The main function of a concrete vibrator is to vibrate or shake fresh concrete in the formwork. This helps remove air bubbles trapped in the concrete (referred to as voids) and compresses the concrete into the formwork better. Concrete vibrators are available in various designs and types. Some types include internal vibrators (also known as poker vibrators) which are inserted directly into the concrete, and external vibrators which are used to vibrate the formwork from the outside. They can also be powered by electricity, a gasoline engine, or air.