Ultrasonic detection device and fingerprint identification device

Abstract

The invention discloses an ultrasonic detection device, 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 smaller 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 smaller than 1 / 4 of the wavelength corresponding to the acoustic impedance group. The matching layer is configured to be at least two acoustic impedance groups with at least two acoustic impedance gradients, and the thickness of each acoustic impedance group is set to be far less than 1 / 4 of the thickness of the wavelength corresponding to the acoustic impedance group under the condition of ensuring that the matching layer has enough acoustic impedance coefficient, so that the thickness of the acoustic impedance group is less than 1 / 4 of the thickness of the wavelength corresponding to the acoustic impedance group. On the basis of the matching layer formed by the at least two acoustic impedance groups, acoustic impedance gradient matching can be achieved, and the thickness can be small under the condition that the transmissivity is guaranteed. Therefore, the thickness of the ultrasonic detection device is reduced, attenuation of transmitted sound waves is reduced, and the sensitivity of ultrasonic detection is improved.

Description

Technical Field

[0001] The embodiments of the present application relate to the field of ultrasonic detection, and in particular to an ultrasonic detection device and a fingerprint recognition device. Background Art

[0002] Ultrasonic testing (UT) (also known as ultrasonic testing) is a technology that uses ultrasonic technology to detect objects or biological tissues. Since the ultrasonic sound beam can be concentrated in a specific direction in the medium and propagates in a straight line, and can produce reflection, refraction and wave type conversion at the interface of heterogeneous media, the transmission characteristics of ultrasonic waves in the medium can be used to obtain the reflected sound waves reflected from the interface of heterogeneous media, and then the texture characteristics of the surface of the heterogeneous medium can be analyzed based on the reflected sound waves. Therefore, ultrasonic testing technology is often used in fingerprint recognition, flaw detection and other scenarios.

[0003] In conventional ultrasonic testing, in order to reduce the acoustic impedance mismatch between the piezoelectric ultrasonic transducer and the sensing layer, which causes ultrasonic attenuation, at least one matching layer is generally configured between the piezoelectric ultrasonic transducer and the sensing layer. The acoustic impedance of the matching layer is between the acoustic impedance of the piezoelectric ultrasonic transducer and the acoustic impedance of the sensing layer, which can reduce the acoustic impedance mismatch between the piezoelectric ultrasonic transducer and the sensing layer to a certain extent.

[0004] However, in order to make the ultrasonic wave as close to full transmission as possible when passing through the matching layer, the conventional technical solution configures the thickness of each matching layer in at least one matching layer to be approximately equal to 1 / 4 times the wavelength of the ultrasonic wave propagating through the matching layer, so that the ultrasonic wave is close to full transmission when passing through each matching layer. However, the thickness of the matching layer configured in the above manner is relatively thick, which may limit the application scenarios of the ultrasonic detection device. For example, an ultrasonic detection device with a matching layer of relatively large thickness may not be suitable for use in scenarios such as fingerprint recognition that require the thickness of the ultrasonic detection device.

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

[0006] The present application provides an ultrasonic detection device, which is used to reduce the thickness of the ultrasonic detection device, reduce the attenuation of propagating sound waves, and improve the sensitivity of ultrasonic detection.

[0007] In the first aspect, the present application provides an ultrasonic detection 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 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, and the detection signal generates an echo signal after reaching the biological tissue through the matching layer and the sensing layer, and the echo signal reaches the piezoelectric ultrasonic transducer after passing through the sensing layer and the matching layer, and the echo signal carries the characteristic information of the biological tissue. The matching layer includes 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, and 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 the preset acoustic transmission coefficient, and the first threshold value is less than 1 / 4 times the wavelength corresponding to the acoustic impedance group.

[0008] In the present application, the matching layer is configured as 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 thickness of the wavelength corresponding to the acoustic impedance group while ensuring a sufficient acoustic impedance coefficient. Therefore, the matching layer composed of the at least two acoustic impedance groups can achieve acoustic impedance gradient matching and have a thinner thickness while ensuring transmittance. Therefore, it is beneficial to reduce the thickness of the ultrasonic detection device, 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.

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

[0010] In a possible implementation, the equivalent resonant frequency of at least two acoustic impedance groups is related to the thickness of each of 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 value. The second threshold value is a real number greater than or equal to 0. The smaller the value of the second threshold value, 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 value is equal to 0, the equivalent resonant frequency of the at least two acoustic impedance groups is equal to the center frequency of the ultrasonic transducer.

[0011] In this embodiment, 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 by adjusting the thickness of the acoustic impedance group, so that the sound wave transmission produces local resonance, thereby enhancing the amplitude of the sound wave.

[0012] In a possible implementation, the total thickness of the 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 satisfies a 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 times the equivalent wavelength, which is beneficial for making the process of the sound waves emitted by the piezoelectric ultrasonic transducer passing through the matching layer and reaching the sensing layer close to full transmission.

[0014] In a possible embodiment, each acoustic impedance group includes a low acoustic impedance layer and a high acoustic impedance layer, two adjacent acoustic impedance groups are connected by the low acoustic impedance layer, the thickness of the low acoustic impedance layer is less than 1 / 8 times the wavelength corresponding to the low acoustic impedance layer, and the thickness of the high acoustic impedance layer is less than 1 / 8 times the wavelength corresponding to the high acoustic impedance layer.

[0015] In this embodiment, since an acoustic impedance group formed by cross-stacking 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 beneficial 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 the valley-ridge contrast and signal-to-noise ratio. In addition, the low acoustic impedance layer and the high acoustic impedance layer are both configured as thin layers less than 1 / 8 times the wavelength, that is, the matching layer is configured as a cross-stack of multiple thin low acoustic impedance layers and high acoustic impedance layers. Compared with a 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 propagating sound waves, improve the sensitivity of ultrasonic detection, and improve the valley-ridge contrast and signal-to-noise ratio.

[0016] In a possible embodiment, 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, and 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 a possible implementation, the low acoustic impedance layer in each acoustic impedance group has an equivalent stiffness coefficient, the high acoustic impedance layer in each acoustic impedance group has an equivalent mass, and 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] Exemplarily, the equivalent acoustic impedance of the acoustic impedance group, the equivalent stiffness coefficient of the low acoustic impedance layer in the acoustic impedance group, and the equivalent mass of the high acoustic impedance layer satisfy the following constraints:

[0019]

[0020] Among them, R m is the equivalent acoustic impedance of the acoustic impedance group, K is the equivalent stiffness coefficient of the low acoustic impedance layer in the acoustic impedance group, and M is the equivalent mass of the high acoustic impedance layer in the acoustic impedance group.

