An ultrasonic transducer backing wave-absorbing structure based on standing wave resonators, a manufacturing method thereof and an ultrasonic transducer

Abstract

This invention provides an ultrasonic transducer backing absorption structure based on a standing wave resonator, comprising a layered backing substrate and at least one resonant unit. The backing substrate includes a first backing layer and a second backing layer. The resonant unit is disposed between the first and second backing layers and is used to locally reflect and interfere with ultrasonic waves entering the backing substrate to form a standing wave and enhance the dissipation absorption of the target frequency band ultrasonic waves in the backing. The resonant unit has an axial dimension set along the main direction of ultrasonic propagation, which is set according to the target operating frequency of the ultrasonic transducer so that the standing wave resonant frequency of the resonant unit matches the target operating frequency of the ultrasonic transducer. This invention has the advantages of adjustable frequency, simple structure, ease of manufacture, and strong engineering applicability, and is suitable for non-destructive testing, structural health monitoring, and other ultrasonic applications.

Description

Technical Field

[0001] This invention belongs to the field of ultrasonic transducer technology, specifically relating to an ultrasonic transducer backing absorbing structure based on a standing wave resonator, its fabrication method, and an ultrasonic transducer. Background Technology

[0002] Ultrasonic transducers are widely used in nondestructive testing, structural health monitoring, medical diagnostics, and related acoustic testing fields. As a commonly used excitation and receiving device, the output signal quality of piezoelectric ultrasonic transducers is influenced not only by the piezoelectric material itself but also by the backing material and the internal structure of the transducer. There are usually acoustic impedance differences between the various components within the transducer. The mechanical waves generated after the piezoelectric element is excited propagate not only towards the object under test but also towards the backing. Some waves that pass through the backing are reflected at the shell or propagate along the internal structure, thus forming multidirectional clutter and trailing waves, affecting the detection accuracy.

[0003] In existing technologies, backing materials are typically required to possess high attenuation characteristics to absorb waves propagating from the piezoelectric element towards the back side. However, most existing solutions focus on impedance matching or the material's inherent damping properties, neglecting to consider how to prolong the wave dissipation process within the backing and improve absorption efficiency at specific frequencies. Standing waves are formed by the reflection and interference of waves within a local structure, enhancing the local acoustic field and energy dissipation. Therefore, it is necessary to propose a novel ultrasonic transducer backing absorption structure that not only relies on the damping absorption capacity of the backing material itself but also constructs a standing wave absorption mechanism within the backing through a resonant structure. This allows for selective absorption of back-propagating waves near the target operating frequency, reducing clutter propagation into subsequent structures and improving the transducer's output signal quality. Summary of the Invention

[0004] The purpose of this invention is to provide an ultrasonic transducer backing absorption structure based on a standing wave resonator, its fabrication method, and an ultrasonic transducer, in order to solve the problems of existing backing materials mainly relying on bulk damping absorption, insufficient absorption efficiency for back propagation waves in the target frequency band, long trailing waves, and low output waveform fidelity.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] An ultrasonic transducer backing absorbing structure based on a standing wave resonator includes:

[0007] The backing substrate has a layered molding structure, including a first backing layer and a second backing layer;

[0008] A resonant unit, at least one in number, is disposed between the first backing layer and the second backing layer to locally reflect and interfere with the ultrasonic waves entering the backing matrix, so as to form a standing wave and enhance the dissipation and absorption of the target frequency band ultrasonic waves in the backing.

[0009] The resonant unit has an axial dimension set along the main direction of ultrasonic propagation. The axial dimension is set according to the target operating frequency of the ultrasonic transducer so that the standing wave resonant frequency of the resonant unit matches the target operating frequency of the ultrasonic transducer.

[0010] Furthermore, the backing substrate is made of one or any combination of epoxy resin, polymer-based damping material, and composite damping material.

[0011] Furthermore, the resonant unit is provided in a plurality of such units, arranged in an array, periodic or spaced manner in the backing substrate along one or more directions.

[0012] Furthermore, the resonant unit is one or any combination of several of the following: columnar resonant unit, prismatic resonant unit, local cavity resonant unit, and solid local resonant body.

