An ultrasonic detection device and a fingerprint recognition device

Abstract

The application discloses an ultrasonic detection device, wherein a matching layer in the ultrasonic detection device comprises at least two acoustic impedance groups for realizing at least two acoustic impedance gradients, and the thickness of each acoustic impedance group is less than or equal to a first threshold value, the first threshold value is the thickness of the acoustic impedance group when the acoustic transmission coefficient of the acoustic impedance group is greater than or equal to a preset acoustic transmission coefficient, and the first threshold value is less than 1 / 4 times the wavelength corresponding to the acoustic impedance group. Since the matching layer is configured to have at least two acoustic impedance groups with at least two acoustic impedance gradients, and the thickness of the acoustic impedance group is set to be much smaller than 1 / 4 times the wavelength corresponding to the acoustic impedance group while ensuring that the acoustic impedance coefficient is sufficient, the matching layer formed by the aforementioned at least two acoustic impedance groups can realize acoustic impedance gradient matching and has a relatively thin thickness while ensuring the transmittance. Therefore, the thickness of the ultrasonic detection device is reduced, the attenuation of the propagating sound wave is reduced, and the sensitivity of the ultrasonic detection is improved.

Description

Technical Field

[0001] This application relates to the field of ultrasonic testing, and more particularly to an ultrasonic testing device and a fingerprint recognition device. Background Technology

[0002] Ultrasonic testing (UT) is a technique that uses ultrasound to inspect objects or biological tissues. Because ultrasound beams can be concentrated and propagate in a straight line in a specific direction within a medium, and because reflection, refraction, and mode conversion occur at interfaces between dissimilar media, the reflected sound waves from the interface can be obtained using these propagation characteristics. The texture features of the dissimilar media surface can then be analyzed based on these reflected sound waves. Therefore, ultrasonic testing technology is commonly used in fingerprint recognition, flaw detection, and other applications.

[0003] In conventional ultrasonic testing, to reduce ultrasonic wave attenuation caused by acoustic impedance mismatch between the piezoelectric ultrasonic transducer and the sensing layer, at least one matching layer is typically placed between them. The acoustic impedance of this matching layer lies between the acoustic impedance of the piezoelectric ultrasonic transducer and the acoustic impedance of the sensing layer, thus reducing the acoustic impedance mismatch between them to some extent.

[0004] However, to ensure near-full transmission of ultrasound waves through the matching layers, conventional techniques typically configure at least one matching layer, with each layer having a thickness approximately equal to one-quarter of the wavelength of the ultrasound wave propagating through it. This ensures near-full transmission of the ultrasound waves through each matching layer. However, the relatively thick matching layers produced by this configuration may limit the application scenarios of the ultrasonic testing device. For example, an ultrasonic testing device with a thick matching layer may not be suitable for applications such as fingerprint recognition, where the thickness of the ultrasonic testing device is critical.

[0005] Therefore, how to reduce the thickness of ultrasonic testing devices while ensuring high transmission efficiency is an urgent problem to be solved. Summary of the Invention

[0006] This application provides an ultrasonic testing device that reduces the thickness of the ultrasonic testing device, reduces the attenuation of propagating sound waves, and improves the sensitivity of ultrasonic testing.

[0007] In a first aspect, this application provides an ultrasonic testing device, which mainly includes a piezoelectric ultrasonic transducer, a sensing layer, and a matching layer located between the piezoelectric ultrasonic transducer and the sensing layer. The sensing layer is used to place the biological tissue to be tested; the matching layer is used to connect the piezoelectric ultrasonic transducer and the sensing layer; the piezoelectric ultrasonic transducer is used to transmit a detection signal and receive an echo signal. The detection signal, after passing through the matching layer and the sensing layer to reach the biological tissue, generates an echo signal. The echo signal, after passing through the sensing layer and the matching layer, reaches the piezoelectric ultrasonic transducer, and carries characteristic information of the biological tissue. The matching layer includes at least two acoustic impedance groups for realizing at least two acoustic impedance gradients. The thickness of each acoustic impedance group is less than or equal to a first threshold, where the first threshold is the thickness of the acoustic impedance group when the acoustic transmission coefficient is greater than or equal to a preset acoustic transmission coefficient, and the first threshold is less than 1 / 4 of the wavelength corresponding to the acoustic impedance group.

[0008] In this application, the matching layer is configured as at least two acoustic impedance groups with at least two acoustic impedance gradients. Furthermore, while ensuring sufficient acoustic impedance coefficients, the thickness of each acoustic impedance group is set to be much less than 1 / 4 the thickness of the wavelength corresponding to that group. Therefore, the matching layer based on the aforementioned at least two acoustic impedance groups can achieve acoustic impedance gradient matching while maintaining a relatively thin thickness. This is beneficial for reducing the thickness of the ultrasonic testing device, reducing the attenuation of propagating sound waves, improving the sensitivity of ultrasonic testing, and enhancing valley-ridge contrast and signal-to-noise ratio.

[0009] For example, the preset sound transmission coefficient is greater than or equal to 60%. For instance, the preset sound transmission coefficient can be 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%, etc. Of course, in practical applications, the preset sound transmission coefficient can also be other values, which will not be listed here.

[0010] In one possible implementation, the equivalent resonant frequencies of at least two acoustic impedance groups are related to the thickness of each of the at least two acoustic impedance groups, and the difference between the equivalent resonant frequencies and the center frequency of the ultrasonic transducer is less than a second threshold. This second threshold is a real number greater than or equal to 0. The smaller the value of the second threshold, the closer the equivalent resonant frequencies are to the center frequency of the ultrasonic transducer, and the easier it is to generate local resonance. Optionally, when the second threshold is equal to 0, the equivalent resonant frequencies of the at least two acoustic impedance groups are equal to the center frequency of the ultrasonic transducer.

[0011] In this embodiment, by adjusting the thickness of the acoustic impedance group, the equivalent resonant frequency of the matching layer can be adjusted to be the same as or close to the center frequency of the piezoelectric ultrasonic transducer, so that the sound wave transmission generates local resonance, thereby enhancing the amplitude of the sound wave.

[0012] In one possible implementation, the total thickness of at least two acoustic impedance groups is less than or equal to 1 / 4 of the equivalent wavelength, and the equivalent wavelength is equal to the sum of the wavelengths corresponding to each of the at least two acoustic impedance groups.

[0013] In this embodiment, it is proposed that, when each acoustic impedance group meets the preset acoustic transmission coefficient, the total thickness of at least two acoustic impedance groups is configured to be less than or equal to 1 / 4 of the equivalent wavelength. This is beneficial to make the process of the sound wave emitted by the piezoelectric ultrasonic transducer passing through the matching layer and reaching the sensing layer close to full transmission.

[0014] In one possible implementation, each acoustic impedance group includes a low acoustic impedance layer and a high acoustic impedance layer. Two adjacent acoustic impedance groups are connected through the low acoustic impedance layer. The thickness of the low acoustic impedance layer is less than 1 / 8 of the wavelength corresponding to the low acoustic impedance layer, and the thickness of the high acoustic impedance layer is less than 1 / 8 of the wavelength corresponding to the high acoustic impedance layer.

[0015] In this embodiment, since an acoustic impedance group composed of a low acoustic impedance layer and a high acoustic impedance layer stacked alternately has a thinner thickness than an acoustic impedance group made of only one material, it is advantageous to further reduce the thickness of the matching layer, further reduce the thickness of the ultrasonic testing device, further reduce the attenuation of propagating sound waves, improve the sensitivity of ultrasonic testing, and improve the valley-ridge contrast and signal-to-noise ratio. Furthermore, configuring both the low acoustic impedance layer and the high acoustic impedance layer as thin layers less than 1 / 8 of the wavelength, i.e., configuring the matching layer as a combination of multiple thin low acoustic impedance layers and high acoustic impedance layers stacked alternately, is advantageous compared to a combination scheme that does not consider the thickness of the low acoustic impedance layer and the high acoustic impedance layer, as it further reduces the thickness of the matching layer, further reduces the thickness of the ultrasonic testing device, further reduces the attenuation of propagating sound waves, improves the sensitivity of ultrasonic testing, and improves the valley-ridge contrast and signal-to-noise ratio.

