A structural element

Abstract

An electromechanically auxetic structural element defined by the application of coated electrodes on the larger two main surfaces encompassing the triply periodic minimal surface structures made of active materials that deform under the actuation of electrical fields. A structural element (10) comprising a base structure (11) defined by a triply periodic minimal surface having a thickness and two main surfaces that separated two disjoint sub-volumes (12, 14), wherein the base structure is made of an electromechanically functional material, wherein the surface (12') of the first sub-volume comprises a first coating of a first electrically conductive material (16), wherein the surface (14') of the second sub-volume comprises a second coating of a second electrically conductive material (16), and wherein the coating of the first sub-volume is arranged to not be in electrical contact with the coating of the second sub-volume. This structural element can fill any 3D-shaped volume, imparting an auxetic electromechanical response to the overall device (sensor, actuator or transducer).

Description

[0001]A STRUCTURAL ELEMENT The present invention relates to developing functional materials, specifically electromechanical active / functional metamaterials. Electromechanically active functional materials, such as electrostrictors and piezoelectrics, undergo strain under an electric field, i.e., the inverse piezoelectric effect, yielding forces in the surrounding environment depending on the mechanical properties of the materials. Ferroelectric piezoceramics are especially paramount for existing and emerging technologies in ultrasounds and hypersounds, piezo-photo-tronics, MEMS, flexible devices, and advanced robotics, to mention a few. However, the current paradigm is mainly based on bidimensional criteria and simple shapes (e.g., disks, plates, cylinders, lenses), with limited influence of the geometry on the resulting performance. Although the strain is relatively precise, it is often inconsequential for certain applications where a large displacement via amplification is needed. The best-performing piezoelectric materials for actuation are ferroelectric relaxors, i.e., lead- based piezoelectrics such as PZT and PT-PMN compounds, which generally deliver up to 0.3 % of strain. Among the lead-free compositions, K0.5Na0.5NbO3 (KNN) is emerging as one of the most promising candidates. The early concepts of electromechanical amplification for these materials rely on a basic piezoelectric-electrodes multi-stack approach, where several piezoelectric layers are under intense electric fields and deliver the maximum possible strain at a low applied voltage. The multilayering approach in multilayer actuators (MLAs) presents several variations in layer / electrode arrangement. The piezoelectric layers in MLAs are stacked along the strain direction and generally actuate in the d33 or d31 modes. Control over the direction of the resulting displacement can be achieved with other supporting frames connected with the main piezoelectric element or a stack of elements, e.g., cymbal, moonie-, rainbow-, bridge-, etc. Although such designs are universally adopted, there are several drawbacks, especially related to the non-trivial fabrication co-firing methodology for ceramic-metallic multilayers with tens or hundreds of layers of tens of microns each. MLAs also possess high capacitance, e.g., PZT multilayers with 10-20 µm actuation (stroke) typically convey high capacitance in the hundreds of nF-µF range. High capacitance requires high voltage and driving power, large losses, and undesired phase shifts, especially for high-frequency operations (kHz). Such limitations arise from the high specific surface of the bi-dimensional capacitor design with a high number of interfaces (10 µm actuation in PZT requires large flat surface areas of ca 100 cm2) combined with the high dielectric constant of the relaxors (1,000 to 10,000). Inspicos / 14 / 03 / 2025 / 13:20 Relevant technology may be found in: WO2020 / 141264, WO2019 / 227082, US9099986, US2021 / 0234089, US2022 / 0066557, WO23 / 224197, KR2023 / 0142923, CN115730494, KR2022 / 0026222, US2017 / 149083, US2017 / 104198, WO17 / 040280, WO15 / 160798, CZ309723, as wel as in: HE Zl-XUAN ET AL: "Effects of CuO additive on properties of high-performance (Ba0.85Ca0.15)(Ti0.9Zr0.1)03 piezoceramics obtained by vat photopolymerization", CERAMICS INTERNATIONAL, ELSEVIER, AMSTERDAM, NL, vol. 49, no. 23, 20 September 2023 (2023-09-20), pages 38973-38981, XP087427189, ISSN: 0272-8842, DOI: 10.1016 / J.CERAMINT.2023.09.233 IMANIAN MOHAMMAD EBRAHIM ET AL: "3D printed flexible wearable sensors based on triply periodic minimal surface structures for biomonitoring applications", SMART MATERIALS AND STRUCTURES, IOP PUBLISHING LTD., BRISTOL, GB, vol. 32, no. 1, 15 December 2022 (2022-12-15), XP020440025, ISSN: 0964-1726, DOI: 10.1088 / 1361-665X / ACA6BC XU HU ET AL: "Piezoelectric properties of triply periodic minimum surface structures", COMPOSITES SCIENCE AND TECHNOLOGY, ELSEVIER, AMSTERDAM, NL, vol. 200, 27 August 2020 (2020-08-27), XP086299122, ISSN: 0266-3538, DOI: 10.1016 / J.COMPSCITECH.2020.108417. 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Song et al., “Additive manufacturing of bi-continuous piezocomposites with triply periodic phase interfaces for combined flexibility and piezoelectricity,” Journal of Manufacturing Science and Engineering, Transactions of the ASME, vol. 141, no. 11, 2019, doi: 10.1115 / 1.4044708. Inspicos / 14 / 03 / 2025 / 13:20 W. Ma et al., “Structure-reinforced periodic porous piezoceramics for ultrahigh electromechanical response manufactured by vat photopolymerization,” Addit Manuf, vol. 93, no. September, p. 104446, 2024, doi: 10.1016 / j.addma.2024.104446. Z. Jiang, Y. Sun, J. Chen, and Y. Zeng, “Control of electromechanical performance in 3D printing lattice-structured BaTiO3 piezoelectric ceramics,” Journal of Advanced Ceramics, vol. 13, no. 7, pp. 987–1001, 2024, doi: 10.26599 / JAC.2024.9220912. E. C. Nelli Silva, J. S. Ono Fonseca, and N. Kikuchi, “Optimal design of piezoelectric microstructures,” Comput Mech, vol. 19, no. 5, pp. 397–410, 1997, doi: 10.1007 / s004660050188. E. C. N. Silva, J. S. O. Fonseca, A. T. Crumm, G. A. Brady, J. W. Halloran, and N. Kikuchi, “Design of Piezocomposite Materials and Piezoelectric Transducers Using Topology Optimization - Part I,” Archives of Computational Methods in Engineering, vol. 6, no. June 1998, p. 3, 1999. O. Sigmund, S. Torquato, and I. A. Aksay, “On the design of 1-3 piezocomposites using topology optimization,” J Mater Res, vol. 13, no. 4, pp. 1038–1048, 1998, doi: 10.1557 / JMR.1998.0145. G. Stankiewicz, C. Dev, M. Weichelt, T. Fey, and P. Steinmann, “Towards advanced piezoelectric metamaterial design via combined topology and shape optimization,” Structural and Multidisciplinary Optimization, vol. 67, no. 2, pp. 1–20, 2024, doi: 10.1007 / s00158-024- 03742-w. It has been found by the present inventor(s) that active electromechanical functional metamaterials with a triply periodic minimal surface (TPMS) structural arrangement yield metamaterial electromechanical responses that go beyond their constitutive components. The new functionality is an electromechanical auxetic response that results from the three- dimensional geometric properties of TPMS structures and the placement of the electrodes on their two larger surfaces. TPMS are, by definition, mere surfaces (without thickness), and different approaches exist to generate solid structures (with volume) from these geometries. Typical TPMS are Gyroid, Neovius Surface, Schwarz, and Diamond. The metamaterial response presented here depends on the exploitation of the piezoelectric (or higher-order electromechanical) effect in these structures if the electrodes are placed on the larger surfaces of the structure. Therefore, in the first aspect, the present invention relates to a structural element comprising Inspicos / 14 / 03 / 2025 / 13:20 a base structure defined by a triply periodic minimal surface having a thickness and two main surfaces that separate two disjoint first and second sub-volumes and an external surface, wherein the base structure is made of an electromechanically functional material, wherein the surface of the first sub-volume comprises a first coating of a first electrically conductive material, wherein the surface of the second sub-volume comprises a second coating of a second electrically conductive material, and wherein the coating of the first sub-volume is arranged to not be in electrical contact with the coating of the second sub-volume. This structural element can fill any 3D-shaped volume, imparting an auxetic electromechanical response to the overall device, such as for use as a sensor, actuator, and / or transducer. In the present context, the base structure can be a solid element, dense or porous, and may be relatively stiff. The base structure may, as will be described below, be made of a range of active materials and may be manufactured in a number of manners. The structural element comprises a base structure defining a triply periodic minimal surface having disjoint first and second sub-volumes. A triply periodic minimal surface is often periodic but always has only two disjoint sub-volumes therein. In this context, a triply periodic minimal surface extends beyond the strict mathematical definition often used for this term. In this context, the TPMS structure will often be defined by a base structural element (a unit cell). The TPMS is often periodic, where the same structure is replicated in one or more directions, such as two or three, which may be perpendicular to each other. The TPMS structures can be geometrically altered, that is, suffer transformations, such as scaled, stretched, rotated, or morphed, as long as the overall shape and the two disjoint sub- volumes is / are retained, separated by two minimal surfaces. Stretching may be linear or may vary along a direction (in more directions), where the stretching factor depends on the position along the direction. Thus, the stretching may vary in a particular direction. Thus, the overall shape is retained, but the stretching will alter the extent of the period or unit element of the structure in the direction. Additionally, or alternatively, the structural element may define a shape that is a basic TPMS that is rotated where some portions of the TPMS are rotated in relation to other portions thereof. Inspicos / 14 / 03 / 2025 / 13:20 Additionally, or alternatively, the structural element may define a shape which may be modified by transitioning from a TPMS to another, i.e., morphed, where the morphing may be a 3D variation from the periodic shape. The morphing may be determined or defined by a morphing description, which may be a mathematical description of the morphing. Another possible morphing operation is to generate a structure that is a hybrid between two (or more) different kinds of TPMS. Mathematically, one can achieve this result by averaging the corresponding underlying functions. The structural element also will normally not be infinitely periodic in that its outer surface exists and defines the outer geometry with various shapes. Thus, the outer portions of the structural element prevent the structure from being indefinitely periodic. The outer surface may be at an outer boundary of a unit cell of the structure or maybe inside this unit cell. Irrespective of the stretching, rotation and / or morphing, the unit cell replication is seen so that the functionality thereof may be seen throughout the structure, irrespective of the fact that the individual instances of the unit cell may differ from a strict periodicity and identity in shape. The sub-volumes are not connected to each other inside the structure but may both open into the surroundings at an outer surface of the structure or element. The structure or element may define walls extending therein and dividing the two sub-volumes from each other. Each wall will then have one side defining the surface of the first sub-volume and another side defining the surface of the second sub-volume. The walls may end at an outer portion or surface of the structure or element, where, e.g., air or other fluids may then flow around the end from one sub-volume to the other. The outer portions of the walls may define one or more surfaces, such as portions of one or more surfaces, with predetermined shapes, such as plane surfaces or surfaces having an axis of symmetry, where the surface, in a plane perpendicular to the symmetry axis, has a predetermined outlining shape, such as a sphere, hemisphere, cube, cylinder, box, or any other 3D shape. That is: a 3D shape infilled with a TPMS structure, and if the electrodes are placed on the two main larger surfaces, the structure will display an auxetic response around the outlining shape. It is noted that the thickness of the wall end at the outer shape portions may define a surface enclosing the structure if the outer portions are provided at least substantially on or at the surface. Since the structure presents inner channels, the outer portions at the walls need not form the complete surface and will normally form only part of the surface. Inspicos / 14 / 03 / 2025 / 13:20 Inside the structural element, each wall preferably has the first sub-volume on one side and the second sub-volume on the other side. Preferably, all portions of all walls are at least substantially of the same thickness, where a wall thickness is determined perpendicular to a general direction or plane or extension of the individual wall portion. The wall or region between these two volumes is made of active material, and the distance between these volumes is defined here as thickness. The thickness can be engineered to vary along the structure to generate a desired deformation. The thickness can also be engineered to be at least substantially the same to e.g. generate a desired torque or the like of a deformation. The base structure is made of an electromechanically functional material. An electromechanically functional material may be a material whose shape may change if exposed to an electrical voltage or which may generate a voltage if deformed. Typical types of electromechanically functional materials would be piezoelectric or electrostrictive, which will be described further below. An auxetic material is a specialized material that exhibits a negative Poisson’s ratio, causing it to expand laterally when subjected to tensile forces and contract laterally when subjected to compressive forces. This behavior is in contrast to conventional materials, which typically become narrower, in one direction, under tension, perpendicular to the one direction, and wider under compression. The auxetic effect is achieved through tailored internal structures, such as re-entrant geometries, rotating units, or specific molecular arrangements, allowing for enhanced mechanical properties, including improved energy absorption, higher resistance to fracture, and superior flexibility. Such materials are applicable in various fields, including impact-resistant equipment, medical implants, flexible electronics, and advanced structural components. TPMS structures do not exhibit auxetic behavior in the conventional definition of the term. Instead, they exhibit an electromechanical response known in the literature as “auxetic piezoelectric behavior”, but this effect