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Title:
BINARY SPATIAL SOUND MODULATOR FOR ADAPTIVE WAVEFIELD SHAPING
Document Type and Number:
WIPO Patent Application WO/2019/122942
Kind Code:
A1
Abstract:
A spatial sound modulator can comprise an array of controllable unit cells, each has a dimension of roughly half the wavelength of the target frequency. The spatial sound modulator can communicate with at least one feedback to achieve meaningful control of the sound field. The unit cell of the spatial sound modulator can include a membrane (200) fixed on a frame (250), a magnet (300) disposed on the membrane (200),and an electromagnet (500) configured to be in contact with the plateau (600) according to a magnetic force between the magnet (300) and electromagnet (500). The membrane (200) corresponding to the plateau (600) is configured to be spaced apart from the plateau (600) under a first state and to be in contact with the plateau (600) under a second state, thereby encode the wavefield by change the phase factor.

Inventors:
SHENG, Ping (Flat Rd, 76/f Tower7 Le Prestige, Lohas Park,Tseung Kwan O, New Town,Sai Wan Ho, Hong Kong, CN)
FAN, Xiying (Room 2-332, Sakura Castle Wuhan Universit, Wuhan Hubei, CN)
MA, Guancong (Flat Rd, 76/f Tower7 Le Prestige, Lohas Park,Tseung Kwan O, New Town, Hong Kong, CN)
FINK, Mathias, Alexandre (16 E. Laferriere, Meudon, 92190, FR)
Application Number:
IB2017/001680
Publication Date:
June 27, 2019
Filing Date:
December 20, 2017
Export Citation:
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Assignee:
THE HONG KONG UNIVERSITY OF SCIENCE AND TECHNOLOGY (Clear Water Bay, Kowloon, Hong Kong, CN)
International Classes:
H04R9/06; H04R7/16
Foreign References:
CN204090135U2015-01-07
CN102111702A2011-06-29
CN102711015A2012-10-03
CN102761810A2012-10-31
CN105657617A2016-06-08
JP2012227647A2012-11-15
US5724429A1998-03-03
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Claims:
CLAIMS

What is claimed is:

1. An actively reconfigurable acoustic device, comprising:

an reconfigurable element that alters the spatial distribution of an audible sound field by imprinting a spatial distribution of phase factors to the audible sound field that coexist in the same environment.

2. The actively reconfigurable acoustic device according to claim 1, wherein the actively reconfigurable acoustic device alters a global property of the audible sound field.

3. The actively reconfigurable acoustic device according to claim 1, wherein the reconfigurable element has a lateral dimension of no larger than 0.5 wavelength of the sound in air.

4. The actively reconfigurable acoustic device according to claim 1, wherein the reconfigurable element is reconfigurable between at least two states.

5. The actively reconfigurable acoustic device according to claim 4, wherein one state gives a first phase factor, while the other state gives a second phase factor that is different from the first phase factor, in either transmitted or reflected waves.

6. The actively reconfigurable acoustic device according to claim 4, wherein when the reconfigurable element has more than two reconfigurable states, the phase factor of each state is more flexible, and in total they cover at least a phase difference, in either transmitted or reflected waves.

7. The actively reconfigurable acoustic device according to claim 1, wherein the actively reconfigurable acoustic device works in either transmission mode or reflection mode, or both.

8. The actively reconfigurable acoustic device according to claim 1, wherein the reconfigurable element comprises at least one of a single unit and multiple sub-units placed at different locations.

9. The actively reconfigurable acoustic device according to claim 7, wherein the transmission mode refers to a situation that the phase factors are imprinted to waves that are transmitted through the device.

10. The actively reconfigurable acoustic device according to claim 7, wherein the reflection mode refers to imprinting the phase factors to waves that are reflected off the device.

11. The actively reconfigurable acoustic device according to claim 1, wherein the actively reconfigurable acoustic device interacts with a feedback.

12. The actively reconfigurable acoustic device according to claim 11, wherein a state of the reconfigurable element is determined by the feedback.

