Vibration sensor

Abstract

The invention relates to a vibration sensor, a method for production thereof, and a wearable device including the sensor. The vibration sensor comprises a pressure detecting arrangement and a pressure generating arrangement. The pressure detecting arrangement is adapted to detect pressure variations and provide an output signal in response thereto. The pressure detecting arrangement comprises a membrane separating a front volume from a back volume, and a capacitor plate provided at a distance to the membrane. The pressure generating arrangement comprises a resilient suspension member and a mass secured thereto for movement of the mass relative to the pressure detecting arrangement. The suspension member is arranged at a distance to the membrane. The pressure generating arrangement generates pressure variations in the front volume of the pressure detecting arrangement in response to movement of the mass.

Description

[0001] VIBRATION SENSOR

[0002] Field of the invention

[0003] The present invention relates to a vibration sensor, a wearable device comprising such a vibration sensor and a method for producing a vibration sensor. In particular, the present invention relates to a vibration sensor comprising a pressure detecting arrangement comprising a membrane and a capacitor plate at a distance to the membrane.

[0004] Background of the invention

[0005] Vibration sensors include a movable mass and means for detecting the movement of said mass. A specific type of vibration sensors is a "voice pick-up unit" or "VPU", tuned to the frequencies of human voice. For example, VPUs can pick up voice by bone conduction.

[0006] In a known type of vibration sensor, the movable mass induces pressure variations in an air volume. These pressure variations are detected by a MEMS microphone. The relatively large surface that supports the movable mass is driving a small pickup surface, namely the membrane of the MEMS microphone. This detection principle is also referred to as "acoustic amplification". An example of such a device is described in EP 3 279 621 Al.

[0007] Description of the invention

[0008] A drawback of known vibration sensors is that they may suffer from damage when exposed to large vibrations. Such large vibrations for example occur in an environment with loud sound sources, e.g. at airports, at construction sites or in factories.

[0009] An object of the present invention is to provide a more durable vibration sensor, or at least to provide an alternative. This object is achieved by the system and method according to the invention.

[0010] According to the invention, the vibration sensor comprises a pressure detecting arrangement and a pressure generating element. The pressure detecting arrangement is adapted to detect pressure variations and to provide an output signal in response to the detected pressure variations. The pressure detecting arrangement comprises a membrane that separates a front volume from a back volume. The pressure generating arrangement comprises a resilient suspension member and a mass. The mass is secured to the resilient suspension member for movement of the mass relative to the pressure detecting arrangement. The resilient suspension member is arranged at a distance to the membrane of the pressure detecting arrangement. The pressure generating arrangement is arranged to generate pressure variations in the front volume of the pressure detecting arrangement in response to movement of the movable mass.

[0011] P355WOOOThe resilient suspension member is adapted to support the moving mass. By securing the mass to the resilient suspension member, rather than to the membrane of the pressure detecting arrangement, damage of the membrane is prevented. Thus, a durable vibration sensor is provided.

[0012] Preferably, the vibration sensor is a VPU, i.e. the vibration sensor is adapted for detecting human voice. For example, the VPU is tuned for detecting vibrations in a frequency range of 20 Hz - 4 kHz, for enabling detecting voice by bone conduction.

[0013] Preferably, the pressure detecting arrangement further comprises a capacitor plate provided at a distance to the membrane. The pressure detecting arrangement is then adapted for capacitive detection of pressure variations. For example, the capacitor plate is a backplate accommodated in the back volume of the pressure detecting arrangement. In another example, the capacitor plate is a front plate accommodated in the front volume of the pressure detecting arrangement. In an embodiment, the distance between the membrane and the capacitor plate of the pressure detecting arrangement is at least 20 pm, preferably between 20 - 50 pm, more preferably between 25-50 pm.

[0014] A distance of at least 20 pm prevents the membrane from hitting the capacitor plate when the sensor is exposed to large vibrations. Hitting the capacitor plate would damage the membrane. Thus, by providing a distance of at least 20 pm between the membrane and the capacitor plate, a more durable vibration sensor is provided.

