Mechanical metamaterial vibration isolation device with local resonance and particle damping synergy

Abstract

This invention discloses a mechanical metamaterial vibration isolation device with synergistic effects of local resonance and particle damping, comprising a dual-oscillator periodic phonon crystal, a flexible connecting device, a self-lubricating panel, and a protective shell. The dual-oscillator periodic phonon crystal includes a large hexagonal grid, a small hexagonal grid, a helical spring assembly, and a group of loose particles. The flexible connecting device includes a porous connecting plate, a force-equalizing beam, and a series of disc springs. The large hexagonal grids are bolted together. The small hexagonal grids, as ordinary local oscillators, are placed inside the large hexagonal grids and connected to the large hexagonal grids via the helical spring assembly. The group of loose particles is spaced apart along the long side of the vibration isolation device within the small hexagonal grids, forming a particle-damped local oscillator with the small hexagonal grids. The large hexagonal grids containing the two types of local oscillators are periodically arranged to form the dual-oscillator periodic phonon crystal. The phonon crystal is connected to the outside via the flexible connecting device. The self-lubricating panel contacts the upper and lower surfaces of the phonon crystal and is embedded in the protective shell.

Description

Technical Field

[0001] This invention relates to the field of artificial mechanical metamaterials technology, and in particular to a mechanical metamaterial vibration isolation device with the synergistic effect of local resonance and particle damping. Background Technology

[0002] Metamaterials are artificially constructed materials or structures with periodic properties, possessing extraordinary static or dynamic characteristics not found in natural materials. Phononic crystals are the most typical example of this type of material. These periodic structures exhibit a mechanical bandgap characteristic due to Bragg scattering, meaning that mechanics rapidly attenuates and cannot propagate within the bandgap (gap) frequency range. Utilizing the bandgap properties of metamaterials, the propagation of vibrations and elastic waves can be suppressed, achieving control over vibrations and noise. However, if the lattice constant of the metamaterial decreases, or the elastic modulus of the matrix material increases, the Bragg scattering bandgap frequency shifts to a higher frequency region, making it difficult for metamaterials to open bandgap structures in the low-frequency range at small scales.

[0003] In the early 21st century, the local resonance mechanism was introduced into the design of phononic crystals. Compared with the traditional Bragg scattering mechanism, this mechanism can achieve a lower frequency wave bandgap within the same geometric dimensions. When vibrations and elastic waves propagate between cells, energy is transferred to the inner and outer masses. When the inner mass blocks of a cell resonate, the amplitude of the outer mass vibration is smaller, reducing the mechanical energy transmitted to adjacent cells. The wave decays rapidly after traveling a certain spatial distance, and the vibrations and elastic waves are blocked.

[0004] Particle damping technology is a passive vibration reduction and isolation technology adapted to extreme conditions. Particle dampers are typically cavity structures containing particles. They utilize the collisions and friction between particles and between particles and the inner wall of the cavity to dissipate vibration energy, thereby achieving vibration isolation. Particle dampers have a simple structure, wide isolation bandwidth, and high reliability, and are used in aerospace, civil engineering, and mechanical engineering fields. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a mechanical metamaterial vibration isolation device that combines the synergistic effect of local resonance and particle damping. It combines the advantages of phononic crystal dampers, local resonance mechanisms and particle dampers to achieve synergistic effects and realize vibration isolation and noise reduction over a wide frequency range.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A mechanical metamaterial vibration isolation device with synergistic effect of local resonance and particle damping includes a dual-oscillator periodic phonon crystal, a flexible connection device, a self-lubricating panel, and a protective shell.

[0008] The upper and lower surfaces of the dual-oscillator periodic phonon crystal are in contact with the self-lubricating panel, and the left and right ends of the dual-oscillator periodic phonon crystal are connected to the flexible connection device. The self-lubricating panel is embedded in the protective shell.

