Air pulse generator with embedded resonant chamber

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

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

[0005] Therefore, the main object 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, where resonance is formed within the resonance chamber, Due to the resonant chamber, the air pulse generator exhibits a peak in the frequency response of its acoustic characteristics at the ultrasonic operating frequency.

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

[0008] [Figure 1] This is a schematic diagram of an air pulse generator according to an embodiment of the present invention. [Figure 2] This is a schematic diagram of an air pulse generator according to an embodiment of the present invention. [Figure 3] This figure shows a resonant chamber according to an embodiment of the present invention. [Figure 4] This figure shows the frequency response of a resonant chamber according to an embodiment of the present invention. [Figure 5] This figure shows a resonant chamber according to an embodiment of the present invention. [Figure 6] This figure shows the frequency response of a resonant chamber according to an embodiment of the present invention. [Figure 7] This is a schematic diagram of an air pulse generator according to an embodiment of the present invention. [Figure 8] This is a schematic diagram of an air pulse generator according to an embodiment of the present invention. [Figure 9] This is a schematic diagram of an air pulse generator according to an embodiment of the present invention. [Figure 10] This is a schematic diagram of an air pulse generator according to an embodiment of the present invention. [Figure 11] This is a schematic diagram of an air pulse generator according to an embodiment of the present invention. [Figure 12] This is a schematic diagram of an air pulse generator according to an embodiment of the present invention. [Figure 13] This is a schematic diagram of an air pulse generator according to an embodiment of the present invention. [Figure 14]This is a top view showing the film structure of an air pulse generator according to an embodiment of the present invention. [Figure 15] This is a top view showing the cover structure of an air pulse generator according to an embodiment of the present invention. [Modes for carrying out the invention]

[0009] The following inventions filed by the applicant are incorporated herein by reference: U.S. Patent No. 1,1323797 relating to a dynamic vent (DV), U.S. Patent No. 1,1943585 relating to an air pulse generator (APG) device, and U.S. Patent No. 18 / 829245 relating 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. 11943585, or shown in Figure 1 or Figure 2), created by etching a film layer made of silicon or other suitable material, are actuated by applying a voltage between the ends of a piezoelectric material such as PZT deposited on the pair of flaps. The pair of opposing flaps produce both common-mode operation with signal SM and differential-mode operation with a pair of signals ±SV, performing the functions of ultrasonic modulation and demodulation, respectively. As a result of this ultrasonic modulation and demodulation to the baseband, air mass motion is generated between the flap pair 101 to 103 via a virtual valve 112 at the baseband frequency. This air pump may be used as an audio speaker to generate audio sound waves by sending air bidirectionally at audio frequencies, or as a unidirectional air pump for other applications such as forced air cooling.

[0011] The airflow through the valve is increased by the pressure difference across the valve. The instantaneous pressure at 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. 11943585. This cap forms a small chamber much smaller in dimensions than the wavelength near the flap and has a small outlet that restricts the airflow. This increases the level of compression / expansion of the air in the chamber, increasing the pressure difference across the valve and consequently increasing the airflow. As disclosed in U.S. Patent No. 11943585, this cap is not strictly necessary, as a considerable airflow can be achieved without it.

[0012] Instead of restricting the airflow into and out of the compression chamber, an alternative method is presented here to increase the local pressure change around the valve. A resonant air cavity may be set 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, together with the volume of air in the chamber acting as a spring, forms a mass-spring system. Standing wave resonance occurs when an acoustic reflector is placed at a favorable distance from the flap. This causes the acoustic wave to bounce off the reflector, and the reflected and incident waves are superimposed to form regions of constructive interference (antinodes) with high-amplitude vibrational pressure and regions of destructive interference (nodes) with minimum pressure. Figure 1 or Figure 2 shows one embodiment in which a pair of flaps 101 and 103 have a Helmholtz resonant chamber 115 on one side where the exit 713 is located. On the other side, in Figure 2, a standing wave cavity 116 is formed with an acoustic reflector 702 spaced at 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 each have anchor portions 131 and 133. 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, particularly 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 toward the cavities 115 and 116 outside, 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 synchronized 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. 11943585, but will not be described in this specification for simplicity. Further, the demodulation signal SV may be obtained from the drive circuit disclosed in U.S. Application No. 18 / 396678, and the modulation signal SM may be obtained from the drive circuit disclosed in U.S. Patent No. 12107546. However, the details thereof will not be described in this specification for simplicity.

