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Antennas – The Radio Frequency Part of an RFID System
 RFID systems involve several major subsystems. The software may be the most important section, since it controls operations and manages the database. The hardware subsystem is also necessary to form a complete system. The front end of the hardware system is the computer, followed by a module called the reader, which is a transmitter/receiver used to communicate with a transponder called a tag.
Tags are available in many formats and the end-user may select a tag from any of several manufacturers to use in the system. The gap in this description is between the reader and the tag, and that gap is filled by the antenna system. It has been our experience that in many cases the antenna subsystem is the last one to be addressed, and in some ways is the most difficult.  The antenna attached to the reader may come in many forms. Some are prepackaged, and some are available as standard units from various distributors or manufacturers. Often they will have to be customized to the specific job in order to optimize the system, since there are so many different applications of this new technology.
In many typical systems a flat panel antenna may be appropriate and two examples of that kind of antenna, as made by Snyder Antenna Systems, are shown in Figure 1. The flat panel can readily be adapted to many applications such as reading articles on a conveyor belt, reading articles going through a passage way, reading articles on a shelf, and others.  Once the appropriate antenna for use in the system has been determined, the next step is how the interconnection can be done. The most basic application uses one computer addressing one reader, and addressing one antenna. This of course is not practical in most systems and other approaches must be used. A reasonable approach to this problem is the use of a multiplexer, which is a radio frequency switch, which can connect the reader to multiple antennas.
These devices are not commonly available and may have to be customized for a given job. One example of this is shown in Figure 2, a unit that is available from Snyder Antenna Systems. This unit is driven by a computer and reader and provides the capability of addressing up to eight antennas. The unit illustrated receives an address command from the computer, selects that antenna, and takes a reading from any tags in the field of the specified antenna. Upon receipt of a new address from the computer, it proceeds to the next antenna, and selects that antenna. In this way, the computer can retrieve the data from multiple tags in multiple antenna fields. In many applications, even reading up to eight antennas may not be satisfactory. The unit shown, can be configured as a master multiplex switch, which can, on each of the eight outputs, address a slave multiplex switch. This multiple system will allow a computer to send up to 64 addresses, and using this master/slave system, address up to 64 antennas.  A system of this kind may be particularly applicable in inventory systems, especially retail stores. An example of this latter application is shown in Figure 3. This was an application in a retail store where each of the shelves shown was integrated with three antennas. The computer could then read the inventory on the array of shelves shown in the figure, complete for the entire store, in only a few minutes, and have an accurate up-to-date inventory of products available on the shelves.
The same technology was used in the back room storage area of this retail store where reserve stock could similarly be located. The software system could then identify where there were shelves needing to be refreshed in the retail area, and indicate the location of these goods in the warehouse area of the store. More complex systems use antennas in an array where they are combined to form a compound antenna called a tunnel. These tunnels, though seemingly complex, are in fact a combination of the flat panel antennas referred to previously, along with the necessary combining and multiplexing circuits so that the reader and the computer may address them. A unique requirement common to these tunnels is that they must be able to read tags passing through the tunnel in any orientation; therefore it is usually a requirement that the tunnel have a three-dimensional reading capability. Antenna arrays of this type of may be used manually, such as removing articles or boxes from a truck and passing them through the tunnel by hand and then to their storage area. By this method, the computer makes a record of all articles arriving at the location. A more complex application is the use of larger tunnels where a conveyor line passes directly through the tunnel. In this way boxes of articles that move along the conveyor belt can be read and catalogued by the computer and thus control the movement of articles through the warehouse. There is of course a requirement that the conveyor speed be appropriate so that all articles in a package may be read as that package moves through the tunnel. These kinds of systems have in some cases been implemented, and at the present time many more are being considered. FAQs 1). What is a good source for general information about RFID and where to buy the necessary equipment? RFID 101 - Link to online guide to selecting and buying radio-frequency ID products. 2). Q: What is a good source for training on implementation of RFID systems? RFID4U.com - Training Info 3). Q: What would you recommend to use as a reader to go with your UHF antennas? A: We like the readers made by AWID, especially the MPR 3014 model which has a superb combination of capability and price. gen2.awid.com - UHF Antenna Guide 4). Q: What are some of the new applications for which you are developing products? A: We are installing systems in casinos for patron tracking and gaming chip counting. We have developed several antennas for use in systems for tracking laundry and uniforms. These use water and heat proof tags the size of a nickel. We are installing systems for large scale inventory of CD ROMS and computer tapes. We have developed a line of very small UHF antennas used for various applications, such as inside RFID label printers. We offer everything from full scale retail inventory antenna systems to antennas smaller than a coin. With a full line of standard products and the ability to handle almost any custom RFID system, let us show you why Snyder Antenna Systems is your gateway to a successful RFID solution. |
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Snyder Antenna Systems
Voice: 626.794.7139 Fax: 626.794.8844 e-mail: snyderelectronics@sbcglobal.net
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