Filter arrangement with an acoustic ultrasonic filter for a microphone module

Abstract

Filter arrangement for a microphone module (100) with an acoustic input tube (105), wherein a cavity (106) is arranged as a resonance chamber between the input tube (105) and a region of the filter arrangement designed for connection to a microphone module (100) or to a device (102) with a microphone module (100), wherein a Helmholtz resonator is formed as an ultrasonic filter (1) through the cavity (106) and the input tube (105), which exhibits a resonance at a defined frequency, wherein the resonance chamber has a significantly larger diameter than the input tube (105) and / or an opening (103) in front of the microphone module (100) to cause a transverse resonance in addition to the Helmholtz resonance.

Description

[0001] The invention relates to a filter arrangement with an acoustic ultrasonic filter for a microphone module and to a device with such a filter arrangement.

[0002] MEMS microphones are sensitive to ultrasonic signals, which can cause audible intermodulation distortion (IMD). In the presence of two inaudible ultrasonic signals, a tone with a frequency equal to the difference between the two ultrasonic frequencies can be demodulated in the audio band within the microphone module. The same problem can also occur with narrowband ultrasonic noise. For example, this can happen in a room with two ultrasonic sources, such as two types of ultrasonic presence detectors or switched-mode power supplies.

[0003] When ultrasound enters the microphone and causes intermodulation distortion, there is no way to distinguish it from normal audio signals at the microphone's electrical output. Therefore, it is necessary to filter ultrasound signals at the microphone module. Since intermodulation distortion is part of the audio signal at the microphone's output, ultrasound signals must be acoustically filtered.

[0004] WO 2024 / 088747 A1 describes an electronic sound recording device, in particular a hearing aid, comprising a housing with a housing wall and an opening formed therein through which sound can enter the housing. A printed circuit board (PCB) is arranged inside the housing. The PCB has a through-hole that serves as a sound channel through the PCB. A microphone with a microphone connector is mounted on the PCB such that the microphone connector faces the PCB and opens towards the through-hole. A sound channel with a sound passage formed therein is arranged between the PCB and the housing wall, connecting the opening in the housing wall to the through-hole in the PCB. The electronic sound recording device further comprises a washer with a hole.The washer is positioned between the circuit board and the sound channel, so that the sound channel is connected to the through-hole of the circuit board via the washer's bore. To achieve effective acoustic low-pass filtering, the bore has a diameter smaller than both the diameter of the circuit board's through-hole and the diameter of the sound channel's opening.

[0005] WO 2018 / 202309 A1 describes a filter for a microphone system of a miniature electronic device. The filter comprises a sound inlet and a sound outlet and is suitable for mounting on a printed circuit board surface.

[0006] The invention is based on the objective of specifying a novel filter arrangement with a microphone module and an acoustic ultrasonic filter, as well as a novel device with such a filter arrangement.

[0007] The problem is solved according to the invention by a filter arrangement with a microphone module and an acoustic ultrasonic filter having the features of claim 1 and by a device having the features of claim 20.

[0008] Advantageous embodiments of the invention are the subject of the dependent claims.

[0009] A filter arrangement for a microphone module is proposed, comprising an acoustic input tube, wherein a cavity is arranged as a resonance chamber between the input tube and a region of the filter arrangement designed for (in particular sealing) connection to a microphone module or to a device with a microphone module, wherein a Helmholtz resonator is formed through the cavity and the input tube as an ultrasonic filter, in particular in the form of a series acoustic mass-spring system, which exhibits a resonance at a defined frequency, wherein the resonance chamber has a significantly larger diameter than the input tube and / or an opening in front of the microphone module to effect a transverse resonance in addition to the Helmholtz resonance.

[0010] In one embodiment, the area is located at a microphone module or a device with a microphone module.

[0011] In one embodiment, the resonance chamber is designed as a circular resonance chamber, which is arranged concentrically with a microphone inlet of the microphone module and the input tube.

[0012] In one embodiment, the microphone inlet is in acoustic contact with the input tube, which is arranged in a mechanical component, for example a housing and / or a sealing part, via an opening in a circuit board.

