WO2008128851A1

WO2008128851A1 - Method for the nondestructive determination of the size of an ultrasound-reflecting structure in the volume of a test sample by means of ultrasound, and device therefor

Info

Publication number: WO2008128851A1
Application number: PCT/EP2008/053702
Authority: WO
Inventors: Wolf-Dietrich Kleinert
Original assignee: Ge Inspection Technologies Gmbh
Priority date: 2007-04-18
Filing date: 2008-03-28
Publication date: 2008-10-30
Also published as: EP2140258A1; DE102007018576A1

Abstract

The invention relates to a device (10) for the nondestructive determination of the size of an ultrasound-reflecting structure (90) in the volume of a test sample (100) by means of ultrasound. The device (10) is based on the use of a first and a second ultrasound transmitter (15, 15') which are spaced apart in the X direction and which are oriented to beam a directed first ultrasound pulse P1 and a directed second ultrasound pulse P2 into the test sample. The first and the second ultrasound pulses P1, P2 are propagated in the test sample along substantially parallel paths S1 and S2 and have different polarities P+, P-. Furthermore, means are provided for summing the reflected first and second ultrasound pulses P1, P2, as are means for detecting the amplitude maximums Amax of the summed reflected first and second ultrasound pulses P1, P2. Finally, the device has means for detecting a displacement (50), of a defined amount ?X, of the first and the second ultrasound transmitters (15, 15') along the X-axis.

Description

Description: Method for the non-destructive determination of the size of an ultrasound-reflecting structure in the volume of a test specimen by means of ultrasound, and device therefor

The present invention is a method for non-destructive determination of the size of an ultrasound-reflecting structure in the volume of a test specimen by means of ultrasound. Furthermore, the present invention relates to a device which is set up using a suitably selected ultrasonic probe to determine the size of an ultrasound-reflecting structure in the volume of a test specimen by means of ultrasound. Finally, the present invention relates to an arrangement which is individualized for the same purpose and which comprises a device according to the invention and a test head.

The invention is advantageously applicable to both biological and non-biological samples, wherein both types of samples are hereinafter referred to as "DUT".

Various methods for determining the size of an ultrasound-reflecting structure in the volume of a test specimen by means of ultrasound are known from the prior art. These methods, based on comparing the error to be measured with a model reflector, provide an estimate of the error magnitude. In practice, it has become common practice to determine from the amplitude level of the ultrasonic signal reflected at the error a so-called equivalent reflector size which is given by the size of an ideal circular disk reflector which would produce an equivalent error signal. In an alternative approach, the error signal is compared to an ultrasonic signal obtained experimentally on test bores, the test bores having different known diameters. Since the sound components reflected from a natural error are influenced not only by the magnitude of the error, but also by the shape, orientation and surface condition of the error, the actual size of the error to be measured is usually inconsistent with the experimentally determined spare reflector size , Because manual testing of ultrasound is difficult and impractical, most ultrasound testing specifications and guidelines place the criteria for finding and registering defects at a given substitute reflector size. The examiner thus determines whether a detected error reaches or exceeds the specified maximum spare reflector size. In addition, he must carry out further investigations, for. As to registration length, echo dynamics, etc., but not discussed further at this point. For further details on the size determination of errors in the volume of a test specimen by means of ultrasound, reference is made to the book Material Testing with Ultrasound, Josef Krautkrämer and Herbert Krautkrämer, Springer, 5th edition (February 1998).

The object of the present invention is therefore to specify a method for determining the size of an ultrasound-reflecting structure in the volume of a test specimen by means of ultrasound, which has an improved accuracy in comparison to the methods known from the prior art. A further object of the present invention is to provide a device which is suitable for carrying out a method for the nondestructive determination of the size of an ultrasound-reflecting structure in the volume of a test object by means of ultrasound, which has an improved accuracy compared with the prior art, and to specify an arrangement. which is set up for the same purpose and which represents a complete testing system.

This object is achieved by a method having the features of claim 1, by an apparatus having the features of claim 11 and by an arrangement having the features of claim 18.

The inventive method is based on the finding that ultrasonic pulses can be generated whose time-resolved sound pressure profile is opposite to each other. So, if one pulse starts with an increase in the sound pressure, so the complementary pulse begins with a decrease in the sound pressure. In the context of the present invention, such complementary pulses are referred to as "pulses of different polarity." Reflecting two ultrasound pulses of different polarity P +, P- on a reflecting structure causes the reflected pulses to overlap as they are detected, the sound pressure amplitudes of the reflected pulses are canceled out Essentially, they are mutually exclusive in their detection, ie one receives a zero signal from the regular structure.

The method according to the invention is now based on the use of a first and a second ultrasonic sound transmitter, which are arranged spaced apart in one spatial direction (in the following: X direction).

In a first method step, a directed first ultrasonic pulse P 1 and a second directed ultrasonic pulse P 2 are sounded into the test object, such that the first and second ultrasonic pulses P 1, P 2 propagate substantially along parallel paths S 1 and S 2 in the test object. It is now of central importance for the present invention that the pulses P1 and P2 have a different polarity P +, P-.

