The invention pertains to a load transfer interface for selectively transferring a mechanical load to an object, a system for selectively applying a mechanical load to an object, a method for designing a load transfer interface and a method for driving an object into the ground.

In many applications, a dynamic mechanical load having a frequency spectrum which encompasses a range of frequencies is applied to an object. This dynamic mechanical load is often applied for a purpose, e.g. moving the object, but the dynamic mechanical load can also produce undesired side effects, such as the production of noise. An example of such a situation is the driving of for example piles or pile sheets into the ground. In this situation, for example a hammer applies a dynamic load having a wide frequency spectrum to the pile or pile sheet. The energy in some of the frequencies will make that the pile or pile sheet is moved into the ground, but other frequencies, for example some resonance frequencies of the pile or pile sheet, cause noise and other undesired vibrations. In case the pile driving or pile sheet driving takes place offshore, such resonance frequencies may cause pressure waves in the water which are detrimental for aquatic life.

It is the object of the invention to provide a load transfer interface for selectively transferring a mechanical load to an object, as well as system for selectively applying a mechanical load to an object, method for designing a load transfer interface and method for driving an object into the ground.

The object of the invention is obtained by a load transfer interface for selectively transferring a mechanical load to an object, which load transfer interface comprises:

- a load input region which is adapted to receive a dynamic mechanical input load having a load frequency spectrum,

- a load output region which is adapted to transmit a dynamic mechanical output load to the object,

- an interface body, which is adapted to transform the dynamic mechanical input load into the dynamic mechanical output load, wherein the interface body comprises a first subwavelength frequency attenuation unit cell which has at least a first energy attenuation frequency.

The load transfer interface is adapted to selectively transfer a mechanical load to an object. The mechanical load is or comprises for example an impact load, a force, a torque and/or mechanical energy.

The load transfer device according to the invention comprises a load input region which is adapted to receive a dynamic mechanical input load having a load frequency spectrum. The load input region is or comprises for example an outer surface or a part of an outer surface of the load transfer interface.

The load transfer device according to the invention further comprises a load output region which is adapted to transmit a dynamic mechanical output load to the object. The load output region is or comprises for example an outer surface or a part of an outer surface of the load transfer interface. In general, the load output region will not coincide with the load input region. For example, the load input region is arranged on one side of the outer surface of the load transfer interface and the load output region is arranged on a different, for example, opposite side of the outer surface of the load transfer interface.

The load transfer interface according to the invention further comprises an interface body, which is adapted to transform the dynamic mechanical input load into the dynamic mechanical output load.

The interface body comprises a first subwavelength frequency attenuation unit cell which has at least a first energy attenuation frequency. Optionally, the first subwavelength frequency attenuation unit cell is a subwavelength multi-frequency attenuation unit cell. Optionally, the interface body comprises a plurality of subwavelength frequency attenuation unit cells and/or one or more subwavelength multi-frequency attenuation unit cells.

Subwavelength frequency attenuation unit cells and subwavelength multi-frequency attenuation unit cells are unit cells that have dimensions that are significantly smaller than their target frequencies and that transfer energy to structures that resonate at these target frequencies in a defined energy attenuation frequency. The use of resonators is different from Bragg scattering. Bragg scattering is for example used in phononic crystal unit cells. For example, at least one subwavelength frequency attenuation unit cell is a locally resonant unit cell. Multiple subwavelength frequency attenuation unit cells and/or subwavelength multifrequency attenuation unit cells can be arranged together to form a metasurface and/or metamaterial.

In use, the load input region of the load transfer interface receives a dynamic mechanical input load having a load frequency spectrum. The dynamic mechanical input load is transferred from the load input region to the interface body of the load transfer interface. The first subwavelength frequency attenuation unit cell in the interface body filters (i.e., reduces or eliminates) the energy of components in the dynamic mechanical input load that are associated with the first energy attenuation frequency. The energy of components in the dynamic mechanical input load that are associated with the first energy attenuation frequency, is to a lesser extent or not at all transferred to the load output region of the load transfer interface. Therewith, these components are to a lesser extent or not at all present in the dynamic mechanical output load (“to a lesser extent” as compared to the dynamic mechanical input load). The frequencies at which the load components are filtered out are in the art sometimes referred to as “band gaps”.

An advantage of the use of the load transfer interface according to the invention is that the object to which the mechanical load is transferred, is not or to a lesser extent (as compared to the situation where the mechanical load would be applied directly) subjected to the components of the dynamic mechanical input load that are associated with the first absorption frequency of the first subwavelength frequency attenuation unit cell. As in the design of the subwavelength frequency attenuation unit cell it is possible to determine the value of the energy attenuation frequency associated with that particular subwavelength frequency attenuation unit cell, respectively, the invention allows to tailor the load transfer interface for filtering out or reducing those components of the dynamic mechanical input load that are associated with undesired frequencies or undesired frequency ranges, for example a frequency corresponding to a resonance frequency of the object to which the load it to be transferred in a certain application of the load transfer interface, or a frequency range around such a resonance frequency.

The load transfer interface according to the invention is suitable for filtering components of the dynamic mechanical input load in a frequency range that is narrow compared to the bandwidth of the load frequency spectrum, for example in a frequency range closely around the resonance frequency of a resonator of the subwavelength frequency attenuation unit cell.

The invention provides a very effective approach to for example noise reduction, as the noise does not have to be damped after it has been generated. Using the load transfer interface according to the invention reduces the noise being generated, as the object is not or to a lesser extent excited at for example a noise generating frequency.

The load transfer interface according to the invention allows the first attenuation frequency to be relatively low, e.g. below 200 Hz, and at the same time allow to keep the dimensions of the load transfer interface within a reasonable and practical range. This is due to the use of a subwavelength frequency attenuation unit cell in the interface body, instead of the use of unit cells that are framed solely or mainly on Bragg scattering. In an embodiment, the interface body comprises a plurality of subwavelength frequency attenuation unit cells, and the plurality of subwavelength frequency attenuation unit cells includes the first subwavelength frequency attenuation unit cell which has a first energy attenuation frequency and a second subwavelength frequency attenuation unit cell which has a second energy attenuation frequency that is different from the first energy attenuation frequency.

