Embroidered Driven Shields for Robust Textile Touch Interfaces

Abstract

We present a fully textile capacitive touch sensor that provides an additional electrode for implementing driven (or active) shielding, which can considerably improve signal-to-noise ratio (SNR) and guard from parasitic capacitance. While driven shields are state-of-the-art for traditional printed sensors, they are still uncommon in contemporary textile user interfaces. Using an enameled copper wire as a bobbin thread in computerized machine embroidery, both sensor and shield electrodes are applied in a single sequence, eliminating manual intermediate or finishing steps and harnessing the design flexibility provided by the embroidery technique. Preliminary finite element analysis indicates significant improvements gained by employing driven shields, in terms of sensing range as well as signal quality, when the sensor is close to other conductors, e.g., when worn on the user’s body. By varying the shield electrode’s pattern properties, such as pattern type, area, and density, we investigate their effects on the resulting SNR, based on characterizations within controlled lab experiments. A major finding of our work is that the impact of density seems minor, while adjustments of the pattern layout seem to adequately compensate for a lower stitch density, with a grid layout yielding the best results.