Despite the ubiquity of computers, paper still occupies a central role in our everyday lives. It is used in a dizzying array of products, from newspapers and calendars, board games, and food packaging, to notepads and post-it notes. Indeed, paper is a convenient, low-cost, high-contrast, and durable means to transport and view information. It also has enviable social, practical, and aesthetic qualities that make it a popular and rapid means for writing text and drawing figures. Despite much prognostications starting in the 1970s about a "paper-less future", global paper consumption has instead continued to grow in lockstep with adoption of information and computing technologies.

Of course, unlike dynamic computing technologies, paper is static. Although we can read from and write on paper, it is not truly interactive – the paper is simply a passive medium. In response, many projects have sought to superimpose computational capabilities, for example, facilitating information retrieval (e.g., barcodes, QRCodes, RFID tags), enhancing paper-based experiences (e.g., augmented reality with printed ARTags), and digitizing pen input. In these systems, the “smarts” are contained in an external object (e.g., optical pen, RFID reader, barcode scanner, camera), but the paper itself is passive.

A second, more involved option is to imbue paper with sensing capabilities, typically touch sensing. This is most frequently achieved by instrumenting paper with conductive traces (e.g., copper stickers/tape, printed inks) to enable capacitive touch-sensing elements, such as buttons and sliders. Such methods generally cannot support continuous touch tracking across the entire surface of a sheet of paper, and instead must be designed in accordance with printed content (i.e., a fixed design). Additionally, most of these methods are targeted for one-off DIY or end-user applications, and are generally impractical for mass production, undermining one of the key qualities of paper’s success: cost so low it can be crumpled up and thrown away after a single use.

In this work, we explore a new approach to enable fully continuous touch tracking on paper at low cost, opening new opportunities. Our input method can support both fingers and writing implements, such as pens, pencils and brushes. In the extremely small volumes that we created for this project, individual sheets were created for little as 30 cents, not including our reusable sensing board. Although we do not see this immediately supplanting more traditional, externally sensed methods (e.g., Anoto pens) – as these are far more practical in the short term – we do believe that our work significantly advances the feasibility of low-cost, interactive, paper-based experiences, especially those that are single use.

As we will discuss in greater detail, we achieve this tracking capability by coating paper, on one side(or sandwiched between two sheets), with a uniform, low-cost conductive layer. This could be applied en masse at the mill, before the paper is cut from bulk rolls into e.g., notepad stock. To this layer, we add conductive traces connecting to different points on the periphery, which could be applied through any number of printing (e.g., offset printing, silk-screening) or mechanical processes (e.g., stamping, die-cutting). We then employ electric field tomography to localize touch inputs, which capacitively couple to our paper. We previously explored this general sensing approach in Electrick for surfaces (e.g., tables, walls) and objects (e.g., toys, controllers). Paper is uniquely single-use, and therefore must be mass-produced at extremely low cost. This required innovation in our touch tracking pipeline, materials, fabrication processes, and writing implements.

Research Team: Yang Zhang and Chris Harrison

Additional media can be found on Yang Zhang's site.