[0018] In addition to this, the APG device 10 / 20 includes 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, 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 with respect to the input velocity at the bottom of chamber 115. This represents the positions of flaps 101 and 103. It can be seen that the pressure amplitude is large inside the chamber and decreases towards the outlet. Figure 4 shows the input acoustic impedance as a function of frequency, looking inside the chamber from the position of the input volume velocity, or simply the input velocity. In this case, the maximum value of the acoustic impedance corresponds to the Helmholtz mode (in this example, set to be around 192 kHz, which is the operating frequency of the ultrasound). This may be set to be near the frequency of a common-mode signal (e.g., SM) by controlling the dimensions between the cavity and the outlet. Maximizing the acoustic impedance at the ultrasonic operating frequency minimizes the ultrasonic energy propagating outward from the flaps and maximizes the pressure buildup near the virtual valve, so that air flows through the valve as desired. At the same time, the ultrasonic impedance of the resonant cavity at the baseband frequency must be kept low, typically lower than other impedances in the system (such as valves or connected acoustic chambers), so as not to obstruct the baseband airflow.

[0020] Figures 3 and 4 demonstrate that the Helmholtz resonant chamber can produce a peak in the frequency response of the acoustic impedance of the APG device (e.g., 10 or 20) at an ultrasonic operating frequency (e.g., 192 kHz).

[0021] [Standing wave resonance] A standing wave reflector may be used to further improve airflow. Common-mode ultrasound generated by flaps 101 and 103 (Figure 2) bounces off reflector 702 and is superimposed and summed with subsequent cycles of ultrasound generated by the flaps. These bounces cause resonance in the cavity, resulting in pressure amplification and increased airflow through valve 112. The optimal distance H116 of reflector 702 from the plane of flaps 101 and 103 is approximately determined by the wavelength of ultrasound in the air.

[0022] In one embodiment, the reflector 702 is a rigid wall with a characteristic acoustic impedance much higher than that of air. When the ultrasonic waves travel in direction 202 and reach the reflector, they are reflected in direction 204 without changing polarity. For in-phase addition of pressure at the flap, the sum of the bidirectional distances between the flap and the reflector is assumed to be a multiple of the wavelength λ corresponding to the ultrasonic operating frequency. Thus, 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., half a wavelength or an integer multiple of half a wavelength).

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

[0024] It should be noted that, depending on the outlet configuration, the standing wave configuration may be set to have a higher quality factor (sharper impedance peak) than the Helmholtz configuration. Since the standing wave configuration does not require a narrow wall, viscous losses can be significantly reduced. As explained in the section on directivity below, ultrasonic emission (loss) can be reduced by placing the outlet on the side rather than in a reflector. This is beneficial for containing a larger proportion of ultrasonic energy within the cavity with less dissipation. However, an increase in the quality factor may mean that it takes longer for the pressure to reach a steady state, and sensitivity to changes in resonant frequency due to temperature, humidity, and other factors may increase. However, if an open valve (not included in the acoustic impedance simulation) is present, the airflow through the valve reduces the quality factor. This can be significantly lower than the quality factor shown in Figure 6.

[0025] The resonant frequency of the standing wave is required for the airflow in the baseband and may be affected by the presence of holes or other outlets, potentially deviating from the given Nλ / 2 condition. Furthermore, the anchor regions 131 and 133 of the flap exhibit different acoustic impedances to ultrasound compared to the movable flap, and together they affect the optimal distance for resonance.

[0026] [Increased conversion from ultrasound to baseband] Ultrasound contained by either Helmholtz waves or standing waves increases the local ultrasonic sound pressure difference, resulting in higher airflow at the baseband frequency. When the valve is open, air flows through the valve from one side of the cavity to the other, 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 shown in Figures 4 and 6 where the effect of the valve is not modeled. Nevertheless, this achieves the desired goal of increased conversion from ultrasound to baseband waves, i.e., increased demodulation efficiency. Therefore, it is beneficial to set up an air cavity with high acoustic impedance at the common-mode operating frequency.

[0027] Simultaneously, another resulting effect is a reduction in the emission of undesirable ultrasonic frequencies. In U.S. Patent No. 11943585, since emitted ultrasound is released and not recaptured as described herein, undesirable strong ultrasound is emitted along with the baseband wave. 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 ultrasound to baseband is effective in increasing baseband output while simultaneously reducing the potentially harmful emission of high-amplitude ultrasound.