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

[0022] Exemplarily, 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] Among them, f R1 is the center frequency of the ultrasonic transducer; K1 is the equivalent stiffness coefficient of the low acoustic impedance layer in the first acoustic impedance group; M1 is the equivalent mass of the high acoustic impedance layer in the first acoustic impedance group; K2 is the equivalent stiffness coefficient of the low acoustic impedance layer in the second acoustic impedance group; M2 is the equivalent mass of the high acoustic impedance layer in the second acoustic impedance group.

[0025] In a possible implementation, the material of the low acoustic impedance layer is a polymer material, and the material of the high acoustic impedance layer is a metal material or an inorganic material. Exemplarily, the acoustic impedance of the low acoustic impedance layer is less than or equal to 4 megarais, and the acoustic impedance of the high acoustic impedance layer is greater than or equal to 20 megarais.

[0026] In this embodiment, a polymer material with adhesive properties is used to make a low acoustic impedance layer, so that the low acoustic impedance layer can connect adjacent high acoustic impedance layers and can be connected to the piezoelectric ultrasonic transducer, without the need to separately configure an adhesive layer to connect each acoustic impedance group. Therefore, it is not only helpful to simplify the structure of the matching layer, but also helpful to reduce the thickness of the matching layer, and further helpful to reduce the thickness of the ultrasonic detection device, 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.

[0027] In a second aspect, the present application provides a fingerprint recognition device, which includes an ultrasonic fingerprint chip and the ultrasonic detection device described in the first aspect and any one of the first aspects. 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 characteristic information of fingerprints based on the echo signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1A is a structural example diagram of an ultrasonic detection device in conventional technology;

[0029] Figure 1B Another structural example diagram of an ultrasonic detection device in the conventional technology;

[0030] Figure 1C Another structural example diagram of an ultrasonic detection device in the conventional technology;

[0031] Figure 2 A schematic diagram of an embodiment of an ultrasonic detection device in the present application;

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

[0033] Figure 3B is an example diagram of the corresponding relationship between the thickness of the middle layer of the laminated structure and the sound transmission coefficient;

[0034] Figure 3C Another example diagram of the corresponding relationship between the thickness of the middle layer of the laminated structure and the sound transmission coefficient;

[0035] Figure 4 is a schematic diagram of another embodiment of the ultrasonic detection device in the present application;

[0036] Figure 5 is an example diagram of at least two acoustic impedance groups constituting a matching layer in the present application;

[0037] Figure 6 An example diagram of a spring oscillator model corresponding to at least two acoustic impedance groups constituting a matching layer in the present application;

[0038] Fig. 7A is another example diagram of at least two acoustic impedance groups constituting a matching layer in the present application;

[0039] Figure 7B is another example diagram of at least two acoustic impedance groups constituting a matching layer in the present application;

[0040] Figure 7C is another example diagram of at least two acoustic impedance groups constituting a matching layer in the present application;

[0041] Figure 8 An example diagram of a piezoelectric ultrasonic transducer in this application;

[0042] Fig.9A Another example diagram of a piezoelectric ultrasonic transducer in the present application;

[0043] Fig. 9B FIG. 4 is another example diagram of a piezoelectric ultrasonic transducer in the present application. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.

[0045] The terms "first", "second", "third", "fourth", etc. (if any) in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way are interchangeable where appropriate, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0046] It should be understood that the term "and / or" in this article is only a description of the association relationship of the associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0047] For ease of understanding, the following is a brief introduction to the professional terms involved in this application:

[0048] Specific acoustic impedance: also known as acoustic impedance or acoustic characteristic impedance, it indicates the ratio of the sound pressure on the wavefront of a sound wave in a medium to the vibration velocity of the particles on the surface. Generally, the specific acoustic impedance is a complex number. The real part of the specific acoustic impedance is called the acoustic resistivity, and the imaginary part of the specific acoustic impedance is called the acoustic reactance. The specific acoustic impedance R can also be expressed by the product of the propagation velocity v of the sound wave in the material and the density ρ of the material, that is, the specific acoustic impedance R = density ρ × sound velocity v. The unit is mega-Rayleigh (MRayl) or kilogram·square meter·second (kg·m -2·s). Among them, 1MRayl=10 6 kg·m -2 ·s. In the embodiments of the present application, the term "acoustic impedance" is used for introduction.

[0049] Sound transmission coefficient: refers to the ratio of the transmitted sound energy flux through the interface (i.e., the interface from one medium to another medium) to the incident sound energy flux under given frequency and conditions. The larger the sound transmission coefficient, the less attenuation of the sound wave during the transmission process of penetrating 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 incident on 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 material that constitutes the acoustic impedance group.

[0050] Resonance: refers to the phenomenon that the amplitude of an oscillating system increases sharply when the frequency of the external force is the same as or very close to the natural oscillation frequency of the system under the action of periodic external force. The frequency when resonance occurs is called the resonance frequency. When sound waves resonate, the amplitude of the sound waves increases.

[0051] To facilitate understanding of the ultrasonic detection device provided by the present application, Figure 1A A brief introduction to the detection principle and internal structure of the ultrasonic detection device in traditional technology:

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

[0053] The matching layer is located between the piezoelectric ultrasonic transducer and the sensing layer, and is used to match the acoustic impedance of the piezoelectric ultrasonic transducer with the acoustic impedance of the sensing layer. The matching layer in the conventional technology can be made of one material or multiple materials. Figure 1B As shown, the matching layer in the conventional technology can be a layer of adhesive (for example, a nonconductive adhesive (NCA) layer) as a bonding layer, which is bonded between the piezoelectric ultrasonic transducer and the sensing layer by a glue coating process. Figure 1CAs shown, the matching layer in the conventional technology can also be a composite laminate composed of a metal layer and an adhesive layer (for example, a composite laminate composed of pressure sensitive adhesives (PSA) / copper (Cu) / PSA), which is bonded between the piezoelectric ultrasonic transducer and the sensing layer by using glue coating and silk screen printing processes. In addition, the sensing layer is used to bond biological tissues or objects with textures. Generally, the concave part constituting the texture is called a valley, and the convex part is called a ridge. The piezoelectric ultrasonic transducer emits an ultrasonic wave (i.e., a detection signal) in the direction of the sensing layer. After the detection signal reaches the biological tissue or object through the matching layer and the sensing layer, it can generate a reflected ultrasonic wave (i.e., an echo signal). The echo signal reaches the piezoelectric ultrasonic transducer after passing through the sensing layer and the matching layer. Since there is a difference between the ultrasonic wave reflected through the valley and the ultrasonic wave reflected through the ridge, the echo signal received by the piezoelectric ultrasonic transducer can reflect the characteristic information of the texture of the biological tissue. The signal processing module connected to the piezoelectric ultrasonic transducer can then extract feature information from the echo signal and compare it with the stored feature information, thereby realizing the recognition of the texture of the biological tissue (eg, fingerprint).

