coil vs. target geometry

Hi

First, conductive fabric will be OK for LDC1000. And it`s possible for detect distance when it is within 0.5 inches of the target, at an accuracy of +/-0.05 inches. But I think it`s diffcult to detect a 1 inch metal disk approaching a 12 inch by 12 inch target area.

You can refer to the FAQ post.

Regards, Sunny.

Sunny,

Thanks for the reply. I think I didn't word my question very well. I've read the FAQ that says the target diameter should be at least half the coil diameter, but that can't happen in my case. On the other hand, I don't need very high resolution, so perhaps I can violate the target_dia = coil_dia / 0.5 rule but by how much? And if I cover my 12" x 12" area with multiple coils, perhaps square-shaped PCB coils, can I get away with 3" or 4" squares to cover my 12" x 12" area? Will the coils need to overlap to avoid blind spots at the coil edges?

I've ordered the evm, but, any insight you can give me from your hands-on experience will help greatly.

Thanks,

Ray

Hi,

For presence detection , a target with a size comparable to the size of the coil can be sensed at a distance of up to the coil diameter,  So I think the max detect range is as the coil diameter. 

Second, Yes, it  need to overlap to avoid blind spots at the coil edges.

Regards, Sunny

OK. I can't increase the size of the target, and if it really can't sense a target smaller than the coil size this won't work for my app. But I already have an EVM on order so I'll spend a couple hours with it to get an idea of how close it comes.

Thanks for the help.

Ray

Is it possible for your app to make the coil larger than 12"?

@Evgeny, the 12" x 12" is approximate. It could be somewhat bigger, but I don't think it could go beyond 14" x 14".

Thanks,

Ray

The biggest challenge in this application is to create uniform magnetic field in this large area.

If magnetic field is non-uniform, the response of the sensor will depend on both distance and position.

A big coil can generate a uniform-enough field (the required resolution is not high).

Another approach is to have a mesh of sensors, each, say, 0.5" diameter, and then to triangulation to determine the position, and then, knowing that, determine the height.

Evgeny, which is better in terms of X-Y uniformity (Z being perpendicular to plane of coil): a PCB coil with traces covering the entire X-Y surface, or a discrete wire coil where all turns are concentrated near the periphery of the X-Y area?

That's a very good question. Unfortunately, I do not have a quick and easy way to model such a system.

But it's something to experiment with. If you have a possibility to try different PCBs, I can give you a few ideas of what may work.

I should get the EVM in a couple days and can provide more feedback after that.

Thanks,

Ray