RFID employs Radio Frequency Communications to exchange data between a portable memory device and a host computer or Programmable Logical Controller (PLC). An RFID system typically consists of a Tag or Label containing data storage, an Antenna to communicate with the RFID Tag, and a Controller to manage the communication between the Antenna and the PC or PLC (the terms Reader or Reader/Writer are used when the Antenna and Controller are combined in a single housing).
The RFID Tag/Label is commonly attached to a product carrier, tote or even the product itself, providing a remote database that travels with the product.
RFID Systems Consist of Three Primary Components
- Tags/Labels
- Antennas
- Controllers
- Tag/Label
An RFID Tag/Label contains a coil, a programmed silicon chip and in Active Read/Write systems, a battery.
RFID Tags come in a variety of sizes, memory capacities, temperature survivability and ranges. Tags can be small enough to inject into animals or large enough to cover an entire desktop. Nearly all tags are encapsulated for durability against shock, chemicals, moisture and dirt. While tags are immune to most environmental factors, their Read/Write ranges may be affected by close proximity to metal and electromagnetic radiation.
Tags can be powered by an internal battery (often called an 'Active Tag') or by inductive coupling ('Passive Tag'). Passive Tags have zero maintenance requirements and virtually an unlimited life span. The life span of an Active Tag can be limited by the battery life, although some Tags offer replaceable batteries or extremely large capacity batteries.
Labels have printed, punched, etched or deposited RF coils on a paper/polyester substrate with a memory chip. Although less resistant to environmental conditions than the encapsulated tags, the labels provide distinct low-cost benefits in open-loop (or disposable) applications. If the Label is involved in an open-loop system, it is affixed onto the product itself and is shipped throughout the complete supply chain. The reference to disposability in this application is the fact that when the item is eventually purchased by the consumer (e.g. a PC), it is taken out of the supply chain loop. This is in contrast to reusable Tag applications such as pallet tracking in which the Tag will remain in the supply chain indefinitely. The low cost makes Labels extremely attractive for high-volume applications.
RFID Antennas
An Antenna is a device which uses radio waves to read and write data to the Tags/Labels/PCBs. Some systems use separate Antennas and Controllers, while other systems integrate the Antenna and Controller into a single Reader or Reader/Writer. Antennas can be found in all shapes and sizes, including Antennas which can fit into very tight spaces and larger Antennas for greater read/write ranges. In addition, the Antennas provide unique solution features. One such example is the submersible Antennas used for media disc drive applications. The Antenna is mounted under de-ionized water to read/write data to the Tags while submerged. Other examples include Antennas that offer portals around conveyors or even dock doors. These portals (also called tunnels and gates) read or write to Tags or Labels as they pass through.
RFID System Controllers
The Controller manages the communication interface between an Antenna and a PC, PLC, Server or Network Interface Module.
The host system interfaces with the Controller and directs the interrogation of the Tag via parallel, serial or bus communications. RFID Controllers can also be programmed to perform process control directly from the data in the Tag memory. Some Controllers even feature direct I/O points that can be activated by the Controller, making it possible to lessen the work load of the host system.
Why RFID?
Read-Only
In its simplest form (read-only), RFID is used as a direct replacement for barcode technology. The advantages it offers include 100% read accuracy, the ability to survive demanding environments, and the elimination of line-of-sight requirements.
Read accuracy is often a critical factor in choosing RFID. With fixed position barcode readers, achieving a first-pass read accuracy of 95% to 98 % is normal. Depending on environmental conditions and maintenance, barcode read rates often decline to less than 90% over time. In most environments, RFID can achieve 99.5% to 100% first-pass read rates. Further, with no moving parts or optical components, maintenance is not an issue.
The demands of industrial environments also favor RFID. Some environments require data collection systems to operate while immersed in fluids, chemicals, dirt and heat. Examples include applications where tags and antennas transfer data while completely submerged in water, or even cases where tags pass through paint ovens at 2400C.
The value of RFID is further realized when considering line-of-sight requirements. With RFID, the tag does not have to be visible to the face of the reader. With the ability to penetrate most non-metallic materials (assuming the proper frequency is used), RFID tags can be embedded in totes, containers or even products. Moreover, these containers and products can be sealed in over-pack materials without any adverse effects on the data capture results.
RFID System Performance Criteria
The performance of a Read/Write RFID system is dictated by the following criteria:
Tags' Memory Capacity,
Data Transfer Speed,
Operating Range,
Multiple-Tags-in-Field Capability,
Operating Temperatures,
RF Carrier Frequency of the Tag-to-Antenna Link,
RFID System Connectivity.
RFID Tags' Memory Capacity:
The general rule with any memory based system has always been that no amount of memory is ever sufficient. Invariably, the response to enlarging the memory capacity of a system is to increase the scope of the application so that it requires even more memory. The amount of memory available on Read Only Tags is 20 bits of information. Active Read/Write Tags vary from 64 Bytes to 32KB, meaning that several pages of type-written text can be stored in a Read/Write Tag. This is usually sufficient to carry build manifests and test data, as well as allowing room for system growth. The memory of Passive Read/Write Tags ranges from 48 Bytes to 736 Bytes and provides many distinct benefits over Active Systems.