[0016] In one possible implementation, at least two acoustic impedance groups include a first acoustic impedance group and a second acoustic impedance group. The low acoustic impedance layer in the first acoustic impedance group is used to connect the piezoelectric ultrasonic transducer and the high acoustic impedance layer in the first acoustic impedance group. The low acoustic impedance layer in the second acoustic impedance group is used to connect the high acoustic impedance layer in the first acoustic impedance group and the high acoustic impedance layer in the second acoustic impedance group. The high acoustic impedance layer in the second acoustic impedance group is connected to the sensing layer through an adhesive layer. The equivalent acoustic impedance of the first acoustic impedance group is equal to the geometric mean of the acoustic impedance of the piezoelectric ultrasonic transducer and the acoustic impedance of the sensing layer. The equivalent acoustic impedance of the second acoustic impedance group is equal to the geometric mean of the acoustic impedance of the first acoustic impedance group and the acoustic impedance of the sensing layer.

[0017] In one possible implementation, the low acoustic impedance layer in each acoustic impedance group has an equivalent stiffness coefficient, and the high acoustic impedance layer in each acoustic impedance group has an equivalent mass. The equivalent resonant frequency is related to the equivalent stiffness coefficient of the low acoustic impedance layer and the equivalent mass of the high acoustic impedance layer in each acoustic impedance group.

[0018] For example, the equivalent acoustic impedance of the acoustic impedance group, the equivalent stiffness coefficient of the low acoustic impedance layer, and the equivalent mass of the high acoustic impedance layer in the acoustic impedance group satisfy the following constraints:

[0019]

[0020] in, The equivalent acoustic impedance of the acoustic impedance group. This represents the equivalent stiffness coefficient of the low acoustic impedance layer in the acoustic impedance group. It represents the equivalent mass of the high acoustic impedance layer in the acoustic impedance group.

[0021] In one possible implementation, each acoustic impedance group has an equivalent acoustic impedance, which is related to the product of the equivalent stiffness coefficient of the low acoustic impedance layer and the equivalent mass of the high acoustic impedance layer in the acoustic impedance group.

[0022] For example, the equivalent stiffness coefficient of the low acoustic impedance layer, the equivalent mass of the high acoustic impedance layer, and the center frequency of the ultrasonic transducer in at least two acoustic impedance groups satisfy the following constraints:

[0023]

[0024] in, The center frequency of the ultrasonic transducer; is the equivalent stiffness coefficient of the low acoustic impedance layer in the first acoustic impedance group; The equivalent mass of the high acoustic impedance layer in the first acoustic impedance group; is the equivalent stiffness coefficient of the low acoustic impedance layer in the second acoustic impedance group; It represents the equivalent mass of the high acoustic impedance layer in the second acoustic impedance group.

[0025] In one possible implementation, the low acoustic impedance layer is made of a polymer material, and the high acoustic impedance layer is made of a metallic or inorganic material. For example, the acoustic impedance of the low acoustic impedance layer is less than or equal to 4 MRayles; the acoustic impedance of the high acoustic impedance layer is greater than or equal to 20 MRayles.

[0026] In this embodiment, a low acoustic impedance layer is made of a polymer material with adhesive properties. This allows the low acoustic impedance layer to connect adjacent high acoustic impedance layers and to the piezoelectric ultrasonic transducer, eliminating the need for separate adhesive layers to connect each acoustic impedance group. Therefore, this not only simplifies the structure of the matching layer but also reduces its thickness, thereby reducing the thickness of the ultrasonic detection device, minimizing the attenuation of propagating sound waves, improving the sensitivity of ultrasonic detection, and enhancing valley-ridge contrast and signal-to-noise ratio.

[0027] Secondly, this application provides a fingerprint recognition device, which includes an ultrasonic fingerprint chip and an ultrasonic detection device as described in the first aspect and any one thereof. The ultrasonic detection device is used to detect signals and receive echo signals carrying characteristic information of the fingerprint; the ultrasonic fingerprint chip is used to identify the characteristic information of the fingerprint based on the echo signals. Attached Figure Description

[0028] Figure 1A This is a structural example diagram of an ultrasonic testing device in traditional technology;

[0029] Figure 1B This is another structural example diagram of an ultrasonic testing device in conventional technology;

[0030] Figure 1C This is another structural example diagram of an ultrasonic testing device in conventional technology;

[0031] Figure 2 This is a schematic diagram of one embodiment of the ultrasonic testing device in this application;

[0032] Figure 3A An example diagram of a laminated structure made of different materials;

[0033] Figure 3B This is an example diagram showing the relationship between the thickness of the intermediate layer in a laminated structure and the acoustic transmission coefficient.

[0034] Figure 3C Another example diagram showing the relationship between the thickness of the intermediate layer in a laminated structure and the acoustic transmission coefficient;

[0035] Figure 4 This is a schematic diagram of another embodiment of the ultrasonic testing device in this application;

[0036] Figure 5 This is an example diagram of at least two acoustic impedance groups that constitute the matching layer in this application;

[0037] Figure 6 This is an example diagram of a spring oscillator model corresponding to at least two acoustic impedance groups that constitute the matching layer in this application;

[0038] Figure 7A This is another example diagram of at least two acoustic impedance groups that constitute the matching layer in this application;

[0039] Figure 7B This is another example diagram of at least two acoustic impedance groups that constitute the matching layer in this application;

[0040] Figure 7C This is another example diagram of at least two acoustic impedance groups that constitute the matching layer in this application;

[0041] Figure 8 This is an example diagram of the piezoelectric ultrasonic transducer in this application;

[0042] Figure 9A This is another example diagram of the piezoelectric ultrasonic transducer in this application;

[0043] Figure 9B This is another example diagram of the piezoelectric ultrasonic transducer in this application. Detailed Implementation

[0044] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0045] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms are interchangeable where appropriate so that the embodiments described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0046] It should be understood that the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0047] To facilitate understanding, a brief introduction to the technical terms used in this application will be provided below:

[0048] Acoustic impedance (specific acoustic impedance): also known as acoustic resistance or acoustic characteristic impedance, it represents the ratio of the sound pressure on the wavefront of a sound wave in a medium to the vibration velocity of a particle on that surface. Generally, acoustic impedance is a complex number; the real part is called the acoustic resistivity, and the imaginary part is called the acoustic reactance. Acoustic impedance R can also be expressed as the product of the sound wave's propagation velocity v in the material and the material's density ρ, i.e., acoustic impedance R = density ρ × sound velocity v. The unit is megarayllite (MRayl) or kilograms per square meter per second (kg∙m). -2 ∙s). Where, 1MRayl = 10 6 kg∙m -2 •s. In the embodiments of this application, the term "acoustic impedance" is used for description.

[0049] The sound transmission coefficient is the ratio of the transmitted sound energy flux to the incident sound energy flux through an interface (i.e., the interface between one medium and another) at a given frequency and under given conditions. A higher sound transmission coefficient indicates less attenuation during the transmission of sound waves through the interface. In this application, the sound transmission coefficient of an acoustic impedance group refers to the ratio of the transmitted sound energy flux through the acoustic impedance group to the incident sound energy flux into the acoustic impedance group when the acoustic impedance group is used as an equivalent interface. The sound transmission coefficient of an acoustic impedance group is related to the materials constituting the acoustic impedance group.

[0050] Resonance refers to the phenomenon where, under the influence of a periodic external force, the amplitude of an oscillating system increases sharply when the frequency of the external force is the same as or very close to the system's natural oscillation frequency. The frequency at which resonance occurs is called the resonance frequency. When sound waves resonate, their amplitude increases.

