Air-pulse generating device with resonant chamber embedded therein

Abstract

To provide an air-pulse generating device with a resonant chamber embedded therein.SOLUTION: An air-pulse generating device (APG device) 10 comprises a film structure (flaps 101 and 103) operating at an ultrasonic operating frequency, and a resonant chamber 115 formed on a side of the film structure. A resonance is formed within the resonance chamber. The resonant chamber causes the APG device to have a peak on a frequency response of an acoustic property at the ultrasonic operating frequency.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This application relates to an air pulse generator, and more particularly to an air pulse generator having an embedded resonance chamber.

Background Art

[0002] Unless otherwise stated in this specification, the approaches described in this section are not prior art to the claims of this application and are not admitted to be prior art by inclusion in this section.

[0003] Speaker drivers and back enclosures are two major design challenges in the speaker industry. It is difficult for conventional speakers to cover the entire audio frequency band, for example, from 20 Hz to 20 kHz. To produce a highly faithful sound at a sufficient sound pressure level (SPL), it is necessary to make both the radiation / moving surface and the volume / size of the back enclosure sufficiently large for conventional speakers.

Summary of the Invention

[0004] An air pulse generation (APG) device is disclosed to overcome the design challenges faced by conventional speakers. However, the previously disclosed APG devices generate a pulsed air flow. For applications that generate sound (or move air), it is necessary to efficiently convert such an air flow into air pressure.

[0005] Therefore, the main objective of this application is to provide an air pulse generator that surpasses the prior art.

[0006] Embodiments of the present invention provide an air pulse generator (APG device). The air pulse generator includes a film structure operating at an ultrasonic operating frequency, and a resonance chamber formed on the side surface of the film structure, wherein resonance is formed within the resonance chamber, Due to the resonance chamber, the air pulse generator has a peak in the frequency response of the acoustic characteristics of the air pulse generator at the ultrasonic operating frequency.

[0007] After reading the following detailed description of the preferred embodiments shown in various figures and drawings, these and other objects of the present invention will become apparent to those skilled in the art without doubt.

Brief Description of the Drawings

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Embodiments for Carrying Out the Invention

[0009] The following inventions filed by the present applicant are incorporated herein by reference. That is, U.S. Patent No. 11,323,797 related to Dynamic Vent (DV), U.S. Patent No. 11,943,585 related to an Air Pulse Generation (APG) device, and U.S. Application No. 18 / 829,245 related to a toothed flap edge.

[0010] In the case of an APG device, a pair of opposing flaps (e.g., flaps 101, 103 of U.S. Patent No. 11,943,585, or those shown in FIG. 1 or FIG. 2) created by etching a film layer made of silicon or other suitable material are actuated by applying a voltage between both ends of a piezoelectric material such as PZT deposited on the pair of flaps. The pair of opposing flaps causes both common-mode operation by signal SM and differential-mode operation by a pair of signals ±SV, and respectively executes functions of modulation and demodulation of ultrasonic waves. As a result of this modulation of ultrasonic waves and demodulation to the baseband, air mass movement occurs between flap pairs 101 to 103 at the baseband frequency via the virtual valve 112. This air pump may be used as an audio speaker that generates audio sound waves by sending air bidirectionally at an audio frequency, or may be used as a unidirectional air pump for other applications such as forced air cooling.

[0011] The airflow passing through the valve increases due to the pressure difference across the valve. The instantaneous pressure on each side of the valve is generated by the movement of the flap, locally compressing or expanding the air. To increase the flow rate through valve 112, a cap with an outlet located over (downstream of) the flap is described in U.S. Patent No. 11,943,585. This cap forms a chamber with dimensions much smaller than the wavelength near the flap and has a small outlet that restricts the airflow. This increases the level of air compression / expansion in the chamber, increasing the pressure difference across the valve, and as a result, increasing the airflow. As disclosed in U.S. Patent No. 11,943,585, this cap is not strictly necessary, as a significant airflow can be achieved without the cap.