[0015] The membrane has a length and a width that define the surface area of the membrane. Likewise, the resilient suspension member has a length and width that define a surface area of the resilient suspension member.

[0016] In an embodiment, the length of the membrane is at least 80% of the length of the resilient suspension member and / or the width of the membrane is at least 80% of the width of the resilient suspension member.

[0017] The pressure detecting arrangement is thus provided with a relatively large surface area, and is thus able to withstand larger pressures. Thus, the durability of the vibration sensor is improved.

[0018] Preferably, the length of the membrane exceeds the length of the resilient suspension member and / or the width of the membrane exceeds the width of the resilient suspension member. For example, the length and / or width of the resilient suspension member exceeds the width of the resilient suspension member by 5-10%.

[0019] In an embodiment, the area of the membrane is at least 80% of the area of the resilient suspension member.

[0020] For example, the resilient suspension member comprises a movable surface on which the mass is provided. In this example, the area of the membrane is preferably at least 80% of the area of the movable surface.

[0021] P355WOOOIn a further embodiment, the area of the membrane is greater than the area of the resilient suspension member. For example, the area of the membrane exceeds the area of the resilient suspension member by 5-25%, e.g. 15%.

[0022] For example, the area of the resilient suspension member is larger than 0.5 mm2, such as larger than 1 mm2, such as larger than 2 mm2, such as larger than 4 mm2, such as larger than 6 mm2, such as larger than 8 mm2, such as larger than 10 mm2.

[0023] Preferably, the mass of the moveable mass is greater than the mass of the membrane of the pressure detecting arrangement, for example at least two times greater, such as at least four times greater, such as at least six times greater, such as at least eight times greater or at least ten times greater.

[0024] For example, the mass of the moveable mass is larger than 0.004 mg, such as larger than 0.04 mg, such as larger than 0.4 mg, such as larger than 1 mg, such as larger than 2 mg, such as around 4 mg.

[0025] Preferably, the length of the vibration sensor exceeds the width of the vibration sensor. In an embodiment, the membrane of the pressure detecting arrangement has a length exceeding a width of the membrane. Preferably, such membrane is combined with a vibration sensor that has a length exceeding its width. The membrane can then span a relatively large portion of the space available in the vibration sensor. This results in a relatively large membrane, and thus in a pressure detecting arrangement that is able to withstand larger pressures. In contrast, MEMS microphones typically comprise a circular membrane. Thus, its length is restricted to its width, resulting in a small pick up surface relative to the overall size of the vibration sensor, which is not able to withstand large pressures. Moreover, increasing the size of the membrane improves the signal-to-noise ratio.

[0026] Preferably, the vibration sensor comprises electronics for sensing charge differences induced by displacement of the membrane relative to the capacitor plate.

[0027] In an embodiment, the membrane or the capacitor plate comprises an electret layer.

[0028] The electret layer for example comprises polytetrafluoroethylene (PTFE). In such case, the vibration sensor senses charge differences induced by displacement of the electret layer of the membrane or capacitor plate, relative to the other element.

[0029] An advantage of using an electret layer is that no charge pump is required for charging the capacitor, since the charge is embedded in the electret layer. The use of an electret layer thus enables operating the vibration sensor at relatively low voltages, while the sensitivity can be similar to the sensitivity of a conventional vibration sensor.

[0030] The use of an electret layer is particular advantageous in combination with a membrane to capacitor plate distance of at least 20 pm (e.g. 20-50 pm) as described above.

[0031] P355WOOOTo illustrate, we compare two exemplary vibration sensors. The first sensor has a capacitor plate with an electret layer, whereas the second sensor has an electrically conductive capacitor plate. In both exemplary sensors, the membrane comprises a metal layer and the distance between the membrane and the capacitor plate is 30 pm. In the first sensor, a charge has been injected into the electret layer, which results in an electric field strength of 14 * 106V / m (at rest, i.e. no vibrations). The second sensor is operated using a charge pump to provide a charge to the capacitor plate. To achieve a similar electric field strength as the first sensor (to achieve similar sensitivity), the charge pump would need to apply a voltage of 420 V. Such high voltages are not feasible in practice. This is particularly true for wearable devices (e.g. hearing aids or headsets), which cannot include a high voltage power supply in view of their small dimensions and / or limited battery.

