Reconfigurable GPR device

Abstract

A reconfigurable GPR device (1) for acquiring radar data about a medium comprises a radar antenna (2) having a first polarization, a processor unit (3) connected to the antenna (2), and a housing (4) around the antenna (2) and the processor unit (3). In addition, the device (1) comprises at least one of a wheel assembly (20) and a direction determination unit (30). If present, the wheel assembly (20) comprises a holder (21), a wheel (22), and a wheel rotation sensor (23). The wheel rotation sensor (23) is connected to the processor unit (3), and an axis (22s) of the wheel (22) pivots relative to the first polarization. If present, the direction determination unit (30) is connected to the processor unit (3) and is adapted to determine direction information. The direction information describes the angle between the direction of movement of the device (1) and the first polarization.

Description

Technical Field

[0001] The present invention relates to a reconfigurable GPR device, an autonomous GPR system and a method for acquiring radar data about a medium. Background Art

[0002] Ground penetrating radar (GPR) is commonly used to image a medium, i.e., to generate an image of its internal structure. In particular, such an image contains information about the location and properties of layers, objects, cracks, and / or voids in the medium. The basic principle of GPR is the propagation of radar waves, for example, having a frequency between 10 MHz and 10 GHz, which are emitted and received by at least one radar antenna. The propagation of radar waves is affected by the structure and properties of the medium. In particular, radar waves are reflected at the boundaries of materials with different dielectric constants and / or diamagnetic constants. Therefore, GPR is commonly used in non-destructive testing (NDT), for example in concrete, masonry, brickwork, or wood. GPR is particularly suitable for locating steel bars or voids in building structures, such as houses and bridges.

[0003] Radar waves are also characterized by their polarization. In particular, radar waves can exhibit different polarization directions. Orthogonally polarized radar waves can have H polarization (horizontal) or V polarization (vertical). It is well known that the penetration depth of radar waves, and therefore the resolution of the resulting image, varies with the polarization of the radar waves and depends on the internal structure of the medium. The steel bars in a concrete wall can be used as an example: radar waves polarized along the steel bars may not penetrate into the deeper parts of the medium behind the steel bars, i.e., further away from the antenna than the steel bars, while radar waves polarized transversely with respect to the steel bars may actually penetrate deeper. For practical applications, it may therefore be beneficial to choose the polarization according to the structure of interest and the depth range.

[0004] Conventional GPR devices used for NDT include handheld devices that can be operated on various surfaces (e.g., with varying inclinations). Such handheld devices are known, for example, from EP2720065A1 and EP1197762B1. By rotating the device (e.g., 90°) to switch between H-polarization and V-polarization, the polarization of the transmitted radio waves relative to the medium can be changed.

[0005] However, such conventional GPR devices have several disadvantages. First, they are relatively large, heavy, and cumbersome for regular manual operation. Second, acquiring data around corners and edges of building structures is difficult, and often impossible. Third, it is not possible to change polarization to acquire data on the same path with both H and V polarizations. Fourth, because information about polarization is not routinely available in the data set, accurate processing and interpretation of the acquired radar data is impossible. Summary of the Invention

[0006] Therefore, the problem to be solved by the present invention is to provide a reconfigurable GPR device that allows acquiring radar data with different polarizations along a defined path on a medium.

[0007] This problem is solved by a reconfigurable GPR device for acquiring radar data about a medium according to the present invention. GPR stands for Ground Penetrating Radar and involves the use of radar waves to image the internal structure of a medium such as soil, rock, ice, concrete, wood, or other construction materials. GPR for concrete structures preferably operates in a frequency range between 50 MHz and 8000 MHz, particularly between 400 MHz and 6000 MHz. Preferably, the device acquires and processes the radar data in real time, i.e., in a time frame of the order of milliseconds, particularly less than 1 second.

[0008] The device includes a radar antenna with a first polarization, a processor unit (particularly an FPGA (field programmable gate array) or a CPU (central processing unit)) connected to the antenna, and a housing surrounding the antenna and the processor unit. The antenna is preferably adapted to transmit and receive radar waves that pass through a medium and to convert the received radar waves into radar data. The radar data is preferably a representation of the radar waves as electrical signals. The term "radar antenna with a first polarization" is used in the sense that the radar waves emitted by the antenna exhibit the first polarization. This should explicitly include antennas adapted to transmit radar waves of different polarizations. The housing preferably protects the antenna and the processor unit, for example, from at least one of dust and liquids. However, the housing need not be enclosed on all sides.

