# Transmittance calculation in COMSOL

• MrTentacles
In summary, the conversation discusses decibels and how they are used in engineering to measure power, particularly in relation to sound waves. The formula for converting a value in normal form to decibels is given, as well as the relationship between pressure and the amplitude of sound waves. It is noted that the power of sound waves is typically measured in decibels, with a different formula of ##20\times\log_{10}\left(T\right)##.
MrTentacles
Homework Statement
I am emulating a transmittance vs frequency plot for a research project I am apart of. However I am having difficulty understanding something. The plot has the transmittance values as a unit of decibels anywhere from 0 to -40, but the equation they’ve given me is attached below. The equation has the absolute value of the pressures so how exactly are they getting negative numbers out of this? Is there something I’m missing?
Any help would be great thank you.
Relevant Equations
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Are you familiar with decibels? If ##T=0.03## in normal form (unitless), then in dB it would be ##10\times \log_{10} \left(T\right)\approx -15.2dB##. Note also that in some cases, especially in engineering it is common to plot power in decibels. I am not sure what your setup is, but if pressure is related to the amplitude of the sound waves, I would guess that the power of the sound-waves is the square of it (with some constants), so the dB expression in this case would be ##20\times\log_{10}\left(T\right)=-30.4 dB##

MrTentacles
This is very helpful thank you!

## 1. What is transmittance and how is it calculated in COMSOL?

Transmittance is a measure of the amount of light that passes through a material, often expressed as a percentage. In COMSOL, transmittance is calculated using the Beer-Lambert law, which takes into account the material's absorption coefficient, thickness, and incident light intensity.

## 2. Can transmittance be calculated for different types of materials?

Yes, transmittance can be calculated for any material as long as its absorption coefficient is known. This includes materials such as liquids, solids, and gases.

## 3. How accurate is the transmittance calculation in COMSOL?

The accuracy of the transmittance calculation in COMSOL depends on the accuracy of the input parameters, such as the absorption coefficient and incident light intensity. If these parameters are known accurately, then the transmittance calculation in COMSOL will also be accurate.

## 4. Is it possible to simulate different incident light angles in the transmittance calculation in COMSOL?

Yes, COMSOL allows for simulation of different incident light angles in the transmittance calculation. This is important for materials with anisotropic properties, where the transmittance may vary depending on the angle of incident light.

## 5. Can transmittance calculations in COMSOL be used for practical applications?

Yes, transmittance calculations in COMSOL can be used for practical applications, such as designing optical devices or predicting the performance of materials under different lighting conditions. However, it is important to validate the results with experimental data for accurate predictions.

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