GB2033579A - Ultrasonic probes - Google Patents

Abstract

With the aim of providing an ultrasonic probe capable of delivering differently angled ultrasonic beams at choice on application of the probe to a surface of a workpiece to be examined by ultrasonic waves, the probe comprises transducers 9/1 to 9/18 in contact with a shoe 2 having a working face 3 adapted to the workpiece surface, wherein a plurality of transducers are arrayed on the shoe along an arc 5 of a cylinder of which the axis 6 lies in the working face of the shoe and are adapted when employed in groups of adjacent transducers, some at least of which groups may overlap one another, to generate or to detect respective working beams of ultrasonic waves in the shoe the axes of which beams are respectively differently angled and all pass through the cylinder axis region of the shoe working face. Delay lines to or from some of the transducers of a transducer group may be employed. <IMAGE>

Description

SPECIFICATION Improvements in and relating to probes for ultrasonic examinations This invention relates to probes for ultrasonically examining the interiors of workpieces in order to detect whether flaws are present and to locate them if present.

In ultrasonic examination a transmitting probe is relatively traversed over a surface of the workpiece while it produces in the interior of the workpiece a beam of electro-acoustical ly generated ultrasonic waves. Flaws encountered by the beam as the moving of the probe sweeps the beam through the workpiece interior are normally capable of reflecting the ultrasonic waves and when echo waves from flaws return to a receiving probe the latter electroacoustically converts them into electric oscillations, the strength of which depends on the character of the flaw and on its distance from the two probes and which can be converted to a visual and/or recorded signal.The location of the flaw is deducible from the position of the probes at the time and a knowledge of the angle of the ultrasonic beam in the workpiece interior which the transmitting probe is designed to project and the angle of the ultrasonic echo beam in the workpiece interior which the receiving probe is designed to receive the frequently also, since the transmitting probe is usually activated to send the ultrasonic waves into the workpiece in short wave trains or pulses, from a measure of the time interval from an ultrasonic pulse leaving the transmitting probe to the corresponding echo pulsearriving back at the receiving probe, for the time interval is determined by and can be coverted into the total distance from the transmitting probe along the beam to the flaw and along the echo beam from the flaw to the receiving probe.The transmitting probe and the receiving probe may be moved together and may be mounted side by side, separated from one another by acoustic insulation, or it is feasible for a probe to serve both as the transmitting probe and as the receiving probe.

Now a flaw that might reflect ultrasonic waves only feebly if the impinging ultrasonic beam is directed on it at one particular angle might nevertheless yield a much stronger reflection if the impinging beam were directed on it at another angle. For the better gauging of the seriousness of flaws, therefore, it is necessary to examine the workpiece interior with the aid of ultrasonic beams of different angles and it is known to examine a workpiece interior repetitively each time with a different probe capable of delivering a differently-angled ultrasonic beam into the workpiece interior. Time could be saved if a probe having the capability of delivering differentlyangled beams at choice were available.

Known kinds of probes have a transducer comprising a plate-like body of piezo-electric material at one face of a shoe having another face adapted to the workpiece surface. In Patent Specification No.

803,551 we proposed a variable-angle probe in which there were in effect two shoes, one shoe for application to the workpiece surface and a second shoe carrying the transducer and having a cylindrically curved face adapted to a cylindrically curved surface on the first shoe; if the second shoe is moved from one angular position on the first shoe to another angular position the probe becomes adapted for operation with a changed angle of beam in the workpiece interior. The arrangement, with a motor for reciprocating the second shoe in relation to the first shoe, would inevitably be bulky for many modern requirements and moreover modern data processing systems can handle a flow of information at a faster rate than could be provided during the reciprocation.

The present invention includes an ultrasonic probe for application to a surface of a workpiece to be examined by ultrasonic waves, comprising transducer means in contact with a shoe having a working face adapted to the workpiece surface, wherein a plurality of transducers are arrayed on the shoe along an arc of a cylinder of which the axis lies in the working face of the shoe and are adapted when employed in groups of adjacent transducers, some at least of which groups may overlap one another, to generate or to detect respective working beams of ultrasonic waves in the shoe the axis of which beams are respectively differently angled and all pass through the cylinder axis region of the shoe working face.

