EP3490727A1 - Transducteur ultrasonore multiéléments capacitif à couplage air - Google Patents
Transducteur ultrasonore multiéléments capacitif à couplage airInfo
- Publication number
- EP3490727A1 EP3490727A1 EP17749639.5A EP17749639A EP3490727A1 EP 3490727 A1 EP3490727 A1 EP 3490727A1 EP 17749639 A EP17749639 A EP 17749639A EP 3490727 A1 EP3490727 A1 EP 3490727A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- transducer
- elements
- ultrasonic
- membrane
- distance
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
- B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
- B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
- B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
- B06B1/0292—Electrostatic transducers, e.g. electret-type
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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
- G01N29/22—Details, e.g. general constructional or apparatus details
- G01N29/24—Probes
- G01N29/2406—Electrostatic or capacitive probes, e.g. electret or cMUT-probes
Definitions
- the present invention relates generally to the field of non-destructive ultrasonic testing.
- the invention more particularly relates to an air-coupled capacitive type ultrasonic transducer for generating and / or detecting ultrasound.
- Non-destructive ultrasonic testing makes it possible to quickly inspect a structure, for example a composite material or metal, without damaging it and sometimes without dismantling it.
- the ultrasonic waves provide information on the mechanical properties of the structure and reveal the presence of defects, on the surface or in depth.
- ultrasonic waves may indicate the presence of cracks, delaminations and porosity zones in the structure, as these defects alter the amplitude and / or shape of the waves.
- the methods of non-destructive ultrasonic testing most often use a liquid coupling medium, good conductor of ultrasonic waves, such as water or a gel.
- This liquid coupling medium makes it possible to achieve an acoustic impedance matching between the emitter and receiver 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 non-destructive liquid coupling methods are, however, heavy to implement, because of the need to provide a tank or a liquid supply device. They also require the cleaning and / or drying of parts, and sometimes their dismantling.
- non-destructive non-destructive contactless methods where ambient air is used as a coupling medium, are simpler to implement and make continuous inspection of structures possible.
- they require the provision of air-coupled transducers whose efficiency is high, in order to compensate for the very high attenuation of the ultrasonic waves experienced at each interface between the air and the solid materials (air interface (s) / transducer (s) and interface (s) air / structure).
- Capacitive ultrasonic transducers now allow the emission of ultrasonic waves into the air at high levels and their reception with sufficient sensitivity to use air as a coupling medium. These transducers also have a better frequency bandwidth than the piezoelectric type transducers. They may 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, in particular linear, annular, matrix and circular.
- the Micromachined Capacitive Ultrasonic Transducer is an example of a multi-element transducer. It consists of a large number of micro-diaphragms organized in a network and operated electrostatically. This transducer is particularly compact because it is made from a silicon substrate using surface micromachining techniques. However, because of the geometry of the array of elements, in the form of a linear array or matrix, the CMUT transducer is not the most adapted to obtain a focus of the waves. ultrasonic. Focusing ultrasonic waves is possible by arranging the elements on a curved substrate whose curvature sets the central value of the focal length. The focusing distance can then vary (or very little), because of the small number of elements arranged on the support.
- CMUT transducer The elements of the CMUT transducer are manufactured in small numbers because the piezoelectric materials that compose them are difficult to machine on a small scale. This inability to change focus distance involves providing as many CMUT transducers as there are possible applications.
- This capacitive transducer comprises a membrane, one side of which is metallized, and a metal back plate on which the membrane is fixed.
- the back 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 ultrasonic wave beam, to adjust the spatial resolution.
- it makes it possible to adjust the focusing distance dynamically, by applying variable delays to the electrical excitation signals sent to the elements ("transmitter” mode) or delivered by the elements ("receiver” mode).
- the capacitive multi-element transducer of the aforementioned document does not simultaneously offer a great flexibility in adjusting the focusing distance, a high pressure level and a satisfactory resolution for the targeted applications.
- an air-coupled capacitive multi-element ultrasonic transducer comprising:
- a plurality of electrically independent conductive elements composed of a central disk and several rings concentrically arranged with the central disk, the conductive elements each having a face disposed facing the membrane and said faces of the elements being likewise area;
- the capacitive transducer according to the invention has a wider range of focus.
