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EP 1 060 637 B1 |
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EUROPEAN PATENT SPECIFICATION |
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Mention of the grant of the patent: |
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03.08.2005 Bulletin 2005/31 |
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Date of filing: 26.04.1999 |
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International application number: |
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PCT/FI1999/000337 |
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International publication number: |
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WO 1999/056498 (04.11.1999 Gazette 1999/44) |
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ACOUSTIC ELEMENT
AKUSTISCHES ELEMENT
ELEMENT ACOUSTIQUE
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Designated Contracting States: |
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AT BE CH CY DE DK ES FI FR GB GR IE IT LI NL PT SE |
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Priority: |
27.04.1998 FI 980926
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Date of publication of application: |
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20.12.2000 Bulletin 2000/51 |
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Proprietor: Panphonics Oy |
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02200 Espoo (FI) |
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Inventor: |
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- KIRJAVAINEN, Kari
FIN-332 30 Tampere (FI)
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Representative: Huhtanen, Ossi Jaakko et al |
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Kolster Oy AB,
Iso Roobertinkatu 23,
P.O. Box 148 00121 Helsinki 00121 Helsinki (FI) |
(56) |
References cited: :
AT-B- 382 490 US-A- 3 740 496 US-A- 4 885 783
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US-A- 3 654 403 US-A- 3 787 642 US-A- 4 887 248
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Note: Within nine months from the publication of the mention of the grant of the European
patent, any person may give notice to the European Patent Office of opposition to
the European patent
granted. Notice of opposition shall be filed in a written reasoned statement. It shall
not be deemed to
have been filed until the opposition fee has been paid. (Art. 99(1) European Patent
Convention).
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[0001] The invention relates to an acoustic element which comprises an arbitrary number
of layers, at least one layer comprising at least one porous layer which is either
electrically conductive or coated at least on one of its surfaces to be electrically
conductive, and at least one film, which is either charged or provided with at least
one electrically conductive surface, at least one porous layer and film being arranged
to come into contact with each other substantially only at support points, thereby
providing an air gap between the porous layer and the film.
[0002] WO publication 97/31506 discloses a plate-like acoustic element comprising fixed
stator plates, with a film secured between the plates at predetermined support points.
Between the stator plate and the film are left small air gaps that allow the film
3 to move. The stator plates and the film are provided with electrically conductive
surfaces, so by applying electric signals to the surfaces, the film 3 can be made
to move to produce sound. The structure is simple and has a very even frequency response,
but its field of application is somewhat limited and, to produce a sufficiently high
air pressure by using a moving film, a fairly strong electric field is required.
[0003] AT-B-382 490 discloses an electrostatic loudspeaker comprising two electrodes and
a film between the electrodes. There are elastic parts made of foam rubber between
the film and an electrode. US 4 885 783 discloses a transducer having opposed first
and second conductive plates for application of an electrical potential difference
therebetween. An elastomeric dielectric material such as neoprene rubber is disposed
between the plates and in contact therewith.
[0004] An object of the present invention is to provide an acoustic element allowing the
above shortcomings to be avoided.
[0005] The acoustic element of the invention is characterized in that the support points
are arranged in such a way that the porous layer being moved by the film is able to
move in such a way that the acoustic element can change its thickness substantially
entirely.
[0006] An essential idea of the invention is that the acoustic element comprises an arbitrary
number of layers, at least one layer comprising a porous layer and a film arranged
at a distance from the layer, the porous layer and the film coming into contact with
each other substantially only at specific support points. The porous layer is either
electrically conductive or coated at least on one of its surfaces to be electrically
conductive, and the film is charged or provided with at least one electrically conductive
surface. The support points at which the film and the porous layer come into contact
with each other are arranged in such a way that the entire structure can change its
thickness. A preferred embodiment is based on the idea that the acoustic element is
coated with an elastic surface material. Another preferred embodiment is based on
the idea that the acoustic element is hermetically sealed.
