Flexible sensor for synchronous monitoring of multiple parameters of respiration and heartbeat, as well as its preparation method and application

Abstract

The present invention discloses a flexible sensor for synchronous monitoring of multiple parameters of respiration and heartbeat, as well as a preparation method and application, and relates to the field of sensor technology. The flexible sensor includes: a respiration sensing layer, including a bottom layer and a plurality of open resonant rings distributed in an array; a heartbeat sensing layer, arranged on the respiration sensing layer, including a middle layer and a plurality of cross-shaped resonant units distributed in an array, wherein the array center of the cross-shaped resonant unit is staggered with the array center of the open resonant ring; and an encapsulation layer, arranged on the heartbeat sensing layer, having a plurality of through holes. The present invention adopts a double-layer unit differentiated layout, and the resonant frequency of the outer layer SRR (respiration-dominant frequency band) and the resonant frequency of the inner layer cross-shaped resonant unit (heartbeat-dominant frequency band) are physically separated by frequency interval, without the need for complex algorithm decoupling, to achieve synchronous monitoring of multiple parameters of respiration and heartbeat.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology, and in particular to a flexible sensor for synchronously monitoring multiple parameters of breathing and heartbeat, and a preparation method and application thereof. Background Art

[0002] Flexible electronics technology has seen rapid development in the wearable health monitoring field in recent years, particularly in respiratory and heart rate monitoring (for sleep apnea screening, postoperative rehabilitation monitoring, and exercise respiratory management). Technical solutions include resistive sensors (such as those in Chinese Patent Publication No. CN117643464A), capacitive sensors (such as those in Chinese Patent Publication No. CN116898452A), optical sensors (such as those in Chinese Patent Publication No. CN117617942A and CN115575357A), and piezoelectric film sensors (such as those in Chinese Patent Publication No. CN119714621A, CN119488373A, and CN119498781A). These existing technologies all indirectly reflect physiological parameters by detecting changes in skin deformation, pressure, or optical signals. However, these technologies suffer from issues such as susceptibility to environmental interference, limited functionality, and wearability.

[0003] To make up for the shortcomings of existing technologies, researchers have applied electromagnetic metamaterial technology to physiological sensing (such as posture, respiration, and heartbeat monitoring). For example, the Chinese patent publication number CN119173201A discloses sensors, systems, and methods for non-contact sensing of the body's physiological parameters. It generates an evanescent electromagnetic field through a metamaterial waveguide (artificial surface plasma mode), detects electromagnetic field disturbances caused by physiological movements (such as respiration and heartbeat), extracts physiological parameters through phase shift changes in the transmitted / received signals, uses a software-defined radio (SDR) system to demodulate the signal, and combines bandpass filtering, fast Fourier transform (FFT), long short-term memory network (LSTM) and other algorithms to separate respiration and heart rate signals, 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, and indirectly senses physiological movements through external electromagnetic field disturbances. Its sensitivity is limited by the evanescent field strength and environmental noise. (2) It is non-contact and has a distance limitation. The sensor needs to be placed 1mm-15mm away from the body. It has a weak direct response capability to tiny deformations (such as micron-level vibrations on the skin surface), making it difficult to effectively capture skin micro-vibration signals such as heartbeats. It needs to rely on complex signal processing algorithms 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. It needs to use multiple sensors (such as back and wrist) and complex algorithms (such as LSTM aligners) to separate respiration, heart rate, and pulse signals. The system is expensive and large in size.

[0004] Chinese patent publication number CN118209223A discloses a multi-layer flexible electronic integrated thin film stress metamaterial sensor and its fabrication method. This sensor utilizes a multi-layer flexible electronic integrated thin film, integrated with a trapezoidal cross-metal resonant structure via 3D printing technology. The sensor leverages the stretchability of the PDMS substrate to alter the metasurface structure dimensions, sensing posture stress through changes in resonant frequency. Nano-metal oxide trapezoidal resonant units are interconnected with an ionically conductive hydrogel, mimicking the structural layout of skin epithelial cells to achieve flexible conformity and interlayer conductivity. This sensor is primarily designed for detecting human posture stress (such as finger bending and wrist movement), acquiring subtle 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), and does not involve dynamic monitoring of physiological parameters (respiration, heartbeat), especially the lack of synchronous detection capability of complex deformation (large strain and micro-vibration) caused by cardiopulmonary movement; (2) The limitation of the resonant structure, the trapezoidal cross metal unit design 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 directly apply to multi-parameter physiological sensing; (3) Signal decoupling depends on the algorithm. Although the integration is improved through multi-layer interconnection, multi-parameter decoupling at the physical structure level is not achieved. If it is used for physiological monitoring, additional algorithms are required to separate the signals, which increases the complexity of the system. Summary of the Invention

[0005] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art and to provide a flexible sensor for synchronous monitoring of multiple parameters of respiration and heartbeat, as well as a preparation method and application thereof.

