Differential ultrasonic transducer based on acoustic differential method and preparation method thereof

Abstract

The invention discloses a differential ultrasonic transducer based on an acoustic differential method and a preparation method of the differential ultrasonic transducer. The differential ultrasonic transducer comprises a shell, a supporting layer, a backing layer, a bottom electrode layer, a top electrode layer and a piezoelectric unit layer. When external stress is received, acoustic differential signals with equal amplitude and opposite phases are output. The acoustic differential pair is creatively introduced into the piezoelectric unit layer, differential signals are generated from a physical source, external noise is effectively suppressed, and the signal-to-noise ratio is remarkably increased; the preparation method of the differential ultrasonic transducer is highly compatible with the process of a traditional transducer, and industrial production is easy to realize. The differential ultrasonic transducer is applied to a photoacoustic microscope system, and the imaging signal-to-noise ratio and contrast ratio in a complex electromagnetic and vibration environment can be remarkably improved under the condition of not depending on additional shielding or multiple averaging. The preparation process has the characteristics of high integration level and excellent anti-interference performance, and provides a reliable device basis for high-sensitivity photoacoustic imaging.

Description

Technical Field

[0001] This invention belongs to the field of piezoelectric devices and biomedical imaging technology, specifically relating to a differential ultrasonic transducer based on acoustic differential method and its fabrication method. Background Technology

[0002] Optical-resolution photoacoustic microscopy (OR-PAM) is a high-resolution biomedical imaging technique based on the photoacoustic effect. It achieves sub-micron resolution imaging with optical absorption as the contrast by detecting the ultrasound signal generated after tissue absorbs pulsed laser light. It shows great potential in fields such as vascular network imaging, tumor detection, and brain function research. The ultrasound transducer, as the core component of the OR-PAM system, is responsible for receiving weak broadband photoacoustic signals, and its performance directly affects the system's imaging quality.

[0003] However, traditional piezoelectric sensors operate based on the piezoelectric effect, and their performance is easily affected by external noise such as electromagnetic interference and mechanical vibration in actual imaging. In complex clinical or industrial environments, electromagnetic noise from power supplies, motors, wireless devices, etc., as well as mechanical vibrations from equipment operation or external transmission, can couple into the signal transmission path as noise, significantly reducing the system's signal-to-noise ratio (SNR). This decrease in SNR not only limits imaging sensitivity but also affects imaging speed and the realization of other functions. Currently used hardware-based noise reduction strategies, such as electromagnetic shielding, and software-based noise reduction strategies, such as signal averaging and filtering, increase system size, imaging time, and have serious limitations in adaptability to multi-source noise. Summary of the Invention

[0004] To address the aforementioned problems in the prior art, this invention provides a differential ultrasonic transducer based on the acoustic differential method and its fabrication method. The technical problem to be solved by this invention is achieved through the following technical solution: In a first aspect, the present invention provides a differential ultrasonic transducer based on an acoustic differential method, comprising: The structure comprises an outer shell, a support layer, a backing layer, a bottom electrode layer, a top electrode layer, and a piezoelectric unit layer; among which, The outer shell encloses the support layer, backing layer, bottom electrode layer, top electrode layer, and piezoelectric unit layer; The support layer is disposed at the bottom of the outer shell; The backing layer, bottom electrode layer, piezoelectric unit layer and top electrode layer are arranged sequentially from bottom to top above the support layer; The top electrode layer achieves acoustic focusing by adding an acoustic lens and acoustic impedance matching by adding a matching layer. The piezoelectric unit layer is composed of acoustic differential pairs; The differential ultrasonic transducer outputs acoustic differential signals with equal amplitude and opposite phase when receiving external stress.

[0005] In one embodiment of the invention, the outer shell has a ring-shaped shape.

[0006] In one embodiment of the invention, the acoustic differential pair includes at least one pair of piezoelectric sensing units with opposite polarization directions.

[0007] In one embodiment of the invention, the backing layer and the bottom electrode layer are segmented according to the characteristics of the acoustic differential pair, and the spatial arrangement of the backing layer and the bottom electrode layer is consistent with the acoustic differential pair.

[0008] In one embodiment of the present invention, the acoustic lens includes: Spherical concave lenses, holographic lenses, and acoustic metasurfaces.

[0009] In one embodiment of the present invention, the matching layer conforms to the quarter-wavelength design rule, and the number of matching layers is at least one.

