RFID Technology Survey
RFID Tags
RFID tags come in three general varieties: passive, active, or semi-passive (also known as battery-assisted). Passive tags require no internal power source, thus being pure passive devices (they are only active when a reader is nearby to power them), whereas semi-passive and active tags require a power source, usually a small battery.
Passive
Passive Tag
The passive tags do not have internal power source, they consist of a circuit CMOS and an antenna.The tags are activated by an electromagnetic signal of a reader that gives energy to the CMOS circuit and to the antenna to transmit or receive a data code. Therefore, the signal power of the reader must be strong enough to allow the establishment of communication (backscatter) and the tags must be in an area that is visible by the antenna of the reader. These factors typically constrain passive RFID operation to 5 meters or less, depending on the vendor and frequency of operation, the range may be as short as a few centimeters.
In these days, the passive tags (class 2) have not only an identification code (as old tags class 0 and 1), but also a non-volatile memory EEPROM (Electrically Erasable Programmable Read-Only Memory ) where data can be saved with a capacity form 1 bit up to 1000 bits (128 bytes). Secondly, the size of these tags are increasingly smaller due to the lack of battery; in these days, have a dimension of only a few decimals of millimeters and a thickness in the order of micrometers including the size and the form of the antenna.The passive tags have the most low price of the market, depending the price on the dimension,memory capacity and quantity of tags.The future purpose is to print a RFID tag with a simple printer to make this technology “free”,where everyone can make tags to own application.
The operation frequency of this tags are LF, HF and UHF,according to standard of EPC/ISO (see below the operation frequency).
Active
Active Tag
The tags have an active form-factor and applicability complementing the passive tags, already described. They have a battery and a radio circuit that allows them to transmit their own signal for the reader, that can make an active and continuous communication to the antenna reader with little power,so this way we can have distances in the order of tens of meters. This is the most advantage of this kind of tags, however, this limits the product lifetime, without maintenance of this equipment.
The active tags have other features that passive tags do not allow, these kind of tags can perform monitoring and independent control as a result of having a battery ; they can take initiative in the establishment of communications; they can run diagnoses; have a higher band than other kind of tags and can be equipped with mechanisms that allow them to detect what the best way to communicate. However the active tags have a considerably higher cost and a higher size comparing the passive tags which is certainly, in some cases, a negative factor.
The operation frequency of this tags are UHF and Microwaves ,according to standard of EPC/ISO (see below the operation frequency).
Semi-Passive
These tags are a mix of other two technologies,grouping some advantages and disadvantages. They allow to have ranges in the order tens of meters, as the active tags and they also use a battery power. The main difference to the active tags is related with semi-passive tags can not be always activated,they need to receive an electromagnetic signal from the antenna reader to establish communication (backscatter).These tags are also cheaper than active tags.
Semi-passive tags are far more reliable and have greater ranges than passive tags,but they also have shorter lives, are more fragile,and are significantly more expensive.
In this way, semi-passive tags can be an alternative technology to be used in some applications.
Operation Frequency
RFID is fundamentally based on wireless communication,making use of radio waves which form part of the electromagnetic spectrum( i.e frequencies from 300 Khz to 3 Ghz).It is not unlike two other wireless technologies,WiFi and Bluetooth. RFID operates in unlicensed spectrum space,sometimes referred to an ISM (Industrial,Scientific and Medical) but the exact frequencies that constitute ISM may vary depending on the regulation in different countries.These operations frequencies are generally considered to be organized into four main frequency bands and the next figures shows more common frequencies used and their characteristics for RFID systems.
RFID Frequencies Used and Their Characteristics
 |
 |
Standards
The number and use of standards within RFID and its associated industries is quite complex, involves a number of bodies and is in a process of development. Standards have been produced to cover four key areas of RFID application and use: air interface standards (for basic tag-to-reader data communication), data content and encoding (numbering schemes), conformance (testing of RFID systems) and interoperability between applications and RFID systems.
There are several standards bodies involved in the development and definition of RFID technologies including:
- International Organization of Standardization (ISO)
- EPCglobal Inc
- European Telecommunications Standards Institute (ETSI)
- Federal Communications Commission (FCC)
EPC Standards
The Auto-ID Center was set up in 1999 to develop the Electronic Product Code and related technologies that could be used to identify products and track them through the global supply chain. Its mission was to develop a low-cost RFID system, because the tags needed to be disposable (a manufacturer putting tags on products shipped to a retailer was never going to get those tags back to reuse them). It had to operate in the ultra-high frequency band, because only UHF delivered the read range needed for supply chain applications, such as reading pallets coming through a dock door.
