A multi-frequency shared air-coupled ultrasonic transducer

Abstract

The present invention discloses a multi-frequency shared air-coupled ultrasonic transducer, comprising a piezoelectric transducer, a matching layer, an excitation layer and an acoustic metasurface layer; the matching layer and the acoustic metasurface layer are respectively arranged on both sides of the excitation layer. The piezoelectric transducer is used to generate an ultrasonic signal; the matching layer is used to achieve acoustic impedance matching between the piezoelectric transducer and the excitation layer; the excitation layer is a uniform chamber filled with a micron / nano ultrasonic contrast agent, which is used to convert the incident sound wave into secondary and higher harmonics; the acoustic metasurface is composed of a substrate and a periodic frame deposited thereon, which is used to achieve acoustic impedance matching between the excitation layer and the air, so that the fundamental wave, secondary or higher harmonics in the excitation layer can enter the air. The present invention can generate single-frequency or multi-frequency shared signals such as fundamental frequency, double frequency and higher harmonic frequency while achieving acoustic impedance matching between the piezoelectric transducer and the air, greatly improving the efficiency and accuracy of non-destructive testing and imaging.

Description

Technical Field

[0001] The invention relates to the field of acoustics, and in particular to a multi-frequency shared air-coupled ultrasonic transducer. Background Art

[0002] Air-coupled ultrasonic testing technology is a non-contact, non-destructive testing method that uses air as the medium for ultrasonic wave propagation. It has the characteristics of non-contact, non-destructive, and fast online scanning, and is suitable for the testing of a variety of materials. This technology is particularly good at scenarios that are difficult to achieve with traditional ultrasonic testing, such as the inability to couple water and oil, and the need to avoid sample contamination. Therefore, it is widely used in the food industry, pharmaceutical testing, wood product testing, environments sensitive to water or other coupling agents, online monitoring of moving parts, and medical fields where direct contact is prohibited.

[0003] Air-coupled ultrasonic transducers are mainly divided into two categories: capacitive and piezoelectric. Capacitive transducers perform well in matching the acoustic impedance of air, but their operating frequencies are often low. For high-frequency applications, a tiny air gap needs to be constructed between the substrate and the diaphragm, which places extremely high demands on micro-nano processing technology and also leads to higher production costs. In contrast, piezoelectric air-coupled transducers are easy to make and low in cost, making them an ideal choice for many applications. However, due to the huge difference in acoustic impedance between piezoelectric materials and air (for example, the commonly used PZT material has an acoustic impedance of about 30 MRayl, while air is only about 400 Rayl), when sound waves are transmitted from the solid transducer to the air, most of the sound energy is reflected, and only a small amount of energy can enter the air for propagation, thus affecting its radiation efficiency, signal-to-noise ratio and resolution.

[0004] In the field of non-destructive testing, low-frequency sound waves have strong penetration ability and a large detection depth, but the resolution is relatively low; while high-frequency sound waves have high resolution, but they decay quickly and have weak penetration ability. Therefore, in practical applications, in order to achieve the best detection effect, it is often necessary to combine multiple ultrasonic transducers to cover different frequency bands, but this will undoubtedly increase the cost and complexity of detection. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a multi-frequency shared air-coupled ultrasonic transducer, which can generate single-frequency or multi-frequency shared signals such as fundamental frequency, second frequency and high-order harmonic frequency while achieving acoustic impedance matching between the piezoelectric transducer and the air, thereby greatly improving detection efficiency and detection accuracy.

[0006] In order to achieve the above technical objectives, the technical solution of the present invention is as follows:

[0007] A multi-frequency shared air-coupled ultrasonic transducer comprises a piezoelectric transducer, a matching layer, an excitation layer and an acoustic metasurface layer; the matching layer and the acoustic metasurface layer are respectively arranged on both sides of the excitation layer.

[0008] The piezoelectric transducer is used to generate an ultrasonic signal.

[0009] The matching layer is used to achieve acoustic impedance matching between the piezoelectric transducer and the excitation layer.

[0010] The excitation layer is a uniform chamber filled with a micron / nano ultrasonic contrast agent, and is used to convert incident sound waves into secondary and higher harmonics.

