Patent Application
20250182729
The invention is related to the development of meta cells which can show both passive material and meta properties (ie, hybrid properties) and multifunctional acoustic metamaterial panel comprising at least one hybrid meta cell in order to decrease the transmission of sound waves and/or attenuate sound waves in a desired narrow or wide frequency band.
Sound or noise isolation/reduction/control basically takes place with two techniques, active and passive. In addition, this reduction or control is generally performed in two different ways, sound absorption and sound transmission loss. In terms of sound absorption, active and passive insulation can be described as:
Active insulation; in general, is carried out with a control sound wave interferencing with the source sound wave that is desired to be reduced without the application of an insulating material. Control sound wave is adjusted as in the opposite phase, and the same frequency of the sound wave desired to be suppressed. This method is quite costly. In addition, since it requires a controlled volume, its application area is limited in practice. In this method, the control sound wave can be produced externally using a sound source, or it can be produced without a sound source by means of various elements called resonators. However, this type of control can generally operate in narrow frequency bands (also known as tonal) and still needs a controlled volume. More resonators are needed to widen the frequency band. This means that the area where the resonators can be placed is increased. To absorb lower frequencies, larger volumes or lengths of resonators are required.
Passive insulation; is realized by placing the insulation elements, such as a sponge, felt, glass wool, rock wool, textile waste, etc., between the noise source and the receiver. Passive insulation materials provide sound absorption by viscous and thermal effects due to their internal spaces, discontinuities, physical and chemical structures. In addition to that, they can increase the propagation path of sound through the material (also known as tortuosity), thereby reducing the energy of sound waves that follow a longer path. These materials, which can absorb by converting sound energy into heat energy, are insufficient in absorbing low-frequency noises where the sound wave has a large wavelength. Because in order for these types of materials to function efficiently, the material characteristic thickness must be at least one quarter of the wavelength of the sound/noise to be controlled. For example, in order to absorb a 100 Hz sound wave (sound speed: 343 m/s), it requires the use of an insulation material with a characteristic thickness of 343/100/4≈86 cm. Since this is not possible both physically and economically in practice, this makes conventional materials not usable efficiently at low frequencies. In addition, the use of these materials in systems such as areas that require air circulation, food and hygiene equipment, flammable and hot environments is quite limited.
In terms of sound transmission reduction/loss, there is no difference between sound absorption or transmission for active isolation by nature. However, sound transmission loss can be realized by increasing the reflection with various acoustic volume-based geometric discontinuities (i.e. expansion chambers). Again, the need for larger volume continues at low frequencies.
When the sound transmission loss is evaluated in the context of passive control; it takes place depending on the material mass and frequency (known as the mass-frequency law). Accordingly, as the mass of the material increases, the sound transmission loss increases. Likewise, as the frequency increases, the sound transmission loss increases. Therefore, larger weights of insulating material must be used to achieve a higher sound transmission loss at lower frequencies. For this purpose, materials such as stone wool or glass wool reinforced concrete, and brick are generally preferred.
Especially in the last 15 years, there has been intense work on the development of artificial insulation materials, known as acoustic metamaterials, instead of traditional materials for low-mid frequency regions. Acoustic metamaterials have a wide range of uses, mainly in the technical field of physics and engineering, in many sectors such as automotive, aerospace, industrial machinery, white goods, household appliances, air conditioning and ventilation systems, defense industry, construction and construction sector. With acoustic metamaterials, high sound absorption and/or sound transmission loss can be achieved at certain singular low frequencies through negative effective mass, negative effective bulk modulus or both by not obeying the mass-frequency law. Cells are usually formed by periodically arranging them side by side or in succession. In these materials, although the material thickness is an important parameter; the main technique is to design and appropriately locate resonance cells which are usually of small size (having characteristic lengths smaller than the wavelength of sound., i.e. subwavelength). However, acoustic metamaterials, which are also in the state of the art, absorb in narrow frequency bands and provide transmission loss in a certain region (in a frequency band) depending on the resonance frequency of the cell. Therefore, it is necessary to develop acoustic metamaterials in order to provide a desired broad spectrum absorption and sound losses. Often a combination of multiple, tuned and periodically arrayed cells is used to broaden the band.
