Designed actuators useful in MEMS active cooling devices

Abstract

A mover is described that can be used in a cooling system. The mover includes an anchor region and a cantilever. The cantilever extends outward from the anchor region. The cantilever includes a step region, an extension region, and an outer region. The step region extends outward from the anchor region and has a step thickness. The extension region extends outward from the step region and has an extension thickness that is less than the step thickness. The outer region extends outward from the extension region and has an outer thickness that is greater than the extension thickness.

Description

[0001] This application is a continuation of PCT Patent Application No. PCT / US2020 / 057760 (International Filing Date: 28 October 2020, Priority Date: 06 December 2019, International Publication Number: WO 2021 / 112977) “Engineered Actuators Useful in MEMS Active Cooling Devices,” entered into the Chinese National Phase on September 30, 2021.

[0002] Cross Reference to Related Applications

[0003] This application is a continuation-in-part of pending U.S. Patent Application No. 16 / 915,912, filed June 29, 2020, entitled CENTRALLY PINNED MEMS-BASED PIEZOELECTRIC COOLING SYSTEM, which claims priority to U.S. Provisional Patent Application No. 62 / 945,001, filed December 6, 2019, entitled CENTRALLY ANCHORED MEMS-BASED ACTIVE COOLING SYSTEMS, both of which are incorporated herein by reference for all purposes. BACKGROUND

[0004] As computing devices increase in speed and computational power, the heat generated by the computing devices also increases. Various mechanisms are proposed to address the generation of heat. Active devices, such as fans, can be used to drive air through larger computing devices, such as laptops or desktop computers. Passive cooling devices, such as heat sinks, can be used in smaller mobile computing devices, such as smartphones, virtual reality devices, and tablets. However, such active and passive devices can not adequately cool both mobile devices, such as smartphones, and larger devices, such as laptops and desktop computers. Thus, additional cooling solutions for computing devices are desired. BRIEF DESCRIPTION OF DRAWINGS

[0005] Various embodiments of the application are disclosed in the following detailed description and the accompanying drawings.

[0006] Figures 1A-1F Embodiments of active cooling systems including engineered actuators are depicted.

[0007] Figures 2A-2E Performance metrics for embodiments of actuators useful in active cooling systems including centrally anchored cooling elements are depicted.

[0008] Figures 3A-3D Embodiments of actuators useful in active cooling systems including centrally anchored cooling elements are depicted.

[0009] Figures 4A-4B An embodiment of an active cooling system including a designed actuator is depicted.

[0010] Figure 5 An embodiment of a designed actuator is depicted.

[0011] Figures 6A-6B An embodiment of a designed actuator is depicted.

[0012] Figures 7-13 An embodiment of a designed actuator is depicted.

[0013] Figures 14A-14B An embodiment of a designed actuator is depicted.

[0014] Figures 15A-15B An embodiment of an active cooling system including a plurality of cooling units configured as tiles and using a designed actuator is depicted.

[0015] Figure 16 An embodiment of an active cooling system including a plurality of cooling units is depicted.

[0016] Figure 17 is a flowchart depicting an embodiment of a technique for driving an actuator. DETAILED DESCRIPTION

[0017] The application can be implemented in numerous ways, including as a process; an apparatus; a system; a composition of matter; a computer program product; 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 application can take, can be referred to as techniques. Generally, the order of the steps of disclosed processes can be altered, unless otherwise specified. Unless otherwise specified, elements of a description that are configured to perform tasks can be implemented as one or more of a general purpose construct such as a processor or memory configured to perform the task during a given time, a special purpose construct specifically manufactured to perform the task, and / or a combination of general purpose constructs and special purpose constructs. 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.

[0018] A detailed description of one or more embodiments of the application is provided with reference to the accompanying drawings below. The application is described in connection with such embodiments, but the application is not limited to any embodiment. The scope of the application is limited only by the claims and the application 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 application. These details are provided for the purpose of example and the application can 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 application has not been described in detail so that the application is not unnecessarily obscured.

[0019] As semiconductor devices become more powerful, the heat generated during operation also increases. For example, processors used in mobile devices such as smartphones, tablets, notebook computers, and virtual reality devices can operate at high clock speeds, but generate a large amount of heat. Due to the generated heat, the processor can only run at full speed for a relatively short period of time. After this time expires, throttling (e.g., the processor clock speed is slowed down) occurs. While throttling can reduce the generation of heat, it also adversely affects the processor speed, and thus the performance of the device using the processor. This problem is expected to worsen as technology progresses to 5G and beyond.

[0020] Larger devices such as laptops or desktop computers include electric fans with rotating blades. The fan can be powered on in response to an increase in the temperature of internal components. The fan drives air through the larger device to cool the internal components. However, such fans are typically too large for mobile devices such as smartphones or thinner devices such as tablets. The fan can also have limited efficacy due to the air boundary layer present at the surface of the components, providing limited air speed for airflow across the hot surface to be cooled, and can generate excessive noise. Passive cooling solutions can include components such as heat sinks and heat pipes or vapor chambers to transfer heat to a heat exchanger. While heat sinks alleviate temperature increases at hot spots to some extent, the heat generated in current and future devices can not be adequately addressed. Similarly, heat pipes or vapor chambers can provide insufficient amounts of heat transfer to remove the excess heat generated. Thus, additional cooling solutions that can be used with smaller mobile devices as well as larger devices are desirable.

[0021] While described in the context of cooling systems, the techniques and / or devices described herein can be used in other applications. For example, the actuators can be used in other applications. Further, the devices are described in the context of a centrally anchored actuator (i.e., cooling element). However, in some embodiments, the actuator can be edge anchored. In some such embodiments, only a portion (e.g., half) of the actuator can be utilized.

[0022] A mover usable in a cooling system is described. The mover includes an anchor region and a cantilever. The cantilever extends outwardly from the anchor region. The cantilever includes a step region, an extension region, and an outer region. The step region extends outwardly from the anchor region and has a step thickness. The extension region extends outwardly from the step region and has an extension thickness that is less than the step thickness. The outer region extends outwardly from the extension region and has an outer thickness that is greater than the extension thickness. In some embodiments, the outer thickness is at least fifty microns thicker than the extension thickness and no more than two hundred microns thicker. The outer region can have a width of at least one hundred microns and no more than three hundred microns. In some embodiments, the extension region has a length extending outwardly from the step region of at least 0.5 millimeters and no more than 1.5 millimeters.

[0023] In some embodiments, the cantilever further includes an additional step region between the step region and the extension region. The additional step region has an additional step thickness that is less than the step thickness and greater than the extension thickness.

[0024] In some embodiments, at least one of the step region, the extension region, and the outer region of the mover includes a recess therein. The recess includes a taper such that a width of the recess increases with distance from the anchor region. For example, the taper can be selected from a linear taper, a quadratic taper, and a cubic taper. Other tapers are possible. In some embodiments, the mover includes a cover configured such that the recess is internal to the mover.

[0025] In some embodiments, the mover includes an additional cantilever. The additional cantilever extends outwardly from the anchor region opposite the cantilever. The additional cantilever includes an additional step region, an extension region, and an outer region. The additional step region has an additional step thickness. The additional extension region extends outwardly from the additional step region and has an additional extension thickness that is less than the additional step thickness. The additional outer region extends outwardly from the additional extension region and has an additional outer thickness that is greater than the additional extension thickness.

[0026] The mover can be used as a cooling element in a cooling system. The cooling system includes an anchor and the mover. The cooling element (i.e., the mover) is secured to the anchor at the anchor region. The cooling element is configured to perform a vibrational motion when actuated to drive fluid toward a heat generating structure. In some embodiments, the cooling system includes an aperture plate having an aperture therein. The aperture plate is disposed between the cooling element and the heat generating structure. In some embodiments, the cooling system includes a cell wall configured such that a top chamber is formed between a portion of the plurality of cell walls and the cooling element, and a bottom chamber is formed between the plurality of cell walls, the aperture plate, and the cooling element. The top chamber is in fluid communication with the bottom chamber.

[0027] In some embodiments, a method for cooling a heat generating structure is described. The method includes driving a cooling element to induce vibrational motion at a frequency. In some embodiments, the cooling element is an actuator described herein. In some embodiments, the cooling element is driven substantially at a structural resonance frequency of the cantilever. In some embodiments, the cooling element is driven at or near a fluid resonance frequency.

[0028] Figures 1A-1F is a diagram depicting an exemplary embodiment of an active cooling system 100 that can be used with a heat generating structure 102 and includes a centrally anchored cooling element 120. For clarity, only certain components are shown. Figures 1A-1F Not to scale. Although shown as symmetric, the cooling system 100 is not necessarily symmetric. Figure 1A and 1C -1F depicts a cooling system using an actuator or cooling element 120. Figure 1B is a side view of the cooling element 120.

[0029] The cooling system 100 includes a top plate 110 having an outlet 112 therein, a cooling element 120, an aperture plate 130 having an aperture 132 therein, a support structure (or "anchor") 160, and chambers 140 and 150 (collectively, chambers 140 / 150) formed therein. The cooling element 120 is supported at its center region by the anchor 160. A region of the cooling element 120 proximate to and including a peripheral portion of the cooling element (e.g., a tip 123) vibrates when actuated. In some embodiments, the tip 123 of the cooling element 120 includes a portion of the periphery that is farthest from the anchor 160 and undergoes the greatest deflection during actuation of the cooling element 120. For clarity, Figure 1A In FIG. 1A, only one tip 123 of the cooling element 120 is labeled.

[0030] Figure 1A depicts the cooling system 100 in a neutral position. Thus, the cooling element 120 is shown as substantially flat. For in-phase operation, the cooling element 120 is driven to vibrate in a direction that is substantially parallel to the plane of the top plate 110. Figure 1C and 1DThe oscillating motion draws fluid (e.g., air) into the outlet 112 at high speed and / or high flow rate, through the chambers 140 and 150, and out the hole 132. For example, the speed at which the fluid impacts the heat generating structure 102 can be at least thirty meters per second. In some embodiments, the fluid is driven by the cooling element 120 toward the heat generating structure 102 at a speed of at least forty-five meters per second. In some embodiments, the fluid is driven by the cooling element 120 toward the heat generating structure 102 at a speed of at least sixty meters per second. In some embodiments, other speeds can be possible. The cooling system 100 is also configured such that little or no fluid is drawn back into the chamber 140 / 150 by the oscillating motion of the cooling element 120 through the hole 132.

[0031] The heat generating structure 102 is desirably cooled by the cooling system 100. In some embodiments, the heat generating structure 102 generates heat. For example, the heat generating structure can be an integrated circuit. In some embodiments, the heat generating structure 102 is desirably cooled but does not itself generate heat. The heat generating structure 102 can conduct heat (e.g., from a nearby heat generating object). For example, the heat generating structure 102 can be a heat sink or a vapor chamber. Thus, the heat generating structure 102 can include semiconductor components, including individual integrated circuit components (such as processors), other integrated circuits and / or chip packages; sensors; optical devices; one or more cells; other components of electronic devices (such as computing devices); heat sinks; heat pipes; other electronic components desirably cooled and / or other devices.

