Arbitrary Waveform

[prisae]

This PR implements (finally) the possibility for an arbitrary waveform

• Convert all loop examples
  • TEMFAST
  • WalkTEM -> Delay necessary? Bandpass filter necessary?
  • IP and VRM -> Check B; dB/dt stuff; Negative waveform times?
  • Others?
  • Ping folks of relevant examples for feedback
  • Compare waveform to signal={-1, 0, 1}
• Create a comprehensive loop example (see info in Document better loops #232)
• Document
• Add tests
  • Test also against step-on, step-off, impulse

Examples that deal in one way or another with loops:

• Figures 4.7 and 4.8 from Ward and Hohmann
• WalkTEM example
• TEMFAST example
• IP and VRM example
• In-phase and Quadrature, with GEM-2 and DUALEM-842 examples
• Difference between magnetic dipole and loop sources

[prisae]

Hi @orerocks - this is the new implementation of the arbitrary waveform in empymod. Could you have a look at your example, and give me feedback (here or in the SimPEG chat) if your example looks OK to you?
Here is a render of your example: https://empymod--253.org.readthedocs.build/en/253/gallery/tdomain/ip_vrm.html

[prisae]

Hi @aignerlukas - this is the new implementation of the arbitrary waveform in empymod. Could you have a look at your example, and give me feedback (here or by email) if your example looks OK to you?
Here is a render of your example: https://empymod--253.org.readthedocs.build/en/253/gallery/tdomain/tem_temfast.html

[nwilliams-kobold]

Looks great. A few general comments:

• "WalkTEM -> Delay necessary? Bandpass filter necessary?": I don't have answers on this, but I think both are good practice:

  1. delay_rst is i think what we usually call "sensor delay" which basically describes the length of pause that happens from when the TX is nominally expected to achieve 0 current and when the timing gates start. It allows for natural variations in the ramp-down. If that's the case, then it should be a user-parameter defaulting to 0.0 seconds.
  2. Aarhus have made good points in the past about including instrumentation filters in modelling workflows, and this is a good example of that. However, most equipment suppliers don't adequately describe their instrument filters. Keeping this around is a good example of how one might do it. But maybe need to include a comment saying that if you don't know what to use, try without one.

• One point that I had a really hard time with on the waveform in my production code was what happens when the waveform doesn't end at t=0, or where the ramp-down starts at t=0, but doesn't finish until later. The simple off-time heuristic in get_time wasn't enough. I ended up having to recompute the times relative to the end of the ramp, and cover a period of at least Ton + Toff. I may be doing overkill but it is working.