Help for Beginners Radio Tags
|Introduction||Tags||Hardware||Application||RFID or Barcode?|
Radio frequency identification (RFID) first appeared in tracking and security applications during the 1980s, and is now a major growth area in the field of automatic identification and data capture (AIDC).
There are three main elements to an RFID system; the radio tag, the scanner and the scanning antenna. RF tags are small electronic / radio circuits programmed to have a unique identity. They are attached to or embedded in the item to be tracked. The scanner system includes an antenna that emits radio signals to activate and communicate with the tag.
The tags and scanner are designed to communicate at a certain radio frequency and within a certain power level. When the two are within range the scanner will interrogate the contents of the tag's memory and (in most cases) it can add to, or modify the stored data. This gives it a distinct advantage over a bar code, where the data remains fixed. It can therefore be used to record the service history of an item, for example.
The read / write process is very quick, typically less than a hundredth of a second. This means effectively the scanner can interrogate and write to many tags within its proximity at the same time. The interrogation process is non-contact. RFID is therefore suitable for use in very harsh environments (where for example bar code labels would not be practical) or applications where moving objects need to be tracked.
There are almost as many different types of tags available as there are applications and many RFID manufacturers produce proprietary equipment. New global standards for tag systems are slowly emerging, but if you need RFID technology now you may need to opt for a proprietary system and the long term risks that may be associated with it.
Whilst still relatively new, the technology is RFID has established itself in a wide range of markets including livestock identification, container tracking and automated vehicle identification (AVI). Synergix has expertise in RFID and supplies RF tag solutions; but because of the diversity of standards, tags and readers we do not generally stock this type of equipment. We strongly recommend our consultancy services if you are considering RFID. Our Milestones to a successful solutions section will give you an outline of the important stages that you must go through when implementing this technology.
There are passive tags and active tags. Passive tags are essentially a silicon chip and a small radio antenna. The circuitry only operates when the tag is within range of the radio signal generated by the scanner. The electromagnetic field of the radio signal provides sufficient power to drive the tag. They can be very small (built into an identification label for example) and effectively have an unlimited operational life. Active tags are the same as passive tags with the addition of some power supply circuitry or a power source and sometimes more memory. They generate a more powerful radio signal and therefore can be interrogated over a longer range. However they are bigger, heavier, more expensive, and in most cases have a limited operational life.
There are read only tags and read/write tags. Read-only tags are typically passive and are programmed with a unique ID (usually 32 to 128 bits) that cannot be modified. They are mainly used as a reference key to a database record, in the same way as linear barcodes reference a database containing modifiable product-specific information.
Tags come in a wide variety of shapes and sizes. Animal tracking tags, inserted beneath the skin, can be as small as a pencil lead in diameter and 1 cm in length. Tags can be screw-shaped to identify trees or wooden items, or credit-card shaped for use in access control applications. The anti-theft hard plastic tags attached to merchandise in stores are RFID tags. Heavy duty 12 by 10 by 5 cm rectangular tags are used to track containers or heavy machinery, trucks, and railroad cars for maintenance and tracking applications.
Tags have several key characteristics that affect how and where they are used.
- Active / passive - active tags operate over longer range but require a power source. Passive tags derive their power from the radio signal of the scanning device.
- Data storage capacity - from a few bytes to (at the time of writing) 64K bits.
- Data transfer rate - generally speaking, the higher the carrier frequency the higher the data transfer rate.
- Range - from close proximity to tens of metres.
- Enclosure - a wide range of packaging is available, often specific to a particular application.
- Cost - both of the tag and the scanning equipment.
Antennas are available in a variety of shapes and sizes; they can be built into a door frame to receive tag data from persons or things passing through the door, or mounted on in a toll gate to monitor traffic passing through on a motorway.
The scanner (or 'Reader' or 'Interrogator') can be either a handheld or a fixed-mount device. It emits radio waves over a range anywhere from 1cm to tens of metres, depending upon its power output and the radio frequency used. When an RFID tag passes through the electromagnetic zone, it detects the reader's activation signal. The reader decodes the data encoded in the tag's integrated circuit (silicon chip) and the data is passed to the host computer for processing.
RFID systems operate on a wide range of frequencies. Low-frequency (30 KHz to 500 KHz) systems have short reading ranges and lower system costs. They are most commonly used in security access, asset tracking, and animal identification applications. Intermediate frequency (10 - 15MHz) systems are still relatively inexpensive, with quite high reading speeds, and are used in smart cards for access control. High-frequency (850 MHz to 950 MHz and 2.4 GHz to 2.5 GHz) systems, offering long read ranges (greater than 20m) and high reading speeds, are used for applications such as automated toll collection. However, the higher performance of high-frequency RFID systems incurs higher system costs.
Here are some typical applications where RFID technology has been successfully introduced.
- Electronic article surveillance - clothing retail outlets being typical.
- Protection of valuable equipment against theft, unauthorised removal or asset management.
- Controlled access to vehicles, parking areas and fuel facilities - depot facilities being typical.
- Automated toll collection for roads and bridges - since the 1980s, electronic Road-Pricing (ERP) systems have been used in Hong Kong.
- Controlled access of personnel to secure or hazardous locations.
- Time and attendance - to replace conventional "slot card" time keeping systems.
- Animal husbandry - for identification in support of individualised feeding programmes.
- Automatic identification of tools in numerically controlled machines - to facilitate condition monitoring of tools, for use in managing tool usage and minimising waste due to excessive machine tool wear.
- Identification of product variants and process control in flexible manufacture systems.
- Sport time recording.
- Electronic monitoring of offenders at home.
- Vehicle anti-theft systems and car immobiliser.
RFID and bar code are complementary technologies. Despite exaggerated claims in the press, one will not replace the other.
Whilst the cost of tags is falling (currently £0.50 to £20, depending on type, packaging and quantity) they remain significantly more expensive than a barcode label. This tends to limit them to applications where they are used repeatedly, and where the item has a relatively high value - tracking beer kegs for example.
The significant advantage of all types of RFID systems is the non-contact, non-line-of-sight nature of the technology. Tags can be read through a variety of substances such as snow, fog, ice, paint, crusted grime, and other visually and environmentally challenging conditions, where barcodes or other optically read technologies would be useless.
The read/write capability of an active RFID system is a significant advantage in interactive applications such as work-in-process or maintenance tracking, where the information in the tag can be continually upgated.
The scanning equipment also tends to be more expensive than the barcode equivalent. Hybrid scanners are now available to work with both technologies. Tag scanning can be less intrusive than barcode scanning, it is often used for access control where the antenna forms part of a gate. We are all familiar with the security gates used be retailers, where crude tags attached to high value items will operate an alarm during an attempted theft.
Developments in RFID technology continue to yield larger memory capacities, wider reading ranges, and faster processing. It is highly unlikely that the technology will ultimately replace barcode - even with the inevitable reduction in raw materials coupled with economies of scale, the integrated circuit in an RF tag will never be as cost-effective as a barcode label