[0013] Furthermore, the resonant unit is made of metal, alloy, ceramic or high-modulus polymer material.

[0014] The present invention also provides a method for manufacturing an ultrasonic transducer backing absorbing structure based on a standing wave resonator, for manufacturing the aforementioned ultrasonic transducer backing absorbing structure based on a standing wave resonator, the method comprising:

[0015] S1. Determine the target operating frequency of the ultrasonic transducer.

[0016] S2. Establish the correspondence between the axial dimension of the resonant unit and the resonant frequency of the standing wave based on the wave propagation characteristics in the backing region.

[0017] S3. Determine the target axial dimension of the resonant unit based on the corresponding relationship;

[0018] S4. Arrange the resonant unit inside the backing substrate to form a backing absorbing structure that selectively absorbs ultrasonic waves in the target frequency band.

[0019] Furthermore, the specific method for step S2 is as follows:

[0020] The axial standing wave model of the resonant unit is expressed as:

[0021] ;

[0022] Assuming the displacement function can be expressed as the product of a spatial function and a time function, its general solution is expressed as: ;

[0023] The top and bottom of the resonant unit satisfy the following free boundary conditions: , ;

[0024] Substituting the above free boundary conditions into the general solution, we get: , , and , ,

[0025] The relationship between the axial dimension of the resonant unit and the resonant frequency of the standing wave is further obtained as follows: ;

[0026] ;

[0027] Where h represents the axial height of the resonant unit, f represents the standing wave resonant frequency, c represents the wave propagation speed in the resonant unit, and n represents the mode order.

[0028] Further, step S4 specifically includes:

[0029] S41. Prepare the backing molding mold and prepare the backing substrate material and resonant unit according to the design requirements;

[0030] S42. Pour the backing substrate material into the backing molding mold to form the first backing layer;

[0031] S43. After the first backing layer reaches the load-bearing state, the prefabricated resonant unit is placed on it, so that the resonant unit is in the preset position and remains suspended.

[0032] S44. Continue to add the remaining backing matrix material to the backing molding die to form a second backing layer, so that the resonant unit is covered and located between the first backing layer and the second backing layer. After further curing, a complete standing wave component layer is formed.

[0033] Finally, the present invention provides an ultrasonic transducer comprising the aforementioned ultrasonic transducer backing absorbing structure based on a standing wave resonator and a piezoelectric element; the ultrasonic transducer backing absorbing structure is disposed on the back side of the piezoelectric element.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. This invention does not rely solely on the damping of the backing material itself for absorption, but rather constructs a standing wave absorption mechanism by setting a resonant unit inside the backing, thereby improving the dissipation capability of ultrasonic waves in the target frequency band.

[0036] 2. This invention can selectively control the absorption frequency by adjusting the axial dimension of the resonant unit, thereby achieving matching with the target operating frequency of the piezoelectric element, and has a high degree of freedom in frequency design.

[0037] 3. This invention can reduce the transmission of back-propagating waves to subsequent structures, reduce the tail length of the output signal, and improve the fidelity of the transducer output waveform.

[0038] 4. The present invention has a simple structure, is compatible with the existing transducer backing manufacturing process, is easy to implement in engineering, and can be extended to multiple resonant units or multi-layer structures. Attached Figure Description

[0039] Figure 1 A schematic diagram of the internal structure of an existing ultrasonic transducer and the mechanism of tail wave formation.

[0040] Figure 2 This is a schematic diagram of the standing wave dissipation principle based on resonant units in this invention, wherein... Figure 2 A is a conceptual diagram of the standing wave dissipation formed by the resonant unit. Figure 2 B is a simulation diagram of the sound field near the resonant unit;

[0041] Figure 3 This is a schematic diagram illustrating the standing wave characteristics of the resonant unit in this invention, wherein... Figure 3 A is a schematic diagram of the transmission coefficient testing device. Figure 3 B is a schematic diagram of the reflection coefficient testing device;

