A method for preparing a silica-epoxy resin composite, an ultrasonic transducer and a preparation process thereof, and an imaging system

Abstract

The application discloses a preparation method of a silica-epoxy resin composite material, adjusts the volume fraction to control the acoustic impedance of the composite material, discloses an ultrasonic transducer prepared by using the composite material and a preparation process thereof, and further discloses an imaging system designed by using the ultrasonic transducer. By designing the matching layer and the backing layer with specific acoustic impedance, seamless fusion of ultrasonic imaging and photoacoustic imaging is realized; the transducer has ultrahigh sensitivity, wide frequency band characteristics and high optical transparency, exhibits bimodal imaging capability with high contrast and high resolution, and solves the problem of insufficient acoustic performance of a traditional transparent ultrasonic transducer.

Description

Technical Field

[0001] This invention relates to a method for preparing a silica-epoxy resin composite material, an ultrasonic transducer and its preparation process, and an imaging system, belonging to the field of transparent ultrasonic transducer technology. Background Technology

[0002] Ultrasound imaging has long held an important position in clinical diagnosis and biomedical research due to its core advantages of simple operation, high safety, controllable cost, and deep penetration. Optical imaging technologies, including photoacoustic imaging (PAI), optical coherence tomography (OCT), and fluorescence imaging (FLI), are characterized by high specificity and high resolution, enabling precise capture of molecular-level information of biological tissues. The integration of these two technologies has become a key direction for improving the sensitivity and specificity of disease diagnosis. By complementing the shortcomings of single-modality imaging, it retains the deep penetration advantage of ultrasound imaging while leveraging the high specificity of optical imaging to achieve precise localization and characterization of lesions, making it particularly suitable for complex scenarios such as early disease screening and dynamic monitoring.

[0003] However, this fusion requirement has long been constrained by the technological bottlenecks of core components. Traditional imaging systems struggle to simultaneously achieve the dual goals of "seamless integration" and "optimal dual-modal performance." If a separate design is adopted, with ultrasound and optical components arranged independently, the system structure becomes complex and bulky. Coaxial calibration of the optical and ultrasound channels is difficult, affecting imaging accuracy and making it unsuitable for miniaturized applications such as in vivo imaging and minimally invasive diagnosis and treatment. Attempts to integrate via transparent components are hampered by the performance defects of early related devices, significantly reducing the overall effectiveness and diminishing the practical value of fused imaging. Before the development of this novel transparent ultrasound transducer, the industry's ultrasound transducers were divided into two camps, both with insurmountable limitations. The following describes two traditional ultrasound transducers:

[0004] First, traditional opaque ultrasonic transducers have mature acoustic performance. The matching layer and backing layer constructed by metal-epoxy resin composite material achieve good acoustic impedance matching. They are stable in core indicators such as bandwidth, signal transmission efficiency, and sensitivity, and can meet the needs of conventional single-modal ultrasonic imaging.

[0005] Disadvantages: The opaque structure blocks light transmission and cannot be seamlessly integrated with optical modalities such as photoacoustic and fluorescence, limiting the development of multimodal imaging; additional optical channels are required, resulting in a large and complex imaging system that is difficult to adapt to miniaturization and in vivo imaging scenarios.

[0006] Second, the early exploration of transparent ultrasonic transducers (TUTs) uses transparent piezoelectric crystals (such as lithium niobate), transparent polymers, or ceramic-polymer composites to replace metal components, and is paired with transparent indium tin oxide (ITO) electrodes to achieve the dual function of "ultrasonic sound generation and optical transmission".

[0007] Disadvantages: The acoustic impedance of the front-end matching layer is mostly 2-3 MRayl (far lower than the ideal 7-9 MRayl), and the impedance of the backing layer is less than 5 MRayl, resulting in low acoustic wave transmission efficiency and severe residual vibration; narrow bandwidth, low peak voltage, and fast signal attenuation, resulting in significant disadvantages in imaging resolution and penetration depth; gaps or weak bonding between layers disrupt the continuity of acoustic transmission, further reducing the quality and stability of the transducer. Summary of the Invention

[0008] This patent proposes an ultrasonic transducer based on a silica-epoxy resin composite material, its fabrication process, and an imaging system. By designing a matching layer and a backing layer with specific acoustic impedance, it achieves seamless integration of ultrasonic imaging and photoacoustic imaging. This transducer combines ultra-high sensitivity, wide bandwidth, and high optical transparency, exhibiting high-contrast and high-resolution dual-modal imaging capabilities, thus solving the problem of insufficient acoustic performance of traditional transparent ultrasonic transducers.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing a silica-epoxy resin composite material includes the following steps:

[0011] (1) Select silica micro powder and silica nano powder as ceramic fillers, mix them with epoxy resin matrix, and prepare a variety of ceramic-epoxy resin composite slurries with different volume fractions V.

[0012] (2) Calculate the corresponding acoustic impedance Z based on the volume fraction of the ceramic-epoxy resin composite slurry prepared in step (1), and fit to form a theoretical curve of the relationship between the volume fraction V of the ceramic-epoxy resin composite slurry and the acoustic impedance Z.

[0013] (3) Based on the theoretical curve obtained in step (2), obtain the volume fraction value corresponding to the acoustic impedance value of the required silica-epoxy resin composite material, and perform positive and negative scaling on the volume fraction value to form a volume fraction range value.

[0014] (4) Within the volume fraction range in step (3), ceramic-epoxy resin composite slurries with different volume fractions are prepared with a set value as a gradient. Each ceramic-epoxy resin composite slurry is used to prepare a corresponding silica-epoxy resin composite chip. The round-trip propagation time t of ultrasound in the chip is measured by an ultrasonic transducer and a pulse receiver. The actual longitudinal sound velocity is calculated in combination with the chip thickness d. Simultaneously measure the chip's weight (m) and volume. Calculate the actual density Finally passed To obtain the actual acoustic impedance value ;

[0015] (5) When the actual acoustic impedance value in step (4) is consistent with the acoustic impedance value of the silica-epoxy resin composite material to be prepared, the actual volume fraction V of the corresponding ceramic-epoxy resin composite slurry is obtained, and the corresponding ceramic-epoxy resin composite material is prepared according to the volume fraction V.

