A multi-physics field time-domain modeling method for giant magnetostrictive underwater acoustic transducer

Abstract

The present invention discloses a multi-physics field time-domain modeling method for a giant magnetostrictive underwater acoustic transducer. First, based on the working mechanism of the transducer, a magnetic field model that simultaneously considers the bias magnetic field and the AC drive is constructed; secondly, based on the loss separation theory, an improved Preisach magnetization model is proposed to describe the dynamic magnetization process of the rod and the internal effective magnetic field distribution; thirdly, considering the distribution characteristics of the rod, a multi-degree-of-freedom dynamic model of the transducer is established; finally, based on the modular idea, a comprehensive equivalent circuit model of the transducer's electro-magnetic-mechanical-acoustic multi-physics field coupling is constructed. The comprehensive dynamic time-domain model proposed in the present invention can effectively characterize the impedance characteristics and the output sound wave time-domain characteristics of the transducer, judge whether the output sound wave is normal under different working conditions, and provide theoretical support for the design and optimization of high-power giant magnetostrictive underwater acoustic transducers.

Description

Technical Field

[0001] The invention belongs to the technical field of underwater acoustic transducer modeling, and in particular relates to a multi-physical field time-domain modeling method of a giant magnetostrictive underwater acoustic transducer. Background Art

[0002] Giant magnetostrictive materials (GMM) are a new type of intelligent material. The most famous and widely used one is a commercial material called Terfenol-D. It has been rapidly developed due to its advantages such as large magnetostrictive strain at room temperature, high Curie temperature, small Young's modulus, low sound velocity, and good frequency response characteristics. The giant magnetostrictive transducer is an electric-acoustic energy conversion device that uses Terfenol-D as the core driving oscillator. It has the advantages of high magnetomechanical coupling coefficient, large output strain, fast response speed, and large output force. It plays a key role in the field of seabed resource exploration and underwater target detection. Therefore, its research is of great strategic significance to maintaining my country's marine national defense security.

[0003] The operation of giant magnetostrictive underwater acoustic transducer (GMUAT) involves changes and mutual coupling of multiple physical fields such as electric, magnetic, mechanical and acoustic. The energy conversion process during this period also has strong nonlinear problems. In addition, the input and output responses of the giant magnetostrictive transducer show different nonlinear effects as the input conditions such as excitation amplitude, bias magnetic field, and input frequency change. This nonlinear effect will cause the transducer output to be distorted and its tracking performance to deteriorate, and at the same time cause some other negative effects such as system oscillation and inaccuracy, which will pose a huge challenge to the further application of GMUAT. However, existing research on GMUAT either focuses on the impact analysis of a single input factor (prestress change, narrow range frequency change, etc.) or focuses on studying the characteristics of the GMM material level, and there is little research on the analysis of the output time domain characteristics of the transducer. Therefore, the present invention proposes a multi-physics field time domain modeling method for a giant magnetostrictive underwater acoustic transducer. The modeling method comprehensively considers electro-magnetic-mechanical-acoustic and their interactions, and can describe the output time domain characteristics under conditions such as different excitation amplitudes, different bias magnetism, and a wide range of input frequencies. The method can effectively characterize the impedance characteristics of the transducer and the time domain characteristics of the output sound wave, and determine whether the output sound wave is distorted, providing strong theoretical support for the design and optimization of high-power giant magnetostrictive underwater acoustic transducers. Summary of the invention

[0004] The purpose of the present invention is to provide a multi-physics field time-domain modeling method for a giant magnetostrictive underwater acoustic transducer, which can perform nonlinear modeling on the electro-magnetic-mechanical-acoustic multi-physics field of GMUAT, and then analyze the impedance characteristics and output sound wave time-domain characteristics of the transducer, so as to provide technical support for the transducer to achieve efficient electro-acoustic conversion.

[0005] In order to achieve the purpose of the present invention, the technical solution adopted by the present invention is:

[0006] A multi-physics field time-domain modeling method for a giant magnetostrictive underwater acoustic transducer comprises the following steps:

[0007] S1. Based on the working principle of giant magnetostrictive underwateracoustic transducer (GMUAT), a magnetic field model of the solenoid excitation tube considering the bias magnetic field is established to obtain the AC driving magnetic field intensity H ac and the bias magnetic field strength H bias ;

[0008] S2, according to the AC driving magnetic field strength H ac and the bias magnetic field strength H bias , combined with the basic theory of Preisach magnetization model, a dynamic magnetization intensity model based on the giant magnetostrictive rod material level under the influence of strong bias magnetization is constructed to obtain the total magnetization intensity M;

[0009] S3, taking the total magnetization intensity M as the input of the strain model, considering the influence of the prestress σ on the output strain of the giant magnetostrictive rods (GMR), constructing the giant magnetostrictive strain model at the material level, and then obtaining the strain λ of the GMR;

[0010] S4. According to the obtained λ, a multi-degree-of-freedom dynamic model based on the giant magnetostrictive rope transducer system level is constructed to obtain the output force F and the vibration velocity v;

[0011] S5. Considering the electro-magnetic-mechanical-acoustic multi-physics coupling effect of the giant magnetostrictive underwater acoustic transducer, a cascade T-type comprehensive equivalent circuit is constructed. The output force F and the vibration velocity v are used as the input sources of the equivalent circuit to calculate the sound pressure p ac , emission current response TCR and time domain acoustic wave a c ; In addition, the total mechanical impedance is converted to the electrical end to obtain the total electrical impedance characteristics of the transducer.

[0012] Furthermore, the bias magnetic field in S1 is applied by a permanent magnet (PM), and the driving magnetic field is generated by passing a current through a hollow cylindrical electromagnetic coil. The total magnetic field intensity Htotal (abbreviated as H) is the AC driving magnetic field intensity H ac With the bias magnetic field strength H bias The sum of is expressed as

[0013] H=H total =H bias +H ac (1)

[0014] (a) When a built-in permanent magnet disk is used to generate a bias magnetic field, the bias magnetic field H at any point on the GMR axis at a distance r from the top surface is bias It can be expressed as

[0015]

[0016] Where, m is the residual magnetization intensity of the permanent magnet disk; t p is the thickness of the permanent magnet disk; r p is the radius of the permanent magnet disk, and z is the coordinate in the axial direction of the rod.

[0017] (b) Ignoring the change in relative permeability after the GMR is placed and the reaction of eddy current to the magnetic field, the GMR permeability is generally small, only about 10, while the permeability of other components in the magnetic circuit is very large. Most of the magnetomotive force generated by the driving coil acts on the GMM rod. Therefore, the driving coil can be designed as an air-core coil.

[0018] The parameters of the hollow cylindrical coil mainly include the inner diameter r1, the outer diameter r2 and the length l. Once the three parameters are determined, the shape of the coil can be completely determined, and the magnetic field intensity distribution at a distance r from the axis inside the coil can be obtained as follows:

[0019]

[0020] Among them, n1 is the number of turns per unit length of the coil, n2 is the number of turns per unit height of the coil, and H ac (r) is the magnetic field strength at a point on the coil axis with a distance r from the center. From formula (3), it can be seen that the magnetic density at the center of the coil is the largest, and the magnetic density at both ends decreases rapidly. Therefore, the length of the coil should be slightly larger than the length of the giant magnetostrictive rod.

