Patent Publication Number: US-2023156983-A1

Title: Air-vent with non-uniform cross section for emi shielding

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of co-pending U.S. provisional patent application Ser. No. 63/263,970 filed Nov. 12, 2021. The aforementioned related patent application is herein incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     Embodiments presented in this disclosure generally relate to vent openings with varying cross-sections. 
     BACKGROUND 
     Air vents on a computing system chassis are designed to shield unwanted electromagnetic energy, while at the same time allow efficient air flow to cool the system. Vent opening/perforation patterns consisting of straight through holes are typically used to balance electromagnetic interference (EMI) and thermal requirements. There is an inherent conflict between thermal design (calling for larger, less restrictive openings) and electromagnetic shielding (which benefits from smaller openings). With the speed and power consumption of a computing system increasing every product generation, the balance between electromagnetic and thermal requirements has become harder to achieve. 
     EMI engineers prefer smaller air vent openings to move the cutoff frequency much higher than the operating frequency, while thermal engineers design bigger air vents for more airflow for efficient cooling. The requirements for these two functions are inverse of each other and often reach at different crossroads with every new generation of products that are more power hungry and operate at higher speeds. Modification of shapes of air vent openings with straight through holes have their limitation in terms of EMI/shielding performance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate typical embodiments and are therefore not to be considered limiting; other equally effective embodiments are contemplated. 
         FIGS.  1 A- 1 F  illustrate different air vents and their cross sections, according to embodiments herein. 
         FIG.  2    illustrates airflow through an air vent, according to one embodiment herein. 
         FIGS.  3 A- 3 C  illustrate chassis sides containing a plurality of air vents, according to embodiments herein. 
         FIG.  4    is a computing system chassis with a side containing a plurality of air vents, according to embodiments herein. 
         FIGS.  5 A and  5 B  illustrate measurement and simulation data for air vents, according to embodiments herein. 
         FIG.  6    illustrates pressure drop data for air vents, according to one embodiment herein. 
         FIG.  7    illustrates pressure drop data for air vents, according to one embodiment herein. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially used in other embodiments without specific recitation. 
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Overview 
     One embodiment presented in this disclosure is a container that includes a body configured to contain a computing system that emits heat and is a source of electromagnetic interference (EMI) and an air vent formed through the body. The air vent configured to enable airflow and absorb the EMI emitted by the computing system. The air vent includes a first opening on a first side of the body and a second opening on a second, opposite side of the body where a diameter of the air vent increases at a non-linear rate when moving from the first opening to the second opening and the first opening has a smaller diameter than the second opening. Moreover, the first and second openings are co-planar with the first and second sides of the body. 
     Another embodiment presented in this disclosure is a container that includes a body configured to contain a computing system that emits heat and is a source of electromagnetic interference (EMI) and a plurality of air vents formed through the body. The plurality of air vents configured to enable airflow and absorb the EMI emitted by the computing system. Each of the plurality of air vents includes a first opening on a first side of the body and a second opening on a second, opposite side of the body where the first opening has a smaller diameter than the second opening and the second openings for the plurality of air vents contacts a second opening of at least one other of the plurality of air vents. 
     Example Embodiments 
     Embodiments herein describe air vents for, e.g., computing systems that provide air flow for cooling but still provide EMI shielding. In one embodiment, the air vents have a first opening on a first side of a panel of a chassis and a second opening on a second, opposite side of the panel. These openings form an aperture through the panel of the chassis. In addition, the first opening has a smaller diameter than the second opening. 
     The EMI shielding is generally tied to the smallest opening of the air vent. That is, the frequencies shielded (or absorbed) by the air vent generally correspond to the size of the smallest opening in the air vent. However, shrinking the opening typically reduces airflow, thereby having a negative impact on cooling. In the embodiments herein, however, the air vents have openings of different sizes which results in a smaller hole for improved EMI shielding but without any (or minimal) loss in airflow. Alternatively, the air vents can have openings of different sizes which result in the same EMI shielding as an air vent with a uniform radius but provide improved airflow and cooling. 
