US20110223043A1

US20110223043A1 - Piezoelectric fan and cooling device

Info

Publication number: US20110223043A1
Application number: US13/027,473
Authority: US
Inventors: Nobuhira TANAKA; Hiroaki Wada
Original assignee: Murata Manufacturing Co Ltd
Current assignee: Murata Manufacturing Co Ltd
Priority date: 2010-03-10
Filing date: 2011-02-15
Publication date: 2011-09-15
Also published as: CN102192136B; CN102192136A; JP5051255B2; JP2011185211A

Abstract

A piezoelectric fan includes reinforcing plates that increase the rigidity of a portion of the vibrating plate corresponding to a gap between a piezoelectric element and a fixing plate. First ends of the reinforcing plates are attached to portions of the vibrating plate on both sides of piezoelectric elements in the width direction, and second ends of the reinforcing plates are attached to a fixed end of the vibrating plate such that the second ends and the fixing plate sandwich the fixed end of the vibrating plate therebetween and such that the reinforcing plates extend over the gap. The reinforcing plates prevent vibration of the portion of the vibrating plate corresponding to the gap, prevent a portion of vibration energy generated by expansion and contraction of the piezoelectric elements from being consumed in the portion corresponding to the gap, and increase the amplitude of the vibration of blade ends.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a piezoelectric fan that discharges warm air from the vicinity of a heat dissipater, and to a cooling device including the piezoelectric fan.
2. Description of the Related Art
Electronic components are mounted with high density in small electronic apparatuses. Therefore, dissipation of heat generated in the apparatuses is an important issue. For example, while the size of personal computers has decreased, the CPU clock rate has increased in order to improve the processing performance. As a result, in such an electronic apparatus, the airflow is reduced due to the high-density mounting of components while the amount of heat generated by the CPU, which is an example of a heat-generating member, has been increased. In such circumstances, it has become an important issue to discharge warm air that is heated by a heat dissipater, such as a heatsink, which is disposed on an upper surface of the CPU, from the vicinity of the heat dissipater so as to prevent an increase in the temperature of the CPU.
For example, Hiroto Kaneko, “Demonstration of Heatsink that Blows Air by Vibration”, Sep. 25, 2009, Nikkei WinPC, searched on Oct. 16, 2009 on the Internet, <URL:http://pc.nikkeibp.co.jp/article/news/20090925/1018872/?f=news> (hereinafter referred to as “Kaneko”) describes a piezoelectric fan that discharges warm air from the spaces between heat-dissipating fins of a heatsink. Referring to FIGS. 1 to 3B, the structures of the piezoelectric fan and the cooling device described in Kaneko will be described.
FIG. 1 is a perspective view of a piezoelectric fan 10 described in Kaneko. FIG. 2 is a side view of the piezoelectric fan 10. FIGS. 3A and 3B are perspective views of a cooling device 9 including the piezoelectric fan 10 described in Kaneko. The piezoelectric fan 10 includes a vibrating plate 11, piezoelectric elements 12A and 12B, and a fixing plate 13. A heatsink 20 includes heat-dissipating fins 22 that extend upward from a base portion 21 so as to be parallel to each other. In FIGS. 3A and 3B, a heat-generating member 50, such as a CPU, is mounted on a circuit board. The heatsink 20 is disposed on the upper surface of the heat-generating member 50 so that the bottom surface of the heatsink 20 is thermally coupled to the upper surface. The cooling device 9 is formed by fixing the piezoelectric fan 10 to the heatsink 20 that is made of aluminum.
As illustrated in FIGS. 1 and 2, the two piezoelectric elements 12A and 12B are affixed to both sides of the vibrating plate 11, and the vibrating plate 11 bends when the piezoelectric elements 12A and 12B expand and contract. Blades 14 are provided on a free end side of the vibrating plate 11, and the blades 14 vibrate when the vibrating plate 11 bends. The fixing plate 13 is fixed to a fixed end of the vibrating plate 11.
The two piezoelectric elements 12A and 12B are affixed to the vibrating plate 11 so as to sandwich the vibrating plate 11, which functions as an intermediate electrode, therebetween. Thus, the piezoelectric elements 12A and 12B and the vibrating plate 11 define a bimorph vibrator. Each of the piezoelectric elements 12A and 12B includes a film electrode that is provided on the surface of piezoelectric ceramic body thereof. When a drive voltage is applied between the film electrodes and the vibrating plate 11, which functions as an intermediate electrode, the vibrating plate 11 is warped in the longitudinal direction and vibrates.
The two piezoelectric elements 12A and 12B are arranged such that the piezoelectric element 12B contacts the fixing plate 13 and such that the piezoelectric elements 12A and 12B sandwich a portion of the vibrating plate 11 therebetween. Then, the piezoelectric elements 12A and 12B are affixed to the vibrating plate 11 (see FIGS. 1 and 2). Each of the seven blades 14 is inserted in a corresponding one of the grooves between the heat-dissipating fins 22 of the heatsink 20 (see FIG. 3A and 3B), and the fixed end of the vibrating plate 11 is fixed, using screws 15, to an upper portion of the heatsink 20 with the fixing plate 13 therebetween.
With the structure described in Kaneko, heat that is generated by the heat-generating member 50 is transferred to the heatsink 20, and air in the spaces between the heat-dissipating fins 22 is heated by the heat-dissipating fins 22. When the piezoelectric fan 10 is driven, the blades 14 vibrate and discharge the warm air from the spaces between the heat-dissipating fins 22.
However, even when the fixing plate 13 and the piezoelectric elements 12A and 12B are affixed to the vibrating plate 11 after being positioned as described above, a gap G is generated between the fixing plate 13 and the piezoelectric elements 12A and 12B (see FIG. 2). This is because there is a limitation on the precision of positioning or because there are microscopic asperities on the surface of the fixing plate 13.
As shown in FIG. 2, the rigidity of a portion of the vibrating plate 11 corresponding to the gap G depends only on the rigidity of the vibrating plate 11. Therefore, the rigidity of this portion is less than the rigidity of a portion of the vibrating plate 11 to which the fixing plate 13 is bonded and the rigidity of a portion of the vibrating plate 11 to which the piezoelectric elements 12A and 12B are bonded. Accordingly, the inventors of the present invention discovered that, with the piezoelectric fan 10 described in Kaneko, the portion of the vibrating plate 11 corresponding to the gap G vibrates, and a portion of the vibration energy that is generated by expansion and contraction of the piezoelectric elements 12A and 12B is consumed in the portion corresponding to the gap G, and thereby the amplitude of the vibration of the ends of the blades 14 is decreased. That is, the gap G impairs the air-moving performance of the piezoelectric fan 10.
Therefore, when the piezoelectric fan 10 described in Kaneko is mounted on the heatsink 20, the piezoelectric fan 10 may not sufficiently dissipate heat from the heat-dissipating fins 22. Because a variety of high-speed CPUs, which generate a large amount of heat, have been used recently, a piezoelectric fan having a cooling performance that is greater than that of the piezoelectric fan 10 described Kaneko is desired.

