JP2023174649A - Air pulse generator generating asymmetrical air pulse - Google Patents

Abstract

To provide an air pulse generator for improving defects of a conventional technology.SOLUTION: An air pulse generator has a membrane structure. The membrane structure is driven so as to form an amplitude modulated ultrasonic air pressure change having an ultrasonic carrier frequency. The membrane structure is driven so as to form an aperture at a rate synchronized with the ultrasonic carrier frequency. The air pulse generator generates a plurality of air pulses according to the amplitude-modulated ultrasonic air pressure change, and the plurality of air pulses are asymmetrical.SELECTED DRAWING: Figure 1

Description

The present invention relates to an air pulse generator, and more particularly to an air pulse generator capable of generating asymmetric air pulses and performing synchronous demodulation.

Speaker drivers and rear enclosures are two major design challenges in the speaker industry. Conventional speakers cannot easily cover the entire audio frequency band from 20Hz to 20kHz, for example. In order to produce sound with sufficiently high sound pressure level (SPL) with high fidelity, both the radiating/transferring surface and the volume/size of the back enclosure of a conventional loudspeaker are required to be sufficiently large. .

Therefore, how to design compact sound generating devices while overcoming the design challenges faced by conventional speakers has become an important objective in this field.

The main object of the present invention is to provide an air pulse generator that improves the drawbacks of the prior art.

In some embodiments of the present disclosure, an air pulse generator comprising:
It has a membrane structure,
the membrane structure is driven to create an amplitude modulated ultrasonic air pressure change having an ultrasonic carrier frequency;
the membrane structure is driven to form an aperture at a speed synchronized with the ultrasound carrier frequency;
An air pulse generating device is provided, the air pulse generating device generating a plurality of air pulses according to the amplitude modulated ultrasonic air pressure change, the plurality of air pulses being asymmetric.

In some embodiments of the present disclosure, an air pulse generator comprising:
modulating means configured to perform a modulating operation such that an amplitude modulated ultrasonic air pressure change having an ultrasonic carrier frequency is generated, the amplitude modulated ultrasonic air pressure change being connected to an input modulating means amplitude modulated according to an audio signal, said input audio signal being an electrical representation of a sound signal;
performing a synchronous demodulation operation on the amplitude modulated ultrasonic air pressure change such that a spectral component of the amplitude modulated ultrasonic air pressure change is shifted by an amount that is an integer multiple of the ultrasonic carrier frequency; demodulating means configured to;
has
The air pulse generator generates a plurality of air pulses by performing the synchronous demodulation operation,
An air pulse generator is provided, wherein the audible spectral components of the plurality of air pulses correspond to the sound signal.

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

1 is a schematic diagram of an air pulse generator according to an embodiment of the invention; FIG. FIG. 3 is a diagram showing waveforms of a demodulated drive signal and a modulated drive signal according to an embodiment of the present invention. 2 is a diagram showing simulation results corresponding to the device of FIG. 1. FIG. 2 is a plot of the simulated frequency response of the sound pressure level of the APG device of FIG. 1; FIG. 2 is a diagram showing simulation results corresponding to the device of FIG. 1. FIG. 2 is a diagram showing simulation results corresponding to the device of FIG. 1. FIG. 1 is a schematic diagram of an air pulse generator according to an embodiment of the invention; FIG. 1 is a schematic diagram of an air pulse generator according to an embodiment of the invention; FIG. 2 is a diagram showing the frequency response of the energy transfer ratio of the device of FIG. 1. FIG. 9 is a diagram showing the frequency response of the energy transfer ratio of the device of FIG. 8. FIG. 9 is a diagram showing one step of the method for manufacturing the device of FIG. 8. FIG. 1 is a schematic diagram of an air pulse generator according to an embodiment of the invention; FIG. FIG. 3 is a diagram showing a drive signal wiring system according to an embodiment of the present invention. FIG. 13 is a diagram showing SPL measurement results with respect to frequency of the device in FIG. 12. 13 is a diagram showing the SPL measurement results for the peak-to-peak voltage of the device in FIG. 12. FIG. 1 is a schematic diagram of an air pulse generator according to an embodiment of the invention; FIG. 1 is a schematic diagram of an air pulse generator according to an embodiment of the invention; FIG. 18 is a diagram showing a snapshot of an FEM (finite element method) simulation pressure profile of a device similar to the device of FIG. 17; FIG. 18 is a diagram showing ear coupler SPL measurement results for frequencies of the device of FIG. 17. FIG. 1 is a schematic diagram of an air pulse generator according to an embodiment of the invention; FIG. 1 is a schematic diagram of an air pulse generator according to an embodiment of the invention; FIG. 1 is a schematic diagram of an air pulse generator according to an embodiment of the invention; FIG. 1 is a schematic diagram of an air pulse generator according to an embodiment of the invention; FIG. 1 is a schematic diagram of an air pulse generator according to an embodiment of the invention; FIG. FIG. 4 is a diagram illustrating timing alignment of opening of a virtual valve according to an embodiment of the present invention. 1 is a schematic diagram of an air pulse generator according to an embodiment of the invention; FIG. FIG. 3 is a diagram illustrating timing alignment of virtual valve openings according to an embodiment of the invention. FIG. 3 shows full-period pulses within one operating cycle with different degrees of asymmetry; 1 is a schematic diagram of a top view of an air pulse generator according to an embodiment of the invention; FIG. 30 is a schematic diagram of a top view of the air pulse generator of FIG. 29; FIG. 1 is a top view of an air pulse generator according to an embodiment of the invention. FIG. 32 is a diagram showing waveforms of two sets of modulation (demodulation) drive signals of the air pulse generator of FIG. 31. FIG. 1 is a top view of an air pulse generator according to an embodiment of the invention. FIG. FIG. 3 shows a system perspective view of the function of each component and their corresponding frequency domain effects;

A fundamental aspect of the invention relates to an air pulse generator, and more particularly to an air pulse generator comprising modulation means and demodulation means, said modulation means comprising ultrasonic air pressure waves/fluctuations having a frequency f _UC . (UAW), the amplitude of which is modulated according to the input audio signal S _IN , which is an electrical (analog or digital) representation of the audio signal SS. This amplitude modulated ultrasonic air pressure wave/change (AMUAW) is then synchronously demodulated by the demodulation means, and the spectral components embedded in the AMUAW are shifted by ±nf _UC (n is a positive integer). Ru. Here, n is a positive integer. As a result of this synchronous demodulation, the spectral components of the AMUAW corresponding to the audio signal SS are partially transferred to baseband, resulting in the reproduction of the audible audio signal SS. Here, the amplitude modulated ultrasonic air pressure wave/change AMUAW corresponds to a carrier component with an ultrasonic carrier frequency f _UC and the modulation component corresponds to the input audio signal S _IN .

FIG. 1 shows a schematic diagram of an air pulse generation (APG) device 100 according to one embodiment of the invention. The device 100 may be applied as a sound generation device that generates an acoustic sound in response to an input (audio) signal S _IN , but is not limited thereto.

Device 100 has device layer 12 and chamber-defining layer 11 . Device layer 12 has walls 124L, 124R and support structures 123R, 123L that support the thin film layers that are etched down to flaps 101, 103, 105, and 107. In one embodiment, the device layer 12 is formed in a MEMS (small electromechanical systems) manufacturing process using, for example, a 250-500 μm thick Si substrate that is etched to form 123L/R and 124R/L. It may be manufactured by. In one embodiment, a thin layer, typically 3-6 μm thick, composed of a silicon-on-insulator SOI or a POLY-on-insulator POI layer is etched on top of this Si substrate, with flaps 101, 103, 105 and 107 is formed.

Chamber-defining layer (which may also be referred to/named a "cap" structure) 11 has a pair of chamber side walls 110R, 110L and a chamber ceiling 117. In one embodiment, chamber-defining layer (or cap structure) 11 may be manufactured using MEMS manufacturing techniques. A resonant chamber 115 is formed between the chamber defining layer 11 and the device layer 12.

In other words, the device 100 may be considered to have a membrane structure 10 and a cap structure 11 with a chamber 115 formed therebetween. Membrane structure 10 can be viewed as including a modulating portion 104 and a demodulating portion 102. (Modulation) The modulation portion 104 with flaps 105 and 107 is configured to form and activate ultrasonic air/sound waves within the chamber 115, where the air/sound waves are a type of air pressure that varies both in time and space. It can be seen as a change. In one embodiment, the ultrasonic air/acoustic wave or air pressure change may be an amplitude DSB-SC (double sideband suppressed carrier) modulated air/acoustic wave with an ultrasonic carrier frequency f _UC . The ultrasound carrier frequency f _UC may be, for example, in the range of 160kHz to 192kHz, which is significantly greater than the maximum frequency of human audible sound.

Hereinafter, the terms air wave and acoustic wave will be used interchangeably.

(Demodulation) A demodulation section 102 having flaps 101 and 103 is configured to operate in synchronization with the modulation section 102, and converts the spectral components of the DSB-SC modulated acoustic wave generated by the modulation section 104 into ±n×f _UC , where n is a positive integer, generates air pulses toward the environment according to the ultrasonic air waves within chamber 115, and the baseband frequency components of the air pulses (within chamber 115) (generated by the demodulator 102 according to the ultrasonic air waves) becomes the input (audio) signal S _IN or corresponds to/is related to the input (audio) signal S _IN . Low frequency components of the air pulses represent frequency components of the air pulses that are within the audible spectrum (eg, below 20 or 30 kHz). In this application, baseband may generally be referred to as, but not limited to, the audio spectrum.

