A stretchable dual-frequency flexible ultrasonic transducer

Abstract

The present invention belongs to the field of medical ultrasound technology and discloses a stretchable dual-frequency flexible ultrasonic transducer, comprising a front encapsulation layer, a back encapsulation 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. The material strength and stretchable fatigue resistance of the wavy flexible electrode far exceed those of currently mainstream island-bridge structures and other flexible probe electrodes of other material structures, improving the overall mechanical performance of the probe. The imaging method of the dual-frequency transducer array can image tissues at different depths, and can achieve higher-quality imaging of deep tissues through harmonic imaging. Compared with other flexible ultrasonic transducers, this transducer has better mechanical properties, better deep tissue imaging quality, and more application scenarios.

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 noninvasive manner, making it the most widely used medical imaging modality. Ultrasound offers advantages such as safety, non-invasiveness, non-ionization, low cost, and real-time imaging, monitoring, and treatment. With significant advances in microelectronics and materials science, ultrasound probes have become an important tool for furthering ultrasound applications beyond the clinical setting, such as in home and monitoring settings.

[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 the operator to manually hold them 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 maintain continuous and conformal contact with the skin and do not require manual translation or rotation by the operator, nor do they require repeated application of coupling agent. Currently, the electrodes of common flexible probes are mostly metal or non-metallic "island-bridge" structures. Although this structure can achieve flexibility and meet stretchability requirements, the fatigue resistance of the flexible electrode and the overall material strength of the flexible electrode are very low, making it very easy to break. Therefore, it is of great significance to design flexible ultrasound transducers with new materials and new structures 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 all dedicated or single-purpose probes, which 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 this invention are: the unsatisfactory tensile and bending fatigue performance of flexible ultrasonic transducers; the unsatisfactory material strength of flexible transducer electrodes; and the low utilization rate of single-frequency flexible ultrasonic transducers. By designing new materials and structures, the performance indicators of the probe can be improved.

[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);

[0007] 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).

[0008] 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 portions of the low-frequency array element (E1) and 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 using a heat-curing conductive adhesive. On the far left 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.

[0009] The flexible electrode-positive electrode (D) is an electrode lead printed on the flexible electrode substrate (C) except for the electrode connected to the copper block (I) on the far left 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 the positive side 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 shaped like a circle.

[0010] The backing layer (F) is located below the flexible electrode substrate (C);

[0011] The flexible electrode-negative electrode (G) consists 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. The other part is an electrode lead connected to the copper block (I).

[0012] The shielding layer (H) is located between the flexible electrode-positive electrode (D) and the front encapsulation layer (A);

[0013] 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.

[0014] The flexible electrode substrate (C) has a wavy structure, and the material of the flexible electrode substrate (C) is a polyimide film with a thickness of 0.015 mm;

[0015] The material of the flexible electrode-positive electrode (D) is conductive ink, which is printed directly on the flexible electrode substrate (C) using a flexible electronic printer using a flexible printing method;

[0016] The backing layer (F) is made of a mixture of aluminum oxide and PDMS. The size of the backing layer (F) is just enough to cover the entire transducer array.

[0017] 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.

[0018] 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 using the same material as the back packaging layer (B) as the front packaging layer (A).

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 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 the human body.

[0021] 2. Compared with the current new flexible ultrasonic transducers, the wavy flexible electrode based on 0.015mm thick polyimide film has a stretchable fatigue resistance that 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.

[0022] 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

[0023] Figure 1 It is the overall structural diagram of the present invention;

[0024] Figure 2 It is an overall exploded view of the present invention;

[0025] Figure 3 It is a schematic diagram of the overall straightening of the present invention;

[0026] Figure 4 This is a schematic diagram of the overall straightening and bending of the present invention;

[0027] Figure 5 is a top view of the probe-electrode of the present invention;

[0028] Figure 6 is a schematic diagram of an array element-electrode of the present invention;

[0029] Figure 7 is a schematic diagram of the flexible electrode of the present invention;

[0030] Figure 8 This is a schematic diagram of the 1-3 piezoelectric composite material and its production process of the present invention;

[0031] Figure 9 It is a schematic diagram of the cross-sectional structure and manufacturing sequence of the present invention;

[0032] Figure 10 is a schematic diagram of the attachment deformation of the present invention;

[0033] Figure 11 It is a schematic diagram of curved surface attachment of the present invention.

[0034] 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

[0035] See Figures 1 to 7 As shown, a stretchable dual-frequency flexible ultrasonic transducer 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);

[0036] The flexible electrode substrate (C) is the base of the entire flexible ultrasonic transducer. The flexible electrode substrate (C) is made of a 0.015mm 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 tensile 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 flexible electrode-positive electrode (D) itself during the stretching process of the probe as a whole.

