Flexible wearable ultrasonic patch based on PMUT chip

Abstract

The invention discloses a flexible wearable ultrasonic patch based on a PMUT chip. The flexible wearable ultrasonic patch sequentially comprises a flexible substrate, a snakelike negative electrode, a matching layer, a PMUT array, a snakelike positive electrode, a backing layer and a flexible packaging layer from bottom to top in the thickness direction. The snakelike negative electrode is arranged on the flexible substrate and is electrically connected with a negative electrode pin of the PMUT array through a through hole penetrating through the matching layer; the snakelike positive electrode is arranged on the PMUT array and is electrically connected with a positive electrode pin of the PMUT array; the backing layer is arranged on the snake-shaped positive electrode and used for absorbing sound, and the flexible packaging layer wraps the backing layer and the peripheral side of the patch to achieve overall protection. The device has the advantages of being low in working voltage, high in skin fitting performance and high in long-time wearing stability, can be used for achieving blood vessel imaging and continuous blood pressure monitoring, and does not need a liquid coupling agent.

Description

Technical Field

[0001] This invention relates to the fields of microelectromechanical systems (MEMS) technology and wearable medical technology, specifically to a flexible wearable ultrasonic patch based on a PMUT chip. Background Technology

[0002] Current mainstream clinical ultrasound equipment uses rigid probes made of piezoelectric ceramic (PZT) sheets, which have significant limitations: First, the probe's acoustic window is geometrically mismatched with the complex curved surfaces of the human neck and wrist, requiring the application of large amounts of liquid coupling agent to eliminate air gaps, which can easily cause patient discomfort. Second, the rigid structure makes it difficult to maintain continuous and stable acoustic contact with the skin, and changes in body position can cause signal drift, making it unsuitable for continuous monitoring during movement or sleep. Third, the probe weighs 100-300g, requiring handheld or robotic arm fixation, which can easily lead to pressure sores and hinder patient movement over time. Fourth, measurement results depend on the operator's technique, with repeatability errors exceeding 10%, which is not conducive to home self-testing and widespread adoption at the grassroots level. Fifth, the liquid coupling agent is prone to drying out and staining clothing, and some patients face the risk of allergies, limiting long-term wear.

[0003] To overcome these bottlenecks, academia and industry have been actively developing "flexible ultrasonic patch" technology in recent years. This technology integrates ultrasonic transducers onto flexible substrates such as polyimide (PI) and polydimethylsiloxane (PDMS), theoretically enabling conformal adhesion to the skin. However, existing flexible ultrasonic technologies still face the following key technical bottlenecks: capacitive micromechanical ultrasonic transducers (CMUTs) require a 30-100V DC bias voltage, resulting in high system power consumption, electromagnetic compatibility challenges, and high-voltage safety hazards; PZT ceramics thinned to 100-200μm are still brittle, prone to microcracks when bent, exhibit rapid sensitivity decay, and their thickness does not meet the requirements for "imperceptible wear"; simultaneously, existing technologies lack systematic acoustic optimization of the matching layer thickness, acoustic impedance, and backing layer attenuation coefficient, affecting ultrasonic transmission efficiency and imaging resolution; furthermore, the large number of array elements and the complexity and bulky wire bundles of traditional gold wire bonding processes, coupled with simple parallel connections leading to a surge in channel count, make it difficult to achieve high-density, stretchable, and low-impedance electrode interconnections on flexible substrates. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a flexible wearable ultrasound patch based on a PMUT chip. This invention has the advantages of low operating voltage, high skin adhesion, and high stability during long-term wear. It can be used to achieve vascular imaging and continuous blood pressure monitoring, and requires no liquid coupling agent.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a flexible wearable ultrasonic patch based on a PMUT chip, comprising, from bottom to top along the thickness direction, a flexible substrate, a serpentine negative electrode, a matching layer, a PMUT array, a serpentine positive electrode, a backing layer, and a flexible encapsulation layer; the serpentine negative electrode is disposed on the flexible substrate and electrically connected to the negative electrode pin of the PMUT array through a through-hole penetrating the matching layer; the serpentine positive electrode is disposed on the PMUT array and electrically connected to the positive electrode pin of the PMUT array; the backing layer is disposed on the serpentine positive electrode for sound absorption, and the flexible encapsulation layer covers the backing layer and the periphery of the patch to achieve overall protection.

