Method and system for evaluating transmission angle of piezoelectric ultrasonic transducer based on lithium niobate

Abstract

The invention relates to the technical field of electronic materials and devices, in particular to a piezoelectric ultrasonic transducer transmission angle evaluation method and system based on lithium niobate, and the method comprises the steps: obtaining a physical parameter matrix of a target cut lithium niobate crystal under a standard coordinate system; performing rotation transformation on the physical parameter matrix according to a preset rotation axis and different transmission angles; extracting a first transmission angle by taking maximization of a target piezoelectric matrix component as a target according to the physical parameter matrix after rotation transformation; extracting a second transmission angle by taking maximization of an electromechanical coupling coefficient as a target according to the physical parameter matrix after rotation transformation; and constructing a transducer simulation model, and simulating and extracting an optimal transmission angle according to the first transmission angle and the second transmission angle. The invention aims to optimize the sensitivity and bandwidth of the piezoelectric ultrasonic transducer prepared from lithium niobate.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic materials and devices, and in particular to a method and system for evaluating the transmission angle of a piezoelectric ultrasonic transducer based on lithium niobate. Background Art

[0002] Ultrasonic transducers are key components of ultrasonic systems, responsible for the conversion between electrical energy and mechanical energy. Traditional ultrasonic transducers are mainly produced using piezoelectric materials through a series of complex manufacturing processes, which result in high costs and low production efficiency. In order to solve these problems, micro-electromechanical systems (MEMS) technology was introduced to prepare miniaturized and integrated ultrasonic transducers, namely micro-machined ultrasonic transducers (MUTS), which include capacitive ultrasonic transducers (CMUTs) and piezoelectric ultrasonic transducers (PMUTs); among them, PMUTs are widely used because they do not require bias voltage and have high sensitivity and reliability.

[0003] In recent years, lithium niobate (LiNbO3, LN) has attracted widespread attention as a crystalline material with strong piezoelectric effect. The LN single crystal film prepared by ion implantation and stripping not only retains the excellent properties of LN, but also performs well in thickness control and surface flatness, which provides new possibilities for the development of high-performance PMUT devices. Compared with traditional piezoelectric materials such as aluminum nitride (AlN) and lead zirconate titanate (PZT), LN has a higher piezoelectric coefficient and dielectric constant, which means stronger electromechanical coupling ability. At the same time, although the piezoelectric coefficient of LN is lower than that of PZT, its much lower dielectric loss enables PMUT based on LN to achieve lower energy consumption while maintaining a high signal-to-noise ratio. In addition, LN material also has excellent biocompatibility and process compatibility, especially single crystal LN in a specific cutting direction can provide a very high electromechanical coupling coefficient, which is crucial to improving the working efficiency of PMUT.

[0004] However, the existing technology is insufficient in research on how to make full use of the unique properties of LN single crystal materials to optimize the performance of PMUT, and lacks analysis methods for the response characteristics of PMUT under different working conditions, resulting in deficiencies in how to effectively adjust the relationship between LN material parameters and PMUT performance indicators under different working conditions, which in turn limits the sensitivity and bandwidth of PMUT devices, especially for situations requiring high-resolution imaging or precise detection tasks. Summary of the invention

[0005] In order to optimize the sensitivity and bandwidth of a piezoelectric ultrasonic transducer prepared from lithium niobate, the purpose of the present invention is to provide a method and system for evaluating the transmission angle of a piezoelectric ultrasonic transducer based on lithium niobate. The technical scheme adopted is as follows:

[0006] The technical solution of the first aspect of the present invention provides a method for evaluating the transmission angle of a piezoelectric ultrasonic transducer based on lithium niobate, the method comprising:

[0007] Obtain the physical parameter matrix of the target cut lithium niobate crystal in the standard coordinate system;

[0008] Rotate and transform the physical parameter matrix according to the preset rotation axis and different transmission angles;

[0009] According to the physical parameter matrix after the rotation transformation, a first transmission angle is extracted with the goal of maximizing the target piezoelectric matrix component;

[0010] According to the physical parameter matrix after the rotation transformation, the second transmission angle is extracted with the goal of maximizing the electromechanical coupling coefficient;

[0011] A transducer simulation model is constructed, and the optimal transmission angle is simulated and extracted according to the first transmission angle and the second transmission angle.