[0011] The acoustic metasurface is used to achieve acoustic impedance matching between the excitation layer and the air, so that the fundamental wave, the second harmonic and the higher harmonic in the excitation layer can enter the air.

[0012] Preferably, the thickness of the matching layer is 1 / 4 of the wavelength of the incident sound wave.

[0013] Preferably, the acoustic impedance of the matching layer is ,in and are the acoustic impedances of the piezoelectric material and water, respectively.

[0014] Preferably, the center frequency of the ultrasonic wave generated by the piezoelectric transducer is f Should be in 1.1 ~1.5 between is the resonance frequency of the bubbles in the excitation layer, which can be expressed as

[0015] .

[0016] In the formula, is the minimum radius of the bubble without bursting of contrast agent, is the radius of the bubble at equilibrium position, is the static pressure of the contrast agent, is the density of the surrounding medium, is the polytropic index of the gas in the contrast agent, is the shear modulus of the bubble envelope.

[0017] Preferably, the acoustic metasurface layer consists of a substrate and a frame deposited thereon.

[0018] Preferably, the frame is composed of periodic units, the shapes of the periodic units include rectangles, triangles and regular hexagons, and each unit has a hollow structure in the middle.

[0019] Preferably, the acoustic metasurface layer, substrate and frame are made of one or more materials including silicon, aluminum, copper, iron and organic polymer materials.

[0020] Preferably, the unit period is 0.1 mm to 50 mm; and the substrate thickness is 1 um to 10 mm.

[0021] Preferably, the frame height is 1 um to 1 mm; the frame hollowing rate is 50% to 90%.

[0022] Preferably, the acoustic metasurface layer can adjust its operating frequency according to specific needs. f When the transducer is required to generate a pure 2 f When the frequency ultrasonic signal is transmitted, the resonance frequency of the acoustic metasurface is designed to be 2 f ; When the transducer is required to generate f、 2 f、 3 f When the multi-frequency shared signal is used, the acoustic metasurface adopts a multi-unit composite structure, and its sub-units are f、 2 f、 3 f The operating frequency of the acoustic metasurface can be estimated by the following formula:

[0023] .

[0024] in is the speed of sound in air, and are the densities of air and metasurface, respectively, and are the thickness of substrate and periodic frame, respectively, is the hollowing ratio of the periodic framework.

[0025] Compared with the prior art, the present invention has the following technical advantages:

[0026] (1) The present invention successfully achieves acoustic impedance matching between the piezoelectric transducer and the air through a precisely designed acoustic matching layer, greatly reducing the reflection of sound waves at the interface and greatly improving the radiation efficiency of the piezoelectric transducer. This improvement means that under the same power drive, the piezoelectric transducer of the present invention can radiate stronger and more concentrated ultrasonic signals into the air, which can significantly improve the signal strength and detection depth in fields such as medical imaging, industrial detection, and environmental monitoring, bringing great performance improvements to related applications.

[0027] (2) Another highlight of the present invention is its unique nonlinear frequency conversion capability, which can efficiently convert the fundamental frequency sound waves originally generated by the piezoelectric transducer into a series of secondary or higher harmonic signals with higher energy through carefully designed internal structures and material properties. This process enables a single ultrasonic transducer to simultaneously generate single-frequency or multi-frequency signals including fundamental frequency, second harmonic frequency and even higher harmonic frequency, greatly broadening the application scope of ultrasonic technology. Whether it is the medical field that requires high-resolution imaging or the industrial detection that pursues multi-frequency detection to improve recognition accuracy, the present invention can provide strong technical support.

[0028] (3) The present invention demonstrates its outstanding comprehensive advantages in improving detection accuracy and reducing use costs. Through the stable output of the baseband signal, a deeper detection depth is ensured, meeting the needs of detection in complex media or thicker structures. At the same time, by utilizing the rich detail information contained in the secondary and higher harmonic signals, the present invention can significantly improve the resolution of the detection image, making it have a stronger detection capability for tiny defects. The synergistic effect of this multi-frequency signal not only enhances the comprehensiveness and accuracy of detection, but also indirectly reduces the cost of subsequent maintenance or repair by reducing false alarms and missed alarms. In addition, due to the adoption of high-efficiency design principles, the present invention optimizes energy utilization efficiency while maintaining high performance, further reducing the cost of long-term use, and has significant economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0030] Figure 1 Schematic diagram of the overall structure of a multi-frequency shared air-coupled ultrasonic transducer in an embodiment of the present invention.