[0032] Devices in which cooling system 100 is expected to be used can also have limited space in which to place the cooling system. For example, cooling system 100 can be used in a computing device. Such computing devices can include, but are not limited to, smartphones, tablet computers, laptop computers, tablets, two-in-one laptop devices, handheld gaming systems, digital cameras, virtual reality headsets, augmented reality headsets, mixed reality headsets, and other devices that are very thin. Cooling system 100 can be a microelectromechanical system (MEMS) cooling system that is capable of residing within a mobile computing device and / or other device that has limited space in at least one dimension. For example, the overall height of cooling system 100 (from the top of heat-generating structure 102 to the top of top plate 110) can be less than 2 millimeters. In some embodiments, the overall height of cooling system 100 is no more than 1.5 millimeters. In some embodiments, the overall height is no more than two hundred and fifty micrometers. In some embodiments, the overall height is no more than 1.1 millimeters. In some embodiments, the overall height is no more than one millimeter. Similarly, the distance y between the bottom of aperture plate 130 and the top of heat-generating structure 102 can be small. In some embodiments, y is at least two hundred micrometers and no more than one millimeter. In some embodiments, y is at least two hundred micrometers and no more than three hundred micrometers. Thus, cooling system 100 can be used in computing devices and / or other devices that have limited space in at least one dimension. However, cooling system 100 is not used in devices that have less restriction on space and / or for purposes other than cooling. Although one cooling system 100 (e.g., one cooling unit) is shown, multiple cooling systems 100 can be used in conjunction with heat-generating structure 102. For example, a one-dimensional or two-dimensional array of cooling units can be used.

[0033] Cooling system 100 is in fluid communication with a fluid used to cool heat-generating structure 102. The fluid can be a gas or a liquid. For example, the fluid can be air. In some embodiments, the fluid includes fluid from outside of the device in which cooling system 100 is located (e.g., provided through an external outlet in the device). In some embodiments, the fluid is circulated within the device in which cooling system is located (e.g., in a closed device).

[0034] Cooling element 120 can be thought of as partitioning the interior of active cooling system 100 into a top chamber 140 and a bottom chamber 150. Top chamber 140 is formed by cooling element 120, the sides, and top plate 110. Bottom chamber 150 is formed by aperture 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., the interior chamber of cooling system 100).

[0035] The dimensions and configuration of the top chamber 140 can be based on the size of the cell (cooling system 100), the movement of the cooling element 120, and the frequency of operation. The top chamber 140 has a height hi. The height of the top chamber 140 can be selected to provide sufficient pressure to drive fluid to the bottom chamber 150 and through the holes 132 at a desired flow rate and / or velocity. The top chamber 140 is also sufficiently high so that the cooling element 120 does not contact the top plate 110 when actuated. In some embodiments, the height of the top chamber 140 is at least fifty microns and no more than five hundred microns. In some embodiments, the top chamber 140 has a height of at least two hundred and no more than three hundred microns.

[0036] The bottom chamber 150 has a height h2. In some embodiments, the height of the bottom chamber 150 is sufficient to accommodate the movement of the cooling element 120. Thus, during normal operation, no portion of the cooling element 120 contacts the orifice plate 130. The bottom chamber 150 is generally smaller than the top chamber 140 and can help reduce backflow of fluid into the holes 132. In some embodiments, the height of the bottom chamber 150 is the maximum deflection of the cooling element 120 plus at least five microns and no more than ten microns. In some embodiments, the deflection (e.g., of the tip 123) z of the cooling element 120 has an amplitude of at least ten microns and no more than one hundred microns. In some such embodiments, the deflection amplitude of the cooling element 120 is at least ten microns and no more than sixty microns. However, the deflection amplitude of the cooling element 120 depends on factors such as the desired flow rate through the cooling system 100 and the configuration of the cooling system 100. Thus, the height of the bottom chamber 150 generally depends on the flow rate through the other components of the cooling system 100.

[0037] The top plate 110 includes an outlet 112 through which fluid can be drawn into the cooling system 100. The top outlet 112 can have dimensions selected based on the desired acoustic pressure in the chamber 140. For example, in some embodiments, the width w of the outlet 112 is at least five hundred microns and no more than one thousand microns. In some embodiments, the width of the outlet 112 is at least two hundred fifty microns and no more than two thousand microns. In the illustrated embodiment, the outlet 112 is a hole in the center of the top plate 110. In other embodiments, the outlet 112 can be located elsewhere. For example, the outlet 112 can be closer to one of the edges of the top plate 110. The outlet 112 can have a circular, rectangular, or other shaped footprint. Although a single outlet 112 is shown, multiple outlets can be used. For example, outlets can be offset toward the edges of the top chamber 140 or located on the sides of the top chamber 140. Although the top plate 110 is shown as substantially flat, in some embodiments, grooves and / or other structures can be provided in the top plate 110 to modify the configuration of the top chamber 140 and / or the region above the top plate 110.

[0038] Cooling element 120 includes an anchor region 122 and a cantilever 121. Anchor region 122 is supported (e.g., held in place) in cooling system 100 by an anchor 160. Cantilever 121 is to vibrate in response to actuated cooling element 120. Each cantilever 121 includes a step region 124, an extension region 126, and an outer region 128. For clarity, cantilever 121, step region 124, extension region 126, and outer region 128 are labeled only in Figure 1B In the embodiment shown in Figures 1A-1F In the embodiment shown in

[0039] Extension region 126 has a thickness (extension thickness) that is less than a thickness (step thickness) of step region 124 and less than a thickness (outer thickness) of outer region 128. Thus, extension region 126 can be considered a recess. Extension region 126 can also be considered to provide 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 than the step thickness of step region 124. The outer thickness of outer region 128 and the step thickness of step region 124 are each at least three hundred micrometers and no more than three hundred sixty micrometers. In other embodiments, other thicknesses are possible. In some embodiments, the outer thickness is at least fifty micrometers and no more than two hundred micrometers thicker than the extension thickness. In other words, the step (difference between the step thickness and the extension thickness) is at least fifty micrometers and no more than two hundred micrometers. In some embodiments, the outer step (difference between the outer thickness and the extension thickness) is at least fifty micrometers and no more than two hundred micrometers. Outer region 128 can have a width o of at least one hundred micrometers and no more than three hundred micrometers. In some embodiments, extension region has a length e extending outward from step region of at least 0.5 millimeters and no more than 1.5 millimeters. In some embodiments, outer region 128 has a mass per unit length that is higher than extension region 126 in a direction from anchor region 122. This difference in mass can be due to the larger size of outer region 128, a difference in density between portions of cooling element 120, and / or another mechanism.

[0040] Anchor (support structure) 160 supports cooling element 120 at a central portion of cooling element 120. Thus, at least a portion of a perimeter of cooling element 120 is not pinned and is free to vibrate. In some embodiments, anchor 160 is along a central axis of cooling element 120 (e.g., perpendicular to a plane of cooling element 120). In some embodiments, anchor 160 is along a central axis of cooling element 120 (e.g., parallel to a plane of cooling element 120). Figures 1A-1FIn such embodiments, the portion of the vibrating cooling element 120 (e.g., the cantilever 121 including the tip 123) moves in a cantilevered manner. Thus, the cantilever 121 of the cooling element 120 can move in a manner similar to the wings of a butterfly (i.e., in phase) and / or similar to a seesaw (i.e., out of phase). Thus, the cantilever 121 of the cooling element 120 that vibrates in a cantilevered manner is in phase in some embodiments and out of phase in other embodiments. In some embodiments, the anchor 160 does not extend along the axis of the cooling element 120. In such embodiments, all portions of the perimeter of the cooling element 120 are free to vibrate (e.g., similar to a jellyfish). In the illustrated embodiment, the anchor 160 supports the cooling element 120 from the bottom of the cooling element 120. In other embodiments, the anchor 160 can support the cooling element 120 in another manner. For example, the anchor 160 can support the cooling element 120 from the top (e.g., the cooling element 120 is suspended from the anchor 160). In some embodiments, the width a of the anchor 160 is at least 0.5 millimeters and no more than 4 millimeters. In some embodiments, the width of the anchor 160 is at least two millimeters and no more than 2.5 millimeters. The anchor 160 can occupy at least ten percent and no more than fifty percent of the cooling element 120.

[0041] The cooling element 120 has a first side that is distal from the heat generating structure 102 and a second side that is proximal to the heat generating structure 102. In the illustrated embodiment, the first side of the cooling element 120 is the top of the cooling element 120 (closer to the top plate 110) and the second side is the bottom of the cooling element 120 (closer to the hole plate 130). As shown in FIG. 1F, the anchor 160 supports the cooling element 120 from the bottom of the cooling element 120. Figures 1A-1F Figure 1A and 1C As shown in FIG. 1F, the cooling element 120 is actuated to perform a vibrational motion. The vibrational motion of the cooling element 120 drives fluid from the first side of the cooling element 120 (e.g., from the top chamber 140) that is distal from the heat generating structure 102 to the second side of the cooling element 120 (e.g., to the bottom chamber 150) that is proximal to the heat generating structure 102. The vibrational motion of the cooling element 120 also draws fluid through the outlet 112 and into the top chamber 140; forces fluid to flow from the top chamber 140 to the bottom chamber 150; and drives fluid from the bottom chamber 150 through the holes 132 of the hole plate 130.

[0042] The length L of the cooling element 120 depends on the frequency at which the cooling element 120 is desired to vibrate. In some embodiments, the length of the cooling element 120 is at least four millimeters and no more than ten millimeters. In some such embodiments, the cooling element 120 has a length of at least six millimeters and no more than eight millimeters. The depth (e.g., the distance from the top of the cooling element 120 to the bottom of the cooling element 120) of the cooling element 120 is at least 0.5 millimeters and no more than 4 millimeters. In some embodiments, the depth of the cooling element 120 is at least two millimeters and no more than 2.5 millimeters. Figures 1A-1F ​The plane normal to the length L shown can vary from one quarter of L to twice L. For example, the cooling element 120 can have a depth that is the same as the length. The thickness t of the cooling element 120 can vary based on the construction of the cooling element 120 and / or the frequency at which the cooling element 120 is expected to be actuated. In some embodiments, for a cooling element 120 having a length of eight millimeters and driven at a frequency of at least twenty kilohertz and no more than twenty-five kilohertz, the cooling element thickness is at least two hundred micrometers and no more than three hundred fifty micrometers. The length C of the chamber 140 / 150 is close to the length L of the cooling element 120. For example, in some embodiments, the distance d between the edge of the cooling element 120 and the wall of the chamber 140 / 50 is at least one hundred micrometers and no more than five hundred micrometers. In some embodiments, d is at least two hundred micrometers and no more than three hundred micrometers.

