• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    The invention relates to an air-coupled capacitive multi-element ultrasonic transducer (100) comprising: - a membrane (120) having an electrically conductive face; and a plurality of electrically independent conductive elements, composed of a central disk (111) and several rings (112) concentrically arranged with the central disk, the conductive elements each having a face arranged facing the membrane ( 120) and said faces of the conductive elements being of the same area; wherein the central disk (111) has a radius (R1) of between 10 mm and 15 mm and wherein the number of conductive elements is between 12 and 18.
    公开号:FR3054768A1
    申请号:FR1657305
    申请日:2016-07-28
    公开日:2018-02-02
    发明作者:Christine BIATEAU；Michel CASTAINGS；Mathieu RENIER
    申请人:Centre National de la Recherche Scientifique CNRS；Universite de Bordeaux；Institut Polytechnique de Bordeaux；
    IPC主号:
    专利说明:

    Holder (s): UNIVERSITY OF BORDEAUX, POLYTECHNICAL INSTITUTE OF BORDEAUX, NATIONAL CENTER FOR SCIENTIFIC RESEARCH.
    Extension request (s)
    Agent (s): CABINET CAMUS LEBKIRI Limited liability company.
    THERE IS AN AIR-COUPLED MULTI-PURPOSE ULTRASONIC TRANSDUCER.
    FR 3 054 768 - A1
    The invention relates to an air coupling capacitive multi-element ultrasonic transducer (100) comprising:
    - a membrane (120) having an electrically conductive face; and
    - A plurality of electrically independent conductive elements, composed of a central disc (111) and several rings (112) arranged concentrically with the central disc, the conductive elements each having a face arranged opposite the membrane (120 ) and said faces of the conductive elements being of the same area;
    in which the central disc (111) has a radius (R1) of between 10 mm and 15 mm and in which the number of conductive elements is between 12 and 18.

    i
    MULTI-ELEMENT CAPACITIVE AIR-COUPLED TRANSDUCER
    TECHNICAL AREA
    The present invention relates generally to the field of non-destructive ultrasonic testing. The invention relates more particularly to an ultrasonic transducer of the air coupling capacitive type making it possible to generate and / or detect ultrasound.
    STATE OF THE ART
    Non-destructive ultrasonic testing makes it possible to quickly inspect a structure, for example made of composite material or metal, without damaging it and sometimes without dismantling it. By propagating in the material of the structure, the ultrasonic waves provide information on the mechanical properties of the structure and reveal the presence of defects, on the surface or at depth. For example, ultrasonic waves can indicate the presence of cracks, delamination and areas of porosity in the structure, since these defects modify the amplitude and / or the shape of the waves.
    Non-destructive ultrasonic testing methods most often use a liquid coupling medium, which is a good conductor of ultrasonic waves, such as water or a gel. This liquid coupling medium makes it possible to carry out an acoustic impedance adaptation between the transmitting and receiving probes of ultrasonic waves, called transducers, and the structure to be inspected. The presence of the liquid coupling medium between the transducers and the structure can be ensured by partial or total immersion of the structure in the liquid or by continuous supply of the liquid, for example in the form of water jets. These liquid-coupled non-destructive testing methods are however cumbersome to implement, due to the need to provide a tank or a device for supplying the liquid. They also require cleaning and / or drying of the parts, and sometimes their disassembly. In addition, they are not suitable for the control of certain types of structures which do not tolerate coupling with a liquid. By way of example, mention may be made of so-called “sandwich” structures incorporating one or more cellular layers (foam, honeycomb, etc.), which are widely used in the aeronautical industry.
    In comparison, non-destructive non-contact ultrasonic testing processes, where ambient air is used as the coupling medium, are simpler to implement and allow continuous inspection of structures. However, they require the provision of air-coupled transducers whose efficiency is high, îo in order to compensate for the very strong attenuation of the ultrasonic waves undergone at each interface between the air and the solid materials (interface (s) air / transducer (s) and air / structure interface (s)).
    Capacitive ultrasonic transducers today allow the emission of ultrasonic waves into the air at high levels and their reception with sufficient sensitivity to use air as the coupling medium. These transducers also have a better frequency bandwidth than piezoelectric type transducers. They can consist of a single capacitive element or a multitude of electrically independent capacitive elements. Compared to single element technology, phased array technology increases the spatial resolution of the transducer. Indeed, by electronically controlling each of the elements, different settings such as angular scanning and focusing can be obtained. Multi-element transducers can adopt different geometries, including linear, annular, matrix and circular.
    The capacitive micromachined ultrasonic transducer (or CMUT, for “Capacitive Micromachining Ultrasonic Transducer”) is an example of a multi-element transducer. It consists of a large number of micro-diaphragms organized in a network and actuated electrostatically. This transducer is particularly compact because it is made from a silicon substrate using surface micromachining techniques. However, due to the geometry of the array of elements, in the form of a linear bar or a matrix, the CMUT transducer is not the most suitable for obtaining a focus of ultrasonic waves. Focusing of the ultrasonic waves is possible, by placing the elements on a curved substrate whose curvature fixes the central value of the focal length. The focusing distance cannot then vary (or very slightly), because of the small number of elements placed on the support. The CMUT transducer elements are produced in small numbers because the piezoelectric materials that compose them are difficult to machine on a small scale. This inability to modify the focusing distance implies to provide as many CMUT transducers as there are possible applications.