In the state of the art, in the patent with CN112728275 document no, it is mentioned that a sound absorption unit which is especially suitable for non-singular low-frequency noise absorption, has ultra-open ventilation and adjustable sound absorption performance. In this cell design; the frequency is adjustable, it allows air passage and it is aimed at sound absorption by trapping the sound wave in a labyrinth dead end. The cell mentioned in the document in question aims to increase the sound path for low frequencies so that it can absorb cavity resonances. The cell specified in this context may only feature a local negative Bulk module at singular but adjustable frequencies. In addition, a moving part inside can provide the frequency tuning (tuning) process. In this way, it has larger thicknesses by design. However, it does not have cell functions that can perform the sound transmission reduction, that is, have a negative mass effect.
In another known state of the art, in the patent with CN111883093 (A) document no., a 3-layer cell is mentioned as 1-micro-perforated plate, 2-double helix coiled structure, 3-back plate. In this cell type, the first plate comprises two micro-sized holes. Right behind these holes, there are two channels in the form of helix to increase tortuosity. With these two channels, it is aimed to provide absorption at two different frequencies at the same time. With the plate on the back, it is aimed to cut the transmission according to the law of mass. These two plates on the front and back do not show meta features. Sound attenuation is achieved through a micro-perforated front panel and a passively comprised dual channel. Again, it only works as a sound absorber at tonal frequency. Although the path is designed as a spiral in order to increase the tortuosity, the combination and metamaterial technique described in the mentioned document is a known technique.
In another known state-of-the-art, numbered WO2017093690A1, a unit cell of an acoustic metamaterial is mentioned. This cell provides high sound transmission at Fabry Perot frequencies with multiple additions of typical Helmholtz resonance cells. In other words, it is not a cell developed to reduce the transmission of sound waves created by a noise source and to absorb sound waves.
In another known state-of-the-art, US2021237394 (A1) patent document numbered; preserves another acoustic metamaterial. This metamaterial; a cell with a classical geometric form comprising a membrane consists of a posterior rigid cavity or a mass. This is a classical dipole type metamaterial. A classical metamaterial stops the sound transmission up to the natural frequency of its membrane. The metamaterial in question provides a small amount of sound absorption according to the material properties of the membrane. Therefore, according to the purpose, some of the said cells, which are counted in the state of the art, perform sound suppression and some perform sound absorption.
It is necessary to develop acoustic metacells that turn the disadvantages listed in the state of the art into advantages.
The purpose of the invention; comprising at least one part, which is both passive material and meta-feature (hybrid), developed with unique geometric forms to stop and/or absorb the transmission of sound waves by tuning to a desired narrow or wide frequency band, is to realize a multifunctional acoustic metamaterial panel comprising at least one acoustic hybrid metacell and said at least one hybrid metacell.
Another aim of the invention is the development of acoustic insulation panels that can be shaped or formed according to the applied section or place; the panels, comprising the aforementioned hybrid acoustic meta cells, can operate in the desired narrow band and/or a certain wide frequency band, can provide both high sound absorption and high sound transmission loss and they, can be very thin, flexible or rigid (inflexible, solid).
The developed cells and the panels comprising these cells can exhibit passive insulation material properties as well as acoustic metamaterial properties. For this reason, it is called hybrid acoustic meta cell and acoustic hybrid meta insulation panel/plate.
Besides, The cells also have a form that can function as a resonator at medium and high frequencies. Thus, a combined cell that can comprise both meta, passive material and resonator is obtained. In the state of the art, these features do not exist together in this way. These panels can be used in a wide range of sectors as sound (acoustic, noise) insulation materials.
In addition, since the insulation panels can be in perforated forms, innovative insulation systems that allow air circulation but not sound/noise transmission are created with the invention.
