Patent Publication Number: US-2023133627-A1

Title: Antenna for a hearing assistance device

Description:
The present invention relates to an antenna for a hearing assistance device. The invention, more particularly, relates to a hearing assistance device having a housing component enclosing processing circuitry arranged in a compact block structure, and at least one actively driven antenna element arranged in between the compact block structure and the housing component. Also, the invention relates to a method of manufacturing such a hearing assistance device. 
     The purpose of the invention is to provide a hearing assistance device with an antenna element adapted for a compact design of the hearing assistance device. 
     This purpose is achieved according to the teaching of claim  1 . By using a parasitic element as claimed, the parasitic element can be used for shaping the radiation pattern and/or improving bandwidth properties. Thereby improved properties for the hearing aid antenna may be obtained despite the limited volume available in the hearing aid. 
     According to a second aspect of the invention, there is provided a method of manufacturing a hearing assistance device according to claim  14 . The dependent claims define various embodiments. 
    
    
     
       The invention will be described in further detail with reference to preferred aspects and the accompanying drawing, in which: 
         FIG.  1    shows a hearing assistive device according to one embodiment of the invention; 
         FIG.  2    illustrates schematically one embodiment of a compact block structure of a hearing aid with actively driven antenna elements and a parasitic element according to the invention; 
         FIG.  3    illustrates in cross section one embodiment of a compact block structure of a hear aid with actively driven antenna elements and a parasitic element according to the invention; 
         FIG.  4    illustrates in cross section another embodiment of a compact block structure of a hear aid with actively driven antenna elements and a parasitic element according to the invention; 
         FIG.  5    illustrates the return loss for the compact block structure of a hear aid with actively driven antenna elements and with and without a parasitic element according to the invention; 
         FIG.  6    illustrates schematically a second embodiment of a compact block structure of a hearing aid with actively driven antenna elements and a parasitic element according to the invention; and 
         FIG.  7    illustrates in cross section a further embodiment of a compact block structure of a hear aid with actively driven antenna elements and a parasitic element according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     A hearing assistive device is according to one embodiment of the invention a hearing aid  10  and is shown in  FIG.  1   . The hearing aid  10  comprises a Behind-The-Ear (BTE) housing component  12  adapted for placement Behind-The-Ear (BTE), and to which there is attached an earpiece component  14 . The major part of the electronics (including some microphones, a processor, a battery and preferably a short-range radio, e.g. Bluetooth based, and an inductive radio) of the hearing aid  10  is located inside of the housing component  12 . 
     In one embodiment, the sound producing parts of the hearing aid  10  (including a speaker) are located inside of the earpiece component  14 . The housing component  12  and the earpiece component  14  are interconnected by a cable  16  comprising two or more wires (not shown) for transferring audio processed in the housing component  12  to the speaker in the earpiece component  14 , for powering components in the earpiece component  14 , and/or for transferring audio picked up by a microphone (not shown) in the earpiece component  14  to the audio processing components in the housing component  12 . 
     In one embodiment, the sound producing parts of the hearing aid  10  (including a speaker) are located inside of the housing component  12 . The housing component  12  and the earpiece component  14  are interconnected by a sound tube (not shown) for passing sound produced by the speaker in the housing component  12  to an outlet in the earpiece component  14 . 
       FIG.  2    illustrates schematically one embodiment of a compact block structure  20  of a hearing aid with two actively driven antenna elements  23  and  24  and a parasitic element  25 ,  26  according to the invention. In one embodiment, each of the two actively driven antenna elements  23  and  24  are resonant loop antennas governed by the intended wavelength of operation. For a loop antenna intended to operate in the ISM band at approximately 2.4 GHz, the wavelength will be around 12.5 cm. 
     The loop antenna can be viewed as a folded dipole split into an open shape, just as a folded dipole is a full-sized loop, bent at two ends and squashed into a line. The shape of loop antenna is in fact a closed polygon limited by the shape of the hearing aid housing  12 . It is only required that its perimeter is slightly over one full wavelength. An antenna feed  21  drives, via a feed line  22 , the two antenna elements  23  and  24 . 