[0010] In one embodiment of the present invention, the piezoelectric unit layer is a material with polarization reversal properties, comprising: Piezoelectric ceramics, piezoelectric single crystals, piezoelectric composite materials, or piezoelectric thin films.

[0011] Secondly, the present invention provides a method for fabricating a differential ultrasonic transducer based on an acoustic differential method, comprising: Select an outer casing that is fixed to a glass substrate; An epoxy resin support layer is formed on the bottom of the casing; A backing layer and a bottom electrode layer are sequentially formed on the upper surface of the support layer; Using sputtering, grinding, and cutting and arranging processes, a piezoelectric unit layer composed of acoustic differential pairs is generated on the upper surface of the bottom electrode layer; A top electrode layer is generated on the upper surface of the piezoelectric unit layer; The spatial arrangement of the backing layer and the bottom electrode layer is consistent with that of the acoustic differential pair; The acoustic differential pair includes at least one pair of piezoelectric sensing units with opposite polarization directions.

[0012] The beneficial effects of this invention are: The solution provided by this invention creatively introduces acoustic differential pairs into the piezoelectric unit layer to generate differential signals from a physical source, effectively suppressing external noise and significantly improving the signal-to-noise ratio. The fabrication method of the differential ultrasonic transducer is highly compatible with the process of traditional transducers, facilitating industrial-scale production. Furthermore, the differential ultrasonic transducer proposed in this invention can significantly suppress external noise and improve the imaging quality of photoacoustic images in noisy environments without relying on complex hardware shielding or high-cost software algorithms, while also possessing both real-time imaging speed and robust signal acquisition. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the structure of a differential ultrasonic transducer based on the acoustic differential method provided in an embodiment of the present invention; Figure 2 This is an exploded view of the structure of a differential ultrasonic transducer based on the acoustic differential method provided in an embodiment of the present invention. Figure 3 This is a schematic diagram illustrating the steps of a method for fabricating a differential ultrasonic transducer based on the acoustic differential method provided in an embodiment of the present invention. Figure 4 This is a schematic diagram of the fabrication method of a differential ultrasonic transducer based on the acoustic differential method provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of a differential ultrasound transducer based on the acoustic differential method applied to an OR-PAM imaging system, as provided in an embodiment of the present invention.

[0014] Figure 6 The figure shows the experimental results of human hair obtained under external noise interference when a differential ultrasonic transducer based on the acoustic differential method is applied to an OR-PAM system according to an embodiment of the present invention.

[0015] Figure Labels 1-Outer shell; 2-Support layer; 3-Backing layer; 4-Bottom electrode layer; 5-Top electrode layer; 6-Piezoelectric unit layer. Detailed Implementation

[0016] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0017] To overcome the low signal-to-noise ratio and insufficient anti-interference capability of existing ultrasonic transducers in complex noise environments, this invention provides a differential ultrasonic transducer based on the acoustic differential method and its fabrication method.

[0018] Below, we will first introduce a differential ultrasonic transducer based on the acoustic differential method provided in the embodiments of the present invention.

[0019] The present invention provides a differential ultrasonic transducer based on an acoustic differential method, such as... Figure 1 As shown, it may include: 1. Outer shell; 2. Support layer; 3. Backing layer; 4. Bottom electrode layer; 5. Top electrode layer; and 6. Piezoelectric unit layer; wherein, The outer shell 1 encloses the support layer 2, the backing layer 3, the bottom electrode layer 4, the top electrode layer 5, and the piezoelectric unit layer 6; The support layer 2 is disposed at the bottom of the outer casing 1; The backing layer 3, the bottom electrode layer 4, the piezoelectric unit layer 6, and the top electrode layer 5 are arranged sequentially from bottom to top above the support layer 2; Top electrode layer 5: acoustic focusing is achieved by adding an acoustic lens, and acoustic impedance matching is achieved by adding a matching layer; The piezoelectric unit layer 6 consists of acoustic differential pairs; Differential ultrasonic transducers output acoustic differential signals with equal amplitude and opposite phase when subjected to external stress.

[0020] An exploded view of the differential ultrasonic transducer provided in this embodiment of the invention is shown below. Figure 2 As shown, the following will be combined with Figure 2 The various structures proposed in the embodiments of the present invention will be described.

[0021] The shape of the outer shell 1 is as follows Figure 2 As shown, it can include a ring shape.

