Patent Application
20090004034
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.
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
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.
Referring still to
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.
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.
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.
