Description:FIELD OF THE INVENTION
The present invention relates to an acoustic absorption coating. More particularly, the present invention relates to an acoustic absorption coating comprising a viscoelastic meta-structure (MS) matrix with unbonded resonators configured to achieve broadband noise attenuation in diverse acoustic environments.

BACKGROUND OF THE INVENTION
The low frequency sound waves have longer wavelengths making it harder to absorb or cancel them. To effectively dampen these sounds usually requires large amounts of absorbing material, making it difficult to develop a compact and lightweight solution that works efficiently across diverse environments. Flexible coatings are widely used for dampening high-frequency noise, but low-frequency signals are more challenging to absorb as they travel farther and remain detectable over longer distances.
To design an effective noise absorber the key factors to be considered are energy dissipation, resonance and impedance matching. Energy dissipation involves converting sound energy into heat or mechanical vibrations. Resonance helps target specific frequencies for better absorption. Impedance matching ensures that sound waves pass through the material efficiently instead of being reflected.
Acoustic metamaterials have gained attention as a new approach to noise control. Unlike traditional coatings, acoustic metamaterials can be engineered to target specific frequency ranges, making them useful for addressing low-frequency noise issues. While many existing systems already incorporate energy dissipation and impedance matching, acoustic metamaterials focus more on low-frequency sound absorption. Different kinds of metamaterials have been developed over the years, including cavity resonators, Helmholtz resonators and membrane-type metamaterials (MAMs), some of which use eccentric masses to improve absorption. Over the past decade, MAMs have been widely researched for their ability to absorb low-frequency noise in both air and water. Studies have analyzed their behavior using vibroacoustic models and found that adding multiple masses to MAMs improves their absorption capacity.
Reference is made to US Patent application US9076429B2 disclosing a modular system built of a metamaterial capable of absorbing sound and pressure. The metamaterial member includes an outer mass having a cavity formed therein in which a stem coupled to an inner mass is disposed or the outer mass can be solid and contain an inner mass embedded therein. The inner mass includes an inner core and an outer shell. Multiple metamaterial members are attached to form a modular system for absorption of sound and pressure providing superior vibro-acoustic damping properties across a wide range of frequencies.
Another reference is made to Chinese Patent CN116564257A disclosing an underwater sound absorption structure of a space coiling perforated plate of a damping lining, which comprises cuboid cells, wherein a perforated upper panel, a space coiling channel and a damping lining layer are arranged in the cuboid cells. The perforated upper panel and the space coiling channel are connected through welding or gluing, the damping lining layer is adhered to the side wall and the bottom wall of the space coiling channel and a plurality of cuboid cell arrays are arranged to form the underwater sound absorption structure of the space coiling perforated plate of the damping lining providing low-frequency underwater sound absorption.
Another reference is made to US Patent Application US9390702B2 disclosing an acoustic metamaterial composite including a plurality of micro-perforated plates alternately and periodically arranged with a plurality of absorbent layers and optional air gaps. The plurality of micro-perforated plates is in the form of a periodically arranged stack and include perforations extending therethrough. Each of the plurality of absorbent layers is formed of a poro-elastic material. The metamaterial layered composite noise control device is designed using the metamaterial acoustics transformation approach for optimized noise control.
Another reference is made to Chinese Patent application no. PCT/CN2017//072100 disclosing an underwater sound absorption metamaterial based on cooperative coupling resonance. It comprises of M multiplied by M subunits which are periodically arranged along a plane. Each subunit consists of N multiplied by N single cells with consistent geometric dimensions and each unit cell comprises an upper substrate layer, a lower substrate layer and a coupling resonance intermediate layer embedded between the upper substrate layer and the lower substrate layer. The coupling resonance intermediate layer is respectively and symmetrically fastened at the center of the middle inserting sheet by an upper dual harmonic oscillator and a lower dual harmonic oscillator and is jointly embedded between the upper substrate layer and the lower substrate layer. A fluid layer and a backing are sequentially distributed below the underlying substrate layer.
One of the primary issues associated with the inventions in the existing state of the art is their inability to effectively address low-frequency noise absorption in a compact, lightweight and scalable manner. Conventional sound absorbing materials struggle with long wavelength, low-frequency acoustic signals due to the requirement for thick, bulky and heavy structures to achieve effective attenuation. While flexible coatings are used for high-frequency damping, they fail to absorb low-frequency signals efficiently, as these signals travel farther and remain detectable over long distances.

