Abstract:
A cochlear implant or other auditory prosthesis utilizes an external portion worn on a recipient&#39;s head and an internal portion implanted therein. Both portions include an associated coil that transmits a signal between the two portions. The external coil has a form factor substantially similar to the implantable coil. This form factor allows the external portion to be manufactured with a smaller footprint, since components that may otherwise interfere with signal transmission (e.g., batteries) may be installed closer to the external coil.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of U.S. Provisional Patent Application No. 61/954,921, filed Mar. 18, 2014, entitled “COIL FOR SIGNAL TRANSMISSION TO IMPLANTABLE DEVICE,” the disclosure of which is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    Auditory prostheses, such as cochlear implants, include an implantable portion having a stimulating assembly with an implanted coil and an external portion having a coil, speech processing hardware and software, as well as a battery. Recipients of such devices desire the external portion to be as light and small as possible, both for comfort and unobtrusiveness. Reducing the size of such external portions is complicated however, since positioning the various components, e.g., the batteries and coil, closer to each other can reduce the quality of signals sent between the external and implanted coils. 
       SUMMARY 
       [0003]    Embodiments disclosed herein relate to systems and apparatuses that are used to transmit data between external and internal portions of medical devices. Those devices include, for example, cochlear implants or other auditory prostheses or devices. The external portion of the auditory prosthesis is powered by an on-board battery and sends signals via a coil. An implanted coil receives the signals and provides stimulation to the device recipient. The form factor of the external coil allows the external portion of the device to be small and discreet, while still providing high quality data transmission to the implantable coil. 
         [0004]    This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The same number represents the same element or same type of element in all drawings. 
           [0006]      FIG. 1  is a perspective view of an auditory prosthesis, including an implantable portion and an external portion. 
           [0007]      FIGS. 2-3  are perspective views of an external portion of an auditory prosthesis. 
           [0008]      FIGS. 4A-4B  depict schematic views of external portions of auditory prostheses. 
           [0009]      FIGS. 5A-5B  depict schematic views of external portions of auditory prostheses in accordance with embodiments of the present disclosure. 
           [0010]      FIGS. 6A-6B  depict a top view and a side sectional view, respectively, of a bobbin utilized in embodiments of the present disclosure. 
           [0011]      FIG. 7  depicts an auditory prosthesis, including an implantable coil portion, an external control coil portion, and an external modified coil portion in accordance with an embodiment of the present disclosure. 
           [0012]      FIG. 8  depicts a comparison plot of coil coupling between coils having different form factors. 
           [0013]      FIG. 9  depicts a top view of another bobbin utilized in embodiments of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    While the technologies disclosed herein have particular application in the cochlear implant devices depicted in  FIG. 1 , it will be appreciated that the systems, methods, and apparatuses disclosed can be employed in other types of hearing prostheses. For example, the embodiments disclosed herein can be used to power active transcutaneous bone conduction devices, passive transcutaneous devices, or other devices that include an external coil and an internal or implantable coil. Furthermore, the embodiments disclosed herein can be utilized to transmit signals to medical devices other than hearing prostheses. The technologies disclosed herein will be described generally in the context of external portions of medical devices where the external portions utilize a coil for transmission of data or other signals. Such signals can also include signals sent by a charging coil that charges a totally-implantable cochlear implant or other medical device. For clarity, however, the technology will be described in the context of cochlear implant auditory prostheses and, more specifically, the external portions and coils used therewith. 
