RFID stands for Radio Frequency Identification and refers to a system for automatically identifying objects.  The easiest way to understand RFID is to imagine a type of BARCODE which is able to exchange information by radio, and update  itself over a period of time.

Many people think that RFID is a form of technology that will allow us to create an INTERNET OF OBJECTS, a kind of network that unites not just people, but also things.

The potential of this concept  are only just being touched on and in the coming years we expect lots of  innovative applications with RFID.

The identification is done by an antenna for reading a digital chip, (also called tag or transponder) that has been applied on the object (see below).

The tag contains information regarding the object to which it is applied ( e.g. product number, production date, manufacturer). This information can be static or can be updated with time.

RFID tags don’t need any kind of power (electricity) to work, thanks to magnetic induction. When they are awoken by the magnetic  field in the antenna, the tag is able to generate just  the right amount of energy needed  to transmit the information that it contains across a short difference. This type of tag is called a PASSIVE TAG

If a more powerful force is needed to transmit across a greater distance, the TAG must be powered by a source of energy such as a battery. In this case the tag is an ACTIVE TAG.

There are many sectors to which RFID technology can be applied.  Tags are moving into the sectors of industrial production, logistics and clothing, but also in health care,  public administration and access control

For private researchers and Universities, RFID is a challenge. In the coming years there will be need to develop tags which are even more sensitive and intelligent.

For those work in hospitals, public administration, libraries, emergency services, and the defense RFID is a certainty  because, thanks to this technology, it is possible to guarantee more control, security, accuracy in crisis management.

For supply chain management,  RFID is a useful tool  and indispensible for the future. Together with other technology  it can provide an extraordinary organisation of packages and single products.

With RFID, management costs can be reduced, efficiency in the warehouses increased and the entire chain improved.

For shopkeepers, RFID is a real opportunity, because in a few years the amount of shop lifting will  be reduced in store, but above all, the whole shopping experience will be improved, in such a way that the consumers can interact with the products that they intend to purchase.

The RFID tag is made up of a chip and a small antenna applied to a small support. While the chip incorporates memories of different kinds and manages all the different  activity of the tag, the antenna  communicates with the RFID reader.

The integrated antenna of the tags, can be of two types either circular or linear.

At the moment, the majority of processors are created using beams of light that are projected onto the silicon with a photosensitive material. On this microprocessor the data is stored, amongst which a unique serial number is written in the silicon

Passive Tags

The principle that allows an RFID tag to receive and transmit data contained in the chip is called magnetic induction.

When the Tag enters the reader’s field of operation (by just a few centimeters to a few meters) the tag is woken up by the ELECTROMAGNETIC FIELD which is generated  by the reader and it responds to it by reflecting back the signal.

This signal is answered when it is received by the reader, that decodifies it. This type of tag, known as a PASSIVE TAG, is the most common type of RFID tag on the market, mostly thanks to the price that makes it suitable for most applications.

Some types of PASSIVE TAGS are specifically designed to offer robust and resistant characteristics against extreme conditions. 

The limited settings of the Passive Tags and the reading distance make it impossible to integrate auxiliary sensors. Furthermore, the fact that they activate only when they are situated within the operating field of a Reader doesn’t make them suitable for applications of REAL TIME positioning.

Active tags

RFID tags can be integrated into a receiver system like the readers and this is the case of Active Tags that need a battery to generate the signal.

Thanks to this integrated source of energy, the Active Tags can turn themselves on independently  from the presence of a nearby reader , they also have a reading distance far more superior than that of the Passive Tags.

Because they are always on, Active Tags are used when there is a necessity to create systems with Real time positioning.

They can operate continually or in timed intervals in order to save the battery life. The battery also allows the added sensors to work, for example in order to detect the temperature or pressure

There are some disadvantages with Active Tags. Usually there are larger than Passive Tags and the cost  of purchasing them is greater  than those of Passive Tags. The cost of carrying out maintenance or changing the battery should also be taken into consideration, and the battery could cause difficulties if they are used in environments with very high temperatures. 

Semipassive Tags

There is a third category of RFID tags called semi passive tags or Battery Assisted Passive (BAP).
These are essentially passive tags that are fitted with a battery. They don’t use the battery’s energy to transmit the signal but like the passive tags reflect the signal which comes from the reader.

