Patent Description:
Piezo-diaphragms or piezoelectric diaphragms are piezoelectric ceramic disks adhered to a metal plate that is typically formed of brass or nickel alloy. A common piezoelectric ceramic material is lead zirconate titanate (PZT). Due to the piezoelectric effect presented by the piezoelectric ceramic disk that converts electrical signals (e.g., voltage, charge) into mechanical signals (e.g., deformation, strain, etc.) and vice versa, piezo-diaphragms are widely used as transducer elements. One typical application of a piezo-diaphragm is a sound buzzer device that converts electrical input energy into mechanical deformation of the piezo-diaphragm, resulting in sound emission. On the other hand, when a piezo-diaphragm is attached to a base structure, the piezo-diaphragm can vibrate once excited by mechanical motion of the base structure and generate a charge or voltage output, thus forming a vibration sensor. If the mechanical motion of the base structure is induced by sound, the piezo-diaphragm in this case becomes essentially a sound sensor that is equivalent to a microphone.

Document <CIT> discloses a vibration sensor for detecting a vibration of a vibrating object including a plurality of detecting members. Each of the detecting members includes a vibrating portion disposed to be separated from the vibrating object, a transmitting portion for transmitting the vibration from the vibrating object to the vibrating portion, and a detecting portion disposed on a vibrating face of the vibration portion. The detecting portion outputs an electrical signal corresponding to a resonance of the vibrating portion. At least two of the vibrating portions of the detecting members have resonance frequencies, which are different from each other.

Document <CIT> discloses a piezoelectric knock sensor comprising a flexing plate at one end of a generally cylindrical case with a mounting stud extending perpendicularly therefrom and a piezoelectric element attached to the flexing plate within the case for flexure with the flexing plate. When the sensor is attached to a component of a multicylinder, internal combustion engine, the case vibrates interactively with at least a portion of the component through the flexing plate and exhibits both an interactive resonance with the component for a wide resonance peak and response to transverse as well as axial vibrations.

Document <CIT> discloses a broadly tuned self resonant knock sensor including a piezoelectric element mounted on a central mounting stud. The element includes a generally annular vibratable portion having a variable radial dimension so as to exhibit resonant vibrations at a plurality of relatively closely spaced resonant frequencies essentially spanning an engine determined knock frequency band. The element comprises a circular plate having piezoelectric generating means and an axis offset from the axis of the mounting stud.

In at least one embodiment, a sound and vibration sensor is provided. The sound and vibration sensor includes a housing, a piezo-diaphragm, and a flexible support plate. The piezo-diaphragm is positioned in the housing to detect an input signal including audio or vibrations. The flexible support plate receives the piezo-diaphragm to enable the sensor to exhibit a frequency response with a plurality of resonant frequencies in response to detecting the audio or the vibrations on the input signal. The piezo-diaphragm and the flexible support plate form a two-degree of freedom system that provides the frequency response with a plurality of resonant frequencies. The flexible support plate includes a mounting post extending therefrom and being configured to receive the piezo-diaphragm to support the piezo-diaphragm in the housing. The mounting post is flexible or rigid. The flexible support plate includes an extending portion that contacts a first end of the housing and a second end of the housing to environmentally seal the housing, and the extending portion extends outwardly from the mounting post.

The embodiments of the present disclosure are pointed out with particularity in the appended claims. However, other features of the various embodiments will become more apparent and will be best understood by referring to the following detailed description in conjunction with the accompany drawings in which:.

Aspects disclosed herein generally relate to a piezo-diaphragm based sensor in which a piezo-diaphragm has a flexible bottom surface mounted thereon to provide a second resonance in a frequency band of interest. This implementation provides a one mechanism to extend a signal bandwidth for the sensor. In another aspect, a plurality of piezo-diaphragms may be provided to generate a plurality of resonances in the frequency band of interest. This aspect provides an active way to extend the signal bandwidth for the sensor.

Piezo-diaphragms or piezoelectric diaphragms are piezoelectric ceramic disks adhered to metal plate of, for example, brass or nickel-alloy. A common piezoelectric piezo-electric ceramic is lead zirconate titanate (PZT). Due to the piezoelectric effect presented by the piezoelectric ceramic disk that converts electrical signals (e.g., voltage, charge) into mechanical signals (e.g., deformation, strain) and vice versa, piezo-diaphragms are widely used as transducer elements. One application of piezo-diaphragms is the sound buzzer device that converts electrical input energy into mechanical deformation of the piezo-diaphragm, resulting in sound emission. On the other hand, when a piezo-diaphragm is attached to a base structure, the piezo-diaphragm can vibrate once excited by mechanical motion of the base structure and generate a charge or voltage output, thus forming a vibration sensor. If the mechanical motion of the base structure is induced by sound, the piezo-diaphragm in this case becomes a sound sensor equivalent to a microphone.

The piezo-diaphragm based sensor includes a printed circuit board (PCB) assembly ("PCBA") and a piezo-diaphragm enclosed in a protective housing. The protective housing includes an upper body and a bottom surface. The PCB assembly with appropriate electrical components serves as a pre-amplifier or signal conditioner for the piezo-diaphragm output and is fixed to the housing body through adhesive or other mechanical mechanisms. Similarly, the piezo-diaphragm may be attached to the bottom surface of the protective housing through adhesive or other mechanical mechanisms. The piezo-diaphragm and the PCBA are interconnected by a pair of electrical wires for power and signal transmitting. When the piezo-diaphragm sensor is attached to a base surface such as a vehicle body (e.g., windshield glass, body panel or bumper), the sensor may sense motions of the base surface through piezoelectric effect of the piezo-diaphragm, whether the motion is induced by vibration sources (e.g., road roughness, engine, etc.) or acoustic sources in the environment (e.g., voice). In the latter case, the piezo-diaphragm sensor functions as a surface-mounted microphone.

The signal bandwidth for the disclosed piezo-diaphragm based sensor may be controlled by the property of the piezo-diaphragm and the manner in which the piezo-diaphragm is mounted inside the housing. Piezo-diaphragms may come with a natural vibration mode or natural resonance frequency residing between <NUM> and <NUM>. Below this resonance frequency, the sensor sensitivity is essentially flat which is characterized as a useful bandwidth of the sensor. Above the resonance frequency, the sensitivity may drop rapidly. When the sensor is used as a surface mounted microphone, a bandwidth up to <NUM> - <NUM> may be relatively narrow compared to the typical audio bandwidth of <NUM> to <NUM>. To increase the signal bandwidth, the bottom surface of the housing to which the piezo-diaphragm is attached can be implemented to provide a second resonance at a higher frequency than the existing resonance. The second resonance helps to boost the sensitivity at high frequencies to increase the signal bandwidth. To fit various application needs, the location of the second resonance may be implemented with the following parameters: bottom surface shape, thickness, size, material and location at which the piezo-diaphragm is attached to the bottom surface. The overall implementation of the bottom surface provides at least one innovative aspect.

