Flexible wearable ultrasonic probe based on low-acoustic-impedance backing layer and gradient matching layer and preparation method thereof

Abstract

The invention provides a flexible wearable ultrasonic probe based on a low-acoustic-impedance backing layer and a gradient matching layer and a preparation method of the flexible wearable ultrasonic probe. The flexible wearable ultrasonic probe comprises a probe body and an elastic body for packaging the probe body, wherein the probe body sequentially comprises a low-acoustic-impedance backing layer, a top electrode, a piezoelectric plate, a bottom electrode and a gradient matching layer from one side to the other side; the low-acoustic-impedance backing layer is a porous polymer, aerogel, cloth or air; the gradient matching layer comprises a plurality of matching layers which are arranged in a stacked mode, and the acoustic impedance of the matching layers is sequentially reduced in the direction from the position close to the bottom electrode to the position away from the bottom electrode; and the elastomer is a coupling material matched with the skin impedance. The flexible wearable ultrasonic probe has the advantages of high bandwidth, low insertion loss and excellent mechanical tensile property, and can be widely adapted to ultrasonic application scenes of various different principles such as A-type ultrasonic, B-type ultrasonic and Doppler ultrasonic.

Description

Technical Field

[0001] The present invention relates to the technical field of medical devices, specifically focusing on the sub-field of flexible wearable ultrasound devices, and particularly relates to a flexible wearable ultrasound probe based on a low acoustic impedance backing layer and a gradient matching layer and a preparation method thereof. Background Art

[0002] Ultrasonic technology, with its unique advantages of being non-destructive, non-radiative, and capable of detecting depth information, has demonstrated irreplaceable value in numerous fields. For example, it has significant application advantages in mechanical detection, ocean exploration, biomedical, and other fields. In the biomedical field, especially when applied to the human body, ultrasound can penetrate deep into the human body to obtain key physiological information in multiple aspects such as the cardiovascular system, respiratory system, and nervous system, playing a crucial role in early screening, disease monitoring, and subsequent treatment of related diseases. However, traditional ultrasonic devices have many inherent defects. They are usually bulky, inconvenient to move, and can only achieve short-term monitoring. These limitations severely restrict the popularization and use of traditional ultrasound in current practical application scenarios such as mobile healthcare and home care, and are difficult to meet the actual needs of people for convenient and long-term health monitoring.

[0003] With the continuous progress of technology, in 2018, the team led by Sheng Xu at the University of California, San Diego, innovatively proposed the concept of piezoelectric-based flexible wearable ultrasound devices (Science Advances 2018, 4 (3), eaar3979; Nature Biomedical Engineering 2018, 2 (9), 687-695), providing a highly valuable idea for the expansion of ultrasonic technology in new application directions and strongly promoting the development of new ultrasonic technology. Such flexible wearable ultrasound devices, with the characteristics of being able to directly adhere to the skin and achieve long-term continuous monitoring, have shown good application effects in many aspects such as blood pressure, blood flow, tissue modulus, bladder volume, cerebral blood flow monitoring, ultrasonic myography, core temperature, cardiac imaging, and in-vivo tissue morphology monitoring, bringing new possibilities to biomedical monitoring.

[0004] However, in the actual application process, some key problems that need to be solved urgently have gradually emerged in flexible wearable ultrasonic devices. Among them, the unsatisfactory insertion loss and bandwidth performance are particularly prominent. This is mainly because most of the core components of such devices use elastomers as the encapsulation layer, acoustic matching layer, and backing layer at the same time. This structural design results in a serious acoustic impedance mismatch between them and piezoelectric materials. On the one hand, this mismatch greatly hinders the forward ultrasonic energy from being transmitted to human tissues and makes it difficult to efficiently penetrate deep into the tissues for detection. On the other hand, obvious acoustic reflection and scattering occur at the elastomer interface for the backward ultrasonic, bringing about the ringing effect, which further deteriorates the acoustic performance of the ultrasonic probe and leads to adverse effects on the overall detection effect and data accuracy.

[0005] In view of the above technical defects existing in the existing flexible wearable ultrasonic probes, there is an urgent need in this field to deeply improve and optimize their designs, and develop a flexible wearable ultrasonic probe that can not only ensure the acoustic performance of low insertion loss and high bandwidth, but also has good mechanical tensile properties, so that it can better adapt to ultrasonic applications based on different principles such as A-mode, B-mode, and Doppler ultrasound, in order to meet the diverse and precise health monitoring and disease diagnosis needs in the biomedical field. Summary of the Invention

[0006] Aiming at the defects of unsatisfactory insertion loss and bandwidth performance existing in flexible wearable ultrasonic probes in the prior art, the present invention provides a flexible wearable ultrasonic probe based on a low acoustic impedance backing layer and a gradient matching layer and a preparation method thereof.

