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    • 专利摘要:
    Laminar structure as part of a piezoelectric ultrasonic transducer. The present invention refers to a laminar structure, its production process and its use as part of a piezoelectric ultrasonic transducer to operate in broadband pulse-echo mode and with high sensitivity and axial resolution in the presence of a pressurized gas at a pressure between 14 bar and 103 bar. Furthermore, the present invention refers to the transducer comprising said laminar or layered structure. Therefore, the present invention can be framed in the area of materials with applications as sensors in ultrasonic systems. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2779956A1
    申请号:ES201930140
    申请日:2019-02-20
    公开日:2020-08-20
    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] Laminar structure as part of a piezoelectric ultrasonic transducer
    [0004] The present invention refers to a laminar structure, its method of obtaining and its use as part of a piezoelectric ultrasonic transducer to operate in broadband pulse-echo mode and with high sensitivity and axial resolution in the presence of a pressurized gas at a pressure between 14 bar and 103 bar. Furthermore, the present invention refers to the transducer comprising said laminar or layered structure.
    [0006] Therefore, the present invention can be framed in the area of materials with applications as sensors in ultrasonic systems.
    [0008] BACKGROUND OF THE INVENTION
    [0010] The so-called pulse-echo ultrasonic technique for the detection of internal discontinuities in solids or their back surface is well known and has numerous industrial applications. This technique always uses liquid couplings (water or gel) or even soft solids (dry coupling) between the ultrasound emitter / receiver (transducer) and the solid to be inspected (part) and it is not particularly complex since this type of coupling transducer / part is an effective way to ensure efficient transmission of ultrasound from the transducer to the solid under inspection. This enables either the detection of internal discontinuities (detection of cracks, cavities or inclusions) in the solid or the opposite surface (measurement of thickness).
    [0012] When ultrasonic transducers operate by air or gas coupling, the detection of echoes from the gas / air interfaces with a solid, from the internal discontinuities of said solid, or from the back surface is much more complex since there is a strong acoustic impedance decoupling at transducer-gas and gas-solid interfaces. This makes:
    [0013] i) the sensitivity of the transducer is very poor,
    [0014] ii) the transducer band is limited
    [0015] iii) the amplitude of the signal reflected in the first interface of the solid is very high, while that of the internal echoes (or of the back face) is very weak.
    [0017] Furthermore, i) and ii) result in the transducers used for coupling by gases having a very long response signal in time, which produces a very long dead zone that makes it impossible to discern the presence of echoes close to it in time, that is, the axial resolution is very poor.
    [0019] For very high gas pressures the above problems can be reduced in such a way that it becomes possible to solve the problem by using conventional transducers for immersion in water. This is due to the fact that in this case of very high pressures the increase in gas density contributes to the fact that the acoustic impedance of the gas increases in the same proportion. For a sufficiently high pressure, the impedance mismatch between transducer and gas and between solid and gas may decrease so much that it may be possible to use a transducer designed to operate by liquid coupling. Although the result is not optimal, if the pressure is high enough and the impedance of the gas increases as necessary, it is possible to obtain an at least acceptable performance. In practice it has been found that it is possible to apply this approach for pressures higher than 69-103 bar (1000-1500 psi (US005587534A). Unfortunately, these pressures are too high for most of the applications that are presented in the industry so that this approach is useless.
    [0021] Indeed, the pressures used in gas transportation and distribution are in the range 14-103 bar (200-1500 psi), so this approach to the problem based on the use of conventional transducers for immersion in water is no longer useful. that at these pressures the transducers designed for coupling by means of liquids do not offer acceptable performance. As the pressure in the gas decreases (below 103 bar), the attenuation of the ultrasound increases and the impedance decreases, which reduces the sensitivity of the immersion transducers and produces a worsening of the signal-to-noise ratio; in addition, it lengthens the response signal, which produces a loss of axial resolution.
    [0023] On the other hand, the existing transducers for air coupling are not useful for this application as they are designed to operate at pressures reduced and because they are designed to work in transmission mode and not in pulse-echo mode, presenting a poor axial resolution that is not acceptable in these applications.
    [0025] Therefore, it is necessary to develop new transducers resistant to high pressures (> 14 bar), with high sensitivity (> -35 dB) and good axial resolution (<5 p, s) to detect echoes generated by a solid body (and their discontinuities internal) in the presence of a pressurized gas and using said gas as a coupling medium.
    [0027] DESCRIPTION OF THE INVENTION
    [0029] The present invention relates to a laminar or laminated structure and to its method of obtaining and to the use of said laminar or laminated structure as part of a piezoelectric ultrasonic transducer and to the transducer comprising said laminar or laminated structure.
    [0031] The piezoelectric ultrasonic transducer referred to in the present invention operates in broadband pulse-echo mode, with high sensitivity (> -35 dB) and with high axial resolution (<5 p, s) in the presence of a pressurized gas at a pressure between 14 bar and 103 bar (200-1500 psi), that is, it operates by generating ultrasonic signals and detecting the echoes generated by a solid body in the presence of a pressurized gas at a pressure between 14 bar and 103 bar (200- 1500 psi).
    [0033] This piezoelectric ultrasonic transducer has a high sensitivity> -30 dB and a bandwidth> 90% and can be used to carry out the following measurements in tanks and pipes that contain or transport gases at pressures between 14 bar and 103 bar (of between 200 psi and 1500 psi).
    [0034] - Profilometry of the internal surface
    [0035] - Measurement of wall thickness.
    [0036] - Detection of corrosion by thickness reduction.
    [0037] - Detection of cracks or other defects.
