Abstract:
A thermal management system for an embedded environment is described. The thermal management system includes a pleumo-jet that has at least one wall defining a chamber, at least one piezoelectric device on the at least one wall, and a compliant material within the at least one wall and encompassing the chamber. The compliant material has at least one opening providing fluid communication between said chamber and the embedded environment. A cooling system is also described. A method for making a pleumo-jet is also described.

Description:
BACKGROUND 
       [0001]    The invention relates generally to thermal management systems, and more particularly to thermal management systems for use in embedded environments. 
         [0002]    Environments having embedded electronic systems, hereinafter embedded environments or heated environments, offer challenges for thermal management. Such systems produce waste heat as a part of their normal operation, heat that must be removed for proper performance and reliability of the embedded electronics. The design of thermal management systems to provide cooling for embedded electronics is a formidable challenge due to space limitations. Examples of embedded electronic systems include single board computers, programmable logic controllers (PLCs), operator interface computers, laptop computers, cell phones, personal digital assistants (PDAs), personal pocket computers, and other small electronic devices, there is a limited amount of available space for thermal management systems. It has been known to use passive cooled heat sinks or forced air-cooling as thermal management systems to assist in the removal of heat from electronic components. Further, it has been known that conducting the heat generated by electronic components to a printed circuit board, on which they are mounted, thereby providing a migration of the heat from a smaller area to a larger area. 
       SUMMARY 
       [0003]    The invention includes embodiments that relate to a thermal management system for a heated environment that includes a pleumo-jet. The pleumo-jet includes at least one wall defining a chamber, at least one active material on the at least one wall, and a compliant material within the at least one wall and encompassing the chamber. The compliant material has at least one opening facilitating fluid communication between the chamber and the heated environment. 
         [0004]    The invention includes embodiments that relate to a pleumo-jet that includes a first flexible structure, a second flexible structure, at least one active material on at least one of the first and second flexible structures, and a compliant material positioned between the first and second flexible structures and defining a chamber. The compliant material includes at least one orifice for facilitating fluid communication between the chamber and an ambient environment. 
         [0005]    The invention includes embodiments that relate to a cooling system for a heated environment. The cooling system includes a substrate having one free end and one anchored end, at least one piezoelectric device positioned on the substrate, and an electrical circuit to provide an electrical current to the at least one piezoelectric device. 
         [0006]    The invention includes embodiments that relate to a method for making a pleumo-jet. The method includes providing a pair of flexible structures, at least one of the structures having an attached active material, attaching a compliant material between the pair of flexible structures, the elastomeric material having at least one orifice, and adding electrical contacts to the pair of flexible structures. 
         [0007]    These and other advantages and features will be more readily understood from the following detailed description of preferred embodiments of the invention that is provided in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a cross-sectional side view of a thermal management system utilizing a pleumo-jet constructed in accordance with an embodiment of the invention. 
           [0009]      FIG. 2  is a cross-sectional side view showing the thermal management system of  FIG. 1  with the pleumo-jet in a different position. 
           [0010]      FIG. 3  is a top view of a thermal management system constructed in accordance with an embodiment of the invention. 
           [0011]      FIG. 4  is a cross-sectional side view of the thermal management system of  FIG. 3  taken along line IV-IV. 
           [0012]      FIG. 5  is a top view of a pleumo-jet constructed in accordance with an embodiment of the invention. 
           [0013]      FIG. 6  is a top view of a pleumo-jet constructed in accordance with an embodiment of the invention. 
           [0014]      FIG.7  is a side view of the pleumo-jet of  FIG. 6 . 
           [0015]      FIG. 8  is a schematic view a thermal management system utilizing a piezoelectrically driven flexible cooling apparatus constructed in accordance with an embodiment of the invention. 
           [0016]      FIG. 9  is a schematic view showing the thermal management system of  FIG. 8  with the piezoelectrically driven flexible cooling apparatus in a different position. 
           [0017]      FIG. 10  illustrates process steps for forming a pleumo-jet in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Referring to  FIGS. 1 and 2 , there is shown a thermal management system  10  that includes a pleumo-jet  12  illustrated in cross-section and placed in proximity to a printed circuit board assembly (PCA)  30  having a plurality of electronic components to be cooled  32   a-d . While a PCA  30  is depicted with reference to an embodiment of the invention, it should be appreciated that the thermal management system  10  may be utilized in any suitable embedded environment and its depiction with reference to the PCA  30  is merely for convenience in description. The PCA  30  may be used in heated environments in any number of small electronic devices, such as, for example, single board computers, programmable logic controllers (PLCs), laptop computers, cell phones, personal digital assistants (PDAs), personal pocket computers, to name a few. The pleumo-jet  12  is sized appropriately for its use, and generally is in the meso-scale or micro-scale. 
