Laser microphone, vehicle with laser microphone, and method for detecting sound waves using a laser microphone

Abstract

The invention relates to a laser microphone for detecting sound waves (14) comprising at least a laser device (12) for emitting and detecting laser radiation (121) and at least one passive transducer (10) comprising a housing (101) and a diaphragm (102) connected to the housing (101) and movable relative to the housing (101).The invention is characterized in that the laser radiation (121) strikes both the housing (101) and the membrane (102), the laser radiation (121) is reflected by the housing (101) and the membrane (102) and forms a reflected laser radiation (20), then at least a part of the reflected laser radiation (20) is detected by the laser device (12) and a membrane vibration (16) and a housing vibration (16) are determined from the detected reflected laser radiation (20), wherein the laser microphone is configured to determine the mechanical vibration (16) caused by the sound waves (14) by comparing the membrane vibration (16) with the housing vibration (16).

Description

[0001] The invention relates to a laser microphone for detecting sound waves, a vehicle with a laser microphone and a method for detecting sound waves using a laser microphone.

[0002] Such a laser microphone can comprise at least one laser device for emitting and detecting laser radiation. The at least one laser device is configured to generate and emit laser radiation, preferably in the visible light range. In particular, the laser device is configured to detect at least a portion of the laser radiation emitted by the laser device and preferably reflected by an object. The object can be an article that reflects the laser radiation. The laser radiation is preferably detected by a detection unit. Detection can be performed, for example, via at least one optical sensor or at least one photodetector, in particular via at least one photodiode and / or a video camera.

[0003] The object at which the laser radiation from the laser device is reflected is preferably at least one passive transducer. A housing and a membrane of the at least one passive transducer are configured to reflect the laser radiation. In particular, the housing and / or the membrane are coated with a layer of a material that reflects the laser radiation, and / or the housing and / or the membrane comprise a material that reflects the laser radiation.

[0004] In addition to the at least one laser device, the laser microphone thus comprises at least one passive transducer, which comprises the housing, which can be attached to a vehicle, for example, and the membrane connected to the housing and movable relative to the housing. Preferably, a surface of the membrane can be divided into an outer region, which completely encloses an inner region, wherein at least a portion of the outer region is connected to the housing and at least a portion of the inner region is configured to be deflected relative to the housing.

[0005] The diaphragm is configured to vibrate mechanically relative to the housing due to the sound waves. When the sound waves strike the diaphragm (in the following, "sound waves" refers only to those sound waves that strike the diaphragm), the diaphragm is configured to vibrate relative to the housing. In other words, the diaphragm is configured to exhibit a mechanical vibration relative to the housing when the sound waves strike the diaphragm. Preferably, the mechanical vibration comprises a relative movement, in particular of the inner region of the diaphragm, relative to the housing.

[0006] In this context, DE 20 2005 006 661 U1 shows a laser-assisted contactless scanning of a membrane deflected by a sound pressure, whereby the laser beam is reflected from the membrane to a receiver.

[0007] US 10 362 409 B1 shows a method for capturing audio signals from a surface using an optical microphone.

[0008] WO 2017 / 085 571 A1 shows a device comprising at least one acoustic and one optical microphone, wherein the signal of the acoustic microphone is improved with the aid of the signal of the optical microphone.

[0009] US 2022 / 0 167 096 A1 discloses an optical microphone whose principle is based on an interference measurement between two light beams, at least one of which strikes a reflecting membrane of the optical microphone.

[0010] One problem with these devices and / or methods is vibrations that are transmitted from the housing to the membrane, thus also contributing to the membrane's vibration. This is particularly the case when a passive transducer is mounted on a vibrating object, such as a vehicle component.

[0011] A solution to this is provided by structure-borne sound sensors, which, however, require a cable to the structure-borne sound sensor and thus to the passive transducer.

[0012] The invention is based on the object of providing a microphone which is characterized in that no cable has to lead to a measuring point at which the sound waves incident there are recorded, which cable is set up for data transmission of signals determined at the measuring point based on the sound waves incident there.

[0013] The problem is solved by the subject matter of the independent patent claims. Advantageous further developments of the invention are described by the dependent patent claims, the following description, and the figures.

[0014] The invention is based on the finding that by using a laser microphone, a laser device for sampling a vibration of a passive transducer can be placed separately from the passive transducer, whereby only the laser device needs to be connected to at least one data and / or power line, while the position of a measuring point at which at least one passive transducer is located is not restricted by a data and / or power line.