In other words, in sound generation applications, the modulating section 104 may be operated to form a modulated air wave according to the input audio signal S _IN , and the demodulating section 102 may be operated synchronously with the modulating section 104. , generates a plurality of air pulses having its low frequency component as (or corresponding to/related _{to) the input audio signal S IN .} Typically, in sound production applications where f _UC is much higher than the highest human audible frequency, such as f _UC ≥ 96 kHz ≒ 5 × 20 kHz, natural/environmental low-pass filtering effects on multiple air pulses (walls, floors, , caused by the physical environment such as ceilings, furniture, or high propagation losses such as sound waves and the human auditory system such as the ear canal, eardrum, malleus, incus, and stapes) that are perceived by the listener. is only the audible sound or music represented by the input audio signal S _IN .

Illustratively, FIG. 34 conceptually/schematically illustrates the effect of the modulation (demodulation) operation by showing the frequency spectra of the signal before and after the modulation (demodulation) operation. In Figure 34, the modulation operation produces an amplitude modulated ultrasonic acoustic/air wave UAW, shown as W(f), according to the input audio signal S _IN which is an electrical (analog or digital) representation of the acoustic signal SS. The spectrum of S _IN /SS with the spectrum represented by S(f) in FIG. A synchronous demodulation operation that produces an ultrasonic pulse array UPA (containing multiple pulses) with a spectrum denoted as Z(f) converts the spectral components of the ultrasonic acoustic/air wave UAW to ±n × f _UC (where n is an integer ), the spectral components of the ultrasonic air wave UAW corresponding to the acoustic signal SS are partially carried to baseband. Therefore, as can be seen from Z(f), the baseband component of the ultrasonic pulse array UPA is significant compared to the amplitude modulated UAW W(f). The ultrasonic pulse array UPA propagates towards the surroundings. Due to the natural/physical environment and the inherent low-pass filtering effects of the human auditory system, the resulting spectrum Y(f) corresponding to the audio signal SS can be reproduced.

Unlike traditional DSB-SC amplitude modulation, which uses a sinusoidal carrier, W(f) can vary from ±3 × f _UC , ±5 × f _UC , and higher harmonics of f _UC (in Figure 34 (not shown). This is because the carrier wave of the modulation of the present invention is not a purely sinusoidal wave.

Referring again to FIG. 1, in one embodiment of synchronous demodulation operation, demodulator 102 may be activated to form aperture 112 at a time and location corresponding to/aligned with the peak of the modulated air wave. . In other words, when the modulated air wave reaches a peak at the location of the aperture 112, the demodulator 102 may operate such that the aperture 112 also reaches its peak.

In the embodiment illustrated in FIG. ) λ _UC , meaning that the tips of flaps 101 and 103 are (substantially) λ _UC /2 apart from side walls 111 L and 111 R, or from side wall surfaces 111 L and 111 R. Here, λ _UC represents the wavelength corresponding to the ultrasonic carrier frequency f _UC , ie, λ _UC =C/f _UC , and C is the speed of sound.

In one embodiment, the demodulator 102 may be operated to form the aperture 112 with a valve opening rate synchronized to the ultrasound carrier frequency f _UC . In the present invention, when the valve opening speed is synchronized with the ultrasonic carrier frequency f _UC , the valve opening speed is usually a value obtained by multiplying the ultrasonic carrier frequency f _UC by a rational number, that is, f _UC × (N/M). It means that. Here, N and M are integers. In one embodiment, the valve opening rate (of aperture 112) may be the ultrasonic carrier frequency f _UC . For example, the valve/aperture 112 may open every actuation period T _CY , where the actuation period T _CY is the reciprocal of the ultrasound carrier frequency f _UC , ie, T _CY =1/f _UC .

Also in the present invention, the modulation (demodulation) section 102/104 is used to indicate a modulation (demodulation) flap pair. Furthermore, the demodulator (or flap pair) 102 that forms the aperture 112 may be regarded as a virtual valve, and may perform opening and closing movements (periodically) according to a specific valve/demodulation drive signal to form the aperture 112.

In one embodiment, the modulator 104 substantially creates a mode 2 (or second harmonic) resonance (or standing wave) within the resonant chamber 115, such as the pressure profile P104 and airflow profile U104 shown in FIG. may be generated. In this regard, the spacing between sidewall surfaces 111L and 111R substantially defines a total wavelength λ _UC corresponding to the ultrasound carrier frequency f _UC , ie, W115≈λ _UC =C/f _UC . Furthermore, in the embodiment shown in FIG. 1, the free ends of modulating flaps 105/107 are located by side walls 110L/110R.

It should be noted that intermodulation (or cross-coupling) may occur between the modulation generating the modulated air wave and the demodulation forming the aperture 112, which may degrade the resulting sound quality. . To improve sound quality, it is desirable to minimize intermodulation (or cross-coupling). To achieve this (i.e. to minimize cross-coupling between modulation and demodulation), modulation flaps 105 and 107 are driven to have common mode movement, and demodulation flaps 101 and 103 are driven to have a common mode movement. driven to have dynamic mode movement. By modulating flaps 105 and 107 having common mode movement is meant that flaps 105 and 107 are actuated/driven at the same time and move toward the same direction. By demodulating flaps 101 and 103 having differential mode movement is meant that flaps 101 and 103 are actuated simultaneously and move in opposite directions. Furthermore, in one embodiment, flaps 101 and 103 may be actuated to move in opposite directions with (substantially) the same displacement/magnitude.

The demodulating section 102 substantially generates mode 1 (or first harmonic) resonance (or standing wave) within the resonant chamber 115 as the pressure profile P102 and air flow profile U102 formed by the demodulating section 102 shown in FIG. may be generated. Therefore, the demodulator 102 operates at a valve operating/driving frequency f _{D_V} (corresponding to the valve/demodulating drive signal) such that W115≈λ _{D_V} /2. Here, λ _{D_V} = C/f _{D_V} and the valve operating/driving frequency is half of the ultrasound carrier frequency Fuc, ie, f _{D_V} = fuc/2.

Common mode movement and differential mode movement can be driven by modulation (demodulation) drive signals. FIG. 2 shows waveforms of demodulated drive signals S101, S103 and modulated drive signal SM. Modulation drive signal SM is used to drive modulation flaps 105 and 107. Demodulation drive signals (or valve drive signals) S101 and S103 are used to drive demodulation flaps 101 and 103, respectively.

In one embodiment, the modulated drive signal SM can be considered a pulse amplitude modulated (PAM) signal that is modulated according to the input audio signal S _IN . Furthermore, unlike conventional PAM signals, the polarity (relative to constant voltage) of signal SM is toggled within one actuation cycle (period) _TCY . In general, the modulated drive signal SM contains pulses with alternating polarity (for a constant voltage), the envelope/amplitude of the pulses being (substantially) the same as the AC (alternating current) component of the input audio signal S _IN . is or is proportional to/corresponds to it. In other words, the modulated drive signal SM can be considered as having a pulse amplitude modulated signal or as having PAM modulated pulses with alternating polarity for a constant voltage. In the embodiment shown in FIG. 2, the toggling rate of the modulated drive signal SM is 2×fuc, which means that the polarity of the pulses in the modulated drive signal SM alternates/toggles twice within one working period T _CY . It means that.

The demodulated drive signals S101 and S103 include two drive pulses with equal amplitude and opposite polarity (for a constant/average voltage). In other words, at a particular time, a given S101 contains a first pulse with a first polarity (for a constant/average voltage) and S103 contains a second pulse (for a constant/average voltage). , the first polarity is opposite to the second polarity. As shown in Figure 2, the toggling speed of the demodulated drive signals S101/S103 is fuc, which means that the polarity of the pulses in the demodulated drive signals S101/S103 alternates once within one operating period T _CY . / means toggle. Therefore, the toggling speed of the modulated drive signal (SM) is twice the toggling speed of the demodulated drive signals S101/S103.

The S101/S103 slope (and associated shadow area) is a simplified diagram representing energy reuse during transitions between voltage levels. Note that the transition periods of the signals S101 and S103 overlap. Energy reuse may be achieved by using the characteristics of the LC oscillator if most of the piezoelectric actuators of the flap 101/R are capacitive loads. For more information on energy recycling concepts, reference may be made to US Pat. No. 11,057,692, which is incorporated herein by reference. Note that the piezoelectric actuator is provided as one embodiment, and it should be noted that the piezoelectric actuator is not limited thereto.

To emphasize that flap pair 102 is driven differentially, signals S101 and S103 may be denoted -SV and +SV, which means that the drive signals of this pair have the same waveform but with different polarities. indicates that they are different. In the explanation, as shown in FIG. 2, -SV is for S101, and +SV is for S103, but the present invention is not limited to this. In one embodiment, S101 may be +SV and S103 may be -SV.

In another embodiment, there is a DC bias voltage V _BIAS and under the circumstances that drive signal S101=V _BIAS -SV, S103=V _BIAS +SV, V _BIAS ≠103. Such variations should be considered within the scope of this disclosure.

Furthermore, FIG. 2 shows the difference in toggling speed between the modulated drive signal SM and the demodulated drive signal ±SV. The relative phase delay between the modulated drive signal SM and the demodulated drive signal ±SV means timing alignment, which may be adjusted according to the actual requirements.

In one embodiment, the drive circuit generating the signals SM and ±SV may have a subcircuit configured to generate a (relative) delay between the modulated drive signal SM and the demodulated drive signal ±SV. good. The details of the subcircuits that generate the delays are not limited. Known techniques can be incorporated into the sub-circuits. This is within the scope of the present invention because as long as the sub-circuit can generate delays to meet timing alignment requirements (detailed below), the requirements of the present invention are met.

It is noted that the tips of flaps 101 and 103 are at substantially the same location (centered between sidewalls 111L and 111R) and are subject to substantially the same air pressure at that location. Additionally, flaps 101 and 103 move differentially. Therefore, the movement of the tips of the flaps 101 and 103 has a common mode rejection behavior similar to that known in the art of analog differential OP amplifier circuits, which This means that the displacement difference, or |d ₁₀₁ −d ₁₀₃ |, is almost unaffected by the air pressure created by the modulation flaps 105 and 107.

