Patent Application
20240302205
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 one or more piezo electric layers and one or more electrodes arranged on the respective piezo electric layers. According to the present invention the shape and the dimensions of a moveable mass, and the layout of the piezo electric read-out arrangement are mutually optimised in order not to increase the overall dimensions of the vibration sensor.
Vibration sensors to be used in modern hearing devices need to be very compact as the available space in modern hearing devices is very limited. Thus, the designers of vibration sensors are constantly faced with demanding challenges with respect to the dimensions and the performance of such vibration sensors. An example of the prior art sensor may for example be found in US 2008/072677 A1 which discloses an accelerometer comprising a piezo electric signal crystal in the form of a cantilever beam having a free portion. A metal shim is secured to the piezo electric signal crystal. The cantilever beam is adapted to bend when exposed to external accelerations. The accelerometer suggested in US 2008/072677 A1 is disadvantageous in that it does not involve moveable masses-the omitted moveable masses reduce the sensitivity of the accelerometer suggested in US 2008/072677 A1. Moreover, the accelerometer suggested in US 2008/072677 A1 relies on a piezo electric signal crystal formed as a cantilever beam-this approach is disadvantageous seen from a manufacturing point of view.
It may be seen as an object of the embodiments of the present invention to optimise the shape and the dimensions of a moveable mass without increasing the overall dimensions of a vibration sensor.
It may be seen as a further object of embodiments of the present invention to optimise the layout of the piezo electric read-out arrangement without increasing the overall dimensions of a vibration sensor.
The above-mentioned objects are complied with by providing, in a first aspect, a vibration sensor comprising
The vibration sensor of the present invention is advantageous with respect to the mutual arrangement of the moveable mass and the one or more piezo electric layers in that 1) at least part of the moveable mass is secured to the cantilever beam between the virtual hinge line and the moveable end, and that 2) the one or more piezo electric layers are secured to the cantilever beam in a manner so that the one or more piezo electric layers intersect the virtual hinge line. Thus, the moveable mass is preferably secured to the cantilever beam (between the virtual hinge line and the moveable end) in a region where the cantilever beam is not intended to bend when the vibration sensor is exposed to external vibrations. Similarly, the one or more piezo electric layers are preferably secured to the cantilever beam at least in a region where the cantilever beam is intended to bend when the vibration sensor is exposed to external vibrations.
Moreover, the vibration sensor of the present invention is advantageous in that the shape and the dimensions of the moveable mass as well as the layout of the piezo electric read-out arrangement are optimised in order not to increase the overall dimensions of the vibration sensor. Finally, the vibration sensor of the present invention is advantageous in that it incorporates only low-cost technologies.
In the present context, and as it will be discussed in further detail below, the term “virtual hinge line” defines a line between the static end and the moveable end of the cantilever beam where the cantilever beam effectively bends when the moveable mass is displaced due to external vibrations.
The vibration sensor of the present invention is advantageous in that it provides a low noise level and has a relatively small overall size. The low noise level is provided due to an incorporation of a large moveable mass (>1 mg).
The vibration sensor of the present invention applies a piezo electric detection principle for detecting the displacements of the moveable mass when the vibration sensor is exposed to external vibrations. As it will be discussed in further detail below, one or more piezo electric layers with one or more electrodes arranged thereon is/are arranged on the suspension member. A displacement of the moveable mass bends the suspension member whereby the one or more piezo electric layers is/are stretched or compressed in the lateral direction. Whether the one or more piezo electric layers is/are stretched or compressed depends on the direction of the displacement of the moveable mass when the suspension member is bent.
The change in the lateral strain of the one or more piezo electric layers will cause a change in electrical field strength across each of the one or more piezo electric layers, i.e. across the thickness of the one or more piezo electric layers. The change in field strength across the one or more piezo electric layers will cause a change in voltage generated between two electrodes arranged on opposite sides of each of the one or more piezo electric layers.
Preferably, the thickness and width of the one or more piezo electric layers are adapted to the thickness and width of the suspension member so that strain induced in the one or more piezo electric layers has uniformly the same sign when they are stretched or compressed.