The invention provides also apparatus for activating in the beam generating sense by the application thereto of pulses of ultrasonic waves an ultrasonic probe as indicated in the preceding paragraph, including electronic delay means arranged to supply to transducers away from the centre of each group of adjacent transducers to be activated pulses so delayed in relation to pulses applied to the transduc erortransducers at the centre of the group asto effect the generation of a plane pulse front working beam in the shoe or a beam of only slightly converging pulse front character.

The invention provides moreover apparatus for activating in the beam generating sense by the application thereto of pulses of ultrasonic waves an ultrasonic probe as indicated in the preceding paragraph but one, including a ring counter arranged for switching from the employment of one group of adjacent transducers to another group of adjacent transducers in a repeated sequence of a plurality of groups and a monostable arranged for determining according to the period of its unstable state the number of pulses supplied to each group of transducers before the switching to the next group in the sequence.

The invention provides also apparatus for detecting beams of pulses of ultrasonic waves received by an ultrasonic probe as-indicated in the preceding paragraph but two, and traversing the shoe thereof to a group of adjacent transducers arranged to be responsive, including electronic delay means arranged to impose on signal responses from transducers away from the centre of the group such delays in relation to the signal response or responses of the transducer or transducers at the centre of the group as will bring together in time the responses of all the transducers of the group; Since each working beam in the shoe is generated or detected by means of a group of transducers arrayed along a cylindrical arc, the probe can be relatively compact.Compactness is generally advantageous and may present a particular advantage in the relative shortness of all the ultrasonic path lengths in the probe if the probe material tends to attenuate ultrasonic waves rather strongly.

The invention will now be described by way of example with reference to the accompanying drawings, in which Figure 1 is a side view and Figure 2 is a plan view of an ultrasonic probe shoe having a curved cylindrical face on which eighteen relatively narrow transducers are mounted side by side.

Figure 3 is a side view in section through a number of the transducers but to a larger scale and showing details of the transducers and of the mounting thereof not represented in Figures 1 and 2, Figure 4is a perspective-sectional view, also to a larger scale than Figures 1 and 2, of a part of a shoe having an arcuate prismatic face instead of a curved cylindrical one, Figure 5is a side view in section similar to Figure 3 but showing transducers mounted on the facets of the shoe arcuate prismatic face, Figures 6, 7 and 8 are diagrams illustrating the formation in the probe shoe, by the activation of a group of transducers, of working beams of different pulse front shapes, Figure 9 is a perspective-sectional view of a butt weld between plates showing a probe scanning path adjacent the weld and illustrating how the probe may detect a flaw by means of ultrasonic beams of different angles and Figure 10 is a block diagram of an electronic system for repetitively activating in sequence a number of groups of adjacent transducers.

With reference to Figures 1 and 2 of the drawings, an ultrasonic probe adapted for application to a plane surface of a workpiece to be examined by ultrasonic waves comprises a transducer array 1 mounted on a shoe 2 which has a plane working face 3 to be urged against the said plane surface of the workpiece during the employment of the probe and which is a shaped block of a material known to be suitable for ultrasonic probe shoes, such as Perspex (Registered Trade Mark).

The block has parallel plane side faces 4 at right angles to the shoe working face 3 and a curved cylindrical face 5 of which the axis 6 lies in the shoe working face 3 and is at right angles to the side faces 4. The curved cyindrical face 5 extends at one end 7 from the shoe face 3; at its other end its starts to approach again towards the shoe face 3 but is terminated by a wide-V sloping cut-out 8 made in the shoe block and having the intended purpose of deflecting some of the ultrasonic waves that may, when the transducers are operated, return within the shoe block as unwanted echoes from the shoe face 3 and thereby ensuring a greater attenuation thereof.

The transducer array 1 consists of eighteen equalwidth relatively narrow transducers 9 mounted side by side on the curved cylindrical shoe face 5. The array extends over an 80 arc of the curved cylindrical face 5. As shown, the transducer nearest the cylindrical face end 7 is arcuately spaced by about 23' therefrom. For the sake of what follows, that transducer is denoted by 9/1 and the remaining transducers in succession are denoted by 9/2, 9/3 and soon to 9/18 at the other end of the array.

