Fine-Feature Additively Dry Printed Passive Wireless Sensor Tag

Abstract

Wireless passive sensors have many applications, from precision agriculture to structural health monitoring. A simple but useful wireless passive sensor tag consists of a planar inductor coupled with a planar interdigitated electrode capacitor, forming an inductor-capacitor (LC) loop. Either the planar inductor or the planar interdigitated electrode capacitor can be used as the sensor. For example, the inductor could be used for proximity detection with an external ferrous object, or the capacitor could be used to measure the relative humidity of the surrounding air. The planar inductor, however, is also used to inductively couple the sensor tag to a base station feedback oscillator. As a result, the LC loop on the sensor tag tunes the base station oscillator’s output frequency accordingly. In this work, the planar inductor and the planar interdigitated electrode capacitor were printed on a polyimide substrate using a novel laser-based additive nanomanufacturing (ANM) and dry printing technology. With this fabrication process, approximately 2 micron thick silver traces were printed to realize a 34 loop planar inductor and a 69 tooth interdigitated electrode capacitor, with a nominal trace and space width of 6 mils (152.4 microns). This recently developed laser-based ANM technique allows for much finer trace and space widths, as well as a much larger variety of electronic materials, to be printed, compared to more traditional ink-based printed electronics manufacturing techniques.