SUMMARY OF THE INVENTION

To overcome the problems described above, preferred embodiments of the present invention provide a piezoelectric fan with which the air-moving performance of a vibrating plate is increased and thereby the cooling performance is improved, and also provide a cooling device including the piezoelectric fan.
According to a preferred embodiment of the present invention, a piezoelectric fan preferably includes a piezoelectric element that expands and contracts in accordance with a voltage applied thereto, a vibrating plate to which the piezoelectric element is attached, the vibrating plate bending and vibrating at a resonant frequency when the piezoelectric element expands and contracts, a fixing member that fixes a fixed end of the vibrating plate to another member, and a reinforcing member arranged on the vibrating plate such that, when the vibrating plate is viewed in a side view in a direction in which a boundary between the piezoelectric element and the fixing member is visible, a first end of the reinforcing member is disposed on a portion of the vibrating plate to which the piezoelectric element is bonded, and a second end of the reinforcing member is disposed on a portion of the vibrating plate to which the fixing member is bonded.
With this structure, heat generated by the heat-generating member is transferred to the heat dissipater, and the heat dissipater generates warm air in the vicinity of the heat dissipater. Preferably, the heat dissipater is, for example, a heatsink or a heat spreader. With this structure, the piezoelectric fan is directly fixed to the heat dissipater or fixed to another member, and the warm air is discharged from the vicinity of the heat dissipater due to vibration of the vibrating plate.
Because the reinforcing member is preferably arranged at the position described above, the rigidity of a portion of the vibrating plate corresponding to the gap between the piezoelectric element and the fixing member is increased, and the following phenomenon occurs. That is, the reinforcing member prevents vibration of the portion of the vibrating plate corresponding to the gap G, and prevents a portion of vibration energy that is generated by expansion and contraction of the piezoelectric element from being consumed in the portion corresponding to the gap G, and thereby the amplitude of the vibration of the free ends of the vibrating plate is significantly increased. Thus, the air-moving performance of the piezoelectric fan is significantly increased.
Therefore, with the piezoelectric fan having this structure, the air-moving performance of the vibrating plate and the cooling performance are significantly increased.
According to a preferred embodiment of the present invention, the first end of the reinforcing member is preferably attached to each side in the width direction of the portion of the vibrating plate to which the piezoelectric element is attached, and the second end of the reinforcing member is preferably attached to the fixed end of the vibrating plate such that the second end and the fixing member sandwich the fixed end of the vibrating plate therebetween.
According to another preferred embodiment of the present invention, the reinforcing member is preferably a portion of the fixing member, and the first end of the reinforcing member is preferably attached to each side in the width direction of a portion of the vibrating plate to which the piezoelectric element is attached.
According to another preferred embodiment of the present invention, the first end of the reinforcing member is preferably attached to an end of the piezoelectric element near the fixing member, and the second end of the reinforcing member is bonded to the fixed end of the vibrating plate such that the second end and the fixing member sandwich the fixed end of the vibrating plate therebetween.
According to another preferred embodiment of the present invention, the vibrating plate preferably includes a cut-out portion on each side in the width direction of the portion to which the piezoelectric element is bonded.
With this structure, an openings or a cut-out portion is provided on each side of a portion of the vibrating plate to which the piezoelectric element is attached.
According to another preferred embodiment of the present invention, the first end of the reinforcing member is preferably attached to the vibrating plate such that the first end and the piezoelectric element sandwich the vibrating plate therebetween, and the second end of the reinforcing member is preferably attached to the fixed end of the vibrating plate such that the second end and the fixing member sandwich the fixed end of the vibrating plate therebetween.
This structure is preferably used when the piezoelectric element and the vibrating plate define a unimorph vibrator.
The number of the piezoelectric elements is preferably two, for example, and the piezoelectric elements sandwich the vibrating plate therebetween.
In this case, the piezoelectric elements and the vibrating plate preferably define a bimorph vibrator. With this structure, the bending displacement relative to the applied voltage is increased and the amplitude of the vibration of the vibrating plate is increased. Therefore, the air-moving performance of the piezoelectric fan is further increased.
The fixing member is preferably fixed to a heat dissipater that dissipates heat that is generated by a heat-generating member.
With this structure, the piezoelectric fan is fixed to the heat dissipater and discharges warm air from the vicinity of the vibrating plate due to vibration of the vibrating plate.
According to another preferred embodiment of the present invention, a cooling device preferably includes the piezoelectric fan according to a preferred embodiment of the present invention and the heat dissipater, wherein the heat dissipater is preferably a heat sink including a plurality of heat-dissipating fins, the vibrating plate preferably includes a plurality of blades provided on a free end side thereof, and the fixing member preferably fixes the fixed end of the vibrating plate to an upper portion of the heatsink such that each of the plurality of blades is inserted in a corresponding one of grooves between the plurality of heat-dissipating fins of the heatsink.
With this structure, the cooling device produces the same effect as that of the piezoelectric fan described above.
According to another preferred embodiment of the present invention, each of the plurality of blades of the vibrating plate is preferably bent toward the grooves between the heat-dissipating fins.
With this structure, the plurality of blades are bent toward the grooves between heat-dissipating fins. Therefore, a low profile cooling device is provided, so that the cooling performance can be increased without increasing the overall size of the cooling device.
With various preferred embodiments of the present invention, the air-moving performance of the vibrating plate and the cooling performance are significantly increased.
The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a piezoelectric fan of the related art.

FIG. 2 is a side view of the piezoelectric fan of the related art.

FIGS. 3A and 3B are perspective views of a cooling device including a piezoelectric fan of the related art.

FIG. 4 is a perspective view of a piezoelectric fan according to a first preferred embodiment of the present invention.

FIG. 5 is a side view of the piezoelectric fan according to the first preferred embodiment of the present invention.

FIGS. 6A and 6B are perspective views of a cooling device including the piezoelectric fan according to the first preferred embodiment of the present invention.

FIG. 7 is a graph illustrating the relationship between the distance from a fixed end of a vibrating plate of the piezoelectric fan to a position on the vibrating plate and the displacement of the vibrating plate at the position.

FIG. 8A is a top view of a fixing plate of a piezoelectric fan according to a second preferred embodiment of the present invention, FIG. 8B is a front view of the fixing plate, and FIG. 8C is a side view of the fixing plate.

FIG. 9 is a top view of the piezoelectric fan according to the second preferred embodiment of the present invention.

FIG. 10 is a side view of the piezoelectric fan according to the second preferred embodiment of the present invention.

FIG. 11 is a perspective view of a modification of the piezoelectric fan of the related art.

FIG. 12 is a perspective view of a piezoelectric fan according to a third preferred embodiment of the present invention.

FIG. 13 is a side view of the piezoelectric fan according to the third preferred embodiment of the present invention.

FIGS. 14A and 14B are perspective views of a cooling device including the piezoelectric fan according to the third preferred embodiment of the present invention.

