Ultrasonic atomization of liquids into micrometer-diameter droplets is widely used for aerosol drug delivery. However, existing systems lack the required precision to tune the droplet size and throughput on-demand, and the underlying droplet formation mechanism under high-frequency ultrasonic actuation remains poorly understood due to experimental constraints. Here, we present an ultrasonically actuated aerosol delivery platform, which can atomize a wide range of liquids from different inlets and generate aerosol droplets with tuneable diameters on-demand. Central to the technique are microfabricated, high aspect ratio channels bounding the liquid to be atomised into a precisely defined narrow region. High frequency oscillation of the channel sidewalls generates tuneable capillary waves at the liquid interface, leading to exceptional control over droplet formation. Throughout the process, any fluid remaining in the inlet continues to be drawn into the channel via a capillary flow. As a result, the width and depth of the liquid to be aerosolised remain constant and the periodicity and amplitude of the capillary waves can be maintained over a narrow and long rectangular region. We demonstrate that the droplet size distribution and flowrates can be modified on-demand. Since the approach does not need nozzles, meshes or impacting jets, stresses exerted on the liquid samples are reduced, hence the device is gentler on delicate samples. These results signify a significant advancement in medical aerosol delivery technology, promising improved patient comfort, treatment efficacy, and application versatility

Ultrasonic atomization of liquids into micrometer-diameter droplets is widely used for aerosol drug delivery. However, existing systems lack the required precision to tune the droplet size and throughput on-demand, and the underlying droplet formation mechanism under high-frequency ultrasonic actuation remains poorly understood due to experimental constraints. Here, we present an ultrasonically actuated aerosol delivery platform, which can atomize a wide range of liquids from different inlets and generate aerosol droplets with tuneable diameters on-demand. Central to the technique are microfabricated, high aspect ratio channels bounding the liquid to be atomised into a precisely defined narrow region. High frequency oscillation of the channel sidewalls generates tuneable capillary waves at the liquid interface, leading to exceptional control over droplet formation. Throughout the process, any fluid remaining in the inlet continues to be drawn into the channel via a capillary flow. As a result, the width and depth of the liquid to be aerosolised remain constant and the periodicity and amplitude of the capillary waves can be maintained over a narrow and long rectangular region. We demonstrate that the droplet size distribution and flowrates can be modified on-demand. Since the approach does not need nozzles, meshes or impacting jets, stresses exerted on the liquid samples are reduced, hence the device is gentler on delicate samples. These results signify a significant advancement in medical aerosol delivery technology, promising improved patient comfort, treatment efficacy, and application versatility