     The hearing aid according to the invention comprises, in addition to the actively driven antenna elements  23  and  24 , a passive radiator or parasitic element  25 ,  26  which is a conductive element. The parasitic element  25 ,  26  is not electrically connected to anything else. The actively driven antenna elements  23  and  24  are connected to the radio transceiver (receiver and transmitter) through a feed line, while the parasitic element  25 ,  26  is not. The parasitic element  25 ,  26  is in one embodiment a metal rod. 
     The purpose of the parasitic element  25 ,  26  is to modify the radiation pattern of the radio waves emitted by the actively driven antenna elements  23  and  24 . The modification of the radiation pattern of the radio waves may involve increasing the antenna&#39;s directivity (gain). Normally parasitic elements are used for increasing the bandwidth of the actively driven antenna element, but for hearing aids the parasitic element  25 ,  26  can be used for shaping the radiation pattern and thereby obtain improved properties for the hearing aid antenna despite the limited volume available in the hearing aid. 
     The parasitic element  25 ,  26  is acting as a passive resonator absorbing the radio waves from the nearby driven antenna elements  23  and  24  and re-radiating radio waves with a different phase. The radio waves from the actively driven antenna elements  23  and  24  and the parasitic element  25 ,  26  interfere and is strengthening the entire antenna&#39;s radiation in the desired direction and cancelling out the waves in undesired directions. 
     The parasitic element  25 ,  26  in the hearing aid antenna according to the embodiment illustrated in  FIG.  2    is mounted parallel to the driven antenna elements  23  and  24 , with all the elements in a line substantially perpendicular to the direction of radiation of the entire antenna. The way the parasitic element  25 ,  26  affects the radiation pattern depends both on the parasitic element&#39;s separation from the actively driven antenna element, and on the length of the parasitic element. 
     The driven antenna element is in one embodiment equivalent to a half-wave dipole. Therefore, the driven antenna element has a length being half a wavelength of the radio waves used. By applying appropriate matching components, including a capacitor and an inductor, it is possible to shorten the physical length of the two branches and obtain the desired electric length. The matching components may be used for antenna tuning. 
     According to the invention, two types of parasitic elements are used, a reflector and a director. A “reflector” is slightly longer (around 5%) than a half-wavelength. It serves to reflect the radio waves in the opposite direction. A “director” is slightly shorter than a half-wavelength; it serves to increase the radiation in directions defined by the actual design. 
     According to the antenna illustrated in  FIG.  2   , it is seen that parasitic element  25 ,  26  is a director (folded di-pole) arranged in the top of a well-known hearing aid antenna design and is extending along this antenna. The parasitic element  25 ,  26  has two main segments  25  extending in parallel with each other and a bridge segment  26  connecting the two main segments  25 . The two driven antenna elements  23  and  24  do each have an upper edge along which one of the two main segments  25  of the parasitic element extends. 
     When designing the overall antenna system, it is important to identify areas of the one or more driven antenna elements  23  and  24  transporting a significant current compared to other parts of the one or more driven antenna elements  23  and  24 . These areas will often provide a significant contribution of the radiation from the antenna. When coupling the one or more driven antenna elements  23  and  24  to the parasitic element  25 ,  26 , the coupling may advantageously take place along edge transporting a significant current. 
     In the embodiment shown in  FIG.  2   , the driven antenna elements  23 ,  24  and the parasitic element  25 ,  26  are coupled by mutual inductance. Mutual inductance occurs in the illustrated embodiment in a section  28  when the change in current in one inductor induces a voltage in another nearby inductor. In the illustrated embodiment, the spacing between the upper edge of one of the actively driven active elements  23  and  24  and one of the two main segments  25  of the parasitic element may in the mutual inductance section  28  be in the range from 0.5 to 5% of the wavelength at which the antenna resonates. In one embodiment, the spacing will be below 2% of the wavelength. The spacing between the upper edge of one of the actively driven active elements  23  and  24  and a respective one of the two main segments  25  of the parasitic element must be sufficiently low to ensure that mutual inductance occurs between the two parts. 
     Referring to  FIG.  2   , the mutual inductance section  28 , in which the upper edge of one of the actively driven active elements  23  and  24  and a respective one of the two main segments  25  of the parasitic element are sufficiently close to ensure that mutual inductance, extends along a significant part of the each of the two main segments  25 . Each of the actively driven active elements  23  and  24  interacts with respective main segments  25  of the parasitic element in respective mutual inductance sections  28  (only one is shown). In one embodiment, the length of the mutual inductance section  28  may be in the range from 8 to 25% of the wavelength at which the antenna resonates. 