[0015] The invention relates to a laser microphone comprising at least one laser device and at least one passive transducer, wherein the at least one laser device is configured to scan both the housing and the diaphragm of the at least one passive transducer using laser radiation from the laser device. The scanning process comprises the following steps: The laser radiation emitted by the laser device (emitted laser radiation) strikes both the housing and the diaphragm of the passive transducer. This can happen either simultaneously or serially. In other words, the laser device can emit a laser beam consisting of directed laser radiation, i.e., laser radiation propagating in a predeterminable direction. The point of impact of the laser beam, i.e., the point at which the laser beam strikes, for example, the diaphragm or the housing, can alternate between at least one point on the housing and at least one point on the diaphragm. Additionally or alternatively, the laser device can emit at least two laser beams, with at least one laser beam striking the housing and at least one other laser beam striking the diaphragm.

[0016] The laser radiation is reflected from the at least one point of incidence by the housing and the membrane, forming the reflected laser radiation. At least a portion of the reflected laser radiation is detected by at least one detection unit of the laser device. The portion of the reflected laser radiation detected by the detection unit is referred to below as the detected laser radiation.

[0017] From the detected laser radiation, a membrane vibration and a housing vibration are determined. In other words, the detected portion of the laser radiation reflected by the housing (housing laser radiation) and the detected portion of the laser radiation reflected by the membrane (membrane laser radiation) are considered separately. The housing vibration, i.e., a vibration of the housing, is determined from the housing laser radiation. The membrane vibration, i.e., a vibration of the membrane, is determined from the membrane laser radiation. The membrane vibration includes, in particular, the mechanical vibration of the membrane due to sound waves impinging on the membrane.In addition to the sound waves hitting the membrane, other factors can lead to movement and / or vibration of the membrane, whereby the vibration generated by the other factors is only part of the membrane vibration, but not part of the sound-induced mechanical vibration.

[0018] The detection of the housing vibration and the detection of the membrane vibration is preferably carried out using a technique known from a scanning vibrometer. The scanning vibrometer can be based on laser Doppler vibrometry, in which, due to the vibration of an object on which emitted laser radiation is reflected, the reflected laser radiation changes frequency due to the Doppler effect. This frequency change of the reflected laser radiation compared to the emitted laser radiation can be determined by interferometry of the emitted laser radiation with the reflected laser radiation.

[0019] The laser microphone is designed to determine the mechanical vibration induced by the sound waves by comparing the diaphragm vibration with the housing vibration. This means that the difference between the diaphragm vibration and the housing vibration is determined, particularly with the housing vibration as the subtrahend. Calculating this difference yields the mechanical vibration, i.e., the information about the sound waves.

[0020] The diaphragm vibration consists of the mechanical vibration generated by the sound waves and a vibration transmitted from the housing to the diaphragm. If the housing vibration and the diaphragm vibration are determined separately, the mechanical vibration can be determined by subtracting the diaphragm vibration transmitted from the housing to the diaphragm from the diaphragm vibration. For the subtraction, the housing vibration signal can be convolved with a transfer function that represents a transfer characteristic from the housing to the diaphragm. The transfer function can be determined using a sound-free test measurement. In other words, the sound-free test measurement can be used to determine the relative movement of the diaphragm to the housing due to housing vibration.The relative movement of the diaphragm to the enclosure in an anechoic chamber results primarily from the diaphragm's inertia, especially when excited by the enclosure. Knowing the enclosure vibration and the relative movement of the diaphragm to the enclosure, the total vibration of the diaphragm, which is not sound-induced, can be determined. By subtracting this non-sound-induced total vibration from the diaphragm vibration, the sound-induced mechanical vibration can be determined. This difference calculation has the advantage that relative movements between the laser device and the passive transducer are zeroed, since they are included in both the enclosure vibration measurement and the diaphragm vibration measurement.

[0021] This has the advantage that no cable is required to reach the measuring point. This provides greater flexibility in choosing the measuring point, i.e., the location where the passive transducer is mounted.

[0022] The invention also includes further developments which result in additional advantages.

[0023] A further development comprises the at least one passive transducer having elements that reflect or non-reflect the laser light for calibrating the at least one laser device. This provides the advantage of facilitating the alignment of the laser device. The calibrating elements are called calibration elements.

[0024] The laser microphone must be designed such that emitted laser radiation strikes the passive transducer, and the laser device is configured to detect at least a portion of the reflected laser light. At least one point of incidence of the emitted laser radiation is located on the diaphragm, preferably centrally on the diaphragm with respect to the attachment of the diaphragm to the housing and / or at the point on the diaphragm where the deflection of the vibration is greatest. This selection results in a particularly strong signal. At least one other point of incidence of the emitted laser radiation is located on the housing.Those points of incidence which are provided and / or which are selected such that, with correct positioning and / or alignment of the at least one passive transducer and / or the laser device, at least a part of the reflected light strikes the detection unit of the laser device, preferably independently of the deflection of the membrane, are referred to as optimal points of incidence.

