An inkjet-printed bendable antenna for wearable electronics

Flexible antennas, which can conform to the skin and transfer signals to terminals, are particularly useful for wearable electronics. Bending, which frequently occurs to flexible devices, significantly affects the performance of flexible antennas. Inkjet printing has been used as an additive manufacturing technology for fabricating flexible antenna in recent years. However, there is little research on the bending performance of inkjet printing antenna in both simulation and experiment. This paper proposes a bendable coplanar waveguide antenna with a small size of 30 x 30 x 0.05 mm3 by combining the advantages of fractal antenna and serpentine antenna, which realizes the ultra-wideband feature and avoids the problems of large dielectric layer thickness (greater than 1 mm) and large volume of traditional microstrip antenna at the same time. The structure of the antenna was optimized by simulation using the Ansys high-frequency structure simulator, and the antenna was fabricated on a flexible polyimide substrate by inkjet printing. The experimental characterization results show that the central frequency of the antenna is 2.5 GHz, the return loss is -32 dB, and the absolute bandwidth is 850 MHz, which is consistent with the simulation results. The results demonstrate that the antenna has antiinterference capability and can meet the ultra-wideband characteristics. When the traverse and longitudinal bending radius are greater than 30 mm and skin proximity greater than 1 mm, the resonance frequency offsets are mostly within 360 MHz, and return losses of the bendable antenna are within the -14 dB compared with the no bending condition. The results exhibit that the proposed inkjet-printed flexible antenna is bendable and promising for wearable applications.