Performance Indicating Acoustic Emission Measurements on a Dry Powder Inhaler

Lars Karlsson, Lisa Holmstén, Mats Josefson, Roland Greguletz, Kyrre Thalberg, Staffan Folestad


In this paper Acoustic Emission (AE) technology is used to assess inhaler performance. The aim of the AE approach is to 1) perform accurate measurements of timings/events related to device performance, 2) improve metadata capacity for analysis, and 3) capture deviations or trends in inhaler performance. By applying this technology consistently and long-term, it is envisioned that AE will provide data as an aid for designing in robustness in the technical and mechanical performance of the inhaler. In this study, two types of Acoustic Emission measurements were performed on a marketed Dry Powder Inhaler (DPI). In the univariate mode, AE was used for measuring timings of inhaler (and analysis robot) operations. The parameter of interest in this particular application was the Time to Trig (TtT), defined as the time from start of the flow until the inhaler triggers. TtT, which is linked to device performance, was easily and accurately determined for 9 device units, and was found to correlate well to trigger flow. In another mode of AE assessment, a chemometrics approach was used. Here, the raw sound data was Fourier transformed to frequency spectra, which were fed into a multivariate analysis software. Principal Components Analysis (PCA), as well as Orthogonal Projections to Latent Structures (OPLS), with unit variance scaled data were used for spectral analysis. Some applications are shown, focusing on how and to what degree the acoustic pattern changes with different actuations within the same device and between devices filled with different formulations. It was concluded that the passive Acoustic Emission chemometric approach described will detect also subtle differences in device performance or formulation characteristics. If the AE data is interpreted correctly, it is envisioned that this technology will be aiding future product and device development projects.

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