[0012] Instead of restricting the airflow into and out of the compression chamber, an alternative method of increasing the local pressure changes around the valve is presented here. A resonant air cavity may be provided on one or both sides of the flap to increase the local ultrasonic pressure by confining ultrasonic energy within the cavity. The resonance may be Helmholtz resonance or standing wave resonance. Helmholtz resonance occurs at a specific frequency when the mass of air at the outlet forms a mass-spring system with the volume of air in the chamber acting as a spring. Standing wave resonance occurs when an acoustic reflector is placed at a preferred distance from the flap. This causes the acoustic wave to bounce off the reflector, and the reflected wave and the incident wave are added in superposition, forming regions of constructive interference with high-amplitude oscillatory pressure (antinodes) and regions of destructive interference with minimum pressure (nodes). FIGS. 1 or 2 show one embodiment, where a pair of flaps 101 and 103 have a Helmholtz resonance chamber 115 on one side with an outlet 713. On the other side, in FIG. 2, a standing wave cavity 116 is configured with an acoustic reflector 702 spaced a distance H116 from the flap.

[0013] In this application, the terms "chamber" and "cavity" are used interchangeably.

[0014] As disclosed in U.S. Patent No. 11,943,585, the APG devices 10 and 20 shown in FIGS. 1 and 2 include a film structure 104. The film structure 104 includes a flap pair 102, and the flap pair 102 includes flaps 101 and 103. The flaps 101 and 103 have anchor portions 131 and 133, respectively. The flap pair 102 performs differential mode operation to form an opening 112 or a virtual valve 112. This "virtual valve" is used to emphasize the ability of the flap pair to be opened and closed. On the other hand, the "opening" is used to emphasize the state of the flap pair, especially when the virtual valve is opened.

[0015] The common mode displacement of the flaps 101 and 103 at the ultrasonic modulation / operating frequency by the common mode signal SM generates ultrasonic pressure bidirectionally from the flaps outward toward the cavities 115 and 116, but with opposite polarities in each direction. The effect of Helmholtz resonance or standing wave resonance is to increase the ultrasonic pressure amplitude while maintaining opposite polarities between the front and back of the flaps. Further, the flaps are simultaneously driven by a differential mode signal ±SV superimposed on the common mode signal, leading to the opening of the virtual valve 112. The opening of the valve 112 is temporally aligned with the pressure difference generated by the common mode displacement, whereby the pressure difference across the flaps causes a net air flow through the valve 112 within the ultrasonic period of the common mode displacement.

[0016] In one embodiment, the ultrasonic modulation / operating frequency of the common mode signal (or modulation drive signal) SM may be 192 kHz, while the demodulation frequency of the differential mode signal (or demodulation drive signal) SV may be 96 kHz, which is half of the ultrasonic modulation / operating frequency, due to the differential mode operation.

[0017] The detailed operating principle of the flap pair, which is driven by the common / differential mode signals SM / SV and performs common / differential mode operations and modulation (demodulation) operations to generate ultrasonic pulses, is introduced in U.S. Patent No. 11,943,585, but will not be described in this specification for the sake of simplicity. Further, the demodulation signal SV may be obtained from the drive circuit disclosed in U.S. Application No. 18 / 396,678, and the modulation signal SM may be obtained from the drive circuit disclosed in U.S. Patent No. 12,107,546. However, the details thereof will not be described in this specification for the sake of simplicity.

[0018] In addition to this, the APG devices 10 / 20 include a cover structure 150. The outlet 713 is formed therein. The cover structure 150 may be a lid, a cap, or the like. The cover structure 150 may be 3D printed, or may be formed of metal or silicon, for example, formed through a semiconductor manufacturing process, but is not limited thereto. As shown in FIGS. 1 and 2, the Helmholtz resonance chamber 115 is formed between the film structure 104 and the cover structure 150. The outlet 713 and the Helmholtz resonance chamber 115 are connected to each other.

