Non-contact characterization of carbon nanotube based strain sensors using millimeter waves

Abstract

Carbon nanotubes (CNTs) are unique tubular structures with high thermal and electrical conductivity, distinct optical characteristics, and high mechanical stiffness and strength. Carbon nanotube (CNT) composites have widely been used as strain sensors because of their electrical-mechanical coupling behavior. Typically, these piezoresistive sensors require direct measurement of electrical resistance change using an external source connected with wires. This research introduces a new, non-contact measurement method to detect the change in electrical conductivity of carbon nanotube-based strain sensors using high-frequency millimeter wave technology. By analyzing the transmission coefficient from the textile-based CNT composite, we were able to observe the piezoresistive effect. Sensors were characterized over a broad frequency band, from 82 GHz to 100 GHz, with applied strain up to 40%. Fabrics were coated with a sizing composed of an aqueous dispersion of multi-walled CNTs. Sets of fabrics with different CNT concentration were examined to investigate the sensitivity, polarization effects and isotropy properties of manufactured sensors under three different case studies.