[0016] The aforementioned method for preparing a silica-epoxy resin composite material is characterized in that: in step (2), the acoustic impedance Z of the ceramic-epoxy resin composite slurry is determined by the longitudinal sound velocity C. L The density ρ is determined by the formula:

[0017] Z = C L *ρ;

[0018] The density of the ceramic-epoxy resin composite slurry follows the law of mixing, namely... ,in This represents the density of the epoxy resin matrix. The density of the silica filler;

[0019] Longitudinal sound speed C L The bulk modulus K and shear modulus G of the composite slurry are determined by the following formula:

[0020] ;

[0021] Where K and G need to be calculated using the Devani model:

[0022] ;

[0023] ;

[0024] In the formula For epoxy resin bulk modulus, For epoxy resin shear modulus, The bulk modulus of silicon dioxide, The shear modulus of silicon dioxide;

[0025] Substitute the specific volume fraction value of the ceramic-epoxy resin composite slurry prepared in step (1) into the above formula to calculate the corresponding acoustic impedance Z, and fit to form a theoretical curve of the volume fraction V of the ceramic-epoxy resin composite slurry versus the acoustic impedance Z.

[0026] The aforementioned method for preparing a silica-epoxy resin composite material is characterized in that: in step (5), in order to meet the viscosity requirements of the composite slurry, it is necessary to calculate the viscosity of the composite slurry corresponding to the determined volume fraction V of the ceramic-epoxy resin composite slurry.

[0027] (a) Several ceramic-epoxy resin composite slurries with different volume fractions V were prepared and divided into three groups of samples: low volume fraction, medium volume fraction, and high volume fraction. After each sample was stirred evenly and degassed, the viscosity of the composite slurry of each sample was measured. ,

[0028] (b) Calculate the intrinsic viscosity of silica :

[0029] ;

[0030] in, To determine the viscosity of the pure epoxy resin matrix, the volume fractions of the low-volume-fraction group samples were substituted, and the average value was taken. ;

[0031] (c) The viscosity values ​​of the composite slurry and the viscosity of the pure epoxy resin matrix measured for all samples with different volume fractions in step (a) are compared. and the intrinsic viscosity of silica Krieg-Doherty model:

[0032] ;

[0033] And calculate the corresponding values ​​for different volume fractions. The theoretical value is fitted using the least squares method: to find a... The value is chosen to minimize the sum of squares of the deviations between the theoretical viscosity calculated by the model and the measured viscosity obtained by the rheometer;

[0034] (d) Substitute the volume fraction V of the ceramic-epoxy resin composite slurry determined in step (5) into the Krieg-Doherty model:

[0035] ;

[0036] The viscosity of the ceramic-epoxy resin composite slurry with this volume fraction was calculated. And determine the viscosity value. Does it meet the viscosity requirements for manufacturing ultrasonic transducers?

[0037] An ultrasonic transducer based on the aforementioned silica-epoxy resin composite material includes a stack and a shell, wherein a transparent polyurethane resin is filled between the stack and the shell, characterized in that: the stack comprises:

[0038] The piezoelectric crystal is a lithium niobate (LNO) crystal sputtered with indium tin oxide (ITO), with dimensions of 5.6 mm × 5.6 mm and a thickness of 100 μm;

[0039] A transparent electrode layer is sputtered on both sides of the piezoelectric crystal. The transparent electrode layer is an indium tin oxide (ITO) layer with a thickness of 200 nm.

[0040] A front matching layer and a back matching layer are disposed outside the transparent electrode layers on the front and back sides of the piezoelectric crystal;

[0041] A conductive epoxy resin layer and a transparent backing layer are disposed outside the back matching layer. The transparent backing layer has a double-layer structure with an acoustic impedance of 4-6 MRayl and is made of silica-epoxy resin composite material.

[0042] The front matching layer includes a first matching layer with an acoustic impedance of 7 MRayl - 9 MRayl and a second matching layer with an acoustic impedance of 2 MRayl - 3 MRayl, and the back matching layer has an acoustic impedance of 3.5 MRayl - 4 MRayl.

[0043] Furthermore, the first matching layer, the second matching layer, and the back matching layer are all prepared using the aforementioned method for preparing silica-epoxy resin composite materials;

[0044] The optical transmittance of the first matching layer, the second matching layer, the back matching layer and the transparent backing layer meets the following requirements: ≥90% in the visible light region (400-760nm) and ≥95% in the near-infrared region (800-1000nm).

[0045] The aforementioned ultrasonic transducer is characterized in that: the first matching layer has an acoustic impedance of 7.5 MRayl and a thickness of 31 μm, and is made of a ceramic filler composed of silica micropowder (3 μm particle size) and nanopowder (15 nm particle size) in a mass ratio of 9:1, combined with epoxy resin, with a ceramic filler volume fraction of 0.49%; the second matching layer has an acoustic impedance of 2.4 MRayl and a thickness of 18 μm, and is made of a silica-epoxy resin composite material, with a ceramic filler volume fraction of 0.25%; the back matching layer has an acoustic impedance of 3.8 MRayl and a thickness of 25 μm, and is made of a ceramic filler composed of silica micropowder (3 μm particle size) and nanopowder (30 nm particle size) in a mass ratio of 95:5, combined with epoxy resin, with a ceramic filler volume fraction of 0.38%; the upper layer of the transparent backing layer has an acoustic impedance of 4.2 MRayl, the lower layer has an acoustic impedance of 5.8 MRayl, both layers are 50 μm thick, and the corresponding ceramic filler volume fractions are 0.4% and 0.4%, respectively. And 0.43.

