Multifunctional fabric-based flexible pressure sensor for fetal movement monitoring, preparation method and system

Abstract

The invention relates to a multifunctional fabric-based flexible pressure sensor for fetal movement monitoring, a preparation method and a system, and belongs to the technical field of vital sign monitoring. The fetal movement monitoring system comprises a waist-surrounding fixing belt, a sensing device, a control circuit and an upper computer subsystem. Wherein the sensing device is sewn on the side, close to the skin, of the waist surrounding fixing belt, and the sensing device is fixed to the abdomen position through the waist surrounding fixing belt; the sensing device is used for monitoring fetal movement signals, and the monitored fetal movement signals are transmitted to the upper computer subsystem through the control circuit to graphically display fetal movement information. The sensing device comprises a plurality of fabric-based flexible pressure sensors arranged in an array, two ends of each sensor are respectively connected with a first wire and a second wire, the first wire and the second wire are respectively connected with the control circuit through a multichannel analog switch, the multichannel analog switch is controlled by the control circuit to sequentially gate all the sensors, and the fabric-based flexible pressure sensors are connected with the control circuit. Therefore, electric signals generated by the sensors can be read out.

Description

Technical Field

[0001] The present invention belongs to the technical field of vital sign monitoring, and relates to wearable electronic devices, health monitoring, and electromagnetic protection, and in particular to a multifunctional fabric-based flexible pressure sensor for fetal movement monitoring, a preparation method, and a system. Background Art

[0002] The rapid development of communication technology and electronic equipment has brought about improved communication, time saving, convenient life and information explosion, but it has also brought about the trouble of electromagnetic waves. On the one hand, electromagnetic waves interfere with electronic equipment through adverse responses and complete operational failures. On the other hand, the thermal and non-thermal effects of electromagnetic waves through radiation seriously affect the health of humans, especially pregnant women and infants. Long-term exposure to excessive electromagnetic radiation may cause varying degrees of damage to the immune system, nervous system, reproductive system and hematopoietic system of pregnant women, which will have a serious impact on the growth and development of newborns.

[0003] Among the physiological indicators of the fetus, fetal movement is the most intuitive form of expression. Fetal movement refers to the activity of the fetus in the uterus, including the movement of the fetus's limbs, swinging, flipping and rolling. The number and intensity of fetal movements can clearly reflect the health status of the fetus. Traditionally, pregnant women count fetal movements by self-feeling, but this counting method is greatly limited. On the one hand, it is caused by the lack of medical knowledge and the inability of pregnant women to concentrate for a long time. On the other hand, pregnant women's perception of fetal movement is highly subjective and individual. At present, there are many devices used for fetal monitoring, but basically they are detected by ultrasound or based on fetal heart sound. There are no more mature products for home-use detection instruments, and most of the tests are often carried out in hospitals. Fetal movement detection in hospitals is mainly through ultrasound imaging and Doppler ultrasound. However, ultrasound equipment can only detect fetal movement for a short time. This is because ultrasound has a thermal effect. Long-term detection is harmful to the fetus and pregnant women. In addition, ultrasound equipment has the disadvantages of large size, high price and professional operation, and cannot be used at home. Common fetal ECG detectors use patch electrodes to collect mixed ECG signals from the pregnant woman's abdominal surface, and then use relevant algorithms to extract fetal ECG signals. This is an indirect way to obtain fetal ECG signals. It is simple to operate, and basically harmless to pregnant women. It is suitable for daily fetal ECG monitoring. However, the hard integrated device for collecting data is in contact with the pregnant belly, and its softness and skin-friendliness are relatively poor. In addition, the collected mixed ECG signals contain baseline drift, a large amount of myoelectric noise, power frequency and electromagnetic interference, which makes the detector have low accuracy and poor practicality.

[0004] Therefore, a household sensor with electromagnetic shielding function, high sensitivity, wide response and instant detection is designed for fetal movement monitoring. It can effectively help pregnant women obtain the fetal movement position, pressure and frequency anytime and anywhere to quickly understand the fetal condition, while reducing the impact of electromagnetic wave radiation caused by surrounding electronic devices to meet the ergonomic needs of pregnant women. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a multifunctional fabric-based flexible pressure sensor, preparation method and system for fetal movement monitoring, which performs fetal movement monitoring based on a multifunctional wearable fabric sensor, while achieving a wide response range and high sensitivity and having an electromagnetic shielding function, effectively helping pregnant women to self-measure the number of fetal movements anytime and anywhere, and quickly understand the condition of the fetus.

[0006] To achieve the above objectives, the present invention provides a system for fetal movement monitoring, which includes a waist-encircling fixing belt, a sensor device, a control circuit and a host computer subsystem.

[0007] The sensor device is sewn on the side of the waist-fixing belt close to the skin, and the sensor device is fixed at the abdomen through the waist-fixing belt; the sensor device is used for fetal movement signal monitoring, and the monitored fetal movement signal is transmitted to the upper computer subsystem through the control circuit. The upper computer subsystem filters, denoises and extracts features for the fetal movement monitoring data, and graphically displays the fetal movement information.

