Air-pulse generating device, wearable sound device, bladeless fan, and airflow producing method

Abstract

A gas pulse generating device includes a membrane structure. The membrane structure is actuated to generate a plurality of gas pulses at an ultrasonic pulse frequency. The plurality of gas pulses generate a unidirectional net airflow.

Description

Pneumatic Pulse Generation Device, Wearable Sound Device, Fanless Exhaust Fan, and Airflow Generation Method This application relates to a pneumatic pulse generation device, a wearable sound device, and its fanless exhaust fan, especially a pneumatic pulse generation device, a wearable sound device, and its fanless exhaust fan that can improve the user experience. As electronic devices (such as smartphones or tablet computers) become thinner and need to perform more and more complex operations, they will consume more battery power. Therefore, thermal management is crucial for the future sustainability of (handheld) electronic devices. In addition, wearing earphones with wet ears may affect the service life of the earphones or make it difficult to dry the ears. Therefore, it may be necessary to dry the ear canal after hydrophilic activities (such as swimming or surfing) or after taking a shower. Therefore, this application mainly provides a pneumatic pulse generation device, a wearable sound device, and its fanless exhaust fan to improve the deficiencies of the existing technology. The present invention discloses a pneumatic pulse generation device, including a membrane structure that is used to be actuated to generate a plurality of pneumatic pulses at an ultrasonic pulse frequency; wherein, the plurality of pneumatic pulses generate a unidirectional net air flow. The present invention discloses a heat dissipation method, including arranging the above-mentioned pneumatic pulse generation device on, under, or beside a heat source. The present invention discloses a ventilation method, including arranging the above-mentioned pneumatic pulse generation device on a host device. The present invention discloses an ear canal ventilation method, including arranging the above-mentioned pneumatic pulse generation device on a wearable sound device. The present invention discloses a method for sensing air quality, including arranging the above-mentioned pneumatic pulse generation device on an air quality sensing device. The present invention discloses a wearable sound device, including a housing; and an airflow generation device that is used to generate a unidirectional airflow. The present invention discloses a fanless exhaust fan, including a membrane structure; wherein, the fanless exhaust fan generates a plurality of pneumatic pulses according to air pressure changes, and the plurality of pneumatic pulses are asymmetric; wherein, the plurality of pneumatic pulses generated by the fanless exhaust fan constitute a unidirectional net air movement or net air flow. The present invention discloses an airflow generation method, including a pneumatic pulse generation device generating an asymmetric plurality of pneumatic pulses at an ultrasonic pulse frequency; wherein, the asymmetric plurality of pneumatic pulses generate a unidirectional net air flow. The present invention essentially relates to a pneumatic pulse generation device, especially a pneumatic pulse generation device including modulation means and demodulation means. The modulation means generates a signal with a frequency f UCultrasonic air pressure wave or variation (UAW), the amplitude of the UAW being modulated according to the input audio signal S IN and the input audio signal S IN is an electrical (analog or digital) representation of the sound signal SS. This amplitude-modulated ultrasonic air pressure wave or variation (AMUAW) is then synchronously demodulated by the demodulation means such that the spectral components embedded in the AMUAW are shifted by ±n·f UC where n is a positive integer. Due to this synchronous demodulation, the spectral components of the AMUAW corresponding to the sound signal SS are partially shifted to the baseband, thereby reproducing the audible sound signal SS. Here, the amplitude-modulated ultrasonic air pressure wave or variation AMUAW may correspond to a carrier component having an ultrasonic carrier frequency f UC and a modulation component corresponding to the input audio signal S IN corresponds. FIG. 1 is a schematic diagram of an air pulse generation (APG) device 100 according to an embodiment of the present invention. The device 100 can be used as a sound generation device that generates acoustic sound according to an input (audio) signal S IN but is not limited thereto. The device 100 includes a device layer 12 and a chamber definition layer 11. The device layer 12 includes walls 124L, 124R and support structures 123R, 123L that support a thin film layer, and the thin film layer is etched into flaps 101, 103, 105 and 107. In one embodiment, the device layer 12 can be fabricated by a microelectromechanical system (MEMS) process, for example, using a Si substrate with a thickness of 250 to 500 μm, and the Si substrate is etched to form 123R, 123L and 124L, 124R. In one embodiment, on top of the Si substrate, a thin layer is etched to form flaps 101, 103, 105 and 107, and the thickness of the thin layer is typically 3 to 6 μM and is made of a silicon-on-insulator (SOI) or polysilicon-on-insulator (POI) layer. The chamber definition layer (which can also be regarded as / called a lid structure) 11 includes a pair of chamber sidewalls 110R, 110L and a chamber top cover 117. In one embodiment, the chamber definition layer (or lid structure) 11 can be fabricated using MEMS manufacturing techniques. A resonant chamber 115 is defined between the chamber definition layer 11 and the device layer 12. In other words, the device 100 can be regarded as including a membrane structure 10 and a lid structure 11, with a chamber 115 formed therebetween. The membrane structure 10 can be regarded as including a modulation section 104 and a demodulation section 102. The modulation section 104 includes (modulation) flaps 105 and 107, which are used to be actuated to form ultrasonic air or sound waves in the chamber 115, where the air / sound waves can be regarded as an air pressure change that varies in both time and space. In one embodiment, the ultrasonic air / sound waves or air pressure change can be an amplitude double-sideband suppressed carrier (DSB-SC) modulated air / sound wave having an ultrasonic carrier frequency f UC . The ultrasonic carrier frequency f UC can be, for example, in the range of 160 KHz to 192 KHz, which is much higher than the maximum frequency of human audible sound. The terms "air wave" and "sound wave" are used interchangeably in the following context. The demodulation section 102 includes (demodulation) flaps 101 and 103, which are used to operate synchronously with the modulation section 104 to shift the spectral components of the DSB-SC modulated sound wave generated by the modulation section 104 by ±n×f UC and generate multiple air pulses to the surrounding environment according to the ultrasonic air wave in the chamber 115, such that the baseband frequency components of the multiple air pulses (generated by the demodulation section 102 according to the ultrasonic air wave in the chamber 115) will be, will correspond to, or will be related to the input (audio) signal S IN , where the low-frequency components of the multiple air pulses refer to the frequency components of the multiple air pulses within the audible spectrum (e.g., below 20 or 30 KHz), and n is a positive integer. Here, the baseband generally refers to the audible spectrum, but is not limited thereto. In other words, when the device 100 is switched to the sound generation application, the modulation section 104 can be actuated according to the input audio signal S IN to form a modulated air wave, and the demodulation section 102 operates synchronously with the modulation section 104, and the demodulation section 102 generates multiple air pulses having low-frequency components that are the same as (or corresponding to, related to) the input audio signal S IN . For the sound generation application, f UC is usually much higher than the highest human audible frequency. For example, f UC ≥ 96 KHz ≈ 5×20 KHz. Then, through the natural or environmental low-pass filtering effect of the multiple air pulses, what the listener perceives will only be the input audio signal S INThe audible sound or music represented. The natural or environmental low-pass filtering effect is caused by the physical environment (such as walls, floors, ceilings, furniture, or high propagation loss of ultrasonic waves, etc.) and the human ear system (such as ear canals, eardrums, malleus, incus, stapes, etc.). By showing the spectra of the signals before and after the demodulation or modulation operations, FIG. 19 conceptually / schematically depicts the effects of the demodulation or modulation operations. In FIG. 19, the modulation operation is based on the input audio signal S IN Generates an amplitude-modulated ultrasonic or air wave UAW with a spectrum of W(f), and the input audio signal S IN Is an electrical (analog or digital) representation of the sound signal SS. The spectrum of S IN Or SS is represented as S(f) in FIG. 19. The ultrasonic pulse array UPA includes multiple pulses. The synchronous demodulation operation generates an ultrasonic pulse array UPA with a spectrum of Z(f), which can be regarded as (including the following steps) shifting the spectral components of the ultrasonic / air wave UAW by ± n× f UC (n is an integer), and partially transfers the spectral components of the ultrasonic air wave UAW corresponding to the sound signal SS to the baseband. Therefore, it can be seen from Z(f) that compared with the amplitude-modulated UAW W(f), the baseband components of the ultrasonic pulse array UPA are significant. The ultrasonic pulse array UPA propagates into the surrounding environment. Through the low-pass filtering effect inherent in the natural or physical environment and the human auditory system, the resulting spectrum Y(f) corresponding to the sound signal SS can be reproduced. Note that different from the conventional DSB-SC amplitude modulation using a sinusoidal carrier, W(f) has components at the higher harmonics of ±3×f UC 、±5×f UC And f UC (not shown in FIG. 19). This is because the carrier modulated in the present invention is not a pure sinusoidal wave. Please refer to FIG. 1 again. As an example of the synchronous demodulation operation, the demodulation unit 102 can be actuated to form an opening 112 at the time and position