Waterproof sound and vibration sensing device

Abstract

A sound and vibration sensing device includes a housing, and a printed circuit board assembly (PCBA) including a sensor element supported within the housing. A flexible and non-porous structural membrane is arranged to seal the housing at one end, thereby creating a first enclosed air volume below the sensor element and a second enclosed air volume above the sensor element, wherein the sensor element measures a change in air pressure in the first enclosed air volume resulting from vibration of the structural membrane caused by external sound pressure and structural vibration to output a combined sound and vibration signal.

Description

Background Art

[0001] The present disclosure relates to sound and vibration sensing devices, and more particularly, to waterproof sound and vibration sensing devices. Technical Field

[0002] With the development of driver assistance technology and autonomous vehicles, the number of sensors on vehicles has grown significantly. As a result of these technological developments, it is necessary to sense sound and vibration from outside the vehicle. Therefore, sensing devices are positioned on the outer surface structures of the vehicle (e.g., body panels, frames, glass) that are directly exposed to various types of harsh environmental conditions. Therefore, the sensing devices must withstand the use of the vehicle in many situations, including but not limited to exposure to water and moisture, high temperature / high pressure water jets, ice, dust, debris, and mud.

[0003] For robust performance, it is desirable to achieve the highest level of environmental protection for the sensing device. This includes, for example, water and dust ingress and close-range high temperature, high pressure spray (up to 85°C and 10 MPa), as described by the IP6K9K rating in ISO 20653. In order to achieve this high level of environmental protection for sound sensing microphones that directly expose the sensing element to the external acoustic environment through a hole, the logical approach is to enclose the microphone element in a housing to physically separate the delicate sensing element from contaminants in the environment. However, this physical separation inevitably modifies the sound transmission path, which will change or degrade the acoustic performance if not carefully designed. Summary of the invention

[0004] A sound and vibration sensing device, the sound and vibration sensing device having: a housing; a support structure in the housing; a flexible non-porous structural membrane, the flexible non-porous structural membrane being arranged to seal the housing so as to produce a first enclosed air volume between a second surface of the structural membrane and a first surface of the support structure and a second enclosed air volume between the housing and the second surface of the support structure. A sensor element arranged on a printed circuit board assembly (PCBA) attached to the second surface of the support structure measures changes in air pressure in the first enclosed air volume caused by vibration of the structural membrane caused by external sound pressure and structural vibration input, and the sound and vibration sensing device outputs a combined sound and vibration signal output.

[0005] In one or more embodiments, the sound and vibration sensing device has a leakage path between the first enclosed air volume and the second enclosed air volume to filter low frequency vibration signals.

[0006] In one or more embodiments, the size of the leakage path depends on a predetermined frequency response shape, an amount of attenuation, and a predetermined frequency range.

[0007] In one or more embodiments, the support structure has a mechanical stop on a surface of the support structure facing the first enclosed air volume.

[0008] In one or more embodiments, the support structure is tapered.

[0009] In one or more embodiments, a damping layer is included. The damping layer can be positioned on the first surface or the second surface of the structural film.

[0010] In one or more embodiments, the housing has a vent from the second enclosed air volume. The vent may be covered by an acoustic mesh.

[0011] In one or more embodiments, the sound and vibration sensing device includes a second sensor element for simultaneously sensing sound and vibration.

[0012] In one or more embodiments, a sound and vibration sensing device has a housing and a printed circuit board assembly (PCBA) including a sensor element supported within the housing.

[0013] A flexible, non-porous structural membrane is arranged to seal the housing at one end, thereby defining a first enclosed air volume below the sensor element and a second enclosed air volume above the sensor element, wherein the sensor element measures changes in air pressure in the first enclosed air volume caused by vibrations of the structural membrane caused by external sound pressure and structural vibrations to output a combined sound and vibration signal.

[0014] In one or more embodiments, a leakage channel in the PCBA connects the first enclosed air volume and the second enclosed air volume to filter low frequency vibration signals.

