Double-matching-layer ultrasonic transducer for craniocerebral ultrasound and application

Abstract

The invention discloses a double-matching-layer ultrasonic transducer for craniocerebral ultrasound, the double-matching-layer ultrasonic transducer sequentially comprises a capacitance and inductance piece, a backing layer, a 1-3 type piezoelectric element, a rigid matching layer and an elastic matching layer from top to bottom, and the material of the elastic matching layer comprises an elastic substrate and a filler for regulating and controlling acoustic impedance. The double-matching-layer ultrasonic transducer for craniocerebral ultrasound provided by the invention can be acoustically matched with a skull through the 1-3 type piezoelectric element and the double-layer matching layer, so that ultrasonic scattering and dissipation caused by acoustic impedance mismatch between the skull and a piezoelectric material of the transducer are reduced; meanwhile, due to the design of the elastic matching layer, a bent skull can be better attached, and the transcranial transmission effect of ultrasound is enhanced.

Description

Technical Field

[0001] The present invention relates to the field of medical health diagnosis and treatment, and in particular to a double matching layer ultrasonic transducer for cranial ultrasound and its application. Background Art

[0002] Ultrasound is a sound wave with a frequency higher than 20kHz. It has good directionality and strong reflection ability, and it is easy to obtain concentrated sound energy. Its medical value in the field of brain has received more and more attention, and cranial ultrasound is considered to have important diagnostic value. Cranial ultrasound therapy has many significant advantages and wide applications in the medical field, such as no radiation, non-invasiveness, high safety and convenience.

[0003] Ultrasonic transducers are one of the most important parts of ultrasonic engineering technology and the fastest growing branch of acoustic transducers. Transducers are devices that convert energy. In the field of acoustic research, transducers mainly refer to electroacoustic transducers, which can realize the mutual conversion between electrical energy and acoustic energy. Piezoelectric ultrasonic transducers are the most widely used acoustic-to-electric conversion elements in the field of ultrasound. In the high-frequency range, piezoelectric ultrasonic transducers can produce a uniform vibration sound generator similar to a rigid piston, and their structure is simple, easy to excite, and easy to form and process, so they can be used in many different applications.

[0004] When ultrasound is applied to the brain, due to the presence of the skull, the acoustic impedance mismatch between the skull and the surrounding environment, human tissue environment, and ultrasonic coupling agent will produce strong reflection and absorption. In addition, the skull itself has a structure of alternating loose and dense layers. The porous layer will scatter and dissipate ultrasound, and when the longitudinal wave is transmitted to the skull, it will produce a conversion between transverse and longitudinal waves, resulting in energy loss. In addition, due to the certain curvature of the skull, the traditional rigid transducer cannot fit, thus affecting the transmission of ultrasound.

[0005] At present, the commonly used methods for improving the efficiency of ultrasound cranial penetration include acoustic metamaterials (such as the Chinese patent with publication number CN118204255A discloses a MEMS ultrasonic transducer array and a preparation method thereof that realizes the functions of acoustic wave focusing guidance and edge vibration stopping by means of acoustic metamaterials, including a MEMS ultrasonic transducer array and a vibration stopping material layer and an acoustic focusing guiding material layer arranged on the surface of the MEMS ultrasonic transducer array, wherein the MEMS ultrasonic transducer array includes a plurality of MEMS ultrasonic transducer units, the vibration stopping material layer is arranged above the common support area between the MEMS ultrasonic transducer units, and the position on the vibration stopping material layer opposite to the MEMS ultrasonic transducer unit is set as a blank area, and the blank area As a sound-permeable hole, the acoustic focusing guide material layer is arranged above the MEMS ultrasonic transducer unit; the invention optimizes the upper surface structure layer of the MEMS ultrasonic transducer array, and can effectively improve the acoustic performance of the silicon MEMS ultrasonic transducer array while realizing the wafer-level packaging of the MEMS ultrasonic transducer. ), acoustic impedance matching layer (such as the acoustic impedance matching layer disclosed in the Chinese patent with publication number CN110270493A, which includes magnetic particles coated with a low-density material layer and an adhesive, wherein the magnetic particles coated with the low-density material layer are gradiently distributed in the adhesive according to their different acoustic impedances, so that the acoustic impedance of the matching layer is gradually distributed from one end to the other end of the matching layer), etc. Traditional uniform dielectric materials cannot meet the development requirements of modern technology in terms of mechanical strength, matching bandwidth, acoustic performance, service life, etc. Non-uniform media can achieve precise control of sound waves and improve the transmission efficiency of ultrasonic energy in the skull and brain, but its preparation process is relatively complicated and the cost is relatively high.