[0028] [Directivity] In the case of standing wave resonance, since the wavelength of the ultrasound is considerably smaller than the wavelength of the baseband wave, the ultrasound has 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 ultrasound, the ultrasound propagates toward the reflector with minimal lateral spreading loss. Conversely, the demodulated baseband wave, being of a much lower frequency, propagates similarly to a spherical wave, and much more of the acoustic energy is directed laterally in direction 206 in Figure 2. Thus, the reflector or slits, holes, or other openings around it may be set off-axis with respect to the ultrasound, allowing for simultaneous containment of the ultrasound and transmission of baseband waves from these openings. To maintain a high baseband airflow, it may be desirable to have large openings around it. This increases the flexibility of the setting, as the openings may be set for baseband that is separate from the ultrasound requirements. While the exits described in U.S. Patent No. 11943585, and the Helmholtz chambers mentioned above, have small, narrow exits that result in large resistive losses, even though these are necessary to contain the ultrasound, standing wave acoustic cavities may be set to have much larger openings to keep the baseband loss low while confining the ultrasound within the cavity.

[0029] [Various embodiments] In other embodiments, the flap may have a standing wave resonant cavity or Helmholtz chamber on one side, or on both sides. Figure 7 (showing the APG device 30) shows a configuration with standing wave cavities on both sides. On both sides of the flap are standing wave resonant cavities (116, 117) and reflectors 701, 702. The distances H116 and H117 may be close to the condition Nλ / 2, respectively, subject to other effects that affect the frequency. This embodiment may be preferred from a manufacturing standpoint because it does not require the creation and assembly of a chamber having a three-dimensional pattern with small features.

[0030] Furthermore, in small areas such as directly above the valve, the standing wave cavity may be partially filled with a solid material (e.g., solid material 151 shown in Figure 8 where the APG device 40 is shown) to suppress acoustic waves laterally. Local air pressure is generated by the displacement of the flap, and for a given displacement, the lateral volume reduction of cavities 116 and 117 results in a larger pressure change that is beneficial to the airflow through the valve. Because the pressure waves are suppressed and directed closer to the valve, the bounce of reflected ultrasonic waves is minimized in ineffective areas such as the anchor and in the flap area close to the anchor. This has the effect of improving the speed at which ultrasonic energy is converted to baseband (requiring less bounce and having a lower quality factor, but still achieving high airflow), which is advantageous for achieving high sound pressure levels at high frequencies with minimal delay or decay time. Furthermore, the filler may improve the structural rigidity of the reflector. However, the cavity should be sufficiently wide to avoid increasing the viscous resistance of the airflow and leading to undesirable acoustic loss. In this embodiment, to allow baseband airflow, the openings in the reflectors 701, 702 or the wall 151 may be spaced out in the out-of-page direction.

[0031] Furthermore, flexible boundary ultrasonic reflectors may be considered for standing waves. Driving ultrasound into open space through narrow slots with a width much smaller than the wavelength (W715 and W716 of exits 715 and 716 in Figure 9 where the APG device 50 is illustrated) can cause impedance mismatch at the open boundary at the ends of the slots. This reverses the polarity of the ultrasound during reflection from the slots to the open boundary. In such cases, the optimal distance from flaps 101 and 103 to ends 703 / 704 is approximately λ(N / 2+1 / 4), where ends 703 / 704 may represent the ends of exits 715 / 716. Compared to a rigid reflector requiring a distance of λ / 2, the fundamental wavelength here is λ / 4, resulting in a lower profile device.

[0032] The APG apparatus 50 in Figure 9 may include resonant chambers 115a and 115b. In this embodiment, the resonant chambers 115a and 115b may be Helmholtz resonant chambers, but are not limited thereto.

[0033] The Helmholtz chambers shown in Figures 1 and 2 have an exit directly beyond flaps 101 and 103, although the exit may be located elsewhere. Figure 10 shows an exit 717 located beyond anchors (or anchor portions) 131 and 133, which are substitutes for flaps (downstream of the over-exit). The acoustic impedance may still be tuned to maximize the impedance at the ultrasonic common-mode frequency. In this configuration, there is no need for a wall between adjacent flap pairs, which can provide ease of manufacture.

