Hearing instrument comprising a rechargeable power source

The present invention relates to a hearing instrument comprising an audio signal source (typically a microphone arrangement) for providing audio signals, an audio signal processing unit for processing the audio signals, means to be worn at or in a user's ear or to be implanted in the user's head for stimulating the user's hearing according to the processed audio signals, and a rechargeable power source.

Hearing instruments are typically powered by an electrochemical battery which may be replaceable (disposable) or rechargeable. Rechargeable batteries store electric energy in chemical form. Since the maximum charging current typically is relatively low, charging of batteries takes quite a long time. Further, the lifetime of rechargeable batteries is limited by the number of charging cycles. However, the energy density is relatively high.

Another option for storing electric energy is to use capacitors, wherein the electric energy is stored as an electric field between two capacitor plates. Wearing of the capacitor due to the charging cycles is very small, and the charging currents may be high. However, the energy density typically is much lower than in electrochemical batteries.

A specific type of capacitors having high energy densities is an electrochemical double layer capacitor (EDLC), wherein an electrolyte layer between the capacitor plates is formed and wherein an electrically conducting material having very high surface area, such as activated carbon, is wetted by the electrolyte. The contact of the electrolyte with the surface of the large surface material creates an electrical double layer of charge carriers of opposed polarity having a thickness of only a few molecular layers which do not move. A separator layer is provided between the electrodes in order to prevent direct electric contact between the two electrodes. Such EDLCs have a very high energy density.

U.S. Pat. No. 8,224,007 B2 relates to a rechargeable electrochemical battery to be used in a hearing aid, wherein the battery is based on thin film technology and consists of a wire-like structure which is wound to form an induction coil which may be used both for charging purposes and as a transmitting or receiving antenna for communication purposes. The wire-like structure consists of a radial sequence of concentric hollow cylindrical layers forming the current collectors, anode, cathode and electrolyte.

International Patent Application Publication WO 99/55131 A2 relates to an electrical energy storage unit for a hearing aid, wherein a foil-like capacitor, i.e., a capacitor film, is provided in the shape of a hollow cylinder which is surrounded by an induction coil used for charging of the capacitor coil.

German Patent Application DE 36 23 304 A1 relates to a film capacitor which is wound in the shape of a hollow cylinder forming an induction coil, with such capacitor arrangement being used for creating high energy electromagnetic pulses. One end of one of the two electrode foils and the opposite end of the other one of the electrode foils are provided with a contact, with the electric circuit for discharging of the capacitor being closed by closing a switch provided between the two contacts, whereby the discharging current creates an electromagnetic induction field. Also examples of a capacitor having more than two electrode layers are described.

European Patent Application EP 0 376 948 B1 relates to an ignition system of internal combustion engines comprising a capacitor comprising two metallic conductor sheets wound in a role, wherein the wound capacitor also serves as the inductance required in the ignition circuit to generate ignition sparks.

U.S. Pat. No. 4,048,593 relates to an inductive-capacitive network used as a filter or a transformer, The network comprises a structure consisting of one or more sheets of dielectric material having one or more conductive sheets positioned on each dielectric sheet, wherein the sheet assembly is turned into a spiral configuration.

U.S. Pat. No. 7,023,687 B2 relates to a capacitor having a very high energy density which is made of a porous shaped body of a catalyst support material, wherein the surface of the porous body is coated with a first electrically conductive layer, a barium-titanate layer and a second electrically conductive layer.

It is an object of the invention to provide for a hearing instrument comprising a rechargeable power source which has a relatively high capacity and requires relatively little space, which can be charged relatively fast and in a convenient manner and which has a relatively long lifetime.

According to the invention, this object is achieved by a hearing instrument as described herein.

The invention is beneficial in that, by providing the rechargeable power source as a wound capacitor comprising a capacitor foil arrangement having at least a first electrically conducting layer, a second electrically conducting layer and a dielectric layer in between and which is wound in a manner so as to form an induction coil for generating a current for charging of the capacitor when exposed to an external alternating electromagnetic field generated by a charging device, the space required by the power source is minimized, while the need for a separate induction coil used for convenient contact-less charging is eliminated, fast charging is enabled due to the relatively high charging currents allowed by a capacitor compared to a battery, and a relatively long lifetime of the rechargeable power source can be achieved due to the low degrading of capacitors per charging/discharging cycle.