[0013] In one embodiment, the geometry of the resonance chamber, in particular its diameter and height, is chosen such that a transverse resonance is caused which absorbs a specific frequency band in the ultrasound range in order to cause a notch effect of the ultrasound filter at a predetermined frequency which is greater than the frequency of the Helmholtz resonator.

[0014] In one embodiment, at least one damper is arranged at or in front of an inlet of the resonance chamber and / or at or behind an outlet of the resonance chamber or at or the microphone inlet.

[0015] In one embodiment, the damper is designed as a part separate from the resonance chamber.

[0016] In one embodiment, the damper has a grid or fabric that is attached by gluing.

[0017] In one embodiment, the damper has a grid that is overmolded or attached to at least one rigid part, in particular a plastic part.

[0018] In one embodiment, the rigid part is designed as a disk.

[0019] In one embodiment, the rigid part is clamped in a cavity or within the cavity.

[0020] In one embodiment, the cavity is formed in a housing of a device or a sealing part.

[0021] In one embodiment, the rigid part is shaped in such a way that it has inside the resonance chamber for the Helmholtz resonance and the transverse resonance.

[0022] In an alternative embodiment, the resonance chamber can be formed by the cavity.

[0023] In one embodiment, two rigid parts, each with damping material attached to it, are arranged opposite each other to form a central resonance chamber between the two parts.

[0024] In one embodiment, the resonance chamber is milled out of the circuit board or formed in a metallic cap that is attached to the circuit board, in particular soldered on.

[0025] In one embodiment, a metallic disc is attached to the circuit board, in particular soldered on, which covers the resonance chamber in the circuit board.

[0026] In one embodiment, a sealing part is arranged to seal the disc or cap against the housing, wherein at least one damper is arranged in the sealing part.

[0027] In one embodiment, the microphone module is a MEMS.

[0028] According to one aspect of the present invention, a device with at least one microphone module is proposed, on which one or more filter arrangements as described above are arranged. The device is, for example, configured as a wireless microphone that can be used as a remote device with a hearing aid. Alternatively, the device can also be configured as a hearing aid. The filter arrangement can be configured as a separate arrangement from the device or as an arrangement wholly or partially integrated into the device.

[0029] The filter can be produced as a separate component that can be easily and intuitively placed, and especially clamped, into one of the openings of a sealing element. This requires minimal time and is less prone to assembly errors. When the microphone and circuit board are mounted to the sealing element and the filter, the filter cavity, together with the acoustic inlet tube, forms a Helmholtz resonator. The transverse resonance within the cavity can be adjusted (diameter-to-height ratio) to achieve improved or optimized attenuation at a target frequency, thus effectively creating an additional notch filter.

[0030] Implementing such a filter requires no additional components, as it simply replaces the existing dust protection, while reducing manufacturing complexity and improving performance. The filter can be manufactured, for example, using plastic injection molding.

[0031] The ultrasonic filter can be used for a remote microphone for a hearing aid.

[0032] In one embodiment, the cavity is milled into the circuit board.

[0033] In one embodiment, dampers are arranged at both ends of the cavity.

[0034] In one embodiment, the cavity is formed in a separate part or between two separate parts.

[0035] In one embodiment, a metallic disc is soldered over the cavity in the circuit board.

[0036] In one embodiment, a sealing element is arranged between the disc and the housing of the device.

[0037] In one embodiment, a metallic cap in which the cavity is formed is soldered to the circuit board.

[0038] In one embodiment, the acoustic filter is manufactured by injection molding.

[0039] In one embodiment, a grid is overmolded onto a rigid plastic part to produce a damper.

[0040] In one embodiment, the damper is clamped into the cavity.

[0041] Exemplary embodiments of the invention are explained in more detail below with reference to a drawing.

