FIELD OF INVENTION
The present invention relates to a hybrid honey comb structure for noise reduction
with improved absorption coefficient as compared to honey combs and negligible
back pressure.
BACKGROUND OF THE INVENTION
It is known that the best technique to reduce noise is generally to curtail it at the
source. However, the possibility of modifications in source may not be always
possible. In that case, making the transmission path modification is found to be the
most feasible option for noise reduction. The present invention relates to
development of an improved noise absorbing panel that can be used for noise
attenuation in the transmission path.
US patent US8727072B2 by Hexcel Corporation describes a method for making
acoustic honeycomb structure with perforated septum caps located in the
honeycomb cells. These septum caps are claimed to be made from flexible and stiff
material providing frictional engagement and locking within the honeycomb cells
during fabrication. The patent includes an adhesive is applied to the septum caps in
the honeycomb cells to provide a permanent bond.
US patent US20030178250A1 describes an acoustically absorbent porous panel
constructed from cured foamed material that has a continuous open-celled porous
structure. The patent describes that the first face of the said panel is planar while
the second face is a geometric pattern of depressions between 50%-90% of the
layer by volume. The patent also states that porous panel is formed from aerated
aqueous foam slurry that contains water, cement, synthetic organic fibers and a
surfactant of various compositions.

US patent US3700067A by Mc Donnell Douglas Corp. describes a three-dimensional
acoustic porous face sheet fabricated from a woven fabric and made rigid by a resin
system as per the required configuration. This three-dimensional acoustic face sheet
is said to be bonded, mechanically attached or laid over a plurality of cavities or
absorbent materials or used singly as an acoustic absorber.
US patent US8651233B2 by Hexcel Corporation describes an acoustic structure that
has coupled honeycomb cells to form pairs of acoustic cells. The patent states that
this pairing results with an effective acoustic or resonator length up to twice that of
either acoustic cell taken alone which in turn leads to increased bandwidth
suppression.
US patent US6871725B2 describes a honeycomb acoustic unit with a metallurgically
secured, deformable septum. The patent includes that the acoustic attenuation is
done by the honeycomb acoustic unit comprising of first and second honeycomb
layers that are separated by the septum.
US patent US6371242B1 by Short Brothers Plc describes a method of manufacturing
a noise attenuation panel that has a cellular component part with front and rear
faces and there are wall portions providing bounding surfaces for a multiplicity of
cells which extend from the front face to the rear face.
US patent US6274216B1 by Hispano Suiza Aero structures describes a conventional
honeycomb structure that is strengthened by intermediate membranes
compartmentalizing cells in height-wise direction. This structure has a perforated
membrane in the front face and states that it has increased mechanical strength and
high acoustic damping properties.

US patent US4235303A by The Boeing Company describes an acoustic panel with a
combination of bulk absorbers that comprises of an impervious back sheet, a
perforated septum sheet, a broadband noise-suppressing bulk absorber layer
mounted between the back sheet and septum sheet which is followed by another
perforated sheet and a rigid noise-suppressing honeycomb layer mounted between
septum and face sheet.
OBJECTS OF THE INVENTION
Object of the invention is a hybrid honey comb device with improved absorption
coefficient and negligible back pressure to reduce noise.
SUMMARY OF THE INVENTION
Accordingly, a hybrid honey comb device is proposed with improved absorption
coefficient and negligible back pressure to reduce noise as compared to honey comb
structures. The acoustic structure provides improved noise attenuation in terms of
better absorption coefficient with reference to the base material (honey combs). The
hybrid honey comb structure includes basic honeycomb structure and an absorptive
material lining parallel to the direction of flow of fluid through the structure. Each
cell in the honeycomb structure consists of absorptive material lined against the wall
of the cell and an additional layer of material to hold the absorptive lining in place is
bonded.
The present invention relates to development of an improved noise absorbing panel
that can be used for noise attenuation in the transmission path. The disclosed Hybrid
honey comb devices are best suitable for use where air flow is involved and
blocking/modification of air flow path is not possible.

The embodiment of the present invention describes a low back pressure device
which can be placed in the path of the flow of air to attain noise reduction without
introducing much back pressure. The current invention identifies this low back
pressure as the advantage for better absorption of noise through lining of the honey
comb device with absorptive materials
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The following drawings accompanying the invention are described as a preferred
embodiment of the invention.
Fig 1: A detailed view of hybrid honey comb device along with the acoustic material
lining.
Fig 2: illustrates the isometric view of the device of Figure 1.
Fig 3: depicts the front view of the embodiment of the device of Figure 1.
DETAILED DESCRIPTION OF THE INVENTION
The invention shall now be described with reference to the drawings. The invention
may be embodied in different forms and is not limited to the embodiments described
here.
Fig. 1 depicts a hexagon celled honeycomb structure in 180. Upon inserting the
acoustic lining 182 in the said honeycomb structure, a novel hybrid honeycomb is
constructed.

Fig. 2 illustratively depicts the isometric view of a hybrid honeycomb that may be
placed in a fan duct for noise attenuation. 201 is a structural architecture made from
any metal/alloy/composition. 165 is the acoustic material lined in the height wise
direction of hybrid honeycomb parallel to the flow of the duct.
Fig. 3 shows one of the configuration of hybrid honeycomb in front view. The
embodiment of the invention may be beyond depicted circular configuration and
depicted hexagonal cells. 145 refer to the encompassing architecture, 150 refers to
the acoustic lining and 155 refers to the mesh holding the absorptive material.

WE CLAIM:
1. A hybrid honey comb device with improved absorption coefficient and
negligible back pressure to reduce noise, the device comprising :-
- a base honey comb structure having a plurality of cells; wherein the base
honey comb material can be metallic or non-metallic and flexible or rigid;
- a boundary lining formed of absorptive material disposed in each cell of the
structure; and
- an additional layer of binding / holding material to hold the acoustic material
bonded in the wall;

2. The device as claimed in claim 1, wherein the acoustic lining can be made by
acoustic absorptive materials like glass wool, rock wool, or any other
absorptive materials.
3. The device as claimed in claim 1, wherein said boundary lining material in
said hybrid honey comb panel has a thickness more than 0.1 mm and consists
of a mesh/woven cloth/insulation material/alloy/composition.

4. The device as claimed in claim 1, wherein the shape of honey comb pattern
of the structure is polygonal;