JP2022160366A - Air-pulse generating device and sound producing method thereof - Google Patents

Abstract

To provide an air-pulse generating device.SOLUTION: An air-pulse generating device includes a membrane structure, a valve structure, and a cover structure. A chamber is formed between the membrane structure, the valve structure and the cover structure. An air wave vibrating at an operating frequency is formed within the chamber. The valve structure is configured to be actuated to perform an open-and-close movement to form at least one opening. The at least one opening connects air inside the chamber with air outside the chamber. The open-and-close movement is synchronous with the operating frequency.SELECTED DRAWING: Figure 1

Description

This application relates to an air-pulse generating device and a sound producing method thereof, and more particularly to increasing the overall air pulse rate and increasing the sound pressure level. An air pulse generator and method for producing sound that can be improved and/or conserve power.

Speaker drivers and rear enclosures are two major design challenges in the speaker industry. It is difficult for conventional speakers to cover the entire audio frequency band, eg, 20Hz-20KHz. Both the radiating/moving surface and rear enclosure volume/size for conventional loudspeakers must be large enough to produce high fidelity sound at a sufficiently high sound pressure level (SPL). is required.

Therefore, how to design a compact sound-producing device while overcoming the design challenges faced by conventional loudspeakers is an important goal in the field.

U.S. Patent Application No. 17/553,806 U.S. Patent Application No. 17/553,808

SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present application to provide an air pulse generator and method of generating sound therefor, in order to overcome the shortcomings and/or limitations of the prior art.

An embodiment of the present invention provides an air pulse generator, a membrane structure and a valve structure; a cover structure, wherein a chamber is formed between the membrane structure, the valve structure and the cover structure. an air wave oscillating at the operating frequency is formed within the chamber; the valve structure is configured to be actuated to perform an opening and closing action to form the at least one opening, the at least one opening comprising: , connects the air inside the chamber with the air outside the chamber; the opening and closing action is synchronized with the operating frequency.

Another embodiment of the present invention provides a method of generating sound applied to an air pulse generator, the method comprising forming an air wave in a chamber, the air wave vibrating at an operating frequency, the chamber is formed in the air pulse generator; and forming at least one opening in the air pulse generator at an opening frequency, the at least one opening directing air in the chamber to the chamber connecting with outside air, and the open frequency is synchronous with the operating frequency.

These and other objects of the present invention will become apparent to those skilled in the art after reading the following detailed description of the preferred embodiments illustrated in the various figures and drawings.

1 is a schematic diagram of an air pulse generator according to an embodiment of the present application; FIG.

1 is a schematic diagram of multiple waveforms according to an embodiment of the present application; FIG.

1 is a schematic diagram of multiple signals according to an embodiment of the present application; FIG.

4 shows a membrane drive signal according to one embodiment of the present application;

Figure 2 is a schematic diagram showing a top view of the air pulse generator shown in Figure 1;

1 is a schematic diagram of a cross-sectional view of an air pulse generator according to an embodiment of the present application; FIG.

1 is a schematic diagram of a cross-sectional view of an air pulse generator according to an embodiment of the present application; FIG.

1 is a schematic diagram of a cross-sectional view of an air pulse generator according to an embodiment of the present application; FIG.

1 is a schematic diagram of a cross-sectional view of an air pulse generator according to an embodiment of the present application; FIG.

9 is a schematic diagram of the air pulse generator shown in FIG. 8 positioned within an arrangement according to an embodiment of the present application; FIG.

9 is a schematic diagram of the air pulse generator shown in FIG. 8 positioned within an arrangement according to an embodiment of the present application; FIG.

1 is a schematic diagram of a mobile device according to one embodiment of the present application; FIG.

1 is a schematic diagram of a cross-sectional view of an air pulse generator according to an embodiment of the present application; FIG.

1 is a schematic diagram of a cross-sectional view of an air pulse generator according to an embodiment of the present application; FIG.

1 is a schematic diagram of a cross-sectional view of an air pulse generator according to an embodiment of the present application; FIG.

1 is a schematic diagram of valve travel according to an embodiment of the present application; FIG.

U.S. Pat. No. 10,425,732 discloses a sound system comprising multiple air pulsing elements capable of generating multiple PAM (Pulse Amplitude Modulation) air pulses at an ultrasonic pulse rate above the maximum human audible frequency. Provide a generator or pneumatic pulse speaker (APPS). US Pat. No. 10,425,732 also discloses that APPS can be placed within an electronic device to function as a fan that can help dissipate heat from the electronic device.

U.S. Pat. No. 10,771,893 discloses a SEAM (SEAM) for sound generators or APPS that can generate single-ended PAM air pulses at ultrasonic pulse rates to further improve sound pressure level performance and low acoustic frequency response. single-ended amplitude modulation) drive signal. The SEAM drive signal includes multiple electrical pulses, the multiple electrical pulses having the same polarity relative to (or relative to) the constant voltage. For SEAM drive signals, each electrical pulse cycle includes a PAM (Pulse, Amplitude Modulation) phase and an RST (Reset) phase, described below. The SEAM drive signal can be the PAM signal in the PAM phase and return to the reset voltage in the RST phase.

U.S. patent application Ser. No. 16/802,569 discloses generating air pulses via chamber compression/expansion induced by membrane movement to achieve significant air pressure in a small size/dimension of a sound generating device. to propagate through a pressure ejection orifice (PEO) formed on a membrane or plate of the sound generating device or APPS.

U.S. Pat. No. 11,043,197 utilizes a membrane to compress/expand air in a chamber, temporarily opening an air shunt so that the air pressure equilibrium process between two faces of the membrane is accelerated. Air pulsing elements and APPS are provided that utilize slits formed on membranes to form virtual valves that can be provided.

In one embodiment, the air pulse generator of the present application may be applied to APPS applications configured to generate PAM air pulses at an ultrasonic pulse rate according to APPS sound generation principles. In another embodiment, the air pulse generator of the present application functions as a fan and can be applied to air movement or fan applications similar to US Pat. No. 10,425,732.

FIG. 1 is a schematic illustration of a cross-sectional view of an air pulse generator 890 according to one embodiment of the present application. An air pulse generator 890 may be applied within the APPS. Air pulse generator 890 includes membrane structure 12 , valve structure 11 and cover structure 804 . A chamber 105 is formed between membrane structure 12 , valve structure 11 and cover structure 804 . Air pulse generator 890 produces its (pneumatic) outputs at ports 707L and 707R. FIG. 1 shows the membrane structure 12 in a state in which the membrane structure 12 is (substantially) flat and parallel to the XY plane (solid outline), and in an operational state in which the membrane structure 12 is curved. (dashed outline).

Membrane structure 12 and valve structure 11 may have a thin film structure, which may be, for example, a MEMS (micro-electromechanical system) using SOI (silicon/Si on insulator) or POI (polySi/polysilicon on insulator) wafers. electromechanical system) manufacturing process, but is not limited to these. In the embodiment shown in FIG. 1, the membrane structure 12 includes a first membrane portion 102a and a second membrane portion 102b. Valve structure 11 includes a first valve portion 101 and a second valve portion 103 . Cover structure 804 includes a top plate 804T and sidewalls 804L and 804R. Chamber 105 is bounded by/between membrane portions 102a and 102b, valve portions 101 and 103, top plate 804T, and sidewalls 804L and 804R. The valve portions 101/103 are fixed at one end to the support structure 110/115 and free to move at the other end, with the free moving end located proximate/adjacent the side walls 804L/804R.

Membrane structure 12 is configured to be actuated to generate air waves AW. Furthermore, by carefully choosing the drive signal(s) supplied to the membrane structure 12, the air waves AW will oscillate at the operating frequency f _CY and in a direction parallel to the membrane structure 12 (e.g., X direction).

In one aspect, an air wave is defined as the mass of air molecules moving forward and backward (e.g., left and right in the X direction in terms of movement of the X-axis component) at regular time intervals due to air pressure fluctuations or air molecular density fluctuations. It can be associated with moving periodically. An air wave oscillating at a particular frequency is associated with an operating frequency f _CY where the particular frequency is the reciprocal of the particular period and vice versa.

The valve structure 11 is configured to operate to perform opening and closing operations at an opening frequency to periodically form at least one opening, the at least one opening allowing air in the chamber 105 to ambient/ Connect with the air outside the chamber 105 . Specifically, the valve portion 101 may be actuated to form-and-unform an opening 112 up and down (in the Z direction), which is referred to as opening and closing the valve 101 . Similarly, the valve portion 103 can be actuated to move up and down (in the Z direction) to cause and not form the opening 114, which is referred to as opening and closing the valve 103. FIG. The opening and closing motion (or opening frequency) of valve structure 11, including valves (parts) 101 and 103, is synchronous with air wave AW, which in turn is synchronous with operating frequency f _CY . The synchronous opening and closing motion of the valve structure/portion with the actuation frequency f _CY means that the opening and closing motion of the valve portion/structure is (preferably) performed at a frequency of the actuation frequency f _CY or (M/N)*f _CY . where M and N are both integers. The open/close, up/down, forming and non-forming movements are described in detail later. In the following description, valves 101/103 may be referred to as valve portions 101/103 for simplicity.

