SAW-based fluid atomization using mass-producible chip devices

Abstract

Surface acoustic wave (SAW)-based fluid atomizers are ideally suited to generate micrometer-sized droplets without any moving parts or nozzles. Versatile application fields can be found for instance in biomedical, aerosol or thin film technology, including medical inhalators or particle deposition for advanced surface treatment. Such atomizers also show great potential for on-chip integration and can lead to economic production of hand-held and even disposable devices, with either a single functionality or integrated in more complex superior systems. However, this potential was limited in the past by fluid supply mechanisms inadequate for mass production, accuracy and reliability. In this work, we briefly discuss existing fluid supply methods and demonstrate a straightforward new approach suited for reliable and cost-effective mass-scale manufacturing of SAW atomizer chips. Our approach is based on a fluid supply at the boundary of the acoustic beam via SU-8 microchannels produced by a novel one-layer/double-exposure photolithography method. Using this technique, we demonstrate precise and stable fluid atomization with almost ideal aerosol plume geometry from a dynamically stabilized thin fluid film. Additionally, we demonstrate the possibility of in situ altering the droplet size distribution by controlling the amount of fluid available in the active region of the chip.

Fast selective trapping and release of picoliter droplets in a 3D microfluidic PDMS multi-trap system with bubbles

“…The applied technique of SAWs is an established practice in the field of microfluidics, and several applications have already been demonstrated [40][41][42] like fluid mixing, 43,44 fluid translation, [45][46][47][48] jetting and atomization, 49,50 particle, droplet and cell sorting, 51-54 reorientation of nano-objects like carbon nanotubes 55 and liquid crystals, 56 pumping of fluids 57 and microcentrifugation. 58,59 Here, the generated water droplets in oil, using a T-junction, are directed to the trapping system.…”

HYbriD Resonant Acoustics (HYDRA)

“…[ 5,[15][16][17][18][19][20] To demonstrate this, we choose a microfl uidic application which requires by far the highest power density-nebulization. Pure SAW devices are typically limited to nebulization rates up to ≈0.4 mL min −1 [21][22][23][24] due to device failure as a result of the large thermal gradients and hence voltages that exceed the threshold value for dielectric breakdown in the material that arise locally on the substrate surface. In contrast, the hybrid combination of the surface and bulk waves, i.e., the SRBW and the SAW in the confi guration shown in Figure 1 c-i, is able to sustain larger increases in the input power as the acoustic energy and hence the thermal gradients are no longer confi ned to the acoustic penetration depth, but are distributed through the entire substrate.…”

“…[11][12][13][14][15][16][17][18][19][20] This use of pure SAWs, while opening up a myriad of possibilities in microfl uidics, may however not always be the most effi cient way to actuate fl uid fl ow at the microscale. As but one example, the nebulization rates with SAW nebulization has to date been limited to 0.2-0.4 mL min −1 , [21][22][23][24] frustrating efforts to translate an otherwise attractive and potentially powerful technology for pulmonary drug administration into clinical practice given its many advantages, such as the ability to generate aerosol sizes that are optimal for deep lung deposition [ 21 ] and the ability to deliver next generation therapeutic molecules (e.g., proteins, peptides, and nucleic acids [ 25 ] ) without degradation. Further increasing the input power and hence the surface vibration amplitude in the attempt to obtain higher nebulization rates is not possible given that there exists a maximum power loading before the device fails.…”

Influence of Viscosity in Fluid Atomization with Surface Acoustic Waves

“…In previous work, the advantages of the boundary fluid supply approach in SAWbased fluid atomization [26] were already demonstrated, including (I) the prevention of a larger fluid volume in the SAW propagation path, (II) a spatial separation of atomization zone and fluid supply and (III) minimized interaction between SAW and the means of fluid supply. Therefore, the experiments described here were carried out using sSAW with a fluid supply via a stainless steel capillary positioned at the boundary of the acoustic path (Figure 1).…”