can be observed in higher-order electromechanical phenomena (like electrostriction, for instance). As an electric potential difference is applied between the electrodes coating either side of the piezoelectric material, the whole structure contracts in all three Cartesian directions (i.e., all the three spatial directions of a global – fixed–coordinate system). This is in sharp contrast with the normal response of piezoelectric structures that contract in one direction and expand in two perpendicular directions or vice versa. It is only when the electric field is applied through the thickness of the electromechanically active TPMS that the resulting transversal strain can build up along the tangential directions Inspicos / 14 / 03 / 2025 / 13:20 isotropically and thus result in an overall contraction of all sides of the cube (or other outlining shape) enveloping the structure. Furthermore, TPMS-based materials can be engineered to exhibit tunable mechanical properties by adjusting parameters such as unit cell size, wall thickness, and structural periodicity. These characteristics allow for precise control over auxetic performance, making TPMS structures advantageous for applications requiring high energy absorption, impact resistance, and flexibility. Integrating such auxetic TPMS architectures into advanced materials enhances their suitability for use in biomedical implants, aerospace components, and protective equipment. In the disclosed piezoelectric auxetic TPMS, the first sub-volume comprises a coating of the first electrically conductive material. As will be described further below, the coating may be provided in any of a number of manners, and the first electrically conductive material may be any type of material, where a number of suitable materials are described below. It is preferred that the first electrically conductive material engages, such as is attached to or adheres to, the surface of the first sub-volume. Preferably at least 90%, such as at least 95%, such as at least 99% of the wall surface facing the first sub-volume is covered by the first electrically conductive material. The second sub-volume comprises a coating of a second electrically conductive material which may be identical to or different from the first electrically conductive material. As will be described further below, the coating may be provided in any of a number of manners, and the second electrically conductive material may be any type of material, where a number of suitable materials are described below. It is preferred that the second electrically conductive material engages, such as is attached to or adheres to, the surface of the second sub- volume. Preferably at least 90%, such as at least 95%, such as at least 99% of the wall surface facing the second sub-volume is covered by the second electrically conductive material. It may be desired that the first and / or second electrically conductive material is configured to remain in engagement with and / or be attached to the surface of the base structure if the base structure wall is deformed. The structural element has an external surface which may be formed by or may comprise the external wall portions. The coating of the first sub-volume is arranged so as not to be in electrical contact with the coating of the second sub-volume. This may be obtained by providing the structural element Inspicos / 14 / 03 / 2025 / 13:20 where the external surface is not electrically conducting and / or where the external wall portions are not electrically conducting. As will be described below, this may be obtained by ensuring that the external wall portions and / or the external surface do not comprise a coating with an electrically conducting coating. It is noted that the coatings of the first and second electrically conducting materials are not in electrical contact when no electrically conducting material extends between these coatings. In this context, the electromechanically functional material is not considered an electrically conductive material. In this context, an electrically conductive material preferably has a conductivity of at least 100 S / m to 108S / m, such as 1000 S / m to 106S / m, such as 105S / m to 106S / m. In one embodiment, the coating of the surface of the first sub-volume is arranged to be in contact with a first external electrode, and wherein the coating of the surface of the second sub-volume is arranged to be further in contact with a second external electrode, and the first and second external electrodes are arranged to provide an electrical potential, i.e. voltage. This potential may be created when the structural element is deformed, as this deformation will deform the base structure and thus the electromechanically functional material which is coated with electrically conductive coatings. Then, all coated portions of the base structure may act in creating the voltage. It is noted that for a range of electromechanically functional materials, providing a voltage over the two coatings could cause the material, and thus the structural element, to deform. It is preferred that the structural element comprises only the base structure and the coating(s). It is preferred that the outer wall portions are not fixed to elements external to the structural element. Such fixing could act to prevent or hamper the deformation of the functional element, either if deformed by external forces or, if desired, deformed by the application of a voltage over the coatings. Then, the external surface is preferably arranged to be free to expand and / or contract (bend, stretch, or both) in more than one direction. In one embodiment, the electromechanically functional material is a piezoelectric or electrostrictive material. Preferred piezoelectric materials could be polymeric or ceramic piezoelectric materials, such as piezoceramics. Preferred electrostrictive materials may be electrostrictive ceramics, such as oxygen- defective metal oxides, such as ceria, ceria-zirconia, zirconia-hafnia, and bismuth oxide. Inspicos / 14 / 03 / 2025 / 13:20 Alternative materials comprise relaxor ferroelectric and other piezoceramics, such as PZT-, PMN-PT-, BNT-, bismuth titanates-, barium titanates-, bismuth ferrites-, niobates- and other KNN-based materials. These materials may initially be provided as a slurry, which is later solidified. Solidification is followed by debinding and thermal treatment by sintering to achieve the ceramic state. Alternatively, the base structure may be printed, such as when using polymer-ceramic composites. The electromechanically functional material may be fully dense or porous. Different manners of generating the electromechanically functional material or the base structure may generate no or some porosity. Clearly, any triply periodic minimal surface may be used, as may any structure defining two sub-volumes divided by one or more walls. Well-known structures of this type are: a gyroid surface, Schwarz H surface, Schwarz primitive (Schwarz P) surface, diamond surface, Split primitive (Split P) surface, Lidinoid surface, Fischer-Koch, and Neovius surface. In one embodiment, the first and / or the second electrically conductive material is a metal. Suitable metals may be nickel, silver, copper, aluminium, or alloys comprising such metals. Other suitable electrically conductive materials comprise carbon-based conductive pastes. As indicated above, the wall thickness of the structural element need not be the same throughout the structural element. In one embodiment, the base structure comprises a first portion having a first wall thickness and a second portion having a second wall thickness, the first wall thickness being different from the second wall thickness. An advantage thereof is that the deformation of a portion of the wall of the base structure will depend on the strength of the electrical field inside the wall. As the potential is provided over the first and second coating, the same potential is seen at all wall portions, so that the thickness of the wall portion will determine the deformation thereof. Inside a thin wall portion, the field is stronger, so that a larger deformation may be obtained compared to a thicker wall portion. A difference in wall thickness may be 1:2 to 1:10, such as 1:2 to 1:5. Also, as the deformation increases with decreasing wall thickness, it may be desired to have a low wall thickness especially in situations where the walls are not expected to exert a large force. Wall thicknesses down to 10-50µm which is the present limit for 3D printers. Wall Inspicos / 14 / 03 / 2025 / 13:20 thicknesses of 50µm to 2mm may be used, such as 100-500µm for certain embodiments such as pumps. Then, when the deformation created by the potential is an increase of the wall thickness, the overall size of the structural element, such as a distance between two predetermined portions of the external surface thereof, may be reduced. If a wall portion extending between such two portions is thinner, the distance will decrease more, compared to portions separated by a thicker wall portion. In this manner, the overall shape of the external surface may be varied in a number of manners. If a curved surface is desired, the rest shape of the base structure may define an external surface which is curved or plane and with a lower wall thickness at positions where a larger deformation is desired and a higher wall thickness at other locations. For example, the base structure may be provided with a reflective surface or element connected to a portion of its external surface. The curvature of this surface / element may then be altered when either the outer portions or the central portion of the external surface has a lower wall thickness than other portions of the base structure. Applying or increasing a potential will then cause a different deformation of the outer and the central portions affecting the shape of the reflective surface / element. It is noted that the structural element and / or the base structure may be provided with any shape. As long as it is monolithic in the sense that the coatings are provided on both sides of all wall portions except at the external surface, the deformation will take place in all wall portions. Thus, the structural element may be box-shaped, elongate, curved, shaped as a sphere, hemisphere, hollow sphere, hollow hemisphere, Helicoidal, Cylindrical, Hollow cylinder, toroid, hollow toroid, ring, hollow ring, cymbals, origami, cube, hollow cube, honeycombs, and other extruded shapes, and their combinations, or the like. The structural element may be L-shaped or C-shaped. For example, a C-shaped structural element may be embodied so as to operate as a pair of tweezers opening and closing as a function of the value of the potential. It is noted that e.g. a portion of the external surface of the structural element may be fixed, such as to a stiff element, so that other portions of the structural element may move to take up the deformation created by the potential. Inspicos / 14 / 03 / 2025 / 13:20 A second aspect of the invention relates to a transducer comprising the structural element according to the first aspect of the invention, and a signal provider, the signal provider being configured to apply an electrical potential over the first and second coatings. The signal provider may be configured to apply a stationary, controllable, varying and / or quazi-stable potential over the coatings. A stationary potential would generate a predetermined deformation which is then maintained for a longer or shorter period of time. A desired deformation may be a desired elongation, thickness, distance change, curvature or any other shape of the structural element. A quazi-stable potential may be a potential varying slowly or in steps and often over an extended period of time. Two or more potentials may be determined which are sequentially fed to the coatings to arrive at a sequence of predetermined deformations. This may be desired in a number of situations, such as during production of equipment where a sequence of positions, elongations, curvatures or the like is repeated. A variable potential may be desired for e.g. allowing the deformation to follow an external, moving element or to allow a continuously varying deformation. Below, actuators such as pumps are explained which require a constantly varying potential to keep operating. It is preferred that the electromechanically functional material behaves as an auxetic material when shaped as a TPMS, so that the applied potential is configured to alter the physical dimensions of the structural element along three directions perpendicular to each other. This material will experience the same direction of the deformation: shrinking in outer dimensions along all directions or an expansion in all directions. In one embodiment the transducer may be configured to have the structural element, as a result of the applied potential, apply a force to an element engaging the structural element. Thus, the transducer may be configured to apply a force to an element, such as for moving the element, deforming the element or the like. To this end, the structural element may comprise an external surface configured to engage with the element, such as over a sufficiently large surface area thereof, so that the structural element is not damaged when the force is applied. An intermediate element may be provided between the structural element and the other element, which intermediate element may conform to a portion of the external surface of the structural element so as to distribute the force over this portion of the external surface to avoid damage to this portion of the structural element. In that or another embodiment, the transducer is configured to have the structural element, as a result of the applied potential, apply a translation to an element engaging the structural element. One manner of obtaining a translation is to fix one portion of the structural element Inspicos / 14 / 03 / 2025 / 13:20 and allow another portion, engaging the element to be translated, to move more freely. A deformation of the structural element may then cause the translation. As mentioned, the signal provider may be configured to apply a potential varying over time. In this manner, the deformation of the structural element varies over time. This may be used in a number of situations. If the structural element provides a force or a translation, this may be varied as a function of e.g. a measured or sensed value to maintain a force, position, translation, deformation or the like. In a particularly interesting embodiment, the structural element comprises a covering element covering an outer surface of the structural element, the covering element having one or more first openings and one or more second openings, each first and second opening opening into the first sub-volume. In this context, the covering element may cover one or more predetermined portions of the external surface so as to prevent ingress or egress of fluid at such portions. The covering element is preferably flexible in order to be able to maintain its function during deformation of the structural element. Suitable materials for such covering elements may be silicone Rubber (PDMS), Polyethylene (PE), Polyvinyl Chloride (PVC), Polyurethane (PU), Ethylene Propylene Diene Monomer (EPDM), Fluoropolymers (PTFE, FEP, PFA), Low-Density Polyethylene (LDPE), Polypropylene (PP), Ethylene-Vinyl Acetate (EVA), Polyvinylidene Chloride (PVDC), Nylon, Thermoplastic Elastomers (TPE, TPU, SBS, SEBS) and the like. An opening may be a channel or the like through which fluid from the surroundings may enter the structural element. The opening(s) may have any shape and may generally be positioned at any position of the external surface. Often, a first or second opening opens into or extends to a portion of the external surface from which fluid may enter the first sub- volume. Multiple first and / or second openings may be provided. Multiple openings may facilitate flow of a fluid into the sub-volume from one opening and out via another. In one embodiment, the transducer further comprises a first one-way valve configured to allow flow of a first fluid from surroundings of the structural element to the first sub-volume via the one or more first openings. . In this manner, flow from the surroundings and to the structural element is directed in that direction only, at least in relation to the one or more first openings. In that or another embodiment, the transducer further comprises a second one-way valve configured to allow flow of a first fluid from the first sub-volume to surroundings of the structural element via the one or more second openings. This is another manner of obtaining a flow directionality. Clearly, both valves may be provided to ensure that a deformation of the structural element creates a flow in the desired direction. In this manner, the actuator will Inspicos / 14 / 03 / 2025 / 13:20 function as a pump. The fluid may be any type of fluid, such as a gas or a fluid or even a suspension. High viscosity fluids are easily handled by this structure. Naturally also the second sub-volume may be taking part in the operation of the transducer, such as when the one or more of the first openings and one or more of the second openings open into also the second sub-volume. In this manner, the deformation and thus volume change of also the second sub-volume may take part in the pumping action. In one embodiment, the covering element further comprises one or more third openings and one or more fourth openings each opening into the second sub-volume. This brings about further manners of using the transducer. As described above, when the structural element further comprises a third one-way valve configured to allow flow of the second fluid from surroundings of the structural element to the second sub-volume via the one or more third openings., a directionality of flow of fluid through the second sub-volume may be obtained. The same is the situation when the structural element further comprises a fourth one-way valve configured to allow flow of the second fluid from the second sub-volume to surroundings of the structural element via the one or more fourth openings. Then, both the first and second sub-volumes may be used for pumping or fluid transport and even of different fluids. It is noted that the pumping action for both fluids may be exactly the same, which may be taken advantage of, for example when the first fluid is delivered to a receptacle from which the second fluid (which could stem from the first fluid) is sourced. It may be desired that the structural element comprises a first and a second non-overlapping outer surface portions, wherein the first opening(s) is / are provided in the first outer surface portion and the second opening(s) is / are provided in the second outer surface portion. Then, the fluid flow may be directed through the first sub-volume as defined by the positions of the first and second outer surface portions. If the portions are neighbouring, such as positioned at one surface portion of the structural element, the inlet and outlet of the fluid will be adjacent so that the movement of fluid in the sub-volume will be in / out from the same area. On the other hand, if the first and second outer surface portions are at opposite ends of the structural element, the flow of fluid will be generally along a direction from the inlet to the outlet. Similarly, the fourth opening(s) may be provided in the first outer surface portion, and the third opening(s) may be provided in the second outer surface portion. In this manner, the flow direction of the first fluid may be opposite to that of the second fluid. This may be an advantage for a number or reasons, such as in the below operation as a heat exchanger. Inspicos / 14 / 03 / 2025 / 13:20 Alternatively, the third opening(s) may be provided in the first outer surface portion, and the fourth opening(s) may be provided in the second outer surface portion. In this manner, the flow of the first and second fluid may be along essentially the same direction. It is noted that for fluid transport, it may be desired that the first and / or second coatings are covered or coated by another material, if the first and second coatings could react with the fluid in a non-desired manner. It may be desired to apply this other material or coating after having provided electrodes contacting the first and second coatings so that also the electrodes are covered by the other material or coating. A third aspect of the invention relates to a pump comprising a first fluid source, a first fluid receiver and a transducer as described above, wherein the first fluid source is fluidly connected to the first opening(s) and the first fluid receiver is fluidly connected to the second opening(s). In this connection, being fluidly connected would mean that a connection exists where fluid may pass from the source to the first opening(s) for example. Different types of fluid guides and other components may be provided, such as the above valves, so that the first fluid may pass from the first fluid source to the first fluid receiver via the first sub- volume, and optionally also the second sub-volume, and any additional components such as one or more valves as described above. Naturally, this pump may also comprise a second fluid source and a second fluid receiver fluidly connected to the third and fourth openings so that fluid may be passed between these via the second sub-volume and optionally also the third / fourth openings / valves. As mentioned above, this pump may be used for a host of fluid types and in any setting in which a pump may be employed. One particularly interesting manner is the use of the present pump in an injector for a drug and combined with an actuator and a needle. Using this pump, a precise controlling of the dispensed dose may be obtained by e.g. controlling a number and / or intensity of pulses from the signal generator. In addition, the structure has a high degree of efficiency and deformation so that it may be made rather small while allowing a large amount of volume pumped and at a very high precision. A fourth aspect of the invention relates to a heat exchanger comprising a first fluid source, a first fluid receiver, a second fluid source, a second fluid receiver and a transducer as described above, wherein the first fluid source is fluidly connected to the first opening(s), the first fluid receiver is fluidly connected to the second opening(s), the second fluid source is fluidly connected to the third opening(s) and the second fluid receiver is fluidly connected to the fourth opening(s). This functionality is described further above. Especially the set-up where the flow of the two fluids are opposite may be interesting. Inspicos / 14 / 03 / 2025 / 13:20 A fifth aspect of the invention relates to a sound generator comprising a signal generator and a structural element as described above, wherein the signal generator is configured to provide an electrical signal representing a sound and apply the electrical signal over the first and second coatings. In this situation, an electrical signal representing a sound often is a digital, optical or analogue signal describing the sound over time, such as an intensity / amplitude of a sound pressure over time. An analogue signal would represent e.g. the movement of a diaphragm playing the sound and this signal may be digitized in known manners. The electrical signal applied over the coatings preferably is an analogue signal so that the deformation of the structural element may drive the air in the same manner as a diaphragm of a standard loudspeaker driver would. Multiple manners exist of doing this. The structural element may simply be used as a transducer and a diaphragm may be attached thereto, so that the diaphragm is driven by the transducer to generate the sound. Alternatively, the outer surface of the structural element may itself drive the air, such as when exposed directly to the body of air into which the sound is desired launched. Further alternatively, the first and / or second sub-volumes may open into the body of air into which the sound is desired launched, so that the increasing and decreasing of the inner volume of the structural element may itself create the sound. A sixth aspect of the invention relates to an ultrasound generator comprising a signal generator and a structural element as described above, wherein the signal generator is configured to provide an electrical signal having one or more frequencies between 20kHz and 10GHz, such as 1MHz-1GHz, such as 5MHz-50MHz, and apply the electrical signal over the first and second coatings. The ultrasound may be generated generally as described above for the sound. However, it may be desired to provide the ultrasound in a liquid, where the structural element may be submerged in the liquid which may also be allowed to enter into the firs and / or second sub-volumes. In relation to the (ultra) sound generation, it may be preferred that the structural element comprises a covering element covering an outer surface of the structural element, the covering element having one or more first openings each opening into the first sub-volume and / or the second sub-volume. In this manner, the generator may act as a standard speaker with a well-defined sound output (multiple may be provided if desired) so that the volume of the sound output in a desired direction may be larger. A seventh aspect of the invention relates to a sensor comprising a signal receiver and the structural element as described above, the signal receiver being configured to receive an Inspicos / 14 / 03 / 2025 / 13:20 electrical potential generated over the first and second coatings. Any deformation of the structural element will result in a potential being built up over the two coatings. This potential may be received and e.g. quantified to quantify the deformation. As mentioned, the deformation may be caused by a number of things. An eighth aspect of the invention relates to a force sensor comprising a signal receiver and a structural element as described above, the signal receiver being configured to receive an electrical potential, generated over the first and second coatings, caused by the force acting to deform the structural element. A calibration may be desired for quantifying the force from the potential received. As mentioned, the deformation may deform the structural element in a number of ways and the deformation may be determined, sensed and quantified. A nineth aspect of the invention relates to a sound sensor comprising a signal receiver and a structural element as described above, the signal receiver being configured to: - receive an electrical potential generated over the first and second coatings caused by the sound acting to deform the structural element, and - generate an electrical signal representing the sound. Sound impacting on an element, such as a diaphragm, engaging the structural element may cause a deformation of the structural element. Detecting or sensing this deformation is a detection or sensing of the sound. Alternatively, the sound may be allowed to impact directly on the structural element, again causing a deformation of the structural element which again creates a potential which may be detected or sensed. Further alternatively, the sound may be allowed to enter one or both sub-volumes and thus impact on the coatings and inner surfaces and thus deform the structural element in this way. Again, this will create a deformation causing the potential to exist. The sound will cause the generation of a signal which varies over time, as defined by the pressure pulses of the sound, so that the receiving of the potential may be a receiving over time, as is known in the art in e.g. microphones. It is noted that the electrical signal may be of any known type of signal representing a sound. Inspicos / 14 / 03 / 2025 / 13:20 A tenth aspect of the invention relates to an ultrasound sensor comprising a signal receiver and a structural element as described above, the signal receiver being configured to: - receive an electrical potential generated over the first and second coatings caused by the ultrasound acting to deform the structural element, and - generate information representing the ultrasound. The manner in which the ultrasound may interact with the structural element to cause the resulting deformation may be as described above in relation to the sound sensor. The information representing the ultrasound may represent any desired property with the ultrasound, such as a frequency thereof, an intensity thereof or the like. As is the situation with the ultrasound generator, it may be desired that the sensor is configured to sense ultrasound in a fluid, such as when submerged therein. Then, the fluid may be allowed to enter into the first and / or second sub-volumes. As is usual in ultrasonic devices, an ultrasound generator may also act as an ultrasound sensor, where the same element, here the structural element, is capable of both generate and output ultrasound and receive ultrasound and output the above information representing the ultrasound sensed. An eleventh aspect of the invention relates to an ultrasound sensor comprising: - an ultrasound generator configured to emit a fan shaped ultrasound beam, - a plurality of ultrasound sensors each comprising a structural element as described above, each ultrasound sensor being directed along a separate portion of the fan shaped ultrasound beam, and - a signal receiver configured to receive, from each ultrasound sensor, an electrical potential generated over the first and second coatings caused by ultrasound travelling along the pertaining portion of the fan shaped ultrasound beam and acting to deform the pertaining structural element. This particular aspect may be an ultrasound sensing head as used in e.g. examining a human body, detecting the shape of the ocean floor, or any other use. The operation is as is usual that the ultrasound beam is output toward the desired area and in a fan shaped beam fanning out from the emitter or sensor. Often the beam is desired more or less in a single Inspicos / 14 / 03 / 2025 / 13:20 plane in which the fan is provided. When the ultrasound is reflected, which may be caused by density interfaces or the like in the area, ultrasound is reflected back toward the sensor. The sensor has an array of individual sensors each configured to receive ultrasound from only a portion of the desired area receiving ultrasound from the source, so that the ultrasound received by a particular sensor describes only a portion of the area, such as an angle interval within the overall angle interval of the fan shaped beam. The sensors may relate to overlapping or non-overlapping areas or angle intervals. Different technologies are known for ensuring that the individual sensors view only a portion of the