THZ measuring device and THZ measuring method for detecting defects in measuring objects

Description

[0001] The invention relates to a THz measuring device and a THz measuring method for detecting defects in objects being measured. Such objects can be made of plastic, but also of other materials that are generally transparent to THz radiation, such as ceramics, concrete, or paper. Defects can include, in particular, cavities (i.e., voids formed during manufacturing), but also cracks, fissures, and inclusions of other materials, e.g., metal fragments.

[0002] In THz measurement of objects, THz radiation, specifically electromagnetic radiation in the frequency range of 0.01–10 THz, is emitted from a THz transceiver onto the object; the emitted electromagnetic radiation can therefore also be in the microwave range. The THz radiation emitted onto the object is partially reflected at the object's interfaces, i.e., at the transition between media with different refractive indices. Thus, layer thicknesses can be determined via this partial reflection, and, for example, air inclusions at their interfaces can be detected; metal fragments can be detected by the complete reflection of the THz radiation.

[0003] The THz transceiver can be optical, for example, by directly measuring the time of flight of the emitted THz beam and the reflected THz radiation. Furthermore, fully electronic THz measurement systems are known in which an antenna dipole generates the THz radiation as a transceiver and receives the reflected THz radiation. In this case, frequency modulation can be used, or pulsed THz radiation can be emitted.

[0004] In phased-array measurement systems, additional THz receivers, for example passive THz antenna dipoles, are connected to the actively transmitting THz transceiver, so that THz radiation reflected non-perpendicular to the THz transceiver can also be detected; accordingly, the THz transceiver and the THz receiver are synchronized with each other to enable coordination of the transmission time for distance measurement as time-of-flight measurement or frequency modulation.

[0005] Defect detection is intended to be carried out particularly directly after the production of plastic pipes or films by passing the objects in front of stationary THz measuring devices, e.g., measuring tubes. However, detecting defects, such as material fatigue and cracks, in stationary objects is generally hardly possible with such stationary THz measuring devices.

[0006] DE 10 2016 111 044 A1 describes a terahertz measuring device and a terahertz measuring method for measuring a test object, in which a terahertz transmitting and receiving unit and at least one, preferably several, passive terahertz receiving devices, whose optical axes are offset or inclined relative to the optical axis of the terahertz transmitting and receiving unit, serve to measure the test object. The multiple units or devices are arranged around a test object and are designed to be stationary.

[0007] DE 10 2016 105 599 A1 describes another terahertz measuring device for measuring test objects, in which terahertz radiation is emitted in a solid angle along an optical axis and reflections are detected. Defects are determined from the signal amplitude, whereby in particular a core region of the emitted terahertz radiation can be filtered out.

[0008] KR 10-2016-0149429 describes a measuring device with femtosecond lasers and suitable semi-transparent mirrors for measuring a disk-shaped test object.

[0009] DE 10 2016 119 728 A1 describes a terahertz measuring device for determining at least one layer thickness of a test object, which is portable by a handle area and has a shaped aperture with a contact contour for contact with a curved surface of a test object at its front end area.

[0010] The invention is based on the objective of creating a THz measuring device and a THz measuring method for detecting defects in objects being measured, which enable reliable detection with relatively little effort.

[0011] This problem is solved by a THz measuring device and a THz measuring method according to the independent claims. The dependent claims describe preferred embodiments. The THz measuring method is carried out in particular with the THz measuring device; the THz measuring device is specifically designed for carrying out the THz measuring method.

[0012] Thus, a THz measuring device with at least one active THz transmitter and several, at least temporarily passive, THz receivers is provided. The THz transmitter and the THz receivers are preferably fully electronic, i.e., designed as antenna dipoles, and thus form an antenna array.

[0013] The THz transmitter can in particular be a THz transceiver, i.e. designed as a combined transmitting and receiving device.

[0014] The control unit receives the THz measurement signals and identifies defects as reflections that have occurred outside proper interfaces of the object being measured; that is, the control unit receives the THz measurement signals and identifies reflections that have occurred outside proper interfaces of the object being measured, and evaluates these as defects.

