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(11) | EP 2 871 860 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | A hearing aid with an antenna |
| (57) A hearing aid having an antenna is provided, the hearing aid being adapted for wireless
communication, such as for wireless communication with accessory and/or other hearing
aids. The hearing aid comprises a hearing aid assembly having a first side and a second
side, a signal processor, and a wireless communications unit. The wireless communications
unit is connected to the signal processor. The hearing aid comprises an antenna for
emission and reception of an electromagnetic field. The antenna is connected to the
wireless communications unit and the antenna has an excitation point. A first branch
of the antenna extends from the excitation point and a second branch of the antenna
extends from the excitation point, and at least a part of the second branch extends
from the first side to the second side. The second branch has at least one ground
connection.
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TECHNICAL FIELD
[0001] The present disclosure relates to the field of hearing aids having antennas, especially adapted for wireless communication, such as for wireless communication with accessory and/or other hearing aids.
BACKGROUND
[0002] Hearing aids are very small and delicate devices and comprise many electronic and metallic components contained in a housing small enough to fit in the ear canal of a human or behind the outer ear. The many electronic and metallic components in combination with the small size of the hearing aid housing impose high design constraints on radio frequency antennas to be used in hearing aids with wireless communication capabilities.
[0003] Moreover, the antenna in the hearing aid has to be designed to achieve a satisfactory ear-to-ear performance despite the limitation and other high design constraints imposed by the size of the hearing aid.
SUMMARY
[0004] It is an object of the present invention to overcome at least some of the disadvantages as mentioned above, and it is a further object to provide a hearing aid. The hearing aid comprises a hearing aid assembly having a first side and a second side, a signal processor, and a wireless communications unit. The wireless communications unit is connected to the signal processor. The hearing aid comprises an antenna for emission and reception of an electromagnetic field. The antenna is connected to the wireless communications unit and the antenna has an excitation point. A first branch of the antenna extends from the excitation point and a second branch of the antenna extends from the excitation point. At least a part of the second branch extends from the first side to the second side. The second branch has at least one ground connection.
[0005] Typically, the antenna is configured so that current flowing in the antenna forms standing waves along the length of the antenna. The length of an antenna may for example be tailored so that the length of the antenna equals a quarter wavelength of the desired electromagnetic field, or any multiple, or any odd multiple, thereof. In one or more embodiments, an absolute relative difference between the total length of the antenna and the wavelength may be less than a threshold, such as less than 10%, 25%, etc. In some embodiments a total length of the antenna is between three quarters of a wavelength and five quarters of a wavelength.
[0006] In some embodiments, a current in the antenna may have a maximum in the second branch, such as for example in the part of the second branch which extends from the first side to the second side.
[0007] The first end may be free, so that the first end may be a free end or an open end. If the first end is free, the current at the end of the first branch may be near zero. Alternatively, the first end may be interconnected with the excitation point via a third branch. The third branch may be different from the first branch. The current in the third branch may have a local maximum near the excitation point, such as a further local maximum. In some embodiments, the third branch extends along the first side of the hearing aid assembly.
[0008] Likewise, the second end may be free, so that the second end may be a free end or an open end. If the second end is free, the current at the end of the second branch may be near zero. Alternatively, the second end may be interconnected with the excitation point via a fourth branch. The fourth branch may be different from the second branch. In some embodiments, the fourth branch extends along the second side of the hearing aid assembly.
[0009] In one or more embodiments, the first and/or second branch may form a loop. The loop formed by the first and/or the second branch may return to the excitation point. An advantage of a loop formed by the first and/or the second branch is that it may provide a relatively long total length of the antenna and therefore may improve the ear-to-ear performance of the hearing aid. In some embodiments, the first and/or second branch may be a plate or a dish of conductive material.
[0010] In some embodiments, the first antenna branch may form a loop along the first side and/or the second antenna branch may form a loop along the second side.
[0011] At least a part of the second branch extends from the first side to the second side. The part of the second antenna branch may thus extend from proximate the first side of the hearing aid assembly to proximate the second side of the hearing aid assembly, such as from adjacent the first side to adjacent the second side, or the at least part of the second branch may extend from a point or position at or along the first side to a point or position at or along the second side.
