Microelectromechanical strain and pressure sensors based on electric field aligned carbon cone and carbon black particles in a silicone elastomer matrix

Abstract

Methods for developing microelectromechanical strain and pressure sensors based on aligned carbon particle strings within dielectric elastomer matrices are presented. Two different types of carbon particles were used: a mixture of carbon cone and carbon disk particles and spherical carbon black particles. The particles were assembled and aligned into strings by an alternating electric field with a strength of 4 kV/cm and a frequency of 1 kHz, utilizing the dielectrophoretic effect. The particle fraction was about 0.1 vol. %, which is an order of magnitude lower than their percolation threshold (∼2 vol. %). The aligned strings were produced in a couple of minutes. The matrices were subsequently cured thus stabilizing the strings. Micromechanical strain sensors with a capacitive readout were produced by aligning the particles into a single string-like formation in the in-plane direction, the string dimensions being 3 μm width and 30 μm length. The pressure sensors with piezoresistive readout were made by aligning the particles into multiple unidirectional strings in the out-of-plane direction, the thickness of the sensors being of the order of 100 μm and the lateral area of 1.5 cm2. The strain and the pressure sensors show reversible piezocapacitive and piezoresistance effects when stretched and compressed, respectively.