Abstract:
The invention relates to a method for processing signals which are generated by the reflection of ultrasonic waves by defects in the surface of objects during the non-destructive testing of objects such as pipes, bars, sheet metal, or uniform and complex carbon-fiber components. Said method comprises the following steps: emission of a complete wavefront onto at least one test section of the object, using a plurality of independent emission elements; receiving a wave reflected by the structure of the object by means of a plurality of receiver elements that are independent of one another; digitalization of the signals received by the receiver elements in digitizing steps; continuous modification of delay values and/or the number of receiver elements for each digitalization step (on-the-fly).

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a method for processing signals, which are generated by the reflection of ultrasonic waves by defects in the surface of objects during the non-destructive testing of objects such as pipes, bars, sheet metal, or uniform and complex carbon-fiber components. 
     A method of the type mentioned at the outset is described in DE-A-10 2005 051 781, which relates to a method for the non-destructive inspection of a test piece using ultrasound. In the case of this method, ultrasound waves are coupled with one or a plurality of ultrasound transducers into the test piece and ultrasound waves reflected inside the test piece are received by a plurality of ultrasound transducers and converted into ultrasound signals. An ultrasound transducer is provided and activated on a surface of the test piece, such that the ultrasound waves coupled to the test piece are propagated spatially and distributed largely uniformly within the test piece. Subsequently, the ultrasound waves reflected within the test piece are received by a plurality m of ultrasound transducers provided on the surface and m ultrasound time signals are generated, in which time-resolved amplitude information is contained. 
     The m ultrasound time signals are saved. Subsequently, a 3-dimensional volume-image, a sector image in the form of a 2-dimensional ultrasound image through the test piece or an A-image in the form of a 1 dimensional time and location resolving ultrasound signal along a presettable intromission angle, is reconstructed exclusively using at least one part of the m ultrasound time signals. 
     DE-A-10 2006 003 978 relates to a method for the non-destructive inspection of a test piece having at least one acoustically anisotropic material area using ultrasound. The direction-specific sound propagation properties describing the acoustically anisotropic material area are determined and provided. Also a coupling of ultrasound waves takes place in the acoustically anisotropic material area of the test piece and a reception of ultrasound waves reflected in the interior of the test piece with a plurality of ultrasonic transducers. 
     The ultrasound signals generated by means of the plurality of ultrasonic transducers are evaluated such that the evaluation takes place in a direction-selective manner using the direction-specific sound propagation properties. 
     In the case of the method, a test piece is employed with n ultrasonic transducers, of which a number i ultrasonic transmitters is established, which are activated at the same time. Via the number i of the ultrasonic transmitters and the concrete assembly of the transmitter group, in particular its arrangement on the surface of the test piece, the entire radiation characteristic (aperture) of the transmitter group and in addition the sensitivity and the resolution power of the measurements is determined. Certainly, the number i is smaller than the total number of the ultrasound transmitters of the test piece. The total radiation characteristic is determined exclusively via the number i of the ultrasonic transmitters. 
     U.S. Pat. No. 4,989,143 relates to a coherent energy beam display and in particular to a new method for the improved adaptive formation of a coherent beam using interactive phase conjugating, in order to counteract effects of the inhomogeneous wave deflection. Details for the improvement of the signal energy and readout for phased array-applications for different defect depths cannot be learned from this publication. 
     A further method is described in EP-B-1 649 301. In the case of this method, a complete wavefront is emitted onto at least one test section of the object using a plurality of independent emission elements. 
     Subsequently, a wave reflected by the structure of the object is received by means of a plurality of receiver elements independent of one another. The signals received from the receiver elements are digitalized in digitalizing steps and processed further. A dynamic depth focusing or an aperture adaption is not raised in EP-B-1 649 301. 
     In U.S. Pat. No. 7,263,888 a two dimensional phased array for the volumetric ultrasound testing as well as a method for the use of the phased array is described. The phased array consists of a plurality of ultrasound oscillators, which are arranged in a right-angled design. The two-dimensional array permits the electronic adjustment of combustion point properties and of the dimensions of the aperture/orifice both in lateral as well as in height directions, so that uniform and/or specified sound-field characteristics can be attained at any or all positions in the tested components. 
     A modulation can be applied to each of the ultrasonic elements, in order to form a sample beam and to scan at least one area of the test material with the sample beam. 
