Patent Publication Number: US-2023137610-A1

Title: Integration of airjets into computing devices

Description:
CROSS REFERENCE TO OTHER APPLICATIONS 
     This application is a continuation in part of U.S. Pat. Application No. 17/683,058 entitled EXHAUST BLENDING FOR PIEZOELECTRIC COOLING SYSTEMS filed Feb. 28, 2022, which claims priority to U.S. Provisional Pat. Application No. 63/155,721 entitled MOUNTING AND USE OF PIEZOELECTRIC COOLING SYSTEMS IN DEVICES filed Mar. 02, 2021, U.S. Provisional Pat. Application No. 63/220,371 entitled MEMS-BASED ACTIVE COOLING SYSTEMS INCLUDING COOLING CELL ARRANGEMENT, TABS, ANCHOR BONDING, INTEGRATED SPREADER, ADHESIVE, AND POWER MANAGEMENT filed Jul. 09, 2021, and U.S. Provisional Application No. 63/277,494 entitled INTEGRATION OF AIRJETS INTO COMPUTING DEVICES filed Nov. 09, 2021, all of which are incorporated herein by reference for all purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     As computing devices grow in speed and computing power, the heat generated by the computing devices also increases. Various mechanisms have been proposed to address the generation of heat. Active devices, such as fans, may be used to drive air through large computing devices, such as laptop computers or desktop computers. Passive cooling devices, such as heat spreaders, may be used in smaller, mobile computing devices, such as smartphones, virtual reality devices and tablet computers. However, such active and passive devices may be unable to adequately cool both mobile devices such as smartphones and larger devices such as laptops and desktop computers. Moreover, incorporating cooling solutions into computing devices may be challenging. Consequently, additional cooling solutions for computing devices are desired. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. 
       Various embodiments of the invention are disclosed in the following detailed description and the accompanying drawings. 
         FIGS.  1 A- 1 G  depict an embodiment of an active MEMS cooling system including a centrally anchored cooling element. 
         FIGS.  2 A- 2 B  depict an embodiment of an active MEMS cooling system including a centrally anchored cooling element. 
         FIGS.  3 A- 3 G  depict an embodiment of an active MEMS cooling system formed in a tile. 
         FIG.  4    depicts an embodiment of an active cooling system that utilizes entrainment integrated into a device. 
         FIGS.  5 A- 5 F  depict embodiments of an active cooling system that may utilize entrainment integrated into a device. 
         FIG.  6    depicts an embodiment of an active cooling system that utilizes entrainment integrated into a device. 
         FIG.  7    depicts an embodiment of an active cooling system that utilizes entrainment integrated into a device. 
         FIG.  8    depicts an embodiment of an active cooling system that utilizes entrainment integrated into a device. 
         FIG.  9    depicts an embodiment of an active cooling system that utilizes entrainment integrated into a device. 
         FIGS.  10 A- 10 B  depict an embodiment of an active cooling system that utilizes entrainment integrated into a device. 
         FIG.  11    depicts an embodiment of an active cooling system that utilizes entrainment integrated into a device. 
         FIG.  12    depicts an embodiment of a method for providing an active cooling system that utilizes entrainment. 
         FIG.  13    depicts an embodiment of a method for using an active cooling system that utilizes entrainment. 
     
    
    
     DETAILED DESCRIPTION 
     The invention can be implemented in numerous ways, including as a process; an apparatus; a system; a composition of matter; a computer program product embodied on a computer readable storage medium; and/or a processor, such as a processor configured to execute instructions stored on and/or provided by a memory coupled to the processor. In this specification, these implementations, or any other form that the invention may take, may be referred to as techniques. In general, the order of the steps of disclosed processes may be altered within the scope of the invention. Unless stated otherwise, a component such as a processor or a memory described as being configured to perform a task may be implemented as a general component that is temporarily configured to perform the task at a given time or a specific component that is manufactured to perform the task. As used herein, the term ‘processor’ refers to one or more devices, circuits, and/or processing cores configured to process data, such as computer program instructions. 
     A detailed description of one or more embodiments of the invention is provided below along with accompanying figures that illustrate the principles of the invention. The invention is described in connection with such embodiments, but the invention is not limited to any embodiment. The scope of the invention is limited only by the claims and the invention encompasses numerous alternatives, modifications and equivalents. Numerous specific details are set forth in the following description in order to provide a thorough understanding of the invention. These details are provided for the purpose of example and the invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the invention is not unnecessarily obscured. 
     As semiconductor devices become increasingly powerful, the heat generated during operations also grows. For example, processors for mobile devices such as smartphones, tablet computers, notebook computers, and virtual reality devices as well as for other computing devices such as servers, can operate at high clock speeds, but produce a significant amount of heat. Because of the quantity of heat produced, processors may run at full speed only for a relatively short period of time. After this time expires, throttling (e.g. slowing of the processor’s clock speed) occurs. Although throttling can reduce heat generation, it also adversely affects processor speed and, therefore, the performance of devices using the processors. As technology moves to 5G and beyond, this issue is expected to be exacerbated. Further, other components in a computing device may generate heat. In addition, even if heat-generating components within a device may be actively cooled, the hot air or other fluid carrying the heat is desired to exit the device to carry the heat away from the device. This fluid is typically quite hot. For example, a processor may reach ninety through ninety-five degrees Celsius during operation. A heat spreader thermally coupled to the processor may be approximately seventy-eight through eighty degrees Celsius. Air used to cool such components may be hot enough when exiting the device that the air may cause the user discomfort and/or burn the user. Thus, thermal management is increasingly an issue for computing devices. 
     A system including a module and an egress passageway is described. The module includes a cooling cells, a heat spreader, and a cover including vents therein. The cooling cells are between the heat spreader and the cover. Each of the cooling cells includes a cooling element configured to draw air in through the vents and drive air out of an aperture between the heat spreader and the cover at a first flow rate. Thus, a stream of hot air having been heated by a heat from a heat-generating structure thermally coupled to the heat spreader is provided. The hot air passes through the egress passageway toward an egress. The egress passageway includes at least one inlet through which cool air is drawn at a second flow rate to be mixed with the hot air. The second flow rate is greater than the first flow rate. The cooling element undergoes vibrational motion to drive cooler air that is heated by the heat due to the heat-generating structure. In some embodiments, the module has a thickness not exceeding three millimeters. In some embodiments, the mixture of the hot air and the cool air at the egress has a temperature not exceeding sixty degrees Celsius for the heat-generating structure being at least seventy degrees Celsius. In some such embodiments, the temperature does not exceed fifty-five degrees Celsius. 
     The system may include a housing having the inlet(s) therein. The housing has a vertical dimension, a first horizontal dimension, and a second horizontal dimensions. The vertical dimension is smaller than the first horizontal dimension and second horizontal dimensions. The module is vertically aligned with a portion of the housing. The inlet(s) and/or egress are distal from the portion of the housing. In some embodiments, the housing includes a keyboard and a back cover opposite from the keyboard. The module may be at least one millimeter from the keyboard and at least 800 micrometers from the back cover. In some embodiments, the aperture has an aperture area, the egress has an egress area, and the aperture area does not exceed the egress area. In some embodiments, the module and the egress passageway are integrated into a computing device selected from a notebook computer, a laptop computer, and a smartphone. 
     In some embodiments, the module includes a top plate having vents therein and an orifice plate having at least one orifice therein for each cooling cell. A top chamber is formed between the cooling element and the top plate for each of the cooling cells. The cooling element is between the top plate and the orifice plate. The cooling element is actuated to drive air through the orifice(s). The orifice plate, the cooling element, the top chamber, and the top plate have a combined height of not more than two millimeters. 
     A method is also described. The method includes driving a cooling element in each of a plurality of cooling cells to induce a vibrational motion at a frequency. The cooling cells are part of a module. The module further includes a heat spreader, and a cover including vents therein. The cooling cells are between the heat spreader and the cover. The vibrational motion draws air in through the vents and drives the air out of an aperture between the heat spreader and the cover at a first flow rate. Thus, a stream of hot air heated by a heat from a heat-generating structure thermally coupled to the heat spreader is provided. The hot air passes through an egress passageway toward an egress. The egress passageway includes at least one inlet through which cool air is drawn and provides a second flow rate to be mixed with the hot air. The second flow rate is greater than the first flow rate. In some embodiments, the frequency corresponds to a structural resonant frequency of the cooling element and an acoustic resonant frequency for the cooling element. The module may have a thickness not exceeding three millimeters. In some embodiments, a mixture of the hot air and the cool air at the egress has a temperature not exceeding fifty-five degrees Celsius for the heat-generating structure being at least seventy degrees Celsius. 
       FIGS.  1 A- 1 G  are diagrams depicting an exemplary embodiment of active MEMS cooling system  100  usable with heat-generating structure  102  and including a centrally anchored cooling element  120  or  120 ′. Cooling element  120  is shown in  FIGS.  1 A- 1 F  and cooling element  120 ′ is shown in  FIG.  1 G . For clarity, only certain components are shown.  FIGS.  1 A- 1 G  are not to scale.  FIGS.  1 A and  1 B  depict cross-sectional and top views of cooling system  100  in a neutral position.  FIGS.  1 C- 1 D  depict cooling system  100  during actuation for in-phase vibrational motion.  FIGS.  1 E- 1 F  depict cooling system  100  during actuation for out-of-phase vibrational motion. Although shown as symmetric, cooling system  100  need not be. 
     Cooling system  100  includes top plate  110  having vent  112  therein, cooling element  120 , orifice plate  130  having orifices  132  therein, support structure (or “anchor”)  160  and chambers  140  and  150  (collectively chamber  140 / 150 ) formed therein. Cooling element  120  is supported at its central region by anchor  160 . Regions of cooling element  120  closer to and including portions of the cooling element’s perimeter (e.g. tip  121 ) vibrate when actuated. In some embodiments, tip  121  of cooling element  120  includes a portion of the perimeter furthest from anchor  160  and undergoes the largest deflection during actuation of cooling element  120 . For clarity, only one tip  121  of cooling element  120  is labeled in  FIG.  1 A . Also shown is pedestal  190  that connects orifice plate  130  to and offsets orifice plate  130  from heat-generating structure  102 . In some embodiments, pedestal  190  also thermally couples orifice plate  130  to heat-generating structure  102 . 
       FIG.  1 A  depicts cooling system  100  in a neutral position. Thus, cooling element  120  is shown as substantially flat. For in-phase operation, cooling element  120  is driven to vibrate between positions shown in  FIGS.  1 C and  1 D . This vibrational motion draws fluid (e.g. air) into vent  112 , through chambers  140  and  150  and out orifices  132  at high speed and/or flow rates. For example, the speed at which the fluid impinges on heat-generating structure  102  may be at least thirty meters per second. In some embodiments, the fluid is driven by cooling element  120  toward heat-generating structure  102  at a speed of at least forty-five meters per second. In some embodiments, the fluid is driven toward heat-generating structure  102  by cooling element  120  at speeds of at least sixty meters per second. Other speeds may be possible in some embodiments. Cooling system  100  is also configured so that little or no fluid is drawn back into chamber  140 / 150  through orifices  132  by the vibrational motion of cooling element  120 . 
     Heat-generating structure  102  is desired to be cooled by cooling system  100 . In some embodiments, heat-generating structure  102  generates heat. For example, heat-generating structure may be an integrated circuit. In some embodiments, heat-generating structure  102  is desired to be cooled but does not generate heat itself. Heat-generating structure  102  may conduct heat (e.g. from a nearby object that generates heat). For example, heat-generating structure  102  might be a heat spreader or a vapor chamber. Thus, heat-generating structure  102  may include semiconductor component(s) including individual integrated circuit components such as processors, other integrated circuit(s) and/or chip package(s); sensor(s); optical device(s); one or more batteries; other component(s) of an electronic device such as a computing device; heat spreaders; heat pipes; other electronic component(s) and/or other device(s) desired to be cooled. In some embodiments, heat-generating structure  102  may be a thermally conductive part of a module containing cooling system  100 . For example, cooling system  100  may be affixed to heat-generating structure  102 , which may be coupled to another heat sink, vapor chamber, integrated circuit, or other separate structure desired to be cooled. 
     The devices in which cooling system  100  is desired to be used may also have limited space in which to place a cooling system. For example, cooling system  100  may be used in computing devices. Such computing devices may include but are not limited to smartphones, tablet computers, laptop computers, tablets, two-in-one laptops, hand held gaming systems, digital cameras, virtual reality headsets, augmented reality headsets, mixed reality headsets and other devices that are thin. Cooling system  100  may be a micro-electro-mechanical system (MEMS) cooling system capable of residing within mobile computing devices and/or other devices having limited space in at least one dimension. For example, the total height, h3, of cooling system  100  (from the top of heat-generating structure  102  to the top of top plate  110 ) may be less than 2 millimeters. In some embodiments, the total height of cooling system  100  is not more than 1.5 millimeters. In some embodiments, this total height is not more than 1.1 millimeters. In some embodiments, the total height does not exceed one millimeter. In some embodiments, the total height does not exceed two hundred and fifty micrometers. Similarly, the distance between the bottom of orifice plate  130  and the top of heat-generating structure  102 , y, may be small. In some embodiments, y is at least two hundred micrometers and not more than 1.2 millimeter. For example, y may be at least two hundred and fifty micrometers and not more than three hundred micrometers. In some embodiments, y is at least five hundred micrometers and not more than one millimeter. In some embodiments, y is at least two hundred micrometers and not more than three hundred micrometers. Thus, cooling system  100  is usable in computing devices and/or other devices having limited space in at least one dimension. However, nothing prevents the use of cooling system  100  in devices having fewer limitations on space and/or for purposes other than cooling. Although one cooling system  100  is shown (e.g. one cooling cell), multiple cooling systems  100  might be used in connection with heat-generating structure  102 . For example, a one or two-dimensional array of cooling cells might be utilized. 
     Cooling system  100  is in communication with a fluid used to cool heat-generating structure  102 . The fluid may be a gas or a liquid. For example, the fluid may be air. In some embodiments, the fluid includes fluid from outside of the device in which cooling system  100  resides (e.g. provided through external vents in the device). In some embodiments, the fluid circulates within the device in which cooling system resides (e.g. in an enclosed device). 
     Cooling element  120  can be considered to divide the interior of active MEMS cooling system  100  into top chamber  140  and bottom chamber  150 . Top chamber  140  is formed by cooling element  120 , the sides, and top plate  110 . Bottom chamber  150  is formed by orifice plate  130 , the sides, cooling element  120  and anchor  160 . Top chamber  140  and bottom chamber  150  are connected at the periphery of cooling element  120  and together form chamber  140 / 150  (e.g. an interior chamber of cooling system  100 ). 
     The size and configuration of top chamber  140  may be a function of the cell (cooling system  100 ) dimensions, cooling element  120  motion, and the frequency of operation. Top chamber  140  has a height, h1. The height of top chamber  140  may be selected to provide sufficient pressure to drive the fluid to bottom chamber  150  and through orifices  132  at the desired flow rate and/or speed. Top chamber  140  is also sufficiently tall that cooling element  120  does not contact top plate  110  when actuated. In some embodiments, the height of top chamber  140  is at least fifty micrometers and not more than five hundred micrometers. In some embodiments, top chamber  140  has a height of at least two hundred and not more than three hundred micrometers. 
     Bottom chamber  150  has a height, h2. In some embodiments, the height of bottom chamber  150  is sufficient to accommodate the motion of cooling element  120 . Thus, no portion of cooling element  120  contacts orifice plate  130  during normal operation. Bottom chamber  150  is generally smaller than top chamber  140  and may aid in reducing the backflow of fluid into orifices  132 . In some embodiments, the height of bottom chamber  150  is the maximum deflection of cooling element  120  plus at least five micrometers and not more than ten micrometers. In some embodiments, the deflection of cooling element  120  (e.g. the deflection of tip  121 ), z, has an amplitude of at least ten micrometers and not more than one hundred micrometers. In some such embodiments, the amplitude of deflection of cooling element  120  is at least ten micrometers and not more than sixty micrometers. However, the amplitude of deflection of cooling element  120  depends on factors such as the desired flow rate through cooling system  100  and the configuration of cooling system  100 . Thus, the height of bottom chamber  150  generally depends on the flow rate through and other components of cooling system  100 . 
