Device and method for testing a test object

Abstract

The invention comprises a device (10) for testing a test object (40), comprising an excitation system (13) for generating broadband ultrasound pulses (12) in the test object, a detection system (20) for detecting ultrasound waves (21), which are generated through the broadband ultrasound pulses (12) in the test object (40) and emitted by the test object (40). The device (10) comprises a processing unit (30) for processing the detected ultrasound waves (21), while the excitation system (13) being one of a thermoacoustic emitter or a pulsed laser and the detection system (20) is a broadband detection system. The excitation system (13) comprises a modulator (11) for modulating the broadband ultrasound pulses (12). Furthermore, the invention comprises a method for testing a test object.

Claims

1. A device for testing a test object, the device comprising: an excitation system for generating broadband ultrasound pulses in the test object; a detection system for detecting ultrasound waves, said detection system being a broadband detection system, and said broadband detection system comprising at least a first membrane-free optical microphone with two partially reflecting non-movable mirrors for reflecting a laser beam in a cavity of the two partially reflecting mirrors, the ultrasound waves being generated through the broadband ultrasound pulses in the test object and emitted by the test object; a processing unit for processing the detected ultrasound waves; and an excitation head connected through a fibre bundle with the excitation system, wherein fibres of the fibre bundle are selectable for generating a specific spatial excitation pattern, the excitation system being a pulsed laser and comprising a modulator for modulating the broadband ultrasound pulses.

2. The device according to claim 1, wherein the processing unit is configured to execute a correlation between a reference signal and the emitted ultrasound waves to calculate a correlation index.

3. The device according to claim 1, wherein the broadband detection system comprises a two-dimensional array of membrane-free optical microphones.

4. The device according to claim 3, wherein the broadband detection system comprises at least a second membrane-free optical microphone, said first membrane-free optical microphone and said second membrane-free optical microphone being arranged non-parallel.

5. The device according to claim 1, wherein the fibres of the fibre bundle are arranged in the excitation head in a two-dimensional array.

6. The device according to claim 1, wherein the broadband detection system and the excitation system are arranged such that a measurement in pitch-catch mode can be done or the broadband detection system and the excitation system are arranged such that a measurement in pulse-echo mode can be done.

7. The device according to claim 6, wherein the broadband detection system is arranged in the excitation head, and the fibre bundle is led through the broadband detection system.

8. The device according to claim 1, wherein the device comprises a housing element shielding at least the broadband detection system, and wherein the housing element comprises a separation element for separating the excitation system from the broadband detection.

9. The device according to claim 1, wherein either the excitation system or the broadband detection system is moveable or both are moveable on the test object.

10. A method for testing a test object, the method comprising: generating broadband ultrasound pulses in the test object with an excitation system, wherein said excitation system is modulated; detecting ultrasound waves which are generated through the broadband ultrasound pulses in the test object and emitted by the test object, the ultrasound waves being detected with a broadband detection system comprising at least a first membrane-free optical microphone with two partially reflecting non-movable mirrors, where a laser beam is reflected in a cavity of the two partially reflecting mirrors; processing the detected ultrasound waves with a processing unit; and selecting fibres of a fibre bundle of an excitation head for generating a specific spatial excitation pattern.

11. The method according to claim 10, wherein the detected ultrasound waves are correlated with a reference signal and a correlation index is calculated.

12. The method according to claim 11, wherein the method steps according to claim 9 are done for a first measuring point and repeated for at least a second measuring point, a correlation index for each measuring point is calculated, and each correlation index is plotted on a display.

13. The method according to claim 11, wherein the broadband ultrasound pulses as well as the ultrasound waves are each transferred into a spectral signal, said spectral signals being correlated with each other for providing a correlation index.

14. The method according to claim 11, wherein the said reference signal being the generated ultrasound pulses or data obtained from a reference object or a measured ultrasound signal at a reference point of the test object.

15. The method according to claim 10, wherein the broadband ultrasound pulses are generated in the form of a code sequence.

16. The method according to claim 10, wherein the excitation of the broadband ultrasound pulses is executed in a two-dimensional array for providing a spatial pattern of ultrasound pulses.

