PI shielding

[Mr.Jaick]

To discharge induced currents fast, you want high resistance.
To discharge capacitor charge fast, you want low resistance.
To discharge inductive and capacitive charge fast at the same time, you want critical damping. Critical damping is the sweet spot where both charges are discharged at the same time.

Thank you Monolith
good info

just a quick check of my understanding:
A_ we want a middle ground on shield material (semiconductor) let's use medium to heavily doped silicon resin (YEEEH)
B_ higher shield eddy = NO small low conductive target sensitivity anymore
C_ higher shield capacitance = longer delay, so basically the same effect
so we want the resonant point between these two, XC = XL or maybe XC = R

now I have two questions :
1_ can we use either high or low conductive shield material and then compensate the negative effect of them with the damping resistor ?
2_ what can i use for PI mono loop with let's say 15 or 20uS sample delays
two choices, the Copper tape in the previous post OR the same tape but Aluminium
I guess Aluminium

[Monolith]

Thank you Monolith
good info

just a quick check of my understanding:
A_ we want a middle ground on shield material (semiconductor) let's use medium to heavily doped silicon resin (YEEEH)
B_ higher shield eddy = NO small low conductive target sensitivity anymore
C_ higher shield capacitance = longer delay, so basically the same effect
so we want the resonant point between these two, XC = XL or maybe XC = R

now I have two questions :
1_ can we use either high or low conductive shield material and then compensate the negative effect of them with the damping resistor ?
2_ what can i use for PI mono loop with let's say 15 or 20uS sample delays
two choices, the Copper tape in the previous post OR the same tape but Aluminium
I guess Aluminium

Aluminium and copper have similar rather long TC's. As far as the tape goes, the thickness plays a very important role.
Woven fabric would be a better solution for 15 to 20uS delay.
Important to leave a minimum spacer of about 3mm or 1/8" between shield and coil wires.
Coil building is a fine art. Any coil will give some kind of result, but to have a really good coil, many factors need to be taken in account.

[kt315]

I was always under the impression that the true purpose of a shield was to eliminate capacitative effect of the ground.
Quite apart from being on mars, by the way ,the perseverance has shielding. The use a very high tc material.

take any protective pocket from/for a PC board/card (same with black strips or slightly mettalized on color) and try to measure
the resistance. you will get infinity on value. while those thing SURE are protecting from electrostatic -!
so maybe NOT resistance you wait to get but SOME ABILITY that you do not see? or do not want to notice??

[Mr.Jaick]

Aluminium and copper have similar rather long TC's. As far as the tape goes, the thickness plays a very important role.
Woven fabric would be a better solution for 15 to 20uS delay.
Important to leave a minimum spacer of about 3mm or 1/8" between shield and coil wires.
Coil building is a fine art. Any coil will give some kind of result, but to have a really good coil, many factors need to be taken in account.

yes Coil has a comprehensive science behind it.
the thinner the tape the better right?
so only scotch 24 and graphite spray is suitable for PI coil shielding... hmm
the problem is scotch 24 is not available in my country and i have to import it very expensive
graphite spray is available but price is beyond insanity
I see in the hammerhead build document Carl suggested Aluminium foil overlapping method, if you can remember that
while hammerhead has a min 10uS delay originally (well we can argue that's for experimenting)

right now i'm trying to shield Felezjoo PI coil to make it less noisy
after that i need a good shield material for MPP or Barracuda which i'm worrying about, not many choices
aluminium tape and foil, copper tape, couldn't find Nickel tape but found Nickel foam which looks very good but only in square shape like 10cm x 10cm and of course very expensive!
I don't think conductive mylar is any different than above
any recommendations ?

[Tinkerer]

yes Coil has a comprehensive science behind it.
the thinner the tape the better right?
so only scotch 24 and graphite spray is suitable for PI coil shielding... hmm
the problem is scotch 24 is not available in my country and i have to import it very expensive
graphite spray is available but price is beyond insanity
I see in the hammerhead build document Carl suggested Aluminium foil overlapping method, if you can remember that
while hammerhead has a min 10uS delay originally (well we can argue that's for experimenting)

right now i'm trying to shield Felezjoo PI coil to make it less noisy
after that i need a good shield material for MPP or Barracuda which i'm worrying about, not many choices
aluminium tape and foil, copper tape, couldn't find Nickel tape but found Nickel foam which looks very good but only in square shape like 10cm x 10cm and of course very expensive!
I don't think conductive mylar is any different than above
any recommendations ?

YX Silver conductive fabric tape, one-way duct tape for laptop, cell phone, LCD screen EMI, 20 meters

YX Серебряная проводящая тканевая лента, односторонняя клейкая лента для ноутбука, сотового телефона, ЖК экран EMI, 20 метров|Лента| | АлиЭкспресс (aliexpress.ru)

[Mr.Jaick]

thank you
i'll try to find a similar thing

[Monolith]

Attempt at measuring hand TC. Used the coil I was playing with. Recorded amplifier out, persistence on to get both Tx polarities.

Some observations.
One Tx polarity effected more than other, a ferrite core(positioned on coil) was used to adjust what no target signal looked like.
It appears X signal dominates R signal out to maybe 4us.
With the nickel, signal reversed end A to end B. With hand as target, signal changed from no target but appears to be the same end A and end B(maybe hand isn't acting as a target?).
Don't know it means? Looking at each end of Tx coil with the scope, similar but not the same.
Hand doesn't seem to be detected with scope disconnected from circuit. Sometimes with scope connected seems it does detect the hand, where the scope is connected can make it worse.
Wish I had some answers not questions.
Anything else I might try?

CH2 not important, should have turned off.

I am not sure if I read your graphs correctly. Do we see a high amplitude response, with a very short TC?, like less than 1uS?

[Monolith]

take any protective pocket from/for a PC board/card (same with black strips or slightly mettalized on color) and try to measure
the resistance. you will get infinity on value. while those thing SURE are protecting from electrostatic -!
so maybe NOT resistance you wait to get but SOME ABILITY that you do not see? or do not want to notice??

The metallized one's react like space blanket. It is difficult to make a connection with probes, but the metal responds with eddy currents.

[Monolith]

thank you
i'll try to find a similar thing

A_ we want a middle ground on shield material (semiconductor) let's use medium to heavily doped silicon resin (YEEEH)

You could try doping some silicate. Silicate is also known as "waterglass"

[green]

I am not sure if I read your graphs correctly. Do we see a high amplitude response, with a very short TC?, like less than 1uS?

Not certain what you are asking. Some scope pictures of amplifier out with regular strength aluminum foil targets. Was playing with unipolar circuit, could connect bipolar circuit and make some more measurements. Didn't see any change on scope when hand was placed near coil. 10mm square was placed on center of one of the Rx coils, 1inch square was above one of the Rx coils.

Small shift right when target was added, guessing X signal greater than R signal?

[Monolith]

Not certain what you are asking. Some scope pictures of amplifier out with regular strength aluminum foil targets. Was playing with unipolar circuit, could connect bipolar circuit and make some more measurements. Didn't see any change on scope when hand was placed near coil. 10mm square was placed on center of one of the Rx coils, 1inch square was above one of the Rx coils.

Small shift right when target was added, guessing X signal greater than R signal?

X signal is an interesting conclusion. I have the feeling that we could learn a lot from looking at this waveform in detail. How much it changes with the target and where it changes with the target. Is that a phase shift what we are seeing?