Iron magnetic materials can be used to shield the magnet field, generally we use the ordinary iron sheets. We need to pay attention to the thickness of the iron sheets, if sheet is too thin or its magnetic is in saturation, it can only shield part of the magnet field and part of magnetic lines will spread out in all directions. The key to conduct magnet field to form into magnetic circuit is to choose a high permeability material with proper size and shape to reduce the magnetic flux leakage.