Stretchable double-frequency flexible ultrasonic transducer

Abstract

The invention belongs to the technical field of medical ultrasound, and discloses a stretchable double-frequency flexible ultrasonic transducer which comprises a front packaging layer, a back packaging layer, a flexible electrode substrate, a flexible electrode-positive electrode, a transducer array, a backing layer, a flexible electrode-negative electrode and a shielding layer. Wherein the material strength and the tensile fatigue resistance of the wave-shaped flexible electrode are far better than those of the current mainstream flexible probe electrode with an island bridge structure and other material structures, so that the overall mechanical property of the probe is improved; according to the imaging mode of the double-frequency transducer array, imaging of tissues with different depths can be achieved, and higher-quality imaging of deep tissues can be achieved through harmonic imaging. Compared with other flexible ultrasonic transducers, the flexible ultrasonic transducer has better mechanical performance, better deep tissue imaging quality and more application scenes.

Description

Technical Field

[0001] The present invention relates to the field of medical ultrasound technology, and in particular to a stretchable dual-frequency flexible ultrasonic transducer. Background Art

[0002] Ultrasound provides real-time imaging of deep tissues, organs, and blood flow in a safe and non-invasive manner. It is the most widely used medical imaging modality. Ultrasound has the advantages of safety, non-invasiveness, non-ionization, low cost, real-time imaging, monitoring, and treatment. With the great progress in microelectronics and materials science, ultrasound probes have become an important means for ultrasound to be further applied outside the clinic (such as home and monitoring applications).

[0003] Ultrasound can be used for in vivo soft tissue imaging, early diagnosis and monitoring of disease progression. Accurate and continuous monitoring of physiological signals is of great value to clinical care and research. However, traditional ultrasound probes are rigid, have a narrow field of view, and rely on operators to manually hold or use bulky devices to fix them for continuous monitoring. Wearable flexible electronic devices can solve this problem. Wearable ultrasound devices can comfortably contact the skin surface to sense physiological signals in deep tissues. They can continuously and conformally contact the skin and do not require operators to manually translate or rotate, nor do they need to repeatedly apply coupling agents. At present, the common flexible probes have mostly metal or non-metal "island-bridge" structures in the electrode part. Although this structure can achieve flexibility and meet the requirements of stretchability, the fatigue resistance of the stretching and the overall material strength of the flexible electrode are very low, and it is very easy to break. Therefore, it is of great significance to design new materials and new structures for flexible ultrasonic transducers that are resistant to stretching and bending.

[0004] Currently, commercial rigid ultrasound probes can achieve broadband or multi-band imaging, that is, they can achieve high-quality imaging of tissues at different depths. However, it is extremely difficult to achieve ideal matching layers and backings on flexible probes. Therefore, current flexible probes are dedicated or single-purpose probes that can only achieve tissue imaging at one depth at a single frequency. Obviously, the utilization rate of single-frequency probes is low. Detection of different parts of the human body requires imaging at different depths, that is, probes of different frequencies. Currently, low-frequency flexible ultrasonic transducers have low imaging resolution, and high-frequency flexible ultrasonic transducers have shallow imaging depths. At this stage, we do not have broadband flexible ultrasonic transducers, and cannot achieve high-quality imaging of organs and tissues at different depths. Therefore, it is of great significance to develop a dual-frequency multi-purpose flexible ultrasonic transducer. Summary of the invention

[0005] The technical problems to be solved by the present invention are: the tensile bending fatigue performance of the flexible ultrasonic transducer is not ideal; the material strength of the flexible transducer electrode is not ideal; the utilization rate of the single-frequency flexible ultrasonic transducer is low. The performance indicators of the probe are improved through the design of new materials and structures.

