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The science behind our tags

Radio frequency identification (RFID) is the technology at work inside every electronic tag. What makes a superior tag is a combination of quality components and great design. Shearwell SET EID tags are always the right choice – tough, tested and trusted. (SET stands for Shearwell Electronic Tag.)


What’s inside?

Every electronic tag contains a transponder - a microchip and a coil of copper wire as an antenna. The microchip is pre-programmed at Shearwell with a unique code that is assigned to the animal when it is tagged.


SET Strip

SET Transponder

SET Closed

 The transponder in a Shearwell SET tag is inserted into a cavity in the body of the tag. This location protects the transponder from any pressure or damage. After insertion the tag is sealed to lock the transponder in place. The EID number is then laser printed on the outside of the tag. 


Empty SET tags
 Transponders Inserted
Tags Sealed

The transponder in a button tag is built inside the female part. The antenna circles the centre hub and is over-moulded with plastic to protect it from moisture and damage.



Underside of female button

Button Tag

Better by design 

 An ear tag is designed to survive some harsh treatment; it gets hot, cold, wet, frozen, bitten, pulled, scraped and squeezed - whatever the ear endures the tag must too.

The challenge is to keep the electronics safe, not just from the weather and animals but from the application process itself.

A one-piece EID tag is quite a feat of engineering – the plastic must be flexible enough to bend without breaking, rigid enough to punch a hole through a sinewy old ear, tough enough to protect the electronics inside, plus small and light enough for a newborn lamb to carry.

 A tag undergoes the most stress and strain as it’s being snapped into the ear.
Applicator Jaws
Flag Spike

Two-piece tags may have a spike with a metal tip, or have a harder grade of plastic in the spike than in the rest of the tag, making this design more suitable for older animals with tougher ears.

Button Spike

Tag Retention

The consequences of losing a tag can be serious so it's important that tag retention is as good as possible.

Tag retention is influenced by:

  • Correct placement in the ear
  • Ensuring the male and female parts of the tag lock together properly
  • Infection – affected by cleanliness, flies, flock/herd health
  • Environmental hazards – twine, wire, fence and feeder design

The size of the puncture hole can also affect the retention rates between different kinds of tags. Loop tags such as the SET tag experience very little movement if properly positioned in the ear, and are unlikely to snag on wire, twine or net.


 Tagged Sheep

Tag Reading

RFID tags have no internal power source such as a battery. Instead the microchip in the tag is energized by the radio frequency of the tag reader. The electrical current is very small but just strong enough to power up the tag to transmit the ID number stored inside.


Several factors affect the read range of an electronic tag.

  • The output power of the tag reader.
  • Size and type of antenna used.
  • Competition from other devices emitting electrical interference. Fluorescent lights and electrical motors running nearby can interfere with the radio signals between the tag and the tag reader.


There are two common technologies used  - FDX and HDX - for communication between the tag reader and the transponder inside the tag. The difference is in how the microchip is energized by the reader. They are functionally equivalent and any ISO compliant reader will read both seamlessly.


Radio Frequency

Low frequency tags are used for animal identification around the world. Standards for EID are set by international committees, and all EID tags sold in the UK must conform to the standards. High frequency or ultra-high frequency tags are not currently approved for use in livestock.


What's Next?

We are constantly exploring new technology and its possible benefits for animal identification. Working closely with our customers, as well as statutory, commercial and industry partners, helps to drive us forward with ever better management solutions to help the livestock farmer.

Shearwell is a founder member of ALIDMA, the industry body for UK animal identification manufacturers and suppliers