Transducer element with electrode supported by flexible film

Abstract

The present disclosure is directed to the field of electroactive polymer transducers, actuators, sensors and generators. In particular, the disclosure pertains to a transducer element comprising an elastic body, a flexible film and an electrode attached to the flexible film. The electrode being in a corrugated state having elevations and depressions, and wherein the corrugated state is provided by a compression force of the elastic body or the flexible film. Moreover the present disclosure is directed to manufacturing of such transducer element and to a transducer with such transducer element.

Description

[0001] TRANSDUCER ELEMENT WITH ELECTRODE SUPPORTED BY FLEXIBLE FILM

[0002] FIELD OF THE INVENTION

[0003] The present disclosure pertains to the field of electroactive polymer transducers, actuators, sensors and generators. In particular, the disclosure pertains to such transducers, actuators, sensors and generators having an elastic body placed between electrodes.

[0004] BACKGROUND OF THE INVENTION

[0005] A transducer element for sensing, actuating and electrical power generation can be made using an elastic body, e.g. in the form of a deformable polymer body, in combination with at least two electrodes placed at either side of the elastic body. The elastic body acts as an insulator between the two electrodes and is made to deflect or stretch upon application of a voltage difference between the electrodes. Such transducer element is signified by having a variable capacitance, where capacitance variation is caused by a deflection or stretching of the transducer.

[0006] One particular type of such transducers is known as the dielectric elastomer actuator (DEA), signified by having a stretchable dielectric body, sandwiched by stretchable electrodes. The stretchable dielectric body is further signified by supporting macroscopic stretch, being electrically insulating with a low leakage current, and having a well-defined permittivity. Generally, for a dielectric elastomer actuator, the actuation pressure Pactfrom an applied voltage V is generally described by the formula:

[0007] Pact = e0erE2= e0erV2 / t2where e0is the vacuum permittivity, eris the relative permittivity of the dielectric body having a thickness t, and E is the electrical field due to an applied voltage V. The mechanical stress Pmech fromstretching the DEA is: r Pmech — V1° where K is the mechanical module of the dielectric body and S is the strain (related to stretch B through B = S + 1).

[0008] These actuators can find use in a wide range of applications and generally provide advantages over other transducer types that operate by means of compressed air, pressurized oil, changes in temperature, chemical combustion, and other such transduction where the principal energy is provided by means other than electrical.

[0009] As the DEA is actuated, the shape of the DEA body changes. However, such shape changes risk challenging the mechanical and electrical performance. For example, as the polymer body stretches, the electrodes also need to stretch, risking cracks and ruptures. The motion should preferably occur in unison, such that electrodes and body move homogenously without delaminating from each other or from attachments to boundaries. Moreover, compression of the polymer body by an external force or due to the actuation itself will reduce the distance between the electrodes, risking a breakdown of the electrical field, causing a spark between the electrodes that may lead to pinholes in the polymer body. Breakdowns are highly undesirable as the charge is lost, whereas the pinhole may cause permanent failure of the DEA. Such breakdowns may also occur due to other effects, such as imperfections, cavities or impurities in the polymer body or conditions on electrode edges.

[0010] Stretchable electrodes should preferably provide several features, including deformability under low applied force to allow unhindered actuation, durability to support multiple stretching cycles with unchanging properties, strong mechanical attachment to the elastic body even under deformation, and practical methods for manufacture. A further requirement may include self-clearing, which enables self-healing of the DEA after an electrical breakdown has occurred; self-clearing utilizes the sparks around the pinhole to evaporate and thereby remove the electrode near the pinhole, until the effective distance between electrodes becomes long enough for no further sparking to occur, and the DEA regains operation.

[0011] Electrode materials and processes that simplify and speed up the manufacture of electrode layers are desirable, and which lend themselves to practical attachment to the external power supply by supporting one or more electrical interface connections that are stable over the lifetime of the DEA.

[0012] The polymer body of the DEA is commonly chosen as an elastomer, characterized by being macroscopically stretchable over 1%. Elastomers can retract to their original configuration with low permanent deformation. Many elastomers are hyper-elastic, having macroscopic stretchability over 100% stretch, with complex non-linear stress-strain behaviour. Electrically, common pure elastomers have relatively low electrical conductivity and relatively low relative permittivity below 10. Other materials may also be used, commonly having modified mechanical, electrical or dielectric properties.

[0013] A transducer may further be used as a generator to generate electric energy from an external motion, such that mechanical energy is converted to electrical energy. The mechanical energy can be obtained from any moving source, e.g. from ocean waves.

[0014] EP1221180 discloses an electroactive polymer-based transducer, where the electroactive polymers are pre-strained to improve conversion from electrical to mechanical energy. Compliant electrodes are provided by forming electrodes on the pre-strained polymer during fabrication resulting in a corrugated electrode when the polymer is relaxed.

[0015] EP1330867 discloses an electroactive polymer-based transducer, where an elastomer body is provided with a corrugated surface section to provide elevations and depressions. The corrugated section is covered by an electrode resulting in a waved electrode. One purpose of the corrugation is to reduce the mechanical force of the electrode by allowing it to stretch via bending, and to avoid mechanical failures in the electrode and subsequent reduction in ability to conduct electricity.

[0016] Nevertheless, there is still a need in the art to provide further ways of addressing the challenges of an electroactive polymer device, and it is against this background that the invention has been devised.

[0017] SUMMARY OF THE INVENTION

[0018] The present invention relates to electroactive polymer actuators generally, and dielectric elastomer actuators specifically, of the kind wherein electrostatic attraction between two electrodes located on each side of an elastic body, e.g. a polymer body or an elastomeric body, leads to a compression of the body in a first direction and a corresponding extension of the body in a second direction.

[0019] It would be advantageous to achieve a transducer element for use in an electroactive polymer actuator / sensor / generator structure which is easy to produce and tolerant of production defects such as pinholes, cracks and inclusions in the elastic body, and which supports prolonged use without degradation of the structure while being protected against electromechanical pull-in failure modes.

[0020] Accordingly, in a first aspect, there is provided a transducer element comprising: an elastic body with a first surface and a second surface; a flexible film with an upper surface and a lower surface, wherein the lower surface of the flexible film is attached to the first surface of the elastic body; an electrode attached to the flexible film at the upper surface or lower surface; wherein the electrode is in a corrugated state having elevations and depressions. The corrugated state is preferably provided by and / or obtained by a compression force of the elastic body. As described in the following sections, the compression force may originate from different sources. For example, for a pre-strained elastic body, the compression force originates via the interplay between the elastic body and the flexible film. In another embodiment, for a non pre-strained transducer, an external force can be applied on two ends of a transducer element, such as a transducer element in a roll configuration. Such a force results in a compression force that originates on the elastic body and acts on the electrode.

[0021] The corrugated state is provided by a force imposed by the elastic body to the flexible film. By corrugating the flexible film, also the electrode becomes corrugated. An elastic body capable of imposing such compression force can be obtained in different ways. One way is to strain the elastic body and then attach the flexible film when the elastic body is in the strained state. Upon release of the flexible body, it will impose a compression force to the elastic film and the electrode. The compression force is maintained in the transducer element, and leads the electrode to be in a corrugated state.

[0022] Another way is to compress the elastic body, e.g. by application of a force to the sides of the elastic body. For example when the transducer element is in a roll configuration. By application of a force to the sides of the elastic body, the elastic body becomes shorter in the direction of the applied force and thereby imposes a compressing force to the flexible film and the electrode. As a result, the compression force is the force exerted by the elastic body to the electrode, and such a compression force maintains the corrugated state of the transducer element, until an additional force or voltage makes the transducer element to expand, thereby diminishing the corrugated structure. It is possible to obtain a transducer from a fabrication process where no pre-straining has been made to any of the elements of the transducer. In an embodiment, the flexible film is attached to the elastic body without prestretch of the film. The desired corrugated state of the electrode is achieved by subsequent application of a force to two opposing sides of a transducer, optionally in the direction along a multitude of electrode layers. As a result to that force, the elastic body may be compressed, creating corrugations on the electrode. In this embodiment, the corrugations are a result of the compression force provided by the electrode being attached on the elastic film. The compressive force may also be achieved by attaching the assembled transducer onto a separate pre-stretched elastic body.

[0023] The transducer element geometry gives rise to an interplay between the elastic body and the flexible film, leading to a compression force that is applied on the electrode. The compression force can be generated by that interplay. Without the compression force, the electrode would not be maintained in a corrugated state.

[0024] Due to the attachment of the flexible film to the elastic body, shape changes of the elastic body is reflected in shape changes of the flexible film. A compression of the elastic body is thereby also a compression of the flexible film.

[0025] A transducer element of this kind can be used to provide at least three functions, including: as an actuator, where the shape of the element can be controlled by a voltage difference applied between the electrodes using a suitable power source; as a generator, where, with a suitable electrical circuit, the variation in the electric energy storing capacity of the element can be utilized for electrical energy harvesting, e.g. from ocean waves; or as a sensor, where the variation in shape of the element due to an externally coupled motion can be detected by a suitable sensing electrical circuit. Hence, the present disclosure in further embodiments relate to an actuator (for example as described above and herein) comprising one or more of the presently disclosed transducer elements, a generator (for example as described above and herein) comprising one or more of the presently disclosed transducer elements, and a sensor (for example as described above and herein) comprising one or more of the presently disclosed transducer elements.

[0026] A transducer element of this kind possesses several advantages. A main feature for many of the advantages is the provision of the flexible film. One advantage is that the electrode can be attached to the flexible film. Flexible films are relatively easy to handle in a production setup as they can be unwound from reels. Use of wound films on reels is suitable for automated mass production. Additionally, while not essential, the use of a flexible film as a support for the electrode makes it possible to fabricate the electrode in a separate production step and then afterwards combine the compound of the electrode and the flexible film with the elastic body. Combining a flexible film with an elastic body in a production setup is for a large number of materials easier to handle than providing an electrode directly onto the elastic body. In this manner, the intrinsically hard and stiff material of the electrode is made functionally soft by virtue of the flexible film being in a corrugated state and therefore being easier to combine with the soft elastic body.

[0027] A further advantage is that by a proper adaptation of the structural aspects of the flexible film and the elastic body, sufficient potential energy stored in, or externally provided to, the elastic body can be converted into a compression force which provides a wrinkling of the electrode in the form of a corrugated state having elevations and depressions. Having the electrode in a corrugated state when the elastic body is in a compressed state ensures that upon imposing a shape change and thereby a stretching of the elastic body, the flexible film and the electrode unwrinkle or reduce the corrugation as the elastic body gets larger and thereby ensure that the surface of the elastic body with the flexible film element is still covered with the electrode without a rupture or breaking of the electrode. This mechanism will have the effect of protecting the actuator against several electro-mechanical failure modes, e.g. pull-in failure or excessive thinning.

[0028] By the provision of the flexible film as a support for the electrode, an element is introduced which reduces some of the difficulties with providing a corrugated electrode to electroactive actuators.

[0029] The flexible film is generally arranged as a film suitable for carrying the electrode whereas the elastic body is arranged as the transducer body which on one hand provides a dielectric separation between the electrodes and on the other hand provides the shape change for the transducer. The flexible film and the elastic body are normally made of different materials. The flexible film is generally thinner than the elastic body, and generally has a higher Young’s modulus. The flexible film provides the advantageous feature of a built-in maximum strain, i.e. when corrugation is exhausted at a certain strain, the stiffness against any further increase of a strain becomes higher by several orders of magnitude. This feature helps to protect against general mechanical over-stretching and over-actuation. Additionally, the flexible film further reduces the risk of pull-in-failure and related failure run-away actuation modes. Such safeguard against pull-in-failure is improved with increased Young's modulus of the flexible film.