- 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 finely adjusting the focusing distance, that is to say with a smaller pitch.
- 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 changing 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 of thickness.
- the transducer can also be used to adjust the focus characteristics, including the size of the focal spot, to detect defects whose dimensions are beyond of a certain critical size, without being sensitive to inhomogeneities of material of smaller sizes and not to 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 composition.
- the adjustment of the focusing distance of a phased array transducer operating in "transmission” mode can be carried out by applying phase shifts to the excitation signals sent to the various elements, for example by means of multi-channel electronics.
- the adjustment of the focusing distance of a phased array transducer operating in "reception” mode can be carried out by applying phase shifts to the signals delivered by the different elements having detected an acoustic wave, again 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.
- the conductive elements are 16 in number
- the central disk has a radius equal to 10 mm
- the conductive elements are spaced a distance equal to 1.4 mm.
- the invention also relates to a method for manufacturing simply and inexpensively an air-coupled capacitive multi-element ultrasonic transducer with good performance. This process comprises the following steps:
- a rear plate comprising a plurality of electrically independent conductive elements, including a central disk and a plurality of rings arranged concentrically with the central disk, the rear plate having a rear face and a front face, said active face, opposite to the back side;
- the formation of the back plate comprising the following operations: Machining in a metal plate a plurality of concentric annular grooves;
- micro-sandblasting step of the active face of the back plate so as to form microcavities
- a step of 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 back plate;
- the electrically insulating glue is an epoxy resin.
- FIG. 1 schematically represents an air-coupled capacitive multi-element ultrasonic transducer according to a preferred embodiment of the invention
- FIG. 2 is a top view of a rear plate of the ultrasonic transducer of FIG. 1;
- FIG. 3 represents the maximum acoustic pressure at the distance of Fresnel radiated by the transducer according to the invention, as a function of the number of elements of the rear plate;
- FIG. 4 represents the lateral resolution for a focusing distance equal to the Fresnel distance of the transducer of FIG. 1, as a function of the number of elements of the rear plate;
- FIG. 5 shows the variations of 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;
- FIG. 6 represents the variations of the amplitude of the transverse pressure field at the distance of Fresnel radiated by the transducer according to the invention and by the transducer of the prior art;
- FIGS. 7A to 7E show steps of a method of manufacturing the rear plate according to FIG. 2 and its support made of insulating material
- FIG. 8 represents a particular way of assembling the capacitive multi-element transducer with air coupling according to the invention.
- FIG. 1 represents a preferred embodiment of a capacitive type multi-element ultrasonic transducer 100.
- the ultrasonic array transducer 100 is optimized in terms of working frequency and spatial resolution for non-destructive testing of materials.
- the objective of this check may 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 to say that it uses ambient air as a coupling medium for ultrasonic waves. There is therefore no contact between this transducer and the material to be controlled.
- the advantages of this type of transducer are the ease of implementation of the control procedures and the absence of contamination or pollution of the material.
- the transducer 100 comprises a rear plate 1 10 and a membrane 120 arranged facing the rear plate 1 10.
- the back plate 1 10 is rigid and massive compared to the membrane 120, which is (by definition) flexible and thin.
- the thickness of the back plate 11 is between 4 mm and 10 mm, while the thickness of the membrane 120 is between 3 ⁇ m and 8 ⁇ m.
- the backplate 1 and the diaphragm 120 are both disk-shaped. At least one face of the membrane 120 is electrically conductive.
- the membrane 120 is formed of a layer of polymer 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 back plate 1 10 ).
- the membrane 120 can thus be arranged in contact with the rear plate 1 10 and fixed to the edges thereof, without creating a short circuit between the metal layer 122 and the rear plate 1 10.
- the rear plate 1 10, shown in plan view in FIG. 2, comprises several conductive elements spaced from each other, and more particularly a central disc 1 1 1 and rings 1 12.
- the rings 1 12 are arranged concentrically with the central disc 1 1 1 .
- These elements are preferably metal, for example aluminum.
- the disk 1 1 1 and the rings 1 12 are advantageously of the same thickness and nested in each other, so that the rear plate 1 10 has planar and parallel main faces (ie front and rear) (see FIG. ).
