CN117929541A - Air coupling ultrasonic guided wave array transducer and variable-mode excitation method thereof - Google Patents
Air coupling ultrasonic guided wave array transducer and variable-mode excitation method thereof Download PDFInfo
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Abstract
The invention relates to an air coupling ultrasonic guided wave array transducer and a variable mode excitation method thereof, belonging to the field of ultrasonic guided wave nondestructive detection, wherein a planar array arrangement mode is adopted in the sensor, a 1-3 type piezoelectric composite material is selected as an excitation receiving sensitive element, and the sensor is combined with an acoustic impedance matching layer, a backing layer, an upper electrode, a lower electrode, a wire, a foam insulating element, a BNC joint and the like to form the air coupling ultrasonic guided wave array transducer.
Description
Technical Field
The invention relates to an air coupling ultrasonic guided wave array transducer and a variable mode excitation method thereof, belonging to the technical field of ultrasonic guided wave nondestructive detection. According to the method, the air coupling array transducer is used for realizing ultrasonic guided wave variable-mode excitation, and the problem that the traditional air coupling ultrasonic guided wave transducer is limited by a single specific center frequency during detection is solved.
Background
The high acoustic impedance difference and the strong attenuation are problems faced by the air coupling ultrasonic detection technology, and the acoustic impedance of the traditional PZT material is larger (> 30 MRayl), so that the traditional PZT material is difficult to realize acoustic impedance matching with light load materials (such as water, human bodies and the like) and is difficult to couple with air. The piezoelectric composite material overcomes the defects of a single-phase piezoelectric material, retains the high-voltage electrical property of the PZT material, and has lower acoustic impedance and lower Q value (about 3-10), so that the piezoelectric composite material is suitable for manufacturing an air coupling ultrasonic sensor.
The multimode characteristics and the dispersion characteristics of the ultrasonic guided wave make the guided wave signal difficult to analyze, and different guided wave modes have different sensitivities to damage, so that the selection of different single guided wave modes is the key of ultrasonic guided wave detection. The traditional air coupling ultrasonic guided wave transducer adopts single-crystal unit to excite ultrasonic waves, and has the defect that only ultrasonic guided waves with single center frequency can be excited. Under the occasion that different ultrasonic guided wave modes need to be applied, probes with different center frequencies need to be replaced frequently or the incidence angles of the probes need to be rotated to meet the requirements, the adaptability is poor, and the cost is greatly increased. Compared with the traditional single transducer, the multi-element array transducer has the advantages of flexible beam control, higher signal gain, extremely strong anti-interference inhibition capability, higher spatial resolution capability and the like, so that the multi-element array based on the piezoelectric composite material is expected to become a favorable tool for improving the efficiency and the sensitivity of the air-coupled ultrasonic transducer.
Disclosure of Invention
The invention aims to provide an air coupling ultrasonic guided wave array transducer and a variable mode excitation method thereof, which are used for meeting the requirements of non-contact ultrasonic guided wave detection.
Aiming at the problems mentioned in the background art, the invention adopts the following scheme to solve and perfect: the piezoelectric chip is made of 1-3 piezoelectric composite material, which can reduce the difference between the acoustic impedance of the piezoelectric element and the acoustic impedance of air, so as to improve the transmission efficiency of signal energy.
As a further improvement of the present invention; the piezoelectric wafers are cut into strips by 1-3 piezoelectric composite materials, wherein each single piezoelectric wafer is connected with each other at intervals by adopting an insulating material to improve the overall stability, and the insulating element is made of a low-density low-acoustic-impedance foam material to greatly reduce the acoustic crosstalk between array elements.
As a further improvement of the present invention; the matching layer of the piezoelectric element is strip-shaped, the thickness of the matching layer is about one quarter of the wavelength, the bandwidth and the transmission efficiency of the transducer are improved, and each array element is respectively adhered with the matching layer, so that the strong crosstalk generated between the array elements is reduced.
