WO1996012924A1

WO1996012924A1 - Piezoelectric cooling device

Info

Publication number: WO1996012924A1
Application number: PCT/US1995/011806
Authority: WO
Inventors: Edward D. Suski
Original assignee: Ast Research, Inc.
Priority date: 1994-10-20
Filing date: 1995-09-15
Publication date: 1996-05-02
Also published as: AU3677295A

Abstract

A device (120) attached to a heat source (124) that includes a thermally conductive element (104) and a piezoelectric element (102a, 102b) that induces the thermally conducting element (104) into motion where the motion facilitates dissipation of heat energy absorbed by the thermally conductive element (104) from the heat source (124) into the ambient environment. The device (120) is comprised of a member (122) that consists of multiple layers of piezoelectric material (102a, 102b) and thermally conducting layers (107a, 107b).

Description

Piezoelectric Cooling Device

Background of the Invention Field of the Invention

The present invention relates to a device for dissipating excess heat and, in particular, concerns a device comprised of a piezoelectric element and a thermally conductive element, where the thermally conductive element is connected to a heat source and the piezoelectric element induces the device to move in response to an electrical voltage being applied to the piezoelectric element, to thereby facilitate dissipation of heat by the device. Description of the Related Art

Heat energy is a natural byproduct of most electronic devices. Generally, it is necessary to dissipate excess heat produced by electronic devices to protect the components of the device and to ensure that the electronic device operates in a desired fashion. One common method of dissipating heat in electronic devices is to attach heat sinks to heat sources in the electronic devices.

A typical heat sink is comprised of a structure which is in thermal contact with the heat source and extends outward from the heat source into a comparatively cooler ambient environment. The typical heat sink usually has a large surface area so that the interface between the heat sink and the cooler ambient environment is maximized to allow for greater transfer of heat energy from the heat sink to the ambient environment.

However, in some applications, heat sinks by themselves are incapable of providing the amount of cooling needed for some electronic components in light of other design constraints. Specifically, the typical desktop computer includes electronics which produce a significant amount of heat A simple heat sink which has the dimensions to fit within a standard computer is generally not capable of providing the needed amount of cooling to keep the computer components at a desired temperature. Consequently, most desktop computers include a fan which forces air over the heat producing electronics or over heat sinks attached to the heat producing electronics to dissipate the heat and cool the computer through the use of convection currents.

The problem of cooling electronics within computers is becoming increasingly troublesome as new generations of computer processors are generating larger amounts of heat. For example, computer processors of the 386 family produced approximately two to three watts of heat energy during operation. However, the latest computer processors contemplated by designers are expected to produce greater than eight watts of heat during operation This heat must be dissipated to protect the computer, to ensure that the computer electronics function correctly and also to keep the outer casing of the computer cool enough to be comfortable to the touch of the computer operator Hence, these computers will generally require larger, higher power fans to provide sufficient cooling to dissipate the heat produced by these computers.

Most fans used in computer applications consume a comparatively significant amount of power. The fans that are currently used in the standard desktop computer consume somewhere between 0.5 and 1.5 watts of power during operation These fans are generally always operating to ensure that the computer components are sufficiently cooled Hence, these tans represent a significant dram on the power supply powering the computer However battery operated computers, such as the typical laptop or notebook computer, are becoming increasingly popular due to their ability to be used in the absence of a permanent power supply. It can be appreciated that the cooling fans included in these types of computers consume a significant amount of the limited stored energy in the battery and thereby limit the length of time that the computer can be used. Hence, cooling battery operated computers using known technology generally reduces the ability of the operator to use the computer for long periods. The problem of providing cooling for battery operated computers, while minimizing the drain on the battery, will become an even greater problem once portable computers incorporating the next generation of high speed processors are produced. A further difficulty associated with using cooling devices such as fans in portable computers is that these devices often occupy a large amount of the limited space inside of the computer. Increasingly, portable computers are being made smaller to augment their portability. This requires that all of the space inside of the computer be used in an optimum fashion. Consequently, large fans and heat sinks often occupy a significant amount of the available space inside of the computer thereby increasing the overall size of the computer.

In the prior art, there have been previous attempts to provide a comparatively low power cooling device which is small in size. One such attempt is a piezoelectric fan which, for example, was described in an article entitled "A New Electromotional Device" by M. Toda et al., published in the June/July 1979 edition of RCA Engineer. As described in this article, a piezoelectric fan includes a member comprised of piezoelectric material that is mounted in a cantilevered fashion. The member includes electrodes through which voltages can be applied to the piezoelectric material.

As is generally understood, a piezoelectric material is a material which, upon receiving an electrical stimulus, will undergo a mechanical deflection. The size of the mechanical deflection is dependent upon the type of piezoelectric material used, the size of the electrical stimulus and the configuration of the piezoelectric material. As explained in the above-identified article by Toda et al., a member which is mounted in a cantilevered fashion and which includes one or more layers of a piezoelectric material can be induced to move back and forth to thereby produce an air flow. Further, as described in an article entitled "High Field Dielectric Loss of PVF, and The Electromechanical Conversion Efficiency of a PVF- Fan" by M. Toda published in 1979 in Volume 22 of Ferroelectrics, these types of fans can be very efficient in that they produce a comparatively large quantity of air flow while consuming comparatively little power.