Alternatively or in addition, the interface body comprises a first subwavelength multifrequency attenuation unit cell which has at least a third energy attenuation frequency and a fourth energy attenuation frequency that is different from the third energy attenuation frequency. The third energy attenuation frequency can be the same as or different from the first energy attenuation frequency. The third energy attenuation frequency can be the same as or different from the second energy attenuation frequency. The fourth energy attenuation frequency can be the same as or different from the first energy attenuation frequency. The fourth energy attenuation frequency can be the same as or different from the second energy attenuation frequency.

In use, in this embodiment, the load input region of the load transfer interface receives a dynamic mechanical input load having a load frequency spectrum. The dynamic mechanical input load is transferred from the load input region to the interface body of the load transfer interface. The first and second subwavelength frequency attenuation unit cells and/or the first subwavelength multi-frequency attenuation unit cell in the interface body filter (i.e. reduce or eliminate) the energy of components in the dynamic mechanical input load that are associated with the first energy attenuation frequency and the second first energy attenuation frequency and/or with the third energy attenuation frequency and fourth energy attenuation frequency, respectively. The energy of components in the dynamic mechanical input load that are associated with the first energy attenuation frequency and the second first energy attenuation frequency and or with the third energy attenuation frequency and fourth energy attenuation frequency, respectively, is to a lesser extent or not at all transferred to the load output region of the load transfer interface. Therewith, these components are to a lesser extent or not at all present in the dynamic mechanical output load (“to a lesser extent” as compared to the dynamic mechanical input load). The frequencies at which the load components are filtered out are in the art sometimes referred to as “band gaps”.

An advantage of the use of the load transfer interface according to the invention is that the object to which the mechanical load is transferred, is not or to a lesser extent (as compared to the situation where the mechanical load would be applied directly) subjected to the components of the dynamic mechanical input load that are associated with the first and second absorption frequency of the subwavelength frequency attenuation unit cells. As in the design of these subwavelength frequency attenuation unit cells and/or the first subwavelength multi-frequency attenuation unit cell it is possible to determine the value of the energy attenuation frequency associated with that particular subwavelength frequency attenuation unit cells and/or the first subwavelength multi-frequency attenuation unit cell, respectively, the invention allows to tailor the load transfer interface for filtering out or reducing those components of the dynamic mechanical input load that are associated with undesired frequencies or undesired frequency ranges, for example a frequency corresponding to a resonance frequency of the object to which the load it to be transferred in a certain application of the load transfer interface, or a frequency range around such a resonance frequency.

The load transfer interface according to this embodiment allows the first and second energy attenuation frequency and/or the third energy attenuation frequency and fourth energy attenuation frequency, respectively, to be relatively low, e.g. below 200 Hz, and at the same time allow to keep the dimensions of the load transfer interface within a reasonable and practical range. This is due to the use of subwavelength frequency attenuation unit cells and/or subwavelength multi-frequency attenuation unit cell in the interface body, instead of the use of unit cells that are framed solely or mainly on Bragg scattering.

In an embodiment, the interface body is connected to the load input region and/or the load output region of the load transfer interface. Optionally, the interface body is mechanically connected to and/or in mechanical contact with the load input region and/or the load output region of the load transfer interface.

In an embodiment, the interface body is arranged between the load input region and the load output region. Optionally, in addition the interface body is mechanically connected to and/or in mechanical contact with the load input region and/or the load output region of the load transfer interface.

In an embodiment, at least one of the first subwavelength frequency attenuation unit cell and/or the optional second subwavelength frequency attenuation unit cell and/or the optional first subwavelength multi-frequency attenuation unit cell is a passive subwavelength frequency attenuation unit cell.

In an embodiment, at least one of the first subwavelength frequency attenuation unit cell and/or the optional second subwavelength frequency attenuation unit cell and/or the optional first subwavelength multi-frequency attenuation unit cell is an actuatable subwavelength frequency attenuation unit cell. This allows to tune the energy attenuation frequency. In an embodiment, the interface body comprises a first and a second subwavelength frequency attenuation unit cell, and the first subwavelength frequency attenuation unit cell has a first geometry and a second subwavelength frequency attenuation unit cell has a second geometry that is different from the first geometry.

The first and second energy absorption frequencies are influenced by the geometry of the first and second subwavelength frequency attenuation unit cell, respectively. Therefore, providing the first and second subwavelength frequency attenuation unit cell with a mutually different geometry is a suitable way of achieving different energy absorption frequencies for the first and second subwavelength frequency attenuation unit cell.

In an embodiment, the first subwavelength frequency attenuation unit cell and/or the optional second subwavelength frequency attenuation unit cell are made of a single material.

Optionally, in this embodiment, the first subwavelength frequency attenuation unit cell and the second subwavelength frequency attenuation unit cell are both made of the same single material.

Optionally, in this embodiment, the first subwavelength frequency attenuation unit cell has a first geometry and a second subwavelength frequency attenuation unit cell has a second geometry that is different from the first geometry. In this case, the different geometries are used to obtain the mutually different first energy attenuation frequency and the second energy attenuation frequency.

Making at least one of the first and/or second subwavelength frequency attenuation unit cell of a single material allows for easier manufacturing. It also makes the subwavelength frequency attenuation unit cell better and easier to recycle after decommissioning of the load transfer interface. Therewith, it can be used within the concept of a circular economy.

For example, the material that is used for the first subwavelength frequency attenuation unit cell and/or the second subwavelength frequency attenuation unit cell is a metal, for example aluminum, an aluminum alloy, or steel.

In an embodiment, the first subwavelength multi-frequency attenuation unit cell is made of a single material.

