Antenna system for a hearing aid

Abstract

A hearing aid includes a hearing aid assembly having an antenna for emission of an electromagnetic field, a transceiver for wireless data communication, the transceiver interconnected with the antenna, and a housing for accommodation of the antenna, wherein the antenna comprises a first section having a length between at least one sixteenth wavelength and a full wavelength of the electromagnetic field, the antenna being positioned so that current flows in the first section in a direction that corresponds with an ear-to-ear axis of a user when the housing is worn in its operational position by the user, whereby the electromagnetic field emitted by the antenna propagates along a surface of a head of the user with its electrical field substantially orthogonal to the surface of the head of the user.

Claims

1. A hearing aid, comprising: an antenna for emission of an electromagnetic field; a transceiver for wireless data communication, the transceiver interconnected with the antenna; and a housing for accommodation of the antenna, wherein the antenna is inside the housing; wherein the antenna comprises a first section having a length between at least one sixteenth wavelength and a full wavelength of the electromagnetic field, the antenna being positioned so that current flows in the first section in a direction that corresponds with an ear-to-ear axis of a user when the housing is worn in its operational position by the user; and wherein the antenna is a passively excited antenna.

2. A hearing aid, comprising: an antenna for emission of an electromagnetic field; a transceiver for wireless data communication, the transceiver interconnected with the antenna; and a housing for accommodation of the antenna, wherein the antenna is inside the housing; wherein the antenna comprises a first section having a length between at least one sixteenth wavelength and a full wavelength of the electromagnetic field, the antenna being positioned so that current flows in the first section in a direction that corresponds with an ear-to-ear axis of a user when the housing is worn in its operational position by the user; and wherein the antenna further comprises a parasitic antenna element.

3. The hearing aid according to claim 2, wherein the first section of the antenna is actively excited.

4. The hearing aid according to claim 2, wherein the hearing aid further comprises a primary antenna element.

5. The hearing aid according to claim 4, wherein the primary antenna element and the parasitic antenna element are positioned on opposite sides of the hearing aid.

6. The hearing aid according to claim 4, wherein the first section forms a ground potential plane for the primary antenna and the parasitic antenna element.

7. The hearing aid according to claim 4, wherein an excitation point for the parasitic antenna element is opposite to an excitation point for the primary antenna element.

8. The hearing aid according to claim 4, wherein the primary antenna element and the parasitic antenna element have a same length.

9. The hearing aid according to claim 2, wherein the antenna has a total length that is at least a quarter wavelength of the electromagnetic field, or longer.

10. The hearing aid according to claim 2, wherein the parasitic antenna element comprises a patch geometry, a rod geometry, a monopole geometry, a meander line geometry, or any combination thereof.

11. The hearing aid of claim 2, wherein the antenna is completely surrounded by the housing.

12. A hearing aid, comprising: an antenna for emission of an electromagnetic field; a transceiver for wireless data communication, the transceiver interconnected with the antenna; and a housing for accommodation of the antenna, wherein the antenna is inside the housing; wherein the antenna comprises a first section having a length between at least one sixteenth wavelength and a full wavelength of the electromagnetic field, the antenna being positioned so that current flows in the first section in a direction that corresponds with an ear-to-ear axis of a user when the housing is worn in its operational position by the user; and wherein the current of the antenna has its maximum amplitude in the first section during emission of the electromagnetic field.

13. The hearing aid according to claim 12, wherein the antenna is configured to operate at a frequency that is at least 1 GHz.

14. The hearing aid according to claim 12, wherein the antenna is configured to operate at a frequency that is between 1.5 GHz and 3 GHz.

15. The hearing aid according to claim 12, wherein the antenna is configured to operate at a frequency that is 2.4 GHz.

16. The hearing aid according to claim 12, wherein an electrical field associated with an operation of the hearing aid is substantially orthogonal to a surface of a head of the user when the hearing aid is at an intended operational position with respect to the user.

17. The hearing aid according to claim 12, wherein the first section extends in a direction that forms an angle with the ear-to-ear axis of the user when the hearing aid is at an intended operational position with respect to the user, the angle being anywhere between −18° and 18°.

18. The hearing aid according to claim 12, wherein the antenna has a total length that is more than a quarter wavelength of the electromagnetic field.

