This paper presents a wearable hand module which was made of five fiber Bragg grating (FBG) strain sensor and algorithms to achieve high accuracy even when worn on different hand sizes of users. For real-time calculation with high accuracy, FBG strain sensors move continuously according to the size of the hand and the bending of the joint. Representatively, four algorithms were proposed; point strain (PTS), area summation (AREA), proportional summation (PS), and PS/interference (PS/I or PS/I_ $\alpha$ ). For more accurate and efficient assessments, 3D printed hand replica with different finger sizes was adopted and quantitative evaluations were performed for index~little fingers (77 to 117 mm) and thumb (68~78 mm). For index~little fingers, the optimized algorithms were PS and PS/I_ $\alpha$ . For thumb, the optimized algorithms were PS/I_ $\alpha$ and AREA. The average error angle of the wearable hand module was observed to be 0.47 ± 2.51° and mean absolute error (MAE) was achieved at 1.63 ± 1.97°. These results showed that more accurate hand modules than other glove modules applied to different hand sizes can be manufactured using FBG strain sensors which move continuously and algorithms for tracking this movable FBG sensors.

Massive efforts to build walking aid platforms for the disabled have been made in line with the needs of the aging society. One of the core technologies that make up these platforms is a realization of the skin-like electronic patch, which is capable of sensing electromyogram (EMG) and delivering feedback information to the soft, lightweight, and wearable exosuits, while maintaining high signal-to-noise ratio reliably in the long term. The main limitations of the conventional EMG sensing platforms include the need to apply foam tape or conductive gel on the surface of the device for adhesion and signal acquisition, and also the bulky size and weight of conventional measuring instruments for EMG, limiting practical use in daily life. Herein, we developed an epidermal EMG electrode integrated with a wireless measuring system. Such the stretchable platform was realized by transfer-printing of the as-prepared EMG electrodes on a SiO₂ wafer to a polydimethylsiloxane (PDMS) elastomer substrate. The epidermal EMG patch has skin-like properties owing to its unique mechanical characteristics: i) location on a neutral mechanical plane that enables high flexibility, ii) wavy design that allows for high stretchability. We demonstrated wireless EMG monitoring using our skin-attachable and stretchable EMG patch sensor integrated with the miniaturized wireless system modules.

A novel inertial measurement unit (IMU) was proposed to measure the three-axis linear/angular acceleration of a body using six fiber Bragg grating (FBG) optical fiber acceleration sensors sharing the same rotational center. The six acceleration sensors were shown to accurately distinguish between movements in different directions using a vibration generator and rotary motor/encoder device. The results also indicated that the measurement range of the FBG linear acceleration sensor was ±14 g, its average sensitivity was approximately 229.4 pm/g, and its nonlinearity was under 0.05%. Furthermore, the average sensitivity and nonlinearity of the FBG angular acceleration sensor were 21°/s ² /pm and 0.23%, respectively. When measuring linear and angular acceleration, the cross-axis sensitivity of the IMU was within 2.0%. The measurement accuracy of the roll and pitch angle during 360° rotation as well as that of the yaw angle during 720° rotation were both in the range of 0.54%–1.31%. Most of results indicated that the FBG-based IMU sensor was within the performance specifications of an equivalent conventional IMU sensor. Thus, the concept underlying the proposed sensor can be confidently used as a basis to develop a high-precision IMU sensor that is unaffected by electromagnetic interference.

In this study, a double-ring erbium-doped fiber (EDF) laser with an optical switch and a fiber Bragg grating (FBG)-referenced interrogating system was developed and demonstrated. This double-ring configuration can achieve high power amplified spontaneous emission, enabling laser oscillation even within the L-band. The output range and signal-to-noise ratio (SNR) of the double-ring EDF laser were measured to be 1512–1610 nm and 55 dB. In addition, the interrogating system using FBGs for reference resulted in precision improvement of ∼25 pm over those achieved in previous studies, reaching a precision of about 7 pm. The high power, broad tuning range, and sufficiently high precision of the proposed interrogating system make it promising for use in FBG-based sensing applications.

We present a high-accuracy distributed bend sensor suitable for high-curvature structures based on Brillouin frequency measurement using a multi-fiber probe. Brillouin optical correlation domain analysis (BOCDA) with differential measurement is adopted for distributed strain sensing with a cm-order spatial resolution (minimum 1 cm), and a specially designed sensing probe embedding three optical fibers is used to enhance the minimum measurable bending radius and accuracy of bend sensing. Analysis on the reconstruction accuracy is performed for various spatial resolutions (10, 20, 30, 40 mm) and steps (1, 5, 10, 15, 20 mm) of the BOCDA system. Our results show that the maximum measurable curvature of three-dimensional bending is 143 m-1, which is the highest curvature so far measured by Brillouin sensors in three-dimensional space, with about 0.7 % of tip position error. Additionally, both pseudo-discrete sensing and fully distributed sensing are performed together to analyze the relation between the methods of sensing (discrete or distributed) and the accuracy of probing multi-bend curvatures according to the measurement step.

Standard flexible colonoscopy is a powerful diagnostic tool for detecting colorectal cancer. However, the procedure entirely depends on the skill and perception of the colonoscopist, leading to unpredictable outcomes such as loop formation, potentially leading to severe complications. Consequently, there is a growing demand for a real-time shape monitoring system for colonoscopes. Despite various research efforts and commercial products that use magnetic sensors, challenges such as signal vulnerability, cost, and limited applicability persist. Optical fiber sensors (OFS), which address these drawbacks, are gaining increasing attention. However, measuring the shape of long colonoscopes accurately remains challenging for OFS due to twist-induced noise. In this study, we developed a twist-suppressed fiber Bragg grating (FBG) sensor to measure long 3-D shapes by enhancing the linearity of the sensor and introducing a node-type structure. We also introduced an insertion length measurement algorithm for stable monitoring with this shape sensor. The twist-suppressed shape sensor exhibited a torsion angle suppression of 92% compared to conventional FBG shape sensors, achieving a torsional angle of 0.48°/cm. We evaluated the performance of the sensor by measuring bending directions and various loop shapes. Clinical tests with FBG sensors demonstrated their potential for real-time monitoring and reducing the time required for loop reduction. A colonoscopic monitoring system capable of precise shape measurements can facilitate safer and quicker procedures.