[0008] The sensing device comprises a first multi-channel analog switch, a second multi-channel analog switch and a plurality of multifunctional fabric-based flexible pressure sensors arranged in an array, wherein the two ends of each multifunctional fabric-based flexible pressure sensor are respectively connected with a first wire and a second wire; the first wire of each multifunctional fabric-based flexible pressure sensor is connected to a first flexible electrode through the first multi-channel analog switch; the second wire of each multifunctional fabric-based flexible pressure sensor is connected to a second flexible electrode through the second multi-channel analog switch. The first flexible electrode and the second flexible electrode are respectively connected to a control circuit, which sequentially selects each multifunctional fabric-based flexible pressure sensor by controlling the multi-channel analog switch to read out the electrical signal generated by each multifunctional fabric-based flexible pressure sensor.

[0009] Optionally, the waist-wrap is made of a flexible breathable material, with Velcro provided at both ends of the belt to adapt to the waist and abdominal circumference of pregnant women in different pregnancy stages.

[0010] Optionally, the multifunctional fabric-based flexible pressure sensor includes a strain layer, electrode layers respectively attached to both sides of the strain layer, and protective layers respectively used to protect the two electrode layers. The side of the electrode layer attached to the strain layer is loaded with conductive nanoparticles, and the sides of the two electrode layers not in contact with the strain layer are respectively connected to the first wire and the second wire through conductive glue.

[0011] Optionally, the control circuit includes a charge amplifier, a microcontroller and a power management module. The charge amplifier amplifies the electrical signal collected by the sensor device and outputs it to the microcontroller, the microcontroller converts the electrical signal into digital form and stores it, and transmits the collected data to the host computer subsystem via Bluetooth communication; the power management module is connected to the charge amplifier and the microcontroller respectively to provide power.

[0012] Optionally, the multifunctional fabric-based flexible pressure sensor may be a piezoresistive flexible pressure sensor, a pressure-capacitive flexible pressure sensor or a piezoelectric flexible pressure sensor.

[0013] In the piezoresistive flexible pressure sensor, the strain layer includes a fabric substrate and a film formed on the surface of the fabric substrate and mixed with polymer materials and magnetic nanoparticles, and the electrode layer is a nanofiber membrane loaded with conductive nanoparticles.

[0014] In the pressure-capacitive flexible pressure sensor, the strain layer includes a fabric substrate and a film formed on the surface of the fabric substrate and mixed with dielectric material and magnetic nanoparticles, and the electrode layer is a nanofiber membrane loaded with conductive nanoparticles.

[0015] In the piezoelectric flexible pressure sensor, the strain layer includes a fabric substrate and a piezoelectric fiber layer mixed with piezoelectric material and magnetic nanoparticles formed on the surface of the fabric substrate, and the electrode layer is a nanofiber membrane loaded with conductive nanoparticles.

[0016] In another aspect, the present invention provides a method for preparing a fabric-based flexible pressure sensor, the method comprising:

[0017] uniformly dispersing magnetic nanoparticles into a strain material solution to obtain a spinning solution;

[0018] The spinning solution is spun on a fabric substrate by using an electrospinning process to form a thin film, thereby obtaining a strain layer;

[0019] Weigh a certain mass of polymer material particles, clean the attached oil stains and pollutants and then soak them in ethanol for rinsing; remove the ethanol with deionized water and then dry; add the dried polymer material particles into a mixed solution of DMF and acetone, stir to completely dissolve the polymer material particles, prepare an electrospinning precursor solution, and make the precursor solution into a nanofiber membrane through an electrospinning process;

[0020] The nanofiber membrane is clamped and pre-stretched along the four vertex directions by an X-shaped tensile load method, and the stress applied in the four directions is the same; the stretched nanofiber membrane is fixed horizontally, and the conductive nanoparticle solution is sucked by a syringe and sprayed on the nanofiber membrane; the clamp is removed, and the nanofiber membrane is laid flat on the cardboard and covered with a layer of cardboard; the cardboard is clamped with a clamp and placed in an oven for drying to obtain an electrode layer;

[0021] The strain layer is sandwiched between two electrode layers, wherein the side of the electrode layer loaded with conductive nanoparticles is in contact with the strain layer; an adhesive is used to encapsulate the sensor to protect it from the external environment;

[0022] Then, wires are connected to each electrode layer respectively and fixed with conductive glue to obtain a piezoresistive flexible pressure sensor.

[0023] Optionally, the parameters of the electrospinning process include: voltage of 10 kV; distance from the spinneret tip to the collector of 10 cm; spinneret speed of 3500 r / min; spinning needle diameter of 0.21 mm; relative humidity of 50%; indoor temperature of 25° C.; and the receiving roller is coated with aluminum foil.

[0024] Optionally, in the mixed solution of DMF and acetone, the volume ratio of DMF to acetone is 1:1.

[0025] Optionally, when preparing the electrode layer, the conductive nanoparticles include but are not limited to multi-walled carbon nanotubes, carbon fibers, carbon black, metal nanoparticles, metal powders, metal nanowires, transition metal carbonitrides, graphene, etc., and the material of the nanofiber membrane includes but is not limited to polycaprolactone, polyurethane, polysuccinate, etc.

[0026] Optionally, for a piezoresistive flexible pressure sensor, the strain material is a polymer material, such as PDMS; for a pressure-capacitive flexible pressure sensor, the strain material is a dielectric material, such as silicone rubber, polyimide, etc.; for a piezoelectric flexible pressure sensor, the strain material is a piezoelectric material, such as PVDF, P (VDF-Tr FE), etc.

