Hybrid acoustic material for wide-bandwidth sound energy control, including low, mid, and high frequencies.

Description

/ 8 “HYBRID ACOUSTIC MATERIAL FOR WIDEBAND SOUND ENERGY CONTROL INCLUDING LOW, MEDIUM AND HIGH FREQUENCIES” FIELD OF THE INVENTION

[01] The present invention pertains to the field of sound energy control over a wide frequency spectrum. In particular, this invention relates to a geometric configuration that combines a layer of traditional porous material and an acoustic metamaterial based on symmetrical rolled spaces, which enables extended sound absorption including the low frequency region. BACKGROUND OF THE INVENTION

[02] In the field of acoustic physics, the control of sound energy is achieved through two important coefficients: the sound absorption and transmission coefficients; this control is of broad interest in various potential applications, such as industry, ambient acoustics, the aerospace sector, among others.

[03] Considering the control of sound energy solely through the sound absorption coefficient, it is known that traditional acoustic materials such as perforated panels and porous materials (cellular, granular and fibrous) act efficiently in the mid-range (1000 - 2000 Hz) and mid-high frequency range (>1000 Hz), respectively. However, considering the low frequency range (<1000 Hz) these materials require physical dimensions on the order of the wavelength of the frequency at which they act to be efficient.

[04] Thus, the simultaneous control of sound energy at low, medium, and high frequencies by means of versatile acoustic materials with small dimensions has proven to be a challenge over time. In this context, due to a combination of different materials, a specifically designed geometric configuration, and above all, because they exhibit unique properties and behaviors, especially for long wavelengths, the Petition 870240110127, dated 12 / 26 / 2024, page 9 / 27 / 8 hybrid acoustic materials have enabled a new way to control sound energy across a wide range of frequencies.

[05] That said, hybrid acoustic materials, when compared to traditional materials, stand out primarily due to two important peculiarities: 1) In general, they exhibit sub-length scale (E), meaning their total thickness (T) is much smaller than the wavelength (λ) of the lowest frequency (f) at which they operate, (Eq. 1) where co = 343 m / s is the speed of sound in air. 2) They enable the effective conversion of sound energy into other forms of energy, for example, thermal or viscous energy.

[06] Absorbers made solely of traditional materials are generally efficient at absorbing sound in the high and mid-frequency range and inefficient in the low-frequency range, so, depending on the need and application, these materials become unsuitable. In this context, one of the main needs in the current scenario is to obtain effective control of sound energy over a wider frequency spectrum.

[07] For this, the development of new sound absorbers based on the coupling of porous materials and acoustic metamaterials with symmetrical air cavities of rolled spaces becomes a viable solution to this need.

[08] The current state of the art presents some patents in accordance with the subject matter of the invention application presented here. For example, document US2015279345 discloses a layered acoustic metamaterial composite for noise control consisting of microperforated plates interspersed with absorbent layers and optional air spaces, arranged in an alternating and periodic manner. Petition 870240110127, dated 12 / 26 / 2024, page 10 / 27 / 8 The micro-perforated plates, stacked periodically, exhibit perforations. Each absorbent layer is composed of poroelastic material. The device is designed using a metamaterial acoustic transformation approach to optimize noise control. However, this invention patent does not constitute a sound-absorbing device with a coupling of a porous material and a double symmetrical air cavity of coiled spaces attenuating noise in the low, medium, and high frequencies.

[09] Document US11037543, in turn, discloses a structure and acoustic absorption system, composed of a material with channels, each with an opening on the surface of the material. The channels have specific shapes and dimensions to resonate at low frequencies in response to sound waves, giving the structure a predetermined response characteristic to acoustic signals. The document also discusses techniques for operating the acoustic absorption system. However, this invention patent does not constitute a sound-absorbing device with coupling of a porous material and a double symmetrical air cavity of coiled spaces attenuating noise at low, medium and high frequencies.

[010] Document US10032445 discloses a device that attenuates sound across a range of audible frequencies. The exemplary device consists of a planar membrane with two honeycomb structures, each containing unit cells fixed on opposite sides of the membrane. Each unit cell has rigid walls perpendicular to the planar membrane. Within these cells, supports are mounted, the dimensions of which alter the attenuation characteristic with respect to frequency, especially at audible frequencies. This configuration aims to improve the effectiveness of sound attenuation compared to a device without supports. However, this invention patent does not constitute a sound-absorbing device. Petition 870240110127, dated 12 / 26 / 2024, page 11 / 27 / 8 with coupling of a porous material and a double symmetrical air cavity of coiled spaces attenuating noise in low, medium and high frequencies.