[0054] In the conventional technology, in order to make the ultrasonic wave as close to full transmission as possible when passing through the matching layer, the thickness of the matching layer is configured to be approximately equal to n / 4 times λ of the ultrasonic wave propagating through the matching layer, where n is an odd number greater than 0, and λ is the equivalent wavelength of the ultrasonic wave signal in the matching layer. It can be seen that the thickness of the matching layer in the conventional technology is greater than or equal to 1 / 4 times the wavelength.

[0055] Therefore, the matching layer configured in the aforementioned manner is relatively thick, and the ultrasonic detection device having a matching layer with a relatively thick thickness may not be suitable for use in scenarios such as fingerprint recognition that have requirements on the thickness of the ultrasonic detection device.

[0056] In this regard, the present application provides an ultrasonic detection device, which is used to reduce the thickness of the matching layer while ensuring the transmittance of sound waves, thereby reducing the thickness of the ultrasonic detection device, thereby increasing the energy of the detection signal transmitted to the sensing layer and improving the sensitivity of ultrasonic detection.

[0057] Combine the following Figure 2 The ultrasonic detection device provided in this application is introduced.

[0058] like Figure 2 As shown, the ultrasonic detection device provided by the present 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 since this embodiment is mainly aimed at Figure 2The matching layer 03 in the figure is optimized and designed, and other layers in the figure (for example, the sensing layer 02 and the piezoelectric ultrasonic transducer 01) are simplified to be described as a single layer. However, in actual applications, the sensing layer 02 and the piezoelectric ultrasonic transducer 01 may include multiple layers of materials respectively.

[0059] Among them, 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 a detection signal and receive an echo signal. The detection signal generates an echo signal after passing through the matching layer 03 and the sensing layer 02 and reaching the biological tissue. The echo signal reaches the piezoelectric ultrasonic transducer 01 after passing through the sensing layer 02 and the matching layer 03. The echo signal carries the characteristic information of the biological tissue.

[0060] Among them, the matching layer 03 includes at least two acoustic impedance groups for realizing at least two acoustic impedance gradients. The acoustic impedance group refers to a component made of one or more materials with a certain acoustic impedance. The acoustic impedances of different acoustic impedance groups in the at least two acoustic impedance groups are different, and the acoustic impedances of the at least two acoustic impedance groups present a gradient change from the piezoelectric ultrasonic transducer 01 to the sensing layer 02. Therefore, at least two acoustic impedance groups can realize at least two acoustic impedance gradients. It should be understood that the acoustic impedance gradient can be a linear acoustic impedance gradient or a nonlinear acoustic impedance gradient, which is not limited here. The at least two acoustic impedance groups can realize the transition of acoustic impedance between the piezoelectric ultrasonic transducer 01 and the sensing layer 02. Exemplarily, if the acoustic impedance of the sensing layer 02 is less than the acoustic impedance of the piezoelectric ultrasonic transducer 01, the equivalent acoustic impedance of the acoustic impedance group close to the piezoelectric ultrasonic transducer 01 is greater than the equivalent acoustic impedance of the acoustic impedance group close 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 decreases. Exemplarily, 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 close to the piezoelectric ultrasonic transducer 01 is less than the equivalent acoustic impedance of the acoustic impedance group close to the sensing layer 02. For example, the equivalent acoustic impedances of the at least two acoustic impedance groups gradually increase from the piezoelectric ultrasonic transducer 01 to the sensing layer 02.

[0061] In addition, in addition to having a certain acoustic impedance, each acoustic impedance group also needs to have a thinner thickness when a certain acoustic transmission coefficient is reached. Specifically, 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. In other words, the thickness of the acoustic impedance group is not only less than 1 / 4 times the wavelength corresponding to the acoustic impedance group (i.e., the wavelength of the sound wave when it is transmitted in the acoustic impedance group), but also less than the thickness corresponding to the preset acoustic transmission coefficient.

[0062] like Figure 3A As shown, assume that the intermediate layer material 2 with a thickness of D and an acoustic impedance of R2 = ρ2×v2 is placed between material 1 with an acoustic impedance of R1 = ρ1×v1 and material 3 with an acoustic impedance of 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 part of it is transmitted into material 2 and further transmitted into material 3 behind the intermediate layer. During this process, the acoustic transmission coefficient and the thickness of the intermediate layer material 2 satisfy the following formula:

[0063]

[0064] where t represents the acoustic transmission coefficient of the intermediate layer impedance material 2, k2 represents the wave number (where k2 = 2π / λ2), D represents the thickness of the intermediate layer material 2, R1 represents the acoustic impedance of material 1, R2 represents the acoustic impedance of material 2, and R3 represents the acoustic impedance of material 3.

[0065] The proportion of the sound wave that can be transmitted when the sound wave passes through the intermediate layer is not only related to the acoustic impedance of the materials (i.e., R1, R2, and R3), but also related to the ratio of the thickness of the intermediate layer material 2 (i.e., D) to the wavelength of the sound wave when it propagates in the intermediate layer material 2 (i.e., λ2) (i.e., ).

[0066] In one example, if , and when R1≈R3, cosk2D≈1, sink2D≈0, based on formula 0.1, t≈1.

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

[0068] In another example, when (i.e., , that is, the thickness of the intermediate layer is an odd multiple of 1 / 4 of the wavelength, where n is an integer greater than 0), and when , based on formula 0.1, t≈1.

[0069] In this example, when the thickness of the intermediate layer is an odd multiple of 1 / 4 of the wavelength, the sound wave 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 acoustic 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 acoustic transmission coefficient is close to 1.

[0070] It can be seen from this that the relationship between the acoustic transmission coefficient of the impedance material and the thickness of the intermediate layer material has a periodically changing pattern.