     Top plate  110  includes vent  112  through which fluid may be drawn into cooling system  100 . Top vent  112  may have a size chosen based on the desired acoustic pressure in chamber  140 . For example, in some embodiments, the width, w, of vent  112  is at least five hundred micrometers and not more than one thousand micrometers. In some embodiments, the width of vent  112  is at least two hundred fifty micrometers and not more than two thousand micrometers. In the embodiment shown, vent  112  is a centrally located aperture in top plate  110 . In other embodiments, vent  112  may be located elsewhere. For example, vent  112  may be closer to one of the edges of top plate  110 . Vent  112  may have a circular, rectangular or other shaped footprint. Although a single vent  112  is shown, multiple vents might be used. For example, vents may be offset toward the edges of top chamber  140  or be located on the side(s) of top chamber  140 . Although top plate  110  is shown as substantially flat, in some embodiments trenches and/or other structures may be provided in top plate  110  to modify the configuration of top chamber  140  and/or the region above top plate  110 . 
     Anchor (support structure)  160  supports cooling element  120  at the central portion of cooling element  120 . Thus, at least part of the perimeter of cooling element  120  is unpinned and free to vibrate. In some embodiments, anchor  160  extends along a central axis of cooling element  120  (e.g. perpendicular to the page in  FIGS.  1 A- 1 F ). In such embodiments, portions of cooling element  120  that vibrate (e.g. including tip  121 ) move in a cantilevered fashion. Thus, portions of cooling element  120  may move in a manner analogous to the wings of a butterfly (i.e. in phase) and/or analogous to a seesaw (i.e. out of phase). Thus, the portions of cooling element  120  that vibrate in a cantilevered fashion do so in phase in some embodiments and out of phase in other embodiments. In some embodiments, anchor  160  does not extend along an axis of cooling element  120 . In such embodiments, all portions of the perimeter of cooling element  120  are free to vibrate (e.g. analogous to a jellyfish). In the embodiment shown, anchor  160  supports cooling element  120  from the bottom of cooling element  120 . In other embodiments, anchor  160  may support cooling element  120  in another manner. For example, anchor  160  may support cooling element  120  from the top (e.g. cooling element  120  hangs from anchor  160 ). In some embodiments, the width, a, of anchor  160  is at least 0.5 millimeters and not more than four millimeters. In some embodiments, the width of anchor  160  is at least two millimeters and not more than 2.5 millimeters. Anchor  160  may occupy at least ten percent and not more than fifty percent of cooling element  120 . 
     Cooling element  120  has a first side distal from heat-generating structure  102  and a second side proximate to heat-generating structure  102 . In the embodiment shown in  FIGS.  1 A- 1 F , the first side of cooling element  120  is the top of cooling element  120  (closer to top plate  110 ) and the second side is the bottom of cooling element  120  (closer to orifice plate  130 ). Cooling element  120  is actuated to undergo vibrational motion as shown in  FIGS.  1 A- 1 F . The vibrational motion of cooling element  120  drives fluid from the first side of cooling element  120  distal from heat-generating structure  102  (e.g. from top chamber  140 ) to a second side of cooling element  120  proximate to heat-generating structure  102  (e.g. to bottom chamber  150 ). The vibrational motion of cooling element  120  also draws fluid through vent  112  and into top chamber  140 ; forces fluid from top chamber  140  to bottom chamber  150 ; and drives fluid from bottom chamber  150  through orifices  132  of orifice plate  130 . Thus, cooling element  120  may be viewed as an actuator. Although described in the context of a single, continuous cooling element, in some embodiments, cooling element  120  may be formed by two (or more) cooling elements. Each of the cooling elements as one portion pinned (e.g. supported by support structure  160 ) and an opposite portion unpinned. Thus, a single, centrally supported cooling element  120  may be formed by a combination of multiple cooling elements supported at an edge. 
     Cooling element  120  has a length, L, that depends upon the frequency at which cooling element  120  is desired to vibrate. In some embodiments, the length of cooling element  120  is at least four millimeters and not more than ten millimeters. In some such embodiments, cooling element  120  has a length of at least six millimeters and not more than eight millimeters. The depth of cooling element  120  (e.g. perpendicular to the plane shown in  FIGS.  1 A- 1 F ) may vary from one fourth of L through twice L. For example, cooling element  120  may have the same depth as length. The thickness, t, of cooling element  120  may vary based upon the configuration of cooling element  120  and/or the frequency at which cooling element  120  is desired to be actuated. In some embodiments, the cooling element thickness is at least two hundred micrometers and not more than three hundred and fifty micrometers for cooling element  120  having a length of eight millimeters and driven at a frequency of at least twenty kilohertz and not more than twenty-five kilohertz. The length, C of chamber  140 / 150  is close to the length, L, of cooling element  120 . For example, in some embodiments, the distance, d, between the edge of cooling element  120  and the wall of chamber  140 / 150  is at least one hundred micrometers and not more than five hundred micrometers. In some embodiments, d is at least two hundred micrometers and not more than three hundred micrometers. 
     Cooling element  120  may be driven at a frequency that is at or near both the resonant frequency for an acoustic resonance of a pressure wave of the fluid in top chamber  140  and the resonant frequency for a structural resonance of cooling element  120 . The portion of cooling element  120  undergoing vibrational motion is driven at or near resonance (the “structural resonance”) of cooling element  120 . This portion of cooling element  120  undergoing vibration may be a cantilevered section in some embodiments. The frequency of vibration for structural resonance is termed the structural resonant frequency. Use of the structural resonant frequency in driving cooling element  120  reduces the power consumption of cooling system  100 . Cooling element  120  and top chamber  140  may also be configured such that this structural resonant frequency corresponds to a resonance in a pressure wave in the fluid being driven through top chamber  140  (the acoustic resonance of top chamber  140 ). The frequency of such a pressure wave is termed the acoustic resonant frequency. At acoustic resonance, a node in pressure occurs near vent  112  and an antinode in pressure occurs near the periphery of cooling system  100  (e.g. near tip  121  of cooling element  120  and near the connection between top chamber  140  and bottom chamber  150 ). The distance between these two regions is C/2. Thus, C/2 = nλ/4, where λ is the acoustic wavelength for the fluid and n is odd (e.g. n = 1, 3, 5, etc.). For the lowest order mode, C = λ/2. Because the length of chamber  140  (e.g. C) is close to the length of cooling element  120 , in some embodiments, it is also approximately true that L/2 = nλ/4, where λ is the acoustic wavelength for the fluid and n is odd. Thus, the frequency at which cooling element  120  is driven, v, is at or near the structural resonant frequency for cooling element  120 . The frequency v is also at or near the acoustic resonant frequency for at least top chamber  140 . The acoustic resonant frequency of top chamber  140  generally varies less dramatically with parameters such as temperature and size than the structural resonant frequency of cooling element  120 . Consequently, in some embodiments, cooling element  120  may be driven at (or closer to) a structural resonant frequency than to the acoustic resonant frequency. 
     Orifice plate  130  has orifices  132  therein. Although a particular number and distribution of orifices  132  are shown, another number and/or another distribution may be used. A single orifice plate  130  is used for a single cooling system  100 . In other embodiments, multiple cooling systems  100  may share an orifice plate. For example, multiple cells  100  may be provided together in a desired configuration. In such embodiments, the cells  100  may be the same size and configuration or different size(s) and/or configuration(s). Orifices  132  are shown as having an axis oriented normal to a surface of heat-generating structure  102 . In other embodiments, the axis of one or more orifices  132  may be at another angle. For example, the angle of the axis may be selected from substantially zero degrees and a nonzero acute angle. Orifices  132  also have sidewalls that are substantially parallel to the normal to the surface of orifice plate  130 . In some embodiments, orifices may have sidewalls at a nonzero angle to the normal to the surface of orifice plate  130 . For example, orifices  132  may be cone-shaped. Further, although orifice place  130  is shown as substantially flat, in some embodiments, trenches and/or other structures may be provided in orifice plate  130  to modify the configuration of bottom chamber  150  and/or the region between orifice plate  130  and heat-generating structure  102 . 
     The size, distribution and locations of orifices  132  are chosen to control the flow rate of fluid driven to the surface of heat-generating structure  102 . The locations and configurations of orifices  132  may be configured to increase/maximize the fluid flow from bottom chamber  150  through orifices  132  to the jet channel (the region between the bottom of orifice plate  130  and the top of heat-generating structure  102 ). The locations and configurations of orifices  132  may also be selected to reduce/minimize the suction flow (e.g. back flow) from the jet channel through orifices  132 . For example, the locations of orifices are desired to be sufficiently far from tip  121  that suction in the upstroke of cooling element  120  (tip  121  moves away from orifice plate 13) that would pull fluid into bottom chamber  150  through orifices  132  is reduced. The locations of orifices are also desired to be sufficiently close to tip  121  that suction in the upstroke of cooling element  120  also allows a higher pressure from top chamber  140  to push fluid from top chamber  140  into bottom chamber  150 . In some embodiments, the ratio of the flow rate from top chamber  140  into bottom chamber  150  to the flow rate from the jet channel through orifices  132  in the upstroke (the “net flow ratio”) is greater than 2:1. In some embodiments, the net flow ratio is at least 85:15. In some embodiments, the net flow ratio is at least 90:10. In order to provide the desired pressure, flow rate, suction, and net flow ratio, orifices  132  are desired to be at least a distance, r1, from tip  121  and not more than a distance, r2, from tip  121  of cooling element  120 . In some embodiments r1 is at least one hundred micrometers (e.g. r1 ≥ 100 µm) and r2 is not more than one millimeter (e.g. r2 ≤ 1000 µm). In some embodiments, orifices  132  are at least two hundred micrometers from tip  121  of cooling element  120  (e.g. r1 ≥ 200 µm). In some such embodiments, orifices  132  are at least three hundred micrometers from tip  121  of cooling element  120  (e.g. r1 ≥ 300 µm). In some embodiments, orifices  132  have a width, o, of at least one hundred micrometers and not more than five hundred micrometers. In some embodiments, orifices  132  have a width of at least two hundred micrometers and not more than three hundred micrometers. In some embodiments, the orifice separation, s, is at least one hundred micrometers and not more than one millimeter. In some such embodiments, the orifice separation is at least four hundred micrometers and not more than six hundred micrometers. In some embodiments, orifices  132  are also desired to occupy a particular fraction of the area of orifice plate  130 . For example, orifices  132  may cover at least five percent and not more than fifteen percent of the footprint of orifice plate  130  in order to achieve a desired flow rate of fluid through orifices  132 . In some embodiments, orifices  132  cover at least eight percent and not more than twelve percent of the footprint of orifice plate  130 . 
     In some embodiments, cooling element  120  is actuated using a piezoelectric. Thus, cooling element  120  may be a piezoelectric cooling element. Cooling element  120  may be driven by a piezoelectric that is mounted on or integrated into cooling element  120 . In some embodiments, cooling element  120  is driven in another manner including but not limited to providing a piezoelectric on another structure in cooling system  100 . Cooling element  120  and analogous cooling elements are referred to hereinafter as piezoelectric cooling element though it is possible that a mechanism other than a piezoelectric might be used to drive the cooling element. In some embodiments, cooling element  120  includes a piezoelectric layer on substrate. The substrate may include or consist of stainless steel, a Ni alloy, Hastelloy, Al (e.g. an Al alloy), and/or a Ti (e.g. a Ti alloy such as Ti6Al-4V). In some embodiments, piezoelectric layer includes multiple sublayers formed as thin films on the substrate. In other embodiments, the piezoelectric layer may be a bulk layer affixed to the substrate. Such a piezoelectric cooling element  120  also includes electrodes used to activate the piezoelectric. The substrate functions as an electrode in some embodiments. In other embodiments, a bottom electrode may be provided between the substrate and the piezoelectric layer. Other layers including but not limited to seed, capping, passivation or other layers might be included in piezoelectric cooling element. Thus, cooling element  120  may be actuated using a piezoelectric. 
     In some embodiments, cooling system  100  includes chimneys (not shown) or other ducting. Such ducting provides a path for heated fluid to flow away from heat-generating structure  102 . In some embodiments, ducting returns fluid to the side of top plate  110  distal from heat-generating structure  102 . In some embodiments, ducting may instead direct fluid away from heat-generating structure  102  in a direction parallel to heat-generating structure  102  or perpendicular to heat-generating structure  102  but in the opposite direction (e.g. toward the bottom of the page). For a device in which fluid external to the device is used in cooling system  100 , the ducting may channel the heated fluid to a vent. In such embodiments, additional fluid may be provided from an inlet vent. In embodiments, in which the device is enclosed, the ducting may provide a circuitous path back to the region near vent  112  and distal from heat-generating structure  102 . Such a path allows for the fluid to dissipate heat before being reused to cool heat-generating structure  102 . In other embodiments, ducting may be omitted or configured in another manner. Thus, the fluid is allowed to carry away heat from heat-generating structure  102 . 
     Operation of cooling system  100  is described in the context of  FIGS.  1 A- 1 F . Although described in the context of particular pressures, gap sizes, and timing of flow, operation of cooling system  100  is not dependent upon the explanation herein.  FIGS.  1 C- 1 D  depict in-phase operation of cooling system  100 . Referring to  FIG.  1 C , cooling element  120  has been actuated so that its tip  121  moves away from top plate  110 .  FIG.  1 C  can thus be considered to depict the end of a down stroke of cooling element  120 . Because of the vibrational motion of cooling element  120 , gap  152  for bottom chamber  150  has decreased in size and is shown as gap  152 B. Conversely, gap  142  for top chamber  140  has increased in size and is shown as gap  142 B. During the down stroke, a lower (e.g. minimum) pressure is developed at the periphery when cooling element  120  is at the neutral position. As the down stroke continues, bottom chamber  150  decreases in size and top chamber  140  increases in size as shown in  FIG.  1 C . Thus, fluid is driven out of orifices  132  in a direction that is at or near perpendicular to the surface of orifice plate  130  and/or the top surface of heat-generating structure  102 . The fluid is driven from orifices  132  toward heat-generating structure  102  at a high speed, for example in excess of thirty-five meters per second. In some embodiments, the fluid then travels along the surface of heat-generating structure  102  and toward the periphery of heat-generating structure  102 , where the pressure is lower than near orifices  132 . Also in the down stroke, top chamber  140  increases in size and a lower pressure is present in top chamber  140 . As a result, fluid is drawn into top chamber  140  through vent  112 . The motion of the fluid into vent  112 , through orifices  132 , and along the surface of heat-generating structure  102  is shown by unlabeled arrows in  FIG.  1 C . 
     Cooling element  120  is also actuated so that tip  121  moves away from heat-generating structure  102  and toward top plate  110 .  FIG.  1 D  can thus be considered to depict the end of an up stroke of cooling element  120 . Because of the motion of cooling element  120 , gap  142  has decreased in size and is shown as gap  142 C. Gap  152  has increased in size and is shown as gap  152 C. During the upstroke, a higher (e.g. maximum) pressure is developed at the periphery when cooling element  120  is at the neutral position. As the upstroke continues, bottom chamber  150  increases in size and top chamber  140  decreases in size as shown in  FIG.  1 D . Thus, the fluid is driven from top chamber  140  (e.g. the periphery of chamber  140 / 150 ) to bottom chamber  150 . Thus, when tip  121  of cooling element  120  moves up, top chamber  140  serves as a nozzle for the entering fluid to speed up and be driven towards bottom chamber  150 . The motion of the fluid into bottom chamber  150  is shown by unlabeled arrows in  FIG.  1 D . The location and configuration of cooling element  120  and orifices  132  are selected to reduce suction and, therefore, back flow of fluid from the jet channel (between heat-generating structure  102  and orifice plate  130 ) into orifices  132  during the upstroke. Thus, cooling system  100  is able to drive fluid from top chamber  140  to bottom chamber  150  without an undue amount of backflow of heated fluid from the jet channel entering bottom chamber  140 . Moreover, cooling system  100  may operate such that fluid is drawn in through vent  112  and driven out through orifices  132  without cooling element  120  contacting top plate  110  or orifice plate  130 . Thus, pressures are developed within chambers  140  and  150  that effectively open and close vent  112  and orifices  132  such that fluid is driven through cooling system  100  as described herein. 
     The motion between the positions shown in  FIGS.  1 C and  1 D  is repeated. Thus, cooling element  120  undergoes vibrational motion indicated in  FIGS.  1 A- 1 D , drawing fluid through vent  112  from the distal side of top plate  110  into top chamber  140 ; transferring fluid from top chamber  140  to bottom chamber  150 ; and pushing the fluid through orifices  132  and toward heat-generating structure  102 . As discussed above, cooling element  120  is driven to vibrate at or near the structural resonant frequency of cooling element  120 . Further, the structural resonant frequency of cooling element  120  is configured to align with the acoustic resonance of the chamber  140 / 150 . The structural and acoustic resonant frequencies are generally chosen to be in the ultrasonic range. For example, the vibrational motion of cooling element  120  may be at frequencies from 15 kHz through 30 kHz. In some embodiments, cooling element  120  vibrates at a frequency/frequencies of at least 20 kHz and not more than 30 kHz (e.g. 23 kHz-25 kHz). The structural resonant frequency of cooling element  120  is within ten percent of the acoustic resonant frequency of cooling system  100 . In some embodiments, the structural resonant frequency of cooling element  120  is within five percent of the acoustic resonant frequency of cooling system  100 . In some embodiments, the structural resonant frequency of cooling element  120  is within three percent of the acoustic resonant frequency of cooling system  100 . Consequently, efficiency and flow rate may be enhanced. However, other frequencies may be used. 