     Compared to a 1-dimensional linear array, the 2-dimensional phased array offers the advantage that this is separated and/or divided in a plurality of discrete ultrasound oscillators, which extend both in the X as well as in the Z-direction. As a result, the formation of a sample beam can occur both in the X-Y plane as well as in the Z-Y plane. This permits a 3-dimensional steering/control of the sample beam with regard to the focal distance depth, steering angle and focal distance geometry. The steering of the aperture also contributes to the formation of the sample beam. The aperture of the array can be selected by multiplexing the sample beam by connecting synchronous channels with individual ultrasonic oscillators of the array. Also, the dimensions of the aperture can be controlled and/or adjusted both in the X as well as in the Z direction. 
     A method and a device for the ultrasonic testing of different zones of a workpiece are described in U.S. Pat. No. 5,533,401. A plurality of ultrasound transducers with focus zones with different sized depths is thereby arranged, in order to test a bar-shaped titanium-body with regard to its thickness. The focus zones partially overlap the adjacent focus zones, so that a complete inspection of the thickness of the entire bar section is ensured. The reflected signals of the transducer-receiver are processed in digital form, in order to generate an image of the bar-section. 
     Such a method, however, is expensive, since each probe must be adjusted individually and an adjustment of the surface unevenness is difficult. 
     SUMMARY OF THE INVENTION 
     Consequently, the task of the present invention is to further develop a method and a device of the type mentioned at the outset, to the effect that the signal energy and resolution is improved for phased array-applications for different defect depths. 
     The task, according to the present invention, is solved among other things by the characteristics of claim  1 . Through the invention it is achieved, that already during reception, a continuous modification of delay values and/or the number of receiver elements occurs for each digitalizing step. An improvement of the sound energy and the resolution for phased array-applications is achieved for different defect depths “on-the-fly” with a receiver/transmit clocking with a continuous focal law, i.e., modification of the delay values and number of transmit/receive elements or optionally by combination of different focal laws. 
     The continuous modification of delay values and/or number of transmit/receiver elements for a virtual probe occur during the reception of the HF-signals by a suitable firmware-program “on-the-fly.” 
     Overall, higher performance and improved error detection is achieved with reduced testing costs compared to the prior art. 
     Through the method according to the present invention, a dynamic depth focusing (run-time controlled focusing) and dynamic aperture-adaption (run-time controlled receiving aperture) of the receiving part of a phased-array application are carried out. The focal law or the delay values and the number of transmit/receiver elements of the virtual probe are changed next by a digitalization step. 
     According to a preferred procedural method the delay values of a stored start delay (focal law for the surface position) up to an end delay (focal law for the rear wall position) are calculated by means of a distance function 1/R with R=radius. 
     Optionally, the delay values can be stored in a reference table, particularly in the case of complex coherence. 
     A further procedural method is characterized by the fact that an aperture-adaption occurs through linear modification of the start elements of the virtual probe to the number of the end elements. 
     The start of the aperture-change can be triggered with the “time-of-flight”-position of the surface-interface-echo. 
     A further method step is characterized by the fact that the summation of different focused transmitter-shots at a signal occurs through use of a digital TGC-function. It is thereby provided, that the sensitivity difference occurring in the assembly of transmitter-shots focused in different depths at a signal during the zone transition are balanced out by use of a digital TGC-function. 
     According to an independent inventive concept, the invention additionally relates to a method and a device for the definition of time delays for phased array probes through functional dependencies, such as for example by means of a BEZIER-function, a polynomial or other type of function. The function uses the indices of the ultrasonic transducer element as a criterion and displays the delay as result, while the parameters are set depending on the application. 
     A further property of the invention consists in that all of the above-mentioned methods according to the present invention can be combined in any form with each other or carried out in succession. 
     Moreover, it is the subject matter of the invention, that the digitalized signals received by the ultrasonic transducers are stored in a suitable electronic device. For the expansion of the evaluation, for example in the above-mentioned form, the stored data can then be consulted. 
     In the case of the prior art, the problem is that the number of applicable delay-sets for the arrangements is ultimately limited by the capacity of the hardware and processing times for the data transfer. With a greater number of elements and additional zones, which are to be tested, the demand for storage space increases. 
