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    • 专利摘要:
    Focusing system for an air-coupled focused ultrasound emitter, receiver or transducer. The present invention refers to a focusing system characterized by comprising a concave lens that comprises a flat central area and a polymeric coating that covers the lens, capable of being used as part of a focused and air-coupled ultrasound emitter, a receiver air coupled focused ultrasound device or a focused air coupled ultrasound transducer comprising said transducer and/or said receiver. Furthermore, the present invention relates to said emitter, said receiver and said transducer comprising the aforementioned focusing system. The present invention is framed in the field of design and manufacture of ultrasonic transducers, more specifically in the manufacture of ultrasonic, piezoelectric, focused and air-coupled transducers to operate in transmission and reception mode. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2812373A1
    申请号:ES201930801
    申请日:2019-09-16
    公开日:2021-03-16
    发明作者:Alvarez-Arenas Tomás Gómez
    申请人:Consejo Superior de Investigaciones Cientificas CSIC；
    IPC主号:
    专利说明:

    [0002] Focusing system for an air-coupled focused ultrasound emitter, receiver or transducer
    [0004] The present invention refers to a focusing system characterized by comprising a concave lens that comprises a flat central area and a polymeric coating that covers the lens, capable of being used as part of a focused and air-coupled ultrasound emitter, a receiver air-coupled focused ultrasound device or a focused air-coupled ultrasound transducer comprising said transducer and / or said receiver. Furthermore, the present invention relates to said emitter, said receiver and said transducer comprising the aforementioned focusing system.
    [0006] The present invention is framed in the field of the design and manufacture of ultrasonic transducers, more specifically in the manufacture of ultrasonic, piezoelectric, focused and air-coupled transducers to operate in transmission and reception mode.
    [0008] BACKGROUND OF THE INVENTION
    [0010] The main problem in the design and development of air-coupled piezoelectric transducers is the enormous impedance mismatch between the piezoelectric material and air. This results in very poor sensitivity and low bandwidth transducers, which greatly limits the practical utility of this technology. However, it is extremely interesting in some applications, while in some others it is the only viable alternative.
    [0012] The reason why there are certain cases in which air coupling is required and not conventional ultrasonic techniques based on the use of coupling liquids (water, gel, water jet, etc.), is because there are certain materials and components that cannot come into contact with such liquids. In these cases, the only alternative is air-coupled inspection, although this is extraordinarily difficult given the enormous losses an ultrasonic signal experiences as it passes through these components and the limited sensitivity of conventionally used transducers.
    [0014] Among the components and materials in which the use of air coupling is necessary are all those with internal cavities, with porous components (open porosity) or with elements susceptible to being affected by liquids (corrosion, contamination, dilution, etc.). An example is sandwich structures with a honeycomb core and fiber-reinforced polymer walls. This type of component is widely used in the aeronautical industry (for example, in the acoustic panels that surround turbojets in commercial aircraft), aerospace (antenna support structure), energy (wind turbine blades), civil engineering (beams made of composite material) and that of sports material, since they combine rigidity, lightness, thermal and acoustic insulation and resistance to impacts. However, and due to this multilayer structure, the inspection of these components by means of air coupling is extremely difficult and requires extremely sensitive and efficient transducers, which demands an extremely effective adaptation of the impedances of the transducers to the air.
    [0016] The resolution of the transducer / air impedance mismatch problem is not easy since the realization of these transducers faces two types of strong restrictions that prevent the implementation of conventional designs used in other applications. These restrictions refer to:
    [0018] a) The materials to be used: There are no materials with the acoustic impedance that the ideal design requires to use. The available materials present losses that are not negligible.
    [0020] b) The assembly / manufacture of the transducer itself: The union between the different materials is not ideal (perfect cohesion and negligible thickness transition). Furthermore, it is sometimes necessary to use a thin (but not negligible) layer of adhesive.
    [0022] Focused transducers make use of lenses or other modifications in their structure to focus the beam. This targeting allows increasing spatial resolution, both axial and transverse, which enables applications related to obtaining an ultrasonic image and applications related to therapy (acting on the insonic medium) that require greater spatial precision. In general, focusing the beam leads to an increase in the complexity of the transducer design and a decrease in its sensitivity or efficiency. Said loss of sensitivity is critical in the case of air-coupled transducers, which already suffer from reduced sensitivity due to the aforementioned impedance decoupling. Furthermore, as also mentioned above, stacking of matching layers is critical to overcome this problem and the presence of a lens can result in excessive distortion.
    [0023] US4184094 presents a focusing system for ultrasonic transducers that allows optimal energy transmission without blurring the beam. However, this design can only be applied to transducers coupled to relatively high impedance media (water, biological tissues, etc.) and it would not work for air coupled transducers since in this case the difference in impedances between the piezoelectric material is much greater. and the materials that would be necessary to implement this design are not available. Another system for targeting ultrasonic transducers that has been used successfully in the case of high-frequency and water-coupled transducers has been the use of annular arrays of different geometries (US4138895, US4155259, EP0104929A2), whose utility for transducers coupled to air and intermediate frequencies (<1MHz) is limited (TE Gómez Álvarez-Arenas, J. Camacho, and C. Fritsch, “Passive focusing techniques for piezoelectric air-coupled ultrasonic transducers,” Ultrasonics, vol. 67, no. January, pp. 85-93, 2016.).
