Overview

This script performs passive magnetic shimming to improve the homogeneity of a magnetic field. Below is a breakdown of the code:

1. Reading Magnetic Field Data

• The script loads magnetic field data from a .npy file.
• Converts the field and position data into meters and filters the data within a defined spherical region (DSV - Diameter Spherical Volume).
• The magnetic field data is visualized in 3D scatter plots.

2. Defining Shim Geometry

• Specifies the geometry of the shim array, including magnet dimensions, diameter, and magnetization.
• Creates shim ring templates using the make_shim_ring_template function.
• Saves the initial shim tray arrangement as an STL file for visualization.

3. Field Computation

• Computes the magnetic field generated by the shim tray template.
• Visualizes the computed field and its combination with the measured field.

4. Optimization for Homogeneity

• Defines an optimization problem using the shimming_problem function to minimize field inhomogeneity.
• Uses the MixedVariableGA algorithm from the pymoo library to solve the optimization problem.
• Outputs the optimized shim tray configuration.

5. Generating Optimized Shim Tray

• Creates an optimized shim tray based on the optimization results.
• Saves the optimized shim tray as an STL file and visualizes the shimmed magnetic field.

6. Saving and Loading Shim Tray

• Saves the optimized shim tray configuration to a .pkl file.
• Demonstrates how to reload and visualize the saved shim tray.

Key Functions and Libraries

• magpylib: Used for magnetic field computations and visualization.
• pymoo: Provides optimization algorithms for solving the shimming problem.
• Custom Functions:
  • get_field_pos, filter_dsv: Process and filter magnetic field data.
  • make_shim_ring_template: Creates shim tray templates.
  • cost_fn: Evaluates the field homogeneity.
  • write2stl: Exports shim tray configurations to STL files.

Outputs

• Visualizations of the magnetic field before and after shimming.
• STL files for initial and optimized shim tray configurations.
• A .pkl file containing the optimized shim tray for future use.

This script automates the process of designing and optimizing passive shim trays for magnetic field correction.