WO2008119748A1 - Method for controlling an array test head of a device for the ultrasonic testing of an animate or inanimate test object and device for carrying out said method - Google Patents

Abstract

The invention relates to a method for controlling an array test head (10) of a device (1) for the ultrasonic testing of an animate or inanimate test object, the array test head comprising a plurality (N) of individually controllable ultrasonic transmitters (15). The method comprises the following steps: a. selecting a set (M) of the plurality (N) of individually controllable ultrasonic transmitters (15), b. subdividing the set (M) into at least two subsets (U1 and U2), c. controlling the ultrasonic transmitters (15) comprised by the subset (U1) by means of an amplitude (A1) which is higher than the amplitude average value (FA) across all ultrasonic transmitters (15) contained in the set (M), and d. controlling the ultrasonic transmitters (15) comprised by the subset (U2) by means of an amplitude (A2) which is lower than the amplitude average value (FA) across all ultrasonic transmitters (15) contained in the set (M). The invention also relates to a device which is adapted to carry out said method.

Description

 Description: Method for controlling an array test head of a device for ultrasound testing of a live or inanimate test specimen and device for carrying out the method

The present invention is a method for controlling an array probe of a device for non-destructive ultrasonic testing of a specimen, and a device for non-destructive ultrasonic testing of a specimen, which is suitable for carrying out the method according to the invention. The invention particularly relates to the field of material testing by means of ultrasound and here to the improvement of the lateral resolution of an array probe. The invention can furthermore be used in the field of investigation of animated and inanimate biological samples by means of ultrasound, in particular for medical diagnostics. The invention will be explained below using the example of material testing by means of ultrasound.

An array probe is basically a single transducer that is divided into many individual elements. Typical element widths range from 0.5 mm to approx. 2.5 mm, other dimensions are also possible. The term array also includes so-called ring phased arrays, ie round oscillators or elements which are divided into concentrically shaped individual elements.

The use of several small oscillators makes dynamic focusing and oscillation of the beam possible. In addition, a particularly effective sound transmission results because smaller elements require less excitation energy. As a receiver, they respond extremely efficiently because of their low mass to be excited. While a large transducer provides a large level scan, its relatively low fanning (the small divergence) limits fault findability. Small swingers, on the other hand, have a much larger divergence angle. Another advantage of an array probe is its ability to create a dynamically modifiable ultrasound beam to provide a "virtual probe." For this purpose, a subset of the individual transducers encircled by an array probe are jointly driven, thus becoming one "Virtual probe" summarized because position along the array by driving different subsets can be moved.

So-called phased array probes excite the individual elements at different times, whereby a wavefront is generated, which is characterized by mutually delayed einstrahlende sound lobes. This wavefront looks like the sound field of a conventional angle probe. By varying the delay times, different sound fields can be generated; in particular, the insonification angle of the sound field within the sound beam characteristic of the individual oscillator can be set practically as desired. By gradually varying the delay times, the entire sound field can thus be "swiveled." The use of a phased array test head thus makes possible an angle scan with a stationary test head.

In addition to sound beam tilting, phased array probes also allow dynamic focusing of the sound beam. This is achieved by an electronic unit that allows control of the individual elements and at the same time can cause pulse delays. In principle, a focal point is driven through the test specimen. The combination of dynamic focusing and beam oscillation causes a beam of sound that is simultaneously focused and incident at an angle, whereby the depth of the focal point in the specimen and the insonification angle can be adjusted specifically.

Larger array probes can also be used for a so-called linear scan, in which the combined groups of oscillators are controlled one after the other. This creates a sampling effect. The width of the sound lobe traveling through the test specimen and the scanning step size can be determined by the number of simultaneously activated individual elements and by the impulse to impulse offset. In this way, the achievable resolution of the "virtual test head" is limited in principle to such a called "pitch" of the probe, ie the center distance of two single oscillator (= width single oscillator + gap between single oscillator).

For further details on the technique of ultrasonic testing by means of array probes, reference is made, for example, to the publication Ultrasonic Array Technique for Industrial Applications by the authors Bill Waldron & Gerd Kauth, ZfP-Zeitung 69, March 2000, pp. 50-52.