If the first and second ultrasonic pulses P1 and P2 in the test object meet an ultrasound-reflecting structure such as a discontinuity or a crack, they are at least partially reflected back and returned to the surface of the test object via which ultrasonic pulses P1 and P2 have been coupled into the test object were referred to below as the test area. Preferably, but not necessarily, vertical scanning is used so that the pulses P1 and P2, after being reflected by the ultrasound-reflecting structure, return along the same paths S1 and S2 as reflected pulses P1, P2 to the first and second ultrasonic transmitters. Therefore, in this configuration, the first and second ultrasonic transmitters can be advantageously used as ultrasonic receivers.

In an alternative configuration, we worked in oblique sound, possibly using separately trained ultrasonic transmitter and receiver are used. In the subsequent method step, the reflected first and second ultrasound pulses Pi, P2 are summed, which can be done acoustically by means of an ultrasound receiver, which collects both reflected pulses collectively, or electronically, eg by connecting two separately formed ultrasound receivers electrically to a receiver or by electrical signals of the receiver are summed up electronically (analog or digital).

In the resulting sum signal of the reflected pulses, the value of the amplitude maximum Amax is determined in the subsequent method step, e.g. by a suitable digital signal processing of the sum signal. It should be noted that each "echo pulse" has a positive and a negative maximum value AmX +, Amax-, so that the sum echo signal also has both a positive and a negative "maximum value", as illustrated by FIG. Figure 1 shows a first echo pulse £ 1 with positive polarity P +, a second echo pulse P2 with negative polarity P- and the result of a superposition of both pulses. The maximum values "Amax-t" and "Amax" are also drawn in. Both maximum values are basically equivalent for the present invention, but for reasons of signal quality it is preferred to use the larger maximum value for the processing in the context of the inventive method The maximum value Amax + is therefore shown in the example according to Figure 1. Both maximum values are interchangeable within the scope of the invention, also a (possibly separate) evaluation of both maximum values Amax +, Amax- may be advantageous under certain circumstances.

Depending on the configuration of the receiver, the signal detected by the ultrasound receiver can be both the sound pressure and the sound intensity. For the present invention, both sizes are basically equivalent. If reference is made in the context of this application to the determination of an echo signal amplitude, then it can be both the sound pressure amplitude and the amplitude of the sound intensity.

Subsequently, the first and second ultrasonic transmitters are displaced along the X-axis defined above by a defined amount ΔX. These process steps are repeated, whereby an experimental curve can be obtained which maps the course of the reflected amplitude maximum Amax +/- typical for the special test configuration as a function of the displacement ΔX.

According to the invention, in a subsequent method step, the points of maximum curvature X1, X2 are determined in the experimentally obtained profile of the maximum amplitude over the displacement ΔX. If an ultrasound-reflecting structure was recorded and scanned along the crossed-out interval on the X-axis, it is possible to convert its size from the position of the points of maximum curvature X1, X2 determined in the last method step in the course of the amplitude maximum Amax to estimate the shift ΔX.

It has proven to be particularly advantageous if, for the determination of the points of maximum curvature X1, X2 in the obtained curve of the amplitude maximum Amax, the discontinuities with change of sign in the third derivative of the detected amplitude maximum Amax are determined after the displacement ΔX. On the basis of theoretical investigations, it has been found that in the points of maximum curvature X1, X2 to be determined according to the invention a "kink" actually occurs in the curvature of the course of the amplitude maximum, ie the second derivative of the course of the amplitude maximum after the shift ΔX is at this point The result of this is that the third derivative of the curve of the maximum amplitude Amax after the shift ΔX at this point has a discontinuity, ie a discontinuity at which a sign change in the third derivative occurs at the same time Jumping points occurring jump can be used as a measure of the reflectivity r of the ultrasound-reflecting structure.

Due to the fact that the measured amplitude characteristic is generally not present as a continuous curve, but rather is represented by a plurality of discrete measured values, the problem may arise here that the third derivative of the experimentally determined amplitude characteristic after the displacement has a very high noise , In such cases, it has proved to be advantageous if, to determine the points of maximum curvature in the amplitude curve, the maxima and minima of the second derivative of the detected reflected amplitude after the shift .DELTA.X be determined. Even if a "kink" in the second derivative actually occurs at the desired points, these kinks nevertheless appear as (possibly local) maxima and minima in the second derivative (compare in particular FIG. 5b of the following exemplary embodiments).

A value for the geometric size d of the measured ultrasound-reflecting structure can now be determined from the information obtained above by determining the distance between adjacent points of maximum curvature X1, X2 in the experimentally determined profile of the maximum amplitude Amax.

To identify a pair of adjacent points of maximum curvature X1, X2 as belonging to a single ultrasound-reflecting structure, one or more of the following criteria may be used:

1. Between the first and second maximum curvature points X1, X2, the curvature changes sign (i.e., from "right-curved" to "left-curved" or vice versa),

2. The amount of curvature is in the immediate vicinity of both points Xl, X2 on the flanks of the measured curve of the maximum amplitude, each of which is oriented maximally towards the supposedly complementary point (ie, for example, Xl-δX and X2 + 5X or Xl + δX and X2 + 5X, see Fig. 5b), substantially the same, and

3. the second derivative of the course of the amplitude maximum Amax after the shift ΔX is continuous in both points X1, X2, but not differentiable.

While the first criterion essentially serves to ensure that the selected points are actually adjacent points, the second criterion is based on the assumption that the reflectivity r of the detected ultrasound-reflecting structure along its entire extent along the X -Axis substantially has a constant reflectivity. It has been proven in practice that this assumption is met with good accuracy for many measured errors, so that the second criterion is well suited to finding the right and left bounds of the measured error. The two However, the criterion is not fulfilled if the reflectivity of the ultrasound-reflecting structure varies along its extent. The third criterion is intended to ensure that the maxima or minima found are actually correlated with the boundary of an ultrasound-reflecting structure.