Common mode cancellation or modulator-demodulator separation can be explained with reference to FIG. 3. FIG. 3 shows simulation results generated from the equivalent circuit model of the device 100. Curves d ₁₀₁ and d ₁₀₃ represent the movement/displacement of the tips of flaps 101 and 103, respectively. As can be seen from Fig. 3, d ₁₀₁ and d ₁₀₃ vary considerably (P104) due to the sound pressure generated by the modulating flaps 105/107, but the curve shown by d ₁₀₁ - d ₁₀₃ in Fig. 3 The differential motion represented by remains (substantially) constant. That is, the width/gap of the valve opening 112 remains constant as the modulating portion 104 operates. In other words, the movement of the modulator has a negligible effect on the functionality and characteristics of the demodulator, and this is what is meant by "modulator-to-demodulator-isolation." It is.

On the other hand, regarding demodulator-to-modulator-isolation, as can be seen from FIG. The pressures exerted by P102 on flaps 105 and 107 have substantially the same magnitude and opposite polarity, causing changes in the movement of flaps 105 and 107 of equal magnitude but opposite polarity. (according to P102). This produces two ultrasound waves (one 105, the other 107) of the same magnitude but varying in opposite polarity. When these two ultrasound waves propagate to a position above the valve opening 112 (indicated by the dotted area shown in FIG. 1), they are combined into one pressure. This "meeting" location occurs at the center of the device 100 along the X-axis or A net residual is produced that is largely free from the interference of vessel/virtual valve operation.

Illustratively, Figure 4 shows that under conditions where S _IN is a 10-tone equal-amplitude test signal (within 650 to 22 kHz and with equal logarithmic scale spacing) and an equivalent circuit simulation model of device 100 is used. , the simulated frequency response of SPL (sound pressure level) measured 1 meter away from the device 100 is plotted. In the current simulation, the ultrasound carrier frequency is set to fuc=192kHz and the valve operating frequency is set to _{fD_V} = _fUC /2=96kHz.

The demodulator-to-modulator separation can be explained by the absence of extraneous spectral components around about 96 kHz (indicated by the block arrow in FIG. 4). This indicates a high level of separation.

As a result, the motion interference of these two flap pairs (101/103 vs. 105/107) is minimized through the orthogonality/arrangement of the differential mode (on the demodulator) to the common mode (on the modulator).

Additionally, the percentage of time that the valve remains open, ie, the duty factor, is an important factor affecting the output of the device 100. Increasing the amplitude of the driving voltages S101 and S103 increases the amplitude of the movement of the flaps 101 and 103, which increases the maximum opening width of the valve opening 112, and by increasing the driving voltage, the duty factor of the valve opening increases. will also rise. That is, the duty factor of the valve opening 112 and the maximum opening width/gap of the valve opening 112 can be determined by the driving voltages S101 and S103.

As the duty factor of valve opening approaches 50%, as in the example shown in Figure 5 generated from one of the equivalent circuit simulation models mentioned above, it is shown as the curve labeled V(Opening) > 0. The period of each valve opening overlaps with the same half-period of the amplitude modulated ultrasonic standing wave at the top of the valve opening 112 (indicated by the dotted area in FIG. 1). By synchronizing and timing the opening and closing of the valve opening 112 with the standing wave in the chamber, shown as the curve labeled V(p_vlv) in FIG. 5, the curve labeled V(ep_vlv) , a well-shaped output pressure pulse is produced.

In Figure 5, the curve labeled V(d2)-V(d3) represents the difference in displacement of flaps 101 and 103, i.e. d101-d103, and the curve labeled V(aperture) represents the virtual It represents the degree of opening of the valve 112. When |V(d2)−V(d3)|>TH, V(open)>0, where TH is the thickness of flaps 101 and 103, and the width of the slit between flaps 101 and 103. , a threshold defined by parameters such as boundary layer thickness. A suitably shaped V(ep_vlv) may represent that the pulse denoted by V(ep_vlv) is highly asymmetric, unlike V(p_vlv) which has a high degree of symmetry. The asymmetry of the output pressure pulse indicates a low frequency content (i.e., a frequency content in the audio range) of the air pulses produced by the air pulse generator, or APG device for short, which is a desirable feature for an APG device. The higher the asymmetry, the stronger the baseband frequency component of the air pulse. A reduced view of FIG. 5 is shown in FIG. 6, which shows the asymmetry of V(ep_vlv) corresponding to the envelope of a 1.68 kHz baseband audio signal. In the present invention, the opening (112) is opened/opened when the difference in displacement between the flap (101) and the flap (103) is larger than a threshold value, for example, |V(d2)−V(d3)|>TH. formed or in an open state; otherwise closed or in a closed state.

Furthermore, the maximum power output occurs when the duty factor of valve opening, defined as |V(d2)−V(d3)|>TH, is 50% or slightly greater, e.g. in the range 55-60%. are observed, but are not limited to this. However, when the duty factor of valve opening is sufficiently higher than 50%, such as 80-85%, more than half a period of the ultrasonic standing wave in the chamber passes through the valve, and the constant wave with different polarity passes through the valve. The active portions cancel each other out, resulting in a lower net SPL output from the device 100. Therefore, it is usually desirable to keep the valve opening duty factor close to 50%, typically in the 50% to 70% range (duty factors in the range of 45% to 70% are within the scope of the invention).

In addition to the duty factor, in order to ensure modulator-to-demodulator isolation, the resonant frequency f _{R_V} of the demodulation flaps 101/103 is proposed to deviate sufficiently from the ultrasound carrier frequency fuc, which is different from the design Become a factor.

For any given thickness of the flaps 101/103, under the constraint of a duty factor of valve opening equal to 50%, the higher the resonance-to-drive ratio (f _{R_V} : f _{D_V} or f _{R_V} / f _{D_V} ) , it can be observed (from the equivalent circuit simulation model) that the valve can be opened wider. The output of the device 100 is positively related to the maximum width that the valve opens, so it is desirable to have a resonance-to-drive ratio greater than one.

However, when f _{R_V} is within the range of f _UC ±max (f _SOUND ), flaps 101/103 begin to resonate with the AM ultrasound standing waves, and a portion of the ultrasound energy is transferred to the flaps 101/103. converted to common mode deformation. Here, max(f _SOUND ) may represent the maximum frequency of the input audio signal S _IN . Such a common mode deformation of the flaps 101/R changes the volume of the upper part of the flaps 101/103, resulting in pressure fluctuations in the chamber 105 in the vicinity of the valve opening 112 over the affected frequency range. occurs, resulting in a decrease in SPL output.

To avoid frequency response variations induced by valve resonance, it is preferable to design the flaps 101/103 with a resonant frequency outside the range of (f _UC ±max(f _SOUND ))×M. Here, M is a safety margin to cover factors such as, but not limited to, manufacturing tolerances, temperature, and height. As a rule of thumb, it is usually significantly lower than f _UC , such as when f _{R_V} ≤ (f _UC - 20kHz) × 0.9, or significantly higher than f _UC , such as f _{R_V} ≥ (f _UC + 20kHz) × 1.1. It is desirable to have f _{R_V} . It should be noted that 20kHz is used because it is well accepted as the highest human audible frequency. For applications such as HD/Hi-Res audio, 30kHz or 40kHz may be taken as max(f _SOUND ) and the above formula may be modified accordingly.

It is also assumed that w(t) and z(t) represent functions of time for the amplitude modulated ultrasonic acoustic/air wave UAW and the ultrasonic pulse array UPA (including multiple pulses). Since the apertures 112 are formed periodically with an aperture ratio of the ultrasonic carrier frequency f _UC , they are denoted as r(t) and can be expressed as r(t) = z(t)/w(t), The function of the ratio of z(t) to w(t) has an aperture ratio of the ultrasound carrier frequency f _UC and is periodic. In other words, z(t) can be considered as the multiplication of w(t) and r(t) in the time domain, i.e., z(t) = r(t)・w(t), and for UAW The synchronous demodulation operation performed can be viewed as a multiplication of w(t) and r(t) in the time domain. This means that Z(f) can be seen as the convolution of W(f) and R(f) in the frequency domain, i.e. Z(f)=R(f)*W(f), where: * represents a convolution operator, meaning that the synchronous demodulation operation performed on the UAW can be considered as a convolution of W(f) and R(f) in the frequency domain. When r(t) is periodic in the time domain with a rate of frequency f _UC , R(f) is discrete in the frequency domain and the frequency/spectral components of R(f) are equal by f _UC . Note that they are spaced apart at intervals. Therefore, the convolution of W(f) with R(f), or the synchronous demodulation operation, involves the step of shifting W(f) (or the spectral components of the UAW) by ±n × f _UC (where n is an integer). have/contain. Here, r(t)/w(t)/z(t) and R(f)/W(f)/Z(f) form a Fourier transform pair.

FIG. 7 is a schematic diagram of an APG device 200 according to an embodiment of the invention. Device 200 is similar to device 100 and therefore the same reference numerals are used. Unlike device 100, device 200 further includes an enclosure 14. A chamber 125 is formed between the surrounding structure 14 and the cap structure 11. Vents 113L/R may be formed in the ceiling 117 located at λ _UC /4 from the side walls 111L/R, respectively, on the nodes of the ultrasonic steady pressure wave P104, as indicated by lines 135/137. Be noted.

The purpose of vent 113L/R in FIG. This minimizes the difference between the average pressure inside chamber 115 and the average pressure outside the surrounding area, and the function of chamber 125 is to allow air to flow into chamber 125 by the air flow. The objective is to prevent these airflows from forming additional audible acoustic signals. By placing the vents 113L/R on the nodes of the steady pressure wave, the spectral components surrounding f _UC are prevented from exiting the chamber 115, and demodulation forms a UPA (Ultrasonic Pulse Array) that produces the desired APPS ( pneumatic pulse speaker) effect is produced.