     In addition, the zone for varying delay laws requires special treatment, so that no discontinuity occurs within the images produced by the ultrasound device. In order to resolve this, modern instruments calculate the delay based on a distance-algorithm for very small zones or for each scanned point. This distance-algorithm is only suited for sufficiently homogeneous media without strong discontinuities, as these are common in the case of non-destructive testing. During the distance calculation, fixed relationships were already utilized, in which, however, a significantly higher number of parameters was required. 
     According to the inventive concepts of one&#39;s own described here, this problem is solved through the use of functional descriptions for the delay-generating switching circuits. The delays, which are generally used for ultrasound problems, can be defined by a static and differential function between the first element of the arrangement and the last element of the arrangement. The functional descriptions permit the generation of a curve for the delays of all elements, in which the delay value is a function of the arrangement number. For a 1-dimensional arrangement, this is a function with one variable, for 2-dimensional arrangements, it is a function of at least two variables, etc. 
     The functional description contains, in addition, a limited number of parameters. These parameters change for each of the selected delay zones and are to be adjusted individually. 
     A 1-dimensional virtual probe with 32 transmitter/receiver elements, for example, requires 64 delay values for a second zone. If a functional description is used in the form of a cubic BEZIER-function, the number of required parameters for a second zone can be reduced to 8 values: 4 values for emission and four values for receiving. 
     In order to even the transition between the delay zones, linear interpolations can be made between the functionally described values of two zones depending on the time difference between the currently viewed scan and two reference-time positions. The same formula can be used for the apodization or the overlap weighting. Here the result of the functional description is the amplitude for the element of the arrangement. The criterion is the element itself and the parameters are transferred within the ultrasound system or calculated in advance for higher-dimensional cases and filed in a table for the transfer. 
     Through the solution according to the present invention, the advantages are achieved compared to the prior art, that considerably fewer parameters are to be transferred, so that less storage space is required. Also the number of cycles can be augmented and an adaption to highly complex geometrical situations is also possible. 
     In summary, the method according to the present invention is characterized in that parameterizable functions for the delay-zones are employed instead of fixed formulas or delay-sets. 
     According to a further inventive concept of one&#39;s own the invention relates to a use of a 2-dimensional phased array probe and a probe mount for the testing of plate-like material such as thin or thick sheet metal. For this a 2-dimensional phased array is employed using dynamic depth focusing and dynamic depth aperture for improvement of the signal quality. 
     In the prior art dual, contact probes are used with water-film coupling and plastic-interface. Each of up to 100 probes must be set down individually, which requires a high expense for control technology. In addition, the probes must be inspected regularly for suitable ultrasonic coupling quality. 
     Since each probe can only be operated, when the latter is completely covered by the plate to be tested, plate edges have a non-inspected maximum zone, which is as wide as the width of the individual probe. This width is at present in the range of 50 mm. 
     The task of the further inventive conceptions is to further develop a device for the testing of two-dimensional material such as thin or thick sheet metal, such that a uniform sensitivity is achieved regarding a wide range of thickness. Also, the device should be improved to the effect that no mobile parts are required and this is applicable, without additional equipment to test the two-dimensional materials close to the edge. A novel and inventive use of a phased array is suggested. 
     To solve the task it is provided, that a 2-dimensional phased array probe is employed using dynamic depth focusing and dynamic aperture adjustment for the improvement of the signal quality and resolution. The mechanical design of the probe and probe mount is simplified by an ultrasound coupling via segment immersion technique. 
     Through replacement of matrix-array scanning units, which are individually programmable to individual thickness zones, the poor resolution of conventional immersion technique scanning units can be overcome. 
     In contrast to the conventional water-gap technique, the immersion technique permits a much simpler mechanical solution and requires no additional scanning units tracking the edges, in order to permit an inspection close to the plate edges. 
     Compared to the prior art, a greater mechanical simplification and higher resolution of defects are achieved. In addition, the on-site immersion technique is less sensitive to unevenness on the surface of the material to be tested. 
     The method and the device are suitable for testing thin or thick sheet metal in the thickness range of 4 to 400 mm. 
     The pixelization over a plate width is conventionally between 12 and 17 mm, whereas 4 to 8 mm can be achieved with the technology according to the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further particulars, advantages and characteristics of the invention arise not only from the claims, the characteristics to be drawn from these—in themselves and/or in combination—, but also from the preferred execution examples to be drawn from the description of the drawings. 