[0019] [Helmholtz Resonance] The acoustic simulation of the Helmholtz chamber (Figure 3) shows the pressure amplitude distribution near the Helmholtz resonance according to the input velocity at the bottom of the chamber 115. This represents the positions of the flaps 101 and 103. It can be seen that the pressure amplitude is large inside the chamber and decreases at the outlet towards the outside. Figure 4 shows the input acoustic impedance as a function of frequency, looking into the chamber from the position of the input volume velocity, or simply the input velocity. The maximum value of the acoustic impedance in this case corresponds to the Helmholtz mode (which is set to be near 192 kHz, the operating frequency of the ultrasonic wave in this example). This can be set to be near the frequency of the common mode signal (e.g., SM) by controlling the dimensions of the cavity and the outlet. Maximizing the acoustic impedance at the ultrasonic operating frequency minimizes the ultrasonic energy propagating out from the flaps, maximizes the pressure accumulation near the virtual valve, and thus the air flows through the valve as desired. At the same time, the ultrasonic impedance of the resonant cavity at the baseband frequency should be low so as not to impede the baseband air flow, typically kept lower than the other impedances of the system (such as valves and connected acoustic chambers).

[0020] From Figures 3 and 4, it can be verified that the Helmholtz resonance chamber generates a peak in the frequency response of the acoustic impedance of the APG device (e.g., 10 or 20) at the ultrasonic operating frequency (e.g., 192 kHz).

[0021] [Resonance of standing waves] A standing wave reflector may further be used to improve the air flow. The common mode ultrasonic waves generated by the flaps 101 and 103 (Figure 2) bounce off the reflector 702 and superimpose and sum with the subsequent cycles of the ultrasonic waves generated by the flaps. These bounces generate resonance in the cavity, resulting in pressure amplification and an increase in the air flow through the valve 112. The optimal distance H116 of the reflector 702 from the plane of the flaps 101, 103 is determined approximately by the ultrasonic wavelength in air.

[0022] In one embodiment, the reflector 702 is a hard rigid wall having a characteristic acoustic impedance much higher than that of air. When traveling in direction 202 and reaching the reflector, the ultrasonic wave is reflected in direction 204 without changing its polarity. For the in-phase addition of the pressures at the flaps, the total of the bidirectional distances between the flaps and the reflector shall be a multiple of the wavelength λ corresponding to the ultrasonic operating frequency. Therefore, the optimal distance H116 between the reflector and the flap is assumed to be approximately Nλ / 2, where N is a positive integer (i.e., it may be a half wavelength or an integer multiple of the half wavelength).

[0023] FIG. 5 shows the pressure amplitude distribution of a simulated standing wave cavity with N = 1, where the high-pressure antinodes are in the plane of the flap and the reflector 702, and the low-pressure nodes are at the center of the cavity. Periodic boundary conditions are used to simulate such an array of flaps, and small outlets are arranged in the reflector 702. However, as will be described in the directivity section below, there are other possibilities for the outlets. The input acoustic impedance (FIG. 6) seen from the position of the input velocity as a function of frequency shows several peaks. The first peak corresponds to the Helmholtz mode, and the second peak corresponds to the λ / 2 standing wave mode near the common mode frequency (192 kHz in this case). On the other hand, the impedance drop at approximately 96 kHz corresponds to destructive interference, which is effective in further suppressing the differential mode pressure generated by the movement of the valve, as described previously in U.S. Patent No. 11943585.

[0024] Note that the standing wave configuration may be set to have a higher quality factor (a sharper impedance peak) than the Helmholtz configuration, depending on the outlet configuration. Since the standing wave configuration does not require a narrow wall, viscous losses can be significantly reduced. As will be described in the directivity section below, the emission (loss) of ultrasonic waves can be reduced by arranging the outlet on the side rather than as a reflector. This is beneficial for confining a larger proportion of the ultrasonic energy in the cavity with less dissipation. However, when the quality factor increases, it may take time for the pressure to reach a steady state, and the sensitivity to changes in the resonance frequency due to temperature, humidity, and other factors may increase. However, if there is an open valve (not included in the simulation of acoustic impedance), the air flow through the valve reduces the quality factor. This can be significantly lower than the quality factor shown in FIG. 6.

