Thin Panel Surface Mount Microphone

Abstract

A sound and vibration sensor has a sealed cavity defined between a microphone element and a structural panel and an area below the microphone element, wherein the microphone element senses changes in sound pressure inside the sealed cavity caused by sound waves impinging on the structural panel.

Description

Technical Field

[0001] The present disclosure relates to an acoustic sensing device, and more particularly, to a surface mounted and environmentally sealed acoustic sensing device. Background Art

[0002] With the development of driver assistance technology and autonomous vehicles, the number of sensors on vehicles has increased significantly. With the development of these technologies, it has become necessary to sense the sound outside the vehicle. Currently, sound sensing devices are set on the external structural panels of the vehicle (such as body panels, frames, glass), which are directly exposed to various harsh environmental conditions, such as water and dust ingress and close-range high-temperature, high-pressure spray (up to 85°C and 10MPa), as described in the IP6K9K rating in ISO 20653.

[0003] In order to achieve good acoustic performance, such as high sensitivity and wide bandwidth, microphone elements require port holes in their design to provide a direct air path between the sensing element and the external environment. This makes the microphone element susceptible to damage from harsh environmental conditions or foreign contaminants.

[0004] One way to solve this problem is to add an acoustic mesh or an acoustic membrane in front of the port hole of the microphone element. The acoustic mesh or membrane is usually made of a material (or structure) with very small pores or micropores, which are usually a few microns to hundreds of microns in diameter. The micropores are large enough to allow air molecules to pass through, but small enough to block dust particles. Due to the large surface tension formed between liquid molecules, it is also difficult for liquid molecules to pass through, thus having a waterproof effect. Therefore, the acoustic mesh or acoustic membrane forms a physical layer to isolate and protect the delicate sensing element from the external environment. Examples of acoustic mesh or membrane materials are PTFE (polytetrafluoroethylene) and PDMS (polydimethylsiloxane).

[0005] It is important to note that although the terms acoustic mesh and acoustic membrane are used interchangeably, there is a subtle difference between them in that a mesh generally refers to a material (or structure) with a larger pore size, while a membrane generally refers to a material (or structure) with a smaller pore size. Nevertheless, in order to achieve acoustic breathability and not significantly degrade the acoustic performance of the microphone, such an acoustic mesh or membrane needs to be thin, flexible, and lightweight, which may make it easily damaged by sharp objects (such as road debris). In addition, when pressurized, liquids such as water may penetrate through the pores, making it impossible to meet the IPx9K rating under high-pressure and high-temperature spray.

[0006] Another approach to solving this problem is to attach an accelerometer to a structural surface (e.g., a glass window or door panel of a vehicle) to measure the sound-induced vibrations of the panel that are correlated with and representative of the sound in the environment. Since the accelerometer is designed to be completely sealed to the environment, this approach perfectly solves the weatherproofing problem. An example of such an accelerometer-based sound sensing solution using a piezoelectric diaphragm can be found in the recent U.S. Patent No. 11,533,568B1. However, piezoelectric diaphragms are typically much larger in size than microphone elements (e.g., MEMS or ECM microphone elements), making it more difficult to integrate them into a protective housing while achieving good electromagnetic interference and electromagnetic compatibility (EMI / EMC) performance.

[0007] There is a need for a surface mounted acoustic sensing device that forms a seal around the microphone element of the acoustic sensing device when the device is mounted to a surface to make the acoustic sensing device weatherproof and still achieve good acoustic performance. Summary of the invention

[0008] A sound and vibration sensor having a housing, a PCBA attached to a perimeter edge of the interior of the housing, and a bonding member sealed to both the perimeter edge of one end of the housing and a structural panel defining a sealed cavity, wherein a microphone element senses changes in sound pressure inside the sealed cavity caused by sound waves striking the structural panel.

[0009] In one or more embodiments, a leakage channel in the PCBA forms a ventilation path between the sealed cavity and the cavity inside the housing.

[0010] In one or more embodiments, the structural panel is thinned in the area receiving the bonding member.The thinned area may be configured to match the periphery of the bonding member.

[0011] In one or more embodiments, the structural panel is a vehicle body panel.The bonding member may be adhered to the B-side of the vehicle body panel.

[0012] In one or more embodiments, the PCBA is flush mounted on one end of the housing, and the thickness of the adhesive member defines a small gap distance.

[0013] In one or more embodiments, the sound and vibration sensor has vents in the cavity inside the housing to equalize static air pressure.

