NL2037579B1

NL2037579B1 - Non-contact sensor for measuring an energy flux in a metallic mag-netic structure

Info

Publication number: NL2037579B1
Application number: NL2037579A
Authority: NL
Inventors: Vladimirovich Metrikine Andrey; Christiaan Meijers Peter; Greco Francesca
Original assignee: Univ Delft Tech
Priority date: 2024-04-29
Filing date: 2024-04-29
Publication date: 2025-11-17
Also published as: WO2025230411A1

Abstract

l 4 The present invention is in the ﬁeld of a measuring system for measuring physical properties of a magnetic metallic structure, in particular for measuring an energy ﬂux in said magnetic structure, a method Wherein said sensor system is used, such as for driving piles, and a computer program for driving said piles and/or for carrying out said method.

Description

NON-CONTACT SENSOR FOR MEASURING AN ENERGY FLUX IN A METALLIC MAG-

NETIC STRUCTURE

FIELD OF THE INVENTION

The present invention is in the field of a measuring system for measuring physical properties of a magnetic metallic structure, in particular for measuring an energy flux in said magnetic struc- ture, a method wherein said sensor system is used, such as for driving piles, and a computer pro- gram for driving said piles and/or for carrying out said method.

BACKGROUND OF THE INVENTION

In mechanics, strain is defined as a relative deformation, compared to a reference position configuration. Typically, strain therefore has a dimension of a length ratio (m/m), and are usually expressed as a decimal fraction or a percentage. Mathematically, strain is typically expressed as a tensor. Normal strain and shear strain may be considered, within a deforming physical body. A state of strain at a material point of the physical body may be defined as the totality of all the changes in length of material lines, the normal strain, which pass through that point and also the totality of all the changes in the angle between pairs of lines initially perpendicular to each other, the shear strain, radiating from this point. If there is an increase in length of the material line, the normal strain is called tensile strain; otherwise, if there is reduction or compression in the length of the material line, it is called compressive strain.

Determining strain typically requires a sensor or the like in contact with the object to be sensed. Currently, mechanical strain levels and structural velocity of steel structures are measured with sensors (strain gauges and/or accelerometers) that are in physical contact with the structure.

Quite often this is not possible, such as when a measurement is performed on an object with varying strain, having impact on the object to be measured, and therefore distorting a measurement. Some- times it is too cumbersome or practically difficult or impossible to make contact between the sensor and the object to be sensed. For instance. when driving piles, an impact of a hammer driving the pile into the soil, makes contact measurements rather difficult due to the high forces acting on the meas- uring equipment. Also, it is often too time-consuming to add a sensor or the like. Furthermore, the sensors are prone to being damaged when they are exposed to high stress levels, e.g. during an im- pact.

The present invention relates to an improved method of measuring, in particular of an en- ergy flux, which overcomes one or more of the above disadvantages, without jeopardizing function- ality and advantages.