area. From the received signals, information may be derived from the area. It may be desired to implement the sensors as a type of Lidar or Sonar, where a distance to the reflecting portion is determined by a delay from output of the ultrasound and until reception of the reflected ultrasound. In this aspect, the sensors are implemented with structural elements so that the advantages thereof are obtained. Clearly, the ultrasound emitter may also be implemented as the above-mentioned ultrasound generator. A twelfth aspect of the invention relates to a method of manufacturing the structural element according to the first aspect of the invention. This method may comprise the steps of: i) providing a base structure arranged to provide a triply periodic minimal surface having disjoint first and second sub-volumes, ii) dipping said base structure in a fluid comprising at least one coating element, such as a coating element comprising at least one metal, to provide a coated base structure, iii) optionally removing any coating from an external surface, so that the first coating of the first sub-volume is not electrically connected to the second coating of the second sub-volume. Inspicos / 14 / 03 / 2025 / 13:20 Naturally, all aspects, embodiments, considerations, materials, structures, alternatives, and the like mentioned in relation to the first aspect are equally relevant to the second aspect of the invention. Thus, the structural element, the base structure, the coating(s), and the materials may be as described above. The base structure may be provided in any desired manner. As described below, a host of manners exist for manufacturing this element, such as additive manufacturing methods, also known as 3D printing. Dipping the base structure in the fluid allows the fluid to contact all internal wall portions of the base structure. This is a simple manner of coating the inner surfaces of the base structure. Alternative methods may be to flow the fluid through the base structure, such as by pouring it into openings of the base structure. Naturally, two different coatings or coating materials may be desired, one for each sub- volume. In that situation, one sub-volume may be sealed while the other is coated and vice versa. The base structure is now coated by the fluid. This coating may be dried, solidified or otherwise treated in order to ensure that it stays in place during subsequent steps and use. Naturally, the dipping may be complete so that all surfaces of the base structure are covered. Alternatively, only a portion of the base structure may be dipped if desired. A final but optional step is to remove any coating from the external surface of the structural element, such as from the outer wall portions described above. Such coating could act to short-circuit the coatings in the first and second sub-volumes, which is not desired. Such removal could be a mechanical removal, chemical removal, or the like. Alternatively, such external surface and / or outer wall portions could be protected before dipping so that no coating is provided on these portions. A protection could be a physical covering, e.g., using a masking coating on the external surface, or a covering using a material to which the fluid will not attach itself. Inspicos / 14 / 03 / 2025 / 13:20 In one embodiment, the step of providing the base structure comprises 3D printing the base structure. 3D printing may be additive manufacturing so that the printing realizes a triply periodic minimal surface CAD model. The step of providing the base structure may comprise providing the base structure: a) by photopolymerization of a resin provided in a VAT, b) by printing using a composite molten filament, c) by direct deposition of a suspension, slipcasting or d) by molding, such as where an inverse structure is generated and where the electromechanically functional material, or a precursor thereof, is added to the inverse structure, which is then removed. This removal may be by dissolution, evaporation, or physical removal. The above are already known manufacturing techniques. Photopolymerization using a VAT of a resin is a method where the already manufactured portion of the base structure is immersed in the vat so that a small proportion thereof extends over the surface of the portion of the base structure. This resin is then exposed to radiation, typically UV radiation, causing the resin to solidify and thus attach to the underlying base structure portion so that the base structure grows and then is slightly lowered to extend again under the surface of the resin in the VAT. Printing using a molten filament is another manner of manufacturing the base structure bit by bit, which may melt a filament, such as a polymer, which is then provided on a portion of an already manufactured portion of the base structure so that the base structure gradually is manufactured. Deposition of a suspension is a method using Slip casting, or slipcasting. It is a ceramic forming technique, and is widely used by commercial industry as well as contemporary fine artists as a way of making various ceramic forms. This technique is suitable for simple, functional objects such as cups and plates, as well as more complicated shapes like figurative ceramics that would be difficult to reproduce by hand or other forming techniques. The technique involves a clay body slip, which is essentially a liquid version of clay, usually Inspicos / 14 / 03 / 2025 / 13:20 prepared in a blunger, being poured into plaster molds and allowed to form a layer, the cast, on the internal walls of the mold. Molding using an inverse structure is also a known manner in which an inverse structure of the base structure is generated. This method is also known as free injection molding. It may be generated in a number of manners, such as by embedding an element with the desired shape in a moldable material, such as glue, resin, polymer, or the like, which is then, if required, solidified whereafter this element is removed leaving space for the electromechanically functional material. This removal may, e.g., be a dissolution of the element. Alternatively, the inverse structure may be 3D printed. The material added to the inverse structure may be the electromechanically functional material or a precursor thereof. The final structure may be post-treated to arrive at the electromechanically functional material, such as by sintering or further manufacturing steps. The removal of the inverse structure may be by dissolution, melting, physical removal, evaporation, or the like, depending, a.o., on what type of material it consists of and what type of removal process the material therein can withstand. As mentioned, the base structure is made of or comprises an electromechanically functional material, whereby the resin, in the method a), preferably is an electromechanically functional material. If method b) is used, the filament preferably is an electromechanically functional material suspended in a liquid. If method c) is used, the suspension preferably comprises an electromechanically functional material suspended in a liquid. If method d) is used, the material added to the inverse structure, preferably an electromechanically functional material, in a thermoplastic material to be injected, which cannot be dissolved with the mold. An alternative manner of manufacturing the base structure comprises: Inspicos / 14 / 03 / 2025 / 13:20 - providing a preliminary base structure of a material of a binder and an electromechanically functional material, - debinding said first preliminary base structure to provide a second preliminary base structure and - sintering said second preliminary base structure. The preliminary base structure may have the same shape as the desired base structure or may be, e.g., larger if a shrinking is expected in the debinding or sintering steps. The binder may be any type of binder, such as glue or resin. Typically, the binder is a material evaporating / incinerating at a temperature between room temperature and the sintering temperature (see below). Then, debinding may take place in the course of heating the preliminary base structure for also sintering the material. Debinding may remove all or part of the binder. It may be desired that part of the binder remains in the structure to provide structural integrity before the sintering is completed. Some binders are capable of debinding by incineration, leaving behind a layer of carbon, which may act to provide sufficient structural integrity until and during sintering. Sintering often acts to have the electromechanically functional material remain in the structure but is now in a state with sufficient structural integrity and microstructural continuity. Sintering may, e.g., interconnect individuals, touching particles by having part of the particles flow to the intersection between the particles. Then, the step of providing the preliminary base structure may be to provide this structure with a material comprising the binder and particles of the electromechanically functional material. Then, the final result may be the desired base structure comprising only or at least substantially only the electromechanically functional material. As mentioned above, the base structure may be a ceramic base structure, preferably a fully ceramic base structure such as a fully dense base structure. Alternatively, the base structure may be a porous ceramic base structure. A porous ceramic may be generated by a pore-forming material in the ceramic material or a precursor thereof, such as particles. This may be in a state where the initial material is moldable or flexible. Inspicos / 14 / 03 / 2025 / 13:20 Such pore-forming material may then be removed during solidification of the ceramic material. Solidification may be a sintering of the type described above. In one situation, the step of dipping said base structure comprises dipping said base structure in a paste comprising at least one conductive element, preferably at least one metal or alloy. Even more preferably, the base structure is dipped in a metal conductive paste, such as a paste comprising nickel, copper, silver and / or gold. The step of removing any external coating from the external surface may, as described above, comprise mechanically removing any external coating from the external surface. This removal is preferably performed by mechanical grinding or polishing. Alternatively, a removable material may be provided to the base structure, such as on outer wall portions thereof, before dipping or evaporating and condensing the metals so that the coating adheres to this removable material, or does not adhere thereto, and not on the base structure in such positions. Then, the removal step may comprise removing this removable material and thus also any coating adhering thereto. A removable material may be a polymeric material that works as a physical mask and may be applied to the external surface of the structural element and may be removed by selective dissolution. Another aspect of the invention relates to using the structural element according to the first aspect of the invention or manufactured according to the second aspect of the invention, the method comprising applicating an electrical potential, i.e., voltage, over the first and the second coatings. This may cause the electromechanically functional material to deform and, thus, the overall shape of the structural element to alter. Another aspect of the invention relates to using the structural element according to the first aspect of the invention or manufactured according to the second aspect of the invention, the method comprising deforming the structural element and determining a voltage difference between the first and second coatings. In this manner, the deformation may be correlated with the voltage and thus function as a sensor. As indicated above, the method may be a method of altering a physical dimension of the structural element as described above, the method comprising applying an electrical potential over the first and the second coatings. As mentioned above, it may be desired that the base structure comprises a first portion having a first wall thickness and a second portion having a second wall thickness, the first wall thickness being larger than the second wall thickness, where the deformation of the Inspicos / 14 / 03 / 2025 / 13:20 second portion being larger than the deformation of the first portion. A difference in wall thickness may be 1:2 to 1:10, such as 1:2 to 1:5. In one embodiment, the applying step comprises the structural element altering its physical dimensions along three directions perpendicular to each other, where the altering for all directions is a contraction or an expansion. This is the so-called auxetic behaviour which is obtained in this type of materials provided by this particular structure. Clearly, the application of the signal could be the application or a DC signal or a signal which varies in time, depending on the desired deformation and the use thereof as explained above and below. In one embodiment, the applying step comprises the structural element applying a force to an element engaging the structural element. The force may be applied one or sequentially and is controlled or defined by the signal, such as a frequency or voltage thereof. In one embodiment, the applying step comprises the structural element applying a translation to an element engaging the structural element. The translation may be applied one or sequentially and is controlled or defined by the signal, such as a frequency or voltage thereof. As mentioned, for a number of applications, it is desired that the applying step comprises applying a potential varying over time. The variation may be swift, such as when generating sound or ultrasound, or slower such as when imparting a force or translation on a physical element such as when controlling a valve or the like. The signal may be used for arriving at a desired deformation, after which it may be kept constant. In a particularly interesting embodiment, the structural element comprises a covering element covering an outer surface of the structural element, the covering element having one or more first openings and one or more second openings each opening into the first sub- volume, wherein the applying step comprises a first fluid entering the first sub-volume through the first opening(s) and exiting the structural element through the second opening(s). The covering element and the openings are described above where it is seen that the covering element may be used when transporting, inputting or outputting fluid, such as liquid, suspensions or gas. It may be desired to that the applying step comprises a first one-way valve allowing flow of the a first fluid from surroundings of the structural element to the first sub-volume via the Inspicos / 14 / 03 / 2025 / 13:20 one or more openings. This may create a unidirectional flow in the structural element between the first and second openings. Another manner of obtaining a unidirectional flow is when the applying step comprises a second one-way valve allowing flow of a first fluid from the first sub-volume to the surroundings via the one or more second openings. Naturally the first and second valves may be used in the same embodiment. Also the second sub-volume may be employed, such as when the one or more first openings and one or more second openings open into also the second sub-volume, where the applying