0
\$\begingroup\$

All other variables being equal, how does waveform complexity of a plane wave affect shielding effectiveness? Is it easier to attenuate a sine wave or a complex waveform?

\$\endgroup\$
  • \$\begingroup\$ You should be more clear about what you mean when you say, "wave." It sounds like you are asking about how to shield something from radio-frequency (RF) electromagnetic radiation (also known as, "radio waves"). Is that correct? If so, then knowing roughly what frequency band the signal occupies will be more important than knowing the bandwidth/wave-shape/information content. \$\endgroup\$ – Solomon Slow Feb 28 '18 at 16:03
  • \$\begingroup\$ A sine wave has only one frequency. A complex waveform has many component frequencies that can extend far lower and far higher than that single frequency. A shielding effective for the single sine frequency might not be as effective at such extreme frequencies, so some part of the signal might slip in. \$\endgroup\$ – Sredni Vashtar Feb 28 '18 at 17:04
  • \$\begingroup\$ @james, yes, you're right. I thought the tag "electromagnetic" and the term "shielding effectiveness" would have made that clear, but I'll consider adding clarification to my question. \$\endgroup\$ – dcorsello Feb 28 '18 at 19:04
3
\$\begingroup\$

In almost all cases, where linearity holds, it makes no difference.

You can analyse a complex waveform into a superposition of component sinewaves. An attenuator will reduce each, possibly by a different amount.

If the attenuator shifts the phases of the components, this may shift where the peak occurs, and so the ratio of peaks of output to input may be slightly different to the ratio of powers.

If your fields are so large the attenuator goes non-linear, then the complex waveform will likely send it non-linear at a lower power, as its peak to RMS ratio will be higher than that of a sinewave. Whether that means it attenuates more or less will depend on the detail of the non-linearity.

\$\endgroup\$
  • \$\begingroup\$ The question is about "shielding". Shielding is usually a set of conductive elements of various shapes and sizes, frequently with gaps and different grounding methods. Thus the shields may have resonances, and usually don't attenuate all things uniformly over wide frequency ranges. \$\endgroup\$ – Ale..chenski Feb 28 '18 at 16:00
  • \$\begingroup\$ @AliChen ... and a shield amplifies or attenuates a signal? 'Possibly by a different amount' === 'don't attenuate all things uniformly over wide frequency ranges'. \$\endgroup\$ – Neil_UK Feb 28 '18 at 16:10
  • \$\begingroup\$ I am not sure what do you mean. My English is poor. If a shield has pieces hanging out of the size of 1/4 of some wavelength, it will amplify emission at that frequency. Or magnify susceptibility to external radiation... \$\endgroup\$ – Ale..chenski Feb 28 '18 at 17:29
  • \$\begingroup\$ @AliChen unless it's powered, so the shield is receiving power from some external source, it cannot add power to a signal. It may act as a transformer between a mismatched source and receiver to improve the matching and so power transfer. Normally when we talk about a shield, we assume that there aren't resonators engineered into it, which can be false if it has slots in it! \$\endgroup\$ – Neil_UK Feb 28 '18 at 17:35
  • \$\begingroup\$ This is a philosophical topic. Yes, a shield can't add power to a signal. However, a specially-formed conductive elements can collect power from bigger area, and create fairly strong signals at specific isolated points. Especially if this point is connected to input of a RF amplifier. These arrangements are called "directional antennas", a horn in road radar detector is an example. And when we talk about shields, the reason of the talks is to avoid accidental engineering of resonator cavities and quarter-way receiving antennas. It looks like we are approaching the question from opposite ends. \$\endgroup\$ – Ale..chenski Feb 28 '18 at 18:12
2
\$\begingroup\$

Any "complex waveform" is a superposition of "sine waveforms". Therefore each "sine waveform" will be affected in accord with your shielding technique, and should be addressed individually. So yes, complex waveform needs more work.

\$\endgroup\$
  • \$\begingroup\$ in my application, the attenuator is a passive, ungrounded, sealed enclosure, which needs to attenuate a broadband signal. So, in my case, I don't need additional attenuators to address multiple, individual frequencies. Rather, I need to choose a material that attenuates well across the entire bandwidth. \$\endgroup\$ – dcorsello Feb 28 '18 at 20:04
  • 1
    \$\begingroup\$ @dcorsello, how broad is your "broadband signal"? If it is from 30 Mhz to 30 GHz, then you might need to pay close attention to possible gaps in your enclosure. And what choice of "materials" do you have in mind, other than copper foil? \$\endgroup\$ – Ale..chenski Feb 28 '18 at 20:16
  • \$\begingroup\$ The frequencies are 1-1000 MHz. \$\endgroup\$ – dcorsello Feb 28 '18 at 20:30
  • \$\begingroup\$ @dcorsello, I took some look into your other questions. As I see you need a protection from a strong electromagnetic pulse, weapon-grade. AFAIK, copper doesn't shield magnetic fields much. To shield against magnetic field, you need magnetic materials with high permeability. magnetic-shield.com/pdf/magnetic_fields_shields_overview.pdf \$\endgroup\$ – Ale..chenski Feb 28 '18 at 20:37

Your Answer

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

Not the answer you're looking for? Browse other questions tagged or ask your own question.