Piezoresistive flexible composite for robotic tactile applications

• We present a flexible tactile sensor based on a piezoresistive tunneling composite.
• The functional composite is based on nanostructured Ni particles in silicone matrix.
• This piezoresistive behavior is based on tunneling conduction mechanism.
• Huge variation of electrical conduction in response to an applied deformation.
• A logarithmic trans-impedance amplifier is used in the electronic readout circuit.

We present a robust and flexible tactile sensor based on piezoresistive sensing material, constituted by a polymeric composite with nanostructured spiky particles as filler. The composite is able to exploit tunneling conduction mechanism when subjected to a compressive load. We have here integrated this quantum tunneling composite (QTC) with an ad-hoc electronic read-out circuit. In addition a software interface can monitor and visualize the applied mechanical pressure, thus leading to a complete tactile sensor device.Concerning the sensing material, the piezoresistive composite shows an enhanced tunneling conduction due to the presence of nickel particles with nanostructured sharp tips embedded in a silicone matrix. We registered an increase up to nine orders of magnitude of the composite electrical conduction in response to a mechanical strain. The sensor consisted in a continuous layer of functional composite sandwiched between a matrix of patterned top and bottom electrodes. The planar sensor can thus be modeled as a two-dimensional array of resistors whose value decreases by increasing the applied pressure. We also designed an ad-hoc electronic read-out circuit, able to read and process the resistance variations of the sensor upon a compressive load, thus providing not only the pressure intensity but also the pressure distribution data. A software interface was able to achieve the real-time tridimensional response and lead to the visualization of the compressed regions on the sensor.The present device is an efficient and low-cost prototype of tactile sensing skin, thus readily enabling its use for human robotic applications.