         FIG. 1  shows a block diagram of a control unit for phased array probes, 
         FIG. 2   a )- d ) shows a diagram of a top view of a probe in the transmit/receive state, 
         FIG. 3  shows a diagram of a probe with different test clockings, 
         FIG. 4   a ),  b ) shows a diagram of a probe above a non-ideal switch-on geometry as well as an illustration of a parallel B-scan, 
         FIG. 5  shows a diagram of a first embodiment of a probe arrangement in local immersion for the testing of a two-dimensional material from the bottom 
         FIG. 6  shows a top view of the probe arrangement according to  FIG. 5 , 
         FIG. 7   a )- d ) shows a diagram of a top view of a probe in the transmit and receive state, 
         FIG. 8  shows a diagram of a probe with different test clockings, 
         FIG. 9   a ),  b ) shows a lateral view of a probe bar as well as the top view of a probe bar, 
         FIG. 10  shows a front view of a second embodiment of a probe-arrangement in the form of a probe bar, 
         FIG. 11  shows a lateral view of the probe bar according to  FIG. 7  and 
         FIG. 12  shows a lateral view of a further embodiment of a probe bar. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a block diagram of a control unit comprising preferably N=128 channels. For each of the up to N=128 ultrasonic transducer elements  10 , a pulser  12  is provided, which is controllable via an input  14 . A delay time, for example, of 5 ns can be switched on or off via a further input  16 . The signals received by the ultrasonic transducer elements  10  are collected on two channels, in which each channel includes an operational amplifier  18 ,  20 , a low-pass filter  22 ,  24  as well as an A/D-transducer  26 ,  28 . The operational amplifiers  18 ,  20  of the individual channels have different amplification. The A/D-transducers are connected to their digital outlet, i.e., with a programmable integrated switching circuit  30 . The digital outlet of the A/D-transducer  26 ,  28  is connected to an input of a De-Serial-device  32 ,  34 . An outlet of the De-Serial-device is connected to the input of an offset-correction-device  36 ,  38 , whose outlets are connected to a multiplexer  40 . The multiplexer  40  is connected on the outlet side to an external memory element  42  such as RAM and to a processing unit  44 . 
     In the processing unit  44 , a channel selection and also a depth focusing as well as a dynamic aperture-adjustment occur. By way of example, 5 ns is provided as delay time. An output of the external memory element  42  is connected to the aperture-processing unit  44 . Also, an internal memory element  46  is provided, which is also connected to the aperture-processing unit  44 . 
     An outlet of the unit  44  having a summing member is connected to a processor  48 , in which the amplification, filtering, time-control amplification a real-time HF-amplitude scaling is carried out in a digital manner. 
     A signal is transferred to the outlet of the processor  48 , which is connected to a first input  52 . 1  of a multiplexer  50 . A header, a sequence number or a control word can be connected to a second input  52 . 2  of the multiplexer. The respective input can be selected via a third input  52 . 3 . For example, a 17 bit signal abuts the outlet of the multiplexer  50 , which is made available via a fast serial link  54  for further processing. A further component of the switching mechanism is an input-device  56  for the input of signals to different units of the switching circuit  30 . 
     The method according to the present invention is carried out as follows. First, a complete wavefront is emitted via the pulser  12  through simultaneous (phase-fixed) control of all ultrasonic transducer elements perpendicular to at least one section of the object to be tested. Subsequently, a wave reflected by the structure of the object is received by means of a plurality of ultrasonic transducer elements  10  independent of one another. The signals received by the ultrasonic transducer elements  10  are digitalized in a digital signal processing unit in digitalization steps, processed electronically and stored in the memory element  42  or  46 . 
     At the same time, a continuous change of delay values and/or the number of ultrasonic transducer elements of a virtual probe takes place for each digitalization step on-the-fly, since for each digitalization step on-the-fly the delay values and/or number of ultrasonic transducer elements are adjusted. The delay values are calculated from a stored start delay (focal law for the surface position) up to an end delay (focal law for a real wall position) by means of a distance function such as, by way of example, 1/R with R=radius. The delay values can be stored in a reference table, particularly in the case of complex coherence. In the present case, the delay values are filed in the form of a curve. 
     The aperture-adaption is effected through linear modification of the number of receive elements, preferably in the summing member  44 . 
