A transducer optimization method based on backing parameter simulation

Abstract

The application discloses a transducer optimization method based on backing parameter simulation; the method is as follows: 1, constructing a geometric model for transducer simulation; 2, setting the density, Young's modulus and Poisson's ratio of the backing and the composite matching layer; 3, selecting the physical field of the geometric model, determining the multi-physical field involved in the physical field boundary; 4, exciting the piezoelectric element using an impulse voltage; 5, simulating the terminal voltage data of the transducer; 6, calculating the sensitivity and bandwidth of the transducer; 7, adjusting the material type and thickness of the backing, and re-executing steps 1-6; preferably, the material type and thickness of the final backing; 8, using the backing material type and thickness obtained in step 7 to construct the transducer. The application optimizes the substrate thickness and material of the transducer through the simulation method of constructing a geometric model, thereby obtaining a transducer that meets the design requirements, and can significantly reduce the research and development time cost and material cost of the transducer.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of manufacturing ultrasonic transducers, and particularly relates to a transducer optimization method based on backer parameter simulation. BACKGROUND

[0002] An ultrasonic transducer is widely used in the field of ultrasonic, and a structure of the ultrasonic transducer is shown in FIG. 1. Figure 1 The piezoelectric element functions to receive an electric signal and convert electric energy into acoustic energy, and to receive acoustic signals and convert acoustic energy into electric energy. The matching layer functions to realize impedance transition from the piezoelectric element to a medium to be detected, and improve the sensitivity and energy transmission efficiency of the ultrasonic transducer. The backer functions to reduce waveform tailing, improve the axial resolution of the transducer, provide a heat dissipation channel, and provide physical support for the piezoelectric element.

[0003] In ultrasonic nondestructive testing, the pulse width of the transducer directly affects the axial resolution. When the piezoelectric element is excited by a pulse, acoustic energy is not only radiated forward, but also backward. If the backward radiated acoustic energy is reflected back, serious clutter interference will be caused, resulting in a waveform with serious tailing produced by the transducer. In order to eliminate such clutter interference, in addition to reducing the pulse width of the excitation signal and using a piezoelectric material with a low Q value, a high-impedance and high-attenuation backer layer is usually added to the back side of the piezoelectric element. m

[0004] The method of adding the backer usually includes two methods: (1) bonding method: after the backer block is made, glue is used to realize the close combination of the backer and the piezoelectric element; and (2) injection molding method: the backer is made by using a mold forming method and adding fillers to the epoxy resin, and the close combination of the piezoelectric element and the backer is realized after the epoxy resin is cured.

[0005] Sensitivity and bandwidth are two important indicators for measuring an ultrasonic transducer, and the three parts of the ultrasonic transducer will affect the indicators. It is inconvenient to separately study the influence of the backer on the sensitivity and the bandwidth. For the injection molding method, the piezoelectric element is expensive, and once the backer is injection molded, only the thickness of the backer can be adjusted. Therefore, under the premise of fixed backer material, the most suitable backer thickness is searched, which increases the research and development cost of the ultrasonic transducer to a certain extent. SUMMARY

[0006] The application aims to provide a transducer optimization method based on backer parameter simulation.

[0007] A transducer optimization method based on backer parameter simulation includes the following steps:

[0008] ​Step one, constructing a geometric model for transducer simulation; the geometric model contains a transducer composed of a backing, a piezoelectric element and a composite matching layer arranged in sequence.

[0009] Step two, setting the density, Young's modulus and Poisson's ratio of the backing and the composite matching layer.

[0010] Step three, selecting physical fields for the geometric model, determining the multi-physical fields involved in the physical field boundary;

[0011] Step four, in the geometric model, using a pulse voltage to excite the piezoelectric element.

[0012] Step five, using simulation software to simulate the geometric model to obtain the terminal voltage data of the transducer.

[0013] Step six, after exporting the terminal voltage data obtained in step five, the sensitivity and bandwidth of the transducer are calculated.

[0014] Step seven, adjusting the material type and thickness of the backing, and re-executing steps one to six; obtaining the material type and thickness of the different backings and their corresponding transducer sensitivity and bandwidth. Select the combination of the material type and thickness of the backing whose transducer sensitivity and bandwidth both meet the requirements as the final material type and thickness of the backing.

[0015] Step eight, using the material type and thickness of the backing obtained in step seven to construct the transducer.