[0030] The flexible film advantageously provides a barrier to leakage current. Such barrier further provides the advantage of protection against electrical breakdowns caused by various defects in an elastic body, e.g. pinholes, bubbles, impurities, or other weak spots. A further advantage of the flexible films is the effect of dielectric barrier protection against electric treeing breakdown, a slow and on-going degradation of any dielectric placed under large electric fields, which is mostly trapped on the boundary between a flexible film and an elastic body.

[0031] A corrugated electrode may also be provided in a manner which support self-healings of failures due to an electrical breakdown of the elastic body. This is because even if some of the electrode is eroded away in the self-clearing process, a coherent electrode on the general surface of the flexible film will still be present after the self-clearing process and thereby support the same operating voltage as the actuator was initially specified for.

[0032] The electrode can be attached to the flexible film at the upper surface or lower surface of the flexible film. This entails that the flexible film may be placed against the elastic body such that the electrode faces the elastic body or faces away from the elastic body.

[0033] In an embodiment, the elastic body is strained resulting in a compression force acting from the elastic body to the electrode and to the flexible film, thereby shaping the electrode in a corrugated state. For example, it can be considered that the compression force arises from a manufacturing process where the elastic body was pre-strained when the flexible film and the electrode was attached to the elastic body.

[0034] In this embodiment, the elastic body is pre-strained, i.e. a straining force is applied to the elastic body to enlarge the elastic body, while the flexible film is attached to the elastic body. The flexible film being attached in an unstrained, or slightly strained, state, e.g. directly from a reel.

[0035] By pre-straining the elastic body, a potential energy is introduced into the structure which is capable of providing the compressive force when the elastic body is relaxed from the prestraining. The relaxed pre-strained elastic body with a flexible film (and electrode) in a compressed state ensures a corrugated electrode in the relaxed state of the elastic body.

[0036] The elastic body may in embodiments be pre-strained in a single direction and in another embodiment be pre-strained in a first and a second orthogonal direction. In such embodiment, the same or different strains may be applied in the two directions.

[0037] Depending on the use case of the final transducer, the energy used in the pre-straining is adjusted so that appropriate corrugated states arise in the relaxed state and in suitable operating states.

[0038] In an embodiment, an externally applied force acts on the transducer element, thereby resulting into a compression force configured to shape the electrode in a corrugated state. In such an embodiment, the transducer element is manufactured without pre-straining of the elastic body, and after manufacturing of the transducer element, the transducer element is arranged in a structure which introduces the compression force as a mechanical force.

[0039] Depending on the use case of the final transducer, the specific pre-strain and resulting energy used in manufacturing is adjusted so that an appropriate corrugated state arises in the relaxed and operating state. Additionally, the thickness and stiffness of the flexible film may be selected in relation to providing an appropriate corrugated state in the relaxed state.

[0040] In an embodiment, the elastic body is stretchable above 5% and / or is having a Young’s modulus between 1 kPa and 100 MPa.

[0041] The elastic body may be pre-strained along at least one of its axes by a factor up to 15 times the original unstrained configuration. The elastic body can be made of a suitable material capable of being stretched and capable of withstanding a suitable large electric field with suitable low leakage current. An elastic body may for example be of a material having elastic, hyper-elastic, plastic and / or viscoelastic properties. In general, the elastic body can be made of both incompressible and compressible materials. However, an incompressible material is normally preferable since this provides a more direct response between voltage signal and shape change.

[0042] An elastic body may be synthesized from materials with network properties supporting strain-hardening, such that they are initially very soft at low strains, then become very stiff as strain is increased, which may further protect an actuator made of this material against electro-mechanical pull-in failure. Elastic bodies may be synthesized with chemical moieties supporting self-healing of material properties after a macroscopic tear.

[0043] In general, the elastic body may be a polymer material, preferably selected from the group of: an elastomer material, a dielectric elastomer material, a chemically crosslinked elastomers, a physically crosslinked thermoplastic elastomers, an adhesive, a gel or combinations thereof.

[0044] Specifically, the elastic body may be a natural rubber, styrene-butadiene rubber, polybutadiene rubber, neoprene rubber, ethyl ene-propylene rubber, silicone rubber, polyurethane rubber, fluorocarbon rubber, butyl rubber, nitrile rubber, chloro-sulfonated polyethylene rubber, polyacrylic rubber, chlorinated polyethylene rubber, ethyl ene-butadiene rubber, ethylene-acrylic rubber, ethylene-vinyl acetate rubber, isoprene rubber, chloroprene rubber, or a polyether block amide rubber.

[0045] Elastomers may be polymers having physical crosslinks, including copolymers and block copolymers, including combination achieved by simple mixing or by chemical synthesis, e.g. as blends, random copolymers, block copolymers, brushes.

[0046] Polymer materials may be mixed or grafted with solvents, plasticizers or other polymers, aided by various agents, further including any of the previously mentioned materials or combinations thereof combined with other agents through blending or grafting e.g. solvents, plasticizers, interface agents. The elastic body may comprise a component provided for the purpose of adjusting mechanical properties, e.g. for the purpose of modifying elastic or hyper-elastic properties to achieve suitable mechanical properties, e.g. adjusted Young’s modulus, strain-hardening, or self-healing, for example by means of embedded microcapsules or dynamic reversible covalent bonds.

[0047] The elastic body may comprise a component that enhances the relative permittivity, including such materials that are coated with an insulating material, e.g. ceramic particles, liquid crystal moieties, ionic liquids, oligomeric ionic liquids, highly polarizable molecules such as conducting oligomers and polymers, phthalocyanines, zwitterions, and conducting particles to achieve sub-percolative enhancement, and all their variants achieved by suitable coating with insulating materials.

[0048] Furthermore, electro-mechanically active polymer materials can be used as the elastic body, e.g. relaxor ferroelectric polymers and copolymers, inter-penetrating polymer metal composites (IPMCs), inter-penetrating network conducting polymers (IPN actuator), and other such materials undergoing microscopic or macroscopic polarization or ionic migration transformations due to applied voltage.

[0049] In embodiments the elastic body may be stacked to tailor the properties of a final actuator. By stacking the elastic bodies, the final properties and responses of the actuator can be finely tuned. The flexible film is attached to the first surface of a top elastic body in the stack of elastic bodies. In embodiments, at least two elastic bodies in the stack may be of different materials and / or of a different thickness and / or is pre-strained with different strains. In alternative embodiments, the elastic bodies in the stack may be of same materials. If the stack is to be placed under a pulling force applied to the end-most layers of the stack, it is advantageous to ensure that every single layer throughout the stack adheres well to its neighbouring layers.

[0050] The flexible film can be made of any suitable material capable of supporting an electrode. Moreover, the flexible film should be sufficiently flexible to support wrinkling upon exposure to the compressive force of the elastic body, which may be achieved by having a suitable thickness of the flexible film. The flexible film may be of a metal oxide, a semiconductor metal oxide, a polymer, or a copolymer material, which may have been processed by biaxial orientation. The flexible film may be made from a material which is stretchable to a strain level that is lower than for the elastic body.

[0051] The flexible film may be made from a biaxially pre-stretched polymer, which commonly support strains below 50% before breaking, and commonly have Young’s modulus above 100 MPa and below 100 GPa. A flexible film may, however, also be made from metal oxides or semiconductor metal oxides, or their alloys.

[0052] The flexible film material may be an electrical insulator, and may be of polyethylene terephthalate, polyethylene naphthalate, polypropylene, polycarbonate, poly-(ethylene- propylene-norbomene), polyvinylidene fluoride, polyethylene, polyvinyl chloride, polyimide, polyphenylene sulfide, polystyrene, polytetrafluoroethylene, polyetheretherketone, polybutylene terephthalate, or poly-(ethylene-co-tetrafluoroethylene), and may include various agents for the purpose of modifying dielectric, conductive, or machinability properties.

[0053] The flexible film may in embodiments be attached to the elastic body by adhesion, e.g. selfadhesion, by use of adhesives or glues, or by use of adhesion promoting components provided in the elastic body.

[0054] Self-adhesion occurs when the surface energies of the flexible film and the elastic body are similar or matched. Such matching may be done by proper selection of materials of the flexible film and the elastic body or by modifying their surface properties by plasma treatment or treatment with surface activation agents.

[0055] Reference is made to elastic bodies and flexible films being strained or stretched. It is noted that strain and stretch are intimately correlated. For example, a strain of 0.05 is the same as stretch of 1.05. The terms strain and stretch, pre-strain and pre-stretch are used interchangeably, unless specific values of either strain or stretch are mentioned.

[0056] In an embodiment, the transducer element is configured such that the elevations and depressions comprise a peak-to-peak amplitude, wherein the peak-to-peak amplitude may be larger than 1 gm, preferably larger than 5 pm, or more preferably larger than 10 pm, or most preferably larger than 50 pm. The peak-to-peak amplitude can be customizable depending on the type of application for the transducer element. Larger peak-to-peak amplitude may result in enhanced mechanical flexibility and resilience, as the corrugated structure allows for significant deformation before reaching the strain limits of the electrode or flexible film. This increased tolerance can prevent cracking or delamination during repeated actuation cycles, particularly in high-strain or high-voltage environments.

[0057] Furthermore, a larger peak-to-peak amplitude can contribute to improved self-clearing behaviour by preserving conductive continuity even after localized electrical breakdowns, thereby extending the operational lifetime of the device. In contrast, smaller peak-to-peak amplitudes can be advantageous in applications requiring compact form factors, rapid response times, or high-precision actuation, where only minimal deformation is desirable. Therefore, the peak-to-peak amplitude may be tuned during fabrication or by structural design to optimize the transducer’s performance for actuation, sensing, or energy harvesting tasks.

[0058] Moreover, the transducer element can be configured, such that the peak-to-peak amplitude is associated to a ratio, the ratio obtained by dividing the length of the transducer element when extended, to the length of the transducer element in the corrugated state, wherein the length is the length along the axis of the elevations and depressions.

[0059] In addition, the transducer element can be configured, such that the ratio is larger than 1.05, preferably larger than 1.1, more preferably larger than 1.15, such as 1.2. Certain ratios can be associated with specific levels of mechanical stretchability and energy absorption characteristics. A higher ratio indicates a greater degree of stored mechanical potential due to the corrugated geometry, allowing the transducer to undergo more substantial elongation before the electrode becomes fully extended. This can be particularly advantageous in actuation scenarios requiring large stroke lengths or dynamic range. Furthermore, a higher ratio enables the device to operate at lower internal mechanical stress during initial stages of actuation, thereby minimizing material fatigue and improving operational lifespan. In energy harvesting applications, a larger ratio can allow for greater deformation under external forces, which translates into increased electrical output due to the larger capacitance variation. Conversely, more moderate ratios may be preferred in precision sensing applications, where linearity, response time, and compact geometry are more critical. Thus, the ratio serves as a tunable design parameter, allowing optimization of the transducer element's mechanical and electrical performance across diverse applications.

