Abstract:
A method is provided for operating a thermal management system which includes providing a set of synthetic jet actuators A={a 1 , . . . , a n } ( 309, 311, 313 ), wherein n≧3, and wherein each member of A has a diaphragm which oscillates along a principle axis. The members of set A are arranged and operated such that they have corresponding forces F 1 , . . . , F n  at any given time during their operation, wherein any force F k  ε {F 1 , . . . , F n } has vector components along mutually orthogonal axes x, y and z of F kx , F ky , and F kz , wherein at least one of the sets S x ={|F 1x |, . . . , |F nx |}, S y ={|F 1y |, . . . , |F ny |} and S z ={|F 1z |, . . . , |F nz |} has more than one member, and wherein the sum T F =Σ i=1   n  F i  is essentially zero.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. provisional application No. 61/771,289, filed Mar. 1, 2013, having the same title, and the same inventors, and which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    The present disclosure relates generally to synthetic jet ejectors, and more particularly to systems and methods for affecting vibration cancellation in the same. 
       BACKGROUND OF THE DISCLOSURE 
       [0003]    A variety of thermal management devices are known to the art, including conventional fan based systems, piezoelectric systems, and synthetic jet ejectors. The latter type of system has emerged as a highly efficient and versatile thermal management solution, especially in applications where thermal management is required at the local level. 
         [0004]    Various examples of synthetic jet ejectors are known to the art. Earlier examples are described in U.S. Pat. No. 5,758,823 (Glezer et al.), entitled “Synthetic Jet Actuator and Applications Thereof”; U.S. Pat. No. 5,894,990 (Glezer et al.), entitled “Synthetic Jet Actuator and Applications Thereof”; U.S. Pat. No. 5,988,522 (Glezer et al.), entitled Synthetic Jet Actuators for Modifying the Direction of Fluid Flows”; U.S. Pat. No. 6,056,204 (Glezer et al.), entitled “Synthetic Jet Actuators for Mixing Applications”; U.S. Pat. No. 6,123,145 (Glezer et al.), entitled Synthetic Jet Actuators for Cooling Heated Bodies and Environments”; and U.S. Pat. No. 6,588,497 (Glezer et al.), entitled “System and Method for Thermal Management by Synthetic Jet Ejector Channel Cooling Techniques”. 
         [0005]    Further advances have been made in the art of synthetic jet ejectors, both with respect to synthetic jet ejector technology in general and with respect to the applications of this technology. Some examples of these advances are described in U.S. 20100263838 (Mahalingam et al.), entitled “Synthetic Jet Ejector for Augmentation of Pumped Liquid Loop Cooling and Enhancement of Pool and Flow Boiling”; U.S. 20100039012 (Grimm), entitled “Advanced Synjet Cooler Design For LED Light Modules”; U.S. 20100033071 (Heffington et al.), entitled “Thermal management of LED Illumination Devices”; U.S. 20090141065 (Darbin et al.), entitled “Method and Apparatus for Controlling Diaphragm Displacement in Synthetic Jet Actuators”; U.S. 20090109625 (Booth et al.), entitled Light Fixture with Multiple LEDs and Synthetic Jet Thermal Management System”; U.S. 20090084866 (Grimm et al.), entitled Vibration Balanced Synthetic Jet Ejector”; U.S. 20080295997 (Heffington et al.), entitled Synthetic Jet Ejector with Viewing Window and Temporal Aliasing”; U.S. 20080219007 (Heffington et al.), entitled “Thermal Management System for LED Array”; U.S. 20080151541 (Heffington et al.), entitled “Thermal Management System for LED Array”; U.S. 20080043061 (Glezer et al.), entitled “Methods for Reducing the Non-Linear Behavior of Actuators Used for Synthetic Jets”; U.S. 20080009187 (Grimm et al.), entitled “Moldable Housing design for Synthetic Jet Ejector”; U.S. 20080006393 (Grimm), entitled Vibration Isolation System for Synthetic Jet Devices”; U.S. 20070272393 (Reichenbach), entitled “Electronics Package for Synthetic Jet Ejectors”; U.S. 20070141453 (Mahalingam et al.), entitled “Thermal Management of Batteries using Synthetic Jets”; U.S. 20070096118 (Mahalingam et al.), entitled “Synthetic Jet Cooling System for LED Module”; U.S. 