Spray-Deposited Graphite Nanoplatelet Metasurfaces for Chipless Wireless Strain Sensing

Chipless passive wireless sensors (CLPWSs) are gaining traction for applications requiring battery-free, compact, and wireless monitoring capabilities. Among these, strain sensors leveraging metasurfaces offer a promising approach due to their tunable electromagnetic responses. This study presents the fabrication and characterization of a frequency-selective CLPWS using a spraydeposited nanocomposite based on graphite nanoplatelets (GNPs) on a polyetherimide (PEI) substrate. Characterized of electrical conductivity, strain sensitivity, and electromagnetic response in the X band (8–12 GHz) of samples with different composition have been performed to evaluate the best case for the fabrication of the sensor array. A maximum electrical conductivity (~7.16 × 10⁴ S/m) was found for samples based on oriented GNPs at low frequencies (quasi-static condition). Strain sensitivity tests demonstrated a minimal resistance change under strain. X-band measurements and equivalent transmission line modeling were used to estimate material conductivity at high frequencies. The results highlight the feasibility of spraydeposited GNP-based metasurfaces for wireless strain sensing. Indeed, an array sensor of 10 x 10 cm2 has been fabricated and preliminary tested in X-band.