Abstract:
Water resistant acoustic ports and electronic hearing protection devices incorporating such ports are described. More specifically, water proof acoustic ports that provide water protection for an internal sealed chamber by providing acoustically transparent inlets that are capable of withstanding external water pressure at given depth due to their volume relation to that of the internal chamber, as well as hearing protection devices incorporating such ports, are described.

Description:
FIELD 
       [0001]    The present description relates to ports used in hearing devices, and more specifically, water resistant acoustically transparent ports in ear-mounted hearing devices. 
       BACKGROUND 
       [0002]    The use of hearing protective and noise attenuating devices are well known, and various types of devices have been considered. Such devices include earplugs and semi-aural devices that may be inserted into, or placed over, the ear canal of a user to obstruct passage of sound waves to the inner ear. Certain hearing devices may contain microphones for sensing sounds from the external environment and re-transmitting to the user&#39;s ear using a speaker in the protective device. A challenge with such a system is how to properly receive all sound from the external environment while protecting the microphone and its surroundings from water intrusion. 
       SUMMARY 
       [0003]    In one aspect, the present description relates to a water resistant acoustic port. The water resistant acoustic port includes a housing, a sealed chamber within the housing, an inlet microtube positioned in the wall of the housing and a hydrophobic coating that covers at least a portion of the walls of the inlet microtube. The chamber has a volume, V C . The inlet microtube fluidically connects the chamber to an environment external to the housing and has an inlet microtube volume, V I . The inlet microtube volume is sized to be greater than or equal to the combined volume of V C  and V I  multiplied by the quantity (1−(External pressure in air/External pressure when submerged)). In some embodiments, the weatherproof acoustic port may further include at least a second inlet microtube positioned in the wall of the housing. The second inlet microtube may, as with the first inlet microtube, also be fluidically connect the chamber to the environment external to the housing and also be covered with a hydrophobic coating. The volume of the second inlet microtube is also a portion of the inlet microtube volume. 
         [0004]    In another aspect, the present description relates to a weatherproof acoustic port that includes a housing, a sealed chamber within the housing, an inlet microtube positioned in the wall of the housing and a semi-permeable diverter positioned on the surface of the housing over the inlet microtube. The inlet microtube fluidically connects the chamber to an environment external to the house and has an inlet microtube volume and is capable of resisting water intrusion from ambient water at a submersion of at least one meter. The semi-permeable diverter further protects the inlet microtube from water intrusion due to an impulse event. In some embodiments, the inlet microtube is one of a plurality of inlet microtubes and the diverter is positioned over all of the inlet microtubes. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a cross-sectional view of an acoustic port according to the present description. 
           [0006]      FIG. 2  is a cross-sectional view of an acoustic port according to the present description. 
           [0007]      FIG. 3  is a cross-sectional view of an electronic hearing protection device according to the present description. 
           [0008]      FIG. 4  is a cross-sectional view of an electronic hearing protection device according to the present description. 
       
    
    
