Ultrasonic transducer gradient matching layer based on PVDF and preparation method thereof

Abstract

The invention discloses an ultrasonic transducer gradient matching layer based on PVDF and a preparation method thereof. The PVDF film is obtained by uniformly mixing PVDF and additives and forming a film, the thickness after film formation is 1 [mu] m to 80 [mu] m. The additive is one or more of hollow glass beads, barium titanate, niobium magnesium lead titanate and tungsten powder. According to the method, the matching layers with different acoustic impedances can be obtained by doping different types of additives with different contents into the PVDF, so that the matching layers with the impedance values changing in a gradient manner are made by stacking the matching layers with the acoustic impedances sequentially reduced. When the acoustic impedance of the five matching layers from inside to outside is 10 <-12 > MRayls, 6 <-8 > MRayls, 3 <-4 > MRayls, 2 <-3 > MRayls and 1.5 <-2 > MRayls in sequence, the transmissivity of the ultrasonic transducer is obviously improved and can be improved to 0.70-0.72, and the performance of the ultrasonic transducer can be effectively improved. In addition, the prepared matching layer sample is uniform in density distribution and good in transmission stability.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrasonic transducers, and in particular to an ultrasonic transducer, a gradient matching layer design and a preparation method thereof. Background Art

[0002] An ultrasonic transducer is a complex electronic device that converts electrical signals into ultrasonic signals and is able to receive ultrasonic signals returned from the object being detected (such as the human body) and reconvert them into electrical signals. In the working mechanism of ultrasonic transducers, piezoelectric composites play a core role. Using the piezoelectric effect, this material can convert the electrical signal applied to it into mechanical vibrations, thereby generating ultrasonic signals. Similarly, when an ultrasonic signal is incident on a piezoelectric composite, the vibration of the material generates an electrical signal, thereby realizing the signal receiving function.

[0003] In the field of medical ultrasound, the acoustic impedance of piezoelectric composites is usually in the range of 16 to 30 MRayls, while the acoustic impedance of typical human tissue is about 1.5 MRayls. Due to the significant difference in acoustic impedance between piezoelectric composites and human tissue, if there is no appropriate matching layer, a large amount of ultrasonic reflection will occur at the interface between the transducer and human skin, resulting in the loss of ultrasonic energy. This energy loss directly affects the working efficiency and imaging quality of the ultrasonic transducer.

[0004] The main function of the acoustic matching layer is impedance matching, which is responsible for efficiently channeling the acoustic energy flow into the medium, improving the energy utilization efficiency, and playing a great role in improving the sensitivity and bandwidth of the ultrasonic transducer. Traditional acoustic matching layers are often single-layered, and the transmission efficiency of ultrasonic waves is not high. The design of multi-layer matching is still mainly double-layered. Since the preparation process of the acoustic matching layer should be convenient, inexpensive, and easy to produce, it is very necessary to design a truly low-loss, high-bandwidth, and easy-to-process acoustic matching layer. The present invention will focus on designing and manufacturing high-frequency ultrasonic transducers with multi-layer gradient acoustic matching layers, increasing the sensitivity and bandwidth of ultrasonic transducers, and making contributions to the field of medical ultrasound. Summary of the invention

[0005] Currently in the field of high-frequency transducers, the thickness of the matching layer often needs to be very thin, and most of the time, the matching layer is made to reach the optimal thickness by reducing friction. However, this solution often has problems such as insufficient precision when making particularly thin matching layers. Based on the deficiencies in the prior art, the present invention proposes an ultrasonic transducer with a gradient matching layer and a method for making the same. A strategy of gradient superposition of multiple matching layers with different acoustic impedances is adopted to achieve a better acoustic impedance matching between the piezoelectric composite material and the human tissue. By using the PVDF drying and molding method, the thickness of the manufactured matching layer is made thinner, and it can be better used in high-frequency ultrasonic transducers with a frequency greater than 10M.