    [0025] In the case of air-coupled focused transducers, the main application refers to the generation of C-scan ultrasonic images in the field of non-destructive testing. The main objective is to locate and size defects such as delaminations, insertions, corrosion, cracks, loss of thickness and / or porosity, with sufficient resolution.
    [0027] To achieve focusing an air-coupled ultrasonic transducer, mirror-like structures or Fresnel masks have been proposed (US7719170B1, US8616329B1), which add additional elements to the transducer and complicate its design, manufacture and use. Piezoelectric elements carved according to the geometry of the field have also been proposed (US3732535A), which makes manufacturing difficult and expensive while reducing the vibration efficiency of the piezoelectric, or the use of specific lenses for each application (for example, for water-coupled transducers: US5577507A). Likewise, one of the known problems in these focused transducers is caused by the use of embedded lenses in the transducer structure, which affect their effectiveness as they cause adverse effects such as de-tuning and loss of tuning. efficiency of impedance matching layers. These efficiency losses make current designs not useful for the most demanding applications such as curved components manufactured with asymmetric sandwich structures with a honeycomb core.
    [0028] Therefore, it is necessary to develop new focused air-coupled ultrasonic transducers with high sensitivity and spatial resolution, which allow non-destructive inspection of industrial materials and components.
    [0030] DESCRIPTION OF THE INVENTION
    [0032] The object of this patent refers to a focusing system characterized by comprising a concave lens that comprises a flat central area and a polymeric coating that extends over the lens, where said focusing system is capable of being used as part of an emitter. air-coupled focused ultrasound device, an air-coupled focused ultrasound receiver or an air-coupled focused ultrasound transducer comprising said transducer and said receiver. Furthermore, the present invention relates to said emitter, said receiver and said transducer comprising the aforementioned focusing system and a piezoelectric foil.
    [0034] The air-coupled focused transducer of the present invention exhibits high sensitivity and spatial resolution that enables non-destructive inspection of the most demanding materials and components, such as the aforementioned sandwich structures for which the industry does not have an efficient solution. The focused and air-coupled ultrasound transducer of the present invention is designed so that: i) the negative effect of the focusing system on the sensitivity of the transducer is minimal, ii) so that the transmission of energy to the material to be inspected is optimal and iii) so that the spatial resolution is sufficient for the detection and dimensioning of defects.
    [0036] The piezoelectric transducers referred to in the present invention operate in air under normal conditions and in emission-reception mode (in English mode called pitchcatch), within the frequency range between 0.1 and 2.0 MHz, with a width Relative moderate band (> 30% @ -20dB), with high sensitivity (> -25 dB) and a focal point diameter (transverse direction, to the beam, 6 dB drop) less than 5 mm.
    [0038] These features allow the use of these transducers for scanning and obtaining images using the automated C-Scan ultrasound scanning technique in transmission mode and using air coupling for non-destructive tests. In particular, they allow the use of these transducers in this type of application when the component under inspection has such high transmission losses that it is impossible to use other available techniques. Examples can be cited:
    [0039] 1. Sandwich structures with high impedance skins (> 3MRayl) and a very porous core: “honeycomb” type honeycomb (aluminum, nomex, etc.) or polymeric foam; for the detection of impact defects on the surface, delaminations within the skins, detachments between the skin and the core, continuity failures in the core, the presence of insertions either in the skins or between the skin and the core.
    [0041] Note that by "sandwich structure" is meant in the present invention a multilayered structure composed of three layers. Two identical ones located on the external faces, also called skins, and an internal one, between both skins, also called the nucleus.
    [0043] 2. Same objective as in (1), with structures as in (1), but with curved geometry.
    [0045] 3. Same objective as in (1), with structures as in (1) or (2), but with asymmetric skins or of variable thickness.
    [0047] 4. Same objective as in (1), with sandwich-type structures with very high impedance skins (metals,> 30 MRayl) and a rubber core.
    [0049] 5. Very attenuating media, such as porous media, foams, cellular solids, composite materials with a high concentration of dispersants (concrete, food compounds, etc.), to determine the presence of porosity, cracks, inserts, etc.
    [0051] In addition, the sender and the receiver can be used autonomously when the only interest is either transmission or reception because reception or transmission are resolved by alternative methods, respectively. Examples of these applications are:
    [0053] - Non-destructive tests and / or characterization of materials: for the reception of ultrasonic waves generated in a solid by means of laser or other techniques.
    [0054] - Non-destructive tests and / or characterization of materials, for the generation of waves that are later detected by other means: laser, contact ultrasound, etc.