[0025] The resonance frequency of the standing wave is required for the air flow in the baseband and may be affected by the presence of holes or other outlets, deviating from the predetermined Nλ / 2 condition. Also, the anchor regions 131 and 133 of the flap exhibit different acoustic impedances to ultrasonic waves compared to the movable flap and, together, affect the optimal distance for resonance.

[0026] [Increased conversion from ultrasonic to baseband] Ultrasonic waves confined by either Helmholtz waves or standing waves increase the local ultrasonic sound pressure difference, resulting in a higher air flow at the baseband frequency. When the valve is open, air flows through the valve from one side cavity to the other side, resulting in an attenuation or loss mechanism that reduces the pressure gain, or an attenuation or loss mechanism that reduces the quality factor more than that shown in FIGS. 4 and 6 where the effect of the valve is not modeled. Nevertheless, this achieves the desired goal of increased conversion from ultrasonic waves to baseband waves, i.e., increased demodulation efficiency. Therefore, it is beneficial to set an air cavity having a high acoustic impedance at the common mode operating frequency.

[0027] At the same time, another resulting effect is the reduction of the emission of unwanted ultrasonic frequencies. In U.S. Patent No. 11943585, the emitted ultrasonic waves are emitted and not recaptured as described herein, so as a result, strong unwanted ultrasonic waves are emitted along with the baseband waves. For health and safety reasons, it is often desirable that the emitted ultrasonic energy be limited to a certain threshold level. This increased conversion from ultrasonic waves to the baseband is effective in increasing the baseband output while reducing the potentially harmful emission of high-amplitude ultrasonic waves.

[0028] [Directivity] In the case of standing wave resonance, since the wavelength of the ultrasonic wave is much smaller than the wavelength of the baseband wave, the ultrasonic wave has a much higher directivity than the baseband wave. When the dimensions of the flap or the array of flaps 101, 103 are larger than the wavelength of the ultrasonic wave, the ultrasonic wave propagates toward the reflector while minimizing the spreading loss in the lateral direction. Conversely, since the demodulated baseband wave has a much lower frequency, it propagates like a spherical wave, and more of the acoustic energy is directed laterally in the direction 206 of FIG. 2. Thus, the reflector or the slits, holes, or other openings around it may be set off-axis with respect to the ultrasonic wave, enabling the confinement of the ultrasonic wave and the transmission of the baseband wave from these openings simultaneously. To maintain a high baseband air flow, it may be desirable to have large openings around. Thereby, the openings may be set for the baseband separated from the ultrasonic requirements, increasing the degree of freedom in setting. The outlets described in U.S. Patent No. 11943585 and, further, the Helmholtz chambers described above have small and narrow outlets that are required to confine the ultrasonic wave but cause large resistance losses. In comparison, the standing wave acoustic cavity may be set to have much larger openings in order to keep the ultrasonic wave confined in the cavity while keeping the baseband loss low.

[0029] [Various Embodiments] In other embodiments, a standing wave resonance cavity or a Helmholtz chamber may be provided on one side of the flap, or on both sides. FIG. 7 (showing the APG device 30) shows a configuration having standing wave cavities on both sides. On both sides of the flap, there are standing wave resonance cavities (116, 117) and reflectors 701, 702. The distances H116 and H117 may be close to the condition of Nλ / 2 each, subject to other effects that affect the frequency. This embodiment may be preferable from the perspective of fabrication because it does not require fabricating and assembling a chamber having a three-dimensional pattern with small features.