[0006] In a first aspect, the present invention provides an ultrasonic transducer matching layer, which is obtained by uniformly mixing PVDF and an additive to form a film; the thickness of the film after forming is 1 μm to 80 μm. The additive is one or more of hollow glass microspheres, barium titanate, lead magnesium niobate titanate, and tungsten powder.

[0007] Preferably, the particle size of the additive is less than 1 μm.

[0008] Preferably, the additive in step 2 is hollow glass microspheres; the weight ratio of the hollow glass microspheres to PVDF is (1-10):(1-10).

[0009] Preferably, the additive in step 2 is barium titanate; the weight ratio of barium titanate to PVDF is (10-50):(1-10).

[0010] Preferably, the additive in step 2 is lead magnesium niobate titanate; the weight ratio of lead magnesium niobate titanate to PVDF is (40-80):(1-10).

[0011] Preferably, the additive in step 2 is tungsten powder; the weight ratio of tungsten powder to PVDF is (150-300):(1-10).

[0012] In a second aspect, the present invention provides a method for preparing the aforementioned ultrasonic transducer matching layer, which comprises the following steps: Step 1: Dissolve PVDF in DMF solvent Step 2: Add additives to the solution obtained in step 1 and stir evenly.

[0013] Step 3: vacuum the product obtained in step 2.

[0014] Step 4: solidify and dry the product obtained in step 3 to obtain an ultrasonic transducer matching layer.

[0015] Preferably, the amount of the PVDF particles relative to the DMF solvent is 20 g / L to 200 g / L.

[0016] Preferably, the stirring method in step 2 is to use a magnetic stirrer to stir for 24 hours to 48 hours; the vacuum treatment time in step 3 is 30 minutes to 50 minutes. The curing condition in step 4 is to cure at a constant temperature.

[0017] In a third aspect, the present invention provides an ultrasonic transducer, which includes a backing, a flexible circuit board, a piezoelectric material, and a plurality of matching layers stacked in sequence. All matching layers adopt the ultrasonic transducer matching layer described above. Along the direction away from the piezoelectric material, the acoustic impedance of each matching layer decreases in sequence.

[0018] Preferably, the matching layer has five layers, namely, the first matching layer, the second matching layer, the third matching layer, the fourth matching layer, and the fifth matching layer, which are stacked in sequence in the direction away from the piezoelectric material. The additives corresponding to the first matching layer, the second matching layer, and the third matching layer are hollow glass microspheres, barium titanate, and lead magnesium niobate titanate, respectively; the additives corresponding to the fourth matching layer and the fifth matching layer are both tungsten powder. The acoustic impedance of the first matching layer is 10MRayls to 12MRayls; the acoustic impedance of the second matching layer is 6MRayls to 8MRayls; the acoustic impedance of the third matching layer is 3MRayls to 4MRayls; the acoustic impedance of the fourth matching layer is 2MRayls to 3MRayls; and the acoustic impedance of the fifth matching layer is 1.5MRayls to 2MRayls.

[0019] The beneficial effects of the present invention are: 1. The ultrasonic transducer matching layer made of PVDF in the present invention has the characteristics of low acoustic impedance, which can make the last layer of the gradient matching layer better matched with the load.

[0020] 2. The present invention can obtain matching layers with different acoustic impedances by doping PVDF with different types and contents of additives, thereby stacking matching layers with increasing acoustic impedances to make matching layers with gradient impedance values. The acoustic impedance of the five matching layers from the inside to the outside decreases in a gradient, and the transmittance of the ultrasonic transducer is significantly improved, which can be increased to 0.70-0.72, which can effectively improve the performance of the ultrasonic transducer.

[0021] 3. The matching layer sample prepared by the present invention has uniform density distribution and good transmission stability, thus breaking the bottleneck of the development of ultrasonic transducers and expanding the application field of ultrasonic transducers. It is crucial for the later development of ultrasonic transducers and has great significance for the later development of ultrasonic transducers.