[0034] [structure] The resonant cavity wall may be made from a solid material that forms part of the speaker module. Part of the speaker module may be a printed circuit board used for electrical wiring, or copper traces, or a cover (stainless steel, brass, etc.) used to protect against mechanical, chemical, dust, and other unwanted materials. Furthermore, it may be set up as part of a structural assembly, such as in earphones or headphones. In such cases, there is little additional cost to incorporate such an acoustic resonant cavity.

[0035] Non-rigid, flexible reflectors are also available, often made from polymers (such as polyimide, polyethylene, or polyvinyl chloride), and can be easily added to speaker packages at low cost. The optimal position of such flexible reflectors may vary depending on the contributions of mass and rigidity.

[0036] Furthermore, the standing wave reflector may have a slight concave curvature toward the flaps 101, 103, or an inwardly curved end, in order to help suppress ultrasonic waves within 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, Figure 11 shows the appearance of an APG device 70 or 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 cap). Figures 12 and 13 are cross-sectional views of APG devices 80 and 82 according to embodiments of the present invention. The APG devices 80 and 82 include a plurality of flap pairs 102 and a plurality of outlets 723. In Figure 12, the outlets 723 are formed on a virtual valve or opening 112 and aligned with it (i.e., located beyond it). The APG devices 80 and 82 include a plurality of flap pairs 102 and a plurality of outlets 723. In Figure 12, the outlets 723 are formed on an anchor portion 134 and aligned with it (i.e., located 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] Figure 14 shows a top view of the film structure 90 of an APG apparatus according to an embodiment of the present invention, and Figure 15 shows a top view of the cover structure 92 of an APG apparatus according to an embodiment of the present invention. The film structure 90 and the cover structure 92 may be applied to APG apparatuses 80 and 82. The alignment of the exit 723 with respect to the flap pair 102 may be set according to practical requirements.

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

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

Claims

1. A film structure that operates at ultrasonic operating frequencies, The film structure comprises a resonant chamber formed on the side surface, A resonance is formed within the resonance chamber. Due to the aforementioned resonant chamber, the air pulse generator has a peak in the frequency response of the acoustic impedance of the air pulse generator at the ultrasonic operating frequency. Air pulse generator (APG device).

2. The APG apparatus according to claim 1, wherein the resonance is a Helmholtz resonance.

3. Equipped with a cover structure, The APG apparatus according to claim 1, wherein the resonance chamber is formed between the film structure and the cover structure.

4. The APG apparatus according to claim 3, wherein the outlet is formed within the cover structure and connected to the resonant chamber.

5. The film structure includes a pair of flaps configured to perform differential mode operation to form a virtual valve, The APG device according to claim 4, wherein the outlet is located beyond the virtual valve.

6. The APG apparatus according to claim 4, wherein the outlet is located beyond the anchor portion of the flap of the film structure.

7. A first resonance chamber formed on the first side surface of the film structure, The APG apparatus according to claim 1, further comprising a second resonance chamber formed on the second side surface of the film structure opposite to the first side surface.

8. The first outlet connected to the first resonant chamber, The APG apparatus according to claim 7, further comprising a second outlet connected to the second resonant chamber.

9. Equipped with a resonant cavity, The resonance chamber is formed on the first side surface of the film structure, The APG apparatus according to claim 1, wherein the resonant cavity is formed on the second side surface of the film structure opposite to the first side surface.

10. Equipped with a reflector, The APG apparatus according to claim 9, wherein the resonant cavity is formed between the film structure and the reflector.

11. The APG apparatus according to claim 10, 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.

12. The APG apparatus according to claim 1, wherein the resonance is a standing wave resonance.

13. The APG apparatus according to claim 1, wherein the film structure includes a pair of flaps configured to perform common-mode operation and differential-mode operation.

14. A first resonant cavity formed on the first side surface of the film structure, The film structure comprises a second resonant cavity formed on the second side surface of the film structure opposite to the first side surface, The APG apparatus according to 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.

15. It comprises a first reflector and a second reflector. The APG apparatus according to claim 14, 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.

16. The APG apparatus according to claim 1, wherein the film structure includes a plurality of flap pairs and a plurality of outlets.

17. The APG apparatus according to claim 16, wherein the plurality of outlets are located beyond a plurality of openings formed by differential mode operation performed by the plurality of flap pairs.

18. The APG device according to claim 16, wherein the plurality of outlets are located beyond the plurality of anchor portions of the plurality of flap pairs.

19. Equipped with a cover structure, The APG apparatus according to claim 16, wherein the plurality of outlets are formed within the cover structure.

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