DE102014106892B3 - Inverse Synthetic Aperture Radar (ISAR) and Method for Detecting Impurities in a Material - Google Patents

Abstract

The invention relates to an inverse synthetic aperture radar (ISAR) and a method for detecting impurities (101) in a material (102), in particular in bulk, in particular in sugar, which moves through a measuring volume of interest (VOI). The Synthetic Aperture Radar (ISAR) comprises: a radar transmitter (103) for transmitting radar signals to the measurement volume (VOI), a first radar receiver (104) and a second radar receiver (105) for receiving the radar signals scattered in the measurement volume (VOI), wherein the radar transmitter (103), the first (104) and the second (105) Radarempfänger are arranged around the volume of interest (VOI) such that the first Radarempfänger (104) a scattered portion of the radar signals from the measuring volume (VOI) with a Scattering angle in a range of 0 ° ± 30 ° or 0 ° ± 20 ° or 0 ° ± 10 ° and the second radar receiver (105) a scattered proportion of the radar signals with a scattering angle in a range of 90 ° ± 30 ° or 90 ° ± 20 ° or 90 ° ± 10 ° from the measurement volume (VOI), a control unit (106) for controlling the radar transmitter (103), the first (104) and the second (105) radar receiver, and an evaluation unit (107) for detection one There is one contaminant in the material (102) based on an evaluation of the scattered radar signals received by the radar receivers (104, 105).

Description

The invention relates to an inverse synthetic aperture radar (ISAR) and a method for detecting impurities in a material, in particular in bulk, in particular in bulk food such as sugar, corn, rice, flour, cereals, potatoes, etc., which is characterized by measuring volume of interest (VOI) moves. The ISAR is used today, for example, in the observation of near-earth space objects in order to obtain there two-dimensional radar images of satellites or other objects with such a quality that a target identification is made possible.

The invention is based on the following problem. In the case of bulk solids, in particular food bulk solids (sugar, corn, rice, flour, cereals, potatoes, etc.), high purity, i. Minimal contamination by foreign particles, required at the end of the production chain. Depending on the materials and nature of the bulk material, detection of such foreign particles is difficult. Optical and infrared-based processes tend to be ruled out, since they make a certain transparency of the bulk material necessary during the measuring process for these wavelengths, which is usually not the case. Ultrasonic and acoustic measurement methods are experiencing difficulties in achieving the necessary spatial resolution, and they can easily be rendered unusable by noise in the current production or transport process of the bulk material. Furthermore, their range is limited depending on the acoustic wavelength and bulk material. X-ray techniques involve high safety measures during operation (safety distance, shielding) and long measurement times, making them less easy to use in an industrial production environment. Magnetic screening methods only work for ferromagnetic foreign particles. Mass-selective sieving methods (e.g., settling by shaking, centrifuging) require a high overhead and are ineffective when foreign particles and bulk particles have a similar mass. Furthermore, it is usually desirable to use a detection method in existing production facilities without immense additional effort by conversion measures.

From the DE 10 2009 047 300 A1 For example, there is known a non-contact food analysis apparatus comprising: means for generating high frequency electromagnetic radiation for irradiating the food, means for receiving electromagnetic high frequency radiation reflected from the food, and means for analyzing the food based on the food reflected electromagnetic radio frequency radiation.

From the DE 10 2010 051 207 A1 a sensor arrangement and a method for three-dimensional imaging of a relative to the sensor arrangement moving object by means of a combination of radar technology and optical imaging is known. In the method, a three-dimensional radar image of the object is detected and fused with a 3D surface model of the object generated with optical 3D sensors in such a way that the radar image is focused on the surface or the immediate vicinity of the surface of the 3D surface model. The 3D surface model is also used for accurate projection of radar data and optical texture data.

The invention has for its object to provide an apparatus and a method which are able to reliably and as far as possible, without having the disadvantages mentioned above, to allow impurities in a material, especially in bulk, especially in sugar.

The invention results from the features of the independent claims. Advantageous developments and refinements are the subject of the dependent claims. Other features, applications and advantages of the invention will become apparent from the following description, as well as the explanation of embodiments of the invention, which are illustrated in the figures.

The inventors have first recognized that microwave measurement methods offer themselves to solve this problem. Microwaves can very well penetrate many dielectric materials depending on the frequency range, as well as a variety of common bulk materials (e.g., rocks, plastics, food products, etc.). Also, depending on the measurement method and frequency range, a very high spatial resolution can be achieved and the measurement times are kept sufficiently short by modern electronics. Microwaves are not ionizing, so they can be used anywhere in a production process without any health risks, as they can also work with the lowest possible output. Microwaves can detect very well dielectric differences with appropriate measuring methods, so that a foreign body is detectable as soon as it is dielectrically separated from the bulk material sufficiently, which is in most cases correct. Microwave measuring methods are particularly sensitive to metallic foreign bodies of any material type.