[0006] The aforementioned flexible wearable ultrasonic patch based on PMUT chips consists of a PMUT array composed of 3×3 PMUT chips arranged in an array, with each PMUT chip containing 9 PMUT elements.

[0007] The aforementioned flexible wearable ultrasonic patch based on a PMUT chip includes a PMUT element comprising a substrate and a vibration structure disposed on the substrate; The substrate includes a base having cavities and a buried oxide layer formed on the base; The vibration structure includes a structural layer above the buried oxygen layer, a piezoelectric layer above the structural layer, a grounding electrode layer below the piezoelectric layer, and a top electrode layer above the piezoelectric layer.

[0008] The aforementioned flexible wearable ultrasonic patch based on a PMUT chip has a substrate made of silicon; the cavity in the substrate is either a cavity with a gradually changing diameter or a cavity with a fixed diameter; the thickness of the substrate is 400 μm, and the cavity diameter or maximum diameter is 1000 μm; the buried oxide layer is made of silicon dioxide and has a thickness of 1 μm.

[0009] The aforementioned flexible wearable ultrasonic patch based on the PMUT chip has the following characteristics: the structural layer is made of silicon and has a thickness of 10 μm; the piezoelectric layer is made of aluminum nitride, scandium-doped aluminum nitride, lead zirconate titanate, or lithium niobate and has a thickness of 1 μm; the ground electrode layer has a thickness of 1 μm; and the top electrode layer is made of gold, platinum, tin, or aluminum and has a thickness of 0.5 μm.

[0010] The aforementioned flexible wearable ultrasonic patch based on a PMUT chip includes a top electrode layer comprising a central ring electrode and an outer ring electrode; the central ring electrode and the outer ring electrode are arranged concentrically, with the central ring located inside the outer ring electrode; the central ring electrode is connected to a first pin probe, and the outer ring electrode is connected to a second pin probe.

[0011] The aforementioned flexible wearable ultrasonic patch based on a PMUT chip has a flexible substrate material of medical thermoplastic polyurethane or polydimethylsiloxane with a thickness of 20-25µm; and a flexible encapsulation layer material of one of polydimethylsiloxane, polyimide or medical thermoplastic polyurethane with a thickness of 20-25µm.

[0012] The aforementioned flexible wearable ultrasonic patch based on the PMUT chip uses copper, gold, or silver as the material for the serpentine negative electrode and the serpentine positive electrode, both of which employ an island-bridge structure. In the island-bridge structure, the island element radius is 300µm, the bridge structure is a half-circle flip structure with a semi-circle radius of 500µm, a line width of 10µm, and an electrode thickness of 5µm. The serpentine negative electrode is connected to a negative electrode pin, which is electrically connected to the negative electrode pin of the PMUT array through a through-hole penetrating the matching layer; the serpentine positive electrode is connected to the positive electrode pin of the positive electrode pin.

[0013] The aforementioned flexible wearable ultrasonic patch based on a PMUT chip has a backing layer material of a mixture of rubber and tungsten powder; the thickness of the backing layer is 500µm.

[0014] The aforementioned flexible wearable ultrasonic patch based on a PMUT chip has a matching layer material that is a composite material of silver nanowires and PDMS, with a thickness of one-quarter of the wavelength.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention uses a PMUT array as its core, operates at a low voltage, and eliminates the need for high-voltage driver chips and large-capacity batteries. This eliminates high-voltage safety hazards and reduces system power consumption, perfectly meeting the lightweight requirements of wearable medical devices. Furthermore, this invention employs a fully flexible layered structure, with both the substrate and encapsulation layer made of flexible materials. This allows for close contact with the complex curves of human skin, eliminating the need for liquid coupling agents and solving the problems of poor fit and discomfort associated with traditional rigid probes. This enables "unobtrusive" long-term continuous wear. This invention requires no professional adjustment; the patch can be applied directly for wearing. It is suitable for home self-testing by patients and facilitates standardized monitoring in primary healthcare institutions, broadening its application scope.