[0032] In an embodiment, the electret layer has been injected with a charge that results in an electric field strength between the membrane and capacitor plate of at least 5 * 106V / m (at rest, i.e. no vibrations). Preferably, the electric field strength created by the electret layer is at least 10 * 106V / m, more preferably at least 12 * 106V / m, even more preferably at least 14 * 106V / m.

[0033] In one particular example, the pressure detecting arrangement comprises an electret microphone. In an embodiment, the vibration sensor comprises a first housing, and the membrane of the pressure detecting arrangement is provided in the first housing.

[0034] In a further embodiment, the first housing comprises support members. The capacitor plate of the pressure detecting arrangement is supported by said support members. This enables accurate positioning of the capacitor plate, thereby allowing accurately setting the distance between the membrane and the plate. Preferably, the support members protrude from a wall of the first housing.

[0035] In an embodiment, the first housing comprises metal. This increases the durability of the pressure detecting arrangement, and thus of the vibration sensor. In a further embodiment, the first housing comprises two pairs of opposing side walls comprising metal (e.g. are made of metal). In another embodiment, the first housing is made of metal.

[0036] In an embodiment, the vibration sensor further comprises a printed circuit board (PCB). The PCB is electrically connected to the pressure detecting arrangement and forms part of the first housing. Preferably, the first housing comprises a recess for receiving the PCB. In another example, the PCB is integrated into a wall of the first housing.

[0037] In an embodiment, an intermediate volume exist between the first housing and the pressure generating arrangement, and the first housing comprises an inlet opening connected to the front volume of the pressure detecting arrangement. The inlet opening thus connects the front volume to the intermediate volume.

[0038] P355WOOOFor example, the intermediate volume is smaller than 5 mm3, such as smaller than 2 mm3, such as smaller than 1 mm3, such as smaller than 0.75 mm3, such as smaller than 0.5 mm3, such as smaller than 0.25 mm3, such as smaller than 0.1 mm3.

[0039] In an embodiment, the pressure generating element comprises a second housing in which the resilient suspension member and the mass are provided. The second housing is attached to the first housing.

[0040] Optionally a spacer is provided between the first housing and the second housing. In one example, the spacer creates the intermediate volume between the first housing and the pressure generating element.

[0041] In an embodiment, the resilient suspension member comprises a hinged member. For example, the hinged member comprises a plate comprising a free end and a fixed end (e.g. fixed to a housing of the vibration sensor), wherein the fixed end acts as a hinge. For example, the hinged member is formed by cutting or punching a plate, e.g. a metal plate. In an embodiment, the membrane comprises a metal layer. For example, the membrane is made of metal, or a metal layer is provided on a non-metallic membrane. Preferably, the membrane comprises a metal layer and the capacitor plate comprises an electret layer. Preferably, the membrane does not comprise a semiconductor material. For example, the membrane does not comprise silicon. The capacitor plate preferably does not comprise a semiconductor material either, e.g. the capacitor plate does not comprise silicon.

[0042] The invention further relates to a wearable device including a vibration sensor according to any of the embodiments described herein. In addition, the invention relates to a method for producing a vibration sensor. The same technical effects as described above in relation to the vibration sensor apply to the headset and the production method. Moreover, any features of the vibration sensor described above can similarly be applied in the headset and method, and vice versa.

