Abstract:
A method of expelling a fluid includes filling a nozzle with a fluid using a capillary force, generating an ion wind by ionizing air near an outlet of the nozzle, and expelling the fluid from the nozzle as the ion wind decreases a pressure around the outlet of the nozzle. An ink-jet printhead utilizing the method includes a manifold formed in a passageway plate to supply ink, a nozzle to be supplied with ink formed in a nozzle plate provided on the passageway plate, and a ground electrode and a source electrode arranged near an outlet of the nozzle, the ground electrode and the source electrode forming an electric field due to an application of a voltage thereto and ionizing air near the outlet of the nozzle to produce an ion wind to decrease a pressure near the outlet of the nozzle to expel the ink contained in the nozzle.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a method of expelling a fluid. More particularly, the present invention relates to a method of expelling a fluid from a nozzle using an ion wind and an ink-jet printhead utilizing the method.  
           [0003]    2. Description of the Related Art  
           [0004]    Typically, ink-jet printheads are devices for printing a predetermined image, color or black, by ejecting a small volume droplet of printing ink at a desired position on a recording sheet. In conventional ink-jet printheads, ink ejection mechanisms are largely categorized into two types. Conventionally, there have been used a thermally driven type in which a heat source is employed to generate bubbles in ink to cause ink droplets to be ejected by an expansion force of the generated bubbles, and a piezoelectrically driven type in which ink is ejected by a pressure applied to ink due to deformation of a piezoelectric element.  
           [0005]    [0005]FIGS. 1A and 1B illustrate examples of a conventional thermally driven ink-jet printhead. FIG. 1A illustrates a cutaway perspective view of a structure of a conventional ink-jet printhead. FIG. 1B illustrates a cross-sectional view of an ink ejection mechanism of the conventional ink-jet printhead shown in FIG. 1A.  
           [0006]    The conventional thermally driven ink-jet printhead shown in FIGS. 1A and 1B includes a manifold  22  provided on a substrate  10 , an ink channel  24  and an ink chamber  26  defined by a barrier wall  14  installed on the substrate  10 , a heater  12  installed in the ink chamber  26 , and a nozzle  16  that is provided on a nozzle plate  18  and through which ink droplets  29 ′ are expelled. When a pulse current is supplied to the heater  12  and heat is generated in the heater  12 , ink  29  filled in the ink chamber  26  is heated, and a bubble  28  is generated. The formed bubble  28  continuously expands and exerts pressure on the ink  29  contained within the ink chamber  26 . This pressure causes the ink droplets  29 ′ to be expelled through the nozzle  16 . Subsequently, the ink  29  is absorbed from the manifold  22  into the ink chamber  26  through the ink channel  24 , thereby refilling the ink chamber  26  with ink  29 .  
           [0007]    However, in the thermally driven ink-jet printhead, when ink droplets are expelled due to the expansion of bubbles, a portion of the ink in the ink chamber  26  flows backward to the manifold  22 , and an ink refill operation is performed after ink is expelled. Thus, there is a limitation in implementing high-speed printing.  
           [0008]    In addition to the above-described ink droplet ejection mechanisms, a variety of different ink droplet ejection mechanisms are used in ink-jet printheads, and another example is shown in FIG. 2. FIG. 2 illustrates an example of a conventional ink droplet ejection mechanism utilizing a principle of an atomizer.  
           [0009]    Referring to FIG. 2, unmixed ink  40  of multiple colors is contained in a reservoir  34  of an ink cartridge  32 . The reservoir  34  has a printhead  35  at a bottom surface thereof. The printhead  35  operates to dispense unmixed ink  40 . The ink  40  dispensed through the printhead  35  is mixed in a mixing chamber  42 , and a nozzle tube  44  is filled with the mixed ink. Compressed air delivered via a conduit  52  of an atomizer  50  is sprayed onto a front portion of an outlet  46  of the nozzle tube  44 , causing a reduction in pressure at the front portion of the outlet  46  of the nozzle tube  44 . Accordingly, ink in the nozzle tube  44  is expelled and atomized onto an object  49  in the form of droplets  48 .  
