Wednesday, May 13, 2015

Introduction to RFID Technology (part 2)

NOTE: If you haven't read about part 1, then please do so.

Types of RFID Tags

Active Tags

In active RFID systems, tags have their own transmitter and power source. Usually, the power source is a battery. Active tags broadcast their own signal to transmit the information stored on their microchips.

Active RFID systems typically operate in the ultra-high frequency (UHF) band and offer a range of up to 100 m. In general, active tags are used on large objects, such as rail cars, big reusable containers, and other assets that need to be tracked over long distances.

There are two main types of active tags: transponders and beacons

Transponders are “woken up” when they receive a radio signal from a reader, and then power on and respond by transmitting a signal back. Because transponders do not actively radiate radio waves until they receive a reader signal, they conserve battery life.

Beacons are used in most real-time locating systems (RTLS), in order to track the precise location of an asset continuously. Unlike transponders, beacons are not powered on by the reader’s signal. Instead, they emit signals at pre-set intervals. Depending on the level of locating accuracy required, beacons can be set to emit signals every few seconds, or once a day. Each beacon’s signal is received by reader antennas that are positioned around the perimeter of the area being monitored, and communicates the tag’s ID information and position.
Tag Power Source : Internal to tag
Tag Battery : Yes
Availability of Tag Power : Continuous
Required Signal Strength from Reader to Tag : Very Low
Available Signal Strength from Tag to Reader : High
Communication Range : Long Range (100m or more) 
Sensor Capability : Ability to continuously monitor and record sensor input.

Passive Tags

In passive RFID systems, the reader and reader antenna send a radio signal to the tag. The RFID tag then uses the transmitted signal to power on, and reflect energy back to the reader. This is called Backscatter Modulation.

Passive RFID systems can operate in the low frequency (LF), high frequency (HF) or ultra-high frequency (UHF) radio bands. 

As passive system ranges are limited by the power of the tag’s backscatter (the radio signal reflected from the tag back to the reader), they are typically less than 10 m. Because passive tags do not require a power source or transmitter, and only require a tag chip and antenna, they are cheaper, smaller, and easier to manufacture than active tags.

Passive tags can be packaged in many different ways, depending on the specific RFID application requirements. For instance, they may be mounted on a substrate, or sandwiched between an adhesive layer and a paper label to create smart RFID labels. Passive tags may also be embedded in a variety of devices or packages to make the tag resistant to extreme temperatures or harsh chemicals.

Passive RFID solutions are useful for many applications, and are commonly deployed to track goods in the supply chain, to inventory assets in the retail industry, to authenticate products such as pharmaceuticals, and to embed RFID capability in a variety of devices. Passive RFID can even be used in warehouses and distribution centers, in spite of its shorter range, by setting up readers at choke points to monitor asset movement.
Tag Power Source : Energy transfer from the reader via RF
Tag Battery : No
Availability of Tag Power : Only within field of reader
Required Signal Strength from Reader to Tag : Very high (must power the tag)
Available Signal Strength from Tag to Reader : Very Low
Communication Range : Short range (up to 10m) 
Sensor Capability : Ability to read and transfer sensor values only when tag is powered by                                                                                                                                                          reader

Semi-Passive / Battery Assisted Passive (BAP) Tags

A Battery-Assisted Passive RFID tag is a type of passive tag which incorporates a crucial active tag feature. While most passive RFID tags use the energy from the RFID reader’s signal to power on the tag’s chip and backscatter to the reader, BAP tags use an integrated power source (usually a battery) to power on the chip, so all of the captured energy from the reader can be used for backscatter. 

Unlike transponders, BAP tags do not have their own transmitters.

Tag Power Source : Tag uses internal power source to power on, and energy transferred from                                                                                                                 the reader via RF to backscatter
Tag Battery : Yes
Availability of Tag Power : Only within field of reader
Required Signal Strength from Reader to Tag : Moderate (does not need to power tag, but must                                                                                                                                     power backscatter)
Available Signal Strength from Tag to Reader : Moderate
Communication Range : Moderate range (up to 100m) 
Sensor Capability : Ability to read and transfer sensor values only when tag receives RF signal                                                                                                                                                 from reader

Other RFID tags (active/passive/BAP)

Reference : (in part3)

Tuesday, May 12, 2015

Introduction to RFID Technology (Part 1)

what is RFID?

RFID, short for Radio Frequency IDentification, is a technology that enables identification of a tag (that is normally attached with an entity) by using electromagnetic waves. The function served by RFID is similar to bar code identification, but line of sight signals are not required for operation of RFID.