[0027] The beneficial effects of the present invention are:

[0028] (1) The present invention prepares the electrode layer through electrospinning technology, and adopts the "X-shaped stretching method" to load a large amount of conductive nanoparticles onto the nanofibers; the basic structure of the flexible capacitive pressure sensor is formed by the strain layer and the two electrode layers, and the instantaneous tensile strain is converted into the change of the electrical signal to obtain the relevant data of the fetal movement signal such as frequency, amplitude, etc., and feedback is given in a visual form. Home detection can be achieved while observing the health status of the fetus, which greatly reduces the time cost and operation complexity.

[0029] (2) The base material selected for the strain layer and the electrode layer in the present invention has good air permeability and is suitable for attachment to the surface of human skin without causing damage to the skin; magnetic nanoparticles are added to the sensor, which helps to absorb and reflect electromagnetic waves based on their own magnetic response and certain conductivity. Through reasonable particle distribution and structural design, a continuous or semi-continuous shielding layer can be formed to protect the internal signal of the sensor from external interference. The flexible sensor in the present invention can be measured by a microwave vector analyzer to have excellent high-frequency adaptability from the X band (8 to 12 GHz) to the Ku band (12 to 18 GHz), which is suitable for high-frequency electromagnetic interference (EMI) suppression scenarios. It can effectively shield the electromagnetic waves emitted by surrounding electronic products during fetal movement monitoring and reduce radiation to pregnant women and babies.

[0030] (3) Based on the conductive network formed by the introduced magnetic nanoparticles, heat is generated through the Joule heating effect after the current is applied. By finely controlling the continuity and current density of the conductive network, a fast-response, uniformly distributed local heating function can be achieved to meet the application requirements of temperature control, dehumidification or low-temperature protection. The Joule heating effect enables the sensor to generate heat efficiently in a short period of time, which is very suitable for application scenarios that require rapid temperature regulation, such as local heating of the knees, abdomen and waist of pregnant women, providing a warm and comfortable experience while maintaining low voltage operation to ensure safety of use.

[0031] (4) The present invention adopts a waist fixing belt made of flexible breathable fabric material, which can adapt to the size of the waist and abdomen of pregnant women in different cycles. At the same time, the good air permeability and skin-friendliness can increase the comfort of pregnant women, and it can be used in any scenario.

[0032] 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

[0033] 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:

[0034] Figure 1 It is a schematic diagram of the structure of the flexible pressure sensor;

[0035] Figure 2 It is a schematic diagram of the principle of piezoresistive flexible pressure sensor;

[0036] Figure 3 It is a schematic diagram of the principle of a pressure-capacitive flexible pressure sensor;

[0037] Figure 4 It is a schematic diagram of the principle of a piezoelectric flexible pressure sensor;

[0038] Figure 5 It is a schematic diagram of the structure of the fetal movement monitoring system;

[0039] Figure 6 This is a schematic diagram of a fetal movement monitoring platform;

[0040] Figure 7 It is a schematic diagram of the gating principle of each sensor of the sensing device;

[0041] Figure 8 It is a skin-friendly waist fixing belt;

[0042] Fig. 9 This is the electromagnetic shielding effectiveness curve of the flexible pressure sensor using magnetic nanoparticles in the present invention. DETAILED DESCRIPTION

[0043] 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.

[0044] 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.

[0045] 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.

[0046] Example 1

[0047] This embodiment provides a multifunctional fabric-based flexible pressure sensor for fetal movement monitoring, such as Figure 1 As shown, the multifunctional fabric-based flexible pressure sensor includes a first protective layer, a first electrode layer, a strain layer, a second electrode layer, and a second protective layer. The first protective layer is arranged opposite to the second protective layer, and the first electrode layer is arranged opposite to the second electrode layer.

[0048] The protective layer is located on the top of the sensor. It uses a material with good air permeability and flexibility (such as non-woven fabrics, polyurethane films, etc.) to protect the internal structure of the sensor, prevent the external environment from affecting the performance of the sensor, and has a certain mechanical strength.

[0049] According to the material used in the strain layer, sensors can be divided into piezoresistive, piezocalytic, piezoelectric, etc. For piezoresistive flexible pressure sensors, the strain layer usually needs to have strain sensitivity.

[0050] In this embodiment, for the piezoresistive flexible pressure sensor, the strain layer material includes magnetic nanoparticles (Fe 3 O 4 ) and a flexible polymer (PDMS can be used) are electrospinned to form a thin film on both sides of a non-woven fabric substrate to form a strain layer. 3 O 4 The particles are added to PDMS and Fe 3 O 4 The particles are evenly dispersed to avoid aggregation, and a spinning solution is obtained. 3 O 4 The content of the particles in the spinning solution was 15 wt%.

[0051] The electrospinning process parameters were set, including: voltage of 10 kV; distance from spinneret tip to collector of 10 cm; spinneret speed of 3500 r / min; spinning needle diameter of 0.21 mm; relative humidity of 50%; room temperature of 25° C.; and the receiving roller was wrapped with aluminum foil.