[0046] The aforementioned ultrasonic transducer is characterized in that: the stack is fixed in the outer shell and connected to a coaxial cable through conductive epoxy resin; the outer shell is grounded on the front side of the piezoelectric crystal and connected to a signal wire on the back side.

[0047] The aforementioned ultrasonic transducer is characterized in that the viscosity of the silica-epoxy resin composite material of the first matching layer, the second matching layer and the back matching layer is between 80 and 100 McPs.

[0048] A fabrication process for an ultrasonic transducer based on the aforementioned silica-epoxy resin composite material includes the following steps:

[0049] The lithium niobate crystal sputtered with indium tin oxide is used as a piezoelectric crystal. Two layers of composite slurry prepared by the aforementioned method for preparing silica-epoxy resin composite material are sequentially coated on the front side of the piezoelectric crystal. After curing and grinding to the set thickness, it serves as the front matching layer.

[0050] A composite slurry prepared by the aforementioned method for preparing silica-epoxy resin composite material is coated on the back of the piezoelectric crystal as a back matching layer.

[0051] Apply backing material to the backing layer to form a stack, and vacuum degas for 30 minutes to avoid interlayer bubbles;

[0052] Remove the four corners of the front and back matching layers to connect the electrode layer of the piezoelectric crystal to the coaxial cable, ensuring that the conductive path is unobstructed;

[0053] The gap between the outer shell and the stack is filled with transparent polyurethane resin to complete the overall encapsulation.

[0054] An imaging system includes a collimator and an imaging head, wherein,

[0055] The imaging head includes two angle-adjustable silver film reflectors, a right-angle prism reflector, and two parabolic reflectors. The imaging head also includes the aforementioned ultrasonic transducer.

[0056] The two angle-adjustable silver film reflectors are located below the collimator, the right-angle prism reflector is located below the two angle-adjustable silver film reflectors, the ultrasonic transducer is located between the two parabolic reflectors, and the acoustic center of the ultrasonic transducer coincides with the optical axis of the parabolic reflector. The laser beam can penetrate the ultrasonic transducer vertically and then be incident on the parabolic mirror.

[0057] The beneficial effects of this invention are:

[0058] 1. Core material innovation: Developing silica-epoxy resin composite materials. By controlling the volume fraction of SiO2 micro powder / nano powder, the target acoustic impedance of the matching layer and backing layer is achieved while maintaining high optical transparency. This solves the problem of the conflict between acoustic performance and transparency of traditional transparent materials and lays the foundation for dual-modal imaging materials.

[0059] 2. Impedance matching structure design: adopts a stepped structure of "double front matching layer + single back matching layer", combined with piezoelectric crystal and transparent electrode to achieve acoustic impedance step transition, reduce ultrasonic reflection loss, achieve wide bandwidth performance, and the acoustic performance is comparable to traditional opaque transducers.

[0060] 3. The seamless integrated manufacturing process uses the matching layer and backing layer materials as adhesives. After coating, vacuum degassing, two-step curing and precision grinding and polishing, the layer thickness tolerance is controlled to avoid acoustic attenuation caused by interlayer gaps, thereby improving transmission efficiency and transducer stability.

[0061] 4. Ultrasonic-photoacoustic coaxial dual-mode integration: By leveraging the performance advantages of the transducer, a specially designed imaging head is used to achieve coaxial focusing of the laser and ultrasonic beams, and simultaneously acquire high-resolution ultrasonic and photoacoustic imaging, thus overcoming the problem of optical-acoustic path misalignment in traditional dual-mode systems.

[0062] 5. Low-cost and highly compatible system design: The dual-modal imaging system does not require complex optical components. It relies on commercial equipment and software to achieve signal acquisition and imaging. The laser energy density meets safety standards and is suitable for imaging live animals and humans, taking into account both safety and clinical compatibility. Attached Figure Description

[0063] Figure 1 This is a schematic diagram showing the disassembled ultrasonic transducer made of silica-epoxy resin composite material according to the present invention;

[0064] Figure 2 This is a schematic diagram of the structure of an imaging system according to the present invention. Detailed Implementation

[0065] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. Example 1

[0066] A method for preparing a silica-epoxy resin composite material includes the following steps:

[0067] (1) Select silica micro powder and silica nano powder as ceramic fillers, mix them with epoxy resin matrix, and prepare a variety of ceramic-epoxy resin composite slurries with different volume fractions V.

[0068] (2) Calculate the corresponding acoustic impedance Z based on the volume fraction of the ceramic-epoxy resin composite slurry prepared in step (1), and fit to form a theoretical curve of the relationship between the volume fraction V of the ceramic-epoxy resin composite slurry and the acoustic impedance Z.

[0069] The specific calculation process is as follows:

[0070] The acoustic impedance Z of the ceramic-epoxy resin composite slurry is determined by the longitudinal sound velocity C. L The density ρ is determined by the formula:

[0071] Z = C L *ρ;

[0072] The density of the ceramic-epoxy resin composite slurry follows the law of mixing, namely... ,in The density of the epoxy resin matrix is ​​1.1 g / cm³. The density of the silica filler is 2.6 g / cm³; it can be seen that the higher the V, the better. The larger the impedance, the more it lays the foundation for increased impedance.

[0073] Longitudinal sound speed C L The bulk modulus K and shear modulus G of the composite slurry are determined by the following formula:

[0074] ;

[0075] Where K and G need to be calculated using the Devani model:

[0076] ;

[0077] ;

[0078] In the formula The bulk modulus of epoxy resin is 3 GPa; The shear modulus of epoxy resin is 1.2 GPa. The bulk modulus of silicon dioxide is 70 GPa; The shear modulus of silica is 30 GPa;

[0079] Based on the above theory, the specific volume fraction values ​​of the ceramic-epoxy resin composite slurry prepared in step (1) are substituted into the above formula to calculate the corresponding acoustic impedance Z, and a theoretical curve is formed relating the volume fraction V of the ceramic-epoxy resin composite slurry to the acoustic impedance Z. In this embodiment, volume fractions of 0.3, 0.35, 0.4, 0.45, and 0.5 are substituted into the above formula to initially obtain the "VZ" theoretical curve.

