A multi-functional fabric-based flexible pressure sensor for fetal movement monitoring, method of manufacture and system

Abstract

The present application relates to a kind of multifunctional fabric-based flexible pressure sensor for fetal movement monitoring, preparation method and system, belong to vital sign monitoring technical field.Fetal movement monitoring system includes waist fixing belt, sensing device, control circuit and host computer subsystem.Wherein, sensing device is sewn in waist fixing belt close to the side of skin, and sensing device is fixed in abdominal position by waist fixing belt;Sensing device is used for fetal movement signal monitoring, and the fetal movement signal monitored is transmitted to host computer subsystem by control circuit and graphically shows fetal movement information.Sensing device includes a plurality of fabric-based flexible pressure sensors arranged in array, and the two ends of each sensor are respectively connected with first wire and second wire, and first wire and second wire are respectively connected with control circuit by a multi-channel analog switch, and each sensor is sequentially selected by control circuit control multi-channel analog switch, to read out the electrical signal generated by each sensor.

Description

TECHNICAL FIELD

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

[0002] The rapid development of communication technology and electronic devices has brought about improved communication, time saving, convenient life and information explosion, but at the same time, it has also brought about the trouble of electromagnetic waves. On the one hand, electromagnetic waves interfere with electronic devices through bad response and complete operation failure, and on the other hand, electromagnetic waves seriously affect the health of humans, especially pregnant women and infants, through the heat effect and non-thermal effect generated by radiation. Long-term exposure to excessive electromagnetic radiation environment may cause different 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, turning and rolling, etc. 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 due to the lack of medical knowledge of pregnant women and the inability to concentrate for a long time, and on the other hand the perception of fetal movement by pregnant women has high subjectivity and individual difference. There are many devices for fetal monitoring at present, but basically they are detected by ultrasonic or based on fetal heart sound, and there is no mature product for home type detection instrument, and most of the detection is usually carried out in hospitals. Fetal movement detection in hospitals is mainly through ultrasonic imaging and Doppler ultrasound. But the ultrasonic device can only detect fetal movement for a short time, because ultrasonic waves have a heat effect, and long-term detection is harmful to the fetus and the pregnant woman, and the ultrasonic device has the disadvantages of large size, high price and the need for professional operation, and cannot be used in the family. The common fetal electrocardiogram detector uses a patch electrode to collect mixed electrocardiogram signals from the abdominal surface of the pregnant woman, and then uses a related algorithm to extract the fetal electrocardiogram signal, which is an indirect way to obtain the fetal electrocardiogram signal, simple to operate, basically harmless to the pregnant woman, and suitable for daily fetal electrocardiogram monitoring, but the hard integrated device for collecting has relatively poor softness and skin friendliness, and the mixed electrocardiogram signals collected contain baseline drift, a large amount of electromyographic noise, power frequency and electromagnetic interference, so that the detector has the problems of low accuracy and poor practicability.

[0004] Therefore, a household sensor with electromagnetic shielding function, high sensitivity, wide response and instant detection is designed for fetal movement monitoring, which can effectively help pregnant women to obtain fetal movement position, pressure and frequency at any time and anywhere, quickly understand the fetal condition, and reduce the influence of electromagnetic wave radiation caused by surrounding electronic equipment, so as to meet the needs of pregnant women in ergonomics. SUMMARY

[0005] Therefore, the present application aims to provide a multifunctional fabric-based flexible pressure sensor for fetal movement monitoring, a preparation method and a system, which can monitor fetal movement based on a multifunctional wearable fabric sensor, has electromagnetic shielding function while realizing wide response range and high sensitivity, and effectively helps pregnant women to self-test fetal movement frequency at any time and anywhere, quickly understand the fetal condition.

[0006] To achieve the above-mentioned purpose, in one aspect, the present application provides a system for fetal movement monitoring, which comprises a waist fixing belt, a sensing device, a control circuit and an upper computer subsystem.

[0007] The sensing device is sewn on the side close to the skin of the waist fixing belt, and the sensing device is fixed on the abdominal position through the waist fixing belt; the sensing 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 performs filtering, denoising and feature extraction on the fetal movement monitoring data, and displays the fetal movement information in a graphical manner.

[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, and the two ends of each multifunctional fabric-based flexible pressure sensor are respectively connected with a first lead wire and a second lead wire; the first lead wire of each multifunctional fabric-based flexible pressure sensor is connected with a first flexible electrode through the first multi-channel analog switch; and the second lead wire of each multifunctional fabric-based flexible pressure sensor is connected with a second flexible electrode through the second multi-channel analog switch. The first flexible electrode and the second flexible electrode are respectively connected with the control circuit, and the control circuit sequentially selects each multifunctional fabric-based flexible pressure sensor through the multi-channel analog switch to read the electric signal generated by each multifunctional fabric-based flexible pressure sensor.

