Patent Publication Number: US-2010124352-A1

Title: Micro magnetic device with magnetic spring

Description:
BACKGROUND 
     Speakers are acoustical elements that are common is today&#39;s society. Speakers are present in radios, stereo systems, televisions, computers, earphones/headphones and other personal equipment that is configured to emit sound. Without speakers, one could not enjoy music, a television program, or a movie, to its full extent. 
     A traditional speaker (also referred to as a loud speaker or variation thereof) has a large magnet in close proximity to a movable current coil which drives a cone/diaphragm. The oscillating cone/diaphragm generates sound. A single loud speaker, however, typically does not have sufficient frequency bandwidth to amplify an audio signal at the full bandwidth. To expand the overall bandwidth of a speaker system, a multi-speaker system is compiled where each speaker is responsible for a limited bandwidth range. This type of system consumes a large amount of power, occupies larger space and is expensive. This issue also exists in headphones or earphones products. 
     Attempts have been made to miniaturize speakers using micro-system technology (MST). Although low cost and good reproducibility of electronic circuitry has been obtained, the number of realized loudspeakers using MST is small and these loudspeakers generally do not fulfill the requirements for a hearing instrument such as headphone or earphones. Better micro-speakers and methods of making them are needed. 
     BRIEF SUMMARY 
     The present disclosure is directed to micro magnetic devices (e.g., micro-speakers) suitable for use with a broadband acoustic range. The micro magnetic devices can be made by batch microfabrication processing using thin film or micro-electromechanical system (MEMS) techniques. A plurality of the monolithic elements can be provided as an array to provide a broader bandwidth of acoustic range. 
     In one exemplary embodiment, this disclosure provides a micro magnetic device having a body defining at least part of an enclosed chamber, the body comprising a first sidewall and a second sidewall. A pole comprising a soft magnetic material is within the chamber and an electrically conductive coil is positioned around the pole. A diaphragm is connected to the first sidewall and a permanent dipole magnet is connected to the second sidewall at a first end and to the diaphragm at a second end. The dipole magnet is offset centrally from the pole. The diaphragm may also be offset centrally from the first pole. 
     These and various other features and advantages will be apparent from a reading of the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawing, in which: 
         FIG. 1  is a schematic cross-sectional view of a micro magnetic speaker device; 
         FIG. 2  is a schematic cross-sectional view of a first embodiment of a micro magnetic speaker device according to this disclosure;  FIG. 2A  is an alternate schematic cross-sectional view of the micro magnetic speaker device of  FIG. 2 ; 
         FIG. 3  is a schematic cross-sectional view of a second embodiment of a micro magnetic speaker device according to this disclosure; 
         FIG. 4  is a schematic cross-sectional view of a third embodiment of a micro magnetic speaker device according to this disclosure; 
         FIG. 5  is a schematic top view of an array of micro magnetic devices according to this disclosure; 
         FIG. 6  is a graphical representations of peak frequency/bandwidth versus amplitude for multiple micro-speakers according to this disclosure; 
         FIGS. 7A-7C  are schematic cross-sectional views of a process for making a first half of a micro magnetic device; 
         FIGS. 8A-8D  are schematic cross-sectional views of a process for making a second half of a micro magnetic device; and 
         FIGS. 9A and 9B  are schematic cross-sectional views of a process for combining the first half of  FIGS. 7A-7C  with the second half of  FIGS. 8A-8D  to form a micro magnetic device. 
     
    
    
     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 
     In the following description, reference is made to the accompanying set of drawings that form a part hereof and in which are shown by way of illustration several specific embodiments. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense. 
     The present invention is directed to miniaturized, micro magnetic devices such as micro-speakers. The elements can be used in high performance speaker devices, such as headphone or earphone devices, or in acoustic signal detection devices. The applications for the micro magnetic devices are not limited to entertainment or other audible uses, but can also include applications above that audible by humans (i.e., above about 20 kHz) such as military, biomedical and marine uses. 
     The micro magnetic devices of this invention are built on a single semiconductor chip using micro magnetic actuator technology (e.g., thin film or micro-electro-mechanical (MEMS) techniques). An array of micro magnetic devices can be built on a single chip. In an array, each micro element covers a predefined bandwidth based on its unique physical and mechanical structure. A combination of a plurality of micro elements can offer broad bandwidth coverage for any audio signal which is delivered or received. 
