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[FAQ] Inductive Sensing Fundamentals Part 2: What is the Ideal Target Thickness for Inductive Sensing?

Materials with high conductivity for inductive sensing may be expensive, so limiting the amount of material used for a target in an inductive system is of paramount importance, but what is the ideal target thickness for inductive sensing?

  • For target thickness, we must acknowledge that the eddy currents induced by the AC magnetic field flow near the surface of the conductor and are reduced in amplitude the deeper we go into the conductive target. This depth is typically measured in “skin depths”.  The equation for skin depths can be found below.


    A good rule of thumb is that the target thickness should be at least 2 to 3 skin depths. The reason for this rule is that at ~3 skin depths thick, 95% of the total current will be induced by the target.


    Another option to achieve ideal inductance is to increase the sensors frequency. At high frequencies the skin depth will decrease which will result in eddy currents concentrating at the surface of the conductor. In order to achieve the best performance, a thick target could be used or the frequency of the sensor could be increased.

    When working with inductive touch buttons it is important to take into consideration the deflection of the conductive target. The deflection produced in the target surface with a given amount of force is inversely proportional to the material’s tensile strength and thickness. A constant force will produce a larger deflection in a thinner/less rigid target than a thicker/more rigid one.

    For more information please refer to the following documents:

    LDC Target Design

    Inductive Touch Buttons for HMIs

    Inductive Touch Buttons for Wearables