[0009] The dual-oscillator periodic phononic crystal comprises: a large hexagonal grid, a small hexagonal grid, a helical spring assembly, and a group of loose particles;

[0010] The large hexagonal grid consists of several sections, each with a through hole at its center, and all are connected to each other by bolts. Each small hexagonal grid also has a through hole at its center and serves as a common local oscillator within the large hexagonal grid, connected to it via the helical spring assembly. The granular particle group is spaced along the long side of the mechanical metamaterial vibration isolation device within the small hexagonal grid, serving together with the small hexagonal grid as particle-damped local oscillators. The large hexagonal grid containing both common and particle-damped local oscillators is periodically arranged along a plane, forming a dual-oscillator periodic phonon crystal.

[0011] Two flexible connection devices are provided, symmetrically arranged on the left and right sides of the dual-oscillator periodic phonon crystal, including a porous connection plate, a force-equalizing beam, and a series of disc springs; the porous connection plate has several through holes of different diameters, and is connected to the force-equalizing beam through the series of disc springs; the side of the porous connection plate away from the force-equalizing beam is connected to the external component by bolts; the force-equalizing beam is bolted to the adjacent large hexagonal grid.

[0012] The self-lubricating panel has two parts, which are respectively embedded in the limiting slots of the upper and lower protective shells;

[0013] The protective shell has two parts, including a limiting slot and a through hole. There are several through holes, and the protective shells are fixedly connected by bolts.

[0014] Furthermore, the granular group comprises several rigid large spheres and rigid small spheres, with the rigid small spheres dispersed in the gaps between the rigid large spheres and the small hexagonal grid.

[0015] Furthermore, the dual-oscillator periodic phononic crystal has a Bragg scattering bandgap and a local resonance bandgap. Vibrations decay rapidly within the bandgap frequency range and cannot propagate. Vibrations within the passband frequency range are dissipated by particle friction and collision damping in the particle-damped local oscillator.

[0016] Furthermore, the flexible connection device also includes a self-lubricating bushing and a limiting bolt; the self-lubricating bushing is nested in the through holes corresponding to the force equalizing beam and the multi-hole connecting plate; the limiting bolt is a semi-threaded bolt, with the optical axis part contacting the multi-hole connecting plate, the series disc spring assembly and the self-lubricating bushing, and the threaded part contacting the nut.

[0017] Furthermore, the series disc spring assembly includes long series disc springs and short series disc springs, wherein the long series disc springs are between the perforated connecting plate and the force equalizing beam, and the short series disc springs are between the perforated connecting plate and the head of the nut and the limiting bolt. The number of disc springs in the long series disc springs is twice the number of the short series disc springs, so that the flexible connecting device has elasticity under tension and compression, and the elastic coefficient is consistent under tension and compression.

[0018] Furthermore, the surfaces of the rigid large sphere and the rigid small sphere, as well as the inner wall of the small hexagonal grid, are all sandblasted to increase the roughness of the contact surface, improve the damping performance of particle friction and collision, suppress the generation of friction screaming noise, and reduce the intensity of friction noise.

[0019] Furthermore, the vibration isolation device of the mechanical metamaterial with synergistic effect of local resonance and particle damping has the most significant vibration isolation effect in the frequency bands of 255-498Hz, 735-891Hz and above 1146Hz.

[0020] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0021] 1. The local oscillator in this invention provides a new local resonant bandgap, which expands the effective isolation frequency range of the vibration reduction device, overcomes the shortcomings of the traditional phonon crystal vibration isolator with too narrow an effective isolation frequency band, and the local resonant bandgap is flexible to adjust and can be adjusted in a targeted manner according to the actual situation, thereby achieving a better vibration isolation effect on the target frequency band.

[0022] 2. The granular particle group in this invention uses particles of different diameters to make reasonable use of limited space, improve the cavity filling rate, and can fully dissipate energy through particle damping, thereby weakening the propagation of vibration in the passband frequency range. At the same time, it can be equivalent to the added mass of a local oscillator. By arranging them at intervals, a dual-oscillator periodic phonon crystal is formed, which widens the original Bragg scattering band gap and works synergistically with the local resonance band gap. Compared with the traditional single-oscillator periodic phonon crystal vibration isolation device, it has a wider range and more vibration isolation frequency bands.