[0071] like Figure 3B As shown in the figure, the periodic variation law is: when the thickness of the material is thin enough (for example, much less than 1 / 4 times the wavelength), the acoustic transmission coefficient is close to 1; when the thickness of the material is equal to an odd multiple of 1 / 4 times the wavelength, the acoustic transmission coefficient is also close to 1; when the thickness of the material is equal to an even multiple of 1 / 4 times the wavelength, the acoustic transmission coefficient is the lowest. Figure 3B In the example shown, the thickness of the acoustic impedance group is not only smaller than 1 / 4 times the wavelength corresponding to the acoustic impedance group (i.e., the wavelength of the sound wave when it is transmitted in the acoustic impedance group), but when the value of the preset sound transmission coefficient is high, the thickness of the acoustic impedance group may also be smaller than 1 / 8 times 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 a material is equal to an even multiple of 1 / 4 times the wavelength, the acoustic transmission coefficient of sound waves in different materials is different. Figure 3C As shown in the figure, when the thickness of the metal material is much smaller than 1 / 4 times the wavelength (i.e., the wavelength of the sound wave when propagating in the metal material) or the thickness of the metal material is equal to an odd multiple of 1 / 4 times the wavelength, the sound transmission coefficient is close to 1; when the thickness of the polymer material is much smaller than 1 / 4 times the wavelength (i.e., the wavelength of the sound wave when propagating in the polymer material) or the thickness of the polymer material is equal to an odd multiple of 1 / 4 times the wavelength, the sound transmission coefficient is also close to 1. However, when the thickness of the metal material is equal to an even multiple of 1 / 4 times the wavelength, the sound transmission coefficient of the intermediate layer made of the metal material is close to 0.5 (i.e., 50%); and when the thickness of the polymer material is equal to an even multiple of 1 / 4 times the wavelength, the sound transmission coefficient of the intermediate layer made of the polymer material is close to 0.1 (i.e., 10%).

[0073] It can be seen that when the thickness of each acoustic impedance group in the matching layer is much smaller than 1 / 4 times the wavelength corresponding to the acoustic impedance group (i.e., the wavelength of the sound wave when it is transmitted in the acoustic impedance group), the sound wave can have a higher sound transmission coefficient when passing through the acoustic impedance group. Therefore, the thickness of the acoustic impedance group can be selected based on the preset sound transmission coefficient from 0 to 1 / 4 times the wavelength. Exemplarily, the preset sound transmission coefficient is greater than or equal to 60%. For example, the preset sound transmission coefficient is equal to 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95%, etc. Of course, in actual applications, the preset sound transmission coefficient can also be other values, which are not listed here one by one.

[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 the acoustic impedance groups contained in the matching layer. For example, taking the matching layer #1 including the acoustic impedance group 1 and the acoustic impedance group 2 as an example, the preset acoustic transmission coefficient is 70%. If the acoustic transmission coefficient is 90% when the thickness of the acoustic impedance group 1 is configured to be 0.08 times λ1 (i.e., the wavelength corresponding to the acoustic impedance group 1, i.e., the wavelength of the sound wave when propagating in the acoustic impedance group 1), and the acoustic transmission coefficient is 80% when the thickness of the acoustic impedance group 2 is configured to be 0.12 times λ2 (i.e., the wavelength corresponding to the acoustic impedance group 2, i.e., the wavelength of the sound wave when propagating in the acoustic impedance group 2), then the thickness of the matching layer #1 is (0.08λ1+0.12λ2), and the acoustic transmission coefficient of the 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, and the thickness of the acoustic impedance group is set to be much smaller than 1 / 4 of the thickness of the wavelength corresponding to the acoustic impedance group while ensuring a sufficient acoustic impedance coefficient. Therefore, the matching layer composed of the at least two acoustic impedance groups can achieve acoustic impedance gradient matching and have a thinner thickness while ensuring transmittance. Therefore, it is beneficial to reduce the thickness of the ultrasonic detection device, 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.

[0076] The specific implementation of at least two acoustic impedance groups is further introduced below:

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

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

[0079] In this embodiment, it is proposed that when each acoustic impedance group satisfies a 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 times the equivalent wavelength, which is beneficial for making the process of the sound waves 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 have multiple implementations. In one implementation, an acoustic impedance group can be formed by stacking two sheets made of different acoustic impedance materials. In another implementation, an acoustic impedance group can be formed by filling another acoustic impedance material in a hole etched on an acoustic impedance material. In another implementation, an acoustic impedance group can be formed by mixing metal particles and thermoplastic polymer particles and then pressing them at high temperature. The at least two acoustic impedance groups contained in a matching layer can both adopt one of the aforementioned implementations, or they can adopt different implementations respectively, which will not be listed one by one in this embodiment.

[0081] This embodiment is described by taking as an example the implementation method in which an acoustic impedance group includes two sheets made of different acoustic impedance materials stacked together. Figure 4 As shown, each acoustic impedance group in the matching layer 03 includes a low acoustic impedance layer and a high acoustic impedance layer, and two adjacent acoustic impedance groups are connected through the low acoustic impedance layer. Figure 4 The acoustic impedance group 1 is adjacent to the acoustic impedance group 2, and the high acoustic impedance layer of the acoustic impedance group 1 is connected to the high acoustic impedance layer of the acoustic impedance group 2 through the low acoustic impedance layer of the acoustic impedance group 2. In addition, the low acoustic impedance layer of the acoustic impedance group close to the piezoelectric ultrasonic transducer 01 (for example, the low acoustic impedance layer of the acoustic impedance group 1) is connected to the piezoelectric ultrasonic transducer 01, and the acoustic impedance group close to the sensing layer 02 is connected to the sensing layer 02 through the adhesive layer. In other words, the matching layer 03 is formed by staggered stacking of at least two low acoustic impedance layers and at least two high acoustic impedance layers, and an acoustic impedance gradient is formed by adjacent low acoustic impedance layers and high acoustic impedance layers. Since an acoustic impedance group formed by cross-stacked low acoustic impedance layers and high acoustic impedance layers has a thinner thickness than an acoustic impedance group made of only one material, 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 propagating sound waves, improve the sensitivity of ultrasonic detection, and improve the valley-ridge contrast and signal-to-noise ratio.

