Redes y Servicios de Radio. RFID Systems

Transcription

1 Redes y Servicios de Radio RFID Systems Alumno 1: Dietl Marcus Alumno 2: Maier Karl Fecha de la presentación:

2 1. Introduction The term RFID refers to the use of an object ( tag ) on a product, animal or person for the purpose of contactless identification and tracking using radio waves. The functional range of this system, depending of the used technique, include distances from a few centimeters (LF) up to several meters (in UHF/SHF >20m, the frequency bands are mentioned and explained later in this paper). The standard RFID system consists of two parts, the so called reader (also called: interrogator) and tags (also referred as labels ). Tag: The tag also consists of two parts: 1. an integrated circuit (IC) for modulating, demodulating, storing and processing information 2. an antenna for physical transmission and reception of the signal The tags carries information about the object/subject which it is attached to, this can be, for example, an article number which is associated to the respective article in a supermarket. If the tag receives a so called Query request from the reader it sends the information back. We can distinguish between the following types of tags: -passive tags: don t contain a battery and use the EM-field of the reader as power supply -active tags: contain a battery and can transmit signals autonomously -battery assisted passive tags (BAP tags): need an external source for the wake up - process (reader signal), but provide much higher range capability. Figure 1: RFID tags,;uhf (on the right), HF (upper left), smart label HF (lower left) Reader: The reader emits an alternating electromagnetic field which operates also as a power supply for the tags (just in case of passive tags), sends his commands to the tags ( query requests ) and receives the information from them. The reader can be connected to a host computer to process and handle the obtained information (e.g. database). In the LF and HF case, the information transmission process is done by load modulation (inductive coupling in the near field), in the UHF and SHF case by wave propagation and reflection (so called backscattering ).

3 Figure 2: RFID readers; handheld (on the left) Operating frequencies: We distinguish between 4 frequency bands: LF: 125kHz HF: 13.56MHz UHF: MHz SHF: 2.45GHz While the LF, HF and SHF bands are all the same around the globe, for UHF there are differencies between Europe, USA and Japan. The reason are the different operating frequencies for mobile phones in this regions which must not interfere with RFID equipment. Figure 3: Frequency bands for RFID around the globe

4 2. Applications In general, the main purpose and main application area is in logistics. Nowadays the barcode is very popular in this area, for example in supermarkets, warehouses, etc. RFID systems offer a much bigger amout of information to be stored, with the additional advantage of the possibility to be read from distance and bunchwise (saves time). Figure 4: barcode Logistic in warehouses (and supermarkets): If in a warehouse every pallet (or even every product) gets his own tag, it becomes simple for the owner to (coupled to a database) create an inventory list of all the products stored in his warehouse, which can help avoid out of stock -problems. RFID antennas could be placed at the entrance of the warehouse, registering every incoming and outgoing product. In supermarkets it is also possible to tag every product (low price of tags requiered) and simply pass by a so called gate (where the reader antennas are mounted) and register all the products that the customer is going to buy. This would avoid queues in front of the cashpoint and would increase the efficiency. Figure 5: An example for a logistic application in a warehouse Public Transport: RFID systems are already widely used for this purpose, many cities around the globe use RFID in their public transport services to offer the customer the oportunity to pay for the ride easy and fast. As the range in this application is not important (or would be troublesome), exclusively LF or HF tags are used. In 2007 already 300 billion tags were in use, with growing tendency.

5 Figure 6: Application: Public Transport Animal identification management: This is one of the oldest uses of RFID technology, it gives the farmer the opportunity to get easily information about his cattle. The idea is to attach a tag to each one of the animals (mostly as an ear-tag). The tag can identify the cow and store additional information such as date of birth, weight, etc. Figure 7: Application Animal identification Identification and tracking of pharmaceutical products: An UID (unique identification number) allows verification and tracking (owner, destination, package, ) of the product from its manufactoring to its destiny and makes it much more difficult to steal products out of the supply chain by replacing it with placebo medicaments. Electronic passport (Biometric passport): Representative for many possible applications of human identification a already used application of RFID is the Electronic passport. The first country in installing this system was Malaysia in 1998, in Europe it has been installed from 2005 on. In 2008 already 300 million tags were sold. Figure 8: Electronic (biometric) passport

6 The image above shows the countries in which the electronic passport is already in use (green). The countries filled with yellow color use this type of passport just for diplomats and countries in grey don't use it. Vehicle Identification: A application field of SHF-tags is vehicle identification. The tag works as a electronic licence plate of a car. By passing the reader system (which can be installed for example at toll stations or on-ramps) the car or truck is identified. Possible applications can be: Admission control Road charge systems Speed measurement (section control) Figure 9: Inner city road charge system Access control: An also already well-used application is access control for humans based on RFID. The kind of admission can be access to a room/building or also access control of vehicles, such as anti-theft devices in cars.