[0021] Furthermore, in S2, a dynamic magnetization intensity model based on the improvement of the giant magnetostrictive rod material level under the influence of strong bias magnetization is constructed, and the specific process is as follows:

[0022] (a) The Preisach magnetization model theory holds that ferromagnetic materials can be composed of a large number of magnetic dipoles, and the macroscopic properties of the material are expressed as the linear superposition of all magnetic dipoles. Therefore, the definition of the classic Preisach magnetization model (continuous) can be expressed as:

[0023] B(t)=∫∫ T μ(α,β)γ(α,β,H(t))dαdβ (4)

[0024] Among them, H(t) is the system input (here is the magnetic field intensity), B(t) is the system output (here is the magnetic induction intensity), μ(a, β) is the distribution function in the model,

[0025] γ(α, β, H(t)) is defined as the hysteresis operator, and its expression is as shown in equation (5),

[0026] T is the integral triangular area, called the Preisach plane or triangle, and its expression is as shown in formula (6):

[0027]

[0028] Among them, α and β correspond to the “rising” and “falling” thresholds of the system input, respectively, and t - represents the previous moment, therefore, the hysteresis operator γ(α, β, H(t)) can only take the value of +1 or -1;

[0029] T3{(α, β)∈R 2 |α≥β, β≥β0, α≤α0} (6)

[0030] Among them, α0 and β0 correspond to the boundaries of the integral triangle respectively. In practice, α and β cannot be infinite, so β≥β0, α≥α0; without loss of generality, assuming that α0=-β0=R>0, the Preisach triangle plane region Γ has normal values, and outside T, the density function μ is all 0;

[0031] In order to numerically realize the Preisach magnetization model, the Preisach plane needs to be discretized, the discretization interval of the triangular area is L, and the boundaries of the two coordinate axes are R. It can be seen that the total number of discretized hysteresis operators n = L × (L + 1) / 2;

[0032] Therefore, the continuous Preisach model is numerically discretized, and the discrete Preisach model is obtained as follows:

[0033]

[0034] Where B(t) is the output of the discrete Preisach magnetization model system, γ jk (α, β, H(t) is the hysteresis operator, μ jk is the weight of the relay operator, γ jk (α, β, H(t)) is the hysteresis operator, Δs = ΔαΔβ is the area of ​​the discrete region, where Δα = Δβ = 2R / L;

[0035] To further facilitate the solution, the density function can use the Lorentz distribution, factorized-Lorentz distribution and Gauss-Gauss distribution. The present invention takes Gauss-Gauss distribution as an example for analysis, and its analytical expression is:

[0036]

[0037] Among them, N, h0 and σ are the three parameters corresponding to the Gaussian-Gaussian distribution function;

[0038] (b) The output of the Preisach magnetization model is generally the magnetic induction intensity B p , in order to facilitate the superposition with the subsequent dynamic magnetization intensity component, therefore, the present invention uses the magnetization intensity M p represents the output of the static Preisach model, M p With B p The conversion expression is:

[0039]

[0040] Where H is the system input magnetic field strength, μ0 is the magnetic permeability in vacuum, and its value is 4π×10 -7 H / m,B p is the magnetic induction intensity, M p is the static magnetization output by the Preisach magnetization model;

[0041] As the operating frequency of the giant magnetostrictive transducer increases, its dynamic loss can no longer be ignored. Therefore, based on the principle of energy conservation, the present invention decouples the eddy current loss and the abnormal loss by magnetic energy, thereby separating the corresponding magnetization components, and the expression is:

[0042]

[0043] The two terms on the left side of the equation are the magnetic energy expressions of eddy current loss and abnormal loss, and the two terms on the right side of the equation are the actual physical expressions of eddy current loss and abnormal loss. e is the eddy current loss, d M anom is the magnetization intensity component corresponding to the abnormal loss; D is the size of the magnetostrictive material (the diameter for a cylinder); ρ is the resistivity of the material, β is the geometric factor (16 for a cylinder and 6 for a slice); G0 is a constant independent of size; A r is the cross-sectional area of ​​the GMR; H0 is a parameter related to the material domain wall; M is the actual total magnetization intensity; H e is the effective magnetic field inside the GMR, which is expressed as:

[0044] H e =H+αM+Hσ (11)

[0045] Where H is the total magnetic field of the external drive, including the AC excitation H ac and the bias magnetic field H bias ; αM is the magnetic field generated by the interaction between the magnetic domains of the material; H σ The magnetic field induced by the prestress is:

[0046]

[0047] Among them, λ s is the saturation magnetostrictive strain of GMR, M s is the saturation magnetization, σ is the axial prestress of GMR;

[0048] In order to further separate the magnetization components of eddy current loss and abnormal loss, the two terms dH on the left side of equation (10) are e The equivalent transformation is (dH e / dt)×dt, and at the same time, divide both sides of equation (10) by μ0 to obtain:

[0049]

[0050] According to the principle of equal correspondence of sub-items, the transformation of formula (13) can be obtained:

[0051]

[0052] Furthermore, divide both sides of equation (14) by (dH e / dt), we can get:

[0053]

[0054] From formula (15), it can be seen that the eddy current loss and abnormal loss and their corresponding magnetization intensity have been decoupled, which are M ed 、M anom , further, using the superposition principle, combined with the output of the classic Preisach model, the magnetization intensity M p , we can get the dynamic magnetization intensity M of the system dy for:

[0055] M dy =M p +M ed +M anom (16)

[0056] In addition, the bias magnetic field H bias The generated bias magnetization M bias It can be expressed by formula (17)

[0057]

[0058] In formula (17), M s is the saturation magnetization, M an is the hysteresis-free magnetization, a is the hysteresis-free magnetization shape coefficient, and α is the domain wall interaction coefficient.

[0059] Therefore, the total magnetization M in the GMR is

[0060] M=M dy +M bias (18)

[0061] At this point, an improved dynamic magnetization model that takes into account the influence of prestress and bias magnetic field and comprehensively considers loss components such as eddy current and anomaly has been constructed.

[0062] Furthermore, in S3, the magnetostriction model considering the influence of prestressing includes the following specific processes:

[0063] The magnetostrictive model of giant magnetostrictive materials is constructed based on the structural characteristics of the material itself. The magnetostrictive mechanism of the magnetic-mechanical coupling of GMR is quite complex and is easily affected by factors such as stress and lattice anisotropy. It is generally divided into two processes: magnetic domain movement and magnetic domain rotation. When a certain compressive prestress is applied along the GMR axis, the magnetic domain of the material will be mainly distributed in the direction of easy magnetization perpendicular to the axis, and its main magnetization process is magnetic domain rotation. At this time, the relationship between the magnetostrictive strain of the GMM rod and the dynamic magnetization intensity M can be expressed as:

[0064]

[0065] Among them, σ s is the saturated compressive stress, σ max is the maximum stress that the material can withstand, λ s is the saturation magnetostriction, M s is the saturation magnetization.

