Flexible sensor for synchronously monitoring multiple parameters of respiration and heartbeat as well as preparation method and application of flexible sensor

Abstract

The invention discloses a flexible sensor for synchronously monitoring multiple parameters of respiration and heartbeat as well as a preparation method and application thereof, and relates to the technical field of sensors. The flexible sensor comprises a respiration sensing layer which comprises a bottom layer and a plurality of split-ring resonators distributed in an array; the heartbeat sensing layer is arranged on the respiration sensing layer and comprises a middle layer and a plurality of cross-shaped resonance units distributed in an array mode, and the array center of the cross-shaped resonance units and the array center of the split-ring resonators are arranged in a staggered mode; and the packaging layer is arranged on the heartbeat sensing layer and is provided with a plurality of through holes. According to the invention, a double-layer unit differentiation layout is adopted, the outer-layer SRR resonant frequency (breathing dominant frequency band) and the inner-layer cross-shaped resonant unit resonant frequency (heartbeat dominant frequency band) realize physical signal separation through frequency interval, complex algorithm decoupling is not needed, and breathing and heartbeat multi-parameter synchronous monitoring is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of sensors, and particularly to a flexible sensor for synchronous monitoring of multiple respiratory and heartbeat parameters, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, flexible electronic technology has developed rapidly in the field of wearable health monitoring, especially in the direction of respiratory and heartbeat monitoring (sleep apnea screening, postoperative rehabilitation monitoring, and sports respiratory management). Technical solutions include resistive sensors (such as the Chinese patent with publication number CN117643464A), capacitive sensors (such as the Chinese patent with publication number CN116898452A), optical sensors (such as the Chinese patents with publication numbers CN117617942A and CN115575357A), and piezoelectric thin film sensors (such as the Chinese patents with publication numbers CN119714621A, CN119488373A, and CN119498781A). These existing technologies indirectly reflect physiological parameters by detecting skin deformation, pressure, or changes in optical signals, but there are problems such as susceptibility to environmental interference, single function, and wearing comfort.

[0003] To make up for the deficiencies of the existing technologies, researchers have applied electromagnetic metamaterial technology to physiological sensing (such as posture, respiration, and heartbeat monitoring). For example, the Chinese patent with publication number CN119173201A discloses a sensor, system, and method for non-contact sensing of physiological parameters of the body. It generates an evanescent electromagnetic field through a metamaterial waveguide (artificial surface plasmon mode), detects the electromagnetic field perturbation caused by physiological movements (such as respiration and heartbeat), extracts physiological parameters through the phase shift change of the transmitted / received signal, demodulates the signal using a software-defined radio (SDR) system, separates respiration and heart rate signals by combining algorithms such as band-pass filtering, fast Fourier transform (FFT), and long short-term memory network (LSTM), and calculates blood pressure through pulse transit time (PTT). However, this solution has the following limitations: (1) It relies on electromagnetic coupling and signal processing, indirectly senses physiological movements through external electromagnetic field perturbations, and the sensitivity is limited by the evanescent field intensity and environmental noise; (2) There is a non-contact distance limitation. The sensor needs to be placed 1 mm - 15 mm away from the body, and its direct response ability to minute deformations (such as micrometer-level vibrations on the skin surface) is weak. It is difficult to effectively capture skin micro-vibration signals such as heartbeat, and complex signal processing algorithms are required for compensation, resulting in insufficient detection accuracy of parameters such as heart rate, high system complexity, and increased power consumption; (3) The complexity of multi-parameter integration is high. Multiple sensors (such as on the back and wrist) and complex algorithms (such as LSTM aligners) are required to separate respiration, heart rate, and pulse signals, resulting in high system cost and large volume.

[0004] The Chinese patent with the publication number CN118209223A discloses a multi-layer flexible electronic integrated film stress metamaterial sensor and its preparation method. It uses a multi-layer flexible electronic integrated film, integrates a trapezoidal cross-metal resonant structure through 3D printing technology, utilizes the stretchability of the PDMS substrate to change the size of the metasurface structure, and senses posture stress through the change of the resonant frequency. It uses nano-metal oxide trapezoidal resonant units and ion-conductive hydrogels for interconnection, simulates the layout of skin epithelial cells, and realizes flexible fitting and interlayer conductivity. It mainly aims at detecting human posture stress (such as finger bending, wrist movement), and obtains tiny strain information through spectral analysis. However, this solution has the following limitations: (1) The application scenario is single, focusing on posture stress (such as joint movement), not involving the dynamic monitoring of physiological parameters (breathing, heartbeat), especially lacking the ability to synchronously detect the complex deformation (large strain and micro-vibration) caused by cardiopulmonary movement; (2) Limitations of the resonant structure, the design of the trapezoidal cross-metal unit focuses on mechanical stress response, and does not distinguish the frequency domain requirements in physiological movement (low-frequency strain of breathing and high-frequency vibration of heartbeat), making it difficult to be directly applied to multi-parameter physiological sensing; (3) Signal decoupling depends on algorithms. Although the integration degree is improved through multi-layer interconnection, multi-parameter decoupling at the physical structure level has not been achieved. If used for physiological monitoring, additional algorithms are needed to separate signals, increasing the system complexity. Summary of the Invention

[0005] An object of the present invention is to solve at least one of the technical problems existing in the prior art, and provide a flexible sensor for synchronous monitoring of multiple parameters of breathing and heartbeat, its preparation method and application.

