Thanks for the feedback, Bob. You have a good question, and I don't have a good answer. The core material should ideally be completely soft, i.e. no area enclosed in the B/H curve, so no losses due to magnetic cycling. However, I can imagine that eddy-current losses might be significant at these frequencies. The end effect should simply be some heating of the core, and a phase shift between the drive and sense signals. The demodulation electronics would need to deal with this, but I don't think it fundamentally affects the measurement principle. But I'm just speculating - perhaps someone else actually knows the answer? -- Philip

Funny you should ask... ;-) Springer is about to publish a book, "Magnetic Measurement Techniques for Materials Characterization" (www.springer.com/gp/book/9783030704421), for which I wrote a chapter, "Magnetic Field Sensing Techniques". In that chapter I give a short overview of Hall sensors, fluxmeters, fluxgates, anisotropic magnetoresistive (AMR) and giant magnetoresistive (GMR) sensors, and nuclear magnetic resonance (NMR) magnetometers. The references I used for fluxgates are: - K. Evans, Fluxgate Magnetometer Explained-Mar. 2006 (Invasens, Cheltenham, 2006) invasens.co.uk/FluxgateExplained.PDF. Accessed 26.07.2019 - Texas Instruments (2016) DRV425 Fluxgate Magnetic-Field Sensor. www.ti.com/lit/ds/symlink/drv425.pdf. Accessed 26.07.2019 - Korepanov V, Marusenkov A (2008) Modern Flux-Gate Magnetometers Design. In proceedings of International Scientific Conference on Magnetism-Geomagnetism-Biomagnetism MGB-2008, Sežana, Slovenija, Nov 7-8 2008, pp. 31-36. www.viviss.si/download/viviss/ZBORNIK%20MGB/Korepanov_paper_31_36.pdf. Accessed 26.07.2019 Hope that helps! -- Philip

@@MetrolabTechnology Thank you so much! I found some resources in the last few days, but these are just extraordinary and they will help me immensely.

@@MJAlberts Excellent! Happy to help.

HI Jace, By "second version", I assume you mean the second core geometry shown, at roughly 04:08 in the video? The same iron loop can be used for fields pointing either to the right or to the left; that would just change the sign of the detected flux change as the core goes into and out of saturation. Does that answer the question?

@@MetrolabTechnology no I meant the 2 dimensional version Sorry my question was so unclear. Thanks, this is an informative video! Will be making one soon

OK, I see: you're talking about the diagram at roughly 04:53 in the video. Yes, one can use the same iron core for the two directions; the diagram was just intended to show how that was equivalent to two independent sensors.

@@MetrolabTechnology on thanks for the clarification

Khalid

Hi Vadim. Thanks for watching. The simplified diagram in the introduction only shows some of the physical effects that can be used to measure magnetic flux density; as you undoubtedly know, there are well over a dozen, and my talks focus on the ones we use in Metrolab instruments. You are absolutely correct that optically pumped NMR is a family of very sensitive field measurement techniques, suitable for precision measurements at low fields. Perhaps you can refer us to a good technical talk on the subject? Philip

@@MetrolabTechnology thanks for for answer. I found your description of NMR sensors in another video on your channel. For me that topic is interesting because i have master of science degree in plasma physics and i want to build own magnetometr setup in my home workshop. Right now im in process of planning future construction works. I think i able design a something new if i will combine computer vision and that NMR magnetometr sensor.

@@vmened Ambitious! I'd be interested in learning more, if and when you're ready to talk about it. Sincerely, Philip

@@MetrolabTechnology My skype is vadimedition. I will be grateful if at a difficult moment you can help me with advice. Thank you in advance.