Electromagnetic Material Characterization

Material characterization is the process of defining precisely the electrical properties of materials. In electromagnetics, a set of equations called Maxwell's equations describe electromagnetic behavior in the presence of real-world objects, materials, and conditions. Three equations, called the constitutive relationships, specifically describe how both electric and magnetic fields behave in the presence of these real-world materials. They are:

where:
E = electric field intensity
D = electric flux density
J_c = conduction current density
H = magnetic field intensity
B = magnetic flux density

If you can describe the (permittivity), (permeability), and σ (conductivity) of a material, you can describe completely how electromagnetic energy behaves within that material. The definitions of these parameters are:

Note that, for a given material, the electrical properties change under various conditions such as frequency, temperature, humidity, and physical orientation to the electromagnetic field.

Most real-world materials fall into one of three categories: insulators, conductors, and absorbers. Insulators are, for the most part, transparent to electromagnetic energy.

Their electrical properties are usually described by permittivity ( ) only, where the permeability  = , and the conductivity σ < 10-7 ohms/meter. Conductors are materials that conduct electrical current and reflect electromagnetic energy. The electrical properties of conductors need only be described by their conductivity σ and permeability  . Absorbers are materials that absorb electromagnetic energy without reflecting it. The electrical properties of absorbers are usually described by all three parameters: permittivity, permeability, and conductivity.

An EMI gasket is considered a conductor and is characterized by its conductivity.

Testing the permittivity, conductivity, and permeability of materials can be difficult. The main problem is the lack of available standards. For example, if you wanted to develop a method to measure the dielectric constant of a material using a custom sensor, you would not be able to purchase a dielectric standard to calibrate or evaluate your test method.

At Gore, we have chosen a variety of methods, some based on industry standards, some not, to fulfill our needs.