[0042] Figure 4 This is a schematic diagram showing the operating frequency and absorption performance of the resonant unit of the present invention, wherein... Figure 4 A shows the variation of sound pressure level inside the resonant unit at different frequencies. Figure 4 B is a comparison diagram of sound pressure levels in the case of a single resonant unit and multiple resonant units. Figure 4 C is a graph showing the variation of reflection coefficient and transmission coefficient with frequency;

[0043] Figure 5 This is a schematic diagram of the structure of the present invention. Detailed Implementation

[0044] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The specific implementation methods of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] Example 1:

[0046] like Figure 1 As shown, during the operation of an ultrasonic transducer, the wave generated by the piezoelectric element propagates not only towards the object under test but also towards the backing, thus creating an unwanted propagation component inside the transducer. Figure 2As shown, in order to enhance the absorption capacity of the backing region for back-propagating waves, a resonant unit is set inside the backing substrate, so that the wave is reflected and interfered near the resonant unit, thereby forming a local standing wave field.

[0047] The formation of standing waves can enhance local energy accumulation and improve wave dissipation efficiency within the backing region. Compared to structures that rely solely on the bulk damping of the backing material, such as... Figure 5 As shown, this embodiment establishes an additional local standing wave absorption mechanism by introducing a resonant unit inside the backing substrate, thereby exhibiting a stronger absorption capability for fluctuations near the target frequency.

[0048] This embodiment provides an ultrasonic transducer backing absorbing structure based on a standing wave resonator, including:

[0049] The backing substrate has a layered molding structure, including a first backing layer and a second backing layer; the backing substrate is made of one or any combination of epoxy resin, polymer-based damping material and composite damping material.

[0050] A resonant unit, at least one in number, is disposed between the first backing layer and the second backing layer. It is used to locally reflect and interfere with the ultrasonic waves entering the backing matrix to form a standing wave and enhance the dissipation and absorption of the target frequency ultrasonic waves in the backing. When there are multiple resonant units, they are arranged in the backing matrix in an array, periodic or spaced manner along one or more directions. The resonant unit has an axial dimension set along the main direction of ultrasonic propagation. The axial dimension is set according to the target operating frequency of the ultrasonic transducer so that the standing wave resonant frequency of the resonant unit matches the target operating frequency of the ultrasonic transducer.

[0051] When multiple resonant elements have the same axial dimension, selective absorption in a specific target frequency band can be enhanced; when multiple resonant elements have different axial dimensions, they can correspond to different target frequency bands, thereby achieving multi-band absorption. Multiple resonant elements of the same size can be periodically arranged in the backing substrate to further enhance wave dissipation.

[0052] The resonant unit in this embodiment is one or a combination of several of the following: a columnar resonant unit, a prismatic resonant unit, a localized cavity resonant unit, and a solid localized resonator. The resonant unit is made of metal, alloy, ceramic, or high-modulus polymer material. In this embodiment, the resonant unit is made of 17-4PH stainless steel.

[0053] Example 2:

[0054] This embodiment provides a method for manufacturing the ultrasonic transducer backing absorbing structure based on a standing wave resonator in Embodiment 1, comprising:

[0055] S1. Determine the target operating frequency of the ultrasonic transducer.

[0056] S2. Establish the correspondence between the axial dimension of the resonant unit and the resonant frequency of the standing wave based on the wave propagation characteristics in the backing region.

[0057] The axial standing wave model of the resonant unit is expressed as:

[0058] ;

[0059] Assuming the displacement function can be expressed as the product of a spatial function and a time function, its general solution is expressed as: ;

[0060] The top and bottom of the resonant unit satisfy the following free boundary conditions: , ;

[0061] Substituting the above free boundary conditions into the general solution, we get: , , and , ,

[0062] The relationship between the axial dimension of the resonant unit and the resonant frequency of the standing wave is further obtained as follows: ;

[0063] ;

[0064] Where h represents the axial height of the resonant unit, f represents the standing wave resonant frequency, c represents the wave propagation speed in the resonant unit, and n represents the mode order.

[0065] S3. Determine the target axial dimension of the resonant unit based on the corresponding relationship;

[0066] S4. Arrange the resonant unit inside the backing substrate to form a backing absorbing structure that selectively absorbs ultrasonic waves in the target frequency band.

