A Winning Backscatter Modulator: A Quarter-Gram, Ultrahigh-Frequency RFID for On-Metal Operation

Wireless sensors have become commonplace in our daily lives for such tasks as tracking temperature, measuring humidity, and sensing light and gas. Many technologies capable of relaying sensor information are continually being refined, but the search for a robust and customizable technology to satisfy the exponentially increasing demand for largescale and low-cost deployment of these wireless sensor nodes while minimizing power consumption has led to backscatter radio as a potential solution. Backscatter radio, first proposed in the 1940s as "communication by means of reflected power" [1], is a fairly mature technology that has been used in a variety of modern applications, especially those employing passive RFID technology in the ultrahigh-frequency band. The tags used in these applications are usually made up of just a transistor or switch and an antenna. These tags can be activated using only the RF power from an interrogating signal and, as a result, can be operated without any external energy source. Communication ranges of up to a few meters have been reported using this technology [2], [3].