A Brief Description of Radio Frequency Identification (RFID) Technology
In a nutshell, RFID works like this: A radio-sensitive "tag" is placed on an item. The tag could be concealed in an adhesive label, affixed to the shirt collar tag on an item of clothing, attached to the packaging for a product, or even injected under the skin of a dog or a cat (or a human - as is being offered by a sports club in Brazil to uniquely identify members!) When an RFID "reader" scans the tag a pulse of radio energy is sent out and the tag sends back the inventory control number. In its essence, RFID is "wireless UPC bar coding". But there's more... While "read-only RFID tags" are simply read, "read-write RFID tags" can have their information content updated by the reader. This is being proposed by Toyota whereby they would place a read-write tag under the VIN number plate in 2005 vehicles and the complete maintenance history of the vehicle would be encoded on the tag. Suffice it to say, there is a significant amount of discussion taking place regarding people's right to privacy and the potential for RFID technology to track a person's purchases, and even their physical location. The State of California passed a law in 2004 restricting the information content of an RFID tag to that of a static UPC bar code. While it's uncertain how far RFID technology will go towards documenting private information there's no question that the RFID tag will replace the UPC bar code over time. Some of the advantages of using Radio Frequency Identification are: The ability to scan and identify an entire shopping cart full of merchandise without removing individual items. The ability to locate a "lost" product in a warehouse or a "lost" piece of equipment on a corporate campus. The ability to track a person's or vehicle's location inside a building when GPS (Global Positioning System) signals can't be received. The ability to read tag information from up to 30-feet away without having to "scan" anything with a laser, the way a UPC bar code scanner is required to do today.
RFID Is Not a Wi-Fi Radio Standard The key thing to remember, relative to Connect802, is that RFID is not a Wi-Fi technology. The radio standards for RFID are unrelated to those of 802.11 (although there is RFID specified in the 2.4 GHz band also used by 802.11b/g).

"If RFID isn't a Wi-Fi technology, why is being discussed in a 'Just the Facts' page?"

There's every reason to expect RFID tagging to completely replace the common UPC bar codes found on essentially every product sold in every retail store around the world. The RFID readers (referred to as "RFID interrogators") may be handheld, they may be mobile (attached, for example, to a fork lift in a warehouse), or they may be fixed (at a point-of-sale location, on a door frame for entry control, or on a warehouse loading dock door to track inventory as it enters and leaves the warehouse). Here's the key thought: The RFID readers must have a way to communicate back to the in-building network to send information to, and receive information from the central database system that understands what to do with the identification information read from the tags.

The communication link between the RFID reader and the in-building network is the 802.11 Wi-Fi network infrastructure. That's the link between RFID and Wi-Fi. It means that the Wi-Fi network will have to be designed to provide sufficient capacity and throughput and sufficient RF signal coverage, to support the use of whatever types of RFID readers are in use. In addition, the Wi-Fi network will probably be used for data communications, web browsing, email, and possibly wireless Voice-over-IP telephony. This is where Connect802 enters into the picture, providing RF design services through the Suite Spot Predictive Site Survey to make sure the Wi-Fi wireless LAN does its job supporting RFID, data, voice, and possibly even streaming video for security cameras.

To provide a perspective on how RFID works you are invited to read this 'Just the Facts' tutorial. To build a Wi-Fi backhaul network to support the connection of RFID interrogators / readers to the in-building or corporate campus network, you're invited to call Connect802 in California at (925) 552-0802.

When you are considering implementing an RFID solution for vehicle yard management, equipment yard management, asset tracking, reusable transport item tracking, personnel monitoring or as part of your maintenance and repair process you'll need to involve a professional RFID solutions provider. Your solutions provider will have the software and RFID readers that will collect tag data and Connect802 will provide the Wi-Fi wireless infrastructure to carry that data back to the central software system.

An Overview of RFID Technology

The Evolution of RFID Technology

Universal Product Code (UPC) barcode labels are inadequate for the sophisticated requirements of today's supply chain management systems. Barcodes may be extremely cheap, but their stumbling block is their low storage capacity and the fact that they cannot be reprogrammed. The technically optimal solution would be the storage of data in a silicon chip. The most common form of electronic data carrying device in use in everyday life is the chip card based upon a contact field (telephone chip card, bank cards). However, the mechanical contact used in the chip card is often impractical. A contactless transfer of data between the data carrying device and its reader is far more flexible. In the ideal case, the power required to operate the electronic data carrying device would also be transferred from the reader using contactless technology. Because of the procedures used for the transfer of power and data, contactless ID systems are called RFID systems (Radio Frequency Identification).

RFID (Radio Frequency Identification) is used in all areas of automatic data capture allowing contactless identification of objects using RF. With applications ranging from secure internet payment systems to industrial automation and access control, RFID technology solutions are receiving much attention in the research and development departments of large corporations. RFID is a major growth are in auto ID, allowing emergency vehicles to safely trip traffic signals, and providing the technology behind contactless smart cards, "autopiloting" cars, and production automation.

The RFID Transponder / Interrogator System

An RFID system contains two basic components:

• The RFID transponder (referred to as a "tag") located on the object to be identified
• The RFID interrogator / detector (referred to as a "reader" or "scanner") which sends pulses of RF energy to activate the tag, and then read the resulting response from the tag

A reader typically contains a high frequency module (transmitter and receiver), a control unit and a coupling element to the transponder. In addition, 802.11 Wi-Fi radios are often included with the reader to allow communication to a central database or control software system.

