Flexible Pressure Sensors with Wide Linearity Range and High Sensitivity Based on Selective Laser Sintering 3D Printing

Abstract

applications in electronic skin (E-skin), human-machine interfaces, and healthcare monitoring. [1][2][3][4] Among the various types of sensors employing piezoresistive, [5][6][7] capacitive, [8][9][10] piezoelectric, [11][12][13] and triboelectric [14][15][16] sensing mechanisms, the piezoresistive mechanisms have been intensively investigated due to their high sensitivity, simple structures, easy fabrication, and convenient data processing, resulting in significantly promising commercialization prospects. [17][18][19] To achieve success in practical applications, excellent performances in the pressure range related to human activity and scalable, low-cost, and reproducible manufacturing processes are decidedly required. [20][21][22][23] Piezoresistive pressure sensors based on composite materials consisting of elastic matrixes and conductive fillers have been comprehensively investigated and adopted in commercial applications due to their good performance and compatibility with scalable printing technology. [3,21,24] However, the sensors based on bulk resistance changes generally exhibited poor sensitivity in low pressure ranges, which limited their applications in E-skin or wearable devices. To break the bottleneck, flexible pressure sensors composed of surface microstructures and conductive layers were proposed, in which the signals were typically generated from the variation of the contact resistance. [25,26] The transformed working mechanism greatly promoted the sensitivity up to 10-100 kPa −1 (especially in the low pressure range) and decreased the limit of detection (LOD) to 1 Pa or less. [26][27][28] Nonetheless, for plenty of microstructure-based sensors, the response ranges with high sensitivity were limited to several kPa since the contact areas of the microstructures were easily saturated under small pressure. First, the narrow range would limit their applications in the medium-pressure range [29,30] (10-100 kPa), which is closely related to daily human activity. Second, the background stress that is generated from nontest objects can easily disable a sensor with a narrow sensing range. [31,32] In addition to the sensing range, a linear relationship between the pressure and the electrical signals was typically desired to facilitate data processing. [21,33] Considering that the sensitivity was usually different in the whole range, the available range would be further narrowed down, which set To achieve practical applications of flexible pressure sensors, good performance and scalable manufacturing processes are both desired. Here, flexible pressure sensors with excellent performance are fabricated via selective laser sintering (SLS). Having benefitted from the irregular microstructures generated in the powder sintering process, the sensors exhibit high sensitivity of 55 kPa −1 in a wide linearity range of 100 kPa, and they maintain decent sensitivity (>10 kPa −1 ) over a high-pressure range (100-400 kPa), which is among the best results for flexible pressure sensors. The working mechanism of the sensor...

Flexible Waterproof Piezoresistive Pressure Sensors with Wide Linear Working Range Based on Conductive Fabrics

“…Flexible pressure sensor, especially the piezoresistive sensor, is widely employed in electronic skin [1][2][3][4], healthcare monitoring [5][6][7][8], and human-machine interactions (HMI) [9][10][11]. To expand the feasibility of the piezoresistive sensor for diversified practical applications, they should have a linear pressure-sensing capability within large dynamic sensing ranges to constantly maintain their high sensitivity from lowpressure (< 10 kPa) to high-pressure region (> 100 kPa, even near 1 MPa) [12][13][14]. So far, however, this is still a great challenging task for this kind of pressure sensor [15].…”

“…The reason is that a small increase in the contact area between the electrode and the active material leads to a significant decrease in the contact resistance. Inspired by this, constructing ordered rough architectures (e.g., the planar, microdome, micropyramid, and the micropillar structure) on the sensing materials were extensively studied to increase the contact variation in improving the sensitivity and working range [12,[19][20][21][22]. Fewer reports, however, including our previous studies, achieved a wide working range of over 100 kPa with superior sensitivity were studied through the development of the sensing materials [23][24][25].…”

Current advances and future perspectives of additive manufacturing for functional polymeric materials and devices

“…In view of the integration of structural design and tunable property, 3D printed electronic conductive parts have unique advantages for the use of sensing devices. Zhang et al 62 . constructed an irregular microstructure during the powder sintering process, and the assembled sensor exhibited high sensitivity over 10 kPa–1 in the wide range of 0‐400 kPa, which performed well in the tactile test, pulse monitoring, and plantar pressure measurement (Figure 2G).…”

“…In view of the integration of structural design and tunable property, 3D printed electronic conductive parts have unique advantages for the use of sensing devices. Zhang et al 62 constructed an irregular microstructure during the powder sintering process, and the assembled sensor exhibited high sensitivity over 10 kPa-1 in the wide range of 0-400 kPa, which performed well in the tactile test, pulse monitoring, and plantar pressure measurement ( Figure 2G). Moreover, the printing-induced alignment of filler, 63 structural design-induced localized strain, 59 and dual-material printing 64 can significantly enhance the gauge factor, responsive range, and stability of the printed sensors, making them of a great potential for applications in electronic skin, human-machine interface, and healthcare monitoring.…”

“…Reproduced with permission: Copyright 2019, Elsevier. 62 and the printed structure showed a high electronic conductivity of 100 S/m after annealing ( Figure 2F). However, the conductive inks for inkjet printing should have proper viscosity, volatile solvents, low-temperature curing capability, which limited the application of inkjet printing in manufacturing conductive parts or devices on a large scale.…”