EMI and RFI Shielding by thin films
- Aki Matilainen
- Dec 11, 2025
- 2 min read
Updated: Jan 2
Electromagnetic energy, as we know it, is present from high energy/ frequency gamma waves to long wavelength AM radio frequencies. We can sense a narrow frequency range from it in terms of heat or visible light. Electromagnetic interference (EMI) or radio frequency interference (RFI) shielding refers to shielding of electrical and electronic devices, or living organism, from unwanted electromagnetic disturbance.
How EMI and RFI Shielding Works
Nature of electromagnetic energy is determined by it's source and distance to it. By a shield energy can be transformed permanently or temporarily into another form of energy and it's direction can be altered. A set of electric- and magnetic fields perceived in a material is dictated by a three parameters, conductivity, permittivity and permeability.
Reflection
When an EM wave hits an electrically conductive shield, it generates surface current in free charge carriers such as electrons by electric force field and magnetic induction. Such currents generates opposing field towards original field. The magnitude of reflection is roughly proportional to charge carrier density and mobility. Vacuum coating technology enables to deposit highly conductive metal films on surfaces of economically manufactured enclosed.
Absorption
Materials can absorb electromagnetic energy, converting it into a heat which is emitted in infrared frequencies. This reduces the energy of the interfering wave as it passes through the shield. Becomes more dominant as frequency increases.
Static and Low Frequency Magnetic shielding
Time dependent magnetic field induces electrical current so purely conductive shield works as medium level shield. Static magnetic fields can be redirected only trough a shield with high permeability magnetic materials.
Multiple Layers
Effective shielding can consist of vacuum deposited conductive- and high permeability layers. Thin films has further advantages to offer also to pure magnetic shielding, as multi-layer structure allows to design a shield with the small fraction of magnetic material compared to that in equally effective single layer shield.
Reason for that being that for high permeability materials effective permeability becomes higher as the magnetic field becomes weaker and due to the coupling in between separated magnetic layers the shielding effectiveness increase when the permeability and number of layers increase, for same total amount of magnetic material.
Be it electric-, magnetic- or far fields, in NextGen Surfaces Finland Oy we have the knowledge on shield design, materials selection, manufacturing and characterization.
Common Shielding Materials
Choosing the right material depends on the frequency range, operating environment, and device requirements. For mobile enclosures NextGen Surfaces Finland Oy offers a multi layer metallic shield in which adhesion, shielding effectiveness, durability and manufacturing costs can be balanced.
Characterization
Shielding effectiveness is measured using standardized tests such as:
Shielding Effectiveness (SE): Expressed in decibels (dB), it quantifies how much the shield reduces electromagnetic energy.
MIL-STD-285: A military standard for measuring shielding performance.
IEEE and IEC standards: Provide guidelines for commercial and industrial applications.
Manufacturers often test shields in an-echoic chambers to simulate real-world electromagnetic environments. NextGen Surfaces Finland Oy can develop and characterize shield system materials complying with ASTM D4935.