[0009] Furthermore, the device includes at least one of a wheel assembly and a direction determination unit. If present, the wheel assembly includes a holder, a wheel, and a wheel rotation sensor. The wheel rotation sensor is connected to the processor unit. The wheel axis pivots relative to the first polarization. That is, the rolling direction of the wheel, and therefore preferably the rolling direction of the device, can be changed by pivoting the wheel. This allows radar data with different polarizations to be collected along the same path, which in turn improves the quality and resolution of the resulting image of the internal structure of the medium.

[0010] Preferably, the wheel rotation sensor is adapted to sense the path length of the device's movement and, in particular, to determine position information based on the path length. The wheel rotation sensor may be, for example, a rotary encoder. Advantageously, the path length, and preferably the position information, is used in the display and / or interpretation of radar data, for example, to locate objects within a medium, such as rebar or voids in concrete or building structures.

[0011] If present, the direction determination unit is connected to the processor unit and is adapted to determine direction information. The direction information describes the angle between the direction of motion of the device and the first polarization. Such direction information can support processing and / or interpretation of radar data. In particular, the direction information is used to process and / or interpret radar data acquired along the same path but with different polarizations. Therefore, the processor unit is advantageously adapted to generate a data set comprising at least one of the position information and the direction information, together with the radar data.

[0012] The direction determination unit can be adapted to determine the direction information in different ways. In one embodiment, the wheel assembly includes an angle sensor adapted to sense the angle between the axis of the wheel and the holder. In particular, the angle sensor is connected to the direction determination unit. In another embodiment, the direction determination unit is connected to different direction sensors, such as optical encoders, which are adapted to sense the direction of at least one of the movement and acceleration of the device. Furthermore, the processor unit can be adapted to determine fused direction information based on the direction information from the different direction sensors. In the following, the term "direction sensor" is understood to include "orientational sensors", such as compass sensors or accelerometers.

[0013] As mentioned above, it is advantageous if the device exhibits at least two preferred directions of movement relative to the first polarization, so that the antenna can be oriented in two different orientations relative to the direction of movement of the device. This allows the polarization of the radar waves to be adjusted in order to optimize the quality and / or resolution of the resulting image, for example, depending on the internal structure of the medium.

[0014] In one embodiment, the wheel (i.e., its axis) exhibits two stable orientations relative to the housing, which differ by a pivot angle, which can be, for example, 90°, and which are particularly capable of emitting waves with H and V polarizations. Preferably, the wheel's orientations other than the two stable orientations are unstable. In particular, the stable orientation requires the application of a torque or force above a given threshold in order to change the orientation. Such a stable orientation can be achieved, for example, by a snap-fit ​​mechanism, for example by an elastic force, such as from a spring, or by a magnetic force, which needs to be overcome in order to change the orientation.

[0015] In an advantageous embodiment, the wheel assembly is removably attachable to the housing, i.e. it is non-destructively attachable to and removable from the housing. In particular, the wheel assembly can be attached to several side walls of the housing. This allows changing the polarization of the movement relative to the device by attaching the wheel assembly to different side walls. Preferably, the wheel assembly is manually attachable, in particular by means of a snap-fit ​​attachment. "Manually" means that the attachment and / or removal can be done with the bare hands, i.e. without using any tools, such as a screwdriver. "Snap-fit" describes a fastening device, wherein the attached wheel assembly can only be detached if the separation force is greater than a certain threshold value. Such a snap-fit ​​can be achieved, for example, by elastic force (e.g. by a spring) or magnetic force.

[0016] In another embodiment, the device comprises a communication unit adapted to transmit the radar data to a remote computing unit via a wireless connection, in particular wherein the wireless connection comprises Wi-Fi or Bluetooth. Preferably, the communication unit is one of located in the housing or part of the device.