[0051] To facilitate understanding of the ultrasonic testing device provided in this application, the following will first be combined with... Figure 1A This article provides a brief introduction to the detection principle and internal structure of ultrasonic testing devices in traditional technologies:

[0052] like Figure 1A The diagram shown is a structural example of an ultrasonic testing device in conventional technology. This ultrasonic testing device includes a piezoelectric ultrasonic transducer, a matching layer, and a sensing layer.

[0053] The matching layer, located between the piezoelectric ultrasonic transducer and the sensing layer, is used to match the acoustic impedance of the piezoelectric ultrasonic transducer with that of the sensing layer. In conventional technologies, the matching layer can be made of one material or multiple materials. For example, ... Figure 1BAs shown, in conventional technologies, the matching layer can be a layer of adhesive (e.g., a nonconductive adhesive (NCA) layer) used as a bonding layer, bonded between the piezoelectric ultrasonic transducer and the sensing layer using an adhesive coating process. For example, such as... Figure 1C As shown, the matching layer in conventional technology can also be a composite stack composed of overlapping metal and adhesive layers (e.g., a composite stack composed of pressure-sensitive adhesives (PSA) / copper (Cu) / PSA), bonded between the piezoelectric ultrasonic transducer and the sensing layer using adhesive coating and screen printing processes. Furthermore, the sensing layer is used to bond textured biological tissues or objects. Generally, the recessed portions constituting this texture are called valleys, and the protruding portions are called ridges. The piezoelectric ultrasonic transducer emits ultrasonic waves (i.e., a detection signal) towards the sensing layer. This detection signal, after passing through the matching and sensing layers, reaches the biological tissue or object and generates reflected ultrasonic waves (i.e., an echo signal). This echo signal, after passing through the sensing and matching layers, reaches the piezoelectric ultrasonic transducer. Because there is a difference between the ultrasonic waves reflected through the valleys and those reflected through the ridges, the echo signal received by the piezoelectric ultrasonic transducer can reflect the characteristic information of the texture of the biological tissue. Furthermore, the signal processing module connected to the piezoelectric ultrasonic transducer can extract feature information from the echo signal and compare it with the stored feature information to realize the recognition of the texture of biological tissue (e.g., fingerprint).

[0054] In traditional techniques, to ensure near-full transmission of ultrasound waves through the matching layer, the thickness of the matching layer is approximately equal to n / 4 times the wavelength (λ) of the ultrasound wave propagating through it. Here, n is an odd number greater than 0, and λ is the equivalent wavelength of the ultrasound signal in the matching layer. Therefore, the thickness of the matching layer in traditional techniques is greater than or equal to 1 / 4 of the wavelength.

[0055] Therefore, the matching layer configured in the aforementioned manner is relatively thick. Ultrasonic detection devices with a large matching layer may not be suitable for applications such as fingerprint recognition where the thickness of the ultrasonic detection device is required.

[0056] In response, this application provides an ultrasonic testing device that reduces the thickness of the matching layer while ensuring the transmittance of sound waves, thereby reducing the thickness of the ultrasonic testing device, increasing the energy of the detection signal transmitted to the sensing layer, and improving the sensitivity of ultrasonic testing.

[0057] The following is combined Figure 2 The ultrasonic testing device provided in this application is described below.

[0058] like Figure 2As shown, the ultrasonic testing device provided in this application includes a piezoelectric ultrasonic transducer 01, a sensing layer 02, and a matching layer 03 located between the piezoelectric ultrasonic transducer 01 and the sensing layer 02. It should be noted that this embodiment mainly targets... Figure 2 The matching layer 03 in the figure is optimized. Other layers in the figure (e.g., sensing layer 02 and piezoelectric ultrasonic transducer 01) are simplified to single-layer descriptions. However, in actual applications, sensing layer 02 and piezoelectric ultrasonic transducer 01 may each include multiple layers of materials.

[0059] The sensing layer 02 is used to place the biological tissue to be detected; the matching layer 03 is used to connect the piezoelectric ultrasonic transducer 01 and the sensing layer 02; the piezoelectric ultrasonic transducer 01 is used to transmit detection signals and receive echo signals. After the detection signal passes through the matching layer 03 and the sensing layer 02 to reach the biological tissue, it generates an echo signal. After the echo signal passes through the sensing layer 02 and the matching layer 03, it reaches the piezoelectric ultrasonic transducer 01. The echo signal carries the characteristic information of the biological tissue.

[0060] The matching layer 03 includes at least two acoustic impedance groups for achieving at least two acoustic impedance gradients. Each acoustic impedance group refers to a component made of one or more materials and possessing a certain acoustic impedance. Different acoustic impedance groups within the at least two acoustic impedance groups have different acoustic impedances, and the acoustic impedances of the at least two acoustic impedance groups exhibit a gradient change from the piezoelectric ultrasonic transducer 01 to the sensing layer 02. Therefore, the at least two acoustic impedance groups can achieve at least two acoustic impedance gradients. It should be understood that the acoustic impedance gradient can be a linear or non-linear acoustic impedance gradient, and this is not limited thereto. The at least two acoustic impedance groups can achieve a transition in acoustic impedance between the piezoelectric ultrasonic transducer 01 and the sensing layer 02. For example, if the acoustic impedance of the sensing layer 02 is less than the acoustic impedance of the piezoelectric ultrasonic transducer 01, then the equivalent acoustic impedance of the acoustic impedance group closer to the piezoelectric ultrasonic transducer 01 is greater than the equivalent acoustic impedance of the acoustic impedance group closer to the sensing layer 02. For example, the equivalent acoustic impedance of the at least two acoustic impedance groups gradually decreases from the piezoelectric ultrasonic transducer 01 to the sensing layer 02. For example, if the acoustic impedance of the sensing layer 02 is greater than the acoustic impedance of the piezoelectric ultrasonic transducer 01, the equivalent acoustic impedance of the acoustic impedance group closer to the piezoelectric ultrasonic transducer 01 is less than the equivalent acoustic impedance of the acoustic impedance group closer to the sensing layer 02. For example, from the piezoelectric ultrasonic transducer 01 to the sensing layer 02, the equivalent acoustic impedance of the at least two acoustic impedance groups gradually increases.

[0061] In addition to having a certain acoustic impedance, each acoustic impedance group also needs to have a relatively thin thickness to achieve a certain acoustic transmission coefficient. Specifically, the thickness of each acoustic impedance group is less than or equal to a first threshold, which is the thickness of the acoustic impedance group when its acoustic transmission coefficient is greater than or equal to a preset acoustic transmission coefficient. The first threshold is less than 1 / 4 of the wavelength corresponding to the acoustic impedance group. In other words, the thickness of the acoustic impedance group is not only less than 1 / 4 of the wavelength corresponding to the acoustic impedance group (i.e., the wavelength of the sound wave when it propagates in the acoustic impedance group), but also less than the thickness required to achieve the preset acoustic transmission coefficient.

[0062] like Figure 3A As shown, assume that an intermediate layer material 2 with thickness D and acoustic impedance R2 = ρ2 × v2 is placed between material 1 with acoustic impedance R1 = ρ1 × v1 and material 3 with acoustic impedance R3 = ρ3 × v3. When a plane sound wave (p0, v0) is incident perpendicularly from material 1 onto the interface of the intermediate layer material 2, a portion is transmitted into material 2 and further into material 3 behind the intermediate layer. During this process, the sound transmission coefficient and the thickness of the intermediate layer material 2 satisfy the following formula:

[0063] ;(Formula 0.1)

[0064] in, This represents the acoustic transmission coefficient of the intermediate layer impedance material 2. Denotes the wave number (where, ), R1 represents the thickness of the intermediate layer material 2, R2 represents the acoustic impedance of material 1, R3 represents the acoustic impedance of material 2, and R3 represents the acoustic impedance of material 3.

[0065] The proportion of sound waves that can be transmitted through the interlayer depends not only on the acoustic impedance of the material (i.e., R1, R2, and R3), but also on the ratio of the thickness of the interlayer material 2 (i.e., D) to the wavelength of the sound wave propagating through the interlayer material 2 (i.e., λ2). )related.

