# Development of High-Power Ultrasonic System Dedicated to Metal Powder Atomization
## 4 Results and Discussion
### Working Plate Deflection Measurements  
In order to verify the model and confirm the amplitude distribution on the surface of the sonotrode plate, measurements of the amplitude of vibrations on its surface were conducted. Due to the fact that sonotrodes are solids with rotational symmetry, the amplitude study was carried out at a series of points along the radius of the plate with a measuring step of 0.5 mm.  
The ultrasonic transducers (20 kHz and 70 kHz) were tested together with mounted plates, each having a diameter of 140 mm. The ultrasonic waveguides were installed on a measuring table (Figure 7, as an example of 70 kHz set-up). The Keyence LK-H008 laser displacement sensor was directed at the surface of the sonotrode. It was moved along the plate by a precise micrometer screw.  
Figure 6: Distribution of vibration amplitudes with vibrations forced at a frequency of 70 kHz.  
Figure 7: The measurement stand for testing the amplitude of the sonotrode vibrations.  
Measurements were made cyclically by moving the optical sensor away from the axis of the sonotrode. At each point, the measurement was made four times by changing the generator amplitude setting. For the purpose of testing the 20 kHz system, amplitudes at four levels of 10%, 20%, 30% and 40% of the range were used, while for the 70 kHz system, 60%, 70%, 80% and 90% settings were used, whereas 100% of the energization corresponds to a maximum value of 1.8 kV supply voltage for a 20 kHz transducer and 300 V for a 70 kHz transducer. The obtained results are presented on a graph of the amplitude distribution depending on the distance from the center of the plate (Figure 8).  
The results of numerical calculations and those obtained experimentally show a good correspondence. This mainly concerns the distribution of the amplitude of vibrations along the radius of the plate, in particular the position of the maxima and minima of the amplitude of the standing wave.  
Figure 8: Amplitude distribution depending on the distance from the axis of the plate: (**a**) for the 20 kHz system and (**b**) for the 70 kHz system.  
The amplitude values of the FEM model compared to those measured on the real object turned out to be lower. The differences result from the heterogeneity of material properties and the necessary approximations of the finite element method. In addition, the system was not powered by the maximum possible power (only 40% for the 20 kHz system) due to the lack of liquid load for atomization. A further increase in power without loading the system would risk damaging it. This does not change the fact that the study clearly confirmed the proper nature of vibrations of both sonotrodes, which was the most important goal of this experiment.  
In addition, the results obtained from analytical calculations show that the amplitude of vibrations required to produce the atomization process is relatively small compared to the amplitude values obtained in the arrows (maxima) on the surface of the plate. Analyzing the vibration amplitude distribution for both vibration systems (20 kHz and 70 kHz), it can be seen that over 90% of the plate surface meets the theoretical amplitude condition, i.e., Am > 1.223 \(\upmu\)m for 20 kHz and Am > 0.805 \(\upmu\)m for 70 kHz for water (Table 1). For liquid metals, the required amplitudes have a mixed value, respectively, Am > 0.595 \(\upmu\)m for 20 kHz and Am > 0.392 \(\upmu\)m for 70 kHz, which confirms the suitability of both systems for atomization.