[0015] Thus, the THz transmitter, which is located, for example, in the center of the antenna array, sends the THz transmission beam along an optical axis, specifically with an outgoing transmission cone around the optical axis. The THz radiation can be reflected at defects and at least partially reflected back towards the antenna array, so that one of the THz receivers or the THz transmitter itself, configured as a THz transceiver, receives the reflected radiation.

[0016] The measurement signal from the THz transmitter can initially be used to measure the thickness of the object being measured. The angle of arrival of the reflected radiation at the receivers can be evaluated from the time-shifted arrival of the reflected radiation, thus determining the distance and position of the reflection source in space. For example, from a curved surface of a defect, such as air inclusions, the THz transmission beam is reflected as a wavefront to the antenna array. A reflection peak can then be received by several THz receivers and, if necessary, by the THz transceiver itself. This allows the position and shape of the defect's surface to be determined or estimated with higher accuracy from the travel times or relative time shifts between the signals. The antenna array can initially be configured as a linear sensor strip, so that its extent or...lateral width determines the angle of the detectable reflected THz radiation.

[0017] This also offers the advantage that even curvatures of the defect can be very well tracked, since the multiple, adjacent THz receivers allow for estimation or triangulation from several reflection peaks.

[0018] According to further training, the THz receivers also function, at least temporarily, as transmitters, specifically as THz transceivers. This creates an antenna array in which several THz transceivers are arranged in a row, for example, as a sensor array. Each THz transceiver transmits the THz signal beam intermittently along its optical axis, preferably perpendicular to the sensor array, towards the object being measured, while the other THz transceivers then passively function as THz receivers. The THz array can thus be operated, in particular, with alternating active function of the THz transceivers.

[0019] This allows for a high number of measurement signals, as different THz transmission beams, especially those emitted in parallel with their own transmission cones, are directed at the object being measured, thus enabling a multitude of measurements to be recorded. This allows curved surfaces to be located three-dimensionally in space. The additional equipment required to operate the other dipole antennas temporarily as active THz transceivers is relatively low.

[0020] Another advantageous configuration is achieved through a two-dimensional design of the antenna array. For example, two intersecting sensor strips can be used, perhaps with a 90° angle between them. Again, only the central dipole antenna can be configured as an active THz transceiver, while the other dipole antennas act as passive THz receivers. However, it is advantageous that all dipole antennas are, at times, active THz transceivers and, conversely, passive at other times.

[0021] Even with this type of training, a depth profile of defects can be determined. This allows, for example, the reliable detection and measurement of the object being measured, including its external surfaces. Furthermore, the position, location, and extent of a defect, such as a void, within the object can be determined and visualized, for example, on a display, particularly an external display unit connected to a computer. Thus, in addition to the position within the material, the volume of a void can also be estimated.

[0022] Such a two-dimensional array arrangement can, for example, consist of just two intersecting sensor strips; in principle, a 2D matrix of antenna arrays can also be configured. However, it turns out that the additional equipment required for a complete 2D arrangement does not offer a significant advantage over the intersecting sensor strips; even the two intersecting sensor strips enable good two-dimensional detection with a relatively small number of antenna dipoles.

[0023] A further advantage arises from the combination with an accelerometer, particularly accelerometers for the three-dimensional detection of accelerations, i.e., in the three spatial dimensions. Thus, the control unit can both receive the THz measurement signals from the individual THz transceivers and evaluate them in combination with the accelerometer signals. Through temporal integration of the acceleration signals, three-dimensional positions in space can be assigned to the measurement signals.

[0024] According to the invention, a portable THz measuring device is designed in which the user can preferably perform a very precise measurement by handling and adjusting the measuring device, in particular by moving it along the object being measured. The THz measuring device is portable, at least with its antenna array, and its portable part has a grip area for the user to grasp and position at various points in front of the object being measured.

[0025] The control unit determines the respective three-dimensional position of the THz measuring device relative to the object being measured from the acceleration signals and can thus assign the numerous measurement signals to the points. Upon detecting a potential defect, the user can therefore measure this area more precisely with the THz measuring device and, for example, adjust the THz measuring device translationally or rotate and swivel it to acquire further measurement signals. Thus, a void can be subsequently detected more accurately after a single detection, and the curvature profile of its surface, and therefore its location and volume, can also be precisely determined. Consequently, even this simple and easy-to-handle array, formed from crossed sensor strips, can deliver a comparable number of measurement signals to a more complex and expensive 2D matrix arrangement.

