4. AC motors starting and protection
6.7 RFID -Radio Frequency IDentification- detection
6 - Data acquisition:
detection
6.7 RFID -Radio Frequency IDentification- detection
This section describes devices that use a radio frequency signal to store and use data in electronic tags.
b Overview
Radio Frequency IDentification (RFID) is a fairly recent automatic identification technology designed for applications requiring the tracking of objects or persons (traceability, access control, sorting, storage).
It works on the principle of linking each object to a remotely accessible read/write storage capacity.
The data are stored in a memory accessed via a simple radio frequency link requiring no contact or field of vision, at a distance ranging from a few cm to several metres. This memory takes the form of an electronic tag, otherwise known as a transponder (TRANSmitter + resPONDER), containing an electronic circuit and an antenna.
b Operating principles
A RFID system consists of the following components (CFig.27 and 28):
- An electronic tag,
- A read/write station (or RFID reader).
v The reader
Modulates the amplitude of the field radiated by its antenna to transmit read or write commands to the tag processing logic. Simultaneously, the electromagnetic field generated by its antenna powers the electronic circuit in the tag.
v Tag
This feeds back its information to the reader antenna by modulating its own consumption. The reader reception circuit detects the modulation and converts it into digital signals (CFig.29).
b Description of components v Electronic tags
Electronic tags consist of three main components inside a casing.
• Antenna (CFig.30):
This must be adjusted to the frequency of the carrier and so can take several forms:
- coil of copper wire, with or without a ferrite core (channelling of field lines), or etched on a flexible or rigid printed circuit, or printed (with conductive ink) for frequencies of less than 20MHz;
- dipole etched onto a printed circuit, or printed (with conductive ink) for very high frequencies (>800MHz).
AFig. 28 View of components in a RFID system (Telemecanique Inductel system)
AFig. 30 Inside of an RFID tag AFig. 29 Operation of a RFID system AFig. 27 Layout of a RFID system
6.7 RFID -Radio Frequency IDentification- detection
6 - Data acquisition:
detection
• Logical processing circuit
This acts as an interface between the commands received by the antenna and the memory.
Its complexity depends on the application and can range from simple shaping to the use of a microcontroller (e.g. payment cards secured by encryption algorithms).
• Memory
Several types of memory are used to store data in electronic tags (CFig.31).
“Active” tags contain a battery to power their electronic components. This configuration increases the dialogue distance between the tag and the antenna but requires regular replacement of the battery.
v Casing
Casings have been designed for each type of application to group and protect the three active components of a tag: (CFig.32a)
- credit card in badge format to control human access, - adhesive support for identification of library books,
- glass tube, for identification of pets (injected under the skin with a syringe),
- plastic “buttons”, for identification of clothing and laundry, - label for mail tracking.
There are many other formats, including: key ring, plastic “nails” to identify wooden pallets, shockproof and chemical-resistant casings for industrial applications (surface treatment, furnaces, etc.) (CFig.32b).
v Stations
A station (CFig.33a)acts as an interface between the control system (PLC, computer, etc.) and the electronic tag via an appropriate communication port (RS232, RS485, Ethernet, etc.).
It can also include a number of auxiliary functions suited to the particular
6
AFig. 31 Storage capacities range from a few bytes to several dozen kilobytes
AFig. 32 a et b a - RFID formats designed for different uses
b - RFID industrial
(Telemecanique Inductel)
Type Advantages Disadvantages
ROM • Good resistance to high temperatures • Read only
• Inexpensive
EEPROM • No battery or backup battery • Fairly long read/write access time
• Number of write operations limited to 100,000 cycles per byte
RAM • Fast data access • Need for backup battery built into tag
• High capacity
FeRAM • Fast data access • Number of write operations limited to 1012 (ferroelectric) • No battery or backup battery
• High capacity
a b
6.7 RFID -Radio Frequency IDentification- detection
6 - Data acquisition:
detection
v Antennas
Antennas are characterised by their size (which determines the shape of the zone where they can exchange information with the tags) and the frequency of the radiated field. Ferrite cores are used to concentrate the electromagnetic field lines to increase the reading distance (CFig.34) and reduce the influence of any metal bodies in the vicinity of the antenna.
The frequencies used by the antennas cover several distinct bands, all of which have advantages and disadvantages (CFig.35).
AFig. 34 Influence of a ferrite antenna on electromagnetic field lines
Power ratings and frequencies used vary with the applications and countries. There are three major zones: North America, Europe and Rest of World. Each zone and each frequency has an authorised emission spectrum range (CISPR standard 300330) within which every RFID station/antenna must operate.
v Codes and protocols
The exchange protocols between stations and tags are defined by international standards (ISO 15693 – ISO 14443 A/B).
More specialised standards are in the definition process, such as those intended for mass retailing (EPC - Electronic Product Code) or
identification of animals (ISO 11784).
b Advantages of RFID
Compared to barcode systems (labels or marks and readers), RFID has the following advantages:
- data in the tag can be modified,
- read/write access through most non-metallic materials, - insensitive to dust, soiling, etc.,
- several thousand characters can be recorded in a tag, - data confidentiality (tag data access lock).
These advantages all contribute to its development in the service sector (e.g. ski run access control) and retailing.
Furthermore, the ongoing fall in the cost of RFID tags will probably result in their replacing conventional barcodes on containers (boxes, parcels, baggage) in logistics and transport and also on products in the industrial manufacturing process.
It should be noted however that the appealing idea of using these systems for automatic identification of trolley contents without having to unload them at supermarket checkouts is not yet feasible for physical and technical reasons.
Frequency Advantages Disadvantages Typical applications
125-134 khz (LF) • Immune to the environment • Small storage capacity • Identification of pets (metal, water, etc.) • Long access time
13.56 Mhz (HF) • Standard antenna/tag dialogue • Sensitive to metallic environments • Library book tracking
protocols (ISO 15693 - • Access control
ISO 14443 A/B) • Payment systems
850 - 950 Mhz (UHF) • Very low-cost tags • Frequency ranges differ • Product control in retailing
• Long dialogue range (several metres) with the country
• Interference in dialogue zones caused by obstacles (metal, water, etc.)
2.45 Ghz ) • Very high speed of transfer between • “Dips” that are hard to control in • Vehicle tracking
(microwaves) tag and antenna the dialogue zone (motorway tollgates)
• Long dialogue range • Cost of reading systems (several metres)
AFig. 35 Description of frequency bands used in RFID