[0025] In order for the impact points, in particular some or all of the optimal impact points, to be hit by the emitted laser radiation, the laser device must have a predeterminable alignment relative to the at least one passive transducer. In particular, after a repair and / or replacement of at least one passive transducer and / or the laser device, an alignment (calibration) of the laser device may be necessary, preferably to establish the predeterminable alignment of the laser device relative to the passive transducer.

[0026] The calibration elements are designed to enable easy alignment of the laser device. This can be achieved, for example, by reflective elements in a non-reflective region of the passive transducer, by reflective elements whose reflection differs from the reflection of the passive transducer, and / or by non-reflective elements in a reflective region of the passive transducer. If the emitted laser radiation strikes at least one of the calibration elements, the reflection behavior of the emitted laser radiation differs from its reflection behavior upon impact with the passive transducer.For example, by moving the laser device and / or the passive transducer, where movement can be understood as a shift and / or tilt about at least one axis, the reflection behavior of the emitted laser radiation changes when the point of incidence changes from a point on the passive transducer where no calibration element is located to a point on the passive transducer where a calibration element is located. The positions of the calibration elements can be detected by moving the passive transducer and / or the laser device. The calibration elements are located at positions that can be specified relative to at least one optimal point of incidence.If the positions of the calibration elements relative to at least one optimal point of impact as well as the positions of the calibration elements in space are known, the laser device can be aligned such that the points of impact of the emitted laser radiation correspond to the optimal points of impact.

[0027] A further development comprises the at least one passive transducer having a light limiter to prevent reflection of scattered light from the at least one passive transducer if the scattered light comes from a direction other than the at least one direction of the at least one laser device. This means that scattered light, i.e. light whose origin is not in the laser device, for example light from the sun or light from a light source, for example an LED (light emitting diode), which is not laser light and / or which does not come from the direction of the laser device and / or does not have the same direction as the laser beam, is not reflected from the at least one passive transducer due to the light limiter.This results in the advantage that a person is not dazzled, especially by scattered light reflected by at least one passive transducer, for example, the driver of a vehicle with at least one laser microphone. This can contribute to safer driving. In particular, the light limitation can lead to a less noisy measurement.

[0028] The light limitation can be designed, for example, as an LCF (light control film) and / or as a device, particularly a tubular or hollow-cylindrical device, which shields stray light from all directions except for at least one predeterminable direction. In particular, a direction refers to a solid angle range.

[0029] A further development provides that a single laser device is configured to repeatedly scan at least two passive transducers one after the other. In other words, this means that the laser radiation from a single laser device strikes the impact points of at least two passive transducers, with the scanning taking place repeatedly one after the other. This means that with N passive transducers, the laser radiation from the laser device first strikes the impact points of the first passive transducer, then those of the second passive transducer, and so on, until after the Nth passive transducer the laser radiation again strikes the impact points of the first passive transducer. This can be achieved, for example, by a movable laser device and / or movable mirrors and / or lenses in the laser device.

[0030] This has the advantage that a single laser device can scan multiple passive transducers and thus record mechanical vibrations caused by the sound waves at multiple measuring points. This is particularly advantageous because the laser device is at least one expensive component of the laser microphone, while the at least one passive transducer is very inexpensive in comparison. Since the number of passive transducers determines the number of measuring points, the number of measuring points can be increased cost-effectively by scanning multiple passive transducers using a single laser device. The increased number of measuring points can, for example, lead to better localization of a sound, which in turn enables better suppression of background noise, for example by removing noise from other spatial angles.In particular, a microphone arrangement (microphone array) can be realized cost-effectively by increasing the number of measuring points.

[0031] As a further solution, the invention encompasses a vehicle with a laser microphone according to the invention. By comparing the housing vibration with the diaphragm vibration, even in vibrating systems—that is, in systems such as a vehicle in which the housing exhibits vibrations that it transmits to the diaphragm—the mechanical vibration due to sound waves can be distinguished from the vibration transmitted via the housing to the diaphragm, thus allowing sound waves to be detected.

[0032] A further development of the vehicle comprises that the passive transducers are arranged in at least one group and one laser device per group is configured to carry out the repeated, successive scanning of all passive transducers in the respective group. This means that all passive transducers in a group are located within a predeterminable solid angle range under which the laser device sees the group, so that scanning can be carried out at at least one predeterminable frequency, for example 8 kHz. A suitable parameter can be the distance between the laser device and the group or the distance between the passive transducers in the group. This means that the laser device and / or movable parts in the laser device can be moved so quickly that all passive transducers in a group are scanned by the laser device at the predeterminable frequency.