[0007] The present invention is realized through the following technical solutions: In a first aspect, the present invention provides a flexible wearable ultrasonic probe based on a low acoustic impedance backing layer and a gradient matching layer, including a probe body and an elastomer encapsulating the probe body. The probe body sequentially includes a low acoustic impedance backing layer, a top electrode, a piezoelectric sheet, a bottom electrode, and a gradient matching layer from one side to the other side; the low acoustic impedance backing layer is a porous polymer, aerogel, fabric, or air; the gradient matching layer includes several stacked matching layers, and along the direction from near the bottom electrode to far from the bottom electrode, the acoustic impedance of each matching layer decreases in turn; the elastomer is a coupling material with impedance matching to the skin.

[0008] Preferably, the top electrode and the bottom electrode are stretchable metal electrodes.

[0009] Further, both the bottom electrode and the top electrode are of an island-bridge structure, and the island elements in the island-bridge structure are connected by serpentine wires; the number of island elements included in each of the bottom electrode and the top electrode is the same as the number of piezoelectric wafers; the multiple piezoelectric wafers are connected to the island elements of the top electrode in a one-to-one correspondence and to the island elements of the bottom electrode in a one-to-one correspondence; the multiple low acoustic impedance backing layers are connected to the island elements of the top electrode in a one-to-one correspondence, and the multiple gradient matching layers are connected to the island elements of the bottom electrode in a one-to-one correspondence.

[0010] Preferably, the thickness of the low acoustic impedance backing layer is 0.5 - 1 mm.

[0011] Preferably, the gradient matching layer includes a first matching layer and a second matching layer, the acoustic impedance of the first matching layer is higher than that of the second matching layer, and the first matching layer is located between the bottom electrode and the second matching layer.

[0012] Further, the first matching layer is an epoxy resin doped with micron metal, nano metal, oxide, carbide or nitride, and the second matching layer is an epoxy resin.

[0013] Preferably, the thicknesses of the first matching layer and the second matching layer are each one-quarter wavelength of the ultrasonic wave propagating in each layer.

[0014] Preferably, one side surface of the low acoustic impedance backing layer is connected to the top electrode, and the opposite side surface is encapsulated by an elastomer; one side surface of the gradient matching layer is connected to the bottom electrode, and the opposite side surface is encapsulated by an elastomer.

[0015] Preferably, the elastomer is polydimethylsiloxane, polyurethane, silicone rubber or hydrogenated styrene-butadiene-styrene block copolymer.

[0016] In a second aspect, the present invention provides a method for preparing the flexible wearable ultrasonic probe based on the low acoustic impedance backing layer and the gradient matching layer, comprising the following steps: S1, connecting the two side surfaces of the piezoelectric wafer to one side surface of the bottom electrode and one side surface of the top electrode respectively, and connecting the low acoustic impedance backing layer and the gradient matching layer to the other side surface of the top electrode and the other side surface of the bottom electrode respectively, to obtain an ultrasonic device; S2, placing the ultrasonic device on the elastomer, enclosing it to form a mold all around, injecting the elastomer solution into the mold to submerge the low acoustic impedance backing layer; after the elastomer is cured, a wearable ultrasonic probe encapsulated by the elastomer is obtained.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The flexible wearable ultrasonic probe based on a low acoustic impedance backing layer and a gradient matching layer of the present invention breaks through the traditional thinking that the existing flexible wearable ultrasonic probe uses an elastomer as both the encapsulation layer, the acoustic matching layer, and the backing layer. Using a porous polymer, aerogel, fabric, or air as the low acoustic impedance backing layer can avoid the ringing effect caused by obvious acoustic reflection and scattering of the backward ultrasonic wave at the elastomer interface, and can effectively utilize the backward ultrasonic energy; using a gradient matching layer can avoid the obstruction of the forward ultrasonic energy during transmission to human tissues; therefore, the acoustic impedance mismatch in the backward and forward directions of the ultrasonic wave can be effectively avoided, thereby enhancing the relative bandwidth and reducing the insertion loss. The elastomer serves as the encapsulation layer, providing mechanical support, and it eliminates the interfacial compressive stress of the elastomer in the vertical direction in the reported flexible wearable ultrasonic probe, thereby effectively improving the mechanical stretching ability of the ultrasonic probe; at the same time, the elastomer serves as a solid coupling layer, which can effectively avoid the problem of water loss of the liquid ultrasonic coupling agent or hydrogel coupling agent, and enhances the long-term monitoring stability of the acoustic performance. Thus, the flexible wearable ultrasonic probe of the present invention has high bandwidth, low insertion loss, and excellent mechanical stretching performance, and can be widely adapted to various ultrasonic application scenarios with different principles such as A-mode, B-mode, and Doppler ultrasound, aiming to provide more efficient and accurate ultrasonic detection means for human health monitoring and disease diagnosis in the biomedical field.

[0018] The preparation method of the flexible wearable ultrasonic probe based on a low acoustic impedance backing layer and a gradient matching layer of the present invention can prepare a flexible wearable ultrasonic probe with high relative bandwidth, low insertion loss, and high mechanical stretching, and has the advantages of simple operation and suitability for large-scale production. Brief Description of the Drawings

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0020] Figure 1 It is a schematic structural diagram of the flexible wearable ultrasonic probe based on a low acoustic impedance backing layer and a gradient matching layer of the present invention. In the figure: low acoustic impedance backing layer 1, top electrode 2, piezoelectric wafer 3, bottom electrode 4, gradient matching layer 5, and elastomer 6.