[0043] For example, the wearable device comprises a hearing aid or a headset. Generally, a headset includes speakers (e.g. headphones or earbuds) and a microphone. The headset preferably comprises a microphone arm comprising the vibration sensor. The microphone arm and vibration sensor may also be referred to as a "boom mic". Alternatively or additionally, the headset may be integrated in a helmet. For example, a helmet includes one or more speakers and one or more vibration sensors according to any of the embodiments disclosed herein. The production method comprises a step of providing a pressure detecting arrangement. The pressure detecting arrangement comprises a membrane separating a front volume from a back volume. The method further comprises a step of providing a pressure generating arrangement. The pressure generating element comprises a resilient suspension member. A mass is secured to the resilient suspension member for movement of the mass relative to the pressure detecting arrangement. The method further comprises a step of combining the

[0044] P355WOOOpressure generating arrangement and the pressure detecting arrangement. In this step, the pressure generating arrangement is arranged to generate pressure variations in the front volume of the pressure detecting arrangement in response to movement of the movable mass.

[0045] The step of combining for example comprises attaching a first housing in which the pressure detecting arrangement is provided to a second housing in which the pressure generating element is provided. For example, attaching comprises welding the first housing to the second housing.

[0046] Brief description of the drawings

[0047] In the following, example embodiments will be described with reference to the drawings, wherein:

[0048] Figure 1 shows a schematic cross-section of a vibration sensor according to a first embodiment;

[0049] Figure 2 shows a schematic cross-section of a vibration sensor according to a second embodiment;

[0050] Figure 3 shows a schematic cross-section of a vibration sensor according to a third embodiment;

[0051] Figure 4 shows a schematic cross-section of a vibration sensor according to a fourth embodiment;

[0052] Figure 5 shows a cross-sectional side view of a vibration sensor according to a fifth embodiment;

[0053] Figure 6 shows a cross-sectional perspective view of the vibration sensor of figure 5;

[0054] Figure 7 shows, in perspective view, details of the electret microphone of the vibration sensor of figures 5 and 6;

[0055] Figure 8 shows, in perspective view, details of the pressure generating arrangement of the vibration sensor of figures 5-7; and

[0056] Figure 9 schematically illustrates an example of a wearable device according to an embodiment of the invention.

[0057] Detailed description of the drawings

[0058] Elements in a figure that correspond to elements in a different figure have been given the same reference numeral, increased by a multiple of 100, and the same description applies to such elements - unless otherwise specified.

[0059] P355WOOOFigure 1 shows a vibration sensor 2 comprising an electret microphone 4 and a pressure generating arrangement 6. The electret microphone 4 comprises a membrane 8 that separates a front volume F from a back volume B. A capacitor plate 10 is arranged in the back volume, and may thus also be referred to as "back plate". In this example, the capacitor plate 10 is a metal plate (e.g. stainless steel) that is provided with an electret layer of PTFE. The membrane 8 is electrically conductive. In particular, the membrane 8 comprises a metal (e.g. gold, copper, brass). In this example, the membrane 8 comprises a non-conductive membrane provided with a metal layer. Specifically, the membrane 8 comprises a mylar membrane with a gold layer. Alternatively, the membrane 8 is made of a conductive material, e.g. a metal.

[0060] The electret microphone 4 further comprises a housing 12, in which the membrane 8 and the plate 10 are arranged. The housing 12 includes an inlet opening 14 connected to the front volume F. The housing 12 is made of metal.

[0061] The pressure generating arrangement 6 comprises a resilient suspension member 16. A mass 18 is secured to the resilient suspension member 16. Vibrations induce movement of the mass together with the suspension member 16, in the direction of arrows M (i.e. substantially perpendicular to the lane of the suspension member 16).

[0062] Optionally, a pair of openings 22, 24 extend through the suspension member 16 and mass 18, respectively. These openings 22, 24 may be provided to finetune the frequency response of the vibration sensor 2.

[0063] The pressure generating arrangement 6 further comprises a housing 20 in which the suspension member 16 and mass 18 are arranged. The housing 20 is made of metal, e.g. steel or mu-metal. The housing 20 of the resilient suspension member 16 is attached to the housing 12 of the electret microphone 4, in this case by welding the metal housings 12, 20 together.

