Laminated multi-mode ultrasonic phased array probe and preparation method thereof

Abstract

The invention discloses a laminated multi-mode ultrasonic phased array probe and a preparation method thereof.According to the laminated multi-mode ultrasonic phased array probe, a low-frequency piezoelectric array and a high-frequency piezoelectric array element are vertically stacked up and down, and a frequency selection isolation layer is arranged between the low-frequency piezoelectric array and the high-frequency piezoelectric array, the low-frequency piezoelectric array elements and the high-frequency piezoelectric array elements are independently selected from nonlinear piezoelectric array elements or linear piezoelectric array elements respectively, so that the piezoelectric array elements in the high-frequency piezoelectric array are used as a first matching layer of low-frequency signals, and the high-frequency transmitting array elements are used as efficient transmission channels of low-frequency receiving signals at the same time; and the composite impedance transition is realized by the second matching layer at the lowest end, so that the transmission path of the low-frequency nonlinear signal is fundamentally optimized, the reflection loss of the low-frequency nonlinear signal penetrating through the front end of the probe is reduced by more than 60%, and the receiving sensitivity is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of ultrasonic phased array probe technology, specifically relating to a stacked multimodal ultrasonic phased array probe and its preparation method. Background Technology

[0002] In the field of ultrasonic nondestructive testing, the functional completeness of the testing probe needs to be reflected in its multimodal coverage of both linear and nonlinear acoustic responses. In linear detection mode, ultrasonic waves interact with macroscopic defects within the material (such as macroscopic cracks and pores), and the location, quantification, and qualitative assessment of defects are achieved through the extraction and analysis of linear acoustic features such as reflected and scattered waves. However, when ultrasonic waves interact with early damage mechanisms within the material (such as dislocations and microcracks), nonlinear distortion of the waveform is induced, exciting nonlinear components such as zero-frequency, second-order harmonics, higher-order harmonics, mixed-frequency harmonics, and subharmonics. These nonlinear acoustic indicators are extremely sensitive to the early evolution of the material's microstructure, providing a new technical approach for component life prediction and health status assessment. Therefore, developing multimodal ultrasonic testing technology that can balance high-efficiency linear defect detection with high-precision nonlinear early damage identification has become an important research direction in this field. However, existing ultrasonic probes still face a series of technical bottlenecks that urgently need to be addressed in achieving high-performance reception and processing of wide-bandwidth, multimodal signals.

[0003] Traditional single-frequency probes (e.g., probes with a center frequency of 3MHz) often employ a one-dimensional linear array element layout, which has limited detection bandwidth. This makes it difficult to simultaneously meet the high spatial resolution required for linear detection and the wide spectral coverage required for nonlinear detection, especially in terms of response to low-frequency components (such as zero-frequency signals, typically below 0.5MHz) and high-frequency harmonic signals. In terms of acoustic matching design, conventional matching layers are usually optimized only for the probe's single dominant frequency, leading to severe impedance mismatch when the probe operates over a wide bandwidth and in multiple modes. This not only significantly reduces the transmission efficiency and receiving sensitivity of nonlinear harmonic signals but also limits the signal fidelity and imaging resolution in linear detection mode. Regarding probe structural layout, using a horizontally staggered arrangement of high- and low-frequency array elements increases the overall probe size and expands the acoustic field focus, hindering high-resolution imaging of minute defects. Conversely, using a compact, stacked structure presents a series of technological challenges, including complex interlayer electrical interconnections, stress concentration at the isolation layer interface, and poor contact reliability, affecting the independent and stable extraction of multimodal signals. In addition, existing manufacturing processes rely heavily on multi-step machining and manual assembly, which can easily introduce array element size errors and interlayer alignment deviations. It is also difficult to achieve integrated molding of acoustic functional layers with gradient impedance and complex topology, which ultimately restricts the performance consistency, sensitivity and long-term reliability of the probe in broadband and multimodal detection scenarios.

[0004] In summary, existing technologies lack an ultrasonic probe solution that achieves high structural integration, broadband impedance matching acoustically, high-precision linear detection and high-sensitivity nonlinear early damage identification simultaneously, and high-precision and process-controllable manufacturing. Therefore, there is an urgent need to propose an innovative multimodal ultrasonic probe design and fabrication method to drive the development of ultrasonic nondestructive testing technology towards a more comprehensive, accurate, and stable direction. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the first objective of this invention is to provide a stacked multimodal ultrasonic phased array probe.

[0006] The second objective of this invention is to provide a method for fabricating a multimodal ultrasonic phased array probe.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] The present invention provides a stacked multimodal ultrasonic phased array probe, which comprises, from top to bottom, a backing layer, a low-frequency piezoelectric array composed of low-frequency piezoelectric elements, a frequency-selective isolation layer, a high-frequency piezoelectric array composed of high-frequency piezoelectric elements, and a second matching layer.

[0009] The low-frequency piezoelectric array element and the high-frequency piezoelectric array element are each independently selected from nonlinear piezoelectric array elements or linear piezoelectric array elements, and the low-frequency piezoelectric array element and the high-frequency piezoelectric array element are not both nonlinear piezoelectric array elements or linear piezoelectric array elements at the same time.

[0010] The high-frequency piezoelectric array also serves as the first matching layer for low-frequency signals, with a thickness of t. h From equation (1):

[0011] t h =1 / 4λ l Equation (1);

[0012] Where λ l The wavelength of the low-frequency piezoelectric array element;

[0013] The upper and lower surfaces of the frequency selective isolation layer are respectively provided with slots for inserting low-frequency piezoelectric elements and high-frequency piezoelectric elements. The surface of any slot is provided with a microchannel, which serves as an embedding channel for the vertical electrical interconnection structure and a positioning reference for the low-frequency and high-frequency piezoelectric elements.