To achieve the object, therefore, an inverse synthetic aperture radar (ISAR) is proposed for detecting impurities in a material, in particular in bulk material, in particular in sugar, which moves through a measuring volume of interest VOI. The proposed ISAR comprises a radar transmitter for transmitting radar signals to the measurement volume VOI, a first radar receiver and a second radar receiver for receiving the radar signals scattered in the measurement volume VOI, the radar transmitter, the first and the second radar receiver being arranged around the measurement volume VOI of interest in that the first radar receiver has a portion of the radar signals scattered (substantially backwards parallel to the transmission direction) from the measurement volume VOI with a scattering angle in a range of 0 ° ± 30 ° or 0 ° ± 20 ° or 0 ° ± 10 ° and the second radar receiver receives a (substantially perpendicular) scattered portion of the radar signals having a scattering angle in a range of 90 ° ± 30 ° or 90 ° ± 20 ° or 90 ° ± 10 ° from the measurement volume (VOI). Due to the two scattering angles around 0 ° and around 90 °, different types of scattering processes are detected, resulting in a decisive increase in detection and information. Furthermore, the ISAR comprises a control unit for controlling the radar transmitter, the first and the second radar receiver, and an evaluation unit for detecting a presence of an impurity in the material on the basis of an evaluation of the scattered radar signals received by the radar receivers. The impurities are assumed to be detectable objects (eg particles, etc.).

The moving or moving material through the measuring volume is thus exposed to detect the impurities in the material with radar radiation. The scattered radiation resulting from the interaction of the radar radiation with the material or with the impurities contained therein is detected and evaluated under the described scattering angles. The coherent evaluation of the transmission signal received by the radar receivers scattered radiation signals (principle of the synthetic aperture) allows the determination of individual impurities, which will be explained in more detail below.

A development of the proposed inverse synthetic aperture radar ISAR is characterized in that a third radar receiver for receiving a (substantially forward) scattered portion of the radar signals with a scattering angle in a range of 180 ° ± 30 ° or 180 ° ± 20 ° or 180 ° ± 10 ° from the measuring volume VOI is arranged. As a result, the recorded data volume is increased by different types of scattering processes, which allows a more accurate and reliable statement about impurities contained in the material.

The information on the scattering angles relate in each case to the main radiation direction of the radar signals emitted by the radar transmitter.

An advantageous development of the inverse synthetic aperture radar ISAR comprises a conveyor belt which moves the material with the contamination through the measurement volume VOI of interest or a tube through which the material moves with the contamination by the measurement volume VOI of interest. Both variants make it possible to construct the ISAR as a module, which can be easily integrated into existing installations which, for example, move the material on a conveyor belt or in which the material falls through a downpipe, for example. Of course, for this purpose, the ISAR for the conveyor belt or the pipe must have on both sides a corresponding interface for integration into an existing system. This makes it possible to integrate the proposed ISAR into existing production systems simply and without great additional effort and with identical quality for multiple use. The preferably large spatial proximity of the sensor (radar transmitter / radar receiver) to the bulk material allows a compact design of such a module, which is provided with, for example, to a conveyor system matching interfaces.

Advantageously, in the proposed Inverse Synthetic Aperture Radar ISAR, the material is moved in one direction through the measurement volume of interest VOI having an angle in the range of 90 ° ± 30 ° or 90 ° ± 20 ° or 90 ° ± 10 ° or preferably 90 ° a central direction of radar signals radiated from the radar transmitter.

A development of the proposed inverse synthetic aperture radar ISAR has a plurality of first radar receivers for receiving in each case one (back) scattered portion of the radar signals with a scattering angle in the range of 0 ° ± 30 ° or 0 ° ± 20 ° or 0 ° ± 10 ° from the measurement volume VOI on. Alternatively or additionally, the ISAR has a plurality of second radar receivers for receiving one (vertically) scattered portion of the radar signals with a scattering angle in the range of 90 ° ± 30 ° or 90 ° ± 20 ° or 90 ° ± 10 ° or 90 ° from the measurement volume ( VOI). The other receivers enable the acquisition of 3D radar data, which in turn allows a more accurate detection of the geometry as well as the position of a pollution imaged in the 3D radar data.

A further development of the proposed inverse synthetic aperture radar ISAR comprises a plurality of radar transmitters (i.e., at least two or more radar transmitters) each arranged to transmit radar signals to the measurement volume VOI. Advantageously, these radar transmitters radiate orthogonal radar signals, so that a clear assignment of stray signals to each radar transmitter is possible. This is particularly helpful if you want to work simultaneously with all radar transmitters in the same frequency band and all should be evaluated completely independently.

Alternatively, multiple or all of the radars may emit non-orthogonal but coherent radar signals. In the case of coherent radar signals, for example, a sharper, pivotable antenna pattern can be generated together via the individual transmit antennas (eg, phased array). It would also be conceivable to use a combination of orthogonal and non-orthogonal radar signals, for example in the time multiplex for a measurement, in order to temporarily supplement the signal-to-smoke ratio by sharpening the antenna pattern (increase of the antenna gain).