The piezo-diaphragm sensor may include the PCBA and the piezo-diaphragm enclosed in the protective housing. The sensor may include a flexible bottom surface implementation that generates a second resonance to aid in extending the signal bandwidth of the sensor. The flexible bottom surface generally includes a bottom surface shape, predetermined thickness, predetermined size, and predetermined material and the location at which the piezo-diaphragm is attached to the bottom surface. For example, considering a circular piezo-diaphragm and housing design, mounting the piezo-diaphragm concentrically with the bottom surface at a center point versus along the rim may result in different resonance locations and frequency response characteristics.

The embodiments disclosed herein may provide a response for recent applications in connection with, for example, automotive Original Equipment Manufacturers (OEMs) that may need a surface-mountable microphone for external voice activity detection. The disclosed piezo-diaphragm sensor relates to sensing audio signals inside or outside of the vehicle. As such, the sensor should include sufficient sound sensing bandwidth. For external vehicle applications, the sensor should also be environmentally robust and insensitive to wind noise. The sensor may be sensitive to voice induced structural vibrations in the case of the surface-mounted vibration sensor. Other microphone (or sensor) applications may benefit from the aspects disclosed herein. For example, microphones that are traditionally difficult to position in the vehicle such as spaces like a full glass rooftop versus a traditional headliner and for sound and vibration sensing for active noise cancellation (ANC)/road noise cancellation (RNC), vehicle noise compensation (VNC), and external siren detection may utilize any one or more of the sensors disclosed herein.

Some acoustic microphones may have acceptable bandwidth and sensitivity, but such microphones may be difficult to be packaged in a way that can resist water/dust contamination. Accelerometers, on the other hand, may be environmentally robust and may be implemented in a sealed package and can pick up vibrations caused by voice and transmitted through structures. The disclosed microphones (or piezo-diaphragm sensors) may be implemented as surface mounted microphones that may be environmentally robust as well.

In general, existing lab level precision accelerometers may serve as microphones to detect external audio. However, such accelerometers may be too expensive to be used for automotive implementations. In addition to lab level precision accelerometers, commercial, off the shelf Micro-Electro-Mechanical System (MEMS) accelerometers typically have a limited bandwidth (e.g., up to <NUM>) or low sensitivity compared to what is needed in terms of an ideal bandwidth for audio applications. In general, external voice detection in the automotive industry is gaining interest by OEMs with a desired objective of developing sensor solutions that can meet environmental robustness, signal bandwidth, higher sensitivity, packaging constraints and low cost. The sensor solutions disclosed herein may meet such OEM objectives.

<FIG> depicts a vehicle <NUM> including a plurality of sound and vibration sensors 102a - 102n ("<NUM>") for detecting sound that is external to the vehicle <NUM>. The plurality of sound and vibration sensors <NUM> may include microphones or accelerometers (or a combination thereof). The plurality of sound and vibration sensors <NUM> are distributed about the vehicle <NUM> and are configured to detect voice commands that are external (or internal) to the vehicle <NUM>. A controller <NUM> is positioned in the vehicle <NUM> and receives signals from the various sound and vibration sensors <NUM>.

OEMs generally desire that the plurality of sound and vibration sensors <NUM> may be implemented as surface-mountable sensors for external (or internal) voice detection. Thus, the plurality of sound and vibration sensors <NUM> may transmit signals indicative of detected voice commands to the controller <NUM>. The controller <NUM> may then activate or deactivate a predetermined vehicle operation (e.g., open/close a trunk, vehicle door, liftgate, etc.) in response to the voice commands. Given that the plurality of sound and vibration sensors <NUM> is configured to detect voice audio from an environment exterior <NUM> to the vehicle <NUM>, the sensors <NUM> may be positioned on external portion of the vehicle <NUM> and may be exposed to a variety of environmental factors. As such, the sensors <NUM> need to be environmentally robust and insensitive to, for example, wind. Additionally, the sensors <NUM> need to provide a sufficient wideband for voice sensing and remain sensitive enough to voice induced structural vibrations in the case of a surface-mounted vibration sensor. This piezo-diaphragm based sensor <NUM> measures the vibration (i.e., acceleration) of the base structure surface on which the sensor <NUM> is attached to, regardless the source of the vibration. In the case, where the structure vibration is excited by sound, the sensor <NUM> then picks up the sound signal and functions as a traditional microphone. Furthermore, whether the sound corresponds to voice commands or background noise, the sensor <NUM> may be one way to use the sensed signal. In case of speech detection, the sensor <NUM> may be used in connection with voice command applications. In case of background noise, the sensor <NUM> may detect signals that can be used in the ANC/RNC system.

<FIG> depicts an example of a piezo-diaphragm <NUM>. The piezo-diaphragm <NUM> may be a piezoelectric diaphragm that includes a ceramic disk <NUM> and a metal substrate plate <NUM>. The ceramic disk <NUM> may be adhered to the metal substrate plate <NUM> which may be formed of brass (or nickel alloy). The material for the ceramic disk <NUM> may be lead zirconate titanate (PZT). The piezoelectric effect presented by the piezoelectric ceramic disk converts electrical signals (e.g., a voltage or charge) into mechanical signals (e.g., deformation, strain, etc.) and vice versa. Piezo-diaphragms may be used as sensing or actuating elements for a transducer. One typical application of a piezo-diaphragms is that of a sound buzzer that converts electrical input energy into mechanical deformation of the piezo-diaphragm resulting in a sound emission.

When the piezo-diaphragm <NUM> is attached to a base structure (not shown), the piezo-diaphragm can vibrate once excited by the mechanical motion of the base structure and generate a charge or voltage output, thus forming a vibration sensor. If the mechanical motion of the base structure is induced by sound, the piezo diaphragm <NUM> becomes a sound sensor equivalent to a microphone.