[0014] The stacked multimodal ultrasonic phased array probe provided by this invention employs a vertically stacked low-frequency piezoelectric array and high-frequency piezoelectric elements. A frequency-selective isolation layer is set between the low-frequency and high-frequency piezoelectric arrays for electrical insulation and suppression of crosstalk between high-frequency and low-frequency signals. The low-frequency and high-frequency piezoelectric elements are independently selected from either nonlinear or linear piezoelectric elements, and the piezoelectric elements in the low-frequency and high-frequency arrays are not simultaneously nonlinear or linear. This allows the piezoelectric elements in the high-frequency array to serve as the first matching layer for low-frequency signals, while the high-frequency transmitting elements simultaneously act as an efficient transmission channel for low-frequency receiving signals. A composite impedance transition is achieved through the bottommost second matching layer, fundamentally optimizing the transmission path of low-frequency nonlinear signals. This reduces the reflection loss of low-frequency nonlinear signals at the probe tip by more than 60%, significantly improving receiving sensitivity.

[0015] Furthermore, to achieve the alignment and stacking of the low-frequency piezoelectric array with the high-frequency piezoelectric array, this invention sets microchannels in the slots of the isolation layer. The positions of these microchannels correspond one-to-one with the electrodes of the upper and lower piezoelectric array elements. While serving as vertical electrical interconnection channels, they also serve as mechanical positioning references. During assembly, by inserting the electrode leads or alignment features of the upper and lower array elements into the corresponding microchannels, sub-micron level precise positioning (error <20μm) of the high-frequency and low-frequency piezoelectric array elements in the horizontal direction can be automatically achieved. This integrates electrical interconnection, acoustic isolation, and precision alignment functions into a single structure, significantly improving the probe's assembly accuracy, structural stability, and long-term reliability.

[0016] In a preferred embodiment, the linear piezoelectric array element is used to transmit and receive fundamental frequency ultrasonic signals, while the nonlinear piezoelectric array element is used to receive nonlinear harmonic signals, including zero-frequency signals and harmonic signals. Therefore, when a nonlinear piezoelectric array element is used to receive the zero-frequency signal, the low-frequency piezoelectric array element is a nonlinear piezoelectric array element, and the corresponding high-frequency piezoelectric array element is a linear piezoelectric array element. When the nonlinear piezoelectric array element receives the zero-frequency signal or harmonic signals, it functions as a high-frequency piezoelectric array element.

[0017] The stacked multimodal ultrasonic phased array probe provided by this invention comprises low-frequency piezoelectric elements and high-frequency piezoelectric elements, each independently selected from nonlinear or linear piezoelectric elements. Furthermore, the piezoelectric elements in the low-frequency and high-frequency piezoelectric arrays are not simultaneously nonlinear or linear piezoelectric elements. Therefore, the ultrasonic phased array probe of this invention necessarily contains one nonlinear piezoelectric element and one linear piezoelectric element. The piezoelectric array is simultaneously composed of both nonlinear and linear piezoelectric elements. The linear piezoelectric elements are used to transmit and receive linear ultrasonic signals, while the nonlinear piezoelectric elements are used to receive nonlinear harmonic signals. This design, by stacking nonlinear and linear piezoelectric wafers, constructs a multimodal detection system. Its core advantage lies in its ability to simultaneously receive linear and nonlinear signals caused by material damage, while also possessing a compact structure that facilitates the localization and imaging of multi-scale defects.

[0018] In a further preferred embodiment, the linear piezoelectric element operates at a frequency of 2MHz to 5MHz, the nonlinear piezoelectric element operates at a frequency of 0.1MHz to 1MHz when receiving a zero-frequency signal, and the nonlinear piezoelectric element operates at a frequency of 4MHz to 15MHz when receiving a frequency-doubled signal.

[0019] In a preferred embodiment, the lengths of both the low-frequency piezoelectric element and the high-frequency piezoelectric element are 10mm to 15mm.

[0020] In a preferred embodiment, the spacing between any two low-frequency piezoelectric elements or any two high-frequency piezoelectric elements is 0.1~0.3mm.

[0021] In a preferred embodiment, the thickness of the linear piezoelectric element is 0.5mm to 1.3mm; the thickness of the nonlinear piezoelectric element is 3mm to 5mm when receiving zero-frequency signals and 0.1mm to 0.65mm when receiving harmonic signals.

[0022] In a preferred embodiment, both the low-frequency piezoelectric element and the high-frequency piezoelectric element are PZT piezoelectric wafers with Ag electrodes coated on their surfaces.

[0023] In a preferred embodiment, the backing layer is made of an epoxy resin mixture with tungsten powder as filler. The backing layer is located at the top of the probe and is made of an epoxy resin mixture with tungsten powder as filler. It is a high-impedance, high-attenuation material used to absorb reverse acoustic energy and reduce signal aliasing.

[0024] In a preferred embodiment, the microchannel is disposed on the central axis of the slot of the frequency selective isolation layer. The microchannel is semi-circular with a diameter of 90-110μm and a dimensional tolerance of ≤10μm.

[0025] Experiments have shown that placing the microchannel on the central axis of the slot, and controlling its shape and size within the limits of this invention, results in the optimal probe performance. Excessive dimensional deviations in the microchannel can impair its function as a precision positioning reference, affecting assembly accuracy. Poor shape or rough inner walls of the channel can cause uneven gaps between the wires and the channel walls, resulting in uneven filling of the conductive adhesive and ultimately poor electrical contact. Ultimately, these defects significantly reduce the probe's manufacturing yield.

[0026] In a preferred embodiment, the frequency selection isolation layer is made of a transparent photosensitive resin. It can be formed using a DLP photopolymerization printer.

[0027] In a preferred embodiment, the thickness t at the slot in the frequency selection isolation layer... i From equation (2):

[0028] t i ≤1 / 4λ2 Equation (2);

[0029] Where λ2 is the wavelength of the high-frequency piezoelectric array element.

[0030] In this invention, the thickness of the slot in the frequency selective isolation layer is the spacing between the low-frequency piezoelectric element and the high-frequency piezoelectric element. On the one hand, when the thickness of the isolation layer is 1 / 4 of the wavelength of the high-frequency fundamental wave, the two pulses reflected before and after the isolation layer will be synchronized, thereby increasing the amplitude of the transmitted pulse. On the other hand, this thickness is very small for the wavelength of the received static component and will not interfere with the propagation of the static component. The function of the frequency selective isolation layer is to isolate high-frequency ultrasonic waves and suppress their interference with the transmission of low-frequency ultrasonic signals.

