Title:
PIEZOELECTRIC FAN
Kind Code:
A1


Abstract:
A piezoelectric fan comprising two or more prongs and a bulk flow portion.



Inventors:
Lee, Seri (Beaverton, OR, US)
Application Number:
11/771566
Publication Date:
01/01/2009
Filing Date:
06/29/2007
Primary Class:
International Classes:
F04B17/00
View Patent Images:
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Primary Examiner:
KASTURE, DNYANESH G
Attorney, Agent or Firm:
Cool Patent, C/o Intellevate P. C. (P.O. BOX 52050, MINNEAPOLIS, MN, 55402, US)
Claims:
What is claimed is:

1. An apparatus comprising: a piezoelectric fan assembly comprising; at least one piezoelectric actuator capable of causing vibration in a flexible blade; and the flexible blade coupled to the piezoelectric actuator at a first end, the blade comprising; a bulk flow portion capable of generating a bulk media flow, the bulk flow portion positioned between the first end and a second end of the blade; and two or more prongs coupled to the bulk flow portion and positioned at the second end.

2. The apparatus of claim 1, wherein at least one prong comprises: holes, scalloped edges, notches, or rounded edges, or combinations thereof.

3. The apparatus of claim 1, further comprising a heat sink comprising a base portion and at least one projection extending from the base portion, wherein at least a portion of one or more prongs is positioned over the base portion and adjacent to the at least one projection.

4. The apparatus of claim 3, wherein at least a portion of the piezoelectric fan assembly is contained within an enclosure.

5. The apparatus of claim 3, wherein the one or more prongs are positioned at an angle which is transverse to a plane of the base portion of the heat sink.

6. The apparatus of claim 3, wherein the piezoelectric actuator is coupled to the heat sink.

7. A method, comprising: dissipating heat from a heat source to a heat dissipating device; forming a thermal boundary layer of air and a thermal ambient layer of air proximate to a surface of the heat dissipating device; generating a bulk airflow with a piezoelectric fan capable of displacing at least a portion of the thermal ambient layer; and generating a local turbulent airflow with a piezoelectric fan capable of breaking up the thermal boundary layer.

8. The method of claim 7 further comprising interweaving a portion of the piezoelectric fan with projections protruding from the heat dissipating device.

Description:

BACKGROUND

Piezoelectric fans may be used to remove heat from a variety of devices, such as integrated circuits, for example. In a particular embodiment, utilizing a piezoelectric actuator, a piezoelectric fan may operate by vibrating a plate attached to a piezoelectric element at a first end. The plate may be suspended at a second end in free space, similar to a cantilever beam. An alternating electrical current may cause a lateral vibration of the plate. Resonant vibration of the plate may generate airflow. According to a particular embodiment, a piezoelectric fan may be part of an electronic assembly and may be positioned adjacent to an integrated circuit package coupled to a heat sink. The piezoelectric fan may generate airflow across the heat sink and may facilitate removal of heat from the integrated circuit package. Addition of the piezoelectric fan to such an electronic assembly increases the form factor requirement for a circuit board assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram side view of an electronic assembly comprising a piezoelectric fan according to a particular embodiment;

FIG. 2 is a plan view of an electronic assembly comprising a piezoelectric fan according to a particular embodiment,

FIG. 3 is a block diagram side view of an electronic assembly comprising a piezoelectric fan according to a particular embodiment;

FIG. 4 is a block diagram side view of an electronic assembly comprising a piezoelectric fan according to a particular embodiment.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of claimed subject matter. However, it will be understood by those skilled in the art that claimed subject matter may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure claimed subject matter.

Although, the embodiments described herein refer to a piezoelectric fan capable of generating airflow across a heat sink, such embodiments are meant for illustrative purposes and are not intended to limit the scope of the disclosure. The disclosed device and method may be useful in any of a variety of applications involving airflow or other medium flow. Such applications may include cooling integrated circuits or moving a medium about an environment such as with Laminar airflow applications, for instance. The disclosed device may find utility in a variety of products such as room deodorizers, pool filters, handheld products, consumer electronics products, low power micro-processor applications, chipset cooling, and low-velocity turbulent flow applications. Additionally, the disclosed device may be made from a variety of materials, such as flexible metals and/or plastic. Further, the disclosed device may be enclosed, mounted and/or secured in a variety of ways depending on the specifications of the particular application to which it is applied.

