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The anguilliform swimmer, like eels, has a relatively flexible body, while the thunniform swimmer, like the swordfishes, has a much stiffer body. Correspondingly, in the design of biomimetic robotic fish, how to balance the non-uniform stiffness to achieve better propulsion performance is an essential question needed to be answered. In this paper, we conduct an experimental study on this question. First, a customized experimental platform is built, which eases the adjustment of the non-uniform stiffness ratio, the stiffness of the flexible part, the flapping frequency, and the flapping amplitude. Second, extensive experiments are carried out, finding that to maximize the propulsion performance of the biomimetic robotic fish, the non-uniform stiffness ratio is required to adapt to different locomotor parameters. Specifically, the non-uniform stiffness ratio needs to be reduced when the robotic fish works at low frequency, and it needs to be increased when the robotic fish works at high frequency. Finally, detailed discussions are given to further analyze the experimental results. Overall, this study can shed light on the design of a non-uniform biomimetic robotic fish, which helps to increase its propulsion performance.<\/jats:p>","DOI":"10.3390\/biomimetics7040187","type":"journal-article","created":{"date-parts":[[2022,11,4]],"date-time":"2022-11-04T03:28:10Z","timestamp":1667532490000},"page":"187","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":11,"title":["How Non-Uniform Stiffness Affects the Propulsion Performance of a Biomimetic Robotic Fish"],"prefix":"10.3390","volume":"7","author":[{"given":"Changzhen","family":"Zheng","sequence":"first","affiliation":[{"name":"School of Artificial Intelligence, Shenzhen Polytechnic, Shenzhen 518055, China"},{"name":"College of Mechanical Engineering, Guangxi University, Nanning 530004, China"},{"name":"Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8481-0913","authenticated-orcid":false,"given":"Jiang","family":"Ding","sequence":"additional","affiliation":[{"name":"College of Mechanical Engineering, Guangxi University, Nanning 530004, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Bingbing","family":"Dong","sequence":"additional","affiliation":[{"name":"School of Artificial Intelligence, Shenzhen Polytechnic, Shenzhen 518055, China"},{"name":"College of Mechanical Automation, Wuhan University of Science and Technology, Wuhan 430000, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4845-6632","authenticated-orcid":false,"given":"Guoyun","family":"Lian","sequence":"additional","affiliation":[{"name":"School of Artificial Intelligence, Shenzhen Polytechnic, Shenzhen 518055, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8615-3520","authenticated-orcid":false,"given":"Kai","family":"He","sequence":"additional","affiliation":[{"name":"Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3947-2916","authenticated-orcid":false,"given":"Fengran","family":"Xie","sequence":"additional","affiliation":[{"name":"School of Artificial Intelligence, Shenzhen Polytechnic, Shenzhen 518055, China"},{"name":"Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2022,11,3]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"771","DOI":"10.1093\/icb\/38.4.771","article-title":"Muscles, elastic energy, and the dynamics of body stiffness in swimming eels","volume":"38","author":"Long","year":"1998","journal-title":"Am. 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