Radio Frequency Identification System

Positioning and Remote Sensing M Ing. Enrico Tarantino [email protected]

Introduction (1/3) ◊

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Radio Systems for Automatic Data Collection = TLC systems that can provide information on an object by means of radio communication between a transponder and physically associated with the object containing the information about it and Interrogator-Receiver must acquire them; Communication system consisting essentially of 4 macroblocks: a. The Interrogator-Receiver; the transponder; the radio interface; IT infrastructure that manages the interaction

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Note: Radio-communication -> Contactless -> "read" potentially possible even in the absence of direct visibility between devices;

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"Cooperative Systems" means the acquisition and transfer of information occurs through the interaction of devices

Introduction (2/3) ◊

The 'Interrogator-Receiver typically incorporates a module for the received radio frequency transmission, a control unit and a "coupling element" (element coupling o coupling unit) al Transponder;

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The transponder is almost always consists of a coupling element interrogator and device control, processing and memory required to process commands received from the reader and for their implementation; In many cases, the coupling element comprises a receive antenna for the transmission of EM waves

Introduction (3/3) ◊

In most applications, the transponder does not have any power / autonomy to operate any transmission that must somehow be authorized (the transponder must be "enabled" from the interrogator by means of an appropriate signal "query"); In summary, the main function of the tag is to transmit their data to answer the question made ​by the player. In general, the transponder is required, the following functional capabilities: - receipt / activation; - reception / demodulation; - modulation; - transmission;

Classification ◊

passive transponders:  have no battery or other power source directly. Are then fed through the interrogator that not only active coupling mechanism and enables the transponder but also provides the energy needed to perform the modulation and transmission;

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semi-passive transponder (semi-active): have a battery that provides power to the power of memory and the modulation performed by its control logic. The energy required to transmit the signal from the interrogator continues to be provided by means of the coupling mechanism;

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active transponders: have a real transmitter / receiver radio and a battery that provides power to both the memory is to provide the energy needed to modulation and transmission. Transponders are active then "self" and potentially capable of independent transmissions from interrogation by the reader.

Examples ◊

Radio Frequency Identification (RFID) - passive systems in most cases Automatic debiting systems and access control (Telepass) - semi-passive; Secondary Radar (SSR) - active system

Radio Frequency Identification (RFID)

RFID - Introduction ◊

In the RFID, the Interrogator is commonly called a reader (Reader), while the transponder is often referred to as "tags" or "Smart Label";

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Technology has long used low-frequency (HF - 13.56 MHz) in a number of short-range applications (eg anti-theft systems in shops and businesses);

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The recent standardization of RFID systems operating in the UHF band (~ 870 MHz) has amplified the interest in RFID technology, as increased operating frequency allows (at least in theory) more reading distances and speed of data transfer;

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Alternative / complementary to the barcode, against which the "reading" can take place even in the absence of visibility between devices;

RFID classification Different possible classification methods: a. Transponder alimentation ▪ Passiv ; ▪ semi-passiv (or semi-active) ▪ active; b. principle of operation


inductive coupling;
EM backscatter modulation;
… c. operative frequencies
Low Frequency (LF);
High Frequency (HF);
Ultra High Frequency (UHF);
Microonde (µW); d. range (close coupling, remote coupling, long range) e. Memoriy (1 bit / n bits, read-only / re-writeble, …) f. ……

Principle of operation (1/2) Given a source that generates and sustains an EM field of frequency f, we identify the following regions of space: : 1. “far field region”: r >> λ ; r >> D ; r >> 2D2/ λ 2. “near field region” : r ≤ λ The electromagnetic field is presented and an EM wave propagates as usually spherical, non-uniform, locally flat (radiation field) ◊

The EM field has the characteristics of a field "static" -> the near-field coincides with the static field "instantaneously", ie generated by the instantaneous value of the source

The total EM field is always the sum of two contributions, a radiation and a static type. However, in the far field region of the former shall prevail, and prevail in the near field region of the second

