Flexible pressure sensor for BCG monitoring, monitoring system and preparation method

Abstract

The invention relates to a flexible pressure sensor for BCG monitoring, a monitoring system and a preparation method, and belongs to the technical field of physiological status monitoring. The special flexible pressure sensor is integrated in the cushion type monitoring system, and the signal processing circuit is combined, so that the physiological states such as the heart rate and the respiratory rate of a human body in a static sitting state can be monitored; meanwhile, the independent signals of the heart rate and the respiratory frequency are separated from the original fusion signals collected by the sensor through a decomposition algorithm, and the method can be used for heart health management and auxiliary diagnosis of related diseases. Vital signs can be monitored in an unconstrained mode under the condition of not making contact with the skin, discomfort possibly brought by a traditional monitoring method is eliminated, and the method is suitable for heart health management and related disease auxiliary diagnosis of sedentariness people or old people.

Description

Technical Field

[0001] The invention belongs to the technical field of physiological state monitoring, and relates to a flexible pressure sensor for ballistocardiogram (BCG) signal monitoring, a monitoring system and a preparation method. Background Art

[0002] As the global population ages, chronic disease management becomes increasingly important, especially the prevention and treatment of cardiovascular disease. At the same time, modern lifestyles have led to more and more people being sedentary, increasing the risk of heart disease and other health problems. Against this backdrop, physiological monitoring technologies have developed rapidly, especially those that can continuously monitor vital signs such as heart rate, respiratory rate, etc. Traditional physiological monitoring methods, such as electrocardiograms (ECGs), although effective, may cause skin irritation or other discomfort when worn for a long time, especially in the elderly, which limits their application in long-term health monitoring.

[0003] Existing physiological signal monitoring technologies mostly rely on wearable devices, such as smart watches or chest strap heart rate monitors. These devices collect data by directly contacting the skin and can provide accurate ECG records. In addition, there are seated BCG signal monitoring devices that use technologies such as accelerometers, pressure sensors, and vibration sensors, which attempt to monitor cardiac activity in a non-contact manner. However, although methods based on accelerometers, pressure sensors, and vibration sensors have achieved non-contact BCG signal monitoring to a certain extent, in practical applications, especially under conditions of greater static pressure, these devices often have difficulty in accurately capturing weak BCG signals. Signal interference, unstable signal quality, and difficulty in achieving continuous real-time monitoring have become major problems, limiting the effectiveness of existing unconstrained monitoring devices, especially in medical environments where precise data is required. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a flexible pressure sensor, a monitoring system and a preparation method for BCG monitoring, so as to accurately monitor the respiratory signal and the cardiac impact signal in a sitting position, thereby supporting the evaluation of heart rate variability and early warning of heart health.

[0005] To achieve the above-mentioned object, one aspect of the present invention provides a flexible pressure sensor for BCG monitoring, which comprises a second substrate, a second electrode, an array microstructure, a first substrate and a first electrode stacked in sequence, wherein a plurality of regularly distributed microstructures are formed on one surface of the array microstructure, the surface is in contact with the first substrate, and the other surface is in contact with the second electrode. Furthermore, the microstructure comprises one or more of a convex hemisphere, a concave hemisphere, a triangular prism, a cylinder, a terrace, a cube and a cuboid, and the microstructure has a plurality of different size characteristics.

[0006] Furthermore, the first electrode and the second electrode are both obtained by growing conductive fillers, wherein the conductive fillers include but are not limited to carbon materials such as graphene and carbon nanotubes, and metal nanowires such as iron nanowires and silver nanowires.

[0007] The first substrate is made of a flexible elastomer material, including but not limited to PDMS, hydrogel, TPU, latex, etc. The second substrate is made of a flexible substrate, including but not limited to PET, PI, PVA, etc.

