Large-bandwidth electret transducer and designing and manufacturing method thereof

Abstract

The invention provides a large-bandwidth electret transducer and a designing and manufacturing method thereof. The prepared transducer comprises a top cover, an electret film, conductive adhesive, a backing layer, an internal supporting mold, a lead, a shell and an electrical interface. The backing layer is adhered to the back surface of the electret film through an adhesive, and the electret film and the lead are conducted through the conductive adhesive; wherein the back lining layer is matched with the acoustic impedance of the electret thin film, and the back lining layer is used for absorbing the acoustic wave energy transmitted backwards by the electret thin film so as to suppress vibration trailing, thereby widening the bandwidth. According to the electret thin film, the backing layer matched with the acoustic impedance of the electret thin film is introduced, and the backing layer can effectively absorb backward sound waves and restrain trailing. In addition, the electret film is attached by using the same composite material as the backing layer as an adhesive, so that the introduction of an additional mismatching layer is avoided, and the influence on the acoustic performance is minimized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of air-coupled ultrasonic transducers, and particularly relates to a large-bandwidth electret transducer and a design and manufacturing method thereof. BACKGROUND

[0002] The electret air-coupled transducer has a wide application prospect in medical diagnosis, industrial nondestructive testing, human-computer interaction and other fields due to its simple structure, low cost, high sensitivity and easy flexibility. However, the existing electret transducer adopts a simple structure without a backing or a rigid backing (such as a metal block). When the acoustic impedance of the backing is seriously mismatched with the electret film (the acoustic impedance is usually lower than 1 MRayl), most of the backward radiated acoustic waves will be reflected back to the film at the interface, resulting in long vibration tail and long pulse duration, which seriously limits the-6dB bandwidth and axial resolution of the transducer, and further affects the imaging quality. SUMMARY

[0003] In order to solve the above problems in the prior art, the application provides a large-bandwidth electret transducer and a design and manufacturing method thereof. The technical problems to be solved by the application are solved by the following technical solutions: The application provides a large-bandwidth electret transducer, which comprises a top cover, an electret film, conductive glue, a backing layer, an internal support mold, a lead wire, a shell and an electrical interface; the internal support mold is arranged in the shell; the top cover is arranged at the front end of the shell; the electret film is arranged below the top cover; the backing layer is adhered to the back of the electret film by an adhesive; the electret film is connected to one end of the lead wire penetrating through the backing layer through the conductive glue, and the other end of the lead wire penetrates through the shell and is connected to the interface; wherein the acoustic impedance of the backing layer and the electret film is matched, the backing layer is used for absorbing the acoustic wave energy backwardly propagated by the electret film, so as to suppress the vibration tail and widen the bandwidth.

[0004] A design and manufacturing method of a large-bandwidth electret transducer, which is prepared, and the design and manufacturing method comprises the following steps: S100, a porous polypropylene film is selected as an electret film, and a 3D printing device is used to print an internal support mold; S200, based on the impedance matching relationship between the electret film and the backing layer, hollow glass microspheres and PDMS-based glue are mixed according to a predetermined proportion to obtain HGMP, and the HGMP is injected into the mold to be solidified and formed to obtain the backing layer; S300, a slurry of HGMP is coated on the surface of the backing layer to form an adhesive, and the adhesive is used to complete the flat attachment of the backing layer and the electret film; and the electret film and the lead wire are electrically connected through the conductive glue; S400, installing the electret film, the backing layer, the internal support mold in the shell, and connecting one end of the lead wire to the electrical interface through the shell and the other end to the electret film through the backing layer and the conductive adhesive; S500, installing the top cover on the top of the electret film to clamp the electret film to obtain a large-bandwidth electret transducer.