[0066] In one example, if And, when R1≈R3, , Based on formula 0.1, we can obtain .

[0067] In this example, if the thickness D of the intermediate layer is small compared to the wavelength of the sound wave propagating in the intermediate layer, then the sound wave can achieve full transmission in the intermediate layer.

[0068] In another example, when (Right now , that is, the thickness of the intermediate layer is an odd multiple of 1 / 4 wavelength, where n is an integer greater than 0), and, when, based on Equation 0.1, we can obtain .

[0069] In this example, when the thickness of the intermediate layer is an odd multiple of 1 / 4 wavelength, sound waves can also achieve total transmission. For example, when (R1 + R3) > [R2 + (R1R3 / R2)], and D = n / 4λ (n is an odd number greater than 0), the sound transmission efficiency is the highest, that is, the sound transmission coefficient is close to 1; when R1 + R3 < R2 + R1R3 / R2, and D = n / 2λ (n is an integer greater than 0), the sound transmission efficiency is the highest, that is, the sound transmission coefficient is close to 1.

[0070] It can be seen from this that the relationship between the sound transmission coefficient of the impedance material and the thickness of the intermediate layer material has a periodic change rule.

[0071] As Figure 3B shown, this periodic change rule is: when the thickness of the material is thin enough (for example, much less than 1 / 4 wavelength), the sound transmission coefficient is close to 1; when the thickness of the material is an odd multiple of 1 / 4 wavelength, the sound transmission coefficient is also close to 1; when the thickness of the material is an even multiple of 1 / 4 wavelength, the sound transmission coefficient is the lowest. In Figure 3B the shown example, the thickness of the acoustic impedance group is not only less than 1 / 4 of the wavelength corresponding to the acoustic impedance group (that is, the wavelength when sound waves propagate in this acoustic impedance group), when the value of the preset sound transmission coefficient is relatively high, the thickness of the acoustic impedance group may also be less than 1 / 8 of the wavelength corresponding to the acoustic impedance group.

[0072] It should be understood that different materials have different acoustic impedance characteristics. When the thickness of the material is an even multiple of 1 / 4 wavelength, the sound transmission coefficients of sound waves in different materials are different. As Figure 3C shown, when the thickness of the metal material is much less than 1 / 4 wavelength (that is, the wavelength when sound waves propagate in the metal material) or the thickness of the metal material is an odd multiple of 1 / 4 wavelength, the sound transmission coefficient is close to 1; when the thickness of the polymer material is much less than 1 / 4 wavelength (that is, the wavelength when sound waves propagate in the polymer material) or the thickness of the polymer material is an odd multiple of 1 / 4 wavelength, the sound transmission coefficient is also close to 1. However, when the thickness of the metal material is an even multiple of 1 / 4 wavelength, the sound transmission coefficient of the intermediate layer made of this metal material is close to 0.5 (that is, 50%); while when the thickness of the polymer material is an even multiple of 1 / 4 wavelength, the sound transmission coefficient of the intermediate layer made of this polymer material is close to 0.1 (that is, 10%).

[0073] Therefore, when the thickness of each acoustic impedance group in the matching layer is much smaller than 1 / 4 of the wavelength corresponding to the acoustic impedance group (i.e., the wavelength of the sound wave propagating in that acoustic impedance group), the sound wave can have a high acoustic transmission coefficient when passing through that acoustic impedance group. Therefore, the thickness of the acoustic impedance group can be selected between 0 and 1 / 4 of the wavelength based on a preset acoustic transmission coefficient. For example, the preset acoustic transmission coefficient is greater than or equal to 60%. For instance, the preset acoustic transmission coefficient can be 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%, etc. Of course, in practical applications, the preset acoustic transmission coefficient can also be other values, which will not be listed here.

[0074] It should be noted that the acoustic transmission coefficient of the matching layer is equal to the product of the acoustic transmission coefficients of each acoustic impedance group contained in the matching layer. For example, taking matching layer #1 containing acoustic impedance group 1 and acoustic impedance group 2 as an example, with a preset acoustic transmission coefficient of 70%, if the acoustic transmission coefficient is configured to be 90% when the thickness of acoustic impedance group 1 is 0.08 times λ1 (i.e., the wavelength corresponding to acoustic impedance group 1, i.e., the wavelength when the sound wave propagates in acoustic impedance group 1), and the acoustic transmission coefficient is 80% when the thickness of acoustic impedance group 2 is 0.12 times λ2 (i.e., the wavelength corresponding to acoustic impedance group 2, i.e., the wavelength when the sound wave propagates in acoustic impedance group 2), then the thickness of matching layer #1 is (0.08λ1 + 0.12λ2), and the acoustic transmission coefficient of matching layer #1 is 90% × 80% = 72%.

[0075] In this embodiment, the matching layer is configured as at least two acoustic impedance groups with at least two acoustic impedance gradients. Furthermore, while ensuring sufficient acoustic impedance coefficients, the thickness of the acoustic impedance group is set to be much less than 1 / 4 the thickness of the wavelength corresponding to the acoustic impedance group. Therefore, the matching layer based on the aforementioned at least two acoustic impedance groups can achieve acoustic impedance gradient matching while maintaining a relatively thin thickness. This is beneficial for reducing the thickness of the ultrasonic testing device, reducing the attenuation of propagating sound waves, improving the sensitivity of ultrasonic testing, and enhancing valley-ridge contrast and signal-to-noise ratio.

[0076] The following section provides a further introduction to the specific implementation methods of at least two acoustic impedance groups:

[0077] In one possible implementation, the total thickness of at least two acoustic impedance groups is less than or equal to 1 / 4 of the equivalent wavelength, meaning the total thickness of the matching layer 03 is less than or equal to 1 / 4 of the equivalent wavelength. The equivalent wavelength is the wavelength of the sound wave (e.g., a detection signal) propagating in the matching layer. The equivalent wavelength is equal to the sum of the wavelengths corresponding to each of the at least two acoustic impedance groups, i.e., the sum of the wavelengths of the sound wave (e.g., a detection signal) propagating in each acoustic impedance group.

[0078] For example, taking the matching layer #1 as containing acoustic impedance group 1 and acoustic impedance group 2, if the thickness of acoustic impedance group 1 is configured to be 0.08 times λ1 (i.e., the wavelength corresponding to acoustic impedance group 1, i.e., the wavelength of the sound wave when it propagates in acoustic impedance group 1), and the thickness of acoustic impedance group 2 is configured to be 0.12 times λ2 (i.e., the wavelength corresponding to acoustic impedance group 2, i.e., the wavelength of the sound wave when it propagates in acoustic impedance group 2), then the thickness of matching layer #1 is (0.08λ1+0.12λ2), and (0.08λ1+0.12λ2)≤0.25λ0, where λ0 is the equivalent wavelength of matching layer #1.

[0079] In this embodiment, it is proposed that, when each acoustic impedance group meets the preset acoustic transmission coefficient, the total thickness of at least two acoustic impedance groups is configured to be less than or equal to 1 / 4 of the equivalent wavelength. This is beneficial to make the process of the sound wave emitted by the piezoelectric ultrasonic transducer passing through the matching layer and reaching the sensing layer close to full transmission.

[0080] Furthermore, each acoustic impedance group can be implemented in multiple ways. In one implementation, an acoustic impedance group can be formed by stacking thin sheets made of two different acoustic impedance materials. In another implementation, an acoustic impedance group can be formed by filling another acoustic impedance material into holes etched into one acoustic impedance material. In yet another implementation, an acoustic impedance group can be formed by mixing metal particles and thermoplastic polymer particles and then pressing them at high temperature. At least two acoustic impedance groups contained in a matching layer can both adopt one of the aforementioned implementation methods, or they can each adopt different implementation methods; these will not be listed in detail in this embodiment.