17. The method according to claim 10, wherein the broadband ultrasound pulses in the test object or the ultrasound waves which are generated through the broadband ultrasound pulses are transmitted at least partially through a contact fluid.

18. The method according to claim 10, wherein the method is executed while the excitation system and/or the broadband detection system is moved above the test object.

19. The method according to claim 10, wherein the ultrasound waves are detected in a two-dimensional array.

20. The method according to claim 10, wherein the method is executed while the broadband detection system is moved above the test object.

21. A device for testing a test object, the device comprising: an excitation system for generating broadband ultrasound pulses in the test object; a detection system for detecting ultrasound waves, said detection system being a broadband detection system, and said broadband detection system comprising at least a first membrane-free optical microphone with two partially reflecting non-movable mirrors for reflecting a laser beam in a cavity of the two partially reflecting mirrors, the ultrasound waves being generated through the broadband ultrasound pulses in the test object and emitted by the test object; a processing unit for processing the detected ultrasound waves; and an excitation head connected through a fibre bundle with the excitation system, wherein a set of plural fibres of the fibre bundle is selectable for generating a specific spatial excitation pattern, the excitation system being a pulsed laser and comprising a modulator for modulating the broadband ultrasound pulses, wherein the excitation system emits a temporal code, consisting of a defined number of pulses, with a defined length L, L, L, L per pulse and a defined pause P, P between each pulse and a defined pulse shape.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: A first embodiment of a device for testing a test object;

(2) FIG. 2: A second embodiment of a device for testing a test object

(3) FIG. 3: A temporal code sequence

(4) FIG. 4: A fibre bundle with several fibres

(5) FIG. 5: A third embodiment of a device for testing a test object

(6) FIG. 6: A forth embodiment of a device for testing a test object

(7) FIG. 7: A fifth embodiment of a device for testing a test object

(8) FIG. 8: A sixth embodiment of a device for testing a test object

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(9) FIG. 1 shows a first embodiment of a device 10 for testing a test object 40. The device 10 comprises a pulsed laser as an excitation system 13 and an optical microphone as detection system 20. The excitation system 13 and the detection system 20 are arranged in transmission mode. The excitation system 13 comprises a modulator 11 for modulating the excitation wave 12 and subsequently the broadband ultrasound pulses 12. The modulator 11 is able to temporally and/or spatially modulate the excitation wave 12 and/or the broadband ultrasound pulses 12. A test object is thus arranged between said excitation system 13 and said detection system 20. The detection system 20 and the excitation system 13 having an electrical connection to a processing unit 30, i.e. they are connected through wires with the processing unit 30. The processing unit 30 is electrically connected through wires with a display 35.

(10) Within the test object 40 a material defect 41 is shown. Said material defect 41 can e.g. be caused due to delamination, porosities or inhomogeneous material distributions.

(11) The device 10 of FIG. 1 works as follows (one basic working principle):

(12) The excitation system 13 emits an exaction wave 12in case a pulsed laser, a pulsed laser beam is emittedinto a sound propagating medium which in this case is air. The pulsed laser beam hits a first surface 42 of the test object 40 and generates a broadband ultrasound pulse 12 due to the thermoelastic effect or due to rapid compression and relaxation following surface ablation. The broadband ultrasound pulse 12 propagates through the test object 40 and can be influenced by the material defect 41 in the test object 40. Induced by interfering with the material defect 41 or zone of interest, the broadband ultrasound pulse 12 generates an ultrasound wave 21 while propagating through the test object 40 to a second surface 43 of the test object 40. The ultrasound wave 21 exits the test object 40 at the second surface 43 and enters into the surrounding sound propagating medium. Afterwards, the ultrasound wave 21 is detected by the detection system 20, which in case is a membrane-free optical microphone. In this case, the membrane-free optical microphone is an optical microphone as described in EP 3 173 781 A1.

(13) Therefore, the optical microphone detects the alteration of the density of the sound propagating medium which is caused through the ultrasonic wave 21.

(14) In an alternative embodiment, the sound propagating medium can be e.g. inert gas or a liquid.