FIG. 15A is a perspective view of a piezoelectric fan according to another preferred embodiment of the present invention, and FIG. 15B is a perspective view of a piezoelectric fan according to another preferred embodiment of the present invention.

FIG. 16A is a perspective view of a piezoelectric fan according to another preferred embodiment of the present invention, and FIG. 16B is a side view of the piezoelectric fan according to the other preferred embodiment of the present invention.

FIG. 17A is a perspective view of a piezoelectric fan according to another preferred embodiment of the present invention, and FIG. 17B is a side view of the piezoelectric fan according to the other preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Preferred Embodiment

Hereinafter, a piezoelectric fan according to a first preferred embodiment of the present invention will be described.
FIG. 4 is a perspective view of a piezoelectric fan 101 according to the first preferred embodiment, and FIG. 5 is a side view of the piezoelectric fan 101. FIGS. 6A and 6B are perspective views of a cooling device 1 including the piezoelectric fan 101. In FIG. 5, a vibrating plate is seen in side view in a direction in which the boundary between piezoelectric elements and a fixing member is visible. A gap G is illustrated in a slightly enlarged scale for convenience of illustration.
The piezoelectric fan 101 include a vibrating plate 111, piezoelectric elements 112A and 112B, a fixing plate 113, and reinforcing plates 151 and 152. A heatsink 20 preferably includes heat-dissipating fins 22 that extend upward from the base portion 21 so as to be parallel to each other. In FIGS. 6A and 6B, a heat-generating member 50 (heat-generating component), such as a CPU, for example, is mounted on a circuit board P so that the bottom surface of the heatsink 20 is thermally coupled to the upper surface of the heat-generating member 50. The cooling device 1 includes the piezoelectric fan 101 and the heatsink 20, which is preferably made of aluminum, for example.
As illustrated in FIGS. 4 and 5, two piezoelectric elements 112A and 112B are affixed to both sides of the vibrating plate 111. The vibrating plate 111 bends when the piezoelectric elements 112A and 112B expand and contract. Seven blades 141, for example, are preferably provided on the free end side of the vibrating plate 111. The seven blades 141 vibrate due to bending of the vibrating plate 111. The seven blades 141 of the vibrating plate 111 are preferably bent at 90 degrees, for example, toward grooves between the heat-dissipating fins 22.
The vibrating plate 111 is preferably a stainless steel plate having the following dimensions: a total width (i.e., the width of the seven blades 141) of about 45 mm, a width of each blade of about 2.0 mm, a total length of about 50 mm, a length from the fixed end of the vibrating plate 111 to the edge of the vibrating plate 111 (i.e., the bent portion) of about 25 mm, a length from the ends of the seven blades 141 to the edge (i.e., bent portion) of the vibrating plate 111 of about 25 mm, and a thickness of about 0.1 mm, for example.
Each of the piezoelectric elements 112A and 112B preferably has the following dimensions: a width of about 30 mm, a length of about 15 mm, and a thickness of about 0.05 mm, for example. The two piezoelectric elements 112A and 112B are affixed to the vibrating plate 111 so as to sandwich the vibrating plate 111, which functions as an intermediate electrode, therebetween. Thus, the piezoelectric elements 112A and 112B and the vibrating plate 111 preferably define a bimorph vibrator, for example. Each of the piezoelectric elements 112A and 112B preferably includes a film electrode, for example, that is provided on the front and back surfaces of the piezoelectric ceramic body thereof. The piezoelectric elements 112A and 112B are preferably poled such that, when a drive voltage in accordance with the polarization directions of the piezoelectric elements 112A and 112B is applied between the film electrodes and the vibrating plate 111, which functions as an intermediate electrode, the vibrating plate 111 is warped in the longitudinal direction and vibrates. Because the vibrator preferably has the bimorph structure, the bending displacement of the vibrating plate 111 relative to the voltages applied to the piezoelectric elements 112A and 112B is increased, whereby the amplitude of the vibration of the blades 141 is more efficiently increased.
The two piezoelectric elements 112A and 112B are preferably arranged such that the piezoelectric element 112B contacts the fixing plate 113 and such that the piezoelectric elements 112A and 112B sandwich a portion of the vibrating plate 111 therebetween. Then, the piezoelectric elements 112A and 112B are affixed to the vibrating plate 111 (see FIGS. 4 and 5). The fixing plate 113 is preferably made of glass epoxy, for example, and preferably has the following dimensions: a width of about 50 mm, a length of about 5 mm, and a thickness of about 2 mm, for example. Each of the seven blades 141 is inserted in a corresponding one of the grooves between the heat-dissipating fins 22 of the heatsink 20 (see FIGS. 6A and 6B), and the fixed end of the vibrating plate 111 is fixed, preferably using screws 115, for example, to an upper portion of the heatsink 20 with the fixing plate 113 therebetween.
