Flexible RFID Tag Inductor Printed by Liquid Metal Ink Printer and Its Characterization

In order to fulfill various growing needs of application fields, the development of low-cost directly printable radio-frequency identification (RFID) tag is essential for item level tracking. Currently, there lacks an easily available way to directly write out functional consumer electronicslike typewriting on paper by an office printer. Here, we show a desktop printing of RFID tag inductors on flexible substrates via developing liquid metal ink and related working mechanisms. The directly printing inductor on various flexible substrates with extremely low cost and rapid speed was designed based on the sympathetic oscillations of multiple LC (inductor–capacitor) circuits. In order to better meet the demands of the distinct resonant circuits, a series of conceptual experiments for investigating the relationship between the character of the inductor and its parameters—shape, number of coils, line width, spacing, etc.,—have been designed. The parameters are all working upon the performance of the printed inductors by liquid metal ink printer, and the relationship laws are consistent with those of the conventional inductors. The coils number as the biggest effect factor has a linear relationship with the inductance of the spiral-type inductors. An inductor with excellent properties can be well chosen by adjusting its parameters according to various applications. The present work demonstrated the way for a low cost and easy going method in directly printing RFID tag inductors on flexible substrates.