Abstract:
A synthetic jet actuator is provided which includes a voice coil, a yoke consisting of a back iron ( 303 ) and pole piece, a plate ( 307 ), a first magnet ( 305 ) disposed on a first side of said plate, and a second magnet ( 309 ) disposed on a second side of said plate. The second magnet is disposed on said pole piece, and the first and second magnets and the plate cooperate to produce and direct magnetic flux which drives the voice coil.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. provisional application No. 61/772,064, filed Mar. 4, 2013, having the same title, and the same inventor, and which is incorporated herein by reference in its entirety, and of U.S. provisional application No. 61/774,974, filed Mar. 8, 2013, entitled “Synthetic Jet Actuator Equipped with Means for Magnetic Flux Profiling”, having the same inventor, 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 motors for synthetic jet actuators that are equipped with a means for profiling magnetic flux. 
       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. 1A-1C  are illustrations depicting the manner in which a synthetic jet actuator operates. 
           [0007]      FIG. 2  is an illustration of a conventional motor for a synthetic jet ejector. 
           [0008]      FIG. 3  is an illustration of a motor for a synthetic jet ejector in accordance with the teachings herein. 
           [0009]      FIG. 4  depicts the results of an FEMM simulation for a standard magnet arrangement, a  2 / 3  magnet volume, an NS-SN arrangement with a back iron, and an NS-SN arrangement with an iron ring. 
           [0010]      FIG. 5  is a graph of the normal B-field component for each of the arrangements of  FIG. 4 . 
           [0011]      FIG. 6  is an illustration of an embodiment of a motor for a synthetic jet actuator in accordance with the teachings herein. 
           [0012]      FIG. 7  is an illustration of a motor for a synthetic jet ejector in accordance with the teachings herein. 
       
    
    
     SUMMARY OF THE DISCLOSURE 
       [0013]    In one aspect, a synthetic jet actuator is provided which comprises (a) a voice coil; (b) a yoke consisting of a back iron and pole piece; (c) a plate; (d) a first magnet disposed on a first side of said plate; and (e) a second magnet disposed on a second side of said plate. The second magnet is disposed on said pole piece, and the first and second magnets and the plate cooperate to produce and direct magnetic flux which drives the voice coil. 
         [0014]    In another aspect, a synthetic jet actuator is provided which comprises (a) a voice coil; (b) a plate; (c) a first magnet disposed on a first side of said plate; (d) a second magnet disposed on a second side of said plate; and (e) a ring. The first and second magnets and the plate cooperate to produce and direct magnetic flux which drives the voice coil. 
         [0015]    In a further aspect, a synthetic jet actuator is provided which comprises (a) a voice coil; (b) a yoke consisting of a back iron and pole piece; (c) a plate; and (d) at least first and second magnets disposed radially about said pole piece, and wherein the first and second magnets and the plate cooperate to produce and direct magnetic flux which drives the voice coil. 
       DETAILED DESCRIPTION 
       [0016]    Despite the many advances in synthetic jet ejector technology, a need for further advances in this technology still exists. For example, conventional synthetic jet actuators and the motors they utilize typically feature a back iron that acts as a yoke, in combination with a magnet and top plate, to produce and direct the magnetic flux required to move the motor coil in the actuator. However, it has been found that this configuration can produce magnetic flux profiles that are sufficiently asymmetric so as to give rise to significant harmonic distortions. 
         [0017]    It has now been found that the foregoing infirmity may be overcome with the devices and methodologies disclosed herein. In a preferred embodiment, synthetic jet ejectors are provided which are equipped with two opposing magnets sandwiched around an iron plate. Such a configuration allows the magnetic field to be directed radially outwards from the structure and to avoid shorting of the field lines, and allows a very symmetric, strong field to be obtained. 
         [0018]    Prior to further describing the systems and methodologies disclosed herein, a brief overview of synthetic jet actuators may be helpful. The operation of a synthetic jet ejector and the formation of a synthetic jet are illustrated in  FIGS. 1   a - 1   c.    
