At 03:14 AM 5/21/2006, Eugen Leitl wrote:
Smith explains that Intel's sensor devices use off-the-shelf components: an antenna to send and receive data and collect energy from a reader, and a sensor-containing microcontroller -- a tiny computer that requires only a couple hundred microwatts of power to collect and process data.
The antenna harvests this power directly from the radio waves emitted by an RFID reader. When a tag comes within range of a reader, the reader's radio signal passes through the antenna, generating a voltage that activates the tag. The tag is then able to send information to the reader through a process called backscattering, in which the antenna essentially reflects a data-encoded variation of the received radio signal.
One of the first uses of backscatter or passive transmission was when the Russians bugged the U.S. embassy in Moscow in the 1960s using resonant 'nails'. The heads of the nails (no larger than the standard variety) were actually hollow with two resonant cavities (I think at non-harmonic frequencies) formed by a 'wall' and covered by a metal diaphragm. The nail shaft was an antenna. The nails had been placed just below painted surfaces. Sound pressure caused the diaphragm to alternately cover and uncover the cavities leading to a change in resonance at audio frequencies. Nearby, a microwave transmitter operated by Russian agents beamed energy into the embassy. They could listen in on conversations by detecting the changes in reflected power from nails. From reported stories it took quite a while to discover these babies, but then a gain it might not have and the embassy security people used them to run 'false flag' operations. Steve