     Usually a strong change in the delay values and/or aperture-adaption is triggered by the “time-of-flight”-position (run-time position) of the surface-interface-echo. In the summing device  44 , a summation occurs of differently focused transmitter-shots on a signal by using a digital TGC-function. In addition, the delay values can be defined by functional dependencies by means for example of a BEZIER-function, polynomial or other type of function, in which the function indices of the ultrasonic transducer elements are used as criterion and the delay values are displayed as a result, while parameters are set depending on the application. 
     In the  FIGS. 2   a  to  2   d , purely diagrammatic top views of a probe  62  are depicted in the form of a matrix-phased-array probe. The latter consists of a plurality of individual ultrasonic transducer elements  10 , which are individually controllable. 
     As already previously explained, all ultrasonic transducer elements  10  are activated simultaneously for sending, as is depicted in  FIG. 2   a.    
     In  FIGS. 2   b  to  2   d  for focal zones to be interested in, according to the principle of run-time controlled focusing (dynamic depth focusing) as well as run-time receive-aperture (dynamic aperture), one element, as in  FIG. 2   b , five elements, as in  FIG. 2   c , or nine elements as in  FIG. 2   d , are switched to receive, in order to focus on zones of different depths. 
     Each probe  62 , by way of example, can have 128 ultrasonic transducer elements  10 . Preferably, probes are employed with 5×25=125 elements, whereby an active surface, for example, is achieved in the range of 35 mm×175 mm. 
     In order to cover sheet widths in the range of 1000 mm to 5300 mm, approx. 36 probes  62  are required. 
     A system probe  64  with 24 elements is depicted in  FIG. 3 , in which according to the system test clocking T 1  . . . Tn in each case nine ultrasonic transducer elements  10  are gradually switched on and are switched to receive. 
     Through the method according to the present invention compared to the conventional attachment technique a greater coupling reliability is achieved in the case of rough surfaces. Also all probes can be arranged without a gap over the entire sheet metal width, in the case of a width pixelization, for example, of 6 mm. Edge and top/bottom testing are integrated into the concept. Also, more significant reconstruction methods can be incorporated through early digitalization of all test data. Also, the parallel-B-scan principle is permitted, i.e., transmitting and receiving all ultrasonic transducer elements simultaneously. 
     Through the parallel-B-scan-method, robust testing is also permitted in non-ideal switch-on geometries  66 , as depicted in  FIG. 4   a . The non-ideal switch-on geometry  66  can, for example, have a curved front wall and/or curved rear wall, as depicted in  FIG. 4   b.    
     A first embodiment of a test arrangement  68  is depicted in  FIG. 5  in lateral view. An object  70  to be tested in the form of a two-dimensional material such as thin sheet metal or thick sheet metal is stored on rollers  72 ,  74  and is transportable in the direction of the arrow  76 . On a rear side  78  of the material  70  to be tested, a probe arrangement  80  is provided, by means of which the individual probes PK 1 -PKn are coupled via a segment technique to the material  70  to be tested. The probe arrangement  80  is designed as a water chamber opened upwards, which via a constant coolant inlet counterbalances the water loss, which arises in the crack of the object  70  to be tested and thus guarantees a flawless coupling of the ultrasound. The probe arrangement  80  is preferably sealed with a lip-seal on the rear side of the material to be tested, in order to reduce the water loss. Alternatively, start-up and outlet sliding blocks can also be provided in the direction of movement  76  of the device under test  70 , in order to protect the probe arrangement  80  against damage in the case of too great unevenness of the device under test. The probe arrangement  80  can be lowered via an actuator  84  and dynamically readjusted with further actuators  86 ,  88 ,  90  for waviness adjustment. A preliminary purification or preliminary wetting  92  as well as a security sensor  94 , which in the case of failure arranges a cut-off, is upstream of the probe arrangement  80 . 