[0017] Another aspect of the present invention relates to an autonomous GPR system for acquiring radar data. The system comprises the aforementioned apparatus and a power supply unit electrically connected to the apparatus and adapted to supply power to the apparatus. In particular, the power supply unit can be attachable to the apparatus, preferably manually attachable. The power supply unit can include at least one battery, such as at least one rechargeable battery. Such a system is autonomous in that it can operate autonomously, i.e., without attached cables. The system can be connected to a separate electronic device, such as a remote computing unit and / or a unit with a display. This facilitates ease of use and allows for application in inaccessible areas, such as corners in building structures.

[0018] Yet another aspect of the present invention relates to a method for acquiring radar data about a medium, and in particular, a method for operating the aforementioned device. The method comprises the steps of moving a GPR device including a radar antenna along the medium, repeatedly transmitting radar waves of a first polarization into the medium via the antenna, repeatedly receiving the radar waves via the antenna, and converting the received radar waves into radar data. Furthermore, the method comprises at least one of changing the angle between the device's direction of motion and the first polarization (and repeating the aforementioned steps) and determining directional information describing the angle between the device's direction of motion and the first polarization.

[0019] Further advantageous embodiments are listed in the dependent claims and in the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be better understood and objects other than those set forth above will become apparent from the following detailed description, which is made with reference to the accompanying drawings, in which:

[0021] Figure 1 and 2 A perspective view of a reconfigurable GPR device according to an embodiment of the present invention is shown from the rear side and the front side, respectively;

[0022] Figure 3 and 4 Shown Figure 1 and 2 A perspective view of the apparatus further comprising a wheel assembly;

[0023] Figure 5 and 6 shows a perspective view of a wheel assembly according to an embodiment of the present invention;

[0024] Figure 7 A block diagram of a GPR device or a GPR system according to an embodiment of the present invention is shown;

[0025] Figure 8 and 9 shows a perspective view of an autonomous GPR system including a power supply unit according to an embodiment of the present invention;

[0026] Figure 10 and 11 Shown Figure 8 and 9 A perspective view of a system further comprising a wheel assembly;

[0027] Figure 12 A flow chart of a method for acquiring radar data about a medium according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0028] Figure 1 and 2 Perspective views of a reconfigurable GPR device 1 according to an embodiment of the present invention are shown from the rear and front sides, respectively. The reconfigurable GPR device 1 for acquiring radar data about a medium includes a housing 4 enclosing a radar antenna 2 (indicated by dashed lines) and a processor unit (not shown) connected to the antenna. The inclusion of the processor unit in the device 1 makes the device 1 autonomous, i.e., the GPR is not "dependent" on another external device, e.g., via a cable. The antenna 2 is adapted to transmit and receive radar waves of a first polarization (the antenna "has" the first polarization). The housing 4 includes a top side 5, a bottom side 6 opposite the top side 5, and four side walls, namely, a rear side wall 7, a front side wall 8 opposite the rear side wall 7, and two lateral side walls 9 and 9' opposite each other. In general, the housing 4 may alternatively include more or fewer than four side walls. The antenna 2 is located in the lower portion of the housing 4, i.e., closer to the bottom side 6 than to the top side 5, preferably in the lowermost quarter of the housing 4. Typically, bottom side 6 corresponds to the transmitting side of antenna 2 , and the medium of interest is located near (ie, “under”) bottom side 6 when apparatus 1 is operating (ie, acquiring radar data about the medium).

[0029] The housing 4 of the device 1 is preferably made of a durable and / or strong material, for example, polycarbonate (e.g., Lexan), so that the device is not damaged under the harsh operating conditions of field use. Advantageously, the housing 4 is dustproof and / or protected against splashing water, for example, according to IP 54 or, more preferably, according to IEC standard 60529. In particular, the bottom side 6 of the housing 4 is made of a scratch-resistant and preferably smooth material. Preferably, the bottom side 6 is easily interchangeable, for example, by hand, meaning that no additional tools are required.

[0030] In one embodiment, the length, width and height of the housing 4 are all less than 10 cm, and preferably less than 9 cm. The height of the housing 4, i.e. its dimension between the top side 5 and the bottom side 6, is preferably less than 8 cm, preferably less than 7 cm. Such dimensions make the device 1 ergonomic and enable access to compact spaces. Typically, the device is preferably a handheld device, which means that the device can be operated when held by hand, preferably with only one hand. This allows the device 1 to be operated in difficult-to-access areas, such as corners of building structures, or between pipes suspended from a ceiling and the ceiling itself, or between pipes and other structural features. The small size and weight also allow the device 1 to be operated on vertical walls and in overhead situations.

