NSF-BSF: CCSS: Resistance Tomography with 2D Sensor Membranes

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Touchpads and touchscreens in today's computers and cell phones have two disadvantages - first, they are rigid, and second, they require a complex manufacturing process with many individual sensors. A flexible and easy-to-manufacture pressure sensor could function as an artificial skin for people and objects and could lead to cheap and convenient solutions for wearable computer interfaces, touch enabled spaces, and biomedical movement diagnostics. Such a device with a wireless interface will allow for ease-of-use in sensor interfaces. With the help of an unconventional sensor mapping method called resistive tomography, it is possible to create such a platform using only a single piece of easy-to-manufacture pressure-sensitive material to map pressures. Device fabrication for such a flexible sensor is trivial in comparison to standard sensor arrays, with the complexity shifted to the signal processing needed to interpret the pressure pattern. Multiple measurements using various combinations of contacts can create the full pressure map. It is expected that the technology that is developed from this effort will lead to new kinds of flexible sensors for wearable touch-pad like interfaces and biomedical movement diagnostics.Most of today's two dimensional (2D) touch sensors and strain sensors require an indexed array of individual sensors in order to gather spatial information, requiring significant complexity in the fabrication stage, while impairing durability and broader applicability. This work proposes a new means of gathering 2D spatial data combining touch sensing and strain mapping that uses a trivial fabricated composite membrane to serve as the spatial pressure sensor, with the complexity shifted from fabrication to the computational domain through a tomographic mapping algorithm. This research will develop new tomographic algorithms based on a Zernike moment analysis to convert resistive four-point measurements at the periphery of a strain-sensitive membrane into a 2D map of the local pressures applied throughout the area of the membrane. The membrane will be made of a nanotube-silicone conducting composite rubber developed for this purpose. An energy-efficient measurement architecture and wireless interface to the membrane will allow this strain-sensor map to be easily employed in-the-field for various mechanical, medical, engineering, and personal-user applications. The low cost of fabrication will lend itself to ubiquitous touch sensors and novel modes of interaction for wearable and Internet-of-Everything applications. The trivial fabrication method of the sensor component and the conformability of the sensor around any shape make for a mass-producible, easily implemented, and highly versatile strain sensor and flexible touchpad. The exact algorithms to be investigated here can be applied on a much broader class of systems, expanding the utility of tomographic methods in sensing. The conducting elastomer sensor material will be developed to optimize the tomography application envisioned here. The ideas generated in the course of this proposal are expected to generate new intellectual property in the area of sensors, such as flexible, wearable touchpads for computer interfaces, likely to spawn new industry products. The conformal ability to shape such a sensor will lead to broader applications in the health industry for rehabilitation, such as a tomographic sock to sense bending and mechanical strain at the elbow, knee, or torso for health monitoring. Durable, long-lasting, zero-maintenance haptic skin for prosthetic limbs and robotics can be produced at extremely low cost with the technology proposed here. This effort will train graduate students in essential skills for critical thinking and design methodologies, as well as developing skills in applied math, physics, and materials design with newly developed courses including subject matter developed under this research.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.