Maximizing read accuracy by optimally locating RFID interrogators

Lin Wang, Bryan A. Norman, Jayant Rajgopal

Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review

1 Scopus citations


In recent years there has been a rapid growth in interest in the implementation of RFID technologies to better manage supply chain operations by tracking the movement of products or assets through a system. RFID implementations have also been motivated by mandates from large organizations like the U.S. Department of Defense and Wal-Mart. In typical logistics or supply chain applications, portals have been commonly chosen to streamline the automatic RFID scanning processes so that tags which move through portals are automatically tracked, read, and recorded into a suitable information system. The primary motivation of course, is labor savings since RFID technology can be used to simultaneously read multiple tagged items (typically, pallets or cases today) going through the portal, as opposed to having a human being manually read and record bar-coded information or process RFID tags manually. Portals are currently used by companies at several points within the overall supply chain. These could include shipping (e.g., at a plant or warehouse loading docks), receiving (e.g., at warehouse receiving docks), floor replenishment (e.g., between the backroom=storage area and the retail floor), sales (e.g., at check-out lanes), or packaging materials disposition (e.g., at a box crusher area). In its simplest form a portal is merely a wide doorway with one or more RFID reader antennas mounted at locations along the portal perimeter. In supply chain applications, such portals are designed primarily to read passive tags that receive their power from the reader. Although their sizes and specific configurations might vary depending on individual applications, RFID-equipped portals are all designed with the objective of maximizing read accuracy as tagged objects move through the portal. Read accuracy is of great importance to the success of RFID applications. A missed read at the pallet or case level gives rise to discrepancies between recorded inventory and physical inventory, which in turn leads to various inefficiencies within the supply chain. For example, suppose 10 tagged cases are received, but only 9 are read and recorded in the system by the receiving dock portal reader. This could lead to nonvalue added activities such as manually reconciling stock for payment purposes or potentially costly outcomes such as inaccurate reorder points within the inventory control system. Missed reads at the item level can be even more worrisome as these could lead to lost sales from stock sitting in a backroom but not being available on the shelf; this directly affects revenue. It is fair to say that despite steadily decreasing costs of tags and readers, a major factor inhibiting the increased adoption of RFID technology in supply chain and logistics applications is the less-than-perfect reliability of the tag-reading process that is prevalent today. Even if the cost of RFID tags falls to the level of barcode labels, their use will not become ubiquitous until read accuracy levels are close to 100%. It is worth noting that although using barcodes for tracking is a slow and manually intensive process, it is rare to miss a read other than by human error. With RFID tags, this human element can be eliminated but unfortunately, the technology usually cannot guarantee 100% accuracy in real-world applications. Read accuracy at a portal obviously depends on factors such as the quality, reliability, and capabilities of the tags and readers used, as well as the specific application domain. However, when considering a fixed technology (tag=reader) and application, the design of the RFID-equipped portal becomes critical. Tag reads can be missed because of many factors including limitations in the read range, tag orientation, or interference (fromwater, metal, or other tags). Another complicating factor is that in an automated RFID-scanning process the locations of tags are often not fixed because items are of different sizes andmight bemoving on a truck, ormaterial-handling equipment such as a pallet, forklift, or conveyor belt. In fact, not only the location but also the orientation of each tag may differ when the interrogation process starts within a portal-this is especially true with item-level applications. To compensate for the problem of imperfect read-rates, multiple reader antennas are commonly used in portal design, and a major determinant of read accuracy is the correct placement of reader antennas at the portal. Given that tag locations cannot be isolated and fixed, it is important to optimize and fix the locations of multiple RFID reader antennas so that the probability of a tag being read is maximized. The readability of a passive tag is directly related to the amount of power it receives, which in turn, is a function of the distance between the tag and reader antennas as well as their orientations relative to each other. Thus the objective of optimal reader antenna placement is equivalent to maximizing the powering region, that is, the area within the portal where tags can receive the minimal power required for them to be read at almost all likely orientations of the tag.

Original languageEnglish
Title of host publicationRFID Handbook
Subtitle of host publicationApplications, Technology, Security, and Privacy
PublisherCRC Press
Number of pages18
ISBN (Electronic)9781420055009
ISBN (Print)1420054996, 9781420054996
StatePublished - Jan 1 2017


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