Bioinspired Gradient Conductivity and Stiffness for Ultrasensitive Electronic Skins

Abstract

Hierarchical and gradient structures in biological systems with special mechanical properties have inspired innovations in materials design for construction and mechanical applications. Analogous to the control of stress transfer in gradient mechanical structures, the control of electron transfer in gradient electrical structures should enable the development of high-performance electronics. This paper demonstrates a high performance electronic skin (e-skin) via the simultaneous control of tactile stress transfer to an active sensing area and the corresponding electrical current through the gradient structures. The flexible e-skin sensor has extraordinarily high piezoresistive sensitivity at low power and linearity over a broad pressure range based on the conductivity-gradient multilayer on the stiffness-gradient interlocked microdome geometry. While stiffness-gradient interlocked microdome structures allow the efficient transfer and localization of applied stress to the sensing area, the multilayered structure with gradient conductivity enables the efficient regulation of piezoresistance in response to applied pressure by gradual activation of current pathways from outer to inner layers, resulting in a pressure sensitivity of 3.8 × 10 5 kPa −1 with linear response over a wide range of up to 100 kPa. In addition, the sensor indicated a rapid response time of 0.016 ms, a low minimum detectable pressure level of 0.025 Pa, a low operating voltage (100 μV), and high durability during 8000 repetitive cycles of pressure application (80 kPa). The high performance of the e-skin sensor enables acoustic wave detection, differentiation of gas characterized by different densities, subtle tactile manipulation of objects, and real-time monitoring of pulse pressure waveform.

Pushing detectability and sensitivity for subtle force to new limits with shrinkable nanochannel structured aerogel

“…In principle, electrical resistance changes are governed by the structure and electrical features of piezoresistive materials, while material deformation critically depends on their geometry and mechanical properties 7 , 9 . Over the past few years, extensive investigations have focused on improving the detectability and/or sensitivity of piezoresistive sensors by optimizing the structural and electrical properties of sensing materials 8 , 10 – 14 . While conventional piezoresistive sensors made of bulk composites of conductive fillers and insulating polymers exhibit a low sensitivity 15 , recent studies have demonstrated that hierarchical nano/microstructured materials (e.g., cellular monolith/sponges 8 , 16 , 17 , nanomesh 18 , microdomes/micropillars/microspines 10 , 11 , 19 , bristled nanoparticles 12 , 20 , and microchannels/multilayers 21 , 22 ) provide decent sensing performance (sensitivity >100 kPa −1 ).…”

Recent Progress in Essential Functions of Soft Electronic Skin

“…The commonly used method to sense these tactile stimuli is to convert them into electrical signals, including resistance or capacitance, which can be collected and processed by computer. Based on different mechanisms, the existing tactile sensors can be divided into resistive-type sensors [16,45,46] and capacitive-type sensors. [47,48] Resistive-type sensors normally transduce the above stimuli into a change in resistance, while the working principle of capacitance -based sensors is due to the change in capacitance induced by the stimuli.…”

Recent Advances in Graphene Electronic Skin and its Future Prospects

“…Chunggi Baig and Hyunhyub Ko, [99] Ulsan University of Science and Technology in South Korea, proposed a gradient conductive structure based on a gradient mechanical structure and achieved high linearity, wide detection range (100 kPa), and ultra‐high pressure sensitivity (3.8×10 5 kPa −1 ) of e‐skin by accurately adjusting the current in the gradient conductive structure and transferring stress in the gradient mechanical structure. The PDMS microspheres used to achieve interlocking are coated with three layers of poly (3,4‐ethylene dioxythiophene): poly (styrene sulfonate) (PEDOT: PSS)/polyurethane dispersion (PUD) active layers with different conductivities, which are gradually increased from the outer to the inner layer by adding different amounts of ethylene glycol (Figure 7h).…”