In the present invention, an APG device with an APPS effect generally means that the baseband frequency component (particularly the frequency component in the audio band) embedded in the air pulse output by the APG device at the ultrasonic carrier frequency is observable. It means that it not only exists, but also has a certain amount of strength. In an APG device that produces the APPS effect, the spectrum of the electrical input signal S _IN is converted into an acoustic signal within the baseband of the audible spectrum (low frequency compared to the carrier frequency) through the generation of multiple air pulses by the APG device. , which is suitable for use in sound generation applications. The baseband strength produced through the APPS effect is related to the amount or degree of asymmetry in the air pulse produced by the APG device. Note that the asymmetry will be described later.

It is noted that the support structures 123L and 123R of the device 100 or 200 have parallel and straight walls (to the X axis) and the space/channel between 123L and 123R acts as an acoustic outlet. . Simulation results using FEM (Finite Element Method) show that when the frequency exceeds 350kHz, a lateral standing wave along the X direction begins to form between the 123L/123R walls, and the output begins to self-annihilate. It has been shown that Such transverse resonance induced self-nullification phenomenon reduces the energy transfer ratio over the 123L-123R wall height (Z direction).

To avoid this problem, a horn-shaped outlet is proposed. For example, FIG. 8 is a schematic diagram of a portion of an APG device 300 according to an embodiment of the invention. Similar to device 100, device 300 has flaps 101 and 103 fixed on support structures 123L'' and 123R'', respectively, and openings that generate a plurality of air pulses directed to the surrounding environment via outlet 320. 112. Unlike support structures 123L and 123R of apparatus 100, which have straight, parallel walls, the walls of support structures 123L" and 123R of apparatus 300 are oblique and are at an angle θ non-perpendicular to the X axis or direction. has. A horn-shaped outlet 320 is formed. The non-orthogonal angle θ may be designed according to actual requirements. In one embodiment, the non-orthogonal angle θ may be 54.7°, but is not limited thereto. In the present invention, a horn-shaped outlet generally refers to an outlet whose outlet or tunnel dimensions gradually widen from the membrane structure toward the surrounding environment.

9 and 10 show the frequency response of the energy transfer ratio of devices 100 and 300 for eight different displacements of flaps 101 and 103, respectively. Here, Dvv=k means that the displacement of the tip of each flap is kμM, resulting in a differential movement of 2kμM. 9 and 10 were simulated using FEM. By comparing Figures 9 and 10, it can be seen that the device 100 has an energy transfer ratio such that the frequency increases above 170kHz and begins to roll off beyond 170kHz, with some jumps and dips. generate. On the other hand, the device 300 maintains an upward trend above about 120 kHz and produces an energy transfer ratio with a smoother frequency response for frequencies above 170 kHz. This means that the frequency response of the energy transfer ratio of device 300 (above 170 kHz) is much smoother than that of device 100, which means that the ultrasonic pulse rate (i.e., the ultrasonic carrier frequency f _UC ) and its higher harmonics (e.g., n×f _UC ). Additionally, device 300 produces an energy transfer ratio that is approximately five times higher than that produced by device 100. Therefore, it can be explained from FIGS. 9 and 10 that the horn-shaped outlet provides a better energy transfer ratio for the APG device.

FIG. 11 shows an embodiment of a two-step etch/fabrication method that etches the wall at two different angles. First, the 123R”/123L” walls are etched with a taper angle (as shown in Figure 11(b)), then the tapered walls are etched using a spray coating method (as shown in Figure 11(c) ) covered by photoresist or spin-on dielectric. Next, the photoresist or spin-on dielectric is patterned by a photolithographic method (as shown in Figure 11(d)), and then the 124L and 124R walls are aligned at right angles (as shown in Figure 11(e)). etched. The manufacturing method described above is for illustrative purposes only and the scope of the invention is not limited thereto.

FIG. 12 is a schematic diagram of an APG device 400 according to one embodiment of the invention. Apparatus 400 is modified from FIG. 7 of US patent application Ser. No. 17/553,806 and is similar to apparatus 100 shown in FIG. 1 of the present invention. Unlike device 100, device 400 includes only flap pair 102 (and not flap pair 104). The flap pair 102 performs a modulating operation (forming an amplitude modulated air pressure fluctuation at the ultrasonic carrier frequency f _UC ) and a demodulating operation (forming the aperture 112 in synchronization with the amplitude modulated ultrasonic carrier wave at the frequency f _UC ). and generating an air pulse according to an envelope of said amplitude modulated ultrasonic air pressure change.

In FIG. 12, U104 and P104 represent the pressure profile and airflow profile formed by the flap pair 102 in response to the modulated drive signal SM, and U102 and P102 represent the pressure profile and airflow profile formed by the flap pair 102 in response to the demodulated drive signal ±SV. represents the pressure profile and airflow profile formed by the Here, the demodulation drive signals are expressed as ±SV and the flap pair 102 is driven differentially to perform the demodulation operation (the demodulation drive signals +SV and -SV have the same magnitude but opposite polarity). It is emphasized that For example, S101 and/or S103 above may be represented by -SV and/or +SV.

In other words, the modulator and demodulator are co-located in/as the flap pair 102. Similar to device 100, the membrane structure 10 of flap pair 102 of device 400 is operated to have common mode movement to perform modulation as well as differential mode movement to perform demodulation.

That is, the "modulation operation" and the "demodulation operation" are performed simultaneously by the same pair of flaps 102. As a result, "modulation operation" and "demodulation operation" can be co-located using a new drive signal wiring method as shown in FIG. 13. If the device 400 has an actuator 101A/103A disposed on the flap 101/103, and the actuator 101A/103A has an upper electrode and a lower electrode, both the upper electrode and the lower electrode are connected to the modulated drive signal SM and the demodulated drive Signals ±SV may also be received.

In one embodiment, one electrode of actuator 101A/103A receives a common mode modulated drive signal SM and the other electrode receives a differential mode demodulated drive signal S101(-SV)/S103(+SV). You may. For example, diagrams 431 and 433 shown in FIG. 13 show details of region 430 shown in FIG. 12. As shown in diagrams 431 and 432, the bottom electrodes of actuators 101A/103A receive the common mode modulated drive signal SM, and the top electrodes of actuators 101A/103A receive the differential mode demodulated drive signal S101 (-SV )/S103 (+SV) is received. A suitable bias voltage V BIAS may be applied to either the bottom electrode (shown in diagram 432) or the top electrode (shown in diagram 433), and the bias voltage V _BIAS can be determined according to actual requirements.

In some embodiments (shown in FIG. 433), one electrode of actuators 101A/103A receives both the common mode modulated drive signal SM and the differential mode demodulated drive signal S101(-SV)/S103(+SV). The other electrode may be biased appropriately. In the embodiment shown in diagram 433, the bottom electrode receives the common mode modulated drive signal SM and the differential mode demodulated drive signal S101(-SV)/S103(+SV), and the top electrode is biased.

In the drive signal wiring scheme shown in FIG. 13, the applied signal of one actuator (e.g., 101A) is -SM-SV or has -SM-SV, and the applied signal of the other actuator (e.g., 103A) is −SM+SV, or achieves the goal of having −SM+SV (V _BIAS is not considered). It is noted that the drive signal wiring scheme may be modified or changed according to the actual situation/requirements. The common mode signal component between the two applied signals applied to the flap pair 102 has a modulating drive signal SM (+V _BIAS ), and the differential signal component between the two applied signals applied to the flap pair 102 has a demodulated drive signal SM (+V BIAS ). As long as the drive signal SV is present, the requirements of the invention are met and the invention falls within the scope of the invention. Here (or in general), the common mode signal component between two arbitrary signals a and b is expressed as (a + b)/2, while the differential signal component between two arbitrary signals a and b The signal components of the mode may be expressed as (ab)/2.

Furthermore, to minimize cross-coupling between modulation operation (as a result of drive signal SM) and demodulation operation (as a result of drive signal ±SV), in one embodiment flaps 101 and 103 are It is noted that they are arranged in mirror/symmetrical pairs both in their mechanical structure, dimensions, and electrical properties. For example, the cantilever length of flap 101 should be equal to that of 103, the membrane structure of flap 101 should be the same as flap 103, and the position of virtual valve 112 should be equal to that of flap 101 and flap 103. The actuator pattern deposited on the flap 101 should mirror the pattern of the flap 103 and should be centered between and equidistantly spaced from the two supporting walls 110 of the flap 101. The metal wiring for the actuator deposited on and 103 needs to be symmetrical. Here, some items are named because of the mirror/symmetrical pair (or flaps 101 and 103 are mirror/symmetrical), but are not limited thereto.

FIG. 14 shows a set of frequency response measurements of a physical embodiment of device 400 in an IEC711 occluded ear emulator. The device 400 is driven using the drive scheme shown in diagram 431, the Vrms for the modulated drive signal SM for the bottom electrode is 6Vrms, and the Vpp (peak-to-peak for the demodulated drive signal ±SV for the top electrode) is 6Vrms. The peak voltage) is swept from 5Vpp to 30Vpp and a GRAS RA0401 ear simulator is used to measure the acoustic results. The operating frequency of the device 400 (i.e. the ultrasound carrier frequency f _UC ) is 160 kHz and the device dimensions are designed accordingly (e.g. for C = 336 m/s, W115≈λ _UC = C/f _UC ≒2.10mm). As can be seen from FIG. 14, the device 400 is capable of producing high SPL sound in the low frequency band (at least 99 dB for frequencies below 100 Hz).

Furthermore, FIG. 15 shows an analysis of the measurement results of the device 400 shown in FIG. 14. In Figure 15, the SPL at 100Hz (thick dashed line) and 19Hz (thick solid line) in Figure 14 is plotted against Vvtop (Vpp), where Vvtop (Vpp) is, as shown in connection diagram 431 This is the voltage between the peaks of the demodulated drive signal applied to the upper electrode. It can be seen from FIGS. 14 and 15 that as Vvtop increases, SPL increases. Simulation results of an equivalent lumped circuit model of device 100 also show that as the amplitude of the demodulated drive signal (valve drive or) increases, the SPL increases. It can therefore be seen that the volume of sound produced by the air pulse generator of the invention can be controlled via the amplitude of the demodulated drive signal.

