Ray Tracing
The Ray Tracing () study and study step are used to compute the trajectories of rays. The Ray Tracing study step is a special case of the Time Dependent study step. The time steps taken by the solver can either be specified directly or by specifying a set of path lengths and a characteristic group velocity. Built-in stop conditions can be used to stop the solver when no active rays remain, or when the intensity of active rays is negligibly small. Except for the section below, see Time Dependent for all settings. This study requires the Ray Optics Module or the Acoustics Module.
For example, this study is used with the Geometrical Optics or Ray Acoustics interfaces to compute ray trajectories. By specifying the range of time steps in terms of the maximum path length, it is possible to deduce the optimal study settings from the geometry size and ray properties.
Study Settings
Select a Time step specification: Specify time steps (the default) or Specify maximum path length.
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If Specify time steps is selected, select a Time unit from the list to use a convenient time unit for the time span of the simulation. The default is ms (milliseconds) for models that use the Ray Acoustics interface and ns (nanoseconds) for models that use the Geometrical Optics interface. Then, in the Times field, specify the time interval for the output from the simulation using the selected time unit.
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If Specify maximum path length is selected, select a Length unit from the list (the default is m). Then specify a list of Lengths using the selected unit. Enter a Characteristic group velocity (SI unit: m/s). For Ray Acoustics simulations the default is 343 m/s, the approximate speed of sound in air at standard temperature and pressure. For Geometrical Optics simulations the default is c_const, the speed of light in a vacuum. The time steps taken by the solver are computed by dividing the list of lengths in the Lengths field by the characteristic group velocity.
From the Tolerance list, choose Physics controlled (the default) to use the tolerance suggested by the physics. Choose User controlled to override the suggested relative tolerance with a value that you enter in the Relative tolerance check field. The tolerance settings control the internal time steps taken by the solver, so selecting large time steps for the output times does not affect the accuracy in the time stepping.
Select a Stop condition: None (the default), No active rays remaining, Active rays have intensity below threshold, or Active rays exceed maximum number of reflections. If No active rays remaining is selected, the solver terminates immediately when all rays are stuck, frozen, or have disappeared.
If Active rays have intensity below threshold is selected, enter a Threshold ray intensity (the default is 1[W/m^2]). The solver terminates immediately when all rays are either stuck, frozen, have disappeared, or have intensity less than the threshold. This setting can only be used if the ray intensity is computed for the Geometrical Optics or Ray Acoustics physics interface (select any option other than None from the Intensity Computation list in the physics interface Intensity Computation section.
If Active rays exceed maximum number of reflections is selected, enter a Number of reflections (the default is 5). The solver terminates immediately when all rays are either stuck, frozen, have disappeared, or have been reflected or refracted at least the specified number of times. This setting can only be used if the Count reflections check box has been selected in the Additional Variables section for the Geometrical Optics or Ray Acoustics interface.