[0081] This embodiment only uses the example of an acoustic impedance group consisting of stacked thin sheets made of two different acoustic impedance materials as an example for illustration. Figure 4 As shown, each acoustic impedance group in matching layer 03 consists of a low acoustic impedance layer and a high acoustic impedance layer, with adjacent acoustic impedance groups connected through the low acoustic impedance layer. For example, Figure 4Acoustic impedance group 1 and acoustic impedance group 2 are adjacent to each other. The high acoustic impedance layer of acoustic impedance group 1 and the high acoustic impedance layer of acoustic impedance group 2 are connected through the low acoustic impedance layer of acoustic impedance group 2. Furthermore, the low acoustic impedance layer of the acoustic impedance group near the piezoelectric ultrasonic transducer 01 (e.g., the low acoustic impedance layer of acoustic impedance group 1) is connected to the piezoelectric ultrasonic transducer 01, and the acoustic impedance group near the sensing layer 02 is connected to the sensing layer 02 through an adhesive layer. In other words, the matching layer 03 is formed by alternating stacking of at least two low acoustic impedance layers and at least two high acoustic impedance layers, forming an acoustic impedance gradient through adjacent low and high acoustic impedance layers. Since an acoustic impedance group formed by alternating stacking of a low acoustic impedance layer and a high acoustic impedance layer has a thinner thickness than an acoustic impedance group made of only one material, it is advantageous to further reduce the thickness of the matching layer, further reduce the thickness of the ultrasonic detection device, further reduce the attenuation of propagating sound waves, improve the sensitivity of ultrasonic detection, and improve valley-ridge contrast and signal-to-noise ratio.

[0082] In one possible implementation, the thickness of the low acoustic impedance layer is less than 1 / 8 of the wavelength corresponding to the low acoustic impedance layer, and the thickness of the high acoustic impedance layer is less than 1 / 8 of the wavelength corresponding to the high acoustic impedance layer. For example, the thickness of the low acoustic impedance layer is less than 0.1 times the wavelength corresponding to the low acoustic impedance layer, and / or the thickness of the high acoustic impedance layer is less than 0.1 times the wavelength corresponding to the high acoustic impedance layer. For example, the thickness of the low acoustic impedance layer is less than 0.05 times the wavelength corresponding to the low acoustic impedance layer, and / or the thickness of the high acoustic impedance layer is less than 0.05 times the wavelength corresponding to the high acoustic impedance layer. It should be understood that the thicknesses of the low acoustic impedance layer and the high acoustic impedance layer within the same acoustic impedance group can be the same or different, and this application is not limiting.

[0083] In this embodiment, both the low acoustic impedance layer and the high acoustic impedance layer are configured as thin layers less than 1 / 8 of the wavelength. That is, the matching layer is configured as a combination of multiple thin low acoustic impedance layers and high acoustic impedance layers stacked in a cross manner. Compared with the combination scheme that does not consider the thickness of the low acoustic impedance layer and the high acoustic impedance layer, it is beneficial to further reduce the thickness of the matching layer, further reduce the thickness of the ultrasonic detection device, further reduce the attenuation of the propagating sound wave, improve the sensitivity of ultrasonic detection, and improve the valley-ridge contrast and signal-to-noise ratio.

[0084] In one possible implementation, the low acoustic impedance layer is made of a polymer material, and the high acoustic impedance layer is made of a metallic or inorganic material. For example, the acoustic impedance of the low acoustic impedance layer is less than or equal to the average acoustic impedance of the polymer material (e.g., 4 MRayles). For example, the low acoustic impedance layer is any one of polymer materials such as polyimide (PI), polyester (PET), pressure-sensitive adhesives (PSA), and optically clear adhesives (OCA). For example, the acoustic impedance of the high acoustic impedance layer is greater than or equal to the average acoustic impedance of the metallic material or the average acoustic impedance of the inorganic material (e.g., 20 MRayles). For example, the high acoustic impedance layer is made of metallic materials such as copper (Cu), tungsten (W), silver (Ag), iron (Fe), nickel (Ni), and titanium (Ti), or inorganic materials such as aluminum oxide (Al₂O₃).

[0085] In this embodiment, a low acoustic impedance layer is made of a polymer material with adhesive properties, enabling it to connect adjacent high acoustic impedance layers and to the piezoelectric ultrasonic transducer 01, eliminating the need for separate adhesive layers to connect each acoustic impedance group. Therefore, this not only simplifies the structure of the matching layer 03 but also reduces its thickness, thereby reducing the thickness of the ultrasonic detection device, minimizing attenuation of propagating sound waves, improving ultrasonic detection sensitivity, and enhancing valley-ridge contrast and signal-to-noise ratio.

[0086] In one example, such as Figure 5 As shown, at least two acoustic impedance groups include a first acoustic impedance group and a second acoustic impedance group. A low acoustic impedance layer l1 in the first acoustic impedance group connects the piezoelectric ultrasonic transducer 01 and the high acoustic impedance layer h1 in the first acoustic impedance group. A low acoustic impedance layer l2 in the second acoustic impedance group connects the high acoustic impedance layer h1 in the first acoustic impedance group and the high acoustic impedance layer h2 in the second acoustic impedance group. The high acoustic impedance layer h2 in the second acoustic impedance group is connected to the sensing layer 02 via an adhesive layer (i.e., a low acoustic impedance layer l3). The equivalent acoustic impedance of the first acoustic impedance group is equal to the geometric mean of the acoustic impedance of the piezoelectric ultrasonic transducer 01 and the acoustic impedance of the sensing layer 02. The equivalent acoustic impedance of the second acoustic impedance group is equal to the geometric mean of the acoustic impedance of the first acoustic impedance group and the acoustic impedance of the sensing layer 02. For example, if the acoustic impedance of the piezoelectric ultrasonic transducer is R1 and the acoustic impedance of the sensing layer is R2, then the equivalent acoustic impedance of the first acoustic impedance group... (Formula 1.1), the equivalent acoustic impedance of the second acoustic impedance group is (Equation 1.2).

[0087] In one possible implementation, each acoustic impedance group is equivalent to a spring oscillator model. The low acoustic impedance layer in each acoustic impedance group has an equivalent stiffness coefficient, meaning the low acoustic impedance layer is equivalent to a spring; the high acoustic impedance layer in each acoustic impedance group has an equivalent mass, meaning the high acoustic impedance layer is equivalent to an oscillator. In this case, the equivalent acoustic impedance of the acoustic impedance group is related to the product of the equivalent stiffness coefficient of the low acoustic impedance layer and the equivalent mass of the high acoustic impedance layer.

[0088] For example, the equivalent acoustic impedance of the acoustic impedance group, the equivalent stiffness coefficient of the low acoustic impedance layer, and the equivalent mass of the high acoustic impedance layer in the acoustic impedance group satisfy the following constraints:

[0089] (Formula 2.0)

[0090] in, The equivalent acoustic impedance of the acoustic impedance group. This represents the equivalent stiffness coefficient of the low acoustic impedance layer in the acoustic impedance group. It represents the equivalent mass of the high acoustic impedance layer in the acoustic impedance group.

[0091] For ease of understanding, Figure 5 Taking the matching layer shown as an example, Figure 5 The acoustic impedance group in the model can be equivalent to a spring oscillator model. For example... Figure 6 As shown, the low acoustic impedance layer l1 in the first acoustic impedance group can be equivalent to a spring with a spring constant K1, and the high acoustic impedance layer h1 in the first acoustic impedance group can be equivalent to an oscillator with mass M1. The low acoustic impedance layer l2 in the second acoustic impedance group can be equivalent to a spring with a spring constant K2, and the high acoustic impedance layer h2 in the second acoustic impedance group can be equivalent to an oscillator with mass M2. Based on the spring oscillator model, the equivalent acoustic impedance of the first acoustic impedance group can be obtained. (Formula 2.1), the equivalent acoustic impedance of the second acoustic impedance group is (Equation 2.2).