[0060] In embodiments, the Young’s modulus of the flexible film is larger than the Young’s modulus of the elastic body, such as a Young’s modulus being at least two times larger, preferably 10 times larger, more preferably 25 times larger, most preferably 50 times larger, such as between 10 and 100 times larger, or even more than 100 times larger, such as even more than 1000 times larger, or even larger than that. In embodiments, the flexible film may have a Young’s modulus of 1 GPa and the elastic body may have a Young’s modulus of 50 kPa.

[0061] Having a Young’s modulus of the flexible film being larger than the Young’s modulus of the elastic body may support an increased corrugated state.

[0062] A broad range of materials can be used as electrodes for transducers, from simple metals to complex hierarchical composites of conducting particles in insulating support materials such as elastomers and adhesives, which may be applied in homogeneous layers or arranged in patterns, e.g. by printing. Electrodes having a thickness above 1 micrometres may also be suitable, e.g. at least up to 200 micrometres. Electrodes may have adhesive properties to ensure the integrity of some transducer architectures, e.g. a stack, where an externally applied force pulls on the ends of the stack.

[0063] Not all relevant electrode materials are self-clearing. When self-clearing is sought, the electrode material should be thin, e.g. having a thickness in the range of 1 nanometres to 10 micrometres, depending upon the specific material. The stiffness of the electrode material is rarely well-defined for self-clearing electrodes, as it depends both on the nature of the material itself, it’s structure and the method by which it was applied.

[0064] The electrode can be made of any pure or composite material capable of conducting electricity. The electrode may be provided as a film, network or mesh, in embodiments the electrode material is a metal, metal oxides, semiconductors, semiconductor oxides, metal alloys or alloy oxides, carbon allotropes and their precursors. The materials can be provided as homogeneous films or as particulates such as flakes, wires, horns, brushes, networks, agglomerates, where the residual particle may have a dominant feature size between 1 nm to several micrometres, e.g. a graphene flake having a thickness of a few atomic layers and a diameter of several 100 micrometres. Homogeneous or particulate material may consist of metals, metal oxides, semiconductors, semiconductor oxides and carbon allotropes, or their precursors. Further, said particulates may be provided in a composite comprising a matrix of elastomer, adhesive or gel material.

[0065] The electrode may in embodiments be deposited onto the flexible film in a step prior to the fabrication. This is advantageous as the flexible film and the electrode can be handled separately as a unit and, e.g., rolled up for easy further handling. When an electrode is made of a thin metal film, the flexible film provides an advantage in that it can provide a stable substrate for metal deposition, contrary to elastic bodies which may have a surface which is more difficult for metal deposition due to having a lower mechanical surface stability and high surface roughness. Further deposition of an electrode onto a flexible film may generally be faster than when deposited onto an elastic body due to easier handling of a flexible film web.

[0066] In embodiments the electrode may however also be deposited onto the flexible film during fabrication of the transducer element. The electrode may be provided by such techniques as vapor deposition or spraying, and may be provided as a continuous layer or masked, e.g. in a photolithographic or shadow patterning. Further methods of application of electrodes include reel-to-reel or web-based methods where conductive adhesive is provided as a transfer tape, suitably pre-cut using dies, or where conductive material including composites is deposited using known printing methods including inkjet, flexo, screen, litho, or gravure.

[0067] The electrode may be provided in a manner so that it is not covering the entire surface of the flexible film. The electrode may typically be uniformly provided over the surface of the flexible film to increase the durability of the expansions and compressions of a working transducer, however a pattern may be provided, the pattern may be provided during fabrication or in a prior step. Electrodes may be provided having locally varying thickness, e.g. for the purpose of adjusting the electrode properties on edges of an electrode area. The edges of an electrode may be deposited in such a way that conductivity is reduced or tapering in a suitable zone or area near edges of an electrode, which can be achieved by reducing or tapering the deposition thickness on the edges. The reduced conductivity on the electrode edges suppresses edge concentration of the electric field and thereby minimizes or mitigates localized electrical erosion or degradation related to such electric field concentration.

[0068] In embodiments, the electrode has a maximum thickness between 1 nanometres to 200 micrometres. An actual thickness may be selected depending on use case. A thin electrode supports better self-clearing, which may be advantageous for actuation. A thick electrode increases conductivity, which may be advantageous when the transducer is used to generate electrical energy.

[0069] Several electrode materials may be combined at various steps during manufacture of a transducer, serving such purposes as ensuring a moderate amount of conductivity between adjacent electrodes, to transfer mechanical loads between adjacent electrodes and throughout a multi-layer or stack actuator, to enable layer-to-layer electrode rail connection, and to facilitate attachment of electrical wire lead components for suitable mechanical strength and electrical conductivity.

[0070] A first flexible film having a first coated electrode may be combined with a second flexible film having a second coated electrode. The combination may be such that the electrodes face each other while the flexible films face away from each other, so that the electrodes are mostly sandwiched by the flexible films. The electrodes may be attached to each other by means of a suitable adhesive, ensuring a strong bond capable of transferring mechanical load. Electrical connectivity between the two electrode layers while maintaining advantageous self-clearing is enabled by use of an adhesive that includes a low volume concentration of conducting particles, such that the adhesive is electrically insulating in the planar directions and electrically conducting in the direction between the electrodes, a property commonly referred to as anisotropic z-axis conductivity.

[0071] The surface of the transducer element may in embodiments be coated to cover the electrode and the upper surface or lower surface of the flexible film, to provide encapsulation of a transducer in relation to electrical safety.

[0072] In an embodiment, the transducer element is in a roll configuration, the roll configuration having a substantially cylindrical shape, wherein the roll configuration comprises a first and a second base. The roll configuration may be obtained by spirally winding a flat or multi- layered laminate around a central axis to form a compact cylindrical structure. A laminate is consisting of alternating dielectric and electrode layers, optionally with additional adhesive, spacer, or insulating films. The first and second base may correspond to the axial end faces of the cylinder, and may serve as mechanical interfaces or electrical contact zones.

[0073] This substantially cylindrical geometry may facilitate space-saving deployment in compact actuation or sensing applications. The roll may be configured such that electrode layers are exposed at the ends for terminal connections, or electrically connected internally and encapsulated externally.

[0074] Rolling the transducer into a substantially cylindrical configuration may allow the transformation of planar actuation forces into axial or radial movement, depending on boundary conditions. This makes the design suitable for applications such as artificial muscles, compact linear actuators, or tubular pumps. The design may also benefit from inherent mechanical stability along the radial axis, and may be robust against local defects due to the distributed layering.

[0075] In an embodiment, the roll configuration is in a compression mode, wherein the compression mode for example relates to an application of an external force, for example parallel to the first and second base. The compression mode may be defined as a mechanical loading condition in which the roll structure is compressed along its longitudinal axis, i.e., the axis perpendicular to the first and second base, thereby reducing the axial length of the cylindrical transducer, and expanding its diameter and circumference as shown in Fig. 10.

[0076] External compressive force may be applied using a fixed-weight load, spring mechanism, or rigid fixture. The compressive force may be constant, variable, or even passively regulated based on environmental conditions. The compression mode may result in mechanical buckling or wrinkling within the actuator layers, particularly in the direction perpendicular to the applied load. These mechanical deformations may act as compliant energy reservoirs, enabling the actuator to extend when voltage is applied and internal electrostatic forces are generated.

[0077] Operating in a compression mode may allow the transducer to convert internal actuation pressure into axial expansion against the applied load. This mode of operation may be particularly suitable for high-displacement or load-bearing applications, such as lifting elements, compliant grippers, or vertical actuators. Furthermore, the compression mode may improve mechanical compliance, reduce stiffness in the direction of motion, and support reversibility of actuation over many cycles. A further advantage of the compression mode is that if the transducer element is placed in an enclosed space, it can be beneficial to have it in compression mode in order to ensure that its enlarged circumference can fit the enclosed space.

[0078] Moreover, the compression mode may relate to a length reduction of the transducer preferably larger than 5%, or larger than 10%, or larger than 15%, such as 20%. The length reduction refers to the difference between the relaxed (uncompressed) axial length of the roll and its length under compression. This reduction may arise from the externally applied load that establishes the compression mode. Different length reductions may be used depending on the type of application.

[0079] The extent of length reduction may be adjusted during assembly, or dynamically applied using a spring-based housing or load-adjustable frame. In some implementations, the actuator may be preloaded during installation into a device, thereby achieving the compression state passively during operation. The use of controlled length reduction may also be combined with feedback systems to actively tune the actuation profile. After the application of an external force, a voltage may be applied on the ends of the transducer, resulting in an expansion of the transducer element. By turning on and off the voltage, a repeated expansion / shrinkage of the transducer can be achieved. Such a process forms an actuator.

[0080] In one embodiment of the present disclosure, the elastic body is pre-strained. The pre-strain in this context refers to the initial mechanical deformation applied to the dielectric elastomer material before the transducer is rolled into the cylindrical configuration. Pre-strain may be applied uniaxially, for example along the rolling direction, or biaxially across the film surface, depending on desired wrinkle orientation and actuation characteristics.

[0081] Pre-straining the elastic body prior to rolling may result in the formation of internal stress fields that facilitate wrinkling or buckling under compressive loads. The pre-strain may enhance the electromechanical coupling efficiency, promote strain-hardening behaviour, and prevent uncontrolled thinning or rupture during operation. The magnitude of pre-strain may be selected based on material type, mechanical properties, and expected operating voltages. Pre-strain may be implemented using stretching frames, web tension in roll-to-roll processing, or pre-tensioned laminates. It may also be combined with selective curing to lock the pre-strained geometry into place.

[0082] In an embodiment, the roll configuration comprises a cavity in the center of the substantially cylindrical shape. The cavity may be defined as an axial void within the core of the rolled structure and may extend along the full length of the cylinder. This cavity may be formed during rolling by using a central mandrel, a removable insert, or by wrapping around a soft, deformable core. The cavity may remain empty or be filled with a compliant material that does not significantly impede deformation.

[0083] The presence of a central cavity may provide space for inward material displacement when the roll is compressed, allowing the outer layers to shift towards the center. This displacement mechanism may help form wrinkles and relieve mechanical constraints imposed by surrounding electrode films. Importantly, the presence of the cavity can be beneficial as it enables the application of a voltage in order to perform actuation tasks. The cavity may thus act as a volume buffer that enables radial compliance and facilitates axial actuation in compression mode.

[0084] Furthermore, the cavity may also serve as a mechanical interface, allowing the transducer to be mounted around a rod or shaft. In some implementations, the cavity may be part of a fluidic or pneumatic system, or may accommodate sensing elements, optical fibers, or wiring.

[0085] In addition, the cavity may comprise air and / or a polyolefin material, such as polypropylene foam. The polyolefin material may be introduced during the rolling process as a core insert, or it may be moulded or extruded separately and inserted into the cavity after rolling. Polypropylene foam may be selected for its combination of mechanical compliance, thermal stability, chemical resistance, and low cost. Other polyolefin foams, such as polyethylene or ethylene-vinyl acetate, may also be used depending on the mechanical demands and processing methods. Filling the cavity with a soft foam core may provide structural support while still allowing sufficient deformation to enable actuation. In one embodiment of the present disclosure, the transducer element comprises a stack of transducer elements, wherein each transducer element arranged on a dielectric layer. The dielectric layers may be used to separate the various transducer elements from one another. In an embodiment, the elastic body on each transducer element can act as a dielectric layer, therefore there may not be a need for an additional dielectric layer. The stack configuration may include any number of individual transducer elements, wherein each element includes a flexible film with an electrode and an underlying elastic body, as described herein. The dielectric layer may act as both an electrical insulator and a mechanical spacer, and may be provided as a separate sheet or as an integral part of an electrode film. The dielectric material may be selected from polymeric materials such as polypropylene, polyethylene terephthalate (PET), polyimide, or silicone-based elastomers, optionally reinforced with fillers to modify mechanical or dielectric properties.