[0014] In one or more embodiments, the vents are covered by a dense mesh layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The features, objects and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which like reference numerals refer to like elements.

[0016] Figure 1A is a cross-sectional view of one or more embodiments of a sound sensing device prior to installation to a structural panel;

[0017] Figure 1B Is mounted on a thin panel surface Figure 1A A cross-sectional view of the sound sensing device shown in ;

[0018] Figure 2 shows an exemplary location for mounting the acoustic sensing device on a vehicle;

[0019] Figure 3 is a cross-sectional view of one or more embodiments of an acoustic sensing device; and

[0020] Figure 4 is a cross-sectional view of one or more embodiments of a sound sensing device. DETAILED DESCRIPTION

[0021] Figure 1A 1 is a cross-sectional view of an acoustic sensing device 100 according to one or more embodiments. A printed circuit board assembly (PCBA) 102 is flush mounted inside the housing 104 at one end thereof to form a waterproof seal between the housing 104 and a perimeter edge 106 of the PCBA 102 .

[0022] PCBA 102 is a printed circuit board (PCB) 108 having a port hole or holes 110, and includes any components required for the operation of the sound sensing device 100. Other circuit components may include, but are not limited to, a preamplifier, an analog-to-digital converter, a microphone element 112, and any other components required for the operation of the sound sensing device. The microphone element 112 has an acoustic port 114 and is mounted on the PCB 108 so that the acoustic port 114 is aligned with the port hole 110 on the PCB 108 to allow sound waves outside the sound sensing device 100 to reach the first diaphragm (not shown) exposed via the acoustic port 114 of the microphone element 112. In one or more embodiments, the microphone element 112 may be a micro-electromechanical system (MEMS) device. In one or more embodiments, the microphone element 112 may be an electret condenser microphone (ECM) device. In one or more embodiments, the sound sensing device 100 may include a bonding member 116 that is shaped in a manner that matches the periphery of the housing 104. In one or more embodiments, the adhesive member 116 is annular, for example, as in the case of a circular housing 104 .

[0023] Figure 1B1 is a cross-sectional view of the acoustic sensing device 100 mounted to a structural panel 120. The adhesive member 116 is aligned with and attached to the bottom perimeter 118 of the housing 104, while also being attached to and forming a seal with the structural panel 120 (e.g., a body panel). When the acoustic sensing device 100 is used in an automobile, the adhesive member 116 should be rugged for typical automotive applications and should be able to withstand extreme temperatures and humidity. Additionally, or alternatively, the adhesive member 116 can be conformable, such as having a foam core, to ensure good contact between surfaces that may be even slightly mismatched, thereby achieving a good seal.

[0024] The good contact of the adhesive member 116 with the housing 104, the good contact of the adhesive member 116 with the structural panel 120, and the thickness h of the adhesive member 116 form a sealed cavity 122 between the structural panel 120 and the bottom surface 124 of the PCBA 102. The sealed cavity 122 defines a first sealed volume V1 based on the thickness h of the adhesive member 116 and the size of the housing 104. The sound sensing device 100 is mounted to the structural panel 120 in a sealed manner through the adhesive member 116 to form a surface mounted microphone. When the sound wave 126 hits the structural panel 120, a surface vibration 121 in the form of displacement (or velocity or acceleration) is caused in a direction perpendicular to the structural panel 120. The displacement of the structural panel 120 dynamically changes the first sealed volume V1, thereby generating a sound pressure proportional to the volume change inside the sealed cavity 122, which can be sensed by the microphone element 112. The structural panel 120 acts as a second diaphragm for sound sensing. The first diaphragm (not shown) is located inside the microphone element 112.

[0025] An advantage of the present subject matter is that the acoustic sensing device 100 utilizes the structural panel 120 to seal the cavity 122 and provide environmental protection for the microphone element 112 of the acoustic sensing device 100. In the example of an automotive application, a body panel made of sheet metal (e.g., steel or aluminum alloy) or plastic is undoubtedly strong enough to meet the IP6K9K protection rating.

[0026] The sensitivity, frequency response characteristics, and bandwidth of the acoustic sensing device 100 may be determined by the volume V1 of the sealed cavity 122, the area of ​​the structural panel 120 surrounded by the bonding member 116, the material properties of the structural panel 120, and the thickness of the bonding member 116. To improve sensitivity, a smaller sealed cavity 122 or first sealed volume V1 is preferred. This requires a small gap distance 128 between the structural panel 120 and the bottom surface 124 of the PCBA 102. A thicker bonding member 116 will form a larger sealed cavity 122, while a thinner bonding member will form a smaller sealed cavity 122.