- the elements 1 1 1 1 -1 12 12 of the back plate 1 10 are separated by a dielectric material 1 13, preferably a resin epoxy.
- "x" designates the radial position of the rings 1 12 with respect to the center "O" of the central disc 1 1 1.
- Each element 1 1 1 1 -1 12 of the back plate 1 10 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 (to the way of a speaker).
- the membrane 120 constitutes the first armature (or electrode), movable, of the capacitor, while the relevant element of the rear plate 1 10 is the second armature of the capacitor, which is instead fixed.
- each of the elements, the disk 1 1 1 and the rings 1 12 constitutes with a portion of the membrane 120 an active element of the capacitive type.
- the ultrasonic transducer multielements 100 can therefore be seen as a multitude of capacitive transducers mono-element, integrated in the same housing and sharing the same membrane.
- the membrane 120 of the transducer 100 is permanently prestressed by a DC bias voltage VDC and vibrates at a resonance frequency under the effect of an AC excitation voltage VAC applied to each conductive element 1 1 1 -1 12 of the back plate 1 10.
- This movement of the membrane 120 gives rise to an ultrasonic wave beam 130, corresponding to the superposition of the acoustic beams generated by the different capacitive transducers mono-element.
- the axis of revolution Oz of the central disk 1 1 1 and rings 1 12 coincides with the propagation direction of the ultrasonic wave beam 130. This axis Oz is hereinafter called the "acoustic axis" of the transducer ultrasound 100.
- the ultrasonic phased array transducer 100 inherently has a large frequency bandwidth because it is of the capacitive type. This wide bandwidth makes the transducer 100 compatible with many materials, because the frequency of the AC excitation signal VAC, called the working frequency, is chosen according to the material to be controlled.
- This surface roughness is for example obtained by a micro-sandblasting of the front face of the elements.
- the sound pressure field of the ultrasonic beam generated by a single-element plane 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 distant (or Fraunhofer area) where the pressure field diverges.
- Fresnel distance Df is the distance from the near-field zone to the far-field zone. This distance Df is that at which the ultrasonic beam presents the most interesting characteristics: a high sound pressure (when the attenuation in the air is negligible, it is the position of the last pressure maximum) and reduced lateral dimensions ( in other words, a good lateral resolution).
- the distance Df is proportional to the ratio of the active surface S on the emitted wavelength ⁇ , ie in the case of a disk-shaped source of radius r:
- the ray n of the active surface S to be taken into account is:
- the central disc 1 1 1 and the concentric rings 1 12 of the back plate 1 10 are here dimensioned so that they have the same active surface S.
- the front faces of the central disc 1 1 1 and rings 1 12 are of the same area.
- the central disc 1 1 1 and the rings concentric 1 12 necessarily have different widths.
- This configuration has the advantage of minimizing the amplitude of the side lobes of the acoustic pressure field.
- These secondary lobes represent a part of the acoustic energy which is radiated in different directions from the acoustic axis Oz of the transducer 100 (ie the axis of the disc 1 1 1 and rings 1 12, see Fig.1). They can induce artifacts on the images of the inspected materials and lead to the detection of "false defects".
- the irregularity in the width of the transducer elements is therefore an asset for obtaining a beam with few side lobes, or even without side lobes.
- 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 occur naturally.
- the ultrasonic beam certainly has a certain directivity, but it is comparable to that of a single-element transducer formed of a single disk of radius equal to the outer 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 offsets are introduced between the excitation signals of the disc 1 1 1 and rings 1 12.
- the ultrasound beam 130 then converges to a focal area where it becomes locally plane. At greater distance, the beam diverges.
- the focusing distance, denoted hereinafter Zf is measured from the source (i.e. the membrane 120) along the axis Oz and may be equal to the Fresnel distance Df.
- This focusing makes it possible to detect finer defects, with a better signal-to-noise ratio.
- the other advantage of the multi-element transducer according to the invention is that it is then easy to modify the focusing distance Zf and thus the depth of detection.
- 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 focusing zone depend on the focusing distance Zf and the wavelength ⁇ .
