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Optical modelling of biomedical applications using TracePro
O
ptical-based biomedical systems can span a wide range of applications
from wearables, pulse oximeters, absorption spectroscopy, fluorescence microscopy and many others. These systems use light sources of varying types and wavelength ranges, including UV, visible, and infrared. Optical design and analysis programs, such as TracePro, allow designers and engineers to design, analyse and optimise these types of systems in a virtual environment. This allows for easy and efficient modification of the system parameters, and helps to speed the design process and reduce development costs. TracePro allows for an easy
file exchange with different CAD programs. Designers and engineers can use their preferred CAD program for the mechanical design, then export the model to TracePro for the optical analysis. Typical file formats are SAT, STEP and IGES. TracePro is
based on a 3D solid modelling CAD kernel, so users can also use TracePro for their CAD design. TracePro features an
interactive optimiser that gives engineers and designers the capability of optimising the design of light guides, lenses, reflectors, or almost any other optical element automatically to meet a user-defined goal such as flux, illumination pattern or uniformity. The saying 'garbage in equals
garbage out' can be applied to many things, including optical analysis software. To get the best results from an optical analysis, it is necessary to have accurate properties. This can include material properties, surface properties, scattering properties, as well as light source properties. TracePro includes a built-in catalogue on many optical properties, as well as the ability for users to easily add their own properties to the database at any time. The modelling of the light
Figure 2- Pulse oximeter example shows the path of rays getting to the detector through a finger model.” Designing, modelling and analysing biomedical systems requires an optical design program that combines excellent CAD tools, accurate properties, accurate source modelling and tools to analyse results. Special features such as fluorescence and bulk scattering are often also required. TracePro provides all these tools and more
“Being able to model the spatial, angular and spectral distribution of the source is extremely important”
sources is a critical part of the process.
Being able to model the
spatial, angular and spectral distribution of the source is extremely important. Some examples of source modelling tools are grid sources, surface source properties and rayfiles. Rayfiles can be downloaded from many LED manufacturer’s websites. TracePro can use all of these types of light source models. Light source models can also be mixed and matched. Once a raytrace has been
Figure 1- Fluorescence microplate reader excitation and emission beams A red LED shines through a model of a human finger. The finger model includes skin, bone, blood vessels and tendons. A detector on the opposite side of the finger from the source detects light that has passed through the finger. A major factor in this type of device is accurately modelling the scattering of the skin, bone, blood vessels and tendons. TracePro’s Bulk Scatter property and included catalogue of tissue properties makes this a straightforward process
www.electrooptics.com | @electrooptics
run, the results need to be analysed. Analysis can include illumination patterns, flux on a detector, angular/intensity distributions, luminance and radiance, polarisation plots, 3D irradiance/illuminance, photorealistic rendering, optical path length, and time-of- flight plots. Results may also need to be displayed in either radiometric or photometric units. TracePro gives users the ability to show all of these results and more. The design and analysis of biomedical applications often requires specialised tools
and capabilities in the optical analysis software. These can include fluorescence, birefringence, bulk or internal scattering, and importance sampling. TracePro includes all of these tools. Accurate modelling and analysis of biomedical systems without these capabilities can be difficult, if not impossible. The following examples will illustrate some of these capabilities in TracePro. The first example is a fluorescence microplate reader. This model was made using TracePro, Oslo, and RayViz for Solidworks. This method allowed each program to be used for what it does best. Oslo was used to design and optimise the lenses, RayViz for Solidworks was used for the mechanical design, and then the system was imported into TracePro for a full optical analysis. In this example an excitation
source is used to illuminate a sample in a sample holder. A fluorescence property is applied to the sample. This sample will then fluoresce according to the fluorescent property applied. An important note is that the fluorescence emission will be from a 3D volume and not just from a surface. Figure 1 shows the excitation and emission beams. EO
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April 2021 Electro Optics 17
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