Carbon nanotubes and graphene-based microsonar for embedded monitoring of microporosity

Nanoporosities play a most significant role in the durability of cementitious materials, so that nanoscale features are a promising target for SHM. However, to this day, no sensor features the resolution required to investigate non-destructively these nanofeatures. To fill in this loophole, we are devising a SHM-targeted, carbon nanotubes and graphene based capacitive ultrasonic nanotransducer for microporosity assessment in concrete. In this paper, we report on the feasibility of the key building block of the proposed sensor: we have fabricated ultra-thin graphene and single-walled carbon nanotubes membranes. A breakthrough laser vibrometry experiment shows that the membranes can feature above-nanometer amplitudes of vibration over a large range of frequencies spanning from 100 kHz to 5 MHz. A detailed numerical model of the nanotransducer shows that upon embedding in a cementitious material it could determine the volume and content of the porosity in its vicinity. Such information would be invaluable in the evaluation of structural durability.