BIG Vizibility 101

RFID

RFID (radio frequency identification) is a technology that incorporates the use of electromagnetic or electrostatic coupling in the radio frequency (RF) portion of the electromagnetic spectrum to uniquely identify an object, animal, or person. RFID is coming into increasing use in industry as an alternative to the bar code. The advantage of RFID is that it does not require direct contact or line-of-sight scanning. There are three essential components of Radio Frequency Identification solutions:

• A transceiver (with decoder)
• An antenna
• A tag or transponder

In most cases, the antenna is joined together with the transceiver and decoder and becomes a reader (or interrogator). RFID Readers can be configured in three standard platforms - as a handheld device , a fixed-mount device, or a mobile device.

To explain how the three components work together, imagine that a company is using RFID as a security tool for laptop computers stored in a computer lab.

Requirements

• Each laptop computer would be affixed with a small “passive” RFID tag.
• Any ingress or egress (doorways) into the lab would have antennae positioned within the doorframe.
• The transceiver is connected to either a computer network or alarm system to react to any “events”.

An example of an event would be someone taking a tagged laptop out of the computer lab. The system works with the antenna emitting a low powered signal within the doorway that generates a response from the circuitry within the tag as the laptop (and tag) pass through. The resulting radio wave transmission is received and interpreted by the transceiver. The transceiver, in turn, registers a preprogrammed response to the event whether that response is an alarm, an e-mail, an SMS text message, or any type of response needed.

Passive and Active RFID Tags

Both active and passive RFID technologies use radio frequency energy to communicate between a tag and a reader, the method of powering the tags is different. Active RFID uses an internal power source (battery) within the tag to continuously power the tag and its RF communication circuitry, whereas Passive RFID (or unpowered) relies on RF energy transferred from the reader to the tag to power the tag.

Passive RFID tags either reflect energy from the reader or absorb and temporarily store a very small amount of energy from the reader’s signal to generate its own quick response. In either case, Passive RFID operation requires very strong signals from the reader, and the signal strength returned from the tag is constrained to very low levels by the limited energy. Because of this low signal strength being returned from the tag, Passive tags are considered to be near-field tags with average read ranges from up to a couple of meters.

Active RFID tags allow very low-level signals to be received by the tag since the reader does not need to power the tag. Therefore, the tag can generate high-level signals back to the reader, driven from its internal power source. In addition, the Active RFID tag is continuously powered, whether in the reader field or not. Active tags are considered to be far-field tags with average read ranges from 20 to 100 meters.

RFID Readers

An RFID reader is basically a radio frequency (RF) transmitter and receiver, controlled by a microprocessor. The reader, using an attached antenna, captures data from the tags and passes the data to a computer for processing. As with tags, readers come in a wide range of sizes and offer different features.

• Stationary (e.g. beside a conveyor belt in a factory or dock doors in a warehouse)
• Portable (Integrated into a mobile computer that also might be used for scanning bar codes)
• Embedded in electronic equipment such as print-on-demand label printers.
  
  
  

RFID Antennas

Antennas used within an RFID visibility solution are integrated into two different areas of the system, the reader and the tag. Both the reader and tag use antenna to perform their given tasks. The antenna in an RFID tag is a conductive element that permits the tag to exchange data with the reader. In Passive RFID tags, the antenna create a magnetic field through coiling of the antenna make use of a coiled antenna and uses the energy provided by the reader's carrier signal. In the reader configuration, the antenna emits radio waves from which the tag responds by sending back its data.

GPS

Global Positioning System (GPS) was developed and is operated by the U.S. Department of Defense. GPS is a worldwide MEO satellite navigational system formed by 24 satellites orbiting the earth and their corresponding receivers on the earth. GPS satellites orbit the earth at more than 12,000 miles above the surface and make a complete orbit every 12 hours. The GPS satellites continuously transmit digital radio signals that contain data on the satellites location and the exact time to the earth-bound receivers. Based on these precise time calculations the earth based receivers know how long it takes for the signal to reach the receiver from the satellite. As each signal travels at the speed of light, the longer it takes the receiver to get the signal, the farther away the satellite is. By knowing how far away a satellite is, the receiver knows that it is located somewhere on the surface of an imaginary sphere centered at the satellite. By using a minimum of three satellites (triangulation), GPS can calculate the longitude and latitude of the receiver based on where the three spheres intersect. By using four satellites, GPS can also determine altitude.

The 24 satellites are positioned in 6 planes of 4 satellites each. At any given time, the receiver can have line of sight visibility of 5 to 8 different satellites. Today, there are actually 31 satellites which provide an extra layer of redundancy and improves reliability and availability of the system.