Preferably, the material of the suspension member is selected so that the one or more piezo elastic layers can be arranged directly on the suspension member. Moreover, the material of the suspension member is preferably electrically conducting so that the suspension member can be used as one of the electrodes sandwiching the one or more piezo electric layers.
Preferably, the one or more electrodes arranged on the respective piezo electric layers are dimensioned so that they do no influence the stiffness of the suspension member.
With respect to the geometry of the suspension member, the geometry is chosen so that the required resonance frequency is obtained with the required moveable mass, and so that no plastic deformation can occur if the vibration sensor is exposed to extreme mechanical shocks, e.g. when being dropped. With respect to the resonance frequency the length of the suspension member is preferably adjusted to the thickness and width of the suspension member in order to meet the required stiffness. With respect to plastic deformation, the thickness and width of the suspension member should be as small as possible, such as a thickness in the range of 10-50 μm and a width in the range of 200-500 μm.
The vibration sensor of the present invention is preferably suitable for being incorporated into hearing devices, such as a hearing aid, a hearable, a headset, an earbud, personal audio and personal communication devices or a similar device. The roles of the vibration sensor may be numerous, such as detecting voice induced vibrations via bone conduction in the skull. Detection of such voice induced vibrations in the skull is preferably used in relation to voice recognition where the user's own voice is separated or recognised in an otherwise acoustically noisy environment.
In one embodiment of the vibration sensor, at least part of the moveable mass preferably extends from the moveable end to the virtual hinge line of the cantilever beam. The moveable mass comprises a first part preferably being substantially aligned with the moveable end of the cantilever beam, and a second part preferably being substantially aligned with the virtual hinge line of the cantilever beam. Thus, the moveable mass extends from the moveable end of the cantilever beam to the virtual hinge line of the cantilever beam. Optionally, the moveable mass may extend beyond the moveable end of the cantilever beam, or the moveable mass may, for other reasons, not extend entirely from the moveable end of the cantilever beam to the virtual hinge line of the cantilever beam.
As already mentioned, the mass of the moveable mass needs to be relatively high, such as higher than 1 mg. As the moveable mass typically has a thickness in the range of 100-200 μm, the surface areas of the moveable mass can be up to 2.5 mm2. In terms of manufacturing the moveable mass may be made of a variety of materials including steel, tantalum or tungsten.
Preferably, the width of the second part of the moveable mass is smaller than the width of the first part of the moveable mass. It is advantageous in that the smaller width of the second part of the moveable mass facilitates that one or more piezo electric layers may be arranged next to the second part of the moveable mass. Preferably, at least part of the second part of the moveable mass is arranged between two piezo electric layers secured to the cantilever beam in a manner so that the two piezo electric layers intersect the virtual hinge line. Arranging the two piezo electric layers so that they intersect the virtual hinge line is advantageous in that the sensitivity of the read-out arrangement of the vibration sensor then becomes high since the cantilever beam effectively bends at the virtual hinge line. Moreover, as the two piezo electric layers and the second part of the moveable mass spatially overlap, the overall size of the vibration sensor can be kept at a minimum thus providing a compact vibration sensor.
In another embodiment the first part of the moveable mass is preferably secured to the cantilever beam, while the second part of the moveable mass forms an overhang above the cantilever beam so that an air gap is formed between the second part of the moveable mass and the cantilever beam. The first part of the moveable mass is preferably secured to the cantilever beam between the moveable end and the virtual hinge line of the cantilever beam. Thus, the area where the moveable mass is secured to the cantilever beam does not intersect the virtual hinge line. In this embodiment the one or more piezo electric layers are preferably secured to the cantilever beam in a manner so that the one or more piezo electric layers extend into the air gap between the second part of the moveable mass and the cantilever beam, and intersect the virtual hinge line. Arranging the piezo electric layer so that it intersects the virtual hinge line is advantageous in that the sensitivity of the read-out arrangement of the vibration sensor then becomes high since the cantilever beam effectively bends at the virtual hinge line. Moreover, as the piezo electric layer and the second part of the moveable mass spatially overlap the overall size of the vibration sensor can be kept at a minimum thus providing a compact vibration sensor.