The battery has two uses: to power the added sensors if the Tag is fitted with them, or rather to help the chip “wake up” keeping it in standby mode rather than completely switched on.

Given that often Tags have difficult  in “waking up” because of the limited reading distance which might not stimulate sufficient energy from the field of the reader, the help of the battery in the BAP tags means that they can offer far more superior reading distance.

With regards to prices, the BAP tags place themselves in line between the passive tags and the active tags.

RFID systems use various frequencies that can be classified as:
LOW frequency (LF between 125 and 134kHz)
HIGH frequency (HF, around 13Mz)
ULTRA HIGH frequency (UHF between 860  and 960 MHz)
Microwaves (superior of 2,45 GHz)

The  frequency bands have different characteristics and are suitable for different applications.

Low frequency tags use little power , they are able to pass through non metal material and liquids but the reading signal doesn’t pass 30-40 cm.

The High frequency tags work better with metal objects and are capable of covering  a distance of around one  meter. 

The Ultra High frequency tags offer the greatest range of reading and allow the transfer of data extremely quickly however they don’t pass through material easily.

Usually Tags operate at  with 2,45 GHZ are used for  operations such as Motorway tolls and port access control.

There are 3 types of RFID TAGS:

1. Read only: SOLA LETTURA

2. Write once & read many o WORM

3. Read & write

The first of the two forms, the RFID tag represents the technological evolution of the barcode,  that is the information stored on the microchip, once written on cannot be modified. The Read and Write tags however are more flexible. The tag can be used like a dynamic memory in which the information  on the chip can be updated  in every moment along the supply chain. Generally this kind is a little more expensive than Read only Tags.

WHAT ADVANTAGES CAN RFID OFFER OVER THE BARCODE?

With regards to barcodes and other identification technology  RFID technology offers numerous advantages. The reading does not require direct contact or eye contact. It isn’t necessary to point the tags towards the Scanner.

The tags can be read at the same time, they can work in contaminated or dry environments and can cope with difficult conditions such as extreme temperatures, chemical or physical damage.
They are durable. They can hold more data as opposed to the barcode and depending on the kind of Tag they can also be rewritten on and updated with new information. They can work even if they are submerged in a liquid or from within an object if identification is required from inside a container. Furthermore where the Barcode can only indentify one lot of a product, but not the single item. The RFID tag instead can contain a unique serial number  that can indentify each and every product manufactured in the world.

The RFID tags are more costly in respect to barcodes but the cost/benefit relationship is generally greater. It would be wrong to thing that RFID technology can replace the barcode, the two will coexist.

How much distance can really be covered?
The reading distance varies according to the type of tag ACTIVE or PASSIVE and the frequency.

For Passive technology the indicative reading  distances vary from  just a few millimeters to tens of centimeters.  For LF from 10cm to 20 cm for HF up to 4m to 7m for the UHF, these values vary depending on the dimensions of the tag and of its antenna.

For example an HF tag in the shape of a button with a diameter of 14mm has a reading distance of at least 25cm, whilst an HF tag in the shape of credit card 80x50mm can be read over a distance of 100cm. For active tags the distances increase up to at least tens of metres.

With regards to the reading angle we are faced with a similar situation as described above.  Passive LF and HF tags are extremely sensitive to the angle of exposure.  By moving the  angle even by 45 degrees the behaviour of the tag can be effected

For UHF tags, however this depends on the  reader and the antenna. Naturally the cost of the two different types of tags is different.

This applies more significantly for applications with PASSIVE TAGS that structurally are designed to be applied in large volumes and therefore in contexts where many tags must be read in a short amount of time. See table below:

The memory capacity within in the Tag can be assured by using 3 different types of memories:

• Read only memories (ROM), they can be used to memorise the unique Identification code that is written on the Tag when it produced, according to the ISO standards.
• Writable once memories and therefore only readable
• Memories which are rewritable a number of times ( flash memories)

Read only memories have a lifespan similar to other electronic devices fitted with ROM about 10 years.

Rewritable memories have a lifespan of at least 10 years.

These lifespans can generally satisfy the majority of the identification applications: problems could be caused by special asset management identification applications over a long period (for example in libraries).

Naturally for these applications there isn’t accurate data on the actual life span of the information written on the  rewritable memory of the tags. The exposure of the TAGS to strong magnetic fields to other sources of radiation could also cause the loss of memorized data.