DK177431B2

DK177431B2 - Hearing aid with an antenna

Info

Publication number: DK177431B2
Application number: DKPA201000931A
Authority: DK
Inventors: Özden Sinasi
Original assignee: Gn Hearing A/S
Priority date: 2010-10-12
Filing date: 2010-10-12
Publication date: 2019-04-08
Also published as: DK201000931A; DK177431B1

Abstract

A binaural hearing aid system is provided with a hearing aid comprising a microphone for reception of sound and conversion of the received sound into a corresponding first audio signal, a signal processor for processing the first audio signal into a second audio signal compensating a hearing loss of a user of the hearing aid, a receiver that is connected to an output of the signal processor for converting the second audio signal into an output sound signal, a transceiver for wireless data communication interconnected with an antenna for emission and reception of an electromagnetic field, and a housing for accommodation of the antenna, characterized in that the antenna comprises a first section that is positioned so that current flows in the first section in a direction substantially in parallel with an ear to ear axis of the user when the housing is worn in its operational position by the user, whereby an electromagnetic field emitted by the first section propagates along the surface of the head of the user with its electrical field substantially orthogonal to the surface of the head of the user.

Description

The present disclosure relates to a binaural hearing aid system that is adapted for wireless data communication. During operation, the hearing aids worn at opposite ears of the user communicate wirelessly with each other.

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 be located 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.

Conventionally, antennas in hearing aids have been used for receiving radio broadcasts or commands from a remote control. Typically, such antennas are designed to fit in the hearing aid housing without special concern with relation to the obtained directivity of the resulting radiation pattern. For example, behind-the-ear hearing aid housings typically accommodate antennas positioned with their longitudinal direction in parallel with the longitudinal direction of the banana shaped behind-the-ear hearing aid housing. In-the-ear hearing aids have typically been provided with patch antennas positioned on the face plate of the hearing aids as for example disclosed in WO 2005/081583; or wire antennas protruding outside the hearing aid housing in a direction perpendicular to the face plate as for example disclosed in US 2010/20994.

It is an object of the present invention to provide a binaural hearing aid system with an improved wireless ear to ear communication between the hearing aids worn at opposite ears of the user.

In accordance with the present invention the above-mentioned and other objects are obtained by the provision of a binaural hearing aid system with a hearing aid comprising a microphone for reception of sound and conversion of the received sound into a corresponding first audio signal, a signal processor for processing the first audio signal into a second audio signal compensating a hearing loss of a user of the hearing aid, a receiver that is connected to an output of the signal processor for converting the second audio signal into an output sound signal, a transceiver for wireless data communication interconnected with an antenna for emission and reception of an electromagnetic field, and a housing for accommodation of the antenna, characterized in that the antenna comprises a first section that is positioned so that current flows in the first section in a direction substantially in parallel with an ear to ear axis of the user when the housing is worn in its operational position by the user, whereby an electromagnetic field emitted by the first section propagates along the surface of the head of the user with its electrical field substantially orthogonal to the surface of the head of the user.

The first section of the antenna may be connected to the transceiver so that the first section conducts current of a large amplitude at the desired transmission frequency of the electromagnetic field whereby a major part of the power of the electromagnetic field emitted by the antenna and propagating from one ear to the opposite ear of the user is emitted by the first section of the antenna.

The first section of the antenna may be a first linear section, e.g. a rod-shaped section, that is positioned so that the longitudinal direction of the first section is parallel to the ear to ear axis, or in other words perpendicular to, or substantially perpendicular to, the surface of the head proximate the operational position of the first section.

The positioning of the first section of the antenna so that current flows in the first section in a direction in parallel with, or substantially in parallel with, an ear to ear axis of the user makes the antenna suitable for wireless communication between devices located in opposite ears or proximate opposite ears due to advantageous features of the emitted electromagnetic field as further explained below.

The first section of the antenna emits an electromagnetic field that travels around the head of the user thereby providing a wireless data communication that is robust and has low loss.

The first section of the antenna does not emit an electromagnetic field in the direction of its current path, and therefore the first section does not, or substantially does not, emit an electromagnetic field in the direction of the ear to ear axis of the user when the hearing aid housing is positioned in its operational position at the ear of the user; rather, the first section 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. 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 with the surface of the head. Diffraction around the head makes the electromagnetic field emitted by the first section propagate from one ear and around the head to the opposite ear.