[0026] According to further training, an optical camera, particularly an RGB camera, can be additionally attached to the measuring device and thus provide additional image signals that are evaluated and combined by the control unit. This allows an image of the object being measured to be displayed on a connected display device, corresponding to the image signals, and enhanced with the additional information obtained from the THz measurement signals.

[0027] With such a display, even when measuring an object from only one side, the front and back can be shown, for example, since these interfaces can be reliably determined by the THz radiation, and furthermore the position and arrangement of the defects can be shown, so that the user can, for example, place a mark on the workpiece that indicates the position and size of the defect.

[0028] Thus, movements of the measuring device do not lead to measurement inaccuracies, but to further measurement information, which can be evaluated as further measurements from other positions in space and used to determine defects more accurately.

[0029] Furthermore, the amplitude of the THz measurement signal can also be evaluated to determine the height of the measurement peaks of a defect and assign it to a specific size or the measured area of ​​the defect. This allows, for example, the determination of the area of ​​the defect, particularly through measurements taken in multiple swivel positions of the THz measuring device.

[0030] Thus, a complete 3D model of the workpiece, including its interfaces, formation and extent of its defects, can be replicated and visualized on a display.

[0031] In addition to applications such as the extrusion of plastic articles like plastic pipes and films, the measuring device can also be used for subsequent material testing. For example, wind turbine rotors can be measured safely and accurately as static objects using a portable device. Hairline cracks and delaminations can be detected as defects, for example, by measuring air inclusions within the cracks and delaminations, and their dimensions can be determined. Furthermore, pipe breaks can be detected from the outside. Metal pipes in plastic or earthenware environments can also be detected.

[0032] The invention is explained below with reference to the accompanying drawings, using several embodiments as examples. The drawings show: Fig. 1 shows the measurement of a measuring object with a measuring device according to a first embodiment, as shown in a measurement plane; Fig. 2 shows a perspective view of the three-dimensional measurement of a measuring object with a THz measuring device according to an embodiment; Fig. 3 shows another perspective view of the measurement of a measuring object with a measuring device according to a further embodiment with an additional RGB camera; Fig. 4 shows an example of an irregular measuring object with a void; Fig. 5 shows the measurement of a wall as a measuring object with a portable measuring device; Fig. 6 shows an example of a signal diagram of a THz measurement signal.

[0033] According to Fig. 1 A THz measuring device 1 is intended for measuring a stationary object 2, for example made of plastic or of a ceramic or stone material. The object 2 has interfaces 2a, 2b, for example a front 2a and a back 2b. Defects 3, for example as in Fig. 1 shown as voids (free space) or cracks and fissures that are not visible from the outside, for example also on the back side 2b, which is not directly visible to the user from the front.

[0034] The THz measuring device 1 has an antenna array 4, a control unit 5, an internal memory 6, and an output device 7. The output device can be, for example, an optical display device 7 for visualizing the object being measured 2 and the defects 3, and / or an acoustic indicator that, for example, emits a signal when a defect 3 is detected.

[0035] Furthermore, the THz measuring device 1 advantageously has a Fig. 5 The shown grip area 8 for grasping by the user, an actuating device 9 and at a front end area 10 a contact contour 11 or contour lines for contact with the interfaces, i.e. the front 2a and, if applicable, the back 2b of the object being measured 2.

[0036] According to the embodiment of the Fig. 1 The antenna array 4 initially comprises a central transceiver 12 as a transmitter, which is configured as an antenna dipole and emits a THz transmission beam 15 along its optical axis A. The antenna array 4 further comprises several receivers 14, which are similarly configured as antenna dipoles and detect THz radiation 16 reflected from the object 2 under test. The transceiver 12 and the receivers 14 are synchronized with each other or via the control unit 5, so that transmission and reception times can be compared.

