RFID
RFID products fall into two basic categories: Passive and Active.
Passive tags do not have batteries and have indefinite life
expectancies. Active Tags are powered by batteries and either have
to be recharged, have their batteries replaced or be disposed of
when the batteries fail.
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RFID products are then broken up into different frequencies. Tags
and Antennas are tuned or matched much the same way as a radio is
tuned to a frequency to receive different channels. These
frequencies are grouped into Four basic ranges: Low Frequency, High
Frequency, Very High Frequency and Ultra-High Frequencies.
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Each frequency range has its advantages and disadvantages. Europe
use 868 MHz. for its UHF applications while the US uses 915 MHz. for
its UHF applications. Japan does not allow the use of the UHF
frequency for RFID applications. Low Frequency tags (LF) are less
costly to manufacturer than Ultra High Frequency (UHF) tags. UHF
tags offer better read/write range and can transfer data faster then
other tags. HF tags work best at close range but are more effective
at penetrating non-metal objects especially objects with high water
content.
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Once a frequency range is determined, then it is time to choose an
antenna that best fits the application. Antennas come in all sorts
of sizes and shapes. The size of the antenna determines the range of
the application. Large antennas used with Active Tags can have a
range of 100 feet or more. Large antennas used with Passive Tags
generally have a range of 10 feet of less. There are dock door
antennas (some times called Portals) that allow a forklift driver to
drive between two antennas. Information can be collected from the
tags without the forklift driver having to stop. There are antennas
that mount between rollers on conveyors for reading/writing from
below. While other antennas are available that mount to the side of
or above the conveyors. Handheld Reader/Writers are available as
well.
Controllers are available to communicate with most Networks (Ethernet, DeviceNet, ProFibus, etc). They typically have serial ports for programming and data transfer. Controllers are usually shipped with programming software to set-up and customize the application. Controllers typically operate on 120VAC or 24VDC. |
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The interference issue in RF protocols
In order to communicate between many simple transponders and a reader, a set of instructions(rules) implemented in the transponders and readers is needed. This set of instructions is known as the RF protocol. RF protocols have been developed which allow up to 1000 transponders to communicate reliably with the reader on a single frequency, even if the all have the same identity, and yet preserve their properties of frequency agility and simple design.
There are basically two types of protocols for implementing multi-transponder situations, namely "Tag-talks-first(TTF)" and "Reader-talks-first(RTF)".
Tag talks first protocol
In a "tag-talks-first" situation, the reader puts out an energising field which
is generally a carrier wave signal with no modulation at the operating frequency
of the system. Tags entering the field, collect this energy in their transponder
aperture, convert it to operating energy, and communicate their identity to the
reader. In some cases the reader communicates the successful receipt of the
message back to the transponder by a short burst of modulation on the energising
field. These systems use minimal RF bandwidth for the energising field and hence
cause minimum interference for other users of the RF spectrum. Many readers can
operate at distances of a few meters from each other using this type of protocol
with small frequency offsets between readers. The identitiy information is
communicated by the tags which operate at power levels of up to 1 million times
less than that of the energising field of the reader.
Reader talks first protocol
In a "reader-talks-first" situation the reader puts out an energising field which is modulated with call messages to the transponders. Tags entering the field, collect this energy in their transponder aperture, convert it to operating energy, and listen for messages from the reader which is modulated on the energising field. The reader polls for transponders in its reading field by asking "Transponder number 1, are you there?" If transponder number 1 is there, then it replies "Yes" and its identity is known to the reader. This is repeated for all the possible numbers of transponders present, or a more compact "treeing" method is used. The disadvantage of this system is that the reader has to be continually calling for transponders, modulating its high power signal and causing widespread interference around the reader, even if no transponders are in the field at the time. Also this interrogation has to be repeated faster than the time it would take for a transponder to pass through its field so as not to possibly miss a transponder in transit through the field. This requires high bandwidth and widespread interference to other radio users.
To explain the difference between reader-talks-first and
tag-talks-first protocols - imagine you were at a picnic in a quiet park trying
to whisper to your companion, but close by you have another group of picnickers
with a radio playing rock music full blast - that is the situation with reader
talks first. Now imagine that back in the radio station the music source is
disconnected or comes to an end of the music track - the radio is still
receiving a signal but is quiet as there is no modulation on the carrier signal
- that is tag-talks-first. In both situations the radio is still broadcasting a
signal, the difference being the amount of interference it causes.
The following table compares the two technologies for UHF transponder systems
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"Tag-talks-first" |
"Reader-talks-first" |
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Energising signal |
Carrier wave |
Modulated energising signal |
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Modulation bandwidth |
10kHz |
Up to 1 Mhz |
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RF power of modulated signal |
20uWatts |
0.5 to 4 watts |
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Interference zone for other readers |
4 meters |
1 km |
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Speed of transit of zone to detect tag |
300kph |
3kph |
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Interference when no tags present |
Carrier wave only |
Modulated energising signal |
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Transponder receiver complexity |
Very simple |
Needs to have good dynamic range |
The choice of protocol impacts many decisions regarding the use of multiple RFID reader systems in close proximity. TTF systems are able to operate two readers within only four metres of each other due to the very small bandwidth(10kHz) used and the stable transmitted signals.
Note The EPC Global Gen 2 protocol approved in December 2004 is a RTF type protocol with high interference levels. The EPC Global has approved three levels of designs regarding interference levels for readers - namely
Level 1 - no other reader operating within 1 kilometer
Level 2 - A few readers operating within 1 kilometer
Level 3 - More than 50 readers operating within 1 kilometer
In addition RTF designs are very susceptible to interference from cell phones - whereas TTF protocols generally work well with cell phones and allow readers to operate together with spacing as close as 4 meters. In the long term both the EPC Global and the ISO 18000-6 specifications will be forced to migrate to TTF type protocols due to the high levels of interference caused.
