Mechanical-property measurement of enhanced flexible antenna graphene-electrode substrates on curved surfaces using spatial compensation temporal Fourier-transform profilometry

Abstract

To enhance the mechanical strength of flexible antenna electrode substrates for wearable devices and address the challenge of non-contact mechanical property measurement on curved, flexible structures, this study proposes a spatial-compensation temporal Fourier-transform profilometry (SC-TFTP) technique. The proposed method employs novel image-filling technology and integrates temporal fast Fourier transform with bandpass filtering. It measures the height distribution of laser-induced graphene antenna electrodes on polyimide substrates, including the microstrip-patch electrode structure (MPES) and Hilbert fractal electrode structure (HFES), under various curvatures and touch loads. Subsequently, mechanical characterization principle (MCP) is employed for stress analysis and comparison. The results show that, compared with the finite element method, the minimum relative error of local mean height deformation was as low as 0.003 mm, whereas the maximum relative percentage error of the stress was 19.66%. Furthermore, the stress of the HFES was reduced by approximately 20% compared with the traditional MPES under the same curvature and load. These findings demonstrate that the fractal geometry of HFES distributes stress, and significantly enhances the mechanical-damage resistance of the antenna-electrode substrate. The proposed SC-TFTP combined with MCP provides a rapid, stable, and nondestructive approach for characterizing the mechanical properties of curved flexible thin films, enabling the effective quantification and enhancement of the mechanical performance of flexible antenna-electrode substrates under bending conditions.