Furthermore, the invention also provides an air-coupled ultrasonic guided wave array transducer and a variable mode excitation method thereof, wherein the method comprises the following steps:
(1) Amplitude of mode n for an air-coupled transducer array The method comprises the following steps:
wherein, For particle displacement, F (ω) is the frequency response of the transducer element for a given input signal, C n (x) is the coupling coefficient between waveguide surface drag and guided wave mode,/>The superposition factor representing the frequency response of all the array elements, the coupling coefficient or the frequency response of each array element is uncontrollable, so the amplitude of the guided wave mode can be regulated only by changing H (omega):
Wherein + -corresponds to a propagation direction along the x-axis; p is the array element spacing, N is the number of units, k is the wave number, lambda is the wavelength of harmonic mode N, Is the center position of the transducer array;
When (when) Time,/>Maximum is reached where m is any integer where the wavelength of the harmonic mode n isBy selecting a specific time delay t 0, a specific guided wave mode can be enhanced;
Taking the array element spacing to be much smaller than the wavelength, i.e. p ≪ lambda, where m=0, the excitation of the array transducer is no longer frequency dependent and is only related to the phase velocity:
(2) The air coupling transducer array excites ultrasonic guided waves with specific phase velocity, and can be obtained according to Snell's law:
wherein, To excite the incident angle of the ultrasonic wave,/>Is the air wave velocity,/>For guiding wave target phase velocity, air wave velocity is unchanged, and incident angle/> is obtained according to guiding wave target phase velocity；
Further, phase delay techniques are used to excite the ultrasonic waves along a particular angleIncidence, introducing a time delay on each element:
Wherein the method comprises the steps of For the delay time corresponding to the ith array element,/>Is array element spacing and/>The transducer is vertically arranged to regulate and control the delay time/>, of the piezoelectric array elementExcitation guided waves form wave fronts at specific angles along specific directions, so that specific phase velocities/>, are excitedTo regulate the guided wave mode;
(3) Selecting a specific frequency in the frequency band range of the transducer as a center frequency, and modulating an excitation signal by a narrow-band raised cosine (Hanning) window function to obtain a sine signal:
Wherein t is the time of the time, For the excitation signal center frequency,/>For modulating the cycle number, pass cycle number/>Regulation of bandwidth/>The mode that only needs to excite exists in the bandwidth range is kept, and the specific guided wave mode excitation at the center frequency is realized.
After the technical scheme is adopted, the invention has the following beneficial effects:
According to the array transducer for air coupling ultrasonic guided wave detection, the signal transmission efficiency is improved through the design of the piezoelectric composite material, the matching layer, the insulating element and the like. Meanwhile, the method solves the problem that the traditional air coupling ultrasonic guided wave transducer can only excite the mode corresponding to a single specific center frequency during detection, realizes excitation of different ultrasonic guided wave modes in different frequency channel ranges of the sensor, envelopes a low-order mode and a high-order mode, and provides a direction for realizing quantitative detection of different types of defects at different parts of a structure.
Drawings
FIG. 1 is a schematic cross-sectional structure of an air-coupled array transducer;
FIG. 2 is a schematic diagram of detection of a variable mode excitation method based on an air-coupled array transducer;
FIG. 3 is a schematic diagram of the sound velocity deflection principle;
FIG. 4 is a refractive diagram of an air coupled transducer excitation propagating to a bulk acoustic wave to be measured;
FIG. 5 is a solution of the phase velocity dispersion curve of a 4.76mm thick aluminum plate;
fig. 6-8 show two-dimensional fourier transform recognition results of exciting different modes by the method, namely an a 0、S0、A1、S1 mode.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail below with reference to the accompanying drawings and detailed description. It should be understood that the detailed description set forth herein is intended only to illustrate the present invention. An example of a 4.76mm thick aluminum plate is described below.
In one embodiment, referring to fig. 1, an air-coupled ultrasonic guided wave array transducer according to the present embodiment includes:
The piezoelectric ceramic comprises a matching layer (1), a piezoelectric wafer (2), a plastic insulator (3), a glass fiber board (4), a backing layer (5), a shell (6), a lower electrode (7), an upper electrode (8), a wire (9) and a BNC connector (10);
The core component of the whole transducer is a piezoelectric wafer (2), the number of the piezoelectric wafer can be customized and regulated, the sensitive element is a strip-shaped body formed by cutting 1-3 piezoelectric composite materials, and each single piezoelectric wafer is bonded and supported at intervals by adopting a plastic insulator (3) to improve the overall stability; and, additionally bonding glass fiber plates (4) from two sides of the array to fix the transducer assembly in the shell (6); the matching layers (1) are respectively adhered to the lower surface of the piezoelectric wafer, the backing layer (5) is fixed on the upper surface of the piezoelectric wafer and is adhered and fixed with the shell (6), and the shell is an aluminum shell; the piezoelectric wafer, the plastic insulator, the glass fiber plate, the back lining layer and the like are fixed at different positions inside the shell, so that the overall stability of the transducer is ensured.
The signal connection end consists of a lower electrode (7), an upper electrode (8), a lead (9) and a BNC connector (10), wherein the BNC connector is fixed outside the shell (6), and the lead (9) is respectively connected with the upper electrode and the lower electrode of each piezoelectric wafer and is used for independently exciting and transmitting ultrasonic signals to each piezoelectric wafer.