[0021] Figure 2 It is a stretchable electrode obtained by laser engraving a copper foil with a micron-level thickness according to the present invention; a, bottom electrode; b, top electrode.

[0022] Figure 3 It is the morphological characteristics of the 1-3 type lead zirconate titanate (PZT) composite piezoelectric ceramic used according to the present invention.

[0023] Figure 4 It is the variation relationship of the mass fractions of the acoustic impedance material, epoxy resin and curing agent of the present invention.

[0024] Figure 5 It is the morphological characteristics of the tungsten powder nanoparticles adopted by the present invention; a, scanning electron microscope picture; b, particle size distribution statistical chart; c, variation relationship between the acoustic impedance of the matching layer and the mass fraction of tungsten powder.

[0025] Figure 6 It is the morphological characteristics of the porous polymer low acoustic impedance backing layer adopted by the present invention.

[0026] Figure 7 It is the physical picture of the flexible wearable ultrasonic probe of the present invention.

[0027] Figure 8 It is the cross-sectional morphological picture of a single element of the flexible wearable ultrasonic probe of the present invention.

[0028] Figure 9 It is the resonance characteristics of different types of flexible wearable ultrasonic probes of the present invention; a, without a matching layer (Comparative Example 1); b, with a single matching layer (Comparative Example 2); c, the gradient matching layer of the present invention.

[0029] Figure 10 It is the response characteristics of different types of flexible wearable ultrasonic probes of the present invention; a, without a matching layer (Comparative Example 1); b, with a single matching layer (Comparative Example 2); c, the gradient matching layer of the present invention.

[0030] Figure 11 It is the response characteristics of the flexible wearable ultrasonic probe with Ecoflex elastomer as the backing layer and the matching layer of the present invention; a, with a thickness of 1 mm; b, with a thickness of 5 mm.

[0031] Figure 12 It is the acoustic performance of different types of flexible wearable ultrasonic probes of the present invention; a, relative bandwidth; b, insertion loss; different types of flexible wearable ultrasonic probes include the flexible wearable ultrasonic probe based on a low acoustic impedance backing layer and a gradient matching layer in Example 1 (abbreviation: gradient matching layer), the flexible wearable ultrasonic probe based on a low acoustic impedance backing layer without a matching layer in Comparative Example 1 (abbreviation: without a matching layer), the flexible wearable ultrasonic probe based on a low acoustic impedance backing layer and a single matching layer in Comparative Example 2 (abbreviation: single matching layer), and the flexible wearable ultrasonic probe with Ecoflex elastomer as the backing layer and the matching layer in Comparative Example 3 (including Ecoflex-1mm and Ecoflex-5mm).

[0032] Figure 13 It is the test result of the adhesion performance of the flexible wearable ultrasonic probe based on a low acoustic impedance backing layer and a gradient matching layer of the present invention.

[0033] Figure 14 These are the test results of the mechanical stability of the flexible wearable ultrasonic probe based on the low acoustic impedance backing layer and the gradient matching layer of the present invention; a, torsion test; b, tensile test.

[0034] Figure 15 These are the schematic diagrams of the polytetrafluoroethylene template structure when the flexible wearable ultrasonic probe based on the low acoustic impedance backing layer and the gradient matching layer of the present invention uses air as the low acoustic impedance backing layer; a, top view; b, side view. Specific embodiments

[0035] The following specific examples illustrate the implementation manners of the present invention. Those skilled in the art can easily understand the other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0036] It should be noted that the process equipment or devices not specifically noted in the following embodiments all adopt the conventional equipment or devices in the art.

[0037] It should be noted that the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily limit to those clearly listed steps or units, but may include other steps or units not clearly listed or inherent to these process, method, product or device. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, rather than limiting the arrangement order of each method step or the scope of implementation of the present invention. The change or adjustment of their relative relationship, without substantial change in technical content, should also be regarded as the scope of implementation of the present invention.

[0038] In addition, it should be noted that the terms "first", "second", etc. in the present invention are used to distinguish similar objects and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. The orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation of the present invention; in addition, unless otherwise clearly specified and limited, the terms "installation", "connection", "connection" should be understood in a broad sense. For example, it can be a fixed connection or a detachable connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements.

[0039] The flexible wearable ultrasonic probe of the present invention is based on a low acoustic impedance backing layer and a gradient matching layer 5, as Figure 1 shown, which is a multi-layer composite structure, including a probe body and an elastomer encapsulating the probe body. The probe body sequentially includes a low acoustic impedance backing layer 1, a top electrode 2, a piezoelectric sheet 3, a bottom electrode 4, and a gradient matching layer 5 from one side to the other side; the low acoustic impedance backing layer 1 is a porous polymer, aerogel, cloth or air; the gradient matching layer 5 includes several stacked matching layers, and along the direction from close to the bottom electrode 4 to far from the bottom electrode 4, the acoustic impedance of each matching layer decreases in turn; the elastomer serves as both a coupling layer and an encapsulating layer, and the elastomer is an elastomer with impedance matching with the skin and a small acoustic attenuation coefficient, and is also used to dissipate the random stress with the human skin.

