Types of RFID tags
Contenido
Las etiquetas RFID pueden ser activas, semipasivas (también conocidos como semiactivos o asistidos por batería) o pasivos. Las etiquetas pasivas no requieren ninguna fuente de alimentación interna y son dispositivos puramente pasivos (solo se activan cuando un lector se encuentra cerca para suministrarles la energía necesaria). Los otros dos tipos necesitan alimentación, típicamente una pila "Pila (electricidad)") pequeña.
La gran mayoría de las etiquetas RFID son pasivas, que son mucho más baratas de fabricar y no necesitan batería. En 2004, estas etiquetas tenían un precio desde 0.40 $, en grandes pedidos, para etiquetas inteligentes, según el formato, y de 0.95 $ para etiquetas rígidas usados frecuentemente en el sector textil encapsulados en PP o epoxi. El mercado de RFID universal de productos individuales será comercialmente viable con volúmenes muy grandes de 10 000 millones de unidades al año, llevando el coste de producción a menos de 0.05 $ según un fabricante. La demanda actual de chips de circuitos integrados con RFID no está cerca de soportar ese coste. Los analistas de las compañías independientes de investigación como Gartner and Forrester Research convienen en que un nivel de precio de menos de 0.10 $ (con un volumen de producción de 1 000 millones de unidades) solo se puede lograr en unos 6 u 8 años,[9] lo que limita los planes a corto plazo para una adopción extensa de las etiquetas RFID pasivas. Otros analistas creen que esos precios serían alcanzables dentro de 10 a 15 años.
A pesar de que las ventajas en cuanto al coste de las etiquetas RFID pasivas con respecto a las activas son significativas, otros factores, incluyendo exactitud, funcionamiento en ciertos ambientes como cerca del agua o metal, y fiabilidad, hacen que el uso de etiquetas activas sea muy común hoy en día.
Para comunicarse, las etiquetas responden a peticiones o preguntas generando señales que a su vez no deben interferir con las transmisiones del lector, ya que las señales que llegan de las etiquetas pueden ser muy débiles y han de poder distinguirse. Además de la reflexión o backscatter, puede manipularse el campo magnético del lector por medio de técnicas de modulación de carga"). El backscatter se usa típicamente en el campo lejano") y la modulación de carga en el campo próximo") (a distancias de unas pocas veces la longitud de onda del lector).
Passive tags
Passive tags do not have electrical power. The signal that reaches them from the readers induces a small electrical current sufficient to operate the CMOS integrated circuit of the tag, so that it can generate and transmit a response. Most passive tags use backscatter on the received carrier; That is, the antenna must be designed to obtain the energy necessary to operate at the same time as transmitting the response by backscatter. This response can be any type of information, not just an identifier code. A tag may include non-volatile, possibly writable memory (e.g. EEPROM).
Passive labels usually have distances of practical use between 10 cm (ISO 14443) and reaching up to a few meters (EPC and ISO 18000-6"), depending on the operating frequency and the design and size of the antenna. Due to their conceptual simplicity, they are obtainable through a printing process of the antennas. As they do not require power supply, the device can be very small: they can be included in a sticker or inserted under the skin (low frequency tags).
In 2006, Hitachi developed a passive device called µ-Chip with a size of 0.15 × 0.15 mm without antenna, thinner than a sheet of paper (7.5 µm).[10][11] SOI (Silicon-on-Insulator) is used to achieve this integration. This chip can transmit a unique 128-bit identifier fixed to it at manufacture, which cannot be modified and confers authenticity to it. It has a maximum reading range of 30 cm. In February 2007 Hitachi presented a device even smaller than 0.05x0.05 mm and thin enough to be embedded in a sheet of paper.[12] These chips have storage capacity and can operate at distances of up to a few hundred meters. Its main drawback is that its antenna must be at least 80 times larger than the chip.
Alien Technology") (Fluidic Self Assembly), SmartCode") (Flexible Area Synchronized Transfer) and Symbol Technologies (PICA) claim to have processes in various stages of development that can further reduce costs through parallel manufacturing processes. These means of production could further reduce costs and drive the economies of scale models of an important sector of silicon manufacturing. This could lead to further expansion of passive tag technology.
There are labels made with polymer-based semiconductors developed by companies around the world. In 2005 PolyIC and Philips introduced simple tags in the 13.56 MHz range that used this technology. If successfully introduced to the market, these labels would be printable like a magazine, with much lower production costs than silicon labels, serving as a fully printed alternative, like current barcodes. However, this requires that they overcome technical and economic aspects, taking into account that silicon is a technology that has been enjoying multimillion-dollar development investments for decades that have resulted in a lower cost than that of conventional printing.