    [0055] - Generation of waves or mechanical displacements in organic tissues that are then measured by laser or any other technique, for example, for applications in elastography.
    [0056] In a first aspect, the present invention refers to a focusing system characterized by comprising
    [0058] • a concave lens having an acoustic impedance between 0.2 MRayl and 0.9 MRayl and a focal length between 5mm and 100mm and comprising a concentric concave surface with a radius of curvature between 20mm and 90mm , and • a polymeric coating with a thickness between 70 pm and 200 pm and a porosity greater than 70%, presenting an acoustic impedance between 0.05 MRayl and 0.09 MRayl,
    [0060] and wherein said polymeric coating is arranged over the entire concentric concave surface of the concave lens.
    [0062] The term "acoustic impedance" refers to the physical property of a material medium determined by the product of the density of said medium and the speed of propagation of ultrasound in said medium.
    [0064] The focal length of a lens is a term that refers to the distance from the surface of the lens to the point where the lens concentrates energy.
    [0066] In the present invention, the lens is concave, that is, it is defined by a concave surface with a radius of curvature between 20 mm and 90 mm.
    [0068] By "angular aperture of the lens" is understood in the present invention as the angle formed by the axis of the transducer and the line that joins the edge of the transducer with the focal point. The angular aperture of the concave lens of the present invention must be such that all of the ultrasound generated is capable of passing through the air / solid interface to be inspected.
    [0070] In a preferred embodiment of the focusing system, the concentric concave surface of the concave lens comprises a concentric planar central region with a diameter of between 1mm and 5mm and a thickness of between 0.3mm and 3.0mm. Said flat central area must have a diameter equal to or less than the size of the focus (diameter of the focal point) of a perfectly spherical lens with the same radius of curvature.
    [0072] In the present invention, the concave lens is manufactured using a material with an acoustic impedance value between 0.2 MRayl and 0.9 MRayl.
    [0073] The concave lens of the focusing system of the present invention is made of material with an ultrasound attenuation coefficient between 500 Np / m and 3000 Np / m, preferably less than 2000 Np / m at a frequency of 1 MHz.
    [0075] Preferably the concave lens is made of a syntactic foam.
    [0077] "Syntactic foam" is understood as that foam that is composed of a polymeric matrix to which hollow microspheres of glass or other material with similar characteristics are added, preferably smaller than 20 µm in size, randomly distributed. For example, these syntactic foams are used in flotation systems for deep-sea submarines, for depths from 700 m to 10,000 m.
    [0079] The focusing system of the present invention comprises a concave lens and a polymeric coating with a thickness between 70 pm and 200 pm and a porosity greater than 70%. Said coating is arranged over the entire concave surface of the concave lens. It has an acoustic impedance of between 0.05 MRayl and 0.09 MRayl, an ultrasound attenuation coefficient of between 500 Np / m and 3000 Np / m and is made of a polymer that is selected from among polypropylene, polyethersulfone, nylon, nitrate of cellulose or any of its combinations.
    [0081] Another aspect of the present invention refers to a focused and air-coupled ultrasound emitter with a central frequency comprised between 0.1 MHz and 2.0 MHz and an angular aperture of between 3 ° and 20 ° characterized in that it comprises
    [0083] • the aforementioned focusing system, where the thickness of the concave lens is equal to a quarter of the wavelength of the ultrasound in the lens at the center frequency of the emitter.
    [0085] In a preferred embodiment of the air-coupled focused ultrasound emitter with a central frequency comprised between 0.1 MHz and 2.0 MHz and an angular aperture of between 30 and 20 °, it is characterized in that it comprises
    [0087] • the aforementioned focusing system, where the thickness of the concave lens is equal to a quarter of the wavelength of ultrasound in the lens at the center frequency of the emitter,
    [0088] • a piezoelectric foil selected from a lead zirconate titanate PZT type ceramic PbZr03-PbTi03, a ceramic composite material piezoelectric and resin with type 1-3 connectivity and with a volumetric concentration of ceramic between 25% and 80%, or a piezoelectric single crystal type Pb (Mgi / 3Nb2 / 3) 03-PbTi03, where said piezoelectric sheet comprises a coating electrical conductor of gold, silver, carbon, aluminum, copper or any of their combinations, where said piezoelectric sheet is polarized along its thickness and where the thickness of said piezoelectric sheet is between 20 nm and 100 nm,
    [0089] • an electronic excitation equipment, and
    [0090] • an inductance in parallel or in series between 1 pH and 500 pH configured to connect the piezoelectric foil with the electronic excitation equipment and suitable for it,
    [0092] where the focusing system and the piezoelectric foil are in contact.
    [0094] Commercial examples of electronic excitation equipment are PR Olympus 5058, 5072 or 5054, AirScope from DASEL, JSR, etc.
    [0096] The angular aperture in the emitter is configured so that all the generated ultrasound is able to pass through the air / solid interface to be inspected.