[0066] Furthermore, in S4, the multi-degree-of-freedom dynamic model based on the giant magnetostrictive transducer system level includes the following specific processes:

[0067] First, considering the connection stiffness of the pressure-applying part and the stiffness characteristics of the disc spring, it is considered that the load is a mass-spring-damping type load; secondly, compared with the rod material, the permanent magnet has a greater stiffness, and it is assumed that there is no deformation during its vibration process; furthermore, the driving vibrator is formed by staggered bonding of GMR and PM disks, and this structure is bound to lead to uneven distribution of GMR bias and driving magnetic field, and its axial strain and vibration velocity will also be different; therefore, the present invention constructs a multi-degree-of-freedom dynamic model of the transducer according to the distribution characteristics of different rod materials;

[0068] PM stiffness is generally much greater than GMR stiffness, so it is assumed that PM does not deform. Therefore, it is only necessary to divide the GMR in the driving vibrator into n equal parts with equal spacing, and PM does not need to be divided into micro-elements. Each GMR is divided into n equal parts, and the length of each micro-element is Δz = l r / n, and Δz is much smaller than the wavelength; the mass of each microelement is M i =M = ρA r Δz, whose stiffness is K i =K=E r A r / Δz, each microelement is regarded as a mass-spring vibration system, and all microelements are connected in series to obtain the distributed parameter model of GMR. In addition, the PM disk and the output mass block in the driving oscillator can also be regarded as a second-order unit composed of mass-stiffness-damping. For the i-th microelement in GMR, according to Newton's second law, its dynamic equation can be obtained as follows:

[0069]

[0070] Among them, x i is the displacement of the ith element. The vibration of the bar is generally a simple harmonic motion, that is, x i Satisfy the following formula:

[0071]

[0072] Among them, v i is the vibration velocity of the ith element. Combined with formula (21), formula (20) is converted into:

[0073]

[0074] Furthermore, the ith infinitesimal element in equation (22) can be converted into an equivalent circuit corresponding thereto. Similarly, the equivalent circuit of the multi-degree-of-freedom dynamic model of the entire system of the giant magnetostrictive transducer can be obtained. Then, by using the electromechanical analogy method and according to Kirchhoff's law, the general formula of the ith term of GMR can be written as:

[0075]

[0076] Among them, v 1.i is the vibration velocity of the ith element, M 1.i , K 1.i 、x 1.i are the equivalent mass, stiffness and displacement of the ith infinitesimal element in the first GMM rod respectively. Combining similar terms in equation (23) and moving the terms together yields:

[0077]

[0078] Among them, the left side of the equation is all vibration velocity terms, and the ones in brackets can be regarded as coefficient terms, which are determined by parameter identification. The right side of the equation is the magnetostrictive force generated after GMR segmentation.

[0079] Furthermore, in S5, a comprehensive equivalent circuit of the electric-magnetic-mechanical-acoustic multi-physical field coupling of the transducer is considered, and the specific process includes:

[0080] (a) The four GMR rods in the giant magnetostrictive underwater acoustic transducer of the present invention are connected in parallel to drive the front and rear mass blocks to vibrate. Therefore, according to the physical characteristics of parallel connection, the force exerted on the front and rear mass blocks is the sum of the output forces of the four rods individually, and the total displacement is the same as the displacement of a single rod;

[0081] The mechanical system of the entire transducer includes the front and rear mass blocks, and four GMR rods. The rods and mass blocks are rigidly connected and can be regarded as a whole. The following boundary conditions exist: the force at the left end of the front mass block is equal to the force at the right end of the magnetostrictive rod, the force at the right end of the rear mass block is equal to the force at the left end of the rod, and the mass block also vibrates longitudinally. Each part can be replaced by a T-type impedance two-port network. By cascading all parts and connecting an equivalent underwater acoustic radiation impedance at the front mass block, a comprehensive equivalent circuit of a complete giant magnetostrictive underwater acoustic transducer can be constructed.

[0082] The impedance of each part in the equivalent circuit can be expressed by the following formula:

[0083]

[0084] Among them, Z ga , Z ha , Z ta are the cross-branch impedances in the T-type equivalent circuit of the rod, front mass block, and rear mass block, respectively. gb , Z hb , Z tb are the vertical branch impedances in the T-type equivalent circuit of the rod, front mass block, and rear mass block, respectively; ρ, c, A, k, and l are density, sound velocity, cross-sectional area, wave number, and length, respectively; subscripts g, h, and t represent the rod, front mass block, and rear mass block, respectively;

[0085] When the transducer works underwater, the sound waves it emits will produce a reaction force on the transducer itself, which is equivalent to adding a radiation impedance to the vibration system. The reaction force is:

[0086]

[0087] Among them, J1() and H1() are the first-order Bessel function of the first kind and the third-order Bessel function, respectively. The subscript w represents water. It is easy to get the acoustic radiation impedance Z of the transducer by the electromechanical analogy. rfor:

[0088] Z r =F r / v r (27)

[0089] Calculate the vibration velocity v of the radiating surface based on the equivalent circuit r Finally, according to the far-field sound pressure calculation formula on the acoustic axis, the sound pressure of the transducer at a distance of d meters can be obtained as:

[0090]

[0091] Among them, ρ w , A h are the water density and the radiation surface, respectively. When the input current I0=1A, the emission current response of the giant magnetostrictive underwater acoustic transducer is:

[0092] TCR=20lg(p(1) / I0)+120(dB) (29)

[0093] To further obtain acoustic wave information, TCR can be converted into the time domain open circuit voltage v of the hydrophone. oc , whose expression is:

[0094]

[0095] Among them, M e is the sensitivity of the hydrophone, v oc is the time domain open circuit voltage of the hydrophone, that is, the time domain acoustic wave signal emitted by the giant magnetostrictive hydroacoustic transducer;

[0096] (b) Calculate the total mechanical impedance Z based on the equivalent circuit in (a) mec After that, the mechanical impedance is calculated to the electrical equivalent circuit. The total impedance of the electrical equivalent circuit is the electrical impedance of the transducer, which is expressed as

[0097] Z e =Z total =Z coil +Z edd +N 2 Z mec (31)

[0098] Among them, Z coil , Z edd are coil impedance and equivalent eddy current impedance respectively, and N is the electromechanical conversion coefficient.

[0099] Compared with the prior art, the advantages of the present invention are:

[0100] The present invention proposes a multi-physics field time-domain modeling method for a giant magnetostrictive underwater acoustic transducer. Through the modular modeling concept, the method clearly analyzes the complex electric-magnetic-mechanical-acoustic energy conversion process of the giant magnetostrictive transducer, explains the time-domain characteristics of the entire physical quantity process, and focuses on the analysis of the output sound wave characteristics of the transducer, which helps to determine whether the sound wave is distorted and provides technical support for the design and optimization of high-power transducers. BRIEF DESCRIPTION OF THE DRAWINGS

[0101] Figure 1 The internal structure diagram of the giant magnetostrictive underwater acoustic transducer of the present invention;

[0102] Figure 2 This is the overall assembly effect diagram of the transducer;

[0103] Figure 3 This is a working principle diagram of the super magnetostrictive underwater acoustic transducer in the present invention;

[0104] Figure 4 It is a flow chart of multi-physics field time domain modeling of the giant magnetostrictive underwater acoustic transducer in the present invention;

[0105] Figure 5 It is a schematic diagram of the mechanical structure of 4 groups of bars;

[0106] Figure 6 This is a schematic diagram of a single-rent bar;

[0107] Figure 7 It is a set of multi-degree-of-freedom dynamic structures of bars;

[0108] Figure 8 It is a comprehensive equivalent circuit of multiple groups of rod longitudinal vibration type underwater acoustic transducers in the present invention;

[0109] Fig. 9 The giant magnetostrictive underwater acoustic transducer of the present invention transmits the current response;

[0110] Fig.10 is the impedance characteristic curve of the giant magnetostrictive underwater acoustic transducer in the present invention;