    [0039] In a first aspect, the present invention refers to a laminar or laminated structure (hereinafter "the structure of the present invention") characterized in that it comprises
    [0040] a resonant adaptive polymeric membrane (7) with a thickness between 50 pm and 150 pm that presents
    [0042] o quarter wave resonance conditions at a central frequency ( fc) greater than or equal to 1 MHz, between 1 MHz and 4 MHz,
    [0044] or an acoustic impedance between 0.1 MRayl and 0.5 MRayl,
    [0045] or a porosity greater than 70% and
    [0046] or interconnected pores;
    [0047] a pressure sensitive adhesive sheet (6), with a thickness less than 60 pm,
    [0048] or placed on the resonant sheet (7) and covering said sheet (7) completely;
    [0049] or that has an acoustic impedance between 0.5 MRayl and 1.5 MRayl; a sheet of syntactic foam (5), with a thickness of between 100 pm and 500 pm or placed on the sheet (6) and covering said sheet (6) completely, or that has an acoustic impedance of between 0.5 MRayl and 2 MRayl ; a polymeric sheet (4) with a thickness between 100 pm and 500 pm
    [0051] or located on the sheet (5) and covering said sheet (5) completely, or having an acoustic impedance of between 1.5 MRayl and 3.5 MRayl; a first conductive sheet (2e), with a thickness of between 20 nm and 100 nm, located on the sheet (4) and covering said sheet (4) completely; a piezoelectric sheet (1) comprising an internal face (i) and an external face (e)
    [0053] or thickness between 0.5 mm and 2 mm,
    [0054] or which is located on the conductive sheet (2e), where the external face (e) is in direct contact with the conductive sheet (2e), and
    [0055] or that it is partially covering said conductive sheet (2e); a second conductive sheet (2i), with a thickness of between 20 nm and 100 nm, located on the internal face (i) of the piezoelectric sheet (1) and covering said sheet (1) completely;
    [0056] a block (3), with anechoic conical finish,
    [0057] or thicknesses between 15 mm and 30 mm,
    [0058] or located on the conductive sheet (2i) and extending around the sheets (2i) and (1) until contacting the conductive sheet (2e),
    [0059] or that presents an acoustic impedance between 5 MRayl and 10 MRayl, or and which is composed of an epoxy resin comprising particles with a diameter between 1 pm and 50 pm selected from among tungsten, zirconia, alumina and any of their combinations;
    [0060] where (1), (2i), (2e), (3), (4), (5), (6) and (7) withstand hydrostatic pressures up to 3800 psi (262 bar),
    [0061] where the piezoelectric foil is polarized along its thickness, and
    [0062] where the plates (4), (5) and (6) form a set that presents quarter-wave resonance conditions at the central frequency of the transducer (fc) which in this case is a frequency greater than or equal to 1 MHz, between 1 MHz and 4 MHz. This condition is met when it is verified that:
    [0064] fc = 1 / [4 (í 4 / ^ 4 + ts / vs t 6 / v 6)]
    [0066] where v¡ and ti are the speed of the ultrasound and the thickness in layer i, where i = 3, 4, 5. The thickness of the piezoelectric sheet (1) is determined from the resonance frequency of the transducer, fixing in such a way that the frequency of the electrical resonance of the sheet (1) is equal to fc.
    [0068] The laminar or laminated structure of the present invention can have any section: circular, rectangular, square, etc.
    [0070] In the present invention, "resonant adaptive polymeric membrane" is understood as that sheet with a porosity greater than 70% and with interconnected pores that presents an acoustic impedance of between 0.1 MRayl and 0.5 MRay and resonance conditions of a quarter of wave at a central frequency greater than or equal to 1 MHz, between 1 MHz and 4 MHz. Said sheet is adaptive because, thanks to its open pore nature, the gas inside the pores is in equilibrium with the external gas and this allows its acoustic impedance to be modified in accordance with the pressure of the external gas. Said sheet is resonant because its thickness is equal to a quarter of the wavelength of ultrasound at the working frequency of the transducer (fc). By varying the gas pressure external, the density of the same also varies and due to this nature of open pore, the effective density of the sheet is also modified and does it in the same sense. A change in density in the gas implies a change proportional impedance of the same, in such a way that, to maintain an optimal coupling of the transducer, it would also be necessary to modify the impedance of the material on the outside, which is not possible. This problem is addressed through the use of this open-pore sheet whose impedance varies as necessary as the pressure of the external gas varies. For this reason it is classified as adaptive.
    [0072] In the present invention, "pressure sensitive adhesive sheet" is understood as that adhesive tape configured for the permanent bonding of two solid surfaces that does not present any physical support. By the term "pressure sensitive" is understood herein invention to one whose adhesive is activated under pressure.
    [0074] In the present invention, "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 of size <20 pm, randomly distributed. For example, these syntactic foams are used in flotation systems for deep-sea submarines, for depths of 700 m to 10,000 m.
    [0076] In the present invention, "anechoic conical finish" is understood as that cone-shaped finish that presents an internal anechoic structure designed to completely disperse the reflections produced by acoustic waves on any of the surfaces that comprise it.
    [0078] In a preferred embodiment of the structure of the present invention, the resonant adaptive polymeric membrane (7) is selected from polypropylene, cellulose nitrate, cellulose ester, polyethersulfone and nylon.
    [0080] In another preferred embodiment of the structure of the present invention, the pressure sensitive adhesive sheet (6) is selected from an acrylic sheet or a polyurethane sheet.
    [0082] In another preferred embodiment of the structure of the present invention, the syntactic foam sheet (5) is composed of an epoxy resin with hollow spheres of diameter between 1 pm and 20 pm. The hollow spheres are preferably glass or polyolefin.
    [0084] The polymeric sheet (4) is preferably an epoxy resin.
    [0085] In another preferred embodiment of the structure of the present invention, the conductive sheets (2e) and (2i) are independently composed of a conductive material selected from Au, Ag, Cu, Sn and any of their combinations.
