Patent Description:
Most vibration sensors of today have a flat low-frequency response curve, i.e. the frequencies below the mechanical resonance frequency of typical vibrations sensors are not damped, acoustically or any other way. For various reasons, such as for example noise or overload reasons, it is advantageous to remove, or at least damp, the low frequencies. One often used approach is to remove or damp the low frequencies electronically using an electronic filter in for example the signal processing device. However, this approach is disadvantageous in that the mechanical system of the sensor or the input stage of the signal processing device might still be overloaded by precisely the low frequency signals that the electronic filter is intended to remove. Also, electronic filters take up valuable space on the ASIC, could cause distortion of the signal and cause thermal noise which may degrade the signal-to-noise ratio. Typical prior art solutions are discussed in <CIT> and <CIT>.

Moreover, <CIT> discloses various condenser microphone embodiments each comprising a protective barrier diaphragm for improved environmental resistance without causing a sensitivity reduction. <CIT> also discloses a contact-type vibration sensor. The condenser microphone embodiments and the contact-type vibration sensor are however not disclosed as being sensitive to vibrations thereof. <CIT> discloses a seismic vibration sensor for measuring low-frequency seismic waves generated by moving targets. However, measuring of low-frequency seismic waves is remote compared to the present vibration sensor where the low frequencies are attenuated.

Moreover, <CIT> discloses a pressure sensor that relies on altered resonance conditions in an ultrasound cavity, <CIT> discloses an optical microscope that utilizes a phase shift of a reflected light from a flexible acoustic membrane, <CIT> discloses displaceable electrodes with slits for an acceleration sensor, and <CIT> discloses a vibration sensor that relies on transmission of vibrations through two mutually connected vibration transmission units.

It may be seen as an object of embodiments of the present invention to provide a vibration sensor having a predetermined low-frequency response curve.

It may be seen as a further object of embodiments of the present invention to provide an arrangement where the predetermined low-frequency response curve of the vibration sensor is not provided by electronic means.

It may be seen as an even further object of embodiments of the present invention to provide a vibration sensor having a predetermined damping of a mechanical resonance frequency.

The above-mentioned objects are complied with by providing, in a first aspect, a vibration sensor comprising.

Thus, according to the first aspect the present invention relates to a vibration sensor where pressure variations generated by movements of a moveable mass are detected by an appropriate pressure detection arrangement. The generated pressure variations propagate across a pressure transmitting arrangement, which is in the form of a pressure transmitting volume, before reaching the appropriate pressure detection arrangement. As explained later the vibration sensor may comprise a plurality of moveable masses, a plurality of pressure transmitting arrangements as well as a plurality of pressure detection arrangements.

In the present disclosure a predetermined low-frequency roll-off response should be taken to mean that the vibration sensor response below a predefined frequency may be damped in a predetermined manner. In case the input signal contains high level unwanted (noise) signals below the predefined frequency this sort of damping is advantageous in that traditional overload of the processing electronics, such as ASICs, may then be completely avoided. Alternatively, the predetermined low-frequency roll-off response may be provided by the first acoustical impedance and the processing electronics in combination.

It is advantageous that the predetermined low-frequency roll-off response may open up the possibility to increase the amplification of signals with a frequency above the predefined frequency, without possible overload of the processing electronics by noise signals.

The first acoustical impedance may set a predefined damping at selected frequencies by providing a low-frequency roll-off of the response curve. The frequency below which the response may start to roll off, the so-called -<NUM> dB point, may be varied by varying the value of the first acoustical impedance, and may in principle be chosen arbitrary.

However, the -<NUM> dB point may be in the frequency range of <NUM>-<NUM>, such as around <NUM>, <NUM>, <NUM> or <NUM>.

The first acoustical impedance results in a rate at which the response curve rolls off of - 6dB/octave. Higher roll-off rates can be obtained by combining the acoustic roll-off of with other known filter/damping means, electronically, acoustically or in any other way, resulting in higher order filtering/damping.

The movable mass may be implemented in various ways, such as a solid structure. In order to be able to move in responds to vibrations the moveable mass may be suspended in a resilient suspension member. The following disclosure will reveal that the resilient suspension member may be implemented in various ways.

As indicated above the pressure transmitting arrangement involves a pressure transmitting volume where pressure variations generated by the moveable mass is allowed to propagate in order to reach an appropriate pressure detection arrangement.

