Wearable device applications ushered in a new era of human-computer interaction with a variety of purposes, underlying concepts, and forms. These devices are widely used in medical and health fields such as physiological signal evaluation, athletics, and pollution detection.
Study: Synthesis of a nitrogen-doped reduced graphene oxide-based ceramic polymer composite nanofiber film for wearable device applications. Image Credit: magic pictures/Shutterstock.com
Developing an efficient electrode with optimal dielectric permittivity for wearable device applications, however, remains a major challenge.
A recent study published in Scientific Reports addresses this problem by fabricating a piezoelectric composite nanofiber film-based electrode for novel wearable device applications.
Materials for Wearable Device Applications: Overview and Challenges
Piezoelectric composites based on polymer materials and ceramics have attracted considerable interest for wearable device applications due to their excellent mechanical and electrical qualities, such as adaptability, dielectric properties and resilience. The electrical characteristics of untreated materials can be improved by incorporating piezoelectric ceramics into the composite materials.
Although piezoelectric composite materials have been successfully developed for wearable device applications, their resistive characteristics limit their ability to improve piezoelectric capabilities. Conductive materials can be introduced into piezoelectric composites to increase their electrical characteristics, freeing themselves from these constraints.
Two-dimensional reduced graphene oxide (rGO) is commonly used as a conductive substance in wearable device applications. It can be mixed with other materials to improve mechanical and electrical qualities.
Therefore, the incorporation of rGO into piezoelectric materials can increase their piezoelectric characteristics. However, many defects are formed during the reduction reaction of rGO, compromising its electron transport characteristics.
These defects can be very damaging for piezoelectric-based wearable device applications because they disturb the electric field. To compensate for the reduced conductive characteristics, nitrogen can be incorporated into the two-dimensional rGO, resulting in N-rGO with improved electrical properties.
Piezoelectric Nanofiber Films: The Future of Wearable Device Applications
Piezoelectric nanofiber films made from copolymers and ceramic materials have various advantages over conventional composites, including adaptability and dielectric properties. A nanofiber film is more flexible than other ceramic composites and polymers due to its large aspect ratio.
Although many techniques can be used to create piezoelectric nanofiber films for wearable device applications, the electrospinning method is commonly used because it offers several advantages over other physical production methods.
Electrospinning is a process that uses an electric field to create nanofibers of polymeric materials, ceramics and metals. This method can create nanofibers from complex compounds and work at low temperatures.
Moreover, the highly conductive N-rGO and piezoelectric hybrid nanofibers can be carefully combined during the preparation procedure before electrospinning. Therefore, N-rGO doped piezoelectric composite nanofibers suitable for various wearable device applications can be easily fabricated.
Interdigital electrodes for portable device applications
Almost all wearable device applications have a planner-type electrode structure, and traditional vertical-type electrodes cannot be used in next-generation wearable device applications. It is well established that piezoelectric nanofibrous films with planner-type electrodes offer unique electrical capabilities for a wide range of wearable device applications.
This study created interdigital planner type electrodes and applied them to N-rGO doped piezoelectric hybrid nanofiber films for wearable device applications.
The researchers selected synthetic N-rGO to enrich the piezoelectric composite nanofibers because it has a higher conductivity than rGO. Nitrogen is essential for removing defects from the rGO surface. Thanks to this higher conductance, the properties of floating electrodes in piezoelectric composite materials can be improved.
The researchers used the conformal mapping procedure to extract various combinations of dielectric permittivity by simulating and calculating the functional dielectric properties of the prepared electrodes. These electrodes have also been used to develop adaptable piezoelectric energy extractors for wearable device applications.
Important Study Findings
The characteristics of the floating electrodes enhanced the nanofiber-based energy generator created in this work and improved the power output. The output power has been optimized by refining the manufacturing technique and the architecture of the interdigital electrodes. The stored potential, open-circuit voltage, and output power were 3.78 V, 12.4 V, and 6.3 μW, respectively.
The overall dielectric permittivity of piezoelectric hybrid nanofiber films was increased from 8.2 to 15.5 by including ceramics and N-rGO conductors. This improved effective dielectric constant is most likely due to increased electric flux intensity due to higher conductance.
Based on these results, it is plausible to conclude that interdigital electrodes composed of N-rGO doped piezoelectric nanofiber films have high potential for use in a variety of wearable device applications in the future.
Ji, J.-H. et al. (2022). Synthesis of a nitrogen-doped reduced graphene oxide-based ceramic polymer composite nanofiber film for wearable device applications. Scientific reports. Available at: https://www.nature.com/articles/s41598-022-19234-0
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