[0022] The housing 1 completely encompasses the sides of the other structures in the differential ultrasonic transducer.

[0023] The material of the support layer 2 may include epoxy resin.

[0024] The backing layer 3 uses a two-component room-temperature curing silver paste E-solder 3022, whose acoustic impedance is matched with that of the piezoelectric material, which can effectively absorb back acoustic waves and shorten the impulse response.

[0025] The backing layer 3 and the bottom electrode layer 4 are divided according to the characteristics of the acoustic differential pair. The spatial arrangement of the backing layer 3 and the bottom electrode layer 4 is consistent with the acoustic differential pair to ensure the coordination and unity of acoustic and electrical performance.

[0026] The backing layer 3 and the bottom electrode layer 4 are designed to be segmented according to the characteristics of the acoustic differential pair, and are arranged in a 1001 diagonal pattern to ensure that their spatial arrangement is consistent with the acoustic differential pair.

[0027] The top electrode layer 5 may include an acoustic lens and a matching layer.

[0028] The top electrode layer 5 can achieve acoustic focusing by adding an acoustic lens and acoustic impedance matching by adding a matching layer.

[0029] Acoustic lenses may include: Spherical concave lenses, holographic lenses, and acoustic metasurfaces.

[0030] The matching layer conforms to the quarter-wavelength design rule, and the number of matching layers is at least one. For example, the number of matching layers includes, but is not limited to, one, two, and three layers.

[0031] An acoustic lens is provided at the front end of the top electrode layer 5. In this embodiment of the invention, a concave lens made of epoxy resin is used to focus sound waves. The acoustic lens also serves as an acoustic impedance matcher.

[0032] Piezoelectric unit layer 6 is a material with polarization reversal properties and may include: Piezoelectric ceramics, piezoelectric single crystals, piezoelectric composite materials, or piezoelectric thin films.

[0033] The piezoelectric unit layer 6 is composed of acoustic differential pairs, which may include at least one pair of piezoelectric sensing units with opposite polarization directions.

[0034] For example, such as Figure 2 As shown, the piezoelectric unit layer 6 can be composed of two pairs of piezoelectric sensing units with opposite polarization directions. The material of the piezoelectric unit layer 6 can be lithium niobate (LiNbO3) single crystal, with a size of 4mm × 4mm. The operating frequency is designed to be 25MHz. The piezoelectric material is processed to the required thickness (110µm) using a precision grinding process to meet the resonant frequency requirements.

[0035] This differential ultrasonic transducer has two independent signal output ports, which are respectively connected to the positive polarization unit and the anti-polarization unit in piezoelectric unit layer 6. The output ports are led out through SMA connectors to ensure isolation between the two signal paths. One port outputs the positive polarization unit signal, and the other port outputs the anti-polarization unit signal. The two signals constitute acoustic differential signals with equal amplitude and opposite phase.

[0036] The differential ultrasonic transducer provided in this invention utilizes an innovative acoustic differential pair design to generate differential signals from a physical source, effectively suppressing external noise and significantly improving the signal-to-noise ratio. This differential ultrasonic transducer can directly output acoustic differential signals with equal amplitude and opposite phase when receiving external stress, and combined with a differential processing unit, effectively suppresses external noise.

[0037] Secondly, embodiments of the present invention also provide a method for fabricating a differential ultrasonic transducer based on an acoustic differential method, such as... Figure 3 As shown, it may include: S1, Select the outer casing 1 and fix it to the glass substrate; S2, using epoxy resin to form a support layer 2 at the bottom of the outer shell 1; S3, a backing layer 3 and a bottom electrode layer 4 are sequentially generated on the upper surface of the support layer 2; S4. Using sputtering, grinding and cutting arrangement processes, a piezoelectric unit layer 6 composed of acoustic differential pairs is generated on the upper surface of the bottom electrode layer 4. S5, a top electrode layer 5 is formed on the upper surface of the piezoelectric unit layer 6; The spatial arrangement of the backing layer 3 and the bottom electrode layer 4 is consistent with the acoustic differential pair. Acoustic differential pairs include at least one pair of piezoelectric sensing units with opposite polarization directions.

