RFID Passive

Active RFID tags generally cost at least double figures, although they provide greater range and typically more functionality than their passive counterparts. RFID passive tags cost far less, although price can vary depending on a range of factors.

The amount of memoryon the chip is a major factor, and different sizes are suitable for different applications. Lower cost tags might only offer 96 bits of storage. That’s 12 characters, assuming 8 bits per character. While this might be enough to hold a product key or a unique serial number, it will need an external database to hold further details, which your reader will need to be able to connect to. A tag with 512 bits providing 64 characters might  negate the need for database connectivity, while larger chips storing 1-8 Kb could store both current and historical data directly on thechip without ever needing to refer to an external source.

High frequency tags can cost from twice to four times as much as ultra high frequency tags with the same characteristics.

The tag housing needs to be considered: tags embedded in fobs or cards will cost more than a simple tag mounted on a substrate. Another common tag format is smart labels: RFID passive transponders inserted between printed labels and an adhesive backing.

Tags which are shielded to function in harsher conditions, or to work near metal surfaces which would normally interfere with the signal, will be more expensive.

Increasing the range of the transponder will add to the expense, particularly as RFID passive tags have a much shorter range than active tags, due to their need to draw their power from the RFID reader.

Quantity, as always, can be a major factor. Bulk order of hundreds of thousands might save as much as 20% against order measured in the tens ofthousands.

These are some of the main factors influencing the cost of passive RFID tags. The other side of the RFID cost equation is the cost of RFID readers.

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.