The aforementioned procedure can also be combined well with a conventional pulse-echo method, as known from the prior art. By means of the conventional pulse-echo method, the position of the error is determined in the test object, with the subsequent inventive method, the error can thus be measured with increased accuracy.

The implementation of the method according to the invention is particularly simple if the first and second ultrasonic pulses P1 and P2 have substantially the same pulse height and the same pulse duration. However, this is not absolutely necessary for the process according to the invention. It is also advantageous, but not mandatory, for the first and second ultrasonic pulses P1 and P2 to be generated substantially simultaneously. In certain circumstances, a time-delayed generation of the first and second ultrasonic pulses P1 and P2 can also be advantageous. In order to realize the summation / superimposition of the reflected first and second ultrasound pulses Pi and P2 required in the context of the method according to the invention, this superimposition can take place, for example, electronically by processing the first and second ultrasound pulses separately detected by means of the ultrasound receiver.

In turn, the method according to the invention is particularly simple if the first and second ultrasound transmitters have substantially the same beam characteristic. However, this is likewise not absolutely necessary for the method according to the invention.

The method according to the invention is therefore a specially designed pulse-echo method which is based on the use of pulses of different polarity propagating in parallel. As mentioned above, the term "different polarity" of the ultrasonic pulses P1 and P2 in the context of the present invention is to be understood to mean that the chronological course of the sound pressure amplitude of the second pulse is just opposite the first pulse. is over. This means that when the first pulse begins, for example, with a pressure increase, the second pulse begins with a magnitude equal pressure drop. If you bring such pulses in phase to the superposition, they cancel each other out completely.

The method according to the invention can be further developed such that it is suitable for determining the reflectivity r of an ultrasound-reflecting structure in the volume of a test specimen by means of ultrasound. For this purpose, in a first step, the position of the ultrasound-reflecting structure in the volume of the test object is determined by means of a suitable ultrasound algorithm, which in turn can be based, for example, on a pulse-echo method and in particular as a method according to claim 1.

Subsequently, the first four method steps (steps a to d) of the method according to the invention according to claim 1 are repeated, in order to determine the course of the amplitude maximum Amax of the echo pulse as a function of the displacement .DELTA.X. From the experimentally determined course of the amplitude maximum Amax, the third derivative of the detected curve of the amplitude maximum can then be determined after the shift ΔX.

Finally, in the last step of the process, the magnitude of the jump in the third derivative, which occurs when the first and second ultrasonic pulses injected into the device under test detect the edge of the structure, i. when the test beam collimated by the test head is symmetrically over the edge of the structure.

A quantification of the reflectivity r of the measured ultrasound-reflecting structure is possible, for example, by comparing the size of the above-determined jump in the third derivative with that jump occurring in the third derivative of a reference structure which has been measured by means of the method according to the invention.

An apparatus according to the invention for non-destructive determination of the size of an ultrasound-reflecting structure in the volume of a test specimen by means of ultrasound is based on the use of a first and a second ultrasound transmitter operating in one spatial direction (hereinafter again referred to as X direction). draws) are arranged spaced from each other. These first and second ultrasonic transmitters should be set up to resonate a directed first ultrasonic pulse P 1 and a directed ultrasonic pulse P 2 into the test object, the first and second ultrasonic pulses P 1 and P 2 being propagated in the test object along substantially parallel paths S 1 and S 2. Furthermore, the first and second ultrasonic pulses P1 and P2 generated by the first and second ultrasonic transmitters should have a different polarity P +, P-.

Furthermore, the device according to the invention is intended to be used in conjunction with a means for summing the reflected first and second ultrasonic pulses £ 1, P2 and a means for detecting the amplitude maximum Amax of the summed reflected first and second ultrasonic pulses Pi, P2. The first means can be realized, for example, by the first and second ultrasound transmitters, which are combined electronically into a common ultrasound receiver.

Furthermore, the device according to the invention is intended, in conjunction with a means for detecting the common displacement .DELTA.X of the first and the second ultrasonic transmitter in the direction of the X-axis on the test surface of the test object. Such means may be configured, for example, as a path detection unit which is mechanically connected to the first and the second ultrasound transmitters and which may be designed, for example, in the form of a follower wheel. The means for detecting the shift can also be embodied in a purely electronic form. An example of this is the use of an array probe, which has a multiplicity of ultrasound transmitters arranged side by side in a spatial direction, wherein a displacement of the first and second ultrasound transmitters can be realized by the i-th and (i + 1) in a first step ) -th ultrasonic transmitter of the array probe are controlled. In the following step, the i + lth as well as the (i + 2) th ultrasonic transmitter are then activated, etc. Practically, this means that the sound beam emitted by the array is at each cycle by a "pitch" of the arrays, ie Thus, the displacement .DELTA.X from one cycle to the next is exactly the same as the pitch of the array probe, ie the distance between two ultrasound-active elements. However, a particular advantage of the method according to the invention and also of the device consists in the fact that based on a measured progression of the amplitude maximum Amax with relatively few or far apart measuring points on the X-axis, a size determination of the measured error with an accuracy is possible is significantly better than the distance of the measuring points on the X-axis. This is a significant advantage, especially when using array probes.

