Ultrasonic nozzle devices without a central channel but employing a design of cascaded multiple Fourier horns in resonance produce micrometer-sized monodisperse or narrowly-sized droplets with greatly reduced electrical drive power requirements. The liquid to be atomized is brought externally to or adjacent to the endface of the nozzle tip. The above liquid transport method is equally applicable to the ultrasonic nozzle-array devices that are made up of a plurality of ultrasonic single-nozzle devices configured in parallel. The longitudinal length, transverse width, shape, and area of the nozzle endface of single-nozzle and nozzle-array devices may be tailored or designed (e.g. enlarged) to obtain optimum or large quantities of product droplets to achieve high throughput. By increasing the drive frequency to 8 MHz or higher, sub-micrometer-sized monodisperse or narrowly-sized droplets can be produced using the ultrasonic single-nozzle and nozzle-array devices or any solid endface.