[0012] Furthermore, obtaining the physical parameter matrix of the target cut lithium niobate crystal in the standard coordinate system includes:

[0013] Obtain the piezoelectric constant matrix, dielectric constant matrix, and elastic constant matrix of the target cut lithium niobate crystal in the standard coordinate system.

[0014] Furthermore, performing a rotation transformation on the physical parameter matrix according to a preset rotation axis and different transmission angles includes:

[0015] The Bond matrix method is used to rotate the piezoelectric constant matrix, dielectric constant matrix and elastic constant matrix respectively.

[0016] Furthermore, the piezoelectric constant matrix, the dielectric constant matrix and the elastic constant matrix are rotated and transformed using the Bond matrix method, including:

[0017] Define the orthogonal transformation matrix and stress tensor transformation matrix according to the preset rotation axis and different transmission angles;

[0018] The dielectric constant matrix is ​​rotated by using the orthogonal transformation matrix to obtain the rotated dielectric constant matrix;

[0019] The piezoelectric constant matrix and the elastic constant matrix are respectively rotated and transformed using the stress tensor transformation matrix to obtain the rotated piezoelectric constant matrix and the elastic constant matrix.

[0020] Further, according to the physical parameter matrix after the rotation transformation, extracting the first transmission angle with the goal of maximizing the target piezoelectric matrix component includes:

[0021] The transmission angle corresponding to the maximum value of the target piezoelectric matrix component is selected from the rotated piezoelectric constant matrix as the first transmission angle.

[0022] Further, according to the physical parameter matrix after the rotation transformation, extracting the second transmission angle with the goal of maximizing the electromechanical coupling coefficient includes:

[0023] According to the physical parameter matrix after rotation transformation at different transmission angles, the electromechanical coupling coefficient at different transmission angles is calculated;

[0024] The second transmission angle is extracted according to the variation relationship between the electromechanical coupling coefficient and the transmission angle.

[0025] Furthermore, the expression of the electromechanical coupling coefficient is:

[0026]

[0027] In the formula, represents the electromechanical coupling coefficient; represents the piezoelectric constant after rotation transformation; ε ij represents the dielectric constant after rotation transformation; c ij The elastic constant after rotation transformation; i and j represent the row and column indices in the matrix.

[0028] Further, constructing a transducer simulation model, simulating and extracting the optimal transmission angle according to the first transmission angle and the second transmission angle includes:

[0029] Construct a finite element simulation model of the transducer;

[0030] Selecting a transmission angle constant from a closed interval between the first transmission angle and the second transmission angle, extracting the piezoelectric constant, dielectric constant and elastic constant under different transmission angle constants and inputting them into a finite element simulation model, and outputting an amplitude response result;

[0031] The optimal transmission angle is extracted based on the amplitude response results.

[0032] The technical solution of the second aspect of the present invention provides a piezoelectric ultrasonic transducer transmission angle evaluation system based on lithium niobate, the system comprising:

[0033] A physical parameter acquisition module, configured to acquire a physical parameter matrix of a target cut lithium niobate crystal in a standard coordinate system;

[0034] A rotation transformation module, configured to perform rotation transformation on the physical parameter matrix according to a preset rotation axis and different transmission angles;

[0035] A first transmission angle extraction module is configured to extract a first transmission angle based on the physical parameter matrix after the rotation transformation with the goal of maximizing the target piezoelectric matrix component;

[0036] A second transmission angle extraction module is configured to extract a second transmission angle according to the physical parameter matrix after the rotation transformation with the goal of maximizing the electromechanical coupling coefficient;

[0037] The optimal transmission angle extraction module is configured to construct a transducer simulation model, simulate and extract the optimal transmission angle according to the first transmission angle and the second transmission angle.