The device according to the invention now has a drive unit for controlling the first and second ultrasonic transmitters, so that they emit sequences of ultrasonic pulses P1 and P2 of different polarity P +, P-, respectively.

Furthermore, the device according to the invention comprises an evaluation unit which is set up to detect the detected amplitude maximum Amax of the summed reflected first and second pulses Pi and P2 as a function of the displacement ΔX of the first and second ultrasound transmitters on the X-axis. Furthermore, the evaluation unit is set up to determine the points of maximum curvature in the course of the detected amplitude maximum Amax plotted over the displacement ΔX.

In advantageous embodiments, the evaluation unit of the device according to the invention is adapted to implement one or more of the advantageous embodiments of the method according to the invention with respect to the determination of the points of maximum curvature in the experimentally detected amplitude curve.

In a further advantageous embodiment of the device according to the invention, the drive unit included is set up to control the first and second ultrasonic transmitters in such a way that the first and second ultrasonic pulses P1 and P2 have substantially the same pulse shape, pulse height and / or pulse duration. Furthermore, advantages can result if the drive unit is set up to generate the first and second ultrasonic pulses P1 and P2 at substantially the same time. It is particularly advantageous if the drive unit is set up to set the relative timing of the first and second ultrasonic pulses P1 and P2 in a targeted manner. The inventive arrangement for non-destructive determination of the size of an ultrasound-reflecting structure in the volume of a test specimen by means of ultrasound comprises a first and a second ultrasound transmitter, which are arranged spaced apart in a spatial direction, which is referred to below as the X direction. As a rule, the first ultrasound transmitter will be arranged directly adjacent to the second ultrasound transmitter. In this case, the first and second ultrasound transmitters are set up to surround a directed first ultrasound pulse P 1 and a directed second ultrasound pulse P 2 into the test object. In particular, the first and second ultrasonic transmitters are arranged and set up in such a way that the first and second ultrasonic pulses P1 and P2 propagate in the test object along substantially parallel paths S1 and S2. Furthermore, the first and second ultrasonic transmitters are configured to generate first and second ultrasonic pulses P1 and P2 of different polarity. In the context of the present invention, this "being set up" of the first and second ultrasound transmitters means, in particular, that they are capable of producing ultrasound pulses of different polarity Realized ultrasonic transmitter by means of the further included drive unit.

Furthermore, the arrangement according to the invention comprises a means for summing the superimposed reflected first and second ultrasonic pulses Pi, P2, wherein it has already been explained above that such a means can be realized for example in the form of a common ultrasonic receiver. The ultrasonic receiver is then followed by means for detecting the amplitude maximum Amax of the summed reflected first and second ultrasonic pulses Pi, P2.

In a test configuration suitable in particular for perpendicular sounding, the first and second ultrasound transmitters can be combined to form a common reception unit, on which the first and second reflected ultrasound pulses are superimposed. In this case, this superimposition can be a spatial superimposition on the large-sized detector surface of the ultrasound receiver. But it can also be an electronic overlay, in which the with separate ultrasonic receivers detected reflected first and second ultrasonic pulses £ i and P2 are superimposed on each other electrically (analog (raw) signal) or electronically (digitized signal).

Furthermore, the device according to the invention comprises a means for detecting a (collective) displacement ΔX of the first and second ultrasonic transmitters along the X-axis on the surface of the test object. Possible embodiments of the means for detecting the shift have already been discussed above.

Finally, the arrangement according to the invention comprises a device according to claim 11.

Particular advantages arise when the first and second ultrasonic transmitters encompassed by the arrangement have substantially the same beam characteristic. In this case, the first and the second ultrasonic transmitter can advantageously be arranged in a common test head housing.

Particular advantages arise when the first and second ultrasound transmitters are each formed by an individually controllable element of an array probe. If an array probe with a plurality of individually controllable ultrasonic transmitters is used, then the first and the second ultrasonic transmitters can advantageously also be formed from a group of individually controllable ultrasonic transmitters of the array probe that are combined electronically into a common ultrasonic transmitter. This can be done for example by a phase and possibly also the same amplitude control of these individual controllable elements.

Further advantages and features of the method according to the invention, the device according to the invention and the arrangement according to the invention will become apparent from the subclaims and the exemplary embodiments, which are explained in more detail below with reference to the drawing: In this show:

1 shows a schematic representation of a first reflected test pulse

Pi with a first polarity P +, a second reflected test pulse this P2 with an opposite polarity P and the superimposition of these two pulses,

2 shows a schematic representation of a first exemplary embodiment of an arrangement according to the invention for nondestructive determination of the size of an ultrasound-reflecting structure in the volume of a test specimen by means of ultrasound,

3 shows an enlarged view of the test head of the arrangement used in the first exemplary embodiment,

4 is an enlarged view of a test head of the assembly used in a second embodiment;

5 a shows a schematic representation of the profile of the maximum amplitude Amax, which was obtained with the arrangement according to the invention according to FIG. 2 during the scanning of an ultrasound-reflecting structure, and FIG

5b shows a schematic representation of the second and third derivative of the curve of the maximum amplitude Amax from FIG. 5a.

FIG. 2 shows a schematic representation of an arrangement 1 according to the invention which comprises a device 10 according to the invention for nondestructive determination of the size of an ultrasound-reflecting structure 90 in the volume of a test object 100 and an array ultrasound test head 20. In the exemplary embodiment shown, the array test head 20 comprises a plurality N = 12 of individually controllable ultrasound transmitters 15, which are arranged in a common housing. The ultrasonic probe 20 is connected to the test apparatus 10 via a control line.