SUMMARY OF THE INVENTION

The present invention relates in a first aspect to a non-contact sensor system. The in- vention relates to a sensor system, which comprises as (sub)-sensors a magnetic field sensor to measure the change of the magnetic field of a metallic (magnetic) structure to infer the strain state, and a motion sensor, such as an optical sensor, to measure the velocity of the surface of the metallic structure. The term “metallic” is used to indicate a material property of the structure. In view of the magnetic field sensor, the metal is a metal having measurable magnetic properties, or comprises said metal, or is a combination of such metals. In princi- ple also paramagnetic metals could be measured. but typically ferromagnetic materials, such as iron, cobalt, nickel, gadolinium, and their alloys, anti-ferromagnetic materials, such as chromium, ferrimagnetic materials, such as ferrites, in particular wherein the magnetic mate- rial selected from Group 3-12, Period 4-6 elements, such as Fe, Co, Ni, and some rare earth metals, and comprising such a magnetic material, such as FePd, FeCo and FePt, and combi- nations thereof, may be considered. A structure is a 3D-item. Within the structure an energy flux is expected, e.g. to a hammer driving a pile into the soil. This energy flux is sensed by the two non-contact sensors, at a specific relatively small region of the structure. The motion sensor is configured to sense motion at a surface or of the surface of the structure. The mag- netic field sensor senses the magnetic field, in particular a variation of the magnetic field, in said structure, which is found to be proportional to the strain in the structure. A multiplica- tion of these two quantities (strain times velocity) is found to provide the flux of mechanical energy in the structure. at the point of measurement. A primary field of application is pile driving, where the energy flux is considered quite important to determine an efficiency of an installation procedure. Due to the non-contact nature of the present sensor system, it is easy to employ, e.g. it can be “integrated” into an impact hammer. Contrary to other non-contact systems to monitor e.g. pile driving, the present sensor system does not require any prepara- tion of the structure, e.g. the pile. Other non-contact methods are in principle possible; how- ever, these require advance measures to be taken, such as visual patterns to be applied to the structure's surface, or attachment of reflectors for the used laser light. Moreover, in the pre- sent invention strain and velocity are both measured, whereas in other, non-contact, methods only deformation is measured. The strain is typically induced from the measured variation of the magnetic field of the pile. The motion, e.g. velocity, of the pile's surface may be meas- ured by Laser Doppler Velocimetry or by Surface Length Velocimetry; both methods require no visual patterns to be added to the structure's surface. The motion sensor preferably has a relatively high sampling rate, in the order of kHz or higher. In an exemplary embodiment the present sensor system comprises of a magnetic field sensor for measuring (radial and vertical field components), a motion sensor, such as an optical velocity sensor, and typically a data acquisition device, a controller, and a processing unit, which later two may be combined.

Multiple sensors could be used in a ring provided around the pile to improve the accuracy by combining the data from multiple positions of around the circumference of the pile. Addi- tional sensors might be added to correct for potential disturbing factors. For instance, a tem- perature sensor to correct for drift in the magnetic field sensor caused by temperature: a (MEMS-type) gyroscope to track the rotation of the sensor box and hammer; and a linear ac- celerometer to track the vibrations of the sensor. Using primary data (strain and velocity) obtained from the sensors, the flow of energy from the hammer to the soil can be monitored.

This can be used in a feedback loop to optimize such a pile driving process, by changing the hammer settings based on the measured energy flux.

The present sensor system may replace contact-based sensors, by a non-contact meas- urement, i.¢. a magnetic field measurement for the strain and an optical sensor for the veloc- itv. There is no need to physically attach this new sensor to the structure, resulting in easter deployment, reusability of the same sensor, improvement safety for personnel, reduction the risk of damage to the sensor. The non-contact nature of the chosen measurement principles is considered an essential element of this invention. The present sensor system can be used in an offshore environment, in which conventional sensors are very rarely used, due to the high cost related to preparing such a measurement. It may also be used for monitoring of magnetic metallic structures. such as bridges. railways. etc. Albeit the present sensor-system might slightly more costly. the reusability thereof makes the OPEX much lower.

In a first aspect, the present invention relates to a non-contact sensor system 3 com- prising at least one magnetic field sensor 5 for measuring variation in magnetic flux density, in particular for measuring radial and/or axial magnetic field components (B, and 5:), more in particular for measuring a variation in said magnetic field components, the magnetic field sensor providing magnetic flux density output, at least one motion sensor (6) for measuring motion, in particular motion selected from at least one of motion v: in a direction parallel to the magnetic field component Bz, and from motion v; in a direction tangential to the mag- netic field component B, the motion sensor providing motion output, wherein the magnetic field sensor and the motion sensor have an at least partially overlapping field of view, that is, sensors substantially overlap in terms of a part of an object to be measured, and in terms of a time domain in which said measurement takes please, the time domain being substan- tially the same, that is, starting at a (same) starting point in time and ending at a (same) end point in time, so 50-100% overlap is typically applicable, in particular 90-100% overlap, at least one controller configured for controlling the magnetic field sensor and the motion sen- sor, in particular for controlling said sensors such that measuring strain and measuring mo- tion occur in the same time domain, as mentioned above, a data acquisition system (DAQ) (7) receiving input from the magnetic field sensor and from the motion sensor, and a data processor for processing the input of the sensors and for providing a flux of mechanical en- ergy based on said input, in particular wherein the processor is configured to obtaining elas- tic strain from variation in magnetic flux density and motion. The DAQ, and the at least one controller may be combined, such as wherein the DAQ (also) is the at least one controller; optionally also the data processor may be combined, such as also into the DAQ. In other words, one processor, acting as at least one controller, a DAQ, and a data processor could be sufficient. The energy flux is expressed in W/m?. The elastic strain is determined using the data obtained by the magnetic field sensor. The mechanical energy flux Sis then found to be the product of the strain tensor and velocity vector:

Exx Exy Exz] [Vx

S=¢gv= es Eyy 6

Exz Eyz Ezz] Vy

For impact pile driving, the expression for the energy flux much simpler, since most terms 1n the expression above can be neglected. This results in the following expression for the mechanical energy flux along the pile’s axis:

Sz = &,,0,.