However, while a fan of this type may produce air flow more efficiently than standard electrically powered fans, this type of fan has generally not been adequately adapted to be used to cool electronic components, which produce a large amount of heat energy, in confined spaces such as portable computers. Specifically, this type of fan only produces a forced air current which must be directed over the heat producing electronics. Hence, in applications where space is at a premium, such as portable computers, cooling systems incorporating fans of this type would still often require large heat sinks, electric fans and other devices.

Further, fans in general are inefficient in cooling particular components as the fans have to produce an air flow to cool the heat source. Generally, the air flow produced by a fan is distributed over a wide area. Hence, to cool a particular heat source, the overall air flow must be large enough to generate a desired air flow in the region of the heat source. Both the rotating fans and the piezoelectric fans of the prior art must be large enough and powerful enough to produce an overall air flow that will have the desired effect on the heat source. Consequently, the fans of the prior art are inefficient in that they are consuming energy to produce an air flow wherein a large portion of the air flow does not contribute to cooling the particular heat source.

Consequently, there is still a need in the prior art for a cooling device which is suited to be used in systems where space and power consumption are to be minimized. To this end, there is a need in the prior art for a cooling device which can efficiently dissipate heat generated bγ electronic components of a device while consuming a minimum amount of power and while occupying a minimum amount of space inside of the device enclosure.

Summary of the Present Invention The aforementioned needs are satisfied by the present invention which is essentially comprised of a thermally conducting element, adapted to be thermally connected to a heat source, and a piezoelectric element which is engaged with the thermally conducting element so that when the piezoelectric element receives an electric signal, the piezoelectric element induces the thermally conducting element to move. The movement of the thermally conducting element causes air to flow over the thermally conducting element and thereby dissipate the heat energy absorbed by the thermally conducting element into the ambient environment. Further, the movement of the thermally conducting element also generates an air current which can be used to dissipate heat energy through convection cooling.

In one particular aspect of the present invention, the thermally conducting element is comprised of a thermally and electrically conducting layer of material which is adhered to the outer surface of a piezoelectric element. In another particular aspect of the present invention, the thermally conducting element is comprised of a thermally conducting layer of material that is mounted adjacent to the piezoelectric element but is electrically isolated from the piezoelectric element. By isolating the thermally conducting element from the piezoelectric element, the heat source can also be isolated from the electric voltages carried by the piezoelectric element.

In one embodiment, the piezoelectric element is comprised of multiple layers of piezoelectric material. Interposed between each of the layers of piezoelectric material are electrodes which carry voltages. In one preferred embodiment, the electrodes carry voltages of opposite polarity to opposite sides of each of the layers of piezoelectric elements to induce the layers of piezoelectric material to produce the torque needed to move the piezoelectric element in a desired direction. In this embodiment, the layers of piezoelectric material are assembled so that the electric fields contained within the layers of material are oriented so that, when the opposite voltages are applied to the different layers of material, each layer of material generates torque to move the piezoelectric element in the same direction. Further, applying an alternating voltage results in the element oscillating back and forth.

In another embodiment of the present invention, the thermally conducting element is comprised of a thermally conducting substrate interposed between two piezoelectric elements. The two piezoelectric elements can be comprised of multiple layers of piezoelectric material assembled in the above-described manner. The thermally conducting element is preferably mounted on a heat source in a cantilevered fashion. When alternating voltage signals are applied to the two piezoelectric elements, the cantilevered end of the thermally conducting element moves in a back and forth fashion. Preferably, the cantilevered end of the thermally conducting element is exposed to the ambient environment and the movement of the thermally conducting element results in dissipation of the heat energy at the tip of the thermally conducting element into the ambient environment. Further, since more heat energy is dissipated towards the tip of the thermally conducting element, a heat gradient is produced within the thermally conducting element which facilitates removing heat energy from the heat source. In one particular application of the present invention, the embodiment comprised of the cantilevered thermally conducting element and the piezoelectric elements is mounted on a first surface of a heat generating computer chip so that the thermally conducting member extends outward from the first surface of the computer chip. A heat sink is preferably mounted on top of the portion of the thermally conducting member which is positioned on the first surface of the heat source. The heat sink is comprised of a base having a plurality of members which extend generally perpendicularly out of the base. In this particular application, the cantilevered thermally conducting member not only dissipates heat due to its motion, the thermally conducting member also produces a forced air current which can be directed through the heat sink to further dissipate heat produced by the computer chip that has been absorbed by the heat sink. Further, in this particular application, some or all of the perpendicularly extending members of the heat sink can be comprised of thermally conducting elements which have piezoelectric elements engaged therewith to produce motion of these members to further dissipate heat produced by the computer chip.

As can be appreciated, the present invention can be adapted to be used to cool electronic components such as computer chips. The piezoelectric elements which induce the movement of the thermally conducting elements can be selected so that the motion of the thermally conducting elements can be produced with a minimum of power consumption by the piezoelectric elements. Hence, the cooling capabilities of the present invention can be used in environments, such as battery powered computers, where power consumption by cooling apparatuses is a concern.

Further, the present invention also provides a cooling device which is significantly more efficient than prior art fans as it dissipates heat that is produced by the heat source without expending unnecessary energy. Specifically, the cooling device of the present invention directly transfers heat from the heat source to the ambient environment without expending energy to cool other regions of the ambient environment. Hence, the cooling device of the present invention is more efficient than prior art cooling devices.