The transponder, which represents the actual data carrying device of an RFID system, normally consists of a coupling element and an electronic microchip. When the transponder, which does not usually possess its own voltage supply (battery), is not within the response range of a reader it is totally passive. The transponder is only activated when it is within the response range of a reader. The power required to activate the transponder is supplied to the transponder through the coupling unit (contactless) in the form of a timing pulse and data.

Passive and Active RFID Tags

There are two basic designs for RFID tags: passive tags and active tags. Passive tags obtain power from the interrogation pulse from the reader. They use this power to send back their information message. Because they have no battery they essentially last forever and can't wear out. A passive RFID tag is very little more than a loop of antenna with the most basic circuitry. Active tags have a battery. Because of this they are able to respond with a signal that can travel perhaps as much as 50-feet or more to a remote reader.

Tag and Reader Coupling and Data Transfer

There are two basic methods for acquiring information from the RFID tag: inductive coupling and backscatter coupling. Inductively coupled transponders are almost always operated passively. This means that all the energy needed for the operation of the microchip has to be provided by the reader. For this purpose, the reader's antenna coil generates a strong, high frequency electro-magnetic field, which penetrates the cross-section of the coil area and the area around the coil. Because the wavelength of the frequency range used (< 135 kHz: 2400 m, 13.56 MHz: 22.1 m) is several times greater than the distance between the reader's antenna and the transponder, the electro-magnetic field may be treated as a simple magnetic alternating field with regard to the distance between transponder and antenna. In the language of electromagnetic wave theory we refer to this as "near field coupling".

Near-field coupling is the electromagnetic effect that occurs within roughly 1-wavelength of a radiating element. In the near-field the energy field fluctuates outward from the radiating element, and then back in to the radiating element in a "push - pull" manner. Beyond the near-field the electromagnetic energy simply radiates outwards (never "back in") and the power drops off based on the inverse-square law ("twice as far away = 1/4 as powerful"). Consequently, the RFID reader and the tag become part of a bi-directional electromagnetic system in which energy can be exchanged and, thereby, information can be exchanged.

Inductive Coupling in the Near-Field

A small part of the emitted field penetrates the antenna coil of the transponder, which is some distance away from the coil of the reader. By induction, a voltage is generated in the transponder's antenna coil. This voltage is rectified and serves as the power supply for the data carrying device (microchip). A capacitor is connected in parallel with the reader's antenna coil, the capacitance of which is selected such that it combines with the coil inductance of the antenna coil to form a parallel resonant circuit, with a resonant frequency that corresponds with the transmission frequency of the reader. Very high currents are generated in the antenna coil of the reader by resonance step-up in the parallel resonant circuit, which can be used to generate the required field strengths for the operation of the remote transponder.

Inductively coupled systems are based upon a transformer-type coupling between the primary coil in the reader and the secondary coil in the transponder. This is true when the distance between the coils does not exceed 0.16 wavelength , so that the transponder is located in the near field of the transmitter antenna

Backscatter Coupling in the Far-Field

Outside the radius of the near-field the interrogation pulse from the reader propagates outwards, never giving energy back to the radiating element. This RF signal travels outwards and encounters the antenna element in the tag. We know from the field of RADAR technology that electromagnetic waves are reflected by objects with dimensions greater than around half the wavelength of the wave. The efficiency with which an object reflects electromagnetic waves is described by its reflection cross-section. Objects that are in resonance with the wave front that hits them, as is the case for antenna at the appropriate frequency for example, have a particularly large reflection cross-section.

An electromagnetic field propagates outwards from from the reader's antenna and a small proportion of that field (reduced by free space attenuation) reaches the transponder's antenna. The power is supplied to the antenna connections as HF voltage and after rectification by diodes this can be used as turn on voltage for the deactivation or activation of the power saving "power-down" mode. The voltage obtained may also be sufficient to serve as a power supply for short ranges.

A proportion of the incoming RF energy is reflected by the antenna and reradiated outwards. The reflection characteristics (= reflection cross-section) of the antenna can be influenced by altering the load connected to the antenna. In order to transmit data from the transponder to the reader, a load resistor connected in parallel with the antenna is switched on and off in time with the data stream to be transmitted. The strength of the signal reflected from the transponder can thus be modulated (a technique referred to as modulated backscatter).

The signal from the transponder is radiated into free space. A small proportion of this signal is picked up by the reader's antenna. The reflected signal therefore travels into the antenna connection of the reader in the "backwards direction" and can be decoupled using a directional coupler and transferred to the receiver input of a reader. The "forward" signal of the transmitter, which is stronger by powers of ten, is to a large degree suppressed by the directional coupler.

Avoiding Interference in RFID Systems

The need to exercise care with regard to other radio services significantly restricts the range of suitable operating frequencies available to an RFID system. For this reason, it is usually only possible to use frequency ranges that have been reserved specifically for industrial, scientific or medical applications or for short range devices. These are the frequencies classified worldwide as ISM frequency ranges (Industrial-Scientific-Medical) or SRD frequency ranges, and they can also be used for RFID applications.