     Fluid driven toward heat-generating structure  102  may move substantially normal (perpendicular) to the top surface of heat-generating structure  102 . In some embodiments, the fluid motion may have a nonzero acute angle with respect to the normal to the top surface of heat-generating structure  102 . In either case, the fluid may thin and/or form apertures in the boundary layer of fluid at heat-generating structure  102 . As a result, transfer of heat from heat-generating structure  102  may be improved. The fluid deflects off of heat-generating structure  102 , traveling along the surface of heat-generating structure  102 . In some embodiments, the fluid moves in a direction substantially parallel to the top of heat-generating structure  102 . Thus, heat from heat-generating structure  102  may be extracted by the fluid. The fluid may exit the region between orifice plate  130  and heat-generating structure  102  at the edges of cooling system  100 . Chimneys or other ducting (not shown) at the edges of cooling system  100  allow fluid to be carried away from heat-generating structure  102 . In other embodiments, heated fluid may be transferred further from heat-generating structure  102  in another manner. The fluid may exchange the heat transferred from heat-generating structure  102  to another structure or to the ambient environment. Thus, fluid at the distal side of top plate  110  may remain relatively cool, allowing for the additional extraction of heat. In some embodiments, fluid is circulated, returning to distal side of top plate  110  after cooling. In other embodiments, heated fluid is carried away and replaced by new fluid at the distal side of cooling element  120 . As a result, heat-generating structure  102  may be cooled. 
       FIGS.  1 E- 1 F  depict an embodiment of active MEMS cooling system  100  including centrally anchored cooling element  120  in which the cooling element is driven out-of-phase. More specifically, sections of cooling element  120  on opposite sides of anchor  160  (and thus on opposite sides of the central region of cooling element  120  that is supported by anchor  160 ) are driven to vibrate out-of-phase. In some embodiments, sections of cooling element  120  on opposite sides of anchor  160  are driven at or near one hundred and eighty degrees out-of-phase. Thus, one section of cooling element  120  vibrates toward top plate  110 , while the other section of cooling element  120  vibrates toward orifice plate  130 /heat-generating structure  102 . Movement of a section of cooling element  120  toward top plate  110  (an upstroke) drives fluid in top chamber  140  to bottom chamber  150  on that side of anchor  160 . Movement of a section of cooling element  120  toward orifice plate  130  drives fluid through orifices  132  and toward heat-generating structure  102 . Thus, fluid traveling at high speeds (e.g. speeds described with respect to in-phase operation) is alternately driven out of orifices  132  on opposing sides of anchor  160 . Because fluid is driven through orifices  132  at high speeds, cooling system  100  may be viewed as a MEMs jet. The movement of fluid is shown by unlabeled arrows in  FIGS.  1 E and  1 F .The motion between the positions shown in  FIGS.  1 E and  1 F  is repeated. Thus, cooling element  120  undergoes vibrational motion indicated in  FIGS.  1 A,  1 E, and  1 F , alternately drawing fluid through vent  112  from the distal side of top plate  110  into top chamber  140  for each side of cooling element  120 ; transferring fluid from each side of top chamber  140  to the corresponding side of bottom chamber  150 ; and pushing the fluid through orifices  132  on each side of anchor  160  and toward heat-generating structure  102 . As discussed above, cooling element  120  is driven to vibrate at or near the structural resonant frequency of cooling element  120 . Further, the structural resonant frequency of cooling element  120  is configured to align with the acoustic resonance of the chamber  140 / 150 . The structural and acoustic resonant frequencies are generally chosen to be in the ultrasonic range. For example, the vibrational motion of cooling element  120  may be at the frequencies described for in-phase vibration. The structural resonant frequency of cooling element  120  is within ten percent of the acoustic resonant frequency of cooling system  100 . In some embodiments, the structural resonant frequency of cooling element  120  is within five percent of the acoustic resonant frequency of cooling system  100 . In some embodiments, the structural resonant frequency of cooling element  120  is within three percent of the acoustic resonant frequency of cooling system  100 . Consequently, efficiency and flow rate may be enhanced. However, other frequencies may be used. 
     Fluid driven toward heat-generating structure  102  for out-of-phase vibration may move substantially normal (perpendicular) to the top surface of heat-generating structure  102 , in a manner analogous to that described above for in-phase operation. Similarly, chimneys or other ducting (not shown) at the edges of cooling system  100  allow fluid to be carried away from heat-generating structure  102 . In other embodiments, heated fluid may be transferred further from heat-generating structure  102  in another manner. The fluid may exchange the heat transferred from heat-generating structure  102  to another structure or to the ambient environment. Thus, fluid at the distal side of top plate  110  may remain relatively cool, allowing for the additional extraction of heat. In some embodiments, fluid is circulated, returning to distal side of top plate  110  after cooling. In other embodiments, heated fluid is carried away and replaced by new fluid at the distal side of cooling element  120 . As a result, heat-generating structure  102  may be cooled. 
     Although shown in the context of a uniform cooling element in  FIGS.  1 A- 1 F , cooling system  100  may utilize cooling elements having different shapes.  FIG.  1 G  depicts an embodiment of engineered cooling element  120 ′ having a tailored geometry and usable in a cooling system such as cooling system  100 . Cooling element  120 ′ includes an anchored region  122  and cantilevered arms  123 . Anchored region  122  is supported (e.g. held in place) in cooling system  100  by anchor  160 . Cantilevered arms  123  undergo vibrational motion in response to cooling element  120 ′ being actuated. Each cantilevered arm  123  includes step region  124 , extension region  126  and outer region  128 . In the embodiment shown in  FIG.  1 G , anchored region  122  is centrally located. Step region  124  extends outward from anchored region  122 . Extension region  126  extends outward from step region  124 . Outer region  128  extends outward from extension region  126 . In other embodiments, anchored region  122  may be at one edge of the actuator and outer region  128  at the opposing edge. In such embodiments, the actuator is edge anchored. 
     Extension region  126  has a thickness (extension thickness) that is less than the thickness of step region  124  (step thickness) and less than the thickness of outer region  128  (outer thickness). Thus, extension region  126  may be viewed as recessed. Extension region  126  may also be seen as providing a larger bottom chamber  150 . In some embodiments, the outer thickness of outer region  128  is the same as the step thickness of step region  124 . In some embodiments, the outer thickness of outer region  128  is different from the step thickness of step region  124 . In some embodiments, outer region  128  and step region  124  each have a thickness of at least three hundred twenty micrometers and not more than three hundred and sixty micrometers. In some embodiments, the outer thickness is at least fifty micrometers and not more than two hundred micrometers thicker than the extension thickness. Stated differently, the step (difference in step thickness and extension thickness) is at least fifty micrometers and not more than two hundred micrometers. In some embodiments, the outer step (difference in outer thickness and extension thickness) is at least fifty micrometers and not more than two hundred micrometers. Outer region  128  may have a width, o, of at least one hundred micrometers and not more than three hundred micrometers. Extension region has a length, e, extending outward from the step region of at least 0.5 millimeter and not more than 1.5 millimeters in some embodiments. In some embodiments, outer region  128  has a higher mass per unit length in the direction from anchored region  122  than extension region  126 . This difference in mass may be due to the larger size of outer region  128 , a difference in density between portions of cooling element  120 , and/or another mechanism. 
     Use of engineered cooling element  120 ′ may further improve efficiency of cooling system  100 . Extension region  126  is thinner than step region  124  and outer region  128 . This results in a cavity in the bottom of cooling element  120 ′ corresponding to extension region  126 . The presence of this cavity aids in improving the efficiency of cooling system  100 . Each cantilevered arm  123  vibrates towards top plate  110  in an upstroke and away from top plate  110  in a downstroke. When a cantilevered arm  123  moves toward top plate  110 , higher pressure fluid in top chamber  140  resists the motion of cantilevered arm  123 . Furthermore, suction in bottom chamber  150  also resists the upward motion of cantilevered arm  123  during the upstroke. In the downstroke of cantilevered arm  123 , increased pressure in the bottom chamber  150  and suction in top chamber  140  resist the downward motion of cantilevered arm  123 . However, the presence of the cavity in cantilevered arm  123  corresponding to extension region  126  mitigates the suction in bottom chamber  150  during an upstroke. The cavity also reduces the increase in pressure in bottom chamber  150  during a downstroke. Because the suction and pressure increase are reduced in magnitude, cantilevered arms  123  may more readily move through the fluid. This may be achieved while substantially maintaining a higher pressure in top chamber  140 , which drives the fluid flow through cooling system  100 . Moreover, the presence of outer region  128  may improve the ability of cantilevered arm  123  to move through the fluid being driven through cooling system  100 . Outer region  128  has a higher mass per unit length and thus a higher momentum. Consequently, outer region  128  may improve the ability of cantilevered arms  123  to move through the fluid being driven through cooling system  100 . The magnitude of the deflection of cantilevered arm  123  may also be increased. These benefits may be achieved while maintaining the stiffness of cantilevered arms  123  through the use of thicker step region  124 . Further, the larger thickness of outer region  128  may aid in pinching off flow at the bottom of a downstroke. Thus, the ability of cooling element  120 ′ to provide a valve preventing backflow through orifices  132  may be improved. Thus, performance of cooling system  100  employing cooling element  120 ′ may be improved. 
     Further, cooling elements used in cooling system  100  may have different structures and/or be mounted differently than depicted in  FIGS.  1 A- 1 G . In some embodiments, the cooling element may have rounded corners and/or rounded ends but still be anchored along a central axis such that cantilevered arms vibrate. The cooling element may be anchored only at its central region such that the regions surrounding the anchor vibrate in a manner analogous to a jellyfish or the opening/closing of an umbrella. In some such embodiments, the cooling element may be circular or elliptical in shape. In some embodiments, the anchor may include apertures through which fluid may flow. Such an anchor may be utilized for the cooling element being anchored at its top (e.g. to the top plate). Although not indicated in  FIGS.  1 A- 1 G , the piezoelectric utilized in driving the cooling element may have various locations and/or configurations. For example, the piezoelectric may be embedded in the cooling element, affixed to one side of the cooling element (or cantilevered arm(s)), may occupy some or all of the cantilevered arms, and/or may have a location that is close to or distal from the anchored region. In some embodiments, cooling elements that are not centrally anchored may be used. For example, a pair of cooling elements that have offset apertures, that are anchored at their ends (or all edges), and which vibrate out of phase may be used. Thus, various additional configurations of cooling element  120  and/or  120 ′, anchor  160 , and/or other portions of cooling system  100  may be used. 
     Using the cooling system  100  actuated for in-phase vibration or out-of-phase vibration of cooling element  120  and/or  120 ′, fluid drawn in through vent  112  and driven through orifices  132  may efficiently dissipate heat from heat-generating structure  102 . Because fluid impinges upon the heat-generating structure with sufficient speed (e.g. at least thirty meters per second) and in some embodiments substantially normal to the heat-generating structure, the boundary layer of fluid at the heat-generating structure may be thinned and/or partially removed. Consequently, heat transfer between heat-generating structure  102  and the moving fluid is improved. Because the heat-generating structure is more efficiently cooled, the corresponding integrated circuit may be run at higher speed and/or power for longer times. For example, if the heat-generating structure corresponds to a high-speed processor, such a processor may be run for longer times before throttling. Thus, performance of a device utilizing cooling system  100  may be improved. Further, cooling system  100  may be a MEMS device. Consequently, cooling systems  100  may be suitable for use in smaller and/or mobile devices, such as smart phones, other mobile phones, virtual reality headsets, tablets, two-in-one computers, wearables and handheld games, in which limited space is available. Performance of such devices may thus be improved. Because cooling element  120 / 120 ′ may be vibrated at frequencies of 15 kHz or more, users may not hear any noise associated with actuation of cooling elements. If driven at or near structural and/or acoustic resonant frequencies, the power used in operating cooling systems may be significantly reduced. Cooling element  120 / 120 ′ does not physically contact top plate  110  or orifice plate  130  during vibration. Thus, resonance of cooling element  120 / 120 ′ may be more readily maintained. More specifically, physical contact between cooling element  120 / 120 ′ and other structures disturbs the resonance conditions for cooling element  120 / 120 ′. Disturbing these conditions may drive cooling element  120 / 120 ′ out of resonance. Thus, additional power would need to be used to maintain actuation of cooling element  120 / 120 ′. Further, the flow of fluid driven by cooling element  120 / 120 ′ may decrease. These issues are avoided through the use of pressure differentials and fluid flow as discussed above. The benefits of improved, quiet cooling may be achieved with limited additional power. Further, out-of-phase vibration of cooling element  120 / 120 ′ allows the position of the center of mass of cooling element  100  to remain more stable. Although a torque is exerted on cooling element  120 / 120 ′, the force due to the motion of the center of mass is reduced or eliminated. As a result, vibrations due to the motion of cooling element  120 / 120 ′ may be reduced. Moreover, efficiency of cooling system  100  may be improved through the use of out-of-phase vibrational motion for the two sides of cooling element  120 / 120 ′. Consequently, performance of devices incorporating the cooling system  100  may be improved. Further, cooling system  100  may be usable in other applications (e.g. with or without heat-generating structure  102 ) in which high fluid flows and/or velocities are desired. 
       FIGS.  2 A- 2 B  depict an embodiment of active MEMS cooling system  200  including a top centrally anchored cooling element.  FIG.  2 A  depicts a side view of cooling system  200  in a neutral position.  FIG.  2 B  depicts a top view of cooling system  200 .  FIGS.  2 A- 2 B  are not to scale. For simplicity, only portions of cooling system  200  are shown. Referring to  FIGS.  2 A- 2 B , cooling system  200  is analogous to cooling system  100 . Consequently, analogous components have similar labels. For example, cooling system  200  is used in conjunction with heat-generating structure  202 , which is analogous to heat-generating structure  202 . 
     Cooling system  200  includes top plate  210  having vents  212 , cooling element  220  having tip  221 , orifice plate  230  including orifices  232 , top chamber  240  having a gap, bottom chamber  250  having a gap, flow chamber  240 / 250 , and anchor (i.e. support structure)  260  that are analogous to top plate  110  having vent  112 , cooling element  120  having tip  121 , orifice plate  130  including orifices  132 , top chamber  140  having gap  142 , bottom chamber  150  having gap  152 , flow chamber  140 / 150 , and anchor (i.e. support structure)  160 , respectively. Also shown is pedestal  290  that is analogous to pedestal  190 . Thus, cooling element  220  is centrally supported by anchor  260  such that at least a portion of the perimeter of cooling element  220  is free to vibrate. In some embodiments, anchor  260  extends along the axis of cooling element  420 . In other embodiments, anchor  460  is only near the center portion of cooling element  420 . Although not explicitly labeled in  FIGS.  2 A and  2 B , cooling element  220  includes an anchored region and cantilevered arms including step region, extension region and outer regions analogous to anchored region  122 , cantilevered arms  123 , step region  124 , extension region  126  and outer region  128  of cooling element  120 ′. In some embodiments, cantilevered arms of cooling element  220  are driven in-phase. In some embodiments, cantilevered arms of cooling element  220  are driven out-of-phase. In some embodiments, a simple cooling element, such as cooling element  120 , may be used. 
     Anchor  260  supports cooling element  220  from above. Thus, cooling element  220  is suspended from anchor  260 . Anchor  260  is suspended from top plate  210 . Top plate  210  includes vent  213 . Vents  212  on the sides of anchor  260  provide a path for fluid to flow into sides of chamber  240 . 
     As discussed above with respect to cooling system  100 , cooling element  220  may be driven to vibrate at or near the structural resonant frequency of cooling element  220 . Further, the structural resonant frequency of cooling element  220  may be configured to align with the acoustic resonance of the chamber  240 / 250 . The structural and acoustic resonant frequencies are generally chosen to be in the ultrasonic range. For example, the vibrational motion of cooling element  220  may be at the frequencies described with respect to cooling system  100 . Consequently, efficiency and flow rate may be enhanced. However, other frequencies may be used. 
     Cooling system  200  operates in an analogous manner to cooling system  100 . Cooling system  200  thus shares the benefits of cooling system  100 . Thus, performance of a device employing cooling system  200  may be improved. In addition, suspending cooling element  220  from anchor  260  may further enhance performance. In particular, vibrations in cooling system  200  that may affect other cooling cells (not shown), may be reduced. For example, less vibration may be induced in top plate  210  due to the motion of cooling element  220 . Consequently, cross talk between cooling system  200  and other cooling systems (e.g. other cells) or other portions of the device incorporating cooling system  200  may be reduced. Thus, performance may be further enhanced. 