[0013] At least a part of the first branch may extend along the first side, and/or at least a part of the second branch may extend along the second side. The first side may be a longitudinal side of the hearing aid assembly and the second side may be another longitudinal side of the hearing aid assembly. The first side may be opposite the second side. The second branch may be partly parallel to the first branch. In some embodiments, the part of the first branch extending along the first side of the hearing aid, and the part, i.e. the other part, of the second branch extending along the second side of the hearing aid may be symmetric parts, i.e. so that the said parts form symmetric antenna structures about a plane through the antenna, and/or so that the said parts may have an, at least substantially, same shape.
[0014] In general, various branches of the antenna may be formed having different geometries, the branches may be wires or patches, bend or straight, long or short as long as they obey the above relative configuration with respect to each other. In some embodiments, a total length of the antenna is between three quarters of a wavelength and five quarters of a wavelength.
[0015] The hearing aid may be a behind-the-ear hearing aid configured to be positioned behind the ear of the user during use, and the first side may be a first longitudinal side of the hearing aid and the second side may be a second longitudinal side of the hearing aid. The antenna may be accommodated in the housing with its longitudinal direction along the length of the housing. Preferably, the antenna is accommodated within the hearing aid housing, preferably so that the antenna is positioned inside the hearing aid housing without protruding out of the housing.
[0016] Typically, an excitation point is electrically connected to a source, such as the wireless communication unit, such as a radio chip, such as a transceiver, a receiver, a transmitter, etc. The antenna may be excited using any conventional means, using a direct or an indirect or coupled feed, and for example be fed using a feed line, such as a transmission line. The current induced in the antenna may have a first local maximum at a proximate excitation point of the antenna.
[0017] The first branch of the antenna may extend from the excitation point to a first end of the antenna, and the second branch of the antenna may extend from the excitation point to a second end of the antenna. The antenna may be structured with two branches extending from the same excitation point.
[0018] A first distance from the excitation point to the first end may be smaller than a second distance from the excitation point to the second end. In some embodiments, the relative difference between the first distance and the second distance may be less than 25%, such as less than 10%. The distance may be measured along the first branch and along the second branch, respectively.
[0019] In some embodiments, the excitation point may be provided at an edge part of the hearing aid assembly. The excitation point may be interconnected with the wireless communications unit for example via transmission lines.
[0020] The antenna may be configured with a length and a structure so that a current in the antenna may have a magnitude of zero at a point on the first branch and/or at a point on the second branch.
[0021] The hearing aid with the antenna may be configured so that the second branch of the antenna has a ground connection. By providing a ground connection at the second branch, the antenna may have better tuning properties, and may be less dependent on the ground potential of the printed circuit board.
[0022] The antenna may be interconnected with the ground plane at some point along the second branch, for example by providing a transmission line from the antenna to a ground plane of the hearing aid, such as for example to a printed circuit board of the hearing aid.
[0023] The ground connection may be provided along the second side of the hearing aid, such as at any point of the antenna extending along the second side of the hearing aid. In some embodiments, the ground connection is provided at at least a distance of 1/8 of a wavelength from the second end.
[0024] In one or more embodiments, the hearing aid with the antenna may be structured so that the antenna excitation point is positioned at the first side of the hearing aid and the antenna ground connection is positioned at the second side of the hearing aid.
[0025] The part of the second branch extending from the first side to the second side, may extend from the first side to the second side via a midpoint of the hearing aid. The midpoint may be an absolute geometric midpoint, or the midpoint may be an approximate midpoint provided within an interval, such as within an interval of +/-5%, +/- 10%, +/- 15%, etc. of the geometric midpoint. Typically, the midpoint will be a midpoint at an outer side of the hearing aid assembly for the antenna to extend from the first side to the second side via the midpoint.
[0026] The midpoint of the hearing aid may be positioned at a partition plane for the hearing aid, so that the partition plane defines a partitioning of the hearing aid in a first part and a second part. The partition plane may partition the hearing aid in two equal parts, and may e.g. define a middle of the hearing aid.
A distance from the midpoint to the excitation point and a distance from the midpoint to the ground connection may be of equal size. The relative difference between the distance from the midpoint to the excitation point and the distance from the midpoint to the ground connection may be less than a threshold T2. The threshold T2 may be e.g. 25%, or 10%.
