Fluxgate Magnetometer

Farita Tasnim Woojeong Elena Byun

Jack Erdozain

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What is a Fluxgate Magnetometer?

- Incredibly sensitive (1/1000th of Earth’s magnetic field)

- Affordable, rugged, compact

- Earthquakes, solar phenomena, no-boom magnetometers on NASA satellites

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Toroid and Coil Construction

Proof of concept: ferrite cores from EDS

Actual circuit: “metglas” or “permalloy” cores

Magnetic wire: EDS

Magnetic field B = µNI/ (2πr) Saturation current from BH curve

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Generating Drive and Demodulation Frequencies

• Sawtooth Generator • Comparator • Signal Inverter

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Toroid Drive Circuitry

• Board Consolidates Drive Circuitry • Regulated Power Supply • Indication LED • Dead Band Delay Circuitry • Gate Drivers and Totem Pole

(MOSFET Stage)7

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Filtering the Signal

Lower cutoff: 1/(2*pi*R1C1) Upper cutoff: 1/(2*pi*R2C2)

Purpose: Filter out any signals outside of the range of signal

frequencies 5 KHz < f < 20 KHz

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Extracting the Correct Signal

Purpose: Filter out any signals that are not in phase with the original

drive frequency φ

Av

π/2-π/2

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Integrating the Signal

Purpose: Capture the magnitude and directionality

of external magnetic field

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Demo: Servo Actuation

• Differential Amplifier, for voltage gain and subtraction of Earth’s signal

• Adder Circuit for centering of signal

• PWM: Sawtooth Generator and Comparator

• MATLAB: headphone jack

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Active Current Feedback Control

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Timeline and Labor

Week of Tasks People

April 111) Proof of Concept 2) Order parts (high permeability

cores, special op-amps)All

April 18

1) Phase Demodulation Block 2) MATLAB 3) Servo Actuation 4) Integration 5) Testing and Debugging

1) Farita and Elena 2) Farita and Elena 3) Jack 4) All 5) All

April 25 1) Testing and Debugging 2) Add extras if time

All

May 2 1) Testing and Debugging 2) Demonstration of Final Project

All

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Conclusion

Results: • One Axis Fluxgate Magnetometer • Toroidal Drive • Signal Extraction (Phase Demodulation) • Signal Display • Signal Actuation

Risks: • Incorporation of Physics: Magnetics • Novelty: Phase Demodulation • Extra: Multiple Axes • Extra: Feedback

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Questions?

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