VIBRATION SENSOR WITH AIR VENTING CHANNELS

Abstract

The present invention relates to a vibration sensor comprising a carrier substrate comprising a first surface and a second surface, a suspension member and a moveable mass secured thereto, wherein the moveable mass and/or at least part of the suspension member is/are adapted to vibrate when the vibration sensor is exposed to external vibrations, a read-out arrangement for detecting vibrations of the moveable mass and/or at least part of the suspension member, and a signal processor for at least processing an electric signal from the read-out arrangement, wherein the read-out arrangement comprises a capacitor formed by a first capacitor electrode and a second capacitor electrode separated by an air gap, and wherein the first capacitor electrode and/or the second capacitor electrode comprises one or more air venting channels in order to reduce squeeze film damping effects between the first and second capacitor electrodes. The present invention further relates to a hearing device comprising such a vibration sensor and use of the vibration sensor for voice recognition in a hearing device.

Claims

1. A vibration sensor comprising a) a carrier substrate comprising a first surface and a second surface, b) a suspension member and a moveable mass secured thereto, wherein the moveable mass and/or at least part of the suspension member is/are adapted to vibrate when the vibration sensor is exposed to external vibrations, c) a read-out arrangement for detecting vibrations of the moveable mass and/or at least part of the suspension member, and d) a signal processor; for at least processing an electric signal from the read-out arrangement, wherein the read-out arrangement comprises a capacitor formed by a first capacitor electrode and a second capacitor electrode separated by an air gap, wherein the first capacitor electrode and/or the second capacitor electrode comprise(s) one or more air venting channels in order to reduce squeeze film damping effects between the first and second capacitor electrodes.

2. A vibration sensor according to claim 1, wherein at least part of the suspension member is electrically conducting, and in that at least the electrically conducting part of the suspension member forms the first capacitor electrode.

3. A vibration sensor according to claim 1, wherein the second capacitor electrode is provided on the first surface of the carrier substrate.

4. A vibration sensor according to claim 3, wherein the second capacitor electrode; comprises one or more air venting channels, and in that the one or more air venting channels of the second capacitor electrode extend into at least part of the carrier substrate.

5. A vibration sensor according to claim 1, wherein the first capacitor electrode is electrically connected to ground, and in that the second capacitor electrode is electrically biased by the signal processor.

6. A vibration sensor according to claim 1, wherein the one or more air venting channels form a three-dimensional pattern in the first capacitor electrode and/or in the second capacitor electrode.

7. A vibration sensor according to claim 6, wherein the one or more air venting channels are adapted to lead air to and/or from the air gap between the first and second capacitor electrodes.

8. A vibration sensor according to claim 1, wherein the moveable mass; and the signal processor are arranged on opposite sides of the carrier substrate.

9. A vibration sensor according to claim 1, wherein the carrier substrate comprises a first PCB comprising first and second opposing surfaces.

10. A vibration sensor according to claim 9, wherein the signal processor is secured to the second surface of the first PCB.

11. A vibration sensor according to claim 9, wherein the vibration sensor further comprises a spacer-secured to the second surface of the first PCB, and in that the spacer comprises one or more vias electrically connected to the second surface of the first PCB.

12. A vibration sensor according to claim 11, wherein the vibration sensor further comprises a second PCB comprising first and second opposing surfaces, and in that the one or more vias of the spacer, are electrically connected to the first surface of the second PCB, and in that one or more contact pads are provided on the second surface of the second PCB for connecting the vibration sensor to external electronic devices.

13. A vibration sensor according to claim 1, wherein the air gap between the first and second capacitor electrodes is at least partly provided by a spacer arranged between at least part of the first and second capacitor electrodes.

14. A vibration sensor according to claim 1, wherein the air gap between the first and second capacitor electrodes is at least partly provided by one or more embossed elements of the suspension member.

15. A vibration sensor according to claim 1, wherein the acoustic resistance of any one of the one or more air venting channels of the first capacitor electrode and/or the second capacitor electrode is/are lower than the acoustic resistance of any part of the air gap between the first and second capacitor electrodes.

16. A hearing device comprising a vibration sensor according to claim 1, wherein the hearing device comprises a hearing aid, a hearable, a headset, an earbud or a similar device.