[0042] It shows: Fig. 1 A schematic view of an acoustic ultrasonic filter arranged between an acoustic input of a device and a microphone module, Fig. 2 a schematic view of another embodiment of the acoustic ultrasonic filter with two dampers, Fig. 3 a schematic equivalent circuit diagram of the microphone module and the ultrasonic filter, Fig. 4 a schematic equivalent circuit diagram of the microphone module, the ultrasonic filter and the dampers, Fig. 5 a schematic view of the acoustic ultrasound filter when Helmholtz resonance occurs, Fig. 6 a schematic view of the acoustic ultrasonic filter when transverse resonance occurs, Fig. 7 A schematic diagram of the magnitude of a signal filtered by the ultrasonic filter as a function of frequency to illustrate the effect of cavities of the same volume with different diameter-to-height ratios, Fig. 8 A schematic diagram of the magnitude of a signal filtered by the ultrasonic filter as a function of frequency to illustrate the effect of attenuators with different input resistance, Fig. 9 A schematic diagram of the magnitude of a signal filtered by the ultrasonic filter as a function of frequency to illustrate the effect of dampers with different resistance in front of the microphone inlet, Fig. 10 a schematic diagram of the magnitude of a signal filtered by the ultrasonic filter as a function of frequency to illustrate the combined effect of attenuators with different resistance at the input and before the microphone inlet, Fig. 11 a schematic view of another embodiment of the acoustic ultrasonic filter, Fig. 12 a schematic view of another embodiment of the acoustic ultrasonic filter, Fig. 13 a schematic view of another embodiment of the acoustic ultrasonic filter, Fig. 14 a schematic view of another embodiment of the acoustic ultrasonic filter, Fig. 15 a schematic view of another embodiment of the acoustic ultrasonic filter, Fig. 16 a schematic view of another embodiment of the acoustic ultrasonic filter, Fig. 17 a schematic view of another embodiment of the acoustic ultrasonic filter, Fig. 18 a schematic view of another embodiment of the acoustic ultrasonic filter, Fig. 19 a schematic view of another embodiment of the acoustic ultrasonic filter, and Fig. 20 a schematic view of another embodiment of the acoustic ultrasonic filter.

[0043] Corresponding parts are marked with the same reference symbols in all figures.

[0044] Fig. Figure 1 is a schematic view of a filter arrangement with an acoustic ultrasonic filter 1 arranged between an acoustic input 105 of a device 102 and a microphone module 100. The device 102 is, for example, a wireless microphone that can be used as a remote device 102 with a hearing aid. However, the ultrasonic filter 1 can also be used with a device 102 of another type, for example, a hearing aid or any device 102 that has a microphone module 100.

[0045] The microphone module 100, for example, is of the MEMS type (microelectromechanical system - Micro Electronic Mechanical System).

[0046] The microphone module 100 has a microphone inlet 101 which is in acoustic contact with the acoustic input 105 of the device 102, for example via an opening 103 in a circuit board 104 and an input tube 105 through a mechanical component, for example a housing 116 and / or a sealing part 109.

[0047] A cavity 106 is arranged as a resonance chamber between the input tube 105 and the microphone module 100, wherein a Helmholtz resonator is formed as an ultrasonic filter 1 through the cavity 106 and the input tube 105. The cavity 106, in particular a circular cavity 106, can be arranged concentrically with the microphone inlet 101 and the acoustic input 105 of the device 102. The cavity 106 acts as a series acoustic mass-spring system (Helmholtz resonance) with the input tube 105.

[0048] Fig. Figure 2 is a schematic view of a further embodiment of the acoustic ultrasonic filter 1, in which the ultrasonic filter 1 is further equipped with at least one damper 107 at the entrance of the cavity 106 and / or with a damper 108 at the microphone inlet 101.

[0049] Microphones are normally coupled to the environment via a simple input tube 105, which causes resonances and increases the sensitivity to ultrasound. The addition of a cavity 106, which acts as a Helmholtz resonator with the input tube 105, and a damper produces a steeper slope.

[0050] In one embodiment, the cavity 106 has a significantly larger diameter than the inlet tube 105 and the opening 103 in the circuit board 104. This enables a transverse resonance in addition to the Helmholtz resonance to improve the filtering of ultrasonic signals.

[0051] The damper 107, 108 can be designed as a separate part from the cavity 106 to simplify manufacturing.

[0052] Fig. Figure 3 is a schematic equivalent circuit diagram of the microphone module 100 with the opening 103 in the circuit board 104, the input tube 105 and the cavity 106.

[0053] Fig. Figure 4 is a schematic equivalent circuit diagram of the microphone module 100 with the opening 103 in the circuit board 104, the input tube 105, the cavity 106 and the dampers 107, 108.