[0067] S41. Prepare the backing molding mold and prepare the backing substrate material and resonant unit according to the design requirements. In this embodiment, the resonant unit is pre-formed by CNC cutting with a cutting accuracy of about ±0.2 mm and a cutting speed of about 10 mm / min. No polishing is performed, thus forming a surface roughness of about 1 μm.

[0068] S42. The backing matrix material is poured into the backing molding mold to form the first backing layer; in this embodiment, epoxy resin is first poured into the backing molding mold to fill about half of the volume.

[0069] S43. After the first backing layer reaches a load-bearing state, the prefabricated resonant unit is placed on it, so that the resonant unit is in a preset position and kept suspended; in this embodiment, the resonant unit is placed in after the epoxy resin has cured for about 30 minutes.

[0070] S44. Continue adding the remaining backing substrate material to the backing molding die to form a second backing layer, so that the resonant unit is covered and located between the first and second backing layers. After further curing, a complete standing wave assembly layer is formed. This process is also applicable to the fabrication of multilayer standing wave assemblies.

[0071] like Figure 3 As shown, to verify the absorption performance of the backing absorber structures obtained in Examples 1 and 2, the transmission coefficient and reflection coefficient of the resonant unit can be measured respectively. During the transmission coefficient test, the resonant unit is placed in the test area, and the transmitted signal is measured using a test transmitting transducer and a test receiving transducer.

[0072] During reflection coefficient testing, an appropriate angle is set between the resonant unit and the transducer, and a reflective isolation plate is used to separate the direct wave propagation path to ensure that the received signal mainly consists of reflected waves. In the above embodiment, the angle is approximately 35°. To reduce the influence of boundary reflections, the relevant spacing parameters can be significantly larger than twice the characteristic size.

[0073] During testing, when the reflected signal changes relatively little at a certain frequency while the transmitted signal changes significantly more, that frequency can be identified as the standing wave frequency. Furthermore, the absorption performance can be quantitatively characterized using the transmission coefficient and reflection coefficient.

[0074] like Figure 4 As shown, based on Embodiments 1 and 2, the designed resonant units are arranged in the backing material to absorb unwanted back-propagating waves and reduce their propagation to subsequent structures. Simulation results show that standing waves increase the sound pressure level inside the resonant units and form a peak near the target frequency; when multiple resonant units of the same size are arranged periodically, wave dissipation can be further enhanced.

[0075] Experimental results show that the reflection coefficient of the resonant unit changes little around 200 kHz, while the transmission coefficient decreases significantly, indicating that the absorption enhancement near this frequency mainly comes from local standing wave dissipation rather than simple reflection; the obtained resonant unit can absorb about 40.4% of the background noise.

[0076] The viscoelastic properties of the backing material can also be characterized through dynamic mechanical analysis to obtain the loss factor, and the absorption bandwidth and absorption intensity can be estimated in combination with the target standing wave frequency. Based on Examples 1 and 2, measurements were performed at 20°C, and the corresponding loss factor was obtained at the resonant frequency of approximately 200 kHz. The half-power bandwidth estimated based on this loss factor showed good agreement with the attenuation valley of approximately 30 kHz in the experiment. Transmission could be significantly suppressed at this frequency, with energy absorption of approximately 40.4%.

[0077] Example 3:

[0078] This embodiment provides an ultrasonic transducer based on Embodiments 1 and 2. The ultrasonic transducer includes the ultrasonic transducer backing absorption structure based on a standing wave resonator mentioned in the above embodiments and a piezoelectric element; the ultrasonic transducer backing absorption structure is disposed on the back side of the piezoelectric element.

[0079] The standing wave resonant frequency of the ultrasonic transducer backing absorber structure is designed to be consistent with or close to the center operating frequency of the piezoelectric element in order to improve the consistency between the transducer output signal and the theoretical excitation waveform. In this embodiment, the resonant frequency is approximately 199±1 kHz.

[0080] The above embodiments are for illustrative purposes only and are not intended to limit the scope of this invention. Although this invention has been described in detail with reference to the embodiments, those skilled in the art should understand that various combinations, modifications, or equivalent substitutions of the technical solutions of this invention do not depart from the spirit and scope of the technical solutions of this invention and should be covered within the scope of the claims of this invention.

