Metal over Touch (MoT) involves detecting the deflection of a metal overlay upon a touch. MoT uses a metal overlay separated from the sensor using a thin spacer or etched surfaces of metal overlay as shown in the figure below. When you touch the metal, the metal deflects. This deflection is detected by the inductive sensor. An example of front and back (with etched cavities) of a metal overlay is also shown below. The sensitivity of touch detection depends on the following parameters.
Note that the amount of metal deflection for the applied force depends on metal material, thickness, and flexural rigidity.
Metal over Touch Arrangement
Example Metal Overlay
To find out more on MoT designs, please see the Inductive Sensing Design Guide.