Even with the use of array probes for material testing or in medical technology, the test is performed in most cases with the pulse-echo technique. The probe preferably emits ultrasonic pulses periodically, which are coupled into the test specimen. A receiver (e.g., the probe itself in the case of perpendicular sound) then receives echo signals of the delivered ultrasonic pulses. The echo signals originate from the test object and in particular from a rear wall of the workpiece. In that regard, the test method is suitable for workpieces whose coupling surface is substantially parallel to the rear wall, so that it comes to the formation of several outgoing and longitudinal courses of the ultrasonic pulse in the workpiece. In the case of oblique sound, however, "echoes" essentially only originate from edges or defects of the test object.

For the technique of non-destructive material testing by means of ultrasound, in particular by means of pulse-echo method is generally referred to the book Material Testing with Ultrasound, Josef Krautkrämer & Herbert Krautkrämer, Springer, 5th edition (February 1998).

As a general rule, in a test method which uses fixed phase array probes to determine magnitudes of errors in a sample, the resolution of the technique is essentially limited to the size of the individual phased array probe. This is where the invention is based, which has set itself the task of specifying a method which involves shifting a sound field enclosed by a phased array test head into a live or inanimate test specimen with a fixed test head by fractions of the size of the individual oscillators used Array probe allowed. It is another object of the present invention to provide a device for ultrasonic testing of a live or inanimate test specimen by means of a Ultraschallprüfkopfs, which allows the aforementioned electronic displacement of the phased array probe into the test specimen ultrasonic field.

This object is achieved by a method having the features of claim 1 and by an apparatus having the features of claim 7.

The inventive method is based on the finding that in addition to the relative phase position of the ultrasonic pulses generated by the individual elements of a phased array probe and their relative amplitude has an impact on the total resulting sound field.

For example, it has been found in the course of extensive theoretical and experimental investigations that the sound field, which is collimated by a total of, for example, eight individual oscillators of a linear array into a test head, can be electronically displaced by fractions of the dimensions of a single oscillator along the array The totality of the eight individual oscillators is divided into groups of four adjoining individual oscillators and a targeted reduction or increase in the amplitude of the ultrasound pulses emitted by the individual oscillators of the individual groups. In a simple embodiment of the method according to the invention, for example, the amplitude of the ultrasound pulses emitted by the first group of individual oscillators is increased by a substantially equal amount, for example 10%, compared to the mean amplitude of the ultrasound pulses emitted by all the individual oscillators. The amplitude of the second group, however, is lowered by a substantially equal amount to the average. This results in a shift of the maximum of the resulting in the superposition of the emitted from the individual oscillators of the array ultrasonic pulses sound field by an amount corresponding to a fraction of the structure size of a single oscillator. At the same time a slight deformation of the resulting from the superposition of the individual pulses sound field occurs, but in practice is not usually relevant. More generally, the method according to the invention relates to the activation of an array probe of a device for ultrasound testing of an animated or inanimate test object, via which the array test head comprises a plurality N of individually controllable ultrasound transmitters. The method comprises the following method steps:

a) selecting a subset M of the plurality N individually controllable ultrasound transmitter of the array probe, b) dividing the subset M in at least two subsets Ul and U2, c) driving the ultrasonic transmitter comprised of the subset Ul with an amplitude Al, compared to the amplitude mean value 0 A is increased over all ultrasound transmitters contained in the subset M, and d) driving the ultrasound transmitters, which are encompassed by the subset U 2, with an amplitude A 2 which is reduced in relation to the mean amplitude A 0 across all ultrasound transmitters contained in the subset M.

In this case, the subset M may comprise in particular all the individually controllable ultrasonic transmitters of the array test head, or else only a subset of this total number. The subset M advantageously comprises an even number of individually controllable ultrasound transmitters, but this is not absolutely necessary. In principle, a subset M can also comprise only two individually controllable ultrasound transmitters.

It should also be noted that the subset M can also be subdivided into more than just two subsets. In particular, the subset M can be divided into so many subsets U that each subset U comprises only a single controllable ultrasonic transmitter.

In the exemplary embodiment, evidence is presented that the inventive method allows controlled by a plurality of individually controllable ultrasound transmitters sound field electronically controlled by an amount smaller than the dimensions of a single controllable ultrasonic transmitter, which is a single element of an array - Probe may be, wherein the displacement is substantially independent of the depth of the sound field in the device under test. In the following, the probe elements are referred to as ultrasonic transmitters. In a particularly preferred development of the method according to the invention, all ultrasound transmitters with the same amplitude Al encompassed by the subset Ul and all the ultrasound transmitters encompassed by the subset U2 are actuated with the same amplitude A2. This embodiment of the method according to the invention allows a particularly simple design of the control electronics for the array probe.