[0086] The stacking of multiple transducer elements, optionally arranged on dielectric layers, may be implemented as a laminated ribbon or module, prepared via roll-to-roll manufacturing or by individual layer-by-layer assembly. Each layer may be aligned mechanically and electrically to form a compact actuator unit. This stacked configuration may enable the actuator to generate higher force or displacement for a given excitation compared to a singlelayer design. It may also allow for modular control of actuation by selectively addressing subsets of layers, for example in multi-degree-of-freedom actuation schemes. The design may be particularly suitable for applications requiring compact form factors with high output, such as haptics, robotics, medical devices, or soft automation systems.

[0087] The dielectric layers may be designed to support electric field isolation between electrodes, ensuring that actuation remains confined within desired active regions. Thickness and material composition of each dielectric layer may be tailored to balance mechanical compliance and electrical insulation. In some implementations, adhesive layers may be integrated between dielectric layers and transducer elements to provide additional bonding strength and environmental sealing. The stacking approach may support symmetric or asymmetric designs, depending on whether identical transducer elements are used throughout the stack or varied according to function or location.

[0088] Moreover, the distance between adjacent dielectric layers can preferably be less than 10 mm, or less than 5 mm, or less than 1 mm, or less than 50 pm, or less than 10 pm. This distance refers to the spacing between the planar surfaces of adjacent dielectric layers that separate the transducer elements within the stack. The spacing may be determined by the thickness of intermediate materials, such as elastomer films, adhesives, or structural spacers. The distance can also be described as interlayer distance. Controlling the interlayer distance may be achieved through lamination techniques, pressure-based compression during assembly, or use of fixed-thickness interleaving sheets. Reducing the distance between layers may increase the overall packing density of the actuator, improving volumetric efficiency and energy density. When the spacing is minimized, the effective actuation force per unit volume may be enhanced due to the closer proximity of active elements. A smaller spacing may also improve thermal dissipation across the stack, especially in high-duty-cycle applications. Additionally, close interlayer spacing may contribute to mechanical robustness and reduce susceptibility to layer delamination under cyclic loading.

[0089] The target interlayer distance may vary based on the intended operating voltage, dielectric breakdown strength of the materials used, and desired mechanical stiffness. For example, in applications operating in low voltage ranges, dielectric layers may be as thin as 50 pm to 200 pm, allowing for sub-millimeter spacing. In higher-voltage applications, thicker dielectric spacers may be employed while still maintaining spacing below 5 mm. These values may be tailored through empirical testing or simulation to ensure safe operation while maximizing performance.

[0090] In an embodiment, a first group of the stack of transducer elements are horizontally retracted towards a first direction, such that the first group of the stack of transducer elements is in contact with a first electrode, and wherein a second group of the stack of transducer elements are horizontally retracted towards a second direction, such that the second group of the stack of transducer elements is in contact with a second electrode. The term “horizontally retracted” refers to the displacement or offset of electrode-bearing films or layers in the plane of the stack, such that selected electrodes terminate short of one edge of the stack while extending fully to the opposite edge. This retraction may be implemented during lamination by using staggered alignment of electrode films, patterned deposition, or by trimming after lamination.

[0091] This alternating exposure pattern allows electrical contact to be made from the sides of the stack, enabling group-wise electrical connection of electrode layers. In this way, multiple layers can be connected in parallel or series, depending on the desired electrical configuration. Side contacts may be formed using conductive cladding materials, such as silver-loaded pastes, carbon-based coatings, curing dispensed liquid tracks, or printed metallic traces. These materials may be applied post-assembly to the exposed sides of the stack using brushing, dispensing, or stencil printing. Curing dispensed liquid tracks can be understood as using a liquid precursor to a soft electrically conductive material to be dispensed as one or more patterns, thereby connecting a plurality of electrodes. Having a plurality of individual curing dispensed liquid tracks may enhance reliability of the transducer.

[0092] The configuration may support actuation schemes where the entire stack is energized simultaneously, thereby maximizing force or displacement, or where only subsets are addressed for independent control. The use of side contacts may simplify wiring and reduce the need for through-layer vias or other complex electrical interconnects. It may also allow better thermal and electrical integration with external circuitry. This approach may be especially beneficial in stacked actuators used in wearable devices, compact robotics, or embedded systems where lateral access is preferable to vertical access.

[0093] In an embodiment, the horizontal retraction is preferably less than 5 mm, or less than 2.5 mm, or less than 1 mm, such as 0.5 mm. This dimension refers to the extent of lateral offset of each electrode layer from the stack edge, as described above. Keeping the retraction distance small may be advantageous for several reasons. It minimizes inactive edge regions that do not contribute to actuation, thus increasing the proportion of active material within the overall device footprint. This may improve the mechanical and electrical efficiency of the stack. Moreover, smaller retraction distances may reduce the amount of conductive or insulating cladding material required to interface with the electrode layers, simplifying assembly and reducing material costs. It may also allow a higher density of actuating layers per unit width, which may be beneficial when scaling up force output or packing multiple stacks in parallel. Additionally, minimal retraction may reduce the risk of edge-related electrical failures, such as arcing, especially when insulating cladding is applied promptly and uniformly to seal the stack sides.

[0094] The retraction distance may be implemented through design of the electrode film layout or trimming processes during assembly. Precision control over this dimension may be achieved through laser cutting, mechanical die-cutting, or patterned printing of electrodes. The actual retraction value selected may depend on the tolerances of the manufacturing process, the viscosity of cladding materials, and the desired mechanical overlap between adjacent components in the assembled actuator.

[0095] In one embodiment of the present disclosure, one or more of the transducer elements in the stack is pre-strained. The term “pre-strained” refers to the mechanical stretching of the elastic body or the dielectric elastomer before or during assembly. The pre-strain may be introduced uniaxially or biaxially, and may range from a few percent up to several hundred percent, depending on the properties of the elastomer material. Pre-straining may be achieved using frame stretching, web tensioning in roll-to-roll processing, or clamp-based mechanical fixtures.

[0096] The introduction of pre-strain may improve actuation performance by increasing the initial stored elastic energy. In particular, as described herein, pre-strain can promote wrinkle formation upon compression, allowing for greater compliance and reversible actuation in configurations such as hollow rolled actuators or stack-based compression actuators. Pre-strain may be applied selectively to certain layers in the stack to create mechanical asymmetries or to localize actuation.

[0097] Furthermore, each of the electrodes of the stack of transducer elements may be arranged to face towards the same direction. In this context, the "facing direction" refers to the orientation of the conductive surface (e.g., electrode) of the transducer element relative to the stack. When all conductive surfaces face the same direction, such as all upwards or all downwards, the electrical layout may be simplified, and insulation strategies between opposing electrodes may be standardized.

[0098] Uniform orientation of electrode films may facilitate consistent stacking, reduce the chance of alignment errors, and minimize unexpected short circuits between layers. It may also ensure that every dielectric elastomer layer is consistently insulated on one side by the polymer carrier of the electrode film, reducing the likelihood of leakage currents. This may be particularly useful when employing thin metallized films that have sharp edges or variable coverage. The electrode films may be stored on reels and fed through the lamination process such that orientation is preserved throughout.

[0099] The present disclosure further relates to a method of fabrication of a transducer element comprising the steps of providing an elastic body, the elastic body comprises a first surface and a second surface, providing a flexible film with an upper surface and a lower surface, providing an electrode attached to the flexible film at the upper surface or lower surface, attaching the flexible film with the electrode, the flexible film being attached to the first surface of the elastic body, thereby forming a transducer element, and optionally repeating the above steps at least once and stacking consecutive transducer elements, thereby obtaining a multi-layer transducer element. By performing such a process, it is possible to create multilayer transducer elements where the elastic bodies are not pre-strained. As a result, an external force can be applied parallel to the surface of the electrodes, thereby compressing the transducer element and forming a corrugated structure to the electrodes. Then, a voltage difference can be applied between electrodes, thereby de-compressing the transducer element and effectively forming an actuator.

[0100] The present disclosure also relates to a method of fabrication of a transducer element comprising the steps of providing an elastic body, the elastic body comprises a first surface and a second surface, providing a flexible film with an upper surface and a lower surface, providing an electrode attached to the flexible film at the upper surface or lower surface, attaching the flexible film with the electrode, the flexible film being attached to the first surface of the elastic body, thereby forming a layer of a transducer element, and rolling the transducer element, thereby obtaining a substantially cylindrical transducer element in a roll configuration.

[0101] The present disclosure further relates to a method of fabrication of a transducer element comprising: pre-straining an elastic body into a pre-strained state, the elastic body comprises a first surface and a second surface; provide a flexible film with an upper surface and a lower surface; provide an electrode attached to the flexible film at the upper surface or lower surface; while the elastic body is maintained in the pre-strained state attach the flexible film and the electrode, the flexible film being attached to the first surface of the elastic body; relax the elastic body from the pre-strained state to obtain a corrugated state of the electrode, the corrugated state having elevations and depressions, and wherein the corrugated state is provided by a compression force of the elastic body.

[0102] As an alternative to relaxing the elastic body from the pre-strained state to obtain a corrugated state of the electrode, the compression force may be provided by an externally applied force. Such externally applied force may be provided by placing the transducer element into a structure that provides externally applied mechanical force.

[0103] One advantage of the method of fabrication is that the electrode is provided onto the flexible film and not directly onto the elastic body. In this manner the fabrication steps of the transducer elements can be handled separately in different manners. In particularly the handling of the electrode can be handled separately.

[0104] In an advantageous embodiment, the flexible film comprises an electrode being attached in a prior step. In this manner the flexible film and the electrode may be fabricated in a prior step to form a compound.

[0105] While it may be advantageous to fabricate the flexible film and the electrode as a compound in a prior step, there may nevertheless be situations where the electrode is attached at a surface of the flexible film during fabrication of the transducer element prior to relaxing the elastic body.

[0106] In embodiments, a stack of transducer elements may be provided, wherein at least two transducer elements in the stack are of a different material and / or of a different thickness and / or is pre-strained with different strains. By stacking up transducer elements, the flexible response of the combined transducer elements of the stack may be tailor very precisely and fine-tuned to a particular use case.

[0107] The elastic body, or elastic bodies in a stack, may, or may each, be pre-strained in a first and a second orthogonal direction. The pre-straining in the orthogonal directions may be of same or different strains. In an embodiment, the pre-straining in a longitudinal direction may be larger than the pre-straining in a transverse direction. In an embodiment, the method further comprises the step of using one or more liners to separate transducer elements during fabrication of a plurality of transducer elements, wherein each liner is configured to carry electrodes, flexible films, or elastic bodies. The term "liner" may refer to a flexible or semi-rigid sheet, web, or carrier material that facilitates the transport, positioning, or temporary support of one or more transducer components during fabrication. The liner may be made of polymeric materials such as PET, polyimide, silicone- coated paper, or fluoropolymer films, and may have surface properties tailored for adhesion control, release behaviour, or dielectric insulation.

