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Wearable pressure sensors can help monitor human health and realize human-computer interaction. Efforts are ongoing to create pressure sensors with a universal device design and high sensitivity to mechanical stress.
Study: Weave pattern dependent textile piezoelectric pressure transducer based on electrospun polyvinylidene fluoride nanofibers with 50 nozzles. Image Credit: African Studio/Shutterstock.com
An article published in the journal npj Flexible Electronics reports on the fabrication of piezoelectric pressure transducers for fabrics using polyethylene terephthalate (PET) warp yarns and polyvinylidene fluoride (PVDF) weft yarns. The performance of the developed pressure sensor in relation to pressure measurement based on the weave pattern is demonstrated on a cloth scale of approximately 2 meters.
The results show that the sensitivity of a pressure sensor optimized using the 2/2 canard design is 245% higher than that of the 1/1 canard design. In addition, various inputs were used to evaluate the performance of the optimized fabrics, including flexion, squeezing, wrinkling, twisting, and various human movements. In this work, a tissue-based pressure sensor with a sensor pixel array exhibits stable perceptual characteristics and high sensitivity.
Rice. 1. Preparation of PVDF threads and multifunctional fabrics. a Diagram of a 50-nozzle electrospinning process used to produce aligned mats of PVDF nanofibers, where copper rods are placed in parallel on a conveyor belt, and the steps are to prepare three braided structures from four-layer monofilament filaments. b SEM image and diameter distribution of aligned PVDF fibers. c SEM image of a four-ply yarn. d Tensile strength and strain at break of a four-ply yarn as a function of twist. e X-ray diffraction pattern of a four-ply yarn showing the presence of alpha and beta phases. © Kim, DB, Han, J., Sung, SM, Kim, MS, Choi, BK, Park, SJ, Hong, H. R et al. (2022)
The rapid development of intelligent robots and wearable electronic devices has given rise to many new devices based on flexible pressure sensors, and their applications in electronics, industry, and medicine are rapidly developing.
Piezoelectricity is an electrical charge generated on a material that is subjected to mechanical stress. Piezoelectricity in asymmetric materials allows for a linear reversible relationship between mechanical stress and electrical charge. Therefore, when a piece of piezoelectric material is physically deformed, an electrical charge is created, and vice versa.
Piezoelectric devices can use a free mechanical source to provide an alternative power source for electronic components that consume little power. The type of material and structure of the device are key parameters for the production of touch devices based on electromechanical coupling. In addition to high voltage inorganic materials, mechanically flexible organic materials have also been explored in wearable devices.
Polymers processed into nanofibers by electrospinning methods are widely used as piezoelectric energy storage devices. Piezoelectric polymer nanofibers facilitate the creation of fabric-based design structures for wearable applications by providing electromechanical generation based on mechanical elasticity in a variety of environments.
For this purpose, piezoelectric polymers are widely used, including PVDF and its derivatives, which have strong piezoelectricity. These PVDF fibers are drawn and spun into fabrics for piezoelectric applications including sensors and generators.
Figure 2. Large area tissues and their physical properties. Photograph of a large 2/2 weft rib pattern up to 195 cm x 50 cm. b SEM image of a 2/2 weft pattern consisting of one PVDF weft interleaved with two PET bases. c Modulus and strain at break in various fabrics with 1/1, 2/2 and 3/3 weft edges. d is the hanging angle measured for the fabric. © Kim, DB, Han, J., Sung, SM, Kim, MS, Choi, BK, Park, SJ, Hong, H. R et al. (2022)
In the present work, fabric generators based on PVDF nanofiber filaments are constructed using a sequential 50-jet electrospinning process, where the use of 50 nozzles facilitates the production of nanofiber mats using a rotating belt conveyor belt. Various weave structures are created using PET yarn, including 1/1 (plain), 2/2 and 3/3 weft ribs.
Previous work has reported the use of copper for fiber alignment in the form of aligned copper wires on fiber collection drums. However, the current work consists of parallel copper rods spaced 1.5 cm apart on a conveyor belt to help align the spinnerets based on electrostatic interactions between incoming charged fibers and charges on the surface of the fibers attached to the copper fiber.