[0022] 4. The present invention adopts a drying-molding process, so that the thickness of the matching layer can be thinner and more precise, and can be applied to high-frequency ultrasonic transducers with a frequency greater than 10M, and the process is simple, the technology is reasonable, and the raw material cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic diagram of the structure of an ultrasonic transducer provided in Example 4 of the present invention Figure 2 A graph showing changes in acoustic impedance of five matching layers along with gradients in an ultrasonic transducer provided in Example 4 of the present invention; Figure 3 A curve diagram showing changes in the transmittance of an ultrasonic transducer as a function of the gradient provided in Example 4 of the present invention; DETAILED DESCRIPTION

[0024] In order to more clearly illustrate the embodiments of the present invention or the prior art solutions, the present invention is further described below in conjunction with the accompanying drawings. It is worth noting that only a part of the embodiments of the present invention are shown below. For those skilled in the relevant art, other drawings and variants can be derived based on these embodiments without creative work.

[0025] Example 1 A method for preparing an ultrasonic transducer matching layer comprises the following steps: S1. Mix DMF solvent and PVDF particles, and stir to dissolve. In this embodiment, 50 ml of DMF solution is taken; 1 g to 10 g of PVDF particles are taken.

[0026] S2. Add an additive to the product obtained in step S1 and stir it in a stirrer. In this embodiment, the additive is hollow glass microspheres, and the amount of addition is 1 to 10 g. The stirring time in the stirrer is 10 min to 15 min, and the stirring speed is 10000 r / min to 15000 r / min. This step ensures uniform mixing through high-speed stirring in the stirrer, which lays the foundation for uniform density distribution and transmission stability of the ultrasonic transducer matching layer prepared later.

[0027] S3, placing the product obtained in step S2 in a vacuum box and evacuating the vacuum box for 30 minutes to 50 minutes; the vacuum pressure of the vacuum box in this embodiment is -100 kPa. The vacuum box has sufficient pressure to extract the air in the mixture, so as to avoid air remaining in the mixture after stirring, and the density of the ultrasonic transducer matching layer is evenly distributed, further ensuring the transmittance and stability of the ultrasonic transducer matching layer prepared later.

[0028] S4. The product obtained in step S3 is placed in a constant temperature environment and cured for 24 hours.

[0029] S5, drying and molding the product obtained in step S4 to obtain a thin film ultrasonic transducer matching layer.

[0030] The acoustic impedance of the ultrasonic transducer matching layer prepared in this embodiment ranges from 1.5 MRayls to 2.0 MRayls, and the thickness ranges from 1 μm to 80 μm. The acoustic impedance of the ultrasonic transducer matching layer increases with the increase in the amount of hollow glass microspheres added.

[0031] In this embodiment, a matching layer with an acoustic impedance of 1.5 MRayls to 2.0 MRayls is selected as the fifth matching layer of the ultrasonic transducer.

[0032] Example 2 A method for preparing a matching layer of an ultrasonic transducer. The difference between this embodiment and embodiment 1 is that the additive in step S2 is barium titanate; the addition amount of barium titanate is 10g to 50g.

[0033] The acoustic impedance of the ultrasonic transducer matching layer prepared in this embodiment ranges from 2 MRayls to 3 MRayls, and the thickness of the matching layer sample ranges from 1 μm to 80 μm. The acoustic impedance of the ultrasonic transducer matching layer increases with the increase of the amount of barium titanate added.

[0034] In this embodiment, a matching layer with an acoustic impedance of 2.0 MRayls to 3.0 MRayls is selected as the fourth matching layer of the ultrasonic transducer.

[0035] Example 3 A method for preparing a matching layer of an ultrasonic transducer. The difference between this embodiment and embodiment 1 is that the additive in step S2 is lead magnesium niobate titanate; the additive amount of lead magnesium niobate titanate is 40g to 80g.

[0036] The acoustic impedance of the ultrasonic transducer matching layer prepared in this embodiment ranges from 3.0 MRayls to 4.0 MRayls, and the thickness of the matching layer sample ranges from 1 μm to 80 μm. The acoustic impedance of the ultrasonic transducer matching layer increases with the increase of the amount of lead magnesium niobate titanate added.

