RFID Solution

Design of UHF-based RFID Systems

One key factor when it comes to designing solutions using passive UHF RFID is to understand how exactly the technology works, with its benefits and limitations, and to ensure that products are designed to address business needs successfully to provide a return on investment (ROI). This article will provide a high-level overview of how to utilize the technology in the right way to design and implement a UHF solution successfully. These concepts can be used for any industry, based on the application being designed and the environment in which it will be used.

Basic components of any UHF RFID solution could encompass the following segments: readers, antennas, general-purpose input/output (GPIO) devices, power sources, middleware to process tag data, software, handheld readers, printers and tags. Usually, depending on the application being developed to serve a business need, any or all of these hardware components could be used, in addition to other hardware infrastructure available on the market. But before we start designing a solution, the first question to ask is what business need we are trying to solve with the application.

Understanding of the problem statement is the first step toward designing the right application that will actually work in the field and provide the expected results. Sometimes, companies try to create an RFID-based product without considering the actual benefits and limitations of the technology, but understanding these correctly can put a company on the right path.

The outcome of understanding the problem statement will help us to understand the most important factor in designing an RFID solution, which is deciding the frequency on which the hardware will operate. Solutions that need or have the ability to operate tags and antennas over a large distance typically work with passive or active UHF RFID solutions. For simplicity of our discussion, we will discuss passive UHF technology. On the flipside, if an application being designed needs close proximity of the tags to the antenna, we would go the high-frequency (13.56 Mhz) route.

Therefore, based on the actual application, it is very important to consider what frequency would be used to design the solution. High-frequency (HF) and passive ultrahigh-frequency (UFH)—the exact frequency range depends on the country of operation—have the same principle of data transfer (tag-antenna-reader) but have a few different aspects to their functionality. HF antennas have a very limited range (usually inches) compared to UHF antennas (which could be several feet). Also, the tags and readers utilized for each frequency and application are different. The basic understanding that RF is absorbed by liquids and reflected by metals can help us decide the right direction for tag selection.

While the advantages of UHF are long range and readability capacity, at the same time we need to understand the environment in which the technology will be deployed before we can determine if there will be an increase or decrease in the readability of the tags. Therefore, the challenges common to both frequencies could be used to benefit the actual application as well. Liquids absorb UHF energy, whereas metal reflects it. Incorporating this into our solution design turns them into an advantage and not a challenge, based on the environment and circumstances in which the product operates.

When designing solutions for UHF or HF reader applications, important aspects to consider include the loss of signal from reader to antenna, the distance of the tag from the antenna and the orientation of the tags to the antennas, which would determine where we should use linear- or circular-polarized antennas. If the antennas are being custom-designed in-house, the impedance matching of the antenna with the cable connecting to the reader needs to ensure maximum power transfer with minimal loss. This will also impact its ability to read multiple tags.

The basic data flow of the solution can be described as tag – antenna – reader – software. The data transfer from the tag to the software is what would determine how efficient the RFID system is in its design. When designing a UHF solution, one very important factor is the workflow in which the RFID hardware would operate. To be specific, the tag's workflow, or its movement throughout the ecosystem in which the application will be used, will determine the actual location of the antennas, readers, motion sensors and so forth.

For example, if we are designing an application in which a tag would be attached to an item that would, in turn, be tracked throughout a building, it is important to understand where we would establish read points in order for the system to read the tags successfully without missing any tags. In addition, placing minimal RFID hardware whenever we design an application is the best way to reduce interference and increase read rates. Therefore, the placement of the antennas, the readers, the GPIO devices and the tags needs to be streamlined and minimal, and understanding the workflow in which the tags will operate is vital.

If the workflow does not work in favor of the application, it is highly recommended to evaluate it and consider this an opportunity to improve it. Be sure to work with the least amount of hardware at the lowest cost, so as to achieve the ROI goals and maximum the system's efficiency. Having large numbers of RFID hardware parts to track items only increases the complexity of the system and leads to errors in reading the tags from the antennas, due to external induced noise. Design problems that are usually seen with passive UHF RFID solutions end up reducing tag readability.

When the application is developed with all of these factors considered, we can expect a good amount of tag flow from the antennas to the reader. The next step in the design would be to transfer this tag data from the readers to a middleware solution, if needed, which would compile the information being collected from the reader into meaningful data that could then be used by the software designed for the RFID application. The software would enable user interaction with this data and perform the required activities needed to complete the business and user needs.

Many RFID applications run into deployment challenges that result from design limitations. For example, the application might be designed with excessive hardware with maximum read points, due to complex workflows—which, in turn, increase the cost of the entire solution. The environment in which the application is deployed may induce RF interference and reduce tag reads.

Therefore, a good understanding of the environment in which the application will be deployed is a must. Every installation could be different, as every area has its own workflow, which is why it is important to consider how and where to install the readers and antennas before actually deploying them, so as to find out whether or not it works. Considering end-user requirements will help us provide them with the confidence they would need in using the system, as most RFID systems need users to embrace the technology to make it successful. This is because the system may not be self-correcting due to the nature of the technology, so the antennas or portals would not read 100 percent of tags all the time.

That is why user engagement is important to understand the limitations of a workflow, and to come up with backup applications (like handheld readers to interrogate any tags missed by an antenna) to increase the readability to its maximum level. Therefore, to ensure the successful deployment of a product, the design needs to be carefully considered before the actual work is carried out. In the end, it's the customer usability acceptance of the product which will make it a success.

A few best practices that would ensure a successful deployment include surveying a site for potential RF interference, including other RF systems in the ecosystem in which the product is being installed. Doing this before the actual deployment will help to reduce errors in the system post-installation. Another example could be to make sure the tags are placed in the right location for tracking—for example, leave air gaps in between a tag and the surface of the item to which it is attached when tracking metal or liquids. If the application uses motion detectors, a combination of antennas, along with the readers, needs to be optimized to reduce any interference between devices.

When it comes to scaling the solution to larger areas, there are two major aspects to ensuring that the product is able to scale successfully: The architecture of the product needs to support multiple read points (readers, antennas and so on) and should process all tags with minimal or no errors, and the software created for the application needs to be designed to accommodate the database requirements of all tag data being collected over time. The product also needs to be designed to adapt to changes in customer requirements and feedback, in order to improve the efficiency and features of the system.

In summary, understanding the problem statement of what we are trying to resolve using RFID technology will help us to choose the right frequency, and we need to ensure that the system design is simple yet efficient. Designing the solution by considering real-life usage scenarios of the product by an end user, and taking into account the deployment scalability and support while understanding the technology and its limitations, will help us to use RFID to its maximum potential and serve business needs.