<FIG> depicts an example of a piezo-diaphragm based sound and vibration sensor <NUM>. The sensor <NUM> includes the piezo-diaphragm <NUM> (see <FIG>), a housing <NUM>, and a bottom cover or (lid) <NUM>. The piezo-diaphragm <NUM> may be supported circumferentially along an edge of the substrate plate <NUM> within the housing <NUM>. A bottom cover or lid <NUM> is positioned below the piezo-diaphragm <NUM> and is also attached to the housing <NUM> circumferentially. The housing <NUM> and lid <NUM> encapsulate the piezo-diaphragm <NUM>. It is recognized that the lid <NUM> may or may not be implemented. If implemented, the lid <NUM> may be merely used for environmental protection A printed circuit board (PCB) assembly <NUM> (or PCBA <NUM>) is coupled to the piezo-diaphragm <NUM> via a pair of electrical wires <NUM> to transmit a signal indicative of detected sound (or audio) external (or internal) to the vehicle <NUM> to at least one integrated circuit (or microprocessor) (not shown) positioned on a substrate <NUM> of the PCBA assembly <NUM>. The microprocessor may process the signal and transmit another signal to a controller (e.g., the controller <NUM>).

The signal bandwidth for the sensor <NUM> is generally determined based on a resonance frequency of the piezo-diaphragm <NUM> itself which is typically limited to an upper frequency of <NUM> - <NUM>. Such a bandwidth may be too narrow for a speech or sound system when compared to a typical audio bandwidth of <NUM> - <NUM> that is audible to human ears. In general, a frequency range of <NUM> - <NUM> is an acoustic signal bandwidth that is audible to human ears. Thus, an ideal acoustic sensor should be sensitive and maintain the same sensitivity (e.g., flat frequency response) across the entire audible band.

The sensor <NUM> maintains the flat frequency response region up to the natural resonance frequency of the piezo-diaphragm which is typically between <NUM> and <NUM> (e.g., depending on the properties of the piezo-diaphragm design and manufacturing). Above its resonance frequency, the sensitivity reduces rapidly with increasing frequency (e.g., the sensor <NUM> still picks up signal, but it is not as sensitive). In comparison with the entire audible range, a frequency band of <NUM>-<NUM> Hz is relatively narrow. A wideband speech application generally requires a bandwidth at least up to <NUM>. Therefore, generating a second resonance in the frequency band of interest through the use of a flexible bottom plate (see below flexible bottom plate <NUM>) may increase the bandwidth of the sensor.

The single piezo-diaphragm based sound and vibration sensor is based, among other things, on a single piezo-diaphragm that mounted on a flexible bottom plate. A second resonance associated with the bottom plate will work together with the natural resonance of the piezo-diaphragm itself to expand the overall signal bandwidth of the sensor.

<FIG> depicts a cross-sectional view of a single piezo-diaphragm based sound and vibration sensor <NUM> in accordance to one embodiment. The sensor <NUM> includes the piezo-diaphragm <NUM> and the housing <NUM>. The sensor <NUM> includes a first plate <NUM> (e.g., support plate or bottom plate <NUM>). The bottom plate <NUM> is flexible and includes a post <NUM> (or mounting post <NUM>) that extends above the bottom plate and an extending portion <NUM>. It is recognized that the post <NUM> is flexible or rigid. In the event, the post <NUM> is rigid, the post <NUM> may be packaged as a separate component from the extending portion <NUM> which remains flexible. The extending portion <NUM> is substantially flat and is axially displaced from the piezo-diaphragm <NUM>. The extending portion <NUM> is flexible and vibrates which generates a second resonance which aids in the overall sensor output. In conventional designs, the bottom portion of the housing or a lid coupled to the housing are rigid by default or are irrelevant to the acoustical performance of the sensor.

The bottom plate <NUM> supports the piezo-diaphragm <NUM> via the mounting post <NUM>. The extending portion <NUM> of the flexible bottom plate <NUM> may have a uniform thickness and is connected circumferentially to an inner wall of the housing <NUM>. The extending portion <NUM> environmentally seals the housing <NUM>. An optional damping mechanism <NUM> (e.g. a layer of damping material such as, for example, memory foam) surrounds the mounting post <NUM>. The damping mechanism <NUM> may be positioned below the piezo-diaphragm <NUM>. The flexible bottom plate <NUM> connects to the housing <NUM> circumferentially at ends of <NUM> and <NUM> of the housing <NUM>. The bottom plate <NUM> may be positioned directly adjacent to the damping mechanism <NUM> and covers the damping mechanism <NUM>. Thus, the damping mechanism <NUM> is positioned between the bottom plate <NUM> and the piezo-diaphragm <NUM>. When implemented, the damping mechanism <NUM> may help dampen the vibration response amplitudes of the piezo-diaphragm <NUM> at resonant frequencies, and thus maintain a flat and smooth amplitude frequency response in a bandwidth as wide as possible.

The bottom plate <NUM> is compressible and are engineered (or tuned) to provide a second resonance at high frequencies. For example, the mass and stiffness properties of the mounting post <NUM> and the flat portion <NUM> are engineered and provided to generate a second resonance in a frequency response of the sensor <NUM>. The second resonance is achievable since the piezo-diaphragm <NUM> and the bottom plate <NUM> upon which the piezo-diaphragm <NUM> is mounted form a two degree-of-freedom (DOF) system that provides two resonances.

The manner in which the piezo-diaphragm <NUM> and the bottom plate <NUM> form a two degree-of-freedom (DOF) system that provides two resonances will be described in more detail. For example, while still referring to <FIG>, in theory and considering the transverse vibration of the piezo-diaphragm <NUM> in the vertical direction (e.g., perpendicular to the surface of the piezo-diaphragm <NUM>), the piezo-diaphragm <NUM> can be modeled as a lumped mass supported on a spring. The allowed vibration motion of the lumped mass is the translational displacement along the axis of the spring (i.e., the direction perpendicular to the surface of the piezo-diaphragm <NUM>). Thus, this spring-mass system is termed as a one-degree-of-freedom (1DOF) system. The 1DOF spring-mass system has a mechanical resonance frequency determined by and is proportional to the square root of the ratio of its spring stiffness to its mass. Similarly, the flexible bottom plate <NUM> can be modeled as a second 1DOF spring-mass system that comes with its own mechanical resonance frequency. When the piezo-diaphragm <NUM> is positioned (i.e., stacked) on top of the flexible bottom plate <NUM> as depicted in <FIG>, the two 1DOF systems are combined to become a two DOF (2DOF) system that provides two mechanical resonance frequencies.