[0031] In a preferred embodiment, the material of the second matching layer is an Al2O3 / epoxy resin composite material.

[0032] Preferred solution: The thickness d of the second matching layer p From equation (3):

[0033] d p =λ m,h / (4f h Equation (3);

[0034] Where, λ m,h f is the wavelength of the high-frequency signal in the material under test. h The center frequency of the high-frequency piezoelectric array element is denoted as .

[0035] Preferred solution: The acoustic impedance Z of the material of the second matching layer match From equation (4):

[0036] Z match = (0.98~1.02)Z mEquation (4); where Z m The acoustic impedance of the material being tested is denoted as .

[0037] Experiments have shown that when the acoustic impedance of the second matching layer material is related to Z... m When they are close, the efficient transmission of low-frequency signals can be best achieved because Z... eq =√Z match ·Z PZT ≈√Z m ·Z probe Among them, Z eq Z represents the impedance of the composite matching layer. PZT Z represents the acoustic impedance of the piezoelectric material. m Z represents the acoustic impedance of the material being measured. probe This represents the equivalent acoustic impedance inside the probe (including piezoelectric elements, insulating layers, etc.). Since the acoustic impedance of the resin insulating layer is much lower than that of the PZT ceramic material, Z... probe ≈Z PZT Therefore, Z can be obtained. match ≈Z m The second matching layer Z match It can be obtained by adjusting the ratio of Al2O3 to epoxy resin in Al2O3 / epoxy resin composite materials.

[0038] In a preferred embodiment, the stacked multimodal ultrasonic phased array probe further includes a vertical interconnect electrode structure, which is embedded in the microchannels of a frequency-selective isolation layer. This structure forms low-resistance, high-reliability leads for interlayer electrode signals by pre-setting microchannels in the isolation layer region, inserting wires after assembly, and injecting conductive adhesive for curing.

[0039] This invention also provides a method for fabricating a multimodal ultrasonic phased array probe. A slurry containing PZT ceramic powder is used to perform photopolymerization 3D printing on a low-frequency piezoelectric array model containing substrate A and a high-frequency piezoelectric array model containing substrate B, respectively, to obtain low-frequency and high-frequency piezoelectric array blanks. These blanks are then subjected to debinding, sintering, silver plating, and polarization to obtain the low-frequency piezoelectric array containing substrate A and the high-frequency piezoelectric array containing substrate B. An isolation layer slurry is used to perform photopolymerization 3D printing on a model of a frequency-selective isolation layer to obtain a frequency-selective isolation layer. Then, using the microchannels of the frequency-selective isolation layer as a positioning reference, the high-frequency piezoelectric array elements, the frequency-selective isolation layer, and the low-frequency piezoelectric array elements are aligned sequentially and bonded with resin adhesive. Substrate A and substrate B are removed by grinding, and then a second matching layer and a backing layer are bonded to obtain the final probe.

[0040] The preparation method of this invention, through photopolymerization 3D printing integrated molding technology, overcomes the limitations of traditional subtractive manufacturing in processing complex irregular structures (such as irregularly shaped piezoelectric elements and resin isolation layers containing microchannels), achieving high-precision manufacturing of sub-millimeter feature dimensions (accuracy ±10μm) and ensuring the high piezoelectric properties of the piezoelectric wafer (d 33 With a thickness of >500 pC / N and high polarization uniformity (deviation <5%), it is also used for the microchannel design of subsequent wire insertion, eliminating the need for solid wire soldering between layers. Instead, after the upper and lower layers are bonded together, wires are inserted through the reserved 3D-printed microchannels and externally connected to the flexible circuit board, eliminating the thickness abrupt changes caused by interlayer solder joints. At the same time, the microchannels can also serve as positioning references during the bonding of piezoelectric elements.

[0041] In the preferred embodiment, the process of obtaining low-frequency piezoelectric array blanks and high-frequency piezoelectric array blanks by photopolymerization 3D printing is as follows: PZT ceramic powder, No. 1 photopolymerization monomer, and No. 1 additive are mixed to obtain a slurry containing PZT ceramic powder. The slurry containing PZT ceramic powder is added to the photopolymerization 3D printing equipment, and photopolymerization 3D printing is performed based on the low-frequency piezoelectric array model containing substrate A and the high-frequency piezoelectric array model containing substrate B to obtain the piezoelectric array blank.

[0042] The PZT ceramic powder has a particle size of d. 50 It consists of ceramic powder with a particle size of 0.25~1.5μm.

[0043] In the slurry containing PZT ceramic powder, the mass fraction of PZT ceramic powder is 80wt.%~91wt.%, the mass fraction of No. 1 photocurable monomer is 6wt.%~17wt.%, and the mass fraction of No. 1 additive is 1wt.%~5wt.%.

[0044] In this invention, photopolymerization 3D printing is used to achieve continuous forming of sub-millimeter-scale thin-walled piezoelectric wafers. The piezoelectric wafers obtained by photopolymerization 3D printing using this invention have high density and a piezoelectric coefficient d. 33 The polarization uniformity deviation inside the wafer is increased to 450pC / N, and the edge polarization weakening problem caused by traditional cutting processes is solved.

[0045] Further preferably, the No. 1 photocurable monomer is composed of dipentaerythritol hexaacrylate (DPHA), polyethylene glycol o-phenyl phenyl ether acrylate (OPPEA), and ethoxylated trimethylolpropane triacrylate (EO3-TMPTA), with a mass ratio of dipentaerythritol hexaacrylate (DPHA): polyethylene glycol o-phenyl phenyl ether acrylate (OPPEA): ethoxylated trimethylolpropane triacrylate (EO3-TMPTA) = 5~10: 60~80: 10~15.

[0046] In this invention, DPHA with high functional groups (n=6) is used as the first photocurable monomer to improve the crosslinking density during the photocuring process; OPPEA with high refractive index (refractive index=1.542, @405nm) is used as the main component of the photosensitive resin to reduce the refractive index difference between it and the ceramic powder and improve the precision; EO3-TMPTA with ethoxy groups (EO-) can act as an active diluent, which can significantly improve the flexibility and elongation of the cured material.