These and other objects and features of the present invention will become more fully apparent from the following description and appended claims taken in conjunction with the accompanying drawings. Brief Description of the Drawings

Figure 1A is a perspective view of a prior art piezoelectric element; Figure 1B is a side view of the prior art piezoelectric element of Figure 1A;

Figure 1 C is a side view of the prior art piezoelectric element of Figure 1A, used to illustrate the motion of the piezoelectric element in response to voltages being applied thereto; Figure 2A is a perspective view of a plurality of a first preferred embodiment of thermally conducting piezoelectric members of the present invention which are mounted on a heat source; Figure 2B is a side view of the plurality of thermally conducting piezoelectric members of Figure 2A; Figure 3A is a perspective view of a second embodiment of a thermally conducting piezoelectric member mounted on a heat source;

Figure 3B is a side view of the thermally conducting piezoelectric member of Figure 3A; Figure 4A is a perspective view of a third embodiment of a thermally conducting piezoelectric member which is comprised of a thermally conducting element and two piezoelectric elements engaged therewith; Figure 4B is a side view of the thermally conducting piezoelectric member of Figure 4A; Figure 4C is a side view of the thermally conducting piezoelectric member of Figure 4A illustrating the motion of the thermally conducting piezoelectric members; Figure 5A is an exploded perspective view of a cooling assembly of the present invention used to dissipate heat produced by a computer chip;

Figure 5B is a perspective view of the cooling assembly of Figure 5A illustrating the cooling assembly as it is mounted on the computer chip; and

Figure 5C is a side view of the assembly of Figure 5A illustrating the operation of the cooling assembly.

Description of the Preferred Embodiments Reference will now be made to the drawings wherein like numerals refer to like parts. Figures 1A, 1B and 1C illustrate the basic structure of a prior art multi-layer piezoelectric element 100. The element 100 has two layers of piezoelectric material 102a and 102b. Interposed between the two layers of piezoelectric material 102a and 102b is a layer of electrically conductive material 104, forming an electrode, which is adhered to the inner surfaces of the piezoelectric layers 102a and 102b to form an electrical contact therebetween. Two layers of electrically conductive material 106a and 106b forming two electrodes, are also respectively adhered to the outside of the two piezoelectric layers 102a and 102b.

As is diagrammatically illustrated in Figures 1A • 1C, the conductive layers 104, 106a and 106b include contacts which permit a voltage signal V, to be applied to the conductive layer 104 and a voltage signal V_b to be applied to the conductive layers 106a and 106b from an external voltage source (not shown). Further, the piezoelectric element 100 is preferably mounted in a cantilevered fashion on a support 110.

As is generally understood in the prior art, when V, and V_b are applied to the conductive layers 104 and 106, the voltages induce the piezoelectric material to experience a mechanical deflection. The direction and magnitude of the mechanical deflection is dependent upon the composition of the piezoelectric layers 102a and 102b and the magnitude and frequency of the applied voltages. The piezoelectric material used in the preferred embodiments described herein are comprised of a polarized polyvinylidene fluoride (PVF₂) material. However, a person skilled in the art can appreciate that any material which produces a piezoelectric effect, i.e., any material wherein a mechanical deflection can be induced by an applied electrical signal, can be used without departing from the teachings of the present invention. In general, piezoelectric materials are materials which are polarized in that a permanent electric field is produced inside of the material. In the piezoelectric layers 102a and 102b, the material is preferably polarized in the same direction along a thickness axis of the layers of material 102a and 102b (denoted by line 112 in Figures

1A and 1B). In the preferred embodiment, the piezoelectric layers 102a and 102b are polarized in the direction of arrow 114 (Figure 1B).

As is generally understood in the art, when different voltage signals V, and V_b are applied to the conductive layers 104 and 106a and 106b, one of the layers of piezoelectric material 102 is induced to shrink and the other layer 102 is induced to elongate. For example, in Figure 1C, when a voltage V, and a voltage V„ is applied to the conductive layers 104 and 106, where V, > V_b, the layer 102a is induced to shrink and the layer 102b is induced to elongate. This results in a torque being applied to the piezoelectric element 100 causing it to bend to the left in the manner shown in Figure 1 C. However, when a voltage V, and a voltage V_b, where V, < V_b, is applied to the conductive layers 104 and 106, the layer 102b shrinks and the layer 102a expands thereby causing the piezoelectric element 100 to bend to the right in the manner shown in phantom in Figure 1 C.

Hence, applying different voltage signals to a multi-layer piezoelectric element like the element 100 shown in Figures 1A - 1 C can result in the element bending back and forth. Typically, as described in the article "A New Electromotional Device" by M. Toda et al., published in the June/July 1979 edition of RCA Engineer, for a PVF₂-type film which is 9 μm thick, a 10 volt voltage difference between V, and V_b can cause an expansion or contraction of about 0.3μm for each centimeter of film length in each layer of piezoelectric film. Increasing the number of layers of piezoelectric material can further increase the amount of bending that results from application of voltage signals to the layers of piezoelectric material. Multilayer piezoelectric materials of the type described above are described in greater detail in the paper entitled "Electromotional Device using PVF- Multilayer Bimorph" by M. Toda published in The Transactions of the IECE of Japan, Vol E61, No. 7, in July 1978.