           [0010]    The ink-jet printhead expelling ink utilizing the principle of an atomizer requires a compressor for supplying compressed air. In particular, in order to adopt the above-described ink ejection mechanism to an ink-jet printhead having a plurality of nozzles, there is a demand for a complex series of air supply passages from the compressor to the plurality of nozzles. Thus, the printhead becomes bulky, which reduces the number of nozzles per unit area, i.e., a nozzle density. In addition, it is quite difficult to manufacture a printhead having several hundred or more nozzles. As a result, an operational printing resolution of the ink-jet printhead adopting the above-described ink ejection mechanism still remains at a level of several tens of dots per inch (DPI).  
           [0011]    Accordingly, in order to implement an ink-jet printhead having high printing speed and high resolution, a new ink droplet ejection mechanism is needed.  
         SUMMARY OF THE INVENTION  
         [0012]    The present invention provides a method of expelling a fluid from a nozzle by reducing a pressure in a front portion of an outlet of the nozzle using an ion wind.  
           [0013]    The present invention also provides a high-integration, high-resolution ink-jet printhead utilizing the fluid expelling method.  
           [0014]    According to a feature of an embodiment of the present invention, there is provided a method of expelling a fluid including filling a nozzle with a fluid using a capillary force, generating an ion wind by ionizing air near an outlet of the nozzle, and expelling the fluid from the nozzle as the ion wind decreases a pressure around the outlet of the nozzle.  
           [0015]    In the method, the ionizing of air may be performed by an electric field formed between two electrodes disposed near the outlet of the nozzle. A volume and speed of the fluid expelled may be adjusted by varying voltages applied between the two electrodes and a time duration of voltage application. An expelling frequency of the fluid may be adjusted by varying a pulse period of the voltage applied to the electrodes.  
           [0016]    In the method, the ion wind may flow toward the outlet of the nozzle and upward at a front portion of the outlet of the nozzle and may flow in an inclined direction toward the front portion of the outlet of the nozzle.  
           [0017]    In the method, the fluid may be ink, the ink being expelled from an ink-jet printhead.  
           [0018]    According to another feature of an embodiment of the present invention, there is provided an ink-jet printhead including a manifold formed in a passageway plate to supply ink, a nozzle to be supplied with ink formed in a nozzle plate provided on the passageway plate, the ink being supplied by a capillary force, and a ground electrode and a source electrode arranged near an outlet of the nozzle, the ground electrode and the source electrode forming an electric field due to an application of a voltage thereto and ionizing air near the outlet of the nozzle to produce an ion wind to decrease a pressure near the outlet of the nozzle to expel the ink contained in the nozzle.  
           [0019]    In the ink-jet printhead, the ground electrode may be disposed adjacent the outlet of the nozzle and the source electrode may be disposed a predetermined distance from the ground electrode away from the outlet of the nozzle. The ion wind may flow toward the outlet of the nozzle and may flow upward at a front portion of the outlet of the nozzle.  
           [0020]    An embodiment of the ink-jet printhead may further include a recess having a predetermined depth formed at a periphery of the outlet of the nozzle on a surface of the nozzle plate, the ground electrode and the source electrode being arranged within the recess. The recess may have a shape of a ring surrounding the nozzle. A side of the recess adjacent the outlet of the nozzle may be inclined to permit the ion wind to flow in an inclined direction toward a front portion of the outlet of the nozzle. The ground electrode may be disposed on a bottom of the recess or on the inclined side of the recess.  
           [0021]    Another embodiment of the ink-jet printhead may further include an ion wind path for guiding the ion wind formed in the nozzle plate to surround the nozzle, the ground electrode and the source electrode being arranged within the ion wind path. The ion wind path may be shaped as a ring surrounding the nozzle. An outlet side of the ion wind path may be inclined to permit the ion wind to flow in an inclined direction toward a front portion of an outlet of the ion wind path. The ground electrode may be disposed on the inclined side of the ion wind path and the source electrode may be disposed a predetermined distance apart from the ground electrode. This embodiment of the ink-jet printhead may further include an air path for supplying the ion wind path with air formed in the nozzle plate to communicate with the ion wind path. The air path may be formed in a vertical, horizontal, or inclined direction and communicates with a lower portion of the ion wind path.  
           [0022]    In the ink-jet printhead, the nozzle may have a tapered shape in which a cross-sectional area of the nozzle decreases gradually toward the outlet of the nozzle. The ground electrode and the source electrode may surround the outlet of the nozzle. A shape of the ground electrode and the source electrode may be circular, oval, or polygonal. The source electrode may have a cross-sectional area smaller than a cross-sectional area of the ground electrode.  