The function of the valve opening is similar to that of a variable resistance where the resistance to airflow Z _VALVE is controlled by the valve opening. The magnitude of _{Z_VALVE} is high (Hi-Z) when the valve is closed, ie, when Z101<Z _O/C or Z103<Z _O/C . When the valve is open, i.e., Z101>Z _O/C or Z103>Z _O/C , the magnitude of Z _VALVE is inversely proportional to the degree of opening, or Z101-Z _O/C and Z101-Z _O/C . do. The wider the valve opens, the lower the value of Z _VALVE and the higher the air flow rate for a given internal chamber pressure.

chamber resonance

Considering that sidewalls 804L and 804R may act as reflective walls, it should be noted that air waves AW generated by membrane structure 12 may include incident and reflected waves. In one embodiment, the width of chamber 105, indicated as W ₁₀₅ , or the distance between sidewalls 804L and 804R, is designed such that incident and reflected waves can be collected and form standing waves within chamber 105. can be

In one embodiment, the distance or width W ₁₀₅ between sidewalls 804L and 804R may be equal to an integer multiple of half wavelengths (λ/2) corresponding to the operating frequency f _CY of airwaves AW, where λ=C/ f _CY , C is the speed of sound.

In one embodiment, the distance or width W ₁₀₅ between sidewalls 804L and 804R is such that the first (1 ^st ) mode (or n=1 mode) resonance, also called fundamental mode resonance or first harmonic resonance, is within chamber 105 . can be designed to be formed in In this case, only one air-motion antinode (with peak amplitude) is present in chamber 105 (which may be in the middle of chamber 105); ) are located on sidewalls 804L and 804R; only one pneumatic node exists within chamber 105 (which may be located in the middle of chamber 105); only two pneumatic antinodes are located on sidewalls 804L and 804R. Located in

Here, in terms of chamber resonances or standing waves, the antinode of the air motion represents the position at which the amplitude of the velocity/displacement of the air molecules reaches a maximum in the air motion across the X-axis in the chamber; represents the position at which the air molecule velocity/displacement amplitude reaches a minimum in air motion across the X-axis within the chamber (usually zero motion); the air pressure node represents the position where the amplitude of the air pressure variation reaches a minimum in air pressure across the X-axis in the chamber.

In FIG. 1, curve U102 schematically represents the displacement of air particles distributed in the X direction at different times, and curve W102 schematically represents the pressure distribution in the chamber at different times. For example, the dashed lines of curves U102 and W102 correspond to time _t0 , and the solid lines of curves _U102 and W102 correspond to time t1. P0 in FIG. 1 may refer to ambient pressure, which may be 1 atmosphere. In one embodiment, to achieve first-order (or n=1 mode) resonance, the distance or width W ₁₀₅ between sidewalls _804L and 804R is half a wavelength (λ _CY /2).

Further details of the 101/103 valve travel are shown in FIG. At time t ₀ (or when t=t ₀ ), valve 101 is actuated to bend upwards to open or form opening 112 and valve 103 (substantially) seals opening 114 . , which means that the opening 114 is closed or not formed, as shown in the upper part of FIG. _On the _other hand, at time t1 (or when t=t1), valve 101 may be actuated to (substantially) seal opening 112, which means opening 112 is closed or not formed. That is to say, the valve 103 is actuated to bend upwards such that an opening 114 is opened or formed, as shown at the bottom of FIG. In one embodiment, at some time t2 ₍ or _{t =} t2, where t2 ≠ _t0 and t2 ≠ t1), valves 101 and _{103 are} opened with opening 112 and 114 are in a nearly unopened or nearly unclosed state, corresponding to Z101=ZO _/C and _Z103 =ZO/C, respectively, as shown in FIG.

FIG. 2 is a schematic diagram of multiple waveforms according to one embodiment of the present application. Waveform Z101 schematically represents the displacement of the free moving end of valve portion 101 in the Z direction; while waveform Z103 schematically represents the displacement of the free moving end of valve portion 103 in the Z direction. ZO _/C represents a level of displacement and the suffix O/C represents the line separating the open and closed states. If the displacement of the free moving end of valve Z101 is greater than (above) the displacement level ZO _/C , opening 112 is formed or valve 101 is opened. If the displacement of the free moving end of valve Z103 is greater than the displacement level ZO _/C , opening 114 is formed or valve 103 is opened. If the displacement of the free moving end of valve Z101 is less than (below) the displacement level ZO _/C , no opening 112 is formed or the valve 101 is closed. If the displacement of the free moving end of valve Z103 is less than the displacement level ZO _/C , then opening 114 is not formed or valve 103 is closed.

Waveform P112 schematically represents the air pressure at opening 112 (within chamber 105). Waveform P114 schematically represents the air pressure at opening 114 (within chamber 105). Waveform Z102a represents the displacement of membrane portion 102a, which may share a similar waveform as P112. Waveform Z102b represents the displacement of membrane portion 102b, which may share a similar waveform with P114. Waveform P707L schematically represents the air pressure (or air pressure-like quantity) at port 707L (outside chamber 105). Waveform P707R schematically represents the air pressure (or air pressure-like quantity) at port 707R (outside chamber 105). Waveform P890 represents the sum/superposition of P707L and P707R and corresponds to the aggregated on-axis output acoustic pressure of device 890. FIG. Waveforms Z102a/Z102b, which are lengths in units such as μM, generally have different amplitudes than waveforms P112/P114, which are pressures in units such as Pa. FIG. However, since the purpose of FIG. 2 is primarily to show timing relationships between different parts of operation, these waveforms are merged into FIG. 2 for simplicity.

FIG. 3 is a schematic diagram of multiple signals according to one embodiment of the present application. S _IN represents the input audio signal. S101/S103 represent valve drive signals configured to drive valve portions 101/103. S102a/S102b represent membrane drive signals configured to drive membrane portions 102a/102b.

AM modulated waveform

As can be seen from the plots/waveforms P112 and P114 of FIG. 2, P112 and P114 are/include amplitude modulated waveforms, and the amplitude modulated waveforms P112/P114 are generally expressed as the product of the carrier component and the modulating component. can be The carrier component, usually expressed as cos(2πf _CY t), oscillates at an operating frequency f _CY where f _CY =1/T _CY , where f _CY denotes the operating cycle. The modulation component, denoted as m(t), is reflected by the envelope of the amplitude-modulated waveform (shown in dashed lines in FIGS. 2 and 3) corresponding to the _input audio signal SIN. In one embodiment, the modulation component m(t) may correspond to or be proportional to the _input audio signal SIN.

Amplitude modulated waveforms P112/P114 may be achieved by driving membrane structure 12 with a pulse amplitude modulated drive signal. For example, the membrane drive signals S102a/S102b shown in FIG. 3, which drive the membrane portions 102a/102b, are pulse amplitude modulated signals generated according to the input audio signal S _IN .

Membrane drive signal

In other words, membrane drive signal S102a comprises a first pulse amplitude modulated signal comprising a plurality of first pulses for a particular bias voltage _VB . The first pulses are temporally distributed/located by the operating frequency f _CY . Similarly, membrane drive signal _S102b includes a second PAM signal including a plurality of second pulses for bias voltage VB. The second pulses are distributed/positioned in time by the operating frequency f _CY .

In addition, the first pulse includes first transition edges; while the second pulse includes second transition edges. The first transition edge of the first pulse in PAM signal S102a coincides with the second transition edge of the second pulse in PAM signal S102b. Further, at a coincidence time with the first transition edge and the second transition edge, the first transition edge corresponds to the first transition polarity and the second transition edge corresponds to the second transition polarity. corresponds to The first transition polarity is opposite to the second transition polarity at some coincident time. Details of the coincidence of the first and second transition edges and the opposite of the first and second transition polarities may be found in FIG. 3 of this application or see US Pat. References may be made, which are not described here for the sake of brevity.

It should be noted that the film drive signals S102a/S102b that drive the film portions 102a/102b are bipolar (or double _- ended) with respect to the bias voltage VB, but are not limited thereto. For example, FIG. 4 shows the second type of membrane drive signals S102a' and S102b'. Membrane portions 102a and 102b may be driven by membrane drive signals S102a' and S102b', respectively. Note that membrane drive signals S102a' and _S102b ' are SEAM drive signals that are unipolar with respect to bias voltage VB. Similar to monopolar membrane drive signals S102a and S102b, the first pulse in drive signal S102a' and the second pulse in drive signal S102b' are interleaved with each other, as shown in FIG. It has simultaneous transition edges and opposite transition polarities. Details of unipolar SEAM drive signals can be found in US Pat. No. 10,771,893, which is not described here for the sake of brevity.

FIG. 4 also shows a third type of membrane drive signal S102a″ (lower solid line) and S102b″ (lower dashed line, S102a″). and the membrane portion 102b may be driven by the membrane drive signal S102b″. The membrane drive signal S102b″ is either S102b″=V _B −S102a″ (equation 1) or S102b″=−S102a″ ( 2). In other words, the sum of the membrane drive signals S102a'' and S102b'' can be a constant. The constant is the voltage level V _B (if Eq. ) or 0 V (if Equation 2 applies).As with membrane drive signals S102a and S102b, the first pulse in drive signal S102a″ and the second pulse in drive signal S102b″ are simultaneously (coincidence) transition edges and opposite transition polarities, which can be observed from FIG.

pressure gradient

In one aspect, during the first interval (which may be the first half of TCY of the operating cycle), the membrane drive signal pair (S102a, _S102b )/(S102a', S102b')/(S102a'', S102b) ) to membrane portions 102a and 102b, membrane portion 102a can be actuated to move in the positive Z direction and membrane portion 102b can be actuated to move in the negative Z direction. Thus, during the first interval, membrane portion 102a may be actuated to compress a first portion/volume 105a (the top of membrane portion 102a) within chamber 105, and membrane portion 102b may be compressed within chamber 105. can be actuated to inflate the second portion/volume 105b (top of the membrane portion 102b) of the, resulting in a first air pressure gradient from the first portion/volume 105a towards the second portion/volume 105b. (indicated by block arrow 116 in FIG. 1) is formed.