         [0015]      FIG. 1  is a perspective view of an auditory prosthesis  100 , in this case, a cochlear implant, including an implantable portion  102  and an external portion  104 . The implantable portion  102  of the cochlear implant includes a stimulating assembly  106  implanted in a body (specifically, proximate and within the cochlea  108 ) to deliver electrical stimulation signals to the auditory nerve cells, thereby bypassing absent or defective hair cells. The electrodes  110  of the stimulating assembly  106  differentially activate auditory neurons that normally encode differential pitches of sound. This stimulating assembly  106  enables the brain to perceive a hearing sensation resembling the natural hearing sensation normally delivered to the auditory nerve. 
         [0016]    The external portion  104  includes a speech processor that detects external sound and converts the detected sound into a coded signal  112  through a suitable speech processing strategy. The coded signal  112  is sent to the implanted stimulating assembly  106  via a transcutaneous link. The signal  112  is sent from an external coil  114  located on the external portion  104  to an implantable coil  116  on the implantable portion  102 , via a radio frequency (RF) link. The signal  112  can be data, power, audio, or other types of signals, or combinations thereof. These coils  114 ,  116  are typically both circular in shape to maximize the coupling of magnetic flux. The efficiency of power transfer and integrity of the data transmission from one coil to the other is affected by the coil coupling coefficient (k). Coil coupling coefficient k is a unitless value that indicates the amount of the shared magnetic flux between a first coil and a second, coupled (associated) coil. As the amount of shared magnetic flux decreases (i.e., as the coil coupling coefficient k decreases), efficient power transfer between the two coils becomes increasingly difficult. Therefore it is advantageous to maximize the coil coupling coefficient k in a system where power and/or data are transferred between two coils. The stimulating assembly  106  processes the coded signal  112  to generate a series of stimulation sequences which are then applied directly to the auditory nerve via the electrodes  110  positioned within the cochlea  108 . The external portion  104  also includes a battery and a status indicator  118 . Permanent magnets  120 ,  122  are located on the implantable portion  102  and the external portion  104 , respectively. In the depicted device, the external portion includes a microphone port  124  connected to a microphone that receives sound. The microphone is connected to one or more internal processors that process and convert the sound into stimulation signals that are sent to the implantable portion  102 . 
         [0017]      FIGS. 2-3  are perspective views of an external portion  200  of an auditory prosthesis and are described simultaneously. The external portion  200  includes a body  202  and an external coil  204  connected thereto. The body  202  can include a permanent magnet  206  as described above. The external portion  200  can include an indicator  208  such as a light emitting diode (LED). A battery door  210  (depicted removed in  FIG. 3 ) covers a receptacle  212  that includes a battery  214  that provides internal power to the various components of the external portion  200  and the implantable portion. The battery  214  is matingly received in the receptacle  212 . A microphone  216  receives sound that is processed by components within the external portion  200 . As can be seen, the battery  214  is installed proximate the coil  204 , generally above the coil  204  itself. It is desirable that auditory prostheses maintain a high coil quality factor (Q). Coil quality factor Q is a unitless value that indicates the how much energy is lost relative to the energy stored in the resonant circuit that includes the coil. A higher coil quality factor Q indicates a lower rate of energy loss relative to the stored energy of the resonant circuit. Coil quality factor Q can be calculated for an ideal series RLC circuit as depicted in Equation I: 
         [0000]    
       
