Electroactive sound transducer foil having a structured surface

Abstract

An electroactive sound transducer foil includes a composite foil made up of at least one carrier foil, at least one first and one second electrode, and at least one piezoelectric layer including an electroactive polymer, the surface of the sound transducer foil including a structuring having different slopes, and the slope of the sound transducer foil surface changing the sign at least twice.

Claims

1. An electroactive sound transducer foil, comprising: a composite foil having: a carrier foil; a first electrode; a second electrode; and a piezoelectric layer including an electroactive polymer; a vibration-soft bed to which the composite foil is applied; and vibration-hard spacers crisscrossing the vibration-soft bed, thereby dividing a surface of the transducer foil into a plurality of areas having different natural frequencies; wherein: a modulus of elasticity of material of which the vibration-hard spacers are made is greater than a modulus of elasticity of material of which the vibration-soft bed is made; the transducer foil includes at least one surface, a slope of which changes sign at least twice; and at least one of: (a) one of the at least one surface is a surface of the piezoelectric layer; (b) one of the at least one surface is a surface of the first electrode; (c) one of the at least one surface is a surface of the second electrode; and (d) when viewed in a direction that is perpendicular to the at least one surface, the at least one surface forms a two-dimensional plane that is perpendicular to a stacking direction in which the first electrode, second electrode, and piezoelectric layer are stacked over each other.

2. The sound transducer foil as recited in claim 1, wherein the electroactive polymer includes PVDF.

3. The sound transducer foil as recited in claim 1, wherein elasticity of the composite foil varies along the slope.

4. The sound transducer foil as recited in claim 1, further comprising a third electrode, wherein electrode edges of the first, second, and third electrodes extend in parallel to areas having a constant surface slope.

5. The sound transducer foil as recited in claim 1, further comprising an additional protective or cover layer applied at least partially to an outer side of the composite foil.

6. A method for manufacturing an electroactive sound transducer having a structured sound transducer foil, the method comprising: producing a sound transducer foil from a carrier layer, a first electrode layer, a second electrode layer, and a piezoelectric layer including an electroactive polymer, wherein: the carrier layer, first electrode layer, second electrode layer, and piezoelectric layer form a composite foil; the composite foil is applied to a vibration-soft bed, and vibration-hard spacers crisscross the vibration-soft bed, thereby dividing a surface of the transducer foil into a plurality of areas having different natural frequencies; and a modulus of elasticity of material of which the vibration-hard spacers are made is greater than a modulus of elasticity of material of which the vibration-soft bed is made; one of mechanically and chemically structuring the sound transducer foil to include at least one surface, a slope of which changes sign at least twice, wherein at least one of: (a) one of the at least one surface is a surface of the piezoelectric layer; (b) one of the at least one surface is a surface of the first electrode; (c) one of the at least one surface is a surface of the second electrode; and (d) when viewed in a direction that is perpendicular to the at least one surface, the at least one surface forms a two-dimensional plane that is perpendicular to a stacking direction in which the first electrode, second electrode, and piezoelectric layer are stacked over each other; and joining the structured sound transducer foil to one of a frame and a surface.

7. The method as recited in claim 6, further comprising attaching vibration-hard spacers at least in subareas of a rear side of the structured sound transducer foil prior to the joining step.

8. The method as recited in claim 6, further comprising contacting at least subareas of a rear side of the structured sound transducer foil with a vibration-soft bed prior to the joining step.

9. An electroactive sound transducer, producible using a method for manufacturing an electroactive sound transducer having a structured sound transducer foil, the method comprising: producing a sound transducer foil from a carrier layer, a first electrode layer, a second electrode layer, and a piezoelectric layer including an electroactive polymer, wherein: the carrier layer, first electrode layer, second electrode layer, and piezoelectric layer form a composite foil; the composite foil is applied to a vibration-soft bed, and vibration-hard spacers crisscross the vibration-soft bed, thereby dividing a surface of the transducer foil into a plurality of areas having different natural frequencies; and a modulus of elasticity of material of which the vibration-hard spacers are made is greater than a modulus of elasticity of material of which the vibration-soft bed is made; one of mechanically and chemically structuring the sound transducer foil to include at least one surface, a slope of which changes sign at least twice, wherein at least one of: (a) one of the at least one surface is a surface of the piezoelectric layer; (b) one of the at least one surface is a surface of the first electrode; (c) one of the at least one surface is a surface of the second electrode; and (d) when viewed in a direction that is perpendicular to the at least one surface, the at least one surface forms a two-dimensional plane that is perpendicular to a stacking direction in which the first electrode, second electrode, and piezoelectric layer are stacked over each other; and joining the structured sound transducer foil to one of a frame and a surface.

10. A method comprising using an electroactive sound transducer as one of a microphone, a loudspeaker, a human machine interface (HMI), and a sensor, wherein: the electroactive sound transducer includes: a composite sound transducer foil that includes a carrier layer, a first electrode layer, a second electrode layer, and a piezoelectric layer including an electroactive polymer; a vibration-soft bed to which the composite foil is applied; and vibration-hard spacers crisscrossing the vibration-soft bed, thereby dividing a surface of the transducer foil into a plurality of areas having different natural frequencies; a modulus of elasticity of material of which the vibration-hard spacers are made is greater than a modulus of elasticity of material of which the vibration-soft bed is made; the composite foil includes at least one a surface, a slope of which changes sign at least twice; and at least one of: (a) one of the at least one surface is a surface of the piezoelectric layer; (b) one of the at least one surface is a surface of the first electrode; (c) one of the at least one surface is a surface of the second electrode; and (d) when viewed in a direction that is perpendicular to the surface, the at least one surface forms a two-dimensional plane that is perpendicular to a stacking direction in which the first electrode, second electrode, and piezoelectric layer are stacked over each other.