       FIGS.  1 A- 1 F  illustrate different air vents and their cross sections, according to embodiments herein. The air vents in  FIGS.  1 A- 1 F  can be implemented on any chassis that includes a heat source which is cooled by air flowing through the air vents. Further, the chassis can contain an EMI emitter or contain EM sensitive components where EMI shielding is desired. As such, the air vents in  FIGS.  1 A- 1 F  may be made from any material that absorbs EM energy (e.g., an electrical conductor such as metal). 
       FIG.  1 A  illustrates a front view and a cross sectional view of an air vent  100 A formed in a panel  120  that is part of a body of a chassis. The panel  120  has a thickness where the air vent  100 A defines an aperture through the panel  120 . In this example, the air vent  100 A has a first opening  105 A and a second opening  110 A where the first opening  105 A has a larger radius and diameter than the second opening  110 A. Specifically, when moving from the first opening  105 A to the second opening  110 A, the radius of the air vent  100 A increases linearly. As such, the cross section of the air vent  100 A forms a trapezoidal shape, and as such, the air vent  100 A can be referred to as a trapezoidal air vent. 
     In  FIG.  1 A , the radius of the aperture formed by the air vent  100 A changes at a linear rate when moving from left to right, and thus, the change in the radius can be expressed as a linear function. 
       FIG.  1 B  illustrates a front view and a cross sectional view of an air vent  100 B formed in the panel  120  of a chassis. The panel  120  has a thickness where the air vent  100 B defines an aperture through the panel  120 . In this example, the air vent  100 B has a first opening  105 B and a second opening  110 B where the first opening  105 B has a larger radius and diameter than the second opening  110 B. Specifically, when moving from the first opening  105 B to the second opening  110 B, the radius of the air vent  100 B increases at a different rate. In this example, the radius increases at a slower rate nearer the first opening  105 B but at a faster rate nearer to the second opening  110 B. As such, the cross section of the air vent  100 B forms a horn, and as such, the air vent  100 B can be referred to as a horn air vent. 
     In  FIG.  1 B , the radius of the aperture formed by the air vent  100 B changes at a varying rate when moving from left to right, and in one embodiment, the change in the radius can be expressed as a parabolic function. 
       FIG.  1 C  illustrates a front view and a cross sectional view of an air vent  100 C formed in the panel  120  of a chassis. The panel  120  has a thickness where the air vent  100 C defines an aperture through the panel  120 . In this example, the air vent  100 C has a first opening  105 C and a second opening  110 C where the first opening  105 C has a larger radius and diameter than the second opening  110 C. Specifically, when moving from the first opening  105 C to the second opening  110 C, the radius of the air vent  100 C increases at a non-linear rate. In this example, the radius increases at a faster rate nearer the first opening  105 C but at a slower rate nearer to the second opening  110 C. As such, the cross section of the air vent  100 C forms a bell shape, and as such, the air vent  100 B can be referred to as a bell air vent. 
     In  FIG.  1 C , the radius of the aperture formed by the air vent  100 C changes at a varying rate when moving from left to right, and in one embodiment, the change in the radius can be expressed as a parabolic function. 
       FIG.  1 D  illustrates a front view and a cross sectional view of an air vent  100 D formed in the panel  120  of a chassis. The panel  120  has a thickness where the air vent  100 D defines an aperture through the panel  120 . In this example, the air vent  100 D has a first opening  105 D and a second opening  110 D where the first opening  105 D has a larger radius and diameter than the second opening  110 D. Specifically, when moving from the first opening  105 D to the second opening  110 D, the radius of the air vent  100 D increases at a linear rate. In this example, the radius remains constant (i.e., does not change) for a first distance through the panel  120 . However, the radius then increases until reaching the second opening  110 D. In this example, the radius increases in a linear fashion (e.g., at a constant rate) when approaching the second opening  110 D. However, in another embodiment, the radius may increase at a varying rate (e.g., like shown in  FIG.  1 B  or  FIG.  1 C ) when approaching the second opening  110 D. Thus,  FIG.  1 D  illustrates an air vent  100 D where the radius does not always increase when moving from the first opening  105 D to the second opening  110 D such that a portion of the aperture of the air vent  100 D has the same radius. 