[0052] The assembly method of the piezoresistive flexible pressure sensor is as follows: the strain layer is contacted with the side of the two electrode sheets loaded with conductive nanoparticles, the strain layer is sandwiched between the two electrode sheets for assembly, and then the device is encapsulated with an adhesive to protect the device from the external environment. Then, a wire (copper wire, silver wire or copper foil) is connected to each electrode sheet separately, and fixed with a conductive adhesive (conductive adhesive is conductive silver paste or conductive carbon paste) to obtain a flexible capacitive pressure sensor. Among them, the adhesive is one of polyimide insulating tape, polydimethylsiloxane, and polyurethane medical tape.

[0053] Use Fe 3 O4 The dispersion of particles in PDMS forms a conductive network close to the critical point of conductivity, so that a small strain can cause the reconstruction of the network, resulting in a significant change in the overall resistance, such as Figure 2 As shown, the effective detection of fetal movement signals is achieved. 3 O 4 The magnetic and electrical conductivity of the particles themselves can absorb, reflect or scatter electromagnetic waves to form a shielding layer. When current is applied to the sensor, the internal resistance in the conductive network converts electrical energy into thermal energy, which can also realize the heating function.

[0054] Example 2

[0055] This embodiment provides a pressure-capacitive flexible pressure sensor. Compared with the piezoresistive flexible pressure sensor, the pressure-capacitive sensor works based on the principle of capacitance change. Figure 3 As shown in the figure, when external pressure is applied, the electrode spacing or dielectric constant of the sensor changes, resulting in an increase or decrease in capacitance. In order to enhance the capacitance response performance, the strain layer of the pressure-capacitive flexible pressure sensor uses a dielectric material (such as silicone rubber) as a substrate, and introduces electromagnetic shielding and Joule heating functions by doping magnetic nanoparticles.

[0056] The strain layer is woven on a non-woven fabric substrate by an electrospinning process. Specifically, magnetic nanoparticles are first dispersed in a dielectric material solution, and ultrasonic or mechanical stirring is used to evenly disperse the magnetic nanoparticles to avoid forming agglomerate structures to obtain a spinning solution; then the spinning solution is spun on both sides of the non-woven fabric substrate by an electrospinning process to obtain a strain layer. The content of magnetic nanoparticles in the spinning solution is 10wt%, and the specific ratio can be adjusted according to the response sensitivity requirements of the sensor.

[0057] When magnetic nanoparticles are added to dielectric materials in appropriate amounts, they can improve the shielding capability of the dielectric layer and prevent external electromagnetic interference. In addition, when an AC or DC electric field is applied between electrodes, local heating is achieved by controlling the conductive path, helping to stabilize dielectric properties or achieve thermal management.

[0058] The assembly method of the pressure-capacitive flexible pressure sensor is as follows: the strain layer is contacted with the side of the two electrode sheets loaded with conductive nanoparticles, the strain layer is sandwiched between the two electrode sheets for assembly, and then the device is encapsulated with an adhesive to protect the device from the external environment. Then, a wire (copper wire, silver wire or copper foil) is connected to each electrode sheet separately, and fixed with a conductive adhesive (conductive adhesive is conductive silver paste or conductive carbon paste) to assemble a flexible pressure sensor. Among them, the adhesive is one of polyimide insulating tape, polydimethylsiloxane, and polyurethane medical tape.

[0059] Example 3

[0060] This embodiment provides a piezoelectric flexible pressure sensor, which realizes force-to-electricity conversion based on the piezoelectric effect. Figure 4 As shown, specifically, when external pressure or strain is applied to the sensor, the electric dipoles inside the piezoelectric material in the sensor will rearrange, resulting in charge accumulation, and a voltage signal related to the size and direction of the external force will be generated on the electrode layer of the sensor. By measuring this voltage change, the external force can be detected.

[0061] The strain layer of the piezoelectric flexible pressure sensor adopts a fabric substrate, and a piezoelectric material (PVDF can be used) is formed on the surface thereof. Among them, the piezoelectric material is required to form a specific crystal phase (usually β phase).

[0062] Specifically, the method for preparing the strained layer includes:

[0063] 1) Prepare PVDF (polyvinylidene fluoride) precursor solution. According to the required solution concentration, weigh an appropriate amount of PVDF to a mass ratio of 20%. Add PVDF powder to a solvent (such as DMF or NMP). For example, add 10 grams of PVDF powder to 90 milliliters of DMF.

[0064] 2) Stir the solution with a magnetic stirrer and heat to 70°C to ensure that the PVDF is completely dissolved. The dissolution process generally takes 4 to 6 hours until the solution is transparent and free of particulate matter.

[0065] 3) Adding magnetic nanoparticles to a PVDF precursor solution and uniformly dispersing the magnetic nanoparticles in the PVDF precursor solution by stirring. The content of the magnetic nanoparticles in the PVDF precursor solution is 5wt%. When introducing the magnetic nanoparticles, it is necessary to ensure that the particle surface is modified or optimized to avoid interfering with the formation of the piezoelectric crystal phase and appropriately promote the β-phase orientation.

[0066] 4) The piezoelectric fiber layer is formed on both sides of the fabric substrate by electrospinning process, thereby obtaining a strain layer.

[0067] In this embodiment, the assembly method of the piezoelectric flexible pressure sensor is consistent with that in Embodiment 1 or Embodiment 2. By adding magnetic nanoparticles, the magnetic nanoparticles are distributed in the piezoelectric layer to form a local conductive network, which can absorb or scatter external electromagnetic waves. At the same time, appropriate conductive paths can generate local heating when current is applied to the sensor, which is convenient for temperature control and prevents low temperature environment from affecting the sensing performance.

