notas soltas rfid

http://www.rfidexchange.com/forum/topic.asp?TOPIC_ID=10&SearchTerms=range,frequency

frequ?ncias t?picas
– 125Khz (magnetic) — This frequency range was the RFID industry’s first, since the early 1980’s. Read ranges are typically inches to several feet.
– 13.56 MHz (magnetic) => 60-80cm — “you get natural noise from all around (mainly the sun) that gives you a read range of about 2-3 feet max, and barely any motion detection. It is just difficult to get any passive backscatter energy from 13.56 because you have to use the near field for interrogation purposes (way too much resistance in a half wavelength antenna). However, in certain applications, 13.56 MHz is extremely useful”
– 860Mhz to 956 MHz (UHF) (electric) => 1m-4m — At 433 MHz and 915 MHz, you can start producing more results in the asset tracking realm, because you can interrogate tags moving at decent speed (faster than a person can run at 915) and don’t get much antenna loss.
– 2.45GHz ( electric) => 30cm — At 2.4 GHz, you can’t produce enough power to get a read range more than a foot, unless you incorporate some kind of active tag system. (well you can produce enough power, technically, but you’d better hope the FCC doesn’t find you).

“For all intents and purposes 433 MHz-915 MHz gives you the best read range under normal environmental conditions (i.e. not a lot of moisture during the daytime), but lower bands and upper bands definitely have their place in integrated RFID systems for a multitude of reasons.”
“The read range is a function of the frequency that is employed. The higher the frequency, the greater the range. This is way some organizations are persuing UHF frequencies to obtain range.”

activo/passivo
– 400Mhz to 2.45Ghz => em principio passivo
– >2.4 em principio activo

problemas
– liquidos
– outros campos electromagn?ticos

memoria
– 64bits…1kb…

— velocidade acesso
“Passive transponder speed depends on a lot of variables: environment, polarization of tag and antenna, bit length and efficiency of IC of tag, frequency, ”
“To put it in non-scientific terms, identifying one tag with 902-930 MHz, Class 1 EPC, is possible over 20 m.p.h. ”
“ISO tags at 13.56 MHz, which should be intderrogate faster than 2 Mhz, have a 2 m.p.h limit, or close to that”

— orienta??o
“Circular vs linear should consider tag orientation. If the tags are oriented with the electric field, linear polarized antennas should give a better read range. but if you have tags in all different directions then circular polarized antenna and its less, would probably be better. ”
“double dipole antenna, which enables them to be read regardless of their orientation to the reader.”

— transmiss?o de informa??o
– rs232 – 10/15feet +/-4m => Introduction to RS 422 & RS 485
– bluetooth – +/- 10m
– wifi – +/-100m