corresponding to or aligned with the peak of the modulated air wave. In other words, when the modulated air wave reaches its peak at the position of the opening 112, the demodulation unit 102 can be actuated so that the opening 112 also reaches its peak (the largest opened size). In the embodiment shown in FIG. 1, the demodulation unit 102 forms an opening 112 at the central position between the side walls 110L and 110R, and there is (substantially) λ between the side walls 110L and 110R UC The surface-to-surface (or 111L to 111R) spacing, which means that the tips of flaps 101 and 103 are (substantially) separated from side walls 110L and 110R (or side wall surfaces 111L and 111R) by λ UC / 2, where λ UC represents the wavelength corresponding to the ultrasonic carrier frequency f UC i.e., λ UC = C / f UC , where C is the speed of sound. In one embodiment, demodulator 102 can be actuated to form an opening 112 at an opening valve frequency that is synchronized with the ultrasonic carrier frequency f UC In the present invention, the opening valve frequency being synchronized with the ultrasonic carrier frequency f UC generally means that the opening valve frequency is the ultrasonic carrier frequency f UC multiplied by a rational number, i.e., f UC × ( N / M), where N and M represent integers. In one embodiment, the opening valve frequency (of opening 112) can be the ultrasonic carrier frequency f UC . For example, the valve or opening 112 can be opened in each operation period T CY , where the operation period T CY is the reciprocal of the ultrasonic carrier frequency f UC , i.e., T CY = 1 / f UC . In the present invention, the (de)modulation units 102 / 104 are also used to represent the (de)modulation vane pairs. In addition, the demodulation unit (or vane pair) 102 that forms the opening 112 can be regarded as a virtual valve (VV), which performs opening and closing movements according to a specific valve or demodulation drive signal and (periodically) forms the opening 112. In one embodiment, the modulation unit 104 can substantially generate a mode 2 (or second harmonic) resonance (or standing wave) in the resonant chamber 115, such as the pressure distribution P104 and the air flow distribution U104 shown in FIG. 1. In this regard, the distance between the side wall surfaces 111L and 111R substantially defines the full wavelength λ f UC corresponding to the ultrasonic carrier frequency UC , that is, W115≈λ UC =C / f UC . In addition, in the embodiment shown in FIG. 1, the free ends of the modulation vanes 105 / 107 are arranged beside the side walls 110L / 110R. Note that intermodulation (or cross-coupling) may occur between the modulation that generates the modulated air wave and the demodulation that forms the opening 112, which will reduce the final sound quality. To improve the sound quality, it is necessary to minimize the intermodulation (or cross-coupling). To minimize the cross-coupling between modulation and demodulation, the modulation vanes 105 and 107 are driven to have a common-mode motion, and the demodulation vanes 101 and 103 are driven to have a differential-mode motion. The modulation vanes 105 and 107 having a common-mode motion mean that the vanes 105 and 107 are simultaneously actuated or driven to move in the same direction. The demodulation vanes 101 and 103 having a differential-mode motion mean that the vanes 101 and 103 are simultaneously actuated to move in opposite directions. In addition, in one embodiment, the vanes 101 and 103 can be actuated to move in opposite directions and have (substantially) the same displacement or amplitude. The demodulation unit 102 can substantially generate a mode 1 (or fundamental harmonic) resonance (or standing wave) in the resonant chamber 115, such as the pressure distribution P102 and the air flow distribution U102 formed by the demodulation unit 102 shown in FIG. 1. Therefore, the demodulation unit 102 should operate at the valve operation or drive frequency f D_V such that W115≈λ D_V / 2, where λ D_V =C / f D_V, and the valve operation / driving frequency f D_V should be the ultrasonic carrier frequency f UC half of, i.e., f D_V = f UC / 2. The common-mode motion and the differential-mode motion can be driven by the (de)modulation driving signal. FIG. 2 shows the waveforms of the demodulation driving signals S101, S103 and the modulation driving signal SM. The modulation driving signal SM is used to drive the modulation flaps 105 and 107. The demodulation driving signals (or valve driving signals) S101 and S103 are respectively used to drive the demodulation flaps 101 and 103. In one embodiment, the modulation driving signal SM can be regarded as a pulse amplitude modulation (PAM) signal modulated according to the input audio signal S IN Moreover, different from the existing PAM signal, the polarity of the signal SM (relative to a constant voltage) is switched within one operation period T CY Generally speaking, the modulation driving signal SM includes a plurality of pulses with alternating polarities (relative to the constant voltage), and the envelope or amplitude of these pulses is (substantially) the same as, proportional to or corresponding to the alternating current (AC) component of the input audio signal S IN In other words, the modulation driving signal SM can be regarded as including a pulse amplitude modulation signal or including PAM modulation pulses with alternating polarities (relative to the constant voltage). In the embodiment shown in FIG. 2, the switching rate of the modulation driving signal SM is 2×f UC , which means that the polarity of the pulses of the modulation driving signal SM alternates or switches twice within one operation period T CY In other words, the modulation driving signal SM can be regarded as including a pulse amplitude modulation signal or including PAM modulation pulses with alternating polarities (relative to the constant voltage). In the embodiment shown in FIG. 2, the switching rate of the modulation driving signal SM is 2×f The demodulation driving signals S101 and S103 include two driving pulses with equal amplitudes but opposite polarities (relative to a constant or average voltage). In other words, at a specific time, if S101 includes a first pulse with a first polarity (relative to the constant / average voltage) and S103 includes a second pulse with a second polarity (relative to the constant / average voltage), then the first polarity and the second polarity are opposite. As shown in FIG. 2, the switching rate of the demodulation driving signal S101 or S103 is f UC, which means that the polarities of multiple pulses of the demodulated drive signals S101 / S103 alternate or switch once within an operation period T CY Therefore, the switching rate of the modulation drive signal (SM) is twice that of the demodulated drive signals S101 / S103. The slopes of S101 or S103 (and the corresponding shaded areas) are simplified illustrations that represent the energy recycle during the transition between voltage levels. Note that the transition periods of signals S101 and S103 overlap. Considering that the piezoelectric actuators of flaps 101 or 103 are mainly capacitive loads, the characteristics of an LC oscillator can be utilized to achieve energy recycle. Details of the energy recycle concept can be referred to in U.S. Patent 11,057,692, which is incorporated herein by reference. Note that the piezoelectric actuator is one example but not limited thereto. To emphasize that the flap pair 102 is differentially driven, signals S101 and S103 can also be represented as -SV and +SV, indicating that this pair of drive signals has the same waveform but different polarities. For illustrative purposes, in Figure 2, -SV is used for S101 and +SV is used for S103, but not limited thereto. In one embodiment, S101 can be +SV and S103 can be -SV. In another embodiment, there may be a DC bias voltage V BIAS and V BIAS ≠0, in which case the drive signals are S101 = V BIAS – SV, S103 = V BIAS + SV. Such variations should be considered within the scope of this disclosure. In addition, Figure 2 illustrates the difference in toggling rate between the modulation drive signal SM and the demodulated drive signals ±SV. The relative phase delay (i.e., timing alignment) between the modulation drive signal SM and the demodulated drive signals ±SV can be adjusted according to actual needs. In one embodiment, the drive circuit for generating signals SM and ±SV may include a sub - circuit that is used to generate a (relative) delay between the modulation drive signal SM and the demodulated drive signals ±SV. The details of the sub - circuit for generating the delay are not limited. Known techniques can be incorporated into the sub - circuit. As long as the sub - circuit can generate a delay that meets the timing alignment requirements (to be described in detail later), that is, meets the requirements of the present invention, then the sub - circuit will be within the scope of the present invention. Note that the tips of flaps 101 and 103 are located at substantially the same position (at the central position between side walls 111L and 111R), and are subject to substantially the same air pressure at that position. In addition, flaps 101 and 103 move in different ways. Therefore, the movement of the tips of flaps 101 and 103 has a common-mode rejection behavior, similar to the common-mode rejection known in the field of analog differential operational amplifier circuits, which means that demodulating the displacement difference of the tips of flaps 101 and 103 (or |d 101 -d 103 |) is hardly affected by the air pressure formed by modulating flaps 105 and 107. Common-mode rejection (or modulator-to-demodulator isolation) can be demonstrated from Figure 3. Figure 3 shows the simulation results generated from the equivalent circuit model of device 100. Curves d 101 and d 103 represent the movement or displacement of the tips of flaps 101 and 103 respectively. As shown in Figure 3, even if the acoustic pressure (P104) generated by modulating flap 105 or 107 causes d 101 and d 103 to fluctuate quite a lot, the differential movement (represented by the curve marked d 101 -d 103 in Figure 3) remains (substantially) consistent. That is to say, even when the modulation unit 104 operates, the width or gap of the valve opening 112 will be consistent. In other words, the influence of the movement of the modulator on the function and performance of the demodulator is negligible, which is what "modulator-to-demodulator isolation" means. On the other hand, for demodulator-to-modulator isolation, since the vanes 101 / 103 generate a first-order harmonic resonance or standing