         [0019]    With reference to  FIG. 1   a , the structure of a synthetic jet ejector may be appreciated. 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 . 
         [0020]    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 . 
         [0021]    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. 
         [0022]    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 . 
         [0023]      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 . 
         [0024]      FIG. 2  depicts a portion of a conventional motor structure (in air) for the voice coil actuator of a synthetic jet ejector. The details of the remainder of the voice coil actuator have been omitted for simplicity of illustration but may be found, for example, in U.S. Pat. No. 7,768,779 (Heffington et al.), which is incorporated herein by reference in its entirety (see, e.g.,  FIGS. 28-31  thereof), or in U.S. Pat. No. 8,066,410 (Boothe et al.), which is also incorporated herein by reference in its entirety (see, e.g.,  FIGS. 4-6  and  12 - 14  thereof). 
         [0025]    The motor structure  201  depicted in  FIG. 2  comprises a back iron  203  which acts as a yoke, a magnet  205  and a top plate  207 . In the particular structure depicted, the back iron  203  and top plate  207  consist of pure iron, while the magnet  205  consists of a Neodymium Iron Boron (NdFeB) magnet with a maximum energy product (BHmax) rating of 40 MgOe. These elements act together to produce and direct the magnetic flux needed to move the motor coil in the voice coil actuator. 
         [0026]      FIG. 3  depicts a portion of a particular, non-limiting embodiment of a motor structure (in air) for a synthetic jet actuator in accordance with the teachings herein. The motor structure  301  depicted therein comprises a back iron  303  which acts as a yoke, and first  305  and second  309  magnets which are separated by an intervening plate  307 . In a preferred embodiment of the particular structure depicted, the back iron  303  and intervening plate  307  consist of pure iron, while the first  305  and second  309  magnets are Neodymium Iron Boron (NdFeB) magnets with a maximum energy product (BHmax) rating of 40 MgOe. The first  305  and second  309  magnets are arranged with opposing polarities. These elements act together to produce and direct the magnetic flux needed to move the motor coil in the voice coil actuator. 
         [0027]    The motor structure  301  of  FIG. 3  differs from the motor structure  201  of  FIG. 2  in that the single larger magnet  205  of  FIG. 2  has been replaced with two smaller magnets  305  and  309  of lesser total volume. Also, the shape of the back iron  303  in  FIG. 3  is more U-shaped than the back iron  203  of  FIG. 2 . 
         [0028]    The symmetry of the magnetic field produced by the motor of a synthetic jet actuator is important to reduce harmonic distortions. The embodiment of  FIG. 3  provides a means for generating more symmetric and focused magnetic fields with radial symmetry and with high radial-normal field strength, while also reducing the total magnet volume (a cost savings). In particular, by using two magnets  305  and  309  sandwiched around an iron plate  307 , the magnetic field may be directed radially outwards from the structure  301  and the shorting of field lines may be avoided. If a back-iron structure is replaced with an iron ring (see  FIG. 4 ), then a very symmetric and strong field may be achieved. 
         [0029]      FIG. 7  illustrates another particular, non-limiting embodiment of a motor structure (in air) for a synthetic jet actuator in accordance with the teachings herein. The motor structure  501  depicted therein lacks a back iron altogether, but is equipped instead with a ring  503 , as well as first  505  and second  509  magnets which are separated by an intervening plate  507 . In a preferred embodiment of the particular structure depicted, the ring  503  and intervening plate  507  consist of pure iron, while the first  505  and second  509  magnets are Neodymium Iron Boron (NdFeB) magnets with a maximum energy product (BHmax) rating of 40 MgOe. The first  505  and second  509  magnets are arranged with opposing polarities. These elements act together to produce and direct the magnetic flux needed to move the motor coil in the voice coil actuator. 