Conversely, during a second interval (which may be the second half of the operating cycle _TCY ), membrane portion 102b may be actuated to move in the positive Z direction and membrane portion 102a may move in the negative Z direction. can be actuated to move to Thus, during the second interval, membrane portion 102b can be actuated to compress second portion/volume 105b and membrane portion 102a can be actuated to expand first portion/volume 105a. , resulting in a second air pressure gradient (opposite of 116, not shown in FIG. 1) from the second portion/volume 105b towards the first portion/volume 105a.

The pressure gradient direction of the air pressure gradient (eg, 116 shown in FIG. 1) generated by membrane structure 12, including membrane portions 102a and 102b, is parallel to the X direction shown in FIG. The propagation direction of the air wave AW propagating inside the chamber 105 is also parallel to the X direction. That is, the pressure gradient direction is parallel to the air wave propagation direction. In addition, the pressure gradient direction parallel to the X direction is perpendicular to the membrane displacement direction of the membrane structure 12, mainly the Z direction, which refers to the direction in which the membrane is actuated to move. . Therefore, the pressure gradient direction is parallel to the XY plane, the plane of the membrane structure, and orthogonal to the direction of membrane displacement (Z). By considering the membrane structure to be actuated or deformed, the pressure gradient direction (generated by the membrane structure) is substantially parallel to the membrane structure and/or substantially relative to the direction of membrane displacement/movement. can be considered to be perpendicular/orthogonal to

Spatial location of valve opening

When a standing wave is formed in the chamber 105, it is suggested that the aperture(s) be located at or near the pneumatic antinode(s) of the standing wave in order to increase the audio output efficiency. be. For the air pulse generator 890, the aperture may be spatially formed at the location where the air/standing wave peak is achieved, where the air/standing wave peak is (for APPS applications) It can be in terms of air pressure.

For APPS, assume that the air pressure in the chamber can be expressed as a single-variable function p(x) or a two-variable function p(x,t), where x denotes the variable on the X-axis and t is Show variables on the time axis. The peak is where the first (partial) derivative is zero, i.e. dp(x)/dx=0 or ∂p(x,t)/∂x=0 (to find the optimal spatial position of the valve opening ). In other words, the peaks (for some fixed time t ₀ ) can be interpreted as maxima or minima of p(x)/p(x,t ₀ ) across the X-axis.

In this case, openings 112 and 114 are formed near sidewalls 804L and 804R because the pneumatic antinodes of the standing wave are located on sidewalls 804L and 804R for air pulse generation APPS device 890. FIG.

Temporal alignment of valve opening

In another aspect, to increase the efficiency of air pulsing, valve opening(s) is increased during the interval when the peak pressure of the air wave is achieved at the location of the valve opening, as shown at 112 and 114 in FIG. It is suggested that timing is formed. Peak pressure timing herein refers to the first (partial) time derivative of zero, given that the air pressure in the chamber can be expressed as a single-variable function p(t) or a two-variable function p(x,t). ie dp(t)/dt=0 or ∂p(x,t)/∂x=0 (to determine the optimal timing of valve opening, ie temporal behavior). In other words, the peak (for some fixed position x ₀ , which can be the position of the valve opening 112 or 114) is the local maximum of p(x)/p( _{x 0 ,} t) across the t axis. or can be interpreted as a local minimum.

For example, referring to FIG. 2, the time intervals in which opening 112 is formed (i.e., valve portion 101 is actuated open or valve 101 is opened) is shown as the dotted area within plot Z101. the time intervals in which the opening 114 is formed (ie, the valve portion 103 is actuated open or the valve 103 is opened) is shown as the cross-hatched area in plot Z103. Aperture 112 is formed during the ( _first ) interval T1; while aperture 114 is formed during the ( _second ) interval T2. _{Both intervals} T1 and T2 are within the working cycle _TCY , meaning _T1≤TCY , _T2≤TCY and T1 _{+ T2≤} ( _{1 +} d)* _TCY , where _TCY = 1/f _CY and d<0.5.

To improve efficiency, the first opening 112 is formed within a _first interval T1, during which the first peak pressure pk1 of the airwave AW at the _first location (corresponding to sidewall 804L). is achieved; the second aperture 114 is formed within a _second interval T2, during which a second peak pressure pk2 of the airwave AW at the _second location is achieved.

In one aspect, the opening frequency of valves 101 and 103 is equal to the operating frequency f _CY in the embodiment shown in FIG.

It should be noted that in the embodiment shown in FIG. 2, the first interval T ₁ (representing the opening interval of valve 101) covers half of the working cycle T _CY and the second interval T ₂ (representing the opening interval of valve 103). ) covers the other half of the working cycle T _CY , which is T ₁ =T ₂ ≈T _CY /2 (ie the length of the interval T _y is half the length of the working cycle T _CY means that T _y ≈ T ₁ or T _y ≈ T ₂ ), but is not limited to this. Intervals T ₁ or T ₂ may be slightly shorter or longer than T _CY /2 (eg, within ±10% or ±20%). As long as the opening interval of valve 101 covers the first peak pk ₁ and the opening interval of valve 103 covers the second peak pk ₂ , the requirements of this application are satisfied and this is within the scope of this application. .

Furthermore, the first interval T ₁ (representing the opening interval of valve 101) is the first overpressure/underpressure during which the air pressure P112 generated by the movement of the membrane is greater/less than the constant pressure _Pth . /under-pressure) interval, the first over-pressure/under-pressure _interval overlapping T1 in the embodiment shown in FIG. Similarly, the _second interval T2 (representing the opening interval of valve 103) is a second overpressure/underpressure during which the air pressure _P114 generated by membrane movement is above/below a particular pressure Pth. A _second overpressure/underpressure interval that may cover the interval overlaps T2 in the embodiment shown in FIG. _In this case, the air pulse generator 890 generates positive/negative air pulses during the valve opening _intervals T1 and T2, where the positive/negative air pulses correspond to the valve opening interval(s). It can be propagated from the chamber 105 to the surroundings in the meantime.

The AW pressure waves generated by the drive waveforms S102a'/S102b' in FIG. 4 are simple AM, and the AW pressure waves generated by the drive waveforms S102a/S102b in FIG. 3 or S102a''/-S102a'' in FIG. Note that it is DSB-SC (double-sideband, suppress carrier). The timing relationship shown in FIG. 2 corresponds to a simple AM modulated AW pressure wave, with peaks pk ₁ , pk ₂ not crossing the line of P _th . However, for DSB-SC modulated AW pressure waves, pk ₁ , pk ₂ cross the line of P _th whenever S _IN changes polarity, then over pressure becomes negative pressure and vice versa. is.

Note that the total pressure in the chamber can have two component pressures: one caused by membrane movement and the other caused by valve movement. Both components can be in the form of standing waves. Pressures P112 and P114 shown in FIG. 2 refer only to component pressures caused by membrane transport.

Synchronous valve open

Further, valve portion 101 may form openings 112 within or during a plurality of first valve opening intervals, wherein air pressure P112 is greater than a specified pressure _Pth within or during a plurality of first overpressure intervals. obtain. In the embodiment shown in FIG. 2, the plurality of first valve opening intervals (of valve 101) and the plurality of first overpressure intervals (of pressure P112) are aligned or overlapped in time and the first The valve opening interval of (for valve 101) and the _first overpressure interval (for pressure P112) are annotated as T1 in FIG.

Similarly, the valve portion 103 may form openings 114 within or during a plurality of second valve opening intervals, and the air pressure P114 may be greater than a certain pressure _Pth within a plurality of second overpressure intervals. . The plurality of second valve opening intervals (of valve 103) and the plurality of second overpressure intervals (of pressure P114) may also be aligned or overlapped in time such that the valve opening intervals (of valve 103) and overpressure intervals (of valve 103) The pressure interval (of pressure P114) is annotated as T2 as in _FIG .

In this application, temporal alignment or overlap of the plurality of first time intervals and the plurality of second time intervals means: 1) the plurality of first time intervals and the plurality of second time intervals; are temporally located (or appear temporally) at the same frequency, or 2) the first time interval and the second time interval overlapping the first time interval form an overlapping region. and that the length of the overlapping region is at least 50% of the length of the first (or second) time interval.

By aligning the valve opening interval and the overpressure interval, the air pulse generator 890 delivers a plurality of first air pulses AP ₁ (shown as P707L in FIG. 2) at port 707L through aperture 112. ) and through aperture 114 may generate a plurality of second air pulses AP ₂ (shown as P707R in FIG. 2) at port 707R. In addition, the times corresponding to the peak valve openings of Z101/Z103 are preferably aligned with the times corresponding to the peak pressures of P112/P114 generated by membrane transport.

In different perspectives, T ₁ in FIG. 2 are respectively: first valve opening interval of valve 101 (perspective of Z101); a first membrane transfer interval of membrane portions 102a (perspective of Z102a) and 102b (perspective of Z102b), creating a pressure gradient (vector) directed towards; a first overpressure interval (perspective of P112); 1 air pulse AP ₁ may refer to the first duty period. Similarly, T2 in FIG. ₂ are respectively: the second valve opening interval of valve 103 (perspective of Z103'); from volume 105b over membrane portion 102b; a second membrane displacement interval of membrane portion 102a (perspective view of Z102a') and membrane portion 102b (perspective of Z102b') creating a pressure gradient (vector) directed towards; a second overpressure interval (perspective of P114'); and the second duty period of the _second air pulse AP2 at port 707R.