[0111] Fig.11 It is the time domain acoustic wave characteristic curve of the current under small excitation working condition in the present invention;

[0112] Fig.12 It is the time domain acoustic wave characteristic curve of the output force of the bar under the medium and small excitation working condition of the present invention;

[0113] Fig.13 The time domain acoustic wave characteristic curve of the hydrophone open circuit under the medium and small excitation working condition of the present invention;

[0114] Fig.14 It is the time domain acoustic wave characteristic curve of the current under large excitation condition in the present invention;

[0115] Fig.15 It is the time domain acoustic wave characteristic curve of the output force of the rod under large excitation conditions in the present invention. DETAILED DESCRIPTION

[0116] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined purpose, the multi-physics field time-domain modeling method of a giant magnetostrictive underwater acoustic transducer proposed by the present invention is described in detail as follows in combination with the accompanying drawings and preferred examples:

[0117] In the embodiment, Figure 1 As shown in FIG2 , the giant magnetostrictive underwater acoustic transducer mainly includes components such as a GMM rod 6, a permanent magnet 7, an excitation coil 8, a top rod 12, a circular magnetic conductive yoke 5, a base 11, a disc spring 3 and a shell 10. One group of rods is formed by bonding three Φ30×35mm GMM rods and four Φ30×10mm samarium cobalt permanent magnet blocks. The transducer is composed of a total of four groups of rods to achieve high-power acoustic energy emission.

[0118] Further, if Figure 3 As shown in the figure, the entire energy conversion of the giant magnetostrictive underwater acoustic transducer is specifically as follows: the permanent magnet provides a bias magnetic field for the GMM rod, so that the mechanical frequency of the GMM rod is equal to the frequency of the driving magnetic field, eliminating the "frequency doubling" phenomenon of the GMT output, and the excitation coil is passed with alternating current. According to the principle of electromagnetic induction, an alternating excitation magnetic field is generated, thereby controlling the expansion and contraction changes of the GMM rod in the axial direction, thereby promoting the output displacement and force of the push rod, realizing the conversion of electromagnetic energy to mechanical energy. In addition, the push rod promotes the vibration of the front mass block, thereby emitting sound waves, realizing the conversion of electrical energy to sound energy.

[0119] Furthermore, in this example, a multi-physics field time-domain modeling method of a giant magnetostrictive underwater acoustic transducer is proposed, such as Figure 4 As shown, it is mainly composed of a magnetic field model considering bias, a dynamic magnetization model, a strain model, a structural dynamics model, and a comprehensive equivalent impedance circuit model, and specifically includes the following steps:

[0120] S1. Based on the working mechanism of GMUAT, a solenoid excitation tube magnetic field model considering the bias magnetic field is established, in which the bias magnetic field is provided by a permanent magnet and the AC excitation magnetic field is generated by passing AC current through the coil.

[0121] S2. Combining the basic theory of Preisach magnetization model, an improved dynamic magnetization intensity model based on giant magnetostrictive rod material level is constructed under the influence of strong bias magnetization.

[0122] S3. Considering the influence of prestress on the output strain of giant magnetostrictive rod, a magnetostrictive model at the material level is constructed.

[0123] S4. Based on the distribution characteristics of giant magnetostrictive rods, a multi-degree-of-freedom structural dynamics model based on the giant magnetostrictive transducer system level is constructed.

[0124] S5. Considering the electro-magnetic-mechanical-acoustic multi-physics coupling effect of the giant magnetostrictive underwater acoustic transducer, a cascaded T-type comprehensive equivalent circuit is constructed to calculate the sound pressure p ac , emission current response TCR and time domain acoustic wave a c ; In addition, the total mechanical impedance is converted to the electrical end to obtain the total electrical impedance characteristics of the transducer.

[0125] Furthermore, in step S1, the bias magnetic field is applied by a permanent magnet, and the driving magnetic field is generated by passing a current through a hollow cylindrical electromagnetic coil. The total magnetic field strength H total (abbreviated as H) is the AC driving magnetic field intensity H ac With the bias magnetic field strength H bias The sum of is expressed as

[0126] H=H total =H bias +H ac (1)

[0127] (a) When a built-in permanent magnet disk is used to generate a bias magnetic field, the bias magnetic field H at any point on the GMR axis at a distance r from the top surface is bias It can be expressed as

[0128]

[0129] Where, m is the residual magnetization intensity of the permanent magnet disk; t p is the thickness of the permanent magnet disk; r p is the radius of the permanent magnet disk.

[0130] (b) Ignoring the change in relative permeability after the GMR is placed and the reaction of eddy current to the magnetic field, the GMR permeability is generally small, only about 10, while the permeability of other components in the magnetic circuit is very large. Most of the magnetomotive force generated by the drive coil acts on the GMM rod. Therefore, the drive coil can be designed as a hollow coil. The parameters of the hollow cylindrical coil mainly include the inner diameter r1, the outer diameter r2 and the length l. When the three parameters are determined, the shape of the coil can be completely determined, and the magnetic field intensity distribution at a distance r from the axis in the coil can be obtained as follows:

[0131]

[0132] Among them, n1 is the number of turns per unit length of the coil, n2 is the number of turns per unit height of the coil, and H ac(r) is the magnetic field strength at a point on the coil axis with a distance r from the center. From formula (3), it can be seen that the magnetic density at the center of the coil is the largest, and the magnetic density at both ends decreases rapidly. Therefore, the length of the coil should be slightly larger than the length of the giant magnetostrictive rod.

[0133] Furthermore, in step S2, an improved dynamic magnetization intensity model based on the giant magnetostrictive rod material level under the influence of strong bias magnetization is considered, and the specific process includes:

[0134] (a) The Preisach magnetization model theory holds that ferromagnetic materials can be composed of a large number of magnetic dipoles, and the macroscopic properties of the material are expressed as the linear superposition of all magnetic dipoles. Therefore, the definition of the classical Preisach magnetization model (continuous) can be expressed as

[0135] B(t)=∫∫ T μ(α,β)γ(α,β,H(t))dαdβ (4)

[0136] Where H(t) is the system input (here the magnetic field intensity), B(t) is the system output (here the magnetic induction intensity), μ(α, β) is the distribution function in the model, γ(α, β, H(t)) is defined as the hysteresis operator, and its expression is as shown in equation (5). T is the integral triangular area, called the Preisach plane or triangle, and its expression is as shown in equation (6):

[0137]

[0138] Among them, α and β correspond to the “rising” and “falling” thresholds of the system input, respectively, and t - represents the previous moment, therefore, the hysteresis operator γ(α, β, H(t)) can only take the value of +1 or -1.

[0139]

[0140] Among them, α0 and β0 correspond to the boundaries of the integral triangle respectively. In practice, α and β cannot be infinite, so β≥β0, α≥α0. Without loss of generality, assuming that α0=-β0=R>0, the Preisach triangle plane region T has normal values, and outside T, the density function μ is all 0.

[0141] In this embodiment, in order to numerically realize the Preisach magnetization model, the Preisach plane needs to be discretized, the discretization interval of the triangular area is L, and the boundaries of the two coordinate axes are R. It can be seen that the total number of discretized hysteresis operators n = L × (L + 1) / 2. Therefore, the continuous Preisach model is numerically discretized, and the discrete Preisach model can be obtained as

[0142]

[0143] Where B(t) is the output of the discrete Preisach magnetization model system, γ jk (α, β, H(t)) is the hysteresis operator, μ jk is the weight of the relay operator, Δs=ΔαΔβ is the area of ​​the discrete region, where Δα=Δβ=2R / L. To further facilitate the solution, the density function can be selected from the Lorentz distribution, factorized-Lorentz distribution, and Gaussian-Gaussian distribution. The present invention takes the Gaussian-Gaussian distribution as an example for analysis, and its analytical expression is

[0144]

[0145] Among them, N, h0 and σ are the three parameters corresponding to the Gaussian-Gaussian distribution function.