[0006] The technical solution of the present invention is as follows: In a first aspect of the present invention, there is provided a flexible sensor for synchronous monitoring of multiple parameters of breathing and heartbeat, the flexible sensor comprising: A breathing sensing layer, the breathing sensing layer includes a bottom layer and a plurality of split ring resonators, the split ring resonators are arranged in an array on the bottom layer, and the split ring resonators have openings; A heartbeat sensing layer, arranged on the breathing sensing layer, the heartbeat sensing layer includes a middle layer and a plurality of cross-shaped resonant units, the cross-shaped resonant units are arranged in an array on the middle layer, wherein the array center of the cross-shaped resonant units is offset from the array center of the split ring resonators; A packaging layer, arranged on the heartbeat sensing layer, and the packaging layer has a plurality of through holes.

[0007] Wherein, the resonant frequency of the breathing sensing layer is different from the resonant frequency of the heartbeat sensing layer.

[0008] The present invention adopts a double-layer unit differential layout, using a large-sized split-ring resonator (SRR) array and integrating small-sized cross-shaped resonator units. The resonance frequency of the outer-layer SRR (breathing-dominated frequency band) and the resonance frequency of the inner-layer cross-shaped resonator unit (heartbeat-dominated frequency band) are physically separated through a frequency interval, without the need for complex algorithm decoupling, realizing synchronous monitoring of multiple parameters such as breathing and heartbeat.

[0009] Optionally, the resonance frequency of the breathing sensing layer is 2.9 GHz to 3.4 GHz, and the resonance frequency of the heartbeat sensing layer is 5.5 GHz to 7.3 GHz.

[0010] Optionally, the thickness of the bottom layer is 40 μm to 60 μm; The thickness of the split-ring resonator is 30 μm to 40 μm, the outer radius of the split-ring resonator is 3 mm to 7 mm, the ring width of the split-ring resonator is 0.2 mm to 0.7 mm, and the width of the opening is 0.1 mm to 0.5 mm.

[0011] Optionally, the split-ring resonators are distributed in a 10×10 matrix, and the distance between adjacent split-ring resonators is 1 mm to 3 mm.

[0012] Optionally, the thickness of the middle layer is 70 μm to 90 μm; The cross-shaped resonator unit includes four symmetrically distributed connecting arms, and the ends of the connecting arms are pointed; The length of the connecting arm is 1 mm to 5 mm, the width of the connecting arm is 0.1 mm to 0.3 mm, and the radius of curvature of the end of the connecting arm < 10 μm.

[0013] Optionally, the cross-shaped resonator units are distributed in a 5×5 matrix, and the distance between the connecting arms on adjacent cross-shaped resonator units is 0.1 mm to 0.2 mm; The distance between the array centers of the split-ring resonator array and the cross-shaped resonator unit array is 4 cm to 6 cm.

[0014] Optionally, the thickness of the encapsulation layer is 15 μm to 25 μm; The diameter of the through hole is 5 μm - 10 μm.

[0015] Optionally, the preparation raw material of the bottom layer is polydimethylsiloxane, and the Young's modulus of the bottom layer is 1.0 MPa to 1.4 MPa; The preparation raw material of the split-ring resonator is liquid metal gallium-indium-tin alloy, wherein the mass ratio of gallium, indium, and tin is 68.5%: 21.5%: 10%; The preparation raw material of the middle layer is TPU; The preparation raw material of the cross-shaped resonant unit is silver nanowires; The encapsulation layer is a porous polyurethane film.

[0016] The second aspect of the present invention provides a preparation method of a flexible sensor for synchronous monitoring of multiple respiratory and heartbeat parameters, including the following steps: S1. Preparation of the respiratory sensing layer: Mix the PDMS prepolymer with a curing agent (hydrogen-containing silicone oil), spin-coat it on a silicon wafer, and heat-cure it to form a bottom layer; Use femtosecond laser direct writing to process on the surface of the bottom layer to form a number of grooves; Use a piezoelectric inkjet printer to deposit liquid metal gallium-indium-tin alloy drop by drop into the grooves to form open resonant rings; S2. Preparation of the heartbeat sensing layer: Dissolve TPU particles in tetrahydrofuran to obtain a TPU solution; Cast the TPU solution into a film and dry it to form a middle layer; Imprint the middle layer through a nanoimprint template to form a number of cross-shaped grooves; Coat the silver nanowire solution in the cross-shaped grooves and sinter it to form a cross-shaped resonant unit; S3. Bond the respiratory sensing layer prepared in S1 and the heartbeat sensing layer prepared in S2 together through a silane coupling agent, and then cover it with a porous polyurethane film to form an encapsulation layer; After thermal compression sealing, a flexible sensor is obtained.