17. Use of a vibration sensor according to a claim 1 in a hearing device, wherein the vibration sensor is used for detecting voice

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will now be described with reference to the accompanying drawings where

[0030] FIG. 1 shows a cross-sectional view of an embodiment of the present invention,

[0031] FIG. 2 shows a top view of a carrier substrate of the embodiment shown in FIG. 1,

[0032] FIG. 3 shows a cross-sectional view of an embodiment where the air venting channels extend into the carrier substrate,

[0033] FIG. 4 shows a cross-sectional view of an embodiment where the air venting channels are provided in a movable capacitor electrode, and

[0034] FIG. 5 shows a cross-sectional view of an embodiment comprising a thin spacer and an embossed suspension member.

DETAILED DESCRIPTION OF THE INVENTION

[0035] In general, the present invention relates to a vibration sensor for a hearing device. The vibration sensor comprises, among other features, a suspension member and a moveable mass adapted to vibrate when the vibration sensor is exposed to external vibrations. The vibration sensor further comprises a capacitive read-out arrangement for detecting vibrations of the moveable mass and/or at least part of the suspension member. The capacitive read-out arrangement comprises first and second capacitor electrodes, wherein one or more air venting channels is/are provided in the first and/or second capacitor electrode in order to reduce squeeze film damping effects.

[0036] Referring now to FIG. 1, a cross-sectional view of an embodiment of the vibration sensor is depicted. Generally, the vibration sensor relies on a capacitive detection scheme where the distance between a first capacitor electrode 11 and a second capacitor electrode 10 (see FIG. 2) comprising second capacitor electrode portions 10, 10, 10, and thus the capacitance, is adapted to change when the vibration sensor is exposed to external vibrations. In the embodiment shown in FIG. 1 the first capacitor electrode 11 is electrically connected to ground, whereas the second capacitor electrode portions 10, 10, 10 are electrically biased by the signal processor 6. The signal processor 6 is moreover adapted to process voltage changes caused by capacitance changes between the first capacitor electrode 11 and the second capacitor electrode portions 10, 10, 10. The signal processor 6 is electrically connected to the second capacitor electrode portions 10, 10, 10 through wire bonding 8 and via 9 in the first PCB 1.

[0037] Around or on the outside of the second capacitor electrode portions 10, 10, 10 a rim 13 forming a periphery is provided. Preferably, the rim 13 forms part of the same layer as second capacitor electrode portions 10, 10, 10 so that the second capacitor electrode portions 10, 10, 10 and the rim 13 has exactly the same thickness. A spacer 13 is arranged on top of the rim 13. Preferably, both the rim 13 and the spacer 13 are electrically conductive. Moreover, the rim 13 and the spacer 13 are preferably electrically connected to ground through via 9 in the first PCB 1 and through via 4 in the spacer 3 between the first PCB 1 and the second PCB 2.

[0038] As seen in FIG. 1, the first capacitor electrode 11 and the second capacitor electrode portions 10, 10, 10 are separated by an air gap 15 defined by the spacer 13. As already mentioned, the size this air gap 15, i.e. the distance between the first capacitor electrode 11 and the second capacitor electrode portions 10, 10, 10, is adapted to change when the vibration sensor is exposed to external vibrations as the first capacitor electrode 11 also acts as a suspension member for the moveable mass 16 secured thereto. The air gap is typically in the range of 5-15 m when no acceleration is applied. The resilient properties of the combined suspension member/first capacitor electrode 11 (in the following referred to as the first capacitor electrode 11) is provided by an elastic member 12 either secured to, or forming part of, the first capacitor electrode 11. A housing 18 defining a cavity 17 is provided over the moveable mass 16 and the first capacitor electrode 11.

[0039] As also depicted in FIG. 1, the vibration sensor further comprises a first PCB 1 and a second PCB 2. The second PCB 2 comprises first and second opposing surfaces, wherein one or more contact pads 5 are provided on the second surface of the second PCB 2. The one or more contact pads 5 facilitate easy connection of the vibration sensor to external electronic devices. Moreover, the spacer 3 is provided between the first PCB 1 and the second PCB 2 so that a cavity 7 is formed by the first PCB 1 and second PCB 2 and the spacer 3. The spacer 3 comprises one or more vias 4 for electrically interconnecting the first PCB 1 and the second PCB 2.