       [0009]    The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number. 
       DETAILED DESCRIPTION 
       [0010]    In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which illustrate specific embodiments in which the invention may be practiced. The illustrated embodiments are not intended to be exhaustive of all embodiments according to the invention. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. 
         [0011]    Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. 
         [0012]    As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” encompass embodiments having plural referents, unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
         [0013]    Spatially related terms, including but not limited to, “proximate,” “distal,” “lower,” “upper,” “beneath,” “below,” “above,” and “on top,” if used herein, are utilized for ease of description to describe spatial relationships of an element(s) to another. Such spatially related terms encompass different orientations of the device in use or operation in addition to the particular orientations depicted in the figures and described herein. For example, if an object depicted in the figures is turned over or flipped over, portions previously described as below or beneath other elements would then be above those other elements. 
         [0014]    As used herein, when an element, component or layer for example is described as forming a “coincident interface” with, or being “on,” “connected to,” “coupled with,” “stacked on” or “in contact with” another element, component or layer, it can be directly on, directly connected to, directly coupled with, directly stacked on, in direct contact with, or intervening elements, components or layers may be on, connected, coupled or in contact with the particular element, component or layer, for example. When an element, component or layer for example is referred to as being “directly on,” “directly connected to,” “directly coupled with,” or “directly in contact with” another element, there are no intervening elements, components or layers for example. 
         [0015]      FIG. 1  illustrates a cross-sectional view of a water resistant acoustic port  100  according to the present description. Water resistant acoustic port  100  includes a housing  102 , and a sealed chamber  104  that is located within the housing. Housing  102  may be made up of any number of appropriate materials that allow the housing to be molded into an appropriate shape and enable a potentially hollow chamber within, for example plastic materials, such as ABS or polypropylene, amongst others. The housing may be made up of thermoform or thermoset polymers. Additionally, housing  102  could be formed of composites, alloys, or other materials. In some embodiments, the housing may be constructed from multiple different materials, such that, e.g., the material surrounding the inlet microtubes is different from that in the remainder of the housing. Chamber  104  will be understood to have a given volume, V C . In some embodiments, the volume of chamber may be between about 5 mm 3  and about 10 mm 3 , though smaller or larger volumes may be appropriate. Water resistant acoustic port further includes an inlet microtube  106  that is positioned in the wall  108  of the housing. Inlet microtube  106  fluidically connects the chamber  104  to an environment  110  that is external to the housing. For purposes of this description, a “sealed chamber” means that the chamber is entirely sealed with the exception of the inlet microtubes that connect it to the external environment. As the acoustic port will generally be part of a wearable electronic hearing protection device, the external environment will be that in which the user is surrounded. Accordingly, at times, the external environment may be air. At other times, the external environment may be water, e.g., when the user wearing the hearing protection device happens to be submerged. Inlet microtube also has a given volume V I . In one embodiment, the inlet microtube volume, V I , is greater than 10% of the chamber volume, V C . Generally, the inlet microtube volume will be between about 0.5 mm 3  and about 1.0 mm 3 , though again, V I  can be larger or smaller in certain embodiments. 
         [0016]    Additionally, a hydrophobic coating  112  can cover at least a portion of the walls of the inlet microtube  106 . This hydrophobic coating  112  may, in some embodiments, be a 3M Novec™ Coating, such as 3M Novec™ 1720 (from 3M Company, St. Paul, Minn.), though other low surface energy coatings may also be appropriate. The hydrophobic coating works to prevent capillary action in the inlet microtube from water external to or partially filling the inlet microtube. Capillary action occurs when the adhesive forces between water and a tube wall exceed the cohesive forces between the water and the molecules themselves. The greater the affinity water has for a material, the greater the distance water will travel into a tube. The height to which the water will rise and fall in a capillary tube is given by Jurin&#39;s Law. The height, h, of a liquid column is given by Equation 1: 
         [0000]    
       
         
           
             
               
                 
                   h 
                   = 
                   
                     
                       2 
                        
                       
                           
                       
                        
                       γ 
                        
                       
                           
                       
                        
                       cos 
                        
                       
                           
                       
                        
                       θ 
                     
                     
                       ρ 
                        
                       
                           
                       
                        
                       g 
                        
                       
                           
                       
                        
                       r 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   1 
                 
               
             
           
         
       
     