The first acoustical opening defining the first acoustical impedance comprises a through-going opening having predetermined dimensions, said predetermined dimensions setting the first acoustical impedance. Generally, the larger the dimensions of the through-going opening the smaller the acoustical impedance.

The first acoustical impedance is provided between the pressure transmitting arrangement and the exterior of the vibration sensor, i.e. an open and infinite volume. Alternatively or in combination therewith the first acoustical impedance may be provided across the pressure detection arrangement, such as between the pressure transmitting arrangement and a substantially closed volume. In this configuration the pressure transmitting arrangement may act as an acoustical front volume, whereas the substantially closed volume may act as an acoustical rear volume.

The vibration sensor of the present invention further comprises a second acoustical opening defining a second acoustical impedance between the pressure transmitting arrangement and a substantially closed damping volume. The second acoustical impedance may, in combination with the moveable mass and substantially closed damping volume, set a predetermined damping of a mechanical resonance frequency of the vibration sensor.

Typically, the mechanical resonance frequency of the vibration sensor is a few kHz, such as between <NUM> and <NUM>, with peak levels up to several <NUM>'s of dB's, such as between <NUM> dB and <NUM> dB. The level of damping of the mechanical resonance frequency may range from a small damping up to complete damping of the peak, i.e. between <NUM> and <NUM> dB. The pressure transmitting arrangement and the substantially closed damping volume may be essentially oppositely arranged relative to the moveable mass, i.e. the moveable mass may, optionally in combination with a suspension member, separate the pressure transmitting arrangement and the damping volume. Thus, the suspension member and/or the moveable mass may define at least part of a boundary of the substantially closed damping volume.

The second acoustical impedance between the pressure transmitting arrangement and the damping volume comprises a through-going opening in the moveable mass and/or in a suspension member suspending the moveable mass. The predetermined dimensions of said through-going opening may determine the second acoustical impedance. Again, the larger the dimensions of the through-going opening the smaller the acoustical impedance.

The pressure detection arrangement may comprise a pressure sensitive device adapted to detect the transmitted pressure variations. As stated previously the pressure sensitive device may form part of a microphone, such as an electret microphone or a MEMS microphone.

The suspension member and/or the moveable mass may, in combination with the pressure sensitive device, define at least part of a boundary of the pressure transmitting arrangement. Moreover, a primary direction of movement of the moveable mass and a direction of movement of at least part of the pressure sensitive device, such as a detecting membrane, may be substantially parallel to each other. Alternatively, a primary direction of movement of the moveable mass and a direction of movement of at least part of the pressure sensitive device, such as a detecting membrane, may be angled relative to each other.

The vibration sensor may further comprise one or more additional moveable masses being adapted to generate pressure variations in response to respective movements thereof, wherein the one or more additional moveable masses may be adapted to move in either different directions or in essentially the same direction. Thus, the vibration sensor may for example comprise three moveable masses having the primary directions of movement in either the same direction or in directions being angled relative to each other, such as in three directions being angled essentially <NUM> degrees relative to each other in order to be sensitive to 3D vibrations.

The moveable masses may be arranged such that they generate a combined pressure difference in one pressure transmitting arrangement, said pressure difference being detected by one pressure detecting arrangement. Alternatively, the moveable masses may generate pressure differences in a plurality of pressure transmitting arrangements being detected by a plurality of pressure detecting arrangements.

In addition the moveable masses may be arranged, via their respective suspension arrangements, to provide linear and/or rotational movements in response to incoming vibrations.

The vibration sensor of the present invention may further comprise signal processing means, such as one or more ASICs, for processing the output signal from the pressure detection arrangement.

In a second aspect the present invention relates to a vibration sensor according to claim <NUM>.

Thus, according to the second aspect the present invention relates to a pressure generating arrangement that is secured to a PCB This PCB of the pressure detecting arrangement may preferably be the largest exterior surface of the pressure detecting arrangement. The reason for this being that the area of the active components of the pressure generating arrangement, such as a suspension member and a moveable mass, may then be maximized.

The suspended moveable mass generates pressure variations in response to movements of the vibration sensor.

Thus, according to the second aspect the present invention relates to a vibration sensor where pressure variations generated by movements of a moveable mass are detected by an appropriate pressure detection arrangement comprising a microphone unit comprising a microphone cartridge and a signal processing unit. The generated pressure variations propagate across a pressure transmitting arrangement, which is in the form of a pressure transmitting volume or intermediate volume, before reaching the appropriate pressure detection arrangement.