[0006] The present invention comprises a front encapsulation layer (A), a back encapsulation layer (B), a flexible electrode substrate (C), a flexible electrode-positive electrode (D), a transducer array (E), a backing layer (F), a flexible electrode-negative electrode (G), and a shielding layer (H); The flexible electrode substrate (C) is the base of the entire flexible ultrasonic transducer. The flexible electrode substrate (C) is located between the front packaging layer (A) and the back packaging layer (B), and is located below the shielding layer (H). The transducer array (E) is located above the flexible electrode substrate (C) and the flexible electrode-positive electrode (D). The entire transducer array has a total of 60 array elements. The piezoelectric material of the transducer is a 1-3 piezoelectric ceramic composite material. The transducer array (E) is a two-dimensional array with two columns, including a column of low-frequency array elements (E1) and a column of high-frequency array elements (E2). The number of array elements of the low-frequency array element (E1) and the high-frequency array element (E2) is 30 each. The frequency of the low-frequency array element (E1) is 3.5MHz, and the frequency of the high-frequency array element (E2) is 7MHz. The positive electrode parts of the low-frequency array element (E1) and the high-frequency array element (E2) are connected to the flexible electrode-positive electrode (D). The transducer array (E) and the flexible electrode-positive electrode (D) are bonded by thermally cured conductive glue. The leftmost of the low-frequency array element (E1) array and the high-frequency array element (E2) array is a copper block (I) of the same size as the array element; The flexible electrode-positive electrode (D) is an electrode lead printed on the flexible electrode substrate (C) except the electrode connected to the copper block (I) on the leftmost side of the transducer array (E). The flexible electrode-positive electrode (D) is closely attached to the flexible electrode substrate (C). The number of electrode channels is 60. One end of the electrode is aligned with one side of the transducer, and the other end is connected to one side of the positive electrode of the transducer array (E). Channels 1-30 are connected to the low-frequency array element (E1), and channels 31-60 are connected to the high-frequency array element (E2). The electrode is in the shape of a U-shaped letter. The backing layer (F) is located below the flexible electrode substrate (C); The flexible electrode-negative electrode (G) is composed of two parts, the first part is located above one side of the low-frequency array element (E1) and the high-frequency array element (E2), the material of the flexible electrode-negative electrode (G) is conductive silver glue, and the other part is an electrode lead connected to the copper block (I); The shielding layer (H) is located between the flexible electrode-positive electrode (D) and the front encapsulation layer (A); The front encapsulation layer (A) and the back encapsulation layer (B) are encapsulation layers of the flexible probe. The front encapsulation layer (A) and the back encapsulation layer (B) are located on the front and back of the flexible probe, respectively, and the material is silicone of model ecoflex-0030.

[0007] The flexible electrode substrate (C) has a wavy structure, and the material of the flexible electrode substrate (C) is a 0.015 mm thick polyimide film; The material of the flexible electrode-positive electrode (D) is conductive ink, which is directly printed on the flexible electrode substrate (C) using a flexible electronic printer using a flexible printing method; The material of the backing layer (F) is a mixture of aluminum oxide and PDMS, and the size of the backing layer (F) is just enough to cover the entire transducer array; The shielding layer (H) is a wavy structure that matches the flexible electrode substrate (C), and the material of the shielding layer (H) is flexible carbon cloth.

[0008] The manufacturing process of the stretchable dual-frequency flexible ultrasonic transducer of the present invention is divided into five steps. First, a back packaging layer (B) is made in a mold using ecoflex-0030 silicone. Then, a backing layer (F) is attached to the back packaging layer (B). The manufactured flexible electrode and shielding layer (H) are attached to the back packaging layer (B) and the backing layer (F). The piezoelectric transducer is bonded to the attached flexible electrode and backing layer (F). Flexible silver glue is used to connect the negative electrode of the transducer as a flexible electrode-negative electrode (G). Finally, a layer of silicone is spin-coated with the same material as the back packaging layer (B) as a front packaging layer (A).

[0009] Compared with the prior art, the present invention has the following beneficial effects:

[0010] 1. Compared with traditional rigid commercial ultrasound probes, it has relatively low cost, is flexible, stretchable, conformable, and wearable, does not require repeated application of ultrasound coupling agent, and can realize real-time and continuous physiological signal acquisition of multiple parts of human tissue.

[0011] 2. Compared with the current new flexible ultrasonic transducers, the stretchable fatigue resistance of the wavy flexible electrode based on 0.015mm thick polyimide film far exceeds the current mainstream island bridge structure and other material structures of flexible probe electrodes, and the material strength of this type of flexible electrode is also significantly higher than other forms of flexible electrodes.