         [0017]    where γ is the liquid surface tension, θ is the contact angle of the liquid on the tube wall, ρ is the density of the liquid, g is local acceleration due to gravity, and r is the radius of the tube. 
         [0018]    The cos(θ) term can take on any value between −1 and +1, and therefore dramatically impacts the extent to which water will migrate into the tube. Material with an angle of θ&gt;90 degrees is considered hydrophobic. When the contact angle exceeds 150 degrees, the material is considered superhydrophobic. The plastic material used in some embodiments of the acoustic port housing has a contact angle with water of less than 90 degrees. This may enable capillary action which can act to either pre-fill the inlet microtube or microtubes with some water, in which case a subsequent immersion of the acoustic port into water could cause flooding of the chamber, or a “bridging over” of the inlet microtubes. It has been founded that treating the inlet microtubes with a hydrophobic coating ensures that the contact angle rises above 100 degrees, and avoids these issues with capillary action. 
         [0019]    The combination of the inlet microtube volumes noted along with the use of a hydrophobic coating allows the acoustic port to be essentially waterproof up to certain depths. In at least some embodiments described herein, the inlet microtube or inlet microtubes in the case of a plurality of inlet microtubes (as discussed below) are capable of withstanding water intrusion into the cavity at a submersion depth of 1 m. One of skill in the art will understand that this means that the water resistant acoustic port is capable of meeting IP-67 standards. Despite its ability to prohibit water intrusion, the water resistant acoustic port of the present description is sound transparent, i.e., compression waves of air are capable of traveling substantially unrestricted through the port. 
         [0020]    The ability to waterproof the acoustic port is due, in part, to the creation of a pressure differential between the chamber and external environment which aids in prohibiting water intrusion from the external environment into the chamber.  FIG. 2  illustrates a cross-sectional view of a water resistant acoustic port according to the present description in an external environment  110  of water. As water moves down inlet microtube  106 , it displaces air in the inlet V DIS , which results in compression of the air in the chamber volume, V C . This compression raises the air pressure P INT  of the internal volume. The system will reach equilibrium once the external water pressure P EXT  (determined by submersion depth) is balanced by the internal air pressure. As long as the increase in water pressure does not force water past the entirety of the inlet microtube and into the chamber, water present in the inlet microtube will be expelled when the acoustic port returns to an external environment of air. We can refer to total internal volume of the device as V, made up of volume of the inlet (V I ) and volume of the chamber (V C ) (V=V I +V C ). If we define further that the external pressure above water is P a  and the external pressure submerged is P s , and further that the total volume V of air above water is understood as V a  and submerged is V s , the ideal gas law tells us the following (assuming a temperature being held constant): 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       P 
                       s 
                     
                     
                       P 
                       a 
                     
                   
                   = 
                   
                     
                       V 
                       a 
                     
                     
                       V 
                       s 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   2 
                 
               
             
           
         
       
     
         [0000]    In order to keep water from entering the chamber, the overall reduction in volume (V a −V s ), must be less than the inlet microtube volume V I . Therefore, to ensure that water does not enter the chamber: 
         [0000]        V   I   ≧V   a   −V   s   Equation 3:
 
         [0000]    Solving Equation 1 for V s  yields Equation 4: 
         [0000]    
       
         
           
             
               
                 
                   
                     V 
                     s 
                   
                   = 
                   
                     
                       
                         P 
                         a 
                       
                       
                         P 
                         s 
                       
                     
                     * 
                     
                       
                         V 
                         a 
                       
                       1 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   4 
                 
               
             
           
         
       
     
         [0000]    Substituting the value of V s  from Equation 3 into Equation 2 yields the following: 
         [0000]    
       
         
           
             
               
                 
                   
                     V 
                     I 
                   
                   ≥ 
                   
                     
                       V 
                       a 
                     
                     * 
                     
                       ( 
                       
                         1 
                         - 
                         
                           
                             P 
                             a 
                           
                           
                             P 
                             s 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   5 
                 
               
             
           
         
       
     
