WO2010012809A2 - Method and device for the air-coupled ultrasonic non-destructive testing of a structure - Google Patents

Method and device for the air-coupled ultrasonic non-destructive testing of a structure Download PDF

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Publication number
WO2010012809A2
WO2010012809A2 PCT/EP2009/059888 EP2009059888W WO2010012809A2 WO 2010012809 A2 WO2010012809 A2 WO 2010012809A2 EP 2009059888 W EP2009059888 W EP 2009059888W WO 2010012809 A2 WO2010012809 A2 WO 2010012809A2
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WO
WIPO (PCT)
Prior art keywords
ultrasonic waves
probe
frequency band
frequency
band
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PCT/EP2009/059888
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French (fr)
Inventor
Nicolas Colin
Didier Simonet
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European Aeronautic Defence And Space Company Eads France
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Application filed by European Aeronautic Defence And Space Company Eads France filed Critical European Aeronautic Defence And Space Company Eads France
Publication of WO2010012809A2 publication Critical patent/WO2010012809A2/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/34—Generating the ultrasonic, sonic or infrasonic waves, e.g. electronic circuits specially adapted therefor
    • G01N29/348—Generating the ultrasonic, sonic or infrasonic waves, e.g. electronic circuits specially adapted therefor with frequency characteristics, e.g. single frequency signals, chirp signals
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/36—Detecting the response signal, e.g. electronic circuits specially adapted therefor
    • G01N29/42—Detecting the response signal, e.g. electronic circuits specially adapted therefor by frequency filtering or by tuning to resonant frequency
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/023—Solids
    • G01N2291/0231—Composite or layered materials
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/10—Number of transducers
    • G01N2291/104—Number of transducers two or more emitters, one receiver
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/26—Scanned objects
    • G01N2291/269—Various geometry objects
    • G01N2291/2694—Wings or other aircraft parts

Definitions

  • the present invention belongs to the field of non-destructive ultrasonic testing of structures. More particularly, the present invention relates to a method and device for non-destructive ultrasonic air-coupled control.
  • the non-destructive control methods make it possible to control a structure for detecting defects on the surface and / or in the depth of said structure without degrading it. These methods are used in a production phase of the structure to check the quality of manufacture and / or in a maintenance phase to check if defects have appeared.
  • non-destructive ultrasonic testing methods ultrasonic acoustic waves are emitted in the direction of the structure to be monitored, and a portion of the emitted ultrasonic waves is received after propagation in said structure. Characteristics (amplitude, flight time, etc.) of the received waves are used to evaluate structural characteristics of the inspected structure.
  • the ultrasonic non-destructive testing methods most often use a liquid coupling medium, which is a good conductor of ultrasonic waves, for example water or gel, between one or more ultrasonic probes and the structure, in order to produce, in particular, a acoustic impedance matching between said probes and said structure.
  • a liquid coupling medium which is a good conductor of ultrasonic waves, for example water or gel
  • the presence of the liquid coupling medium between the probes and the structure is for example provided by partial or total immersion of the structure in said medium, or by continuous supply of said medium for example in the case of a coupling by water jets.
  • a disadvantage of non-destructive liquid coupling methods lies in the fact that they are relatively disadvantageous to implement by the very fact of the implementation of tanks or liquid supply devices, and in the fact that they are not suitable for controlling certain types of structures.
  • one possible solution consists in implementing non-destructive ultrasonic air-coupling control methods for which the coupling medium is gaseous, typically ambient air.
  • Such methods use a device comprising a transmitting probe for emitting ultrasonic waves and a receiving probe for receiving waves, said probes not being in contact with the structure.
  • the probes have very similar spectral characteristics in order to avoid introducing losses related to a filtering by the receiving probe of the ultrasonic waves emitted by the emitting probe, that is to say to limit as much as possible the losses inherent in the transmission / reception chain.
  • this configuration imposes very strong constraints on the manufacture of the probes, and it is not uncommon for the emission transducer and the reception transducer to be made not only according to the same technology, for example piezoelectric ceramics, but also in the same block of the ceramic material, to have spectral characteristics as close as possible.
  • the spectral characteristics of the probes evolve independently over time, and spectral characteristics initially almost identical may no longer be after a certain time, with the effect of introducing significant losses by filtering the ultrasonic waves by the receiving probe.
  • the second probe if a probe is damaged, the second probe generally becomes unusable in association with another probe that will not be matched.
  • the level of the ultrasonic waves measured is then low because of the frequency selectivity of the receiving probe, especially in the case of a narrow-band receiving probe.
  • the present invention proposes to solve the aforementioned problems by introducing a device for non-destructive ultrasonic air-coupling control of a structure, comprising at least one emitting probe, for the emission of ultrasonic waves towards the structure and the least one receiving probe, for the reception of ultrasonic waves after propagation in the structure.
  • the at least one emitter probe and the at least one receiving probe physically disjoint, have frequency bands respectively of emission and reception of different widths, the frequency band of emission of the at least one a transmitting probe being of width less than the width of the frequency band of reception of the at least one receiving probe, and included in the frequency band of reception of the at least one receiving probe.
  • the at least one emitter probe comprises at least one transducer made of a composite piezoelectric ceramic or piezoelectric material
  • the at least one receiving probe comprises at least one electro-capacitive transducer, preferably comprising at least one membrane of material polymer or copolymer.
  • the device comprises, in a particular embodiment, a plurality of probes transmitting transmission frequency bands that are different and narrow with respect to the reception frequency band of the at least one receiver probe. and included in said frequency reception band.
  • the device comprises:
  • the invention also relates to a method of non-destructive ultrasonic air-coupling control in which ultrasonic waves are emitted in the direction of the structure, ultrasonic waves are measured after propagation in the structure, and structural characteristics of the structure are evaluated. structure from characteristics of the measured ultrasonic waves.
  • the aerial ultrasonic waves are emitted on a frequency transmission band, and the aerial ultrasonic waves returned by the structure are measured on a wide reception frequency band with respect to the frequency transmission band.
  • a signal obtained is filtered by measuring the ultrasonic waves returned by the structure with a frequency band filter adapted to the frequency band of emission on which the waves have been transmitted. aerial ultrasound.
  • ultrasound waves are emitted over a plurality of different narrow emission frequency bands, and a signal obtained is filtered by measuring the ultrasonic waves returned by the structure with frequency band filters adapted to frequency transmission bands on which the ultrasonic air waves have been emitted.
  • FIGS. 1a and 1b are diagrammatic representations of a first embodiment of a device according to the invention, according to two modes of use;
  • FIGS. 2a and 2b examples of spectral characteristics of an emitting probe (FIG. 2a) and a receiving probe (FIG. 2b) of a device according to the invention,
  • FIG. 1a a schematic representation of a second embodiment of a device according to the invention.
  • An airborne ultrasound non-destructive testing device 1 as represented in FIG. 1a, comprises, in a known manner, the following elements:
  • a so-called transmitting ultrasound probe 10 used for the emission of ultrasonic waves, provided with at least one transducer for the conversion of an electrical signal into an ultrasonic wave,
  • receiver ultrasound probe 11 used for the reception of ultrasonic waves, provided with at least one transducer for the conversion of an ultrasonic wave into an electrical signal, and physically disjunct from the emitting probe 10; electrical pulses 12 connected to the emitter probe 10,
  • an analysis unit 13 of the electrical signals obtained by measuring the ultrasonic waves received by the receiving probe 11, comprising, for example, a module for sampling said electrical signals in digital signals, a processing module for said digital signals, a module for displaying said digital signals, etc.
  • the emitter 10 and receiver 11 probes are probes suitable for airborne ultrasound non-destructive testing, in which the probes are not in contact with a structure 2 to be inspected, and the space separating said probes from said structure to inspect is occupied by a gaseous medium such as ambient air.
  • the ultrasonic waves emitted and received propagate in the gaseous medium and are called aerial ultrasonic waves.
  • Said ultrasonic air waves have generally low frequencies, that is to say less than 1 MHz, but the invention is not limited to this frequency range.
  • the spectral characteristics of the emitter probe 10 and those of the receiver probe 11 are different.
  • spectral characteristics is meant the frequency behavior of said probes, which can be represented, for the emitting probe 10, in the form of a frequency spectrum representing, for example, the power spectral density of the different frequency components of the emitted ultrasonic waves or, for the receiving probe 11, in the form of a frequency response characterizing the filtering which will be introduced on the received ultrasonic waves.
  • the frequency characteristics of the emitter 10 and receiver 11 probes differ at least in the width of their frequency bands, that is to say for the emitter probe 10 the frequency range in which is comprised most of the radiated power and for the receiver probe 11 the frequency range outside which received frequency components of ultrasonic waves will be greatly attenuated by said receiver probe 11, according to its frequency response.