     For example, a micro magnetic device or speaker of this disclosure may have a body defining at least part of a first enclosed chamber, the body comprising a first sidewall and a second sidewall. A first pole comprising a soft magnetic material is within the first chamber and a first electrically conductive coil is positioned around the first pole. A diaphragm is connected to the first sidewall and a permanent dipole magnet is connected to the second sidewall at a first end and to the diaphragm at a second end. The dipole magnet is offset centrally from the pole. The diaphragm may also be offset centrally from the first pole. Such a micro magnetic device may have two chambers, each having a pole and a coil therearound. 
     As another example, a micro magnetic device or speaker of this disclosure may have a first enclosed chamber having therein a first pole comprising a soft magnetic material and a first electrically conductive coil positioned around the first pole, and a second enclosed chamber having therein a second pole comprising a soft magnetic material and a second electrically conductive coil positioned around the second pole. The first chamber and the second chamber can share a first sidewall and a second sidewall. A diaphragm is connected to the first sidewall and a permanent dipole magnet is connected to the second sidewall at a first end and to the diaphragm at a second end. The dipole magnet is offset centrally from the pole. The diaphragm may also be offset centrally from the first pole. 
     As yet another example, a micro magnetic device or speaker of this disclosure may have a first enclosed chamber having therein a first pole comprising a soft magnetic material and a first electrically conductive coil positioned around the first pole, and a second enclosed chamber having therein a second pole comprising a soft magnetic material and a second electrically conductive coil positioned around the second pole. A diaphragm and a permanent dipole magnet extend between the first chamber and the second chamber and are oscillatable into and out from the first chamber and the second chamber based on a magnetic spring constant. The diaphragm and permanent dipole magnet may also be oscillatable into and out from the first chamber and the second chamber based on a mechanical spring constant. 
     While the present invention is not so limited, an appreciation of various aspects of the invention will be gained through the discussion provided below. A general embodiment of a micro magnetic device is illustrated in  FIG. 1  as micro-speaker  10 . It should be understood that although the following discussion will be directed to a micro-speaker, the micro magnetic device could alternately be a micro sensor or the like. 
     The micro magnetic device micro-speaker  10  has a body  11  that forms the overall shape of micro-speaker  10 .  FIG. 1  is a side view of micro-speaker  10 , from a top view, micro-speaker  10  may be circular or rectangular (e.g., square), although in most embodiments, is circular. 
     In most embodiments, micro-speaker  10  and other micro magnetic devices of this disclosure, such as those described below, are no more than about 10 mm, in some embodiments, about 5 to 10 mm in their largest dimension. For a circular micro magnetic device, the largest dimension is usually the diameter across body  11 . In other embodiments, micro magnetic devices of this invention have a largest dimension of no more than about 4 mm, in some embodiments about 2 to 4 mm, and often, about 1 mm in largest dimension. 
     Body  11  may be a dielectric material (for example, a polyamide or polyimide material), a metal, or other semiconductor or chip material. Silicon (Si) is a common material for body  11 . Body  11  at least partially defines an enclosed inner chamber  12 . Chamber  12  is defined by body  11  and a diaphragm  14  extending across chamber  12 . Diaphragm  14  is integral with body  11 , in that diaphragm  14  is an extension of body  11  and is formed from the same material as body  11 . 
     Present proximate diaphragm  14  is a magnetic thin film  15 . Magnetic thin film  15  is a hard or permanent magnet, the magnetization orientation of which does not change. Examples of permanent magnet materials include iron (Fe), chromium (Cr), cobalt (Co), nickel (Ni), platinum (Pt), vanadium (V), manganese (Mn), bismuth (Bi), and combinations thereof. Magnetic thin film  15  may be made of bulk material or may be electrochemical deposited (e.g., plated). In most embodiments, magnetic thin film  15  is about 1 to 200 micrometers thick, and may be thicker or thinner than diaphragm  14  which supports it. In some embodiments, magnetic thin film  15  is about 1 to 100 micrometers thick. 
