DESCRIPTION JP2015104134

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DESCRIPTION JP2015104134
The object of the present invention is to have good vibration characteristics and to be easily and
reliably fixed to various surface geometries due to its structure and geometry, and in that case
the film's vibration characteristics To provide an electroactive acoustic transducer film that is not
significantly compromised. The surface of the acoustic conversion film comprises structured
parts with different gradients, wherein the sign of the gradient of the surface of the acoustic
conversion film changes at least twice. [Selected figure] Figure 5
Electroactive acoustic conversion film comprising a structured surface
[0001]
The present invention comprises a film combination comprising at least one support film, at least
one first electrode, at least one second electrode, and at least one piezoelectric layer comprising
an electroactive polymer. With respect to the active acoustic transducing film, the surface of the
acoustic transducing film has structured portions with different gradients, the sign of the
gradient of the acoustic transducing film surface changing at least twice.
[0002]
The current electrodynamic acoustic transducer concept is usually connected to an
electromagnetic vibration coil at the center and utilizes a diaphragm that is vibrated by Lorentz
force or air flow induced by current. There is.
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In such acoustic transducers, depending on the mode of operation, the current is converted to
mechanical motion or the motion of the diaphragm is converted to current. By means of this form
of construction, for example, moving coil loudspeakers or microphones are obtained. This form
of construction is, to date, excellent in that the level of sound intensity is high and natural tone
reproduction is performed.
[0003]
However, due to the special electrodynamic coupling by the suspension of the diaphragm and the
magnets, certain structural heights and vibration characteristics result, which are not suitable for
any structural state and application. For this reason, in the last few decades, a number of acoustic
transducers have also been developed which use the piezoelectric effect for acoustic conversion
without being based on a combination of diaphragms, coils and magnets. These acoustic
transducers comprise electroactive ceramics or plastics, and also realize direct acoustic
transformations due to macroscopic dimensional changes of the acoustic transducers in response
to electric fields. That is, for example, the application of a voltage to the piezoelectric diaphragm
or film causes a change in dimension in the longitudinal direction (d31 mode) and a change in
the thickness direction (d33 mode). In particular, the effect of the d31 mode causes bending of
the layer, which can be used effectively for sound wave radiation. By contrast, mechanical
loading causes charge transfer in the layer, which can generally be used for acoustic wave
detection. These piezoelectric acoustic transducers require very little displacement. In the case of
a loudspeaker, the displacement is typically in the range of a few hundred μm, whereas in the
field of microphone applications the displacement is in the range of only a few μm to a few nm
or a few pm. The displacement is strongly frequency dependent in both the speaker and the
microphone. At relatively high frequencies, the displacement is smaller than at relatively low
frequencies. This ambient condition makes it possible to realize a film converter, in particular
with a very short distance to other surfaces, but such film converters are used today in the
current electromagnetic diaphragm-coil systems. Not done.
[0004]
One possible embodiment relating to unusual transducer geometry is disclosed, for example, in
US Pat. No. 4,638,207 A, which discloses polyvinylidene fluoride (PVDF) in order to produce
balloon-like loudspeakers. The use of piezoelectric polymers based on is described. Here, a PVDF
strip embedded between the outer coating and the inner coating is deposited on the balloon or
the balloon itself is formed from such a strip.
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[0005]
With regard to one alternative configuration, U.S. Patent No. 5,677,095 discloses a piezoelectric
acoustic transducer using a piezoelectric plastic material. In particular, an acoustic transducer is
disclosed, which consists essentially of a support layer and a layer of a piezoelectric plastic
support deposited on the support layer, wherein the piezoelectric element is piezoelectric The
plastic layer does not completely cover the support layer, but has a plurality of recesses.
[0006]
However, to date, the concept of a piezoelectric transducer that is as effective and reliable as
possible requires a compromise process in fixing the conversion film. By fixing the conversion
film directly to the whole surface, for example by gluing, the fixing of the converter is more
reliable, but as a result the displacement is largely disturbed, which adversely affects the
efficiency of the converter. Exert. For this reason, in order to achieve as unobtrusive vibrational
properties as possible, an electroactive film as a combination is arranged on a flexible support
film and the edge of the combination is mechanical. It is held. This results in a structure that can
be freely oscillated despite the fact that the coupling is sufficiently mechanically fixed and thus
stabilized. This provides favorable radiation or reception characteristics, but as a whole this
arrangement is disadvantageous as it reduces the mechanical load resistance of the transducer at
the non-fixed point.
