Aromarest uses ultrasonic diffuser technology. The system, hidden carefully in the base of the lamp, creates ultrasonic vibrations (sound waves that vibrate at a frequency higher than human ears can detect)). These waves agitate the water and separate the water particles. Those negatively charged particles become lighter than air, causing a light mist. When you add essential oils to the WAKE and SLEEP diffuser bays, the oil's particles are carried into the air along with the particles of water.