    [0098] In another preferred embodiment of the emitter of the present invention, it comprises a focusing system where the concentric concave surface of the concave lens comprises a concentric flat central zone with a diameter of between 1 mm and 5 mm and a thickness of between 0.3 mm. and 3.0 mm and where the thickness of the flat central area of the concave surface of the concave lens is equal to a quarter of the wavelength of the ultrasound in the lens at the central frequency of the emitter.
    [0100] Another aspect of the present invention refers to a focused and air-coupled ultrasound receiver with a central frequency between 0.1 MHz and 2.0 MHz and an angular aperture of between 3 ° and 20 ° characterized in that it comprises
    [0102] • the focusing system according to claims 1 to 4, wherein the thickness of the concave lens is equal to a quarter of the wavelength of the ultrasound in the lens at the center frequency of the receiver,
    [0103] In a preferred embodiment of the air-coupled focused ultrasound receiver with a central frequency between 0.1 MHz and 2.0 MHz and an angular aperture of between 3 ° and 20 °, it is characterized in that it comprises
    [0105] • the focusing system according to claims 1 to 4, wherein the thickness of the concave lens is equal to a quarter of the wavelength of the ultrasound in the lens at the center frequency of the receiver,
    [0106] • a piezoelectric sheet selected from among a PbZr03-PbT¡03 lead zirconate titanate PZT ceramic, a composite material of piezoelectric ceramic and resin with type 1-3 connectivity and with a volumetric concentration of ceramic between 25% and the 80%, or a Pb (Mgi / 3Nb2 / 3) 03-PbTi03 type piezoelectric single crystal, where said piezoelectric sheet comprises an electrically conductive coating of gold, silver, carbon, aluminum, copper or any of their combinations, where said piezoelectric sheet is polarized along its thickness and where the thickness of said piezoelectric sheet is between 20 nm and 100 nm,
    [0107] • an electronic reception team, and
    [0108] • a parallel or series inductance between 1 pH and 500 pH configured to connect the piezoelectric foil with the electronic receiving equipment
    [0110] where the focusing system and the piezoelectric foil are in contact.
    [0112] Commercial examples of electronic receiving equipment are PR Olympus 5058, 5072 or 5054, AirScope from DASEL and JSR.
    [0114] The angular aperture in the receiver is configured so that all of the (generated) ultrasound is able to pass through the air / solid interface to be inspected.
    [0116] In another preferred embodiment of the receiver of the present invention, it is characterized by comprising the aforementioned focusing system, where the concentric concave surface of the concave lens comprises a concentric planar central zone with a diameter of between 1 mm and 5 mm and a thickness between 0.3 mm and 3.0 mm and where the thickness of the flat central area of the concave surface of the concave lens is equal to a quarter of the wavelength of the ultrasound in the lens at the central frequency of the emitter .
    [0118] Another aspect of the present invention relates to a focused and air-coupled ultrasound transducer with a central frequency between 0.1 MHz and 2.0 MHz and a angular aperture of between 30 and 200 characterized in that it comprises an emitter as described previously and / or a receiver as described previously, where the emitter and receiver are aligned and facing each other and where the central frequency of the emitter is different to that of the receiver.
    [0120] In a preferred embodiment of the present invention, the ultrasound transducer comprises an emitter as described above and a receiver as described above, where the thickness of the piezoelectric sheet (114) of the receiver is different from the thickness of the piezoelectric sheet ( 114) of the emitter and where the mechanical resonance frequency of the piezoelectric sheet (114) in the receiver Rx is equal to the electrical resonance frequency of the piezoelectric sheet (114) in the emitter Tx and and where both frequencies are at the frequency transducer center.
    [0122] Throughout the description and claims the word "comprise" and its variants are not intended to exclude other technical characteristics, additives, components or steps. For those skilled in the art, other objects, advantages and characteristics of the invention will emerge partly from the description and partly from the practice of the invention. The following examples and figures are provided by way of illustration, and are not intended to be limiting of the present invention.
    [0124] BRIEF DESCRIPTION OF THE DRAWINGS
    [0126] Figure 1: Cross-sectional view of the transducer of the invention and its components:
    [0128] Figure 2: Plane of the lens and its different parts.
    [0130] Figure 3: Cross section and geometric relationships present in the inspection of a component with the transducer of the invention: Illustration of the parameters involved in determining the optimal geometry of the lens.
    [0132] Figure 4: Modulus of the electrical impedance of the piezoelectric discs used to manufacture Tx and Rx
    [0134] Figure 5: Stages of assembly of the transducer of the invention.
    [0136] Figure 6: Response of the transducers (temporal signal and frequency sensitivity band) manufactured.
    [0137] EXAMPLES
    [0139] The invention will be illustrated below by means of tests carried out by the inventors, which show the effectiveness of the product of the invention.
