Micropower Object Range and Bearing Sensor for Smart Contact Lenses

In this article, we present an eye-tracking system for distance ranging, developed for varifocal contact lens applications. The system comprises of a set of four ~150 μm-thick, semi-circular coils, which are patterned on flexible Kapton substrates and can easily conform to the sclera. The object-distance from the eyeballs is determined via triangulation of the eye gaze angles, which is calculated from the induced electromagnetic voltage between the coils. Preliminary experiments with the coil-system, placed on eyeball simulated polymeric spheres resulted in accurate prediction of object distance in the range of 0.1-15 D (Diopter) with an RMS error of 0.1 D and object direction in the range of -15 to 15-degree arc with 0.4 degree RMS error, respectively. Diopter is the reciprocal of the object distance (in meters). The energy required to perform a single range reading was ~ 20 μJ.