[0005] Advantages: The present application provides a large-bandwidth electret transducer and a design and manufacturing method thereof. The prepared transducer includes a top cover, an electret film, conductive adhesive, a backing layer, an internal support mold, a lead wire, a shell, and an electrical interface. The backing layer is bonded to the back of the electret film by an adhesive. The conductive adhesive connects the electret film and the lead wire. The backing layer matches the acoustic impedance of the electret film, and the backing layer is used to absorb the acoustic energy of the electret film propagating backward to suppress vibration tailing, thereby widening the bandwidth. The present application introduces a backing layer that matches the acoustic impedance of the electret film. The backing layer can effectively absorb backward acoustic waves and suppress tailing. In addition, the same composite material as the backing layer is used as an adhesive to attach the electret film, avoiding the introduction of an additional mismatched layer and minimizing the impact on acoustic performance.

[0006] The present application will be further described in detail below with reference to the accompanying drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 A structural diagram of a large-bandwidth electret transducer with a backing layer is provided for the present application. Figure 2 A flowchart of a design and manufacturing method of a large-bandwidth electret transducer with a backing layer is provided for the present application. Figure 3 A manufacturing process diagram of a large-bandwidth electret transducer is provided for the present application. Figure 4 A vibration mode change diagram before and after adding a backing layer is provided for the present application. Figure 5 A diagram showing the propagation of acoustic waves between the piezoelectric layer and the backing layer is provided for the present application. Figure 6 A diagram showing the change trend of frequency, sensitivity, and bandwidth performance with the increase of acoustic impedance of the backing material is provided for the simulation results of the present application. Figure 7 A diagram of impedance phase testing of an electret transducer with a backing layer is provided. Figure 8 A comparison diagram of one-transmitting and one-receiving performance and -6 dB bandwidth performance between transducers of the same type for three different acoustic impedance backing transducers is provided. DETAILED DESCRIPTION

[0008] The application will be further described in detail below in connection with specific embodiments, but the embodiments of the application are not limited thereto.

[0009] The application is based on the transmission theory of acoustic waves in multi-layer media and the KLM equivalent circuit model. By establishing an accurate transducer model, the acoustic impedance of the backing layer is parameterized and scanned as a key variable for simulation. Simulation analysis reveals that the bandwidth performance of the transducer does not change monotonously with the acoustic impedance of the backing, but there is an optimal interval. When the acoustic impedance of the backing is much smaller or much larger than that of the film, the interface acoustic energy transmission rate is low and the bandwidth is narrow; when the acoustic impedance of the two is close, the acoustic energy can be effectively coupled into the backing and absorbed, thereby shortening the pulse width and widening the bandwidth. Based on this, the application determines that the optimal matching range of the acoustic impedance of the backing is 0.02~1 MRayl.

[0010] Based on the optimal matching range, the transducer structure is designed, including an aluminum shell, a top cover, an electret film, conductive glue, a backing layer, a lead wire and an electrical interface. The innovation of the application lies in that a backing layer such as HGMP matching the acoustic impedance of the electret film is introduced, which can effectively absorb the backward acoustic wave and suppress the tailing.

[0011] The key of the design and manufacturing method of the application and the transducer lies in that the impedance matching of the backing layer and the electret film is designed, and the same composite material such as HGMP as the adhesive is used to attach the film, avoiding the introduction of an additional unmatched layer. The lead wire passes through the backing layer by pre-buried or perforated way, and only a small amount of conductive glue is used at the connection point, minimizing the impact on the acoustic performance.

[0012] In a first aspect, as shown in the accompanying drawings, the application provides a large-bandwidth electret transducer, comprising: a top cover 1, an electret film 2, conductive glue 3, a backing layer 4, an internal support mold 5, a lead wire 6, a shell 7 and an electrical interface 8; the internal support mold 5 is arranged in the shell 7; the top cover 1 is arranged at the front end of the shell 7; the electret film 2 is arranged below the top cover 1; the backing layer 4 is adhered to the back of the electret film 2 by an adhesive; the electret film 2 is connected to one end of the lead wire 6 passing through the backing layer 4 through the conductive glue 3, and the other end of the lead wire 6 passes through the shell 7 and is connected to the interface 8; wherein the acoustic impedance of the backing layer 4 matches that of the electret film 2, and the backing layer 4 is used to absorb the acoustic energy of the electret film 2 propagating backward to suppress vibration tailing, thereby widening the bandwidth. Figure 1 The acoustic impedance of the backing layer 4 of the application is preferably matched in the range of 0.02~1 MRayl.

