STUDIES ON MICRO-PUMP EMPLOYING ELECTRO-HYDRO-DYMAMIC STREAM

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We have developed micro pumps that use ion dragging generated by DCvoltage. Positive and negative electrodes are alternately placed, and a half of each electrode is covered with insulating film. The operating liquid is a mixture of 1-butyl alcohol : silicone=1 : 1. With three pairs of metal mesh electrodes, 18mm in diameter and 30mm in total length, pressure is proportional to the number of active pairs were obtained. Much smaller devices were fabricated on silicon wafers with 250 pairs of interdigitated electrodes. The width and spacing of the electrode fingers are both 20mm. Liquid flow rate of 2 mm/s was observed at the applied voltage of 50V,where the current was 10mA.When the composition of operating liquid is changed, flow of liquid was not observed even at the same current level. It is concluded that ion-drag micro pumps are possible when appropriate ion species are supplied and the liquid has appropriate resistivity for acceleration of ions at acceptably low voltages.When a set of subsidiary electrodes covered with insulating film was used instead of covering a half of each electrode, the flow direction was reversed. This is explained by formation of an ion sheath around each subsidiary clectrode, since the subsidiary electrode is covered with insulating film, and charge exchange is prohibited on it. The ion sheath will build up a new electric field opposite to that of the applied voltage. This effect has then been applied to a novel ion-drag motor, which has subsidiary covered electrodes between each of the main bare electrodes. In this new device, the polarity of the voltage applied to the subsidiary electrodes can successfully control the rotating direction of motor.