[0047] Further preferably, the No. 1 additive is composed of a dispersant, an anti-settling agent, a leveling agent, a defoamer, and a photoinitiator, with the following mass ratio: dispersant: anti-settling agent: leveling agent: defoamer: photoinitiator = 1~3:0.1~3:1~3:0.1~3:0.1~5; the dispersant is KMT3331, the anti-settling agent is Sago-8810, the leveling agent is Rad2500, the defoamer is SRE-2022A, and the photoinitiator is ethyl 2,4,6-trimethylbenzoylphenylphosphonate (TPO-L).

[0048] Further optimization involves mixing PZT ceramic powder, No. 1 photocurable monomer, and No. 1 additive in a mixer under vacuum. The mixing speed is 800~1800 rpm, and the mixing time is 5~30 min.

[0049] In a further preferred embodiment, when using the low-frequency piezoelectric array blank and the high-frequency piezoelectric array blank, the exposure energy is controlled to be 8~30 mJ / cm. 2 The layer thickness is 10~30μm.

[0050] In a preferred embodiment, the degreasing is carried out in a vacuum environment, the degreasing temperature is 400~600℃, and the degreasing time is 2500~3000min.

[0051] In a preferred embodiment, the sintering temperature is 1150~1250℃ and the sintering time is 1~3h.

[0052] In a preferred embodiment, the polarization process is as follows: the silver-coated sintered blank is placed in silicone oil at 120°C under an electric field of 2~5kV / mm for 5~20 minutes for polarization.

[0053] The preferred method is to use an isolation layer slurry to obtain a frequency-selective isolation layer by photopolymerization 3D printing based on a model of a frequency-selective isolation layer. The process is as follows: mix No. 2 photopolymerizable monomer and No. 2 additive to obtain an isolation layer slurry, add the photopolymerizable slurry to the photopolymerization 3D printing equipment, and perform photopolymerization 3D printing based on the model of the frequency-selective isolation layer to obtain a frequency-selective isolation layer.

[0054] In a further preferred embodiment, the second photocurable monomer is composed of trimethylolpropane triacrylate (TMPTA) and 1,6-hexanediol diacrylate (HDDA) in a mass ratio of 10~30:70~90.

[0055] In a further preferred embodiment, the No. 2 additive is composed of a light absorber, a dispersant, a defoamer, a photoinitiator, and a surfactant, in a mass ratio of 0.1~3:0.1~3:0.1~5:0.1~0.5:0.1~0.2; the light absorber is Tinuvin-384-2, the dispersant is KMT-3331, the defoamer is SRE-2022A, the photoinitiator is ethyl 2,4,6-trimethylbenzoylphenylphosphonate (TPO-L), and the surfactant is BYK-333.

[0056] In this invention, since the frequency-selective isolation layer has microchannels, and microchannel printing requires the slurry to have a suitable viscosity (300-800 mPa·s, @25℃), this invention controls the viscosity by adjusting the ratio of TMPTA to HDDA monomers: TMPTA, with higher functionality (n=3), is used to improve the crosslinking density and stiffness of the cured sample, while HDDA, with lower functionality (n=2), is used to reduce viscosity and enhance fluidity. Combined with appropriate amounts of dispersant and defoamer, the slurry possesses suitable viscosity and shear-thinning characteristics, ensuring smooth flow during printing and structural stability after forming. A small amount of surfactant BYK-333 is introduced into the slurry to enhance its wettability on the printing platform or support structure, reducing printing defects. A light absorber (Tinuvin-384-2) is added to effectively suppress ultraviolet light scattering, precisely limiting the curing reaction to the exposure area, thereby significantly improving the sharpness and dimensional accuracy of the microchannel contour (inner diameter tolerance ±10). The solidified microchannels (μm) not only serve as electrical insulation but also provide a smooth and precise channel for subsequent wire insertion, ensuring the long-term reliability of electrode interconnection.

[0057] Further optimization involves mixing No. 2 photocurable monomer and No. 2 additive in a mixer under vacuum, with a mixing speed of 400~800 rpm and a mixing time of 2~30 min.

[0058] Further preferably, when using the photopolymerizable 3D printing isolation layer, the exposure energy is controlled to be 2.41~9.63 mJ / cm². 2 The layer thickness is 50~100μm.

[0059] In a preferred embodiment, wires are inserted into the microchannels in the frequency-selective isolation layer and externally connected to the flexible circuit board. The wires are connected to the electrodes through conductive adhesive, and epoxy resin is used to fill the remaining pores to fix and form a vertical interconnect electrode structure.

[0060] In a preferred embodiment, the preparation process of the second matching layer is as follows: the acoustic impedance of the second matching layer is calculated based on the acoustic impedance of the material being tested; then, according to the acoustic impedance of the second matching layer, a corresponding proportion of Al2O3 ceramic powder and bisphenol A type liquid epoxy resin are prepared, and then additive No. 3 is added to the mixture to obtain a matching layer slurry; the matching layer slurry is injected into a mold and cured to obtain the second matching layer; in the matching layer slurry, the mass fraction of additive No. 3 is 1wt.%~5wt.%.

[0061] In a further preferred embodiment, the particle size of the Al2O3 ceramic powder is 100nm~500nm.

[0062] In a further preferred embodiment, the No. 3 additive is composed of a dispersant and a curing agent, consisting of a silane coupling agent (KH-560) and a polyetheramine curing agent (Jeffamine D-230), with a mass ratio of silane coupling agent (KH-560): polyetheramine curing agent (Jeffamine D-230) = 60~85: 15~40.

[0063] Further optimization involves mixing Al2O3 ceramic powder, epoxy resin matrix, and additives in a mixer under vacuum, with a mixing speed of 800~1500 rpm and a mixing time of 5~30 min.

[0064] In a preferred embodiment, the preparation process of the backing layer is as follows: tungsten powder, bisphenol A type liquid epoxy resin and additive No. 4 are mixed to obtain a backing layer slurry, and the backing layer slurry is injected into a mold and cured to obtain the backing layer.

[0065] The slurry containing tungsten powder has a volume fraction of 65 wt.% to 90 wt.% for tungsten powder and a volume fraction of 5 wt.% to 34 wt.% for epoxy resin.