wave in the chamber 115, as shown in Fig. 1, the pressures applied to the vanes 105 and 107 by P102 will have substantially the same amplitude but opposite polarities, resulting in changes in the motion of the vanes 105 and 107 (due to P102) that also have the same amplitude but opposite polarities. This will generate two ultrasonic waves, (one generated by 105 and the other by 107), and these two ultrasonic waves also change with the same amplitude but opposite polarities. When these two ultrasonic waves propagate to the position above the valve opening 112, such as the position indicated by the dashed region in Fig. 1, the two ultrasonic waves combine into one pressure. Since this "combination" position occurs at the center of the device 100, along the X-axis or X-direction, and at an equal distance from the tips of 105 and 107, the changes caused by P102 will cancel or compensate each other, and a net rest will be generated, and this net rest is hardly affected by the demodulator or the operation of the virtual valve. As an illustration, Fig. 4 shows the simulated frequency response of the sound pressure level (SPL) measured at a distance of 1 meter from the device 100, with the condition that S IN is a test signal of 10 tones with equal amplitudes (at equally logarithmic scale intervals in the range of 650 - 22 KHz), and an equivalent circuit simulation model of the device 100 is used. In the current simulation, the ultrasonic carrier frequency is set to f UC = 192 KHz, and the valve operation frequency is set to f D_V = f UC / 2 = 96 KHz. Demodulator-to-modulator isolation can be demonstrated by the absence of extraneous spurious spectral components near 96 KHz and 96 KHz, which indicates a very high degree of isolation. Fig. 4 indicates 96 KHz with a square arrow. Therefore, the motion interference of these two vane pairs (101 / 103 vs. 105 / 107) is minimized by the orthogonality or alignment of the common mode (in the modulator) to the differential mode (in the demodulator). In addition, the percentage of time the valve remains open (or duty factor) is a key factor affecting the output of the device 100. Increasing the amplitudes of the driving voltages S101 and S103 can increase the motion amplitudes of the vanes 101 and 103, which will increase the maximum opening width of the valve opening 112. Increasing the driving voltage also increases the duty factor of the valve opening. In other words, the duty factor of the valve opening 112 and the maximum opening width or gap of the valve opening 112 can be determined by the driving voltages S101 and S103. When the opening duty factor of the valve approaches 50%, as in the example shown in Figure 5, the period during which each valve is open can be as shown by the curve labeled V(opening) where V(opening)>0, and the period during which each valve is open overlaps with the same half period of the amplitude-modulated ultrasonic standing wave at the position at the top of the valve opening 112 (shown by the dashed line area in Figure 1). This example shown in Figure 5 is generated by one of the equivalent circuit simulation models mentioned previously. The curve labeled V(p_vlv) in Figure 5 depicts the standing wave in the chamber. By synchronizing and timing the opening-closing of the valve opening 112 with the in-chamber standing wave, a well-shaped output pressure pulse is generated, as shown by the curve labeled V(ep_vlv). In Figure 5, the curve labeled V(d2)-V(d3) represents the displacement difference between the flaps 101 and 103 (i.e., d 101 -d 103 ), and the curve labeled V(opening) represents the degree of opening of the virtual valve 112. When |V(d2)-V(d3)|>TH, V(opening)>0, where TH is a threshold defined by parameters such as the thickness of the flaps 101 and 103, the slit width between the flaps 101 and 103, or the boundary layer thickness, etc. The well shape of V(ep_vlv) may indicate that the pulse shown by V(ep_vlv) is highly asymmetric, unlike V(p_vlv) which is highly symmetric. The asymmetry of the output pressure pulse will exhibit the low-frequency components (i.e., the frequency components in the audible frequency band) of the gas pulse generated by the gas pulse generating device (or simply referred to as the APG device), which is an ideal characteristic of the APG device. The higher the asymmetry, the stronger the baseband frequency component of the gas pulse. Figure 6 depicts a magnified view of Figure 5. Figure 6 shows the asymmetry of V(ep_vlv) (corresponding to the envelope of the 1.68 KHz baseband sound signal). In the present invention, when the displacement difference between the flaps 101 and 103 is greater than the threshold (e.g., |V(d2)-V(d3)|>TH), the opening (112) is opened, formed, or in an open state, otherwise it is closed or in a closed state. In addition, it can be observed that the maximum output will occur when the duty factor of the valve opening (i.e., |V(d2)-V(d3)|>TH) is equal to or slightly greater than 50% (for example, in the range of 55-60%), but not limited thereto. However, when the duty factor of the valve opening is significantly higher than 50% (for example, in the range of 80-85%), more than half a cycle of the ultrasonic standing wave in the chamber will pass through the valve, resulting in the cancellation of the standing waves of the parts with different polarities, thereby resulting in a lower net SPL output of the device 100. Therefore, it is generally preferred to keep the duty factor of the valve opening close to 50%, usually in the range between 50% and 70% (where the duty factor in the range between 45% and 70% is also within the scope of the present invention). In addition to the duty factor, to ensure modulator-to-demodulator isolation, the resonant frequency f of the demodulation diaphragms 101 / 103 R_V is preferably sufficiently offset from the ultrasonic carrier frequency f UC , which is another design element. It can be observed (from the equivalent circuit simulation model) that, under the limitation that the duty factor of the valve opening is equal to 50%, for any given thickness of the diaphragms 101 / 103, the higher the resonance drive ratio (f R_V : f D_V or f R_V / f D_V ), the greater the amplitude by which the valve can be opened. Since the output of the device 100 is positively correlated with the maximum width of the valve opening, a resonance drive ratio higher than 1 is preferred. However, when f R_V falls within the range of f UC ±max(f SOUND ), the diaphragms 101 / 103 will start to resonate with the AM ultrasonic standing wave, converting part of the ultrasonic energy into the common-mode deformation of the diaphragms 101 / 103, where max(f SOUND ) can represent the maximum frequency of the input audio signal S IN . This common-mode deformation of the diaphragms 101 / 103 will cause a change in the volume at the top of the diaphragms 101 / 103, resulting in fluctuations in the pressure in the chamber 115 and near the valve opening 112 within the affected frequency range, thereby resulting in a reduction in the SPL output. To avoid frequency response fluctuations caused by valve resonance, it is preferably to design the resonant frequency of the diaphragms 101 / 103 at ( f UC ±max( f SOUND )) × M outside the range, where M is a safety margin used to cover factors such as manufacturing tolerances, temperature, altitude, etc., but not limited to this. Generally, an empirical method is to tend to f R_V significantly lower than f UC (e.g., f R_V ≤ ( f UC – 20KHz) × 0.9) or significantly higher than f UC (e.g., f R_V ≥ ( f UC + 20KHz) × 1.1). Note that 20KHz is used here because 20KHz is the recognized highest human audible frequency. In applications such as HD- / Hi-Res Audio, 30KHz or even 40KHz may be used as max( f SOUND ), and accordingly, the above formula should be modified. In addition, assume that w(t) and z(t) represent functions of the amplitude-modulated ultrasonic / air wave UAW and the ultrasonic pulse array UPA varying with time, where the ultrasonic pulse array UPA includes multiple pulses. Since the opening 112 is periodically formed at the ultrasonic carrier frequency f UC 's opening rate, the ratio function of z(t) and w(t) (which can be denoted as r(t) and can be expressed as r(t) = z(t) / w(t)) and the ultrasonic carrier frequency f UCThe opening rate is periodic. In other words, z(t) can be regarded as the product of w(t) and r(t) in the time domain, that is, z(t)=r(t)·w(t), and the synchronous demodulation operation performed on the UAW can be regarded as the product of w(t) and r(t) in the time domain. This means that Z(f) can be regarded as the convolution of W(f) and R(f) in the frequency domain, that is, Z(f)=R(f)*W(f), where * represents the convolution operator, and the synchronous demodulation operation performed on the UAW can be regarded as the convolution of W(f) and R(f) in the frequency domain. Note that when r(t) is periodic at a frequency of f UC in the time domain, R(f) is discrete in the frequency domain, where the frequencies or spectral components of R(f) are evenly distributed at f UC and so on. Therefore, the convolution of W(f) and R(f) or the synchronous demodulation operation involves or includes steps of shifting (frequency shifting) W(f) (or the spectral components of the UAW) by ±n×f UC . Here, n is an integer, and r(t) / w(t) / z(t) and R(f) / W(f) / Z(f) form a Fourier transform pair. FIG. 12 is a schematic diagram of an APG device 400 according to an embodiment of the present invention. The device 400 is modified based on FIG. 7 of U.S. Application No. 17 / 553,806 and is similar to the device 100 shown in FIG. 1 of the present invention. Different from the device 100, the device 400 only includes the vane pair 102 (but does not include the vane pair 104). The vane pair 102 is used to perform modulation operations and demodulation operations. The modulation operation is used to form an amplitude-modulated air pressure change with an ultrasonic carrier frequency f UC , and the demodulation operation is used to synchronize with the amplitude-modulated ultrasonic carrier at the frequency f UC to form an opening 112 to generate a plurality of air pulses according to the envelope of the amplitude-modulated ultrasonic air pressure change. In FIG. 12, U104 and P104 represent the pressure distribution and air flow distribution formed by the vane pair 102 in response to the modulation drive signal SM, and U102 and P102 represent the pressure distribution and air flow distribution formed by the vane pair 102 in response to the demodulation drive signals ±SV. Here, the demodulation drive signal is represented by ±SV to emphasize that the vane pair 102 is differentially