[0054] In addition to the mass-spring effect due to the acoustic mass of the inlet (i.e., the opening 103 and the inlet tube 105) and the acoustic spring action of the cavity 106, the geometry of the cavity 106 can be optimized to generate a transverse resonance that absorbs a specific frequency band in the ultrasonic range.

[0055] Fig. Figure 5 is a schematic view of the acoustic ultrasonic filter 1 when Helmholtz resonance occurs through the cavity 106 as a spring and the input tube 105 as a mass, providing a second-order filter in front of the microphone module 100, which has a resonance at a defined frequency fc, optimized by the volume of the cavity 106 and the dimensions of the acoustic input (the input tube 105).

[0056] Fig. Figure 6 is a schematic view of the acoustic ultrasonic filter 1 when transverse resonance occurs in the cavity 106, causing a notch effect of the ultrasonic filter 1 at a predetermined frequency greater than the frequency fc, optimized by the diameter of the cavity 106.

[0057] Fig. Figure 7 is a schematic diagram of the magnitude y of a signal filtered by the ultrasonic filter 1 as a function of frequency f, illustrating the effect of cavities 106 of the same volume with different diameter-to-height ratios, resulting in the same cutoff frequency but different behavior in the ultrasonic range. Curve K1 shows the magnitude y for a cavity 106 with a diameter of 5 mm and a height of 1 mm, resulting in a notch at 35 kHz and greater attenuation between 20 kHz and 60 kHz, compared to curve K2, where the cavity 106 has a diameter of 2.9 mm and a height of 2.97 mm.

[0058] Fig. Figure 8 is a schematic diagram of the magnitude y of a signal filtered by the ultrasonic filter 1 as a function of the frequency f to illustrate the effect of attenuators 107 with different input impedances. The attenuator 107 essentially attenuates the level at the Helmholtz resonance of the volume of the cavity 106 containing the input tube 105.

[0059] Fig. Figure 9 is a schematic diagram of the magnitude y of a signal filtered by the ultrasonic filter 1 as a function of the frequency f to illustrate the effect of dampers 108 with different resistance at the opening 103, that is, in front of the microphone inlet 101. The damper 107 essentially dampens the mechanical resonance of the microphone diaphragm.

[0060] Fig. Figure 10 is a schematic diagram of the magnitude y of a signal filtered by the ultrasonic filter 1 as a function of the frequency f to illustrate the combined effect of dampers 107, 108 with different resistance at the inlet and at the opening 103. This allows for fine-tuning of the frequency response of the microphone arrangement.

[0061] The design of the ultrasonic filter 1, in particular the way in which the dampers 107, 108 are attached to the mechanical parts, is intended to simplify the manufacturing process of the arrangement as far as possible.

[0062] Acoustic dampers 107, 108 are generally made from a damping material, for example a thin mesh (fabric), which is attached to a double-sided adhesive strip. This is then attached to the device 102, for example, manually. This solution makes the manufacturing process of the device 102 difficult, time-consuming, and prone to assembly errors.

[0063] Instead, the grid can be overmolded or attached to a rigid plastic part, for example, overmolded. This part can then be easily clamped into a cavity 106 in the device.

[0064] In one embodiment, the plastic part can be a simple disc that can be clamped at the end of the cavity 106, which may be formed in another part of the device, for example a housing or a soft intermediate part (for example made of rubber or rubber-like material), which ensures the tightness of the system, in particular between the microphone module 100 and the input tube 105, in order to avoid certain resonances.

[0065] In another embodiment, the plastic part can be shaped not as a simple disc, but in such a way that it also has the cavity 106 itself.

[0066] In another embodiment, two plastic parts, each containing damping material, are arranged opposite each other to form a central cavity 106. This can be used as a filter arrangement that includes an additional microphone damper.

[0067] The invention essentially has three aspects: 1. The principle of acoustic filtering: By adjusting the height and / or diameter of the cavity 106 and the size of the input tube 105, a second-order filter with a notch at a predetermined frequency is obtained, combined with an acoustic damper 107 at the input. 2. The damping material can be arranged on a rigid support that can be clamped to the device to simplify the device's manufacturing process. The support may contain the cavity, but this is not mandatory. 3. Two filter elements, each with a damper 107, 108, at least one of which has a cavity 106, can be combined to obtain a filter arrangement having a damper 107 at the inlet, a cavity 106 and a damper 108 at the microphone.