13. A spatial sound modulator unit cell, comprising:

a membrane fixed on a frame;

a magnet disposed on the membrane;

an electromagnet configured to face the magnet; and

a plateau disposed over the membrane,

wherein the membrane is configured to be in contact with the plateau according to a magnetic force between the magnet and the electromagnet.

14. The spatial sound modulator unit cell according to 13, further comprising a ring disposed on the membrane, wherein the ring is placed between the magnet and the frame.

15. The spatial sound modulator unit cell according to 14, further comprising a support fixing the electromagnet and the plateau.

16. The spatial sound modulator unit cell according to claim 15, wherein the plateau has a ring shape and a diameter of the plateau is smaller than a diameter of the ring.

17. The spatial sound modulator unit cell according to claim 15, wherein the frame has a ring shape and the magnet is placed at a center of the membrane.

18. The spatial sound modulator unit cell according to claim 15, wherein the membrane has one fixed boundary when the magnetic force is a repulsion force, and two fixed boundaries when the magnetic force is an attraction force.

19. A spatial sound modulator, comprising:

an array of a plurality of spatial sound modulator unit cells of 13;

an electric relay connected to each of the plurality of spatial sound modulator unit cells; and

a micro-controller controlling the electric relay.

20. A spatial sound modulator, comprising:

a two-dimensional array of a plurality of unit cells;

a sensor monitoring sound and generating feedback; and

a micro-controller manipulating a phase of each of the plurality of unit cells based on the feedback,

wherein each of the plurality of unit cells comprises:

a frame;

a membrane having a first boundary fixed on the frame;

a magnet disposed on a center of the member;

a ring disposed on the membrane between the magnet and the frame;

an electromagnet disposed over the magnet;

a plateau disposed over the membrane; and

a support fixing the electromagnet and the plateau, and

wherein a second boundary of the membrane corresponding to the plateau is configured to be spaced apart from the plateau or to be fixed on the plateau according to a movement of the magnet.

Description:
BINARY SPATIAL SOUND MODULATOR FOR ADAPTIVE WAVEFIELD SHAPING

BACKGROUND

Field of the Invention

This invention relates to a binary phase modulator for airborne sound field at audible frequencies. It can be used to imprint a sound field with a specific phase distribution to reshaping its spatial distribution. A feedback mechanism based on live measurement and an optimization scheme are adopted to achieve local optimization of sound field.

Description of the Background Art

From music halls to office rooms, reverberant cavities are extremely common for audible sound. Due to the complexity of reverberant fields, existing means of controlling reverberant audible sound only provide very limited functionality. Changing a room’s "acoustic quality" usually amounts to changing reverberations. Conventionally, this is accomplished by either adding lossy materials (such as sound-attenuating ceilings, rugs, curtains, etc.) so to make the room more dissipative; and/or adding diffusive designs to increase mode density. This is also the reason why the“acoustic quality” must be considered at the stage of building design to suit the preordained functionality of the room, and its alteration after construction usually means an overhaul of interior decorations. Refined control of a reverberant sound field is challenging.

A reverberant environment is essentially a large, complex acoustic cavity. Two most important properties of an acoustic cavity are its eigenmodes and their quality factors. A cavity’s eigenmodes are standing waves, characterized by a spatial pattern that comprises more than one nodes and anti-nodes. A direct consequence is that the sound intensity inside the cavity is not evenly distributed. For a three-dimensional cavity, the density of modes is larger at higher frequencies. There exists certain degree of broadening for these eigenmodes, owing to their quality factors that characterize the dissipation of the modes. When the frequency is sufficiently high, modes can be very close to each other in terms of their frequency separations. Due to the broadening effect (from dissipation), distinguishing each individual mode can become impossible. For these reasons, a wave with a sufficiently high frequency can simultaneously excite a multitude of modes. With enough modes, their interference eventually yields a wave field whose spatial variation is relatively small. When this happens, the cavity is considered to be operating in the reverberant regime.

The richness in modes offers a very large degree of freedom, the modulation of which can change the wave field inside the cavity. In essence, the modulation is achievable by changing the phase of each eigenmode. By changing the phases, interferences between modes can be controlled to be constructive (or destructive) in one or multiple positions, thereby leading to increased or decreased field intensity. Such modulation is equivalent to harnessing the energy within these modes, and redistributing them spatially to form desired patterns.

