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BlogsAsk The Experts ForumHow Can I Shield LF RFID Antennas from Nearby Electric Motors Generating Noise?

How Can I Shield LF RFID Antennas from Nearby Electric Motors Generating Noise?

Posted By RFID Journal, 09.30.2014

What design considerations are important for creating this shielding? I am very new to this, so the simpler the explanation, the better.

—Name withheld


Almost any material that blocks RF energy would work. You could use a thin sheet of aluminum or Mylar between the reader and the motors, or you could utilize metal mesh, such as chicken wire.

—Mark Roberti, Founder and Editor, RFID Journal


Mark Roberti 2014-10-08 07:31:18 AM
After I posted an answer to this question, our executive editor, Paul Prince wisely questioned whether you could use an aluminum sheet, Mylar or metal mesh to shield the LF reader. LF reader antennas use electromagnetic coupling (not RF energy), so Paul asked me: "If an electric motor generates RF noise, will the noise even have any effect on a passive LF RFID system?” He also noted that motors create a magnetic field and wondered if this would interfere with LF systems and if so, whether aluminum or Mylar would solve the interference issue. I reached out to James E. Heurich, president of RFID Inc., which makes LF systems. James responded by saying that over the years he has seen electromagnetic interference (EMI) from a number of sources, including motors, lighting systems, welders, CRT screens and other equipment that affected both LF and HF RFID hardware. "There are a number of ways to combat EMI,” he says. “First, troubleshoot to see if EMI is the problem. You can do this by simply turning off the suspected sources of EMI and then testing the performance of your RFID gear. Another method is to use shields, and it’s easy to make down and dirty shields for testing, using cardboard and household tin foil. I've completely wrapped a cardboard box in tin foil and placed it over the reader with one side open to where the tag passes.” If the tests show EMI is the culprit, you will need to use metal to shield the LF reader from the source of EMI. However, James points out that these tests will only tell you if EMI in the air is affecting the LF reader. EMI can also affect the electrical line to the reader. “Some RFID gear can only use a regulated power supply, as a switching supply generates noise on its own,” he says. “If the RFID gear shares the same power source with the motor in question, that could be a problem. Troubleshoot by using separate power supplies and lines. Don't forget about grounding. Try a common ground with your own supply first, then try grounding your RFID gear on a completely separate ground.” —Mark Roberti

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