[0015] In one or more embodiments, the structural membrane has a footing member that is attached to the bottom surface of the housing and also supports the PCBA within the housing. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The features, objects and advantages of the present disclosure will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which like reference numerals refer to like elements.

[0017] Figure 1 is a schematic diagram of a sensing device according to one or more embodiments;

[0018] Figure 2 It is a lumped parameter model that represents the vibration of the structural membrane;

[0019] Figure 3 is a measured frequency response of one or more embodiments of a sensing device;

[0020] Figure 4 is a simulated frequency response of one or more embodiments of a sensing device;

[0021] Figure 5 is a schematic diagram of a sensing device according to one or more embodiments;

[0022] Fig. 6A is a bottom view of a support structure showing one or more embodiments of a mechanical stop;

[0023] Figure 6B is a bottom view of a support structure showing one or more embodiments of a mechanical stop;

[0024] Figure 7 is a schematic diagram of a sensing device having a damping layer according to one or more embodiments;

[0025] Figure 8 is a partial view of a sensing device having a damping layer according to one or more embodiments;

[0026] Fig. 9 is a schematic diagram of a sensing device having a micro-electromechanical system (MEMS) microphone element according to one or more embodiments;

[0027] Fig.10 is a schematic diagram of a hybrid sensing device according to one or more embodiments;

[0028] Fig.11 is a schematic diagram of a sensing device according to one or more embodiments;

[0029] Fig.12 is a schematic diagram of a sensing device according to one or more embodiments;

[0030] Fig.13 is a schematic diagram of a sensing device according to one or more embodiments;

[0031] Fig.14 is a schematic diagram of a sensing device according to one or more embodiments; and

[0032] Fig.15 is a flow chart of a method according to one or more embodiments. DETAILED DESCRIPTION

[0033] Figure 11 is a schematic diagram of a sound and vibration sensing device 100 according to one or more embodiments. The housing 102 has an opening 104 at one end. The support structure 106 is attached to the interior of the housing 102 at the opening 104 in a sealed manner. The structural membrane 108 is attached to the support structure 106 and / or the housing 102 in a sealed manner so that there is no opening to the environment outside the housing 102. In practical applications, the housing 102 of the sound and vibration sensing device 100 can be mounted and mechanically fixed to Figure 1 The base structure is not shown in the figure, which can be, for example, a body panel, a frame, or a glass surface of the vehicle.

[0034] The first surface 110 of the structural membrane 108 is exposed to the external environment outside the housing 102. The second surface 112 of the structural membrane 108 is inside the housing 102. The sealed attachment between the housing 102, the support structure 106, and the structural membrane 108 defines a first enclosed air volume V1 inside the housing 102 between the second surface 112 of the structural membrane 108 and the first surface 114 of the support structure 106. The use of "enclosed" with respect to the first enclosed air volume means that V1 is isolated from the environment outside the housing 102.

[0035] The sound pressure 109 acting on the first surface 110 of the structural membrane 108 causes the structural membrane 108 to bend, which changes the volume of the first enclosed air volume V1 and causes a dynamic (or acoustic) pressure inside the first enclosed air volume V1. The second enclosed air volume V2 is defined between the housing 102 and the second surface 116 of the support structure 106. The use of "enclosed" with respect to the second enclosed air V2 also means that V2 is isolated from the environment outside the housing 102. Vibration (e.g., acceleration) input 111 is transmitted via the support structure 106. As described above, the sound and vibration sensing device 100 can be attached to the base structure through the housing 102. Structural vibration (e.g., acceleration) input 111 from the base structure can also be transmitted to the support structure 106 through the housing 102, thereby causing the structural membrane 108 to bend.

[0036] A printed circuit board (PCB) 118 is mounted to the second surface 116 of the support structure 106. A sensor element 120 is placed on the PCB 118. The sensor element 120 may be, for example, a microphone device such as a micro-electromechanical system (MEMS) microphone device or an electret condenser microphone (ECM) device. Other circuit components ( Figure 1 The PCB 118 (not shown) may also be placed on the PCB 118. The PCB 118, the sensor element 120, and any other necessary components on the PCB 118 are referred to as a PCB assembly (PCBA).