The evaluation unit is advantageously designed on the basis of the scattered radar signals received by the radar receivers in addition to the detection for determining the position of an impurity in the material.

Furthermore, the evaluation unit is advantageously designed and set up such that a 2D or 3D data record is generated on the basis of the radar signals received by the radar receivers, in which each pixel / voxel indicates at least one scattering amplitude in the 2D or 3D data set cluster C are determined whose pixels / voxels have scatter amplitudes which are within predetermined range limits, those clusters C _{G1 are} determined whose pixels / voxels have scatter amplitudes which are greater than a predetermined limit G1, and individual impurities based on the shape and / or the size the cluster C _{G1 are} determined. In the present case, a cluster is a contiguous region of the 2D or 3D data set whose scatter amplitudes are all within a range defined by a lower and an upper range limit.

The frequency range of the radar signals emitted by the radar transmitter (s) is preferably one or more of the frequency ranges: L-band, S-band, C-band, X-band, Ku-band, K-band, Ka-band, V Band, W band or G band, adjustable, the radar signals having a relative bandwidth: Δf / f ₀ of 1-50% or 10% -50% or 20% -50% or 30% -50% or 20% -40%, where f _{0 is} the average frequency of the radar signals. The band designations follow the IEEE standard (where G band corresponds to the range 110-300 GHz).

A technically and application specific preferred and also adapted to the radar bands graduation of the relative bandwidth is the following, in which the distance resolution of the radar (d _r = c ₀ / (2B) is never worse than 15 cm, and in the best case up to 5 mm can: L-band: 67%, S-band: 33-67%, C-band: 17-67%, X-band: 10-40%, Ku-band: 7-40%, K-band: 4 -40%, Ka-band: 3-40%, V-band 2-50%, and W-band: 1-40% Of course, you can also work across bands, so that the minimum and maximum bandwidth may change significantly (For example, a combination of L and S band: 40-120% or a combination of L, S, and C band: 22-155%.) In the G band, even with usually reduced penetration depth, a range resolution is up to reachable to 1 mm (eg Δf / f ₀ = 67%).

In a further development of the proposed inverse synthetic aperture radar ISAR, the control unit is embodied and configured in such a way that, based on the evaluation of the radar signals received by the radar receivers, a purely signal processing-based adaptation of a directional characteristic of the radar receivers to focus on an area in which an impurity has been determined , This is done in particular in the context of digital beamforming.

The frequency range advantageously used by the radar transmitter depends in particular on the bulk material damping. A rough classification for a maximum usable radar frequency is for the case that conventional dielectrics are assumed with a real part of the permittivity <10 and a maximum purely material-related two-way attenuation of 20 dB, refer to the following table. Imaginärteil permittivity 1.0 0.1 0.01 0.001 Penetration depth [m] 0.1 <15 GHz <150 GHz 1 <1.5 GHz <15 GHz <150 GHz 10 <0.15 GHz <1.5 GHz <15 GHz <150 GHz

The imaginary part of the permittivity is a measure of the damping of a dielectric (the larger the value, the greater the damping). As an example, water can have values up to 20, depending on the frequency considered here. Plastics usually have frequency-independent values in the range 0.01 ... 0.0001. Other values are easily accessible to the person skilled in the art (only for information: unfortunately this is not the case).

For a signal path of radar transmitter volume radar receiver of <2 m, it is possible to work with a CW (continuous wave) radar (for example with a frequency-modulated CW radar transmitter), while with signal paths> 2 m, preferably with a pulse radar is worked, the pulse amplitude can also be modulated in addition.

If the presence of an impurity has been detected by the evaluation unit, at least one control signal is generated by the evaluation unit in a development that activates a controllable mechanism for sorting out or removing the identified contamination.

The invention furthermore relates to a method for detecting impurities in a material, in particular in bulk material, in particular in sugar, which moves through a measuring volume of interest (VOI) by means of an inverse synthetic aperture radar (ISAR), in which radar signals are radiated onto the sensor by a radar transmitter A first radar receiver and a second radar receiver in the measurement volume VOI receive scattered radar signals, wherein the radar transmitter, the first and the second radar receiver are arranged around the volume of interest VOI such that the first radar receiver a (back) scattered proportion of Radar signals from the measurement volume VOI with a scattering angle in a range of 0 ° ± 30 ° or 0 ° ± 20 ° or 0 ° ± 10 ° and the second radar receiver a vertically scattered proportion of the radar signals with a scattering angle in a range of 90 ° ± 30 ° or 90 ° ± 20 ° or 90 ° ± 10 ° from the Messvo A control unit controls the radar transmitter, the first and the second radar receiver, and an evaluation unit determines the presence of an impurity in the material on the basis of an evaluation of the scattered radar signals received by the radar receivers.

The method thus makes it possible to detect foreign bodies (contaminants), in particular in bulk solids, by means of an ISAR which generates two-dimensional or three-dimensional radar images in a mono-, bi- or multistatic measurement configuration and carries out their automatic evaluation. Preferably, in the proposed method a radar transmitter and three radar receivers are used in a bistatic arrangement with the bistatic angles Ψ around 0 °, Ψ around 90 ° and Ψ around 180 °. Also several radar transmitters and a different number of receivers are possible.