[0031] exist Figure 1 and 2 In the embodiment of the present invention, the housing 4 further comprises a connector 10 on each side wall, in particular a four-pin connector. Such a connector can be used to communicate with components such as wheel assemblies, see Figure 3-6 Alternatively, the connector 10 can be used to communicate with a different component, for example comprising a camera, in particular a CCD camera, or an optical mouse, in particular for determining the movement of the device 1. Furthermore, the housing 4 comprises a second connector 11, for example a threaded hole, for mechanically connecting the component to each side wall, for example by means of screws on the component.

[0032] Figure 1 and 2 The housing 4 in the device also includes a cap 12, such as a rubber seal, covering at least one slot. Specifically, the device 1 includes a slot for a communication unit 13, such as a Wi-Fi 802.11a / b / g / n device or a Bluetooth dongle, for communicating with a remote processing unit. Furthermore, the device 1 may include an additional slot, such as a USB-C connector 14. This additional slot may be suitable for communication, such as for data transmission, and / or for receiving power from a remote power source.

[0033] Figure 1 and 2The device 1 also includes buttons 15 and 15' on the lateral side walls 9 and 9'. The buttons are functionally connected to a processor unit for controlling the device 1. In particular, a user can control at least one of the following actions by pressing only one of the buttons 15 and 15': turning the device on, starting the acquisition of radar data, marking a specific location (e.g., the location of a rebar) during the acquisition (e.g., by pressing the button twice during a short time interval (e.g., within 1 second)), and turning the device off (e.g., by pressing the button for a longer duration, e.g., for more than 1 second). The presence of at least two buttons 15 and 15' allows for two-sided operation of the device, i.e., the device can be operated in a simple manner with the left and / or right hand. Generally, the device 1 may optionally include only one button. Operation of the device by pressing only one button (or one of two or more equivalent buttons) is simple and makes acquiring radar data using the device user-friendly.

[0034] Figure 3 and 4 Shown Figure 1 and 2 , which also includes a wheel assembly 20. The wheel assembly 20 includes a holder 21, a wheel 22, and a wheel rotation sensor 23 (indicated but not visible in the figure). The wheel rotation sensor 23 measures the amount of rotation of the indicator wheel 22 about its axis 24 (see Figure 4 The wheel rotation sensor 23 may be, for example, a rotary encoder and is connected to the processor unit ( Figure 3 and 4 (not shown in the figure). Preferably, the wheel rotation sensor 23 is adapted to sense the path length of the device's movement. In particular, the wheel rotation sensor 23 is adapted to determine position information based on the path length, i.e., the coordinates of the position within a given reference frame. Thus, the radar data can be linked to their corresponding positions on the medium.

[0035] Furthermore, the axis 24 of the wheel 22 (see Figure 4 ) is pivoted relative to the housing 4 and thus pivoted to the first polarization. In particular, the wheel 22 has two stable orientations relative to the housing 4, which differ by a pivot angle α, which is in particular 90°, as shown in FIG. Figure 3 As shown by the thick arrows in . Therefore, the device exhibits at least two preferred directions of motion relative to the first polarization. Figure 4As shown by the thick arrows in , the device 1 can move in particular in a forward direction F (rear wheel), a rearward direction B (front wheel), a left direction L and a right direction R (all wheels are in a sidecar configuration, not shown). Note: in the sidecar configuration, the axis 22' of the wheel 22 is perpendicular to the sidewall to which the wheel assembly 20 is attached; in the rear wheel configuration and the front wheel configuration, the axis 22' is parallel to the sidewall. Therefore, by pivoting the wheel from the rear wheel / front wheel configuration to the sidecar configuration and measuring a second time along the same path, the polarization of the radar data acquired along the same path can be changed, for example from H polarization to V polarization, or vice versa. Radar data with different polarizations can, in turn, produce better resolution and / or quality of data about the medium, particularly in a specific depth range of the medium.