    The document [“Numerical modeling for the optimization of multi-element, capacitive, ultrasonic, air coupled transducer”, D. Zhang et al., Journal of Physics: Conférence Sériés, Volume 457, 012011, 2013] describes another example of a transducer ultrasonic capacitive multi-element with air coupling, annular configuration.
    This capacitive transducer comprises a membrane, one face of which is metallized, and a metal back plate on which the membrane is fixed. The rear plate has eight elements of identical active surface, distributed in a central disc and seven concentric rings. This transducer has a wide frequency bandwidth, a high efficiency and allows to focus the beam of ultrasonic waves, in order to adjust the spatial resolution. In addition, it allows the focusing distance to be adjusted dynamically, by applying variable delays to the electrical excitation signals sent to the elements ("emitter" mode) or delivered by the elements ("receiver" mode).
    However, the multi-element capacitive transducer of the above-mentioned document does not simultaneously offer great flexibility in adjusting the focusing distance, a high pressure level and a satisfactory resolution for the targeted applications.
    SUMMARY OF THE INVENTION
    There is therefore a need to provide a multi-element air-coupled capacitive ultrasonic transducer with great flexibility in adjusting the focusing distance, while having optimal spatial resolution and pressure level, in order to widen the field of application of this type of transducer.
    According to the invention, there is a tendency to satisfy this need by providing an air coupling capacitive multi-element ultrasonic transducer comprising:
    - a membrane having an electrically conductive face; and
    - A plurality of electrically independent conductive elements, composed of a central disc and several rings arranged concentrically with the central disc, the conductive elements each having a face îo disposed opposite the membrane and said faces of the elements being of same area;
    in which the central disc has a radius of between 10 mm and 15 mm and in which the number of conductive elements is between 12 and 18.
    With such an active surface (the selected radius fixes the active surface of the central disc and consequently that of all the conductive elements) and such a number of conductive elements, the capacitive transducer according to the invention benefits from a more focused range. extent. In addition, thanks to the number of elements selected, the transducer according to the invention has a better pressure efficiency and spatial resolution than those of the transducer of the prior art. Such a number of elements finally offers the possibility of more finely adjusting the focusing distance, that is to say with a smaller step.
    The possibilities for adjusting the frequency and the focusing distance are therefore increased, which makes it possible to satisfy a greater number of applications. For example, in the case of non-destructive testing of structures, the transducer according to the invention makes it possible to detect finer defects located at a greater depth in the structures. Without moving the transducer, just by modifying the focusing distance, it is possible to adapt to structures whose surface geometry would be variable, for example a composite plate with a step or a variation in thickness. The transducer can also make it possible to adjust the focusing characteristics, in particular the size of the focal spot, so as to detect defects whose dimensions are beyond a certain critical size, without being sensitive to inhomogeneities of material of smaller sizes and should not be considered as defects. The transducer according to the invention thus adapts to a greater variety of structures and needs, with regard to their shape or their composition.
    The adjustment of the focusing distance of a multi-element transducer operating in “emission” mode can be carried out by applying phase shifts to the excitation signals sent to the different elements, for example by means of multi-channel electronics. The adjustment of the focusing distance of a multi-element transducer operating in “reception” mode can be carried out by applying phase shifts to the signals delivered by the various elements having detected an acoustic wave, still by means of multi-channel electronics.
    The conductive elements are advantageously separated by a distance of between 1 mm and 1.8 mm, and preferably between 1.4 mm and 1.6 mm.
    According to an exemplary embodiment of the transducer according to the invention, the conductive elements are 16 in number, the central disc has a radius equal to 10 mm and the conductive elements are spaced by a distance equal to 1.4 mm.
    The invention also relates to a method allowing the simple and inexpensive manufacture of an air coupling capacitive multi-element ultrasonic transducer with good performance.
    This process includes the following steps:
    forming a rear plate comprising a plurality of electrically independent conductive elements, including a central disc and several rings arranged concentrically with the central disc, the rear plate having a rear face and a front face, called the active face, opposite to the back side; and
    - have on the active face of the rear plate a membrane having an electrically conductive face;
    the formation of the back plate comprising the following operations:
    • machining a plurality of concentric annular grooves in a metal plate;
    • fill the grooves with an electrically insulating adhesive; and • remove a portion of the metal plate so that the glue-filled grooves pass through.
    The method according to the invention may also have one or more of the characteristics below, taken individually or in any technically possible combination:
    io - a step of micro-sandblasting of the active face of the back plate, so as to form microcavities;
    a step consisting in applying a bias voltage, preferably between 30 V and 100 V, between the electrically conductive face of the membrane and the conductive elements of the rear plate;
    a step of fixing the rear plate inside a support by means of electrically insulating adhesive, a portion of the support advantageously being removed at the same time as the portion of the metal plate so as to form a flat surface, the membrane being arranged on this flat surface;
    - The annular grooves have the same width; and
    - the electrically insulating adhesive is an epoxy resin.
