No abstract

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.

Smart wearable technology is exceedingly desirable in athletic sports due to being lightweight, flexible to bend, soft and comfortable. It can continuously deliver accurate information and deformation. During knee flexion, the upper knee perimeter increases with the shrinkage of the knee joint flexor, and it can be monitored. In this study, a fiber Bragg grating (FBG) smart belt is fabricated by embedding FBG sensors at the center of a special silica gel (with unique adhering characteristics to fix FBG on the surface of the belt) for sensing knee joint movements. Polyvinyl chloride strips were adhered to the surface of the smart wearable belt for better protection. The smart belt was calibrated in the laboratory by a systematical changing knee posture and used to identify body postures at various static and kinematic postures of a male subject. The FBG-based smart wearable belt presented a consistent wavelength change after each step by angle changes at the knee joint position. The wavelength increment of FBG sensors increases linearly with the increasing of the bend angle of the knee joint in static tests, and the related slope ratio was 0.3 nm/°. In a jogging test, the measurement sensitivity achieved by the FBG smart wearable belt was within a range between 0.018/° and 0.021 nm/° for the male subject at the velocities of 2 and 3 km/h, respectively. The smart wearable belt could be a useful index to characterize a simple design and ease of implementation, and could also applied for knee posture circumferential strain measurements, especially for sports activities and monitoring stroke patients. This FBG smart belt can be fabricated to produce smart sensing fabrics.

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.

The analysis of plantar pressure distribution is essential in the field of biomedical and sports-related applications. In this study, a smart insole was developed for the measurement of plantar pressure distribution and the evaluation of body postures using optical fiber Bragg grating (FBG) sensing technology. Four FBG sensors characterized by four different center Bragg wavelengths, 1528 ± 0.3, 1532 ± 0.3, 1535 ± 0.3 and 1539 ± 0.3 nm, were located at the first metatarsus, third metatarsus, fifth metatarsus and heel position, respectively. The measurement sensitivity of all the FBG sensors was 0.000412 nm/kPa, approximately. Silica gel material of modulus = 10 MPa was selected to incorporate the FBG sensors. All FBG sensors were multiplexed together with one optical fiber cable. The performance and functional properties of all FBG-based pressure sensors were calibrated in the laboratory to evaluate plantar pressure distribution. A male subject was selected for performing four tasks, namely standing in an upright position, leaning forward, squat position and forward fold. During standing tests, plantar pressure observed at the heel position was around 57% higher than that at the first and third metatarsus, while the pressure of the fifth metatarsus position presents minimal pressure, which is only 37% that of the pressure of the heel position. When the subject performs leaning forward, the squat position and forward fold posture, the first and third metatarsi show maximum pressure, while the pressure decreases at the fifth metatarsus position. However, almost zero pressure is observed at the heel position when the subject changes the body postures of leaning forward, squat and forward fold posture. The extreme pressure of the forward fold posture was 1750 kPa acquired at the first metatarsus, which is 52% and 62% higher than those at the fifth and third metatarsi, respectively. Therefore, the smart insole successfully recorded both plantar pressure distribution and body posture changes regarding the wavelength values collected by the FBG sensors.