BRIEF SUMMARY

Embodiments of the subject invention provide a novel and advantageous spatial sound modulator that comprises a membrane fixed on a frame and a plateau disposed over the membrane, thereby manipulating a phase and making up the sound field.

In an embodiment, a spatial sound modulator unit cell can comprise a membrane fixed on a frame, a magnet disposed on the membrane, an electromagnet configured to face the magnet, and a plateau disposed over the membrane, wherein the membrane is configured to be in contact with the plateau according to a magnetic force between the magnet and the electromagnet.

In another embodiment, an acoustic device can comprise a frame, a membrane having a first boundary fixed on the frame, a magnet disposed on a center of the member, and an electromagnet disposed over the magnet, wherein the acoustic device provides two states by moving the magnet by the electromagnet.

In yet another embodiment, a spatial sound modulator can comprise a two- dimensional array of a plurality of unit cells, a sensor monitoring sound and generating feedback, and a micro-controller manipulating the state of each of the plurality of unit cells based on the feedback, wherein each of the plurality of unit cells comprises: a frame, a membrane having a first boundary fixed on the frame, a magnet disposed on a center of the member, a ring disposed on the membrane between the magnet and the frame, an electromagnet disposed over the magnet, a plateau disposed over the membrane, and a support fixing the electromagnet and the plateau, and wherein a second boundary of the membrane corresponding to the plateau is configured to be spaced apart from the plateau or to be fixed on the plateau according to a movement of the magnet. BRIEF DESCRIPTION OF DRAWINGS

Figure 1 shows spatial phase modulator for sound in an enclosed acoustic environment according to an embodiment of the subject invention.

Figure 2 shows a spatial sound modulator unit cell according to an embodiment of the subject invention.

Figure 3 shows a cross sectional view of a spatial sound modulator unit cell according to an embodiment of the subject invention.

Figure 4 shows a spatial sound modulator unit cell under OFF state and ON state according to an embodiment of the subject invention.

Figure 5 shows simulated vibration profiles of a membrane’s eigenmode under OFF state and ON state according to an embodiment of the subject invention.

Figure 6 shows amplitude transmission coefficients and phases of a spatial sound modulator unit cell under OFF state and ON state according to an embodiment of the subject invention.

Figure 7 shows a spatial sound modulator according to an embodiment of the subject invention.

Figure 8 shows spectral responses at the optimization position by the spatial sound modulator according to an embodiment of the subject invention.

Figure 9 shows silence zone creation at the optimization position by the spatial sound modulator according to an embodiment of the subject invention.

Figure 10 shows pressure reduction at the optimization position by the spatial sound modulator according to an embodiment of the subject invention averaged over many realizations.

Figure 11 shows minimization histories using iterative scheme of a spatial sound modulator according to an embodiment of the subject invention.

Figure 12 shows increased amplitude of a sound intensity at the optimization position by thespatial sound modulator according to an embodiment of the subject invention.

Figure 13 shows creation of hot spot at the optimization position by the spatial sound modulator according to an embodiment of the subject invention.

Figure 14 shows pressure increase at the optimization position by the spatial sound modulator according to an embodiment of the subject invention.

Figure 15 shows maximization histories using iterative scheme of a spatial sound modulator according to an embodiment of the subject invention. Figure 16 shows supercells of a spatial sound modulator according to an embodiment of the subject invention.

DETAILED DESCRIPTION

Embodiments of the subject invention provide novel and advantageous a spatial sound modulator that comprises a membrane fixed on a frame and a plateau disposed over the membrane, thereby manipulating a phase and making up the sound field.

Embodiments of the subject invention provide a reconfigurable device, called spatial sound modulator (SSM) for the control of the complex airborne sound fields, such as reverberating sound. The SSM achieves its functionality through the manipulation of phase of a sufficient number of modes that make up the sound field. The SSM of the subject invention comprises an array of pixels, each with a lateral dimension at the order of half of wavelength of the airborne sound. Each pixel is switchable between at least two states, each generating a different phase factor in either the transmitted or the reflected waves. For a two-state pixel, which is a binary SSM, the two different phase factors shall be 0 and p in the ideal case,. Each pixel must interact with a feedback through an optimization mechanism to achieve the desirable outcome sound field.