       FIGS.  3 A- 3 G  depict an embodiment of active MEMS cooling system  300  including multiple cooling cells configured as a module termed a tile, or array.  FIG.  3 A  depicts a perspective view, while  FIGS.  3 B- 3 E  depict side views.  FIG.  3 G  indicates the flow of a fluid, such as air, during use of cooling system  300 .  FIG.  3 G  depicts module  395  including multiple cooling systems  300 .  FIGS.  3 A- 3 G  are not to scale. Cooling system  300  includes four cooling cells  301 A,  301 B,  301 C and  301 D (collectively or generically  301 ), which are analogous to one or more of cooling systems described herein. More specifically, cooling cells  301  are analogous to cooling system  100  and/or  200 . Tile  300  thus includes four cooling cells  301  (i.e. four MEMS jets). Although four cooling cells  301  in a 2x2 configuration are shown, in some embodiments another number and/or another configuration of cooling cells  301  might be employed. In the embodiment shown, cooling cells  301  include shared top plate  310  having apertures  312 , cooling elements  320 , shared orifice plate  330  including orifices  332 , top chambers  340 , bottom chambers  350 , anchors (support structures)  360 , and pedestals  390  that are analogous to top plate  110  having apertures  112 , cooling element  120 , orifice plate  130  having orifices  132 , top chamber  140 , bottom chamber  150 , anchor  160 , and pedestal  190 . In some embodiments, cooling cells  301  may be fabricated together and separated, for example by cutting through top plate  310 , side walls between cooling cells  301 , and orifice plate  330 . Thus, although described in the context of a shared top plate  310  and shared orifice plate  330 , after fabrication cooling cells  301  may be separated. In some embodiments, tabs (not shown) and/or other structures such as anchors  360 , may connect cooling cells  301 . Further, tile  300  includes heat-generating structure (termed a heat spreader hereinafter)  302  (e.g. a heat sink, a heat spreader, and/or other structure) that also has sidewalls, or fencing, in the embodiment shown. Cover plate  306  having apertures therein is also shown. Heat spreader  302  and cover plate  306  may be part of an integrated tile  300  as shown or may be separate from tile  300  in other embodiments. Heat spreader  302  and cover plate  306  may direct fluid flow outside of cooling cells  301 , provide mechanical stability, and/or provide protection. Electrical connection to cooling cells  301  is provided via flex connector  380  (not shown in  FIGS.  3 B- 3 G ) which may house drive electronics  385 . Cooling elements  320  are driven out-of-phase (i.e. in a manner analogous to a seesaw). Further, as can be seen in  FIGS.  3 B- 3 C  and  FIGS.  3 D- 3 E  cooling element  320  in one cell is driven out-of-phase with cooling element(s)  320  in adjacent cell(s). In  FIGS.  3 B- 3 C , cooling elements  320  in a row are driven out-of-phase. Thus, cooling element  320  in cell  301 A is out-of-phase with cooling element  320  in cell  301 B. Similarly, cooling element  320  in cell  301 C is out-of-phase with cooling element  320  in cell  301 D. In  FIGS.  3 D- 3 E , cooling elements  320  in a column are driven out-of-phase. Thus, cooling element  320  in cell  301 A is out-of-phase with cooling element  320  in cell  301 C. Similarly, cooling element  320  in cell  301 B is out-of-phase with cooling element  320  in cell  301 D. By driving cooling elements  320  out-of-phase, vibrations in cooling system  300  may be reduced. Cooling elements  320  may be driven in another manner in some embodiments.  FIG.  3 F  indicates the flow of a fluid, such as air, driven by the cooling elements of cooling system  300 . As discussed herein, cooling system  300  not only drives direct flow of the fluid (e.g. air) through the cooling cells  310 , but also entrains fluid from nearby regions. In particular, the entrained air flow may be substantially the same as or exceed the direct fluid flow. Thus, as indicated in the embodiment shown in  FIG.  3 F , operation of the cooling cell may result in more fluid flow being entrained than directly driven. 
     In some embodiments, two sets of four cooling cells  301  may be combined and integrated in a manner analogous to system  300 .  FIG.  3 G  is an exploded view of module  395  including two cooling systems  300  and, therefore, eight cooling cells  301 . Cooling system  300  are enclosed in copper heat spreader  392  and cover  396  having vents  397  therein. Also shown is connector  396  that may house drive electronics analogous to drive electronics  385 . Although not shown, vents  397  may have a dust cover that reduces or prevents the flow of dust (e.g. carried by the fluid flowing into vents  397 ) from reaching the internal portion of module  395  Such standardized modules  395  may facilitate incorporation into devices. Aperture  398  through which flow exits module  395  is between cover  396  and heat spreader  392 . In some embodiments, aperture  398  occupies most or all of the side of module  395 . In some embodiments, module  395  may be approximately forty to sixty millimeters on a side (e.g. forty-five millimeters by fifty-five millimeters) and not more than three millimeters thick. Module  395  may be capable of dissipating 10 W of power (while consuming not more than approximately 3 W of power). Direct flow through module  395  may be at least 0.3 cfm (e.g. on the order of 0.35 cfm) and entrained flow may be at least 0.5 cfm (e.g. 0.7 cfm or approximately twice the direct flow). Thus, the entrained airflow achieved using module  395  is at least the same as the direct airflow. In some embodiments, the entrained airflow is at least 1.5 multiplied by the direct airflow through module  395 . In some embodiments, the entrained airflow may be twice the direct airflow through module  395 . At such flows, the back pressure for module  395  may be not more than 2 kPa-2.2 kPa. Further, module  395  may have a top surface temperature that is significantly lower than the heat spreader (not shown in  FIG.  3 G ) to which module  395  is coupled or heat spreader  392 . This occurs because the active heat dissipation of module  395  starts from the region the fluid enters vents  397  opposite to heat spreader  392 . Consequently, during operation the top surface of module  395  may be at least ten degrees Celsius cooler than a heat spreader  392  or other component to which module  395  is thermally coupled via heat spreader  392 . In some embodiments, the top surface of module  395  is at least fifteen degrees Celsius cooler than heat spreader  392  during operation. The thin form factor (e.g. less than three millimeters thick), high back pressure and flow, little to no noise (e.g. less than 27 dBA) and low top surface temperature may facilitate use of module  395  in devices including but not limited to notebook computers. Thus, the techniques and systems described herein include but are not limited to use in notebook computers. 
     Cooling cells  301  of cooling system  300  and module  395  functions in an analogous manner to cooling system(s)  100 ,  200 , and/or an analogous cooling system. Consequently, the benefits described herein may be shared by cooling system  300  and module  395 . Because cooling elements in nearby cells are driven out-of-phase, vibrations in cooling system  300  may be reduced. Because multiple cooling cells  301  are used, cooling system  300  may enjoy enhanced cooling capabilities. Further, multiples of individual cooling cells  301   and/or cooling system  300  may be combined in various fashions to obtain the desired footprint of cooling cells. 
       FIG.  4    depicts an embodiment of active cooling system  400  that utilizes entrainment as integrated into a device.  FIG.  4    is not to scale and for clarity, only some structures are shown. The device may be a laptop computer, a tablet or notebook computer, a smart phone, and/or other mobile device. Device may also be another device, such as a server in a rack, a game console, or a desktop computer. In some embodiments, therefore, the device is thin. For example, in some embodiments, the device has a thickness (height along the smallest dimension, the z-direction in  FIG.  4   ) of not more than twenty-five millimeters. The thickness is not more than ten millimeters in some embodiments. In some such embodiments, the thickness of the device is not more than eight millimeters. However, other thicknesses are possible. 
     The device into which cooling system  400  is integrated includes heat-generating structure  401 , additional components  402 ,  403 , and  404 , substrate  406 , and housing  407 . Heat-generating structure  401  is a component that is desired to be cooled. For example, heat-generating structure  401  may be an integrated circuit, such as a processor, or other device. During use, heat-generating structure  401  may rise significantly in temperature. For example, for heat-generating structure  402  being a processor, the top near heat spreader  420  may be on the order of ninety degrees Celsius and the junction temperature may be on the order of ninety-three to ninety four degrees Celsius. Substrate  406  may be a printed circuit board (PCB) or other substrate on which heat-generating structure  401  and additional components  402  and  403  are mounted. In some embodiments, substrate  404  may be omitted. Components  402 ,  403 , and  404  may also generate heat. Thus, cooling system  400  may be used for thermal management of not only heat-generating structure  401 , but also components  402 ,  403 , and/or  404 . 
     Cooling system  400  includes MEMS cooling system  410 , heat spreader  420 , egress passageway  430 , inlets  440 A and  440 B (collectively or generically  440 ), and egress  450 . In some embodiments, heat spreader  420  may be omitted and/or another structure used to mount MEMS cooling system  410 . MEMS cooling system  410  includes one or more cooling cells analogous to cooling systems  100  and/or  200 . In some embodiments, MEMS cooling system  410  includes multiple cooling cells configured as a module termed a tile. For example, MEMS cooling system  410  may include one or more tiles  300  and/or module  395 . Thus, MEMS cooling system  410  includes cooling element(s) configured to undergo vibrational motion when actuated to drive a fluid. MEMS cooling system  410  may also include top plate(s), anchor(s), orifice plate(s), and/or pedestal(s) analogous to those described in the context of cooling system  100  and/or  200 . MEMS cooling system  410  may also include an integrated heat spreader and cover analogous to those described in the context of tile  300 . MEMS cooling system  410  may have a thickness of not more than three millimeters. In some embodiments, MEMS cooling system  410  has a thickness of not more than 2.5 millimeters. MEMS cooling system  410  may have a thickness of not more than two millimeters. 
     Inlets  440 A and  440 B and egress  450  allow for an exchange in fluid (e.g. air) internal to housing  407  with fluid external to the device. For example, inlets  440 A and  440 B and egress  450  may be vents. Although two inlets  440 A and  440 B and one egress  450  are shown, in some embodiments, another number of inlet(s) and/or egress(es) may be present. Although termed inlets, inlet(s)  440 A and/or  440 B may allow some fluid to exit the device. Similarly, although termed an egress, egress  450  may allow some fluid to enter the device. Thus, the terms inlet and egress are intended to indicate the primary function of the structures  440 A,  440 B, and  450 . 
     In the embodiment shown, fluid entering the device via inlet  440 A and driven via MEMS cooling system  410  primarily flows through MEMS cooling system  410 . Thus, fluid may enter via inlet  440 A, enter MEMS cooling system  410  via apertures (not shown in  FIG.  4   ), be driven through MEMS cooling system  410  by vibrational motion of cooling elements (not shown in  FIG.  4   ), and exit MEMS cooling system  410 . More specifically, cooler fluid enters via inlet  440 A. This flow of cooler fluid is shown by dashed arrows. The cool fluid may be the temperature of the ambient in which the device operates. For example, the cool fluid may be at or near room temperature (e.g. 22-28° C.). Heat from heat-generating structure  401  is transferred to heat spreader  420  (e.g. via conduction) and from heat spreader  420  to the fluid driven through MEMS cooling system  410 . In traversing MEMS cooling system  410 , the fluid is heated. Thus, hot fluid exits MEMS cooling system  410 . The flow of heated fluid is shown by the dotted/dashed arrows in  FIG.  4   . In some embodiments, the heated fluid exiting MEMS cooling system  410  has a temperature of at least sixty degrees Celsius. In some embodiments, the heated fluid exiting MEMS cooling system  410  is at least sixty-five degrees Celsius. In some embodiments, the heated fluid exiting MEMS cooling system  410  is at least seventy degrees Celsius. 
     As described herein, the heated fluid driven by MEMS cooling system  410  travels at high speeds. For example, fluid leaving the orifice plate may travel at the speeds described herein (e.g. greater than thirty-five meters per second). The flow of heated fluid outside of MEMS cooling system  410  is also at a high speed. Consequently, a region of low pressure may be developed within egress passageway  430 . The low pressure and/or high fluid flow of egress passageway  430  due to MEMS cooling system  410  entrains fluid into inlet  440 B. Stated differently, fluid is drawn into egress passageway  430  from inlet  440 B. In the embodiment shown, the entrained fluid is from the ambient and thus may have a temperature similar to the fluid drawn into inlet  440 A. The flow of cooler fluid into inlet  440 B is indicated by dashed arrows in  FIG.  4   . The flow of cool fluid through inlet  440 B is at least one-half multiplied by the fluid flow from MEMS cooling system  410 . In some embodiments, the flow of cool fluid through inlet  440 B is at least as large as the fluid flow from MEMS cooling system  410 . The flow of cool fluid from inlet  440 B in egress passageway  430  may be greater than the flow of fluid through MEMS cooling system  410 . In some embodiments, the flow of cool fluid from inlet  440 B in egress passageway  430  is at least 1.5 multiplied by the flow of fluid through MEMS cooling system  410 . In some embodiments, the flow of cool fluid from inlet  440 B in egress passageway  430  is at least two multiplied by the flow of fluid through MEMS cooling system  410 . 
     Egress passageway  430  receives hot fluid from MEMS cooling system  410  and the cool fluid from inlet  440 B. The hot fluid from MEMS cooling system  410  mixes with the cooler fluid from inlet  440 B in egress passageway  430 . Thus, the hot fluid from MEMS cooling system  410  is cooled. The flow of the mixture of the heated fluid from MEMS cooling system  410  and cool fluid from inlet  440 B is shown by solid arrows in  FIG.  4   . The mixture of heated and cool fluid exits egress passageway via egress  450 . Because cool fluid is mixed with hot fluid in egress passageway  430 , the mixture of fluid exiting via egress  450  may have a significantly lower temperature than the hot fluid leaving MEMS cooling system  410 . For example, the mixture of the hot air and the cool air at egress  450  may have a temperature not exceeding sixty degrees Celsius for the heat-generating structure being at least seventy degrees Celsius (e.g. for the heat-generating component having a temperature of at least ninety degrees Celsius). In some embodiments, the temperature of the fluid mixture at egress  450  does not exceed fifty-five degrees Celsius. For example, the mixture of fluid may have a temperature of at least fifty and not more than fifty-five degrees Celsius. In some embodiments, the temperature at egress  450  may be lower. For example, the fluid mixture exiting the device via egress  450  may be forty through forty-five degrees Celsius. 
     In addition to cooling the hot fluid from MEMS cooling system  410 , the cool air entrained through inlet  440 B may also be used to cool other components. Stated differently, the cool(er) air entering via inlet  440 B may pass and remove heat from other components. For example, components  402 ,  403 , and/or  404  might be cooled. 
     Cooling system  400  may improve thermal management of the device(s) in which cooling system  400  is incorporated. MEMS cooling system  410  may provide efficient cooling in a low profile package. For example, in some embodiments, MEMS cooling system  410  may provide up to ten Watts of power dissipation while consuming three Watts of power. Further, MEMS cooling system  410  is thin (e.g. MEMS cooling system  410  is not more than three millimeters thick). Thus, cooling system  400  may be used in confined spaces and thin devices. Further, entrainment provided via egress passageway  430  may provide higher flow and greater cooling. In addition, fluid used in cooling the device exits the device at a lower temperature. For example, fluid exiting egress  450  may be 50-55° C. in some cases. Thus, the fluid is less likely to cause discomfort to or burn a user. Thus, performance of devices incorporating cooling system  400  may be improved. 
       FIGS.  5 A- 5 F  depict embodiments of active cooling system  500 A,  500 B,  500 C,  500 D,  500 E and  500 F that utilize MEMS cooling systems and, optionally, entrainment as integrated into devices.  FIGS.  5 A- 5 F  are not to scale and for clarity, only some structures are shown. The device in each cooling system  500 A,  500 B,  500 C,  500 D,  500 E and  500 F may be a laptop computer, a tablet or notebook computer, a smart phone, and/or other mobile device. Device may also be another device, such as a server in a rack, a game console, or a desktop computer. In some embodiments, therefore, the device is thin. For example, in some embodiments, the device has a thickness (height along the smallest dimension, the z-direction in  FIGS.  5 A- 5 F ) of not more than twenty-five millimeters. The thickness is not more than twenty millimeters in some embodiments. The thickness is not more than fifteen millimeters in some embodiments. The thickness is not more than ten millimeters in some embodiments. In some such embodiments, the thickness of the device is not more than eight millimeters. However, other thicknesses are possible. 