driven (which means that the demodulation drive signals +SV and -SV have the same amplitude but opposite polarities) to perform the demodulation operation. For example, the above-mentioned S101 and / or S103 can be represented by -SV and / or +SV. In other words, the modulator and the demodulator are co-located at or arranged as the pair of vanes 102. Similar to the device 100, the membrane structure 10 of the pair of vanes 102 of the device 400 is actuated, so as to have not only a common-mode motion to perform modulation, but also a differential-mode motion to perform demodulation. In other words, the "modulation operation" and the "demodulation operation" are simultaneously performed by the same pair of vanes 102. This co-location of the "modulation operation" and the "demodulation operation" is achieved by a new driving signal wiring scheme (such as that shown in FIG. 13). Given that the device 400 may include actuators 101A / 103A disposed on the vanes 101 / 103, and the actuators 101A / 103A include a top electrode and a bottom electrode, both the top electrode and the bottom electrode can receive a modulation driving signal SM and a demodulation driving signal ±SV. In one embodiment, one electrode of the actuator 101A / 103A can receive a common-mode modulation driving signal SM; and the other electrode can receive a differential-mode demodulation driving signal S101(-SV) / S103(+SV). For example, illustrations 431 to 433 shown in FIG. 13 illustrate details of the area 430 shown in FIG. 12. As shown in illustrations 431 and 432, the bottom electrode of the actuator 101A / 103A receives the common-mode modulation driving signal SM; and the top electrode of the actuator 101A / 103A receives the differential-mode demodulation driving signal S101(-SV) / S103(+SV). An appropriate bias voltage V can be applied to the bottom electrode (as shown in illustration 432) or to the top electrode (as shown in illustration 433) BIAS , the bias voltage V BIAS can be determined according to actual requirements. In one embodiment (as shown in illustration 433), one electrode of the actuator 101A / 103A can receive both the common-mode modulation driving signal SM and the differential-mode demodulation driving signal S101(-SV) / S103(+SV); and the other electrode is appropriately biased. In the embodiment shown in illustration 433, the bottom electrode receives the common-mode modulation driving signal SM and the differential-mode demodulation driving signal S101(-SV) / S103(+SV); and the top electrode is biased. The driving signal wiring scheme shown in FIG. 13 achieves the goal that (without considering V BIAS ), the applied signal of one actuator (such as 101A) is or includes -SM - SV and the applied signal of the other actuator (such as 103A) is or includes -SM + SV. Note that the driving signal wiring scheme can be modified or changed according to actual situations / requirements. As long as a common-mode signal component between the two applied signals applied to the pair of vanes 102 includes the modulation driving signal SM (plus V BIAS ), and a differential-mode signal component between the two applied signals applied to the flap pair 102 includes the demodulation drive signal SV, which meets the requirements of the present invention and is within the scope of the present invention. Here (or generally), a common-mode signal component between any two signals a and b can be expressed as (a + b) / 2, and a differential-mode signal component between any two signals a and b can be expressed as (a - b) / 2. Please further note that in order to minimize the cross-coupling between the modulation operation (caused by the drive signal SM) and the demodulation operation (caused by the drive signals ±SV), in one embodiment, the flaps 101 and 103 are made into a mirror image or a symmetric pair in terms of their mechanical structure, dimensions, and electrical characteristics. For example, the cantilever length of the flap 101 should be equal to the cantilever length of the flap 103; the membrane structure of the flap 101 should be the same as the membrane structure of the flap 103; the position of the virtual valve 112 should be at the center between the two support walls 110 of the flap 101 and the flap 103 or equidistant from the two support walls 110; the actuator pattern provided on the flap 101 should be symmetric with the actuator pattern provided on the flap 103; the wires of the actuators provided on the tops of the flaps 101 and 103 should be symmetric. Only some items are listed here as the mirror image / symmetric pair (or to make the flaps 101 and 103 be mirror image / symmetric), but it is not limited to this. FIG. 14 shows a set of frequency response measurement results of the physical embodiment of the device 400 in the IEC711 closed ear simulator, where the drive scheme shown in FIG. 431 is used to drive the device 400, the Vrms of the modulation drive signal SM of the bottom electrode is 6 Vrms, the peak-to-peak voltage (Vpp) of the demodulation drive signals ±SV of the top electrode varies from 5 Vpp to 30 Vpp, and the GRAS RA0401 ear simulator is used to measure the acoustic results. The operating frequency of the device 400 (i.e., the ultrasonic carrier frequency f UC ) is 160 KHz, and the device dimensions are designed accordingly (e.g., W115≈λ UC = C / f UC ≈2.10 mm, where C is 336 m / s). It can be seen from FIG. 14 that the device 400 can generate sounds with high SPL in the low-frequency band (at least 99 dB for frequencies less than 100 Hz). In addition, FIG. 15 illustrates and analyzes the measurement results of the device 400 shown in FIG. 14. FIG. 15 shows a graph of SPL versus Vvtop (Vpp) at 100 Hz (thick dashed line) and 19 Hz (thick solid line) of FIG. 14, where, as shown in the connection diagram 431, Vvtop (Vpp) is the peak-to-peak voltage of the demodulated drive signal applied to the top electrode. As can be seen from FIGS. 14 and 15, as Vvtop increases, the SPL also increases. In addition, the simulation results of the equivalent lumped circuit model of the device 100 also confirm that the SPL increases as the amplitude of the (valve drive or) demodulated drive signal increases. Thus, it can be known that the volume of the sound generated by the pneumatic pulse generating device of the present invention can be controlled by the amplitude of the demodulated drive signal. Based on the results of FIGS. 14 and 15, it can be concluded that the concept of modulator-demodulator juxtaposition is correct, which means that the modulation (used to form amplitude-modulated ultrasonic air pressure changes) and demodulation (used to form an opening to synchronously generate asymmetric pneumatic pulses) performed by the device 400 successfully produce the APPS effect. Therefore, it may be possible to reduce the chamber width (e.g., W115 of the device 100). FIG. 17 is a schematic diagram of an APG device C00 according to an embodiment of the present invention. The device C00 is similar to the previously introduced APG device and includes flaps 101 and 103. The flaps 101 and 103 can also be driven by the driving scheme shown in FIG. 13. Different from those devices including a lid structure, the device C00 does not include a lid structure. Compared with the APG device introduced above, the structure of the device C00 is much simpler, requiring fewer photolithography etching steps, eliminating the complex conduit manufacturing steps, and avoiding the need to bind two sub-components or sub-assemblies together. The production cost of the device C00 is greatly reduced. Since no chamber to be compressed is formed below the lid structure, the acoustic pressure generated by the device C00 is mainly generated by the acceleration of the movement of the flaps (101 and 103). By aligning the opening timing of the virtual valve 112 (responsive to the demodulated drive signal ±SV) with the acceleration timing of the common-mode movement of the flaps 101 and 103 (responsive to the modulated drive signal SM), the device C00 can generate asymmetric air (pressure) pulses. Note that the space around flaps 101 and 103 is divided into two sub-spaces: one at Z>0 (or +Z sub-space) and the other at Z<0 (or -Z sub-space). For any common-mode movement of flaps 101 and 103, a pair of acoustic pressure waves will be generated, one in the +Z sub-space and the other in the -Z sub-space. These two acoustic pressure waves have the same amplitude but opposite polarities. Therefore, when the virtual valve 112 is opened, the pressure difference between the two air volumes near the virtual valve 112 will neutralize each other. The timing when the differential-mode movement reaches its peak is the timing when the virtual valve 112 reaches its maximum opening. Therefore, when the timing when the differential-mode movement reaches its peak is aligned with the timing when the acceleration of the common-mode movement reaches its peak, it is expected that the acoustic pressure generated by the common-mode movement should be suppressed or eliminated due to the opening of the virtual valve 112, resulting in automatic neutralization between the two acoustic pressures on the two opposite sides of flaps 101 and 103, where these two acoustic pressures have the same magnitude but opposite polarities. This means that when the virtual valve 112 is opened, device C00 will generate (near) net-zero air pressure. Therefore, when the opening period of the virtual valve 112 overlaps with the time period of one of the (two) polarities of the acceleration of the common-mode flap movement, device C00 will generate a single-ended (SE) or pseudo-single-ended air pressure waveform or pulse, which is highly asymmetric. In the present invention, a (pseudo-)single-ended waveform may refer to a waveform that is (substantially) unipolar with respect to a certain level. A single-ended acoustic pressure wave may refer to a waveform that is (substantially) unipolar with respect to the ambient pressure (e.g., 1 ATM). Note that the opening of the virtual valve 112 does not determine the intensity or amplitude of the acoustic pressure pulse, but rather determines the intensity of the "near net-zero pressure" (or automatic neutralization) effect. When the opening width of the virtual valve 112 is wide (fully opened to a large extent), the "net-zero pressure" effect is strong, the automatic neutralization is completed or complete, the asymmetry is strong / obvious, resulting in a strong / significant baseband signal or APPS effect. Conversely, when the opening of the virtual valve 112 is narrow (slightly opened), the "net-zero pressure" effect is weak, the automatic neutralization is not completed or incomplete, the