![]() The Impedance boundary condition is appropriate if the skin depth is much smaller than the object. ![]() From the point of view of the electromagnetic wave, this is true, since L_c \gg \delta means that the wave does not penetrate through the object. In this situation, it is appropriate to use the Impedance boundary condition, which treats any material “behind” the boundary as being infinitely large. So, from a modeling point of view, we can treat the currents as flowing on the surface. Although there are currents flowing inside of the object, the skin effect drives these currents to the surface. That is, the object is much larger than the skin depth. Let’s consider an object in which L_c \gg \delta. Depending on the situation, the characteristic size can be defined as the ratio of volume to surface area or as the thickness of the thinnest part of the object being simulated. There are different ways of defining L_c. ![]() Now that we have the skin depth, we will want to compare this to the characteristic size, L_c, of the object we are simulating. The skin depth, along with your knowledge of the dimensions of the part, will determine if it is possible to use the Impedance boundary condition or the Transition boundary condition. \nabla \times \left( \mu_r^īefore you even begin your modeling in COMSOL Multiphysics, you should compute or have some rough estimate of the skin depth of all of the materials you are modeling. ![]()
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