    [0087] In another preferred embodiment of the structure of the present invention, where the composition of the piezoelectric sheet (1) is selected from a ceramic type PZT of lead zirconate titanate PbZrO 3 -PbTiO 3 , a composite material of piezoelectric ceramic and resin with Type 1-3 connectivity and with a volumetric concentration of ceramic between 25% and 80%, and a piezoelectric single crystal type Pb (Mg1 / 3Nb2 / 3) O3-PbTiO3 (PMN-PT).
    [0089] Another aspect of the invention refers to the process for obtaining the structure of the present invention (hereinafter "the process of the invention") characterized in that it comprises the following steps:
    [0090] (a) join the piezoelectric sheet (1) covered by the conductive sheets (2i) and (2e) to a sacrificial sheet, preferably polycarbonate, by means of adhesive tape (6) on a first side,
    [0091] (b) join a metal receptacle (8), to the sacrificial sheet with the help of adhesive tape (6),
    [0092] (c) filling the space formed between the piezoelectric sheet (1) and the metal receptacle with resin (3) and curing said resin (3),
    [0093] (d) remove sacrificial sheet,
    [0094] (e) metallize the first face of the piezoelectric sheet (1) so that the conductive sheet (2e) completely covers the piezoelectric and the edge of the cap, (f) deposit the polymeric sheet (4) on the conductive sheet (2e) cure and polish,
    [0095] (g) gluing the syntactic foam sheet (5) to the polymer sheet (4) preferably the adhesive has the same composition as the polymer sheet (4),
    [0096] (h) adhering the pressure sensitive adhesive sheet (6) onto the syntactic foam sheet (5),
    [0097] (i) gluing the resonant adaptive polymeric membrane (7) to the pressure sensitive adhesive sheet (6),
    [0098] (j) fix the set of blades (1), (2e), (2i), (3), (4), (5), (6) and (7) for example with a protective crown (11) and flip , and
    [0099] (k) filling the interior space of the metal receptacle with the help of a conical mold to form a block (3) with conical shape.
    [0101] The method of the present invention can be verified by measuring the electrical impedance at the terminals (plates (2i) and (2e)) in each stage thereof.
    [0103] In a preferred embodiment of the process of the present invention, the step (e) of metallizing the first face of the piezoelectric sheet (1) to form the conductive sheet (2e) that completely covers the piezoelectric and the edge of the cap, is carried out performed by techniques selected from sputtering, vacuum plating, evaporation plating, screen printing plating, dip deposition and spin coating.
    [0105] In another preferred embodiment of the process of the present invention, the deposition of step (f) is carried out by deposition techniques selected from among dip deposition, spin coating, and screen printing.
    [0107] In another preferred embodiment of the process of the present invention, step (g) regarding the gluing of the syntactic foam sheet (5) to the polymer sheet (4) is carried out using an adhesive that has the same chemical composition as polymeric sheet (4).
    [0109] Another aspect of the present invention refers to the use of the structure of the present invention as part of a piezoelectric ultrasonic transducer to detect echoes generated by a solid body in the presence of a pressurized gas at a pressure of 14 bar and 103 bar (from between 200 psi and 1500 psi), for example to detect echoes from natural gas pipelines.
    [0111] It has been mentioned above that the laminar or laminated structure of the present invention can have any section: circular, rectangular, square, etc. The section of said structure will be selected according to the final section that is desired for the transducer; The shape of the metal receptacle (8) of step (b) of the method of the present invention will determine the final section of the transducer. For example, if it is intended to obtain a circular section transducer, then the metal receptacle (8) used in stage (b) of the procedure for obtaining the structure of the present invention will be cylindrical.
    [0113] In the present invention, "piezoelectric ultrasonic transducer" is understood as that ultrasound generator and receiver based on the use of a piezoelectric material.
    [0115] In the present invention, the piezoelectric ultrasonic transducer works in an echo pulse mode, that is, between the transducer and the solid to be inspected through a pressurized gas, at a pressure between 14 bar and 103 bar (between 200 psi and 1500 psi).
    [0117] The last aspect of the present invention refers to a piezoelectric ultrasonic transducer for detecting echoes generated by a solid body in the presence of a pressurized gas at a pressure between 14 bar and 103 bar (between 200 psi and 1500 psi), characterized by that understands
    [0118] • the structure of the present invention mentioned above,
    [0120] or where the resonant adaptive polymeric membrane (7) is configured to act as a quarter wave resonant layer at the center frequency of the transducer,
    [0122] or where the set formed by (4), (5) and (6) is configured to act together as a single resonant layer at the center frequency of the transducer and gradually reduce the acoustic impedance of the structure,
    [0124] or where the first conductive sheet (2e) and the second conductive sheet (2i) are configured to act as an electrode and enable the application / measurement of electric field in piezoelectric sheet (1),
    [0125] or where the block (3) is configured to damp the vibration of the piezoelectric sheet (1) and avoid any background echo,
    [0126] • a metal receptacle (8) comprising a coaxial connector (9) with ground connection and an internal connector (10) of a rear cover (12) of the metal receptacle (8) and which is configured to house the laminated structure and provide electromagnetic shielding.
    [0128] or where (2e), (3), (4), (5), (6) and (7) are in contact with the internal walls of the receptacle (8);
    [0129] • a coaxial connector (9) that joins the internal connector (10) of the rear cover (12) of the metal receptacle (8) with the second conductive sheet (2i) that is configured to apply a voltage to the piezoelectric element through the connector or to measure the voltage generated in the piezoelectric element; and • a protective crown (12) configured to protect the resonant adaptive polymeric membrane (7) and the lateral edge of the resonant adaptive polymeric membrane (7), the set formed by (4), (5) and (6), the block (3), the first conductive sheet (2e) and the second conductive sheet (2i).
    [0131] 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.