(15) The processing unit 30 consists of hardware and software and is used to trigger excitation system 13 and matches the signal excitation and the signal detection and the modulation. In detail, the hardware of the processing unit 30 comprises a signal generator and a signal-analysis hardware with a signal processing unit.

(16) The processing unit 30 is able to examine correlations, based on the measured data. This correlation can be based on a temporal, spatial, or spectral data analysis or signal analysis. The reference signal, used for correlation can be 1) the excitation signal itself; 2) scan data of a different sample, which can be C-Scan data or a time signal, where measured data of a Sample A are correlated with a Sample B; or 3) an ultrasound response, measured with the detection device 20 where the excitation system 13 is triggered by the processing unit 30 with a defined code sequence (see for example FIG. 3). The excitation system 13 is subsequently sending a first excitation wave 12, which generating a first ultrasound pulse 12 according to the code sequence onto a first measuring point (which is considered as having no material defects) of the test object 40.

(17) Regarding point 3) of the before mentioned correlation options, the correlation is performed as in the following described:

(18) The ultrasound response of the test object 40, namely the generated ultrasound wave 41 is saved as a reference signal.

(19) A time signal measured on each point of the test object is correlated with the reference signal to increase SNR.

(20) To perform a spectral analysis, the spectrum of the ultrasound response recorded at said measuring point is used as reference signal. This reference signal can be correlated with a spectrum measured at each point of the test object. These steps can be repeated for a plurality of measuring points. Signal shape differences, both in temporal and spatial direction lead to a lower correlation index. A lower correlation index indicates differences between the reference signal and the compared signal. If the reference signal is supposed to represent a healthy structure a low correlation index indicates a defect.

(21) In case the broadband ultrasound pulses 12 are generated in an array for example with an excitation head, the measurements of a plurality of measurement points can be done simultaneously and preferably also detected in an array. Thus, the process is shortened and the evaluation of a plurality of signals can be made simultaneously.

(22) The display 35 can be part of a computer, which is used for data recording and further analysis. Furthermore, the processing unit 30 can be part of the computer.

(23) FIG. 2 shows a second embodiment of a device 100 for testing a test object 140. The device 100 comprises a pulsed laser as an excitation system 113 emitting an excitation wave 112 and an optical microphone as detection system 120. The excitation system 113 and the detection system 120 are arranged side by side in pitch-catch mode on one side of a test object. The detection system 120 and the excitation system 113 are electrically connected to a processing unit 130. The processing unit 130 is electrically connected through wires with a display 135.

(24) Alternatively, the excitation system 113 and the detection system 120 can be arranged in pulse-echo mode which means, that the detection system 120 can be directly placed in the optical path of the excitation system 113. In this embodiment ultrasound waves 122 reflected from the first surface 142 of the test object 140 as well as ultrasound waves 121 influenced by a material defect 141 are detectable in the detection system 120. The detection system 120 and the excitation system 113 having an electrical connection to a processing unit 130, i.e. they are connected through wires with the processing unit 130. The processing unit 130 is electrically connected through wiresor by wireless technologywith a display 135.

(25) The working principle and the alternatives of the device 100 as explained to FIG. 1 are applicable to the device 100 of FIG. 2. The difference lies in the fact, that in the second embodiment according to FIG. 2 at least some of the detected ultrasound waves 121 are reflected and not transmitted as in the first embodiment according to FIG. 1.

(26) The ultrasound wave 121 propagates through the test object 140 and can be influenced by the material defect 141 in the test object 140. Induced by interfering with the material defect 141, namely reflection, the ultrasound wave 121 is altered while propagating through the test object 140 to a second surface 143 of the test object 140. The altered ultrasound wave 121 exits the test object 140 at the first surface 142 again and enters into the surrounding sound propagating medium. Afterwards, the ultrasound wave 121 is detected by the detection system 120 which in case is membrane-free optical microphone. In this case, the membrane-free optical microphone is an optical microphone as described in EP 3 173 781 A1.

(27) FIG. 3 shows a possible temporal code, emitted by the excitation system 13 (see FIGS. 1 and 2). This code consists of a defined number of pulses, with a defined length L, L, L, L per pulse and a defined pause P, P between each pulse and a defined pulse shape.

