Abstract:
This invention relates to a method and apparatus for high-speed fluid flow control. More particularly, the invention is directed to a valve formed, at least in part, of an actuating material, such as piezoelectric or anti-ferro-electric material. The valve is used for controlling fluid flow (including air flow) in a variety of devices including imaging devices (e.g. printers, copiers, etc.) for which air flow is used to handle paper. In one embodiment, the subject valve takes advantage of the phenomenon of buckling, resultant bistability and other structural mechanics to efficiently, and in a high-speed manner, open and close to regulate fluid flow. In another embodiment, the valve includes implementation of the actuating material to bend an s-shaped blocking element within the valve. The valve is also advantageously implemented in matrices and formed using batch fabrication techniques.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to a method and apparatus for high-speed fluid flow control. More particularly, the invention is directed to a valve formed, at least in part, of an actuating material, such as piezoelectric or anti-ferro-electric material. The valve is used for controlling fluid flow (including air flow) in a variety of devices including imaging devices (e.g. printers, copiers, etc.) for which air flow is used to handle paper. In one embodiment, the subject valve takes advantage of the phenomenon of buckling, resultant bistability and other structural mechanics to efficiently, and in a high-speed manner, open and close to regulate fluid flow. In another embodiment, the valve includes implementation of the actuating material to bend an s-shaped blocking element within the valve. The valve is also advantageously implemented in arrays and formed using batch fabrication techniques.  
           [0002]    While the invention is particularly directed to the art of high-speed valves for regulating fluid flow in certain applications such as paper handling, and will be thus described with specific reference thereto, it will be appreciated that the invention may have usefulness in other fields and applications. For example, the invention may be used for controlling concentrations of chemicals over a volume to regulate chemical reactions, liquids, or for controlling sorting processes such as those known in the food processing and drug fields.  
           [0003]    By way of background, micro-device valves for use in, for example, paper-handling applications are known. In this regard, U.S. Pat. Nos. 5,839,722; 5,897,097; 5,941,501; and, 5,971,355, all commonly assigned and incorporated herein by this reference, disclose various such valves in an exemplary environment of a microdevice support system for a paper handling system  110 . Referring now to FIG. 1, valve and sensor arrays can be used for moving objects, including flexible objects such as papers. As shown, a paper handling system  110  can be optimized for handling sheets of paper  112  without requiring direct physical contact by rollers, belts, or other mechanical transport devices. The paper handling system  110  has a conveyor  120 , divided into a lower section  122  and an upper section  124 . For clarity, the upper section  124  is cut away to better illustrate paper movement, however, it will be appreciated that the I upper section  124  and lower section  122  are substantially coextensive. The sections  122  and  124  are maintained in spaced apart relationship to define a passage  123  therebetween, with the passage sized to accommodate non-contacting passage therethrough of paper  112 . Each section  122  and  124  has a plurality of independently or semi-independently controlled adjustable air jets  126  for dynamically supporting, moving, and guiding paper  112  through the system  110 . The intensity or directionality of air jets  126  can be controlled by microdevice valves in air jets  126 , or even by use of alternative microdevices for directing air flow, such as directional vanes, louvers, or other mechanical air flow redirectors that can be embedded within or adjacent to air jets  126 .  
           [0004]    The conveyor  120  is constructed from multiple laminate layers with embedded microelectromechanical controllers and sensors. As will be appreciated, using opposed and precisely controllable air jets in sections  122  and  124  having multiple angled orientations is one mechanism for advantageously permitting adjustable application of air flow to opposing sides of paper  112 , dynamically holding the paper between sections  122  and  124 , while allowing precise control of paper position, velocity, and orientation through application of vertical, lateral, or longitudinal forces (again by directed air jets). As an added advantage, the use of independent or semi-independent controlled adjustable air jets allows for dynamically increasing or decreasing air flow directed against portions of paper  112 , allowing straightening, flattening, curling, decurling, or other desired modification in paper topography, as well as adjustments to paper position, orientation and velocity. In addition, paper of various weights, sizes, and mechanical characteristics can be easily supported and accelerated by appropriate modification of the airflow applied by air jets  126 . For example, a heavy, thick, and relatively inflexible cardboard type paper may require more air flow from the jets  126  for support and maneuvering, while a lightweight paper sheet may require less overall air flow, but may need quicker and more frequent air flow adjustments directed by the independent or semi-independent air jets  126  to compensate for flutter or edge curling effects. Advantageously, the use of large numbers of independent valve controlled air jets allows diverse paper types and sizes to simultaneously be transported, with appropriate modifications to air flow characteristics being made for each paper in the conveyor  120 .  