     During use of speaker  10 , the suspended combination of diaphragm  14  and magnetic thin film  15  oscillates in a vertical direction, toward and away from chamber  12 , at a frequency to produce sound waves. Through different designs of diaphragm  16 , the bandwidth of micro-speaker  10  can be adjusted for a desired frequency range. The peak frequency (f peak ) for micro-speaker  10  is dependent on the thickness of diaphragm  16 , the width of diaphragm  16 , and also the Young&#39;s Modulus of diaphragm  16 . Thus, the physical design of diaphragm  14  affects the bandwidth and peak frequency of speaker  10 . 
     Diaphragm  16 , which oscillates, is fairly thin, typically about 1 to 100 micrometers thick, and in most embodiments, has a diameter of about 0.5 to 2 mm. In some embodiments, including that illustrated in  FIG. 1 , diaphragm  14  does not extend across the entire width of chamber  12 , but rather, a portion of body  11  extends over chamber  12  and transitions into diaphragm  14 . 
     Positioned within chamber  12  is a pole  16  of a soft magnetic material with high momentum, the magnetization of which can be altered by being exposed to a magnetic field. Examples of soft magnetic materials include ferromagnetic materials such as nickel (Ni), iron (Fe), cobalt (Co), iron oxide (Fe 2 O 3 ), and combinations thereof. In this illustrated embodiment, pole  16  is present on an interior surface of inner chamber  12 ; in alternate embodiments, pole  16  may be recessed into body  11 , i.e., the lower edge of pole  16  is below the lower wall of chamber  12 . 
     An electrically conducting coil  18  is positioned around pole  16 . Coil  18  is formed from an electrically conducting material, typically metal. Examples of suitable metals for coil  18  include copper (Cu), aluminum (Al), silver (Ag) and gold (Au). In  FIG. 1 , coil  18  is illustrated being a single layer with three turns; other designs for a coil may be useful, such as more or less turns, or multiple layers. Coil  18  may have, for example, from one to  100  (one hundred) turns around pole  16 . 
     In use, an electrical current is applied to coil  18 . The current in coil  18  will generate a magnetic field and polarize (e.g., charge) soft magnetic pole  16 . The total magnetic field from pole  16  will produce an attraction or repelling force on magnetic thin film  15 , which will drive diaphragm  14  toward and away from pole  16  (e.g., down and up), thereby creating waves (e.g., sound waves). 
     Other configurations of micro magnetic devices, e.g., speakers, are illustrated in  FIGS. 2 and 2A  and  FIGS. 3 and 4 . The various elements of the following micro magnetic devices as similar to the respective elements of micro-speaker  10 , described above, unless otherwise indicated. 
       FIG. 2  illustrates a micro-speaker  20  having a body  21  that forms the overall shape of micro-speaker  20 .  FIG. 2  is a side view of micro-speaker  20 ; from a top view, micro-speaker  20  may be circular or rectangular (e.g., square), although in most embodiments, micro-speaker  20  is circular. Body  21  includes sidewall non-magnetic portions  23  and a magnetic portion  27  extending between sidewall non-magnetic portions  23 . In this embodiment, a beam portion  23 ′ of sidewall non-magnetic portions  23  extends out from the sidewall. An enclosed inner chamber  22  is defined by body  21  (i.e., by non-magnetic portions  23  and magnetic portion  27 ), a diaphragm  24  and a magnetic member  25 , which are connected together. Each of diaphragm  24  and magnetic member  25  is connected to non-magnetic sidewall portions  23 , and are also connected together. 
     Unlike body  11  of micro-speaker  10  of  FIG. 1 , body  21  is formed from at least two different materials, a non-magnetic material for non-magnetic portions  23  and soft magnetic material for magnetic portion  27 . Examples of suitable materials for non-magnetic portions  23  include dielectric materials (for example, a polyamide or polyimide material), non-magnetic metal, and semiconductor or chip material. Silicon (Si) is a common material for non-magnetic portions  23 . In micro-speaker  20 , two non-magnetic portions  23  are present; these two portions  23  may be made from the same or different non-magnetic material. Soft magnetic portion  27  has a high momentum, the magnetization of which can be altered by being exposed to a magnetic field. Examples of suitable materials for soft magnetic portion  27  include ferromagnetic materials such as nickel (Ni), iron (Fe), cobalt (Co), iron oxide (Fe 2 O 3 ), and combinations thereof. 