[0108] Each liner may be pre-configured or prepared in-line to carry specific functional layers. For instance, a liner may serve as a carrier for a flexible film that has been pre-metallized to form an electrode, or it may support a dielectric elastomer sheet with a pre-applied adhesive. Liners may also be used to handle elastic bodies during pre-stretching and lamination steps, particularly in roll-to-roll or web-based manufacturing. In some embodiments, a liner may comprise surface textures, registration marks, or patterns to ensure accurate layer alignment. The use of liners may also enable partial or selective release of specific layers at defined stages in the process, for example to expose electrodes for electrical contact.

[0109] The use of liners may support modular and scalable fabrication by providing clean separation between adjacent transducer units. This separation may allow for easy cutting, handling, or stacking without cross-contamination or mechanical damage. Liners may further serve as temporary dielectric barriers or tensioning media during winding, pressing, or curing operations. In high-throughput production environments, liners may be continuously fed through lamination stations, UV-curing chambers, or nip rollers, and may be rewound or discarded after use. In some configurations, liners may remain part of the final product, for example as encapsulating or insulating boundary layers, or they can be discarded.

[0110] In an embodiment, the method further comprises the step of utilizing a reel-to-reel process, roll-to-roll process, and / or a sheet-to-sheet process to fabricate a plurality of transducer elements. These fabrication techniques refer to continuous or semi-continuous production processes commonly used in flexible electronics, film-based components, and web-laminated systems. A roll-to-roll process may involve feeding material layers from one roller (unwinder) to another (rewinder) through a series of processing stations, including lamination, coating, printing, stretching, curing, and cutting. A sheet-to-sheet process may instead process discrete panels or segments using pick-and-place, press-based, or vacuum table systems.

[0111] The reel-to-reel or roll-to-roll configuration may be used to fabricate a multi-layer laminate comprising alternating dielectric elastomer films and electrode films. Each layer may be introduced onto a moving web using rollers, tensioning devices, and precision registration mechanisms. This setup may allow for simultaneous lamination of several hundred meters of film, significantly improving throughput compared to manual or batch processes. For example, electrode films carried on liners may be laminated onto pre-stretched elastomer webs using pressure rollers. Intermediate adhesive layers may be applied via slot-die coating or flexographic printing units integrated within the same line.

[0112] The roll-to-roll process may support incorporation of pre-stretch by using tension zones in the elastomer handling section. Alternatively, mechanical stretching units such as gripper frames or expansion mandrels may be used in a modular layout. At defined intervals, the web may be transversely cut to form discrete rectangular or custom-shaped transducer modules, which may then be stacked, rolled, or integrated into cylindrical devices.

[0113] Utilizing reel-to-reel or sheet-based processes may reduce manufacturing cost per unit, improve consistency of layer thickness and alignment, and enable inline quality control (e.g., via machine vision or electrical inspection). These processes may also facilitate integration of cladding layers, electrode patterning, and terminal connection steps in a continuous flow.

[0114] The present disclosure further relates to a transducer comprising: a transducer element compound of a first transducer element in accordance with an embodiment provided in accordance with the first aspect and a second transducer element in accordance with an embodiment provided in accordance with the first aspect, wherein the first transducer element is combined with the second transducer element by attaching the second surface of each transducer element to each other, thereby providing a transducer compound with an electrode pair with a first electrode and a second electrode, or, a first transducer element in accordance with an embodiment provided in accordance with the first aspect, the first transducer element further comprising: a second flexible film with an upper surface and a lower surface, wherein the lower surface of the second flexible film is attached to the second surface of the elastic body; a second electrode attached to the second flexible film at the upper surface or lower surface; wherein the second electrode is in a corrugated state having elevations and depressions, and wherein the corrugated state is provided by a compression force of the elastic body, thereby providing a transducer compound with an electrode pair with a first electrode and a second electrode.

[0115] A transducer of the type being based on electrostatic attraction between two electrodes located on each side of an elastic body to provide a compression of the body in a first direction and a corresponding extension of the body in a second direction, naturally needs two electrodes, one on each side of the elastic body. In the transducer element according to the first and the second aspect of the invention a single electrode is provided on one side of the elastic body. In order to provide two electrodes, two transducer elements are combined by attaching the two transducer elements to each other, thereby providing a transducer compound with an electrode pair between two elastic bodies (or stack of elastic bodies).

[0116] Alternatively, two flexible films each with an electrode is provided on either side of an elastic body (or stack of elastic bodies).

[0117] A transducer may in embodiments comprise a number of transducer element compounds in a predefined arrangement and wherein the electrode pairs of at least a some of the transducer compounds are electrically connected together.

[0118] For a stack of transducer elements, a transducer with a number of transducer element compounds and / or a number of transducer element compounds in a predefined arrangement may advantageously be arranged in a manner where the compression force arises from an externally applied force to the stack of elastic bodies, to the transducer element compounds and / or to the number of transducer element compounds in the predefined arrangement. One or more externally applied forces may for example be provided to one or more sides of a stack of elastic bodies, the transducer element compounds and / or the number of transducer element compounds in a predefined arrangement.

[0119] A transducer element can be obtainable by the process according to any of the methods of fabrication described herein. In an embodiment, a transducer element can be obtained by prestraining an elastic body into a pre-strained state, the elastic body comprises a first surface and a second surface, providing a flexible film with an upper surface and a lower surface, providing an electrode attached to the flexible film at the upper surface or lower surface. Then, while the elastic body is maintained in the pre-strained state, the flexible film can be attached to the electrode, where the flexible film is attached to the first surface of the elastic body. Then, the elastic body can be relaxed from the pre-strained state to obtain a corrugated state of the electrode, the corrugated state having elevations and depressions, and wherein the corrugated state is provided by a compression force of the elastic body. In another embodiment, as also described in the previous paragraphs, a transducer element can be obtained without any pre-straining of the elastic body. Instead, an external force can be applied on the transducer, thereby triggering a compression force by the elastic body towards the electrode, forming a corrugated structure on the electrode. Such a corrugated structure can be utilized as an actuator, since by applying a voltage it is possible to extend and retract the corrugations.

[0120] In general the various aspects of the present disclosure may be combined and coupled in any way possible within the scope of the present disclosure. These and other aspects, features and / or advantages of the present disclosure will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0121] BRIEF DESCRIPTION OF THE DRAWINGS

[0122] Embodiments of the present disclosure will be described, by way of example only, with reference to the drawings, in which

[0123] Fig. 1 schematically illustrates the principle of an actuator;

[0124] Fig. 2 schematically illustrates an elastic body;

[0125] Fig. 3 schematically illustrates an embodiment of a fabrication a transducer element; Fig. 4 illustrates an embodiment with two flexible films each with an electrode attached;

[0126] Figs. 5 and 6 schematically illustrate embodiments of a transducer;

[0127] Fig. 7 schematically illustrates stacking of transducer elements;

[0128] Fig. 8 schematically illustrates a transducer element where the compression force arises from an externally applied force; and

[0129] Fig. 9 schematically illustrates examples of transducers comprising a plurality of transducer compounds in a predefined arrangement.

[0130] Fig. 10 schematically illustrates a transducer element in a roll configuration.

[0131] Fig. 11 schematically illustrates a transducer element in a roll configuration comprising a cavity.

[0132] Fig. 12 schematically illustrates a stack of transducer elements.

[0133] Fig. 13 schematically illustrates sets of transducer elements stacks.

[0134] DESCRIPTION OF EMBODIMENTS

[0135] Fig.l schematically illustrates the principle of an actuator where an insulating dielectric elastic body 1 is placed between two electrodes 2 which upon application of an increased voltage difference 3 between the two electrodes cause an attraction between the two electrodes resulting in a shape change of the elastic body. By a controlled variation of the voltage difference the shape change can be controlled and the system used as an actuator. In a reverse situation, by imposing a shape change of the elastic body, a changed voltage difference can be detected / generated, and the system can be used as a sensor or a generator. Fig. 1 A illustrates a situation with a low, or no, voltage difference between the electrodes and Fig. IB illustrates a situation with a higher voltage difference between the two electrodes, leading to a stretching of the elastic body due to the increased attraction of between the electrodes causing the electrodes to move closer together imposing the shape change of the elastic body. Figure 1 illustrates the basic principle of an electroactive polymer transducer. Embodiments of the present invention relate to aspects of such a transducer as will be disclosed in the following.

[0136] Figure 2 schematically illustrates an embodiment of a transducer element 20 in accordance with the invention. The transducer element comprises an elastic body 1 with a first surface 21 and a second surface 22. Attached to the first surface is a flexible film 23. The flexible film has an upper surface 24 and a lower surface 25, and the lower surface of the flexible film is attached to the first surface of the elastic body. An electrode 26 is attached to the flexible film at the upper surface. The electrode 26 is wrinkled in a corrugated state having elevations and depressions, the corrugated state is provided by a compression force of the elastic body. The corrugated state is generated by a force applied by the elastic body to the elastic film and to the electrode. Embodiment of how to provide a compression force from the elastic body is disclosed below. In general a compression force pulls the elastic body towards a reduced size and by ensuring a sufficiently strong adhesion between the flexible film and the elastic body the compression force compress the flexible film, curling it up, leading to the corrugated state, which again from the adhesion between the flexible film and the elastic body impose the shape of the corrugated state upon the surface of the elastic body.

[0137] Figure 2 illustrates a transducer element with only one electrode, however by way of comparison with Fig. 1 A and Fig. IB it can be envisaged that as two electrodes attract each other the stretching of the elastic body will induce a stretching of the flexible film and the electrode. By having the electrode in a corrugated state when the elastic body is in a relaxed state, the electrode can accommodate to the elastic body in a stretched state without breaking. In a similar manner, when an external force is applied to compress the elastic body, the electrode becomes corrugated. As the external force is removed and the elastic body stretches back to a less compressed or relaxed state, the electrode can smoothly accommodate this shape change by unfolding its corrugations. This allows the electrode to remain intact and conform to the elastic body without mechanical failure during the expansion phase.

[0138] The corrugations arise as a subtle interplay between the mechanical energy available in the elastic body to laterally compress the flexible film attached to its surface. The energy is related to the hyper-elastic properties, as signified by the Young’s modulus at low strain and a non-linear behaviour at higher strains, of the elastic body, and the amount of lateral strain (compressive or tensile). The Young’s modulus is also known as elastic modulus, and together with the hyper-elastic properties these mechanical properties are commonly described, for simplicity, as the stiffness of an object. The wavelength of the corrugations is related to the ratio of the stiffness of the flexible film and the elastic body, as well as the thickness of the flexible film. Shorter wavelengths are obtained when the flexible film is thinner and when the ratio between the stiffness of the flexible film and the elastic body is lower. The amplitude is proportional to the wavelength and is related to the strain difference between flexible film and elastic body, the strain difference which may be applied as initial pre-stretch or as subsequent external compression. Hence, the amplitude may vary during operation and become zero when the flexible film is fully stretched.

[0139] When the transducer element is used for purposes of actuation, it may be advantageous to employ materials of such mechanical properties as to reduce the overall thickness of the elastic body material, as this will generally enable a lower operation voltage. When the transducer element is used for purposes of generation of electrical energy, the operation voltage can be higher to reduce conversion or transmission losses. Higher operation voltages may permit higher thickness of the transducer element and also larger wavelength of the corrugations. The wavelength of corrugations may depend upon material properties and the application, and preferably be in the range from 100 nanometres to 10 millimetres.