[0038] The present invention has the following beneficial effects:

[0039] The present invention provides a lithium niobate-based piezoelectric ultrasonic transducer transmission angle evaluation method and system, which performs a rotational transformation on a physical parameter matrix of a lithium niobate crystal of a target cut type, and according to the physical parameter matrix after the rotational transformation, extracts a first transmission angle with the goal of maximizing a target piezoelectric matrix component, and extracts a second transmission angle with the goal of maximizing an electromechanical coupling coefficient, and then determines the optimal transmission angle of the lithium niobate piezoelectric ultrasonic transducer through simulation, and prepares a lithium niobate piezoelectric ultrasonic transducer within a closed interval between the first transmission angle and the second transmission angle, so that a lithium niobate piezoelectric ultrasonic transducer with a large bandwidth and high sensitivity under the target cut type can be prepared, thereby providing more efficient and more accurate ultrasonic detection and imaging capabilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0041] Figure 1 A method flow chart of a method for evaluating the transmission angle of a piezoelectric ultrasonic transducer based on lithium niobate provided by one embodiment of the present invention;

[0042] Figure 2 A schematic diagram of the linear relationship between piezoelectric matrix components, electromechanical coupling coefficients and transmission provided by one embodiment of the present invention;

[0043] Figure 3 A schematic diagram of a signal waveform of a LN PMUT provided by an embodiment of the present invention;

[0044] Figure 4 A schematic diagram of the bandwidth of an LN PMUT provided by an embodiment of the present invention;

[0045] Figure 5 A schematic diagram of the structure of a piezoelectric ultrasonic transducer transmission angle evaluation system based on lithium niobate provided by one embodiment of the present invention;

[0046] Figure 6 A schematic diagram of the structure of a LN PMUT provided by an embodiment of the present invention;

[0047] Icon: 101-metal electrode, 102-lithium niobate film, 103-silicon dioxide, 104-silicon substrate. DETAILED DESCRIPTION

[0048] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is a detailed description of the transmission angle evaluation method and system of the piezoelectric ultrasonic transducer based on lithium niobate proposed by the present invention, its specific implementation method, structure, characteristics and effects, in combination with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "another embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics in one or more embodiments may be combined in any suitable form.

[0049] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0050] The specific scheme of a piezoelectric ultrasonic transducer transmission angle evaluation method and system based on lithium niobate provided by the present invention is described in detail below with reference to the accompanying drawings.

[0051] See also Figure 1 , which shows a method flow chart of a method for evaluating the transmission angle of a piezoelectric ultrasonic transducer based on lithium niobate provided by an embodiment of the present invention. The technical solution of the first aspect of the present invention provides a method for evaluating the transmission angle of a piezoelectric ultrasonic transducer based on lithium niobate, and the method comprises:

[0052] Step S100: obtaining a physical parameter matrix of a target-cut lithium niobate crystal in a standard coordinate system; specifically, common cuts of lithium niobate crystals include X-cut, Y-cut, and Z-cut, and each cut has different performance advantages in different applications; in this embodiment, the physical parameter matrix of an X-cut lithium niobate crystal is mainly used; lithium niobate material is an anisotropic material, and the physical parameter matrices of lithium niobate with different transmission angles are quite different; therefore, it is necessary to maximize the performance advantages of the piezoelectric properties and electromechanical coupling coefficient of lithium niobate crystals in order to prepare a piezoelectric ultrasonic transducer with high sensitivity and large bandwidth;

[0053] Step S100 specifically includes:

[0054] Step S110: obtaining a piezoelectric constant matrix, a dielectric constant matrix, and an elastic constant matrix of a target-cut lithium niobate crystal in a standard coordinate system;

[0055] Step S200: performing a rotation transformation on the physical parameter matrix according to a preset rotation axis and transmission angle; specifically, using the Bond matrix method to perform a rotation transformation on the piezoelectric constant matrix, the dielectric constant matrix, and the elastic constant matrix respectively;

[0056] Step S200 specifically includes:

[0057] Step S210: defining an orthogonal transformation matrix and a stress tensor transformation matrix according to a preset rotation axis and different transmission angles; for example, for a physical parameter matrix of an X-cut lithium niobate crystal, taking the coordinate transformation matrix when rotating about the x-axis by an angle θ as an example, the orthogonal transformation matrix can be expressed as:

