ferrite simulation

[pustareka]

The parallel resistor, inductor(time constant>10,000usec) target simulation matches what I get with my PI with ferrite beads, not ground(earth). 100,000use time constant is better. Seems to work with a VLF simulation if I did it right. Do you see something wrong with the simulations?

Added VLF simulation. click on Tx and Rx, try 5kHz and 50kHz with V1. Get a small shift at 5kHz, more shift at 2kHz. Probably shouldn't see any shift. Is the problem with the spice simulation or ferrite simulation?

yes problem big is.all simulator wrong. finite variable problem.ferite have many variable imposibile simulate. every pulse-sin(x) wave modifikuje ferit properte to jest variable. many variable do no have any simulator. similar komvi vojadzer problem - imposibile solve, very mach variable play game. similare put finger in no run water. make waves. variable waters change. finger change water variable. ALL TRUTH. albedo sistem play game.

[Carl-NC]

I'm not sure I completely understand everything that's being posted in this thread, but the parallel RL circuit generally models an eddy current target. A small tau approaches 90° (salt) and a large tau approaches 180° which would be a superconductor. So the "big L small R" (tau = 10,000us) models a high conductor, not a ferrite.

The RL model is incapable of modeling a purely magnetic target and probably even a ferrous target. I've not thought a lot about this so I may be wrong, but that's what I see at first glance. The sims I've done over the years have always used RL target models for eddy targets, and I never considered trying to model ferrite. It would seem to me that ferrite would be modeled in a mono coil by coupling the inductance of the coil to the current through the coil to simulate the effect of ferrite on µ. In an IB system, you would probably need to add a dependency to the k term. If these dependencies are instantaneous, you have ideal ferrite. If they have a decay, then maybe that makes a ferrous target.

[Davor]

I believe it was PiTec (I'm not sure) that once suggested the very same, and it worked for me ever since. If I combine the inductance or mutual inductance increase, the response becomes a ferrite, or in case of added conductive target - a ferrous one.
There are no native primitives in LTspice to do inductance or K modulation, so I created my own models. Otherwise you may only observe differences between discrete steps.
If you have some measured values of ferrous targets vs frequency, I'll be able to tune a few such targets for everyone here to use.

[Ferric Toes]

Initially (perhaps mistakenly) I thought this thread was about modelling the magnetic viscosity in mineralised ground. Hence my comment about frequency dependent susceptibility. I couldn't see why one would want to model ferrite unless it was to design a ferrite cored coil as in a pinpointer probe. Ideally, a rod for this purpose should have high susceptibility, but no frequency dependence within the band of frequencies transmitted. If you had the latter, then with a PI pinpointer a unwanted decay signal would result and which would be superimposed on the decay of a detected object.

Modelling the response from soils and rocks that contain superparamagnetic minerals is probably difficult. You would need to model a magnetic core coupled to a TX coil driven by a sine wave, where the susceptibility halves for each decade change in frequency. You would then need to couple it into an RX circuit. That is how I understand it, which may or may not be correct. P.I. seems rather less straightforward, but it is easy to see the decay waveform resulting from frequency dependence after a bit of amplification. Also, it is easy to see that it is not an exponential decay, by displaying on log/linear or log/log scales. Maybe you can simulate it by summing a suitable number of exponentials.

I have not looked back on Davor's previous work as yet, and I believe I have some geophysical papers that deal with this subject. However, before delving further, is this thread to do with soil magnetics, commercial ferrites, or ferrous metal objects?

Interestingly, black magnetic sand from California which has a high percentage of magnetite, has high susceptibility but very low viscosity (freq. dependence). Hardly affects a PI but plays havoc with IB.

Eric.

[Davor]

OP green asked about ferrite in general, and in a subsequent post it turned to be a ferrite as a target. It is not very different from ferrites in soils, or when combined with a conductive target - a ferrous target altogether. Point is that we are mostly using conductive targets in simulation, and ferrous targets fall into a mystery department.

I made a viscous target model before. See "Target models for simulation" topic. Apparently it works well for both PI and CW.

[Skippy]

I brought up the additional topics of ferrous targets, and ground pickup modelling mainly because it seemed an important, yet never-discussed theme.

I was thinking that if the behaviour of a ferrous target could be modelled, then the ground could then be modelled by treating it as a large square grid of ferrous targets, all contributing to make up the total ground signal. My interests were specifically for VLF machines with DD IB coils.

[Skippy]

I forgot to add:
As a real physical experiment, I was looking out for a large quantity of ferrite beads, and was going to lay them out on a grid, and compare to single ferrite beads (or small clusters) .
Getting the beads cheap was the problem. I'm still looking. I have quite few, so I could do some worthwhile experiments, but to do the full array would probably need 500 of them....