[0008] The preparation method of the flexible pressure sensor comprises:

[0009] A silicon wafer is selected and cleaned and degreased, and a photoresist is spin-coated on the treated silicon wafer;

[0010] The silicon wafer with the spin-coated photoresist is exposed through a mask, and then placed in a developer to remove excess photoresist, thereby obtaining a number of regularly distributed microstructure patterns;

[0011] The photoresist is melted by high-temperature heat reflow, and low-temperature gas is blown to prevent the photoresist from being over-melted; after the photoresist is cooled and solidified, a stable microstructure is obtained;

[0012] Covering the silicon wafer with microstructures with silica gel to make a mold, removing the mold and injecting microarray material into the grooves formed by the microstructures, and peeling off the mold after the microarray material is solidified;

[0013] Obtain a conductive filler electrode; mix a flexible elastomer material prepolymer and a curing agent in a certain proportion to obtain a flexible elastomer material substrate, attach the conductive filler electrode to the surface of the flexible elastomer material substrate, and dissolve the copper mesh with an etchant to obtain a first electrode; wherein the area of ​​the flexible elastomer material substrate needs to be larger than the area of ​​the first electrode; obtain a second electrode in the same manner, wherein the flexible elastomer material substrate of the second electrode needs to be peeled off;

[0014] The side of the flexible elastomer material substrate to which the first electrode is not attached is closely fitted to the side of the microarray material with microstructures, the second electrode is closely fitted to the side of the microarray material without microstructures, and then a layer of flexible substrate is used to fix the second conductive filler electrode between the microarray material and the flexible substrate, thereby obtaining the flexible triboelectric pressure sensor;

[0015] The flexible elastomer material prepolymer and the curing agent are mixed in a certain proportion, poured on the surface of the conductive filler electrode after vacuum treatment, heated and cured to form a packaging layer, and the sensor packaging is completed.

[0016] In another aspect of the present invention, a flexible pressure sensor for BCG monitoring may adopt a single electrode structure. Specifically, the flexible pressure sensor with a single electrode structure includes a flexible elastomer material substrate, a conductive filler electrode formed on the surface of the flexible elastomer material substrate, a flexible substrate, and an array microstructure formed on the surface of the flexible substrate. The flexible pressure sensor can be formed by closely fitting the side of the flexible elastomer material substrate to which the conductive filler electrode is not attached and the side of the array microstructure with a shape distribution.

[0017] Another aspect of the present invention provides a cushion-type BCG monitoring system for BCG monitoring, which includes: a signal processing circuit, a cushion, a host computer, and a flexible pressure sensor. The flexible pressure sensor and the signal processing circuit are arranged in the cushion, and the flexible pressure sensor and the signal processing circuit are electrically connected; the signal processing circuit is wirelessly connected to the host computer.

[0018] The flexible pressure sensor is fixed to the seat surface inside the seat cushion and fits the seat cushion to capture the tiny forces generated by human breathing or heartbeat. The host computer decomposes the signal collected by the flexible pressure sensor through the VMD algorithm to obtain the heart rate signal and respiratory rate signal.

[0019] Furthermore, the signal processing circuit includes a signal amplifier, a filter, an analog-to-digital converter and a wireless transmission module. The signal amplifier is used to amplify the electrical signal output by the flexible pressure sensor, the filter is used to filter the electrical signal, the analog-to-digital converter performs analog-to-digital conversion on the filtered electrical signal, and the wireless transmission module is used to transmit the analog-to-digital converted electrical signal to the host computer.