[0007]
DE 10 2010 043 108 A1
[0008]
The object of the invention is therefore to have good vibrational properties and, because of its
structure and geometry, can be fixed simply and reliably to various surface geometries, and in
that case, It is an object of the present invention to provide an electroactive acoustic conversion
film in which the vibrational properties of the film are not significantly impaired.
[0009]
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Electroactive acoustics comprising a film combination comprising at least one support film, at
least one first electrode, at least one second electrode, and at least one piezoelectric layer
comprising an electroactive polymer The transducing film is characterized in that the surface of
the transducing film has structured parts with different gradients and the sign of the gradating of
the surface of the transducing film changes at least twice and is flat according to the prior art It
has been found that the emission characteristics are improved and the efficiency is increased
compared to electro-active acoustic transducer surfaces having only one heel or arch.
Without being bound by theory, it is possible to improve the transducer characteristics by
structuring the film surface, which also leads to a larger total area of film per unit area.
This is advantageous in comparison to conventional film surfaces which are simply formed flat or
which have only one arched part. Furthermore, the structuring of the surface can improve the
mechanical properties of the film. The reason is that the mechanical dimensional change of the
film is better sterically better due to different surface gradients, for example, depending on the
applied electric field, without undesired interactions of the different partial regions of the
transducer. It is because it can be produced. The improvement of this property is in particular
based on the fact that the transducer surface has a plurality of zones with different slopes and
that the sign of the surface slope changes many times. Different gradients of the surface can give
rise to different mechanical load profiles each time strain / displacement, so that the load peaks
of the surface so structured can also be better compensated. .
[0010]
The electroactive acoustic conversion film according to the invention is a film combination
consisting of at least one film layer with piezoelectric properties, at least two electrodes and one
support film. Preferably, one support film is at the bottom and at least two electrodes are
provided on each side of the electroactive film so that an electroactive piezoelectric layer is
formed between the electrodes. A structure in which is intervened is obtained. However, the
combination can also have more than one support film and / or more than one electrode. In
particular, the individual layers may not be present on the entire surface in the film combination.
This means that the individual regions of the film bond can also have defects in the individual
layers. The film combination can have a thickness of 10 μm or more and 5000 μm or less,
preferably at least 30 μm or more and 2500 μm or less, more preferably 50 μm or more and
1500 μm or less. If the thickness of the bond is relatively thin, it is not advantageous because
the mechanical rigidity of the bond may no longer be maintained. If the layer thickness is
relatively large, on the other hand, excessively high rigidity and excessively large mass may
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occur, which may be disadvantageous, for example, in recording (microphone) applications. The
thickness of the individual layers can be varied depending on the material and application
purpose.
[0011]
The support film can advantageously be formed from a material of low specific gravity and high
rigidity. Thus, for example, thin paper layers or PET films can be used as support films. The
support film can have a thickness of 10 μm or more and 2000 μm or less, preferably 30 μm or
more and 1000 μm or less, more preferably 50 μm or more and 500 μm or less. Relatively
thin layer thicknesses can be disadvantageous to the mechanical stability of the overall
combination. A relatively thick layer thickness can lead to a mechanically inactive excessively
large mass, which can also reduce the sensitivity of the conjugate.
[0012]
The electrodes can be formed of metal layers or other conductive materials. For the metallized
layer, metals known to those skilled in the art such as aluminum, copper, silver, gold and the like
are used. Conductive materials which may be considered include, for example, conductive
plastics such as Pedot: PSS (poly-3,4-ethylenedioxythiophene: polystyrene sulfonate). The
electrodes can advantageously be arranged on both sides of the piezoelectric layer comprising
the electroactive polymer. In that case, the two electrode layers can be provided over the entire
surface, or only partially. This means that one or both electrode surfaces cover the entire
transducer surface, or one or both electrodes cover only a partial area of the transducer surface.
In particular, one of the electrodes can have multiple defects, in which case there is no
uninterrupted, consistent electrical contact of the electrodes. Furthermore, individual electrodes
can be provided with one or more feed lines.