[0036] As from Figure 3 and 4 As will be understood in the foregoing, the wheel assembly 20 can alternatively be attached to a side wall of the device other than the rear side wall 7 (shown). Furthermore, in this way, the polarization of the acquired radar data can be changed when measuring a second time along the same path. Preferably, the wheel assembly 20 is detachably attached to the housing 4. Typically, the wheel assembly 20 can be attached to multiple side walls, in particular to at least four side walls (as shown). Advantageously, the wheel assembly 20 can be attached to (and removed from) the housing 4 manually (i.e., by hand) without the use of additional tools. This attachment method is simple and time-saving, and in particular, it can be achieved by snap-fitting. Figure 5 and 6 An embodiment of such a snap-fit ​​mechanism is shown in FIG.

[0037] Figure 5 and 6 A perspective view of a wheel assembly 20 according to an embodiment of the present invention is shown. The retaining member 21 includes four balls 24 which are mounted to the retaining member by springs. The balls 24 fit into corresponding recesses 16 in the housing 4 (see FIG. Figure 2 ), so that snapping the ball 24 into the recess 16 results in a mechanical connection between the wheel assembly 20 and the housing 4. Alternatively, such a snap-in mechanism can be implemented by magnets on the holder 21 and on the housing 4. In addition, the holder 21 includes a screw 25 suitable for interlocking with the second connector 11 on the housing 4. Thus, the screw 25 can be used to fix the wheel assembly 20 on the housing 4. Advantageously, the screw 25 can be screwed into the housing 4 manually (i.e. without the use of additional tools). The holder 21 also includes a plug 26, which is suitable for establishing an electrical connection between the wheel assembly 20 and the components inside the housing 4 when the connector 10 is inserted.

[0038] Preferably, the wheel assembly 20 includes a suspension 28 for the wheel 22. The suspension 28 is resilient, for example, implemented by a spring, and is adapted to press the wheel 22 against the surface of the medium as the device 1 moves along the medium. This makes the path length and position information determined from the measurements of the wheel rotation sensor 23 more accurate and reliable, for example, in the case of rough surfaces.

[0039] In one embodiment, the apparatus 1 may comprise a direction determining unit. Figure 7 1 shows a block diagram of a GPR device according to an embodiment of the present invention, comprising the direction determination unit 30. The direction determination unit 30 is connected to the processor unit 3 and is adapted to determine direction information. The direction information describes the angle between the direction of movement of the device and the first polarization. In this case, it is advantageous if the wheel assembly 20 comprises an angle sensor 27 (at the position of the wheel assembly 20) adapted to sense the angle between the wheel axis 22' and the holder 21. Figure 6 ). The angle sensor 27 is connected to the direction determination unit 30 and may be, for example, a resistive or capacitive angle sensor.

[0040] As an alternative to or in addition to the angle sensor 27 in the wheel assembly 20, the direction determination unit 30 may be connected to a direction sensor 31 adapted to sense the direction of at least one of the movement and acceleration of the device 1. The direction sensor 31 may include at least one of the following components: (i) It may include a camera 32, i.e., an optical encoder, such as a CCD camera, with a camera viewing angle at least partially directed toward the bottom side 6 of the housing 4. In this case, the direction determination unit 30 is adapted to determine direction information from subsequent images captured by the camera 32, e.g., using conventional image processing techniques, in order to retrieve the direction of the movement and / or acceleration of the device 1. Advantageously, the surface of the medium exhibits a texture that facilitates retrieving the direction. (ii) The direction sensor 31 may include an accelerometer 33, such as a piezoelectric, piezoresistive, or capacitive component. In this case, the direction determination unit 30 is adapted to determine the direction of the device's acceleration. (iii) The direction sensor 31 may include a compass sensor 34, i.e., a sensor that measures a quantity indicating the sensor's orientation relative to the direction of a magnetic field in the surrounding environment (e.g., the Earth's magnetic field). Generally, the orientation sensor 31 may be implemented in an assembly similar to the wheel assembly 20 that is attachable to the housing 4, such as an assembly having a camera, or it may be implemented within the housing 4, such as an onboard accelerometer of the device.

[0041] If more than one type of directional information is present, the processor unit is preferably adapted to determine fused directional information based on the directional information from the different directional sensors. The (fused) directional information indicates the polarization of the acquired radar data, such as H polarization or V polarization. This directional information facilitates processing and / or interpretation of the radar data to determine a high-quality image of the interior of the medium. The processing and / or interpretation can, for example, take into account the polarization of the acquired radar data and / or vary depending on the polarization. Therefore, the directional information is preferably stored and / or transmitted together with the radar data.