    [0141] The exemplary embodiment refers to an air-coupled transducer with quasi-spherical targeting that is used for ultrasonic inspection by air-coupled transmission of composite materials with high losses, specifically, for the inspection of components with a sandwich-type structure with a nest core. of bees, skins made of asymmetric carbon fiber reinforced resin laminate material, and non-planar geometry, which are commonly used in the aeronautical and aerospace industry, and which must be inspected using air-coupled ultrasound because ultrasound presents enormous transmission losses through these parts.
    [0143] Table I summarizes the main transducer design specifications for the application.
    [0145] Table I.
    [0150] * When the material to be inspected is a multilayer material, the inspection is carried out on the external face
    [0152] ** A lateral resolution <5 mm is chosen according to the inspection requirements in the aeronautical industry of sandwich structures with carbon fiber reinforced resin skin (CFRP) and honeycomb core.
    [0153] *** High sensitivity> -25 dB is chosen (extraordinarily high for a transducer
    [0154] with air coupling) because it has been observed that lower values can give
    [0155] result in a very poor signal-to-noise ratio that does not allow the correct identification of
    [0156] defects.
    [0158] Figure 1 refers to the transducer components listed below:
    [0160] (101) Metal bushing rear cover
    [0161] (102) Conductive wire
    [0162] (103): Resin for fixing the piezoelectric element (sheet or disk) (114) to the bushing ( 112 )
    [0163] (104): Metallization of the internal face of the piezo
    [0164] (105): Conductive layer (metallization)
    [0165] (106): Adhesive layer
    [0166] (107): Adhesive layer
    [0167] (108): Quarter wave layer
    [0168] (109): Rear connector
    [0169] (110): Inductance in parallel
    [0170] (111): Series inductance
    [0171] (112): Cap
    [0172] (113): Welding the lead wire to the piezo
    [0173] (114): Piezoelectric foil or disc
    [0174] (115): Lens
    [0175] (116): Cap front crown
    [0177] The lens is specifically designed to ensure that the transmission of energy from the
    [0178] transducer to air and from air to the component to be inspected is maximum. Therefore, the lens
    [0179] It has been designed based on the type of material to be inspected and the spatial resolution that
    [0180] the specific application demands (a).
    [0182] Figure 2 refers to the parts of the lens listed below:
    [0184] (201) Outer edge of lens;
    [0185] (202) Concave lens surface (spherical ring);
    [0186] (203) Circular, flat section of the lens;
    [0187] (204) Thickness of the lens in the flat area;
    [0188] (205) Width of the outer flat ring of the lens;
    [0189] (206) Diameter of the flat central disc of the lens;
    [0190] (207) External diameter of the spherical section of the lens;
    [0191] (208) Total diameter of the lens.
    [0193] The parameters involved in determining the optimal geometry of the lens
    [0195] (301) Piezoelectric disc diameter
    [0196] (302) Piezoelectric disc radius
    [0197] (303) Maximum angle of incidence of radiation on the material to be inspected, which is equal to the limit angle (0_lim)
    [0198] (304) Fa: Focal length (acoustic focus)
    [0199] (305) Fg: Lens curvature radius (geometric focus)
    [0200] (306) 0r: Angle of refraction at the lens / air interface;
    [0201] (307) 0i: Nominal angular aperture
    [0202] (308) Material on the surface of the component to be inspected (can be CFRP),
    [0203] (309) Material in the core of the component to be inspected (it can be honeycomb).
    [0205] Additionally, the geometry of said lens has been designed in such a way that:
    [0207] i) the angular opening of the transducer (303) is equal to the value of the limit angle, d Um, for the transmission of ultrasound from the air to the material under inspection (for example, 0 | im ~ 9o for transmission of air to a composite carbon fiber reinforced resin such as those used in the aeronautical sector, CFRP),
    [0208] ii) the focal length Fa (304) is within the near field zone of the transducer, defined by a2 / X, where a is the radius of the transducer (302) aperture and A is the wavelength in air at the center frequency of the transducer.
    [0209] iii) the thickness of the lens in the central zone (204) is equal to a quarter wave,
    [0210] XJ4 where X is the wavelength of the ultrasound at the lens at the transducer's center frequency ( fcent ).
    [0211] iv) the beam width at the focal point ( W) corresponding to an equivalent transducer but with perfectly spherical focusing and radius of curvature Fg is less than or equal to the required resolution (a).
    [0213] Afg
    [0214] W = 1 . 4 - - < or 2 a
    [0216] v) The diameter of the flat central disc of the lens (203) is less than or equal to a.