           [0023]    In an embodiment of the ink-jet printhead, the source electrode may include a protrusion extending toward the ground electrode. The protrusion may be a plurality of protrusions provided at equidistant intervals along a lengthwise direction of the source electrode.  
           [0024]    In the ink-jet printhead, the nozzle may be a plurality of nozzles, each formed in the nozzle plate, and one of a plurality of ground electrodes and one of a plurality of source electrodes are arranged near each of the plurality of nozzles, and wherein ink may be expelled from each of the plurality of nozzles simultaneously, sequentially, or individually. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
         [0026]    [0026]FIGS. 1A and 1B illustrate an exemplary conventional ink-jet printhead, in which FIG. 1A illustrates a cutaway perspective view of a structure thereof and FIG. 1B illustrates a cross-sectional view for explaining an ink ejection mechanism thereof;  
         [0027]    [0027]FIG. 2 illustrates another exemplary conventional ink-jet printhead for explaining an ink ejection mechanism using an atomizer;  
         [0028]    [0028]FIG. 3A illustrates a planar structure of an ink-jet printhead according to a first embodiment of the present invention and FIG. 3B illustrates a vertical cross-sectional view of the ink-jet printhead taken along line A-A′ of FIG. 3A;  
         [0029]    [0029]FIG. 4 is a diagram illustrating a mechanism of producing an ion wind;  
         [0030]    [0030]FIG. 5 illustrates a modification of a source electrode shown in FIG. 3A;  
         [0031]    [0031]FIG. 6 illustrates an exemplary ink-jet expelling method according to an embodiment of the present invention adopted to an ink-jet printhead having a plurality of nozzles;  
         [0032]    [0032]FIG. 7 illustrates a vertical cross-sectional view of an ink-jet printhead according to a second embodiment of the present invention; and  
         [0033]    [0033]FIG. 8 illustrates a vertical cross-sectional view of an ink-jet printhead according to a third embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0034]    Korean Patent Application No. 2003-2728, filed on Jan. 15, 2003, and entitled: “Method of Expelling Fluid Using Ion Wind and Ink-Jet Printhead Adopting the Method,” is incorporated by reference herein in its entirety.  
         [0035]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the thickness of layers and regions are exaggerated for clarity. Like reference numerals refer to like elements throughout.  
         [0036]    [0036]FIG. 3A illustrates a planar structure of an ink-jet printhead according to a first embodiment of the present invention. FIG. 3B illustrates a vertical cross-sectional view of the ink-jet printhead taken along line A-A′ of FIG. 3A.  
         [0037]    Although only a unit structure of the ink-jet printhead is shown in the drawings, a plurality of nozzles are provided in the ink-jet printhead manufactured in a form of chips.  
         [0038]    Referring to FIGS. 3A and 3B, a manifold  112  is formed in a passageway plate  110  to supply ink  101 , a nozzle  122  filled with ink  101  to be expelled is formed in a nozzle plate  120  formed on the passageway plate  110 . The passageway plate  110  and the nozzle plate  120  may be integrally formed.  
         [0039]    Ink  101  is supplied to the manifold  112  from an ink reservoir (not shown). Ink  101  in the manifold  112  moves to the nozzle  122  by a capillary force to fill the nozzle  122 . Although the nozzle  122  preferably has a circular cross-sectional area, the nozzle  122  may have various shapes, including an oval or polygonal shape. Preferably, the nozzle  122  has a tapered shape in which a cross-sectional area of the nozzle  122  decreases gradually toward an outlet.  
         [0040]    A ground electrode  131  and a source electrode  132  are spaced a predetermined distance apart from each other near an outlet of the nozzle  122 . The ground electrode  131  is grounded, and a predetermined DC pulse or AC voltage is applied to the source electrode  132 . The voltage applied to the ground electrode  131  and the source electrode  132  forms an electric field and ionizes ambient air present near the outlet of the nozzle  122 , thereby producing an ion wind, which will be subsequently described in greater detail.  
         [0041]    The ground electrode  131  and the source electrode  132  are preferably shaped to surround the outlet of the nozzle  122 . For example, as shown, if the nozzle  122  has a circular cross-sectional shape, the ground electrode  131  and the source electrode  132  will also have a circular ring cross-sectional shape. However, if the nozzle  122  has an oval or polygonal cross-sectional shape, the cross-sectional shapes of the ground electrode  131  and the source electrode  132  may vary accordingly.  