7 Figure 10: Applications: Access control

8 3. LF Low frequencies RFID The LF tag was the first RFID invention and is nowadays worldwide regulated and implemented into the laws of each country. The standard you have to use for a Reader - Tag communication depends on what you want to do with the tag, so: ISO 11784/85: for Read-Only ISO 14223/1: Read/Write ISO : Item Management The operating frequency is normally 125, respectivamente 134KHz. Normally there are strict regulations by law but for this frequencies it is much more rare to disturb components of other frequency bands. Low- and high-frequency tags use inductive coupling. Essentially, a coil in the reader antenna and a coil in the tag antenna form an electromagnetic field. The tag draws power from the field, uses the power to run the circuitry on the chip and then changes the electric load on the antenna. The reader antenna senses the change in the magnetic field and converts these changes into the ones and zeros. Because the coil in the tag antenna and the coil in the reader antenna must form a magnetic field, the tag must be fairly close to the reader antenna, which limits the read range of these systems. Fig. 11: Inductive Coupling in Near Field between a Reader and a Transponder So with the magnetic field a voltage with a certain value is induced in the transponder (law of induction): whereas: ω = 2*Π*f... whereas f en LF is either 125kHz or 134kHz Ф 0... magnetic flux Considering that we will not take care of the time shift that comes from the cosine and the magnetic flux can also be represented by following equation:

9 we can obtain a fixed value for the voltage: But how is the answer of the transponder acomplished? Well this is made with the so called load modulation. It is a form of an extern modulation which occur when the magnetic moment of the transponder causes changes in the feedback of the reader antenna. So it can be compared with the reception of an electromagnetic wave with fc +/- fsc (whereas fc is the carrier and fsc the subcarrier frequency. Fig. 12: Creating the answer of the transponder Now we want to look at the procedure of talking between the Transceiver and the Transponder when there is a magnetic field:

10 Fig. 13: Establishement of a communication between a Transponder and a Reader Phase A: Reader recognizes the data answer with standard ISO11785 from the transponder. Because of certain received bits, the Reader knows that the Transponder is an advanced one. Phase B: Reader switches the H-field for more than 5 ms off to make a RESET in the Transponder (HDX is Tag-Form, ADV-advanced... nochmal nachschaun) Phase C: Reader sends either a command called SOF which signals the transponder a positive request or a command so the transponder switches into his advanced mode. Phase D: Read / Write or Inventory-Operation in Advanced Mode. Phase E: After all procedures, the Reader switches the H-field again for more than 5ms off and starts a search for new added Transponders (Polling) Advantages: there are nearly no regulations by law are very reliable when used in short range there is nearly no attenuation through water, aluminium or wood Disadvantages: huge problems occur when tag is used in environments like steel or iron need of huge antennas (in contrary to the size of the tag) just for short range the transponder is much thicker, expensive and more complex than in systems RFID-HF Typical applications: animal identification access control, for example music concerts RFID chips to measure the competition time in sport events tool identification poker chips

11 4. HF High frequencies RFID The HF tecnology can be considered as a further developement of the LF technique. The main difference lays in the frequency band. For HF technique is a frequency equal to 13.56MHz used. Until recently many countries had different law regulations but with the further developement and years of using HF readers and transponders, now it has worldwide the same regulations. It is distinguished whether you want to use HF tags with a read range up to 10 cm or up to 1.3m. The first one is called Vicinity (reader) and the last one Proximity. So there are following standards: ISO Proximity Card ISO Vicinity Card ISO Item Management HF EPC Gen2 Why would someone want a transponder with a very low read range? Simply said sometimes you have a RFID chip which transmits sensible data and you do not want to have other people getting this data. An example would be your passport or your ID-card which are holding sensible information. Advantages: the antenna is more simple than the LF antenna and therefore much cheaper it is possible to create thinner Tags the data rate is much higher than for LF tags just light attenuation en water and textiles Disadvantages: like for LF there is the problem with metal environments read range just up to 1.3m Typical applications: Health care

12 smart cards ticketing library 5. UHF Ultra high frequencies RFID Whereas LF / HF tags use the principal of inductive coupling, UHF tags are using the principe of electromagnetic wave propagation and are operating in a frequency range of MHz. The exact frequency depends on the country in which you want to use the tag: Fig. 14: Frequency regulations for the use of UHF tags worldwide However the standards are worldwide equal and are defined in: ISO Item Management EPC Class I Gen2

13 Fig. 15: Evolution of protocolls for the use of UHF tags Like we mentioned before for HF tags, there are also two different types of UHF tags depending on the reading range. In contrast they are not completely different but rather there is a difference in whether you are using the near or the far field of the radiated electromagnetic field. So you can read tags up to a distance of 7m when using the far field but just 10cm if you are using the near field. But how is a communication between the reader and the tag (and viceversa) established? Reader to Tag (Transponder) Communication: The Reader can send more or less two starting signals. The first one is to start a new inventory round. So with this command he is able to find new tags respectivamente to send a query-command to all tags in his inventory list: Fig. 16: Data transmitted by the reader for searching new tags Where Tari a logical 1 and the return to 0 significate. For all other signals will be the first frame a short syncronisation frame:

