Patent Publication Number: US-11653143-B2

Title: Helmholtz-resonator for microphone assembly

Description:
RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 62/954,918 filed on Dec. 30, 2019, entitled “Helmholtz-Resonator for Microphone Assembly,” the entire contents of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to microphone assemblies and more particularly to microphones with Helmholtz-resonators and other structures for modifying sound input to the microphone assembly. 
     BACKGROUND 
     Microphones are used in various devices including hearing aids, mobile phones, smart speakers, personal computers among other devices and equipment. A microphone generally includes a transducer, and in some devices, an integrated circuit disposed in a housing formed by a can or cover mounted on a base. A sound port typically extends through the base (for a bottom port device) or through the top of the housing (for a top port device). In any case, sound traverses through the sound port and is converted into an electrical signal by the transducer. 
     For certain applications, the microphone is exposed to ultrasonic frequencies emitted by motion sensors, proximity detectors and other sources. These ultrasonic devices can interfere with the resonance response of the microphone and induce audible artifacts in its output. Thus, users can benefit from improved microphone designs that reduce the adverse effects associated with ultrasonic or other signals otherwise detectable by known microphone assemblies. 
     The various aspects, features and advantages of the present disclosure will become more fully apparent to those having ordinary skill in the art upon consideration of the following Detailed Description and the accompanying drawings described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure is described in more detail below in connection with the appended drawings and in which like reference numerals represent like components: 
         FIG.  1    is a cutaway view of a microphone assembly with a Helmholtz-resonator formed in a base of the microphone assembly; 
         FIG.  2    is a transparent view of the base of the microphone assembly of  FIG.  1   ; 
         FIG.  3    is a transparent view of another configuration of the base of the microphone assembly of  FIG.  1   ; 
         FIG.  4    is a transparent view of yet another configuration of the base of the microphone assembly of  FIG.  1   ; 
         FIG.  5    is a bottom view of a sound port adapter with a Helmholtz-resonator in a first configuration; 
         FIG.  6    is a transparent view of the sound port adapter of  FIG.  5    coupled to a microphone assembly; 
         FIG.  7    is a bottom view of a sound port adapter with a Helmholtz-resonator in a second configuration; 
         FIG.  8    is a transparent view of the sound port adapter of  FIG.  7    coupled to a microphone assembly; 
         FIG.  9    is a bottom view of a sound port adapter with a Helmholtz-resonator in a third configuration; 
         FIG.  10    is a transparent view of the sound port adapter of  FIG.  9    coupled to a microphone assembly; 
         FIG.  11    is a cross-sectional view of another embodiment of the microphone assembly of  FIG.  1   ; and 
         FIG.  12    is a transparent view of the base of the microphone assembly of  FIG.  11   . 
     
    
    
     DETAILED DESCRIPTION 
     According to one aspect of the disclosure, a sensor assembly comprises a housing having an external-device interface and a sound port to an interior of the housing. A transducer is disposed within the housing and acoustically coupled to the sound port. An electrical circuit is also disposed within the housing and electrically coupled to the transducer and to the electrical contacts on the external-device interface. A cavity is formed in a portion of the sensor assembly and acoustically coupled to the interior of the housing via the sound port. The cavity has a wall portion structured to modify an acoustic property of the sensor assembly, such as any one or more of an inertance, resistance, compliance, or resonance. In one example, the sensor assembly is a microphone. In other examples, the sensor assembly includes other sensor types such as a pressure sensor, an accelerometer, a gas sensor, a mass flow sensor, etc. 
     In various embodiments, the cavity and wall portion form a Helmholtz-resonator that modifies any one or more of a frequency of resonance or an amplitude of resonance of the sound propagating through the sound port. The Helmholtz-resonator is configured with a neck connected to one or more chambers, where the sound port is acoustically coupled to the one or more chambers via the neck. 
     In some embodiments, the cavity and wall portion forming the Helmholtz-resonator are disposed in a base of the sensor assembly. The base is part of the housing and includes the external-device interface and the sound port. In one implementation, the neck and the one or more chambers are formed in or on a same layer of the base. In another implementation, the neck and the one or more chambers are formed in or on different layers of the base, with the neck being formed in or on a first layer and the one or more chambers being formed in or on a second different layer. Other suitable neck and chamber implementations may be contemplated in other embodiments. 