[0043] The cooling element 120 can be driven at a frequency at or near both the resonant frequency of the pressure wave acoustic resonance with respect to the fluid in the top chamber 140 and the resonant frequency of the structural resonance with respect to the construction of the cooling element 120. The portion of the cooling element 120 that is in vibrational motion is driven at or near the resonant frequency of the cooling element 120 ("structural resonance"). In some embodiments, this portion of the cooling element 120 that is in vibration can be the cantilever 121. The frequency of vibration of the structural resonance is referred to as the structural resonance frequency. Using the structural resonance frequency in driving the cooling element 120 reduces the power consumption of the cooling system 100. The cooling element 120 and the top chamber 140 can also be constructed such that this structural resonance frequency corresponds to the resonance of a pressure wave in the fluid driven through the top chamber 140 (the acoustic resonance of the top chamber 140). The frequency of such a pressure wave is referred to as the acoustic resonance frequency. At acoustic resonance, a pressure node occurs near the outlet 112 and a pressure antinode occurs near the periphery of the cooling system 100 (e.g., near the end 123 of the cooling element 120 and near the junction between the top chamber 140 and the bottom chamber 150). The distance between these two regions is C / 2. Thus, C / 2 = nλ / 4, where λ is the acoustic wavelength with respect to the fluid and n is an odd number (e.g., n = 1, 3, 5, etc.). For the lowest order mode, C = λ / 2. Since the length of the chamber 140 (e.g., C) is close to the length of the cooling element 120, in some embodiments, L / 2 = nλ / 4 is also approximately correct, where λ is the acoustic wavelength of the fluid and n is an odd number. Thus, the frequency v at which the cooling element 120 is driven is at or near the structural resonance frequency with respect to the cooling element 120. The frequency v is also at or near the acoustic resonance frequency with respect to at least the top chamber 140. The acoustic resonance frequency of the top chamber 140 varies substantially less dramatically with parameters such as temperature and size than the structural resonance frequency of the cooling element 120. Thus, in some embodiments, the cooling element 120 can be driven at (or near) the structural resonance frequency rather than the acoustic resonance frequency.

[0044] Orifice plate 130 has holes 132 therein. Although a particular number and distribution of holes 132 are shown, other numbers and / or another distribution can be used. A single orifice plate 130 is used for a single cooling system 100. In other embodiments, multiple cooling systems 100 can share an orifice plate. For example, multiple units 100 can be provided together in a desired configuration. In such embodiments, the units 100 can have the same size and configuration or different sizes and / or configurations. Holes 132 are shown as having an axis oriented normal to the surface of heat-generating structure 102. In other embodiments, the axis of one or more holes 132 can be at another angle. For example, the angle of the axis can be selected from a degree substantially zero and a non-zero acute angle. Holes 132 also have sidewalls that are substantially parallel to the normal of the surface of orifice plate 130. In some embodiments, the holes can have sidewalls that are at a non-zero angle to the normal of the surface of orifice plate 130. For example, holes 132 can be conical. Further, although orifice plate 130 is shown as being substantially flat, in some embodiments, grooves and / or other structures can 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.

[0045] The size, distribution, and location of the holes 132 are selected to control the flow rate of fluid driven to the surface of the heat-generating structure 102. The location and configuration of the holes 132 can be configured to increase / maximize the flow of fluid from the bottom chamber 150 through the holes 132 to the ejection channel (the region between the bottom of the orifice plate 130 and the top of the heat-generating structure 102). The location and configuration of the holes 132 can also be selected to reduce / minimize the suction flow (e.g., backflow) from the ejection channel through the holes 132. For example, it is desirable for the location of the holes to be far enough from the tip 123 to reduce the suction force that pulls fluid through the holes 132 into the bottom chamber 150 in the upward stroke of the cooling element 120 (movement of the tip 123 away from the orifice plate 130). It is also desirable for the location of the holes to be close enough to the tip 123 that the suction force in the upward stroke also allows the higher pressure from the top chamber 140 to push fluid from the top chamber 140 into the bottom chamber 150. In some embodiments, the ratio of the flow rate from the top chamber 140 into the bottom chamber 150 to the flow rate from the ejection channel through the holes 132 in the upward stroke (“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. To provide the desired pressure, flow rate, suction force, and net flow ratio, it is desirable for the holes 132 to be at least r1from the tip 123 and no more than r2from the tip 123 of the cooling element 120. In some embodiments, r1is at least one hundred microns (e.g., r1> 100 pm) and r2is no more than one millimeter (e.g., r2< 1000 pm). In some embodiments, the holes 132 are at least two hundred microns (e.g., r1> 200 pm) from the tip 123 of the cooling element 120. In some such embodiments, the holes 132 are at least three hundred microns (e.g., r1> 300 pm) from the tip 123 of the cooling element 120. In some embodiments, the holes 132 have a width o of at least one hundred microns and no more than five hundred microns. In some embodiments, the holes 132 have a width of at least two hundred microns and no more than three hundred microns. In some embodiments, the hole spacing s is at least one hundred microns and no more than one millimeter. In some such embodiments, the hole spacing is at least four hundred microns and no more than six hundred microns. In some embodiments, it is also desirable for the holes 132 to occupy a particular portion of the area of the orifice plate 130. For example, the holes 132 can cover at least five percent and no more than fifteen percent of the footprint of the orifice plate 130 to achieve the desired flow rate of fluid through the holes 132. In some embodiments, the holes 132 cover at least eight percent and no more than twelve percent of the footprint of the orifice plate 130.

[0046] In some embodiments, the cooling element 120 is actuated using a piezoelectric body. Thus, the cooling element 120 can be a piezoelectric cooling element. The cooling element 120 can be driven by a piezoelectric body mounted on or integrated into the cooling element 120. In some embodiments, the cooling element 120 is driven in another manner, including but not limited to providing a piezoelectric body on another structure in the cooling system 100. The cooling element 120 and similar cooling elements are referred to hereinafter as piezoelectric cooling elements, but it is possible that the cooling element can be driven using a mechanism other than a piezoelectric body. In some embodiments, the cooling element 120 includes a piezoelectric layer on a base. The base can be a stainless steel, nickel alloy, and / or Hastelloy base. In some embodiments, the piezoelectric layer includes a plurality of sub-layers formed as a thin film on the base. In other embodiments, the piezoelectric layer can be a bulk layer affixed to the base. Such piezoelectric cooling elements 120 also include electrodes for activating the piezoelectric body. In some embodiments, the base serves as an electrode. In other embodiments, a bottom electrode can be provided between the base and the piezoelectric layer. Other layers, including but not limited to a seed layer, a capping layer, a passivation layer, or other layers, can be included in the piezoelectric cooling element. Thus, the cooling element 120 can be actuated using piezoelectricity.

[0047] In some embodiments, the cooling system 100 includes a vent (not shown) or other duct. Such a duct provides a path for the heated fluid to exit the heat generating structure 102. In some embodiments, the duct returns the fluid to a side of the top plate 110 distal from the heat generating structure 102. In some embodiments, the duct can instead direct the fluid away from the heat generating structure 102 in a direction parallel to the heat generating structure 102 or perpendicular to the heat generating structure 102 but in an opposite direction (e.g., toward the bottom of the page). For devices that use fluid external to the device in the cooling system 100, the duct can direct the heated fluid to an outlet. In such embodiments, additional fluid can be provided from an inlet. In device-enclosed embodiments, the duct can provide a circuitous path back to a region proximal to the outlet 112 and distal from the heat generating structure 102. Such a path allows the fluid to dissipate heat before being reused to cool the heat generating structure 102. In other embodiments, the duct can be omitted or constructed in another manner. Thus, the fluid is allowed to carry heat away from the heat generating structure 102.

[0048] The operation of the cooling system 100 is described in the context of Figures 1A-1F The operation of the cooling system 100 is described in the context of Figures 1C-1D The in-phase operation of the cooling system 100 is depicted. Referring to Figure 1C The cooling element 120 is actuated such that the cantilever 121 and the tip 123 move away from the top plate 110. Thus, it can be considered that Figure 1Cdepicts the end of the downward stroke of the cooling element 120. Due to the oscillating motion of the cooling element 120, the gap 152 with respect to the bottom chamber 150 decreases in size and is shown as gap 152B. Conversely, the gap 142 with respect to the top chamber 140 increases in size and is shown as gap 142B. During the downward stroke, when the cooling element 120 is in the neutral position, a lower (e.g., minimum) pressure is created at the periphery. As the downward stroke continues, the bottom chamber 150 decreases in size and the top chamber 140 increases in size as shown in Figure 1C size and the top chamber 140 increases in size. Thus, fluid is driven from the top chamber 140 to the bottom chamber 150 in a direction that is perpendicular or near perpendicular to the surface of the orifice plate 130 and / or the top surface of the heat generating structure 102. The fluid is driven from the orifice 132 toward the heat generating structure 102 at high speeds (e.g., over thirty-five meters per second). In some embodiments, the fluid then travels along the surface of the heat generating structure 102 and toward the periphery of the heat generating structure 102 where the pressure is lower than near the orifice 132. Also during the downward stroke, the top chamber 140 increases in size and a lower pressure exists in the top chamber 140. As a result, fluid is drawn into the top chamber 140 through the outlet 112. The movement of fluid into the outlet 112, through the orifice 132 and along the surface of the heat generating structure 102 is shown by the unlabelled arrows in Figure 1C

[0049] The cooling element 120 is also motivated such that the cantilever 121 and the tip 123 move away from the heat generating structure 102 and toward the top plate 110. Thus, it can be considered that Figure 1D depicts the end of the upward stroke of the cooling element 120. Due to the motion of the cooling element 120, the gap 142 decreases in size and is shown as gap 142C. The gap 152 increases in size and is shown as gap 152C. During the upward stroke, when the cooling element 120 is in the neutral position, a higher (e.g., maximum) pressure is created at the periphery. As the upward stroke continues, the bottom chamber 150 increases in size and the top chamber 140 decreases in size as shown in Figure 1D size and the top chamber 140 increases in size. Thus, fluid is driven from the top chamber 140 to the bottom chamber 150 in a direction that is perpendicular or near perpendicular to the surface of the orifice plate 130 and / or the top surface of the heat generating structure 102. The fluid is driven from the orifice 132 toward the heat generating structure 102 at high speeds (e.g., over thirty-five meters per second). In some embodiments, the fluid then travels along the surface of the heat generating structure 102 and toward the periphery of the heat generating structure 102 where the pressure is lower than near the orifice 132. Also during the downward stroke, the top chamber 140 increases in size and a lower pressure exists in the top chamber 140. As a result, fluid is drawn into the top chamber 140 through the outlet 112. The movement of fluid into the outlet 112, through the orifice 132 and along the surface of the heat generating structure 102 is shown by the unlabelled arrows in Figure 1D

[0050] ​​The motion between the positions shown in Figure 1C and 1D is repeated. Thus, the cooling element 120 performs Figure 1A and 1C the vibrational motion indicated in -1D, drawing fluid from the distal side of the top plate 110 through the outlet 112 into the top chamber 140; passing fluid from the top chamber 140 to the bottom chamber 150; and pushing fluid through the hole 132 and toward the heat generating structure 102. As described above, the cooling element 120 is driven to vibrate at or near the structural resonance frequency of the cooling element 120. In some embodiments, this corresponds to the structural resonance of the cantilever 121. Further, the structural resonance frequency of the cooling element 120 is configured to align with the acoustic resonance of the chambers 140 / 150. The structural and acoustic resonance frequencies are generally selected to be in the ultrasonic range. For example, the frequency of the vibrational motion of the cooling element 120 can be from 15 kHz to 30 kHz. In some embodiments, the cooling element 120 vibrates at a frequency of at least 20 kHz and no more than 30 kHz. The structural resonance frequency of the cooling element 120 is within ten percent of the acoustic resonance frequency of the cooling system 100. In some embodiments, the structural resonance frequency of the cooling element 120 is within five percent of the acoustic resonance frequency of the cooling system 100. In some embodiments, the structural resonance frequency of the cooling element 120 is within three percent of the acoustic resonance frequency of the cooling system 100. Thus, efficiency and flow rate can be enhanced. However, other frequencies can be used.