20070081027 (Beltran et al.), entitled “Acoustic Resonator for Synthetic Jet Generation for Thermal Management”; U.S. 20070023169 (Mahalingam et al.), entitled “Synthetic Jet Ejector for Augmentation of Pumped Liquid Loop Cooling and Enhancement of Pool and Flow Boiling”; U.S. 20070119573 (Mahalingam et al.), entitled “Synthetic Jet Ejector for the Thermal Management of PCI Cards”; U.S. 20070119575 (Glezer et al.), entitled “Synthetic Jet Heat Pipe Thermal Management System”; U.S. 20070127210 (Mahalingam et al.), entitled “Thermal Management System for Distributed Heat Sources”; U.S. 20070141453 (Mahalingam et al.), entitled “Thermal Management of Batteries using Synthetic Jets”; U.S. Pat. No. 7,252,140 (Glezer et al.), entitled “Apparatus and Method for Enhanced Heat Transfer”; U.S. Pat. No. 7,606,029 (Mahalingam et al.), entitled “Thermal Management System for Distributed Heat Sources”; U.S. Pat. No. 7,607,470 (Glezer et al.), entitled “Synthetic Jet Heat Pipe Thermal Management System”; U.S. Pat. No. 7,760,499 (Darbin et al.), entitled “Thermal Management System for Card Cages”; U.S. Pat. No. 7,768,779 (Heffington et al.), entitled “Synthetic Jet Ejector with Viewing Window and Temporal Aliasing”; U.S. Pat. No. 7,784,972 (Heffington et al.), entitled “Thermal Management System for LED Array”; and U.S. Pat. No. 7,819,556 (Heffington et al.), entitled “Thermal Management System for LED Array”. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIGS. 1   a - 1   c  are illustrations depicting the manner in which a synthetic jet actuator operates. 
           [0007]      FIG. 2  is a side view illustration of a configuration of actuators that has only a single direction of force, and wherein the actuators are arranged so that the forces are equal and opposite. They also have no net moment about the axis of the cone. An arrangement of this type may be utilized to provide straightforward vibration minimization. 
           [0008]      FIG. 3  is a side view illustration of a configuration with two of the actuators positioned similarly to those in  FIG. 2 , except they have been tilted to follow the outline of the cone. In this case there is a net force along the z-axis of the cone. The third actuator is positioned symmetrically about the cone axis. In this arrangement, the third actuator may be driven so that its force is opposite in phase and cancels the z component of the first two actuators. An arrangement of this type may be utilized to achieve zero net force and moment, thus providing the desired vibration elimination. 
           [0009]      FIG. 4  is a top view illustration of the end view of a cone or cylinder, typical for a standard (PAR/R) light bulb or lighting fixture. In this configuration, the three actuators are placed with 120° spacing and with their forces perpendicular to, and passing through, the z-axis of the cone. An arrangement of this type may be utilized to achieve cancellation of the x and y force components when the three actuators are driven in phase. Moreover, the individual net forces of the actuators pass through the cone axis so there is zero moment. Thus, arrangement of this type may be utilized to eliminate vibration. 
           [0010]      FIG. 5  is a top view illustration of an arrangement similar to  FIG. 4 , except that the embodiment depicted includes four actuators which are arranged such that they are not attached in paired equal and opposite positions, but are mounted with their individual force vectors passing the through the axis of the cone. For this case, zero force is obtained by modifying the magnitude of the displacement drive signals and/or the mass of the moving elements of the actuators so as to give a net zero force. This approach provides more package design flexibility to meet external constraints or to optimize cooling, and eliminates vibration. 
           [0011]      FIG. 6  is an illustration that extends the  FIG. 5  arrangement to include compensation for the more general case when the  FIG. 5  actuators are mounted such that there is a net z-axis force. In this case, the actuator at the base of the cone provides the balancing force similar to the description above for  FIG. 3 . 