[0040] In the probe body of the present invention, each layer is connected by an elastomer to achieve mechanical stretching.

[0041] In the flexible wearable ultrasonic probe of the present invention, the low acoustic impedance backing layer 1 is a porous polymer, aerogel, cloth or air, so as to achieve high reflection of the backward ultrasound.

[0042] In a preferred embodiment of the present invention, the low acoustic impedance backing layer 1 is a porous polymer, which can not only provide the function of the low acoustic impedance backing layer 1, but also play a role in encapsulating and protecting the flexible wearable ultrasonic probe. The thickness of the low acoustic impedance backing layer 1 of the present invention is 0.5 - 1 mm.

[0043] In a preferred embodiment of the present invention, the gradient matching layer 5 may be a matching layer prepared by selecting two or more different acoustic impedance materials. These materials are usually solid powders such as micro-nano metals, oxides, carbides, and nitrides, and are easily mixed with epoxy resin to form a homogeneous dispersion solution with different concentrations, so as to facilitate the preparation of matching layers with different acoustic impedances to achieve high transmission of forward ultrasound.

[0044] In a preferred embodiment of the present invention, the gradient matching layer 5 includes a first matching layer and a second matching layer. The acoustic impedance of the first matching layer is higher than that of the second matching layer, and the first matching layer is located between the bottom electrode 4 and the second matching layer. The first matching layer is prepared from a high acoustic impedance material, and the second matching layer is prepared from a low acoustic impedance material. The high acoustic impedance material and the low acoustic impedance material in the present invention are relative, that is, the acoustic impedance of the high acoustic impedance material is higher than that of the low acoustic impedance material.

[0045] Specifically, the first matching layer is prepared from an epoxy resin doped with micron metal, nano metal, oxide, carbide or nitride, and the second matching layer is prepared from pure epoxy resin.

[0046] In the present invention, the thicknesses of the first matching layer and the second matching layer are each one-quarter wavelength of the ultrasonic wave propagating in each layer.

[0047] In a preferred embodiment of the present invention, one side of the low acoustic impedance backing layer 1 is connected to the top electrode 2, and the opposite side is encapsulated by an elastomer; one side of the gradient matching layer 5 is connected to the bottom electrode 4, and the opposite side is encapsulated by an elastomer.

[0048] The elastomer 6 in the present invention can be polydimethylsiloxane (PDMS), polyurethane (PU), EcoFlex (random copolyester) or hydrogenated styrene-butadiene-styrene block copolymer (SEBS) elastomer suitable for thermal curing, photocuring or radiation curing methods, and more preferably Ecoflex elastomer and polyurethane elastomer; at the same time, they should have a small acoustic attenuation coefficient (less than 0.4 dB / mm), which needs to be adjusted by the elastomer components. The EcoFlex elastomer has excellent mechanical tensile properties and is convenient for polymerization by heating; the polyurethane elastomer also has excellent mechanical tensile properties and can be polymerized by ultraviolet light or heating temperature.

[0049] In a preferred embodiment of the present invention, both the bottom electrode 4 and the top electrode 2 have an island-bridge structure, and the island elements in the island-bridge structure are connected by serpentine wires, as Figure 2As shown. The number of island elements included in each of the bottom electrode 4 and the top electrode 2 is consistent with the number of piezoelectric sheets 3. Specifically, a plurality of piezoelectric sheets 3 are respectively connected to the island elements of the top electrode 2 in a one-to-one correspondence, and are respectively connected to the island elements of the bottom electrode 4 in a one-to-one correspondence. A plurality of low acoustic impedance backing layers 1 are respectively connected to the island elements of the top electrode 2 in a one-to-one correspondence, and a plurality of gradient matching layers 5 are respectively connected to the island elements of the bottom electrode 4 in a one-to-one correspondence. The stretchability of the top electrode 2 and the bottom electrode 4 is greater than 10%, more preferably greater than 30%.

[0050] The piezoelectric sheet 3 of the present invention can be a polymer, a piezoelectric ceramic, or a polymer-piezoelectric ceramic composite.

[0051] In a preferred embodiment of the present invention, the piezoelectric sheet 3 is a 1-3 type lead zirconate titanate (PZT) composite piezoelectric ceramic. Among them, the thickness of the piezoelectric sheet 3 is preferably 600 μm, the pitch of the piezoelectric ceramic columns in the piezoelectric sheet 3 is preferably 120 μm, and the pitch of the slits is preferably 30 μm. This structure of the present invention not only retains the high electromechanical coupling coefficient and piezoelectric properties of the piezoelectric ceramic, but also improves the flexibility, processability, and acoustic impedance matching with human tissues by adding an elastomeric polymer.