[0031] Figure 2 A cross-sectional view of an acoustic metasurface of a multi-frequency shared air-coupled ultrasonic transducer in an embodiment of the present invention.

[0032] Figure 3 Schematic diagram of an acoustic metasurface framework of a multi-frequency shared air-coupled ultrasonic transducer in an embodiment of the present invention.

[0033] Figure 4 This is a spectrum diagram of acoustic waves when the transmitting frequency of the piezoelectric transducer is 2 MHz and there is an excitation layer according to an embodiment of the present invention (the signal amplitudes are all normalized).

[0034] Figure 5 This is a spectrum diagram of acoustic waves when the transmitting frequency of the piezoelectric transducer is 2 MHz and there is no excitation layer (the signal amplitudes are all normalized) according to an embodiment of the present invention.

[0035] Figure 6 It is the transmission coefficient of the acoustic metasurface layer at the water-air interface of Example 1 of the present invention.

[0036] Figure 7 It is the transmission coefficient of the acoustic metasurface layer at the water-air interface of Example 2 of the present invention.

[0037] Figure 8 This is a schematic diagram of the surface layer structure of the acoustic metastructure according to Example 3 of the present invention.

[0038] Fig. 9 This is a transmission coefficient diagram of the acoustic metasurface layer at the water-air interface of Example 3 of the present invention.

[0039] Among them, 1. piezoelectric transducer; 2. impedance matching layer; 3. excitation layer; 4. metasurface layer; 41. periodic frame; 42. substrate; 421. solid area; 422. hollow area. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] like Figure 1 As shown, a multi-frequency shared air-coupled ultrasonic transducer includes a piezoelectric transducer 1, a matching layer 2, an excitation layer 3 and an acoustic metasurface layer 4; the matching layer 2 and the acoustic metasurface layer 4 are respectively arranged on both sides of the excitation layer 3.

[0042] The matching layer 2 is used to achieve acoustic impedance matching between the piezoelectric transducer 1 and the excitation layer 3. Its thickness is 1 / 4 of the wavelength of the incident sound wave, and its acoustic impedance is ,in and are the acoustic impedance of the transducer piezoelectric material and the acoustic impedance of water, respectively.

[0043] The excitation layer 3 is a uniform cavity filled with a micron / nano ultrasonic contrast agent, and is used to convert incident sound waves into secondary and higher harmonics.

[0044] The piezoelectric transducer 1 is used to generate ultrasonic signals. At the resonant frequency, bubbles in the excitation layer 3 may burst due to the cavitation effect. Therefore, the center frequency of the ultrasonic wave emitted by the piezoelectric transducer is f Take 1.1 ~1.5 ,in is the resonant frequency of the bubble, which can be expressed as

[0045] .

[0046] In the formula, is the minimum radius of the bubble without bursting of contrast agent, is the radius of the bubble at equilibrium position, is the static pressure of the contrast agent, is the density of the surrounding medium, is the polytropic index of the gas in the contrast agent, is the shear modulus of the bubble envelope.

[0047] The acoustic metasurface is used to achieve acoustic impedance matching between the excitation layer and the air, so that the second and higher harmonics generated in the excitation layer can enter the air. Figure 2 and Figure 3 As shown, the acoustic metasurface is composed of a substrate 42 and a periodic frame 41 deposited thereon, wherein the frame 41 is composed of periodically arranged rectangular units, and each unit has a hollow structure in the middle. The operating frequency of the acoustic metasurface layer, substrate and frame can be estimated by the following formula:

[0048] .

[0049] in is the speed of sound in air, and are the densities of air and metasurface, respectively, and are the thickness of substrate and periodic frame, respectively, is the hollowing ratio of the periodic framework.