The current flowing in a linear antenna forms standing waves along the length of the antenna; and for proper function, a linear antenna is operated at, or approximately at, a resonance frequency at which the length of the linear antenna equals a quarter wavelength of the emitted electromagnetic field. Thus, the first section may be interconnected with a second section, and possibly further sections, of the antenna in order to obtain a combined length of the antenna appropriate for emission of the desired wavelength of the electromagnetic field.

When the first linear section of the antenna has a sufficient length and conducts current flowing in the antenna at and proximate a maximum of the standing wave(s) formed by the current, the first linear section emits a major part of the radiated power of the electromagnetic field emitted by the antenna and received at the opposite ear of the user thereby rendering the orientation of the second linear section and possible other linear sections of the antenna unimportant since these other linear sections do not contribute significantly to the electromagnetic field that can be received at the opposite ear of the user.

Thus, the orientation of current paths of sections of the antenna other than the first section can be determined in response to limitations imposed by the shape and small size of the hearing aid housing and desirable positioning and shape of other components in the housing. For example, second and possible further sections of the antenna other than the first section may be positioned so that current flows in the sections in directions in parallel with the surface of the head when the hearing aid housing is worn in its operational position at the ear of the user.

The hearing aid may further comprise one or more parasitic antenna elements in order to obtain a desired directional pattern of the emitted electromagnetic field and possibly a desired polarization.

Thus, the antenna formed by the combination of sections including the first section positioned so that current flows in the first section in a direction that is parallel with the ear to ear axis of the user during use, has the desired length for effective emission of the desired electromagnetic field but path of current flowing in the antenna exhibits a number of bends due to the different orientations of the sections provided in such a way that the antenna fits inside the hearing aid housing while simultaneously being configured for emission of the desired radiation pattern and polarization at the desired radio frequency.

The required physical length of the antenna may be decreased by interconnecting the antenna with an electronic component, a so-called antenna shortening component, having an impedance that modifies the standing wave pattern of the antenna thereby changing its effective length. The required physical length of the antenna may for example be shortened by connecting the antenna in series with an inductor or in shunt with a capacitor.

Thus, the antenna may have a single linear section of a relative short length positioned in the hearing aid housing in such away that its longitudinal direction is parallel with an ear to ear axis of the user when the hearing aid housing is worn in its operational position at the ear of the user. Furthermore, the single linear section is connected in series with antenna shortening component, e.g. a serial inductor.

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:

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,

Fig. 2a is a top view of the magnitude of the electric field (E) around the head for a parallel antenna configuration (prior art),

Fig. 2b is a top view of the magnitude of the electric field (E) around the head for an orthogonal antenna configuration,

Fig. 3 is the total efficiency of a parallel as well as an orthogonal antenna configuration as a function of antenna length,

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

Fig. 5a is a view from the left hand side of various parts of another exemplary BTE hearing aid with an orthogonal antenna, and

Fig. 5b is a view from the right hand side of the parts shown in Fig. 5b.

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.

In the following, a parallel antenna designates an antenna 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 an orthogonal antenna designates an antenna 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.

According to the invention passive or active antenna elements are implemented in a hearing aid of limited size and proportion. An antenna or an aerial is a transducer that radiates electromagnetic waves. When an electromagnetic wave is radiated it propagates from the antenna and into the space surrounding the antenna. The signal in the electromagnetic wave can then be picked up at a point in the surroundings thereby achieving a wireless transfer of information. In the present invention the signal needs to go from one side of the head to the other side of the head.

An example of an antenna consist of conducting elements where charges or currents are set up. When the charges are varied over time the electromagnetic field originating from the charges will vary in time and a wave is transmitted through space. The specific geometry of the antenna dictates the radiation pattern of the antenna. The radiation pattern is the geometric pattern of the relative field strengths of the field emitted by the antenna. It shows the directional dependence of radiation from the antenna. For an antenna that is ideal isotropic, the radiation pattern will have the geometry of a sphere. For a typical dipole antenna, the radiation pattern will have the geometry of a toroid.

The radiation pattern of an antenna is typically represented by polar plots of the horizontal and vertical cross sections far away from the antenna. The variable in the plot can be the field strength, the power per unit solid angle or directive gain. The peak radiation occurs in the direction where the gain is highest.

When designing antennas for wireless communication between nodes on the human body, the human head can advantageously be modelled as a sphere where sensory organs as the nose, ears, mouth and eyes are attached thereto. Such a sphere 9 is illustrated in the accompanied fig. 1. In the figure the phantom head model is shown together with an ordinary rectangular three dimensional coordinate system with an x, y and z axis for defining the geometries of the head.