As a result, the gap G is generated in the piezoelectric fan 101 of the first preferred embodiment (see FIG. 5), in a similar manner to the piezoelectric fan 10 of the Kaneko. That is, even when the fixing plate 113 and the piezoelectric elements 112A and 112B are affixed to the vibrating plate 111 after being positioned, the gap G is generated between the fixing plate 113 and the piezoelectric elements 112A and 112B. This is because there is a limitation on the precision of positioning and/or because there are microscopic asperities on the surface of the fixing plate 113.
Therefore, the piezoelectric fan 101 according to the first preferred embodiment includes the reinforcing plates 151 and 152, which are preferably made of stainless steel, for example, so that the rigidity of a portion of the vibrating plate 111 corresponding to the gap G is increased. First ends of the reinforcing plates 151 and 152 are preferably attached to both sides in the width direction of a portion of the vibrating plate 111 to which the piezoelectric elements 112A and 112B are bonded. Second ends of the reinforcing plates 151 and 152 are preferably attached to the fixed end of the vibrating plate 111 such that the reinforcing plates 151 and 152 and the fixing plate 113 sandwich the fixed end of the vibrating plate 111 therebetween. Each of the reinforcing plates 151 and 152 preferably has a thickness of about 0.05 mm, for example.
With the structure described above, heat that is generated by the heat-generating member 50 is transferred to the heatsink 20, and air in the spaces between the heat-dissipating fins 22 is heated by the heat-dissipating fins 22. Each of the seven blades 141 of the piezoelectric fan 10 vibrates between a corresponding pair of the heat-dissipating fins 22 that are next to each other without contacting the heat-dissipating fins 22. Thus, the piezoelectric fan 101 discharges the warm air from the spaces between the heat-dissipating fins 22.
A comparison between the air-moving performance of the piezoelectric fan 10 of Kaneko and the air-moving performance of the piezoelectric fan 101 of the first preferred embodiment will be described below.
FIG. 7 is a graph illustrating the relationship between the distance from a fixed end of a vibrating plate of the piezoelectric fan to a position on the vibrating plate and the displacement of the vibrating plate at the position. This graph illustrates the results of an experiment. In the experiment, the amplitude of the vibration of ends of the blades was measured when a sinusoidal alternating voltage of 24 Vpp at the resonant frequency was applied between the electrodes of the piezoelectric elements and the vibrating plate of each of the piezoelectric fan 10 and the piezoelectric fan 101.
In the experiment, the vibrating plate 11, the piezoelectric elements 12A and 12B, and the fixing plate 13 of the piezoelectric fan 10, respectively, had the same dimensions and were made of the same materials as those of the vibrating plate 111, the piezoelectric elements 112A and 112B, and the fixing plate 113 of the piezoelectric fan 101.
According to the results of the experiment, for the piezoelectric fan 10 of Kaneko, the average amplitude of the vibrations of the ends of the blades was about 8.0 mm at the resonant frequency of about 89.1 Hz. In contrast, for the piezoelectric fan 101 of the first preferred embodiment, the average amplitude of the vibrations of the ends of the blades was significantly increased to about 8.9 mm at the resonant frequency of about 95.5 Hz. This experiment shows that the average amplitude and the frequency of the piezoelectric fan 101 of the first preferred embodiment were greater than those of the piezoelectric fan 10 of Kaneko. Therefore, the air-moving performance of the blades of the piezoelectric fan of the first preferred embodiment, which is represented by “average amplitude×frequency”, was significantly improved.
This result is presumably due to the following phenomenon, which occurs because the rigidity of the portion of the vibrating plate 111 corresponding to the gap G is increased preferably by providing the reinforcing plates 151 and 152 on the vibrating plate 111. That is, the reinforcing plates 151 and 152 prevent the vibration of the portion of the vibrating plate 111 corresponding to the gap G and thereby prevent a portion of vibration energy, which is generated due to expansion and contraction of the piezoelectric elements 112A and 112B, from being consumed in the portion corresponding to the gap G, and thereby increases the amplitude of the vibrations of the ends of the blades 141.
As heretofore described, the blades 141 of the piezoelectric fan 101 of the first preferred embodiment have an air-moving performance greater than that of the blades of the piezoelectric fan 10, whereby the cooling performance is significantly increased.
The vibrating plate 111, which has a relatively large overall length, is bent so that a low-profile cooling device 1 is provided, whereby the cooling performance is increased without significantly increasing the size of the cooling device 1.