The cells of the invention show negative mass properties with a membrane or plate with a sub-wavelength, and a negative bulk modulus with cavities and channels (working like a special resonator with sub-wavelengths). These negativities imply metamaterial effects creating exotic behaviours leading to higher sound transmission loss and sound absorption. In addition, the geometry, thickness and length of the channels provide a high visco-thermal and tortuosity effects. These effects mean passive material behaviour. This hybrid combination is quite different from the systems mentioned in the state of the art. Thanks to these features, it can take a very thin form compared to the state of the art. Frequency tuning is performed with a calculation that comprises the geometric parameters of both the membrane/plate and the form of cavity, channel and slits.
The invention is a hybrid acoustic single cell in any geometric form, preferably circle, triangle, square, rectangular, polygon or arbitrary, which can be used in many sectors such as automotive, aviation, industrial machinery, white goods, household appliances industry, air conditioning and ventilation systems, defense industry, construction and building sector. These cells can create multicells by connecting single cells to each other through an acoustic volume channel. These cells are designed to stop the transmission in a very wide frequency range of sound waves created by a noise source or to provide sound absorption, with at least one first layer (or front or entrance layer) in any geometric form and physical feature, with at least one second layer (or intermediate layer) in any geometric form and physical feature, with at least one third layer (or output or back layer) of any geometric form and physical properties. These cells have at least one inner frame in any geometric form and physical properties, and at least one internal acoustic volume that fills the said inner frame as much as the inner volume and conforms to the geometric form of the inner frame or in any geometric form and physical properties. It also comprise at least one external acoustic volume channel of any geometric form and physical feature, positioned at a predetermined distance relative to the said inner frame and in the outer region of the inner frame, together with the acoustic volume. In addition, at least one outer frame in any geometric form and physical properties in the cell completely or partially covers a surface of the said external acoustic volume channel and said second layer of the said inner acoustic volume. Due to the geometrical form and physical feature formed by combining said first layer and said third layer, which completely or partially covers another surface, with the said second layer, two separate sections are formed in the cell for each of the first layer and the third layer at a predetermined thickness; first and second part. Each part exhibits different physical properties according to its natural frequencies.
For a better understanding of the invention, the corresponding numbers in the figures are given below:
Hybrid single acoustic metacell (1), which is the subject of the invention, in order to stop the transmission and/or absorb the sound waves in a wide frequency range; It comprises at least one first layer (1.1) (or front or entrance layer) in any geometric form and physical properties, in order to be a resonant cell with characteristic dimensions smaller than the wavelength of the sound (i.e at subwavelength scale), at least one second layer (1.2) (or intermediate layer) in any geometric form and physical properties and at least one third layer (1.3) (or output layer or back layer) in any geometric form and physical properties (
In order to realize another aim of the invention; Acoustic hybrid metamaterial insulation panels are formed by positioning at least one hybrid metamaterial cell (1) on top of and/or back-to-back and/or back-to-back and/or side-to-side and/or in any arbitrary manner. Therefore, the insulation panel comprises at least one hybrid metamaterial cell (1) that is positioned as desired and has different or the same geometric forms. Acoustic channels between cells can be connected to each other according to the desired frequency setting. Here, the term insulation comprises sound transmission stopping or sound absorption feature or both.
