Data transmission and power supply for smart contact lens

• Main Author: Kim, Moobum
• Other Authors: Lee Seok Woo
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Electrical and electronic engineering::Applications of electronics; Engineering::Chemical engineering::Industrial electrochemistry
• Online Access: https://hdl.handle.net/10356/152693
• Institution: Nanyang Technological University

The industry of wearable device is dramatically growing with the development of smart sensors, battery, and internet of things (IoT) in the stream of 4th industrial revolution. Among the wearable devices, smart contact lens has great potential to grow in the aspect of giving information to user directly. For collecting information, smart sensors can be used in noninvasive method to detect vital sign from the components in tear, intraocular pressure, and dangerous elements which are attached on the surface of contact lens. Also, computer vision can be used to get the information from the image taken by integrated camera on smart contact lens. From the previous researches on integration of sensor into smart contact lens, wireless power supply and communication were used to activate sensor and transfer the data with complex circuit and additional receiver. Lithium ion battery was integrated for giving power to smart contact lens in another research. However, wireless data transmission and power supply require high power consumption, additional antenna and external receiver. Furthermore, lithium ion battery requires additional electrolyte and has potential of explosion. In this thesis, direct electrochromic data transmission is suggested for smart contact lens instead of wireless communication. Prussian Blue (PB) is used for color change with voltage application, because it has electrochemical reaction with sodium and potassium ion in tear which shows clear color change between transparency and blue. Diverse signals are demonstrated by controlling the duration and magnitude of voltage application. Computer vision is used to detect the position and amount of color change for real-time application. For the safe power supply of smart contact lens, safe battery with self-recharging system is demonstrated. Prussian Blue analogues (PBAs) are safe battery materials which have electrochemical reaction with sodium and potassium ions in tear. This battery works in narrow voltage window without additional electrolyte which means removing the potential of explosion. Also, photodiode is integrated into system for charging the battery with solar energy. Furthermore, electrochemical kinetic energy harvesting is introduced as preliminary study for the energy harvesting using the flow of tear made by blinking. Voltage gap is induced on the surface of battery material and supercapacitor material by the flow of electrolyte, because the ways of attachment of ions on each material’s surface are different. Ions which are inserted into the structure of battery material maintain the original status under the flow of electrolyte, but ions which are attached on the surface of supercapacitor material are easily detached by the flow of electrolyte. This selective ion sweeping is characterized, and energy is harvested during 500 cycles without dramatic decrease of performance.