Optionally, in this embodiment, the first subwavelength frequency attenuation unit cell (which optionally is a subwavelength multi-frequency attenuation unit cell) and the first subwavelength multi-frequency attenuation unit cell are both made of the same single material.

Making the first subwavelength multi-frequency attenuation unit cell of a single material allows for easier manufacturing. It also makes the first subwavelength multi-frequency attenuation unit cell better and easier to recycle after decommissioning of the load transfer interface. Therewith, it can be used within the concept of a circular economy.

For example, the material that is used for the first subwavelength multi-frequency attenuation unit cell is a metal, for example aluminum, an aluminum alloy, or steel.

In an embodiment, the interface body comprises a plurality of first subwavelength frequency attenuation unit cells. Optionally, the first subwavelength frequency attenuation unit cell are subwavelength multi-frequency attenuation unit cells.

In an embodiment, the interface body comprises a plurality of first subwavelength frequency attenuation unit cells and a plurality of second subwavelength frequency attenuation unit cells.

Optionally, in addition a plurality of further subwavelength frequency attenuation unit cells is provided which have a further energy attenuation frequency which is different from the first energy attenuation frequency and from the second energy attenuation frequency.

Optionally, a further subwavelength frequency attenuation unit cell of the plurality of further subwavelength frequency attenuation unit cells has a further geometry that is different from both the first geometry and from the second geometry.

Optionally, a further subwavelength frequency attenuation unit cell of the plurality of further subwavelength frequency attenuation unit cells is made of a single material.

Optionally, a further subwavelength frequency attenuation unit cell of the plurality of further subwavelength frequency attenuation unit cells is made of the same single material as a first subwavelength frequency attenuation unit cell and/or a second subwavelength frequency attenuation unit cell.

In an embodiment, the interface body comprises a plurality of first subwavelength multifrequency attenuation unit cells.

Optionally, in addition a plurality of further subwavelength multi-frequency attenuation unit cells is provided which have further energy attenuation frequencies which is different from the third energy attenuation frequency and from the fourth energy attenuation frequency.

Optionally, a further subwavelength multi-frequency attenuation unit cell of the plurality of further subwavelength multi-frequency attenuation unit cells has a geometry that is different from the geometry of a first subwavelength multi-frequency attenuation unit cell.

Optionally, a further subwavelength multi-frequency attenuation unit cell of the plurality of further subwavelength multi-frequency attenuation unit cells is made of a single material. Optionally, a further subwavelength multi-frequency attenuation unit cell of the plurality of further subwavelength multi-frequency attenuation unit cells is made of the same single material as a first subwavelength multi-frequency attenuation unit cell.

In an embodiment, the first subwavelength frequency attenuation unit cell comprises:

- a frame, which frame has an opening,

- resonance mass, which is arranged in the opening of the frame,

- a beam which connects the resonance mass to the frame.

Optionally, the first subwavelength frequency attenuation unit cell comprises a plurality of resonance masses. These resonance masses may be associated with the same different energy attenuation frequency or with mutually different energy attenuation frequencies.

In an embodiment, the first subwavelength frequency attenuation unit cell and the second subwavelength frequency attenuation unit cell each comprise:

- a frame, which frame has an opening,

- resonance mass, which is arranged in the opening of the frame,

- a beam which connects the resonance mass to the frame.

So, in this embodiment, the first subwavelength frequency attenuation unit cell has a frame with an opening, a resonance mass which is arranged in the opening of the frame and a beam which connects the resonance mass to the frame. In this embodiment, in addition, the second subwavelength frequency attenuation unit cell has a frame with an opening, a resonance mass which is arranged in the opening of the frame and a beam which connects the resonance mass to the frame.

Optionally, in this embodiment, the first subwavelength frequency attenuation unit cell and the second subwavelength frequency attenuation unit cell differ from each other in at least one of:

- the mass of the resonance mass,

- an outer dimension of the resonance mass,

- an inner dimension of the opening in the frame,

- the number of beams,

- a dimension of a beam, e.g. width, height, length or diameter of a beam.

These parameters influence the value of the energy attenuation frequency of the respective subwavelength frequency attenuation unit cells. Therefore, changing these parameters allows to tailor the value of the respective energy absorption frequencies to a specific application of the load transfer interface. The energy attenuation frequency of a subwavelength frequency attenuation unit cell corresponds to the resonance frequency of that subwavelength frequency attenuation unit cell, so any changes in e.g. geometry and/or other parameters (like stiffness) that influence the resonance frequency of the subwavelength frequency attenuation unit cell can be used to tailor the energy attenuation frequency of the subwavelength frequency attenuation unit cell.

In an embodiment, the first subwavelength multi-frequency attenuation unit cell, and/or the first subwavelength frequency attenuation unit cell if it is a subwavelength multi-frequency attenuation unit cell, comprises a first resonance mass and a second resonance mass. The first and second resonance mass are optionally connected to a frame by one or more beams. The value of the energy attenuation frequencies of the (first) subwavelength multi-frequency attenuation unit cell can for example be tailored to the desired energy attenuation frequencies for a specific application by changing for example ore or more of:

- the mass of a resonance mass,

- an outer dimension of a resonance mass,

- the number of beams,

- a dimension of a beam.

The energy attenuation frequencies of a subwavelength multi-frequency attenuation unit cell correspond to resonance frequencies of that subwavelength multi-frequency attenuation unit cell, so any changes in e.g. geometry and/or other parameters (like stiffness) that influence the resonance frequencies of the subwavelength multi-frequency attenuation unit cell can be used to tailor the energy attenuation frequencies of the subwavelength multifrequency attenuation unit cell.

In an embodiment, the interface body comprises a first metasurface. A first subwavelength frequency attenuation unit cell and/or an optional second subwavelength frequency attenuation unit cell and/or an optional first subwavelength multi-frequency attenuation unit cell is/are arranged in the first metasurface. The metasurface allows the interface body to be of limited height, which makes the load transfer interface easy to handle and to apply in a practical situation.