         
           
             Q 
             = 
             
               
                 
                   1 
                   R 
                 
                  
                 
                   
                     L 
                     C 
                   
                 
               
               = 
               
                 
                   
                     ω 
                     0 
                   
                    
                   L 
                 
                 R 
               
             
           
         
       
     
         [0000]    Here, L is the measured inductance of the coil, R is the measured resistance of the coil, and ω 0 =2×Pi×Frequency. As the coil quality factor Q decreases, it becomes increasingly difficult to transfer power efficiently from one coil to an associated coil. Therefore, it is advantageous to maximize the coil quality factor Q in a system where power is transferred between two coils. 
         [0018]    A high coil quality factor Q is desirable, even while the electronics and batteries are in close proximity to the coil, as depicted in  FIGS. 2 and 3 . Placing metallic components, e.g., a battery  214 , above the coil  204 , as depicted in  FIGS. 2 and 3 , has an adverse effect on coil Q, but does keep to a minimum the effective length L CB  of the coil/battery arrangement which is directly related to the size of the external portion  200 . In  FIG. 3 , the effective length Lcb is limited to the outer diameter of the coil  204 . A reduced coil Q, however, results in a lower efficiency RF link, which ultimately results in a shorter battery life. To address this in the configuration depicted in  FIGS. 2 and 3 , a shielding material such as ferrite may be disposed between the battery  214  and coil  204 . This can help alleviate the adverse effect on coil Q, but adds weight and size to the device, which is also undesirable, since the external portion  200  is worn on the head of a recipient. 
         [0019]      FIGS. 4A-4B  depict schematic views of external portions  300  of auditory prostheses. In  FIG. 4A , the external portion  300   a  includes an external coil  302   a  and, in this case, two batteries  304   a . In contrast to the device of  FIGS. 2 and 3 , the external portion  300   a  of  FIG. 4A  is arranged such that the batteries  304   a  are disposed next to the coil  302   a , where a center  308   a  of the coil  302   a  is a distance Da from a center  310   a  of the battery  304   a . This configuration results in an increase in coil Q as compared to the device of  FIGS. 2 and 3 , but also a significant increase in the effective length La of the coil/battery arrangement. In testing, it has been discovered that the depicted arrangement has a coil Q of about 89.3 when the coil is made to resonate at about 5 MHz. Thus, in Equation I, L=5.288 μH, R=1.86 Ohms, and Frequency=5 MHz. This coil also has a coupling coefficient k to a second coil of about k=0.25 when the two coils are separated by about 3.0 mm. However, as apparent from  FIG. 4A , this configuration ultimately increases the total footprint of a housing  306   a  of the external portion  300   a , which is undesirable. 
         [0020]    In  FIG. 4B , the batteries  304   b  are arranged so as to only partially overlap the coil  302   b , where a center  308   b  of the coil  302   b  is a distance Db from a center  310   b  of the battery  304   b . Here, the distance Db is less than the distance Da of the device depicted in  FIG. 4A . This shorter distance Db decreases the effective length Lb of the coil/battery arrangement (relative to the effective length La of  FIG. 4A ) and thus the housing  306   b  size. However, due to the proximity of the batteries  304   b  and the coil  302   b , the drop in coil Q is significant and undesirable. In testing, it has been discovered that the depicted arrangement has a coil Q of about 36.4 when the coil is made to resonate at about 5 MHz. Thus, in Equation I, L=5.1 μH, R=4.4 Ohms, and Frequency=5 MHz. The coupling coefficient k is largely unchanged in this configuration because the size, shape, and relative position of the two coils has not changed. 
         [0021]      FIGS. 5A-5B  depict schematic views of external portions  400   c ,  400   d  of auditory prostheses in accordance with embodiments of the present disclosure. In  FIG. 5A , the external portion  400   c  includes an external coil  402   c  and two batteries  404   c . The centers  408   c ,  410   c , respectively, are a distance Dc from each other. Notably, this distance Dc is the same as the distance Db depicted in  FIG. 4B , above. In this embodiment, however, the batteries  404   c  do not overlap the coil  402   c . Instead, the outer perimeter of the coil  402   c  has been modified to decrease the total perimeter length as compared to the coils  302   a ,  302   b  depicted above, by including a curved (in this case, substantially circular) portion  412   c  and a substantially linear portion  414   c . Coil  402   c  has a truncated circle shape. This modification from the round coils  302   a ,  302   b  depicted above enables the