asymmetry is reduced, resulting in a weak baseband signal or APPS effect. In the FEM simulation, device C00 can generate 145 dB SPL at 20 Hz. It can be seen from the FEM simulation that even though the SPL generated by device C00 is about 12 dB lower than the SPL generated by device 600 (about 157 dB SPL at 20 Hz), under the same driving conditions, the total harmonic distortion (THD) of device C00 is 10 - 20 dB lower than that of device 600. Therefore, the simulation verifies the efficacy of device C00 (i.e., an APG device without a lid structure or without a chamber formed therein). Note that the statement "the timing of the virtual valve opening is aligned with the timing of the peak pressure in the chamber or the peak velocity or acceleration of the common-mode diaphragm movement" implicitly implies that a tolerance of ±e% is acceptable. That is, the case where the timing of the virtual valve opening is aligned with the timing of the peak pressure in the chamber (1 ± e%) or the peak velocity or acceleration of the common-mode diaphragm movement is also within the scope of the present invention, where e% can be 1%, 5%, or 10%, and the specific value depends on the actual needs. Regarding the asymmetry of the pulse, FIG. 18 shows full-cycle pulses with different degrees of asymmetry (within an operating period T CY ). In the present invention, the degree of asymmetry can be evaluated by p 2 and p 1 ratio, where p 1 > p 2 , p 1 represents the peak of the first half-cycle pulse with a first polarity relative to a reference level, p 2 represents the peak of the second half-cycle pulse with a second polarity relative to the reference level. In the field of acoustics, the reference level can correspond to environmental conditions (ambient pressure (zero acoustic pressure) or zero acoustic airflow), where the air pulse of the present invention can refer to an airflow pulse or an air pressure pulse. FIG. 18(a) shows r = p 2 / p 1 > 80% of a full-cycle pulse. The full-cycle pulse shown in FIG. 18(a) or r = p 2 / p 1 ≈ 1 full-cycle pulse has a low degree of asymmetry. FIG. 18(b) shows 40% ≤ r = p 2 / p 1 ≤ 60% of a full - cycle pulse. The full - cycle pulse shown in (b) of Fig. 18 or r = p 2 / p 1 ≈ 50% of the full - cycle pulses have a medium degree of asymmetry. Fig. 18(c) shows r = p 2 / p 1 < 30% of a full - cycle pulse. The full - cycle pulse shown in (c) of Fig. 18 or r = p 2 / p 1 → 0 full - cycle pulses have a high degree of asymmetry. As described above, the higher the degree of asymmetry, the stronger the APPS effect and the base - band spectral components of the ultrasonic air pulse. In the present invention, an asymmetric air pulse refers to an air pulse having at least a medium degree of asymmetry, that is r = p 2 / p 1 ≤ 60%. Note that the demodulation operation of the APG device of the present invention generates an asymmetric air pulse according to the amplitude of the ultrasonic air pressure change, and the amplitude of the ultrasonic air pressure change is generated through a modulation operation. From a certain perspective, the demodulation operation of the present invention is similar to the rectifier of an amplitude - modulation (AM) envelope detector in a radio communication system. In a radio communication system (as known in the art), an envelope detector is a radio amplitude - modulation (non - coherent) demodulator. The envelope detector includes a rectifier and a low - pass filter. The envelope detector will generate an envelope corresponding to its input amplitude - modulated signal. The input amplitude - modulated signal of the envelope detector usually has ( r = p 2 / p 1 →1) high symmetry. One purpose of the rectifier is to convert a symmetric amplitude-modulated signal such that the rectified amplitude-modulated signal is ( r = p 2 / p 1 →0) highly asymmetric. After low-pass filtering the highly asymmetric rectified AM signal, the envelope corresponding to the amplitude-modulated signal can be recovered. The demodulation operation of the present invention will ( r = p 2 / p 1 →1) symmetric ultrasonic air pressure variations into ( r = p 2 / p 1 →0) asymmetric air pulses. The demodulation operation of the present invention is similar to a rectifier as an envelope detector for an AM demodulator, where the low-pass filtering operation is left to the natural environment and the human auditory system (or a sound sensing device such as a microphone), such that the sound / music corresponding to the input audio signal S IN can be recovered, perceived by the listener, or measured by the sound sensing device. It is crucial that the demodulation operation of the APG device generates asymmetry. In the present invention, the asymmetry of the pulses depends on the appropriate opening timing, which is aligned with the movement of the diaphragm (flap) that generates the ultrasonic air pressure variations. Different APG structures will have different timing alignment methods. In other words, the timing of forming the opening 112 is specified such that the multiple air pulses generated by the APG device are asymmetric. The APG device that generates asymmetric air pulses can also be applied to an air pump or air movement applications, which can be used for heat dissipation, ventilation, or have functions such as temperature reduction, drying, or others. In this regard, the APG device of the present application can also be regarded as (a type of) air flow generating device. Note that existing loudspeakers (such as dynamic drivers) that use physical surface motion to generate sound waves suffer from the problem of forward / backward radiation wave cancellation. When physical surface motion causes air mass motion, a pair of sound waves (i.e., forward radiation wave and backward radiation wave) is generated. These two sound waves mostly cancel each other out, resulting in a net SPL much lower than the sound pressure levels of the forward / backward radiation waves measured separately. Commonly adopted solutions to the forward / backward radiation wave cancellation problem are to use an enclosure or an open flap. Both of these solutions require physical dimensions or sizes comparable to the wavelength of the lowest frequency of interest, such as a wavelength of 1.5 meters at a frequency of 230 Hz. Compared with existing loudspeakers, the APG device of the present invention occupies only a few tens of square millimeters (much smaller than existing loudspeakers) and generates a huge sound pressure level (especially at low frequencies). This is achieved by generating asymmetric amplitude-modulated air pulses, where the modulation part generates symmetric amplitude-modulated air pressure changes through diaphragm motion, and the demodulation part generates asymmetric amplitude-modulated air pulses through a virtual valve. The modulation part and the demodulation part are implemented by a pair of flaps manufactured on the same fabrication layer, thereby reducing the complexity of manufacturing / production. The modulation operation is performed through the common-mode motion of the pair of flaps, and the demodulation operation is performed through the differential-mode motion of the pair of flaps, where the modulation operation (through common-mode motion) and the demodulation operation (through differential-mode motion) can be carried out by a single pair of flaps. Proper timing alignment between the differential-mode motion and the common-mode motion enhances the asymmetry of the output air pulses. As described above, the APG device of the present application can be used as a (miniature) air pump that can generate asymmetric air pulses and can be applied to cooling, drying, dehumidifying, heat dissipation, and / or ventilation applications. (Asymmetric) air pulses are generated to form a continuous unidirectional net air flow. In addition, the APG device of the present application for air flow applications can be disposed within an air quality sensing device that is used to sense the density of, for example, specific particles (such as PM 2.5 or PM 10) or compounds (such as ozone (O 3 ), nitrogen dioxide (NO 2 ), sulfur dioxide (SO 2 ), and carbon monoxide (CO)). Therefore, the size of the air quality sensing device can be significantly reduced. (PM in PM 2.5 is an abbreviation for particulate matter). For example, FIG. 20 is a schematic diagram of the pneumatic pulse AP of an embodiment of the present application. The pneumatic pulse can be generated by the APG device of the present application (such as C00, 500 or 100), and the APG device includes a membrane structure (such as 10). As described above, the membrane structure of the APG device can be actuated to perform motion, and a pneumatic pulse AP is generated at an ultrasonic pulse frequency (rate) f pulse (such as 96 kHz or 192 kHz), and the ultrasonic pulse frequency f pulse can be, for example, the operating period T UC of the ultrasonic carrier frequency f CY The reciprocal. In this case, the ultrasonic pulse frequency f pulse can be the ultrasonic carrier frequency f UC . The pneumatic pulse AP can generate a net air flow in a single direction. Therefore, the APG device can be used as a (micro) air pump. In one embodiment, the first pneumatic pulse AP1 can generate a first net air flow that continuously faces a single direction (such as the first direction D1). Taking FIG. 20 as an example, during the first time period T1, all the pneumatic pulses AP face the first direction D1. When the first time period T1 is at least equal to or longer than the reciprocal of the minimum audible frequency, the first net air flow generated by the first pneumatic pulse AP1 can be regarded as continuously facing a single direction D1. For example, when the minimum audible frequency is 10 Hz, when the first time period T1 is at least equal to or longer than 0.1 second, the first net air flow can be regarded as continuously facing a single direction D1. Note that the first amplitudes corresponding to the first pneumatic pulses AP1 facing the first direction D1 can be the same or different from each other. On the other hand, the APG device can generate a second pneumatic pulse AP2, and the second pneumatic pulse AP2 can generate a second net air flow that continuously faces the second direction D2, and the second direction D2 is opposite to the first direction D1. In one embodiment, when the APG device generates a significant air flow or air movement, and the pneumatic pulses switching between the first direction D1 and the second direction D2 are indistinguishable, the first net air flow can be regarded as continuously facing the direction D1 during the time period T1, and / or the second net air flow