[0052] The flexible wearable ultrasonic probe of the present invention can effectively utilize the backscattered ultrasound and forward ultrasound energy, so as to achieve a relative bandwidth greater than 50% and an insertion loss less than -10 dB for the acoustic performance requirements of typical wearable ultrasonic devices in the field. At the same time, it has a mechanical tensile performance greater than 10% and is applicable to various ultrasonic applications with different principles such as A-mode, B-mode, and Doppler ultrasound.

[0053] In a preferred embodiment of the present invention, it has comprehensive performance with a relative bandwidth greater than 70%, an insertion loss less than -10 dB, and a mechanical stretch greater than 30%. A large number of comparative tests prove that the performance parameters of the flexible wearable ultrasonic probe based on the low acoustic impedance backing layer 1 and the gradient matching layer 5 of the present invention are within the above ranges. Compared with the existing flexible wearable ultrasonic probes, it has a better relative bandwidth and a lower insertion loss, and also has good mechanical flexibility. This can not only effectively improve the accuracy and sensitivity of ultrasonic detection, but also ensure the stability and reliability of the probe during long-term use and when fitting different body parts, meeting the performance requirements in all aspects during use.

[0054] The preparation method of the flexible wearable ultrasonic probe based on the low acoustic impedance backing layer and the gradient matching layer of the present invention includes the following steps: S1, connect the two sides of the piezoelectric sheet to one side of the bottom electrode and one side of the top electrode respectively, and connect the low acoustic impedance backing layer and the gradient matching layer to the other side of the top electrode and the other side of the bottom electrode respectively to obtain an ultrasonic device; S2. Place the ultrasonic device on the elastomer, enclose it all around to form a mold, inject the elastomer solution into the mold, and submerge the low acoustic impedance backing layer. After the elastomer cures, a wearable ultrasonic probe encapsulated with the elastomer is obtained.

[0055] In a preferred embodiment of the present invention, a copper foil with a micron-level thickness is engraved using a laser device to prepare a stretchable top electrode 2 and bottom electrode 4 having an island-bridge structure.

[0056] The laser device described in the present invention can be a fiber laser marking machine, an ultraviolet laser marking machine, a green laser marking machine, or a YAG laser marking machine.

[0057] In a preferred embodiment of the present invention, the laser device is a 1064nm fiber laser marking machine with high marking accuracy, high speed, small volume, low power consumption, and long service life; the thickness of the top electrode 2 and the bottom electrode 4 is 10 - 100μm, and the mechanical stretchability is maintained at more than 30%.

[0058] In a preferred embodiment of the present invention, the piezoelectric sheet 3 is connected to both the top electrode 2 and the bottom electrode 4 through a conductive adhesive, and the low acoustic impedance backing layer 1 is connected to the top electrode 2 through an adhesive. The gradient matching layer 5 is connected to the bottom electrode 4 through an epoxy resin. The conductive adhesive is a silver-based, copper-based, carbon-based, metal oxide, or composite conductive adhesive for achieving good electrical connection. Preferably, a composite conductive adhesive is used, which can quickly volatilize organic solvents below 75°C, adapt to various processing techniques such as coating and screen printing, and can be reliably connected to the piezoelectric sheet 3 at the same time; furthermore, it will not reduce the piezoelectric performance of the piezoelectric sheet 3 when heated, and can obtain good electrical and mechanical properties of the piezoelectric sheet 3 and the electrode after curing, and has good stability performance when the mechanical deformation is greater than 30%.

[0059] In a preferred embodiment of the present invention, the viscosity of the elastomer solution is adjustable to ensure good fluidity, so as to completely submerge all the voids of each layer of the ultrasonic probe, and at the same time, the volume of the formed polymer does not change significantly.

[0060] In a preferred embodiment of the present invention, when heat curing is used, the crosslinking temperature of heat curing needs to be lower than 75°C to avoid reducing the piezoelectric performance of the piezoelectric sheet 3; ultraviolet curing can be completely cured within a few seconds or dozens of seconds.

[0061] During specific implementation, place the assembled ultrasonic device on an elastomer 6 with a certain thickness, attach tapes with a certain thickness all around, enclose to form a mold, and inject the elastomer solution into all the voids of the ultrasonic device. After the elastomer cures, a wearable ultrasonic probe can be obtained.

[0062] The basic structure of the flexible wearable ultrasonic probe based on a low acoustic impedance backing layer and a gradient matching layer of the present invention is as follows Figure 1 shown, which has excellent acoustic and mechanical properties. The acoustic properties include the relative bandwidth of the ultrasonic probe. The relative bandwidth refers to the frequency range that the device can cover in its effective working state; the relative bandwidth is expressed by the formula (where f c is the center frequency, f 1 and f 2 are the frequencies corresponding to the maximum value in the spectrum dropping to -6 dB). The acoustic properties also include the insertion loss of the ultrasonic probe. The insertion loss is a key index to measure the sensitivity of the transceiver integrated ultrasonic transducer, reflecting the conversion efficiency of the ultrasonic transducer in the process of converting an electrical signal into an acoustic signal and converting the acoustic signal back into an electrical signal; the insertion loss is expressed by the formula , in units of dB (where V i is the input voltage of the excitation power supply, V 0 is the output signal after being converted by the ultrasonic transducer, D is the distance between the ultrasonic probe and the glass plate, in units of mm, 1.9 dB is the compensation value for the loss of the ultrasonic wave signal caused by the incomplete reflection of the quartz target, 2.2×10 −4 dB mm -1 MHz -2 is the compensation coefficient for the attenuation of the ultrasonic wave signal in water). The mechanical properties include the mechanical properties of the ultrasonic probe that can withstand bending, stretching, twisting, adhesion, etc., and the influence on its acoustic properties.

