Automatic identification though RFID tags
The new frontier of automatic identification

When it made its appearance, some saw it as something that would replace bar codes and make them obsolescent; others imagined applications for coding and controlling human beings.

Also known as transponders, RFID tags are essentially memories equipped with a radio transceiver, often inserted in the same silicon chip.

The tag is excited by an external apparatus (fixed or portable) that establishes a dialogue via radio and then returns its identification code or any other information contained. Rewritable tags can also be remote programmed with additional data, or reprogrammed entirely with a new "identity."

Their size and final assembly can vary enormously depending on the application and performance required, although the chip on which they are based remains the same.

The classic disk form is inserted into various types of casings for the objects to be codified, while those with a hole in the middle can be fastened with a screw or rivet. Some have a form that can be directly "nailed" to soft materials (such as wooden pallets). The teardrop form is typically used for key chains.

Small glass bulbs (in a variety of sizes) can be inserted into non-ferromagnetic material or beneath the skin of animals using special syringes. It can take on the shape of a bracelet, single use string, watch, credit card and much more.

Many manufacturers provide tags that are not inserted into specific containers , known as In-Let, which are clearly more economical and smaller. They can be assembled during the company's production cycle: for example, in items of clothing, footwear, watches, equipment, and furniture.

Some companies codify pallets using this kind of tag, inserting them into special holes and then protecting them with silicone or other sealants.

INTERNAL MEMORY

The first important distinction between tags is the kind of memory they contain.

The least expensive utilize ROM (READ ONLY MEMORY), typically about ten bytes, which the manufacturer precodifies with a chronological number so that it will never be repeated.

Thus, when reading, an online data base that can show the real code used by the company is often necessary.

They are certainly less expensive, but their use is not flexible, and they are primarily utilized in "one time" applications. In general, the market tends to use tags with a larger memory that can be rewritten.

The company can thus memorize them with a code along with the information desired; they can easily be reused when their use cycle is complete. Some producers calculate that by maximizing volumes of production on rewritables, their cost is almost the same as ROMs.

They rarely contain SRAM (STATIC RANDOM ACCESS MEMORY), because they need to be constantly powered. They almost always use EEPROM (ELECTRICALLY ERASABLE PROGRAMMABLE READ ONLY MEMORY) and FLASH, which are powered only when used, without losing the data.

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ACTIVE AND PASSIVE TAGS

This is an important distinction, as are the relative technical differences and costs.

Active tags have an internal battery. There is thus enough power for high performance in terms of radio capacity (100 meters or more), speed, quantity of memory and to support any additional functions.

They cost at least ten times more than passive tags, and even the smallest are always larger.

An example of an active tag is the common TELEPASS used in automobiles. The gate lifts automatically after the toll booth transmitters activate it to ask it for an identifying code. Everything takes place at a distance of about 20 meters.

In addition to automatic identification, active tags are created to locate objects or persons. They are fastened to the object or worn as a bracelet. Then, through radio coverage with special Access Points and sophisticated triangulation systems, it is possible to determine the position within less than a meter.

Usually triangulation occurs by measuring the radio power received from at least three Access points. This system is susceptible to possible errors caused by attenuation and reflections of surrounding objects. Using triangulation and measuring the signal propagation time, the required calculation power is enormous.

Suffice it to consider that in 1 second a radio signal can travel the distance from the earth to the moon, and can travel 3 meters in less than one billionth of a second.

Passive tags do not have an internal battery: the current required for them to function is taken directly from the outside RF source that is dialoguing with the tag; in other words, RF energy, converted into electrical energy by the antenna, is directed and carried to a capacitor (similar to what happens in a feeder) which then acts as a tiny battery with enough charge to complete the transaction.

This method does not allow for a very powerful radio emission. Passive tags in fact have capabilities that at best reach just a few meters. Active tags are much more economical and can be extremely tiny, down to just a few square millimeters (excluding the antenna).

In our daily lives, we find them inserted in car ignition keys: through an antenna placed around the lock, the exchange can dialogue with the key's tag, and if it does not recognize it, prevent the car from starting. This prevents theft that is accomplished by short-circuiting the ignition wires or making a physical copy of the key, even when the copy is perfect.

It is important to distinguish passive tags from common shoplifting prevention systems used in shops, department stores and highway cafes. In fact, the latter almost always use much simpler, inexpensive technologies: in most cases a magnetized Mumetal sheet is hidden in the product (which is demagnetized at the cash register), or else the tag has a resonant L-C circuit (which is short-circuited at the register). This latter type looks like certain passive tags, but in reality it has no intelligent chip or memory.

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TAGS IN RFID AUTOMATIC IDENTIFICATION SYSTEMS

Radio frequency, normally a technology applied to communications of reporting and/or data input apparatuses, is extended to traditional, tested automatic identification techniques, which until now have been handled by bar code, magnetic strip or smart card management systems.

Now proven Radio Frequency Identification technology is in fact gaining more and more ground in both production and commercial areas.

There are three components involved:

RFID TAGS AT 13.56 MHz - 125 kHz - 134.2 kHz - 2.45Ghz - 5.8 GHz

Tags (or transponders), which have different forms, dimensions and consistencies depending on the field of application, may be, as we have noted, active (using an internal battery to independently transmit the signal; they can be used in situations that require reading/writing at a distance of up to 10-15 meters) or passive (less expensive, with no battery, they have only a chip, an antenna and a capacitor, which when activated by a magnetic field make it possible to transmit and receive data at a distance of 25-80 cm).

The radio frequency tag technique ( RFID), unlike competing identification systems, such as bar codes, magnetic strips or smart cards, often has no alternative in many automatic identification applications.

This is due to its unique features, primarily the absence of contact between the tag and the reader.