According to the invention, the microphone unit comprises a stand-alone and self-contained MEMS microphone unit comprising a MEMS microphone cartridge and the signal processing unit. In the present context a stand-alone and self-contained MEMS microphone unit should be understood as a fully functional microphone unit. The MEMS cartridge of the microphone unit may comprise a read-out arrangement comprising a piezo, a biased plate capacitor or an electret plate capacitor.

Is it advantageous to use a stand-alone and self-contained MEMS microphone in that at least the following advantages are associated therewith: low development costs, low price of the MEMS microphone unit itself, easy to brand, reflowable, digital as well as analog variants, various sizes available (trade off with performance (sensitivity/noise) etc..

The stand-alone and self-contained MEMS microphone unit comprises a PCB to which PCB the MEMS microphone cartridge and the signal processing unit are electrically connected.

An intermediate volume exists between an outer surface of the PCB of the MEMS microphone unit and a surface of the suspension member. This intermediate volume is considered a pressure transmitting volume through which volume the generated pressure variations propagate the MEMS microphone unit. In order to allow generated pressure variations to enter the MEMS microphone unit and thereby reach the MEMS cartridge the PCB comprises a through-going opening being acoustically connected to the intermediate volume. The intermediate volume is smaller than <NUM><NUM>, such as smaller than <NUM><NUM>, such as smaller than <NUM><NUM>, such as smaller than <NUM><NUM>, such as smaller than <NUM><NUM>, such as smaller than <NUM><NUM>, such as smaller than <NUM><NUM>.

In order to provide sufficient pressure variations the area of the suspension member may be larger than <NUM><NUM>, such as larger than <NUM><NUM>, such as larger than <NUM><NUM>, such as larger than <NUM><NUM>, such as larger than <NUM><NUM>, such as larger than <NUM><NUM>, such as larger than <NUM><NUM>. The mass of the moveable mass is larger than <NUM>, such as larger than <NUM>, such as larger than <NUM>, such as larger than <NUM>, such as larger than <NUM>, such as around <NUM>.

The present invention will now be described in further details with reference to the accompanying figures, wherein.

While the invention is susceptible to various modifications and alternative forms specific embodiments have been shown by way of examples in the drawings and will be described in details herein. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed.

In its broadest aspect the present invention relates to a vibration sensor where pressure variations generated by one or more moveable masses are detected using appropriate detection means, such as one or more microphones. The microphones may in principle be of any suitable type, including electret or MEMS microphones.

Referring now to <FIG> the principle underlying the present invention is depicted. Generally, the vibration sensor <NUM> of the present invention comprises a moveable mass <NUM> which is adapted to move as indicated by the arrow <NUM> in response to vibrations as indicated by arrow <NUM>. The moveable mass <NUM> is suspended is some sort of resilient suspension member <NUM> whereby the moveable mass <NUM> is allowed to move as indicated by the arrow <NUM>. The suspension member <NUM> may be implemented in various ways as depicted in <FIG>. Returning now to <FIG> a microphone <NUM> is provided in order to detect the pressure variations being transmitted through the pressure transmitting volume <NUM> in response to the vibration induced movements of the moveable mass <NUM>. A vibration sensor of the type depicted in <FIG> typically has a mechanical vibration frequency around a few kHz, such as between <NUM> and <NUM>.

Referring now to <FIG> various implementations of the resilient suspension member for suspending the moveable mass are depicted.

In <FIG> the moveable mass <NUM> is suspended to the sides via the suspension member <NUM>. The moveable mass <NUM> is adapted to respond to vibrations as indicated by the arrow <NUM>, i.e. in a direction being essentially perpendicular to the main direction of extension of the suspension member <NUM>. Pressure variations generated by movements of the moveable mass <NUM> is transmitted via the pressure transmitting volume <NUM> and detected using the microphone <NUM>.

In <FIG> the moveable mass <NUM> is positioned on top of the suspension member <NUM>. The moveable mass is <NUM> adapted to respond to vibrations as indicated by the arrow <NUM>. Associated pressure variations generated in the pressure transmitting volume <NUM> are detected using the microphone <NUM>.