[0063] To better explain the present invention, the following three specific embodiments are given: Embodiment 1 Step 1: Use a 1064 nm fiber laser marking machine to engrave a 20 μm thick copper foil with a power of 150 W, a cutting speed of 600 mm / s, and a cutting frequency of 20 kHz to obtain the bottom electrode 4 and the top electrode 2 with an island-bridge structure. The line width of the serpentine wires of the bottom electrode 4 and the top electrode 2 is 450 μm, and the island element size is 2 mm (as Figure 2 shown).

[0064] Step 2: Precisely paste the PZT-based piezoelectric sheet 3 (as Figure 3 shown) onto the corresponding island elements of the bottom electrode 4 through a composite conductive adhesive, and heat-cure the conductive adhesive at 75 °C; coat a conductive silver paste adhesive on the metal electrode facing up of the piezoelectric sheet 3 and paste it onto the corresponding island elements of the top electrode 2, and heat-cure the conductive adhesive at 275 °C; in order to facilitate the subsequent testing of the acoustic and mechanical properties of the ultrasonic probe, flexible cables are used to lead out the top electrode 2 and the bottom electrode 4.

[0065] Step 3: In this embodiment, two different acoustic impedance materials are used to fabricate the gradient matching layer 5. According to the KML classical matching layer theory, the acoustic impedances of these two different acoustic impedance materials are 2.13 MRayls and 6.14 MRayls respectively. For the low acoustic impedance material (the second matching layer), it can be directly prepared by adjusting the ratio of epoxy resin to curing agent. As can be seen from Figure 4 , when the mass ratio of epoxy resin to curing agent is 1:1, the set acoustic impedance value of 2.13 MRayls can be obtained. For the high acoustic impedance material (the first matching layer), 350 nm tungsten powder is added as a filler to the epoxy resin solution (the morphological characteristics of the tungsten powder are as shown in Figure 5 a and b), thereby adjusting the mass fraction of the tungsten powder. As can be seen from Figure 5 c, when the mass fraction of the tungsten powder is 70%, the set acoustic impedance value of 6.14 MRayls can be achieved. Subsequently, the solution of uniformly mixed epoxy resin and tungsten powder is drop-coated into a groove with a certain thickness, and air bubbles are removed by a vacuum pumping method, and then heated at 180 °C until completely cured to obtain the first matching layer. The epoxy resin solution with a mass ratio of epoxy resin to curing agent of 1:1 is drop-coated into a groove with a certain thickness, and air bubbles are removed by a vacuum pumping method, and then heated at 180 °C until completely cured to obtain the second matching layer. The first matching layer and the second matching layer are finely polished with sandpaper to meet the requirement of the corresponding quarter-wavelength thickness of the matching layer, where the thicknesses of the first matching layer and the second matching layer are adjusted to approximately 205 μm and approximately 175 μm respectively; then, the first matching layer is adhered to the island element of the bottom electrode 4 through the epoxy resin solution, and then the second matching layer is adhered to the first matching layer, and thus the preparation of the gradient matching layer 5 can be obtained.

[0066] Step 4: A porous polymer with a thickness of 0.5 mm (such as Figure 6 shown, this porous polymer is plastic foam) is directly pasted on the island element of the top electrode 2, and thus the low acoustic impedance backing layer 1 can be obtained.

[0067] Step 5: The ultrasonic device assembled in Step 4 is placed on the elastomer 6 with a thickness of 100 μm, and a tape with a certain thickness is attached around it. The Ecoflex elastomer solution used to prepare the elastomer 6 is injected into all the voids of the ultrasonic device and completely submerges the low acoustic impedance backing layer 1; after the Ecoflex elastomer is cured, the elastomer-encapsulated wearable ultrasonic probe ( Figure 7 ) can be obtained.

[0068] To better illustrate the unique advantages of the flexible wearable ultrasonic probe of the present invention based on a low acoustic impedance backing layer and a gradient matching layer, the present invention is illustrated by flexible wearable ultrasonic probes with three different structures as comparative examples (Comparative Example 1: a flexible wearable ultrasonic probe with a low acoustic impedance backing layer and no matching layer; Comparative Example 2: a flexible wearable ultrasonic probe with a low acoustic impedance backing layer and a single matching layer; Comparative Example 3: a flexible wearable ultrasonic probe with Ecoflex elastomer serving as both the matching layer and the backing layer).

[0069] Comparative Example 1 It is basically the same as Example 1, except that step 3 is omitted to obtain a flexible wearable ultrasonic probe with a low acoustic impedance backing layer 1 and no matching layer.

