Patent Publication Number: US-2023146074-A1

Title: Mems microphone with ingress protection

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a non-provisional application claiming priority from U.S. Provisional Application Ser. No. 62/982,429, filed Feb. 27, 2020 entitled “MEMS Microphone with Ingress Protection” and incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     The present description relates generally to micro-electro-mechanical systems (MEMS) microphones and more particularly to a MEMS microphone assembly with ingress protection. 
     BACKGROUND OF RELATED ART 
     In general, the application of MEMS technology to microphones has led to the development of small microphones with very high performance. For example, MEMS microphones typically offer high signal to noise ratio (SNR), relatively low power consumption, and good sensitivity. A typical MEMS microphone, however, has a frequency response which is not compliant with IEC61672 Class 2 limits. 
     Accordingly, there remains a strong desire for improved MEMS microphones, and more particularly for a more simplified and easily assembled, MEMS microphone complete with ingress protection that achieves class 2 response by adding different components around the MEMS microphone to form a special construction as disclosed herein. 
     SUMMARY 
     In one embodiment, A microphone assembly comprises a microphone housing defining an acoustic cavity and comprising a sound inlet for transmitting a sound into the acoustic cavity. A micro-electro-mechanical (MEMS) microphone is operatively mounted at least partially within the microphone housing and comprising an aperture acoustically coupled with the acoustic cavity for receiving the sound. A MEMS microphone support is adjustably coupled to the microphone housing for supporting the MEMS microphone within the microphone housing, the MEMS microphone support being movable relative to the acoustic cavity to vary the acoustic characteristics of the microphone assembly. An acoustic vent is located between the acoustic cavity and the aperture to substantially allow the sound to pass through the acoustic vent while substantially preventing a foreign contaminant from entering the aperture. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a side elevational view of an example MEMS microphone with ingress protection in accordance with an example of the teachings of the present disclosure. 
         FIG.  2    is an exploded perspective view of the example MEMS microphone of  FIG.  1   . 
         FIG.  3    is a top plan view of the example MEMS microphone of  FIG.  1   . 
         FIG.  4    is a cross section view of the example MEMS microphone taken along line  4 - 4  of  FIG.  1   . 
         FIG.  5    is a graphical plot of a typical prior art MEMS microphone response. 
         FIG.  6    is a graphical plot of the free field response of the example MEMS microphone of  FIG.  1   . 
         FIG.  7    is an exploded perspective view of another example MEMS microphone with ingress protection. 
         FIG.  8    is a top plan view of the example microphone of  FIG.  7   . 
         FIG.  9    is a side elevational view of the example microphone of  FIG.  7   . 
         FIG.  10    is a cross section view of the example MEMS microphone of  FIG.  7   , taken along line  10 - 10  of  FIG.  9   . 
     
    
    
     DETAILED DESCRIPTION 
     The following description of example methods and apparatus is not intended to limit the scope of the description to the precise form or forms detailed herein. Instead the following description is intended to be illustrative so that others may follow its teachings. 
     Currently known and typical MEMS microphones have a frequency response which is not compliant with IEC 61672 Class 2 limits. In order to achieve Class 2 response from a known commercial MEMS microphone, its frequency response has to be altered. This is achieved by adding different components around the microphone to form a special construction, such as disclosed herein. 
     Referring now to  FIGS.  1 - 4   , an example MEMS microphone assembly  10  is illustrated. The example MEMS microphone assembly  10  generally comprises a stack built into a 0.5 inch microphone, although it will be appreciated by one of ordinary skill in the art that the size of the example MEMS microphone assembly  10  may vary as desired. As best illustrated in  FIGS.  2  and  4   , the example MEMS microphone assembly  10  includes a microphone printed circuit board (PCB)  12  defining an aperture  13  and a MEMS microphone  15  as is known in the art to for detecting sound. The aperture  13  may be any suitable wave guide such as an acoustic wave guide. It will be understood that the MEMS microphone  15  may be top-ported (i.e., the hole is in a top cover) or bottom-ported (i.e., the hole is in the microphone PCB) as desired. In the illustrated example, the microphone PCB  12  is a 0.5 mm microphone PCB, although any suitable PCB and/or MEMS microphone may be utilized. The microphone PCB  12  is supported by a PCB support  14 , which in turn is housed within a microphone housing  16 . The space defined between the microphone housing  16  and the microphone PCB  12  is an acoustic cavity having acoustic characteristics that may be varied by any suitable means including varying the size of the acoustic cavity and/or the materials defining the acoustic cavity. 
