Exam Essentials

Know the differences between and characteristics of the various frequencies (LF, HF, UHF, and microwave), their specific use, performance, and pros and cons. LF systems are used for applications requiring very short read distances. LF has the advantage of working through water, metal, and other challenging applications. It is often used for access control and automobile security (embedding tags in a car key with a reader in the steering column).

HF is the system that has the most maturity. It has been used for decades in industrial applications, from tracking totes carrying work in process to tracking cows and pigs. It uses inductive coupling and can transfer relatively high data rates over distances up to three feet. The readers are not very expensive. However, the tags are more expensive because they require several loops for the antenna to function.

UHF has been brought to prominence by the U.S. Department of Defense requiring its 50,000 plus suppliers and Wal-Mart requiring its 7,000 plus suppliers to use the technology developed out of the Massachusetts Institute of Technology called the electronic product code (EPC). UHF has very fast data-transfer rates and long read ranges. The tags also have the potential to be the cheapest of all systems, with the holy grail being the 5¢ tag. UHF is affected by water and metals in a way that HF is not.

Microwave functions like a UHF tag, although microwave systems are not nearly as prevalent and are therefore more expensive. As the frequency increases, the read rate and data-transfer rate increases. However, the challenges around metal and liquids also increase. Microwave systems work well for closed-loop applications in which speed is critical-for example, automobile toll tags.

Know the key criteria for antenna selection. The two basic types of UHF antennas are linearly polarized and circularly polarized. A linearly polarized antenna has a more-focused and concentrated beam of energy. A circularly polarized antennas is like a tornado of RF. Linearly polarized are best to use if the tag's orientation is going to be constant vis-à-vis the antenna. The linearly polarized antenna will allow you to keep a tight beam and not read adjacent tags if you do not want to read them. The circularly polarized antenna will allow many different tags and orientations to be read-for example, when a case of items comes in through a dock door and the tags are all over the place.

HF antennas are coiled loops of wire (usually copper) that can be made in many shapes and sizes and then tuned based on where they are set up and installed-for instance, in a smart-shelf type of application.

Know the proper way to select an RFID reader. All RFID readers are not created equal. Understanding the key functionality for your business requirements will help you select between the trade-offs of various readers. After you know the key differences among readers (cost, read distance, interference rejection, and so forth), you can determine the one or two parameters that are most important to you and your business requirements. Knowing how to test for those parameters will make you a better RF technician and more capable of setting up an accurate RFID network.

Be aware of the important considerations when choosing and installing a cable from reader to antenna.

The cable composition and thickness both determine how well a signal is carried across the cable to the antenna. The longer the cable run, the more insulation the cable requires to prevent signal loss. When using LMR cable, the thickness is designated by the number after LM. It ranges from LMR-100 to LMR-1700, with the number designating measurement in 1/100th of an inch. The other thing to keep in mind is not to exceed the manufacturer's recommended radius for bending the cable during install. You should also make sure to use cable lengths that are in increments of ¼ wavelength.

Know the regional differences between frequencies used in RFID. Low frequency (125–134 kHz), high frequency (13.56 MHz), and microwave frequency (2.45 GHz) are used globally. Ultra-high frequency differs by region. The United States uses 902–928 MHz (South America, South Africa, China, and Australia use a similar band), while Europe uses 865–868 MHz up to 870 MHz (as do North Africa, India, Hong Kong, New Zealand, and Singapore). Japan operates at 952–954 MHz, which is out of the U.S. and European bands. Active tags usually operate on the UHF frequency around 433 MHz internationally.

Understand the basics of RFID middleware. RFID middleware simply filters the thousands of reads that would happen each second down to a handful of important reads. The filtering and smoothing of data is the primary function of RFID middleware. Some of the more-sophisticated programs can control RFID peripherals such as light stacks and motion sensors, or can set up reading based on time sequences (a work shift) or with a manual switch.

Ensure a correct tag orientation for a reader's antenna. Tags should face the antenna (parallel to the antenna's radiator) for maximum performance. When using a single dipole tag and a linear antenna, the tag antenna should be in the same plane as the plane of wave propagation. When using a circular antenna, or when using a dual dipole tag, the orientation does not matter.