This study proposed a new fiber Bragg grating-based smart ring for monitoring body joint postures occurred at elbow joint and knee joint positions. A single-mode fiber Bragg grating sensor was embedded into a 3D printed ring for sensing occurred deformation of the ring. The raw material used for fabricating the smart ring was polylactic acid, which was found to have the advantages of being flexible in nature and having ease of fabrication using fused deposition modeling method. The fabrication process of the fiber Bragg grating smart ring was characterized by the advantages of ease of handling, quick prototyping, high resolution, low cost, and time-saving. Bare fiber Bragg grating sensors were successfully embedded into hot printed polylactic acid material during the fused deposition modeling process, even the printing temperature of the printing nozzle exceeded 200℃. Two new smart wearable rings were fabricated and used to monitor systematic bend motion of elbow joint and knee joint. The measurement sensitivities of the two smart rings mounted at the elbow joint and knee joint were 0.0056 nm/° and 0.0276 nm/°, respectively. The corresponding maximum measurement angle within current calibration tests were 90° and 100°, respectively. The method of using both fiber Bragg grating and fused deposition modeling for sensor design can be extended for the fabrication of other sensors such as temperature sensors, strain sensors, pressure sensors, stress sensors, displacement sensors, and tilt sensors.

Posture monitoring and investigation in wearable technology play a significant role in the analysis of body postures. This study aims to develop a new flexible smart garment realized by stitching flex sensors at different joint positions for sensing flexion angles in static and kinematic motions. Calibration tests were conducted by systematically flexing wrist, elbow, and knee joints, respectively. A male subject then wore the developed flexible smart garment to sense different body postures. The measured data from flex sensors inside the smart garment exhibited immediate response after each joint movement of the male subject. The minimum measurement sensitivities of flex sensors mounted at the knee, elbow, and wrist was 0.94°, 0.8°, and 0.56°, respectively. Measured flexion angle changes were within 80°, 95°, and 140° ranges from knee, elbow, and wrist. Both stand and walk tests at a velocity of 4 km/h indicate that the flexion angles of three joint positions include wrist, elbow, and knee joints can be effectively monitored using the flex sensor–based smart garment. Flex sensor can be employed to monitor body joint movement and future to identify different postures of body joints in practice. The flexible smart garments cannot be washed.

This study aims to fabricate smart insoles using wireless Flexi force and bend sensing technology. Polyvinyl chloride (PVC) film was chosen as the substrate to hold all the sensors. The developed smart insole has a three-layer structure (insole-PVC layer-fabric layer) and is calibrated in an isolation laboratory to evaluate its measurement performance. One male volunteer subject exhibited four different body postures, namely tree pose, forward-leaning, squatting, and forward folding pose. Changes in pressure distribution were considered to be similar for the forward, squat, and forward-folded positions. When subjects performed a full squat, the flex sensor exhibited maximum flexion during the squat position, and the flex sensor response against the squat pose was found to be higher by about 18.18% than in the forward lean, respectively. The tree pose has the highest error rate at the first metatarsal, about 18.6%, of which the maximum absolute relative error of the sensor is less than 5%. Plantar pressure distribution and body posture measurements were successfully validated using Flexi force and flex sensors embedded in the smart insole. The smart insole proposed in this research work has broader prospects for clinical application.

The present study designed the dual-point liquid level measuring sensor using the polymer optical fiber. The sensor measures the liquid level variation based on the optical power intensity variation. The sensor structure is based on the twisting of two fibers and introduces cascading to achieve a dual-point detection. In our work, two liquid-level sensors are combined in series to form a dual-point liquid level sensor. Meanwhile, the system relies on a single input source, and the outputs of both sensors are individual. The individual output source of each sensor independently measures the liquid level variation that doesn’t require any decoupling technique to extract the sensing information. The liquid level variation is sensed by dual-point sensor by the change in the refractive index due to medium change. The increasing liquid level led to change in medium from air to water. Where the power coupling varies due to the change in liquid level. For present study we achieved the liquid level detection in the range of 0cm to 12 cm. The overall both sensors have the liner response of coupled optical power with respect to change in liquid level. The R-squared value of both sensors (Sensor-A and Sensor-B) is measured as 0.9924 and 0.9925. At repeated times, both sensors have a close response curve. The dual-point liquid level sensor is capable to response for continuous and discontinuous liquid level variations.