To obviate the need for a battery or other power source, a keyboard may transmit keystroke signals to a tablet computer via a passive antenna, such as a passive Near Field Communication (NFC) antenna and/or radio-frequency identification (RFID) antenna. The tablet computer may transmit signals to the keyboard via an active antenna such as an active NFC antenna and/or RFID antenna. When the user presses a key on the keyboard, the passive antenna may modulate the signal received from the tablet computer. The modulation of the signal may include completing and/or closing a circuit in response to the user pressing the key on the keyboard. The modulation of the signal may be unique to the keystroke, and/or combination of keystrokes, entered by the user. The tablet computer may receive the modulated signal and interpret the modulated signal as the keystroke entered by the user.
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Asrani, Vijay and Tanner, James, "Wireless Keyboard Without Need For Battery", Technical Disclosure Commons, (April 29, 2015)