[0013]
The piezoelectric layer comprising the electroactive polymer can comprise or be formed of an
electroactive polymer. This layer is characterized in that it can be deformed upon application of a
voltage and that a voltage is induced in the layer upon occurrence of mechanical deformation. It
is also possible to provide a plurality of piezoelectric layers one on top of the other. In that case,
only one piezoelectric layer comprising an electroactive polymer can be provided, or preferably
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from 1 to 5 and more preferably from 1 to 10 individual piezoelectric layers. The layer
combination can be obtained, for example, by providing the individual layers one after the other
and characterized by interruptions at the layer transitions. This can be confirmed by common
optical methods, for example using a microscope. As electroactive polymers, in principle,
polymers with groups of silicone elastomers, acrylic elastomers, polyurethanes, thermoplastic
materials, copolymers with PVDF (polyvinylidene fluoride), pressure-sensitive adhesives,
fluorinated elastomers, and silicone or acrylics It can be used. The piezoelectric layer with the
electroactive polymer may further have other additives, such as plasticizers, polymeric oils,
antioxidants, viscosity modifiers, and / or additional dielectric particles with high dielectric
constants. . The piezoelectric layer can have a thickness of 1 μm or more and 1000 μm or less,
preferably 2 μm or more and 500 μm or less, more preferably 5 μm or more and 250 μm or
less.
[0014]
Since the film bond has structured parts, different gradients occur in the surface area. The
gradient of the surface area occurs in a mathematical sense, so the surface has a plurality of
areas of different lengths and heights. Preferably, the surfaces are structured symmetrically and,
viewed as one surface cross section, have at least one plane of symmetry or, particularly
preferably, two planes of symmetry perpendicular to one another. Have. Various gradients can be
seen from the cross section of the surface of the film bond. Here, the slope of the surface is the
slope of the tangent of the outermost layer of the surface. Discontinuities in the surface where
gradients can not be determined are not taken into account in the determination of gradients.
According to the invention, the surface is provided with a structured part in which the sign of the
gradient changes more than once. The surface of the conventional film-type acoustic transducer
is fixed flat to the outer frame or fixed to the outer frame in a prestressed manner, within the
scope of the application. As a result, in the former case (when stretched linearly) the surface
gradient does not change across the transducer surface and is therefore constant (see FIG. 1a). If
the transducer surface is stretched in a curved manner, the curvature of the film causes a change
in the gradient (see FIG. 1b), but such a gradient is different from the present invention And the
sign of the surface gradient has changed only once. The number of gradient sign changes can
preferably be determined by viewing the film surface in cross section and placing a reference
point at one edge of the surface. The sign of the slope changes when the positive slope (surface
rise) transitions to a negative slope (surface fall) or when the negative slope transitions to a
positive slope. On the surface of the acoustic conversion film, there are partial areas which are
linear and neither rise nor fall, but those areas are not taken into consideration.
[0015]
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The structured transducer surface can also be applied to different rigid objects, for example to
relatively small objects such as casings of component parts, glass plates, walls or postcards, in an
application-specific manner. Or can be attached.
[0016]
In the following, the invention will be described in detail with reference to other aspects and
embodiments.
Those aspects and embodiments can be arbitrarily combined with each other as long as no
obvious contradiction is caused by the combination.
[0017]
In one advantageous embodiment, the acoustic conversion film can comprise PVDF as
electroactive polymer. This PVDF has proven particularly suitable as an electroactive polymer in
the piezoelectric layer. In particular, the piezoelectric layer can comprise PVDF, or the
piezoelectric layer can be formed from PVDF. This material exhibits good piezoelectric properties
so that sufficiently high mechanical displacements can be achieved even at relatively low
voltages. This is, of course, also effective in converting sound waves into current. Furthermore,
since the PVDF layer exhibits a sufficiently high mechanical load resistance, a mechanically
sufficiently stable bond can be obtained even if the strength of the material is relatively low. The
material is furthermore flexible enough to be deformed into various shapes without breakage
within the framework of mechanical or chemical construction. Piezoelectric layers with PVDF as
the electroactive polymer have a sign change of more than 20 times, preferably more than 50
times, more preferably more than 100 times, per transducer surface. It can have. Just such a
large number of sign changes can contribute to a larger surface and can also contribute to the
improved vibrational dynamics of the structured surface.
