RFID and PIT Technology Explained

Radio frequency identification (RFID) uses a signal transmitted between an electronic device, such as a "tag", "transponder" or "microchip" and a reading device, such as a "scanner", "reader" or "transceiver". RFID technology identifies objects remotely through the use of radio frequencies.

The RFID or EID devices most widely used in animals are passive. Passive integrated transponders have no battery so the microchip remains inactive until read with a scanner. The scanner sends a low frequency signal to the microchip within the tag providing the power needed to send its unique code back to the scanner and positively identify the animal. Passive tags are designed to last the life of the animal providing a reliable, long term identification method.
The distance from which a tag can be read is called read range. Many factors contribute to the read range of passive tags including operation frequency, antenna power, tag orientation and interference from other devices. Low frequency tags are detected in milliseconds at close range from a few inches to about a foot (0.33 meter) in distance. Tags can be read through materials such as soil, wood and water. Ferrous metals and noisy environments can cause interference between the electromagnetic communication of the reader and tag.

PIT tags are typically injected subcutaneously using a 12-gauge hypodermic needle and syringe; they can also be externally attached using adhesives. Implant location varies depending on the species being studied, animal size and in some cases the behavior of the animal. Tags that are pre-loaded into an implanter, gas sterilized and individually packaged are available and convenient for tagging in the field.

The use of passive tags for animal identification and research provides many benefits including the reduction of error in recording data, rapid data collection and long term reliability. The value of PIT tags has been successfully demonstrated in studies of mark and recapture, survival, movement, behavior and distribution for a variety of species.

Frequently Asked Questions
Q.  What is the best read range for a tag and reader?
A.

The distance from which a tag can be read is the read range. There are environmental and application factors that may limit read range. Optimal conditions exist in an air environment with the tag placed perpendicular to the antenna field. Factors such as tag frequency, electromagnetic noise, metals and antenna power may affect the read range. Typically, the larger the tag the better the read range. Some tag and antenna combinations can read passive tags as far away as 18 inches. Most read ranges using hand-held readers are 3 to 9 inches depending on the reader.

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Q.  Are duplicate codes ever produced?
A.

Codes for the tags are computer generated and programmed into the microchip before the tag is assembled. Each manufacturer employs redundant quality control checks prior to distribution. There are international standards (ISO) that also regulate the manufacturing of many tags and how the codes are formatted. The chance of duplicate codes reaching a customer is very rare.

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Q.  Why should I be concerned about the tag frequency?
A.

PIT tag technology and development is constantly evolving. There are currently three basic tag frequencies. The 400-kHz tag was one of the first developed and it is still in use today, though readers are getting scarce. These tags have a limited read range. As microchip technology evolved, the 125-kHz and the ISO 134.2-kHz tags became available. Compared to the older 400-kHz tags, they have a much better read range and reduced read time. The ISO 134.2-kHz tag was developed to meet international standards for code format. If you are starting a new project and working with different agencies or organizations the tag type and equipment should be compatible. Most readers are capable of detecting both 125-kHz and ISO 134.2-kHz frequencies.

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Q.  How small an animal can I tag?
A.

The size of an animal to be tagged using PIT tags varies and depends on the species. Fish less than 55-mm have been successfully tagged using the small 12.5-mm tags. These tags weigh about 0.1 grams. Small mice, frogs and salamanders have also been tagged with good success for years. Information about tagging techniques for individual species can usually be found in relevant biological references. Please feel free to ask us for more information.

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Q.  Where is the best place to implant a tag?
A.

The implant site is dependent upon the species, size of the animal and the size of the tag. Biomark can provide guidelines on tagging location for most species. We can also refer you to customers working with specific species.

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Q.  Will tags I buy from Biomark be read with other manufacturers' readers?
A.

Yes, as long as the reader is designed for the frequency of the tag used. Biomark does not sell encrypted tags. The use of encrypted tags makes it difficult to have compatible equipment and gives you fewer options in choosing readers.

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Q.  How long will a PIT tag last?
A.

Design engineers' calculations suggest that PIT tags can last as long as 75 years or more. There is no battery to fail and the glass encapsulation is impervious to almost everything. PIT tags can be removed or recovered from a primary location and reused indefinitely.

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Q.  What is a PIT tag?
A.

A Passive Integrated Transponder tag is a radio frequency device that transmits a unique individual code to a reader where it is displayed in a numeric or alphanumeric form. The tag has no internal battery, hence the term “passive". The reader powers or excites the tag circuitry by radio frequency induction and receives the code back from the tag. Radio frequency identification does not require line of sight, tags can be read as long as they are within the range of a reader.

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Q.  What materials can a PIT tag be read through?
A.

Tags can be detected through materials like plastics, water, wood products, animal tissue and bone, fabrics, fiberglass, rock and most nonferrous metals.

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Q.  Do I need to sedate/anesthetize an animal before tag implanting?
A.

Reducing animal stress should be a consideration in evaluating your research project. Fish should be anesthetized and most other animals should be restrained during the implantation of PIT tags. Species, size and age should be considered when making a decision about anesthetization and restraint.

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Q.  Should my tags be sterilized before I implant them?
A.

Sterile implants are advised but many field conditions do not allow for sterile implants. Equipment can be disinfected prior to use with alcohol and iodine-based solutions. Biomark provides sterile tag packages in which the tag is implanted into the syringe, packaged and gas sterilized. These products are very convenient for use in field situations.

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Q.  Will the animal's survival be affected by the implantable tag?
A.

Many studies have addressed this subject and there is virtually no negative impact on animals provided they have sufficient body size and behavior is not inhibited by the tag.

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Q.  Are PIT tags used to track animals?
A.

PIT tags were designed for positive identification; because they are passive they are not capable of long-distance tracking. Many researchers use PIT tags and readers to study migration habits and movement to and from specified areas. Please call us for details on how the technology can be used in this way.

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Q.  What happens if two or more tags are in the read field?
A.

Tag collision occurs when more than one transponder (of the same frequency) is in the antenna field at once. Transponders are detected by the reader in milliseconds. If there is some degree of separation between tags, they have a better chance of being read. This is an issue that depends on the antenna design, the orientation of the tag, number of tags in the field and the ambient conditions of the installation. However, having a 134.2 kHz and a 125 kHz tags in the same read field at the same time will not cause collision with an ISO reader. This is because the reader switches between the two tag types. Therefore, it is possible to re-tag animals with ISO tags after they have been tagged with pre-ISO tags.

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