Access Control Doctor: Token questions

28 Apr 09

Q: Are all proximity tokens the same?

A: No they're not. We can define 'proximity token' as an RF device used for identification. Here's a summary of the main types used.

Passive: A passive proximity token does not contain a battery. The token is given the energy to transmit its number by being placed near the reader. An electrical current is induced by placing the token's inductance coil within the electromagnetic field of the reader. There are varying types of passive tokens ranging from low cost Electromarin tokens through to higher security solutions such as Hitag2. These higher security tokens require matching security passwords at both reader and token, meaning that they are much more difficult to reproduce.

Active: Active tokens (you may have guessed what I'm about to say) contain a battery. As they have their own power source these tokens can often be read while much further away from the proximity reader. This can mean hands-free operation and can be useful when using a proximity token to open a barrier to a car park, for example. Batteries will need to be changed and active tokens are usually larger and more expensive.

High frequency: 'Normal' proximity readers operate at around 125KHz. 'High frequency' generally refers to readers and tokens working from 13.5MHz right up to 2.4GHz (microwaves). This higher frequency offers a couple of significant benefits. One is that the rate of data transfer is much higher. This difference is imperceptible when transmitting a simple identification number but can be an advantage when handling the more complex data exchanges common with smartcard applications. In addition, high frequency tokens can have a simpler construction as they can operate with a very simple inductance coil. This coil can be printed onto a PCB, or even paper, reducing the cost and opening up markets such as baggage tracking. Predictably, there are drawbacks. The higher frequency means a shorter wavelength which is more susceptible to interference and doesn't have the reach of lower frequencies. Just like short-wave, medium-wave and long-wave on your radio in fact.

Q: What are smartcards?

A: The term 'smartcard' refers to a token's ability to have its stored information changed and updated when communicating with a reader. This can be very useful for applications such as cashless vending where a user's allowance is stored on the card itself. The Oyster card is used in this way for cashless travel using London's public transport. Bank cards are smartcards and use this technology to store your PIN. However, they rely on the card making contact with the card reader rather than contactless proximity. Popular smartcard formats are Mifare and HID iClass. These both operate at 13.5GHz.

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