step comprises the first fluid also entering the second sub-volume through the one or more first openings and exiting the second sub-volume through the one or more second openings, optionally via the first and / or second valves. In another embodiment, the covering element has one or more third openings and one or more fourth openings each opening into the second sub-volume, wherein the applying step further comprises a second fluid entering the second sub-volume through the third opening(s) and exiting the structural element through the fourth opening(s). In this manner, two different fluids may be transported at the same time. In this situation, the structural element further may comprise a third one-way valve allowing flow of the second fluid from the surroundings to the second sub-volume via the one or more third openings and / or a fourth one-way valve allowing flow of the second fluid from the the second sub-volume to the surroundings via the one or more fourth openings. The third and fourth valves may be employed and may operate in the same manner as the first / second valves. Then, the method may be used for transporting two fluids at the same time. One situation where this may be especially interesting is when the applying step comprises transporting heat between the first and second fluids. Then, a heat exchanger may be obtained which in addition to the heat exchanging also pumps the fluids through the heat exchanger. Then, the operation of the valves may be set so that the applying step comprises flowing the first fluid, between the first and second openings, in a first general direction and flowing the second fluid, between the third and fourth openings, in a second general direction at least substantially opposite to the first direction which is often desired in heat exchangers so that the cooling profile of one fluid through the heat exchanger follows the heating profile of the other fluid. Naturally, if desired, the two fluids may alternatively flow in generally the same direction as described further up. Inspicos / 14 / 03 / 2025 / 13:20 A thirteenth aspect of the invention relates to a method of generating sound, the method comprising: - providing a structural element according to the first aspect, - providing an electrical signal representing the sound, - applying the electrical signal over the first and second coatings. This is described further above. A fourteenth aspect of the invention relates to a method of generating ultrasound, the method comprising: - providing a structural element according to the first aspect, - providing an electrical signal having one or more frequencies between 20kHz and 10GHz, - applying the electrical signal over the first and second coatings. This is described further above. When generating (ultra) sound, the step of providing the structural element may comprise providing the structural element comprising a covering element covering an outer surface of the structural element, the covering element having one or more first openings each opening into the first sub-volume. As mentioned above, both sub-volumes may be employed for the generation of the (ultra) sound. A fifteenth aspect of the invention relates to a method of operating a transducer according to the second aspect, wherein the signal provider applies a potential over the first and second coatings. As mentioned, the signal may be a DC signal, a varying signal and / or a repeating signal such as a signal with one or more frequencies. Preferably, the signal provider applies a potential varying over time over the first and second coatings. This may be used for many different purposes as described above and below. Inspicos / 14 / 03 / 2025 / 13:20 A sixteenth aspect of the invention relates to a method of operating a heat exchanger according to the fourth aspect of the invention, wherein the signal provider applies a potential varying over time over the first and second coatings. In relation to both the pump embodiments and the heat exchanger embodiments, it may be desired that the signal is periodic in order to provide a steady flow of the fluids. Clearly, a frequency and / or intensity of the signal may be used for controlling the flow. An eighteenth aspect of the invention relates to a method of operating a sound generator according to the fifth aspect, wherein the signal generator provides an electrical signal representing a sound and applies the electrical signal over the first and second coatings. The signal and the manners of embodying the sound generator are explained above. A nineteenth aspect of the invention relates to a method of operating an ultrasound generator according to the sixth aspect, wherein the signal generator provides an electrical signal having one or more frequencies between 20kHz and 10GHz and applies the electrical signal over the first and second coatings A twentieth aspect of the invention relates to a method of sensing a deformation of a structural element according to the first aspect, the method comprising sensing a potential generated over the first and second coatings by the deformation. This is described above. A calibration or the like may be generated for converting the potential into a measure of the deformation. A twenty first aspect of the invention relates to a method of sensing a force acting to deform a structural element according to the first aspect, the method comprising allowing the force to deform the structural element and sensing a potential generated over the first and second coatings by the deformation. This is described above. A calibration or the like may be generated for converting the force into a measure of the deformation. A twenty second aspect of the invention relates to a method of sensing sound, the method comprising: - allowing the sound to impact on a structural element according to the first aspect so that the sound deforms the structural element, - sensing a potential generated over the first and second coatings by the deformation, and - generating an electrical signal representing the sound. Inspicos / 14 / 03 / 2025 / 13:20 Different manners of embodying this and different types of electrical signals are described above. A twenty third aspect of the invention relates to a method of sensing ultrasound, the method comprising: - allowing the ultrasound to impact on a structural element according to the first aspect so that the sound deforms the structural element, - sensing a potential generated over the first and second coatings by the deformation, and - generating information representing the ultrasound. Different manners of embodying this and different types of information are described above. A twenty fourth aspect of the invention relates to a method of operating a sensor according to the eleventh aspect of the invention, the method comprising: - the ultrasound generator launching the fan shaped beam into a target substance comprising a plurality of elements each reflecting part of the ultrasound, - each ultrasound sensor being impacted by reflected ultrasound, deforming and generating an electrical potential over its first and second coatings, - the signal receiver receiving, from each ultrasound sensor, the electrical potential and generating information representing the potential and a direction of the pertaining ultrasound sensor. This sensor and its operation is described above. In the following, preferred embodiments are described with reference to the drawing wherein: Fig. 1 illustrates the first example of a structural element according to the invention, Fig. 2 illustrates a unit cell of the structural element of Figure 1, Fig. 3 illustrates electrodes over a wall portion, Fig. 4 illustrates a second example of a structural element according to the invention, Inspicos / 14 / 03 / 2025 / 13:20 Fig. 5 illustrates a third example of a structural element according to the invention, Fig. 6 illustrates seven different examples of structural elements according to the invention, Figs. 7A-C illustrates the first manner of manufacturing a structural element according to the invention, Fig. 8 illustrates a second manner of manufacturing a structural element according to the invention, Fig. 9 illustrates the Fischer-Koch TPMS shape, Fig. 10 illustrates a Boolean intersection of the Gyroid infinite surface with a sphere, Fig. 11 illustrates a Gyroid with anisotropic scaling, Fig. 12 illustrates a Gyroid with variable scaling, Fig. 13 illustrates a Gyroid with variable rotation, defined from a cylindrical coordinate system, Fig. 14 illustrates variable morphing between two different kinds of minimal surfaces, Fig. 15 illustrates a TPMS structure with electrodes for deforming, actuating or sensing, Fig. 16 illustrates deformation of different TPMS structures, Fig. 17 illustrates a TPMS structure embodied as a pump and Fig. 18 illustrates a TPMS structure embodied as a heat exchanger. Definitions A pure Triply Periodic Minimal Surface structure A pure minimal surface is a surface for which the total surface area is invariant with respect to any sufficiently small deformation of the surface. Minimal surfaces are thus relevant points Inspicos / 14 / 03 / 2025 / 13:20 of the functional that expresses the total area. It has been proved that this invariance requirement implies that the mean curvature of the surface is equal to zero at any point. A pure Triply periodic minimal surface is a minimal surface that is also periodic along three spatial dimensions. This means that the pure shape is obtained by arranging multiple copies of a representative elementary volume (REV) in a three-dimensional array. The resulting structure is thus periodic, in the sense that there exist three linearly independent directions along which the structure exhibits discrete translational symmetry. If it is translated by an amount equal to the length of the REV along that direction (or any multiple), the resulting structure is identical to the original one. TPMS are free of self-intersections, orientable, and divide space into two disjoint sub- volumes. The gyroid is an exemplary structure (space group I4132) among the twelve TPMS symmetries. The gyroid is a non-trivial Schwarz surface that separates space into two oppositely congruent sub-volumes. The short equation sin x cos y + sin y cos z + sin z cos x = 0 trigonometrically approximates its surface. The gyroid is also a congruent geometry with a symmetry mapping of one sub-volume onto the other, i.e., a balance surface [ref]. A Triply Periodic Minimal Surface structure is obtained from the ideal two-dimensional infinite surface by thickening the surface. The thickening operation consists of constructing the portion of volume that is comprised between two surfaces that are obtained by expanding the original surface in each point along the local direction corresponding to the normal vector on either side of the surface. Additionally, only a finite portion of the original infinite surface is considered, typically corresponding to a given number of REV along each of the three dimensions of the periodic array. A TPMS is invariant under a rank-3 lattice of translations and combines orientable surface- periodic arrangements, dividing space into two disjoint sub-volumes, i.e., free of self- intersections. Known pure Triply Periodic Minimal Surface comprises Gyroids, Lidinoid, and the many surfaces named after Schoen, Schwarz, or Neovius. Mean curvature For a planar curve, the curvature κ is the reciprocal of the radius of curvature R, which is simply the radius of the circle that best approximates the curve at a given point (i.e. the radius of the so-called osculating circle). Inspicos / 14 / 03 / 2025 / 13:20 For each point of a surface embedded in a three-dimensional space, we have to consider the two principal directions. The mean curvature, H, in a given point of the surface is thus defined as the arithmetic mean of the principal curvatures, κ and κ2, i.e., the curvatures along the principal directions. A surface S can be defined implicitly via the equation F (x) = F (x, y, z) = 0 (2) The gradient of F is normal to S. The unit normal n̂ is thus given by: It has been proved that the mean curvature is equal to the negative of the divergence of the unit normal multiplied by 1 / 2, i.e.: Relation between surface area and mean curvature It has been proved that surfaces with minimal surface area are also having zero mean curvature at any point, and vice versa. Therefore, the property of having zero mean curvature can be used as a definition of minimal surfaces. Without loss of generality, we consider the case of a surface that can be expressed as graph of a function, i.e.: z = u(x, y) (5) Implicitly, this surface is defined as F (x, y, z) = 0, where F is given by: F (x, y, z) = z − u(x, y) (6) Inspicos / 14 / 03 / 2025 / 13:20 The implicit function theorem guarantees that for any continuously differentiable function such a local parameterization can be constructed at any point, possibly along a different direction than the z direction. Curvature Let us now calculate the mean curvature of the surface. The gradient of F is: The norm of the gradient is thus given by: Since the unit normal ∇F / ∥∇F ∥ does not depend on the variable z, the divergence contains only the derivatives with respect to x and y: Where uxand uydenote the partial derivatives of u with respect to x and y,respectively. Surface area For a surface defined by z = u(x, y) the functional giving the area of the surface is expressed as: The condition that the area is minimized is expressed by the mathematical requirement that the surface is a critical “point” of the functional expressing the Inspicos / 14 / 03 / 2025 / 13:20 surface area. For a given functional, the equation giving the critical point is known as Euler-Lagrange equation. The Euler-Lagrange equation for the functional under consideration is: This equivalence, (see equation 9) links the concepts of zero curvature surface and minimal area surface. Although we briefly showed here how this link emerges for the case of surfaces defined as graph of functions (i.e. as in Equation 5) the same result remains true regardless of the way the surface is defined. From surface to structure In order to obtain a realizable structure from the ideal infinite surface, it is first necessary to restrict it to a surface of a finite extent. Typically, this can be done by considering a given number of REV along each of the three dimensions of the periodic array. However, it is also possible to consider the boolean intersection between the infinite surface and a finite shape. For example, in the case shown in Figure 10 the gyroid has been intersected with a sphere. The object that the TPMS is intersected with may have arbitrary topology, e.g., have holes. The last step is converting the infinitely flat surface S, (defined by F(x, y, z) = 0), into a solid object, i.e., thickening the surface. There are two main methods of performing this geometrical procedure. The first method consists of constructing the portion of volume that is comprised between two surfaces, S+ and S−, that are obtained by expanding the original surface S in each point along the local direction corresponding to the normal vector on either side of the surface. With this method, the thickness t of the resulting solid is constant. However, neither of the two external surfaces S+ and S− will strictly obey the condition of zero mean curvature originally verified by S. The thickness can be deliberately be made variable by