[0082] In a possible embodiment, the thickness of the low acoustic impedance layer is less than 1 / 8 times the wavelength corresponding to the low acoustic impedance layer, and the thickness of the high acoustic impedance layer is less than 1 / 8 times the wavelength corresponding to the high acoustic impedance layer. Exemplarily, 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. Exemplarily, 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 thickness of the low acoustic impedance layer and the thickness of the high acoustic impedance layer in the same acoustic impedance group may be the same or different, and the present application is not limited thereto.

[0083] In this embodiment, the low acoustic impedance layer and the high acoustic impedance layer are configured as thin layers less than 1 / 8 times the wavelength, that is, the matching layer is configured as a cross-stack of multiple thin low acoustic impedance layers and high acoustic impedance layers. 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 waves, improve the sensitivity of ultrasonic detection, and improve the valley-ridge contrast and signal-to-noise ratio.

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

[0085] In this embodiment, a polymer material with adhesive properties is used to make a low acoustic impedance layer, so that the low acoustic impedance layer can connect adjacent high acoustic impedance layers and can be connected to the piezoelectric ultrasonic transducer 01, without the need to configure a separate adhesive layer to connect each acoustic impedance group. Therefore, it is not only helpful to simplify the structure of the matching layer 03, but also helpful to reduce the thickness of the matching layer 03, and further helpful to reduce the thickness of the ultrasonic detection device, 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.

[0086] In one example, if Figure 5 As shown, at least two acoustic impedance groups include a first acoustic impedance group and a second acoustic impedance group. The low acoustic impedance layer l1 in the first acoustic impedance group is used to connect the piezoelectric ultrasonic transducer 01 and the high acoustic impedance layer h1 in the first acoustic impedance group. The low acoustic impedance layer l2 in the second acoustic impedance group is used to connect 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 through an adhesive layer (i.e., the 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 The equivalent acoustic impedance of the second acoustic impedance group is

[0087] In a 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, that is, the low acoustic impedance layer is equivalent to a spring; the high acoustic impedance layer in each acoustic impedance group has an equivalent mass, that is, the high acoustic impedance layer is equivalent to a oscillator. At this time, 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 in the acoustic impedance group and the equivalent mass of the high acoustic impedance layer.

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

[0089]

[0090] Among them, R m is the equivalent acoustic impedance of the acoustic impedance group, K is the equivalent stiffness coefficient of the low acoustic impedance layer in the acoustic impedance group, and M is the equivalent mass of the high acoustic impedance layer in the acoustic impedance group.

[0091] For ease of understanding, Figure 5 Take the matching layer shown as an example, Figure 5 The acoustic impedance group in can be equivalent to a spring oscillator model. Figure 6 As shown, the low acoustic impedance layer l1 in the first acoustic impedance group can be equivalent to a spring with a stiffness coefficient of K1, the high acoustic impedance layer h1 in the first acoustic impedance group can be equivalent to a vibrator with a mass of M1, the low acoustic impedance layer l2 in the second acoustic impedance group can be equivalent to a spring with a stiffness coefficient of K2, and the high acoustic impedance layer h2 in the second acoustic impedance group can be equivalent to a vibrator with a mass of M2. Based on the spring vibrator model, it can be obtained that: the equivalent acoustic impedance of the first acoustic impedance group The equivalent acoustic impedance of the second acoustic impedance group is

[0092] Since, the stiffness coefficient K of the low acoustic impedance layer can be expressed as Furthermore, the mass M of the high acoustic impedance layer can be expressed as M = ρ h D h (Formula 3.2), where ρ l represents the density of the material of the low acoustic impedance layer, v l The speed of sound waves transmitted in the low acoustic impedance layer, D l represents the thickness of the low acoustic impedance layer, ρ h Indicates the density of the material of the high acoustic impedance layer, D h Represents the thickness of the high acoustic impedance layer. Based on formula 1.1, formula 2.1 and formula 3.1, the following relationship 4.1 can be obtained:

[0093]

[0094] Among them, ρ l1 represents the density of the material of the low acoustic impedance layer l1 in the first acoustic impedance group, v l1 represents the acoustic velocity of the acoustic wave transmitted in the low acoustic impedance layer l1 in the first acoustic impedance group, D l1 represents the thickness of the low acoustic impedance layer l1 in the first acoustic impedance group, ρ h1 represents the density of the material of the high acoustic impedance layer h1 in the first acoustic impedance group, D h1 represents the thickness of the high acoustic impedance layer h1 in the first acoustic impedance group.

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

[0096]

[0097] Among them, ρ l2 represents the density of the material of the low acoustic impedance layer l2 in the second acoustic impedance group, v l2 represents the acoustic velocity of the acoustic wave transmitted in the low acoustic impedance layer l2 in the second acoustic impedance group, D l2represents the thickness of the low acoustic impedance layer l2 in the second acoustic impedance group, ρ h2 represents the density of the material of the high acoustic impedance layer h2 in the second acoustic impedance group, D h2 represents 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 formula 1.1. m1 , R m1 Substituting into equation 4.1, we can obtain the density ρ of the low acoustic impedance layer in the first acoustic impedance group: l1 、Sound speed v l1 and thickness D l1 and the density ρ of the high acoustic impedance layer in the first acoustic impedance group h1 and thickness D h1 When a certain material is selected as the low acoustic impedance layer, the density ρ of the low acoustic impedance layer l1 It is possible to determine the sound velocity v of the sound wave in the low acoustic impedance layer material. l1 It can also be determined that when a certain material is selected as the high acoustic impedance layer, the density ρ of the high acoustic impedance layer h1 Therefore, by adjusting the test material, it is possible to find a solution that makes D l1 +D h1 The first acoustic impedance group is composed of a low acoustic impedance layer material and a high acoustic impedance layer material with a smaller value.

[0099] Similarly, based on R m1 R can be determined by using formula 1.2 m2 , R m2 Substituting into equation 4.2, we can obtain the density ρ of the low acoustic impedance layer in the second acoustic impedance group: l2 、Sound speed v l2 and thickness D l2 and the density ρ of the high acoustic impedance layer in the second acoustic impedance group h2 and thickness D h2 When a certain material is selected as the low acoustic impedance layer, the density ρ of the low acoustic impedance layer l2 It can be determined that the sound velocity v of the sound wave in the low acoustic impedance layer material l2 It can also be determined that when a certain material is selected as the high acoustic impedance layer, the density ρ of the high acoustic impedance layer h2 Therefore, by adjusting the test, we can find the l2 +D h2 The second acoustic impedance group is composed of a low acoustic impedance layer material and a high acoustic impedance layer material with a smaller value.