11. The sound transducer foil as recited in claim 1, wherein the first and second electrodes are arranged along only a portion of the piezoelectric layer.

12. The sound transducer foil as recited in claim 1, wherein the modulus of elasticity of the vibration-hard spacers is greater than or equal to 5,000 N/mm.sup.2 and the modulus of elasticity of the vibration-soft bed is less than or equal to 5,000 N/mm.sup.2.

13. The sound transducer foil as recited in claim 1, wherein the modulus of elasticity of the vibration-hard spacers is greater than or equal to 10,000 N/mm.sup.2 and the modulus of elasticity of the vibration-soft bed is less than or equal to 1,000 N/mm.sup.2.

14. The sound transducer foil as recited in claim 1, wherein the modulus of elasticity of the vibration-hard spacers is greater than or equal to 30,000 N/mm.sup.2 and the modulus of elasticity of the vibration-soft bed is less than or equal to 500 N/mm.sup.2.

15. The sound transducer foil as recited in claim 3, wherein changes in the elasticity of the composite foil along the slope occur at locations in which a sign of the slope changes.

16. The sound transducer foil as recited in claim 3, wherein changes in the elasticity of the composite foil along the slope are due to differences in elasticity of sublayers of the composite foil at different locations along the slope.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1a shows a schematic cross section of a conventional sound transducer design including a straight sound transducer foil composite;

(2) FIG. 1b shows a schematic cross section of a conventional sound transducer design including a curved sound transducer foil composite;

(3) FIG. 2 shows a schematic section of a structured sound transducer surface;

(4) FIGS. 3a through 3e show schematic sections through different embodiments of a structured sound transducer foil;

(5) FIG. 4 shows a schematic section through a structured sound transducer surface without a carrier layer and including a piezoelectric layer and multiple electrodes;

(6) FIG. 5 shows a schematic section through a sound transducer including a sound transducer foil having a structured surface on a vibration-hard spacer and a vibration-soft bed;

(7) FIG. 6 shows a schematic top view onto a transducer substructure made of a vibration-soft bed and vibration-hard spacers.

DETAILED DESCRIPTION

(8) FIG. 1a shows the schematic cross section of a conventional sound transducer design 1 including a component surface 2 on the rear side of the transducer, two frames or mountings 3 on the two sides of the sound transducer foil composite including a carrier layer 4 and, situated thereabove, a composite 5 made up of a piezoelectric layer and two electrode layers. The surface of the sound transducer foil is not structured, and the foil is clamped straight between the mountings 3. This results in a constant surface slope of the sound transducer foil.

(9) FIG. 1b shows the schematic cross section of a conventional sound transducer design including a sound transducer foil composite made up of a carrier layer 4 and, situated thereabove, a piezoelectric layer and two electrode layers 5. The surface of the sound transducer foil is not structured. The composite is clamped between mountings 3 in a curved manner. This results (from left to right) first in a positive slope of the sound transducer foil surface and then, after the maximum has been exceeded, in a negative slope of the sound transducer foil surface. The sign of the slope of the sound transducer foil surface changes once, and this number of changes of signs is thus not in accordance with the present invention.

(10) FIG. 2 shows a schematic section of a structured sound transducer surface. From left to right, this results first in a positive slope, a maximum, a negative slope, a minimum, and then again in a positive slope. The the surface slope thus changes its sign twice. A surface which is structured according to the present invention is thus present in this subarea.

(11) FIGS. 3a through 3e show a section through different embodiments of a structured sound transducer foil, the surface slope of the sound transducer foil changing the sign more than once. In particular preferred specific embodiments are illustrated here, which have a sequence of recurring individual elements and accordingly have a symmetrical design. However, non-periodically structured surfaces or mixed forms of the shown surfaces are also conceivable.

(12) FIG. 4 shows a section through a structured sound transducer surface 8 without carrier layer 4. The figure shows a piezoelectric layer 9 and multiple electrodes, for example 10, 11, which do not extend across the entire surface of piezoelectric layer 9. The individual edges of the electrodes extend in parallel to areas having a constant surface slope (not shown here in the section). It is in particular also within the sense of the present invention that the polarity of individual electrodes on the top side/bottom side of the piezoelectric layer is not constant, but variable. In this way, different surface areas of the piezoelectric layer including an electroactive polymer may be differently polarized in the same unit of time.

(13) FIG. 5 shows a section through a sound transducer including a sound transducer foil having a structured surface 5. The sound transducer is situated on a solid body 2 and is stabilized by vibration-hard spacers 7 and a vibration-soft bed 6. Situations in which the sound transducer foil is stabilized either only by vibration-hard spacers 7 or only by a vibration-soft bed 6 are also within the sense of the present invention. Vibration-soft bed 6 may fill the entire rear space of solid body 2 to the sound transducer foil. However, designs in which vibration-soft bed 6 is in contact only with subareas of the sound transducer foil having structured surface 5 may also be in accordance with the present invention. The sound transducer foil having structured surface 5 may both include a further purely mechanical carrier foil and have a design without a carrier foil.

(14) FIG. 6 shows a schematic top view onto a transducer substructure made of vibration-soft bed 6 and vibration-hard spacers 7. The structured sound transducer foil is not shown in the schematic top view. Due to the arrangement of the vibration-hard spacers 7, it is possible to form different transducer subareas, which may have a different surface and thus also different resonance properties. In this way, the sound transducer may be matched to the particular designed field of application by the selection of the substructure. Specific embodiments in which only vibration-hard spacers 7 without vibration-soft bed 6 are present are also in accordance with the present invention.