The term “thermal boundary layer” may be used herein to describe the layer of air that is in immediate contact with the surfaces of a heat dissipating device, absorbing the heat from the convective surfaces. Also, convective surfaces may be used herein to describe the surface that is directly exposed to the surrounding air flow, dissipating heat into the thermal boundary layer. Additionally, the term “thermal ambient layer” may be used herein to describe the layer of ambient air that carries the bulk flow over and through the heat sink but not substantially a part of the thermal boundary layers

FIG. 1 depicts a particular embodiment of an electronic cooling assembly 100 comprising integrated circuit 112, heat sink 114 and piezoelectric fan 116. According to a particular embodiment, piezoelectric fan 116 may comprise blade 102 made from a suitable material. Such suitable material may be flexible metal and/or plastic, for example. In a particular embodiment, piezoelectric actuator 104 may be attached to one end of blade 102 with the rest of blade 102 being suspended in free space. Additionally, piezoelectric actuator 104 may comprise, for example, a ceramic material capable of expanding or contracting in response to an electric current. According to a particular embodiment, power source 106 may provide power to piezoelectric actuator 104. When an electric current flows through piezoelectric actuator 104 in one direction, piezoelectric actuator 104 may contract causing blade 102 to flex upward. Similarly, when an electrical current flows through piezoelectric actuator 104 in the opposite direction, piezoelectric actuator 104 may expand causing blade 102 to flex downward. Thus, when alternating current (AC) power is provided to piezoelectric fan 116 at an appropriate frequency (e.g. substantially near a resonant frequency) blade 102 may oscillate or vibrate (e.g. in the direction of arrow 108). The appropriate frequency may depend on, for example, the sizes, materials, and proportions associated with blade 102.

In a particular embodiment, heat sink 114 may be coupled to integrated circuit 112 and may be capable of dissipating heat generated by integrated circuit 112. According to a particular embodiment, heat sink 114 may comprise a number of projections 122 (e.g. pins and/or fins) extending in a lateral direction with respect to base 115 of heat sink 114 increasing the surface area of heat sink 114. In a particular embodiment, heat may be dissipated from integrated circuit 112 to the air surrounding the projections 122, a thermal boundary layer of air and a thermal ambient layer of air. The vibration of blade 102 may generate an airflow (e.g. predominantly in the direction of arrow 10) toward heat sink 114 and through channels (not shown) between projections 122. Such airflow may improve the performance of heat sink 114. According to a particular embodiment, addition of piezoelectric fan 116 may significantly increase form factor 118 of electronic cooling assembly 100 and may not substantially break-up thermal boundary layers that build-up upon convective surfaces of heat sink 114.

FIG. 2 is a plan view of a particular embodiment of electronic assembly 200. In a particular embodiment, electronic assembly 200 may comprise piezoelectric fan 216 and heat sink 214. Heat sink 214 may be capable of dissipating heat from a heat source to a thermal boundary layer of air and to a thermal ambient layer of air. In a particular embodiment, piezoelectric fan 216 may comprise piezoelectric actuator 202 coupled to a piezoelectric fan blade 217. Piezoelectric fan blade 217 may comprise a bulk flow portion 204 and rake shaped portion 205. However, this is merely an example of a configuration of a piezoelectric fan and claimed subject matter is not so limited. For instance, in another particular embodiment, a piezoelectric fan may comprise a plurality of actuators coupled to a plurality of blades.

Referring still to FIG. 2, in a particular embodiment, heat sink 214 may comprise a base 226, projections 222 and channels 225 defined by projections 222. According to a particular embodiment, piezoelectric actuator 202 may be coupled to a power source (not shown) that may enable piezoelectric fan 216 to vibrate as described above with reference to FIG. 1. In a particular embodiment, a portion of prongs 218 may be positioned within channels 225. This configuration may decrease the form factor of electronic assembly 200. Additionally, according to a particular embodiment, a portion of or the entire electronic assembly 200 may be contained within an enclosure (not shown).

In a particular embodiment, rake shaped portion 205 may comprise two or more prongs 218. Prongs 218 may be uniformly shaped or may have a variety of shapes. For example, prongs 218 may comprise holes 220, notches (not shown), scalloped edges 223 and/or rounded edges 224. Additionally, prongs 218 may have a variety of dimensions (e.g. varied length, thickness and/or width). However, these are merely examples of a variety of shapes prongs of a piezoelectric fan may comprise and claimed subject matter is not limited in this regard.

