Unsymmetrical Alveolate PMMA/MWCNTs Film as Piezoresistive E-skin with Four-dimensional Resolution and Application for Detecting Motion Direction and Airflow Rate.

Flexible and piezoresistive electronic skins (E-skins) with high spatial resolution are highly desired in artificial intelligence and human-machine interactions. In this study, a simple method is developed to pattern a piezoresistive layer using lithography, which can realize real-time tactile sensing and spatial resolution. The piezoresistive layer with a honeycomb hole array based on polymethyl methacrylate (PMMA)/multiwalled carbon nanotubes (MWCNTs) was fabricated using a reverse mold with a ZnO nanorod array. The device exhibits an ultrahigh sensitivity of 88 kPa-1 in the low-pressure regime (< 10 kPa) and a fast response time of 110 ms owing to the conductive honeycomb structure. The E-skin-based PMMA/MWCNTs honeycomb array film can be applied to monitor bending and vibration by changing the contact area of the hole walls. A 4 × 4 piezoresistive matrix was fabricated by lithography for a 16-pixel tactile-sensing E-skin, which realizes a four-dimensional resolution including the space and time resolutions of pressure points. In addition, using the unsymmetrical structure of alveolate PMMA/MWCNTs film, the detection of direction and velocity for the movement and gas flow are realized. The obtained piezoresistive and unsymmetrical tactile sensor realized a four-dimensional resolution, including a three-dimensional space and a fourth dimension of timeline, which enables future applications of human-machine interactions.