges, and future directions. Priority was
given to articles that offered in-depth discussions, empirical studies, or novel insights, as they provided
valuable contributions to the review. By employing this systematic process of data extraction and synthesis,
the review provides a thorough analysis of the current literature on self-powered wearable IoT sensors as
human-machine interfaces. This method ensures the comprehensive synthesis of relevant information,
identification of trends, and derivation of critical insights, thereby making a significant contribution to the
field.