[0050] The main principle of the above technical solution is as follows: the piezoelectric transducer 1 generates a center frequency of f Since the acoustic impedance of piezoelectric material and water is not much different, the acoustic impedance matching between the two can be achieved by using the traditional 1 / 4 wavelength matching layer 2, so that the ultrasonic signal generated by the transducer can enter the excitation layer 3. There are a large number of contrast agent microbubbles in the excitation layer 3. fClose to the resonance frequency of contrast agent microbubbles, a large part of the fundamental frequency sound energy will be converted into secondary and higher harmonic sound. Finally, the impedance matching of water and air is achieved through the acoustic metasurface layer 4, so that the fundamental frequency sound waves, secondary or higher harmonics in the excitation layer 3 can be smoothly transmitted to the air, realizing subsequent non-destructive testing.

[0051] In order to verify the ability of the excitation layer 3 to generate secondary and higher harmonics, the normalized spectrum with and without the excitation layer was measured experimentally under the action of an acoustic field with a center frequency of 2 MHz. The results are shown in Figure 4 and Figure 5 .Depend on Figure 4 and Figure 5 It can be seen that the external sound field can generate obvious second and higher harmonic signals under the action of the contrast agent in the excitation layer, which proves the ability of the excitation layer to generate second and higher harmonics.

[0052] Example 1.

[0053] Assuming that the center frequency of the sound wave generated by the transducer is 41.7kHz, when only a 41.7kHz sound field is required, no ultrasound contrast agent is added to the excitation layer 3, that is, no second harmonic and high harmonic will be generated in the excitation layer. At the same time, the acoustic metasurface parameters are as follows:

[0054] The acoustic metasurface is made of aluminum, and its material density is ρ=2700 kg∕m 3 ; Young's modulus E = 70 Gpa; Poisson's ratio v = 0.3. The substrate thickness is 40um, the periodic frame thickness is 21um, the unit period is 500um, the periodic frame width is 40um, and the hollowing ratio is 84.64%.

[0055] In order to verify the acoustic impedance matching effect of the acoustic matching layer 4 on air and water, COMSOL Multiphysics was used to simulate and calculate its acoustic performance. Figure 6 The transmission coefficient of acoustic power when an acoustic matching layer is set at the interface between water and air is given. Figure 6 It can be seen that after setting the acoustic matching layer, at 41.7kHz, the acoustic energy transmission coefficient can be increased from 0.1% in the natural state to more than 95%, indicating that it can effectively improve the transmission of sound waves in two media with extremely different acoustic impedances. Therefore, the acoustic metamaterial matching layer can effectively increase the intensity of the acoustic signal transmitted from the excitation layer to the air, thereby improving the detection sensitivity.

[0056] Example 2.

[0057] Assuming that the center frequency of the sound wave generated by the transducer is 41.7kHz, when only an 83.4kHz sound field is required, the working frequency can be adjusted by adjusting the particle size of the micron / nano ultrasound contrast agent. Between 45.87kHz and 65.55kHz, the acoustic metasurface parameters are as follows:

[0058] The acoustic metasurface is made of aluminum, with a substrate thickness of 20um, a periodic frame thickness of 10um, a unit period of 500um, a periodic frame width of 40um, and a hollowing ratio of 84.64%. Figure 7 The transmission coefficient of sound power when an acoustic matching layer is set at the interface between water and air is given. As can be seen from the figure, after setting the acoustic matching layer, at 83.4kHz, the sound energy transmission coefficient can be increased from 0.1% in the natural state to more than 95%, while at 41.7kHz the transmission coefficient is still only 0.1%. Therefore, in this case, the transducer can generate a pure second harmonic signal, and other frequency component sound signals can be fully filtered.

[0059] Example 3.