It is recognized that the two resonance frequencies of the combined 2DOF system may not have exactly the same values as those in the two individual 1DOF systems. However, the two resonance frequencies of the combined 2DOF system can be implemented to be close enough to the two resonance frequencies of the two individual 1DOF systems or implemented to have otherwise desired values. For example, the first resonance frequency in the 2DOF system may be designed to be close to the resonance frequency of the piezo-diaphragm <NUM> when considered as a 1DOF system (i.e., decoupled from the flexible bottom plate <NUM>). Likewise, the second resonance frequency in the 2DOF system may be designed to be higher than the first resonance frequency and close to the resonance frequency of the flexible bottom plate <NUM> when considered as a 1DOF system (i.e., decoupled from the piezo-diaphragm <NUM>). Due to the generation of the <NUM>nd resonance frequency by using the flexible bottom plate <NUM>, the sensor output becomes more sensitive at high frequencies compared to the case of only using the 1DOF system formed by the piezo-diaphragm <NUM> (e.g., the conventional design depicted in <FIG>). Therefore, by providing the second higher resonance, the sensor <NUM> can extend the signal bandwidth to higher frequency regions that may not have been achieved with prior implementations. This aspect will be discussed further in connection with <FIG>.

<FIG> depicts a first block diagram <NUM> of a two-wire electrical interface circuit of the sensor <NUM> that is based on a single piezo-diaphragm <NUM> in accordance to one embodiment. The first block diagram <NUM> generally represents a circuit design that may be used in two-wire VDA applications. The sensor <NUM> includes the piezo diaphragm <NUM>, a power supply reference circuit (or power supply) <NUM>, and an amplifier circuit <NUM>. The amplifier circuit <NUM> and the power supply <NUM> share a common terminal <NUM> (e.g., first wire).

In general, a reference voltage is provided from a power source that is external to the sensor to the power supply <NUM> via the terminal <NUM>. The power supply <NUM> provides the reference voltage to the piezo-diaphragm <NUM> (e.g., the sensing element) and the amplifier circuit <NUM>. The amplifier circuit <NUM> amplifies the signal detected by the piezo-diaphragm <NUM> and provides an amplified output on the output terminal <NUM> which is then provided external to the sensor <NUM>.

A ground connection <NUM> (e.g., second wire) is provided for the sensor <NUM>. The power supply <NUM> receives power from an external regulated voltage source (e.g., vehicle head unit or amplifier) through connection <NUM> and provides a reference voltage to the piezo-diaphragm <NUM> and the amplifier circuit <NUM>. The piezo-diaphragm <NUM> provides a signal to the amplifier <NUM>. The signal corresponds to a detected audio input that is external (or internal) to the vehicle <NUM>. The amplifier circuit <NUM> applies signal conditioning (e.g., amplification and filtering) to the signal and outputs to connection <NUM>. It is recognized that the power supply reference <NUM> and the amplifier circuit <NUM> may be positioned on an integrated circuit (or microprocessor) that is positioned on the PCBA <NUM> of the sensor <NUM>.

<FIG> depicts a second block diagram <NUM> of a three-wire electrical interface circuit of the sensor <NUM> that is based on a single piezo-diaphragm <NUM> in accordance to one embodiment. The sensor <NUM> includes the piezo-diaphragm <NUM>, the power supply <NUM>, and the amplifier circuit <NUM>. The operation of the circuit in the second block diagram <NUM> is similar to the operation of the circuit in the first block diagram <NUM>. The amplifier circuit <NUM> provides an electrical output on the first output <NUM> (e.g., first wire). The ground connection <NUM> (e.g., second wire) is provided to the sensor <NUM>. The power supply <NUM> receives power from an external regulated voltage source (e.g., vehicle head unit or amplifier) through connection <NUM> (or terminal, wire, etc. hence third wire) and provides a reference voltage to the piezo-diaphragm <NUM> and the amplifier circuit <NUM>. The difference between the first block diagram <NUM> and the second block diagram <NUM> is that the power input terminal and the signal output terminal in the first block diagram <NUM> are shared at the same connection <NUM>, while all three interface wires are separate in the second block diagram <NUM>.

<FIG> is a plot <NUM> illustrating simulated frequency responses for a conventional piezo-diaphragm sensor and for the single piezo-diaphragm sensor <NUM> in accordance to one embodiment. For example, waveform <NUM> depicts the simulated frequency response for the conventional piezo-diaphragm sensor. As shown, the waveform <NUM> illustrates that a single resonance is generated somewhere between <NUM> and <NUM> corresponding to the spring-mass properties of the piezo-diaphragm <NUM>. Below the resonance frequency, the amplitude response of the sensor is fundamentally flat over the frequency range. At higher frequencies above the resonance frequency of the waveform <NUM>, e.g., ><NUM>, the amplitude response is substantially lower than that in the flat portion. This makes the conventional piezo-diaphragm sensor insensitive to high frequency signals, thus limiting its bandwidth.

Waveform <NUM> depicts the simulated frequency response for the single piezo-diaphragm sensor <NUM> in accordance to one embodiment illustrated in <FIG>. As shown, waveform <NUM> provides a first resonance at roughly <NUM> and a second resonance at roughly <NUM>. Below the first resonance, the amplitude response of the sensor depicted by the waveform <NUM> is fundamentally flat over the frequency range. Above the first resonance, although the amplitude response reduces with increasing frequency, the amplitude response is boosted again by the second resonance around <NUM>. It can be seen that the second resonance makes the amplitude response noticeably higher than that of the waveform <NUM>. Therefore, the second resonance provided by the sensor <NUM> extends the signal bandwidth such that audible voice commands may be better detected either external to the vehicle <NUM> (or internal within the vehicle <NUM>). As the frequency contents above <NUM> is advantegous to speech intelligibility, the single piezo-diaphragm sensor <NUM> is more advantegous than the conventional piezo-diaphragm sensor in voice commend applications. Waveform <NUM> shows the frequency response for the case depicted by waveform <NUM> but with the damping mechanism <NUM> as illustrated in <FIG>. It is demonstrated that, when a damping mechanism <NUM> is added, the response amplitudes at resonance peaks are attenuated, therefore resulting in a smoother frequency response shape.

