Diagram of the shift in nodal positions of a SSAW resulting from a change in applied SAW frequency. The electronics used to excite the SAWs are as follows: I—impedance matching networks; II—power divider; III—radio frequency (RF) power amplifier with 25 V bias; and IV—RF signal generator.
(a) Schematic of polymeric microfluidic device, separated from the SAW device by a layer of ultrasound coupling gel and, (b) scattering parameter measurements for SAW transmission prior to integration with a fluidic device.
Fluorescence micrographs of an array of micron-sized latex particles at 31 MHz (a) and 32.8 MHz (b). The fluorescence intensity was measured in the regions highlighted by the large white boxes in (a) and (b) and is plotted in (c). The centre of the acoustic path is highlighted by an arrow in (c). A line at the edge of the array in (a) splits into two neighbouring lines in (b), highlighted by a small white box.
Enlarged images of the highlighted region in Figure 3(a) at 31 MHz (a) and at intervals of 1 s ((b)–(h)) after changing the SSAW frequency to 32.8 MHz. The arrow indicates the line that splits between two neighbouring lines after the frequency change. Black lines have been added to indicate the location of particle lines at 32.8 MHz for clarity.
(a) Fluorescence micrographs of 1 m diameter latex spheres held in array by a SSAW showing array transportation by sequential increases in the SSAW frequency. (b) The distance travelled by each line in the array was calculated for each frequency increment and the average distance moved by the entire array is plotted as a function of frequency. Standard errors were calculated during averaging. The solid line is a guide to the eye, showing the order in which the frequency increments were applied.
Plots of (a) latex particle acceleration during coalescence by standing-SAW at a range of power levels and (b) the calculated time constants of particle coalescence for a range of particle sizes (data points) and theoretically calculated time constants (solid line).
Fluorescence micrographs of a suspension of polydisperse microbubbles (a) prior to SSAW activation and (b) 10 s after SSAW activation with an applied frequency equal to 31.6 MHz with a power level of 7 dBm applied to each IDT. A digital magnification of the microbubble cluster highlighted in (b) is shown in (c). The scale bars are 30 m wide in (a) and (b), and 2.5 m wide in (c). The contrast has been digitally enhanced in all three figures equally for clarity.
(a) Fluorescence image of an array of microbubbles. Plots of the fluorescence intensity measured across a microbubble array at SSAW frequencies of (b) 32 MHz, (c) 31.6 MHz, and (d) 31.2 MHz. Fluorescence images (e), (f), and (g) show the microbubble arrays from which plots (b), (c), and (d) were measured, respectively.
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