[0023] 3. The large and small hexagonal grids in this invention are both made of ABS material, which is inexpensive, easy to process, and has excellent elasticity and toughness. The lower density makes the structure of the vibration isolation device lighter. The noise generated by the collision and friction between the ABS material cavity and the loose particle group is lower in frequency and decibel, avoiding the high-frequency noise problem of stainless steel particle dampers during operation.

[0024] 4. The self-lubricating panel in this invention is made of PTFE (polytetrafluoroethylene), which has a very low coefficient of friction. It provides pressure along the plane normal only to the dual-oscillator periodic phonon crystal, enabling each component in the dual-oscillator periodic phonon crystal to vibrate fully along the plane and improving the vibration isolation performance of the metamaterial.

[0025] 5. The limiting bolt in the flexible connection device of the present invention is a semi-threaded bolt. Its optical axis part serves as a guide rod, which guides the series disc spring assembly, the force equalizing beam and the multi-hole connecting plate. The threaded part cooperates with the nut to perform the fastening and limiting function. The self-lubricating bushing is nested in the through hole corresponding to the force equalizing beam and the multi-hole connecting plate, which can avoid direct contact between the through hole of the force equalizing beam and the multi-hole connecting plate and the optical axis part of the limiting bolt, thus avoiding scratching noise.

[0026] 6. The flexible connection device in this invention can better protect the dual-oscillator periodic phonon crystal structure from damage under extreme working conditions, enabling the vibration isolation device to adapt to more complex working conditions.

[0027] 7. All components in this invention are connected by bolts, making the structure flexible and easy to assemble and disassemble. The number of periods of the dual-oscillator periodic phonon crystal can be changed according to actual needs to obtain better vibration isolation effect.

[0028] 8. The surfaces of the rigid large sphere and the rigid small sphere, as well as the inner wall of the small hexagonal grid, are all sandblasted; this increases the roughness of the contact surface, improves the damping performance of particle friction and collision, suppresses the generation of friction screaming noise, and reduces the intensity of friction noise. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structural explosion of the mechanical metamaterial vibration isolation device in an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the overall assembly of the mechanical metamaterial vibration isolation device in an embodiment of the present invention;

[0031] Figure 3 This is an enlarged schematic diagram of the protective shell limiting groove structure of the mechanical metamaterial vibration isolation device in an embodiment of the present invention;

[0032] Figure 4 This is a schematic diagram of the dual-oscillator periodic phononic crystal dual-oscillator periodic structure according to an embodiment of the present invention;

[0033] Figure 5 This is a cross-sectional structural diagram of the flexible connection device according to an embodiment of the present invention;

[0034] Figure 6 This is a schematic diagram of a large hexagonal grid structure with a particle-damped local oscillator according to an embodiment of the present invention.

[0035] Figure 7 This is an exploded view of the structure of the large hexagonal grid with a particle-damped local oscillator according to an embodiment of the present invention.

[0036] Figure 8 This is a comparison of the output frequency response curves with and without a local oscillator in an embodiment of the present invention;

[0037] Figure 9 This is a comparison chart of the output frequency response curves of the local oscillator with and without particle damping in an embodiment of the present invention.

[0038] Figure 10 This is a comparison of the output frequency response curves of the localized oscillator with and without particle damping in an embodiment of the present invention.