[0020] Furthermore, the host computer decomposes the signal collected by the flexible pressure sensor through the VMD algorithm, including:

[0021] S1, input the signal collected by the sensor, initialize the number of modes, bandwidth constraint parameters and the center frequency of each mode;

[0022] S2, construct an optimization model to minimize the sum of the energy of all modes and the sum of the bandwidth penalty term, while ensuring that the sum of the modes is equal to the original signal;

[0023] S3, iteratively update the function and center frequency of each mode using the alternating direction multiplier method, and ensure that the sum of all modes is equal to the original input signal by adjusting the Lagrange multiplier;

[0024] S4. When the update amplitude of all modes is less than a preset threshold or reaches the maximum number of iterations, the iteration is stopped, and the decomposed mode function and its corresponding center frequency are output;

[0025] S5. Determine whether the center frequency of each modal function is within the frequency range of the heart rate signal or the respiratory rate signal according to the center frequency of each modal function; if it is within the frequency range of the heart rate signal, identify it as a heart rate signal; if it is within the frequency range of the respiratory rate signal, identify it as a respiratory rate signal.

[0026] The beneficial effects of the present invention are:

[0027] (2) The sensor proposed in the present invention can achieve a frequency response range of at least 0.1 Hz to 20 Hz. This wide frequency range can cover human respiratory signals (usually less than 0.5 Hz) and cardiac shock signals (0.1 Hz to 20 Hz), making the sensor suitable for a variety of physiological signal monitoring scenarios.

[0028] (4) The design of the sensor proposed in the present invention allows for unconstrained vital sign monitoring without direct contact with the skin, eliminating the discomfort that may be caused by traditional monitoring methods, and is particularly suitable for long-term continuous monitoring of sensitive groups such as the elderly. By integrating the sensor into a cushion-type physiological signal monitoring system, the present invention can achieve unconstrained health monitoring in daily life, which is particularly suitable for cardiac health management and auxiliary diagnosis of related diseases for sedentary people, and can assist in heart rate variability analysis, providing technical support for cardiac health management and early diagnosis of diseases.

[0029] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0031] Figure 1 Schematic diagram of the structure distinction between single-electrode and double-electrode flexible pressure sensors;

[0032] Figure 2 A partial schematic diagram of a single-electrode flexible pressure sensor combining different microarray material array microstructures;

[0033] Figure 3 An example of microstructure distribution provided by an embodiment of the present invention;

[0034] Figure 4 (a) is a schematic diagram of the force-to-electricity conversion principle of the capacitive flexible pressure sensor. Figure 4 (b) is a schematic diagram of the force-to-electricity conversion principle of the triboelectric flexible pressure sensor. Figure 4(c) is a schematic diagram of the force-to-electricity conversion principle of the resistive flexible pressure sensor, where C is the output capacitance, R is the output resistance, and I is the output current;

[0035] Figure 5 A schematic diagram of the process of preparing an array microstructure according to an embodiment of the present invention;

[0036] Figure 6 The electrode preparation process;

[0037] Figure 7 A three-dimensional layered schematic diagram of a single-electrode flexible pressure sensor is provided for an embodiment of the present invention

[0038] Figure 8 A schematic diagram of the structure of a BCG monitoring system provided by an embodiment of the present invention;

[0039] Fig. 9 This is a schematic diagram of the correlation between BCG and ECG cycles;

[0040] Fig.10 The heart rate signal and respiratory rate signal are decomposed. DETAILED DESCRIPTION

[0041] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0042] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0043] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0044] The flexible pressure sensor provided by the present invention can be divided into a single electrode and a double electrode. Compared with the single electrode flexible pressure sensor, the double electrode flexible pressure sensor has a layer of conductive filler electrode disposed between the array microstructure and the second substrate. Figure 1 As shown. The array microstructure can have a variety of different styles, such as Figure 2 Shown is a partial pattern of array microstructures (taking a single-electrode flexible pressure sensor as an example).

[0045] The single-electrode flexible pressure sensor realizes force-to-electricity conversion based on the principle of contact friction electrification. Figure 4 (b); The flexible pressure sensor with two electrodes can realize the force-electric conversion based on the principle of pressure capacitance; The flexible pressure sensor with two electrodes can realize the force-electric conversion based on the principle of ionization, piezoresistance or pressure capacitance. The specific implementation method is shown in Example 1, wherein the principles of pressure capacitance and pressure resistance are respectively as follows: Figure 4 (a) and Figure 4 (c) as shown.