[0017] Optionally, in S1, the mass ratio of the PDMS prepolymer to the curing agent (hydrogen-containing silicone oil) is 9-11:1, the spinning speed is 1500 rpm - 2500 rpm, the spinning time is 25 s - 35 s, the curing temperature is 70 °C - 90 °C, and the curing time is 1.5 h - 2.5 h; The wavelength of femtosecond laser direct writing is 750 nm - 850 nm, the pulse width is 80 fs - 120 fs, and the energy density is 150 mJ / cm² - 250 mJ / cm²; The nozzle diameter of the piezoelectric inkjet printer is 8 μm - 12 μm, and the pulse frequency is 8 kHz - 12 kHz; In S2, the concentration of the TPU solution is 10 wt% - 20 wt%, the drying temperature is 50 °C - 70 °C, and the drying time is 10 h - 14 h; The solid content of the silver nanowire solution is 15% - 25%, the sintering temperature is 50 °C - 70 °C, and the sintering time is 20 min - 30 min; In S3, the temperature of thermal compression sealing is 70 °C - 90 °C, the pressure is 8 kPa - 12 kPa, and the time is 8 s - 12 s.

[0018] The third aspect of the present invention provides a respiratory and heartbeat monitoring system, including a radio frequency chip and a flexible sensor, and the flexible sensor transmits the collected respiratory signal and heartbeat signal to an intelligent terminal through the radio frequency chip.

[0019] The present invention has at least one of the following beneficial effects: (1) The sensor of the present invention significantly improves the detection accuracy of physiological parameters and simplifies the system complexity through metamaterial structures and frequency-domain design. Specifically, on the one hand, the outer large-sized SRR array (split-ring resonator) and the inner cross-shaped resonant unit respectively respond to the large strain of breathing and the micro-vibration of the heartbeat; on the other hand, material properties such as the high stretchability of the liquid metal in the split-ring resonator and the high electrical conductivity stability of the silver nanowires in the cross-shaped resonant unit, combined with the frequency filtering effect of the PDMS / TPU substrate, enable the physical decoupling of the breathing (0.1Hz - 0.8Hz) and heartbeat (0.9Hz - 5Hz) signals due to the resonant frequency interval, and the signals can be separated without complex algorithms. Compared with the existing technologies that rely on external electromagnetic fields for indirect sensing and multi-sensor layouts, the detection accuracy is higher and the system power consumption is lower.

[0020] (2) The sensor of the present invention adopts a three-layer flexible composite structure. The bottom layer of PDMS and the middle layer of TPU are integrated by chemical bonding. The top layer (encapsulation layer) of the skin-friendly waterproof PU film ensures long-term wearing comfort. The single-piece design replaces the traditional multi-sensor layout, realizing the synchronous monitoring of breathing and heartbeat at the physical structure level, and avoiding the problems of large volume and high cost in the existing technologies. Description of the Drawings

[0021] Figure 1 It is a schematic structural diagram of the flexible sensor for synchronous monitoring of multiple parameters of breathing and heartbeat in Embodiment 1 of the present invention; Figure 2 It is a schematic structural diagram of the split-ring resonator in Embodiment 1 of the present invention; Figure 3 It is a schematic structural diagram of the cross-shaped resonant unit in Embodiment 1 of the present invention; Figure 4 It is the resonant frequencies of the breathing layer and the heartbeat layer in Embodiment 1 of the present invention; Figure 5 It is the electromagnetic response characteristics corresponding to different unit periods of the breathing layer in Embodiment 1 of the present invention; Figure 6 It is the breathing signal in Embodiment 1 of the present invention; Figure 7 It is the heartbeat signal in Embodiment 1 of the present invention; Figure 8 It is a schematic diagram of the usage state of the flexible sensor for synchronous monitoring of multiple parameters of breathing and heartbeat in Embodiment 2 of the present invention.

[0022] Reference numerals: 1. Breathing sensing layer; 11. Bottom layer; 12. Split-ring resonator; 2. Heartbeat sensing layer; 21. Middle layer; 22. Cross-shaped resonant unit; 23. Connecting arm; 3. Encapsulation layer; 31. Through hole. Detailed Embodiments

[0023] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] Embodiment 1 This embodiment provides a flexible sensor for synchronous monitoring of multiple respiratory and heartbeat parameters and a preparation method thereof, which are as follows: The structure of a flexible sensor for synchronous monitoring of multiple respiratory and heartbeat parameters is as Figures 1-3 shown, and the resonance frequency and sensing signal are as Figures 4-7 shown. The flexible sensor includes a respiratory sensing layer 1, a heartbeat sensing layer 2 and a packaging layer 3 arranged in sequence from bottom to top. The respiratory sensing layer 1 is used to monitor respiration, and the heartbeat sensing layer 2 is used to monitor heartbeat. The specific structure is as follows: The respiratory sensing layer 1 includes a bottom layer 11 and a plurality of split-ring resonators (SRRs) 12. The plurality of split-ring resonators 12 are arranged on the bottom layer 11. Specifically, the split-ring resonators 12 are arranged in an array on the bottom layer 11. As Figure 2 shown, the split-ring resonator 12 has an opening 13.