In <FIG> the moveable mass <NUM> is suspended to the sides via the external suspension member <NUM>. The moveable mass <NUM> is adapted to respond to vibrations as indicated by the arrow <NUM>. Associated pressure variations generated in the pressure transmitting volume <NUM> are detected using the microphone <NUM>.

Finally, in <FIG> the moveable mass <NUM> is suspended in the external suspension member <NUM>. The moveable mass <NUM> is adapted to respond to vibrations as indicated by the arrow <NUM>, i.e. in the longitudinal direction of the suspension member <NUM>. Associated pressure variations generated in the pressure transmitting volume <NUM> are detected using the microphone <NUM>.

In the various implementations depicted in <FIG> the suspension member <NUM>, <NUM>, <NUM>, <NUM> may be in the form of a spring, such as a helical spring, a leaf spring, tensionless membrane or any other resilient material. As already addressed the microphones <NUM>, <NUM>, <NUM>, <NUM> may in principle be of any type, including electret or MEMS microphones.

Turning now to <FIG>, both <FIG> show embodiments where acoustical impedances in the form of acoustical openings <NUM>, <NUM> are provided. The acoustical impedances ensure that the vibration sensor has a predetermined low-frequency roll-off response curve, i.e. a predetermined damping of the response curve below a predetermined frequency.

<FIG> shows an embodiment of the vibration sensor where an acoustical opening <NUM> is provided between the pressure transmitting volume <NUM> and the exterior of the vibration sensor. The acoustical impedance of the acoustical opening <NUM> determines, together with the other mechanical/acoustical properties of the system, the behaviour of the low-frequency roll-off response curve of the vibration sensor, cf. <FIG> and <FIG>. In addition to the acoustical opening <NUM> the embodiment shown in <FIG> comprises a moveable mass <NUM> being suspended in a resilient suspension member <NUM>. The moveable mass <NUM> is adapted to move in the direction of the arrow <NUM>. The moveable mass <NUM> in combination with the resilient suspension member <NUM> separates the two volumes <NUM> and <NUM> - the latter being the pressure transmitting volume <NUM>. The third and optional volume <NUM> may be provided as well. The pressure variations induced by the moveable mass <NUM> is detected by the microphone <NUM>.

<FIG> shows an embodiment of the vibration sensor where an acoustical opening <NUM> is provided between the pressure transmitting volume <NUM> and a substantially closed volume <NUM>. The pressure transmitting volume <NUM> and the substantially closed volume <NUM> act as respective front and rear volumes relative to the microphone <NUM>. Similar to the embodiment of <FIG> the acoustical impedance of the acoustical opening <NUM> determines the behaviour of the low-frequency roll-off response curve of the vibration sensor, cf. <FIG> and <FIG>. In addition to the acoustical opening <NUM> the embodiment shown in <FIG> comprises a moveable mass <NUM> being suspended in a resilient suspension member <NUM>. The moveable mass <NUM> is adapted to move in the direction of the arrow <NUM>. The moveable mass <NUM> in combination with the resilient suspension member <NUM> separates volume <NUM> from the pressure transmitting volume <NUM>. The pressure variations induced by the moveable mass <NUM> is detected by the microphone <NUM>.

Turning now to <FIG> an embodiment <NUM> comprising a first acoustical opening <NUM> and a second acoustical opening <NUM> is depicted. The first acoustical opening <NUM> provides a predetermined low-frequency roll-off response curve of the vibration sensor, whereas the second acoustical opening <NUM> provides a predetermined damping of the mechanical resonance frequency of the vibration sensor. In <FIG> the first acoustical opening <NUM> connects the pressure transmitting volume <NUM> to a substantially closed rear volume <NUM>. Alternatively, the first acoustical opening <NUM> could connect the pressure transmitting volume <NUM> (front volume) with the exterior of the vibration sensor. The second acoustical opening <NUM> is provided through the moveable mass <NUM>. Alternatively or in combination therewith, the second acoustical opening <NUM> could be provided through the resilient suspension member <NUM> to which the moveable mass <NUM> is secured. The moveable mass <NUM> is adapted to move as indicated by the arrow <NUM>. The pressure variations induced by the moveable mass <NUM> is detected by the microphone <NUM>.

Still referring to <FIG> a combined low-frequency roll-off and resonance peak damping may be provided by acoustically connecting volumes <NUM> and <NUM>. Alternatively, the volumes <NUM> and <NUM> could be acoustically connected to the exterior of the vibration sensor whereby the low-frequencies will be boosted.