The second layer (1.2) of a predetermined thickness, an outer frame (1.20) of any geometric form (circle, square, rectangle or arbitrary) and inside said outer frame (1.20) conforming to the geometric form of the outer frame (1.20) or any comprises at least one inner frame (1.21) of any geometric form, positioned within the outer frame (1.20) and at a predetermined distance from the outer frame (1.20) (
In an example implementation of this cell form (
In different embodiments of the invention, each same or different metacell (1) can be connected to each other by acoustic volume channels (1.201) to form a new meta-cell (1) with double, triple or multiple and different acoustic characteristics. As an example of this application of the invention, two meta-cells (1) with different mouth openings in form and positions are connected to each other via acoustic volume channels (
The first layer (1.1) and third layer (1.3); for entrance of sound wave (or air), respectively, according to embodiments of the invention; at least one entrance hole (1.10) in predetermined sizes, numbers, various geometric forms (circle, triangle, square, rectangle, polygon or arbitrary) and/or in predetermined sizes, numbers, depending on the cell character, depending on the cell character, may comprise at least one exit hole (1.30) in various geometric forms (circle, triangle, square, rectangle, polygon or arbitrary) (
The first layer (1.1), the second layer (1.2), and the third layer (1.3) have predetermined thicknesses and can be the same or different thicknesses. The first layer (1.1) and the third layer (1.3) may each be a membrane and/or plate according to embodiments of the invention.
On the first layer (1.1) and the third layer (1.3), a single, multiple or distributed mass or masses of any form and weight can be added to any part. The frequency region to be effective can be changed by changing the geometric dimensions, material, geometric shapes and the value and position of the mass brought on the first layer (1.1), the second layer (1.2) and the third layer (1.3).
If the general working principle of the cells is summarized technically, the specially designed second layer (1.2) provides high absorption by increasing the tortuosity with the channel type space it comprises, allowing the sound to consume more energy than the thickness. This situation is shown as the “e” channel in
Single cell (1); due to the inner frame (1.21) and the outer frame (1.20) and the small internal acoustic volume (1.210) between these frames and bounded by the membrane on both sides, it exhibits dipolar* properties and provides more than 50 percent sound at the natural frequency of the cell (1) and the volume. (*Note: cavities that do not comprise small closed volumes or comprise long volumes are monopole and provide absorption up to a maximum of 50 percent.)
The negative effective mass and the negative effective Bulk modulus can be provided simultaneously in the same frequency region by changing the geometry, material, shape and the physical properties of the inner frame (1.21), the outer frame (1.20), the inner acoustic volume (1.210), the outer acoustic volume channel (1.201), the first part (B1) (peripheral membrane) and the second part (B2) (middle membrane). In this way, double negative metamaterial can be obtained in a desired frequency band. When they are vibrated by the sound wave, it stops the propagation of the sound in a certain frequency region depending on the mass, if there is no mass on them, up to their natural frequency, if there is mass on them, it stops the propagation of the sound (it stops the transmission, creates a band gap, makes sound filtering). At the same time, a passive sound absorption occurs due to the elastic properties of the membranes.
The entrance hole (1.10) (or the wave entrance hole) located in the first layer (1.1) allows the sound wave to enter the cell and proceed through the acoustic volume channel (1.210). It is not necessary to have an exit hole in the third layer (1.3), it is determined by the desired character of the cell. As the path (Leffective) gets longer, the energy of the sound along the path is reduced. Thus, a significant amount of sound absorption is obtained. Therefore, absorption in the cell is increased. For this purpose, it is necessary to have at least one inlet hole (1.10) in order to provide impedance matching. However, the exit hole (1.30) need not always be. If a material that requires ventilation or does not block the air inlet and outlet is desired, there should be inlet and outlet holes (1.10 and 1.30). For example, in applications where air inlet and outlet are required, such as compressors or generators, metamaterials with cells with inlet and outlet holes (1.10 and 1.30) can be used to filter the sound (sound transmission stopping). The transmission and absorption spectrum of the cell (1) can be changed depending on whether each technical unit (such as the entrance hole (1.10), neck, internal acoustic volume (1.210) . . . ) comprised in the unit cell (1), which is the subject of the invention, is in the cell (1) or not. For example, the geometric form of the entrance hole (1.10) (circle, square or rectangle . . . etc) or even whether the said form exists or is positioned on the layer can completely change the behavior of the cell (1). As mentioned above, the first layer (1.1) and the third layer (1.3) can be at least one, as well as be made of membrane and/or plate of a predetermined thickness, or any material.