Embodiments of the subject invention provide an acoustic device that is capable to re- distribute a complex sound field at audible frequencies. The device is essentially a phase modulator for sound. It comprises a two-dimensional array of reconfigurable elements that are no larger than of half the wavelength of sound in air. The elements are reconfigurable between at least two states, each gives a different phase factor in either the transmitted or the reflected waves. Such phase factors are imprinted to the sound field in a controllable way to construct desirable interference, thereby controlling the spatial distribution of the complex sound field. The device interacts with a feedback through an optimization mechanism. In an embodiment, membrane-type metamaterials with actively tunable resonances are used to construct the SSM. The SSM according to an embodiment of the subject invention provides the creation of a zone of silence and a hotspot in a realistic reverberating environment.

Figure 1 shows a schematic drawing of the spatial phase modulator for sound in an enclosed acoustic environment according to an embodiment of the subject invention. Referring to Figure 1, a sensor monitors a sound signal in an acoustic environment and measures some sound factors, such as pressure amplitude, and then provides feedback to a micro-controller performing optimization mechanism. The micro-controller controls the state of the phase modulator so as to manipulating the sound in the environment, thereby creating a silent zone or a hotspot zone in the acoustic environment.

To manipulate the phase of eigenmodes, it is necessary to use one or more phase modulator(s) to control a sufficient number of eigenmodes, as shown in Figure 1. One or more than one pre-defme target(s) shall be defined to guide the operation of the phase modulator(s). One or multiple feedback(s) shall be employed to interact with the phase modulator(s) through an optimization mechanism that may or may not locate in the same environment.

Figure 2 shows a schematic of spatial sound modulator unit cell according to an embodiment of the subject invention, Figure 3 shows a cross sectional view of a spatial sound modulator unit cell according to an embodiment of the subject invention, and Figure 4 shows a spatial sound modulator unit cell under OFF state and ON state according to an embodiment of the subject invention. In particular, Figure 2 shows a perspective view from a top of the spatial sound modulator unit cell and Figure 4 show a perspective view from a bottom of the spatial sound modulator unit cell.

Referring to Figures 2-4, a spatial sound modulator unit cell 100 comprises a membrane 200 fixed on a frame 250, a magnet 300 disposed on a center of the membrane 200, and an electromagnet 500 disposed over the magnet 300 while facing the magnet 300. The membrane 200 is fixed on the rigid frame 250, thereby forming a first boundary 210 that is a fixed boundary. The spatial sound modulator unit cell 100 further comprises a plateau 600 disposed over the membrane 200 and a ring 400 disposed on the membrane 200. The magnet 300 and the ring 400 are in contact with the membrane 200, and the plateau 600 is spaced apart from the membrane 200. The electromagnet 500 and the plateau 600 are fixed by a support 550 through a support arm 560. The support 550 is rigid and can be formed monolithically with the rigid frame 250.

The frame 250, the support 550, and the plateau 600 have a ring shape similar to the ring 400. The magnet 300 has a disk shape and the magnet 300, the ring 400, and the frame 250 are arranged concentric while the ring 400 is disposed between the magnet 300 and the frame 250. The plateau 600 is also arranged concentric with respect to the frame 250 when viewed from a top of the spatial sound modulator unit cell 100 while the plateau 600 is disposed between the magnet 300 and the ring 400. That is, a diameter of the plateau 600 is configured to be smaller than a diameter of the ring 400.