In the embodiments depicted in <FIG> the moveable masses and the microphones are oppositely arranged relative to the pressure transmitting volumes. In alternative embodiments the pressure transmitting volume may be curved, bended or in other ways twisted so that the moveable mass and the microphone are no longer oppositely arranged, but rather angled relative to each other, cf.

In <FIG> various simulated low-frequency roll-off responses are depicted. The shape of the low-frequency roll-off is determined by the dimensions of the first acoustical opening <NUM>, cf. A large acoustical opening results in a small first acoustical impedance which causes a large low-frequency roll-off.

Similar to <FIG> various simulated low-frequency roll-off responses are depicted in <FIG>. In addition to the first acoustical opening <NUM>, cf. <FIG>, the damping effect of the second acoustical opening <NUM> is depicted as well. Again, a large acoustical opening results in a small second acoustical impedance which causes a low resonance frequency, i.e. high damping.

<FIG> shows an embodiment <NUM> with two moveable masses <NUM>, <NUM> being suspended in respective resilient suspension members <NUM>, <NUM>. As depicted in <FIG> the moveable masses <NUM>, <NUM> are adapted to move in essentially perpendicular directions as indicated by the respective arrows <NUM>, <NUM>. Thus, the vibration sensor depicted in <FIG> is sensitive to vibrations in two perpendicular directions.

In order to provide a predetermined low-frequency roll-off response curve of the vibration sensor a first acoustical opening <NUM> is provided between the common pressure transmitting volume <NUM> and a substantially closed volume <NUM>.

Second acoustical openings <NUM>, <NUM> are provided between the common pressure transmitting volume <NUM> and the respective volumes <NUM>, <NUM> which are acoustically separated by the wall <NUM>. It should be noted that the wall <NUM> can optionally be omitted so that volumes <NUM> and <NUM> becomes a single volume, and second acoustical openings <NUM> and <NUM> act as a single acoustical opening. The second acoustical openings <NUM>, <NUM> ensure a predetermined damping of the mechanical resonance frequency of the vibration sensor. A microphone <NUM> is provided in the common pressure transmitting volume <NUM>.

Turning now to <FIG> a vibration sensor <NUM> with separate pressure transmitting volumes <NUM>, <NUM> and separate microphones <NUM>, <NUM> is depicted. Similar to the embodiment of <FIG>, the embodiment <NUM> shown in <FIG> comprises two moveable masses <NUM>, <NUM> being suspended in respective resilient suspension members <NUM>, <NUM>. The moveable masses <NUM>, <NUM> are adapted to move in essentially perpendicular directions as indicated by the respective arrows <NUM>, <NUM>.

Again, second acoustical openings <NUM>, <NUM> are provided between the separated pressure transmitting volumes <NUM>, <NUM> and the respective volumes <NUM>, <NUM> which are acoustically separated by the wall <NUM>. Similar to <FIG> the wall <NUM> can optionally be omitted so that volumes <NUM> and <NUM> becomes a single volume, and second acoustical openings <NUM> and <NUM> act as a single acoustical opening.

In order to provide a predetermined low-frequency roll-off response curve of the vibration sensor first acoustical openings <NUM>, <NUM> are provided between the separated pressure transmitting volumes <NUM>, <NUM> and respective substantially closed volumes <NUM>, <NUM>. Separate microphones <NUM>, <NUM> are provided in the respective pressure transmitting volumes <NUM>, <NUM>. It should be noted that the pressure transmitting volumes <NUM>, <NUM> may optionally be combined into a single pressure transmitting volume. Similarly, the substantially closed volumes <NUM>, <NUM> may be combined as well.

The second acoustical openings <NUM>, <NUM> ensure a predetermined damping of the mechanical resonance frequency of the vibration sensor.

Similar to the vibration sensor depicted in <FIG> the vibration sensor of <FIG> is sensitive to vibrations in two perpendicular directions. It should be noted however that vibration sensors having more than two moveable masses may be implemented as well. For example a 3D vibration sensor involving three moveable masses may be implemented if the movements of the respective three moveable masses are essentially perpendicular to each other.

Generally and as previously addressed, the moveable masses may be suspended to perform rotational movements instead of, or in combination with, linear movements.

