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

Jin-Chern Chiou; Shun-Hsi Hsu; Yu-Chieh Huang; Guan-Ting Yeh; Wei-Ting Liou; Cheng-Kai Kuei

doi:10.3390/s17010108

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

Sensors (Basel). 2017 Jan 7;17(1):108. doi: 10.3390/s17010108.

Authors

Jin-Chern Chiou^{1

2}, Shun-Hsi Hsu³, Yu-Chieh Huang⁴, Guan-Ting Yeh⁵, Wei-Ting Liou⁶, Cheng-Kai Kuei⁷

Affiliations

¹ Department of Electrical and Computer Engineering, National Chiao-Tung University, Room 617, Engineering Building 5, No. 1001, Ta Hsueh Rd., Hsinchu 30010, Taiwan. chiou@mail.nctu.edu.tw.
² Institute of Electrical Control Engineering, National Chiao-Tung University, Room 617, Engineering Building 5, No. 1001, Ta Hsueh Rd., Hsinchu 30010, Taiwan. chiou@mail.nctu.edu.tw.
³ Department of Electrical and Computer Engineering, National Chiao-Tung University, Room 617, Engineering Building 5, No. 1001, Ta Hsueh Rd., Hsinchu 30010, Taiwan. shhsu.eed01g@g2.nctu.edu.tw.
⁴ Institute of Electrical Control Engineering, National Chiao-Tung University, Room 617, Engineering Building 5, No. 1001, Ta Hsueh Rd., Hsinchu 30010, Taiwan. yuchieh.ece99g@g2.nctu.edu.tw.
⁵ Institute of Electrical Control Engineering, National Chiao-Tung University, Room 617, Engineering Building 5, No. 1001, Ta Hsueh Rd., Hsinchu 30010, Taiwan. x210469@nctu.edu.tw.
⁶ Institute of Electrical Control Engineering, National Chiao-Tung University, Room 617, Engineering Building 5, No. 1001, Ta Hsueh Rd., Hsinchu 30010, Taiwan. steven61617@yahoo.com.tw.
⁷ Institute of Electrical Control Engineering, National Chiao-Tung University, Room 617, Engineering Building 5, No. 1001, Ta Hsueh Rd., Hsinchu 30010, Taiwan. gloooomylife@gmail.com.

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.

Keywords: UHF RFID Class1 Gen2; capacitance-to-digital converter (CDC); capacitive sensor; soft contact lens.