SNOA951 June   2016 LDC1312 , LDC1312-Q1 , LDC1314 , LDC1314-Q1 , LDC1612 , LDC1612-Q1 , LDC1614 , LDC1614-Q1

 

  1.   Inductive Sensing Touch-On-Metal Buttons Design Guide
    1.     Trademarks
    2. 1 ToM Basics
    3. 2 How Are Inductive Touch-On-Metal Buttons Implemented?
    4. 3 System Design Procedure
      1. 3.1 Mechanical System Design
        1. 3.1.1 Designing for Natural Button Force
          1. 3.1.1.1 Metal Composition
          2. 3.1.1.2 Metal Thickness
          3. 3.1.1.3 Mechanical Structure of the Button
        2. 3.1.2 Target Distance
        3. 3.1.3 Mechanical Isolation
        4. 3.1.4 Mounting Techniques
      2. 3.2 Sensor Design
        1. 3.2.1 PCB Design
        2. 3.2.2 Sensor Frequency Selection
        3. 3.2.3 Sensor Amplitude Selection
      3. 3.3 Other Considerations
        1. 3.3.1 Button Quantity and Multiplexing
        2. 3.3.2 Power Consumption
        3. 3.3.3 Software Algorithm
        4. 3.3.4 EMI Emissions Testing
      4. 3.4 Design Implementation
    5. 4 Results
    6. 5 Summary
    7. 6 Additional resources

3.1.1.1 Metal Composition

The material choice can have a large impact on how much force is required to achieve the required deflection at a given metal thickness. The key parameter is Young’s modulus, which is a measure of the elasticity of the metal and is measured in units of pascal (Pa). Materials with a lower Young’s Modulus are typically more flexible. Aluminum (AL6061-T6) has a Young’s modulus of 68.9 GPa, while Stainless Steel (SS304) has a higher Young’s modulus of 203 GPa, which makes it about 3 times less flexible than aluminum. Aluminum is an excellent material choice for inductive sensing because it is both flexible and asserts a high inductance change on an inductive sensing coil. Materials such as SS304, can also be used and provide robust results. The difference in deflection for a given amount of pressure between the two materials is shown in Figure 6.

D001_SNOA951.gifFigure 6. Force vs Peak Deflection for Different Materials, Diameter = 20 mm, Thickness = 0.25 mm