[0058]

[0059] In the formula, A represents the orthogonal transformation matrix; θ represents the transmission angle, that is, the angle between the electrode arrangement direction and the x-axis direction of the material; Represents the array element of the orthogonal transformation matrix;

[0060] The stress tensor transformation matrix M is used to describe the transformation of stress and strain in the rotated coordinate system. For rotation in 3D space, the stress tensor transformation matrix M can be expressed as:

[0061]

[0062] Step S220: Using the orthogonal transformation matrix to perform a rotation transformation on the dielectric constant matrix, a rotated dielectric constant matrix is ​​obtained, which can be expressed as:

[0063] [ε`]=[A][ε][A] T

[0064] Where [ε`] represents the rotated dielectric constant matrix; [A] T represents the transposed matrix of the orthogonal transformation matrix;

[0065] Step S230: Using the stress tensor transformation matrix, the piezoelectric constant matrix and the elastic constant matrix are respectively rotated to obtain the rotated piezoelectric constant matrix and the elastic constant matrix, which can be expressed as:

[0066] [e`]=[M][e][M] T

[0067] [c`]=[M][c][M] T

[0068] Where [e`] represents the piezoelectric constant matrix after rotation; [M] T represents the transposed matrix of the stress tensor transformation matrix; [c`] represents the elastic constant matrix after rotation;

[0069] In this embodiment, the physical parameter matrix in the standard coordinate system can be accurately converted to a new coordinate system under different transmission angles through the orthogonal transformation matrix and the stress tensor transformation matrix. The physical parameter matrix under different transmission angles reflects the performance difference of the lithium niobate crystal in different directions.

[0070] Step S300: extracting the first transmission angle according to the physical parameter matrix after the rotation transformation with the goal of maximizing the target piezoelectric matrix component; specifically, according to Figure 6 The schematic diagram of the LN PMUT structure is shown in Figure 1. The target piezoelectric matrix component is preferably 11 , i.e., the component of the first row and first column of the piezoelectric matrix; it should be noted that, for different structures, different piezoelectric matrix components can be selected as optimization targets;

[0071] Step S300 specifically includes:

[0072] Step S310: Selecting the transmission angle corresponding to the maximum value of the target piezoelectric matrix component from the rotated piezoelectric constant matrix as the first transmission angle; specifically, see Figure 2 As shown, e 11 The value of is the largest when the transmission angle is 29°, so 29° can be selected as the first transmission angle; it should be noted that the amplitude response of LN PMUT is similar to e 11 Correlation, the selection of 29° as the first transmission angle represents the optimal amplitude response;

[0073] Step S320: extracting a second transmission angle according to the physical parameter matrix after the rotation transformation with the goal of maximizing the electromechanical coupling coefficient;

[0074] Step S320 specifically includes:

[0075] Step S321: Calculate the electromechanical coupling coefficient at different transmission angles according to the physical parameter matrix after rotation transformation at different transmission angles; the expression of the electromechanical coupling coefficient is:

[0076]

[0077] In the formula, represents the electromechanical coupling coefficient; represents the piezoelectric constant after rotation transformation; ε` ij represents the dielectric constant after rotation transformation; c` ij The elastic constant after rotation transformation; i and j represent the row and column indexes in the matrix;

[0078] Step S322: extracting the second transmission angle according to the variation relationship between the electromechanical coupling coefficient and the transmission angle; specifically, the electromechanical coupling coefficient As an example, it is used to describe the coupling between the electric field and mechanical strain along the X-axis. It can be expressed as:

[0079]

[0080] See also Figure 2 As shown in the figure, the electromechanical coupling coefficient under different transmission angles is Plotted as a curve graph, where the horizontal axis is the transmission angle, it can be understood that according to The extreme value of , the transmission angle 30° can be extracted as the second transmission angle;

[0081] Step S400: constructing a transducer simulation model, simulating and extracting the optimal transmission angle according to the first transmission angle and the second transmission angle;

[0082] Step S400 specifically includes:

[0083] Step S410: Construct a finite element simulation model of the transducer; specifically, according to the actual design parameters, establish a geometric model of the X-cut LNPMUT. Figure 6 As shown, a basic structural embodiment of a piezoelectric ultrasonic transducer based on lithium niobate is shown, wherein the longitudinal structure is sequentially a metal electrode 101, a lithium niobate film 102, silicon dioxide 103 and a silicon substrate 104, and the dotted line represents a cavity. By applying an alternating voltage to the metal electrode, the piezoelectric effect causes the film to expand and contract regularly, and vibrate;

[0084] Step S420: selecting a transmission angle constant from a closed interval of the first transmission angle and the second transmission angle, extracting the piezoelectric constant, dielectric constant and elastic constant under different transmission angle constants and inputting them into the finite element simulation model, and outputting the amplitude response result; specifically, the average of the first transmission angle and the second transmission angle is preferably used as the transmission angle constant; and according to the closed interval of [first transmission angle, second transmission angle], a preset number of transmission angle constants can be selected starting from the first transmission angle according to a preset transmission angle selection step, and simulating these transmission angle constants respectively. For each transmission angle constant, the physical parameter matrix is ​​rotated and transformed using the orthogonal transformation matrix and the stress tensor transformation matrix in step S200, and the physical parameter matrix after the rotation transformation is updated to the finite element simulation model, and the amplitude response under each transmission angle constant is recorded;

[0085] As a further preferred technical solution, a selection method based on Bayesian optimization is also provided. For example, 5 transmission angles are randomly selected from a closed interval and finite element simulation is performed, and the amplitude responses are recorded respectively. The RBF kernel function Hou Jian Gaussian process regression model can be expressed as:

[0086]

[0087] In the formula, k(θ i ,θ j ) represents the i-th transmission angle θ i and the jth transmission angle θ j The similarity between them; l represents the length scale parameter, which is used to control the smoothness of the kernel function;

[0088] Then, the predicted mean and predicted variance are obtained by training the Gaussian process regression model, and the expected improvement is finally used as the acquisition function for iterative optimization. In each iteration, the acquisition function values ​​of all transmission angles in the search interval are calculated; the transmission angle that maximizes the acquisition function value is selected for finite element simulation, and the amplitude response is recorded; the training set is updated and the Gaussian process regression model is retrained; the above process is repeated until the maximum number of iterations (for example, 20 times) is reached or the amplitude response is no longer significantly improved; the transmission angle that maximizes the amplitude response is selected from all simulated transmission angles as the optimal transmission angle; where the expression of the acquisition function is:

[0089]

[0090] Wherein, μ(θ) represents the predicted mean value of the transmission angle θ; σ(θ) represents the predicted variance of the transmission angle θ; f* represents the current optimal amplitude response value; Φ represents the cumulative distribution function of the standard normal distribution; σ represents the probability density function of the standard normal distribution; this embodiment can find the optimal transmission angle within a relatively small number of simulations through Bayesian optimization, thus saving a large amount of computing resources;

[0091] Preferably, the sound pressure can also be calculated according to the amplitude response result to extract the sensitivity simulation data, and the expression is:

[0092]

[0093] Wherein, P represents the sound pressure; d0 represents the amplitude response result, that is, the maximum displacement of the transducer during vibration; f0 represents the center frequency of the transducer; S represents the area of ​​the transducer; z represents the preset propagation distance; ρ represents the medium density; Finally, the optimal transmission angle is verified based on the sensitivity simulation data; When the sound pressure is the largest, the PMUT sensitivity is also the highest; After obtaining the optimal transmission angle, the PMUT under the optimal transmission angle can be prepared; For example, according to this method, a piezoelectric ultrasonic transducer based on X-cut lithium niobate (LN) is designed (PMUT), whose longitudinal structure is 0.3μm gold electrode for applying voltage excitation, deposited on the surface of lithium niobate by sputtering or evaporation, 0.7μm X-cut lithium niobate film as piezoelectric layer, 2μm silicon dioxide as insulating layer to prevent short circuit between electrodes, 350μm thick silicon substrate for mechanical support; the direction of the electrode is 29° with the X-axis of the crystal; and a cavity with a length of 80μm and a width of 50μm is opened on the silicon substrate to form a diaphragm; we will package the prepared LN PMUT device and test the receiving sensitivity in water, including the prepared transducer, receiving sensor and signal processing equipment; apply voltage excitation to make the transducer work, and record the signal of the receiving sensor; perform Fourier transform on the received signal to obtain the frequency domain response, so as to determine the bandwidth; see Figure 3 and Figure 4As shown, the signal waveform of the LN PMUT and the bandwidth after Fourier transformation are recorded. It can be understood that the LN PMUT device prepared according to the transmission angle determined by this method has the characteristics of high sensitivity and large bandwidth compared with the traditional method; therefore, this method can effectively improve the sensitivity and bandwidth of the piezoelectric ultrasonic transducer prepared by lithium niobate.