[0016] 2. This invention, through the collaborative design of a matching layer, PMUT element, and backing layer, reduces ultrasonic signal interface loss, suppresses back-side reflection interference, and improves beam focusing performance, enabling clear imaging and meeting the monitoring needs of fine vascular structures. Furthermore, the serpentine electrode of this invention solves the interconnection problem of high-density elements on a flexible substrate, simplifies back-end processing, and facilitates industrial mass production. The PMUT element of this invention uses a piezoelectric material with superior toughness, combined with fully flexible packaging, which can withstand repeated bending and environmental interference, avoiding problems such as device brittleness and poor contact, ensuring long-term reliability. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a patch device in a specific embodiment of the present invention; Figure 2 This is a schematic diagram of the side structure of a patch device in a specific embodiment of the present invention; Figure 3 This is a schematic diagram of the flexible bending of the patch device in a specific embodiment of the present invention; Figure 4 This is a schematic diagram of a 3x3PMUT chip array in a specific embodiment of the present invention; Figure 5 This is a schematic diagram showing the layering of the serpentine negative electrode and the serpentine positive electrode in a specific embodiment of the present invention; Figure 6 This is a schematic diagram of the structure of a single PMUT chip in a specific embodiment of the present invention; Figure 7 This is a schematic diagram of the top electrode layer in a specific embodiment of the present invention; Figure 8 This is a schematic diagram of the structure of a single vibration element of PMUT in a specific embodiment of the present invention. Figure 9 This is a schematic diagram of the island bridge structure of the serpentine electrode of the patch device in a specific embodiment of the present invention; Figure 10 This is a schematic diagram of the serpentine electrode row and column multiplication of a patch device in a specific embodiment of the present invention; Figure 11 This is a diagram of patch signal transmission and reception in a specific embodiment of the present invention; Figure 12 This is a voltage waveform corresponding to the transmitted pulse signal and the received echo signal during patch operation in a specific embodiment of the present invention; Figure 13 This is an image showing the imaging effect obtained by patching in a specific embodiment of the present invention; Figure 14 This is a schematic diagram of a test system for surface mount devices in a specific embodiment of the present invention.

[0018] Figure Labels 1. Flexible substrate; 2. Serpentine negative electrode; 3. Matching layer; 4. PMUT array; 5. Serpentine positive electrode; 6. Backing layer; 7. Flexible encapsulation layer; 201. Negative electrode pin of serpentine negative electrode; 401. Central ring electrode; 402. Outer ring electrode; 403. Piezoelectric layer; 404. Ground electrode layer; 405. Structural layer; 406. Buried oxide layer; 407. Substrate; 408. First pin probe; 409. Second pin probe; 4001. Negative electrode pin of PMUT chip; 4002. Positive electrode pin of PMUT chip; 501. Positive electrode pin of serpentine positive electrode. Detailed Implementation

[0019] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0020] Example 1: A flexible wearable ultrasonic patch based on a PMUT chip, such as Figures 1-5 As shown, from bottom to top along the thickness direction, the structure includes a flexible substrate 1, a serpentine negative electrode 2, a matching layer 3, a PMUT array 4, a serpentine positive electrode 5, a backing layer 6, and a flexible encapsulation layer 7. The serpentine negative electrode 2 is disposed on the flexible substrate 1 and is electrically connected to the negative electrode pin of the PMUT array 4 through a through-hole penetrating the matching layer 3. The serpentine positive electrode 5 is disposed on the PMUT array 4 and is electrically connected to the positive electrode pin of the PMUT array 4. The backing layer 6 is disposed on the serpentine positive electrode 5 for sound absorption, and the flexible encapsulation layer 7 covers the backing layer 6 and the periphery of the patch to achieve overall protection.

