Ultrasonic (My favorite)
These diffusers use electronic oscillators to create high frequency ultrasonic waves. This causes the disc in the bottom of the water reservoir to vibrate at a high frequency and break up the essential oil and water into a fine mist. Ultrasonic diffusers are very gentle and mild. They usually have an automatic shut off when the water runs out. Also, they tend to be pretty quiet.
Candle
They come in all different shapes and sizes, beautifully crafted from glass, ceramic and sometimes with a metal base. You add water to the small dish, a few drops of essential oils, and light a votive candle or tealight underneath. They are completely silent, and the soft candlelight adds to a relaxing ambience. Best if you want essential oil in a small space for mood, ambience and a gentle aroma.
Ceramic
A few drops of essential oils on something ceramic is a simple method for diffusing the oils in a small, personal space. All you do is add essential oils to the ceramic, and the aroma naturally fills the space.
Mini Electric
Some electrical devices use low heat for dispersing the oils. These include plug-in diffusers for cars, and portable little night light diffusers. The heating unit warms the oils just enough for better evaporation.
Fan (cold wind)
These diffusers use fans to blow essential oils into the air. The oils are usually placed on an absorbing pad inside the diffuser, so no water needs to be added. There are many shapes, sizes and styles of fan diffusers. They’re usually electric.