[0068] According to the first aspect of the invention, the transverse resonance of the cavity 106 of the Helmholtz resonator is used as its additional notch filter, which is obtained by the geometry of the cavity 106.

[0069] In addition to its acoustic properties, the filter arrangement can also help protect the microphone against dust and liquids.

[0070] Fig. Figure 11 is a schematic view of an embodiment of the acoustic ultrasonic filter 1 similar to that shown in Fig. 1, however with a different ratio of the diameter to the height of the cavity 106 and the entrance tube 105.

[0071] Fig. Figure 12 is a schematic view of an embodiment of the acoustic ultrasonic filter 1 similar to that shown in Fig. 2, however with only one damper 107 at the entrance, which is glued into the cavity 106. In Fig. 2. The damper 108 can also be glued to the circuit board 104.

[0072] Fig. Figure 13 is a schematic view of an embodiment of the acoustic ultrasonic filter 1 similar to that shown in Fig. 12, wherein the damper 107 is mounted at the inlet on a rigid disc 110 which is clamped at the end of the cavity 106.

[0073] Fig. Figure 14 is a schematic view of an embodiment of the acoustic ultrasonic filter 1 similar to that shown in Fig. 13, wherein the damper 107 is designed as a separate part 111, which includes the cavity 106, and is clamped in a housing 109 or a soft sealing part 109 or intermediate part. The filter function can be realized by the combination of the inlet tube 105 and the cavity 106. The rigid separate part 111 with the damper 107 (grid), which can be overmolded during a plastic injection molding process, can be manufactured as a separate part 111. The rigid separate part 111 can be attached to the soft sealing part 109, and in this way the ultrasonic filter can be formed by the inlet tube 105 and the cavity 106.

[0074] Fig. Figure 15 is a schematic view of an embodiment of the acoustic ultrasonic filter 1 similar to that shown in Fig. 14, wherein a damper 108 is also arranged in front of the microphone, which is designed as a separate part 113, which together with the separate part 112 of the damper 107 forms the cavity 106 and is also clamped in the housing 109 or intermediate part.

[0075] Instead of cavities 106 formed in the mechanical part in front of the circuit board 104, the cavity 106 can also be milled out of the circuit board 104 or be formed as a metallic cap 117 soldered onto the circuit board 104.

[0076] Fig. Figure 16 is a schematic view of an embodiment of the acoustic ultrasonic filter 1 similar to that shown in Fig. 3, wherein the cavity 106 is milled out of the circuit board 104 and closed by a mechanical component 109 which contains the input tube 105.

[0077] Fig. Figure 17 is a schematic view of an embodiment of the acoustic ultrasonic filter 1 similar to that shown in Fig. 16, however with a damper 107 at the entrance, which is glued to the mechanical component 109.

[0078] Fig. Figure 18 is a schematic view of an embodiment of the acoustic ultrasonic filter 1 similar to that shown in Fig. 16, but with a metallic disc 114 soldered onto the circuit board 104, which covers the cavity 106. A sealing element 115 seals the disc 114 against the housing 116. The damper 107 is arranged in the sealing element 115.

[0079] Fig. Figure 19 is a schematic view of an embodiment of the acoustic ultrasonic filter 1 similar to that shown in Fig. 18, however, with a metallic cap 117 instead of the disc 114, which is soldered onto the circuit board 104 and forms the cavity 106. In this case, no cavity is milled out of the circuit board 104.

[0080] Fig. Figure 20 is a schematic view of another embodiment of the acoustic ultrasonic filter 1 similar to that shown in Figure 20. Fig. 14, wherein the damper 107 is designed as a separate part 111 that includes the cavity 106 and is clamped in a housing 109 or a soft sealing part 109 or intermediate part that is attached to a front plate of the housing 116. In particular, in this case, the intermediate part 109 or sealing part 109 may be formed from a soft material. REFERENCE MARK LIST 1 ultrasonic filter 100 microphone modules 101 Microphone inlet 102 device 103 Opening 104 circuit board 105 Input tube, acoustic input 106 Cavity, resonance chamber 107 dampers 108 dampers 109 mechanical component, housing, sealing part, intermediate part 110 disc Part 111 Part 112 Part 113 114 disc 115 Sealing part 116 cases 117 cap f frequency K1, K2 curve y Magnitude QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2024 / 088747 A1