[0012] 3. Compared with the most advanced flexible transducers currently available, it has higher imaging quality for deeper tissues, and the flexible probe with a dual-frequency structure can achieve high-quality imaging of organs and tissues at different depths. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is the overall structural diagram of the present invention; Figure 2 It is an overall exploded view of the present invention; Figure 3 It is a schematic diagram of the overall straightening of the present invention; Figure 4 This is a schematic diagram of the overall straightening and bending of the present invention; Figure 5 is a top view of the probe-electrode of the present invention; Figure 6 is a schematic diagram of an array element-electrode of the present invention; Figure 7 is a schematic diagram of a flexible electrode of the present invention; Figure 8 It is a 1-3 piezoelectric composite material of the present invention and a schematic diagram of its manufacture; Fig. 9 It is a schematic diagram of the cross-sectional structure and manufacturing sequence of the present invention; Fig.10 is a schematic diagram of the attachment deformation of the present invention; Fig.11 It is a schematic diagram of curved surface attachment of the present invention.

[0014] In the figure: A, front packaging layer; B, back packaging layer; C, flexible electrode substrate; D, flexible electrode-positive electrode; E, transducer array; F, backing layer; G, flexible electrode-negative electrode; E1, low-frequency array element; E2, high-frequency array element; H, shielding layer; I, copper block. DETAILED DESCRIPTION

[0015] See also Figures 1 to 7 As shown, a stretchable dual-frequency flexible ultrasonic transducer comprises a front packaging layer (A), a back packaging layer (B), a flexible electrode substrate (C), a flexible electrode-positive electrode (D), a transducer array (E), a backing layer (F), a flexible electrode-negative electrode (G), and a shielding layer (H); The flexible electrode substrate (C) is the base of the entire flexible ultrasonic transducer. The material of the flexible electrode substrate (C) is a 0.015 mm thick polyimide film. The flexible electrode substrate (C) is located between the front encapsulation layer (A) and the back encapsulation layer (B), and is located below the shielding layer (H). Its main function is to provide support for the flexible electrode-positive electrode (D). The first function is to facilitate the printing of the flexible electrode-positive electrode (D), and the second function is to prevent the flexible electrode-positive electrode (D) from breaking during bending and stretching. Since the polyimide film itself does not have stretching properties, the wavy structure of the flexible electrode substrate (C) can achieve a certain degree of stretching of the probe as a whole, without stretching or damaging the electrode flexible electrode-positive electrode (D) itself during the overall stretching of the probe.

[0016] The flexible electrode - positive electrode (D) is the electrode lead printed on the flexible electrode substrate (C) other than the electrode connected to the copper block (I) on the left - most side of the transducer array (E). The flexible electrode - positive electrode (D) is closely attached above the flexible electrode substrate (C). The number of electrode channels is 60. One end of the electrode is aligned with one side of the transducer, and the other end is connected to the positive - electrode side of the transducer array (E). Channels 1 - 30 are connected to the low - frequency elements (E1), and channels 31 - 60 are connected to the high - frequency elements (E2). The electrode as a whole is in a shape of a double - loop. The material of the flexible electrode - positive electrode (D) is conductive ink, which is printed directly on the flexible electrode substrate (C) by means of flexible printing.

[0017] The transducer array (E) is located above the flexible electrode substrate (C) and the flexible electrode - positive electrode (D). There are a total of 60 elements in the whole transducer array. The piezoelectric material of the transducer is 1 - 3 piezoelectric ceramic composite. The transducer array (E) is a two - column two - dimensional array, which includes a column of low - frequency elements (E1) and a column of high - frequency elements (E2). The number of elements in both the low - frequency elements (E1) and the high - frequency elements (E2) is 30. The frequency of the low - frequency elements (E1) is 3.5 MHz, and the frequency of the high - frequency elements (E2) is 7 MHz. The positive - electrode parts of the low - frequency elements (E1) and the high - frequency elements (E2) are connected to the flexible electrode - positive electrode (D). The bonding method between the transducer array (E) and the flexible electrode - positive electrode (D) is bonding with thermosetting conductive glue. The left - most side of the low - frequency element (E1) array and the high - frequency element (E2) array is a copper block (I) with the same size as the element, and its function is to connect the negative electrode of the whole transducer array (E) to a unified negative - electrode lead.