[0006] Therefore, it is necessary to design a double matching layer ultrasonic transducer for cranial ultrasound to solve the above technical problems. Summary of the invention

[0007] The purpose of the present invention is to provide a double matching layer ultrasonic transducer for cranial ultrasound and its application. The transducer achieves acoustic matching with the skull through 1-3 type piezoelectric elements and a double matching layer, thereby reducing ultrasonic scattering and dissipation caused by the mismatch of acoustic impedance between the skull and the transducer piezoelectric material. At the same time, the design of the elastic matching layer can better fit the curved skull and enhance the transcranial transmission effect of ultrasound.

[0008] The present invention provides the following technical solutions:

[0009] The present invention proposes a double matching layer ultrasonic transducer, which comprises, from top to bottom, a capacitor and an inductor, a backing layer, a 1-3 type piezoelectric element, a rigid matching layer and an elastic matching layer, wherein the material of the elastic matching layer comprises an elastic substrate and a filler for regulating acoustic impedance.

[0010] The capacitor and inductor, backing layer and 1-3 type piezoelectric element are packaged, and after packaging, a rigid matching layer and an elastic matching layer are sequentially arranged at the front end, the transducer is connected to the SMA wire, and the rear end of the backing layer is connected to the capacitor and inductor and connected to the signal generator through the SMA wire.

[0011] Furthermore, the 1-3 type piezoelectric element includes a top electrode, a 1-3 type piezoelectric composite material and a bottom electrode. The 1-3 type piezoelectric composite material includes lead zirconate titanate and epoxy resin, and the thickness is selected based on the thickness vibration mode theory.

[0012] Furthermore, the rigid matching layer is connected to the front end of the 1-3 type piezoelectric element, and its material is epoxy resin and alumina, and the thickness is selected based on the traditional 1 / 4 wavelength matching layer theory.

[0013] Furthermore, the elastic matching layer is independent of the packaged device, and its material is polydimethylsiloxane and tungsten powder, and the thickness is selected based on the traditional 1 / 4 wavelength matching layer theory.

[0014] Furthermore, the backing layer is connected to the rear end of the 1-3 type piezoelectric element, and its material is epoxy resin, tungsten powder and boron nitride.

[0015] Furthermore, the elastic matching layer comprises an elastic substrate and a filler, wherein the elastic substrate is selected from polydimethylsiloxane, sodium alginate or Ecoflex, and the filler is selected from tungsten powder, alumina powder or silicon dioxide powder.

[0016] The present invention also provides an application of the double matching layer ultrasonic transducer in cranial ultrasound.

[0017] Furthermore, when the dual-matching layer ultrasonic transducer is in use, the elastic matching layer is directly attached to the outer surface of the skull.

[0018] The implementation principle of the present invention is as follows:

[0019] (1) Design principle of 1-3 type piezoelectric element composite material

[0020] The emission of ultrasound is based on the inverse piezoelectric effect, which means that when a voltage signal is applied to the surface of a piezoelectric material along the axial direction, the piezoelectric material will produce corresponding elastic deformation under the action of the voltage signal.

[0021] When thickness vibration occurs, the thickness d of the piezoelectric ceramic sheet and its resonant frequency f r The following relationship exists:

[0022]

[0023] Where c prepresents the propagation speed of sound waves in piezoelectric materials. n is an odd number. When n is 1, f r is the fundamental resonant frequency.

[0024] Type 1-3 piezoelectric composite material is a two-phase piezoelectric composite material composed of one-dimensionally connected piezoelectric ceramic columns arranged in parallel in a three-dimensionally connected polymer. It can improve the electromechanical coupling coefficient, increase the conversion efficiency between electrical energy and acoustic energy, and at the same time reduce the acoustic impedance of the piezoelectric element, making it easier to match the impedance with the skull, thereby further improving the transmission efficiency of sound waves.

[0025] (2) Design principle of matching layer

[0026] The acoustic matching layer is a transition layer placed between two media with large impedance differences. The existence of the acoustic matching layer will reduce the impedance difference. The calculation formula for acoustic impedance is as follows:

[0027]

[0028] when When , Z = ρv, where Z is the acoustic impedance, ρ is the density, ω is the angular velocity, k is the wave number, v is the longitudinal wave velocity, and α is the attenuation coefficient.