     Diaphragm  24  is formed from a flexible material, one that can readily oscillate. Examples of suitable materials for diaphragm  24  include silicon (Si), polyimides, polyamides, and metallic foils, such as foils of NiCr, Al, W, Nb and Ta. In some embodiments, diaphragm  24  may be formed from the same material as non-magnetic portion  23  of body  21 , whereas in other embodiments, diaphragm  24  is a material different that for non-magnetic portion  23 . In most embodiments, diaphragm  24  is about 1 to 200 micrometers thick, often about 50 to 100 micrometers thick. Diaphragm  24  is offset from the center of chamber  22 , in that it is not centrally or symmetrically positioned over the speaker pole and coil (described below). In some embodiments, diaphragm  24  may extend over all or a portion of the pole, but does not center itself over the pole. 
     Magnetic member  25  also is offset from the center of chamber  22 , in that it is not centrally or symmetrically positioned over the speaker pole and coil (described below). In some embodiments, magnetic member  25  may extend over all or a portion of the pole, but does not center itself over the pole. Magnetic member  25  is a hard or permanent magnet, the magnetization orientation of which does not change. Examples of permanent magnet materials include iron (Fe), chromium (Cr), cobalt (Co), nickel (Ni), platinum (Pt), vanadium (V), manganese (Mn), bismuth (Bi), and combinations thereof. In most embodiments, magnetic member  25  is about 1 to 200 micrometers thick, often about 50 to 100 micrometers thick. In the illustrated embodiment, magnetic member  25  has the same or similar thickness as diaphragm  24 . In  FIG. 2 , magnetic member  25  is a dipole magnet, positioned with its south pole attached to body  21  at non-magnetic portion  23  and with its north pole connected to diaphragm  24 . 
     Positioned within chamber  22  is a pole  26  made of soft magnetic material with high momentum, the magnetization of which can be altered by being exposed to a magnetic field. Examples of soft magnetic materials include ferromagnetic materials such as nickel (Ni), iron (Fe), cobalt (Co), iron oxide (Fe 2 O 3 ), and combinations thereof. In this illustrated embodiment, pole  26  is present on an interior surface of inner chamber  22 ; in alternate embodiments, pole  26  may be integral with body  21 , e.g., with soft magnetic portion  27 . With pole  26  positioned proximate or on magnetic portion  27 , magnetic portion  27  functions as a return pole for micro-speaker  20 . 
     An electrically conducting coil  28  is around centrally positioned pole  26 . Coil  28  is formed from an electrically conducting material, typically metal. Examples of suitable metals for coil  28  include copper (Cu), aluminum (Al), silver (Ag) and gold (Au). Coil  28  is electrically connected to a circuit (not shown) that provides electric current to coil  28 . 
     In use, an electrical current is applied to coil  28 , which generates a magnetic field and polarizes (e.g., charges) pole  26  and optionally magnetic portion  27 . The total magnetic field from pole  26  and portion  27  produces an attractive or repelling force on magnetic material  25 , driving magnetic material  25  toward and away from pole  26  (e.g., down and up) in an oscillating motion. Because the south end of magnetic material  25  is fixed to non-magnetic material sidewall  23 , the north end of magnetic material  25  oscillates toward and away from pole  26 . Diaphragm  24 , connected to magnetic member  25  at an end, likewise oscillates, toward and away from chamber  22 , at a frequency to produce sound waves. Both non-magnetic material  23  and diaphragm  24  have a spring constant, which affects the oscillation of magnetic member  25 ; diaphragm  24  generally has a lower spring constant than non-magnetic material  23 , allowing more movement proximate diaphragm  24  than proximate non-magnetic material  23 . Magnetic member  25  and diaphragm  24  may oscillate up (e.g., away from pole  26 ) the same distance as it oscillates down (e.g., toward pole  26 ), or may move away from less than is moves toward pole  26 . Although magnetic member  25  is a dipole, as mentioned above, during oscillation it functions as a monopole, due to only one end (i.e., the end proximate diaphragm  24 ) being readily able to oscillate and the other end (i.e., the end proximate non-magnetic material  23 ) being fixed. 