[0037] The first surface 110 of the structural membrane 108 is exposed to the external environment. The housing 102 is sealed by the structural membrane 108. The structural membrane 108 and the support structure 106 define a closed air volume V1. The material and configuration of the seal created between the housing 102, the support structure 106, and the structural membrane 108 can vary based on design criteria, as long as the attachment of the elements creates a seal between the structural membrane 108 and the support structure 106 to define the first closed air volume V1 and protect the sensor element 120 from contaminants.

[0038] Holes or port holes 122 in the PCB 118 and the support structure 106 open the first enclosed air volume V1 to the sensor element 120. The sensor element (e.g., a MEMS microphone or an ECM) measures pressure changes in V1 caused by the vibratory movement of the structural membrane 108 as a result of the sound pressure 109 acting on the first surface 110 of the structural membrane 108. Alternatively or additionally, the vibratory movement of the structural membrane 108 may also be caused by the base structure vibration input 111. It should be noted that in case a MEMS microphone arrangement is used, the sensor element 120 may be a bottom port MEMS or a top port MEMS microphone, as long as the port hole 122 is open to the first enclosed air volume V1.

[0039] The structural membrane 108 is not an acoustic membrane or mesh that is usually used to protect the microphone from external contamination. The structural membrane 108 is a structurally durable membrane made of a solid material such as engineering plastic or metal. The structural membrane 108 is not only non-porous to liquid and dust, but also non-porous to air.

[0040] Figure 2 is a lumped parameter model 200 that represents how the structural membrane 108 vibrates under external excitation. The structural membrane 108 is represented as supported on a support structure ( Figure 2 ) and / or the mass m on the housing 102 s . The first spring k s represents the structural spring stiffness of the structural membrane 108. The second parallel spring k a represents the air spring stiffness of the first enclosed air volume V1. The structural damping of the structural membrane 108 is determined by the parameter c s When an external sound wave strikes the first surface 110 of the structural membrane 108, vibrations (e.g., in the form of displacement, velocity, and acceleration) are induced in a direction perpendicular to the first surface of the structural membrane 108. Additionally, the structural vibration input 111 may be transmitted to the support structure 106 ( Figure 2 ), resulting in vibration energy being transferred directly to the structural membrane 108 attached to the support structure 106 and / or the housing 102.

[0041] The displacement amplitude d (i.e., displacement sensitivity) of the structural membrane 108 to a unit input (the input being the sound pressure input 109 and / or the support structure vibration input 111) can be calculated from the total stiffness (k s + k a ) is controlled. The measurement bandwidth of the sensor element 120 can be determined by the resonant frequency of the mass-spring vibration system and is related to the total stiffness (k s + k a ) Effective mass m of the structural membrane s Finally, the peak displacement amplitude at the resonant frequency is mainly determined by the structural damping c of the structural membrane 108. s Sure.

[0042] The displacement of the structural membrane 108 due to, for example, an external acoustic input (primary sound pressure) 109 causes a change in the enclosed air volume V1, which in turn causes the sound pressure (secondary sound pressure) within V1. The sensor element 120 (e.g., a MEMS microphone or ECM) on the PCB 118 is directly exposed to the first air volume V1 through a port hole 122 to measure the secondary sound pressure. For a small sealed air cavity such as V1, the sound pressure generated due to the volume change in the air cavity is proportional to the area of ​​the structural membrane and the membrane displacement, but inversely proportional to the enclosed air volume. The material of the structural membrane can be one or more sheets of plastic, polymer or metal such as acrylonitrile butadiene styrene (ABS), polybutylene terephthalate (PBT), nylon and / or aluminum.

[0043] Figure 3 Shows Figure 1 Measured frequency responses 300 of one or more embodiments of a waterproof sound and vibration sensor are shown. Curve 302 is the response amplitude normalized to 1 kHz sensitivity for a direct measurement of a MEMS microphone element without a structural membrane. In contrast, curve 304 is a 0.1 mm thick aluminum structural membrane. In contrast, curve 306 is a 0.4 mm thick plastic membrane. In each example, the height h and diameter D (see Figure 1 ) are 0.5 mm and 25 mm respectively. This example design results in approximately 245 mm 3 The enclosed air volume V1.

