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ECE 480 – Team 6

How to Choose/Use Capacitive Sensors for Various Applications. ECE 480 – Team 6. In Order of Presentation: Ishaan Sandhu Danny Kang Anuar Tazabekov Arslan Qaiser Eric Otte. Background. Three Main Types: Displacement Touch Sensor and iPod Click Wheel Accelerometer

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ECE 480 – Team 6

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  1. How to Choose/Use Capacitive Sensors for Various Applications ECE 480 – Team 6 In Order of Presentation: Ishaan Sandhu Danny Kang Anuar Tazabekov Arslan Qaiser Eric Otte

  2. Background • Three Main Types: • Displacement • Touch Sensor and iPod Click Wheel • Accelerometer • Automobile Suspension System, Air Bag System, ABS • Pressure • Tire Pressure

  3. Background (cont...) Capacitance Electric Fringe Fields Dielectric differences

  4. Advantages of Capacitive Sensor Higher accuracy Smaller size More reliable (compared to mechanical) No moving parts (more durable) No direct contact with the sensor Sealed from dirt Cheaper Background (cont...)

  5. Metal electrode Ground vessel Dielectric change causes change in capacitance Water level sensor

  6. Water Level Sensor (cont...) • Figure shows simplified view • Typical Applications: • Gas Tank Sensor • Water Reservoir • Production Vats • Cheaper than similar sensors • More Accurate

  7. Required by Government law since 1999 model year Capacitive Pressure Sensor and Capacitive Accelerometer Sensorare used for passenger protection Airbag System

  8. Sense a passenger. Capacitive Pressure Sensor Use a thin diaphragm Pressure is detected based on change in the capacitance between the diaphragm and the electrode Airbag System

  9. Sense a crash Capacitive Accelerometer Sensor A change in electrical capacitance with respect to acceleration Airbag System

  10. Touch sensor Electrical disturbance Two plate sensor Surface charge Overlay of 1-3mm

  11. Touch sensor (cont...) Interaction with E-fields E-fields projects through material Responsive to conductive devices

  12. Touch sensor (cont...) Change in capacitance Dielectric permittivity influence Common applications Touch screens (ex. iPhone, Nexus1) Track pads

  13. Vehicle Identification Capacitive Sensor • Used at road toll stations • Current Inductive sensors • Drawbacks: • Covers large area • Senses only metal • Not very accurate • Solution: Use a capacitive sensor

  14. Capacitive sensor structure • 11 Excitation and 30 detection electrodes • B0 (detection circuit and CtD) • B0 connects to B1-B30 • Capacitance between plates A and B

  15. Structure (cont...) • Sensor embedded into a ramp • Help slow the cars down • Stray capacitance

  16. Capacitance measuring circuit • Cx is very small • Cs1 and Cs2 are large • Measured Cx: • V3 = 2fVcCxRf + V1-V2 • Detection of 0.001 pF • Sensitivity 1V/pF

  17. Capacitive Sensors for Thickness Measurement Utilizes high-performance, complex sensors Resolution down to less than one nanometer Thickness measurement: capacitive vs. inductive Ex: Measuring the thickness of silicon wafers

  18. Capacitive Sensors for Thickness Measurement Components: Probe: Device which emits the electric field Probe Guard: Shapes the electric field Circuitry: Measures very small changes in capacitance using complex algorithms

  19. Capacitive Sensors for Thickness Measurement Single channel: Only one sensor probe Non-flat surfaces produce error Dual channel: Uses two sensors placed on opposite sides of object to be measured Nulls out curved surface errors due to differential operation

  20. Capacitive Sensors for Thickness Measurement Typical Applications? Machining Manufacturing Precision thickness measurements

  21. Conclusion Background Water Level Air Bag deployment systems Touch sensors Vehicle detection system Thickness Measurement Questions?

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