[0006] The technical solutions of the present invention are as follows:

[0007] A first aspect of the present invention provides a flexible sensor for synchronously monitoring multiple parameters of respiration and heartbeat, the flexible sensor comprising:

[0008] A respiratory sensing layer, comprising a bottom layer and a plurality of split resonant rings, wherein the split resonant rings are arranged in an array on the bottom layer and each split resonant ring has an opening;

[0009] A heartbeat sensing layer is provided on the respiration sensing layer, the heartbeat sensing layer comprising a middle layer and a plurality of cross-shaped resonant units, the cross-shaped resonant units being distributed in an array on the middle layer, wherein the array center of the cross-shaped resonant units is staggered with the array center of the open resonant ring;

[0010] The packaging layer is arranged on the heartbeat sensing layer, and has a plurality of through holes.

[0011] Wherein, the resonant frequency of the respiration sensing layer is different from the resonant frequency of the heartbeat sensing layer.

[0012] The present invention adopts a differentiated double-layer unit layout, using a large-sized split ring resonator (SRR) array and an integrated small-sized cross-shaped resonant unit. The resonant frequency of the outer SRR (the dominant frequency band for breathing) and the resonant frequency of the inner cross-shaped resonant unit (the dominant frequency band for heartbeat) are physically separated by frequency intervals, without the need for complex algorithm decoupling, to achieve synchronous monitoring of multiple parameters of breathing and heartbeat.

[0013] Optionally, the resonant frequency of the respiratory sensing layer is 2.9 GHz to 3.4 GHz, and the resonant frequency of the heartbeat sensing layer is 5.5 GHz to 7.3 GHz.

[0014] Optionally, the bottom layer has a thickness of 40 μm to 60 μm;

[0015] The thickness of the open resonant ring is 30 μm to 40 μm, the outer radius of the open resonant ring is 3 mm to 7 mm, the ring width of the open resonant ring is 0.2 mm to 0.7 mm, and the width of the opening is 0.1 mm to 0.5 mm.

[0016] Optionally, the split resonant rings are distributed in a 10×10 matrix, and the spacing between adjacent split resonant rings is 1 mm to 3 mm.

[0017] Optionally, the thickness of the middle layer is 70 μm to 90 μm;

[0018] The cross-shaped resonance unit includes four symmetrically distributed connecting arms, and the ends of the connecting arms are pointed;

[0019] 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 curvature radius of the end of the connecting arm is less than 10 μm.

[0020] Optionally, the cross-shaped resonant units are distributed in a 5×5 matrix, and the spacing between the connecting arms on adjacent cross-shaped resonant units is 0.1 mm to 0.2 mm;

[0021] The distance between the array center of the open resonant ring and the array center of the cross-shaped resonant unit is 4 cm to 6 cm.

[0022] Optionally, the encapsulation layer has a thickness of 15 μm to 25 μm;

[0023] The diameter of the through hole is 5 μm-10 μm.

[0024] Optionally, the raw material for preparing the bottom layer is polydimethylsiloxane, and the Young's modulus of the bottom layer is 1.0 MPa to 1.4 MPa;

[0025] The raw material for preparing the split resonant ring is liquid metal gallium indium tin alloy, wherein the mass ratio of gallium, indium and tin is 68.5%:21.5%:10%;

[0026] The raw material for preparing the middle layer is TPU;

[0027] The raw material for preparing the cross-shaped resonance unit is silver nanowire;

[0028] The encapsulation layer is a porous polyurethane film.

[0029] A second aspect of the present invention provides a method for preparing a flexible sensor for synchronously monitoring multiple parameters of respiration and heartbeat, comprising the following steps:

[0030] S1. Preparation of the respiratory sensing layer: PDMS prepolymer is mixed with a curing agent (hydrogenated silicone oil), spin-coated onto a silicon wafer, and heated to cure to form a base layer. Several grooves are formed on the surface of the base layer using femtosecond laser direct writing. Liquid metal gallium indium tin alloy is dropwise deposited into the grooves using a piezoelectric inkjet printer to form an open resonant ring.