     In certain embodiments, the cavity and wall portion forming the Helmholtz-resonator are disposed in a sound port adapter that can be fitted to the sensor assembly. The sound port adapter includes an acoustic channel acoustically coupled to the cavity. The sound port adapter includes a sound outlet and a sound inlet disposed on a mounting surface. The sound outlet is acoustically coupled to the sound port when the mounting surface is coupled to a surface (e.g., base) of the sensor assembly. 
     According to another aspect of the disclosure, a sound port adapter for a microphone assembly comprises a body member having a mounting surface and an acoustic channel disposed through the body member. The acoustic channel includes a sound inlet and a sound outlet. The body member is configured to mount on a surface (e.g., top or bottom surface) of the microphone assembly on which a sound port is disposed. A Helmholtz-resonator comprising a neck and one or more chambers is disposed in the body member. The acoustic channel is acoustically coupled to the one or more chambers by the neck. 
     In some embodiments, the body member includes a wall portion configured to form a non-straight acoustic path in the acoustic channel to modify any one or more of an inertance or resistance of the acoustic channel. In other embodiments, the body member includes a wall portion configured to obstruct the entry of debris into the acoustic channel for ingress protection. 
     In various applications, a sound attenuation device, such as a Helmholtz-resonator, can be employed to reduce or dampen the acoustic signal at specific frequencies (e.g., high frequencies) at the input of the microphone or other sensor.  FIGS.  1 - 10    show different configurations of a Helmholtz-resonator for such a sensor assembly. In  FIGS.  1 - 4   , the Helmholtz-resonator is constructed in a base of the microphone assembly. In  FIGS.  5 - 10   , the Helmholtz-resonator is constructed in a sound port adapter that can be fitted to a sound port of the microphone assembly. If desired, the sound port adapter can be configured for other acoustic tuning (e.g., inertance, resistance, compliance) and/or for ingress protection (e.g., prevent debris from entering the sound port). 
     A sensor assembly generally includes various components enclosed in a housing.  FIG.  1    shows a cutaway view of a microphone assembly  100 . The microphone assembly includes a transducer  102  and an electrical circuit  104  (e.g., an integrated circuit) disposed in a housing  105  having a lid or cover  106  mounted on a base  108  having a sound port  110 . The transducer, electrical circuit, and sound port are all disposed in an interior of the housing. The transducer is acoustically coupled to the sound port, while the electrical circuit is electrically coupled to the transducer and to electrical contacts  112  on an external-device interface (see  FIG.  2   ). In one implementation, the external-device interface is a surface-mount interface suitable for integrating the microphone assembly to a host device, for example by reflow or wave soldering or some other known or future surface-mount technology. While  FIG.  1    shows a microelectromechanical systems (MEMS) capacitive transducer with one or more diaphragms  103 , other types of transducers (e.g., capacitive, piezoelectric, optical, electro-acoustic, etc.) may be contemplated in other embodiments. Also, the transducer is not necessarily limited to an acoustic transducer. 
     The transducer is configured to convert sound into an electrical signal. Once converted, the electrical circuit conditions the electrical signal before providing the conditioned signal at the external-device interface. Such conditioning may include buffering, amplification, filtering, analog-to-digital (A/D) conversion for digital devices, and signal protocol formatting among other processing. The microphone assembly of  FIG.  1    shows a bottom port device having the transducer mounted on the base in acoustic communication with the sound port. In other embodiments, the microphone assembly may be a top port device having the transducer mounted over a sound port on the lid. 
     To modify an acoustic property of the microphone assembly, a tuning structure may be formed in a portion of the microphone assembly. In  FIGS.  1 - 2   , the tuning structure is a cavity  114  with a wall portion  116  formed in the base of the microphone assembly. The cavity is acoustically coupled to the interior of the housing via or by the sound port. The cavity is defined in part by sidewalls  118 ,  120 . The wall portion includes wall segments  122 ,  124  and defines an opening  126  connected to the sound port. The opening allows sound to enter the cavity and move to the sound port. The cavity and wall portion can be made by using laser drilling, manual drilling, or other suitable techniques. 