[0027] In some embodiments, the first antenna branch has a first length and the second antenna branch has a second length, and wherein the sum of the first length and the second length may correspond to at least 90% of a total length of the antenna.
[0028] The length of the first branch and/or the length of the second branch may be at least λ/4, such as substantially λ/4, such as at least λ/4 +/-10%.
[0029] The first length may correspond to the second length, so that the first and second branches have a same length, or the first length of the first branch may be different from the length of the second branch.
[0030] The first branch may have a first length and the second branch may have a second length. The first length may be different from the second length, and in one or more embodiments, the second length may be longer than the first length. The length of the first or the second branch may be equal to, such as substantially equal to λ/4, where λ corresponds to the frequency of the wireless communications unit. The first length and/or the second length may be at least λ/4.
[0032] The hearing aid disclosed herein may be configured for operation in ISM frequency band. Preferably, the antennas are configured for operation at a frequency of at least 1 GHz, such as at a frequency between 1.5 GHz and 3 GHz such as at a frequency of 2.4 GHz.
[0033] In the following the invention is described primarily with reference to a hearing aid, such as a binaural hearing aid. It is however envisaged that the disclosed features and embodiments may be used in combination with any aspect of the invention.
[0034] The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
[0035]
Fig. 1 shows a block-diagram of a hearing aid,
Figs. 2a-b show schematically an exemplary implementation of a hearing aid comprising an antenna according to an embodiment of the present disclosure,
Fig. 3 shows schematically an exemplary implementation of a hearing aid comprising an antenna according to an embodiment of the present disclosure,
Fig. 4 shows schematically an exemplary implementation of a hearing aid comprising an antenna according to an embodiment of the present disclosure,
Figs. 5a and 5b show schematically an exemplary implementation of an antenna for a hearing aid according to an embodiment of the present disclosure,
Fig. 6 shows schematically an exemplary implementation of an antenna according to an embodiment of the present disclosure,
Fig. 7 shows schematically an exemplary implementation of an antenna according to an embodiment of the present disclosure,
Fig. 8 is a 3D illustration of a behind-the-ear hearing aid having an exemplary antenna,
Figs. 9a-b show a hearing aid positioned on the right and left ear of a user's head with the hearing aid comprising an antenna according to an embodiment of this disclosure.
DETAILED DESCRIPTION OF THE DRAWINGS
[0036] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
As used herein, the term "antenna" refers to an electrical device which converts electric power into radio waves. An antenna, such as an electric antenna, may comprise an electrically conductive material connected to e.g. a wireless communications unit, such as a radio chip, a receiver or a transmitter.
[0037] Fig. 1 shows a block-diagram of a hearing aid. In Fig. 1, the hearing aid 10 comprises a microphone 11 for receiving incoming sound and converting it into an audio signal, i.e. a first audio signal. The first audio signal is provided to a signal processor 12 for processing the first audio signal into a second audio signal compensating a hearing loss of a user of the hearing aid. A receiver is connected to an output of the signal processor 12 for converting the second audio signal into an output sound signal, e.g. a signal modified to compensate for a users hearing impairment, and provides the output sound to a speaker 13. Thus, the hearing instrument signal processor 12 may comprise elements such as amplifiers, compressors and noise reduction systems etc. The hearing aid may further have a feedback loop for optimizing the output signal. The hearing aid has a wireless communication unit 14 (e.g. a transceiver) for wireless communication interconnected with an antenna 15 for emission and reception of an electromagnetic field. The wireless communication unit 14 may connect to the hearing aid signal processor 12 and an antenna 15, for communicating with external devices, or with another hearing aid, located at another ear, in a binaural hearing aid system.
[0038] The specific wavelength, and thus the frequency of the emitted electromagnetic field, is of importance when considering communication involving an obstacle. In the present invention the obstacle is a head with a hearing aid comprising an antenna located closed to the surface of the head. If the wavelength is too long such as a frequency of 1 GHz and down to lower frequencies greater parts of the head will be located in the near field region. This results in a different diffraction making it more difficult for the electromagnetic field to travel around the head. If on the other hand the wavelength is too short, the head will appear as being too large an obstacle which also makes it difficult for electromagnetic waves to travel around the head. An optimum between long and short wavelengths is therefore preferred. In general the ear to ear communication is to be done in the band for industry, science and medical with a desired frequency centred around 2.4 GHz.