       FIG. 6  shows a top view of the probe arrangement  80 , in which individual probes PK 1 -PK 6  or PKn are arranged within a water basin  96 . The water basin is covered by means of a preferably circumferential sealing element  98  such as lip seal for the rear side  78  of the material  70  to be tested. Thereby, the probes PK 1 , PK 3 , PK 5  are arranged along a first longitudinal axis  98  at a distance from each other, in which the probes PK 2 , PK 4 , PK 6  are arranged along a second axis  100  running parallel to the first axis such that these run offset to the probes PK 1 , PK 3 , PK 5 . In this manner, an overall width B of the area to be inspected is covered by ultrasonic transducer elements. Each of the ultrasound probes Pk i is connected here to one of the ultrasound control units i (according to  FIG. 1 ). In this manner, the testing can be carried out simultaneously parallel to each individual probe and thus the test performance can be increased. Within a probe depending on the test requirement a group of preferably 5×5 elements of the matrix probe is emitted focused on the rear wall of the device under test. The evaluation of the same receive group then occurs depending on the depth zone via the described dynamic aperture adjustment through the selection of the corresponding receive elements and/or a dynamic depth focusing via the adjustment of the delay times. In order to cover the entire probe area, the described group continues to be clocked in the next ultrasound shot, a matrix element, until the entire probe aperture was scanned. Alternatively, in a further test mode the transmit side aperture (for example, only the center element or a 3×3 element group) can be activated with appropriate focusing and the stored received ultrasonic signal from the different transmit shots assembled according to the depth zone can be reevaluated with aperture and focusing adjustment. A further test mode exists in a transmit shot of the entire aperture of the probe (for example, 5×25 matrix elements) with a linear focusing on the rear wall of the device under test and an evaluation of the stored receive signals corresponding to the method described at the outset of the through-clocking of a 5×5 element group. 
     The probe arrangement  80  is able to carry out a test of 100% of the area of untrimmed rolled plates in the process of manufacture. Thereby, test sheet metal dimensions with lengths up to 30,000 mm, widths of 1000 to 5300 mm and thicknesses in the range of 4 mm to 300 mm can be treated and inspected. 
     The testing can take place in a flow, in particular surface and edge zone testing, in which these can take place longitudinally and transversely. The test speed is approx. 0.5 m/sec at 1000 ultrasound-shots/sec. 
     The coupling occurs—as explained above—via water gaps per cycle of water supply. 
     The method according to the present invention permits a reliable detection depending on the material thickness, in which in the case of a thickness of 8 mm to 240 mm ERG Ø 3  up to a distance of 3 mm to the surfaces and in a thickness range of 240 mm to 400 mm ERG Ø 5  up to a distance of 5 mm to the surfaces are reliably detected. 
     Overall, a modular design is aimed at in order to increase functional reliability, availability and maintainability. 
     The method can be verified for example under the following conditions. 
     Testing method: Pulse echo—method in the case of a water distance of 80 mm 
     Probe  1 : 
     
         
         Material: carbon steel 
         Dimensions: length=200 mm, width=100 mm 
         Thickness: 280 mm 
         Test defects: shallow saddle holes, diameter 3 or 5 mm
 
Probe  2 :
 
         Material: carbon steel 
         Dimensions: length=100 mm, width=100 mm 
         Thickness: 20 mm 
         Test defects: blind hole, diameter 3 or 5 mm
 
Transducer (Probe  1 ):
 
         Type: 2D-Face Array Transducer (18 elements) 
         Frequency: 4 MHz 
         Element dimensions: 7×7 mm 2  
 
Transducer (Probe  2 ):
 
         Type: 2D-Face Array Transducer (24 elements) 
         Frequency: 5 MHz 
         Element dimensions: 6×6 mm 2    
       
    
     The diagram of a matrix-probe is depicted in  FIG. 7 . According to  FIG. 7   a , the probe PK includes 5×5−25 individual transmit/receive elements  10 . The principle of the run-time controlled focusing (dynamic deep focusing) of the run-time controlled receive aperture (dynamic aperture) is to be learned from  FIGS. 7   b ) to  7   d ). According to the evaluation of the number of received ultrasound signals of probe PK, different zones (Zone  1 , Zone  2 , Zone  3 ) of a test object can be inspected, as purely schematically depicted in  FIG. 7   e ). 
       FIG. 8  shows, for example, a gapless sequence of individual probes PK 1  . . . PKn for a system probe APK or a probe bar PKL, which in turn arises through a gapless sequence of system probes APK. 
     After the emission of the wavefront by all probes PK 1  . . . PKn all ultrasound receivers  10  of the probes PK 1 . 