(28) The used pulse lengths are variable. The most significant improvement of the signal-to-noise ration can be observed if the chosen pulse length is in the same magnitude as the expected range of the signal frequency. The signal frequency can be proportional to the inverse pulse length, i.e., a short pulse will lead to a broad frequency signal, whereas a long pulse will lead to a signal containing lower frequencies in the first place.

(29) The pulse sequence can consist of a defined number of pulses, each having the same pulse length or with different pulse lengths. The pauses between the pulses can have a constant duration for each pause or alternating durations.

(30) FIG. 4 shows a fibre bundle 16 with several single fibres 16 applicable to the above described embodiments of the device 10, 100 (FIG. 1 or FIG. 2) for realizing a spatially encoded signal. The spatial encoded signal is generated by the modulator 11, 111, while some of the single fibres 16 are illuminated with a laser beam (dark fibres) and some of the single fibres 16 are not illuminated (bride fibres). The fibre bundle 16 is directed to the surface of a test object (not shown) and is used to generate a specific spatial excitation pattern.

(31) FIG. 5 shows a third embodiment of a device 200 for testing a test object 240, which is basically described in the above embodiments (FIG. 1 or FIG. 2). In addition, the basic working principle of the device 200 is described in especially in FIG. 2 to FIG. 4. The excitation system 213 generates a laser pulse as excitation wave 212. The optical device 215, e.g. a collimator, redirects the laser beam 214 into each single fibre 216 of the fibre bundle 216. The fibre bundle 216 is lead through a medical device 217, which can be for example a laparoscopic, endoscopic or thoracoscopic device. In addition, the laser beam 214 is redirected to several single fibres 2016. The broadband ultrasound pulse 212 is generated by the laser beam 214 and is coupled into the test object 240, preferably using a coupling agent 218, e.g. a liquid, and generates a broadband ultrasound pulse 212. Within the test object 240, the generated broadband ultrasound pulse 212 is absorbed by an absorber 241 which is generating an ultrasound wave 221 due to thermo-elastic expansion. This ultrasound wave 221 is reflected and detected with the detection device 240. The detected signal is displayed in the display 235 of the computer. The computer comprises the aforementioned processing unit in the computer.

(32) FIG. 6 shows a fourth embodiment of the device 250 for testing the test object 240, which describes basically a combination of some of the features disclosed embodiments 200 (FIG. 5) and the above described working principles. In addition, the functionality of the device 250 is described basically in FIG. 2 to FIG. 5. The excitation system 243 is a laser, which emits a pulsed laser beam 244. The pulsed laser beam 244 is sent to a galvanometer mirror system 245 an afterword to the laser bundle 216. The laser bundle 216 is directed to the surface of the test object 240. Hereby, broadband ultrasound pulses are generated at different locations, distributed over the surface of the test object 240 (as described in FIG. 5). Due to a potentially uneven distribution of the defect inside the test object 240, the generated ultrasound waves from the test object 240 will depend on the location of the ultrasound pulse excitation. Scanning the laser fibre bundle 216, e.g. by means of a galvanometer mirror system 245, enables a fast testing device 250 without the need to physically move the testing device over the surface of the test object 240.

(33) This embodiment allows illuminating a specific spatial pattern on the test object 240 at once, simultaneously. The laser fibre bundle 216, e.g., consist of 10.000 fibres. A selected number of these fibres may be carrying a laser pulse at the same time (see FIG. 4), hereby generating a specific spatial excitation pattern. This pattern may stay the same for subsequent laser pulses, or it may change.

(34) FIG. 7 shows a fifth embodiment of a device 300 for testing a test object 340, which describes basically a combination of some of the features disclosed embodiments 10, 100, 200, 250 (FIG. 1 to FIG. 6) and the above described working principles. In addition, the functionality of the device 300 is described basically in FIG. 1 to FIG. 6. The excitation system 313 generates a laser pulse as excitation wave 312, which finally generates a broadband ultrasound pulse 312 and is either absorbed and converted into an ultrasound wave 321 at the first surface 342 of the test object 340 or by an absorber 341 within the test object 340. The housing element 317 shields the surrounding area from the reflected laser light. The housing element 317 comprises an interlock element 319 connected to the test object 340 to guarantee contact to the test object 340 by an electric feedback loop connection 318 to the processing unit 330. If the housing element 317 is disconnected with the test object 340 a signal to the processing unit 330 stops the triggering of the excitation system 313. The detected signal is displayed in the display 335 of the computer. Said interlock element 319 may comprise a distance measurement sensor, like a laser distance sensor, for measuring the distance between said test object 340 and said housing element 317.