[0140] Depending on the use case of the final transducer, a suitable peak-to-peak amplitude 27 of the corrugations may be desired. A peak-to-peak amplitude of the corrugations between 1 and 10 micrometres may typically be selected.

[0141] The material of the elastic body 1 may be selected depending on the use case. In embodiments the elastic body is of a polymer material or an elastomer material, but other materials may be used. In embodiments, the thickness 28 of the elastic body is between 1 micrometres and 5 millimetres. The thickness depends on use case and working voltage. As an example, the elastic body has a relative permittivity between 1 and 10.000 at a penetrating time-varying electrical signal of one hertz.

[0142] Figure 2 illustrates a single elastic body 1, in embodiments, the elastic body may be a stack of flexible bodies and the flexible film provided to the upper surface of the top elastic body. At least two flexible bodies in the stack may be of a different material and / or of a different thickness and / or is pre-strained with different strains, however, the flexible bodies may also be of same material. In such embodiment, the elastic body is thus provided as a compound of a stack of flexible bodies.

[0143] The material of the flexible film 23 may be selected depending on the use case. In embodiments the flexible film is a of a polymer material, an elastomer material, a polypropylene material or a PVDF material. In embodiments, the thickness of the flexible film is between 0.02 micrometre and 200 micrometres and may be selected based on the use case. It is desirable to reduce the flexible film thickness

[0144] Figure 3 illustrates a schematic embodiment of a method of fabrication a transducer element 1. In the illustrated embodiment, a fabrication process is illustrated where the elastic body is pre-strained when the flexible film and the electrode is attached to the elastic body, resulting in an elastic body being able to impose a compression force onto the electrode to obtain the corrugated state.

[0145] The figure illustrates two general steps, however in a typical method of fabrication more steps are present.

[0146] In Fig. 3 A the elastic body 1 is pre-straining by a force 30 into a pre-strained state. The flexible film 23 with the electrode 26 attached is provided as a pre-fabricated compound. The flexible film is provided in a relaxed state, or slightly strained state. The figure shows the flexible film as a sheet or layer, but may in embodiments be provided from a roll and rolled onto the pre-strained elastic body. Importantly, while the elastic body is maintained in the pre-strained state, the flexible film and the electrode is attached 31 to the elastic body.

[0147] Once attached, as schematically illustrated in Fig. 3B, the elastic body is relaxed from the pre-strained state resulting in a compression of the elastic body as a straining force is no longer provided. In this manner the corrugated state of the electrode is obtained.

[0148] In figure 3 the electrode is illustrated to be provided to the flexible film in a prior step. However, as long as the electrode is provided onto the film prior to relaxing the straining force applied to the elastic body, the electrode may be provided to the film during the fabrication of the transducer element. Figure 3 illustrates a pre-straining force 30 applied in one direction, in embodiments, the elastic body may be pre-strained in both a first and a second orthogonal direction.

[0149] In figures 2 and 3 the electrode is illustrated to be provided to the upper surface of the flexible film, however the electrode may also be provided to the lower surface of the flexible film. The electrode may in such embodiment be provided between the flexible film and the elastic body and thereby be in direct contact with the surface of the elastic body.

[0150] In an embodiment, a glue or another way of increasing the adhesion, may be provided between the flexible film and the elastic body.

[0151] Once the elastic body is relaxed from its pre-strained state, the flexible film and the electrode enter their maximally compressed configuration, forming the corrugated state, as shown in Fig. 2 and in Fig. 3B. At this point, the elastic body exerts a compression force on the flexible film. This force is counteracted by the internal restoring force of the flexible film, which inherently tends to return to its original, flat (relaxed) shape. However, due to the adhesion between the flexible film and the elastic body, the flexible film remains constrained and cannot expand back on its own. If however the electrode and the flexible film would not be adhered to the elastic body, then the electrode and the flexible film would return to their original un-corrugated state, as illustrated in the schematic of Fig. 3 A.

[0152] Fig. 4 illustrates an embodiment where two flexible films 23 A, 23B each with an electrode attached 26A, 26B are combined, e.g. by lamination, such that the electrodes are facing each other. The lamination may be performed by application of a suitably thin adhesive, which may be anisotropically conductive only in the z-direction, to one electrode on a flexible film, then bringing the second electrode on a second flexible film against it, e.g. using a reel-to- reel or plate-to-plate method, thereby a compound electrode is formed with mechanical integrity from the encapsulation within two flexible films. By z-direction is meant a direction that is along the thickness direction of the flexible films, elastic bodies. It may be advantageous to provide one or both flexible films with suitable openings or cut-outs, to support electrical connection to this compound electrode.

[0153] In figure 4 the electrode is provided as a compound 40 of a first electrode 26A attached to a first flexible film 23 A and a second electrode 26B attached to a second flexible film 23B to be provided 42 onto the elastic body 1. As shown, the first and second electrode / flexible film units may not completely overlap to create an exposed electrode connection area 41.

[0154] Figure 5 schematically illustrates a transducer 50. The transducer comprises two transducer elements 1. Each transducer element 1 are made in the same way as disclosed in connection with Fig. 3, to provide a first transducer element 1 and a second transducer element 1. The two transducer elements are combined by attaching the second surface of each transducer element to each other, thereby providing a transducer compound with an electrode pair 51 with a first electrode and a second electrode.

[0155] Figure 6 schematically illustrates an alternative embodiment of a transducer 60 where a single transducer element 1 is provide as disclosed in connection with Fig. 3. In a further fabrication step a second flexible film with a second electrode attached to the opposite surface of the elastic body. In this manner an electrode pair 61 with a first electrode and a second electrode is provided on opposite sides of the elastic body 1.

[0156] Figure 7 schematically illustrates stacking of transducer elements 20. In Fig. 7A two individual transducer elements are shown, and in Fig. 7B a number of transducer elements are stacked 70. In embodiments, the stack of transducers elements may be of same or different material and / or of same or different thickness and / or is pre-strained with same or different strains. Different materials, thickness, pre-strain may be used for finely tailoring the properties of the transducer stack.

[0157] As illustrated, each transducer element is partly covered with the electrode leaving an area 71 without electrode. In this manner a side of the transducer element (the side with the uncovered area 71) will not be in contact with the electrode if covered by a conductive layer, whereas the other side 72 will be in contract with the electrode if covered by a conductive layer.

[0158] In the transducer element stack 70, each transducer element in the stack is arranged so that the non-covered area is alternatingly arranged to the right and to the left. In this manner, an electrode connection can be made on each side, 73, 74 by covering the side of the stack with a conductive layer, to provide electrodes pairs of the transducer elements of the stack. Fig. 7C provides more detail to a possible hierarchy of electrical connections in a stack transducer suitable for actuation, but also being relevant as a generator or a sensor. A plurality of elastic bodies A provides the bulk volume of the transducer. Electrode material B is provided on the surface of flexible film C, however, having been previously glued to a second electrode B and flexible film C by means of a thin layer D of z-axis anisotropically conducting adhesive. However, as illustrated by 41 in Fig. 4, an area of one flexible film may be left uncovered, such that an electrode material E can be applied to and connect electrically with an electrode B on a flexible film A, while the electrode material E may extend to one surface of the transducer. The electrode material E is characterized by being a solid, and by having a suitable electrical conductivity and a suitable mechanical stiffness. The electrode material E may connect to a surface electrode material F, which may be applied to one surface of the transducer to establish an electrical connection between a subset of electrode layers. In this manner, at least two separate subsets of electrodes are connected electrically to electrodes 75 and 76 on at least one surface of the transducer. The stack transducer may be coupled to an external mechanical feature at either surface 77 and 78, or it may be coupled at the surfaces indicated by 75 and 76. This enables coupling of mechanical force to the stack transducer along a z-direction or along an x or y direction, as is suitable for the application.

[0159] Figure 8 schematically illustrates a transducer element where the compression force arises from an externally applied force.

[0160] In Fig. 8A, a stack 80 of uncompressed transducer elements / transducer element compounds 81 is shown. At each end of the stack, connection elements 82 are attached. By externally apply a mechanical force 83, a resulting compression force 84 arises, as shown in Fig. 8B.

[0161] Figure 8C schematically illustrates that the actuator element may be used to lift a weight 85. By providing a voltage difference between the electrodes 86, 87 the weight can be lifted / moved in the vertical direction 88.

[0162] Fig. 8D schematically illustrates another actuator, where a voltage difference between the electrodes will result in the structures 89 move. Fig. 8E schematically illustrates yet another actuator, where the compression force is provided by springs 800, and where a voltage difference between the electrodes will result in the extension 801 of the structure along the vertical direction. Figure 9 schematically illustrates examples of transducers comprising a plurality of transducer compounds in a predefined arrangement. Electrode pairs of at least a some of the transducer compounds are electrically connected together. Electrode pairs are not illustrated but can be arranged in accordance with a desired type of actuation of the arrangement. The geometry of the transducer arrangement strongly influences the output properties.

[0163] A transducer may in embodiments be provided as a laminate of flexible films 90, 91 having electrodes in suitable predefined patterns and flexible bodies which are combined with suitable electrode materials, forming a multi-layer or stack configuration, which may be rolled up into a roll configuration. Such roll configuration is illustrated in Fig. 9A.

[0164] A transducer may in embodiments comprise a multitude of transducer elements, e.g. formed as a ribbon element 92 made by combining a multitude of elements, e.g. 32 active layers. A further layer (not shown) within the ribbon element may be a stretchable temperature sensor, which is electrically insulated from the actuator layers. The ribbon element thus formed may be millimetres thick. The ribbon element may be rolled in a flattened roll as illustrated in Figs. 9B and 9C, which are variants of a flattened roll. Such flattened roll can be combined with further flattened rolls to achieve an elongated transducer element, suitable for a robotic or automated production setup. In Fig. 9D two ribbons are alternately folded into the “paper spring” element, whereby adhesive between each layer in the paper spring ensures force can be transferred through this stack actuator element to actuate along the longitudinal direction of the transducer.

[0165] In an example, a silicone elastomer sheet having a thickness of 200 micrometres is prestretched by 50% in one direction, forming a pre-stretched elastic body. Beams are glued to the elastic body. Flexible films are made from a biaxially oriented cast polypropylene web having a thickness of 2.5 micrometres, which is sprayed with a carbon nanotube dispersion from a suitable solvent. The flexible films are placed on either side of the elastic body with electrodes facing out, taking care to land the flexible films to partially cover a suitable beam. A liquid precursor of an elastomer composite comprising conductive carbon black particles is used to glue metal foils to the flexible films resting on a beam, such that a flexible film, a beam and a metal foil form a solid combination. The two metal foils can be attached to an external electrical circuit capable of measuring capacitance, such that the transducer is capable of providing a macroscopic strain signal up to a strain of 50%.