[0016] As a preferred, the geometric model in step one further includes a water area and a perfect matching layer attached together. The composite matching layer in the transducer is attached to the water area.

[0017] As a preferred, the geometric model in step one is established by COMSOL.

[0018] As a preferred, the physical fields in step three include electrostatics, solid mechanics, piezoelectric effect, pressure acoustics-transient. The multi-physical fields include acoustic-structural boundary.

[0019] As a preferred, in step four, the waveform of the pulse voltage v(t) is:

[0020]

[0021] Wherein, T0 is the clock period corresponding to the center frequency of the transducer; t is time.

[0022] As a preferred, the sensitivity Srel of the transducer in step six is:

[0023]

[0024] Wherein, Uc U is the peak-to-peak voltage before echo amplification from the specified reflector; U a U is the peak-to-peak voltage applied to the piezoelectric element.

[0025] As a preference, the width BW of the transducer in step six is:

[0026] BW = (fu - f1) / fc * 100%

[0027] Wherein, f1 and f u are two frequencies of the maximum pulse-echo response (-6dB) respectively; f c is the pulse-echo center frequency.

[0028] The expression of the pulse-echo center frequency f c is as follows:

[0029] f c = (f1 + f u ) / 2.

[0030] The present application has the beneficial effects that:

[0031] The present application, by constructing a geometric model for simulation, optimizes the substrate thickness and material of the transducer, thereby obtaining a transducer that meets the design requirements, and can significantly reduce the research and development time cost and material cost of the transducer. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a schematic diagram of the geometric model constructed in the present application.

[0033] Figure 2 is a schematic diagram of the setting of the physical field, multi-physical field and boundary conditions of the geometric model in the present application.

[0034] Figure 3 is a time-frequency diagram corresponding to the transducer using different thicknesses of backer a in the embodiment of the present application.

[0035] Figure 4 is a graph of the relationship between the transducer sensitivity, bandwidth and backer a thickness in the embodiment of the present application.

[0036] Figure 5 is a time-frequency diagram corresponding to the transducer using different thicknesses of backer b in the embodiment of the present application.

[0037] Figure 6 is a graph of the relationship between the transducer sensitivity, bandwidth and backer b thickness in the embodiment of the present application.

[0038] Figure 7 is a time-frequency diagram corresponding to the transducer using different thicknesses of backer c in the embodiment of the present application.

[0039] Figure 8 A graph of the relationship between the transducer sensitivity, bandwidth and the backing c thickness in the embodiment of the present application.

[0040] Figure 9 A performance comparison graph of three backings set in the embodiment of the present application. DETAILED DESCRIPTION

[0041] The present application is further described below in conjunction with the accompanying drawings.

[0042] A transducer optimization method based on backing parameter simulation, comprising the following steps:

[0043] Step one, set the material type and thickness of the backing; use the geometric module in the COMSOL software to establish a geometric model for simulation, as shown in Figure 1 The geometric model includes a transducer, a water area and a perfect matching layer. The transducer includes a backing, a piezoelectric element and a composite matching layer arranged in sequence.

[0044] Step two, import the pre-set density, Young's modulus and Poisson's ratio of the matching layer and the backing into the material library of the COMSOL software.

[0045] Step three, as shown in Figure 2 , select the physical field for each part in the geometric model, and determine the multi-physical field involved in the physical field boundary; the physical field includes electrostatic, solid mechanics, piezoelectric effect, pressure acoustics-transient. The multi-physical field includes acoustic-structural boundary.

[0046] Step four, in the geometric model, use a pulse voltage to excite the piezoelectric element, and the waveform of the pulse voltage v(t) used is:

[0047]

[0048] Wherein, T0 is the clock period corresponding to the center frequency of the transducer; t is time.

[0049] Step five, select the transient analysis module in the COMSOL software, determine the simulation time and step size, and then perform simulation calculation to obtain the terminal voltage data of the transducer.

[0050] Step six, after exporting the terminal voltage data obtained in step five, perform sensitivity and bandwidth calculation of the transducer.

[0051] The sensitivity is calculated as follows: the transducer is excited with a burst of constant amplitude and variable carrier frequency. The transducer, when excited, emits an ultrasonic pulse in the forward direction to a standard reflector located at a distance of one near field length from the transducer. The peak-to-peak voltage of the excitation pulse and the peak-to-peak voltage of the first echo received by the transducer are used to determine the pulse-echo sensitivity of the transducer. In addition, the first echo signal is analyzed to determine the center frequency and bandwidth of the transducer, as follows:

[0052] The relative pulse-echo sensitivity Srel is:

[0053]

[0054] where U c is the peak-to-peak voltage of the first echo from the specified reflector before amplification; U a is the peak-to-peak voltage applied to the piezoelectric element.