[0066] In a further preferred embodiment, the particle size of the tungsten powder is 100nm~500nm.

[0067] In a further preferred embodiment, the No. 4 additive is composed of a dispersant and a curing agent, consisting of a silane coupling agent (KH-560) and a polyetheramine curing agent (Jeffamine D-230), with a mass ratio of silane coupling agent (KH-560): polyetheramine curing agent (Jeffamine D-230) = 70~85: 15~30.

[0068] Further optimization involves mixing tungsten powder, epoxy resin matrix, and additives in a mixer under vacuum conditions. The mixing speed is 800~1200 rpm, and the mixing time is 5~30 min.

[0069] In actual operation, epoxy resin is used to assemble the backing layer and matching layer with the piezoelectric array element. During assembly, the assembly error is controlled to be <20μm by mold limiting.

[0070] Beneficial effects

[0071] 1. Significantly improved wideband multimodal acoustic performance. Based on a layered acoustic transparency design, the high-frequency transmitting array element simultaneously serves as a high-efficiency transmission channel for low-frequency receiving signals. Furthermore, a composite impedance transition is achieved through a front-end matching layer, fundamentally optimizing the transmission path of low-frequency nonlinear signals. This design increases the overall low-frequency signal transmittance at the probe front end to over 85%, and improves the receiving sensitivity for nonlinear signals by more than 40% compared to traditional single-frequency probes. The -6dB detection bandwidth covers 0.2MHz to 5.0MHz, enabling wideband, high-sensitivity simultaneous detection of fundamental, zero-frequency, and second harmonic signals.

[0072] 2. High-precision integrated manufacturing and assembly. Utilizing photopolymerization 3D printing technology, the PZT piezoelectric array elements and the insulating resin layer with built-in microchannels are precisely integrated and formed. This is achieved through dual-particle-size graded ceramic slurry and refined process parameter control (exposure energy 8-30 mJ / cm²). 2 With a layer thickness of 10-30 μm, the prepared piezoelectric wafers have a density higher than 93% and a piezoelectric coefficient d. 33 Achieving a polarization ratio of up to 500 pC / N with an internal polarization uniformity deviation of less than 5%, effectively suppressing edge effects caused by traditional cutting processes. Combining the microstructural positioning characteristics of the printed model with the limiting design of a dedicated assembly mold, submicron-level integration with an array element spacing accuracy of ±20 μm and an interlayer assembly error of <20 μm is achieved, ensuring the consistency of acoustic wave excitation and reception.

[0073] 3. Enhanced electrical interconnect reliability and stability. 3D-printed microchannels are pre-installed within the high-frequency array elements to serve as pathways for the subsequent insertion of alloy conductive wires to form conductive interconnect electrodes, replacing traditional interlayer soldered wires. This structure avoids issues such as welding thermal stress, poor contact, and additional thickness, ensuring that the interlayer contact resistance remains stable below 1Ω. This significantly improves the electrical connection reliability and signal transmission stability of the probe in long-term high-frequency vibration environments. Simultaneously, the microchannels themselves serve as positioning structures, further reducing assembly errors. Attached Figure Description

[0074] Figure 1 This is a schematic diagram of the structure of a stacked multimodal ultrasonic phased array probe.

[0075] Figure 2This is a schematic diagram of the fabrication process of the multimodal ultrasonic phased array probe with a stacked structure provided in the embodiment.

[0076] Figure 3 This is a magnified view of a portion of the resin isolation model.

[0077] Figure 4 This is a comparison of the bandwidth of the multimodal ultrasonic phased array probe and the single-frequency probe provided in Example 1 and Comparative Example 1 at -6dB.

[0078] Figure 5 This is a comparison of the focusing effects of the multimodal ultrasonic phased array probe with a stacked structure and the ultrasonic phased array probe with a flat structure provided in Example 1 and Comparative Example 1. Detailed Implementation

[0079] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0080] Example 1:

[0081] Fabrication and Testing of a 32-Element Stacked Multimodal Nonlinear Ultrasonic Phased Array Probe

[0082] Step 1: Photopolymerization 3D Printing of PZT Piezoelectric Wafers. Two PZT piezoelectric wafers with a thickness of 0.34 mm (6 MHz, high-frequency piezoelectric element, nonlinear piezoelectric element) and 0.68 mm (3 MHz, low-frequency piezoelectric element, linear piezoelectric element) were prepared. 70 g of PZT ceramic powder with a particle size of 2 μm, 30 g of PZT powder with a particle size of 100 nm, 0.757 g of DPHA, 12.873 g of OPPEA, 1.514 g of EO3TMPTA, 4 g of KMT-3331, 1.0 g of Sago-8810, 0.5 g of Rad2500, 0.5 g of SRE-2022A, and 0.228 g of TPO-L were mixed. All raw materials were mixed using a vacuum mixer at 1200 r / min for 20 minutes to obtain the desired ceramic slurry. The ceramic slurry has a solid content of 50 vol% and uses 29.8 mJ / cm³. 2Using energy and a 20μm slice thickness, a single-step forming of piezoelectric wafer blanks with thicknesses of 0.68mm and 4mm is achieved. During photopolymerization 3D printing of piezoelectric array element blanks, the geometric thickness of the blank is directly controlled by precisely setting the layer thickness (e.g., 20μm) and total number of layers in the digital model. After calibration with sintering shrinkage (38.5%), the final product thickness matching the design value is obtained. Sampling verification is performed using a micrometer, with tolerances controlled within 20 μm. Following gradient degreasing (600℃ / 3000min), high-temperature sintering (1200℃ / 3h), and silicone oil environmental polarization (120℃ / 5kV / mm), the wafer density reaches 93.2%, the piezoelectric constant d33 = 500pC / N, and the polarization uniformity deviation is <3%, making it particularly suitable for the alternating thin-thickness arrangement requirements of 3-6MHz array elements.