[0013]

[0014] ​The backing layer 4 is a composite material made of hollow glass microspheres and a polymer, wherein the polymer is PDMS and the composite material is HGMP. The adhesive is the same composite material used in the backing layer. The electret film 2 is a porous polypropylene film, and the conductive adhesive is a nano-silver-copper particle conductive adhesive. This application can use the K-808 nano-silver-copper particle conductive adhesive from Zhuhai Jinsheng Technology Co., Ltd.

[0015] Firstly, combining Figure 2 and Figure 3 As shown, this application provides a method for designing and fabricating a large-bandwidth electret transducer, which fabricates the large-bandwidth electret transducer as described in the first aspect. The design and fabrication method includes: S100, a porous polypropylene film is selected as the electret film 2, and an internal support mold 5 is printed using a 3D printing device. S200, based on the impedance matching relationship between the electret film 2 and the backing layer 4, hollow glass microspheres and PDMS-based adhesive are mixed at a predetermined mass ratio to obtain HGMP, and then the HGMP is injected into a mold and cured to form the backing layer 4. The predetermined mass ratio can be selected from 40:1 to 20:3. A predetermined mass ratio of 40:1, 20:3, or any mass ratio within this range can be selected. All mass ratios within this selection range are within the scope of protection of this application. In this application, the acoustic impedance value of the HGMP is minimized when a predetermined mass ratio of 8:1 is selected.

[0016] This application describes a PDMS base adhesive obtained by mixing PDMS components A and B at a mass ratio of 10:1, stirring, and removing air bubbles under vacuum. Hollow glass microspheres are then added at a predetermined mass ratio to obtain a PDMS-glass microsphere composite material, defined as HGMP. After thorough mixing, the mixture is injected into the corresponding mold and cured at 60°C for 60 minutes to obtain backing layer 4.

[0017] PDMS stands for polydimethylsiloxane. Its A component is usually vinyl-terminated polydimethylsiloxane + platinum catalyst, and its B component is usually hydrogen-containing silicone oil crosslinking agent + inhibitor.

[0018] This application requires the backing layer 4 to be sanded to make its surface smooth.

[0019] S300, HGMP slurry is coated on the surface of the backing layer 4 to form an adhesive, and the adhesive is used to complete the smooth attachment of the backing layer 4 to the electret film 2; then the electret film 2 and the lead wire 6 are electrically connected by conductive adhesive 3. S400, installing the electret film 2, the backing layer 4, the internal support mold 5 in the shell 7, and connecting one end of the lead wire 6 to the electrical interface 8 through the shell 7 and connecting the other end of the lead wire 6 to the electret film 2 through the backing layer 4 and the conductive glue 3; S500, installing the top cover 1 on the top of the electret film 2, so as to clamp the electret film 2 to obtain a large-bandwidth electret transducer.

[0020] In a specific embodiment of the present application, S200 comprises: S210, mixing and uniformly stirring PDMS-based glue and hollow glass microspheres according to a mass ratio of 8:1 to obtain HGMP; S220, injecting the HGMP into a mold to be cured and formed into the backing layer 4.

[0021] In a specific embodiment of the present application, before S100, the design and manufacturing method further comprises: S000, establishing an electret transducer model based on the transmission theory of sound waves in a multilayer medium and the KLM equivalent circuit model; S001, taking the acoustic impedance of the backing layer of the electret transducer model as a key variable, and scanning and simulating the electret transducer model to obtain the impedance matching relationship between the backing layer and the electret film.

[0022] This step takes the acoustic impedance of the backing layer of the electret transducer model as a key variable, and scans and simulates the electret transducer model to obtain the change relationship between the bandwidth performance of the electret transducer and the acoustic impedance of the backing layer; and determines the impedance matching relationship between the backing layer and the electret film based on the change relationship.

[0023] S002, determining that the optimal matching range of the acoustic impedance of the backing layer is 0.02-1 MRayl based on the impedance matching relationship.