As shown, the flexible bottom plate <NUM> enables the sensor <NUM>, <NUM>', <NUM>'', and <NUM>''' to generate a second resonance in the frequency response of the sensor <NUM>, <NUM>', <NUM>'', and <NUM>''' at a frequency region of interest to the application (e.g.,, within an audible band) as illustrated in the waveform <NUM>. Due to inherent multiple resonances in the frequency response of the sensor <NUM>, <NUM>', <NUM>", or <NUM>"' for a certain sound and vibration input, the output of the sensor <NUM>, <NUM>', <NUM>", or <NUM>"' at the frequencies of interest to the application may be more sensitive than conventional designs that only have one resonance in the frequency response.

<FIG> depicts a cross-sectional view of another single piezo-diaphragm based sound and vibration sensor <NUM>'. The sensor <NUM>' includes the piezo-diaphragm <NUM> and the housing <NUM>. As noted above, the piezo-diaphragm <NUM> may be positioned on the bottom plate <NUM> (or flexible bottom plate <NUM>). Similarly, the sensor <NUM>' includes the PCBA <NUM> that is coupled to the piezo-diaphragm <NUM> via the at least one pair of electrical wires (not shown) to transmit a signal indicative of detected sound external (or internal) to the vehicle <NUM> to at least one integrated circuit (or microprocessor) (not shown) and/or other electronics positioned on the PCBA assembly <NUM>. The housing <NUM> defines a cavity <NUM> for receiving the PCBA <NUM> including the microprocessor and/or the electronics positions thereon. By inserting the PCBA <NUM> into the cavity <NUM> and coupling it thereto, this may reduce the overall packaging height of the sensor <NUM>' which may be advantageous for packaging the sensor <NUM> in various locations in the vehicle <NUM>. The microprocessor may process the signal and transmit another signal to a controller (e.g., the controller <NUM>) located somewhere in the vehicle <NUM>.

The sensor <NUM>' also includes the bottom plate <NUM> (or flexible bottom plate <NUM>) having the post <NUM> and the extending portion <NUM>. As shown, the extending portion <NUM> has a variable thickness as the extending portion <NUM> extends between the ends <NUM> and <NUM>. The piezo-diaphragm <NUM> is mounted on a top surface of the post <NUM> of the flexible bottom plate <NUM> through adhesive or other mechanical mechanism. While not shown, it is recognized that the sound and vibration sensor <NUM>' may optionally include the damping mechanism <NUM> that surrounds at least the post <NUM> of the flexible bottom plate <NUM>. The damping mechanism <NUM> may be positioned in between and in contact with the piezo-diaphragm <NUM> and the extending portion <NUM> of the flexible bottom plate <NUM>. The flexible bottom plate <NUM> is connected to the housing <NUM> circumferentially along the ends <NUM> and <NUM> and may optionally form an environmental seal to an inner volume defined by an interior of the housing <NUM>. The extending portion <NUM> of the bottom plate <NUM> has a thickness that varies between a center point (or center area) thereof and its circumference. It is recognized that the thickness of the extending portion <NUM> of the flexible bottom plate <NUM> may increase from the end <NUM> and the second end <NUM> to the center area of the post <NUM> or that the thickness of the extending portion <NUM> of the bottom plate <NUM> may decrease from the ends <NUM>, <NUM> to the center area of the post <NUM>. As noted above, it is desirable to achieve or provide a second resonance at a proper frequency location to expand the signal bandwidth of the sensor <NUM>'. The second resonance frequency may be determined by the mass and stiffness values of the spring-mass system formed by the flexible bottom plate <NUM>. Varying the thickness provides one approach to adjust the mass and stiffness values of the flexible bottom plate <NUM> to result in a proper secondary resonance frequency.

<FIG> depicts a cross-sectional view of another single piezo-diaphragm based sound and vibration sensor <NUM>". The sensor <NUM>" includes the piezo-diaphragm <NUM> and the housing <NUM>. The piezo-diaphragm <NUM> may be positioned on the bottom plate <NUM> (or the flexible bottom plate <NUM>). Similarly, the sensor <NUM>" includes the PCBA <NUM> that is coupled to the piezo-diaphragm <NUM> via the at least one pair of electrical wires (not shown) to transmit a signal indicative of detected sound external (or internal) to the vehicle <NUM> to at least one microprocessor (not shown) and/or other electronics positioned on the PCBA <NUM>. The housing <NUM> defines a support feature <NUM> for receiving the PCBA <NUM> including the microprocessor and/or the electronics positions thereon. The microprocessor may process the signal and transmit another signal to a controller (e.g., the controller <NUM>) in the vehicle <NUM>.

The flexible bottom plate <NUM> includes the post <NUM> and the extending portion <NUM>. The piezo-diaphragm <NUM> is mounted on the top of the post <NUM> of the flexible bottom plate <NUM> through adhesive or other mechanical mechanism. While not shown, it is recognized that the sound and vibration sensor <NUM>" may optionally include the damping mechanism <NUM> that surrounds at least a portion <NUM> of the post <NUM> and is positioned between and in contact with the piezo-diaphragm <NUM> and the extending portion <NUM> of the flexible bottom plate <NUM>. The flexible bottom plate <NUM> is connected to the housing <NUM> circumferentially along the ends <NUM>, <NUM>. The extending portion <NUM> of the flexible bottom plate <NUM> may include at least one perforation <NUM> (or cavity) formed through the entire surface of the extending portion <NUM>. The number of perforations <NUM> on the mounting post <NUM> may vary based on the desired criteria of a particular implementation. As noted above, it is desirable to achieve or provide a second resonance at a proper frequency location to expand the signal bandwidth of the sensor <NUM>". The second resonance frequency may be determined by the mass and stiffness values of the spring-mass system formed by the flexible bottom plate <NUM>. The one or more perforations <NUM> provides another approach to adjust the mass and stiffness values of the flexible bottom plate <NUM> to result in a proper secondary resonance frequency.

