Electrical and Mechanical Characterization of Printed Antennas under Uniaxial and Biaxial Bending
During usage, the printed electronic components are often stretched, bent, folded, and/or twisted to conform to the underlying structure. In this work, 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. The 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, the S11 (return loss) response 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 images have been taken to examine the mechanical damages of the printed structure and to verify the mechanical simulation results. High-frequency electrical simulations have also been performed to correlate with the bending experimental data. It’s seen that the conductivity of the printed structure changes differently in different zones, due to the various values of strain they undergo. Although the cracks are observed in the printed structures, the maximum shift in the measured resonant frequency is less than 100 MHz in both tests.