Each transducer 9 consists of piezo-electric ceramic material with electrodes on opposite faces thereof and the whole array is covered in an appropriate tungsten-loaded epoxy-resin cement backing, not shown in Figures 1 and 2. With reference more particularly to Figure 3, the whole array is composed of a single large curved slab 10 of appropriate thickness of piezo-electric material having an electrode sheet 11 on each face thereof. In the mounting of the transducer array on the shoe, firstly the slab 10 is bonded to the shoe face 5 by means of a thin layer 12 of an appropriate epoxy-resin cement.

Thereafter the outer of the two electrode sheets 11 is sub-divided by making grooves 13 parallel to the cylinder axis which excise the sheet in lines so that the eighteen transducers 9 may become independent ultrasonic wave generators or receivers. It is not advantageous if, for abundant certainty of subdividing of the outer electrode sheet, the grooves 13, as shown also excise subjacent parts of the slab 10 and if desired, in a modification, the grooves may extend to the inner electrode sheet, which, however, is preferably not also sub-divided by such grooves.

Electrical connectors 14 are then soldered to the outer electrodes, now isolated from one another, of the respective transducers, and also an electrical connector, not shown, is soldered to the inner electrode sheet, and the transducer array is then covered in the mentioned cement backing 15, through which the various electrical connectors extend.

In a modification, more onerous however of construction and of transducer mounting, the shoe face 5, or at least the part thereof on which the transducer array is mounted, instead of being curved cylindrical, might, as illustrated in Figure 4, be formed with relatively narrow side-by-side plane facets 21, all parallel to and equidistant from the axis 6 in the shoe working face 3, so that the shoe face 5, or the appropriate part of it, is now arcuate prismatic. With reference to Figure 5, on such facets 21 the respective transducers 109, which may now be strictly flat, of the array will be mounted. For the sake of reducing in number the necessary electrical connectors the inner electrodes of the transducers are provided by a single electrode sheet 111 extending over the whole of the faceted shoe face area on which the transducer array is mounted.

Transmitting probes are commonly activated to send ultrasonic waves at an ultrasonic frequency of a few megahertz into a workpiece in short wave trains or pulses of a considerably lower but nevertheless high repetition frequency of, say, one kilohertz. With reference again to the arrangements of Figures 1 and 2, the transducers 9/1 to 9/18, though individually narrow, are capable of generating working beams of ultrasonic waves in the shoe when employed in groups of say, six adjacent transducers of the array.

With reference to this connection to Figure 6, in which, however, the curvature of the shoe face 5 is exaggerated, if the six adjacent transducers 9/1 to 9/6 are activated together in the wave-generating sense to deliver synchronous pulses of ultrasonic waves, they will generate a working beam in the shoe of pulse front 22, of concave cylindrical shape advancing in the direction of the arrows 23 with central plane repressented by the line 24 which passes through the axis 6 in the shoe working face 3.

If instead of the group of six adjacent transducers 9/1 to 9/6 the group of six adjacent transducers 9/2 to 9/7 is activated in the same way, then there will be generated in the shoe a similar working beam differing only in that its central plane makes, where it passes through the axis 6 in the shoe working face 3, a different angle to the perpendicular to the shoe working face. Since there are eighteen transducers 9, no fewer than thirteen different working beams with central planes all passing through the same axis 6 are available by activating different groups of six adjacent transducers.

The described working beams have a strongly converging character and may be of only limited use. Since the ultrasonic waves from each relatively narrow transducer diverge laterally in the shoe, to an extent depending upon the relation between the wavelength in the shoe corresponding to the ultrasonic frequency and the transducer width, the working beam in the shoe may be given a non-converging character by arranging that transducers away from the centre pair of each group of six, when activated to deliver pulses of ultrasonic waves corresponding to those delivered by said centre pair, are activated to do so with approproate delays. Such delays may readily be imposed by electronic means in the lines via which the transducers are stimulated.Most ultrasonic inspections are carried out with probes which, when used for transmitting, direct onto the workpiece surface through the probe working face an ultrasonic working beam of plane pulse front.