           [0005]    Active flexible object guidance (of paper  112 ) to correct for flutter and other dynamic problems of flexible objects is enabled by provision of a sensing unit  140  that is connected to the plurality of sensors embedded in the conveyor  120 . The sensing unit  140  senses the motion state of paper  112  by integrating information received from the embedded sensors, giving spatial and dynamic information to a motion analysis unit  150  capable of calculating relative or absolute movement of paper  112  from the received sensory information, with movement calculations generally providing overall position, orientation, velocity of paper  112 , as well as position, orientation, and velocity of subregions of the paper  112 (due to flexure of the paper  112 ). Typically, the motion analysis unit  150  is a general purpose computer, embedded microprocessor, digital signal processor, or dedicated hardware system capable of high speed image processing calculations necessary for determining object movement. Using this calculated movement information, a motion control unit  152  connected to the motion analysis unit  150  sends control signals to conveyor  120  to appropriately modify movement of paper  112  by selectively increasing or decreasing application of directed air jets to subregions of the paper  112  to reduce flutter, buckling, curling, or other undesired deviations from the desired motion state. As will be appreciated, use of discrete sensors, motion analysis units, and motion control units is not required, with integrated motion analysis and motion control assemblies being contemplated. In fact, it is even possible to provide a plurality of integrated sensors, motion analysis units, and motion control units as integrated microcontroller assemblies on the conveyor, with each air jet being locally or semi-locally controlled in response to locally sensed information.  
           [0006]    Whether the sensing unit  140  is discrete or integrated with microcontrollers, in order to ascertain object position properly the sensing unit  140  must be reliable and accurate, ideally having two dimensional spatial and temporal resolution sufficient for overall tracking of the paper through the paper transport path with submillimeter precision, and three dimensional tracking ability for even small areas of the flexible object (typically at less than about one square centimeter, although lesser resolution is of course possible). Further, in many processes the object is moving quickly, allowing less than about 1 to 100 milliseconds for tracking measurements. Fortunately, optical sensors, video imaging systems, infrared or optical edge detectors, or certain other conventional detectors are capable of providing suitable spatial and temporal resolutions. For best results, two-dimensional optical sensors (such as charge coupled devices (CCD&#39;s)), or position sensitive detectors are utilized. However, suitably arranged one-dimensional sensor arrays can also be used. As will also be appreciated, sensors other than optical sensors may be used, including but not limited to pressure sensors, thermal sensors, acoustic sensors, or electrostatic sensors.  
           [0007]    In operation, use of a sensing unit  140  for feedback control of object movement allows for precise micromanipulation of object motion state. For an illustrative example, in FIG. 1 paper  112  is sequentially illustrated in four distinct positions along conveyor  120 , respectively labeled as paper position  108 , paper position  114 , paper position  116 , and paper position  118 . In initial position  108 , the paper  112  moves along a curving path defined by a flexible portion  130  of the conveyor, constructed at least in part from a flexible laminate. In position  114 , the paper  112  becomes slightly misaligned. As paper  112  is moved along conveyor  120  toward position  116  by air jets  126 , the embedded sensors provide information that allows sensor unit  140  to calculate a time series of discrete spatial measurements that correspond to the instantaneous position fo paper  112 . These elements of a time series of spatial measurement information are continuously passed to the motion analysis unit  150 . The motion analysis unit  150  uses the received information (i.e. the sensor measured one, two or three-dimensional spatial information) to accurately determine motion state of paper  112 , including its position, velocity, and internal paper dynamics (e.g. trajectory of areas of the paper undergoing curl or flutter). This information (which may be collectively termed “trajectory”) is passed to the motion control unit  152 , which computes a new desired trajectory and/or corrective response to minimize deviation from the desired trajectory. The motion control unit  152  sends signals to selected air jets  126  to correct the misalignment, bringing the paper  112  closer to a correct alignment as indicated by position  116 . This feedback control process for properly orienting paper  112  by feedback controlled corrections to paper trajectory (the paper  112  now spatially located at position  116 ) is repeated, with the trajectory of paper  112  finally being correctly aligned as shown at position  118 . As will be appreciated, this feedback control process for modifying the trajectory of flexible objects can be quickly repeated, with millisecond cycle times feasible if fast sensor, motion processing, and air jet systems are employed. Faster cycle times are feasible as a function of the processing used, computational load, and particular implementation.  
