LDC1000 thickness of conductive target

Sammy Peiren

Hello,

I am designing an application in which a very thin target needs to be detected. Is it possible to detect something that is thinner than the skin depth with a high resolution if the metal is very close to the coil (a few mm)?

The skin depth:

$\text{[math]}$

for my parameters:

w=2*pi*f=2*pi*5000000

µr=1.000022

rho=2.6548

I get a skin depth of about 36µm. Can my conductive target still be thinner than that?

over 11 years ago

0 Evgeny Fomin over 11 years ago

TI__Genius 9300 points

Hello,

What resolution are you trying to achieve?

Resolution will also depend on the diameter of the coil.

Rough estimate: calculate 1-e^(-d/σ) - this is how much your sensitivity will be reduced compared to a thick metal target.

0 Evgeny Fomin over 11 years ago in reply to Evgeny Fomin

TI__Genius 9300 points

Sorry, should have been δ in the last formula. d - thickness of your metal.

0 Sammy Peiren over 11 years ago in reply to Evgeny Fomin

Prodigy 95 points

thickness	skin depth	sensitivty loss
10	30	0,283468689
15	30	0,39346934
20	30	0,486582881
25	30	0,565401791
30	30	0,632120559
35	30	0,688596776
40	30	0,736402862
45	30	0,77686984
50	30	0,811124397
55	30	0,840120254
60	30	0,864664717
65	30	0,885441156
70	30	0,903028032
75	30	0,917915001
80	30	0,930516549
85	30	0,941183528
90	30	0,950212932

Alright so about 3 times the skin depth for 95% sensitivity. At half the skin depth I lose about 60% of sensitivity.

I'm trying to measure vibrations in a very thin stretched membrane (a few tens of microns). Displacement of the membrane will only be a few microns, depending on the thickness, stifness and size of the membrane. So ideally my resolution should be as fine as possible (sub micron).

The membrane will be very close to the coil, probably less than a mm.

I have another question regarding my application can I ask this in the same thread or do you prefer a new thread?

Thanks for the help

Sensors

Sensors forum

LDC1000 thickness of conductive target