[0037] The flexible electrode-positive electrode (D) is the electrode lead printed on the flexible electrode substrate (C), excluding the electrode connected to the copper block (I) on the far left of the transducer array (E). The flexible electrode-positive electrode (D) is tightly attached to the flexible electrode substrate (C). It has 60 electrode channels, one end of which is aligned with one side of the transducer, and the other end is connected to the positive side of the transducer array (E). Channels 1-30 connect to the low-frequency array element (E1), and channels 31-60 connect to the high-frequency array element (E2). The overall electrode is shaped like a U-shaped triangle. The flexible electrode-positive electrode (D) is made of conductive ink and is printed directly on the flexible electrode substrate (C) using flexible printing.

[0038] 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 thermosetting conductive glue. On the far left of the low-frequency array element (E1) and the high-frequency array element (E2) is a copper block (I) of the same size as the array element. Its function is to connect the negative electrode of the entire transducer array (E) to a unified negative lead.

[0039] The backing layer (F) is located below the flexible electrode substrate (C). The material of the backing layer (F) is a mixture of aluminum oxide and PDMS. The size of the backing layer (F) can just cover the entire transducer array. Its main function is to absorb the acoustic energy on the back of the array element and to make the signals of the array element transmitting and receiving ultrasonic waves attenuate as quickly as possible to obtain a narrow pulse signal.

[0040] The flexible electrode-negative electrode (G) consists 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. The elasticity of the conductive silver glue can ensure that the array element and the negative electrode can maintain an effective connection when the probe is bent. The other part is the electrode lead connected to the copper block (I).

[0041] The shielding layer (H) is located between the flexible electrode-positive electrode (D) and the front encapsulation layer (A). The shielding layer (H) is made of flexible carbon cloth. Its main function is to shield the electric and magnetic fields of human skin tissue and improve the signal-to-noise ratio.

[0042] The front encapsulation layer (A) and the back encapsulation layer (B) are the encapsulation layers of the flexible probe, used to protect the electrodes and 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 ecoflex-0030 silicone, which plays a protective role for the entire probe.

[0043] Manufacturing process of the present invention: see Figure 8 and Figure 9 shown.

[0044] The manufacturing process of the stretchable dual-frequency flexible ultrasonic transducer of the present invention is five steps, such as Figure 9 Follow steps e to i in the previous step. First, use ecoflex-0030 silicone to make a back encapsulation layer (B) in the mold. Next, attach a backing layer (F) to the back encapsulation layer (B). Attach the prepared flexible electrode and shielding layer (H) to the back encapsulation layer (B) and the backing layer (F). Bond the piezoelectric transducer to the attached flexible electrode and backing layer (F). Use flexible silver glue to connect the transducer cathode as the flexible electrode-cathode (G). Finally, spin-coat a layer of silicone using the same material as the back encapsulation layer (B) as the front encapsulation layer (A).

[0045] 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, a whole piece of piezoelectric ceramic (PZT-5H) is first cut with a knife to obtain ceramic pillars with a width of about 50 microns. Epoxy resin is then filled into the pillars. After curing, the surface is polished. Finally, the polished surface is sputtered with array element electrodes.

[0046] Working principle of the present invention: Figure 10 and Figure 11 shown.

[0047] The stretching, deformation, and attachment process of the stretchable dual-frequency flexible ultrasonic transducer of the present invention to the human tissue surface can be divided into four steps, as shown in steps j to i. First, in a natural state without external forces, the packaging materials on both sides are not stretched, and the flexible electrodes have a wavy curved structure. Next, the transducer is stretched as a whole to straighten the flexible electrodes to a certain extent according to the needs of the attachment surface. The flexible electrodes are then bent to a certain extent according to the shape of the human tissue surface to be attached to facilitate more perfect attachment to the skin surface. Finally, the flexible ultrasonic transducer is attached to the irregular human tissue surface in a highly conformable manner.

[0048] The greatest feature and advantage of the present invention is the design of a dual-frequency transducer array. The transducer array is a two-dimensional linear array with one column of low-frequency elements and the other column of high-frequency elements. Because the rate 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 tissue, its 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 with the deeper imaging depth of low-frequency ultrasound, and can achieve high-quality imaging of deeper tissue. The present invention has two imaging modes. The first is deep tissue imaging. The low-frequency array is used to transmit ultrasound and the high-frequency array is used to receive echoes. Imaging is performed using harmonic imaging. The low-frequency array elements transmit 3.5MHz ultrasound. After reflection at various tissue interfaces, 7MHz and second harmonics are generated. The 7MHz high-frequency array elements receive the second harmonics for imaging. The second 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 array elements of the low-frequency array elements (E1) and the high-frequency array elements (E2) is 30 each. The frequency of the low-frequency array elements (E1) is 3.5MHz, and the frequency of the high-frequency array elements (E2) is 7MHz. The positive electrode parts of the low-frequency array elements (E1) and the high-frequency array elements (E2) are connected to the flexible electrode-positive electrode (D). The transducer array (E) and the flexible electrode-positive electrode (D) are bonded by heat-curing conductive glue. The leftmost side 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 for the electrode connected to the copper block (I) on the far left 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 the positive side 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 shaped like a circle. The backing layer (F) is located below the flexible electrode substrate (C); The flexible electrode-negative electrode (G) consists 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. 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) has 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) using 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) can just 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.

Images