           [0008]    Advantageously, known systems such as this allow for manipulation and control of a wide variety of objects and processes. In addition to paper handling, other rigid solids such as semiconductor wafers, or flexible articles of manufacture, including extruded plastics, metallic foils, wires, fabrics, or even optical fibers can be moved in accurate three-dimensional alignment. As will be appreciated, modifications in layout of conveyor  120  are contemplated, including but not limited to use of curved conveyors (with curvature either in a process direction or perpendicular to the process direction to allow for vertical or horizontal “switchbacks” or turns), use of cylindrical or other non-linear conveyors, or even use of segmented conveyors separated by regions that do not support air jets. In addition, it may be possible to construct the conveyer  120  from flexible materials, from modular components, or as interlocking segmented portions to allow for quick and convenient layout of the conveyor in a desired materials processing path.  
           [0009]    The valves used in the above referenced systems disclosed in the prior noted patents, however, are electrostatic valves. Such valves have physical and mechanical characteristics that do not render them entirely conducive to certain applications. For example, electrostatic valves tend to be formed with membranes that are flexible and thin, thus lacking robustness. In addition, electrostatic valves typically lack compatibility with liquid that is regulated in liquid fluid flow systems.  
           [0010]    Further, these electrostatic valves do not maintain a physical state or configuration in the absence of power. The valves may be bistable with power applied thereto; however, the devices return to a default state once the power is removed. The significance of this characteristic becomes amplified in circumstances where arrays of valves are formed and individually addressing the valves is desired. If for example, a 1000×1000 array of valves is fabricated, one million wires would be needed to address and power each valve. This excessive amount of wiring is problematic in many applications.  
           [0011]    Bimorph actuators have also been proposed to construct air flow valves. However, these valves are not bistable and are normally closed.  
           [0012]    The present invention contemplates a new and improved high-speed valve that overcomes the above-referenced difficulties and others.  
         SUMMARY OF THE INVENTION  
         [0013]    A method and apparatus for high-speed fluid flow control are provided.  
           [0014]    In one aspect of the invention, the apparatus comprises a valve body having a base portion and wall portions, at least one aperture defined in the base portion for ingress or egress of the fluid, an actuating element attached between the wall portions—the actuating element comprising a material having a plurality of physical states that varies as a function of applied voltage and being positioned to transition from a first physical state to a second physical state to selectively open and close the aperture, the transition including a buckling of the actuating element, and electrodes positioned to apply the voltage to the actuating element.  
           [0015]    In another aspect of the invention, the actuating element is formed of piezoelectric material.  
           [0016]    In another aspect of the invention, the actuating element is formed of one of anti-ferro-electric material and a ferro-electric material.  
           [0017]    In another aspect of the invention, the actuating element is formed of ferro-electric material.  
           [0018]    In another aspect of the invention, the actuating element is a diaphragm.  
           [0019]    In another aspect of the invention, the actuating element comprises multiple layers.  
           [0020]    In another aspect of the invention, the multiple layers are selectively actuated by the applied voltage.  
           [0021]    In another aspect of the invention, the actuating element maintains the second state in the absence of the applied voltage.  
           [0022]    In another aspect of the invention, the apparatus is adaptable to be addressable in a matrix.  
           [0023]    In another aspect of the invention, the method of actuation is comprised of steps of applying the voltage to the electrodes to actuate the actuating element while the actuating element is in a first physical state, maintaining the application of the voltage to buckle the actuating element into a second physical state, and removing the application of the voltage such that the actuating element remains in the second physical state.  
           [0024]    In another aspect of the invention, the method further comprises selectively applying the voltage to corresponding electrodes of multiple layers of the actuating element.  
           [0025]    In another aspect of the invention, the apparatus comprises a valve body having a base portion and wall portions, an aperture defined in the base portion for ingress and egress of the fluid, a blocking element attached between the base portion and a wall portion—the blocking element having at least one actuating element formed thereon, the actuating element comprising a material having a plurality of physical states that varies as a function of applied voltage and being positioned to transition from a first physical state to a second physical state to selectively open and close the aperture, and electrodes positioned to apply the voltage to the actuating element.  