    BRIEF DESCRIPTION OF THE FIGURES
    Other characteristics and advantages of the invention will emerge clearly from the description which is given below thereof, by way of indication and in no way limiting, with reference to the appended figures, among which:
    - Figure 1 schematically shows a multi-element ultrasonic transducer with air coupling capacitive according to a preferred embodiment of the invention;
    - Figure 2 shows a top view of a rear plate of the ultrasonic transducer of Figure 1;
    - Figure 3 shows the maximum sound pressure at the Fresnel distance radiated by the transducer according to the invention, as a function of the number of elements of the back plate;
    - Figure 4 shows the lateral resolution for a focusing distance equal to the Fresnel distance of the transducer of Figure 1, depending on the number of elements of the back plate;
    - Figure 5 shows the variations in the amplitude of the axial pressure field radiated by the transducer according to the invention and by the transducer of the prior art, at the focusing distance equal to the Fresnel distance of each of the transducers ;
    - Figure 6 shows the variations in the amplitude of the pressure field transverse to the Fresnel distance radiated by the transducer according to the invention and by the transducer of the prior art;
    - Figures 7A to 7E show steps in a manufacturing process of the back plate according to Figure 2 and its support in insulating material; and
    - Figure 8 shows a particular way of assembling the air-coupled capacitive multi-element transducer according to the invention.
    For the sake of clarity, identical or similar elements are identified by identical reference signs in all of the figures. Furthermore, in FIGS. 3, 5 and 6, the sound pressure is expressed in arbitrary unit (“a.u.”, for “arbitrary unit” in English).
    DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT
    FIG. 1 represents a preferred embodiment of a multi-element ultrasonic transducer 100 of the capacitive type.
    The phased array ultrasonic transducer 100 is optimized, in terms of working frequency and spatial resolution, for non-destructive testing of materials.
    The objective of this control can be to detect the presence of defects, such as cracks, voids or porosity, in mechanical parts or structures, to measure the thickness of the materials and / or to analyze their properties .
    The transducer 100 is air-coupled, that is, it uses ambient air as the coupling medium for the ultrasonic waves. There is therefore no contact between this transducer and the material to be checked. The advantages of this type of transducer are the ease of implementing control procedures and the absence of contamination or pollution of the material.
    The transducer 100 comprises a rear plate 110 and a membrane 120 arranged opposite the rear plate 110. The rear plate 110 is rigid and massive compared to the membrane 120, which is (by definition) flexible and thin. Preferably, the thickness of the back plate 110 is between 4 mm and 10 mm, while the thickness of the membrane 120 is between 3 pm and 8 pm. The back plate 110 and the membrane 120 both have the shape of a disc. At least one face of the membrane 120 is electrically conductive.
    In the preferred embodiment of Figure 1, the membrane 120 is formed of a layer of polymeric material 121, such as polyethylene terephthalate (PET), covered with a thin layer of metal 122, for example aluminum. The metal layer 122 advantageously covers the front face of the polymer layer 121, that is to say the face facing the material to be controlled (the rear face of the polymer layer 121 being directed towards the rear plate 110) . The membrane 120 can thus be placed in contact with the rear plate 110 and fixed to the edges thereof, without creating a short circuit between the metal layer 122 and the rear plate 110.
    The rear plate 110, shown in top view in FIG. 2, comprises several conductive elements spaced apart from each other, and more particularly a central disc 111 and rings 112. The rings 112 are arranged concentrically with the central disc 111 These elements (disc and rings) are preferably made of metal, for example aluminum. The disc 111 and the rings 112 are advantageously of the same thickness and nested one inside the other, so that the rear plate 110 has main faces (i.e. front and rear) planar and parallel (cf. FIG. 1). The elements 111-112 of the back plate 110 are separated by a dielectric material 113, preferably an epoxy resin. In FIG. 2, "x" designates the radial position of the rings 112 relative to the center "O" of the central disc 111.
    Each element 111-112 of the back plate 110 interacts with the membrane 120 in the manner of a capacitor, to convert an ultrasonic wave into an electrical signal (in the manner of a microphone), and vice versa (in the manner of a speaker). The membrane 120 constitutes the first movable armature (or electrode) of the capacitor, while the element concerned of the rear plate 110 constitutes the second armature of the capacitor, which is on the contrary fixed. In other words, each of the elements, the disc 111 and the rings 112, constitutes with a portion of the membrane 120 an active element of the capacitive type. The multi-element ultrasonic transducer 100 can therefore be seen as a multitude of single-element capacitive transducers, integrated in the same housing and sharing the same membrane.
    To generate ultrasound, the membrane 120 of the transducer 100 is permanently prestressed by a DC bias voltage Vdc and vibrates at a resonant frequency under the effect of an alternating excitation voltage Vac applied to each conductive element 111- 112 of the rear plate 110. This movement of the membrane 120 gives rise to a beam of ultrasonic waves 130, corresponding to the superposition of the acoustic beams generated by the various capacitive single-element transducers. In FIG. 1, the axis of revolution Oz of the central disc 111 and of the rings 112 coincides with the direction of propagation of the beam of ultrasonic waves 130. This axis Oz is hereinafter called "acoustic axis" of the ultrasonic transducer 100.
    The phased array ultrasonic transducer 100 inherently has a wide frequency bandwidth due to the fact that it is of the capacitive type. This wide bandwidth makes the transducer 100 compatible with many materials, because the frequency of the alternating excitation signal Vac, called the working frequency, is chosen according to the material to be checked.
    The active surface S of the elements 111-112, that is to say the surface facing the ίο membrane 120, advantageously comprises microcavities sized to increase the bandwidth and the efficiency of the transducer. This surface roughness is for example obtained by micro-sandblasting of the front face of the elements.