The Auto-ID Center also wanted its RFID system to be global and to be based on open standards. It needed to be global because the aim was to use it to track goods as they flowed from a manufacturer in one country or region to companies in other regions and eventually to store shelves. For Company A to read a tag put on a product by Company B, the tag had to use a standardized air interface protocol. The Auto-ID Center developed its own protocol and licensed it to EPCglobal on the condition that it would be made available royalty-free to manufacturers and end users.
Tags Classes
The Auto-ID Center developed its own UHF protocol. Originally, the center planned to have one protocol that could be used to communicate with different classes of tags. Each successive class of tags would be more sophisticated than the one below it. The classes changed over time, but here is what was originally proposed:
- Class 0 - passive, read-only tag that is programmed at the time the microchip is made.
- Class 1 - passive, read-only backscatter tag with one-time, field-programmable non-volatile memory.
- Class 2 - passive backscatter tag with up to 65 KB of read-write memory.
- Class 3 - semi-passive backscatter tag, with up to 65 KB read-write memory;a Class 2 tag with a built-in battery to support increased read range.
- Class 4 - active that uses a built-in battery to run the microchip's circuitry and to power a transmitter that broadcasts a signal to a reader.
- Class 5 - active RFID tag that can communicate with other Class 5 tags and/or other devices.
Gen 2 Tags
In 2004, EPCglobal began developing a second-generation protocol (Gen 2). The aim was to create a single, global standard that would be more closely aligned with ISO standards, Gen 2 was approved in December 2004. RFID vendors that had worked on the ISO UHF standard also worked on Gen 2.EPC Gen 2 tag features:
- The EPC Gen 2 RFID tags can operate globally in the US, Europe, Japan, Asia in the 860- to 960-MHz UHF band.
- Reading data rates are significantly better in EPC Gen 2 compared with EPC Gen 1. Reading data rates of up to 640 kpbs represent a tenfold increase compared with 60-80 kpbs in EPC Gen 1.
- Compared to EPC class 1 tags, EPC Gen 2 tags can be read about 1,000 tags per second (versus 300 in EPC Gen 1) and be written about 7 tags per second (versus 4 EPC Gen 1).
- EPC Gen 2 RFID tag has a 32bit password versus 8bit in EPC Gen 1.
- EPC Gen 2 RFID tag memory and reading can be password protected.
- Enhanced air protocol security with an encrypted communication between the Reader and the tags.
- EPC Gen 2 RFID tag has a kill feature which cannot be reversed once activated.
- EPC Gen 2 tags are more power efficient meaning they should work better in tougher environments such as with the presence of metal and fluids
ISO Standards
The International Organization for Standardization (ISO) is based in Geneva, and its standards carry the weight of law in some countries. All ISO standards are required to be available for use around the world, so users of ISO RFID standards will not have to worry if their systems comply with the different regulations on frequencies and power output for each country where they do business. The ISO is very active in developing RFID standards for supply chain operations and is nearing completion on multiple standards to identify items and different types of logistics containers.
Air Interface
RFID frequencies are governed by the ISO 18000–RFID Air Interface family of standards, and a complete set of standards was released in September 2004:
- 18000–1 – Generic Parameters for Air Interface Communication for Globally Accepted Frequencies
- 18000-2 - Parameters for Air Interface Communications below 135 KHz
- ISO standard for Low Frequency
- 18000-3 - Parameters for Air Interface Communications at 13.56 MHz
- ISO standard for High Frequency
- Read \ Write capability
- 18000-4 - Parameters for Air Interface Communications at 2.45 GHz
- ISO standard for Microwave Frequency
- Read \ Write capability
- 18000-5 - Parameters for Air Interface Communications at 5.8 GHz
- 18000-6 - Parameters for Air Interface Communications at 860 – 930 MHz
- ISO standard for UHF Frequency
- Read \ Write capability
- 18000-6C - Submitted to EPC GEN 2
- 18000-7 - Parameters for Air Interface Communications at 433.92 MHz
- Manifest tag for Department of Defense (DOD)
Proximity Cards
- ISO 14443 for “proximity” cards and ISO 15693 for “vicinity” cards both recommend 13.56 MHz as its carrier frequency.
- ISO 14443 proximity cards offer a maximum range of only a few inches. It is primarily utilized for financial transactions such as automatic fare collection, bankcard activity and high security applications. These applications prefer a very limited range for security.
- ISO 15693 vicinity cards, or Smart Tags, offer a maximum usable range of out to 28 inches from a single antenna or as much as 4 feet using multiple antenna elements and a high performance reader system.
Animal Identification
- ISO 11748 / 11785: Standard for Animal Identification
Supply Chain
These are used to identify different types of logistics containers and packaging, in addition to individual items.