[0046] The present invention will be described in detail below through several embodiments.

[0047] Example 1

[0048] This embodiment provides a triboelectric flexible pressure sensor for BCG monitoring, which includes a flexible elastomeric material substrate (first substrate), a conductive filler electrode, an array microstructure and a flexible substrate (second substrate).

[0049] Among them, the array microstructure is arranged on a surface of a flexible substrate, the array microstructure is made of triboelectric material, and the triboelectric material is formed into an array microstructure with at least one shape distribution by a photoresist hot melt method. Specifically, the array microstructure includes a number of regularly distributed microstructures. The shape of the microstructure includes but is not limited to a convex hemisphere, a concave hemisphere, a triangular prism, a cylinder, a terrace, a cube, a cuboid, or a mixture of multiple shapes, and the microstructures have different sizes. The performance of the sensor can be enhanced or changed by combining microstructures of different shapes and sizes. In this embodiment, the array microstructure adopts a spherical crown shape, and the distribution of the microstructure is as follows: Figure 3 As shown, it can be distributed symmetrically.

[0050] It should be noted that the distribution form of the microstructures in the array microstructure is not limited to the symmetrical distribution form. The symmetrical distribution form is only an example of a distribution form. During the sensor preparation process, the microstructure distribution can also adopt other forms as long as the distribution has a certain regularity.

[0051] The conductive filler electrode is combined with a flexible elastomer material substrate, wherein the conductive filler electrode is attached to the surface of the flexible elastomer material substrate to collect electrical signals generated by friction.

[0052] The structure of the flexible triboelectric pressure sensor is specifically that a combination of a conductive filler electrode and a flexible elastomer material substrate is laminated and bonded with an array microstructure, wherein the bonding surfaces of the two parts are respectively a side of the flexible elastomer material substrate to which the conductive filler electrode is not attached and a side of the array microstructure having a shape distribution.

[0053] like Figure 4 (b) is a diagram showing the force-to-electricity conversion principle of the flexible triboelectric pressure sensor proposed in this embodiment. Specifically, when the flexible elastomer material contacts the array microstructure of the triboelectric material, the flexible elastomer material gains electrons and becomes negatively charged, while the array microstructure loses electrons and becomes positively charged; when the flexible elastomer material is separated from the array microstructure, an electric potential difference is generated.

[0054] For capacitive flexible pressure sensors, the core working principle is based on the property that the capacitance of a capacitor changes with the change of geometric structure. In such a sensor, a dielectric material is sandwiched between two parallel conductive plates (electrodes). When an external force, such as pressure or strain, is applied, the distance between the electrodes or the coverage area will change, resulting in a change in capacitance. Specifically, when the applied pressure brings the electrodes closer to each other, the thickness of the capacitor decreases and the capacitance increases accordingly; conversely, when the electrodes are separated by external force, the thickness of the capacitor increases and the capacitance decreases. Therefore, by accurately measuring the change in capacitance, the size and distribution of the external force applied to the sensor can be effectively detected.

[0055] A special capacitive flexible pressure sensor is an ion capacitive flexible pressure sensor, which uses ion gel as a capacitor. As a special dielectric material, ion gel plays an important role in capacitive flexible pressure sensors. Ion gel contains a large number of free-moving ions, which not only provides good electrochemical properties and mechanical flexibility, but also allows internal ions to migrate under the action of the electric field, further affecting the capacitance. When an external force is applied to compress or separate the electrode plates, the thickness of the ion gel will change accordingly, and it will also cause a change in the ion concentration gradient. In this case, compression will make the ion gel thinner and increase the capacitance; separation will make the ion gel thicker and reduce the capacitance. In addition, the concentration change caused by ion migration can significantly enhance the change amplitude of the capacitance, allowing the sensor to respond more sensitively to external pressure changes.

