[ RFID ] 17. What's the difference between passive and active tags?
- Active RFID tags have a transmitter and their own power source (typically a battery). The power source is used to run the microchip's circuitry and to broadcast a signal to a reader (the way a cell phone transmits signals to a base station). Passive tags have no battery. Instead, they draw power from the reader, which sends out electromagnetic waves that induce a current in the tag's antenna. Semi-passive tags use a battery to run the chip's circuitry, but communicate by drawing power from the reader. Active and semi-passive tags are useful for tracking high-value goods that need to be scanned over long ranges, such as railway cars on a track, but they cost more than passive tags, which means they can't be used on low-cost items. (There are companies developing technology that could make active tags far less expensive than they are today.) End-users are focusing on passive UHF tags, which cost less than 40 cents today in volumes of 1 million tags or more. Their read range isn't as far-typically less than 20 feet vs. 100 feet or more for active tags-but they are far less expensive than active tags and can be disposed of with the product packaging.
[ RFID ] 18. What is the read range for a typical RFID tag?
- There really is no such thing as a "typical" RFID tag, and the read range of passive tags depends on many factors: the frequency of operation, the power of the reader, interference from other RF devices and so on. In general, low-frequency tags are read from a foot (0.33 meter) or less. High-frequency tags are read from about three feet (1 meter) and UHF tags are read from 10 to 20 feet. Where longer ranges are needed, such as for tracking railway cars, active tags use batteries to boost read ranges to 300 feet (100 meters) or more.
[ RFID ] 19. What is tag collision?
- Tag collision occurs when more than one transponder reflects back a signal at the same time, confusing the reader. Different vendors have developed different systems for having the tags respond to the reader one at a time. These involve using algorithms to "singulate" the tags. Since each tag can be read in milliseconds, it appears that all the tags are being read simultaneously.
[ RFID ] 20. What is energy harvesting?
- Most passive RFID tags simply reflect back waves from the reader. Energy harvesting is a technique in which energy from the reader is gathered by the tag, stored momentarily and transmitted back at a different frequency. This method may improve the performance of passive RFID tags dramatically.
[ RFID ] 21. What is a chipless RFID tag?
- "Chipless RFID" is a generic term for systems that use RF energy to communicate data but don't store a serial number in a silicon microchip in the transponder. Some chipless tags use plastic or conductive polymers instead of silicon-based microchips. Other chipless tags use materials that reflect back a portion of the radio waves beamed at them. A computer takes a snapshot of the waves beamed back and uses it like a fingerprint to identify the object with the tag. Companies are experimenting with embedding RF reflecting fibers in paper to prevent unauthorized photocopying of certain documents. Chipless tags that use embedded fibers have one drawback for supply chain uses-only one tag can be read at a time.
[ RFID ] 22. I've heard that RFID doesn't work around metal and water. Does that mean I can't use it to track cans or liquid products?
- No. Radio waves bounce off metal and are absorbed by water at ultra-high frequencies. That makes tracking metal products or those with high water content problematic, but good system design and engineering can overcome this shortcoming. Low- and high-frequency tags work better on products with water and metal. In fact, there are applications in which low-frequency RFID tags are actually embedded in metal auto parts to track them.
[ RFID ] 23. What is an agile reader?
- An agile reader is one that can read tags operating at different frequencies or using different methods of communication between the tags and readers.
[ RFID ] 24. What are intelligent and dumb readers?
- These terms are not precise, but many people use "intelligent reader" to describe one that has the ability not just to run different protocols, but also to filter data and even run applications. Essentially, it is a computer that communicates with the tags. A "dumb" reader, by contrast, is a simple device that might read only one type of tag using one frequency and one protocol. This type typically has very little computing power, so it can't filter reads, store tag data and so on.
[ RFID ] 25. What is reader collision?
- One problem encountered with RFID is that the signal from one reader can interfere with the signal from another where coverage overlaps. This is called reader collision. One way to avoid the problem is to use a technique called time division multiple access, or TDMA. In simple terms, the readers are instructed to read at different times, rather than both trying to read at the same time. This ensures that they don't interfere with each other. But it also means any RFID tag in an area where two readers overlap will be read twice. So the system has to be set up so that if one reader reads a tag, another reader does not read it again.
[ RFID ] 26. What is "dense reader" mode?
- This is a mode of operation that prevents readers from interfering with one another when many are used in close proximity to one another. Readers hop between channels within a certain frequency spectrum (in the United States, they can hop between 902 MHz and 928 MHz) and may be required to listen for a Signal before using a channel. If they "hear" another reader using that channel, they go to another channel to avoid interfering with the reader on that channel.
[ RFID ] 27. What is automatic identification?
- Automatic identification, or auto ID for short, is the broad term given to a host of technologies that are used to help machines identify objects. Auto identification is often coupled with automatic data capture. That is, companies want to identify items, capture information about them and somehow get the data into a computer without having employees type it in. The aim of most auto-ID systems is to increase efficiency, reduce data entry errors and free up staff to perform more value-added functions, such as providing customer service. There is a host of technologies that fall under the auto-ID umbrella. These include bar codes, smart cards, voice recognition, some biometric technologies (retinal scans, for instance), optical character recognition (OCR) and radio frequency identification (RFID).
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