Principle of operation (2/2) In accordance with the principle of operation, the RFID systems can be divided into 2 main categories: 1. Inductively coupled systems: communication between Tag and Reader takes place in the near field region, and therefore does not exploit any EM wave propagation. The interaction between the devices is usually due to inductive coupling to the magnetic field. The coupling element consists of a coil with a suitable number of windings

2. EM propagation systems: communication between Tag and Reader takes place in the far field region and thus through the propagation of EM waves. The coupling element comprises a receive antenna for the transmission of EM waves

Inductively coupled systems ◊ time-varying magnetic field generated by the reader induces (1) a voltage (and current) to the terminals of the tag, and so provides the energy needed to power the memory and logic attached (if passive); ◊ Tagged by the current path in turn generates a magnetic field induction (1) is to alter the voltage at the terminals of the Reader, this change is detected by the reader and thus so is the interaction between devices; ◊ information transfer is often done by means of the so-called load modulation: the internal logic to tag produces a change in the load terminals of the coil between two distinct values ZL1 and ZL2 (according to the

sequence to be transmitted) -> this change affects the current in the loop -> field H -> on the induced voltage at the terminals of the Reader, which thus receives the bits stored in the Tag (1)

Faraday’s law

Example: Anti-Theft RFID Systems ◊

The most famous (and most common) application of inductively coupled RFID is probably represented by the anti-theft systems in shops of goods;

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The tag stores a single bit (with values ​1 and 0 states are "ON" and "OFF");

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When the reader finds his range of action in the presence of a "Tag On" the alarm, as if the payment tag is set to OFF (or removed).

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Usual operation of inductively coupled is at 13.56 MHz

Electronic Article Surveillance

EM propagation systems ◊ Reader radiates a signal "interrogation" is received by the radio frequency tags and used (in part) to power memory and logic attached (if passive);

◊ Part of the energy supplied by the signal instead of the query is re-radiated (backscattered) toward the reader in ways that depend on the properties of radiation of the antenna of tag (1). The reader receives the signal transmitted by the transponder and thus brings about the interaction between the devices (if passive and semi-passive); ◊ The transfer of information is usually by means of the so-called load

modulation (the variation of load impedance to the antenna terminals of the values ​and ZL1 ZL2 affects the EM field re-radiated -> signal on the terminals of the Reader, that in thus receives the bits stored in the Tag (1)

Radar’s principle

operative frequecies ◊

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The operating frequency is by definition the transmission frequency of the reader (which may not coincide with that used by the Tag for the transmission of data); The process of international standardization has occurred in recent planned operation in the following main bands (Italy): a. LF: 120 ÷ 145 kHz d. (UHF “alta”): near 2.45 GHz b. HF: 13.56 MHz; e. (5.4 ÷ 5.9 GHz) c. UHF: 865 ÷ 870 MHz; f. near 24.125 GHz Each band is regulated by one or more standards, despite the recent integration between ISO 18000-6 and EPC Global Gen 2 (07/06), still sometimes differences between various countries and geographic areas, which is an obstacle to the widespread diffusion of technology.

RFId in LF band Frequency: 125 kHz & 134.2 kHz Standard: ISO 18000-2 Coupling: inductive (magnetic ) Alimentation: mainly passiv tag Read Range: usually additional distortion and weakening of the signal; Obstruction of the wireless link => Additional weakening of the signal; EM coupling phenomena with nearby objects and / or other Tags => unexpected changes in the parameters of the tag antenna (impedance, efficiency, radiation digraph)

data in VDD

data out

Digital Section (Control logic & memory)

Multipath ◊

The increase in frequency (from HF to UHF), however, determines the onset of all the problems of the propagation of radio frequency (albeit in a restricted environment), thus increasing the criticality of the systems because of greater sensitivity to the characteristics of 'operating environment; The presence of objects and / or obstacles in the vicinity of the device generates the phenomenon of multiple paths (multipath): radiated signal to the receiver that comes in different replicas (or echoes), each characterized by a different propagation path length and number and type of interactions with the environment (reflections, diffractions, transmission, etc.). The feedback received from different paths interfere with each other and can therefore significantly affect the received power (and more generally distort the waveform actually received) compared to the ideal case in which the only contribution is received "direct"