making the parameter t space dependent, i.e. t = t(x, y, z). Inspicos / 14 / 03 / 2025 / 13:20 The second method consists of constructing the two external surfaces S+ and S− from the equations: where c is a constant that will determine the average of thickness of the resulting solid. The thickness of the resulting solid may be variable across each REV when the surface is constructed in this way, although the periodicity would still be satisfied, as long as c is a constant. Conversely, thickness variation can be deliberately controlled by making the parameter c space dependent, i.e. c = c(x, y, z). Transformations We consider a surface defined implicitly, such as in Eq. 13. A number of transformations can be applied before performing the thickening operation described above. These operations can be applied to these surfaces regardless of how they are defined. It is important to notice that the properties originally satisfied by minimal surfaces may not be satisfied anymore after these transformations have been applied. Scaling A change of scale may be obtained by the following transformation: where kx, ky, and kz are the scaling factors, which might be different from each other if the scaling is anisotropic as in the example shown in Figure 11. These parameters can be themselves space dependent (e.g. kx = kx(x, y, z)) in order to achieve a variable scaling as in the example shown in Figure 12. Rotation Inspicos / 14 / 03 / 2025 / 13:20 The surface can of course be rotated with a corresponding transformation. The most relevant case is that of a space-dependent rotation. Among these, it is worth mentioning the rotation that is obtained when considering a coordinate transformation between orthogonal coordinate systems (e.g.: Cartesian to cylindrical coordinates). When the original coordinates (x, y, z) are transformed to another orthogonal system (u, v,w), the corresponding operation is equivalent to a space-dependent rotation that follows the new coordinate system. Figure 13 shows an example of such a rotation, obtained by considering cylindrical coordinates as (u,v,w), where the left illustration is seen from the side and the right illustration is a top view.. Two (or more) different kinds of triply periodic minimal surfaces can be morphed into each other. This is achieved by making a linear combination of the corresponding function. Let us denote by FGyroid(x, y, z) the function that implicitly defines the gyroid with the equation FGyroid(x, y, z) = 0, as expressed by Equation 13. Similarly, we denote by FSchwarz(x, y, z) the function corresponding to the Schwarz Primitive surface. Then, we can morph these two kinds of surfaces by considering the equation: 20 where a and b are two parameters. As in the previous examples, the parameters a and b may be space dependent, in order to achieve a variable morphing. This is illustrated in the example of Figure 14. Figure 1 illustrates an example of a structural element 10 according to the invention. This element has the so-called gyroid shape and its unit cell is illustrated in figure 2. The structure 10 has a base structure 11 made of an electromechanically functional material, such as a piezoelectric ceramic, and defines two inner sub-volumes 12 and 14, the walls, 12’ and 14’, respectively, of each of which is coated by an electrically conductive material 16. The walls 12’ and 14’ may be coated with the same or different materials. Inspicos / 14 / 03 / 2025 / 13:20 When the base structure is made of an electromechanically functional material, providing electrodes 19 and a voltage over these (see figure 3) may activate the electromechanically functional element to deform and / or a deformation of the base structure may cause a voltage to exist between the electrodes 19. Naturally, the electrodes may be provided in any desired manner, such as as two symmetric surfaces with no intersections and constant mean curvature. Especially if the base structure has the shape of a TPMS, the latter property is linked to balance surface area variation being zero under small deformations. Figure 4 illustrates another shape of a structural element 10 which again has the sub- volumes 12 and 14, the coatings and the like. Figure 5 illustrates another shape of a structural element 10 which again has the sub- volumes 12 and 14, the coatings and the like. In common of the structural elements is the two sub-volumes, coatings and the walls dividing these (formed by the base structure). The two sub-volumes 12, 14 are not connected within the structural element, but as the structural element naturally has a finite extent, outer portions thereof will exist where the two sub-volumes open into eg. the surroundings. At these outer portions, the walls of the base structure have outer portions 20 facing the surroundings and thus not forming part of the wall portions defining the two sub-volumes. These outer portions 20 are not covered by the conductive material(s) 16, so that the coatings of the two sub-volumes are not electrically connected. In this manner, a voltage provided between the two coatings is seen over all inner wall portions of the base structure 11. Naturally, when the base structure has different shapes (see also figure 6), the outer portions 20 have different shapes. Figure 6 illustrates seven different types of TPMS’, the Schwarz D and P, Diamond, Gyroid, Neovius, Primitive and I-WP shapes. In figure 9, the Fischer-Koch shape is seen. Methods of manufacture A base structure may be provided or manufactured in a number of manners. One way to provide the base structure is additive manufacturing (AM), such as 3D printing. Inspicos / 14 / 03 / 2025 / 13:20 In Figure 7A-C, manufacturing of a gyroid-shaped structural element is seen where, in figure 7A, the base structure is provided, such as by 3D printing (see also below). This base structure is provided with a coating on all surfaces as seen in figure 7B, where-after the outer wall portions 20 are ground or polished to remove the electrically conducting coating at these portions so that the coatings of the two sub-volumes is electrically disconnected. This results in the structural element seen in figure 7C. Additive manufacturing methods may be used for manufacturing the base structure such as digital light processing (DLP) or stereolithographic (SLA) 3d printing or free-injection moulding and filament deposition methods (FDM). In principle, other subtractive methods, such as carving, are possible but not practical. A precursor basic structure may be made of a mixture of a binder and the desired electromechanically functional material or a precursor thereof. This mixture may shaped in the desired shape, whereafter, in a debinding step, the binder may be removed or partly removed, whereafter the desired base structure may be obtained. Further steps may be required, such as a sintering, in order to arrive at the base structure. The base structure may be porous or fully dense. A pore former may be added to the electromechanically functioning material if porosity is desired and this does not in itself form the desired porosity. In figure 8, another manufacturing method is illustrated, i.e. moulding where a precursor shape is made and the piezoelectric or electrostrictive material is added there-into and subsequently solidified. This resuting shape may be sintered if desired to arrive at the final shape. This shape may then be coated as desired to arrive at the final product. Any piezoelectrical or electrostrictive material may be used, such as a renowned lead-free piezoceramic, i.e. K0.5Na0.5NbO3 (KNN). In the following various types of TPMS based actuators, sensors as well as combinations thereof (in the form of transducers) will be disclosed with reference to Figs. 15 to 18. With reference to Fig. 15 the electrodes of a TPMS structure are electrically connected to a voltage source which is here exemplified as an AC voltage source. However, and as also depicted in the lower part of Fig. 15, other types of voltage sources, such DC voltage sources and pulsed DC voltage sources, are also applicable. The dynamic range may be from 20 kHz to THz. Inspicos / 14 / 03 / 2025 / 13:20 As previously disclosed, the TPMS structure will, in general, deform (expanding or contracting) in an auxetic manner in response to an applied voltage. In Fig. 15 the TPMS structure contracts in response to an applied voltage. The degree of expansion / contraction depends on various parameters, including the thickness of the walls separating the two volumes within the TPMS structure. As a general rule, a thin wall (between the two volumes) expanse / contracts more compared to a thick wall. Moreover, the expansion / contraction may be controlled by varying the voltage level applied to the TPMS structure. In terms of actuator-related applications, TPMS structure may be used in various types of actuators, including displacement, force, pump, positioning and motion actuators. Moreover, actuators for generating pressure variations, such as in the pressure variations in the ultrasound frequency range, may be provided. Turning now to Fig. 16, TPMS structures with varying wall thicknesses are depicted. As the expansion / contraction of TPMS structures depends on the wall thicknesses, TPMS actuators with tailored properties may be provided if different wall thicknesses are incorporated into the same TPMS structure. The ratio between the smallest and largest thicknesses may for example be in the range of 5-10. In addition, or in combination therewith, TPMS structures may comprise walls of different materials that expand / contract differently when a voltage is applied to the electrodes on the walls. Referring now to Fig. 16b, a TPMS structure with thinner walls in the middle section is depicted. When a voltage is applied to this TPMS structure the structure will deform as depicted in Fig. 16d, where the upper illustration is a top view, whereas the lower illustration in Fig. 16d is a side view. The bottom surface / side is fixated in Fig. 16d. As seen in the upper illustration, the TPMS structure contracts in the middle section. In the lower illustration the bottom surface / side is fixated whereas the top surface / side of the TPMS structure contracts. Similarly, a clamp shaped TPMS structure is depicted in Fig. 16a (lower illustration) where the jaws of the TPMS clamp structure are configured to open when a voltage is applied to the TPMS structure, cf. Fig. 16c (lower illustration). In the upper illustrations of Figs. 16a and 16c show examples of programmable piezoelectric TPMS metamaterial. Figure 16a illustrates simulated non-cubic architectures with multi- morphic actuation that preserves auxetic properties and concentrates displacement in desired directions, such as spherical omnidirectional (hemisphere) and punctual (C-shape). Due to the wall-thickness-strain relation, the auxetic multi-morphic actuation can be functionally Inspicos / 14 / 03 / 2025 / 13:20 graded structures (Figure 16b) and spatial parameterized (Figure 16c). The latter can be achieved by replacing the constant in the TPMS level-set equation with a scalar field, c(x,y,z), allowing for spatial control of the structural thickness, as shown in Figure 16c. Turning now to Fig. 17, a TPMS actuator in the form of a pump is depicted. As depicted in Fig. 17 the TPMS structure (with an optimized shape) is encapsulated in silicone so that the silicone seals the outer shape of the TPMS structure while keeping the inner volumes of the TPMS structure free so that fluidic drugs in the form a liquids or gasses may flow freely inside the TPMS structure. The silicone (or similar soft material) encapsulation is flexible so that it can deform with the TPMS structure. The silicone encapsulation further incorporates suitable tubing and wiring for the actuator. Two one-way valves are applied to ensure flow in one direction (from left to right). In a non-contracted state, the fluidic drug is allowed to enter the volumes of the TPMS structure. When a voltage is applied to the TPMS structure the TPMS structure contracts and the fluidic drug is pumped out of the volumes of the TPMS structure in the direction towards right. Fig. 18 shows a double-flow configuration where the two volumes in the TPMS structure pump fluids in opposite directions with the help of four one-way valves. As illustrated in Fig. 18 one volume pumps fluids in one direction, whereas the other volume pumps fluids in the opposite direction. With this arrangement, two fluids can be pumped simultaneously, and / or heat exchangers for liquids and / or gases may be provided where the thermal exchange properties of the fluids and the materials allow it. In case of TPMS structure based actuators for generating pressure variations in for example the ultrasound frequency range the electrodes of the TPMS structure may act as membranes / diaphragms. Alternatively, or in combination therewith, external membranes / diaphragms may be driven by the electrodes of the TPMS structure in order to generate pressure variations in the ultrasound frequency range. Turning now to the area of sensors, TPMS structures may be applied in different kinds of sensors, including pressure sensors, force sensors, acceleration sensors (accelerometers), vibration sensors, ultrasound sensors, acoustic sensors, strain sensors, impact sensors and gas and chemical sensors. In case of TPMS structure based sensors for measuring pressure variations in for example the ultrasound frequency range the electrodes of the TPMS structure may act as membranes / diaphragms. Alternatively, or in combination therewith, external membranes / diaphragms may be operatively connected to the electrodes of the TPMS structure. In case of vibration sensors a suspended moveable mass may be operatively Inspicos / 14 / 03 / 2025 / 13:20 connected to the electrodes of the TPMS structure so that the electrodes vibrate when the vibration sensor as a whole is exposed to mechanical vibrations. With respect to TPMS based transducers involving both actuators and sensors an example of an ultrasound transducer will be disclosed in the following. The TPMS based transducer may involve one or more TPMS actuators for generating pressure variations in the ultrasound frequency range. As already mentioned, the electrodes of the TPMS structure may act as membranes / diaphragms. Alternatively, or in combination therewith, external membranes / diaphragms may be driven by the electrodes of the TPMS structure in order to generate pressure variations in the ultrasound frequency range. The TPMS based transducer may further involve one or more TPMS sensors for measuring pressure variations in the ultrasound frequency range. As already mentioned, the electrodes of the TPMS structure may act as membranes / diaphragms. Alternatively, or in combination therewith, external membranes / diaphragms may be operatively connected to the electrodes of the TPMS structure. In case the TPMS based transducer comprises a plurality of TPMS actuators and a plurality of the TPMS sensors these may be arranged in a matrix like manner with dedicated TPMS actuators as well as dedicated TPMS sensors. Alternatively, the very same TPMS structure may be used as both an ultrasound actuator and an ultrasound sensor. With proper signal processing TPMS based transducer may be used for ultrasound imaging, including ultrasound echo imaging, such as medical echography or marine sonars for seabed imaging. Inspicos / 14 / 03 / 2025 / 13:20