[0068] Example 4

[0069] This embodiment provides a system for fetal movement monitoring, such as Figure 5 and Figure 6As shown in the figure, it includes a sensor device, a charge amplifier, an ESP32 microcontroller, a power management module and a host computer subsystem. The fetal movement monitoring sensor device and the fetal movement signal acquisition instrument are connected by a medical ECG lead wire, which can well shield the external interference noise. The fetal movement signal generated by the sensor device is output as an analog signal through the charge amplifier. The internal ADC of the STM32 microcontroller converts the analog signal into a digital signal, and the collected data is sent to the host computer subsystem in real time through the built-in Bluetooth module for monitoring, so that the family doctor can understand it in time.

[0070] The sensing device is sewn into a skin-friendly waist-fixing belt, which includes a multi-channel analog switch and a plurality of fabric-based flexible pressure sensors arranged in an n×n array. Any sensor proposed in Embodiments 1 to 3 can be selected, and the multi-channel analog switch can be TMUX1308A. In this embodiment, a pressure-capacitive flexible pressure sensor is used, and a 7×7 array is formed, such as Figure 7 As shown, in the array, both ends of each sensor are connected to a first wire and a second wire (the first wire and the second wire are connected to the two electrode layers of the sensor respectively), wherein the first wire of each sensor in each column is connected to the first multi-channel analog switch, and the second wire of each sensor in each row is connected to the second multi-channel analog switch, the output end of the first multi-channel analog switch is connected to the column electrode (i.e., the first flexible electrode), and the output end of the second multi-channel analog switch is connected to the row electrode (i.e., the second flexible electrode), and the first and second flexible electrodes are connected to the charge amplifier. The two multi-channel analog switches are both controlled by the ESP32 microcontroller to control the on and off of each channel switch, so that the gating of a single sensor can be realized.

[0071] For the sensing device, the signal readout of each sensor in its array is completed by sequential scanning. Specifically, the sensors with smaller rows in the array are scanned first, and then the sensors with smaller columns in the array are scanned, that is, the scanning is performed in the order of: row 1, column 1, row 2, column 1, row 3, column 1, …, row 1, column 2, row 2, column 2, row 3, column 2, …, row 1, column 3, row 2, column 3, …, row 1, column 3, row 2, column 3, row 3, …, and during the scanning process, the channel switches corresponding to the rows and columns of the scanned sensors are closed in turn, so that the electrical signals generated by the scanned sensors are read out through the first and second flexible electrodes.

[0072] The charge amplifier is used to amplify the signal output by the sensor device. The amplifier can use the OPA2206 chip from TI. OPA2206 has excellent performance and is an ideal choice for high-precision and low-power systems. Its single-power supply feature simplifies the design of the power supply circuit and reduces the size of the instrument. It uses a vertical dual-op-amp instrumentation amplifier circuit to achieve high input impedance, high common-mode rejection ratio (CMRR), low distortion and low noise, etc., to reduce interference with fetal movement signals.

[0073] ESP32 is a high-performance dual-core microcontroller from Espressif, with a maximum operating frequency of 240MHz and built-in 520KB SRAM. In the design of the fetal movement monitoring system, ESP32's 12-bit multi-channel ADC is used to collect analog signals from fetal movement sensors with high precision, and supports multi-channel solutions to achieve real-time collection of fetal movement signals. The sampling rate of the ADC is set to 100Hz to ensure the real-time nature of the signal. The DMA module of ESP32 is used to achieve automatic data transmission, further reducing the CPU load and improving data processing efficiency. The timer is used to control the sampling cycle to ensure the uniformity of the collected data. In addition, ESP32 integrates Wi-Fi and low-power Bluetooth (BLE) modules, which can meet high data processing requirements and support local and remote transmission of fetal movement data. Its BLE module supports both BLE 4.2 and Bluetooth classic mode. Through this module, wireless transmission of fetal movement data can be achieved at low power consumption, while supporting near-field connection to mobile devices or host computers to build a flexible wireless communication system. The Bluetooth communication mode of ESP32 is UART serial communication. The default baud rate is set to 115200, the data bit is 8 bits, and the stop bit is 1 bit. It supports multiple baud rate configurations and has high communication flexibility.

[0074] Considering the portability and safety of fetal movement signal acquisition equipment, the fetal movement monitoring system uses lithium batteries for power supply. The power management module mainly includes three parts: voltage stabilization circuit, charging circuit and power on / off control circuit.

[0075] The voltage stabilization circuit uses T1's TLV70033 voltage stabilization chip to achieve voltage stabilization. Its quiescent current is as low as 31μA and its maximum output current is 200mA. The chip is small in size and simple in circuit, making it suitable for portable devices. The charging circuit uses a circuit based on Microchip's MCP73831 lithium battery charging management controller. The MCP73831 uses a constant voltage charging method to charge lithium batteries, and can automatically limit the charging current to reduce the chip temperature under high ambient temperatures. This thermal regulation optimizes the charging time while ensuring device reliability. The power on / off control circuit uses the dual MOS tube NTJD1155L based on ON Semiconductor. This device is particularly suitable for portable electronic devices that require control signals, low battery voltages, and high load currents.