ADVANTAGES OF THE INVENTION OVER THE EXISTING STATE OF ART:
The present invention provides a noise absorption coating with a viscoelastic meta-structure (MS) comprising a plurality of resonators, without any masses attached. The resonators can be configured to undergo multimode vibrations by varying their shapes, dimensions and spatial distribution. The meta-structure coating effectively dissipates acoustic energy by converting incident sound waves into vibrational energy providing broadband noise absorption across both the low and high frequency ranges. The coating is simple in structure, easy to fabricate, and scalable, and does not require bulky absorbers. The present invention provides a noise absorption solution with structural simplicity and enhanced acoustic stealth capabilities in diverse areas including marine, aerospace, automobile, industrial, architectural, and so on.

OBJECTS OF THE INVENTION
In order to obviate the drawbacks in the existing state of the art, the main object of the present invention is to provide a noise absorption coating comprising a viscoelastic meta-structure matrix that enables broadband noise absorption in different media such as air or water.
Another object of the present invention is to provide a noise absorption coating comprising a plurality of resonators formed as a result of unbonded regions within the viscoelastic meta-structure matrix being capable of vibrating freely in response to incident acoustic waves.
Yet another object of the present invention is to provide a noise absorption coating with unbonded resonators arranged in a patterned array with varying shapes and diameters for any given coating thickness such that their eigen frequencies are designed to achieve a desired level of noise absorption across low and high frequency ranges.
Yet another object of the present invention is to provide a noise absorption coating with unbonded resonators optimized and distributed in a predetermined patterned array using finite element analysis (FEA) to ensure multi-frequency resonance and maximize acoustic energy dissipation by conversion to vibrational energy.
Yet another object of the present invention is to provide a noise absorption coating with unbonded resonators being configured to maximize insertion loss and echo reduction within the frequency range of interest based on application specific noise profiles in different media.
Yet another object of the present invention is to provide a noise absorption coating that is simple in structure, easy to fabricate, scalable and that enables effective noise attenuation without the need for bulky absorbers.

SUMMARY OF THE INVENTION
The present invention relates to a noise absorption coating (100) with a viscoelastic meta-structure comprising a plurality of unbonded resonators (120) for broadband noise attenuation. The viscoelastic matrix (110) is made of a material having viscoelastic and acoustic damping properties with a loss factor (tan δ) of at least 0.1 within a frequency range of interest in the acoustic spectrum. The coating is designed to be applied to an external substrate (130), made of a material selected from metal, alloy or composite or any material providing structural support. The resonators (120) are the regions within said viscoelastic matrix (110) that are not bonded to the substrate (130) and are arranged in spatial patterns with varying shapes and diameters.
The unbonded resonators (120) are configured to undergo multi-mode vibrations and vibrate at respective eigen frequencies in response to incident acoustic waves, converting acoustic energy into vibrational energy, which is then absorbed and damped within the meta-structure coating. This enhances the insertion loss (IL) and echo reduction (ER) resulting in noise attenuation across a broad frequency range. The spatial distributions, shape and dimension of the unbonded resonators are designed based on application-specific noise profiles using finite element analysis (FEA) providing effective noise absorption across low and high-frequency ranges and ensuring that the coating effectively mitigates noise in different settings. The coating (100) is designed to function in diverse acoustic environments including industrial noise control, aerospace, marine and architectural acoustics.
A method of fabricating the acoustic absorption meta-structure coating (100) comprises selecting a viscoelastic material having a loss factor (tan δ) of at least 0.1 exhibiting viscoelastic and acoustic damping properties, creating unbonded resonators within the viscoelastic matrix (110) by defining air interfaces and applying the coating to an external substrate (130). The spatial distribution, dimensions and eigen frequencies of the unbonded resonators are optimized using FEA, allowing for enhanced acoustic energy dissipation which manifests as an increased insertion loss (IL) or echo reduction (ER) in different media.
The present invention provides a significant technical advancement over the inventions in the existing state of the art containing bulky acoustic absorbers, Helmholtz resonators or thick polymeric layers. It provides a noise absorption coating with structural simplicity and enhanced acoustic stealth capabilities in diverse acoustic environments including naval, aerospace, automotive, industrial and architectural noise control.
The acoustic absorption meta-structure coating (100) is a simple, easy to fabricate, scalable and technologically advanced solution capable of providing efficient and broad-spectrum acoustic attenuation suitable for diverse applications requiring noise attenuation in varying complex environments.

BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 illustrates the geometric model of the meta-structure coating (MS coating).
Fig.2 illustrates the functioning of the meta-structure coating for noise absorption.
Fig. 3 illustrates the surface displacement of the meta-structure coating in water at different frequencies based on FEA - 3(a) 600 Hz, 3(b) 6000 Hz, 3(c) 10000 Hz, 3(d) 15000 Hz, 3(e) 25000 Hz
Fig. 4 illustrates the insertion loss for low frequencies in water based on FEA
Fig. 5 illustrates the insertion loss for high frequencies in water based on FEA.
Fig. 6 illustrates the surface displacement of the meta-structure coating in air at different frequencies based on FEA - 6(a) 10 Hz, 6(b) 100 Hz, 6(c) 500 Hz, 6(d) 1000 Hz, 6(e) 5000 Hz, 6(f) 9910 Hz
Fig. 7 illustrates the echo reduction for low frequencies in air based on FEA.
Fig. 8 illustrates the echo reduction for high frequencies in air based on FEA.

DETAILED DESCRIPTION OF THE INVENTION WITH ILLUSTRATIONS AND NON-LIMITING EXAMPLES
While the invention has been disclosed with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made, and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the invention without departing from its scope. However, one of the ordinary skills in art will readily recognize that the present disclosure including the definitions listed here below are not intended to be limited to the embodiments illustrated but is to be accorded with the widest scope consistent with the principles and features described herein.
Throughout the specification and claims, the following terms take the meanings explicitly associated herein unless the context clearly dictates otherwise. The meaning of “a”, “an”, and “the” include plural references. Additionally, a reference to the singular includes a reference to the plural unless otherwise stated or inconsistent with the disclosure herein.
A person of ordinary skill in art will readily ascertain that the illustrated steps detailed in the figures and here below are set out to explain the exemplary embodiments shown, and it should be anticipated that ongoing technological development will change the way functions are performed. It is to be noted that the drawings are to be regarded as being schematic representations and elements that are not necessarily shown to scale. Rather, the various elements are represented such that their function and general purpose becomes apparent to a person skilled in the art.
The reference numerals for Fig. 1 used in the present invention are tabulated below in Table 1 and for Fig. 2 in Table 2
Table 1: Legend of Reference numerals
Reference Numeral Component / Description
110 Viscoelastic matrix / coating
120 Meta-structure / resonators
130 External substrate or Substrate
140 Perfectly Matched Layer (PML)
150 Medium (Air/Water)

Table 2: Legend of Reference numerals
Reference Numeral Component / Description
110 Viscoelastic matrix / coating
120 Meta-structure / resonators
130 External substrate or Substrate
160 Displacement of coating at low frequency when sound wave hits
170 Displacement of coating at high frequency when sound wave hits
180 long wavelength
190 low frequency wave
200 Short wavelength
300 High frequency wave
400 Speaker source