<FIG> depicts a cross-sectional view of a another single piezo-diaphragm based sound and vibration sensor <NUM>"'. The sensor <NUM>"' includes the piezo-diaphragm <NUM>, the PCBA <NUM> and the housing <NUM>. The PCBA <NUM> includes the electronics mounted on a substrate board <NUM> and is secured to the housing <NUM> through adhesive or other mechanical mechanism. The piezo-diaphragm <NUM> may be connected to and supported directly by the substrate board <NUM> of the PCBA <NUM> through a mounting post <NUM> (or spacer). Similarly, the sensor <NUM>"' includes the PCBA <NUM> that is coupled to the piezo-diaphragm <NUM> via the at least one pair of electrical wires (not shown) to transmit a signal indicative of detected sound external (or internal) to the vehicle <NUM> to at least one integrated circuit (or microprocessor (not shown)) and/or other electronics positioned on the PCBA <NUM>. The cavity <NUM> of the housing <NUM> receives the PCBA <NUM> including the (or the microprocessor) and/or the electronics positions thereon. The microprocessor may process the signal and transmit another signal to a controller (e.g., the controller <NUM>) positioned in the vehicle <NUM>. Similar to the functionality of the bottom plate <NUM> as set forth in connection with <FIG>, when the first spring-mass system formed by the piezo-diaphragm <NUM> is directly supported by the substrate board <NUM> of the PCBA <NUM>, the substrate board <NUM> may be flexible and form the second spring-mass system to provide the second resonance to the sensor <NUM>"'. The desired value of the second resonance frequency may be achieved by adjusting the size and thickness of the substrate board <NUM>. In the example of arrangement depicted in <FIG>, the bottom plate <NUM> is optional. If provided, the bottom plate <NUM> serves to environmentally seal the sensor housing <NUM>.

The embodiments described above are utilized as a single piezo-diaphragm based sound and vibration sensor and are capable of detecting structure-borne sound and vibration signals that is external (or internal) to the vehicle. Such embodiments may be more environmentally robust than conventional acoustical sensors (e.g., acoustical microphones). As noted above, the embodiments also provide a higher bandwidth for improved audio sensing and automatic speech recognition (ASR) accuracy than conventional piezo-diaphragm based sensors. Similarly, the embodiments provide higher sensitivity and higher signal to noise (SNR) ratio compared to conventional off-the-shelf accelerometers and generally provide for a more cost-effective implementation for automotive applications. As also noted above, the embodiments provide an extended bandwidth by adding a second resonance.

<FIG> depict examples not encompassed by the wording of the claims. <FIG> depicts a cross-sectional view of a multi-stage piezo-diaphragm based sound and vibration sensor <NUM>. The sensor <NUM> includes a number of the features disclosed in connection with the single piezo-diaphragm based sensors <NUM>, <NUM>', <NUM>", and <NUM>"'. The sensor <NUM> includes a plurality of piezo-diaphragms 110a - 110b that are stacked in series and positioned on the bottom plate <NUM> through the mounting post <NUM> of the bottom plate <NUM> The mounting post <NUM> may be integrated with the bottom plate <NUM>. The bottom plate <NUM> as referenced in connection with the multi-stage piezo-diaphragms may or may not be flexible. As shown in <FIG>, the piezo-diaphragm 110b is supported on the mounting post <NUM> by adhesive or other mechanical mechanism. The piezo-diaphragm 110a is axially spaced apart by the piezo-diaphragm 110b via a spacer <NUM>. In other words, the piezo-diaphragm 110a is parallel to the piezo-diaphragm 110b. The piezo-diaphragms 110a and 110b and the spacer <NUM> can be connected together using adhesive or other mechanical mechanism.

In another arrangement, a center opening can be formed in the piezo-diaphragms 110a and 110b. The post <NUM> may be made as a step axle with a thinner diameter at the top portion thereof and a thicker diameter at the bottom portion thereof. The center opening of the piezo-diaphragm 110b is placed and secured over the top thinner diameter of the post <NUM> via interference fit or adhesive. When assembled, the piezo-diaphragm 110b then sits on the step created by the thicker diameter of the post <NUM>. Then similarly, the spacer <NUM> may be formed of a step axle that has a thinner diameter at the top portion thereof and a thicker diameter at a bottom portion thereof. The center opening of the piezo-diaphragm 110a is placed and secured over the top thinner diameter of the spacer <NUM> via interference fit or adhesive.

Each of the piezo-diaphragms 110a - 110b may come with different sizes and mechanical properties, therefore different resonance frequencies with the second resonance frequency being higher than the first resonance frequency. Each of the piezo-diaphragms 110a - 110b may generate a signal output and when such signals are combined, the combined output signal provides a wider bandwidth and higher sensitivity than a single piezo diaphragm implementation. A first pair of wires 158a couples the piezo-diaphragm 110a to the PCBA <NUM>. A second pairs of wires 158b couples the piezo-diaphragm 110b to the PCBA <NUM>. The post <NUM> and the extending portion <NUM> are generally stiff and may not be compressible or flexible as noted in connection with the sensors <NUM>, <NUM>', <NUM>" noted above. In this manner, the post <NUM> and/or the extending portion <NUM> function to support or mount the piezo-diaphragms 110a, 110b inside the housing <NUM>.

<FIG> depicts a first block diagram <NUM> of a two-wire electrical interface circuit of the sensor <NUM> that is based on a multi-stage piezo-diaphragm implementation. The first block diagram <NUM> generally represents a circuit design that may be used in connection with a circuit design for a two-wire VDA application. The sensor <NUM> includes the plurality of piezo diaphragms 110a - 110b, the power supply reference circuit (or the power supply) <NUM>, and the amplifier circuit <NUM>. The output or connection <NUM> (e.g., first wire) is shared between the amplifier circuit <NUM> and the power supply <NUM>. The ground connection <NUM> (e.g., second wire) is provided for the sensor <NUM>. The power supply <NUM> receives power from an external regulated voltage source (e.g., vehicle head unit or amplifier) on the connection <NUM> and provides a reference voltage to the plurality of piezo diaphragms 110a and 110b and to the amplifier circuit <NUM>. Each of the piezo diaphragms 110a, 110b provides a signal to the amplifier circuit <NUM>. Each of the signals corresponds to a detected audio input that is external (or internal) to the vehicle <NUM>. The amplifier circuit <NUM> applies signal conditioning (e.g., amplification and filtering) to both of the output signals from the piezo-diaphragms 110a, 110b and electronically adds (or sums) them together and outputs the combined signal to connection <NUM>. Given that the piezo-diaphragms 110a and 110b are provided with distinct electromechanical properties, each piezo-diaphragm 110a and 110b provides a resonance in its frequency response curve. Below this resonance, the response amplitude (e.g., sensitivity) of each piezo-diaphragm 110a, 110b is fundamentally constant (e.g., flat) versus the frequency. This flat frequency response region defines the signal bandwidth of the output of the piezo-diaphragm 110a and 110b. The constant amplitude value may be generally inverse proportional to the resonance frequency value. For illustration and referring to <FIG>, it is assumed that the piezo-diaphragm 110a provides a first resonance that is lower than the second resonance provided by the piezo-diaphragm 110b. This entails that the piezo-diaphragm 110b has a wider bandwidth and lower sensitivity compared to those of the piezo-diaphragm 110a. When the outputs from the plurality of piezo diaphragms 110a -110b are combined together, the effective sensitivity and bandwidth of the sensor <NUM> are improved compared to either piezo-diaphragm being used alone. This will be explained further in <FIG>. In general, the power supply <NUM> generates a reference voltage that is half of the input voltage it receives from a battery of a car or other controller in the vehicle <NUM>. The power supply <NUM> provides this input voltage (e.g., half amount of voltage) to the piezo-diaphragms 110a, 110b and the amplifier circuit <NUM>. It is recognized that the power supply <NUM> and the amplifier circuit <NUM> may be positioned on an integrated circuit (or microprocessor) that is positioned on the PCBA <NUM> of the sensor <NUM>.