  • the frequency bands differ in particular in their width.
  • one of the bands, called narrow band has a width less than that of the other band, said broad band, preferably of a factor of ten or more.
  • the narrow band corresponds to the transmission band of the transmitting probe 10
  • the wide band corresponds to the receiving band of the receiving probe 11. This is the case which is considered in the remainder of the description.
  • the emitter 10 and receiver 11 probes have different spectral characteristics, they are preferably made with technologies adapted to said spectral characteristics, and advantageously with different materials chosen for example to optimize the operation of said probes on the one hand, and on the other hand.
  • the emitter probe 10 comprises one or more transducers made of a composite piezoelectric ceramic and / or piezoelectric material, for example based on lead titano-zirconate (or "PZT").
  • PZT lead titano-zirconate
  • Such materials can be used to produce powerful transducers with emission and narrow emission band (of the order of ten kilohertz or less), which makes them good transducers for the emission of aerial ultrasonic waves.
  • the receiving probe 11 comprises, for example, one or more electro-capacitive transducers, preferably comprising membranes made of a polymer material such as polyvinylidene fluoride (or "PVDF"), or of copolymeric material such as comprising PVDF and trifluoroethylene.
  • PVDF polyvinylidene fluoride
  • Such materials can be implemented to produce high sensitivity and wide bandwidth transducers (on the order of one hundred kilohertz or more), making them good transducers for the reception of aerial ultrasonic
  • spectral characteristics of a narrowband transmitter probe and a wideband receiver probe 11 are shown in Figs. 2a and 2b, respectively.
  • FIG. 2a shows the impedance Z (in Ohms) measured as a function of the frequency f for a transducer probe 10 with a ceramic piezoelectric material transducer.
  • the frequencies for which a maximum is observed correspond to resonant frequencies of the emitter probe 10, corresponding to the frequencies at which said probe is to be excited to efficiently produce ultrasound.
  • there are essentially two resonance frequencies one around 140 kHz corresponding to a radial resonance mode not used for the non-destructive air-coupling control, and one around 360 kHz corresponding to a longitudinal resonance.
  • the transmission band denoted by the reference B E , centered on the central frequency 360 kHz, has a width of a few kilohertz.
  • FIG. 2b shows the efficiency E (in Volts / Pascals) measured as a function of frequency for a receiving probe 11 with an electro-capacitive transducer.
  • the receive band denoted by the reference B R , has a width of about 300 kHz for a center frequency of about 280 kHz.
  • the examples of FIGS. 2a and 2b illustrate a preferred embodiment in which the narrow emission band of the emitter probe 10 is included in the wide reception band of the receiving probe 11.
  • This embodiment is particularly advantageous because the bulk of the ultrasonic waves emitted by the emitter probe 10 is picked up by the receiving probe 11 after propagation in the structure 2, at least in the absence of a frequency shift of the received ultrasonic waves. relative to the ultrasonic waves emitted by the emitter probe 10. In fact, the frequency components of the ultrasonic waves received are then essentially comprised in the receiving band of the receiving probe.
  • This embodiment also has the advantage of a low sensitivity to a possible frequency shift of the received ultrasonic waves with respect to the ultrasonic waves emitted by the emitting probe 10. It can be seen in FIGS. 2a and 2b that if the ultrasonic waves transmitted are received with a frequency offset of less than 50 kHz (for the example shown in FIGS. 2a and 2b) the frequency components of the received ultrasonic waves are always included in the reception band of the receiving probe 11, that is, that is, most of the ultrasonic waves are picked up by said receiver probe.
  • the device 1 also finds a particularly advantageous application in the non-destructive ultrasonic air-coupled control of structures characterized by a nonlinear transfer function, which said nonlinearities introduce frequency offsets of the received ultrasonic waves with respect to the emitted ultrasonic waves.
  • the emitter probe 10 may be replaced by another emitter probe with a narrow emission band, with characteristics that may or may not be similar to those of the emitter probe 10, without it being necessary to change the receiving probe 11 because of its wide reception band.
  • the receiver probe 11 is not sensitive to an evolution of the spectral characteristics of the emitter probe 10.
  • a signal obtained by measuring the received ultrasonic waves, returned by the structure 2 comprises a noise, measured on the same wide frequency band as said ultrasonic waves, which is for example of thermal origin, caused by interference, etc.
  • the device 1 comprises a filtering module 14, included in the analysis unit 13 in the nonlimiting example of FIG. 1a, implementing a filtering whose transfer function is adapted to reduce the level of the noise frequency components measured outside the transmission band of the transmitting probe 10, for example characteristics (bandwidth, center frequency, etc.) close to those of said transmission band.
  • the filtering is adapted to the received offset transmission band.
  • the reception band is deliberately shifted with respect to the transmission band so that ultrasonic waves received with an expected shift in frequency with respect to the ultrasound waves emitted, because of a function of non-linear transfer of the structure 2, are received with minimal attenuation.
  • said device comprises a plurality of emitter probes 10.
  • the emitter probes 10 are preferably all narrow-band, and of different frequency bands, overlapping partially or not, and preferably all included in the wide reception band of the receiving probe 10.
  • Such a device makes it possible to carry out a broadband characterization of a structure 2 by an airborne ultrasonic non-destructive testing, by performing a plurality of simultaneous or successive narrow-band inspections, using the same receiver probe 11.
  • the device 1 comprises a selection module 15 of one or more emitter probes to be used.
  • the selection module 15 changes emitter probe used substantially periodically.
  • the device 1 preferably comprises a filter module 14 comprising one or more analog or digital filters used to reduce the level of the noise measured with the received ultrasonic waves.
  • the filtering module 14 comprises a filter
  • the characteristics of said filter are preferably modifiable to be adapted to the different emission bands of the different emitter probes 10 considered.
  • each filter is preferably adapted to a transmission band of one of the emitting probes 10.
  • the device 1 comprises in another embodiment not shown a plurality of receiving probes 11, wide bands partially overlapping or not.
  • the number of emitting probes 10 is greater than the number of receiving probes 11 because a wide-band receiving probe is adapted to receive ultrasonic waves emitted by a plurality of different narrow-band transmitting probes.
  • the emitter 10 and receiver 11 probes of the device 1 are physically disjoint and are arranged in different positions with respect to the structure 2. In a conventional manner, the emitter 10 and receiver 11 are arranged in "transmission” mode or in "reflection” mode. "Following a" tandem “configuration (also known as” pitch and catch "in the Anglo-Saxon literature).
  • the emitter 10 and receiver 11 probes are arranged so that the structure 2 is interposed between said probes, and the ultrasonic waves received by the probe receiver 11 are ultrasonic waves that have been emitted by the emitter probe 10 and after propagation in the structure 2.
  • the emitter 10 and receiver 11 probes are arranged on the same side of the structure 2, and the ultrasonic waves received by the receiving probe 11 are ultrasonic waves that have been emitted by the probe emitter 10 and having been returned by the structure 2, for example reflected on the faces of said structure and / or propagated on the surface of said structure.
  • the device 1 according to the invention is adapted to the implementation of a method of non-destructive ultrasonic air-coupling control of the structure 2.
  • the method comprises an inspection step in which air ultrasonic waves are emitted in the direction of the structure 2, and in which ultrasonic waves returned by said structure are measured.
  • Characteristics of the measured ultrasonic waves are used to evaluate the structural characteristics of the structure 2, such as the presence of internal defects which may be in the case of sandwich structures a crushing of the layer alveolar, an omission of separator, etc.
  • aerial ultrasonic waves are emitted in the direction of the structure 2 over a narrow frequency band, for example by means of the emitter probe 10 of the device 1 used in a longitudinal resonance mode, and ultrasonic waves returned are measured. by said structure 2 over a wide frequency band, for example by means of the receiving probe 11.
  • a signal obtained is filtered by measuring the ultrasonic waves returned by the structure 2 with a selective filter of transfer function adapted to reduce the power of the frequency components measured outside the band.
  • narrow emission on which the above-mentioned ultrasonic waves have been emitted eg characteristics (bandwidth, central frequency, etc.) adjacent to those of said emission band.
  • the transfer function of the filtering is adapted to the transmitted offset transmission band received.
  • aerial ultrasonic waves are transmitted on different narrow frequency bands simultaneously or successively. The different narrow frequency bands overlap partially or not, and are preferably all included in the wide reception band on which the ultrasonic waves are measured overhead.
  • the signal corresponding to the received ultrasonic waves is filtered with selective filters of transfer functions adapted to the different narrow frequency bands on which ultrasonic waves, possibly frequency shifted, have been emitted.
  • the device and the method according to the invention make it possible to carry out a non-destructive ultrasonic air-coupling control which is insensitive to the spectral characteristics of the emitter and receiver probes, and which is not very sensitive to the frequency shifts of the ultrasonic waves received with respect to the ultrasonic waves. issued.