    The acoustic pressure field of the ultrasonic beam generated by a flat single-element transducer emitting a purely sinusoidal wave conventionally comprises two zones: the near field zone (or Fresnel zone) where the pressure field is inhomogeneous, and the field zone far (or io Fraunhofer area) where the pressure field diverges. The Fresnel distance Df is the distance at which one passes from the near field zone to the far field zone. This distance Df is that at which the ultrasonic beam has the most interesting characteristics: a high acoustic pressure (when the attenuation in air is negligible, it is the position of the last maximum pressure) and reduced lateral dimensions ( in other words good lateral resolution). The distance Df is proportional to the ratio of the active surface S to the emitted wavelength λ, that is to say in the case of a disc-shaped source of radius r:
    (1)
    For an annular source, the radius of the active surface S to be taken into account is:
    with rext and nnt respectively the external and internal radii of the ring.
    The central disc 111 and the concentric rings 112 of the rear plate 110 are here dimensioned so that they have the same active surface S. In other words, the front faces of the central disc 111 and the rings 112 are likewise area. Thus, if each of these elements 111-112 is excited by the same purely sinusoidal signal, the field radiated by each of the elements will have the same Fresnel distance Df. Consequently, the amplitude of the pressure at this distance Df will be equal to the sum of the fields radiated by the different elements.
    To have an identical active surface, the central disc 111 and the rings n
    concentric 112 necessarily have different widths. This configuration has the advantage of minimizing the amplitude of the secondary lobes of the sound pressure field. These secondary lobes represent part of the acoustic energy which is radiated in directions different from the acoustic axis Oz of the transducer 100 (i.e. the axis of the disc 111 and the rings 112; cf. Fig. 1). They can induce artifacts on the images of the materials inspected and lead to the detection of "false defects". The irregularity in the width of the transducer elements is therefore an advantage for obtaining a beam with few side lobes, or even without side lobes.
    In practice, the elements of the transducer are not excited by purely sinusoidal signals, but by wave trains. Consequently, when the excitation signals are all in phase, the focusing of the transducer at the Fresnel distance (common to all the rings) does not take place naturally. The ultrasonic beam certainly has a certain directivity, but it is comparable to that of a single-element transducer formed by a single disc of radius equal to the external radius of the peripheral element. The lateral resolution of such a system is not sufficient.
    In order to be able to effectively improve the lateral resolution and increase the amplitude of the maximum pressure at the Fresnel distance, phase shifts are introduced between the excitation signals of the disc 111 and the rings 112. This has the effect of concentrating, or focus, the beam of ultrasonic waves 130 emitted by the transducer 100 around a point located on the acoustic axis Oz of the transducer 100. The ultrasonic beam 130 then converges towards a focal zone where it becomes locally plane. At a greater distance, the beam diverges. The focusing distance, denoted below Zf, is measured from the source (i.e. the membrane 120) along the axis Oz and can be equal to the Fresnel distance Df.
    This focusing makes it possible to detect finer faults, with a better signal-to-noise ratio. The other advantage of the multi-element transducer according to the invention is that one can then easily modify the focusing distance Zf and therefore the detection depth. The focusing distance Zf is adjusted by modifying the relative phase shifts between the excitation signals, for example using multi-channel electronics. The amplitude of the pressure and the lateral dimensions of the ultrasonic beam at the level of the focusing zone depend on the focusing distance Zf and on the wavelength λ.
    The performance of the multi-element capacitive transducer 100, in terms of spatial resolution and efficiency in particular, also depends on its geometry. Numerical simulations have made it possible to identify the geometric characteristics of the transducer 100, such as the number N of elements (central disc and concentric rings) of the rear plate 110 and the active surface S of these elements, which have a strong impact. on the performance of the transducer. The results of these digital simulations (at a frequency of 300 kHz) are given below in relation to Figures 3 and 4.
    By definition, the efficiency of a transducer is defined as the ratio between the acoustic power delivered and the electric power consumed. The sound power is roughly proportional to the square of the sound pressure generated by the beam of ultrasonic waves. Consequently, the higher the sound pressure of the beam, the higher the efficiency of the transducer.
    FIG. 3 represents the amplitude p (z = Df) of the maximum pressure located at the Fresnel distance Df when this distance is chosen as the focusing distance Zf on the axis Oz (ie in the plane of FIG. 2, at x = 0), as a function of the number N of elements of the transducer 100 and for values of the radius R1 of the central element 111 of between 5 mm and 12 mm. As a reminder, the radius R1 fixes the active surface S of all the elements 111-112 (S = π. Æl 2 ). The distance d between two consecutive 111-112 elements is constant and here fixed at 1 mm.
    This figure shows that the amplitude p (z = Df) of the maximum pressure increases with the number N of elements of the rear plate 110, for a fixed surface S (ie a fixed radius R1). It also shows that the maximum pressure p (z = Df) (reached at the Fresnel distance Df) does not necessarily increase with the active surface S of the elements. For example, for a number N of elements equal to 8, the maximum pressure developed by surface elements S = π. 12 2 mm 2 is less (almost half) than the maximum pressure obtained with surface elements S = π. 5 2 mm 2 .
    FIG. 4 represents the lateral resolution R (z = Df) (ie the dimension of the beam along the axis Ox) at the Fresnel distance Df, as a function of the number N of elements and for values of radius R1 of between 5 mm and 12 mm. The lower the value indicated on the ordinate, the better the lateral resolution.
