Patent Application
20080218972
The disclosed embodiments of the invention relate generally to cooling systems, and relate more particularly to piezoelectric cooling devices.
Computer chips and other microelectronic devices generate heat during their operation that, if not properly addressed, is capable of negatively affecting the performance of, or even damaging, the system of which the microelectronic device is a part. One technique for addressing such heat makes use of a heat sink in combination with a piezoelectric assembly having blades that vibrate or otherwise move to create airflow. However, existing cooling devices of this type require relatively high voltages and relatively long blades in order to achieve an effective blade vibration amplitude. Accordingly, there exists a need for a piezoelectric cooling device that does not share the problems that characterize the existing solutions.
The disclosed embodiments will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying figures in the drawings in which:
For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the discussion of the described embodiments of the invention. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present invention. The same reference numerals in different figures denote the same elements.
The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Similarly, if a method is described herein as comprising a series of steps, the order of such steps as presented herein is not necessarily the only order in which such steps may be performed, and certain of the stated steps may possibly be omitted and/or certain other steps not described herein may possibly be added to the method. Furthermore, the terms “comprise,” “include,” “have,” and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under,” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. The term “coupled,” as used herein, is defined as directly or indirectly connected in an electrical or non-electrical manner. Objects described herein as being “adjacent to” each other may be in physical contact with each other, in close proximity to each other, or in the same general region or area as each other, as appropriate for the context in which the phrase is used. Occurrences of the phrase “in one embodiment” herein do not necessarily all refer to the same embodiment.
In one embodiment of the invention, a cooling device comprises a heat sink having a plurality of fins and a piezoelectric assembly comprising an actuator and a plurality of blades coupled to the actuator. The actuator comprises multiple piezoelectric layers sandwiched between metal electrodes. The fins of the heat sink are intertwined with the blades of the piezoelectric assembly. Because the piezoelectric assembly has a plurality of blades that resemble the prongs of a rake, the piezoelectric assembly may be referred to as a “rake piezoelectric assembly,” which in turn may be abbreviated as “rake piezo.”
The cooling device described in the preceding paragraph offers several advantages over existing cooling devices, including existing rake piezo cooling devices. For example, as compared to existing cooling devices, the cooling device according to embodiments of the present invention is capable of obtaining a given strain at a significantly reduced voltage (or achieving greatly increased performance at the same voltage), is capable of achieving much greater amplitudes, and may be constructed to have significantly reduced length.
Referring now to the figures,
As an example, plurality of blades 122 can be made of plastic, steel, or the like. As another example, metal electrode 225 can be made of a highly electrically conductive material such as nickel, silver palladium, or the like. In one embodiment, metal electrode 225 has a thickness of between approximately three and approximately eight micrometers. In the same or another embodiment, actuator 121 comprises at least three metal electrodes, one of which may be metal electrode 225. In general, performance increases with the number of layers making up actuator 121. Care must be taken, however, to keep the total number of layers (including metal electrode layers and piezoelectric layers) small enough that the stiffness of actuator 121 does not become too great.
As another example, piezoelectric layer 226 can be made of lead zirconium titanate (PZT) or a lead-free piezoelectric material such as bismuth titanate or the like. Alternatively, piezoelectric layer 226 can be made of another piezoelectric material, including piezoelectric polymers. In one embodiment, piezoelectric layer 226 has a thickness no greater than approximately 30 micrometers. In the same or another embodiment, actuator 121 comprises at least two piezoelectric layers, one of which may be piezoelectric layer 226.
As an example, each metal electrode in plurality 227 of metal electrodes can be similar to metal electrode 225. As another example, each piezoelectric layer in plurality 228 of piezoelectric layers can be similar to piezoelectric layer 226. Plurality 227 of metal electrodes and plurality 228 of piezoelectric layers are in alternating relationship with each other as shown. In the illustrated embodiment, metal electrode 225 is immediately adjacent to neck 123 and the outermost layer (farthest from neck 123) is another metal electrode such that each piezoelectric layer in plurality 228 of piezoelectric layers lies between two metal electrodes.
Governed by what may be called the reverse piezoelectric effect, piezoelectric material undergoes a small change in length when it is subjected to an externally applied voltage. If the applied voltage takes the form of an alternating current then the piezoelectric material can be caused to cycle rapidly between relaxed and constricted states and, as known in the art, this provides a way to induce a lateral vibration in a blade or other object attached to the piezoelectric material. This concept may be put to use with cooling device 100 by applying an alternating current to piezoelectric layer 226 in order to cause a simultaneous lateral vibration of blades 122. By electrically connecting each one of plurality 228 of piezoelectric layers to each other in parallel, such lateral vibration may be achieved at much lower voltages than are possible with single-layer piezoelectric actuators, as will be further discussed below.