[0021] Specifically, in this embodiment, the flexible substrate 1 can be a polydimethylsiloxane film with a Young's modulus of approximately 2 MPa, which can be repeatedly bent without plastic deformation. To reduce interfacial stress and improve adhesion to the subsequent PDMS encapsulation layer, a double-sided spin-coating process is used to deposit 2 µm thick PDMS layers on both sides of the original film as stress buffer layers. After spin-coating, the entire assembly is pre-cured in an 80°C oven for 30 min, and then vacuum-annealed at 120°C for 1 h to eliminate internal stress and ensure thickness uniformity. In other embodiments, the flexible substrate 1 can also be medical-grade thermoplastic polyurethane.

[0022] In this embodiment, the serpentine negative electrode 2 and the serpentine positive electrode 5 are made of copper, gold, or silver, and both adopt an island-bridge structure. Figure 9 As shown.

[0023] In the island-bridge structure, the island element has a radius of 300µm, the bridge structure is a half-circle flip structure with a semi-circle radius of 500µm, a linewidth of 10µm, and an electrode thickness of 5µm. like Figure 5and Figure 10 As shown, the row and column multiplexing of the serpentine negative electrode 2 compresses 9 channels into 1 channel, ultimately forming a negative electrode pin 201. The serpentine negative electrode is connected to the chip negative electrode pin 4001 via a hole in the matching layer 2; the hole radius is 100 μm and the hole thickness is 10 μm. The thickness of the serpentine negative electrode is 5 μm. The serpentine positive electrode 5 is made of copper, gold, or silver, preferably gold. The serpentine positive electrode 5 is connected to a positive electrode pin 501, and the serpentine positive electrode is connected to the positive electrode pin 4002 of the PMUT array 4, as shown... Figure 6 As shown. The serpentine negative electrode is made by pouring copper, gold, or silver paste into the hole and curing it to connect and conduct with the negative electrode pin of the PMUT chip. The serpentine positive electrode is also made by curing copper, gold, or silver paste and connecting and conducting with the positive electrode pin of the PMUT chip. The curing process involves attaching a carrier layer to the groove surface of a stainless steel mold in an island-bridge serpentine shape, then injecting metal paste, vacuum degassing for 3 minutes, and then curing in a 120℃ oven for 30 minutes. After complete cross-linking, it is naturally cooled to room temperature, and the carrier layer is peeled off along the edge of the mold for complete demolding. The resulting electrode thickness is 5μm.

[0024] In this embodiment, the matching layer 3 is a composite material of silver nanowires and PDMS, with a specific gravity ratio of 1:1. Its thickness at 5MHz is λ / 4, where λ is the wavelength, which is 75µm in this embodiment. Using a matching layer 3 with a thickness of λ / 4 enables efficient coupling of ultrasound at the skin-soft tissue interface. The matching layer 3 is prepared by slowly dripping pretreated silver nanoparticle slurry into a vacuum-degassed PDMS prepolymer while stirring and evacuating to ensure no air bubbles. Then, it is screen-printed to cover a 3x3 PMUT chip array, followed by curing.

[0025] Specifically, the PMUT array 4 consists of 3×3 PMUT chips arranged in an array, each PMUT chip containing 9 PMUT elements, and each PMUT element includes a substrate and a vibration structure located on the substrate.

[0026] like Figure 8 As shown, the substrate includes a base 407 having a cavity and a buried oxide layer 406 formed on the base 407; The vibration structure includes a structural layer 405 disposed above the buried oxygen layer 406, a piezoelectric layer 403 disposed above the structural layer 405, a ground electrode layer 404 disposed below the piezoelectric layer 403, and a top electrode layer disposed above the piezoelectric layer 403.