         [0042]    The ground electrode  131  may be disposed relatively near the outlet of the nozzle  122  while the source electrode  132  is disposed relatively far from the outlet of the nozzle  122 , or the positions of the ground electrode  131  and the source electrode  132  may be reversed. The source electrode  132  has a cross-sectional area smaller than that of the ground electrode  131 .  
         [0043]    The ink-jet printhead according to the first embodiment of the present invention is driven by an ink expelling mechanism in which ink is expelled from a nozzle using an ion wind generated in such a manner as shown in FIG. 4. Referring to FIG. 4, if a DC pulse or AC voltage of a sufficiently high voltage is applied to a source electrode  62  spaced a predetermined distance apart from a ground electrode  61 , an electric field is formed between the ground electrode  61  and the source electrode  62 . The electric field ionizes air present between the electrodes  61 ,  62 , and the ionized air moves toward the ground electrode  61  having the opposite polarity, thus producing an ion wind W. The ion wind W is generated by a Coulomb force (F) equal to a product of an intensity (E) of the electric field and a quantity of ion charges (q), that is, F=q*E. If the ground electrode  61  has a shape of a plate having a relatively wide cross section and the source electrode  62  has a relatively narrow cross section, particularly if the source electrode  62  has a shape of a sharp tip, as shown in FIG. 4, a relatively strong electric field is formed at the end of the sharp tip, and the Coulomb force F producing the ion wind W increases accordingly.  
         [0044]    Referring back to FIGS. 3A and 3B, an ink expelling mechanism of the ink-jet printhead according to the first embodiment of the present invention will now be described.  
         [0045]    When a DC pulse or AC voltage of a voltage sufficiently high to ionize air is applied to the source electrode  132 , an electric field is formed between the ground electrode  131  and the source electrode  132 . The electric field ionizes air present between the electrodes  131 ,  132 , and the ionized air moves toward the ground electrode  131  by a Coulomb force (F=q*E), and the ion wind W is produced accordingly. A speed of the produced ion wind W increases as the Coulomb force (F=q*E) applied to the ions within the electric field increases. As described above, if the ion wind W is generated near the outlet of the nozzle  122 , a pressure near the outlet of the nozzle  122  is reduced, so that ink  101  within the nozzle  122  is expelled in the form of a droplet  102  based on the principle of an atomizer. As the ink droplet  102  is expelled, the nozzle  122  is refilled with ink  101  due to a capillary force.  
         [0046]    In the above-described ink expelling mechanism, a volume and speed of the droplet  102  expelled may be adjusted by varying a voltage applied between the two electrodes  131 ,  132  and a time duration of voltage application. That is, if a voltage applied to the electrodes  131 ,  132  is increased, the speed of the ion wind W is increased and a difference in the pressure between an interior and outside the nozzle  122  is increased, thereby increasing the expelling speed of the droplet  102 . Therefore, a response speed of the nozzle  122 , which depends on a signal indicative of ink expelled, the signal transferred via the source electrode  132 , is increased. If the voltage application time is reduced, a volume of the droplet  102  of ink expelled becomes reduced. An expelling frequency of the droplet  102  may be adjusted by varying a pulse period of the voltage applied. Therefore, a desired volume of the ink droplet  102  may be expelled at a desired frequency. As the ink droplet  102  is expelled, the ink  101  refills the nozzle  122  by a capillary force. In addition, backflow of the ink  101  does not occur in the nozzle  122 . Thus, only a short period of time is required for ink refill, thereby allowing the ink droplet  102  to be expelled at a high frequency.  
         [0047]    Although the ink  101  in the nozzle  122  is driven by the ion wind W that horizontally moves from one side of the nozzle  122  to the opposite side thereof, it is preferable to make the ion wind W converge and flow upward at a front portion of an outlet of the nozzle  122 , which is because the ion wind W preferably adaptively moves in an expelling direction of the ink droplet  102 . To this end, the electrodes  131 ,  132  are arranged to surround the nozzle  122 , respectively. Preferably, the ground electrode  131  is disposed adjacent to the outlet of the nozzle  122  and the source electrode  132  is disposed a predetermined distance apart from the ground electrode  131  away from the outlet of the nozzle  122 . Such an arrangement of the electrodes  131 ,  132  allows the ion wind W to flow toward the outlet of the nozzle  122  and allows the ion wind W to flow upward at the front portion of the outlet of the nozzle  122 .  