[0030] Furthermore, in order to suppress acoustic waves laterally in a small area such as directly above the valve, the standing wave cavity may be partially filled with a solid material (e.g., the solid material 151 shown in FIG. 8 where the APG device 40 is shown). The local air pressure is generated by the displacement of the flap, and for a given displacement, the lateral volume reduction of the cavities 116 and 117 results in a larger pressure change beneficial to the air flow through the valve. Since the pressure wave is suppressed and can be directed near the valve, the bounce-back of the reflected ultrasonic waves is minimized in the ineffective area such as the anchor and the flap area near the anchor. This has the effect of improving the speed at which ultrasonic energy is converted to the baseband (requiring less bounce-back and having a lower quality factor but still achieving a high air flow), which is advantageous for achieving a high sound pressure level at high frequencies with a minimum delay time or attenuation time. Furthermore, the filler may improve the structural rigidity of the reflector. However, to avoid increasing the viscous resistance of the air flow and leading to undesirable acoustic losses, the cavity shall be wide enough. In this embodiment, in order to enable the baseband air flow, the openings in the reflectors 701, 702 or the wall 151 may be spaced in the out-of-page direction.

[0031] Furthermore, a soft boundary ultrasonic reflector may be considered for the standing wave. Letting ultrasonic waves flow into the open space through a narrow slot having a width (W715 and W716 of the outlets 715 and 716 in FIG. 9 where the APG device 50 is illustrated) much smaller than the wavelength may cause an impedance mismatch at the open boundary at the end of the slot. Thereby, during the reflection from the slot to the open boundary, the ultrasonic wave has its polarity reversed. In such a case, the optimal distance from the flaps 101 and 103 to the ends 703 / 704 may be about λ(N / 2 + 1 / 4), and these ends 703 / 704 may mean the ends of the outlets 715 / 716. Compared with the rigid reflector that requires a distance of λ / 2, the fundamental wavelength here is λ / 4, and as a result, a lower profile device can be achieved.

[0032] Incidentally, the APG device 50 in FIG. 9 may include resonance chambers 115a and 115b. In an embodiment, the resonance chambers 115a and 115b may be Helmholtz resonance chambers, but are not limited thereto.

[0033] The Helmholtz chambers shown in FIGS. 1 and 2 have an outlet at a location directly beyond the flaps 101 and 103, but the outlet may be located elsewhere. FIG. 10 shows an outlet 717 located beyond (downstream of) the anchors (or anchor portions) 131 and 133 that replace the flaps. The acoustic impedance may still be adjusted to maximize the impedance at the ultrasonic common mode frequency. In this situation, there is no need for a wall between adjacent flap pairs, which can provide ease of manufacture.

[0034] [Structure] The resonance cavity wall may be made of a solid material that forms part of the speaker module. Part of the speaker module includes a printed circuit board used for electrical wiring, or a copper trace, or a lid (such as stainless steel or zinc alloy) used to protect against mechanical substances, chemical substances, dust, and other unwanted substances. Further, it may be set as part of the structural assembly, such as in earphones or headphones. In such cases, there is little additional cost to incorporate such an acoustic resonance cavity.

[0035] A non-rigid flexible reflector can also be used, which may be made of a polymer (such as polyimide, polyethylene, polyvinyl chloride, etc.), and can be easily added to the speaker package at low cost. The optimal position of such a flexible reflector may vary depending on the contributions of mass and stiffness.

[0036] Furthermore, the standing wave reflector may have a slight concave curvature towards the flaps 101, 103 or an inwardly curved end to help suppress ultrasonic waves in the cavity.

[0037] Furthermore, the APG device of the present invention may include a plurality of outlets and a plurality of flap pairs. For example, FIG. 11 shows the appearance of the APG device 70 or the cover structure according to an embodiment of the present invention. The APG device 70 may have a plurality of outlets formed on a cover structure (e.g., a lid or a cap). FIGS. 12 and 13 are cross-sectional views of the APG devices 80 and 82 according to an embodiment of the present invention. The APG devices 80 and 82 include a plurality of flap pairs 102 and a plurality of outlets 723. In FIG. 12, the outlet 723 is formed in and aligned with a virtual valve or opening 112 (i.e., disposed beyond it). The APG devices 80 and 82 include a plurality of flap pairs 102 and a plurality of outlets 723. In FIG. 12, the outlet 723 is formed in and aligned with an anchor portion 134 (i.e., disposed beyond it). To increase the air pressure or sound pressure level (SPL) of the APG device 80 / 82, a Helmholtz resonance chamber may be formed between the cover structure 850 and the film structure 104 of the APG device 80 / 82.