In an alternative embodiment, the ultrasound transmitters included in a subset U1 are not driven with a substantially constant amplitude, rather they are driven with different amplitudes. It is inventively provided that in the second subset U2 to each ultrasonic transmitter of the first subset a complementary ultrasonic transmitter is provided in the second subset U2, wherein in each pairing of the ultrasonic transmitter is that the average of the amplitude of the ultrasonic transmitter from the subset of Ul and the amplitude of the complementary ultrasound transmitter from the subset U2 is just equal to the mean value of the amplitudes of all the ultrasound transmitters 0A contained in the subset U. ,

In order to actually use the method according to the invention for lateral displacement of the sound field generated by the phased array probe, the method steps c) and d) are preferably repeated, wherein the amplitudes A1 and A2 are changed between the individual passes. By deliberately varying the amplitudes A1 and A2, the maximum of the sound field can be shifted in a controlled manner along the longitudinal axis of the phased array probe.

The evaluation of the resulting ultrasound echo signals is particularly simple in this case if, during the individual passes, the mean amplitude value 0 A is kept essentially constant over all ultrasound transmitters contained in the subset M.

Of course, the method according to the invention can also be used with the methods for dynamic focusing established from the field of phased array ultrasonic probes, for the stepwise displacement of the sound field across the width of an individually controllable ultrasound transmitter and for blurring. ken of the sound bundle. In order to achieve the best possible spatial resolution in the measurement of errors in the DUT, therefore, the sound field, which is generated by the ultrasound transmitters of the amount of sound M, usually be impressed by phase-shifted control of individually controllable ultrasound transmitters focus. Here, too, the exact position of the focus in the specimen can be adjusted by varying the phase shift between the individually controlled ultrasound transmitters.

In order to use the inventive method, for example, to accurately determine the error size of an error in a device under test, one will usually combine the prior art prior art test methods, which are based on the use of a phased array probe, with the inventive method. In particular, to locate a fault in a device under test, a focused ultrasound field will be incrementally translated along the array until the intensity of the error found is maximum. After the error is roughly localized in this way, then the scanning method according to the invention for highly accurate determination of the size of the error is applied. In addition to the linear displacement of the focused ultrasound beam along the array, pivoting of the focused ultrasound beam is of course also possible in order to allow for errors whose main direction of reflection is not perpendicular to the coupling surface of the device under test, to maximize the error signal by searching that insonification angle below which the reflectivity maximum error.

An apparatus according to the invention for non-destructive ultrasonic testing of a live or inanimate test specimen comprises an array test head which comprises a plurality of individually controllable ultrasound transmitters. Furthermore, the device comprises a control electronics for the array probe, wherein the control electronics is set up to control the individually controllable ultrasonic transmitter individually or in groups and in particular with respect to their phase position and their respective transmission amplitude controlled. In this case, the control electronics is especially adapted to drive the array probe according to the inventive method. In general, the previously known from the prior art array probes are suitable for the inventive device, comprising a plurality N individually controllable ultrasonic transmitter. In particular, both linear and areal stretched array probes suitable. The corresponding design of the control electronics for the array test head can be hardware implemented. In the majority of applications, however, the control electronics of the array probe will work digitally and the method according to the invention will be implemented by executing a software program on the digital control electronics.

Further advantages and features of the method according to the invention and the device according to the invention will become apparent from the dependent claims and the embodiment, which is explained below with reference to the drawing. In this show:

1 shows a schematic representation of a device according to the invention for non-destructive ultrasonic testing of a test specimen with an array probe,

2 is a graphical representation of the course of the first derivative of

Sound pressure amplitude signal along the longitudinal axis X of the test head array to indicate the position of the sound pressure maximum.

3: the resulting shift of the amplitude maximum as a function of the amplitude difference ΔA between the first subset U1 and the second subset U2, and

4 shows the position of the amplitude maximum for a given amplitude difference ΔA as a function of the depth Z in the test object.

