the desired flow ratio it should be possible also to introduce full two dimensional sheath flow in this method a 1 dimensional sheath flow is first generated introduction of sheath streams from below and above then act to compress the sample stream in the vertical direction creating a true two dimensional sheath there are a large number of methods termed u201c inertial u201d these rely to varying degrees on the discreteness of the particles themselves to create focusing not merely on the flow paths generated within the streamlines of the liquid as above some inertial methods also have a focusing component due to creation of focused streamlines as well nearly all of these methods operate at very low flow rates that cannot be obviously extended to the range required for quick analyses e g the flow of several hundred ul of liquid in less than 1 minute a secondary problem of most of these flow methods is that the fabrication demands are beyond what is reasonable to expect in high volume manufacture in the near to mid term since the sizes of structures are on the order of the sizes of the particles to be focused an inertial focusing method that could be implemented in a microfluidic disc is illustrated in fig1 this method uses expansions and contractions in the flow stream to induce vortices which have the effect of focusing the sample stream for total flow rates lt 5 5 ml hour and sample sheath ratios of 1 10 a structure with multiple contractions expansions 350 um square and 53 um deep connected by channels 50 umw u00d7 53 umd and 300 um long has.