     In this example, the PCB support  14  and the microphone housing  16  are generally cylindrical and coaxial aligned along their respective longitudinal axis when the PCB support  14  is inserted within the microphone housing  16 . A lock ring  20  and a support spacer  22  are provided within the microphone housing  16  to secure the PCB support  14  within the microphone housing  16 . As will be understood, the lock ring  20  may be fitted or otherwise secured within the microphone housing  16  by threads, friction fitting, etc. 
     While the microphone PCB  12  is mounted to and supported by the PCB support  14 , an acoustic vent  24  is positioned over the aperture  13  in the microphone PCB  12  and sealingly mounted thereto. In the illustrated example, the acoustic vent  24  is a GORE® Portable Electronic Vent for Acoustic and Immersion applications available from W. L. Gore &amp; Associates, Inc, Elkton, Md., USA, model GAW334. The provided acoustic vent comprises an expanded polytetrafluoroethylene (ePTFE) material that allows for the transmission of air and sound, while effectively repelling water, other fluids and particulates, thus substantially preventing and/or minimizing ingress of any foreign contaminant into the aperture  13 . It will be understood by one of ordinary skill in the art that while a specific acoustic vent is identified, other suitable acoustic vents may be utilized as desired. 
     As further illustrated, a porous material, such as a foam disk  26 , which, in this example optionally defines another aperture  27 , is provided over the microphone PCB  12  and the acoustic vent  24 . Finally, the assembly is enclosed by a microphone front grill  28  having yet another aperture  29  (e.g., a sound inlet), and being mounted to the microphone housing  16 , such as by a screw thread, friction fit or other suitable closure. In this example, a ring  30  surrounding an upper portion of the microphone housing  16  and contacts an inner surface of the microphone front grill  28  to provide a spacing. In some examples, the microphone front grill  28  may be slidably coupled to the microphone housing  16  such that the space defined between the microphone front grill  28  and the foam disk  26  may be varied, hence the defined cavity may be a bespoke design. The PCB support  14  may, therefore, support the microphone PCB  12  proximate the microphone front grill  28  such that the aperture  29 , acoustic cavity, and aperture  13  are acoustically coupled. In addition, as illustrated, the position of the lock ring  20  within the microphone housing  16  may allow for the formation of an upper air gap  37   a  and a lower air gap  37   b.  If the lock ring  20  is screwed in (direction arrow I), the lower air gap  37   b  will close up and the MEMS microphone  15  will move closer to the microphone front grill  28 . If, however, the lock ring is un-screwed (direction arrow O), the upper air gap  37   a  will close up and the MEMS microphone  15  will move further away from the microphone front grill  28 . Accordingly, the MEMS microphone assembly  10  may be tunable as desired. 
     The MEMS microphone assembly  10  may also be tuned by selection of various microphone PCBs with a sufficient dynamic range. The acoustically transparent, acoustic vent  24 , meanwhile, provides for ingress protection. The designed simple stack of different materials achieves acoustically tuned, sealed, resonance cavity, overcoming problems with repeatability and also resulting in ease of assembly. For instance, the construction of tuning cavities around the microphone PCB  12  is very simple when compared to known prior art assemblies. By utilizing layers of some soft materials and precisely designed hard layers in a unique way, the MEMS microphone assembly  10  achieves the target Class 1&amp;2 response. Further, the present design provides a unique way of adjusting the microphone height to aid tuning of the resonant cavity. 
       FIG.  5    illustrates a microphone response of a typical prior art MEMS microphone assembly. More precisely, the plot illustrates a normalized frequency response by plotting a sensitivity against a frequency.  FIG.  6   , meanwhile illustrates a plot of a measured response of the example MEMS microphone assembly  10 , as compared to Class  2  limits. 
