Patent ID: 12209817

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference to the accompanying drawings.

The present disclosure is related to systems and methods for dynamically controlling the radiative thermal emission profile from a surface, both in amplitude and in direction of emission, so that the surface thermal impedance can be changed by >10×, and so that the direction of emission of the low impedance flow can be dynamically controlled over a full 360° range.

The various embodiments described herein a thermal emission control system which in some embodiments makes use of a base layer having a high emissivity surface, and which is adapted to operate at high temperatures (e.g., 300 degrees C. or even higher). The system also includes a segmented array having a plurality of actuation elements and a plurality of shutter elements. The actuation elements are supported on the high emissivity surface of the base and support the shutter elements above the high emissivity surface. The shutter elements are movable, and their movements are controlled by the actuation elements. The high emissivity surface of the base dissipates heat, while the segmented array suppresses the surface's emissions unless the shutter elements are tilted to provide an enlarged gap through which high flux emissions can occur. In this manner the degree of opening of the shutter elements controls the degree of high flux emissions that can be released through the segmented array. The orientation of the shutter elements thus controls the overall thermal emissivity of the device, and may be further controlled to control a direction of the thermal emissivity from the base as well.

Referring toFIG.1one embodiment of a thermal management system10is shown in accordance with the present disclosure. The system10includes a segmented array12, and in some implementations an electronic control system14as well. An optional thermal sensing system16may be included which is in thermal communication with the segmented array12and electrical communication with the electronic control system14.

The segmented array12includes a base layer18which may be made from any thermally conductive material, but in some preferred embodiments, and without limitation, is made of silicon or silicon carbide via microfabrication. The base layer18is able to function at a high temperature (e.g., up to 300° C. or even higher), and optionally may include a high emissivity layer or coating on a surface18ato produce a high thermal radiative flux. The base layer18in one example supports a plurality of actuation elements20, which in turn are coupled to a plurality of shutter elements S1-Sn. The actuation elements20may also be supported adjacent the base layer18on an independent component, rather than supported from the base layer itself, and the present disclosure therefore contemplates both types of assembly configurations.

In one embodiment a separate actuation element or set of actuation elements20is used for each shutter element S1-Sn, which enables maximum flexibility in tiling movement and translational movement of the shutter elements S1-Sn about all three of X, Y and Z axes. However, in other embodiments a single actuation element20could be used to activate two or more shutter elements, although such an arrangement would limit the range of motion of the shutter elements to one axis (i.e., either X or Y axes) of tilting movement and translational movement (i.e., up and down about the Z axis), as will become apparent from the following discussion. In this latter embodiment, for example, one actuation element20could be used to simultaneously control tilting or translation movement of an entire row or an entire column of shutter elements S1-Sn.

FromFIG.1, the shutter elements S1-Sn can be seen to be laid out in an X/Y grid pattern, with a small gap or spacing20a(i.e., typically 5 μm-10 μm) between them. In the example ofFIG.1, the shutter elements S1-Sn have a hexagonal shape, although this is but one suitable shape, and other shapes (e.g., and without limitation, square, rectangular, octagonal, pentagonal, triangular, round, etc.) could be used. Preferably, whatever shape is selected will allow for a uniform repeating pattern of the shutter elements S1-Sn. Hexagonally shaped shutter elements S1-Sn are especially desirable as they readily enable tilting, tipping and translational movement, while still enabling the dimension of the gap20ato be closely controlled and defined. The gap or spacing20abetween the shutter elements S1-Sn is also such to allow free tiling, tipping and translational movement of adjacently positioned shutter elements S1-Sn without interference with one another, while still forming a substantially solid surface, parallel to the surface18aof the base layer18, when the shutter elements are all in their closed positions. In their closed positions, the shutter elements S1-Sn form a flat plane arranged parallel to the base layer18, and are able to suppress substantially all thermal radiation from the base layer18. The controlled tiling, tipping, rotational or translational movement of the shutter elements S1-Sn effectively enlarges the gaps20abetween adjacent shutter elements S1-Sn, and these movements of the shutter elements can be used to effectively control the amplitude of thermal radiation that is radiated through the segmented array12, while the controlled degree of tilting and tipping movements may be used to control the direction in which the thermal radiation is emitted, as will be described further in the following paragraphs. When in their fully opened orientations, the shutter elements S1-Sn enable maximum transmission of thermal radiation out through the gaps20a. In most applications it is expected that the segmented array12may incorporate anywhere from just a few dozen shutter elements S1-Sn to possibly thousands or more of shutter elements S1-Sn, and the specific application will have a large bearing on the precise number of shutter elements needed.