[0076] The Qt-based host subsystem connects to ESP32 via Bluetooth to collect and graphically display fetal movement information in real time to help pregnant women and medical staff understand the health status of the fetus. The host subsystem includes multiple core modules: the Bluetooth communication module uses Qt Bluetooth to achieve wireless communication with the sensor device, and is responsible for data search, connection and reception to ensure stable transmission; the data processing module filters, denoises and extracts features of fetal movement data through the Qt data processing library or custom algorithms, and calculates key indicators such as fetal movement frequency, amplitude and duration; the graphical interface module builds an intuitive user interface based on Qt Widgets or Qt Quick (QML), displays real-time curves, historical data tables and statistical information, and supports parameter settings and personalized display; the data storage module uses Qt SQL or file storage system to save data to the local database or file system, and supports exporting CSV or PDF reports for sharing; the alarm and reminder module has a built-in threshold library for fetal movement frequency and amplitude, and reminds users through sound or messages when abnormalities are detected. The host subsystem has cross-platform compatibility and supports systems such as Windows, macOS and Linux.

[0077] The host computer subsystem also has a Bluetooth connection management function, which can automatically search for connected sensor devices and reconnect when interrupted; it has a real-time data visualization function, which allows fetal movement data to be intuitively displayed in the form of a curve, and supports data zooming and dragging; it has historical data analysis and trend display functions to help analyze long-term fetal movement patterns; it has a personalized setting function that allows adjustment of monitoring parameters; it has data security and privacy protection functions, supports data encryption and backup, and ensures data security and user privacy.

[0078] In addition, in the waist-wrap fixing belt, since magnetic nanoparticles are added to the sensors that make up the sensing device, the magnetic response and certain conductivity of the magnetic nanoparticles help absorb and reflect electromagnetic waves. Through reasonable particle distribution and structural design, a continuous or semi-continuous shielding layer can be formed to protect the internal signal of the sensor from external interference. Fig. 9 The figure shows the electromagnetic shielding effectiveness curve of the sensor using magnetic nanoparticles under high-frequency electromagnetic interference. Fig. 9 It can be seen that the shielding effectiveness (SE) varies with the change of electromagnetic frequency, and the EMI value is less than -18dB in the range of 8 to 13GHz. The shielding performance of magnetic nanoparticles is steadily improved in a wide frequency band (≥5GHz), which solves the limitation of insufficient high-frequency attenuation of traditional materials. Fig. 9It can be seen that the average electromagnetic shielding effectiveness of the sensor in the range of 8 to 18 GHz reaches -22dB, indicating that the sensor has excellent high-frequency adaptability from the X band (8 to 12 GHz) to the Ku band (12 to 18 GHz), and is suitable for high-frequency electromagnetic interference (EMI) suppression scenarios. The sensor is verified by a vector network analyzer (VNA) in a standard test environment to comply with IEEE 299 and other electromagnetic shielding effectiveness test specifications. The above data shows that the sensor has SE ≤ -20dB at 8 to 9 GHz and 10 to 13 GHz, meeting the industrial-grade high-frequency shielding requirements (SE ≤ -20dB).

[0079] On the other hand, the conductive network formed by nanoparticles generates heat through the Joule heating effect after applying current. By finely controlling the continuity and current density of the conductive network, a fast-response, uniformly distributed local heating function can be achieved to meet application requirements such as temperature control, dehumidification or low-temperature protection.

[0080] Example 5

[0081] This embodiment provides a method for preparing a piezoresistive flexible pressure sensor, the method comprising:

[0082] 1. Prepare the strain layer: Prepare PDMS solution and mix Fe 3 O 4 The particles were added to the PDMS solution and the Fe 3 O 4 The particles are evenly dispersed to obtain a spinning solution. 3 O 4 The content of particles in the spinning solution is 15wt%. The spinning solution is made into a film on both sides of a fabric substrate using an electrostatic spinning process to obtain a strain layer. The thickness of the film is controlled between 50 and 200 μm. The fabric can be a non-woven fabric.

[0083] 2. Preparation of polyurethane nanofiber precursor: Weigh a certain mass of TPU particles, clean the attached oil stains and pollutants with detergent, and then soak them in ethanol for 5 minutes; then wash them with deionized water for several times, and after removing the ethanol, put the TPU particles into a 50°C oven and dry them for 5 minutes; then add them to a mixed solution of DMF: acetone = 1: 1 (V / V), and stir magnetically at room temperature for 8 hours to completely dissolve the TPU particles to obtain a spinning solution with a mass fraction of 5%, which is the precursor solution before the electrospinning process.

[0084] 3. Preparation of polyurethane nanofibers: The parameters for preparing TPU nanofiber membrane by electrospinning were set, including: voltage of 10 kV; distance from spinneret tip to collector of 10 cm; spinneret speed of 0.3 mL / h; spinning needle diameter of 0.21 mm; relative humidity of 50%; room temperature of 25°C; and the receiving roller was coated with aluminum foil.

[0085] By using the above process parameters, a TPU nanofiber membrane with uniform size distribution and smooth surface can be obtained, with a breaking stress of 15MPa and a breaking strain of 361%. The average thickness of the electrospun membrane is 0.05-0.5mm, the length is 25.01mm, and the width is 25.03mm.

