Voice Coil Dispenser
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The electro-magnetic "voice coil" actuated dispenser incorporates the "collapsing wall" dispensation technique, which can be an inexpensive method for controlling dispensations ranging from nl to ml with sufficient accuracy.

 

Resilient small ID tubing is filled with reagent through capillary action (See "Micro-Fluidics" section).  The tubing is placed between opposing poles of a magnet. An elongated, flexible, coil carrying current is positioned with one segment attached along the tubing. A pulse of current through the coil exerts force perpendicular both to the magnetic field and current, thereby "squeezing" or collapsing the tubing.  Liquid in the tubing is forced out with a force proportional to the applied current. Control over the current pulse (amperage and timing) enables control over dispensation. The memory resilience of the tubing and capillary action restore the tubing to its original shape and thus refills the tubing. A current pulse of the opposite polarity can also enhance the restoration of the tubing shape after collapse. Soft, resilient tubing made from various materials such as TeflonTM, silicone, rubber, ChemrezTM, or CalrezTM can be used depending on application.

 

During tubing collapse, liquid flows in both directions outside and back towards the reservoir. The flow back towards the reservoir is impeded by the mass and resistance of the interconnecting tubing and can be reduced further by installing a dynamic check valve.  The dynamic check valve is a small tapered orifice, which widens in the direction of the desired liquid motion. Due to the fluid dynamics of such a configuration, the fast moving liquid has a much higher resistance going into the taper than out of the taper, unidirectional flow is thus achieved. 

 

                Another technique of creating unidirectional flow is to make use of the high dynamic resistance of an open cell sponge.  Properly located inside the tubing, the sponge has low static resistance to the "normal" flow of liquid and do not impede refilling of the tube.  On the other hand, during fast liquid motion, the dynamic resistance of these sponges is very high due to internal turbulence.

 

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