I am a senior industrial design major and I am have been asked to give a brief presentation on RFID tags and how they work. I understand the general concept but I am not sure the specific technical aspects of the system. I was wondering if someone could explain the basic principle of how these tags work (in layman's terms!) I have conducted some research but I am not sure I completely understand the difference between active, passive and semi active. Another thing I am a little confused with is that I read that they are used in library's and theft deterrent devices in retail. I have taken some of these tags apart (specifically the ones found in CD's ) and it appears they are a plastic housing with thin sheets of steel in them. Are these considered RFID or strictly magnetic detectors that must be demagnetized in order to pass through the detector. If anyone can shed some light on this issue, I would be most appreciative. Thank you very much.