[0056] For resistive flexible pressure sensors, piezoelectric conversion is achieved based on the principle that resistance changes with external physical quantities (such as pressure, strain, etc.). Specifically, when the sensor is subjected to external force, the piezoresistive material inside it will deform. If the piezoresistive material is compressed, its length will shorten, the cross-sectional area will increase, and the resistance value will decrease. On the contrary, if the piezoresistive material is stretched, its length will increase, the cross-sectional area will decrease, and the resistance value will increase. This change can be detected by the measurement circuit, thereby realizing the measurement of pressure.

[0057] Example 2

[0058] This embodiment provides a preparation method for preparing the triboelectric flexible pressure sensor described in Embodiment 1. The preparation method is as follows:

[0059] S1. Obtain array microstructure, such as Figure 5 As shown, including:

[0060] First, a silicon wafer is selected and pre-processed, including cleaning and degreasing, to remove pollutants and organic residues on the surface of the silicon wafer;

[0061] Then a layer of photoresist is spin-coated on the processed silicon wafer by a spin coater, and the spin-coating speed and time are adjusted according to the required photoresist thickness;

[0062] The spin-coated silicon wafer is placed in a UV exposure machine, and the photoresist is exposed and etched using a mask, and the exposure time and intensity are adjusted according to the required microstructure size; the exposed photoresist and silicon wafer are placed in a developer, and the unexposed photoresist is removed by the developer to form the required microstructure pattern; the coaxial double-layer cylindrical photoresist array structure is prepared by exposure and development technology;

[0063] The developed photoresist and silicon wafer are placed in an oven for heating, and the cylindrical photoresist structure is thermally melted into a spherical crown structure by a high-temperature thermal reflow method. At the same time, low-temperature gas blowing is used in parallel for cooling assistance to prevent the double-layer cylindrical photoresist structure from being thermally melted into a single spherical crown structure; after the photoresist is cured, a stable microstructure is obtained;

[0064] The formed microstructure is covered with silica gel to make a mold, and after removing the mold, a triboelectric material is injected into the surface of the mold so that the triboelectric material fills the microstructure grooves in the mold;

[0065] A flexible substrate is used to cover the triboelectric material so that the flexible substrate and the triboelectric material are well bonded, and then the mold is peeled off to obtain an array microstructure.

[0066] S2, firstly, a conductive filler is grown on a copper grid substrate by radio frequency plasma chemical vapor deposition (PECVD), such as Figure 6 As shown, during the growth process, it is necessary to control the parameters such as RF frequency, RF power, temperature, gas flow rate, etc. to form the desired conductive filler electrode; the flexible elastomer material prepolymer and the curing agent are mixed in a certain proportion to obtain a flexible elastomer material substrate; the conductive filler electrode is attached to the surface of the flexible elastomer material substrate, and the copper mesh is dissolved by an etchant to obtain a flexible elastomer material substrate with a mesh conductive filler electrode attached to the surface;

[0067] S3. Assemble the array microstructure, the conductive filler electrode, and the flexible elastomer material substrate. Specifically, fit the side of the array microstructure with the shape distribution to the side of the flexible elastomer material substrate to which the conductive filler electrode is not attached, ensuring that the fitting surfaces are in close contact to form the basis of the triboelectric effect.

[0068] S4, encapsulating the sensor, specifically, mixing the flexible elastomer material prepolymer and the curing agent in a certain proportion, pouring the mixed flexible elastomer material solution into a container, and vacuumizing to remove bubbles; then pouring it on the surface of the conductive filler electrode, and forming an encapsulation layer with excellent mechanical properties and chemical stability after curing to protect the sensor from the external environment; the formed flexible triboelectric pressure sensor is as follows Figure 7 shown.