The ultrasound test head 20 is used for testing a test object 100, which in the exemplary embodiment shown is designed as a plane-parallel metal plate, on its upper side surface, referred to below as the test surface 110. The individually controllable ultrasound transmitters 15 contained in the array test head 20 are acoustically connected to the previously known from the prior art Test surface 110 of the device under test 100 coupled, for example by using water, a hydrous gel or oil as a coupling agent.

The test apparatus 10 comprises an integrated drive unit 30 and an integrated evaluation unit 35, wherein the drive unit 30 is adapted to control the individually controllable ultrasound transmitters 15 contained in the test head 20 at the same time or using a controlled phase shift, the transmit amplitude and the polarity of the ultrasound pulses generated Each individually controlled ultrasonic transmitter 15 can be individually controlled by the drive unit 30.

The evaluation unit 35 is provided for subjecting and evaluating reflected ultrasonic pulses recorded by one or more ultrasonic receivers to digital signal processing. In particular, the evaluation unit 35 is provided to process the reflected ultrasound signals received from one or more ultrasound transmitters.

Furthermore, the test apparatus 10 includes a plurality of operating elements 45, which are formed in the embodiment shown as a keypad and as knobs. Finally, the test apparatus 10 includes a display device 40, which is configured in the embodiment shown as a high-resolution LCD display.

The embodiment of the method according to the invention by means of the first exemplary embodiment of an arrangement according to the invention will now be explained with reference to FIG. 3, this arrangement comprising an array test head 20, which comprises N = twelve individually controllable ultrasonic transmitters 15. These individually controllable ultrasonic transmitters 15 are made of the same piezoelectric material and have substantially identical transmission and reception properties. The drive unit 30, not shown in FIG. 3, of the test apparatus 10 is now set up to drive two of the twelve individually controllable ultrasonic transmitters 15 of the test head 20 according to the method according to the invention. In this case, the drive unit 30 always selects two ultrasound transmitters 15 which are arranged directly adjacent to one another and are referred to below as first ultrasound transmitters 15 'and second ultrasound transmitters 15 "All ultrasound transmitters 15, including the first and second ultrasound transmitters 15' and 15 "are configured to generate high pulse repetition rate ultrasonic pulses, which may be in the range of a few megahertz, and to wave them perpendicular to the test area 110 into the test piece 100. Each ultrasonic transmitter 15 produces a focused sound beam, the depth of focus being the same for all ultrasonic transmitters 15 The control unit 30 is now set up to control the selected first ultrasonic transmitter 15 in such a way that it samples a sequence of first ultrasonic pulses P1 into the test object 100, the ultrasonic pulses P1 having a first polarity P + The polarity P + of the ultrasonic pulse P1 is selected such that the wave train of the ultrasonic pulse P1 begins with increasing sound pressure. The first ultrasonic pulses P1 generated by the first ultrasonic transmitter 15 'propagate along the first S in the test object 100 Challweg Sl.

The second ultrasonic transmitter 15 "is controlled by the drive unit 30 in such a way that it generates a sequence of ultrasonic pulses P2 which has the same pulse repetition rate as the sequence of the first ultrasonic pulses P1 On the other hand, the polarity P of the second ultrasonic pulses P2 is opposite to the polarity P + of the first ultrasonic pulses P1, ie the second pulses P2 begin with a falling sound pressure arranged that between the first ultrasonic pulses Pl and the second ultrasonic pulses P2 substantially no phase shift occurs.

After being coupled into the test 100, the first and second ultrasonic pulses P1 and P2 propagate along substantially parallel paths S1 and S2, which are oriented substantially perpendicular to the test surface 110 of the test object. If there is now an ultrasound-reflecting structure 90 in the sound path S1 and / or S2 of the first and second ultrasound pulses P1, P2, these are (partially) reflected back (as reflected pulses Pi, P2) and travel along the paths S1 and S2, respectively reverse direction back to the first and second ultrasonic transmitters 15 'and 15 ". The evaluation unit 35 is now set up to interconnect the first and second ultrasound transmitters 15 'and 15 "selected by the drive unit 30 to a common ultrasound receiver, for this purpose the first and second ultrasound transmitters 15' and 15" reflected by the first and second ultrasound pulses reflected back Pi and P2 generated electrical signals superimposed on each other and only subsequently subjected to the aforementioned digital signal processing. In the case of oblique sounding, instead of the first and second ultrasonic transmitters 15 'and 15 ", a separately formed ultrasonic receiver could be used whose ultrasound-sensitive element could consist of a single large-area piezoelectric element, from which both reflected pulses £ 1 and P2 are recorded.

In order to realize the displacement of the first and second ultrasonic transmitters 15 'and 15 "in the direction of the X-axis marked in FIG. 3, which coincides with the longitudinal axis of the array probe 20, the actuation unit 30 is to be realized designed to select a new pair of ultrasound transmitters 15 in successive process steps and to make the first and second ultrasound transmitters 15 'and 15 ", respectively. If the drive unit 30 in the illustration according to FIG. 2 has selected the eighth and ninth ultrasound transmitters 15 of the test head 20 as the first and second ultrasound transmitters 15 ', 15 ", then it is set up for the ninth and the tenth ultrasound transmitters 15 in the following cycle and as the second ultrasonic transmitter 15 'and 15 ", respectively. The displacement of the first and second ultrasound transmitters 15 'and 15 "to be realized according to the invention is therefore implemented electronically by selecting ever new pairs of ultrasound transmitters 15, whereby the area of the test object 100 detected by the test head 20 is electronically in the X direction is scanned.