[0080] (3) Based on the theoretical curve obtained in step (2), obtain the volume fraction value corresponding to the acoustic impedance value of the required silica-epoxy resin composite material, and perform positive and negative scaling on the volume fraction value to form a volume fraction range value.

[0081] (4) Within the volume fraction range in step (3), ceramic-epoxy resin composite slurries with different volume fractions are prepared with a set value as a gradient. Each ceramic-epoxy resin composite slurry is used to prepare a corresponding silica-epoxy resin composite chip. The round-trip propagation time t of ultrasound in the chip is measured by an ultrasonic transducer and a pulse receiver. The actual longitudinal sound velocity is calculated in combination with the chip thickness d. Simultaneously measure the chip's weight (m) and volume. Calculate the actual density Finally passed To obtain the actual acoustic impedance value ;

[0082] (5) When the actual acoustic impedance value in step (4) is consistent with the acoustic impedance value of the silica-epoxy resin composite material to be prepared, the actual volume fraction V of the corresponding ceramic-epoxy resin composite slurry is obtained, and the corresponding ceramic-epoxy resin composite material is prepared according to the volume fraction V.

[0083] In the actual preparation process, since the ceramic-epoxy resin composite material needs to be used as an adhesive for coating and curing in the later stage of ultrasonic transducer fabrication, the viscosity needs to be below 100 McPs, otherwise it is difficult to spread evenly. Therefore, it is necessary to determine the upper limit of the volume fraction of the ceramic-epoxy resin composite material through viscosity testing.

[0084] Specifically, in step (5), it is necessary to calculate the viscosity of the composite slurry corresponding to the determined volume fraction V of the ceramic-epoxy resin composite slurry:

[0085] (a) Several ceramic-epoxy resin composite slurries with different volume fractions V were prepared and divided into three groups of samples: low volume fraction, medium volume fraction, and high volume fraction. After each sample was stirred evenly and degassed, the viscosity of the composite slurry of each sample was measured. ,

[0086] (b) Calculate the intrinsic viscosity of silica :

[0087] ;

[0088] in, The viscosity of the pure epoxy resin matrix is ​​10 McPs; the volume fractions of the low volume fraction array samples are substituted and the average value is taken to obtain the viscosity. ;

[0089] (c) The viscosity values ​​of the composite slurry and the viscosity of the pure epoxy resin matrix measured for all samples with different volume fractions in step (a) are compared. and the intrinsic viscosity of silica Krieg-Doherty model:

[0090] ;

[0091] And calculate the corresponding values ​​for different volume fractions. The theoretical value is fitted using the least squares method: to find a... The value is chosen to minimize the sum of squares of the deviations between the theoretical viscosity calculated by the model and the measured viscosity obtained by the rheometer;

[0092] (d) Substitute the volume fraction V of the ceramic-epoxy resin composite slurry determined in step (5) into the Krieg-Doherty model:

[0093] ;

[0094] The viscosity of the ceramic-epoxy resin composite slurry with this volume fraction was calculated. And determine the viscosity value. Does it meet the viscosity requirements for manufacturing ultrasonic transducers?

[0095] Specifically, in this embodiment, a series of ceramic-epoxy resin composite slurries with different volume fractions V were first prepared: the value range of V covered low volume fraction (V=0.05, 0.1, 0.15), medium volume fraction (V=0.2, 0.25, 0.3, 0.35, 0.4, 0.45), and high volume fraction (V=0.48, 0.5, 0.51), for a total of 12 groups of samples, to ensure that the viscosity variation trend from low to high was covered;

[0096] No curing agent was added during slurry preparation (to avoid viscosity changes caused by curing). Only ceramic filler and epoxy resin matrix were mixed, stirred evenly, and then degassed (to remove the interference of air bubbles on viscosity). The dynamic viscosity was tested under fixed conditions using a rheometer (TA Instruments HR20). Temperature 25℃ (room temperature, to avoid temperature affecting viscosity), angular frequency 10 rad / s, oscillation displacement 2% (these conditions simulate the shear state during slurry coating, and the data are for process reference).

[0097] The core data trend obtained from actual measurements is: as V increases, The viscosity gradually increases, and the rate of increase accelerates significantly after V > 0.45—for example, when V = 0.45. ≈60 McPs, V=0.48 ≈85 McPs, V=0.5 When ≈100 McPs, V=0.51 ≈150 McPs (far exceeding the 100 McPs process limit).

[0098] Select low volume fraction array data (V=0.05, 0.1, 0.15) and substitute it with the viscosity of pure epoxy resin matrix. =10 McPs (measured value), calculate for each group Take the average of the three sets of data to obtain =2.7.

[0099] The volume fractions of all 12 sample groups were compared with the corresponding measured values. Data, and known parameters ( =10McPs =2.7) Substitute into the Krieg-Doherty model and fit using the least squares method: find a The value is adjusted to minimize the sum of squares of the deviations between the theoretical viscosity calculated by the model and the measured viscosity obtained by the rheometer. This is achieved through iterative adjustments. Observe the changes in deviation when the value of is taken: When V=0.48, the model predicts that when V=0.5, ≈130 McPs, which deviates significantly from the measured 100 McPs; when When V=0.5, the model predicts that when V=0.5, ≈102 McPs, with a deviation of <2% from the measured 100 McPs, and the sum of squared deviations across all data points is minimized; when When V=0.52, the model predicts that when V=0.5, The value is approximately 85 McPs, which deviates too much from the measured value and cannot explain the sudden increase in viscosity when V=0.51.