Claims

CLAIMS 1. A structural element comprising a base structure defining a triply periodic minimal surface having disjoint first and second sub-volumes and an external surface, wherein the base structure is made of an electromechanically functional material, wherein the surface of the first sub-volume comprises a first coating of a first electrically conductive material, wherein the surface of the second sub-volume comprises a second coating of a second electrically conductive material, and wherein the coating of the first sub-volume is arranged to not be in electrical contact with the coating of the second sub-volume.

2. The structural element according to claim 1, wherein the coating of the surface of the first sub-volume is arranged to be in contact with a first external electrode, and wherein the coating of the surface of the second sub-volume is arranged to be further in contact with a second external electrode, and the first and second external electrode are arranged to provide an electrical potential.

3. The structural element according to any preceding claims, is wherein the external surface is arranged to be free to expand and / or contract in more than one direction.

4. The structural element according to any one of the preceding claims, wherein the electromechanically functional material is a piezoelectric or electrostrictive material.

5. The structural element according to claim 4, wherein the electromechanically functional material is an electrostrictive material comprising a ceramic electrostrictor.

6. The structural element according to any one of the preceding claims, wherein the base structure is arranged to provide a triply periodic minimal surface selected from a gyroid surface, Schwarz H surface, Schwarz primitive (Schwarz P) surface, diamond surface, Split primitive (Split P) surface, Lidinoid surface, Fischer-Koch and a Neovius surface.

7. The structural element, according to any one of the preceding claims, wherein the first and / or the second electrically conductive material is a metal.

8. The structural element according to any of the preceding claims, wherein the base structure comprises a first portion having a first wall thickness and a second portion having a second wall thickness, the first wall thickness being different from the second wall thickness. Inspicos / 14 / 03 / 2025 / 13:

209. A transducer comprising the structural element according to any of claims 1-8, and a signal provider, the signal provider being configured to apply an electrical potential over the first and second coatings.

10. A transducer according to claim 9, wherein the applied potential is configured to alter the physical dimensions of the structural element along three directions perpendicular to each other.

11. A transducer according to claim 9 or 10, configured to have the structural element, as a result of the applied potential, apply a force to an element engaging the structural element.

12. A transducer according to any of claims 9-11, configured to have the structural element, as a result of the applied potential, apply a translation to an element engaging the structural element.

13. A transducer according to any of claims 9-12, wherein the signal provider is configured to apply a potential varying over time.

14. A transducer according to claim 13, wherein the structural element comprises a covering element covering part of the external surface of the structural element, the covering element having one or more first openings and one or more second openings, each first and second opening opening into the first sub-volume.

15. A transducer according to claim 14, further comprising a first one-way valve configured to allow flow of a first fluid from surroundings of the structural element to surroundings of the first sub-volume via the one or more first openings.

16. A transducer according to claim 14 or 15, further comprising a second one-way valve configured to allow flow of a first fluid from the first sub-volume to surroundings of the structural element via the one or more second openings.

17. A transducer according to any of claims 14-16, wherein the one or more first openings and one or more second openings open into also the second sub-volume.