    It can be seen from this figure that the lateral resolution improves by increasing the number N of elements (with fixed surface S) and by decreasing the active surface S of the elements (for a fixed number N of elements). The dimensions of the focal spot are proportional to the focusing distance and inversely proportional to the total radius of the phased array transducer (and therefore to the number of elements). However, since the Fresnel distance is proportional to the active surface, (square of the radius of the central element), an increase in the active surface S of the elements deteriorates the spatial resolution.
    Thus, to obtain the best performance in terms of efficiency (Fig. 3) and spatial resolution (Fig. 4), the transducer 100 should have a high number of elements of small area S. The efficiency and the spatial resolution are not however, not the only criteria to be taken into consideration for the dimensioning of the transducer 100.
    The inventors have found, surprisingly, that by choosing a number N of elements between 12 and 18 and a radius R1 of the central disc 111 between 10 mm and 15 mm, the focusing range of the phased array transducer 100 is extended significantly. In addition, its performance is close to the maximum level, its spatial resolution is very good and the dimensions and spacings of its various elements make it possible to achieve it with common machining and assembly means. In addition, the technology based on the "capacitive" effect of the transducer gives it a wide bandwidth, which ranges from 100 kHz to 500 kHz at -20 dB. This wide bandwidth makes it possible to choose the operating frequency so as to tune it to one of the resonance frequencies of the structure to be checked. As the characteristics of the focal task (pressure amplitude and dimensions) depend on the frequency, the focusing distance can be adjusted so as to optimize the beam to be emitted.
    Once the control frequency has been chosen, this focusing distance Zf can be adjusted from Zf-min = 40 mm up to a distance Zf-max equal to approximately twice the Fresnel distance (up to 350 mm at 300 kHz for 16 elements and R1 = 15 mm). By way of comparison, the bandwidth of the multi-element transducer of the prior art (8 surface elements S = π. 7.87 2 mm 2 is equal to 100 kHz - 500 kHz and its focusing range is approximately 30 mm to 110 mm.
    Furthermore, with a number N of elements between 12 and 18, the transducer 100 makes it possible to adjust the focusing distance more finely, compared to the transducer of the prior art equipped with only 8 elements. Indeed, the higher this number N, the more precisely the delay law applied to the excitation signals can be defined.
    Finally, the geometric characteristics of the transducer 100 offer good compromises between performance and difficulties in manufacturing the back plate. Indeed, a backplate with a very high number of rings (> 20) of small area (R1 <10 mm) can be particularly difficult to machine, especially if it is made of a metal such as aluminum.
    The distance d between two consecutive elements 111-112 is advantageously between 1 mm and 1.8 mm, and preferably between 1.4 mm and 1.6 mm. Thanks to this small spacing between the elements 111-112, the multi-element ultrasonic transducer 100 remains compact and can therefore be used more easily.
    According to a particular embodiment, the multi-element ultrasonic transducer 100 comprises a central disc of radius R1 equal to 10 mm and 15 concentric rings of the same active surface, ie a total of 16 conducting elements. The distance between two consecutive elements is constant and equal to 1.4 mm.
    FIG. 5 represents a calculation of the amplitude of the axial acoustic pressure p (z) (ie along the axis Oz) radiated by this example of the transducer according to the invention (curve in solid line) and, by way of comparison, that developed by the transducer of the prior art (curve in dotted lines). In this figure, each of the transducers focuses at its own Fresnel distance. Similarly, Figure 6 îo represents the transverse sound pressure p (x) at the focusing distance (i.e. Zf = Df) for these two transducers. The frequency is the same in both cases (300 kHz).
    Figure 5 shows that the axial resolution (in the direction of the acoustic axis Oz) is also improved, since the main lobe of the axial acoustic pressure p (z) is narrower for the 16-element transducer than for the 8 elements. The improvement here is around 25% (9 mm instead of 12 mm).
    Figure 6 shows that the lateral resolution of the ultrasonic beam calculated for the 16-element transducer is about 12% finer than that of the 8-element transducer (1.4 mm versus 1.6 mm). This lateral resolution is measured, for each curve, by taking the width at mid-height (Pmax / 2) of the main lobe from the transverse acoustic pressure p (x).
    It can also be seen in these figures that the amplitude Pmax of the maximum sound pressure (at the Fresnel distance Df) of the 16-element transducer is almost twice that of the 8-element transducer (945 against 492 in arbitrary units ). The efficiency of the 16-element transducer is therefore significantly higher (by a factor of 4) than that of the 8-element transducer.
    Following numerical calculations carried out for different focusing distances (always at a frequency of 300 kHz), the table below gives the orders of magnitudes of the performances for the transducer of the prior art and two examples of the transducer according to the invention .
    Distance fromZf focus (mm) Pressure p ma x (ua) Resolutionlateral (mm) Resolutionaxial (mm) N = 8 30 "250 1.1 6 R1 = 7.87 mm 54 "490 1.6 12 110 "330 3.0 42 180 "160 4.9 99 N = 16 40 "500 0.8 5 R1 = 10 mm 87.5 "950 1.4 9 d = 1.4 mm 180 "500 2.8 31 N = 16 40 "590 0.7 6 R1 = 15 mm 160 "750 1.8 15 d = 1.4 mm 350 "350 3.8 62
    The values given in italics for the transducer of the prior art at a focusing distance of 180 mm, outside the advertised focus range, are given for comparison only (the pressure there is much lower compared to the transducer at 16 elements).