(35) FIG. 8 shows a sixth embodiment of a device 400 for testing a test object 440, which describes basically a further embodiment of the above described embodiments (FIG. 5 to FIG. 7). In addition, the functionality of the device 400 is described basically in FIG. 2 to FIG. 7 and the above described working principles. The excitation system 413 as well as the broadband detection system 420 are placed in the housing element 417 and are connected to the processing unit 430 via a fibre bundle 416. The housing element 417 comprises a separating element 443, e.g. a wall, for separating the excitation system from the broadband detection system. The excitation system 413 generates a laser pulse as excitation wave 412, which generates and afterwards propagates as ultrasound pulse 412. The ultrasound pulse 412 is either absorbed and converted into an ultrasound wave 421 at the first surface 442 of the test object 440 or by an absorber 441 within the test object 440. The separating element 417 prevents parasitic waves, e.g. structure-borne waves or air-borne waves from the first surface 442, to reach the broadband detection system 420. The housing element 417 comprises a contact element 419, like a sliding contact, which is connected to the test object 440 to guarantee contact to the test object 440 by an electric feedback loop connection 418 to the processing unit 430. If the housing element 417 is moved away from the test object 440 a signal to the processing unit 440 stops the triggering of the excitation system 413. The detected signal is displayed in the display 435 of the computer. Said contact element or interlock element 419 may comprise a distance measurement sensor, like a laser distance sensor, for measuring the distance between said test object 340 and said housing element 317.

(36) In the embodiments of the device 10, 100, 200, 250, 300, 400 the pulsed laser is replaceable with a thermoacoustic transmitter. The thermoacoustic transmitter generates ultrasound pulses by a short time heating of a metallized glass surface and thereby induced moving of the surrounding gas molecules. The thermoacoustic transmitter emits broadband Dirac-shaped short broadband ultrasound pulses with a signal duration minimum of 1 s. The emitted pulses can be single pulses or a pulse sequence. Those pulses propagate through the gas into the test object. The following signal processing is according to the description of FIG. 1 to FIG. 8.

(37) The claims and the reference list are part of the disclosure.

LIST OF REFERENCE SIGNS

(38) 10 device 11 modulator 12 excitation wave 12 broadband ultrasound pulse 13 excitation system 16 single fibres 16 fibre bundle 20 detection system 21 ultrasound waves 30 processing unit 35 display 40 test object 41 material defect 42 first surface 43 second surface 100 device 111 modulator 112 excitation wave 112 broadband ultrasound pulse 113 excitation system 120 detection system 121 ultrasound waves 122 reflected ultrasound waves 130 processing unit 135 display 140 test object 141 material defect 142 first surface 143 second surface 200 device 212 excitation wave 212 broadband ultrasound pulse 213 excitation system 214 laser beam 215 optical device 216 single fibres 216 fibre bundle 217 medical device 218 coupling agent 220 detection system 221 ultrasound waves 235 display 240 test object 241 absorber 250 device 243 excitation system 244 laser beam 245 galvanometer mirror system 246 fibre bundle 300 device 312 excitation wave 312 broadband ultrasound pulse 313 excitation system 317 housing element 318 feedback loop connection 319 interlock element 320 detection system 321 ultrasound waves 330 processing unit 335 display 340 test object 341 absorber 342 first surface 400 device 412 excitation wave 412 broadband ultrasound pulse 413 excitation system 416 fibre bundle 417 housing element 418 feedback loop connection 419 interlock element 420 detection system 421 ultrasound waves 430 processing unit 435 display 440 test object 441 absorber 442 first surface 443 separating element L-L different lengths per pulse P, P different pauses between each pulse