DRAFT: This module has unpublished changes.

When deciding which RFID tag to use, many considerations need to be taken into account.  There are three main options for tags: passive, active, and a combination of both.  Each one has its own advantages and disadvantages that need to be considered.  The three types have different costs, different hardware components, and different abilities.  All three options work similarly in that they can store up to 2 kilobytes of data and are composed of a microchip, antenna and, in the case of active and semi-passive tags, a battery. The tag's components are enclosed within plastic, silicon or sometimes glass.

Passive

• A passive 96-bit EPC inlay (chip and antenna mounted on a substrate) costs from 7 to 15 U.S. cents, which is pretty inexpensive.
• The passive RFIDs are not dependent on a battery to work.
• Able to be disposed of if necessary.
• These tags are usually much smaller and can fit on a wide variety of surfaces.

• Depend on the reader for the supply of power to enable signal transmission, because it doesn’t have a battery.
• Since passive RFID tags are constrained by the need for strong signals to power the tag and the small amount of power to respond to the reader, the communication range of a passive tag is limited to 3 meters or less
• In a passive RFID, the data storage is less than 128 bytes with no search capabilities or data manipulation features.
• It can collect about 100 tags, since the communication range is limited to 3 meters or less.

Active

• Can transmit wireless signals on its own to the reader autonomously and can continuously monitor and record sensor input.
• Active tags do not have the constraint of power and can thus transmit to as far as 100 meters or more.
• Active RFID tags have large read and write data storage almost 128 kilobytes and sophisticated data search and access capabilities.
• An active tag can collect more than 100 tags from a seven acre region using a single reader.
• Can provide a better layer of security than passive RFID.

• Depend on a battery to be able to work and power internal circuits.  The tag cannot function without battery power, which limits the lifetime of the tag.
• Active tags are more expensive, ranging from $25 and up. Active tags with special protective housing, extra-long battery life or sensors can run$100 or more.
• The tag is physically larger, which may limit applications.
• Battery outages in an active tag can result in expensive misreads.

Semi-passive

• Broadcast high frequencies from 850 to 950 MHz that can be read 100 meters or more away.
• Once the battery dies, it can still act as a passive RFID tag.
• Can collect more than 100 tags from a seven acre region using a single reader.
• They have large read and write data storage almost 128 kilobytes and sophisticated data search and access capabilities.
• Can provide a better layer of security than passive RFID.

• Uses a battery to power their circuits.
• A semi-passive tag relies on the reader to supply its power for broadcasting.
• Usually more expensive, because they contain more hardware.

How RFID Works

Passive RFID Basics

Radio Frequency Identification (RFID) systems use radio frequency to identify, locate and track people, assets, and animals (Sorrels, 2004).  Passive RFID systems are composed of three components – an interrogator (reader), a passive tag, and a host computer.  The tag is composed of an antenna coil and a silicon chip that includes basic modulation circuitry and non-volatile memory.  The tag is energized by a time-varying electromagnetic radio frequency (RF) wave that is transmitted by the reader.  This RF signal is called a carrier signal.  When the RF field passes through an antenna coil, there is an AC voltage generated across the coil.  This voltage is rectified to supply power to the tag.  The information stored in the tag is transmitted back to the reader.  This is often called backscattering.  By detecting the backscattering signal, the information stored in the tag can be fully identified.

LANDMARC: Indoor Location Sensing Using Active RFID