14 Fig. 17: syncronization frame For a Multireader environment exist beside the law regulations a transmission mask: Fig. 18: Transmission mask for multireader environment Tag to Reader Communication: There is a principle of electromagnetic theory, the principle of reciprocity, which say that any structure that receives a wave can also transmit a wave. The radiated wave can make its way back to the transmitting antenna, induce a voltage, and therefore, produce a signal that can be detected. This is called a backscattered signal. The UHF reader transmits a continous, constant modulated signal which provides not only the power for the transponder as well as the back-modulation of the data. Additionaly defines this signal the reference clock for the backtransmission. To transmit a binary "0", the transponder switches his antenna to absorption. So the Reader will not receive any reflection. To transmit a binary "1", the transponder switches his antenna to reflection. The Reader will now definitely receive an answer whereas the propagation time of the signal is not important. The cause for this is that the Reader transmits a constant signal which is not depending on the elapsed time. This procedure is shown in the following pictures:

15 Fig. 19: backscattered signal at time T 1 Fig. 20: backscattered signal at time T 2 Interferences: This topic is way more important than in the RF / HF area. UHF uses electromagnetic waves and those can be amplified when there is a metal environment and constructive interference occur. For a complete list, see: Absorption / Attenuation: absorbing materials are influencing the reading range of a transponder. Water is very strong absorbing UHF radiation and so it is advisable to avoid any contact Reflections: Electromagnetic waves can be reflected for example on metal, water and concrete and can occur severe behaviour. Constructive Interference leads to overrange whereas destructive Interference leads to leaks in supply. Diffractions Refractions: If the relative permitivity coefficient between 2 medias is different, the wave might change direction Fluids: The observed influence depends on the electrical conductivity. Water has a high electrical conductivity and will absorbe and reflect electromagentic waves Polarisation Advantages: only system for ranges more than 1.5m metal environment can be positive for the field (constructive interference) smaller inlays support high data rates

16 Disadvantages: variability of power complicated chips operating frequency is in the same range as the operating frequency of mobile phones nearly totally absorbed by water Typical applications: logistics, warehouse container management Airline baggage 6. Controversy There are many concerns about the wide spread use of RFID technology within the society. Critics argue that due to the small dimensions of RFID tags, people won't be even aware of the presence of such a tag or won't be able to remove it from a purchased item. Especially in the UHF and SHF case where tags can be read from distance the discussion is held very polemically. One of the main fears is related to privacy in general, to be tracked wherever a person goes or to collect information about buying behavior, property, etc. Another criticised point is tags remain functional after the purchase of the product, so critics claim that a possible scenario would be that for a example a thief could scan a house with a handheld scanner and figure out this way if it would pay off to rob a house. A possible offered solution is the so called clipped tag, designed to increase consumer privacy. The consumer can tear of a part of the tag, transforming it from a long-range- into a proximity-tag which just can be read from a distance of a few centimeters. The remaining proximity-tag function it could be used later for possible returns or recalls. A more realistic scenario is that, given the case of RFID in supermarkets, companies could tie every sold product to the customer. This is only possible if the purchaser pays using his credit card or show his loyalty card. As mentioned before, the whole discussion is very polemically and in certain cases critics contain even partially false information, like that a thief could achieve a complete inventory list of a house from outside, even if the tags in the house are LF types, just by using a high-gain antenna. Although it would be possible induce enough energy in the tags to wake them up, it is simply impossible that the reader could recognize and treat the responses of the tags, given the distance and the resulting SNR.

17 Figure 21: Logo of the anti-rfid campaign by German privacy group FoeBuD 7. Resumen RFID can be a very useful technology and will or is already replacing the barcode in many applications. The possibilty of both contactless reading and writing is a great advantage of this technology, followed by the increased amount of storable data. The disadvange of a higher price with respect to the barcode can in a few applications be compensated by reusing the tags, though the price of the tags is a very critically point of this technology. That, from the security point of view, data can be read by any (equal) RFID system is another disadvantage, which has to be mentioned. Trends in RFID technology: In the last years along with the increasing use of RFID systems came decreasing prices for the necessary equipment in general and tags in particular, so RFID is increasingly prevalent. For example, Envego announced a price of 5.9 cents per tag and in March 2010 a Korean laboratory announced that they would be able to offer a price of 3 cents per tag by late At the same time, tags and readers became better and more efficient in terms of read range and, even more important, read rate. Sales worldwide In 2007 RFID sales around the world hit the 5 billion $ mark, a number pushed by a 2 billion $ investment of China establishing their national ID card based on RFID. This number even increased in 2008 when sales worth 5.3 billion $ were recorded, topped once more in 2009 with 5.56 billion $.

18 Fuentes Texas Instruments, M. Gebhart, RFID Systems, Second Edition, 2009