Abstract:
Provided is an electrohydrodynamic (EHD) micro-pump and a method of operating the same. The EHD micro-pump includes a plurality of electrodes alternately disposed on a substrate, an insulating layer covering the electrodes on the substrate, a carbon nanotube (CNT) layer formed on the insulating layer, a cover that forms a chamber with the substrate to accommodate the plurality of electrodes on the substrate where the cover includes a fluid inlet and a fluid outlet, an upper electrode formed on an inner surface of the cover facing the plurality of electrodes, and a power supplier that applies a voltage to the plurality of electrodes.

Description:
CLAIM OF PRIORITY 
       [0001]    This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for ELECTRO-HYDRODYNAMIC MICRO-PUMP AND METHOD OF OPERATING THE SAME earlier filed in the Korean Intellectual Property Office on the 20 Nov. 2006 and there duly assigned Serial No. 10-2006-0114719. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a micro-pump, and more particularly, to an electro-hydrodynamic micro-pump having improved characteristics and a method of operating the same. 
         [0004]    2. Description of the Related Art 
         [0005]    Micro-pumps that pump minute amounts of solution can be used for micro-chemical analysis systems, medical equipments for organ transplantation, micro liquid medicine injectors, and cooling systems for electronic devices. 
         [0006]    Example of such micro-pumps include mechanical micro-pump having a rotation pump or a vibration diaphragm, electro-hydrodynamic (EHD) micro-pumps, magneto-hydrodynamic (MHD) micro-pumps, and phase change micro-pumps as a pumping mechanism. 
         [0007]    An EHD micro-pump is able to move a polar liquid without a mechanical driving unit. The polar liquid can be a polar solvent such as ethanol, propanol, or acetone. The EHD micro-pump induces flow of a polar liquid by forming an electric field in the polar liquid, and the polar liquid flows along a direction of a traveling electric field. 
         [0008]    Contemporary EHD micro-pump, however, requires high electric field to induce a flow of a polar liquid, or requires a bulky structure that is not convenient to flow liquid in a micro-device such as a semiconductor chip. 
         [0009]    Present invention provides a novel structure of EHD micro-pump, which requires low electric field to induce a flow of a polar liquid, and can be manufactured in a smaller size. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention provides an electro-hydrodynamic (EHD) micro-pump using a mechanical driving force generated by carbon nanotubes. The present invention also provides a method of operating the EHD micro-pump. 
         [0011]    According to an aspect of the present invention, there is provided an electro-hydrodynamic micro-pump including a substrate, a plurality of electrodes arranged on a surface of the substrate along a direction, an insulation layer formed on the electrodes to cover the electrodes, a carbon nanotube layer formed on the insulation layer, a cover for covering the carbon nanotube layer and the plurality of the electrodes, an upper electrode formed on the inner surface of the cover where the upper electrode facing the plurality of electrodes, and a power supplier for supplying voltages to the plurality of electrodes. The cover has a fluid inlet and a fluid outlet, and the cover forms a channel between an inner surface of the cover and the carbon nanotube layer. 
         [0012]    Each of the plurality of the electrodes is a first electrode, a second electrode, or a third electrode. The first electrode is connected to a first electrode pad, the second electrode to a second electrode pad, and the third electrode to a third electrode pad. The electrodes are sequentially arranged in order of one electrode from the first electrode, one electrode from the second electrode, and one electrode from the third electrode. The power supplier supplies a first voltage to the first electrode, a second voltage to the second electrode, and a third voltage to the third electrode. The power supplier supplies the second voltage after supplying the first voltage, and supplies the third voltage after supplying the second voltage. 
         [0013]    The electro-hydrodynamic micro-pump of the present invention can further includes a circuit unit connected to the plurality of electrodes and connected to the power supplier. The power supplier supplies a first voltage signal having a first phase to a first number of electrodes, a second voltage signal having a second phase to a second number of electrodes, and a third voltage signal having a third phase to a third number of electrodes. 
         [0014]    According to another aspect of the present invention, there is provided a method of operating the electro-hydrodynamic micro-pump described above. The method includes steps of applying a common voltage to the upper electrode, applying a first voltage to a first number of the electrodes of the plurality of the electrodes where the first number of electrodes is included in a first electrode, and applying a second voltage to a second number of electrodes of the plurality of the electrodes where the second number of electrodes is included in a second electrode. 