The head is constrained by its surface. Every point on the surface of the head will have 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 with the surface of the head while an object extending from a point on the surface of the head and radial away from the head into the surrounding space is said to be orthogonal to the head.

As an example the point 8 furthest to the left on the surface of the head in fig. 1 can be considered. The point is on the left of the head but on the right of the figure. Being the point furthest to the left of the head it will have the y-axis and z-axis as tangential vectors while it will have the x-axis as normal vector. 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.

The user modelled with the phantom head of fig. 1 is standing erect on the ground (not shown in the figure) where the ground is defined as being spanned by the xyplane. The torso axis from top to toe of the user is thus parallel with the z-axis whereas the nose of the user is pointing out of the paper along the y-axis.

The axis going through the right ear canal and the left ear canal is parallel with the xaxis 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 of the present invention.

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.

The hearing aid for the user can be located in the ear canal or behind the ear. Different types of hearing aids are manufactured to the different placements. When looking directly at a user as in fig. 1, the hearing aid will in most cases not be visible.

The in the ear canal type of hearing aid will have a 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 will thus have a longitudinal axis parallel with the surface of the head of the user.

Considering the behind the ear type of hearing aid as an example it will be located behind the ear. A signal connection to the ear extends from the front of the hearing aid and to the ear canal. The front of the hearing aid will for this apparatus be defined as the part being closest to the entry point of the ear canal.

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 as is typically done when measuring the height of elements.

Conventionally, an elongated antenna located along the surface of the head is denoted a parallel antenna, since it is positioned so that its longitudinal direction is parallel to the surface of the head. Hearing aids with parallel antennas for wireless communication with other devices, such as a remote control device, are well-known in the art.

An elongated antenna, such as an antenna shaped as a rod, located so that its longitudinal direction is orthogonal to the surface of the head in the operational position of the antenna is denoted an orthogonal antenna. For proper operation, a rod-shaped antenna must have a length approximately equal to a quarter of the wavelength of the emitted electromagnetic field at the desired radio frequency. Typically, orthogonal rod-shaped antennas have been too long to be accommodated in a hearing aid housing.

Figs. 2a and fig. 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.

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 magnitude of the electric field is plotted around the head. The scale is in RGB so that it goes from high magnitudes (red) over medium magnitudes (green) to low magnitudes (blue). The magnitude around the radiating antenna is completely red. Thus the field around the antenna has a high magnitude. It gradually decreases with the distance to the antenna such that it goes into yellow colours and further on to green colours. On the opposite side of the head at the receiving antenna it can be seen that the field is low (blue colour).

Thus, in order to obtain reliable wireless communication between devices 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.

The reduced magnitude is due to the fact that the electromagnetic fields of the prior art antennas are either radiated in a direction orthogonal to the surface of the head or radiated with an electric field that is parallel with the surface of the head. Both instances causes the magnitude shown in fig. 2a.

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 white as a white rod.

The magnitude of the electric field is plotted around the head. The scale is in RGB so that it goes from high magnitudes (red) over medium magnitudes (green) to low magnitudes (blue). With the present invention the magnitude of the electric field at the opposite side of the head around the receiving antenna is now at medium magnitude (green) and no longer at low magnitude (blue) as in the prior art, and therefore reliable wireless communication between devices at the two ears of a human can be established without the requirement of powerful amplifiers.

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 causing resistive transmission loss in the tissue of the head. 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.

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 can have one or more bends without deteriorating its performance significantly provided that the part of the rod-shaped antenna that emits most of the power of the emitted electromagnetic field maintains its orthogonal orientation.

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, i.e. the charges at the node are stationary. Thus, the part of the rod-shaped antenna proximate its free end does not contribute with a significant part of the power 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 rodshaped antenna proximate the root of the antenna, or the feed-point of the antenna, contribute with a significant part of eh power of the emitted electromagnetic field.

Thus, preferably, a part of the antenna proximate the root of the antenna, or the feedpoint of the antenna, constitutes a first linear 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.

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 on the opposite side of the head than the longest parallel antenna.

Fig. 4 shows various parts 1 of a BTE hearing aid with an antenna 10, 5 having a first linear section 10 that is positioned with a longitudinal direction substantially in parallel with 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 of the hearing aid housing, and it extends along the entire width of the top side of the housing. The first linear section 10 is fed with a 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 housing. 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 of the BTE hearing aid housing.

