Patent Publication Number: US-11659337-B1

Title: Balanced armature receiver having improved shock performance

Description:
FIELD OF THE DISCLOSURE 
     The present disclosure relates generally to balanced armature (BA) receivers and more particularly to nickel-iron (Ni—Fe) alloy armature having improved robustness and performance for BA receivers, as well as to BA motors and BA receivers comprising such Ni—Fe alloy armatures. 
     BACKGROUND 
     BA receivers (also referred to herein as “receivers”) capable of producing an acoustic output signal in response to an electrical audio signal are commonly used in hearing aids, wired and wireless earphones, True Wireless Stereo (TWS) devices, among other hearing devices. BA receivers generally comprise a housing in the form of a cup and cover enclosing a diaphragm that separates an interior of the housing into a back volume and a front volume. An electromagnetic motor located in the back volume includes an electrical coil disposed about an armature (also referred to herein as a “reed”) having a free end portion movably disposed between permanent magnets retained by a yoke. A drive rod or other link mechanically connects the movable portion of the reed to a movable portion of the diaphragm known as a paddle. The reed vibrates between the magnets in response to an electrical signal (representing sound) applied to the coil; otherwise, the reed is balanced between the magnets. The moving diaphragm expels sound out of a sound port of the housing via the front volume. 
     The motor and particularly the reed and yoke of known balanced armature receivers comprise ASTM A753-2 Type 2 (UNS K94840) nickel-iron (Ni—Fe) alloy having a nickel content between 47% and 49% by weight. Type 2 Ni—Fe alloy is desired for its characteristically low coercivity, low core loss, low distortion and high magnetic permeability. ASTM A753-02 Type 1 (UNS K94490) Ni—Fe alloy has a lower nickel content than Type 2 Ni—Fe alloy. Type 1 Ni—Fe alloy has not been used for armatures due to its low magnetic permeability and high coercivity compared to Type 2 Ni—Fe alloy. However Type 2 Ni—Fe alloy is relatively inelastic and susceptible to plastic deformation, which can result from an impact or other shock imparted to the receiver. A bent or otherwise deformed reed adversely affects the acoustical performance of the receiver. Thus there is a desire to provide BA receivers, and motors and armatures for such receivers that are more robust. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects, features and advantages of the present disclosure will become more fully apparent from the following detailed description and the appended claims considered in conjunction with the accompanying drawings. The drawings depict only representative embodiments and are therefore not considered to limit the scope of the disclosure. 
         FIG.  1    is a representative balanced armature receiver U-reed. 
         FIG.  2    is a representative balanced armature receiver E-reed. 
         FIG.  3    is a representative receiver armature having multiple grains across a thickness dimension of the armature. 
         FIG.  4    is a representative receiver armature having a single grain across a thickness dimension of the armature. 
         FIG.  5    is a cross-sectional view of a balanced armature receiver. 
     
    
    
     Those of ordinary skill in the art will appreciate that the figures are illustrated for simplicity and clarity and therefore may not be drawn to scale and may not include well-known features, that the order of occurrence of actions or steps may be different than the order described or be performed concurrently unless specified otherwise, and that the terms and expressions used herein have the meaning understood by those of ordinary skill in the art except where different meanings are attributed to them herein. 
     DETAILED DESCRIPTION 
     The disclosure relates generally to balanced armature receivers and more particularly to armatures comprising nickel-iron (Ni—Fe) alloy compositions having improved robustness and performance for BA receivers. The disclosure also related to receiver motors and receivers comprising such armatures. BA receivers are commonly used in hearing aids, wired and wireless earphones, True Wireless Stereo (TWS) devices, among other hearing devices that are susceptible to shock when handling or dropped. 
