Background to RFID
RFID tags are going in and on many products from pharmaceuticals, toys, key chains, season tickets to clothes and even on animals and children.
RFID stands for Radio Frequency IDentification, a technology that has been used for many years in inventory tracking and secure access applications. More recently, RFID technology has been a major thrust in the tag and label industry, as small labels and tags include RFID transponder inlays that, unlike bar codes, allow users to read without line of sight. This membrane-thin inlay can also identify multiple articles simultaneously. In addition, it offers read/write capabilities so users can update information.
In a typical RFID label construction, the inlay is one additional layer in a typical pressure sensitive label construction. In the label or tag manufacturing process, the inlay is laminated between layers to become part of the label or tag. Inlays can be incorporated into existing stickers, labels, tickets or badges. Anywhere a pressure sensitive label can be placed, an inlay can be placed. Whether it is part of the packaging or part of the product, an RFID label can be embedded and hidden from sight.
Are you Using RFID?
RFID applications are all around us. Frequent users of toll roads and bridges users carry an RFID transponder mounted on the windscreen. Many car manufacturers such as BMW use an RFID transponder embedded in the ignition key. Many big city marathon races use RFID tags to track the progress of each runner. In this application, the runner wears an RFID tag on their shoelaces that can be read at specific points in a race. Pet passports use an RFID tag inserted under the skin of the animal. The London Underground Oyster card uses an RFID tag. More and more libraries are tagging books.
How RFID Works
At its most basic level, RFID is a wireless link used to uniquely identify objects. RFID systems use electronic devices called transponders or tags, and readers to communicate. These systems communicate via radio signals that carry data either unidirectionally or bidirectionally.
When a transponder enters a read zone, data is captured by the reader and then transferred through standard interfaces to a host computer for storage or action.
What's on the Inside?
At the core of an RFID tag or label is a transponder inlay. The inlays, which are commonly battery-less consist of two primary parts, the RFID silicon chip, and an antenna that circles the perimeter of the inlay. Tags can come be read only, write once or fully writable. The writeable memory can be as little as 64 bits for passive tags and up to as much as 32 KB for active tags. This memory can be read or written very quickly, in some cases as fast as 1000 tags per second!
Writing Data
Many applications of RFID labels include thermal direct or thermal transfer human-readable printing and bar codes on the face of the label. Therefore, the logical place for data to be written to RFID labels is at the bar code printer. Printer vendors such as Zebra technologies, Datamax and Intermec have developed RFID writers that are built into their printers.
Varieties of tags
Active RFID tags use an internal power source (a battery) within the tag to continuously power the tag and its RF communication circuitry. Active RFID allows extremely low-level RF signals to be received by the tag (since the reader/interrogator does not power the tag) and the tag can generate high-level signals back to the reader/interrogator. Active RFID tags are continuously powered, whether in the reader/interrogator field or not and are normally used when a longer tag read distance is desired. This can be many (even 00s of) metres, but the downsides are significant extra cost and the need to replace the battery at some point.
Passive RFID relies on RF energy transferred from the reader/interrogator to the tag to power the tag. Passive RFID tags reflect energy from the reader/interrogator or receive and temporarily store a small amount of energy from the reader/interrogator signal in order to generate the tag response. Passive RFID requires strong RF signals from the reader/interrogator, and the RF signal strength returned from the tag is constrained to very low levels by the limited energy. Passive RFID tags are best used when the tag and interrogator will be close to one another.
Semi-passive RFID uses an internal power source to monitor environmental conditions, but requires RF energy transferred from the reader/interrogator similar to passive tags to power a tag response. Semi-passive RFID tags use a process to generate a tag response similar to that of passive tags. Semi-passive tags differ from passive in that semi passive tags possess an internal power source (battery) for the tag's circuitry which allows the tag to complete other functions such as monitoring of environmental conditions (temperature, shock) and which may extend the tag signal range.
Frequencies of tags
The antenna used for an RFID tag is affected by the intended application and the frequency of operation.
- Low-frequency is 30kHz to 300 kHz. LFID or LowFID passive tags like glass-encapsulated tags used in animal and human identification, use a multilayer coil
- High frequency is 3MHz to 30 MHz. At 13.56 MHz, a HFID or HighFID tag can be used to provide ranges of several centimetres.
- Ultra high-frequency or UHF is 300 MHz to 3 GHz.
Standards
Low-frequency (125–134.2 kHz and 140–148.5 kHz) (LowFID) tags and high-frequency (13.56 MHz) (HighFID) tags can be used globally without a licence. Ultra-high-frequency (UHF: 868–928 MHz) (Ultra-HighFID or UHFID) tags cannot be used globally as there is no single global standard. In North America, UHF can be used unlicensed for 902–928 MHz. In Europe RFID operation is allowed from 865–868 MHz. However there are some ISO standards for animal, passport, smart payments, cargo containers and retail (EPCglobal with GEN2).
