RFID
RFID relates to that branch of automatic identification that uses radio-frequency devices to obtain data.
Usually, the component containing the data, namely the "transponder" or TAG, consists of a passive microchip and an antenna. The latter device is capable of picking up a radio emission at a certain frequency that activates the microchip and releases the data.
The radio-frequency sender, contained in the "reader", is also equipped with a decoding system and an interface with the host system.
This identification system is suitable for those applications where the use of barcodes is not convenient, for example in external environments exposed to the weather, or when the identification label must not be visible, or when it is necessary to modify the label content such as in stepped payment systems.
The transponder (TAG) containing the identification data may have different shapes and sizes, thus allowing many applications: industrial automation, animal identification, production monitoring, access control, pallet and container identification, luggage sorting and materials management.
How a tag works
The TAG or Transponder, the automatic radio-frequency identification element (RFID) is mostly a passive component, i.e. without a battery, made of an integrated circuit (chip) and an antenna. The reader, which is also equipped with an antenna, emits a magnetic field. When the transponder enters into the reader range, it receives through the antenna the energy necessary to activate the integrated circuit, which starts transmitting data to the reader. No contact is required for the reading. The reader can also invert the data flow thus becoming a "writer" and modifying the TAG content.
The TAGs have an internal memory that varies, depending on the model, from some ten to some thousand of bytes and can be of the following type:
- Reading only - the code is unique and is customised during production
- Reading and writing - the information contained in the TAG can be modified by the reader
- Anti-collision - these are special TAGs that can be simultaneously identified by the reader, compared to the others that must enter individually into the range of the reading system
Maximizing the RFID readings in a SUPPLY CHAIN
A certain way of publicising results at fairs - results which do not exist and which in many cases will never exist, or which if they come into existence will only do so in many or in at least five years time, an altogether American way, (but lately not only American), of marketing, selling the product of tomorrow - has created an aura of unbelievable expectations, almost magical, around RFID. Moreover, it is never specified whether these expectations are due to the magic of UHF or HF or some other frequency band, but in any event since it's magic what difference does it make?
The result of all this is that people are surprised when the tags cost much more than 5c (NB: dollars not Euro cents), for many millions of pieces, not for a few thousand. Those that expect the RFID, almost as if by magic, to be capable of performing the instant and ongoing inventory of the warehouse at the simple push of a button, marvel that a gateway or an ordinary reading system is not able to read 100% of the hundreds of tags contained in a pallet or simply in a box that contains only 4 small electrical appliances in pressure die-casting aluminium - things that happen to anyone who has to do with RFID in one way or another.
As a consequence reality intrudes rather brutally, when for the first time a pallet composed of real cardboard boxes crosses a real gateway. Result: reading of very few tags.
Problems presented by the reality
At this point an introductory discussion is required. In writing this article, we took our cue from an interesting white paper published recently by Texas Instruments, which takes a very practical approach to the problems relating to the reliability of the reading for the UHF world, taking it for granted however, as do almost all Americans, that other RFIDs, outside UHF, do not exist. In Europe, as in the rest of the world, we use and will continue to use on a widespread basis the HF. Given that with the forthcoming liberalisation of the ORE in Italy too, this technology will allow one to finally implement those solutions that FIF did not allow; we will look at both technologies in this article. Vice versa the Americans, despite their "UHF centricity" are starting to take account of the fact that if one wishes to carry out item tagging, it is very difficult to do so with UHF, if not impossible with near field UHF, and thus even EPC is finally starting to open its standards to HP. That which seems to be a simple and linear process, writes Texas Instruments, simply adding a tag with a small radio to each box and tuning in the receiver, the reader and the right transmitter can crystallise into a variety of problems in reading the smart label.
Various factors can cause these problems, the main problem is however only one: one demands high performance with very limited power. It must be borne in mind that passive smart tags that are used in a Supply Chain do not have their own power source and must receive the energy required to answer the reader, from the reader itself; there are many things that can interfere with these weak signals: environmental RF interference, the physics of the tagged product and slight damage to the tag caused by handling are some but not all of the causes of a decline in the reading performance. Many types of products allow one to come close to a 100% reading with 101fF1 or to reach even 100% with HF without any problems. Generally, they are products that do not contain moisture, in the case of the UHF and, in both cases do not contain metal. Products loaded on to a pallet present greater difficulties when the readers try to identify the tag located inside the pallet. Even though REID is not strictly speaking a technology that requires optic lines to read, the weak signals that try to leave the pallet are easily pink-shielded ... can be easily read if it is found outside a pallet, but not so easily if it is on the inside.
If one uses a tag-pallet, which in essence, as specified by various standards, can contain information with reference to all the tags contained in the pallet, this limitation does not constitute an insuperable problem.
What can one realistically expect
The EEC has in fact accepted, with certain quite strict limits, the standards on UHF from November last year; in Italy, for the time being, these can be used only indoors, with effect from May, except for last minute surprises. The discussion that follows, relating to the past implementation of the UHF, thus essentially relates to the USA.
Anyone who implemented a UHF system, knows that a 100% legibility is not a realistic expectation; instead this may be very different with HF because whether for good or bad, they behave in a much more predictable and constant manner.