    [0133] BRIEF DESCRIPTION OF THE FIGURES
    [0135] FIG. 1 Schematic representation of the piezoelectric ultrasonic transducer
    [0136] (1) Piezoelectric foil
    [0137] (2) Conductive foil:
    [0139] or first conductive sheet (2e) and second conductive sheet (2i) (3) Damping block
    [0140] (4) Polymeric sheet
    [0141] (5) Syntactic foam sheet
    [0142] (6) Pressure sensitive adhesive sheet
    [0143] (7) Resonant adaptive polymeric membrane
    [0144] (8) Metal receptacle
    [0145] (9) Cable or coaxial connector
    [0146] (10) Internal connector of the coaxial connector (9)
    [0147] (11) Protective crown
    [0148] (12) Metal receptacle rear cover (8)
    [0150] FIG. 2 Cap, back cap and front crown. Dimensions.
    [0152] FIG. 3 Modulus of the electrical impedance (ohm) of the piezoelectric composite disc [(1), (2i), (2e)] versus the frequency (MHz) measured in the vicinity of the frequency of resonance (1 MHz). Dashed line: experimental measurement, dotted line: theoretical calculation.
    [0154] FIG. 4 Side view of the piezoelectric disc after soldering (1) the wire (2) to the metallized surface of the piezoelectric (3)
    [0156] FIG. 5 Side view of the fixation of the piezoelectric disk to a polyurethane sheet (2) using a double-sided adhesive (1).
    [0158] FIG. 6 Side view of the piezoelectric disc and the cylindrical bushing (1) ready to be fixed concentrically.
    [0160] FIG. 7 Side view of the piezoelectric disc fixed to the bushing using epoxy resin (1).
    [0162] FIG. 8 Side view of the piezoelectric disc attached to the bushing already released from the manufacturing support.
    [0164] FIG. 9 Side view of the piezoelectric disc fixed to the socket and with the external face completely metallized (1).
    [0166] FIG. 10 Electrical impedance of the free piezoelectric disc (dashed line) and of the disc attached to the sleeve (solid line).
    [0168] FIG. 11 Side view of the deposition of the resin layer (1) on the metallized surface.
    [0170] FIG. 12 Side view of the transducer with the ground and polished resin sheet (1).
    [0171] FIG. 13 Electrical impedance of the transducer before (dashed line) and after (solid line) depositing and sanding the resin layer.
    [0173] FIG. 14 Side view of the transducer with the layers of epoxy adhesive (1) and syntactic foam (2) deposited.
    [0174] FIG. 15 Electrical impedance of the transducer before (dashed line) and after (solid line) depositing the syntactic foam layer.
    [0176] FIG. 16 Side view of the transducer with the layers of adhesive tape (2) and membrane (1).
    [0178] FIG. 17 Electrical impedance of the transducer before (dashed line) and after (solid line) placing the membrane.
    [0180] FIG. 18 Side view of transducer with front crown (1).
    [0182] FIG. 19 Side view of the transducer with the mold (1) for the completion of the counter mass
    [0184] FIG. 20 Side view of the transducer with the counter mass (1) completed.
    [0186] FIG. 21 Electrical impedance of the transducer before (dashed line) and after (solid line) placing the counter mass.
    [0188] FIG. 22 Side view of the transducer with the free end of the cable soldered to the internal pin (3) of the coaxial connector (2) housed in the rear cover (1).
    [0190] FIG. 23 Side view of the transducer closed from the back.
    [0192] FIG. 24 Spectrum of the transmission coefficient (magnitude and phase) of the membrane used for the outer layer of the transducer. Solid line: theoretical calculation of the magnitude, dashed line: theoretical calculation of the phase, points: measurements.
    [0194] FIG. 25 Impulse response (a) and sensitivity band (b) of the 1 MHz transducer in air under normal conditions.
    [0196] FIG. 26 Impulse response (a) and sensitivity band (b) of the 1 MHz transducer in air with an overpressure of 5 bar.
    [0197] EXAMPLES
    [0199] The invention will now be illustrated by means of tests carried out by the inventors, which show the effectiveness of the product of the invention.
    [0201] The following example of embodiment refers to a piezoelectric ultrasonic transducer with a circular section. The following table 1 lists and describes the elements that make up the transducer.
    [0203] Table 1: Transducer elements with their description
    [0205]
    [0206]
    [0209] * It is a composite material of piezoelectric ceramic and resin. The resin is the matrix and the ceramic comes in the form of a stack of abutments. This type of compound is known as 1-3, 1 because the ceramic is connected only in 1 direction, which are the pillars, and 3 because the resin is connected in the three directions of space, which is a matrix.
    [0210] Dice and fill refers to the standard manufacturing method of this material: a ceramic disc is taken, a series of regularly spaced cuts are produced in two orthogonal directions that form the pillars, and the gaps are then filled with resin.
    [0212] The materials used in manufacturing are listed below:
    [0214] Structural elements [(8), (9), (11)]:
    [0215] • Conductive metallic bushing (cylinder with internal diameter 11 mm and wall thickness 1 mm). 25 mm in length.
    [0216] • Flat back cover with circular through hole in the center for SMB connector.
    [0217] • Metallic frontal crown for protection of the radiant face.
    [0219] Cap, back cover and front crown according to Figure 2.
    [0221] Other materials:
    [0222] • Coaxial panel connector, SMB type.
    [0223] • Cable (0.2 mm) [(9)].
    [0224] • Piezoelectric composite disc [(1), (2i), (2e)], 1-3 connectivity, PZT5A ceramic and 50% epoxy resin. Manufactured by the dice and fill technique . Polarized in the thickness direction and metallized on both flat faces (100 nm thick CuSn coating). 9.83mm diameter disc, 1.54mm thickness. Resonance frequency: 1 MHz.
    [0225] • Epoxy resin, density 1150 kg / m3, ultrasound speed 2450 m / s [(4)]
    [0226] • Syntactic foam [(5)] (epoxy resin loaded with hollow spheres, diameter <20. ^ M (acoustic impedance of 0.7 MRayl and ultrasound speed of 2100 m / s).