         [0030]      FIG. 4  illustrates the results of a finite element simulation with four different motor structures and calculations. The first of these (upper left) motor structures is for a conventional structure of the type depicted in  FIG. 2 . The second (upper right) of these motor structures is the same as the first, except that the magnet volume has been reduced to ⅔ for better comparison with the following NS-SN structures. The third of these motor structures is of the type depicted in  FIG. 3  (that is, an NS-SN structure with a back iron). The fourth of these motor structures is of the type depicted in  FIG. 3  (that is, it has an NS-SN structure without a back iron, but with an iron ring). 
         [0031]    The normal B-field component for the four motor structures of  FIG. 4  is shown in  FIG. 5 . As seen therein, the motor structure of  FIG. 3  provides an improvement in the symmetry of the magnetic flux profile (B field component) of the motor structure as compared to either the standard motor structure of  FIG. 2 , or the ⅔ magnet volume variant of that structure. The motor structure of  FIG. 7  provides a further improvement in magnetic flux profile. 
         [0032]    Variations modifications to and extensions of the foregoing systems are possible. For example, in some embodiments, a transducer may be provided that has two motor structures and two voice coils driving one diaphragm to create a driver with a symmetric flux field. In other embodiments, a transducer may be provided that has two non-symmetric flux field motor structures combined to produce one drive unit that has a symmetric flux field. In still other embodiments, a transducer may be provided that has two motor structures and two voice coils driving one diaphragm, and that utilizes a shorted ring of non-ferrous material within the magnetic circuit that may reduce harmonic distortion. 
         [0033]      FIG. 6  is an illustration of another particular, non-limiting embodiment of a motor structure for a synthetic jet actuator in accordance with the teachings herein which may be utilized to create a symmetric, strong magnetic field. The motor structure  401  depicted therein comprises a back iron  403 , a yoke  405 , and a plurality of magnets  407  disposed within a plastic ring  409  and backed up against the surface of the yoke  405  so as to close the flux lines. These elements cooperate to produce and direct the magnetic flux required to move the motor coil of the synthetic jet actuator. In the particular embodiment depicted, magnets  407  are placed inside the yoke  405  in such a way that a radial magnetic field is created. 
         [0034]    The magnets  407  may have any shape that fits within the motor structure, so long as the magnets create the desired magnetic field properties. Similarly, the number of magnets  407  utilized may vary but is preferably two or more, preferably 2 to 14, more preferably 6 to 10, and most preferably 8, with the particular number for a given implementation or application being selected to ensure that field strength and uniformity matches the requirements. Likewise, the magnets  407  are preferably evenly spaced, and are preferably all the same size. 
         [0035]    In some embodiments, the magnets may be placed inside the yoke, or may be placed into or onto the back iron surfaces without being fully enclosed. Thus, for example, the magnets may be placed into preformed recesses, flat areas or drilled holes. 
         [0036]    The magnets may be placed on the inner yoke surface or on the inside of the outer yoke surface. In some cases, this may provide cost reduction (due to less magnet material required), easier assembly (since pre-magnetized magnets may be utilized and adhesives won&#39;t be necessary) better control over field/flux shape and strength, and adaptability of the design to vary field strength by adjusting the number of magnets. 
         [0037]    It will be appreciated that the embodiment of  FIG. 6  may have other advantages as well. For example, this structure allows for more design freedom in the shape of the back iron. For example, the back iron may be configured with a central hole (for example, to provide air flow, cooling, structural aid, to serve as a guide, or for other purposes), so long as the required magnetic properties are provided. 
         [0038]    Various types of magnets may be utilized in the devices and methodologies described herein. However, the use of Neodymium Iron Boron (NdFeB) magnets is preferred. Preferably, the NdFeB magnets utilized have BHmax ratings within the range of 27 MGOe to 52 MGOe and a maximum operating temperature rating which ranges from +60+80° C. to +220/+230° C. (that is, from Ny up to NyVH/NyAH, where y is the Maximum Energy Product in MGOe). 
         [0039]    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.