  • the preferred field of application of the invention is that of non-destructive ultrasonic airborne coupling control of aeronautical structures made of composite material, in particular sandwich structures incorporating one or more honeycomb layers (foam, nest bee, etc.), widely used in the aviation industry, which could be damaged and / or polluted by a liquid coupling medium.

Abstract

A device (1) for the air-coupled ultrasonic non-destructive testing of a structure (2) comprises at least one emitting probe (10) for emitting ultrasonic waves towards said structure and at least one receiving probe (11) for receiving ultrasonic waves after propogation through said structure, the ultrasonic waves being emitted and received through a gaseous medium without contact between said probes and the structure (2). The emission frequency band (BE) of the at least one emitting probe (10) is narrower than the receiving frequency band (BR) of the at least one receiving probe (11) and lies within the latter. According to one method for the air-coupled ultrasonic non-destructive testing of a structure (2), airborne ultrasonic waves are emitted over an emission frequency band (BE) narrower than the receiving frequency band (BR).

Description

Procédé et dispositif de contrôle non-destructif par ultrasons à couplage aérien d'une structure Method and device for non-destructive ultrasonic airborne coupling control of a structure
La présente invention appartient au domaine du contrôle non-destructif par ultrasons de structures. Plus particulièrement, la présente invention concerne un procédé et un dispositif de contrôle non-destructif par ultrasons à couplage aérien. Les procédés de contrôle non-destructif permettent de contrôler une structure pour détecter des défauts en surface et/ou en profondeur de ladite structure sans la dégrader. Ces procédés sont utilisés dans une phase de production de la structure pour en vérifier la qualité de fabrication et/ou dans une phase de maintenance pour vérifier si des défauts sont apparus. Dans les procédés de contrôle non-destructif par ultrasons, des ondes acoustiques ultrasonores sont émises en direction de la structure à contrôler, et une partie des ondes ultrasonores émises est reçue après propagation dans ladite structure. Des caractéristiques (amplitude, temps de vol, etc.) des ondes reçues sont utilisées pour évaluer des caractéristiques structurelles de la structure inspectée.The present invention belongs to the field of non-destructive ultrasonic testing of structures. More particularly, the present invention relates to a method and device for non-destructive ultrasonic air-coupled control. The non-destructive control methods make it possible to control a structure for detecting defects on the surface and / or in the depth of said structure without degrading it. These methods are used in a production phase of the structure to check the quality of manufacture and / or in a maintenance phase to check if defects have appeared. In non-destructive ultrasonic testing methods, ultrasonic acoustic waves are emitted in the direction of the structure to be monitored, and a portion of the emitted ultrasonic waves is received after propagation in said structure. Characteristics (amplitude, flight time, etc.) of the received waves are used to evaluate structural characteristics of the inspected structure.
Les procédés de contrôle non-destructif par ultrasons utilisent le plus souvent un milieu de couplage liquide, bon conducteur des ondes ultrasonores comme par exemple de l'eau ou du gel, entre une ou des sondes ultrasonores et la structure, afin de réaliser notamment une adaptation d'impédance acoustique entre lesdites sondes et ladite structure. La présence du milieu de couplage liquide entre les sondes et la structure est par exemple assurée par immersion partielle ou totale de la structure dans ledit milieu, ou par apport continu dudit milieu par exemple dans le cas d'un couplage par jets d'eau.The ultrasonic non-destructive testing methods most often use a liquid coupling medium, which is a good conductor of ultrasonic waves, for example water or gel, between one or more ultrasonic probes and the structure, in order to produce, in particular, a acoustic impedance matching between said probes and said structure. The presence of the liquid coupling medium between the probes and the structure is for example provided by partial or total immersion of the structure in said medium, or by continuous supply of said medium for example in the case of a coupling by water jets.
Un inconvénient des procédés de contrôle non-destructif à couplage liquide réside dans le fait qu'ils sont relativement pénalisants à mettre en œuvre du fait même de la mise en œuvre de cuves ou de dispositifs d'apport de liquide, et dans le fait qu'ils ne sont pas adaptés au contrôle de certains types de structures.A disadvantage of non-destructive liquid coupling methods lies in the fact that they are relatively disadvantageous to implement by the very fact of the implementation of tanks or liquid supply devices, and in the fact that they are not suitable for controlling certain types of structures.
C'est le cas par exemple des structures sandwich intégrant une ou des couches alvéolaires (mousse, nid d'abeille, etc.), largement répandues dans l'industrie aéronautique, qui peuvent être endommagées et/ou polluées par un milieu de couplage liquide, notamment lorsqu'on utilise des jets d'eau.This is the case, for example, of sandwich structures incorporating one or more honeycomb layers (foam, honeycomb, etc.), widely used in the aeronautical industry, which can be damaged and / or polluted by a liquid coupling medium, especially when using jets of water.
Pour pallier à ce problème, une solution possible consiste à mettre en œuvre des procédés de contrôle non-destructif par ultrasons à couplage aérien, pour lesquels le milieu de couplage est gazeux, typiquement de l'air ambiant.To overcome this problem, one possible solution consists in implementing non-destructive ultrasonic air-coupling control methods for which the coupling medium is gaseous, typically ambient air.
De tels procédés utilisent un dispositif comportant une sonde émettrice pour l'émission d'ondes ultrasonores et une sonde réceptrice pour la réception d'ondes, lesdites sondes n'étant pas au contact de la structure. Les sondes ont des caractéristiques spectrales très voisines afin d'éviter d'introduire des pertes liées à un filtrage par la sonde réceptrice des ondes ultrasonores émises par la sonde émettrice, c'est-à-dire pour limiter au maximum les pertes inhérentes à la chaîne d'émission/réception.Such methods use a device comprising a transmitting probe for emitting ultrasonic waves and a receiving probe for receiving waves, said probes not being in contact with the structure. The probes have very similar spectral characteristics in order to avoid introducing losses related to a filtering by the receiving probe of the ultrasonic waves emitted by the emitting probe, that is to say to limit as much as possible the losses inherent in the transmission / reception chain.
De telles pertes seraient d'autant plus préjudiciables que l'air étant moins bon conducteur des ondes ultrasonores qu'un milieu liquide, les pertes par propagation sont déjà très importantes. De plus les structures de type sandwich sont également très absorbantes dans le domaine acoustique, ce qui fait que les ondes ultrasonores reçues sont difficilement exploitables pour évaluer les caractéristiques structurelles de la structure. En pratique, cette configuration exige de mettre en œuvre des sondes émettrice et réceptrice dont les caractéristiques spectrales sont quasiment identiques, les sondes étant appariées pour obtenir ce résultat, et le plus souvent à bande étroite (généralement inférieure à quelques dizaines de kilohertz) pour améliorer le rapport signal sur bruit en réception, ce qui présente divers inconvénients.Such losses would be all the more damaging as air is less conducive to ultrasonic waves than a liquid medium, propagation losses are already very important. Moreover sandwich structures are also very absorbent in the acoustic field, so that the ultrasonic waves received are difficult to exploit to evaluate the structural characteristics of the structure. In practice, this configuration requires the implementation of emitter and receiver probes whose spectral characteristics are almost identical, the probes being matched to obtain this result, and most often narrowband (generally less than a few tens of kilohertz) to improve the signal-to-noise ratio on reception, which presents various disadvantages.
Tout d'abord, cette configuration impose des contraintes très fortes sur la fabrication des sondes, et il n'est pas rare que le transducteur d'émission et le transducteur de réception soient réalisés non seulement suivant une même technologie, par exemple piézoélectrique céramique, mais également dans un même bloc du matériau céramique, pour avoir des caractéristiques spectrales aussi voisines que possible.Firstly, this configuration imposes very strong constraints on the manufacture of the probes, and it is not uncommon for the emission transducer and the reception transducer to be made not only according to the same technology, for example piezoelectric ceramics, but also in the same block of the ceramic material, to have spectral characteristics as close as possible.
De plus, les caractéristiques spectrales des sondes évoluent indépendamment dans le temps, et des caractéristiques spectrales initialement quasiment identiques peuvent ne plus l'être au bout d'un certain temps, avec pour effet une introduction de pertes importantes par filtrage des ondes ultrasonores par la sonde réceptrice. En outre, si une sonde est endommagée, la deuxième sonde devient généralement inutilisable en association avec une autre sonde qui de fait ne sera pas appariée.In addition, the spectral characteristics of the probes evolve independently over time, and spectral characteristics initially almost identical may no longer be after a certain time, with the effect of introducing significant losses by filtering the ultrasonic waves by the receiving probe. In addition, if a probe is damaged, the second probe generally becomes unusable in association with another probe that will not be matched.