     Through different designs of diaphragm  24  (e.g., thickness, length, etc.), the bandwidth of micro-speaker  20  can be adjusted for a desired frequency range. The peak frequency (f peak ) for micro-speaker  20  is dependent on the thickness of diaphragm  24 , the width of diaphragm  24 , and also the Young&#39;s Modulus of diaphragm  24 . Thus, the physical design of diaphragm  24  affects the bandwidth and peak frequency of speaker  20 . Additionally, the physical design of magnetic member  25  (e.g., thickness, width, and material) affects the performance of speaker  20 . In the embodiment illustrated in  FIG. 2 , the north pole of magnetic member  25  is positioned at a far edge of pole  26 ; in alternate embodiments, magnetic member  25  may extend past pole  27  or may not extend across the width of pole  26 . Still further, non-magnetic material  23  and the physical connection between magnetic member  25  and non-magnetic material  23  (in this embodiment, at the south pole of magnetic member  25 ) affect the performance of speaker, by at least partially defining the properties of chamber  22  and the position of magnetic member  25 . The configuration of non-magnetic material  23 , where it is connected to magnetic member  25 , also affects the performance of micro-speaker  20 . The spring constant of non-magnetic member  23  can be adjusted by changing the physical design of non-magnetic member  23 , thus affecting the oscillation of magnetic member  25  and thus the bandwidth and peak frequency of micro-speaker  20 . These various elements allow micro-speaker  20  to be tuned to a desired bandwidth and/or peak frequency. Each of these tunable elements, for micro-speaker, is a physical or mechanical element. 
     A variation of micro-speaker  20  is illustrated in  FIG. 2A  as micro-speaker  20 A. The various elements of micro-speaker  20 A are the same as for micro-speaker  20 , unless indicated otherwise. 
     Micro-speaker  20 A has a body  21 A that forms the overall shape of micro-speaker  20 A. Body  21 A includes two non-magnetic portions  23 A and soft magnetic portion  27 A. An enclosed inner chamber  22 A is defined by body  21 A, a diaphragm  24 A and a magnetic member  25 A, which are connected together. In  FIG. 2A , magnetic member  25 A is positioned with its north pole attached to body  21 A at non-magnetic portion  23 A and with its south pole connected to diaphragm  24 A. Positioned within chamber  22 A is a pole  26 A of a soft magnetic material with an electrically conducting coil  28 A therearound. In use, because the north end of magnetic material  25 A is fixed, the south end of magnetic material  25 A oscillates toward and away from pole  26 A. 
     Micro-speakers  20 ,  20 A described above have a single chamber with the pole and coil positioned on one side of the oscillating diaphragm and magnetic member. The bandwidth and peak frequency of speakers  20 ,  20 A are generally dependant on mechanical features of the speaker, e.g., the spring constants of non-magnetic material  23  and diaphragm  24 , configuration of diaphragm  24 , and configuration of magnetic member  25 . Micro-speakers having multiple chambers may also be design, with a chamber with a pole and coil positioned on each side of the diaphragm and the magnetic member. 
       FIG. 3  illustrates a multi-chambered micro-speaker  30  having a body  31  that forms the overall shape of micro-speaker  30 , which in this embodiment, can be generalized as a micro-speaker with two chambers, or, as two micro-speakers sharing one diaphragm. Body  31  includes two opposite sidewall non-magnetic portions  33  separated by two magnetic portions  37 A and  37 B extending between non-magnetic portions  33 . A first enclosed inner chamber  32 A is defined by non-magnetic portions  33 , magnetic portion  37 A, a diaphragm  34  and a magnetic member  35 , which are connected together. A second enclosed inner chamber  32 B is defined by non-magnetic portions  33 , magnetic portion  37 B, diaphragm  34  and magnetic member  35 . Magnetic member  35  is fixedly attached to non-magnetic sidewall member  33  at a first end (at its south pole in  FIG. 3 ) and to diagraph  34  at a second end (at its north pole in  FIG. 3 ). 
     Positioned within chamber  32 A is a pole  36 A of a soft magnetic material with high momentum, the magnetization of which can be altered by being exposed to a magnetic field. With pole  36 A positioned proximate or on magnetic portion  37 A, magnetic portion  37 A functions as a return pole for pole  36 A of micro-speaker  3 O. An electrically conducting coil  38 A is positioned around pole  36 A. Coil  38 A is electrically connected to a circuit that provides electric current to coil  38 A. Positioned within chamber  32 B is a pole  36 B of a soft magnetic material with high momentum, the magnetization of which can be altered by being exposed to a magnetic field. With pole  36 B positioned proximate or on magnetic portion  37 B, magnetic portion  37 B functions as a return pole for pole  36 B of micro-speaker  30 . An electrically conducting coil  38 B is positioned around pole  36 B. Coil  3   8 B is electrically connected to a circuit that provides electric current to coil  38 B. Coils  38 A,  38 B may be electrically connected or may be electrically separate and controlled individually. 