Second Preferred Embodiment

FIG. 8A is a top view of a fixing plate 213 of a piezoelectric fan 201 according to a second preferred embodiment of the present invention, FIG. 8B is a front view of the fixing plate 213, and FIG. 8C is a side view of the fixing plate 213. FIG. 9 is a top view of the piezoelectric fan 201 according to the second preferred embodiment. FIG. 10 is a side view of the piezoelectric fan 201. In FIG. 10, a vibrating plate is shown in a side view in a direction in which the boundary between piezoelectric elements and a fixing member is visible.
The piezoelectric fan 101 according to the first preferred embodiment includes the reinforcing plates 151 and 152 arranged to increase the rigidity of the portion of the vibrating plate 111 corresponding to the gap G. The piezoelectric fan 201 according to the second preferred embodiment includes the fixing plate 213 preferably made of glass epoxy, for example, which is illustrated in FIGS. 8A to 8C. The fixing plate 213 preferably includes reinforcing portions 214A and 214B. First ends of the reinforcing portions 214A and 214B are preferably attached, so as to extend over the gap G, to both sides of the portion of the vibrating plate 111 to which the piezoelectric elements 112A and 112B are attached.
A comparison between the air-moving performance of the piezoelectric fan 10 of Kaneko and the air-moving performance of the piezoelectric fan 201 of the second preferred embodiment will be described below based on the results of an experiment. In the experiment, the amplitude of the vibration of ends of the blades was measured when a sinusoidal alternating voltage of about 24 Vpp at the resonant frequency was applied between the electrodes of the piezoelectric elements and the vibrating plate of each of the piezoelectric fan 10 and the piezoelectric fan 201.
In the experiment, the vibrating plate 11, the piezoelectric elements 12A and 12B, and the fixing plate 13 of the piezoelectric fan 10 respectively had the same or substantially the same dimensions and were made of the same or substantially the same materials as those of the vibrating plate 111, the piezoelectric elements 112A and 112B, and the fixing plate 213 (excluding the reinforcing portions 214A and 214B) of the piezoelectric fan 201.
According to the result of the experiment, for the piezoelectric fan 10 of Kaneko, the average amplitude of the vibrations of the ends of the blades was about 8.0 mm at the resonant frequency of about 89.1 Hz. In contrast, for the piezoelectric fan 201 of the second preferred embodiment, the average amplitude of the vibrations of the ends of the blades was increased to about 8.6 mm at the resonant frequency of about 89.8 Hz. That is, the average amplitude and the frequency of the piezoelectric fan 201 of the second preferred embodiment were greater than those of the piezoelectric fan 10 of. Therefore, the air-moving performance of the blades of the piezoelectric fan according to the second preferred embodiment was significantly improved.
This result is presumably due to the same phenomenon as that for the piezoelectric fan 101 of the first preferred embodiment, which occurs because the rigidity of the portion of the vibrating plate 111 corresponding to the gap G is increased by attaching the reinforcing portions 214A and 214B of the fixing plate 213 to the vibrating plate 111.
As heretofore described, the blades 141 of the piezoelectric fan 201 of the second preferred embodiment have an air-moving performance greater than that of the blades of the piezoelectric fan 10, whereby the cooling performance is significantly increased. Therefore, when a cooling device includes the fixed end of the vibrating plate 111 of the piezoelectric fan 201 of the second preferred embodiment fixed to an upper portion of the heatsink 20 as illustrated in FIGS. 6A and 6B, the cooling performance of the cooling device is significantly increased.
The vibrating plate 111 is preferably bent so that a low-profile cooling device is provided, whereby the cooling performance can be increased without increasing the size of the cooling device.