It can be further appreciated that application of voltage signals V, and V_b, where these voltage signals are alternating voltage signals which are opposite in polarity, can result in the piezoelectric element 100 vibrating back and forth in the direction of the arrow 116 in Figure 1C. The piezoelectric element 100 will vibrate at a frequency which is proportional to the frequency of the alternating voltages V, and V_b. Further, the movement of the piezoelectric element 100 in the direction of the arrow 116 is maximized when applied alternating voltage signals induce the element 100 to vibrate back and forth at its resonance frequency. The resonance frequency of a cantilevered member can be readily calculated using well known formulas. Hence, by selecting the appropriate frequency of the voltage signals V, and V_b, the piezoelectric element 100 can be induced into motion where the cantilevered end of the element 100 will move a significant amount.

Turning now to Figures 2A - 2B, one preferred embodiment of a heat sink 120 incorporating thermally conducting piezoelectric members 122 of the present invention is illustrated. Specifically, Figures 2A - 2B illustrate a plurality of thermally conducting piezoelectric members 122 which are mounted in a cantilevered fashion on the top of a heat source 124. Each of the thermally conducting piezoelectric members 122 includes an electrode 104 and two layers of piezoelectric material 102a and 102b which are substantially the same in construction as the materials described above in reference to Figures 1A ^■ 1C.

However, in this preferred embodiment, the outside conductive layers 107a and 107b are comprised of a material which is not only electrically conductive, but is also thermally conductive. Further, a bottom portion 126 of the thermally conductive layers 107 is thermally connected to the heat source 124 so that the thermally conductive layers 107 receive heat energy from the heat source 124. The conductive layers 104, 107a and 107b are also configured to receive the voltages V, and V„ in the manner described above in reference to Figures 1 A - 1C. Specifically, as shown in Figure 2A, the heat sink 120 includes two tabs 121a and 121b which respectively receives voltages V, and V_b from an external voltage source (not shown). A plurality of conductors 123, which are shown in phantom in Figure 2A, then connect each of the conductive layers 104 and 107 on each of the members 122 to the appropriate tab 121. Preferably, the conductors 123 can be electrically insulated from the heat source 124. Hence, when alternative voltage signals are applied to the conductive layers 104, 107a and 107b, the outer end 130 of each of the members 122 is induced to move back and forth in the direction of the arrows 116 in Figure 2B in substantially the same manner as described above in reference to Figure 1C. Further, as shown in Figures 2A and 2B, an insulator 131 can also be positioned so as to electrically insulate the piezoelectric layers 102a and 102b and the conducting layer 104 from the surface of the heat source 124. Since different voltages are being applied to the layers 107a and 107b and the layer 104, it may be desirable to isolate these conducting layers to prevent short circuit conditions.

As can be appreciated, the movement of the outer end 130 of the cantilevered member 122 through the ambient air surrounding the heat sink 120 results in heat energy absorbed by the member 122 from the heat source 124 dissipating into the ambient environment. Specifically, the member 122 is induced to move in a direction which is substantially normal to the plane of the thermally conducting layers 107a and 107b. Hence, the movement of the member 122 results in air being forced over the surface of the thermally conducting layers 107a and 107b which, as is generally understood in the art, substantially increases the transfer rate of heat energy from the thermally conducting layers 107a and 107b to the ambient environment.

Further, the movement of the member 122 in response to the applied voltages is maximized towards the outer end 130 of the member 122. Consequently, the amount of heat energy dissipated by the member 122 increases towards the outer end 130 of the member 122 thereby producing a thermal gradient in the thermally conducting layers 107a and 107b which facilitates the removal of heat energy out of the heat source 124. The thermally conducting layers 107a and 107b are preferably made out of a material which is flexible, a good thermal conductor and a good electrical conductor. Further, as is generally understood in the art, the amount of heat energy that can be carried by the conducting layers is dependent upon the heat mass of the material forming the layers and upon the cross sectional area of the layers. In this preferred embodiment, the layers 107a and 107b can either be silver ink or a rolled annealed copper material which is adhered to both the heat source 124 and to the piezoelectric layers 102a and 102b. These materials are both good electrical and thermal conductors and they are also generally flexible to be able to withstand the repeated bending motion of the member 122 without significant 96/12924 PO7US95/11806

-8- fatigue. The exact composition and dimensions of the thermally conducting layers 107a and 107b is dependent upon several factors including the amount of heat energy to be dissipated by the member 122.

Hence, the movement of the members 122 causes heat energy to be drawn out of the heat source 124 into the outer layers 107a and 107b of the members 122. The heat energy is then also dissipated by the movement of the members 122 through the ambient environment surrounding the heat sink 120. Further, the movement of the members 122 also generates forced air currents in the ambient environment surrounding the heat sink 120 which can also contribute to removal and dissipation of heat energy from the heat source 124.

In general, it is understood that heat sources generally radiate heat energy into the surrounding ambient environment. Typically, heat sources are surrounded by air and a boundary layer is formed between the heat source and the surrounding environment. However, air is not very efficient in transferring heat so it is often desirable to generate air currents to transfer the heat energy out of the proximity of the heat source to thereby cool the heat source.

