Suppression of short-range exposure to infectious aerosols using multiple paths of midair ultrasound acoustic streaming

Figures & data

Figure 1. Three types of acoustic streaming discussed in this study. (a) airflow toward the user’s face, (b) airflow toward the user’s head, and (c) airflow toward the left and right sides of the user.

Figure 2. The prototype system used in the experiment. The point O shows the origin point of experimental data. Bold yellow arrows show the direction of coordinate axes.

Figure 3. Outline of five conditions (a1), (a2-i), (b1-i), (b2), and (c). All coordinates are indicated in meters.

Figure 4. Outline of the other four conditions (a2-ii), (a2-iii), (b1-ii), and (b1-iii) to assess the validity of our method when the left manikin was moved. The lengths in the figures are in meters. Note that the Bessel beams were tilted upward and passed above the user’s head as conditions (b1-i) and (b2).

Figure 5. The movement of ejected smoke under the conditions (a1), (a2-i), (b1-i), (b2), (c), (a2-ii), (a2-iii), (b1-ii), and (b1-iii). The top left picture is unprocessed, and the other ten pictures were obtained via image processing against raw images.

Figure 6. Average values of captured particle numbers for the five experimental sets (excluding the maximum and minimum trial values from calculation) under (a1), (a2-i), (b1-i), (b2), and (c). “Noult” in the graph means the case under the phased array was inactivated. The error bars show the standard deviations and the symbols × and ○ show the maximum and minimum trial values, respectively.

Figure 7. $z$ components (left column) and the vector plots (middle column) of measured flow fields and simulated acoustic intensity field corresponding to the flow acceleration field (right column) under the five conditions (a1), (a2-i), (b1-i), (b2), and (c). Black dots show the position of the dual acoustic focal points, and black lines show the central axis of each Bessel beam. In the cases of (a1), (a2-i), and (c), flow fields on the $\mathit{\text{xz}}$ plane were measured. In the cases of (b1-i) and (b2), flow fields on the $\mathit{\text{yz}}$ plane were measured. In the cases of (a1) and (a2-i), the ‘intentional flows’ referred to the main text are surrounded by dotted lines. The ‘unintentional flows’ in those cases refer to the flows outside the dotted lines.

Table 1. The maximum absolute value of the $z$-component of the flow fields on the measurement plane at the time, as shown in Figure 7.

	(a1)	(a2-i)	(b1-i)	(b2)	(c)
intentional flow	0.690 m/s	1.147 m/s	0.691 m/s	0.704 m/s	0.447 m/s
unintentional flow	0.986 m/s	0.794 m/s			0.420 m/s

Figure 8. The average, standard deviation, maximum value, and minimum value of experimental sets under (a2-ii), (a2-iii), (b1-ii), and (b1-iii). The graphs were created in line with the same procedures as in Figure 6.

Figure 9. The relationship between $P_{\mathrm{\text{OFF}}}$ and $P_{\mathrm{\text{ON}}},$ as calculated by Equation (7)(7) $$\begin{array}{c}{P}_{\mathrm{\text{ON}}}=1-{\left(1-P_{\mathrm{\text{OFF}}}\right)}^{\epsilon }.\end{array}$$(7) , with the average value of $N_{\mathrm{\text{ON}}}/N_{\mathrm{\text{OFF}}}$ in each condition.