The demand for high performance multifunctional wearable devices is more and more pushing towards the development of novel low-cost, soft and flexible sensors with high sensitivity. In the present work, we describe the fabrication process and the properties of new polydimethylsiloxane (PDMS) foams loaded with multilayer graphene nanoplatelets (MLGs) for application as high sensitive piezoresistive pressure sensors. The effective DC conductivity of the produced foams is measured as a function of MLG loading. The piezoresistive response of the MLG-PDMS foam-based sensor at different strain rates is assessed through quasi-static pressure tests. The results of the experimental investigations demonstrated that sensor loaded with 0.96 wt.% of MLGs is characterized by a highly repeatable pressure-dependent conductance after a few stabilization cycles and it is suitable for detecting compressive stresses as low as 10 kPa, with a sensitivity of 0.23 kPa⁻¹, corresponding to an applied pressure of 70 kPa. Moreover, it is estimated that the sensor is able to detect pressure variations of ~1 Pa. Therefore, the new graphene-PDMS composite foam is a lightweight cost-effective material, suitable for sensing applications in the subtle or low and medium pressure ranges.

The development of lightweight microwave absorber, operating in a wide range of frequencies, is still a challenging task. A novel broadband lightweight radar absorbing material is developed using a phenolic aramid honeycomb (HC) coated with a graphene-filled polymeric paint, which is made of a colloidal suspension of graphene nanoplatelets (GNPs) dispersed in a mixture of polyvinyl-alcohol, water, and 1-propanol. This study describes the production process of the GNP-filled paint and of the lossy HC, and investigates the morphological and electromagnetic properties of the new nanostructured material. A multiscale effective-medium model of the GNP-coated HC, which takes into account the morphology and properties of the nanostructured material from micro- to macroscale, is developed and validated through the comparison with experimental data in the X-band. Findings demonstrate a feasible way to develop lightweight and broadband absorbers for various practical applications.

In this work we investigate the piezoresistive effect in multilayer graphene (MLG) based films produced by two different cost-effective techniques, spray coating and drop casting. Both techniques enable the direct deposition of the sensor over the structure to be monitored. The piezoresistive behavior of the MLG-based sensors has been investigated experimentally by measuring the variation of the electrical resistance during three point bending tests. The sensor response has been stabilized through an optimized mechanical treatment. The obtained results show that the produced sensors are characterized by a gauge factor in the range 20-50 at very small strains (i.e. below 0.2%).

In this work we investigate the shielding properties of graphene-based films, produced by spray casting deposition, which is a cost-effective technique that can be directly scaled to industrial applications. The deposition process is optimized in order to produce uniform films made of well dispersed graphene nanoplatelets (GNP), having thicknesses in the range 3-8 microns. The sheet resistance and the shielding effectiveness up to 18 GHz of films produced using GNP-suspensions at different concentrations are measured and compared with the ones of carbon nanotube (CNT)-based films, produced in the same conditions. The obtained results demonstrate the superior shielding properties of graphene-based films with respect to CNT-ones, mainly due to the bi-dimensional shape of GNPs, which contributes to minimizing the contact resistances among adjacent nanostructures. It is also demonstrated that after a thermal annealing at 250°C, the final measured shielding effectiveness of the produced GNP-film triplicates in linear scale, reaching the value of 30.6 dB.