rfid power supply

This is really old news. I first heard of it around 1999. The idea goes back to Tesla around the late 1800s. Nowdays all mainstream RFID chips use this method of powering so it's no longer a "trick" -- its common.

Google "Radio power transmission" (Isn't it the most obvious thing to inject into google in this case?, Lacking google-fu?). The first hit is a wikipedia article on the subject.

This is probably true by volume of RFID devices sold, but there are still plenty of self-powered units out there as well. The main drawbacks of field-powered RFID tags is a relatively short read distance (it's difficult to get more than a foot, although some people have managed better than a yard) and slow read rate. Both are really due to the same problem -- with very low power available, it's hard to transmit hard or fast.

reply: Art Bell had a antenna located at his residence that covered about a mile,about 800 feet high using copper cable.He had measured about 20k watts on end fed system.A high value cap was used for storage.I do not know the amp's available.But was tuned to about 7 meter's.

Passive EPC Global RFID tags get up to 7metres with a 4watt 900MHz RFID reader used.

Paper RFID tags ~ 10 c to 15c in million pcs qty.

All doable!

Joe

Where did you get the idea that energy needs to be stored? An RFID or any transponder can perform the receive and retransmit simultaneously. Incoming on one frequency is used to power the RFID circuitry AND a portion goes into powering the transmitter to power the response. Or the RFID is used to modulate the amount of power the transmitter is putting out - similar to a grid dip meter.

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I doubt there's enough energy available to operate a charge pump to drive EEPROM cells, so nonvolatile storage is probably out as well.

Best regards, Spehro Pefhany

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RichD wrote in news:1191985183.525647.21920@

19g2000hsx.googlegroups.com:

They basically send out a series of pulses at 125Khz or 13Mhz, and listen for responses between the pulses.

"Spehro Pefhany" schreef in bericht news: snipped-for-privacy@4ax.com...

Elektor had an article about RFID last year. They concentrated on the Mifare Ultralight ICs which are meant to be used for entry tickets. This RFIDs have

512 bits of memory of which 384 bits are read/write. Some other figures:

- ISO/IEC 14443-3A

- read/write distance up to 10cm

- 106 kbps

- unique serial number and some more.

Other technics are available for logistics in food and pharmacy for instance. EasyLogic RFID Distribution and RSI-ID developed a new RFID-tag, AG-38, that can be read and written from distances up to 26m. Have a look at:

No surprise this new ones are way too expensive for Wal Mart but there are many others out there.

petrus bitbyter

Joel Kolstad snipped-for-privacy@yahoo.com posted to sci.electronics.design:

And now it is time to start asking some of the hard questions: How can this be used/abused to invade privacy? Or do we have any left?

Spehro Pefhany snipped-for-privacy@interlogDOTyou.knowwhat posted to sci.electronics.design:

But of course there is, but you have to get closer for longer with a higher power source.