     Cooling system  500 A and the device into which it is incorporated are analogous to cooling system  400  and the device housing cooling system  400 . The device into which cooling system  500 A is integrated includes heat-generating structure  501 , additional components  502  and  503 , substrate  506 , housing  507  and  508  that are analogous to heat-generating structure  401 , additional components  402  and  403 , substrate  406 , and housing  407 . The portion of housing  507  includes a keyboard, while portion housing  508  is near the support (e.g. a table or other structure) on which the device is located. Heat-generating structure  501  is a component that is desired to be cooled, such as a processor. During use, heat-generating structure  501  may reach temperatures analogous to those described in the context of heat-generating structure  401 . Also shown is thermal interface material (TIM)  509  that may be used to improve thermal coupling between heat-generating structure  501  and heat spreader  520 . In some embodiments, TIM  509  may be omitted. Components  502  and  503  may also generate heat. Thus, cooling system  500 A may be used for thermal management of not only heat-generating structure  501 , but also components  502  and/or  503 . 
     Cooling system  500 A includes MEMS cooling system  510 , heat spreader  520 , egress passageway  530 , inlets  540 A and  540 B (collectively or generically  540 ), and egress  550  that are analogous to cooling system  410 , heat spreader  420 , egress passageway  430 , inlets  440 , and egress  450 , respectively. MEMS cooling system  510  includes cooling cells  512  and surrounding structure  514  which may be analogous to cooling cells  301 , heat spreader  302 , and cover plate  306 . Thus, MEMS cooling system  510  may correspond to one or more modules  395  or cooling systems  300 . In some embodiments, heat spreader  520  may be omitted and/or another structure used to mount MEMS cooling system  510 . In some embodiments, heat spreader  520  may be part of structure  514  surrounding cooling cells  512 . In some embodiments, heat spreader  520  may be considered to be integrated into MEMS cooling system  510 . Although a single set of cooling cells  512  and surrounding structure  514  (e.g. a tile) is shown, multiple tiles may be present in some embodiments. Thus, MEMS cooling system  510  (i.e. cooling cells  512 ) includes cooling element(s) configured to undergo vibrational motion when actuated to drive a fluid. Cooling cells  512  may also include top plate(s), anchor(s), orifice plate(s), and/or pedestal(s) analogous to those described in the context of cooling system  100  and/or  200 . MEMS cooling system  510  may have a thickness of not more than three millimeters. MEMS cooling system  510  may have a thickness of less than three millimeters. In some embodiments, MEMS cooling system  510  has a thickness of not more than 2.5 millimeters. MEMS cooling system  510  have a thickness of not more than two millimeters. 
     Inlets  540 A and  540 B and egress  550  allow for an exchange in fluid (e.g. air) internal to housing  507  with fluid external to the device. For example, inlets  540 A and  540 B and egress  550  may be vents. Although two inlets  540 A and  540 B and one egress  550  are shown, in some embodiments, another number of inlet(s) and/or egress(es) may be present. The function of inlets  540 A and  540 B and egress  550  are analogous to that of inlets  440 A and  440 B and egress  450 , respectively. 
     Cooling system  500 A functions in a manner analogous to cooling system  400 . In the embodiment shown, fluid (e.g. air) enters the device from the region between housing  508  and the underlying support. Thus, cool fluid enters the device via inlet  540 A and primarily flows through MEMS cooling system  510 . The cool fluid may be the temperature of the ambient in which the device operates (e.g. 22-28° C.). This flow of cooler fluid is shown by dashed arrows. The cool fluid is driven via cooling cells  512  of MEMS cooling system  510 . In so doing, heat is transferred from heat-generating structure  501  (via heat spreader  520 ) to the fluid. The heated fluid flows between portions of surrounding structure  514 , toward egress  550 . The flow of heated fluid is shown by dotted/dashed arrows. In some embodiments, the heated fluid exiting MEMS cooling system  510  has a temperature of at least sixty degrees Celsius. In some embodiments, the heated fluid exiting MEMS cooling system  510  is at least sixty-five degrees Celsius. In some embodiments, the heated fluid exiting MEMS cooling system  510  is at least seventy degrees Celsius. 
     The heated fluid driven by MEMS cooling system  510  travels at high speeds discussed herein. Consequently, a region of low pressure may be developed within egress passageway  530 . The low pressure and/or high fluid flow of egress passageway  530  due to MEMS cooling system  510  entrains fluid into inlet  540 B. In the embodiment shown, the entrained fluid is from the ambient and thus may have a temperature similar to the fluid drawn into inlet  540 A. The flow of cooler fluid into inlet  540 B is indicated by dashed arrows in  FIG.  5 A . The flow of cool fluid through inlet  540 B is at least one-half multiplied by the fluid flow from MEMS cooling system  510 . In some embodiments, the flow of cool fluid through inlet  540 B is at least as large as the fluid flow from MEMS cooling system  510 . The flow of cool fluid from inlet  540 B in egress passageway  530  may be greater than the flow of fluid through MEMS cooling system  510 . In some embodiments, the flow of cool fluid from inlet  540 B in egress passageway  530  is at least 1.5 multiplied by the flow of fluid through MEMS cooling system  510 . In some embodiments, the flow of cool fluid from inlet  540 B in egress passageway  530  is at least two multiplied by the flow of fluid through MEMS cooling system  510 . 
     Egress passageway  530  receives hot fluid from MEMS cooling system  510  and the cool fluid from inlet  540 B. The hot fluid from MEMS cooling system  510  mixes with the cooler fluid from inlet  540 B in egress passageway  530 . Thus, the hot fluid from MEMS cooling system  510  is cooled. The flow of the mixture of the heated fluid from MEMS cooling system  510  and cool fluid from inlet  540 B is shown by solid arrows in  FIG.  5 A . The mixture of heated and cool fluid exits egress passageway via egress  550 . Because cool fluid is mixed with hot fluid in egress passageway  530 , the mixture of fluid exiting via egress  550  may have a significantly lower temperature than the hot fluid leaving MEMS cooling system  510 . For example, the mixture of the hot air and the cool air at egress  550  may have a temperature not exceeding sixty degrees Celsius for the heat-generating structure being at least seventy degrees Celsius (e.g. for the heat-generating component having a temperature of at least ninety degrees Celsius). In some embodiments, the temperature of the fluid mixture at egress  550  does not exceed fifty-five degrees Celsius. For example, the mixture of fluid may have a temperature of at least fifty and not more than fifty-five degrees Celsius. In some embodiments, the temperature at egress  550  may be lower. For example, the fluid mixture exiting the device via egress  550  may be forty through forty-five degrees Celsius. 
     In addition to cooling the hot fluid from MEMS cooling system  510 , the cool air entrained through inlet  540 B may also be used to cool other components. Stated differently, the cool(er) air entering via inlet  540 B may pass and remove heat from other components. For example, components  502  and/or  503  might be cooled. In some embodiments, other mechanisms are used to cool component(s)  502  and/or  503 . In some embodiments, no additional thermal management is used for component(s)  502  and/or  503 . 
     Referring to  FIG.  5 B , cooling system  500 B and the device (e.g. a notebook computer or other portable computing device) into which it is incorporated are analogous to cooling systems  400  and  500 A and the device housing cooling system  400  and  500 A. The device into which cooling system  500 B is integrated includes heat-generating structure  501  (e.g. a central processing unit), additional components (not shown in  FIG.  5 B ), substrate  506 , housing  507  (e.g. having a keyboard) and  508  (e.g. back cover) that are analogous to heat-generating structure  401 / 501 , additional components  402 / 502  and  403 / 503 , substrate  406 / 506 , and housing  407 / 507 . During use, heat-generating structure  501  may reach temperatures analogous to those described in the context of heat-generating structure  401 . Although not shown, a TIM may be used to improve thermal coupling between heat-generating structure  501  and heat spreader  520  and/or MEMS cooling system  510 . 
     Cooling system  500 B includes MEMS cooling system  510 , which is analogous to MEMS cooling system  510  depicted in  FIG.  5 A . Thus, MEMS cooling system  510  may be a module analogous to module  395 . In some embodiments, MEMS cooling system  510  may include multiple modules  395 . MEMS cooling system  510  is coupled directly to (i.e. aligned with) heat-generating structure  501  via heat spreader  520 . For example, heat spreader  392  of module  395  of MEMS cooling system  510  may be coupled with heat spreader  520 . In some embodiments, heat spreader  520  may be formed of a layer of graphite and a layer of copper (e.g. a 500 micrometer thick layer of copper with a 100 micrometer thick layer of graphite). In other embodiments, for example embodiments in which MEMS cooling system  510  includes multiple modules  395 , item  320  may be a vapor chamber. 
     Directly coupling MEMS cooling system  510  to heat-generating structure  501  may reduce complexity of design and thermal resistance between heat-generating structure  501   and MEMS cooling system  510 . As discussed with respect to module  395 , the surface of MEMS cooling system  510  opposite to heat-generating structure  501  may be significantly cooler than heat spreader  520 . Thus, a lower temperature of back cover of housing  508  may be maintained. 
     Referring to  FIG.  5 C , cooling system  500 C and the device (e.g. a notebook computer or other portable computing device) into which it is incorporated are analogous to cooling systems  400 ,  500 A, and  500 B and the device housing cooling system  400 ,  500 A, and  500 B. The device into which cooling system  500 C is integrated includes heat-generating structure  501  (e.g. a central processing unit), additional components  502  and  503 , substrate  506 , housing  507  (e.g. having a keyboard) and  508  (e.g. back cover) that are analogous to heat-generating structure  401 / 501 , additional components  402 / 502  and  403 / 503 , substrate  406 / 506 , and housing  407 / 507 . During use, heat-generating structure  501  may reach temperatures analogous to those described in the context of heat-generating structure  401 . Although not shown, a TIM may be used to improve thermal coupling between heat-generating structure  501  and heat spreader  520  and/or MEMS cooling system  510 . 
     Cooling system  500 C includes MEMS cooling system  510 , which is analogous to MEMS cooling system  510  depicted in  FIG.  5 A . Thus, MEMS cooling system  510  may be a module analogous to module  395 . In some embodiments, MEMS cooling system  510  may include multiple modules  395 . MEMS cooling system  510  is offset from (i.e. not directly aligned with) heat-generating structure  501 . However, MEMS cooling system  510  is still thermally coupled with heat-generating structure  501  via heat spreader  520 . For example, heat spreader  392  of module  395  of MEMS cooling system  510  may be coupled with heat spreader  520 . In some embodiments, heat spreader  520  may be a vapor chamber to account for the higher thermal resistance between heat-generating structure  501  and MEMS cooling system  510 . Offsetting MEMS cooling system  510  from heat-generating structure  501  may allow for MEMS cooling system  510  to provide its cooling power despite a reduced thickness of the device in which it is incorporated. 
     Referring to  FIG.  5 D , cooling system  500 D and the device (e.g. a notebook computer or other portable computing device) into which it is incorporated are analogous to cooling systems  400 ,  500 A,  500 B, and  500 C and the device housing cooling system  400  and  500 A. The device into which cooling system  500 D is integrated includes heat-generating structure  501  (e.g. a central processing unit), additional components (not shown), substrate  506 , housing  507  (e.g. having a keyboard) and  508  (e.g. back cover) that are analogous to heat-generating structure  401 / 501 , additional components  402 / 502  and  403 / 503 , substrate  406 / 506 , and housing  407 / 507 . During use, heat-generating structure  501  may reach temperatures analogous to those described in the context of heat-generating structure  401 . Although not shown, a TIM may be used to improve thermal coupling between heat-generating structure  501  and heat spreader  520  and/or MEMS cooling system  510 . 
     Cooling system  500 D includes two MEMS cooling systems  510 , which are analogous to MEMS cooling system  510  depicted in  FIG.  5 A . Thus, each MEMS cooling system  510  may be a module analogous to module  395 . In some embodiments, each MEMS cooling system  510  may include multiple modules  395 . MEMS cooling systems  510  are offset from (i.e. not directly aligned with) heat-generating structure  501 . However, MEMS cooling systems  510  are still thermally coupled with heat-generating structure  501  via heat spreader  520 . For example, heat spreader  392  of module  395  of MEMS cooling system  510  may be coupled with heat spreader  520 . In some embodiments, heat spreader  520  may be a vapor chamber to account for the higher thermal resistance between heat-generating structure  501  and MEMS cooling system  510 . Offsetting MEMS cooling system  510  from heat-generating structure  501  may allow for MEMS cooling system  510  to provide its cooling power despite a reduced thickness of the device in which it is incorporated. Also shown in cooling system  500 D is stage  511 , to which heat spreader  520  and/or MEMS cooling system  510  may be mounted. In some embodiments, stage  511  is thermally conductive. 
     Also indicated in  FIG.  5 D  are thickness, T, of the device, Gap A between heat spreader  520  and/or MEMS cooling systems  510  and housing  508 , and Gap B between substrate  506  (or heat-generating device  501 ) and housing/keyboard  507 . Gap A and Gap B may be desired in order to thermally insulate housing  507  and  508  from heat-generating structure  501  and heat spreader  520 . Air is one of the best insulators. Consequently, Gap A and Gap b are generally desired to be airgaps. Adjusting the Gap A and Gap B between the hot spots and the housing/keyboard  507  and housing/back cover  508  may be a practical means of balancing the thermal resistance. Because air gap size affects the system pressure resistance, the thermal resistance balance must be considered with entrainment in mind. The added entrainment from the MEMS cooling systems  510 A and  510 , targets the skin hot spots (back cover and the keyboard) from inside the notebook. This results in lowering the skin temperature without lowering the vapor chamber/heat spreader  520  temperature. In some embodiments, air Gap A is desired to be not less than 800 micrometers thick in order for the temperature of back cover  508  to be less than 48° C. Air Gap B may be not less than one millimeter thick for housing/keyboard  507  to maintain a temperature of less than 42° C. In the embodiment shown in  FIG.  5 D , these gaps may be maintained for a device thickness T of nine millimeters. Further, air Gap A and air Gap B may be sufficiently large to allow for entrained flow of air through these gaps. The sizes and functions of air gaps analogous to Gap A and Gap B may be similar for other embodiments. 
     Referring to  FIG.  5 E , cooling system  500 E and the device (e.g. a notebook computer or other portable computing device) into which it is incorporated are analogous to cooling systems  400 ,  500 A,  500 B,  500 C, and  500 D and the device housing cooling system  400  and  500 A. The device into which cooling system  500 E is integrated includes heat-generating structure  501  (e.g. a central processing unit), additional components (not shown), substrate  506 , housing  507  (e.g. having a keyboard) and  508  (e.g. back cover) that are analogous to heat-generating structure  401 / 501 , additional components  402 / 502  and  403 / 503 , substrate  406 / 506 , and housing  407 / 507 . During use, heat-generating structure  501  may reach temperatures analogous to those described in the context of heat-generating structure  401 . Although not shown, a TIM may be used to improve thermal coupling between heat-generating structure  501  and heat spreader  520  and/or MEMS cooling system  510 . Heat spreader  520  may be a vapor chamber. 
     Cooling system  500 E includes MEMS cooling system  510 , which is analogous to MEMS cooling system  510  depicted in  FIG.  5 A . Thus, MEMS cooling system  510  may be a module analogous to module  395 . In some embodiments, MEMS cooling system  510  may include multiple modules  395 . MEMS cooling system  510  and heat-generating structure  501  are thermally coupled to heat spreader  520 . In cooling system  500 E, heat spreader  520  may be substantially flat. In addition, MEMS cooling system  510  is mounted such that the heated air leaves MEMS cooling system  510  in the direction of keyboard  507 . The inlets to the device housing MEMS cooling system  510  may be between the back cover (e.g. a vent in a surface that is not shown in  FIG.  5 E  or a vent in housing  508 ) and heat spreader  520 . Thus, cooler air flows between heat spreader  520  and housing  508 . Heated air from MEMS cooling system  510  flows between keyboard  507  and MEMS cooling system  510  to an egress. Cooler air, at least some of which may be entrained, thus flows over a number of components of the device. As such, cooling may be improved. 
     Referring to  FIG.  5 F , cooling system  500 F and the device (e.g. a notebook computer or other portable computing device) into which it is incorporated are analogous to cooling systems  400 ,  500 A,  500 B,  500 C,  500 D, and  500 E and the device housing cooling system  400  and  500 A. The device into which cooling system  500 F is integrated includes heat-generating structure  501  (e.g. a central processing unit), additional components (not shown), substrate  506 , housing  507  (e.g. having a keyboard) and  508  (e.g. back cover) that are analogous to heat-generating structure  401 / 501 , additional components  402 / 502  and  403 / 503 , substrate  406 / 506 , and housing  407 / 507 . During use, heat-generating structure  501  may reach temperatures analogous to those described in the context of heat-generating structure  401 . Although not shown, a TIM may be used to improve thermal coupling between heat-generating structure  501  and heat spreader  520  and/or MEMS cooling system  510 . Heat spreader  520  may be a vapor chamber. 
