Regole di concezione

THE FIRST APPROACH

  • Before searching for a solution, we must consider the following parameters:
    - am I in a continuous field or in an alternating field?
    - am I in the presence of a weak field or a strong field?
    - should I shield the perturbation or the sensitive part?
    - what attenuation do I need?
    - are data or measured values reliable?
    - are data averages or peak values?
    - how much space is there to install a shield?
    - what do I have to consider: air, place, mechanical stress, climate, accessibility ...
    - what is my budget? 
 

DESIGN: MAGNETIC AND MECHANICAL APPROACH

  • Magnetically designing a shield will consist of:
    - checking the non-saturation of the material
    - defining materials and the thickness
    - defining the number of layers to use
    - choosing the suitable heat treatment
         
  • Mechanically designing a shield will consist of:
    - breaking down the part
    - taking into account the manufacturing process (shaping, assembly, heat treatment...) and customer demand (opening, protection, ...)
         
  • Shielding design may require several iterations.

HOW TO DESIGN

  • Using relatively simple formulas, which can quickly give an idea of the solution in a continuous field.
     
  • Using slightly more complex formulas (with abacuses), formalized among others by J. Albrecht Mager in 1970 and which refined solutions in AC or DC from simple shapes.
     
  • Using finite element simulations (including Maxwell's equations). This solution is an approach for complex forms and relies heavily on the software, the user and the integrated BH curves of the raw material.

 

 

A FEW PRINCIPLES

  • The least effective shape of a shield is a simple plate, the most effective is a sphere.
     
  • To have the most effective shielding possible, it will be necessary to gi ve preference to round angles, to limit the openings and to use smaller sizes.
     
  • The most common form is the cylinder. It should be placed with its axis perpendicular to the field.
     
  • The thickness of the material should be determined based on avoiding saturation but also being well positioned in the BH curve around the µmax.
     
  • Two 1 mm layers with a gap shield better than a thickness of 2 mm (if there is no problem of saturation).