19. The hearing aid according to claim 12, wherein the antenna has a total length that is less than a quarter wavelength of the electromagnetic field.

20. The hearing aid of claim 12, wherein the antenna is fixedly coupled to the transceiver.

21. The hearing aid of claim 12, wherein the antenna is completely surrounded by the housing.

22. A hearing aid, comprising: an antenna for emission of an electromagnetic field; a transceiver for wireless data communication, the transceiver interconnected with the antenna; and a housing for accommodation of the antenna; wherein the antenna comprises a first section having a length between at least one sixteenth wavelength and a full wavelength of the electromagnetic field, the antenna being positioned so that current flows in the first section in a direction that corresponds with an ear-to-ear axis of a user when the housing is worn in its operational position by the user; and wherein the antenna further comprises a parasitic antenna element, and the parasitic antenna element comprises an antenna shortening component.

23. The hearing aid according to claim 22, wherein the antenna shortening component comprises a serial inductor.

24. A hearing aid, comprising: an antenna for emission of an electromagnetic field; a transceiver for wireless data communication, the transceiver interconnected with the antenna; and a housing for accommodation of the antenna, wherein the antenna is inside the housing; wherein the antenna comprises a first section having a length between at least one sixteenth wavelength and a full wavelength of the electromagnetic field, the antenna being positioned so that current flows in the first section in a direction that corresponds with an ear-to-ear axis of a user when the housing is worn in its operational position by the user; and wherein the antenna comprises a second section, wherein a magnitude of the current in the first section is larger than a magnitude of a current in the second section.

25. The hearing aid according to claim 24, wherein the first section is a first linear section that is positioned with a longitudinal direction substantially in parallel with the ear-to-ear axis of the user when the housing is worn in its operational position by the user.

26. The hearing aid according to claim 24, wherein the first section is accommodated in the housing with its longitudinal direction along a width of the housing.

27. A binaural hearing aid system comprising at least one hearing aid according to claim 24.

28. The hearing aid according to claim 24, wherein the antenna is configured to operate at a frequency that is at least 1 GHz.

29. The hearing aid according to claim 24, wherein the antenna is configured to operate at a frequency that is between 1.5 GHz and 3 GHz.

30. The hearing aid according to claim 24, wherein the antenna is configured to operate at a frequency that is 2.4 GHz.

31. The hearing aid according to claim 24, wherein the antenna comprises a monopole antenna.

32. The hearing aid according to claim 24, wherein the electromagnetic field has an associated electrical field that is substantially orthogonal to a surface of a head of the user.

33. The hearing aid according to claim 24, wherein the first section extends in a direction that forms an angle with the ear-to-ear axis of the user when the housing is worn in its operational position by the user, the angle being anywhere between −18° and 18°.

34. The hearing aid according to claim 24, wherein the electromagnetic field emitted by the antenna propagates along a surface of a head of the user.

35. The hearing aid according to claim 24, wherein the antenna has a total length that is more than a quarter wavelength of the electromagnetic field.

36. The hearing aid according to claim 24, wherein the antenna has a total length that is less than a quarter wavelength of the electromagnetic field.

37. The hearing aid according to claim 24, wherein at least a majority of the antenna is inside the housing.

38. The hearing aid of claim 24, wherein the antenna is fixedly coupled to the transceiver.

39. A device configured to be worn at a head of a user, comprising: a structure to be worn at the head of the user, the structure comprising a hearing aid housing of a hearing aid; an antenna for emission of an electromagnetic field, the antenna located underneath an exterior wall of the hearing aid housing; and a transceiver for wireless data communication, the transceiver interconnected with the antenna and located inside the hearing aid housing; wherein the antenna comprises a first section having a length being between at least one sixteenth wavelength and a full wavelength of the electromagnetic field, the antenna being positioned so that current flows in the first section in a direction substantially orthogonal to a body of a user when the antenna system is worn in its operational position by the user; and wherein the antenna comprises a second section, wherein a magnitude of the current in the first section is larger than a magnitude of a current in the second section.

40. The device according to claim 39, wherein the antenna comprises a monopole antenna.

41. The device according to claim 39, wherein the electromagnetic field has an associated electrical field that is substantially orthogonal to a surface of a head of the user when the hearing aid is at an intended operational position with respect to the user.