A metasurface comprises a two-dimensional array of subwavelength frequency attenuation unit cells.

Optionally, the first metasurface comprises a plurality of first subwavelength frequency attenuation unit cells.

Optionally, the first metasurface comprises a plurality of second subwavelength frequency attenuation unit cells.

Optionally, the first metasurface comprises a plurality of first subwavelength frequency attenuation unit cells and a plurality of second subwavelength frequency attenuation unit cells. Optionally, the first metasurface comprises a plurality of further subwavelength frequency attenuation unit cells.

Optionally, the first metasurface comprises a plurality of first subwavelength frequency attenuation unit cells and a plurality of second subwavelength frequency attenuation unit cells and a plurality of further subwavelength frequency attenuation unit cells.

Optionally, the first metasurface comprises one or more further subwavelength multifrequency attenuation unit cells.

Optionally, the first metasurface comprises a plurality of first subwavelength frequency attenuation unit cells and a plurality of second subwavelength frequency attenuation unit cells and one or more first subwavelength multi-frequency attenuation unit cells.

Optionally, the interface body comprises metamaterial element, which metamaterial element comprises the first metasurface and a further metasurface. Optionally, the interface body comprises metamaterial element, which metamaterial element comprises the first metasurface and a plurality of further metasurfaces. Optionally, the further metasurface comprises a first subwavelength frequency attenuation unit cell and/or a second subwavelength frequency attenuation unit cell and/or a further subwavelength frequency attenuation unit cell and/or a subwavelength multi-frequency attenuation unit cell. Optionally, the first metasurface and the further metasurface are stacked on top of each other.

Optionally, the interface body comprises metamaterial element, which metamaterial element comprises a three-dimensional array of subwavelength frequency attenuation unit cells and/or subwavelength multi-frequency attenuation unit cells.

The invention further pertains to a system for selectively applying a mechanical load to an object, which system comprises:

- a load transfer interface according to the invention,

- a load application device, which is adapted to exert, during operation, the dynamic mechanical input load on the load input region of the load transfer interface, wherein the load output region of the load transfer interface is adapted to exert the dynamic mechanical output load on an object.

In this system, a load application device is provided which cooperates with the load transfer interface according to the invention to apply a load to an object. The load application device produces a dynamic mechanical input load having a load frequency spectrum. The load transfer interface of the system modifies the dynamic mechanical input load into a dynamic mechanical output load. The dynamic mechanical output load is then exerted on an object. The dynamic mechanical input load as exerted by the load application device is or comprises for example an impact load, a force, a torque and/or mechanical energy.

The first subwavelength frequency attenuation unit cell in the interface body filters (i.e. , reduces or eliminates) the energy of components in the dynamic mechanical input load that are associated with the first energy attenuation frequency. The energy of components in the dynamic mechanical input load that are associated with the first energy attenuation frequency, is to a lesser extent or not at all transferred to the load output region of the load transfer interface. Therewith, these components are to a lesser extent or not at all present in the dynamic mechanical output load (“to a lesser extent” as compared to the dynamic mechanical input load). The frequencies at which the load components are filtered out are in the art sometimes referred to as “band gaps”.

The system according to the invention therewith allows to remove or reduce certain load components that are - sometimes inevitably - produced by the load application device, but that are not desirable to transmit to the object to which the load is to be applied, for example because they may excite a resonance frequency in the object.

The system according to the invention may be used for many applications, for example, but not limited to pile driving, pile sheet driving, mechanical testing of objects (including building structures), vibration control and/or positioning control within machinery, resonance shielding of objects.

In an embodiment, the interface body of the load transfer device according to the invention comprises a plurality of subwavelength frequency attenuation unit cells, and the plurality of subwavelength frequency attenuation unit cells includes the first subwavelength frequency attenuation unit cell which has a first energy attenuation frequency and a second subwavelength frequency attenuation unit cell which has a second energy attenuation frequency that is different from the first energy attenuation frequency.

Alternatively or in addition, the interface body of the load transfer device according to the invention comprises a first subwavelength multi-frequency attenuation unit cell which has at least a third energy attenuation frequency and a fourth energy attenuation frequency that is different from the third energy attenuation frequency. The third energy attenuation frequency can be the same as or different from the first energy attenuation frequency. The third energy attenuation frequency can be the same as or different from the second energy attenuation frequency. The fourth energy attenuation frequency can be the same as or different from the first energy attenuation frequency. The fourth energy attenuation frequency can be the same as or different from the second energy attenuation frequency. In use, in this embodiment, the load input region of the load transfer interface receives a dynamic mechanical input load having a load frequency spectrum. The dynamic mechanical input load is transferred from the load input region to the interface body of the load transfer interface. The first and second subwavelength frequency attenuation unit cells and/or the first subwavelength multi-frequency attenuation unit cell in the interface body filter (i.e. reduce or eliminate) the energy of components in the dynamic mechanical input load that are associated with the first energy attenuation frequency and the second first energy attenuation frequency and/or with the third energy attenuation frequency and fourth energy attenuation frequency, respectively. The energy of components in the dynamic mechanical input load that are associated with the first energy attenuation frequency and the second first energy attenuation frequency and or with the third energy attenuation frequency and fourth energy attenuation frequency, respectively, is to a lesser extent or not at all transferred to the load output region of the load transfer interface. Therewith, these components are to a lesser extent or not at all present in the dynamic mechanical output load (“to a lesser extent” as compared to the dynamic mechanical input load). The frequencies at which the load components are filtered out are in the art sometimes referred to as “band gaps”.

In an embodiment of the system, the load application device is or comprises a hammer, for example a pile driving hammer.

In an embodiment, the load output region of the load transfer interface has a shape which is adapted to engage the object, for example wherein the shape of the load output region is adapted to engage the top of a pile or piling sheet.

