RFID Passive

What is passive RFID?

RFID, or radio-frequency identification, involves the use of a “tag” for the purposes of identification, authentication, or tracking. The tag can store information on an integrated circuit, convert this to a radio-frequency (RF) signal, and transmit or receive these RF signals to an RF reader.The distance at which the tag can be read depends on a number of factors, including the strength of the signal, and the size of the antennae on the tag and the reader.RFID tags can be active or passive. RFID active tags are typically larger and more expensive, but are capable of transmitting signals with the need for an external prompt. RFID passive tags are cheaper, have no battery, but remain dormant until prompted to transmit a signal by an external source.Here we will be focusing mainly on RFID passive tags, which are becoming more common in daily use due to their lower cost.

RFID passive tags

RFID passive tags need to be activated by a reader in order to access the information stored on them.The distance from which a tag can be read depends on a number of factors, including the size of the tag antenna and the amount of power it can draw from the tag reader. Modern RFID tags can be miniaturized to a great degree, the better to be easily embedded in other objects. However, the smaller the tag’s antenna, the lower its range, so the smallest tags can only be read at a very short distance. Various RFID passive tag types are suitable for different applications.

RFID passive applications

As the cost of mass-producing modern RFID passive tags becomes progressively cheaper, use of them has become increasingly common. Inventory systems, road tolls, logistics, animal tracking are just some of the current applications of RFID passive tags. In recent years, a number of countries have started including tags in passports.In other articles, we will look in more detail at some of the current and possible future uses of RFID passive tags.

RFID issues and concerns

Unlike other systems such as the barcode, no single international standard governing RFID is in place. Many countries have their own protocols for governing the allocation of RFID frequencies. As a result, tags of certain frequencies cannot be used worldwide due to conflicting with other uses of these frequencies in certain countries. Security of tags is a major concern. While tag data can be encrypted, this is problematic due to the limited resources available on the tag itself. There is concern that unencrypted tags can be read, possible from a greater distance than originally intended, by a reader which provides additional power to the tag. Many people worry about privacy issues raised by RFID passive tags. These might be used to track stock from manufacture through to point of sale. However, if they remain attached to the product after sale and remain functional, they may be activated at a future date. The security issues mentioned above also have a number of privacy implications. Again, we will look at some of these concerns and what can be done to address them in other articles

Further Reading

Coca-Cola has begun testing a new soft drinks dispenser which uses passive RFID technology. The new system will allow a machine to offer over 100 choices of beverage while taking up no more space than the current 8-valve dispenser.

Cartridges containing concentrated flavouring will dispense a small amount of the appropriate flavour, which will then be mixed with the other ingredients, such as sweetener, water, and carbonating agent, and dispensed to the customer. Maintaining a wide variety of cartridges in a single dispenser is problematic, which is where RFID comes in.

When the cartridge is produced, it is fitted with an RFID passive tag, which will contain details of the flavour it contains and the quantity. RFID readers in the dispensers can then register the cartridge as it is inserted, and ensure it is placed in the correct slot, which will be identified to the user by a LED.

Once the cartridge has been correctly installed, the data on the cartridge’s passive RFID tag can be updated each time a drink is dispensed, to keep track of the quantity of flavouring remaining. This information can also be relayed back to Coca-Cola’s management system, and used to automatically detect when a cartridge is nearing depletion, allowing a replacement to be prepared. This also allows the company up-to-date information on consumption patterns, and finally the direct link to the dispenser allows a particular cartridge to be instantly disabled for any reason, be it a recall or withdrawal of a product line.

Four years in development, the Freestyle dispenser is currently being tested in selected restaurants in Atlanta and southern California before a planned wider roll-out next year.

Modern RFID passive tags all share certain basic characteristics. They are composed of an antenna and a microchip, and a battery for active and semi-passive tags. They work in the same manner:

The passive tag remains dormant until activated by energy from an RFID reader’s antenna. The tag then sends the data stiored on the microchip as radio waves to the reader, powered by energy derived from the reader’s electromagnetic field. The reader interprets the radio waves as data, and can also update the data on the chip.

With decreasing production costs, and without the need for their own power source, passive RFID tags have now reach the point where they can be used disposably.

While the word “tag” is generally used when talking about RFID systems, an RFID tag is specifically an RFID transponder (the microchip and antenna) mounted on an underlying layer. While this is the cheapest option, other possibilities exist:

• the transponder can be placed within a printed adhesive label to form a smart label, which can be used like a barcode, but with the ability to be read without line of sighth and have its data modified;
• it can be embedded in a plastic card, and used in access control or transport pass systems;
• it can be integrated into a container to enable tracking of the contents;
• the transponder can be protected by special packaging to withstand extremes of temperature or other harsh conditions which would otherwise damage it.

The production cost will obviously increase if the transponder is packaged in such a manner.

We will continue to use the term “tag” as an inclusive reference to any of these alternatives.

Whether tag data can be updated is another point of differentiation.

• Read only tags can’t be updated and store a unique serial number, which can be used to uniquely identify them but will need to reference an external database to find more information about the tag.
• Read/write tags can have their information updated many times.
• Write once, read many, or WORM, tags can only be written to once, after which the stored data cannot be updated.

Thus there are a variety of passive RFID tag types, with the most appropriate dependent on the nature of the application in question.