[0051] Fluid driven toward the heat generating structure 102 can move substantially normal (perpendicular) to the top surface of the heat generating structure 102. In some embodiments, fluid movement can have a non-zero acute angle with respect to the normal of the top surface of the heat generating structure 102. In either case, the fluid can thin and / or form a hole in the fluid boundary layer at the heat generating structure 102. As a result, heat transfer from the heat generating structure 102 can be improved. Fluid is deflected from the heat generating structure 102, traveling along the surface of the heat generating structure 102. In some embodiments, the fluid moves in a direction substantially parallel to the top of the heat generating structure 102. Thus, heat from the heat generating structure 102 can be extracted by the fluid. The fluid can exit the region between the orifice plate 130 and the heat generating structure 102 at the edge of the cooling system 100. A vent or other conduit (not shown) at the edge of the cooling system 100 allows the fluid to be carried away from the heat generating structure 102. In other embodiments, the heated fluid can be transferred away from the heat generating structure 102 in another manner. The fluid can exchange heat transferred from the heat generating structure 102 to another structure or the ambient environment. Thus, the fluid at the distal side of the top plate 110 can remain relatively cool, allowing additional heat extraction. In some embodiments, the fluid is circulated, returning to the distal side of the top plate 110 after cooling. In other embodiments, the heated fluid is carried away and replaced by new fluid at the distal side of the cooling element 120. As a result, the heat generating structure 102 can be cooled.

[0052] Figures 1E-1F An embodiment of an actively cooled system 100 is depicted including a centrally anchored cooling element 120, in which the cooling element is driven out of phase. More particularly, the cantilevered arms 121 of the cooling element 120 on opposite sides of the anchor 160 are driven to vibrate out of phase. In some embodiments, the cantilevered arms 121 of the cooling element 120 on opposite sides of the anchor 160 are driven 180 degrees out of phase or near 180 degrees out of phase. Thus, one cantilevered arm 121 of the cooling element 120 vibrates toward the top plate 110, while the other cantilevered arm 121 of the cooling element 120 vibrates toward the orifice plate 130 / heat generating structure 102. Movement of the cantilevered arms 121 of the cooling element 120 toward the top plate 110 (upstroke) drives fluid in the top chamber 140 to the bottom chamber 150 on that side of the anchor 160. Movement of one section of the cooling element 120 toward the orifice plate 130 drives fluid through the orifice 132 and toward the heat generating structure 102. Thus, fluid traveling at high speed (e.g., relative to the speeds described for in-phase operation) is alternately driven away from the orifices 132 on opposite sides of the anchor 160. Movement of the fluid is represented by the unlabelled arrows in Figure 1E and 1F

[0053] Repeating in Figure 1E and 1F ​the motion between the positions shown in FIGS. 1A-1F. Thus, the cooling element 120 is driven to vibrate Figure 1A , 1E and the vibrational motion indicated in FIGS. 1A-1F, alternately draws fluid from the distal side of the top plate 110 through the outlet 112 into the top chamber 140 on each side of the cooling element 120; passes the fluid from each side of the top chamber 140 to the corresponding side of the bottom chamber 150; and pushes the fluid through the holes 132 on each side of the anchor 160 and toward the heat generating structure 102. As described above, the cooling element 120 is driven to vibrate at or near the structural resonance frequency of the cooling element 120. In addition, the structural resonance frequency of the cooling element 120 is configured to align with the acoustic resonance of the chambers 140 / 150. The structural and acoustic resonance frequencies are generally selected to be in the ultrasonic range. For example, the vibrational motion of the cooling element 120 can be at the frequencies described for in-phase vibration. The structural resonance frequency of the cooling element 120 is within ten percent of the acoustic resonance frequency of the cooling system 100. In some embodiments, the structural resonance frequency of the cooling element 120 is within five percent of the acoustic resonance frequency of the cooling system 100. In some embodiments, the structural resonance frequency of the cooling element 120 is within three percent of the acoustic resonance frequency of the cooling system 100. Thus, efficiency and flow rate can be enhanced. However, other frequencies can be used.

[0054] Fluid driven toward the heat generating structure 102 to vibrate out of phase can move substantially normal (perpendicular) to the top surface of the heat generating structure 102 in a manner similar to the in-phase operation described above. Similarly, vents or other ducts (not shown) at the edges of the cooling system 100 allow fluid to be carried away from the heat generating structure 102. In other embodiments, the heated fluid can be passed further from the heat generating structure 102 in another manner. The fluid can exchange heat passed from the heat generating structure 102 to another structure or the ambient environment. Thus, the fluid at the distal side of the top plate 110 can remain relatively cool, allowing additional heat extraction. In some embodiments, the fluid is circulated, returning to the distal side of the top plate 110 after cooling. In other embodiments, the heated fluid is carried away and replaced by new fluid at the distal side of the cooling element 110. As a result, the heat generating structure 102 can be cooled.

[0055] Using the cooling system 100 actuated for in-phase or out-of-phase vibration, fluid drawn in through the outlet 112 and driven through the aperture 132 can effectively dissipate heat from the heat generating structure 102. Because the fluid impacts the heat generating structure at a sufficient velocity (e.g., at least thirty meters per second) and in some embodiments substantially normal to the heat generating structure, the fluid boundary layer at the heat generating structure can thin and / or partially remove. As a result, heat transfer between the heat generating structure 102 and the moving fluid is improved. As a result of more effectively cooling the heat generating structure, a corresponding integrated circuit can run at a higher speed and / or power for a longer period of time. For example, if the heat generating structure corresponds to a high speed processor, such a processor can run for a longer period of time before throttling. As a result, performance of a device utilizing the cooling system 100 can be improved. Further, the cooling system 100 can be for a MEMS device. As a result, the cooling system 100 can be suitable for smaller devices and / or mobile devices with limited available space, such as smartphones, other mobile phones, virtual reality headsets, tablets, 2-in-l computers, wearable devices, and handheld game consoles. Performance of such devices can thus be improved. Because the cooling element 120 can vibrate at a frequency of 15 kHz or higher, a user can not hear any noise associated with actuation of the cooling element. If driven at or near a structural and / or acoustic resonance frequency, power used in operating the cooling system can be significantly reduced. The cooling element 120 does not physically contact the top plate 110 or the aperture plate 130 during vibration. As a result, resonance of the cooling element 120 can be more easily maintained. More particularly, physical contact between the cooling element 120 and other structures disrupts the resonance conditions of the cooling element 120. Disrupting these conditions can drive the cooling element 120 out of resonance. As a result, additional power would be required to maintain actuation of the cooling element 120. Further, fluid flow driven by the cooling element 120 can be reduced. These issues are avoided by using a differential pressure and fluid flow as discussed above. The benefits of improved, quiet cooling can be achieved with limited additional power. Further, out-of-phase vibration of the cooling element 120 allows the center of mass position of the cooling element 100 to remain more stable. Although torque is applied to the cooling element 120, the force due to motion of the center of mass is reduced or eliminated. As a result, vibration due to motion of the cooling element 120 can be reduced. Further, efficiency of the cooling system 100 can be improved by using out-of-phase vibration motion to both sides of the cooling element 120. For out-of-phase vibration of the cantilever 121, vibration through the cooling system 100 can also be reduced. As a result, performance of a device incorporating the cooling system 100 can be improved. Further, the cooling system 100 can be used in other applications (e.g., with or without the heat generating structure 102) where high fluid flow and / or velocity is desired.

[0056] The use of the designed cooling element 120 can further improve the performance of the cooling system 100. The extended region 126 is thinner than the stepped region 124 and the outer region 128. This results in a cavity in the bottom of the cooling element 120 corresponding to the extended region 126. The presence of this cavity helps to improve the efficiency of the cooling system 100. As discussed with respect to Figure 1A and 1C -1F, the cantilever 121 oscillates toward the ceiling 110 on the upward stroke and away from the ceiling 110 on the downward stroke. As the cantilever 121 moves toward the ceiling 110, the high pressure fluid in the top chamber 140 resists the movement of the cantilever 121. In addition, the suction force in the bottom chamber 150 also resists the upward movement of the cantilever 121 during the upward stroke. On the downward stroke of the cantilever 121, the increased pressure in the bottom chamber 150 and the suction force in the top chamber 140 resist the downward movement of the cantilever 121. However, the presence of the cavity in the cantilever 121 corresponding to the extended region 126 relieves the suction force in the bottom chamber 150 during the upward stroke. During the downward stroke, the cavity also reduces the increase in pressure in the bottom chamber 150. Because the suction force and the increase in pressure are reduced in magnitude, the cantilever 121 can more easily move through the fluid. This can be accomplished while substantially maintaining the high pressure of the drive fluid in the top chamber 140 flowing through the cooling system 100. Thus, the efficiency can be improved.

[0057] In addition, the presence of the outer region 128 can improve the ability of the cantilever 121 to move through the fluid being driven through the cooling system 100. The outer region 128 has a higher mass and thus a higher momentum. Thus, the outer region 128 can improve the ability of the cantilever 121 to move through the fluid being driven through the cooling system 100. The magnitude of the deflection of the cantilever 121 can also be increased. By using a thicker stepped region 124, these benefits can be achieved while maintaining the stiffness of the cantilever 121. Thus, the efficiency of the cooling system 100 can again be improved.

[0058] The improvement can also be understood as follows. Q can be thought of as a measure of the efficiency of the cooling element 120. The value of Q is at least partially determined by the interaction of the cooling element 120 with the surrounding fluid (i.e., a gas such as air or a liquid), structural losses within the cooling element 120, anchoring of the cooling element 120, and / or other characteristics. Q can be thought of as being defined by res = Q * δ static where δ res is the deflection at resonance, and δ staticis the corresponding static deflection. The higher the Q value, the greater the deflection at resonance and the slower the deflection decays (i.e., the lower the damping). Due to the designed configuration of the cooling element 120, the cooling element is better able to move through the surrounding fluid. As a result, a higher static deflection can be achieved, the deflection can be amplified better at resonance, the power consumed to drive the cooling element 120 can be reduced, and the deflection can decay more slowly (i.e., be subject to reduced damping). The Q of the cooling element 120, and thus the efficiency of the cooling system 100, can thus be enhanced by the configuration of the cooling element 120.