[0024] The present application has strong scientificity, starts from a theoretical model, quantitatively determines the optimization direction through simulation, and makes the backing design have a basis to avoid blind trial and error. By using the optimized backing, the transducer-6dB bandwidth can be improved by more than 90%, and the longitudinal resolution is greatly improved. By using the same material to paste the film and the backing, the acoustic continuity is ensured, and the process is simple and reliable.

[0025] Firstly, the present application considers that, before and after adding the backing layer, due to the change of boundary conditions, the vibration mode of the transducer is converted from half-wavelength vibration in the thickness direction to quarter-wavelength vibration, so that the working frequency after adding the backing layer is reduced to half of that without the backing layer, as shown in Figure 4 .

[0026] Secondly, the schematic diagram of acoustic wave transmission is as shown in Figure 5 Since the interface between the piezoelectric layer and the backing layer is between materials with different acoustic impedances, when the acoustic wave reaches the surface of the piezoelectric element, part of the acoustic wave will be reflected back into the piezoelectric element, and part of the acoustic wave will continue to transmit and propagate to the rear. If the acoustic impedance of the backing material is too low or too high (too different) compared with the piezoelectric element, the acoustic wave will almost completely bounce back to the piezoelectric medium after reaching the interface, and cannot absorb acoustic energy, resulting in low acoustic energy transmission efficiency and low bandwidth performance. If the acoustic impedance of the backing material is close to that of the piezoelectric element, more energy at the interface can be projected and coupled into the backing layer, reducing the continuous oscillation of the piezoelectric element and improving the bandwidth and resolution.

[0027] Finally, the KLM equivalent circuit model of the electret transducer is established in the application. In the model, the acoustic impedance of the electret film (cPP) is 0.02 MRayl. The acoustic impedance of the backing layer is varied as a variable in the range of 0.0004 MRayl (air) to 40 MRayl (metal) for simulation.

[0028] The simulation results are as shown in Figure 6 It is clearly shown that the variation trend of the center frequency, sensitivity and -6dB bandwidth of the transducer with the acoustic impedance of the backing. It can be seen that the bandwidth appears a peak when the acoustic impedance of the backing is close to the acoustic impedance of the cPP film. Accordingly, the application can determine that the optimal range of the acoustic impedance of the backing is 0.02-1 MRayl.

[0029] In order to verify the effect of the application, three kinds of transducers with backing are prepared: no backing (air), copper backing (39.8 MRayl) and HGMP backing (0.98 MRayl).

[0030] The material parameters of the transducer are shown in Table 1.

[0031] Table 1 Material parameters of each layer of the transducer

[0032] The impedance phase test diagram of the transducer with backing is as shown in Figure 7 The one-transmit-one-receive test results are as shown in Figure 8 Figure 8 The specific test method is as follows: one-transmit-one-receive test is performed on two transducers with the same backing and a spacing of 3 cm. The excitation voltage is a sine pulse with a peak-to-peak value of 5V, a period of one cycle and a trigger interval of 1ms. Since the cPP piezoelectric film has large attenuation, the transmitted signal is amplified at the transmitting end and the receiving end, and then the received echo signal is recorded on the oscilloscope. After FFT transformation, the -6dB bandwidth is taken. The specific performance is shown in Table 2.

[0033] Table 2 Test performance parameters of transducers with different backings ​

[0034] The -6dB bandwidth of HGMP-backed transducer reaches 38.5%, far exceeding that of air-backed (20.2%) and copper-backed (20.1%), with bandwidth improvement of over 90%.

[0035] Although the sensitivity (Vpp=150mV) of HGMP-backed transducer is sacrificed, it has the narrowest pulse width and the highest resolution, fully embodying the significant effect of the application on bandwidth and resolution optimization.

[0036] The application successfully proposes and verifies a design and preparation method capable of greatly improving the bandwidth of electret air-coupled transducer by combining theoretical simulation with experiment. The method is scientific and effective, and the prepared transducer has superior performance and good application prospect.

[0037] The above is a further detailed description of the application in combination with specific preferred embodiments, and the specific implementation of the application cannot be limited to these descriptions. For ordinary skilled persons in the technical field to which the application belongs, some simple deductions or substitutions can be made without departing from the concept of the application, and all of them should be regarded as falling within the protection scope of the application.