    [0218] Additionally, the design of said lens has involved:
    [0220] i) the calculation of the geometric design parameters of the lens taking into account the refraction suffered by the ultrasound when passing from the lens to the air (Figure 3), so that the radius of curvature of the lens, or geometric focal length Fg (305), does not match the real or acoustic focal length Fa (304). Thus, the acoustic or real focal length, Fa (304), and is obtained from the angle of refraction at the exit of the lens at a point on the outer edge dR (306). This angle is calculated from Snell's law at the lens surface and the angle of incidence of the ultrasonic radiation on the lens surface at that point: 0¿ (307):
    [0222] dR = asin ( yM / v LsinBUm) (Equation 1)
    [0224] Where vM is the speed of the ultrasound in the external environment (air: -350 m / s) and vl the speed of the ultrasound in the lens (syntactic foam -2500 m / s). Since the angles involved in the problem meet the following geometric relationship (see figure 3):
    [0226] Qiím 9r = 9í (Equation 2)
    [0228] We can get 0¿:
    [0230] tandi = - vL / v M syndlim / (1.0 - vL / v M cos9lim) (Equation 3)
    [0232] ii) In addition, it has been imposed that the position of the geometric focus is within the near field area of the transducer:
    [0234] Fg = Sa2 / A , where: 0 <5 <1 (Equation 4)
    [0235] That is, the value of 5 is determined.
    [0237] Therefore, the opening of the transducer (o) is determined according to (Equation 5):
    [0239] a = 2 <t / (1.45) (Equation 5)
    [0241] With which the radius of curvature of the lens or geometric focus Fg (305) is given, finally, by:
    [0243] Fg = a / sindí (Equation 6)
    [0245] Determine the minimum frequency of the transducer to achieve the desired resolution (Equation 6):
    [0246] fm in T4l7jvf / (2o'SÍW 0¡¿m) (ECU3CÍÓH 7)
    [0248] With the data in table I, the limiting angle (303) (incidence of the ultrasonic beam on the material to be inspected (308)), in this case is 0i¡m = 7.44 °
    [0250] As piezoelectric material (114), a 1-3 composite disc of PZT5A (60% by volume) and epoxy resin is used, polarized in the thickness direction and metallized on the flat faces (SnCu 200 nm thick).
    [0252] The acoustic impedance of this material is: Zp = 17 MRayl. The material to be used in the lens (115) must have an impedance ZL = (ZP Z Cae) 1/2, where CAE is the external adaptation layer (108) for which a material with Zcae = 0.07 MRayl is used , that is, Zl «1.09 MRayl. The material selected in this case is a syntactic foam: an epoxy resin compound loaded with hollow glass microspheres (concentration 60% by volume and diameter of the microspheres 20 um). A wafer is manufactured with a circular section (diameter equal to the transducer aperture) and a thickness of 3 mm. The speed of propagation of ultrasound in this material is 2100 m / s and the acoustic impedance of 1.02 MRayl, very close to that required.
    [0254] It is determined that the position of the geometric focus is 0.6 x distance from the near field, that is: 5 = 0.6 is taken.
    [0256] These parameters and the values in Table I determine the remaining specifications for the transducers and lens:
    [0258] Table II. Transducer design parameters
    [0260]
    [0263] Given these design parameters, a transducer whose center frequency is 400 kHz is manufactured. Two piezoelectric discs of the mentioned material are used, with a diameter of 25 mm. For the transmitter transducer, the electrical resonance of the disk thickness mode is tuned to fcent = 400 kHz (which requires a disk thickness of 3.92 mm) and for the receiver the mechanical resonance is tuned to fcent = 400 kHz (which requires a disc thickness of 4.66 mm).
    [0265] For the external adaptation layer (108) a polyethersulfone membrane manufactured by phase inversion (precipitation by immersion) with 140 p, m thickness is used, suitable as an adaptation layer for this case since it presents an acoustic impedance of Z Cae = 0.07 MRayl and a resonance frequency (A./4) of 400 kHz, tuned to the central frequency to which the transducer is to be designed, fcent , (see table II), where tuned means that the resonance frequency from the thickness mode of the sheet (quarter wave or A./4, where X denotes the wavelength) is taken equal to the resonant frequency of the transducer. As this frequency in the sheet is given by: f = v / 4t, where v is the speed of ultrasound in the material with which the sheet is manufactured and t the thickness, this allows, once the material to be used has been determined, to calculate the necessary thickness.
    [0267] To verify that for the aperture (302) selected the thickness mode of the piezoelectric disc is free of interference with radial modes and the correct tuning of the transmitter and receiver transducer operating frequencies, the electrical impedance is measured in a network analyzer to verify enough decoupling between thickness mode and radial modes.
    [0269] Table III. Components of the transducers in this embodiment.
    [0271]
    [0272]
    [0273]
    [0276] Figure 6 shows the response of the two transducers thus manufactured. Spacing: 140mm, Excitation: Olympus Pulser / Receiver, Model 5077, Excitation 100V. Receiver connected directly to a digital oscilloscope to represent the received signal (Tektronix DPO7054).
    [0278] Manufacturing procedure:
    [0280] ( 1) Procedure for the initial verification of piezoelectric discs and their correct tuning by electrical impedance measurement.