[0146] (b) The output of the Preisach magnetization model is generally the magnetic induction intensity B p , in order to facilitate the superposition with the subsequent dynamic magnetization intensity component, therefore, the present invention uses the magnetization intensity M p represents the output of the static Preisach model, M p With B p The conversion expression is

[0147]

[0148] Where H is the system input magnetic field strength, μ0 is the magnetic permeability in vacuum, and its value is 4π×10 -7 H / m,B p is the magnetic induction intensity, M p Static magnetization output for the Preisach magnetization model.

[0149] As the operating frequency of the giant magnetostrictive transducer increases, its dynamic loss (mainly eddy current loss and abnormal loss) can no longer be ignored. Therefore, based on the principle of energy conservation, the present invention decouples the eddy current loss and abnormal loss by magnetic energy, thereby separating the corresponding magnetization components, which are expressed as follows:

[0150]

[0151] The two terms on the left side of the equation are the magnetic energy expressions of eddy current loss and abnormal loss, and the two terms on the right side of the equation are the actual physical expressions of eddy current loss and abnormal loss. ed 、M anomare the magnetization intensity components corresponding to eddy current loss and abnormal loss respectively; D is the size of magnetostrictive material (diameter for cylinder); ρ is the resistivity of the material, β is the geometric factor (16 for cylinder and 6 for slice); G0 is a constant independent of size; A r is the cross-sectional area of ​​the GMR; H0 is a parameter related to the material domain wall; M is the actual total magnetization intensity; H e is the effective magnetic field inside the GMR, which is expressed as

[0152] H e =H+αM+H σ (11)

[0153] Where H is the total magnetic field of the external drive (including AC excitation H ac and permanent magnet bias H bias );αM is the magnetic field generated by the interaction between the magnetic domains of the material; H σ The magnetic field induced by the prestress is

[0154]

[0155] Among them, λ s is the saturation magnetostrictive strain of GMR, M s is the saturation magnetization, and σ is the axial prestress of the GMR.

[0156] In this example, in order to further separate the magnetization components of eddy current loss and abnormal loss, the two terms dH on the left side of equation (10) are e The equivalent transformation is (dH e / dt)×dt, divide both sides of equation (10) by μ0, and we can get

[0157]

[0158] In addition, according to the principle of equal correspondence of sub-items, formula (13) can be transformed to obtain

[0159]

[0160] Furthermore, divide both sides of equation (14) by (dH e / dt), we can get

[0161]

[0162] From formula (15), it can be seen that the eddy current loss and abnormal loss and their corresponding magnetization intensity have been decoupled, which are M ed 、M anom , further, using the superposition principle, combined with the output of the classic Preisach model, the magnetization intensity M p , we can get the dynamic magnetization intensity M of the systemdy for

[0163] M dy =M p +M ed +M anom (16) In addition, the bias magnetic field H bias The generated bias magnetization M bias It can be expressed by formula (17)

[0164]

[0165] In formula (17), M s is the saturation magnetization, M an is the hysteresis-free magnetization, a is the hysteresis-free magnetization shape coefficient, and α is the domain wall interaction coefficient.

[0166] Therefore, the total magnetization M in the GMR is

[0167] M=M dy +M bias (18)

[0168] In this example, an improved dynamic magnetization model was constructed that takes into account the influence of prestress and bias magnetic field, and comprehensively considers loss components such as eddy current and anomaly. It can realize accurate simulation of hysteresis characteristics under different working conditions and broaden the working frequency band of the magnetization model.

[0169] Furthermore, in step S3, the magnetostriction modeling method considering the influence of prestressing includes:

[0170] The magnetostrictive model of giant magnetostrictive materials is constructed based on the structural characteristics of the material itself. The magnetostrictive mechanism of the magnetic-mechanical coupling of GMR is quite complex and is easily affected by factors such as stress and lattice anisotropy. It is generally divided into two processes: magnetic domain movement and magnetic domain rotation. When a certain compressive prestress is applied along the GMR axis, the magnetic domain of the material will be mainly distributed in the direction of easy magnetization perpendicular to the axis, and its main magnetization process is magnetic domain rotation. At this time, the relationship between the magnetostrictive strain of the GMM rod and the dynamic magnetization intensity M can be expressed as

[0171]

[0172] Among them, σ s is the saturated compressive stress, σ max is the maximum stress that the material can withstand, λ s is the saturation magnetostriction, M s is the saturation magnetization.

[0173] Further, in step S4, a multi-degree-of-freedom structural dynamics model of the giant magnetostrictive transducer system level is constructed, such as Figure 5-7 As shown, the specific process includes:

[0174] First, considering the connection stiffness of the pressure-applying part and the stiffness characteristics of the disc spring, the load is considered to be a mass-spring-damping type load; second, compared with the rod, the permanent magnet has a greater stiffness, and it is assumed that there is no deformation during its vibration process; third, the driving vibrator is made of GMR and PM discs staggered and bonded together. This structure is bound to lead to uneven distribution of GMR bias and driving magnetic field, and its axial strain and vibration velocity will also be different;

[0175] The present invention constructs a multi-degree-of-freedom dynamic model of the transducer according to the distribution characteristics of different rods, which can achieve accurate characterization of the time-domain output force, displacement or vibration velocity on the overall level of the transducer.

[0176] Furthermore, the PM stiffness is generally much greater than the GMR stiffness, so assuming that the PM does not deform, it is only necessary to divide the GMR in the driving vibrator into n equal parts with equal spacing, and the PM does not need to be divided into micro-elements. Each GMR is divided into n equal parts, and the length of each micro-element is Δz = l r / n, and Δz is much smaller than the wavelength; the mass of each microelement is M i =M = ρA r Δz, whose stiffness is K i =K=E r A r / Δz, each microelement is regarded as a mass-spring vibration system, and all microelements are connected in series to obtain the distributed parameter model of GMR. In addition, the PM disk and output mass block in the driving oscillator can also be regarded as a second-order unit composed of mass-stiffness-damping. Analyzing the i-th microelement in GMR, according to Newton's second law, its dynamic equation can be obtained as

[0177]

[0178] Among them, x i is the displacement of the ith element, the vibration of the bar is simple harmonic motion, then x i Satisfy the following formula

[0179]

[0180] Among them, v i is the vibration velocity of the ith element. Combining equation (21), equation (20) is converted into

[0181]

[0182] Furthermore, the ith infinitesimal element in equation (22) can be converted into its corresponding equivalent circuit. Similarly, the equivalent circuit of the multi-degree-of-freedom dynamic model of the entire giant magnetostrictive transducer system can be obtained. Then, using the electromechanical analogy method and according to Kirchhoff's law, the general formula of the ith term of GMR can be written as

[0183]

[0184] Among them, v 1.i is the vibration velocity of the ith element, M 1.i , K 1.i 、x 1.i are the equivalent mass, stiffness, and displacement of the ith infinitesimal element in the first GMM rod, respectively. Combining similar terms and moving terms in equation (23) yields

[0185]

[0186] Among them, the left side of the equation is all vibration velocity terms, and the ones in brackets can be regarded as coefficient terms, which are determined by parameter identification. The right side of the equation is the magnetostrictive force generated after GMR segmentation.