[0027] On the other hand, a larger enclosed area helps to introduce a larger volume change in the cavity 122. Therefore, for a circular acoustic sensing device 100, an enclosed area equivalent to a circular area having a diameter between 10 mm and 80 mm may be preferred.

[0028] The total volume of the sealed cavity 122 can be maintained below 350 cubic millimeters. The gap distance 128, which is primarily controlled by the thickness of the bonding member 116, may preferably be between 0.1 and 0.5 millimeters. Finally, automotive body panels are typically 0.5 millimeters to 2 millimeters thick, depending on the type of material (e.g., steel sheets are thinner). This thickness range, combined with the preferred range of enclosed area, gap distance 128, and sealed cavity 122 volume V1, is suitable for generating sufficient sound pressure in a small sealed cavity 122 under the excitation of a typical external sound pressure level in the environment (e.g., on the order of 50-120 dB sound pressure level (SPL)).

[0029] Figure 2 Exemplary locations 202a-202n of a vehicle 200 for mounting sound sensing devices on the vehicle 200 are shown. More than one sound sensing device may be positioned on the vehicle, and the locations may be selected based on the sounds that need to be detected. For example, but not limited to, the sound sensing device is surface mounted for exterior or interior voice detection to transmit a signal indicative of a voice command to one or more controllers 204 on the vehicle. The one or more controllers 204 may be responsible for activating or deactivating vehicle operations (e.g., opening / closing a trunk, doors, liftgate, etc.). Additionally or alternatively (and without limitation), the sound sensing device may be used to detect background noise signals that may be used by one or more controllers 204 in an active noise cancellation (ANC) and / or road noise cancellation (RNC) system. Microphone element ( Figure 2 ) may include an analog or digital interface (such as A2B) to communicate with one or more controllers 204 on the vehicle 200.

[0030] The sound sensing device may be mounted on any thin structural panel of the vehicle 200, such as a door panel, roof panel, front / rear bumper panels, etc. Additionally, or alternatively, the sound sensing device may be mounted on the inner side (B side) of the structural panel to completely hide the device from view.

[0031] Changes in altitude or ambient temperature may cause static pressure differences between the cavity 122 and the external environment. Static pressure differences may pre-stress the structural panels 120, causing unwanted changes in sensitivity and frequency response characteristics. Figure 31 is a cross-sectional view of one or more embodiments of an acoustic sensing device 300 having a leakage channel 302 in the PCBA 102 and a vent 304 in the housing 104. The leakage channel 302 and the vent 304 define a ventilation path connecting the cavity 122 and the external environment, wherein the ventilation path balances the static air pressure between the cavity 122 and the external environment.

[0032] In order to have a minimal impact on the low frequency response of the microphone element 112, the cross-sectional area of ​​the leakage channel 302 should be as small as possible. For example, a circular (or equivalent) area with a diameter less than 0.4 mm. The vent 304 in the housing may have a circular (or equivalent) area with a diameter less than 1 mm.

[0033] Optionally, a dense mesh layer 306 may be positioned inside the housing 104 to cover the vents 304. The dense mesh layer 306 may have a smaller pore size than the air permeable acoustic mesh to not only prevent foreign matter, water, and moisture from entering the housing and ultimately the microphone element 112, but also have a high resistance to the passage of air molecules. However, when the difference between the internal and external static air pressures becomes large, the dense mesh layer 306 still allows static pressure equalization. An exemplary dense mesh layer 306 may be made of an expanded polytetrafluoroethylene (ePTFE) material having a thickness in the range of 0.1 to 0.5 mm.

[0034] Figure 4 is a cross-sectional view of one or more embodiments of an acoustic sensing device 400 that is shaped to match a pre-formed or built-in recessed area 402 on a structural panel 120. Advantageously, the recessed area 402 of the structural panel that receives the bonding member 116 of the acoustic sensing device is thinner than the surrounding vehicle body panel, thereby increasing the sensitivity and signal-to-noise ratio (SNR) of the acoustic sensing device 400. The recessed area 402 also helps ensure that the acoustic sensing device 400 is positioned and mounted in the correct location on the vehicle body during assembly.

[0035] The acoustic sensing device 100, 300, 400 of the subject invention is attached to a structural panel 120, such as a vehicle body panel, thereby providing an environmentally sealed surface mounted microphone suitable for exterior microphone applications. Mounting the acoustic sensing device to the structural panel in a completely sealed manner not only provides environmental protection for the microphone element, but also allows the structural panel 120, 420 to act as a second diaphragm for the microphone element 112.