Due to power and cost concerns, the response of a passive RFID tag is necessarily brief, typically just a single identification number (GUID). The lack of its own power source means the device can be quite small: there are commercially available products that can be inserted under the skin. In practice, passive tags have reading distances that vary from about 10 millimeters to about 6 meters, depending on the size of the tag's antenna and the power and frequency at which the reader operates. In 2007, the smallest commercially available device of this type measured 0.05 millimeters × 0.05 millimeters, and thinner than a sheet of paper; These devices are practically invisible.
Active tags
Unlike passive tags, active tags have their own autonomous energy source, which they use to power their integrated circuits and propagate their signal to the reader. These are much more reliable (have fewer errors) than passive ones due to their ability to establish sessions with the reader. Thanks to their energy source, they are capable of transmitting more powerful signals than passive ones, which makes them more efficient in environments that are difficult for radiofrequency such as water (including humans and livestock, mostly made up of water), metal (containers, vehicles). They are also effective at greater distances and can generate clear responses from weak receptions (unlike passive receptions). On the contrary, they tend to be larger and more expensive, and their useful life is generally much shorter.
Many active tags have effective ranges of hundreds of meters and battery life of up to 10 years. Some of them integrate temperature recording sensors and other variables that can be used to monitor food environments or pharmaceutical products. Other sensors associated with RFID include humidity, vibration, light, radiation, temperature, and atmospheric components such as ethylene. In addition to much greater range (500 m), they have greater storage capacities and the ability to store additional information sent by the transceiver.
Currently, the smallest active tags are about the size of a coin. Many active tags have practical ranges of ten meters, and battery life of up to several years.
Characteristics
The main advantage of active RFID tags over passive ones is the high reading range, on the order of tens of meters. As disadvantages, it is worth highlighting the price, which is much higher than the passive ones, and the dependence on battery power. The lifespan of the batteries depends on each label model and also on its activity; it is normally on the order of years. To facilitate battery management, it is common for active RFID tags to send battery level information to the reader, allowing those that are about to run out to be replaced in advance.
These batteries provide the tags with power in standby mode in which the current consumed is very small (generally 3uA) and in operating mode (where 24mA is consumed) these batteries can last from 1 to 10 years, which makes them more robust. The most used are lithium and manganese dioxide such as CR2032 and CR2320. Below are its technical characteristics:
It has the following dimensions according to IEC 60086:.
The discharge performance based on temperature and load resistance is shown in the following graphs:
There are also ultra-thin printed batteries for active packaging design. These batteries are flexible, powerful and less than a millimeter thick, making them ideal for active tags in RFID systems.
Another alternative is paper batteries, which have applications in RFID devices, smart cards and paper LEDs, among others. It is a battery that is made up of thin sheets of chemical compounds embedded in paper, obtaining electrical energy from oxidation-reduction reactions, producing at the terminals a nominal voltage of 1.5 V and a charge of approximately 1.5 mAh.
Semi-passive tags
Semi-passive tags are similar to active tags in that they have their own power supply, although in this case it is mainly used to power the microchip and not to transmit a signal. The energy contained in the radio frequency is reflected towards the reader as in a passive tag. An alternative use for the battery is to store information propagated from the reader to emit a response in the future, typically using backscatter. Batteryless tags must respond by reflecting carrier power from the reader on the fly.
The battery can allow the tag's integrated circuit to be constantly powered and eliminate the need to design an antenna to collect power from an incoming signal. Therefore, antennas can be optimized to use backscattering methods. Semi-passive RFID tags respond faster, so they are stronger in read rate" than passive ones.
This type of tag has a reliability comparable to that of active tags, while being able to maintain the operating range of a passive one. They also tend to last longer than active ones.
What are the differences between barcode and RFID tags?.
One of the essential functions of security seals is to guarantee the correct identification and traceability of the products and merchandise to which they are associated. What are the differences between barcode and RFID tags? The security seal then functions as a vehicle of information thanks to the codes that are integrated into it.
The main differences between identification systems: What are the differences between barcode and RFID tags?
It is interesting to compare more traditional systems such as barcodes against the alternative presented by RFID tags. Let's review the behavior of each one focusing on four main characteristics:.
Information storage capacity.
Versatility and scanning speed.
System cost.
Outstanding advantage.
- Bar code.
The outstanding advantage of the barcode is its standardization in a multitude of sectors. The simplicity of its use and its correct level of precision make it the most widespread system in the retail or commerce sector and in inventory and logistics management.
However, its information storage capacity is more limited by space: it records up to 20 characters. On the other hand, barcode scanning requires human intervention and direct contact of the reader with the printed information, something that slows down the process.
Regarding cost, barcodes can be printed with simple systems and therefore are not burdensome, but it is true that they are more prone to deterioration in aggressive environments and cannot be modified once they have been printed.
- RFID tags.
