If you're really intersted, Texas Instruments makes several different RFID sensors (and readers). Some are active, requiring a battery, I think, while others are passive and can be read by the disturbance caused in a magnetic field (very much like NMRI). One of the TI sensors requires an antenna that is 22.5mm (1.5 in) long. The RFID device is 48mm (1.89 in) square and about as thick as a piece of thin aluminum foil. A data sheet can be found at the company website mini-RFID.
(http://www.ti.com/tiris/docs/manuals/pdfSpecs/RI-I03-112A.pdf)
Hope this helps with the discussion.
Barry
pete wrote:
On Mon, 23 Jun 2003, [EMAIL PROTECTED] wrote:From: Stephen Straker [mailto:[EMAIL PROTECTED]] Sent: Monday, June 23, 2003 8:58 AMWAL-MART EMBEDDING RADIO FREQUENCY ID SENSORS INTO CERTAIN RETAIL PRODUCTS...These chips, researched at M.I.T.'s Auto-ID Center are about the size of a grain of sand. Chipsters say the technology will only be used to help retailers keep track of inventory --- like bar codes. But privacy-loving consumers question the very concept of a device that sends out radio waves to "readers" that not only identify the article, but where and with whom it's going.!!??? This has to be a paranoid hoax of some kind ... Or have I fallen so far behind that I don't realize that it's obsolete to ask how in the world a thing the size of a grain of sand could find the energy to broadcast rf waves to anybody even if across the room? Inquiring old minds want to know. Stephen Straker <[EMAIL PROTECTED]> Vancouver, B.C.It is certainly puzzling...Here is some background. ================================== COMPUTER IDENTIFICATION (RFID) TAGS IN PRODUCTS A number of new consumer products from companies such as Gillette, Procter & Gamble, and Prada will come with embedded RFID (radio frequency identification) "tags" (actually, tiny computer chips), that will contain scannable information such as the product's serial number. The goal is to dramatically improve inventory processes, and other big companies poised to join the RFID movement are Johnson & Johnson, Coca-Cola, Pepsi, Home Depot and Target.[...]. Embedded processor technologies, such as RFID, or radio frequency identification, will allow companies that use the system to keep consumer belongings under surveillance in stores, in homes and on the street.Nothing to explain the process there. I suspect that the way they would work might be sort of like my new (terrorism paranoia) magic name tag - it has an inductor loop which acquires power from the interrogating transmitter in order to transmit a response about one foot. However, in order to acquire enough power to work, the inductor loop has to be the size of a credit card. Perhaps with a higher frequency and higher transmitter power that could be shrunk somewhat, but I can't see how it could work if the whole device was the size of a chip. The required power would fry the little part as it tried to absorb it, and the interrogator power would be large enough to be a regulatory problem. The other possibility is more complicated - a built in battery and a switch, so it would broadcast briefly after receiving an initiating signal from the interrogator. That way it can retain power and release little bursts when required. But I would think the antenna would need to be an area the size of a button, or perhaps an aspirin, as would the battery. I presume they are using the terms "RF" and "sand grain" rather loosely, as it is patently impossible (under normal circumstances) for something the size of a sand grain to interact with frequencies in the range we normally regard as RF; the circuitry to operate even a tiny short range transmitter would be more like the size of a sesame seed, even neglecting the antenna, and I would expect it must operate in the high microwaves. ...You can get an interaction with RF and small amounts of material like salt solutions, using nuclear magnetic resonance - NMR, which is how the medical "MRI" scanners work - the marketing drones having deleted the N from the acronym as they assume most of their customers will be too stupid to understand the context - but the trick there is that the whole subject sample is immersed in a very powerful magnetic field. I suppose this is also a possible solution to the puzzle, but I didn't see any reference to powerful magnets, and NMR signals are not trivial to interpret unambiguously. Ah, well, when I went to school, they carefully explained how it was impossible to send a digital signal down a phone line at more than 2400 bits per second, but I have a half megabit dsl line disappearing down my phone jack, so you never know... -Pete Vincent _______________________________________________ Futurework mailing list [EMAIL PROTECTED] http://scribe.uwaterloo.ca/mailman/listinfo/futurework