Un autre problème apparaît en cas de décalage en fréquence des ondes ultrasonores reçues par rapport aux ondes ultrasonores émises, par exemple dû à un comportement non-linéaire de la structure. Le niveau des ondes ultrasonores mesurées est alors faible du fait de la sélectivité fréquentielle de la sonde réceptrice, notamment dans le cas d'une sonde réceptrice à bande étroite.Another problem arises in the case of a frequency shift of the received ultrasonic waves with respect to the emitted ultrasonic waves, for example due to a non-linear behavior of the structure. The level of the ultrasonic waves measured is then low because of the frequency selectivity of the receiving probe, especially in the case of a narrow-band receiving probe.
Il n'est pas connu d'autre configuration de contrôle non-destructif par ultrasons à couplage aérien permettant de résoudre les problèmes susmentionnés tout en limitant les pertes inhérentes à la chaîne d'émission/réception.No other non-destructive airborne ultrasound control configuration is known to solve the aforementioned problems while limiting the inherent losses in the transmit / receive chain.
La présente invention propose de résoudre les problèmes susmentionnés en introduisant un dispositif de contrôle non-destructif par ultrasons à couplage aérien d'une structure, comportant au moins une sonde émettrice, pour l'émission d'ondes ultrasonores en direction de la structure et au moins une sonde réceptrice, pour la réception d'ondes ultrasonores après propagation dans la structure.The present invention proposes to solve the aforementioned problems by introducing a device for non-destructive ultrasonic air-coupling control of a structure, comprising at least one emitting probe, for the emission of ultrasonic waves towards the structure and the least one receiving probe, for the reception of ultrasonic waves after propagation in the structure.
Selon l'invention, l'au moins une sonde émettrice et l'au moins une sonde réceptrice, physiquement disjointes, ont des bandes fréquentielles respectivement d'émission et de réception de largeurs différentes, la bande fréquentielle d'émission de l'au moins une sonde émettrice étant de largeur inférieure à la largeur de la bande fréquentielle de réception de l'au moins une sonde réceptrice, et comprise dans la bande fréquentielle de réception de l'au moins une sonde réceptrice.According to the invention, the at least one emitter probe and the at least one receiving probe, physically disjoint, have frequency bands respectively of emission and reception of different widths, the frequency band of emission of the at least one a transmitting probe being of width less than the width of the frequency band of reception of the at least one receiving probe, and included in the frequency band of reception of the at least one receiving probe.
Avantageusement, l'au moins une sonde émettrice comporte au moins un transducteur réalisé avec un matériau piézoélectrique céramique ou piézoélectrique composite, et l'au moins une sonde réceptrice comporte au moins un transducteur électro-capacitif, comportant de préférence au moins une membrane en matériau polymère ou copolymère. Pour effectuer une inspection large bande de la structure, le dispositif comporte dans un mode particulier de réalisation une pluralité de sondes émettrices de bandes fréquentielles d'émission différentes et étroites par rapport à la bande fréquentielle de réception de l'au moins une sonde réceptrice, et comprises dans ladite bande fréquentielle de réception. Suivant d'autres caractéristiques, le dispositif comporte :Advantageously, the at least one emitter probe comprises at least one transducer made of a composite piezoelectric ceramic or piezoelectric material, and the at least one receiving probe comprises at least one electro-capacitive transducer, preferably comprising at least one membrane of material polymer or copolymer. In order to carry out a broadband inspection of the structure, the device comprises, in a particular embodiment, a plurality of probes transmitting transmission frequency bands that are different and narrow with respect to the reception frequency band of the at least one receiver probe. and included in said frequency reception band. According to other features, the device comprises:
- un module de sélection d'une ou plusieurs sondes émettrices,a module for selecting one or more emitting probes,
- un module de filtrage muni d'au moins un filtre à bande fréquentielle étroite par rapport à la bande fréquentielle de réception de l'au moins une sonde réceptrice, et adaptée à une bande fréquentielle démission d'une sonde émettrice. L'invention concerne également un procédé de contrôle non-destructif par ultrasons à couplage aérien dans lequel on émet des ondes ultrasonores aériennes en direction de la structure, on mesure des ondes ultrasonores après propagation dans la structure, et on évalue des caractéristiques structurelles de la structure à partir de caractéristiques des ondes ultrasonores mesurées.a filtering module provided with at least one narrow frequency band filter with respect to the frequency band of reception of the at least one receiving probe, and adapted to a frequency band resigning from an emitting probe. The invention also relates to a method of non-destructive ultrasonic air-coupling control in which ultrasonic waves are emitted in the direction of the structure, ultrasonic waves are measured after propagation in the structure, and structural characteristics of the structure are evaluated. structure from characteristics of the measured ultrasonic waves.
Selon l'invention, on émet les ondes ultrasonores aériennes sur une bande fréquentielle d'émission, et on mesure les ondes ultrasonores aériennes renvoyées par la structure sur une bande fréquentielle de réception large par rapport à la bande fréquentielle d'émission.According to the invention, the aerial ultrasonic waves are emitted on a frequency transmission band, and the aerial ultrasonic waves returned by the structure are measured on a wide reception frequency band with respect to the frequency transmission band.
Pour réduire le niveau du bruit mesuré sur la bande fréquentielle de réception large, on filtre un signal obtenu en mesurant les ondes ultrasonores renvoyées par la structure avec un filtre de bande fréquentielle adaptée à la bande fréquentielle d'émission sur laquelle on a émis les ondes ultrasonores aériennes.In order to reduce the level of the noise measured on the wide reception frequency band, a signal obtained is filtered by measuring the ultrasonic waves returned by the structure with a frequency band filter adapted to the frequency band of emission on which the waves have been transmitted. aerial ultrasound.
Pour effectuer une inspection large bande de la structure, on émet des ondes ultrasonores sur une pluralité de bandes fréquentielles d'émission étroites différentes, et on filtre un signal obtenu en mesurant les ondes ultrasonores renvoyées par la structure avec des filtres de bandes fréquentielles adaptées aux bandes fréquentielles d'émission sur lesquelles on a émis les ondes ultrasonores aériennes.To perform a broadband inspection of the structure, ultrasound waves are emitted over a plurality of different narrow emission frequency bands, and a signal obtained is filtered by measuring the ultrasonic waves returned by the structure with frequency band filters adapted to frequency transmission bands on which the ultrasonic air waves have been emitted.
La description suivante de modes de l'invention est faite en se référant aux figures, dans lesquelles des références identiques désignent des éléments identiques ou analogues, qui représentent de manière non limitative :The following description of modes of the invention is made with reference to the figures, in which like references designate elements identical or similar, which represent in a non-limiting way:
- Figures 1 a et 1 b : des représentations schématiques d'un premier mode de réalisation d'un dispositif selon l'invention, suivant deux modes d'utilisation, - Figures 2a et 2b : des exemples de caractéristiques spectrales d'une sonde émettrice (figure 2a) et d'une sonde réceptrice (figure 2b) d'un dispositif selon l'invention,FIGS. 1a and 1b are diagrammatic representations of a first embodiment of a device according to the invention, according to two modes of use; FIGS. 2a and 2b: examples of spectral characteristics of an emitting probe (FIG. 2a) and a receiving probe (FIG. 2b) of a device according to the invention,
- Figure 3 : une représentation schématique d'un second mode de réalisation d'un dispositif selon l'invention. Un dispositif 1 de contrôle non-destructif par ultrasons à couplage aérien, tel que représenté sur la figure 1 a, comporte notamment de manière connue les éléments suivants :- Figure 3: a schematic representation of a second embodiment of a device according to the invention. An airborne ultrasound non-destructive testing device 1, as represented in FIG. 1a, comprises, in a known manner, the following elements:
- une sonde ultrasonore dite émettrice 10, utilisée pour l'émission d'ondes ultrasonores, munie d'au moins un transducteur pour la conversion d'un signal électrique en onde ultrasonore,a so-called transmitting ultrasound probe 10, used for the emission of ultrasonic waves, provided with at least one transducer for the conversion of an electrical signal into an ultrasonic wave,
- une sonde ultrasonore dite réceptrice 11 , utilisée pour la réception d'ondes ultrasonores, munie d'au moins un transducteur pour la conversion d'une onde ultrasonore en signal électrique, et physiquement disjointe de la sonde émettrice 10, - un générateur d'impulsions électriques 12 connecté à la sonde émettrice 10,a so-called receiver ultrasound probe 11, used for the reception of ultrasonic waves, provided with at least one transducer for the conversion of an ultrasonic wave into an electrical signal, and physically disjunct from the emitting probe 10; electrical pulses 12 connected to the emitter probe 10,
- une unité d'analyse 13 des signaux électriques obtenus en mesurant les ondes ultrasonores reçues par la sonde réceptrice 11 , comportant par exemple un module d'échantillonnage desdits signaux électriques en signaux numériques, un module de traitement desdits signaux numériques, un module d'affichage desdits signaux numériques, etc.an analysis unit 13 of the electrical signals obtained by measuring the ultrasonic waves received by the receiving probe 11, comprising, for example, a module for sampling said electrical signals in digital signals, a processing module for said digital signals, a module for displaying said digital signals, etc.
