# Development of High-Power Ultrasonic System Dedicated to Metal Powder Atomization
## 5 Conclusions  
The article presents an analysis of the operation of two ultrasonic systems with different operating frequencies (20 kHz and 70 kHz). All stages of the design of these systems (FEM calculations, harmonic analysis and obtained forms of vibrations) are presented in this work. After the manufacturing of both ultrasonic systems, the results of sonotrode deflection measurements are presented. This allowed us to verify and confirm the correctness of the designing process and construction. By comparing the expected amplitude distribution in the numerical model to the experimental results, it can be concluded that the assumptions to the model, as well as the calculation process, was correct.  
The functional tests of both devices were carried out for different operating parameters (amplitude of voltage powering the sonotrode). The atomization process of the distilled water was recorded with a high-speed camera, which allowed us to confirm that the frequency of the transducer significantly affects the size of the atomized droplets. However, both systems proved to be highly effective in terms of atomization. In addition, it can be noted that:  
* FEM simulation results and experimental measurements show a very similar distribution of vibration amplitude, especially when comparing the range of maxima and minima of the standing wave for both working plates.
* The calculated minimum vibration amplitude thresholds required to initiate the atomization process were reached for both developed ultrasonic atomization systems for more than 90% of the surface, in both set-ups (20 kHz and 70 kHz).
* The size of the atomized water droplets during the tests indicates that the 20 kHz system generates droplets in the range of 10-25 \(\upmu\)m and the 70 kHz system in the range of 35-55 \(\upmu\)m.
* The obtained results of the morphological analysis are in agreement with the results of the analytical calculations. The lower droplet diameters were obtained for individual systems experimentally when compared to those calculated analytically. However, the mutual trend is maintained, i.e., for a system with a higher frequency, the droplets have on average an over 50% smaller diameter.  
The obtained results confirm the effectiveness of the developed atomization system for water, and according to the calculations, the systems should allow production of metal powder particles with a desired size distribution. In further research, the developed ultrasonic atomization systems will be loaded with a stream of molten metal droplets to see if the atomization can be still effectively performed.  
**Author Contributions:** Conceptualization, P.K. ([PERSON]), M.K. and P.S.; methodology, P.K. ([PERSON]), M.K., A.S. and P.S.; investigation, P.K. ([PERSON]), M.K., A.S., T.P., P.K. ([PERSON]) and P.S.; writing--original draft preparation, P.K. ([PERSON]), M.K., A.S. and P.S.; and writing--review and editing, P.K. ([PERSON]), M.K., A.S., T.P. and P.S. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the National Center for Research and Development in Poland, under the LIDER program (LIDER/42/0230/L-10/18/NCBR/2019).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data generated and/or analyzed during the presented study are available from the corresponding author upon request.  
**Acknowledgments:** The authors would like to acknowledge the financial support provided by the National Center for Research and Development in Poland, under the LIDER program (LIDER/42/0230/L-10/18/NCBR/2019) awarded to the Faculty of Mechanical Engineering at Wroclaw University of Science and Technology.  
**Conflicts of Interest:** The authors declare no conflict of interest.