[0033] This has the advantage that multiple measuring points, particularly multiple measuring points within a single solid angle range, enable better angular resolution than fewer measuring points. This means that the greater number of measuring points allows the source of a noise to be determined more precisely. Particularly in a vehicle, where the solid angle range from which the relevant noises are coming is known, background noise can be effectively removed by using multiple measuring points, for example for operating predefined functions, particularly via voice commands and / or for telephone calls. Background noise can be removed by filtering out noises from solid angle ranges other than those identified as relevant.Relevant spatial angle ranges can be identified, for example, as the spatial angle range in which the driver's head and / or the driver and / or at least one person and / or the head of a person are located. By using multiple passive transducers in groups, improved spatial resolution of the noise, particularly of the noise sources, can be achieved at low cost (the only costs are for additional passive transducers, which are, however, inexpensive compared to the laser device), thereby enabling cost-effective background noise suppression.

[0034] Additionally or alternatively, better spatial resolution of the noise enables more precise identification of the noise source. In particular, it can be provided that activation and / or deactivation of certain functions can only be carried out by the driver. In the case of voice input, this requires that a distinction must be made, particularly by localizing the noise source, as to whether the noise, in this case the voice command, is coming from the driver or from another person, for example someone leaning towards the driver. In particular, with driving-relevant and / or safety-relevant functions such as driver assistance systems, precise spatial resolution, in particular of a voice command, can be safety-relevant so that the function cannot be deactivated without the driver's knowledge, for example.

[0035] A further development of the vehicle includes the vehicle comprising a plurality of passive transducers and a central scanning arrangement, wherein the central scanning arrangement comprises at least one laser device and is configured to scan all passive transducers within the vehicle. This means that all laser devices installed in the vehicle are combined in a single scanning arrangement. The scanning arrangement is characterized in that all laser devices are arranged in a single housing and / or are powered by a common driver circuit.

[0036] This has the advantage that the cabling effort is significantly reduced, which is accompanied by cost and / or effort savings, particularly during assembly and / or repair. The reduction in cabling effort results from the fact that only the laser device of a laser microphone requires a cable connection, with all laser devices being located in a central scanning arrangement and in particular at a single installation location in the vehicle, whereas the at least one passive transducer does not require a cable connection since it does not transmit signals to a receiver and does not require a power supply. The central scanning arrangement in combination with at least one passive transducer advantageously enables the implementation of a laser microphone in a vehicle for recording sound waves with a single cable to the installation location.

[0037] A further development of the vehicle comprises that the at least one passive transducer is fastened to a surface in the vehicle and / or behind the surface of the vehicle at a measuring point, wherein the surface is at least partially permeable to both the laser radiation and the sound waves, at least at the measuring point. This results in the advantage of particularly simple assembly and / or installation of a laser microphone in the rest of the vehicle, since the at least one passive transducer can be attached, in particular by selecting a suitable shape adapted to the rest of the vehicle, for example by gluing it to a surface or behind a surface, preferably a sound- and laser-transparent surface and / or a surface with a sound- and laser-transparent hole.

[0038] A further development of the vehicle comprises the at least one passive transducer and / or the at least one laser device and / or the scanning arrangement being mounted at a fastening point so as to be movable relative to the rest of the vehicle in order to reduce the transmission of vibrations from the vehicle to the at least one passive transducer and / or the at least one laser device and / or the scanning arrangement. The fastening point is the point at which the at least one passive transducer and / or the at least one laser device and / or the scanning arrangement is connected to the rest of the vehicle / held in the vehicle. The advantage of the movable mounting is that the vibrations of the rest of the vehicle, which are transmitted to the membrane via the housing, are attenuated and thus fewer and / or less strong vibrations which do not originate from sound waves influence the membrane vibration.

[0039] As a further solution, the invention comprises a method for detecting sound waves by means of the laser microphone according to the invention, wherein the at least one laser device scans both the housing and the membrane of the at least one passive transducer by means of the laser radiation in that the laser radiation strikes both the housing and the membrane, the laser radiation is reflected by the housing and the membrane and forms a reflected laser radiation, at least a part of the reflected laser radiation is detected by the laser device and a membrane vibration and a housing vibration are determined from a detected reflected laser radiation, wherein the mechanical vibration caused by the sound waves is determined from a comparison of the membrane vibration, which comprises at least the mechanical vibration, with the housing vibration.

[0040] For use cases or application situations that may arise during the method and which are not explicitly described here, it may be provided that, in accordance with the method, an error message and / or a request to enter user feedback is issued and / or a default setting and / or a predetermined initial state is set.

[0041] The invention also includes further developments of the method according to the invention that have features already described in connection with the further developments of the vehicle according to the invention and / or the laser microphone according to the invention. For this reason, the corresponding further developments of the method according to the invention are not described again here.