    [0227] • Double-sided pressure sensitive adhesive tape [(6)]. Without support, thickness:
    [0228] 60 microns, acoustic impedance 0.6 MRayl.
    [0229] • Resonant polymeric membrane [(7)] at the center frequency of the transducer (1MHz ± 10%). Material: Polypropylene; Impedance: 0.095 MRayl (± 10%); Porosity: 70%, Porosity type: open (interconnected). Thickness: 90 p, m Diameter: 14 mm.
    [0231] Materials for the counter mass [(3)]:
    [0232] • Epoxy resin, density 1150 kg / m3, ultrasound speed 2450 m / s • Rubber powder (particle size <120 microns).
    [0233] • Tungsten powder (particle size: 12 microns).
    [0235] Auxiliary materials:
    [0236] • Low-density polyurethane foam (100-300 kg / m3) for the manufacture of the conical mold for finishing the counter mass [(3)].
    [0237] • Demolition agent.
    [0238] • Plastic sheet (200 um, polycarbonate).
    [0239] • Tin and solder paste.
    [0241] Manufacturing procedure:
    [0243] ( 1) Procedure for the initial verification of the piezoelectric disk by measurement of electrical impedance and for successive verifications during the manufacturing process.
    [0245] The integrity and suitability of the piezoelectric disk is checked by measuring its electrical impedance in an impedance analyzer or network analyzer in the vicinity of the thickness mode resonance frequency provided by the manufacturer, in this case 1 MHz. To measure the electrical impedance of the disc, the metallized faces are connected to the output terminals of the impedance analyzer. The electrical resonance is verified to be at 1 MHz (tolerance 5%). This will be the center frequency of the transducer to be manufactured. The integrity of the piezoelectric resonance is also verified, comparing the measured impedance curve with that provided by the manufacturer. Likewise, the almost negligible influence of radial modes of vibration is verified (lower frequency resonances and their harmonics that can overlap with the thickness mode resonance located at 1 MHz).
    [0247] Figure 3 shows the Modulus of the electrical impedance (ohm) of the piezoelectric composite disc [(1), (2i), (2e)] versus the frequency (MHz) measured in the vicinity of the resonance frequency (1 MHz ). The curve with the dashed line is the experimental measurement and the dotted curve is the one calculated theoretically (model 1D). The small oscillations at low frequencies are the radial modes on the disk that are practically negligible compared to the thickness mode that appears at 1 MHz.
    [0249] This same electrical impedance measurement taken at the piezoelectric disk terminals is repeated at each step of the process to verify the integrity of the piezoelectric response and the correct assembly and dimensioning of the layers and elements placed at each step by comparing the impedance curve. Measure with which it is calculated knowing the properties (thickness, impedance and damping) of each deposited layer.
    [0251] ( 2) Fixing the piezoelectric disc to the socket and preparing electrical connections.
    [0253] Take a piece of wire with a length approximately equal to twice the length of the bushing (60 mm in this case) and both ends are stripped to a length, approximately 3 mm). It is wound in the form of a solenoid (with an approximate diameter of 1/3 the internal diameter of the bushing, 4 mm in this case, and a similar length to that of the bushing, 28.2 mm in this case) and one of its ends to one of the faces of the piezoelectric disc using tin and solder paste. The other end of the cable is free. See figure 4. Side view of the piezoelectric disc after soldering the cable.
    [0255] A demolition agent is applied to the other face of the piezoelectric disc.
    [0257] Take a plastic sheet (polycarbonate 200 um, 30 x 30 mm) and stick double-sided adhesive tape on a surface of 40 x 40 mm. This will act as a support for fixing the piezoelectric disk to the socket. The piezoelectric disc is glued to this sheet on the face on which the demolder was applied. See figure 5. Side view of the piezoelectric disc with the cable fixed to the bracket for fixing to the bushing.
    [0259] The metal sleeve is glued to the plastic film concentrically to the piezoelectric disk, ensuring the tightness of the cavity formed by the sleeve, piezoelectric disk and polycarbonate sheet. See figure 6. Side view of the piezoelectric disc and the cap, ready to be fixed.
    [0260] The edge between the bushing and the piezoelectric disc (width of 1 mm in the present example) is filled with epoxy resin filled with tungsten powder and rubber powder, manufactured following the procedure explained in (3). See figure 7. Side view of the piezoelectric disc fixed to the socket.
    [0262] The resin deposited between the cap and the piezoelectric disk is allowed to cure.
    [0264] After the resin has cured, the polycarbonate sheet attached to the piezoelectric disc and cylinder is removed. The outer surface of the piezoelectric disc and the edge of the metal cap are cleaned of any remaining adhesive residue, preserving the metallization of the piezoelectric disc. The end result in this step is that the piezoelectric disc is fixed to the bushing by means of a ring of resin loaded with 1 mm thick particles (in this case). See figure 8. Side view of the piezoelectric disk fixed to the bushing already released from the manufacturing support.
    [0266] The surface that has just been cleaned is metallized: piezoelectric disc resin ring cap edge. Any available technique can be used, either sputttering, evaporation or screen printing. See figure 9. Side view of the piezoelectric disc fixed to the socket and with the external face completely metallized.
    [0268] Finally, the electrical conductivity between the surface that has just been metallized and the metal cap of the transducer is verified and the electrical impedance measurement is repeated to verify that the piezoelectric resonance remains unchanged except for the introduction of a slight damping due to the fixation. from the piezoelectric disc to the bushing. The result of the impedance measurement is shown in figure 10 where the measurements corresponding to the free piezoelectric disk and the disk fixed in the socket can be seen and the damping effect introduced when fixing the piezoelectric disk to the socket can be verified both in the mode thickness as in radial modes that disappear completely.
