In Order of Presentation: Ishaan Sandhu Danny Kang Anuar Tazabekov Arslan Qaiser Eric Otte How to Choose/Use Capacitive Sensors for Various Applications

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

Capacitance Electric Fringe Fields Dielectric differences

Background (cont...) 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

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

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

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

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

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

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

Interaction with E-fields E-fields projects through material Responsive to conductive devices

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

Used at road toll stations Current Inductive sensors Drawbacks: Covers large area Senses only metal Not very accurate Solution: Use a capacitive sensor

11 Excitation and 30 detection electrodes B 0 (detection circuit and CtD) B 0 connects to B 1 -B 30 Capacitance between plates A and B

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

C x is very small C s1 and C s2 are large Measured C x : V 3 = 2fV c C x R f + V 1 -V 2 Detection of pF Sensitivity 1V/pF Capacitance measuring circuit

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

Components: Probe: Device which emits the electric field Probe Guard: Shapes the electric field Circuitry: Measures very small changes in capacitance using complex algorithms

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

Typical Applications? Machining Manufacturing Precision thickness measurements

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