With reference to Figure 7, which reproduces the part of Figure 6 with transducers 9/1 to 9/7 on an exaggeratedly curved shoe face 5, if pulses of ultrasonic waves in the shoe are generated by the two transducers 9/3 and 9/4 in synchronism with one another and if corresponding pulses are delivered by the two transducers 9/2 and 9/5 synchronously with one another but with an appropriate delay in relation to the pulses generated by the transducers 9/3 and 9/4 and moreover corresponding pulses are delivered by the two transducers 9/1 and 9/6 synchro nously with one another but with an appropriate longer delay in relation to the pulses delivered by the transducers 9/3 and 9/4, the group of six adjacent transducers 9/1 to 9/6 will generate a non-coverging working beam in the shoe of plane pulse front 122 advancing in the direction of the arrows 123 with central plane represented by the line 124 which passes through the axis 6 in the shoe working face 3.

Again, thirteen different working beams centred on different central planes, all passing through the same axis 6, are available by activating different groups of six adjacent transducers.

If desired, by using delays in the manner referred to, but of smaller values than are appropriate to result in beams in the shoe of plane pulse fronts, ultrasonic beams may be produced in the shoe which have a converging character but not a strongly converging character, such that in the workpiece each corresponding ultrasonic beam may tend to converge towards a linear region in the workpiece interior, the expectation being that any flaws in any of the regions so focused on will yield stronger echoes than otherwise.

With reference to Figure 8, which again reproduces the part of Figure 6 with transducers 9/1 to 9/7 on an exaggeratedly curved shoe face 5, by the activation of the group of transducers 9/1 to 9/6 in the manner described with reference to Figure 7 but with smaller values of the delays mentioned, a slightly converging working beam may be generated in the shoe of pulse front 222 advancing in the direction of the arrows 223 with central plane, represented by the line 224, which passes through the axis 6 in the shoe working face 3. As before, thirteen different working beams with different central planes, all passing through the same axis 6, are available by activating different groups of six adjacent transducers.

Aworkpiece interior may be ultrasonically examined by operating a probe of the character described to transmit an ultrasonic beam into the workpiece, varying the groups of adjacenttransducers activated thereby the change the angle of the working beam in the shoe and thereby the angle of the working beam in the workpiece and giving the probe a systematic scanning movement over the workpiece surface, in the pattern of, for example, a raster. Arrangements are made to detect echo waves from a flaw when they return to the probe or to a different probe used only for receiving and moved simultaneously over the workpiece surface with the transmitting probe.Usually in a large industrial workshop information as to the occurrence of echoes, their strengths and their travel times from flaws will be recorded and interpreted by a data processing system simultaneously recording also the probe position as it is mechanically systematically scanned over the workpiece surface and information gained from prior experiments as to the angle of ultrasonic beam in the workpiece associated with each transducer group will also have been supplied to the data processing system in order that it may identify a flaw detected with the aid of an angled beam when the probe is in one position in the scan with the same flaw detected with the aid of a differently angled beam when the probe is in another position in the scan.

Prior experiments will have also given information as to the generation by the employment of some transducer groups of compression wave beams in the workpiece as well as shear wave beams and information enabling signals from any echo pulses due to compression wave beams to be gated-out, or, alternatively, information from such signals collated with the remainder of the gained data.

With reference to Figure 9, an ultrasonic inspection to detect the presence of flaws in or in the neighbourhood of a butt weld 25 between two plates 26 is commonly made by activating a probe in the transmitting sense while moving it over a plate face in a systematic raster scanning path such as 27 extending along the length of the weld and to one side of the weld, the proceeding being then repeated to the other side of the weld.The probe described, assumed operating at a position Ato supply plane pulse front beams, may, when one group of six adjacent transducers is activated, deliver a beam All which impinges directly on a flaw 28 whereby the latter is detected and it may, when another group of six adjacent transducers is activated, effect detection of the same flaw 28 by means of a beam A/2 which impinges on the flaw indirectly after an internal reflection from the opposite face of the appropriate plate 26. When the probe is at another position B on the plate, the flaw 28 is capable of being impinged on directly and indirectly by differently angled beams B/1 and B/2 from the probe; similarly, the flaw 28 can receive directly and indirectly other angled beams C/1 and C/2 when the probe is in position C.Thus the one probe is adapted to achieve multiple detections of any flaw. The flaw, moreover, receives inspecting beams from a multiplicity of angles during the ultrasonic examination.

The thirteen differently angled working beams in the shoe which are achievable by activating different groups of six adjacent transducers have their central planes only 4.4 apart.

As the probe is moved over the workpiece surface, preferably a sequence of different groups of six adjacent transducers is repetitively activated.