[0025] The heartbeat sensing layer 2 includes a middle layer 21 and a plurality of cross-shaped resonant units 22. The plurality of cross-shaped resonant units 22 are arranged on the middle layer 21. Specifically, the cross-shaped resonant units 22 are arranged in an array on the middle layer 21; as Figure 3 shown, the cross-shaped resonant unit 22 includes four symmetrically distributed connecting arms 23, and the ends of the connecting arms 23 away from the center are pointed.

[0026] The packaging layer 3 is arranged on the heartbeat sensing layer 2, and the packaging layer 3 has a plurality of through holes 31.

[0027] In this embodiment, the specific structure and material composition of the respiratory sensing layer 1 are as follows: (1) Substrate material and parameter materials: The raw material for preparing the bottom layer 11 is polydimethylsiloxane (PDMS, Dow Corning SYLGARD 184). After curing, the performance parameters of polydimethylsiloxane are: thickness 50 μm (controlled by a spin coater), and Young's modulus 1.2 MPa.

[0028] (2) SRR array structural unit structure: Shape: As Figure 3 shown, the unilateral opening of the split-ring resonator 12, and the opening direction is uniformly towards the edge of the sensor.

[0029] Geometric parameters: Outer radiusr = 5 mm, the width of the ring w = 0.5 mm, the thickness t = 35 μm, the unit period (the distance between the geometric centers of two adjacent resonant units in the row / column direction) P = 12 mm, the opening width g = 0.3 mm.

[0030] Material: liquid metal gallium-indium-tin alloy (GaInSn, mass ratio of gallium, indium, and tin is 68.5%: 21.5%: 10%, purity > 99.9%); Array layout: 10×10 unit matrix, covering an area of 120 mm×120 mm, centered on the central region of chest breathing movement (the 4th - 6th intercostal space of the mid-sternal line).

[0031] In this embodiment, the design basis of the respiratory sensing layer 1: (1) Physiological signal characteristic matching The chest strain frequency generated by respiratory movement is 0.1 Hz - 0.8 Hz (corresponding to a resting respiratory rate of 12 breaths / min - 20 breaths / min), accompanied by a 5% - 15% periodic tensile strain (such as an increase in chest circumference of about 2 cm - 5 cm during inspiration, corresponding to a 5% - 15% strain of the sensor substrate). The demand for low-frequency large-strain sensitivity: The sensor unit needs to be sensitive to large-size changes (circumference changes). Therefore, a large-size open resonant ring 12 (outer radius r = 5 mm, the width of the ring w = 0.5 mm, the thickness t = 35 μm, the unit period P = 12 mm) is designed. A concentrated capacitance is introduced through the open-ring structure (opening width g = 0.3 mm) to form an LC resonant unit.

[0032] (2) LC resonance formula and structural parameter calculation According to The initial frequency of the respiratory sensing layer 1: LC resonance frequency formula , f is the LC resonance frequency of the respiratory sensing layer 1, L is the toroidal inductance of the respiratory sensing layer 1, C is the capacitance of the respiratory sensing layer 1 。 Toroidal inductance L is determined by the geometric dimensions of the open resonant ring 12 (outer radius R , the width of the ring w ), and the capacitance C is determined by the opening width g of the open resonant ring 12. The specific calculation formula is as follows: Toroidal inductance , where the vacuum permeability , the permeability of the bottom layer 11 (The PDMS used as the raw material for preparing the bottom layer 11 is a non-magnetic material), the average radius of the split ring resonator 12 , substituting into the calculation gives the toroidal inductor L = 15.4 nH. The capacitance , where, the air permittivity , the permittivity of the bottom layer 11 (the permittivity of the PDMS used as the raw material for preparing the bottom layer 11), the ring width of the split ring resonator 12 w = 0.5 mm, the thickness of the split ring resonator 12 t = 35 μm, the opening width of the split ring resonator 12 g = 0.3 mm, substituting into the calculation gives the capacitance C = 0.138 pF. The resonance frequency f : Substituting the toroidal inductor L , the capacitance C into the LC resonance frequency formula gives f = 3.4 GHz.

[0033] When the breathing sensing layer 1 undergoes a 5% strain: The average radius of the split ring resonator 12 , the opening width of the split ring resonator 12 , substituting into the calculation, the toroidal inductor , the capacitance , therefore, the LC resonance frequency when the breathing sensing layer 1 undergoes a 5% strain .