[0037] The THz transceiver 12 emits THz radiation, generally in the frequency range between 0.01 THz and 10 THz, in particular frequency-modulated or pulsed; however, direct time-of-flight measurements are also possible. Thus, a THz transmit beam 15 is emitted along an optical axis A towards the object 2 and partially reflected at the interfaces 2a, 2b, for measuring distances, in particular the thickness d of the object 2 as the distance between the interfaces 2a, 2b, when the optical axis A is positioned perpendicular to the interfaces 2a, 2b.

[0038] Fig. 6 Figure 1 shows an example signal diagram of a measurement in which a signal amplitude S is plotted as a function of time t. A first measurement peak P1 is determined at time t1 when the THz transmission beam 15 enters the front interface 2a, and a measurement peak P4 is determined at a later time t4 when the THz radiation exits the rear interface 2b. In this measurement over the time period t4-t1, a time difference t4-t1 can thus be assigned to the thickness d of the object 2 as it is known. A measurement and evaluation can be performed accordingly using frequency modulation.

[0039] The THz transceiver 12 emits the THz transmit beam 15 within a radiation cone 15a around the optical axis A, so that radiation also propagates at an angle to the optical axis A. This radiation does not result in a measurement signal at the THz transceiver 12 itself when the optical axis A is positioned orthogonally at the interfaces 2a, 2b. However, the THz transmit beam 15 is reflected in various directions, particularly at irregular interfaces, such as a curved surface 3a of the void 3 depicted as a defect. As a result, the THz transceiver 12 itself, and at least one or more of the THz receivers 14, receive reflected THz radiation 16 that was not reflected by the interfaces 2a, 2b.

[0040] In Fig. 3 A void occurring, for example, during a casting process is shown as defect 3; according to, for example, Fig. 5 A defect 3 can also occur as a hairline crack or delamination in the plastic material and can be recognized as such by the additionally formed interfaces, i.e., in particular as an air inclusion.

[0041] In Fig. 6 Example measurement peaks P2 and P3 at times t2 and t3 are shown, which are generated upon entering and exiting the defect 3. The thickness of the defect 3, i.e., its extent in the direction of the THz transmission beam, is determined by the time difference t3-t2; the position of the defect 3 in the object 2 can be determined by its distances to the interfaces 2a and 2b, i.e., by the time differences t4-t3 and t2-t1, respectively. Furthermore, the signal amplitude S can preferably also be evaluated, where the height ΔS of the signal amplitude can be interpreted as the area extent or size of the defect perpendicular to the THz transmission beam.

[0042] The measurement signal from a single receiver 14 does not initially determine the exact position of the defect 3, nor its size and shape; first, the total travel time of the THz radiation is determined as the path of the transmitted THz beam 15 and the reflected THz radiation 16 back to the receiver 14, so that for a reflection peak in the measurement signal, the points where the reflection could have occurred generally lie on an ellipse whose foci are determined by the THz transceiver 12 and the THz receiver 14. Even with a linear antenna array 4 with a central THz transceiver 12 and adjacent THz receivers 14, several measurement signals can be acquired, allowing the direction of the defect 3 to be roughly estimated.

[0043] The antenna array 4 according to Fig. 1 Advantageously, the system does not only have one active THz transceiver 12; rather, it can have several THz transceivers 12, whereby the THz receivers 14 can also advantageously be configured as transceivers at certain times. For example, the active function of the THz transceiver 12 can be switched on alternately, so that one of the antenna dipoles is active at any given time and emits the THz transmit beam 15, while the other antenna dipoles passively receive reflected THz radiation 16. Fig. 1 As an example, a second THz transceiver 12 for emitting a THz transmit beam 15 is shown.

[0044] By means of such a configuration of an antenna array 4 with alternating function of the active THz transceiver 12, the THz transmit beam 15 can be directed towards the object 2 and the defect 3 from different directions or angles, and the reflected radiation 16 can be detected by correspondingly differently positioned passive receivers, so that in the plane shown the Fig. 1 A better measurement of the interface 3a of the void 3 is possible.