Based on the results from Figures 14 and 15, the concept of a modulator-demodulator co-location is verified, and the modulation (forming amplitude modulated ultrasonic air pressure changes) and demodulation (forming an asymmetric air pressure change) performed by the device 400 is It can be concluded that forming the apertures synchronously to generate pulses) means that the APPS effect is favorably generated. Accordingly, it may be possible to reduce the chamber width (eg, W115 of device 100).

For example, FIG. 16 is a schematic diagram of an APG device 500 according to one embodiment of the invention. Apparatus 500 is similar to apparatus 400, with flap pair 102 being driven via one of the drive schemes shown in FIG. 13, but not limited thereto. Compared to device 400, the chamber width W115' of device 500 is reduced by half. In one embodiment, the chamber width W115' of the device 500 may be λ _UC /2.

Furthermore, standing waves in the chamber such as 115 in Figure 12 or 115' in Figure 16 are not required, which requires that the chamber width (W115) be λ _UC or λ _UC /2. This means that there is no need to form/maintain/reflect plane waves between the side walls 111R/111R' and 111L/111L'. It is free/flexible to change the shape of the chamber and optimize other factors, e.g. the length of the chamber can be reduced to increase sound production efficiency, which reduces the area of the device. It can be evaluated by SPL per (mm ² ).

FIG. 17 is a schematic diagram of an APG device 600 according to one embodiment of the invention. Device 600 may include subassemblies 610 and 640. In one embodiment, subassemblies 610 and 640 may be fabricated via known MEMS processes, using bonding or adhesive materials such as dry film or other suitable die attach materials/methods. They may be bonded to each other via layer 620. The subassembly 610 itself can be viewed as an APG device (detailed below in FIG. 26 and related paragraphs) that includes a pair of flaps 102 or a membrane structure 10. Subassembly 640 may be viewed as a cap structure.

Similar to device 500, device 600 has a flap pair 102 with flaps 101 and 103 driven via one of the drive schemes shown in FIG. 13, but is not limited thereto. The flap pair 102 of the device 600 forms an amplitude modulated ultrasonic air pressure change with an ultrasonic carrier frequency f _UC , and forms an aperture 112 at a rate synchronized with the ultrasonic carrier frequency f _UC , according to the ultrasonic air pressure change. , is actuated to produce a plurality of air pulses through the outlet and towards the surroundings.

Unlike device 500, a conduit 630 is formed within device 600. Conduit 630 connects the air volume above virtual valve 112 (the slit between flaps 101 and 103) to the external environment. Conduit 630 has a chamber 631, a passageway 632, and an outlet 633 (or zones 631-633). Chamber 631 is formed between membrane structure 10 and cap structure (subassembly) 640. A passageway 632 and an outlet 633 are formed within a cap structure (subassembly) 640.

Chamber 631 may be considered a semi-occlusive compression chamber, and the air pressure within compression chamber 631 may be compressed or rarefied in response to a common mode modulated drive signal SM, and ultrasonic air pressure changes/waves. may be generated and fed directly to passageway 632 via orifice 613. The passageway 632 acts as a waveguide, and its shape and dimensions are optimized so that the pressure fluctuations/pulses generated within the zone/chamber 631 can efficiently propagate outward. The outlet 633 is configured to minimize reflection/deflection and maximize acoustic energy coupling to the surroundings. To achieve this, the tunnel dimensions (eg, the width in the X direction) of the outlet 633 gradually widen toward the periphery, and the outlet 633 may have a horn shape.

In one embodiment, the length/distance L ₆₃₀ of the conduit 630 between the opening 112 (equal to the flap pair 102 or membrane structure 10) and the surface 650 is (substantially) a quarter corresponding to f _UC The wavelength may be λ _UC /4 (eg, with a tolerance of ±10%). For example, if f _UC =192 kHz, L ₆₃₀ may be, but is not limited to, 450 μm. (Referring again to Figure 16) An air pressure wave (as a type of air pressure change) propagates along the ) 112 and the sidewall surfaces 111L'/111R' is observed to be λ _UC /4. In Figure 17, the device 600 folds/rotates the air wave propagation path by 90° to align with the Z direction, and assumes that the air wave or air pressure pulse is emitted directly towards the environment via the Z direction. may be done.

FIG. 18 shows a snapshot of a FEM simulated pressure profile of a device similar to device 600, according to one embodiment of the invention. In FIG. 18, supplementary arrows are presented to represent the polarity/sign of the pressure values. The difference between device 600 and the device shown in FIG. 18 is the addition of a chamfer 635 to subassembly 640 at the interface between chamber 631 and passageway 632 to minimize airflow turbulence. It is. In FIG. 18, the pressure in zone 631 is about +500 Pa and the pressure in zone 632, near 633, is about -500 Pa. The brightest zone provides the pressure nodal plane.

The nodal plane within the zone 632 shows proper formation of wave propagation, and the space/distance between the nodal plane 632 and the nodal plane outside the device is approximately 1.2*λ/2 (where λ=346( m/s)/192 (kHz)), which is close to (and slightly larger than) λ/2. This means that there is uninterrupted pressure wave propagation at the speed of sound. In other words, as shown in FIG. 18, the pressure pulses or air waves generated by the membrane structure of the device 600 are radiated towards the surroundings.

FIG. 19 shows the results of an IEC711 occluded ear coupler SPL measurement versus frequency for the physically implemented device 600. Results corresponding to demodulated drive signals ±SV with 20Vpp and 15Vpp are plotted. Also in Table 1, the parameters of devices 400 and 600 for producing maximum SPL are compared.

As can be seen from FIGS. 14, 19 and Table 1, device 600 is able to achieve slightly higher SPL than device 400 at lower input amplitudes while reducing die size by 40%. This means that the device 600 with conduit 630 is more efficient, both in terms of power consumed and silicon space/area occupied.

Generally, the width W631 of the chamber 631 is significantly smaller than λ _UC /2, for example, in the example of device 600, W631≈570 μM and λ _UC /2≈900 μM. In order for zone 631 to perform chamber compression, the dimensions of chamber 631 must be sufficiently smaller than λ _UC . In one embodiment, the height H631 of chamber 631 may be less than λ _UC /5, ie, H631 < λ _UC /5. It is noted that the width (ie, the dimension in the X direction) of the chamber 631 may be stepped or tapered from the membrane structure 10 towards the passageway 632. All of these cases fall within the scope of the present invention.

FIG. 20 is a schematic diagram of an APG device 700 according to one embodiment of the invention. Similar to device 600, device 700 includes subassemblies 710 and 740 and has a conduit 730 formed therein. Subassembly 710 may be manufactured by a MEMS process and may be considered an APG device. A chamber 705 is formed within subassembly 710. The subassembly 710 may itself be an APG device, with the squeeze mode operation disclosed in U.S. Pat. No. 11,172,310, the virtual valve disclosed in U.S. Pat. Nos. 11,172,310 and 11,043,197, which may be viewed in combination, are herein incorporated by reference.

The conduit 730 has a chamber 731, a passageway/waveguide 732, and a horn-shaped outlet 733 (or zones 731-733) connecting the air volume below the virtual valve 112 to the outside ambient atmosphere. . Unlike device 600, subassembly 740 may be formed/manufactured via techniques such as 3D printing, precision injection molding, stamping, etc. Passageway/waveguide 732 has a first section, which is an orifice 713 etched on the cap of subassembly 740, and a second section formed within subassembly 710, with a gap between the two. , a chamfer 735 may be added to minimize disturbance. Chambers 705 and 731 overlap. The pressure fluctuations/waves generated by flaps 101 and 103 are fed directly into passageway/waveguide 732.

FIG. 21 is a schematic diagram of an APG device 800 according to one embodiment of the invention. Device 800 includes subassemblies 810 and 840. Subassembly 810 may have the same or similar structure as device 500, which can be fabricated by a MEMS process and can be viewed as an APG device, driven by one of the schemes shown in FIG. It may have flaps 101 and 103 that are A virtual valve (opening) 112 is formed. Subassembly 840 may be formed/manufactured via techniques such as 3D printing, precision injection molding, precision stamping. It is noted that subassembly 810 generates multiple airflow pulses through a modulation (demodulation) operation.

A conduit 830 connecting the air volume below the virtual valve 112 to the surrounding external environment is formed within the device 840. Conduit 830 has a (compression) chamber 831, a passage/waveguide 832, and a horn-shaped outlet 833 (or zones 631-633). Compression chamber 831 is configured to convert a plurality of airflow pulses into a plurality of air pressure pulses. Specifically, chamber 831 generates a pressure pulse ΔP _n ∝P _{0_n} ·ΔM _n /M _{0_n} (Equation 1), where M _{0_n} is the air mass within chamber 831 before the start of pulse cycle n. and ΔM _n is the air mass associated with the airflow pulse of pulse cycle n. Equation 1 represents converting the airflow pulse to an air pressure pulse, which propagates into the passageway/waveguide 832. In one embodiment, subassembly 840 within zone 831 may have a brass mouthpiece-like cross-sectional profile.

The passageway/waveguide 832 has an impedance that is close to, matched with, or within ±15% of the compression chamber 831 to efficiently propagate the pressure pulses generated within the zone 831 outward toward the periphery. may be maximized. In one embodiment, propagation efficiency may be optimized by appropriately selecting the cross-sectional area of passageway 832.

In the embodiment shown in FIG. 21, the tunnel dimensions (e.g. _, width in _the Accordingly, it gradually widens towards the periphery. It is noted that the horn shape of the outlet may be designed according to actual specifications. The exit tunnel dimensions can be widened according to, but are not limited to, polynomial, pure line, piecewise line, parabolic, exponential, hyperbolic, etc. As long as the exit tunnel dimensions gradually widen towards the periphery, the specifications of the invention are met and this falls within the scope of the invention.