[0055] The pulse-echo center frequency fc is:

[0056] f c = (f1+f u ) / 2

[0057] where f1 and f u are the two frequencies at which the maximum pulse-echo response (-6 dB) occurs.

[0058] The relative bandwidth BW is:

[0059] BW = (fu-f1) / fc*100%

[0060] Step seven, adjust the material type and thickness of the backing, and re-perform steps one to six; obtain the material type and thickness of the different backings and their corresponding transducer sensitivity and bandwidth. Select the combination of the material type and thickness of the backing whose transducer sensitivity and bandwidth both meet the requirements as the final material type and thickness of the backing.

[0061] Step eight, use the material type and thickness of the backing obtained in step seven to construct the transducer.

[0062] COMSOL 5.6 multi-physics simulation is based on the finite element theory. A tree-shaped operation index is set in the software platform, which realizes all the steps involved in the modeling workflow from top to bottom: multi-physics selection, geometry modeling, material property definition, physical field definition, meshing, model solving, and post-processing of the results. All steps can be operated in a graphical interface without the need to write code to realize user-defined differential equations that can be coupled with physical field interfaces. COMSOL has a series of predefined physical field interfaces, involving structural mechanics and electrostatics. These interfaces can be freely combined and coupled with professional models to make multi-physics simulation more simple.

[0063] For this transducer optimization method, the following specific optimization cases are provided:

[0064] The sensitivity requirement is set to be above -42dB; the bandwidth requirement is greater than 30%, and three types of materials with different thicknesses of backings are provided for the design of the transducer. The sensitivity and bandwidth of the transducer under different backing types and different backing thicknesses are compared. The three backings are backing a, b, and c, and their performance parameters are shown in Table 1:

[0065] Table 1

[0066] Class Density (kg / m3 3 )]]> Young's modulus (GPa) Poisson's ratio Backing a 2867.2 5.86 0.39 Backing b 2797 7.57 0.33 Backing c 2666 6.79 0.38

[0067] The three backings are used with a matching layer with a density of 2921 kg / m 3 , a Young's modulus of 13.716 GPa, and a Poisson's ratio of 0.317.

[0068] Set alternative group 1: select backing a as the backing of the transducer, and set 5 thicknesses, 1mm, 5.5mm, 10mm, 14.5mm, and 19mm. The waveforms received by the transducers with five different backing thicknesses are shown in Figure 3 It can be seen that the thickness of the backing has an effect on the received waveform, including the shape of the pulse waveform and the amplitude of each peak of the waveform. The sensitivity and bandwidth obtained after frequency spectrum analysis of the received waveform are shown in Figure 4 The sensitivity of the transducer increases first and then decreases with the increase of the thickness of the backing, and when the thickness of the backing is 10mm, the sensitivity of the transducer reaches the maximum value of -40.83dB; the bandwidth of the transducer presents a trend of first decreasing and then increasing, and when the thickness of the backing is 10mm, the bandwidth appears the minimum value of 30.9%, and when the thickness of the backing is 19mm, the bandwidth of the transducer appears the maximum value of 34.04%.

[0069] Set-up alternative 2: Select backing b as the backing of the transducer and set 5 thicknesses, 1mm, 5.5mm, 10mm, 14.5mm, 19mm respectively. The received waveforms of the transducer with five different thicknesses of backing are shown in Fig. 2. Figure 5 It can be seen from Fig. 2 that the thickness of the backing has an impact on the received waveform, including the shape of the pulse waveform and the amplitude of each peak of the waveform. The sensitivity and bandwidth of the transducer after the spectral analysis of the received waveform are shown in Fig. 3. Figure 6 It can be seen from Fig. 3 that the sensitivity of the transducer presents a trend of first decreasing and then increasing with the increase of the thickness of the backing, and the sensitivity of the transducer reaches the minimum value of -42.41dB when the thickness of the backing is 10mm. The bandwidth of the transducer presents a trend of first increasing and then decreasing, and the bandwidth reaches the maximum value of 30.1% when the thickness of the backing is 14.5mm.

