The three primary components that make RFID “Work” are Tags, Readers, and Software that collects data from the readers and helps turn it into actionable information.
RFID Readers are devices that read/write data from/to RFID tags and transfer this data to back end IT systems. Fixed Readers are mounted to a specific location (e.g. a dock door or similar portal) and generally require one or more external antennas and associated cabling for an increased read area. Less powerful Mobile readers offer greater flexibility but with a decreased read range as compared to fixed readers.
RFID Tags fall into three primary categories: Passive, Battery Assisted Passive (BAP), and Active. The most common tags in use today in North America are passive UHF RFID tags. For this reason the focus of this document will be on passive UHF RFID tags supporting the EPC Global EPC Gen2 Standard.
Passive RFID tags operate by harvesting energy through electromagnetic waves provided by the RFID reader to power up an integrated circuit in the tag which then transmits and receives information? using either inductive coupling or backscatter:
- Inductive coupling (Near Field) works when a tag and reader transfer energy through a shared magnetic field. Near Field RFID tags have a relatively short read range (< 36”).
- Backscatter (Far Field) works by reflecting electromagnetic waves back in the direction which they came from. Far Field tags such as EPC Gen2 tags can support read distances of up to 30’ or more depending on tag size and , environmental conditions.
High Frequency (HF) passive tags which operate at 13.56 MHz and typically follow the ISO 14443 of ISO 15693 standards use inductive coupling. HF tags are commonly used to support transit ticketing, item level tagging, and library applications.
Ultra-High Frequency (UHF) passive tags (e.g. EPC Gen2 tags) harvest energy from the RFID reader which stimulates the tag antenna to power up the chip. The tag then uses backscatter to send data from the chip back to the reader.
Battery Assisted Passive (BAP) tags operate in a way similar to UHF passive tags with the exception that they use battery power to significantly boost the read range of the tags (up to 100’). BAP tags must first be contacted by the RFID reader (a.k.a Reader Talks First) before the battery is engaged to power up the chip and broadcast data back to the reader. The downside to BAP tags is that the batteries on RFID tags typically last 2-5 years, after which the tag is no longer operational.
Active Tags use battery power to broadcast data to any active reader within range. Active tags have a read range of up to 300’, but suffer the same limitations as BAP tags, when the batteries run out they stop working.
EPC Gen2 UHF Passive RFID Tags – The Global Standard
In North America EPC Gen2 tags are by far the most common. The reasons behind this are as follows:
- Wal-Mart and the US DoD mandates that suppliers apply EPC Gen2 tags to cases and pallets of products shipped to their respective distribution centers
- Numerous RFID tag and hardware vendors jumped in to support the EPC Gen2 standard, driving costs down to promote industry adoption
- EPC Gen2 has been adopted by ISO (ISO 18000-6) and is truly a global standard
Because different regions of the world use dissimilar frequencies in the UHF range, most UHF tags are tuned to perform best in a particular region (e.g. 915 MHz for the US, 868 MHz for the EU). However, a growing number of tag providers are developing tags that perform equally well in all regions.
Using EPC Gen2 labels to tag cases and pallets of goods in support of supply chain applications is now much easier than when mandate programs were first initiated; most RFID labels work sufficiently well to support Wal-Mart and DoD RFID programs. Using UHF Gen2 tags to support asset tracking applications is more challenging as metallic surfaces can have a significant impact on tag performance.
Standard RFID labels applied directly to metal simply will not work. Supply chain labels with a small “stand off” or RF insulator will work, but the read distance is often compromised as compared to the same tags operating in free space. Tags designed to operate when placed directly on metal, typically durable “hard tags” with advanced antenna designs, work very well on metal do not work as well when not placed directly on metal. “Flag Tags” and “Hang Tags” that are designed to operate in free space while fastened to metal items perform differently based on the environment in which they must function.
Selecting the Proper EPC Gen2 Tag
To determine which tag is best for your application you first need to gather detailed application requirements and speak with a knowledgeable source. To get started review the information on our website and then contact us to discuss your specific RFID needs.