However, if the sequence comprises all thirteen possible groups the repetition frequency would be relatively low and during an initial scanning movement of the probe over the workpiece it may be preferred to employ a sequence of only some groups, for example, the five-group sequence comprising the group 9/1 to 9/6, the group 9/3 to 9/8, the group 9/5 to 9/10, the group 9/11 to 9/16 and the group 9/13 to 9/18. After such initial scanning movement, if a flaw has been detected at any locality, such flaw may be further investigated by placing the probe at the appropriate area of the workpiece surface and moving it over said area while activating in sequence all thirteen possible groups of six adjacent transducers.

Most ultrasonic shear wave inspections of workpiece interior regions where flaws are more likly employ plane pulse front beams to search through those regions and there has been described with reference to Figure 7 how plane pulse front working beams may be generated by the appropriate activations of groups of six adjacent transducers. It may frequently be safely assumed that the echo waves from a flaw in such a region arrive back at the probe position with an approximation to a plane pulse front. It will be appreciated from Figure 7, if one mentally reverses the arrows 123, that a plane pulse front in the shoe 2 approaching the group of six adjacent transducers 9/1 to 9/6 will not arrive at all the transducers simultaneously.If the probe is used for echo-wave-detecting the responses of the three pairs of transducers 9/1 and 9/6, 9/2 and 9/5, 9/3 and 9/4 will be spread out in time; if appropriate delays are imposed by electronic means in the signaltransmitting lines from the first two of the said three pairs of transducers the responses from the three pairs of transducers may be brought together in time, so that therefrom there may be formed a joint signal from which the timing of the echo-wave reception and the echo magnitude may be more effectively determined.

The same expedient, but with appropriately different values of the delays, may be employed if an echo-wave arrives at the transducers with a known degree of divergence, as from a region focused upon by means of a converging pulse front generated in the manner described with reference to Figure 8.

For the switching from the employment of one group of six transducers to another group in a repeated predetermined sequence, as well as for the allowance of times for the same group of transducers as transmits waves also to receive corresponding echo waves, a monostable and a ring counter may be used. With reference to Figure 10, a pulse generator and receiver 41 is arranged for generating pulses at a repetition frequency of, say, one kilohertz of ultrasonic waves of a frequency of, say, five megahertz. The pulses after being given a sharper leading edge by a pulse shaper 42 are led to a transmitter 43, simultaneously through electronic delay means 44 to a transmitter 45 and simul taneouslythrough electronic delay means 46to a transmitter 47.The transmitters 43,45 and 47 convey the pulses they receive into respective lines 43A, 45A and 47Awhich lead into a selective switching unit 48. The pulses from the pulse shaper 42 are also led to a monostable 49, the output of which leads to a ring counter 50 the outputs of which also lead into the unit 48. Eighteen lines 51 provide for the leading of pulses from the unit 48 to activate the respective transducers of the transducer array 1 mounted on the shoe 2.

The selective switching unit 48 is arranged for the transmitting of pulses received through the lines 43A, 45A and 47A to only one group of six adjacent transducers of the array 1 at a time but which particular group of transducers is selected for the purpose depends upon which of the outputs from the ring counter 50 is activated. For example, and as represented, the ring counter 50 may have five outputs, one of which, when activated, selects the group of adjacent transducers 9/1 to 9/6, another of which, when activated, selects the group 9/3 to 9/8, a third selects the group 9/5 to 9/10, a fourth selects the group 9/11 to 9/16 and the fifth selects the group 9/13 to 9/18. The unit 48 is also so arranged that, within each selected group of six transducers, the pulses in the line 43A activate the central transducer pair, the pulses in the line 45A activate the two transducers one at each side of the central pair and the pulses in the line 47A activate the two outer transducers of the group of six.

The monostable 49 is arranged to be triggered by the reception of a pulse to is unstable state and upon its return to its stable state to trigger the ring counter to select the next transducer group in the sequence.

If the monostable's period of instability if less than the periodic time of the pulses, a fresh transducer group is selected before every fresh pulse is gener ated; with the 1 kilohertz pulse repetition frequency the probe will be switched through the range of five beam angles 200 times per second. If the monostable's period of instability is longer than the periodic time of the pules, and if it does not respond to pulses received while it is still in its unstable state, a fresh transducer group is selected only after a number of pulses has been generated.