       FIG.  1 E  illustrates a front view and a cross sectional view of an air vent  100 E formed in the panel  120  of a chassis. The panel  120  has a thickness where the air vent  100 E defines an aperture through the panel  120 . In this example, the air vent  100 E has a first opening  105 E and a second opening  110 E where the first opening  105 E has a larger radius and diameter than the second opening  110 E. Specifically, when moving from the first opening  105 E to the second opening  110 E, the radius decreases for a first distance through the panel  120  and then increases until reaching the second opening  110 E. The radius of the air vent  100 E can decrease and increase at a constant rate, or at a varying rate. 
     The first opening  105 E for the air vent  100 E may have a larger radius and diameter than the first openings  105 A-D for the air vents  100 A-D. In the air vents  100 A-D the first openings  105 A-D corresponded to the portion of the aperture formed by the air vents  100 A-D that had the smallest radius. In contrast, the portion of the aperture formed by the air vent  100 E with the smallest radius or diameter is in the interior of the panel  120 . In either case, the amount of EMI shielding provided by the air vents  100 A-E is determined by the portion of the aperture with the smallest radius. If the smallest portions of the apertures formed by the air vents  100 A-E have the same radius, then the EMI shielding provided by the air vents  100 A-E is substantially the same, regardless if the portions of the apertures with the smallest radius is at an opening as is the case for the air vents  100 A-D or in the interior of the panel  120  as is the case for the air vent  100 E. The radius r i  illustrates the portions of the air vents  100 A-E with the smallest radius while the radius r o  illustrates the portions of the air vents  100 A-E with the largest radius. 
     The concept of non-uniform vent openings as shown in the air vents  100 A-E can work for any geometrical function of the radius—i.e., the vent openings have improved EMI shielding relative to uniform openings. But for simplicity in manufacturing it may be desired to use a function in which the radius only increases (or decreases) from one panel to the other. 
     Further, the air vents  100 A-E in  FIGS.  1 A- 1 E  illustrates circular openings, but other shapes are also possible. For example, the openings could be rectangular, oval, triangular, pentagonal, hexagonal, or any polygon shapes. 
     In one embodiment, the thickness of the panel  120  (and the width of the air vents) is between 0.5 and 2.5 mm. In one embodiment, the thickness of the panel  120  (and the width of the air vents) is between 0.75 and 1.5 mm. 
     In one embodiment, the radius of the (small) first openings  105 A-E is between 0.5 to 3 mm. In another embodiment, the radius of the (small) first openings  105 A-E is between 0.1 to 2 mm. However, the radius of the first openings  105  can vary depending on the frequency of the signals being shielded or absorbed. If the air vents are to be used in a system with higher frequency EMI, then the smaller openings  105  may be smaller than air vents used in the presence of lower frequency EMI. 
     In one embodiment, the radius of the (large) second openings  110 A-E is between 0.5 to 3 mm. In another embodiment, the radius of the (small) first openings  105 A-E is between 0.1 to 2 mm. In one embodiment, the difference between the radiuses of the first and second openings is between 0.01 and 0.1 mm. In another embodiment, the difference between the radiuses of the first and second openings is between 0.04 and 0.08 mm. As one non-limiting example, the radius of the first opening  105  may be 1.61 mm while the radius of the second opening  110  is 1.67 mm for a radius difference of 0.06 mm between the two openings. 
       FIG.  1 F  illustrates a front view and a cross sectional view of an air vent  100 F formed in the panel  120  of a chassis. The panel  120  has a thickness where the air vent  100 F defines an aperture through the panel  120 . In this example, the air vent  100 F has a first opening  105 F and a second opening  110 F with the same radius and diameter. Specifically, when moving from the first opening  105 F to the second opening  110 F, the radius of the air vent  100 F is constant, thereby forming an aperture with a cylindrical shape. 