[0064] The resilient suspension member 16 is arranged at a distance to the membrane 8 of the electret microphone 4. In the example of figure 1, the resilient suspension member 16 is at a distance to the housing 12 of the electret microphone, such that an intermediate volume I is formed between the electret microphone's housing 12 and the suspension member 16. The intermediate volume I is connected to the front volume F of the microphone 4 via inlet opening 14 in the housing 12 of the microphone 4.

[0065] Figure 2 shows a vibration sensor 102 according to a second embodiment. The second embodiment is the same as the first embodiment, except that the capacitor plate 110 of electret microphone 104 is positioned in the front volume F, i.e. the plate 110 forms a "front plate" rather than a "back plate". The front plate has a through-going opening 111 to ensure that pressure variations in the front volume F induced by the movement of suspension member 116 and mass 118 are able to travel to the membrane 108 for detection of vibration of membrane 108.

[0066] P355WOOOIn the example of figure 2, the front plate 110 is attached to two opposing side walls of the housing 104. Said side walls comprise cams or other protrusions to which the front plate 110 is attached, e.g. by glueing or welding.

[0067] Figure 3 shows a vibration sensor 202 according to a third embodiment. The vibration sensor 202 is a variant of the vibration sensor 102 of figure 2, wherein the front plate F is attached to the housing 212 via cams 213 protruding from a top wall of the housing 212. The top wall of housing 212 is the wall adjacent to the intermediate volume I. The top wall comprises inlet opening 214. In figure 3, the front plate F is spaced apart from two opposing side walls of the housing 212. Alternatively, the front plate F may contact the side walls.

[0068] Figure 4 shows a vibration sensor 302 according to a fourth embodiment. This embodiment is the same as the first embodiment of figure 1, except that the membrane 308 of the electret microphone 308 and the resilient support member 316 of the pressure generating arrangement 306 are provided in the same housing 320. In this embodiment, there is no intermediate volume. The front volume F of the electret microphone 304 is adjacent to both the membrane 308 and the resilient support member 316. As before, the membrane 308 and member 316 are at a distance to each other. Movement of mass 318 generates pressure variations in the front volume F that cause a detectable movement of membrane 308.

[0069] In the example of figures 1-3, the intermediate volume I is 0,2 mm3. In the example of figures 1-4, the distance between the capacitor plate 10, 110, 210, 310 and the membrane 8, 108, 208, 308 is 30 pm. However, the invention is not limited to these specific dimensions. In figures 1-4, the electret layer is provided on the capacitor plate 10, 110, 210, 310.

[0070] Alternatively, the electret layer may be provided on membrane 8, 108, 208, 308.

[0071] Figures 5 and 6 show a vibration sensor 402 according to a fifth embodiment. This embodiment is similar to the third embodiment of figure 3. The sensor 402 comprises an electret microphone 404 and a pressure generating arrangement 406. The electret microphone 404 comprises a membrane 408 that separates a front volume F from a back volume B.

[0072] The membrane 408 comprises a mylar membrane onto which a metal layer is deposited, particularly a gold layer. Capacitor plate 410 is provided with an electret layer, particularly a layer of PTFE. The electret layer of the plate 410 holds an electrical charge, which is provided by injecting charged particles into the layer.

[0073] The pressure generating arrangement 406 comprises a suspension member 416 to which a mass 418 is secured. A viscoelastic substance 419 is provided between the mass 418 and a portion of the suspension member 418 for providing damping. In this example, the viscoelastic substance is a viscoelastic gel, particularly a viscoelastic silicone gel.

[0074] The microphone 404 is provided in a first housing 412 and the pressure generating arrangement 406 is provided in a second housing 420. A spacer 434 is provided between the

[0075] P355WOOOfirst housing 412 and the second housing 420 to form the intermediate volume I (see Fig. 5). The first housing 412, spacer 434 and second housing 420 are joined together e.g. by welding or glueing.

[0076] The first housing 412 comprises a first part 412a and a second part 412b that are joint together. The first housing part 412a comprises side walls that enclose the membrane 408, and a top wall extending perpendicular to the side walls and forming a cover of the housing part 412a. The top wall comprises the inlet opening 414. The first housing part 412a is made of metal.

