Active RFID Tags

Definition

Active RFID is a form of Auto ID (automatic identification) characterised by the use of ID tags which are self powered. They have their own battery, and typically emit a signal at a predefined rate, usually with an interval of about one second between transmissions.

Advantages of Active RFID tags vs Passive RFID tags

Benefits of active RFID tags include range and independence from surroundings.

Range

An active RFID tag can typically be read at a range of 100 metres. This compares well against passive tags, where the read range varies according to the frequency of the tag. For LF tags, range can be less than an inch. for HF tags, range can be to a twelve inches. For UHF tags, range can be up to twenty feet. But long range is now always a good thing. In systems where the tag is used as a locator , range can be deliberately reduced, and this is often done by reducing the "gain" of the reader.

Effect of surroundings and orientation.

The orientation of the tag tends to be less critical for active RFID tags than for passive RFID tags, and the tag is less affected by its surroundings, especially the proximity of water or metals. In fact, testing of systems using active tags can be problematic. When testing we typically use a tin box to shield unwanted tags and make them unavailable to the reader. This is fine when testing for passive RFID Tags, but when testing many Active RFID tags we find they can be read even when placed in a tin box with a closed lid. Of course, in theory this is not possible, but if the lid is less than a perfect fit, enough signal leaks through to give a reading. This has obvious implications in real world deployments, meaning that an accidental partial screening of a tag can be accommodated without the tag being unreadable.

Disadvantages of Active RFID tags vs Passive RFID tags

Disadvantages include cost, size, life, operating temperature range.

Cost

Depending on type, manufacturer and quantity, as a general guide assume that an active RFID tag is going to fall in the range $5 to $30 each. This compares to $1 to $3 for HF tags, and 50c to $6 for UHF tags. (Prices are changing rapidly, these are rough numbers as a general guide).

Size

Active RFID tags are generally larger than their passive counterparts. An active RFID tag can be in one of several formats. In credit card format, it is typically the thickness of four or five credit cards, say 1/8 inch or 3mm. More commonly it is in a format two or three inches long, perhaps 3/4 wide and 1/4 inch thick. Construction is usually sealed, and tags vary in how robust they might be. Passive tags vary in size according to frequency. An LF RFID tag is perhaps the size and shape of a beer bottle cap, although tags in the form of a "plastic nail" are sometimes used where appropriate, especially for identifying trees. A HF RFID tag is commonly packaged as a credit card, typically used for building access, but can also be incorporated into a key fob, as with the tags used to "pay at the pump". UHF RFID tags are smallest of all, due in part to their construction, which requires printing on only one side of the laminate. So UHF tags are typically three or four inches long, between 1/4 inch and one inch wide, and less than 1mm thick. (please excuse the mixed units).

Life

The life of an active RFID tag is limited by the battery. Manufacturers claim typically five years. The battery cannot be changed, and the tag must be discarded at end of life. Note that this is a little difficult to test, and as the technology is new, we are still collecting data on effective life in real world conditions. But then, I have Christmas tie that plays Rudolf, and that is approaching five years old, and still going strong. And it came from the buck store. The life of a passive RFID tag is theoretically unlimited, determined only by the reliability of the components.

Temperature Range.

The strength of the Active RFID tag comes from its on board battery, but in some circumstances that can also be a weakness. At extreme low temperatures the chemical reaction of the battery is slowed, and the tag becomes unresponsive. Normal performance generally resumes when the tag is warmed. Depending on the design, tags can work down to minus twenty degrees Celsius.

Applications

Active RFID tags are commonly used for tracking high value assets over a large area. They might be used for tracking vehicles in a lot, or for tracking valuable items or essential equipment within a building.

SageData is based in Ottawa, Ontario, Canada.

For further information, please contact us...
Send email to "info@sagedata.com"
Contact us by phone...
within Ottawa, dial (613) 225-4404
outside Ottawa, dial (888) 838-1067