Third Preferred Embodiment

FIG. 11 is a perspective view of a piezoelectric fan 30, which is a modification of the piezoelectric fan 10 described in Kaneko. FIG. 12 is a perspective view of a piezoelectric fan 301 according to a third preferred embodiment of the present invention. FIG. 13 is a side view of the piezoelectric fan 301 according to the third preferred embodiment. FIGS. 14A and 14B are perspective views of a cooling device 3 including the piezoelectric fan 301 according to the third preferred embodiment. In FIG. 13, a vibrating plate is shown in side view in a direction in which the boundary between piezoelectric elements and a fixing member is visible.
First, in order to compare the air-moving performance of the piezoelectric fan 301 of the third preferred embodiment with the air-moving performance of the piezoelectric fan 30, which is a modification of the piezoelectric fan 10, the structure of the piezoelectric fan 30 will be described.
The piezoelectric fan 30 differs from the piezoelectric fan 10 in the shape of the vibrating plate. In other respects, the piezoelectric fan 30 and the piezoelectric fan 10 have the same or substantially the same structure. As illustrated in FIG. 11, a vibrating plate 311 is a stainless steel plate preferably having the following dimensions: a width of about 45 mm, a length of about 50 mm, and a thickness of about 0.1 mm, for example. Cut-out portions 118 are formed by punch pressing the stainless steel plate. To be specific, the cut-out portions 118 are provided on both sides of a portion of the vibrating plate 311 to which the piezoelectric elements 112A are 112B are affixed, i.e., both sides in a direction perpendicular or substantially perpendicular to the longitudinal direction of the blades. The width the portion of the vibrating plate 311 to which the piezoelectric elements 112A and 112B are affixed is about 35 mm. Other dimensions of the vibration plate 311 are the same as those of the vibrating plate 111.
The piezoelectric fan 301 of the third preferred embodiment, which is illustrated in FIGS. 12 and 13, differs from the piezoelectric fan 30 of the comparative example in that the piezoelectric fan 301 includes a reinforcing plate 313, which is preferably made of glass epoxy, for example, in order to increase the rigidity of a portion of the vibrating plate 311 corresponding to the gap G. In other respects, the piezoelectric fan 301 and the piezoelectric fan 30 have the same or substantially the same structure. A first end of the reinforcing plate 313 is preferably attached to an end of the piezoelectric element 112A near the fixing plate 113. A second end of the reinforcing plate 313 is preferably attached to the fixed end of the vibrating plate 311 such that the reinforcing plate 313 and the fixing plate 113 sandwich the fixed end of the vibrating plate 311 therebetween. The thickness of the reinforcing plate 313 is preferably about 0.1 mm, for example.
Next, a comparison between the air-moving performance of the piezoelectric fan 30 the air-moving performance of the piezoelectric fan 301 of the third preferred embodiment will be described based on the results of an experiment. In the experiment, the amplitude of the vibration of ends of the blades was measured when a sinusoidal alternating voltage of about 24 Vpp at the resonant frequency was applied between the electrodes of the piezoelectric elements and the vibrating plate of each of the piezoelectric fan 30 and the piezoelectric fan 301.
According to the results of the experiment, for the piezoelectric fan 30, the average amplitude of the vibrations of the ends of the blades was about 9.0 mm at the resonant frequency of about 82.0 Hz. In contrast, for the piezoelectric fan 301 of the third preferred embodiment, the average amplitude of the vibrations of the ends of the blades was increased to about 9.5 mm at the resonant frequency of about 84.1 Hz. That is, this experiment shows that the average amplitude and the frequency of the piezoelectric fan 301 of the third preferred embodiment were larger than those of the piezoelectric fan 30. Therefore, the air-moving performance of the blades of the piezoelectric fan 301 according to the third preferred embodiment was significantly improved.
