Electronic Design

RFID FAQs

If you're designing or implementing an RFID system, consider the following key questions and answers:

What kind of problem are you trying to solve?

RFID is a solution looking for a problem. It may or may not be for you. If you need a basic ID solution, check out bar codes first. They are mature and easy to implement. RFID is a cool technology, but it may be overkill for your application.

What is the value of the item to be tagged?

Tag prices range from a low of about 25 cents to over a dollar, depending on the type and quantity. If the item value is less than that, forget it. Anything with a value of over $10 can probably be profitably tagged. Don't hold your breath for the 5- or even 10-cent tag. It probably won't happen for a long time, if ever.

Is the item big enough to hold a tag?

Most things are, but a larger tag can overwhelm small items. Most tags are a few inches square, but smaller ones are available. The antenna eats up all of the space, and you want the biggest antenna possible as it increases read range and reliability.

What frequency tag should I use?

That depends upon the application and the desired read range. Low-frequency tags (125 kHz) have a read range of only up to a foot or so. But their main advantage is that they work best in the presence of lots of surrounding metal and/or water. Animals and people are mostly water, so these tags work best in those uses. The 13.56-MHz tags are the most versatile and cost the least. Read range is up to three feet or so. UHF tags have the longest read range, up to 20 to 25 feet. Once the new Gen2 products become available, this will be a great choice if you need interoperability worldwide. Finally, don't forget that the higher the operating frequency, the faster the read data rate. It may only be a few tens of kilobits per second at the low frequencies, but it can be several hundred kilobits per second at the higher frequencies.

What is the maximum read range?

Most RFID works at a range of several inches to several feet. Anything beyond that is going to require special tags, readers, or antennas. The UHF tags have the longest range of up to 20 feet or so, but no more. If you need more range, consider the active tags that have a battery to transmit higher power over longer distances.

What is the tag orientation with respect to the reader?

Tags read best when they parallel the reader antenna. This is true of the loop-type antennas used in most applications. Tags generally can be read in almost any orientation if they are close enough. Yet most reader antennas have a directional characteristic, so you could have blind spots. Tags that end up at a perfect 90° orientation to the reader may not read.

Does your application require a write capability?

Most tags become preprogrammed, but your application may require you to write to them as they move through a process or during some transportation. Writeable tags are more expensive, and the write range is only 30% to 50% of the read range. Your reader also must be able to write to your chip. Memory size in the chip must fit your application.

Does the application require reading tags in close proximity to one another, or will each item be isolated from the others?

If you must read many items close together, you will need a tag and reader with anticollision capability to avoid read errors or no-read conditions. These are more expensive, but they make some otherwise impossible applications practical.

Is security an issue?

Do you want your tags potentially to be read by someone other than those authorized, or do you really care? Maybe the application is noncritical, so perhaps unauthorized reads are unlikely. There isn't too much you can do with just a part number. But in sensitive applications, you may wish to make your tags unreadable by anyone. If so, get tags and readers with built-in encryption and authentication. Again, these are more expensive, but the applications may demand it.

What are the environmental conditions in the read area?

Tags and readers are pretty tough, but they also have their temperature, moisture, vibration, and physical limitations. Visit the site and match the conditions to the tag and reader specs. Also, look at the presence of surrounding metal, water, and other liquids. All of these can affect read range and reliability. Don't forget to survey the site for other wireless applications and noise sources. Noise from motors, switch gears, fluorescent lights, and other traditional sources can greatly reduce the read range and reliability. In fact, existing radio sources also may interfere if they are on or near the same frequency or in close proximity.

Will multiple readers be nearby?

A reader in one location can interfere with another reader nearby. For example, using readers on adjacent loading docks could cause massive interference between the readers. Increasing the space between readers and reorienting the antennas can help mitigate such interference. Handheld readers can wreak havoc if care isn't taken to evaluate where they will operate.

Will your product tag only be used internally, or will others read it in multiple settings and conditions?

If your tag finds use outside your proprietary setting, be sure its features and characteristics match the other potential systems. Conformance to existing standards will help you select a workable tag and system.

Have you determined how tag-reader data will be used?

Once you read the tag, you have to do something with the data. You can store and process it in a variety of ways, depending on your usage. The key to a successful system is the software that handles this processing. Specialized RFID middleware is available, and most of it ties into existing database, manufacturing, or ERP software packages.

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