    The multi-element ultrasonic transducer according to the invention therefore has higher performance in terms of spatial resolution and efficiency compared to the capacitive multi-element translator of the prior art. The high efficiency and resolution favor the detection and localization of small defects (of the order of a millimeter), while the large frequency bandwidth allows a large number of applications. More particularly, the transducer 100 makes it possible to control parts or structures of complex shape, made up of very diverse materials (metals, polymeric or composite materials, wood, ceramics, etc.). Finally, unlike other capacitive type transducers, the transducer 100 has the ability to dynamically change the focus distance. Indeed, it is possible to create a focal task with an amplitude greater than half of the maximum amplitude over distances between 40 mm and approximately twice the Fresnel distance from the transducer. It can therefore replace a plurality of transducers each having a fixed focusing distance.
    In addition to non-destructive testing, which mainly concerns industrial applications (space, aeronautics, civil engineering, etc.), the multi-element ultrasonic transducer according to the invention may be suitable for applications in the field of telemetry.
    One way of manufacturing and assembling the components of the phased array ultrasonic transducer 100 will now be described in relation to FIGS. 7A-7E and 8.
    io
    FIGS. 7A to 7E represent steps S1 to S5 of a process for manufacturing the back plate 110 comprising the central disc and the concentric rings. This process allows a simple back plate with a central disc and at least one concentric ring to be made simply and inexpensively. It is applicable whatever the number N of elements, the radius R1 of the central disc and the spacing d between the elements (within the limits of manufacture by machining). It turns out to be particularly beneficial for a high number of rings (N> 10), as in the case of the transducer according to the invention.
    In step S1 of FIG. 7A, annular grooves 800 are machined in a metal disc 801, preferably made of aluminum. The grooves 800 are concentric and intended to delimit the elements of the rear plate. In the example shown, the thickness of the metal disc 801 is 10 mm, while the grooves 800 have a depth of about 7 mm. Therefore, the grooves 800 do not get along the entire thickness of the metal disc 801. The grooves are preferably the same width, for example 1.4 mm, so that the elements of the back plate are evenly spaced.
    In step S2 (FIG. 7B), a dielectric material is deposited in the grooves 800 until forming a layer 802 of surplus dielectric material on the upper face of the metal disc 801. The dielectric material is an adhesive, preferably a two-component epoxy resin.
    Then, in S3 (FIG. 7C), the metal disc 801 covered with the resin layer 802 is inserted into a backplate support 803 made of electrically insulating material, for example polyvinyl chloride (PVC). The support 803 comprises a housing 804 arranged to receive the metal disc 801. The metal disc 801 is pushed into the housing 804 until the resin layer 802 comes into contact with the bottom of the housing 804. The resin fulfills several functions , including that of gluing the metal disc 801 into the support 803. Preferably, the housing 804 has a height equal to the thickness of the metal disc 801 (10 mm) and the total thickness of the support 803 is for example 15. mm. The housing 804 has a diameter slightly greater than that of the disc 801, so that the resin overflows at the periphery of the disc, in the space between the metal disc 801 and the side wall of the support 803.
    A groove 806 is advantageously arranged through the bottom of the housing 804, up to the upper face of the support 803. When the metal disc 801 is pressed against the bottom of the housing 804, the excess resin flows and is evacuated by this orifice. A drilling hole (not shown in FIG. 7C) can also be arranged in the side wall of the support 803, in substitution or in addition to the groove 806, in order to evacuate the excess resin.
    Step S4 of FIG. 7D consists in machining, preferably by means of a lathe, the lower portions of the metal disc 801 and of the support 803 until reaching the resin located in the grooves 800, for example on a thickness of about 4 mm. The glue-filled grooves 800 thus pass through, that is to say that they extend from one face to the other of the metal plate. This separates the different portions of the metal disc 801 intended to form the conductive elements of the rear plate of the transducer. The resin placed between the conductive elements keeps them in a single block and electrically isolates them from each other.
    The machining of step S4 is advantageously carried out so that the rear plate 110 and the support 803 have a flat "rectified" surface. Thus, the risk of damaging (by shearing) the membrane 120 subsequently arranged on this surface is reduced.
    In step S4, the groove 806 can also be enlarged by milling, in order to provide access, on the rear face 110a of the rear plate, to all the conducting elements of the rear plate. This access is intended for the electrical connectors of the back plate.
    Preferably, the manufacturing process further comprises a step of preparing S5 of the active surface of the back plate 110 (glued in the support 803), in order to create microcavities (of the order of pm). This step S5 is illustrated in FIG. 7E and includes at least one micro-sandblasting operation. The microcavities are formed on the front face 110b of the rear plate 110 by the projection of hard grains, the diameter of which is decisive in order to impart a wide frequency bandwidth and optimal performance to the ultrasonic multi-element transducer.
    The preparation step S5 of the front face 110b is preferably composed of several sub-steps: at least one polishing operation, a micro-sandblasting operation and a cleaning operation. In fact, the dressing tool used when machining the back plate 110 (in step S4) leaves a rough surface state. In particular, the front (active) face 110b of the rear plate 110 has roughness of much larger dimensions than the desired microcavities. It is therefore necessary to remove these irregularities before creating the microcavities by sandblasting.