     A balanced armature receiver generally comprises a housing having a sound port between an interior and exterior thereof, and a diaphragm disposed in the housing and separating the interior thereof into a front volume and a back volume. A motor disposed at least partially within the housing comprises a coil located proximate an armature having a free-end portion balanced between permanent magnets retained by a yoke. The free-end portion of the armature is connected to a movable portion of the diaphragm and vibrates between the magnets in response to an audio signal applied to the coil, whereby the moving diaphragm emits sound from the sound port. A representative balanced armature receiver is described in greater detail below. 
     The Ni—Fe alloy armatures described herein can take many forms. Most all of these armatures generally comprise a planar member having a longitudinal dimension, a width dimension transverse to the longitudinal dimension, and a thickness dimension less than the width dimension. An end portion of the planar member is positionable between magnets retained by a yoke when the armature is connected to the yoke. In one implementation, shown in  FIG.  1   , the armature is a U-reed  100  comprising a first portion  102  and second portion  104  connected by a U-portion  106 . The first portion of the armature  100  corresponds to the planar member and includes a movable end portion  103  connectable to a diaphragm of the receiver. The second portion includes an end portion  105  connectable to a yoke of the receiver. In another implementation, shown in  FIG.  2   , the armature is an E-reed  200  comprising a first arm  202  and second arm  204  located on opposite sides of a central arm  206  corresponding to the planar member. The central arm includes a movable end portion  207  connectable to the diaphragm. The first, second and central arms each have a corresponding end portion connected to a common base portion  208 . The first and second arms have opposite end portions  203 ,  205 , respectively, connectable to the yoke. Other armatures suitable for use in balanced armature receivers have other shapes and structures. These and other armature configurations can be fabricated in stamping and forming operations and can comprise a unitary structure or can be an assembly of components. The armature can also have other known or future structural configurations. 
     According to one aspect of the disclosure, generally, the armature is a nickel-iron (Ni—Fe) alloy comprising a nickel content of 45% or less by weight, 5% or less additives and impurities by weight, and the balance Fe. This representative Ni—Fe alloy armature has a modulus of elasticity not greater than 120 gigapascals (GPa), a density of less than 8.20 g/cm{circumflex over ( )}3, and a yield strain, after annealing, of 0.001 or greater. 
     The mechanism of elastic deformation in a reed is dominating by bending, which includes tensile, compressive, and shear stresses and strains. As such, the effective modulus seen in bending, also called the flexural modulus, may differ slightly from the more commonly measured tensile modulus. For the purposes of this disclosure, the terms bending modulus, flexural modulus, Young&#39;s modulus, effective elastic modulus, elastic modulus, and modulus of elasticity are all understood to mean the material property that dictates the stress-strain relationship of the reed in operation and during shock events. Similarly, for the purposes of this disclosure, the term yield strain is used interchangeably to refer to the strain seen in tension, compression, bending, or combined modes of deflecting the reed. 
     In a more particular implementation, the armature is a Ni—Fe alloy comprising a nickel content between 36.5% and 45% by weight, 5% or less additives and impurities by weight and the balance Fe. In this implementation, the Ni—Fe alloy armature has a modulus of elasticity between 80 GPa and 120 GPa, a density between 8.1 g/cm{circumflex over ( )}3 and 8.20 g/cm{circumflex over ( )}3, and a yield strain, after annealing, between 0.001 and 0.004. 
     In another more particular implementation, the armature is a Ni—Fe alloy comprising a nickel content between 38.5% and 41.5%, 2% or less additives and impurities by weight, and the balance Fe. In this implementation, the Ni—Fe alloy armature has a modulus of elasticity between 80 GPa and 100 GPa, a density between 8.10 g/cm{circumflex over ( )}3 and 8.15 g/cm{circumflex over ( )}3, and a yield strain, after annealing, between 0.002 and 0.003. 
