What are the criteria of selecting frequency for RFID?

Hi, i am a newbie in RFID. I have questions:

1. Some RFIDs work at frequency less than 1MHz, why are they call "RF"ID?
2. What is the criterial of selecting frequency for the RFID? or what is the relation between transmission distance, loss, absorption, power consumption and frequency?

Question about RFID.

Hi,

1) For RFID, it does not mean the carrier frequency is very high. In fact most RFID is located in the low frequency range (<100MHz). From this point maybe we call it wireless or contact-less ID is more reasonable. RFID is just a name for it.

2) For the frequency range, currently we have a lot of standards for RFID. e.g. ISO/IEC 14443, is a good standard for 13.56MHz middle distance contactless card. Due to these standards, the developement should follow these standards, otherwise nobody buy your product. For the loss, distance, power, frequency and physical layer signal format, each standard specifies them in detail. Also each standard has its FOM and application field. You can read some standards or get some books on RFID to get the idea. Thank you.

Question about RFID.

Hi alanphydenics, thanks a lot.
My colleague has such an idea: design a transponder that is powered by the radio signal sent from the reader, the transponder, which is implanted inside an animal body, has a simple sensor monitoring something, temperature for example, it sends back the sensing data to the reader whenever the reader comes close.

So can the transponder get enough power supply for the sensing circuit, and the trnasmiter that sends back the data? Is there any product doing similar job in the market? If power is not an issue, then which frequcny is suitable for this application? If the frequency is low, the antenna is large thus not possible to implant into a body. If the frequency is high (GHz), then the absorption by the body is high, and the transmitter's power should be high. So, is this idea possible?

Re: Question about RFID.

everything is possible if you have theory standing for, but why not using Thermo Life
to get electricity energy instead of radio signal energy?

Re: Question about RFID.

In the early days the used tow halves of a pot core for inductive coupling. One was just below the animal skin. The other was held next to it on the outside of the skin.

This transferred enough power to power the electronics inside the animal including the transmitter.

I have heard of such methods for recharging the battery of items inside humans such as heart stimulators.

The RFID term was originated for serial numbered transponders. Originally it was used for door keys. When the price became lower it was used for stock room inventory keeping.

Transponders without serial numbers (one bit of data) were used for security of store merchandise. Many of the above early methods used 'field disturbance sensor" methods where the mobile part coupled to the fixed part and upset a bridge circuit.

Re: Question about RFID.

yeah, soon they'll be implanted into people... pretty crazy

Added after 1 minutes:

wait, i take that back, they are already being implemented into certain societies/small parts of cities-- soon to be distributed world-wide when the opportunity arises.