     As can be seen by comparing the air vent  100 F to the air vents  100 A-E, the air vents  100 A-E have second openings  110 A-E that have the same radius or diameter as the radius or diameter of the air vent  100 F. However, the air vents  100 A-E have portions with a much smaller radiuses than the radius of the air vent  100 F. As mentioned above, the amount of EMI shielding provided by the air vents  100 A-F is primarily determined by the smallest radius of the air vents  100 A-F. As such, the air vents  100 A-E provide greater EMI shielding than the air vent  100 F since their smaller radius will absorb higher frequency EM signals than the larger radius of the air vent  100 F. 
     Moreover, the cross sectional shapes of the air vents  100 A-E result in them having substantially equal air flow properties as the air vent  100 F. That is, despite the air vents  100 A-E having portions with a smaller radius, the cross sectional shape still permit substantially the same air flow, and thus, have the same cooling benefits as the air vent  100 F. Thus, the air vents  100 A-E have improved EMI shielding than air vent  100 F but still have similar air flow properties as the air vent  100 F. 
     In one embodiment, the air vents  100 A-E do not have any protrusions. That is, the air vents  100  are contained within the width of the panel  120  (e.g., a panel of a chassis). For example, a milling or laser cutting process can be used to form the air vents  100 A-E within the panel  120 . As shown, the first and second openings  105  and  110  of the air vents  100 A-E are co-planar with respective sides of the panel  120 . That is, the first openings  105 A-E are co-planar with a first side of the panel  120  while the second openings  110 A-E are co-planar with a second side of the panel  120  which is opposite the first side. As such, in the embodiments illustrated in  FIGS.  1 A- 1 E  the air vents  100  do have portions that protrude from the panel  120 . In one embodiment, the entirety of the air vent  100  is contained within the panel  120 . Thus, the air vents  100  can be formed by cutting apertures through a flat panel  120  without adding any conical or other shaped protrusions to the panel. 
     In one embodiment, the air vents  100 A-E can be covered with an EMI coating that can improve their EMI shielding properties. For example, the EMI coating can be deposited on both sides of the panel  120 . 
       FIG.  2    illustrates airflow through the air vent  100 C in  FIG.  1 C , according to one embodiment herein.  FIG.  2    illustrates that the air flow volume (AFV) into the air vent  100 C (i.e., AFV input ) and the AFV out of the air vent  100 C (i.e., AFV output ).  FIG.  2    illustrates that the AFV into the air vent  100 C is essentially the same as the AFV out of the air vent  100 C, indicating that the smaller radius of the first opening  105 C has little to no impact of the air flow through the air vent  100 C. That is, AFV input  is approximately the same as air flow volume output AFV output . 
     The principle illustrated in  FIG.  2    can also apply to the other air vents with non-uniform radiuses illustrated in  FIGS.  1 A- 1 E . 
       FIGS.  3 A- 3 C  illustrate chassis panels containing a plurality of air vents, according to embodiments herein.  FIG.  3 A  illustrates a front view and a cross sectional view of the panel  120  that contains a plurality of the air vents  100 C illustrated in  FIG.  1 C .  FIG.  3 B  illustrates a front view and a cross sectional view of the panel  120  that contains a plurality of the air vents  100 B illustrated in  FIG.  1 B .  FIG.  3 C  illustrates a front view and a cross sectional view of the panel  120  that contains a plurality of the air vents  100 A illustrated in  FIG.  1 A . The air vents  100  in  FIGS.  3 A- 3 C  create a web or webbing of air vents. 
     In  FIGS.  3 A- 3 C , the individual air vents  100  have second openings  110  that contact second openings  110  for neighboring air vents  100 . However, in other embodiments, there may be a small spacing between the second openings  110  of neighboring air vents  100 . For example, the spacing between the second openings  110  of neighboring air vents  100  may range from 0 to 5 mm. 
     Minimizing the spacing between the second openings  110  can increase the density of the air vents  100  in the panel  120  which may in turn improve air flow and cooling. However, the air vents  100  reduce the structural integrity of the panel  120 . Thus, the number of air vents  100  in the panel  120  can be a tradeoff with maintaining the strength of the panel  120 . 