This result is presumably due to the same phenomenon as that for the piezoelectric fan 101 of the first preferred embodiment, which occurs because the rigidity of the portion of the vibrating plate 311 corresponding to the gap G is increased by providing the reinforcing plate 313 on the vibrating plate 311.
Next, the airflow in the piezoelectric fan 301 will be described. As illustrated in FIGS. 14A and 14B, each of the seven blades 141 are inserted in a corresponding one of the grooves between the heat-dissipating fins 22 of the heatsink 20, the cut-out portions 118 are preferably arranged above the grooves between the heat-dissipating fins 22, and the fixed end of the vibrating plate 311 is preferably fixed to an upper portion of the heatsink 20. Thus, in the third preferred embodiment, the cooling device 3 including the piezoelectric fan 301 and the heatsink 20 is provided. With this structure, when the piezoelectric fan 301 is driven and the blades 141 vibrate, airflow is produced due to the existence of the cut-out portions 118 as follows. That is, cool air flows downward through the cut-out portions 118 into the grooves between the heat-dissipating fins 22 and warm air generated between the heat-dissipating fins 22 flows upward through the cut-out portions 118. Therefore, with the piezoelectric fan 301 of the third preferred embodiment, not only the air-moving performance of the piezoelectric fan 301 but also the airflow to the heat-dissipating fins 22 are significantly improved.
As heretofore described, with the piezoelectric fan 301 of the third preferred embodiment, the air-moving performance of the blades 141 and the airflow to the heat-dissipating fins 22 are improved, whereby the cooling performance is significantly improved.
The vibrating plate 311 is preferably bent so that a low-profile cooling device is provided, whereby the cooling performance can be increased without increasing the size of the cooling device.
In the preferred embodiments of the present invention described above, the piezoelectric fans 101, 201, and 301 preferably include the vibrating plate 111 and the vibrating plate 311 that are bent towards the grooves between the heat-dissipating fins 22. However, as illustrated in FIG. 15A, a piezoelectric fan 401, which includes the vibrating plate 111 or the vibrating plate 311 that is preferably not bent, may be used. Alternatively, as illustrated in FIG. 15B, a piezoelectric fan 501, which includes the vibrating plate 111 or the vibrating plate 311 that is preferably bent at an appropriate angle (for example, 45 degrees), may be used.
In the preferred embodiments of the present invention described above, the piezoelectric fans 101, 201, and 301 are preferably bimorph-type piezoelectric fans, in which the piezoelectric elements 112A and 112B are attached to both sides of the vibrating plate 111. However, as illustrated in FIGS. 16A and 16B, a unimorph piezoelectric fan 601, which includes the vibrating plate 111 and only one piezoelectric element 112A that is attached to the upper surface of the vibrating plate 111, may be used. Alternatively, as illustrated in FIGS. 17A and 17B, a unimorph piezoelectric fan 701, which includes the vibrating plate 111 and only a piezoelectric element 112B that is attached to the lower surface of the vibrating plate 111, may preferably be used.
The piezoelectric fan 701 includes, instead of the reinforcing plates 151 and 152, a reinforcing plate 153 that is preferably made of stainless steel, for example. The reinforcing plate 153 is preferably attached to the upper surface of the vibrating plate 111 such that a first end of the reinforcing plate 153 is located at a position corresponding to a portion of the vibrating plate 111 to which the piezoelectric element 112B is attached and a second end of the reinforcing plate 153 is located at a position corresponding to a portion of the vibrating plate 111 to which the fixing plate 113 is attached.
In the preferred embodiments of the present invention described above, each of the vibrating plate 111 and the vibrating plate 311 preferably includes a plurality of blades provided on the free end side thereof. However, a vibrating plate including a free end that is not branched into a plurality of blades may be used.
In the preferred embodiments of the present invention described above, the blades 141 need not be made of stainless steel, and may preferably be made of an elastic metal, such as phosphor bronze, or a resin, for example.
While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.