The electromagnet 500 is connected to a DC power source, thereby providing a magnetic force, such as attraction force or repulsion force, with respect to the magnet 300. When the repulsion force is applied or there is no magnetic force between the magnet 300 and the electromagnet (i.e., OFF state), the membrane 200 has one fixed boundary of the first boundary 210 and a first membrane area 260 between the first boundary 210 and the centre of the magnet 300 vibrates. By contrast, when the attraction force is applied between the magnet 300 and the electromagnet 500 (i.e., ON state), the free magnet 300 and the membrane 200 move toward the fixed electromagnet 500, accordingly, a portion of the membrane 200 corresponding to the plateau 600 is in contact with the plateau 600. As a result, the membrane 200 has two fixed boundaries including the first boundary 210 fixed on the frame 250 and a second boundary 220 fixed on the plateau 600 under ON state. Under ON state, a second membrane area 270 between the first boundary 210 and the second boundary 220 vibrates while a third membrane area 280 between the second boundary 220 and the centre of the magnet 300 does not vibrate.

Figure 5 shows the simulated vibration profiles of a membrane’s eigenmode under OFF state and ON state according to an embodiment of the subject invention. Referring to Figure 5, the first membrane area 260 vibrates under OFF state and the second membrane area 270 vibrates under ON state. Thus, the spatial sound modulator unit cell 100 generates different phase factors based on different vibration profile under OFF state and ON state.

The subject invention includes, but is not limited to, the following exemplified embodiments.

Embodiment 1. A spatial sound modulator unit cell, comprising:

a membrane fixed on a frame;

a magnet disposed on the membrane;

an electromagnet configured to face the magnet; and

a plateau disposed over the membrane,

wherein the membrane is configured to be in contact with the plateau according to a magnetic force between the magnet and the electromagnet.

Embodiment 2. The spatial sound modulator unit cell according to embodiment

1, wherein the membrane is in contact with the plateau when the magnetic force is an attraction force. Embodiment s. The spatial sound modulator unit cell according to any of embodiments 1-2, further comprising a ring disposed on the membrane, wherein the ring is placed between the magnet and the frame.

Embodiment 4. The spatial sound modulator unit cell according to any of embodiments 1-3, further comprising a support fixing the electromagnet and the plateau.

Embodiment 5. The spatial sound modulator unit cell according to embodiment

4, wherein the support is connected to the electromagnet and the plateau through a support arm.

Embodiment 6. The spatial sound modulator unit cell according to any of embodiments 4-5, wherein the support and the frame are monolithically formed.

Embodiment 7. The spatial sound modulator unit cell according to any of embodiments 3-6, wherein the plateau has a ring shape and a diameter of the plateau is smaller than a diameter of the ring.

Embodiment 8. The spatial sound modulator unit cell according to any of embodiments 1-7, wherein the frame has a ring shape and the magnet is placed at a center of the membrane.

Embodiment 9. The spatial sound modulator unit cell according to any of embodiments 1-8, wherein the membrane has one fixed boundary when the magnetic force is a repulsion force, and two fixed boundaries when the magnetic force is an attraction force.

Embodiment 10. The spatial sound modulator unit cell according to embodiment 9, wherein the two fixed boundaries includes a first boundary fixed on the frame and a second boundary fixed on the plateau.

Embodiment 11. A spatial sound modulator, comprising:

an array of a plurality of spatial sound modulator unit cells of claims 1-10;

an electric relay connected to each of the plurality of spatial sound modulator unit cells; and a micro-controller controlling the electric relay.

Embodiment 12. The spatial sound modulator according to embodiment 11, further comprising a sensor monitoring sound and providing feedback to the micro-controller such that the micro-controller controls each of the plurality of spatial sound modulator unit cells.

Embodiment 13. The spatial sound modulator according to any of embodiments 11-12, wherein a lateral dimension of each of the plurality of spatial sound modulator unit cells is equal to or less than half of a wavelength of the sound.

Embodiment 14. An acoustic device, comprising:

a frame;

a membrane having a first boundary fixed on the frame;

a magnet disposed on a center of the member; and

an electromagnet disposed over the magnet,

wherein the acoustic device provides two states by moving the magnet by the electromagnet.

Embodiment 15. The acoustic device according to embodiment 14, further comprising a plateau disposed over the membrane.

Embodiment 16. The acoustic device according to embodiment 15, wherein a second boundary of the membrane corresponding to the plateau is configured to be spaced apart from the plateau under a first state of the two states and to be in contact with the plateau under a second state of the two states.

Embodiment 17. The acoustic device according to embodiment 16, wherein the acoustic device generates a different phase factor in the sound in the environment with respect to the first and second states.