[0029] When a plane wave is incident vertically on the interface between two media, if Z1 and Z2 represent the acoustic impedance of the first medium and the second medium respectively, then:

[0030] Reflection coefficient:

[0031]

[0032] Transmission coefficient:

[0033]

[0034] The traditional 1 / 4 wavelength matching theory refers to when the thickness of the intermediate layer is an odd multiple of 1 / 4 wavelength and the impedance satisfies:

[0035]

[0036] At this time, T=1, which means that the correct selection of the thickness and impedance of the matching layer can greatly improve the transmission effect of the sound wave.

[0037] (3) Design principle of backing layer

[0038] The backing structure attenuates the sound waves facing away from the transducer by scattering the sound waves and utilizing the friction between particles caused by viscosity to achieve unidirectional transmission of the sound wave signal. This can effectively suppress the interference of sound waves in other directions on the front sound waves during operation of the transducer, thereby improving the performance of the transducer.

[0039] The beneficial effects of the double matching layer ultrasonic transducer for cranial ultrasound provided by the present invention are as follows:

[0040] (1) By cutting the piezoelectric crystal and filling it with epoxy resin, a 1-3 type piezoelectric element is prepared, thereby improving the electromechanical coupling coefficient, increasing the conversion efficiency between electrical energy and acoustic energy, achieving a higher transmission efficiency, and reducing the acoustic impedance of the piezoelectric element, making it easier to match the impedance with the skull, thereby further improving the transmission efficiency of the sound wave;

[0041] (2) By designing a double-layer matching layer for the transducer, the strong reflection of sound waves at the interface caused by acoustic impedance mismatch is reduced, thereby improving the transmission efficiency of sound waves and optimizing the transmission process of sound waves from the transducer to the skull, ensuring that more sound energy can reach the target area, thereby improving the ultrasonic transcranial transmittance of the transducer;

[0042] (3) By designing an elastic matching layer for the transducer, it can be better fitted with the skull, solving the problem that the traditional rigid ultrasonic transducer is difficult to fit well with the uneven skull of the human body due to its rigid material properties, thereby reducing its application and effect in medical testing. The restrictions, while reducing the attenuation of sound wave transmission and the increase in reflection caused by poor fit. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Schematic diagram of the structure of a double matching layer ultrasonic transducer for cranial ultrasound in an embodiment;

[0044] Figure 2 It is a simulation diagram of the emitted sound pressure and radiation direction of the piezoelectric element in the double matching layer ultrasonic transducer for cranial ultrasound in the embodiment in the water area;

[0045] Figure 3 This is an appearance diagram of a double matching layer ultrasound transducer for cranial ultrasound in an embodiment;

[0046] Figure 4 The front and side enlarged views of the 1-3 type piezoelectric element in the double matching layer ultrasound transducer for cranial ultrasound in the embodiment;

[0047] Figure 5 A comparison diagram of the bonding conditions between the double matching layer ultrasonic transducer for cranial ultrasound in the embodiment and the single matching layer ultrasonic transducer provided in comparative example 1 and a curved object;

[0048] Figure 6 1 is a comparison chart of the sound pressure transmission coefficient of the double matching layer ultrasonic transducer for cranial ultrasound in the embodiment and the commercial transducer in comparative example 2 for the skull phantom. DETAILED DESCRIPTION

[0049] The present invention will be further described below in conjunction with the accompanying drawings and embodiments. Here, the embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0050] The internal structure of the double matching layer ultrasonic transducer for cranial ultrasound is as follows: Figure 1 The device includes: a backing layer 1, a top electrode 2, a 1-3 type piezoelectric composite material 3, a bottom electrode 4, a rigid matching layer 5 and an elastic matching layer 6. When in use, the elastic matching layer 6 is attached to the outside of the skull and in close contact, and the rear end of the backing layer 1 is connected to the capacitor and inductor and connected to the signal generator through an SMA line. The simulated diagram of the emitted sound pressure and radiation direction of the piezoelectric element in the water is shown in Figure 2 As shown in the figure, the electric oscillation signal sent from the output stage of the excitation power supply causes the change of the electric field in the transducer, and the mechanical vibration system enters the vibration state through the inverse piezoelectric effect, thereby driving the medium in contact with the transducer vibration system to vibrate and radiate sound waves into the medium. The excitation electric field is parallel to the propagation direction of the elastic wave, generating longitudinal effect vibration, and emitting ultrasound to the front end of the transducer.

