Elastomeric Electronic Skin for Prosthetic Tactile Sensation

Abstract

Human skin is capable of transducing pressures in the range of 100 Pa (light touch) to 1 MPa (full body weight bearing); common tasks such as object manipulation develop contact pressures on the order of 10 kPa. [ 21,22 ] Moreover, sensitivity of human skin to applied pressures is complex and varies widely by type of mechanoreceptor and type of stimulation (normal pressure, shear pressure, frequency, magnitude). [ 23 ] Although distributed sensing using arrays of thin-fi lm transistors on ultrathin plastic foils combined with soft mechanical sensors has also been demonstrated, [ 11,[24][25][26] most reported skin-like sensors are discrete elements. An unmet demand for truly wearable e-skin is mechanical compliance. Natural skin is soft and elastic. Electronic skins should therefore wrap over the external surface of the body and accompany movement, in particular over joints and articulations. To date, pressure sensing data gloves and tactile skins are mainly prepared with fl exible polymers [27][28][29] and conductive textiles. [ 30,31 ] These constructs conform well to developable surfaces (e.g., the arm and fi nger phalanges) but wrinkle and often fail when placed over articulations (e.g., the elbow and fi nger joints). [ 32 ] E-skins prepared entirely with stretchable materials appear as a necessary starting point. Over the last decade, multiple designs of stretchable tactile sensors using elastomers, thin fi lms, composites, [ 19,33 ] and conductive liquids [34][35][36] have been reported, but their systematic characterization in real-life conditions is often incomplete. Stretchable strain sensors are often demonstrated in complex real-life scenarios, [ 37,38 ] but in the literature related to stretchable tactile sensors, demonstrations involving dynamic states where bending and stretching of the sensors occur simultaneously are not common, likely due to the challenges of removing cross-sensitivities to strain and noise received from the body. [ 19,20,39 ] In this paper, we report on a stretchable e-skin designed to be worn over the hand, monitor live fi nger movement, and register distributed pressure along the entire length of the fi nger. The sensory skin is thin and made entirely of elastic materials, thereby can be mounted on a glove and worn without impeding hand movement ( Figure 1 ). The read-out electronics are integrated in a small printed circuit board (PCB) located immediately at the base of each fi nger. Capacitive pressure sensors combine stretchable gold thin-fi lm electrodes with porous silicone foam (Figure 1 a) and display high sensitivity across much of the large dynamic pressure range of human skin. Six adjacent pressure sensors cover the entire length of the fi nger; two soft metallic shielding layers eliminate noise and cross-sensitivity over the skin and enable multi-touch with This report demonstrates a wearable elastomer-based electronic skin including resistive sensors for monitoring fi nger articulation and capacitive tactile pressure sensors that register distributed pressure along ...

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