- the performance of the capacitive multi-element transducer 00 in terms of spatial resolution and efficiency in particular, also depends on its geometry. Numerical simulations have made it possible to identify the geometrical characteristics of the transducer 100, such as the number N of elements (central disk and concentric rings) of the rear plate 1 10 and the active surface S of these elements, which have a strong impact. on the performance of the transducer. The results of these numerical simulations (at a frequency of 300 kHz) are given below in relation to FIGS. 3 and 4.
- the efficiency of a transducer is defined as the ratio between the acoustic power delivered and the electrical power consumed.
- the acoustic power is substantially proportional to the square of the sound pressure generated by the ultrasonic wave beam. Therefore, the higher the sound pressure of the beam, the higher the efficiency of the transducer.
- the distance d between two consecutive elements 1 1 1 1 -1 12 is constant and fixed here to 1 mm.
- 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 task are proportional to the focusing distance and inversely proportional to the total radius of the multi-element transducer (and thus to the number of elements).
- the Fresnel distance is proportional to the active area, (square of the radius of the central element)
- an increase of the active surface S of the elements deteriorates the spatial resolution.
- 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 considered for sizing 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 disk 11 between 10 mm and 15 mm, the focusing range of the multielement transducer 100 is extended significantly. In addition, its efficiency is close to the maximum level, its spatial resolution is very good and the dimensions and spacings of its various elements make its realization possible with current machining and assembly means.
- the technology based on the "capacitive" effect of the transducer gives it a wide bandwidth, which extends from 100 kHz at 500 kHz to -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 controlled. Since the characteristics of the focal task (amplitude of the pressure and dimensions) depend on the frequency, the focusing distance can be adjusted so as to optimize the beam to be emitted.
- the transducer 100 makes it possible to adjust the focus distance finer, compared with the prior art transducer equipped with only 8 elements. Indeed, the higher this number N, the more the delay law applied to the excitation signals can be precisely defined. Finally, the geometric characteristics of the transducer 100 offer good compromises between performance and manufacturing difficulties of the back plate. Indeed, a back plate with a very large 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 1 1 1 1 -1 12 is advantageously between 1 mm and 1, 8 mm, and preferably between 1, 4 mm and 1, 6 mm. Due to this small spacing between the elements 1 1 1 -1 12, the ultrasonic transducer multielements 100 remains compact and can therefore be used more easily.
- the ultrasonic multielement transducer 100 comprises a central disk of radius R1 equal to 10 mm and 15 mm. concentric rings with the same active surface, ie a total of 16 conductive 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 Oz axis) radiated by this example of the transducer according to the invention (curve in solid line) and, as a comparison, that developed by the transducer of the prior art (curve in dashed lines).
- each of the transducers focuses at its own Fresnel distance.
- FIG. 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 transducer 8 elements.
- the improvement here is about 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% thinner than that of the 8-element transducer (1.4 mm vs. 1.6 mm). This lateral resolution is measured, for each curve, by raising the width at half height (Pmax / 2) of the main lobe of the transverse acoustic pressure p (x). Moreover, it can be seen from these figures that the amplitude Pmax of the maximum acoustic pressure (at the Fresnel distance Df) of the 16-element transducer is nearly twice that of the 8-element transducer (945 versus 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.
- the table below gives the orders of magnitude of the performances for the transducer of the prior art and two examples. of the transducer according to the invention.
- the ultrasonic phased array transducer according to the invention therefore has higher performances in terms of spatial resolution and of efficiency with respect to the capacitive multi-element transducer of the prior art.
- the high efficiency and high resolution allow the detection and localization of small defects (of the order of a millimeter), while the wide frequency bandwidth allows a large number of applications.
- the transducer 100 makes it possible to control pieces or structures of complex shape, made of very diverse materials (metals, polymer materials or composites, wood, ceramics, etc.).
- the transducer 100 has the ability to dynamically change the focus distance.
- the ultrasonic phased array transducer according to the invention may be suitable for applications in the field of telemetry.
- FIGS. 7A to 7E show steps S1 to S5 of a method of manufacturing the backplate 1 comprising the central disc and the concentric rings.