FIG. 2 illustrates a first valve opening interval of valve 101, a first chamber pressure gradient interval, movement of membrane portions 102a and 102b, a first overpressure interval and a first duty period of _first pneumatic pulse AP1. are temporally aligned (peak-to-peak) and overlapped (periodic). Similarly, a second valve opening interval for valve 103, a second chamber pressure gradient interval, movement of membrane portions 102a and 102b, a second overpressure interval (in terms of P114'), and a _second air pressure pulse AP2. are aligned in time (peak-to-peak) and overlapped (periodic).

Combining two half-wave rectified pulses into one full-wave rectified pulse

In one aspect, by comparing waveforms P112 and P707L, P707L can be interpreted as a half-wave rectified version of P112 rectified by the timing variation impedance associated with valve 101 movement Z101. Also, by comparing waveforms P114 and P707R, P707R can be interpreted as a half-wave rectified version of P114 rectified by the timing variation impedance associated with valve 103 movement Z103. Waveform P890, which sums waveforms P707L and P707R and represents the on-axis output sound pressure of device 890, can be interpreted as a full wave rectified version of P112 or P114.

Referring to plot P707L, a plurality of first air pulses AP ₁ are generated at a first (air) pulse rate APR ₁ corresponding to operating frequency f _CY . Referring to plot P707R, a plurality of _{second air pulses AP2 are generated at a second (} air) pulse rate _APR2 corresponding to operating frequency fCY.

Referring to plot P890, the first plurality of air pulses AP ₁ and the second plurality of air pulses AP ₂ are temporally and mutually interleaved such that air pulse generator 890 produces a plurality of aggregate air pulses (aggregated air pules) can be interpreted as generating APs. The plurality of aggregate air pulses AP includes a _first air pulse AP1 having a _first pulse rate APR1 and a _second air pulse AP2 having a _second pulse rate APR2. Aggregate air pulses AP are generated at an overall (air) pulse rate PRO.

Under the condition of APR ₁ =APR ₂ =f _CY as in the embodiment shown in FIG. 2, the overall pulse rate PRO is twice the pulse rate APR ₁ (or APR ₂ ). In other words, the overall pulse rate PRO corresponds to twice the operating frequency f _CY , i.e., PRO = 2*f _CY , where a 110 VAC sine waveform at 60 Hz becomes a half sine waveform at 120 Hz after full-wave rectification. to generate similar to

Analogy with AM radio demodulation

In one aspect, the effect of membrane transport can be compared to an AM radio station that produces EM waves that are amplitude modulated by a sound signal and emits AMEM waves into the atmosphere. Instead of EM waves, device 890 generates amplitude modulated ultrasound waves and transmits such AM ultrasound waves into chamber 105 . Such ultrasound waves are further amplified by the standing wave construct of chamber 105 at the valve location. The standing wave structure of chamber 105 resembles an EM waveguide in which signal strength is maximized by placing ports at the node(s) and antinode(s) of the waveguide. The signal received at the valve position is then demodulated by the periodic operation of the valve(s), analogous to the synchronized local oscillator of an AM receiver, and the non-linear characteristics of the Z _VALVE , analogous to the mixer of an AM receiver. and produces outputs P707R/P707R by dividing P112/P114 by its corresponding valve impedance Z _VALVE (t).

As an example, assume plots Z101, P112, Z103, and P114 are sinusoidal for simplicity, i.e., interleaved drive signals S101, S103 yield Z101∝sin(ωt), Z103∝-sin( ωt); in the example shown in FIG. 1, due to the n=1 standing wave, there is a phase reversal between P112 and P114, so these two local pressures are ∝S _IN sin( ωt), P114∝−S _IN ·sin(ωt), where the minus sign “−” represents a phase difference of 180° and ω=2πf _CY . Assuming Z _VALVE ∝1/(Z101−Z _O/C ) when Z101>Z _O /C and Z _VALVE =∞ otherwise, P707L is P707L∝S _IN when Z101>Z _O/C • sin ² (ωt), otherwise P707L=0. Similarly, P707R can be expressed as P707R∝S _IN ·sin ² (ωt) if Z103>Z _O/C and P707R=0 otherwise. Quantity P890 is P707L+P707R and represents the audio sound produced by device 890. FIG. After replacing P707L and P707R, we have P890=P707L+P707R∝S _IN ·sin ² (ωt) for all times that device 890 operates.

When a DSB-S AM radio waveform having the mathematical representation of S _IN ·sin(ωt) is demodulated using a multiplier with a carrier signal sin(ωt) generated by a synchronous local oscillator, the result is , S _IN *sin(ωt)*sin(ωt)=S _IN *sin ² (ωt), which is exactly the same formula as P890 derived in the paragraph above. .

As known to those skilled in the art, after multiplying the AM modulated signal/waveform S _IN ·sin(ωt) by the demodulated signal sin(ωt), the resulting signal (i.e., S _IN ·sin ² (ωt) ) is in the baseband and 1/3 of the energy of the resulting signal is on the frequency band centered at twice the carrier frequency, ie 2·ω or 2·f _CY . As an example, it was assumed that P890∝S _IN ·sin ² (ωt)=S _IN ·(1/2−1/2cos(2ωt)) (equation 3). The first term in Equation 3, 1/2 S _IN represents the demodulated component on baseband; while the second term in Equation 3, 1/2 S _IN cos(2ωt), represents the Represents the components of an acoustic band. As can be seen from Equation 3, the first energy of the first term in the baseband is twice the second energy of the second term. As used herein, baseband refers to the frequency band of the _input audio signal SIN, which covers/overlaps the human audible frequency band.

In FIG. 1 (or FIG. 6), the oxide substrate material, membrane portion 102a/102b, under valve 101/103 may be removed by photolithographic process/process(es) to form support 110 and wall 111. In FIG. obtain. According to very fine line patterns, the Si or POLY layer(s) can be etched to form openings/slits. Such slits form free moving ends on the valves 101/103 (e.g. these slits may form openings 112/114 when the displacement of the free moving ends of the valves exceeds ZO _/C ). ). Alternatively, slits can increase the compliance of membrane portions 102a/102b (eg, by forming slits 113a, 113b on membrane portions 102a/102b).

FIG. 5 is a schematic diagram showing a top view of the air pulse generator 890 shown in FIG. The air pulse generator 890 may (optionally) include cross linked beams 871, 872 to break the (long) valves 101/103 or (long) membrane portions 102a/102b into shorter pieces and to support 110 and reinforce 891. The air pulse generator 890 may (optionally) have a slot 873 that cuts through one slit on the membrane portion to act as an air channel to allow pressure to be released. It can be formed by spreading. Here, the slit generally has a width corresponding to the etching resolution of the MEMS fabrication process, for example, a width of 0.5-1.8 μM across a Si film with a thickness of 3-7 μM; It means the line geometry width, which is unlimited.

harmonic

Harmonic resonances can occur in air pulse generators. For example, FIG. 7 is a schematic diagram of a cross-sectional view of an air pulse generator 850 according to one embodiment of the present application. In air pulse generator 850, width W ₁₀₅ between sidewalls 804L and 804R is one wavelength (λ) corresponding to operating frequency f _CY to achieve second-order mode (or n=2 mode) resonance. can be At second mode resonance, two air-motion antinodes exist within chamber 105 (e.g., one-quarter (1/4) width W ₁₀₅ from either side wall 804L or side wall 804R). three air-motion nodes located near the center and sidewalls 804L, 804R of the chamber 105; two air-motion nodes within the chamber 105 (e.g., either from side wall 804L or 804R to/near one quarter (1/4) of width W ₁₀₅ ); Curve W102, which schematically represents the pressure distribution within chamber 105 over time, may result from movement of membrane portions 102c and 102d of air pulse generator 830 and may be symmetrical about centerline 703. FIG. As shown at W102 in FIG. 7, when an n=2 mode standing wave is formed in chamber 105 of apparatus 850, films 102e and 102f are driven synchronously with one common waveform such as S102a''. This causes the pneumatic waveforms near sidewalls 804L and 804R to be in phase with each other, producing a phase-inverted pneumatic waveform of similar amplitude in the center of chamber 105. Thus, the antinode of the pneumatic pressure is equal to chamber ₁₀₅ (or width W105). , valve opening 112 of air pulse generator 850 may be located at/near the center position between sidewalls 804L and 804R.In other words, the harmonic resonance (i.e., n≧2) For, in addition to next to sidewalls 804L and 804R, the opening of the air pulsing orifice(s) may be at/near any air pressure antinode between the two sidewalls that causes resonance.

The same description in the immediately preceding paragraph is also applicable to device 830 of FIG.

In an air pulse generator such as device 830 of FIG. 6, device 850 of FIG. 7, or device 890 of FIG. Causes a net air mass change in the chamber 105 over time to increase/decrease the pressure P 0 in the chamber 105 . Since such back pressure will reduce the output SPL, it is suggested to relieve such pressure.

For the air pulse generator 830 of FIG. 6, the slit openings 113a*/113b* may be designed to be proximate a pneumatic node located W ₁₀₅ /4 away from the sidewalls 804L/804R. Due to the audio filtering effect of the pneumatic node of the n=2 standing wave, widened slits 113a*/113b*, as shown by waveform W102 across P0, demodulate valves 101 and 103 shown by valve opening 112. Minimal impact on the operation of device 830 while relieving pressure build-up due to operation.