[0042] The vehicle according to the invention is preferably designed as a motor vehicle, in particular as a passenger car or truck, or as a passenger bus or motorcycle.

[0043] The invention also includes an evaluation unit for evaluating the housing vibration and the diaphragm vibration, as well as for calculating the difference between the diaphragm vibration and the housing vibration. The evaluation unit can comprise a data processing device or a processor device configured to carry out an embodiment of the method according to the invention. For this purpose, the processor device can comprise at least one microprocessor and / or at least one microcontroller and / or at least one FPGA (Field Programmable Gate Array) and / or at least one DSP (Digital Signal Processor). In particular, a CPU (Central Processing Unit), a GPU (Graphical Processing Unit), or an NPU (Neural Processing Unit) can be used as the microprocessor.Furthermore, the processor device can have program code configured to implement the embodiment of the method according to the invention when executed by the processor device. The program code can be stored in a data memory of the processor device. The processor device can be based, for example, on at least one circuit board and / or on at least one SoC (System on Chip).

[0044] The invention also encompasses combinations of the features of the described embodiments. The invention therefore also encompasses implementations that each comprise a combination of the features of several of the described embodiments, unless the embodiments are described as mutually exclusive.

[0045] Exemplary embodiments of the invention are described below. Shown are: Fig. 1 is a schematic representation of an embodiment of a laser microphone; Fig. 2 a possible embodiment of the passive converter with calibration elements; and Fig. 3 an embodiment of the vehicle with at least one laser microphone.

[0046] The exemplary embodiments explained below are preferred embodiments of the invention. In the exemplary embodiments, the described components of the embodiments each represent individual features of the invention that can be considered independently of one another, each of which also develops the invention independently of one another. Therefore, the disclosure is intended to encompass combinations of the features of the embodiments other than those shown. Furthermore, the described embodiments can also be supplemented by further features of the invention already described.

[0047] In the figures, the same reference symbols designate elements with the same function.

[0048] Fig. 1 shows a schematic representation of an embodiment of a laser microphone. The laser microphone comprises at least one passive transducer 10 and at least one laser device 12. The passive transducer 10 comprises a housing 101 and a diaphragm 102, which is designed to be movable relative to the housing 101 and can bend and / or oscillate, for example, under the influence of air pressure changes caused by sound waves 14. The bending and / or oscillation of the diaphragm 102 due to the sound waves 14 is referred to as mechanical vibration 16, which is represented by the double arrow marked with the reference number 16 on the diaphragm 102. The diaphragm 102 is attached to the housing 101 via at least one attachment 103 such that the mechanical vibration 16 of the diaphragm 102 can be enabled.In order for the membrane 102 to be configured to carry out the mechanical oscillation 16, the passive transducer 10 may comprise a cavity 104, for example similar to a loudspeaker.

[0049] The laser device 12 comprises a device for generating laser radiation, known for example from the prior art, so that the laser device 12 is configured to emit emitted laser radiation 121. This emitted laser radiation 121 strikes at least one point of impact 18 on the passive transducer 10. According to the invention, at least one point of impact 18 lies on the housing 101 of the passive transducer 10, the housing point of impact 18G, and at least one other point of impact 18 lies on the membrane 102, the membrane point of impact 18M. This can be realized by a laser beam 122, which can consist of directed laser radiation 121, alternately striking the points of impact 18 on the passive transducer 10. In the Fig. 1, this would mean that the laser beam 122 alternately strikes the housing impact point 18G and the membrane impact point 18M. Alternatively, the emitted laser radiation 121 may comprise a plurality of laser beams 122, i.e., the laser device 12 emits a plurality of laser beams 122, each laser beam 122 striking at least one impact point 18. In the example shown in Fig. 1, the laser device 12 can, for example, emit two laser beams 122, wherein of the two emitted laser beams 122, a housing laser beam 122G impinges on the housing impact point 18G and a membrane laser beam 122M impinges on the membrane impact point 18M.

[0050] The housing 101 and the membrane 102 of the passive transducer 10 are characterized, at least at the respective point of impact 18, preferably on the entire surface facing the laser device 12, apart from any calibration elements 26 present, in that they reflect the laser radiation 121 or at least a portion of the laser radiation 121, which, when laser radiation 121 impinges on at least one point of impact 18, results in the reflected laser radiation 20. The laser device 12 and the passive transducer 10 are aligned relative to one another such that the reflected laser radiation 20 impinges on a detection unit 123 of the laser device 12.