    [0270] ( 3) Manufacture of multilayer material for optimal adaptation of impedances to gas / air.
    [0272] Deposition of a resin sheet of 300-350 microns, using a technique of screen printing, deep coating or any similar technique on the external surface of the piezoelectric disc. For this purpose, both components of the resin are mixed, trapped air is removed using a vacuum hood and deposited, while in a liquid state, on the metallized surface, covering it completely. The deposited layer does not need to lie flat or flat parallel. The amount of resin deposited, equivalent to a layer of 300-350 microns, is controlled by weighing on a precision balance. The final result can be seen in figure 11 Side view of the deposition of the resin layer on the metallized surface.
    [0274] The resin thus deposited is allowed to cure following the resin manufacturer's instructions.
    [0276] Once cured, its external surface is polished using an automatic polisher to leave a finish flat and normal to the axis of the bushing. The final thickness of this layer should be 260 p, m, the roughness <5 p, m. The result after this stage can be seen in figure 12. Side view of the transducer with the rectified and polished resin sheet.
    [0278] At this point, the electrical impedance measurement of the transducer is repeated to verify the correct deposition of the resin sheet, as explained in (1). For this, the free end of the cable and the gland are connected to the terminals of the impedance analyzer. The result is shown in figure 13.
    [0280] From a block of syntactic foam, cut a 1 mm thick sheet, side> 25 mm.
    [0282] The thickness of the previous sheet is lowered, either by means of a numerical control lathe or by using a polishing machine to a thickness of 330 pm, guaranteeing the plane parallelism of both sides of the sheet. From this sheet, a disc is cut with the same diameter as the external diameter of the transducer sleeve (13.3 mm in this case). This operation can be done using a punch.
    [0284] The syntactic foam sheet is glued to the surface of the transducer using the same epoxy resin that was deposited on the surface of the piezoelectric. The added thickness of epoxy resin to achieve this bond should be 100 pm. The amount of resin added is controlled by weighing on a weighing scale. precision. See figure 14. Side view of the transducer with the layers of epoxy resin and syntactic foam deposited.
    [0286] Once the previous layer has cured and therefore the syntactic foam sheet has been glued, the electrical impedance measurement is repeated connecting the free end of the cable and the bushing to the terminals of the impedance analyzer to verify the correct placement of this sheet as explained. in 1). The result is shown in Figure 15. Electrical impedance of the transducer before (dashed line) and after (solid line) depositing the syntactic foam layer.
    [0288] Once verified, a sheet of pressure sensitive double-sided adhesive tape (thickness 60 | j, m) is placed on the outer surface of the syntactic foam layer. On this sheet of adhesive tape the adaptive and resonant polymeric membrane is placed. See figure 16. Side view of the transducer with the layers of adhesive tape and membrane. To ensure correct bonding of the double-sided adhesive tape sheet to both the syntactic foam and the membrane, it is subjected to a pressure in the normal direction of the bonding plane of about 150 kN / m2. And at a temperature of 50 ° C for 30 minutes.
    [0290] Once this cycle is finished and the transducer has cooled, the electrical impedance measurement is repeated, connecting the free end of the cable and the cap to the terminals of the impedance analyzer to verify the correct placement of this sheet as explained in (1). The result is shown in figure 17.
    [0292] ( 4) Front crown.
    [0294] Once the last layer of the stack of layers has been deposited, both the front and side faces are protected by placing the front protection ring, which can simply be fitted or fitted and glued on the cap. See figure 18. Side view of the transducer with frontal crown.
    [0296] ( 5) Placement of the backing.
    [0298] Once the frontal protection crown is in place, the transducer is placed in a vertical position, resting on the front crown. The cavity formed by the bushing and The surface of the piezoelectric disc is filled with the mixture of epoxy resin, tungsten and rubber powder before the mixture begins to cure, up to a height of 2/3 of the total height of the ferrule, ensuring that the free end of the wire welded to the piezoelectric disc is free. Allow the mixture to cure. See figure 19. Side view of the transducer with the counter mass deposited.
    [0300] Manufacture of the mold for the conical finish of the counter mass. A disc is cut from the low-density polyurethane foam (100-300 kg / m3), with a diameter equal to the internal diameter of the metal sleeve and a thickness equal to the radius. A conical surface with a generatrix at 45 degrees from the axis is carved on one of the faces of this disc. A small hole (<1mm diameter) is made at the vertex.
    [0302] The mold thus manufactured is placed on the counter mass deposited in the bushing by passing the free end of the cable welded to the piezoelectric disk through the hole made at the apex of the conical surface. See figure 20. Side view of the transducer with the mold for the completion of the counter mass.
    [0304] The conical space between the mold and the counter mass is filled with the same mixture of resin, tungsten and rubber powder with which the counter mass was made. It is allowed to heal. See figure 20. Side view of the transducer with the counter mass completed.
    [0306] Once the counter mass is in place, correct operation is checked again by measuring the electrical impedance of the transducer. The result is shown in figure 21.
    [0308] ( 6) Fitting the connector and back cover.
    [0310] The panel SMB coaxial connector is attached to the rear cover. The connector ground connects to the back cover. The free end of the cable is soldered to the internal pin of the coaxial connector (SMB). See figure 22. Side view of the transducer with the free end of the cable soldered to the internal pin of the coaxial connector housed in the rear cover.
    [0312] The back cover is attached to the socket ensuring electrical connectivity between the back cover and the socket body and between the internal pin of the connector and the transducer cable. See fig. 23. Side view of the transducer closed from the rear.
    [0313] ( 7) Manufacture of the material to make the backing of the transducer and of the material to fix the piezoelectric disc to the socket. Both materials are identical.
    [0315] The material consists of epoxy resin, tungsten powder (12 microns) and rubber powder (<120 microns). Weight proportion: Resin: 22%, Tungsten powder: 72%, Rubber powder: 6%
    [0317] Additives (tungsten powder and rubber powder) are added to component A of the resin.
