Hi Everyone, I have issues with understanding electromagnetic waves.
From https://www.bbc.co.uk/bitesize/guides/z9bw6yc/revision/4
I found the following sentence "When radio waves are absorbed by a conductor, they create an alternating current. This electrical current has the same frequency as the radio waves."
I assume the conductor means metal.
My first question is, if I point these electromagnetic waves (low frequency or high frequency), let's say from radio frequency identification (RFID), towards a coated steel pipeline. Does it generate AC current on the place where coating defect is present (e.g. bare metal surface)?
Second question: If the same steel pipeline is cathodically protected by anode, can the electromagnetic waves from radio frequency interfere with cathodic protection (CP) system and vice versa? Has anyone encountered this?
If the coating is an electrical insulator, then the RFID will generate currents on and inside the surface of the steel pipeline. It is likely that defects in the coating will not make any difference to this. RFID goes through insulators a bit like light through glass.
I don't expect RFD will interfere with the cathodic protection. RFID will generate currents that change direction millions of times a second that should balance out and not cause problems, and the power levels for RFID are very low, so the currents will be very small, like a milliamp or less crossing each cm of surface width, even with the RFID reader very close.
Malcolm White , I am not sure how RF currents can be generated _inside_ the steel pipeline, coated or not, particularly buried into the ground. Maybe I have little experience, so can you please comment on this model of excitation?
I should also mention that a conductive media includes semiconductors and weak ionic conductors, which is a natural soil. And despite that there are ground penetrating radars for finding pipelines, cables, and underground cavities, and they may operate even in RFID band, it is a very specific class of equipment, dealing with strong surface reflections and high loss. Hardly RFID signal can be even detected at the typical municipal pipeline depths.
Hi Andrey Porokhnyuk . You are right, RFID would get nowhere near a pipeline buried underground. Underground wasn't in the question. The currents won't get inside the pipe in any case, but would only be on the outside few hundred microns or less of the steel. Look up skin depth effects, if you don't already know about them - I can't tell if you are being sarcastic.
Radar does go into the ground, but it is attenuated quickly, particularly in damp or wet ground. In good conditions microwaves are useful at decimetres and RF at metres, but the power left at these depths is not enough to produce the effects the question was asking about.
yes, that's exactly what I mean. I did not know that "underground" was added later to the question.
Thank you Sovan Mohanty , Andrey Porokhnyuk and Malcolm White for the answers. So to conclude, RFID has very little or negligible effect on the CP system and vice versa.
I would not say about versa that easily. The metal pipe electrically is a very large object. And if some anomalously large AC currents flow in it, it may emit some noise, which can eventually get into RFID receiver's LF band. It is a purely hypothetical situation, which may be related to lighting. In that case many other electronic devices operation will also be disrupted, and even people nearby may receive electrical shock. But it is more probable than RFID creating serious parasitic currents on the pipeline surface.
Dear Yoga Sugama Salim ,
I would like to second the colleagues above and add: The cathodic protection system is a direct current system with normally relatively low DC resistance so any e.m.f. induced by the radio frequency waves from the RFID system will have negligible effect on the cathodic protection system since the induced e.m.f. will be small and have high resistance because of its much higher frequency. One would expect depending on the frequency of the high frequency RFID, the rf frequency current will be much smaller than the DC protective current.
You can easily test this hypothesis by measuring the DC and the AC current at feeding points of the cathodic protection system.
Best wishes
Hello everyone,
I want to ask whether is there any relationship between the power supply and signal transmitted by the active RFID tags? In other words, if the power supply to active RFID tags is less then the signal transmitted by the active RFID tags will be less, is it so?
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