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Electromagnetic Sensors

Electromagnetic Sensors. Group 249 Andy Kottsick Jeremy Lee Michael Newell Jeremy Purcell. Overview. Goal is to create a “suite” of sensors to measure everyday electric and magnetic fields These sensors are not readily available together

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Electromagnetic Sensors

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  1. Electromagnetic Sensors Group 249 Andy Kottsick Jeremy Lee Michael Newell Jeremy Purcell

  2. Overview • Goal is to create a “suite” of sensors to measure everyday electric and magnetic fields • These sensors are not readily available together • These devices can be used in a laboratory setting to help students better understand electric and magnetic fields

  3. Requirements Sensors should measure magnetic and electric field for: • DC (static) • 1Hz-1kHz (low) • 1MHz-10MHz (mid) • 1-3GHz (high) • Display field strength on a LCD • Inexpensive as possible • Collection of sensors need to be easy to transport.

  4. Options-Low Frequency Electric Field Measurement • Field Mill • J-FET Transistor • Charge Plates

  5. Options-Mid Frequency Electric Field Measurement • Electric Dipole • PCB Patch Antenna • Loop Antenna

  6. Options-High Frequency Magnetic/Electric Field Measurement • Loop-coil Probe • Single-Probe Method

  7. Options-Low Frequency Magnetic Field Measurement • Giant Magnetoresistive (GMR) • SQUID • Fluxgate

  8. Options-Mid Frequency Magnetic Field Measurement • SQUID • GMR • Loop-coil Probe

  9. Sensor Selection • Static Field and Low Frequency Electric – • Field Mill • Low Frequency Magnetic – • Fluxgate • Mid Frequency Magnetic and Both High Frequency Magnetic and Electric – • Loop-coil Probe • Low and Mid Frequency Electric – • Dipole

  10. Field Mill Electrometer • Advantages • High Voltage Readings • High Input Impedance • Relatively cheap to build • Disadvantages • Size compared to alternate solutions

  11. Flux Gate Magnetometer • Disadvantages • Does not Work well at higher frequencies • Overall operation is fairly complicated Advantages Works well at low frequencies Easy, and relatively cheap to build

  12. Loop Coil Probe • Advantages • Very small • Easy to build • Disadvantages • Durability • Frequency Dependent

  13. Dipole Antenna • Advantages • Easy to adjust to frequency range of interest • Very available technology • Disadvantages • Low frequencies create unrealistic specifications for the dipole • Operation depends on length of antenna

  14. Field Mill Sensor

  15. Conversion of Charge to Voltage Case 1 Case 2 i i ++++++++ ++++++++ R R Block Plate Block Plate e - - - - - - - - - - - - - - - - - - - e- + Vout Vout + As the block plate moves from the area between the charge and sensing plate, more electrons are attracted to the sensing plate. This creates electrons to flow in the direction of the grey arrow. Thus, we have current in the opposite direction as seen in the purple arrow. As this current flows through R, a negative voltage is created at Vout. This output continues to become negative till the plate no longer blocks. As the block plate moves into the area between the charge and sensing plate, electrons return to the sensing plate. This creates electron flow in the direction of the grey arrow. Thus, we have current in the opposite direction as seen in the purple arrow. As this current flows through R, a positive voltage is created at Vout. This output continues to become negative till the plate fully blocks.

  16. Field Mill Operation Top View ++++++++++++++ Rotor Plate ------- ------ Sensing Plate ++++

  17. Flux Gate Sensors

  18. Flux Gate Diagram + Drive Circuit - Vo Sensing Circuit

  19. Theory of flux gate Flux - Magnetic field No Flux net Net Flux has a value when external field is present Flux + Vo

  20. 555 Timer D Flip Flop (x2) x6 Offset Drive Coil +-12V Output Push-pull Amp Fluxgate Drive Circuit Diagram

  21. Magnetic Loop Sensors

  22. d dt Loop Coil Probe a N Turns B Field Signal (S) - Vemf + - Vemf B = π*N* SIn*a2 Note: For a sinusoidal input, B will be frequency dependent

  23. Loop Coil Probe Circuit Diagram Signal Probe Frequency Counter Vemf Circuit Pic Processor Display

  24. Product Layout Fluxgate Loop Coil Probe Main Unit/LCD Field Mill Dipole • Centralized Main unit for interfacing to each sensor

  25. Budget

  26. Timeline

  27. Questions?

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