- This method makes it possible to manufacture simply and inexpensively a back plate provided with a central disk and at least one concentric ring. It is applicable regardless of the number N of elements, the radius R1 of the central disk and the spacing d between the elements (within the limits of manufacturing by machining). It is particularly beneficial for a large number of rings (N> 10), as in the case of the transducer according to the invention.
- annular grooves 800 are machined into a metal disk 801, preferably of aluminum. The grooves 800 are concentric and intended to delimit the elements of the back plate.
- the thickness of the metal disk 801 is 10 mm, while the grooves 800 have a depth of about 7 mm. Therefore, the grooves 800 do not agree over the entire thickness of the metal disc 801.
- the grooves preferably have the same width, for example 1, 4 mm, so that the elements of the back plate are evenly spaced.
- a dielectric material is deposited in the grooves 800 to form a layer 802 of surplus dielectric material on the upper face of the metal disc 801.
- the dielectric material is an adhesive, preferably a bi-component epoxy resin.
- the metal disk 801 covered with the resin layer 802 is inserted into a back plate 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 disk 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 sticking the metal disk 801 in the support 803.
- the housing 804 has a height equal to the thickness of the metal disk 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 protrudes beyond 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.
- a drilling hole (not shown in Figure 7C) can also be arranged in the side wall of the support 803, in substitution or in addition to the groove 806, to remove the excess resin.
- Step S4 of FIG. 7D consists in machining, preferably by means of a lathe, the lower portions of the metal disk 801 and the support 803 until reaching the resin situated in the grooves 800, for example on a thickness of about 4 mm.
- the grooves 800 filled with glue thus become 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 disposed between the conductive elements ensures their maintenance in a single block and isolates them electrically from each other.
- step S4 is advantageously carried out so that the rear plate 1 10 and the support 803 have a planar "ground” surface. Thus, it reduces the risk of damaging (shearing) the diaphragm 120 disposed later on this surface.
- step S4 the groove 806 can also be enlarged by milling, in order to provide access, on the rear face 1 10a of the back plate, to all the conductive elements of the back plate. This access is for the electrical connectors on the backplate.
- the manufacturing method further comprises a preparation step S5 of the active surface of the back plate 1 (glued in the support 803), in order to create microcavities (of the order of the pm).
- This step S5 is illustrated in FIG. 7E and comprises at least one micro-sandblasting operation.
- the microcavities are formed on the front face 1 10b of the back plate 1 10 by the projection of hard grains whose diameter is critical to confer a broad frequency bandwidth and optimal performance of the ultrasound transducer multielements.
- the preparation step S5 of the front face 1 10b is preferably composed of several sub-steps: at least one polishing operation, a micro-sandblasting operation and a cleaning operation.
- the dressing tool used during the machining of the back plate 1 10 leaves a coarse surface condition.
- the (active) front face 1 10b of the rear plate 1 10 has asperities of much greater dimensions than the desired microcavities. It is therefore necessary to remove these irregularities before creating micro-cavities by sanding.
- a so-called mirror-like reference surface is made by polishing, for example by successively passing glass papers of increasing particle size (180, 400, 800 and then 1200 grains / cm 2 ) and then successively using diamond-shaped pastes. 3 pm, 1 pm and 1 ⁇ 4 pm in roughness.
- the sanding is then carried out by projecting on the front face 1 10b of the back plate 1 10 an abrasive powder (for example F400 white corundum of average particle size equal to 17 ⁇ m), preferably under a pressure of 5 bar with a nozzle of 1, 8 mm in diameter.
- the assembly consisting of the back plate 1 10 and the support 803 is preferably held about ten centimeters from the nozzle.
- the sanding is carried out until a uniform surface (with the naked eye) is obtained on the front face 1 10b of the rear plate 1 10.
- the back plate-support assembly is cleaned to eliminate the particles generated. by polishing and sanding operations, then dried.
- the cleaning is for example carried out in an ultrasonic bath.
- Fig. 8 shows a preferred embodiment of the backplate assembly step 1 with the membrane 120 and other components of the multielement ultrasonic transducer 100.
- the membrane 120 is deposited on the front face 1 10b of the rear plate 1 10, by orienting its metallized conductive face (aluminum) outwards.