[0100] To facilitate understanding, the following is an example:

[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 acoustic impedance of the first acoustic impedance group is expected to be And, it is expected that the acoustic impedance of the second acoustic impedance group R m1 and R m2 By substituting into equations 4.1 and 4.2 respectively, and 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, and we can 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] <![CDATA[v l1 (m / s)]]> <![CDATA[ρ l1 (kg / m 3 )]]> <![CDATA[v h1 (m / s)]]> <![CDATA[ρ h1 (kg / m 3 )]]> <![CDATA[D l1 (μm)]]> <![CDATA[D h1 (μm)]]> <![CDATA[R m1 (MRayl)]]> 1800 1100 4400 8900 3 6 7.9 1800 1100 4400 8900 10 21 8.1 1800 1100 5200 19300 3 3 8.2 1800 1100 5200 19300 10 9 7.8 2500 1000 4400 8900 4 5 8.3 2500 1000 4400 8900 12 14 8.1

[0104] In the example shown in Table 1-1, if material 1 (i.e., the speed of sound is 1800 m / s and the density is 1100 kg / m 3 The material 2 (i.e., the sound velocity is 4400 m / s and the density is 8900 kg / m) is the low acoustic impedance layer of the first acoustic impedance group and the material 3 (i.e., the sound velocity is 4400 m / s and the density is 8900 kg / m 3 The material of the first acoustic impedance group is the high acoustic impedance layer, then two sets of thickness solutions can be obtained. In the two sets of thickness solutions, if the thickness D of the low acoustic impedance layer in the first acoustic impedance group is l1 =3 μm, and the thickness D of the high acoustic impedance layer in the first acoustic impedance group h1 =6μm, then the actual acoustic impedance of the first acoustic impedance group is R m1 =7.9 MRayl. Among them, D l1 =3μm=3 / (v l1 / f0)=3 / (1800 / 13)≈0.022λ l1 , D h1 =6μm=6 / (v h1 / f0)=6 / (4400

[0105] / 13)≈0.018λ h1 Among them, D l1 <0.125λ l1 , which meets the above requirements on the thickness of the low acoustic impedance layer; D h1 <0.125λ h1 , which meets the above requirements on the thickness of the high acoustic impedance layer.

[0106] Similarly, if the thickness D of the low acoustic impedance layer in the first acoustic impedance group l1 =10μm≈0.072λ l1, and the thickness D of the high acoustic impedance layer in the first acoustic impedance group h1 =21μm≈0.062λ h1 , then the actual acoustic impedance of the first acoustic impedance group R m1 =8.1 MRayl. Among them, D l1 Meet the above requirements on the thickness of the low acoustic impedance layer, D h1 It also meets the aforementioned requirements regarding the thickness of the high acoustic impedance layer.

[0107] Similarly, if material 1 (i.e., the speed of sound is 1800 m / s and the density is 1100 kg / m 3 The material 3 (i.e., the sound velocity is 5200 m / s and the density is 19300 kg / m) is the low acoustic impedance layer of the first acoustic impedance group and the material 4 (i.e., the sound velocity is 5200 m / s and the density is 19300 kg / m 3 The material of the first acoustic impedance group is the high acoustic impedance layer, then two sets of thickness solutions can also be obtained. In the two sets of thickness solutions, if the thickness D of the low acoustic impedance layer in the first acoustic impedance group is l1 =3μm≈0.022λ l1 , and the thickness D of the high acoustic impedance layer in the first acoustic impedance group h1 =3μm≈0.0075λ h1 , then the actual acoustic impedance of the first acoustic impedance group R m1 =8.2 MRayl; if the thickness D of the low acoustic impedance layer in the first acoustic impedance group l1 =10μm≈0.072λ l1 , and the thickness D of the high acoustic impedance layer in the first acoustic impedance group h1 =9μm≈0.0225λ h1 , then the actual acoustic impedance of the first acoustic impedance group R m1 =7.8 MRayl.

[0108] Similarly, if material 4 (i.e., the speed of sound is 2500 m / s and the density is 1000 kg / m 3 The material 2 (i.e., the sound velocity is 4400 m / s and the density is 8900 kg / m) is the low acoustic impedance layer of the first acoustic impedance group and the material 3 (i.e., the sound velocity is 4400 m / s and the density is 8900 kg / m 3 The material of the first acoustic impedance group is the high acoustic impedance layer, then two sets of thickness solutions can also be obtained. In the two sets of thickness solutions, if the thickness D of the low acoustic impedance layer in the first acoustic impedance group is l1 =4μm≈0.0208λ l1 , and the thickness D of the high acoustic impedance layer in the first acoustic impedance group h1 =5μm≈0.015λ h1 , then the actual acoustic impedance of the first acoustic impedance group R m1 =8.3MRayl; if the thickness D of the low acoustic impedance layer in the first acoustic impedance group l1=12μm≈0.0624λ l1 , and the thickness D of the high acoustic impedance layer in the first acoustic impedance group h1 =14μm≈0.041λ h1 , then the actual acoustic impedance of the first acoustic impedance group R m1 =8.1 MRayl.

[0109] It can be seen that in the acoustic impedance group composed of the above-mentioned multiple materials combined in pairs, when material 1 (i.e., the sound velocity is 1800m / s and the density is 1100kg / m 3 The material 3 (i.e., the sound velocity is 5200 m / s and the density is 19300 kg / m) is the low acoustic impedance layer of the first acoustic impedance group and the material 4 (i.e., the sound velocity is 5200 m / s and the density is 19300 kg / m 3 When the material of the first acoustic impedance group is the high acoustic impedance layer of the first acoustic impedance group, the thickness of the first acoustic impedance group (i.e., D l1 +D h1 ) has the smallest value. Therefore, it can be determined that material 1 (i.e., the speed of sound is 1800m / s and the density is 1100kg / m 3 The material 3 (i.e., the sound velocity is 5200 m / s and the density is 19300 kg / m) is the low acoustic impedance layer of the first acoustic impedance group and the material 4 (i.e., the sound velocity is 5200 m / s and the density is 19300 kg / m 3 It should be understood that, since there are other examples of thicknesses in Table 1-1 that meet the requirements of the thickness of the low acoustic impedance layer and the thickness of the high acoustic impedance layer, if the thickness can meet the use requirements of the application scenario, the first acoustic impedance group can also be made of materials corresponding to other groups of thicknesses.

