Ultrasonic removal of coarse and fine droplets in air

•PM2.5 and PM2.5-10 in air can be filtered by ultrasound.•Nonlinear effects of ultrasound are used in the filtering process.•The device would be competitive in light weight and structural compactness.

It has been a big challenge to effectively collect coarse and fine droplets from the air by compact and light equipment. In this report, a novel strategy of collecting coarse and fine droplets from the air, which employs an ultrasonic field in an air gap between a flat radiation surface and reflector, is demonstrated. Coarse and fine droplets (PM2.5-10 and PM2.5) can be effectively collected onto the reflector’s surface when the air gap thickness is proper. The radiation surface works in a flexural vibration mode at 56.9 kHz, and the collected droplets may form concentric rings and irregular shape on the reflector’s surface. Analyses show that both the acoustic streaming and acoustic radiation force contribute to the collection.

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