[0166] In another example, an elastomer precursor comprising a filler which enhances the relative permittivity fills a nip between two rollers to allow a controlled coating thickness on one roller of 5 mm. The roller passes under a UV lamp which provides a partial curing of the elastomer precursor, which is adequate to allow the prepared web to be lifted from the roller. A suitable mechanism comprising a multitude of grabbers is capable of attaching to either of the free sides of the web, pulling it sideways and along the length of the web to build up a pre-stretch. A flexible film having a thickness of 10 micrometres is prepared with a metal alloy electrode having a thickness of 15 nanometres, and is provided on a reel. As the reel unwinds, it passes through a corona treatment station providing a thin silica coating of 15 nanometres thickness. An identical reel with an identical corona treatment is placed on the other side of the elastic body web. The three webs are brought together in a nip. The laminated web is carried under a strong UV source which cures the elastic body and creates a strong adhesive bond between the two flexible films and the elastic body, which is then wound up on a reel. The laminated is brought to a second station where it is suitably combined with a second such web, to encapsulate the high voltage electrode layer which is provided with an electrical lead. This web is wound on a mechanism which allows it to couple to ocean waves. With a suitable electrical control it is possible to generate electricity from ocean energy at voltage levels of 50 kilovolts.

[0167] In yet another example, a flexible film made of 0.9 micrometre of PEN is used. The flexible film is coated with an electrode consisting of 50 nm aluminium placed on a reel. An elastic body made of the material VHB 4905 from 3M is pre-stretched and attached to a stiff frame while the flexible film is attached. This results in a transducer element which by used of a switching voltage between 0 and 5000 V will cause the transducer to actuate with an actuation strain of about 5%-l 0%, depending upon the chosen prestretch and load.

[0168] Fig. 10 shows an example of a transducer element in a roll configuration 100. The roll configuration can be substantially cylindrical, comprising a first 101 and a second 102 base. A cross section of a roll configuration is shown 103, illustrating a possible way of biasing the transducer element with a voltage. Fig. 11 shows an example of a transducer element in a roll configuration comprising a cavity 110. The cavity may either be void 111, or the cavity may be filled with a material 112, such as polypropylene foam. As described herein, a purpose of the cavity is to accommodate the expansion of the transducer element when an external force is applied.

[0169] Fig. 12 shows an example of a stack of transducer elements 120 wherein a first group is retracted towards one direction 121 and a second group is retracted towards a second direction 122. As described above, electrodes can be used to selectively contact a number of the transducer elements, by utilizing the retraction process. For example, a positive electrode 123 can contact the first group, while a negative electrode 124 can contact the second group.

[0170] Sets of transducer element stacks may also be utilized to form an extended structure. Fig. 13 shows such an example, where a series of stacks of transducer elements 130 are connected by a conductive cladding layer 131. The conductive cladding layer may be a conductive paste or paint or similar flowable composite material that can be applied to the sides of the electrodes. As a result, the various electrodes can be connected together.

[0171] CLAUSES

[0172] The present disclosure and embodiments of the present disclosure are set out in the following numbered clauses:

[0173] 1. A transducer element comprising: an elastic body with a first surface and a second surface; a flexible film with an upper surface and a lower surface, wherein the lower surface of the flexible film is attached to the first surface of the elastic body; an electrode attached to the flexible film at the upper surface or lower surface.;

[0174] 2. The transducer element according to clause 1, wherein the electrode is in a corrugated state having elevations and depressions, and wherein the corrugated state is provided by a compression force of the elastic body.

[0175] 3. The transducer element according to any one of the preceding clauses, wherein the elevations and depressions comprise a peak-to-peak amplitude, wherein the peak-to- peak amplitude is larger than 1 pm, or larger than 5 pm, or larger than 10 pm, or larger than 50 pm. . The transducer element according to clause 3, wherein the peak-to-peak amplitude is associated to a ratio, the ratio obtained by dividing the length of the transducer element when extended, to the length of the transducer element in the relaxed state, wherein the length is the length along the axis of the elevations and depressions.

[0176] 5. The transducer element according to clause 4, wherein the ratio is larger than 1.05, or larger than 1.1, or larger than 1.15, such as 1.2.

[0177] 6. The transducer element according to any one of the preceding clauses, wherein the elastic body is strained resulting in a compression force acting from the elastic body to the electrode and to the flexible film, thereby shaping the electrode in a corrugated state.

[0178] 7. The transducer element according to any one of the preceding clauses, wherein an externally applied force acts on the transducer element, thereby resulting into a compression force configured to shape the electrode in a corrugated state.

[0179] 8. The transducer element according to any one of the preceding clauses, wherein the elastic body is stretchable above 5% and is having a Young’s modulus between 1 kPa and 100 MPa.

[0180] 9. The transducer element according to any one of the preceding clauses, wherein the elastic body is a polymer material, an elastomer material, a dielectric elastomer material, a chemically crosslinked elastomers, a physically crosslinked thermoplastic elastomers, an adhesive, or a gel.

[0181] 10. The transducer element according to any one of the preceding clauses, wherein a thickness of the elastic body is between 1 micrometres and 5 millimetres. 11. The transducer element according to any one of the preceding clauses, wherein the elastic body has a relative permittivity between 1 and 10.000 at a penetrating timevarying electrical signal of one hertz.

[0182] 12. The transducer element according to any one of the preceding clauses, wherein the elastic body is a stack of elastic bodies and wherein the flexible film is attached to the first surface of a top elastic body, optionally wherein at least two elastic bodies in the stack are of a different material and / or of a different thickness and / or is pre-strained with different strains.

[0183] 13. The transducer element according to any one of the preceding clauses, comprises a stack of transducer elements, optionally wherein at least two transducer elements in the stack comprise elastic bodies of a different material and / or of a different thickness and / or is pre-strained with different strains.

[0184] 14. The transducer element according to clause 13, wherein the compression force arises from an externally applied force to the stack of elastic bodies.

[0185] 15. The transducer element according to any one of the preceding clauses, wherein the transducer element comprises a stack of transducer elements, wherein each transducer element arranged on a dielectric layer.

[0186] 16. The transducer element according to clause 15, wherein the distance between adjacent dielectric layers is preferably less than 10 mm, or less than 5 mm, or less than 1 mm, or less than 50 pm, or less than 10 pm.

[0187] 17. The transducer element according to any one of clauses 15-16, wherein a first group of the stack of transducer elements are horizontally retracted towards a first direction, such that the first group of the stack of transducer elements is in contact with a first electrode, and wherein a second group of the stack of transducer elements are horizontally retracted towards a second direction, such that the second group of the stack of transducer elements is in contact with a second electrode. The transducer element according to clause 17, wherein the horizontal retraction is preferably less than 5 mm, or less than 2.5 mm, or less than 1 mm, such as 0.5 mm. The transducer element according to any one of the clauses 13-18, wherein one or more of the transducer elements in the stack is pre-strained. The transducer element according to any one of the clauses 15-19, wherein each of the electrodes of the stack of transducer elements are arranged to face towards the same direction. The transducer element according to any one of the preceding clauses, wherein the flexible film is stretchable to a strain level that is lower than the strain level of the elastic body. The transducer element according to any one of the preceding clauses, wherein the flexible film is a of a metal oxide, a semiconductor metal oxide, a polymer, a copolymer material which may have been processed by biaxial orientation. The transducer element according to any one of the preceding clauses, wherein the flexible film has a thickness between 0.02 micrometre and 100 micrometres. The transducer element according to any one of the preceding clauses, wherein the flexible film is attached to the elastic body by adhesion, e.g. self-adhesion, by use of glue, or by use of adhesion-promoting components provided in the elastic body. The transducer element according to any one of the preceding clauses, wherein the electrode is a metal, metal oxides, semiconductors, semiconductor oxides, metal alloys or alloy oxides, carbon allotropes and their precursors, composites of elastomer and composites of gel materials comprising conducting particles. The transducer element according to any one of the preceding clauses, wherein the electrode has a thickness between 1 nanometres to 200 micrometres, 27. The transducer element according to any one of the preceding clauses, further comprises a coating covering the electrode and the upper surface of the flexible film.

[0188] 28. The transducer element according to any one of the preceding clauses, comprising a compound of a first flexible film with a first electrode attached and a second flexible film with a second electrode attached, wherein the first electrode and the second electrode face each other, optionally with an adhesive in-between, and wherein the compound is attached to the first surface of the elastic body.

[0189] 29. The transducer element according to any one of the preceding clauses, wherein the transducer element is in a roll configuration, the roll configuration having a substantially cylindrical shape, wherein the roll configuration comprises a first and a second base.

[0190] 30. The transducer according to clause 29, wherein the roll configuration is in a compression mode, wherein the compression mode relates to an application of an external force parallel to the first and second base.

[0191] 31. The transducer according to clause 30, wherein the compression mode relates to a length reduction of the transducer preferably larger than 5%, or larger than 10%, or larger than 15%, such as 20%.

[0192] 32. The transducer according to any one of clauses 29-31, wherein the elastic body is prestrained.

[0193] 33. The transducer according to any one of clauses 29-32, wherein the roll configuration comprises a cavity in the center of the substantially cylindrical shape.

[0194] 34. The transducer according to clause 33, wherein the cavity comprises air and / or a polyolefin material, such as polypropylene foam.

[0195] 35. A method of fabrication of a transducer element comprising: provide an elastic body, the elastic body comprises a first surface and a second surface; provide a flexible film with an upper surface and a lower surface; provide an electrode attached to the flexible film at the upper surface or lower surface; attach the flexible film with the electrode, the flexible film being attached to the first surface of the elastic body, thereby forming a layer of a transducer element. The method according to clause 35, further comprising the step of rolling the transducer element, thereby obtaining a substantially cylindrical transducer element in a roll configuration. A method of fabrication of a multi-layer transducer element comprising: provide an elastic body, the elastic body comprises a first surface and a second surface; provide a flexible film with an upper surface and a lower surface; provide an electrode attached to the flexible film at the upper surface or lower surface; attach the flexible film with the electrode, the flexible film being attached to the first surface of the elastic body, thereby forming a layer of a transducer element. repeat the above steps at least once and stack consecutive layers of transducer elements, thereby obtaining a multi-layer transducer element. A method of fabrication of a transducer element comprising: pre-straining an elastic body into a pre-strained state, the elastic body comprises a first surface and a second surface; provide a flexible film with an upper surface and a lower surface; provide an electrode attached to the flexible film at the upper surface or lower surface; while the elastic body is maintained in the pre-strained state attach the flexible film and the electrode, the flexible film being attached to the first surface of the elastic body; relax the elastic body from the pre-strained state to obtain a corrugated state of the electrode, the corrugated state having elevations and depressions, and wherein the corrugated state is obtained from a compression force of the elastic body.

[0196] 39. The method according to any one of the clauses 35-38, wherein the flexible film comprises an electrode being attached at the upper surface or lower surface in a prior step.

[0197] 40. The method according to any one of the clauses 35-39, wherein the electrode is attached at the upper surface or lower surface of the flexible film during fabrication of the transducer element prior to relaxing the elastic body.

[0198] 41. The method according to any of the clauses 35 to 40, wherein the elastic body is prestrained in a first and a second orthogonal direction.

[0199] 42. The method according to any of the clauses 35 to 41, wherein the elastic body is prestrained up to 15 times the original area.

[0200] 43. The method according to any of the clauses 35 to 42 wherein the electrode comprises a pattern, wherein the pattern is provided during fabrication or in a prior step.

[0201] 44. A method of fabrication of a transducer element comprising: pre-straining an elastic body into a pre-strained state, the elastic body comprises a first surface and a second surface; provide a flexible film with an upper surface and a lower surface; provide an electrode attached to the flexible film at the upper surface or lower surface; apply an external force to obtain a corrugated state of the electrode, the corrugated state having elevations and depressions, and wherein the corrugated state is provided by a compression force of the elastic body.

