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I just read this news and got very curious: http://www.takepart.com/article/2014/07/23/goodbye-finger-pricking-how-googles-smart-contact-lens-really-helps-diabetics enter image description here

Google is designing "Google Contact lens", through which people can read Glycemic Index. How power system is designed for this kind of electronic system? Is there a battery inside? If so, how is it charged?

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  • \$\begingroup\$ I'm not sure about this specific case so I'm leaving a comment instead of an answer, but it looks like they beam power with radio waves like an RFID chip. Devices on this scale usually use radio waves or high density batteries like thin film lithium. \$\endgroup\$
    – EternityForest
    Commented Jul 25, 2014 at 8:40
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    \$\begingroup\$ There is salt water in the eye, I bet you could use copper and zinc electrodes.</kidding> \$\endgroup\$
    – jippie
    Commented Jul 25, 2014 at 16:00

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Although the article you linked to doesn't mention it, other articles like this one do confirm that the device gets its power using RFID technology. That is the way a passive RFID employee ID badge, for example, can work without needing a battery installed.

Besides being used to receive and transmit the RF frequencies used for communication with the tiny transceiver IC, the antenna is also used to receive a relatively higher-powered RF signal that is rectified and used to power the circuit (this article mentions a capacitor). I have no idea what the power requirement is for the Google contact lens device, but a typical power level for a passive RFID tag at maximum range is 1 µW -- 1 V at 1 µA.

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  • \$\begingroup\$ Thanks for your explanation, which is great. But I would like to leave it open for greater detail. :) \$\endgroup\$
    – richieqianle
    Commented Aug 4, 2014 at 10:26

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