     Cooling system  500 F is analogous to cooling system  500 E. In particular, the locations of inlets and egresses may be analogous to those for cooling system  500 E. Thus, air enters the device of cooling system  500 F and travels between housing  508  and heat spreader  520 . MEMS cooling system  510  is mounted such that the heated air leaves MEMS cooling system  510  in the direction of keyboard  507 . Heated air from MEMS cooling system  510  flows between keyboard  507  and MEMS cooling system  510  to an egress. Further, cooling system  500 E includes two MEMS cooling systems  510 . MEMS cooling systems  510  are offset from (i.e. not directly aligned with) heat-generating structure  501 . Offsetting MEMS cooling systems  510  from heat-generating structure  501  may allow for MEMS cooling system  510  to provide its cooling power in a device having a reduced thickness. 
     Cooling systems  500 A,  500 B,  500 C,  500 D,  500 E, and  500 F may improve thermal management of the device(s) in which cooling systems  500 A,  500 B,  500 C,  500 D,  500 E, and  500 F are incorporated. MEMS cooling systems  510  may provide efficient cooling in a low profile package. Further, entrainment provided via egress passageway  530  may provide higher flow and greater cooling. In addition, fluid used in cooling the device exits the device at a lower temperature. For example, fluid exiting egress  550  may be 50-55° C. in some cases. Thus, the fluid is less likely to cause discomfort to or burn a user. Thus, performance of devices incorporating cooling systems  500 A,  500 B,  500 C,  500 D,  500 E and/or  500 F may be improved. 
       FIGS.  6 - 11    depict embodiments of systems  600 ,  700 ,  800 ,  900 ,  1000 , and  1100  that utilize cooling systems analogous to systems  100 ,  200 ,  300 ,  395 ,  400 ,  500 A,  500 B,  500 C, and/or  500 D. In some embodiments, the devices integrate the cooling systems (e.g. module  395  and/or MEMS cooling systems  510 ) in order to utilize entrainment for cooling. In some embodiments, cooling systems  600 ,  700 ,  800 ,  900 ,  1000 , and/or  1100  may produce entrained flow of greater than 1 cfm and a total flow (i.e. the flow that enters and exits the device) of greater than 1.5 cfm. For example, in some embodiments, entrained flows of 1.3 cfm and total flows of 2 cfm may be achieved. Thus, although the direct flow through a module such as module  395  may be on the order of 0.35 cfm, the entrained flow may be greater than the direct flow. Thus, entrained flow may significantly increase the cooling provided and allow for an improvement in maximum steady power of the device. In general, to improve entrained flow, inlets are located distal from the cooling modules (e.g. module  395 ). For example, the inlets may be not in a direct line (e.g. in the keyboard region or back cover) to the vents in the cooling module (e.g. vents  397 ). In some embodiments, side inlets are the primary inlets for flow entrained in system. A rear inlet (or other inlet) distal from the cooling module (e.g. module  395 ) may provide additional flow through the device. Egresses for such devices are generally in proximity to MEMS cooling system to provide an egress passageway with a lower resistance path for the heated air to leave the device. Such egress passageways may also allow for mixing of the heated air with cooler entrained air without significantly heating other components of the device. In some embodiments, egresses are desired to have an area that is of equal size or larger than the egresses of the cooling systems modules (e.g. not smaller than aperture  398 .) In some embodiments the cool air entering the module/MEMS cooling system as part of the direct flow is desired to not mix with the heated air being driven to the egress(es). Thus, a gasket may be used on the side of MEMS cooling system proximate to the egresses. In some embodiments, the mixture of the hot air and the cool air at the egress(es) has a temperature not exceeding sixty degrees Celsius for the heat-generating structure being at least seventy degrees Celsius. In some such embodiments, the temperature does not exceed fifty-five degrees Celsius. 
       FIG.  6    is a plan view of an embodiment of active cooling system  600  that utilizes entrainment integrated into a device.  FIG.  6    is not to scale and for clarity, only some structures are shown. The device may be a laptop computer, a tablet or notebook computer, a smart phone, and/or other mobile device. Device may also be another device, such as a server in a rack, a game console, or a desktop computer. In some embodiments, therefore, the device is thin. For example, in some embodiments, the device has a thickness (height along the smallest dimension, perpendicular to the page in  FIG.  6   ) analogous to those described for the devices of  FIGS.  4  and  5 A- 5 F . 
     Cooling system  600  and the device into which it is incorporated are analogous to cooling system(s)  400 ,  500 A,  500 B,  500 C,  500 D,  500 E, and/or  500 F and the device housing cooling MEMS system(s)  410  and/or  510 . The device into which cooling system  600  is integrated includes heat-generating structure(s) (not shown) and housing  607  that are analogous to heat-generating structure  401  and  501  and housing  407  and  507 / 508 . During use, the heat-generating structure cooled by system  600  may reach temperatures analogous to those described in the context of heat-generating structure(s)  401  and/or  501 . 
     Cooling system  600  includes MEMS cooling system  610 , heat spreader  620 , egress passageway  630 , inlets  640 A,  640 B,  640 C, and  640 D (collectively or generically  640 ), and egress  650  that are analogous to cooling system  410  and/or  510 , heat spreader  420  and/or  520 , egress passageway  430  and/or  530 , inlets  440  and/or  540 , and egress(es)  450  and/or  550 , respectively. MEMS cooling system  610  includes cooling cells  612  (which are not individually denoted) and surrounding structure  614  which may be analogous to cooling cells  301 , heat spreader  302 , and cover plate  306 . In some embodiments, heat spreader  620  may be omitted and/or may be part of structure  614  surrounding cooling cells  612 . Although a single set of cooling cells  612  and surrounding structure  614  (e.g. a tile) is shown, multiple tiles may be present in some embodiments. Thus, MEMS cooling system  610  includes cooling element(s) configured to undergo vibrational motion when actuated to drive a fluid. Cooling cells  612  may also include top plate(s), anchor(s), orifice plate(s), and/or pedestal(s) analogous to those described in the context of cooling system  100  and/or  200 . MEMS cooling system  610  may have a thickness analogous to those described for cooling systems  300 ,  395 ,  410  and/or  510 . 
     Inlets  640 A,  640 B,  640 C, and  640 D and egress  650  allow for an exchange in fluid (e.g. air) internal to housing  607  with fluid external to the device. For example, inlets  640  and egress  650  may be vents. Although four inlets  640 A,  640 B,  640 C, and  640 D and one egress  650  are shown, in some embodiments, another number of inlet(s) and/or egress(es) may be present. For example, inlet  640 D may be omitted, inlet  640 D and one of inlets  640 B and  640 C may be omitted, or one or both of inlets  640 B and  640 C may be omitted. The function of inlets  640  and egress  650  are analogous to that of inlets  440  and  540  and egresses  450  and  550 , respectively. 
     Cooling system  600  functions in a manner analogous to cooling system(s)  400 ,  500 A,  500 B,  500 C,  500 D,  500 E, and/or  500 F. Thus, cool fluid that enters the device via inlet  640 A primarily flows through MEMS cooling system  610 . The cool fluid may be the temperature of the ambient in which the device operates (e.g. 22-28° C.). The cool fluid is driven via cooling cells  612  of MEMS cooling system  610 . In so doing, heat is transferred from the heat-generating structure to the fluid. The heated fluid flows between portions of surrounding structure  614 , toward egress  650 . The flow of heated fluid is shown by dotted/dashed arrows. In some embodiments, the heated fluid exiting MEMS cooling system  610  has a temperature of at least sixty degrees Celsius. In some embodiments, the heated fluid exiting MEMS cooling system  610  is at least sixty-five degrees Celsius. In some embodiments, the heated fluid exiting MEMS cooling system  610  is at least seventy degrees Celsius. 
     The heated fluid driven by MEMS cooling system  610  travels at high speeds and may develop a low pressure, as discussed herein. Consequently, fluid is entrained into inlets  640 B,  640 C, and  640 D. In the embodiment shown, fluid is entrained into inlets  640 B and  640 C even though inlets  640 B and  640 C are not between cooling cells  612  and egress  650 . In the embodiment shown, the entrained fluid is from the ambient and thus may have a temperature similar to the fluid drawn into inlet  640 A. The flow of cooler fluid through inlets  640 B,  640 C, and  640 D is indicated by dashed arrows in  FIG.  6   . The flow of cool fluid through inlets  640 B,  640 C, and  640 D as compared to the fluid flow from MEMS cooling system  610  is analogous to that described for cooling systems  410  and  510 . For example, the fluid flow through inlets  640 B,  640 C, and  640 D may be greater than the flow of fluid through MEMS cooling system  610 . 
     Egress passageway  630  receives hot fluid from MEMS cooling system  610  and the cool fluid from inlets  640 B,  640 C, and  640 D. The hot fluid from MEMS cooling system  610  mixes with the cooler fluid from inlet  640 B in egress passageway  630 . Thus, the hot fluid from MEMS cooling system  610  is cooled. The flow of the mixture of the heated fluid from MEMS cooling system  610  and cool fluid from inlets  640 B,  640 C, and  640 D is shown by solid arrows in  FIG.  6   . The mixture of heated and cool fluid exits egress passageway via egress  650 . Because cool fluid is mixed with hot fluid in egress passageway  630 , the mixture of fluid exiting via egress  650  may have a significantly lower temperature than the hot fluid leaving MEMS cooling system  610 . For example, the mixture of the hot air and the cool air at egress  650  may have a temperature(s) in the ranges described for egresses  430  and/or  530 . In addition to cooling the hot fluid from MEMS cooling system  610 , the cool air entrained through inlets  640 B,  640 C, and  640 D may also be used to cool other components (not shown). 
     Cooling system  600  may improve thermal management of the device(s) in which cooling system  600  is incorporated. MEMS cooling system  610  may provide efficient cooling in a low profile package. Further, entrainment provided via egress passageway  630  may provide higher flow and greater cooling. In addition, fluid used in cooling the device exits the device at a lower temperature. For example, fluid exiting egress  650  may be 50-55° C. in some cases. Thus, the fluid is less likely to cause discomfort to or burn a user. Thus, performance of devices incorporating cooling system  600  may be improved. 
       FIG.  7    depicts a perspective view of an embodiment of active cooling system  700  that utilizes entrainment integrated into a device.  FIG.  7    is not to scale and for clarity, only some structures are shown. The device may be a laptop computer, a tablet or notebook computer, a smart phone, and/or other mobile device. Device may also be another device, such as a server in a rack, a game console, or a desktop computer. In some embodiments, therefore, the device is thin. For example, in some embodiments, the device has a thickness (height along the smallest dimension) analogous to those described for the devices of  FIGS.  4  and  5 A- 5 F . 
     Cooling system  700  and the device into which it is incorporated are analogous to cooling system(s)  400 ,  500 A,  500 B,  500 C,  500 D,  500 E,  500 F, and/or  600  and the device that houses cooling system(s)  410 ,  510  and/or  610 . The device into which cooling system  700  is integrated includes heat-generating structure(s) (not shown) and housing  707  that are analogous to heat-generating structure  401  and  501  and housing  407  and  507 / 508 . During use, the heat-generating structure cooled by system  700  may reach temperatures analogous to those described in the context of heat-generating structure(s)  401  and/or  501 . 
     Cooling system  700  includes MEMS cooling systems  710 A and  710 B (collectively or generically  710 ), heat spreader  720 , egress passageway  730 , inlets  740 A,  740 B,  740 C,  740 D,  740 E, and  740 F (collectively or generically  740 ), and egresses  750 A and  750 B (collectively or generically  750 ) that are analogous to cooling system  410 ,  510  and/or  610 , heat spreader  420  and/or  520 , egress passageway  430 ,  530  and/or  630 , inlets  440 ,  540  and/or  640 , and egress(es)  450 ,  550 , and/or  650 , respectively. MEMS cooling systems  710  may each be analogous to cooling system (i.e. tile)  300 . Each MEMS cooling system  710  may include cells, a heat spreader, and cover plate that are analogous to cells  301 , heat spreader  302 , and cover plate  306 . In some embodiments, heat spreader  720  may be omitted. In some embodiments, the heat-generating structure may be thermally connected to heat spreader  720  (e.g. may be located near the center of heat spreader  720 ). Thus, the heat-generating structure may, but need not, be offset from MEMS cooling systems  710 . MEMS cooling systems  710  include cooling elements configured to undergo vibrational motion when actuated to drive a fluid. MEMS cooling systems  710  may have a thickness analogous to those described for cooling systems  410  and  510 . 
     Inlets  740  and egresses  750  allow for an exchange in fluid (e.g. air) internal to housing  707  with fluid external to the device. For example, inlets  740  and egresses  750  may be vents. Although six inlets  740  and two egresses  750  are shown, in some embodiments, another number of inlet(s) and/or egress(es) may be present. For example, in some embodiments, inlets  740 E and  740 F are omitted. In some embodiments, omission of inlets  740 E and  740 F is desired. In such embodiments, more flow may be drawn in through remaining inlets  740 A,  740 B,  740 C, and/or  740 D. In some embodiments, side inlets  740 B and  740 C are the primary inlets for flow entrained in system  700 . Rear inlet  740 A may be desired to provide additional flow through the device. Egresses  750  may be in proximity to MEMS cooling system  710 . In some embodiments, egresses have an area that is of equal size or larger than the egresses of MEMS cooling systems  710  (e.g. not smaller than aperture  398 .) In some embodiments the cool air entering MEMS cooling system  710  as part of the direct flow is desired to not mix with the heated air being driven to egresses  750 . Thus, a gasket may be used on the side of MEMS cooling system  710  proximate to egresses  750 . This high flow may be desirable for cooling the heat-generating structure that is thermally connected to heat spreader  720 , for cooling other components (not shown), and/or for the blending and cooling of fluid exhaust. The function of inlets  740  and egresses  750  are analogous to that of inlets  440  and  540  and egresses  450  and  550 , respectively. 
     Cooling system  700  functions in a manner analogous to cooling system(s)  400 ,  500 A,  500 B,  500 C,  500 D,  500 E,  500 F, and/or  600 . Thus, cool fluid that enters the device via inlets  740 E and  740 F primarily flows through MEMS cooling systems  710 A and  710 B. The cool fluid may be the temperature of the ambient in which the device operates (e.g. 22-28° C.). The cool fluid is driven via MEMS cooling systems  710 . In so doing, heat is transferred from the heat-generating structure to the fluid. The heated fluid flows toward egresses  750 A and  750 B. In some embodiments, the heated fluid exiting MEMS cooling systems  710  has a temperature of at least sixty degrees Celsius. In some embodiments, the heated fluid exiting MEMS cooling systems  710  is at least sixty-five degrees Celsius. In some embodiments, the heated fluid exiting MEMS cooling systems  710  is at least seventy degrees Celsius. 
     The fluid driven by MEMS cooling systems  710  travels at high speeds and may develop a low pressure in various portions of the device (e.g. in egress passageway  730 ). Although termed an “egress passageway”, passageway  730  is between inlets  740  and egresses  750 . Thus, egress passageway  730  is not only between the exit of MEMS cooling system  710  and egresses  750 . Consequently, fluid is entrained into inlets  740 A,  740 B,  740 C, and  740 D. In the embodiment shown, the entrained fluid is from the ambient and thus may have a temperature similar to the fluid drawn into inlets  740 E and  740 F. The flow of cooler fluid through inlets  740 A,  740 B,  740 C, and  740 D is indicated by dashed arrows in  FIG.  7   . The flow of cool fluid through inlets  740 A,  740 B,  740 C, and  740 D as compared to the fluid flow from MEMS cooling systems  710  is analogous to that described for cooling systems  400 ,  500 A,  500 B,  500 C,  500 D,  500 E,  500 F, and/or  600 . For example, the fluid flow through inlets  740 A,  740 B,  740 C, and  740 D that does not pass through MEMS cooling systems  710  may be greater than the flow of fluid through MEMS cooling systems  710 . 
     Egress passageway  730  receives hot fluid from MEMS cooling systems  710  and the cool fluid from inlets  740 A,  740 B,  740 C, and  740 D. The hot fluid from MEMS cooling systems  710  mixes with the cooler fluid from inlet  740 B in egress passageway  730 . Thus, the hot fluid from MEMS cooling systems  710  is cooled. The flow of the mixture of the heated fluid from MEMS cooling systems  710  and cool fluid from inlets  740 A,  740 B,  740 C, and  740 D is shown by solid arrows in  FIG.  7   . The mixture of heated and cool fluid exits egress passageway via egresses  750 . Because cool fluid is mixed with hot fluid in egress passageway  730 , the mixture of fluid exiting via egresses  750  may have a significantly lower temperature than the hot fluid leaving MEMS cooling systems  710 . For example, the mixture of the hot air and the cool air at egresses  750  may have a temperature(s) in the ranges described for egresses  430  and/or  530 . In addition to cooling the hot fluid from MEMS cooling systems  710 , the cool air entrained through inlets  740 A,  740 B,  740 C, and  740 D may also be used to cool other components (not shown). 
