RF performance through ITO or touch film

[Tom]

Hi there,

We're looking to improve the touch performance of our products by moving from PCB electrodes to a dedicated touch film. Can anyone provide any references to info on how 2.4GHz RF is impacted by touch film? Specifically I'm wondering how much a full ITO matrix will degrade RF performance, assuming the touch surface is the only window in the product for RF. An alternative to an ITO matrix would be specific touch buttons or using silver electrodes, but again, I'd like some info on the impact they have.

Thanks,

Tom

[run_ar]

Hi Tom,

Not sure what the touch film is made of / how it is constructed. Have you checked the specification from the manufacturer? I would assume this contains some kind of metal, which in case it would not be very RF friendly.

[Tom]

Hi run_ar,

At this stage I don't have a film selected, I'm just trying to make the right architecture choices for the product. In general the electrodes on the touch film are going to be an alloy (so a metal).

Given that, the questions I have are to understand if there are any workarounds:

• Can I just have the antenna behind an aperture in the touch film where there are no electrodes? What should that stackup and alignment look like to maximise performance given the constraints?
• Or can I design the spacing of the electrodes such that the RF will be able to propagate between them?

Obviously this is where an RF engineer would be helpful. Short of that, does anyone have some good recommendations for resources I can look at to understand a little better?

Thanks,

Tom

[ketiljo]

Any metal close to the antenna will affect it. So keep the antenna as free as possible. If the touch film is completely metalized, it will block the radiation from the antenna. You will need an aperture over the antenna. This would need to extend some 5 mm from the antenna, so it will be quite large.