[0083] Step 2: Forming the second matching layer

[0084] Taking aluminum alloy (Z≈17MRayl) as the test material as an example, the impedance of the second matching layer is set to 17.1MRayl. The calculated mass ratio of Al2O3 ceramic powder to bisphenol A epoxy resin is 100:45.1. Additionally, based on the thickness d of the second matching layer... p= λ m,h / (4f h ), obtain d p= 0.46mm;

[0085] Take 100g of Al2O3 ceramic powder, 45.1g of bisphenol A epoxy resin, 4.433g of silane coupling agent (KH-560), and 0.354g of polyetheramine curing agent (Jeffamine D-230). Mix all raw materials and use a vacuum mixer at 1200 r / min for 20 minutes to obtain the desired ceramic slurry. Pour the slurry into a precision mold and cure it at 80℃. The impedance of this composite material is 17.1MRayl, enabling a 92.5% acoustic energy transmission efficiency for a 3MHz array element and reducing the interface reflection loss to 3.8dB for a 6MHz array element.

[0086] Step 3: Molding of the backing layer

[0087] Take 100g of tungsten powder, 42.664g of bisphenol A epoxy resin, 5.542g of silane coupling agent (KH-560), and 0.152g of polyetheramine curing agent (Jeffamine D-230). Mix all raw materials and use a vacuum mixer at 1200 r / min for 20 minutes to obtain the desired slurry. Use a rectangular mold to injection mold to obtain a high-impedance backing layer. This increases the -6dB bandwidth to 75% of the center frequency and reduces the signal aliasing rate by 30%.

[0088] Step 4: Photopolymerization 3D Printing of the Resin Isolation Layer

[0089] Take 30g TMPTA, 70g HDDA, 2g KMT-3331, 4g Clariant-2R, 2g SRE-2022A, 0.2g TPO-L, and 0.3g BYK-333. Mix all ingredients and use a vacuum mixer at 1200 r / min for 20 minutes to precisely manufacture a 0.2mm resin isolation layer and a 0.1mm diameter semi-circular microchannel.

[0090] Step 5: Assembly of stacked multimodal ultrasonic phased array

[0091] This invention relates to a multimodal ultrasonic phased array probe, comprising, from bottom to top, a double-peak matching layer, an Ag lower electrode, a high-frequency piezoelectric crystal, a resin insulating layer, a low-frequency piezoelectric crystal, an Ag upper electrode, a flexible circuit board, and a backing layer. The matching layer is matched to the corresponding piezoelectric array element frequencies according to a λ / 4 matching mechanism. The printed channels of the flexible circuit board correspond one-to-one with the array element electrodes via alloy wires. The flexible circuit board is used to lead out the wiring of the ultrasonic phased array probe for easy connection to external devices. Its fabrication and assembly method includes the following steps:

[0092] 1. In this embodiment, the PZT piezoelectric ceramic array includes an array of 32 array elements with a spacing of 1.4 mm between each array element. The 6MHz array elements and the 3MHz array elements are arranged opposite each other, with 16 array elements in each array. The 6MHz array elements have a thickness of 0.34 mm and a width of 12 mm, and the 3MHz array elements have a thickness of 0.68 mm and a width of 12 mm. The 6MHz array elements are used as frequency doubling array elements, and the 3MHz array elements are used as fundamental frequency array elements.

[0093] 2. After printing the piezoelectric array using photopolymerization 3D printing technology, it was then degreased in a vacuum environment at 600℃ for 3000 min. After sintering at 1250℃ for 3 h, electrodes were fabricated. Then, the electrodes were polarized for 60 min in a silicone oil environment at 120℃ under a 5kV / mm electric field.

[0094] 3. A photosensitive resin isolation layer containing microchannels was printed using photopolymerization 3D printing technology. The isolation layer was 0.2 mm thick and the microchannel size was 100 μm.

[0095] 4. Using the microchannel position as a positioning reference, assemble the piezoelectric array elements with the isolation layer. Insert metal wires into the microchannels and connect them to the flexible circuit board, ensuring that the channels on the flexible circuit board correspond to each array element. Connect the metal wires to the electrodes using conductive adhesive, and fill the remaining pores with epoxy resin for fixation.

[0096] 5. Precisely grind away 1mm of the substrate in the piezoelectric array element to obtain the assembled mixing piezoelectric array element.

[0097] 6. The alumina (Al2O3) matching layer was formed using gel casting technology, with the model thickness meeting the requirement of d=λ / 4. The piezoelectric elements were then bonded to the matching layer with epoxy resin.

[0098] 7. A high-impedance tungsten powder backing layer is obtained through injection molding. This layer is then assembled with the mixing piezoelectric array elements according to the microchannel positions, achieving an error of <15μm. Epoxy resin is used for bonding. The final result is a multi-modal ultrasonic phased array probe.

[0099] Comparative Example 1 is identical to Example 1 in all structure, materials, and fabrication process except that all 6MHz frequency doubling array elements in Example 1 are replaced with 3MHz array elements. This yields a traditional single-frequency ultrasonic phased array probe containing only 3MHz array elements. Both the probe of Example 1 and the probe of Comparative Example 1 employ the same single-element excitation-reception mode to emit ultrasonic waves and acquire reflected echo signals from the same object under test, and then perform spectral analysis on the echo signals.

[0100] Test results are as follows Figure 4 As shown: Figure 4 (a) shows the received signal spectrum of the stacked multimode probe in Example 1. The -6dB bandwidth of its high-frequency (multiplier) receiving channel is 2.87MHz ~ 8.71MHz, and the -6dB bandwidth of its low-frequency (fundamental frequency) transmitting / receiving channel is 1.12MHz ~ 4.98MHz, indicating that the probe can effectively cover and respond to zero-frequency signals. Figure 4 In Figure (b), the received signal spectrum of the single-frequency probe in Comparative Example 1 is shown. The -6dB bandwidth of its array elements is only 1.464MHz to 4.576MHz, and there is almost no response in the zero-frequency band near 0.2MHz. The comparison confirms that the stacked multimode structure proposed in this invention has significantly better receiving sensitivity for nonlinear harmonic signals such as zero-frequency signals than the traditional single-frequency probe.