Claims

1. An ultrasonic transducer backing absorbing structure based on a standing wave resonator, characterized in that, include: The backing substrate has a layered molding structure, including a first backing layer and a second backing layer; A resonant unit, at least one in number, is disposed between the first backing layer and the second backing layer to locally reflect and interfere with the ultrasonic waves entering the backing matrix, so as to form a standing wave and enhance the dissipation and absorption of the target frequency band ultrasonic waves in the backing. The resonant unit has an axial dimension set along the main direction of ultrasonic propagation. The axial dimension is set according to the target operating frequency of the ultrasonic transducer so that the standing wave resonant frequency of the resonant unit matches the target operating frequency of the ultrasonic transducer.

2. The ultrasonic transducer backing absorbing structure based on a standing wave resonator according to claim 1. Its characteristic is that... The backing substrate is made of one or any combination of epoxy resin, polymer-based damping material and composite damping material.

3. The ultrasonic transducer backing absorbing structure based on a standing wave resonator according to claim 1. Its characteristic is that... The resonant unit comprises several units, arranged in an array, periodic or spaced manner in the backing substrate along one or more directions.

4. The ultrasonic transducer backing absorbing structure based on a standing wave resonator according to claim 1. Its characteristic is that... The resonant unit is one or any combination of several of the following: columnar resonant unit, prismatic resonant unit, local cavity resonant unit, and solid local resonant body.

5. The ultrasonic transducer backing absorbing structure based on a standing wave resonator according to claim 1. Its characteristic is that... The resonant unit is made of metal, alloy, ceramic or high-modulus polymer material.

6. A method for manufacturing an ultrasonic transducer backing absorbing structure based on a standing wave resonator, used to manufacture the ultrasonic transducer backing absorbing structure based on a standing wave resonator as described in any one of claims 1 to 5, characterized in that, The methods include: S1. Determine the target operating frequency of the ultrasonic transducer. S2. Establish the correspondence between the axial dimension of the resonant unit and the resonant frequency of the standing wave based on the wave propagation characteristics in the backing region. S3. Determine the target axial dimension of the resonant unit based on the corresponding relationship; S4. Arrange the resonant unit inside the backing substrate to form a backing absorbing structure that selectively absorbs ultrasonic waves in the target frequency band.

7. The manufacturing method of an ultrasonic transducer backing absorbing structure based on a standing wave resonator according to claim 6, characterized in that, The specific method for step S2 is as follows: The axial standing wave model of the resonant unit is expressed as: ； Assuming the displacement function can be expressed as the product of a spatial function and a time function, its general solution is expressed as: ; The top and bottom of the resonant unit satisfy the following free boundary conditions: , ; Substituting the above free boundary conditions into the general solution, we get: , , and , , The relationship between the axial dimension of the resonant unit and the resonant frequency of the standing wave is further obtained as follows: ; ； Where h represents the axial height of the resonant unit, f represents the standing wave resonant frequency, c represents the wave propagation speed in the resonant unit, and n represents the mode order.

8. The manufacturing method of an ultrasonic transducer backing absorbing structure based on a standing wave resonator according to claim 6, characterized in that, Step S4 specifically includes: S41. Prepare the backing molding mold and prepare the backing substrate material and resonant unit according to the design requirements; S42. Pour the backing substrate material into the backing molding mold to form the first backing layer; S43. After the first backing layer reaches the load-bearing state, the prefabricated resonant unit is placed on it, so that the resonant unit is in the preset position and remains suspended. S44. Continue to add the remaining backing matrix material to the backing molding die to form a second backing layer, so that the resonant unit is covered and located between the first backing layer and the second backing layer. After further curing, a complete standing wave component layer is formed.

9. An ultrasonic transducer, characterized in that, The ultrasonic transducer backing absorbing structure based on a standing wave resonator as described in any one of claims 1 to 5 and a piezoelectric element are included; the ultrasonic transducer backing absorbing structure is disposed on the back side of the piezoelectric element.

Images