Some of the advantages of RFID over the mag-swipe ID cards:
- There are no moving parts, anywhere. This means dust, corrosion and wear and tear have a much smaller impact on RFID than mag-stripes, and mischief with chewing gum is ineffective.
- It is contactless. The card doesn't even have to be on a line of sight from the reader in order to be detected. With enough range on an RFID lock, one just walks up to a door with the ID card still in a pocket, and it opens.
- Greater security is possible on RFID systems. For example, code hopping can be implemented so a tag transmits a different ID code each time. Each card can still be distinguished from all others, but even if someone can get a copy of one transmission from a card, that one transmission, when reproduced, will be rejected by the interrogator later.
- RFID is more transparent to the users than mag-stripes. A flexible tag on sticky paper could be attached to grocery items instead of a price tag, for example, then a checkout counter could read the contents of a shopping bag and total the prices without a clerk even having to open it.
RFID tags generally come in two types: FDX (Full duplex) and HDX (Half duplex). Either type can be made with or without a battery, though it's rare to find an FDX tag with a battery. FDX tags transmit their ID codes while the reader's activator signal is on - most of them actually get their energy from the activator signal, which is why they rarely have batteries. HDX tags transmit their ID codes after the signal turns off - sometimes the tag has a large capacitor, and gathers energy while the activator is on, sometimes it has a battery (in which case the activator merely is a signal for the HDX tag indicating when it should transmit its ID).
There are generally three types of modulation used in RFID - Amplitude modulation (ASK), Frequency modulation (FSK), and Phase modulation (PSK). There are several encoding schemes: NRZ, Manchester encoding, Differential bi-phase encoding, variants, and more exotic types. The bit rate may vary from one tag format to another, as may the length of the tag, and the logical arrangement of bits within the tag; all these variables make for a very wide variety of tag formats. On top of that, more sophisitcated tags implement query-response protocols for authentication, and anticollision routines so that multiple tags in a field don't interfere with each others transmissions.