[0039] Reference numerals: 1-Protective outer shell, 2-Self-lubricating panel, 3-Dual-oscillator periodic phonon crystal, 4-Flexible connection device, 10-Limiting slot, 11-Bolt through hole, 30-Large hexagonal grid, 31-Small hexagonal grid, 32-Helical spring assembly, 33-Particle group, 34-Through hole, 40-Force equalizing beam, 41-Porous connecting plate, 42-Bolt, 43-Limiting bolt, 44-Flat washer, 45 - Series disc spring assembly, 46- Self-lubricating bushing, 47- Spring washer, 48- Nut, 320- Lightweight helical spring, 321- Bolt, 322- Flat washer, 323- Spring washer, 324- Nut, 325- Spring seat, 330- Rigid large ball, 331- Rigid small ball, 400- Through hole, 410- Large through hole, 411- Small through hole, 450- Long series disc spring, 451- Short series disc spring. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0041] In the description of this invention, unless otherwise stated, "several", "multiple", or "a variety" means two or more; the terms "upper", "lower", "inner", "outer", "left", "right", "lateral", "center", "elevation", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0042] The bandgap characteristics of mechanical metamaterials or phononic crystals make it difficult for vibrations to propagate within the bandgap frequency range, thus enabling effective vibration isolation within the bandgap frequency band. This invention proposes a mechanical metamaterial vibration isolation device that combines the advantages of traditional phononic crystals, local resonance mechanisms, and particle dampers, achieving vibration isolation and noise reduction over a wider frequency range. It possesses two different bandgap mechanisms—Bragg scattering bandgap and local resonance bandgap—at different frequency bands, effectively blocking vibrations within the bandgap; the particle damper dissipates vibration energy within the passband and also enhances the bandgap's vibration isolation effect, thus achieving effective vibration reduction and isolation across a wider frequency range.

[0043] like Figures 1 to 2 As shown, the planar mechanical metamaterial vibration isolation device with local resonance and particle damping characteristics according to an embodiment of the present invention includes: a protective shell 1, a self-lubricating panel 2, a dual-oscillator periodic phonon crystal 3, and a flexible connecting device 4. The upper and lower surfaces of the dual-oscillator periodic phonon crystal 3 are in contact with the self-lubricating panel 2, and the left and right ends of the dual-oscillator periodic phonon crystal 3 are connected to the flexible connecting device 4. The self-lubricating panel 2 is embedded in the protective shell 1. In this embodiment, the protective shell 1 is made of ABS material, and the self-lubricating panel 2 is made of PTFE (polytetrafluoroethylene). Due to the extremely low coefficient of friction between the self-lubricating panel 2 and the dual-oscillator periodic phonon crystal 3, each component in the dual-oscillator periodic phonon crystal 3 can vibrate fully under the excitation conducted by the flexible connecting device 4, thus better exhibiting bandgap characteristics. Simultaneously, it can also drive the rigid spheres in the granular particle group 33 to rub and collide, dissipating vibration energy.

[0044] like Figure 3 As shown, the limiting groove 10 of the protective shell 1 restricts the displacement of the self-lubricating panel 2, and the upper and lower protective shells 1 can be bolted together using the bolt through hole 11.

[0045] like Figure 4 As shown, a small hexagonal grid 31 is placed inside a large hexagonal grid 30 and connected by a helical spring assembly 32. The bolts of the helical spring assembly 32 are also used to fix adjacent large hexagonal grids 30. The bulk particle group 33 is placed laterally spaced within the small hexagonal grid 31, forming a particle-damped local oscillator with the small hexagonal grid 31. It also serves as additional mass for the small hexagonal grid 31. The spaced arrangement makes the dual-oscillator periodic phonon crystal 3 a dual-oscillator periodic structure. In this embodiment, both the large hexagonal grid 30 and the small hexagonal grid 31 are made of ABS (acrylonitrile-butadiene-styrene copolymer), and the rigid spheres in the bulk particle group 33 are made of stainless steel.