         [0048]    [0048]FIG. 5 illustrates a modification of a source electrode shown in FIG. 3A.  
         [0049]    Referring to FIG. 5, a protrusion  133  protruding toward the ground electrode  131  is provided in the source electrode  132 ′. Preferably, a plurality of protrusions  133  is provided at equidistant intervals along a lengthwise direction of the source electrode  132 ′. The source electrode  132 ′ having the protrusions  133  is able to form a relatively strong electric field between the electrodes  131 ,  132 ′ as shown in FIG. 4, and the Coulomb force producing an ion wind W increases accordingly, thereby creating a sufficiently fast ion wind using only a relatively low voltage.  
         [0050]    [0050]FIG. 6 illustrates an exemplary ink expelling method according to an embodiment of the present invention adapted to an ink-jet printhead having a plurality of nozzles. Referring to FIG. 6, a manifold  112  is formed in a passageway plate  110  and a plurality of nozzles  122  in communication with the manifold  112  are arranged in the nozzle plate  120  in an exemplary three rows. Although only a unit structure of the ink-jet printhead having the plurality of nozzles  122  arranged in three rows has been shown in the drawings, they may be arranged in one or two rows, or in four or more rows to achieve a higher resolution in an ink-jet printhead. The ground electrode  131  and the source electrode  132  are arranged near each of the plurality of nozzles  122  as described above.  
         [0051]    In this structure, the ink droplet  102  may be simultaneously expelled from the respective nozzles  122  by simultaneously applying a voltage to the respective source electrodes  132 . In addition, the ink droplet  102  may be sequentially expelled from the respective nozzles  122  by applying voltages at a time interval to the respective source electrodes  132 . Alternatively, the ion wind W may be produced only around the outlet of one selected nozzle by applying a voltage to only one of the source electrodes  132 , thereby expelling the ink droplet  102  only from the selected nozzle.  
         [0052]    Since the electrodes  131 ,  132  are formed in a form of micro droplets using a semiconductor manufacturing process, the ink-jet printhead according to this embodiment of the present invention has a simplified structure, as compared to the conventional ink-jet printhead in which ink is expelled by compressed air. Therefore, the ink-jet printhead having the plurality of nozzles  122  can be easily manufactured, thereby implementing a high-integration, high-resolution ink-jet printhead. Since a relatively small voltage, i.e., several to several tens of volts, is applied to the source electrode  132 , that is, a relatively small amount of power is consumed in producing the ion wind W, an ink-jet printhead having a small power consumption can be manufactured.  
         [0053]    [0053]FIG. 7 illustrates a vertical cross-sectional view of an ink-jet printhead according to a second embodiment of the present invention.  
         [0054]    As shown in FIG. 7, the ink-jet printhead according to the second embodiment of the present invention has a similar structure as that of the ink-jet printhead according to the first embodiment of the present invention, except that a recess  224  having a predetermined depth is formed at a periphery of an outlet of a nozzle  222 . An explanation of a difference between the ink-jet printheads according to the first and second embodiments of the present invention follows.  
         [0055]    Referring to FIG. 7, a manifold  212  containing ink  101  is formed in a passageway plate  210 , a nozzle  222  filled with the ink  101  is formed in a nozzle plate  220  formed on the passageway plate  210 . The recess  224  having a predetermined depth is formed at a periphery of the outlet of the nozzle  222  on a surface of the nozzle plate  220 . A ground electrode  231  and a source electrode  232  are arranged within the recess  224 .  
         [0056]    The recess  224  is preferably shaped as a ring surrounding the nozzle  222  to accommodate a ring-shaped ground electrode  231  and source electrode  232 . A side  225  of the nozzle  222  adjacent the outlet of the nozzle is preferably inclined to permit the ion wind W produced in the recess  224  to flow in an inclined direction toward a front portion of an outlet of the nozzle  222 , thereby facilitating an upward flow of the ion wind W at the front portion of the outlet of the nozzle  222 .  
         [0057]    The ground electrode  231  may be installed on a bottom of the recess  224 , or it may be installed on the inclined side  225  of the recess  224  for the purpose of facilitating flow of the ion wind W. In this embodiment, the source electrode  232  is installed on a bottom at an outer peripheral side of the recess  224 .  
         [0058]    The nozzle  222  preferably has a tapered shape in which a cross-sectional area decreases gradually toward an outlet. As is well known, this configuration permits a meniscus formed on a surface of the ink  101  in the nozzle  222  to extend upward quickly to be stabilized. The shape of the nozzle  222  conforms to that of the recess  224  formed in the periphery thereof.  