[0007] An advantage of the invention is that the structure of the acoustic element is very
light, solid, inexpensive and easy to manufacture. Further, because the gap between
the porous layer and the film is fairly small, a reasonably high pressure is obtained
by applying a fairly low control voltage. The porous material provides the element
with a large air capacity, whereby the air displaced by the film is able to enter
the porous layer, which reduces counter pressure and increases movement. The air entering
the porous layer causes flow losses and therefore the structure does not resonate
strongly. Further, due to the flow losses the material of the element also attenuates
sound passively. An element coated with an elastic surface material can be used for
a number of different applications (e.g. floors). Hermetic sealing of the element
allows it to be used also in fairly humid conditions.
[0008] The invention will be described in greater detail in the accompanying drawings, of
which
Figure 1 is a schematic sectional side view of an acoustic element of the invention;
Figure 2 is a schematic sectional side view of another acoustic element of the invention:
and
Figure 3 is a schematic view of a third embodiment of the invention.
[0009] Figure 1 shows an acoustic element 1 comprising a plural number of porous layers
2. A typical porous layer is, for example, 0.5 to 1 mm thick, about 70% of the layer
being air. The porous layer 2 can be made of cellulose, glass fibre, mineral fibre,
metal fibre or by sintering plastic or metal powder. The porous layer 2 is either
electrically conductive or coated at least on one of its surfaces to be electrically
conductive, for example, by sputtering the surface to provide a metallization 3 thereon.
The metallization 3 of the porous layer 2 is typically about 40 nanometers thick.
The metallization 3 on the porous layer 2 is also porous in order to allow air to
pass through the porous layer 2 and the metallization 3.
[0010] The acoustic element 1 further comprises a film 4 arranged between the porous layers
2. The porous layer 2 and the film 4 come into contact with each other only at support
points 5, an air gap 6 being thus formed between the porous layer 2 and the film 4.
The thickness of the film 4 is typically about 5 micrometers and the width of the
air gap 6, correspondingly about 10 micrometers.
[0011] Figure 1 shows an embodiment in which two films 4 are arranged one on the other,
a metallization 7 typically about 40 nanometers thick being arranged between the films.
The films are charged and they can be made of polypropylene, polymethyl pentene or
cyclic olefin copolymer, for example. The films 4 can be further provided with a bubble
structure comprising flat bubbles.
[0012] Porous layers 2 and films 4 are arranged one on the other to provide the acoustic
element 1 with a layered structure as shown in Figure 1. Control electrodes A are
connected to the metallizations 7 between the films 4 and earth electrodes B. correspondingly,
to the metallizations 3 of the porous layers 2. The support points 5 are arranged
in such a way that the film 4 is not supported to the porous layers 2 at exactly the
same points on opposite sides of the film. Consequently, when a signal is supplied
to the control electrode A, the film 4 changes is form. Since the film 4 is secured
to the porous layer 2 at the support point 5, the porous layer 2 also moves and, since
the support points 5 are at different places in the acoustic element, the acoustic
element 1 can change its thickness substantially entirely.
[0013] Pressure P caused by the acoustic element 1 is obtained from the following formula
where
s is the width of the air gap 6,
U is voltage acting over the air gap 6, and
ε is a dielectricity constant of an intermediate medium.
[0014] Since the width s of the air gap 6 in the element concerned is very small, the voltage
U need not be very high to provide a fairly high pressure P.
[0015] Figure 2 shows an acoustic element with a plural number of different layers arranged
one on the other. In the embodiment shown in Figure 2 one side of the film 4 is secured
substantially entirely to a first porous layer 2. The other side of the film 4 is
secured to a second porous layer 2 substantially only at support points 5. between
the second porous layer 2 and the film 4 being then the air gap 6. When the film 4
moves, it also makes the porous layer 2 move to which it is secured. The support points
5 of successive air gaps 6 are at different places, thereby allowing the entire acoustic
element to change its thickness.
[0016] The support points 5 can be formed on the porous plates 2, for example, by pressing
the plates at suitable places to form bulges. The places of the support points 5 can
vary symmetrically or randomly, but it is essential that the support points 5 of successive
layers are arranged at substantially different places.
[0017] A strong electric field reduces the elastic constant of the structure, i.e. due to
pressure the thickness of the structure changes essentially more than without the
electric field, thereby substantially increasing the attenuating capability of the
structure and lowering its resonance frequency. When the control electrodes A and
the earth electrodes B are connected with each other, the structure can function in
an attenuating manner, control electronics being not needed then. Between the control
electrodes A and earth electrodes B can also be applied a static pre-voltage which
allows the elastic constant of the structure to be controlled in a desired manner.