[0031] S2. Preparation of the heartbeat sensing layer: dissolving TPU particles in tetrahydrofuran to obtain a TPU solution; casting the TPU solution into a film and drying it to form a middle layer; imprinting the middle layer using a nanoimprint template to form a plurality of cross-shaped grooves; coating a silver nanowire solution in the cross-shaped grooves and sintering them to form a cross-shaped resonant unit;

[0032] S3. The respiratory sensing layer prepared in S1 and the heartbeat sensing layer prepared in S2 are bonded together using a silane coupling agent, and then covered with a porous polyurethane film to form an encapsulation layer; and hot-pressed and sealed to obtain a flexible sensor.

[0033] Optionally, in S1, the mass ratio of PDMS prepolymer to curing agent (hydrogenated silicone oil) is 9-11:1, the spin coating speed is 1500 rpm-2500 rpm, the spin coating 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;

[0034] In S2, the concentration of the TPU solution is 10wt%~20wt%, the drying temperature is 50℃~70℃, and the drying time is 10h~14h; the solid content of the silver nanowire solution is 15%~25%, the sintering temperature is 50℃~70℃, and the sintering time is 20min~30min;

[0035] In S3, the temperature of the hot pressing seal is 70°C to 90°C, the pressure is 8 kPa to 12 kPa, and the time is 8 s to 12 s.

[0036] A third aspect of the present invention provides a respiratory and heartbeat monitoring system, comprising a radio frequency chip and a flexible sensor, wherein the flexible sensor transmits collected respiratory signals and heartbeat signals to a smart terminal via the radio frequency chip.

[0037] The present invention has at least one of the following beneficial effects:

[0038] (1) The sensor of the present invention significantly improves the accuracy of physiological parameter detection and simplifies the system complexity through the metamaterial structure and frequency domain design. Specifically, on the one hand, the outer large-scale SRR array (open resonant ring) and the inner cross-shaped resonant unit respond to large respiratory strain and heartbeat micro-vibration respectively; on the other hand, the material properties such as the high stretchability of the liquid metal in the open resonant ring and the high conductive stability of the silver nanowires in the cross-shaped resonant unit, combined with the frequency filtering effect of the PDMS / TPU substrate, enable the respiratory (0.1Hz-0.8Hz) and heartbeat (0.9Hz-5Hz) signals to be physically decoupled due to the resonant frequency interval. The signals can be separated without complex algorithms. Compared with the existing technology that relies on indirect sensing of external electromagnetic fields and multi-sensor layout, the detection accuracy is higher and the system power consumption is lower.

[0039] (2) The sensor of the present invention adopts a three-layer flexible composite structure. The bottom layer PDMS and the middle layer TPU are integrated through chemical bonding. The top layer (encapsulation layer) skin-friendly and waterproof PU film ensures long-term wearing comfort. The single-piece design replaces the traditional multi-sensor layout and realizes breathing and heartbeat monitoring simultaneously at the physical structure level, avoiding the problems of large size and high cost of existing technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a schematic structural diagram of a flexible sensor for synchronously monitoring multiple parameters of respiration and heartbeat in Example 1 of the present invention;

[0041] Figure 2 Schematic diagram of the structure of the split resonant ring in Example 1 of the present invention;

[0042] Figure 3 Schematic diagram of the structure of the cross-shaped resonance unit in Example 1 of the present invention;

[0043] Figure 4 is the resonant frequency of the respiratory layer and the cardiac layer in Example 1 of the present invention;

[0044] Figure 5 The electromagnetic response characteristics corresponding to different unit periods of the breathing layer in Example 1 of the present invention;

[0045] Figure 6 is the respiratory signal in Example 1 of the present invention;

[0046] Figure 7 The heartbeat signal in embodiment 1 of the present invention;

[0047] Figure 8 This is a schematic diagram of the usage status of the flexible sensor for synchronous monitoring of multiple parameters of respiration and heartbeat in Example 2 of the present invention.

[0048] Figure numerals: 1, breathing sensing layer; 11, bottom layer; 12, open resonant ring; 2, heartbeat sensing layer; 21, middle layer; 22, cross-shaped resonant unit; 23, connecting arm; 3, packaging layer; 31, through hole. DETAILED DESCRIPTION

[0049] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is 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 intended to limit the present invention.