These and further objects, features and advantages of the present invention will become apparent from the following description when taken in connection with the accompanying drawings which, for purposes of illustration only, show several embodiments in accordance with the present invention.

FIG. 1 is a schematic block diagram of an example of a hearing instrument according to the invention;

FIG. 2 is a schematic perspective view of an example of a rechargeable power source to be used with the present invention, shown together with an example of a circuitry to be used for charging and discharging the power source;

FIG. 3 is a view, like FIG. 2 , wherein an alternative embodiment is shown;

FIG. 4 is a schematic view of an example of a hearing instrument according to the invention including a rechargeable power source;

FIG. 5 is a schematic view of an example of a layer structure of a rechargeable power source to be used with the invention; and

FIG. 6 is a schematic view of another example of a layer structure of a rechargeable power source according to the invention.

In FIG. 1 a schematic block diagram of a hearing aid 10 is shown which comprises a microphone arrangement 12 which typically comprises at least two spaced-apart microphones 14 A, 14 B for capturing audio signals from ambient sound, an audio signal processing unit 16 for processing the captured audio signals, a driver/amplifier 18 for driving an output transducer 20 (typically a loudspeaker) according to the processed audio signals, and a rechargeable power source 22 . In order to enable contactless, i.e., wireless, charging of the power source 22 , typically an induction coil 24 is used which is connected via a charging circuitry 26 to an electrical energy storage element 23 of the power source 22 in order to supply a charging current to the electrical energy storage element 23 which is generated from the voltage induced at the charging coil 24 by an alternating electromagnetic field generated by a coil 28 of a corresponding charging device 30 . Typically, the power source 22 is charged during times when the hearing aid 10 is not used, for example, during night.

According to the present invention, the induction coil is formed by the electrical energy storage element. More in detail, the rechargeable power source is formed by a wound capacitor comprising a capacitor foil arrangement which forms both a capacitor for storing electric energy and an induction coil for generating a current for charging of the capacitor when exposed to an external alternating electromagnetic field generated by the charging device 30 . The capacitor foil arrangement comprises at least a first electrically conducting layer, a second electrically conducting layer and a dielectric layer in between. Also, the wound capacitor comprises a charging circuitry 26 connected to the capacitor foil arrangement.

In the example shown in FIG. 2 , the capacitor foil arrangement 23 comprises two electrically conducting layers, namely a first layer 32 and a second layer 34 , which are separated by a dielectric layer 36 in between. The layers 32 , 34 , 36 are arranged parallel to each other and are wound in a manner so as to form an induction coil having the shape of a hollow cylinder.

Each layer comprises two axial ends (which correspond to the two ends of a cylinder) and two “peripheral ends” 32 A, 32 B and 34 A, 34 B, respectively (these “peripheral ends” form the ends of the layers 32 , 34 , 36 with regard to the winding direction and extend in the axial direction of the cylinder formed by the foil arrangement 23 ). The peripheral end of the first electrically conducing layer 32 which is adjacent to the peripheral end 34 A of the second electrically conducting layer 34 is designated by 32 A, and the peripheral end of the first electrically conducting layer 32 adjacent to the other peripheral end 34 B of the second electrically conducting layer 34 is designated by 32 B.

In the example shown in FIG. 2 the adjacent peripheral ends 32 A and 34 A are provided with electrical contacts 33 A and 35 A, respectively, and the other peripheral end 34 B of the second electrically conducting layer 34 is provided with an electrical contact 35 B. The peripheral end 32 B of the first electrically conducting layer 32 adjacent to the peripheral end 34 B does not comprise an electrical contact and thus is insulated. The contacts 33 A, 35 A at the adjacent peripheral ends 32 A, 34 A are used for discharging the wound capacitor 23 , whereby inductive electromagnetic radiation caused by the discharging current is avoided (such electromagnetic radiation would be generated if the capacitor 23 was discharged by using the contact 35 B at the opposite peripheral end 34 B rather than using the contact 35 A). In the example of FIG. 2 , the load, i.e., the hearing aid electronics, is supplied at 38 with the discharge voltage provided by the capacitor 23 . Alternatively, the load may be connected to the contact 35 B of the second electrically conducting layer 34 rather than to the contact 35 A.