In the illustrated embodiment, plurality of blades 122 are inserted substantially all the way into spaces defined by and located between adjacent ones of plurality of fins 111 such that approximately one hundred percent of each one of plurality of blades 122 overlaps with at least one of the plurality of fins 111. In a non-illustrated embodiment, less than approximately one hundred percent but at least approximately ten percent of each one of plurality of blades 122 overlaps with at least one of the plurality of fins of the heat sink. In other embodiments the overlap may be even less than ten percent. In certain embodiments of the invention, the lesser overlap percentage may result in performance gains for cooling device 100, possibly in terms of increased cooling efficiency or the like.
Also in the illustrated embodiment, plurality of blades 122 are arranged so as to be approximately parallel to plurality of fins 111, which fins extend substantially perpendicularly from base 112 of heat sink 110. In a non-illustrated embodiment, plurality of blades 122 lie approximately horizontally to base 112, which may also, in certain embodiments of the invention, result in performance gains for cooling device 100. Other geometries may also be constructed in which plurality of fins 111 lie at other angles with respect to base 112.
A step 320 of method 300 is to provide a piezoelectric assembly comprising an actuator with a plurality of metal electrodes and a plurality of piezoelectric layers and further comprising a plurality of blades that are electrically and mechanically coupled to the actuator. As an example, the piezoelectric assembly, the actuator, and the plurality of blades can be similar to, respectively, piezoelectric assembly 120, actuator 121, and plurality of blades 122, all of which were first shown in
In one embodiment, step 320 comprises providing blades that are approximately 70 millimeters long. In that and possibly other embodiments, an input voltage of no greater than approximately 15 volts is capable of generating a vibration amplitude of at least approximately 40 millimeters. The situation is depicted in
In the embodiment described immediately above, the blades of the piezoelectric assembly were approximately 70 millimeters long. In some cases, such as those where space is constrained by a small form factor, a 70 millimeter blade may be too long. Embodiments of the invention are able to generate sufficient air flow to perform adequate cooling even where the piezoelectric assembly comprises blades that are no longer than approximately 55 millimeters. Referring again to
When blade 122 is made to vibrate in accordance with embodiments of the invention, air flow is generated in the direction of arrows 530. As indicated, blade 122 has a width 521. In a particular embodiment, width 521 is between approximately 12 and 13 millimeters, distance 522 is between approximately six and seven millimeters, and distance 523 is between approximately seven and eight millimeters. In the same or another particular embodiment, wires 573 are approximately 150 millimeters long.
A step 330 of method 300 is to interweave the blades of the piezoelectric assembly between the fins of the heat sink such that the blades and the fins are in alternating relationship with each other. Having this relationship, any air flow generated by the blades will flow around the fins of the heat sink, therefore significantly improving the heat transfer coefficient.
A step 340 of method 300 is to cause the blades of the piezoelectric assembly to vibrate. In one embodiment, step 340 comprises electrically connecting the plurality of piezoelectric layers to each other in parallel and subjecting the plurality of piezoelectric layers to an alternating current. In the same or another embodiment, the performance of step 340 generates air flow that disturbs a boundary layer of air near the plurality of heat sink fins, thus reducing the thermal resistance of the heat sink.
Although the invention has been described with reference to specific embodiments, it will be understood by those skilled in the art that various changes may be made without departing from the spirit or scope of the invention. Accordingly, the disclosure of embodiments of the invention is intended to be illustrative of the scope of the invention and is not intended to be limiting. It is intended that the scope of the invention shall be limited only to the extent required by the appended claims. For example, to one of ordinary skill in the art, it will be readily apparent that the cooling device and related methods and systems discussed herein may be implemented in a variety of embodiments, and that the foregoing discussion of certain of these embodiments does not necessarily represent a complete description of all possible embodiments.
Additionally, benefits, other advantages, and solutions to problems have been described with regard to specific embodiments. The benefits, advantages, solutions to problems, and any element or elements that may cause any benefit, advantage, or solution to occur or become more pronounced, however, are not to be construed as critical, required, or essential features or elements of any or all of the claims.
Moreover, embodiments and limitations disclosed herein are not dedicated to the public under the doctrine of dedication if the embodiments and/or limitations: (1) are not expressly claimed in the claims; and (2) are or are potentially equivalents of express elements and/or limitations in the claims under the doctrine of equivalents.