[0050] Example 1

[0051] This embodiment provides a flexible sensor for synchronously monitoring multiple parameters of breathing and heartbeat and a method for preparing the same, as follows:

[0052] The structure of a flexible sensor for synchronous monitoring of multiple parameters of breathing and heartbeat is as follows: Figure 1-Figure 3 As shown, the resonant frequency and sensor signal are Figure 4-Figure 7 The flexible sensor includes a breathing sensing layer 1, a heartbeat sensing layer 2, and an encapsulation layer 3, arranged sequentially from bottom to top. The breathing sensing layer 1 is used to monitor breathing, and the heartbeat sensing layer 2 is used to monitor heartbeat. The specific structure is as follows:

[0053] The respiratory sensor layer 1 includes a bottom layer 11 and a plurality of split-ring resonators 12 (SRRs). The plurality of split-ring resonators 12 are arranged on the bottom layer 11. Specifically, the split-ring resonators 12 are distributed in an array on the bottom layer 11. Figure 2 As shown, the split resonant ring 12 has an opening 13 .

[0054] 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 distributed in an array on the middle layer 21. Figure 3 As shown, the cross-shaped resonance unit 22 includes four symmetrically distributed connecting arms 23 , and the ends of the connecting arms 23 away from the center are pointed.

[0055] The packaging layer 3 is disposed on the heartbeat sensing layer 2 , and has a plurality of through holes 31 .

[0056] In this embodiment, the specific structure and material composition of the respiratory sensor layer 1 are as follows:

[0057] (1) Base material and parameter material:

[0058] The raw material for preparing the bottom layer 11 is polydimethylsiloxane (PDMS, Dow Corning SYLGARD 184). The performance parameters of the polydimethylsiloxane after curing are: thickness 50 μm (controlled by a spin coater) and Young's modulus 1.2 MPa.

[0059] (2) SRR array unit structure:

[0060] Shape: As Figure 3 As shown, the split resonant ring 12 is open on one side, and the opening direction is uniformly toward the edge of the sensor.

[0061] Geometric parameters: outer radius r =5mm, ring width w =0.5mm, thickness t =35μm, unit period (the distance between the geometric centers of two adjacent resonant units in the row / column direction) P =12mm, opening width g =0.3mm.

[0062] Material: Liquid metal gallium indium tin alloy (GaInSn, gallium, indium, tin mass ratio is 68.5%:21.5%:10%, purity>99.9%);

[0063] Array layout: 10×10 element matrix, covering an area of ​​120mm×120mm, centered on the central area of ​​thoracic respiratory motion (the 4th to 6th intercostal space at the midsternal line).

[0064] In this embodiment, the design of the respiratory sensor layer 1 is based on:

[0065] (1) Physiological signal characteristic matching

[0066] The chest strain frequency generated by respiratory movement is 0.1Hz-0.8Hz (corresponding to a resting respiratory rate of 12 times / minute to 20 times / minute), accompanied by a periodic tensile strain of 5%-15% (e.g., the chest circumference increases by about 2cm-5cm during inhalation, corresponding to a 5%-15% strain on the sensor base). Low-frequency and high-strain sensitivity requirements: The sensor unit needs to be sensitive to large size changes (circumference changes), so a large-sized open resonant ring 12 (outer radius r =5mm, ring width w =0.5mm, thickness t=35μm, unit period P = 12mm), through the open ring structure (opening width g =0.3mm) to introduce concentrated capacitance to form an LC resonance unit.

[0067] (2) LC resonance formula and structural parameter calculation based on

[0068] Initial frequency of the respiratory sensing layer 1: LC resonant frequency formula , f is the LC resonant frequency of the respiratory sensing layer 1, L is the toroidal inductor of the breathing sensing layer 1, C is the capacitance of the breathing sensing layer 1 。 Toroidal Inductor L The geometric dimensions of the split resonant ring 12 (outer radius R , ring width w ) determines the capacitance C The opening width of the split resonant ring 12 g The specific calculation formula is as follows: , where the vacuum permeability , the magnetic permeability of the bottom layer 11 (The raw material PDMS for preparing the bottom layer 11 is a non-magnetic material), the average radius of the open resonant ring 12 , substitute into the calculated toroidal inductance L =15.4nH. Capacitor , where the dielectric constant of air is , the dielectric constant of the bottom layer 11 (dielectric constant of the PDMS raw material used to prepare the bottom layer 11), the ring width of the open resonant ring 12 w =0.5mm, the thickness of the split resonant ring 12 t =35μm, the opening width of the split resonant ring 12 g =0.3mm, substitute the calculated capacitance C =0.138pF. Resonant frequency f :Toroidal inductor L , capacitor C is substituted into the LC resonant frequency formula to obtain f =3.4GHz.