[0086] 4. Preparation of electrode layer: Use X-shaped tensile load method to clamp and pre-stretch the TPU nanofiber membrane along the four vertex directions, apply the same stress in four directions, and the area of ​​the fiber membrane after stretching is expanded by 25%; fix it on the laboratory bench with tape, use a 1mL syringe to absorb the conductive nanoparticle solution, and spray it on the TPU nanofiber membrane; remove the clamp, lay the loaded fiber membrane flat on the cardboard, and cover it with a layer of cardboard; clamp the cardboard with a clamp, place it in a 60℃ oven and dry it for 1h before taking it out.

[0087] In the prepared electrode sheet, the mass percentage of the conductive nanoparticles in the electrospinning membrane is 1.5%, the thickness of the electrode sheet is 0.3 mm, and the conductivity is 300 S / m.

[0088] 5. Assemble the flexible pressure sensor: assemble the strain layer by sandwiching it between two electrode sheets. Specifically, make the strain layer contact the side of the two electrode sheets that are loaded with conductive nanoparticles. Use adhesive packaging to protect the device from the external environment.

[0089] 6. Connect a wire (copper wire, silver wire or copper foil) to each electrode sheet of the sensor and fix them with a conductive adhesive (conductive adhesive is conductive silver paste or conductive carbon paste) to obtain a piezoresistive flexible pressure sensor. The adhesive is one of polyimide insulating tape, polydimethylsiloxane and polyurethane medical tape.

[0090] Based on the prepared piezoresistive flexible pressure sensor, this embodiment also provides Figure 8The assembly method of the skin-friendly waist-circling fixing belt shown. Specifically, the flexible pressure sensors are first arranged in a 7×7 array and sewn on the side of the fabric close to the skin. The sensing device is connected to the external circuit through a wire. Specifically, one of the electrode layers of each sensor is connected to a first wire, and the other electrode layer is connected to a second wire. In the array, the first wire of each sensor in each column is connected to the first multi-channel analog switch, and the second wire of each sensor in each row is connected to the second multi-channel analog switch. The output end of the first multi-channel analog switch is connected to the first flexible electrode, and the output end of the second multi-channel analog switch is connected to the second flexible electrode. The first and second flexible electrodes are then connected to the charge amplifier. This wiring method not only reduces the number of wire connections, making the overall line clearer, but also reduces costs.

[0091] Among them, the fabric base and the skin-friendly waist-protecting strap are both woven by shuttle weaving knitting technology, which ensures the softness and comfort between the strap and the abdomen; a male Velcro and a female Velcro are respectively provided at the two ends of the strap away from the abdomen attachment body, and the user can adjust the tightness according to the length of the strap for adhesion.

[0092] Example 6

[0093] This embodiment provides a method for preparing a pressure-capacitive flexible pressure sensor, which is different from the method for preparing a piezoresistive flexible pressure sensor described in Example 5 only in the preparation method of the strain layer.

[0094] Specifically, in this embodiment, the strain layer is prepared as follows:

[0095] The magnetic nanoparticles are dispersed in a dielectric material solution, and an ultrasonic cleaner or a high shear force dispersion device is used to disperse the magnetic nanoparticles so that the magnetic nanoparticles are evenly distributed in the solution to avoid agglomeration. The content of the magnetic nanoparticles in the solution is adjusted to 10 wt%.

[0096] The electrospinning process was used to spin the solution containing magnetic nanoparticles onto both sides of the nonwoven fabric. The electrospinning parameters were set as follows: voltage of 10 kV; distance from the spinneret tip to the collector of 10 cm; spinneret speed of 3500 r / min; spinning needle diameter of 0.21 mm; relative humidity of 50%; room temperature of 25°C; and the receiving roller was wrapped with aluminum foil.

[0097] Example 7

[0098] This embodiment provides a method for preparing a piezoelectric flexible pressure sensor, which is different from the method for preparing a piezoresistive flexible pressure sensor described in Example 5 only in the preparation method of the strain layer.

[0099] Specifically, the preparation method of the strain layer of the piezoelectric flexible pressure sensor is as follows:

[0100] 1) Prepare PVDF (polyvinylidene fluoride) precursor solution, weigh an appropriate amount of PVDF to a mass ratio of 20% according to the required solution concentration. Add PVDF powder to a solvent (such as DMF or NMP), for example, add 10 grams of PVDF powder to 90 ml of DMF.

[0101] 2) Stir the solution with a magnetic stirrer and heat to 70°C to ensure that the PVDF is completely dissolved. The dissolution process generally takes 4 to 6 hours until the solution is transparent and free of particulate matter.

[0102] 3) Adding magnetic nanoparticles to a PVDF precursor solution and uniformly dispersing the magnetic nanoparticles in the PVDF precursor solution by stirring. The content of the magnetic nanoparticles in the PVDF precursor solution is 5wt%. When introducing the magnetic nanoparticles, it is necessary to ensure that the particle surface is modified or optimized to avoid interfering with the formation of the piezoelectric crystal phase and appropriately promote the β-phase orientation.

[0103] 4) The piezoelectric fiber layer is formed on both sides of the fabric substrate by electrospinning process, thereby obtaining a strain layer.

[0104] The electrospinning process parameters are as follows: voltage of 10 kV; distance from spinneret tip to collector of 10 cm; spinneret speed of 3500 r / min; spinning needle diameter of 0.21 mm; relative humidity of 50%; indoor temperature of 25°C; and receiving roller wrapped with aluminum foil.