[0110] Table 1-2

[0111] <![CDATA[v l2 (m / s)]]> <![CDATA[ρ l2 (kg / m 3 )]]> <![CDATA[v h2 (m / s)]]> <![CDATA[ρ h2 (kg / m 3 )]]> <![CDATA[D l2 (μm)]]> <![CDATA[D h2 (μm)]]> <![CDATA[R m2 (MRayl)]]> 1800 1100 4400 8900 3 3 5.6 1800 1100 4400 8900 10 10 5.6 1800 1100 5200 19300 6 3 5.8 1800 1100 5200 19300 10 4 5.3 2500 1000 4400 8900 5 3 5.7 2500 1000 4400 8900 10 5 5.3

[0112] The meaning of the contents in Table 1-2 is similar to that in Table 1-1 and is not described in detail here.

[0113] In one example, the material corresponding to the thinnest solution is determined to be the material of the second acoustic impedance, that is, material 1 (i.e., the sound velocity is 1800 m / s and the density is 1100 kg / m 3 The material 2 (i.e., the sound velocity is 4400 m / s and the density is 8900 kg / m) is the low acoustic impedance layer of the second acoustic impedance group and the material 2 (i.e., the sound velocity is 4400 m / s and the density is 8900 kg / m 3 The material) is the high acoustic impedance layer of the second acoustic impedance group. At this time, the thickness D of the low acoustic impedance layer in the second acoustic impedance group l2 =3μm≈0.022λ l1 , and the thickness D of the high acoustic impedance layer in the second acoustic impedance group h2 =3μm≈0.0088λ h1 , the actual acoustic impedance of the second acoustic impedance group R m2=5.6 MRayl.

[0114] It should be noted that the material of the low acoustic impedance layer of the first acoustic impedance group can be the same as or different from the material of the low acoustic impedance layer of the second acoustic impedance group; the material of the high acoustic impedance layer of the first acoustic impedance group can be the same as or different from the material of the high acoustic impedance layer of the second acoustic impedance group. Fig. 7A As shown in FIG. 1 , the low acoustic impedance layer in the matching layer is made of the same material and the high acoustic impedance layer is made of a different material. Figure 7B As shown in FIG. 1 , the high acoustic impedance layer in the matching layer is made of the same material and the low acoustic impedance layer is made of a different material. Figure 7C As shown, the low acoustic impedance layer in the matching layer is made of a different material and the high acoustic impedance layer is made of a different material.

[0115] In this embodiment, the matching layer is configured as a "low-high-low-high-low" stacked structure, and the acoustic impedance gradient matching function is realized by stacking multiple low-high acoustic impedance groups, which reduces sound wave attenuation and parasitic reflections, is beneficial to improving the sensitivity of ultrasonic detection, and is beneficial to improving the valley-ridge contrast and signal-to-noise ratio.

[0116] Furthermore, the thickness of the matching layer 03 may be further optimized so that the matching layer 03 can achieve local resonance and increase the amplitude of the sound wave, thereby improving the detection sensitivity.

[0117] 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 value. The second threshold value is a real number greater than or equal to 0. The smaller the value of the second threshold value, the closer the equivalent resonant frequency is to the center frequency of the ultrasonic transducer, and the easier it is to produce local resonance. Optionally, when the second threshold value 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 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, which can cause local resonance in the sound wave transmission, thereby enhancing the amplitude of the sound wave.

[0118] In a possible implementation, the equivalent resonant frequencies of the 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.

[0119] Exemplarily, 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:

[0120]

[0121] Among them, f R1is the center frequency of the ultrasonic transducer; M1 is the equivalent mass of the high acoustic impedance layer in the first acoustic impedance group; K1 is the equivalent stiffness coefficient of the low acoustic impedance layer in the first acoustic impedance group; M2 is the equivalent mass of the high acoustic impedance layer in the second acoustic impedance group; K2 is the equivalent stiffness coefficient of the low acoustic impedance layer in the second acoustic impedance group.

[0122] From the formula 3.1 introduced above, we can know that the stiffness coefficient K of the low acoustic impedance layer can be calculated from the density ρ of the low acoustic impedance layer material. l 、Sound speed v l and thickness D l It is shown that, according to the formula 3.2 introduced above, the mass M of the high acoustic impedance layer can be obtained from the density ρ of the high acoustic impedance layer material. h and thickness D h Indicates. When the center frequency f of the piezoelectric ultrasonic transducer is known R1 In the case of , the density ρ of the low acoustic impedance layer in the two acoustic impedance groups can be obtained by substituting formula 3.1 and formula 3.2 into formula 5.1. l 、Sound speed v l and thickness D l and the density of the high acoustic impedance layer ρ h and thickness D h By adjusting the test material, we can find the constraints that make D l1 +D h1 +D l2 +D h2 The matching layer is composed of a low acoustic impedance layer material and a high acoustic impedance layer material with a smaller value, and the equivalent resonant frequency of the matching layer is close to the center frequency of the piezoelectric ultrasonic transducer.

[0123] For ease of understanding, the following is an example in which the material of the low acoustic impedance layer of the first acoustic impedance group is the same as the material of the low acoustic impedance layer of the second acoustic impedance group, and the material of the high acoustic impedance layer of the first acoustic impedance group is the same as the material of the high acoustic impedance layer of the second acoustic impedance group:

[0124] If the sound velocity v of the low acoustic impedance layer material l =1800m / s, density of low acoustic impedance layer material ρ l =1100kg / m 3 ; The sound velocity of the high acoustic impedance layer material is v h =4400m / s, density of high acoustic impedance layer material ρ h =8900kg / m 3 , piezoelectric ultrasonic transducer operating frequency f R1 =13MHz, then at least two sets of solutions can be obtained as shown in Table 2-1.

[0125] Table 2-1

[0126]

[0127] In this embodiment, the equivalent resonant frequencies of at least two acoustic impedance groups are configured to be 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 enhancing signal strength and improving sensitivity.

