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Sensors 2017, 17(1), 108; doi:10.3390/s17010108

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

1
Department of Electrical and Computer Engineering, National Chiao-Tung University, Room 617, Engineering Building 5, No. 1001, Ta Hsueh Rd., Hsinchu 30010, Taiwan
2
Institute of Electrical Control Engineering, National Chiao-Tung University, Room 617, Engineering Building 5, No. 1001, Ta Hsueh Rd., Hsinchu 30010, Taiwan
*
Author to whom correspondence should be addressed.
Academic Editors: Pak Kwong Chan and Holden King-Ho Li
Received: 14 November 2016 / Revised: 19 December 2016 / Accepted: 30 December 2016 / Published: 7 January 2017
(This article belongs to the Special Issue Smart Sensor Interface Circuits and Systems)
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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. View Full-Text
Keywords: capacitance-to-digital converter (CDC); capacitive sensor; soft contact lens; UHF RFID Class1 Gen2 capacitance-to-digital converter (CDC); capacitive sensor; soft contact lens; UHF RFID Class1 Gen2
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Chiou, J.-C.; Hsu, S.-H.; Huang, Y.-C.; Yeh, G.-T.; Liou, W.-T.; Kuei, C.-K. A Wirelessly Powered Smart Contact Lens with Reconfigurable Wide Range and Tunable Sensitivity Sensor Readout Circuitry. Sensors 2017, 17, 108.

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