[0039] Fig. 2a shows schematically an embodiment of a hearing aid 20 comprising an antenna 25, a wireless communications unit 24 and a ground plane 26. Antenna 25 comprises an excitation point 23, a first branch 21, and a second branch 22. The first branch 21 extends from the excitation point 23. The second branch 22 extends from the excitation point 23. The first branch 21 and the second branch 22 may extend from the excitation point 23 in different directions. The excitation point 23 is connected to the wireless communications unit 24 via a transmission line 27. A part 221 of the second branch 22 extends from a first side of the hearing aid 20 to a second side of the hearing aid 20.
[0040] Fig. 2b shows schematically another embodiment of a hearing aid 20. The hearing aid 20 corresponds to the hearing aid in Fig. 2a. Additionally, the hearing aid as shown in Fig. 2b has a ground connection 223, connecting the second branch 22 with the ground plane 26 which may be a printed circuit board. The ground connection 223 is positioned across from the excitation point for the antenna, and the distance from the midpoint 222 to the excitation point 23 and the distance from the midpoint 222 to the ground connection 223 may be substantially equal.
[0041] A distance from the midpoint 222 to the excitation point 23 and a distance from the midpoint 222 to the ground connection 223 may be of equal size. The relative difference between the distance from the midpoint 222 to the excitation point 23 and the distance from the midpoint 222 to the ground connection 223 may be less than a threshold T2. The threshold T2 may be e.g. 25%, or 10%.
[0042] The partition plane 224 may be a symmetry plane 224 for the antenna 25 so that the shape of the first branch 21 of the antenna is symmetric with the shape of the second branch 22 of the antenna with respect to the symmetry plane 224, irrespective of the ground connection 223. The partition plane 224 may extend exactly mid through the hearing aid, or the partition plane may extend anywhere between a first side of the hearing aid and a second side of the hearing aid.
[0043] In general, various branches of the antenna may be formed with different geometries, they may be wires or patches, bend or straight, long or short as long as they obey the above relative configuration with respect to each other such that the antenna comprises an excitation point, a first branch of the antenna extending from the excitation point and a second branch of the antenna extending from the excitation point and such that the first branch has a first end, the first end being free or being interconnected with the excitation point via a third branch and such that at least a part of the second branch extends from the first side to the second side.
[0044] Fig. 3 shows schematically an embodiment of a hearing aid 30 according to the present disclosure. The hearing aid 30 comprises an antenna 35. The antenna 35 comprises an excitation point 33, a first branch 31, and a second branch 32. The first branch 31 extends from the excitation point 33. The second branch 32 extends from the excitation point 33. The second branch 32 comprises a part 321 that extends from the first side to the second side, wherein the part 321 extends from the excitation point 33 to the second side in a curve. The first branch 31 and/or the second branch 32 may have any width and/or any shape configured according to hearing aid restrictions and/or antenna optimization.
[0045] Fig. 4 shows schematically an embodiment of a hearing aid 40 according to the present disclosure. The hearing aid 40 comprises an antenna 45. The antenna 45 comprises an excitation point 43, a first branch 41, and a second branch 42. The first branch 41 extends from the excitation point 43 to a first end 412. The second branch 42 extends from the excitation point 43 to a second end 422. In Fig. 4, the second branch 42 comprises a part 421 that extends from a first side of the hearing aid 40 to a second of the hearing aid 40. The part 421 extends from the excitation point 43 positioned at an intersection of the first branch 41 with the second branch 42, wherein the part 421 extends from a first side to a second side directly from the excitation point to thereby obtain a high current at the bridge. The first end 412 and/or the second end 422 may be a free end. The current is seen to be zero at the free ends 412, 422 of the antenna 45. The ends 412, 422 may also be open or have an infinite impedance. Alternatively, the first end 412 and/or the second end 422 may be interconnected with the excitation point 43 via a third and/or forth branch.
[0046] The third branch may be different from the first branch, and/or the forth branch may be different from the second branch.