[0004] WO 2018 / 202309 A1

[0005]

Claims

[1] Filter arrangement for a microphone module (100), with an acoustic input tube (105), wherein a cavity (106) is arranged as a resonance chamber between the input tube (105) and a region of the filter arrangement designed for connection to a microphone module (100) or to a device (102) with a microphone module (100), wherein a Helmholtz resonator is formed as an ultrasonic filter (1) through the cavity (106) and the input tube (105), which has a resonance at a defined frequency, wherein the resonance chamber has a significantly larger diameter than the input tube (105) and / or an opening (103) in front of the microphone module (100) to cause a transverse resonance in addition to the Helmholtz resonance. [2] Filter arrangement according to claim 1, wherein the area is located on a microphone module (100) or a device (102) with a microphone module (100). [3] Filter arrangement according to claim 1 or 2, wherein the resonance chamber is designed as a circular resonance chamber which is arranged concentrically with a microphone inlet (101) of the microphone module (100) and the input tube (105). [4] Filter arrangement according to one of the preceding claims, wherein the microphone inlet (101) is in acoustic contact with the input tube (105) via an opening (103) in a circuit board (104), which is arranged in a mechanical component, for example a housing (116) and / or a sealing part (109, 115). [5] Filter arrangement according to one of the preceding claims, wherein the geometry of the resonance chamber, in particular its diameter and height, is selected such that a transverse resonance is caused which absorbs a specific frequency band in the ultrasonic range in order to cause a notch effect of the ultrasonic filter (1) at a predetermined frequency which is greater than the frequency of the Helmholtz resonator. [6] Filter arrangement according to one of the preceding claims, wherein at least one damper (107, 108) is arranged at or in front of an inlet of the resonance chamber and / or at or behind an outlet of the resonance chamber or at or the microphone inlet (101). [7] Filter arrangement according to claim 6, wherein the damper (107, 108) is designed as a part separate from the resonance chamber. [8] Filter arrangement according to claim 6 or 7, wherein the damper (107, 108) has a grid or fabric which is attached by gluing. [9] Filter arrangement according to claim 6 or 7, wherein the damper (107, 108) has a grid which is overmolded or attached to at least one rigid part (110 to 113), in particular a plastic part. [10] Filter arrangement according to claim 9, wherein the rigid part (110 to 113) is designed as a disk (110). [11] Filter arrangement according to claim 9 or 10, wherein the rigid part (110 to 113) is clamped in a cavity (106) or in the cavity (106). [12] Filter arrangement according to one of the preceding claims, wherein the cavity (106) is formed in a housing (116) of a device (102) or a sealing part (109, 115). [13] Filter arrangement according to one of claims 9 to 12, wherein the rigid part (110 to 113) is shaped such that it has inside the resonance chamber (106) for the Helmholtz resonance and the transverse resonance. [14] Filter arrangement according to one of claims 9 to 12, wherein the resonance chamber is formed by the cavity (106). [15] Filter arrangement according to claims 9 to 12, wherein two rigid parts (110 to 113), on each of which damping material is arranged, are arranged opposite each other to form a central resonance chamber between the two parts (110 to 113). [16] Filter arrangement according to one of claims 4 to 15, wherein the resonance chamber is milled out of the printed circuit board (104) or formed in a metallic cap (117) which is attached to the printed circuit board (104), in particular soldered on. [17] Filter arrangement according to claim 16, wherein a metallic disk (114) is attached to the circuit board (104), in particular soldered on, which covers the resonance space in the circuit board (104). [18] Filter arrangement according to claim 16 or 17, wherein a sealing part (115) is arranged for sealing the disk (114) or the cap (117) against the housing (116), wherein at least one damper (107) is arranged in the sealing part (115). [19] Filter arrangement according to one of the preceding claims, wherein the microphone module (100) is a MEMS. [20] Device (102) with at least one microphone module (100) on which one or each of a filter arrangement according to one of the preceding claims is arranged, wherein the device (102) is designed as a wireless microphone which can be used as a remote device (102) with a hearing aid device, or wherein the device (102) is designed as a hearing aid device.

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