An ultra-low power, optically-interrogated smart tagging and identification system

We present a wireless identification system that employs an optical communications link between an array of uniquely identifiable smart tags and an interrogator flashlight. As the tags consume a quiescent current of under 2 microamperes and are woken up directly by the interrogator´s modulated illumination, they are able to last nearly the shelf life of their battery with moderate use. Unlike RFID, which requires a large antenna to achieve significant range, our system requires only a small photodiode, which enables very compact tags to be rapidly queried at a range of over 8 meters with a handheld flashlight interrogator. Our tags are currently aimed at an asset location scenario, where they pulse an onboard LED when their stored ID matches a query broadcast by the interrogator. We also present two different techniques that allow the tags to talk back to the interrogator-one that uses an onboard IR LED to send data a meter away when the interrogator illumination is off and another that uses the onboard green indicator LED for proximate operation. We present our hardware and system design, analyze its performance, and discuss powering the tag from ambient illumination sources.