The invention further pertains to a method for designing a load transfer interface, which method comprises the following steps:

- for a combination of a mechanical load application device and an associated object, determining the dynamic mechanical input load to be delivered by the mechanical load application device and a load frequency spectrum associated with this dynamic mechanical input load,

- determining a first part of load frequency spectrum which is undesirable to subject the associated object to and a second part of the load frequency spectrum to which the associated object should be subjected,

- designing an interface body of a load transfer interface, which interface body comprises a plurality of subwavelength frequency attenuation unit cells, which plurality of subwavelength frequency attenuation unit cells includes a first subwavelength frequency attenuation unit cell which has a first energy attenuation frequency and a second subwavelength frequency attenuation unit cell which has a second energy attenuation frequency that is different from the first energy attenuation frequency, and/or wherein the interface body comprises a first subwavelength multi-frequency attenuation unit cell which has at least a third energy attenuation frequency and a fourth energy attenuation frequency that is different from the third energy attenuation frequency, wherein the first and second subwavelength frequency attenuation unit cells are designed such that the first energy attenuation frequency and the second energy attenuation frequency are in the first part of the load frequency spectrum and/or wherein first subwavelength multi-frequency attenuation unit cell is designed such that the third energy attenuation frequency and the fourth energy attenuation frequency are in the first part of the load frequency spectrum.

Optionally, this method further comprises the step of manufacturing the interface body of the load transfer device, the interface body comprising the first and second subwavelength frequency attenuation unit cells of which the first energy attenuation frequency and the second energy attenuation frequency are in the first part of the load frequency spectrum and/or comprising the first subwavelength multi-frequency attenuation unit cell of which the third energy attenuation frequency and the fourth energy attenuation frequency are in the first part of the load frequency spectrum.

In a variant, the invention further pertains to a method for designing a load transfer interface, which method comprises the following steps:

- for a combination of a mechanical load application device and an associated object, determining the dynamic mechanical input load to be delivered by the mechanical load application device and a load frequency spectrum associated with this dynamic mechanical input load,

- determining a first part of load frequency spectrum which is undesirable to subject the associated object to and a second part of the load frequency spectrum to which the associated object should be subjected,

- designing an interface body of a load transfer interface, wherein the interface body comprises a first subwavelength frequency attenuation unit cell which has at least a first energy attenuation frequency, wherein the first subwavelength frequency attenuation unit cell is designed such that the first energy attenuation frequency is in the first part of the load frequency spectrum.

Optionally, the first and second subwavelength frequency attenuation unit cell is designed such that the first energy attenuation frequency is in the first part of the load frequency spectrum. Optionally, this method further comprises the step of manufacturing the interface body of the load transfer device, the interface body comprising the first subwavelength frequency attenuation unit cell of which the first energy attenuation frequency is in the first part of the load frequency spectrum.

The above methods for designing a load transfer interface can be used to design a load transfer interface according to the invention.

The above methods for designing a load transfer interface can be used to design a system as described above for selectively transferring a mechanical load to an object.

In an embodiment, in the method for designing a load transfer interface, the step of determining a part of load frequency spectrum which is undesirable to subject the associated object to includes characterizing the dynamic behaviour of the object to which energy is to be transferred, for example including determining at least one resonance frequency of the associated object.

In an embodiment, in the method for designing a load transfer interface, the first subwavelength frequency attenuation unit cell and the optional second subwavelength frequency attenuation unit cell comprises:

- a frame, which frame has an opening,

- resonance mass, which is arranged in the opening of the frame,

- a beam which connects the resonance mass to the frame,

In this embodiment, the method step of designing of the first and second subwavelength frequency attenuation unit cells includes selection of at least one of the following parameters:

- the mass of the resonance mass,

- an outer dimension of the resonance mass,

- an inner dimension of the opening in the frame,

- the number of beams,

- a dimension of a beam,

In this embodiment, optionally at least one of these parameters has a different value for the first subwavelength frequency attenuation unit cell and for the second subwavelength frequency attenuation unit cell.

In this embodiment, the values of specific parameters of the geometry of the first and optional second subwavelength frequency attenuation unit cells are adapted to obtain the desired energy absorption frequencies of the respective subwavelength frequency attenuation unit cells. This is an example of how the subwavelength frequency attenuation unit cells of the load transfer interface can be tailored for use in a specific application.

In an embodiment, in the method for designing a load transfer interface, the first subwavelength multi-frequency attenuation unit cell and/or the first subwavelength frequency attenuation unit cell if it is a subwavelength multi-frequency attenuation unit cell, comprises a first resonance mass and a second resonance mass. The first and second resonance mass are optionally connected to a frame by one or more beams. The value of the energy attenuation frequencies of the (first) subwavelength multi-frequency attenuation unit cell can for example be tailored to the desired energy attenuation frequencies for a specific application by changing for example ore or more of:

- the mass of the resonance mass,

- an outer dimension of the resonance mass,

- the number of beams,

- a dimension of a beam.

In an embodiment, the method for designing a load transfer interface includes a band structure analysis, in which a first subwavelength frequency attenuation unit cell is modelled with appropriate material properties and geometry. Bloch-Floquet periodic boundary conditions are applied, thus assuming an infinite number of first subwavelength frequency attenuation unit cells. Then, a series of complex eigenvalue problems is solved for different wave vectors along the Irreducible Brillouin Zone (IBZ). The band structure is then a plot of frequency as a function of wave vector. In this diagram the bandgaps can be found, as they are the ranges of frequencies for which no mode can be found.

Optionally, this type of band structure analysis is also carried out for at least one of a second subwavelength frequency attenuation unit cell, a first subwavelength multi-frequency attenuation unit cell, a further subwavelength frequency attenuation unit cell and/or a further subwavelength multi-frequency attenuation unit cell.

In an embodiment, the method for designing a load transfer interface includes a transmissibility analysis.