     Further, increasing the radius or diameter of the largest opening in the air vents (the second openings  110 A-C in the examples illustrated in  FIGS.  3 A- 3 C ) means the radius or diameter of the smaller opening can be reduced without having a negative impact on the airflow or cooling properties. Thus, by increasing the diameter of the second openings  110 , the diameters of the first openings  105  can be reduced which, as discussed above, improves the EMI shielding of the air vents. 
     However, increasing the size of the second openings  110  reduces the density of the air vents  100 . Put differently, the number of air vents  100  that can be placed on the panel  120  is reduced as the diameter of the second openings  110  is increased. Thus, the size of the second openings  110  can be balanced between the desired density of the air vents on the panel  120  and the EMI shielding. For example, the designer may know the frequencies of the EMI that should be blocked or absorbed by the air vent and can set the size of the smaller opening to block those frequencies. The size of the larger opening can then be set according to the desired air flow through each air vent and the desired density of the air vents  100  on the panel  120 . 
       FIG.  4    is a computing system  400  with a chassis  405  (e.g., a container) having a body with at least one panel  120  with a plurality of air vents  100 , according to embodiments herein. For example, the air vents  100  can be any of the designs illustrated in  FIGS.  1 A- 1 E  above. Further, the openings of the air vents  100  can be circular, oval, triangular, rectangular, etc. 
     In this example, the chassis  405  contains fans  410  and an EM emitter  415 . The fans  410  may be arranged in the chassis  405  to cool the air in the chassis by pushing or pulling air through the air vents  100 . The chassis  405  can include any number of fans  410 . 
     The EM emitter  415  can include a computing system that emits undesirable EMI. For example, the computing system  400  may be disposed in a data center with other computing systems. To prevent the EMI generated by the EM emitter  415  from escaping, the chassis  405  can include the air vents  100  which are designed to absorb the EMI signals emitted by the EM emitter  415  to prevent them from affecting other computing devices in the same shared space. 
     In one embodiment, the EM emitter  415  is also the source of heat which heats the air in the chassis  405 . The fans  410  may be tasked with cooling the EM emitter  415 . In other embodiments, the chassis  405  may include other heat sources which are cooled by the fans  410  and the air flowing through the air vents  100 . 
     Additionally or alternatively, the computing system  400  can include EM sensitive computing components which can be negatively impacted by EMI that may enter into the chassis  405 . In that case, the air vents  100  can be designed to absorb the EM at the frequencies that affect the EM sensitive computing components. Thus, the air vents  100  can be used to prevent EMI from being emitted from the chassis  405  as well as prevent EMI from entering into the chassis  405 , while enabling the interior of the chassis  405  to be cooled. 
     Although the air vents  100  are disposed on one panel of the body of the chassis  405 , the air vents  100  can be disposed on any number of panels of the chassis body. The panels of the chassis  405  that do not have the air vents can be solid sheets (without holes) of conductive material (e.g., metal) to prevent EMI from leaving or entering the chassis  405 . 
     In some embodiments, the computing system  400  may be a server, server node, expansion box, or a networking device (e.g., router or switch). 
       FIGS.  5 A and  5 B  illustrate measurement and simulation data for air vents, according to embodiments herein.  FIG.  5 A  includes a chart  500  illustrating measurements captured by testing a uniform air vent (i.e., the cylindrical shaped air vent  100 F in  FIG.  1 F ) and a horn air vent (i.e., the air vent  100 B in  FIG.  1 B ). The radius of the uniform air vent used to capture the data illustrated in  FIGS.  5 A and  5 B  is 1.64 mm and the radius of the small opening of the horn air vent is 1.6 mm and the radius of the larger opening of the horn air vent is 1.67 mm. The thickness of the panel in which the uniform and horn air vents are formed is 1 mm. 