Data Transfer Speed:
Speed is an important factor for most data capture systems. With today's decreasing production cycle times, the amount of time needed to access or update the RFID pallet identification system must fit within a very small time window. Microwave systems can operate at high speeds, but the concerns inherent in microwave technology can far outweigh any benefits gained from the speed (see below for details).
Read Only Speed - The speed of a Read Only RFID system is dictated by the length of the code, the speed of data transfer from the Tag, the range at which they will operate, the RF carrier frequency of the Tag to Antenna link, and the modulation technique used to transfer data. This speed will vary according to the specific products used in each application. For example a generic Read Only system transmits its data in a 20-bit frame at a rate of 8750 bits per second.
Passive Read/Write Speed - The speed of a Passive Read/Write RFID system is based on the same criteria as Read Only systems, except now one must consider the speed of data transfer both to and from the Tag. Speed will again vary according to the specific products used in each application. For example a generic HS system transfers data at a rate of 1000 bytes per second.
Operating Range:
The Read/Write range for presently available systems varies from less than one inch to over 29 inches; increased Read/Write ranges of up to eight feet using low frequency 13.56Mhz. (Contact an EMS Sales Engineer for further details).
Oftentimes in an RFID application, the need to have long read/write distances can be quickly overcome by choosing the most appropriate Antenna. For instance, the FastTrack Conveyor Antenna is designed to be mounted on a conveyor between the rollers or even in place of the rollers. An RFID Tag can then be mounted on the bottom of a tote, pallet or even the product itself, ensuring the Tag passes directly over the Conveyor Antenna. In this example, read/write range requirements are greatly reduced since the Tag is placed on the bottom of the tote and effortlessly slides over the Conveyor Antenna to achieve 100% reading accuracy each time.
Multiple-Tags-In-Field Capability:
Depending upon the Tag and Antenna configuration, reading and writing data to Multiple-Tags-In-Field is possible with the FastTrack family. The FastTrack Tunnel Antenna was specifically designed to read many tags simultaneously. In post office applications, FastTrack Labels are placed inside envelopes which are then placed inside tagged letter sacks. As the sacks pass through the Tunnel Antenna, data is simultaneously read and written to all Tags. Operating Temperatures:
EMS is considered the foremost expert on high-temperature RFID applications, and has numerous high-temperature installations throughout the world. EMS' field-proven history in high-temperature applications originated with the Passive Read Only ES-Series Tags. Designed to survive up to 4010F (2400C), in addition to sub-freezing levels of -400F (-400C).
The third generation of high-temperature Tags provide an additional benefit to any high-temperature application -- the Tags are disposable! The FastTrack LRP250HT-FLX Tags incorporate a patent-pending manufacturing process which makes these flexible Labels the best solution for any high-temperature application. Using their adhesive backing, simply attach RFID FLX Tags to products (automobiles for example). The Tags will then remain with the products throughout the entire production cycle, and can even be used for after sale information at the retail level.
RF Carrier Frequency of the Tag-to-Antenna Link:
A very important consideration in choosing an RFID system is the carrier frequency band used to transfer information between the Tag and Antenna. The FCC restricts operation to frequencies in either the very low (50 to 500khz), medium (13.56Mhz) or microwave (0.9 to 2.5 Gigahertz) range. The microwave systems have the advantage of potentially longer range, but exhibit a crippling phenomenon known as 'Standing Wave Nulls.' Standing Wave Nulls are dead areas within the reading field in which the Tag cannot be accessed. These arise due to the short wavelengths of microwave radiation (12 to 30 centimeters). When the signal bounces between metal at a distance equal to a multiple of its half wavelength, it forms a standing wave pattern with some points where there is an insufficient signal to operate the Tag. This is the same phenomenon that causes 'cold spots' in food cooked in microwave ovens. The solution for the microwave oven industry is to move the food on a rotating platter so that the location of the null is not constant. Similarly, microwave-based RFID systems have tried mechanically manipulating the Antenna using a 'wobulator,' but this method has proven impractical.
The location of nulls is unpredictable, since nulls will change depending on the configuration of metal in the field. In practical terms, this indicates that in a microwave system the Tag cannot be reliably operated while standing still, since it could be located in a null area.
Lower frequency systems do not exhibit this concern. In addition, these systems are not affected by moisture in the reading field. This high tolerance to different operating environments tends to make low and medium frequency systems the preferred solutions for most applications.
RFID System Connectivity:
As an extension of an automation system, RFID must be able to integrate with both existing and developing automation technologies. Importantly, EMS' RFID systems reduce installation costs by interfacing directly to personal computers, Programmable Logic Controllers (PLC's) and Industrial Network Interface Modules. This connectivity allows EMS to provide RFID systems that are flexible and easy to integrate in a diverse set of industries. |