- the membrane 120 has previously been cut around a cylindrical template of diameter greater than the diameter of the back plate 1 10, so that the peripheral edge of the membrane 120 rests on the insulating support 803.
- the membrane 120 covers the entire surface active the back plate 1 10 and, for example, half the width of the insulating support 803.
- a retaining ring 900 (for example made of aluminum), of internal diameter slightly greater than the diameter of the rear plate 1 10, is deposited on the front face of the membrane 120, directly above the support 803 located on the other side membrane, that is to say on the back side.
- the retaining ring 900 advantageously has a chamfer on its inside diameter and a mirror-rectified surface condition so as not to damage the membrane later during assembly or operation of the transducer 100.
- 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 subsequently be used to convey alternating 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 back plate 1 10, while the electrically conductive holding ring 900 ensures that the mass of the membrane 120 (see also Fig. 1). Under the effect of this bias voltage, the membrane 120 is stretched. The DC bias voltage is maintained during transducer mounting, and then during operation. A perfectly stretched membrane, without any air bubbles trapped between the membrane and the back plate 1 10, guarantees an optimal final yield.
- a DC bias voltage preferably between 30 V and 100 V
- a cylindrical housing 903 (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 suggests the membrane 120.
- a rear cover 905 (electrically conductive material, for example aluminum) is attached to the cylindrical housing 903, facing the rear plate 1 10, 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 1 10. 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 in abutment against the retaining ring 900 (which is snuggled to the bottom of the housing 903).
- the ultrasonic phased array transducer 100 is operational.
Abstract
Description
Claims
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
FR1657305A FR3054768B1 (fr) | 2016-07-28 | 2016-07-28 | Transducteur ultrasonore multielements capacitif a couplage air |
PCT/EP2017/068663 WO2018019778A1 (fr) | 2016-07-28 | 2017-07-24 | Transducteur ultrasonore multiéléments capacitif à couplage air |
Publications (1)
Publication Number | Publication Date |
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EP3490727A1 true EP3490727A1 (fr) | 2019-06-05 |
Family
ID=57396588
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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EP17749639.5A Withdrawn EP3490727A1 (fr) | 2016-07-28 | 2017-07-24 | Transducteur ultrasonore multiéléments capacitif à couplage air |
Country Status (4)
Country | Link |
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US (1) | US20190160491A1 (fr) |
EP (1) | EP3490727A1 (fr) |
FR (1) | FR3054768B1 (fr) |
WO (1) | WO2018019778A1 (fr) |
Families Citing this family (4)
Publication number | Priority date | Publication date | Assignee | Title |
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JP6606034B2 (ja) * | 2016-08-24 | 2019-11-13 | 株式会社日立製作所 | 容量検出型超音波トランスデューサおよびそれを備えた超音波撮像装置 |
DE102017115923A1 (de) | 2017-07-14 | 2019-01-17 | Infineon Technologies Ag | Mikroelektromechanischer Transducer |
US11181627B2 (en) * | 2018-02-05 | 2021-11-23 | Denso Corporation | Ultrasonic sensor |
CN114887864B (zh) * | 2022-03-08 | 2024-02-20 | 南京邮电大学 | 一种摩擦电空气耦合超声换能器 |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
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US5520188A (en) * | 1994-11-02 | 1996-05-28 | Focus Surgery Inc. | Annular array transducer |
US6613004B1 (en) * | 2000-04-21 | 2003-09-02 | Insightec-Txsonics, Ltd. | Systems and methods for creating longer necrosed volumes using a phased array focused ultrasound system |
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2016
- 2016-07-28 FR FR1657305A patent/FR3054768B1/fr not_active Expired - Fee Related
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2017
- 2017-07-24 EP EP17749639.5A patent/EP3490727A1/fr not_active Withdrawn
- 2017-07-24 WO PCT/EP2017/068663 patent/WO2018019778A1/fr unknown
- 2017-07-24 US US16/320,856 patent/US20190160491A1/en not_active Abandoned
Also Published As
Publication number | Publication date |
---|---|
WO2018019778A1 (fr) | 2018-02-01 |
FR3054768A1 (fr) | 2018-02-02 |
US20190160491A1 (en) | 2019-05-30 |
FR3054768B1 (fr) | 2018-08-10 |
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