COMSOL 6.4 - Material Discontinuity

Add the node to model at any (interior) boundary where there is a discontinuity in the material properties or when an interior boundary represents a thin absorbing layer.

Select the option as (the default) or .

When is selected, the feature represents a material discontinuity. The feature applies reflection and refraction using a deterministic ray splitting approach. The direction of the refracted ray is computed using Snell’s law, based on the speed of sound on either side. If extra degrees of freedom have been allocated for secondary rays, a reflected ray is also released. If the incident ray undergoes total internal reflection, no refracted ray is produced and no secondary rays are needed to release the reflected ray. The associated reflection coefficient R and transmission coefficient T is automatically computed.

If is selected, the feature represents a general internal condition that can be used to model, for example, a thin absorbing surface like a curtain. For this option, enter the R (SI unit: 1) and the T (SI unit: 1). This can be an analytical expression that depends on, for example, frequency or angle of incidence.

If the ray intensity or power is solved for in the model, the feature computes the new values of these variables for the reflected and refracted rays.

	The maximum number of reflected rays can be controlled via the Maximum number of secondary rays text field, which is found under the Ray Release and Propagation section for the physics interface.

The Accumulator (Boundary) subnode is available from the context menu (right-click the parent node) or from the toolbar, menu.

For the option (the condition represents a material discontinuity), then use the inputs in this section to control whether the incident ray is split into a reflected and refracted ray at the material discontinuity. Select an option from the list: (the default), , or .

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If is selected, whenever a ray hits the material discontinuity, the incident ray is refracted across the boundary, and a reflected ray is produces using some of the preallocated degrees of freedom for secondary rays.

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If is selected, the incident ray is refracted, but no reflected ray is produced. This does not prevent a ray from undergoing total internal reflection at the boundary.

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If is selected, enter a value or expression for the e (dimensionless). The default is 1. A reflected ray is produced only if the value of this expression is nonzero for the incident ray.

If the ray intensity is solved for in the model, enter a Ith (SI unit: W/m2). The default is 1 mW/m2. If the interaction of a ray with a material discontinuity would create a reflected ray of intensity less than the threshold intensity, the release of this reflected ray is suppressed.

If the ray power is solved for in the model, enter a Qth (SI unit: W). The default is 10-3 mW. If the interaction of a ray with a material discontinuity would create a reflected ray of power less than the threshold power, the release of this reflected ray is suppressed.

If both the and the are specified, a reflected ray is only released if the value of the expression is nonzero and the intensity of the reflected ray exceeds the threshold. In other words, a ray must satisfy all of the criteria in the section in order to be released, not just one of them.

The release of reflected rays at a material discontinuity can be suppressed to prevent an arbitrarily large number of degrees of freedom from being used to model rays of extremely low intensity. Keep in mind that this can lead to a reduction in the total energy of the system.

For the option the intensity of the transmitted ray is computed based on the entered transmission coefficient.

If an Auxiliary Dependent Variable has been added to the model then there is an option to reinitialize the values of auxiliary dependent variables for the refracted ray. These settings are the same as in the New Value of Auxiliary Dependent Variables section for the Wall feature.

If an Auxiliary Dependent Variable has been added to the model then there is an option to reinitialize the values of auxiliary dependent variables for the reflected ray. These settings are the same as in the New Value of Auxiliary Dependent Variables section for the Wall feature.