FIG. 5a now shows the resulting amplitude profile of the signal present at the ultrasound receiver during scanning of the ultrasound-reflecting structure 90, which lies below the test surface 110 in the volume of the test object 100. If the ultrasound-reflecting structure 90 has substantially constant reflection properties for the ultrasound pulses P 1 and P 2 which have been injected in, a characteristic mountain-valley profile results, as can be seen from FIG. 5 a. The central zero crossing, which is marked X ₀ in FIG. 5a, is In this case, it is precisely correlated with the test situation in which the first and second ultrasound pulses P1 and P2 detect the ultrasound-reflecting structure 90 equally, ie centrally. This situation exists when the first and second ultrasonic transmitters 15 'and 15 "are arranged symmetrically with respect to the axis of symmetry of the structure 90, which is denoted by S _{0 in} Figure 3. Right and left of the central zero crossing X ₀ results in the amplitude maximum Amax Depending on the experimental resolution, these may also appear as simple zero crossings Figure 5b shows correspondingly the course of the third derivative of the curve of the maximum amplitude Amax according to Figure 5a, wherein the third derivative has characteristic zero crossings, which are arranged symmetrically to the position X ₀ .

In the context of complex theoretical and experimental investigations, it has been found that these extreme values with kink occur in the curvature of the measured curve of the maximum amplitude Amax precisely when the ultrasound-reflecting structure 90 is no longer detected in any one of the first and second ultrasound pulses P1, P2 , By determining the distance of the aforementioned points, a measure of the actual geometric dimension d of the structure 90 in the direction of the X-axis can be given. Experimental studies have shown that the value obtained in this way shows a high correlation with the actual dimensions of the structure 90, wherein the actual geometric dimensions were subsequently determined by means of destructive methods.

A scan of the structure 90 in a direction Y perpendicular to the X direction finally provides a 2d image of the geometric dimensions of the ultrasound reflecting structure 90.

Furthermore, FIG. 5b shows the curve of the second derivative of the profile of the maximum amplitude Amax as a function of the displacement ΔX, the points of maximum curvature X1, X2 from FIG. 5a corresponding to the zeros of the third derivative having maxima or minima of the second derivative are correlated. If, for example, due to insufficient measurement accuracy, the extraction of a third derivative of the experimentally determined Runs the maximum amplitude Amax after the shift ΔX not possible, so alternatively the second derivative of the curve of the maximum amplitude Amax can be determined by the location and analyzed for adjacent pairs of points consisting of a maximum and a minimum, the second derivative in the maximum and in the minimum should not be differentiable. Furthermore, the second derivative should have a maximum opposite sign to the minimum. In order to ensure that a considered pair of points, at which in each case an extreme value of the curvature occurs in the course of amplitude and which are adjacent to each other, are actually controlled with the outer boundaries of an ultrasound-reflecting structure 90, it is possible to have the test criteria mentioned in the subclaims apply what may be done, for example software implemented in the evaluation unit 35.

In the exemplary embodiment according to FIG. 2, the display device 40 of the test apparatus 10 is set up to display, in addition to the immediate pulse-echo signal, the signal for the amplitude maximum Amax and its second or third derivative obtained during a displacement in the direction of the X-axis.

Finally, FIG. 4 shows the test head 20 of a second exemplary embodiment of an arrangement 1 according to the invention in an enlarged view. Except for the test head 20 and the path detection unit 15, the arrangement 1 corresponds to the arrangement according to FIG. 1. In the second exemplary embodiment, the test head 20 comprises only two ultrasound transmitters 15, one of which is the first ultrasound transmitter 15 'and a second second ultrasound transmitter 15 "of the control unit 30 and the evaluation unit 35. The first and second ultrasonic transmitters 15 'and 15 "are configured analogously to the ultrasonic transmitters 15 of the first exemplary embodiment. Here, too, the drive unit 30 is set up to control the first and second ultrasound transmitters 15 'and 15 "analogously to the first exemplary embodiment." In the second exemplary embodiment too, the evaluation unit 35 holds the first and second ultrasound transmitters 15' and 15 "electrically or electronically to a large ultrasonic receiver, so that the reflected first and second ultrasonic pulses Ei and P2 picked up by the first and second ultrasonic transmitters 15 'and 15 ", respectively, are superimposed by this interconnection of the first and second ultrasonic transmitters 15' and 15", respectively. The resulting signal is subsequently subjected by the evaluation unit 35 to a digital signal processing analogous to the first embodiment.

In contrast to the first exemplary embodiment, however, in order to carry out the method according to the invention, the test head 20 of the arrangement 1 must be displaced in the X direction on the test surface 110 of the test object 100 in the X direction. In order to detect the shift ΔX that occurs in this case, a travel detection unit 50 is attached to the test head 20. This is formed in the embodiment shown as a follower wheel whose rotation is detected by means of an angle sensor. The signals of the angle sensor are then translated by the evaluation unit 35 into the actual displacement ΔX of the test head 20 on the test surface 110. When carrying out the method according to the invention, when the test head 20 is displaced on the test surface 110, the amplitude curve according to FIG. 4a is again obtained, which is also correlated with a curve of the second or third derivative according to FIG. The subsequent evaluation of the resulting measured amplitude curve can therefore be carried out analogously to the first exemplary embodiment.