One method of transferring air is by using a fan which produces an air current in the proximity of the boundary layer to remove the heat energy in this boundary layer. This produces a thermal gradient across the boundary layer which facilitates heat energy dissipating from the heat source into the boundary layer. However, fans are often an inefficient means for cooling a heat source as a significant amount of the fan's energy is not directed towards cooling the heat source but is directed towards creating air currents which do not remove heat energy from the boundary layer. The heat sink 120 utilizing the members 122 provide a more efficient solution to dissipating heat from the heat source as the energy consumed to move the members 122 directly contributes to dissipating the heat absorbed by the members 122 from the heat source 124.

Figures 3A and 3B illustrate another embodiment of a thermally conducting piezoelectric member 140 of the present invention. As illustrated, the center layers of the member 140 are substantially identical to the piezoelectric element 100 illustrated in Figures 1A-1C. Specifically, the member 140 includes a center electrically conducting layer 104, two piezoelectric layers 102a and 102b and two outer electrically conducting layers 106a and 106b. The voltage signals V, and V_b are applied to the electrically conducting layers 104 and 106a and 106b to induce the vibratory bending motion of the member 140 in the same manner as described above.

However, the layers 104, 102a, 102b, 106a and 106b are all preferably electrically insulated from the surface of the heat source 124 by an insulator 141. The insulator 141 ensures that the upper surface of the heat source 124 is not energized by the voltages applied to the conducting layers 104, 106a and 106b. As can be appreciated, many heat sources in electrical devices are electrically conducting. Applying a voltage to the heat source can result in the heat source being energized which can interfere with the function of the device or create a hazardous condition for an individual working on the device containing the heat source.

To address this particular problem, the member 140 includes the insulator 141. Further, both of the outer electrically conducting layers 106a and 106b are also coated with a dielectric layer 142 which also acts as an insulator to electrically insulate the electrically conducting layers 106a and 106b. Two thermally conducting layers 144a and 144b are then respectively adhered to the dielectric layers 142a and 142b so that the thermally conducting layers 144a and 144b are positioned on the outer surfaces of the member 140. The thermally conducting layers 144a and 144b each include a bottom portion 146 which is thermally connected to a surface of the heat source 124. As is generally understood, many thermal conductors are also electrical conductors. By isolating the thermal conductors 144 from the electrical conductors 106 with the dielectric layers 142, the heat source 124 can be electrically insulated from the voltages applied to the member 140.

The operation of the member 140 is, in all other respects, the same as the operation of the member 122 described in reference to Figures 2A and 2B above. Hence, this embodiment of the present invention provides for a cantilevered thermally conductive piezoelectric member which can be induced to move so that the outer end of the member oscillates back and forth. The thermal conductors 144 are positioned so that the surface area of the thermal conductors 144a and 144b is generally normal to the direction of motion of the member 140. Hence, the motion of the member 140 causes heat absorbed by the thermal conductors 144 from the heat source 124 to be dissipated into the ambient environment in the same manner as described above. Hence, the member 140 can either be used individually to cool a heat source or can be substituted for the members 122 in the heat sink 120.

Figures 4A - 4C illustrate another embodiment of the present invention. As is generally understood in the art, increasing the number of layers of piezoelectric material and conducting material in a piezoelectric element, like the element shown in Figures 1A - 1C, results in a greater amount of mechanical deflection of the element when voltages are applied to the piezoelectric layers. However, the middle layers of piezoelectric element contribute significantly less to the overall deflection of the element than the layers located towards the outside surface of the element. Consequently, piezoelectric elements have been developed in the prior art where a middle substrate of flexible, non-piezoelectric material has been interposed between two piezoelectric elements which are comprised of one or more layers of piezoelectric material. With these types of devices, the non-piezoelectric substrate will be bent by the forces exerted by the layers of piezoelectric material in response to voltage signals being applied to the piezoelectric elements. The embodiment of the present invention illustrated in Figures 4A • 4C comprises a piezoelectric thermally conductive member 160 which has this substrate structure. Specifically, the piezoelectric thermally conductive member 160 includes two piezoelectric elements 162a and 162b and a thermally conductive element 164 interposed between the piezoelectric elements 162a and 162b. The piezoelectric elements 162 can be comprised of a multiple layer piezoelectric element like the element 100 described above in reference to Figures 1A-1C. The thermally conducting element or substrate 164 is generally planar in configuration and is comprised of a flexible, thermally conducting material. In one embodiment, the thermally conducting element 164 is comprised of a rolled annealed copper member where the thickness of the member has been selected based upon the amount of heat energy that must be dissipated by the element 164 and the desired flexibility of the element 164. In another embodiment, the thermally conducting element 164 is comprised of a plastic member, substantially the same as the plastic members used in prior art piezoelectric structures having a center substrate, that has been coated with a thermally conducting material, such as silver ink. The thermally conducting element 164 is thermally connected to a heat source 124 and is mounted on a surface of the heat source in a cantilevered fashion. Specifically, in the embodiment shown in Figures 4A - 4C, the member 160 is mounted on a first surface 165 of the heat source 124. Preferably, the member 160 includes several clamping surfaces 166 which allow the member 160 to be clamped into an opening in the heat source 124. Further, the clamping surfaces 166 are also preferably configured to receive electrical conductors 167