Preferably, the moveable mass and the signal processor are arranged on opposite sides of the carrier substrate. In the present context the term opposite means that the moveable mass is arranged on one side of the carrier substrate, whereas the signal processor is arranged on another side of the carrier substrate. With this arrangement the carrier substrate becomes arranged between the moveable mass and the signal processor. This is advantageous in that it reduces the overall size of the vibration sensor as projections of the moveable mass and the signal processor overlap spatially in a plane defined by the carrier substrate.
The plane defined by the carrier may coincide with the first surface or the second surface of the carrier substrate, or it may be a virtual plane being parallel with the first surface or the second surface of the carrier substrate. In the present context spatially overlapping of the moveable mass and the signal processor occur when a projected area of the moveable mass overlaps with a projected area of the signal processor in the plane defined by the carrier substrate.
Preferably, the carrier substrate comprises a first printed circuit board (PCB) comprising first and second opposing surfaces. Thus, the carrier substrate is preferably implemented as a PCB comprising the first and second surfaces which may be considered upper and lower surfaces, respectively. Implementing the carrier substrate as a PCB is advantageous in that electronics, such as electrodes, the signal processor etc., can be connected directly to the PCB. In this respect, the signal processor is preferably secured to the second surface of the first PCB.
Preferably the vibration sensor further comprises a spacer, secured to the second surface of the first PCB, wherein the spacer comprises one or more vias electrically connected to the second surface of the first PCB. Preferably the vibration sensor further comprises a second PCB comprising first and second opposing surfaces, wherein the one or more vias of the spacer are electrically connected to the first surface of the second PCB, and wherein one or more contact pads are provided on the second surface of the second PCB for connecting the vibration sensor to external electronic devices. Thus, the incorporation of the spacer, the one or more vias and the second PCB is advantageous in that these elements facilitate that the internal electrical connections of the vibration sensor can be easily implemented. In the present context external electronic devices may include power supplies and additional signal processors, such as amplifiers, filters etc.
In a second aspect the present invention relates to a hearing device comprising a vibration sensor according to the first aspect, wherein the hearing device comprises a hearing aid, a hearable, a headset, an earbud or a similar device.
In a third aspect the present invention relates to a use of a vibration sensor according to the first aspect, wherein the vibration sensor is used for detecting voice induced vibrations in the skull of the user of the hearing device, and wherein the detected voice induced vibrations are used for voice recognition of the user's own voice.
In general, the various aspects of the present invention may be combined and coupled in any way possible within the scope of the invention. These and other aspects, features and/or advantages of the present invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
The present invention will now be described with reference to the accompanying drawings where
In general the present invention relates to a vibration sensor suitable for being incorporated into hearing devices. The vibration sensor is advantageous due to its mutual arrangement of a moveable mass and one or more piezo electric layers of a read-out arrangement for detecting displacements of the moveable mass when the vibration sensor is exposed to external vibrations. Moreover, the vibration sensor of the present invention is advantageous in that the shape and the dimensions of a moveable mass as well as the layout of the piezo electric read-out arrangement are optimised in order not to increase the overall dimensions of the vibration sensor.
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 compared to the sensitivity at 1 KHz. With this approach Q will typically be smaller than 3. Moreover, the input referred noise, or equivalent input noise of the vibration sensor should be low, i.e. <−98 dB re. 1 g in ⅓rd octave band at the resonance frequency. In order to meet these requirements the mass of the moveable mass needs to be relatively high, such as higher than 1 mg. As the moveable mass typically has a thickness in the range of 100-200 μm, the large surface areas of the moveable mass can be up to 2.5 mm2. In terms of manufacturing, the moveable mass may be made of a variety of materials including steel, tantalum or tungsten.
Referring now to
As already mentioned, the vibration sensor applies a piezo electric detection principle for detecting the displacements of the moveable mass 12, 13 when the vibration sensor is exposed to external vibrations. In the embodiment shown in
The vibration sensor depicted in
Turning now to
Referring now again to
Turning now to
As seen in
As already addressed, the vibration sensor applies a piezo electric detection principle for detecting the displacements of the moveable mass 12, 13 when the vibration sensor is exposed to external vibrations. In the embodiment shown in
Similar to the embodiment depicted in
Referring now to
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| PA202170316 | Jun 2021 | DK | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/066187 | 6/14/2022 | WO |
