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
* Reference: Ben Kasemsadeh, Luke LaPointe (Texas Instruments) Inductive Sensing Touch-On-Metal Buttons Design Guide
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.
Video
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