Les sondes émettrice 10 et réceptrice 11 sont des sondes adaptées au contrôle non-destructif par ultrasons à couplage aérien, dans lequel les sondes ne sont pas au contact d'une structure 2 à inspecter, et l'espace séparant lesdites sondes de ladite structure à inspecter est occupé par un milieu gazeux comme par exemple de l'air ambiant. Les ondes ultrasonores émises et reçues se propagent dans le milieu gazeux et sont dites ondes ultrasonores aériennes. Lesdites ondes ultrasonores aériennes ont des fréquences généralement basses, c'est-à-dire inférieures à 1 MHz, mais l'invention n'est pas limitée à cette gamme de fréquences.The emitter 10 and receiver 11 probes are probes suitable for airborne ultrasound non-destructive testing, in which the probes are not in contact with a structure 2 to be inspected, and the space separating said probes from said structure to inspect is occupied by a gaseous medium such as ambient air. The ultrasonic waves emitted and received propagate in the gaseous medium and are called aerial ultrasonic waves. Said ultrasonic air waves have generally low frequencies, that is to say less than 1 MHz, but the invention is not limited to this frequency range.
Selon l'invention, les caractéristiques spectrales de la sonde émettrice 10 et celles de la sonde réceptrice 11 sont différentes.According to the invention, the spectral characteristics of the emitter probe 10 and those of the receiver probe 11 are different.
Par « caractéristiques spectrales », on entend le comportement fréquentiel desdites sondes, pouvant être représenté, pour la sonde émettrice 10, sous la forme d'un spectre fréquentiel représentant par exemple la densité spectrale de puissance des différentes composantes fréquentielles des ondes ultrasonores émises ou, pour la sonde réceptrice 11 , sous la forme d'une réponse en fréquence caractérisant le filtrage qui sera introduit sur les ondes ultrasonores reçues.By "spectral characteristics" is meant the frequency behavior of said probes, which can be represented, for the emitting probe 10, in the form of a frequency spectrum representing, for example, the power spectral density of the different frequency components of the emitted ultrasonic waves or, for the receiving probe 11, in the form of a frequency response characterizing the filtering which will be introduced on the received ultrasonic waves.
En particulier, les caractéristiques fréquentielles des sondes émettrice 10 et réceptrice 11 diffèrent au moins par la largeur de leur bandes fréquentielles, c'est-à-dire pour la sonde émettrice 10 l'intervalle de fréquences dans lequel est compris l'essentiel de la puissance rayonnée et pour la sonde réceptrice 11 l'intervalle de fréquences en dehors duquel des composantes fréquentielles d'ondes ultrasonores reçues seront fortement atténuées par ladite sonde réceptrice 11 , conformément à sa réponse en fréquence. Dans un mode préféré de réalisation de l'invention, les bandes fréquentielles diffèrent notamment par leur largeur. Dans ce cas, l'une des bandes, dite bande étroite, a une largeur inférieure à celle de l'autre bande, dite bande large, de préférence d'un facteur dix ou plus.In particular, the frequency characteristics of the emitter 10 and receiver 11 probes differ at least in the width of their frequency bands, that is to say for the emitter probe 10 the frequency range in which is comprised most of the radiated power and for the receiver probe 11 the frequency range outside which received frequency components of ultrasonic waves will be greatly attenuated by said receiver probe 11, according to its frequency response. In a preferred embodiment of the invention, the frequency bands differ in particular in their width. In this case, one of the bands, called narrow band, has a width less than that of the other band, said broad band, preferably of a factor of ten or more.
Avantageusement, la bande étroite correspond à la bande d'émission de la sonde émettrice 10, et la bande large correspond à la bande de réception de la sonde réceptrice 11. C'est le cas qui est considéré dans la suite de la description. Toutefois il est envisageable, quoique d'un intérêt moindre en raison d'une utilisation moins efficace de l'énergie rayonnée par la sonde émettrice 10, d'avoir une bande d'émission large et une bande de réception étroite dans d'autres modes de réalisation non décrits.Advantageously, the narrow band corresponds to the transmission band of the transmitting probe 10, and the wide band corresponds to the receiving band of the receiving probe 11. This is the case which is considered in the remainder of the description. However, it is possible, although of less interest because of a less efficient use of the energy radiated by the emitter probe 10, to have a broad transmission band and a narrow reception band in other modes. not described.
Les sondes émettrice 10 et réceptrice 11 ayant des caractéristiques spectrales différentes, elles sont de préférence réalisées avec des technologies adaptées auxdites caractéristiques spectrales, et avantageusement avec des matériaux différents choisis par exemple pour optimiser le fonctionnement desdites sondes en émission d'une part, et en réception d'autre part.Since the emitter 10 and receiver 11 probes have different spectral characteristics, they are preferably made with technologies adapted to said spectral characteristics, and advantageously with different materials chosen for example to optimize the operation of said probes on the one hand, and on the other hand.
Par exemple, la sonde émettrice 10 comporte un ou des transducteurs réalisés en matériau piézoélectrique céramique et/ou piézoélectrique composite, par exemple à base de titano-zirconate de plomb (ou « PZT »). De tels matériaux peuvent être mis en œuvre pour réaliser des transducteurs puissants à l'émission et à bande d'émission étroite (de l'ordre de la dizaine de kilohertz ou moins), ce qui en fait de bons transducteurs pour l'émission d'ondes ultrasonores aériennes. La sonde réceptrice 11 comporte par exemple un ou des transducteurs électro-capacitifs, comportant de préférence des membranes réalisées en matériau polymère tel que du polyfluorure de vinylidène (ou « PVDF »), ou en matériau copolymère tel que comportant du PVDF et du trifluoroéthylène. De tels matériaux peuvent être mis en œuvre pour réaliser des transducteurs à sensibilité élevée et à bande passante large (de l'ordre de la centaine de kilohertz ou plus), ce qui en fait de bons transducteurs pour la réception d'ondes ultrasonores aériennes.For example, the emitter probe 10 comprises one or more transducers made of a composite piezoelectric ceramic and / or piezoelectric material, for example based on lead titano-zirconate (or "PZT"). Such materials can be used to produce powerful transducers with emission and narrow emission band (of the order of ten kilohertz or less), which makes them good transducers for the emission of aerial ultrasonic waves. The receiving probe 11 comprises, for example, one or more electro-capacitive transducers, preferably comprising membranes made of a polymer material such as polyvinylidene fluoride (or "PVDF"), or of copolymeric material such as comprising PVDF and trifluoroethylene. Such materials can be implemented to produce high sensitivity and wide bandwidth transducers (on the order of one hundred kilohertz or more), making them good transducers for the reception of aerial ultrasonic waves.
Des exemples de caractéristiques spectrales d'une sonde émettrice 10 à bande étroite et d'une sonde réceptrice 11 à bande large sont représentées respectivement sur les figures 2a et 2b.Examples of spectral characteristics of a narrowband transmitter probe and a wideband receiver probe 11 are shown in Figs. 2a and 2b, respectively.
Sur la figure 2a, on a représenté l'impédance Z (en Ohms) mesurée en fonction de la fréquence f pour une sonde émettrice 10 à transducteur en matériau piézoélectrique céramique. Les fréquences pour lesquelles un maxima est observé correspondent à des fréquences de résonance de la sonde émettrice 10, correspondant aux fréquences auxquelles ladite sonde doit être excitée pour produire efficacement des ultrasons. Sur la figure 2a, on a essentiellement deux fréquences de résonance, une aux alentours de 140 kHz correspondant à un mode de résonance radial non utilisé pour le contrôle non- destructif à couplage aérien, et une aux alentours de 360 kHz correspondant à un mode de résonance longitudinal. La bande d'émission, désignée par la référence BE, centrée sur la fréquence centrale 360 kHz, a une largeur de quelques kilohertz.FIG. 2a shows the impedance Z (in Ohms) measured as a function of the frequency f for a transducer probe 10 with a ceramic piezoelectric material transducer. The frequencies for which a maximum is observed correspond to resonant frequencies of the emitter probe 10, corresponding to the frequencies at which said probe is to be excited to efficiently produce ultrasound. In FIG. 2a, there are essentially two resonance frequencies, one around 140 kHz corresponding to a radial resonance mode not used for the non-destructive air-coupling control, and one around 360 kHz corresponding to a longitudinal resonance. The transmission band, denoted by the reference B E , centered on the central frequency 360 kHz, has a width of a few kilohertz.