Preferably, a sufficiently large signal bandwidth of the radar signals and a sufficiently large footprint of the radar antennas in the azimuth direction is used, so that even small objects with respect to the mean wavelength of the radar radiation can still sufficiently be distinguished from background signals by a sufficiently large spatial resolution.

Preferably, the frequency band of the radar transmitter to be used is adapted to the respective application and the bulk material to be penetrated. For high resolutions of a few millimeters and below as well as for low damping properties of the bulk material, radar signals in the millimeter and submillimeter range are preferably used. With lower requirements for the resolution and higher damping of the bulk material, it is preferable to use microwaves in the GHz range.

When using a plurality of radar receivers (each with receiving antenna), these are preferably arranged in the z-direction at appropriate different distances, so that a three-dimensional radar image is made possible, which allows improved detection and a more accurate localization of a foreign body, especially in the z-direction.

Preferably, multiple radar transmitters are used in the method. Preferably, these generate orthogonal radar signals during simultaneous operation in order to be able to make a clear separation of the signals in each reception branch. Provide the additional images of each transmitter-receiver combination independent information, which improves the detectability of soiling and ambiguity suppression.

With simultaneous and coherent scanning of the individual reception branches in the time domain, digital beamforming is possible on the reception side. For this purpose, the antennas of the radar receiver are preferably arranged in the azimuth direction at suitable intervals, which alone by signal processing allows a subsequent change in the reception-side illumination characteristics and thus an improvement of the signal-to-noise ratio and the ambiguity suppression.

Preferably, in the method as a waveform of the radar signals at short distances of the radar transmitter / receiver to the bulk material or to the measurement volume with modulated CW signals (CW = Continuous Wave) and worked at longer distances with additionally modulated pulse signals. As modulation forms preferably linear frequency modulation, noise or phase shift keyed signals are used.

For evaluating the scattered radar signals detected by the radar receivers or for radar image generation of each transmitter-receiver combination or of several combinations, preferably high-quality radar images are generated with a backprojection method and established methods of image processing, which are used for object detection and thus for detection are suitable for pollution.

The 2D or 3D radar image data sets generated in the evaluation of the scattered radar signals detected by the radar receivers are preferably evaluated by established methods of object detection in order to enable the presence of contamination (foreign bodies) in a bulk material with a high probability of detection with a low false alarm probability. In this case, the use of temporal image sequences, which arise during the passage of a foreign body through the synthetic aperture during the bulk material movement, is also advantageous.

In a development of the method, after detection of one or more contaminants (foreign bodies) in the bulk material, they are advantageously removed by means of a preferably mechanical access according to a time determined from the known system parameters (for example the speed of the conveyor belt, etc.). This removal of the foreign body / s is preferably carried out in the smallest possible distance after the measurement volume.

Preferably, the method and the ISAR can also be used to assess the manufacturing quality of components in mass production, if this production process has a similar transport structure as the bulk goods industry.

Further advantages, features and details will become apparent from the following description in which - where appropriate, with reference to the drawings - at least one embodiment is described in detail. The same, similar and / or functionally identical parts are provided with the same reference numerals. It shows:

1 a schematic structure of the proposed ISAR in a variant embodiment for detecting impurities in the sugar.

In the production of high-quality crystal sugar, as it is provided for consumption, it happens that, despite complex control measures remaining impurities are added in the form of very small particles. These particles have a size of typically a few millimeters to less than 1 mm and usually consist of metal (iron) or iron oxide particles (rust) as well as glass, plastic or sealing particles, which can detach from the production lines during sugar production. Even small animals such as wasps or bumblebees can be found, which inevitably have access to the manufacturing processes over the smallest cracks in the buildings or doors or locks. By mechanical Aussiebverfahren and the use of permanent magnets can be indeed remove magnetic, but by far not all contaminants of this kind. There is therefore interest in significantly increasing the purity of the sugar and thus further increasing the quality of the sugar product. It should be necessary, if possible, no complex intervention in the existing manufacturing process in order not to increase the cost of production unacceptable.

With the help of the proposed ISAR, many of these objects can be detected in sugar. Microwaves are also able to penetrate many dielectric (non-metallic) materials, so that the Detection of optically hidden objects is possible. In addition to a very high spatial resolution, in particular excellent sensitivity can be achieved by means of special imaging or radar measurement methods, so that even the smallest objects can be detected at the appropriate wavelength or frequency of the radiation used. In the present case, millimeter waves appear to be most expedient, since their small wavelength (a few millimeters to 1 mm) is of the order of magnitude of the particles to be detected, and accordingly correspondingly observable radar echoes are to be expected.

An important factor in microwave measurements is the complex permittivity or dielectric constant of the materials used in the measurement of a scene. Permittivity values can either be taken from the literature or determined by measurements. From measurements made by the inventors, it is clear that potential "soil materials" differ significantly in the permittivity of granulated sugar, which supports successful detection.