     In use, an electrical current is applied to either or both coils  38 A,  38 B, which generates a magnetic field and polarizes (e.g., charges) the respective pole  36 A,  36 B and optionally the respective magnetic portion  37 A,  37 B. The total magnetic field from poles  36 A,  36 B and portions  37 A,  37 B produces an attraction or repelling force on magnetic material  35 , driving magnetic material  35  toward and away from pole  36 A and from pole  36 B in an oscillating motion. Because the south end of magnetic material  35  is fixed in  FIG. 3 , the north end of magnetic material  35  oscillates. Diaphragm  34 , connected to magnetic member  35 , likewise oscillates at a frequency to produce sound waves. By having coils  38 A,  38 B separately controlled, the phase of the attractive/repelling force can be controlled by changing the current, thus controlling the oscillation of magnetic material  35  and the bandwidth and peak frequency of speaker  30 . 
     Similar to micro-speaker  20  described above, the bandwidth and peak frequency of micro-speaker  30  can be affected by mechanical features of the speaker, e.g., the spring constants of non-magnetic material  33  and diaphragm  34 , configuration of diaphragm  34 , and configuration of magnetic member  35 , and also by the current through coils  38 A,  38 B. 
     The current through coils  3   8 A,  3   8 B can be independently adjusted, during use of speaker  30 , to modify the bandwidth and peak frequency of speaker  30 . Adjusting the current through coils  3   8 A,  3   8 B, in essence, adjusts a magnetic spring constant affecting magnetic member  35 . 
       FIG. 4  illustrates a multi-chambered micro-speaker  40  having a body  41  that forms the overall shape of micro-speaker  40 , which in this embodiment, can also be generalized as two micro-speakers sharing one diaphragm. Body  41  includes one sidewall non-magnetic portion  43 A and a second, non-sidewall non-magnetic portion  43 B. Body  41  also includes a magnetic portion  47  that has a first portion  47 A, a second portion  47 B opposite first portion  47 A and a third portion  47 C that forms a sidewall of body  41 . First portion  47 A extends from sidewall non-magnetic portion  43 A to third portion  47 C, and second portion  47 B also extends from sidewall non-magnetic portion  43 A to third portion  47 C. A first enclosed inner chamber  42 A is defined by side wall non-magnetic portion  43 A, first magnetic portion  47 A, third magnetic portion  47 C, non-sidewall non-magnetic member  43 B, a diaphragm  44  and a magnetic member  45 , which are connected together. Similarly, a second enclosed inner chamber  42 B is defined by sidewall non-magnetic portion  43 A, second magnetic portion  47 B, third magnetic portion  47 C, non-sidewall non-magnetic portion  43 B, diaphragm  44  and magnetic member  45 . Magnetic member  45  is fixedly attached to non-sidewall non-magnetic member  43 B at a first end (at its south pole in  FIG. 4 ) and to diagraph  44  at a second end (at its north pole in  FIG. 4 ). 
     Positioned within chamber  42 A is a pole  46 A of a soft magnetic material with high momentum, the magnetization of which can be altered by being exposed to a magnetic field. With pole  46 A positioned proximate or on magnetic portion  47 A, magnetic portion  47 A functions as a return pole for pole  46 A of micro-speaker  40 . An electrically conducting coil  48 A is positioned around pole  46 A. Coil  48 A is electrically connected to a circuit that provides electric current to coil  48 A. Positioned within chamber  42 B is a pole  46 B of a soft magnetic material with high momentum, the magnetization of which can be altered by being exposed to a magnetic field. With pole  46 B positioned proximate or on magnetic portion  47 B, magnetic portion  47 B functions as a return pole for pole  46 B of micro-speaker  40 . An electrically conducting coil  48 B is positioned around pole  46 B. Coil  48 B is electrically connected to a circuit that provides electric current to coil  48 B. Coils  48 A,  48 B may be electrically connected or may be electrically separate and controlled individually. 