effective length Lc of the coil/battery arrangement to be substantially the same as the effective length Lb, which results in a similarly-sized housing  406   c . It has been discovered that, by eliminating overlap between the coil  402   c  and batteries  404   c , coil Q is substantially increased in comparison to the arrangement of  FIG. 4B . In testing, the depicted embodiment of external device  400   c  has a coil Q of about 74.6 when the coil is made to resonate at about 5 MHz. Thus, in Equation I, L=5.268 μH, R=2.22 Ohms, and Frequency=5 MHz. This increase in coil Q is in excess of 200%, or double that the coil of  FIG. 4B . A coil with the shape of  402   c  has a slightly smaller coupling coefficient k than a round coil. In testing, it has been discovered that the depicted arrangement has a coupling coefficient to a second coil of about k=0.24 when the two coils are separated by about 3.0 mm. By utilizing a truncated circular coil shape as depicted in  FIG. 5A , instead of a round coil as depicted in  FIG. 4B , coil quality factor Q has more than doubled, while but the coil coupling coefficient k has only reduced by about 4% (from about 0.25 to about 0.24). The resulting power transfer efficiency increase is a significant benefit of the coil shape  402   c.    
         [0022]    In  FIG. 5B , the external portion  400   d  includes a coil  402   d  and two batteries  404   d . The centers  408   d ,  410   d , respectively, are a distance Dd from each other. Notably, this distance Dd is the same as the distance Db depicted in  FIG. 4B , above. In this embodiment, the outer perimeter of the coil  402   d  also has been modified to decrease the total perimeter length, by including a curved (in this case, substantially circular) portion  412   d  and two substantially linear portions  414   d . This modification enables the effective length Ld of the coil/battery arrangement to be substantially the same as the effective length Lb, which results in a similarly-sized housing  406   d . It has been discovered that, by eliminating overlap between the coil  402   d  and batteries  404   d , coil Q is substantially increased in comparison to the arrangement of  FIG. 4B . Coil Q is anticipated to be similar to that of the prosthesis  400   c . In the external portions  400   c ,  400   d , a shielding material such as ferrite may be disposed between the batteries and coil to further increase Q, although, as described above, this may increase weight of the external portion  400   c ,  400   d.    
         [0023]      FIGS. 6A-6B  depict a top view and a side sectional view, respectively, of a bobbin  500  utilized in embodiments of the present disclosure, and are described together. The bobbin  500  is used as a base about which to wind a wire  510  to form an external coil  512  to be utilized in an auditory prosthesis. The bobbin  500  includes a base plate  502  with a ring  504  extending therefrom. A second plate  506  is disposed parallel to the base plate  502  so as to form a channel  508  at least partially defined therebetween. The channel  508  is configured so as to receive the wire  510  that is wound about the ring  504 , in a particular arrangement, so as to form the coil  512 . In the depicted embodiment, the wire  510  is a 40 strand, 46 AWG wire having a diameter of about 420 μm, and is wound ten times to form the coil  512 . Wires having other diameters or sizes can be utilized to form a coil, which can have greater than or fewer than ten turns. 
         [0024]    In certain embodiments, the shape of the bobbin  500  and the coil  512  contained therein, can be defined by the geometric structure thereof. The depicted bobbin  500  (and therefore, the coil  512 ) has a shape of a truncated circle  501 . In other embodiments, the bobbin can be a D-shape. In the depicted embodiment, the diameter D represents an interior diameter of the bobbin  500  and, therefore, the interior diameter of the coil  512 . The diameter D (or radius R) defines a curved portion  512  of the truncated circle shape of the perimeter. In the depicted embodiment, the curved portion  512  is called the primary arc portion and has a primary arc length S 1 . The truncated circle  501  is also defined by a substantially straight portion  514  or a chord. The substantially straight portion  514  can connect to the curved portion  512  at a curved or sharp interface  520 , although a curved interface can be more desirable to reduce or prevent damage, stress, or kinks to the coil  512 . In the depicted embodiment, the chord  514  is a distance R T  from a line parallel to the substantially straight portion  514  that also intersects the center C of the truncated circle  501 . The substantially straight portion  514  has a chord length C L . The truncated circle  501  can also be defined by the absent circular segment  516  partially defined by the substantially straight portion  514  and a secondary arc portion length S 2 . A center point of the secondary arc portion  518  is a distance R S  from the substantially straight portion  514 . The radius of the curved portion  512  of the truncated circle can be defined as Equation II: 
         [0000]    
       
