velocity application_number US 47924795 A description fig1 a shows a plan view drawn to scale of a portion of the surface of a silicon substrate 1 in one embodiment measuring 2 5 mm u00d7 5 mm at any convenient thickness in accordance with one embodiment of the present invention it is to be understood that materials other than those disclosed herein may also be used in the surface of substrate 1 is etched a channel having a wide portion 2a and a narrow portion 2b fig2 and 3 show cross sectional views of a glass or silicon cover 12 and the substrate 1 as viewed along line b b and line a a respectively in fig1 a a groove channel 13a in fig2 and 13b in fig3 is etched in a surface 12a of cover 12 the groove having wide and narrow portions corresponding to the wide and narrow portions of the channel 2a 2b of substrate 1 the cover 12 is anodically or wafer bonded to the substrate 1 so that the channel 13a 13b of cover 12 aligns with the channel 2a 2b of substrate 1 to form a flow path for fluids referring again to fig1 a the wide portion 2a of substrate 1.