[0069] When the respiratory sensing layer 1 is strained by 5%, the average radius of the split resonant ring 12 , the opening width of the split resonant ring 12 , substitute into the calculation, the toroidal inductor ,capacitance Therefore, the LC resonance frequency of the respiratory sensing layer 1 when the strain is 5% is .

[0070] When the respiratory sensing layer 1 is strained by 15%, the average radius of the split resonant ring 12 , the opening width of the split resonant ring 12 , substitute into the calculation, the toroidal inductor ,capacitance Therefore, the LC resonance frequency when the respiratory sensing layer 1 is strained by 15% is .

[0071] Based on the above analysis, the frequency band corresponding to the respiratory sensing layer 1 is 2.9GHz to 3.4GHz. Figure 4 、 Figure 6 shown.

[0072] (3) Subwavelength design principle

[0073] The metamaterial unit cycle must meet the following requirements: ,in, p is the unit period of the split resonant ring 12, λ is the free space wavelength ( , c =3×10 8 mm / s is the speed of light, f is the resonant frequency) ， is 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 respiratory sensing layer 1 is 3.4 GHz, that is, the resonant frequency f is 3.4GHz, substitute into the formula =88.2mm, , it can be seen that , and the unit period of the split resonant ring 12 in this embodiment is , meeting the sub-wavelength design principle and ensuring that the structure avoids electromagnetic wave diffraction interference.

[0074] The setting of the unit period of 12mm is based on electromagnetic simulation optimization. When the unit period is 12mm, the reflection coefficient at the resonance point is about -30dB, there is no spurious mode interference, and it shows a single pure resonance characteristic; when the unit period increases to 20mm, the coupling effect of adjacent units causes the resonance peak to split, forming a double-peak response at 3.2GHz and 3.6GHz, resulting in blurred signal detection; and when the period is reduced to 8mm, the excessive coupling between units will degrade the electromagnetic signal transmission, and the reflection coefficient will be too large (-15dB), affecting the signal detectability. Figure 5 shown.

[0075] In this embodiment, the specific structure and material composition of the heartbeat sensor layer 2 are as follows:

[0076] (1) Base material and parameter material:

[0077] The preparation material of the middle layer 21 is thermoplastic polyurethane (TPU, Bayer Desmopan 9385A), and the performance parameters after tape casting are: thickness 80μm, dielectric constant ;

[0078] (2) Structure of the cross-shaped resonant unit

[0079] Shape: As Figure 3 As shown, the four arms of the cross-shaped resonant unit 22 are symmetrically distributed, and the arm ends are pointed (the curvature radius is less than 10 μm, which enhances the electric field concentration);

[0080] Geometric parameters: arm length L =3mm, arm width w =0.2mm, arm end clearance g =0.15mm, thickness t =35μm;

[0081] Materials: Silver nanowires (50 nm diameter, >10 μm length, 20 wt% concentration) were nanoimprinted onto the TPU substrate to form a dense conductive network.

[0082] Array layout: 5×5 element matrix, covering an area of ​​60mm×60mm, with the array center aligned with the chest cardiac projection area (5mm from the SRR array center to avoid mechanical coupling interference);

[0083] In this embodiment, the design of the heartbeat sensor layer 2 is based on:

[0084] (1) Physiological signal characteristic matching

[0085] The frequency of chest micro-vibration caused by heartbeat is 0.9Hz-5Hz (corresponding to heart rate 54 beats / minute-300 beats / minute), and the vibration amplitude is 1μm-50μm. The sensor unit needs to be sensitive to local high-frequency micro-deformation. High-frequency micro-vibration sensitivity requirements: Design a small-sized cross-shaped unit (arm length L =3mm, arm width w =0.2mm, arm end clearance g =0.15mm, thickness t =35 μm).

[0086] (2) Frequency band selection basis

[0087] The resonant frequency of the cross-shaped resonant unit 22 is mainly determined by the inductance of the connecting arms 23 and the capacitance of the gap between the connecting arms 23 .