      
       R=R 
       T 
       +R 
       S  
      
     
         [0025]    In certain embodiments, the primary arc portion length S 1  can be about 70% to about 90% of the total length of the perimeter, which is the sum of the primary arc portion length S 1  and the chord length C L . In other embodiments, the primary arc portion length S 1  is about 75% of the total length of the perimeter. The truncated circle and the circular segment  516  define areas bound by, respectively, the primary arc portion  512  and chord  514 , and the secondary arc portion  518  and chord  514 . In embodiments, the area of the circular segment  516  can be between about 5% and about 25% of the area of a complete circle (which includes the area of the truncated circle  501  and the circular segment  516 ). In other embodiments, the area of the circular segment  516  is about 10% of the area of the complete circle. 
         [0026]      FIG. 7  depicts an auditory prosthesis  100 , including an implantable portion  102 , an external control portion  104 , and an external modified portion  104 ′ in accordance with an embodiment of the present disclosure. The various elements depicted are described generally in  FIG. 1 , and thus generally are not described further. The implantable portion  102  includes an implantable coil  116  that, in this embodiment, has a generally circular base form factor. The implantable coil  116  has a radius R I  and an area A I  defined by the radius R I . The external control portion  104  includes an external control coil  114 . That also has a generally circular form factor. The external control coil  114  has a radius R C  and an area A C  defined by the radius R I . In certain embodiments, R C  can be greater than R I  to help ensure adequate data transmission from the external control coil  114  to the implantable coil  116 .  FIG. 7  also depicts an external modified portion  104 ′, which is an external portion of the auditory prosthesis  100 . The external modified portion  104 ′ includes the same components as the external control portion  104 , e.g., a magnet  122 ′, an indicator  118 ′, and so on. The coil  114 ′, however is a modified coil, in that it has a modified base form factor substantially similar to the base form factor of the implantable coil  116 , and that has a radius R M  and an area A M  defined at least in part by the radius R M . The substantial similarity stems from the condition that the implantable coil  116  has a circular base form factor, while the modified base form factor of the modified external coil  114 ′ is a truncated circle. In certain embodiments, the radius R M  of the modified external coil  114 ′ is larger than the radius R C  of the control coil  114 . However, due to the truncated circle shape of the modified external coil  114 ′, the area A M  of the modified external coil  114 ′ is less than the area A C  of the external control coil  114 . In other embodiments, the radius R C  of the external control coil  114  is substantially the same as the radius R M  of the modified external coil  114 ′. 
         [0027]      FIG. 8  depicts a comparison plot of coil coupling coefficient k between coils having different form factors. For the auditory prosthesis depicted in  FIG. 7  above, where an implantable coil is utilized with an external control coil or a modified external coil, the coil coupling coefficient k can be measured between the implanted coil and either external coil (i.e., the control coil or the modified coil). As can be seen from the plot, the coil coupling coefficient k between an implanted coil and a truncated circle coil is between about 92% to about 96% of the coil coupling coefficient k between an implanted coil and a full coil, at various implant distances. 
         [0028]      FIG. 9  depicts a top view of another bobbin  600  utilized in embodiments of the present disclosure. As with the embodiment of  FIG. 7 , the bobbin  600  includes a base plate  602  with a ring  604  extending therefrom. A second plate (not shown in this view) is disposed parallel to the base plate  602  so as to form a channel  608 . The bobbin  600  is substantially oval in shape, and thus may be defined by a primary radius R P  and a secondary radius R S . It has been discovered that bobbins (and thus coils) having a form factor such as an oval can also be utilized with an implanted coil having a circular form factor while still maintaining acceptable coil quality Q and coil coupling k. Additionally, the non-round coils described herein need not be formed by wrapping a wire about a bobbin. For example, a non-round coil may be formed by traces on a printed circuit board. 
         [0029]    This disclosure described some embodiments of the present technology with reference to the accompanying drawings, in which only some of the possible embodiments were shown. Other aspects can, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments were provided so that this disclosure was thorough and complete and fully conveyed the scope of the possible embodiments to those skilled in the art. 
         [0030]    Although specific embodiments were described herein, the scope of the technology is not limited to those specific embodiments. One skilled in the art will recognize other embodiments or improvements that are within the scope of the present technology. Therefore, the specific structure, acts, or media are disclosed only as illustrative embodiments. The scope of the technology is defined by the following claims and any equivalents therein.