       
    
    
     SUMMARY OF THE DISCLOSURE 
       [0012]    In one aspect, a method is provided for operating a thermal management system which includes providing a set of synthetic jet actuators A={a 1 , . . . , a n }, wherein n≧3, and wherein each member of A has a diaphragm which oscillates along a principle axis. The members of set A are arranged and operated such that they have corresponding forces F 1 , . . . , F n  at any given time during their operation, wherein any force F k  ε {F 1 , . . . , F n } has vector components along mutually orthogonal axes x, y and z of F kx , F ky , and F kz , wherein at least one of the sets S x ={|F 1x |, . . . , |F nx |}, S y ={|F 1y |, . . . , |F ny |} and S z ={|F 1z |, . . . , |F nz |} has more than one member, and wherein the sum T F =Σ i=1   n  F i  is essentially zero. 
       DETAILED DESCRIPTION 
       [0013]    The structure of a synthetic jet ejector may be appreciated with respect to  FIG. 1   a.  The synthetic jet ejector  101  depicted therein comprises a housing  103  which defines and encloses an internal chamber  105 . The housing  103  and chamber  105  may take virtually any geometric configuration, but for purposes of discussion and understanding, the housing  103  is shown in cross-section in  FIG. 1   a  to have a rigid side wall  107 , a rigid front wall  109 , and a rear diaphragm  111  that is flexible to an extent to permit movement of the diaphragm  111  inwardly and outwardly relative to the chamber  105 . The front wall  109  has an orifice  113  therein which may be of various geometric shapes. The orifice  113  diametrically opposes the rear diaphragm  111  and fluidically connects the internal chamber  105  to an external environment having ambient fluid  115 . 
         [0014]    The movement of the flexible diaphragm  111  may be controlled by any suitable control system  117 . For example, the diaphragm may be moved by a voice coil actuator. The diaphragm  111  may also be equipped with a metal layer, and a metal electrode may be disposed adjacent to, but spaced from, the metal layer so that the diaphragm  111  can be moved via an electrical bias imposed between the electrode and the metal layer. Moreover, the generation of the electrical bias can be controlled by any suitable device, for example but not limited to, a computer, logic processor, or signal generator. The control system  117  can cause the diaphragm  111  to move periodically or to modulate in time-harmonic motion, thus forcing fluid in and out of the orifice  113 . 
         [0015]    Alternatively, a piezoelectric actuator could be attached to the diaphragm  111 . The control system would, in that case, cause the piezoelectric actuator to vibrate and thereby move the diaphragm  111  in time-harmonic motion. The method of causing the diaphragm  111  to modulate is not particularly limited to any particular means or structure. 
         [0016]    The operation of the synthetic jet ejector  101  will now be described with reference to  FIGS. 1   b - FIG. 1   c.    FIG. 1   b  depicts the synthetic jet ejector  101  as the diaphragm  111  is controlled to move inward into the chamber  105 , as depicted by arrow  125 . The chamber  105  has its volume decreased and fluid is ejected through the orifice  113 . As the fluid exits the chamber  105  through the orifice  113 , the flow separates at the (preferably sharp) edges of the orifice  113  and creates vortex sheets  121 . These vortex sheets  121  roll into vortices  123  and begin to move away from the edges of the orifice  109  in the direction indicated by arrow  119 . 
         [0017]      FIG. 1   c  depicts the synthetic jet ejector  101  as the diaphragm  111  is controlled to move outward with respect to the chamber  105 , as depicted by arrow  127 . The chamber  105  has its volume increased and ambient fluid  115  rushes into the chamber  105  as depicted by the set of arrows  129 . The diaphragm  111  is controlled by the control system  117  so that, when the diaphragm  111  moves away from the chamber  105 , the vortices  123  are already removed from the edges of the orifice  113  and thus are not affected by the ambient fluid  115  being drawn into the chamber  105 . Meanwhile, a jet of ambient fluid  115  is synthesized by the vortices  123 , thus creating strong entrainment of ambient fluid drawn from large distances away from the orifice  109 . 