[0105] 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 system for fetal movement monitoring, characterized in that: It includes a waist-encircling fixing belt, a sensor device, a control circuit and a host computer subsystem; the sensor device is sewn on the side of the waist-encircling fixing belt close to the skin, and the sensor device is fixed to the abdomen through the waist-encircling fixing belt; the sensor device is used for fetal movement signal monitoring, and the monitored fetal movement signal is transmitted to the host computer subsystem through the control circuit, and the host computer subsystem filters, denoises and extracts features for the fetal movement monitoring data, and graphically displays the fetal movement information; The sensing device comprises a first multi-channel analog switch, a second multi-channel analog switch and a plurality of multifunctional fabric-based flexible pressure sensors arranged in an array, wherein two ends of each multifunctional fabric-based flexible pressure sensor are respectively connected to a first wire and a second wire; The first wire of each multifunctional fabric-based flexible pressure sensor is connected to the first flexible electrode through the first multi-channel analog switch; the second wire of each multifunctional fabric-based flexible pressure sensor is connected to the second flexible electrode through the second multi-channel analog switch; the first flexible electrode and the second flexible electrode are respectively connected to the control circuit, and the control circuit sequentially selects each multifunctional fabric-based flexible pressure sensor by controlling the multi-channel analog switch to read out the electrical signal generated by each multifunctional fabric-based flexible pressure sensor.

2. The system according to claim 1, characterized in that The multifunctional fabric-based flexible pressure sensor includes a strain layer, electrode layers respectively attached to two sides of the strain layer, and protective layers respectively used to protect the two electrode layers; the side of the electrode layer attached to the strain layer is loaded with conductive nanoparticles; wherein the sides of the two electrode layers not in contact with the strain layer are respectively connected to the first wire and the second wire through conductive glue.

3. The system according to claim 1, characterized in that The control circuit includes a charge amplifier, a microcontroller and a power management module; the charge amplifier is connected to the first flexible electrode and the second flexible electrode respectively, amplifies the electrical signal collected by the sensor device and outputs it to the microcontroller, the microcontroller stores the electrical signal after analog-to-digital conversion, and transmits the collected data to the host computer subsystem via Bluetooth communication; the power management module is connected to the charge amplifier and the microcontroller respectively.

4. The system according to claim 1, characterized in that The multifunctional fabric-based flexible pressure sensor is a piezoresistive flexible pressure sensor, a pressure-capacitive flexible pressure sensor or a piezoelectric flexible pressure sensor.

5. The system according to claim 2 or 4, characterized in that: In the piezoresistive flexible pressure sensor, the strain layer includes a fabric substrate and a film formed on the surface of the fabric substrate and mixed with polymer materials and magnetic nanoparticles, and the electrode layer is a nanofiber film loaded with conductive nanoparticles.

6. The system according to claim 2 or 4, characterized in that: In the pressure-capacitive flexible pressure sensor, the strain layer includes a fabric substrate and a thin film formed on the surface of the fabric substrate and mixed with dielectric materials and magnetic nanoparticles, and the electrode layer is a nanofiber membrane loaded with conductive nanoparticles.

7. The system according to claim 2 or 4, characterized in that: In the piezoelectric flexible pressure sensor, the strain layer includes a fabric substrate and a piezoelectric fiber membrane mixed with piezoelectric material and magnetic nanoparticles formed on the surface of the fabric substrate, and the electrode layer is a nanofiber membrane loaded with conductive nanoparticles.

8. A method for preparing a multifunctional fabric-based flexible pressure sensor for fetal movement monitoring, characterized in that: The method includes: uniformly dispersing magnetic nanoparticles into a strain material solution to obtain a spinning solution; The film is made on both sides of a fabric substrate by using an electrospinning process to obtain a strain layer; Weigh a certain mass of polymer material particles, clean the attached oil stains and pollutants and then soak them in ethanol for rinsing; remove the ethanol with deionized water and then dry; add the dried polymer material particles into a mixed solution of DMF and acetone, stir to completely dissolve the polymer material particles, prepare an electrospinning precursor solution, and make the precursor solution into a nanofiber membrane through an electrospinning process; The nanofiber membrane is clamped and pre-stretched along the four vertex directions by an X-shaped tensile load method, and the stress applied in the four directions is the same; the stretched nanofiber membrane is fixed horizontally, and the conductive nanoparticle solution is sucked by a syringe and sprayed on the nanofiber membrane; the clamp is removed, and the nanofiber membrane is laid flat on the cardboard and covered with a layer of cardboard; the cardboard is clamped with a clamp and placed in an oven for drying to obtain an electrode layer; The strain layer is sandwiched between two electrode layers, wherein the side of the electrode layer loaded with conductive nanoparticles is in contact with the strain layer; an adhesive is used to encapsulate the sensor to protect it from the external environment; Then, wires are connected to each electrode layer respectively and fixed with conductive glue to obtain a piezoresistive flexible pressure sensor.

9. The method according to claim 8, characterized in that The parameters of the electrospinning process include: voltage of 10 kV; distance from the spinneret tip to the collector of 10 cm; spinneret speed of 3500 r / min; spinning needle diameter of 0.21 mm; relative humidity of 50%; indoor temperature of 25° C.; and receiving roller coated with aluminum foil.

10. The method according to claim 8, characterized in that In the mixed solution of DMF and acetone, the volume ratio of DMF to acetone is 1:1.

Images