[0059] The use of the designed cooling element 120 can also improve the reliability of the cooling system 100. Due to its reduced thickness, the extended region 126 can be less rigid than the outer region 128 and the stepped region 124. This reduction in rigidity results in reduced stress on the cooling element 120 during vibration. The cooling element 120 can be less likely to fail. As a result, the reliability of the cooling system 100 can be improved.

[0060] For example, Figures 2A-2E Exemplary embodiments of graphs 200A, 200B, 200C, 200D, and 200E related to the performance of the cooling element 200 are depicted. The graphs 200A, 200B, 200C, 200D, and 200E are for explanatory purposes only and are not intended to represent the performance of all embodiments of the cooling element 120 and / or the cooling system 100. The graph 200A includes curves depicting the deflection 204A (y) of a cooling element having a uniform thickness and the pressure 202A (P) in the chambers 140 and 150. The graph 200B includes curves depicting the pressure 202B (P) in the chambers 140 and 150 and the deflection 204B (y) of the cooling element 120. The magnitude of the deflection of the curves 204A and 204B is the same in the illustrated embodiment. In some embodiments, the magnitude of the deflection is four microns. Due to the presence of the cavity under the extended region 126, the pressure curve 202B indicates that the pressure generated in the chamber of the cooling element 120 is less than the pressure indicated by the pressure curve 202A for a uniform actuator. The cantilever 121 can thus more easily and efficiently move through the fluid in the cooling system 100. The efficiency can thus be improved.

[0061] Similarly, plots 200C, 200D, and 200E depict stress (σ) versus deflection (y) for the cooling element of a uniform cooling element (plot 200C) and two embodiments of cooling element 120 (plots 200D and 200E). Plot 200C indicates a single high stress region near the edge of anchor 160. This is where the highest stress occurs as the uniform cooling element is deflected. Plots 200D and 200E indicate that the stress of cooling element 120 is concentrated in two locations: near anchor 160 (i.e., where cooling element 120 is free to vibrate) and near the transition between step region 124 and extension region 126. However, the construction of cooling element 120 reduces the magnitude of the stress experienced by cooling element 120 at these regions. Because cooling element 120 is subjected to less stress, cooling element 120 can be less likely to fail. Thus, reliability can be improved.

[0062] Figures 3A-3D Plan views of embodiments of cooling systems 300A, 300B, 300C, and 300D similar to active cooling systems such as cooling system 100 are depicted. Figures 3A-3D Not to scale. For simplicity, only portions of cooling elements 320A, 320B, 320C, and 320D and anchors 360A, 360B, 360C, and 360D are shown, respectively. Cooling elements 220A, 320B, 320C, and 320D are similar to cooling element 120. Thus, dimensions and / or materials used for cooling elements 320A, 320B, 320C, and / or 320D can be similar to dimensions and / or materials used for cooling element 120. Anchors (support structures) 360A, 360B, 360C, and 360B are similar to anchor 160 and are indicated by dashed lines.

[0063] For cooling elements 320A and 320B, anchors 360A and 360B are located centrally and extend along the central axis of cooling elements 320A and 320B, respectively. Thus, cantilevered portions (i.e., cantilevers) that are urged to vibrate are located to the right and left of anchors 360A and 360B. In some embodiments, cooling elements 320A and / or 320B are continuous structures with two portions that are urged (e.g., cantilevered portions outside of anchors 360A and 360B). In some embodiments, cooling elements 320A and / or 320B include separate cantilevered portions, each attached to and urged by anchors 360A and 360B, respectively. The cantilevered portions of cooling elements 320A and 320B can thus be configured to vibrate in a manner similar to the wings of a butterfly (in phase) or a seesaw (out of phase). In some embodiments, cooling elements 320A and / or 320B include a single cantilevered portion that is attached to and urged by anchors 360A and 360B. The cantilevered portion of cooling elements 320A and 320B can thus be configured to vibrate in a manner similar to a single wing of a butterfly (in phase) or a seesaw (out of phase). Figure 3A and 3B In, L is the length of the cooling element, similar to that depicted in Figures 1A-1F In, L is the length of the cooling element, similar to that depicted in Figure 3A and 3BIn some embodiments, the depth P of the cooling elements 320A and 320B is indicated.

[0064] Also shown by the dashed lines in Figures 3A-3B is the piezoelectric 323. The piezoelectric 323 is used to drive the cooling elements 320A and 320B. Although described in the context of a piezoelectric, another mechanism for actuating the cooling elements 320A and 320B can be utilized. Such other mechanisms can be at the location of the piezoelectric 323 or can be located elsewhere. In the cooling element 320A, the piezoelectric 323 can be fixed to the cantilevered portion or can be integrated into the cooling element 320A. Further, although the piezoelectric 323 is shown in Figure 3A and 3B as having a particular shape and size, other configurations can be used.

[0065] In the embodiment shown in Figure 3A , the anchor 360A extends the entire depth of the cooling element 320A. Thus, a portion of the perimeter of the cooling element 320A is pinned. The unpinned portion of the perimeter of the cooling element 320A is part of the cantilevered section that is moved in vibration. In other embodiments, the anchor need not extend the entire length of the central axis. In such embodiments, the entire perimeter of the cooling element is unpinned. However, such cooling elements still have a cantilevered section configured to vibrate in the manner described herein. For example, in Figure 3B , the anchor 360B does not extend to the perimeter of the cooling element 320B. Thus, the perimeter of the cooling element 320B is unpinned. However, the anchor 360B still extends along the central axis of the cooling element 320B. The cooling element 320B is still actuated such that the cantilevered portion vibrates (e.g., like the wings of a butterfly).

[0066] Although the cooling element 320A is depicted as rectangular, the cooling element can have another shape. In some embodiments, the corners of the cooling element 320A can be rounded. Figure 3B The cooling element 320B of Figure 3BIn the embodiments shown in FIGS. 3A and 3B, the anchors 360B are hollow and include holes 363. In some embodiments, the cooling elements 320B have holes in the regions of the anchors 360B. In some embodiments, the cooling elements 320B include multiple portions, such that holes exist in the regions of the anchors 360B. As a result, fluid can be drawn through the cooling elements 320B and through the anchors 360B. Thus, the cooling elements 320B can be used in place of a top plate, such as the top plate 110. In such embodiments, the holes in the cooling elements 320B and the holes 363 can function in a manner similar to the outlets 112. Further, although the cooling elements 300A and 300B are depicted as being supported in the central regions, in some embodiments, one cantilevered segment of the cooling elements 320A and / or 320B can be omitted. In such embodiments, the cooling elements 320A and / or 320B can be considered to be supported or anchored at or near one edge, while at least a portion of the opposite edge is free to perform vibrational motion. In some such embodiments, the cooling elements 320A and / or 320B can include a single cantilevered segment that performs vibrational motion.

[0067] Figures 3D-3D FIGS. 3C and 3D depict plan views of embodiments of cooling systems 300C and 300D similar to active cooling systems, such as the cooling system 100. For simplicity, only the cooling elements 320C and 320D and the anchors 360C and 360D, respectively, are shown. The cooling elements 320C and 320D are similar to the cooling element 120. Thus, the dimensions and / or materials used for the cooling elements 320C and / or 320D can be similar to the dimensions and / or materials used for the cooling element 120. The anchors 360A and 360D are similar to the anchor 160 and are indicated by dashed lines.

[0068] For the cooling elements 320C and 320D, the anchors 360C and 360D, respectively, are limited to the central regions of the cooling elements 320C and 320D, respectively. Thus, the regions surrounding the anchors 360C and 360D perform vibrational motion. The cooling elements 320C and 320D can thus be configured to vibrate in a manner similar to a jellyfish or in a manner similar to the opening / closing of an umbrella. In some embodiments, the entire perimeters of the cooling elements 320C and 320D vibrate in phase (e.g., all move up or down together). In other embodiments, portions of the perimeters of the cooling elements 320C and 320D vibrate out of phase. In some embodiments, the cooling elements 320C and 320D can be configured to vibrate in a manner similar to a flag. Figure 3C and 3D In the embodiments depicted in FIGS. 3C and 3D, L is the length (e.g., diameter) of the cooling element, similar to Figures 1A-1F Although the cooling elements 320C and 320D are depicted as being circular, the cooling elements can have another shape. Further, piezoelectric bodies (not shown in FIGS. 3C and 3D) and / or other mechanisms can be used to drive the vibrational motion of the cooling elements 320C and 320D. Figures 3C-3D ​

[0069] exist Figure 3D In the embodiment shown, the anchor 360D is hollow and has a hole 363. In some embodiments, the cooling element 320D has a hole in a region of the anchor 360D. In some embodiments, the cooling element 320D comprises multiple portions such that the hole exists in a region of the anchor 360D. As a result, fluid can be drawn through the cooling element 320D and the anchor 360D. Fluid can exit through the hole 363. Therefore, the cooling element 320D can be used instead of a top plate, such as top plate 110. In such embodiments, the hole and hole 363 in the cooling element 320D can function in a manner similar to outlet 112.

[0070] Cooling systems such as cooling system 100 can utilize cooling elements 320A, 320B, 320C, 320D, and / or similar cooling elements. Such cooling systems also enjoy the benefits of cooling system 100. Cooling systems using cooling elements 320A, 320B, 320C, 320D, and / or similar cooling elements can more effectively drive fluid toward the heat-generating structure at high speeds. Therefore, heat transfer between the heat-generating structure and the moving fluid is improved. Because the heat-generating structure is more effectively cooled, the corresponding device can exhibit improved operation, such as operating at higher speeds and / or power for longer periods. Cooling systems employing cooling elements 320A, 320B, 320C, 320D, and / or similar cooling elements are suitable for smaller devices and / or mobile devices with limited available space. Therefore, the performance of such devices can be improved. Because cooling elements 320A, 320B, 320C, 320D, and / or similar cooling elements can vibrate at frequencies of 15 kHz or higher, the user cannot hear any noise associated with actuating the cooling elements. If the acoustic and / or structural resonant frequencies of cooling elements 320A, 320B, 320C, 320D and / or similar cooling elements are driven, the power used in operating the cooling system can be significantly reduced. Cooling elements 320A, 320B, 320C, 320D and / or similar cooling elements do not need to physically contact the plate during use, thus allowing for easier maintenance of resonance. The benefits of improved, quieter cooling can be achieved with limited additional power. Therefore, the performance of devices incorporating cooling elements 320A, 320B, 320C, 320D and / or similar cooling elements can be improved.

[0071] Figures 4A-4B An embodiment of an active cooling system 400 including a cooling element anchored at the top center is depicted. Figure 4A A side view depicting the cooling system 400 in a neutral position. Figure 4B A top view depicting the cooling system 400. Figures 4A-4B Not to scale. For simplicity, only a portion of the cooling system 400 is shown. Reference Figures 4A-4BCooling system 400 is similar to cooling system 100. Accordingly, similar components have similar labels. For example, cooling system 400 is used in conjunction with a heat generating structure 402 similar to heat generating structure 102.