[0187] In step S5, Figure 8 As shown in the figure, a comprehensive equivalent circuit considering the transducer is constructed, and the specific process includes:

[0188] (a) The four GMR rods in the giant magnetostrictive underwater acoustic transducer in this embodiment are connected in parallel to drive the front and rear mass blocks to vibrate. Therefore, according to the physical characteristics of parallel connection, the force on the front and rear mass blocks is the sum of the output forces of the four rods alone, 4×F rod It is the driving source of the entire circuit, and the total displacement is the same as the displacement of a single rod.

[0189] (b) The mechanical system of the entire transducer includes the front and rear mass blocks, and four GMR rods. The rods and mass blocks are rigidly connected and can be regarded as a whole. The following boundary conditions exist: the force at the left end of the front mass block is equal to the force at the right end of the magnetostrictive rod, the force at the right end of the rear mass block is equal to the force at the left end of the rod, and the mass block also vibrates longitudinally. Each part can be replaced by a T-type impedance two-port network. All parts are cascaded and an equivalent underwater acoustic radiation impedance is connected in series at the front mass block, thus forming a complete comprehensive equivalent circuit of a giant magnetostrictive underwater acoustic transducer.

[0190] Furthermore, the impedance of each part in the equivalent circuit can be expressed as follows:

[0191]

[0192] Among them, Z ga , Z ha , Z taare the cross-branch impedances in the T-type equivalent circuit of the rod, front mass block, and rear mass block, respectively. gb , Z hb , Z tb are the vertical branch impedances in the T-type equivalent circuit of the rod, the front mass block and the rear mass block, respectively. ρ, c, A, k and l are the density, sound velocity, cross-sectional area, wave number and length, respectively. The subscripts g, h and t represent the rod, the front mass block and the rear mass block, respectively.

[0193] When the transducer works underwater, the sound waves it emits will produce a reaction force on the transducer itself, which is equivalent to adding a radiation impedance to the vibration system. The reaction force is

[0194]

[0195] Among them, J1() and H1() are the first-order Bessel function of the first kind and the third-order Bessel function, respectively. The subscript w represents water. It is easy to get the acoustic radiation impedance Z of the transducer by the electromechanical analogy. r for

[0196] Z r =F r / v r (27)

[0197] Calculate the vibration velocity v of the radiating surface based on the equivalent circuit r Then, according to the far-field sound pressure calculation formula on the acoustic axis, the sound pressure of the transducer at a distance of d meters can be obtained as

[0198]

[0199] Among them, ρ w , A h are the water density and the radiation surface respectively. When the input current I0=1A, the emission current response of the giant magnetostrictive underwater acoustic transducer is

[0200] TCR=20lg(p(1) / I0)+120(dB) (29)

[0201] The TCR of GMUAT calculated based on the equivalent circuit is compared with the experimental data, such as Fig. 9 As shown, the error at the resonance point (1000 Hz) is 0.5%, and the maximum error in the test frequency band of 800-1300 Hz is 2%, which proves that the present embodiment can effectively reflect the emission current response of the transducer.

[0202] (b) Further, the total mechanical impedance Z is calculated based on the equivalent circuit in (a). mec After that, the mechanical impedance is calculated to the electrical equivalent circuit. The total impedance of the electrical equivalent circuit is the electrical impedance of the transducer, which is expressed as

[0203] Z e =Z total =Z coil +Z eddy +N 2 Z mec (32)

[0204] Among them, Z coil , Z eddy are coil impedance and equivalent eddy current impedance respectively, and N is the electromechanical conversion coefficient.

[0205] Therefore, it is easy to obtain the electrical impedance characteristic curve of the equivalent circuit and compare it with the experimental impedance, such as Fig.10 As shown, it can be seen that the result is in good agreement with the experiment near the resonance point, and the maximum error in the entire test frequency band of 800-1300 Hz is 8.3%, which further confirms that the comprehensive equivalent circuit in this embodiment can effectively reflect the impedance characteristics of the giant magnetostrictive underwater acoustic transducer.

[0206] Furthermore, in order to obtain the acoustic information, TCR can also use the time domain open circuit voltage v of the hydrophone oc

[0207] To solve, the expression is

[0208] TCR=20lg(v oc ×d)-M e (30)

[0209] Further comparison of equations (29) and (30) yields the hydrophone open circuit voltage v oc ,for

[0210]

[0211] Among them, M e is the sensitivity of the hydrophone, which is generally defined as a negative value, v oc is the time domain open circuit voltage of the hydrophone, that is, the time domain acoustic wave signal emitted by the giant magnetostrictive hydroacoustic transducer.

[0212] Furthermore, the input and output characteristics of GMUAT are focused on. In this embodiment, the time domain waveform signals of input current, output force and sound wave under two typical working conditions are plotted, such as Figure 11-15 As shown, under small excitation conditions, the current amplitude here is 1A, the output force and the sound wave waveform have good sinusoidality, and the distortion is small. However, under large excitation conditions, the output force and the sound wave show "fat head" and "double frequency" phenomena, and the waveform is obviously distorted, which can effectively reflect the sound wave output situation.

[0213] A multi-physics field time-domain modeling method for a giant magnetostrictive underwater acoustic transducer proposed in this embodiment mainly includes: a magnetic field calculation method considering a bias magnetic field; an improved dynamic magnetization intensity model at the GMM material level considering the influence of strong bias magnetism; a magnetostriction calculation method considering the influence of prestress; a multi-degree-of-freedom dynamic model at the GMUAT system level based on the distribution characteristics of giant magnetostrictive rods; and a cascaded T-type comprehensive equivalent circuit considering the electro-magnetic-mechanical-acoustic multi-physics field coupling effect of the GMUAT.

[0214] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any technician familiar with the profession, without departing from the scope of the technical solution of the present invention, makes any simple modifications, equivalent changes and modifications to the above embodiments based on the technical essence of the present invention, which still fall within the scope of the technical solution of the present invention.

Claims

1. A multi-physics field time-domain modeling method for a giant magnetostrictive underwater acoustic transducer, characterized in that: The following steps are involved: S1. Based on the working principle of giant magnetostrictive underwater acoustic transducer (GMUAT), a magnetic field model of the solenoid excitation tube considering the bias magnetic field is established to obtain the AC driving magnetic field intensity H ac and the bias magnetic field strength H bias ; S2, according to the AC driving magnetic field strength H ac and the bias magnetic field strength H bias , combined with the basic theory of Preisach magnetization model, a dynamic magnetization intensity model based on the giant magnetostrictive rod material level under the influence of strong bias magnetization is constructed to obtain the total magnetization intensity M; S3, taking the total magnetization intensity M as the input of the strain model, considering the influence of the prestress σ on the output strain of the giant magnetostrictive rods (GMR), constructing the giant magnetostrictive strain model at the material level, and then obtaining the strain λ of the GMR; S4. According to the obtained λ, a multi-degree-of-freedom dynamic model based on the giant magnetostrictive rope transducer system level is constructed to obtain the output force F and the vibration velocity v; S5. Considering the electro-magnetic-mechanical-acoustic multi-physics coupling effect of the giant magnetostrictive underwater acoustic transducer, a cascade T-type comprehensive equivalent circuit is constructed. The output force F and the vibration velocity v are used as the input sources of the equivalent circuit to calculate the sound pressure p ac , emission current response TCR and time domain acoustic wave a c ; In addition, the total mechanical impedance is converted to the electrical end to obtain the total electrical impedance characteristics of the transducer.