For air pulse generator 850 of FIG. 7 also operating at frequency f _CY corresponding to n=2 mode resonance across the width of chamber W ₁₀₅ , membranes 102e and 102f are each one of the thin flaps attached to respective supports 110. Contains one single piece. In contrast to the situation in device 830, membranes 102c, 102d in device 850 consist of two sub-portions separated by slits 113a and 113b, respectively, allowing free movement of membranes 102e and 102f. Slits 112 and 114 formed to align are located at air pressure antinodes within chamber 105 of device 850, so the width of these slits should be minimized to limit air pressure leakage. Accordingly, one or more vents 713T can be created on the top cap at pneumatic node locations, eg, a distance W ₁₀₅ /4 away from sidewalls 804L and 804R. Theoretically, one such vent is sufficient for back pressure relief purposes, but in order to consider the optimum balance of air pressure within chamber 105, generally a pair of vents, as shown in FIG. Vents 713T are preferably arranged in a central mirror fashion.

For the air pulse generator 890 of FIG. 1, the pressure pulses of acoustic tones (e.g., acoustic tone P890) from valves 112 and 113 have the same polarity, which increases or decreases the pressure P0 in chamber 105. to join together. Accordingly, vent openings 713T on the top plate located at or near the pneumatic nodes, as indicated by the alignment to the position where pneumatic profile W102 passes through P0, allow airflow to pass through. to release the pressure build-up due to the demodulating action of valves 101 and 103 .

The length and width of vent opening(s) 713T may be adjusted to form a suitable acoustic low pass filter (LPF) with the volume of chamber 105. FIG. The location of the vent opening(s) 713T may be at the antinode(s) of the air pressure relative to the operating frequency f _CY such that the amplitude of the frequency component corresponding to the standing wave is near zero. As a result, an acoustic notch filter is formed such that the pressure corresponding to the amplitude modulated standing wave can be suppressed near/at the vent opening(s) 713T within the chamber 105, such that only pressure changes due to the demodulation operation May reside near/at 713T(s). For devices operating at second mode resonance (e.g., device 850), the air pulse vent opening 713T is from either side wall 804R or 804L differently than for devices operating at first mode resonance (e.g., device 890). It may be positioned approximately one quarter of the width W ₁₀₅ (W ₁₀₅ /4), where the vent opening 713T (of the air pulse generator 890) is near the midpoint between the two sidewalls 804R and 804L. obtain.

The structure of air pulse generator 850 may be varied according to different design considerations. For example, membrane 102e/102f may have, but is not limited to, two membrane sub-portions, or two pieces, such as membrane 102a/102b or 102c/102d. The maximum Z-direction displacement of a one-piece membrane structure such as 102e/102f in FIG. Note that there is In contrast, in a two-piece per membrane structure, there is no such limit on Z-direction membrane displacement, since the two sub-parts always move in tandem, and larger displacements may be possible, thus , leading to improved unit-device-area effectiveness (SPL/m).

Further, valve portions 101 and 103 shown in FIG. 7 can be considered virtual valves. In other words, the slit formed between valve portions 101 and 103 can become a temporarily formed/opened valve opening (112') when valve portions 101 and 103 are fully actuated. In addition, the temporarily created/opened valve openings are created periodically. When the opening is opened, the chamber and ambient environment are connected through the opening (112'). When the aperture is not open, the air flowing through the slit is negligible or below threshold. Details of virtual valves (temporarily formed openings) can be found in US Pat. No. 11,043,197, which is not described here for brevity.

Additionally, similar to the device 890 shown in FIG. 1, a pressure gradient is also created within the device 850 through the properties of membrane movement and standing waves. Unlike device 890, membrane portions 102e and 102f are actuated to move in an in-phase manner, and at a given time both membrane portions 102e and 102f are actuated to move upward (or downward). point to In this case the pressure gradient is also established by exploiting the properties of n=2 standing waves. Similar to the description of FIG. 1, in FIG. 7 the dashed lines of curves U102 and W102 correspond to time _t0 and the solid lines of curves _U102 and W102 correspond to time t1. At time _t0 , membrane portions 102e and 102f are actuated to move upward (positive Z direction) and a pressure gradient develops inward (X direction) as indicated by the dashed slope of W102. do. _At time t1, membrane portions 102e and 102f are actuated to move downward (negative Z direction) and a pressure gradient develops outward (X direction) as indicated by the solid slope of W102. do. Similarly, the direction of membrane movement is substantially perpendicular to the pressure gradient direction.

Air moving or fan applications

The structure/mechanism of the device 890/830/850 can be regenerated/adapted for air movement or fan applications. Unlike sound waves traveling at the speed of sound C, the motion of the air, like that of the wind, is air flow related to the motion of air particles, the membrane portions 102a-102d/ caused by displacement of membrane portion(s), corresponding to 102 . In air movement or fan applications/modes of these devices, the air particles within the device can be described primarily according to hydrodynamics or aerodynamics; in contrast, in air pulse (APPS) generation applications/modes of these devices, The behavior of air in a device can be described primarily according to acoustics.

For air movement or fan applications, valve openings, such as openings 112 and 114 shown in devices 890/830/850, are positioned spatially and temporarily in time so that air movement is maximized. The air movement peak may be in terms of the velocity of air moved or the volume of air moved.

The drive signal(s) of the device for airflow generation or fan applications are different from APPS applications. For example, in an air movement or fan application, device 890 can be operated by applying the same drive signal to both membranes 102a and 102b to create a pressure differential between the volume within chamber 105 and the surroundings outside device 890. , may actuate its two membranes (102a and 102b) to move synchronously. In contrast, for APPS applications, device 890 uses two interleaved (S102a/S102b, etc.) or polarity reversed (S102a″, S102a″, The two membranes (102a and 102b) are actuated to move synchronously in opposite directions (along the Z-axis) by applying drive signals to the membranes 102a and 102b (eg S102a″).

The key difference between these two modes of operation is the different relationship between the chamber size of the device and the operating frequency. As described in connection with apparatus 890/830/850 for APPS applications, the operating frequency may be selected to generate a mode n standing wave in the chamber. In other words, the operating frequency f _CY is related to the chamber width W ₁₀₅ by the equation W ₁₀₅ =n/2·λ _CY , where λ _CY =C/f _CY is the characteristic length or wavelength of f _CY . , n is a small positive integer such as 1-3. On the other hand, for air movement or fan applications of the devices 890/830/850, the conversion rate of membrane movement to air flow generally increases as the ratio λ _CY /W _chamber increases, where W _chamber is the width of the chamber 105 of the air pulse generator 890/830/850, the chamber width of the device corresponding to W ₁₀₅ ; In other words, the conversion rate of membrane movement to airflow is typically greater than the chamber of the airflow generator for air movement or fan applications (corresponding to chamber 105 of the air pulse generator 890/830/850). As the pressure within becomes more uniform, it increases and is in direct opposition to the desire to maximize the pressure gradient (or pressure non-uniformity within the chamber 105) of the air pulse generator 890/830/850.

For example, in the air pulse generator 890, the resonant frequency f of the cantilever beam can be related to its length L by f∝1/L ³ , so that W ₁₀₅ =λ _CY =3.6 mm at an operating frequency of 96 KHz. be. On the other hand, the operating frequency of the air pulse generator for air moving or fan applications is reduced from 96 KHz to 24 KHz, and the membrane portion(s) and the valve portion(s) of the air moving or fan application ( By lowering both resonance frequencies to 24 KHz as well, the width of the membrane portion can be increased from 0.94 mm to 1.44 mm, and the width of the valve portion can be increased from 0.46 mm to 0.73 mm, resulting in The width of the resulting chamber can be 2 x (0.1 + 0.73 + 0.2) + 1.44 = 3.5 mm, which is much shorter than the wavelength of 14.6 mm at a frequency of 24 KHz and the airflow of the membrane travels. shows a high conversion rate to Thus, air pulse generators and air for air movement or fan applications that have a resonant frequency of 24 KHz for both membrane portion(s) and valve portion(s), despite nearly identical cross-sectional views. Driving both air pulse generators for motion or fan applications with the same waveform at 24 KHz may be suitable for air motion applications, but with membrane portions 102a and 102b interleaved waveforms S102a', S102b' or symmetrical. An air pulse generator 890 driven by waveforms S102a″, −S102a″ and producing nearly zero net air movement over each operating cycle T _CY can be optimized for sound generation applications and is not suitable as an air mover. may not.

In short, symmetrical membrane displacements of membrane portions 102a/102b or 102c/102d of device 890 can be used to maximize the intra-chamber pressure gradient for APPS applications, but with signals of the same polarity (membrane portions Synchronous/identical membrane displacement can be employed to maximize the conversion of membrane movement to airflow. In another aspect, for APPS applications, the chamber width (in the X direction) W ₁₀₅ is n/2× λ _CY , where n is a small positive integer; while for air movement applications, the chamber width (in the X direction) of the air pulse generator for air movement or fan applications ) can be much smaller than λ _CY /2 to maximize the conversion of membrane transport to airflow.