For other pile driving methods, e.g. the GDP vibratory shaker, less terms from the full expression can be neglected. Hence, the strain and velocity must be determined in more di- rection.

In a second aspect the present invention relates to a method for driving a pile, com- prising providing the pile, positioning the present sensor system of in proximity of the pile, driving the pile into a soil using a pile driver, in particular using a driver selected from an impact hammer, a weight, and a driver providing a combination of vertical and torsional vi- bration (GDP), and measuring a flux of mechanical energy through the pile to the soil. Fora gentle driver of Piles (GDP) reference can be made to WO 2021/040523 Al, of the present applicant. The impact of the GDP on the pile can be measured with the present sensor sys- tem. The same applies for an impact of a hammer and or weight providing impact energy to the pile.

In a third aspect the present invention relates to a computer program or integrated cir- cuit comprising instructions, in particular wherein the computer program is loaded on a pro- cessor or in a memory, the instructions causing the computer to carry out (or conduct) the following: instructing a pile driver to drive the said pile into a soil, in particular an impact hammer, and instructing the present sensor system to measure a flux of mechanical energy through the pile to the soil.

Thereby the present invention provides a solution to one or more of the above-men- tioned problems.

Advantages of the present description are detailed throughout the description. Refer- ences to the figures are not limiting, and are only intended to guide the person skilled in the art through details of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates in a first aspect to the non-contact sensor system accord- ing to claim 1.

In an exemplary embodiment of the present sensor system the at least one motion sensor is selected from at least one of a non-contact electromagnetic field sensor, an ultra- sonic sensor, and an optical sensor, such as using IR or laser light, more in particular at least one motion sensor configured to detect motion v: of a said magnetic material in at least the direction parallel to the central vertical axis of the said magnetic material, in par- ticular an optical sensor, more in particular an optical velocity sensor.

In an exemplary embodiment of the present sensor system the at least one motion sensor has a sampling rate of > 500 Hz, in particular > 1000 Hz, more in particular > 5000

Hz, such as > 10 kHz.

In an exemplary embodiment of the present sensor system the at least one optical 5 sensor is selected from an optical Doppler sensor, in particular a Laser Doppler Veloci- metry sensor, from a high-speed optical sensor comprising a multitude of pixels, from a surface length sensor, in particular a Surface Length Velocimetry sensor, more in particular wherein the optical sensor is configured to provide light and to sense reflected light. This method is found to work by reflecting a laser beam from the surface. It requires no prepara- tion, such as visual marking, or reflectors of the surface of an object to be measured, which is needed in other methods that monitor pile driving. This optical sensor in particular works by analysing pictures at very high speeds, such as > 10° frames/sec. It typically uses a large number of pixels, per frame, such as > 10° pixels. Even then, it still does not require visual markers on the surface.

In an exemplary embodiment of the present sensor system the strain and the motion are measured in a said magnetic material, in particular wherein the said magnetic material is selected from a driving pile, a support pile, a windmill pile, an infrastructural element, in particular a bridge, a railway or part thereof. In other words, as long as the material to be measured is somewhat magnetic, the present system can be used to measure a variation of magnetic field and motion thereof. The system therefore is broadly applicable.

In an exemplary embodiment of the present sensor system the sensor system is config- ured for measuring at a distance of the said magnetic material, such as in a flying object.

In an exemplary embodiment of the present sensor system the sensor system is pro- vided in a housing.

In an exemplary embodiment of the present sensor system the sensor system is config- ured to receive electrical power.

In an exemplary embodiment of the present sensor system the sensor system is config- ured to transmit data.

In an exemplary embodiment of the present sensor system the sensor system is config- ured to receive data.