[0027] In this embodiment, both the substrate 407 and the structural layer 405 of the PMUT element can be made of silicon, with the substrate 407 having a thickness of 400 μm. The buried oxide layer 406 is made of silicon dioxide with a thickness of 1 μm. The buried oxide layer 406 is grown into silicon dioxide using a thermal oxidation epitaxial growth method. The buried oxide layer 406 separates the substrate 407 and the structural layer 405, which is beneficial for manufacturing three-dimensional structures of MEMS. Furthermore, the thicknesses of the substrate 407 and the structural layer 405 can be flexibly designed according to the device and application during manufacturing. A cavity with a diameter of 1000 μm is formed in the substrate 407 and the buried oxide layer 406. In other embodiments, the diameter of the cavity can adopt a gradient structure, with a minimum diameter of 500 μm and a maximum diameter of 1000 μm. The structural layer 405 is formed by vacuum silicon-silicon bonding of another silicon wafer onto the front side of the substrate 407, followed by high-temperature annealing, serving as the top silicon material. The bonded silicon wafer is thinned to near the designed silicon device layer thickness. Then, chemical mechanical polishing is used to further refine the top silicon thickness. Finally, surface treatment completes the manufacturing process. The thickness of the structural layer 405 is 10 μm. The piezoelectric layer 403 is made of aluminum nitride. In other embodiments, the piezoelectric layer 403 can be made of scandium-doped aluminum nitride, zinc oxide, or lead zirconate titanate piezoelectric ceramic. The piezoelectric layer 403 is formed by growing a thin layer of aluminum nitride on the silicon surface of the structural layer 405 as a seed layer using magnetron sputtering, followed by dry etching for patterning. The ground electrode layer 404 can be made of gold, platinum, or aluminum. The electrode material can be grown on the piezoelectric layer using physical vapor deposition, including electron beam evaporation and magnetron sputtering, followed by electrode patterning. The thickness is 1 μm.

[0028] like Figure 7 As shown, the top electrode layer includes a central ring electrode 401 and an outer ring electrode 402. The central ring electrode 401 and the outer ring electrode 402 are arranged concentrically, with the central ring 401 located inside the outer ring electrode 402. They do not contact each other to avoid electrical signal interference. The central ring electrode 401 is connected to a first pin probe 408, and the outer ring electrode 402 is connected to a second pin probe 409. This separate structure can drive the piezoelectric layer to generate lateral expansion and contraction strain by applying an electrical signal between the two electrodes, thereby causing the diaphragm to bend and vibrate. This is the key structural basis for the PMUT element to achieve both inverse and direct piezoelectric effects. The first pin probe 408 and the second pin probe 409 both extend to the outside of the PMUT element for electrical connection with external electrode structures such as the serpentine positive electrode. Figure 11 As shown, when emitting ultrasound, the external electrical signal is transmitted to the central ring electrode and the outer ring electrode through two probes, driving the piezoelectric layer to vibrate; when receiving the echo, the polarization charge signal generated by the vibration of the piezoelectric layer is transmitted to the external signal processing module through the two electrodes and probes, ultimately realizing the conversion and transmission of the ultrasound signal.

[0029] In this embodiment, to suppress back-side acoustic wave reflection and shorten ringing time, the backing layer 6 is made of a rubber-tungsten powder composite material with a specific gravity of 1:1. The rubber and tungsten powder are mixed in a mixer, degassed under vacuum, and then uniformly coated using a scraping method before curing. This design of the patch backing layer reduces the loss and reflection of ultrasonic energy to the side of the patch away from the skin, allowing more ultrasonic energy to propagate towards the skin and deeper tissues—the "forward" direction. This is also the target direction for ultrasound to achieve functions such as vascular imaging and blood flow monitoring, thereby improving the efficiency of ultrasonic energy utilization and imaging / monitoring effects.

[0030] In this embodiment, the patch is encapsulated with a flexible encapsulation layer for overall protection. The flexible encapsulation layer 7 is made of polydimethylsiloxane and has a thickness of 20-25 μm. In other embodiments, the flexible encapsulation layer 7 may also be made of polyimide or medical-grade thermoplastic polyurethane.

