Design and Analysis of a Bent Antenna-coil for a HF RFID Transponder

In this work, the design of a bent antenna-coil for a 13.56 MHz RFID transponder is presented. The tag is integrated into a plastic ballpoint pen, optimally making use of the marginal volume inside the cylindrical geometry of the casing. The coil is designed with a 50% higher inductance in its planar state, so that the required inductance of nearly 6 muH to ensure resonance is obtained when the bent tag is inside the pen. Quasi-static and full-wave methods for the electromagnetic simulation of the coil are compared and an analysis of the influence of the bend radius on the inductance of the coil is conducted. Furthermore, the designed tag was manufactured using two technologies comprising copper windings on a polyimide substrate and conductive polymer paste on a polyester foil for experimental verification. With a mid-range RFID reader configuration, read-ranges of up to 23 cm and 12 cm, respectively, were obtained with the bent tag inside the pen.