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There are many parts to an RFID system and a lengthy list of factors that may influence their performance. Often, a system malfunction can create a chain of blame that extends from end-user to manufacturer, the assumption being that if a problem is not immediately solvable, the reader is simply defective. In reality, many RFID failures are caused not by the reader itself but by issues with system design, hardware, setup, environment, and other influences that are entirely within the end user’s control. Yet, with so many potential sources to choose from, it can be near impossible to decide where to start your search, especially if you are unfamiliar with the details of RFID systems and operations.
A good starting point when troubleshooting read failures is at the system’s basic hardware, as improper and/or misplaced components are a common cause. Luckily, they are also typically simple to address.
The first step in determining if the hardware is the root of your malfunction is checking the level of electrical noise interfering with any HF system using either the tools provided by the manufacturer or some other noise measurement devices.
Cable length and type are a common concern of those utilizing RFID systems as well as a common site of errors. While 50-ohm antenna cables are the standard, not all are equal. Close attention must be paid to ensure that the ones you select are capable of supplying the desired signal and installed to do so as efficiently as possible.
With HF antennas, the cable length is instrumental; while it is common to assume that a shorter cable will provide a better performance, cables in an HF application suffer higher losses as they shrink. Rather, they should exactly match the recommendation given by your manufacturer.
In contrast, UHF antenna cables do perform best with as short a cable as possible but require a specific type of cable carefully selected based on its attenuation. Cables at the lower end of the market have far more attenuation, causing huge portions of your signal to be lost.
With RFID, the antenna’s primary responsibility is communicating with the transponder, thereby, determining the range in which tags can be detected. It is very important to select the size and type of transponder that fulfills the needs of the system.
All HF systems utilize loop antennas, which generate a symmetrical magnetic field whose size can be adjusted based on signal strength and size of the antenna. Meanwhile, UHF systems use antennas that produce a directional field whose specifications vary based on their individual design. Of the two, UHF environments are more likely to be the source of poor antenna performance, as directional fields can be easily disrupted by objects within their beam angles, causing reflections as well as reading holes and islands.
The frequency a reader operates on forms the foundation of its capabilities. HF and UHF, the two most common passive RFID frequencies, each have a unique mechanism to transfer energy and perform couplings between the reader and transponder. HF, at 13.56 megahertz, utilizes a magnetic field or inductive coupling to perform these tasks, while UHF, sitting between 860 and 960 megahertz for FCC countries, employs an electrical field known as backscatter coupling. Although it may seem simple to select the correct frequency for your application, the fact is that many are unaware of the intricacies where failures can occur.
RFID reception is heavily influenced by the materials a frequency must pass through to deliver information to the reader; particularly, their density is an important determining factor in which frequency is best suited to your application. When using an incorrect frequency, materials like water, human bodies, and metal can cause reflections and absorptions that can be construed as poor reader performance.
Applications that involve high-density materials are best served by lower frequencies that use magnetic coupling, such as HF and nearfield UHF.
In the same vein, tag density is a major determining factor of the proper frequency one should use. If your application requires reading a large number of tags bundled close together (such as a stack of documents or poker chips) that are collected in a single, small area, using an improper frequency can cause antennas to detune, rendering the reader unable to detect any tags at all.
In these cases, an ISO18000-3M3 HF transponder will provide the best performance.
Although the reading speeds of various RFID frequencies can be found listed from various sources throughout the market, they are often far off from the results observed in real-life settings. For instance, ISO 18000-3M3 transponders are presented as reading as many as 800 tags per second. In UHF, the same can be said of EPC Class 1 Gen 2 transponders, which are often said to read up to 1,000 tags per second. In testing, we’ve found each to perform far below these estimates in real world environments.
When purchasing RFID readers, people often ask for a straightforward answer on the distance capabilities of particular readers. Yet, it is near impossible to provide an accurate estimate without testing the reader in its intended application first. This is because reading distance is subject to an extreme number of influences: environmental factors, densities at play, sensitivity, tag type, size, and location, plus many more.
For example, in a case where multiple tags in a low density are collected in a small space, HF and nearfield UHF each appear as options. However, if unrelated tags are nearby, HF will prove the most appropriate; unlike UHF antennas, the range of HF antennas can be precisely controlled.
One place perhaps underlooked when attempting to trace and resolve RFID malfunctions is system security. While this may not be a problem in applications such as inventory tracking, where no private data is recorded, there are many in which choosing the proper protection for your system is a crucial concern.
Several security strategies are available for use with RFID systems, the least of which is password protection on data collected by the transponder. Above that, encryption keys can be used to lock down user memory or data; however, these keys must be carefully kept to prevent a compromise of the entire system. Cryptographic authentication is the highest level of security available, utilizing transponders running either a cryptographic engine or processor that allows each reader to transponder interaction to be uniquely encrypted.
In most cases, failures in RFID systems are not due to misunderstanding the technology, misstepping in your setup, or overlooking important factors, but the result of not realizing the wide variety of options available on the market, particularly when many companies offer only one flavor of RFID technology. If you continue to have reader failures that your manufacturer cannot resolve, it may be that they simply do not offer the best solution for your needs. At the end of the day, gathering the specifics of your application and using them to guide your decisions will always be the best route to optimal RFID performance.
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