[0034] When the breathing sensing layer 1 undergoes a 15% strain: The average radius of the split ring resonator 12 , the opening width of the split ring resonator 12 , substituting into the calculation, the toroidal inductor , the capacitance , therefore, the LC resonance frequency when the breathing sensing layer 1 undergoes a 15% strain .

[0035] Based on the above analysis, the corresponding frequency band of the breathing sensing layer 1 is 2.9 GHz to 3.4 GHz, specifically as Figure 4 , Figure 6 shown.

[0036] (3) Sub-wavelength design principle The period of the metamaterial unit needs to satisfy: , where, p is the unit period of the split ring resonator 12, λ is the free space wavelength ( , c = 3×10 8 mm / s is the speed of light, f is the resonance frequency)， The effective dielectric constant of the mixture of the bottom layer 11 and air ( , is the dielectric constant of the bottom layer 11). Specifically, when the frequency of the breathing sensing layer 1 is 3.4 GHz, that is, the resonance frequency f is 3.4 GHz, substituting into the formula = 88.2 mm, , it can be known that , and in this embodiment, the unit period of the split ring resonator 12 satisfies the sub-wavelength design principle, ensuring that the structure avoids electromagnetic wave diffraction interference.

[0037] The setting of the unit period of 12 mm is based on electromagnetic simulation optimization. When the unit period is 12 mm, the reflection coefficient at the resonance point is about -30 dB, without spurious mode interference, showing a single and pure resonance characteristic; when the unit period increases, such as 20 mm, the coupling effect between adjacent units causes the resonance peak to split, forming a double-peak response at 3.2 GHz and 3.6 GHz, resulting in signal detection blurring; while when the period decreases, such as 8 mm, the over-strong coupling between units will deteriorate the electromagnetic signal transmission, and the reflection coefficient is too large (-15 dB), affecting the signal detectability. As Figure 5 shown.

[0038] In this embodiment, the specific structure and material composition of the heartbeat sensing layer 2 are as follows: (1) Substrate material and parameter materials: The preparation material of the middle layer 21 is thermoplastic polyurethane (TPU, Bayer Desmopan 9385A). After casting molding, the performance parameters are: thickness 80 μm, dielectric constant ; (2) Structure of the cross-shaped resonant unit Shape: As Figure 3 shown, the four arms of the cross-shaped resonant unit 22 are symmetrically distributed, and the arm ends are pointed (radius of curvature < 10 μm, enhancing electric field concentration); Geometric parameters: arm length L = 3 mm, arm width w = 0.2 mm, arm end gap g = 0.15 mm, thickness t = 35 μm; Material: Silver nanowires (diameter 50 nm, length > 10 μm, concentration 20 wt%), forming a dense conductive network on the surface of the TPU substrate through nanoimprinting; Array layout: 5×5 unit matrix, covering an area of 60 mm×60 mm, and the center of the array is aligned with the chest heart projection area (5 mm away from the center of the SRR array, avoiding mechanical coupling interference); In this embodiment, the design basis of the heartbeat sensing layer 2: (1) Physiological signal characteristic matching The frequency of the chest micro-vibration caused by the heartbeat is 0.9 Hz - 5 Hz (corresponding to a heart rate of 54 beats per minute - 300 beats per minute), and the vibration amplitude is 1 μm - 50 μm. The sensor unit needs to be sensitive to local high-frequency micro-deformation. Requirements for high-frequency micro-vibration sensitivity: Design a small-sized cross-shaped unit (arm length L = 3 mm, arm width w = 0.2 mm, gap at the arm end g = 0.15 mm, thickness t = 35 μm).

[0039] (2) Band selection basis The resonance frequency of the cross-shaped resonance unit 22 is mainly determined by the inductance of the connecting arm 23 and the capacitance of the gap between the connecting arms 23.

[0040] The initial frequency of the heartbeat sensing layer 2: LC resonance frequency , f 0 is the LC resonance frequency of the heartbeat sensing layer 2, L arm is the toroidal inductance of a single arm (one connecting arm 23) of the cross-shaped resonance unit 22, C gap is the gap capacitance of the cross-shaped resonance unit 22. Specifically, the toroidal inductance of a single arm: , where the vacuum permeability , the permeability of the middle layer 21 (the preparation material TPU of the middle layer 21 is a non-magnetic material), the arm length L = 3.0 mm of the cross-shaped resonance unit 22, the arm width w = 0.2 mm of the cross-shaped resonance unit 22. Substituting into the calculation, the toroidal inductance of a single arm can be obtained as L arm = 1.2 nH. The total inductance of the cross-shaped resonance unit 22 is in a parallel structure. Therefore, the actual total inductance of the cross-shaped resonance unit L total = 0.3 nH. The gap capacitance of the cross-shaped resonance unit 22: C gap , where the air permittivity , the permittivity of the middle layer 21 (the permittivity of the preparation material TPU of the middle layer 21), the arm width w = 0.2 mm of the cross-shaped resonance unit 22, the thickness t = 35 μm of the cross-shaped resonance unit 22, the gap at the arm end g = 0.15 mm of the cross-shaped resonance unit 22. Substituting into the calculation, we getC gap = 0.035 pF. Resonant frequency: Substituting the inductance and capacitance into the LC resonant frequency formula gives f f0 = 7.3 GHz When the heartbeat sensing layer 2 vibrates by 1 μm: The arm - end gap of the cross - shaped resonant unit 22 , and the gap capacitance of the cross - shaped resonant unit 22 , so the frequency when the heartbeat sensing layer 2 vibrates by 1 μm .