42. The device according to claim 39, wherein the antenna has a total length that is at least a quarter wavelength of the electromagnetic field, or longer.

43. The device according to claim 39, wherein the electromagnetic field emitted by the antenna propagates along a surface of a head of the user.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other features and advantages 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:

(2) FIG. 1 is a phantom head model of a user together with an ordinary rectangular three dimensional coordinate system with an x, y and z axis for defining the geometrical anatomy of the head of the user,

(3) FIG. 1a shows a block-diagram of a typical hearing aid,

(4) FIG. 2a is a plot of the strength of the electric field (E) around the head for a parallel antenna configuration seen from above the head (prior art),

(5) FIG. 2b is a plot of the strength of the electric field (E) around the head for an orthogonal antenna configuration seen from above the head,

(6) FIG. 3 shows the total efficiency of a parallel as well as an orthogonal antenna configuration as a function of antenna length,

(7) FIG. 4 is a view from the side of various parts of an exemplary BTE hearing aid with an orthogonal antenna,

(8) FIG. 5a is a view from the left hand side of various parts of another exemplary BTE hearing aid with an orthogonal antenna,

(9) FIG. 5b is a view from the right hand side of the parts shown in FIG. 5a,

(10) FIG. 6 is a plot of the current distribution across the at least first section of the supporting element in accordance with some embodiments,

(11) FIGS. 7a-c show schematically exemplary implementations of the primary antenna element and the at least one parasitic antenna element, and

(12) FIGS. 8a-d are plots showing the electromagnetic field distribution around the head of a user with the hearing aid being positioned on a right hand side and a left hand side of a user, respectively.

DETAILED DESCRIPTION

(13) Various embodiments are described hereinafter with reference to the figures. It should be noted that the figures are not drawn to scale and that elements of similar structures or functions are represented by like reference numerals throughout the figures. It should also be noted that the figures are only intended to facilitate the description of the embodiments. They are not intended as an exhaustive description of the claimed invention or as a limitation on the scope of the claimed invention. In addition, an illustrated embodiment needs not have all the aspects or advantages shown. An aspect or an advantage described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced in any other embodiments even if not so illustrated. Also, reference throughout this specification to “some embodiments” or “other embodiments” means that a particular feature, structure, material, or characteristic described in connection with the embodiments is included in at least one embodiment. Thus, the appearances of the phrase “in some embodiments” or “in other embodiments” in various places throughout this specification are not necessarily referring to the same embodiment or embodiments.

(14) In the following, a parallel antenna or a parallel section of an antenna designates an antenna or a section of an antenna, respectively, in a device that is worn at the ear of a user during use and that conducts current solely in directions parallel to the surface of the head at the ear of the user, or in other words perpendicular to the ear to ear axis of the user, and

(15) an orthogonal antenna or an orthogonal section of an antenna designates an antenna or a section of an antenna, respectively, in a device that is worn at the ear of a user during use and that, at least in a section of the antenna, conducts current in a direction that is orthogonal to the surface of the head at the ear of the user, or in other words parallel to the ear to ear axis of the user.

(16) The radiation pattern of an antenna is typically illustrated by polar plots of radiated power in horizontal and vertical planes in the far field of the antenna. The plotted variable may be the field strength, the power per unit solid angle, or directive gain. The peak radiation occurs in the direction of maximum gain.

(17) When designing antennas for wireless communication proximate the human body, the human head can be approximated by a rounded enclosure with sensory organs, such as the nose, ears, mouth and eyes attached thereto. Such a rounded enclosure 9 is illustrated in FIG. 1. In FIG. 1, the phantom head model is shown together with an ordinary rectangular three dimensional coordinate system with an x, y and z axis for defining orientations with relation to the head.

(18) Every point of the surface of the head has a normal and tangential vector. The normal vector is orthogonal to the surface of the head while the tangential vector is parallel to the surface of the head. An element extending along the surface of the head is said to be parallel to the surface of the head while an object extending from a point on the surface of the head and radially outward from the head into the surrounding space is said to be orthogonal to the head.

(19) As an example, the point with reference numeral 8 in FIG. 1 furthest to the left on the surface of the head in FIG. 1 has tangential vectors parallel to the yz-plane of the coordinate system, and a normal vector parallel to the x-axis. Thus the y-axis and z-axis are parallel to the surface of the head at the point 9 and the x-axis is orthogonal to the surface of the head at the point 9.