In an exemplary embodiment of the present sensor system the sensor system com- prises a transceiver.

In an exemplary embodiment of the present sensor system the sensor system com- prises a positioner for maintaining the sensor system in a location in space, in particular wherein the positioner is a flying object, such as a drone.

In an exemplary embodiment of the present sensor system the sensor system com- prises a positioning sensor configured for maintaining the sensor “in place”, that is, in sub- stantially the same spatial location, that might be considered also relative to an object to be measured. The positioning sensor may control a positioner, such as a step-motor, correcting for small deviation by moving the sensor system (back) to it’s “original” position, that it, a position where it originally at the start was located.

In an exemplary embodiment the present sensor system the comprises at least one fur- ther sensor, wherein the at least one further sensor is selected from a temperature sensor for correcting drift in any other sensor, an orientation sensor, and angular velocity sensor, con- figured for monitoring relative rotation of the sensor system and/or pile driver, in particular a gyroscope (such as a MEMS), an accelerometer configured for monitoring vibrations of the sensor system, such as a linear accelerometer, in particular wherein the at least one fur- ther sensor is integrated in the sensor system.

In an exemplary embodiment the present sensor system the comprises at least one controller, wherein the at least one controller is configured to process the motion sensor output and the magnetic field output, and configured to control energy provided to the said magnetic material, in particular to control impact energy, and/or to provide feedforward and/or feedback, and/or wherein the at least one controller, the data acquisition system, and data processor are provided as one or more processors.

In an exemplary embodiment of the present method the measured mechanical energy flux is used to control the energy provided by the pile driver to the pile, in particular to in- crease the energy provided, to decrease the energy provided, or to maintain the energy level provided. This may be achieved by an increase/decrease of pile driver hammer fall dis- tance; or likewise, by an increase/decrease in driving frequency/amplitude of a pile driver.

In an exemplary embodiment of the present method the energy/time is controlled, in particular by increasing a number of quantized energy provisions per unit time, by decreas- ing a number of quantized energy provisions per unit time, or to maintain a number of quantized energy provisions per unit time at a present level. That is, a driving frequency of a hammer of weight is adapted accordingly.

In an exemplary embodiment the present computer program further comprises instruc- tions for instruction the pile driver to control the impact energy provided by the pile driver to the pile based on the measured energy flux, in particular to increase the impact energy, to decrease the impact energy, or to maintain the impact energy.

The invention is further detailed by the accompanying figures and examples. which are exemplary and explanatory of nature and are not limiting the scope of the invention. To the person skilled in the art, it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protection, defined by the present claims.

SUMMARY OF FIGURES

Figure 1-4 show details of the present invention.

DETAILED DESCRIPTION OF FIGURES

1 steel pile 2 hydraulic impact hammer 3 non-contact sensor

4 anvil conventional sensor (for reference measurement) 6 motion sensor & magnetic field sensor 7 data acquisition system (DAQ) 5 8 processor 9 controller

B: magnetic filed strength in vertical direction

B, magnetic filed strength in radial direction

Figure 1 shows a pile 1 and the present non-contact sensor system 6 comprising a motion sen- sor and a magnetic field sensor.

Fig. 2 schematically show a steel pile 1, a hydraulic impact hammer 2, an anvil 4, a non-con- tact sensor 3, and magnetic and motion vectors enforced by the impact hammer.

Fig. 3 shows schematics of the present non-contact sensor system with, integrated in one unit, a CPU 8, a controller 9, and a DAQ 7, a conventional contact sensor for reference measurements 5, and further the sensor box 6 comprising magnetic field sensor and optical velocity sensor, as well as vectors being measured. A field of view is schematically indicated, as well as the part of the pile surface which is measured by the respective sensors.

Fig. 4 shows a practical implementation of the sensor box.

The figures are further detailed in the description of the experiments below.

EXAMPLES/EXPERIMENTS

An exemplary sensor system was designed. A working prototype is attached to an impact hammer to finalize the hammer integration. Then, this configuration is tested onshore and finally offshore.