Based on this, model calculations show that the radiant power transmitted through a 30 cm thick layer of sugar is approximately 80% of the original power incident on the layer. Therefore, the detection of a dirt particle is still sufficiently possible through a layer of sugar.

The proposed ISAR uses the possibility of matter bodies to reflect the microwave radiation impinging on them at least in part back to the radar. In addition to the reflection or scattering properties of an object, the success of a useful radar measurement depends on many other factors such as the nature of the scene, the observation geometry, the exact measurement method and the sensor itself.

1 shows a schematic structure of the proposed ISAR in a variant embodiment for detecting impurities 101 in sugar 102 , The illustrated angles are adjusted for clarity and clarity and are not true. The illustration shows a side view, in which the bulk material (sugar) on a conveyor belt 109 is transported through the measuring volume VOI. The conveyor belt 109 extends perpendicular to the image plane.

The ISAR includes a radar transmitter 103 for transmitting radar signals to the measurement volume VOI, a first radar receiver 104 , a second radar receiver 105 and a third radar receiver 108 for receiving the radar signals scattered in the measurement volume VOI. The radar transmitter 103 , the first 104 , the second 105 And the third 108 Radar receiver are arranged in such a way around the measurement volume of interest VOI that the first radar receiver 104 a backscattered portion of the radar signals from the measurement volume VOI with a scattering angle in a range of 0 ° ± 10 °, the second radar receiver 105 a vertically scattered portion of the radar signals with a spread angle in a range of 90 ° ± 10 °, and the third radar receiver 108 receives a forward scattered portion of the radar signals having a scattering angle in a range of 180 ° ± 10 ° from the measurement volume VOI. To control the radar transmitter 103 and the radar receiver 104 . 105 . 108 is a control unit 106 available. This control unit 106 is still with an evaluation unit 107 for detecting an existence of an impurity in the sugar 102 based on an evaluation of the radar receivers 104 . 105 . 108 received scattered radar signals connected. If a contamination or a foreign body is detected in the measurement volume VOI, a control signal is generated by the evaluation unit and sent to a mechanism 110 sent, which ensures that the part of the sugar that contains the pollution is eliminated. This mechanism 110 may be a flap, a mechanical slide or a blower or a suction device, etc.

The ISAR is not on a conveyor belt 109 set, but the sugar 102 can also be at the sensor 103 . 104 . 105 . 108 To be drilled or pumped eg in a pipe. Only the relative movement between sensors and bulk material is necessary. Furthermore, there must be no metallic shield between sensor and bulk material. However, these circumstances are usually met in the industrial production of bulk products.

The ISAR is an extension of a coherent radar with multiple radar transmitters 103 and several radar receivers 104 . 105 . 108 etc., so that each transmitter-receiver combination allows a sufficiently accurate amplitude and phase measurement with respect to a reference signal.

Radarsender and radar receiver of the ISAR can be operated in one embodiment via a common antenna, which corresponds to the exact monostatic operating case. Preferably, however, they are operated via separate antennas, which brings the technical advantage of a better decoupling or minimal crosstalk, but in particular also allows the bistatic operating case. Of the bistatic angles Ψ can now be set or used in a variety of ways and in a variety of sizes. On the one hand, it can be realized in the horizontal direction as a difference of the viewing angles Φ, on the other hand and also simultaneously on the difference of the viewing angles Θ in the vertical direction. Preferably, a quasi-monostatic case with eg Ψ = 0 °, a bistatic case with Ψ = 180 ° and a bistatic case with Ψ be used by 90 °. The first case involves backscattering of the transmitted signals, which is the classic situation of most radar applications and leads to high signal strengths of the radar returns for many types of objects (eg objects with corners or dipole-shaped objects). The second case is so-called forward scattering, which often causes significant radar signals on smooth and bulky objects. The third case is a bistatic angular range, where strong resonance effects in a frequency band as a function of the frequency are observed, which could also be confirmed experimentally. Of course, in all other bistatic angle settings, signals are also measurable, but in many cases, on average, they cause a less strong radar signal. In the case of two-dimensional ISAR, the direction transverse to the relative movement between the radar and the scene is referred to as the distance direction (for example, the y direction in FIG 1 ). The direction of the relative movement is usually called azimuth direction (eg x-direction in 1 ). The mapping takes place in that a so-called distance profile for the transverse direction y is recorded for each increment of the relative movement δx. Due to the known geometric relationships of the relative movement, each point in the scene to be imaged can be predicted to have an amplitude and phase course. If this is correlated with the coherently measured signal curve of all N sample points i × δx, i = 0 ... N - 1, a focused image of the intensity of the scattering behavior of the scene results, which is also generally used as a spatial distribution of the radar scattering cross section (RCS radar Cross Section). The mathematical signal processing for this is also called SAR processing and executed in a SAR processor (usually by software in a digital computer, but also analog via eg optical methods possible).