[0092] Since the stiffness coefficient K of the low acoustic impedance layer can be expressed as (Equation 3.1), and the mass M of the high acoustic impedance layer can be expressed as... (Formula 3.2), where, This indicates the density of the material in the low acoustic impedance layer. This represents the speed of sound as it travels through a layer with low acoustic impedance. Indicates the thickness of the low acoustic impedance layer. This indicates the density of the material in the high acoustic impedance layer. This represents the thickness of the high acoustic impedance layer. Based on formulas 1.1, 2.1, and 3.1, the following relationship 4.1 can be obtained:

[0093] (Relation 4.1)

[0094] in, This represents the density of the material in the low acoustic impedance layer l1 of the first acoustic impedance group. This represents the speed of sound propagating in the low acoustic impedance layer l1 of the first acoustic impedance group. This indicates the thickness of the low acoustic impedance layer l1 in the first acoustic impedance group. This represents the density of the material in the high acoustic impedance layer h1 of the first acoustic impedance group. This indicates the thickness of the high acoustic impedance layer h1 in the first acoustic impedance group.

[0095] Similarly, based on formulas 1.2, 2.2, and 3.2, the following relationship 4.2 can be obtained:

[0096] (Relation 4.2)

[0097] in, This represents the density of the material in the low acoustic impedance layer l2 of the second acoustic impedance group. This represents the speed of sound propagating in the low acoustic impedance layer l2 of the second acoustic impedance group. This indicates the thickness of the low acoustic impedance layer l2 in the second acoustic impedance group. This represents the density of the material in the high acoustic impedance layer h2 of the second acoustic impedance group. This indicates the thickness of the high acoustic impedance layer h2 in the second acoustic impedance group.

[0098] It should be understood that the acoustic impedance R1 of the piezoelectric ultrasonic transducer 01 and the acoustic impedance R2 of the sensing layer 02 are known, and R can be determined based on Equation 1.1. m1 , will R m1 Substituting into equation 4.1, the density of the low acoustic impedance layer in the first acoustic impedance group can be obtained. Speed ​​of sound and thickness and the density of the high acoustic impedance layer in the first acoustic impedance group and thickness The relationship between them. When a certain material is selected as the low acoustic impedance layer, the density of the low acoustic impedance layer... It can be determined that the sound velocity in this low acoustic impedance layer material is... It can also be determined that when a certain material is selected as the high acoustic impedance layer, the density of the high acoustic impedance layer is... It can be determined. Therefore, by adjusting the test materials, it is possible to find the optimal method. The first acoustic impedance group is composed of low acoustic impedance layer material with smaller values ​​and high acoustic impedance layer material.

[0099] Similarly, based on R m1R can be determined using Formula 1.2. m2 , will R m2 Substituting into Equation 4.2, the density of the low acoustic impedance layer in the second acoustic impedance group can be obtained. Speed ​​of sound and thickness and the density of the high acoustic impedance layer in the second acoustic impedance group and thickness The relationship between them. When a certain material is selected as the low acoustic impedance layer, the density of the low acoustic impedance layer... It can be determined that the sound velocity in this low acoustic impedance layer material is... It can also be determined that when a certain material is selected as the high acoustic impedance layer, the density of the high acoustic impedance layer is... It can be determined. Therefore, by adjusting the test, it is possible to find the solution. The second acoustic impedance group is composed of low acoustic impedance layer material with smaller values ​​and high acoustic impedance layer material.

[0100] To facilitate understanding, specific examples are provided below:

[0101] If the acoustic impedance of the piezoelectric ultrasonic transducer is R1 = 16 MRayl and the acoustic impedance of the sensing layer is R2 = 4 MRayl, then the expected acoustic impedance of the first acoustic impedance group is... MRayl, and, the expected acoustic impedance of the second acoustic impedance group MRayl. R m1 and R m2 Substituting into equations 4.1 and 4.2 respectively, and by substituting into the density and sound velocity of various materials, we can obtain the thickness of various materials to be used to form the first acoustic impedance group and the actual acoustic impedance of the first acoustic impedance group as shown in Table 1-1. We can also obtain the thickness of various materials to be used to form the second acoustic impedance group and the actual acoustic impedance of the second acoustic impedance group as shown in Table 1-2.

[0102] Table 1-1

[0103]

[0104] In the examples shown in Table 1-1, if material 1 (i.e., the speed of sound is 1800 m / s and the density is 1100 kg / m³) 3 Material 2 (i.e., sound velocity of 4400 m / s and density of 8900 kg / m³) is the low acoustic impedance layer of the first acoustic impedance group. 3 If the material is a high acoustic impedance layer in the first acoustic impedance group, then two sets of thickness solutions can be obtained. In these two sets of thickness solutions, if the thickness of the low acoustic impedance layer in the first acoustic impedance group... Furthermore, the thickness of the high acoustic impedance layer in the first acoustic impedance group The actual acoustic impedance R of the first acoustic impedance group m1 =7.9 MRayl. Wherein, , .in, This meets the requirements for the thickness of the low acoustic impedance layer mentioned above. This meets the requirements for the thickness of the high acoustic impedance layer mentioned earlier.

[0105] Similarly, if the thickness of the low acoustic impedance layer in the first acoustic impedance group... Furthermore, the thickness of the high acoustic impedance layer in the first acoustic impedance group The actual acoustic impedance R of the first acoustic impedance group m1 =8.1MRayl. Wherein, It meets the requirements for the thickness of the low acoustic impedance layer mentioned above. This also meets the requirements for the thickness of the high acoustic impedance layer mentioned earlier.

[0106] Similarly, if material 1 (i.e., the speed of sound is 1800 m / s and the density is 1100 kg / m³) 3 The material is the low acoustic impedance layer of the first acoustic impedance group, and material 3 (i.e., the sound velocity is 5200m / s and the density is 19300kg / m³) is the material of the first acoustic impedance group. 3 If the material is a high acoustic impedance layer in the first acoustic impedance group, then two sets of thickness solutions can also be obtained. In these two sets of thickness solutions, if the thickness of the low acoustic impedance layer in the first acoustic impedance group... Furthermore, the thickness of the high acoustic impedance layer in the first acoustic impedance group The actual acoustic impedance R of the first acoustic impedance group m1 =8.2MRayl; if the thickness of the low acoustic impedance layer in the first acoustic impedance group Furthermore, the thickness of the high acoustic impedance layer in the first acoustic impedance group The actual acoustic impedance R of the first acoustic impedance group m1 =7.8MRayl.

[0107] Similarly, if material 4 (i.e., the speed of sound is 2500 m / s and the density is 1000 kg / m³) 3 Material 2 (i.e., sound velocity of 4400 m / s and density of 8900 kg / m³) is the low acoustic impedance layer of the first acoustic impedance group. 3 If the material is a high acoustic impedance layer in the first acoustic impedance group, then two sets of thickness solutions can also be obtained. In these two sets of thickness solutions, if the thickness of the low acoustic impedance layer in the first acoustic impedance group... Furthermore, the thickness of the high acoustic impedance layer in the first acoustic impedance group The actual acoustic impedance R of the first acoustic impedance group m1=8.3MRayl; if the thickness of the low acoustic impedance layer in the first acoustic impedance group Furthermore, the thickness of the high acoustic impedance layer in the first acoustic impedance group The actual acoustic impedance R of the first acoustic impedance group m1 =8.1MRayl.

[0108] Therefore, it can be seen that in the aforementioned acoustic impedance groups composed of pairs of various materials, when material 1 (i.e., the sound velocity is 1800 m / s and the density is 1100 kg / m³) 3 The material is the low acoustic impedance layer of the first acoustic impedance group, and material 3 (i.e., the sound velocity is 5200m / s and the density is 19300kg / m³) is the material of the first acoustic impedance group. 3 When the material is a high acoustic impedance layer of the first acoustic impedance group, the thickness of the first acoustic impedance group (i.e., the material) is the high acoustic impedance layer of the first acoustic impedance group. The value of ) is the smallest. Therefore, it can be determined that material 1 (i.e., sound velocity of 1800 m / s and density of 1100 kg / m³) has the smallest value. 3 The material is the low acoustic impedance layer of the first acoustic impedance group, and material 3 (i.e., the sound velocity is 5200m / s and the density is 19300kg / m³) is the material of the first acoustic impedance group. 3 The material is used as the high acoustic impedance layer of the first acoustic impedance group. It should be understood that since there are other examples in Table 1-1 with thicknesses that meet the requirements for the thickness of the low acoustic impedance layer and the high acoustic impedance layer mentioned above, the first acoustic impedance group can also be made of materials corresponding to the thicknesses of other groups, provided that the thickness can meet the usage requirements of the application scenario.

