High-temperature-resistant air coupling type ultrasonic transducer without adhesion layer

Abstract

The invention discloses a high-temperature-resistant air coupling type ultrasonic transducer without an adhesion layer. The high-temperature-resistant air coupling type ultrasonic transducer comprises a sealing shell, a sealing cover plate, a prestressed bolt, an insulating spacer, piezoelectric ceramics, a matching layer and an insulating wrapping layer, the matching layer is arranged at the front end in the sealing shell, the piezoelectric ceramic is arranged behind the matching layer, and the front end face of the piezoelectric ceramic is attached to the back face of the matching layer; the insulating wrapping layer wraps the outer periphery of the piezoelectric ceramic, and an insulating spacer is arranged behind the piezoelectric ceramic; the prestressed bolt is arranged behind the insulating spacer; the outer periphery of the prestressed bolt is provided with an external thread, the inner wall of the sealing shell is provided with a matched internal thread, and the external thread of the prestressed bolt is matched with the internal thread of the sealing shell and compresses the insulating spacer, the piezoelectric ceramic and the matching layer, so that the piezoelectric ceramic and the matching layer are tightly attached. The ACUT has high-temperature adaptability, the transmitting sound pressure sensitivity and the receiving voltage sensitivity of the ACUT are improved, and the effective propagation distance is prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ultrasonic transducers, in particular to a high-temperature-resistant air-coupled ultrasonic transducer without adhesion layer. BACKGROUND

[0002] With the start of the carbon emission trading market, the authenticity and traceability of enterprise carbon emission data have become the core basis for regulation and transaction. Direct measurement method on the emission side is considered as the key technical route for calculating fuel consumption and greenhouse gas emissions due to its high accuracy and easy regulation. Among them, the flue gas ultrasonic flowmeter realizes online measurement by measuring the flue gas flow rate combined with the concentration of greenhouse gases, which is an important means for high-temperature flue gas emission monitoring. Air-coupled ultrasonic transducer (ACUT) is the core component of such ultrasonic flowmeter.

[0003] Due to the large difference in acoustic impedance between piezoelectric ceramics and air, most ultrasonic waves are reflected at the interface, which seriously limits the transmission and reception efficiency of ACUT. In order to improve the transmission efficiency of acoustic energy, an acoustic matching layer is usually arranged between the piezoelectric ceramic and the air. The existing typical technical solutions mainly include:

[0004] 1. Single-layer matching layer scheme based on epoxy resin-based composite material

[0005] The existing ACUT generally uses epoxy resin as the matrix, and mixes hollow glass beads or microporous materials to prepare the acoustic matching layer. The volume fraction of the filler is adjusted to reduce the acoustic impedance of the matching layer and control the attenuation coefficient. This kind of matching layer is widely used in room temperature or low-temperature air-coupled ultrasonic probes.

[0006] 2. Matching layer scheme based on low-impedance materials such as hydrogel, foam material, etc.

[0007] Some studies use a composite matching layer of hydrogel + hollow glass beads to obtain an acoustic impedance close to 1.0 MRayl and a lower attenuation coefficient; some schemes use polystyrene foam and other porous materials as matching layers to further reduce the acoustic impedance and improve the air coupling ability. However, the softening point or thermal stability of such materials is relatively low, and most of them are difficult to withstand high-temperature flue gas environments of more than 80-120℃ for a long time.

[0008] 3. Multi-layer or gradient matching structure scheme

[0009] In order to make the overall acoustic impedance closer to the theoretical optimal value, some schemes use double-layer or multi-layer gradient matching structure to gradually transition the acoustic impedance through multiple layers in series, thereby improving the bandwidth and sensitivity. However, the gradient structure inevitably increases the process complexity, the number of internal reflection interfaces in the matching layer, and the additional loss, and the multi-layer structure is more prone to interface peeling and failure in high-temperature environments.