In a second embodiment, the method is implemented by the transducer according to the first embodiment, and the specific embodiment adopts the following technical scheme:
(1) The detection device is composed of an ultrasonic signal generator, a multiplexer, an air coupling array transducer, a laser vibrometer, a data processing unit, a display device and the like, as shown in fig. 2. The ultrasonic signal transmitter is mainly responsible for transmitting electric pulses; the multiplexer is responsible for converting the single-channel transmission signal into a plurality of channel transmission signals; the air coupling ultrasonic array probe is responsible for realizing the excitation of ultrasonic waves; the laser vibration meter is used for detecting displacement distribution of the surface points of the aluminum plate and receiving guided wave signals; the data processing unit is responsible for setting an excitation guided wave signal and processing and analyzing a received signal; the display device is responsible for displaying the processed signals.
(2) Further, fig. 3 is a schematic diagram of the transmission guided wave of the hollow coupling excitation ultrasonic wave incident on the aluminum plate. In air coupling detection, ultrasonic waves are excited to air to enter the aluminum plate to form lamb waves, the direction of the guided waves is parallel to the plate surface, and the relation between the incident angle and the air sound velocity and the guided wave phase velocity can be known as follows:
wherein, To excite the incident angle of the ultrasonic wave,/>Is the air wave velocity,/>Is the phase velocity of the guided wave.
(3) Further, fig. 4 is a schematic diagram of controlling delay time of each array element of the probe to excite ultrasonic waves based on the air-coupled ultrasonic guided wave array transducer, where the delay time of each array element is as follows:
Wherein the method comprises the steps of For the delay time corresponding to the ith array element,/>Is the array element spacing. In this example,/>Taking the array element of 0.4mm and the number of the array elements of 64.
(4) Further, FIG. 5 is a graph of the dispersion curve of a 4.76mm thick aluminum plate, whereinFor the center frequency of the excitation signal,/>Is the target phase velocity of the mode,/>Is a frequency bandwidth and is regulated by the number of excitation signal cycles. Determining phase velocity/>, of mode from dispersion curveThen the delay time/>, of each array element is adjustedRealizing the deflection of sound beams, and selecting an excitation signal to regulate and control the center frequency/>Sum bandwidth/>The excitation of a single mode can be completed.
Fig. 6-8 show graphs of results of identifying guided wave modes by two-dimensional fourier transforms. Selecting a Hanning window modulated pulse signal excitation with a period number of 20, which isLower/>About/>To achieve bandwidth control. Wherein FIGS. 6 and 7 are compared at the same frequency/>The excited A 0 and S 0 modes in the lower aluminum plate, and the same phase velocity/> at different frequencies are compared in FIG. 7 and FIG. 8The S 0 and a 1 modes of time excitation.
The air coupling ultrasonic guided wave array transducer has the characteristics of low acoustic impedance, large bandwidth, high energy transmission efficiency and the like. Based on the transducer and the method, the delay time of each array element and the bandwidth of an excitation signal are regulated, and the ultrasonic guided wave excitation of a variable mode can be realized without rotating a probe. Therefore, different ultrasonic guided wave modes, including a low-order mode and a high-order mode, can be excited in different 'channels' of the sensor by adopting different center frequencies, and more possibility is provided for realizing quantitative detection of different types of defects at different parts of the waveguide.
While the invention has been described in detail in connection with specific preferred embodiments, it is not to be construed as limited to the specific embodiments of the invention, but rather as a matter of course, it will be understood by those skilled in the art that various modifications and substitutions can be made without departing from the spirit and scope of the invention.
Claims (4)
1. An air-coupled ultrasonic guided wave array transducer, characterized in that: the transducer comprises a matching layer (1), a piezoelectric wafer (2), a plastic insulator (3), a glass fiber plate (4), a backing layer (5), a shell (6), a lower electrode (7), an upper electrode (8), a wire (9) and a BNC connector (10);
The piezoelectric wafers (2) are made by cutting 1-3 type piezoelectric composite materials into strips, the piezoelectric wafers (2) are fixed in the plastic insulator (3) at intervals in an adhesive mode, and two sides of the plastic insulator (3) are fixed in the shell (6) through the adhesive glass fiber plates (4); the matching layer (1) is correspondingly adhered to the lower surface of the piezoelectric wafer (2), the backing layer (5) is fixed on the upper surface of the piezoelectric wafer (2), and the backing layer (5) is adhered and fixed with the shell (6);
The signal connection end is formed by the lower electrode (7), the upper electrode (8), the lead (9) and the BNC connector (10), the BNC connector (10) is fixed outside the shell (6), the lead (9) is respectively connected with the upper electrode and the lower electrode of each piezoelectric wafer (2), and the lead (9) is used for independently exciting and transmitting ultrasonic signals to each piezoelectric wafer.