     According to another aspect of the disclosure, the Ni—Fe alloy armature comprising a nickel content of 45% or less by weight is subject to an annealing operation after formation of the armature. Ni—Fe alloy material as delivered from a steel mill tends to have small grains before annealing.  FIG.  3    shows a Ni—Fe alloy strip material having relatively small grains  302 ,  304  between opposite side surfaces  305 ,  306  prior to annealing. Small grain size improves the workability of the Ni—Fe alloy material during formation (e.g., stamping, bending . . . ) of the armature. A typical armature has a thickness between 100 microns and 200 microns. After the Ni—Fe material is formed into an armature it will be annealed to improve the magnetic properties of the armature. During the anneal process the grains will grow in size and provide improved magnetic properties at the expense of some mechanical properties. Generally, the average grain size of the Ni—Fe alloy armature depends on the annealing temperature and time duration, armature thickness and other factors. According to this aspect of the disclosure, a fully annealed Ni—Fe armature comprises a grain size generally greater than 100 micron and possibly as high as 400 microns. In  FIG.  4   , the annealed armature has many relatively large grains that are as thick as, or thicker than, the thickness of the armature in the z-direction. 
       FIG.  5    is a representative balanced armature receiver  500  comprising an armature having a Ni—Fe alloy as described herein. The various armatures comprising the Ni—Fe alloy described herein can be used in the receiver of  FIG.  5    as well as in other known or future BA receivers. In  FIG.  5   , the receiver  500  comprises a housing  510 , a diaphragm  520  disposed within a housing and separating an interior thereof into a front volume  512  and a back volume  514 . The front volume is acoustically coupled to an exterior of the housing via a sound port  516  located on an end wall portion. Alternatively, the sound port can be located on some other part of the housing, for example on a wall portion parallel to the diaphragm, among others. The representative receiver also includes a nozzle  518  disposed over the sound port and coupled to an end wall on which the sound port is located. Other receivers do not include a nozzle. The sound port can be located on different wall portion of the housing. For example, the sound port can be located on a wall portion  511  parallel to the diaphragm and partially defining the front volume. Alternatively, the sound port can be on a wall portion defining another part of the interior of the housing. 
     In  FIG.  5   , a motor disposed in the back volume comprises a coil  524  supported by a bobbin  526  located about an armature  530  having a free-end portion  532  movably located between permanent magnets  540 ,  542  retained in space apart relation by a yoke  544 . The free-end portion of the armature is coupled to a movable portion of the diaphragm known as a paddle  522  by a drive rod or other link  546 . The armature in  FIG.  5    is a U-reed having a first arm  534  coupled to the yoke and a second arm  538  from which the free-end portion  532  extends. A U-portion  536  of the armature interconnects the first and second arms. The receiver generally comprises a terminal located on an outer portion or surface of the housing. The terminal includes contacts electrically coupled to the coil within the housing, wherein the contacts are accessible from an exterior of the receiver. Other receivers can have a variety of other forms. For example, the armature can be an E-reed or have some other configuration, the bobbin is not required, and the motor can be located in the front volume instead of the back volume, among other known and future balanced armature designs. 
     In some receiver implementations, the armature and yoke both comprise the same Ni—Fe composition, namely a nickel content of 45% or less by weight as described herein. In other receiver implementations, however, a Ni—Fe alloy yoke comprises a different nickel content than the Ni—Fe alloy armature described in the embodiments disclosed herein. The yoke does not require enhanced strain characteristics to survive a shock as it is physically well constrained by magnets, reed welding and case. The yoke only requires optimized for magnetic properties. Type 2 Ni—Fe alloys provide the best magnetic properties for the yoke. The reed must balance magnetic properties with elastic modulus and resistance to damage when larger strains occur during shock events. In one particular implementation, the armature is a Ni—Fe alloy comprising a nickel content of 45% or less by weight and the yoke is a Ni—Fe alloy comprising a nickel content between 46% and 51% by weight. For example, the yoke can be a Type 2 Ni—Fe alloy comprising a nickel content between 47% to 49% by weight. 
     While the disclosure and what is presently considered to be the best mode thereof has been described in a manner establishing possession and enabling 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 representative embodiments described herein and that myriad modifications and variations may be made thereto without departing from the scope and spirit of the invention, which is to be limited not by the embodiments described but by the appended claims and their equivalents.