         [0015]    The method can further include a step of applying a third voltage to a third number of the electrodes of the plurality of the electrodes where the third number of electrodes is included in a third electrode. Each of the plurality of the electrodes can be the first electrode, the second electrode, or the third electrode. The electrodes are sequentially arranged in order of one electrode from the first electrode, one electrode from the second electrode, and one electrode from the third electrode. The step of applying the second voltage can be performed after the step of applying the first voltage, and the step of applying the third voltage can be performed after the step of applying the second voltage. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    A more complete appreciation of the invention and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein: 
           [0017]      FIG. 1  is a cross-sectional view illustrating an electro-hydrodynamic micro-pump constructed as an embodiment of the present invention; 
           [0018]      FIG. 2  is a partial plan view of the electro-hydrodynamic micro-pump of  FIG. 1 ; 
           [0019]      FIGS. 3  is a simulation result illustrating electric field formed in the EHD micro-pump of  FIG. 1 ; 
           [0020]      FIG. 4  is a simulation result illustrating an alignment of carbon nanotubes responding to the electric field shown in  FIG. 3 ; and 
           [0021]      FIG. 5  is a plan view illustrating a portion of an electro-hydrodynamic micro-pump constructed as another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    The present invention will now be described more completely with reference to the accompanying drawings in which exemplary embodiments of the invention are shown. In the drawings, like reference numerals refer to like elements. 
         [0023]      FIG. 1  is a cross-sectional view illustrating an electro-hydrodynamic (EHD) micro-pump constructed as an embodiment of the present invention.  FIG. 2  is a partial plan view of the EHD micro-pump of  FIG. 1 . 
         [0024]    Referring to  FIGS. 1 and 2 , first electrode  11 , second electrode  12 , and third electrode  13  are sequentially formed on a surface of substrate  10  along a direction. Insulation layer  20  is formed to cover first, second, and third electrodes  11 ,  12 , and  13  that are formed on substrate  10 . Carbon nanotube (CNT) layer  30  is formed on insulation layer  20 . Cover  40  is formed on substrate  10  to cover carbon nanotube layer  30  and first, second, and third electrodes  11 ,  12 , and  13 . Cover  40  forms channel  44  between an inner surface of cover  40  and carbon nanotube layer  30 . Fluid inlet  41  and fluid outlet  42  are formed in cover  40 . Upper electrode  50 , which faces first, second, and third electrodes  11 ,  12 , and  13 , is formed on the inner surface of cover  40 . 
         [0025]    Insulation layer  20  can be a silicon oxide layer. Substrate  10  can be made of a non-conductive material such as glass. Cover  40  can be made of a non-conductive material such as plastic. 
         [0026]    Second electrode  12  is connected to second electrode pad  22 , third electrode  13  is connected to third electrode pad  23 , and first electrode  11  is connected to first electrode pad  21 . As shown in  FIG. 2 , first electrode  11  crosses third electrode pad  23 . In this case, an insulation layer (not shown) can be formed on portions of first electrode  11  and third electrode pad  23  where first electrode  11  crosses third electrode pad  23 . First, second, and third electrode pads  21 ,  22 , and  23  are connected to power supplier  60 . 
         [0027]    Power supplier  60  supplies a three-phase direct current pulse voltages to first, second, and third electrode pads  21 ,  22 , and  23  in a predetermined sequence. In other words, a pulse voltage is applied to first electrode pad  21  for a first time period, while no voltage is applied to second and third electrode pads  22  and  23 . After the first time period, a pulse voltage is applied to second electrode pad  22  for a second time period, while no voltage is applied to first and third electrode pads  21  and  23 . In this way, pulse voltages are sequentially applied to first, second, and third electrode pads  21 ,  22 , and  23 . Because EHD micro-pump of this embodiment has three sets of electrodes, three types of pulse voltage signals may exist to drive the three sets of electrodes, respectively. Each of the pulse voltage signals has a pulse voltage at a different phase from the other pulse voltage signals. Therefore, the phases of the voltage signals, which are applied to first, second, and third electrode pads  21 ,  22 , and  23 , respectively, are different from each other. In this case, it can be described that three-phase voltages are applied to first electrode  11 , second electrode  12 , and third electrode  13 , which means that a first voltage signal having a first phase is applied to first electrode  11 , a second voltage signal having a second phase is applied to second electrode  12 , and a third voltage signal having a third phase is applied to third electrode  13 . 
         [0028]    A constant voltage, for example a ground voltage, is applied to upper electrode  50 . The voltage applied to upper electrode  50  can be referred to as a common voltage. There is voltage difference between upper electrode  50  and electrodes to which the pulse voltage is applied. As a result, a first electric field is formed between upper electrode  50  and electrodes to which the pulse voltage is applied. On the region where the first electric field is formed, CNTs of CNT layer  30  are arranged in a perpendicular direction with respect to equipotential lines of the first electric field. The CNTs in the region, where the first electric field is formed, are vertically aligned with respect to the surface of substrate  10 . Mechanical force is generated by the motion of the CNTs, and a flow of fluid is induced due to the mechanical force. 
         [0029]    When a pulse voltage is sequentially applied to first, second, and third electrode pads  21 ,  22 , and  23 , a traveling electric field is formed in channel  44 . Accordingly, the polar liquid filled in channel  44  moves along the traveling electric field. 
