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Original question:

FDC1004: thickness between a sensor and its associated shield

FDC1004: thickness between a sensor and its associated shield

Michael T Schneider
Expert 3790 points
Part Number: FDC1004

Team, 

My customer has a question concerning the thickness between a sensor and its associated shield when using the FDC1004.

 

From Application Report SNOA928A, Capacitive Proximity Sensing Using the FDC1004, Page 6:

The size of the shield and distance to the sensor electrode significantly affects the sensing range. A shield

that is larger than and closer to the sensor electrode reduces the sensitivity and maximum range, but it

limits the amount of interference seen by the sensor electrode. A smaller shield further away from the

sensor electrode has an opposite effect on sensitivity and detection range. For more information on

shielding effects, refer to the Capacitive Sensing: Ins and Outs of Active Shielding application note.

What is the tradeoff for the shield to sensor distance versus sensing range? While most of the application notes reference FR4 at a thickness of approximately 60 mils, Application Report SNOA926A uses Plexiglas at a thickness of approximately 23.6 mils. I’m primarily interested in thicknesses less than Plexiglas.?

Thank you for your help

  • 0
    TI__Genius 11015 points
    Hi,

    We have received your question & our application engineer will respond to your query soon.
  • 0
    TI__Mastermind 23810 points
    Actually, app report SNOA926A only uses a piece of dielectric tape between the shield and CIN, so it is about as thin as you can get.

    Figure 14 shows how the sensitivity decreases with the shield in such close proximity, while Figure 15 shows how the shield does its job by reducing interference from the side.

    Taking this experiment further, you could show that the sensor with no shield would see a very similar response if the target approached from the reverse side of the sensor. With the shielding, the interference will be greatly reduced.