[0202] 45. The method according to any one of clauses 35-44, further comprising the step of using one or more liners to separate transducer elements during fabrication of a plurality of transducer elements, wherein each liner is configured to carry electrodes, flexible films, or elastic bodies. The method according to any one of clauses 35-45, further comprising the step of utilizing a reel-to-reel process, roll-to-roll process, and / or a sheet-to-sheet process to fabricate a plurality of transducer elements. A transducer comprising: a transducer element compound of: a first transducer element in accordance with any of the clauses 1 to 34 and a second transducer element in accordance with any of the clauses 1 to 34, wherein the first transducer element is combined with the second transducer element by attaching the second surface of each transducer element to each other, thereby providing a transducer compound with an electrode pair with a first electrode and a second electrode, or, a first transducer element in accordance with any of the clauses 1 to 34, the first transducer element further comprising: a second flexible film with an upper surface and a lower surface, wherein the lower surface of the second flexible film is attached to the second surface of the elastic body; a second electrode attached to the second flexible film at the upper surface or lower surface; wherein the second electrode is in a corrugated state having elevations and depressions, and wherein the corrugated state is provided by a compression force of the elastic body, thereby providing a transducer compound with an electrode pair with a first electrode and a second electrode. A transducer according to clause 47 comprising a plurality of transducer compounds in a predefined arrangement and wherein the electrode pairs of at least a some of the transducer compounds are electrically connected together. 49. A transducer element obtainable by the process according to any one of clauses 35- 46.

[0203] Although the present disclosure has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The presently disclosed approach can be implemented by any suitable means; and the scope of the present disclosure is to be interpreted in the light of the accompanying claim set. Any reference signs in the claims should not be construed as limiting the scope. Example embodiments of the present disclosure have been described for the purposes of illustration only, and not to limit the scope of the invention as defined in the accompanying claims.

Claims

CLAIMS1. A transducer element comprising: an elastic body with a first surface and a second surface; a flexible film with an upper surface and a lower surface, wherein the lower surface of the flexible film is attached to the first surface of the elastic body; an electrode attached to the flexible film at the upper surface or lower surface; wherein the electrode is in a corrugated state having elevations and depressions, and wherein the corrugated state is provided by a compression force of the elastic body.

2. The transducer element according to claim 1, wherein the elevations and depressions comprise a peak-to-peak amplitude, wherein the peak-to-peak amplitude is larger than 1 pm, or larger than 5 pm, or larger than 10 pm, or larger than 50 pm.

3. The transducer element according to claim 2, wherein the peak-to-peak amplitude is associated to a ratio, the ratio obtained by dividing the length of the transducer element when extended, to the length of the transducer element in the relaxed state, wherein the length is the length along the axis of the elevations and depressions.

4. The transducer element according to claim 3, wherein the ratio is larger than 1.05, or larger than 1.1, or larger than 1.15, such as 1.2.

5. The transducer element according to any one of the preceding claims, wherein the elastic body is strained resulting in a compression force acting from the elastic body to the electrode and to the flexible film, thereby shaping the electrode in a corrugated state.

6. The transducer element according to any one of the preceding claims, wherein an externally applied force acts on the transducer element, thereby resulting into a compression force configured to shape the electrode in a corrugated state.

7. The transducer element according to any one of the preceding claims, wherein the elastic body is stretchable above 5% and is having a Young’s modulus between 1 kPa and 100 MPa.

8. The transducer element according to any one of the preceding claims, wherein the elastic body is a polymer material, an elastomer material, a dielectric elastomer material, a chemically crosslinked elastomers, a physically crosslinked thermoplastic elastomers, an adhesive, or a gel.

9. The transducer element according to any one of the preceding claims, wherein a thickness of the elastic body is between 1 micrometres and 5 millimetres.

10. The transducer element according to any one of the preceding claims, wherein the elastic body has a relative permittivity between 1 and 10.000 at a penetrating timevarying electrical signal of one hertz.

11. The transducer element according to any one of the preceding claims, wherein the elastic body is a stack of elastic bodies and wherein the flexible film is attached to the first surface of a top elastic body, optionally wherein at least two elastic bodies in the stack are of a different material and / or of a different thickness and / or is pre-strained with different strains.

12. The transducer element according to any one of the preceding claims, comprises a stack of transducer elements, optionally wherein at least two transducer elements in the stack comprise elastic bodies of a different material and / or of a different thickness and / or is pre-strained with different strains.

13. The transducer element according to claim 12, wherein the compression force arises from an externally applied force to the stack of elastic bodies.

14. The transducer element according to any one of the preceding claims, wherein the transducer element comprises a stack of transducer elements, wherein each transducer element arranged on a dielectric layer.

15. The transducer element according to claim 14, wherein the distance between adjacent dielectric layers is preferably less than 10 mm, or less than 5 mm, or less than 1 mm, or less than 50 pm, or less than 10 pm.

16. The transducer element according to any one of claims 14-15, wherein a first group of the stack of transducer elements are horizontally retracted towards a first direction, such that the first group of the stack of transducer elements is in contact with a first electrode, and wherein a second group of the stack of transducer elements are horizontally retracted towards a second direction, such that the second group of the stack of transducer elements is in contact with a second electrode.

17. The transducer element according to claim 16, wherein the horizontal retraction is preferably less than 5 mm, or less than 2.5 mm, or less than 1 mm, such as 0.5 mm.

18. The transducer element according to any one of the claims 12-17, wherein one or more of the transducer elements in the stack is pre-strained.

19. The transducer element according to any one of the claims 14-18, wherein each of the electrodes of the stack of transducer elements are arranged to face towards the same direction.

20. The transducer element according to any one of the preceding claims, wherein the flexible film is stretchable to a strain level that is lower than the strain level of the elastic body.

21. The transducer element according to any one of the preceding claims, wherein the flexible film is a of a metal oxide, a semiconductor metal oxide, a polymer, a copolymer material which may have been processed by biaxial orientation.

22. The transducer element according to any one of the preceding claims, wherein the flexible film has a thickness between 0.02 micrometre and 100 micrometres.

23. The transducer element according to any one of the preceding claims, wherein the flexible film is attached to the elastic body by adhesion, e.g. self-adhesion, by use of glue, or by use of adhesion-promoting components provided in the elastic body.

24. The transducer element according to any one of the preceding claims, wherein the electrode is a metal, metal oxides, semiconductors, semiconductor oxides, metalalloys or alloy oxides, carbon allotropes and their precursors, composites of elastomer and composites of gel materials comprising conducting particles.

25. The transducer element according to any one of the preceding claims, wherein the electrode has a thickness between 1 nanometres to 200 micrometres,26. The transducer element according to any one of the preceding claims, further comprises a coating covering the electrode and the upper surface of the flexible film.

27. The transducer element according to any one of the preceding claims, comprising a compound of a first flexible film with a first electrode attached and a second flexible film with a second electrode attached, wherein the first electrode and the second electrode face each other, optionally with an adhesive in-between, and wherein the compound is attached to the first surface of the elastic body.

28. The transducer element according to any one of the preceding claims, wherein the transducer element is in a roll configuration, the roll configuration having a substantially cylindrical shape, wherein the roll configuration comprises a first and a second base.

29. The transducer according to claim 28, wherein the roll configuration is in a compression mode, wherein the compression mode relates to an application of an external force parallel to the first and second base.

30. The transducer according to claim 29, wherein the compression mode relates to a length reduction of the transducer preferably larger than 5%, or larger than 10%, or larger than 15%, such as 20%.

31. The transducer according to any one of claims 28-30, wherein the elastic body is prestrained.

32. The transducer according to any one of claims 28-31, wherein the roll configuration comprises a cavity in the center of the substantially cylindrical shape.

33. The transducer according to claim 32, wherein the cavity comprises air and / or a polyolefin material, such as polypropylene foam.

34. A method of fabrication of a transducer element comprising: provide an elastic body, the elastic body comprises a first surface and a second surface; provide a flexible film with an upper surface and a lower surface; provide an electrode attached to the flexible film at the upper surface or lower surface; attach the flexible film with the electrode, the flexible film being attached to the first surface of the elastic body, thereby forming a layer of a transducer element, roll the transducer element, thereby obtaining a substantially cylindrical transducer element in a roll configuration.

35. A method of fabrication of a transducer element comprising: pre-straining an elastic body into a pre-strained state, the elastic body comprises a first surface and a second surface; provide a flexible film with an upper surface and a lower surface; provide an electrode attached to the flexible film at the upper surface or lower surface; while the elastic body is maintained in the pre-strained state attach the flexible film and the electrode, the flexible film being attached to the first surface of the elastic body; relax the elastic body from the pre-strained state to obtain a corrugated state of the electrode, the corrugated state having elevations and depressions, and wherein the corrugated state is obtained from a compression force of the elastic body.

36. The method according to any one of the claims 34-35, wherein the flexible film comprises an electrode being attached at the upper surface or lower surface in a prior step.

37. The method according to any one of the claims 35-36, wherein the electrode is attached at the upper surface or lower surface of the flexible film during fabrication of the transducer element prior to relaxing the elastic body.

38. The method according to any of the claims 35 to 37, wherein the elastic body is prestrained in a first and a second orthogonal direction.

39. The method according to any of the claims 35 to 38, wherein the elastic body is prestrained up to 15 times the original area.

40. The method according to any of the claims 34 to 39 wherein the electrode comprises a pattern, wherein the pattern is provided during fabrication or in a prior step.

41. A method of fabrication of a transducer element comprising: pre-straining an elastic body into a pre-strained state, the elastic body comprises a first surface and a second surface; provide a flexible film with an upper surface and a lower surface; provide an electrode attached to the flexible film at the upper surface or lower surface; apply an external force to obtain a corrugated state of the electrode, the corrugated state having elevations and depressions, and wherein the corrugated state is provided by a compression force of the elastic body.

42. The method according to any one of claims 34-41, further comprising the step of using one or more liners to separate transducer elements during fabrication of a plurality of transducer elements, wherein each liner is configured to carry electrodes, flexible films, or elastic bodies.

43. The method according to any one of claims 34-42, further comprising the step of utilizing a reel-to-reel process, roll-to-roll process, and / or a sheet-to-sheet process to fabricate a plurality of transducer elements.

44. A transducer comprising: a transducer element compound of: a first transducer element in accordance with any of the claims 1 to 33 and a second transducer element in accordance with any of the claims 1 to 33, wherein the first transducer element is combined with the second transducerelement by attaching the second surface of each transducer element to each other, thereby providing a transducer compound with an electrode pair with a first electrode and a second electrode, or, a first transducer element in accordance with any of the claims 1 to 33, the first transducer element further comprising: a second flexible film with an upper surface and a lower surface, wherein the lower surface of the second flexible film is attached to the second surface of the elastic body; a second electrode attached to the second flexible film at the upper surface or lower surface; wherein the second electrode is in a corrugated state having elevations and depressions, and wherein the corrugated state is provided by a compression force of the elastic body, thereby providing a transducer compound with an electrode pair with a first electrode and a second electrode.

45. A transducer according to claim 44 comprising a plurality of transducer compounds in a predefined arrangement and wherein the electrode pairs of at least a some of the transducer compounds are electrically connected together.

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