[0094] In summary, the transmission angle evaluation method of the piezoelectric ultrasonic transducer based on lithium niobate provided by the present invention is to rotate and transform the physical parameter matrix of the lithium niobate crystal of the target cut type, and according to the physical parameter matrix after the rotation transformation, extract the first transmission angle with the goal of maximizing the target piezoelectric matrix component, and extract the second transmission angle with the goal of maximizing the electromechanical coupling coefficient, and then determine the optimal transmission angle of the lithium niobate piezoelectric ultrasonic transducer by simulation, and prepare the lithium niobate piezoelectric ultrasonic transducer in the closed interval between the first transmission angle and the second transmission angle, so as to prepare a lithium niobate piezoelectric ultrasonic transducer with large bandwidth and high sensitivity under the target cut type, thereby providing more efficient and more accurate ultrasonic detection and imaging capabilities. This method ensures the scientificity and reliability of the design of the lithium niobate piezoelectric ultrasonic transducer through systematic theoretical calculation, simulation and experimental verification, and finally prepares a piezoelectric ultrasonic transducer with excellent performance, which is suitable for various high-frequency ultrasonic application fields such as medical imaging and non-destructive testing.

[0095] See also Figure 5 , which shows a schematic structural diagram of a piezoelectric ultrasonic transducer transmission angle evaluation system based on lithium niobate provided by an embodiment of the present invention. The technical solution of the second aspect of the present invention provides a piezoelectric ultrasonic transducer transmission angle evaluation system based on lithium niobate, and the system includes:

[0096] A physical parameter acquisition module, configured to acquire a physical parameter matrix of a target cut lithium niobate crystal in a standard coordinate system;

[0097] A rotation transformation module, configured to perform rotation transformation on the physical parameter matrix according to a preset rotation axis and different transmission angles;

[0098] A first transmission angle extraction module is configured to extract a first transmission angle based on the physical parameter matrix after the rotation transformation with the goal of maximizing the target piezoelectric matrix component;

[0099] A second transmission angle extraction module is configured to extract a second transmission angle according to the physical parameter matrix after the rotation transformation with the goal of maximizing the electromechanical coupling coefficient;

[0100] The optimal transmission angle extraction module is configured to construct a transducer simulation model, simulate and extract the optimal transmission angle according to the first transmission angle and the second transmission angle.

[0101] It should be noted that the sequence of the above embodiments of the present invention is only for description and does not represent the advantages and disadvantages of the embodiments. The processes depicted in the accompanying drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0102] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

Claims

1. A method for evaluating the transmission angle of a piezoelectric ultrasonic transducer based on lithium niobate, characterized in that: The method comprises: Obtain the physical parameter matrix of the target cut lithium niobate crystal in the standard coordinate system; Rotate and transform the physical parameter matrix according to the preset rotation axis and different transmission angles; According to the physical parameter matrix after the rotation transformation, a first transmission angle is extracted with the goal of maximizing the target piezoelectric matrix component; According to the physical parameter matrix after the rotation transformation, the second transmission angle is extracted with the goal of maximizing the electromechanical coupling coefficient; A transducer simulation model is constructed, and the optimal transmission angle is simulated and extracted according to the first transmission angle and the second transmission angle.