We can in any event expect that the tags will be read more than once in the Supply Chain. Certain reading points are:
- manufacturer's production line
- manufacturer's shipment area
- distributor's receiving and dispatch area
- gdo's distribution centre
- retailer's receiving area
- retailer's warehouse exit point
- retailer's box opening point
A certain product may have only a 50% legibility in a particular reading point, but after 5 reading points, according to the theory of probabilities, one will obtain an accumulated global reading of 97%, i.e. one product in 33 will not be read. It is from this type of consideration that in the USA the target comes of a five niner, i.e. a legibility of 99.999% at 5 reading stations, probably even in different companies of the Supply chain.
The first problem that must be dealt with is how to improve the system as a whole.
The first choice to be made is obviously which system to use, UHF or HF; it is definitely an important choice because it involves the whole Supply Chain. The choice can differ depending on the type of 51W or even on the item that one wants to tag. Then one can give consideration to the tags: for example by seeking more sensitive tags. One can then move on to the reading area, using the most sensitive antennas
There are many choices, one is dealing with choosing between options that are more suitable for each organisation and its objectives.
In the case that one opts for a UHF system, one should bear in mind that if the supply chain ends beyond the ocean, whether West or East, the frequencies are different and vary from 865 MHz in Europe to 915 throughout North America and 960 in Japan and various other frequencies in other Asian countries.
If this situation arises, the performances must be measured in the different frequency ranges.
There is also a question of standards not yet completely resolved between EPC and ISO. On every score the Gen2 (EPCglobal) Texas Instruments tags - "die or strap" type - are capable of solving many problems when the goods must leave the country; it goes without saying that this problem of the frequencies does not present itself with the FIF systems in that one is dealing with a single worldwide standard in regard to both the frequency and the protocols.
A few introductory remarks
In the first instance one must choose certain parameters of the existing process or in any event define them, as they will be useful to compare the expectations with what one obtains in reality. These parameters - time to complete a determined operation, reading percentages, efficiency of the reading area, human intervention required, measured and checked for a certain lapse of time - will enable one to understand the process and will give a good line of comparison with the incoming process allowing us to show the improvement or the need to change.
The best way of measuring the success of the change is to understand how the new dynamics that were introduced, influence the performance as a whole.
A very important aspect of this process is choosing the tags which are best suited to the purpose.
Above all in the case in which one chooses the UHF systems one may not simply trust to data obtained from air in an anechoical chamber; it is essential to carry out tests which are specific to the application. Each company has its own mix of products and processes that determine the needs of the tag labelling.
One should always bear in mind:
- Material and identity of the products
- Packaging material
- Position of the labels on the product or the packaging
- Size of the pallet and number of boxes per pallet
The tags can be supplied already written, according to the customer's specifications or written at the time of use; in the latter case one must assess the times required to carry out the writing which depends on the type of tag originally chosen. One must then carry out tests on a significant population of tags prepared in this way, reading them not in a laboratory but in an environment similar to that where they will be read, and thus including metal structures and multiple sources of RE interference. This is particularly important for UHF systems.
Next one must then carry out a series of static tests to obtain more simplified data, which can be easily reproduced and compared.
These tests are typically:
- Determination of the maximum reading distance; one should note that whereas this test gives fairly uniform results in the case of I-lE tag, the results can differ significantly in the case of UHF depending on the test set-up environment
- Determination of the best point to apply the tag. This is a test that requires time if carried out on many products or packages; it is particularly important and complex if the products are liquids, creams or packages containing such products; the same applies, with greater reason for metal products even in the case of HP. The subsequent dynamic tests add a new level of complexity insofar as the labelled products are put into motion. However they have the significant advantage of supplying the user with real use parameters and make a useful contribution in the choice of the tags
- The tagged products are placed on a conveyor, typically a ring conveyor, and pass through a gateway, in this case UHF, or even through a tunnel, in this case HF, at a variable speed and up to 3 or 5 readings per passage; the percentage reading of the tags with respect to the total, for each passage is determined
- A full pallet of tagged products is passed through a gateway with between 2 and 8 antennas; the number of readings per passage and the percentage of readings of the tags with respect to the total, for passage is determined
- A full pallet of tagged products is made to go around a shrink-wrapping machine, where a wrapping is applied before shipment; the percentage of readings of the tags with respect to the total is determined, on completion of the operation
Risks of tags
Bad treatment of the tags can create many problems in the system; tags are electronic components and as such they must be managed with care. If a box of smart labels falls or if the boxes are thrown, this could result in about 10% or more of them becoming unusable; one must also bear in mind that before the smart label is applied to the final packaging it is in the most fragile stage of its life, and it is thus indispensable to train the staff and the receiving carriers properly on how to take care of the boxes containing the smart labels.
It is also important to control the whole process of application of the tag and the system of transport upstream of the application. It is just as important to train the outgoing carriers making them aware that they can damage the tags applied to the boxes, by crushing or rubbing them against other boxes or walls or even by letting them become wet. If one knows from the start that the tags will be subjected to rough treatment, one can bear this in mind when choosing the tags by carrying out in-house test or even by sending them to specialised laboratories.