Antenna Types
The type of antenna used in a tag depends on the application for which it is designed and the frequency of operation. Low frequency or LF tags normally use electromagnetic induction. Since the induced voltage is proportional to the frequency, the voltage needed to power an integrated circuit can be produced using a sufficient number of turns. There are compact LF tags (such as those encapsulated in glass, used for human and animal identification) that use an antenna in several levels (three of 100-150 turns each) around a ferrite core "Ferrite (ferromagnetic ceramic)").
At high frequency (HF, 13.56 MHz) a flat spiral with 5 to 7 turns and a form factor similar to that of a credit card is used to achieve distances of tens of centimeters. These antennas are cheaper than LF antennas since they can be produced by means of lithography instead of spiration, although two metal surfaces and one insulator are necessary to make the cross connection from the outer level to the inside of the spiral, where the resonance capacitor and the integrated circuit are located.
Passive ultra-high frequency (UHF) and microwave tags are usually radio-coupled to the reader's antenna and use classic dipole antennas "Dipole (antenna)"). Only one layer of metal is necessary, which reduces cost. Dipole antennas, however, do not fit very well with the characteristics of typical integrated circuits (high input impedance, slightly capacitive). Folded dipoles or short loops can be used as complementary inductive structures to improve power supply. Half-wave dipoles (16 cm at 900 MHz) are too large for most applications (e.g. RFID tags for label use cannot be larger than 10 cm), so antennas must be doubled to meet size needs. Broadband structures can also be used. The gain "Gain (electronic)") of compact antennas is usually lower than that of a dipole (less than 2 dB) and they can be considered isotropic in the plane perpendicular to their axis.
Dipoles undergo coupling with radiation that is polarized on their axes, so the visibility of a tag with a single dipole antenna depends on its orientation. Tags with two octagonal antennas (double dipole tags) are much less dependent on it and the polarization of the reader's antenna, but are typically larger and more expensive than their single counterparts.
Patch antennas can be used to provide service in the vicinity of metal surfaces, although a thickness of 3 to 6 mm is necessary to achieve good bandwidth, in addition to having a ground connection which increases the cost compared to simpler single layer structures.
HF and UHF antennas are usually made of copper or aluminum. Conductive inks have been tested on some antennas, finding problems with adhesion to the integrated circuit and stability of the environment.
Tag association
There are three basic types of labels due to their relationship with the objects they identify: associable, implantable and insertable (attachable, implantable, insertion).[13] In addition to these types of labels, Eastman Kodak has filed two patent applications that deal with monitoring the consumption of medicine in the form of a “digestible” label.[14].
Label positioning
Orientation can affect the performance of UHF tags through the air. In general, optimal reader power reception is not necessary to operate passive tags. However, there may be cases in which the distance between both parts is fixed as well as the effective power emitted. In this case, it is necessary to know in which cases you can work optimally with them.
The points called R (resonance spot*), L (live spot*) and D (dead spot*) are defined to specify the location of the tags on a marked object, so that they can still receive the necessary energy based on certain levels of emitted power and distance.[15].
Tag environments
The concept of the RFID tag is associated with its ubiquity. This means that readers may require the selection of tags to be explored from among many possible candidates. They may also want to scan tags in their environment to take inventory or, if the tags are associated with sensors and can maintain their values, identify environmental conditions. If an RFID reader tries to work with a set of tags, it must know the devices that are in its area of action and then go through them one by one, or use collision avoidance protocols.
To read the data from the tags, the readers use a singulation algorithm based on tree traversal, resolving any collisions that may occur and sequentially processing the responses. There are blocking tags that can be used to prevent readers from accessing the tags in an area without resorting to suicide commands to disable them. These masquerade as normal labels but have certain specific characteristics; Specifically, they can take any identification code as their own, and can answer any questions they hear, securing the environment by nullifying the usefulness of these questions.
In general, a spurious signal can be emitted if tag activity is detected to block weak tag transmissions. If the labels are expendable or are not needed again, they can be rendered useless by inducing high currents in them that render their circuits useless.
Apart from this, a tag can be promiscuous, if it responds to all requests without exception, or secure, if it requires authentication (this involves the typical aspects of cryptographic and access key management). A tag can be set to activate or deactivate in response to commands from the reader.
Readers in charge of a group of tags in an area can operate in autonomous mode, as opposed to interactive mode. Working this way, they perform periodic identification of all tags in their environment and maintain a presence list with timeouts and control information. If an entry expires, it is removed from the table.
Often a distributed application requires the use of both extreme types of tags. Passive ones cannot perform continuous monitoring tasks, but instead perform tasks on demand when readers request them. They are useful for carrying out regular and well-defined activities with limited storage and security needs. If there are frequent, continuous or unpredictable accesses, or there are real-time or data processing requirements (such as searching internal tables), it is usually convenient to use active tags.