Sur la figure 2b, on a représenté l'efficacité E (en Volts / Pascals) mesurée en fonction de la fréquence pour une sonde réceptrice 11 à transducteur électro-capacitif. La bande de réception, désignée par la référence BR, a une largeur d'environ 300 kHz pour une fréquence centrale d'environ 280 kHz. Les exemples des figures 2a et 2b illustrent un mode préféré de réalisation dans lequel la bande d'émission étroite de la sonde émettrice 10 est comprise dans la bande de réception large de la sonde réceptrice 11.FIG. 2b shows the efficiency E (in Volts / Pascals) measured as a function of frequency for a receiving probe 11 with an electro-capacitive transducer. The receive band, denoted by the reference B R , has a width of about 300 kHz for a center frequency of about 280 kHz. The examples of FIGS. 2a and 2b illustrate a preferred embodiment in which the narrow emission band of the emitter probe 10 is included in the wide reception band of the receiving probe 11.
Ce mode de réalisation est particulièrement avantageux du fait que l'essentiel des ondes ultrasonores émises par la sonde émettrice 10 est capté par la sonde réceptrice 11 après propagation dans la structure 2, au moins en l'absence de décalage en fréquence des ondes ultrasonores reçues par rapport aux ondes ultrasonores émises par la sonde émettrice 10. En effet, les composantes fréquentielles des ondes ultrasonores reçues sont alors essentiellement comprises dans la bande de réception de la sonde réceptrice. Ce mode de réalisation présente en outre l'avantage d'une faible sensibilité à un éventuel décalage en fréquence des ondes ultrasonores reçues par rapport aux ondes ultrasonores émises par la sonde émettrice 10. On voit sur les figures 2a et 2b que si les ondes ultrasonores émises sont reçues avec un décalage en fréquence inférieur à 50 kHz (pour l'exemple représenté sur lesdites figures 2a et 2b) les composantes fréquentielles des ondes ultrasonores reçues sont toujours comprises dans la bande de réception de la sonde réceptrice 11 , c'est-à-dire que l'essentiel des ondes ultrasonores est capté par ladite sonde réceptrice.This embodiment is particularly advantageous because the bulk of the ultrasonic waves emitted by the emitter probe 10 is picked up by the receiving probe 11 after propagation in the structure 2, at least in the absence of a frequency shift of the received ultrasonic waves. relative to the ultrasonic waves emitted by the emitter probe 10. In fact, the frequency components of the ultrasonic waves received are then essentially comprised in the receiving band of the receiving probe. This embodiment also has the advantage of a low sensitivity to a possible frequency shift of the received ultrasonic waves with respect to the ultrasonic waves emitted by the emitting probe 10. It can be seen in FIGS. 2a and 2b that if the ultrasonic waves transmitted are received with a frequency offset of less than 50 kHz (for the example shown in FIGS. 2a and 2b) the frequency components of the received ultrasonic waves are always included in the reception band of the receiving probe 11, that is, that is, most of the ultrasonic waves are picked up by said receiver probe.
Du fait de la faible sensibilité à certains décalages en fréquence, le dispositif 1 trouve également une application particulièrement intéressante dans le contrôle non-destructif par ultrasons à couplage aérien de structures caractérisées par une fonction de transfert non linéaire, lesquelles dites non- linéarités introduisent des décalages en fréquence des ondes ultrasonores reçues par rapport aux ondes ultrasonores émises. II est à noter que la sonde émettrice 10 peut être remplacée par une autre sonde émettrice à bande d'émission étroite, de caractéristiques voisines ou non de celles de la sonde émettrice 10, sans qu'il soit nécessaire de changer la sonde de réception 11 du fait de sa bande de réception large. De même, la sonde réceptrice 11 n'est pas sensible à une évolution des caractéristiques spectrales de la sonde émettrice 10.Because of the low sensitivity to certain frequency offsets, the device 1 also finds a particularly advantageous application in the non-destructive ultrasonic air-coupled control of structures characterized by a nonlinear transfer function, which said nonlinearities introduce frequency offsets of the received ultrasonic waves with respect to the emitted ultrasonic waves. It should be noted that the emitter probe 10 may be replaced by another emitter probe with a narrow emission band, with characteristics that may or may not be similar to those of the emitter probe 10, without it being necessary to change the receiving probe 11 because of its wide reception band. Of even, the receiver probe 11 is not sensitive to an evolution of the spectral characteristics of the emitter probe 10.
Il apparaît clairement que la contrainte de fort appahement des sondes, imposée aux dispositifs de contrôle non-destructif par ultrasons à couplage aérien connus, est levée.It is clear that the constraint of strong attachment of the probes imposed on the known non-destructive ultrasonic coupling devices is removed.
L'utilisation d'une bande étroite à l'émission permet d'avoir à puissance totale d'émission constante des composantes fréquentielles de puissance en moyenne plus élevée qu'avec une bande large, ce qui est avantageux pour améliorer le rapport signal sur bruit en réception. Un signal obtenu en mesurant les ondes ultrasonores reçues, renvoyées par la structure 2, comporte un bruit, mesuré sur la même bande fréquentielle large que lesdites ondes ultrasonores, qui est par exemple d'origine thermique, causé par des interférences, etc. Avantageusement, le dispositif 1 comporte un module de filtrage 14, compris dans l'unité d'analyse 13 dans l'exemple non limitatif de la figure 1 a, mettant en œuvre un filtrage dont la fonction de transfert est adaptée pour réduire le niveau des composantes fréquentielles du bruit mesurées en dehors de la bande d'émission de la sonde émettrice 10, par exemple de caractéristiques (largeur de bande, fréquence centrale, etc.) voisines de celles de ladite bande d'émission. En cas de décalage en fréquence des ondes ultrasonores reçues par rapport aux ondes ultrasonores émises, le filtrage est adapté à la bande d'émission décalée reçue.The use of a narrow band on transmission makes it possible to have constant total power transmission power frequency components on average higher than with a wide band, which is advantageous for improving the signal-to-noise ratio. in reception. A signal obtained by measuring the received ultrasonic waves, returned by the structure 2, comprises a noise, measured on the same wide frequency band as said ultrasonic waves, which is for example of thermal origin, caused by interference, etc. Advantageously, the device 1 comprises a filtering module 14, included in the analysis unit 13 in the nonlimiting example of FIG. 1a, implementing a filtering whose transfer function is adapted to reduce the level of the noise frequency components measured outside the transmission band of the transmitting probe 10, for example characteristics (bandwidth, center frequency, etc.) close to those of said transmission band. In case of a frequency shift of the received ultrasonic waves with respect to the emitted ultrasonic waves, the filtering is adapted to the received offset transmission band.
Dans un mode particulier de réalisation, la bande de réception est décalée volontairement par rapport à la bande d'émission de telle sorte que des ondes ultrasonores reçues avec un décalage attendu en fréquence par rapport aux ondes ultrasonores émises, du fait d'une fonction de transfert non- linéaire de la structure 2, soient reçues avec une atténuation minimale.In a particular embodiment, the reception band is deliberately shifted with respect to the transmission band so that ultrasonic waves received with an expected shift in frequency with respect to the ultrasound waves emitted, because of a function of non-linear transfer of the structure 2, are received with minimal attenuation.
Dans un autre mode de réalisation du dispositif 1 , représenté schématiquement sur la figure 3, ledit dispositif comporte une pluralité de sondes émettrices 10.In another embodiment of the device 1, shown schematically in FIG. 3, said device comprises a plurality of emitter probes 10.
Dans ce mode de réalisation, les sondes émettrices 10 sont de préférence toutes à bande étroite, et de bandes fréquentielles différentes, se recouvrant partiellement ou non, et de préférence toutes comprises dans la bande de réception large de la sonde réceptrice 10.In this embodiment, the emitter probes 10 are preferably all narrow-band, and of different frequency bands, overlapping partially or not, and preferably all included in the wide reception band of the receiving probe 10.
Un tel dispositif permet de réaliser une caractérisation large bande d'une structure 2 par un contrôle non-destructif par ultrasons à couplage aérien, en effectuant une pluralité d'inspections à bande étroite, simultanées ou successives, en utilisant une même sonde réceptrice 11.Such a device makes it possible to carry out a broadband characterization of a structure 2 by an airborne ultrasonic non-destructive testing, by performing a plurality of simultaneous or successive narrow-band inspections, using the same receiver probe 11.