[0041] When the heartbeat sensing layer 2 vibrates by 50 μm: The arm - end gap of the cross - shaped resonant unit 22 , and the gap capacitance of the cross - shaped resonant unit 22 , so the frequency when the heartbeat sensing layer 2 vibrates by 50 μm .

[0042] Based on the above analysis, the frequency band corresponding to the heartbeat sensing layer 2 is 5.5 GHz to 7.3 GHz, specifically as shown in Figure 4 、 Figure 7 .

[0043] (3)Frequency - domain decoupling requirements Maintain a 2.1 - GHz frequency interval from the breathing frequency band (2.9 GHz - 3.4 GHz), use the natural separation of the frequency spectrum to avoid signal crosstalk, and avoid common communication frequency bands (such as Bluetooth 2.4 GHz) to reduce electromagnetic interference.

[0044] In summary, the resonant frequency range (2.9 GHz - 3.4 GHz, 5.5 GHz - 7.3 GHz) is the theoretical design result based on the frequency - strain characteristics of physiological signals, the optimization of the metamaterial unit structure parameters, and the physical decoupling requirements, and is determined by the LC resonant formula and the sub - wavelength principle. This design ensures the differential response of the sensor to large breathing strains and small heartbeat vibrations, and realizes high - precision and low - complexity multi - parameter synchronous monitoring.

[0045] In this embodiment, the specific structure and material composition of the encapsulation layer 3 are as follows: (1)Encapsulation layer material: Porous polyurethane (PU) film, performance parameters: thickness 20 μm, pore diameter 5 μm - 10 μm (moisture permeability 6000 g / m 2 / 24 h), waterproof grade IPX7 (no failure after soaking in 1 m water depth for 30 minutes); (2)Inter - layer connection and bonding method: The middle - layer TPU and the bottom - layer PDMS are chemically bonded through a silane coupling agent (KH - 570).

[0046] This embodiment also provides a preparation method for a flexible sensor for synchronous monitoring of multiple parameters of breathing and heartbeat, including the following steps: S1. Preparation of the respiration sensing layer 1: Mix the PDMS prepolymer with a curing agent (hydrogen-containing silicone oil), spin-coat it on a silicon wafer, and cure it by heating to form the bottom layer 11. Use femtosecond laser direct writing to process on the surface of the bottom layer 11 to form a number of grooves. Use a piezoelectric inkjet printer to deposit drops of liquid metal gallium-indium-tin alloy into the grooves to form the split-ring resonator 12. S2. Preparation of the heartbeat sensing layer 2: Dissolve TPU particles in tetrahydrofuran to obtain a TPU solution. Cast the TPU solution into a film and dry it to form the middle layer 21. Imprint the middle layer 21 through a nanoimprint template to form a number of cross-shaped grooves. Coat the silver nanowire solution in the cross-shaped grooves and sinter it to form the cross-shaped resonant unit 22. S3. Bond the respiration sensing layer 1 prepared in S1 and the heartbeat sensing layer 2 prepared in S2 together through a silane coupling agent, then cover it with a porous polyurethane film to form the encapsulation layer 3, and modify the encapsulation layer 3 with polyethylene glycol. After thermal compression sealing, a flexible sensor is obtained.

[0047] In this embodiment, the specific process of the preparation method is as follows: (1) Preparation of the respiration sensing layer 1 Step 1: Mix the PDMS prepolymer with a curing agent (hydrogen-containing silicone oil) at a mass ratio of 10:1, spin-coat it on a silicon wafer (rotation speed 2000 rpm, time 30 s), and cure it at 80 °C for 2 h to form a 50-μm substrate. Step 2: Use femtosecond laser direct writing (wavelength 800 nm, pulse width 100 fs, energy density 200 mJ / cm 2 ) to process SRR grooves (depth 35 μm, opening width 0.3 mm) on the PDMS surface. Step 3: Use a piezoelectric inkjet printer, set the nozzle diameter to 10 μm and the pulse frequency to 10 kHz, deposit drops of liquid metal into the grooves to form a conductive SRR array.

[0048] (2) Preparation of the heartbeat sensing layer 2 Step 1: Dissolve TPU particles in tetrahydrofuran (concentration 15 wt%), cast it into an 80-μm film, and dry it at 60 °C for 12 h. Step 2: Imprint the TPU film with a nanoimprint template (made of SU-8 photoresist, accuracy ±5 μm) to form cross-shaped grooves (depth 5 μm). Step 3: Coat the silver nanowire solution (solid content 20%) by slit coating and sinter it at 60 °C for 30 min to form a conductive cross unit.