[0051] The detection unit 123 is characterized in that it can detect laser radiation 121 when the laser radiation 121 strikes the detection unit 123. Vibrations at the impact points 18 can lead to changed travel times of the laser radiation 121 and / or changed frequencies of the laser radiation 121, which can be determined, for example, using a technique known from laser scanning vibrometry. Using the reflected laser radiation 20 detected by the detection unit 123, a housing vibration can be determined by the at least one housing laser beam 122G reflected at the at least one housing impact point 18G, and a membrane vibration, which includes the mechanical vibration 16 of the membrane 102, can be determined by the at least one membrane laser beam 122M reflected at the at least one membrane impact point 18M.The sound wave-induced mechanical vibration 16 can be determined from the difference between the housing vibration and the membrane vibration.

[0052] Since the housing 101 and the membrane 102 of the passive transducer 10 can have a surface that reflects at least the laser radiation 121, it can be disruptive if scattered light 22, with the exception of the laser radiation 121 emitted by the laser device 12, is reflected by the passive transducer 10. In particular, the laser microphone can be integrated into a vehicle, whereby scattered light 22 reflected by the passive transducer 10 can, for example, disturb a driver, especially if the scattered light 22 is reflected in such a way that it falls into the driver's eye.

[0053] In order to avoid dazzling the driver, it can be provided that the laser microphone has a light limiter 24 through which the laser radiation 121 can pass from the laser device 12 to the passive transducer 10 and from the at least one point of impact 18 on the passive transducer 10 to the detection unit 123 of the laser device, but no scattered light 22 from another direction can be reflected at the passive transducer 10. This can, as in Fig. 1, for example, via a tubular or cylindrical arrangement. In Fig. 1 shows by way of example that the laser radiation 121 coming from the laser device 12 can enter through an inlet opening 241 of the light limiter 24, can be reflected by the passive converter 10 and can exit again through the inlet opening 241 from the light limiter 24 and can strike the detection unit 123 of the laser device 12. Scattered light 22, however, which as in Fig. 1 shown by way of example, from the side which hits the light barrier 24 which is opaque apart from the inlet opening 241, is blocked by the light barrier 24 and cannot reach the passive converter 10.

[0054] The passive transducer 10 can be based on the technology of a MEMS microphone (MEMS = Micro Electro Mechanical System). The electrical components of the MEMS microphone, for example an A / D converter (analog-to-digital converter) and / or a preamplifier and / or an application-specific integrated circuit (ASIC), can be omitted. The passive transducer 10 can comprise a mechanically movable plate as a membrane 102 above a cavity 104, for example in a wafer, in particular a silicon wafer. MEMS microphones offer the advantage that a technology already exists to manufacture them, they can be manufactured cost-effectively, and they can be very small, measuring less than 1 cm. This offers the advantage that the small space requirement of the MEMS microphones allows for simple and / or space-saving installation, for example in a vehicle.The disadvantage, however, is that MEMS microphones require at least one cable connection for power supply and / or data transmission, which reduces the flexibility in positioning.

[0055] For this reason, it may be advantageous to outsource the electronic components into the laser device 12 so that the passive transducer 10 comprises the acoustic sensor comprising the plate as a membrane 102 over a cavity 104 in the wafer, so that the advantages of the MEMS microphone can be retained and the disadvantage of restricted positioning is eliminated since a cable routing to the passive transducer 10 is eliminated.

[0056] Fig. 2 shows a possible embodiment of the passive transducer 10 with calibration elements 26. The calibration elements 26 can be surfaces on the passive transducer 10 that have different reflection properties than the passive transducer 10 and / or the surface of the passive transducer 10. This can be achieved, for example, by using or applying a material that differs from the material of the passive transducer. For example, the surface of the passive transducer 10, in particular the surface of the housing 101 and / or the surface of the membrane 102, can reflect the laser radiation 121 better, in particular significantly better, than the calibration elements 26.Due to the difference in reflection behavior, it can be determined from the reflected laser radiation 20 detected by the detection unit 123 whether the at least one laser beam 122 emitted by the laser device 12 is reflected by the passive transducer 10 or by a calibration element 26. The calibration element 26 can be designed, for example, as a toroidal calibration element 261 or as a circular calibration element 262. A toroidal calibration element 261 can be a calibration element 26 with a shape in which a circle with a radius r is cut out of a circle with a larger radius R with the same center point.

[0057] By knowing the shape and position of the at least one calibration element 26, the laser device 12 can, for example, be aligned such that the emitted laser beam 122 strikes at least one optimal point of incidence 18* on the passive transducer 10, which, for example, forms the center point of the toroidal calibration element 261 or is located centrally of circular calibration elements 262 arranged, for example, along the outer edge of a circle.