Optionally, in this transmissibility analysis, the interface body of the load transfer interface composed of a finite number of subwavelength frequency attenuation unit cells is modelled. The finite number of subwavelength frequency attenuation unit cells for example comprises a plurality of first subwavelength frequency attenuation unit cells and/or second subwavelength frequency attenuation unit cells and/or subwavelength frequency attenuation unit cells and/or first subwavelength multi-frequency attenuation unit cells and/or further subwavelength multi-frequency attenuation unit cells. Then the mechanical input load is applied load on one side of the modelled interface body and the response load (i.e., the mechanical output load) at the other side of the modelled interface body is determined for a pre-determined range of frequencies. The transmissibility is the ratio between output quantities and input quantities (output/input quantities being for instance displacement). This analysis is conducted by assuming a harmonic response of the system, so already the steady state response is considered.

In an embodiment, the method for designing a load transfer interface includes a band structure analysis, in which a first subwavelength frequency attenuation unit cell is modelled with appropriate material properties and geometry. Bloch-Floquet periodic boundary conditions are applied, thus assuming an infinite number of first subwavelength frequency attenuation unit cells. Then, a series of complex eigenvalue problems is solved for different wave vectors along the Irreducible Brillouin Zone (IBZ). The band structure is then a plot of frequency as a function of wave vector. In this diagram the bandgaps can be found, as they are the ranges of frequencies for which no mode can be found.

Optionally, this type of band structure analysis is also carried out for at least one of a second subwavelength frequency attenuation unit cell, a first subwavelength multi-frequency attenuation unit cell, a further subwavelength frequency attenuation unit cell and/or a further subwavelength multi-frequency attenuation unit cell.

In this embodiment, in addition a this transmissibility analysis in carried out in which the interface body of the load transfer interface composed of a finite number of subwavelength frequency attenuation unit cells is modelled. The finite number of subwavelength frequency attenuation unit cells for example comprises a plurality of first subwavelength frequency attenuation unit cells and/or second subwavelength frequency attenuation unit cells and/or subwavelength frequency attenuation unit cells and/or first subwavelength multi-frequency attenuation unit cells and/or further subwavelength multi-frequency attenuation unit cells. Then the mechanical input load is applied load on one side of the modelled interface body and the response load (i.e., the mechanical output load) at the other side of the modelled interface body is determined for a pre-determined range of frequencies. The transmissibility is the ratio between output quantities and input quantities (output/input quantities being for instance displacement). This analysis is conducted by assuming a harmonic response of the system, so already the steady state response is considered.

The invention further pertains to a method for driving an object into the ground, which method comprises the following steps: - arranging the object at or above the ground surface at the location where the object has to be driven into the ground,

- arranging a load transfer region of the load application device of a system as described above in line with a load receiving surface of the object,

- arranging a load transfer interface of a system as described above on the load receiving surface of the object or on a load transfer region of the load application device,

- driving the object into the ground by the load application device of the system as described above, while maintaining the load transfer interface of the system as described above in a position between the load receiving surface of the object and the load transfer surface of the load application device.

The system as described above refers to the system for selectively applying a mechanical load to an object, which system comprises:

- a load transfer interface according to the invention,

- a load application device, which is adapted to exert, during operation, the dynamic mechanical input load on the load input region of the load transfer interface, wherein the load output region of the load transfer interface is adapted to exert the dynamic mechanical output load on an object.

The invention will be described in more detail below under reference to the drawing, in which in a non-limiting manner exemplary embodiments of the invention will be shown. The drawing shows in:

Fig. 1 : schematically, a first embodiment of the load transfer interface according to the invention,

Fig. 2A: schematically, an example of a subwavelength frequency attenuation unit cell, in top view,

Fig. 2B: schematically, an example of a subwavelength frequency attenuation unit cell, in isometric view,

Fig. 3: schematically, an example of a metasurface as can be used in an embodiment of the load transfer interface according to the invention,

Fig. 4: schematically, an example of a metamaterial element as can be used in an embodiment of the load transfer interface according to the invention,

Fig. 5: schematically, an embodiment of the system according to the invention for selectively applying a mechanical load to an object.

Fig. 1 shows, schematically, a first embodiment of the load transfer interface 1 according to the invention. The load transfer interface 1 of fig. 1 is adapted to selectively transfer a mechanical load to an object. The mechanical load is or comprises for example an impact load, a force, a torque and/or mechanical energy.

The load transfer device of fig. 1 comprises a load input region 2 which is adapted to receive a dynamic mechanical input load 10 having a load frequency spectrum. Curve 12 in fig. 1 represents energy or amplitude related to the dynamic mechanical input load 10 on the vertical axis, and frequency on the horizontal axis. In the embodiment of fig. 1, the load input region comprises a part of an outer surface of the load transfer interface 1.

The load transfer device 1 of fig. 1 further comprises a load output region 3 which is adapted to transmit a dynamic mechanical output load 11 to the object. Curve 13 in fig. 1 represents energy or amplitude related to the dynamic mechanical output load 11. Curve 12 is replicated as a dashed line just above curve 13 in order to show the difference between energy or amplitude related to the dynamic input load 10 (represented by curve 12) and the energy or amplitude related to dynamic output load 11 (represented by curve 13).

The load output region 3 comprises in the embodiment of fig. 1 a part of an outer surface of the load transfer interface 1. In the embodiment of fig. 1 , the load output region 2 does not coincide with the load input region 3, as in this embodiment, the load input region 2 is arranged on one side of the outer surface of the load transfer interface 1 and the load output region 3 is arranged on an opposite side of the outer surface of the load transfer interface 1.

The load transfer interface 1 of fig. 1 further comprises an interface body 4, which is adapted to transform the dynamic mechanical input load 10, 12 into the dynamic mechanical output load 11,13.

The interface body 4 in the embodiment of fig. 1 comprises a plurality of subwavelength frequency attenuation unit cells 20. Subwavelength frequency attenuation unit cells 20 are unit cells that transfer energy to a resonator or resonators of that subwavelength frequency unit cell in a defined energy attenuation frequency. Multiple subwavelength frequency attenuation unit cells 20 can be arranged together to form a metasurface and/or metamaterial.