         [0059]    In the second embodiment, the arrangement and shape of the electrodes  231 ,  232  are the same as those of the first embodiment. The source electrode  232  according to the second embodiment also may have the same shape as shown in FIG. 5. In addition, the ink-jet printhead according to the second embodiment also may have a plurality of nozzles, as shown in FIG. 6.  
         [0060]    [0060]FIG. 8 illustrates a vertical cross-sectional view of an ink-jet printhead according to a third embodiment of the present invention.  
         [0061]    As shown in FIG. 8, the ink-jet printhead according to the third embodiment of the present invention has a structure similar to the structure of the ink-jet printhead according to the first embodiment of the present invention, and only an explanation of a difference between the ink-jet printheads according to the first and third embodiments of the present invention will be given.  
         [0062]    Referring to FIG. 8, a manifold  312  containing ink  101  is formed in a passageway plate  310 , a nozzle  322  filled with the ink  101  by a capillary force is formed in a nozzle plate  320 . An ion wind path  324  for guiding the ion wind W is formed in the nozzle plate  320  to surround the nozzle  322 . A ground electrode  331  and a source electrode  332  are arranged within the ion wind path  324 .  
         [0063]    The ion wind path  324  is preferably shaped as a ring surrounding the nozzle  322  to accommodate a ring-shaped ground electrode  331  and source electrode  332 . An outlet side of the ion wind path  324  is preferably inclined to permit the ion wind W produced in the ion wind path  324  to flow in an inclined direction toward a front portion of the outlet of the ion wind path  324 , thereby facilitating an upward flow of the ion wind W at the front portion of the outlet of the nozzle  322 .  
         [0064]    The ground electrode  331  is disposed at an inclined portion of the ion wind path  324 , and the source electrode  332  is spaced a predetermined distance apart from the ground electrode  331  to be disposed at a deeper portion of the ion wind path  324 . Such an arrangement is preferred in view of the formation of the flow of the ion wind W.  
         [0065]    An air path  326  for supplying the ion wind path  324  with air is formed in the nozzle plate  320  to communicate with the ion wind path  324 . The air path  326  is preferably formed in a vertical direction, as shown in FIG. 8, and communicates with the ion wind path  324  at a lower portion thereof. The air path  326  may also be formed either in a horizontal direction or in an inclined direction. Accordingly, the position and shape of the air path  326  may vary within a limit in which it is capable of supplying the ion wind path  324  with air.  
         [0066]    In addition, for the foregoing reasons, it is preferable that the nozzle  322  has a tapered shape in which a cross-sectional area decreases gradually toward an outlet.  
         [0067]    In the third embodiment, the arrangement and shape of the electrodes  331 ,  332  are the same as those of the first embodiment. The source electrode  332  according to the third embodiment may also have the same shape as shown in FIG. 5. In addition, the ink-jet printhead according to the third embodiment may also have a plurality of nozzles, as shown in FIG. 6.  
         [0068]    As described above, according to the fluid expelling method of the present invention, a volume and speed of the fluid expelled may be adjusted finely and accurately by varying voltages applied between two electrodes and a time duration of voltage application. An expelling frequency of the fluid may be adjusted by varying a pulse period of the voltage applied. As the fluid is expelled from nozzles, the fluid refills the nozzles. In addition, backflow of the fluid does not occur in the nozzles and a separate time for refilling is not required, thereby enabling the fluid to be expelled at a higher frequency.  
         [0069]    Since the ink-jet printhead according to the embodiments of the present invention is constructed such that electrodes producing an ion wind are arranged near a plurality of nozzles and the electrodes are miniaturized, it has a simplified structure as compared to the conventional ink-jet printhead in which ink is expelled by compressed air. Since manufacture of an ink-jet printhead having a plurality of nozzles may be performed easily, a high-integration, high-resolution ink-jet printhead may be easily implemented. Further, since power consumption for producing an ion wind is relatively small, low power consuming ink-jet printheads can be manufactured.  
         [0070]    Preferred and exemplary embodiments of the present invention have been disclosed herein and, although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. For example, the ink expelling method according to the present invention may be applied to a general fluid ejection system in which a small amount of fluid is expelled through nozzles as well as the ink-jet printheads shown and described in the exemplary embodiments of the present invention. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.