    [0319] The three components are mixed well.
    [0321] The resin hardener (part B) is added.
    [0323] The mixture is placed in a vacuum to remove trapped gas.
    [0325] The mixture is deposited in its final location. The mixture is again degassed in a vacuum hood.
    [0327] It is subjected to hydrostatic pressure to eliminate the smallest bubbles (30 min, 6 bar).
    [0329] The resin is cured following the manufacturer's instructions.
    [0331] ( 8) Verification of membrane properties: resonance frequency and impedance.
    [0333] To verify the correct selection of the membrane, the characterization technique described in the following references is applied
    [0334] [1] T. Gómez Álvarez-Arenas, "Air-coupled ultrasonic spectroscopy for the study of membrane filters," J. Memb. Sci., Vol. 213, no. 1-2, pp. 195-207, Mar.
    [0335] 2003.
    [0336] [2] TE Gómez Alvarez-Arenas, "A nondestructive integrity test for membrane filters based on air-coupled ultrasonic spectroscopy.," IEEE Trans.
    [0337] Ultrason. Ferroelectr. Freq. Control, vol. 50, no. 6, pp. 676-85, Jun. 2003.
    [0338] [3] T. E. Gómez Álvarez-Arenas. Device for the characterization of ultrasonic materials with coupling by gases (air) and its application to carry out a non-destructive test to verify the integrity of porous membranes. Patent ES 2239500B1, 2003
    [0339] which consists of the measurement of the membrane transmission coefficient to ultrasound using normal incidence and air as a coupling medium in a frequency range where the membrane thickness resonance appears. Under these conditions, said resonance appears at the frequency in which the wavelength is equal to twice the thickness (that is, A./2 resonance). This frequency has to be twice the central frequency of the transducer, since when the membrane is deposited on the transducer its resonance will be A / 4. That is, you need a membrane whose resonance frequency is 2.0 MHz, the tolerance for this criterion is 5%.
    [0341] In addition, from the theoretical analysis of the magnitude and phase of the transmission coefficient it is also possible to determine the impedance of the material [4].
    [0342] [4] TE Gómez Alvarez-Arenas, "Simultaneous determination of the ultrasound velocity and the thickness of solid plates from the analysis of thickness resonances using air-coupled ultrasound.," Ultrasonics, vol. 50, no. 2, pp. 104- 9, Feb. 2010.
    [0344] The spectrum of the transmission coefficient of the selected membrane (magnitude and phase) and the theoretical adjustment that allows to determine the impedance are shown in figure 24. The resonance frequency A./2 is at 1.95 MHz, therefore the A./4 resonance will be 0.98 MHz, and the impedance value is 0.088 MRayl.
    [0346] Figure 24 shows the spectrum of the transmission coefficient (magnitude and phase) of the membrane used for the outer layer of the transducer. Blue line: theoretical calculation, green points: measurement.
    [0348] To measure the impulse response and the sensitivity band at ambient pressure and with an air overpressure of 5 bar, an Olympus receiver transmitter (5072) is used from the manufactured transducer, a 90 V amplitude excitation pulse and the received signal is leads directly to the oscilloscope, without any extra amplification. I know Place a 22 uH inductance in parallel with the transducer terminals. The reflector was a block of steel located at 7 mm.
    [0350] Figure 25 shows the impulse response and the sensitivity band of the pulse-echo mode transducer obtained at ambient pressure.
    [0352] Figure 26 shows the impulse response and pulse-echo mode transducer sensitivity band obtained with an overpressure of 5 bar (73 psi) of air.
    权利要求:
    Claims (13)
    [1]
    laminar structure characterized by comprising
    a resonant adaptive polymeric membrane (7) with a thickness between 50 pm and 150 pm that presents
    o quarter-wave resonance conditions at a central frequency greater than or equal to 1 MHz, between 1 MHz and 4 MHz,
    or an acoustic impedance between 0.1 MRayl and 0.5 MRayl,
    or a porosity greater than 70% and
    or interconnected pores;
    a pressure sensitive adhesive sheet (6), with a thickness less than 60 pm,
    or placed on the resonant sheet (7) and covering said sheet (7) completely;
    or that has an acoustic impedance between 0.5 MRayl and 1.5 MRayl; a sheet of syntactic foam (5), thickness between 100 pm and 500 pm
    or located on the sheet (6) and covering said sheet (6) completely, or having an acoustic impedance of between 0.5 MRayl and 2 MRayl; a polymeric sheet (4) with a thickness between 100 pm and 500 pm
    or located on the sheet (5) and covering said sheet (5) completely, or having an acoustic impedance of between 1.5 MRayl and 3.5 MRayl; a first conductive sheet (2e), with a thickness of between 20 nm and 100 nm, located on the sheet (4) and covering said sheet (4) completely; a piezoelectric sheet (1) comprising an internal face (i) and an external face (e)
    or thickness between 0.5 and 2 mm,
    or which is located on the conductive sheet (2e), where the external face (e) is in direct contact with the conductive sheet (2e), and
    or that it is partially covering said conductive sheet (2e); a second conductive sheet (2i), with a thickness of between 20 nm and 100 nm, located on the internal face (i) of the piezoelectric sheet (1) and covering said sheet (1) completely;
    a block (3), with anechoic conical finish,
    or thicknesses between 15 mm and 30 mm,
    or located on the conductive sheet (2i) and extending around the sheets (2i) and (1) until contacting the conductive sheet (2e), or that presents an acoustic impedance between 5 MRayl and 10 MRayl,
    or and which is composed of an epoxy resin comprising particles with a diameter between 1 pm and 50 pm selected from among tungsten, zirconia, alumina and any of their combinations;
    where (1), (2i), (2e), (3), (4), (5), (6) and (7) resist hydrostatic pressures up to 262 bar,
    where the piezoelectric foil is polarized along its thickness, and
    where the sheets (4), (5) and (6) form a set that presents resonance conditions of quarter wave at a central frequency greater than or equal to 1 MHz, between 1 MHz and 4 MHz.