         [0018]    Despite the many advances in synthetic jet ejector technology, a need for further advances in this technology still exists. For example, the moving diaphragm in many synthetic jet ejectors creates a force that may be transmitted from the synthetic jet ejector to the assembly to which it is attached. It is desirable, or required, to minimize this force transmission and the related vibration of the overall assembly to which it is attached. 
         [0019]    In applications that permit it, the actuators may be symmetrically disposed in a housing in a face-to-face or back-to-back arrangement, and on the same central axis. Consequently, when they are driven to move in equal and opposite motion and at the same frequency, their forces and moments will cancel each other, thereby minimizing or eliminating vibration problems. 
         [0020]    Such a configuration is depicted in  FIG. 2 . The illumination device  201  depicted therein has a cone  203  with a PAR/R standard shape and an electrical/mechanical attachment  205  (this is typically a threaded screw cap and electrical contact of the type that rotatingly engages an Edison socket). An assembly  207  of one or more light sources and optical components are seated within the cone  203 . First  209  and second  211  synthetic jet ejectors are positioned in the cone in an arrangement in which the respective forces F a  and F b  (and associating moments) are equal in magnitude but opposite in sign, and hence cancel each other out. 
         [0021]    However, when it is not possible or feasible to package the synthetic jet ejectors in a symmetrical arrangement as in  FIG. 2 , the cancellation of moments and forces may not occur, and hence, vibration may become a problem. This problem is especially pronounced when the synthetic jet ejectors need to be placed on the surfaces of cones or cylinders, as would be the case in various standard lighting and light bulb fixtures. In such applications, it may be necessary for the synthetic jet actuators to be placed off-axis and/or at various angles on the sides of a cone, or at intermediate positions between the cone axis and its sides (e.g., higher or lower along such lines). Such a disposition may result in essentially no symmetry with respect to the position or direction of the resultant forces. This may also ban issue for other applications where package geometries do not allow the symmetry required for simple vibration cancellation of the type depicted in  FIG. 2 . 
         [0022]    It has now been found that the foregoing problem may be addressed through arrangements of synthetic jet actuators in such a way that the forces and moments cancel each other, even when straightforward symmetry is not possible, not practical or does not give adequate vibration elimination. 
         [0023]      FIG. 3  is an illustration of a particular, non-limiting embodiment of an illumination device  301  with two synthetic jet ejectors positioned similarly to those in  FIG. 2 , except that they have been tilted to follow the outline of the cone. 
         [0024]    The illumination device  301  depicted therein has a cone  303  with a PAR/R standard shape and an electrical/mechanical attachment  305  (this is typically a threaded screw cap and electrical contact of the type that rotatingly engages an Edison socket). An assembly  307  of one or more light sources and optical components are seated within the cone  303 . First  309  and second  311  synthetic jet ejectors or synthetic jet actuators are positioned in the cone in an arrangement in which the respective forces F a  and F b  (and associating moments) are equal in magnitude but opposite in sign, and hence cancel each other out. In this embodiment, and unlike the situation in the illumination device  201  of  FIG. 2 , there is a net force along the z-axis of the cone  303 . However, in this embodiment, a third synthetic jet ejector  313  or synthetic jet actuator is positioned symmetrically about the axis of the cone  303 . This synthetic jet ejector  313  can be driven so that its force is opposite in phase and cancels the z-component of the forces and moments of the first  309  and second  311  synthetic jet ejectors. The resulting zero net force and moment give the desired vibration reduction or elimination. 
         [0025]      FIG. 4  is an illustration (end view) of a particular, non-limiting embodiment of an illumination device  401  having a configuration featuring a cone  403  or cylinder of the type typical for a standard (PAR/R) light bulb or lighting fixture. In this configuration, three synthetic jet ejectors  409 ,  411  and  413  or synthetic jet actuators are positioned with 120° degree spacing and with their forces perpendicular to, and passing through, the z-axis of the cone  403 . Thus, on balance, and assuming equality of mass and frequency, the x and y force components are cancelled when the three actuators  409 ,  411  and  413  are driven in phase. The individual net forces pass thru the axis of the cone  403  so there is also zero moment. Thus, vibration is reduced or eliminated, even though there is no single synthetic jet ejector in this configuration that completely cancels out the forces or moments of any other single synthetic jet ejector. 