     Cooling system  700  may improve thermal management of the device(s) in which cooling system  700  is incorporated. MEMS cooling systems  710  may provide efficient cooling in a low profile package. Further, entrainment provided via egress passageway  730  may provide higher flow and greater cooling. In addition, fluid used in cooling the device exits the device at a lower temperature. For example, fluid exiting egresses  750  may be 50-55° C. in some cases. Thus, the fluid is less likely to cause discomfort to or burn a user. Thus, performance of devices incorporating cooling system  700  may be improved. 
       FIG.  8    depicts a perspective view of an embodiment of active cooling system  800  that utilizes entrainment integrated into a device.  FIG.  8    is not to scale and for clarity, only some structures are shown. The device may be a laptop computer, a tablet or notebook computer, a smart phone, and/or other mobile device. Device may also be another device, such as a server in a rack, a game console, or a desktop computer. In some embodiments, therefore, the device is thin. For example, in some embodiments, the device has a thickness (height along the smallest dimension) analogous to those described for the devices of  FIGS.  4  and  5 A- 5 F . 
     Cooling system  800  and the device into which it is incorporated are analogous to cooling system(s)  400 ,  500 A,  500 B,  500 C,  500 D,  500 E,  500 F,  600  and/or  700  and the device that houses cooling system(s)  400 ,  500 A,  500 B,  500 C,  500 D,  500 E,  500 F,  600 , and/or  700 . The device into which cooling system  800  is integrated includes heat-generating structure(s) (not shown) and housing  807  that are analogous to heat-generating structure  401  and  501  and housing  407 ,  507 / 508 , and/or  707 . During use, the heat-generating structure cooled by system  800  may reach temperatures analogous to those described in the context of heat-generating structure(s)  401  and/or  501 . 
     Cooling system  800  is most analogous to cooling system  700 . Cooling system  800  includes MEMS cooling systems  810 A and  810 B (collectively or generically  810 ), heat spreader  820 , egress passageway  830 , inlets  840 A,  840 B, and  840 C (collectively or generically  840 ), and egresses  850 A and  850 B (collectively or generically  850 ) that are analogous to MEMS cooling systems  710  (and thus  410 ,  510  and/or  610 ), heat spreader  720  (and thus heat spreader  420 ,  520  and/or  620 ), egress passageway  730  (and thus  430 ,  530 , and/or  630 ), inlets  740  (and thus  440 ,  540 , and/or  640 ), and egresses  750  (and thus  450 ,  550 , and/or  650 ), respectively. However, cooling system  800  omits inlets that would be analogous to inlets  740 E and  740 F. As a result, cool air driven by MEMS cooling systems  810  is drawn in through the inlets  840 . The absence of inlets under MEMS cooling systems  810  may increase the flow through inlets  840 . A back inlet analogous to inlet  740 D has also been omitted. 
     MEMS cooling systems  810  may each be analogous to cooling system  300 . MEMS cooling system  810  may each include cells, a heat spreader and a cover plate that are analogous to cells  301 , heat spreader  302 , and cover plate  306 . In some embodiments, heat spreader  820  may be omitted. In some embodiments, the heat-generating structure may be thermally connected to heat spreader  820  (e.g. may be located near the center of heat spreader  820 ). Thus, the heat-generating structure may, but need not, be offset from MEMS cooling systems  810 . MEMS cooling systems  810  include cooling elements configured to undergo vibrational motion when actuated to drive a fluid. MEMS cooling systems  810  may have a thickness analogous to those described for cooling systems  410  and  510 . 
     Inlets  840  and egresses  850  allow for an exchange in fluid (e.g. air) internal to housing  807  with fluid external to the device. For example, inlets  840  and egresses  850  may be vents. Although three inlets  840  and two egresses  850  are shown, in some embodiments, another number of inlet(s) and/or egress(es) may be present. Flow is drawn in through inlets  840 A,  840 B, and/or  840 C. This high flow may be desirable for cooling the heat-generating structure that is thermally connected to heat spreader  820 , for cooling other components (not shown), and/or for the blending and cooling of fluid exhaust. The function of inlets  840  and egresses  850  are analogous to that of inlets  740  and egresses  750 , respectively. 
     Cooling system  800  functions in a manner analogous to cooling system(s)  400 ,  500 A,  500 B,  500 C,  500 D,  500 E,  500 F,  600  and/or  700 . Cool fluid enters the device via inlets  840 A,  840 B, and  840 C. Some of the flow is driven through MEMS cooling systems  810 A and  810 B. The cool fluid entering via inlets  840 A,  840 B, and  840 C may be the temperature of the ambient in which the device operates (e.g. 22-28° C.). The cool fluid is denoted by dashed arrows in  FIG.  8   . Some of this cool fluid is driven through MEMS cooling systems  810 . In so doing, heat is transferred from the heat-generating structure to the fluid. The heated fluid flows toward egresses  850 A and  850 B. In some embodiments, the heated fluid exiting MEMS cooling systems  810  has a temperature of at least sixty degrees Celsius. In some embodiments, the heated fluid exiting MEMS cooling systems  810  is at least sixty-five degrees Celsius. In some embodiments, the heated fluid exiting MEMS cooling systems  810  is at least seventy degrees Celsius. 
     The fluid driven by MEMS cooling systems  810  travels at high speeds and may develop a low pressure, for example in egress passageway  830 . Although termed an “egress passageway”, passageway  830  is between inlets  840  and egresses  850 . Thus, egress passageway  830  is not only between the exit of MEMS cooling system  810  and egresses  850 . Consequently, fluid is entrained into inlets  840 . Although some of the cool fluid entering via inlets  840  is driven by MEMS cooling systems  810 , some of the entrained cool fluid does not pass through MEMS cooling systems  810 . Some of the cool fluid cools other portions of the device and/or mixes with the hot fluid exiting MEMS cooling systems  810 . The flow of cool fluid through inlets  840  that does not pass through MEMS cooling system  810  as compared to the fluid flow from MEMS cooling systems  810  is analogous to that described for cooling systems  400 ,  500 A,  500 B,  500 C,  500 D,  500 E, and/or  500 F. For example, the fluid flow through inlets  840  that does not pass through MEMS cooling systems  810  may be greater than the flow of fluid through MEMS cooling systems  810 . 
     Egress passageway  830  receives hot fluid from MEMS cooling systems  810  and the cool fluid from inlets  840  that is not driven by MEMS cooling systems  810 . The hot fluid from MEMS cooling systems  810  mixes with the cooler fluid in egress passageway  830 . Thus, the hot fluid from MEMS cooling systems  810  is cooled. The flow of the mixture of the heated fluid from MEMS cooling systems  810  and cool fluid from inlets  840  is shown by solid arrows in  FIG.  8   . The mixture of heated and cool fluid exits egress passageway via egresses  850 . Because cool fluid is mixed with hot fluid in egress passageway  830 , the mixture of fluid exiting via egresses  850  may have a significantly lower temperature than the hot fluid leaving MEMS cooling systems  810 . For example, the mixture of the hot air and the cool air at egresses  850  may have a temperature(s) in the ranges described for egresses  430  and/or  530 . 
     Cooling system  800  may improve thermal management of the device(s) in which cooling system  800  is incorporated. MEMS cooling systems  810  may provide efficient cooling in a low profile package. Further, entrainment provided via egress passageway  830  may provide higher flow and greater cooling. In addition, fluid used in cooling the device exits the device at a lower temperature. For example, fluid exiting egresses  850  may be 50-55° C. in some cases. Thus, the fluid is less likely to cause discomfort to or burn a user. Thus, performance of devices incorporating cooling system  800  may be improved. 
       FIG.  9    depicts a perspective view of an embodiment of active cooling system  900  that utilizes entrainment integrated into a device.  FIG.  9    is not to scale and for clarity, only some structures are shown. The device may be a laptop computer, a tablet or notebook computer, a smart phone, and/or other mobile device. Device may also be another device, such as a server in a rack, a game console, or a desktop computer. In some embodiments, therefore, the device is thin. For example, in some embodiments, the device has a thickness (height along the smallest dimension) analogous to those described for the devices of  FIGS.  4  and  5 A- 5 F . 
     Cooling system  900  and the device into which it is incorporated are analogous to cooling system(s)  400 ,  500 A,  500 B,  500 C,  500 D,  500 E,  500 F,  600 ,  700 , and/or  800  and the device that houses cooling system(s)  400 ,  500 A,  500 B,  500 C,  500 D,  500 E,  500 F,  600 ,  700 , and/or  800 . The device into which cooling system  900  is integrated includes heat-generating structure(s) (not shown) and housing  907  that are analogous to heat-generating structure  401  and  501  and housing  407 ,  507 / 508 ,  707 , and/or  807 . During use, the heat-generating structure cooled by system  900  may reach temperatures analogous to those described in the context of heat-generating structure(s)  401  and/or  501 . 
     Cooling system  900  is most analogous to cooling systems  700  and  800 . Cooling system  900  includes MEMS cooling systems  910 A and  910 B (collectively or generically  910 ), heat spreader  920 , egress passageway  930 , inlets  940 B,  940 C, and  940 D (collectively or generically  940 ), and egresses  950 A and  950 B (collectively or generically  950 ) that are analogous to MEMS cooling systems  710  and  810 , heat spreader  720  and  820 , egress passageway  730  and  830 , inlets  740  and  840 , and egresses  750  and  850 , respectively. However, cooling system  900  omits inlets that would be analogous to inlets  740 E and  740 F. As a result, cool air driven by MEMS cooling systems  910  is drawn in through the inlets  940 . The absence of inlets under MEMS cooling systems  910  may increase the flow through inlets  940 . A front inlet analogous to inlet  740 A has also been omitted. 
     MEMS cooling systems  910  may each be analogous to cooling system  300 . MEMS cooling system  910  may each include cells, a heat spreader and a cover plate that are analogous to cells  301 , heat spreader  302 , and cover plate  306 . In some embodiments, heat spreader  920  may be omitted. In some embodiments, the heat-generating structure may be thermally connected to heat spreader  920  (e.g. may be located near the center of heat spreader  920 ). Thus, the heat-generating structure may, but need not, be offset from MEMS cooling systems  910 . MEMS cooling systems  910  include cooling elements configured to undergo vibrational motion when actuated to drive a fluid. MEMS cooling systems  910  may have a thickness analogous to those described for cooling systems  410  and  510 . 
     Inlets  940  and egresses  950  allow for an exchange in fluid (e.g. air) internal to housing  907  with fluid external to the device. For example, inlets  940  and egresses  950  may be vents. Although three inlets  940  and two egresses  950  are shown, in some embodiments, another number of inlet(s) and/or egress(es) may be present. Flow is drawn in through inlets  940 . This high flow may be desirable for cooling the heat-generating structure that is thermally connected to heat spreader  920 , for cooling other components (not shown), and/or for the blending and cooling of fluid exhaust. The function of inlets  940  and egresses  950  are analogous to that of inlets  740  and  840  and egresses  750  and  850 . 
     Cooling system  900  functions in a manner analogous to cooling system(s)  400 ,  500 A,  500 B,  500 C,  500 D,  500 E,  500 F,  600 ,  700  and/or  800 . Cool fluid enters the device via inlets  940 B,  940 C, and  940 D. Some of the flow is driven through MEMS cooling systems  910 A and  910 B. The cool fluid entering via inlets  940  may be the temperature of the ambient in which the device operates (e.g. 22-28° C.). The cool fluid is denoted by dashed arrows in  FIG.  9   . Some of this cool fluid is driven through MEMS cooling systems  910 . In so doing, heat is transferred from the heat-generating structure to the fluid. The heated fluid flows toward egresses  950 A and  950 B. In some embodiments, the heated fluid exiting MEMS cooling systems  910  has a temperature of at least sixty degrees Celsius. In some embodiments, the heated fluid exiting MEMS cooling systems  910  is at least sixty-five degrees Celsius. In some embodiments, the heated fluid exiting MEMS cooling systems  910  is at least seventy degrees Celsius. 
     The fluid driven by MEMS cooling systems  910  travels at high speeds and may develop a low pressure, for example in egress passageway  930 . Although termed an “egress passageway”, passageway  930  is between inlets  940  and egresses  950 . Thus, egress passageway  930  is not only between the exit of MEMS cooling system  910  and egresses  950 . Consequently, fluid is entrained into inlets  940 . Although some of the cool fluid entering via inlets  940  is driven by MEMS cooling systems  910 , some of the entrained cool fluid does not pass through MEMS cooling systems  910 . Some of the cool fluid cools other portions of the device and/or mixes with the hot fluid exiting MEMS cooling systems  910 . The flow of cool fluid through inlets  940  that does not pass through MEMS cooling system  910  as compared to the fluid flow from MEMS cooling systems  910  is analogous to that described for cooling systems  400 ,  500 A,  500 B,  500 C,  500 D,  500 E,  500 F,  600 ,  700 , and/or  800 . For example, the fluid flow through inlets  940  that does not pass through MEMS cooling systems  910  may be greater than the flow of fluid through MEMS cooling systems  910 . 
     Egress passageway  930  receives hot fluid from MEMS cooling systems  910  and the cool fluid from inlets  940  that is not driven by MEMS cooling systems  910 . The hot fluid from MEMS cooling systems  910  mixes with the cooler fluid in egress passageway  930 . Thus, the hot fluid from MEMS cooling systems  910  is cooled. The flow of the mixture of the heated fluid from MEMS cooling systems  910  and cool fluid from inlets  940  is shown by solid arrows in  FIG.  9   . The mixture of heated and cool fluid exits egress passageway via egresses  950 . Because cool fluid is mixed with hot fluid in egress passageway  930 , the mixture of fluid exiting via egresses  950  may have a significantly lower temperature than the hot fluid leaving MEMS cooling systems  910 . For example, the mixture of the hot air and the cool air at egresses  950  may have a temperature(s) in the ranges described for egresses  430  and/or  530 . 
     Cooling system  900  may improve thermal management of the device(s) in which cooling system  900  is incorporated. MEMS cooling systems  910  may provide efficient cooling in a low profile package. Further, entrainment provided via egress passageway  930  may provide higher flow and greater cooling. In addition, fluid used in cooling the device exits the device at a lower temperature. For example, fluid exiting egresses  950  may be 50-55° C. in some cases. Thus, the fluid is less likely to cause discomfort to or burn a user. Thus, performance of devices incorporating cooling system  900  may be improved. 
       FIGS.  10 A- 10 B  depict perspective views of an embodiment of active cooling system  1000  that utilizes entrainment integrated into a device.  FIGS.  10 A and  10 B  are not to scale and for clarity, only some structures are shown.  FIG.  10 A  depicts fluid flow generally, while  FIG.  10 B  indicates the temperatures of fluid in various portions of the device. The device may be a laptop computer, a tablet or notebook computer, a smart phone, and/or other mobile device. Device may also be another device, such as a server in a rack, a game console, or a desktop computer. In some embodiments, therefore, the device is thin. For example, in some embodiments, the device has a thickness (height along the smallest dimension) analogous to those described for the devices of  FIGS.  4  and  5 A- 5 F . 
     Cooling system  1000  and the device into which it is incorporated are analogous to cooling system(s)  400 ,  500 A,  500 B,  500 C,  500 D,  500 E,  500 F,  600 ,  700 ,  800 , and/or  900  and the device that houses cooling system(s)  400 ,  500 A,  500 B,  500 C,  500 D,  500 E,  500 F,  600 ,  700 ,  800 , and/or  900 . The device into which cooling system  1000  is integrated includes heat-generating structure(s) (not shown) and housing  1007  that are analogous to heat-generating structure  401  and  501  and housing  407 ,  507 / 508 ,  707 ,  807 , and/or  907 . During use, the heat-generating structure cooled by system  1000  may reach temperatures analogous to those described in the context of heat-generating structure(s)  401  and/or  501 . 
     Cooling system  1000  is most analogous to cooling systems  700 ,  800  and  900 . Cooling system  1000  includes MEMS cooling systems  1010 A and  1010 B (collectively or generically  1010 ), heat spreader  1020 , egress passageway  1030 , inlets  1040 A,  1040 B,  1040 C, and  1040 D (collectively or generically  1040 ), and egresses  1050 A and  1050 B (collectively or generically  1050 ) that are analogous to MEMS cooling systems  710 ,  810  and  910 ; heat spreader  720 ,  820 , and  920 ; egress passageway  730 ,  830  and  930 ; inlets  740 ,  840 , and  940 ; and egresses  750 ,  850 , and  950 , respectively. However, cooling system  1000  omits inlets that would be analogous to inlets  740 E and  740 F. As a result, cool air driven by MEMS cooling systems  1010  is drawn in through the inlets  1040 . The absence of inlets under MEMS cooling systems  1010  may increase the flow through inlets  1040 . 