[0051] Example

[0052] The manufacturing method of the double matching layer ultrasonic transducer provided in this embodiment includes steps S1 to S7:

[0053] S1. Cut the lead zirconate titanate PZT-5H sheet by a dicing machine, and precisely control the cutting depth and width during the process to ensure the neatness and parallelism of the array. Pour epoxy resin into the gaps of the piezoelectric sheet, place it in a vacuum environment for 15 minutes, discharge the bubbles generated in the mixture, and perform vacuum degassing. After curing, obtain a 1-3 type piezoelectric composite material 3.

[0054] S2, using a gold spraying instrument to plate electrodes on both sides of the 1-3 type piezoelectric composite material 3, the electrodes plated on the surface of the piezoelectric crystal are used as the application points of the electric field, and the top electrode 2 and the bottom electrode 4 are connected by conductive silver paste;

[0055] S3, the rigid matching layer 5 is connected to the front end of the 1-3 type piezoelectric element by direct casting. The materials are epoxy resin and alumina. Alumina powder filler is slowly added to the epoxy resin A liquid. After the addition is completed, the mixed liquid is fully stirred until the mixture is muddy, and then an appropriate amount of epoxy resin B liquid is added and stirred again until the mixture is free of lumps and the whole is viscous and colloid. The stirred mixture is placed in a vacuum environment for 15 minutes to discharge the bubbles generated in the mixture. Then, the matching layer material is evenly cast above the top electrode of the transducer array element and pressed to shape, keeping its surface flat, and curing at room temperature for 5 hours. After curing, the rigid matching layer 5 is polished to the required thickness;

[0056] S4, the backing layer 1 is connected to the rear end of the 1-3 type piezoelectric element by direct casting. The preparation of the backing layer 1 is also carried out by applying filler in the epoxy resin base material. The filler used here is tungsten powder with a particle size of 1 μm. At the same time, extremely low-density boron nitride powder is applied to alleviate the tungsten powder flocculation phenomenon;

[0057] S5. Test the impedance parameters of the piezoelectric element at the resonant frequency, use the Smith chart to perform impedance matching on the acquired data and the intrinsic impedance of the transmission line, and connect the corresponding capacitor and inductor elements in series and parallel with the device;

[0058] S6, using epoxy resin to encapsulate the prepared piezoelectric element, backing layer 1 and capacitor and inductor together in a steel pipe, and connect the wire to the SMA wire;

[0059] S7, the elastic matching layer 6 material is polydimethylsiloxane and tungsten powder, tungsten powder filler is slowly added to the polydimethylsiloxane, and the mixture is fully stirred until the mixture is free of lumps and the whole is viscous and colloid-like. The stirred mixture is placed in a vacuum environment for 15 minutes, and the bubbles generated in the mixture are discharged and then cured at room temperature for 24 hours.

[0060] The appearance of the double matching layer ultrasonic transducer for cranial ultrasound provided in this embodiment is as follows: Figure 3 As shown, the basic structure of the piezoelectric element is encapsulated in a steel tube 7, the rigid matching layer 5 is directly cast on the front end of the encapsulated transducer, the elastic matching layer 6 is independent of the transducer body, the wire 8 is connected to the SMA wire, and can be further connected to the signal generator. The outer diameter of the steel tube is 25 mm, the wall thickness is 1 mm, and the height is 30 mm.

[0061] The piezoelectric element in this embodiment has a size of 16*16 mm, a thickness of 1 mm, and a volume fraction of the piezoelectric phase of 44%. Figure 4 The width of the ceramic column shown is 240μm, the column spacing is 120μm, the gold color in the front view is the sprayed gold electrode, and the side view shows that the epoxy resin is evenly filled between the ceramic columns without any bubbles.

[0062] In this embodiment, the mass fractions of epoxy resin, tungsten powder and boron nitride in the backing layer are 23%, 70% and 7% respectively, and the thickness is 3 mm; the mass fractions of epoxy resin and alumina in the rigid matching layer are 40% and 60% respectively, and the thickness is 0.75λ; the mass fractions of polydimethylsilazane and tungsten powder in the elastic matching layer are 60% and 40% respectively, and the thickness is 2.25λ, where λ is not a fixed value, but the wavelength of sound waves in different materials.

[0063] Comparative Example 1

[0064] Comparative Example 1 uses a single matching layer ultrasonic transducer without an elastic matching layer. Its piezoelectric element, backing and rigid matching layer are the same as those of the double matching layer ultrasonic transducer for cranial ultrasound in the embodiment. The comparison of the two with the curved object is shown in the figure below. Figure 5 As shown, when a single matching layer ultrasonic transducer fits a curved surface, it can only fit tightly in the center, and the two ends cannot fit with the curved phantom. However, a double matching layer ultrasonic transducer containing an elastic matching layer can achieve a certain degree of deformation and can fit well with the curved phantom, so that the device is in close contact without leaving any gaps, which can better improve the transcranial transmittance of ultrasound.