[0018]
In one further aspect of the invention, the film combination can have areas with different
elasticity, the edges of those areas extending parallel to the area of constant slope of the surface
There is. The acoustic conversion film combination can be configured such that the material has
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different elasticity or stiffness in different flat areas of the combination. The regions are
preferably oriented parallel to the point of the surface where the sign of the gradient changes,
such that a change in the elasticity of the film bond occurs. In particular, it is disadvantageous if
the elastic change of those areas of the film bond occurs at an angle of more than 20 ° or 45 °
or 90 ° and less than 180 ° with respect to the linear part of the constant surface gradient. It
is. Such a change in the elasticity of the film bond can, for example, realize different surface areas
which can be displaced differently depending on the gradient. As such, the resonant properties of
the conversion film according to the invention can be controlled. The different elasticity of the
combination can be achieved by using a plurality of sublayers of different elasticity (e.g. a
support layer). However, it is also possible to provide additional elasticity in the deep-drawn area
of the film combination by mechanical structuring, for example by deep-drawing. However, it is
also possible to provide the partial regions with further layers which contribute to a relatively
low elasticity in those regions. Similar effects can also be achieved by partial chemical or thermal
treatment of the film bond followed by mechanical embossing. Another example of the
relationship between elastic area and surface gradient is shown in the drawings.
[0019]
As an additional feature, the film combination can have more than one electrode with electrode
edges extending parallel to the area of constant surface gradient. The various structures of the
film can be individually controlled and displaced by means of their special structure comprising a
plurality of electrodes with electrode edges extending parallel to the area where the surface
gradient is constant. In addition, this arrangement also makes it possible to separately detect
mechanical displacements of a plurality of regions with a constant gradient. In this way, both the
selectivity of the mechanical displacement of the partial area of the surface as well as the
vibration properties of the entire film assembly can be controlled individually. Thus, the film
bond can provide an adjustment that can not be achieved with conventional film bonds.
Advantageously, the edge boundaries of the electrodes can extend not only parallel to the area
where the surface gradient is constant, but also parallel to the optionally provided plane of
symmetry of the film. . This can contribute to the very uniform sound emission of the acoustic
conversion film.
[0020]
In one additional configuration, the outer surface of the film bond can be provided at least in part
with an additional protective layer or cover layer. In order to increase the mechanical rigidity of
the film bond, for protection against UV radiation, as an electrical contact protection or as
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protection for the outermost transducer layer from moisture or dust, another layer It can be
provided on a film bond. This layer is preferably not piezoelectrically active and can be applied
subsequently by methods known to the person skilled in the art or can be connected to the film
bond within the framework of production. A suitable material of this layer is a chemically inert
polymer such as poly-p-xylylene (parylene) or another polymer such as Teflon. This can extend
the life of the film bond and can increase the reliability. The protective layer may suitably have a
layer thickness of 0.01 μm or more and 30 μm or less, preferably 0.1 μm or more and 15 μm
or less, more preferably 0.5 μm or more and 10 μm or less.
[0021]
Further according to the invention, a method of manufacturing an electroactive acoustic
transducer comprising a structured acoustic transducer film comprises the following features: a)
The acoustic transducer film comprises at least one support B) acoustically produced according
to step a), produced from a layer, at least one first electrode, at least one second electrode, and at
least one piezoelectric layer comprising an electroactive polymer The transducing film is
mechanically or chemically structured, the surface of the acoustic transducing film has a plurality
of regions with different slopes, and the sign of the slope of the surface of the acoustic
transducing film changes at least twice. c) Structured acoustic conversion film is connected with
the frame or surface. It has surprisingly been found that this method results in an acoustic
transducer with improved radiation and / or detection properties. This can be achieved, without
being bound by theory, by means of the expanded acoustic transducer surface and its
characteristic structuring. In particular, it is believed that different gradients of the film surface
can achieve better displacement of the individual surface sections as compared to conventional
unstructured surfaces. This can contribute to higher sound pressure and better frequency
passband width of the transducer frequency. The combination can be formed in step a) from the
individual components in a manner which is conventional in the prior art. This is done, for
example, by bringing together the already completed individual films by post lamination, or by
printing, coating etc. in a wet manner. The person skilled in the art is familiar with the general
processing techniques for forming film bonds.