<FIG> depicts a second block diagram <NUM> of a three-wire electrical interface circuit for the sensor <NUM> that is based on a multi-stage piezo-diaphragm implementation. The sensor <NUM> includes the piezo diaphragms 110a and 110b, the power supply <NUM>, and the amplifier circuit <NUM>. The operation of the circuit in the second block diagram <NUM> is similar to the operation of the circuit in the first block diagram <NUM>. The amplifier circuit <NUM> provides an electrical output on the first output <NUM> (e.g., first wire). The ground connection <NUM> (e.g., second wire) is provided to the sensor <NUM>. The power supply <NUM> receives power from an external regulated voltage source (e.g., vehicle head unit or amplifier) through connection <NUM> (e.g., terminal, wire, etc. hence third wire) and provides the voltage reference to the plurality of piezo diaphragms 110a -110b and the amplifier circuit <NUM>. The difference between the first block diagram <NUM> and the second block diagram <NUM> is that the power input terminal and the signal output terminal are shared at the connection <NUM> in the first block diagram <NUM>, while all three interface wires are separate in the second block diagram <NUM>.

<FIG> is a plot <NUM> illustrating simulated frequency responses for a conventional single piezo-diaphragm sensor and for the multi-stage piezo-diaphragm sensor <NUM> that includes the plurality of piezo diaphragms 110a -110b. For example, waveforms <NUM> and <NUM> depict the simulated frequency responses for the conventional single piezo-diaphragm. As shown, the waveforms <NUM> and <NUM> illustrate that a single resonance is generated somewhere between <NUM> and <NUM> (see waveform <NUM>) and around <NUM> (see waveform <NUM>), respectively. The waveform <NUM> has a resonance frequency higher than the waveform <NUM> and presents a much lower sensitivity in the flat response region than that of the waveform <NUM>. Waveform <NUM> depicts the simulated frequency response for the multi-stage piezo-diaphragm sensor <NUM>, which is an electrical combination of the waveforms <NUM> and <NUM>. As shown, waveform <NUM> provides a first resonance at roughly <NUM> to <NUM> and a second resonance at roughly <NUM>. The second resonance provided by the sensor <NUM> extends the signal bandwidth and the combination of all signals from the plurality of piezo diaphragms 110a -110b increases the sensitivity. Therefore, the sensor <NUM> may present significantly improved performance in detecting the structure-borne sound, such as the audible voice commands external (or internal) to the vehicle.

<FIG> depicts a cross-sectional view of another multi-stage piezo-diaphragm based sound and vibration sensor <NUM>'. The sensor <NUM>' includes a number of the features disclosed in connection with the multi-stage piezo-diaphragm based sensor <NUM> and the single piezo-diaphragm based sensors <NUM>, <NUM>', <NUM>'', and <NUM>"'. The sensor <NUM>' includes a plurality of piezo-diaphragms 110a - 110c that are stacked and positioned on the post <NUM> of the bottom plate <NUM>. Each of the piezo-diaphragms 110a - 110c generates an output signal with a distinct resonance frequency and when such signals are electronically combined, the combined output signal provides the wide bandwidth and high sensitivity.

The housing <NUM> defines the cavity <NUM> for receiving the PCBA <NUM> including the microprocessor and/or the electronics positions thereon. The microprocessor may process the signal and transmit another signal to a controller (e.g., the controller <NUM>) that is external (or internal) to the vehicle <NUM>. As shown, the overall sizes (e.g., length or diameter) of each of the piezo diaphragms 110a - 110c are different from one another. Since the resonance frequency and sensitivity is closely related with various parameters such as the sizes of each piezo-diaphragm, the differences in sizes of the piezo diaphragms 110a - 110c provide respective resonance frequencies with desired values. Therefore, when the outputs from the plurality of the piezo-diaphragms 110a - 110c are electronically combined, the sensor <NUM>' will have improved bandwidth and sensitivity compared to each of the piezo-diaphragms 110a - 110c being used alone.

The piezo-diaphragm 110a is axially spaced apart by the piezo-diaphragm 110b via a spacer <NUM>. The piezo-diaphragm 110a is parallel to the piezo-diaphragm 110b. The piezo-diaphragms 110a and 110b and the spacer <NUM> can be connected together using adhesive or other mechanical mechanism. The piezo-diaphragm 110b is axially spaced apart by the piezo-diaphragm 110c via a spacer <NUM>. The piezo-diaphragm 110b is parallel to the piezo-diaphragm 110c. The piezo-diaphragms 110b and 110c and the spacer <NUM> can be connected together using adhesive or other mechanical mechanism.

In another arrangement, a center opening can be formed in the piezo-diaphragms 110a, 110b, and 110c. The post <NUM> may be made as a step axle with a thinner diameter at the top portion thereof and a thicker diameter at the bottom portion thereof. The center opening of piezo diaphragm 110c fits (or forms an interference fit) with the top thinner diameter of the post <NUM>. similarly, the spacer <NUM> may be formed as a step axle with a thinner diameter at a top portion thereof. When assembled, the piezo-diaphragm 110b then sits on the thinner diameter of the spacer <NUM> via interference fit and/or an adhesive. Likewise, the spacer <NUM> may be formed as a step axle with a thinner diameter at a top portion thereof. When assembled, the piezo-diaphragm 110a then sits on the thinner diameter of the spacer <NUM> via interference fit and/or an adhesive.