[011] Finally, document US11727909 aims to improve the acoustic performance of sound-absorbing materials. A device is proposed that utilizes a negative refractive index with double negative parameters, such as negative effective mass density and effective bulk modulus scheme, through acoustic elements. The technique involves the architecture of metamaterials with strategically positioned open inductive acoustic tubes around the outer surfaces of the porous medium and perforated screens inserted within the porous medium. These components generate a complex acoustic impedance load of the porous medium, with the inductance determined by the lengths of the open tubes. The device generates a desired reactive load in the broadband frequency region of the complex acoustic impedance of the porous medium, using open tubes that extend into the external environment.The perforated tubes and screens generate a conjugate acoustic impedance corresponding to the complex acoustic impedance of the porous medium. However, this invention is not configured as a sound-absorbing device at low, medium, and high frequencies.

[012] It is clear that there is a constant demand, in the state of the art, for solutions in sound absorption. SUMMARY OF THE INVENTION

[013] The core of the present invention is to propose an efficient solution for controlling sound energy by means of the sound absorption coefficient in a wide frequency spectrum (100-6000 Hz).

[014] To achieve this objective, the present invention proposes a series combination of two different materials: initially a layer of cellular-type porous material (CMP) and an acoustic metamaterial (MMA); the geometric configuration of the MMA being based on a rigid panel with a microPetition 870240110127, dated 12 / 26 / 2024, page 12 / 27 / 8 slot-type perforation coupled to a double and symmetrical cavity of rolled spaces.

[015] The solution according to the present invention differs substantially from other known geometric configurations in that: - It allows for greater control of sound energy because the different materials combined act on distinct frequency ranges, resulting in an overlap of sound absorption curves; - It guarantees broadband sound absorption, meaning it acts simultaneously in the low, medium, and high frequency ranges; - It allows for versatile and expanded adjustment capabilities for small-dimension geometry, mainly through the number of symmetrical rolled spaces in the symmetrical cavity; - It allows for a predominant conversion of sound energy into viscous-type dissipation, mainly due to the micro-perforation of the acoustic metamaterial panel. BRIEF DESCRIPTION OF THE DRAWINGS

[016] Figure 1 is an overview of a unit cell of the hybrid acoustic material composed of a CMP and an MMA with n = 6 symmetrical rolled spaces.

[017] Figure 2 is a front view of the parts that make up a unit cell of the hybrid acoustic material.

[018] Figure 3 is a top view in the plane of different coupled hybrid acoustic material cells. The MMAs have configurations with n = 4 and 6 coiled spaces each.

[019] Figures 4(a) and 4(b) illustrate the theoretical and experimental behavior of the sound absorption coefficient in accordance with the analyzed samples of the present invention. Petition 870240110127, dated 12 / 26 / 2024, page 13 / 27 / 8 DETAILED DESCRIPTION OF THE INVENTION

[020] The present invention proposes an efficient, versatile and advanced acoustic material, its effectiveness being due to the possibility of controlling a wide range of sound energy. The model of the hybrid acoustic material proposed in this invention is the result of a delineated geometric combination of different materials, which allows for efficient (sound absorption coefficient close to unity α « 1) and extended sound absorption in the low, medium and high frequency range (100-6000 Hz). Acoustic absorber composition:

[021] The basic cell of the hybrid acoustic material structure (100) is shown in Figure 1. The structure is composed of the series coupling of the porous material layer - CPM (110) and the acoustic metamaterial - MMA (120). The MMA is composed of a rigid front panel (121) which contains a slot-type microperforation (122), coupled to a cavity of symmetrical rolled spaces (125), as illustrated in Figure 2. The internal structure has rigid walls (123) that promote the division of the rolled spaces and a rigid wall (124) that prevents the leakage of sound waves from the symmetrical cavity.

