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.

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.

Polymer actuators are important components in lab-on-a-chip and micromechanical systems because of the inherent properties that result from their large and fast mechanical responses induced by molecular-level deformations (e.g., isomerization). They typically exhibit bending movements via asymmetric contraction or expansion with respect to changes in environmental conditions. To enhance the mechanical properties of actuators, a strain gradient should be introduced by regulating the molecular alignment; however, the miniaturization of polymer actuators for microscale systems has raised concerns regarding the complexity of such molecular control. Herein, a novel method for the fabrication of micro-actuators using a simple molecular self-alignment method is presented. Amphiphilic molecules that consist of azobenzene mesogens were located between the hydrophilic and hydrophobic surfaces, which resulted in a splayed alignment. Thereafter, molecular isomerization on the surface induced a large strain gradient and bending movement of the actuator under ultraviolet-light irradiation. Moreover, the microelectromechanical systems allowed for the variation of the actuator size below the micron scale. The mechanical properties of the fabricated actuators such as the bending direction, maximum angle, and response time were evaluated with respect to their thicknesses and lengths. The derivatives of the polymer actuator microstructure may contribute to the development of novel applications in the micro-robotics field.