[0045] In this process, the THz transmission beam 15 initially travels from the THz transceiver 12 through air or the surrounding environment to the first interface, i.e., the front surface 2a. Here, a small portion of the intensity, for example 2-5%, is reflected, while the majority penetrates the object 2. Similarly, if a void forms as a defect 3, a portion of the THz transmission beam 15 is reflected at its interface 3a, which, for example, surrounds an internal gas or air inclusion. This reflects THz radiation 16 back, which can then be detected by a suitably positioned THz receiver 14. Furthermore, the THz transmission beam 15 also penetrates the void and is partially reflected on the back side of the void, i.e., upon re-entry from the void 3 into the material of the object 2. This reflects THz radiation 16 back as well.Thus, in such a measurement not only a front area but also a rear area of ​​the void 3 can be detected, whereby multiple reflections are generally rather weak, so that the interfaces can be directly detected.

[0046] According to the training of Fig. 2 The antenna array 4 is advantageously not merely linear, but with two-dimensional extent, that is, as a 2D antenna array. According to Fig.2 For this purpose, two linear configurations, i.e., two non-parallel sensor strips 4a, 4b, can be provided, which are preferably aligned at an angle α of 90° to each other and thus span a plane, e.g., with a central THz transceiver 12. If only the central antenna dipole is configured as the active THz transceiver 12, the other THz receivers 14 can detect in two dimensions or two directions, so that a three-dimensional detection of the interface 3a of the defect 3 is already possible. This thus creates a depth image of the defect 3. The antenna array 4 according to Fig. 2 This indicates.

[0047] Even in the embodiment of the Fig. 2 Advantageously, the antenna dipoles of each transmitter strip 4a, 4b can each be active and output a THz transmit beam 15 as a THz transceiver 12, and each passively receive reflected radiation 16 as a pure THz receiver 14. Thus, a single antenna dipole can actively transmit as a THz transceiver 12, while the other antenna dipoles act as passive receivers 14.

[0048] A THz measurement signal S1 obtained in this way can be evaluated by the control unit 5 accordingly to create a three-dimensional image of the object being measured 2 and the position of the defect 3 in the object being measured 2, that is, the relative position of the defect 3, its extent and size.

[0049] Furthermore, according to Fig. 2 Additionally, an acceleration sensor 18 is provided, preferably capable of detecting accelerations in three spatial directions. Thus, when the user handles and moves the THz measuring device 1, the acceleration sensor 18 can measure the acceleration in the three spatial directions, allowing the acceleration signals S3 to be integrated over time in the control unit 5. The acceleration sensor can measure translational or rotational accelerations. Therefore, translational adjustments, as well as rotational or pivoting movements of the THz measuring device 1, can be detected.

[0050] Thus, the user can handle and move the THz measuring device 1 and continuously perform measurements, allowing the control unit 5 to assign the measurement signals S1 to the current positions of the THz measuring device and therefore of the antenna array 4. Assuming a stationary object 2, the accuracy of the measurement can be increased by handling the THz measuring device 1, as continuous measurements are taken from multiple measurement positions and multiple swivel positions.

[0051] This enables precise three-dimensional recording of the object 2 and its defects 3. The entire object 2, including its defects 3, can then be displayed on the output device 7, for example, as a corresponding three-dimensional graphic representation. The output device 7 can also be positioned outside the portable THz measuring device 1. If a potential defect 3 is displayed on the output device 7, the user can adjust the THz measuring device 1 accordingly, further aligning it to this position and increasing the accuracy of the measurement data, for example, by scanning the corresponding area.

[0052] According to the embodiment of the Fig. 3 The THz measuring device 1 can also include an optical camera, e.g., an RGB camera 20, which captures the surrounding area in front of the THz measuring device 1 around the optical axis A and provides image signals S2. Thus, the control unit 5 can receive the THz measurement signals S1 and the image signal S2 and process them together with the acceleration signals S3, and display a representation of the measured object 2 on the output unit 7, including information such as the thickness d, with simulated or displayed position, dimensions, extent, and, if applicable, the volume of the defect 3.

[0053] The user can thus mark the position of the defect 3 on the outer surface 2a of the object being measured 2.