Embodiment 18. The acoustic device according to any of embodiments 16-17, wherein the membrane has a different vibrating area with respect to the first and second states. Embodiment 19. The acoustic device according to any of embodiments 16-18, further comprising a support fixing the electromagnet and the plateau, and a ring disposed on the membrane between the second boundary and the frame.

Embodiment 20. A spatial sound modulator, comprising:

a two-dimensional array of a plurality of unit cells;

a sensor monitoring sound and generating feedback; and

a micro-controller manipulating states of each of the plurality of unit cells based on the feedback,

wherein each of the plurality of unit cells comprises:

a frame;

a membrane having a first boundary fixed on the frame;

a magnet disposed on a center of the member;

a ring disposed on the membrane between the magnet and the frame;

an electromagnet disposed over the magnet;

a plateau disposed over the membrane; and

a support fixing the electromagnet and the plateau, and

wherein a second boundary of the membrane corresponding to the plateau is configured to be spaced apart from the plateau or to be fixed on the plateau according to a movement of the magnet.

Embodiment 21. An actively reconfigurable acoustic device, comprising:

an reconfigurable element altering the spatial distribution of an audible sound field by imprinting a spatial distribution of phase factors to the audible sound field that coexist in the same environment.

Embodiment 22. The actively reconfigurable acoustic device according to embodiment 21, wherein the actively reconfigurable acoustic device alters a global property of the audible sound field ( e.g ., an average sound level).

Embodiment 23. The actively reconfigurable acoustic device according to any of embodiments 21-22, wherein the reconfigurable element has a lateral dimension of no larger than 0.5 wavelength of the sound in air. Embodiment 24. The actively reconfigurable acoustic device according to any of embodiments 21-23, wherein the reconfigurable element is reconfigurable between at least two states.

Embodiment 25. The actively reconfigurable acoustic device according to embodiment 24, wherein one state gives a first phase factor ( e.g ., 0), while the other state gives a second phase factor that is different from the first phase factor (e.g., the second phase factor is ideally p), in either transmitted or reflected waves.

Embodiment 26. The actively reconfigurable acoustic device according to embodiment 24, wherein when the reconfigurable element has more than two reconfigurable states, then the phase factor of each state is more flexible, in total they cover at least a phase difference (e.g., ideally p), in either transmitted or reflected waves.

Embodiment 27. The actively reconfigurable acoustic device according to any of embodiments 21-26, wherein the actively reconfigurable acoustic device works in either transmission mode or reflection mode, or both.

Embodiment 28. The said device actively reconfigurable acoustic device according to any of embodiments 21-27, wherein the reconfigurable element comprises at least one of a single unit and multiple sub-units placed at different locations.

Embodiment 29. The actively reconfigurable acoustic device according to embodiment 27, wherein the transmission mode refers to the a situation that the phase factors are imprinted to the waves that transmitted through the device.

Embodiment 30. The actively reconfigurable acoustic device according to embodiment 27, wherein the reflection mode refers to imprinting the phase factors to the waves that are reflected off the device.

Embodiment 31. The actively reconfigurable acoustic device according to any of embodiments 21-30, wherein the actively reconfigurable acoustic device interacts with a feedback or multiple feedbacks. Embodiment 32. The actively reconfigurable acoustic device according to embodiment 31, a state of the reconfigurable element is determined by the feedback or feedbacks through an optimization scheme.

A greater understanding of the present invention and its many advantages may be had from the following example, given by way illustration. The following example shows some of the methods, applications, embodiments and variants of the present invention. They are, of course, not to be considered as limiting the invention. Numerous changes and modifications can be made with respect to the invention.

