Choosing RFID For Industrial Applications; Part 4


In the first three parts of this blog series, I provided an introduction to the 3 most common frequencies/systems used in industrial RFID, then detailing Low Frequency (LF) and High Frequency (HF) based systems. In this post, I will provide more details specifically on UHF or Ultra High Frequency based RFID.

Ultra High Frequency

Image 5, Back scatter dipole antenna example

UHF RFID systems typically operate between 865 MHz and 960 MHz. Unlike LF or HF based systems, UHF systems are based on an operating principal known as “Backscatter Coupling”, where the reader uses a dipole antenna (see image 5) that transmits electromagnetic waves, creating mostly magnetic power, which is modulated and reflected from the dipole antenna of the tag (or sometimes also referred to as a transponder).

This electromagnetic wave propagation is used for data transmission (see image 6) and powering the tags, thus making them “passive”. Unlike inductive based systems, where the propagation waves transect (Example seen in image 6, wave patterns E & H), the signal can create a “dead zone” where a tag may not be powered or detected.

Image 6, Electromagnetic wave propogation example

Most UHF systems today are based on “Gen 2” (second generation) hardware and the tags will comply with the EPC (Electronic Product Code) data and memory standards. Gen 2 provides multiple frequency capability from a system based on what part of the world the system is located, making these systems very flexible in complying with international radio spectrum frequency usage restrictions. The EPC standard allows the data written to the tag to be referred to a common database to describe the product the data represents, similar to its UPC (Universal Product Code) barcode based counterpart.

Some of the advantages of UHF over its LF or HF RFID counterparts are that it can be used for much longer read/ write distances, as far as 4 to 5 meters reliably, sometimes farther depending on antenna and tag designs. Because of the nature of the propagating wave transmission method, UHF can also be reflected off conductive or partially conductive surfaces like metal, water, concrete, etc. This reflection property can be helpful by causing the waves to be redirected around objects allowing greater flexibility, for example when locating and reading tags while mobile from a fork lift (see image 7).

Image 7, Ultra high frequency Balluff tag sample

But this can also be a disadvantage when trying to isolate a specific tag when a large quantity of tags is present in the field. The system will detect all of the tags in its field and can make isolating a specific tag difficult. It can also lead to reading the wrong tag because of reflected waves from another location. Newer “near field” forms of UHF are entering the market that may help resolve this condition.

Read and write speeds with UHF can vary greatly and many vendors claim reads of 20 to 1000 per second can be achieved. But be careful as these claims can be misleading. There are many factors that can significantly reduce the reliability of such claims. A “read rate” is typically defined as the ratio of the number of times a tag is read per number of seconds reads were performed. Many times the only way to determine a reliable read rate is to perform a site survey and actually test the system’s performance with the environmental factors that can affect read rate performance.

Most UHF tags are divided into to memory spaces. There is typically an EPC space only, but some have a user memory area. Many lower cost tags are limited to 96 bits or bytes of data for the EPC data with no user data memory. There are tags becoming available now with user memory, but are generally limited to less than their LF or HF counterparts.

In the fifth and final blog post of this series, I will provide some application guidance based on the frequency/system types previously defined and introduce some criteria to consider as guidance when choosing the right RFID system for your next application.

Click here to learn more about Balluff industrial RFID.
Click hereto read a whitepaper on “Choosing RFID For Industrial Applications”.


3 Responses

  1. hello thanks for the reading.

  2. Does Balluff have a UHF system available and is there information available on the website?

    • Hello Jeremy,
      We will be releasing a UHF system here in North America early next year. The system is already available in Europe, but because of the frequency difference, the NA version is behind the EU system. The information will be appearing soon. Please stay tuned.

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