A Wirelessly Powered Smart Contact Lens with Reconfigurable Wide Range and Tunable Sensitivity Sensor Readout Circuitry

Abstract

This study presented a wireless smart contact lens system that was composed of a reconfigurable capacitive sensor interface circuitry and wirelessly powered radio-frequency identification (RFID) addressable system for sensor control and data communication. In order to improve compliance and reduce user discomfort, a capacitive sensor was embedded on a soft contact lens of 200 μm thickness using commercially available bio-compatible lens material and a standard manufacturing process. The results indicated that the reconfigurable sensor interface achieved sensitivity and baseline tuning up to 120 pF while consuming only 110 μW power. The range and sensitivity tuning of the readout circuitry ensured a reliable operation with respect to sensor fabrication variations and independent calibration of the sensor baseline for individuals. The on-chip voltage scaling allowed the further extension of the detection range and prevented the implementation of large on-chip elements. The on-lens system enabled the detection of capacitive variation caused by pressure changes in the range of 2.25 to 30 mmHg and hydration level variation from a distance of 1 cm using incident power from an RFID reader at 26.5 dBm.

Electronic Contact Lens: A Platform for Wireless Health Monitoring Applications

“…Advances in nanotechnology have made it technically feasible to put together electronic devices such as sensors, transmitters, amplifiers, and even displays within the confines of standard‐size contact lenses . Delivering small amounts of power to these electronic components in a contact lens is a challenge.…”

Recent Advances in Smart Contact Lenses

“…d) Proposed smart contact lens system architecture. Reproduced with permission . Copyright 2017, MDPI.…”

Stretchable Electronic Platform for Soft and Smart Contact Lens Applications

“…Moreover, their fabrication process needs to be robust, reliable and if possible compatible with reproducible and high volume fabrication techniques . The forming of polymers, including polyethylene terephthalate (PET) and parylene‐C, has been introduced as a suitable process to shape smart contact lenses with electronics. Although PET‐based platforms can be easily thermoformed at temperatures starting at 80 °C (its glass transition temperature is 85 °C), the resulting spherical shape is relatively more rigid compared to conventional soft contact lenses mainly due to its hardness level (ASTM D75 Rockwell R117) .…”

“…Although PET‐based platforms can be easily thermoformed at temperatures starting at 80 °C (its glass transition temperature is 85 °C), the resulting spherical shape is relatively more rigid compared to conventional soft contact lenses mainly due to its hardness level (ASTM D75 Rockwell R117) . Although the forming of parylene‐C structures can be made by cast molding of an embedding polymer (i.e., hydrogels, silicones), the initial electronics platform would be flat thus hindering the subsequent alignment steps. Parylene‐C based electronics platforms could be thermoformed as well (to have an initial curved platform), however, this process demands a high temperature and long duration process (i.e., 6 to 48 h at 170 or 200 °C) because of its high molecular weight and crystallinity, which would be incompatible with industrial scalability of smart contact lenses.…”