[0049] (3) Overall integration The two-layer structure is bonded by a silane coupling agent (KH-570), the edges are cut (laser cutting, accuracy ±10 μm), covered with a PU encapsulation film, and heat-pressed and sealed (temperature 80°C, pressure 10 kPa, time 10 s).

[0050] The working principle and signal decoupling mechanism of the flexible sensor for synchronous monitoring of multiple respiratory and heartbeat parameters prepared in Example 1 are as follows: (1) Respiratory signal detection principle: Respiratory movement causes periodic expansion and contraction of the chest, resulting in strain (5% - 15%) in the flexible sensor substrate (PDMS). The respiratory sensing layer is composed of an array of split-ring resonators (SRRs), whose opening direction is along the main stretching direction of the chest cavity. Using the deformation effect, the resonant frequency shifts from the initial 3.4 GHz to a lower frequency (such as dropping to 2.9 GHz when stretched by 15%). The frequency shift is negatively correlated with the respiratory depth. By real-time monitoring of the dynamic changes in the SRR resonant frequency band (2.9 GHz - 3.4 GHz), the respiratory frequency and amplitude are mapped.

[0051] (2) Heartbeat signal detection principle: The chest wall micro-vibrations (1 μm - 50 μm) caused by the heartbeat are transmitted through the TPU substrate to the array of cross-shaped resonant units in the heartbeat sensing layer. The sharp structure design at the arm ends of the cross-shaped resonant units enhances the electric field concentration effect. The tiny vibrations cause changes in the arm end gap, significantly changing the equivalent capacitance value, and the resonant frequency shifts from the initial 7.3 GHz to a lower frequency (such as dropping to 5.5 GHz). This layer operates in the high-frequency band (5.5 GHz - 7.3 GHz), and by capturing the frequency shift caused by local high-frequency micro-deformations, the heart rate and vibration intensity are analyzed.

[0052] (3) Frequency domain decoupling mechanism: The respiratory sensing layer (split-ring resonator 12) and the heartbeat sensing layer (cross-shaped resonant unit 22) adopt a differential resonant unit design and operate in independent frequency bands (respiratory layer 2.9 GHz - 3.4 GHz, heartbeat layer 5.5 GHz - 7.3 GHz), and the frequency band interval reaches 2.1 GHz. The low-frequency large strain of the respiratory signal and the high-frequency micro-vibrations of the heartbeat signal are naturally decoupled through physical frequency domain isolation without relying on algorithms for separation. The central misalignment layout (4 cm - 6 cm) of the double-layer array further suppresses mechanical coupling interference.

[0053] Example 2 This example provides a respiratory and heartbeat monitoring system, including a radio frequency chip and the flexible sensor prepared in Example 1.

[0054] As Figure 8The figure shows a schematic diagram of the usage state of the flexible sensor (respiration and heartbeat sensor patch) prepared in Example 1. When monitoring the respiration and heartbeat of a tester, the flexible sensor prepared in Example 1 is placed on the chest of the tester. The respiration signal and heartbeat signal of the tester are collected by the flexible sensor, and then the collected respiration signal and heartbeat signal are transmitted to the intelligent terminal through the radio frequency chip, so that the respiration, heartbeat and monitoring data can be displayed through the intelligent terminal.

[0055] In this embodiment, the radio frequency chip is a miniaturized radio frequency chip with the model of NORDIC nRF5340. The miniaturized radio frequency chip integrates the functions of swept-frequency transmission and reception, and its size is 3mm×3mm. The smart phone is connected to the radio frequency chip through Bluetooth and serves as a display terminal. Since the structure and principle of the miniaturized radio frequency chip are well known to those skilled in the art, they will not be specifically described in this embodiment.

[0056] As mentioned above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered by the protection scope of the present invention.

Claims

1. A flexible sensor for synchronous monitoring of multiple parameters of respiration and heartbeat, characterized in that, The flexible sensor includes: A respiration sensing layer (1), the respiration sensing layer (1) includes a bottom layer (11) and a plurality of split ring resonators (12), the split ring resonators (12) are arranged in an array on the bottom layer (11), and the split ring resonators (12) have openings (13); A heartbeat sensing layer (2), arranged on the respiration sensing layer (1), the heartbeat sensing layer (2) includes a middle layer (21) and a plurality of cross-shaped resonant units (22), the cross-shaped resonant units (22) are arranged in an array on the middle layer (21), wherein the array center of the cross-shaped resonant units (22) is offset from the array center of the split ring resonators (12); A packaging layer (3), arranged on the heartbeat sensing layer (2), and the packaging layer (3) has a plurality of through holes (31); Wherein, the resonant frequency of the respiration sensing layer (1) is different from the resonant frequency of the heartbeat sensing layer (2).