2. The multi-physics field time-domain modeling method of a giant magnetostrictive underwater acoustic transducer according to claim 1, characterized in that: The bias magnetic field in S1 is applied by permanent magnets (PM), while the driving magnetic field is generated by passing current through the hollow cylindrical electromagnetic coil. The total magnetic field intensity H total (abbreviated as H) is the AC driving magnetic field intensity H ac With the bias magnetic field strength H bias The sum of is expressed as H=H total =H bias +H ac (1) (a) When a built-in permanent magnet disk is used to generate a bias magnetic field, the bias magnetic field H at any point on the GMR axis at a distance r from the top surface is bias It can be expressed as Where, m is the residual magnetization intensity of the permanent magnet disk; t p is the thickness of the permanent magnet disk; r p is the radius of the permanent magnet disk, and z is the coordinate in the axial direction of the rod. (b) Ignoring the change in relative permeability after the GMR is placed and the reaction of eddy current to the magnetic field, the GMR permeability is generally small, only about 10, while the permeability of other components in the magnetic circuit is very large. Most of the magnetomotive force generated by the driving coil acts on the GMM rod. Therefore, the driving coil can be designed as an air-core coil. The parameters of the hollow cylindrical coil mainly include the inner diameter r1, the outer diameter r2 and the length l. Once the three parameters are determined, the shape of the coil can be completely determined, and the magnetic field intensity distribution at a distance r from the axis inside the coil can be obtained as follows: Among them, n1 is the number of turns per unit length of the coil, n2 is the number of turns per unit height of the coil, and H ac (r) is the magnetic field strength at a point on the coil axis with a distance r from the center. From formula (3), it can be seen that the magnetic density at the center of the coil is the largest, and the magnetic density at both ends decreases rapidly. Therefore, the length of the coil should be slightly larger than the length of the giant magnetostrictive rod.

3. The multi-physics field time-domain modeling method of a giant magnetostrictive underwater acoustic transducer according to claim 1, characterized in that: In S2, a dynamic magnetization intensity model based on the improvement of the giant magnetostrictive rod material level under the influence of strong bias magnetization is constructed, and the specific process is as follows: (a) The Preisach magnetization model theory holds that ferromagnetic materials can be composed of a large number of magnetic dipoles, and the macroscopic properties of the material are expressed as the linear superposition of all magnetic dipoles. Therefore, the definition of the classic Preisach magnetization model (continuous) can be expressed as: B(t)=∫∫ T μ(α,β)γ(α,β,H(t))dαdβ (4) Among them, H(t) is the system input (here is the magnetic field intensity), B(t) is the system output (here is the magnetic induction intensity), μ(α,β) is the distribution function in the model, γ(α, β, H(t)) is defined as the hysteresis operator, and its expression is as shown in equation (5), T is the integral triangular area, called the Preisach plane or triangle, and its expression is as shown in formula (6): Among them, α and β correspond to the "rising" and "falling" thresholds of the system input, respectively, and t - represents the previous moment, therefore, the hysteresis operator γ(α, β, H(t)) can only take the value of +1 or -1; T≡{(α,β)∈R 2 |α≥β,β≥β0,α≤α0} (6) Among them, α0 and β0 correspond to the boundaries of the integral triangle respectively. In practice, α and β cannot be infinite, so β≥β0, α≥α0; without loss of generality, assuming that α0=-β0=R>0, the Preisach triangle plane area T has normal values, and outside T, the density function μ is all 0; In order to numerically realize the Preisach magnetization model, the Preisach plane needs to be discretized, the discretization interval of the triangular area is L, and the boundaries of the two coordinate axes are R. It can be seen that the total number of discretized hysteresis operators n = L × (L + 1) / 2; Therefore, the continuous Preisach model is numerically discretized, and the discrete Preisach model is obtained as follows: Where B(t) is the output of the discrete Preisach magnetization model system, γ jk (α, β, H(t)) is the hysteresis operator, μ jk is the weight of relayoperator, γ jk (α, β, H(t)) is the hysteresis operator, Δs = ΔαΔβ is the area of ​​the discrete region, where Δα = Δβ = 2R / L; To further facilitate the solution, the density function can use the Lorentz distribution, factorized-Lorentz distribution and Gauss-Gauss distribution. The present invention takes Gauss-Gauss distribution as an example for analysis, and its analytical expression is: Among them, N, h0 and σ are the three parameters corresponding to the Gaussian-Gaussian distribution function; (b) The output of the Preisach magnetization model is generally the magnetic induction intensity B p , in order to facilitate the superposition with the subsequent dynamic magnetization intensity component, therefore, the present invention uses the magnetization intensity M p represents the output of the static Preisach model, M p With B p The conversion expression is: Where H is the system input magnetic field strength, μ0 is the magnetic permeability in vacuum, and its value is 4π×10 -7 H / m,B p is the magnetic induction intensity, M p is the static magnetization output by the Preisach magnetization model; As the operating frequency of the giant magnetostrictive transducer increases, its dynamic loss can no longer be ignored. Therefore, based on the principle of energy conservation, the present invention decouples the eddy current loss and the abnormal loss by magnetic energy, thereby separating the corresponding magnetization components, and the expression is: The two terms on the left side of the equation are the magnetic energy expressions of eddy current loss and abnormal loss, and the two terms on the right side of the equation are the actual physical expressions of eddy current loss and abnormal loss. e is the eddy current loss, d M anom is the magnetization intensity component corresponding to the abnormal loss; D is the size of the magnetostrictive material (the diameter for a cylinder); ρ is the resistivity of the material, β is the geometric factor (16 for a cylinder and 6 for a slice); G0 is a constant independent of size; A r is the cross-sectional area of ​​the GMR; H0 is a parameter related to the material domain wall; M is the actual total magnetization intensity; H e is the effective magnetic field inside the GMR, which is expressed as: H e =H+αM+H σ (11) Where H is the total magnetic field of the external drive, including the AC excitation H ac and the bias magnetic field H bias ; αM is the magnetic field generated by the interaction between the magnetic domains of the material; H σ The magnetic field induced by the prestress is: Among them, λ s is the saturation magnetostrictive strain of GMR, M s is the saturation magnetization, σ is the axial prestress of GMR; In order to further separate the magnetization components of eddy current loss and abnormal loss, the two terms dH on the left side of equation (10) are e The equivalent transformation is (dH e / dt)×dt, and at the same time, divide both sides of equation (10) by μ0 to obtain: According to the principle of equal correspondence of sub-items, the transformation of formula (13) can be obtained: Furthermore, divide both sides of equation (14) by (dH e / dt), we can get: From formula (15), it can be seen that the eddy current loss and abnormal loss and their corresponding magnetization intensity have been decoupled, which are M ed 、M anom , further, using the superposition principle, combined with the output of the classic Preisach model, the magnetization intensity M p , we can get the dynamic magnetization intensity M of the system dy for: M dy =M p +M ed +M anom (16) In addition, the bias magnetic field H bias The generated bias magnetization M bias It can be expressed by formula (17) In formula (17), M s is the saturation magnetization, M an is the hysteresis-free magnetization, a is the hysteresis-free magnetization shape coefficient, and α is the domain wall interaction coefficient. Therefore, the total magnetization M in the GMR is M=M dy +M bias (18) At this point, an improved dynamic magnetization model that takes into account the influence of prestress and bias magnetic field and comprehensively considers loss components such as eddy current and anomaly has been constructed.

