# Numerical Analyses of Ultrasonic Atomization Utilizing Acoustic Effects of a Beam Diaphragm
## 2 Summary of the Experiments  
Experimental setup and results from the experiments, which are going to be numerically modeled in later sections, are summarized in this section. and indirectly excited the diaphragm, as shown in Figure 1b. Machined aluminum plates were used to clamp the transducer with a silicone O-ring with a 14 mm inner diameter. A high-frequency power of 2.4 MHz was applied to the transducer (HM-124, Honda Electronics, Aichi, Japan) from a high-frequency power supply through an impedance-matching system. The impedance-matching system was adjusted to achieve a standing wave ratio (SWR) of 1.5 and 95% transmission of RF power to the transducer (IM3570, Hioki, Nagano, Japan). The net power applied to the transducer was measured based on the difference between the incident and reflected waves using a power meter (Bird 4421, Bird, Solon, OH, USA). The bottom tip of the diaphragm was soaked in a water container in the aluminum plate. Distilled water was continuously supplied onto the transducer throughout the experiment so that the volume (approximately 650 mL) and depth (approximately 1 mm) of the water on the transducer remained constant. All experiments were performed at a temperature of 24 \({}^{\circ}\)C and 55% humidity. In the experiments, a water film was formed on the surface of the oscillating diaphragm, as shown in Figure 1c, and atomization occurred from the water film under a limited condition, as discussed later. The experiments conducted were roughly divided into 3 types: one with hydrophobic diaphragm, one with hydrophilic diaphragm and one with atomization ceased by contact with a glass sheet. Figure 2a-d show water film formed on the surface of the diaphragm. Results of the experiments related to water film are shown in Table 1. In the experiment with hydrophobic diaphragm, the shape of the water film was column-like, as shown in Figure 2a,b. With an increase in the power of the transducer, height of the water pillar was increased, but its aspect ratio almost remained constant. The percentage of water coverage on the diaphragm was small, and no atomization occurred in the hydrophobic case. In the cases with a hydrophilic diaphragm, the diaphragm was widely covered by water film, with a surface coverage of as much as 73.5%. Continuous atomization was observed in the hydrophilic case, with 6.0 W of incident power, as shown in Figure 2d. Figures 3 and 4 show acoustic signals processed by fast Fourier transform from the experiments with hydrophobic and hydrophilic diaphrags. For both types of diaphrags, it was observed that peak frequencies shifted in direction to lower frequency with an increase in the incident power of the transducer. Significant peak frequencies are marked as vertical dashed lines **a** to **f**. Figure 1: Apparatus used for the experiments of ultrasonic jet atomization [26]. (**a**) experimental setup, (**b**) layout of diaphragm, (**c**) formation of water film. It is important to note that attenuation of the signals in the hydrophilic case where atomization occurred was larger in the overall frequency range than that in the hydrophobic case where no atomization occurred. In the experiment with the hydrophilic diaphragm, atomization was forcibly ceased by putting a thin glass sheet in contact with the water film. The glass sheet was moved so that it touched only the water film and never touched the diaphragm, as shown in Figure 5a,b. Therefore, the diaphragm kept oscillating after the contact. The surface wave appeared to be attenuated, and the atomization ceased as intended. However, coverage of the water film on the diaphragm did not significantly change, as shown in Figure 5b. The FFT signal in the last experiment is shown in Figure 6. It was found that peak signals in the higher frequency range, such as **e** and **f**, significantly reduced after the cessation of atomization. This result suggested that the resonation of the diaphragm in the higher frequency region was intimately related to conditions of the atomization.