Miniaturized multiple Fourier-horn ultrasonic droplet generators for biomedical applicationsElectronic supplementary information (ESI) available: Video I. Spray of water droplets from the 2 MHz nozzle. See DOI: 10.1039/c005262k

Here we report micro-electro-mechanical system (MEMS)-based miniaturized silicon ultrasonic droplet generators of a new and simple nozzle architecture with multiple Fourier horns in resonance but without a central channel. The centimetre-sized nozzles operate at one to two MHz and a single vibration mode which readily facilitates temporal instability of Faraday waves to produce monodisperse droplets. Droplets with diameter range 2.2-4.6 μm are produced at high throughput of 420 μl min −1 and very low electrical drive power of 80 mW. We also report the first theoretical prediction of the droplet diameter. The resulting MHz ultrasonic devices possess important advantages and demonstrate superior performance over earlier devices with a central channel and thus have high potential for biomedical applications such as efficient and effective delivery of inhaled medications and encapsulated therapy to the lung. MEMS-based miniaturized silicon ultrasonic nozzles of a simple architecture with multiple Fourier horns excite MHz Faraday waves and produce monodisperse droplets of diameter 2.2-4.6 μm at high throughput and very low electrical drive power.