4. The multi-physics field time-domain modeling method of a giant magnetostrictive underwater acoustic transducer according to claim 1, characterized in that: In S3, the magnetostrictive model considering the influence of prestress includes the following specific processes: The magnetostrictive model of giant magnetostrictive materials is constructed based on the structural characteristics of the material itself. The magnetostrictive mechanism of the magnetic-mechanical coupling of GMR is quite complex and is easily affected by factors such as stress and lattice anisotropy. It is generally divided into two processes: magnetic domain movement and magnetic domain rotation. When a certain compressive prestress is applied along the GMR axis, the magnetic domain of the material will be mainly distributed in the direction of easy magnetization perpendicular to the axis, and its main magnetization process is magnetic domain rotation. At this time, the relationship between the magnetostrictive strain of the GMM rod and the dynamic magnetization intensity M can be expressed as: Among them, σ s is the saturated compressive stress, σ max is the maximum stress that the material can withstand, λ s is the saturation magnetostriction, M s is the saturation magnetization.

5. The multi-physics field time-domain modeling method of a giant magnetostrictive underwater acoustic transducer according to claim 1, characterized in that: In S4, the multi-degree-of-freedom dynamic model based on the giant magnetostrictive transducer system level includes the following specific processes: First, considering the connection stiffness of the pressure-applying part and the stiffness characteristics of the disc spring, it is considered that the load is a mass-spring-damping type load; secondly, compared with the rod material, the permanent magnet has a greater stiffness, and it is assumed that there is no deformation during its vibration process; furthermore, the driving vibrator is formed by staggered bonding of GMR and PM disks, and this structure is bound to lead to uneven distribution of GMR bias and driving magnetic field, and its axial strain and vibration velocity will also be different; therefore, the present invention constructs a multi-degree-of-freedom dynamic model of the transducer according to the distribution characteristics of different rod materials; PM stiffness is generally much greater than GMR stiffness, so it is assumed that PM does not deform. Therefore, it is only necessary to divide the GMR in the driving vibrator into n equal parts with equal spacing, and PM does not need to be divided into micro-elements. Each GMR is divided into n equal parts, and the length of each micro-element is Δz = l r / n, and Δz is much smaller than the wavelength; the mass of each microelement is M i =M = ρA r Δz, whose stiffness is K i =K=E r A r / Δz, each microelement is regarded as a mass-spring vibration system, and all microelements are connected in series to obtain the distributed parameter model of GMR. In addition, the PM disk and the output mass block in the driving oscillator can also be regarded as a second-order unit composed of mass-stiffness-damping. For the i-th microelement in GMR, according to Newton's second law, its dynamic equation can be obtained as follows: Among them, x i is the displacement of the ith element. The vibration of the bar is generally a simple harmonic motion, that is, x i Satisfy the following formula: Among them, v i is the vibration velocity of the ith element. Combined with formula (21), formula (20) is converted into: Furthermore, the ith infinitesimal element in equation (22) can be converted into an equivalent circuit corresponding thereto. Similarly, the equivalent circuit of the multi-degree-of-freedom dynamic model of the entire system of the giant magnetostrictive transducer can be obtained. Then, by using the electromechanical analogy method and according to Kirchhoff's law, the general formula of the ith term of GMR can be written as: Among them, v 1.i is the vibration velocity of the ith element, M 1.i , K 1.i 、x 1.i are the equivalent mass, stiffness and displacement of the ith infinitesimal element in the first GMM rod respectively. Combining similar terms in equation (23) and moving the terms together yields: Among them, the left side of the equation is all vibration velocity terms, and the ones in brackets can be regarded as coefficient terms, which are determined by parameter identification. The right side of the equation is the magnetostrictive force generated after GMR segmentation.

6. The multi-physics field time-domain modeling method of a giant magnetostrictive underwater acoustic transducer according to claim 1, characterized in that: In S5, a comprehensive equivalent circuit of the electric-magnetic-mechanical-acoustic multi-physical field coupling of the transducer is considered, and the specific process includes: (a) The four GMR rods in the giant magnetostrictive underwater acoustic transducer of the present invention are connected in parallel to drive the front and rear mass blocks to vibrate. Therefore, according to the physical characteristics of parallel connection, the force exerted on the front and rear mass blocks is the sum of the output forces of the four rods individually, and the total displacement is the same as the displacement of a single rod; The mechanical system of the entire transducer includes the front and rear mass blocks, and four GMR rods. The rods and mass blocks are rigidly connected and can be regarded as a whole. The following boundary conditions exist: the force at the left end of the front mass block is equal to the force at the right end of the magnetostrictive rod, the force at the right end of the rear mass block is equal to the force at the left end of the rod, and the mass block also vibrates longitudinally. Each part can be replaced by a T-type impedance two-port network. All parts are cascaded, and an equivalent underwater acoustic radiation impedance is connected in series at the front mass block to form a complete comprehensive equivalent circuit of a giant magnetostrictive underwater acoustic transducer. The impedance of each part in the equivalent circuit can be expressed by the following formula: Among them, Z ga , Z ha , Z ta are the cross-branch impedances in the T-type equivalent circuit of the rod, front mass block, and rear mass block, respectively. gb , Z hb , Z tb are the vertical branch impedances in the T-type equivalent circuit of the rod, front mass block, and rear mass block, respectively; ρ, c, A, k, and l are density, sound velocity, cross-sectional area, wave number, and length, respectively; subscripts g, h, and t represent the rod, front mass block, and rear mass block, respectively; When the transducer works underwater, the sound waves it emits will produce a reaction force on the transducer itself, which is equivalent to adding a radiation impedance to the vibration system. The reaction force is: Among them, J1() and H1() are the first-order Bessel function of the first kind and the third-order Bessel function, respectively. The subscript w represents water. It is easy to get the acoustic radiation impedance Z of the transducer by the electromechanical analogy. r for: With r =F r / in r (27) Calculate the vibration velocity v of the radiating surface based on the equivalent circuit r Then, according to the far-field sound pressure calculation formula on the acoustic axis, the sound pressure of the transducer at a distance of d meters can be obtained as: Among them, ρ w , A h are the water density and the radiation surface, respectively. When the input current I0=1A, the emission current response of the giant magnetostrictive underwater acoustic transducer is: TCR=20lg(p(1) / I0) / 120(dB) (29) To further obtain acoustic wave information, TCR can be converted into the time domain open circuit voltage v of the hydrophone. oc , whose expression is: Among them, M e is the sensitivity of the hydrophone, v oc is the time domain open circuit voltage of the hydrophone, that is, the time domain acoustic wave signal emitted by the giant magnetostrictive hydroacoustic transducer; (b) Calculate the total mechanical impedance Z based on the equivalent circuit in (a) mec After that, the mechanical impedance is calculated to the electrical equivalent circuit. The total impedance of the electrical equivalent circuit is the electrical impedance of the transducer, which is expressed as WITH e =Z total =Z coil +Z edd +N 2 WITH mec (31) Among them, Z coil , Z edd are coil impedance and equivalent eddy current impedance respectively, and N is the electromechanical conversion coefficient.

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