Each of the piezo-diaphragms 110a - 110c may come with different sizes and mechanical properties, therefore different resonance frequencies. Each of the piezo-diaphragms 110a - 110c may generate a signal output and when such signals are combined, the combined output signal provides a wider bandwidth and higher sensitivity than a single piezo diaphragm implementation. As noted above, the post <NUM> and the extending portion <NUM> are generally stiff and may not be compressible or flexible as noted in connection with the sensors <NUM>, <NUM>', <NUM>" noted above. In this manner, the post <NUM> and/or the extending portion <NUM> function to support or mount the piezo-diaphragms 110a, 110b, 110c inside the housing <NUM>.

<FIG> depicts a cross-sectional view of another multi-stage piezo-diaphragm based sound and vibration sensor <NUM>". The sensor <NUM>" includes a number of the features disclosed in connection with the multi-stage piezo-diaphragm based sensors <NUM>, <NUM>' and the single piezo-diaphragm based sensors <NUM>, <NUM>', <NUM>", and <NUM>"'. The sensor <NUM>" includes a plurality of piezo-diaphragms 110a - 110b that are positioned concentrically on the bottom plate <NUM>. A cavity <NUM> is formed by the bottom plate <NUM>, the post <NUM>, and the piezo-diaphragms 110a - 110b. Each of the piezo-diaphragms 110a - 110b generates an output signal with a distinct resonance frequency and when such signals are electronically combined, the combined output signal provides the wide bandwidth and high sensitivity.

The housing <NUM> defines the cavity <NUM> for receiving the PCBA <NUM> including the microprocessor and/or the electronics positions thereon. The microprocessor may process the signal and transmit another signal to a controller (e.g., the controller <NUM>). As shown, the piezo-diaphragms 110a and 110b are positioned concentrically on the same plane as one another and supported on the bottom plate <NUM>. To enable the concentric mounting arrangement, the piezo-diaphragm 110b has a disk shape and is positioned on the post <NUM> of the bottom plate <NUM> while the piezo-diaphragm 110a has a ring shape and is secured along its edge to a mounting ring <NUM> on the bottom plate <NUM>. The circular ring shaped piezo-diaphragm 110a and the circular disk shaped piezo-diaphragm 110b are positioned concentrically inside the housing <NUM> of the sensor <NUM>". An inner diameter <NUM> of the ring shaped piezo-diaphragm 110a is slightly larger than the outer diameter <NUM> of the disk shaped piezo-diaphragm 110b, which separate them by a space (or gap) <NUM> and allow them to vibrate independently. Due primarily to the dramatic differences in their shapes and the resulting mechanical parameters, the piezo-diaphragms 110a and 110b provide distinct resonance frequencies of the desired values.

<FIG> depicts a top view of the multi-stage piezo-diaphragm based sound and vibration sensor <NUM>" of <FIG>. As shown, the piezo-diaphragm 110a includes the ring shaped piezo ceramic disk 112a and the ring shaped metal substrate plate 114a. The piezo-diaphragm 110b includes the circular disk shaped piezo ceramic disk 112b and the circular disk-shaped metal substrate plate 114b). The piezo-diaphragms 110a, 110b are packaged concentrically within the housing <NUM> which is also concentric (or circular).

<FIG> depicts a cross-sectional view of another multi-stage piezo-diaphragm based sound and vibration sensor <NUM>"'. The sensor <NUM>''' includes a number of the features disclosed in connection with the multi-stage piezo-diaphragm based sensors <NUM>, <NUM>', <NUM>" and the single piezo-diaphragm based sensors <NUM>, <NUM>', <NUM>'', and <NUM>'". The sensor <NUM>" includes a plurality of piezo-diaphragms 110a - 110b. Each of the piezo-diaphragms 110a - 110b generates an output signal with a distinct resonance frequency and when such signals are electronically combined, the combined output signal provides the wide bandwidth and high sensitivity.

The housing <NUM> defines the cavity <NUM> for receiving the PCBA <NUM> including the microprocessor and/or the electronics positions thereon. The microprocessor may process the signal and transmit another signal to a controller (e.g., the controller <NUM>). As shown, the overall sizes (e.g., length or diameter) of each of the piezo diaphragms 110a - 110b are different from one another. Since the resonance frequency and sensitivity are closely related with the mechanical parameters such as the sizes of each piezo-diaphragm 110a - 110b. The differences in sizes of the piezo diaphragms 110a - 110b arrange their respective or corresponding resonance frequencies with desired values. Therefore, when the outputs from the plurality of the piezo-diaphragms 110a - 110b are electronically combined, the sensor <NUM>"' will have improved bandwidth and sensitivity compared to each of the piezo-diaphragms 110a - 110b being used alone.

The housing <NUM> includes a plurality of flanges 410a - 410b that extend inwardly toward the PCBA <NUM>. Each of the flanges 410a - 410b is axially spaced apart from one another (or is parallel to one another). The piezo-diaphragm 110a is positioned on the flange 410a. The piezo-diaphragm 110b is positioned on the flange 410b. <FIG> illustrates that the bottom plate <NUM> is not present. However, it is recognized that the bottom plate <NUM> may be implemented and may be connected to the housing <NUM> circumferentially at the ends <NUM> and <NUM> if necessary to seal the housing. In the event the bottom plate <NUM> is not required (or provided), then the housing <NUM> forms a bottom opening thereof.

Claim 1:
A sound and vibration sensor (<NUM>) comprising:
a housing (<NUM>);
a piezo-diaphragm (<NUM>) positioned in the housing (<NUM>) to detect an input signal including audio or vibrations; and
a flexible support plate (<NUM>) to receive the piezo-diaphragm (<NUM>) to enable the sensor to exhibit a frequency response with a plurality of resonant frequencies in response to detecting the audio or the vibrations on the input signal,
wherein the flexible support plate (<NUM>) includes a mounting post (<NUM>) extending therefrom and being configured to receive the piezo-diaphragm (<NUM>) to support the piezo-diaphragm (<NUM>) in the housing (<NUM>),
wherein the mounting post (<NUM>) is flexible or rigid, and
characterized in that the flexible support plate (<NUM>) includes an extending portion (<NUM>) that contacts a first end of the housing (<NUM>) and a second end of the housing (<NUM>) to environmentally seal the housing (<NUM>), wherein the extending portion (<NUM>) extends outwardly from the mounting post (<NUM>),
such that the piezo-diaphragm (<NUM>) and the flexible support plate (<NUM>) form a two- degree of freedom, DOF, system that provides the frequency response with a plurality of resonant frequencies.