The cell (1) that is the subject of the invention functions as both a sound absorber and a sound transmission stopper due to its structure. That is, the first layer (1.1) or the second layer (1.2) or the third layer (1.3) alone cannot exhibit these features. However, the aforementioned features (absorption and transmission section) can only be realized with the cell (1) subject to the invention, when the first layer (1.1), the second layer (1.2) and the third layer (1.3) come together to form a combined structure.
The aim of the invention is to obtain a cell (1) structure that performs better sound absorption and sound transmission loss. For better absorption, the surface impedance should be reduced. At least one hole must be drilled in the first layer (1.1) to reduce the impedance. While doing this, the entrance hole (1.10) and/or the exit hole (1.30) should be opened in such a way as not to disturb the properties of the layers themselves. If an entrance hole (1.10) and/or exit hole (1.30) is opened in the middle of the cell (1), almost as large as the volume of the cell, the membrane does not show the desired vibration feature. The dimensions of the inlet hole (1.10) and/or the outlet hole (1.30) are made in such a way that they do not disturb the membrane (plate) feature. In addition, the mentioned holes allow the sound wave to enter and/or exit the cell, and with the predetermined geometric form, size and positioning, the path of the sound (Leffective) increases. In addition, the positioning of the holes is such that the sound travels the farthest path from the hole it enters to the hole where it exits. So thus a large effective length (Leffective) is created. Thus, the middle of the cell (1) functions like another membrane, and its surroundings work like another membrane. When sound or air enters from the inlet hole (1.10), the cell (1) shows a negative effective mass feature. As the sound progresses, the metamaterial begins to transform into a negative Bulk modulus. With the design of the cell (1) that is the subject of the invention, the air entering through the holes travels within the external acoustic volume channel (1.201), and the thickness of the material is extended at least 5 times in one application with the path taken by the sound. In other words, without the need for the material to be very thick, the conditions needed to reduce the energy of the sound are provided with the invention. In case of mouth opening, the internal acoustic volume (1.210) works like a Helmholtz resonator. Thus, the geometry of the cell (1) dampens the sound by showing a wave effect at a singular frequency, opposite to the sound, and can stop the sound propagation up to this frequency region. Therefore, the wave can be absorbed due to a phase difference (in opposite phase (180°)) of the wave at the same frequency. When a part of the wave is not passed, sound transmission loss occurs. However, when sound enters the cell and the sound is exposed to the specified geometry of the cell (friction increases when it is passed through a narrow channel), the energy of the sound is also reduced due to friction (heat exchange). Considering that a passive material provides absorption due to viscothermal effects, the cell (1) which is the subject of the invention, has this geometric form and the cell (1) begins to behave like a passive material. Therefore, as mentioned above, a hybrid material is formed by combining passive material and metamaterial.
The acoustic volume-based character of the metacell has a multifunctional feature according to whether there is an inlet hole (1.10) positioned on the mouth (A) and the first layer (1.1) in the second layer (1.2) (i.e, in the form layer) and an outlet hole (1.30) located on the third layer (1.30), and whether the neck connected to the mouth (A). Thus, different meta-cells (1), whose character can be easily changed, are obtained depending on whether there is only a hole/neck/mouth, depending on the application area. Some combinations showing the acoustic volume-based sound transmission loss character of these metacells (1) can be seen in Table 1.
An example description for Table 1:
In an application of the invention, if there are holes in the first layer (1.1) and the third layer (1.3) that the cell (1) comprises, that is, if an entrance hole (1.10) and an exit hole (1.30) are located in both layers (H1), the entire acoustic space will have the character of an expansion chamber. While only the inlet hole (1.10) is present, the meta cell (1) turns into a quarter-wave resonator (H2). While the inlet (A) is present, an additional Helmholtz resonator is formed in the cell (1) (H3 and H4).