[0058] Fig. 3 shows an example of the interior of a vehicle 28. The vehicle 28 comprises at least one laser microphone according to the invention. Fig.In the embodiment shown in Figure 3, the laser microphone is designed such that several passive transducers 10 are each arranged in a group 30, wherein all passive transducers 10 of a group 30 are scanned by the same laser device 12. In the present example, two groups 30, each with six passive transducers 10, are shown. The passive transducers 10 of each of the two groups 30 are each scanned by a laser device 12, wherein the passive transducers 10 of the driver-side group 30F are scanned by a driver-side laser device 12F, and the passive transducers 10 of the passenger-side group 30B are scanned by a passenger-side laser device 12B. Any number of groups 30 can be present in a vehicle 28, and each group can have its own number of passive transducers 10. In particular, the number of passive transducers 10 in a group 30 can differ from six.

[0059] Preferably, the laser devices 12 in the vehicle 28 are combined into a single scanning arrangement 32, which allows for a single cable 34, comprising at least one data line and / or one power line, to be used, thus minimizing the cabling effort. All passive transducers 10 present in the vehicle 28 can be scanned by the scanning arrangement 32.

[0060] In one embodiment, the passive transducers 10 are mounted on a surface in the vehicle 28 or behind a surface that is sound- and light-permeable and / or contains a sound- and light-permeable element, for example, a hole. The passive transducers 10 can be mounted on the vehicle 28 via a movable mounting, in particular on or behind the surface of the vehicle 28, so that vibrations of the vehicle, in particular those caused by driving and / or the engine, are only transmitted to the passive transducer 10 in a weakened manner or are not transmitted at all.

[0061] A particularly preferred embodiment is given below.

[0062] To capture spoken words as clearly as possible, at least one microphone should be positioned as close to the head as possible. This can be particularly problematic if cables cannot be routed to the intended location, such as a glass roof in a vehicle.

[0063] One type of microphone is a condenser microphone. For condenser microphones, sound transducers in the form of MEMS components can be used. These consist of a membrane shaped as a capacitor electrode with at least one counter electrode and an ASIC for regulating the capacitor charge and signal extraction.

[0064] The microphone requires a data line (signal line) and a power supply. The power supply can be provided either separately from the data line at the microphone location or via phantom power (power over data line). This requires considerable cabling effort, especially given the increasing use of microphone arrays to utilize direction-dependent sound information, as well as spatially distributed microphone arrangements to utilize location-specific sound information. Modern microphone systems can therefore utilize data transmission systems such as the Automated Audio Bus (Analog Devices) or 10base T1S-based systems to minimize this effort.

[0065] A key aspect of most sound transduction methods is that a membrane moves relative to its mount, and this movement is converted into an electrical signal. Determining such relative movement is also possible using laser scanning. For this purpose, the deflection of a moving object and the deflection of its mount and / or housing can be scanned simultaneously or serially, and the relative deflection calculated by subtracting the difference. A method of this type is used, for example, in laser vibrometry. Two laser heads and / or a scanning vibrometer can be used to record relative deflections. Such devices can be large and expensive. However, laser technology is becoming ever smaller, so it is now also used in glasses, heads-up displays, and MEMS microphones from Sensibel.

[0066] The invention comprises a miniaturized laser scanning vibrometer and at least one passive transducer (electronically passive transducer, EPW). A passive transducer can convert sound waves into a mechanical vibration using a membrane. This vibration can be measured by the laser scanning vibrometer and compared with the vibration of the membrane's suspension and / or the housing. The differential vibration can correspond to a transducer signal. The evaluation of the differential vibration between the membrane and the attachment and / or the housing of the passive transducer has the particular advantage that relative movements between the passive transducer and the laser unit (laser device) no longer play a role, since they are automatically canceled out during the difference calculation. Thus, the method can also be applied in deformable and / or self-vibrating systems such as a car.

[0067] A passive transducer can be manufactured cost-effectively, like a conventional MEMS microphone, but requires only a circuit board and / or a wafer with the diaphragm and a closed back volume. The electronics and counter electrons are not required. With a suitable shape, the passive transducer can be easily attached to a surface or glued behind it from behind, provided the surface has a suitable sound and laser entry hole.

[0068] Using scanning technology, or serial scanning (repeated sequential scanning of multiple passive transducers using a laser device), it is possible to easily scan passive transducers distributed across different locations, preferably arranged in groups (arrays). If the spatial scanning is fast enough, the signals can be "multiplexed."

[0069] Since the cost of a passive transducer is significantly lower than that of a standard microphone, the number of passive transducers used is of little importance. Price and performance are determined solely by the laser system (at least one laser device).