can be regarded as continuously facing the direction D2 during the time period T2. The membrane structure can be actuated by a demodulated drive signal (such as ±SV) and a modulated drive signal (such as SM). Note that in the present application, SM can be referred to as a modulation signal, which is also a type of drive signal. Similarly, ±SV can be referred to as a demodulation signal, which is also a type of drive signal. Except for Figure 2, Figure 21 is a schematic waveform diagram of the demodulated signal ±SV and the modulated signal SM of another embodiment of the present application, where the transition between high / low voltages is ignored. As shown in Figure 21, the modulation / drive signal SM can be generated according to an input signal (such as S IN ), and the input signal includes a (nonzero) direct current (DC) offset. In other words, the input signal can be just a DC signal, but is not limited thereto. In one embodiment, the DC offset can be related to the direction of the net air flow. For example, during a first time period T1, in response to a positive DC offset, an air pulse (AP) can generate a first net air flow continuously towards a first direction D1. On the other hand, during a second time period T2, in response to a negative DC offset, the air pulse generated by the APG device can generate a second net air flow continuously towards a second direction D2, and the second direction D2 is opposite to the first direction D1. In this regard, the APG device or the air flow generating device of the present application can be regarded as a voltage-air flow converter, which can convert voltage into air flow. In addition to the polarity of the DC offset, the direction of the net air flow can also be determined or controlled by the phase between the modulation signal (SM) and the demodulation signal (±SV). For example, in Figure 21, the transition of the demodulation signal ±SV is aligned with the time period when the modulation signal SM is at a low level. In this case, the APG device can generate an air flow towards a third direction, for example. When the phase of the demodulation signal ±SV is shifted such that the transition of the demodulation signal ±SV is aligned with the time period when the modulation signal SM is at a high level, the APG device can generate an air flow towards a fourth direction, and the fourth direction is opposite to the third party. In short, the direction of the net air flow generated by the APG device can be determined or controlled by the phase (difference) between the modulation signal and the demodulation signal. The intensity or volume of the net air flow can be a function of the DC offset or related to the magnitude of the DC offset. By maintaining the air flow direction (whether it is the first direction or the second direction), the APG device can dissipate heat, dehumidify, ventilate, or promote air circulation. In this case, the APG device can be regarded as a fanless blower. That is to say, C00, 500, or 100 can also be regarded as a fanless blower, especially when the drive signal or modulation drive signal applied thereto is generated according to an input signal, and this input signal contains a non-zero DC component or offset. In the present application, the terms "APG device", "air flow generating device", and "blower" can be used interchangeably, which means that the device (such as 100, 500, C00, or K00) can also be regarded as an air flow generating device or a blower. Alternatively, as shown in Figure 2, the input audio signal S INIt can be an electrical representation of an audio sound signal (such as music). Note that the input audio signal S includes an alternating current (AC) audio component IN It may also include a non-zero DC voltage or offset. The modulation signal SM can be based on the input (audio) signal S including the DC offset IN In this case, the APG device or the fanless exhaust fan can emit sound while generating a unidirectional clean air flow. In one embodiment, the APG device, the air flow generating device or the fanless exhaust fan can be disposed within a wearable sound device (such as an earbud), details of which will be described later. When the APG device, the air flow generating device or the fanless exhaust fan is disposed within the wearable sound device, the APG device, the air flow generating device or the fanless exhaust fan can simultaneously achieve ear canal drying (or cooling) and music playback. As mentioned above, the air flow generating device, the APG device or the fanless exhaust fan can be used for heat dissipation applications. To dissipate the heat of the heat source, the APG device can be strategically located close to the heat source. For example, FIG. 22 is a schematic diagram of different configurations of the APG device G00 of an embodiment of the present application. FIGS. 22(a), (b) and (c) respectively illustrate the case where the APG device G00 is disposed above, below or beside the heat source HS. The heat source HS can be a central processing unit (CPU), a graphics processing unit (GPU) or any heat generating component. The APG device G00 and / or the heat source HS can be disposed within a housing of an electronic / host device (such as a host computer, a wearable sound device, a laptop computer, a tablet computer, a mobile phone, an augmented reality device, a virtual reality device or a mixed reality device). FIG. 23 is a schematic diagram of the APG device H00 of the host device 23HD of an embodiment of the present application. To enable the APG device H00 integrated within the host device 23HD to generate an air flow, the host device 23HD can include one or more appropriate ports VNT to establish this air flow. The ports VNT can be holes along the edge or side of the host device 23HD, which are strategically arranged to facilitate the desired (cooling or drying) air flow. In one embodiment, the host device 23HD can be a personal or portable device, such as a personal or portable phone, but is not limited thereto. When a chamber (or main device 23HD) houses an APG device (such as H00), the APG device (H00) can operate in a pump-in mode. In the pump-in mode, air enters the main device 23HD through the APG device H00, and the port VNT can be used as an outlet for establishing an air flow. When the APG device H00 detects water, the APG device H00 for preventing water damage (such as waterproofing) can immediately stop pumping to prevent water from entering the main device 23HD. Alternatively, the APG device H00 can operate in a net pump-out mode, and the internal space of the main device 23HD can be in an underpressurized state to draw a net air flow into the main device 23HD through the port VNT. The main device may include one or more APG devices disposed within the main device. For example, FIG. 24 is a schematic diagram of the APG devices J00a and J00b of the main device 24HD according to an embodiment of the present application. The two APG devices J00a and J00b disposed within the main device 24HD are used to ventilate the space within the main device 24HD. In one embodiment, the main device 24HD can be a main computer, and its size (such as width, length, or height) is not limited. The space within the main device 24HD can be irregular or undivided. The main device 24HD may lack a specific pattern for guiding the air flow. However, the arrangement of the APG devices J00a and J00b may be crucial for proper cross-ventilation. As shown in FIG. 24(a), the APG devices J00a and J00b can be arranged diagonally or non-facing or misaligned non-alignedly, and are arranged on or adjacent to opposite or non-adjacent faces (such as Wa, Wb) of the main device 24HD, but not limited thereto. Arranging the APG devices J00a and J00b opposite to each other but not directly facing can optimize the path of air through the main device 24HD. Therefore, the air flow can be guided to the places where cold air is most needed. In addition, low-frequency sounds can be blocked from passing through the APG devices J00a or J00b because, with the help of the opposite faces or walls (such as Wa, Wb) of the main device 24HD, the back waves (such as backward radiation waves) of the APG devices J00a and J00b are less likely to leak through each other and thus will not cancel out their respective front waves (such as forward radiation waves). In one embodiment, there is no direct mixing between the sound pressures from APG devices J00a and J00b, such that the host device 24HD can employ an adaptive compensation algorithm, which can utilize real-time chamber pressure data to control the operations of APG devices J00a and J00b, ensuring optimal performance without introducing unexpected errors into the adaptive compensation algorithm by APG devices J00a and J00b. In one embodiment, APG devices J00a and J00b can be substantially parallel. In one embodiment, the planes (such as Wa, Wb) where APG devices J00a and J00b are located can be the farthest apart. In one embodiment, APG devices J00a and J00b may not be aligned when viewed from the top view (Figure 24(a)), and may be aligned when viewed from the side view (Figure 24(b)). The DC offset of APG device J00a and the DC offset of APG device J00b can have opposite polarities. This polarity difference helps to create a push-pull active air flow cooling path. Over time, dust accumulates at the air flow inlet, and may gradually block the air flow. In one embodiment, for self-cleaning, the DC offset of APG device J00a can be switched or alternated between a first value (such as a positive value or higher than a threshold) and a second value (such as a negative value or lower than the threshold) to periodically or irregularly reverse the air flow (such as every few minutes), thereby minimizing dust accumulation. Similarly, the DC offset of APG device J00b can be switched between a third value (such as the second value, negative value or lower than a threshold) and a fourth value (such as the first value, positive value or higher than the threshold), and the switching of APG device J00b is synchronized with the switching of APG device J00a. Accordingly, the accumulated dust can be mostly blown off, and the air flow can be maintained. This self-cleaning mechanism is particularly applicable to situations of high-heat generation applications that require maintaining the air flow for a long time (such as watching an action movie or playing a dungeon game). In one embodiment, for self-cleaning, a "puff" operation may sometimes be employed. For example, the APG device J00a may pump air continuously at a medium rate (in the first time slot), and the APG device J00b may pump out air intermittently (e.g., 2 - 3 