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Know Your RFID Frequency Basics

In 2008, I purchased my first toll road RFID transponder, letting me drive through and pay my toll without stopping at a booth. This was my first real-life exposure to RFID, and it was magical. Back then, all I knew was that RFID stood for “radio frequency identification” and that it exchanged data between a transmitter and receiver using radio waves. That’s enough for a highway driver, but you’ll need more information to use RFID in an industrial automation setting. So here are some basics on what makes up an RFID system and the uses of different radio frequencies.

At a minimum, an RFID system comprises a tag, an antenna, and a processor. Tags, also known as data carriers, can be active or passive. Active tags have a built-in power source, and passive tags are powered by the electromagnetic field emitted by the antenna and are dormant otherwise. Active tags have a much longer range than passive tags. But passive tags are most commonly used in industrial RFID applications due to lower component costs and no maintenance requirements.

Low frequency (LF), high frequency (HF), ultra-high frequency (UHF)

The next big topic is the different frequency ranges used by RFID: low frequency (LF), high frequency (HF), and ultra-high frequency (UHF). What do they mean? LF systems operate at a frequency range of 125…135 kHz, HF systems operate at 13.56 MHz, and UHF systems operate at a frequency range of 840…960 MHz. This tells you that the systems are not compatible with each other and that you must choose the tag, antenna, and processor unit from a single system for it to work properly. This also means that the LF, HF, and UHF systems will not interfere with each other, so you can install different types of RFID systems in a plant without running a risk of interference or crosstalk issues between them or any other radio communications technology.

Choosing the correct system frequency?

How do you choose the correct system frequency? The main difference between LF/HF systems and UHF systems is the coupling between the tags and the antenna/processor. LF and HF RFID systems use inductive coupling, where an inductive coil on the antenna head is energized to generate an inductive field. When a tag is present in that inductive field, it will be energized and begin communications back and forth. Using the specifications of the tag and the antenna/processor, it is easy to determine the read/write range or the air gap between the tag and the antenna head.

The downside of using LF/HF RFID technology based on inductive coupling is that the read/write range is relatively short, and it’s dependent on the physical size of the coils in the antenna head and the tag. The bigger the antenna and tag combination, the greater the read/write distance or the air gap between the antenna and the tag. The best LF and HF RFID uses are in close-range part tracking and production control where you need to read/write data to a single tag at a time.

UHF RFID systems use electromagnetic wave coupling to transmit power and data over radio waves between the antenna and the tag. The Federal Communications Commission strictly regulates the power level and frequency range of the radio waves, and there are different frequency range specifications depending on the country or region where the UHF RFID system is being used. In the United States, the frequency is limited to a range between 902 and 928MHz. Europe, China, and Japan have different operating range specifications based on their regulations, so you must select the correct frequency range based on the system’s location.

Using radio waves enables UHF RFID systems to achieve a much greater read/write range than inductive coupling-based RFID systems. UHF RFID read/write distance range varies based on transmission power, environmental interference, and the size of the UHF RFID tag, but can be as large as 6 meters or 20 feet. Environmental interferences such as metal structures or liquids, including human bodies, can deflect or absorb radio waves and significantly impact the performance and reliability of a UHF RFID system. UHF RFID systems are great at detecting multiple tags at greater distances, making them well suited for traceability and intralogistics applications. They are not well suited for single tag detection applications, especially if surrounded by metal structures.

Because of the impact an environment has on UHF signals, it is advisable to conduct a full feasibility study by the vendor of the UHF RFID system before the system solution is purchased to ensure that the system will meet the application requirements. This includes bringing in the equipment needed, such as tags, antennas, processors, and mounting brackets to the point of use to ensure reliable transmission of data between the tag and the antenna and testing the system performance in normal working conditions. Performing a feasibility study reduces the risk of the system not meeting the customer’s expectations or application requirements.

Selecting an industrial RFID system

There are other factors to consider when selecting an industrial RFID system, but this summary is a good place to start:

- Most industrial RFID applications use passive RFID tags due to their lower component costs and no battery replacement needs.
- For applications requiring short distance and single tag detection, LF or HF RFID systems are recommended.
- For applications where long-distance and multi-tag detection is needed, UHF RFID systems are recommended.
- If you are considering UHF, a feasibility study is highly recommended to ensure that the UHF RFID system will perform as intended and meet your requirements.

