Advanced PI coils

[ppodg]

Compensating coil?

Another approach: let's add a compensatig/decompensating tx or rx coil...

[ppodg]

Elliptical Tx coil?

Hi Aziz & Davor,

And how about elliptical Tx coil, where a>r(Rx1)>b ?
This way you can obtain ANY degree of balance between the Tx and external Rx coils.
Tx and Rx1 can be interchanged; Tx (Rx) can be square etc. as well.

Regards,

[Aziz]

How much off-balance is it with perfect AI?

Hi Davor,

in the example above with with RX+ N=50, RX- N=100 (125 optimal for IB):
TX: 300 µH, 1A coil current, f=10 kHz
Induced voltages:
RX+: -13.399 V
RX-: +10.707 V
Sum: -2.692 V
Too much for an IB coil IMHO.
Aziz

[Davor]

How much off-balance is it with perfect AI?

[Aziz]

Ok guys, I have tried different configurations.

Now the ultimate result (Davor's + Sergey's proposal):
Not possible to meet the AI and IB condition at the same time. You're always screwing one of the criterias.
Aziz

[Aziz]

Thanks!

I am actually very much interested in Rx+ : Tx = 1 and with coupling near 1. With this setup I really wish to know what is the residual unbalance, so that if I make the smaller coil big enough and squeezable I can easily achieve a perfect balance.

My reasoning is that this coil, being coplanar, has all the wires in practically same proximity to the ground, and may achieve very good ground suppression.

Ok, with RX+ being TX size, there is an easy (but rough) IB balancing feature: the slight co-axial (vertical) distance variation (coil coupling variation) of RX+ and TX coil. But the RX- coil requires to be large enough. A significant amount of target response will be cancelled therefore.
I'll see, what my software says. Stay tuned..
Aziz

PS: The Result:
Nope! Forget it. You can't make the RX+ coil as big as the TX coil. The magnetic flux is very strong near the TX coil. We have to make the RX+ coil smaller (at least 0.8 times TX size) or have to rise it much higher (co-axial height).

[Aziz]

Just a picture of my latest 25in noise cancelling coil arrangement. Bottom coil TX.RX1, top coil RX2. Quiet as a mouse, but if you are in an area with little emi, the top coil can be removed.

Eric.

[ATTACH]22319[/ATTACH]

Nice coils Eric. Thanks for sharing your coil picture.
Aziz

[Ferric Toes]

Just a picture of my latest 25in noise cancelling coil arrangement. Bottom coil TX.RX1, top coil RX2. Quiet as a mouse, but if you are in an area with little emi, the top coil can be removed.

Eric.

[Davor]

Thanks!

I am actually very much interested in Rx+ : Tx = 1 and with coupling near 1. With this setup I really wish to know what is the residual unbalance, so that if I make the smaller coil big enough and squeezable I can easily achieve a perfect balance.

My reasoning is that this coil, being coplanar, has all the wires in practically same proximity to the ground, and may achieve very good ground suppression.

[Aziz]

I'm aware of all this, but please do the simulation when you are up to it and see what unbalanced residual percentage of the excitation is present in the Rx coil. In case it is not too big there may be several methods of compensating the residual unbalance. For some odd reason I believe it could do just fine.

Ok, an IB case just calculated:
TX: 1 unit diameter, turns count any
RX+: 0.8*TX unit diameter, 50 turns
RX-: RX+/sqrt(2) unit diameter, 125 turns for IB (optimal for AI = 100 turns)

We have to optimize for AI condition:
N(RX+)*A(RX+) = 2* N(RX-)*A(RX-),
where N() = turns count of the coils,
A() = flux surface area for single turn of the coils

If we slightly make the inner RX- coil bigger, we could achieve the IB balance + AI feature.
But this coil is difficult to build. Nevertheless, a resonable EMI rejection is there.
It doesn't achieve the same depth performance as the tophat coil however.
Aziz

[Davor]

Sure Davor, when I have more time. I already analysed such a coil configuration in the past and it didn't give the benefit. It isn't easy to build too.
The flux surface area of A(RX+) - 2*A(RX-) = 0 works only, when the magnetic field in it is homogenous. But it isn't homogenous and therefore you would need much more winding turns at the inner RX coil (RX-).
We could make the TX much larger and focus to the center region, where the magnetic field is nearly homogenous. It could then work a bit but not as perfect as our tophat coil.

The tophat coil is one of the best IB coils ever.
Aziz

I'm aware of all this, but please do the simulation when you are up to it and see what unbalanced residual percentage of the excitation is present in the Rx coil. In case it is not too big there may be several methods of compensating the residual unbalance. For some odd reason I believe it could do just fine.

[Aziz]

The problem I see with the top hat coil, is that it needs a perfect GB for it to work. Without a perfect GB, any bump the wheels go over, will trigger the indicator, if it is a motion system.

So this will work for you but, unless you give us access to your perfect GB, it will not work for us.

Hi Tinkerer,

no problem, you can make smaller hand-held & stable coils. But the GB is a total different topic.
My "WBGB" is a thermo nuclear weapon and is reserved for the total thermo nuclear metal detector war.
("Wollt ihr den totalen Metalldetektorkrieg?" Oooops, the infamous evil guy has said it differently.. I'm not that evil. But surely much more mad.)

Hey, most people don't even believe in the existence of the "WBGB".
Aziz

[WM6]

The problem I see with the top hat coil, is that it needs a perfect GB for it to work. Without a perfect GB, any bump the wheels go over, will trigger the indicator, if it is a motion system.

So this will work for you but, unless you give us access to your perfect GB, it will not work for us.

So called "Tophat" configurations are known and already patented things at least in industrial use, as proximity sensors, applied and works.

[Tinkerer]

Sure Davor, when I have more time. I already analysed such a coil configuration in the past and it didn't give the benefit. It isn't easy to build too.
The flux surface area of A(RX+) - 2*A(RX-) = 0 works only, when the magnetic field in it is homogenous. But it isn't homogenous and therefore you would need much more winding turns at the inner RX coil (RX-).
We could make the TX much larger and focus to the center region, where the magnetic field is nearly homogenous. It could then work a bit but not as perfect as our tophat coil.

The tophat coil is one of the best IB coils ever.
Aziz

The problem I see with the top hat coil, is that it needs a perfect GB for it to work. Without a perfect GB, any bump the wheels go over, will trigger the indicator, if it is a motion system.

So this will work for you but, unless you give us access to your perfect GB, it will not work for us.

[Aziz]

Could you see about this configuration anyway? In case there is not much extra to compensate, perhaps there are some non-inductive ways to do that in order to keep the anti-interference goodies.
Say, if Tx coil is at 1.1*r ?

Sure Davor, when I have more time. I already analysed such a coil configuration in the past and it didn't give the benefit. It isn't easy to build too.
The flux surface area of A(RX+) - 2*A(RX-) = 0 works only, when the magnetic field in it is homogenous. But it isn't homogenous and therefore you would need much more winding turns at the inner RX coil (RX-).
We could make the TX much larger and focus to the center region, where the magnetic field is nearly homogenous. It could then work a bit but not as perfect as our tophat coil.

The tophat coil is one of the best IB coils ever.
Aziz