times) at a high rate (in the first time slot). Then, the roles are reversed: the APG device J00b may pump air continuously at a medium rate (in the second time slot), and the APG device J00a may pump out air intermittently (e.g., 2 - 3 times) at a high rate (in the second time slot). The entire cycle may take approximately 1 second. This puff operation may be activated as frequently as pressing the power button of the host device each time, and is masked by playing a motorcycle starting sound (e.g., "pon", "pon", "pon", "pon"). Accordingly, most of the accumulated dust can be removed, and the air flow can be maintained. The APG device may be disposed within a wearable sound device (such as an in-ear sound device, earbuds, headphones, or a hearing aid) to ventilate the ear canal. Ventilating or drying the ear canal can prevent infections caused by the growth of bacteria or fungi over long-term use. For example, FIG. 25 is a schematic diagram of the air flow generating device K00 of the host device 25HD according to an embodiment of the present application. The host device 25HD may be a wearable sound device (such as earbuds or a hearing aid). The wearable sound device 25HD includes an air flow generating device K00. The air flow generating device K00 is used to provide a continuous air flow or (net) air movement into or out of the ear canal when the user is wearing it, so as to achieve ear canal drying, dehumidification, or ventilation. FIG. 25(a) shows the host device 25HD; FIGS. 25(b) and (c) respectively provide front and rear views of the air flow generating device (or APG device) K00. The air flow generating device (or APG device) K00 within the host device 25HD (i.e., the wearable sound device) can generate a continuous air flow within or into and out of the host device 25HD, which is beneficial for ear canal cooling or drying, thereby preventing infections caused by the growth of bacteria or fungi over long-term use. In addition, the host device 25HD may include a suitable vent (such as provided on its housing K04) to release the pressure generated by the low-volume air flow, so as to continuously freshen the air within the host device 25HD or the ear canal, and bring a more comfortable long-term wearing experience. In one embodiment, the vent may be designed to remain permanently open, but is not limited thereto. In addition, the size, shape, or position of the housing K04 is not limited and can be designed according to actual requirements. Note that the airflow generating device (such as K00) disposed within the wearable sound device is not limited to the APG device. Any device that can generate a continuous airflow and is disposed within the wearable sound device should meet the requirements of this application and is also within the scope of this application. The intensity or flow rate of the net airflow can be dynamically, programmatically, automatically, in response to the output of sensors (such as humidity sensors or thermometers) disposed within the host device 25HD, or manually controlled or adjusted by the user. In other words, the host device 25HD or the wearable sound device 25HD may include a sensor (such as K02 in Figure 25), and the flow rate of the airflow generated by the airflow generating device (or APG device) K00 can be adjusted according to the sensing result of the sensor (K02). In one embodiment, the sensor K02 can be a humidity or temperature sensor, and the flow rate of the airflow generated by the airflow generating device (or APG device) K00 can be adjusted according to the sensing result of the sensor K02, but is not limited thereto. Note that the position of the sensor K02 within the host device 25HD can be optimized according to actual needs, but is not limited thereto. The user can manually control the wearable sound device to change or adjust the intensity or flow rate of the net airflow; or, the airflow generating device K00 can be triggered / activated according to the command signal from the sensor, and the sensor is disposed within the host device 25HD or communicatively coupled to the airflow generating device K00 via a wireless or wired connection. The intensity or flow rate of the net airflow can be adjusted via the amplitude of the demodulation (driving) signal (such as ±SV) and / or the modulation (driving) signal (such as SM). By utilizing the above energy recovery, the APG device (such as K00) that generates a constant amplitude air pulse can be designed to have low power consumption. In short, in applications where audio is not required, the host device 25HD (operating in the exhaust fan mode) can be powered by or without a battery, and the air pulse (AP) can still generate a continuous net air movement in a single direction to dry the ear canal (or dissipate the heat previously generated by the host device 25HD). Different from traditional speaker technologies (such as electrodynamic or electrostatic speaker technologies) that lack the ability to move air in a single direction, the APG device or airflow generating device (such as K00) of this application has the one-way airflow ability and provides a ventilation solution. Details or variations of wearable sound devices, sound generating devices, APG devices, and circuits for energy recovery can be found in U.S. Patent Application Nos. 62 / 572,405, 62 / 575,672, 62 / 579,088, 62 / 579,914, and 63 / 437,371, the disclosures of which are incorporated herein by reference in their entirety and form a part of this specification. In summary, the pneumatic pulse generating device of the present application generates asymmetric pneumatic pulses at ultrasonic pulse frequencies and can be used as a pneumatic pump. Multiple pneumatic pulses generate a net air flow continuously in a single direction and can be applied to air movement applications (such as cooling, drying, dehumidifying, heat dissipation, and / or ventilation, etc.). The above is only the preferred embodiment of the present application, and all equivalent changes and modifications made according to the scope of the patent application of the present application shall fall within the scope of the present application. 10: Membrane structure 100~900, A00~F00, G00, H00, J00a, J00b, K00: Pneumatic pulse generating device 101, 103, 105, 107: Flap 101A, 103A: Actuator 102: Demodulation unit 104: Modulation unit 11: Chamber definition layer 110R, 110L, 122R, 122L, 111R, 111R', 111L, 111L', 110R', 110L': Side wall 112: Opening 113L, 113R: Through port 115, 125, 115', 631, 705, 731, 805, 831, 905, 931, A05, B05, B15: Chamber 117, 404: Chamber lid 12: Device layer 123H, CP, D113, H125, L 630: Distances 123R, 123L, 123L'', 123R'': Support structures 124L, 124R, 121, 121': Walls 126R, 126L, 413T, B12, B13: Holes 135, 136, 137, 403: Line segments 14: Coating structures 23HD, 24HD, 25HD: Main device 320, 407, 633, 733, 833, 933, A33, B33: Exits 416R, 416L: Directions 430: Areas 431~433: Solutions 610, 640, 710, 740, 810, 840, 910, 940, A10, A40, B10: Sub-assemblies 613, 713: Orifice 620: Layers 630, 730, 830, 930, A30, B30: Conduits 632, 732, 832, 932, A32, B32: Channels 635, 735, A35: Chamfers 650: Surfaces A, B: Groups AP, AP1, AP2: Air pulse B11 Cover structures D01~D08, E11~E12, F11~F22: Units D1, D2: Direction d 101 , d 103 , d 101 -d 103 , V(opening), V(d2)-V(d3), V(ep_vlv), V(p_vlv): Curve f: Frequency f pulse : Ultrasonic pulse frequency f UC : Operating frequency H 631 , H 705 , H 831 , H 834 , H 931 , H 934 , H A31 , H A34 : Height HS: Heat source K02: Sensor K04: Housing p 1 , p 2: Peak values P104, P102, P104'; Airflow distributions S(f), W(f), Y(f), Z(f); Spectra S101, S103, -SV, +SV, -SV', +SV': Demodulated drive signal S IN : Input audio signals SM, SM'; Modulation drive signal SS; Sound signal t 0 ~t 6 : Time points T1, T2; Time period T 22 : Time segment T CY : Operating cycles U104, U102, U104'; Pressure distribution UAW; Ultrasonic air pressure wave UPA; Ultrasonic pulse array V BIAS : Bias voltage VNT; Ports W115, W115'; Chamber widths W631, W 705 ,W 732 ,W 734 ,W 805 ,W 815 ,W 832 ,W 905 ,W 932 ,W CP ,Z 2 : Widths Wa, Wb; Wall θ, θ 1 , θ 2 : Angle FIG. 1 is a schematic diagram of a gas pulse generating device according to an embodiment of the present application. FIG. 2 is a schematic diagram of waveforms of a modulation driving signal and a demodulation driving signal according to an embodiment of the present application. FIG. 3 shows a simulation result corresponding to the device shown in FIG. 1. FIG. 4 shows a simulated frequency response of the sound pressure level corresponding to the APG device shown in FIG. 1. FIG. 5 shows a simulation result corresponding to the device shown in FIG. 1. FIG. 6 shows a simulation result corresponding to the device shown in FIG. 1. FIG. 7 is a schematic diagram of a gas pulse generating device according to an embodiment of the present application. FIG. 8 is a schematic diagram of a gas pulse generating device according to an embodiment of the present application. FIG. 9 shows the frequency response of the energy transfer ratio of the device shown in FIG. 1. FIG. 10 shows the frequency response of the energy transfer ratio of the device shown in FIG. 8. FIG. 11 shows the process of the manufacturing method of the device shown in FIG. 8. FIG. 12 is a schematic diagram of a gas pulse generating device according to an embodiment of the present application. FIG. 13 is a schematic diagram of a driving signal wiring scheme according to an embodiment of the present application. FIG. 14 shows the relationship between the SPL measurement result and the frequency of the device shown in FIG. 12. FIG. 15 shows the relationship between the SPL measurement result and the peak-to-peak voltage of the device shown in FIG. 12. FIGS. 16 to 17 are schematic diagrams of a gas pulse generating device according to an embodiment of the present application. FIG. 18 shows a full-cycle pulse of an operation period with different degrees of asymmetry. FIG. 19 shows the function of each element from the system perspective and its corresponding frequency domain effect. FIG. 20 is a schematic diagram of a gas pulse according to an embodiment of the present application. FIG. 21 shows waveforms of a demodulation signal and a modulation signal according to another embodiment of the present application. FIG. 22 is a schematic diagram of different configurations of the APG device according to an embodiment of the present application. FIGS. 23 to 25 are schematic diagrams of the APG device of the host device according to an embodiment of the present application. AP, AP1, AP2: Gas pulse D1, D2: Direction f pulse : Ultrasonic pulse frequency T1, T2: Time period T CY : Operation period