[0036] An advantage over conventional microphones used on the exterior of a vehicle is that the acoustic sensing device 100, 300, 400 has a fully sealed attachment to the structural panel, thereby ensuring that the acoustic sensing device 100, 300, 400 will be able to meet the highest ingress protection ratings (e.g., IP6K9K). Another advantage of the acoustic sensing device 100, 300, 400 over conventional microphones is that the acoustic sensing device 100, 300, 400 is integrated into the vehicle structure by means of a bonded component, thereby allowing it to be used externally but still remain completely hidden for aesthetic reasons.

[0037] Compared to piezoelectric diaphragms, the advantage is that the size, thickness and height of the acoustic sensing device 100, 300, 400 are much smaller than those of piezoelectric diaphragms. The device 100, 300, 400 can be integrated into a smaller module housing 104 and provide improved EMI / EMC performance.

Claims

1. A sound and vibration sensor, comprising: shell; a printed circuit board assembly (PCBA), the PCBA including a microphone element, the PCBA being attached to a perimeter edge within the housing; and a bonding member having a first side sealingly adhered to a perimeter edge of one end of the shell, the bonding member having a second side sealingly adhered to a structural panel; as well as a sealed cavity defined between the structural panel and an area below the PCBA; The microphone element senses changes in sound pressure inside the sealed cavity caused by sound waves striking the structural panel.

2. The sensor of claim 1 , further comprising a ventilation path formed by a leakage channel in the PCBA between the sealed cavity below the PCBA and an area of ​​the housing above the printed circuit board assembly and a vent in the housing above the PCBA.

3. The sensor of claim 2, wherein the leakage channel further comprises a circular cross-sectional area having a diameter less than 0.4 mm, and the vent further comprises a circular cross-sectional area having a diameter less than 1.0 mm.

4. The sensor of claim 2, further comprising a dense mesh layer covering the vents. 5 . The sensor of claim 1 , wherein a portion of the structural panel that receives the second side of the bonding member is thinned compared to surrounding structural panels.

6. The sensor of claim 5, wherein an outer perimeter of the thinned structural panel is configured to match an outer perimeter of the bonding member to receive the bonding member in a completely sealed manner.

7. The sensor of claim 1, wherein the bonding member has a conformable foam core.

8. The sensor of claim 1, wherein the structural panel is a vehicle body panel.

9. The sensor of claim 8, wherein the second side of the adhesive member is adhered to the B side of the vehicle body panel.

10. A surface mounted microphone module, comprising: shell; a printed circuit board assembly (PCBA) having an aperture, the peripheral edge of the PCBA being flush mounted inside the housing at one end of the housing; a microphone element mounted to the PCBA, the microphone element having an acoustic port aligned with the hole of the PCBA; and an adhesive member having a first side sealingly adhered to an outer periphery of the housing at an end of the housing below the PCBA, the adhesive member having a second side sealingly adhered to a structural panel defining a sealed cavity; When a sound wave hits the structural panel, it causes surface vibration in the form of displacement in a direction perpendicular to the structural panel, and the surface vibration dynamically changes the volume of the sealed cavity, thereby generating a sound pressure proportional to the volume change inside the sealed cavity, and the sound pressure is sensed by the microphone element.

11. The module of claim 10, further comprising a ventilation path formed by a leakage channel in the PCBA and a vent in the housing.

12. The module of claim 11, wherein the leakage channel is aligned with the vent.

13. The module of claim 11 further comprising a dense mesh layer covering the vents.

14. The module of claim 10, wherein an area of ​​the structural panel that receives the second side of the bonding member is thinned compared to surrounding structural panels.

15. The module of claim 14, wherein the periphery of the thinned structural panel is configured to match the periphery of the bonding member so as to receive the bonding member in a completely sealed manner.

16. The module of claim 10, wherein the bonding member has a conformable foam core.

17. The module of claim 10, wherein the structural panel is a vehicle body panel.

18. The module of claim 17, wherein the second side of the bonding member is adhered to the B-side of the body panel.

19. The module of claim 10, wherein the sealed cavity has a volume less than 350 cubic millimeters.

20. The module of claim 10, wherein the bonding member has a thickness between 0.1 mm and 0.5 mm, the structural panel has a thickness between 0.1 mm and 2.0 mm, and the area of ​​the structural panel surrounded by the bonding ring is equivalent to a circular area with a diameter between 10 mm and 80 mm.

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