[0128] In addition, if Figure 8As shown, the piezoelectric ultrasonic transducer in the present application mainly includes an upper electrode layer, a lower electrode layer, a piezoelectric transceiver layer, a substrate and a functional layer. Among them, the upper electrode layer is located between the piezoelectric transceiver layer and the matching layer, and the thickness can be several microns to tens of microns. The material can be a metal material (for example, aluminum (Al), gold (Au), silver (Ag), platinum (Pt), copper (Cu), molybdenum (Mo), titanium (Ti), etc.) or a conductive polymer material (for example, indium tin oxide (Indium-Tin Oxide, ITO) and other conductive materials). The piezoelectric transceiver layer is located between the upper electrode layer and the lower electrode layer. The thickness of the piezoelectric transceiver layer depends on the resonant frequency of the entire acoustic module. The resonant frequency of the acoustic module is about 5 to 20 MHz, and the thickness of the piezoelectric transceiver layer is several microns to tens of microns. The material of the piezoelectric transceiver layer can be an organic polymer material (for example, polyvinylidene fluoride resin (PVDF) and its copolymer polyvinylidene fluoride trifluoroethylene (PVDF-TRFE) or blend PVDF-graphene oxide, etc.), or a piezoelectric ceramic material (for example, PZT and its alloy materials (lead lanthanum zirconate titanate ceramic PLZT, lead magnesium niobate PNZT), KNN (KxNa1-xNbO3), lead magnesium niobate-lead titanate (PMN-PT)), or an inorganic piezoelectric material aluminum nitride (AlN) and its alloy materials (ScxAl1-xN), zinc oxide (ZnO) and its alloy materials (VxZn1-xO), etc.). The lower electrode layer is located between the piezoelectric transceiver layer and the substrate. The lower electrode layer can be a pixelated electrode structure that can pixelate the echo signals of the fingerprint valleys and ridges. In order to achieve the resolution of fingerprint recognition, the center spacing of the pixelated electrodes is usually less than 100μm. The thickness of the lower electrode layer is usually very thin, at the nanometer level, to reduce the impact on the flatness of the piezoelectric transceiver layer deposited on its surface. The material of the lower electrode layer can be various conductive materials, including metal materials (for example, Al, Au, Ag, Pt, Cu, Mo, Ti, etc.) and conductive polymer materials (for example, ITO). The substrate is located below the lower electrode layer and is electrically connected to the substrate, and is responsible for processing the electrical signals collected by the lower electrode layer. The substrate can be a thin film transistor (TFT) circuit, the material of which can be a glass material; the substrate can also be a complementary metal oxide semiconductor circuit (CMOS) circuit, the material of which is a silicon material. The functional layer is located below the substrate, and the functions of the functional layer include but are not limited to sound reflection, sound absorption, mechanical support, etc., so the functional layer can be multilayer, which is not shown in the figure.

[0129] It should be noted that the order of some layers in the piezoelectric ultrasonic transducer can be reversed. For example, the piezoelectric transceiver layer can be located above the substrate or below the substrate. Fig.9AAs shown, the piezoelectric transceiver layer is located above the substrate, and the corresponding matching layer and the piezoelectric transducer are directly in contact with the electrode layer material; Fig. 9B As shown, the piezoelectric transceiver layer is located below the substrate, and the corresponding matching layer and the piezoelectric transducer are in direct contact with the substrate material. The acoustic impedance of general substrate materials (e.g., glass, silicon, etc.) is different from that of electrode materials (e.g., Al, Au, Ag, Pt, Cu, Mo, Ti, etc.), and the corresponding matching layer configuration is adjusted.

[0130] In addition, the present 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 fingerprints; the ultrasonic fingerprint chip is used to identify the characteristic information of the fingerprint based on the echo signal.

[0131] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0132] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. An ultrasonic detection 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, wherein the detection signal generates the echo signal after passing through the matching layer and the sensing layer and reaching the biological tissue, and the echo signal reaches the piezoelectric ultrasonic transducer after passing through the sensing layer and the matching layer, and the echo signal carries characteristic information of the biological tissue; In which, 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, the first threshold 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 is less than 1 / 4 times the wavelength corresponding to the acoustic impedance group.

2. The ultrasonic detection device according to claim 1, characterized in that: The equivalent resonant frequencies of the 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 frequency and the center frequency of the ultrasonic transducer is less than a second threshold.

3. The ultrasonic detection device according to claim 1 or 2, characterized in that: The total thickness of the at least two acoustic impedance groups is less than or equal to 1 / 4 times of an equivalent wavelength, and the equivalent wavelength is equal to the sum of wavelengths corresponding to each of the at least two acoustic impedance groups.

4. The ultrasonic detection device according to any one of claims 1 to 3, characterized in that: Each acoustic impedance group includes a low acoustic impedance layer and a high acoustic impedance layer, and 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 times the wavelength corresponding to the low acoustic impedance layer, and the thickness of the high acoustic impedance layer is less than 1 / 8 times the wavelength corresponding to the high acoustic impedance layer.

5. The ultrasonic detection device according to claim 4, characterized in that: The low acoustic impedance layer in each acoustic impedance group has an equivalent stiffness coefficient, the high acoustic impedance layer in each acoustic impedance group has an equivalent mass, and 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.

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

7. The ultrasonic detection device according to any one of claims 4 to 6, 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, and 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.

8. The ultrasonic detection device according to claim 6 or 7, characterized in that: The equivalent acoustic impedance of the acoustic impedance group, the equivalent stiffness coefficient of the low acoustic impedance layer in the acoustic impedance group, and the equivalent mass of the high acoustic impedance layer satisfy the following constraints: Among them, the R m is the equivalent acoustic impedance of the acoustic impedance group, K is the equivalent stiffness coefficient of the low acoustic impedance layer in the acoustic impedance group, and M is the equivalent mass of the high acoustic impedance layer in the acoustic impedance group.

9. The ultrasonic detection device according to claim 7, 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 f R1 is the center frequency of the ultrasonic transducer; K1 is the equivalent stiffness coefficient of the low acoustic impedance layer in the first acoustic impedance group; M1 is the equivalent mass of the high acoustic impedance layer in the first acoustic impedance group; K2 is the equivalent stiffness coefficient of the low acoustic impedance layer in the second acoustic impedance group; M2 is the equivalent mass of the high acoustic impedance layer in the second acoustic impedance group.

10. The ultrasonic detection device according to any one of claims 4 to 9, characterized in that: The material of the low acoustic impedance layer is a polymer material, and the material of the high acoustic impedance layer is a metal material or an inorganic material.

11. The ultrasonic detection device according to any one of claims 4 to 10, characterized in that: The acoustic impedance of the low acoustic impedance layer is less than or equal to 4 mega-Rayles; the acoustic impedance of the high acoustic impedance layer is greater than or equal to 20 mega-Rayles.

12. The ultrasonic detection device according to any one of claims 1 to 11, characterized in that: The preset sound transmission coefficient is greater than or equal to 60%.

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

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