    [2]
    Structure according to claim 1, wherein the resonant adaptive polymeric membrane (7) is selected from polypropylene, cellulose nitrate, cellulose ester, polyethersulfone and nylon.
    [3]
    Structure according to any one of claims 1 or 2, wherein the pressure sensitive adhesive sheet (6) is selected from an acrylic sheet or a polyurethane sheet.
    [4]
    4. Structure according to any of claims 1 to 3, wherein the syntactic foam sheet (5) is composed of an epoxy resin with hollow spheres with a diameter between 1 pm and 20 pm.
    [5]
    5. Structure according to any one of claims 1 to 4, wherein the polymeric sheet (4) is an epoxy resin.
    [6]
    6. Structure according to any of claims 1 to 5, wherein the conductive sheets (2e) and (2i) are independently composed of a conductive material selected from Au, Ag, Cu, Sn and any of their combinations.
    [7]
    7. Structure according to any one of claims 1 to 6, wherein the composition of the piezoelectric sheet (1) is selected from a ceramic type PZT of lead zirconate titanate PbZrO3-PbTiO3, a composite material of piezoelectric ceramic and resin with connectivity type 1-3 and with a volume concentration ceramic between 25% and 80%, and a piezoelectric monocrystal type Pb (Mg 1/3 Nb 2/3) O 3 -PbTiO 3.
    [8]
    8. Process for obtaining the structure according to any of claims 1 to 7, characterized in that it comprises the following steps:
    (a) join the piezoelectric sheet (1) covered by the conductive sheets (2i) and (2e) to a sacrificial sheet by means of adhesive tape (6) on a first side,
    (b) join a metal receptacle (8) to the sacrificial sheet with the help of adhesive tape (6),
    (c) filling the space formed between the piezoelectric sheet (1) and the metal receptacle with resin (3) and curing said resin (3),
    (d) remove sacrificial sheet,
    (e) metallize the first face of the piezoelectric sheet (1) so that the conductive sheet (2e) completely covers the piezoelectric and the edge of the cap, (f) deposit the polymeric sheet (4) on the conductive sheet (2e), cure and polish,
    (g) gluing the syntactic foam sheet (5) to the polymer sheet (4),
    (h) adhering the pressure sensitive adhesive sheet (6) onto the syntactic foam sheet (5),
    (i) gluing the resonant adaptive polymeric membrane (7) to the pressure sensitive adhesive sheet (6),
    (j) fix the set of sheets (1), (2e), (2i), (3), (4), (5), (6) and (7) and flip, and (k) fill the interior space of the metal receptacle with the help of a conical mold to form a block (3) with a conical shape.
    [9]
    The process according to claim 8, wherein step (e) is carried out by techniques selected from among sputtering, vacuum metallization, evaporation metallization, screen printing metallization, dip deposition and spin coating.
    [10]
    10. The method according to any of claims 8 or 9, wherein the deposition of step (f) is carried out by deposition techniques selected from among dip deposition, spin coating, and screen printing.
    [11]
    The process according to any one of claims 8 to 10, wherein step (g) is carried out using an adhesive having the same composition as the polymeric sheet (4).
    [12]
    12. Use of the structure according to any one of claims 1 to 7, as part of a piezoelectric ultrasonic transducer to detect echoes generated by a solid body in the presence of a pressurized gas at a pressure between 14 bar and 103 bar.
    [13]
    13. Piezoelectric ultrasonic transducer to detect echoes generated by a solid body in the presence of a pressurized gas at a pressure between 14 bar and 103 bar, characterized in that it comprises
    • the structure according to any of claims 1 to 7,
    or where the resonant adaptive polymeric membrane (7) is configured to act as a quarter wave resonant layer at the center frequency of the transducer,
    or where the set formed by (4), (5) and (6) is configured to act together as a single resonant layer of the center frequency of the transducer and gradually reduce the acoustic impedance of the structure,
    or where the first conductive sheet (2e) and the second conductive sheet (2i) are configured to act as an electrode and enable the application / measurement of the electric field in the piezoelectric sheet (1),
    or where the block (3) is configured to damp the vibration of the piezoelectric sheet (1),
    • a metal receptacle (8) comprising a coaxial connector (9) with ground connection and an internal connector (10) of the rear cover (12) of the metal receptacle (8) and that is configured to house the structure and provide shielding electromagnetic,
    or where (2e), (3), (4), (5), (6) and (7) are in contact with the walls of the receptacle (8);
    • a coaxial connector (9) that joins the internal connector (10) of the rear cover (12) of the metal receptacle (8) with the second conductive sheet (2i) that is configured to apply a voltage to the piezoelectric element through the connector or to measure the voltage generated in the piezoelectric element; and a protective crown (12) configured to protect the resonant adaptive polymeric membrane (7) and the lateral edge of the resonant adaptive polymeric membrane (7), the set formed by (4), (5) and (6), the block ( 3), the first conductive sheet (2e) and the second conductive sheet (2i).
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    同族专利:
    公开号 | 公开日
    ES2779956B2|2021-08-30|
    EP3929578A1|2021-12-29|
    WO2020169869A1|2020-08-27|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US20050075571A1|2003-09-18|2005-04-07|Siemens Medical Solutions Usa, Inc.|Sound absorption backings for ultrasound transducers|
    US5587534A|1994-10-28|1996-12-24|The United States Of America As Represented By The Secretary Of Commerce|Wall thickness and flow detection apparatus and method for gas pipelines|
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    PCT/ES2020/070122| WO2020169869A1|2019-02-20|2020-02-20|Laminar structure as part of a piezoelectric ultrasonic transducer|
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