Different structural embodiments (air pulse generation) devices are described in the following paragraphs. For example, FIG. 8 is a schematic diagram of a cross-sectional view of an air pulse generator 880 according to one embodiment of the present application. The membrane structure 12 of air pulse generator 880 includes one membrane portion, which is divided into membrane subparts 102e', 102f' and 102g. Membrane sub-portions 102e' and 102g can be distinguished according to slits 113e and 113f on the membrane portion. The membrane structure 12 of air pulse generator 880 having membrane sub-portions 102e′ and 102g may serve/function as membrane portions 102a and 102b of air pulse generator 890 (or membrane portions 102c and 102d of air pulse generator 830). can.

In APPS applications, membrane subsections 102e' and 102g may be driven by membrane drive signal pairs similar to membrane drive signal pairs (S102a, S102b)/(S102a', S102b')/(S102a, S102b'). As a result, membrane sub-portions 102e' and 102g can move in substantially opposite directions to have symmetrical membrane displacements. Similar to downward bending membrane portion 102a and upward bending membrane portion 102b, membrane sub-portions 102e' and 102f' may be curved concavely to bend downward and membrane sub-portions 102f' and 102g to bend upward. It can be convexly curved and vice versa.

FIG. 9 is a schematic diagram of a cross-sectional view of an air pulse generator 800 according to one embodiment of the present application. Membrane structure 12 of air pulse generator 800 includes membrane portions 102 g and 102 h , which are fixed on support 110 at the center of air pulse generator 800 . The slits/tips of membrane portions 102g and 102h are located proximate sidewalls 804L and 804R.

Valves 101 and 103 of air pulse generator 890/830/850/880 are not present in air pulse generator 800 . When the membrane portions 102g and 102h are driven by the pair of membrane drive signals (S102a, S102b)/(S102a', S102b')/(S102a'', S102b''), the membrane portions 102g and 102h are driven by the air pulse generator. By utilizing slits between membrane portions 102g, 102h and wall 111 to perform the AM ultrasonic carrier rectification function of openings 112, 114 of valves 101, 103 of 890, valve 101 of air pulse generator 890 , 103 and the pressure generating function of the membrane portions 102 a , 102 b of the air pulse generator 890 .

As a result, membrane portion 102g can vibrate to form opening 112g that functions as opening 112 of valve 101, while producing a maximum/minimum change in pressure (e.g., first peak pressure pk ₁ ). can. Membrane portion 102h can vibrate to form opening 114h that functions as opening 114 of valve 103, while producing a maximum/minimum change in pressure (eg, a second peak pressure pk ₂ ). obtain.

The pneumatic waveform P707L may be expressed as P707L∝(S _IN ·sin(ωt)+Z _0AC ) ² when Z102a>Z _O/C , and P707L=0 otherwise. When Z102b>Z _O/C , the pneumatic waveform P707R∝(S _IN ·sin(ωt)+Z _0AC ) ² can be expressed, otherwise P707R=0. Here, waveforms Z102a, Z102b represent displacement of membrane portions 102g, 102h, respectively; waveforms P707L, P707R represent air pressure (outside chamber 105) at ports 707L, 707R, respectively.

A negative bias voltage is applied to the bottom electrode(s) of the actuator(s) of the membrane portion 102g/102h, such that when the input AC voltage is 0V, the (leading edge) of the membrane portion 102g/102h in the Z direction. ) position is raised to be equal to or slightly above the displacement level ZO _/C . In other words, Z _0AC can be positive. If the (tip) position of the membrane portion 102g/102h in the Z direction is less than the displacement level ZO _/C when the input AC voltage is 0V, then _ZOAC may be negative and the low level input signal(s) ) can experience the same clipping phenomenon as a class B amplifier. The clipping phenomenon may not fully open the membrane portion 102g/102h.

If Z _0AC is a positive number, the aggregated on-axis output sound pressure of air pulse generator 800 (ie, P800=P707R+P707L) can be expressed as:
P800∝(S _IN ·sin(ω・t)+Z _0AC ) ² +(S _IN・sin(−ω・t)+Z _0AC ) ² =S _IN ²・(1−cos ² (2ω・t))+2・Z _0AC ² , when |S _IN ·sin(ω·t)|<Z _0AC (equation 5a),
P800 ∝ (S _IN · sin(ω·t) + Z _0AC ) ² ≈ 1/2 sin ² · (1-cos ² (2ω · t)) + 2 · S _IN · sin(ω · t) · Z _0AC , |S If _IN ·sin(ω·t)|>> _{Z 0AC} (equation 5b), and P800∝(S _IN ·sin(ω·t)) ² ≈½sin ² ·(1−cos ² (2ω·t) ), if Z _0AC →0+ (equation 5c).
_ZOAC is the displacement of the membrane relative to the displacement level ZO _/C when the input AC voltage is 0V.

In an embodiment, Z _0AC is a small positive value to reduce the second term 2·Z _0AC ² of Equation 5a and the inaudible second term 2·S _IN ·sin(ω·t)·Z _0AC of Equation 5b. can be set to the value of For example, Z _0AC can range between 1% and 10% of maximum membrane displacement.

In one embodiment, linearity compensation may be performed by a DSP functional block embedded within the host processor to compensate for the non-linearity of S _IN ² in Equations 5a-5c.

By setting Z _0AC to a small positive value, the membrane portions 102g/102h can open slightly when the input AC voltage is 0V. Given the symmetry of the membrane drive signals (S102a, S102b)/(S102a', S102b')/(S102a'', S102b''), at least one of the apertures 112g, 114h may be slightly open at any time/ can be formed. Thus, pressure changes within chamber 105 due to the rectifying effects of apertures 112g, 114h may be balanced and vent aperture(s) 713T or wider slit apertures (113a*/113b*) present in air pulse generator 800. do not do.

With the air pulse generator 800, the effects of full-wave rectification and synchronous demodulation can be produced by the air pulse generator 800 regardless of whether resonance occurs within the chamber 105 or not. Even if there were no standing waves to produce maximum sound pressure at or near sidewalls 804L and 804R, such maximum sound pressure would simply depend on the physical location of openings 112g, 114h in membrane portions 102g, 102h. , and symmetrical membrane drive signals (S102a, S102b)/(S102a', S102b')/(S102a'' that drive the actuators of membrane portions 102g, 102h to produce maximum displacement in the vicinity of sidewalls 804L and 804R. , S102b''). For example, membrane portion 102g can be actuated to compress a first portion/volume 105a (top of membrane portion 102g) within chamber 105 to maximize local pressure. Membrane portion 102h may be actuated to inflate a second portion/volume 105b (top of membrane portion 102h) within chamber 105 to minimize local pressure. The pressure profile over time within portions/volumes 105a and 105b may be identical to that of a standing wave at first mode resonance. In other words, air pulse generator 800 can achieve full-wave rectification and synchronous demodulation without chamber 105 resonance, thereby increasing flexibility in air pulse generator design.

If resonance occurs in the air pulse generator 800, the output of the air pulse generator 800 can benefit from standing waves of such resonance. For example, if the width W ₁₀₅ of the chamber 105 of the air pulse generator 800 is equal to half the wavelength (λ/2) corresponding to the operating frequency f _CY , then a pressure profile similar to that of the standing wave is produced by the membrane portion 102g and 102 h thus enhancing the power caused by standing waves already established in chamber 105 .

Enclosure-less

The air pulse generator 890/850/830 generates a pair of out-of-phase baseband radiations such as those produced by conventional loudspeakers (i.e., forward radiation and phase-reversed back radiation). , the air pulse generator 890/850/830 does not require any back enclosure (the purpose of which is to contain or transform the rear radiation, so that the phase-reversed rear radiation is forward is to avoid canceling the radiation) is also not required. Thus, the sound generating air pulse generator 890/850/830 can be enclosureless.

For device 890, by exploiting the first mode resonance of chamber 105 and the interleaved timing of valve opening, air pulse generator 890 produces two radiations that are in phase instead of being 180° out of phase. Generate. Proper timing alignment between the opening timing of the valves 101/103 (indicated by Z101/Z103 in FIG. 2) and the pressure waves P112/P114 will properly phase the acoustic energy so that the ultrasonic radiation is It is converted to double the baseband output SPL, increasing the utilization of the total acoustic energy and eliminating the need for an enclosure while achieving effective demodulation of ultrasonic AM signals.

acoustic filter

An acoustic filter may be added in front of the air pulse generator. For example, FIG. 10 is a schematic diagram of an air pulse generator 890 located in configuration A00 according to one embodiment of the present application. FIG. 11 is a schematic diagram of an air pulse generator 890 located in configuration A30 according to one embodiment of the present application. The acoustic air pressure measured at ports 707L and 707R of air pulse generator 890 includes not only demodulated AM ultrasound waves P707L and P707R, but also ultrasound waves generated by movement of valves 101 and 103. obtain. The symmetrical motion of valves 101 and 103 can be characterized as a dipole. The ultrasonic superposition generated by the motion of valves 101 and 103 peaks along the plane of valves 101 and 103 and is zero on the center plane between sidewalls 804L and 804R. Configurations A00/A30 may be configured to minimize ultrasonic waves generated by movement of valves 101 and 103, and thus may act as acoustic filters.

In FIG. 10, configuration A00 may include a funnel structure A05 configured to filter out ultrasonic waves generated by movement of valves 101/103. Funnel structure A05 may have a wide opening on the inside of configuration A00, sloped sides, and a narrow tube near the outside of configuration A00. The wide opening of the funnel structure A05 may be smaller than the width W105 of the chamber ₁₀₅ . Funnel structure A05 coalesces the outputs from ports 707L and 707R, causing the ultrasonic waves produced by the symmetrical motion of valves 101 and 103 to annihilate each other, leaving wave P890, which is the sum of waves P770L and P770R. It is superimposed.