In the interface body 4, the plurality of subwavelength frequency attenuation unit cells 20 includes a first subwavelength frequency attenuation unit cell 21 which has a first energy attenuation frequency 14 and a second subwavelength frequency attenuation unit cell 22 which has a second energy attenuation frequency 15 that is different from the first energy attenuation frequency 14.

Optionally, the interface body 4 further comprises one or more first subwavelength multi-frequency attenuation unit cells. The first subwavelength multi-frequency attenuation unit cell has at least a third energy attenuation frequency and a fourth energy attenuation frequency that is different from the third energy attenuation frequency. Optionally, the first subwavelength frequency attenuation unit cell 21 is a subwavelength multi-frequency attenuation unit cell.

In use, the load input region 2 of the load transfer interface 1 receives a dynamic mechanical input load 10, 12 having a load frequency spectrum. The dynamic mechanical input load 10, 12 is transferred from the load input region 2 to the interface body 4. The subwavelength frequency attenuation unit cells 20, 21, 22 in the interface body 4 filter (i.e. reduce or eliminate) the energy of components in the dynamic mechanical input load 10, 12 that are associated with the first energy attenuation frequency 14 and the second first energy attenuation frequency 15. This can be seen by comparing lines 12 and 13 in fig. 1. The energy of components in the dynamic mechanical input load 10, 12 that are associated with the first energy attenuation frequency 14 and the second first energy attenuation frequency 14 is to a lesser extent or not at all transferred to the load output region 3 of the load transfer interface 1. Therewith, these components are to a lesser extent or not at all present in the dynamic mechanical output load 11, 13 (“to a lesser extent” as compared to the dynamic mechanical input load).

In the embodiment of fig. 1 , the interface body 4 is connected to the load input region 2 and to the load output region 3. For example, the interface body 4 is mechanically connected to and/or in mechanical contact with the load input region 2 and/or the load output region 3.

In this embodiment, the interface body 4 is arranged between the load input region 2 and the load output region 3.

In the embodiment of. fig. 1, the first subwavelength frequency attenuation unit cell 21 can be either a passive subwavelength frequency attenuation unit cell or an actuatable subwavelength frequency attenuation unit cell.

In the embodiment of. fig. 1, the second subwavelength frequency attenuation unit cell 22 can be either a passive subwavelength frequency attenuation unit cell or an actuatable subwavelength frequency attenuation unit cell.

In the embodiment of fig. 1 , the first subwavelength frequency attenuation unit cell 21 has a first geometry and the second subwavelength frequency attenuation unit cell 22 has a second geometry that is different from the first geometry.

In the embodiment of fig. 1 , the first subwavelength frequency attenuation unit cells 21 and the second subwavelength frequency attenuation unit cells 22 are made of a single material. In this embodiment, the first subwavelength frequency attenuation unit cells 21 and the second subwavelength frequency attenuation unit cells 22 are both made of the same single material. In this case, the different geometries are used to obtain the mutually different first energy attenuation frequency 14 and the second energy attenuation frequency 15.

For example, the material that is used for the first subwavelength frequency attenuation unit cells 21 and the second subwavelength frequency attenuation unit cells 22 is a metal, for example aluminum, an aluminum alloy, or steel.

In the embodiment of fig. 1 , the interface body 4 comprises a plurality of first subwavelength frequency attenuation unit cells 21 and a plurality of second subwavelength frequency attenuation unit cells 22.

Optionally, in addition a plurality of further subwavelength frequency attenuation unit cells is provided which have a further energy attenuation frequency which is different from the first energy attenuation frequency and from the second energy attenuation frequency.

Fig. 2A shows, schematically, an example of a subwavelength frequency attenuation unit cell 20, in top view and fig. 2B shows, schematically, an example of a similar subwavelength frequency attenuation unit cell 20, in isometric view. In fig. 2B, “x”, “y” and “z” indicate three orthogonal directions of a Cartesian coordinate system.

A subwavelength frequency attenuation unit cell 20 of the type as shown in fig. 2A and 2B can be used as a first subwavelength frequency attenuation unit cell 21, a second subwavelength frequency attenuation unit cell 22 and/or as a further subwavelength frequency attenuation unit cell 23.

In the embodiments of fig. 2A and 2B, the subwavelength frequency attenuation unit cell 20 comprises:

- a frame 30, which frame 30 has an opening 33,

- resonance mass 31 , which is arranged in the opening 33 of the frame 30,

- four beams 32 beam which connect the resonance mass 31 to the frame 30.

In an alternative embodiment, instead of four beams 32, a different number of beams can be present, e.g. 2 beams 32, 3 beams 32, 8 beams 32.

In an alternative embodiment, the shape of the resonance mass 31 and/or the opening 22 may be different, for example elliptical, rectangular or square.

The geometry of the subwavelength frequency attenuation unit cell 20 influences the resonance frequency and therewith the energy attenuation frequency of the subwavelength frequency attenuation unit cell 20. This allows to tailor the subwavelength frequency attenuation unit cell 20 to a desired energy attenuation frequency by changing the geometry of the subwavelength frequency attenuation unit cell 20.

For example, in the embodiments of fig. 2A and fig. 2B, the following geometry parameters can be changed in order to obtain a desired energy attenuation frequency :

- the mass of the resonance mass 31,

- an outer dimension of the resonance mass 31 , e.g. the outer diameter of the resonance mass 31 ,

- an inner dimension of the opening 33 in the frame 30, e.g. the inner diameter of the opening 33 in the frame 30,

- the number of beams 32,

- a dimension of a beam 32.

