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AMC-331 – Active Magnetic Field Canceller

If magnetic field fluctuations occur, they will adversely affect electron beam application devices such as electron microscopes. The AMC-331 is a system that suppresses magnetic field fluctuations by detecting magnetic field fluctuations with a high-sensitivity magnetic field sensor and using a Helmholtz coil to generate magnetic fields of opposite phases.

Causes of Fluctuating Magnetic Fields

  • Due to the movement of magnetic material (cars, elevators, trains, etc.)
  • Power noise (50 or 60 Hz)
  • Influence of peripheral devices

Helmholtz Coil

  • A coil connected in a series with the same number of turns in parallel arrangement.
  • When a current passes, a magnetic field is generated in the axial direction of the coil.
Magnetic flux density contour map
Parallel magnetic field by Helmholtz coil
Theoretical calculation 1

 

Theoretical calculation 2: The magnetic flux density in the X-axis direction is obtained by using Pio-Savart’s law.

 

Theoretical calculation 3 Analysis result 1
Theoretical calculation 4 Analysis result 4
  • High performance: Excellent attenuation performance up to 40-60 dB
  • Low cost: Achieves approximately 1/10 the cost compared to the magnetic field measures of a shield
  • Easy installation: Achieves easy installation by fixing the coil around the device

Control method: DC representative value control + independent feedback control for each axis
Control range: ± 15 μT (approvable)
Control frequency: Quasi DC ~ 1kHz
Attenuation rate: 40-60 dB

1) Measured data 200Hz disturbance
2) Measured data Environmental disturbance
  • Scanning electron microscope (SEM)
  • Transmission electron microscope (TEM)
  • Focused ion beam (FIB)
  • Mass spectrometer (MASS)
  • Electron beam lithography apparatus (EBL)
  • Mask inspection device
  • Wafer observation measurement SEM