With further reference toFIG.1, the electronic control system14, if included as part of the system10, may include a non-volatile memory22(e.g., RAM/ROM, etc.), as well as a control software module22afor assisting in generating commands for controlling movement of the shutter elements S1-Sn. A communications transceiver24(e.g., RS-232; parallel, wireless, analog wiring, etc.) may be used to communicate control signals to the actuation elements20to perform the needed tilting, tipping, rotational and/or translational (i.e., piston-like) movement. The control signals may be applied independently, in one embodiment in parallel simultaneously to all of the actuation elements20. Optionally, a lesser plurality of control signals could be applied to control select groups of actuation elements20, while still controlling all of the actuation elements as a single subsystem. In one embodiment the system10may be operated in a closed loop fashion with the electronic control system14, for example using signals received from the thermal sensing subsystem16or any other external component as feedback signals, to help control movement of the shutter elements S1-Sn. Alternatively, the system10could be controlled in an open loop fashion. An open loop control scheme may involve a database stored in the memory22which contains one or more lookup tables for helping to determine the needed positioning signals for the shutter elements S1-Sn. The needed positioning signals may be based on information obtained from an on-board subsystem (i.e., carried by the electronic control system14) or information obtained from an external subsystem in communication with the electronic control system (e.g., thermal sensing subsystem16or a remote subsystem in wired or wireless communication with the electronic control system14. Still further, select ones of the shutter elements S1-Sn could be tiled, tipped, rotated or translated to open by differing amounts or degrees, and/or at different times, through either closed loop or open loop control schemes. As such, thermal radiation can be released in a highly controlled fashion from the base layer18, for example from a fore to an aft location of the base layer, over a period of time.

FIG.2shows a highly simplified side view of a portion of the segmented array12illustrating how one of the shutter elements S1-Sn is supported above the surface18aof the base layer18by a set distance, indicated by arrows26. The distance defined by arrows26is selected to provide sufficient room for the actuation elements20on the base layer18to drive the shutter elements S1-Sn. This means there must be room for the shutter elements S1-Sn to rotate. In the case of designs using flexible linkages between the actuation elements20and the shutter elements S1-Sn, there must be sufficient space for linkages to be designed which can bend over the full desired range of motion. This tends towards designs of approximately 200 μm-500 μm spacing between the actuation elements20and the shutter elements S1-Sn. In this regard, tilting motion may be considered to be about one axis, for example the X axis, while tipping motion may be considered to be about the perpendicular Y axis. Translational movement of the shutter element S1may be along the Z axis. Rotational motion of each of the shutter elements by the actuation elements20may also be about the Z axis (i.e., parallel to, towards and away from, the transmissive surface18a. The size (i.e., surface area) of the shutter elements S1-Sn may vary considerably to meet the needs of a specific application, and the present disclosure is not limited to use with shutter elements S1-Sn of any specific diameter or surface area, but in most applications it is expected that shutter elements will perform well if formed with a general diameter of about 0.5 mm-2 mm, or a general surface area of about 1 mm2.

The actuation elements20each form low thermal conductivity linkage subsystems that provide the ability to tilt, tip, rotate and translate their respective shutter elements S1-Sn. One construction suitable for forming the actuation elements20and the shutter elements S1-Sn is disclosed in U.S. Pat. No. 10,444,492 to Hopkins et al., assigned to the assignee of the present disclosure. The entire disclosure of U.S. Pat. No. 10,444,492 is hereby incorporated by reference into the present application. This patent describes a Lightfield Directing Array (“LDA”) having a large plurality of independently controllable shutter/mirror elements that can be tilted, tipped and translated about three perpendicular axes. The applicability of this LDA to help form the segmented array12of the present disclosure will be discussed further in the following paragraphs.