[0037] In this embodiment, a matching layer with an acoustic impedance of 3.0 MRayls to 4.0 MRayls is selected as the third matching layer of the ultrasonic transducer.

[0038] Example 4 A method for preparing a matching layer of an ultrasonic transducer. The difference between this embodiment and embodiment 1 is that the additive in step S2 is tungsten powder; the amount of tungsten powder added is 150g to 300g.

[0039] The acoustic impedance of the ultrasonic transducer matching layer prepared in this embodiment ranges from 6.0 MRayls to 12.0 MRayls, and the thickness of the matching layer sample ranges from 1 μm to 80 μm. The acoustic impedance of the ultrasonic transducer matching layer increases with the increase in the amount of lead magnesium niobate titanate added.

[0040] In this embodiment, a matching layer with an acoustic impedance of 6.0 MRayls to 8.0 MRayls is selected as the second matching layer of the ultrasonic transducer; and a matching layer with an acoustic impedance of 10.0 MRayls to 12.0 MRayls is selected as the first matching layer of the ultrasonic transducer.

[0041] Example 5 like Figure 3As shown, an ultrasonic transducer comprises a backing 1, a flexible circuit board 2, a piezoelectric material 3, a first matching layer 4, a second matching layer 5, a third matching layer 6, a fourth matching layer 7, and a fifth matching layer 8, which are stacked in sequence from bottom to top. The first matching layer 4, the second matching layer 5, the third matching layer 6, the fourth matching layer 7, and the fifth matching layer 8 are respectively the matching layers prepared in Examples 1, 2, 3, and 4, and their acoustic impedances are 10.0 MRayls to 12.0 MRayls, 6.0 MRayls to 8.0 MRayls, 3.0 MRayls to 4.0 MRayls, 2.0 MRayls to 3.0 MRayls, and 1.5 MRayls to 2.0 MRayls, respectively.

[0042] In some other embodiments, the number of matching layers may be increased or decreased.

[0043] The effect of different numbers of matching layers on the acoustic intensity transmittance between the piezoelectric composite material of the ultrasonic transducer and the load is as follows: First, the calculation formula of acoustic impedance Z is: Z=ρ·c Where ρ is the density of the medium and c is the speed of sound in the medium.

[0044] Reflection and transmission at the interface of different acoustic media, the reflection coefficient and the transmission coefficient represent the ratio of reflection to transmission, and the sum of the two is 1.

[0045] The formula for calculating the sound intensity reflectivity of ultrasonic waves at the interface is: reflection coefficient for: Formula (1) The formula for calculating the sound intensity transmittance of ultrasound at the interface is: Transmission coefficient Formula (2) Among them, Z1 is the acoustic impedance of the previous medium during the propagation of ultrasonic waves, and Z2 is the acoustic impedance of the subsequent medium during the propagation of ultrasonic waves.

[0046] When there is no matching layer, when the acoustic impedance of the piezoelectric composite material is 20.0-22.0 MRayls, the acoustic impedance of the load is 1.5 MRayls. From formula (2), it can be calculated that the acoustic intensity transmittance of the ultrasonic wave between the piezoelectric composite material and the load is 0.23-0.26.

[0047] like Figure 2 and 3As shown, when a matching layer is added between the piezoelectric composite material and the load, when the acoustic impedance of the piezoelectric composite material is 20.0-22.0 MRayls, the matching layer adopts the matching layer with an acoustic impedance of 10.0-12.0 MRayls obtained in Example 4, and the load acoustic impedance is 1.5 MRayls. According to formula (2), the acoustic intensity transmittance between the piezoelectric composite material and the matching layer is 0.89-0.91, the acoustic intensity transmittance between the matching layer and the load is 0.40-0.45, and the acoustic intensity transmittance between the piezoelectric composite material and the load is 0.36-0.40.