[0022]
In step b), the acoustic conversion film can be structured by physical or chemical processes to
produce multiple regions of different slope. Mechanical steps include, for example, stretching and
compression of partial film bonds, deep engraving, hot pressing, cold pressing, whereby
permanent deformation of the film surface with various gradients is achieved . Further
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advantageously, the structuring can be provided symmetrically. This means that the structuring
portions are not provided arbitrarily but at predetermined intervals with a substantially constant
distance. A particularly effective structured acoustic conversion film can thereby be obtained.
Furthermore, mechanical structuring methods include partial heating, sonication or partial
removal (for example by means of a laser). Chemical methods for structuring include, for
example, partial etching with acid or alkaline solution, partial deposition of another material as
well as partial elevation. All of these physical or chemical structuring schemes are common in
that they provide permanent changes in the height profile of the individual areas of the acoustic
conversion film. Such a change in height profile results in various gradients of the conversion
film, which according to the invention change the sign of this gradient at least twice.
[0023]
In the following step c), a structured conversion film is connected to the frame. This connection
can be made purely mechanically by sandwiching, but also by bonding the materials together by
adhesion. The structured conversion film can be fitted flat on the frame or in a prestressed state.
[0024]
In a particularly advantageous embodiment of the invention, vibration-stable spacers can be
attached at least in part of the back of the structured acoustic transducer film before step c). The
vibrationally stable spacer is in contact with both the film assembly and the component. Due to
the transducer properties of the structured transducer surface, partial areas of the film bond can
also be supported by the mechanically rigid spacer on its back side, but this greatly reduces the
overall efficiency of the transducer There is nothing to be done. Without being bound by theory,
the slight drop in efficiency is based on the structuring of the surface with various gradient
regions. The mechanically hard spacer forms as much as possible an oscillating mechanically
hard component. This advantageously results in a relatively high mechanical stiffness of the
entire transducing film, since the section over which the acoustic transducing film can freely
vibrate freely is reduced. The structured acoustic conversion film can simply be freely mounted
on the spacer or it can be permanently and mechanically connected with the spacer. This can be
done, for example, by gluing or welding. For each acoustic conversion film, it is possible to
provide only one or more vibration-stable spacers on the back side of the film assembly, or to
provide a plurality. In one particular embodiment, by introducing a plurality of vibrationally
stable spacers, the entire transducer surface can be divided into a plurality of subsurfaces in
mutually symmetrical area ratios. By this, the whole sound conversion film can be divided into a
plurality of regions with different natural frequencies. This can contribute to the equalization of
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the converter's radiation characteristics at widely different frequencies. Further advantageously,
by mechanically supporting the acoustic conversion film by means of vibration-stable spacers,
the stiffness of the film itself can be reduced, which leads to a relatively high sensitivity, and also
to a better acoustic conversion as a whole. It can contribute. The vibration stable spacer of the
present invention is advantageous in that a material or combination of materials having a
relatively high modulus of elasticity is used. Advantageously, those vibrationally stable spacers
have a modulus of elasticity of at least 5000 N / mm <2>, preferably at least 10000 N / mm <2>,
more preferably at least 30000 N / mm <2>. it can. The modulus of elasticity of the material can
be obtained from those described in the literature, or it can be determined rheologically (for
example using a plate / plate rheometer or by vibrational mechanical measurement of the
sample) .
This elastic modulus has been found to be very suitable for the sufficiently vibration-stable fixing
of structured acoustic transducer surfaces.
[0025]
Vibration stable spacers can be formed from various materials. Metal, wood, plastic or various
adhesives are also conceivable. For example, epoxy-based two-part adhesives, thermosetting
adhesives or UV-curable adhesives are used here. Vibration-stable spacers can be mounted
purely mechanically, before the acoustic conversion film is applied to the surface of the object, or
by printing methods (eg silk screen printing or flexographic printing) or by lamination steps It
can be applied. Typically, the vibrationally stable spacer can have a width of 5 μm or more and
5 cm or less, preferably 5 μm or more and 2 cm or less, more preferably 10 μm or more and 1
cm or less.
[0026]
In one further aspect of the invention, before step c), at least a partial area of the back of the
structured acoustic transducer film can be brought into contact with a bed of vibrational
variability. By structuring the acoustic conversion film in this way, the back side of the
combination produces a pronounced support point which can be supported by the vibrationally
variable bed without significant loss of transducer characteristics. it can. The vibrating bed is in
contact with the component on which the film bond is provided, and also in at least partial areas,
in contact with the film bond. This allows the acoustic conversion film to be mechanically easily
configured, which advantageously improves the vibrational properties of the overall combination.