The present system was placed at a distance of 20-50 cm from the pile to be driven. The magnetic field flux could be measured accurately, at a field of view location. Also, the motion at field of view is measured accurately. Based thereon the flux of mechanical energy at the field of view location is determined, typically with an accuracy of better than £2% relative, e.g. better than +£1% relative. Measurements are performed in a rather continuous manner, e.g. a sample rate of 1Hz-50 kHz, or. sampling is aligned in time with the impact of the hammer, that is, at each impact time, a measurement is performed. A standard computer, including dedicated software, is used to calculate the flux of mechanical energy. Based thereon, if con- sidered appropriate, the impact of the hammer is adjusted. For instance, the number of quan- tized energy provisions per unit time 1s increased, or likewise the energy o the hammer. As a result, the energy consumption is reduced with 5-25%, compared to standard operation. A similar result is obtained when driving a pile with a pile shaker.

Further, the driving frequency of the impact hammer was increased and decreased. Also, the energy impact per blow was increased and decreased. A clear distinction in mechanical energy flux between the different set-ups was found. Based on the mechanical energy fluxes for the different set-ups optimal settings were determined, e.g. in impact energy, and driving frequency.

The invention although described in detailed explanatory context may be best under- stood in conjunction with the accompanying figures.

It should be appreciated that for commercial application it may be preferable to use one or more variations of the present system, which would similar be to the ones disclosed in the present application and are within the spirit of the invention.

For the sake of searching the following section is added, of which the subsequent section re- lates to a translation into Dutch thereof, representing the extent of the scope of protection, that is de- fine the matter for which protection is sought, of the patent or patent application, wherein further the description and drawings shall be used to interpret these. 1. A non-contact sensor system (3) comprising

At least one magnetic field sensor (6) for measuring variation in magnetic flux den- sity, in particular for measuring radial and/or magnetic field components (B: and B;), more in particular for measuring a variation in said magnetic field components, the magnetic field sensor providing magnetic flux density output,

At least one motion sensor (6) for measuring motion, in particular motion selected from at least one of motion J: in a direction parallel to the magnetic field component B:, and from motion V; in a direction tangential to the magnetic field component B, the motion sensor providing motion output,

Wherein the magnetic field sensor and the motion sensor have an at least partially overlapping field of view,

At least one controller configured for controlling the magnetic field sensor and the motion sensor, in particular for controlling said sensors such that measuring strain and measuring motion occur in the same time domain,

A data acquisition system (DAQ) (7) receiving input from the magnetic field sensor and from the motion sensor, and

A data processor for processing the input of the sensors and for providing a flux of mechanical energy based on said input, in particular wherein the processor is configured to obtaining elastic strain from variation in magnetic flux density and motion. 2. The sensor system according to embodiment 1, wherein the at least one motion sensor is selected from at least one of a non-contact electromagnetic field sensor, an ultrasonic sen- sor, and an optical sensor, such as using IR or laser light, more in particular at least one mo- tion sensor configured to detect motion J’: of a said magnetic material in at least the direc- tion parallel to the central vertical axis of the said magnetic material, in particular an optical sensor, more in particular an optical velocity sensor, and/or

Wherein the at least one motion sensor has a sampling rate of > 500 Hz, in particular > 1000 Hz, more in particular > 5000 Hz, such as > 10 kHz. 3. The sensor system according to embodiment 2, wherein the at least one optical sensor is selected from an optical Doppler sensor, in particular a Laser Doppler Velocimetry sensor,

from a high speed optical sensor comprising a multitude of pixels, from a surface length sensor, in particular a Surface Length Velocimetry sensor, more in particular wherein the optical sensor is configured to provide light and to sense reflected light 4. The sensor system according to any of embodiments 1-3, wherein the strain and the mo- tion are measured in a said magnetic material, in particular wherein the said magnetic mate- rial 1s selected from a driving pile, a support pile, a windmill pile, an infrastructural ele- ment, in particular a bridge, a railway or part thereof. 5. The sensor system according to any of embodiments 1-4, wherein the sensor system is configured for measuring at a distance of the said magnetic material, such as in a flying ob- ject, and/or wherein the sensor system is provided in a housing. 6. The sensor system according to any of embodiments 1-5, wherein the sensor system is configured to receive electrical power, and/or