[0047] Fig. 5a shows schematically an embodiment of a hearing aid having an antenna according to the present disclosure. The antenna 55 comprises an excitation point 53, a first branch 51, and a second branch 52. The first branch 51 has a first length and the second branch 52 has a second length. The first length and the second length are seen to be different. The second length is longer than the first length. In Fig. 5a, a first distance d1 from the excitation point to the first end is smaller than a second distance d2 from the excitation point to the second end. The first or second length may be equal to the first distance d1 or the second distance d2 respectively. The distance is typically measured along the first branch 51 and the second branch 52, respectively.
[0048] The relative difference between the first distance d1 and the second distance d2 may be less than a threshold T1. The threshold T1 may be e.g. 25%, or 10%. The antenna 55 may be formed so that the distances d1 and d2 fulfil the following:
wherein λ is the wavelength. In one or more embodiments, the first length and/or the second length is at least λ/4.
[0049] Fig. 5b shows schematically another embodiment of a hearing aid having an antenna according to the present disclosure. The antenna 55 comprises an excitation point 53, a first branch 51, and a second branch 52. The first branch 51 has a first length and the second branch 52 has a second length. The first length and the second length are seen to be similar or identical. The second length is the same length as the first length. In Fig. 5b, a first distance d1 from the excitation point to the first end is the same as a second distance d2 from the excitation point to the second end. The first or second length may be equal to the first distance d1 or the second distance d2 respectively. The distance is typically measured along the first branch 51 and the second branch 52, respectively.
[0050] The length of the first and/or second branches 51, 52 is at least λ/4 (where λ is the resonance wavelength for the wireless communications unit).
[0051] Fig. 6 shows schematically an embodiment of a hearing aid having an antenna according to the present disclosure. The antenna 65 comprises an excitation point 63, a first branch 61, and a second branch 62. The first branch 61 is a plate. The second branch 62 comprises a plate and a bridge 621. The bridge 621 is a conducting element connecting the two plates, i.e. the first branch 61 and the second branch 62. In one or more embodiments, the length of the antenna branch may be measured along a top part of a plate forming the first and/or second branch 61, 62 is at least λ/8 and the length along a side part of a plate forming the first and/or second branch 61, 62 is at least λ/8, thus having a total first and/or second length along the current path of at least λ/4.
[0052] Fig. 7 shows schematically an embodiment of a hearing aid having an antenna according to the present disclosure. The antenna 75 comprises an excitation point 73, a first branch 71, and a second branch 72. The first branch 71 forms a loop. The second branch 72 forms a loop and further comprises a bridge 721. The length d3 of the loop forming part of the second branch 72 may be small or it may be greater than λ/4. If the length d3 is greater than λ/4, the current has a zero at a point on the loop. The exact location of the zero depends on the magnitude of the current at the start of the loop (where the loop of the second branch 72 connects with the bridge 721) and the length d3 of the loop.
[0054] Fig. 8 shows a behind-the-ear hearing aid 110 configured to be positioned behind the ear of the user during use. The behind-the-ear hearing aid 110 comprises an antenna 115, a wireless communication unit 119 (e.g. a radio chip) with a transmission line 119a to an antenna 115, a battery 116, a signal processor 117 and a sound tube 118 leading to the entrance of the ear canal. The antenna 115 comprises an excitation point 113, a first branch 111, and a second branch 120. The second branch 120 comprises a part 121 extending from a first side 130 of the hearing aid assembly to a second side 140 of the hearing aid assembly. The first side 130 of the hearing aid assembly is opposite the second side 140 of the hearing aid assembly 110. The excitation point 113 is at the first side 130 of the hearing aid assembly. The first branch 111 may in one or more embodiments be a first structure, such as a first resonant structure, provided proximate the first side 130 of the hearing aid, and the second part 120 of the antenna 115 may in one or more embodiments a second structure, such as a second resonant structure, provided proximate a second side 140 of the hearing aid. At least a part of the first branch 111 extends on the first side 130. At least a part of the second branch 120 extends on the second side 140. The first side 130 or the second side 140 is positioned parallel with the surface of the head of the user when the hearing aid is worn in its operational position by the user. The first side 130 is a first longitudinal side of the hearing aid 110. The second side 140 is a second longitudinal side of the hearing aid 110.
[0055] Figs. 9a-b show an exemplary behind-the-ear hearing aid worn in its operational position by a user. Fig. 9a shows the behind-the-ear hearing aid 150 placed on the right ear of the user. The behind-the-ear hearing aid 150 comprises an antenna 155.