[0100] Therefore, the fitted result A viscosity of V=0.5 must meet the practical requirements of the process: when V=0.5, the measured viscosity is approximately 100 McPs (which is exactly the upper limit of viscosity for "uniform spreadability"); if V>0.5 (e.g., 0.51), the viscosity will drastically exceed 100 McPs, making the slurry unable to spread and difficult to degas, which does not meet the process requirements. Therefore, combining the minimum deviation of the model fitting with process constraints, the final viscosity is determined as follows: ≈0.5, V must be less than 0.5 to avoid excessively high viscosity that makes processing impossible. Example 2

[0101] An ultrasonic transducer based on the aforementioned silica-epoxy resin composite material includes a stack and a housing, wherein a transparent polyurethane resin is filled between the stack and the housing, characterized in that: the stack comprises:

[0102] The piezoelectric crystal 10 is a lithium niobate (LNO) crystal sputtered from indium tin oxide (ITO), with a size of 5.6 mm × 5.6 mm and a thickness of 100 μm, serving as the core component for ultrasonic transmission and reception.

[0103] A transparent electrode layer is sputtered on both sides of the piezoelectric crystal 10. The transparent electrode layer is an indium tin oxide (ITO) layer with a thickness of 200 nm.

[0104] A front matching layer 20 and a back matching layer 30 are disposed outside the transparent electrode layers on the front and back sides of the piezoelectric crystal 10;

[0105] A conductive epoxy resin layer 40 and a transparent backing layer 50 are disposed outside the back matching layer. The transparent backing layer has a double-layer structure with an acoustic impedance of 4-6 MRayl and is made of silica-epoxy resin composite material. The core function of the backing layer is to absorb the acoustic energy radiated to the back by the piezoelectric element, and to adjust the acoustic Q factor by regulating its own acoustic impedance and damping characteristics. The magnitude of ) is such that it is related to the electric Q factor ( Matching – If the two are unbalanced (e.g.) Much higher Acoustic energy cannot be dissipated in time and will continue to drive the piezoelectric element to vibrate, forming residual vibration; if properly matched ( Acoustic and electrical energy decay synchronously, significantly reducing residual vibration. The Q factor (quality factor) describes the "energy loss rate" of a vibrating system: a higher Q value indicates slower energy loss and slower vibration decay (easier to generate residual vibration); a lower Q value indicates faster energy loss and faster vibration decay (reduced residual vibration, but signal amplitude may decrease). For ultrasonic transducers, there exists an electrical Q factor (…). ) and acoustic Q factor ( Two types of key parameters:

[0106] electric Q factor ( The dielectric loss and electrode resistance of a piezoelectric element are determined by its electrical characteristics, reflecting the rate of electrical energy dissipation. Excessive levels will cause the electrical signal to attenuate slowly, and when superimposed on the acoustic signal, it will exacerbate the residual vibration.

[0107] Acoustic Q factor ( The acoustic loss is determined by the piezoelectric element, matching layer, and backing layer, reflecting the rate of acoustic energy dissipation. Excessive vibration can cause the mechanical vibration of the piezoelectric element to decay slowly, resulting in a "long tail of vibration" (i.e., residual vibration), which directly reduces the axial resolution of ultrasound imaging.

[0108] The acoustic impedance of a piezoelectric element is approximately 30-40 MRayl. If the impedance of the backing layer is too low (e.g., only 3 MRayl for traditional epoxy resin backing), the impedance difference between the backing layer and the piezoelectric element will be too large. This will cause strong reflection (reflection coefficient >80%) at the piezoelectric element-backing layer interface. The reflected energy will then act on the piezoelectric element again, causing it to vibrate again, resulting in "secondary excitation" and prolonged after-vibration time (e.g., the after-vibration time of a traditional TUT is more than twice that of this study). However, a 4-6 MRayl backing layer significantly reduces the impedance difference between the backing layer and the piezoelectric element, lowering the reflection coefficient to 15%-25%. Most of the backing energy can be directly transferred to the backing layer (rather than reflected), avoiding secondary excitation and reducing the possibility of after-vibration at its source. Simultaneously, the impedance difference between this range and the back matching layer (3.8 MRayl) is <1 MRayl, forming a gradient impedance transition between the piezoelectric element, back matching layer, and backing layer, further reducing interface reflection and ensuring efficient energy transfer to the backing layer for absorption. The damping capacity (energy absorption capacity) of the backing layer is positively correlated with its acoustic impedance: the higher the impedance, the greater the density and elastic modulus of the material, and the stronger its ability to absorb acoustic energy. The lower the impedance, the weaker the absorption capacity. (Higher). 4-6 MRayl impedance range: allows the backing layer Controlled between 12-18, with the transducer (10-20) Highly matched, acoustic energy and electrical energy decay synchronously—avoiding both Excessive height caused aftershocks, and this was avoided. To avoid signal attenuation and resolution reduction caused by excessively low Q-factors, a balance of "low residual vibration + high sensitivity" is achieved. Therefore, a transparent composite material of 4-6 MRayl is used to fill the back of the transducer to balance the electrical Q-factor and acoustic Q-factor and reduce residual vibration.

[0109] The front matching layer includes a first matching layer 21 with an acoustic impedance of 7 MRayl - 9 MRayl and a second matching layer 22 with an acoustic impedance of 2 MRayl - 3 MRayl, and the back matching layer has an acoustic impedance of 3.5 MRayl - 4 MRayl.

[0110] Furthermore, the first matching layer, the second matching layer, and the back matching layer are all prepared using the aforementioned method for preparing silica-epoxy resin composite materials;

[0111] The optical transmittance of the first matching layer, the second matching layer, the back matching layer and the transparent backing layer meets the following requirements: ≥90% in the visible light region (400-760nm) and ≥95% in the near-infrared region (800-1000nm).

[0112] The transmission efficiency of ultrasonic energy at the interface of two media with different impedances is inversely proportional to the impedance difference; the smaller the difference, the less energy is reflected and the more is transmitted. The acoustic impedance of the piezoelectric element (LNO) of an ultrasonic transducer is approximately 30-40 MRayl, while the impedance of biological tissue / water is approximately 1.5-1.8 MRayl. Direct coupling would result in over 90% energy reflection. By introducing a frontal matching layer, a gradient impedance transition can be constructed between the piezoelectric element, the matching layer, and the imaging medium, reducing interface reflection.