[0044] As can be expected, the frequency response of curve 302 without a structural membrane has the highest sensitivity and the widest effective measurement bandwidth of the sensor element, as represented by the flat portion of curve 302. For a structural membrane made of aluminum, curve 304 shows that the sensitivity is slightly reduced (by about 1 dB at 1 kHz), and the bandwidth is narrowed to about 4 kHz. For a structural membrane made of plastic, the sensitivity is even slightly reduced (by about 2.5 dB at 1 kHz), and the bandwidth is also further narrowed. The choice of structural membrane material will depend on meeting the target environmental protection requirements as well as the sensitivity and bandwidth requirements.

[0045] For example, for a structural membrane 108 and housing 102 having a circular shape, the diameter of the structural membrane 108 may range between 10 mm and 35 mm. The thickness of the structural membrane may range, for example, between 0.2 mm and 0.8 mm (for plastic or polymer materials) and between 0.02 mm and 0.2 mm (for metal materials).

[0046] The sound pressure generated in the enclosed air volume V1 caused by the displacement of the structural membrane 108 is inversely proportional to V1. An effective way to increase sensitivity and subsequently increase the signal-to-noise ratio (SNR) is to minimize the volume of V1. Therefore, the height h of the first sealed air volume V1 can be as small as practically possible to minimize the enclosed air volume. An example range can be 0.1 mm to 1 mm.

[0047] The total mass of the structural membrane 108 can be, for example, two to three orders of magnitude higher than a membrane that is part of a MEMS microphone or ECM sensor element 120. It should be noted that the ranges described herein are for exemplary purposes only. One skilled in the art will appreciate that the sensitivity of the microphone to vibration input transmitted from the underlying structure in the housing is proportional to the mass of the structural membrane, making the waterproof sound and vibration sensor with a closed housing and structural membrane described herein more sensitive to vibration input when compared to a conventional microphone element (e.g., a MEMS microphone or ECM).

[0048] Those skilled in the art will appreciate that the high vibration sensitivity of one or more embodiments described herein is advantageous when both a vibration (e.g., base acceleration) input and an acoustic pressure input are of interest because the sensor effectively measures both and outputs a combined signal. On the other hand, acoustic sensing microphone designs typically require minimizing vibration sensing sensitivity. For example, in some practical automotive applications, structural vibrations are primarily at low frequencies (e.g., <300 Hz to 500 Hz), while the acoustic input is broadband up to 10 kHz or higher. Therefore, the inclusion of a high-pass filter will filter out low-frequency vibrations from the sensor output signal. Since the acoustic pressure sensed by the sensor element 120 is inversely proportional to the sealed volume directly in front of the sensor element 120, a larger effective volume at lower frequencies will reduce the sensitivity in the corresponding low-frequency range where, for example, most of the vibration energy in the vehicle structure exists. A larger effective volume can be achieved by including a second enclosed volume V2 that will be sensed by the sensor element 120. Reference Figure 1 , the first closed volume V1 and the second closed volume V2 can be connected via an optional leakage channel 124.

[0049] The low frequency sensitivity of the waterproof sound and vibration sensing device 100 can be attenuated by controlling the size of V2 relative to V1. For example, when V2 is significantly larger (e.g., about 10 times larger) than V1, the low frequency sensitivity can be attenuated by about 7 dB to 12 dB, as shown in FIG. Figure 4 As shown, the figure shows the simulated results of the normalized frequency response amplitude at 1 kHz.

[0050] Depending on the preferred frequency response shape, amount of attenuation, and frequency range, the sensitivity can be attenuated by adjusting the size of the leakage channel 124 (which modifies the size of V2 relative to V1). Curve 402 shows the frequency response of a leakage channel with a diameter of 0.1 mm. Curve 404 shows the frequency response of a leakage channel with a diameter of 0.2 mm. Curve 406 shows the frequency response of a leakage channel with a diameter of 0.3 mm. Curve 408 shows the frequency response of a leakage channel with a diameter of 0.4 mm, which shows how the low frequency sensitivity is attenuated by approximately 12 dB.