[0109] Table 1-2

[0110]

[0111] The meanings of the examples shown in Table 1-2 are similar to those in Table 1-1, and will not be described in detail here.

[0112] In one example, the material corresponding to the thinnest solution is determined to be the material with the second acoustic impedance, i.e., material 1 (i.e., sound velocity of 1800 m / s and density of 1100 kg / m³). 3 The material is a low acoustic impedance layer of the second acoustic impedance group, and material 2 (i.e., sound velocity is 4400 m / s and density is 8900 kg / m³) is used. 3 The material is the high acoustic impedance layer of the second acoustic impedance group, and at this time, the thickness of the low acoustic impedance layer in the second acoustic impedance group is... Furthermore, the thickness of the high acoustic impedance layer in the second acoustic impedance group The actual acoustic impedance R of the second acoustic impedance group m2 =5.6 MRayl.

[0113] It should be noted that the material of the low acoustic impedance layer in the first acoustic impedance group can be the same as or different from the material of the low acoustic impedance layer in the second acoustic impedance group; similarly, the material of the high acoustic impedance layer in the first acoustic impedance group can be the same as or different from the material of the high acoustic impedance layer in the second acoustic impedance group. In one example, such as... Figure 7A As shown, the low acoustic impedance layer in the matching layer is made of the same material, while the high acoustic impedance layer is made of a different material. In another example, such as Figure 7B As shown, the high acoustic impedance layer in the matching layer is made of the same material, while the low acoustic impedance layer is made of a different material. In another example, such as Figure 7C As shown, the low acoustic impedance layer in the matching layer is made of a different type of material and the high acoustic impedance layer is made of a different type of material.

[0114] In this embodiment, the matching layer is configured as a "low-high-low-high-low" stacked structure. The acoustic impedance gradient matching function is achieved by stacking multiple low-high acoustic impedance groups, which reduces sound wave attenuation and parasitic reflection, which is beneficial to improving the sensitivity of ultrasonic detection and improving the valley-ridge contrast and signal-to-noise ratio.

[0115] Furthermore, the thickness of the matching layer 03 can be further optimized so that the matching layer 03 can achieve local resonance to increase the amplitude of the sound wave, thereby improving the detection sensitivity.

[0116] Specifically, at least two acoustic impedance groups have an equivalent resonant frequency, and the difference between the equivalent resonant frequency and the center frequency of the ultrasonic transducer is less than a second threshold. This second threshold is a real number greater than or equal to 0. The smaller the value of the second threshold, the closer the equivalent resonant frequency is to the center frequency of the ultrasonic transducer, and the easier it is to generate local resonance. Optionally, when the second threshold is equal to 0, the equivalent resonant frequency of at least two acoustic impedance groups is equal to the center frequency of the ultrasonic transducer. By adjusting the thickness of the acoustic impedance groups, the equivalent resonant frequency of the matching layer can be adjusted to be the same as or close to the center frequency of the piezoelectric ultrasonic transducer, enabling local resonance in sound wave transmission and thus enhancing the amplitude of the sound wave.

[0117] In one possible implementation, the equivalent resonant frequencies of at least two acoustic impedance groups are related to the equivalent stiffness coefficient of the low acoustic impedance layer and the equivalent mass of the high acoustic impedance layer in each acoustic impedance group.

[0118] For example, the equivalent stiffness coefficient of the low acoustic impedance layer, the equivalent mass of the high acoustic impedance layer, and the center frequency of the ultrasonic transducer in at least two acoustic impedance groups satisfy the following constraints:

[0119] (Formula 5.1)

[0120] in, The center frequency of the ultrasonic transducer; The equivalent mass of the high acoustic impedance layer in the first acoustic impedance group; is the equivalent stiffness coefficient of the low acoustic impedance layer in the first acoustic impedance group; The equivalent mass of the high acoustic impedance layer in the second acoustic impedance group; It is the equivalent stiffness coefficient of the low acoustic impedance layer in the second acoustic impedance group.

[0121] As shown in Formula 3.1 above, the stiffness coefficient K of the low acoustic impedance layer can be determined by the density of the low acoustic impedance layer material. Speed ​​of sound and thickness As shown in Formula 3.2 above, the mass M of the high acoustic impedance layer can be determined by the density of the high acoustic impedance layer material. and thickness This indicates that, given the center frequency of a piezoelectric ultrasonic transducer... In this case, substituting Equations 3.1 and 3.2 into Equation 5.1 yields the density of the low acoustic impedance layer in both acoustic impedance groups. Speed ​​of sound and thickness and the density of the high acoustic impedance layer and thickness The constraints that need to be satisfied between them can be found by adjusting the test materials. The matching layer is composed of low acoustic impedance layer material and high acoustic impedance layer material with smaller values, and the equivalent resonant frequency of the matching layer is close to the center frequency of the piezoelectric ultrasonic transducer.

[0122] For ease of understanding, the following example will be used: the material of the low acoustic impedance layer in the first acoustic impedance group is the same as that in the second acoustic impedance group, and the material of the high acoustic impedance layer in the first acoustic impedance group is the same as that in the second acoustic impedance group.

[0123] If the sound velocity of the low acoustic impedance layer material =1800m / s, density of low acoustic impedance layer material =1100kg / m 3 The sound velocity of the high acoustic impedance layer material is =4400 m / s, density of high acoustic impedance layer material =8900kg / m 3 piezoelectric ultrasonic transducer operating frequency =13MHz, then at least two sets of solutions can be obtained as shown in Table 2-1.

[0124] Table 2-1

[0125]

[0126] In this embodiment, at least two acoustic impedance groups are configured with equivalent resonant frequencies equal to or close to the center frequency of the ultrasonic transducer, so that the overall thickness of the matching layer and the piezoelectric ultrasonic transducer form a local resonance, which is beneficial to enhance signal strength and improve sensitivity.

[0127] In addition, such as Figure 8As shown, the piezoelectric ultrasonic transducer in this application mainly includes an upper electrode layer, a lower electrode layer, a piezoelectric transceiver layer, a substrate, and a functional layer. The upper electrode layer is located between the piezoelectric transceiver layer and the matching layer, and its thickness can range from a few micrometers to tens of micrometers. The material can be a metallic material (e.g., aluminum (Al), gold (Au), silver (Ag), platinum (Pt), copper (Cu), molybdenum (Mo), titanium (Ti), etc.) or a conductive polymer material (e.g., conductive materials such as indium-tin oxide (ITO)). The piezoelectric transceiver layer is located between the upper and lower electrode layers. The thickness of the piezoelectric transceiver layer depends on the resonant frequency of the entire acoustic module, which is approximately 5~20MHz. The piezoelectric transceiver layer can be made of organic polymer materials (e.g., polyvinylidene fluoride (PVDF) resin and its copolymers such as polyvinylidene fluoride-trifluoroethylene (PVDF-TRFE) or blends such as PVDF-graphene oxide), piezoelectric ceramic materials (e.g., PZT and its alloys (lead zirconate titanate lanthanum ceramic PLZT, lead magnesium niobate PNZT, KNN (KxNa1-xNbO3), lead magnesium niobate-lead titanate (PMN-PT)), or inorganic piezoelectric materials such as aluminum nitride (AlN) and its alloys (ScxAl1-xN), zinc oxide (ZnO) and its alloys (VxZn1-xO). The lower electrode layer is located between the piezoelectric transceiver layer and the substrate. This lower electrode layer can be a pixelated electrode structure, capable of receiving the echo signals from fingerprint valleys and ridges in a pixelated manner. To achieve the resolution of fingerprint recognition, the center-to-center spacing of the pixelated electrodes is typically less than 100 μm. The lower electrode layer is typically very thin, on the nanometer scale, to minimize its impact on the flatness of the piezoelectric transceiver layer deposited on its surface. The lower electrode layer can be made of various conductive materials, including metals (e.g., Al, Au, Ag, Pt, Cu, Mo, Ti, etc.) and conductive polymers (e.g., ITO). The substrate is located below the lower electrode layer and electrically connected to it, responsible for processing the electrical signals acquired by the lower electrode layer. The substrate can be a thin-film transistor (TFT) circuit, made of glass; or a complementary metal-oxide-semiconductor (CMOS) circuit, made of silicon. The functional layer is located below the substrate. Its functions include, but are not limited to, sound reflection, sound absorption, and mechanical support; therefore, this functional layer can be multilayered, as shown in the figure.