[0040] In relation to the capacitive detection scheme, the electrically active part of the first capacitor electrode 11 is the centre electrode portion 11 secured to the moveable mass 16. Similarly, the electrically active part of the second capacitor electrode 10 are the three centre electrode portions 10, 10, 10 which are separated by air venting channels 14 in order to reduce squeeze film damping effects between the first capacitor electrode portion 11 and the second capacitor electrode portions 10, 10, 10. Thus, when the distance between the electrically active parts of the first capacitor electrode 11 and the second capacitor electrode portions 10, 10, 10 is reduced air is allowed to escape via the air venting channels 14 whereby squeeze film damping effects are reduced. As seen in FIG. 1 the air venting channel 14 in the second capacitor electrode 10 extends through the entire thickness of the second capacitor electrode 10.

[0041] In order to detect voice induced vibration signals via bone conduction, the bandwidth of the vibration sensor is typically larger than 6 kHz. In addition to this, the resonance frequency of the vibration sensor is typically close to the upper limit of bandwidth, e.g. above 4 kHz, and the resonance peak is typically less than 10 dB higher compared to the sensitivity at 1 KHz. With this approach Q will typically be smaller than 3. Moreover, the noise floor of the vibration sensor should be low, i.e. <98 dB re. 1 g in .sup.rd octave band at the resonance frequency. In order to meet these requirements the mass of the moveable mass 16 needs to be relatively high, such as higher than 1 mg. As the moveable mass 16 typically has a thickness in the range of 100-200 m, the surface areas of the moveable mass 16 can be up to 2.5 mm.sup.2. In terms of manufacturing the moveable mass may be made of a variety of materials including steel, tantalum or tungsten.

[0042] Turning now to FIG. 2, a top view of the second capacitor electrode 10 comprising electrode portions 10, 10 and 10 is depicted. As seen in FIG. 2 the second capacitor electrode portions 10, 10 and 10 are electrically connected and thus form one half of the second capacitor electrode 10. Also the surrounding rim 13 is depicted in FIG. 2. As seen in FIG. 2 the second capacitor electrode 10 comprises a total of six centre electrode portions and a total of six laterally arranged air venting channels 14 which extend through the entire thickness of the second capacitor electrode 10.

[0043] A surrounding air venting channel 14, which is fluidly connected to the air venting channels 14, surrounds the six centre electrode portions. The two vias 9, 9 arranged through the first PCB 1, cf. FIG. 1, are also depicted in FIG. 2. It should be noted that the number of electrode portions may differ from the six portions shown in FIG. 2. Similarly, the number of air venting channels 14 may differ from the six channels shown in FIG. 2. Moreover, both the electrode portions and the air venting channels may be arranged differently compared to the patterns shown in FIG. 2.

[0044] Referring now to FIG. 3, an enlarged cross-sectional view of another embodiment of the vibration sensor is depicted. Similar to the embodiment shown in FIG. 1, the second capacitor electrode 10 (see FIG. 2) including its centre electrode portions 10, 10, 10 are arranged on the first PCB 1 having vias 9, 9 provided therein. The spacer 13 is arranged between the rim 13 and the first capacitor electrode 11 so that an air gap 15 is provided therebetween. The resilient properties of the first capacitor electrode 11 is provided by the elastic member 12 which is either secured to, or forms part of, the first capacitor electrode 11. A part of the housing 18 is also depicted in FIG. 3.

[0045] Still referring to FIG. 3, the electrically active part of the first capacitor electrode 11 is the centre electrode portion 11 to which the moveable mass 16 is secured. Similarly, the electrically active parts of the second capacitor electrode 10 (see FIG. 2) are the three centre electrode portions 10, 10, 10 which are separated by air venting channels 14 in order to reduce squeeze film damping effects between the first capacitor electrode portion 11 and the second capacitor centre electrode portions 10, 10, 10. Air venting channels 14 are also provided between the electrode portions 10, 10 and the rim 13. The air venting channels 14 extend through the entire thickness of the second capacitor electrode 10. In order to further reduce squeeze film damping effects between the first capacitor electrode portion 11 and the second capacitor centre electrode portions 10, 10, 10 the one or more air venting channels 14 are extended into the first PCB 1 thereby the acoustic resistance of the one or more air venting channels 14 are reduced. As a consequence larger amounts of air can escape through the one or more air venting channels 14.