[0038] A schematic diagram of the fabrication process of a differential ultrasonic transducer, as shown below. Figure 4 As shown, the outer shell is fixed to the glass substrate, epoxy resin is poured into the outer shell 1, and a support layer 2 is formed at the bottom of the outer shell 1. A backing layer 3 and a bottom electrode layer 4, segmented according to the characteristics of the acoustic differential pairs, are formed on the support layer 2. Figure 4 As can be seen from this, the fabrication process of piezoelectric unit layer 6 may include: A whole block of piezoelectric material of a specified thickness is cut into piezoelectric units of a certain size through a cutting process. One part of the units remains unchanged as a positive (reverse) polarization unit, marked as 1 (0); the other part is rotated 180 degrees around its axis so that its polarization direction is reversed relative to the other half of the element, and is marked as a negative (positive) polarization unit, marked as 0 (1). Take two positively polarized and two negatively polarized units respectively, and arrange them in a diagonal form, that is, an acoustic difference pair in the form of positive-negative-positive (1001).

[0039] The 1001-type acoustic differential pairs are integrated with the backing layer 3, the support layer 2, and the outer shell 1 to form a complete differential ultrasonic transducer.

[0040] Piezoelectric materials of a specified thickness can be obtained by grinding according to the required frequency.

[0041] For example, the fabrication process of the piezoelectric unit layer 6 may include: The lithium niobate single crystal bulk material, which has been sputtered with gold electrodes on both sides, is precision ground to a thickness of 110μm and then cut into 4.2mm×4.2mm square units using a cutting machine.

[0042] The key steps in preparing acoustic differential pairs may include: dividing the cut piezoelectric units into two groups, one group retaining its original orientation as a positive polarization unit, marked "1"; and rotating the other group 180 degrees around its axis to reverse its polarization direction, as an anti-polarization unit, marked "0".

[0043] The prepared E-solder 3022 was filled into the positive polarization unit and the anti-polarization unit respectively. After drying, it was ground to 1mm and then cut into 4mm×4mm square units by a cutting machine.

[0044] Two units are selected from each of the two groups and arranged diagonally in a "1001" pattern to form an acoustic differential pair. Specifically, two positively polarized units ("1") and two anti-polarized units ("0") are arranged in a 2×2 matrix, where the units on the diagonal are those with the same polarization direction.

[0045] The arranged acoustic differential pairs are connected by wires to form two output ports. Finally, they are assembled with the housing and potted with epoxy resin to complete the assembly of the differential ultrasonic transducer.

[0046] The fabrication method provided in this invention has high compatibility with traditional transducer processes and is easy to industrialize. Furthermore, the differential ultrasonic transducer proposed in this invention can significantly suppress external noise and improve the imaging quality of photoacoustic images in noisy environments without relying on complex hardware shielding or high-cost software algorithms, while also possessing both real-time imaging speed and robust signal acquisition.

[0047] An exemplary schematic diagram of a differential ultrasound transducer applied to an OR-PAM imaging system, as shown below. Figure 5 As shown, a differential ultrasonic transducer is integrated into a photoacoustic microscopy imaging system as a photoacoustic signal receiver; a 532nm pulsed laser source is used, and the laser is focused onto the sample through a water immersion objective; a three-dimensional electric platform is used to control the laser and the differential ultrasonic transducer to scan the sample; based on the differential ultrasonic transducer with two output ports, the imaging system is used for two independent acquisition channels, and data is acquired by a dual-channel data acquisition card; the acquired data from the two channels are subtracted to obtain a high-quality differential photoacoustic image.

[0048] Understandably, a photoacoustic microscopy imaging system is an optical resolution photoacoustic microscopy system.

[0049] Differential ultrasonic transducers can be focused differential ultrasonic transducers.

[0050] The specific steps for applying the differential ultrasonic transducer provided in this embodiment of the invention in an optical microscopic imaging system may include: The system configuration may include: a 532nm pulsed laser source with a pulse width of 2ns and a repetition frequency of 10kHz; a water immersion objective (numerical aperture 0.25); a three-axis motorized scanning platform; a dual-channel data acquisition card with a sampling rate of 200MHz; and two low-noise amplifiers.

[0051] The fabricated differential ultrasonic transducer was fixed in a water immersion tank, ensuring its acoustic focus coincided with its optical focus. The transducer's two output ports were connected to two independent signal channels. A waveform generator was used to synchronously control the laser pulses, scanning motion, and data acquisition.

[0052] During imaging, a pulsed laser is focused onto the sample through a water immersion objective, generating a photoacoustic signal. A differential ultrasonic transducer simultaneously receives the photoacoustic signal and outputs two raw signals with opposite phases. These two signals are then amplified with low noise and simultaneously acquired by a dual-channel data acquisition card.