<FIG> shows a vibration sensor <NUM> comprising a MEMS microphone and a pressure variation generator arranged on top of the MEMS microphone. The MEMS microphone may apply various technologies, including piezo, charged plate capacitor etc. The signal processing of the MEMS microphone may be analog or digital applying any digital coding scheme.

The MEMS microphone comprises a housing having a top PCB <NUM> and a bottom PCB <NUM> on which electrodes <NUM>, <NUM> for electrically connecting the vibration sensor <NUM> are provided. The electrodes <NUM>, <NUM> may be in the form of solder pads.

An acoustical opening <NUM> is provided in the top PCB <NUM>. A wall portion <NUM> is provided between the top PCB <NUM> and the bottom PCB <NUM>. Within the MEMS microphone a MEMS cartridge <NUM> comprising a membrane <NUM> and a front chamber <NUM> is provided. The MEMS microphone further comprises a back chamber <NUM> within which back chamber <NUM> a signal processor <NUM> and one or more via's <NUM> are provided. As addressed above a pressure variation generator is arranged on top of the MEMS microphone. As seen in <FIG> the pressure variation generator is secured to the top PCB <NUM>. The pressure variation generator comprises a housing <NUM>, a suspension member <NUM> and a moveable mass <NUM> secured to the suspension member <NUM>. The suspension member <NUM> and the moveable mass <NUM> comprise respective acoustical openings <NUM> and <NUM>.

The housing <NUM> of the pressure variation generator can be made of any suitable material as long as it seals the inside completely. Preferably, a thin metal shield is applied. A small hole with a low-frequency roll off below <NUM> may be allowed as such a small hole does not introduce acoustic noise.

The mass of the moveable mass <NUM> is preferable around <NUM>. It is estimated that the practical minimum mass would be around <NUM> as this would add +<NUM> dB to the noise.

Similarly, a mass of <NUM> would add +<NUM> dB to the noise, and a mass of <NUM> would add +<NUM> dB to the noise. Thus, the higher the mass of the moveable mass the lower is the effect of the thermal movement noise of the vibration sensor.

The area of the suspension member <NUM> and the moveable mass <NUM> should be as large as possible, and preferably larger than <NUM><NUM>, such as larger than <NUM><NUM>, such as larger than <NUM><NUM>, such as larger than <NUM><NUM>, such as larger than <NUM><NUM>, such as larger than <NUM><NUM>, such as larger than <NUM><NUM>. A large area of the suspension member <NUM> and the moveable mass <NUM> is advantageous as this requires a smaller amplitude of the movement of the moveable mass <NUM> in order to reach certain volume displacement and thereby sensitivity.

As seen in <FIG> a small volume exists between the suspension member <NUM> and the upper side of the top PCB <NUM>. The volume should be as small as possible, and preferably smaller than <NUM><NUM>, such as smaller than <NUM><NUM>, such as smaller than <NUM><NUM>, such as smaller than <NUM><NUM>, such as smaller than <NUM><NUM>, such as smaller than <NUM><NUM>, such as smaller than <NUM><NUM>.

A compliant sealing <NUM> in the form of for example a foil, membrane or gel is preferably provided along the edges of the suspension member <NUM>. Preferably, the compliant sealing should have a low stiffness and it should be able to withstand reflow temperatures.

Optionally the volume above the suspension member <NUM> of the pressure variation generator may be acoustically connected to the back volume <NUM> of the MEMS microphone. This acoustical connection (not shown) may be provided by for example a tube.

<FIG> shows a vibration sensor <NUM> also comprising a MEMS microphone and a pressure variation generator arranged on top of at least part of the MEMS microphone. Again, the MEMS microphone may apply various technologies, including piezo, charged plate capacitor etc., and the signal processing of the MEMS microphone may be analog or digital applying any digital coding scheme.

Referring to <FIG> the MEMS microphone comprises a housing having a shield <NUM> and PCB <NUM> on which electrodes <NUM> for electrically connecting the vibration sensor <NUM> are provided. The electrode <NUM> may be in form of solder pads.