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The mechanical rigidity of the structured transducer surface can thereby be improved, which can
further contribute to a prolonged product life. The vibrationally variable bed is a metal-filled area
on the back side of the acoustic conversion film that is at least partially in contact with the
acoustic conversion film. This region thus hydrostatically produces a connection between the
rigid base and the acoustic conversion film. In the important frequency range of the transducer,
this material is elastic and thereby minimizes the motion of the transducer surface. The
oscillatory mechanical effects exerted on the resonant properties of the transducer can be taken
into account in the design, material selection and thickness of the film combination.
[0027]
The vibrationally variable bed can partially fill the back side of the transducer, or can fill the
entire back side, and more preferably 1 μm to 2000 μm, preferably 1 μm to 1500 μm, more
preferably Can have a thickness of 2 μm or more and 1000 μm or less. Materials suitable for
forming a bed of vibrational variation include silicone elastomers or silicone rubbers, two-part
silicones, such as Fermasil (Sondaloff), elastic or hollow bodies connected by adhesive, plastic
solid spheres Or glass solid spheres, or similar materials. Furthermore, it is also conceivable for a
small air content to be present in the vibrationally variable bed, or such a small air content may
be provided, which advantageously compresses the back space of the transducer. The rate can be
increased. A variation of this conversion particularly advantageously keeps the laminate in a
fixed position, but in the desired frequency range the acoustic transducer resists dynamic
vibrations and exhibits a slight resistance (ie It relates to the characteristics of the bed with high
plasticity, vibrational fluctuation). Here, in the present invention, vibrational variability means
that the material or material composition has a large mechanical plasticity related to the surface.
This property is achieved with a modulus of elasticity of less than 5000 N / mm <2>, preferably
less than 1000 N / mm <2>, more preferably less than 500 N / mm <2> for the material of the
vibration variable. The modulus of elasticity of the material can be obtained from those described
in the literature or it can be determined by rheological measurements (for example using a plate
/ plate rheometer or by oscillatory mechanical measurement of the sample). The modulus of
elasticity of the material corresponds to the frequency range from 20 Hz up to 150 kHz,
preferably 100 Hz up to 100 kHz, to which the acoustic transducer is applicable, as considered
here.
[0028]
In one advantageous embodiment of the invention, the space on the back side of the conversion
film can be supported either by a bed of vibrational variability or by spacers of vibrational
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stability. This combination of vibrationally variable components and vibrationally stable
components can contribute to a very good mechanical support of the structured acoustic
conversion film.
[0029]
Furthermore, according to the invention, an electroactive acoustic transducer can be produced
with the method according to the invention. The acoustic transducer produced by the method of
the invention can exhibit improved transducer properties, such as sensitivity and sound pressure,
by means of a structured transducer surface.
[0030]
The electroactive acoustic transducer according to the invention comprising a microstructured
surface film can be used as a microphone, a speaker, a human machine interface (HMI), a sensor.
The improved transducer characteristics are particularly suitable for use in the above-mentioned
areas, in particular where only limited surfaces can be used and / or high efficiencies are to be
achieved.
[0031]
Also, with regard to the further advantages and features of the electroactive acoustic transducer
described above, reference is explicitly made to the electroactive acoustic transducer film
according to the invention and the description associated with the method according to the
invention. Furthermore, the inventive features and advantages of the electroactive acoustic
transducer film according to the invention are also applicable to the method according to the
invention and the acoustic transducer according to the invention and are considered as disclosed.
be able to. This is also true for the reverse. All combinations of at least two of the features
disclosed in the specification and / or claims are also included in the present invention.
[0032]
The present invention will be described in detail below based on the attached drawings.
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[0033]
Fig. 1 shows a schematic cross-sectional view of a conventional acoustic transducer structure
comprising a linear acoustic transducing film assembly.
FIG. 1 shows a cross-sectional view of a conventional acoustic transducer structure comprising a
curved acoustic transducing film assembly. Fig. 1 shows a schematic cross-sectional view of a
structured acoustic transducer surface. FIG. 1 shows a schematic cross-sectional view of various
examples of the construction of a structured acoustic conversion film. FIG. 1 shows a schematic
cross-sectional view of a structured acoustic transducer surface without a support layer and
having a piezoelectric layer and a plurality of electrodes. FIG. 1 shows a schematic cross-sectional
view of an acoustic transducer having an acoustic conversion film with a structured surface on a
vibration-stable spacer and a bed of vibrational fluctuation. Fig. 2 shows a schematic plan view of
a transducer base consisting of a bed of vibration variable and a spacer of vibration stability.