[Ferric Toes]

For those interested in magnetic viscosity soil response, both for PI and CW detectors, here is further reading much of which is available as .pdf via Google.

a) Mapping of quadrature magnetic susceptibility/magnetic viscosity of soils by using multi-frequency EMI. (Recent paper. Oct.2016)

b) Magnetic viscosity, quadrature susceptibility, and frequency dependance of susceptibility in single domain assemblies of magnetite and maghemite.

c) The influence of magnetic viscosity on electromagnetic sensors. (Paper deals with frequency domain and time domain).

d) Time-domain magnetisation of soils (VRM), experimental relationship to quadrature susceptibility.

There is much more, but some papers on this subject are quite heavy going in the maths department.
One more point, some papers refer to ferrite minerals (magnetite and maghemite) in the soil, so this is a valid term. Sorry to have questioned it, but we still have to be careful of man-made ferrites which can have quite different characteristics than natural soils and rocks.

Eric.

[green]

First, I am just trying to learn something. When I recorded a ferrite bead with a IB coil and a constant rate Tx the Rx signal was constant amplitude during Tx. I was thinking VLF Rx signal amplitude should be constant with frequency if the Tx amplitude is constant. Don't have a VLF detector so I was wondering if I could simulate with spice. (How to simulate a ferrite bead with spice?) Looked at VLF simulation again this morning, change L1 resistance to .1 ohms and the phase and amplitude stay constant with frequency so I'm thinking the parallel L R might be a good ferrite simulation. Don't know how to simulate the California ground with a positive slope during Tx. Any suggestions would be appreciated.

More targets. Some observations. The flatter the Rx signal during Tx the lower the signal after Tx off. The nail orientation was adjusted for the flattest and steepest Rx signal during Tx. The razor and ferrite bead look very close, would they act the same with a VLF detector? When I joined this site you could type what I knew about metal detectors on a postage stamp with 1inch letters. Hopefully you could use smaller letters now. For me, keeping the brain active in my old age, learning something about spice and metal detectors and making a PI detector are my goals.

[Carl-NC]

I forgot to add:
As a real physical experiment, I was looking out for a large quantity of ferrite beads, and was going to lay them out on a grid, and compare to single ferrite beads (or small clusters) .
Getting the beads cheap was the problem. I'm still looking. I have quite few, so I could do some worthwhile experiments, but to do the full array would probably need 500 of them....

I use a "ferrite board" with maybe a 20x20 array of small P-type pot core ferrites, I think it's 25-30cm square overall. It presents a much broader signal than a single piece of ferrite, valuable for DD coils and other complex geometries. Digikey has ferrite plates which are much cheaper and even have a peel-n-stick surface. They come in round and square, up to 1" I think. I have some intending to make another (bigger) ferrite board but haven't gotten around to it. Plus I still need to test the plates to make sure they have good behavior.

[Skippy]

That's roughly what I had in mind, something like 25 x 25 array, on 2cm spaced grid. A few years ago, in a previous job, I had access to loads of beads, bags of 100, and plenty of them, but couldn't think of any use for them....

I had also consider the same arrangement but with steel ball-bearings, 2mm / 3mm diameter.

[pustareka]

No, no, easy road to GOLD tresure. mineral world DEFEND atak humans.
ferite is wide poem. many ferite are no one equal two.

read important.NATURE Page 795, October 29, 1938
Variation in the Longitudinal Incremental Permeability due to a Superimposed Circular Field
magcore.PDFFerromagneticMats.pdfMA012000a.pdf

[green]

I recorded amplifier out with a ferrite bead and some California ground using an IB coil and my bench PI awhile back. Tx 160usec constant rate(6250 amps/sec). Copied scope signal to Excel to see slope better, both looked flat on the scope trace. Been playing with spice today, constant rate pulse. 10uH parallel with .001 ohms(10,000usec time constant)gives a fairly flat signal during Tx. 1000usec TC has some decay slope. Something over 10,000usec should be flat. The ground signal is higher at the end of Tx. Ferrite doesn't show a R signal after Tx off delay, ground does.

Added cr.zip, Rx(c)out
Don't know how to simulate ground with spice but I think the Rx signal during Tx on time should be fairly flat with constant rate and an IB coil.

If I remove the ferrite bead on the bench the Rx signal with Tx on goes to zero. If I cut the target out of spice the Rx signal stays the same. One problem is I don't understand spice.

[Davor]

Your R3 is below any realistic value, hence nothing happens. With 1 ohm you'll get something like bronze. If you want a nearly realistic ferrite simulation, just add a statement: K3 L1 L5 .001

[green]

Your R3 is below any realistic value, hence nothing happens. With 1 ohm you'll get something like bronze. If you want a nearly realistic ferrite simulation, just add a statement: K3 L1 L5 .001

Thanks for the reply. I'm trying to simulate my IB coil. Two round Rx coils, one inverted to cancel with a Tx coil surrounding the Rx coils. I see know I have only one Rx coil(L5). I want the Rx coil to be zero during Tx with no target then read the target when I add it like the bench circuit.