Mechanical and High-Frequency Electrical Study of Printed, Flexible Antenna Under Deformation

During usage, printed electronic components are often stretched, bent, folded, and/or twisted to conform to underlying structure. In this article, tests have been developed for characterizing the mechanical and high-frequency electrical behavior of inkjet-printed patch antennas on flexible polyethylene terephthalate (PET) substrates under uniaxial and biaxial bending. A patch antenna is designed to have a single resonant frequency of 5 GHz in free space. Polycarbonate cylindrical mandrels of 1.25” diameter and special sculptured surfaces have been used as uniaxial and biaxial bending fixtures, respectively. Up to 2000 bending cycles have been performed in both uniaxial and biaxial bending tests. During bending tests, $S_{11}$ (return loss) has been measured by a vector network analyzer (VNA) in both bent and flat configurations. Mechanical simulations have also been performed to determine the strain distribution in the printed elements which will lead to changes in electrical behavior. Scanning electron microscope (SEM) images have been taken to examine the physical damage in the printed structure and to correlate with the strain values obtained through mechanical simulation. High-frequency electrical simulations have also been performed to correlate with the bending experimental data. It is seen that the conductivity of the printed structure changes differently in different zones, due to various values of strain they undergo. Although the cracks are observed in the printed structures, the maximum relative shift in the measured resonant frequency is less than 1.66% in both uniaxial and biaxial bend tests.