[0010] 4. Piezoelectric materials and assembly structure scheme for high-temperature ACUTs

[0011] In high-temperature applications, some solutions use single crystals or ceramics with high Curie temperatures (such as AlN, YCOB, LiNbO3, etc.) to fabricate high-temperature transducers. However, due to their low piezoelectric constants, sensitivity is often sacrificed. PZT series piezoelectric ceramics commonly used in industry have good piezoelectric properties and Curie temperatures, but traditional ACUTs typically use adhesives to bond the matching layer to the piezoelectric ceramic. At high temperatures, the adhesive layer is prone to softening, failure, or detachment, making long-term stable operation difficult.

[0012] In summary, existing ACUT technology for measuring high-temperature flue gas flow still has significant shortcomings in terms of acoustic matching layer materials, high-temperature reliability, assembly structure, and electrical matching, making it difficult to simultaneously achieve high-temperature stability and high sensitivity. Summary of the Invention

[0013] To address the shortcomings of existing technologies, this invention aims to provide a high-temperature resistant air-coupled ultrasonic transducer without adhesive layers.

[0014] To achieve the above objectives, the present invention adopts the following technical solution:

[0015] A high-temperature air-coupled ultrasonic transducer without adhesive layers includes a sealed housing, a sealed cover plate, prestressed bolts, an insulating gasket, a piezoelectric ceramic, a matching layer, and an insulating wrapping layer;

[0016] The matching layer is located at the front end of the sealing housing, and the piezoelectric ceramic is located behind the matching layer with its front end face adhering to the back side of the matching layer. An insulating wrapping layer is wrapped around the outer periphery of the piezoelectric ceramic, and an insulating gasket is located behind the piezoelectric ceramic. A prestressed bolt is located behind the insulating gasket. The outer periphery of the prestressed bolt is provided with an external thread, and the inner wall of the sealing housing is provided with a matching internal thread. The external thread of the prestressed bolt and the internal thread of the sealing housing engage and compress the insulating gasket, the piezoelectric ceramic, and the matching layer, so that the piezoelectric ceramic and the matching layer are tightly adhered. The sealing cover plate is fixedly installed on the back side of the sealing housing.

[0017] Furthermore, the insulating gasket, prestressed bolt, and sealing cover are all provided with wire outlet holes for the piezoelectric ceramic wires to extend out.

[0018] Furthermore, the piezoelectric ceramic uses longitudinally polarized PZT-5G discs.

[0019] Furthermore, the matching layer is a single-layer structure made of organosilicon-based composite material; the organosilicon-based composite material uses organosilicon material as the matrix and hollow glass microspheres as filler.

[0020] Furthermore, the hollow glass microspheres account for 15% of the mass of the organosilicon-based composite material.

[0021] Furthermore, the thickness of the sealing cover is 0.5 mm.

[0022] Furthermore, the sealing shell and sealing cover are made of 316L stainless steel or titanium alloy.

[0023] Furthermore, a wrench slot is provided on the rear side of the prestressed bolt.

[0024] Furthermore, an LC-type matching network is connected in series between the excitation source and the piezoelectric ceramic.

[0025] The beneficial effects of this invention are as follows:

[0026] 1. This invention eliminates the adhesive layer between the piezoelectric ceramic and the matching layer, and uses prestressed bolts to press the piezoelectric ceramic and the matching layer together, thereby enabling the air-coupled ultrasonic transducer to work stably for a long time in a high-temperature (at least 200°C) flue gas environment.

[0027] 2. By using 316L stainless steel or titanium alloy as the shell material, this invention improves the transmission sound pressure and receiving voltage sensitivity of the air-coupled ultrasonic transducer while ensuring high-temperature adaptability, and extends the effective propagation distance.

[0028] 3. The present invention uses organosilicon material as the matrix material of the matching layer and hollow glass microspheres as filler. The resulting matching layer takes into account both low acoustic impedance and acceptable attenuation under air coupling conditions. Furthermore, the softening temperature of the organosilicon matrix is ​​about 220°C, which can meet the requirements of high-temperature flue gas conditions.