[0101] Comparative Example 2

[0102] Except for replacing the stacked structure of 6MHz and 3MHz array elements vertically stacked in Example 1 with a tiled structure arranged alternately in the same plane, all other conditions are the same as in Example 1, thus obtaining a tiled structure multi-frequency ultrasonic phased array probe. Under the same detection conditions, the focal point is imaged using a full-focusing imaging algorithm, and the sound field focusing performance of the two probe structures is compared.

[0103] The results are as follows Figure 5 As shown: Figure 5 As shown in (a), the sound pressure level of the stacked structure probe in Example 1 is 0.02~0.12 Pa; Figure 5As shown in (b), the sound pressure level of the flat-structure probe in Comparative Example 2 is 0.005~0.035 Pa. The comparison shows that, with the same array aperture, the stacked structure of the present invention can generate a higher test sound pressure level and has a higher longitudinal resolution, thus exhibiting higher sensitivity for the detection of minute defects.

[0104] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A stacked multimodal ultrasonic phased array probe, characterized in that: The stacked multimodal ultrasonic phased array probe comprises, from top to bottom, a backing layer, a low-frequency piezoelectric array composed of low-frequency piezoelectric elements, a frequency-selective isolation layer, a high-frequency piezoelectric array composed of high-frequency piezoelectric elements, and a second matching layer. The low-frequency piezoelectric array element and the high-frequency piezoelectric array element are each independently selected from nonlinear piezoelectric array elements or linear piezoelectric array elements, and the low-frequency piezoelectric array element and the high-frequency piezoelectric array element are not both nonlinear piezoelectric array elements or linear piezoelectric array elements at the same time. The high-frequency piezoelectric array also serves as the first matching layer for low-frequency signals, with a thickness of t. h From equation (1): t h =1 / 4λ l Equation (1); Where λ l The wavelength of the low-frequency piezoelectric array element; The upper and lower surfaces of the frequency selective isolation layer are respectively provided with slots for inserting low-frequency piezoelectric elements and high-frequency piezoelectric elements. The surface of any slot is provided with a microchannel, which serves as an embedding channel for the vertical electrical interconnection structure and a positioning reference for the low-frequency and high-frequency piezoelectric elements.

2. The stacked multimodal ultrasonic phased array probe according to claim 1, characterized in that: The linear piezoelectric array element is used to transmit and receive fundamental frequency ultrasonic signals, and the nonlinear piezoelectric array element is used to receive nonlinear harmonic signals, including zero-frequency signals and harmonic signals. The linear piezoelectric array element operates at a frequency of 2MHz to 5MHz. When receiving a zero-frequency signal, the nonlinear piezoelectric array element operates at a frequency of 0.1MHz to 1MHz. When receiving a frequency-doubled signal, the nonlinear piezoelectric array element operates at a frequency of 4MHz to 15MHz. The lengths of both the low-frequency piezoelectric array element and the high-frequency piezoelectric array element are 10mm~15mm; The spacing between any two low-frequency piezoelectric elements or any two high-frequency piezoelectric elements is 0.1~0.3mm; The thickness of the linear piezoelectric array element is 0.5mm~1.3mm; the thickness of the nonlinear piezoelectric array element is 3mm~5mm when receiving zero-frequency signals and 0.1mm~0.65mm when receiving harmonic signals. Both the low-frequency piezoelectric array element and the high-frequency piezoelectric array element are PZT piezoelectric wafers with Ag electrodes coated on their surfaces. The backing layer is made of an epoxy resin mixture with tungsten powder as filler.

3. The stacked multimodal ultrasonic phased array probe according to claim 1, characterized in that: The microchannel is located on the central axis of the slot of the frequency selective isolation layer. The microchannel is semi-circular with a diameter of 90-110μm and a dimensional tolerance of ≤10μm. The frequency-selective isolation layer is made of transparent photosensitive resin; The thickness t at the slot in the frequency selection isolation layer i From equation (2): t i ≤1 / 4λ2 Equation (2); Where λ2 is the wavelength of the high-frequency piezoelectric array element.

4. The stacked multimodal ultrasonic phased array probe according to claim 1, characterized in that: The material of the second matching layer is an Al2O3 / epoxy resin composite material; The thickness d of the second matching layer p From equation (3): d p = λ m,h / (4f h ) Equation (3); Where, λ m,h f is the wavelength of the high-frequency signal in the material being tested. h The center frequency of the high-frequency piezoelectric array element; The acoustic impedance Z of the material of the second matching layer match From equation (4): Z match = (0.98~1.02)Z m Equation (4); where Z m The acoustic impedance of the material being tested is denoted as .

5. A stacked multimodal ultrasonic phased array probe according to claim 1, characterized in that: The stacked multimodal ultrasonic phased array probe also includes a vertical interconnect electrode structure, which is embedded in the microchannels of the isolation layer.

6. A method for fabricating a stacked multimodal ultrasonic phased array probe according to any one of claims 1-5, characterized in that: Using a slurry containing PZT ceramic powder, low-frequency piezoelectric array blanks and high-frequency piezoelectric array blanks were obtained by photopolymerization 3D printing based on a low-frequency piezoelectric array model containing substrate A and a high-frequency piezoelectric array model containing substrate B, respectively. After debinding, sintering, silvering, and polarization, the low-frequency piezoelectric array containing substrate A and the high-frequency piezoelectric array containing substrate B were obtained. Using an isolation layer slurry, a frequency-selective isolation layer was obtained by photopolymerization 3D printing based on a model of a frequency-selective isolation layer. Then, using the microchannel of the frequency-selective isolation layer as a positioning reference, the high-frequency piezoelectric array elements, the frequency-selective isolation layer, and the low-frequency piezoelectric array elements were aligned in sequence and bonded with resin adhesive. Substrate A and substrate B were removed by sanding, and then the second matching layer and the backing layer were bonded to obtain the final product.