[0046] like Figure 5 and Figure 6As shown, both the large hexagonal grid 30 and the small hexagonal grid 31 have through holes at their center for fixing the lightweight helical springs and for fixing adjacent large hexagonal grids 30. All three lightweight helical springs 320 have a certain pre-compression and remain compressed during vibration. A flat washer 322 is provided between the bolt 321 and the hexagonal grid surface, and a spring washer 323 and a flat washer 322 are sequentially provided between the nut 324 and the hexagonal grid surface. The flat washer 322 effectively protects the ABS material from being crushed, and the spring washer 323 prevents the nut 324 from loosening and falling off during structural vibration. A spring seat 325 is nested at both ends of the lightweight helical spring 320, and its inner wall contacts the outer sides of the nut 324, spring washer 323, and flat washer 322. A group of loose particles 33 is placed inside the small hexagonal grid 31, and rigid small balls 331 are dispersed in the gaps between the rigid large balls 330 and the small hexagonal grid 31. The surfaces of the rigid large ball 330 and the rigid small ball 331, as well as the inner wall of the small hexagonal grid 31, are all sandblasted to increase the roughness of the contact surface, improve the particle damping performance, and at the same time avoid the high-intensity frictional screeching noise caused by wear on smooth surfaces, suppressing the generation of frictional screeching noise and reducing its noise intensity. In this embodiment of the invention, the lightweight helical spring 320 and the spring washer 323 are both made of 50CrVA (spring steel), the bolt 321, the nut 324 and the flat washer 322 are made of stainless steel, and the spring seat 325 is made of rubber.

[0047] like Figure 7As shown, in this embodiment, the force-equalizing beam 40 is made of rectangular steel tubing, with through holes 400 evenly spaced on its facade for connecting to the large hexagonal grid 30 and the porous connecting plate 41. This allows external excitation to be evenly distributed to the dual-oscillator periodic phonon crystal 3, ensuring that the contacting large hexagonal grids 30 experience essentially the same force. The porous connecting plate 41 has multiple through holes 410 and 411 of different diameters on its facade for easy connection to external structures. A long series disc spring 450 connects the porous connecting plate 41 to the force-equalizing beam 40, while a short series disc spring 451 connects the porous connecting plate 41 to the head of the nut 48 and the limiting bolt 43. In this embodiment, there are 8 long series disc springs 450 and 4 short series disc springs 451. The flexible connecting device 4 is elastic under both tension and compression, and its elastic coefficient is consistent under tension and compression. The self-lubricating bushing 46 is nested in the through hole used to connect the force-equalizing beam 40 and the perforated connecting plate 41, reducing friction and noise between the limiting bolt 43 and the force-equalizing beam 40 during relative movement. The limiting bolt 43 is a semi-threaded bolt, and its smooth shaft portion acts as a guide rod, preventing the perforated connecting plate 41 from tilting during vibration. A spring washer 47 and a flat washer 44 are provided at the nut 48 connected to the bolt 42. No spring washer is needed at the nut 48 connected to the limiting bolt 43 to prevent loosening. In the embodiment of the invention, the force-equalizing beam 40, the perforated connecting plate 41, the flat washer 44, the limiting bolt 43, the bolt, and the nut 48 are all made of stainless steel, the tandem disc spring assembly 45 is made of 60Si2MnA, the spring washer 47 is made of 50CrVA, and the self-lubricating bushing 46 is made of PTFE.

[0048] This invention provides simulation results of the 0–1800 Hz harmonic response of a vibration isolation device under different configurations. The simulation results show that the synergistic effect of the local resonance mechanism and the particle damping mechanism employed in this invention has a significant suppression effect on vibration and elastic waves.

[0049] like Figure 8 As shown, in the absence of particle damping, the vibration isolation device with a local oscillator has a significant vibration isolation effect in the frequency band of 741–1800 Hz compared to the vibration isolation device without a local oscillator, indicating that the introduction of a local resonance mechanism can broaden the effective operating frequency band of the phononic crystal.

[0050] like Figure 9 As shown, comparing the local oscillator with and without particle damping, the vibration response of the vibration isolation device with particle damping is reduced in most frequency bands compared to the vibration isolation device without particle damping. In particular, in the frequency ranges of 240-609Hz and 639-738Hz, particle damping effectively reduces the response of the vibration isolation device in the above frequency bands, indicating that the particle damping characteristics can effectively dissipate the vibration energy in the passband and achieve effective vibration reduction and isolation in a wider frequency range.