The charging circuitry 26 comprises an auxiliary capacitor 40 , a first diode 42 and a second diode 44 . A first contact of the auxiliary capacitor 40 is connected to the peripheral end 34 B of the second electrically conducting layer 34 via contact 35 B, whereas the other contact of the auxiliary capacitor 40 is connected in parallel via the first diode 42 to the contact 35 A of the other peripheral end 34 A of the second electrically conducting layer 34 and via the second diode 44 to the peripheral end 32 A of the first electrically conducting layer 32 adjacent to the peripheral end 34 A to which the first diode 42 is connected to. The diodes 42 , 44 are connected with opposite polarities to the auxiliary capacitor 40 , i.e., for a given current direction one of the diodes conducts the current while the other one is reverse-biased. By arranging the diodes 42 , 44 in reverse directions it is ensured that during the first half of the cycle of the alternating external magnetic field only one of the diodes allows a current to flow through it, while during the second half of the cycle of the alternating external electromagnetic field only the other one of the diodes allows a current to flow through it.

In the following, it will be assumed that during the first half of the cycle of the alternating external electromagnetic field the first diode 42 allows a current to flow through it, i.e., it is assumed that the voltage induced in the capacitor foil arrangement of the capacitor 22 is such that it drives a current from the second electrically conducting layer 34 via contact 35 A through the first diode 42 to the auxiliary capacitor 40 , thereby charging the auxiliary capacitor 40 (this is illustrated by the arrow 46 in FIG. 2 ). During the second half of the cycle of the alternating external electromagnetic field, the voltage induced in the capacitor foil arrangement has an opposite polarity with regard to the first half of the cycle, so that now a current from the auxiliary capacitor 40 is driven through the second diode 44 to the first electrically conducting layer 32 of the capacitor 22 via the contact 32 A (see arrow 48 in FIG. 2 ). By this mechanism, during each cycle of the external magnetic field, charge is transferred from the second electrically conducting layer 34 to the first electrically conducting layer 32 , thereby charging the capacitor foil arrangement, i.e., a capacitor voltage is generated between the two layers 32 and 34 , which, once charging is completed, may be supplied to the load at 38 .

In the above charging process, the voltage induced in the capacitor foil arrangement during the first half of the cycle serves to charge the auxiliary capacitor 40 , whereas during the second half of the cycle of the alternating external electromagnetic field the voltage at the auxiliary capacitor 40 , together with the voltage induced in the capacitor foil arrangement, serves to drive a charging current to the capacitor foil arrangement.

Anti-polar arrangements may also provide solutions where both cycles can be used.

According to one embodiment, the capacitor foil arrangement may have the structure of an electrochemical double layer capacitor (EDLC), wherein the dielectric layer 36 is formed by an electrolyte 50 which wets the first and second electrically conducting layer 32 , 34 and which is suitable to form, when a charging voltage is applied between the first and second electrically conducting layer 32 , 34 , thin ionic layers of opposite polarity at the surface of the first electrically conducting layer 32 and at the surface of the second electrically conducting layer 34 , respectively. In the schematic example of FIG. 5 , the electrolyte 50 forms a thin layer 52 of negative ions at the surface of the first electrically conducting layer 32 (which carries positive charges) and a thin layer 54 of positive ions at the surface of the second electrically conducting layer 34 which carries negative charges. Thereby each of the ionic layers 52 , 54 forms an electrical double layer with the charges at the surface of the respective layer 32 , 34 . Each of the ionic layers 52 , 54 forms a dielectric layer having a thickness of only a few Ångström (the EDLC shown in FIG. 5 may be described as an in-series connection of two capacitors, as indicated at the bottom of FIG. 5 ). A separator layer 56 is provided within the electrolyte 50 between the two electrodes 32 , 34 in order to prevent direct electrical contact between the electrodes 32 , 34 (in the example shown in FIG. 5 , the first electrically conducting layer 32 forms the positive electrode, while the second electrically conducting layer 34 forms the negative electrode).

In order to achieve a high energy density, the electrodes 32 , 34 are made of a material having a very high surface area, typically a porous material, such as activated carbon.