     PKn are switched to receive, so that the incoming ultrasound signals can be digitalized in digitalization steps and can be stored. Based on the temporally incoming digitalization, in which the signals are digitalized at any point in time, the signals receive depth information, which can be evaluated. In a first test clocking T 1 , the 25 individual signals of each probe PK 1  . . . PKn are evaluated “on-the-fly,” i.e., during the reception of the signals. In the further test clockings T 2  . . . T 5  an evaluation takes place of already stored ultrasound signals, as they continue to be clocked in a “virtual probe,” considering a continuous change of the delay values and/or the number of receive elements for each digitalization step. Based on the digitalization, each stored value also receives depth information, which can be evaluated. In the execution example depicted with probes PK with 25 transmit/receive elements, an evaluation can thus be made within 5 test clockings. 
     An individual probe PK 1  . . . PKn thereby consists, for example, of 5×5=25 individual transmit/receive elements  10  with dimensions in each case, for example, of 6×6 mm. Thus, dimensions result for a probe housing PKG depicted in  FIG. 9   a  in the range of approx. 35 mm×34 8 mm with 25 transmit/receive elements. A probe bar PKL is depicted in  FIG. 9   b.    
     In the case of a sheet metal width, for example, of maximally 5350 mm and an assumed probe housing width in the case of 25 transmit/receive elements of 35 mm a required probe number results of 5350/35=153 for covering the sheet metal width. 
     Assuming that for each control unit SE  125  channels are available, a probe number results of 5 per electronic unit. For a required probe number of 153, 31 electronic units are necessary. 
     Using 31 electronic units, which can each process 5 probes, a maximum probe number results of 155, from which it results, that a width coverage of 155×35 mm=5425 mm is possible. This corresponds in the case of a sheet metal width of 5350 mm to an overlap of 75 mm. 
       FIG. 10  shows a front view of a second embodiment of a test arrangement  102  in the form of a probe bar. With this arrangement, the probes PK 1  . . . PKn are placed in a gapless row according to  FIG. 9  as probe bar PK 1 , in order to permit the complete testing of a two-dimensional material such as, for example, a sheet metal  104 . 
     A lateral view of a first embodiment of the probe bar  102  is depicted in  FIG. 11 . The probe bar  102  is arranged on a stationary or mobile support  106 , which is not described in detail. 
     On this support, carriers  108 ,  110  run, which are designed for water intake. On the carriers  108 ,  110  a lifting device  112  is provided, by means of which the probe bar  102  can be moved towards the sheet metal  104  to be tested. The lift device can be designed pneumatically and can have a range of approximately 20 m in the extended state. The lift device  112  includes a height-adjustable platform  114 , under which channels  116 ,  118  are arranged for the air supply. 
     In the preferred embodiment, the probe bar  102  is designed with an angle adjustment device  120 , including a curved tray  122 , which are pivot mounted on rollers  124 ,  126  and is adjustable via an adjustment mechanism  128 . The angle can be adjusted in the range of +/−5°. 
     The tray is provided with carriers  130 ,  132  running longitudinally, by which the probe bar  134  is carried securely. For the arrangement of the probe bar  134 , particularly in the case of the initial assembly, adjustment elements  136 ,  138  are provided, which are supported on an upper surface of the carrier  130 ,  132 , On the side of the probe bar  134 , collecting channels  140 ,  142  are arranged for draining or stripping of coupling water. Above the probe bar a groove  144  is provided for the coupling of the water to the material to be tested, which is limited laterally by rubber diaphragms  146 ,  158 , which abut on a rear side of the material to be tested. 
       FIG. 12  shows a further embodiment of a probe bar  150  in lateral view, which corresponds significantly to the embodiment according to  FIG. 11 , so that the same elements are identified with the same reference numerals. 
     In the case of this embodiment, the probe bar  134  leads to a test tray  152 , which is limited laterally by stripping and sealing lips  154 ,  156 . Parallel to the test tray, a preliminary moistening-channel  158  is provided in the direction contrary to the running direction of the sheet metal, by means of which the material to be tested is moistened. The channel is limited laterally by a stripping and sealing lip  160  as well as by the stripping and sealing lip  154 . 
     In the running direction of the sheet metal, a collecting channel  162  runs parallel to the test tray  152 , in which water emerging from the test tray is received. The collecting channel is limited laterally by a stripping and sealing lip  64  as well as the stripping and sealing lip  156 .