Ultralow Power Flexible Ocular Microsystem for Vergence and Distance Sensing Based on Passive Differential Magnetometry

We report the theory, construction, and testing of a flexible ocular, on-the-eye microsystem used for ultra-low power object distance sensing suitable for smart adaptive contact lenses. The microsystem determines object distance by vergence angle triangulation. Vergence angle is determined from passive measurements of the earth's magnetic field at each eye. Vergence measurements were performed every 5-degree interval over 35 degrees in total for each eye to accommodate the entire human visual range. Vergence angle measurements had an RMS error of 1.74 degrees and a distance ranging RMS error of 14.04 mm. The energy requirement per magnetic field measurement was estimated to be approximately 2 mu J per eye.