An acoustical opening <NUM> is provided in the PCB <NUM>. Within the MEMS microphone a MEMS cartridge <NUM> comprising a membrane <NUM> and a front chamber <NUM> is provided. The MEMS microphone further comprises a back chamber <NUM> within which back chamber <NUM> a signal processor <NUM> is provided. As addressed above a pressure variation generator is arranged on top of at least part of the MEMS microphone. As seen in <FIG> the pressure variation generator is secured to the PCB <NUM>. The pressure variation generator comprises a housing <NUM>, a suspension member <NUM> and a moveable mass <NUM> secured to the suspension member <NUM>. The moveable mass <NUM>, which has an opening <NUM>, and the suspension member <NUM> may be implemented as disclosed in relation to the embodiment shown in <FIG>.

Similar to the embodiment shown in <FIG> a small volume <NUM> exists between the suspension member <NUM> and the upper side of the PCB <NUM>. Again, this volume should be as small as possible, and preferably smaller than <NUM><NUM>, such as smaller than <NUM><NUM>, such as smaller than <NUM><NUM>, such as smaller than <NUM><NUM>, such as smaller than <NUM><NUM>, such as smaller than <NUM><NUM>, such as smaller than <NUM><NUM>.

<FIG> shows yet another vibration sensor <NUM> also comprising a MEMS microphone and a pressure variation generator arranged on top of a MEMS microphone. Compared to <FIG> and <FIG> the vibration sensor depicted in <FIG> is turned up-side down. Again, the MEMS microphone may apply various technologies, including piezo, charged plate capacitor etc., and the signal processing of the MEMS microphone may be analog or digital applying any digital coding scheme.

In <FIG> the MEMS microphone comprises a housing having a shield <NUM>, PCB <NUM> and a support structure <NUM> on which electrodes <NUM> for electrically connecting the vibration sensor <NUM> are provided. The electrodes <NUM> may be in form of solder pads.

An acoustical opening <NUM> is provided in the PCB <NUM>. Within the MEMS microphone a MEMS cartridge <NUM> comprising a membrane <NUM> and a front chamber <NUM> is provided. The MEMS microphone further comprises a back chamber <NUM> within which back chamber <NUM> a signal processor <NUM> is provided. As seen in <FIG> the pressure variation generator is secured to the PCB <NUM>. The pressure variation generator comprises a housing <NUM>, a suspension member <NUM> and a moveable mass <NUM> secured to the suspension member <NUM>. The moveable mass <NUM>, which comprises an opening <NUM>, and the suspension member <NUM> may be implemented as disclosed in relation to the embodiment shown in <FIG>.

Claim 1:
A vibration sensor (<NUM>, <NUM>) comprising
<NUM>) a pressure detecting arrangement adapted to detect generated pressure variations, and provide an output signal in response to the detected pressure variations, wherein the pressure detecting arrangement comprises a MEMS microphone comprising a housing having a PCB (<NUM>, <NUM>), wherein an acoustical opening (<NUM>, <NUM>) is provided in the PCB (<NUM>, <NUM>), and wherein the MEMS microphone further comprises a MEMS cartridge (<NUM>, <NUM>) comprising a membrane (<NUM>, <NUM>) and a front chamber (<NUM>, <NUM>), and a back chamber (<NUM>, <NUM>) within which back chamber (<NUM>, <NUM>) a signal processor (<NUM>, <NUM>) is provided,
<NUM>) a pressure generating arrangement adapted to generate pressure variations in response to vibrations thereof, wherein the pressure generating arrangement comprises a housing (<NUM>, <NUM>), a suspension member (<NUM>, <NUM>) and a moveable mass (<NUM>, <NUM>) secured to the suspension member (<NUM>, <NUM>)
wherein the pressure generating arrangement is secured to the PCB (<NUM>, <NUM>) and is arranged on top of the MEMS microphone, and wherein a volume (<NUM>, <NUM>) exists between the suspension member (<NUM>, <NUM>) and an upper side of the PCB (<NUM>, <NUM>), and wherein the acoustical opening (<NUM>, <NUM>) in the PCB (<NUM>, <NUM>) is acoustically connected to the volume (<NUM>, <NUM>), and wherein the suspension member (<NUM>, <NUM>) and the moveable mass (<NUM>, <NUM>) comprise respective acoustical openings, and
wherein the volume (<NUM>, <NUM>) is smaller than <NUM><NUM>, such as smaller than <NUM><NUM>, such as smaller than <NUM><NUM>, such as smaller than <NUM><NUM>, such as smaller than <NUM><NUM>, such as smaller than <NUM><NUM>, such as smaller than <NUM><NUM>.