    [0282] The integrity and correct tuning of the piezoelectric discs are checked by measuring their electrical impedance in an impedance analyzer or a network analyzer in the vicinity of the thickness mode resonance frequency provided, in this case 0.4 MHz. For To measure the electrical impedance of the disk, connect the metallized faces to the output terminals of the impedance analyzer. It is verified that the electrical resonance of Tx and the mechanical resonance of Rx are at 0.4 MHz (tolerance 10%). This will be the center frequency of the transducer to be manufactured. The almost negligible influence of the radial modes of vibration is verified.
    [0284] Figure 4 shows the modulus of the electrical impedance (ohm) of the piezoelectric composite discs used to construct Tx and Rx, versus the frequency (MHz) and measured in the vicinity of the resonance frequency (0.4 MHz). As mentioned, firstly it is verified that the electrical resonance frequency of Tx coincides with the mechanical resonance frequency of Rx and both are located at the frequency at which the transducer is to be designed (400 kHz). Secondly, it is verified that the oscillations observed at low frequencies, which correspond to the radial modes in the disk, practically do not interfere with the thickness mode that appears at 0.4 MHz.
    [0286] ( 2) Manufacture of the lens.
    [0287] Any known method can be used to manufacture the lens. In particular, since it is a syntactic foam, made up of epoxy resin and hollow glass microspheres, it is possible to mix both components with the resin in a liquid state and pour into a mold that reproduces the geometry of the lens. Alternatively, it is possible to manufacture a chip and from it carve the geometry of the calculated lens (table II: radius of curvature of the lens, thickness of the lens at the center point and diameter of the central flat disk of the lens) using a lathe with numerical control. In this case, this second option has been used.
    [0289] ( 3) Mounting the transducer.
    [0291] The transducer assembly process is outlined in figure 5.
    [0293] (502) Plastic support sheet for mounting the piezoelectric disc (114) to the bushing (112);
    [0295] (503) Double-sided adhesive tape to fix piezoelectric disc (114) and bushing (112) to the sheet (502)
    [0297] a) A conductive wire (102) is soldered to the piezoelectric disk using tin and solder paste (113). A demolition agent is applied to the other face of the piezoelectric disk. Take a plastic sheet (polycarbonate 200 um, 30 x 30 mm) (502) and stick double-sided adhesive tape (503) on it. This will act as a support for fixing the piezoelectric disc to the socket. The piezoelectric disk is glued to this sheet on the face on which the demolder was applied.
    [0298] b) The metallic sleeve (112) is glued to the plastic film (502) concentrically to the piezoelectric disk, ensuring the sealing of the cavity formed by the sleeve, piezoelectric disk and polycarbonate sheet. The edge between the bushing and the piezoelectric disk (width 1 mm in the present example) is filled with epoxy resin (103).
    [0299] c) Once the resin (103) has cured, the film (502) is removed, the surface of the piezoelectric disk and the cap is cleaned and the front surface is covered with a thin layer (100 pm) of conductive resin (105). The electrical conductivity between the surface that has just been metallized and the metallic cap of the transducer is verified d) The lens (104) is glued to (105) using a layer of 100 µm urethane adhesive (106).
    [0300] e) The polymeric membrane quarter wave adaptation layer (107) is glued to the lens using double-sided adhesive tape (108).
    [0301] f) Attach the front crown (116) to the edge of the cap using urethane adhesive. The series inductance (111) is soldered to the conductive wire (102)
    [0302] g) The parallel inductance (110) is soldered to the BNC connector (109) housed in the rear cover (101)
    [0303] h) Fix the cap to the cap using conductive epoxy resin.
    [0305] The resin deposited between the ferrule and the piezoelectric disk is allowed to cure.
    权利要求:
    Claims (12)
    [1]
    1. - A focus system characterized by understanding
    • a concave lens (115) having an acoustic impedance between 0.2 MRayl and 0.9 MRayl and a focal length between 5 mm and 100 mm comprising a concentric concave surface with a radius of curvature between 20 mm and 90 mm, and • a polymeric coating (108) with a thickness between 70 pm and 200 pm and with a porosity greater than 70%, which presents an acoustic impedance of between 0.05 MRayl and 0.09 MRayl,
    and wherein said polymeric coating (108) is disposed over the entire concentric concave surface of the concave lens (115).
    [2]
    The focusing system according to claim 1, wherein the concentric concave surface of the concave lens (115) comprises a concentric planar central zone with a diameter of between 1mm and 5mm and a thickness of between 0.3mm and 3mm. , 0 mm.
    [3]
    3. The focusing system according to any of claims 1 or 2, wherein the concave lens is made of a syntactic foam.
    [4]
    4. The focusing system according to any one of claims 1 to 3, wherein the coating comprises a polymer selected from a polypropylene polyethersulfone, polyethersulfone, nylon, cellulose nitrate or any combination thereof.
    [5]
    5. A focused ultrasound emitter coupled to air with a central frequency between 0.1 MHz and 2.0 MHz and an angular aperture between 3 0 and 20 0 characterized in that it comprises
    • the focusing system according to claims 1 to 4, wherein the thickness of the concave lens (115) is equal to a quarter of the wavelength of the ultrasound in the lens at the central frequency of the emitter.