[0034]
In FIG. 1a, there is a structural element surface 2 on the back side of the transducer, as well as a
combination 5 consisting of a support layer 4 and a piezoelectric layer and two electrode layers
provided on the support layer 4. Fig. 1 shows a schematic cross-sectional view of a conventional
acoustic transducer structure 1 comprising two frames or holding parts 3 on either side of an
acoustic conversion film assembly having a. The surface of the acoustic conversion film is
unstructured and the film is stretched straight between the holders 3. This gives a constant
surface gradient of the acoustic conversion film.
[0035]
FIG. 1 b comprises a sonication film combination formed of a support layer 4 and a combination
5 of a piezoelectric layer and two electrode layers provided on the support layer 4. A schematic
cross-sectional view of a conventional acoustic transducer structure is shown. The surface of the
acoustic conversion film is not structured. The combined body is curved and stretched between
the holding portions 3. This first results in a positive slope of the acoustic conversion film surface
(from right to left), and subsequently a negative slope of the acoustic conversion film surface
beyond the highest point. The sign representing the slope of the acoustic conversion film surface
changes only once, so the number of sign changes is not according to the invention.
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[0036]
FIG. 2 shows a schematic cross-sectional view of a structured acoustic transducer surface. From
left to right, a positive slope, a highest point, a negative slope, a lowest point, and again a positive
slope are represented. That is, the surface gradient changes its sign twice. In this partial area
there is therefore a surface structured according to the invention.
[0037]
Figures 3a-e show cross-sectional views of various configurations of the structured acoustic
transducer film, in which the sign of the surface gradient of the acoustic transducer film changes
more than once. In particular, the figures show an advantageous embodiment which repeatedly
comprises a series of individual elements and is thus constructed symmetrically. However,
periodically unstructured surfaces or mixed forms of the illustrated surfaces are also conceivable.
[0038]
In FIG. 4 a cross-sectional view of a structured acoustic transducer surface 8 without the support
layer 4 is shown. The piezoelectric layer 9 and a plurality of electrodes not extending over the
entire surface of the piezoelectric layer 9, for example, the electrodes 10 and 11 are shown. The
individual edges of the electrodes extend parallel to the area having a constant surface slope (not
shown in this cross-sectional view). Particularly in the present invention, the polarities of the
individual electrodes on the upper and lower surfaces of the piezoelectric layer are not constant
but variable. In that way, different surface areas of the piezoelectric layer comprising the
electroactive polymer can be provided with different polarities in the same time unit.
[0039]
FIG. 5 shows a cross-sectional view of an acoustic transducer comprising an acoustic conversion
film comprising a structured surface 5. The acoustic transducer is arranged on a rigid body 2 and
is fixed by means of a vibration-stable spacer 7 and a bed 6 of vibrational variability. In the
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present invention, situations are also conceivable in which the acoustic conversion film is fixed
only by the vibration-stable spacer 7 or only by the vibration-variable bed 6. In the latter case,
the vibrationally variable bed 6 can occupy the entire back space from the rigid body 2 to the
acoustic conversion film. According to the invention, however, it is also conceivable for the
vibrationally variable bed 6 to be in contact only with the partial area of the acoustic conversion
film provided with the structured surface 5. In that case, the acoustic conversion film provided
with the structured surface 5 may also comprise another purely mechanical support film, and the
acoustic conversion film is constructed without the support film. You can also.
[0040]
FIG. 6 shows in a schematic plan view a transducer base consisting of a bed 6 of vibrational
variability and a spacer 7 of vibrational stability. The structured acoustic conversion film is not
shown in this schematic plan view. The arrangement of the vibration-stable spacers 7 makes it
possible to variously shape several transducer subregions which can have different areas and
thus also different resonance properties. The choice of the base thus allows the acoustic
transducer to be tailored to the desired application. According to the invention, an embodiment is
also conceivable in which the vibration-variable bed 6 is not provided and only the vibrationstable spacers 7 are provided.
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