[0070] Comparative Example 2 It is basically the same as Example 1, except that in step 3, a matching layer is prepared with an acoustic impedance material having an acoustic impedance of 5.06 MRalys to obtain a flexible wearable ultrasonic probe with a low acoustic impedance backing layer 1 and a single matching layer.

[0071] Comparative Example 3 It is basically the same as Example 1, except that both the low acoustic impedance backing layer 1 and the gradient matching layer 5 are replaced with Ecoflex elastomer to obtain a flexible wearable ultrasonic probe with Ecoflex elastomer serving as both the backing layer and the matching layer. Two flexible wearable ultrasonic probes with thicknesses of 1 mm and 5 mm are prepared in this comparative example.

[0072] The flexible wearable ultrasonic probe based on the low acoustic impedance backing layer and the gradient matching layer is characterized and tested, and then its preparation process is further optimized.

[0073] Specifically, a super-depth-of-field industrial microscope is used to characterize the cross-section of a single element of the flexible wearable ultrasonic probe, as Figure 8 shown, it can be seen that the connection between its layers is tight, ensuring effective electrical, acoustic, and mechanical properties.

[0074] In particular, to verify the advantages and beneficial effects of the flexible wearable ultrasonic probe of the present invention based on the low acoustic impedance backing layer and the gradient matching layer, the resonance characteristics (as Figure 9 shown) and response characteristics (as Figure 10 shown) of the flexible wearable ultrasonic probe with a low acoustic impedance backing layer 1 and no matching layer (Comparative Example 1) and the flexible wearable ultrasonic probe with a low acoustic impedance backing layer 1 and a single matching layer (Comparative Example 2) are also compared, as well as the acoustic performance (as Figure 11 shown) of the flexible wearable ultrasonic probe usually using Ecoflex elastomer as both the backing layer and the matching layer (Comparative Example 3). FromFigure 9 It can be seen that the wearable ultrasonic probe of the present invention based on a low acoustic impedance backing layer and a gradient matching layer has three resonance peaks, which can greatly enhance the bandwidth of the ultrasonic probe; while the bandwidths of the wearable ultrasonic probes without a matching layer and with a single matching layer are significantly narrower than that of the wearable ultrasonic probe of the present invention based on a low acoustic impedance backing layer and a gradient matching layer. From Figure 10 It can be seen that the wearable ultrasonic probe of the present invention based on a low acoustic impedance backing layer and a gradient matching layer can achieve a low insertion loss of -10 dB and a high bandwidth of 70%, while the wearable ultrasonic probe without a matching layer has an insertion loss of -16.68 dB and a bandwidth of 27%, and the wearable ultrasonic probe with a single matching layer has an insertion loss of -16.88 dB and a bandwidth of 31%. Further, comparing the insertion losses and bandwidths of the wearable ultrasonic probes with typical 1 mm and 5 mm thick Ecoflex elastomers as the backing layer and the matching layer are -16.72 dB @ 28% and -17.64 dB @ 28% ( Figure 11 ), which are much lower than the acoustic performance of the wearable ultrasonic probe of the present invention based on a low acoustic impedance backing layer and a gradient matching layer. Figures 9 - 11 The results show that the flexible wearable ultrasonic probe of the present invention based on a low acoustic impedance backing layer and a gradient matching layer has more excellent resonance characteristics and response characteristics, and thus exhibits a better relative bandwidth and a lower insertion loss (as Figure 12 shown). Based on the above results, the performance of the wearable ultrasonic probe of the present invention with a low acoustic impedance backing layer and a gradient matching layer is superior to that of the wearable ultrasonic probes with a low acoustic impedance backing layer without a matching layer, a low acoustic impedance backing layer with a single matching layer, and Ecoflex as the matching layer and the backing layer.

[0075] Finally, the flexible wearable ultrasonic probe of the present invention based on a low acoustic impedance backing layer and a gradient matching layer also has good adhesion (as Figure 13 shown), and can conformally adhere to the surface of a hard and curved glass tube; at the same time, it still maintains good mechanical stability after 160 stretches under the condition of 50% strain (as Figure 14 shown), which provides strong technical support for its wide biomedical applications.

[0076] Comprehensively Figure 12 and Figure 14 it can be concluded that the flexible wearable ultrasonic probe of the present invention based on a low acoustic impedance backing layer and a gradient matching layer has comprehensive performance with a relative bandwidth greater than 70%, an insertion loss less than -10 dB, and a mechanical stretch greater than 30%.

[0077] Example 2 Replace the thermosetting Ecoflex elastomer in Example 1 with a polyurethane (PU) elastomer that can be ultraviolet polymerized within 30 seconds, which can further expand the application scenarios of the present invention to be applicable to 1-3 type PZT piezoelectric wafers with lower Curie temperature points, avoiding the decline of piezoelectric performance caused by thermal shock, thereby affecting the acoustic performance of the entire ultrasonic probe. Other processes are the same as those in Example 1.

[0078] Example 3 Steps 1-3 of this example are the same as those in Example 1, mainly differing in the low acoustic impedance backing layer. The acoustic impedance of air is only 425 Ralys, with a difference of 3-4 orders of magnitude from that of the piezoelectric wafer, which is a typical representative of low acoustic impedance materials.