The spatial resolution in the direction of removal is achieved via the signal bandwidth B and is approximately Δr ≈ c / 2B, where c is the speed of light in the respective medium (in the case of air c = c ₀ ≈ 3 × 10 ⁸ m / s). The final resolution Δy in the y direction is finally given by the projection of the oblique view onto the xy plane. The scene size in the y-direction is determined by the width of the antenna lobes ΔΘ and the uniqueness range of the image determined by the sampling interval δf of the frequency spectrum used (within B). In the azimuth direction, the spatial resolution Δx is determined by the azimuth angle range of the observation ΔΦ with Δx ≈ λ ₀ / 2sin (ΔΦ), within which each scene location is seen during the relative movement. λ ₀ is the mean wavelength at the center frequency f _{0 of} the observation. The scene size in the azimuth direction is also determined by the width of the antenna lobe ΔΦ and the uniqueness range given by the sampling interval δx.

Preferably, a detection process with the in 1 presented a radar transmitter 103 and the three reception branches of the radar transmitter 104 . 105 . 108 completed. This has the advantage that more or less each object provides a detectable scatter signal in at least one of the transmitter-receiver combinations, provided that it differs sufficiently in terms of dielectric from the actual bulk material (in the present case sugar). Of course, further transmitters or receive branches can also be implemented, which further increases the detection probability. The use of multiple transceiver combinations also allows for improved ambiguity suppression since such ghost targets appear in a different location in each frame of each transceiver combination, while real targets are at the same location of a common coordinate system.

The orientations of the transmitter and receiver antennas are preferably designed such that their directional diagrams projected onto the measurement volume VOI form, if possible, a largest common intersection, which thus also defines the common imaging area (i.e., the image size). In this case, the main lobe widths of the directional diagrams in the azimuth direction Δδ should preferably be selected to be approximately the same for the preferred bistatic angles Ψ. In the elevation direction, the club widths .DELTA.Θ depending on the position and viewing direction of the antenna with respect to the conveyor belt are to be selected so that they illuminate only the region of interest, so as to ensure maximum suppression of ambiguity and a maximum signal-to-noise ratio (optimum antenna gain for a given scene size).

The distances or positions of the transmitter and receiver antennas are to be selected so that preferably the entire width of the conveyor belt 109 can be detected with the respective transmitter-receiver combination. Furthermore, such a distance to the conveyor belt is preferably 109 It should also be ensured that the near range of the measuring range VOI is sufficiently in the far field of the transmitter and receiver antennas.

Become several radar transmitters 103 are used, they are preferably to operate with orthogonal signals, so that a simultaneous operation, a separation of the scattered radar signals of all transmitter branches in each receiver branch is possible. This operation then provides N transmitters and M receivers with the number of N × M independent radar images (transceiver combinations) which are preferably for suppression of ghost echoes (ambiguities) and homogenization of locally variable background echoes of the scene. This allows an improved target-to-background separation.

If all the receiver channels are individually sampled in their full bandwidth B in the time domain with at least the Nyquist frequency (f _Nyq ≥ 2B) and the values stored, a digital beamforming of the overall _{timing diagram of} all individual diagrams or even only parts thereof can be variably provided on the receiving side by suitable signal processing be synthesized (DBF - "Digital Beam Forming").

If one works with mutually coherent transmission signals for all transmitter branches, it is also possible to carry out beamforming on the transmitter side. The preferably to be used receiving side DBF has the great benefit that the maximum possible information that can be recorded by a particular antenna group, is present and thus simultaneously in a digital computer different overall timing diagrams can be generated. Thus, in addition to the wide illumination of the entire scene, e.g. at the same time the adaptive illumination of subregions with a higher signal-to-noise ratio possible. Furthermore, a suppression of unwanted false echoes is also possible thereby.

The use of several spatially suitably separated transmitter-receiver combinations also allows the creation of three-dimensional (3D) distributions of the scattering cross-section of an entire volume. The spatially correct assignment of a scattering cell (spatial area of the resolution cell) into a three-dimensional coordinate system is advantageous in order, for example, to be able to precisely locate the foreign body and then be able to remove it in a targeted manner. Preferably, this is in 1 to arrange a suitable number of receiver antennas along the z- and also partially the y-direction in order to achieve a sufficiently large unambiguity range in the z-direction.

For structurally related short distances of transmitter and receiver antennas to be examined measuring range VOI preferably with the bandwidth B modulated continuous wave signals (CW - Continuous Wave) to choose the center frequency f ₀ . The modulation may be, for example, a linear frequency ramp (FMCW - Frequency-Modulated CW) over time or else noise or coding (eg Phasenumtastung), if, for example, several orthogonal signals are needed. With permissible larger distances, pulsed operation in, for example, combination with a frequency modulation (chirp signal) or noise or coding can preferably also be used in order to be able to better hide additionally disturbing echoes from the scene environment.

Two or three-dimensional radar images of the scatter intensity distribution are preferably generated from the radar measured values of a synthetic aperture length using a SAR processor. The SAR processor is a mathematical image reconstruction algorithm derived from those of the radar receivers 104 . 105 . 108 received radar raw data (sequence of distance profiles) generates a radar image.