EM coupling ◊

objects in the immediate vicinity of the tag can determine EM coupling phenomena can also significantly affect efficiency (δ) and antenna impedance (Z) compared with the project -> variations ρT, ρS and m and can lead to performance degradation the system; the magnitude of the coupling depends on the distance but also the shape and EM properties of the object (material); water and metals are particularly critical for systems in the UHF band;

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EM coupling problem affects virtually all systems of TLC, but if RFID is particularly critical because it plausible that the identified object (to which the tag is physically associated) is necessarily in close contact (or almost) with the transponder

Em analysis ◊

In the presence of EM coupling phenomena effective impedance of the antenna of tag can therefore only be assessed through numerical analysis by means of a suitable electromagnetic simulator

Some results PSK (m=0.8)

Free Space

Real Case

Life Cycle & Privacy The life cycle of the tag often exceeds, by far, one of the objects to which they are associated. Especially the passive tags, it does not require batteries, have theoretically infinite life expectancy. => Possibility to continue for some time to interrogate the objects in the possession of private owners, drawing from this information on the habits of the owners themselves. RFID and privacy: type applications related to ILT (item level tagging), or to tag applications to individual articles of consumption and usual objects in private hands (or access to payment cards, electronic equipment, tickets, etc..). Potential threat: improper acquisition of information on the end user. Possible solution: ability to permanently disable the tag at the end of the distribution chain, or when objects are in the possession of the end user => Killing In Italy: the Authority for the Protection of Personal Data has issued an order: Guarantees for the use of "smart labels" (RFID) - 09/03/05, defining measures to make the processing of personal data in 'field of RFID systems in accordance with the provisions in force.

Security The electronic tags have been created for an automatic acquisition => acritical Viable operations on sensitive data (hacking): fraudulently acquire alteration destruction

• tracking illegal Cloning or theft of ID Violation of privacy

Easy operation by the use of technologies that do not require physical contact, or the visibility of the equipment Efficient solutions: killing: Disabling the final tag so that it can not be read (all tags recognize the command last generation killing) cloaking: we adopt measures that can be detected only a Tag Reader and appears instead to be determined "in disguise", hidden from all other encryption methods (creation of a 'secure channel') => encryption / authentication

Application (1/2) ◊

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SmartWear Tech. (San Diego, CA) has introduced two new products designed to give parents additional protection against child abduction and to aid in recovery of missing children. Use of RFID transponders sewn into clothing (2.4 GHz) The company’s first products incorporate RFID tags embedded in clothing of children, which allow parents to monitor the child’s whereabouts and trigger an alarm if the child leaves a designated area or crosses a boundary Readers would be placed strategically at doors, windows or gates and the system could be programmed to respond if the child moves out of a designated area Knowing combine "creativity" and technical expertise, RFID lends itself to many possible applications

Application (2/2) •Access control: the reader near the door recognizes the ID tags worn by employees, enabling the opening of the door Tracking of goods or products: we monitored the movement of goods (by means of suitable reading gate) along the distribution chain and / or production in order to identify any inefficiencies in the system (eg postal system) Identification: the presence is detected and the location of an object by detecting the associated tags (eg identification fleet) Health care: the patient is fitted with a bracelet (wristband) on which can be transcribed medical records to keep track of personal data, treatment, doses Retailing: all items for sale are labeled with tags (Item Level Tagging - ILT) containing the information of the price, which is transferred to the reader

Conclusion ◊

RFID technology is very flexible which lends itself to a variety of interesting applications; There are many applications for inductive coupling, however, limited by the limited read range (1 to 2 m at most); Extension / standardization of the operating frequency in the UHF band "promises" marked increase in reading distance -> very interesting and strong attention to studies and experiments on these systems Problems in the real environment mainly due to multipath and coupling EM -> research and development of innovative applications and solutions that such promises can be effectively maintained