An ultrasonic humidifier produces a warm or cool mist via a metal diaphragm that vibrates at a high frequency. This produces sound vibrations that are then able to emit the moisture or oil into the surrounding air. You won’t see any residue on nearby items as the molecules are no more than one micron in diameter and are absorbed almost immediately. Ultrasonic humidifiers are quieter than traditional humidifiers because there is no fan built into the technology and there is also no filter included in most models.