Preferably, a backprojection method is to be used for the desired observation geometry, although other known methods also exist. The individual radar images of each transmitter-receiver combination are processed using suitable known image processing methods (noise reduction, side lobe suppression, smoothing filter, contrast enhancement) either already in the SAR processor or in subsequent steps after the basic radar image generation. In the case of DBF application, the signals of the involved transmitter-receiver combinations are coherently and processed together to form an image product.

From the image product or the image products, foreign object detection is preferably carried out using segmentation and threshold methods. This can be done with frame-by-frame evaluation as well as by evaluation of fused concurrent images, the latter methodology providing greater robustness with respect to false targets, i. Misdetections, offers. Also, the evaluation of whole temporal image sequences is advantageous because dynamic and geometric changes in the image sequence support object detection.

If a detection has been carried out with an embodiment of the previously described radar methods or combinations thereof and by a corresponding image evaluation, then it is possible to proceed as follows in order to remove the foreign body.

During detection, the location x ₀ , y ₀ and possibly also z ₀ (in the case of 3D images) of the foreign body in the radar image or the radar images is known with sufficient accuracy at time t ₀ . Since the transport speed v of the bulk material is assumed to be constant and known, there results a new location x ₁ ≈ x ₀ + vΔt, y ₁ ≈ y ₀ and z ₁ ≈ z _{0 of} the foreign body after the time Δt = t ₁ -t ₀ . At this point x ₁ can thus be attached a device which removes the foreign body away from the transport medium. The removal is possible, for example, by a sufficiently fast mechanical separation transversely to the direction of movement (eg mechanical slide or plunger, compressed air nozzle, suction device, etc.), which also small amounts of the bulk material around the foreign body are removed with. In more difficult cases of mechanical sorting (eg because of bulk material size or weight) can then be done automatically at the location x _1, for example, a color coding, with the help of which later suitable manual or mechanical removal of the foreign body is possible.

The proposed ISAR has the advantage that it can preferably be integrated into an existing manufacturing process without any special and expensive conversion measures. Only a sufficiently accessible point in the transport system of the bulk material, which has no metallic shield, is required. Since the sensors can be arranged relatively close to the measuring volume, overall a compact design is possible, which is the smaller, the higher the operating frequency range of the radar can be selected. In many production facilities with quite similar transport structures for bulk materials and large numbers of required test centers of the type of detection method presented is also preferable to design an adapter platform with defined input and output interface of the conveyor mechanism, in which then exactly defined and optimized the sensor system are installed can. Thus, in every production process with transported bulk materials, the identical interface can only be created at suitable locations, and absolutely identical and qualitatively equivalent test standards of bulk material quality can be created everywhere.

The presented ISAR is also suitable for the detection of flaws in the mass production of components in an assembly line structure. It should preferably be ensured that each component is always in almost exactly the same pose with respect to the sensor when it passes through the synthetic aperture.

Although the invention has been further illustrated and explained in detail by way of preferred embodiments, the invention is not limited by the disclosed examples, and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention. It is therefore clear that a multitude of possible variations exists. It is also to be understood that exemplified embodiments are really only examples that are not to be construed in any way as limiting the scope, applicability, or configuration of the invention. Rather, the foregoing description and description of the figures enable one skilled in the art to practice the exemplary embodiments, and those skilled in the art, having the benefit of the disclosed inventive concept, can make various changes, for example, to the function or arrangement of individual elements recited in an exemplary embodiment, without Protected area, which is defined by the claims and their legal equivalents, such as further explanation in the description.

LIST OF REFERENCE NUMBERS

101

Contamination / s

102

Material / bulk material

103

Radar transmitter / transmitter

104

Radar receiver / receiver

105

Radar receiver / receiver

106

control unit

107

evaluation

108

Radar receiver / receiver

109

conveyor belt

110

Mechanism for discarding

Claims (11)