     In the mutual inductance section  28 , the spacing between the upper edge of one of the actively driven active elements  23  and  24  and a respective one of the two main segments  25  of the parasitic element may vary, and for shorter segments exceed the range given above, but the accumulated length range fulfilling the spacing range must be in the range from 8 to 25% of the wavelength at which the antenna resonates. 
     The bridge segment  26  of the parasitic element provides an electrical connection main segments  25  of the parasitic element. In some embodiments that bridge segment  26 , may be connected to a flex print in the compact block structure  20 , and thereby grounded. 
     In one embodiment, the parasitic element according to the invention is not rod-shaped, a parasitic microstrip patch antenna can mounted above a driven patch antenna. This antenna combination resonates at a slightly lower frequency than the original element. However, the main effect is to greatly increase the impedance bandwidth (up to 10 times) of the antenna. 
     According to the invention, the parasitic elements are not electrically connected to the transmitter or receiver, and serve as passive radiators, re-radiating the radio waves to modify the radiation pattern. The directors are slightly shorter than the driven element, while the reflector(s) are slightly longer. 
     In many applications for use of passive elements for shaping the radiation pattern of an actively driven active antenna element, the spacings between the actively driven active element and passive elements vary from about 10 to 25% of a wavelength, depending on the specific design. However, according to one embodiment of the present invention, the spacings between the actively driven active element and passive elements used in a hearing aid will be just around 1 mm (0.8% of a wavelength) for an antenna operating according to the Bluetooth™ specification in the globally unlicensed (but not unregulated) industrial, scientific and medical (ISM) short-range radio frequency band at 2.4 GHz. The wavelength in free air at 2.4 GHz will be around 12.5 cm. The spacing between the actively driven active element and passive elements may in one embodiment vary from about 0.5 to 5% of a wavelength. In one embodiment of the invention, the minimum spacing between the actively driven active element and passive elements is below 2% of a wavelength. In some embodiments the actively driven active element and a passive element is separated by an insulating material. In some embodiments the passive element is embedded in a plastic wall of the hearing aid housing. 
       FIG.  3    illustrates in cross section of a compact block structure  20  of a hear aid  10  with actively driven antenna elements  23  and  24  and a parasitic element  25 ,  26  according to one embodiment of the invention. The compact block structure  20  hosts a transceiver  30  outputting and receiving radio signals via the two actively driven antenna elements  23  and  24 . The transceiver  30  is via a feed line  31  connected to the antenna feed  21 , acting as a branching point, and further via the feed line  22 , provided as metalized lanes on the compact block structure  20 , to the two actively driven antenna elements  23  and  24 . The two actively driven antenna elements  23  and  24  are in this embodiment provided as loop antennas. The housing component  12  comprises a top housing part  32  and a bottom housing part  33 . 
     The two main segments  25  of the parasitic element are embedded into the top housing part  32 . The parasitic element  25 ,  26  is provided by embedding a U-shape metal rod into the top housing part  32  during the manufacturing. The U-shaped metal rod may be over-molded or insert-molded in an injection molding process for integrating the parasitic element  25 ,  26  into the top housing part  32 . In the mutual inductance section  28 , the spacing between the upper edge of one of the actively driven active elements  23  and  24  and one of the two main segments  25  is marked as di and will be in the range from 0.5 to 5% of the wavelength at which the antenna resonates. 
     Hereby it is easily ensured that the parasitic element  25 ,  26  in  FIG.  3    is not electrically connected to the two actively driven antenna elements  23  and  24 . 
       FIG.  4    also illustrates in cross section of a compact block structure  20  of a hear aid  10  with actively driven antenna elements  23  and  24  and a parasitic element  25 ,  26  according to one embodiment of the invention. The transceiver  30  operates as described with reference to  FIG.  3   . The two actively driven antenna elements  23  and  24  are provided as loop antennas. The housing component  12  comprises a top housing part  32  and a bottom housing part  33 . 
     The two main segments  25  of the parasitic element are embedded into the top housing part  32  as metallic path&#39;s or lanes during the manufacturing. The U-shaped parasitic element  25 ,  26  is manufactured by adding a metallic pattern to housing component in a Laser Direct Structuring (LDS) process. The metallic pattern is in one embodiment provided on the inner surface of the top housing part  32 , and subsequently covered by an insulating layer  34 , e.g. an insulating foil. 