[0038] FIG. 14 shows a top view of the film structure 90 of the APG device according to an embodiment of the present invention, and FIG. 15 shows a top view of the cover structure 92 of the APG device according to an embodiment of the present invention. The film structure 90 and the cover structure 92 may be applied to the APG devices 80 and 82. The alignment of the outlet 723 with respect to the flap pair 102 may be set according to practical requirements.

[0039] In summary, the present invention utilizes a resonance chamber to bring a peak in the frequency response of the acoustic impedance at the ultrasonic operating frequency, efficiently generating air pressure, thereby improving the sound pressure level (SPL).

[0040] Those skilled in the art will readily understand that numerous modifications and changes may be made to the devices and methods while maintaining the teachings of the present invention. Accordingly, the above disclosure is to be construed as being limited only by the scope of the appended claims.

Claims

1. a film structure operating at an ultrasonic operating frequency; a resonating chamber formed on a side of the film structure; A resonance is formed in the resonance chamber; due to the resonant chamber, the air pulse generator has a peak in the frequency response of the acoustic characteristic of the air pulse generator at the ultrasonic operating frequency. Air Pulse Generator (APG device).

2. The APG device of claim 1 , wherein the resonance is a Helmholtz resonance.

3. The APG device of claim 1 , wherein the acoustic property is an acoustic impedance.

4. Equipped with a cover structure, The APG device of claim 1 , wherein the resonating chamber is formed between the film structure and the cover structure.

5. The APG device of claim 4 , wherein an outlet is formed in the cover structure and is connected to the resonating chamber.

6. the film structure includes a flap pair configured for differential mode operation to form a virtual valve; The APG apparatus of claim 5 , wherein the outlet is located beyond the virtual valve.

7. The APG device of claim 5 , wherein the outlet is disposed beyond an anchor portion of a flap of the film structure.

8. a first resonating chamber formed on a first side of the film structure; 2. The APG device of claim 1, further comprising a second resonating chamber formed on a second side of said film structure opposite said first side.

9. a first outlet connected to the first resonating chamber; 9. The APG device of claim 8, further comprising a second outlet connected to the second resonating chamber.

10. Equipped with a resonant cavity, the resonating chamber is formed on a first side of the film structure; The APG device of claim 1 , wherein the resonant cavity is formed in a second side of the film structure opposite the first side.

11. Equipped with a reflector, The APG device of claim 10 , wherein the resonant cavity is formed between the film structure and the reflector.

12. 12. The APG device of claim 11, wherein the distance between the film structure and the reflector is a half wavelength corresponding to the ultrasonic operating frequency, or an integer multiple of the half wavelength.

13. The APG device of claim 1 , wherein the resonance is a standing wave resonance.

14. The APG device of claim 1 , wherein the film structure includes a flap pair configured for common mode and differential mode operation.

15. a first resonant cavity formed on a first side of the film structure; a second resonant cavity formed on a second side of the film structure opposite the first side; The APG device of claim 1 , wherein a first standing wave resonance is formed in the first resonant cavity and a second standing wave resonance is formed in the second resonant cavity.

16. A first reflector and a second reflector are provided, 16. The APG device of claim 15, wherein the first resonant cavity is formed between the film structure and the first reflector, and the second resonant cavity is formed between the film structure and the second reflector.

17. The APG device of claim 1 , wherein the film structure includes a plurality of flap pairs and a plurality of exit ports.

18. The APG apparatus of claim 17 , wherein the outlets are disposed beyond a plurality of apertures formed via differential mode motion performed by the plurality of flap pairs.

19. The APG device of claim 17 , wherein the outlets are disposed beyond anchor portions of the pairs of flaps.

20. Equipped with a cover structure, The APG device of claim 17 , wherein the plurality of outlets are formed in the cover structure.

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