(Figure 4A) which provide the voltage signals needed to drive the piezoelectric elements 162a and 162b. The piezoelectric elements 162a and 162b are positioned on the top and bottom surfaces of the thermally conducting element 164 and are electrically connected to an external power supply, not shown, so that when alternating voltage signals are applied to the piezoelectric elements 162a and 162b, the thermally conductive element 164 is induced to move so that a cantilevered outer end 168 of the element 164 bends back and forth in the manner shown in Figure 4C. The bending motion of the element 164 dissipates heat energy that is absorbed by the element 164 from the heat source 124 into the ambient environment. Further, the bending motion of the element 164 generates a forced air current in the surrounding ambient environment which can also be used to dissipate heat energy produced by the heat source 124. It can be appreciated that this movement of the thermally conductive element 164 results in a substantial amount of air flow normal to the top and bottom surfaces of the thermally conductive element 164 which facilitates dissipating the heat energy absorbed by the thermally conductive element 164 into the surrounding environment. Further, since the degree of motion of the thermally conductive element 164 increases towards the outer end of the element 164, the air flow and amount of heat energy dissipated also increases towards the outer end of the element 164. Hence, a thermal gradient is produced in the thermally conductive element 164 which assists the element 164 in extracting heat out of the heat source 124.

In one possible implementation of this embodiment, the cantilevered portion of the thermally conductive member 164 is approximately 4.0 cm wide and 5.0 cm in length and is less than 0.5 mm in thickness. The piezoelectric elements 162a and 162b are both approximately 4.0 cm wide and 3.0 cm in length. Further, the piezoelectric elements 162a and 162b are comprised of multiple layers, e.g., 4 layers, of PVF₂ material which receive an alternating voltage signal where the difference between V, and V_b is approximately 60 - 65 Volts r.m.s. at any given interval. The voltages V, and V_b are applied so as to oscillate the thermally conductive element 164 at its resonance frequency which is dependent upon type and thickness of the material used to construct the thermally conductive element 164. With these design values, it is possible to have the outer end 168 of the thermally conductive element 164 oscillate at a resonance frequency of around 35 - 50 Hz with a peak-to-peak amplitude of approximately 1.0 cm.

This embodiment of the present invention having the above-described dimensions will consume on the order of 30 - 35 mW of power. This level of power consumption is significantly less than prior art fans used to cool computers which generally consume between 0.5 and 1.5 Watts of power. Hence, the present invention can provide cooling for electronic components, and in particular components used in computers, while consuming significantly less power than prior art fans. In the foregoing description, several embodiments of a thermally conducting piezoelectric member have been described which can be used to dissipate heat from a heat source. Advantageously, the present invention is readily adaptable to be used in the context of cooling electronics and, in particular, cooling computer processing chips.

Figures 5A • 5C illustrate how the previously described thermally conducting piezoelectric members can be adapted to cool a computer chip.

Figure 5A is an exploded perspective view which illustrates the components of a cooling assembly 180 to be used with a computer chip 182. The cooling assembly 180 includes a thermally conductive element 184 which is interposed between two piezoelectric elements 186a and 186b to form a member 188 that is substantially similar to the piezoelectric thermally conductive member 160 described above in reference to Figures 4A • 4C. The thermally conductive element 184 has a generally rectangular shape with an inner portion 189 that is preferably positioned on the upper surface of the computer chip 182 and thereby thermally connects the element 184 to the computer chip 182. The piezoelectric elements 186 are electrically connected to a voltage source (not shown) so that these elements 186 can cause the thermally conductive element 184 to move in the same manner as described above in reference to the member 160 in Figures 4A - 4C. The cooling assembly 180 also includes a heat sink assembly 190. The heat sink assembly 190 is essentially comprised of a base 192 which is preferably mounted so as to be thermally connected to the computer chip 182. In the embodiment shown in Figures 5A • 5C, the base 192 of the heat sink assembly 190 is mounted on the inner portion 189 of the thermally conducting member 184. The heat sink assembly 190 also includes a plurality of cantilevered members 196 which extend upward from the base 192 which provide a path for heat energy to be dissipated into the ambient environment. Preferably, at least some of the cantilevered members 196 are comprised of either the thermally conducting piezoelectric members 122 which were described in greater detail in conjunction with Figures 2A and 2B or the thermally conducting members 140 described in conjunction with Figures 3 A and 3B. Finally the cooling assembly 180 also includes a shroud 200 which is positioned over the heat sink assembly 190 and the thermally conducting member 184 to thereby channel air past the heat sink assembly 190. Preferably, the shroud 200 is positioned over the entire assembly 180 to ensure that an air flow is created which flows past the heat sink assembly 190.

The operation of the cooling assembly 180 is as follows. Voltages are applied to the piezoelectric elements 186a and 186b which thereby induces the thermally conducing member 184 to oscillate back in forth in the manner shown in Figure 5C. Further, voltages are also applied to the piezoelectric elements in the members 122 mounted on the base 192 of the heat sink 190 which induce the members 122 to move back and forth in the manner described above in reference to Figures 2A and 2B.