    [6]
    6. The emitter according to claim 5, characterized in that it also comprises a piezoelectric sheet (114) selected from among a PZT type ceramic of lead zirconate titanate PbZr03-PbTi03, a composite material of piezoelectric ceramic and resin with type 1-3 connectivity and with a volumetric concentration of ceramic between 25% and 80%, or a piezoelectric single crystal type Pb (Mgi / 3Nb2 / 3) 03-PbTi03, where said sheet piezoelectric (114) comprises an electrically conductive coating of gold, silver, carbon, aluminum, copper or any of their combinations, where said piezoelectric sheet (114) is polarized along its thickness and where the thickness of said piezoelectric sheet (114 ) is between 20 nrnylOO nm,
    • an electronic excitation equipment, and
    • an inductance (110) in parallel or in series between 1pH and 500 pH configured to connect the piezoelectric foil (114) with the electronic excitation equipment.
    where the focusing system and the piezoelectric foil (114) are in contact.
    [7]
    The emitter according to any of claims 5 or 6 comprising a focusing system according to any of claims 2 to 4, wherein the thickness of the flat central area of the concave surface of the concave lens (115) is equal to a quarter of the wavelength of ultrasound at the lens at the center frequency of the emitter.
    [8]
    8. Focused and air-coupled ultrasound receiver with a central frequency between 0.1 MHz and 2.0 MHz and an angular aperture between 3 0 and 20 0 characterized in that it comprises
    • the focusing system according to claims 1 to 4, wherein the thickness of the concave lens (115) is equal to a quarter of the wavelength of the ultrasound in the lens at the center frequency of the receiver.
    [9]
    9. The receiver according to claim 8, characterized in that it also comprises
    • a piezoelectric sheet (114) selected from a PbZr03-PbTi03 lead zirconate titanate PZT type ceramic, a composite material of piezoelectric ceramic and resin with type 1-3 connectivity and with a volumetric concentration of ceramic between 25% and 80%, or a Pb (Mgi / 3Nb2 / 3) 03-PbTi03 type piezoelectric single crystal, where said piezoelectric sheet (114) comprises an electrically conductive coating of gold, silver, carbon, aluminum, copper or any of their combinations, where said piezoelectric sheet is polarized along its thickness and where the thickness of said piezoelectric sheet is between 20 nm and 100 nm, an electronic receiving equipment, and
    • an inductance (110) in parallel or in series between 1pH and 500 pH configured to connect the piezoelectric foil (114) with the electronic receiving equipment.
    where the focusing system and the piezoelectric foil (110) are in contact.
    [10]
    The receiver according to any of claims 8 or 9 characterized in that it comprises the focusing system according to any of claims 2 to 4, the thickness of the flat central area of the concave surface of the concave lens (115) is equal to a quarter of the wavelength of ultrasound at the lens at the center frequency of the receiver.
    [11]
    11. Focused and air-coupled ultrasound transducer with a central frequency between 0.1 MHz and 2.0 MHz and an angular aperture between 3 0 and 20 0 characterized in that it comprises an emitter according to any of claims 5 to 7 and / or a receiver according to claims 8 to 10, wherein the emitter and the receiver are aligned and facing each other.
    [12]
    12. The transducer according to claim 11, characterized in that it comprises an emitter according to any of claims 5 to 7 and a receiver according to claims 8 to 10, wherein the thickness of the piezoelectric sheet (114) of the receiver is different from the thickness of the piezoelectric sheet (114) of the emitter and where the mechanical resonance frequency of the piezoelectric sheet (114) in the receiver Rx is equal to the electrical resonance frequency of the piezoelectric sheet (114) in the emitter Tx and where both frequencies are set at the center frequency of the transducer.
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    同族专利:
    公开号 | 公开日
    ES2812373B2|2021-10-29|
    WO2021053254A1|2021-03-25|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    EP0107287A2|1982-09-28|1984-05-02|Kabushiki Kaisha Toshiba|Ultrasonic beam focusing device with a concave surface and method of manufacturing the same|
    WO2014035786A2|2012-08-31|2014-03-06|Board Of Regents, The University Of Texas System|Devices, systems, and methods for non-destructive testing of materials and structures|
    CN109212037A|2018-10-09|2019-01-15|南昌航空大学|A kind of Air Coupling ultrasonic phase array detection device|
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    申请号 | 申请日 | 专利标题
    ES201930801A|ES2812373B2|2019-09-16|2019-09-16|Focusing system for a focused, air-coupled ultrasound emitter, receiver or transducer|ES201930801A| ES2812373B2|2019-09-16|2019-09-16|Focusing system for a focused, air-coupled ultrasound emitter, receiver or transducer|
    PCT/ES2020/070553| WO2021053254A1|2019-09-16|2020-09-16|Targeted air-coupled focusing system for an ultrasonic emitter, receiver or transducer|
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