on_by_material(self):
    &#34;&#34;&#34;
    Get the contribution to the transmission by total thickness for each material.

    Layers of the same materials are combined to return one instance with the total thickness.

    Returns
    -------
    `dict`
        Entries are meterials with the total thickness for that material.
    &#34;&#34;&#34;
    material_thickness = dict()
    for name, layers in COMPONENTS.items():
        for material_name, thickness in layers:
            if material_name == &#39;