A simple Read/Write RFID system

 

Tag/Label/PCB
An RFID Tag/Label/PCB contains a coil, a programmed silicon chip and in Active Read/Write systems, a battery.

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.

PCBs (Printed Circuit Boards) are meant to be embedded into a product or carrier, and although impervious to high temperatures, such as is found in plastic pallet manufacturing, the PCB requires some encapsulation if it is to have direct contact with outside environmental conditions (e.g. rain, excessive moisture, etc.) The benefits of RFID PCBs are low cost and the ability to endure environments in which Labels would not survive.

Plastic pallet manufacturing provides a good example of applying an RFID PCB. The PCB is placed inside the plastic pallet prior to the ultrasonically welding phase of the plastic pallet manufacturing cycle. The PCB converts the pallet to a "Smart Pallet," and data can be read and written to the pallet throughout the complete supply chain.

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 deionized 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/Labels/PCBs as they pass through.

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 quite respectable. 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 240°C.

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.
 

Read/Write Tags can record more than 32 KB of data in an assembly process

 

Read/Write (Reusable)
In a more advanced state (read/write), RFID can be used as a dynamic electronic manifest, allowing users to reduce traffic on networks, link remote production stations and to backup host PCs or PLCs.

As an example of this electronic manifest, in automotive engine manufacturing, the tag is attached to an engine carrier. Routing and build instructions are written to the tag. As the engine and carrier approach the first station, the tag is interrogated by a reader/writer to determine whether or not the engine should be at the station. If affirmative, the build information is read off the tag and transferred to the local processor, there decisions are made on how to instruct the automated equipment. After the operations are performed, key quality data and/or production results are stored on the tag. This allows users to later investigate any quality issues across varying lots. In the case where the operation is unsuccessful, this failure is also written to the tag. Then, prior to reaching the next station, the engine is removed from the line and transferred to a remote rework station. At the rework station, the tag is read to determine how the engine must be repaired.

In the electronic industry, several companies are taking the electronic manifests even further, enabling production operations to continue even if the central server or host fails. Since a tag can combine with a local processor at a given station to communicate all build instructions to that station, operations can be conducted without any dependency on the network.

Read/Write (Disposable)
In an even more advanced state, disposable labels are applied to products during manufacturing and utilized throughout the entire supply chain (from manufacturing through retail and out to the customers). In essence, the RFID labels are used to create "smart products" that can communicate with their surroundings.

Applying RFID labels directly to television sets illustrates the value of creating "smart products." During production, RFID labels are applied to the inside of the televisions' housings. After utilizing the labels during production (as explained above), the labels accompany the "smart products" into the warehouse. In the warehouse, the labels are used for both locating a given model or routing different models to intended storage locations. Further, with the ability of reader/writers to communicate with multiple labels in the same field, all televisions can be read or written to as they exit the warehouse, regardless of whether the televisions are stacked on pallets or transported separately. This enables users to write destination information to the "smart products" and to record what has been shipped, providing the trigger for electronic billing.

Upon reaching the retail warehouse, the "smart products" are read upon entering the building, providing instant receipt into inventory and automatic payment clearance for suppliers.
 

The "smart products" are then tracked into the retail outlet where the label is used for anti-theft and real-time inventory. Finally, as the televisions leave the outlet, key customer and product configuration information is written to the RFID labels. If a customer returns a given television set to the Service Center (or affiliated Service Center), the product's complete record is pulled up on a computer monitor prior to the customer reaching the service counter, bringing service to a new level.

The example reveals how "smart products" not only save money throughout the supply chain, but also add value for the customer. This value-added feature is being used by manufacturers (and retailers) to distinguish their products against competitive offerings, enabling the manufacturers to increase sales and/or margins.    This allows the forwarder to offer a service to the customer from the early stage, allowing the final customer to have full control from the very beginning, without any extra cost.    In fact, the final customer enjoys savings in working hours to place the TAGs, as those are already being fitted upon production of the merchandise, most probably on a low labor cost country.

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.

Tags' Memory Capacity:
 

The correct placement of the Tag in the Antenna's range is critical to good performance

 

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 instance, the EMS 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 instance, the EMS HMS system transfers data at a rate of 1000 bytes per second.

Active Read/Write Speed - The speed of an Active Read/Write system is based on the same criteria as a Passive Read/Write system, unless the Passive system relies on charging a capacitor in the Tag to enable communication. Importantly, a typical low-frequency Read/Write system will operate at speeds of only 100 or 200 bytes transferred per second. Since several hundred bytes may be transferred at a station, the transfer of the information could take several seconds longer than the entire mechanical operation. EMS has solved this concern with our line of high speed, low frequency Read/Write RFID products. By incorporating several unique and proprietary techniques, our engineers have designed a low-frequency system with speeds higher than that of most microwave systems. The HS-Series transfers data at speeds of over 3000 bytes per second. In a station transferring 600 bytes of information, the information transfer would take up to six seconds using older technologies, but only 200 milliseconds with the HS-Series products.

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 401°F (240°C), in addition to sub-freezing levels of -40°F (-40°C).

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 halfwavelength, 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 "coldspots" 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.