[0029] 4. In this invention, an LC-type matching network is connected in series between the excitation source and the piezoelectric ceramic of the air-coupled ultrasonic transducer. Using a Smith chart design, a good voltage standing wave ratio (VSWR) of approximately 1.02 can be achieved near the series resonant frequency of the air-coupled ultrasonic transducer. Experimental results show that after adding the electrical impedance matching circuit, the received signal amplitude of the air-coupled ultrasonic transducer is increased by approximately 22% compared to the original value, significantly improving the signal-to-noise ratio and measurement margin. Attached Figure Description

[0030] Fig. 1 This is an exploded view of the transducer in Embodiment 1 of the present invention;

[0031] Fig. 2 This is a cross-sectional view of the transducer in Embodiment 1 of the present invention. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings. It should be noted that this embodiment is based on the present technical solution and provides detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to this embodiment.

[0033] Example 1

[0034] This embodiment provides a high-temperature resistant air-coupled ultrasonic transducer without an adhesion layer, such as... Figs. 1-2 As shown, it includes a sealed housing 1, a sealed cover plate 6, a prestressed bolt 2, an insulating gasket 3, a piezoelectric ceramic 4, a matching layer 5, and an insulating wrapping layer 8.

[0035] The matching layer 5 is located at the front end of the sealing housing 1, and the piezoelectric ceramic 4 is located behind the matching layer 5 with its front end face adhering to the back side of the matching layer 5. The insulating wrapping layer 8 is wrapped around the outer periphery of the piezoelectric ceramic 4, and an insulating gasket 3 is located behind the piezoelectric ceramic 4. The prestressed bolt 2 is located behind the insulating gasket 3. The outer periphery of the prestressed bolt 2 is provided with external threads, and the inner wall of the sealing housing 1 is provided with matching internal threads. The external threads of the prestressed bolt 2 and the internal threads of the sealing housing 1 cooperate to press the insulating gasket 3, the piezoelectric ceramic 4, and the matching layer 5 together, so that the piezoelectric ceramic 4 and the matching layer 5 are tightly fitted together. The sealing cover plate 6 is placed on the back side of the sealing housing 1 and fixed by screws 7. The insulating gasket 3, the prestressed bolt 2, and the sealing cover plate 6 are all provided with wire outlet holes for the wires of the piezoelectric ceramic 4 to extend out.

[0036] In the aforementioned air-coupled ultrasonic transducer, the back of the piezoelectric ceramic 4 contacts the prestressed bolt 2 via an insulating gasket 3 to prevent a short circuit between the prestressed bolt 2 and the electrode of the piezoelectric ceramic 4. The prestressed bolt 2 presses forward to tighten the matching layer 5 and the piezoelectric ceramic 4, enabling stable mechanical and acoustic coupling without an adhesive layer. This eliminates the need for an adhesive layer, allowing the air-coupled ultrasonic transducer to withstand high-temperature conditions. The sealing shell 1 and the sealing cover plate 6 together form a sealed outer shell, protecting the internal structure of the air-coupled ultrasonic transducer and preventing high-temperature airflow from directly eroding the matching layer.

[0037] The preload of the prestressed bolt 2 can be adjusted by changing the screw depth of the prestressed bolt 2 within the sealed housing 1, thereby enabling the mechanical quality factor and resonant frequency of the aforementioned air-coupled ultrasonic transducer to meet design targets. Experiments show that, compared to the bare PZT-5G, the mechanical quality factor of the aforementioned air-coupled ultrasonic transducer is significantly reduced, and the resonant peak is sharper, which is beneficial for reducing signal tailing and improving temporal resolution.

[0038] In this embodiment, a wrench slot 9 is provided on the rear side of the prestressed bolt 2. During the operation of screwing the prestressed bolt 2 into the sealing housing 1, the wrench is first inserted into the wrench slot, and the prestressed bolt 2 is rotated using the wrench.

[0039] In this embodiment, the piezoelectric ceramic 4 is a longitudinally polarized PZT-5G disc with a Curie temperature of about 380°C, exhibiting good vibration modes and piezoelectric properties at around 100 kHz.