(20) The user modelled with the phantom head of FIG. 1 is standing erect on the ground (not shown in the figure), and the ground plane is parallel to xy-plane. The torso axis from top to toe of the user is thus parallel to the z-axis, whereas the nose of the user is pointing out of the paper along the y-axis.

(21) The axis going through the right ear canal and the left ear canal is parallel to the x-axis in the figure. This ear to ear axis (ear axis) is thus orthogonal to the surface of the head at the points where it leaves the surface of the head. The ear-to-ear axis as well as the surface of the head will in the following be used as reference when describing specific configurations of the elements in one or more embodiments.

(22) Since the auricle of the ear is primarily located in the plane parallel to the surface of the head on most test persons, it is often described that the ear to ear axis also functions as the normal to the ear. Even though there will be variations from person to person as to how the plane of the auricle is oriented.

(23) The in the ear canal type of hearing aid will have an elongated housing shaped to fit in the ear canal. The longitudinal axis of this type of hearing aid is then parallel to the ear axis. The behind the ear type of hearing aid will typically also have an elongated housing most often shaped as a banana to rest on top of the auricle of the ear. The housing of this type of hearing aid will thus have a longitudinal axis parallel to the surface of the head of the user.

(24) With reference to FIG. 1, the length of a behind the ear apparatus will primarily be measured along the y-axis whereas the width will be measured along the x-axis and the height be measured along the z-axis.

(25) A block-diagram of a typical (prior-art) hearing instrument is shown in FIG. 1a. The hearing aid comprises a microphone 101 for receiving incoming sound and converting it into an audio signal. A receiver 102 converts output from the hearing instrument processor 103 into output sound, e.g. modified to compensate for a users hearing impairment. Thus, the hearing instrument processor 103 may comprise elements such as amplifiers, compressors and noise reduction systems etc. For proper operation, a rod-shaped antenna typically has a length approximately equal to a quarter of the wavelength of the emitted electromagnetic field at the desired radio frequency. Conventionally, orthogonal rod-shaped antennas have been too long to be accommodated inside a hearing aid housing with no parts protruding from the housing.

(26) FIGS. 2a and 2b illustrate the power of an electromagnetic field radiated around the head of a human, when the electromagnetic field is emitted by an antenna positioned at one of the ears of the human. The electromagnetic field is viewed from above the head of the human. The power values are illustrated in grey-levels, high power is black and low power is white.

(27) In FIG. 2a, the electromagnetic field is emitted by a parallel rod antenna. The antenna is shown to the left in FIG. 2a in white as a white rod. FIG. 2a shows how the parallel antennas of the prior art performs. The plot shows the strength of the electric field around the head. The field strength in the plot is indicated by the tone of the grey-level: The stronger the field the darker the grey level. For example, the plot around the radiating antenna is black. Thus, the field strength around the antenna is high. The grey-levels get paler and paler with increased distance to the antenna. The field strength at the receiving antenna at the opposite side of the head is very low and the plot around the receiving antenna is almost white. Thus, in order to obtain reliable wireless communication with parallel antennas in devices worn at the two ears of a human, the devices have to comprise a powerful amplifier for amplification of the received signal; and/or a powerful amplifier for transmission of a high power electromagnetic signal. In a hearing aid, this is not desirable, since batteries supplying power for hearing aid circuitry are small and have limited power capacity.

(28) In FIG. 2b, the electromagnetic field is emitted by an orthogonal rod antenna. Again, the antenna is shown to the left in FIG. 2b in the form of a white rod.

(29) The strength of the electric field is plotted around the head in the same way as in FIG. 2a. It should be noted that the strength of the electromagnetic field at the opposite side of the head at the receiving antenna is larger than in FIG. 2a, and therefore reliable wireless communication between orthogonal antennas in devices worn at the two ears of a human can be established without the requirement of powerful amplifiers.

(30) The improvement is believed to be caused by the fact that a parallel rod antenna emits an electromagnetic field primarily in a direction perpendicular to the surface of the head at the position of the antenna, and the electrical field of the electromagnetic field is parallel to the surface of the head giving rise to resistive transmission loss in the tissue of the head.