2. A method of variable mode excitation based on an air-coupled ultrasonic guided wave array transducer, the method being implemented in accordance with the air-coupled ultrasonic guided wave array transducer of claim 1, the method comprising:
(1) Amplitude of mode n for transducer array The method comprises the following steps:
wherein, For particle displacement, F (ω) is the frequency response of the transducer element for a given input signal, C n (x) is the coupling coefficient between waveguide surface drag and guided wave mode,/>A superposition factor representing the frequency response of all array elements; the coupling coefficient or frequency response of each array element is fixed and cannot be changed, so that the amplitude of the guided wave mode can be regulated only by changing H (omega):
Wherein + -corresponds to a propagation direction along the x-axis; p is the array element spacing, N is the number of units, k is the wave number, lambda is the wavelength of harmonic mode N, Is the center position of the transducer array;
When (when) Time,/>Maximum is reached where m is any integer where the wavelength of the harmonic mode n is，/>For frequency, by selecting a specific delay/>The specific guided wave mode can be enhanced;
(2) Taking the array element spacing to be much smaller than the wavelength, i.e. p ≪ lambda, where m=0, the excitation of the array transducer is no longer frequency dependent and is only related to the phase velocity:
。
3. The variable mode excitation method based on the air-coupled ultrasonic guided wave array transducer according to claim 2, wherein the method comprises the following steps:
(1) The air coupling transducer array excites ultrasonic guided waves with specific phase velocity, and can be obtained according to Snell's law:
wherein, To excite the incident angle of the ultrasonic wave,/>Is the air wave velocity,/>For the guided wave target phase velocity, the air wave velocity is unchanged, and the incident angle/> can be obtained according to the guided wave target phase velocity；
(2) Exciting ultrasonic waves along a particular angle using phase delay techniquesIncidence, introducing a time delay on each element:
Wherein the method comprises the steps of For the delay time corresponding to the ith array element,/>Is array element spacing and/>The transducer is vertically arranged to regulate and control the delay time/>, of the piezoelectric array elementThe excitation guided wave forms a wave front along a specific angle of a specific direction, thereby exciting a specific phase velocityTo regulate the guided wave mode.
4. A variable mode excitation method based on an air-coupled ultrasonic guided wave array transducer according to claim 2 or 3, characterized in that:
Selecting a specific frequency in a frequency band range of a transducer as a center frequency, and using a sine signal modulated by a narrow-band raised cosine (Hanning) window function as an excitation signal, wherein the expression is as follows:
Wherein t is the time of the time, For the excitation signal center frequency,/>For modulating the cycle number, pass cycle number/>Regulation of bandwidth/>The mode that only needs to excite exists in the bandwidth range is kept, and the specific guided wave mode excitation at the center frequency is realized.
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101325241A (en) * | 2007-06-12 | 2008-12-17 | 富士胶片株式会社 | Composite piezoelectric material, ultrasonic probe, ultrasonic endoscope, and ultrasonic diagnostic apparatus |
| CN101571568A (en) * | 2009-05-15 | 2009-11-04 | 河北省电力研究院 | Ultrasonic planar array sensor suitable for partial discharge detection of transformer |
| CN116441148A (en) * | 2023-03-27 | 2023-07-18 | 中国石油大学(华东) | Piezoelectric composite material transducer with adjustable guided wave excitation mode and working method thereof |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101325241A (en) * | 2007-06-12 | 2008-12-17 | 富士胶片株式会社 | Composite piezoelectric material, ultrasonic probe, ultrasonic endoscope, and ultrasonic diagnostic apparatus |
| CN101571568A (en) * | 2009-05-15 | 2009-11-04 | 河北省电力研究院 | Ultrasonic planar array sensor suitable for partial discharge detection of transformer |
| CN116441148A (en) * | 2023-03-27 | 2023-07-18 | 中国石油大学(华东) | Piezoelectric composite material transducer with adjustable guided wave excitation mode and working method thereof |
Non-Patent Citations (4)
| Title |
|---|
| GEOFFREY VEIT等: "An ultrasonic guided wave excitation method at constant phase velocity using ultrasonic phased array probes", ULTRASONICS, vol. 102, no. 2020, 31 March 2020 (2020-03-31), pages 1 - 9 * |
| RYMANTAS J. KAZYS 等: "Air-Coupled Low Frequency Ultrasonic Transducers and Arrays with PMN-32%PT Piezoelectric Crystals", SENSORS, vol. 17, no. 1, 6 January 2017 (2017-01-06), pages 1 - 20 * |
| RYMANTAS J. KAZYS 等: "Application of Air-Coupled Ultrasonic Arrays for Excitation of a Slow Antisymmetric Lamb Wave", SENSORS, vol. 18, 11 August 2018 (2018-08-11), pages 1 - 22 * |
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