[0113] Through simulation and experimental verification, the study found that optimal transmission efficiency is achieved when the frontal matching layer employs a dual-layer structure (7.5 MRayl for the first layer and 2.36 MRayl for the second layer). The 7.5 MRayl first layer acts as a "high-impedance transition layer," reducing the difference with the piezoelectric element (high impedance) and minimizing initial interface reflection. The 2.36 MRayl second layer further connects to the imaging medium (low impedance), forming a continuous gradient. If the impedance of the first layer is lower than 7 MRayl, the impedance difference with the piezoelectric element increases, leading to increased energy reflection. If it is higher than 9 MRayl, it becomes difficult to find materials compatible with transparency (e.g., opaque metal-based materials). Therefore, 7-9 MRayl represents a balance between "high transmission efficiency + transparency," and 7.5 MRayl was ultimately chosen as the optimal value.

[0114] Specifically, in this embodiment, the first matching layer has an acoustic impedance of 7.5 MRayl and a thickness of 31 μm. It is made of a ceramic filler composed of silica micropowder (3 μm particle size) and nanopowder (15 nm particle size) in a mass ratio of 9:1, combined with epoxy resin, with a ceramic filler volume fraction of 0.49. The second matching layer has an acoustic impedance of 2.4 MRayl and a thickness of 18 μm. It is made of a silica-epoxy resin composite material, with a ceramic filler volume fraction of 0.25. The back matching layer has an acoustic impedance of 3.8 MRayl and a thickness of 25 μm. It is made of a ceramic filler composed of silica micropowder (3 μm particle size) and nanopowder (30 nm particle size) in a mass ratio of 95:5, combined with epoxy resin, with a ceramic filler volume fraction of 0.38. The upper layer of the transparent backing layer has an acoustic impedance of 4.2 MRayl, and the lower layer has an acoustic impedance of 5.8 MRayl. Both layers are 50 μm thick, corresponding to ceramic filler volume fractions of 0.4 and 0.4 respectively. And 0.43.

[0115] The viscosity of the silica-epoxy resin composite material of the first matching layer, the second matching layer and the back matching layer is between 80-100 McPs, which fully meets the requirements for coating and curing as an adhesive.

[0116] The stack is fixed in a housing and connected to a coaxial cable via conductive epoxy resin. The housing is grounded on the front side of the piezoelectric crystal, and the signal wire is connected to the back side. Alternatively, the stack can be fixed in a brass housing and connected to a coaxial cable via conductive epoxy resin (E-solder3022). The housing is grounded on the front side of the LNO crystal, and the signal wire is connected to the back side to ensure stable signal transmission. Example 3

[0117] A fabrication process for an ultrasonic transducer based on the aforementioned silica-epoxy resin composite material includes the following steps:

[0118] The lithium niobate crystal sputtered with indium tin oxide is used as a piezoelectric crystal. Two layers of composite slurry prepared by the aforementioned method for preparing silica-epoxy resin composite material are sequentially coated on the front side of the piezoelectric crystal. After curing and grinding to the set thickness, it serves as the front matching layer.

[0119] A composite slurry prepared by the aforementioned method for preparing silica-epoxy resin composite material is coated on the back of the piezoelectric crystal as a back matching layer.

[0120] Apply backing material to the backing layer to form a stack, and vacuum degas for 30 minutes to avoid interlayer bubbles;

[0121] Remove the four corners of the front and back matching layers to connect the electrode layer of the piezoelectric crystal to the coaxial cable, ensuring that the conductive path is unobstructed;

[0122] The gap between the outer shell and the stack is filled with transparent polyurethane resin to complete the overall encapsulation. Example 4

[0123] An imaging system includes a collimator 1 and an imaging head, wherein the imaging head includes two angle-adjustable silver film mirrors 2, a right-angle prism mirror 3 and two parabolic mirrors 4, and the imaging head also includes the aforementioned ultrasonic transducer.

[0124] The two angle-adjustable silver film reflectors 2 are located below the collimator 1, the right-angle prism reflector 3 is located below the two angle-adjustable silver film reflectors 2, the ultrasonic transducer is located between the two parabolic reflectors 4, and the acoustic center of the ultrasonic transducer coincides with the optical axis of the parabolic reflector. The laser beam can penetrate the ultrasonic transducer vertically and then be incident on the parabolic mirror.

[0125] Coaxial focusing of the laser and ultrasonic beams is achieved through an ultrasonic transducer, a parabolic mirror, an adjustable-angle reflector, and a right-angle prism. The working principle is as follows:

[0126] Ultrasound imaging mode: The sound waves emitted by the transducer are reflected to the sample by a parabolic mirror, and the backscattered waves are received by the transducer. After amplification and digital processing, an anatomical image is generated.

[0127] Photoacoustic imaging mode: The laser penetrates the transducer to irradiate the sample. After the tissue absorbs the light energy, it generates thermal expansion, forming a photoacoustic signal, which is synchronously received by the transducer and combined with the optical absorption characteristics to generate functional imaging.

[0128] Dual-modal fusion: The software synchronously processes ultrasound and photoacoustic signals to generate a superimposed image, providing both anatomical structure (ultrasound) and functional information (photoacoustic).

[0129] Specifically:

[0130] Leveraging the performance advantages of ultrasonic transducers, a specially designed imaging head achieves coaxial focusing of laser and ultrasonic beams, simultaneously acquiring high-resolution ultrasonic and photoacoustic images, overcoming the optical-acoustic path misalignment problem of traditional dual-modal systems. The imaging head is a customized integrated structure, with core components functionally divided into three parts: an "optical path steering module," a "confocal module," and a "transducer fixing module."