2. The flexible sensor according to claim 1, wherein The resonant frequency of the respiration sensing layer (1) is 2.9 GHz to 3.4 GHz, and the resonant frequency of the heartbeat sensing layer (2) is 5.5 GHz to 7.3 GHz.

3. The flexible sensor according to claim 1, wherein The thickness of the bottom layer (11) is 40 μm to 60 μm; The thickness of the split ring resonator (12) is 30 μm to 40 μm, the outer radius of the split ring resonator (12) is 3 mm to 7 mm, the ring width of the split ring resonator (12) is 0.2 mm to 0.7 mm, and the width of the opening (13) is 0.1 mm to 0.5 mm; The split ring resonators (12) are arranged in a 10×10 matrix, and the distance between adjacent split ring resonators (12) is 1 mm to 3 mm.

4. The flexible sensor according to claim 1, wherein The thickness of the middle layer (21) is 70 μm to 90 μm; The cross-shaped resonant unit (22) includes four symmetrically distributed connecting arms (23), and the ends of the connecting arms (23) are pointed; The length of the connecting arm (23) is 1 mm to 5 mm, the width of the connecting arm (23) is 0.1 mm to 0.3 mm, and the radius of curvature of the end of the connecting arm (23) < 10 μm.

5. The flexible sensor according to claim 4, wherein The cross-shaped resonant units (22) are arranged in a 5×5 matrix, and the distance between the connecting arms (23) on adjacent cross-shaped resonant units (22) is 0.1 mm to 0.2 mm; The distance between the array center of the split ring resonators (12) and the array center of the cross-shaped resonant units (22) is 4 cm to 6 cm.

6. The flexible sensor according to claim 1, wherein The thickness of the packaging layer (3) is 15 μm to 25 μm; The diameter of the through hole (31) is 5 μm to 10 μm.

7. The flexible sensor according to claim 1, wherein The raw material for preparing the bottom layer (11) is polydimethylsiloxane, and the Young's modulus of the bottom layer (11) is 1.0 MPa to 1.4 MPa; The raw material for preparing the split-ring resonator (12) is liquid metal gallium-indium-tin alloy, wherein the mass ratio of gallium, indium, and tin is 68.5%: 21.5%: 10%; The raw material for preparing the middle layer (21) is TPU; The raw material for preparing the cross-shaped resonator unit (22) is silver nanowires; The encapsulation layer (3) is a porous polyurethane film.

8. The preparation method of the flexible sensor according to any one of claims 1 to 7, characterized in that, It includes the following steps: S1. Preparation of the respiration sensing layer (1): Mix the PDMS prepolymer and the curing agent, spin-coat it on a silicon wafer, and heat-cure it to form the bottom layer (11); Use femtosecond laser direct writing to process on the surface of the bottom layer (11) to form a number of grooves; Use a piezoelectric inkjet printer to deposit drops of liquid metal gallium-indium-tin alloy into the grooves to form the split-ring resonator (12); S2. Preparation of the heartbeat sensing layer (2): Dissolve TPU particles in tetrahydrofuran to obtain a TPU solution; Cast the TPU solution into a film and dry it to form the middle layer (21); Imprint the middle layer (21) through a nanoimprint template to form a number of cross-shaped grooves; Coat the silver nanowire solution in the cross-shaped grooves and sinter it to form the cross-shaped resonator unit (22); S3. Bond the respiration sensing layer (1) prepared in S1 and the heartbeat sensing layer (2) prepared in S2 together through a silane coupling agent, and then cover it with a porous polyurethane film to form the encapsulation layer (3); After thermal compression sealing, a flexible sensor is obtained.

9. The preparation method according to claim 8, wherein In S1, the mass ratio of the PDMS prepolymer to the curing agent is 9 to 11:1, the spinning speed is 1500 rpm to 2500 rpm, the spinning time is 25 s to 35 s, the curing temperature is 70 °C to 90 °C, and the curing time is 1.5 h to 2.5 h; The wavelength of the femtosecond laser direct writing is 750 nm to 850 nm, the pulse width is 80 fs to 120 fs, and the energy density is 150 mJ / cm² to 250 mJ / cm²; The nozzle diameter of the piezoelectric inkjet printer is 8 μm to 12 μm, and the pulse frequency is 8 kHz to 12 kHz; In S2, the concentration of the TPU solution is 10 wt% to 20 wt%, the drying temperature is 50 °C to 70 °C, and the drying time is 10 h to 14 h; The solid content of the silver nanowire solution is 15% to 25%, the sintering temperature is 50 °C to 70 °C, and the sintering time is 20 min to 30 min; In S3, the temperature of the thermal compression sealing is 70 °C to 90 °C, the pressure is 8 kPa to 12 kPa, and the time is 8 s to 12 s.

10. A respiratory and heart rate monitoring system, characterized in that, It includes a radio frequency chip and the flexible sensor according to any one of claims 1 to 7, and the flexible sensor transmits the collected respiration signal and heartbeat signal to the intelligent terminal through the radio frequency chip.

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