Claims

1. A gas pulse generating device, comprising: A membrane structure is actuated to generate a plurality of air pulses at an ultrasonic pulse frequency; wherein the membrane structure includes a pair of lobes, the pair including a first lobe and a second lobe disposed opposite to each other; wherein each of the first lobe and the second lobe of the pair is provided with an actuator; wherein the actuator includes a first electrode and a second electrode; wherein the first electrode and the second electrode receive a modulation signal for generating a change in ultrasonic air pressure and a demodulation signal for forming an opening; wherein the timing of the modulation signal is substantially aligned with the timing of the demodulation signal; wherein the plurality of air pulses generate a unidirectional net airflow.

2. The gas pulse generating device as described in claim 1, wherein, The flap is actuated to perform a differential motion to form the opening using an opening frequency synchronized with the frequency of the ultrasound pulse.

3. The gas pulse generating device as described in claim 1, wherein, The membrane structure is actuated by a driving signal; wherein the driving signal is generated based on an input signal, the input signal including a non-zero DC offset.

4. The gas pulse generating device as described in claim 3, wherein, In response to a positive DC offset, the plurality of air pulses generate a first net airflow toward a first direction; wherein, in response to a negative DC offset, the plurality of air pulses generate a second net airflow toward a second direction; wherein, the first direction is opposite to the second direction.

5. The gas pulse generating device as described in claim 1, wherein, The membrane structure is actuated by the modulation signal to perform a common-mode motion; wherein the modulation signal is generated based on an input signal, which includes a non-zero DC offset.

6. The gas pulse generating device as described in claim 1, wherein, The membrane structure is actuated by the demodulated signal to perform a differential mode motion to form the opening at an opening frequency synchronized with the ultrasonic pulse frequency.

7. The gas pulse generating device as described in claim 1, wherein, The direction of the clean airflow generated by the air pulse generating device is determined by the phase between the modulation signal and the demodulation signal.

8. The gas pulse generating device as described in claim 1, wherein, This gas pulse generating device is used as an air pump.

9. The gas pulse generating device as described in claim 1, wherein, The gas pulse generating device is installed on, below, or next to a heat source and is used to dissipate heat from the heat source.

10. The gas pulse generating device as described in claim 1, wherein, The gas pulse generator is used for ventilation.

11. The gas pulse generating device as described in claim 1, wherein, The air pulse generating device is installed in a wearable sound device and is used to ventilate the ear canal.

12. The gas pulse generating device as described in claim 1, wherein, The gas pulse generating device is installed in a main unit and is used to ventilate the space inside the main unit.

13. A heat dissipation method, comprising: The gas pulse generating device described in Request 1 is placed on, under, or next to a heat source.

14. A ventilation method, comprising: The gas pulse generating device described in Request 1 is installed in a host device.

15. A method for ventilating the ear canal, comprising: The air pulse generating device described in Request 1 is installed in a wearable sound device.

16. A method for sensing air quality, comprising: The air pulse generating device described in Request 1 is installed in an air quality sensing device.

17. A wearable sound device, comprising: A shell; And an airflow generating device for generating a unidirectional airflow; wherein the airflow generating device includes a membrane structure; wherein the membrane structure includes a pair of lobes, the pair of lobes including a first lobe and a second lobe disposed opposite to each other; wherein the first lobe and the second lobe of the pair of lobes are each provided with an actuator; wherein the actuator includes a first electrode and a second electrode; wherein the first electrode and the second electrode receive a modulation signal for forming an ultrasonic air pressure change and a demodulation signal for forming an opening; wherein the timing of the modulation signal is substantially aligned with the timing of the demodulation signal.

18. The wearable sound device as described in claim 17, wherein, When a user wears the wearable sound device, the airflow generating device generates airflow toward or out of the ear canal.

19. The wearable sound device as described in claim 17, wherein, The membrane structure is actuated by a driving signal; wherein the driving signal is generated based on an input signal, the input signal including a non-zero DC offset.

20. The wearable sound device as described in claim 17, further comprising: A sensor; wherein the flow rate of the airflow generated by the airflow generating device is adjusted according to the sensing result of the sensor.

21. A bladeless fan, comprising: A membrane structure; wherein the membrane structure includes a pair of lobes, the pair of lobes including a first lobe and a second lobe disposed opposite to each other; wherein the first lobe and the second lobe of the pair of lobes are respectively provided with an actuator; wherein the actuator includes a first electrode and a second electrode; wherein the first electrode and the second electrode receive a modulation signal for forming an ultrasonic air pressure change and a demodulation signal for forming an opening; wherein the timing of the modulation signal is substantially aligned with the timing of the demodulation signal; wherein the plurality of air pulses generated by the bladeless fan constitute unidirectional clean air movement or clean airflow.

22. The bladeless fan as described in claim 21, wherein, The bladeless fan is housed within a main unit, which includes a port.

23. The bladeless fan as described in claim 21, wherein, This bladeless fan produces both audio sound and unidirectional airflow.

24. The bladeless fan as described in claim 21, wherein, The plurality of air pulses are generated based on an input audio signal, wherein the input audio signal includes a non-zero DC offset.

25. The bladeless fan as described in claim 21, wherein, The airflow generated by the bladeless fan is controlled in response to the output of a humidity sensor.

26. The bladeless fan as described in claim 21, wherein, The first lobe is driven by the demodulated signal or the modulated signal; wherein the flow rate of the airflow generated by the bladeless fan is adjusted by the amplitude of the demodulated signal or the modulated signal.

27. A method for generating airflow, comprising: A membrane structure of an air pulse generating device generates a plurality of air pulses at an ultrasonic pulse frequency; wherein the membrane structure includes a pair of lobes, the pair of lobes including a first lobe and a second lobe disposed opposite to each other; wherein the first lobe and the second lobe of the lobe pair are each provided with an actuator; wherein the actuator includes a first electrode and a second electrode; wherein the first electrode and the second electrode receive a modulation signal for forming an ultrasonic air pressure change and a demodulation signal for forming an opening; wherein the timing of the modulation signal is substantially aligned with the timing of the demodulation signal; wherein the plurality of air pulses generate a unidirectional net airflow.

28. The airflow generation method as described in claim 27, comprising: The membrane structure of the gas pulse generating device is driven by a driving signal; wherein the driving signal is generated based on an input signal, the input signal including a non-zero DC offset.

29. The airflow generation method as described in claim 27, comprising: The membrane structure of the gas pulse generating device is driven by the modulation signal to perform common-mode motion; wherein the modulation signal is generated based on an input signal, which includes a non-zero DC offset.

30. The airflow generation method as described in claim 27, comprising: The membrane structure of the gas pulse generating device is driven by the demodulated signal to perform differential mode motion; wherein the differential mode motion is used to form the opening at an opening frequency synchronized with the ultrasonic pulse frequency.

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