Unlike in a standard humidifier, which uses a wick/fan system to distribute moisture into a space, an ultrasonic humidifier uses an ultrasonic sensor to form water droplets which are then dispersed into the air in a cool (or sometimes warm) haze.
The ultrasonic humidifier makes use of a transducer, which is a system that transfers an energy signal between one form and another. In the case of the humidifier, it uses its power source (electrical energy) to form ultrasonic energy, sound waves (above 20,000 Hz) that are not perceptible to the human ear.
The action of a vibrating metal diaphragm (again, above 20,000 Hz, so the process is silent) causes the formation of water droplets, which are expelled by the system.
Ultrasonic humidifiers may disperse, along with water droplets, any bacteria present in the water out into the air. To overcome this, many humidifiers make use of antibacterial methods, such as, for instance, ultraviolet light sources.
The water in an ultrasonic humidifier should nevertheless be changed frequently to help prevent potentially irritating or dangerous contamination.