     In use, when an electrical current is applied to second coil  48 B (and no current is applied to first coil  48 A), magnetic member  45  is attracted to second pole  46 B, regardless of the current direction. Similarly, when an electrical current is applied to first coil  48 A (and no current is applied to second coil  48 B), magnetic member  45  is attracted to first pole  46 A, regardless of the current direction. Because the south end of magnetic material  45  is fixed to non-sidewall non-magnetic connection  43 B in  FIG. 4 , the north end of magnetic material  45  oscillates. 
     Similar to micro-speaker  30  described above, the bandwidth and peak frequency of micro-speaker  40  can be affected by mechanical features of the speaker, e.g., the spring constants of non-magnetic material  43 A,  43 B and diaphragm  44 , configuration of diaphragm  44 , and configuration of magnetic member  45 , and also by the current through coils  48 A,  48 B. The current through coils  48 A,  48 B can be independently adjusted, during use of speaker  40 , to modify the bandwidth and peak frequency of speaker  40 . Adjusting the current through coils  48 A,  48 B, in essence, adjusts a magnetic spring constant affecting magnetic member  45 . Non-sidewall non-magnetic member  43 B is present to affect (e.g., decrease) the spring constant at the south end of magnetic member  45 , so that motion of magnetic member  45  and of diaphragm  44  can be better controlled by the magnetic forces from poles  46 A,  46 B via coils  48 A,  48 B. In some embodiments, non-sidewall non-magnetic connection  43 B is not present, but rather, the south end of magnetic material  45  is fixed to magnetic portion  47 C. 
     The micro magnetic devices of this disclosure (e.g., micro-speakers  20 ,  20 A,  30 ,  40 ) can be described as a magnetic monopolar device, due to one end of the magnetic dipole member (e.g., magnetic member  25 ,  25 A,  35 ,  45 ) being fixed to a non-magnetic portion and a sidewall, with the other end having the ability to oscillate, e.g., with the flexible diaphragm  24 ,  24 A,  34 ,  44 . 
     A plurality of micro magnetic devices (e.g., micro-speakers  20 ,  20 A,  30 , etc.) may be combined to form an array of micro magnetic devices on a single chip.  FIG. 5  illustrates an array  50  of micro-speakers, in particular, twenty speakers that include speakers  50 A,  50 B,  50 C,  50 D,  50 E and  50 F, with additional micro-speakers illustrated but not identified. In array  50 , each micro-speaker  50 A,  50 B,  50 C,  50 D,  50 E,  50 F, etc. has a predefined bandwidth; this predefined bandwidth may be based on its unique physical and mechanical structure or may be tunable during use (e.g., by adjusting the current that produces the oscillating diagraph). In some embodiments, each micro-speaker  50 A,  50 B,  50 C,  50 D,  50 E,  50 F, etc. has the same diaphragm thickness but a different diaphragm width, thus providing different frequency peaks. Together, micro-speakers  50 A,  50 B,  50 C,  50 D,  50 E,  50 F, etc. provide broad bandwidth coverage. 
     In embodiments having a speaker array composed of micro-speakers  40  of  FIG. 4 , the frequency range can be tuned by controlling the current in both coils  48 A and  48 B. The higher current makes the higher effective magnetic spring constant for coils  48 A,  48 B. The mechanical parameters including diaphragm thickness, width, and mass also affect the operating frequency. 
       FIG. 6  graphically illustrates multiple individual bandwidths, each from a single speaker, and their distribution over a broad frequency range. It provides a generic frequency distribution for five different speakers, which may differ in their membrane and magnetic member configuration (e.g., have a larger membrane), or which may differ in the amount of current being used to drive the membrane. With the micro magnetic devices of this invention, the total sound wave spatial distribution can be controlled at each individual unit (e.g., speaker  50 A,  50 B, etc. of  FIG. 5 ) to obtain the desired frequency peak and frequency bandwidth with minimum power usage. 
     The micro magnetic devices of this disclosure are easy to optimize to the desired frequency bandwidth. As mentioned above, the peak frequency and the bandwidth are dependent on the geometry of the diaphragm, which can be readily designed and manufactured using micro magnetic actuator technology (e.g., thin film or MEMS techniques). Based on this technology, sound can be tuned or directed to the designated direction with higher acoustic power density. Additionally, the peak frequency and bandwidth can be tuned by adjusting the current through the speaker, which affects the oscillation of the sound producing diaphragm. 