Wherein the sensor system is configured to transmit data, and/or

Wherein the sensor system is configured to receive data, and/or

Wherein the sensor system comprises a transceiver, and/or

Wherein the sensor system comprises a positioner for maintaining the sensor system in a location in space, in particular wherein the positioner is a flying object, such as a drone. 7. The sensor system according to any of embodiments 1-6, wherein the sensor system comprises a positioning sensor configured for maintaining the sensor in place. 8. The sensor system according to any of embodiments 1-7, comprising at least one further sensor, wherein the at least one further sensor is selected from a temperature sensor for cor- recting drift in any other sensor, an orientation sensor, and angular velocity sensor, config- ured for monitoring relative rotation of the sensor system and/or pile driver, in particular a gyroscope (such as a MEMS), an accelerometer configured for monitoring vibrations of the sensor system, such as a linear accelerometer, in particular wherein the at least one further sensor is integrated in the sensor system. 9. The sensor system according to any of embodiments 1-8, comprising at least one control - ler, wherein the at least one controller is configured to process the motion sensor output and the magnetic field output, and configured to control energy provided to the said magnetic mate- rial, in particular to control impact energy, and/or to provide feedforward and/or feedback, and/or wherein the at least one controller, the data acquisition system, and data processor are pro- vided as one or more processors. 10. The sensor system according to any of embodiments 1-9, comprising a receiver, the re- ceiver configured to receive output of the at least one magnetic sensor and the at least one motion sensor, and optionally the DAQ and the data processor, in particular wherein the re- ceiver is ring-shaped, wherein the ring-shape is configured to at least partially surround a said magnetic structure to be measured. 11. A method for driving a pile, comprising

Providing the pile,

Positioning the sensor system of any of embodiments 1-10 in proximity of the pile,

Driving the pile into a soil using a pile driver, in particular using a driver selected from an impact hammer, a weight, and a driver providing a combination of vertical and tor- sional vibration (GDP), and

Measuring a flux of mechanical energy through the pile to the soil. 12. The method according to embodiment 11, wherein the measured mechanical energy flux is used to control the energy provided by the pile driver to the pile, in particular to in- crease the energy provided, to decrease the energy provided, or to maintain the energy level provided . 13. The method according to any of embodiments 11 or 12, wherein the energy/time is con- trolled, in particular by increasing a number of quantized energy provisions per unit time, by decreasing a number of quantized energy provisions per unit time, or to maintain a num- ber of quantized energy provisions per unit time at a present level, 14. Computer program or integrated circuit comprising instructions, in particular wherein the computer program is loaded on a processor or in a memory, the instructions causing the computer to carry out the following: instructing a pile driver to drive the said pile into a soil, in particular an impact ham- mer, and instructing the sensor system according to any of embodiments 1-10 to measure a flux of mechanical energy through the pile to the soil. 15. Computer program according to embodiment 14, further comprising instructions for

Instructing the pile driver to control the impact energy provided by the pile driver to the pile based on the measured energy flux, in particular to increase the impact energy, to decrease the impact energy, or to maintain the impact energy. 16. A system or method comprising at least one element according to any of the embodi- ments 1-15 and optionally an element from the description.

Claims

Conclusions:

1. A contactless sensor system (3) comprising: At least one magnetic field sensor (5) for measuring variation in magnetic flux density, in particular for measuring radial and/or magnetic field components (Bz and Br), more in particular for measuring variation in said magnetic field components, the magnetic field sensor outputting the magnetic flux density, at least one motion sensor (6) for measuring motion, in particular motion selected from at least one of the motions Vz in a direction parallel to the magnetic field component Bz and from motion Vt in a direction tangential to the magnetic field component Bz, the motion sensor providing an output signal for motion, wherein the magnetic field sensor and the motion sensor have an at least partially overlapping field of view, At least one control unit configured for controlling the magnetic field sensor and the motion sensor, in particular for controlling said sensors so that the measurement of voltage and the measurement of motion occur in the same time domain, a data acquisition system (DAQ) (7) receiving input from the magnetic field sensor and from the motion sensor, and a data processor for processing the input from the sensors and providing a flow of mechanical energy based on that input, particularly when the processor is configured to obtain elastic strain from variation in magnetic flux densities and motion.