It is advantageous with the arrangement 1 according to the invention according to the second exemplary embodiment that the same first and second ultrasound transmitters 15 'and 15 "always play no part in variations in the transmission or reception characteristics, however, the faulty mechanical detection of the displacement path ΔX is disadvantageous the test head 20 on the test surface 110th

From the course of the third derivative when sweeping over the ultrasound-reflecting structure 90, which can be seen from FIG. 4 b, information about the reflectivity of the ultrasound-reflecting structure 90 can also be extracted. It has been found in experimental and theoretical investigations that the jump in the third derivative, which is marked A in FIG. 4b when the ultrasound reflecting structure 90 is detected by the first and second ultrasound pulses P1 and P2, directly correlates with the reflectivity of the Ultrasound-reflecting structure 90 is correlated. In particular, it is possible to correlate the reflectivity of different ultrasound-reflecting structures 90 within a device under test 100. In particular, this may also include a riation of the reflectivity within a single reflecting structure 90 are recorded at least qualitatively.

By comparison with a reference structure whose reflectivity is quantitatively known from preliminary investigations, an absolute value of the reflectivity of the ultrasound-reflecting structure 90 can also be obtained by means of the aforementioned method, which can be considered at least as an estimate of the reflectivity of the structure 90.

Arrangement Device Ultrasonic transmitter 'first ultrasonic transmitter' Second ultrasonic transmitter Test head Array test element Control unit Evaluation unit Display device Operating elements Distance detection unit Ultrasonic reflective structure0 DUT 0 Test surface

Claims

claims

1) A method for non-destructive determination of the size d of an ultrasound-reflecting structure (90) in the volume of a specimen (100) by means of ultrasound, using a first and a second ultrasonic transmitter (15 ', 15 ") spaced apart in the X direction , comprising the following method steps:

a) einschallen a directed first ultrasonic pulse Pl and a directed second ultrasonic pulse P2 in the sample, the first and the second ultrasonic pulse Pl, P2: i) propagate in the test piece (100) along substantially parallel paths Sl and S2, and ii) a different polarity P +, P-, and b) summing the reflected first and second ultrasonic pulses Pi, P2, c) detecting the amplitude maximum Amax of the summed reflected first and second ultrasonic pulses Pi, P2, d) shifting the first and second ultrasonic transmitters (15 , 15 ') on the test surface (110) along the X axis by a defined amount .DELTA.X, e) Repeatedly carrying out the method steps a) to d), and f) determining the points of maximum curvature Xl, X2 of the applied over the displacement .DELTA.X detected amplitude maximum Amax.

2) A method according to claim 1, characterized in that for determining the points of maximum curvature Xl, X2 of above the shift ΔX supported amplitude maximum Amax the jump points with sign change of the third derivative of the detected amplitude maximum Amax are determined after the shift .DELTA.X.

3) Method according to claim 1, characterized in that for determining the points of maximum curvature X1, X2 of the amplitude maximum Amax plotted over the displacement ΔX, the maxima and minima of the second derivative of the detected amplitude maximum Amax are determined after the displacement ΔX at which detected amplitude maximum Amax as a function of the displacement ΔX has a kink.

4) A method according to claim 1, characterized in that the size d of the ultrasound-reflecting structure in the volume of the test piece (100) is determined by the distance between adjacent points of maximum curvature Xl, X2 is determined.

5) Method according to claim 4, characterized in that for identifying a pair of adjacent points of maximum curvature Xl, X2 as belonging to an ultrasound-reflecting structure one or more of the following criteria is applied: a) between the first and the second point maximum Curvature X1, X2, the curvature changes sign (ie from "right curved" to "left curved" or vice versa), b) the amount of curvature is in the immediate vicinity of both points Xl, X2 on the edges of the measured curve of the amplitude maximum Amax, the are respectively substantially equal to the supposedly complementary point of maximum curvature, and c) the second derivative of the course of the amplitude maximum Amax after the displacement ΔX is continuous, but not differentiable, in both points X1, X2.

6) Method according to claim 1, characterized in that the first and the second ultrasonic pulse Pl, P2 have substantially the same pulse height and pulse duration. 7) Method according to claim 1, characterized in that the first and the second ultrasonic pulse P 1, P 2 are generated substantially simultaneously.

8) Method according to claim 1, characterized in that the first and the second ultrasonic transmitter (15 ', 15 ") have substantially the same beam characteristic.

9) A method for non-destructive determination of the reflectivity of an ultrasound-reflecting structure (90) in the volume of a test specimen (100) by means of ultrasound, characterized in that: a) the position of the structure (90) is determined by means of a suitable ultrasound algorithm , b) the method steps a) to d) of the method according to claim 1 are repeated to determine the course of the third derivative of the detected amplitude maximum Amax after the displacement ΔX in the region of the ultrasound-reflecting structure, c) determining the size the jump in the third derivative, which occurs when the first and second ultrasonic pulses P 1, P 2, which are immersed in the test object, detect the edge of the structure (90).