         [0026]      FIG. 5  is an illustration of a particular, non-limiting embodiment of an illumination device  501  having a configuration featuring a cone  503  or cylinder of the type typical for a standard (PAR/R) light bulb or lighting fixture. In this configuration, four synthetic jet ejectors  509 ,  511 ,  513  and  515  or synthetic jet actuators are positioned in an arrangement where they are not attached in paired equal and opposite positions, but are mounted with their individual force vectors passing the thru the axis of the cone  503 . For this case, zero force is obtained by modifying the magnitude of the displacement drive signals and/or the mass of the moving elements of the synthetic jet ejectors  509 ,  511 ,  513  and  515  to give a net zero force. This arrangement provides more package design flexibility to meet external constraints or to optimize cooling, and reduces or eliminates vibration. 
         [0027]      FIG. 6  is an illustration of a particular, non-limiting embodiment of an illumination device in accordance with the teachings herein. The illumination device  601  depicted therein has a cone  603  with a PAR/R standard shape and an electrical/mechanical attachment  605  (this is typically a threaded screw cap and electrical contact of the type that rotatingly engages an Edison socket). In this configuration, five synthetic jet ejectors  609 ,  611 ,  613  and  615  or synthetic jet actuators are positioned in an arrangement where they are not attached in paired equal and opposite positions, but are mounted with their individual force vectors passing the thru the axis of the cone  603 . The configuration of the illumination device  601  extends the configuration of the illumination device  501  of  FIG. 5  to include compensation for the more general case when the synthetic jet ejectors or synthetic jet actuators are mounted such that there is a net force along the z-axis. In this case, the synthetic jet ejector  619  at the base of the cone  603  provides the balancing force similar to the description above for  FIG. 3 . 
         [0028]    In some of the systems and methodologies disclosed herein, an accelerometer may be attached or coupled to the housing or components of interest. The accelerometer signal may then be fed into the electronic control circuit to adjust phase and amplitude ratios between actuators. This approach may allow for the dynamic variable control of systems with dissimilar actuators or non-symmetric systems, thus helping to reduce or minimize vibrations. 
         [0029]    It will be appreciated from the foregoing that the novel arrangements of synthetic jet ejectors or actuators described herein provide a more general solution to the vibration minimization in thermal management systems based on synthetic jet ejectors, especially when applied to the geometric, flow, packaging challenges, and other lighting requirements that exist in LED-based illumination devices. The drawings disclosed herein depict embodiments which utilize a cone geometry. However, one skilled in the art will appreciate that the same benefits may be obtained by applying the systems and methodologies disclosed herein to other package shapes and to other applications and products besides LED-based illumination devices. 
         [0030]    It will be appreciated that the systems and methodologies disclosed herein may be utilized to minimize or cancel forces or momenta arising from the operation of a synthetic jet ejector. Typically, at least 90% of the forces and/or momenta are cancelled, preferably at least 95% of the forces and/or momenta are cancelled, more preferably at least 98% of the forces and/or momenta are cancelled, and most preferably, at least 99% of the forces and/or momenta are cancelled. The foregoing may also be expressed by stating that P F  is essentially zero, wherein P F =100*T F /T N , wherein T F =Σ i=1   n  F i , wherein T N =Σ i=1   n  |F i |, and wherein each F i  is one of the n directional components of the forces for all of the synthetic jet ejectors in a device, it being understood that similar relations hold with respect to the momenta. 
         [0031]    The above description of the present invention is illustrative, and is not intended to be limiting. It will thus be appreciated that various additions, substitutions and modifications may be made to the above described embodiments without departing from the scope of the present invention. Accordingly, the scope of the present invention should be construed in reference to the appended claims.