7. The method for fabricating a stacked multimodal ultrasonic phased array probe according to claim 6, characterized in that: The process of obtaining low-frequency piezoelectric array blanks and high-frequency piezoelectric array blanks by photopolymerization 3D printing is as follows: PZT ceramic powder, No. 1 photopolymerization monomer, and No. 1 additive are mixed to obtain a slurry containing PZT ceramic powder. The slurry containing PZT ceramic powder is added to the photopolymerization 3D printing equipment. Based on the low-frequency piezoelectric array model containing substrate A and the high-frequency piezoelectric array model containing substrate B, photopolymerization 3D printing is performed to obtain the piezoelectric array blank. The PZT ceramic powder has a particle size of d. 50 Composed of ceramic powder with a particle size of 0.25~1.5μm; In the slurry containing PZT ceramic powder, the mass fraction of PZT ceramic powder is 80 wt.%~91 wt.%, the mass fraction of No. 1 photocurable monomer is 6 wt.%~17 wt.%, and the mass fraction of No. 1 additive is 1 wt.%~5 wt.%. The No. 1 photocurable monomer is composed of dipentaerythritol hexaacrylate, polyethylene glycol o-phenyl phenyl ether acrylate, and ethoxylated trimethylolpropane triacrylate, with a mass ratio of dipentaerythritol hexaacrylate: polyethylene glycol o-phenyl phenyl ether acrylate: ethoxylated trimethylolpropane triacrylate = 5~10: 60~80: 10~15; The No. 1 additive is composed of a dispersant, an anti-settling agent, a leveling agent, a defoamer, and a photoinitiator, with the following mass ratio: dispersant: anti-settling agent: leveling agent: defoamer: photoinitiator = 1~3:0.1~3:1~3:0.1~3:0.1~5; the dispersant is KMT3331, the anti-settling agent is Sago-8810, the leveling agent is Rad2500, the defoamer is SRE-2022A, and the photoinitiator is ethyl 2,4,6-trimethylbenzoylphenylphosphonate. PZT ceramic powder, No. 1 photocurable monomer, and No. 1 additive are mixed in a mixer under vacuum. The mixing speed is 800~1800 rpm and the mixing time is 5~30 min. When using photopolymerization 3D printing for both low-frequency and high-frequency piezoelectric array preforms, the exposure energy is controlled at 8~30 mJ / cm. 2 The layer thickness is 10~30μm; The degreasing is carried out in a vacuum environment at a temperature of 400-600℃ for a time of 2500-3000 min. The sintering temperature is 1150~1250℃, and the sintering time is 1~3h; The polarization process is as follows: the silver-coated sintered blank is placed in silicone oil at 120℃ and subjected to an electric field of 2~5kV / mm for 5~20min for polarization.

8. The method for fabricating a stacked multimodal ultrasonic phased array probe according to claim 6, characterized in that: The process of obtaining a frequency-selective isolation layer by photopolymerization 3D printing based on the model of the isolation layer using isolation layer slurry is as follows: prepare the isolation layer slurry by mixing No. 2 photopolymer monomer and No. 2 additive, add the photopolymerization slurry to the photopolymerization 3D printing equipment, and perform photopolymerization 3D printing according to the model of the frequency-selective isolation layer to obtain the frequency-selective isolation layer. The No. 2 photocurable monomer is composed of trimethylolpropane triacrylate and 1,6-hexanediol diacrylate, with a mass ratio of trimethylolpropane triacrylate:1,6-hexanediol diacrylate=10~30:70~90. The No. 2 additive is composed of a light absorber, a dispersant, a defoamer, a photoinitiator, and a surfactant, in a mass ratio of 0.1~3:0.1~3:0.1~5:0.1~0.5:0.1~0.

2. The light absorber is Tinuvin-384-2, the dispersant is KMT-3331, the defoamer is SRE-2022A, the photoinitiator is ethyl 2,4,6-trimethylbenzoylphenylphosphonate, and the surfactant is BYK-333. The No. 2 photocurable monomer and the No. 2 additive are mixed in a mixer under vacuum. The mixing speed is 400~800 rpm and the mixing time is 2~30 min. When selecting the isolation layer for the photopolymerization 3D printing frequency, the exposure energy is controlled at 2.41~9.63mJ / cm. 2 The layer thickness is 50~100μm; Wires are inserted into the microchannels in the frequency selective isolation layer and connected to the flexible circuit board. The wires are connected to the electrodes through conductive adhesive. Epoxy resin fills the remaining pores and fixes them to form a vertical interconnect electrode structure.

9. The method for fabricating a stacked multimodal ultrasonic phased array probe according to claim 6, characterized in that: The preparation process of the second matching layer is as follows: The acoustic impedance of the second matching layer is calculated based on the acoustic impedance of the material being tested. Then, according to the acoustic impedance of the second matching layer, a corresponding proportion of Al2O3 ceramic powder and bisphenol A type liquid epoxy resin are prepared, and additive No. 3 is added to obtain a matching layer slurry. The matching layer slurry is injected into a mold and cured to obtain the second matching layer. The mass fraction of additive No. 3 in the matching layer slurry is 1 wt.%~5 wt.%. The particle size of the Al2O3 ceramic powder is 100nm~500nm; The No. 3 additive consists of a dispersant and a curing agent, and is composed of a silane coupling agent and a polyetheramine curing agent. By mass ratio, the ratio of silane coupling agent to polyetheramine curing agent is 60~85:15~40. Al2O3 ceramic powder, epoxy resin matrix, and additives are mixed in a mixer under vacuum. The mixing speed is 800~1500 rpm and the mixing time is 5~30 min.

10. The method for fabricating a stacked multimodal ultrasonic phased array probe according to claim 6, characterized in that: The preparation process of the backing layer is as follows: tungsten powder, bisphenol A type liquid epoxy resin and No. 4 additive are mixed to obtain a backing layer slurry, and the backing layer slurry is injected into a mold and cured to obtain the backing layer. The tungsten powder-containing slurry has a tungsten powder volume fraction of 65 wt.% to 90 wt.% and an epoxy resin volume fraction of 5 wt.% to 34 wt.%. The particle size of the tungsten powder is 100nm~500nm; The No. 4 additive consists of a dispersant and a curing agent, and is composed of a silane coupling agent and a polyetheramine curing agent. By mass ratio, the ratio of silane coupling agent to polyetheramine curing agent is 70~85:15~30. Tungsten powder, epoxy resin matrix, and additives are mixed in a mixer under vacuum. The mixing speed is 800~1200 rpm and the mixing time is 5~20 min.

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