In
In summary, the long and narrow external acoustic volume channel (1.201); By providing high tortuosity, it provides higher absorption at lower frequencies. However, the sound wave entering from the inlet hole (1.10) travels a longer distance than the channel thickness and is exposed to higher visco-thermal effects as it travels inside the cell (1). This allows the sound wave to consume more of its energy and thus the cell has a higher sound absorption capacity. This feature makes the meta cell a hybrid cell. As the viscous absorbance increases, the frequency band becomes wider. With the use of multiple and different cells, the panel comprising hybrid cells having a feature that can provide absorption in a wider band.
In addition to what has been described, the same or different single cells (1) can be connected to each other in double, triple, quadruple and multiple, side-by-side, back-to-back or back-to-back or any other arrangement according to the purpose. Thus, higher absorption is obtained at lower frequencies. All individual cells (1) are binary (for example,
The first layer (1.1), the second layer (1.2), and the third layer (1.3) are joined to each other by any available bonding method, forming single or multiple cells (1). All cell layers can be produced by any fabrication method, such as a single piece or a composite structure.
On the other hand, panels that absorb at various frequencies can be formed by placing at least one of these same or different cells (1) side by side (or by sequential ordering) or on top of each other, or in any arrangement according to the purpose. In order to form a panel, at least one cell (1) mentioned in the same or different geometric form and physical properties can be positioned on the said panel. Thus, panels consisting of meta-cells (1) that are the subject of the invention can be obtained. Since the panel comprises at least one meta cell (1) and each cell (1) will be placed on the panel in such a way as to absorb the sound of the same or different frequencies, sound absorption will be realized in both tonal and wide bands.
The features of the panels obtained from the metacells (1) that are the subject of the invention are as follows:
In summary, the insulation panels formed with metacells (1), which are the subject of the invention, are designed according to the acoustic metamaterial theory. Acoustic metamaterial is simply a kind of artificial composite structure, single or multi-layered, formed by combining one or more base materials by converting them into subwavelength resonance cells. Space and/or vibrating thin plates and/or small weights are placed in the first layer (1.1) and third layer (1.3) of this structure in a planned manner. On the other hand, the geometry, form and dimensions of the second layer (1.2) are specially designed according to the frequency character of the noise to be reduced. When the sound wave of the noise hits this three-layer structure, it vibrates and resonates with this specially tuned three-layer structure. The resonating first layer (1.1), the second layer (1.2), and the third layer (1.3) and the special structure formed by their combination will show a negative mass and/or Bulk Modulus effect up to their resonance frequencies, which will stop the sound propagation in this region and absorb sound energy, thus reduce the sound level to a certain amount. In this way, noise absorption and/or noise transmission stopping is realized with the cell (1), which is the subject of the invention. As it can be understood, the working mechanism of such structures is completely different from that of passive insulation materials. While passive insulation materials provide absorption by converting sound energy into heat energy, these structures reduce sound energy by preventing and manipulating the propagation of sound with cells at lower wavelengths.
In addition to showing acoustic metamaterial properties, the obtained panels perform both sound transmission and sound absorption at the same time in a wider frequency band by taking advantage of the properties of passive materials. That's why it's called a hybrid. Panel cells (1), specially designed and brought to the most optimum form with R&D activities, will operate with maximum efficiency in the wide frequency band of 50 Hz-20000 Hz.
The invention is metamaterial panels comprising at least one cell (1) developed for use in many sectors such as automotive, aerospace, industrial machinery, white goods, household appliances industry, air conditioning and ventilation systems, defense industry, construction and construction industry, and is industrially applicable.
The invention is not limited to the above exemplary embodiments, a person skilled in the art can easily demonstrate different embodiments of the invention. These should be considered within the scope of the protection claimed by the claims of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022/003002 | Mar 2022 | TR | national |
This application is the national phase entry of International Application No. PCT/TR2023/050120, filed on Feb. 9, 2023, which is based upon and claims priority to Turkish Patent Application No. 2022/003002, filed on Mar. 1, 2022, the entire contents of which are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/TR2023/050120 | 2/9/2023 | WO |