         [0030]    In this embodiment of the present invention, three sets of electrodes, which are first electrode  11 , second electrode  12 , and third electrode  13 , are described. The EHD micro-pump of the present invention, however, can have more sets of electrodes. For example, an EHD micro-pump can be constructed to have more than four sets of electrodes. A first number of electrodes can be assigned to a first electrode, a second number of electrodes can be assigned to a second electrode, and so on. In this case, the EHD micro-pump may have voltage signals that has more than four phases. Each voltage signal having a phase is applied to each set of electrodes, and the phases of the voltage signals, which are applied to the sets of electrodes, respectively, are different from each other. 
         [0031]      FIGS. 3  shows a simulation result illustrating electric field formed in the EHD micro-pump of  FIG. 1  when a predetermined voltage is applied between third electrode  13  and upper electrode  50 .  FIG. 4  shows a simulation result illustrating an alignment of carbon nanotubes responding to the electric field shown in  FIG. 3 . 
         [0032]    Width W of each of first, second, and third electrodes  11 ,  12 , and  13  was 70 μm. Interval I between adjacent two electrodes of first, second, and third electrodes  11 ,  12 , and  13  was 30 μm. Gap D between upper electrode  50  and first through third electrodes  11 ,  12 , and  13  was 100 μm. A ground voltage of 0 V was applied to upper electrode  50 , and a voltage of 50 V was applied to first, second, and third electrodes  11 ,  12 , and  13 . The frequency of a pulse voltage applied to first, second, and third electrodes  11 ,  12 , and  13  was 10 Hz˜10 kHz. 
         [0033]    Referring to  FIG. 3 , when a pulse voltage is applied to third electrode  13 , first electric field is formed in a region between upper electrode  50  and third electrode  13 . The lines shown between upper electrode  50  and third electrode  13  are equipotential lines of the first electric field. 
         [0034]    Referring to  FIG. 4 , the CNTs of CNT layer  30  on third electrodes  13 , where the first electric field is formed, are arranged in a perpendicular direction to the equipotential lines of the electric field. The CNTs are vertically aligned from the substrate, and aligned in a direction of the first electric field. At this point, CNT layer  30 , on which CNTs are vertically aligned, induces a flow of the polar liquid. 
         [0035]    If a pulse voltage is applied to an electrode, which is one of first, second, and third electrodes  11 ,  12 , and  13 , the CNTs of CNT layer  30 , which is formed on the electrode, stand up. If the pulse voltage is removed from the electrode, the CNTs of CNT layer  30 , which is formed on the electrode, lie down or disordered. Therefore, if respective pulse voltages are sequentially applied to first, second, and third electrodes  11 ,  12 , and  13 , the CNTs of CNT layer  30 , which are formed on first, second, and third electrodes  11 ,  12 , and  13 , respectively, sequentially stand up and lie down. When a pulse voltage is sequentially applied in order of first electrodes  11 , second electrodes  12 , and third electrodes  13 , traveling electric field is formed along the direction of first, second, and third electrodes  11 ,  12 , and  13 , and a polar liquid moves along the direction of the traveling electric field. In the case shown in  FIG. 3 , the polar liquid moves to the right, which is the moving direction of the second travelling electric field. If the pulse voltage is applied in the opposite order of third electrodes  13 , second electrodes  12 , and first electrodes  11 , the polar liquid moves to the left, which is the moving direction of the travelling electric field. 
         [0036]    Accordingly, the EHD micro-pump of the present invention is a bidirectional micro-pump. The moving direction of the polar liquid is determined by the order of the pulse voltages that is applied to first, second, and third electrodes  11 ,  12 , and  13 . 
         [0037]      FIG. 5  is a plan view illustrating a portion of an EHD micro-pump constructed as another embodiment of the present invention. Referring to  FIG. 5 , electrodes  111  on substrate  10  are connected to circuit unit  160 . Circuit unit  160  applies pulse voltages, which are supplied from power supplier  60 , to electrodes  111  in a predetermined sequence. The pulse voltage applied to electrodes  111  can be a three-phase voltage like the voltage described referring to  FIG. 1 , or can be a voltage having four phases or more. Circuit unit  160  facilitates the connection between electrodes  111  and power supplier  60 . 
         [0038]    Other elements of the EHD micro-pump shown in  FIG. 5  are substantially identical to the elements of the EHD micro-pump shown in  FIG. 1 , and thus, the detailed description thereof will not be repeated. 
         [0039]    As described above, an EHD micro-pump of the present invention moves a polar liquid introduced in a channel in a moving direction of a traveling electric field, and furthermore, the moving efficiency of the polar liquid can be increased using a mechanical force of CNTs that are arranged by an electric field formed by electrodes formed on upper and lower parts of the channel. Accordingly, the magnitude of voltage applying to the electrodes can be reduced. 
         [0040]    Also, the moving direction of the polar liquid can be controlled by changing the sequence of pulse voltages that is applied to the electrodes. 
         [0041]    While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.