Inverse Synthetic Aperture Radar (ISAR) to detect impurities ( 101 ) in a material ( 102 ), in particular in bulk material, in particular in sugar, which moves through a measuring volume of interest (VOI), comprising: a radar transmitter ( 103 ) for transmitting radar signals to the measurement volume (VOI), - a first radar receiver ( 104 ) and a second radar receiver ( 105 ) for receiving the radar signals scattered in the measurement volume (VOI), the radar transmitter ( 103 ), the first ( 104 ) and the second ( 105 ) Radar receivers are arranged around the measurement volume of interest (VOI) such that the first radar receiver ( 104 ) a scattered proportion of the radar signals from the measurement volume (VOI) with a scattering angle in a range of 0 ° ± 30 ° or 0 ° ± 20 ° or 0 ° ± 10 ° and the second radar receiver ( 105 ) receives a scattered portion of the radar signals having a scattering angle in the range of 90 ° ± 30 ° or 90 ° ± 20 ° or 90 ° ± 10 ° from the measurement volume (VOI), - a control unit ( 106 ) for controlling the radar transmitter ( 103 ), of the first ( 104 ) and the second ( 105 ) Radar receiver, and - an evaluation unit ( 107 ) for detecting an existence of an impurity in the material ( 102 ) based on an evaluation of the radar receivers ( 104 . 105 ) received scattered radar signals. Inverse Synthetic Aperture Radar (ISAR) according to claim 1, wherein a third radar receiver (ISAR) 108 ) is arranged to receive a scattered portion of the radar signals having a scattering angle in a range of 180 ° ± 30 ° or 180 ° ± 20 ° or 180 ° ± 10 ° from the measurement volume (VOI). Inverse Synthetic Aperture Radar (ISAR) according to claim 1 or 2, comprising a conveyor belt ( 109 ) that the material ( 102 ) with the impurity ( 101 ) is moved through the measurement volume of interest (VOI) or with a tube ( 110 ) by itself the material ( 102 ) with the impurity ( 101 ) is moved through the measurement volume of interest (VOI). Inverse Synthetic Aperture Radar (ISAR) according to any of claims 1 to 3, wherein the material ( 109 ) is moved in one direction through the measurement volume of interest (VOI) which makes an angle in the range of 90 ° ± 30 ° or 90 ° ± 20 ° or 90 ° ± 10 ° with a central direction of the radar transmitter ( 103 ) radiated radar signals. Inverse Synthetic Aperture Radar (ISAR) according to one of Claims 1 to 4, in which a plurality of first radar receivers (ISAR) 104 ) are arranged to receive in each case a scattered portion of the radar signals with a scattering angle in the range of 0 ° ± 30 ° or 0 ° ± 20 ° or 0 ° ± 10 ° from the measuring volume (VOI), and / or in which a plurality of second radar receivers ( 105 ) are arranged to receive in each case a scattered portion of the radar signals with a scattering angle in the range of 90 ° ± 30 ° or 90 ° ± 20 ° or 90 ° ± 10 ° from the measuring volume (VOI). Inverse Synthetic Aperture Radar (ISAR) according to one of Claims 1 to 5, in which a plurality of radar transmitters (ISAR) 103 ) are each arranged to emit radar signals to the measurement volume (VOI). Inverse Synthetic Aperture Radar (ISAR) according to one of Claims 1 to 6, in which the evaluation unit ( 107 ) based on radar receivers ( 104 . 105 . 108 ) received scattered radar signals for determining a 3D position of the contamination in the material ( 102 ) is executed. Inverse Synthetic Aperture Radar (ISAR) according to one of Claims 1 to 7, in which the evaluation unit ( 107 ) is designed and arranged such that, on the basis of the radar receivers ( 104 . 105 . 108 radar signals), a 2D or 3D data set is generated in which each pixel / voxel indicates at least one scattering amplitude, - clusters C are determined whose pixels / voxels have scatter amplitudes which are within predetermined range limits, - those clusters CG1 are determined, their pixels / voxels have scattering amplitudes which are greater than a predefined limit value G1, - an individual shape and / or size of the impurity can be determined on the basis of the shape and / or the size of the clusters CG1. Inverse Synthetic Aperture Radar (ISAR) according to any one of claims 1 to 8, wherein the frequency range of the radar signals is from one or more of the frequency ranges: L-band, S-band, C-band, X-band, Ku-band, K-band. Band, Ka band, V band, W band, G band is adjustable, the radar signals being a relative Bandwidth: Δf / f0 of 1% -50% or 10% -50% or 20% -50% or 30% -50% or 20% -40%, where f0 is the average frequency of the radar signals. Inverse Synthetic Aperture Radar (ISAR) according to one of Claims 1 to 9, in which the control unit ( 106 ) is designed and set up so that on the basis of the evaluation of the radar receivers ( 104 . 105 . 108 ) received scattered radar signals a purely signal-based adaptation of a directional characteristic of the radar receiver ( 104 . 105 . 108 ) for focusing on an area where contamination has been detected.  Method for detecting impurities in a material, in particular in bulk material, in particular in sugar, which moves through a measuring volume of interest (VOI) by means of an inverse synthetic aperture radar (ISAR), in which radar signals are emitted by the radar transmitter to the measuring volume VOI, a first radar receiver and a second radar receiver in the measurement volume VOI receive scattered radar signals, wherein the radar transmitter, the first and the second radar receiver are arranged around the volume of interest VOI such that the first radar receiver a (back) scattered proportion of the radar signals from the measurement volume VOI with a scattering angle in a range of 0 ° ± 30 ° or 0 ° ± 20 ° or 0 ° ± 10 ° and the second radar receiver a perpendicularly scattered portion of the radar signals with a spread angle in a range of 90 ° ± 30 ° or 90 ° ± 20 ° or 90 ° ± 10 ° from the measuring volume VOI receives, a Steuereinhe it controls the radar transmitter, the first and the second radar receiver, and an evaluation unit determines the presence of an impurity in the material on the basis of an evaluation of the scattered radar signals received by the radar receivers.

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