FIGS.3-5show further examples of how the shutter elements S1-Sn may be controlled (i.e.,FIGS.3and4), as well as further illustrate the tipping and tiling motion that may be used to control each shutter element. The shutters S1-Sn in the segmented array12will suppress thermal radiation when in the fully closed position (i.e., completely flat). A command from the electronic controller14to the actuation elements20associated with the appropriate part of the base layer18will cause the desired shutter(s) to tip or tilt. The rotation causes a gap to appear in the surface of the segmented array, as visible inFIGS.3and4, through which the base layer18can emit its thermal radiative flux. In one preferred implementation as mentioned above, the shutter elements S1-Sn have tip, tilt and piston motion control, so they can be raised (piston motion) and tilted by θmas shown inFIG.5, thus providing a gap along a selected edge of each shutter element S1-Sn, while creating no gap on the other, opposite edge, the shutter element, as shown inFIG.4. In one preferred embodiment each shutter element S1-Sn in the segmented array12can be independently controlled to open at a selected angle in both the tilt axis (e.g., about the X axis) and the tip axis (e.g., about the Z axis), or translated towards and away from the base layer18along the Y axis either with or without one or both of tilting and tipping motion. This enables both the amplitude and direction of the thermal emission to be closely controlled. The direction of propagation of the thermal emission is directionally controlled by choosing which way the shutters S1-Sn tilt. If all are tilted or tipped to full rotation in one orientation, then the hot base layer18is maximally allowed to emit in the controlled direction of tilt or tip.

FIG.6shows a graph100illustrating thermal intensity profile curves with the shutter elements S1-Sn of the segmented array12fully open (curve102) and fully closed (curve104) at a 90° scan angle (θZ=90°). The segmented array open curve102shows the emission profile along the plane defined by the θZ=90° line indicated inFIG.5, when the shutter elements S1-Sn are fully open. The profile is showing maximum emissions at low φ angles, then the emissions drop off to 0 by φ=90° which corresponds to normal to the segmented array. This shows the emission profile is directed largely horizontally (along the X-Y plane) inFIG.5. The segmented array closed curve104shows the emission profile along the plane defined by the θZ=90° line indicated inFIG.5, when the shutter elements S1-Sn are fully closed. In this case, the shutter elements S1-Sn are blocking emissions from the base layer18below and the emission profile is dominated by the standard emission profile from the top of the shutter elements, which is much lower intensity than the open shutter profile102.FIG.7shows a plot200where circle202indicates the radial emission of the open shutter element inFIG.5when taken around the θz=0° line as indicated inFIG.5. The emission is highest at φ=0° then drops off to near 0 when facing in the other direction. This shows that the shutter element can direct the emissivity radiation pattern.

The surface emissivity values for the various components of the segmented array12should be carefully engineered to maximize the effect of the thermal profile control. The base layer18upper surface18aemissivity is preferably set near 1 to maximize its ability to transfer heat out of the segmented array12. The bottom surface of the shutter elements S1-Sn (i.e., the surfaces represented by surface SBinFIG.2facing the base layer18) may also have an emissivity near 1 to keep the shutter element temperature low. This creates a nearly black-body cavity between the base layer18and the shutter elements S1-Sn. When the shutters S1-Sn are opened, this black-body cavity is allowed to dump heat into the environment in a controlled direction defined by the gap20abetween adjacent shutter elements S1-Sn. The top surface STof each of the shutter elements S1-Sn should have the lowest possible emissivity, so little flux passes through the shutter elements and out into the environment. The top (i.e., upper) surfaces STof the shutter elements S1-Sn (shown inFIG.2), which do not face the base layer18) may have a mirror or mirror-like coating, which helps to prevent thermal radiation through the shutter elements to the base layer18. The emissivity difference between the top surfaces of the shutter elements S1-Sn and the base layer18determines the scale of the possible thermal impedance change. High reflectivity upper surfaces on the shutter elements S1-Sn can provide very low emissivity, so aluminum or silver coatings could be used to provide values down to 0.02 for emissivity (see, e.g., “Silver-Based Low-Emissivity Coating Technology for Energy-Saving Window Applications”|IntechOpen). Further tradeoffs could be made based on separating the design requirements for the base layer18top surface18aand shutter element S1-Sn top surface STinFIG.2. The base layer18top surface18ashould be optimized for thermal emission from the base layer, while the shutter element S1-Sn top surface STcould be engineered to manage incoming external radiation while minimizing emissivity in the IR regime. This engineering could be tuned to whether the goal is absorption or emission in specific wavelengths of external radiation. For instance, a highly reflective surface on the top of the shutter element S1-Sn would be ideal to reflect external solar radiation and would also provide a low emissivity surface, maximizing the thermal control of the segmented array12. More complex coatings such as metamaterials or nanoparticles could be used to engineer a detailed spectrally dependent response for the shutter top surface to balance between external radiation requirements and minimizing thermal radiation emissivity as needed for the particular application.