De préférence dans ce mode de réalisation, le dispositif 1 comporte un module de sélection 15 d'une ou plusieurs sondes émettrices à utiliser. Par exemple, le module de sélection 15 change de sonde émettrice utilisée de façon sensiblement périodique. De manière analogue, le dispositif 1 comporte de préférence un module de filtrage 14 comportant un ou plusieurs filtres analogiques ou numériques, utilisés pour réduire le niveau du bruit mesuré avec les ondes ultrasonores reçues. Dans le cas où le module de filtrage 14 comporte un filtre, les caractéristiques dudit filtre sont de préférence modifiables pour être adaptées aux différentes bandes d'émission des différentes sondes émettrices 10 considérées. Dans le cas où le module de filtrage 14 comporte une pluralité de filtres, chaque filtre est de préférence adapté à une bande d'émission d'une des sondes émettrices 10.Preferably in this embodiment, the device 1 comprises a selection module 15 of one or more emitter probes to be used. For example, the selection module 15 changes emitter probe used substantially periodically. Similarly, the device 1 preferably comprises a filter module 14 comprising one or more analog or digital filters used to reduce the level of the noise measured with the received ultrasonic waves. In the case where the filtering module 14 comprises a filter, the characteristics of said filter are preferably modifiable to be adapted to the different emission bands of the different emitter probes 10 considered. In the case where the filtering module 14 comprises a plurality of filters, each filter is preferably adapted to a transmission band of one of the emitting probes 10.
Le dispositif 1 comporte dans un autre mode de réalisation non représenté une pluralité de sondes réceptrices 11 , de bandes larges se chevauchant partiellement ou non. De manière générale, le nombre de sondes émettrices 10 est supérieur au nombre de sondes réceptrices 11 du fait qu'une sonde réceptrice à bande large est apte à recevoir des ondes ultrasonores émises par une pluralité de sonde émettrices différentes à bandes étroites. Les sondes émettrice 10 et réceptrice 11 du dispositif 1 sont physiquement disjointes et sont agencées dans des positions différentes par rapport à la structure 2. De manière conventionnelle, les sondes émettrice 10 et réceptrice 11 sont agencées en mode « transmission » ou en mode « réflexion » suivant une configuration « tandem » (également connu sous le nom de « pitch and catch » dans la littérature anglo-saxonne).The device 1 comprises in another embodiment not shown a plurality of receiving probes 11, wide bands partially overlapping or not. In general, the number of emitting probes 10 is greater than the number of receiving probes 11 because a wide-band receiving probe is adapted to receive ultrasonic waves emitted by a plurality of different narrow-band transmitting probes. The emitter 10 and receiver 11 probes of the device 1 are physically disjoint and are arranged in different positions with respect to the structure 2. In a conventional manner, the emitter 10 and receiver 11 are arranged in "transmission" mode or in "reflection" mode. "Following a" tandem "configuration (also known as" pitch and catch "in the Anglo-Saxon literature).
En mode transmission, représenté sur la figure 1 a, les sondes émettrice 10 et réceptrice 11 sont agencées de sorte que la structure 2 est intercalée entre lesdites sondes, et les ondes ultrasonores reçues par la sonde réceptrice 11 sont des ondes ultrasonores ayant été émises par la sonde émettrice 10 et après propagation dans la structure 2.In transmission mode, represented in FIG. 1a, the emitter 10 and receiver 11 probes are arranged so that the structure 2 is interposed between said probes, and the ultrasonic waves received by the probe receiver 11 are ultrasonic waves that have been emitted by the emitter probe 10 and after propagation in the structure 2.
En configuration tandem, représenté sur la figure 1 b, les sondes émettrice 10 et réceptrice 11 sont agencées d'un même côté de la structure 2, et les ondes ultrasonores reçues par la sonde réceptrice 11 sont des ondes ultrasonores ayant été émises par la sonde émettrice 10 et ayant été renvoyées par la structure 2, par exemple réfléchies sur des faces de ladite structure et/ou s'étant propagées en surface de ladite structure.In the tandem configuration, shown in FIG. 1b, the emitter 10 and receiver 11 probes are arranged on the same side of the structure 2, and the ultrasonic waves received by the receiving probe 11 are ultrasonic waves that have been emitted by the probe emitter 10 and having been returned by the structure 2, for example reflected on the faces of said structure and / or propagated on the surface of said structure.
Le dispositif 1 selon l'invention est adapté à la mise en œuvre d'un procédé de contrôle non-destructif par ultrasons à couplage aérien de la structure 2.The device 1 according to the invention is adapted to the implementation of a method of non-destructive ultrasonic air-coupling control of the structure 2.
De manière classique, le procédé comporte une étape d'inspection dans laquelle on émet des ondes ultrasonores aériennes en direction de la structure 2, et dans laquelle on mesure des ondes ultrasonores renvoyées par ladite structure. Des caractéristiques des ondes ultrasonores mesurées (amplitude, temps de vol, etc.) sont utilisées pour évaluer des caractéristiques structurelles de la structure 2, comme par exemple la présence de défauts internes qui peuvent être dans le cas de structures sandwich un écrasement de la couche alvéolaire, un oubli de séparateur, etc. Selon l'invention, on émet des ondes ultrasonores aériennes en direction de la structure 2 sur une bande fréquentielle étroite, par exemple au moyen de la sonde émettrice 10 du dispositif 1 utilisée dans un mode de résonance longitudinal, et on mesure des ondes ultrasonores renvoyées par ladite structure 2 sur une bande fréquentielle large, par exemple au moyen de la sonde réceptrice 11.In a conventional manner, the method comprises an inspection step in which air ultrasonic waves are emitted in the direction of the structure 2, and in which ultrasonic waves returned by said structure are measured. Characteristics of the measured ultrasonic waves (amplitude, flight time, etc.) are used to evaluate the structural characteristics of the structure 2, such as the presence of internal defects which may be in the case of sandwich structures a crushing of the layer alveolar, an omission of separator, etc. According to the invention, aerial ultrasonic waves are emitted in the direction of the structure 2 over a narrow frequency band, for example by means of the emitter probe 10 of the device 1 used in a longitudinal resonance mode, and ultrasonic waves returned are measured. by said structure 2 over a wide frequency band, for example by means of the receiving probe 11.
La mise en œuvre du procédé selon l'invention introduit les mêmes avantages que ceux décrits précédemment dans le cadre du dispositif 1.The implementation of the method according to the invention introduces the same advantages as those described above in the context of the device 1.
Dans un mode préféré de mise en œuvre du procédé, on filtre un signal obtenu en mesurant les ondes ultrasonores renvoyées par la structure 2 avec un filtre sélectif, de fonction de transfert adaptée pour réduire la puissance des composantes fréquentielles mesurées en dehors de la bande d'émission étroite sur laquelle on a émis les ondes ultrasonores aériennes, par exemple de caractéristiques (largeur de bande, fréquence centrale, etc.) voisines de celles de ladite bande d'émission. En cas de décalage en fréquence des ondes ultrasonores reçues par rapport aux ondes ultrasonores émises, la fonction de transfert du filtrage est adaptée à la bande d'émission décalée reçue. Dans un mode particulier de mise en œuvre du procédé, on émet des ondes ultrasonores aériennes sur des bandes fréquentielles étroites différentes simultanément ou successivement. Les bandes fréquentielles étroites différentes se recouvrent partiellement ou non, et sont de préférence toutes comprises dans la bande de réception large sur laquelle on mesure les ondes ultrasonores aériennes.In a preferred embodiment of the method, a signal obtained is filtered by measuring the ultrasonic waves returned by the structure 2 with a selective filter of transfer function adapted to reduce the power of the frequency components measured outside the band. narrow emission on which the above-mentioned ultrasonic waves have been emitted, eg characteristics (bandwidth, central frequency, etc.) adjacent to those of said emission band. In the case of a frequency shift of the received ultrasonic waves with respect to the emitted ultrasonic waves, the transfer function of the filtering is adapted to the transmitted offset transmission band received. In a particular mode of implementation of the method, aerial ultrasonic waves are transmitted on different narrow frequency bands simultaneously or successively. The different narrow frequency bands overlap partially or not, and are preferably all included in the wide reception band on which the ultrasonic waves are measured overhead.
