Battery-free Display Tag The use of smaller 2.0 inch E-ink screen and further system optimization make the display tag can be powered and updated by a NFC enabled cell-phone. No large energy storage media, like battery or super capacitor rather than 300 µF capacitor is used to buffer enough energy to update the image in run time. Because, the cell-phone is continuously sending dummy data to power the tag even after the the image transmission, therefore the board can keep collecting more energy while E-ink is updating. The updating process of E-ink is also heavily duty-cycled to avoid system brown out.