[0054] In particular, a user can scan and measure a stationary measuring object 2 from the outside. This also includes curved outer surfaces of the measuring object 2, for example, irregular outer surfaces, such as those found in... Fig. 4 Defects that are indicated and also present, for example, in rotor blades, can be detected by appropriate handling and scanning with the THz measuring device 1, whereupon defects 3 can be detected, subsequently scanned in more detail, evaluated and displayed.

[0055] The THz measuring device 1 can be positioned on the outer surface 2a using its contour lines 11. Furthermore, the THz measuring device 1 can also be held, moved, and swiveled by the object being measured 2 in order to better detect the defects 3.

[0056] As in Fig. 3 As indicated, voids can be identified as defects 3. Furthermore, porosities and according to Fig. 5 Cracks caused by material fatigue, especially hairline cracks at the interfaces or delaminations, can be identified as defects. Furthermore, for example, captured metal fragments that directly reflect the THz radiation 15 can also be detected. Reference symbol list

[0057] 1 THz measuring device 2 Object being measured 2a Front of the object being measured 2 2b Rear of the object being measured 2 3 Defects, voids 3a Curved surface, boundary of the void 3 4 Antenna array 4a, 4b Sensor strips of the antenna array 4 5 Control unit 6 Internal memory 7 Output unit, for example, display unit 8 Grip area 9 Actuating unit 10 Front end area 11 System contour, or contour lines 12 THz transceiver 14 THz receiver 15 THz transmit beam 15a Radiation cone 16 Reflected THz radiation 18 Accelerometer 20 Optical camera (RGB camera) A Optical axis d Thickness of the object being measured 2 S Amplitude of the THz measurement signal S1 S1 THz measurement signal S2 Image signal of the RGB camera 20 S3 Acceleration measurement signal of the accelerometer 18 t1, t2 t3, t4 Time points P1, P2, P3, P4 Measurement peaks

Claims

1. THz measuring apparatus (1) for determining impurities (3) in a measured object (2), comprising: an antenna array (4) with at least one active THz transmitter (12) emitting a THz transmission beam (15) along an optical axis (A), a plurality of THz receivers (14) arranged under a fixed spatial arrangement in relation to said THz transmitter (12) and synchronised with said THz transmitter, detecting reflected THz radiation (16) and putting out THz measuring signals (S1), and a control device (5), receiving said THz measuring signals (S1) and determining impurities (3) as reflections that have occurred outside proper boundary surfaces (2a, 2b) of the measured object (2), characterised in that it is portable, at least with its antenna array (4), by a handle region (8) for grabbing by the user and for positioning on various positions in front of or on said measured object (2).

2. THz measuring apparatus (1) according to claim 1, characterised in that said THz transmitter is a THz transceiver (12) detecting reflected THz radiation (16) and putting out a THz measuring signal (S1).

3. THz measuring apparatus (1) according to claim 2, characterised in that at least one of said THz receivers (14) temporarily actively sends out a THz transmission beam (15), where always one THz receiver (14) or said THz transceiver (12) transmits and the other THz receivers (14) or said THz transceiver (12) receives.

4. THz measuring apparatus (1) according to claim 3, characterised in that a plurality, preferably all, of said THz receivers (14) temporarily transmit and said THz transceiver (12) temporarily only passively receives reflected THz radiation (16), in particular, with alternating switching of the active transmission function.

5. THz measuring apparatus (1) according to one of the preceding claims, characterised in that said antenna array (4) comprises at least one sensor strip (4a, 4b) as e.g. linear arrangement made of said at least one THz transmitter (12) and said plurality of THz receivers (14), preferably with a middle arrangement of said THz transmitter (12).

6. THz measuring apparatus (1) according to one of the preceding claims, characterised in that it comprises two non-parallel, e.g. linear, arrangements of THz receivers (14), in particular, as two inter-crossed sensor strips (4a, 4b) or two-dimensional matrix arrangement of THz receivers (14).

7. THz measuring apparatus (1) according to one of the preceding claims, characterised in that it further comprises an acceleration sensor means (18) for measuring accelerations of said THz measuring apparatus (1) and putting out an acceleration measuring signal (S3), preferably for measuring acceleration in the three spatial directions and / or in one or more rotational directions, said control device (5) receiving said acceleration measuring signal (S3) and determining the spatial position of said THz measuring apparatus (1), by double temporal integration, upon transmitting and receiving said THz radiation (15, 16).