2. The method for evaluating the transmission angle of a piezoelectric ultrasonic transducer based on lithium niobate according to claim 1, characterized in that: Obtaining the physical parameter matrix of the target cut lithium niobate crystal in the standard coordinate system includes: Obtain the piezoelectric constant matrix, dielectric constant matrix, and elastic constant matrix of the target cut lithium niobate crystal in the standard coordinate system.

3. The method for evaluating the transmission angle of a piezoelectric ultrasonic transducer based on lithium niobate according to claim 2, characterized in that: The rotation transformation of the physical parameter matrix according to the preset rotation axis and different transmission angles includes: The Bond matrix method is used to rotate the piezoelectric constant matrix, dielectric constant matrix and elastic constant matrix respectively.

4. The method for evaluating the transmission angle of a piezoelectric ultrasonic transducer based on lithium niobate according to claim 3, characterized in that: The Bond matrix method is used to rotate the piezoelectric constant matrix, dielectric constant matrix and elastic constant matrix respectively, including: Define the orthogonal transformation matrix and stress tensor transformation matrix according to the preset rotation axis and different transmission angles; The dielectric constant matrix is ​​rotated by using the orthogonal transformation matrix to obtain the rotated dielectric constant matrix; The piezoelectric constant matrix and the elastic constant matrix are respectively rotated and transformed using the stress tensor transformation matrix to obtain the rotated piezoelectric constant matrix and the elastic constant matrix.

5. The method for evaluating the transmission angle of a piezoelectric ultrasonic transducer based on lithium niobate according to claim 4, characterized in that: According to the physical parameter matrix after the rotation transformation, extracting the first transmission angle with the goal of maximizing the target piezoelectric matrix component includes: The transmission angle corresponding to the maximum value of the target piezoelectric matrix component is selected from the rotated piezoelectric constant matrix as the first transmission angle.

6. The method for evaluating the transmission angle of a piezoelectric ultrasonic transducer based on lithium niobate according to any one of claims 1 to 5, characterized in that: According to the physical parameter matrix after the rotation transformation, the second transmission angle is extracted with the goal of maximizing the electromechanical coupling coefficient, including: According to the physical parameter matrix after rotation transformation at different transmission angles, the electromechanical coupling coefficient at different transmission angles is calculated; The second transmission angle is extracted according to the variation relationship between the electromechanical coupling coefficient and the transmission angle.

7. The method for evaluating the transmission angle of a piezoelectric ultrasonic transducer based on lithium niobate according to claim 6, characterized in that: The expression of electromechanical coupling coefficient is: In the formula, represents the electromechanical coupling coefficient; represents the piezoelectric constant after rotation transformation; ε ij represents the dielectric constant after rotation transformation; c ij The elastic constant after rotation transformation; i and j represent the row and column indices in the matrix.

8. The method for evaluating the transmission angle of a piezoelectric ultrasonic transducer based on lithium niobate according to claim 6, characterized in that: Constructing a transducer simulation model, simulating and extracting the optimal transmission angle according to the first transmission angle and the second transmission angle includes: Construct a finite element simulation model of the transducer; Selecting a transmission angle constant from a closed interval between the first transmission angle and the second transmission angle, extracting the piezoelectric constant, dielectric constant and elastic constant under different transmission angle constants and inputting them into a finite element simulation model, and outputting an amplitude response result; The optimal transmission angle is extracted based on the amplitude response results.

9. A piezoelectric ultrasonic transducer transmission angle evaluation system based on lithium niobate, characterized in that: The system comprises: A physical parameter acquisition module, configured to acquire a physical parameter matrix of a target cut lithium niobate crystal in a standard coordinate system; A rotation transformation module, configured to perform rotation transformation on the physical parameter matrix according to a preset rotation axis and different transmission angles; A first transmission angle extraction module is configured to extract a first transmission angle based on the physical parameter matrix after the rotation transformation with the goal of maximizing the target piezoelectric matrix component; A second transmission angle extraction module is configured to extract a second transmission angle according to the physical parameter matrix after the rotation transformation with the goal of maximizing the electromechanical coupling coefficient; The optimal transmission angle extraction module is configured to construct a transducer simulation model, simulate and extract the optimal transmission angle according to the first transmission angle and the second transmission angle.

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