[0077] The second part 412b comprises a recess 426 for receiving a printed circuit board (PCB) 428. Electronics 430 are mounted to PCB 428 and electrically connected to the membrane 408 via wire 432. The electronics 430 are adapted to sense charge differences induced by displacement of the membrane 408 relative to the front plate 410. In this example, electronics 430 comprise an integrated circuit (IC).

[0078] The second part 412b may also be made of metal, or from a different material (e.g. a polymer). The first part 412a and second part 412b are joint together by welding or glueing. The housing 420 of the pressure generating arrangement 406 has a vent opening 436. During production, the sensor 402 may be subjected to heat, for example as part of a curing process. Heating the sensor 402 may cause build up of air pressure in the sensor 402. The vent opening 436 provides a pressure relief. After production, the vent opening 436 may be sealed. Vent opening 436 is optional.

[0079] Details of the electret microphone 404 are shown in figure 7. Figure 7 shows the capacitor plate 410 in a bottom view (looking in direction of arrow VII in figure 5). For clarity of illustration, membrane 408 is not shown. The capacitor plate 410 is supported by cams 413 extending from the top wall of the housing 412. Membrane 408 is supported by a frame 409 (see also Fig. 6). The frame 409 is attached to the side walls of the housing 412.

[0080] Details of the pressure generating arrangement are shown in figure 8. This figure shows the resilient suspension member 416 in a bottom view. Here, the suspension member 416 is embodied as a hinged member. In particular, the member 416 comprises a plate with a free end A and a fixed end B. At the fixed end, a portion of the plate is cut out, such that the plate is fixed via arms 438. The arms 438 are arranged for allowing a hinging movement of the free end A of the plate. To this end, the arms 438 are thin as compared to the width of the plate. For example, the hinged member is formed plate by cutting or punching a metal plate.

[0081] In all exemplary figures, the length and width of the membrane (8, 108, 208, 308, 408) of the microphone exceeds the length and width of the resilient suspension member (16, 116, 216, 316, 416). Thus, also the area of the membrane exceeds the area of the resilient suspension member. Alternatively, the area of the membrane may exceed the area of the suspension member, while either the length or the width of the membrane is equal to or

[0082] P355WOOOsmaller than the length or width of the suspension member, respectively. In a further alternative, the area of the membrane is at least 80% of the area of the suspension member, e.g. 90%, or the areas are equal.

[0083] In the specific example of figures 5-8, the membrane 408 of the electret microphone 406 has dimensions of 2.27 mm x 3.27 mm = 7.4229 mm2, and the resilient suspension member 416 has dimensions of 2.15 mm x 3 mm = 6.45 mm2. The intermediate volume I is 0,26 mm3. The moveable mass 418 has a mass of 5 mg.

[0084] In the examples of the figures 1-8, the resilient suspension member and the membrane of the electret microphone extend substantially parallel to each other when at rest (i.e. at zero vibration).

[0085] Figure 9 schematically illustrates a wearable device according to an embodiment of the invention. Specifically, figure 9 illustrates a headset 540. The headset 540 includes a headphone comprising two ear cup 544, 546 that are connected via a head band 546. The ear cups 544, 546 each include one or more speakers for generating sound. A microphone arm 548 is attached to the headphone. A microphone unit 550 is provided at the end of the microphone arm 548. The microphone unit 550 includes the vibration sensor 2, 102, 202, 302, 403 according to any of the embodiments disclosed herein.

[0086] Figures 1-8 show exemplary vibration sensors that include an electret microphone. However, the disclosure is not limited to electret microphones, and in each of the embodiments below, a different type of microphone may be employed instead of the electret microphone.

