The vibrating membrane (piezo) uses ultrasonic technology to decompose the water into micro droplets, which are then dispersed into the air by means of a fan, where they evaporate. The visible steam is cold and harmless to health. Ultrasound devices do not require as much electrical energy and have sufficient power. When water vapour is generated by ultrasound, minerals are also released into the air, so it is necessary for devices with this technology to be equipped with water filters. Even in the case of hard water, this principle can lead to the deposition of mineral dust on the furniture and other equipment in the room.