Abstract

Abstract

Abstract
A flexible wearable sensor utilizing a balloon-shaped interferometer structure, created from a bent standard single-mode fiber and a 3D-printed piece, was introduced and shown for respiratory monitoring. The interferometer is a compact, cost-effective, and easily fabricated sensor. The fiber’s curvature causes interference between the core and cladding modes, which in turn results in the sensor operation. In the balloon-shaped curving section, light traversing the core partially escapes and interacts with the cladding. The preliminary results demonstrate an average displacement of 9.3 nm and the capability to evaluate breathing rate. © 2025 SPIE.

Abstract
A sensor based on the fiber Bragg grating (FBG) and additive manufacturing for diameter variation measurement is proposed and experimentally demonstrated in this work. Two designs were proposed: a FBG alone and a FBG in series with a spring. Three tests were developed for each design, and at the end, the statistical treatment was performed. The designs were fabricated using a 3D printer, and the FBG sensor is embedded. The results demonstrated that the structures proposed in this work can be used to monitor diameter variation, among other applications. The sensors, with and without spring in series, presented sensitivities of 0.0671 nm/mm and 0.5116 nm/mm, respectively, with a good linear response greater than 0.99.

Abstract
This work addresses the historical development of techniques and methodologies oriented to the measurement of the internal diameter of transparent tubes since the original contributions of Anderson and Barr published in 1923 in the first issue of Measurement Science and Technology. The progresses on this field are summarized and highlighted the emergence and significance of the measurement approaches supported by the optical fiber.