Science & Technology Review. 2005, 23(0508): 4-9.
We classify the micro systems into two categories, the micro over-all systems and the micro characteristic ones, in the former theover-all sizes must be small and in the latter other and more intrinsic micro characteristics are emphasized. By comparing them, we found thatthe latter are more universal and that smaller over-all sizes do not lead to better intrinsic characteristics in most cases. We proposed that threemicro characteristics, the micro flowing, micro structure and micro comprehensive ones, should be considered for inner flowing under very lowReynolds number Re, which occurs often in fine-long conduits and in micro substance transport and micro heat transfer. We studied the conceptof reasonable flowing form for fluids that flow in micro systems or with very low velocities, and put forward the idea that the flowing pulsesequences, which are predictable and controllable and which are produced artificially, may become the key of dealing with the most intrinsicdifficulty in the field of microfluidic systems that micro flowing readily loses its normality. The existent methods were evaluated of influencing,that is, driving, controlling or disturbing, micro fluids according to the three micro characteristics mentioned above, and the differences betweenour digitalization of microfluids and Kim’s digital microfluidic circuits were pointed put. Then we advanced the pulse influencing method,which is based on pulse inertia force, and its devices. Experimental results showed that the micro characteristics are satisfactory in manyrespects: the flowing normality holds in a wide frequency range, the substance transport resolution reaches the fL order, the minimum flow rateis 3 pL/min, the flowing resistance is minimized especially for fine-long conduits, digital fluidic flowing is realized both in micro conduits andin micro jet streams, some digital microfluidic components with neither micro movable parts nor embedded micro electric circuits have beenmade, the method is suitable universally for ordinary liquid and solid powder driving, controlling and disturbing purposes, no special propertiesof liquids and solid powders are required, and, finally, higher reliability, productivity and automaticity have been reached.