[0042] Typically, directional information not only indicates the polarization of the acquired radar data, but it can also be used to reconstruct the measurement path—that is, the actual path the device moved during data acquisition. Furthermore, directional information can include information about the orientation in which the device is used, such as on the floor, against a wall, on an inclined surface, or in an overhead setup. This information can be evaluated by users and / or manufacturers to support users with measurement and interpretation information, as well as further development of the device and / or acquisition methods.

[0043] Furthermore, the processor unit 3 is adapted to control the antenna 2 and to receive radar data from the antenna 2 and at least one of position information from the wheel rotation sensor 23 (if present) and direction information from the direction determination unit 30 (if present), see Figure 7 The radar data can be stored in the internal memory 40 of the device 1 or sent via the communication unit 13 together with at least one of the position information and the direction information. For this purpose, the device can preferably also include a communication unit 13 that is suitable for transmitting the radar data to a remote computing unit via a wireless connection, for example, via Wi-Fi 802.11a / b / g / n or Bluetooth. The remote computing unit can be, for example, a conventional computer or an iPad, preferably equipped with software for processing the radar data and / or for determining an image of the internal structure of the medium based on the radar data.

[0044] Preferably, the antenna 2 is a radar source with a frequency range between 50 MHz and 8000 MHz, in particular between 400 MHz and 6000 MHz. In particular, the processor unit 3 is configured to control the antenna 2 to transmit a stepped frequency continuous wave (SFCW).

[0045] Typically, the apparatus 1 need not include Figure 7 Although the antenna 2 and the processor unit 3 are essential components, different embodiments include only one or two of the wheel rotation sensor 23 and the direction determination unit 30.

[0046] According to another aspect of the invention, an autonomous GPR system for acquiring radar data comprises an apparatus 1 as described above and a power supply unit 50 adapted to supply power to the apparatus 1, see also Figure 7 Although it is possible to connect the USB-C cable to the slot 14, for example (see Figure 1 ) supplies power to the apparatus 1 , but for certain applications it may be advantageous to attach a power supply unit 50 to the apparatus 1 .

[0047] Figure 8 and 9 A perspective view of an autonomous GPR system 60 according to an embodiment of the present invention is shown, comprising a power supply unit 50 in the form of a battery pack 51. Preferably, the battery pack 51 is manually attachable to the housing 4, for example, via a snap-fit ​​mechanism. In certain embodiments, the snap-fit ​​mechanism is implemented via magnets (e.g., three magnets). The battery pack 51 can comprise conventional batteries, such as rechargeable NiMH batteries. This has the advantage that such batteries are readily available in most locations, and the system is easily transportable, even on an airplane. Advantageously, the battery pack 51 has a height of less than 2 cm, measured from the top side 5 of the device 1. This allows the autonomous system 60 to be small and lightweight, facilitating operation in difficult-to-access areas, such as around corners of buildings, beneath pipes, or overhead. Furthermore, the battery pack 51 can include a light pipe 52, wherein the color or light pattern of one or more LEDs indicates the operating status of the device 1, such as "starting," "on," "ready to acquire data," or "acquiring data." The one or more LEDs can be located in the housing 4 or in the battery pack 51. Figure 10 and 11 Shown Figure 8 and 9 A perspective view of a system comprising, for example Figure 5 and 6 The wheel assembly 20 is shown.

[0048] Advantageously, the autonomous GPR system 60 also comprises a rod 61 for holding the device 1, see Figure 9 This allows for simpler operation in inaccessible areas. In one embodiment, the housing 4 of the device 1 comprises a connector, such as the second connector 11 (see Figure 1 ), and the system 60 further comprises a rod 61 having a joint 62 that can be attached (particularly manually attached) to a connector. In one embodiment, the rod 61 can be screwed onto three of the four second connectors 11, one on each side wall of the housing 4. The rod 61 is adapted to hold the device. Preferably, the joint 62 comprises a ball joint 63, which facilitates the device 1 following the surface of the medium as it moves along the medium. Furthermore, the rod 61 advantageously comprises a telescopic rod, the length of which can be adjusted, for example, up to 2 meters.