[0072] Cooling system 400 includes a top plate 410 having an outlet 412, a cooling element 420, an aperture plate 430 including apertures 432, a top chamber 440 having a gap, a bottom chamber 450 having a gap, and an anchor (i.e., support structure) 460, which are respectively similar to top plate 110 having an outlet 112, cooling element 120, aperture plate 130 including apertures 132, top chamber 140 having a gap 142, bottom chamber 150 having a gap 152, and anchor (i.e., support structure) 160. Accordingly, cooling element 420 is centrally supported by anchor 460 such that at least a portion of the periphery of cooling element 420 is free to vibrate. In some embodiments, anchor 460 extends along the axis of cooling element 420 (e.g., in a manner similar to anchor 360A and / or 360B). In other embodiments, anchor 460 is proximate only a central portion of cooling element 420 (e.g., similar to anchor 360C and / or 360D). Although not explicitly labeled in FIGS. 4A-4D, cooling element 420 includes an anchor region and a cantilever, which includes a step region, an extension region, and an outer region, which are respectively similar to anchor region 122, cantilever 121, step region 124, extension region 126, and outer region 128. In some embodiments, the cantilever of cooling element 420 is driven in phase. In some embodiments, the cantilever of cooling element 420 is driven out of phase. Figure 4A and 4B

[0073] Anchor 460 supports cooling element 420 from above. Accordingly, cooling element 420 is suspended on anchor 460. Anchor 460 is suspended on top plate 410. Top plate 410 includes an outlet 413. Outlet 412 on the side of anchor 460 provides a path for fluid to flow into the side of chamber 440.

[0074] As discussed above with respect to cooling system 100, cooling element 420 can be driven to vibrate at or near a structural resonance frequency of cooling element 420. Further, the structural resonance frequency of cooling element 420 can be configured to align with an acoustic resonance of chamber 440 / 450. The structural and acoustic resonance frequencies are generally selected to be in the ultrasonic range. For example, the vibrational motion of cooling element 420 can be the frequencies described with respect to cooling system 100. Accordingly, efficiency and flow rate can be enhanced. However, other frequencies can be used.

[0075] ​Cooling system 400 operates in a manner similar to cooling system 100. Cooling system 400 therefore enjoys the benefits of cooling system 100. Performance of a device employing cooling system 400 can therefore be improved. Use of cooling elements 420, which are configured in a manner similar to cooling elements 120, can improve efficiency and reliability. Furthermore, suspending cooling elements 420 from anchors 460 can further enhance performance. In particular, vibrations in cooling system 400, which can affect other cooling units (not shown), can be reduced. For example, less vibration due to movement of cooling elements 420 can be induced in top plate 410. Thus, cross-talk between cooling system 400 and other cooling systems (e.g., other units) or other portions of a device incorporating cooling system 400 can be reduced. Performance can therefore be enhanced.

[0076] Figure 5 A side view of an embodiment of a cooling element or actuator 520 is depicted. Figure 5 Not to scale. Cooling element 520 is similar to cooling element 120. Thus, cooling element 520 includes an anchor region 522 and a cantilever 521 similar to anchor region 122 and cantilever 121, respectively. Anchor region 522 is held in place in a cooling system, such as cooling system 100 and / or 400, by an anchor, such as anchor 160 and / or 460. Cantilever 521 is configured to vibrate in response to a driven cooling element 520. Each cantilever 521 includes a step region 524, an extension region 526, and an outer region 528 similar to step region 124, extension region 126, and outer region 128, respectively. In the depicted embodiment, anchor region 522 is located at the center. Step region 524 extends outward from anchor region 522. Extension region 526 extends outward from step region 524. Outer region 528 extends outward from extension region 526. In other embodiments, anchor region 522 can be at one edge of the actuator, and outer region 528 can be at the opposite edge. In such embodiments, the actuator is edge-anchored. The dimensions of extension region 526, step region 524, and outer region 528 can be similar to the dimensions of extension region 126, step region 124, and outer region 128, respectively. Furthermore, outer region 528 can have a higher mass per unit distance from anchor region 522 than extension region 526, as described above with respect to outer region 128.

[0077] Each cantilever 521 also includes an additional step region 529. Additional step region 529 is located between step region 524 and extension region 526. Additional step region 529 has a thickness between the step thickness of step region 524 and the extension thickness of extension region 526. The thickness of the additional step region can be modified based on a desired frequency at which cooling element 520 is to vibrate.

[0078] Cooling element 500 operates in a cooling system, such as cooling system 100 and / or 400, in a manner similar to cooling element 120. A cooling system containing cooling element 500 thus enjoys the benefits of cooling system 100. Performance of a device employing such a cooling system can thus be improved. Use of cooling element 520 can further improve efficiency and reliability. Performance can thus be enhanced.

[0079] Figures 6A-6B An embodiment of a designed actuator 600 is depicted, which can be used as a cooling element in, for example, cooling system 100 and / or 400. Thus, actuator 600 is described as cooling element 600. Figures 6A-6B Not to scale. Figure 6A A side view of cooling element 600 is depicted, including anchor region 602 and cantilevers 601. Figure 6B A bottom perspective view of cantilever 601 is depicted. Anchor region 602 can be used to support or hold cooling element 600 in place in a cooling system, such as cooling system 100 and / or 400, by an anchor, such as anchor 160 and / or 460. Cantilever 601 performs vibrational motion in response to a driven cooling element 600. Each cantilever 601 includes a step region 604 and a recess region 606. In the depicted embodiment, anchor region 602 is located centrally. Step region 604 extends outward from anchor region 602. Recess region 606 extends outward from step region 604. In other embodiments, anchor region 602 can be at one edge of the actuator, and recess region 606 can terminate at the opposite edge. In such embodiments, the actuator is edge-anchored. Further, other regions (not shown) can be included in actuator 600.

[0080] Recess region 606 includes tapers 607, top edge (or cap) 608, and recess 609. Recess 609 between tapers 607 is a depression in cooling element 600. Thus, if cooling element 600 is used in a cooling system, such as cooling system 100 and / or 400, recess 609 provides a cavity that can be considered to increase the size of the bottom chamber. The width of taper 608 decreases as the distance from anchor region 602 increases. Similarly, recess 609 has a recess width that increases as the distance from anchor region 602 increases. For example, the taper (i.e., the change in width) can be selected from a linear taper, a quadratic taper, and a cubic taper. Other tapers are possible. In some embodiments, tapers 607 and recess 609 can have a constant width (i.e., be non-tapered).

[0081] In operation, cooling element 600 functions in a manner similar to cooling element 120. Thus, cooling element 600 can be driven to perform a vibrational motion. When used in a cooling system, such as cooling system 100 and / or 400, cooling element 600 can drive a fluid at the speeds described herein. Thus, cooling element 600 can be used to efficiently cool a heat generating structure. Moreover, recess 609 can reduce the suction / pressure increase during the upward / downward travel of cantilever 601 in a manner similar to extension 126 of cooling element 120. Thus, efficiency can be further improved. Moreover, taper 607 can reduce the stress experienced by cantilever 601 during the vibrational motion. Thus, the reliability of cooling element 600 can be improved.

[0082] Figure 7 is a perspective view of an embodiment of a cantilever 701 that can be part of a cooling element, such as cooling element 600. Figure 7 Not to scale. Cantilever 701 can be adjacent to an anchoring region (not shown) that can be used to support or hold a cooling element of which cantilever 701 is a part. In some embodiments, cantilever 701 can be part of a center-anchored cooling element or part of an edge-anchored cooling element. Cantilever 701 performs a vibrational motion in response to such a driven cooling element. Cantilever 701 includes a step region 704 and a recess region 706. Step region 704 extends outward from an anchoring region (not shown). Recess region 706 extends outward from step region 704. Other regions (not shown) can be included in cantilever 701.

[0083] Recess region 706 includes a taper 707, a bottom edge (or lid) 708, and a recess 709. Taper 707 and recess 709 are similar to taper 607 and recess 609, respectively. If cantilever 701 is used in a cooling system, such as cooling system 100 and / or 400, bottom edge 708 abuts a bottom chamber. Thus, if cantilever 701 is used in a cooling system, such as cooling system 100 and / or 400, recess 709 provides a cavity that can be viewed as increasing the size of a top chamber. The width of taper 708 decreases as the distance from step region 704 increases. For example, the taper (i.e., the change in width) can be selected from a linear taper, a quadratic taper, and a cubic taper. Other tapers are possible. In some embodiments, taper 707 and recess 709 can have a constant width (i.e., non-tapered).

[0084] In operation, the cantilever 701 functions similarly to the cantilever 601 of the cooling element 600. Therefore, the cantilever 701 can be driven to vibrate. When used in a cooling system such as cooling system 100 and / or 400, the cantilever 701 can drive fluid at the speeds described herein. Therefore, the cantilever 701 can be used to effectively cool heat-generating structures. Furthermore, the recess 709 reduces the increase in suction / pressure during the downward / upward stroke of the cantilever 701. Therefore, efficiency is improved. Additionally, the tapered shape 707 reduces the stress experienced by the cantilever 701 during vibrating motion. Therefore, the reliability of the cantilever 701 is improved.

[0085] Figure 8 This is a perspective view of an embodiment of cantilever 801, which may be a portion of a cooling element such as cooling element 600. Figure 8 Not to scale. Cantilever 801 may be adjacent to an anchorage area (not shown) that may be used to support or retain a cooling element to which cantilever 801 is part. In some embodiments, cantilever 801 may be part of a centrally anchored cooling element or a peripherally anchored cooling element. Cantilever 801 oscillates in response to a driven cooling element. Cantilever 801 includes a stepped area 804 and a recessed area 806. Stepped area 804 extends outward from anchorage area (not shown). Cantilever 801 also includes an additional recessed area 816. Recessed area 806 extends outward from additional recessed area 816. Other areas (not shown) may be included in cantilever 800.

[0086] The recessed area 806 includes a cone 807, a top edge 808, and a recess 809, which are similar to the recessed area 606, cone 607, top edge 608, and recess 609 of the cooling element 600. An additional recessed area 816 includes a cone 817, a bottom edge (or cap) 818, a top edge 808, and a groove (…). Figure 8 (Not marked in the text). The cone 817 and the recess are similar to the cone 807 and the recess 809, respectively. However, the cone 817 and the corresponding recess are surrounded by a bottom edge 818 and a top edge 808. In some embodiments, the sides of the recessed area 816 may also be closed. If the cantilever 801 is used in a cooling system such as cooling system 100 and / or 400, the top edge 808 abuts the top chamber and the bottom edge 818 abuts the bottom chamber. Therefore, if the cantilever 801 is used in a cooling system such as cooling system 100 and / or 400, the recess 809 provides a cavity that can be considered as increasing the size of the bottom chamber. Therefore, the suction in the bottom chamber during the upward stroke of the cantilever 801 and the pressure increase during the downward stroke of the cantilever 801 can be mitigated. Therefore, the cantilever 801 can move the fluid through the chamber more efficiently. However, due to the presence of the top edge 808 and the bottom edge 818, the additional recessed section 816 does not significantly affect the pressure in the surrounding chamber. Instead, the additional recessed section 816 reduces stress.