In order to carry out chamber compression in zone 831, it is proposed that the dimensions of chamber/zone 831 be sufficiently smaller than the wavelength λ _UC corresponding to the operating frequency f _UC . For example, for an embodiment with f _UC = 160 kHz and λ _UC = (346/160) = 2.16 mm, the height H ₈₃₁ is in the range λ _UC /10 to λ _UC /60 (e.g., H ₈₃₁ = λ _UC / 35=62 μm), and the width W ₈₁₅ may be in the range of λ _UC /5 to λ _UC /30 (eg, W ₈₁₅ in the range of 115 μm to 350 μm), but is not limited thereto.

The membrane structure 10 subdivides the volume of space into a resonant chamber 805 on one side and a compression chamber 831 on the other side, and the nature of this subdivision causes the It is noted that the displacements due to common mode movement of flaps 101 and 103 are of the same magnitude but in opposite directions/polarity. In other words, together with the common mode movement of flaps 101 and 103, a push-pull motion is formed, and such push-pull motion increases the pressure difference across flaps 101 and 103 (e.g., by a factor of 2). ), thus increasing airflow when virtual valve 112 is opened.

Specifically, for a compression chamber 831 with a volume V1 and a resonant chamber 805 with a volume V2, the membrane/flap movement resulting in a volume difference DV (assuming DV<<V1, V2) is ΔP _V1 = 1 -V1/(V1-DV)=-DV/(V1-DV)≒-DV/V1 as pressure change in V1 and ΔP _V2 =1-V2/(V2+V)=DV/(V2+DV)≈DV/V2 causing a pressure change in V2 as . The pressure difference between the two volumes may be ΔP _V2 −ΔP _V1 = DV/(V2+DV)+DV/(V1−DV). When V1≒V2≒Va, ΔP _V2 - ΔP _V1 ≒DV/(Va+DV)+DV/(Va-DV)=DV・2Va/(Va ² −DV ² )≒2・DV/Va≒2・ΔP _V2 , which means that the push-pull operation can double the pressure difference between the two sub-spaces separated by flaps 101 and 103.

FIG. 22 is a schematic diagram of an APG device 900 according to one embodiment of the invention. Device 900 includes subassemblies 910 and 940. Subassembly 910 may be manufactured by a MEMS process and may be considered an APG device. Subassembly 940 may be manufactured by 3D printing. Also similar to apparatus 700 or subassembly 710, subassembly 940 has a squeeze mode operation as disclosed in U.S. Pat. No. 11,172,310, a virtual valve as disclosed in U.S. Pat. It may be viewed as a combination of drive methods. In the device 900, the squeeze mode operating chamber 905 and the compression chamber 931 are separated, whereas in the device 700, the squeeze mode operating chamber and the compression chamber are integrated as the chamber 731.

Although the effect of subassembly 810 and subassembly 910 is similar for airflow pulsing, their operating principles are different. Subassembly 810 utilizes resonance, whereas assembly 910 utilizes compression and rarefaction of the squeeze mode operating chamber 905 caused by movement of the membrane (flaps 101, 103). Therefore, the chamber width W ₉₀₅ no longer needs to satisfy any relationship with λ _UC and therefore the size of the chamber 905 may be reduced to any practical/desired extent.

FIG. 23 is a schematic diagram of an APG device A00 according to an embodiment of the present invention. Since resonance is not required, the limitation of a rectangular cross-section of a chamber, such as chamber 905, can be eliminated, allowing more flexibility in geometry for optimizing pressure wave generation or wave propagation to the surroundings. For example, chamber A05 or subassembly A40 may have a brass mouthpiece-like cross-section.

Another embodiment of apparatus A00 of FIG. 23 is a "direct pressure connection." Instead of first passing through orifice 913 as in device 900, the pressure wave generated within compression chamber A05 of device A00 is coupled directly to conduit A32 and then released to the surroundings via outlet A33. . Such direct coupling between the compression chamber and the conduit/outlet eliminates losses caused by orifice 913, resulting in significant efficiency improvements over device 900.

FIG. 24 is a schematic diagram of an APG device B00 according to an embodiment of the present invention. Device B00 is similar to device A00. Unlike device A00, device B00 further has a (cap) structure B11, between which a chamber B05 is formed. A push-pull operation may be implemented with chamber A05 formed on one side of membrane structure 10 and chamber B05 formed on the other side of membrane structure 10, whereby airflow pulses are May be strengthened.

The air pulses generated by subassemblies 810 and 910 may be considered airflow pulses, and subassemblies 840 and 940 may be considered airflow to air pressure converters with trumpet-like cross-sectional profiles. is taken into account. On the other hand, the air pulses generated by subassemblies 610, 710, A10, and B10 may be considered as air pressure pulses, which directly form demodulated/asymmetric air pressure pulses and It can also be efficient.

Subassemblies having internal conduits or conduits having a trumpet-like cross-sectional profile are also disclosed in, but are not limited to, U.S. Pat. No. 8,861,752, or other devices such as No. 8,861,752.

FIG. 25 shows a diagram of the timing alignment of the opening of the virtual valve (VV) 112 of the APG device of the present invention. In FIG. 25, the solid curve represents the flap common mode movement produced by the modulated drive signal SM, and the dark background represents the acoustic resistance corresponding to the virtual bulb. Darker shading means higher resistance (VV closed, the volume inside the chamber is disconnected from the surroundings), lighter shading means lower resistance (VV open, the volume inside the chamber is connected to the surroundings) means.

In Figure 25(a), the opening of the virtual valve (VV) 112 is timed such that the maximum value (first peak) of pressure in the chamber is achieved, which typically occurs when the flap just before reaching their most positive (first peak) common mode displacement. On the other hand, the timing of the closed state of virtual valve 112 is timed such that a minimum value (second peak) of pressure within the chamber is achieved, which typically means that the flaps are at their most negative (second peak). peak) just before reaching the common mode displacement. The timing alignment shown in Figure 25(a), where the maximum opening of VV112 is aligned with the first peak of pressure in the chamber, is to maximize the pulse amplitude of the airflow pulse, which is , devices 100-500 (having a chamber but without a conduit formed therein).

On the other hand, in FIG. 25(b), the timing of the open state of the virtual valve 112 is the timing of the opening of the virtual valve 112 of a membrane (flap) moving towards the first direction, as suggested by the valve timing of gas/piston engines in the automotive industry. The timing of the closed state of the virtual valve 112 is matched to the maximum velocity of common mode movement of the membrane (flap) moving towards a second direction opposite the first direction, while being matched to the maximum velocity of common mode movement of the flap. Aligned. The first direction is from the membrane structure toward the periphery. The timing alignment shown in FIG. 25(b) is to maximize the volume of the airflow pulse, which can be achieved by either device 600 or devices 700 through 900, A00, and B00 (the conduits formed therein). may be suitable for use in chambers with

FIG. 26 is a schematic diagram of an APG device C00 according to an embodiment of the present invention. Device C00 is similar to the APG device shown above and has flaps 101 and 103. Flaps 101 and 103 may be driven by the driving method shown in FIG.

Unlike these devices, device C00 does not have a cap structure. Compared to the previously mentioned APG device, the device C00 has a simpler structure, requires fewer photolithographic etching steps, eliminates complex conduit fabrication steps, and allows two sub-members or sub-assemblies to be assembled together. The need to join is avoided. The manufacturing cost of device C00 is significantly reduced.

Since no chamber is formed under the cap structure to be compressed, the sound pressure generated by the device C00 mainly results from the acceleration of the movement of the flaps (101 and 103). By aligning the timing of the opening of virtual valve 112 (in response to demodulated drive signal ±SV) with the timing of the acceleration of the common mode movement of flaps 101 and 103 (in response to modulated drive signal SM), apparatus C00: Asymmetric air (pressure) pulses can be generated.

It is noted that the space surrounding flaps 101 and 103 is divided into two sub-spaces. One is Z>0, ie +Z subspace, and one is Z<0, ie -Z subspace. For any common mode movement of flaps 101 and 103, a pair of acoustic pressure waves are generated, one in subspace +Z and one in subspace -Z. These two acoustic pressure waves are of the same magnitude but opposite polarity. As a result, when the virtual valve 112 is opened, the pressure differences between the two air volumes in the vicinity of the virtual valve 112 are mutually neutralized. Therefore, when the timing of the differential mode movement reaches its peak, i.e., when timing VV112 reaches its maximum opening, the timing of the acceleration of the common mode movement reaching its peak is aligned with the timing of the acceleration of the common mode movement produced by the common mode movement. The supposed sound pressure is suppressed/eliminated by the opening of the virtual valve 112 and an automatic neutralization occurs between the two sound pressures on the two opposite sides of the flaps 101 and 103. Here, the two sound pressures have the same magnitude but opposite polarity. This means that when virtual valve 112 is opened, device C00 produces (almost) a net air pressure of zero. Thus, when the opening period of the virtual valve 112 overlaps with one period of the (two) polarity of acceleration of the common mode flap movement, the device C00 generates an asymmetric high, single-ended (SE) or SE-like pneumatic waveform. /pulse can be generated.

In the present invention, an SE (like) waveform may mean that it is (substantially) unipolar for a certain level. The SE acoustic pressure wave may represent a waveform that is (substantially) unipolar with respect to ambient pressure (eg, 1 ATM).