2. The sensor system according to claim 1, wherein the at least one motion sensor is selected from at least one of a contactless electromagnetic field sensor, an ultrasonic sensor, and an optical sensor, for example using IR or laser light, more in particular a motion sensor configured to detect motion Vz of said magnetic material in at least the direction parallel to the central vertical axis of said magnetic material, in particular an optical sensor, more in particular an optical speed sensor, and/or wherein the at least one motion sensor has a sampling frequency of > 500 Hz, in particular > 1000 Hz, more in particular > 5000 Hz, such as > 10 kHz.

3. The sensor system of claim 2, wherein the at least one optical sensor is selected from an optical Doppler sensor, in particular a laser Doppler velocimeter, a high-speed optical sensor with a large number of pixels, a surface length sensor, in particular a surface length velocimeter, more particularly wherein the optical sensor is configured to supply light and to detect reflected light.

4. The sensor system according to any of claims 1 to 3, wherein the stress and the movement are measured in a magnetic material, in particular wherein the magnetic material is selected from a pile, a support pile, a wind turbine pile, an infrastructure element, in particular a bridge, a railway, or a part thereof.

The sensor system of any of claims 1 to 4, wherein the sensor system is configured to measure at a distance from said magnetic material, such as in a flying object, and/or wherein the sensor system is housed in a housing.

The sensor system of any of claims 1 to 5, wherein the sensor system is configured to receive electrical power, and/or wherein the sensor system is configured to transmit data, and/or wherein the sensor system is configured to receive data, and/or wherein the sensor system comprises a transceiver, and/or wherein the sensor system comprises a positioner for maintaining the sensor system at a location in space, in particular when the positioner is a flying object, such as a drone.

The sensor system of any of claims 1 to 6, wherein the sensor system comprises a positioning sensor configured to keep the sensor “in place.”

8. The sensor system according to any of claims 1 to 7, comprising at least one further sensor, the at least one further sensor being selected from a temperature sensor for correcting drift in another sensor, an orientation sensor, and an angular velocity sensor configured to monitor the relative rotation of the sensor system and/or the pile driver, in particular a gyroscope (such as a MEMS), an accelerometer configured to monitor vibrations of the sensor system, such as a linear accelerometer, in particular when the at least one further sensor is integrated into the sensor system.

9. The sensor system according to any of claims 1 to 8, comprising at least one control unit, wherein the at least one control unit is configured to process the output of the motion sensor and the magnetic field and is configured to control the energy supplied to said magnetic material, in particular to control the impact energy, and/or to provide feedforward and/or feedback, and/or wherein the at least one control unit, the data acquisition system and the data processor are provided as one or more processors.

10. The sensor system of any of claims 1 to 9 comprising a receiver, the receiver being configured to receive output from the at least one magnetic sensor and the at least one motion sensor, and optionally from the DAQ and the data processor, in particular wherein the receiver is annular, the annular configured to at least partially surround a magnetic structure to be measured.

11. A method of driving a pile, including

Providing the pile, placing the sensor system of any of claims 1-10 in the vicinity of the pile, driving the pile into the ground using a pile driver, in particular using a pile driver selected from an impact hammer, a weight, and a pile driver providing a combination of vertical and torsional vibrations (BBP), and measuring a flux of mechanical energy through the pile to the ground.

12. The method of claim 11, wherein the measured mechanical energy flux is used to control the energy supplied to the pile by the pile driver, in particular to increase the supplied energy, decrease the supplied energy, or maintain the supplied energy level.

The method according to any of claims 11 or 12, wherein the energy/time is controlled, in particular by increasing a number of quantified energy supplies per unit time, by decreasing a number of quantified energy supplies per unit time, or by maintaining a number of quantified energy supplies per unit time at a current level.

14. Computer program or integrated circuit comprising instructions, in particular the computer program being loaded onto a processor or into a memory, the instructions causing the computer to perform the following: instructing a pile driver to drive said pile into the ground, in particular a hammer, and instructing the sensor system according to any of claims 1 to 10 to measure a flux of mechanical energy through the pile to the ground.

15. A computer program according to claim 14, further comprising instructions to instruct the pile driver to control the impact energy supplied by the pile driver to the pile based on the measured energy flux, in particular to increase the impact energy, decrease the impact energy, or maintain the impact energy.

16. A system or method comprising at least one element according to any one of claims 1 to 15 and optionally an element from the description.