Inductive touch button - QuickField simulation example
Change in coil inductance when the metal foil of an inductive touch button bends toward the PCB coil, producing detectable eddy-current loading.
How to calculate the inductance change caused by foil deformation in an inductive touch button?
Answer Typical applications Geometry
Given
Task
Solution
Results
Engineering question
First solve the mechanical deformation of the metal foil under finger force, then compare AC-magnetic coil inductance with the foil flat and deformed.
inductive touch sensors, proximity sensing coils, foil-based touch sensors
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Simulation problem
Problem Type
Axisymmetric problem of Stress analysis and AC magnetics.
Metal electrical conductivity 37 MS/m;
Coil current I = 0.1 mA, frequency f = 8 MHz,
Finger force f = 2 N;
Metal foil thickness 0.25 mm, Young's modulus E = 70 GPa, Poisson's ratio ν = 0.33.
Calculate the inductance value change due to the foil deformation.
First the mechanical problem is simulated to calculate the deformed foil shape. Then two AC magnetic problems are simulated: with flat foil and deformed foil.
Foil central part displacement is 30μm. Deformed foil profile:
Nominal coil inductance value is 622 nH. Inductance value decrement for the button pressed state is 2%.
On the picture: the deformed shape of the foil scaled 20 times, the eddy currents distribution in the foil and calculated inductance values.
* Reference: Ben Kasemsadeh, Luke LaPointe (Texas Instruments) Inductive Sensing Touch-On-Metal Buttons Design Guide
Video
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