The line 43A, which will carry a signal response if the transducers to which it is connected at the time receive an echo wave, is connected to a line 43B which leads through buffer amplifiers 51 and 52 back to the pulse generator and receiver 41. The line 45A is connected to a line 45B which leads back to the pulse generator and receiver 41 via a buffer amplifier 53, an electronic delay means 54 and a buffer amplifier 55 and the line 47A is connected to a line 47B leading to the pulse generator and receiver 41 through a buffer amplifier 56, an electronic delay means 57 and a buffer amplifier 58.

In operation, while, as is assumed, the probe is traversed in a scanning path over a workpiece surface, the pulse generating and receiving unit 41 generates ultrasonic waves in pulses which are applied, in a repeated sequence determined by the ring counter 50, to groups of six adjacent transducers of the array 1 causing them to deliver ultrasonic beams, with central planes passing through the axis 6, of plane pulse front, or if desired a pulse front slightly converging. Echo waves arising from a flaw find, on returning to the probe, the same group of transducers selected as that which generated the pulse or pulses from which they derive and the transducer responses thereto pass through the lines 43A, 43B, 51 and 52, through the lines 45A, 45B, 53, 54 and 55 and through the lines 47A, 47B, 56,57 and 58 to yield a joint signal in the unit 41 which will be both timed and evaluated in magnitude.

Claims (10)

1. An ultrasonic probe for application to a surface of a workpiece to be examined by ultrasonic waves, comprising transducer means in contact with a shoe having a working face adapted to the workpiece surface, wherein a plurality of transducers are arrayed on the shoe along an arc of a cylinder of which the axis lies in the working face of the shoe and are adapted when employed in groups of adjacent transducers, some at least of which groups may overlap one another, to generate or to detect respective working beams of ultrasonic waves in the shoe the axes of which beams are respectively differently angled and all pass through the cylinder axis region of the shoe working face.

2. A probe as claimed in Claim 1, wherein the transducer array consists of relatively narrow transducers mounted side by side.

3. A probe as claimed in Claim 2, wherein the transducers are mounted on a curved cylindrical face formed on the shoe.

4. A probe as claimed in Claim 3, the transducers being piezo-electric transducers, wherein the array of mounted transducers has been formed by mounting on the curved cylindrical face of the shoe a single slab of piezo-electric ceramic material having an alectrode sheet on each face thereof and thereafter excising the outer electrode sheet in lines.

5. A probe as claimed in Claim 5, wherein the excising of the outer electrode sheet in lines is achieved by cutting grooves which extend at least part of the way through the thickness of the slab of piezo-electric material.

6. Apparatus for activating in the beam generating sense by the application thereto of pulses of ultrasonic waves an ultrasonic probe as claimed in any of Claims 1 to 6, incuding electronic delay means arranged to supply to transducers away from the centre of each group of adjacent transducers to be activated pulses so delayed in relation to pulses applied to the transducer or transducers at the centre of the group as to effect the generation of a plane pulse front working beam in the shoe or a beam of only slightly converging pulse front character.

7. Apparatus for activating in the beam generating sense by the application thereto of pulses of ultrasonic waves an ultrasonic probe as claimed in any of Claims 1 to 6, including a ring counter arranged for switching from the employment of one group of adjacent transducers to another group of adjacent transducers in a repeated sequence of a plurality of groups and a monostable arranged for determining according to the period of its unstable state the number of pulses supplied to each group of transducers before the switching to the next group in the sequence.

8. Apparatus for detecting beams of pulses of ultrasonic waves received from a workpiece by an ultrasonic probe as claimed in any of Claims 1 to 5, and traversing the shoe thereof to a group of adjacent transducers arranged to be responsive, including electronic delay means arranged to impose on signal responses from transducers away from the centre of the group such delays in relation to the signal response or responses of the transducer or transducers at the centre of the group as will bring together in time the responses of all the transducers of the group.

9. Ultrasonic probes substantially as hereinbefore described with reference to Figures 1 to 4 and 10 of the accompanying drawings.

10. Apparatus both for activating a probe as claimed in Claim 1 in the beam generating sense and for detecting beams of pulses received by such probe, substantially as hereinbefore described with reference to Figure 10 of the accompanying drawings.