[0079] In this example, (1) first use laser engraving to prepare a polytetrafluoroethylene template with grooves ( Figure 15 as shown in a-b), where the groove depth is 0.5 mm and the diameter is the same as that of the top electrode island element (2 mm); pour the Ecoflex elastomer solution into the polytetrafluoroethylene template, heat and cure it, and then separate it from the template to obtain an elastomer with a groove structure; (2) place the assembled ultrasonic device on the 100-μm-thick elastomer 6, attach a certain thickness of tape around it, inject the elastomer solution used to prepare the elastomer 6 into all the voids of the ultrasonic device, and ensure that the height of the elastomer solution is flush with the height of the top electrode 2; after the elastomer is semi-cured, attach the elastomer with the groove structure to the top electrode 2 (where the groove part is aligned with the island element position of the top electrode), and continue to complete the curing to obtain a wearable ultrasonic probe with an elastomer-encapsulated air backing layer and a gradient matching layer.

[0080] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A flexible wearable ultrasound probe based on a low acoustic impedance backing layer and a gradient matching layer, characterized in that: The invention comprises a probe body and an elastomer encapsulating the probe body, wherein the probe body comprises a low acoustic impedance backing layer, a top electrode, a piezoelectric sheet, a bottom electrode and a gradient matching layer in sequence from one side to the other; the low acoustic impedance backing layer is a porous polymer, aerogel, cloth or air; the gradient matching layer comprises a plurality of matching layers arranged in a stacked manner, and the acoustic impedance of each matching layer decreases in sequence from close to the bottom electrode to away from the bottom electrode; the elastomer is a coupling material that matches the skin impedance.

2. The flexible wearable ultrasound probe based on a low acoustic impedance backing layer and a gradient matching layer according to claim 1, characterized in that: The top electrode and the bottom electrode are stretchable metal electrodes.

3. The flexible wearable ultrasound probe based on a low acoustic impedance backing layer and a gradient matching layer according to claim 2, characterized in that: The bottom electrode and the top electrode are both island-bridge structures, and the island elements in the island-bridge structure are connected by serpentine wires; the number of island elements contained in the bottom electrode and the top electrode is consistent with the number of piezoelectric sheets; Multiple piezoelectric sheets are connected to the island elements of the top electrode in one-to-one correspondence, and are connected to the island elements of the bottom electrode in one-to-one correspondence; multiple low acoustic impedance backing layers are connected to the island elements of the top electrode in one-to-one correspondence, and multiple gradient matching layers are connected to the island elements of the bottom electrode in one-to-one correspondence.

4. The flexible wearable ultrasound probe based on a low acoustic impedance backing layer and a gradient matching layer according to claim 1, characterized in that: The thickness of the low acoustic impedance backing layer is 0.5-1 mm.

5. The flexible wearable ultrasound probe based on a low acoustic impedance backing layer and a gradient matching layer according to claim 1, characterized in that: The gradient matching layer comprises a first matching layer and a second matching layer, the acoustic impedance of the first matching layer is higher than the acoustic impedance of the second matching layer, and the first matching layer is located between the bottom electrode and the second matching layer.

6. The flexible wearable ultrasound probe based on a low acoustic impedance backing layer and a gradient matching layer according to claim 5, characterized in that: The first matching layer is epoxy resin doped with micron metal, nano metal, oxide, carbide or nitride, and the second matching layer is epoxy resin.

7. The flexible wearable ultrasound probe based on a low acoustic impedance backing layer and a gradient matching layer according to claim 1, characterized in that: The thickness of the first matching layer and the second matching layer are respectively one quarter of the wavelength of ultrasound propagation in each layer.

8. The flexible wearable ultrasound probe based on a low acoustic impedance backing layer and a gradient matching layer according to claim 1, characterized in that: One side of the low acoustic impedance backing layer is connected to the top electrode, and the other side opposite to it is encapsulated by an elastomer; one side of the gradient matching layer is connected to the bottom electrode, and the other side opposite to it is encapsulated by an elastomer.

9. The flexible wearable ultrasound probe based on a low acoustic impedance backing layer and a gradient matching layer according to claim 1, characterized in that: The elastomer is polydimethylsiloxane, polyurethane, silicone rubber or hydrogenated styrene-butadiene-styrene block copolymer.

10. The method for preparing a flexible wearable ultrasound probe based on a low acoustic impedance backing layer and a gradient matching layer according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1, connecting two side surfaces of the piezoelectric sheet to one side surface of the bottom electrode and one side surface of the top electrode, and connecting the low acoustic impedance backing layer and the gradient matching layer to the other side surface of the top electrode and the other side surface of the bottom electrode, respectively, to obtain an ultrasonic device; S2, placing the ultrasonic device on the elastomer, surrounding it to form a mold, injecting the elastomer solution into the mold to immerse the low acoustic impedance backing layer; after the elastomer is cured, an elastomer-encapsulated wearable ultrasonic probe is obtained.

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