The first, second, and third linear sections of the antenna are interconnected so that current can flow and the interconnected first, second and third linear sections form the antenna of the required length. The connection between the first and second linear sections 10, 5 is typically located where the top of the hearing aid housing and the side of the hearing aid housing intersects. When current flows through the feed point 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. The second linear section 5 and the third linear section extend along the right or left side of the hearing aid housing and the antenna is terminated with a free end with no 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 feed point.

The illustrated parts 1 are accommodated in a hearing aid housing (not shown). In the illustrated BTE hearing aid, the battery 2 is housed in the rear of the hearing aid housing, and the receiver 3 is housed centrally in the hearing aid housing. The battery 2 provides power to the hearing aid circuitry and components including the receiver 3 that generates sound for emission towards the tympanic membrane of the user. The signal processor (not shown) of the hearing aid is located on the printed circuit board 6.

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 of the antenna provide radiation of an electromagnetic field in parallel with the surface of the head of the user and with an electrical field that is orthogonal to the surface of the head.

In a third preferred embodiment of the present invention the conducting parts 5, 6, 7, 10 of the antenna element are configured orthogonal to the surface of the head 9 of the user when the hearing aid is located on the head of the user.

This antenna element will therefore be relatively long but experience a number of bends such that the antenna element can fit inside the hearing aid while ensuring that the electromagnetic field will be radiated alongside or parallel to the surface of the head 9 of the user while the electric field will be orthogonal to the surface of the head.

The current in the first conducting element of such an antenna element will flow parallel to the ear axis. The current will then proceed to a second conducting element which is also configured such that the current will flow parallel in this element as well. This will continue to further conducting elements depending on the overall length of the antenna and length of the single conducting parts. It is desirable that each conducting part is as long as possible within the hearing aid and that the parallel conducting parts are separated a distance.

The first parallel conducting element can for example be located in the front end of the hearing aid while the second parallel part can be in the middle or at the back. Alternatively the first parallel part can be on the top side of the hearing aid and the second conducting part can on the bottom side of the hearing aid.

The start of the first conducting part will be connected to a feed point and the end of the first conducting part will be connected to the start of the next conducting part of the antenna element, this will continue until the end of the last conducting part where the current will have a null.

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 antenna shortening component, e.g. a serial inductor.

Preferably, the hearing aid also has a second antenna for communication with external devices, such as a remote control, a mobile phone, a TV, etc.

In general the 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 with 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.

A typically antenna that can be ordered by suppliers is a quarter wave monopole antenna. In order to meet the design requirements this antenna will be split in two or three parts and located in the hearing aid housing. With a correct relative geometric configuration of the parts the surface of the head will function as a type of lossy ground plane. The length of such an antenna is of course a quarter of a wavelength.

The physical length can then be calculated in the normal way known to a person skilled in the art based on the velocity of the electromagnetic field and the frequency of the signal. However longer or shorter elements can be used such as in the range of a full wave to a sixteenth wave length.

The specific wavelength and thus the frequency 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 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.

Figs. 5a and 5b show opposite sides of internal parts 1 of another BTE hearing aid with another exemplary orthogonal antenna. In the illustrated hearing aid, the orthogonal antenna (not shown) is located on the printed circuit board 6 and interconnects a parallel antenna 7 and a parasitic element 5 as further explained below.

The illustrated parts of the BTE hearing aid include a battery 2, a receiver 3, a printed circuit board 6, internal housing parts 4 and a parallel antenna 7. The signal processor (not shown) is located on the printed circuit board 6.

In fig. 5a, the parallel antenna 7 is located at the right side of the hearing aid housing. However, the parallel antenna may be located at 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 parallel antenna is constrained by 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 parallel antenna 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 even if it not in free space. An antenna with a length of a quarter of a wave will have a current with it maximum magnitude at the feed point and a null at the end of the antenna.

The parallel antenna 7 may act as a passive element where it shields the hearing aid electronics from interference or act as part of an antenna configured to a specific radiation pattern. The parallel antenna 7 can also act as an active element where it is fed from the printed circuit board and radiates an electromagnetic field into the surrounding space. Dependent on which side of the housing the parallel antenna is located on, the radiated electric field will have different characteristics and radiation pattern with respect to the head 9 of the user and where the hearing aid is mounted.

Fig. 5b is a view from the left hand side of the BTE hearing aid components shown in Fig. 5a. In this view a parasitic element 5 is visible. The parasitic element 5 is comprised of metal or similar material in order to conduct a current of electric charges. The parasitic element may be located on any side of the hearing aid housing.

