Exam Essentials

Know the differences between and characteristics of active, passive, and semi-passive tags, their specific use, performance, and pros and cons. Active tags have a battery and a transmitter, which support long read ranges (up to a kilometer). They can carry sensors, support large memory and processing capabilities, and work with GPS, cellular, and other networks. They are expensive but are less susceptible to interference and are suitable for tracking high-value goods. They are heavily used by the U.S. DoD as well as various transportation companies and railroads for container tracking, trailer tracking, and the like. Active tags are also used for RTLS.

Passive tags do not carry a battery or a transmitter and communicate by "reflecting" the energy received from the reader. They are inexpensive and have read ranges from 0.5 to 10 meters, depending on the type. Passive tags are used in item-level, case-level, and pallet-level tracking in retail supply chains, as well as for many other applications.

Semi-passive tags carry a battery but communicate in the same way as passive tags. The battery powers the chip and sensors but does not enable broadcasting the signal to the reader. Semi-passive tags are often used for their sensors, which can monitor temperature and other conditions. Their read ranges can be up to 100 meters.

Know the difference between inductive coupling and passive backscatter. Passive and semi-passive tags receive power and communicate using inductive coupling and passive backscatter. Inductive coupling uses a magnetic field, whereas passive backscatter uses an electric field. Inductive coupled tags (LF, HF, and certain kinds of UHF) have an antenna, usually in the form of an induction coil, whereas tags using passive backscatter (UHF and microwave) have dipole antennas (single or dual dipoles). Inductively coupled tags have short read ranges (a maximum of half a meter); passive backscatter tags can reach distances up to 10 meters.

Distinguish between frequencies and know tag performances within each frequency, including pros and cons. Low-frequency tags have read ranges up to half a meter (passive) and slow data-transfer rates. They penetrate liquids and metals well. They are commonly used for animal tracking, access control, and tracking of RF-difficult items such as laptops in closed-loop systems. They are mostly read-only and without anticollision capabilities; however, there are LF tags that offer these features.

High-frequency tags have read ranges up to a meter (passive) and a data-transfer rate faster than HF but slower than UHF. They work relatively well around liquids and metals. They are commonly used for smart shelves, smart cards, item tracking in pharma and movie rentals, and access control.

Ultra-high-frequency tags have read ranges up to 10 meters (passive) and a data-transfer rate faster than LF and HF. They do not work well around liquids and metals unless they use near-field communication. Passive UHF tags are mandated by the DoD and major retailers and are used for case-level and pallet-level tracking in retail supply chains, as well as for other applications.

Microwave tags have read ranges up to a meter but are usually active (read ranges in hundreds of meters). They have the highest data-transfer rate of all tag types but do not work well around metals and liquids. They are used mostly for toll collection.

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), whereas 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 outside of the U.S. and European bands. Active tags usually operate on the UHF frequency around 433 MHz internationally.

Know the contents of EPC Generation 2 memory. Gen 2 tags have four memory banks. Bank 0 is a reserved memory and holds the Access and Kill passwords (each 32 bits). Bank 1 is an EPC memory that holds the EPC number (96 bits or more) and protocol controls. Bank 2 is a TID memory that holds tag ID and other tag information. Bank 3 is a user memory, which can be defined by the user.

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.

Distinguish between various methods of chip attachment. Chips can be attached to an antenna directly (flip-chip technique) using a robotic hand with a vacuum nozzle that picks up the chip, flips it over, and using pressure and heat affixes the chip to the inlay. Chips also can be attached first to a strap, which is then attached to an antenna. This technique is suitable for very small chips.

Evaluate the package contents and select the right tags and their locations. Although packaging generally is made of cardboard, the contents can be either RF friendly or RF unfriendly. If you are dealing with RF-unfriendly contents such as liquids, metals, chemicals, moist food, or glass, you should utilize the air gaps in the packaging as much as possible and place your tag in the gap, avoiding contact with the product. If you are tagging items or you must place the tag on an RF-unfriendly surface (metal cans, glass bottles), try to use a tag specially designed (tuned) to perform well on these materials. When selecting the tags and their locations, you must test and record everything. You can do this testing yourself or use testing facilities.

Know different types of tag packaging and their possible uses. Tags can come integrated into labels (for use with RFID printers and label applicators), buttons (for clothing maintenance and rentals), cards (used for access control, payment, or memberships), glass beads (animal tracking), wristbands (hospital patient tracking, amusement parks), key fobs (for vehicle access and immobilizers), case (mainly for active and semi-passive tags), or integrated into packaging or the product itself.