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 EID tags are always fit for purpose – tough, tested and trusted.

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 64-bit code that is unique. It contains the four-digit country code where the tag will be used, plus a 12-digit number that will be the animals’ identification.

The transponder in a loop tag has the microchip and antenna inside a miniature water-proof capsule.

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 trauma. After insertion the tag is sealed shut to lock the transponder into place. Then the EID number is laser printed on the outside of the tag.

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

The microchip is programmed with an EID number that can be laser printed on the outside of the 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 tag sustains the most stress and strain as it’s being snapped into the ear.

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.

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.

Tag retention

An animal losing an ear tag is not just the financial loss of a possible fine and the cost of the tag; it can mean the loss of identity, including pedigree and performance information that reduces the sale value of the animal itself.

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, Orf, 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. A loop like the SET tag has very little movement if it’s properly positioned in the ear, and is unlikely to snag on wire, twine or net.

Button tags have a thicker spike to pierce with, and the tags themselves are heavier. Any movement of the tag will enlarge the original puncture, especially if the tag gets caught on something and the animal pulls back. Once the hole becomes sloppy and loose around the spike then the tag can become prone to moving, and the final result might be the entire tag being pulled through the hole and lost.

Tag reading

RFID tags have no internal power source like a battery. 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. This is one reason why the read range of RFID tags is relatively small – the tag and reader must be in close proximity for the tag to absorb enough energy to transfer its number.

Several factors affect the read range of an electronic tag.

  • The output power of the tag reader.
  • The transponder’s ability (power) to respond.
  • Size and type of antennae used.
  • Competition from other devices emitting electrical interference. Florescent 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 for communication between the tag reader and the transponder inside the tag. The difference is in how the microchip is energized by the reader.

  • Full Duplex (FDX) - The tag and tag reader “talk” to each other simultaneously, like two people on a telephone call.
  • Half Duplex (HDX) - The tag and tag reader must take turns; only one can “talk” at a time, like two people using walkie talkies.

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 might be the next generation of RFID technology in the future but they are not currently approved for use in livestock.

What’s next?

We are constantly exploring new technology and its possible benefits for animal identification. Future developments could include read & write tags capable of storing more information (treatment or performance data for example), or new ways to handle, store and transmit that information. 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.