           [0026]    In another aspect of the invention, the blocking element has a substantially s-shaped configuration.  
           [0027]    In another aspect of the invention, the actuating element is formed of a piezoelectric material In another aspect of the invention, the actuating element is formed of one of an anti-ferro-electric material and a ferro-electric material.  
           [0028]    In another aspect of the invention, the at least one actuating element comprises a plurality of actuating elements positioned such that selective actuation of each of the actuating elements generates bending moments in the actuating elements to move the blocking element to vary the configuration.  
           [0029]    In another aspect of the invention, the at least one actuating element comprises two actuating elements.  
           [0030]    In another aspect of the invention, the method is comprised of steps of selectively actuating a first actuating element by applying the voltage thereto to generate a first bending moment in the actuating element to place the actuating element, and concurrently actuating a second actuating element by applying the voltage thereto to generate a second bending moment in the second actuating element such that the first and second bending moments are of opposite sense to alter the configuration of the blocking element.  
           [0031]    In another aspect of the invention, a system comprises a substrate, a plurality of valves positioned on the substrate in a matrix configuration having rows and columns—each valve including a valve body having a base portion and wall portions, an aperture defined in the base portion for ingress and egress of the fluid, an actuating element attached between the wall portions, the actuating element comprising a material having a plurality of physical states that varies as a function of applied voltage and being positioned to transition from a first physical state to a second physical state to selectively open and close the aperture, the transition including a buckling of the actuating element, and electrodes positioned to apply the voltage to the actuating element—a plurality of row address lines, each row address line corresponding to a row of valves, and a plurality of column address lines, each column address line corresponding to a column of valves.  
           [0032]    In another aspect of the invention, each actuating element maintains the second state in the absence of the applied voltage.  
           [0033]    A primary advantage of the present invention is that it provides a valve that performs at relatively high-speed levels.  
           [0034]    Another advantage of the present invention in certain embodiments is that it provides a valve that is bistable, i.e. stable in two configurations, irrespective of whether the valve is supplied with power at all times because of the employment of the principles of buckling.  
           [0035]    Other advantages of the present invention include low cost, insensitivity to surface roughness, relative strength, low power consumption, compatibility with liquid fluid flow applications and ease of fabrication.  
           [0036]    Further scope of the applicability of the present invention will become apparent from the detailed description provided below. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0037]    The present invention exists in the construction, arrangement, and combination of the various parts of the device, and steps of the method, whereby the objects contemplated are attained as hereinafter more fully set forth, specifically pointed out in the claims, and illustrated in the accompanying drawings in which:  
         [0038]    [0038]FIG. 1 is a partial view of a paper handling system having a conveyor with air jets and micro-device sensors;  
         [0039]    FIGS.  2 ( a )-( d ) are cross sectional views of a valve of a first embodiment according to the present invention;  
         [0040]    FIGS.  3 ( a )-( c ) are cross sectional views of a valve of another embodiment according to the present invention;  
         [0041]    [0041]FIG. 4 is a cross sectional view of a valve of still another embodiment of according to the present invention;  
         [0042]    [0042]FIG. 5 illustrates a portion of a matrix of valves according to the present invention; and, FIGS.  6 ( a )-( b ) are cross sectional views of valves according to further embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0043]    The present invention is directed to an improved high-speed valve—advantageously implementing actuating elements formed of, for example, piezoelectric material—for use in the systems described above as well as others. The advantages will become apparent to those skilled in the art upon a reading of the present description. As noted above, such advantages include high-speed performance (10 kHz range and higher), relatively low cost, insensitivity to surface roughness, relative strength when compared to electrostatic valves, low power consumption, bistability (for purposes of being matrix addressable in certain applications), compatibility with liquid fluid applications and ease of fabrication.  
         [0044]    Referring now to the drawings wherein the showings are for purposes of illustrating the preferred embodiments of the invention only and not for purposes of limiting same, FIGS.  2 ( a )-( d ) provide views of a preferred valve according to the present invention. As shown, in FIGS.  2 ( a ) and ( b ), a valve  200  includes a base portion  202  having an aperture  204  defined therein. The valve  200  also includes wall portions  206  that have connected thereto an actuating element  208 . It is to be appreciated that the aperture  204 (as well as other apertures disclosed herein) is only representatively shown and preferably is connected to another volume of fluid from which fluid may flow depending on the state of the valve. It is to be appreciated that the actuating element  208  also has electrodes connected thereto that suitably take the form of layers  208 ′, for example.  