[0053] During the signal processing stage, the acquired data from the two channels are subjected to real-time differential calculation. Since the effective photoacoustic signals are out of phase in the two channels, the signal is enhanced after differential processing; while the common-mode noise is in phase in the two channels, and they cancel each other out after differential processing.

[0054] To verify the system performance, this embodiment of the invention selected to conduct imaging experiments on human hair samples. The experimental results of human hair obtained under external noise interference when the differential ultrasound transducer is applied to the OR-PAM system are shown in the image below. Figure 6 As shown, under the same experimental conditions, the system using the differential ultrasonic transducer can obtain clear hair images in a strong electromagnetic interference environment. Compared with the traditional ultrasonic transducer, the differential ultrasonic transducer provided in this embodiment of the invention improves the contrast signal-to-noise ratio (CNR) from 0.89 to 11.85, which is 13 times higher. The signal-to-noise ratio is significantly improved, and high-quality imaging can be achieved without multiple signal averaging.

[0055] The application of this differential ultrasonic transducer in photoacoustic microscopy shows that it can significantly suppress external noise and improve the imaging quality of photoacoustic images in noisy environments without relying on complex hardware shielding or high-cost software algorithms. It also combines the real-time imaging speed with the robustness of signal acquisition.

[0056] It should be noted that, in the description of this invention, the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0057] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A differential ultrasonic transducer based on the acoustic differential method, characterized in that, include: The shell (1), support layer (2), backing layer (3), bottom electrode layer (4), top electrode layer (5), and piezoelectric unit layer (6); among which, The outer shell (1) encloses the support layer (2), backing layer (3), bottom electrode layer (4), top electrode layer (5) and piezoelectric unit layer (6); The support layer (2) is disposed at the bottom of the outer shell (1); The backing layer (3), bottom electrode layer (4), piezoelectric unit layer (6) and top electrode layer (5) are arranged sequentially from bottom to top above the support layer (2); The top electrode layer (5) achieves acoustic focusing by adding an acoustic lens and acoustic impedance matching by adding a matching layer; The piezoelectric unit layer (6) is composed of acoustic differential pairs; The differential ultrasonic transducer outputs acoustic differential signals with equal amplitude and opposite phase when receiving external stress.

2. A differential ultrasonic transducer based on the acoustic differential method according to claim 1, characterized in that, The outer shell (1) has an annular shape.

3. A differential ultrasonic transducer based on the acoustic differential method according to claim 1, characterized in that, The acoustic differential pair includes at least one pair of piezoelectric sensing units with opposite polarization directions.

4. A differential ultrasonic transducer based on the acoustic differential method according to claim 1, characterized in that, The backing layer (3) and the bottom electrode layer (4) are divided according to the characteristics of the acoustic differential pair, and the spatial arrangement of the backing layer (3) and the bottom electrode layer (4) is consistent with the acoustic differential pair.

5. A differential ultrasonic transducer based on the acoustic differential method according to claim 1, characterized in that, The acoustic lens includes: Spherical concave lenses, holographic lenses, and acoustic metasurfaces.

6. A differential ultrasonic transducer based on the acoustic differential method according to claim 1, characterized in that, The matching layer conforms to the quarter-wavelength design rule, and the number of matching layers is at least one.

7. A differential ultrasonic transducer based on the acoustic differential method according to claim 1, characterized in that, The piezoelectric unit layer (6) is a material with polarization reversal properties, including: Piezoelectric ceramics, piezoelectric single crystals, piezoelectric composite materials, or piezoelectric thin films.

8. A method for fabricating a differential ultrasonic transducer based on the acoustic differential method, characterized in that, include: Select the outer shell (1) and fix it to the glass substrate; A support layer (2) is formed at the bottom of the outer casing (1) using epoxy resin; A backing layer (3) and a bottom electrode layer (4) are sequentially formed on the upper surface of the support layer (2); Using sputtering, grinding and cutting arrangement processes, a piezoelectric unit layer (6) composed of acoustic differential pairs is generated on the upper surface of the bottom electrode layer (4); A top electrode layer (5) is formed on the upper surface of the piezoelectric unit layer (6); The spatial arrangement of the backing layer (3) and the bottom electrode layer (4) is consistent with that of the acoustic differential pair; The acoustic differential pair includes at least one pair of piezoelectric sensing units with opposite polarization directions.

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