     As shown in  FIGS.  1 - 2   , the cavity and wall portion are structured to form a Helmholtz-resonator that operates to modify a frequency of resonance and/or an amplitude of resonance of the sound propagating through the sound port (e.g., dampen the resonance amplitude, shift the resonance frequency, etc.). The Helmholtz-resonator comprises a narrow opening or neck  130  connected to a chamber  131 . In this example, the chamber includes two chambers  132 ,  134 . The neck is formed between the wall segments, while each of the two chambers is formed between a respective wall segment and a sidewall. 
     The neck acoustically couples the sound port to the two chambers. As shown in  FIG.  2   , gaps  202 ,  204  exist between ends  206 ,  208  of the wall segments and a perimeter  210  of the cavity. Respective surfaces  212 ,  214  of the wall segments also interface with a surface  216  of the sound port. In this manner, incoming sound from the opening moves through the neck and enters the chambers via the gaps before traveling back through the neck and into the sound port. Although the chambers in  FIG.  2    are shown as two finger-shaped chambers with rounded tips, any number of other suitably shaped chambers may be contemplated. Indeed, it is the enclosed volume defined by the chambers that constitutes part of Helmholtz-resonator design. Thus, other suitable neck and chamber configurations for the Helmholtz-resonator may be considered in other embodiments. 
     While a microphone is shown in  FIGS.  1 - 2   , the Helmholtz-resonator can be applied to any type of sensor (e.g., pressure sensor, gas sensor, etc.). More generally, any device can be fitted with a Helmholtz-resonator for resonance tuning. If desired, additional structures can be added to achieve other acoustic tuning features such as inertance, resistance, and/or compliance tuning. 
     Different techniques can be employed to embed the Helmholtz-resonator in the base of the microphone assembly. The base may be comprised of various layers of material (e.g., FR-4, epoxy, plastic, ceramic, glass fiber, etc.). In  FIG.  2   , the neck and chambers of the Helmholtz-resonator are formed in or on a same layer of the base. In  FIG.  3   , the neck and chambers of the Helmholtz-resonator are formed in or on different layers of the base. For example, the neck is formed in or on a first layer  302  while the chambers are formed in or on a second different layer  304 . A plurality of columns  306  may be used to support the chambers in the second layer. The first and second layers may be made of the same or different material. As shown in  FIG.  3   , the cavity is split between the first and second layers with the first layer being thinner than the second. However, other configurations of the cavity in different layers may be contemplated in other embodiments. 
       FIG.  4    shows another configuration of the Helmholtz-resonator in the base of the microphone assembly. In this example, the chamber is a single chamber connected to the neck. The single chamber encompasses almost the entirety of the cavity, wherein the cavity encompasses almost the entirety of the base. The single chamber may be created by etching into the base and around the neck, the sound port, and the electrical contacts. In  FIG.  4   , the base is made of a copper material, although other suitable materials are contemplated in other embodiments. 
     In certain embodiments, instead of having the tuning structure in the base of the sensor assembly, a sound port adapter may be configured with the tuning structure to modify various acoustic properties (e.g., inertance, resistance, compliance and/or resonance) of the sensor assembly.  FIGS.  5 - 10    show different configurations of a one-piece sound port adapter that can be fitted to a microphone assembly. The sound port adapter may be made from any suitable material (e.g., metal, plastic, ceramic, glass, etc.) by using any suitable technique such as etching, laser ablation, molding, 3D printing, etc. While  FIGS.  5 - 10    show the sound port adapter as being square in shape, other suitable shapes (e.g., rectangular, trapezoid, oval, etc.) may be contemplated in other embodiments. 
       FIG.  5    shows a sound port adapter  500  that comprises a body member  502  having a mounting surface  506 . The mounting surface includes an acoustic channel  507  defined by sidewalls  508 ,  509 . The acoustic channel is disposed through the body member to create a sound inlet  510  and a sound outlet  512 . 
     The body member includes a Helmholtz-resonator formed by the cavity and wall portion. Here, the wall portion includes wall segments  514 ,  516  that extend horizontally (e.g., parallel with respect to the sound inlet) into the cavity to define the neck of the Helmholtz-resonator. The chamber of the Helmholtz-resonator is defined by the two wall segments and a third sidewall  518 . In this manner, the acoustical channel is acoustically coupled to the chamber by the neck. The chamber is shown to have rounded corners  520 ,  522 , although other shapes may be considered. While one rectangularly-shaped chamber is shown in  FIG.  5   , any number of other suitably shaped chambers may be contemplated in other embodiments. 