(31) Contrary to this, an orthogonal rod antenna emits an electromagnetic field primarily in a direction parallel to the surface of the head facilitating transmission of the electromagnetic field around the head, and the electrical field of the electromagnetic field is perpendicular to the surface of the head whereby transmission loss in the tissue of the head is reduced.

(32) The limited space available in a hearing aid housing makes it difficult to accommodate an orthogonal rod-shaped antenna in a hearing aid housing; however it has been shown that the rod-shaped antenna may have one or more bends without deteriorating its performance significantly, provided that the part of the rod-shaped antenna that contributes significantly to the part of the emitted electromagnetic field received at the opposite ear maintains its orthogonal orientation.

(33) During operation, the rod-shaped antenna conducts a current of a standing wave. The free end of the rod-shaped antenna constitutes a node of the standing wave in which the current is zero. Thus, the part of the rod-shaped antenna proximate its free end does not contribute with a significant part of the magnetic field of the emitted electromagnetic signal. At the root of the rod-shaped antenna that is connected to the transceiver circuitry of the hearing aid and supplied with current, the current has maximum amplitude, and therefore the part of the rod-shaped antenna proximate the root of the antenna, or the feed point or excitation point of the antenna, contribute with a significant part of the magnetic field of the emitted electromagnetic field.

(34) Thus, preferably, a part of the antenna proximate the root of the antenna, or the excitation point of the antenna, constitutes the first section of the antenna having a longitudinal direction that is orthogonal to the surface of the head of the user, when positioned in its desired operational position at the ear of the user. The orientation of the remaining part of the antenna is not critical in order to obtain the desired power of the electromagnetic field at the opposite ear of the user, but further section(s) is/are required in order for the antenna to have the required length for proper operation at the desired radio frequency, e.g. equal to, or approximately equal to, a quarter wavelength of the field or any multiple thereof

(35) In FIG. 3, total efficiencies of a parallel monopole rod antenna and an orthogonal monopole rod antenna with relation to path loss around the head of a human are compared as a function of physical antenna length. The resonance frequency of the antennas is kept the same by using a serial inductance. It should be noted that even the shortest orthogonal antenna is more effective in establishing an electromagnetic field at the opposite side of the head than the longest parallel antenna.

(36) FIG. 4 shows an assembly of various parts 1 of a BTE hearing aid with an antenna 10, 5 having a first section 10 that is positioned with a longitudinal direction substantially in parallel to an ear to ear axis of the user when the housing is worn in its desired operational position by the user. The first linear section 10 is located at the top side 16 of the hearing aid assembly, and it extends along the entire width of the top side 16 of the assembly 1. The first linear section 10 is fed with current from the printed circuit board 6. The antenna further has a second linear section 5 with a longitudinal direction substantially perpendicular to the longitudinal direction of the first linear section 10 and substantially parallel to the side of the BTE hearing aid assembly 1. The antenna ends in a third linear section that has a longitudinal direction that is substantially perpendicular to both the first section 10 and the second linear section 5 and substantially parallel to the side 11 of assembly and thus to the BTE hearing aid housing. The BTE hearing aid housing 15 accommodating the hearing aid assembly 1 in its entirety is illustrated in FIG. 4 with a dashed line.

(37) The first, second, and third linear sections 10, 5, 14 of the antenna are electrically interconnected and the interconnected first, second and third linear sections form the antenna of the required length. The second and third sections form a parasitic antenna element. The connection between the first and second linear sections 10, 5 is typically located where the top 16 of the hearing aid assembly 1 and the side 11 of the assembly intersect. When current flows through the excitation point 17 into the first linear section 10, it will continue into the second linear section 5 while experiencing a bend where the two sections are connected.

(38) The second linear section 5 and the third linear section 14 extend along the right or left side 11, 12 of the hearing aid assembly and thus also extend along the right or left side of the inside of the hearing aid housing 15, and the antenna is terminated with a free end with no electrical connection to other parts. A current in the antenna will thus have a zero or node at the free end, and the antenna current has its largest magnitude at the excitation point.