The movement of the thermally conducting member 184 acts to dissipate heat energy absorbed from the computer chip 182 in the previously described fashion. Similarly, the movement of the members 122 of the heat sink 190 also acts to dissipate heat energy absorbed from the computer chip 182. Hence, heat energy produced by the computer chip 182 is initially dissipated as a result of heat energy being absorbed and then dissipated as a result of piezoelectrically induced motion of the element 184 and the members 122. Further, the piezoelectric movement of the element 184 and the members 122 also produce air currents which act to dissipate heat energy produced by the computer chip 182. Specifically, as discussed above, the thermally conductive element 184 moves in response to the voltages being applied to the piezoelectric elements 186a and 186b. The movement of the thermally conductive element 184 induces air currents in the direction of the arrows 202 in Figure 5C. These air currents preferably induce air currents to flow into the shroud 200, in the direction of the arrow 204, and between the cantilevered members 196 of the heat sink 190. It should be appreciated that this forced air will increase the rate of dissipation of the heat energy that is absorbed by the heat sink 120. Further, the movement of the piezoelectric members 122 of the heat sink 190 generates air currents that also increase the rate of dissipation of the heat energy absorbed by the heat sink 190. Consequently, the cooling assembly 180 cools the computer chip 182 by not only dissipating heat energy absorbed by the moving thermally conductive elements, but also by generating air currents which flow through the heat sink and further remove heat energy from the heat sink.

The foregoing description has described several embodiments of thermally conducting elements which are induced into motion by piezoelectric elements so that heat energy absorbed by the thermally conducting elements can be dissipated as a result of the motion. Further, the foregoing description has also pointed out that the motion by the thermally conducting elements induced by the piezoelectric elements also produces air current which can be channeled to further dissipate heat generated by a heat source. Thus, the foregoing description has described apparatuses which can dissipate heat generated by a heat source, such as electronics, which do not consume a significant amount of power. Further, the elements described above are small in size and are easily adapted to be used in applications where space is at a premium.

Although the foregoing description of the preferred embodiment of the present invention has shown, described and pointed out the fundamental novel features of the invention, it will be understood that various omissions, substitutions, and changes in the form of the detail of the apparatus as illustrates, as well as the uses thereof, may be made by those skilled in the art, without departing from the spirit of the present invention. Consequently the scope of the invention should not be limited to the foregoing discussion, but should be defined by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. An apparatus for cooling a heat source, comprising: a thermally conducting element which is thermally connected to said heat source; and a first piezoelectric element which is engaged with said thermally conducting element so as to piezoelectrically induce said thermally conducting element into motion wherein said motion facilitates dissipation of heat from said heat source.

2. The apparatus of Claim 1, wherein said thermally conducting element is comprised of a thermally conducting member which is mounted in a cantilevered fashion on a surface of said heat source.

3. The apparatus of Claim 2, wherein said first piezoelectric element is engaged with said thermally conducting element so as to induce the cantilevered end of said thermally conducting element to vibrate in response to said piezoelectric element receiving an electrical signal.

4. The apparatus of Claim 3, wherein said thermally conducting member is substantially planar in configuration and said first piezoelectric element is positioned on a first side of said thermally conducting member.

5. The apparatus of Claim 4, further comprising a second piezoelectric element which is positioned on a second side of said thermally conducting member so as to piezoelectrically induce motion of said thermally conducting member.

6. The apparatus of Claim 1, wherein said thermally conducting element has a base and an outer end and generally defines a planar surface and said motion of said thermally conducting element is in a direction which is substantially normal to said planar surface of said thermally conducting element.

7. The apparatus of Claim 6, wherein said base of said thermally conducting element is thermally connected to said heat source and said outer end is mounted in a cantilevered fashion.

8. The apparatus of Claim 7, wherein said motion of said thermally conducting element comprises bending of said thermally conducting element so as to move said outer end of said thermally conducting element back and forth in a direction which is substantially normal to said planar surface of said thermally conducting element.

9. The apparatus of Claim 8, wherein said motion of said thermally conducting element produces a thermal gradient in said thermally conducting element extending from said base of said thermally conducting element to said outer end of said thermally conducting element.

10. The apparatus of Claim 8, wherein said motion of said thermally conducting element results in dissipation of heat energy absorbed by said thermally conducting element into said ambient environment.

11. The apparatus of Claim 1, wherein said motion of said thermally conducting element produces a convection current in said ambient environment.

12. The apparatus of Claim 11, further comprising a channel member which is positioned relative said thermally conducting element and said heat source so as to channel said convection current towards said heat source to thereby facilitate dissipation of heat energy from said heat source.

13. The apparatus of Claim 1, wherein said thermally conducting element is comprised of a first layer of thermally and electrically conducting material and said first piezoelectric element is comprised of a first layer of piezoelectric material and wherein said first layer of thermally and electrically conducting material is adhered to a first face of said first layer of piezoelectric material.

14. The apparatus of Claim 13, further comprising: a middle layer of electrically conducting material which is adhered to a second face of said first layer of piezoelectric material; a second layer of piezoelectric material which is adhered to said middle layer of electrically conducting material on an opposite face of said middle layer of electrically conducting material than said first layer of piezoelectric material; and a second layer of thermally and electrically conducting material which is adhered to said second layer of piezoelectric material on a face opposite said middle layer of electrically conducting material.

15. The apparatus of Claim 1, wherein said thermally conducting element is comprised of a first layer of thermally conducting material which is thermally attached to said heat source and said first piezoelectric element is comprised of a first layer of piezoelectric material positioned adjacent said first layer of thermally conducting material;

16. The apparatus of Claim 15, wherein said first layer of piezoelectric material is electrically isolated from said heat source and said first layer of thermally conducting material.

