A Single Coil TEM field metal detector with simultaneous transmit and recieve.

[Riss]

whether in simulations or real circuits ... resistance is does not affect current sources ... we just dissipate more power.
A 1.0000 amp current source is a 1.0000 amp current source through 1 ohm or 100 ohms.

This is undoubtedly true, but the higher the resistance of L1, the smaller current will fluctuate in L2

[mickstv]

Hi Paul, looks interesting. Any chance you can post a YouTube with it running and showing us how it reacts on the oscilloscope to different objects like ferrite core, aluminium, lead. I guess on the raw input, unless you have a preamp strapped to it now and for a complete cycle, thanks.

[moodz]

Hi Paul, looks interesting. Any chance you can post a YouTube with it running and showing us how it reacts on the oscilloscope to different objects like ferrite core, aluminium, lead. I guess on the raw input, unless you have a preamp strapped to it now and for a complete cycle, thanks.

looking at one of the mosfet gate drives and the raw RX signal.

Blue = no target.
Orange = Iron
Green = aluminium

No amplification. Pulse rate = 10 khz. ( Scope says 20 khz but there are two magnetic transitions per cycle )
Even though the mag pulses are bipolar the RX signal come out as unipolar ... which is nice.

I cant really post a youtube as there is a factor of demonstrating features in the public domain that are the subject of patents.

[mickstv]

Thanks for that. I think I still have the circuit built from when I was playing with the bipolar alternate TX that you posted. So just add a few extra bits and see what happens....

[Aziz]

Hi all,

I for one would still run a concentric co-planar IB coil for this transmitter.

This is the reason for:
Two channel processing. TX is the main target channel (including ground noise).
A small RX coil with a TX bucking coil is the ground channel. It detects 1000 times more ground noise as the coil coupling coefficient k will be affected by the ground mineralization.
This ground channel will be used to clean the TX main channel (removing ground noise).
The TX channel could be integrated over a very large window time (single integrating window).

We don't need much inductance for the RX coil. RX and TX bucking coil could be really small size too. The TX coil will still pick up deep gold.

Now go for it!

[Orbit]

Two months ago I was involved in experiments for the Volvo car industry with a friend who is working on a patent for wireless energy transfer between robots. And I wasn't committed to the detectors. But I was encouraged by this thread using a mono coil for transmission and reception with discrimination decided to repeat my experiment on the GT for which the Altra detector is fully functional with a DD coil works perfectly in the field. So I can't put an oscillogram against it! But I used the GT as a platform and changed the input part and some other things on the basic schematic and attached my mono coil which is wound in a very specific way, nothing like that I haven't noticed anyone mention anywhere. The result is on the video, in the next few days I will set aside to turn off the double tone when the iron is crossed and maybe replace a few other things so that in a few days I could get a fully usable detector with a mono coil and bipolar transmission that has excellent discrimination and ground rejection on one channel.https://youtube.com/shorts/iLerw0GsR...Xi6ea7g0cDw9OG

[Carl-NC]

No amplification. Pulse rate = 10 khz. ( Scope says 20 khz but there are two magnetic transitions per cycle )

I consider the detection edges when quoting the pulse rate. In this case, it's really an effective 20kHz pulse rate.

Even though the mag pulses are bipolar the RX signal come out as unipolar ... which is nice.

Does this mean we need to re-introduce EFE samples? Swing a big magnet and see what happens.

[moodz]

Does this mean we need to re-introduce EFE samples? Swing a big magnet and see what happens.

I would say no ... the coil is reversed on each edge so the EFE induced voltage is too.
Waving a powerful magnet seems to confirm.

[peterr3]

Before any "big reveal" ... you should all read up on this Minelab patent : https://ipsearch.ipaustralia.gov.au/patents/2023204592

Minelab are trying to lockup bipolar pulse induction till 2043.
What is interesting if you follow this document trail you will see at that site that Nokta has raised an objection to that patent since it would appear that Minelab is possibly trying to patent the idea of a controlled constant current bipolar transmit scheme.
Checkout the correspondence paper trail ( the lawyers are finding the gold here )
It is every companies right to protect their own IP however reading the patent seems to indicate they are patenting the method of producing bipolar constant current transmit scheme ( eg using feedback loops, current sensing, controlled high voltage and low voltage connections across a coil at various timings ...etc etc adapted and arranged. )
It is probable that the latest GPZ8000 model utilises this method. However it does require a separate recieve coil hence the horribly complex donut coil required on the GPZ8K.

Food for thought ...

Nokta objection to the patent is 24 pages and i am told is being backed financially by the Turkish Gov. Nokta have lodged their own patent for their new PI detector the Magnetar 9000 which is ZVT based.

[Carl-NC]

After thinking about it some more, that's what I expected. EFE is common-moded on the entire waveform, so if it causes the +peak to increase to +peak+Δv then the -peak should also increase to -peak+Δv. Reflected to the load resistor, you should see a +Δv after the rising edge and -Δv after the falling edge. When averaging multiple sample, EFE disappears.

[Aziz]

Btw,

the coil need not to be IB type. Mono coil as TX, a smaller GB coil placed in the center position (seperate RX) with a few turns should do the GB channel for GB info. The GB coil would detect during the high dI/dt the GB info. There wont be high voltage on the GB coil.
GB response is 1000 x more than target response. Enough for GB without losing much target response.