A Nano-Joule Burst-Mode Eye-Gaze Angle and Object Distance Sensor for Smart Contact Lenses
Chayanjit Ghosh, Sakthidasan Kalidasan, Mohit U. Karkhanis, Alex Mastrangelo, Aishwaryadev Banerjee, Ross M. Walker, Hanseup Kim, Carlos H. Mastrangelo · 2021 IEEE Sensors · 2021
In this article, we demonstrate an ultra-low energy eye gaze tracking system and distance ranger based on scleral coils developed specifically for smart contact lenses. The system comprises of a set of four (two transmitter and two receiver) semi-circular, copper coils which are patterned on flexible Kapton substrates conformally placed on the eye scleras. The thickness of the entire assembly is ~100 µm. A high- frequency amplitude modulated AC signal is transmitted from a transmitter coil in short bursts, which induces an EMF in a receiver coil that is a function of the eye-gaze angle. The induced voltage is demodulated using an AM receiver IC. The observed object distance from the eyeballs can be determined via triangulation of the measured eye-gaze angles. Preliminary results demonstrate that a very short burst of transmitted signal 31 µs long is sufficient for peak envelope detection of the received signal, requiring only 340 nJ of total energy per distance range measurement. This is about 1/500,000 of the energy per measurement required by miniature solid-state time- of-flight distance sensors.