In FIG. 11, configuration A30 may include port A07 and an external chamber A06 that serve as output ports for configuration A30. The width Wa06 between the sidewalls A06T, A06B of the outer chamber A06 may be equal to the width W105 of the chamber ₁₀₅ (eg, half of λ _CY ), so that the standing wave is at frequency f _CY (of the first mode resonance ) and at frequencies 2·f _CY (for second mode resonance). The width Wa07 of port A07 may be smaller than the width W105 of chamber ₁₀₅ . The width Wa07 of port A07 may be equal to half the width W ₁₀₅ of chamber 105 or a quarter of λ _CY .

Configuration A30 is configured to filter out ultrasonic waves generated by movement of valves 101/103. For ultrasonic waves generated by the symmetrical motion of valves 101 and 103 with frequency f _CY , the acoustic energy is directed to an external chamber having a pneumatic node at/near the midpoint between side walls A06T and A06B. There may be a first mode resonance of A06 and the pressure of the standing wave may be coupled to zero across the width Wa07 of port A07. For acoustic wave P890 with a pulse rate of 2·f _CY , the acoustic energy is transferred secondary to external chamber A06, which has a pneumatic antinode at/near the midpoint between sidewalls A06T and A06B, which is also the center of port A07. mode and the maximum output pressure may occur when the pressure of the standing wave is integrated over the width Wa07 of port A07. By utilizing two different resonance modes, the outer chamber A06 eliminates the ultrasonic spectral component at frequency f _CY by first mode resonance and the ultrasonic spectral component at frequency 2·f _CY by second mode resonance (i.e. , waves P890).

In FIG. 11, configuration A30 may include film A08, which may be made of a hydrophobic material. Film A08 filters out the remaining ultrasonic spectral components at frequency 2·f _CY by providing protection (to prevent dust, vapor and moisture ingress) and acoustic resistance (forming a low-pass filter with the volume of the outer chamber A06). to attenuate) can be placed in port A07.

FIG. 12 is a schematic diagram of mobile device A60 according to one embodiment of the present application. Two air pulse generators A02 and A03, each of which can be any of air pulse generators 890/850/830, are mounted on edge A01 of mobile device A60, such as a smart phone or notepad. The ports 707L and 707R of the air pulse generators A02, A04 may face outward and the ultrasonic waves generated by the air pulse generators A02, A03 may pass through the orifice arrays A04, A05. Mobile device A60 utilizes the structure of configuration A00 or A30 to remove ultrasonic spectral components at frequency f _CY produced by the movement of valves 101 and 103, while passing wave P890 at frequency 2·f _CY . A film A08 of configuration A30, which allows for a further reduction of the remaining ultrasound spectral components around frequency 2·f _CY .

FIG. 13 is a schematic diagram of a cross-sectional view of an air pulse generator 300 according to one embodiment of the present application. Similar to the air pulse generator 890, when a standing wave is formed by the chamber 105 of the air pulse generator 300, the motion of the membrane portions 102c, 102d of the air pulse generator 300 is symmetrical, with a net of air movement can be generated. Due to the near zero net air movement over each operating cycle T _CY , most of the energy contributed by the membrane portions 102c/102d will be acoustic energy (in the form of air pressure gradients or standing waves) and the near zero energy will be , resulting in kinetic energy (air mass transfer, ie, wind).

FIG. 14 is a schematic illustration of a cross-sectional view of an air moving device 100 for moving an air volume from one port of the device to another port, according to one embodiment of the present application.

In contrast to the air pulse generators 850/890, the oscillation frequency of the membrane 102 of the air flow generator 100 produces a wavelength λ that is much larger than the width of the chamber 105, and the pressure within the chamber 105 is assumed to be uniform. can be considered. The interleaved valve actuation signals S101/S103 open the valve portions 101/103 in a time-interleaved fashion, or 180° out of phase, allowing air to flow either from port 107 to port 108 or from port 108 to port 107. It can be configured to cause movement. For example, if valves 101/103 are opened and valves 103/101 are closed when membrane 102 moves in the positive Z direction (+Z direction) to compress the volume in chamber 105, air is forced into port 107. / 108 out of chamber 105 . Conversely, when membrane 102 moves in the negative Z direction (-Z direction) to expand the volume of chamber 105, valves 101/103 are opened, and if valves 103/101 are closed, air flows into port 107. /108 into chamber 105.

The cap 104 of the air moving device 100 functions as a heat sink/pad for heat generating components such as, but not limited to, a notebook central processing unit (CPU) or smart phone application processor(s) (AP). come into physical contact with Cap 104 may be made of a thermally conductive material such as aluminum or copper. Fine fins (not shown) may be formed on the surface of the cap 104 within the chamber 105 to improve heat transfer efficiency, but are not limited thereto.

Specifically, in the air pulse generator 850/890, the cap 104 of the air device 100/300 is replaced with a top plate 804T and spacers 804L, 804R that also serve as sidewalls. Top plate 804T may be a printed circuit board (PCB) or land grid array (LGA) substrate and contains metal traces, vias and contact pads that may otherwise be arranged on substrate 109 or plate 115 . The thickness is 0.2-0.3 mm for the top plate 804T, 0.05-0.15 mm for the side walls 804L/804R, and 0.25-0.35 mm for the wall 111 . The total thickness of the air pulse generator can be, but is not limited to, 0.6-0.8 mm.

Additionally, the pulse interleaving concept disclosed in US Pat. No. 10,536,770 can also be applied to the present application. In other words, to improve sound quality while generating ultrasonic acoustic pulses for APPS, in one embodiment, multiple air pulse generators (eg, multiple air pulse generators 100) are combined into a single They can be cascaded together to form a single air pulse generator. The drive signals for the air pulse generator 100 (e.g., membrane drive signals S102a/S102b/S102 or valve drive signals S101/S103) may be interleaved to form interleaved groups, away from the human audible band. However, as a result, the effective air pulse rate can be increased to twice as high frequency. For example, pulses of the membrane drive signal of one air pulse generator 100 may be interleaved with pulses of the membrane drive signal of another air pulse generator 100 so that the aggregate air pulse of one air pulse generator 100 is , may be interleaved with aggregate air pulses of another air pulse generator 100 to increase the effective air pulse rate. Alternatively, each pulse of the membrane drive signal of one air pulse generator 100 is located at/near the midpoint between two successive pulses of the membrane drive signal of the other air pulse generator 100, As a result, each aggregated air pulse of one air pulse generator 100 is located at/near the midpoint of two consecutive aggregated air pulses of the other air pulse generator 100 so as to increase the effective air pulse rate. obtain. In one embodiment, two air pulse generators 100, each designed to operate at an operating frequency T _CY of 24 KHz, are placed side by side or mounted back-to-back and interleaved. resulting in an effective air pulse rate of 48 KHz.

Illustratively, FIG. 15 is a schematic diagram of an air pulse generator 400 according to one embodiment of the present application. Air pulse generator 400 can be viewed as two air pulse generators 100 and 100' stacked back-to-back. In the air pulse generator 400 the two chambers 105 and 105' of the two air pulse generators 100 and 100' are connected to each other via the opening 116 to form the chamber 106 of the air pulse generator 400. .

The air pulse generator 400 can have a first valve portion 101, a second valve portion 103, a third valve portion 101', and a fourth valve portion 103'. A first anchor with valve portion 101 fixed to wall 111 and a second anchor with valve portion 103 fixed to wall 111 are aligned in the X direction; is aligned in the Z direction with a third anchor fixed to wall 111 . Valve portions 101 and 103 (or valve portions 101′ and 103′) are symmetrical with respect to the YZ plane; while valve drive signal S101 (or S103) applied to valve portions 101 and 101′ drops to zero. The (non-actuated) valve portions 101 and 101' (or valve portions 103 and 103') are then symmetrical about a second plane (eg the XY plane) that is not parallel to the YZ plane. Valve portions 101 and 101' (or valve portions 103 and 103') are non-coplanar, while (non-actuated) valve portions 101 and 103 (or valve portions 101' and 103') are:
When the valve drive signals S101 and S103 applied to valve portions 101 and 103 drop to zero, they may be coplanar.

In one embodiment for APPS applications, by interleaving the drive signals of the two air pulse generators 100, the displacement profile(s) of the membrane portion 102 (or valve portions 101, 103) of the air pulse generator 400 is: It may be mirror symmetric with the displacement profile(s) of membrane portion 102 ′ (or valve portions 101 ′, 103 ′) of air pulse generator 400 . Alternatively, by interleaving or inverting the drive signals of the two air pulse generators 100, the displacement profile(s) of the membrane portion 102 (or valve portions 101, 103) of the air pulse generator 400 is The displacement profile(s) of membrane portion 102' and (or valve portions 101', 103') of pulse generator 400 may be the same, so that the displacement (direction and magnitude of) of membrane portion 102 is: It equals (the direction and magnitude of) the displacement of membrane portion 102 ′ and compensates for pressure fluctuations in chamber 106 . Membrane portion 102 may be parallel (or offset to match) with membrane portion 102'.

