Terahertz sensing for non-destructive characterisation of pharmaceutical tablets

Abstract: The pharmaceutical industry is shifting from conventional batch manufacturing to continuous manufacturing. To realise continuous manufacturing, it is crucial to assess the product quality of tablets at different stages of the production line. Therefore, there is a high need for quality control methods that are fast, non-destructive, and compact, with the possibility of implementation in the production line for real-time measurements. However, traditional quality control methods are typically slow and destructive. In our work, we propose the terahertz frequency domain (THz-FD) technique, based on all-electronic solutions, as a fast, sensitive, and non-destructive sensing technique with miniaturization capabilities for a future compact sensing system. In this technique, the effective refractive index of tablets at the terahertz frequency range is extracted from the transmission measurements of the scattering parameters of the tablets using a vector network analyser. Then, the effective refractive index is transferred to tablet density by using an empirical model and later is translated to tablet porosity. The measurement results show that the THz-FD technique could differentiate tablets with different refractive index and detect and quantify the minute changes of tablet density and porosity with the variation of design parameters. The design parameters were compaction force during tableting process, the concentration of the ingredients, and the particle size of the ingredients. It was observed that in our study the compaction force and filler particle size had the major impact on tablet porosity. In conclusion, it was demonstrated that the THz-FD technique based on electronic solutions allows for fast, sensitive, and non-destructive measurements of pharmaceutical tablets that open for compact instrument systems capable of in-line sensing in the tablet manufacturing process.