## 3 Results  
Between the two electrodes, the magnitude of the electromagnetic field along the length of the vertical axis gradually increases toward the center, maintains about 6 mm at the maximum value, and then gradually decreases (Figure 4). Based on this analysis, we designed the distance between two electrodes to be 6 mm to ensure the electric field application. Since the density of electricity would be amplified at the corner of the electrode, the electric field could be non-uniform in between the two parallel electrodes (Figure 5). Uniformity of the electric field could affect the biofilm reduction efficacy based on the principles of the electrostatic force spatial variance that might decrease the net force on biofilms. Hence, we did not expose the corner of the electrode to the media, as the electrode was placed inside the polypropylene package with 0.7 V of electric potential application (Figure 5). \begin{table}
\begin{tabular}{l l l} \hline \hline
**Items** & **Specification** & **Comments** \\ \hline Electrode at the package & SUS, 6 mm separation, 1.5 mm width & Provide the bioelectric effect \\ \hline Package & Polypropylene via 3D printing & Mechanical structure \\ \hline BE technology & 0.7 V DC offset + 0.7 V magnitude of sinusoidal & Bioelectric effect for biofilm removal, previously signal at 10 MHz & characterized [7] \\ \hline Bacterial strain & Escherichia coli & Standard biofilms \\ \hline \multirow{4}{*}{Quantification} & Green fluorescence microscopy image & Image analysis via software ImageJ \\  & (Alexa Fluor 647 Ester) & (surface coverage \%) \\ \cline{1-1}  & Live cell in biofilms assay & \\ \cline{1-1}  & (Colony form unit counting) & Analysis of viable cell in biofilms \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the testing package and analysis method. Figure 3: (**a**) Schematic of the testing package and photo of the biofilm growth testing setup and the power supply, (**b**) a real evaporator block taken from a new automotive part for biofilm growth testing (7 cm \(\times\) 6 cm \(\times\) 4.5 cm, Elandra, Hyundai Motors Korea), (**c**) signal from the electronics for biofilm reduction. The percentage of surface biofilm was calculated as the green fluorescence image was converted to the binary (black and white, in Figure 6), based on the intensity of the green fluorescence wavelength. Figure 6 shows that when the electric field was applied, dramatic biofilm reduction was demonstrated. Overall, six images of each condition were analyzed, and the average surface coverage of biofilm with standard deviation showed significant reduction of total biofilm (Figure 7). The average value reduced approximately 81.8%, compared to the non-treated biofilms (Table 2). Since the biofilms were grown for 48 h, it is assumed to be a well-established biofilm; the results demonstrate that when the BE was applied for one hour for the mature biofilm, the electric treatment removed a significant amount of biofilm. Figure 4: Plot of the magnitude of the electric field along the length of the vertical axis for the different voltage conditions. Figure 5: Contour plot of the estimated value of the electric field for the different voltage conditions. Figure 6: Representative images of biofilms. (**a**) Green fluorescence control biofilm, (**b**) binary converted control image (black area corresponds to the biofilms), (**c**) after one hour electric-field-treated green fluorescence image, and (**d**) binary converted one hour electric-field-treated image (black area corresponds to the biofilms).