18. A transducer according to any of claims 14-16, wherein the covering element further comprises one or more third openings and one or more fourth openings each opening into the second sub-volume. Inspicos / 14 / 03 / 2025 / 13:2019. A transducer according to claim 18, wherein the structural element further comprises a third one-way valve configured to allow flow of a second fluid from surroundings of the structural element to the second sub-volume via the one or more third openings. .

20. A transducer according to claim 18 or 19, wherein the structural element further comprises a fourth one-way valve configured to allow flow of a second fluid from the second sub-volume to surroundings of the structural element via the one or more fourth openings.

21. A transducer according to any of claims 14-20, wherein the structural element comprises a first and a second non-overlapping outer surface portions, wherein the first opening(s) is / are provided in the first outer surface portion and the second opening(s) is / are provided in the second outer surface portion.

22. A transducer according to any of claims 18-20 where the fourth opening(s) is / are provided in the first outer surface portion and the third opening(s) is / are provided in the second outer surface portion.

23. A transducer according to any of claims 18-20 where the third opening(s) is / are provided in the first outer surface portion and the fourth opening(s) is / are provided in the second outer surface portion.

24. A pump comprising a first fluid source, a first fluid receiver and a transducer according to any of claims 9-23, wherein the first fluid source is fluidly connected to the first opening(s) and the first fluid receiver is fluidly connected to the second opening(s).

25. A heat exchanger comprising a first fluid source, a first fluid receiver, a second fluid source, a second fluid receiver and a transducer according to any of claims 18-23, wherein the first fluid source is fluidly connected to the first opening(s), the first fluid receiver is fluidly connected to the second opening(s), the second fluid source is fluidly connected to the third opening(s) and the second fluid receiver is fluidly connected to the fourth opening(s).

26. A sound generator comprising a signal generator and a structural element according to any of claims 1-8, wherein the signal generator is configured to provide an electrical signal representing a sound and apply the electrical signal over the first and second coatings.

27. An ultrasound generator comprising a signal generator and a structural element according to any of claims 1-8, wherein the signal generator is configured to provide an electrical signal having one or more frequencies between 20kHz and 10GHz and apply the electrical signal over the first and second coatings. Inspicos / 14 / 03 / 2025 / 13:2028. A sound generator according to claim 26 or an ultrasound generator according to claim 27, wherein the structural element comprises a covering element covering an outer surface of the structural element, the covering element having one or more first openings each opening into the first sub-volume.

29. A sensor comprising the structural element according to any of claims 1-8, and a signal receiver, the signal receiver being configured to receive an electrical potential generated over the first and second coatings.

30. A force sensor comprising a signal receiver and a structural element according to any of claims 1-8, the signal receiver being configured to receive an electrical potential generated over the first and second coatings caused by the force acting to deform the structural element.

31. A sound sensor comprising a signal receiver and a structural element according to any of claims 1-8, the signal receiver being configured to: - receive an electrical potential generated over the first and second coatings caused by the sound acting to deform the structural element, and - generate an electrical signal representing the sound. (signal will vary over time) 32. An ultrasound sensor comprising a signal receiver and a structural element according to any of claims 1-8, the signal receiver being configured to: - receive an electrical potential generated over the first and second coatings caused by the ultrasound acting to deform the structural element, and - generate information representing the ultrasound.

33. An ultrasound sensor comprising: - an ultrasound generator configured to emit a fan shaped ultrasound beam, - a plurality of ultrasound sensors each comprising a structural element according to any of claims 1-8, each ultrasound sensor being directed along a separate portion of the fan shaped ultrasound beam, and - a signal receiver configured to receive, from each ultrasound sensor, an electrical potential generated over the first and second coatings caused by ultrasound Inspicos / 14 / 03 / 2025 / 13:20travelling along the pertaining portion of the fan shaped ultrasound beam and acting to deform the pertaining structural element.

34. A method of manufacturing the structural element according to any one of claims 1-8, said method comprising the steps of: i) providing a base structure arranged to provide a triply periodic minimal surface having disjoint first and second sub-volumes, ii) dipping said base structure in a fluid comprising at least one coating element, such as a coating element comprising at least one metal, to provide a coated base structure, and iii) optionally removing any coating from an external surface, so that the first coating of the first sub-volume is not electrically connected to the second coating of the second sub-volume.

35. The method according to claim 34, wherein the step of providing the base structure comprises providing the base structure: ^ by photopolymerization of a resin in a vat, ^ using a composite molten filament, ^ using direct deposition of suspensions or ^ by generating an inverse structure of the base structure, adding the electromechanically functional material thereto and finally removing the inverse structure.

36. The method according to claim 34, wherein the step of providing the base structure comprises: - providing a preliminary base structure of a material of a binder and an electromechanically functional material, - debinding said first preliminary base structure to provide a second preliminary base structure and - sintering said second preliminary base structure.

37. The method according to any one of claims 34-36, wherein the step of providing the base structure comprises providing a ceramic base structure.

38. The method according to any one of claims 34-37, wherein the step of providing a base structure comprises providing a porous ceramic base structure. Inspicos / 14 / 03 / 2025 / 13:2039. The method according to any one of claims 34-38, wherein the step of dipping said base structure comprises dipping said base structure in a paste comprising at least one conductive element.

40. The method according to any one of claims 34-39, wherein the step of removing any external coating from the external surface comprises mechanically removing any external coating from the external surface.

41. Use of the structural element according to any one of claims 1-7 or manufactured according to any of claims 34-40, the method comprising applicating an electrical potential over the first and the second coatings.

42. A method of altering a physical dimension of the structural element according to any of claims 1-8, the method comprising applying an electrical potential over the first and the second coatings.

43. A method according to claim 42, wherein the base structure comprises a first portion having a first wall thickness and a second portion having a second wall thickness, the first wall thickness being larger than the second wall thickness, where the deformation of the second portion being larger than the deformation of the first portion.

44. A method according to claim 42 or 43, wherein the applying step comprises the structural element altering its physical dimensions along three directions perpendicular to each other.

45. A method according to any of claims 42-44, wherein the applying step comprises the structural element applying a force to an element engaging the structural element.

46. A method according to any of claims 42-45, wherein the applying step comprises the structural element applying a translation to an element engaging the structural element.

47. A method according to any of claims 42-46, wherein the applying step comprises applying a potential varying over time.

48. A method according to claim 47 and wherein the structural element comprises a covering element covering an outer surface of the structural element, the covering element having one or more first openings and one or more second openings each opening into the first sub-volume, wherein the applying step comprises a first fluid entering the first sub- Inspicos / 14 / 03 / 2025 / 13:20volume through the first opening(s) and exiting the structural element through the second opening(s).

49. A method according to claim 48, wherein the applying step comprises a first one-way valve allowing flow of a first fluid from surroundings of the structural element to the first sub- volume via the one or more openings.

50. A method according to claim 48 or 49, wherein the applying step comprises a second one-way valve allowing flow of a first fluid from the first sub-volume to the surroundings via the one or more second openings.

51. A method according to any of claims 48-50, wherein the one or more first openings and one or more second openings open into also the second sub-volume, where the applying step comprises the first fluid also entering the second sub-volume through the one or more first openings and exiting the second sub-volume through the one or more second openings.

52. A method according to any of claims 48-50, the covering element having one or more third openings and one or more fourth openings each opening into the second sub-volume, wherein the applying step further comprises a second fluid entering the second sub-volume through the third opening(s) and exiting the structural element through the fourth opening(s).

53. A method according to claim 52, wherein the structural element further comprises a third one-way valve allowing flow of the second fluid from the surroundings to the second sub-volume via the one or more third openings.

54. A method according to claim 52 or 53, wherein the structural element further comprises a fourth one-way valve allowing flow of the second fluid from the second sub- volume to the surroundings via the one or more fourth openings.

55. A method according to any of claims 52-54, wherein the applying step comprises transporting heat between the first and second fluids.

56. A method according to any of claims 52-55, where the applying step comprises flowing the first fluid, between the first and second openings, in a first general direction and flowing the second fluid, between the third and fourth openings, in a second general direction at least substantially opposite to the first direction. Inspicos / 14 / 03 / 2025 / 13:2057. A method of generating sound, the method comprising: - providing a structural element according to any of claims 1-8, - providing an electrical signal representing the sound, - applying the electrical signal over the first and second coatings.

58. A method of generating ultrasound, the method comprising: - providing a structural element according to any of claims 1-7, - providing an electrical signal having one or more frequencies between 20kHz and 10GHz, - applying the electrical signal over the first and second coatings.

59. A method according to claim 57 or 58, wherein the step of providing the structural element comprises providing the structural element comprising a covering element covering an outer surface of the structural element, the covering element having one or more first openings each opening into the first sub-volume.

60. A method of operating a transducer according to claim 9-23, wherein the signal provider applies a potential over the first and second coatings.

61. A method of operating a pump according to claim 24, wherein the signal provider applies a potential varying over time over the first and second coatings.

62. A method of operating a heat exchanger according to claim 25, wherein the signal provider applies a potential varying over time over the first and second coatings.

63. A method of operating a sound generator according to claim 26, wherein the signal generator provides an electrical signal representing a sound and applies the electrical signal over the first and second coatings.

64. A method of operating an ultrasound generator according to claim 27, wherein the signal generator provides an electrical signal having one or more frequencies between 20kHz and 10GHz and applies the electrical signal over the first and second coatings. Inspicos / 14 / 03 / 2025 / 13:2065. A method of sensing a deformation of a structural element according to any of claims 1-8, the method comprising sensing a potential generated over the first and second coatings by the deformation.

66. A method of sensing a force acting to deform a structural element according to any of claims 1-8, the method comprising allowing the force to deform the structural element and sensing a potential generated over the first and second coatings by the deformation.

67. A method of sensing sound, the method comprising: - allowing the sound to impact on a structural element according to any of claims 1-8 so that the sound deforms the structural element, - sensing a potential generated over the first and second coatings by the deformation, and - generating an electrical signal representing the sound.

68. A method of sensing ultrasound, the method comprising: - allowing the ultrasound to impact on a structural element according to any of claims 1-8 so that the sound deforms the structural element, - sensing a potential generated over the first and second coatings by the deformation, and - generating information representing the ultrasound.

69. A method of operating a sensor according to claim 33, the method comprising: - the ultrasound generator launching the fan shaped beam into a target substance comprising a plurality of elements each reflecting part of the ultrasound, - each ultrasound sensor being impacted by reflected ultrasound, deforming and generating an electrical potential over its first and second coatings, Inspicos / 14 / 03 / 2025 / 13:20- the signal receiver receiving, from each ultrasound sensor, the electrical potential and generating information representing the potential and a direction of the pertaining ultrasound sensor. Inspicos / 14 / 03 / 2025 / 13:20

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