FIG. 27 shows a diagram of timing alignment of opening of a virtual valve (VV) according to an embodiment of the invention. The timing alignment scheme shown in FIG. 27 may be applied to device C00. In Figure 27(a), the solid/dashed/dotted curves represent the displacement/velocity/acceleration of the common mode movement of the membrane (flaps 101 and 103) in response to the modulated drive signal SM, and similar to Figure 25, the background Density represents the acoustic resistance caused by the opening and closing operations of VV112. For purposes of illustration, the membrane/flap motion waveform in Figure 27(a) is assumed (or approximately plotted) to be a sine wave with constant amplitude, and the velocity/acceleration waveform is assumed to be the first order of the displacement waveform. / is the second derivative. As shown in Figure 27(a), the timing of the opening of the peak VV is aligned with the timing of the first peak acceleration of the common mode membrane/flap movement towards the first direction, as described above. As a result of the perfect timing alignment, a self-neutralization occurs between the two acoustic pressure waves originating in the +Z and -Z subspaces, resulting in a net acoustic pressure, as shown as the flat portion of the SE pneumatic waveform in Figure 27(b). is suppressed.

Also, as shown in Figure 27(a), the timing at which the VV is closed is aligned with the timing of the second peak acceleration of the common mode membrane/flap movement toward the second direction, and the second direction is , which is opposite to the first direction. Since the VV is closed during/near the second peak acceleration, the sound pressure generated by the second peak acceleration of flaps 101 and 103 can radiate away from flaps 101 and 103; As a result, a highly asymmetric sound pressure wave is generated, as shown by the half-sine wave portion of the SE air pressure waveform in FIG. 27(b).

It is noted that the opening of the virtual valve 112 does not determine the intensity/amplitude of the acoustic pressure pulse, but rather how strong the effect of "near net zero pressure" (or auto-neutralization) is. When the opening of the virtual valve 112 is wide, the "net zero pressure" effect is strong, self-neutralization is complete, the asymmetry is strong/clear, and a strong/significant baseband signal or APPS effect is obtained. Conversely, when the opening of the virtual valve 112 is narrow, the effect of "net zero pressure" is weak, the automatic neutralization is incomplete, and the asymmetry is reduced resulting in a weak baseband signal or APPS effect.

In the FEM simulation, device C00 is capable of producing an SPL of 145 dB at 20 Hz. From the FEM simulations, even though the SPL produced by device C00 is approximately 12 dB lower than the SPL produced by device 600 (approximately 157 dB SPL at 20 Hz), under the same driving conditions, the THD (total harmonics) of device C00 distortion) is observed to be 10-20 dB lower than the THD of device 600. Thus, the simulation verifies the effectiveness of device C00, an APG device without a cap structure, or an APG device without a chamber formed therein.

Note that the description of the timing of VV opening to match the timing of peak pressure in the chamber or peak velocity/acceleration of common mode membrane movement implicitly suggests that an error of ±e% is acceptable. be done. That is, it is also within the scope of the invention if the timing of VV opening is matched to (1±e%) of the peak pressure in the chamber or the peak velocity/acceleration of common mode membrane movement, where e% is , may be 1%, 5%, or 10%, depending on the actual specifications.

Regarding pulse asymmetry, FIG. 28 shows full-period pulses (within one working period _TCY ) with different degrees of asymmetry. In the present invention, the degree of asymmetry may be evaluated by the ratio of _p2 to _p1 . where p ₁ > p ₂ and p ₁ represents the peak value of the first half-period pulse with the first polarity with respect to the level and p ₂ represents the peak value of the first half-period pulse with the second polarity with respect to the level. Represents the peak value of 2 half-cycle pulses. In the acoustic domain, the level may correspond to ambient conditions of either ambient pressure (0 sound pressure) or 0 acoustic air flow, and air pulses in the present invention represent either air flow pulses or air pressure pulses. You can.

FIG. 28(a) shows a full period pulse with r=p ₂ /p ₁ >80%. The full-period pulse shown in FIG. 28(a) or the full-period pulse with r=p ₂ /p ₁ ≈1 has small asymmetry. FIG. 28(b) shows a full cycle pulse with 40%≦r=p ₂ /p ₁ ≦60%. The full-period pulse shown in FIG. 28(b), or the full-period pulse with r=p ₂ /p ₁ ≈50%, has a median value of asymmetry. FIG. 28(c) shows a full-period pulse with r=p ₂ /p ₁ <30%. The full-period pulse shown in FIG. 28(c) or the full-period pulse with r=p ₂ /p ₁ →0 has high asymmetry.

As mentioned above, the higher the degree of asymmetry, the stronger the APPS effect and the baseband spectral content of the ultrasonic air pulse. In the present invention, an asymmetric air pulse refers to an air pulse that has at least a median value of asymmetry, and means that r=p ₂ /p ₁ ≦60%.

It is noted that the demodulation operation of the APG device of the present invention is to generate asymmetric air pulses according to the amplitude of the ultrasonic air pressure change produced by the modulation operation. In one aspect, the demodulation operation of the present invention is similar to a rectifier in an AM (amplitude modulation) envelope detector in a wireless communication system.

In wireless communication systems, as is well known, an envelope detector, which is a type of wireless AM (non-coherent) demodulator, includes a rectifier and a low-pass filter. The envelope detector generates an envelope corresponding to its input amplitude modulated signal. The input amplitude modulated signal of the envelope detector usually has a high symmetry, r=p ₂ /p ₁ →1. One goal of the rectifier is to convert a symmetric amplitude modulated signal such that the rectified amplitude modulated signal is highly asymmetric with r=p ₂ /p ₁ →0. After low-pass filtering the highly asymmetric rectified AM signal, the envelope corresponding to the amplitude modulated signal is recovered.

The demodulation operation of the present invention, which converts a symmetric ultrasonic air pressure change (r = p ₂ / p ₁ → 1) into an asymmetric air pulse (r = p ₂ / p ₁ → 0), uses an envelope detector as an AM demodulator. Similar to a rectifier, the low-pass filtering action is left in the natural environment and the human hearing system (or a sound sensing device such as a microphone), and the sound/music corresponding to the input audio signal S _IN is recovered and transmitted to the listener. or can be measured by sound-sensing equipment.

Creating asymmetry is important for the demodulation operation of an APG device. In the present invention, pulse asymmetry is dependent on proper timing of opening, aligned with membrane (flap) movement that produces ultrasonic air pressure changes. As shown in FIGS. 25 and 27, different APG configurations have different methods of timing alignment. In other words, the timing of forming the apertures 112 is specified such that the air pulses produced by the APG device are asymmetric.

APG devices that generate asymmetric air pulses may also be applied in air pump/transfer applications, which may have cooling, drying or other functions.

Furthermore, power consumption can be reduced through proper cell and signal path placement. For example, FIG. 29 shows a top view of APG device D00 according to an embodiment of the present invention, and FIG. 30 shows a cross-sectional view of device D00 along line AA' shown in FIG. 29. Device D00 has cells D01 to D08 arranged in an array. Each cell (D0x) may be one of the aforementioned APG devices (eg, 400-C00). In FIG. 30, the subassembly with the cap structure and conduit formed therein has been omitted for simplicity. It is assumed that all flaps in device D00 are driven by drive signaling 431, with the top electrode receiving either the signal +SV or the signal -SV, and the bottom electrode receiving SM-V _BIAS .

In FIG. 29, the rectangle elongated along the Y direction represents the flap or the upper electrode of the actuator placed on the flap. The background shading may represent the bottom electrode of the actuator or that the bottom electrode of the actuator is electrically connected.

In device D00, the flap (eg, 101) that receives the signal -SV and the flap (eg, 103) that receives the signal +SV are spatially interleaved. For example, when flap 103 of cell D01 receives signal +SV, flap 101 of cell D02 is proposed to receive signal -SV. This is because when the signals +SV, -SV toggle polarity, or during the transition period of the signals +SV, -SV, the (discharge) charging current of the capacitive load flows in the X direction through the bottom electrode, and the This is because the effective resistance R _BT,P (where P represents parallel current flow) is low because L/W≪1, and the power consumption of the device D00 is low. Here, L/W represents the channel length/width in terms of (discharging) charging current.

On the other hand, the drive signals -SV, +SV are {+SV, -SV}, {-SV, +SV}, {+SV, -SV}, {-SV, +SV}, {+SV, -SV}, {-SV, +SV} , {+SV, -SV}, {-SV, +SV} (not shown in Figure 29), where {...,...} is the differential drive signal of one cell D0x , the load (discharge) charging current is in the Y direction, and the effective resistance of the bottom electrode R _BT,S (where S represents the series current flow) is sufficiently large (i.e., L/ Since W≫1 (R _BT,S ≫R _BT,P ), the power consumption of such a scheme will be higher.

In other words, by using the wiring method shown in FIG. 29 (for example, when cells D01 and D02 are adopted), the flap 103 of cell D01 receiving signal +SV is replaced by the flap 103 of cell D02 receiving signal -SV. 101 and the transition periods of the signals ±SV overlap in time, the current from the bottom electrode of one flap (e.g., 103 of D01) will flow as device D00 moves away from the pad and another There is no need to re-enter the device D00 from the pad of , but go directly to the adjacent flap (eg 101 of D02). Therefore, the effective resistance of the lower electrode is significantly reduced, and power consumption is also reduced.

The operating frequency may also be increased by incorporating multiple (eg, two) cells. Specifically, the air pressure pulse speaker (APPS) sound generation method using the APG device of the present invention is a type of discrete time sampling system. On the one hand, it is usually desirable to increase the sampling rate in such sampled systems in order to achieve high fidelity. On the other hand, it is desirable to reduce the operating frequency of the device in order to reduce the required drive voltage and power consumption.

Instead of increasing the actuation frequency as the sampling rate of one APG device, we can increase the high pulse/actuation rate by temporally and spatially interleaving (at least) two groups (subsystems) with low pulse/actuation rates. It is efficient to achieve.

FIG. 31 (illustrating the spatial arrangement) is a top view of APG device E00 according to an embodiment of the invention. The device E00 has two cells E11 and E12 arranged next to each other/side-by-side. Cell E11/E12 may be one of the APG devices of the invention.