[0069] It should be noted that if a dual-electrode flexible pressure sensor is prepared, after the triboelectric material is used to fill the microstructure grooves in the mold in step S1, the triboelectric material needs to be cured and then the mold is directly peeled off. At the same time, two mesh conductive filler electrodes need to be prepared in step S2, one of which is half-coated with a flexible elastomer material (referred to as conductive filler electrode I), and the other conductive filler electrode remains in a bare electrode state (referred to as conductive filler electrode II). When assembling the sensor in step S3, the flexible elastomer material of the conductive filler electrode I is bonded to the side of the triboelectric material with a shape distribution, the conductive filler electrode II is bonded to the other side of the triboelectric material, and then the flexible substrate is used to bond the conductive filler electrode II to form a dual-electrode flexible pressure sensor.

[0070] In addition, resistance, capacitance, and ionization flexible pressure sensors can all be prepared based on the structure of the two-electrode flexible pressure sensor, and only the corresponding components need to be connected between the two electrodes of the pressure sensor.

[0071] Example 3

[0072] This embodiment provides a monitoring system for BCG monitoring, such as Figure 8 As shown, it includes a triboelectric flexible pressure sensor, a signal processing circuit, a seat cushion and a host computer. The signal processing circuit is connected to the triboelectric flexible pressure sensor for processing the original signal captured by the pressure sensor. Both are arranged in the seat cushion, wherein the triboelectric flexible pressure sensor is fixed on the seat surface of the seat cushion, so as to capture the tiny forces generated by human breathing and heartbeat to the maximum extent.

[0073] The signal processing circuit includes an amplifier, a filter, an analog-to-digital converter and a wireless transmission module. The electrical signal output by the sensor is amplified and filtered by the amplifier and the filter, and then converted into a digital signal by the analog-to-digital converter and output to the wireless transmission module, and then transmitted to the host computer for solution and analysis.

[0074] In this embodiment, a VMD algorithm for data decomposition is loaded in the host computer, which can decompose the original signals including the heart rate and respiratory rate collected by the sensor to obtain separate heart rate graphs and respiratory rate graphs.

[0075] Among them, VMD is a completely non-recursive modal variation and signal processing algorithm, which adaptively separates the mixed signal by setting the pre-decomposition scale K value. Specifically, in this embodiment, for the original signal collected by the sensor, the process of decomposing the heart rate signal and the respiratory rate signal by the VMD algorithm is as follows:

[0076] 1. Preprocess the original signal f(t) to remove the trend term and mean in the signal to ensure the accuracy of subsequent analysis. The polydetrend function is used to remove the trend term of the signal to prevent the trend term from affecting subsequent analysis; the signal is de-meaned to make the mean of the signal zero, which is convenient for subsequent spectrum analysis.

[0077] 2. Set parameters, including the number of modes K and bandwidth constraint α, as well as the center frequency ω of each mode k ;

[0078] In this embodiment, the input signal is the original mixed signal collected by the sensor; the number of modes K is 2, corresponding to the heart rate and respiratory rate signals; the bandwidth constraint α=4000 is used to control the bandwidth of the mode;

[0079] In addition, the initialization noise tolerance t au =0, no strict fidelity preservation; set DC=0 to not strengthen the DC component; set the convergence threshold ε=10 -9 , used to control the stopping condition of the iteration.

[0080] 3. Initialize the modal function and center frequency ω k (k=1,2) and parameter λ; then, an optimization model is constructed to minimize the sum of the energies of all modes plus the bandwidth penalty term to ensure that the energy of each mode is concentrated in a specific frequency range and that the modes do not overlap as much as possible;

[0081] 4. In the context of solving the decomposition of the original signal into breathing signals and BCG signals, the optimization model construction part aims to accurately separate the breathing signal and BCG signal by minimizing the sum of the energy of all modes plus the bandwidth penalty term while ensuring that the sum of the modes is equal to the original signal.

