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| RFID Tags |
- How much information can an RFID tag store?
- It depends on the vendor, the application and type of tag, but typically a tag carries no more than 2 kilobytes (KB) of data—enough to store some basic information about the item it is on. Simple "license plate" tags contain only a 96-bit or 128-bit serial number. The simple tags are cheaper to manufacture and are more useful for applications where the tag will be disposed of with the product packaging. The aerospace industry wants to store parts histories on high memory tag, which has led to the introduction of passive UHF tags that store 4KB or 8KB of data.
- What's the difference between read-only and read-write RFID tags?
- Microchips in RFID tags can be read-write, read-only or “write once, read many” (WORM). With read-write chips, you can add information to the tag or write over existing information when the tag is within range of a reader. Read-write tags usually have a serial number that can't be written over. Additional blocks of data can be used to store additional information about the items the tag is attached to (these can usually be locked to prevent overwriting of data). Read-only microchips have information stored on them during the manufacturing process. The information on such chips can never be changed. WORM tags can have a serial number written to them once, and that information cannot be overwritten later.
- 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.
- 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 depends on whether the tag is active or passive. Active tags broadcast a signal, so they have a much longer read range—300 feet or more—than passive tags. 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 and high-frequency tags tags are read from within three feet (1 meter) and UHF tags are read from 10 to 20 feet. Readers with phased array antennas can increase the read range of passive tags to 60 feet or more.
- What is tag collision?
- Tag collision occurs when more than one transponder reflects back a signal at the same time, confusing the reader. Different air interface protocol standards (and different proprietary systems) use different techniques 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.
- 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 briefly and transmitted back to the reader.
- 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. There are inks that reflect back radio waves at certain frequencies, enabling farmers, for example, to tattoo a chipless RFID transponder on an animal for identification purposes.
- 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?
- 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 embedded in metal auto parts to track them. Radio waves bounce off metal and are absorbed by water at ultrahigh frequencies. That makes tracking metal products, or those with high water content, with passive UHF tags challenging. However, in recent years, companies have developed special UHF tags designed to overcome these challenges. There are also ways to tag products with metal or water content to ensure reliable read rates (members, see How to Tag Problem Products.)
- Who are the leading RFID tag vendors?
- There are many different RFID vendors with different areas of expertise. Some make active tags. Some make passive tags. Some focus only on UHF. Others sell low-, high- and ultra-high frequency systems. RFID Journal has created a searchable database of RFID vendors around the world. Visit our online buyer's guide to locate the type of vendor you are looking for.
- What are micro-electro-mechanical systems (MEMS)?
- MEMS (micro-electro-mechanical systems, which are smaller than microscopic dust mites) have been used for several decades in everything from inkjet printers to accelerometers that deploy air bags in cars. A MEMS RFID tag contains micromechanical components that are expected to be rugged and easier to produce, and which could be attached directly to medical devices. Such a tag can withstand exposure to wide temperature ranges and gamma radiation (see MEMS the Word and U.S. Army Developing RFID System to Track Weapons Usage).
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