[0031] This embodiment of the flexible wearable ultrasound patch uses a PMUT array as its core, operates at a low voltage, and eliminates the need for a high-voltage driver chip and a large-capacity battery. This eliminates the safety hazards of high voltage and reduces system power consumption, perfectly meeting the lightweight requirements of wearable medical devices. Furthermore, it employs a fully flexible layered structure, with both the substrate and encapsulation layer made of flexible materials, allowing it to closely conform to the complex curves of human skin (flexible bending states such as...). Figure 3 As shown in the figure, no liquid coupling agent is required, which solves the problems of poor fit and discomfort of traditional rigid probes, and enables "unobtrusive" long-term continuous wear.

[0032] Example 2: This example uses the flexible wearable ultrasound patch from Example 1 to test blood flow in the human neck vessels. It includes a flexible wearable ultrasound patch based on a PMUT chip, a signal generator, a signal receiver, and a signal analysis module.

[0033] Test Preparation: In this embodiment, a flexible patch is attached to the surface of the subject's left common carotid artery, allowing for acoustic coupling with the skin without the need for a coupling agent. An experimental schematic diagram is shown below. Figure 14 After the patch is connected to the ASIC via the serpentine negative electrode 2 and the serpentine positive electrode 5, the row and column multiplexing logic is written into the FPGA: the row and column lines are cross-selected, and only 2 external leads are needed to address all the oscillators.

[0034] Signal Transmission: A built-in DDS signal generator produces a 5MHz sinusoidal transmission signal, which is converted into a 5Vpp unipolar pulse train by a digital-to-analog converter. This pulse is amplified and filtered before being sent to the horizontal driver to ensure sufficient mechanical amplitude for the diaphragm. An electrical pulse is applied between the central ring electrode 401 and the outer ring electrode 402, causing the piezoelectric layer 403 to generate lateral expansion and contraction using the d31 mode, driving the 8µm silicon diaphragm to bend synchronously. The cavity vacuum on the substrate 407 is below 10Pa, forming efficient piston radiation. The 75µm matching layer 3 smoothly transitions the skin from 1.6MRayl to 3.0MRayl, effectively reducing transmission loss.

[0035] Signal reception and imaging: A 5MHz acoustic beam propagates through soft tissue, encountering blood vessel walls, blood flow, and plaques, resulting in reflections. The acoustic impedance difference ΔZ determines the echo amplitude, while blood flow velocity causes a Doppler frequency shift. The echo forces the diaphragm to vibrate, generating polarization charges in the 403 piezoelectric layer, resulting in an output voltage of 0.2–2mV. The channel signal is amplified by a filter amplifier, and delay-superposition beamforming is used to reconstruct color blood flow images in real time (e.g., Figure 13 As shown), the center frequency is 5MHz, the penetration depth is 0-30mm, the lateral resolution is 0.45mm, and the longitudinal resolution is 0.3mm. Simultaneous sampling along the long axis of the vessel displays the grayscale waveform of the arterial wall's expansion and contraction during the cardiac cycle (e.g., ...). Figure 12 As shown in the figure, vascular compliance is calculated and risk classification is output based on this.

[0036] In summary, the flexible wearable ultrasound patch of the present invention overcomes the shortcomings of existing rigid ultrasound probes and flexible ultrasound patches, and has the advantages of low operating voltage, high skin adhesion, and high stability during long-term wear. It can be used to realize vascular imaging and continuous blood pressure monitoring, and does not require liquid coupling agent.

Claims

1. A flexible wearable ultrasonic patch based on a PMUT chip, characterized in that: The structure comprises, from bottom to top along the thickness direction, a flexible substrate (1), a serpentine negative electrode (2), a matching layer (3), a PMUT array (4), a serpentine positive electrode (5), a backing layer (6), and a flexible encapsulation layer (7). The serpentine negative electrode (2) is disposed on the flexible substrate (1) and electrically connected to the negative electrode pin of the PMUT array (4) through a through hole penetrating the matching layer (3). The serpentine positive electrode (5) is disposed on the PMUT array (4) and electrically connected to the positive electrode pin of the PMUT array (4). The backing layer (6) is disposed on the serpentine positive electrode (5) for sound absorption. The flexible encapsulation layer (7) covers the backing layer (6) and the periphery of the patch to achieve overall protection.