[0131] Optical path steering module: Two angle-adjustable silver film reflectors 2 are located on the top of the imaging head and are symmetrically arranged in the horizontal direction. The laser beam propagates vertically downward after being reflected twice. One fixed right-angle prism reflector 3 is located below the angle-adjustable reflectors 2. The laser beam is reflected by it and turns vertically downward, aiming at the center of the parabolic mirror below it.

[0132] Confocal module: Two parabolic mirrors are located at the center of the bottom of the imaging head, and their optical axis (geometric center axis) is the "coaxial reference axis" of the entire imaging head.

[0133] Transducer fixing module: The acoustic center of the ultrasonic transducer coincides with the optical axis of the parabolic mirror, allowing the laser beam to penetrate the ultrasonic transducer perpendicularly and then enter the parabolic mirror. The coaxial focusing of the laser and ultrasonic beams is achieved through the synergy of "reflector optical path calibration" and "parabolic mirror confocalization" within the imaging head, ensuring that the propagation paths of the two beams converge at the parabolic mirror onto the same axis and are focused on the same point within the sample.

[0134] The laser beam first strikes the first adjustable reflector. By fine-tuning the angle of this reflector, the horizontally propagating laser is redirected to propagate vertically upwards, initially calibrating the horizontal position of the laser beam and aligning it with the center of the second adjustable reflector. The laser is then reflected again by the second adjustable reflector, redirecting its propagation horizontally to the right. Simultaneously adjusting the angles of both adjustable reflectors ensures that the center of the laser beam is aligned with the incident center of the lower right-angle prism reflector. After being reflected again by the second adjustable reflector, the laser beam is redirected to propagate horizontally to the right. Again, simultaneously adjusting the angles of both adjustable reflectors ensures that the center of the laser beam is aligned with the incident center of the lower right-angle prism reflector. Upon striking the fixed right-angle prism reflector, the laser beam is redirected to propagate vertically downwards. At this point, the axis of the laser beam coincides with the optical axis (coaxial reference axis) of the parabolic mirror. Subsequently, the laser vertically penetrates the ultrasonic transducer (due to TUT). With a transmittance >80% and laser loss <20%, the laser beam is incident on the reflecting surface of the parabolic mirror. Based on its geometric characteristics, the parabolic mirror focuses the perpendicularly incident parallel laser beam onto a point on its focal plane, which is the subsequent "imaging focus".

[0135] The system features a low-cost and highly compatible design. The dual-modal imaging system requires no complex optical components and relies on commercial equipment and software to achieve signal acquisition and imaging. The laser energy density meets safety standards and is suitable for imaging live animals and humans, balancing safety and clinical compatibility.

[0136] In summary, this invention proposes an ultrasonic transducer based on a silica-epoxy resin composite material, its fabrication process, and an imaging system. By designing a matching layer and a backing layer with specific acoustic impedance, seamless integration of ultrasonic imaging and photoacoustic imaging is achieved. This transducer combines ultra-high sensitivity, wide bandwidth, and high optical transparency, exhibiting high-contrast and high-resolution dual-modal imaging capabilities, thus solving the problem of insufficient acoustic performance of traditional transparent ultrasonic transducers.

[0137] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application.

[0138] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method for preparing a silica-epoxy resin composite material, characterized in that: Includes the following steps: (1) Select silica micro powder and silica nano powder as ceramic fillers, mix them with epoxy resin matrix, and prepare a variety of ceramic-epoxy resin composite slurries with different volume fractions V. (2) Calculate the corresponding acoustic impedance Z based on the volume fraction of the ceramic-epoxy resin composite slurry prepared in step (1), and fit to form a theoretical curve of the volume fraction V of the ceramic-epoxy resin composite slurry versus the acoustic impedance Z. (3) Based on the theoretical curve obtained in step (2), obtain the volume fraction value corresponding to the acoustic impedance value of the required silica-epoxy resin composite material, and perform positive and negative scaling on the volume fraction value to form a volume fraction range value. (4) Within the volume fraction range in step (3), ceramic-epoxy resin composite slurries with different volume fractions are prepared with a set value as a gradient. Each ceramic-epoxy resin composite slurry is used to prepare a corresponding silica-epoxy resin composite chip. The round-trip propagation time t of ultrasound in the chip is measured by an ultrasonic transducer and a pulse receiver. The actual longitudinal sound velocity is calculated in combination with the chip thickness d. Simultaneously measure the chip's weight (m) and volume. Calculate the actual density Finally passed To obtain the actual acoustic impedance value ; (5) When the actual acoustic impedance value in step (4) is consistent with the acoustic impedance value of the silica-epoxy resin composite material to be prepared, the actual volume fraction V of the corresponding ceramic-epoxy resin composite slurry is obtained, and the corresponding ceramic-epoxy resin composite material is prepared according to the volume fraction V. In step (2), the acoustic impedance Z of the ceramic-epoxy resin composite slurry is determined by the longitudinal sound velocity C. L The density ρ is determined by the formula: Z = C L *ρ; The density of the ceramic-epoxy resin composite slurry follows the law of mixing, namely... ,in This represents the density of the epoxy resin matrix. The density of the silica filler; Longitudinal sound speed C L The bulk modulus K and shear modulus G of the composite slurry are determined by the following formula: ； Where K and G need to be calculated using the Devani model: ； ； In the formula For epoxy resin bulk modulus, For epoxy resin shear modulus, The bulk modulus of silicon dioxide, The shear modulus of silicon dioxide; Substitute the specific volume fraction value of the ceramic-epoxy resin composite slurry prepared in step (1) into the above formula to calculate the corresponding acoustic impedance Z, and fit to form a theoretical curve of the volume fraction V of the ceramic-epoxy resin composite slurry versus the acoustic impedance Z.