10) A method according to claim 9, characterized in that the size of the jump in the third derivative is determined relative to a reference structure in a reference body by a) the size of the jump in the third derivative of the detected amplitude maximum Amax of the specimen after the shift ΔX is determined with the magnitude of the jump in the third derivative, b) the magnitude of the jump in the third derivative of the detected amplitude maximum Amax of the reference body is determined after the displacement .DELTA.X which occurs when the first and second ultrasonic pulses injected into the reference body determine the edge capture the reference structure, c) the jump variables determined in steps a) and b) are set in relation to one another. 11) Apparatus (10) for nondestructive determination of the size d of a UIt- fast-reflecting structure (90) in the volume of a test specimen (100) by means of ultrasound using: a) a first and a second ultrasonic transmitter (15 ', 15 ") i) arranged in the X-direction spaced from one another and ii) arranged to be a directed first ultrasonic pulse Pl and a directed second ultrasonic pulse P2 in the DUT, wherein the first and the second ultrasonic pulse Pl, P2 (l) in the DUT propagate along substantially parallel paths Sl and S2, and (2) have a different polarity P +, P-, b) a means for summing the reflected first and second ultrasonic pulses Pi, P2, c) means for detecting the amplitude maximum Amax of the summed reflected first and second ultrasonic pulses £!, P2, d) of a displacement detecting means (50) of the first and second ultrasonic transmitters (15, 15, 15). 15 ') on the X-axis by a defined amount ΔX,

the device (10) having the following features:

e) a drive unit (30) for controlling the first and second ultrasound transmitters (15, 15 ') such that they each emit sequences of ultrasound pulses P1, P2, f) an evaluation unit (35) which is set up to: i) the detected one To detect amplitude maximum Amax as a function of the displacement on the X axis, and ii) to determine the points of maximum curvature X1, X2 of the detected amplitude maximum Amax plotted over the displacement ΔX.

12). Device (10) according to claim 11, characterized in that the evaluation unit (35) is set up to determine the points of maximum curvature X1, X2 of the amplitude amplitude maximum Amax plotted over the displacement ΔX, the jump points with sign change in the third derivative of detected amplitude maximum Amax after the shift ΔX to determine.

13) Device (10) according to claim 11, characterized in that the evaluation unit (35) is adapted to determine the maximum deflection points Xl, X2 of the applied over the shift .DELTA.x detected amplitude maximum Amax the maxima and minima of the second derivative of the detected amplitude maximum Amax after the shift ΔX at which the detected amplitude maximum Amax has a kink as a function of the displacement ΔX

14) Device (10) according to claim 11, characterized in that the evaluation unit (35) is adapted to determine the size d of the ultrasound-reflecting structure (90) in the volume of the test piece (100) by the distance of a pair of adjacent points maximum curvature Xl, X2 is determined.

15) Device (10) according to claim 14, characterized in that the evaluation unit (35) is adapted for identifying a pair of adjacent points of maximum curvature Xl, X2 as belonging to an ultrasound-reflecting structure (90) one or more of the following criteria apply: a) between the first and the second point of maximum curvature X1, X2, the curvature changes sign (ie from "right curved" to "left curved" or vice versa), b) the amount of curvature is in the immediate vicinity of both points Xl, X2 on the flanks of the measured curve of the amplitude maximum Amax, which are respectively oriented towards the supposedly complementary point of maximum curvature, substantially equal, and c) the second derivative of the curve of the amplitude maximum Amax after the shift ΔX is continuous in both points X1, X2 but not differentiable.

16) device (10) according to claim 11, characterized in that the drive unit (30) is adapted to the first and the second ultrasonic transmitter (15 ', 15 ") to control so that the first and the second ultrasonic transmitter (15', 15"). sonic pulse Pl, P2 have substantially the same pulse height and pulse duration.

17) Device (10) according to claim 11, characterized in that the drive unit (30) is adapted to generate the first and the second ultrasonic pulse Pl, P2 substantially simultaneously.

18) Arrangement (1) for nondestructive determination of the size d of an ultrasound-reflecting structure (90) in the volume of a test specimen (100) by means of ultrasound, comprising the following features: a) a first and a second ultrasound transmitter (15 ', 15 i) arranged in the X-direction spaced apart from one another and ii) arranged to introduce a directed first ultrasonic pulse P 1 as well as a directed second ultrasonic pulse P 2 into the test object, the first and the second ultrasonic pulses P 1, P 2 (1) in the DUT along substantially parallel paths Sl and S2, and (2) have a different polarity P +, P-, b) means for summing the reflected first and second ultrasonic pulses Pi, P2, c) means for detecting the amplitude maximum Amax the summed reflected first and second ultrasonic pulses Pi, P2, d) comprise means for detecting a displacement (50) of the first and second ultrasonic transmitters (1 5, 15 ') on the surface of the test piece (110) along the X-axis by a defined amount ΔX, and e) a device (10) according to claim 11.

19) Arrangement (1) according to claim 18, characterized in that the first and the second ultrasonic transmitter (15 ', 15 ") have substantially the same beam characteristic.

20) Arrangement according to claim 18, characterized in that the first and the second ultrasonic transmitter (15 ', 15 ") are arranged in a common probe housing.

21) Arrangement according to claim 18, characterized in that the first and the second ultrasonic transmitter (15 ', 15 ") in each case by an element (27) an array probe (25) are formed.

22) Arrangement according to claim 18, characterized in that the first and the second ultrasonic transmitter (15 ', 15 ") each of a group of ele- ments (27) of an array test head (25) are formed electronically to a Ultrasonic transmitters (15, 15 ') are summarized.