[0046] In the embodiment shown in FIG. 3 the first capacitor electrode 11 is electrically connected to ground, whereas the second capacitor electrode 10, including the three centre electrode portions 10, 10, 10, are electrically biased by the signal processor (not shown), which is also adapted to process voltage changes caused by capacitance changes between the first capacitor electrode portion 11 and the second capacitor electrode portions 10, 10, 10.

[0047] Turning now to the embodiment depicted in FIG. 4, the one or more air venting channels 19 are now provided in the first capacitor electrode 11more particularly between the first capacitor electrode portions 11, 11, 11. The one or more air venting channels 19 extend through the entire thickness of the first capacitor electrode 11. As seen in FIG. 4 no air venting channels are provided in the second capacitor electrode portion 10 which is arranged on the first PCB 1 having vias 9, 9 provided therein. The spacer 13 is arranged between the rim 13 and the first capacitor electrode 11 so that an air gap 15 is provided therebetween. The resilient properties of the first capacitor electrode 11 is provided by the elastic member 12 which is either secured to, or forms part of, the first capacitor electrode 11. A part of the housing 18 is also depicted in FIG. 4. The first capacitor electrode portions 11, 11, 11 are electrically connected to ground, whereas the second capacitor electrode 10, including the centre electrode portions 10, is electrically biased by the signal processor (not shown), which is also adapted to process voltage changes caused by capacitance changes between the first capacitor electrode portions 11, 11, 11 and the second capacitor electrode portion 10.

[0048] Referring now to the embodiment shown in FIG. 5, the air gap 15 between the first capacitor electrode portion 11 and the second capacitor centre electrode portions 10, 10, 10 is provided by the embossed or bent elastic elements 20, 20 of the first capacitor electrode 11. The embossed or bent elastic elements 20, 20 may be either secured to, or form part of, the first capacitor electrode 11. A part of the housing 18 is also depicted in FIG. 5. The electrically active part of the first capacitor electrode 11 is the centre electrode portion 11 to which the moveable mass 16 is secured. Similarly, the electrically active part of the second capacitor electrode 10 (see FIG. 2) are the three centre electrode portions 10, 10, 10 which are separated by air venting channels 14 in order to reduce squeeze film damping effects between the first capacitor electrode portion 11 and the second capacitor centre electrode portions 10, 10, 10. The air venting channels 14 extend through the entire thickness of the second capacitor electrode 10. On the outside of the second capacitor centre electrode portions 10, 10, 10 the rim 13 is provided. Similar to the previous embodiments the first capacitor electrode 11 is electrically connected to ground, whereas the second capacitor electrode 10, including the three centre electrode portions 10, 10, 10, are electrically biased by the signal processor (not shown) which is also adapted to process voltage changes caused by capacitance changes between the first capacitor electrode portion 11 and the second capacitor centre electrode portions 10, 10, 10.

[0049] In the embodiments depicted in FIGS. 1-5 the one or more air venting channels extend through the entire thickness of the first capacitor electrode and/or the second capacitor electrode. It should though be noted that the one or more air venting channels may, as an alternative or in combination therewith, extend only partially through the entire thickness of the first capacitor electrode and/or the second capacitor electrode thus forming one or more recesses or indentations in the first capacitor electrode and/or the second capacitor electrode. Also, the respective air venting channels may have one or more portions that extend through the entire thickness of the first capacitor electrode and/or the second capacitor electrode, and one or more other portions that extend only partially through the entire thickness of the first capacitor electrode and/or the second capacitor electrode.

[0050] Although the present invention has been discussed in the foregoing with reference to exemplary embodiments of the invention, the invention is not restricted to these particular embodiments which can be varied in many ways without departing from the invention. The discussed exemplary embodiments shall therefore not be used to construe the appended claims strictly in accordance therewith. On the contrary, the embodiments are merely intended to explain the wording of the appended claims, without intent to limit the claims to these exemplary embodiments. The scope of protection of the invention shall therefore be construed in accordance with the appended claims only, wherein a possible ambiguity in the wording of the claims shall be resolved using these exemplary embodiments.