[0070] Set-up alternative 3: Select backing c as the backing of the transducer and set 5 thicknesses, 1mm, 5.5mm, 10mm, 14.5mm, 19mm respectively. The received waveforms of the transducer with five different thicknesses of backing are shown in Fig. 4. Figure 7 It can be seen from Fig. 4 that the thickness of the backing has an impact on the received waveform, including the shape of the pulse waveform and the amplitude of each peak of the waveform. The sensitivity and bandwidth of the transducer after the spectral analysis of the received waveform are shown in Fig. 5. Figure 8 It can be seen from Fig. 5 that the sensitivity of the transducer presents a trend of first decreasing and then increasing with the increase of the thickness of the backing, and the sensitivity of the transducer reaches the minimum value of -46.23dB when the thickness of the backing is 14.5mm. The bandwidth of the transducer presents a trend of first decreasing and then increasing, and the bandwidth reaches the minimum value of 28% when the thickness of the backing is 10mm.

[0071] It can be seen from the comparison of the time-frequency diagrams of the transducer using the three kinds of backings that the frequency spectrum diagrams of the received waveforms of the transducer using different backings are different, including the amplitude of the spectrum and the coverage range of the spectrum.

[0072] It can be seen from the combination of the sensitivity, bandwidth and the thickness of the backing of the transducer using the three kinds of backings that: Figure 9 It can be seen that: backing a is the best choice, and the sensitivity and bandwidth of the transducer using backing a are greater than those of the transducers using backing b and backing c. When using backing a, the thickness of backing a needs to be considered. It can be seen that when the transducer requires high bandwidth, the thickness of backing a needs to be adjusted to 19mm, but the bandwidth of the transducer is only 30.9% at this time. When the transducer requires high sensitivity, the thickness of backing a needs to be adjusted to 10mm, but the bandwidth of the transducer is only 30.9% at this time.

Claims

1. A transducer optimization method based on backing parameter simulation, characterized in that: Includes the following steps: Step 1: Construct a geometric model for transducer simulation; the geometric model includes a transducer consisting of a backing, piezoelectric elements, and a composite matching layer stacked sequentially. Step 2: Set the density, Young's modulus, and Poisson's ratio of the backing and composite matching layer; Step 3: Select the physical fields for the geometric model and determine the multiphysics involved in the physical field boundaries; Step 4: In the geometric model, use pulse voltage to excite the piezoelectric element; Step 5: Use simulation software to simulate the geometric model and obtain the transducer's terminal voltage data; Step 6: After exporting the terminal voltage data obtained in Step 5, calculate the sensitivity and bandwidth of the transducer; Step 7: Adjust the material type and thickness of the backing, and repeat steps 1 to 6; obtain different material types and thicknesses of the backing and their corresponding transducer sensitivity and bandwidth; select the combination of backing material type and thickness that meets the requirements of both transducer sensitivity and bandwidth as the final material type and thickness of the backing. Step 8: Using the backing material type and thickness obtained in Step 7, construct the transducer.

2. The transducer optimization method based on backing parameter simulation according to claim 1, characterized in that: The geometric model described in step one also includes the water bodies and the perfectly matched layer that are attached together; the composite matching layer in the transducer is attached to the water bodies.

3. The transducer optimization method based on backing parameter simulation according to claim 1, characterized in that: The geometric model described in step one is created using COMSOL.

4. The transducer optimization method based on backing parameter simulation according to claim 1, characterized in that: The physical fields mentioned in step three include electrostatics, solid mechanics, piezoelectric effect, and pressure acoustics-transient; the multiphysics field includes acoustic-structure boundary.

5. The transducer optimization method based on backing parameter simulation according to claim 1, characterized in that: In step four, the waveform of the pulse voltage v(t) is as follows: Where T0 is the clock period corresponding to the transducer's center frequency; t is time.

6. The transducer optimization method based on backing parameter simulation according to claim 1, characterized in that: In step six, the transducer sensitivity Srel is: Among them, U c U represents the peak-to-peak voltage value from the specified reflector before amplification of the echo; a This represents the peak-to-peak voltage applied to the piezoelectric element.

7. The transducer optimization method based on backing parameter simulation according to claim 1, characterized in that: In step six, the transducer width BW is: BW = (fu - f1) / fc * 100% Among them, f1 and f u These are the two frequencies of the maximum impulse-echo response; f c The pulse-echo center frequency; Pulse-echo center frequency f c The expression is as follows: in c =(f1+f u ) / 2.

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