1
\$\begingroup\$

I have a magnetic field that is being induced onto a power line by a transmitter, which is following the length of the power line to the receiver. The receiver communicates via a loosely coupled coil with the transmitter.

This artificially perceives the transmitter a significant distance away from the receiver. I suspect the AC-DC power supply line may be picking up some of this bringing it within enough distance of the receiver to be perceived.

The problem I am finding is that the copper lines running from the power supply to the receiver cannot be effectively shielded against this phenomena. I have tried graphite sheets ideal for the resonant frequency of the system, however that approach is flawed as the signal is being brought within proximity of the receiver.

What would be a solution to attenuate or reflect the flux lines away from the power cable leading into the receiver?

Edit:

To explain the "phenomena" more technically, what is happening is the RF-field is inducing eddy currents in the non-ferrous metal, which induces a magnetic field opposite to the original field (aka Lenz effect). Of course only part of the field is reflected, so in theory I should be able to use a material with high magnetic permeability to attenuate the signal. I wish there was some sort of flexible graphite sleeve I could use which had a sufficient attenuation at 13.56 MHz.

\$\endgroup\$
  • \$\begingroup\$ What frequency does the transmitter and receiver communicate at? How far is the 'significant' distance, what level is the unintended signal and what level is the intended signal? What filtering do you have between the power supply and receiver? Have you tried operating the receiver from a battery? \$\endgroup\$ – Bruce Abbott Feb 25 at 19:03
  • \$\begingroup\$ @BruceAbbott good point, I can't believe I forgot to mention the frequency of the application as that changes things drastically; 13.56 MHz. The system cannot be operated from a battery in this case, otherwise that may of worked. The DC input has a common mode choke and an over-voltage protection circuit. The receiver is further separated by a split ground plane design stitched with a capacitor and passing through a low-noise LDO. The "significant" distance can be anywhere from a several additional feet to another story in the building (beyond the link-budget of this design, 5 feet). \$\endgroup\$ – Electric Pet Feb 26 at 21:25
  • \$\begingroup\$ At 13.56MHz and distances of 1.5-4m you are in the transition between inductive near and far field, where the relationship between distance and signal strength can be complicated. How are your coils constructed? What is the 'link-budget' of you design? \$\endgroup\$ – Bruce Abbott Feb 27 at 1:19
  • \$\begingroup\$ @BruceAbbott please see some edits I made above. Just a coil antenna on both the transmitter and receiver. The antenna is not a radiating entity. Functions primary in the near-field for this application. \$\endgroup\$ – Electric Pet Mar 6 at 18:20

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.