         [0045]    [0045]FIG. 2( a ) shows the valve  200  in a closed position, i.e. where the actuating element  208  is sealed against the aperture  204 . Conversely, FIG. 2( b ) illustrates the valve in an open position, i.e. where the actuating element  208  is buckled upwardly to allow fluid to flow through the aperture  204 . To induce the transition from the configuration shown in FIG. 2( a ) to the configuration shown in FIG. 2( b ), a voltage is applied to the actuating element  208  to elongate the material against fixed ends shown at  210 . Application of the voltage may be accomplished in a variety of manners that are well known to those skilled in the art. Nonetheless, the resulting axial load generated by the application of the voltage results in the buckling of the actuating element.  
         [0046]    Preferably, the actuating element is formed of piezoceramic (e.g. piezoelectric) material or other material that changes strain state upon the application of a voltage. More specifically, these materials have a plurality of physical states and are consequently capable of changing shape due to an applied voltage and are well known in the art. For example, anti-ferro-electric and ferro-electric materials, similar in nature to piezoelectric material, may also be employed for applications according to the present invention. When structures such as  208  are fabricated using piezoceramic, ferro-electric and anti-ferro-electric materials, once such materials are strained to a given point, i.e., buckled from one physical state to another, they remain in that strained state even if the applied voltage is removed. This feature provides various advantages that will be discussed in detail below in connection with, for example, FIG. 5.  
         [0047]    With reference to FIGS.  2 ( c )-( d ), it is to be appreciated that the configurations of the actuating elements implemented to obtain the advantages of the present invention may vary. For example, as shown in FIG. 2( c ), the valve  200  includes an actuating element  208  that is a substantially circular diaphragm with vent holes as shown at  212 . In FIG. 2( d ), the valve  200  includes an actuating element  208  that is flap-like (e.g. substantially rectangular) with notched areas, such as indicated at  214 , for purposes of facilitating buckling by locally reducing the stiffness of the actuating element. Of course, it should be recognized that the notched areas are not necessary.  
         [0048]    Referring now to FIGS.  3 ( a )-( c ), a valve  300 , which may take the general shapes of the configurations illustrated in FIGS.  2 ( c )-( d ) as well as other suitable configurations, is illustrated. The valve  300  includes a base portion  302  having an aperture  304  formed therein. Wall portions  306  have attached therebetween an actuating element  308 . In this embodiment, the actuating element  308  has multiple layers. As shown, actuating layers  310  and  312  are positioned between electrode layers  314  to effect suitable actuation of the layers. The provision of multiple layers in the embodiment shown in FIGS.  3 ( a )-( c ) allow for the actuating element  308  to be buckled in two directions.  
         [0049]    In this regard, FIG. 3( a ) illustrates the valve in an open state. FIG. 3( b ) illustrates the valve in a closed state. In addition, FIG. 3( c ) illustrates the valve  300  in a nominal state, which may also be considered an open state for certain applications.  
         [0050]    Referring now to FIG. 4, a valve  400  is shown. This valve includes a base portion  402  having an aperture  404  defined therein. The valve  400  also includes wall portions  406  with a multi-layer actuating element  408  connected therein and an additional aperture  410  provided in a top wall portion. The embodiment of FIG. 4 illustrates an advantage of implementation of a multi-layered actuating element described in connection with FIGS.  3 ( a )-( c ). As shown, the actuating element  408  may be buckled in either direction to selectively close the apertures  404  and  410 .  
         [0051]    The multi-layer actuating elements  308  and  408  are preferably actuated by the application of a unique series of voltage signals through their respective electrodes to selectively transition the actuating elements from a first physical state to a second physical state. The transition preferably is achieved by providing a mechanical buckling of the material. In this regard, with exemplary reference to FIG. 3( c ) for convenience (although the following discussion is equally applicable to the valve  400  of FIG. 4), a voltage is provided to the layer  310  to initiate the expansion of the layer to cause movement. Once the actuating element  308  is moving in a direction, the layer  312  is similarly actuated to continue to drive the actuating element in the direction of movement and cause the element to buckle. This configuration is illustrated in FIG. 3( a ). Once buckled, the element will remain in that position irrespective of whether power is supplied to the valve.  