[0056] The antenna 155 comprises a first branch 151 and a second branch 152. The first branch 151 of the antenna is on the side of the hearing aid 150 facing away from the head of the user.
[0058] In Fig. 9b, the second branch 152 (i.e. the other branch than the one shown in Fig. 9a) is on the side of the hearing aid 150 facing away from the head of the user.
[0059] Figs. 9a-b illustrates the symmetry of the antenna implemented in a hearing aid according to this disclosure. The hearing aid disclosed herein is configured to be operational whether it is placed on the right ear or on the left ear.
[0060] The antenna 155 emits an electromagnetic field that propagates in a direction parallel to the surface of the head of the user when the hearing aid housing is positioned in its operational position during use, whereby the electric field of the emitted electromagnetic field has a direction that is orthogonal to, or substantially orthogonal to, the surface of the head during operation. In this way, propagation loss in the tissue of the head is reduced as compared to propagation loss of an electromagnetic field with an electric field component that is parallel to the surface of the head. Diffraction around the head makes the electromagnetic field emitted by the antenna propagate from one ear and around the head to the opposite ear.
1. A hearing aid comprising
a hearing aid assembly having a first side and a second side,
a signal processor,
a wireless communications unit, the wireless communications unit being connected to the signal processor,
an antenna for emission and reception of an electromagnetic field and being connected to the wireless communications unit, the antenna having an excitation point,
wherein a first branch of the antenna extends from the excitation point and a second branch of the antenna extends from the excitation point, at least a part of the second branch extending from the first side to the second side, and wherein the second branch has at least one ground connection.
a hearing aid assembly having a first side and a second side,
a signal processor,
a wireless communications unit, the wireless communications unit being connected to the signal processor,
an antenna for emission and reception of an electromagnetic field and being connected to the wireless communications unit, the antenna having an excitation point,
wherein a first branch of the antenna extends from the excitation point and a second branch of the antenna extends from the excitation point, at least a part of the second branch extending from the first side to the second side, and wherein the second branch has at least one ground connection.
2. A hearing aid according to claim 1, wherein at least a part of the first branch extends
along the first side, and/or wherein at least a part of the second branch extends
along the second side.
3. A hearing aid according to any of the previous claims, wherein the ground connection
is provided along the second side.
4. A hearing aid according to any of the previous claims, wherein the first branch of
the antenna extends from the excitation point to a first end, and wherein the second
branch of the antenna extends from the excitation point to a second end.
5. A hearing aid according to claim 4, wherein the first end and/or the second end is
free or is interconnected with the excitation point via a third and/or forth branch.
6. A hearing aid according to any of claims 4 or 5, wherein the interconnection with
the ground plane is provided at at least a distance of 1/8 of a wavelength from the
second end.
7. A hearing aid according to any of the previous claims, wherein the antenna is a monopole
antenna.
8. A hearing aid according to any of the previous claims, wherein the excitation point
is provided at the first side of the hearing aid.
9. A hearing aid according to any of claims 5-8, wherein the third branch is different
from the first branch, and/or wherein the forth branch is different from the second
branch.
10. A hearing aid according to any of the previous claims, wherein the first and/or second
branch forms a loop.
11. A hearing aid according to any of the previous claims, wherein the first side is opposite
the second side, and wherein the first side is a first longitudinal side of the hearing
aid and the second side is a second longitudinal side of the hearing aid.
12. A hearing aid according to any of the previous claims, wherein the part of the first
branch extending along the first side and the part of the second branch extending
along the second side are symmetric.
13. A hearing aid according to any of the previous claims, wherein the hearing aid is
a behind-the-ear hearing aid configured to be positioned behind the ear of the user
during use, and wherein the first side is a first longitudinal side of the hearing
aid and the second side is a second longitudinal side of the hearing aid.
14. A hearing aid according to any of the previous claims, wherein the part of the second
branch extending from the first side to the second side, extends from the first side
to the second side via a midpoint of the hearing aid.
15. A hearing aid according to claim 14, wherein a relative difference between a distance
from the midpoint to the excitation point and a distance from the midpoint to the
ground connection is less than a threshold T2.