For ease of reference, the terms “external substrate” and “substrate” are used interchangeably throughout this specification.
The present invention provides to an acoustic absorption meta-structure coating (100) comprising a viscoelastic matrix (110) with a plurality of unbonded resonators (120) for broadband noise attenuation capable of absorbing both low and high-frequency acoustic noise. The coating (100) is designed to maximize noise absorption (insertion loss or echo reduction) by efficiently converting incident acoustic wave energy into vibrational energy, which is damped within the viscoelastic matrix (110) as heat.
The present invention utilizes a viscoelastic material with high loss factor and flexibility. The plurality of resonators (120) created as unbonded regions within the viscoelastic matrix (110) are free to vibrate at their characteristic eigen frequencies upon interaction with incident acoustic waves. This structural configuration permits effective conversion and dissipation of acoustic energy into vibrational energy, significantly enhancing noise attenuation. Each unbonded resonator (120) possesses distinct dimensions and shapes carefully determined through computational modeling methods including but not limited to Finite Element Analysis (FEA) to achieve resonance frequencies within the desired acoustic frequency range of interest. The spatial distribution on the unbonded resonators (120) within the meta-structure coating is optimized to facilitate comprehensive broadband noise absorption across low and high frequencies.

STRUCTURAL COMPONENTS:
Meta-Structure (MS) matrix:
The viscoelastic matrix (110) forms the primary noise absorption layer and is applied to an external substrate (130). It comprises a material having viscoelastic and acoustic damping properties with a loss factor (tan δ) of at least 0.1 within a frequency range of interest in the acoustic spectrum. The viscoelastic nature of the material enables efficient energy dissipation for broadband noise absorption in different media. The loss factor (tan δ) is defined as the ratio of the material’s loss modulus to its storage modulus and quantifies the material’s ability to dissipate vibrational energy. A higher tan δ indicates greater internal damping, which is essential for effective acoustic energy absorption in both low and high frequency regimes.
As used herein, the term “external substrate” (130) or simply “substrate” (130) refers to any structural base or support onto which the meta-structure coating is applied. The substrate is not a part of the coating itself.

Unbonded Resonators:
A plurality of unbonded resonators (120) having an interface with air below and the medium (such as air or water) above are distributed within the viscoelastic matrix (110) serving as localized vibrational elements. The resonators (120) are not bonded to the substrate (130), allowing them to undergo multimode vibrations at specific eigen frequencies when exposed to acoustic waves. The geometrical distribution, size and shape of the resonators (120) can be varied to maximize broadband noise absorption efficiency across desired frequency bands.
The arrangement and geometry of the unbonded resonators (120) are critical to ensuring efficient broadband noise absorption. The resonators are distributed in a predetermined pattern using computational models like finite element analysis (FEA) to ensure multi-frequency resonance thereby enhancing insertion loss (IL) and echo reduction (ER) maximizing acoustic energy dissipation by its conversion to vibrational energy. The resonators are arranged in a spatial pattern with varying shapes and diameters such that their eigen frequencies are optimized to achieve a desired level of noise absorption in a frequency range of interest.

Substrate:
The substrate (130) serves as the structural base or support onto which the acoustic absorption meta-structure coating (100) is applied. The substrate (130) is composed of metals, alloys, composites, or other materials with high structural integrity. The substrate (130) material is selected depending on the application specific requirements.
Fig. 1 shows the acoustic absorption meta-structure coating (100) comprising a viscoelastic matrix with a plurality of unbonded resonators. The unbonded resonators (120) of different sizes, shapes and positions are formed within the viscoelastic matrix (110) applied over a substrate (130).
Material and method of fabrication:
In an exemplary embodiment of the invention, polyurethane-urea is selected as the viscoelastic material for noise absorption in water-based environments, while silica aerogel is used in air-based applications. These materials are selected for their high energy dissipation characteristics, flexibility, low density, and acoustic impedance compatibility with the surrounding medium, enabling broadband noise attenuation.
The defining feature of the acoustic absorption meta-structure coating (100) is the presence of unbonded resonators (120) within the viscoelastic matrix (110). These resonators (120) enclose air spaces beneath them ensuring that the coating above that air-space remains free to vibrate in response to incident acoustic waves. The unbonded regions of the coating can be of different shapes, dimensions and spatial distribution. In this embodiment, the unbonded resonators may be circular in shape; however, other geometries may also be employed based on acoustic requirements and application-specific design considerations.
In this embodiment, a stainless steel (SS 304 grade) substrate (130) is used as the base onto which the polyurethane-based meta-structure coating is applied.