         [0019]    The pleumo-jet  12  is positioned such that a pulsating fluid stream of ambient air can be generated from the apparatus  12  and directed at the electronic components to be cooled  32   a-d . As shown, in  FIG. 1 , a fluid stream of ambient air, or other fluid, is directed along direction A toward the electronic component to be cooled  32   b . Alternatively, the pleumo-jet  12  may be positioned to direct a fluid stream of ambient air along direction B toward the electronic component to be cooled  32   b  ( FIG. 2 ). 
         [0020]    The pleumo-jet  12  includes a first structure or wall  14  and a second structure or wall  16 . The walls  14 ,  16  are formed of a flexible material, such as, for example, metal, foil, plastic, or polymer composite material. A compliant material  18  is positioned between the pair of walls  14 ,  16 , and the combination of the walls  14 ,  16  and the compliant material  18  define a chamber  20 . At least one orifice  22  provides a channel between the chamber  20  and the environment outside the apparatus  12 . Although a pair of opposing walls  14 ,  16  are depicted, it should be appreciated that instead of two walls, a single wall (wrapping around to form a cylinder) along with the compliant material  18  may form a pleumo-jet, such as the pleumo-jet  12 . 
         [0021]    Positioned on at least one of the walls  14 ,  16  is an active material, such as, for example, a piezoelectric material. As shown, active materials  24  and  26  are positioned, respectively, on walls  14  and  16 . A suitable active material is one which is capable of creating stress resulting from an electrical stimulus. Examples of suitable active material include piezoelectric material, magnetostrictive material (magnetic fields from coils attract/oppose one another), shape-memory alloy, and motor imbalance (motor with a mass imbalance creates oscillatory motion). Within the subset of piezoelectric materials, suitable active materials include bimorph piezoelectric configurations, where two piezo layers are energized out of phase to produce bending; thunder configurations, where one piezo layer is disposed on a pre-stressed stainless steel shim; buzzer element configurations, where one piezo layer is disposed on a brass shim; and MFC configurations, where a piezo fiber composite on a flexible circuit is bonded to a shim. 
         [0022]    The active material  24 ,  26  may incorporate a ceramic material. Electrical circuitry (schematically depicted in  FIG. 8 ) is attached to the pleumo-jet  12  to provide an electrical current to one or both of the active material  24 ,  26 . The current may be provided as a sine wave, a square wave, a triangular wave, or any other suitable waveform, and it should be appreciated that the current is not to be limited to any specific wave form. Specifically, it has been found that currents having lower harmonics, such as, for example, a sine wave may be used to provide a quieter pleumo-jet  12 . 
         [0023]      FIGS. 3 and 4  illustrate a thermal management system  110  in accordance with another embodiment of the invention. The thermal management system  110  includes a pleumo-jet system  111 , which has a plurality of pleumo-jets in a stacked arrangement. As shown, the pleumo-jet system  111  includes pleumo-jets  112   a ,  112   b , and  112   c  in a stacked arrangement. The pleumo-jet  112   c  is positioned over a base  129  and supported in that location with one or more supports  127 . The pleumo-jets  112   a ,  112   b , and  112   c  have a similar construction to the pleumo-jet  12  ( FIGS. 1 ,  2 ), with the optional exception of the orifices. Specifically, each of the pleumo-jets  112   a ,  112   b , and  112   c  includes flexible walls and a compliant material defining a chamber  120 , and each of the flexible walls has one or more active materials (not shown). Supports between the pleumo-jets  112   a ,  112   b , and  112   c  are necessary to provide sufficient room to accommodate the active materials on one or both flexible walls of each pleumo-jet. 
         [0024]    Each pleumo-jet  112   a ,  112   b , and  112   c  may include a single orifice  122  extending from the chambers  120  through the compliant material. The pleumo-jet system  111  may be arranged such that each of the single orifices  122  of each pleumo-jet  112   a ,  112   b , and  112   c  is positioned in the same direction ( FIG. 4 ). Alternatively, each of the single orifices  122  may be positioned to direct ambient air in a different direction than the other single orifices  122  ( FIG. 3 ). For any two adjacent orifices  122 , the separation between the orifices  122  may be in a range between just above zero degrees (0°) to less than ninety degrees (90°). In one embodiment, adjacent orifices  122  may be separated by a range of about 5° to about 45°. 