FIG. 1 shows schematically a device according to the invention for non-destructive ultrasonic testing of a test object. The device comprises an array test head 10, which is placed on a test surface of a test object 100 in the illustration of FIG. The array test head 10 comprises a plurality N = 16 of individually controllable ultrasound ends 15, which are substantially identical in their dimensions and their ultrasound end and reception properties and which are arranged equidistant. For controlling the array test head 10, in particular for the individual control of the head 10 provided in the array test ultrasound transmitter 15, the array test head 10 with a control electronics 20th In this case, the control electronics 20 include, among other things, a display 25 for the graphic representation of the ultrasonic signals received by the array test head 10 as well as various operating elements 30 for operating the ultrasonic testing device.

FIG. 1 shows the plurality N = 16 of individually controllable ultrasound transmitters 15, of which a subset M = 8 has been selected by ultrasound transmitters 15, which form a coherent group. In this case, this group extends along the longitudinal axis of the array probe 10, the direction of which is marked X in FIG. The direction Z extends into the test piece 100, along which the depth, for example, of the focus or defect in the test piece 100 can be indicated.

The subset M in turn is now subdivided into two equal subsets Ul and U2, the ultrasound transmitters 15, which are assigned to a subgroup U1 or U2, each adjoining each other directly. In the exemplary embodiment shown, the ultrasonic transmitters 15 of the subgroups U1 and U2 are arranged symmetrically about the Z axis.

The control electronics 20 of the device according to FIG. 1 are now configured to carry out the method according to the invention in a preferred embodiment. In the context of the method according to the invention, the designated subset M with 8 elements is selected from the plurality N = 16 individually controllable ultrasonic transmitters 15 of the array test head 10. This is now decomposed in the context of the procedure in the two also marked subgroups Ul and U2 with 4 elements each. Subsequently, the ultrasound transmitters 15 of the first subgroup U1 are actuated with a first uniform amplitude A1 and the ultrasound transmitters 15 of the second subgroup U2 with a second uniform amplitude A2. The average amplitude over all ultrasound transmitters 15 of subset M is given by 0A. The amplitude Al is lowered by an amount ΔA / 2 with respect to 0A, the amplitude A2 is increased by 0A by the amount ΔA / 2. Overall, this results in an amplitude difference of ΔA between the ultrasound transmitters 15 of the first subgroup U1 and the ultrasound transmitters 15 of the second subgroup U2. The starting point of the beam shift is an activation of U1 and U2, each with 0A. This sound beam centered over the geometric center of the subset of the M ultrasound transmitters 15 is displaced by the method according to the invention.

By suitable control of the relative phase position of the ultrasonic pulses generated by the ultrasonic transmitters 15 of the subset M, a maximum of the sound field is formed, which is generated by the subset M of the ultrasonic transmitter. The position of the maximum of this sound field corresponds to the zero crossing of the first derivative of the sound pressure of the sound field along the longitudinal axis X of the array probe 10. In Figure 2, the course of the first derivative of the amplitude signal of the resulting sound field along the longitudinal axis X of the Prüfkopf- Arrays 10 shown for different amplitude differences .DELTA.A. Values for ΔA between 0% and 80% of the mean amplitude 0A were chosen. It can be clearly seen from the resulting family of curves that the zero crossing shifts monotonously with increasing amplitude difference ΔA. In this case, the unit for the abscissa is selected to be 1/10 of the width of an individually controllable ultrasonic transmitter 15 ("dot pitch").

FIG. 3 shows the resulting shift of the amplitude maximum as a function of the amplitude difference ΔA. The strictly monotonous dependence of the resulting shift of the amplitude maximum as a function of the amplitude difference ΔA can also be read from the illustration in FIG. As can also be seen from FIG. 2, FIG. 3 shows that the resulting displacement of the maximum amplitude is already only in the range of fractions of the width of an individually controllable ultrasonic transmitter 15, even though the amplitude differences ΔA are quite high. By varying the amplitude difference .DELTA.A, it is possible, in particular, to shift the maximum of the resulting sound field in a controlled manner along or against the longitudinal axis X of the array test head 10 by at least half the width of an ultrasound transmitter 15.

Finally, FIG. 4 shows the position of the resulting amplitude maximum of the sound field of all ultrasonic transmitters 15 of subset M as a function of depth Z in specimen 100 for a given fixed amplitude difference ΔA be that the position of the amplitude maximum is practically independent of the depth Z in the test piece 100. This means that the method according to the invention actually essentially causes only a displacement of the sound field by fractions of an ultrasonic transmitter width (in addition to the already mentioned slight deformation of the ultrasonic field) and practically causes no tilting of the ultrasonic field against the Z axis.