(39) The illustrated assembly of parts 1 are accommodated in a hearing aid housing 15 (dashed line). In the illustrated BTE hearing aid, the battery 2 is housed in the rear of the hearing aid housing, and the transceiver 3 is housed centrally in the hearing aid assembly 1. The battery 2 provides power to the hearing aid circuitry and components including the transceiver 3 for generating sound for emission towards the tympanic membrane of the user and for wireless data communication and being interconnected with at least a primary antenna element. The transceiver 3 may be also be provided as two separate transceivers for generating sound and for wireless data communication, respectively. The signal processor (not shown) of the hearing aid is located on the printed circuit board 6.

(40) When the hearing aid is worn in its operational position at the ear of the user, the orthogonal angles between the first, second and third linear sections 10, 5, 14 of the antenna provide radiation of an electromagnetic field in parallel to the surface of the head of the user and with an electrical field that is orthogonal to the surface of the head.

(41) In another exemplary BTE hearing aid with an orthogonal antenna, the orthogonal antenna has a single linear section that is relatively short. The single linear section is positioned in the hearing aid housing so that its longitudinal direction is orthogonal to, or substantially orthogonal to, the surface of the head of the user when the hearing aid is positioned in its operational position at the ear of the user. Furthermore, the single linear section is connected in series with an antenna shortening component, e.g. a serial inductor, or a parasitic antenna element.

(42) However, also other embodiments of the antenna and the antenna configurations may be contemplated.

(43) Preferably, the primary antenna element is an antenna element configured also for communication with external devices, such as a remote control, a mobile phone, a TV, etc.

(44) In general, various sections of the antenna can be formed with many different geometries, they can 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 at least one conducting part will carry a current being primarily parallel to the ear axis (orthogonal to the surface of the head 9 of the user at a point 8 in proximity to the ear) such that the field will be radiated in the desired direction and with the desired polarization such that substantially no attenuation is experienced by the surface wave travelling around the head. Preferably, the at least one conducting part is provided in proximity to the excitation point.

(45) The specific wavelength, and thus the frequency of the emitted electromagnetic field, is of importance when considering communication involving an obstacle. In some embodiments, 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.

(46) FIGS. 5a and 5b show opposite sides of a hearing aid assembly of various parts 1 of another BTE hearing aid with another exemplary orthogonal antenna.

(47) The illustrated hearing aid assembly of the BTE hearing aid include a battery 2, a transceiver 3, a printed circuit board 6, internal wall parts, or first and second sides of the hearing aid assembly 11, 12 and a primary antenna element 7. It is seen that the primary antenna element is configured as a parallel antenna. The signal processor (not shown) is located on the printed circuit board 6.

(48) In FIG. 5a, the primary antenna element 7 is located at the first or right side 12 of the hearing aid housing. However, the primary antenna element 7 may be located at a second or the left side of the housing, at the top side of the housing, at the front side of the housing, at the back side of the housing or at the bottom side of the housing. The allowable length of the primary antenna element 7 is constrained by the length of the side of the housing at which it is located. The longer the side, the longer the part can be. In general, the length of the primary antenna element is dictated by the operating frequency, the group velocity of the current flowing on the antenna and the number of nulls that is desired. Normally, the velocity is approximated by the velocity of light in free space. An antenna with a length of a quarter of a wave will have a current with its maximum magnitude at the excitation point and a null at the end of the antenna.

(49) The primary antenna element 7 may act as a passive element where it shields the hearing aid electronics from interference or act as part of an antenna configured for a specific radiation pattern. In the embodiment shown in FIGS. 5a-b, the primary antenna element 7 is an active element being excited from an excitation point 17 on the printed circuit board and radiates an electromagnetic field into the surrounding space. Dependent on which side of the housing the primary antenna element is located on, the radiated electric field will have slightly different characteristics and radiation patterns with respect to the head 9 of the user.

(50) FIG. 5b is a view from the second, or in this case the left hand side, of the BTE hearing aid assembly 1 shown in FIG. 5a and shows a parasitic antenna element 5. The parasitic antenna element 5 is comprised of metal or similar material in order to conduct a current of electric charges. The parasitic antenna element may be located on any side of the hearing aid housing.

(51) The primary antenna element and the parasitic antenna element are interconnected via a supporting or connecting element 6, in this case the printed circuit board 6, which forms a ground plane for the primary antenna element. In this way, upon excitation of the primary antenna element, a current generated by the electromagnetic field has its maximum in at least a first section 19 of the supporting element 6 and flows from the primary antenna element to the parasitic antenna element and excites the parasitic antenna element. The first section may comprise the entire supporting element or any part thereof.