[0051] When the second enclosed volume V2 is connected to the first enclosed volume V1, the sensitivity to vibration input is attenuated, and the sensitivity to sound input is attenuated. This is desirable in some applications when acoustic input above 300 Hz to 500 Hz is the desired signal to be measured with an environmentally sealed sound and vibration sensor. In such applications, the low frequency signals containing the greatest vibration energy can be sensed by a separate, dedicated vibration sensing element (such as an accelerometer).

[0052] The displacement amplitude of the structural membrane 108 can be determined by the dynamic base vibration 111 and the acoustic excitation 109 applied to the structural membrane 108, or directly applied to the first surface 110 of the structural membrane 108 (see Figure 1 ) on the structural membrane. The resulting displacement amplitude corresponding to the dynamic base vibration or acoustic excitation may be on the order of tens to hundreds of microns, which is relatively small. However, under large external force inputs such as the forces that may be applied directly to the surface of the structural membrane under high pressure water spray, the resulting displacement (or deformation) amplitude may be much larger. Large displacements / deformations introduce stresses on the material that may undesirably change the mechanical properties of the structural membrane 108, or even cause damage, rendering the sensor inoperable.

[0053] Figure 5 One or more embodiments of a sound and vibration sensing device 500 are shown that incorporates a mechanical stop 502 into the support structure 106 to prevent excessive deformation of the structural membrane 108 under large external force input. The mechanical stop 502 is located on the first surface 114 of the support structure 106. When the structural membrane 108 is exposed to an external force that causes a large displacement, the displacement / deformation of the structural membrane 108 will be limited by the mechanical stop 502, thereby preventing the structural membrane from being overstressed.

[0054] Additional advantages of the mechanical stop 502 can be achieved by using the design or pattern of the mechanical stop 502 to help increase the sensitivity of the sound and vibration sensing device 500. The structure of the mechanical stop 502 can be implemented in a way that consumes some of the enclosed volume V1. For example, Fig. 6A One example of many is shown in which a pattern 600A of distributed protrusions 602 creates a mechanical stop. Figure 6B Another example 600B of many possible patterns is shown, where rings 604 are concentrically distributed to create a mechanical stop.

[0055] exist Figure 7 In one or more embodiments of the sound and vibration sensing device 700 shown, a damping layer 702 may be added to the structural membrane 108 to attenuate the resonant peak amplitude of the frequency response curve. The damping layer 702 may be a viscoelastic coating such as rubber or other suitable material. The damping layer 702 may be added to the mechanical stop 502, or may be a replacement for the mechanical stop.

[0056] The damping layer 702 may be added to the first surface 110, the second surface 112, or both the first surface 110 and the second surface 112 of the structural membrane 108. The damping layer 702 applied to the second surface 112 of the structural membrane 108 will occupy space that consumes volume in the enclosed volume V1, thereby improving acoustic performance by increasing the sensitivity of the sound and vibration sensing device 700. Figure 8In one or more embodiments shown, the damping layer 702 is applied to the first surface 110 of the structural membrane 108. When the damping layer 702 is applied to the first surface 110 of the structural membrane 108, the damping layer adds additional protection against environmental contaminants that can cause damage to the sensor components.

[0057] The larger second enclosed air volume V2 may improve the signal-to-noise ratio (SNR) of the sound and vibration sensing device. Fig. 9 One or more embodiments of a sound and vibration sensing device 900 having a bottom port MEMS microphone element 902 are shown. The bottom port MEMS microphone element 902 has a MEMS sensing element 908. A first port hole 904 on the bottom of the MEMS sensing element 908 connects an air volume 909 in front of the MEMS microphone element 902 to an enclosed air volume V1. A second hole or port hole 906 vents an air volume 910 behind the MEMS sensing element 908 to an enclosed air volume V2. An advantage of this arrangement is that the rear volume of the MEMS microphone element 902 is connected to V2, resulting in a much larger effective rear volume of the MEMS microphone element 902, which helps reduce microphone self-noise and therefore improves SNR.

