# Effects of Driving Frequency and Voltage on the Performances of Vibrating Mesh Nebulizers
## 3 Results
### Dependence of Nebulization Characteristics on ARFT and IM  
A shown in result Section 3.1, significant changes in nebulization characteristics were observed when driving frequency was altered by only \(\pm\) 1%. Resonance frequencies of PZTs are known to depend on temperature, pressure, and medium viscosity [5; 6; 17], which means the resonance frequencies of individual PZTs should be determined. \begin{table}
\begin{tabular}{c c} \hline
**Experimental Condition** & **Purpose** \\ \hline
50 V\({}_{\text{PP}}\) + Nominal resonance frequency (NF) & Control \\
50 V\({}_{\text{PP}}\) + NF + Impedance matching (IM) & IM effect \\
50 V\({}_{\text{PP}}\) + Automatic resonance frequency tuning (ARFT) & ARFT effect \\
50 V\({}_{\text{PP}}\) + ARFT + IM & ARFT + IM effect \\
40 V\({}_{\text{PP}}\) + ARFT + IM & ARFT + IM + driving voltage effect \\
30 V\({}_{\text{PP}}\) + ARFT + IM & ARFT + IM + driving voltage effect \\ \hline \end{tabular}
\end{table} 
Table 2: Effects of automatic resonance frequency tuning (ARFT) and impedance matching (IM) on experimental conditions. Figure 5: Nebulization characteristics of salbutamol solution by driving frequency and voltage: (**a**) Output rates; (**b**) Power consumptions; (**c**) Particle sizes; All values are means \(\pm\) SDs, * \(p\) < 0.05 versus F\({}_{r}\) at each driving voltage, # \(p\) < 0.05 versus 70 V\({}_{\rm pp}\) at each driving frequency. Figure 6 shows the effects of ARFT and IM on output rate, particle size, and power consumption. Experimental groups were compared with the control (50 VPP and nominal resonance frequency (NF)). Figure 6a shows the output rate of '50 VPP + NF + IM', '50 VPP + ARFT', and '50 VPP + ARFT + IM' changed by \(-\)25%, 60%, and 115% versus the control. In combination, ARFT and IM increased output rates at the same driving voltage. The output rates of 'ARFT + IM' at 40 and 30 VPP were 21% and 33% lower than at 50 VPP. The output rate of '30 VPP + ARFT + IM' was 45% higher than that of the control. For glycerol solution, '50 VPP + NF' and '50 VPP + ARFT + IM' were not nebulized. The output rates of 'ARFT + IM' at 50, 40, and 30 VPP were 350%, 275%, and 125% higher, respectively, than at '50 VPP + ARFT'. Even when the driving frequency was at the resonance frequency, the amplitude of mesh vibration was not enough to nebulize glycerol solution. As shown in Figure 5a, the output rate of salbutamol solution was increased due to increasing driving voltage. We expect a commercial nebulizer output rate of >0.25 mL/min for the glycerol solution when a higher 50 VPP is used in conjunction with 'ARFT + IM'. The output rates of glycerol solution were compared with salbutamol solution for each experimental group ('50 VPP + ARFT', '50 VPP + ARFT + IM', '40 VPP + ARFT + IM', and '30 VPP + ARFT + IM') and were 87.5%, 58.1%, 55.9%, and 69.0% lower, respectively. Power consumptions of '50 V\({}_{\rm pp}\) + NF + IM', '50 V\({}_{\rm pp}\) + ARFT', and '50 V\({}_{\rm pp}\) + ARFT + IM' were 14%, 15%, and 41% higher than that of the control (Figure 6b), which means that ARFT and IM raised power transfer by matching output impedances of the driving system and the PZT. The power consumptions of 'ARFT + IM' at 40 and 30 V\({}_{\rm pp}\) were \(-6\) and \(-31\%\) that of the control, respectively. Considering the tradeoff between output rate and power consumption, '30 V\({}_{\rm pp}\) + ARFT + IM' was deemed acceptable for the achievement of the minimum requirement because it had an output rate of \(>\)0.29 mL/min and 0.69 W. For glycerol solution, power consumptions of 'ARFT + IM' at 50, 40, and 30 V\({}_{\rm pp}\) were 8%, \(-40\%\), and \(-52\%\), respectively, compared with '50 V\({}_{\rm pp}\) + ARFT'. 'ARFT + IM' was more effective at decreasing power consumption than ARFT. Power consumptions required for the nebulization of glycerol solution in the experimental groups were 78.3%, 80.9%, 84.0%, and 82.6% lower than in the correlation salbutamol experimental groups'.