2. The method for preparing a silica-epoxy resin composite material according to claim 1, characterized in that: In step (5), to meet the viscosity requirements of the composite slurry, it is necessary to calculate the viscosity of the composite slurry corresponding to the determined volume fraction V of the ceramic-epoxy resin composite slurry: (a) Several ceramic-epoxy resin composite slurries with different volume fractions V were prepared and divided into three groups of samples: low volume fraction, medium volume fraction, and high volume fraction. After each sample was stirred evenly and degassed, the viscosity of the composite slurry of each sample was measured. , (b) Calculate the intrinsic viscosity of silica : ； in, To determine the viscosity of the pure epoxy resin matrix, the volume fractions of the low-volume-fraction group samples were substituted, and the average value was taken. ; (c) The viscosity values ​​of the composite slurry and the viscosity of the pure epoxy resin matrix measured for all samples with different volume fractions in step (a) are compared. and the intrinsic viscosity of silica Krieg-Doherty model: ； And calculate the corresponding values ​​for different volume fractions. The theoretical value is fitted using the least squares method: to find a... The value is chosen to minimize the sum of squares of the deviations between the theoretical viscosity calculated by the model and the measured viscosity obtained by the rheometer; (d) Substitute the volume fraction V of the ceramic-epoxy resin composite slurry determined in step (5) into the Krieg-Doherty model: ； The viscosity of the ceramic-epoxy resin composite slurry with this volume fraction was calculated. And determine the viscosity value. Does it meet the viscosity requirements for manufacturing ultrasonic transducers? 3. An ultrasonic transducer based on a silica-epoxy resin composite material, comprising a stack and a housing (60), wherein a transparent polyurethane resin is filled between the stack and the housing (60), characterized in that: The stack includes: Piezoelectric crystal (10), wherein the piezoelectric crystal (10) is a lithium niobate crystal sputtered from indium tin oxide; A transparent electrode layer is sputtered on the front and back sides of the piezoelectric crystal (10), wherein the transparent electrode layer is an indium tin oxide layer; A front matching layer (20) and a back matching layer (30) are disposed outside the transparent electrode layers on the front and back sides of the piezoelectric crystal (10). The conductive epoxy resin layer (40) and the transparent backing layer (50) are disposed outside the back matching layer (30). The transparent backing layer (50) is a double-layer structure with an acoustic impedance of 4-6 MRayl and is made of silica-epoxy resin composite material. The front matching layer (20) includes a first matching layer (21) with an acoustic impedance of 7 MRayl -9 Mrayl and a second matching layer (22) with an acoustic impedance of 2 MRayl -3 Mrayl, and the back matching layer (30) has an acoustic impedance of 3.5 MRayl -4 Mrayl. Furthermore, the first matching layer (21), the second matching layer (22), and the back matching layer (30) are all prepared by the method for preparing the silica-epoxy resin composite material as described in claim 1 or 2; The optical transmittance of the first matching layer (21), the second matching layer (22), the back matching layer (30) and the transparent backing layer (50) meets the following requirements: visible light region ≥90%, near infrared region ≥95%; The first matching layer (21) has an acoustic impedance of 7.5 MRayl and a thickness of 31 μm. It is made of a ceramic filler composed of silica micropowder with a particle size of 3 μm and nanopowder with a particle size of 15 nm in a mass ratio of 9:1, and epoxy resin, with a ceramic filler volume fraction of 0.

49. The second matching layer (22) has an acoustic impedance of 2.4 MRayl and a thickness of 18 μm. It is made of a silica-epoxy resin composite material, with a ceramic filler volume fraction of 0.

25. The back matching layer (30) has an acoustic impedance of 3.8 MRayl and a thickness of 25 μm. It is made of a ceramic filler composed of silica micropowder with a particle size of 3 μm and nanopowder with a particle size of 30 nm in a mass ratio of 95:5, and epoxy resin, with a ceramic filler volume fraction of 0.

38. The upper layer of the transparent backing layer (50) has an acoustic impedance of 4.2 MRayl, and the lower layer has an acoustic impedance of 5.8 MRayl. MRayl, with two layers each 50 μm thick, corresponding to ceramic filler volume fractions of 0.4 and 0.43, respectively.

4. An ultrasonic transducer according to claim 3, characterized in that: The stack is fixed in the housing (60) and connected to the coaxial cable by conductive epoxy resin. The housing (60) and the piezoelectric crystal (10) are grounded on the front and connected to the signal wire on the back.

5. An ultrasonic transducer according to claim 4, characterized in that: The viscosity of the silica-epoxy resin composite material of the first matching layer (21), the second matching layer (22) and the back matching layer (30) is between 80 and 100 McPs.

6. A manufacturing process for an ultrasonic transducer as described in any one of claims 3-5, characterized in that: Includes the following steps: The lithium niobate crystal sputtered with indium tin oxide is used as a piezoelectric crystal. Two layers of composite paste are sequentially coated on the front side of the piezoelectric crystal, cured and ground to the set thickness, and used as the front matching layer. A composite paste is applied to the back of the piezoelectric crystal as a back-side matching layer; Apply backing material to the backing layer to form a stack, and vacuum degas for 30 minutes to avoid interlayer bubbles; Remove the four corners of the front and back matching layers to connect the electrode layer of the piezoelectric crystal to the coaxial cable, ensuring that the conductive path is unobstructed; The gap between the outer shell and the stack is filled with transparent polyurethane resin to complete the overall encapsulation.

7. An imaging system, characterized in that: Includes a collimator (1) and an imaging head, wherein, The imaging head includes two angle-adjustable silver film reflectors (2), a right-angle prism reflector (3), and two parabolic reflectors (4). The imaging head also includes an ultrasonic transducer as described in any one of claims 3-5. The two angle-adjustable silver film mirrors (2) are located below the collimator (1), the right-angle prism mirror (3) is located below the two angle-adjustable silver film mirrors (2), the ultrasonic transducer is located between the two parabolic mirrors (4), and the acoustic center of the ultrasonic transducer coincides with the optical axis of the parabolic mirror. The laser beam can penetrate the ultrasonic transducer vertically and then be incident on the parabolic mirror.

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