[0088] Initial frequency of heartbeat sensing layer 2: LC resonant frequency , f0 is the LC resonant frequency of the heartbeat sensing layer 2, L arm is a single-arm (one connecting arm 23) toroidal inductor of the cross-shaped resonant unit 22, C gap is the gap capacitance of the cross-shaped resonant unit 22, specifically, the single-arm ring inductor: , where the vacuum permeability , the magnetic permeability of the middle layer 21 (The preparation material of the middle layer 21 is TPU, which is a non-magnetic material), the arm length of the cross-shaped resonance unit 22 is L =3.0mm, the arm width of the cross-shaped resonant unit 22 w =0.2mm, substitute into the calculation to get the single-arm ring inductor L arm =1.2nH, the total inductance of the cross-shaped resonant unit 22 is a parallel structure, so the total inductance of the actual cross-shaped resonant unit is L total =0.3nH. Gap capacitance of cross-shaped resonant unit 22: C gap , where the dielectric constant of air is , the dielectric constant of the middle layer 21 (dielectric constant of TPU material used for the middle layer 21), arm width of the cross-shaped resonant unit 22 w =0.2mm, the thickness of the cross-shaped resonance unit 22 t =35μm, the arm end gap of the cross-shaped resonant unit 22 g =0.15mm, substitute into the calculation to get C gap =0.035pF. Resonant frequency: Substituting the inductance and capacitance into the LC resonant frequency formula, we get f 0=7.3GHz

[0089] When the heartbeat sensing layer 2 vibrates by 1 μm: the gap between the arms of the cross-shaped resonant unit 22 , the gap capacitance of the cross-shaped resonant unit 22 Therefore, the frequency of the heartbeat sensor layer 2 when it vibrates at 1 μm is .

[0090] When the heartbeat sensing layer 2 vibrates by 50 μm: the gap between the arms of the cross-shaped resonant unit 22 , the gap capacitance of the cross-shaped resonant unit 22 Therefore, the heartbeat sensor layer 2 vibrates at a frequency of 50 μm. .

[0091] Based on the above analysis, the heartbeat sensing layer 2 corresponds to a frequency band of 5.5 GHz to 7.3 GHz. Figure 4 、 Figure 7 shown.

[0092] (3) Frequency domain decoupling requirements

[0093] It maintains a 2.1GHz frequency interval with the breathing frequency band (2.9GHz-3.4GHz), utilizes the natural separation of the spectrum to avoid signal crosstalk, and avoids commonly used communication frequency bands (such as Bluetooth 2.4GHz) to reduce electromagnetic interference.

[0094] In summary, the resonant frequency range (2.9GHz-3.4GHz, 5.5GHz-7.3GHz) is the result of theoretical design based on the frequency-strain characteristics of physiological signals, optimized metamaterial unit structural parameters, and physical decoupling requirements. This design is determined using the LC resonance formula and the subwavelength principle. This design ensures the sensor's differentiated response to large respiratory strains and micro-heartbeat vibrations, achieving high-precision and low-complexity simultaneous multi-parameter monitoring.

[0095] In this embodiment, the specific structure and material composition of the encapsulation layer 3 are as follows:

[0096] (1) Encapsulation layer material: porous polyurethane (PU) film, performance parameters: thickness 20μm, pore size 5μm-10μm (water vapor permeability 6000g / m 2 / 24h), waterproof grade IPX7 (no failure after immersion in 1m water depth for 30 minutes);

[0097] (2) Interlayer connection and bonding method: The middle layer TPU and the bottom layer PDMS are chemically bonded through a silane coupling agent (KH-570).

[0098] This embodiment also provides a method for preparing a flexible sensor for synchronously monitoring multiple parameters of breathing and heartbeat, comprising the following steps:

[0099] S1. Preparation of respiratory sensing layer 1: PDMS prepolymer and curing agent (hydrogenated silicone oil) are mixed, spin-coated on a silicon wafer, and heated and cured to form a bottom layer 11. A femtosecond laser direct writing method is used to process the surface of the bottom layer 11 to form a plurality of grooves. A piezoelectric inkjet printer is used to deposit liquid metal gallium indium tin alloy dropwise into the grooves to form an open resonant ring 12.

[0100] S2. Preparation of the heartbeat sensing layer 2: Dissolving TPU particles in tetrahydrofuran to obtain a TPU solution; casting the TPU solution into a film and drying it to form a middle layer 21; imprinting the middle layer 21 with a nanoimprint template to form a plurality of cross-shaped grooves; coating the silver nanowire solution in the cross-shaped grooves and sintering them to form a cross-shaped resonant unit 22;

[0101] S3. The respiratory sensing layer 1 prepared in S1 and the heartbeat sensing layer 2 prepared in S2 are bonded together using a silane coupling agent, and then covered with a porous polyurethane film to form an encapsulation layer 3, and the encapsulation layer 3 is modified with polyethylene glycol; and hot-pressed and sealed to obtain a flexible sensor.