The films 4 can also be provided with a permanent electret charge, if desired. The
pre-voltage can be applied through a resistor having a high resistance, or the control
electrode A, for example, can have a high resistance.
[0018] Figure 3 illustrates the acoustic element 1 coated with an elastic surface material
8. The thickness of the surface material 8 can be from 0.1 to 10mm, for example. The
surface material 8 can be a rubber carpet, for example, the acoustic element 1 thus
being applicable as a floor covering, for example. The edges of the acoustic element
can be provided with sealing portions 9 to make the element 1 hermetically sealed.
Also the control electronics 10 can be arranged inside the acoustic element. The hermetically
sealed element 1 can be used in very demanding humid conditions. Further, the acoustic
element 1 can be made into a preformed structural board, thereby allowing it to be
used as a construction element. The surface material 8 can be substantially air impermeable
because the entire acoustic element 1 can change its form and thereby produce sound,
although it does not allow air to pass through. The acoustic element in question can
be used, for example, for sound attenuating purposes (as floor mats in cars, for example).
By increasing the mass of the surface material 8. the attenuating capability of the
acoustic element 1 can be enhanced and the resonance frequency further lowered.
[0019] The drawings and the related description are only meant to illustrate the inventive
idea. The details of the invention may vary within the scope of the claims. The acoustic
element 1 may comprise an arbitrary number of layers. To produce sound, at least one
porous layer 2 and at least one film 4 are needed. Instead of two charged films 4
and the metallization 7 between them shown in the embodiment of Figure 1, a film with
polarized charging can be used (i.e. a film having a positive charging on one side
and a negative charging on the other), the control voltage being then applied between
the surfaces of the porous layers 2. The film 4 does not have to be charged if at
least its surface is electrically conductive. The acoustic element of the invention
can be used in various applications relating to sound reproduction and active noise
attenuation. The acoustic element, or some of its layers, can be used for example
as sensors in acoustic systems while, at the same time, the other layers can be used
as actuators.
1. An acoustic element which comprises an arbitrary number of layers, at least one layer
comprising at least one porous layer (2) which is either electrically conductive or
coated at least on one of its surfaces to be electrically conductive, and at least
one film (4), which is either charged or provided with at least one electrically conductive
surface, at least one porous layer (2) and film (4) being arranged to come into contact
with each other substantially only at support points (5), thereby providing an air
gap between the porous layer (2) and the film (4), characterized in that the support points (5) are arranged in such a way that the porous layer (2) being
moved by the film (4) is able to move in such a way that the acoustic element (1)
can change its thickness substantially entirely.
2. An acoustic element according to claim 1, characterized in that the element (1) comprises at least two porous elements (2), at least one film (4)
being arranged between the layers in such a way that on both sides of the film (4),
an air gap (6) is formed, the support points (5) on opposite sides of the film (4)
being arranged at substantially different places.
3. An acoustic element according to claim 1, characterized in that the element (1) comprises at least two porous layers (2), at least one film (4) being
arranged between the layers in such a way that the film (4) is secured to a second
porous layer (2) and between the second porous layer (2) and the film (4) is an air
gap (6).
4. An acoustic element according to claim 3, characterized in that the acoustic element (1) is a layered structure comprising at least two air gaps
(6) arranged one on the other, the support points (5) in successive air gaps (6) being
substantially at different places.
5. An acoustic element according to any one of preceding claims, characterized in that the acoustic element (1) is coated with an elastic surface material (8).
6. An acoustic element according to claim 5, characterized in that the acoustic element (1) is hermetically sealed.
1. Akustisches Element, das umfasst: eine beliebige Anzahl von Lagen, wobei mindestens
eine Lage mindestens eine poröse Lage (2) umfasst, die entweder elektrisch leitfähig
ist oder mindestens auf einer von ihren Oberflächen so beschichtet ist, dass sie elektrisch
leitfähig ist, und mindestens einen Film (4), der entweder geladen oder mit mindestens
einer elektrisch leitfähigen Oberfläche versehen ist, wobei mindestens eine poröse
Lage (2) und ein Film (4) so angeordnet sind, dass sie im Wesentlichen nur an Trägerpunkten
(5) in Kontakt miteinander kommen, wodurch ein Luftspalt zwischen der porösen Lage
(2) und dem Film (4) bereitgestellt wird, dadurch gekennzeichnet, dass die Trägerpunkte (5) auf eine solche Weise angeordnet sind, dass sich die durch den
Film (4) in Bewegung versetzte poröse Lage (2) auf eine solche Weise bewegen kann,
dass das akustische Element (1) seine Dicke im Wesentlichen gänzlich ändern kann.