         [0025]    The pleumo-jets  112   a ,  112   b , and  112   c  are surrounded by fins  128 , which are supported on the base  129 . The fins  128  assist in increasing the surface area for heat transfer for cooling the electronic components  32   a-d . As with the previously described pleumo-jet  12 , the pleumo-jets  112   a ,  112   b , and  112   c  utilize active material, for example a piezoelectric material (not shown), to form streams of ambient air. Briefly, electrical current from electrical circuitry (shown in  FIG. 8 ) is received by the active material, and transformed into mechanical energy. The electrical current can take the form of a sine wave, a square wave, a triangular wave, or any other suitable wave form. The voltage level for the electrical current may be between 1 and 150 volts but is not so limited. The frequency of the current may be between 2 and 300 hertz for embodiments requiring reduced noise, and between 300 hertz and 15 kilohertz for embodiments that do not require reduced noise levels. 
         [0026]    The active material creates stress on the flexible walls, causing them to flex inwardly, resulting in a chamber volume change and an influx of ambient air into the chambers  120 , and then outwardly, thereby ejecting the ambient air from the chambers  120  via the orifices  122 . 
         [0027]    Another alternative embodiment of a pleumo-jet system is illustrated in  FIG. 5 . Specifically, a pleumo-jet system  211  is illustrated as including a base  229  supporting a pleumo-jet  212 . The pleumo-jet  212  has a plurality of orifices  222 , each extending outwardly in different radial directions. An active material  224  is shown on a surface of a flexible wall of the pleumo-jet  212 . For any two adjacent orifices  222 , the separation between the orifices  222  may be in a range between just above 0° to less than 90°. In one embodiment, adjacent orifices  222  may be separated by a range of about 5° to about 45°. 
         [0028]      FIGS. 6 and 7  illustrate a pleumo-jet  312 . The pleumo-jet  312  includes a first flexible wall or structure  314 , a second flexible wall or structure  316 , and a compliant material  318  positioned between the flexible walls  314 ,  316 . The walls  314  and  316  are rectangular in shape and, together with the compliant material  318 , form a chamber (not shown). Orifices  322  extend out through the compliant material  318  from the chamber to the ambient environment. An active material  324  is positioned on the wall  314 , and optionally an active material  326  may be positioned on the wall  316 . The active material can be activated with an electric current provided by electrical circuitry (not shown) to create stress on the wall(s)  314  (and  316 ) to allow for the ingestion of ambient air into the chamber and the expulsion of the ambient air from the chamber to the ambient, heated environment. 
         [0029]      FIGS. 8 and 9  illustrate another embodiment of a thermal management system. A thermal management system  410  is illustrated as including a piezoelectric fan apparatus  412  in working relationship with a PCA  30  containing electronic components to be cooled  32   a-d . The piezo fan apparatus  412  includes one free end and one end fixed to a support member  420 . The piezo fan apparatus includes a substrate  414  and an active material  416 . The active material  416  may utilize, for example, a piezoceramic material. 
         [0030]    An electrical circuit  418  is connected to the piezo fan apparatus  412 . Running an electrical current through the piezo fan apparatus  412  sends an electrical charge through the active material  416 . The active material  416  transforms the electrical energy into mechanical energy by creating a stress on the substrate  414 , causing it to rotate about the fixed end. This creates a current of ambient air to travel in a direction C ( FIG. 8 ) or in a direction D ( FIG. 9 ), depending upon the positioning of the piezo fan apparatus  412  relative to the electronic components to be cooled  32   a-d . 
         [0031]    Next, and with specific reference to  FIG. 10 , will be discussed a process for forming a pleumo-jet in accordance with an embodiment of the invention. At Step  500 , a pair of flexible structures is provided. The flexible structures may be metallic or they may be non-metallic, such as plastic or polymer composite material. Examples of the flexible structures include flexible walls  14 ,  16  ( FIGS. 1 ,  2 ) and flexible walls  314 ,  316  ( FIGS. 6 ,  7 ). One or both of the flexible structures require an active material that is excitable by an electrical stimulus to be affixed thereon. Suitable examples of active material include material  24 ,  26  ( FIGS. 1 ,  2 ) and material  324 ,  326  ( FIGS. 6 ,  7 ). 
         [0032]    At Step  505 , a compliant material is attached between the flexible structures. The compliant material may be compliant material  18  ( FIGS. 1 ,  2 ) or compliant material  318  ( FIGS. 6 ,  7 ). The compliant material is to be provided in such a form as to define a chamber between the flexible structures. One process for providing the compliant material is to dispense the compliant material in a liquid or semi-liquid form onto one of the flexible structures, placing the other conductive structure on the compliant material, and allowing the compliant material to dry. A liquid silicone-based material may be suitable for such a process. Another process for providing the compliant material is to cut the compliant material from a pre-made sheet of compliant material, and bonding the pre-made sheet of cut compliant material to the flexible structures. A pre-made silicone-based sheet of material may be suitable for this process. 
         [0033]    At Step  510 , electrical contacts are provided to the flexible structures. Electrical circuitry will be attached to the electrical contacts. 
         [0034]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.