WORKING OF THE INVENTION:
The working principle of the acoustic absorption meta-structure coating (100) is based on a combination of acoustic structure interaction, resonator-induced vibrations, multi-frequency resonance and energy conversion ensuring efficient broadband noise attenuation. The acoustic absorption meta-structure coating (100) functions by utilizing a viscoelastic matrix (110) embedded with unbonded resonators (120) capable of multi-mode vibrations that dissipate energy of acoustic wave as vibrational energy and heat. The coating (100) is designed to target broadband noise absorption making it effective for applications in naval, aerospace, automotive, industrial and architectural noise control.
When an incident acoustic wave strikes the surface of the coating, it interacts with the unbonded resonators (120) which are part of the viscoelastic matrix (110). The unbonded resonators (120) undergo multi-mode vibrations within the coating (100) at their respective eigen frequencies. These resonators (120) are configured to effectively capture and dissipate acoustic energy providing noise attenuation across a broad frequency spectrum.
The resonators (120) are not physically bonded to the substrate (130) allowing them to vibrate freely when subjected to external acoustic waves. Each resonator (120) is tuned to absorb sound energy in a specific frequency range based on its geometry, size and spatial distribution. Upon excitation by incident sound waves, the unbonded resonators undergo vibrations, leading to a conversion of sound energy into mechanical vibration which propagate through the viscoelastic matrix (110) where it gets absorbed and dissipated as heat.
Fig.2 shows broadband sound incident on the meta-structure coating (100) consisting of different resonators (120). The unbonded resonators vibrate in different modes and dissipate the vibrational energy. The resonators (120) and their distribution can be tuned for maximum sound absorption over a broad frequency range. The multiple vibrational modes of each resonator (120) allow good sound absorption over a large range of frequencies.
As the vibrations propagate into the viscoelastic matrix (110), the viscoelastic properties of the coating (100) ensure effective energy dissipation and enhances insertion loss (IL)/echo reduction (ER)/sound absorption. The viscoelastic matrix (110) with plurality of resonators (120) of varying shapes and dimensions provides multi-mode vibration, enabling the coating to provide noise absorption across a wide range of frequencies in different mediums.

Model design and computational methods:
To achieve the acoustic absorption performance, the meta-structure coating (100) is computationally tuned. Computational methods like finite element analysis (FEA) are used to tune the following parameters:
- the size and dimensions of the unbonded resonators.
- spatial distribution of unbonded resonators (120) to maximize broadband absorption.
- Insertion loss (IL)/echo reduction (ER)/noise absorption coefficient enhancement by evaluating how the meta-structure dissipates acoustic energy across different frequencies.

Case 1: Surface displacement and insertion loss of the coating in the water medium
In an exemplary embodiment, the performance of the meta-structure coating in a water medium is evaluated using a polyurethane-based matrix by assessing the resulting insertion loss (IL).
Six different Meta-structure elements i.e. resonators (120) were incorporated in the coating (100) with diameters ranging from 10 mm to 50 mm. Upon the incidence of a sound wave on the coating, each Meta-structure vibrates in different modes corresponding to their resonant frequencies that match with the frequency of the incident sound wave. To model the acoustic structure interference (ASI), the pressure waves were modelled in acoustic domain, elastic waves in solid domain as well as the interaction between the two were also modelled. For this, the equations in the acoustic and structural domains are solved simultaneously through fully coupled analysis.
To model the acoustic structure interaction, a unit cell comprising the Meta-structure element and the backing steel plate (substrate) was considered. The geometry consists of a backing steel plate, with 3 mm thick polymeric layer is represented in Fig.1. Perfectly matched layer (PML) was modelled on either side of the acoustic domain to ensure anechoic termination of outgoing waves, thereby avoiding formation of standing waves. The configuration of the proposed coating comprised of 3 mm thick with Meta-structure element that function as resonating members. The Meta-structure elements were formed of unbonded areas of coating enclosing an air gap. The diameters of the vibrating membranes were chosen through eigen frequency analysis such that the natural frequency of the eigen nodes of the various meta- structures in the Meta-structure element spans the frequencies of interest of the acoustic noise. Acoustic structure interaction is modelled with plane acoustic wave of 1 atm amplitude and frequencies ranging from 0.6 kHz to 25kHz that travel towards the coating from the water domain in the top of the unit cell. Mesh sizes were ascertained to ensure no slip condition at the ASI interface.

