Abstract
Electronic skins (e-skins) with high sensitivity to multidirectional mechanical stimuli are crucial for healthcare monitoring devices, robotics, and wearable sensors. In this study, we present piezoresistive e-skins with tunable force sensitivity and selectivity to multidirectional forces through the engineered microstructure geometries (i.e., dome, pyramid, and pillar). Depending on the microstructure geometry, distinct variations in contact area and localized stress distribution are observed under different mechanical forces (i.e., normal, shear, stretching, and bending), which critically affect the force sensitivity, selectivity, response/relaxation time, and mechanical stability of e-skins. Microdome structures present the best force sensitivities for normal, tensile, and bending stresses. In particular, microdome structures exhibit extremely high pressure sensitivities over broad pressure ranges (47,062 kPa−1 in the range of <1 kPa, 90,657 kPa−1 in the range of 1–10 kPa, and 30,214 kPa−1 in the range of 10–26 kPa). On the other hand, for shear stress, micropillar structures exhibit the highest sensitivity. As proof-of-concept applications in healthcare monitoring devices, we show that our e-skins can precisely monitor acoustic waves, breathing, and human artery/carotid pulse pressures. Unveiling the relationship between the microstructure geometry of e-skins and their sensing capability would provide a platform for future development of high-performance microstructured e-skins.
Highlights
Electronic skins (e-skins) with high sensitivity to multidirectional mechanical stimuli are crucial for healthcare monitoring devices, robotics, and wearable sensors
Previous e-skins having different microstructures have successfully shown improved tactile sensing performances, specific to some of desired applications, there have been no systematic studies of the effects of microstructure geometry on force-induced microstructure-deformation and the resulting force sensitivity and selectivity in response to multidirectional mechanical stimuli
In the interlocked MWNT/PDMS composite films of the present work, contact resistance is dominated by the tunneling resistance (RT) between microstructured composite films, which is inversely proportional to the variation in contact area according to the equation RT = (V/J) × (1/ACNT), where V is the applied voltage, J is the current density, and ACNT is the electrical contact area between MWNTs, which is in turn proportional to the physical contact area (AC) between interlocked microstructures[25]
Summary
Electronic skins (e-skins) with high sensitivity to multidirectional mechanical stimuli are crucial for healthcare monitoring devices, robotics, and wearable sensors. For accurate and Recently, a large number of electronic skins with cap- reliable monitoring of those signals, e-skins with enhanced abilities of detecting physical/chemical stimuli have been sensitivity, selectivity, response time, and mechanical durreported for applications in robotics, wearable electronics, ability are required In accordance with these demands, eand healthcare monitoring devices[1,2,3,4,5,6,7,8]. The strong adhesion properties of pillar structures provide a new possibility for skinattachable and wearable healthcare devices[1] Considering these geometrical effects of microstructure arrays on the performance of e-skins, previously, geometrical parameters such as shape, size, and space of microstructure arrays have been controlled to enhance the mechanical sensitivity and operation range of piezoresistive[20] and capacitive e-skins[15] and the power generation of self-powered e-skins[16,17,18,21,22,23]. A systematic and in-depth analysis of geometrical effects on sensing performance is important to enable the design of tunable e-skins having high force sensitivity and selectivity, which can be customized for diverse applications
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