[0102] In this embodiment, the specific process of the preparation method is as follows:

[0103] (1) Preparation of respiratory sensing layer 1

[0104] Step 1: PDMS prepolymer and curing agent (hydrogenated silicone oil) were mixed at a mass ratio of 10:1, spin-coated on a silicon wafer (2000 rpm, 30 s), and cured at 80°C for 2 h to form a 50 μm substrate.

[0105] Step 2: Femtosecond laser direct writing (wavelength 800nm, pulse width 100fs, energy density 200mJ / cm 2 ) Processing SRR grooves (depth 35 μm, opening width 0.3 mm) on the PDMS surface;

[0106] Step 3: Using a piezoelectric inkjet printer with a nozzle diameter of 10 μm and a pulse frequency of 10 kHz, liquid metal was deposited dropwise into the grooves to form a conductive SRR array.

[0107] (2) Preparation of heartbeat sensing layer 2

[0108] Step 1: TPU pellets were dissolved in tetrahydrofuran (concentration 15 wt%), cast into 80 μm films, and dried at 60 ° C for 12 h;

[0109] Step 2: A nanoimprint template (made of SU-8 photoresist, accuracy ±5 μm) was used to imprint the TPU film to form a cross-shaped groove (depth 5 μm).

[0110] Step 3: Slit-coat the silver nanowire solution (solid content 20%) and sinter at 60°C for 30 min to form a conductive cross unit.

[0111] (3) Overall integration

[0112] The two-layer structure was bonded using a silane coupling agent (KH-570), edge-cut (laser cutting, accuracy ±10 μm), covered with PU packaging film, and hot-pressed and sealed (temperature 80 °C, pressure 10 kPa, time 10 s).

[0113] The working principle and signal decoupling mechanism of the flexible sensor for synchronous monitoring of multiple parameters of respiration and heartbeat prepared in Example 1 are as follows:

[0114] (1) Principle of respiratory signal detection: 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 a split resonant ring (SRR) array, with its opening direction along the main stretching direction of the chest cavity. The deformation effect causes the resonant frequency to shift from the initial 3.4 GHz to a lower frequency (for example, it drops to 2.9 GHz when stretched by 15%). The frequency shift is negatively correlated with the depth of breathing. 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.

[0115] (2) Principle of heartbeat signal detection: Micro-vibrations (1μm–50μm) of the chest wall caused by the heartbeat are transmitted through the TPU substrate to the cross-shaped resonant unit array of the heartbeat sensing layer. The sharp structure design of the arm ends of the cross-shaped resonant unit enhances the electric field concentration effect. The tiny vibration causes the gap between the arm ends to change, significantly changing the equivalent capacitance value, and the resonant frequency shifts from the initial 7.3GHz to a lower frequency (for example, down to 5.5GHz). This layer operates in the high frequency band (5.5GHz–7.3GHz) and analyzes the heart rate and vibration intensity by capturing the frequency shift caused by local high-frequency micro-deformation.

[0116] (3) Frequency domain decoupling mechanism:

[0117] The breathing sensing layer (open resonant ring 12) and the heartbeat sensing layer (cross-shaped resonant unit 22) utilize differentiated resonant unit designs, operating in independent frequency bands (2.9GHz–3.4GHz for the breathing layer and 5.5GHz–7.3GHz for the heartbeat layer), with a frequency separation of 2.1GHz. Physical frequency domain isolation allows for natural decoupling of the low-frequency, high-strain components of the breathing signal from the high-frequency, micro-vibrations of the heartbeat signal, eliminating the need for algorithmic separation. The dual-layer array's center-staggered layout (4cm–6cm) further minimizes mechanical coupling interference.

[0118] Example 2

[0119] This embodiment provides a respiratory and heartbeat monitoring system, including a radio frequency chip and the flexible sensor prepared in Example 1.

[0120] like Figure 8 The figure shows a schematic diagram of the usage status of the flexible sensor (respiratory 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 tester's chest, and the flexible sensor collects the tester's respiration signal and heartbeat signal. The flexible sensor then transmits the collected respiration signal and heartbeat signal to the smart terminal through the radio frequency chip, so that the respiration, heartbeat and monitoring data can be displayed on the smart terminal.