[0018] The backing layer (F) is located below the flexible electrode substrate (C). The material of the backing layer (F) is a mixture of alumina and PDMS. The size of the backing layer (F) is just large enough to cover the whole transducer array. Its main function is to absorb the acoustic energy on the back of the element and make the signals of the element emitting and receiving ultrasonic waves decay as soon as possible to obtain narrow - pulse signals.

[0019] The flexible electrode - negative electrode (G) consists of two parts. The first part is located above one side of the low - frequency elements (E1) and the high - frequency elements (E2). The material of the flexible electrode - negative electrode (G) is conductive silver glue. The elasticity of the conductive silver glue can ensure that when the probe bends, the element and the negative electrode can still maintain an effective connection. The other part is the electrode lead connected to the copper block (I).

[0020] The shielding layer (H) is located between the flexible electrode - positive electrode (D) and the front - side encapsulation layer (A). The material of the shielding layer (H) is flexible carbon cloth, and its main function is to shield the electric field and magnetic field of the human skin tissue and improve the signal - to - noise ratio.

[0021] The front encapsulation layer (A) and the back encapsulation layer (B) are the encapsulation layers of the flexible probe, which are used to protect the electrodes and the transducer array (E). The front encapsulation layer (A) and the back encapsulation layer (B) are located on the front and back of the flexible probe respectively. The material is silicone of model ecoflex-0030, which plays a protective role for the probe as a whole.

[0022] The manufacturing process of the present invention: Figure 8 and Fig. 9 shown.

[0023] The manufacturing process of the stretchable dual-frequency flexible ultrasonic transducer of the present invention comprises five steps: Fig. 9 Steps e to i in the figure. First, a back encapsulation layer (B) is made in the mold using ecoflex-0030 silicone. Then, a backing layer (F) is attached to the back encapsulation layer (B). The prepared flexible electrode and shielding layer (H) are attached to the back encapsulation layer (B) and the backing layer (F). The piezoelectric transducer is bonded to the attached flexible electrode and backing layer (F). Flexible silver glue is used to connect the negative electrode of the transducer as a flexible electrode-negative electrode (G). Finally, a layer of silicone is spin-coated with the same material as the back encapsulation layer (B) as the front encapsulation layer (A).

[0024] The transducer array of the present invention is a 1-3 piezoelectric ceramic composite material, and the manufacturing process of the material is as follows Figure 8 As shown in steps a to d in the figure, firstly, a whole piece of piezoelectric ceramic (PZT-5H) is cut with a cutter to obtain a ceramic column with a width of about 50 microns, epoxy resin is filled into it, and the surface is polished after curing, and finally, the array electrode is sputtered on the polished surface.

[0025] Working principle of the present invention: Fig.10 and Fig.11 shown.

[0026] The stretching deformation and the process of attaching the stretchable dual-frequency flexible ultrasonic transducer to the human tissue surface of the present invention can be divided into four steps, such as steps j to i. First, in a natural state without external force, the packaging materials on both sides are not stretched, and the flexible electrode is in a wavy curved structure; then, according to the needs of the attached surface, the transducer is stretched as a whole, and the flexible electrode is straightened to a certain extent; then, according to the shape of the attached human tissue surface, it is bent to a certain extent to facilitate a more perfect attachment to the skin surface, and finally, the flexible ultrasonic transducer is attached to the irregular human tissue surface in a very conformable manner.

[0027] The biggest feature and biggest advantage of the present invention is the design of the dual-frequency transducer array. The transducer array is a two-dimensional linear array, one column is low-frequency array elements, and the other column is high-frequency array elements. Because the speed of ultrasonic attenuation is related to the transducer frequency, the higher the frequency of the transducer itself, the higher the frequency of the excited ultrasonic wave, the faster the ultrasonic attenuation, and thus the shallower the imaging depth. The lower the frequency of the transducer itself, the lower the frequency of the excited ultrasonic wave, the slower the ultrasonic attenuation, and the deeper the imaging depth. However, high-frequency ultrasound has better resolution. Although low-frequency ultrasound can image deeper tissues, the resolution is not ideal. The present invention has both a high-frequency transducer array and a low-frequency transducer array. Therefore, the present invention combines the good resolution of high-frequency ultrasound and the deeper imaging depth of low-frequency ultrasound, and can achieve high-quality imaging of deeper tissues. The present invention has two imaging modes. The first one is deep tissue imaging. The low-frequency array is used to transmit ultrasound and the high-frequency array is used to receive echoes. Harmonic imaging is used for imaging. The low-frequency array element transmits 3.5MHz ultrasound. After reflection at various tissue interfaces, 7MHz and second harmonics are generated. The 7MHz high-frequency array element receives the second harmonic for imaging. The second one is shallow tissue imaging. The high-frequency array is directly used for imaging. The array of high-frequency array elements transmits ultrasound and receives echoes for imaging.

