While the piezoresistive effect of nanoparticle-based isolator/conductor composites is known and well described for tension and compression, the case of bending is more complex, as both tensile and compressive loads occur in the part subjected to flexural deformation.

In a recent study published in Nanotechnology, a bulk nanocomposite bending sensor based on multi-wall carbon nanotubes and an epoxy matrix could be produced with a single-step mould casting manufacturing route. The nanocomposite material exhibited a pronounced piezoresistive effect under bending deformation, resulting in a bending sensor capable of resolving small mechanical strains in the elastic regime.

Furthermore, a directional sensitivity could be implied, meaning that the piezoresistive gauge factor may become positive or negative, depending on the direction of flexural deformation. The directional sensitivity was realised by the generation of a gradient in electrical conductivity within the bulk epoxy matrix. It was found that the gradient may be attributed to local variations in carbon nanotube concentration and degree of percolation. The piezoresistive properties of nanocomposite strain sensors can be tuned by controlling the composite morphology.

The implication of a directional sensitivity and the straightforward processing route make these nanocomposite strain sensors interesting candidates for application in structural strain sensing but also in microelectronic systems. Ongoing studies are dealing with the improvement of the morphology of carbon nanotube-based composites and the tuning of the piezoresistive properties of these new types of functional polymers.