[0087] In operation, the cantilever 801 functions in a similar manner to the cantilever 601 of the cooling element 600. Thus, the cantilever 801 can be driven to perform a vibrational motion. When used in a cooling system, such as the cooling systems 100 and / or 400, the cantilever 801 can drive a fluid at the speeds described herein. Thus, the cantilever 801 can be used to effectively cool a heat generating structure. Moreover, the recess 809 can reduce the suction / pressure increase during the upward / downward travel of the cantilever 801. Thus, efficiency can be improved. Moreover, both the taper 808 and the taper 817 can reduce the stress experienced by the cantilever 801 during the vibrational motion. Thus, the reliability of the cantilever 801 can be improved.

[0088] Figure 9 A side view of an embodiment of an actuator or cooling element 900 is depicted. Figure 9 Not to scale. The cooling element 900 is similar to the cooling element 600 and can be used in a cooling system, such as the cooling systems 100 and / or 400. Thus, the cooling element 900 includes an anchor region 902 and cantilevers 901 similar to the anchor region 602 and the cantilevers 601. The anchor region 602 is held in place in a cooling system, such as the cooling systems 100 and / or 400, by an anchor, such as the anchors 160 and / or 460. The cantilevers 901 perform a vibrational motion in response to the driven cooling element 900. In the depicted embodiment, the anchor region 902 is in the center. In other embodiments, the anchor region 902 can be at one edge of the actuator and the recess region 906 can be at the opposite edge. In such embodiments, the actuator is edge anchored.

[0089] Each cantilever 901 is similar to the cantilevers 601, 701, and 801. Thus, each cantilever includes a step region 904, a recess region 906, and an extra region 916. The recess regions 906 and 916 include tapers (not explicitly shown) and recesses (not explicitly shown) similar to the tapers 607 and the recess 609. In the depicted embodiment, the recess region 906 has a top cap and a bottom cap. Thus, the recess region 906 can reduce the vibration-induced stress in that portion of the cantilever 901 without substantially changing the pressure in the surrounding chamber. The extra recess region 916 can both reduce stress and affect the pressure in the top chamber in which the cooling element 900 is mounted.

[0090] Cooling element 900 functions in a manner similar to cooling element 600. Thus, cantilever 901 can be driven in vibrational motion. When used in a cooling system, such as cooling systems 100 and / or 400, cooling element 900 can drive fluid at the speeds described herein. Thus, cooling elements can be utilized to effectively cool heat generating structures. Moreover, recess regions 906 and 916 can reduce the suction / pressure increase during the downstroke / upstroke of cantilever 901. Thus, efficiency can be improved. Moreover, both recess regions 90 and 91 can reduce the stress experienced by cantilever 901 during vibrational motion. Thus, the reliability of cooling element 900 can be improved.

[0091] Figure 10 A side view of an embodiment of an actuator or cooling element 1000 is depicted. Figure 10 Not to scale. Cooling element 1000 is similar to cooling element 600 and can be used in a cooling system, such as cooling systems 100 and / or 400. Thus, cooling element 1000 includes an anchor region 1002 and cantilevers 1001 similar to anchor region 602 and cantilevers 601. Anchor region 1002 is held in place in a cooling system, such as cooling systems 100 and / or 400, by an anchor, such as anchor 160 and / or 460. Cantilevers 1001 are in vibrational motion in response to a driven cooling element 1000. In the depicted embodiment, anchor region 1002 is at the center. In other embodiments, anchor region 1002 can be at one edge of the actuator and recess region 1006 can be at the opposite edge. In such embodiments, the actuator is edge anchored.

[0092] Each cantilever 1001 is similar to cantilevers 601, 701, and 801. Thus, each cantilever includes a step region 1004 and a recess region 1006. Recess region 1006 includes a taper (not explicitly shown) and a recess (not explicitly shown) similar to taper 607 and recess 609. In the depicted embodiment, recess region 1006 has a top cap and a bottom cap. Thus, recess region 1006 can reduce vibration-induced stress in that portion of cantilever 1001 without substantially changing the pressure in the surrounding chamber.

[0093] Cooling element 1000 functions in a manner similar to cooling element 600. Thus, cantilevers 1001 can be driven in vibrational motion. When used in a cooling system, such as cooling systems 100 and / or 400, cooling element 1000 can drive fluid at the speeds described herein. Thus, cooling element 1000 can be utilized to effectively cool heat generating structures. Moreover, recess region 1006 can reduce the stress experienced by cantilevers 1001 during vibrational motion. Thus, the reliability of cooling element 1000 can be improved.

[0094] Figures 11-13Embodiments of cantilevers 1101, 1201, and 1301 are depicted, which can be part of a cooling element such as cooling element 600. Figures 11-13 Not to scale. Cantilevers 1101, 1201, and / or 1301 can be adjacent to an anchor region (not shown), which can be used to support or hold a cooling element of which cantilevers 1101, 1201, and / or 1301 are a part. In some embodiments, cantilevers 1101, 1201, and / or 1301 can be part of a center-anchored cooling element or part of an edge-anchored cooling element. Cantilevers 1101, 1201, and 1301 each undergo vibrational motion in response to such a driven cooling element. Cantilever 1101 includes a step region 1104 and a recess region 1106. Anchor region 1102 is also shown. Step region 1104 extends outward from anchor region 1102. Recess region 1106 extends outward from step region 1104. Cantilever 1201 includes a step region 1204 and a recess region 1206. Anchor region 1202 is also shown. Step region 1204 extends outward from anchor region 1202. Recess region 1206 extends outward from step region 1204. Cantilever 1301 includes a step region 1304 and a recess region 1306. Anchor region 1302 is also shown. Step region 1304 extends outward from anchor region 1302. Recess region 1306 extends outward from step region 1304. Other regions (not shown) can be included in cantilevers 1101, 1201, and / or 1301.

[0095] The recess regions 1106, 1206, and 1306 each include a taper 1107, 1207, and 1307, respectively, and a recess 1109, 1209, and 1309, respectively. The cantilevers 1101, 1201, and 1301 indicate that variations in the tapers 1107, 1207, and 1307 can also be used to tailor the stiffness of the cantilevers 1101, 1201, and 1301, respectively. For example, the width of the tapers 1107, 1207, and 1307 can decrease as the square of the distance from the transition between the step region 1104, 1204, and 1304, respectively, and the recess region 1106, 1206, and 1306, respectively. The dashed lines 1108, 1208, and 1308 indicate how the width of the tapers 1107, 1207, and 1037, respectively, can decrease if the width varied linearly with the distance from the transition between the step region 1104, 1204, and 1304, respectively, and the recess region 1106, 1206, and 1306, respectively. Further, the width of the tapers 1107, 1207, and 1307 decreases at different rates. The taper 1107 decreases the most in width at the edge (e.g., to approximately ninety percent). The taper 1207 decreases to a lesser amount at the opposite edge (e.g., to approximately seventy-five percent). The taper 1307 decreases to the least amount at the opposite edge (e.g., to approximately fifty percent). Other variations in width (e.g., cubic) and other tapering amounts can be used. By tailoring the way in which the taper width varies and / or the amount to which the width varies, the reduction in stiffness and stress of the cantilever can be modified.

[0096] The cantilevers 1101, 1201, and 1301 function in a similar manner to the cantilever 601 of the cooling element 600. Thus, the cantilevers 1101, 1201, and 1301 can be driven to perform vibrational motion. When used in a cooling system, such as the cooling systems 100 and / or 400, the cantilevers 1101, 1201, and 1301 can drive fluid at the speeds described herein. Thus, the cantilevers 1101, 1201, and 1301 can be used to effectively cool heat generating structures. Further, the recess regions can be configured to reduce stress while maintaining stiffness. Thus, the reliability of the cantilevers 1101, 1201, and 1301 can be improved.

[0097] Figure 14A and 14B depicts a side view and a bottom view of an embodiment of an actuator or cooling element 1400. Figures 14A-14BNot to scale. Cooling element 1400 is similar to cooling element 120 and cooling element 600. Cooling element 1400 can be used in a cooling system such as cooling system 100 and / or 400. Thus, cooling element 1400 includes an anchor region 1422 and a cantilever 1421 similar to anchor regions 122 and 602 and cantilevers 121 and 601. Anchor region 1422 is held in place in a cooling system such as cooling system 100 and / or 400 by an anchor such as anchor 160 and / or 460. Cantilever 1421 is responsive to a driven cooling element 1400 to perform vibrational motion. In the illustrated embodiment, anchor region 1422 is at the center. In other embodiments, anchor region 1422 can be at one edge of the actuator.

[0098] Each cantilever 1421 is similar to cantilever 121 and cantilevers 601, 701, and 801. Thus, each cantilever includes a step region 1424, an extension region 1426, and an outer region 1428 similar to step region 124, extension region 126, and outer region 128. Cantilevers 1421 each include a recess region 1406 having a taper 1427 and a recess 1429 similar to taper 627 and recess 629. Thus, a portion of extension region 1426 is also a recess. In some embodiments, step region 1424 and / or outer region 1428 can include a recess and / or a taper in place of or in addition to extension region 1426. Thus, the configuration of cooling element 120 and the recesses and / or cantilevers 701, 801, 1101, 1201, and / or 1301 of cooling elements 600, 900, and / or 1000 can be combined in various ways.

[0099] Cooling element 1400 functions in a manner similar to cooling element 120 and 600. Thus, cantilever 1401 can be driven to perform vibrational motion. When used in a cooling system such as cooling system 100 and / or 400, cooling element 1400 can drive fluid at the speeds described herein. Thus, cooling element 1400 can be used to efficiently cool a heat generating structure. In addition, the ability of cantilever 1401 to move through fluid can be improved and the stresses experienced by cantilever 1401 during vibrational motion are reduced. Thus, the efficiency, performance, and reliability of cooling element 1400 can be improved.

[0100] Various cooling elements 120, 420, 600, 900, 1000, and 1400 and various cantilevers 701, 801, 1101, 1201, and 1301 are described and particular features are highlighted. Various properties of cooling elements 120, 420, 600, 900, 1000, and 1400 and various cantilevers 701, 801, 1101, 1201, and 1301 can be combined in ways not explicitly depicted herein.