EXAMPLE 1

Figure 4 shows a binary spatial sound modulator using membrane-type metamaterial as the basic unit cell to construct the spatial sound modulator. A polyurethane membrane 200 (27 mm in radius and 0.1 mm in thickness) is uniformly stretched and then fixed at the edge of a rigid frame 250. The membrane 200 is transparent and elastic. A neodymium magnet disk 300 with a radius r=6 mm and a mass 0.9 g is attached to the center of the membrane 200. A plastic ring 400 (inner/outer radius of 16/17 mm, weighs 0.15 g) is also attached to membrane 200. One of the membrane’s eigenmode is found at 450 Hz as shown Figure 5. An electromagnet 500 is suspended at 2.5 mm from the membrane 200 by a rigid support 550. In addition, a ring-shaped plateau 600 is embodied to the plastic support. A lmm gap separates the membrane 200 from the plateau 600. The magnet 300 at the center of the membrane 200 snaps to the electromagnet 500 when a suction magnetic force (i.e., attraction force) is established in between. This condition is indicated as the unit’s“ON-state”. Inversing the DC voltage changes the polarity of the electromagnet 500, and releases the magnet 300 and the membrane 200 to its original state, which is indicated as“OFF-state”, with the membrane 200 retaining its circular shape. The membrane 200 at its two states has drastically different eigenmodes.

The simulation of the vibration profile of the mode of interest is shown in Figure 5. Figure 6 shows amplitude transmission coefficients(solid curves) and phases of a spatial sound modulator unit cell(dashed curves) under OFF state and ON state according to an embodiment of the subject invention. Referring to Figures 5 and 6, the resonant peak for OFF-state near 450 Hz is shifted to 800 Hz for ON-state, the vibration profiles of the two states are different. In 580-700 Hz as indicated by shaded yellow, the membrane at its two switchable states has a phase difference of -150°, but they have similar the amplitude transmission coefficients.

Figure 7 shows a spatial sound modulator according to an embodiment of the subject invention. Referring to Figure 7, the spatial sound modulator comprises a two-dimensional array including 360 identical units of membrane resonators. Programmable micro-controllers are used to control the state of each unit. The spatial sound modulator groups 4 units in 2-by- 2 to form a functional pixel. The metasurface formed by the spatial sound modulator now functions as a binary SSM with totally 90 pixels.

The spatial sound modulator according to the subject invention demonstrates the spatial control of this complex field through the creation a“zone of silence” at a certain position in a laboratory. The lab is essentially a cuboid cavity. It is reverberating above a Schroeder frequency estimated to be -108 Hz. The lab is furnished with objects such as desks, chairs, cabinets, etc. as well as various equipment. These objects introduce multiple scattering that further scrambles the sound. At the reverberating regime, the cavity is characterized by its rich eigenmodes. Their interference gives rise to a sound field of complex spatial pattern. The spatial sound modulator adjusts (minimizes or increases) the sound level at a certain position for a specific frequency. To do so, a microphone as a sensor is placed at the chosen position to monitor the sound to measure pressure amplitude P that is used as a feedback to guide the optimization process. The optimization is controlled by an iterative scheme. The measured pressure at the chosen position is compared for each pixel at both of its states. The state that yields the target (a smaller or a bigger) sound amplitude is kept.

Figure 8 shows spectral responses of a spatial sound modulator according to an embodiment of the subject invention. In particular, Figure 8 shows spectral responses at the optimization position before and after minimization by the spatial sound modulator., Especially, the spatial sound modulator reduces the sound intensity by 21 dB at chosen frequency of 636 Hz.

Figures 9 and 10 show silence zone creation of a spatial sound modulator at one and multiple position according to an embodiment of the subject invention, respectively. Referring to Figure 9, it is clear that a region of small sound pressure emerges out of the complex field pattern around the optimization position, which is marked by the green circle. Figure 10 shows the averaged field pattern over 25 independent experiments at uncorrelated positions, and it clearly shows, after optimization, a zone of smaller sound pressure emerging at the optimization position. Figure 11 shows the history of the minimization of all 25 experiments. Clearly, sound pressure continues to decrease throughout the process, further proving the effectiveness of the SSM and the iterative scheme. The black curve is the average of all realizations.

By adapting optimization criteria to keep the pixels’ states that yield a larger sound level, embodiments of the subject invention use the SSM to increase the sound level at a chosen position. This generates an“acoustic hotspot”. Figure 12 shows the result of the spectral response at the optimization position, in particular, increased amplitude of a sound intensity of a spatial sound modulator according to an embodiment of the subject invention. Referring to Figure 12, the chosen frequency is 643 Hz, and 7 dB of increase is observed. Similarly, the field patterns before and after optimization are shown in Figure 13, which show large sound pressure around the optimization position (marked by cyan circles).