[0009] Optionally, the waist fixing belt is made of a flexible and breathable material, and a magic tape is arranged at each end of the fixing belt, which can adapt to the waist circumference of pregnant women in different gestational weeks.

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

[0011] Optionally, the control circuit comprises a charge amplifier, a microcontroller and a power management module, wherein the charge amplifier amplifies the electrical signal collected by the sensing device and outputs the amplified electrical signal to the microcontroller, the microcontroller stores the analog-to-digital converted electrical signal and transmits the collected data to the upper computer subsystem through Bluetooth communication; the power management module is connected with the charge amplifier and the microcontroller respectively and is used for providing power.

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

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

[0014] In the piezocapacitive flexible pressure sensor, the strain layer comprises a fabric substrate and a film formed on the surface of the fabric substrate and containing dielectric material and magnetic nanoparticles, and the electrode layer is a nanofiber film loaded with conductive nanoparticles.

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

[0016] In another aspect, the application provides a method for preparing a fabric-based flexible pressure sensor, which comprises:

[0017] The magnetic nanoparticles are uniformly dispersed in a strain material solution to obtain a spinning solution;

[0018] The spinning solution is spun on a fabric substrate by an electrospinning process to form a film and obtain a strain layer;

[0019] A certain amount of polymer material particles are weighed, cleaned of attached oil stains and contaminants, soaked in ethanol for rinsing, dried after removing ethanol with deionized water, and added to a mixed solution of DMF and acetone, stirred to completely dissolve the polymer material particles, and configured to obtain an electrospinning precursor solution, which is processed into a nanofiber film by an electrospinning process;

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

[0021] The strain layer is clamped between the two electrode layers, and the side of the electrode layer loaded with conductive nanoparticles is in contact with the strain layer; an adhesive is used for packaging to protect the sensor from the external environment;

[0022] Then, a lead wire is connected to each electrode layer respectively, and the lead wire is fixed using conductive glue to obtain a piezoresistive flexible pressure sensor.

[0023] Optionally, the parameters of the electrospinning process include: a voltage of 10 kV; a distance between the spinneret tip and the collector of 10 cm; a spinneret speed of 3500 r / min; a spinning needle diameter of 0.21 mm; a relative humidity of 50%; and an indoor temperature of 25 DEG C; and the receiving roller is wrapped 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, in the preparation of the electrode layer, the conductive nanoparticles include but are not limited to multi-walled carbon nanotubes, carbon fibers, carbon black, metal nanoparticles, metal powder, metal nanowires, transition metal carbonitride, graphene, etc., and the material of the nanofiber membrane includes but is not limited to polycaprolactone, polyurethane, polybutanedioate, etc.

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

[0027] The present application has the following advantages:

[0028] (1) The electrode layer is prepared by the electrospinning technology, and the "X-shaped tensile method" is used to load a large amount of conductive nanoparticles on the nanofiber; the basic structure of the flexible capacitive pressure sensor is formed by the strain layer and the two electrode layers, the real-time tensile strain is converted into the change of the electric signal to obtain the related data of the fetal movement signal such as frequency, amplitude, etc., and the feedback is performed in a visual form, so that the fetal health status can be observed and the home detection can be realized, and the time cost and the operation complexity are greatly reduced.

[0029] (2) The substrate materials selected for the strain layer and electrode layer in this invention have good air permeability, making them suitable for adhesion to the surface of human skin without causing damage. Magnetic nanoparticles are added to the sensor. Based on the inherent magnetic response and certain conductivity of the magnetic nanoparticles, they 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. The flexible sensor in this invention has excellent high-frequency adaptability in the X-band (8-12 GHz) to Ku-band (12-18 GHz) as measured by a microwave vector analyzer. It is suitable for high-frequency electromagnetic interference (EMI) suppression scenarios and can effectively shield electromagnetic waves emitted by surrounding electronic products during fetal movement monitoring, reducing radiation to pregnant women and infants.

[0030] (3) Based on the conductive network formed by the introduced magnetic nanoparticles, heat is generated through the Joule heating effect after an electric current is applied. By precisely controlling the continuity and current density of the conductive network, a fast-response and uniformly distributed local heating function can be achieved, meeting 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 time, making it very suitable for applications requiring rapid temperature adjustment, 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 during use.

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

[0032] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0034] Figure 1 This is a schematic diagram of a flexible pressure sensor structure.

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

[0036] Figure 3 A schematic diagram illustrating the principle of a capacitive flexible pressure sensor.