[0040] In this embodiment, the matching layer 5 is a single-layer structure made of an organosilicon-based composite material. Specifically, the organosilicon-based composite material uses organosilicon material (e.g., a two-component organosilicon of model CC1005, with components A and B mixed in a mass ratio of 10:1) as the matrix, and hollow glass microspheres (K1 type, true density approximately 0.12 g / cm³) as the matrix. 3 The filler material has a particle size distribution of 10–110 μm.

[0041] During preparation, hollow glass microspheres are added to the organosilicon material matrix according to a preset mass fraction. First, the mixture is stirred at 800 rpm for approximately 40 seconds to prevent the microspheres from flying out. Then, it is stirred at 2000 rpm to fully disperse the microspheres. Finally, degassing is performed at 800 rpm to obtain the organosilicon-based composite material. Taking the two-component organosilicon CC1005 as an example, after mixing component A and component B at a mass ratio of 10:1, the mixture is stirred in a planetary gravity mixer at approximately 1200 rpm to obtain a uniform organosilicon material matrix.

[0042] Subsequently, a detachable mold (thickness close to a quarter wavelength at the working frequency) prepared by 3D printing was prepared, and a release agent was coated on the inner surface of the detachable mold. The silicone-based composite material was then injected into the mold and cured at room temperature for 24 hours.

[0043] Finally, the mold is removed, and the thickness is measured with a micrometer. The thickness is then adjusted to the target thickness through polishing so that the matching layer meets the acoustic design requirements.

[0044] The density, sound velocity, acoustic impedance and attenuation coefficient of samples filled with hollow glass microspheres of different mass fractions were tested. It was found that the hollow glass microspheres accounted for 15% of the mass percentage of the organosilicon-based composite material, which was the best. The typical performance of the matching layer obtained was: (1) density of about 495 kg / m³. 3 (2) Sound velocity approximately 2150 m / s; (3) Acoustic impedance approximately 1.06 MRayl; (4) Acoustic attenuation coefficient approximately 0.47 dB / mm. The resulting matching layer balances low acoustic impedance and acceptable attenuation under air coupling conditions, and the softening temperature of the silicone matrix is ​​approximately 220 °C, which can meet the requirements of high-temperature flue gas conditions.

[0045] In this embodiment, the thickness of the sealing cover plate 6 is 0.5 mm.

[0046] In this embodiment, the sealing housing 1 and the sealing cover 6 can be made of 316L stainless steel or titanium alloy. Using titanium alloy results in a lighter overall transducer mass, lower sound attenuation, and higher transmitted sound pressure and received sensitivity. Using 316L stainless steel results in a heavier transducer mass, a slightly lower resonant frequency, and a longer maximum propagation distance. In this embodiment, the sealing housing 1 and the sealing cover 6 are made of titanium alloy.

[0047] Experiments show that the air-coupled ultrasonic transducer made of titanium alloy for the sealed housing 1 and the sealed cover 6 has a higher emission sound pressure sensitivity by about 0.63 dB and a higher receiving voltage sensitivity by about 1.88 dB than the air-coupled ultrasonic transducer made of 316L stainless steel, and the maximum propagation distance is increased by about 24%.

[0048] Since piezoelectric ceramics are equivalent to capacitive loads, in this embodiment, an LC-type matching network is connected in series between the excitation source and the piezoelectric ceramic of the air-coupled ultrasonic transducer. Using a Smith chart design, a good voltage standing wave ratio (VSWR) of approximately 1.02 is achieved near the series resonant frequency of the air-coupled ultrasonic transducer. Experimental results show that after adding the electrical impedance matching circuit, the received signal amplitude of the air-coupled ultrasonic transducer increases by approximately 22% compared to the original value, significantly improving the signal-to-noise ratio and measurement margin.

[0049] Example 2

[0050] This embodiment aims to further test the high-temperature performance of the air-coupled ultrasonic transducer described in Embodiment 1.

