In a recent article published in the journal Polymers, researchers developed a novel wearable smart silicone belt designed for dual functionality: monitoring human motion and harvesting energy from body movements. The study aims to optimize the design and performance of the belt to enhance its effectiveness in real-world applications.
(a) The diagram of the BWS. (b) The photograph of the BWS worn on the waist. The inset is the enlarged view of the BTWS unit. (c) The freestanding working principle of the BWS follows steps (I–IV). (d) The potential distribution of the BWS at various displacements simulated with COMSOL Multiphysics 6.0. Image Credit: https://www.mdpi.com/2073-4360/16/15/2146
Background
Wearable technology has gained significant attention due to its potential to improve health monitoring and personal fitness tracking. Traditional wearable devices often rely on external power sources, which can limit their usability and convenience. The integration of energy harvesting mechanisms into wearable devices represents a significant advancement, allowing them to operate independently without frequent recharging.
In this study, the researchers discuss the triboelectric nanogenerator (TENG) principle, which is foundational to the energy harvesting capabilities of the silicone belt. TENGs exploit the contact electrification phenomenon between different materials to generate electrical energy.
The Current Study
The design of the wearable sensor was inspired by traditional belt structures. The sensor was constructed using a combination of triboelectric materials, specifically polytetrafluoroethylene (PTFE) and polyamide (PA), chosen for their favorable triboelectric properties, including high electronegativity and durability. The fabrication process involved creating multiple sensing units, each consisting of a soft silicone sheet that housed the triboelectric materials.
To optimize the wearable sensor's performance, a series of experiments were conducted to evaluate the influence of various design parameters on its output characteristics. The researchers focused on factors such as the number of divided pieces within a single sensing unit, the size of the friction area, and the connection method between multiple units.
The sensor's output performance was assessed by measuring key electrical parameters, including output voltage, current, and transferred charge. These measurements were taken using a digital multimeter connected to the sensor's output terminals.
To further evaluate the sensor's energy harvesting capabilities, the researchers incorporated an energy storage system, allowing them to charge capacitors and assess the sensor's ability to power electronic devices. Various capacitors were tested, and the time required to charge them to specific voltage levels was recorded. The wearable sensor's performance was also evaluated under different external load resistances to determine its maximum power output.
In addition to energy harvesting, the sensor's capability to monitor various physical activities was tested. The sensor's sensitivity to different physiological states, including normal breathing, deep breathing, and breath-holding, was tested. The output voltage was monitored during these activities, revealing patterns that correlated with changes in breathing intensity. The sensor was also tested during various exercise states, such as standing, walking, and running, with the output voltage increasing in response to higher activity levels.
Results and Discussion
The experimental results revealed that the output voltage of the wearable sensor increased significantly as the number of divided pieces in a single unit decreased. Specifically, the maximum output voltage rose from 16 V with three pieces to 47 V with a single piece, indicating that a complete unit effectively utilizes the entire friction area for charge generation.
The study also found that increasing the size of the friction area led to higher output voltage, current, and transferred charge, confirming the importance of design optimization. The researchers noted that while the output current remained relatively constant across different configurations, reducing the number of divided pieces enhanced the overall energy generation.
Furthermore, the connection method between multiple units was shown to significantly influence output performance. Parallel connections yielded higher voltage, current, and transferred charge compared to series connections, aligning with findings from previous studies.
The researchers successfully manufactured a belt with five parallel-connected units, demonstrating its ability to charge capacitors efficiently. The time required to charge capacitors to 1 V was recorded, with a notable performance observed for a 4.7 μF capacitor, which charged within 20 seconds. The sensor's performance was also evaluated under varying external load resistances, achieving a maximum power output of 35 μW at a resistance of 1 GΩ, surpassing results from earlier studies.
The output voltage remained stable during rest but exhibited significant variations during active breathing, showcasing the sensor's sensitivity to physiological changes. The researchers extended their analysis to monitor various exercise states, such as standing, walking, and running, with the output increasing in correlation with exercise intensity. The long-term performance of the wearable sensor was assessed through stability tests, demonstrating no significant deterioration in output after 12 hours of continuous use.
Conclusion
In conclusion, the study presents a novel belt-type wearable smart sensor that effectively combines motion monitoring and energy harvesting capabilities. The successful demonstration of the sensor's ability to monitor various physical activities while generating electrical energy positions it as a promising solution for the development of self-powered wearable devices. The findings contribute to the growing field of wearable technology, offering insights into the design and functionality of devices that can seamlessly integrate into daily life.
Journal Reference
Zhou L., Liu X., et al. (2024). Wearable Smart Silicone Belt for Human Motion Monitoring and Power Generation. Polymers 16(15):2146. DOI: 10.3390/polym16152146, https://www.mdpi.com/2073-4360/16/15/2146