2. Akustisches Element nach Anspruch 1, dadurch gekennzeichnet, dass das Element (1) mindestens zwei poröse Elemente (2) umfasst, wobei mindestens ein
Film (4) zwischen den Lagen auf eine solche Weise angeordnet ist, dass auf beiden
Seiten des Films (4) ein Luftspalt (6) gebildet ist, wobei die Trägerpunkte (5) auf
entgegengesetzten Seiten des Films (4) an im Wesentlichen unterschiedlichen Orten
angeordnet sind.
3. Akustisches Element nach Anspruch 1, dadurch gekennzeichnet, dass das Element (1) mindestens zwei poröse Lagen (2) umfasst, wobei mindestens ein Film
(4) zwischen den Lagen auf eine solche Weise angeordnet ist, dass der Film (4) an
einer zweiten porösen Lage (2) gesichert ist und sich zwischen der zweiten porösen
Lage (2) und dem Film (4) ein Luftspalt (6) befindet.
4. Akustisches Element nach Anspruch 3, dadurch gekennzeichnet, dass das akustische Element (1) eine Lagenstruktur ist, umfassend mindestens zwei Luftspalte
(6), die übereinander angeordnet sind, wobei sich die Trägerpunkte (5) in aufeinanderfolgenden
Luftspalten (6) im Wesentlichen an unterschiedlichen Orten befinden.
5. Akustisches Element nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass das akustische Element (1) mit einem elastischen Oberflächenmaterial (8) beschichtet
ist.
6. Akustisches Element nach Anspruch 5, dadurch gekennzeichnet, dass das akustische Element (1) hermetisch abgedichtet ist.
1. Elément acoustique comprenant un nombre arbitraire de couches, au moins une couche
comprenant au moins une couche poreuse (2) qui est conductrice d'électricité ou qui
est recouverte sur au moins une de ses surfaces de manière à être conductrice d'électricité,
et au moins un film (4) qui est chargé ou qui comporte au moins une surface conductrice
d'électricité, au moins une couche poreuse (2) et le film (4) étant disposés de manière
à entrer en contact l'un avec l'autre essentiellement et uniquement au niveau de points
de support (5) de manière à former un jour d'air entre la couche poreuse (2) et le
film (4), caractérisé en ce que les points de support (5) sont disposés de sorte que la couche poreuse (2) déplacée
par le film (4) puisse se déplacer de sorte que l'épaisseur de l'élément acoustique
(1) peut changer essentiellement entièrement.
2. Elément acoustique selon la revendication 1, caractérisé en ce que l'élément (1) comprend au moins deux éléments poreux (2), au moins un film (4) étant
disposé entre les couches de sorte qu'un jour d'air (6) soit formé des deux côtés
du film (4), les points de support (5) sur les côtés opposés du film (4) étant situés
en des endroits essentiellement différents.
3. Elément acoustique selon la revendication 1, caractérisé en ce que l'élément (1) comprend au moins deux éléments poreux (2), au moins un film (4) étant
disposé entre les couches de sorte que le film (4) est fixé à une seconde couche poreuse
(2) et qu'un jour d'air (6) se trouve entre la seconde couche poreuse (2) et le film
(4).
4. Elément acoustique selon la revendication 3, caractérisé en ce que l'élément acoustique (1) consiste en une structure stratifiée comprenant au moins
deux jours d'air (6) situés l'un au dessus de l'autre, les points de support (5) dans
les jours d'air (6) successifs se situant en des endroits essentiellement différents.
5. Elément acoustique, selon l'une quelconque des revendications précédentes, caractérisé en ce que ledit élément acoustique (1) est recouvert d'un matériau de surface élastique (8).
6. Elément acoustique selon la revendication 5, caractérisé en ce que l'élément acoustique (1) est scellé hermétiquement.