[0060] Assuming that the center frequency of the sound wave generated by the transducer is 34.7kHz, when it is necessary to generate sound fields of 34.7kHz and 69.4kHz at the same time, the working frequency is adjusted by adjusting the particle size of the micron / nano ultrasound contrast agent. Between 30.8kHz and 42kHz, at the same time, the acoustic metasurface structure such as Figure 8 As shown in the figure, both region 1 and region 2 are made of aluminum alloy, but the specific parameters are different, where region 1 uses parameter 1 and region 2 uses parameter 2. Parameter 1 is: substrate thickness is 100um, periodic frame thickness is 20um, unit period is 500um, periodic frame width is 40um, and hollowing ratio is 84.64%; parameter 2 is: substrate thickness is 24um, periodic frame thickness is 11um, unit period is 500um, periodic frame width is 40um, and hollowing ratio is 84.64%. Fig. 9 The transmission coefficient of acoustic power when an acoustic matching layer is set at the interface between water and air is given. It can be seen from the figure that after setting the acoustic matching layer, the acoustic energy transmission coefficient can be increased from 0.1% in the natural state to more than 77% at 34.7kHz and 69.4kHz. Therefore, in this case, the air-coupled ultrasonic transducer can simultaneously generate a common signal of the fundamental wave and the second harmonic.

[0061] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A multi-frequency shared air-coupled ultrasonic transducer, comprising a piezoelectric transducer, a matching layer, an excitation layer and an acoustic metasurface layer; the matching layer and the acoustic metasurface layer are respectively arranged on both sides of the excitation layer; The piezoelectric transducer is used to generate an ultrasonic signal; The matching layer is used to achieve acoustic impedance matching between the piezoelectric transducer and the excitation layer; The excitation layer is a uniform chamber filled with a micron / nano ultrasonic contrast agent, which is used to convert incident sound waves into secondary and higher harmonics; The acoustic metasurface is used to achieve acoustic impedance matching between the excitation layer and the air, so that the fundamental wave, the second harmonic and the higher harmonic in the excitation layer can enter the air; The acoustic metasurface layer is composed of a substrate and a frame deposited thereon; The framework of the acoustic metasurface layer is composed of periodic units, the shapes of which include rectangles, triangles and regular hexagons, and each unit has a hollow structure in the middle; The acoustic metasurface layer can adjust its operating frequency according to specific needs. When the transducer is required to generate pure f When the transducer is required to generate a pure 2 f When the frequency ultrasonic signal is transmitted, the resonance frequency of the acoustic metasurface is designed to be 2 f ; When the transducer is required to generate f、 2 f、 3 f When a multi-frequency shared signal is generated, the acoustic metasurface adopts a multi-unit composite structure, and its sub-units have a resonance frequency of f、 2 f、 3 f The operating frequency of the acoustic metasurface is estimated by the following formula: in is the speed of sound in air, and are the densities of air and metasurface, respectively, and are the thickness of substrate and periodic frame, respectively, is the hollowing ratio of the periodic framework.

2. A multi-frequency shared air-coupled ultrasonic transducer according to claim 1, characterized in that: The thickness of the matching layer is 1 / 4 of the wavelength of the incident sound wave.

3. The multi-frequency shared air-coupled ultrasonic transducer according to claim 1, characterized in that: The acoustic impedance of the matching layer is ,in and are the acoustic impedances of the piezoelectric material and water, respectively.

4. The multi-frequency shared air-coupled ultrasonic transducer according to claim 1, characterized in that: The center frequency of the ultrasonic wave generated by the piezoelectric transducer f Should be in 1.1 ~1.5 between is the resonance frequency of the bubbles in the excitation layer, which can be expressed as In the formula, is the minimum radius of the bubble without bursting of contrast agent, is the radius of the bubble at equilibrium position, is the static pressure of the contrast agent, is the density of the surrounding medium, is the polytropic index of the gas in the contrast agent, is the shear modulus of the bubble envelope.

5. The multi-frequency shared air-coupled ultrasonic transducer according to claim 1, characterized in that: The acoustic metasurface layer, substrate and frame are made of one or more materials including silicon, aluminum, copper, iron and organic polymer materials.

6. The multi-frequency shared air-coupled ultrasonic transducer according to claim 5, characterized in that: The substrate thickness is 1 um to 10 mm.

7. The multi-frequency shared air-coupled ultrasonic transducer according to claim 5, characterized in that: The frame height is 1um~1mm; the frame hollowing rate is 50%~90%.

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