[0049] In one embodiment, the GPR system 60 further includes an inductive sensor 64 adapted to sense electromagnetic fields. Figure 11 In particular, the inductive sensor 64 is adapted to determine the presence of a cable or pipe based on a sensed electromagnetic field. Preferably, the inductive sensor 64 converts the strength of the magnetic or electric field into a proportional value that can be used to assess the presence of the cable or pipe. For this purpose, the inductive sensor 64 can operate passively, i.e., without emitting an electromagnetic field. In particular, the inductive sensor 64 is adapted to sense electric or magnetic fields with a frequency between 45 Hz and 65 Hz, preferably around 55 Hz, so as to be able to detect cables carrying 50 Hz or 60 Hz AC current. In various embodiments, the inductive sensor 64 can be adapted to transmit an electromagnetic field that, in particular, induces a current in a nearby metallic object (e.g., a cable or pipe). This active transmission facilitates the location of objects that are not live wires, where a live wire is a loaded conductor, i.e., a conductor carrying current. In this case, a signal generator is preferably used to generate the excitation of the object, in particular, where the trace frequency of the excitation is between 400 Hz and 800 Hz or between 4 kHz and 150 kHz. Typically, the inductive sensor 64 is preferably attached to the device 1 via a holder 65. The mechanism of the holder 65 can be similar to the holder 21 of the wheel assembly, see above, i.e. preferably manually attached, for example by snap-fitting. Additionally or alternatively, the inductive sensor 64 can be fixed to the device 1 using screws that can be screwed into the second connector 11. The electrical connection between the inductive sensor 64 and the device 1, in particular the electrical connection with the processor unit 3, is preferably established via the connector 10.

[0050] Yet another aspect of the present invention relates to a method for acquiring radar data about a medium. Figure 12 A flow chart of this method according to an embodiment of the present invention is shown. Generally, this method can be applied when operating the above-mentioned device or system. The method includes the following steps S1 to S4 and at least one of steps S5 and S6:

[0051] Step S1: Moving a GPR device including a radar antenna along the medium. In most cases, "moving along the medium" should be understood as moving / pushing / dragging along a measurement path on the surface of the medium, particularly with the bottom side of the housing in contact with the surface. However, in special applications, the device housing may not be in direct contact with the surface. In an embodiment, the device or system is mounted on a vehicle, such as a drone, that follows the measurement path, facilitating acquisition of radar data over large or otherwise inaccessible areas.

[0052] Step S2: Repeatedly transmit radar waves of a first polarization into the medium via the antenna. The radar waves may be transmitted as radar pulses, continuous waves, or continuous waves with a stepped frequency. The first polarization is defined by the antenna and its control by the processor unit.

[0053] Step S3: Repeatedly receive the radar wave via the antenna. Preferably, radar waves reflected by the medium, such as those reflected by a boundary between regions of different relative permittivity, are received by the same antenna that transmitted the radar wave. However, it is also possible to separate the transmitting and receiving antennas. Steps S2 and S3 are repeated multiple times while acquiring radar measurements.

[0054] Step S4: Converting the received radar waves into radar data, in particular, where the radar data is a representation of the radar waves as electrical signals. Step S4 may include converting analog data into digital data in preparation for data storage, transmission or processing.

[0055] Step S5: Changing the angle between the direction of movement of the device and the first polarization, and repeating the above steps S1 to S4. By changing the angle, the polarization of the radar data is changed, for example, from H polarization to V polarization, or vice versa. Acquiring radar data with different polarizations can produce higher quality images of the interior of the medium. In particular, radar waves with different polarizations can penetrate the medium to different depths, i.e., distances from the antenna, depending on the reflection and / or absorption characteristics of the medium. Therefore, radar data with different polarizations can present high resolution in different depth ranges. Preferably, changing the angle between the direction of movement of the device and the first polarization includes pivoting the axis of the wheel relative to the first polarization, in particular pivoting it by a pivot angle, and rotating the housing by the pivot angle. Generally, for example, if no wheel is present, the device can be rotated by the pivot angle and then moved along the measurement path.