Claims

1. A large bandwidth electret transducer characterized by, It comprises: a top cover (1), an electret film (2), a conductive glue (3), a backing layer (4), an internal support mold (5), a lead wire (6), a shell (7) and an electrical interface (8); the internal support mold (5) is arranged in the shell (7); the top cover (1) is arranged at the front end of the shell (7); the electret film (2) is arranged below the top cover (1); the backing layer (4) is adhered to the back of the electret film (2) by an adhesive; the electret film (2) is connected to one end of the lead wire (6) passing through the backing layer (4) by the conductive glue (3), and the other end of the lead wire (6) passes through the shell (7) and is connected to the interface (8); Wherein, the acoustic impedance of the backing layer (4) matches the acoustic impedance of the electret film (2), the backing layer (4) is used to absorb the acoustic energy of the electret film (2) propagating backward to suppress vibration tailing, thereby widening the bandwidth.

2. The large bandwidth electret transducer of claim 1, wherein, The preferred acoustic impedance range of the backing layer (4) for realizing impedance matching with the electret film (2) is 0.02~1MRayl.

3. The large bandwidth electret transducer of claim 1, wherein, The composite material used by the backing layer (4) is a composite material made of hollow glass microspheres and a high molecular polymer, the high molecular polymer is PDMS, and the composite material is HGMP.

4. The large bandwidth electret transducer of claim 3, wherein, The adhesive used by the backing layer (4) is the same composite material.

5. A method of designing and fabricating a large bandwidth electret transducer, characterized by, The design and manufacturing method of the large bandwidth electret transducer as claimed in any one of claims 1 to 4 comprises: S100, selecting a porous polypropylene film as the electret film (2), and printing an internal support mold (5) by using a 3D printing device; S200, based on the impedance matching relationship between the electret film (2) and the backing layer (4), mixing hollow glass microspheres and PDMS-based glue according to a predetermined mass ratio to obtain HGMP, and then injecting the HGMP into a mold to solidify and form the backing layer (4); S300, coating a slurry of HGMP on the surface of the backing layer (4) to form an adhesive, and using the adhesive to complete the flat attachment of the backing layer (4) and the electret film (2); then electrically connecting the electret film (2) and the lead wire (6) by the conductive glue (3); S400, installing the electret film (2), the backing layer (4) and the internal support mold (5) in the shell (7), and connecting one end of the lead wire (6) to the electrical interface (8) through the shell (7) and the other end to the electret film (2) through the backing layer (4) by the conductive glue (3); S500, installing the top cover (1) on the top of the electret film (2) to clamp the electret film (2) and obtain the large bandwidth electret transducer.

6. The method of claim 5, wherein the method further comprises: S200 comprises: S210, mixing and uniformly stirring PDMS-based glue and hollow glass microspheres according to a predetermined mass ratio to obtain HGMP; S220, injecting the HGMP into a mold to solidify and form the backing layer (4).

7. The method of claim 5, wherein the method further comprises: Before S300, the design and manufacturing method further comprises: Polishing the backing layer (4) to make its surface flat.

8. The method of claim 5, wherein the method further comprises: Before S100, the design and manufacturing method further comprises: S000, based on the transmission theory of sound waves in multilayer medium and KLM equivalent circuit model, an electret transducer model is established; S001, taking the acoustic impedance of the backing layer of the electret transducer model as a key variable, the electret transducer model is simulated to obtain the impedance matching relationship between the backing layer and the electret film.

9. The method of claim 8, wherein the method further comprises: S001 comprises: taking the acoustic impedance of the backing layer of the electret transducer model as a key variable, the electret transducer model is simulated to obtain the change relationship between the bandwidth performance of the electret transducer and the acoustic impedance of the backing layer; based on the change relationship, the impedance matching relationship between the backing layer and the electret film is determined.

10. The method of claim 8, wherein the method further comprises: After S001, the design and manufacturing method further comprises: S002, based on the impedance matching relationship, the optimal matching range of the acoustic impedance of the backing layer is determined to be 0.02~1 MRayl.

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