Of course, this controlled shift of the ultrasound field can be combined by means of the method according to the invention along the longitudinal axis X of the ultrasound array 10 with a pivoting of the ultrasound field by a controlled angle by the relative phase of the ultrasound transmitter 15 of the subset M is selectively controlled. The specific shape of the sound field generated by subset M of ultrasound transmitter 15, in particular the position and the size of a focusing focus, can also be controlled by suitable phase control of ultrasound transmitters 15 of subset M.

Finally, it should be pointed out that the selection of a subset M of the totality N of the ultrasonic transmitters 15 of the array test head 10 is not necessarily required in the context of the method according to the invention. Rather, the method can also be carried out in such a way that always all the ultrasonic transmitters 15 of the array test head 10 are used for the method according to the invention. The division of the totality N of the ultrasonic transmitter 15 of the array probe 10 can be fixed in the context of the method according to the invention, for example, if always one half of the ultrasonic transmitter 15 is combined to form a subgroup U1 and the second half ultrasound transmitter 15 to the second subgroup U2. In this embodiment of the method according to the invention thus the selection of the subset M from the totality N and their division into two subsets Ul and U2 already in the inventive device of the control electronics 25 has taken place and is not repeated each time anew when performing a test task. Nevertheless, this expression of the method according to the invention is to be regarded as a word-appropriate implementation of the method according to the main claim.

Claims

Description: Method for controlling an array test head of a device for ultrasound testing of a live or inanimate test object and device for carrying out the method patent claims 1. A method for driving an array probe (10) of a device (1) for ultrasonic testing of a live or inanimate test specimen, wherein the array probe comprises a plurality N individually controllable ultrasonic transmitter (15), comprising the following steps: a. Selecting a subset M of the plurality N individually controllable ultrasonic transmitter (15), b. Splitting the subset M into at least two subsets Ul and U2, c. Activating the ultrasound transmitter (15), which is encompassed by the subset U1, with an amplitude A1 which is increased in relation to the mean amplitude value 0A over all ultrasound transmitters (15) contained in the subset M, and d. Controlling the ultrasound transmitter (15), which is included in the subset U2, with an amplitude A2 which is reduced compared to the mean amplitude value 0A across all ultrasound transmitters (15) contained in the subset M. 2. Method according to claim 1, characterized in that all the ultrasound transmitters (15) encompassed by the subset U1 with the same amplitude Al and all the ultrasound transmitters (15) included in the subset U2 are driven with the same amplitude A2. 3. Method according to claim 1, characterized in that the ultrasonic transmitters (15) encompassed by the subset U1 with different amplitudes A1 .1 to A1. n and the ultrasonic transmitters (15) encompassed by the subset U2 are driven with different amplitudes A2.1 to A2.n, wherein for each amplitude Al. i a complementary amplitude A2.i exists, so that AU + A2J _ CA Λ 4. The method according to claim 1, characterized in that the method steps c) and d) are repeated several times in succession, wherein between individual passes the amplitudes Al and A2 are changed. 5. The method according to claim 4, characterized in that during the individual runs of the amplitude average value 0A is kept substantially constant over all contained in the subset M ultrasonic transmitter (15). 6. The method according to claim 1, characterized in that the ultrasound transmitters (15) contained in the subset M are driven out of phase in such a way that a focus is formed in the ultrasound beam emitted by the ultrasound transmitters (15) contained in the subset M. 7. A method for determining the size of an ultrasound-reflecting structure in a live or inanimate specimen by means of ultrasound using an array probe (10) comprising a plurality N individually controllable ultrasonic transmitter (15), characterized in that the following method steps executed become: a. Scanning the test specimen by means of a focused ultrasound beam, which is generated by a subset M of the plurality of individually controllable ultrasound transmitters (15), b. Finding that subset M (max) of the plurality N of individually controllable ultrasonic transmitters (15) for which the error signal of a fault in the test object is maximum, and c. Execution of method steps b) to d) according to claim 1. 8. Device (1) for ultrasonic testing of a live or inanimate test specimen, comprising an array probe (10) comprising a plurality N individually controllable ultrasonic transmitter (15), and a control electronics (20) for the array probe (10), characterized in that the control electronics is adapted to drive the array probe (10) according to the method of claim 1.