[0058] exist Fig.10 In one or more embodiments shown, a hybrid waterproof sound and vibration sensing device 1000 is shown. An accelerometer 1002 (e.g., a MEMS accelerometer sensor) is added to the PCB 118. The accelerometer 1002 has an output that is independent of the sound sensing sensor element 120 (e.g., a MEMS microphone or ECM). A leakage channel 124 is provided to configure the sensor element 120 to be insensitive to low frequency vibration and acoustic excitation (see above reference). Figure 4 The enclosed air volume V1 is connected to the enclosed air volume V2 in a manner similar to that discussed in detail above. The leakage path 124 has no effect on the accelerometer 1002 because the accelerometer 1002 directly measures the base structural vibration input 111 transmitted through the housing 102 to the support structure 106 and the PCB 118, regardless of the displacement amplitude of the structural membrane 108 or the volume change of the enclosed air volume V1. The inclusion of the accelerometer 1002 provides simultaneous sound and vibration sensing for vibration inputs of interest at low frequencies (e.g., <350 Hz) and acoustic inputs of interest at frequencies above, for example, 350 Hz.

[0059] In reference Figures 1 to 10In the described embodiment, the sensor element 120 is completely sealed from the external environment. While this is ideal for protecting the sensor from the environment, unwanted static pressure may build up within the first enclosed air volume V1 and the second enclosed air volume V2. Static pressure buildup may occur when there is a temperature difference between the environment and the sealed space within the first enclosed air volume and the second enclosed air volume. Static pressure may also be caused by changes in altitude. Fig.11 In one or more embodiments shown, the waterproof sound and vibration sensor 1100 has a vent or vent hole 1102 in the housing 102. A dense acoustic mesh layer 1104 covers the vent hole 1102 from within the housing 102.

[0060] The size of the vent hole 1102 is set to be as small as possible and only large enough as necessary to equalize the static pressure between the interior of the housing 102 and the external environment. For example, the vent hole 1102 can be less than 1 mm in diameter. The vent hole 1102 is preferably located in the housing 102 as far away from the sensor element 120 as possible.

[0061] The dense acoustic mesh layer 1104 can be thick enough to protect the interior of the housing 102 from an external environment having high flow resistance, while still allowing pressure equalization between the interior and exterior of the housing 102. For example, the dense acoustic mesh layer 1104 can be made of an expanded polytetrafluoroethylene (ePTFE) material having a thickness of approximately 0.1 mm to 0.5 mm.

[0062] The sensitivity of the sound and vibration sensing device can be increased by reducing the first sealed volume V1. Fig.12 In one or more of the embodiments shown, the sensitivity and SNR of the sound and vibration sensing device 1200 is improved by reducing the first sealed volume V1. This can be achieved by changing the configuration of the support structure 1206 in a manner that reduces the size of the first sealed volume V1. Fig.12 The example shown has a conical support structure 1206 configuration that defines a ratio Fig.11 The exemplary flat disk-shaped support structure 116 is shown with a small first sealed volume V1.

[0063] Alternatively, in Fig.13 In one or more embodiments shown, no separate support structure is included within the waterproof sound and vibration sensing device 1300. Instead, the PCB 1318 is attached to the housing 1302 and can be positioned as close to the structural membrane 1308 as possible.

[0064] Alternatively or additionally, in Fig.14In one or more of the illustrated embodiments, the sound and vibration sensing device 1400 has a structural membrane 1408 that is not recessed into the housing 1402 and attached to one end of the housing (eg, Figure 1 , Figure 5 , Figure 7 and Figures 9 and 10 1402) instead, the structural membrane 1408 is attached to one end of the housing 1402 so that the structural membrane can also serve as a support structure. The structural membrane 1408 can be a one-piece configuration with a footing member 1430. The footing member 1430 is directly attached to the outer periphery 1432 of the housing 1402. The PCB 118 is attached within the housing 1402 and supported by the footing member 1430 of the structural membrane 1408. The first surface 1410 of the structural membrane 1408, i.e., the surface exposed to the external environment, can be a smooth surface to help reduce the effects of wind turbulence, which is particularly beneficial when the waterproof sound and vibration sensor 1400 is used on an infrastructure such as the exterior of a vehicle.