(52) Preferably, the excitation point 18 for the parasitic antenna element 5 is located at a distance from the excitation point 17 of the primary antenna element 7 along an axis substantially parallel to the ear to ear axis. Preferably, the excitation point 18 for the parasitic antenna element 5 and the excitation point 17 of the primary antenna element 7 are positioned on opposite sides of the hearing aid assembly 1. However, it is envisaged that at least a part of the parallel or primary antenna element 7 and/or the parasitic antenna element 5 may be provided on any side of the hearing aid, as long as the excitation points 17, 18 are provided at a distance along an axis substantially parallel to the ear to ear axis.

(53) Furthermore, at least a part of the primary antenna element 7 and/or the parasitic antenna element may extend along the supporting element. Preferably, the first section 19 of the supporting element is between one sixteenth wavelength and a full wavelength of the emitted electromagnetic field, the length being measured along the path of maximum current between the excitation points 17,18.

(54) In FIG. 5b, the parasitic antenna element 5 is located on the left side 11 of the assembly 1. The parasitic antenna element 5 can be a separate element with no connections to the other elements in the hearing aid, or it can be operatively connected to the primary antenna element 7, e.g. via the printed circuit board 6.

(55) In FIG. 5b, the conducting part of the circuit board 6 interconnecting the primary antenna element 7 with the parasitic antenna element 5 constitutes the first section of the orthogonal antenna of the illustrated hearing aid due to the positioning of the interconnections at the desired longitudinal axis of the first section thereby forming the desired current path of the first section for emission of the desired part of the electromagnetic field received at the opposite ear of the user.

(56) In the embodiment of FIG. 5b, the three conducting parts, i.e. the primary antenna element 7, the parasitic antenna element 5, and the printed circuit board 6, are configured relative to each other such that when the hearing aid is located on the head 9 of a user and a current flows in the conducting elements the current in the third conducting element 6 will flow in a direction parallel to the ear to ear axis for emission of an electromagnetic field as explained above. The conducting part will thus constitute the first section and be orthogonal because the hearing aid is worn at the ear during use and at this position at the head, a conducting element being parallel to the ear to ear axis will be orthogonal to the surface of the head.

(57) The current in the part of the circuit board 6 interconnecting the primary antenna element 7 and the parasitic antenna element 5 must flow in a direction substantially parallel to the ear to ear axis so that the emitted electromagnetic field propagates substantially in parallel to the surface of the head. The electromagnetic field thus propagates along the surface of the head until it reaches the ear on the other side of the head.

(58) Although the radiation pattern of the antenna configuration may have side lopes, most of the radiated power will propagate in parallel to the surface of the head.

(59) The configuration of the three parts of the orthogonal antenna illustrated in FIG. 5, furthermore has the property that the overall emitted electromagnetic field is polarized in a transverse magnetic mode so that the electrical field is orthogonal to, or substantially orthogonal to, the surface of the head so that the electromagnetic field propagates without, or with low, resistive transmission loss in the tissue of the head.

(60) Preferably, in order to obtain effective radiation, the length of the current path of the first section of the antenna, in the illustrated example located on the printed circuit board 6, that is parallel to the ear to ear axis (orthogonal to the surface of the head proximate the operational position of the hearing aid at the ear of the user) equals the length of the side of the hearing aid assembly at which it is located. This configuration may for example be achieved by placing said conducting part at the top side of the hearing aid assembly and the primary and parasitic antenna element 5 on the right and left side respectively. When the illustrated hearing aid is located in its operational position behind the ear, the third part will constitute the first section and be orthogonal and extend along the entire top side of the housing. Furthermore, to achieve a maximum current in the at least first section of the supporting element, it is preferred that the first section has a length between one sixteenth wavelength and a full wavelength of the emitted electromagnetic field.

(61) An exemplary current distribution in the first section 19 of the first section is shown in FIG. 6. The first section is excited by the excitation point for the primary antenna element 17 and the maximum current 20 is along the shortest path to the excitation point for the parasitic antenna element 18.

