Let Me Tell You Why RFID Tag Doesn’t Work
Radio frequency identification is a technology that enables us to identify almost any object wirelessly using collected data transmitted through radio waves. RFID applications are endless in any industry including healthcare, retail, manufacturing, transportation, and more.
INTELLHYDRO Technology dedicated in Manufacturing of RFID inlay and RFID Tags.
Various components work together to comprise the RFID system functionality and are necessary for the technology to work including RFID tags, antennas, readers, cables, and additional accessories such as multiplexers, and support antennas. Together they form an effective RFID system.
RFID systems are extremely reliable; some enterprises achieve a 99.9% system reliability on their RFID network, but what happens when an RFID system is performing poorly? Or an identification tag is not read? Failures can mean dollars lost for manufacturer’s environments and dangerous risks in a hospital setting. what happens when an RFID system is performing poorly? Or an identification tag is not read? The tag producer? The reader manufacturer? The network integrator? There is enough blame to go around, and let’s face it, the reader and tag are codependent. One can make the other look quite bad.
We have been involved in RFID for more than 50 years so let’s say – we have seen a thing or two. The following discussion does not focus on specific tag malfunctions, but only as they relate to the readers because that is our business, and for the purpose of this blog, we are going to focus on the following RFID frequencies:
|Low frequency||125kHz to 135 kHz|
|High frequency||13.56 MHz|
|Passive UHF||860MHz to 960 MHz|
In our experience, these are some of the factors for RFID reading failures:
- Reader Quality
- Speed and Movement of Tags
- Tag Density
- Antenna Design
- Cable Type and Length
- Mounting Location
- Transponder Sensitivity
- Absorption and Reflection
- Electrical Noise
- Reader Sensitivity
- Material Density
- Operating Frequency/Coupling Factor
- Application Requirements/Security Factors
And there are probably another 20 factors that can affect an RFID reader’s performance but the most common reasons that keep our customer support agents employed are coupling factors, the material density of the tagged item, RFID antenna patterns, antenna cables, RFID tag density, reading speed, noise, and reading distance.
Let’s analyze each of them:
The behavior of frequencies changes below 13.56 MHz, where a magnetic field is used to transfer energy and information between the reader and the transponder. This process is known as inductive coupling. Inductive coupling is limited to a reading distance of about one meter. Higher frequencies, use a “Backscatter” coupling technique with a reading distance well beyond one meter. It is the coupling factor that determines what frequencies are optimal for a specific application.
Material or Product Density
The material density of a tagged item can cause reflection and absorption variances. A polymer is a low-density material, glass is a middle-density material, while substances such as water or liquids have a very high-density. High frequency has almost no change or influence in the transmission of the signal with varying item densities, while in UHF, the transmission characteristics can be significantly affected by subject densities. With Ultra High Frequency the performance of the reading will change due to the material density. So, whenever working with water or the human body (which is 50% to 65% water), the frequency of operation will need to be selected accordingly.
RFID Antenna Patterns
Electromagnetic Near Field of Inductive System (HF)
An HF system uses a loop antenna which creates an asymmetric magnetic field. In the case of a UHF System, the antenna produces a directional field that has an angled beam with specific gain, and polarization that is prone to picking up stray reflections and developing possible reading holes at the farther distances. It is critical to take these antenna patterns into consideration when designing an RFID system.
For optimal performance of your system, it is essential to choose the right transponder for each specific application as every application requires a varying degree of security. Take for example a UID/Inventory & Asset tracking application. These applications requires little to no security and just a simple UID transponder will do the job.
If you require password protection for any kind of information like in anti-counterfeiting applications, a transponder with password protection would be required and that is available on UHF and HF.
For more elevated security, as in the case of encrypted information applications used for instance in access control, a transponder with a secure architecture where you can store access keys would be necessary.
The highest security transponders in the marketplace are used for cryptographic authentication, for access control, ticketing and financial transactions. The readers used in these applications have a cryptographic engine or processor where each transaction is cryptographically challenged in a different way each and every time.
High frequency RFID systems, use a 50-ohm impedance match between the reader and antenna. Cable length and routing can have a huge effect on an HF system. The antenna manufacturers will know what length will provide the best performance for their individual antennas.
In the case of UHF, impendence is equally important but in addition each coaxial cable type also has an attenuation factor according to its length. Signal can be greatly reduced if the planning here is not done correctly.
Some applications have an uncommonly high number of tags in a specific area where tags are stacked or piled mere millimeters away from each other, as in the case of document tracking and Kanban Systems. A few pages in a file folder with several files stacked on top of one another is a recipe for potential reading errors. In these kinds of applications, an HF antenna is ideal, while a UHF antenna would not perform as well if at all. An effective illustration is a stack of tagged playing cards, where HF has a 100% read rate, if you stacked 52 cards on top of one another, a UHF antenna could not read even one card when similarly stacked on top of one another. Under a high-density situation, the UHF antenna cannot read RFID tags unless you separate the items.
Reading Speed (UID reading)
As we can now see, each reader has different capabilities in various applications. These capabilities however can be case specific. Take for example the HF ISO 18000 3M3 that claims to read 800 tags per second and the UHF EPC Class 1 Gen 2 that claims 1000 tags per second according to information found on the Internet. In a test comparing read rates we found the HF ISO 18000 3M3 readers reading at a rate of 300 to 400 tags per second in a live setting while the UHF EPC Class 1 Gen 2 read at a rate somewhere around 250 tags per second. Most of these readers require specialized hardware that differs from a standard reading environment and if this hardware requirement is not met, the reading speeds are substantially compromised. Performance results dramatically change according to the application and the environment.
RFID’s archenemy is noise. We are not talking about acoustical noise here but EMV, and common ground, kind of noise. In the case of HF, this electrical noise can come from various sources including the antenna, the power supply, any communications links, and even cabling issues that could cause a ground loop to create noise. To overcome these possible noise problems, we must use a reader with the capability to measures noise levels. When the noise rises above a normal threshold, the system indicates a problem so managers can inspect these common noise points (antenna, power supply, etc.) to troubleshoot the source of the issue. In the case of UHF, because of the higher frequency level, these kinds of analyzers are unavailable in the marketplace so the networks need to be designed to counteract the noise; one way is by operating on a dense reader mode, meaning the system is designed to operate in a multi reader environment. In the United States, the FCC has allocated 50 channels as UHF frequency band, so we can theoretically have 50 readers in a network, and each would search for an available channel on which to properly function. We conducted tests on this as well in a real-life setting and measured other readers in these kinds of dense reader conditions. We found all readers dropped signal when two readers are on the same channel and noticed a dramatic loss in overall signal and signal strength in several readers when two on neighboring channels In real life, this would result in a typical service call because each time a reader is activated, it starts looking for a free working channel and causes loss of signal as it competes with other readers.
We often hear the question “What distance can I get from this reader?” and the honest answer is, it depends. As we have discussed, all HF and UHF passive readers’ distances depend on a multitude of contributing factors like reader power and sensitivity, antenna tuning (reader and tag) environmental influences (metal, etc.), size and sensitivity of the tag, orientation of the tag to the reader antenna, and add dozens more influencing factors.
Bottom line: It is critical to measure and test the distance from the readers to the tag in a live environment and take all application factors into consideration.