Inkjet-Printed Electromagnet-Based Touchpad Using Spiral Resonators

In this paper, an inkjet-printed electromagnet-based touchpad employing spiral resonators is proposed. The proposed touchpad is fabricated by a direct patterning method using an inkjet printer with a conductive silver nanoparticle ink. The conductive patterns are easily printed on a paper substrate and sintered for achieving good conductivity. The proposed touchpad is composed of two spiral resonators that resonate at 0.94 GHz (f
₁
) and 1.83 GHz (f
₂
), respectively. When the first resonator is touched, f
₁
decreases from 0.94 to 0.81 GHz because of electromagnetic (EM) coupling between the finger and the spiral resonator. Similarly, when the second resonator is touched, f
₂
decreases from 1.83 to 1.55 GHz. Owing to the EM coupling distance between the spiral resonator and the finger, the frequency changes although the finger does not reach beyond a height of 1.27 mm on the spiral resonator. The performance of the proposed touchpad is validated using simulation and measurement results.