[0070] Overall, the examples show how a smart sound sensor and / or a laser microphone can be provided with the least possible cabling effort. LIST OF REFERENCE SYMBOLS 10 passive converters 12 Laser device 12B Passenger-side laser device 12F driver-side laser device 14 sound waves 16 mechanical vibration 18 Point of impact 18G case impact point 18M membrane impact point 18* optimal point of impact 20 reflected laser radiation 22 Scattered light 24 Light limitation 26 calibration element 28 vehicles 30 group 30B passenger side group 30F driver-side group 32 scanning arrangement 34 cables 101 housings 102 Membran 103 Fastening 104 Cavity 121 Laser radiation 122 laser beam 122G housing laser beam 122M membrane laser beam 123 Recording unit 241 Entrance opening 261 torus-shaped calibration element 262 circular calibration element

Claims

[1] Laser microphone for detecting sound waves (14) comprising • at least one laser device (12) for emitting and detecting laser radiation (20, 121) and at least one passive converter (10) comprising ◯ a housing (101) and ◯ a membrane (102) connected to the housing (101) and movable relative to the housing (101), wherein • the housing (101) and the membrane (102) of the at least one passive transducer (10) are each designed to reflect the laser radiation (121), and • the membrane (102) is designed to oscillate in a mechanical oscillation (16) relative to the housing (101) due to the sound waves (14), characterized by , that • the at least one laser device (12) is designed to scan both the housing (101) and the membrane (102) of the at least one passive transducer (10) by means of the laser radiation (121), ◯ by the laser radiation (121) striking both the housing (101) and the membrane (102), ◯ the laser radiation (121) is reflected by the housing (101) and the membrane (102) and forms a respective reflected laser radiation (20), ◯ at least a part of the respective reflected laser radiation (20) is detected by the laser device (12), and ◯ a membrane vibration (16) and a housing vibration (16) are determined from a detected reflected laser radiation (20), • and the laser microphone is configured to determine the mechanical vibration (16) caused by the sound waves (14) from a comparison of the membrane vibration (16), which comprises at least the mechanical vibration (16), with the housing vibration (16). [2] Laser microphone according to claim 1, wherein the at least one passive transducer (10) has elements which reflect or non-reflect the laser light (22) for calibrating the at least one laser device (12). [3] Laser microphone according to one of the preceding claims, wherein the at least one passive transducer (10) has a light limiter (24) for preventing reflection of scattered light (22) at the at least one passive transducer (10) if the scattered light (22) comes from a direction other than the at least one direction of the at least one laser device (12). [4] Laser microphone according to one of the preceding claims, wherein a single laser device (12) is arranged to repeatedly scan at least two passive transducers (10) one after the other. [5] Vehicle (28) with a laser microphone according to one of the preceding claims. [6] Vehicle (28) according to claim 5 in combination with claim 4, wherein the passive transducers (10) are arranged in at least one group (30) and one laser device (12) per group (30) is arranged to carry out the repeated sequential scanning of all passive transducers (10) of the respective group (30). [7] Vehicle (28) according to one of claims 5 or 6, wherein the vehicle (28) comprises a plurality of passive transducers (10) and a central scanning arrangement (32), wherein the central scanning arrangement (32) comprises at least one laser device (12) and is adapted to scan all passive transducers (10) comprising the vehicle (28). [8] Vehicle (28) according to one of claims 5 to 7, wherein the at least one passive transducer (10) is mounted on a surface in the vehicle (28) and / or is mounted behind the surface of the vehicle (28) at a measuring point, wherein the surface is at least partially permeable to both the laser radiation (121) and the sound waves (14) at least at the measuring point. [9] Vehicle (28) according to one of claims 5 to 8, wherein the at least one passive transducer (10) and / or the at least one laser device (12) and / or the scanning arrangement (32) is mounted at a fastening point so as to be movable with respect to the vehicle (28) in order to reduce the transmission of vibrations of the vehicle (28) to the at least one passive transducer (10) and / or the at least one laser device (12) and / or the scanning arrangement (32). [10] Method for detecting sound waves (14) by means of a laser microphone according to one of claims 1 to 4, characterized by, that • the at least one laser device (12) scans both the housing (101) and the membrane (102) of the at least one passive transducer (10) by means of the laser radiation (121), ◯ by the laser radiation (121) striking both the housing (101) and the membrane (102), ◯ the laser radiation (121) is reflected by the housing (101) and the membrane (102) and forms a reflected laser radiation (20), ◯ at least part of the reflected laser radiation (20) is detected by the laser device (12), ◯ and a membrane vibration (16) and a housing vibration (16) are determined from a detected reflected laser radiation (20), • and the mechanical vibration (16) caused by the sound waves (14) is determined from a comparison of the membrane vibration (16), which comprises at least the mechanical vibration (16), with the housing vibration (16).

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