Threadlike Piezoelectric Sensors Based on Ferroelectrets and Their Application in Washable and Breathable Smart Clothing

Abstract

Ferroelectrets, featuring strong piezoelectric activity, flexibility, lightweight, and low cost, are advanced material and have attractive prospects for various sensors and actuators. However, large-scale production of ferroelectret-based devices and their straightforward implementation in complicated structures remain difficult tasks. In this study, a novel self-shielding threadlike piezoelectric pressure sensor based on irradiation cross-linked polypropylene (IXPP) ferroelectrets with a symmetric coaxial structure, named Ferroelectret Coaxial Sensor (FCS), is designed, prepared, and characterized. Besides, such sensors with a length of up to 300 m are successfully produced by an industrial continuous production line, confirming that the fabrication procedure is compatible with it and that the FCS can be mass-produced in the future. The results show that the hydrostatic piezoelectric coefficient up to 55 pC/N is achieved in the FCS, which is around four times of magnitude higher than those of commercially available piezo-cables made of poly (vinylidene fluoride). Smart carpets and wristers weaved with an integrated FCS, that can be produced by an industrial production line, are sensitive, flexible/stretchable, washable, and breathable, demonstrating great potential in motion recognition for health care. A laboratory prototype of traffic sensors based on the FCS indicates its capability in speed meauring and dynamic weighing for vehicles. This study will greatly promote applications of ferroelectrets in wearable devices, smart housing, intelligent transportation, etc.

Smart Cushions with Machine Learning-Enhanced Force Sensors for Pressure Injury Risk Assessment

“…The sensor has an up-and-down structure, with the FCS mounted on the FFS. The FCS features a coaxial structure and consists of a core electrode, a ferroelectret layer as the key functional materials, a shell of conductive layer as the ground and shielding electrode, and a protective outer jacket . The coaxial structure allows it to receive and respond to the external stimuli at 360°, making the FCS as the sensor’s receiving unit.…”

“…The FCS features a coaxial structure and consists of a core electrode, a ferroelectret layer as the key functional materials, a shell of conductive layer as the ground and shielding electrode, and a protective outer jacket. 39 The coaxial structure allows it to receive and respond to the external stimuli at 360°, making the FCS as the sensor's receiving unit. The FFS has a planar structure, with the ferroelectret film sandwiched between polydimethylsiloxane (PDMS) layers, and serves as the calibration unit for the FCS, assisting it in determining the direction of the force.…”

“…Since our previous study characterized the force-electric characteristics of the FCS, 39 this part focuses on the properties of the FFS. The sensitivity of FFS is characterized and the effect of the thickness of the PDMS layer on the sensitivity is investigated.…”

Influence of soft x-ray and ultraviolet irradiations on sensitivity of sensors made with piezoelectret films

“…a significant piezoelectric effect [5][6][7][8], which are one of the most promising materials for constructing high-performance pressure sensors [9][10][11]. Owing to their excellent mechanical flexibility and prominent piezoelectric activity, a variety of applications have been suggested, such as flexible film pressure sensors [11][12][13][14], energy harvesters [15][16][17] and acoustic transducers [18][19][20], which can benefit diversified fields, including wearable energy harvesting, human physiological signal monitoring and human-machine interfaces in the future.…”

“…Decay of charges in an electret is either due to internal phenomena, such as ohmic conduction or drift and diffusion of excess charges, or to the external process of depolarization [21]. For external process, the stability of piezoelectrets under different temperatures, humidities, mechanical excitations has been widely explored [12,[22][23][24]. In our previous work, the sensitivity decay of irradiation cross-linked polypropylene (IXPP) piezoelectret sensors and air-filled parallel-tunnel fluorinated poly(ethylene propylene) (FEP) piezoelectret sensors at different conditions without irradiation was investigated [24,25].…”