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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 tagged, stored momentarily and transmitted back at a different frequency. This method may improve the performance of passive RFID tags dramatically.

Another problem readers have is reading a lot of chips in the same field. Tag collision occurs when more than one chip 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. Since they can be read in milliseconds, it appears that all the tags are being read simultaneously.

One problem encountered with RFID is 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 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.

Microchips in RFID tags can be read-write or read-only. 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, or interrogator. 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. Some read-only microchips have information stored on them during the manufacturing process. The information on such chips can never been changed. Other tags can have a serial number written to it once and then that information can't be overwritten later.

It depends on the vendor and the application, but typically a tag would carry no more than 2KB of data-enough to store some basic information about the item it is on. Companies are now looking at using a simple "license plate" tag that contains only a 96-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 Electronic Product Code, or RFID, was developed by the Auto-ID Center as a successor to the bar code. It is a numbering scheme that will be used to identify products as they move through the global supply chain. For more on EPC technology.

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.

Active RFID tags have a battery, which 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).

Most countries have assigned the 125 kHz or 134 kHz area of the radio spectrum for low-frequncy systems, and 13.56 MHz is used around the world for high-frequency systems. But UHF RFID systems have only been around since the mid-1990s and countries have not agreed on a single area of the UHF spectrum for RFID. Europe uses 868 MHz for UHF and the U.S. uses 915 MHz. Until recently, Japan did not allow any use of the UHF spectrum for RFID, but it is looking to open up the 960MHz area for RFID. Many other devices use the UHF spectrum, so it will take years for all governments to agree on a single UHF band for RFID. Government's also regulate the power of the readers to limit interference with other devices. Some groups, such as the Global Commerce Initiative, are trying to encourage governments to agree on frequencies and output. Tag and reader makers are also trying to develop systems that can work at more than one frequency, to get around the problem.

Different frequencies have different characteristics that make them more useful for different applications. For instance, low-frequency tags are cheaper than ultra high frequency (UHF) tags, use less power and are better able to penetrate non-metallic substances. They are ideal for scanning objects with high-water content, such as fruit, at close range. UHF frequencies typically offer better range and can transfer data faster. But they use more power and are less likely to pass through materials. And because they tend to be more "directed," they require a clear path between the tag and reader. UHF tags might be better for scanning boxes of goods as they pass through a bay door into a warehouse. It is probably best to work with a consultant, integrator or vendor that can help you choose the right frequency for your application.

Microwave (2.45 GHz) is also used in some applications. Radio waves behave differently at different frequency, so you have to choose the right frequency for the right application.

RFID systems use many different frequencies, but ultra-high frequency, or UHF is (850-900 MHz)

RFID systems use many different frequencies, but generally the most common are high- (13.56 MHz)

RFID systems use many different frequencies, but generally the most common are low- (around 125 KHz)

RFID is a proven technology that's been around since at least the 1970s. Up to now, it's been too expensive and too limited to be practical for many commercial applications. But if tags can be made cheaply enough, they can solve many of the problems associated with bar codes. Radio waves travel through most non-metallic materials, so they can be embedded in packaging or encased in protective plastic for weather-proofing and greater durability. And tags have microchips that can store a unique serial number for every product manufactured around the world.

RFID is not necessarily "better" than bar codes. The two are different technologies and have different applications, which sometimes overlap. The big difference between the two is bar codes are line-of-sight technology. That is, a scanner has to "see" the bar code to read it, which means people usually have to orient the bar code towards a scanner for it to be read. Radio frequency identification, by contrast, doesn't require line of sight. RFID tags can be read as long as they are within range of a reader. Bar codes have other shortcomings as well. If a label is ripped, soiled or falls off, there is no way to scan the item. And standard bar codes identify only the manufacturer and product, not the unique item. The bar code on one milk carton is the same as every other, making it impossible to identify which one might pass its expiration date first.

RFID uses the low-end of the electromagnetic spectrum. The waves coming from readers are no more dangerous than the waves coming to your car radio.

An RFID system consists of a tag, which is made up of a microchip with an antenna, and an interrogator or reader with an antenna. The reader sends out electromagnetic waves. The tag antenna is tuned to receive these waves. A passive RFID tag draws power from field created by the reader and uses it to power the microchip's circuits. The chip then modulates the waves that the tag sends back to the reader and the reader converts the new waves into digital data.

Radio frequency identification, or RFID, is a generic term for technologies that use radio waves to automatically identify people or objects. There are several methods of identification, but the most common is to store a serial number that identifies a person or object, and perhaps other information, on a microchip that is attached to an antenna (the chip and the antenna together are called an RFID transponder or an RFID tag). The antenna enables the chip to transmit the identification information to a reader. The reader converts the radio waves reflected back from the RFID tag into digital information that can then be passed on to computers that can make use of it.

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 are 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, and radio frequency identification (RFID).

► What is radio frequency (RF)? How is it measured?
► Is there a health hazard associated with radio frequency?
► How is it regulated? Are there any safety limits on human exposure to wireless and RF fields?
► Where can I go to learn more about regulatory compliance?
► What is a smart meter?
► Are Itron's smart meters certified by the FCC?
► How is Itron addressing the issue of RF Safety?
► Will a smart meter interfere with a security system, pacemaker, cell phone or other RF devices?

Itron defines smart meters as devices that are like mini computers on houses and businesses. They communicate back and forth with the utility to automatically transmit meter information, such as energy consumption, spikes in power usage, and power outage and restoration messages to support various applications beyond monthly billings. Our smart metering solutions have substantially more features and functions than our advanced metering systems and technology. Smart meters are able to collect and store interval data, perform remote service connect/disconnect, send detailed information, receive commands, and interface with other devices, such as in-home displays, smart thermostats and appliances, home area networks, advanced control systems, and more.

The only health effect from RF fields identified in scientific reviews has been related to an increase in body temperature (> 1 °C) from exposure at very high field intensity found only in certain industrial facilities, such as RF heaters. The levels of RF exposure from base stations and wireless networks are so low that the temperature increases are insignificant and do not affect human health.

Electromagnetic waves are measured by wavelength and frequency. Wavelength is the distance covered by one complete cycle of the electromagnetic wave. Frequency is the number of electromagnetic waves in one second, also known as a hertz or Hz. One Hz equals one cycle per second. One megahertz (MHz) equals one million cycles per second. Generally, microwaves are radio frequencies measuring more than 1 GHz.

Electromagnetic fields, radio waves, microwaves and wireless signals are collectively referred to as radio frequency (RF) energy. RF energy is all around us. It's used in various electronics and appliances, including radio and television broadcasting, cellular telephones, satellite communications, microwave ovens, radars, and industrial heaters and sealers, to name a few.