     Referring now to  FIGS.  6 - 9   , there is illustrated another example MEMS microphone assembly  100 . The example MEMS microphone assembly  100  is constructed in a similar fashion as the example MEMS microphone assembly  10 . In this instance, the MEMS microphone assembly  100  comprises a MEMS microphone PCB S/A  110  (Printed Circuit Board Sub-Assembly) comprising a microphone PCB  111  defining an aperture  113  located adjacent a microphone  115 . As with the previous example, it will be understood that any suitable MEMS microphone (e.g., microphone PCB  111 , aperture  113 , and/or microphone  115 ) may be utilized as desired. 
     In this example, the MEMS microphone PCB S/A  110  is supported by a PCB support  114 , which in this instance is generally shaped as a hollow cylinder. The PCB support  114  is, in turn, located within a microphone housing  116 . In this example, the microphone housing  116  is generally shaped as an elongated hollow cylinder that is configured to fit over an outer surface of the PCB support  114 . More precisely, the microphone housing  116  comprises an open end sized, configured, and arranged to accept insertion of the PCB support  114 , and a closed end  116   a  defining an aperture  117 . The aperture  117  may be any suitable size and configured to allow passage of sound therethrough. In the illustrated example, the aperture  117  is acoustically coupled to the aperture  113 . The microphone PCB  111  and/or microphone  115  may be at least partially or completely mounted within the microphone housing  116 . 
     As will be appreciated, the aperture  117  may also allow ingress of various foreign contaminants, such as for instance, fluid, debris, or other similar containment. To assist in the substantial prevention of any ingress of a foreign contaminant, a first acoustic vent  124  is provided adjacent the aperture  117 . As previously noted, the first acoustic vent  124  may be any suitable acoustic vent material and in this example, the first acoustic vent  124  is a GORE® Portable Electronic Vent for Acoustic and Immersion applications available from W. L. Gore &amp; Associates, Inc, Elkton, Md., USA, model GAW112. The first acoustic vent  124  is supported by a porous material  126 , such as an acoustic tuning material, for instance a foam disk. When assembled (see  FIG.  10   ), the first acoustic vent  124  is located between the microphone housing  116  and the porous material  126 . In this example, the first acoustic vent  124  is adhered to the closed end  116   a  (e.g. sealingly mounted) and it will be understood that any suitable method of locating the vent may be utilized, including for instance pressing the first acoustic vent  124  against the closed end  116   a  by the porous material  126 . 
     The porous material  126 , meanwhile, is similarly supported by the PCB support  114  and is separated from the MEMS microphone PCB S/A  110  by a distance. A gasket seal  118  is located between the MEMS microphone PCB S/A  110  and the microphone housing  116 . In this example, the gasket seal  118  is an “O-ring” shaped resilient gasket. As best seen in  FIG.  10   , the MEMS microphone PCB S/A  110  may also comprise a second acoustic vent  125  located adjacent and sealingly mounted to the aperture  113  and further assisting in substantially preventing any foreign containments from entering the aperture  113 . In the illustrated example, the second acoustic vent  125  is a GORE® Portable Electronic Vent for Acoustic and Immersion applications available from W. L. Gore &amp; Associates, Inc, Elkton, Md., USA, model GAW334. It will be understood that in other embodiments, the first acoustic vent  124  or the second acoustic vent  125  may be omitted as desired. Moreover, it will be further understood that while the example acoustic vents are disclosed as being specific models from a specific manufacture, one of ordinary skill in the art will appreciate that any suitable manufacturer or model may be utilized as desired. 
     The PCB support  114  and all supported components may be secured within the microphone housing  116  by a lock ring  120 . In this example, the lock ring  120  is sized and arranged to be inserted into the microphone housing  116  and provide a securable fit between the lock ring  120  and the microphone housing  116  to securely retain the components within the microphone housing  116 . For instance, the lock ring  120  may include a screw thread for coupling with an inner surface of the microphone housing  116 . Other suitable methods of mounting the lock ring  120  may be employed as desired. As with the example of  FIGS.  1 - 5   , the selection of materials and the adjustability of the securing location of the MEMS microphone PCB S/A  110  within the housing allows for tuning of the MEMS microphone assembly  100  and the achievement of various desired acoustical characteristics, including IEC 61672 Class 2 compliance. 
     Although certain example methods and apparatus have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus, and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.