Working:
Fig. 3 shows the surface displacement of Meta-structure resonators (120) arising from their vibrations at different frequencies between 0.6 kHz to 25 kHz. Surface displacement is a key indicator of how the coating responds to sound waves, while IL measures how much sound energy is absorbed or blocked by the coating. The surface displacement of Meta-structure spans different orders of magnitude for the frequency ranges considered. In Fig. 3(a), at low frequencies (0.6 kHz), Meta-structure coatings exhibit significant surface displacement indicating strong resonance, as the coating’s surface moves up and down, allowing better energy dissipation. In Fig.3(b), at 6 kHz, surface displacement for all the Meta-structure is seen with different modes of vibration, suggesting consistent performance across mid-range frequencies. As frequency increases to 10 kHz and beyond, as seen in Fig. 3(c) to Fig. 3(e), the Meta-structure coating (100) enters more complex vibration mode, enhancing energy loss. Insertion loss (IL) was computed through FEA analysis for low frequency range (0.5 kHz to 4 kHz) and high frequency range (5 kHz to 25 kHz).
Fig. 4 compares the IL of Meta-structure coating and regular coating in low frequency range. At 0.6 kHz, regular coatings show an IL of only 0.8 dB, while Meta-structure coatings achieve 7 dB, indicating superior noise attenuation. In the low frequency range of 0.5 to 4 kHz, the IL of Meta-structure coating (100) ranges from 7 dB to 4.5 dB while that of regular coating ranges from 0.8 to 2.2 dB.
Fig. 5 compares the IL of Meta-structure coating (100) and regular coating in high frequency range. In the high frequency range of 5 to 25 kHz, the IL of Meta-structure coating ranges from 5 dB to 12.8 dB while that of regular coating ranges from 1.8 to 10.3 dB. These results prove that Meta-structure coatings are very effective at absorbing and reducing sound across a wide frequency spectrum in underwater domain.

Case 2: Surface displacement of coating and echo reduction of coating in air domain.
In an exemplary embodiment, the performance of the meta-structure coating (100) in an air medium is evaluated using a silica aerogel-based matrix by assessing the resulting echo reduction.
The geometry consists of a backing steel plate coated with silica aerogel as matrix. Silica aerogel was chosen based on its acoustic impedance matching with air. Four different Meta-structure elements i.e. resonators (120) with diameters ranging from 30 mm to 60 mm were used. The eigen frequencies for different modes of vibration for each of the Meta-structure was calculated by the FEA analysis. ASI analysis was performed the frequency range 0.01 kHz to 10 kHz. A unit cell is modelled with four meta-structures of different diameters were arranged in the silica aerogel coating layer.
Fig 1 shows the geometry of ASI model in air; the periodic boundary conditions are provided on all sides of the coating, backing plate and air domain of the unit cell to prevent diffraction of acoustic waves around the edges of the Meta-structure and the plate. ASI is modelled with plane acoustic wave travelling towards the coating at 1 atm amplitude and frequencies ranging from 0.1 kHz to 10 kHz. Mesh sizes were ascertained to ensure no slip condition (equality of pressure and normal velocity) at the ASI interface. Acoustic-structure boundary conditions are provided on top surface of the Meta-structure and bottom surface of the steel plate and all the conditions are same as in case 1.