8. THz measuring apparatus (1) according to claim 7, characterised in that said control device (5) further determining, from said THz measuring signals (S1), boundary surfaces (2a, 2b) of said measured object (2) and a relative position of the impurity (3) in said measured object (2) as well as the three-dimensional arrangement of boundary surfaces (3a) of the impurity (3), preferably including the volume of the impurity (3).

9. THz measuring apparatus (1) according to one of the preceding claims, characterised in that said control device (5) evaluates a height (ΔS) of the amplitude (S) of said THz measuring signal (S1) and determines, from the height (ΔS) of the amplitude (S), in particular in case of measurements in a plurality of pivoting positions and / or positions of said THz measuring apparatus (1), a size or captured surface (A) of the impurity (3).

10. THz measuring apparatus (1) according to claim 10, characterised in that it comprises a contact contour (11) for contacting and defined positioning on said measured object (2).

11. THz measuring apparatus (1) according to one of the preceding claims, characterised in that it further comprises an optical output means (7) for putting out a three-dimensional image of said measured object (2) and the determined impurities (3), said optical output means (7) being provided in a portable or stationary part.

12. THz measuring apparatus (1) according to one of the preceding claims, characterised in that it further comprises an optical camera, preferably RGB camera (20), for capturing the measured object (2) and putting out image signals (S2) to said control device (5), said control device (5) generating, from said image signals (S2) and said THz measuring signals (S1), a three-dimensional representation of said measured object (2) with indicated position, extension and / or shape of the impurity (3) in said measured object (2).

13. THz measuring method for determining an impurity (3) in a measured object (2), where a THz measuring apparatus (1), comprising an antenna array (4) including at least one THz transmitter (12) and a plurality of THz receivers (14), emits a THz transmission beam (15) towards said measured object (2), and said plurality of THz receivers (14) receive THz radiation (16) reflected from said measured object (2), whereby THz measuring signals (S1) are created, a determination is made from said THz measuring signals (S1) as to whether at least part of the received reflected THz radiation (16) was reflected outside ordinary boundary surfaces (2a, 2b) of said measured object (2), where, additionally determined boundary surfaces (3a) in said measured object (2) are associated with an impurity (3), wherein - at least a portable part of said THz measuring apparatus (1) with the antenna array (4) is adjusted by the user in relation to a stationary measured object (2), - wherein the adjustment movements are determined by measuring the acceleration, preferably in three spatial directions, - a relative position of said THz measuring apparatus (1) in relation to said stationary measured object (2) is determined by double temporal integration, and - a position and extension of the detected impurities (3) in said measured object (2) is determined.

14. Method according to claim 13, characterised in that THz radiation (16) is detected which has been reflected in several directions, preferably by means of inter-crossed sensor strips (4a, 4b) of an antenna array (4).

15. Method according to claim 13 or 14, characterised in that said THz-Receivers (14) temporarily actively emit said THz transmission beam (15) and then said THz transmitter (12) as transceiver (12) detects THz radiation merely passively, preferably with alternating switching of transmitting said THz transmission beams (15), wherein the non-active THz receivers (14) or the non-active THz transceiver (12) each detect said THz radiation (15) passively.

16. Method according to one of the claims 13 through 15, characterised in that a height (ΔS) of the signal amplitude (S) of the THz measuring signal (S1) is evaluated and, from the height (ΔS) of the signal amplitude (S), in particular in case of measurement in a plurality of pivoting positions and / or positions of the THz measuring apparatus (1), a size or detected surface (A) of the impurity (3) is determined.

17. Method according to one of the claims 13 through 16, characterised in that further, said THz measuring apparatus (1) captures an optical image of said measured object (2) and generates an image signal (S2), and a three-dimensional association of the THz measuring signals (S1) and the image signals (S2) is carried out by evaluating the image signal (S2), the THz measuring signal (S1) and preferably of the THz acceleration signal (S3), and a three-dimensional representation of the measured object (2) with three-dimensional representation of the positions, size and extensions of the determined impurities (3) is put out.