     One general method of making a single chambered micro magnetic device, such as micro-speaker  20  of  FIG. 2 , is illustrated in  FIGS. 7A-7C ,  8 A- 8 D, and  9 A- 9 B. 
     In  FIGS. 7A through 7C , a first portion of a micro-speaker is step-wise manufactured. A starting support  70  is illustrated in  FIG. 7A ; support  70  is a carrier or support surface for the eventual micro device, and is not illustrated in the illustration of speaker  20  in  FIG. 2 . In many embodiments, support  70  is an inert, dielectric material, such as silica. In  FIG. 7B , applied onto support  70  is a layer of soft ferromagnetic material  72 , which will form the eventual magnetic material portion (e.g., magnetic material portion  27  of micro-speaker  20 ). Soft ferromagnetic material  72  may be plated (e.g., electroplated), deposited (e.g., CVD, PVD, sputtered), or screen printed from a slurry of ferromagnetic particles in a binder material. Applied over soft ferromagnetic material  72  is another soft ferromagnetic material  74 , which will form the eventual pole (e.g., pole  26  of micro-speaker  20 ). Soft ferromagnetic material  74  may be plated (e.g., electroplated), deposited (e.g., CVD, PVD, sputtered), or screen printed from a slurry of ferromagnetic particles in a binder material. Material  74  may be the same or different than material  72 . In some embodiments, material  72  and material  74  may be applied in the same step rather than in sequential steps. An electrically conductive coil  75  is positioned around pole material  74  in  FIG. 7C . Coil  75  may be previously produced and physically placed around pole material  74 , or coil  75  may be fabricated (e.g., plated or deposited) around pole material  74 . The result is first structure  76 . 
     In  FIGS. 8A through 8D , a second portion of a micro-speaker is step-wise manufactured. If referring to micro-speaker  20  of  FIG. 2 , this second portion is the top or upper portion of speaker  20 . A starting non-magnetic material  80  is illustrated in  FIG. 8A . In many embodiments, non-magnetic material  80  is silica. In  FIG. 8B , a recess  81  is formed in non-magnetic material  80 ; in  FIG. 8C , applied into recess  81  are a hard or permanent ferromagnetic material  82 , which will form the eventual magnet of the speaker (e.g., magnetic member  25  of speaker  20 ), and a membrane material  84 , which will form the eventual diaphragm of the speaker (e.g., diaphragm  24  of speaker  20 ). Hard ferromagnetic material  82  may be plated (e.g., electroplated), deposited (e.g., CVD, PVD, sputtered), or screen printed from a slurry of ferromagnetic particles in a binder material. In  FIG. 8D , a cavity  85  is shown formed in support  80  that will form the eventual inner chamber of the speaker (e.g., chamber  22  of speaker  20  in  FIG. 2 ). Support  80  may be etched away by conventional thin film etching processes to form cavity  85 , or, substrate  80  may be built-up. The result is second portion  86 . 
     In  FIG. 9A , first portion  76  from  FIG. 7C  is joined to second portion  86  from  FIG. 8D . This may be done by wafer bonding, under the application of heat and/or pressure. In some embodiments, an adhesive or solder material may be used to facilitate the bonding. The resulting micro-speaker is illustrated in  FIG. 9B  as speaker  90 , similar to micro-speaker  20  of  FIG. 2 . 
     Multiple-chamber speakers, such as micro-speakers  30 ,  40 , could be made by similar methods, but, for example, joining three portions together. It is understood that the micro magnetic devices of this disclosure, whether single chamber or multi-chamber, could be made by any number of alternate methods. 
     Thus, embodiments of the MICRO MAGNETIC DEVICE WITH MAGNETIC SPRING are disclosed. The implementations described above and other implementations are within the scope of the following claims. One skilled in the art will appreciate that the present invention can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation, and the present invention is limited only by the claims that follow. 
     The use of numerical identifiers, such as “first”, “second”, etc. in the claims that follow is for purposes of identification and providing antecedent basis. Unless content clearly dictates otherwise, it should not be implied that a numerical identifier refers to the number of such elements required to be present in a device, system or apparatus. For example, if a device includes a first coil, it should not be implied that a second coil is required in that device.