         [0000]    Therefore, the aggregate volume of the inlet microtube or microtubes, V I , must be greater than or equal to the volume of the inlet and chamber at above water conditions multiplied by the quantity of (1−the external pressure in air over the external pressure when submerged). Satisfying this condition will result in water not traversing the entirety of the inlet microtube(s), and thus not entering the sealed chamber. In other words, the acoustic port is essentially “waterproof.” The volume of the inlet microtube or microtubes in the present invention is chosen according to the relationship in Equation 5. 
         [0021]    A different embodiment of an acoustic port as well as device in which it may be implemented, is provided in  FIG. 3 . Electronic hearing protection device  200  includes acoustic port  201 . In this embodiment, weatherproof acoustic port includes a first inlet tube  206   a  as well as a second inlet microtube  206   b,  each of which is positioned in the wall  208  of housing  202 . In some embodiments, as illustrated, the acoustic port may include a third inlet microtube  206   c,  or any other appropriate number of inlet microtubes, such as 4, 5, 6, 7, 8, 9, 10 or potentially more. The second inlet microtube fluidically connects the sealed chamber  204  to the environment that is external to the housing. As with the embodiment in  FIG. 1 , the second inlet microtube, like the first inlet microtube is covered with a hydrophobic coating  212 . In this embodiment, where more than one inlet microtube is present, the total volume of each microtube is added to provide the total V I . In other words, the inlet microtube volume, V I  is the sum of the volumes of inlets  206   a,    206   b  and  206   c.  The length, L of the inlet microtubes will generally be substantially similar. In one embodiment, the first inlet and second inlet microtubes (as well as the third inlet microtube) will have a length of between about 0.9 and 1.25 mm. It is desirable that the inlet microtube or microtubes not be excessively long. This may result in resonance in the tubes, as well as excessive acoustic impedance. Both of the issues will impact the fidelity of the sound field in the chamber, which, as discussed in  FIG. 3 , may be captured by a microphone. 
         [0022]      FIG. 3  provides further potential detail of acoustic port  201 . Sealed chamber  204  is surrounded in part by housing  202  and inlet microtubes  206   a,    206   b  and  206   c.  However, the chamber may further be surrounded by additional elements, for example, a printed circuit board  214  as illustrated in  FIG. 3 . Additionally, the chamber  204  may be in part surrounded by a seal  216  that separates the housing  202  and circuit board  214 . Circuit board  214  may be an electronic printed circuit board assembly (PCBA). In one embodiment, the seal  216  may be an O-ring. Other appropriate seals, such as other gasket materials, may also be utilized. Additionally, the chamber may, in part, be surrounded by a microphone  218  that is positioned beneath, and connected to, circuit board  214 . The microphone may in one embodiment, be a MEMS type microphone and may be connected to the circuit board by soldering the bottom side of it to the microphone. This microphone may be used to gather the sound that enters acoustic port  201 . The sound may then be re-transmitted by a speaker out a separate sound-emitting opening (not shown) that is positioned within the ear canal of a user. 
         [0023]      FIG. 4  offers further illustration of certain embodiments of the invention. Here, acoustic port again includes a first inlet microtube  406   a,  and may further include a second inlet microtube  406   b  and potentially third inlet microtube  406   c,  as well as potential further inlet microtubes. In this embodiment, the inlet microtube may not have a hydrophobic coating on the walls of the inlet microtubes. As before, inlet microtube or tubes separate the chamber  404  from the external environment  410 . However, in this embodiment, the water resistant acoustic further includes a semi-permeable diverter  420  that is positioned on the surface of the housing  402  over the inlet microtube  406   a,  or tubes  406   a,    406   b,    406   c  such that the semi-permeable diverter  420  eliminate line of sight path to the inlet microtube. The diverter includes small openings  422  that are positioned on sides of the diverter. As such water simply impacting the top of the port will be unable to travel unimpeded into the acoustic port with force. The diverter will likely only be subject to permeation when the acoustic port is submerged. This semi-permeable diverter offers the further protection of protecting the sealed chamber from water intrusion due, not to submersion, but to an impulse event, such as contact with water at a high velocity. Such an impulse event may create peak forces greater than that of water, e.g., at a depth of 1 m, and may flood the inlet microtubes reaching the chamber absent the diverter&#39;s presence.