       FIG.  6    shows the sound port adapter mounted to a microphone assembly, which may be the same as the microphone assembly  100  with the exception that the base does not include the Helmholtz-resonator. When mounted to the base, the sound outlet is acoustically coupled to the sound port and the sound inlet defines a side port location. In other words, the sound port adapter converts the microphone assembly from a bottom port microphone assembly to a side-port microphone assembly. 
     To facilitate mounting of the sound port adapter, a surface  602  of the housing on which the sound port is disposed may include a ground plane  604 . The shape of the ground plane can correspond to the sidewalls of the sound port adapter such that the sidewalls can be attached to the ground plane (e.g., by using solder or cement). The surface may also include a plurality of contacts pads  606 - 610  (e.g., supply voltage, clock, data, etc.) for the external-device interface. 
     In  FIGS.  7 - 8   , in addition to forming the Helmholtz-resonator, the wall portion includes a plurality of discrete wall portions  702 - 712  arranged horizontally across the acoustic channel (e.g., parallel with respect to the sound inlet). The discrete wall portions serve to modify the resistance of the acoustic channel. In this example, the discrete wall portions are embodied as six equally sized cylindrical pillars. However, any number of suitably sized shapes in repeated patterns may be contemplated in other embodiments. 
     The discrete wall portions are arranged in spaced-apart relation with the distance between each of the discrete wall portions being adjustable as desired. The space between each of the discrete wall portions forms the sound inlet to allow sound to travel to the sound outlet. This arrangement also acts like a mesh or screen to prevent debris from entering the acoustic channel. 
     In  FIGS.  9 - 10   , in addition to forming the Helmholtz-resonator, the wall portion includes discrete wall portions in a tortuous acoustic channel. In this example, the wall portion is comprised of the cylindrical pillars  702 - 712  and wall segments  902 - 910 . The wall segments  902 - 908  are disposed horizontally (e.g., parallel), while the wall segment  910  is disposed vertically (e.g., perpendicular) with respect to the sound inlet. In this configuration, the neck of the Helmholtz-resonator is defined between the wall segments  906  and  910 . The chamber of the Helmholtz-resonator is defined by the wall segments  904 ,  906 ,  910  and the sidewalls  508 ,  518 . 
     The sound inlet is narrowed by the placement of the wall segment  908  with respect to the sidewall  509 . This arrangement of also defines a non-straight path  912  with three turns for the sound to follow from the sound inlet to the sound outlet. In general, the wall portion may be configured with various wall segments to form any type of non-straight path (e.g., spiral path, twisting path, S-shape path, sinusoidal path, zigzag path, serpentine path, etc.) to modify the inertance of the acoustic channel and to obstruct debris from entering the acoustic channel. 
     The cylindrical pillars are located near the sound outlet and disposed vertically between the wall segments  902  and  906 . In other examples, the cylindrical pillars may be located near the sound inlet. Other configurations of a tortuous acoustic channel with one or more discrete wall portions may be contemplated in other embodiments. 
       FIGS.  11  and  12    illustrate another embodiment of the microphone assembly  100  with  FIG.  11    showing a cross-section of the microphone assembly along lines A-A (see  FIG.  12   ). In this example, the cavity  114  is defined in part by the sidewalls  118 ,  120  and the wall portion  116 . The wall portion is a single segment that has a height less than the height of the base. This allows the wall portion to form the neck of the Helmholtz-resonator. As shown in  FIGS.  11  and  12   , the chamber of the Helmholtz-resonator is a single circular-shaped chamber embedded in the base. Unlike  FIG.  4   , the chamber does not encompass the entirety of the base. As desired, other shapes of the chamber (e.g., rectangular, oval, etc.) may be contemplated in other embodiments. 
     Among other advantages, employing a Helmholtz-resonator near the entry port of a microphone or another sensor can serve to tune the resonance response the device to thereby improve the quality of the output signal. Other benefits will be recognized by those of ordinary skill in the art. 
     While the present disclosure and what is presently considered to be the best mode thereof has been described in a manner that establishes possession by the inventors and that enables those of ordinary skill in the art to make and use the same, it will be understood and appreciated that there are many equivalents to the exemplary embodiments disclosed herein and that myriad modifications and variations may be made thereto without departing from the scope and spirit of the disclosure, which is to be limited not by the exemplary embodiments but by the appended claims.