Case Study/Electric Magnetic Interference (EMI) Shields

Microwave absorbing materials are used in wireless and electronic applications to suppress electrical magnetic interference (EMI) in such applications as cellular antennae arrays, radio frequency identification (RFID) systems, printed circuit boards, and Wi-Fi on commercial aircraft to name a few.

In the past, these mainly iron based materials were infused into large rubber sheets that would be cut to sizes and shapes to fit into the electrical apparatus. However, rubber is spongy, hard to cut into small, complicated shapes, plus, it is difficult to disperse the iron material uniformly in rubber, which limits EMI shielding effectiveness.

Working with its customer, China Array developed a process whereby microwave absorbing materials could instead be suspended in a high performance polymer and injection molded to create parts of virtually any size and shape with better dispersion and much tighter tolerances than rubber, while also eliminating the expense of hand cutting rubber sheets.

cellular_tower electric_magnetic_interference_shield

  • Enhanced electrical suppression
  • Access to tighter placement in devices
  • Significant per unit cost savings
  • Tighter tolerances and complex geometries
  • Consistent repeatability and quality
  • Asian manufacturing base
  • Intellectual property protection

The key challenge: In order to get the necessary electrical shielding performance, the plastic part would have to be filled with over 80% microwave absorbing material leaving only 20% polymer to hold the shape and dimensions of the parts.

China Array met this challenge producing EMI shielding components with various wall thicknesses, geometries and features (note the notches, holes and inserts, and shape edges and clean lines on the part pictured at left), which allow closer placement to the electrical interference source for more effective suppression.