Here the tiny tags can be seen next to a human hair

The minute devices measure just 0.05mm by 0.05mm (0.002x0.002in) and to the naked eye look like spots of powder.

They are thin enough to be embedded in a sheet of paper, Hitachi spokesman Masayuki Takeuchi says.

RFID tags store data about the objects they are attached to, and companies are vying to create increasingly tiny versions.

Recently, Hitachi unveiled another RFID tag, the Mu-chip, which measures 0.4mm by 0.4mm (0.02x0.02in).

But the latest chips, which are yet to be named, can hold the same amount of data as the Mu even though they are much smaller.

They have one major issue, however - they need an external antenna to work, and the smallest antenna developed so far is about 80 times bigger than the tags.

Hitachi says it wants to study the tags' possible uses, but it does not yet have any plans to put its latest creation into commercial production.

Spy-tags

Unlike its predecessor, the barcode, an RFID tag's data can be extracted from afar - sometimes from hundreds of metres away - by radio-reading devices, and the technology is already widely used.

Stores use it to track stock in warehouses and shops. Some countries are using the tags to hold passport data or for payments in transport systems, and they are even being used for animal identification.

However, some have raised concerns that the technology poses a threat to privacy, and that it could be used in covert monitoring schemes.

And the fact that they are becoming ever more invisible could fuel this apprehension.

However, said Mr Takeuchi: "We are not imagining such uses."