[0065] According to one or more embodiments of the subject matter of the present invention, the sound and vibration sensing device has a closed body that is completely sealed from the external environment. The structural membrane 108, 1408 is mechanically flexible and vibrates under external sound or vibration excitation. The sensor element 120, which can be a microphone (MEMS, ECM, etc.), an accelerometer, or both, measures the sound pressure in the first closed air volume V1 through the vibration of the structural membrane 108, 1408. The above-mentioned waterproof sound and vibration sensing device has many features that can be used alternatively or additionally to make the device configurable for many applications. For example, certain features, such as membrane material, membrane size and thickness, and the presence of leakage channels or vents, will affect sensitivity, SNR, attenuation resonance peak, durability, reliability, etc. Fig.15 Methods are shown for determining and / or selecting which features should be incorporated into a sensing device based on a set of objectives associated with a particular application of the sensing device.

[0066] At steps 1502 and 1504, environmental protection and electro-acoustic targets are set. At step 1502, it should be considered whether the sensing device will be mounted on the exterior of the vehicle. It is also necessary to consider whether the sensing device will be subjected to high temperatures, high pressure spray, etc. Electro-acoustic targets may include sensitivity and bandwidth requirements for the use of the sensing device. For example, detection of emergency vehicle alarms, road noise cancellation, and voice command detection.

[0067] At step 1506, a material for the structural membrane is selected based on the environmental target. The structural membrane may be in the form of a thin sheet made of, for example, engineering plastics, polymers, and metal materials such as ABS, PBT, nylon, aluminum, etc. The structural membrane material should be selected to first meet the target environmental protection requirements and then provide the best possible sensitivity and bandwidth.

[0068] At step 1508, the membrane size (diameter or area) and thickness are selected based on the electroacoustic target. Assuming a circular structure membrane and housing, an exemplary range of membrane diameters may be between 10 mm and 35 mm. An exemplary range of membrane thickness may be 0.2 mm to 0.8 mm for plastic / polymer materials and 0.02 mm to 0.2 mm for metal materials.

[0069] At step 1510, a first enclosed volume V1 is determined based on the electroacoustic target. The height h of the first enclosed air volume V1 should be as small as practically possible to minimize the first enclosed air volume V1. For example, in the range of 0.1 mm to 1 mm. In addition, it should be noted that the first enclosed air volume V1 may also be affected by the configuration of the support structure.

[0070] At step 1512, a second enclosed volume V2 is determined based on the first enclosed volume V1. The second enclosed volume V2 is preferably larger than the first enclosed volume V1. For example, V2 may be approximately ten times larger than V1.

[0071] At step 1514, the size and shape of the closed enclosure that houses V1 and V2 is determined.

[0072] At step 1516, it is determined whether high pass filtering is required for the particular application of the sound and vibration sensing device. If high pass filtering is required 1518, a leakage channel is incorporated 1520 between V1 and V2. The size of the leakage channel is determined based on electroacoustic objectives such as desired sensitivity and bandwidth.

[0073] Although exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the present invention. It should be understood that various changes can be made without departing from the scope of the present invention. Additionally or alternatively, the features of various implementation embodiments can be combined to form other embodiments of the present invention. For example, the configuration of the structural membrane can be combined with a housing vented to the external environment. The waterproof sound and vibration sensor can include a port hole and a leak channel or a leak-free channel. The waterproof sound and vibration sensor can include a leak channel and a vent housing, or does not include a leak channel and a vent housing.

Claims

1. A sound and vibration sensing device, comprising: shell; a support structure within the housing, the support structure having a first surface and a second surface; a structural membrane, the structural membrane being flexible and non-porous, the structural membrane having a first surface and a second surface, the structural membrane being arranged to seal the housing; a first enclosed air volume defined between the second surface of the structural membrane and the first surface of the support structure; a second enclosed air volume defined between the housing and the second surface of the support structure; and a sensor element disposed on a printed circuit board assembly (PCBA) attached to the second surface of the support structure, the sensor element measuring changes in air pressure in the first enclosed air volume caused by vibrations of the structural membrane caused by external sound pressure and structural vibration inputs; and Combined sound and vibration signal output.