     MEMS cooling systems  1010  may each be analogous to cooling system  300 . MEMS cooling system  1010  may each include cells, a heat spreader and a cover plate that are analogous to cells  301 , heat spreader  302 , and cover plate  306 . In some embodiments, heat spreader  1020  may be omitted. In some embodiments, the heat-generating structure may be thermally connected to heat spreader  1020  (e.g. may be located near the center of heat spreader  1020 ). Thus, the heat-generating structure may, but need not, be offset from MEMS cooling systems  1010 . MEMS cooling systems  1010  include cooling elements configured to undergo vibrational motion when actuated to drive a fluid. MEMS cooling systems  1010  may have a thickness analogous to those described for cooling systems  410  and  510 . 
     Inlets  1040  and egresses  1050  allow for an exchange in fluid (e.g. air) internal to housing  1007  with fluid external to the device. For example, inlets  1040  and egresses  1050  may be vents. Although four inlets  1040  and two egresses  1050  are shown, in some embodiments, another number of inlet(s) and/or egress(es) may be present. Flow is drawn in through inlets  1040 . This high flow may be desirable for cooling the heat-generating structure that is thermally connected to heat spreader  1020 , for cooling other components (not shown), and/or for the blending and cooling of fluid exhaust. The function of inlets  1040  and egresses  1050  are analogous to that of inlets  740 ,  840  and  940  and egresses  750 ,  850 , and  950 . 
     Cooling system  1000  functions in a manner analogous to cooling system(s)  400 ,  500 A,  500 B,  500 C,  500 D,  500 E,  500 F,  600 ,  700 ,  800  and/or  900 . Cool fluid enters the device via inlets  1040 A,  1040 B,  1040 C, and  1040 D. Some of the flow is driven through MEMS cooling systems  1010 A and  1010 B. The cool fluid entering via inlets  1040  may be the temperature of the ambient in which the device operates (e.g. 22-28° C.). The cool fluid is denoted by dashed arrows in  FIG.  10 A . Some of this cool fluid is driven through MEMS cooling systems  1010 . In so doing, heat is transferred from the heat-generating structure to the fluid. The heated fluid flows toward egresses  1050 A and  1050 B. In some embodiments, the heated fluid exiting MEMS cooling systems  1010  has a temperature of at least sixty degrees Celsius. In some embodiments, the heated fluid exiting MEMS cooling systems  1010  is at least sixty-five degrees Celsius. In some embodiments, the heated fluid exiting MEMS cooling systems  1010  is at least seventy degrees Celsius. 
     The fluid driven by MEMS cooling systems  1010  travels at high speeds and may develop a low pressure, for example in egress passageway  1030 . Although termed an “egress passageway”, passageway  1030  is between inlets  1040  and egresses  1050 . Thus, egress passageway  1030  is not only between the exit of MEMS cooling system  1010  and egresses  1050 . Consequently, fluid is entrained into inlets  1040 . Although some of the cool fluid entering via inlets  1040  is driven by MEMS cooling systems  1010 , some of the entrained cool fluid does not pass through MEMS cooling systems  1010 . Some of the cool fluid cools other portions of the device and/or mixes with the hot fluid exiting MEMS cooling systems  1010 . The flow of cool fluid through inlets  1040  that does not pass through MEMS cooling system  1010  as compared to the fluid flow from MEMS cooling systems  1010  is analogous to that described for cooling systems  400 ,  500 A,  500 B,  500 C,  500 D,  500 E,  500 F,  600 ,  700 ,  800 , and/or  900 . For example, the fluid flow through inlets  1040  that does not pass through MEMS cooling systems  1010  may be greater than the flow of fluid through MEMS cooling systems  1010 . 
     Egress passageway  1030  receives hot fluid from MEMS cooling systems  1010  and the cool fluid from inlets  1040  that is not driven by MEMS cooling systems  1010 . The hot fluid from MEMS cooling systems  1010  mixes with the cooler fluid in egress passageway  1030 . Thus, the hot fluid from MEMS cooling systems  1010  is cooled. The flow of the mixture of the heated fluid from MEMS cooling systems  1010  and cool fluid from inlets  1040  is shown by solid arrows in  FIG.  10 A . The mixture of heated and cool fluid exits egress passageway via egresses  1050 . Because cool fluid is mixed with hot fluid in egress passageway  1030 , the mixture of fluid exiting via egresses  1050  may have a significantly lower temperature than the hot fluid leaving MEMS cooling systems  1010 . For example, the mixture of the hot air and the cool air at egresses  1050  may have a temperature(s) in the ranges described for egresses  430  and/or  530 . 
     The temperatures of the fluid flowing through inlets  1040 , egress passageway  1030 , and egresses  1050  may also be seen in  FIG.  10 B . Cool fluid having the lower temperatures indicated enters the device via inlets  1040 . The fluid is heated slightly as it traverses the interior of the device. However, the fluid is cooler than MEMS cooling systems  1010 . At least some of the fluid from inlets  1040 A,  1040 B, and  1040 C is driven through MEMS cooling systems  1010 . As indicated in  FIG.  10 B , the temperature of fluid exiting MEMS cooling systems  1010  may be greater than seventy degrees Celsius. As indicated by arrows in  FIG.  10 B , some of the fluid entering via inlet  1040 D returns directly toward egresses  1050 , mixing with the hot fluid from MEMS cooling systems  1010 . Some fluid from inlets  1040 A,  1040 B, and  1040 C also mixes with the heated fluid from MEMS cooling systems  1010 . Thus, the heated fluid is cooled. Fluid exiting egresses  1050  have a reduced temperature. 
     Cooling system  1000  may improve thermal management of the device(s) in which cooling system  1000  is incorporated. MEMS cooling systems  1010  may provide efficient cooling in a low profile package. Further, entrainment provided via egress passageway  1030  may provide higher flow and greater cooling. In addition, fluid used in cooling the device exits the device at a lower temperature. For example, fluid exiting egresses  1050  may be 50-55° C. or less in some cases. Thus, the fluid is less likely to cause discomfort to or burn a user. Thus, performance of devices incorporating cooling system  1000  may be improved. 
       FIG.  11    depicts an embodiment of active cooling system  1100  that utilizes entrainment integrated into a device.  FIG.  11    IS not to scale and for clarity, only some structures are shown.  FIG.  11    depicts fluid flow outside of the device and indicates the temperatures of the fluid device. The device may be a laptop computer, a tablet or notebook computer, a smart phone, and/or other mobile device. Device may also be another device, such as a server in a rack, a game console, or a desktop computer. In some embodiments, therefore, the device is thin. For example, in some embodiments, the device has a thickness (height along the smallest dimension) analogous to those described for the devices of  FIGS.  4  and  5 A- 5 F . 
     Cooling system  1100  and the device into which it is incorporated are analogous to cooling system(s)  400 ,  500 A,  500 B,  500 C,  500 D,  500 E,  500 F,  600 ,  700 ,  800 ,  900 , and/or  1100  and the device that houses cooling system(s)  400 ,  500 A,  500 B,  500 C,  500 D,  500 E,  500 F,  600 ,  700 ,  800 ,  900 , and/or  1000 . The device into which cooling system  1100  is integrated includes heat-generating structure(s) (not shown) and housing  1107  that are analogous to heat-generating structure  401  and  501  and housing  407 ,  507 / 508 ,  707 ,  807 ,  907 , and/or  1007 . During use, the heat-generating structure cooled by system  1100  may reach temperatures analogous to those described in the context of heat-generating structure(s)  401  and/or  501 . 
     Cooling system  1100  is most analogous to cooling systems  700 ,  800 ,  900  and  1000 . Cooling system  1100  includes MEMS cooling systems  1110 A and  1110 B (collectively or generically  1110 ), heat spreader  1120 , egress passageway  1130 , inlets  1140 A,  1140 B,  1140 C,  1140 D, and  1140 E (collectively or generically  1140 ), and a single egress  1150  (i.e. through a rear vent) that are analogous to MEMS cooling systems  710 ,  810  and  910 ; heat spreader  720 ,  820 , and  920 ; egress passageway  730 ,  830  and  930 ; inlets  740 ,  840 , and  940 ; and egresses  750 ,  850 , and  950 , respectively. However, cooling system  1100  omits inlets that would be analogous to inlets  740 E and  740 F, includes two rear inlets  1140 D and  1140 E, and includes a single egress  1150 . As a result, cool air driven by MEMS cooling systems  1110  is drawn in through the inlets  1140 . The absence of inlets under MEMS cooling systems  1110  may increase the flow through inlets  1140 . 
     Cooling system  1100  functions in a manner analogous to cooling system  1000 . Cool fluid is drawn in through inlets  1140 . This high flow may be desirable for cooling the heat-generating structure that is thermally connected to heat spreader  1120 , for cooling other components (not shown), and/or for the blending and cooling of fluid exhaust. The cool fluid entering via inlets  1140  may be the temperature of the ambient in which the device operates (e.g. 22-28° C.). Some of this cool fluid is driven through MEMS cooling systems  1110 . In so doing, heat is transferred from the heat-generating structure to the fluid. The heated fluid flows toward egress  1150 . Cool fluid entering via inlets  1140  that is not driven through MEMS cooling systems  1110  may be used to cool other components, cool heat spreader  1120 , and/or mix with the heated fluid exiting MEMS cooling systems  1110 . Because cool fluid is mixed with hot fluid in egress passageway  1130 , the mixture of fluid exiting via egresses  1150  may have a significantly lower temperature than the hot fluid leaving MEMS cooling systems  1110 . For example, the mixture of the hot air and the cool air at egresses  1150  may have a temperature(s) in the ranges described for egresses  430  and/or  530 . 
     Cooling system  1100  may improve thermal management of the device(s) in which cooling system  1100  is incorporated. MEMS cooling systems  1110  may provide efficient cooling in a low profile package. Further, entrainment provided via egress passageway  1130  may provide higher flow and greater cooling. In addition, fluid used in cooling the device exits the device at a lower temperature. For example, fluid exiting egresses  1150  may be 50-55° C. or less in some cases. Thus, the fluid is less likely to cause discomfort to or burn a user. Thus, performance of devices incorporating cooling system  1100  may be improved. 
       FIG.  12    depicts an embodiment of method  1200  for providing an active cooling system that utilizes entrainment. Method  1200  may include steps that are not depicted for simplicity. Method  1200  is described in the context of system  400 . However, method  1200  may be used with other cooling systems including but not limited to systems  100 ,  200 ,  300 ,  500 A,  500 B,  500 C,  500 D,  500 E,  500 F,  600 ,  700 ,  800 ,  900 ,  1000  and/or  1100  and cells described herein. Method  1200  is also described in the context of forming a single system. However, method  1200  may be used to fabricate multiple systems substantially in parallel. 
     The MEMS cooling system is provided, at  1202 .  1202  includes providing cooling element(s), top plate(s), orifice plate(s), pedestal(s), heat spreader(s), cover plate(s), and/or other portions of the MEMS cooling system. In some embodiments, multiple MEMS cooling systems are fabricated at  1202 . The inlet(s) are provided, at  1204 . In some embodiments,  1204  includes fabricating inlets in the device with which MEMS cooling system(s) are to be used. The egress(es) and egress passageways are provided, at  1206 . In some embodiments,  1206  includes configuring portions of the device in which the MEMS cooling system(s) are incorporated. 
     The MEMS cooling system(s), inlet(s) egress passageway(s), are integrated into the device including heat-generating structure(s), at  1208 . 
     For example, MEMS cooling system  410  may be provided, at  1202 . Inlets  440 A and  440 B and egress  450  may be fabricated at  1204  and  1206 , respectively. System  400  may be integrated into a computing or other device, at  1208 . For example MEMS cooling system  400  may be attached to heat spreader  420  and aligned with inlet  440 A. The distances between inlets  440 , egress  450 , and size of egress passageway  430  may also be configured. Thus, cooling system(s)  400 ,  500 A,  500 B,  500 C,  500 D,  500 E,  500 F,  600 ,  700 ,  800 ,  900 ,  1000  and/or  1100  may be provided and used in a device. Thus, the benefits described herein may be achieved. 
       FIG.  13    depicts an embodiment of method  1300  for using an active cooling system that utilizes entrainment. Method  1300  may include steps that are not depicted for simplicity. Method  1300  is described in the context of system  400 . However, method  1300  may be used with other cooling systems including but not limited to systems and cells described herein. 
     A driving signal at a frequency and an input voltage corresponding to the resonant state of one or more cooling elements is provided to the active MEMS cooling system, at  1302 . In some embodiments, a driving signal having the frequency corresponding to the resonant frequency of a specific cooling element is provided to that cooling element. In some embodiments, a driving signal is provided to multiple cooling elements. In such embodiments, the frequency of the driving signal corresponds to the resonant state of one or more cooling elements being driven, a statistical measure of the resonance, and/or within a threshold of the resonance as discussed above. The MEMS cooling system is utilized in conjunction with an egress passageway and egresses. Thus, activation of the MEMS cooling system at  1302  also entrains fluid into the device. This cooled fluid is mixed with heated fluid driven through the MEMS cooling system. Thus, the mixture of fluid leaving the egress has a reduced temperature. The entrained fluid may also be used to cool other components of the device. 
     Characteristic(s) of the MEMS cooling system are monitored while the cooling element(s) are driven to provide a feedback signal corresponding to a proximity to a resonant state of the cooling element(s), at  1304 . In some embodiments, characteristic(s) of each individual cooling element are monitored to determine the deviation of the frequency of vibration for that cooling element from the resonant frequency of that cooling element. In some embodiments, characteristic(s) for multiple cooling elements are monitored at  1304 . The characteristic(s) monitored may be a proxy for resonance and/or a deviation therefrom. For example, the voltage at the cooling element, the power drawn by the cooling element, power output by the power source, peak-to-peak current output by the power source, peak voltage output by the power source, average current output by the power source, RMS current output by the power source, average voltage output by the power source, amplitude of displacement of the at least one cooling element, RMS current through the cooling element, peak voltage at the cooling element, average current through the at cooling element, average voltage at the at least one cooling element, and/or the peak current drawn by the cooling element may be monitored. Using the characteristic(s) monitored, a deviation from the resonant state of the cooling element (e.g. of the driving/vibration frequency the deviation from the resonant frequency) may be determined. 
     The frequency and/or input voltage is adjusted based on the feedback signal, at  1306 . More specifically,  1306  includes updating the frequency and/or input voltage, based on the feedback signal, to correspond to resonant state(s) of the cooling element(s) at  1306 . For example, the frequency for the drive signal may be updated to more closely match the resonant frequency/frequencies. In some embodiments, updating the frequency includes changing the frequency to correspond to a power drawn corresponding to the vibration of the cooling element(s) being maximized, a voltage provided at the cooling element(s) being maximized, a voltage across the cooling element(s) being minimized, and/or an amplitude of a current drawn by the at least one cooling element being minimized. In some embodiments,  1306  includes determining whether the feedback signal indicates that a drift in the resonant frequency of the cooling element(s) exceeds a threshold and identifying a new frequency in response to a determination that the drift exceeds the threshold. The new frequency accounts for the drift in the resonant frequency. The method also includes setting the new frequency as the frequency for the driving signal in response to the new frequency being identified. 
     For example, cooling elements in MEMS cooling system  410  are driven, at  1302 . Thus, the cooling elements in MEMS cooling system  410  are driven at a frequency that is at or near resonance for one or more of the cooling elements. Characteristics of the cooling elements within MEMS cooling system  410  are monitored, at  1304 . Thus, the drift of the cooling element(s) from resonance may be determined. The frequency may be adjusted based on the monitoring of  1304 , at  1306 . Thus, MEMS cooling system  410  may be kept at or near resonance. 
     Thus, using method  1300 , an active cooling system, such as cooling system(s)  100 ,  200 ,  300 ,  410 ,  510 ,  610 ,  710 ,  810 ,  910 ,  1010  and/or  1110  may be efficiently driven. These cooling systems may entrain fluid, which can be used to cool other components and/or the exhaust that egresses from the devices. Further, because the characteristic(s) of the MEMS cooling system are monitored, drifts in the resonant frequency may be discovered and accounted for. Thus, method  1300  may be used to operate active MEMS cooling systems and achieve the benefits described herein. 
     Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed embodiments are illustrative and not restrictive.