[0087] Specifically, a different type of capacitive microphone may be used instead of the electret microphone. When replacing the electret microphone for a different type of microphone in the embodiment below, the dimensions of the membrane are preferably kept the same. The present disclosure further relates to the following embodiments:

[0088] 1. A vibration sensor, comprising:

[0089] - a pressure detecting arrangement adapted to detect pressure variations and to provide an output signal in response to the detected pressure variations, the pressure detecting arrangement comprising a membrane separating a front volume from a back volume, the membrane having a length and a width that define the surface area of the membrane; and

[0090] - a pressure generating arrangement comprising a resilient suspension member and a mass secured to the resilient suspension member for movement of the mass relative to the pressure detecting arrangement, wherein the resilient suspension member is arranged at a distance to the membrane of the pressure detecting arrangement,

[0091] wherein the pressure generating arrangement is arranged to generate pressure variations in the front volume of the pressure detecting arrangement in response to movement of the movable mass.

[0092] P355WOOO2. The vibration sensor according to embodiment 1, wherein the length of the membrane is at least 80% of the length of the resilient suspension member and / or the width of the membrane is at least 80% of the width of the resilient suspension member.

[0093] 3. The vibration sensor according to embodiment 1 or 2, wherein the length of the membrane exceeds the length of the resilient suspension member and / or the width of the membrane exceeds the width of the resilient suspension member.

[0094] 4. The vibration sensor according to any one or more of the preceding embodiments, wherein the area of the membrane is at least 80% of the area of the resilient suspension member, wherein preferably the area of the membrane is greater than the area of the resilient suspension member.

[0095] 5. The vibration sensor according to any one or more of the preceding embodiments, wherein the membrane of the pressure detecting arrangement has a length exceeding a width of the membrane.

[0096] 6. The vibration sensor of any one or more of the preceding embodiments, wherein the pressure detecting arrangement further comprises a capacitor plate provided at a distance to the membrane, wherein preferably the membrane or the capacitor plate comprises an electret layer.

[0097] 7. The vibration sensor of any one or more of the preceding embodiments, further comprising a first housing, in which the membrane of the pressure detecting arrangement is provided.

[0098] 8. The vibration sensor of the combination of embodiments 6 and 7, wherein the first housing comprises support members, and the capacitor plate of the pressure detecting arrangement is supported by said support members, wherein preferably the support members protrude from a wall of the first housing.

[0099] 9. The vibration sensor of embodiment 7 or 8, further comprising a printed circuit board electrically connected to the pressure detecting arrangement, wherein the printed circuit board forms part of the first housing.

[0100] 10. The vibration sensor of any one or more of embodiments 7-9, wherein an intermediate volume exist between the first housing and the pressure generating arrangement, and the first housing comprises an inlet opening connected to the front volume of the pressure detecting arrangement.

[0101] 11. The vibration sensor of any one or more of the embodiments 7-10, wherein the pressure generating element comprises a second housing in which the resilient suspension member and the mass are provided, wherein the second housing is attached to the first housing, and optionally a spacer is provided between the first housing and the second housing.

[0102] 12. The vibration sensor according to any one or more of the preceding embodiments, wherein the membrane comprises a metal layer.

[0103] P355WOOO13. A wearable device, such as a hearing aid or headset, the wearable device including the vibration sensor of any one or more of the preceding embodiments.

[0104] 14. The wearable device of embodiment 13, wherein the device comprises a headset comprising a microphone arm comprising the vibration sensor.

[0105] 15. A method for producing a vibration sensor, the method comprising:

[0106] - providing a pressure detecting arrangement adapted to detect pressure variations and to provide an output signal in response to the detected pressure variations, the pressure detecting arrangement comprising a membrane separating a front volume from a back volume; and

[0107] - providing a pressure generating arrangement, comprising a resilient suspension member and a mass secured to the resilient suspension member for movement of the mass relative to the pressure detecting arrangement; and

[0108] - combining the pressure generating arrangement and the pressure detecting arrangement, wherein the resilient suspension member is arranged at a distance to the membrane of the pressure detecting arrangement, wherein the pressure generating arrangement is arranged to generate pressure variations in the front volume of the pressure detecting arrangement in response to movement of the movable mass.