[0056] Step S6: Determine directional information describing the angle between the direction of motion of the device and the first polarization. This directional information characterizes the polarization of the acquired radar data, such as H polarization or V polarization. Therefore, it is an important parameter and can support the processing and / or interpretation of the radar data. Step S6 may include a sub-step of sensing the angle between the direction of motion and the first polarization by a directional sensor. The directional information can be determined from measurement results of different sensors, such as an angle sensor, a camera, an accelerometer, or a compass sensor as described above. Step S6 can be performed instead of step S5 or in addition thereto.

[0057] Optionally, the method may include at least one of the following steps (dashed arrow lines indicate optional steps):

[0058] Step S7: Generating a data set comprising said radar data and said direction information.Such a data set may then be stored in an internal memory of the device or transmitted to a remote computing unit, as described above.

[0059] Step S8: Processing the radar data while taking into account the directional information, and generating an image of the structure (i.e., the internal structure) of the medium from the radar data, particularly while taking into account the directional information. As described above, this processing can result in a higher quality structural image than conventional processing methods, particularly in the case of anisotropic reflective and / or absorbing properties of the medium.

Claims

1. A reconfigurable GPR device for acquiring radar data about a medium, comprising: a radar antenna having a first polarization, a processor unit connected to the antenna, the processor unit comprising a field programmable gate array or a central processing unit, a housing surrounding the antenna and the processor unit, as well as a wheel assembly comprising a holder, a wheel, and a wheel rotation sensor, wherein the wheel rotation sensor is connected to the processor unit and the rotation axis of the wheel is pivotable relative to the first polarization, wherein the antenna is movable in two preferred directions of movement relative to the first polarization, wherein the wheel is pivotable to one of a first stable orientation or a second stable orientation, the first stable orientation and the second stable orientation being separated from each other by a pivot angle, and The first stable orientation and the second stable orientation are achieved by elastic force or magnetic force.

2. The reconfigurable GPR device according to claim 1, The pivot angle is 90°.

3. The reconfigurable GPR device according to claim 1, wherein the wheel assembly further comprises a snap mechanism for implementing the elastic force or magnetic force, and in, The spring force or magnetic force is overcome to pivot the wheel from the first stable orientation to the second stable orientation, or to pivot the wheel from the second stable orientation to the first stable orientation.

4. The reconfigurable GPR device according to claim 3, in, Due to the snap-fit ​​mechanism, orientations of the wheel other than the first stable orientation and the second stable orientation are unstable.

5. The reconfigurable GPR device according to claim 1, in, The wheel rotation sensor senses a path length of the motion of the reconfigurable GPR device.

6. An autonomous GPR system (60) for acquiring radar data, comprising: The reconfigurable GPR device (1) according to any one of claims 1 to 5, a power supply unit (50) electrically connected to the reconfigurable GPR device (1) and adapted to supply power to the reconfigurable GPR device (1), In particular, the power supply unit (50) is attachable to the reconfigurable GPR device (1), in particular manually attachable to the reconfigurable GPR device.

7. The autonomous GPR system according to claim 6, in, The housing (4) of the reconfigurable GPR device (1) includes a second connector (11), and the autonomous GPR system further includes: A rod (61) having a joint (62) attachable to the second connector (11), in particular manually attachable to the second connector, wherein the rod (61) is adapted to hold the reconfigurable GPR device (1).

8. The autonomous GPR system according to claim 7, in, The joint (62) comprises a ball joint (63), and in particular, wherein the rod (61) comprises a telescopic rod.

9. The autonomous GPR system of claim 6, further comprising: An inductive sensor (64) is adapted to sense an electromagnetic field, and in particular to determine the presence of a cable or a pipe based on the sensed electromagnetic field.

10. A method for acquiring radar data about a medium, the method being used for operating a reconfigurable GPR device (1) according to any one of claims 1 to 5 or an autonomous GPR system (60) according to any one of claims 6 to 9, the method comprising the steps of: moving a reconfigurable GPR device (1) including a radar antenna (2) along the medium, Repeatedly emitting a first polarized radar wave into the medium through the antenna (2), repeatedly receiving radar waves by means of the antenna (2), Convert the received radar waves into radar data, The angle between the moving direction of the reconfigurable GPR device (1) and the first polarization is changed, and the above steps are repeated.

11. The method according to claim 10, Wherein changing the angle between the direction of motion of the reconfigurable GPR device (1) and the first polarization comprises pivoting an axis (22') of a wheel (22) relative to the first polarization.

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