    First of all, a so-called mirror-type reference surface is produced by polishing, for example by successively passing glass papers of increasing particle size (180, 400, 800 then 1200 grains / cm 2 ) then successively using diamond pastes of 3 pm, 1 pm and% pm in roughness. Sandblasting is then carried out by projecting onto the front face 110b of the rear plate 110 an abrasive powder (for example white corundum F400 with an average particle size equal to 17 μm), preferably under a pressure of 5 bars with a nozzle of 1, 8 mm in diameter. The assembly constituted by the rear plate 110 and the support 803 is preferably held about ten centimeters from the nozzle. Sandblasting is carried out until a uniform surface (with the naked eye) is obtained on the front face 110b of the back plate 110. Finally, the back plate-support assembly is cleaned to remove the particles generated by the polishing and sanding operations, then dried. The cleaning is for example carried out in an ultrasonic bath.
    FIG. 8 represents a preferred embodiment of the step of assembling the back plate 110 with the membrane 120 and other components of the phased array ultrasonic transducer 100.
    The membrane 120 is deposited on the front face 110b of the rear plate 110, orienting its metallized conductive face (in aluminum) towards the outside. The membrane 120 was previously cut around a cylindrical template with a diameter greater than the diameter of the back plate 110, so that the peripheral edge of the membrane 120 rests on the insulating support 803. Thus, the membrane 120 covers the entire active surface. of the back plate 110 and, for example, half the width of the insulating support 803.
    A retaining ring 900 (for example made of aluminum), with an internal diameter slightly greater than the diameter of the rear plate 110, is deposited on the front face of the membrane 120, directly above the support 803 located on the other side of the membrane, that is to say on the rear face. The retaining ring 900 advantageously has a chamfer on its internal diameter and a mirror-rectified surface condition so as not to subsequently damage the membrane during assembly or operation of the transducer 100.
    Furthermore, an electrical connector 901 is disposed in the groove 806 of the support 803, in contact with the rear face of the various conductive elements. The electrical connector 901 is connected by a set of electrical wires 902 to a control electronics (not shown in FIG. 8) comprising a power source and / or a processing circuit. The connector 901 will later be used to route alternative excitation signals to the conductive elements (when the transducer is in transmitter mode) or to recover measurement signals (when the transducer is configured in receiver mode).
    The electrical connector 901 also makes it possible to apply a DC bias voltage (preferably between 30 V and 100 V) to the conductive elements of the rear plate 110, while the retaining ring 900, electrically conductive, provides grounding. membrane 120 (see also Fig. 1). Under the effect of this bias voltage, the membrane 120 stretches. The DC bias voltage is maintained during mounting of the transducer, then during operation. A perfectly tensioned membrane, without any air bubble trapped between the membrane and the back plate 110, guarantees optimal final performance.
    Then, the assembly of these various components (back plate in its support, membrane and retaining ring) is carried out inside a cylindrical housing 903 (made of conductive material, for example aluminum) until the retaining ring 900 comes into abutment against the bottom of the housing 903. The bottom of the housing 903 has a circular opening 904, of diameter equal to the inside diameter of the retaining ring 900, which allows the membrane 120 to be seen.
    Finally, a rear cover 905 (made of electrically conductive material, for example aluminum) is fixed to the cylindrical housing 903, facing the rear plate 110, for example by means of several screws. The rear cover 905 is provided with a projecting portion 906, which abuts against the support 803 of the rear plate 110. When the cover 905 is screwed onto the cylindrical housing 903, this projecting portion 906 presses on the support 803 , so as to bring the membrane 120 into abutment against the retaining ring 900 (which is nestled at the bottom of the housing 903).
    After this assembly, the phased array ultrasonic transducer 100 is operational.
    Many variants and modifications of the manufacturing process according to the invention will appear to a person skilled in the art. In particular, this method is not limited to the order of the assembly steps which has just been described with reference to FIG. 8. It is in particular possible to successively introduce the retaining ring 900, the membrane 120 and the rear plate 110 in the cylindrical housing 903, rather than introducing all of these elements simultaneously. In addition, other ways of connecting the conductive elements of the rear plate to the control electronics can be envisaged.
    权利要求:
    Claims (4)
    [1" id="c-fr-0001]
    1. Air coupled capacitive multi-element ultrasonic transducer (100) comprising:
    5 - a membrane (120) having an electrically conductive face; and
    - A plurality of electrically independent conductive elements, composed of a central disc (111) and several rings (112) arranged concentrically with the central disc, the conductive elements each having a face arranged opposite the membrane (120 ) and said faces of the conductive elements being of the same area (S);
    characterized in that the central disc (111) has a radius (R1) of between 10 mm and 15 mm and in that the number (N) of the conductive elements is between 12 and 18.
    15
    [2" id="c-fr-0002]
    2. Transducer (100) according to claim 1, wherein the conductive elements are separated by a distance (d) between 1 mm and 1.8 mm, and preferably between 1.4 mm and 1.6 mm.
    [3" id="c-fr-0003]
    3. Transducer (100) according to one of claims 1 and 2, wherein the
    There are 20 conductive elements (N) of 16 and in which the central disc (111) has a radius (R1) equal to 10 mm.
    [4" id="c-fr-0004]
    4. A transducer (100) according to claim 3, wherein the conductive elements are spaced by a distance (d) equal to 1.4 mm.