Unlike previously described capacitive or piezoresistive sensors, the tissue pressure sensor proposed in this paper responds to a wide range of input forces from 0.02 to 694 Newtons. In addition, the proposed fabric pressure sensor retained 81.3% of its original input after five standard washes, indicating the durability of the pressure sensor.
In addition, sensitivity values ​​evaluating voltage and current results for 1/1, 2/2, and 3/3 rib knitting showed high voltage sensitivity of 83 and 36 mV/N to 2/2 and 3/3 rib pressure. 3 weft sensors demonstrated 245% and 50% higher sensitivity for these pressure sensors, respectively, compared to the 24 mV/N weft pressure sensor 1/1.
Rice. 3. Expanded application of full-cloth pressure sensor. a Example of an insole pressure sensor made of 2/2 weft ribbed fabric inserted under two circular electrodes to detect forefoot (just below the toes) and heel movement. b Schematic representation of each stage of the individual steps in the walking process: heel landing, grounding, toe contact and leg lift. c Voltage output signals in response to each part of the gait step for gait analysis and d Amplified electrical signals associated with each phase of the gait. e Schematic of a full tissue pressure sensor with an array of up to 12 rectangular pixel cells with conductive lines patterned to detect individual signals from each pixel. f A 3D map of the electrical signal generated by pressing a finger on each pixel. g An electrical signal is only detected in the finger-pressed pixel, and no side signal is generated in other pixels, confirming that there is no crosstalk. © Kim, DB, Han, J., Sung, SM, Kim, MS, Choi, BK, Park, SJ, Hong, H. R et al. (2022)
In conclusion, this study demonstrates a highly sensitive and wearable tissue pressure sensor incorporating PVDF nanofiber piezoelectric filaments. Manufactured pressure sensors have a wide range of input forces from 0.02 to 694 Newtons.
Fifty nozzles were used on one prototype electric spinning machine, and a continuous mat of nanofibers was produced using a batch conveyor based on copper rods. Under intermittent compression, the manufactured 2/2 weft hem fabric showed a sensitivity of 83 mV/N, which is about 245% higher than the 1/1 weft hem fabric.
The proposed all-woven pressure sensors monitor electrical signals by subjecting them to physiological movements, including twisting, bending, squeezing, running and walking. In addition, these fabric pressure gauges are comparable to conventional fabrics in terms of durability, retaining approximately 81.3% of their original yield even after 5 standard washes. In addition, the manufactured tissue sensor is effective in the healthcare system by generating electrical signals based on continuous segments of a person’s walking.
Kim, DB, Han, J., Sung, SM, Kim, MS, Choi, BK, Park, SJ, Hong, HR, et al. (2022). Fabric piezoelectric pressure sensor based on electrospun polyvinylidene fluoride nanofibers with 50 nozzles, depending on the weave pattern. Flexible electronics npj. https://www.nature.com/articles/s41528-022-00203-6.
Disclaimer: The views expressed here are those of the author in his personal capacity and do not necessarily reflect the views of AZoM.com Limited T/A AZoNetwork, the owner and operator of this website. This disclaimer is part of the terms of use of this website.
Bhavna Kaveti is a science writer from Hyderabad, India. She holds MSc and MD from the Vellore Institute of Technology, India. in organic and medicinal chemistry from the University of Guanajuato, Mexico. Her research work is related to the development and synthesis of bioactive molecules based on heterocycles, and she has experience in multi-step and multi-component synthesis. During her doctoral research, she worked on the synthesis of various heterocycle-based bound and fused peptidomimetic molecules that are expected to have the potential to further functionalize biological activity. While writing dissertations and research papers, she explored her passion for scientific writing and communication.
Cavity, Buffner. (August 11, 2022). Full fabric pressure sensor designed for wearable health monitoring. AZonano. Retrieved October 21, 2022 from https://www.azonano.com/news.aspx?newsID=39544.
Cavity, Buffner. “An all-tissue pressure sensor designed for wearable health monitoring”. AZonano. October 21, 2022 . October 21, 2022 .
Cavity, Buffner. “An all-tissue pressure sensor designed for wearable health monitoring”. AZonano. https://www.azonano.com/news.aspx?newsID=39544. (As of October 21, 2022).
Cavity, Buffner. 2022. All-cloth pressure sensor designed for wearable health monitoring. AZoNano, accessed 21 October 2022, https://www.azonano.com/news.aspx?newsID=39544.
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