According to another embodiment, the capacitor foil arrangement 23 may have a structure as described in U.S. Pat. No. 7,023,687 B1, wherein the first electrically conducting layer 132 , the dielectric layer 136 and the second electrically conducting layer 134 are formed on a porous substrate 100 , see FIG. 6 . The porous body 100 may be made of a catalyst support material, for example, a material based on metal oxides. The first and second electrically conducting layer 132 , 134 preferably are made of a metal which is deposited on the surface of the porous body 100 by vapor deposition, sputtering, etc. Once the first layer 132 has been applied, the dielectric layer 136 can be formed by using dispersions of crystalline titanate particles, for example, barium titanate particles, having sizes of less than 10 nm in alcohols, followed by a sintering process. Thereafter the second layer 134 may be applied on top. The dielectric layer 136 preferably has a thickness of 10 to 1,000 nm. Preferably the dielectric layer 136 is ferromagnetic.

The capacitor foil arrangement 123 may comprise more than two electrically conducting layers. An example with three electrically conducting layers 32 , 34 and 37 is shown in FIG. 3 , wherein the third electrically conducting layer 37 is separated from the first electrically conducting layer 32 by a second dielectric layer 39 . By using a third electrically conducting layer the voltage of the capacitor 122 can be increased, whereby the capacity of the capacitor is increased.

In FIG. 3 an example of the charging circuitry 126 is shown which is suitable for a capacitor comprising three electrically conducting layers. The components present in the embodiment of FIG. 2 also are present in the embodiment of FIG. 3 . In addition, a second auxiliary capacitor 41 and two additional diodes 43 , 45 are provided. One of the contacts of the second auxiliary capacitor 41 is connected to the peripheral end 32 B of the first electrically conducting layer 32 via a contact 33 B. The other contact of the second auxiliary capacitor 41 is connected in parallel via the third diode 43 to the contact 33 A at the peripheral end 32 A of the first electrically conducting layer 32 . That peripheral end 37 A of the third electrically conducting layer 37 which is adjacent to the peripheral ends 32 A and 34 A of the first and second layers 32 , 34 is provided with a contact 47 A which is connected to the fourth diode 45 . The second auxiliary capacitor 41 is connected in parallel via the third and fourth diode 43 , 45 to the contact 33 A and 47 A, respectively. The diodes 43 and 45 are connected with opposite polarity to the second auxiliary capacitor 41 . The peripheral end 37 B of the third electrically conducting layer 37 , which is adjacent to the peripheral ends 32 B and 34 B of the layers 32 , 34 , is not provided with a contact, i.e., it is electrically insulated.

The load may be connected, for example, between the contacts 47 A and 35 A or between the contacts 47 A, 33 B.

The capacitor foil arrangement may comprise even more than three electrically conducting layers in order to further increase the capacitor voltage. More complex circuitry, like a Greinacher voltage multiplier circuit, or the like, may be used for utilizing both half-waves of the alternating electromagnetic field. Also, some of the layers of the wound capacitor foil arrangement may serve as the auxiliary capacitor(s) 40 , 41 required for the charging process. By generating in such a manner a cascade of (relatively small) voltages the high voltage resistance of dielectric materials. like barium titanate. may be utilized in an optimized fashion and the density of the stored energy may be enhanced.

In FIG. 4 , an example of a hearing aid according to the invention is shown in a schematic manner, wherein a wound capacitor foil arrangement 23 is located between a microphone arrangement 12 and a speaker 20 , and wherein an electronic unit 25 comprising an audio signal processing unit 16 , an amplifier 18 and a charging circuitry 26 is provided in the hollow interior of the wound capacitor foil arrangement 23 on a support structure 27 . Also the microphone arrangement 12 and the speaker 20 are attached to the support structure 27 .

The present invention in general may be used for all kinds of hearing instruments, such as BTE (behind the ear), ITE (in the ear) or CIC (completely in the canal) type hearing aids.

It also may be used for the external unit of a partially implantable hearing instrument. In such case, the stimulation means is formed by an implantable stimulation assembly for stimulating a middle ear or inner ear component of the hearing of the user, wherein the microphone arrangement and the audio signal processing unit form part of an external unit to be fixed at the patient's head and comprising means for transmitting the processed audio signals via a wireless subcutaneous link to an implantable unit the stimulation assembly.

While various embodiments in accordance with the present invention have been shown and described, it is understood that the invention is not limited thereto, and is susceptible to numerous changes and modifications as known to those skilled in the art. Therefore, this invention is not limited to the details shown and described herein, and includes all such changes and modifications as encompassed by the scope of the appended claims.