Use of a radio frequency tag makes it possible to resolve many environmental problems in the industrial field, as bar codes cannot be used in dirty environments, magnetic strips cannot be used under high temperatures, and smart cards are difficult to use.

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ACTIVE AND PASSIVE TAGS

There are two principal kinds of radio frequency tags. The most common and inexpensive is the passive type, i.e. it contains no battery, just a chip and an antenna that has the task, in addition to receiving and transmitting data, of transforming the electromagnetic energy into electrical energy to power the transmission system.

The intelligent part of each sensor consists of a single signal transmission circuit and a non-volatile memory containing a unique code, which is transmitted to the reading apparatus, or else a microprocessor, which can itself process the signals from readers and retransmit the results thus obtained.

Most passive tags function with electromagnetic field frequencies of 13.56 MHz or 125/134.2 kHz, and they can be very small in size.

Active tags contain their own power source, usually a small lithium battery. In addition to powering the reception and transmission circuits, this can be used to keep static RAM memory active, in which data regarding the tag is memorized.

The advantage to using a power supply is that it becomes possible to create systems that work with a higher frequency signal and that have a range of action of ten or more meters. Some active tags work with a signal band frequency of 900 MHz, for which a vast array of inexpensive electronic components are available to produce the transceiver.

The use of even higher frequencies is anticipated, in the GHz range. For example, in the United States, a proposal to the FCC, which regulates the use of frequencies, requests the use of the 2.45Ghz frequency for electronic radio frequency tags. In Europe, there are other proposals for establishing the use of frequencies around 5.8 GHz.

The various applications so far described require the use of transponders with diversified features; generally speaking, the reading distance, dimensions, environmental operating conditions, type and capacity of memory on the chip and the cost are the factors that determine what kind is selected.

The cost of reading/writing transponders is higher than reading only transponders. Sometimes the choice of a reading/writing transponder seems to be most obvious, as it can store data for changing situations that involve the element to be identified (for example, imagine giving the entire population a health card that could be updated over the years).

The demand for more secure identification systems is also leading to the creation of encrypted reading/writing devices, where identification undergoes complex calculations based on special algorithms, performed by both the reader and the transponder.

All integrated circuits that are applied were designed and implemented to absorb extremely low power (consistent with the energy transmission system necessary for their functioning) and, in general, the capacitor that tunes and stores the energy necessary for the device to function is also integrated.

The antenna consists of a wrapping (sometimes on a ferrite) of copper wire whose ends are welded directly to the bump contacts for the silicon chip through a thermocompression process.

This technological solution using a single chip welded to the coil through hard bording, guarantees dependability, high quality and low costs. This is certainly one of the most advanced production technologies; production is completely authorized and uses machines with an extremely high production capacity, with time cycles of just a few seconds.

In terms of form, two types of structures are utilized. The first is usually used when very small transponders must be produced, In this case, the chip + coil structure is inserted into a small glass cylinder or plastic container that is then hermetically sealed. Dimensions are typically 13 mm long and 2 or 3 mm in diameter for the former, and 10 x 4 x 3 in the latter.

The second type can be used in a remarkable variety of configurations, where the dimensions and form of the antenna can also be easily changed. The chip + coil structure is drowned or laminated in suitable plastic material, creating disks of various diameters (20, 30 and 50 mm are standard), ISO CARDS, and other configurations that may be at the customer's specific request.

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TAG READERS/WRITERS

Tag readers/writers can be a palm type (for reporting in the field), transportable (for installation on forklifts and trolleys) or fixed (to control gaps, production lines or specific areas of activity) and can read/write on one or more tags contemporaneously, with certain limitations.

An RFID system consists of a transceiver (reader) and one or more transponders capable of communicating with each other through a modulated radio frequency signal. If a passive type of transponder is used, the energy necessary for it to function is provided by the transceiver, whose antenna generates the appropriate RF magnetic field. The transponder captures the radio frequency with its antenna, loading a small capacitor integrated into it. When the tension at the ends of the capacitor exceeds a certain value, the transponder sends the transceiver the data contained in its memory, modulating the RF signal.

For a reading only transponder, this data is a unique code, selected from billions of available combinations, which is memorized on the chip during production.

The data can be sent in both directions depending on the characteristics of the transponder (and receiver), which can be incorporated into a chip with a ROM memory (written when the chip is being produced, which is reading only) or an EEPROM type of memory that allows both reading and writing, and on which various types of information can be written (and rewritten) regarding the object to be recognized.

At this point, it is easy to imagine the intrinsic efficiency of this type of identification system and the versatility that can be achieved with a data collection system that uses it.

The possibilities of this new and fascinating technology are thus vast, and will become even more so in the immediate future with the new developments we are already seeing in "SuperTag" applications (the result of research done in South Africa).

Generally speaking, they are particularly useful when we want reading without direct reader contact with the object to be identified, maximum security in transferring information (the percentage of correct reading on the first try exceeds 99.9%), when working in dirty or especially harsh environments where more traditional techniques fail, and when, for example, we do not want to reveal the presence of a control system.

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CONTROLLERS AND ANTENNAE TO RECEIVE AND TRANSMIT DATA

Antennae in different sizes and shapes, depending on the field of application, are usually associated with tag readers/writers or controllers, which act as an interface between them and any personal computers, PLC or host systems, to which they must refer to exchange data. Antennae generate a magnetic field (smaller or larger depending on the size of the antenna) and capture the signal emitted from the tag, which transits the controlled zone.

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SECTORS USING RFID TAGS

Transponders can be drowned in non-metallic materials with no deterioration of performance. It is clear that the utility of the RF identification system is enhanced by its use in an automatic data collection system. There are various possibilities of use for RF identification systems:

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PRINCIPAL DIFFERENCES BETWEEN BAR CODE AND RFID TECHNOLOGIES

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