2. The flexible wearable ultrasonic patch based on a PMUT chip according to claim 1, characterized in that: The PMUT array (4) consists of 3×3 PMUT chips arranged in an array, and each PMUT chip contains 9 PMUT elements.

3. The flexible wearable ultrasonic patch based on a PMUT chip according to claim 2, characterized in that: The PMUT element includes a substrate and a vibration structure disposed on the substrate; The substrate includes a base (407) having a cavity and a buried oxide layer (406) formed on the base (407). The vibration structure includes a structural layer (405) above the buried oxygen layer (406), a piezoelectric layer (403) above the structural layer (405), a ground electrode layer (404) below the piezoelectric layer (403), and a top electrode layer above the piezoelectric layer (403).

4. The flexible wearable ultrasonic patch based on a PMUT chip according to claim 3, characterized in that: The substrate (407) is made of silicon; the cavity in the substrate (407) is a cavity with a gradually changing diameter or a cavity with a fixed diameter; the thickness of the substrate (407) is 400 μm, and the cavity diameter or maximum diameter is 1000 μm; the buried oxide layer (406) is made of silicon dioxide and has a thickness of 1 μm.

5. The flexible wearable ultrasonic patch based on a PMUT chip according to claim 3, characterized in that: The structural layer (405) is made of silicon and has a thickness of 10 μm; the piezoelectric layer (403) is made of aluminum nitride, scandium-doped aluminum nitride, lead zirconate titanate, or lithium niobate; the piezoelectric layer (403) has a thickness of 1 μm; the ground electrode layer (404) has a thickness of 1 μm; and the top electrode layer is made of gold, platinum, tin, or aluminum and has a thickness of 0.5 μm.

6. The flexible wearable ultrasonic patch based on a PMUT chip according to claim 5, characterized in that: The top electrode layer includes a central ring electrode (401) and an outer ring electrode (402); the central ring electrode (401) and the outer ring electrode (402) are arranged in concentric circles, with the central ring (401) located inside the outer ring electrode (402); the central ring electrode (401) is connected to a first pin probe (408), and the outer ring electrode (402) is connected to a second pin probe (409).

7. The flexible wearable ultrasonic patch based on a PMUT chip according to claim 1, characterized in that: The flexible substrate (1) is made of medical thermoplastic polyurethane or polydimethylsiloxane, with a thickness of 20-25µm; the flexible encapsulation layer (7) is made of one of polydimethylsiloxane, polyimide or medical thermoplastic polyurethane, with a thickness of 20-25µm.

8. The flexible wearable ultrasonic patch based on a PMUT chip according to claim 1, characterized in that: The materials of the serpentine negative electrode (2) and the serpentine positive electrode (5) are copper, gold or silver, and both adopt an island-bridge structure; In the island-bridge structure, the island element radius is 300µm, the bridge structure is a half-circle flip structure with a semi-circle radius of 500µm, a line width of 10µm, and an electrode thickness of 5µm. The serpentine negative electrode (2) is connected to a negative electrode pin (201), and the negative electrode pin (201) is electrically connected to the negative electrode pin of the PMUT array (4) through a through hole penetrating the matching layer (3); the serpentine positive electrode (5) is connected to a positive electrode pin (501), and the positive electrode pin (501) is electrically connected to the positive electrode pin of the PMUT array (4).

9. The flexible wearable ultrasonic patch based on a PMUT chip according to claim 1, characterized in that: The backing layer (6) is a mixture of rubber and tungsten powder; the thickness of the backing layer (6) is 500µm.

10. The flexible wearable ultrasonic patch based on a PMUT chip according to claim 1, characterized in that: The matching layer (3) is a composite material of silver nanowires and PDMS, with a thickness of one-quarter of the wavelength.

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