- ISO 17358 - Application Requirements, including
- ISO 17363 - Freight Containers
- ISO 17364 - Returnable Transport Items
- ISO 17365 - Transport Units
- ISO 17366 - Product Packaging
- ISO 17367 - Product Tagging (DoD)
- ISO 10374.2 - RFID Freight Container Identification
RFID Readers
Reader also known as interrogator transmits energy by electromagnetic waves through their antennas next to a tag, that captures these waves and converts it into energy.This energy is used to transmit back the identity of the tag (stored internally) that is captured by the antennas of the reader, which receives the identification and sends to other systems.
Reader Physical Components
An RFID reader typically contains: a module (transmitter and receiver), a control unit and a coupling element (antenna). The reader has three main functions: energizing, demodulating and decoding. In addition, readers can be fitted with an additional interface that converts the radio waves returned from the RFID tag into a form that can then be passed on to another system, like a computer or any programmable logic controller.
Antenna
The antenna make the connection between readers and tags, allowing communication between both.The functionality of the antennas varies according to the supplier, some use the same antenna to send and to receive information, others use independent antennas. Some readers have only one or two antennas, built-in readers themselves; others may be able to manage multiple antennas in remote locations.
A-Desktop Antenna ------------------- B- HF Antenna ------------------ C- Antennas in portal
Lan Interface
The tags identified and recognized are sent to a network or to others devices, through a variety of interfaces.Examples of common network interfaces are the UART (Universal Asynchronous Receiver / Transmitter) communication serial (RS232 and RS485) and the interface Ethernet to ethernet networks (10 BaseT or 100BaseT). In theses days, more and more readers have also used Bluetooth, Wireless and Zigbee.
Control Unit
The two aforementioned systems are coordinated by a controller, which is able to manage all communication protocol, as well as to manage events, to determine which of the information read in an identifier is an event to be sent to a network or other devices. The controller of a reader can vary from a simple state machine, in a single chip, which can be used to a small internal reader in a phone or in a PDA, to a complete microprocessor which is capable of being used in a operational system network. The logical functions of a controller are: the reader API, the communication system, event management system and the antennas system. Logical functions:
- Reader API - Each Reader has an API that allows to check the status of the reader by the connected applications , to order a list of the read tags, to control the configurations of their physical subsystems (such as power of the antennas, configuration parameters of the network interface).
- Communication System - It is responsible for the communication protocol (Ethernet, Serial, Wireless network, Bluetooth) with the middleware to receive and send the API commands.
- Event Management System - An event is when a tag is detected by the reader. This is responsible for define and filter events that are sent to the middleware.
- Antenna System - It is responsible for protocol and for the logical process of how the readers communicate with tags and control the antennas (physical). The system controls the RF subsystem and implement the configured protocols for communication with the tags.
Types of Readers
The readers, as well as tags, differ in many ways.No reader is perfect for all systems.The readers can have many shapes and sizes, can support different protocols and must often comply with certain regulations, which means they can operate in a zone but not operate in another.
The readers are compatible with certain standards and protocols as well as the identifiers that they read, but some readers may support multiple protocols of identifiers. Some readers only support identifiers manufactured by the same vendor. The most important standards include the ISO and the EPC (Tags Survey-Standards).
Permissible levels of energy, variations in frequency and regulatory requirements vary from region to region, even when applied to the same type of tag. For example, readers UHF EPC read the same identifiers at the frequency of 915Mhz in U.S. and the 869Mhz in Europe due to regulatory restrictions.
The readers size vary from half inch to the size of a computer. These may be inserted in portable devices or even in mobile phones. There are a lot of possibilities for the application of readers, ranging from its attachment on walls of a building until implementation in units of shelves. However, there are some typical applications: portals, tunnels, portable devices and smart shelves.
Portals
A RFID portal is an organization antennas and readers designed to recognize identified items, entering or leaving by a "portal". This type of application may be useful to detect an item by in various sections of a factory, allowing the observation of its pathway. The portals also can be mobile, where the antennas and readers are built in a framework with wheels that can be automatically or manually moved, usually used in loading and unloading of materials for registration.
 |  |  |
Tunnels
It is an application in a tunnel form where the antennas are arranged as a small portal. Generally have electromagnetic isolation, that allow to exist any other antennas and readers in the same area with the assurance that will not occur interference. It is used in packaging and assembly lines.
 |  |  |
Portable Reader
A portable reader with an integrated antenna, a controler and communications could allow examining identified items in situations where it is inconvenient or impossible to move the items to a reader. The use of portable RFID readers is similar to the bar codes portable readers. This type of readers can communicate by Wireless, Ethernet, USB.
 |  |  |
Smart Shelves
it is an interesting application of RFID, they are shelves with built-in antennas so that the detection of identified items with tags is made both in the placement and removal of the objects, like this there is a possibility of keeping inventories in real time.
 |  |  |