FIG. 32 (illustrating the temporal relationship) shows the waveforms of two sets of (demodulated) modulation drive signals A and B, intended for cells E11 and E12. The set A includes the demodulated drive signal ±SV and the modulated drive signal SM, and the set B includes the demodulated drive signal ±SV' and the modulated drive signal SM'. As shown in the embodiment of FIG. 32, the demodulated drive signals +SV'/-SV' of signal set B are delayed versions of the demodulated drive signals +SV/-SV of signal set A. Furthermore, the signal +SV'/-SV' of signal set B is the signal +SV/-SV of signal set A delayed by T _CY /2, which is half the operating period, where T _CY = 1/f _UC and f _UC represents the operating frequency of cells E11/E12. The set B modulated drive signals SM' may be considered as inverted or polarized versions of the set A modulated drive signals SM. Signals SM and SM' may have the relationship SM'=-SM or SM+SM'=C, where C is some constant or bias. For example, if the modulated drive signal SM of set A has a pulse of negative polarity with respect to the voltage level (indicated by the dashed line in FIG. 32) within the period T ₂₂ , the modulated drive signal SM' of set B ₂₂ (shown as a dashed line in FIG. 32) with pulses of positive polarity.

By providing one of set A and set B to cell E11 and the other of set A and set B to cell E12, device E00 generates a pulse array with a pulse/sampling rate of 2×f _UC . where f _UC is the operating frequency of each cell.

FIG. 33 is a top view of APG device F00 according to an embodiment of the present invention. Device F00 has cells F11, F12, F21, and F22 arranged in a 2×2 array. The cell in device F00 may be one of the APG devices of the present invention. Two of the cells F11, F12, F21 and F22 may receive signal set A, and the other two cells may receive signal set B.

In one embodiment, cells F11, F22 receive signal set A and cells F21, F22 receive signal set B. In one embodiment, cells F11, F22 receive signal set A and cells F12, F22 receive signal set B. In one embodiment, cells F11, F21 receive signal set A and cells F12, F22 receive signal set B. Similar to device E00, the device also produces a pulse array with a pulse/sampling rate of 2×f _UC .

It is noted that conventional speakers (eg, dynamic drivers) that use physical surface motion to generate acoustic waves face the problem of forward/backward radiated wave cancellation. When the physical surface moves, causing movement of the air mass, a pair of sound waves, a forward radiating wave and a backward radiating wave, are generated. The two sound waves largely cancel each other out, and the net SPL is greatly reduced compared to if the forward/backward radiation waves were measured alone.

A widely adopted solution to the forward/backward radiation cancellation problem is to utilize either a rear enclosure or an open baffle. Both solutions require physical size/dimensions corresponding to a wavelength of 1.5 meters for the lowest frequency wavelength of interest, for example a frequency of 230 Hz.

Compared to conventional loudspeakers, the APG device of the present invention occupies only a few tens of square mm (much smaller than conventional loudspeakers) and produces large SPL, especially at low frequencies.

This is achieved by generating asymmetric amplitude modulated air pulses, where the modulating part generates symmetric amplitude modulated air pressure fluctuations via membrane motion, and the demodulating part generates asymmetric amplitude modulated air pressure fluctuations via a virtual valve. Generate a pulse. The modulation and demodulation sections are realized by flap pairs manufactured in the same processing layer, reducing manufacturing/production complexity. Modulation operation is performed via common mode movement of the flap pair, demodulation operation is performed via differential mode movement of the flap pair, and modulation operation (via common mode movement) and (via differential mode movement) ) The demodulation operation may be performed by a single flap pair. Proper timing alignment between the differential and common mode movements enhances the asymmetry of the output air pulses. Additionally, a horn-shaped outlet or trumpet-shaped conduit helps improve propagation efficiency.

In summary, the air pulse generator of the present invention has modulation means and demodulation means. The modulation means, which may be realized by applying a modulated drive signal to the flap pair (102 or 104), generates an amplitude modulated ultrasonic acoustic/air wave having an ultrasonic carrier frequency according to the acoustic signal. The demodulation means is realized by applying a pair of demodulation drive signals +SV and -SV to the pair of flaps (102) or by periodically driving the pair of flaps (102) to form the aperture (112). A synchronous demodulation operation is performed to shift the spectral components of the ultrasonic acoustic/air wave UAW by ±n×f _UC . As a result, the spectral components of the ultrasonic air waves corresponding to the acoustic signal are shifted to the audible baseband and the acoustic signal is reproduced.

Those skilled in the art will readily appreciate that many modifications and variations of the apparatus and method may be made while retaining the teachings of the invention. Accordingly, the foregoing disclosure should be construed as limited only by the boundaries of the appended claims.

(Publicly known literature)
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100 Air Pulse Generator (APG) Device
12 Equipment layer
11 Chamber definition layer
124L, 124R wall
101, 103, 105, 107 flaps
123R, 123L support structure

Claims (23)

An air pulse generator, comprising:
It has a membrane structure,
the membrane structure is driven to create an amplitude modulated ultrasonic air pressure change having an ultrasonic carrier frequency;
the membrane structure is driven to form an aperture at a speed synchronized with the ultrasound carrier frequency;
The air pulse generating device generates a plurality of air pulses according to the amplitude modulated ultrasonic air pressure change, the plurality of air pulses being asymmetric. 2. The air pulse generator according to claim 1, wherein the timing of forming the opening is specified such that the plurality of air pulses generated by the air pulse generator are asymmetrical. the membrane structure has a pair of flaps;
the flap pair is driven to create the amplitude modulated ultrasonic air pressure change having the ultrasonic carrier frequency;
the pair of flaps is driven such that the aperture is formed at a speed synchronized with the ultrasound carrier frequency;
2. The air pulse generator of claim 1, wherein the air pulse generator generates a plurality of air pulses according to the amplitude modulated ultrasonic air pressure change, and wherein the plurality of air pulses are asymmetric. 2. The air pulse generator of claim 1, wherein the opening time of the aperture is matched to a peak time at which the amplitude modulated ultrasonic air pressure change reaches a peak. a chamber is formed within the air pulse generator;
2. The air pulse generator of claim 1, wherein the membrane structure creates the amplitude modulated ultrasonic air pressure variation within the chamber. the opening is formed when the common mode movement of the pair of flaps is in a first direction;
4. The air pulse generator of claim 3, wherein the aperture is closed when the common mode movement of the pair of flaps is in a second direction opposite the first direction. the time during which the aperture is opened is timed to a time corresponding to a maximum velocity of common mode movement of the pair of flaps moving towards the first direction;
7. The time during which the opening is closed is timed to a time corresponding to a maximum velocity of the common mode movement of the flap pair moving towards the second direction opposite to the first direction. The air pulse generator described. 7. The air pulse generator according to claim 6, wherein the first direction is a direction toward the surroundings. 2. The air pulse generator of claim 1, wherein a conduit is formed within the air pulse generator. the membrane structure has a pair of flaps;
10. The air pulse generator of claim 9, wherein common mode movement of the pair of flaps creates an air wave that propagates through the conduit. 10. The air pulse generator of claim 9, wherein the conduit has a chamber, a passageway, and a horn-shaped outlet. 12. The air pulse generator of claim 11, wherein the dimensions of the chamber narrow toward the passageway. 12. The air pulse generator of claim 11, wherein the horn-shaped outlet dimensions widen towards the periphery. 4. The air pulse generator of claim 3, wherein the time at which the aperture is opened is timed to a time corresponding to a peak acceleration of common mode movement of the pair of flaps. 4. The air pulse generator of claim 3, wherein a time corresponding to a peak of differential mode movement of the flap pair is aligned to a time corresponding to a peak acceleration of common mode movement of the flap pair. 4. The air pulse generator of claim 3, wherein the time at which the aperture is closed is timed to a time corresponding to a peak acceleration of common mode movement of the pair of flaps. the pair of flaps are driven to provide common mode movement to create the amplitude modulated ultrasonic air pressure change having the ultrasonic carrier frequency;
the pair of flaps are driven to perform differential mode movement to form the aperture at a speed synchronized with the ultrasound carrier frequency;
4. The air pulse generator of claim 3, wherein the time of the differential mode movement is matched to the time of the common mode movement such that the air pulse generator generates a plurality of asymmetric air pulses. An air pulse generator, comprising:
modulating means configured to perform a modulating operation such that an amplitude modulated ultrasonic air pressure change having an ultrasonic carrier frequency is generated, the amplitude modulated ultrasonic air pressure change being connected to an input modulating means amplitude modulated according to an audio signal, said input audio signal being an electrical representation of a sound signal;
performing a synchronous demodulation operation on the amplitude modulated ultrasonic air pressure change such that a spectral component of the amplitude modulated ultrasonic air pressure change is shifted by an amount that is an integer multiple of the ultrasonic carrier frequency; demodulating means configured to;
has
The air pulse generator generates a plurality of air pulses by performing the synchronous demodulation operation,
An air pulse generator, wherein the audible spectral components of the plurality of air pulses correspond to the sound signal. The air pulse generator has a pair of flaps,
The demodulation means includes applying a pair of demodulation drive signals to the pair of flaps,
19. The air pulse generator of claim 18, wherein the modulating means includes applying a modulating drive signal to the pair of flaps. The air pulse generator has a first pair of flaps and a second pair of flaps;
The demodulation means includes applying a pair of demodulation drive signals to the first pair of flaps,
19. The air pulse generator of claim 18, wherein the modulating means includes applying a modulating drive signal to the second pair of flaps. The air pulse generator has a pair of flaps,
The demodulating means includes driving the pair of flaps to periodically form an aperture,
19. The air pulse generator of claim 18, wherein the opening speed of the aperture is the ultrasonic carrier frequency. The air pulse generator has a pair of flaps,
The demodulation means includes applying a pair of demodulation drive signals to the pair of flaps,
19. The air pulse generator of claim 18, wherein the pair of demodulated drive signals are periodic and correspond to a drive frequency that is synchronized with the ultrasound carrier frequency. 23. The air pulse generator according to claim 22, wherein the drive frequency of the pair of demodulated drive signals is half the ultrasonic carrier frequency.