         [0052]    To unbuckle the actuating element  308 , the layer  312  is actuated with a voltage of a polarity opposite to the voltage that moved the element in the direction to place it in the position of FIG. 3( a ). Once the actuating element is moving in the direction desired, the layer  310  is actuated with a similarly sensed polarity to return the actuating element to the position of FIG. 3( c ). Of course, it is to be appreciated that the actuating element  308  could be transitioned from the configuration of FIG. 3( c ) to the configuration of FIG. 3( b ) in like manner.  
         [0053]    It should be further recognized that the exemplary valve  300  may not require the nominal state shown in FIG. 3( c ). In this case, the actuating element  308  will preferably toggle between the positions shown in FIGS.  3 ( a ) and ( b ). To effect this toggling, similar sequences of voltage signals should be applied as above except that the actuating element will be driven through the nominal position with the application of suitable voltage signals. The conservation of momentum may be applied in these circumstances to toggle the actuating element from the stable position of FIG. 3( a ) to the stable position of FIG. 3( b ), or vice versa, in a fast and efficient manner. Those skilled in art will further appreciate that the principle of using momentum to drive the actuating element through the nominal position could also be applied to actuating elements of a single layer in appropriate circumstances.  
         [0054]    With reference now to FIG. 5, a matrix or array  500  of the valves positioned on a substrate in a matrix configuration having rows and columns is illustrated. This matrix includes valves  502  that are selectively addressable through row address lines  504  and column address lines  506 . In this configuration, the array of valves is matrix addressable such that any single valve can be addressed by accessing a suitable row address line and a column address line. The valve can thus be opened and closed independent of the surrounding valves. Moreover, the valve array retains its state even if power is removed.  
         [0055]    The primary reason that non-volatile matrix addressability is feasible with the valves of the present invention, but not prior art electrostatic valves, is that the valves take advantage of the principles of buckling. As a consequence, no power is required for any valve to maintain a buckled physical state. Thus, separate lines are not required for each valve. In an array of valves numbering 1000×1000, only 2000 lines are required, not the one million as would be required to individually address a electrostatic array of similar size.  
         [0056]    Referring now to FIG. 6( a ), an alternative embodiment of the present invention is shown. A valve  600  includes a base portion  602  having an aperture  604  formed therein. A top wall portion  606  is also shown. A blocking element  610  is positioned between the base portion  602  and the top wall portion  606 . Significantly, actuating elements such as those shown at  620  and  622  are positioned on a membrane  612 . The actuating element positioned on the membrane can be selectively actuated (through suitably positioned electrodes) to bend (or roll) the s-shaped configuration of the membrane to open and close the aperture  604 . As shown, the s-shape can be moved in the directions indicated by the arrow A. Preferably, the actuating elements on the “comers” of the s-shape are actuated while the other actuating elements are not so actuated.  
         [0057]    Referring now to FIG. 6( b ), a similar device is shown. In this embodiment, a valve  650  includes a base portion  652  having an aperture  654  defined therein. Also shown is a top wall portion  656 . A blocking element  660  includes a membrane  662  having actuating elements  670  and  672  formed thereon. In operation, the actuating elements are actuated to generate bending moments therein to move the s-shaped configuration in the direction of the arrow A as shown to open or close the aperture  654 .  
         [0058]    It is to be appreciated that the valves of the present invention may be constructed of a variety of materials that will be apparent to those skilled in the art, provided that the actuating elements implemented comprise a material that has a plurality of physical states that vary as a function of an applied voltage and, for selected embodiments, are of a mechanical character to allow buckling. For example, lead zirconate titanate (PZT) is the preferred piezoelectric material. However, polyvinylidene difluoride (PVDF or PVF2), zinc oxide (ZnO) and others can be used. In addition, the base and wall portions of the present valves may be formed of metal, plastic or any other rigid material that is advantageously batch fabricated or injection molded. An elastomer material such as Latex or Viton may also be suitably disposed around the aperture for sealing purposes. Further, the membrane for the S-shaped valve may be formed of any suitable flexible material, including Mylar. Similarly, the valves may be constructed in a variety of manners including batch fabrication. In some circumstances, formation processes that take stress and strain forces into account should be implemented.  
         [0059]    The above description merely provides a disclosure of particular embodiments of the invention and is not intended for the purposes of limiting the same thereto. As such, the invention is not limited to only the above-described embodiments. Rather, it is recognized that one skilled in the art could conceive alternative embodiments that fall within the scope of the invention.