Piezocapacitive Flexible E‐Skin Pressure Sensors Having Magnetically Grown Microstructures

Abstract

Flexible pressure sensors are highly desirable in artificial intelligence, health monitoring, and soft robotics. Microstructuring of dielectrics is the common strategy employed to improve the performance of capacitive type pressure sensors. Herein, a novel, low‐cost, large‐area compatible, and mold‐free technique is reported in which magnetically grown microneedles are self‐assembled from a film of curable magnetorheological fluid (CMRF) under the influence of a vertical curing magnetic field (Bcuring). After optimizing the microneedles' fabrication parameters, i.e., magnetic particles' (MPs') concentration and Bcuring intensity, piezocapacitive sensors capable of wide range pressure sensing (0–145 kPa) with ultrafast response time (50 ms), high cyclic stability (>9000 cycles), as well as very low detection limit (1.9 Pa) are obtained. Sensor properties are found dependent on microneedles' fabrication parameters that are controllable, produce variable‐sized microneedles, and allow to govern sensing properties according to desired applications. Finally, the sensor is employed in holding a bottle with different weights, human breath, and motion monitoring, which demonstrate its great potential for the applications of human–machine interaction, human health monitoring, and intelligent soft robotics.

Soft Electronics for the Skin: From Health Monitors to Human–Machine Interfaces

“…[109,111,126,127] Another example is the detection of the deep internal JVP (Figure 4b) which is valuable for diagnosis of cardiac failure or hypervolemia. [81] Pressure detection is mainly based on piezoresistive, [128] piezocapacitive, [129,130] and piezoelectric [117] effects. Flexible piezoresistive pressure sensors have been studied extensively because of their simple sensor structure and manufacturing process, low power consumption, [105,108] wide range of pressure detection, [106] low detection limit, [131] fast response, [131] and high sensitivity.…”

Transduction Mechanisms, Micro-Structuring Techniques, and Applications of Electronic Skin Pressure Sensors: A Review of Recent Advances

“…Through an innovative approach to micro-structure PDMS based on the mixing of the polymer with magnetic particles (silver coated with nickel) and subjecting it to a strong magnetic field to induce the formation of micro-needles as Figure 4 c presents, the group of Run-Wei Li created a low-cost capacitive e-skin, whose micro-needles features could be fairly controlled through the concentration of magnetic particles or magnetic field intensity [ 86 ]. With heights ranging from 275 µm to 856 µm, and diameters ranging from 166 µm to 420 µm, the optimized micro-needles conferred the e-skin a modest sensitivity of 0.159 kPa −1 bellow 1 kPa [ 86 ].…”

“…Polyimide [ 39 , 43 , 171 ] and PET with ITO [ 166 , 170 , 177 ] are common substrates as well. Treatments of the sensing film , such as PDMS heating [ 183 , 184 ], PDMS stretching and UV or oxygen plasma exposure [ 75 , 141 , 185 , 186 ], and self-assembly or chemical reaction [ 86 , 99 , 135 , 184 , 187 , 188 , 189 , 190 , 191 ]. Regarding the latter approach, the most common materials employed to achieve a certain level of micro-structuring are ZnO in several shapes [ 99 , 135 , 188 , 190 ], graphene [ 189 ], and silver particles [ 191 ].…”

“… Capacitive e-skin sensors, developed by ( a ) Zhenan Bao and co-workers in 2013 [ 30 ] (Copyright © 2020, Springer Nature), ( b ) Steve Park and co-workers in 2019 (reprinted with permission from [ 85 ]. Copyright 2019 American Chemical Society, Washington, WA, USA), and ( c ) Run-Wei Li and co-workers in 2020 [ 86 ] (Copyright © 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany). …”

“…of Ag NWs on PDMS. Sandpaper as mold 131.5 (0–1.5) 11.73 (5–28) 1.12 Pa/ 32 kPa 43/71 7000 (L) 0.5 V/- (♡ ) C R.-W. Li [ 86 ] 2020 Micro-needles (diameter between 166 µm and 422 µm, height between 275 µm and 856 µm) of PDMS and Ni-coated magnetic particles of Ag. Self-assembly 0.159 (0–1) 0.019 (1.5–11) 4.1 × 10 −3 (12–145) 1.9 Pa/ 145 kPa 49/51 9200 (L) -/- ( ) C C. F. Guo [ 171 ] 2020 Iontronic protrusions, and elec.…”