In one embodiment for air movement applications, characteristic length λ _CY is generally much longer than the dimensions of air pulse generator 400 . Since the displacement of membrane portion 102 can be equal to the displacement of membrane portion 102', air pulse generator 400 can include only one membrane portion and one of membrane portions 102, 102' can be removed, thereby , reducing power consumption and improving operating efficiency.

power saving

In another aspect, the air pulse generator output is related to A(t)·p(t), where A(t) is the area of the aperture 112/114 and p(t) is the chamber 105 air pressure. In other words, the openings 112/114 of the valves 101/103 are directly related/proportional to the intensity of the air pulse generator output. Specifically, the maximum SPL output is the maximum value of the air pressure p(t) in chamber 105 generated by membrane movement and the maximum value of aperture 112/114 area A(t) generated by valve movement. is a combination of By appropriately modulating/manipulating the area A(t), the operating power of the air pulse generator can be reduced.

The area A(t) may not change at the rate audible to human hearing, but slowly changes the valve drive voltage S101/S103 depending on the volume or envelope of the sound produced. It can be adjusted by changing For example, valve drive voltages S101/S103 may be controlled by envelope sensing with an attack time of 50 milliseconds and a release time of 5 seconds. When the sound produced by the air pulse generator is consistently low volume, the valve drive voltage S101/S103 can be gradually lowered with a 5 second (long) release time. When generating high sound pressure, the valve drive voltages S101/S103 can be boosted with a (short) 50 ms attack time.

In summary, the air pulse generator of the present invention first vibrates its membrane structure and then produces sound pressure (or air movement) in response to the generation of sound pressure (or air velocity) maxima/mins. Sound pressure (or air movement) may be generated by opening/closing its valve structure to filter/reshape and finally output sound waves (or airflow) under full wave rectification effect. Synchronous demodulation by opening/closing the valve structure in a phase-locked and time-aligned manner with respect to the generation of sound pressure maxima/minima (or air velocity) and/or valve portions of the valve structure. can be performed by opening/closing in a temporally interleaved manner.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the scope of the appended claims.

Claims (28)

An air pulse generator comprising:
a membrane structure and a valve structure;
a cover structure, wherein a chamber is formed between the membrane structure, the valve structure, and the cover structure;
forming an air wave within the chamber oscillating at an operating frequency;
said valve structure is configured to be operative to perform an opening and closing action to form at least one opening, said at least one opening connecting air within said chamber with air outside said chamber;
the opening and closing motion is synchronized with the operating frequency;
Air pulse generator. said air pulse generator generating an acoustic sound according to an input audio signal;
the airwave in the chamber generated by the membrane structure includes an amplitude modulated waveform corresponding to a carrier wave component having the operating frequency and a modulated component corresponding to the input audio signal;
2. The air pulse generator of claim 1. The membrane structure is configured to be actuated to generate the airwaves according to a membrane drive signal, the membrane drive signal comprising a pulse amplitude modulated signal, the pulse amplitude modulated signal being generated according to an input audio signal. Ru
2. The air pulse generator of claim 1. The membrane structure has a first membrane portion and a second membrane portion;
the first membrane portion and the second membrane portion are configured to be simultaneously actuated according to a first membrane drive signal and a second membrane drive signal to generate air waves;
2. The air pulse generator of claim 1. said first membrane drive signal comprising a first pulse amplitude modulated signal, said first pulse amplitude modulated signal comprising a plurality of first pulses temporally distributed according to said operating frequency;
said second membrane drive signal comprises a second pulse amplitude modulated signal, said second pulse amplitude modulated signal comprising a plurality of second pulses temporally distributed according to said operating frequency;
5. The air pulse generator of claim 4. a first transition edge of the first pulse temporally coincides with a second transition edge of the second pulse;
6. The air pulse generator of claim 5. the first pulse and the second pulse are temporally interleaved;
6. The air pulse generator of claim 5. the sum of the first membrane drive signal and the second membrane drive signal is constant;
5. The air pulse generator of claim 4. the membrane structure generates a pressure gradient having a pressure gradient direction within the chamber during intervals;
said interval being within half of an operating cycle;
said operating cycle is the reciprocal of said operating frequency;
2. The air pulse generator of claim 1. a pressure gradient direction of the pressure gradient generated by the membrane structure is substantially parallel to the membrane structure;
2. The air pulse generator of claim 1. The membrane structure has a first membrane portion and a second membrane portion;
During intervals, the first membrane portion is actuated to compress the first portion of the chamber and the second membrane portion is actuated to expand the second portion of the chamber. a pressure gradient is formed in the direction of the pressure gradient from the first portion to the second portion;
2. The air pulse generator of claim 1. the membrane structure generates a first air pressure gradient at a location within the chamber during a first interval within the first half of an operating cycle;
the membrane structure generates a second air pressure gradient at the location within the chamber during a second interval within the second half of the operating cycle;
said first air pressure gradient and said second air pressure gradient have opposite directions;
said operating cycle is the reciprocal of said operating frequency;
2. The air pulse generator of claim 1. the first magnitude of the first air pressure gradient and the second magnitude of the second air pressure gradient are substantially the same;
13. The air pulse generator of claim 12. the membrane structure having a membrane portion configured to be actuated to produce membrane movement having a membrane movement direction;
a pressure gradient having a pressure gradient direction is generated due to said membrane transport;
the direction of membrane movement and the direction of pressure gradient are substantially perpendicular to each other;
2. The air pulse generator of claim 1. A sound generation method applied in an air pulse generator, said method comprising:
forming an air wave within a chamber, said air wave oscillating at an operating frequency, said chamber formed within said air pulse generator;
forming at least one opening in the air pulse generator at an open frequency, the at least one opening connecting air within the chamber with air outside the chamber;
the open frequency is synchronous with the operating frequency;
sound generation method. Said step of forming said airwaves at said operating frequency includes:
forming an amplitude modulated waveform according to an input audio signal;
said amplitude modulated waveform comprising a carrier component having said operating frequency and a modulated component corresponding to said input audio signal;
16. A method of generating sound according to claim 15. The air pulse generator has a membrane structure, and the step of forming the air waves at the operating frequency includes:
driving the membrane structure with a membrane drive signal to generate the air waves;
the membrane drive signal comprises a pulse amplitude modulated signal generated according to an input audio signal;
16. A method of generating sound according to claim 15. The air pulse generator has a membrane structure, the membrane structure has a first membrane portion and a second membrane portion, and the step of forming the air waves at the operating frequency includes:
driving the first membrane portion with a first membrane drive signal;
driving the second membrane portion with a second membrane drive signal;
said air wave is generated by simultaneously driving said first membrane portion with said first membrane drive signal and said second membrane portion with said second membrane drive signal;
16. A method of generating sound according to claim 15. generating said first membrane drive signal according to an input audio signal, said first membrane drive signal comprising a first pulse amplitude modulated signal, said first pulse amplitude modulated signal being at said operating frequency; a plurality of first pulses temporally distributed according to;
generating the second membrane drive signal according to the input audio signal, the second membrane drive signal comprising a second pulse amplitude modulated signal, the second pulse amplitude modulated signal including a plurality of second pulses temporally distributed according to frequency;
19. A method of generating sound according to claim 18. generating the first pulse amplitude modulated signal and generating the second pulse amplitude modulated signal, wherein a first transition edge of the first pulse coincides with a second transition edge of the second pulse; temporally coinciding with the transition edge,
20. A method of generating sound according to claim 19. generating the first pulse amplitude modulated signal and generating the second pulse amplitude modulated signal, wherein the first pulse and the second pulse are temporally interleaved;
20. A method of generating sound according to claim 19. generating the first pulse amplitude modulated signal and generating the second pulse amplitude modulated signal, wherein the sum of the first membrane drive signal and the second membrane drive signal is constant. ,
20. A method of generating sound according to claim 19. The air pulse generator has a membrane structure, and the step of forming the air waves at the operating frequency includes:
generating a pressure gradient having a pressure gradient direction within the chamber through a membrane structure;
the pressure gradient direction of the pressure gradient generated by the membrane structure is substantially parallel to the membrane structure;
16. A method of generating sound according to claim 15. The step of generating the pressure gradient having the pressure gradient direction within the chamber includes:
generating said pressure gradient having said pressure gradient direction within said chamber for an interval;
said interval being within half of an operating cycle;
said operating cycle is the reciprocal of said operating frequency;
24. A method of generating sound according to claim 23. The membrane structure has a first membrane portion and a second membrane portion, and the step of generating the pressure gradient having the pressure gradient direction includes:
compressing a first portion of the chamber by actuating the first membrane portion during an interval;
expanding a second portion of the chamber by actuating the second membrane portion during the interval;
the direction of the pressure gradient is from the first portion to the second portion;
24. A method of generating sound according to claim 23. said air pulse generator having a membrane structure, said step of forming said air waves at said operating frequency:
said membrane structure generating a first air pressure gradient at a location within said chamber during a first interval within the first half of an operating cycle;
said membrane structure generating a second air pressure gradient at said location within said chamber during a second interval within the second half of said operating cycle;
said first air pressure gradient and said second air pressure gradient have opposite directions;
said operating cycle is the reciprocal of said operating frequency;
16. A method of generating sound according to claim 15. generating said first air pressure gradient having a first magnitude and said second air pressure gradient having a second magnitude;
the first magnitude of the first air pressure gradient and the second magnitude of the second air pressure gradient are substantially the same;
27. A method of generating sound according to claim 26. wherein the membrane structure comprises a membrane portion and said step of forming said air waves at said operating frequency includes:
actuating the membrane portion to produce a membrane movement having a membrane movement direction such that a pressure gradient is formed;
said pressure gradient having a pressure gradient direction is generated due to said membrane movement;
the direction of membrane movement and the direction of pressure gradient are substantially perpendicular to each other;
16. A method of generating sound according to claim 15.

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