[0051] In a high-temperature furnace, two air-coupled ultrasonic transducers described in Example 1 are placed opposite each other as the transmitter and receiver, with a distance of about 50 cm between them;

[0052] The amplitude variation of the received signal of the above-mentioned air-coupled ultrasonic transducer was collected at various temperature points of 50℃, 100℃, 150℃ and 200℃ respectively.

[0053] The results show that as the temperature increases, the received signal amplitude of the air-coupled ultrasonic transducer decreases linearly. However, under the condition of 200℃ for 24 hours, the air-coupled ultrasonic transducer can still work stably without any obvious failure.

[0054] Example 3

[0055] This embodiment aims to provide an application and testing of the air-coupled ultrasonic transducer described in Embodiment 1 in a flue gas ultrasonic flow meter and a high-temperature wind tunnel.

[0056] The air-coupled ultrasonic transducer described in Example 1 was applied to a flue gas ultrasonic flow meter, and then the flue gas ultrasonic flow meter was placed in a high-temperature wind tunnel for wind speed measurement. The high-temperature wind tunnel provided a fixed flow velocity of approximately 5 m / s, and the test temperatures were 50°C, 100°C, 150°C, and 200°C.

[0057] The flow velocity was calculated using the upstream and downstream time difference method. The results showed that within the above temperature range, the flow velocity measurement error of the flue gas ultrasonic flow meter was approximately 1.67–2.16%, and no significant deterioration was observed with increasing temperature.

[0058] For those skilled in the art, various corresponding changes and modifications can be made based on the above technical solutions and concepts, and all such changes and modifications should be included within the protection scope of the claims of this invention.

Claims

1. A high-temperature resistant air-coupled ultrasonic transducer with no adhesion layer, characterized in that, It includes a sealed housing, a sealed cover plate, prestressed bolts, insulating gaskets, piezoelectric ceramics, a matching layer, and an insulating wrapping layer; The matching layer is located at the front end of the sealing housing, and the piezoelectric ceramic is located behind the matching layer with its front end face adhering to the back side of the matching layer. An insulating wrapping layer is wrapped around the outer periphery of the piezoelectric ceramic, and an insulating gasket is located behind the piezoelectric ceramic. A prestressed bolt is located behind the insulating gasket. The outer periphery of the prestressed bolt is provided with an external thread, and the inner wall of the sealing housing is provided with a matching internal thread. The external thread of the prestressed bolt and the internal thread of the sealing housing engage and compress the insulating gasket, the piezoelectric ceramic, and the matching layer, so that the piezoelectric ceramic and the matching layer are tightly adhered. The sealing cover plate is fixedly installed on the back side of the sealing housing.

2. The high-temperature resistant air-coupled ultrasonic transducer according to claim 1, characterized in that, The insulating gasket, prestressed bolts, and sealing cover are all provided with outlet holes for the piezoelectric ceramic wires to extend out.

3. The high-temperature resistant air-coupled ultrasonic transducer according to claim 1, characterized in that, The piezoelectric ceramic uses longitudinally polarized PZT-5G discs.

4. The high-temperature resistant air-coupled ultrasonic transducer according to claim 1, characterized in that, The matching layer is a single-layer structure made of organosilicon-based composite material; the organosilicon-based composite material uses organosilicon material as the matrix and hollow glass microspheres as filler.

5. The high-temperature resistant air-coupled ultrasonic transducer according to claim 4, characterized in that, The hollow glass microspheres account for 15% of the mass of the organosilicon-based composite material.

6. The high-temperature resistant air-coupled ultrasonic transducer according to claim 1, characterized in that, The thickness of the sealing cover is 0.5 mm.

7. The high-temperature resistant air-coupled ultrasonic transducer according to claim 1, characterized in that, The sealing shell and sealing cover are made of 316L stainless steel or titanium alloy.

8. The high-temperature resistant air-coupled ultrasonic transducer according to claim 1, characterized in that, The rear side of the prestressed bolt has a pre-drilled wrench slot.

9. The high-temperature resistant air-coupled ultrasonic transducer according to claim 1, characterized in that, An LC-type matching network is connected in series between the excitation source and the piezoelectric ceramic.

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