{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,6]],"date-time":"2026-05-06T04:28:34Z","timestamp":1778041714314,"version":"3.51.4"},"reference-count":33,"publisher":"MDPI AG","issue":"19","license":[{"start":{"date-parts":[[2022,10,6]],"date-time":"2022-10-06T00:00:00Z","timestamp":1665014400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"This work was supported by a research grant of the Missouri University of Science and Technology, Rolla, 65401-0040, Rolla, USA in a Post-doc fellowship program for F. Mumtaz.","award":["J. Huang is grateful for support from the Roy A. Wilkens Professorship"],"award-info":[{"award-number":["J. Huang is grateful for support from the Roy A. Wilkens Professorship"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>A highly sensitive strain sensor based on tunable cascaded Fabry\u2013Perot interferometers (FPIs) is proposed and experimentally demonstrated. Cascaded FPIs consist of a sensing FPI and a reference FPI, which effectively generate the Vernier effect (VE). The sensing FPI comprises a hollow core fiber (HCF) segment sandwiched between single-mode fibers (SMFs), and the reference FPI consists of a tunable air reflector, which is constituted by a computer-programable fiber holding block to adjust the desired cavity length. The simulation results predict the dispersion characteristics of modes carried by HCF. The sensor\u2019s parameters are designed to correspond to a narrow bandwidth range, i.e., 1530 nm to 1610 nm. The experimental results demonstrate that the proposed sensor exhibits optimum strain sensitivity of 23.9 pm\/\u03bc\u03b5, 17.54 pm\/\u03bc\u03b5, and 14.11 pm\/\u03bc\u03b5 cascaded with the reference FPI of 375 \u03bcm, 365 \u03bcm, and 355 \u03bcm in cavity length, which is 13.73, 10.08, and 8.10 times higher than the single sensing FPI with a strain sensitivity of 1.74 pm\/\u03bc\u03b5, respectively. The strain sensitivity of the sensor can be further enhanced by extending the source bandwidth. The proposed sensor exhibits ultra-low temperature sensitivity of 0.49 pm\/\u00b0C for a temperature range of 25 \u00b0C to 135 \u00b0C, providing good isolation for eliminating temperature\u2013strain cross-talk. The sensor is robust, cost-effective, easy to manufacture, repeatable, and shows a highly linear and stable response for strain sensing. Based on the sensor\u2019s performance, it may be a good candidate for high-resolution strain sensing.<\/jats:p>","DOI":"10.3390\/s22197557","type":"journal-article","created":{"date-parts":[[2022,10,10]],"date-time":"2022-10-10T05:12:21Z","timestamp":1665378741000},"page":"7557","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":23,"title":["Highly Sensitive Strain Sensor by Utilizing a Tunable Air Reflector and the Vernier Effect"],"prefix":"10.3390","volume":"22","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-5213-608X","authenticated-orcid":false,"given":"Farhan","family":"Mumtaz","sequence":"first","affiliation":[{"name":"Department of Electrical and Computer Engineering, Missouri University of Science and Technology, Rolla, MO 65409-0040, USA"}]},{"given":"Muhammad","family":"Roman","sequence":"additional","affiliation":[{"name":"Department of Electrical and Computer Engineering, Missouri University of Science and Technology, Rolla, MO 65409-0040, USA"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5574-8396","authenticated-orcid":false,"given":"Bohong","family":"Zhang","sequence":"additional","affiliation":[{"name":"Department of Electrical and Computer Engineering, Missouri University of Science and Technology, Rolla, MO 65409-0040, USA"}]},{"given":"Lashari Ghulam","family":"Abbas","sequence":"additional","affiliation":[{"name":"Electrical Engineering Departmesnt, Sukkur IBA University, Sukkur Sindh 65200, Pakistan"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3269-1750","authenticated-orcid":false,"given":"Muhammad Aqueel","family":"Ashraf","sequence":"additional","affiliation":[{"name":"Communications Laboratory, Department of Electronics, Quaid-i-Azam University, Islamabad 45320, Pakistan"}]},{"given":"Yutang","family":"Dai","sequence":"additional","affiliation":[{"name":"National Engineering Laboratory for Fiber Optic Sensing Technology, Wuhan University of Technology, Wuhan 430070, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8659-2910","authenticated-orcid":false,"given":"Jie","family":"Huang","sequence":"additional","affiliation":[{"name":"Department of Electrical and Computer Engineering, Missouri University of Science and Technology, Rolla, MO 65409-0040, USA"}]}],"member":"1968","published-online":{"date-parts":[[2022,10,6]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"106508","DOI":"10.1016\/j.optlaseng.2020.106508","article-title":"Fiber Optic Shape Sensors: A Comprehensive Review","volume":"139","author":"Floris","year":"2021","journal-title":"Opt. 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