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RFID Basics – Gain Key Knowledge to Select the Best Fit System

As digitalization evolves, industrial companies are automating more and more manual processes. Consequently, they transfer paper-based tasks in the field of identification to digital solutions. One important enabling technology is radio frequency identification (RFID), which uses radio frequency to exchange data between two different entities for the purpose of identification. Since this technology is mature, many companies now trust it to improve their efficiency. Strong arguments for RFID technology include its contactless reading, which makes it wear-free. Plus, it’s maintenance-free and insensitive to dirt.

There are myriad applications for RFID in the manufacturing process, which can be clustered into the following areas:

- Asset management e.g. tool identification on machine tools or mold management on injection molding machines in plastic processing companies
- Traceability for work piece tracking in production
- Access control for safety and security purposes by instructed and authorized experts to ensure that only the right people can access the machine and change parameters, etc.

But not all RFID is the same. It is important to select the system type and components that are best suited for your application.

Frequencies and their best applications

RFID runs on three different frequency bands, each of which has its advantages and disadvantages.

Low Frequency (LF)
LF systems are in the range of 30…300 kHz and are best suited for close range and for difficult conditions, such as metallic surroundings. Therefore, they fit perfectly in tool identification applications, such as in machine tools, Additionally, they are used in livestock and other animal tracking. The semiconductor industry (front end) relies on this frequency (134kHz) as well.

High Frequency (HF)
HF in the range of 3…30 MHz is ideal for parts tracking at close range up to 400 mm. With HF you can process and store larger quantities of data, which is helpful for tracking and tracing workpieces in industrial applications. But companies also use it for production control. It comes along with high data transmission speeds. Accordingly, it accelerates identification processes.

Ultra High Frequency (UHF)
UHF systems in the range of 300 MHz…3 GHz are widely used in intralogistics applications and typically communicate at a range of up to 6 m distance. Importantly, they allow bulk reading of tags.

RFID key components

Every RFID system consists of three components.

1. RFID tag (data carrier). The data carrier stores all kinds of information. It can be read and/or changed (write) by computers or automation systems. Read/write versions are available in various memory capacities and with various storage mechanisms. RFID tags are usually classified based on their modes of power supply, including:

– Passive data carriers: without power supply
– Active data carriers: with power supply

2. Antenna or Read/Write head. The antenna supplies the RFID tag with power and reads the data. If desired, it can also write new data on it.

3. Processing unit. The processing unit is used for signal processing and preparation. It typically includes an integrated interface for connecting to the controller or the PC system.

RFID systems are designed for some of the toughest environments and address just most identification applications in the plants. To learn more about industrial RFID applications and components visit www.balluff.us/rifd.

UHF making a big impact on manufacturing

Ultra-High Frequency (UHF) RFID is quickly becoming the go-to identification system for flexible manufacturing lines around the world. While it was once considered to be a system designed primarily for distribution centers and retail stores, UHF technology has evolved to meet the rigors of the manufacturing environment.

Not long ago I was in a discussion with one of my customers who had been using RFID for almost 25 years. He was caught in a tough spot because he had an application which required reading tags from as little as six inches away to as far as two feet away. The HF system he had could easily meet his needs for the six inch read range, but reading at two feet away limited him to using UHF. When I explained that, his bewildered look indicated to me he was reluctant to consider UHF as a real option. He went on to explain that about ten years prior he conducted tests in his plant with UHF and found a host of limitations with the technology. His main concern was how the operators’ two-way radios interfered with the UHF operating frequency of 902-928MHz. Having heard this from other manufacturing organizations who were early adopters I knew right away that he wasn’t aware of how the technology has evolved over the last decade.

Frequency hopping has pretty much eliminated interference with other radio signals. In addition to overcoming radio interference, being able to read and write to tags which are mounted on or near metal and liquids has become a reality with recent advancements. These improvements have led to more flexible read ranges which are a requirement in today’s flexible manufacturing applications.

In a nutshell, the demands of flexible manufacturing have spurred advancements in the process as well as the supporting technology. As it applies to identification of parts or pallets in the manufacturing process, the flexibility of UHF RFID enables manufacturers to gain visibility in their process and provides actionable data that is used to make complex business decisions.

You can learn more about the technology in Balluff’s white paper, What Makes RFID Systems Industrial Strength? or by visiting our website at www.balluff.us.