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Tech Tip Tuesdays with Zemax: Human Tissue Modeling

In my last article I wrote about the power of custom coatings in OpticStudio, how to create them and the ramifications of model detail. In this example, we’ll explore how to extend a model with simplistic assumptions to a more complex multi-physics model with more realistic conditions or even incorporate measured data.

OpticStudio has extensive catalogs of materials and their associated optical properties. Model materials may also be created to address unusual needs not covered by optical catalogs. This allows the user to define custom materials for nearly any discipline, such as heat shields, fiber for lasers, and even human skin.

Building material layers in non-sequential mode is similar to building a volume in a CAD platform. The type of object is selected, then the thickness, position and orientation of each layer is defined. In this case a rectangular volume was used for each layer since we were only interested in a small cross section of the body where a heart rate sensor would sit. It is worth noting that more complex shapes can be used if desired, either leveraging the Part Designer in OpticStudio to create a Boolean object or by importing a STEP, IGES or other standard CAD file format for the volume of interest.

Next, we define the index of refraction for each layer at the given wavelength. In this simple example the indices were generalized from available literature where the blood content was assumed to be evenly distributed throughout the material, data was averaged for all patients from available publications. However, for an actual medical application, this could be refined. Leveraging stratified data from larger data sets instead of the averaged data, conducting your own study by collecting lab data from patients or the model could even be tailored for a specific person, giving an individualized model.

Additionally, an evenly distributed material while good is not as accurate as modeling the actual structures. To gain greater detail, model the complex vascular structure and fat cell distribution. This could be done with other Ansys tools such as Fluent, Rockwell, or Mechanical then tied back to OpticStudio directly or with OptiSlang. In our case we use the standard table and apply it with the model material solve option in OpticStudio. This will allow us to specify a known index for each layer rather than apply the properties of a given material from a catalog.

Author:
Steven LaCava
Senior Application Engineer
Zemax an Ansys Company

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