density of the liquid, ω the angular frequency and r the (radial) distance between the particle and center of the disk. The formula for Coriolis force density is: where u is the flow velocity. The Coriolis force generates when the liquid has a velocity component along the radial direction. This force is generally smaller than the centrifugal force when the rotating speed is not high enough. When it comes to a high angular frequency, the Coriolis force makes a difference to the flow of liquid, which is often used to separate fluid flow in the separation unit. Another basic force is Euler force, which is often defined as the acceleration of angular frequency. For example, when the CD is rotating at a constant speed, the Euler force is relatively slow. The formula for Euler force density is: As for a particle in the fluidic flow, the viscous force is: v is the viscosity of the liquid. As for the entire fluid flow, surface tension plays an important role in flow control. When the flow comes across a varied cross section, the surface tension will balance the centrifugal force and as a result block the flow of liquid. Higher rotation speed is necessary if the liquid would like to enter the next chamber. In this way, due to surface tension, the flowing process is divided into several steps which makes it simpler to realize flow control. Typical component There are various typical units in a centrifugal microfluidic structure, including valves, volume metering, mixing and flow switching. These types of units can make up structures that can be used in a variety of ways. Valves The principle of valves is the balance between centrifugal force and surface tension. When the centrifugal force is smaller than the surface tension, the liquid flow will be held in the original chamber; when the centrifugal force overbalances the surface tension due to a higher rotating speed, the liquid flow will break the valve and flow into the next chamber. This can be used to control the flow process simply by controlling the rotating speed of the disk. The most commonly used valves include the hydrophilic valve, the hydrophobic valve, the syphon valve and sacrificial valve. As for hydrophilic and hydrophobic valves, the generation of surface tension is almost the same. It is the sudden change of cross section of the channel that generates the surface tension.