[0101] Figures 15A-15B An embodiment of an active cooling system 1500 comprising a plurality of cooling units configured as tiles is depicted. Figure 15A A top view is depicted, while Figure 15B A side view is depicted. Figures 15A-15B Not to scale. Cooling system 1500 comprises four cooling units 1501, which are similar to one or more of the cooling systems described herein, such as cooling systems 100 and / or 400. Although four cooling units 1501 are shown in a 2x2 configuration, in some embodiments another number and / or another configuration of cooling units 1501 can be employed. In the depicted embodiment, cooling units 1501 comprise a common top plate 1510 having holes 1512, cooling elements 1520, a common hole plate 1530 comprising holes 1532, a top chamber 1540, a bottom chamber 1550, and anchors (support structures) 1560, which are similar to top plate 110 having holes 112, cooling elements 120, hole plate 130 having holes 132, top chamber 140, bottom chamber 150, and anchors 160. Although depicted in the context of cooling elements 920, any combination of cooling elements 120, 420, 600, 900, 1000, and 1400, and various cantilevers 701, 801, 1101, 1201, and 1301 can be used. Although bottom anchors 1560 are shown, in other embodiments top anchors can be used. In the depicted embodiment, cooling elements 1520 are driven out of phase (i.e., in a manner similar to a seesaw). Moreover, cooling elements 1520 in one unit are driven out of phase with cooling elements in adjacent units.

[0102] Cooling units 1501 of cooling system 1500 function in a manner similar to cooling systems 100 and / or 400. Thus, the benefits described herein can be enjoyed by cooling system 1500. Due to the out-of-phase driving of cooling elements in nearby units, vibration in cooling system 1500 can be reduced. Due to the use of a plurality of cooling units 1501, cooling system 1500 can enjoy enhanced cooling capacity.

[0103] Figure 16 A top view of an embodiment of a cooling system 1600 comprising a plurality of cooling units 1601 is depicted. Figure 16 Not to scale. Cooling units 1601 are similar to one or more of the cooling systems described herein, such as cooling systems 100 and / or 400. As indicated in cooling system 1600, cooling units 1601 can be arranged in a two-dimensional array of desired size and configuration. In some embodiments, cooling system 1600 can be viewed as being composed of a plurality of tiles 160. Thus, desired cooling power and configuration can be achieved.

[0104] Figure 17is a flowchart depicting an exemplary embodiment of a method 1700 for operating a cooling system. The method 1700 can include steps not depicted for simplicity. The method 1700 is described in the context of the piezoelectric cooling system 100. However, the method 1700 can be used with other cooling systems, including but not limited to the systems and units described herein.

[0105] At 1702, one or more cooling elements in the cooling system are actuated to vibrate. At 1702, an electrical signal having a desired frequency is used to drive the cooling elements. In some embodiments, at 1702, the cooling elements are driven at or near a structural and / or acoustic resonance frequency. The drive frequency can be 15 kHz or higher. If multiple cooling elements are driven at 1702, the cooling elements can be driven out of phase. In some embodiments, the cooling elements are driven substantially 180 degrees out of phase. Further, in some embodiments, individual cooling elements are driven out of phase. For example, different portions of a cooling element can be driven to vibrate in opposite directions (i.e., similar to a seesaw). In some embodiments, individual cooling elements can be driven in phase (i.e., similar to a butterfly). Further, the drive signal can be provided to the anchor, the cooling element, or both the anchor and the cooling element. Further, the anchor can be driven to bend and / or translate.

[0106] At 1704, feedback from the piezoelectric cooling elements is used to adjust the drive current. In some embodiments, the adjustment is used to keep the frequency at or near one or more acoustic and / or structural resonance frequencies of the cooling elements and / or the cooling system. The resonance frequency of a particular cooling element can drift, for example, due to changes in temperature. The adjustment made at 1704 allows for the drift in the resonance frequency to be accounted for.

[0107] For example, at 1702, the piezoelectric cooling element 120 can be driven at its structural resonance frequency / frequency. This resonance frequency can also be at or near an acoustic resonance frequency with respect to the top chamber 140. This can be achieved by driving the piezoelectric layer in the anchor 160 (not shown) and / or the piezoelectric layer in the cooling element 120. At 1704, feedback is used to keep the cooling element 120 resonating, and in some embodiments where multiple cooling elements are driven, 180 degrees out of phase. Thus, the efficiency of the cooling element 120 in driving fluid flow through the cooling system 100 and onto the heat generating structure 102 can be maintained. In some embodiments, 1704 includes sampling the flow through the cooling element 120 and / or the flow through the anchor 160 and adjusting the flow to maintain resonance and low input power. Figures 1A-1F

[0108] ​Thus, cooling elements such as cooling elements 120, 420, 600, 900, 1000, and 1400, as well as various cantilevers 701, 801, 1101, 1201, and 1301 can operate as described above. Thus, method 1700 provides for use of the piezoelectric cooling systems described herein. Thus, the piezoelectric cooling systems can cool semiconductor devices more efficiently and quietly at lower power.

[0109] While the foregoing embodiments have been described in some detail for purposes of clarity and understanding, the application is not limited to the details provided. There are many alternative ways of implementing the application. The disclosed embodiments are illustrative and not restrictive.

Claims

1. An actuator, comprising: an anchor region; and a cantilever extending outwardly from the anchor region, wherein the cantilever comprises a step region extending outwardly from the anchor region, the step region having a step thickness; an extension region extending outwardly from the step region, the extension region having an extension thickness that is less than the step thickness; and an outer region extending outwardly from the extension region, the outer region having an outer thickness that is greater than the extension thickness; wherein the actuator resides in a system comprising a chamber, a well plate comprising at least one aperture therein, and a support structure, the actuator residing in the chamber and being supported by the support structure at the anchor region, the actuator dividing the chamber into a top chamber and a bottom chamber in fluid communication with the top chamber, the well plate forming a wall of the bottom chamber, the actuator configured to perform a vibrational motion of the cantilever when actuated to draw fluid into the top chamber, direct the fluid through the top chamber and into the bottom chamber, and expel the fluid from the bottom chamber through the at least one aperture.

2. The actuator of claim 1, wherein the cantilever further comprising: an additional step region between the step region and the extension region, the additional step region having an additional step thickness that is less than the step thickness and greater than the extension thickness.

3. The actuator of claim 1, wherein the outer thickness is at least fifty microns and no more than two hundred microns greater than the extension thickness, wherein the outer region has a width of at least one hundred microns and no more than three hundred microns, and wherein the extension region has a length extending outwardly from the step region of at least 0.5 millimeters and no more than 1.5 millimeters.

4. The actuator of claim 1, wherein at least one of the step region, the extension region, and the outer region comprises at least one recess therein.

5. The actuator of claim 4, wherein, the at least one recess comprises a taper such that a width of the at least one recess increases with distance from the anchor region.

6. The actuator of claim 5, wherein, the taper is selected from a linear taper, a quadratic taper, and a cubic taper.

7. The actuator of claim 4, wherein the actuator further comprising: a cap configured such that the at least one recess is internal to the actuator.

8. The actuator of claim 1, wherein the actuator further comprising: an additional cantilever extending outwardly from the anchor region opposite the cantilever, and wherein the additional cantilever comprises an additional step region extending outwardly from the anchor region, the additional step region having an additional step thickness; an additional extension region extending outwardly from the additional step region and having an additional extension thickness that is less than the additional step thickness; and an additional outer region extending outwardly from the additional extension region and having an additional outer thickness that is greater than the additional extension thickness.

9. A cooling system, comprising: a chamber; a well plate comprising at least one aperture therein; an anchor in the chamber; and a cooling element comprising an anchor region secured by the anchor and a cantilever extending outwardly from the anchor region, wherein the cantilever comprises a step region extending outwardly from the anchor region, the step region having a step thickness; an extension region extending outwardly from the step region, the extension region having an extension thickness that is less than the step thickness; and an outer region extending outwardly from the extension region, the outer region having an outer thickness that is greater than the extension thickness; an extension region extending outwardly from the step region, the extension region having an extension thickness that is less than the step thickness; and an outer region extending outwardly from the extension region, the outer region having an outer thickness that is greater than the extension thickness; wherein the cooling element resides in the chamber and divides the chamber into a top chamber and a bottom chamber in fluid communication with the top chamber, the orifice plate forming a wall of the bottom chamber, the cooling element configured to perform the oscillatory motion of the cantilever when actuated to draw fluid into the top chamber, direct the fluid through the top chamber and into the bottom chamber, and expel the fluid from the bottom chamber through the at least one orifice.

10. The cooling system of claim 9, wherein, The cantilever further comprises: an additional step region between the step region and the extension region, the additional step region having an additional step thickness that is less than the step thickness and greater than the extension thickness.

11. The cooling system of claim 9, wherein, At least one of the step region, the extension region, and the outer region includes at least one recess therein.

12. The cooling system of claim 11, wherein, The cooling element further comprises: a cap configured such that the at least one recess is internal to the cooling element.

13. The cooling system of claim 9, wherein, The cooling element further comprises: an additional cantilever extending outwardly from the anchor region opposite the cantilever, and wherein the additional cantilever comprises an additional step region extending outwardly from the anchor region and having an additional step thickness; an additional extension region extending outwardly from the additional step region and having an additional extension thickness that is less than the additional step thickness; and an additional outer region extending outwardly from the additional extension region and having an additional outer thickness that is greater than the additional extension thickness.

14. A method of cooling a heat generating structure, comprising: actuating a cooling element to induce an oscillatory motion at a frequency, the cooling element comprising an anchor region and a cantilever extending outwardly from the anchor region, wherein the cantilever comprises a step region extending outwardly from the anchor region, the step region having a step thickness, an extension region extending outwardly from the step region, the extension region having an extension thickness that is less than the step thickness, and an outer region extending outwardly from the extension region, the outer region having an outer thickness that is greater than the extension thickness, the cooling element configured to perform the oscillatory motion when actuated to drive fluid toward the heat generating structure; wherein the cantilever includes a step region, an extension region, and an outer region, the step region extending outwardly from the anchor region and having a step thickness, the extension region extending outwardly from the step region and having an extension thickness that is less than the step thickness, the outer region extending outwardly from the extension region and having an outer thickness that is greater than the extension thickness, the cooling element residing in a system that includes a chamber, a orifice plate including at least one orifice therein, and a support structure, the cooling element residing in the chamber and being supported by the support structure at the anchor region, the cooling element dividing the chamber into a top chamber and a bottom chamber in fluid communication with the top chamber, the orifice plate forming a wall of the bottom chamber, the cooling element configured to perform a vibrational motion of the cantilever when actuated to draw fluid into the top chamber, direct the fluid through the top chamber and into the bottom chamber, and expel the fluid from the bottom chamber through the at least one orifice.

15. The method of claim 14, wherein, The actuating further includes: actuating the cooling element at a frequency that is substantially a structural resonance frequency of the cantilever.

16. The method of claim 15, wherein, The actuating further includes: actuating the cooling element at a frequency that is substantially a fluid resonance frequency.

17. The method of claim 14, wherein, The cooling element further includes an additional cantilever extending outwardly from the anchor region opposite the cantilever, the additional cantilever including an additional step region, an additional extension region, and an additional outer region, the additional step region extending outwardly from the anchor region and having an additional step thickness, the additional extension region extending outwardly from the additional step region and having an additional extension thickness that is less than the additional step thickness, the additional outer region extending outwardly from the additional extension region and having an additional outer thickness that is greater than the additional extension thickness, the method further including: actuating the additional cantilever at the frequency.

18. The method of claim 17, wherein, The actuation frequency is substantially at least one of an additional structural resonance frequency of the additional cantilever and a fluid resonance frequency.

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