What applications can benefit from RFID?
| Computer vision for IT systems | Information Technology systems have been built from sophisticated computer networks and application software, but still largely rely on manual or semi automatic data capture. The integration of RFID into labelling objects used with such systems allow the computer to automatically identify objects within 13 meters of the reader and process the data automatically |
| Warehousing | Tracking of containers and pallets, stocktaking |
| Access control | Ability to read the identity of many people at the same time passing through doorways, tube station entrances, lift access and doorways. |
| Identifying capital goods | Ability to read the identity of transponders mounted inside capital goods or packaging, when in the warehouse, when being transported and even when passing through doorways for an asset tracking system. |
| Caselots of low value consumer items | Same system can be used for the producer, wholesaler and retailer at case lot level of consumer goods for transferring via truck, checking in and out of warehouse. |
| Vehicles access control | Ability to read many vehicles in different traffic lanes for parking, toll and access control. |
| Containers labelling | Shipping, airfreighting and rail movement. |
| Courier parcels and documents | Remote identity, sorting, routing and track-and-trace information |
| Parcels and mail bags | Remote identity, routing, track-and-trace information. |
| Airline baggage | Identifying, sorting and routing - not confused by the transponders that will be read from labelled goods within the luggage due to the use of RFID systems. |
| Compact discs and video retailing and rental | EAS, identifying and stock taking |
| Laundry for hospitals and hotels | Identity, sorting and routing after bulk washing |
| Motor vehicle tyres | Transponder embedded into tyre provides positive identification of case for identifying, wear tracking, usage tracking, anti theft. |
| Files and documents | Identifying, track-and-trace, locating, association with person carrying documents past doorways - suitable for insurance industry/ government records. |
| Passport, driver license | Anti-counterfeiting, identifying |
| Manufacture | Labelling components for JIT manufacture, storing, routing, warehousing, identifying |
| Library books | Identifying, EAS, self service checkout/check-in, book location. |
| Loyalty cards for retailing | Remote identification of client and association with database |
| Gaming chips | Identity, anti-counterfeiting |
| Pharmaceutical/ pathology | Tracking controlled and restricted drugs, warehousing, manufacture date, identifying high value drugs. Tracking pathological samples during processing |
| Farm animals | Electronically identifying herd animals for control, for documentation of milk yield, for controlled feeding and dosing and for disease control |
| Labelling clothes and shoes | Identifying, stocktaking, size distribution, self service, EAS. Reading clothes washing properties for an automated washing machine |
| Dismantling items | For green legislation requiring the dismantling and sorting of old capital items, robot identification of parts and type of material. |
| Marking explosives | Identity, track-and-trace, anti-theft |
| Sports events | Timing marathon athletes, cyclists, MotoX, fun runs |
| Hospitals | Tracking patients, access control, preventing baby removal, patient location and identification, computer authorisation of surgical procedures |
| Penal systems | House arrest - verification of presence |
| Marking hotel possessions | Remote identity of possessions in clients luggage |
| Forestry | Tracking logs and products. Inventory control of trees and plants in a nursery |
| Bank notes | Anti-counterfeiting, accurate counting |
| Grocery retailing | High speed scanning of baskets, trolleys and carts, stock-taking, EAS, goods receiving - the ultimate application |
Antenna Types
Low Frequencies
1- The Large Gate Antenna is a fully-packaged antenna for applications like vehicle access to parking lots in an outdoor environment. It can be mounted on a pole or a wall. The antenna is optimized for cable lengths between 0.5 and 4 meters.Recommended connecting cable type: 2.5 mm 2 (14 AWG) flexible conductor.
2- The gate antenna is designed for use in doorways, entrances and corridors, beside conveyers, or in any location where the reading field coverage needs to be maximized.
3- This antenna, connected to a Radio Frequency Module(RFM), forms the interface to the low frequency(134.2kHz) transponders. In combination with the RFM it transmits energy and signals to the transponder and receives the reply. The stick antenna provides a focused read zone and an ability to separate between transponders in close proximity.
4- This stick antenna is specially designed for use with the Mini-RFM. The ferrite rod antenna is a short cylindrical device used in stationary applications where space is limited. An additional benefit of the stick antenna is that it allows a precise discrimination between RFID tags in close proximity to one another through a highly directed field.
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1- OBID i-scan ® Long-range antennas can be used in combination with the Long-range reader and the Long-range reader module Together, the two antennas base antennaand complementary antenna form a gate, which is used for the identification of persons or goods. The maximum gate width (reading range) is 100 cm, as far as there are no orientation limits for the Smart Labels (i.e. all three label directions are possible). If a complementary antenna is connected to the reader in order to configure a triple gate, a maximum gate width of 2x90 cm will be the result. In case that only one of the three label directions is used, even double gates with a gate width of up to 130 cm are possible. In this case, you will have to combine two base antennas to form a gate and, depending on the forward direction of the current in the antennas, the label can be aligned either parallel or crosswise to the antennas.
2-OBID i-scan ® long range antennas are operated in combination with the Long Range Reader and the Long Range Reader module . Depending on the application, single or gate antennas may be used. For applications with only one reading alignment of up to 80 cm, a base antenna (A) in form of a single antenna will be sufficient. For higher ranges of up to approx. 120 cm and applications with multi-directional reading alignment, the use of a complementary antenna (B) becomes necessary.
3- OBID i-scan ® mid range antennas are operated in combination with a mid range reader . The elegant Pad Antenna is perfectly suitable for desk applications with a reading range of up to 30 cm. File and document tracking as well as the registration of rental goods during distribution and return are only two out of many possible applications.
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