     The chart  500  in  FIG.  5 A  illustrates the shielding effectiveness (SE) of the uniform and horn air vents as measured in a testing environment. Specifically, chart  500  illustrates the delta or difference between the SE of the uniform air vent and the SE of the horn air vent. This measured test data indicates the horn air vent has up to a 0.5 dB improvement in EMI shielding compared to the uniform air vent. 
     The chart  550  in  FIG.  5 B  illustrates the SE of the uniform and horn air vents as simulated in a simulator. Like the chart  500 , the chart  550  illustrates the delta between the SE of the uniform air vent and the SE of the horn air vent. This simulated data indicates the horn air vent can have over a 1 dB improvement at lower frequencies and has over an 0.5 dB improvement for all frequencies in the frequency range on the X-axis. Thus,  FIGS.  5 A and  5 B  illustrate that the horn air vent has improved EMI shielding relative to a similarly sized uniform air vent. 
       FIG.  6    illustrates pressure drop data for air vents, according to one embodiment herein.  FIG.  6    includes a chart  600  illustrating simulation data captured by simulating the air flow through a uniform air vent (i.e., the cylindrical shaped air vent  100 F in  FIG.  1 F ) and a horn air vent (i.e., the air vent  100 B in  FIG.  1 B ). The dimensions of the uniform air vent and horn air vent used to capture the simulated data illustrated in  FIGS.  6  and  7    are the same as used to capture the data shown in  FIGS.  5 A and  5 B . 
     As shown, the chart  600  illustrates that the pressure (Y-axis) across the uniform and horn air vents for different air velocities (X-axis) is essentially unchanged, especially at lower air velocities. For example, below 5 m/s, the pressure across the two types of air vents is approximately the same while there is some difference in the pressure at velocities above 5 m/s. 
       FIG.  7    illustrates pressure drop data for air vents, according to one embodiment herein. The chart  700  illustrates the delta or difference between the air pressure across the uniform air vent and the air pressure across the horn air vent. The chart  700  is based on the simulated data illustrated in the chart  600  in  FIG.  6   . 
     As shown, the difference in air pressure between the uniform and horn air vents is essentially zero for air flow velocities below 5 m/s. This means that the cooling characteristics of the air vents as it relates to air flow and pressure is essentially the same for the two types of air vents. However, as mentioned above in charts  500  and  550  in  FIGS.  5 A and  5 B , the horn air vent offers a 0.5-1 dB improvement in EMI shielding. Thus, using the horn air vent has a negligible or no adverse impact on cooling but offers an appreciable improvement for EMI shielding. A similar improvement is offered by the other air vents illustrated in  FIGS.  1 A- 1 E . 
     Further, while  FIGS.  5 - 7    illustrate that switching from the uniform air vent to a horn air vent can offer improved EMI shielding without sacrificing air flow, switching from the uniform air vent to the horn air vent can offer improved air flow without sacrificing EMI shielding. For example, when switching from the uniform air vent to the horn air vent, the radius of the smaller opening of the horn air vent may be set to be equal to the radius of the uniform air vent, thereby ensuring the EMI shielding of the two vents are approximately equal. But by switching to the horn shape, the airflow through the horn air vent is improved relative to the airflow of the uniform air vent due to the non-uniform radius of the horn air vent (e.g., the horn air vent can achieve greater pressure difference than the uniform air vent). 
     In the current disclosure, reference is made to various embodiments. However, the scope of the present disclosure is not limited to specific described embodiments. Instead, any combination of the described features and elements, whether related to different embodiments or not, is contemplated to implement and practice contemplated embodiments. Additionally, when elements of the embodiments are described in the form of “at least one of A and B,” or “at least one of A or B,” it will be understood that embodiments including element A exclusively, including element B exclusively, and including element A and B are each contemplated. Furthermore, although some embodiments disclosed herein may achieve advantages over other possible solutions or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the scope of the present disclosure. Thus, the aspects, features, embodiments and advantages disclosed herein are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s). Likewise, reference to “the invention” shall not be construed as a generalization of any inventive subject matter disclosed herein and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in a claim(s). 
     In view of the foregoing, the scope of the present disclosure is determined by the claims that follow.