According to a particular embodiment, prongs 218 may be coupled to and extend from bulk flow portion 204. Bulk flow portion 204 may have a length L1. Length L1 may comprise a substantial portion of length L2 of piezoelectric fan blade 217. For example, length L1 may be 10.0 cm and length L2 may be 3.0 cm. According to a particular embodiment, in electronic assembly 200, bulk flow portion 204 may be capable of driving bulk motion airflow while prongs 218 may provide local surface turbulences. According to a particular embodiment, a portion of prongs 218 may be positioned within channels 225 defined by projections 322. When actuated, prongs 218 may sweep projection 222 surfaces, preventing thermal boundary layers from building up near convective surfaces. In a particular embodiment, perpendicular airflow caused by the sweeping motion of vibrating prongs 218 may lower the effective cooling air temperature of heat sink 214 and projections 222 by entraining the cooler fin-tip air towards hotter base plate 226. Additionally, when vibrating, bulk flow portion 204 may be capable of generating bulk airflow in the direction of heat sink 214 and may displace thermal ambient layer proximate to heat sink 214. However, this is merely an example of a configuration and function of a piezoelectric fan and claimed subject matter is not limited in this regard.

FIG. 3 is a cutaway view of a particular embodiment of electronic cooling assembly 300 comprising integrated circuit 312, heat sink 314 comprising projections 322 and piezoelectric fan 316. As described above with reference to FIG. 1, when piezoelectric fan 316 is powered on, actuator 305 may cause vibration of bulk flow portion 304 and prongs 318. According to a particular embodiment, a portion of prongs 318 may be positioned within the channels between projections 322. As illustrated, prongs 318 may be interwoven between the projections of heat sink 314, with a portion of the length of prongs 318 overlapping with a portion of the channels between projections 322. In a particular embodiment, an undulating turbulent flow caused by vibration of prongs 318 at or near projection 322 surfaces may break the thermal boundary layers. A portion of the generated airflow may also mix through channels (not shown) in a direction perpendicular to the predominant airflow direction (e.g. in a direction from the projection base to the projection tips). As discussed above with respect to FIG. 2, the perpendicular airflow may lower the effective cooling air temperature of the heat sink by entraining the cooler fin-tip air towards the hotter base plate 326. In a particular embodiment, interweaving prongs 318 within the channels of projections 322 may also enable a significant reduction in form factor 320 of electronic assembly 300.

According to a particular embodiment, bulk flow portion 304 may be positioned close to and outside of the channels and may be capable of generating bulk airflow in the direction of heat sink 314. When piezoelectric fan 316 is powered on, actuator 305 may cause vibration of bulk flow portion 304 and prongs 318. Such vibration may generate bulk airflow in the direction of arrow 310 toward heat sink 314. Such bulk airflow may be capable of substantially displacing a thermal ambient layer of air proximate to heat sink surfaces as a result of undulating turbulence caused by vibration of bulk flow portion 304. The air may flow through channels (not shown) between projections 322 of heat sink 314.

In a particular embodiment, piezoelectric fan 316 may provide a mixture of bulk airflow and local turbulent flows. Providing bulk airflow close to heat sink 314 in addition to breaking up the thermal boundary layer built up at the surface of projections 322, displace thermal ambient layer of air and may enable improved heat removal. Additionally, convective heat transfer from projection 322 surfaces may also be improved. However, this is merely an example of an electronic assembly comprising a piezoelectric fan and claimed subject matter is not so limited.

FIG. 4 is a side view of a particular embodiment of an electronic assembly 400 comprising an integrated circuit 412, piezoelectric fan 416 and pin-fin type heat sink 414. In a particular embodiment, heat sink 414 may comprise an array of protruding cylindrical or rectangular pin-fins 422 defining airflow channels 425 in two directions. In a particular embodiment, piezoelectric fan 416 may be angled with respect to heat sink 414. For example, a substantially common plane to prongs 418 may be transverse to a plane of the base of heat sink 414. In a particular embodiment, piezoelectric fan 416 may be oriented at any desired angle θ with respect to heat sink 414. The position and impinging angle θ may be chosen as desired depending on system design specifications as well as the direction of the gravity vector for enhancement of the convection performance at the target surface.

When piezoelectric fan 416 is powered on, actuator 405 may cause vibration of bulk flow portion 404 and prongs 418. According to a particular embodiment, bulk flow portion 404 may be positioned close to and outside of channels 425. Bulk flow portion 404, when vibrating, may be capable of generating bulk airflow in the direction of heat sink 414 displacing the thermal ambient layer of air. According to a particular embodiment, at least a portion of prongs 418 may be interwoven within channels 425. In a particular embodiment, prongs 418, when vibrating, may be capable of breaking up a thermal boundary layer built up at the surface of projections 422. However, this is merely an example of an electronic assembly comprising an angled piezoelectric fan and claimed subject matter is not so limited.

While certain features of claimed subject matter have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such embodiments and changes as fall within the true spirit of claimed subject matter.