(62) In another exemplary BTE hearing aid with an orthogonal antenna, the orthogonal antenna has a single linear section that is relatively short. The single linear section is positioned in the hearing aid housing so that its longitudinal direction is orthogonal to, or substantially orthogonal to, the surface of the head of the user when the hearing aid is positioned in its operational position at the ear of the user. Furthermore, the single linear section is connected in series with an antenna shortening component, e.g. a serial inductor.

(63) However, also other embodiments of the antenna and the antenna configurations may be contemplated.

(64) A number of possible antenna designs are shown schematically in FIGS. 7a-c. The hearing aid assembly 1 is seen from the top, and the antennas and the position of the antenna excitation points are illustrated.

(65) FIG. 7a shows a primary antenna element 21 having an excitation point 17. The supporting (or connecting) element 23 forms a ground plane for the primary antenna element 21 and the excitation point 18 for the parasitic antenna element 22 is positioned a distance from the primary antenna element excitation point 17 along an axis substantially parallel to the ear to ear axis. The first section 19 of the supporting element 23 does in this example not extend over the entire width of the hearing aid.

(66) FIG. 7b shows an example where the distance between the excitation points 17, 18 corresponds to the width of the hearing aid assembly. In FIG. 7c, an alternative embodiment is shown, wherein the excitation points 17, 18 are positioned at a distance from each other along an axis orthogonal to the ear to ear axis. In this case, the parasitic antenna element 22 is preferably connected to an antenna shortening component to ensure that a maximum current is provided in the part of the antenna orthogonal to the head.

(67) In a preferred embodiment, the primary antenna element 21 and the parasitic antenna element 22 form identical antenna structures. For example, both the primary antenna element 21 and the parasitic antenna element 22 may form an antenna structure having a same form and same dimensions, each antenna element 21, 22 may for example form a meander line antenna having same dimensions and the same form.

(68) It is envisaged that even though only a behind-the-ear hearing aid have been shown in the figures, the described antenna structure may be equally applied in all other types of hearing aids, including in-the-ear hearing aids, as long as the first section is configured to guide the current in a direction parallel to an ear-to-ear axis of a user, when the user is wearing the hearing aid in the operational position.

(69) FIG. 8 shows directivity plots for a hearing aid according to some embodiments, and it is seen that the difference between positioning the hearing aid on a right hand side of a user and a left hand side of the user are minimal. The difference is caused by the mirroring of the antenna placement, so that for the left side device, the primary antenna element is placed further away from the head than for the device on the right hand side. It is thus an advantage of the hearing aid according to some embodiments may be used optionally on a right hand side and a left hand side of a user with only a minimal impact on the wireless connection both to external accessories as to the other of two hearing aids in a binaural hearing aid.

(70) FIG. 8a shows the θ-cut for φ=0° total directivity, and FIG. 8b shows the θ-cut for φ=90° total directivity both at 2441 MHz for a hearing aid according to some embodiments, positioned on a left hand side position of a user.

(71) FIG. 8c shows the θ-cut for φ=0° total directivity, and FIG. 8d shows the θ-cut for φ=90° total directivity both at 2441 MHz for a hearing aid according to some embodiments, positioned on a right hand side position of a user.

(72) In general, various sections of the antenna can be formed with many different geometries, they can 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 at least one conducting part will carry a current being primarily parallel to the ear axis (orthogonal to the surface of the head 9 of the user at a point 8 in proximity to the ear) such that the field will be radiated in the desired direction and with the desired polarization such that no attenuation is experienced by the surface wave travelling around the head.

(73) The specific wavelength, and thus the frequency of the emitted electromagnetic field, is of importance when considering communication involving an obstacle. In some embodiments, 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 opposite side 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.

(74) It should be noted that as used in this specification, the term “substantially” refers to a value variation that is within plus or minus 10%. For example, the term “substantially orthogonal” and similar terms refer to an angle that is 90±9 degrees. Similarly, the term “substantially parallel” and similar terms refer to angle that is 0 (or 180 degrees) ±18 degrees.

(75) Although particular embodiments have been shown and described, it will be understood that they are not intended to limit the claimed invention, and it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present inventions. The specification and drawings are, accordingly, to be regarded in an illustrative rather than restrictive sense. The claimed invention are intended to cover alternatives, modifications, and equivalents.