[022] It is worth highlighting that as the number of coiled spaces increases, a greater effective wavelength of sound wave propagation in the MMA region is guaranteed, which makes it possible to determine the operating frequency of the absorber in the low-frequency region. The choice of material that makes up the CMP layer can be made based on the different existing acoustic materials, for example, cellular, fibrous and other materials. Finally, by coupling two or more cells with different coiled space cavity configurations (see Figure 3), the increased capacity for sound energy control through the proposed hybrid material is guaranteed. Applications: Petition 870240110127, dated 12 / 26 / 2024, page 14 / 27 / 8

[023] Because it operates in an extended frequency range where other traditional materials do not operate efficiently, hybrid acoustic material is applicable to sound energy control in various situations, especially when the acoustic material is required to have a small dimensional scale, such as: aircraft acoustic panels, audio studios, music concert halls, industrial noise control, among others. Advantages:

[024] Unlike traditional materials (perforated panels or bass traps), the structure of the absorber proposed here has a sub-wavelength scale, meaning its total thickness is less than the wavelength of the lowest frequency at which it operates. Furthermore, the versatility and flexibility of different possible configurations stand out, whether through the choice of CMP or the configuration of MMA.

[025] Experimental analyses of samples of the acoustic material were carried out on an experimental bench (impedance tube) considering the direct incidence of sound waves. All tests were governed by the ISO10534-2 standard and are detailed below: • Trial 1 - Number of samples evaluated: 3

[026] Objective: To verify the feasibility of the proposed theoretical and numerical models that describe the behavior of the hybrid acoustic material and to adjust the geometric parameters of the model if necessary. • Trial 2 - Number of samples evaluated: 3

[027] Objective: To evaluate the behavior of hybrid acoustic material with different numbers of symmetrical rolled spaces and to investigate the expanded sound absorption bandwidth guaranteed by the proposed model with different layers of porous acoustic materials. • Trial 3 - Number of samples evaluated: 4 Petition 870240110127, dated 12 / 26 / 2024, page 15 / 27 / 8

[028] Objective: To evaluate the behavior of the hybrid acoustic material in the frequency region between 100 and 1600 Hz and to corroborate the possibility of coupling different configurations to acquire control of sound energy in a wider frequency range.

[029] Experimental studies have corroborated that the geometric configuration of the acoustic material according to the present invention is viable in controlling a wide frequency range, compared to traditional acoustic materials. LIST OF REFERENCE NUMBERS 100 - Hybrid acoustic material for sound energy control with a broad band including low, medium and high frequencies. 110 - Porous material layer (CMP) 120 - Acoustic metamaterial (MMA) 121 - Rigid front panel 122 - Slot-type micro-perforation 123 - Partition walls of channels in symmetrical coiled spaces 124 - Rigid wall that prevents leakage of sound waves from the symmetrical cavity. 125 - Symmetrical coiled space cavity.

[030] It is also important to point out that, when the present application is put into practice, modifications may be made with respect to certain details of construction and form, without departing from the fundamental principles that are clearly set out in the context of the following claims, it being understood that the terminology employed is not intended to limit the present invention. Petition 870240110127, dated 12 / 26 / 2024, page 16 / 27

Claims

1 / 2 CLAIMS 1. Acoustic material capable of controlling a wide range of sound energy associated with low, medium and high frequencies, characterized in that it comprises a basic cell of the hybrid acoustic material structure (100), the structure being composed of the series coupling of a layer of porous material (110) and acoustic metamaterial (120).

2. Acoustic material capable of controlling a wide range of sound energy associated with low, medium and high frequencies, according to claim 1, characterized in that the acoustic metamaterial (120) is composed of a rigid front panel (121) containing a slot-type micro-perforation (122), coupled to symmetrical rolled space cavities (125).

3. Acoustic material capable of controlling a wide range of sound energy associated with low, medium and high frequencies, according to any of claims 1 or 2, characterized in that its internal structure has rigid walls (123) that promote the division of the rolled spaces and a rigid wall (124) that prevents the leakage of sound waves from the symmetrical cavity.

4. Acoustic material capable of controlling a wide range of sound energy associated with low, medium, and high frequencies, according to any one of claims 1 to 3, characterized in that two or more cells with different configurations of wound-space cavities are coupled together.

5. Use of hybrid acoustic material as defined in any one of claims 1 to 4, characterized by the fact that it controls the sound energy associated with low, medium and high frequencies (100-6000 Hz).

6. Use of the hybrid acoustic material as defined in any of claims 1 to 4, characterized by its ability to control sound energy in aircraft acoustic panels, audio studios, music concert halls, and industrial noise control, among others. (Petition 870240110127, dated 12 / 26 / 2024, page 17 / 27)

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