[0048] like Figure 2 and 3 As shown, when two matching layers are added between the piezoelectric composite material and the load, when the acoustic impedance of the piezoelectric composite material is 20.0-22.0 MRayls, the acoustic impedances of the two matching layers from the inside to the outside are 6.0-8.0 MRayls and 10.0-12.0 MRayls respectively, and the load acoustic impedance is 1.5 MRayls. According to formula (2), the acoustic intensity transmittance between the piezoelectric composite material and the first matching layer is 0.89-0.91, the acoustic intensity transmittance between the first matching layer and the second matching layer is 0.94-0.96, and the acoustic intensity transmittance between the second matching layer and the load is 0.53-0.64, and the acoustic intensity transmittance between the piezoelectric composite material and the load is 0.46-0.54.

[0049] like Figure 2 and 3 As shown, when three matching layers are added between the piezoelectric composite material and the load, when the acoustic impedance of the piezoelectric composite material is 20.0-22.0 MRayls, the acoustic impedances of the three matching layers from the inside to the outside are 10.0-12.0 MRayls, 6.0-8.0 MRayls, 3.0-4.0 MRayls, respectively, and the load acoustic impedance is 1.5 MRayls. According to formula (2), the acoustic intensity transmittance between the piezoelectric composite material and the first matching layer is 0.89-0.91, the acoustic intensity transmittance between the first matching layer and the second matching layer is 0.94-0.96, the acoustic intensity transmittance between the second matching layer and the third matching layer is 0.89-0.89, and the acoustic intensity transmittance between the third matching layer and the load is 0.79-0.89. The acoustic intensity transmittance between the piezoelectric composite material and the load is 0.61-0.66.

[0050] like Figure 2 and 3As shown, when four matching layers are added between the piezoelectric composite material and the load, when the acoustic impedance of the piezoelectric composite material is 20.0-22.0 MRayls, the acoustic impedances of the three matching layers from inside to outside are 10.0-12.0 MRayls, 6.0-8.0 MRayls, and 3.0-4.0 MRayls, respectively, and the load acoustic impedance is 1.5 MRayls. According to formula (2), it can be calculated that the acoustic intensity transmittance between the piezoelectric composite material and the first matching layer is 0.89-0.91, the acoustic intensity transmittance between the first matching layer and the second matching layer is 0.94-0.96, the acoustic intensity transmittance between the second matching layer and the third matching layer is 0.89-0.89, the acoustic intensity transmittance between the third matching layer and the fourth matching layer is 0.96-0.98, and the acoustic intensity transmittance between the fourth matching layer and the load is 0.89-0.98. Therefore, the acoustic intensity transmittance between the piezoelectric composite material and the load is 0.68-0.70.

[0051] like Figure 2 and 3 As shown, when five matching layers are added between the piezoelectric composite material and the load, when the acoustic impedance of the piezoelectric composite material is 20.0-22.0 MRayls, the acoustic impedances of the three matching layers from inside to outside are 10.0-12.0 MRayls, 6.0-8.0 MRayls, and 3.0-4.0 MRayls, respectively, and the load acoustic impedance is 1.5 MRayls. According to formula (2), it can be calculated that the acoustic intensity transmittance between the piezoelectric composite material and the first matching layer is 0.89-0.91, the acoustic intensity transmittance between the first matching layer and the second matching layer is 0.94-0.96, the acoustic intensity transmittance between the second matching layer and the third matching layer is 0.89-0.89, the acoustic intensity transmittance between the third matching layer and the fourth matching layer is 0.89-0.89, the acoustic intensity transmittance between the fourth matching layer and the fifth matching layer is 0.96-0.98, the acoustic intensity transmittance between the fifth matching layer and the load is 0.98-0.99, and the acoustic intensity transmittance between the piezoelectric composite material and the load is 0.70-0.72.

[0052] Through the above comparative examples and Figure 3 It can be seen that the gradient matching layer made by multi-layer matching can effectively enhance the acoustic intensity transmittance between the piezoelectric composite material and the load.