Working:
Fig. 6 illustrates how the meta-structure (MS) coatings (100) respond to different frequencies (0.01 kHz to 10 kHz) through surface displacement patterns. Fig. 6(a)at 0.01 kHz, the Meta-structure exhibits out-of-phase vibration with nodal (dark blue) and antinodal (yellow/green) regions. At 0.1 kHz (Fig. 6(b)), displacement is more pronounced at the edges than the center. Fig. 6(c) at 0.5 kHz, the Meta-structure shows nearly uniform surface motion. At 1 kHz (Fig. 6(d)), a shift in mode occurs, dividing the surface into four quadrants moving out of phase, with a central nodal ring. In higher frequencies, the vibration becomes more complex. In Fig. 6(e) at 5 kHz, sharper ring movements appear, with three stationary concentric rings and opposite half-circle movements, Fig. 6(f) shows a complex vibration mode at 10 kHz, characterized by alternating motions across three concentric rings and a single division along the diameter. These patterns indicate a rise in surface displacement, with increased echo reduction (ER).
Fig. 7 plots ER versus frequency (0.01–5 kHz), showing that Meta-structure coatings achieve a peak ER of 0.68 at 0.15 kHz—substantially higher than that of regular coatings. This confirms the Meta-structure effectiveness in low-frequency noise reduction.
In higher frequencies (Fig. 8), Meta-structure and normal coatings show similar ER values, but Meta-structure slightly outperforms. A dip at 6 kHz reflects a weak vibration mode, which can be improved by adding more Meta-structure elements. A peak at 6.5 kHz (ER = 3.5 dB) indicates a mode shift.
Hence, the Meta-structure surface displacement directly influences its acoustic performance. Other factors like damping, stiffness, and impedance matching enhances ER, also contribute, making the Meta-structure coatings (100) highly suitable for noise control.

, Claims:1. An acoustic absorption meta-structure coating (100) comprising:
 a viscoelastic matrix (110) comprising a material having viscoelastic and acoustic damping properties, being configured to be applied to an external substrate (130); and
 a plurality of resonators (120) formed within said viscoelastic matrix (110) as regions that are not bonded to the substrate (130);
wherein,
 said unbonded resonators (120) are configured to vibrate at required eigenfrequencies in response to incident acoustic waves;
 said unbonded resonators (120) are configured to dissipate incident acoustic energy by converting it into vibrational energy which is absorbed and damped within said viscoelastic matrix (110), thereby increasing insertion loss (IL), echo reduction (ER) or acoustic absorption coefficient;
 spatial distribution, shapes, dimensions and eigenfrequencies of said unbonded resonators (120) within said viscoelastic matrix (110) are designed using computational models to achieve broadband noise absorption in various application settings.

2. The acoustic absorption meta-structure coating (100) as claimed in claim 1, wherein said material has a loss factor (tan δ) of at least 0.1 within a frequency range of interest in the acoustic spectrum.

3. The acoustic absorption meta-structure coating (100) as claimed in claim 1, wherein the substrate (130) is selected from a metal, an alloy, a composite or any material providing structural support depending on the application specific requirements.

4. The acoustic absorption meta-structure coating (100) as claimed in Claim 1, wherein the unbonded resonators (120) are arranged in spatial patterns within said viscoelastic matrix (110) with varying shapes and diameters such that their eigenfrequencies are varied to achieve a desired level of noise absorption in a frequency range of interest.

5. The acoustic absorption meta-structure coating (100) as claimed in Claim 1, wherein the unbonded resonators (120) are configured to undergo multi-mode vibrations, thereby enabling broadband noise absorption.

6. The acoustic absorption meta-structure coating (100) as claimed in Claim 1, wherein the unbonded resonators (120) are configured to maximize insertion loss (IL), echo reduction (ER) and acoustic absorption coefficient within said frequency range of interest, based on application-specific sound profiles in diverse acoustic environments.

7. A method of fabricating the acoustic absorption meta-structure coating (100), comprising the steps of:
 selecting a viscoelastic material having a loss factor (tan δ) of at least 0.1 exhibiting viscoelastic and acoustic damping properties to form a viscoelastic matrix (110);
 applying said viscoelastic matrix (110) to a substrate (130); and
 forming a plurality of unbonded regions within the viscoelastic matrix (110);

wherein the unbonded regions function as resonators (120) and are distributed in a predetermined pattern using computational models to ensure multi-frequency resonance, thereby maximizing acoustic energy dissipation through its conversion into vibrational energy.