[0065] Comparative Example 2

[0066] Comparative Example 2 uses a commercial ultrasonic transducer of model 1.5P20, and the comparison of the acoustic pressure transmission coefficient of the skull phantom with that of the double matching layer ultrasonic transducer for cranial ultrasound is shown in the figure below: Figure 6 As shown, the ultrasonic transmitting end uses a commercial transducer with a center frequency of 1.5MHz and a double matching layer ultrasonic transducer for cranial ultrasound in the embodiment, the ultrasonic receiving end uses a commercial transducer with a center frequency of 1.5MHz, the phantom uses an alumina-epoxy skull phantom and an epoxy skull phantom, the skull phantom is kept at the interface of water and air during the test, a medical ultrasonic coupling agent is applied between the commercial transducer and the skull phantom, and the double matching layer ultrasonic transducer for cranial ultrasound in the embodiment is in direct contact with the skull phantom. The sound pressure transmission coefficient of the commercial transducer for the alumina-epoxy skull phantom and the epoxy skull phantom at its center frequency is 7.5% and 18.1%, while the sound pressure transmission coefficient of the double matching layer ultrasonic transducer for cranial ultrasound for the alumina-epoxy skull phantom and the epoxy skull phantom is 26.9% and 61.4%, which are increased by 3.59 times and 3.39 times respectively.

[0067] In summary, this embodiment provides a double matching layer ultrasonic transducer for cranial ultrasound, which can be placed outside the skull to achieve functions such as ultrasonic stimulation. By preparing type 1-3 piezoelectric elements, the electromechanical coupling coefficient is improved, while the acoustic impedance of the piezoelectric elements is reduced. The design of the double matching layer reduces the strong reflection of sound waves at the interface due to impedance mismatch. The elastic matching layer solves the problem that traditional rigid ultrasonic transducers are difficult to fit with the curved skull due to their rigid material properties. Through single-frequency ultrasonic transmission tests, the sound pressure transmission coefficients of commercial transducers and the double matching layer ultrasonic transducers for cranial ultrasound in the embodiment are compared for two skull phantoms, verifying the enhanced effect of the embodiment on ultrasonic transcranial transmission.

[0068] It should be noted that the above is only an embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. For example, the design principle of the matching layer may adopt a traditional single-layer matching layer, or may adopt a multi-layer matching layer, a density gradient, or a matching layer material with a structural design. Any design that can achieve acoustic impedance matching should be included. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A double matching layer ultrasonic transducer for cranial ultrasound, characterized in that: The double matching layer ultrasonic transducer comprises, from top to bottom, a capacitor and an inductor, a backing layer, a 1-3 type piezoelectric element, a rigid matching layer and an elastic matching layer, and the material of the elastic matching layer comprises an elastic substrate and a filler for regulating acoustic impedance.

2. The double matching layer ultrasonic transducer according to claim 1, characterized in that: The capacitor and inductor, backing layer and 1-3 type piezoelectric element are packaged, and after packaging, a rigid matching layer and an elastic matching layer are sequentially arranged at the front end, the transducer is connected to the SMA wire, and the rear end of the backing layer is connected to the capacitor and inductor and connected to the signal generator through the SMA wire.

3. The double matching layer ultrasonic transducer according to claim 1, characterized in that: The material of the backing layer includes epoxy resin, tungsten powder and boron nitride.

4. The double matching layer ultrasonic transducer according to claim 1, characterized in that: The 1-3 type piezoelectric element comprises a top electrode, a 1-3 type piezoelectric composite material and a bottom electrode, and the 1-3 type piezoelectric composite material comprises lead zirconate titanate and epoxy resin.

5. The double matching layer ultrasonic transducer according to claim 1, characterized in that: The material of the rigid matching layer includes epoxy resin and aluminum oxide.

6. The double matching layer ultrasonic transducer according to claim 1, characterized in that: The elastic matching layer comprises an elastic substrate and a filler, wherein the elastic substrate is selected from polydimethylsiloxane, sodium alginate or Ecoflex, and the filler is selected from tungsten powder, alumina powder or silicon dioxide powder.

7. Application of the double matching layer ultrasonic transducer according to any one of claims 1 to 6 in cranial ultrasound.

8. The use according to claim 7, characterized in that: The elastic matching layer in the double matching layer ultrasonic transducer is directly attached to the outer surface of the skull.

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