RFID components

Tag chips or integrated circuits (ICs)
Tag antennas

Reader antenna
Reader control & application software

An RFID tag is comprised of an integrated circuit (called an IC or chip) attached to an antenna that has been printed, etched, stamped or vapor-deposited onto a mount which is often a paper substrate or PolyEthylene Therephtalate (PET). The chip and antenna combo, called an inlay, is then converted or sandwiched between a printed label and its adhesive backing or inserted into a more durable structure.
Tag Chip
The tag's chip or integrated
circuit (IC) delivers performance, memory and extended features to the tag. The chip is pre-programmed with a tag identifier (TID), a unique serial number assigned by the chip manufacturer, and includes a memory bank to store the items' unique tracking identifier (called an electronic product code or EPC).

Electronic Product Code (EPC)
The electronic product code (EPC) stored in the tag chip's memory is written to the tag by an RFID printer and takes the form of a 96-bit string of data. The first eight bits are a header which identifies the version of the protocol. The next 28 bits identify the organization that manages the data for this tag; the organization number
is assigned by the EPCglobal consortium. The next 24 bits are an object class, identifying the kind of product; the last 36 bits are a unique serial number for a particular tag. These last two fields are set by the organization that issued the tag. The total electronic product code number can be used as a key into a global database to uniquely identify that particular product.
Tag Antennas
Tag antennas collect energy and channel it to the chip to turn it on. Generally, the larger the tag antenna's area, the more energy it will be able to collect and channel toward the tag chip, and the further read range the tag will have.

There is no perfect antenna for all applications. It is the application that defines the antenna specifications. Some tags might be optimized for a particular frequency band, while others might be tuned for good performance when attached to materials that may not normally work well for wireless communication (certain liquids and metals, for example). Antennas can be made from a variety of materials; they can be printed, etched, or stamped with conductive ink, or even vapor deposited onto labels.

Tags that have only a single antenna are not as reliable as tags with multiple antennas. With a single antenna, a tag's orientation can result in “dead zones”, or areas on the tag where incoming signals cannot be easily harvested to provide sufficient energy to power on the chip and communicate with the reader. A tag with dual antennas is able to eliminate these dead zones and increase its readability but requires a specialized chip.
RFID Readers
An RFID reader, also known as an interrogator, is a device that provides the connection between the tag data and the enterprise system software that needs the information. The reader communicates with tags that are within its field of operation, performing any number of tasks including simple continuous inventorying, filtering (searching for tags that meet certain criteria), writing (or encoding) to selected tags, etc.

The reader uses an attached antenna to capture data from tags. It then passes the data to a computer for processing. Just like RFID tags, there are many different sizes and types of RFID readers. Readers can be affixed in a stationary position in a store or factory, or integrated into a mobile device such as a portable, handheld scanner. Readers can also be embedded in electronic equipment or devices, and in vehicles.
Reader Antennas
RFID readers and reader antennas work together to read tags. Reader antennas convert electrical current into electromagnetic waves that are then radiated into space where they can be received by a tag antenna and converted back to electrical current. Just like tag antennas, there is a large variety of reader antennas and optimal antenna selection varies according to the solution's specific application and environment.

The two most common antenna types are linear- and circular-polarized antennas. 

Antennas that radiate linear electric fields have long ranges, and high levels of power that enable their signals to penetrate through different materials to read tags. Linear antennas are sensitive to tag orientation; depending on the tag angle or placement, linear antennas can have a difficult time reading tags. Conversely, antennas that radiate circular fields are less sensitive to orientation, but are not able to deliver as much power as linear antennas.

Linear polarization occurs when electromagnetic waves broadcast on a single plane (either vertical or horizontal).  Linear polarized antennas must have a known RFID tag orientation and the RFID tag must be fixed upon the same plane as the antenna in order to get a consistent read. Some examples of linear polarized antennas are the MTI MT-263003 Outdoor Antenna, and the Times-7 A5531 Indoor Antenna. Due to the concentrated emission, linear polarized antennas typically have greater read range than circular polarized antennas of the same gain.

Circular polarized antennas, such as the Laird S9028PCR Indoor RFID Antenna and the MTI MT-242043 Outdoor RFID Antenna, emit electromagnetic fields in a corkscrew-like fashion.  Technically speaking, they are broadcasting electromagnetic waves on two planes making one complete revolution in a single wavelength. Compared to linear polarized antennas, circular polarized antennas lose about 3 dB per read because they split their power across two separate planes.

Choice of antenna is also determined by the distance between the RFID reader and the tags that it needs to read. This distance is called read range. Reader antennas operate in either a "near-field" (short range) or "far-field" (long range). In near-field applications, the read range is less than 30 cm and the antenna uses magnetic coupling so the reader and tag can transfer power. In near-field systems, the readability of the tags is not affected by the presence of dielectrics such as water and metal in the field.

In far-field applications, the range between the tag and reader is greater than 30 cm and can be up to several tens of meters. Far-field antennas utilize electromagnetic coupling and dielectrics can weaken communication between the reader and tags.

Reader Control and Application Software
Reader control and application software, also known as middleware, helps connect RFID readers with the applications they support. The middleware sends control commands to the reader and receives tag data from the reader.
Reference: (See the next part)