In Fig. 5b, the parasitic element 5 is located on the left side of the housing. The parasitic element 5 can be a separate element with no connections to the other elements in the hearing aid, or it can be connected to the parallel antenna 7, e.g. via the printed circuit board 6. The conducting part of the circuit board 6 interconnecting the parallel antenna 7 with the parasitic element 5 constitutes the first section of the orthogonal antenna of the illustrated hearing aid.

In the embodiment of Fig. 5b, the three conducting parts, i.e. the parallel antenna 7, the parasitic 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 with the ear to ear axis for emission of an electromagnetic field as explained above. The conducting part will thus be orthogonal because the hearing aid is under normal use located in close proximity to the ear and at this point of the head a conducting element being parallel with the ear to ear axis will be orthogonal to the surface of the head.

The current in the part of the circuit board 6 interconnecting the parallel antenna 7 and the parasitic 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 with 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.

Although the antenna configuration may have side lopes, most of the radiated power will propagate in parallel with the surface of the head.

The configuration of the three parts of the orthogonal antenna illustrated in Fig. 5, furthermore has the property that the 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 substantially un-attenuated around the head of the user avoiding resistive transmission loss in the tissue of the head.

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 with the ear to ear axis (orthogonal to the surface of the head 10 at a point in close proximity to operational position of the hearing aid at the ear of the user) equals the length of the side of the housing at which it is located. This configuration can for example be achieved by placing said conducting part on the top side of the hearing aid and the first and parasitic element 5 on the right and left side respectively. When the hearing aid is located in its operational position behind the 15 ear the third part will be orthogonal and extend along the entire top side of the housing.

Claims

A rear-ear type hearing aid comprising:

a hearing aid housing designed to be placed behind an ear of the user in use, comprising a hearing aid unit (1) having an antenna (5, 7, 10) for transmitting an electromagnetic field, a transceiver (3) for wireless data communication, which transceiver is coupled to the antenna and where the hearing aid housing holds the antenna;

wherein the antenna (5, 7, 10) comprises a first section (10), the antenna (5, 7, 10) being arranged such that current flows in the first section (10) in a direction corresponding to an ear section. axial axis of a user when the hearing aid housing is carried in its operating position by the user, whereby the electromagnetic field emitted by the antenna (5, 7, 10) propagates along a surface of a head of the user with its electric field in substantially orthogonal to the surface of the user's head, characterized in that the first section (10) is a first linear section disposed longitudinally substantially parallel to an ear-to-ear axis of the user when the hearing aid housing is carried in its operating position by the user and the first section (10) has a length between at least one sixteenth wavelength and one full wavelength of the electromagnetic field.

Hearing aid according to claim 1, wherein the first section (10) of the antenna is actively excited.

Hearing aid according to claim 1, wherein the antenna (5, 7, 10) is a passively excited antenna.

Hearing aid according to claim 1, wherein the antenna (5, 7, 10) further comprises a parasitic antenna element (7), which parasitic antenna element (7) comprises a patch geometry, a rod geometry, a monopoly geometry, a meander line. geometry or any combination thereof.

Hearing aid according to claim 4, wherein the hearing aid further comprises a primary antenna element (5).

Hearing aid according to claim 5, wherein the primary antenna element (5) and the parasitic antenna element (7) are arranged on opposite sides of the hay hearing device unit.

Hearing aid according to claim 5, wherein the first section (10) forms a ground potential plane for the primary antenna (5) and the parasitic antenna element (7).

Hearing aid according to claim 5, wherein an excitation point of the parasitic antenna element (7) is opposite to an excitation point of the primary antenna element (5).

Hearing aid according to claim 5, wherein the primary antenna element (5) and the parasitic antenna element (7) are identical antenna structures.

Hearing aid according to claim 1, wherein the current of the antenna (5, 7, 10) has its maximum amplitude in the first section (10) during emitting of the electromagnetic field.

Hearing aid according to claim 1, wherein the antenna (5, 7, 10) further comprises a parasitic antenna element (7) and the parasitic antenna element (7) comprises an antenna truncation component.

The hearing aid of claim 11, wherein the antenna truncation component comprises a serial inductor.

Hearing aid according to claim 12, wherein the first section (10) is in the housing longitudinally along a width of the hearing aid housing.

Hearing aid according to claim 1, wherein the antenna (5, 7, 10) is designed to emit electromagnetic field.

A binaural hearing aid system comprising at least one hearing aid according to claim 1.