[0053] Therefore, it can be seen that by increasing the sound intensity transmittance, the sensitivity of the ultrasonic transducer can be effectively improved, and the density of the prepared matching layer sample is evenly distributed and the transmission stability is good, thereby breaking the bottleneck of the development of ultrasonic transducers and expanding the application field of ultrasonic transducers. It is crucial for the later development of ultrasonic transducers and has great significance for the later development of ultrasonic transducers.

[0054] The embodiments of the present invention are described in detail above, but the present invention is not limited to the specific embodiments described, and the embodiments only select better results for illustration. For those skilled in the art, various changes, modifications, substitutions and modifications can be made to these embodiments and their components without departing from the basic principles and core spirit of the present invention, and these changes are still within the scope of protection of the present invention.

Claims

1. An ultrasonic transducer matching layer, characterized in that: The film is obtained by mixing PVDF with additives; the thickness of the film is 1 μm to 80 μm; the additive is one or more of hollow glass microspheres, barium titanate, lead magnesium niobate titanate, and tungsten powder.

2. The ultrasonic transducer matching layer according to claim 1, characterized in that: The particle size of the additive is less than 1 μm.

3. The ultrasonic transducer matching layer according to claim 1, characterized in that: The additive in step 2 is hollow glass microspheres; the weight ratio of the hollow glass microspheres to PVDF is (1-10):(1-10).

4. The ultrasonic transducer matching layer according to claim 1, characterized in that: The additive in step 2 is barium titanate; the weight ratio of barium titanate to PVDF is (10-50):(1-10).

5. The ultrasonic transducer matching layer according to claim 1, characterized in that: The additive in step 2 is lead magnesium niobate titanate; the weight ratio of lead magnesium niobate titanate to PVDF is (40-80):(1-10).

6. The ultrasonic transducer matching layer according to claim 1, characterized in that: The additive in step 2 is tungsten powder; the weight ratio of tungsten powder to PVDF is (150-300):(1-10).

7. A method for preparing a matching layer of an ultrasonic transducer, characterized in that: Used to prepare an ultrasonic transducer matching layer as claimed in any one of claims 1 to 6; The preparation method comprises the following steps: Step 1, dissolving PVDF in DMF solvent; the amount of PVDF particles relative to DMF solvent is 20g / L to 200g / L; Step 2, adding additives to the solution obtained in step 1 and stirring evenly; Step 3, vacuuming the product obtained in step 2; Step 4: solidify and dry the product obtained in step 3 to obtain an ultrasonic transducer matching layer.

8. The preparation method according to claim 7, characterized in that: The stirring method in step 2 is to use a magnetic stirrer to stir for 24-48 hours; the duration of the vacuum treatment in step 3 is 30 minutes to 50 minutes; and the curing condition in step 4 is to cure at a constant temperature.

9. An ultrasonic transducer, characterized in that: It comprises a backing (1), a flexible circuit board (2), a piezoelectric material (3) and a plurality of matching layers which are stacked in sequence; all matching layers adopt an ultrasonic transducer matching layer as claimed in claim 1; and the acoustic impedance of each matching layer increases in sequence in a direction away from the piezoelectric material (3).

10. An ultrasonic transducer according to claim 9, characterized in that: The matching layer has five layers, namely a first matching layer (4), a second matching layer (5), a third matching layer (6), a fourth matching layer (7) and a fifth matching layer (8) which are stacked in sequence along a direction away from the piezoelectric material (3); the additives corresponding to the first matching layer (4), the second matching layer (5) and the third matching layer (6) are hollow glass microspheres, barium titanate and lead magnesium niobate titanate respectively; the additives corresponding to the fourth matching layer (7) and the fifth matching layer (8) are both tungsten powder; the acoustic impedance of the first matching layer (4) is 10 MRayls to 12 MRayls; the acoustic impedance of the second matching layer (5) is 6 MRayls to 8 MRayls; the acoustic impedance of the third matching layer (6) is 3 MRayls to 4 MRayls; the acoustic impedance of the fourth matching layer (7) is 2 MRayls to 3 MRayls; and the acoustic impedance of the fifth matching layer (8) is 1.5 MRayls to 2.0 MRayls.

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