[0109] P355WOOO

Claims

Claims1. A vibration sensor for a wearable device, comprising:- a pressure detecting arrangement adapted to detect pressure variations and to provide an output signal in response to the detected pressure variations, the pressure detecting arrangement comprising a membrane separating a front volume from a back volume, the membrane having a length and a width that define the surface area of the membrane, the pressure detecting arrangement further comprising a capacitor plate provided at a distance to the membrane, wherein the membrane or the capacitor plate comprises an electret layer, and the distance between the membrane and the capacitor plate is at least 20 pm; and- a pressure generating arrangement comprising a resilient suspension member and a mass secured to the resilient suspension member for movement of the mass relative to the pressure detecting arrangement, wherein the resilient suspension member is arranged at a distance to the membrane of the pressure detecting arrangement,wherein the pressure generating arrangement is arranged to generate pressure variations in the front volume of the pressure detecting arrangement in response to movement of the movable mass.

2. The vibration sensor according to claim 1, wherein the distance between the membrane and the capacitor plate of the pressure detecting arrangement is between 20-50 pm.

3. The vibration sensor according to claim 1 or claim 2, wherein the length of the membrane is at least 80% of the length of the resilient suspension member and / or the width of the membrane is at least 80% of the width of the resilient suspension member.

4. The vibration sensor according to any one or more of the claims 1-3, wherein the length of the membrane exceeds the length of the resilient suspension member and / or the width of the membrane exceeds the width of the resilient suspension member.

5. The vibration sensor according to any one or more of the claims 1-4, wherein the area of the membrane is at least 80% of the area of the resilient suspension member.

6. The vibration sensor according to any one or more of the claims 1-5, wherein the area of the membrane is greater than the area of the resilient suspension member.P355WOOO7. The vibration sensor according to any one or more of the claims 1-6, wherein the membrane of the pressure detecting arrangement has a length exceeding a width of the membrane.

8. The vibration sensor of any one or more of the claims 1-7, further comprising a first housing, in which the membrane of the pressure detecting arrangement is provided.

9. The vibration sensor of claim 8, wherein the first housing comprises support members, and the capacitor plate of the pressure detecting arrangement is supported by said support members, wherein preferably the support members protrude from a wall of the first housing.

10. The vibration sensor of claim 8 or 9, further comprising a printed circuit board electrically connected to the pressure detecting arrangement, wherein the printed circuit board forms part of the first housing.

11. The vibration sensor of any one or more of the claims 8-10, wherein an intermediate volume exist between the first housing and the pressure generating arrangement, and the first housing comprises an inlet opening connected to the front volume of the pressure detecting arrangement.

12. The vibration sensor of any one or more of the claims 8-11, wherein the pressure generating element comprises a second housing in which the resilient suspension member and the mass are provided, wherein the second housing is attached to the first housing, and optionally a spacer is provided between the first housing and the second housing.

13. The vibration sensor according to any one or more of the preceding claims, wherein the membrane comprises a metal layer.

14. A wearable device including the vibration sensor of any one or more of the preceding claims, the wearable device preferably comprising a headset, wherein the headset for example comprises a microphone arm comprising the vibration sensor.

15. A method for producing a vibration sensor for a wearable device, the method comprising:P355WOOO- providing a pressure detecting arrangement adapted to detect pressure variations and to provide an output signal in response to the detected pressure variations, the pressure detecting arrangement comprising a membrane separating a front volume from a back volume, the pressure detecting arrangement further comprising a capacitor plate at a distance to the membrane, wherein the membrane or the capacitor plate comprises an electret layer, and the distance between the membrane and the capacitor plate is at least 20 pm; and- providing a pressure generating arrangement, comprising a resilient suspension member and a mass secured to the resilient suspension member for movement of the mass relative to the pressure detecting arrangement; and- combining the pressure generating arrangement and the pressure detecting arrangement, wherein the resilient suspension member is arranged at a distance to the membrane of the pressure detecting arrangement, wherein the pressure generating arrangement is arranged to generate pressure variations in the front volume of the pressure detecting arrangement in response to movement of the movable mass.P355WOOO

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