    113 113
    类似技术:
    公开号 | 公开日 | 专利标题
    WO2018019778A1|2018-02-01|Multi-element, capacitive, ultrasonic, air-coupled transducer
    FR2923612A1|2009-05-15|INSONIFYING DEVICE COMPRISING A THREE-DIMENSIONAL NETWORK OF SPIRAL EMITTERS PROVIDED TO GENERATE A HIGH-INTENSITY FOCUSED WAVE BEAM
    FR2866438A1|2005-08-19|Optical reflecting unit for use in e.g. telescope, has set of plates forming stack type structure, where plates have different stiffness depending on orientation and made up of silicon wafers
    EP0385897A1|1990-09-05|Microechographic probe using ultrasound focusing through a deformable surface
    FR2848478A1|2004-06-18|Micromachined ultrasonic transducer device useful in ultrasound imaging systems, comprises transducer array on a substrate, and body of acoustically attenuative material that supports the substrate and flexible electrical connections
    FR2910826A1|2008-07-04|Device for production of longitudinal ultrasonic acoustic vibrations in user element e.g. tube, comprises electro-acoustic converter with pair of piezo-electric ceramics, and intermediate element between the converter and user element
    EP1144948B1|2005-02-16|Gyroscopic sensor and apparatus for measuring rotation
    FR2531298A1|1984-02-03|HALF-WAVE TYPE TRANSDUCER WITH PIEZOELECTRIC POLYMER ACTIVE ELEMENT
    FR3054719A1|2018-02-02|PROCESS FOR MANUFACTURING A CAPACITIVE MULTI-ELEMENTS ULTRASONIC TRANSDUCER WITH AIR COUPLING
    FR3080683A1|2019-11-01|MEANS OF MEASURING FLUID
    EP3509214B1|2020-11-18|Micro or nanomechanical device for detecting particles
    EP2764616B1|2015-12-16|Electroacoustic transducer with periodic ferroelectric polarization produced on a micromachined vertical structure
    EP3213531B1|2019-09-11|Electro-acoustic transducer, related assembly and system
    EP2936140A1|2015-10-28|Reconfigurable device for checking a composite structure using ultrasound
    EP2406625B1|2018-06-27|Device and method for the nondestructive monitoring of complex structures using ultrasonic waves
    FR2655804A1|1991-06-14|MEANS AND METHOD FOR NON-UNIFORM POLARIZATION OF PIEZOELECTRIC TRANSDUCERS.
    EP0538110B1|1996-12-18|Ultrasonic apparatus for testing composite materials and corresponding method
    FR2796153A1|2001-01-12|Automatic non-destructive testing of testing tubes for all manner of internal defects uses a bar of transducer elements, that can be activated in groups according to a phase law, which have a shaped element to direct the beam
    EP1540312A1|2005-06-15|Method and device for measuring a light flux backscattered by a dispersed medium, unperturbed by interface reflections
    EP2887007B1|2017-08-02|Setting device for monitoring components
    EP2361383B1|2018-05-30|Device and method for studying a study area by means of an acoustic wave
    WO2014060574A1|2014-04-24|Ultrasound probe for contact measurement of an object and its manufacturing process
    FR2511571A1|1983-02-18|ELECTROACOUSTIC TRANSDUCER WITH CONDENSER WITH POLARIZED SOLID DIELECTRIC
    FR2596593A1|1987-10-02|METHOD OF SUPPRESSING PARASITE ECHOS IN VOLUME WAVE ELECTROACOUSTIC DELAY LINES, AND DELAY LINE USING THE SAME
    EP3526871A1|2019-08-21|Method for generating a plurality of currents, each having a frequency
    同族专利:
    公开号 | 公开日
    EP3490727A1|2019-06-05|
    WO2018019778A1|2018-02-01|
    FR3054768B1|2018-08-10|
    US20190160491A1|2019-05-30|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US5520188A|1994-11-02|1996-05-28|Focus Surgery Inc.|Annular array transducer|
    US6613004B1|2000-04-21|2003-09-02|Insightec-Txsonics, Ltd.|Systems and methods for creating longer necrosed volumes using a phased array focused ultrasound system|
    JP6606034B2|2016-08-24|2019-11-13|株式会社日立製作所|Capacitive detection type ultrasonic transducer and ultrasonic imaging apparatus including the same|
    DE102017115923A1|2017-07-14|2019-01-17|Infineon Technologies Ag|Microelectromechanical transducer|
    US11181627B2|2018-02-05|2021-11-23|Denso Corporation|Ultrasonic sensor|
    法律状态:
    2017-06-20| PLFP| Fee payment|Year of fee payment: 2 |
    2018-02-02| PLSC| Publication of the preliminary search report|Effective date: 20180202 |
    2018-06-21| PLFP| Fee payment|Year of fee payment: 3 |
    2020-06-23| PLFP| Fee payment|Year of fee payment: 5 |
    优先权:
    申请号 | 申请日 | 专利标题
    FR1657305A|FR3054768B1|2016-07-28|2016-07-28|ULTRASOUND TRANSDUCER MULTIELEMENTS CAPACITIVE AIR COUPLING|
    FR1657305|2016-07-28|FR1657305A| FR3054768B1|2016-07-28|2016-07-28|ULTRASOUND TRANSDUCER MULTIELEMENTS CAPACITIVE AIR COUPLING|
    PCT/EP2017/068663| WO2018019778A1|2016-07-28|2017-07-24|Multi-element, capacitive, ultrasonic, air-coupled transducer|
    US16/320,856| US20190160491A1|2016-07-28|2017-07-24|Multi-element, capacitive, ultrasonic, air-coupled transducer|
    EP17749639.5A| EP3490727A1|2016-07-28|2017-07-24|Multi-element, capacitive, ultrasonic, air-coupled transducer|
    [返回顶部]