This article describes a process of fabricating highly porous paper from cellulosic fibers and carbon black (CB) with tunable conductivity. By embossing such paper, its porosity decreases while its conductivity increases. Tuning the porosity of composite paper alters the magnitude and trend of conductivity over a spectrum of concentrations of conductive particles. The largest increase in conductivity from 8.38 × 10–6 to 2.5 × 10–3 S/m by a factor of ∼300 occurred at a percolation threshold of 3.8 wt % (or 0.36 vol %) with the composite paper plastically compressed by 410 MPa, which caused a decrease of porosity from 88% to 42% on average. Our composite paper showed stable piezoresistive responses within a broad pressure range from 1 kPa up to 5.5 MPa for 800 cycles. The piezoresistive sensitivities of the composite paper were dependent on concentration and decreased with pressure. Composite paper with 7.5 wt % CB had sensitivities of −0.514 kPa–1 over applied pressures ranging from 1 to 50 kPa and −0.215 kPa–1 from 1 to 250 kPa. This piezoresistive paper with embossed patterns enabled touch sensing and detection of damage from darts and punches. Understanding the percolation behavior of three-phase composites (cellulosic fibers/conductive particles/air) and their response to damage, pressure, and processing conditions has the potential to enable scalable applications in prosthetics and robotics, haptic feedback, or structural health monitoring on expansive surfaces of buildings and vehicles.

user interface. In other words, increasing resolution or adding sites for the detection of touch, generally requires augmenting the number of interconnects. With the exception of using a single electrode-based sensing technique to make natural and inanimate objects become user interfaces, there has been a lack of effort in the reduction of the number of wired leads required for scalable sensing of touch. [9] In contrast to electronic touch sensors, skin on humans/vertebrates uses hierarchical neural networks to transmit the relative spatial detection and intensity of force on fleshy surfaces to the brain. [10] These neural networks do not depend on having a pair of running wires for each location. Instead, they have developed mechanisms for sending spatial information about touch along the spinal cord. Inspired by this concept, Tee et al. presented a skininspired organic digital mechanoreceptor, which converted force-based stimuli into digital signals with varied frequencies to mimic the communication between biological mechanoreceptors and the brain. [11] Similarly, there are opportunities to build electrical networks to reduce the number of wired leads required for spatial detection of touch on synthetic electronic skins.The advancements in skin-like sensing with flexible electronics have moved toward the design and fabrication of active electronic components arrayed on flexible sheets with surface areas less than 10 cm in diameter. [12][13][14][15][16] For example, Someya and co-workers demonstrated an application of thin-film transistors in skin-like sensors capable of measuring distributed pressures over a 9 cm × 9 cm footprint. [12] The size of the sensors is typically dependent on the method of fabrication, and current skin-like sensors often cover small areas (i.e., much less area than that of human skin) because of the limited size of semiconductor-based wafers. As mentioned previously, the number of wired leads in conventional arrays of skin-like sensors increases with the square root of the number of buttons. While this scaling may appear favorable, there are still difficulties with making large sensing grids, as a larger quantity of traces requires more space for wired connections and multiplexed measurements.In this work, we present an approach to passive sensing for skin-like sensors consisting of tunable resistive networks and This work presents a unique approach to the design, fabrication, and characterization of paper-based, skin-like sensors that use patterned resistive networks for passive, scalable sensing with a reduced number of interconnects. When touched or wetted with water, the sensors in the resistive networks detect significant changes in electrical impedance. Fabricating these resistive networks and sensors in a single sheet of metallized paper reduces the number of distinct inputs/outputs to the arrayed sensors. For human-electrode interactions, circuit-based models guide the design/material processing of the resistive networks and selection of operating frequencies-typically ranging...