Avantageusement, on filtre le signal correspondant aux ondes ultrasonores reçues avec des filtres sélectifs de fonctions de transfert adaptées aux différentes bandes fréquentielles étroites sur lesquelles on a émis des ondes ultrasonores, le cas échéant décalées en fréquence. Le dispositif et le procédé selon l'invention permettent d'effectuer un contrôle non-destructif par ultrasons à couplage aérien peu sensible aux caractéristiques spectrales des sondes émettrice et réceptrice, et peu sensible aux décalages en fréquence des ondes ultrasonores reçues par rapport aux ondes ultrasonores émises. De plus, il est possible d'optimiser les transducteurs desdites sondes soit pour l'émission (en matériau piézoélectrique céramique et/ou piézoélectrique composite) soit pour la réception (transducteurs électro-capacitifs à base de matériau polymère ou copolymère) d'ondes ultrasonores aériennes.Advantageously, the signal corresponding to the received ultrasonic waves is filtered with selective filters of transfer functions adapted to the different narrow frequency bands on which ultrasonic waves, possibly frequency shifted, have been emitted. The device and the method according to the invention make it possible to carry out a non-destructive ultrasonic air-coupling control which is insensitive to the spectral characteristics of the emitter and receiver probes, and which is not very sensitive to the frequency shifts of the ultrasonic waves received with respect to the ultrasonic waves. issued. In addition, it is possible to optimize the transducers of said probes either for the emission (in ceramic piezoelectric material and / or piezoelectric composite) or for the reception (electro-capacitive transducers based on polymer or copolymer material) ultrasonic waves airline.
Le domaine d'application préféré de l'invention, bien que nullement limitatif, est celui du contrôle non-destructif par ultrasons à couplage aérien de structures aéronautiques en matériau composite, en particulier des structures sandwich intégrant une ou des couches alvéolaires (mousse, nid d'abeille, etc.), largement répandues dans l'industrie aéronautique, qui pourraient être endommagées et/ou polluées par un milieu de couplage liquide. The preferred field of application of the invention, although in no way limiting, is that of non-destructive ultrasonic airborne coupling control of aeronautical structures made of composite material, in particular sandwich structures incorporating one or more honeycomb layers (foam, nest bee, etc.), widely used in the aviation industry, which could be damaged and / or polluted by a liquid coupling medium.

Claims

REVENDICATIONS
1 - Dispositif (1 ) de contrôle non-destructif par ultrasons à couplage aérien d'une structure (2), comportant au moins une sonde ultrasonore, dite sonde émettrice (10), pour l'émission d'ondes ultrasonores en direction de ladite structure et au moins une sonde ultrasonore, dite sonde réceptrice (11 ), pour la réception d'ondes ultrasonores après propagation dans ladite structure, l'émission et la réception d'ondes ultrasonores s'effectuant au travers d'un milieu gazeux sans contact entre lesdites sondes ultrasonores et la structure (2), ledit dispositif étant caractérisé en ce que l'au moins une sonde émettrice (10) et l'au moins une sonde réceptrice (11 ) sont physiquement disjointes, et en ce qu'une bande fréquentielle d'émission1 - Device (1) for non-destructive ultrasonic air-coupling control of a structure (2), comprising at least one ultrasound probe, said emitting probe (10), for the emission of ultrasonic waves towards said structure and at least one ultrasonic probe, called receiving probe (11), for receiving ultrasonic waves after propagation in said structure, the emission and reception of ultrasonic waves being effected through a gaseous medium without contact between said ultrasound probes and the structure (2), said device being characterized in that the at least one emitting probe (10) and the at least one receiving probe (11) are physically disjoint, and in that one frequency of emission
(BE) de l'au moins une sonde émettrice (10) est de largeur inférieure à la largeur d'une bande fréquentielle de réception (BR) de l'au moins une sonde réceptrice (11 ), et est comprise dans ladite bande fréquentielle de réception. 2 - Dispositif (1 ) selon la revendication 1 , dans lequel l'au moins une sonde émettrice (10) comporte au moins un transducteur réalisé avec un matériau piézoélectrique céramique ou piézoélectrique composite. 3 - Dispositif (1 ) selon la revendication 2, dans lequel l'au moins une sonde réceptrice (11 ) comporte au moins un transducteur électro-capacitif. 4 - Dispositif (1 ) selon la revendication 3, dans lequel l'au moins un transducteur électro-capacitif de l'au moins une sonde réceptrice (11 ) comporte au moins une membrane en matériau polymère ou copolymère.(B E ) of the at least one emitting probe (10) is of width less than the width of a reception frequency band (B R ) of the at least one receiving probe (11), and is included in said reception frequency band. 2 - Device (1) according to claim 1, wherein the at least one emitter probe (10) comprises at least one transducer made of a composite piezoelectric ceramic or piezoelectric material. 3 - Device (1) according to claim 2, wherein the at least one receiving probe (11) comprises at least one electro-capacitive transducer. 4 - Device (1) according to claim 3, wherein the at least one electro-capacitive transducer of the at least one receiving probe (11) comprises at least one membrane of polymer material or copolymer.
5 - Dispositif (1 ) selon l'une des revendications 1 à 4, comportant une pluralité de sondes émettrices (10) de bandes fréquentielles d'émission (BE) différentes, étroites par rapport à la bande fréquentielle de réception (BR) de l'au moins une sonde réceptrice (11 ) et comprises dans ladite bande fréquentielle de réception.5 - Device (1) according to one of claims 1 to 4, comprising a plurality of emitting probes (10) of different transmission frequency bands (B E ), narrow with respect to the frequency reception band (B R ) of the at least one receiving probe (11) and included in said reception frequency band.
6 - Dispositif (1 ) selon la revendication 5, comportant un module de sélection6 - Device (1) according to claim 5, comprising a selection module
(15) d'une ou plusieurs sondes émettrices (10) à la fois. 7 - Dispositif (1 ) selon l'une des revendications 1 à 6, comportant un module de filtrage (14) en réception muni d'au moins un filtre à bande fréquentielle de largeur inférieure à la largeur de la bande fréquentielle de réception (BR) de l'au moins une sonde réceptrice (11 ), et adaptée à une bande fréquentielle démission (BE) d'une sonde émettrice (10).(15) one or more emitter probes (10) at a time. 7 - Device (1) according to one of claims 1 to 6, comprising a filtering module (14) in reception provided with at least one frequency band filter of width less than the width of the receiving frequency band (B R ) of the at least one receiving probe (11), and adapted to a resistor frequency band (B E ) of a transmitting probe (10).
8 - Procédé de contrôle non-destructif par ultrasons à couplage aérien d'une structure (2) dans lequel on émet des ondes ultrasonores aériennes en direction de ladite structure, on mesure des ondes ultrasonores après propagation dans ladite structure, et on évalue des caractéristiques structurelles de la structure (2) à partir de caractéristiques des ondes ultrasonores mesurées, ledit procédé étant caractérisé en ce que : - on émet les ondes ultrasonores aériennes sur une bande fréquentielle d'émission (BE), et on mesure les ondes ultrasonores aériennes sur une bande fréquentielle de réception (BR), - la bande fréquentielle d'émission (BE) est de largeur inférieure à la largeur de la bande fréquentielle de réception (BR), et est comprise dans ladite bande fréquentielle de réception.8 - A method of non-destructive ultrasonic airborne coupling of a structure (2) in which airborne ultrasonic waves are emitted towards said structure, ultrasonic waves are measured after propagation in said structure, and characteristics are evaluated. structural elements of the structure (2) from characteristics of the measured ultrasonic waves, said method being characterized in that: - the aerial ultrasonic waves are emitted on a frequency emission band (B E ), and the ultrasonic waves are measured overhead on a reception frequency band (B R ), the transmission frequency band (B E ) is of width less than the width of the reception frequency band (B R ), and is included in said reception frequency band.
9 - Procédé selon la revendication 8, dans lequel on filtre un signal obtenu en mesurant les ondes ultrasonores renvoyées par la structure (2) avec un filtre de bande fréquentielle adaptée à la bande fréquentielle d'émission (BE) sur laquelle on a émis les ondes ultrasonores aériennes. 10 - Procédé selon la revendication 8, dans lequel on émet des ondes ultrasonores sur une pluralité de bandes fréquentielles d'émission (BE) étroites différentes, et on filtre un signal obtenu en mesurant les ondes ultrasonores renvoyées par la structure (2) avec des filtres de bandes fréquentielles adaptées aux bandes fréquentielles d'émission sur lesquelles on a émis les ondes ultrasonores aériennes. 9 - Process according to claim 8, wherein a signal obtained by measuring the ultrasonic waves returned by the structure (2) is filtered with a frequency band filter adapted to the frequency transmission band (B E ) on which it has been transmitted. the aerial ultrasonic waves. 10 - The method of claim 8, wherein emitting ultrasonic waves on a plurality of different narrow transmission frequency bands (B E ), and filtering a signal obtained by measuring the ultrasonic waves returned by the structure (2) with frequency band filters adapted to frequency transmission bands on which the above-mentioned ultrasonic waves have been emitted.
PCT/EP2009/059888 2008-08-01 2009-07-30 Method and device for the air-coupled ultrasonic non-destructive testing of a structure WO2010012809A2 (en)

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US10962506B2 (en) 2016-01-19 2021-03-30 Northrop Grumman Systems Corporation Inspection devices and related systems and methods

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