17. the apparatus of Claim 1, wherein said first piezoelectric element includes a layer of polyvinylidene fluoride (PVF₂) polymer film.

18. The apparatus of Claim 1, wherein said thermally conducting element is comprised of a member fabricated from rolled annealed copper.

19. An apparatus for cooling a heat source, comprising at least one cantilevered thermally conducting piezoelectric member mounted on said heat source wherein said at least one cantilevered thermally conducting piezoelectric member is induced into motion in response to an applied electrical signal and wherein said motion facilitates dissipation of heat from said heat source.

20. The apparatus of Claim 19, wherein said at least one cantilevered thermally conducting piezoelectric member is comprised of: a first and a second layer of piezoelectric material; a first electrical conductor interposed between said first and second layers of piezoelectric material; and a first and second layer of thermally conducting material respectively positioned on an outer surface of said first and said second layers of piezoelectric material.

21. the apparatus of Claim 20, wherein said first and said second layers of piezoelectric material are comprised of polyvinylidene fluoride (PVF₂) polymer film.

22. The apparatus of Claim 20, wherein said first and said second layers of thermally conducting material are comprised of a rolled annealed copper material.

23. The apparatus of Claim 20, wherein said first and said second layers of thermally conducting material are comprised of silver ink material.

24. The apparatus of Claim 19, wherein said at least one cantilevered thermally conducting piezoelectric member includes a thermally conducting surface, which receives heat energy from said heat source, that is exposed on at least one face to said ambient environment.

25. The apparatus of Claim 24, wherein said at least one cantilevered thermally conducting piezoelectric member moves in a direction which is substantially normal to the exposed face of said thermally conducting surface.

26. The apparatus of Claim 25, wherein said movement of said at least one cantilevered thermally conducting piezoelectric member produces a thermal gradient in said thermally conducting surface which facilitates removal of heat energy from said heat source.

27. The apparatus of Claim 19, wherein said heat source is a computer chip and said apparatus is positioned on an upper surface of said computer chip.

28. A cooling assembly for cooling a heat source having a first surface which is positioned in an ambient environment comprising: a first thermally conducting element in thermal contact with said first surface of said heat source and mounted so as to extend in a first direction from said heat source; a first piezoelectric element positioned adjacent said first thermally conducting element so that when an electrical signal is applied to said first piezoelectric element, said first piezoelectric element induces said first thermally conducting element into motion wherein said motion facilitates dissipation of heat energy produced by said heat source; and a heat sink positioned on said first surface of said heat source, said heat sink including a plurality of cantilevered members extending in a second direction.

29. The assembly of Claim 28, wherein said first thermally conducting element is comprised of a planar member having a first and a second face and wherein said first piezoelectric element induces said first thermally conducting element to vibrate back and forth in a direction with is substantially normal to said first and said second faces of said thermally conducting member.

30. The assembly of Claim 29, wherein said vibratory motion of said first thermally conducting element facilitates dissipation of heat energy absorbed by said first thermally conducting element from said heat source into said ambient environment.

31. The assembly of Claim 28, wherein said motion of said first thermally conducting element produces air currents in said ambient environment which induces an air flow over said plurality of cantilevered members of said heat sink.

32. The assembly of Claim 31, further comprising a channel member which is positioned relative said heat sink and said first thermally conducting element to direct air currents produced by said first thermally conducting element into said air flow over said plurality of cantilevered members of said heat sink.

33. The assembly of Claim 28, wherein at least one of said plurality of cantilevered members of said heat sink is comprised of a tnermally conducting element engaged with a piezoelectric element that receives a electrical signal which causes said piezoelectric element to induce said at least one member into motion which facilitates dissipation of heat energy produced by said heat source.

34. The assembly of Claim 28, wherein said heat source is comprised of a computer chip having an upper surface and said first thermally conducting element is positioned so as to extend horizontally outward from said upper surface of said computer chip and said heat sink is positioned so that said plurality of cantilevered members extend vertically upward from said upper surface.

35. A method of dissipating heat energy produced by a heat source in an ambient environment comprising: positioning a thermally conductive element in thermal contact with said heat source; piezoelectrically inducing said thermally conductive element into motion wherein said motion facilitates dissipation of said heat energy produced by said heat source into said ambient environment.

36. The method of Claim 35, wherein said step of positioning said thermally conductive element comprises mounting said thermally conductive element on said heat source so that said thermally conductive element extends outward from said heat source in a cantilevered fashion.

37. The method of Claim 36, wherein said step of piezoelectrically inducing said thermally conductive element into motion comprises applying an electrical signal to a piezoelectric element coupled to said thermally conductive element so that said thermally conductive element vibrates.

38. The method of Claim 35, wherein said thermally conductive element defines a plane and said motion of said thermally conductive element is in a direction which is substantially normal to said plane.

39. The method of Claim 35, wherein said motion of said thermally conductive element produces a thermal gradient in said thermally conductive element which facilitates removal of heat energy from said heat source.

40. The method of Claim 35, wherein said motion of said thermally conductive element produces convection air current in said ambient environment.

41. the method of Claim 40, further comprising the step of channeling said convection air current to further dissipate heat energy produced by said heat source into said ambient environment.

42. The method of Claim 41, wherein said step of channeling said convection air current comprises channeling said air current into an air flow which flows over a heat sink that is thermally connected to said heat source.