Claims

1. A stretchable dual-frequency flexible ultrasonic transducer, characterized in that: It includes a front encapsulation layer (A), a back encapsulation layer (B), a flexible electrode substrate (C), a flexible electrode-positive electrode (D), a transducer array (E), a backing layer (F), a flexible electrode-negative electrode (G), and a shielding layer (H); The flexible electrode substrate (C) is the base of the entire flexible ultrasonic transducer. The flexible electrode substrate (C) is located between the front packaging layer (A) and the back packaging layer (B), and is located below the shielding layer (H). The transducer array (E) is located above the flexible electrode substrate (C) and the flexible electrode-positive electrode (D). The entire transducer array has a total of 60 array elements. The piezoelectric material of the transducer is a 1-3 piezoelectric ceramic composite material. The transducer array (E) is a two-dimensional array with two columns, including a column of low-frequency array elements (E1) and a column of high-frequency array elements (E2). The number of low-frequency array elements (E1) and high-frequency array elements (E2) is 30 each. The frequency of the low-frequency array element (E1) is 3.5MHz, and the frequency of the high-frequency array element (E2) is 7MHz. The positive electrode parts of the low-frequency array element (E1) and the high-frequency array element (E2) are connected to the flexible electrode-positive electrode (D). The transducer array (E) and the flexible electrode-positive electrode (D) are bonded by thermally cured conductive glue. The leftmost of the low-frequency array element (E1) array and the high-frequency array element (E2) array is a copper block (I) of the same size as the array element; The flexible electrode-positive electrode (D) is an electrode lead printed on the flexible electrode substrate (C) except the electrode connected to the copper block (I) on the leftmost side of the transducer array (E). The flexible electrode-positive electrode (D) is closely attached to the flexible electrode substrate (C). The number of electrode channels is 60. One end of the electrode is aligned with one side of the transducer, and the other end is connected to one side of the positive electrode of the transducer array (E). Channels 1-30 are connected to the low-frequency array element (E1), and channels 31-60 are connected to the high-frequency array element (E2). The electrode is in the shape of a U-shaped letter. The backing layer (F) is located below the flexible electrode substrate (C); The flexible electrode-negative electrode (G) is composed of two parts, the first part is located above one side of the low-frequency array element (E1) and the high-frequency array element (E2), the material of the flexible electrode-negative electrode (G) is conductive silver glue, and the other part is an electrode lead connected to the copper block (I); The shielding layer (H) is located between the flexible electrode-positive electrode (D) and the front encapsulation layer (A); The front encapsulation layer (A) and the back encapsulation layer (B) are encapsulation layers of the flexible probe. The front encapsulation layer (A) and the back encapsulation layer (B) are located on the front and back of the flexible probe, respectively, and the material is silicone of model ecoflex-0030.

2. The stretchable dual-frequency flexible ultrasonic transducer according to claim 1, characterized in that: The flexible electrode substrate (C) is a wavy structure, and the material of the flexible electrode substrate (C) is a polyimide film with a thickness of 0.015 mm.

3. The stretchable dual-frequency flexible ultrasonic transducer according to claim 2, characterized in that: The material of the flexible electrode-positive electrode (D) is conductive ink, which is directly printed on the flexible electrode substrate (C) by a flexible electronic printer using a flexible printing method.

4. The stretchable dual-frequency flexible ultrasonic transducer according to claim 3, characterized in that: The material of the backing layer (F) is a mixture of aluminum oxide and PDMS, and the size of the backing layer (F) is just enough to cover the entire transducer array.

5. The stretchable dual-frequency flexible ultrasonic transducer according to claim 4, characterized in that: The shielding layer (H) is a wavy structure that matches the flexible electrode substrate (C), and the material of the shielding layer (H) is flexible carbon cloth.

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