The LDA, described in U.S. Pat. No. 10,444,492 mentioned above, is an example of a segmented array system which has the features and capabilities (base layer, shutter layer, segmented array, tip/tilt/piston control) needed to accomplish the thermal radiation magnitude and directional control of the segmented array12. One preferred approach for the system10may be to use a LDA array adapted for high temperature operation (e.g., using all ceramic linkages in the actuation element20), as the segmented array12, and with the proper surface coatings as described above to maximize thermal emissivity performance.

An LDA-based thermal profile segmented array, such as the segmented array12, has a number of advantages over conventional thermal modification structures like louvers. For one, the LDA approach is solid-state, containing no sliding bearings that could seize after use. Another advantage is that the LDA is a microscale surface structure, so the entire device could simply be bonded to the hot side of an external heat sink structure, without incurring significant size, weight or power penalties. Still another advantage is that the LDA is driven electrostatically which consumes very little power, adding little heat to the system. Still another advantage is that the LDA is manufactured from silicon (although even higher temperature materials are feasible), which means it has high thermal conductivity and can withstand high temperatures (>300° C.) without failure, which enables it to act as an effective uniform heat dissipation surface. Still another advantage is that microelectromechanical system (MEMS) devices like the LDA are compatible with microfabrication techniques, meaning they can easily be coated to correctly engineer the surface emissivity as described previously. Still another advantage is that the linkages between the base layer and the shutter layer in the LDA, which may form the actuation element20, are vertical transmission elements which are ceramic and have extremely low thermal conductivity due to their scale and geometry. This means the shutter elements S1-Sn can be effectively suspended above the hot base layer18with only radiative heat transfer coupling, making them more efficient at controlling thermal impedance than the macro-scale louver approaches. Finally, the LDA tip/tilt/piston capability provides for the full 360° control of the thermal emission profile, in contrast to the limited unidirectional control provided by conventional louvers. From the above, the use of the LDA as the micro electromechanical to form the segmented array12provides a wide range of important benefits and advantages over present day louver-based thermal control systems.

If desired, the LDA-based approach also provides the ability to drive individual shutter elements S1-Sn in piston motion (i.e., translational motion along the Z axis) to allow for thermal emissions in all directions. However, this would likely be less effective than opening all the shutter elements S1-Sn of the segmented array12a particular direction via rotation, since if all the shutter elements were equally pistoned then the shutter surface would merely have been shifted upwards without opening. At best then, only around ½ of the elements could be opened in an array via purely piston translation.

The various embodiments described herein can be used for high performance equipment to control heat sink temperatures, to provide directional IR illumination, as an energy efficient way to selectively heat objects in 3D space, or to help dissipate energy in highly anisotropic environments as might be found by satellites in orbit. The various embodiments described herein provide a highly controllable and directable emission surface that can help ensure that waste heat is directed to the cold part of the environment, while orienting a custom designed surface towards the hot part of the environment. In one specific application, this allows satellites to continue to dissipate operationally generated heat even when the heat sink is illuminated by the sun, as would occur during part of each orbit. In this particular implementation of the system10, the dynamic control provided by the segmented array12ensures that the surface emissions from the satellite will always point away from the sun, regardless of the satellite orientation. For land, sea, air, or space systems attempting to control their thermal signature, the shutter elements S1-Sn of the segmented array12can be fully closed to temporarily suppress thermal emissions. Alternatively, the segmented array12can be controlled so that emissions are directed away from likely threat vectors. Still further, the segmented array12can be controlled so that emissions can be randomly varied in different directions to minimize detection, identification, and/or tracking risk.

Other implementations of the various embodiments described herein may be with other forms of manned or unmanned space systems or vehicles (e.g., rovers). Other commercial implementations may be with dynamic directional room space heaters. Still further applications may be with land, sea and airborne systems where controlling a radiative thermal profile being emitted from one or more heat generating devices is important, and/or where selectively limiting the radiative thermal emission and the incoming thermal radiation from external heat sources during different times of the day, or during different stages of operation of the device, are important.

The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.