[0051] like Figure 10 As shown, particle damping and local oscillators effectively improve the vibration isolation effect of traditional phononic crystal vibration isolation devices in the range of 255–1800 Hz, reducing the lowest effective frequency to 255 Hz and enhancing the original bandgap vibration isolation performance. The vibration isolation effect is best in the frequency bands of 255–498 Hz, 735–891 Hz, and above 1146 Hz, indicating that the synergistic effect of particle damping and local oscillators can enable phononic crystals to obtain a wider vibration isolation frequency band and improve the vibration isolation effect.

[0052] In summary, compared with traditional phonon crystal vibration isolators, the planar mechanical metamaterial vibration isolation device with local resonance and particle damping characteristics of this invention expands the original bandgap frequency range by introducing a local resonance mechanism, making the effective operating frequency band of the vibration isolation device wider; by introducing a particle damping mechanism, the energy of the local oscillator vibration is dissipated by the friction and collision of rigid spheres in the granular particle group, which enhances the vibration attenuation of the device in the passband frequency range; the synergistic effect of local resonance and particle damping enhances the overall vibration isolation effect of the device.

[0053] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0054] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

Claims

1. A mechanical metamaterial vibration isolation device with synergistic effect of local resonance and particle damping, characterized in that, The device comprises a double-oscillator periodic phononic crystal, a flexible connecting device, a self-lubricating panel and a protective shell. The upper and lower surfaces of the double-oscillator periodic phononic crystal are in contact with the self-lubricating panel, and the left and right ends of the double-oscillator periodic phononic crystal are connected with the flexible connecting device. The double-oscillator periodic phononic crystal comprises large hexagonal lattices, small hexagonal lattices, a spiral spring group and a group of granular particles. The large hexagonal lattices are provided with through holes at the centers of each vertical surface and are connected with each other by bolts. The small hexagonal lattices are provided with through holes at the centers of each vertical surface and are arranged inside the large hexagonal lattices as common local oscillators and are connected with the large hexagonal lattices by the spiral spring group. The group of granular particles is arranged in the small hexagonal lattices along the long side direction of the mechanical metamaterial vibration isolation device and is used as a granular damping local oscillator together with the small hexagonal lattices. The large hexagonal lattices containing the common local oscillators and the granular damping local oscillators are arranged periodically along the plane to form the double-oscillator periodic phononic crystal.

2. The mechanical metamaterial vibration isolation device of claim 1, wherein, The flexible connecting device is provided with two symmetrical connecting devices on the left and right sides of the double-oscillator periodic phononic crystal and comprises a porous connecting plate, a uniform force beam and a series disc spring group.

3. The mechanical metamaterial vibration isolation device of claim 1, wherein, The porous connecting plate is provided with through holes of different diameters and is connected with the uniform force beam by the series disc spring group.

4. The mechanical metamaterial vibration isolation device of claim 1, wherein, The self-lubricating panel is provided with two self-lubricating panels embedded in the limiting clamping grooves of the upper and lower protective shells.

5. The mechanical metamaterial vibration isolation device of claim 4, wherein, The protective shell is provided with two protective shells comprising limiting clamping grooves and through holes.

6. The mechanical metamaterial vibration isolation device of claim 2, wherein, The group of granular particles comprises a plurality of rigid large balls and rigid small balls. The double-oscillator periodic phononic crystal has Bragg scattering band gaps and local resonance band gaps. The flexible connecting device further comprises a self-lubricating bushing and a limiting bolt. The self-lubricating bushing is nested in the corresponding through holes of the uniform force beam and the porous connecting plate. The limiting bolt is a half-thread bolt, and the optical axis part is in contact with the porous connecting plate, the series disc spring group and the self-lubricating bushing, and the threaded part is in contact with the nut. The series disc spring group comprises long series disc springs and short series disc springs. The surfaces of the rigid large balls and the rigid small balls and the inner walls of the small hexagonal lattices are subjected to sandblasting treatment. The sandblasting treatment increases the roughness of the contact surface, improves the granular friction and collision damping performance, suppresses the generation of friction squeal noise and reduces the intensity of friction noise.

7. The mechanical metamaterial vibration isolation device of claim 3, wherein, The isolation effect is most significant in the frequency bands of 255-498 Hz, 735-891 Hz and above 1146 Hz.

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