Improving the <inline-formula> <tex-math notation=LaTeX>${Q}$ </tex-math></inline-formula>-Factor of Printed HF RFID Loop Antennas on Flexible Substrates by Condensing the Microstructures of Conductors

High frequency (HF) radio frequency identification (RFID) loop antennas are popular for HF RFID, energy transfer and near field communication applications. One of the major parameters defining the working range of HF RFID antennas is their Q-factor. Printing techniques are the ideal method for mass fabrication of HF RFID loop antennas. However, due to the relatively low conductivity of the inks available on the market, the Q-factor of the printed HF loop antenna tends to be low and in many cases, fails to meet the working range requirements. This paper reports two methods to condense the microstructures of the conductors in order to improve the Q-factors of printed HF RFID loop antennas. Both thermal compression (pressing the sample at elevated temperature) and near-infrared annealing are studied, and the results have demonstrated that both approaches are efficient in improving the Q-factors of printed loop antennas.