Resistive electronic skin

Devices made from traditional conductive bulk materials using complex microfabrication methods often are restricted to being rigid and in some cases, flexible but not strethcable. The main reason is the mismatching mechanics between these traditional materials and the elastomeric materials they were bonded with, which causes materials delimination and/or cracks at soft/hard materials interfaces under strains. Conductive nanomaterials potentially offer new opportunity to tackle this challenge. Their availability in various sizes and shapes enables us to create composites with various dimensions, such as 1D conductive traces, 2D film, and 3D sponge-like architectures. These have opened the door for fabrication of stretchable interconnects, circuits, energy storage devices, antennas, LEDs, etc. The basis of using conductive nanomaterials composites in sensors is that any stimulus or change will generate a measurable electrical impulse. These impulses can be broadly classified as piezoelectric, triboelectric, capacitive, and resistive responses. Depending on the sensitivity required and the preference of electrical impulse to be measured, the device construction maybe tailored to give one of the four kinds of electrical responses. Resistive sensors in addition to being the easiest to construct are also the easiest to measure, which is the crucial reason for a large number of publications in this area. The working mechanism of resistive sensors based on the constituent conductive materials and their percolation network will be discussed in detail. Composition of conductive inks fabricated using wet chemistry methods, and nanomaterials using dry methods, their subsequent applications are covered as well. The exciting applications relating to human health and well-being will also be described. Finally a brief outlook of the future of wearable sensors as ''invisibles'' will be presented.