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. 2017 Mar 1;34(5):890–917. doi: 10.1007/s11095-017-2129-z

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© The Author(s) 2017

Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

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Fig. 5 — Method to determine the porosity of a flat faced tablet by THz-TDS. Tablets of MCC and indomethacin were varied either in porosity ε, height, or API mass fraction x as specified in the legend. (a) Schematic of the terahertz transmission measurement to measure the effective refractive index, n _eff, of a tablet. (b,c) Effective refractive index measured by THz-TDS as a function of the porosity of a tablet. The porosity was calculated from the relative and apparent densities of the sample. The API mass fraction in (a) was kept constant at 10 wt% (modified from [84]).