2. The apparatus of claim 1 further comprising a leakage channel in the support structure, the leakage channel connecting the first enclosed air volume to the second enclosed air volume to filter low frequency vibration signals.

3. The apparatus of claim 2, wherein the size of the leakage channel depends on a predetermined frequency response shape, an amount of attenuation, and a predetermined frequency range.

4. The apparatus of claim 1 further comprising a mechanical stop on the first surface of the support structure.

5. The device of claim 1, wherein the support structure has a conical shape.

6. The apparatus of claim 1 further comprising a damping layer positioned on the structural membrane.

7. The apparatus of claim 6, wherein the damping layer is positioned on the first surface of the structural film.

8. The apparatus of claim 6, wherein the damping layer is positioned on the second surface of the structural film.

9. The apparatus of claim 1 wherein said housing has a vent from said second enclosed air volume.

10. The device of claim 9, further comprising an acoustic mesh layer covering the vent from the interior of the housing.

11. The apparatus of claim 1 , wherein the sensor element is a MEMS microphone having a first aperture vented into the first enclosed air volume and a second aperture vented into the second enclosed air volume.

12. The apparatus of claim 1 further comprising a second sensor element on the PCB assembly for simultaneously sensing sound and vibration.

13. A sound and vibration sensing device, comprising: shell; a printed circuit board assembly (PCBA), the PCBA having an aperture, the PCBA supported within the housing; a sensor element mounted on the PCBA above the hole; a structural membrane, the structural membrane being flexible and non-porous, the structural membrane having a first surface and a second surface, the structural membrane being arranged to seal the housing at one end; a first enclosed air volume, the first enclosed air volume below the sensor element, the first enclosed air volume defined within the housing below the aperture between the PCBA and the structural membrane; and a second enclosed air volume, the second enclosed air volume being above the sensor element, the second enclosed air volume being defined within the housing between the housing and the PCBA; The sensor element measures changes in air pressure in the first enclosed air volume caused by vibrations of the structural membrane caused by external sound pressure and structural vibrations to output a combined sound and vibration signal.

14. The apparatus of claim 13, further comprising a leakage channel in the PCBA, the leakage channel connecting the first enclosed air volume to the second enclosed air volume to filter low frequency vibration signals.

15. The device of claim 14, wherein the size of the leakage path depends on a predetermined frequency response shape, an amount of attenuation, and a predetermined frequency range of the sound and vibration sensing device.

16. The apparatus of claim 13, further comprising a support structure in the housing, the support structure having a first surface and a second surface and a hole therethrough aligned with the hole in the PCBA, the first surface of the support structure facing into the first enclosed air volume and the second surface of the support structure facing into the second enclosed air volume, the PCBA being supported by the support structure.

17. The apparatus of claim 16, further comprising a leakage channel in the PCBA and the support structure, the leakage channel connecting the first enclosed air volume with the second enclosed air volume to filter low frequency vibration signals.

18. The apparatus of claim 16, further comprising a mechanical stop on the first surface of the support structure.

19. The apparatus of claim 16, wherein the support structure is conical.

20. The apparatus of claim 13, wherein a damping layer is positioned on the first surface of the structural film.

21. The apparatus of claim 13, wherein a damping layer is positioned on the second surface of the structural film.

22. The apparatus of claim 13, wherein the structural membrane further comprises feet surrounding the second surface, the feet attached to a bottom surface of the housing to seal the housing and support the PCBA within the housing.

23. The apparatus of claim 13, wherein the sensor element is a MEMS microphone having a first aperture vented into the first enclosed volume of air and a second aperture vented into the second enclosed volume of air.

24. The apparatus of claim 13, further comprising a second sensor element on the PCBA for simultaneously sensing sound and vibration for a combined sound and vibration output signal.

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