[0121] In this embodiment, the RF chip is a miniaturized NORDIC nRF5340 RF chip. The miniaturized RF chip integrates sweep frequency transmission and reception functions and measures 3mm x 3mm. The smartphone is connected to the RF chip via Bluetooth and serves as a display terminal. Since the structure and principles of the miniaturized RF chip are well known to those skilled in the art, they will not be described in detail in this embodiment.

[0122] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. Flexible sensor for synchronous monitoring of multiple parameters of breathing and heartbeat, characterized by: The flexible sensor comprises: A respiratory sensing layer (1), the respiratory sensing layer (1) comprising a bottom layer (11) and a plurality of open resonant rings (12), the open resonant rings (12) being arranged in an array distribution on the bottom layer (11), and the open resonant rings (12) having openings (13); A heartbeat sensing layer (2) is arranged on the breathing sensing layer (1), the heartbeat sensing layer (2) comprising a middle layer (21) and a plurality of cross-shaped resonance units (22), the cross-shaped resonance units (22) being arranged in an array distribution on the middle layer (21), wherein the array center of the cross-shaped resonance units (22) is staggered with the array center of the open resonant ring (12); An encapsulation layer (3) is provided on the heartbeat sensing layer (2), and the encapsulation layer (3) has a plurality of through holes (31); The resonant frequency of the respiratory 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 respiratory 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 open resonant ring (12) is 30 μm to 40 μm, the outer radius of the open resonant ring (12) is 3 mm to 7 mm, the ring width of the open resonant ring (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 open resonant rings (12) are distributed in a 10×10 matrix, and the spacing between adjacent open resonant rings (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 resonance unit (22) comprises 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 curvature radius of the end of the connecting arm (23) is less than 10 μm.

5. The flexible sensor according to claim 4, characterized in that The cross-shaped resonant units (22) are distributed in a 5×5 matrix, and the spacing 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 open resonant ring (12) and the array center of the cross-shaped resonant unit (22) is 4 cm to 6 cm.

6. The flexible sensor according to claim 1, wherein The thickness of the encapsulation 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, characterized in that 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~1.4 MPa; The raw material for preparing the open resonant ring (12) is a 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 resonance unit (22) is silver nanowire; The encapsulation layer (3) is a porous polyurethane film.

8. The method for preparing a flexible sensor according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Preparation of respiratory sensing layer (1): PDMS prepolymer and curing agent are mixed, spin-coated on a silicon wafer, and heated and cured to form a bottom layer (11); a femtosecond laser is used to directly write on the surface of the bottom layer (11) to form a plurality of grooves; a piezoelectric inkjet printer is used to deposit liquid metal gallium indium tin alloy dropwise into the grooves to form an open resonant ring (12); S2. Preparation of the heartbeat sensing layer (2): dissolving TPU particles in tetrahydrofuran to obtain a TPU solution; casting the TPU solution into a film, drying, and forming a middle layer (21); imprinting the middle layer (21) with a nanoimprint template to form a plurality of cross-shaped grooves; coating a silver nanowire solution in the cross-shaped grooves, and sintering to form a cross-shaped resonant unit (22); S3, the respiratory sensing layer (1) prepared in S1 and the heartbeat sensing layer (2) prepared in S2 are bonded together by a silane coupling agent, and then covered with a porous polyurethane film to form an encapsulation layer (3); and hot-pressed and sealed to obtain a flexible sensor.

9. The preparation method according to claim 8, characterized in that In S1, the mass ratio of PDMS prepolymer to curing agent is 9-11:1, the spin coating speed is 1500-2500 rpm, the spin coating time is 25-35 seconds, the curing temperature is 70-90°C, and the curing time is 1.5-2.5 hours. The wavelength of the femtosecond laser direct writing is 750-850 nm, the pulse width is 80-120 fs, and the energy density is 150-250 mJ / cm². The nozzle diameter of the piezoelectric inkjet printer is 8-12 μm, and the pulse frequency is 8-12 kHz. In S2, the concentration of the TPU solution is 10wt%~20wt%, the drying temperature is 50℃~70℃, and the drying time is 10h~14h; the solid content of the silver nanowire solution is 15%~25%, the sintering temperature is 50℃~70℃, and the sintering time is 20min~30min; In S3, the temperature of the hot pressing seal 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 heartbeat monitoring system, characterized in that: The flexible sensor comprises a radio frequency chip and any one of claims 1 to 7, wherein the flexible sensor transmits collected respiratory signals and heartbeat signals to an intelligent terminal through the radio frequency chip.

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