[0082] 5. Next, use the alternating direction multiplier method (ADMM) to iteratively update each mode function μ k (t) and center frequency ω k , and ensure that the sum of all modes is equal to the original signal f(t) by adjusting the Lagrange multipliers;

[0083] 6. The iteration process continues until the update amplitude of all modes is less than the preset threshold tol or the maximum number of iterations is reached, and finally the K modal functions obtained by decomposition and their corresponding center frequencies are output;

[0084] The update amplitude of the mode is calculated by the following formula:

[0085]

[0086] 7. According to the center frequency of each modal function, determine whether it is within the frequency range of the heart rate signal or the respiratory rate signal. If it is within the frequency range of the heart rate signal, then the modal function is used as the heart rate signal; if it is within the frequency range of the respiratory rate signal, then the modal function is used as the respiratory rate signal;

[0087] Specifically, two mode functions are decomposed by VMD algorithm, one of which is It mainly contains low-frequency components, and its frequency range is concentrated in 0.1Hz to 0.5Hz, which is consistent with the frequency characteristics of the respiratory signal, so it is identified as a respiratory signal. The second mode function It mainly contains higher-frequency components, and its frequency range is concentrated in 0.1Hz to 20Hz, which is consistent with the frequency characteristics of the cardiac shock signal (BCG signal), so it is identified as a BCG signal.

[0088] 8. To further verify the accuracy of signal separation, the periodogram function was used to calculate the power spectrum of each modal function. The results showed that the energy of the power spectrum of the respiratory signal was mainly concentrated in the low-frequency area, which was consistent with the frequency characteristics of the respiratory signal; the energy of the power spectrum of the BCG signal was mainly concentrated in the higher-frequency area, which was consistent with the frequency characteristics of the cardiac impact signal. Through the above steps, the VMD algorithm successfully decomposed the original signal into respiratory signals and BCG signals, ensuring the accuracy and reliability of signal separation. Although ECG signals are commonly used in cardiac assessments on the market, BCG signals have been studied to a certain extent, and their period is consistent with that of ECG. Fig. 9 As shown, its characteristic peak J lags behind the characteristic peak R of ECG by about 200ms.

[0089] Example 4

[0090] In this embodiment, a mechanical stability test was conducted on the triboelectric flexible pressure sensor. After the test, the peak-to-peak value of the sensor's output voltage remained stable, indicating that it has excellent mechanical stability and durability. The sensor can still maintain stable performance during long-term use and is suitable for long-term physiological signal monitoring.

[0091] This embodiment also provides the signal measurement results of the BCG monitoring system described in Example 3, such as Fig.10 As shown in Figure 2, the heart rate signal and respiratory rate signal separated from the original signal can be seen, through the proposed BCG monitoring system combined with the VMD algorithm, clear physiological signals can be separated.

[0092] In summary, the flexible pressure sensor and cushion-type physiological signal monitoring system proposed in the present invention show significant advantages in sensitivity, frequency response, stability and non-monitoring, providing strong support for the advancement of physiological signal monitoring technology.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A flexible pressure sensor for BCG monitoring, characterized in that: include: a first substrate, a first electrode, a second electrode, a second substrate, and an array microstructure; The first electrode is located on the first surface of the first substrate; The second surface of the first substrate is in contact with the first surface of the array microstructure; the second surface of the array microstructure is in contact with the second electrode; and the second substrate is in contact with the second electrode.

2. The flexible pressure sensor according to claim 1, characterized in that: The first surface of the array microstructure is formed with a plurality of regularly distributed microstructures; the microstructures include one or more of a convex hemisphere, a concave hemisphere, a triangular prism, a cylinder, a terrace, a cube and a cuboid, and the microstructures have multiple size features.