Claims

1. A piezoelectric fan comprising:

a piezoelectric element arranged to expand and contract in accordance with a voltage applied thereto;

a vibrating plate to which the piezoelectric element is attached, the vibrating plate being arranged to bend and vibrate at a resonant frequency when the piezoelectric element expands and contracts;

a fixing member arranged to fix a fixed end of the vibrating plate to another member; and

a reinforcing member arranged on the vibrating plate such that, when the vibrating plate is viewed in a side view in a direction in which a boundary between the piezoelectric element and the fixing member is visible, a first end of the reinforcing member is located on a portion of the vibrating plate to which the piezoelectric element is attached, and a second end of the reinforcing member is located on a portion of the vibrating plate to which the fixing member is attached.

2. The piezoelectric fan according to claim 1, wherein the first end of the reinforcing member is attached to each side in a width direction of the portion of the vibrating plate to which the piezoelectric element is attached, and the second end of the reinforcing member is attached to the fixed end of the vibrating plate such that the second end and the fixing member sandwich the fixed end of the vibrating plate therebetween.

3. The piezoelectric fan according to claim 1, wherein the reinforcing member is a portion of the fixing member, and the first end of the reinforcing member is attached to each side in a width direction of a portion of the vibrating plate to which the piezoelectric element is attached.

4. The piezoelectric fan according to claim 1, wherein the first end of the reinforcing member is attached to an end of the piezoelectric element near the fixing member, and the second end of the reinforcing member is attached to the fixed end of the vibrating plate such that the second end and the fixing member sandwich the fixed end of the vibrating plate therebetween.

5. The piezoelectric fan according to claim 4, wherein the vibrating plate includes a cut-out portion on each side in a width direction of the portion to which the piezoelectric element is attached.

6. The piezoelectric fan according to claim 1, wherein the first end of the reinforcing member is attached to the vibrating plate such that the first end and the piezoelectric element sandwich the vibrating plate therebetween, and the second end of the reinforcing member is attached to the fixed end of the vibrating plate such that the second end and the fixing member sandwich the fixed end of the vibrating plate therebetween.

7. The piezoelectric fan according to claim 1, wherein a number of the piezoelectric elements is two, and the piezoelectric elements sandwich the vibrating plate therebetween.

8. The piezoelectric fan according to claim 1, wherein the fixing member is fixed to a heat dissipater that dissipates heat that is generated by a heat-generating member.

9. A cooling device comprising:

piezoelectric fan according to claim 8; and

the heat dissipater; wherein

the heat dissipater is a heatsink including a plurality of heat-dissipating fins;

the vibrating plate includes a plurality of blades provided on a free end side thereof; and

the fixing member fixes the fixed end of the vibrating plate to an upper portion of the heatsink such that each of the plurality of blades is inserted in a corresponding one of grooves between the plurality of heat-dissipating fins of the heatsink.

10. The cooling device according to claim 9, wherein the plurality of blades of the vibrating plate are bent toward the grooves between the heat-dissipating fins.