     The LDS process is based on a thermoplastic material doped with a (non-conductive) metallic inorganic compound. The metallic inorganic compound is activated by means of laser. The top housing part  32  is injection molded in a single shot (single-component injection molding), with almost no limitation in the design freedom. A laser then selectively exposes the course of the later circuit trace on the top housing part  32  with a laser beam. 
     Where the laser beam hits the plastic, the metal additive forms a micro-rough track. The metal particles of this track afterwards form the nuclei for a subsequent metallization. In an electroless copper bath, the conductor path layers arise precisely on these tracks. Successively layers of copper, nickel and gold finish can be raised in this way. 
     In the mutual inductance section  28 , the spacing between the upper edge of one of the actively driven active elements  23  and  24  and one of the two main segments  25  is marked as d 2  and will be in the range from 0.5 to 5% of the wavelength at which the antenna resonates. 
     Hereby it is easily ensured that the parasitic element  25 ,  26  in  FIG.  4    is not electrically connected to the two actively driven antenna elements  23  and  24 . 
       FIG.  5    illustrates the return loss for the compact block structure  20  of a hear aid  10  with actively driven antenna elements  23  and  24 . The curve  50  represents the compact block structure  20  shown in  FIG.  2    with the two actively driven antenna elements  23  and  24  without the parasitic element  25 ,  26 . The curve  51  represents the compact block structure  20  shown in  FIG.  2    with the two actively driven antenna elements  23  and  24  with the parasitic element  25 ,  26  according to the invention. It is seen that the return loss, in the interesting frequency band between 2.4 and 2.5 GHz, has been increased with more than 1.5 dB. 
     The return Loss for an antenna indicates the proportion of radio waves (in transmit mode) arriving at the antenna input that are rejected as a ratio against those that are accepted. A high return loss means more power into the antenna. Furthermore, an improvement of the total antenna efficiency in the interesting frequency band between 2.4 and 2.5 GHz, has been increased with more than 0.5 dB. The antenna efficiency is a measure of the electrical efficiency with which a radio antenna converts the radio-frequency power accepted at its terminals into radiated power. 
       FIG.  6    illustrates schematically one embodiment of a compact block structure  20  of a hearing aid with two actively driven antenna elements  23  and  24 . The two actively driven antenna elements  23  and  24  are interconnected by a bridge element  29 , and in operation the bridge element  29  transports a significant current between the two actively driven antenna elements  23  and  24 . 
     The bridge segment  26  of the parasitic element provides an electrical connection between the two main segments  25  of the parasitic element. When coupling the two driven antenna elements  23  and  24  to the parasitic element  25 ,  26 , the coupling may advantageously take place along an edge transporting a significant current. For the embodiment shown in  FIG.  6   , the coupling the two driven antenna elements  23  and  24  to the parasitic element  25 ,  26  takes place between the bridge element  29  and the bridge segment  26 . Mutual inductance occurs in a section  28  when the change in current in one inductor induces a voltage in another nearby inductor. 
       FIG.  7    illustrates in cross section of a compact block structure  20  of a hear aid  10  with actively driven antenna elements  23  and  24  and a parasitic element  25 ,  26  according to one embodiment of the invention. The transceiver  30  drives the two actively driven antenna elements  23  and  24  via the feed line  31 . In this embodiment, the U-shaped parasitic element  25 ,  26  is manufactured embedded in a flex-print in a sandwich structure with the conducting U-shaped parasitic element  25 ,  26  arranged in a filler layer  37  between two isolating layers  36  and  38 . In some embodiment the isolating layer  36  carries the conducting U-shaped parasitic element  25 ,  26 , while filler layer  37  and the isolating layer  38  is omitted. 
     It is important is that the parasitic element  25 ,  26  extending along the at least one actively driven antenna element  23 ,  24 . Preferably, the coupling between the parasitic element  25 ,  26  and the at least one actively driven antenna element  23 ,  24  is provided by mutual induction. Mutual induction occurs when a part of the parasitic element  25 ,  26  and extends closely along a part of the actively driven antenna element  23 ,  24  carrying a significant current. The parasitic element  25 ,  26  is electrically isolated from the at least one actively driven antenna element  23 ,  24 .