3. A method for preparing a flexible pressure sensor, characterized in that: The method includes: A silicon wafer is selected and cleaned and degreased, and a photoresist is spin-coated on the treated silicon wafer; The silicon wafer with the spin-coated photoresist is exposed through a mask, and then placed in a developer to remove excess photoresist, thereby obtaining a number of regularly distributed microstructure patterns; The photoresist is melted by high-temperature heat reflow, and low-temperature gas is blown to prevent the photoresist from being over-melted; after the photoresist is cooled and solidified, a stable microstructure is obtained; Covering the silicon wafer with microstructures with silica gel to make a mold, removing the mold and injecting microarray material into the grooves formed by the microstructures, and peeling off the mold after the microarray material is solidified; Obtaining a conductive filler electrode; mixing a flexible elastomer material prepolymer and a curing agent in a certain proportion to obtain a flexible elastomer material substrate, attaching the conductive filler electrode to the surface of the flexible elastomer material substrate, and dissolving the copper mesh with an etchant to obtain a first electrode; obtaining a second electrode in the same manner, and peeling off the flexible elastomer material substrate of the second electrode; The flexible pressure sensor is obtained by closely fitting the side of the flexible elastomer material substrate to which the first electrode is not attached and the side of the microarray material with microstructures distributed thereon, closely fitting the second electrode and the side of the microarray material without microstructures distributed thereon, and then fixing the second electrode between the microarray material and the flexible substrate using a layer of flexible substrate; The flexible elastomer material prepolymer and the curing agent are mixed in a certain proportion, poured on the surface of the first electrode after vacuum treatment, heated and cured to form a packaging layer, and the sensor packaging is completed.

4. The method according to claim 3, characterized in that The flexible elastomeric material base has an area greater than that of the first electrode.

5. The method according to claim 3, characterized in that: A plurality of the microstructures are regularly distributed on the surface of the microarray material, wherein the microstructures include one or more of convex hemispheres, concave hemispheres, triangular prisms, cylinders, terraces, cubes and cuboids, and the microstructures have multiple size features.

6. A cushion-type BCG monitoring system for BCG monitoring, characterized in that: It comprises a signal processing circuit, a seat cushion, a host computer and the flexible pressure sensor according to any one of claims 1 to 3; the flexible pressure sensor and the signal processing circuit are arranged in the seat cushion, and the flexible pressure sensor and the signal processing circuit are electrically connected; the signal processing circuit is wirelessly connected to the host computer; The flexible pressure sensor is fixed to the seat surface of the seat cushion and fits the seat cushion to capture the tiny forces generated by human breathing or heartbeat; The host computer decomposes the signal collected by the flexible pressure sensor through the VMD algorithm to obtain a heart rate signal and a respiratory frequency signal.

7. The cushion-type BCG monitoring system according to claim 6, characterized in that: The signal processing circuit includes a signal amplifier, a filter, an analog-to-digital converter and a wireless transmission module; the signal amplifier is used to amplify the electrical signal output by the flexible pressure sensor, the filter is used to filter the electrical signal, the analog-to-digital converter performs analog-to-digital conversion on the filtered electrical signal, and the wireless transmission module is used to transmit the analog-to-digital converted electrical signal to the host computer.

8. The cushion-type BCG monitoring system according to claim 6, characterized in that: The host computer decomposes the signal collected by the flexible pressure sensor by using a VMD algorithm, including: S1, input the signal collected by the sensor, initialize the number of modes, bandwidth constraint parameters and the center frequency of each mode; S2, construct an optimization model to minimize the sum of the energy of all modes and the sum of the bandwidth penalty term to ensure that the sum of each mode is equal to the original input signal; S3, iteratively update the function and center frequency of each mode using the alternating direction multiplier method, and ensure that the sum of all modes is equal to the original input signal by adjusting the Lagrange multiplier; S4. When the update amplitude of all modes is less than a preset threshold or reaches the maximum number of iterations, the iteration is stopped, and the decomposed mode function and its corresponding center frequency are output; S5. Determine whether the center frequency of each modal function is within the frequency range of the heart rate signal or the respiratory rate signal according to the center frequency of each modal function; if it is within the frequency range of the heart rate signal, identify it as a heart rate signal; if it is within the frequency range of the respiratory rate signal, identify it as a respiratory rate signal.

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