[0128] It should be noted that the order of some layers in a piezoelectric ultrasonic transducer can be interchanged. For example, the piezoelectric transceiver layer can be located above or below the substrate. Figure 9AAs shown, the piezoelectric transceiver layer is located above the substrate, and the corresponding matching layer and the interface directly in contact with the piezoelectric transducer are made of the electrode layer material; as Figure 9B As shown, the piezoelectric transceiver layer is located below the substrate, and the corresponding matching layer and the interface directly in contact with the piezoelectric transducer are the substrate material. The acoustic impedance of typical substrate materials (e.g., glass, silicon) differs from that of electrode materials (e.g., Al, Au, Ag, Pt, Cu, Mo, Ti, etc.), and the configuration of the matching layer is adjusted accordingly.

[0129] Furthermore, this application also provides a fingerprint recognition device, which includes the ultrasonic detection device and ultrasonic fingerprint chip described above. The ultrasonic detection device is used to detect signals and receive echo signals carrying characteristic information of the fingerprint; the ultrasonic fingerprint chip is used to identify the characteristic information of the fingerprint based on the echo signals.

[0130] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0131] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. An ultrasonic testing device, characterized in that, include: A piezoelectric ultrasonic transducer, a sensing layer, and a matching layer located between the piezoelectric ultrasonic transducer and the sensing layer; The sensing layer is used to place the biological tissue to be detected; The matching layer is used to connect the piezoelectric ultrasonic transducer and the sensing layer; The piezoelectric ultrasonic transducer is used to transmit a detection signal and receive an echo signal. The detection signal passes through the matching layer and the sensing layer to reach the biological tissue and generates the echo signal. The echo signal passes through the sensing layer and the matching layer to reach the piezoelectric ultrasonic transducer. The echo signal carries the characteristic information of the biological tissue. The matching layer includes at least two acoustic impedance groups for achieving at least two acoustic impedance gradients. The thickness of each acoustic impedance group is less than or equal to a first threshold, which is the thickness of the acoustic impedance group when the acoustic transmission coefficient of the acoustic impedance group is greater than or equal to a preset acoustic transmission coefficient. The first threshold is less than 1 / 4 of the wavelength corresponding to the acoustic impedance group. The total thickness of the at least two acoustic impedance groups is less than 1 / 4 of the equivalent wavelength, and the equivalent wavelength is equal to the sum of the wavelengths corresponding to each acoustic impedance group in the at least two acoustic impedance groups.

2. The ultrasonic testing device according to claim 1, characterized in that, The equivalent resonant frequency of the at least two acoustic impedance groups is related to the thickness of each acoustic impedance group in the at least two acoustic impedance groups, and the difference between the equivalent resonant frequency and the center frequency of the ultrasonic transducer is less than a second threshold.

3. The ultrasonic testing device according to claim 1 or 2, characterized in that, Each acoustic impedance group includes a low acoustic impedance layer and a high acoustic impedance layer. Two adjacent acoustic impedance groups are connected through the low acoustic impedance layer. The thickness of the low acoustic impedance layer is less than 1 / 8 of the wavelength corresponding to the low acoustic impedance layer, and the thickness of the high acoustic impedance layer is less than 1 / 8 of the wavelength corresponding to the high acoustic impedance layer.

4. The ultrasonic testing device according to claim 3, characterized in that, The low acoustic impedance layer in each acoustic impedance group has an equivalent stiffness coefficient, and the high acoustic impedance layer in each acoustic impedance group has an equivalent mass. The equivalent resonant frequency is related to the equivalent stiffness coefficient of the low acoustic impedance layer and the equivalent mass of the high acoustic impedance layer in each acoustic impedance group.

5. The ultrasonic testing device according to claim 4, characterized in that, Each acoustic impedance group has an equivalent acoustic impedance, which is related to the product of the equivalent stiffness coefficient of the low acoustic impedance layer and the equivalent mass of the high acoustic impedance layer in the acoustic impedance group.

6. The ultrasonic testing device according to claim 3, characterized in that, The at least two acoustic impedance groups include a first acoustic impedance group and a second acoustic impedance group. The low acoustic impedance layer in the first acoustic impedance group is used to connect the piezoelectric ultrasonic transducer and the high acoustic impedance layer in the first acoustic impedance group. The low acoustic impedance layer in the second acoustic impedance group is used to connect the high acoustic impedance layer in the first acoustic impedance group and the high acoustic impedance layer in the second acoustic impedance group. The high acoustic impedance layer in the second acoustic impedance group is connected to the sensing layer through an adhesive layer. The equivalent acoustic impedance of the first acoustic impedance group is equal to the geometric mean of the acoustic impedance of the piezoelectric ultrasonic transducer and the acoustic impedance of the sensing layer. The equivalent acoustic impedance of the second acoustic impedance group is equal to the geometric mean of the acoustic impedance of the first acoustic impedance group and the acoustic impedance of the sensing layer.

7. The ultrasonic testing device according to claim 6, characterized in that, The equivalent acoustic impedance of the acoustic impedance group, the equivalent stiffness coefficient of the low acoustic impedance layer, and the equivalent mass of the high acoustic impedance layer in the acoustic impedance group satisfy the following constraints: ； Among them, the The equivalent acoustic impedance of the acoustic impedance group is... The equivalent stiffness coefficient of the low acoustic impedance layer in the acoustic impedance group is the... It is the equivalent mass of the high acoustic impedance layer in the acoustic impedance group.

8. The ultrasonic testing device according to claim 6, characterized in that, The equivalent stiffness coefficient of the low acoustic impedance layer, the equivalent mass of the high acoustic impedance layer, and the center frequency of the ultrasonic transducer in the at least two acoustic impedance groups satisfy the following constraints: ； Among them, the The center frequency of the ultrasonic transducer; The equivalent stiffness coefficient of the low acoustic impedance layer in the first acoustic impedance group; The equivalent mass of the high acoustic impedance layer in the first acoustic impedance group; The equivalent stiffness coefficient of the low acoustic impedance layer in the second acoustic impedance group; It is the equivalent mass of the high acoustic impedance layer in the second acoustic impedance group.

9. The ultrasonic testing device according to claim 3, characterized in that, The low acoustic impedance layer is made of polymer material, and the high acoustic impedance layer is made of metallic or inorganic material.

10. The ultrasonic testing device according to claim 3, characterized in that, The acoustic impedance of the low acoustic impedance layer is less than or equal to 4 MRayles; the acoustic impedance of the high acoustic impedance layer is greater than or equal to 20 MRayles.

11. The ultrasonic testing device according to claim 1 or 2, characterized in that, The preset sound transmission coefficient is greater than or equal to 60%.

12. A fingerprint recognition device, characterized in that, include: An ultrasonic fingerprint chip and an ultrasonic detection device as described in any one of claims 1 to 11; The ultrasonic detection device is used to detect signals and receive echo signals carrying characteristic information of fingerprints; The ultrasonic fingerprint chip is used to identify the characteristic information of the fingerprint based on the echo signal.

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