In case a subwavelength frequency attenuation unit cell 20 in accordance with fig. 2A and/or fig. 2B is used as a first subwavelength frequency attenuation unit cell 21 and as a second subwavelength frequency attenuation unit cell 22, the first subwavelength frequency attenuation unit cell 21 and second subwavelength frequency attenuation unit cell 22 are for example made of the same, single material, but differ from each other in one or more geometry parameters, so that the first and second subwavelength frequency attenuation unit cells 21 , 22 have mutually different energy absorption frequencies. For example, the first and second subwavelength frequency attenuation unit cells 21 , 22 differ from each other in the values of one or more of the geometry parameters mentioned above.

Fig. 3 shows, schematically, an example of a metasurface 25 as can be used in an embodiment of the load transfer interface 1 according to the invention.

In an embodiment, the interface body 4 of the load transfer interface 1 comprises a first metasurface 25. This can for example be a metasurface 25 as shown in fig. 3.

In the example of fig. 3, the first subwavelength frequency attenuation unit cell 21 and the second subwavelength frequency attenuation unit cell 21 are arranged in the first metasurface 25. In addition, a further subwavelength frequency attenuation unit cell 23 is present in the metasurface 25. The further subwavelength frequency attenuation unit cell 23 has a further energy attenuation frequency which is different from the first energy attenuation frequency and from the second energy attenuation frequency. Optionally, the further subwavelength frequency attenuation unit cell 23 has a further geometry which is different from the geometry of the first subwavelength frequency attenuation unit cell 21 and the geometry of the second subwavelength frequency attenuation unit cell 22. In the example of fig. 3, optionally, the first metasurface 25 further comprises one or more first subwavelength multi-frequency attenuation unit cells 24.

The metasurface 25 comprises a two-dimensional array of subwavelength frequency attenuation unit cells 21 , 22, 23 and first subwavelength multi-frequency attenuation unit cells 24. In the example of fig. 3, the first metasurface 25 comprises a plurality of first subwavelength frequency attenuation unit cells 21 , a plurality of second subwavelength frequency attenuation unit cells 22, a plurality of further subwavelength frequency attenuation unit cells 23 and a plurality of first subwavelength multi-frequency attenuation unit cells 24.

Fig. 4 shows, schematically, an example of a metamaterial element 26 as can be used in an embodiment of the load transfer interface 1 according to the invention.

In an embodiment, the interface body 4 of the load transfer interface 1 comprises a first metamaterial element 26. This can for example be a metamaterial element 26 as shown in fig. 4.

The metamaterial element 26 comprises a three-dimensional array of subwavelength frequency attenuation unit cells 21 , 22, 23. In the example of fig. 4, the metamaterial element 26 comprises a plurality of first subwavelength frequency attenuation unit cells 21 , a plurality of second subwavelength frequency attenuation unit cells 22, a plurality of further subwavelength frequency attenuation unit cells 23 and a plurality of first subwavelength multifrequency attenuation unit cells 24.

In the example of fig. 4, the metamaterial element 26 which can be used in the interface body 4 comprises the first metasurface 25 twice, and in between the two first metasurface 25, a further metasurface 25*. Many other configurations are possible as well. In this example, the further metasurface 25* comprises a plurality of first subwavelength frequency attenuation unit cells 21 , a plurality of second subwavelength frequency attenuation unit cells 22 and a plurality of further subwavelength frequency attenuation unit cells 23, which are arranged in a different order than in the first metasurface 25..

Fig. 5 shows, schematically, an embodiment of a system 40 according to the invention. The system 40 is suitable for selectively applying a mechanical load to an object 42

The system 40 comprises:

- a load transfer interface 1 , for example a load transfer interface according to fig. 1 ,

- a load application device 41. The load application device 41 is adapted to during operation exert a dynamic mechanical input load 10, 12 on the load input region 2 of the load transfer interface 1.

The load output region 3 of the load transfer interface 1 is adapted to exert the dynamic mechanical output load 11, 13 on an object 42.

In the system of fig. 5, a load application device 41 is provided which cooperates with the load transfer interface 1 to apply a load to an object 42. The load application device 41 produces a dynamic mechanical input load 10, 12 (also see fig. 1) having a load frequency spectrum. The load transfer interface 1 of the system 40 modifies the dynamic mechanical input load 10, 12 into a dynamic mechanical output load 11, 13 (also see fig. 1). The dynamic mechanical output load 11, 13 is then exerted on an object 42. The dynamic mechanical input load 10, 12 as exerted by the load application device 41 is or comprises for example an impact load, a force, a torque and/or mechanical energy.

The subwavelength frequency attenuation unit cells 20 and/or first subwavelength multifrequency attenuation unit cells 24 in the interface body 4 of the load transfer interface 1 filter (i.e. reduce or eliminate) the energy of components in the dynamic mechanical input load 10, 12 that are associated with the first energy attenuation frequency 14 and the second first energy attenuation frequency 15 (also see fig. 1) and/or with the third energy attenuation frequency and fourth energy attenuation frequency, respectively. The energy of components in the dynamic mechanical input load 10, 12 that are associated with the first energy attenuation frequency 14 and the second first energy attenuation frequency 15 and/or with the third energy attenuation frequency and fourth energy attenuation frequency, respectively, is to a lesser extent or not at all transferred to the load output region 3 of the load transfer interface 1. Therewith, these components are to a lesser extent or not at all present in the dynamic mechanical output load 11, 13 (“to a lesser extent” as compared to the dynamic mechanical input load 10, 12).

The system of fig. 5 therewith allows to remove or reduce certain load components that are - sometimes inevitably - produced by the load application device 41, but that are not desirable to transmit to the object 42 to which the load is to be applied, for example because they may excite a resonance frequency in the object 42.

The system of fig. 5 may be used for many applications, for example, but not limited to pile driving, pile sheet driving, mechanical testing of objects (including building structures), vibration control and/or positioning control within machinery resonance shielding of objects.

For example, the load application device 41 is or comprises a hammer, for example a pile driving hammer. For example, the object 42 is a pile or pile sheet. Optionally, the load output region 3 of the load transfer interface 1 has a shape which is adapted to engage the object 42. For example, the shape of the load output region 3 is adapted to engage the top of a pile or piling sheet.