Figure 14 shows pressure increase of a spatial sound modulator according to an embodiment of the subject invention. Referring to Figure 14, the averaged field patterns (over 20 independent experiments at uncorrelated positions) lead to the similar conclusion. Figure 15 shows the history of the maximization of all experiments, in which sound pressure is seen to increase steadily. The black curve is the average of all realizations.

Figure 16 shows supercells of a spatial sound modulator according to an embodiment of the subject invention. Referring to Figure 16, the supercells are formed by grouping units with different operating frequencies together. Each color represents a different type of unit and the spatial sound modulator with such supercells as pixels can control broadband sound field and transient sound field.

According to an example of the subject invention, an actively reconfigurable acoustic device is capable of altering the spatial distribution of audible sound field by imprinting a spatial distribution of phase factors to the audible sound field that coexist in the same environment. The said device can also alter the global property of the sound field, such as the average sound level.

The said device comprises reconfigurable elements, each with the lateral dimension of no larger than 0.5 wavelength of the sound in air, and the property of each element is reconfigurable between at least two states. If each element has two reconfigurable states, then one state shall give a phase factor of 0, while the other state shall give a phase factor that is ideally p, in either the transmitted or the reflected waves. In addition, if each element has more than two reconfigurable states, then the phase factor of each state is more flexible. But in total they shall cover at least a phase difference that is ideally p, in either the transmitted or the reflected waves. The said device can work in either transmission mode or reflection mode, or both. Transmission mode refers to the situation that the phase factors are imprinted to the waves that transmitted through the device. Reflection mode refers to imprinting the phase factors to the waves that are reflected off the device.

The said device interacts with one or multiple feedback(s). The state of each element as mentioned above is determined by the said feedback(s) through an optimization scheme. The said device has a finite working bandwidth, which is determined by the elements. The working frequencies of the elements are tunable, even after the implementation of the device.

The bandwidth may be increased to become broadband by grouping several subwavelength units with different working frequencies into supercells.

The said device can be one single unit, or separated into multiple sub-units and placed at different locations. In a specific, non-binding realization, the device comprises elements that are an array of actively controllable membrane-type metamaterials. The said metamaterial possesses one or more eigenmodes in audible frequencies. The said metamaterial is reconfigurable between two or more states, in which the said eigenmodes have different eigenfrequencies.

The said metamaterial comprises a stretched thin elastic membrane fixed on a rigid frame. In a particular embodiment, the said membrane is decorated with a magnetic disk at the center and a concentric ring. In a non-binding realization, the re-configurability as mentioned above is achieved using magnetic force. The feedback and an optimization scheme are required to guide the optimization of the device to achieve desirable outcome. In a non-binding case, the acoustic pressure amplitude measured by a microphone is used to feedback. In a non binding case, the choice of the optimization scheme is an iterative optimization scheme.

In a non-binding case, the average sound level can be reduced if the said device focuses a large amount of sound energy to a region with localized high absorption, so as to increase overall dissipation.

In a non-binding case, the average sound level can be increased if the said device generates a region of small sound intensity that overlaps with the region with localized high absorption, so as to reduce overall dissipation.

It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application. All patents, patent applications, provisional applications, and publications referred to or cited herein (including those in the“References” section) are incorporated by reference in their entirety, including all figures and tables, to the extent they are not inconsistent with the explicit teachings of this specification.

REFERENCES

[1] H. Kuttruff, Room Acoustics. (CRC Press, 2009).

[2] M. R. Schroeder, K. H. Kuttruff, On Frequency Response Curves in Rooms. Comparison of Experimental, Theoretical, and Monte Carlo Results for the Average Frequency Spacing between Maxima. J. Acoust. Soc. Am. 34, 76-80 (1962).

[3] I. Vellekoop, A. Mosk, Phase Control Algorithms for Focusing Light through Turbid Media. Opt. Commun. 281, 3071-3080 (2008).