[0037] Figure 4 Fig. 8 is a schematic diagram of a piezoelectric flexible pressure sensor principle;

[0038] Figure 5 Fig. 9 is a schematic diagram of a fetal movement monitoring system structure;

[0039] Figure 6 Fig. 10 is a schematic diagram of a fetal movement monitoring platform;

[0040] Figure 7 Fig. 11 is a schematic diagram of a sensing device sensor selection principle;

[0041] Figure 8 Fig. 12 is a skin-friendly waist fixing belt;

[0042] Figure 9 Fig. 13 is a flexible pressure sensor electromagnetic shielding efficiency curve using magnetic nanoparticles in the present application. DETAILED DESCRIPTION

[0043] The embodiments of the present application will be described in detail with specific reference to the drawings. The advantages and effects of the present application can be easily understood by those skilled in the art from the content disclosed in the specification. The present application can also be implemented or applied in other different embodiments, and the details in the specification can be modified or changed in various ways based on different views and applications without departing from the spirit of the present application. It should be noted that the drawings provided in the following examples only illustrate the basic concept of the present application in a schematic manner, and the following examples and features in the examples can be combined with each other without conflict.

[0044] The drawings are only used for illustrative explanation, and the representation is only a schematic diagram, not a physical diagram, and cannot be understood as a limitation of the present application. In order to better illustrate the embodiments of the present application, some components in the drawings may be omitted, enlarged or reduced, and do not represent the actual size of the product. It is understandable for those skilled in the art that some well-known structures and their descriptions in the drawings may be omitted.

[0045] The same or similar reference numerals in the drawings of the embodiments of the present application correspond to the same or similar components; in the description of the present application, it should be understood that the orientation or position relationship indicated by the terms "upper", "lower", "left", "right", "front", "back" and the like is based on the orientation or position relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the terms describing the position relationship in the drawings are only used for illustrative explanation, and cannot be understood as a limitation of the present application. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific situation.

[0046] Example 1

[0047] The embodiment provides a multifunctional fabric-based flexible pressure sensor for fetal movement monitoring, as shown in the accompanying drawings. Figure 1 As shown in the accompanying drawings, the multifunctional fabric-based flexible pressure sensor comprises 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 at the top of the sensor and is made of a material with good air permeability and flexibility (such as non-woven fabric, polyurethane film, etc.), which is used 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 of the strain layer, the sensor can be divided into piezoresistive, piezocapacitive, piezoelectric and other types. For the piezoresistive flexible pressure sensor, the strain layer usually needs to have strain sensitivity.

[0050] In the embodiment, for the piezoresistive flexible pressure sensor, the strain layer material includes magnetic nanoparticles (Fe3O4 can be used) and flexible polymer (PDMS can be used), and a film is prepared on both sides of the non-woven fabric substrate by electrospinning process, thereby forming the strain layer. Specifically, Fe3O4 particles are added to PDMS, and ultrasonic or high shear dispersion technology is used to uniformly disperse the Fe3O4 particles to avoid aggregation, thereby preparing a spinning solution. The content of Fe3O4 particles in the spinning solution is 15wt%.

[0051] The electrospinning process parameters are set as follows: the voltage is 10kV; the distance between the spinneret tip and the collector is 10cm; the spinneret speed is 3500r / min; the spinning needle diameter is 0.21mm; the relative humidity is 50%; the indoor temperature is 25℃; and the receiving roller is 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 assembled between the two electrode sheets, and then an adhesive is used for packaging to protect the device from the external environment. Then, a lead wire (copper wire, silver wire or copper foil) is separately connected to each electrode sheet, and conductive glue (conductive silver paste or conductive carbon paste) is used for fixation, thereby obtaining a flexible capacitive pressure sensor. The adhesive is one of polyimide insulating tape, polydimethylsiloxane and polyurethane medical tape.

[0053] The dispersion of Fe3O4 particles in PDMS forms a conductive network close to the critical point of conductivity, so that a slight strain can cause the reconstruction of the network, thereby causing a significant change in the overall resistance, as shown in the accompanying drawings. Figure 2As shown, thereby achieving effective detection of fetal movement signals. In addition, the magnetic and conductive properties of Fe3O4 particles can absorb, reflect or scatter electromagnetic waves, forming a shielding layer. When an electric current is applied in the sensor, the internal resistance existing in the conductive network causes the electric energy to be converted into heat energy, and the heating function can also be achieved.

[0054] Example 2

[0055] This embodiment provides a pressure-capacitive flexible pressure sensor, which relies on the principle of capacitance change to work compared with the piezoresistive flexible pressure sensor, as shown in Figure 3 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 capacitive response performance, the strain layer of the pressure-capacitive flexible pressure sensor uses a dielectric material (such as silicone rubber) as the substrate, and introduces electromagnetic shielding and Joule heating functions by doping magnetic nanoparticles.

[0056] The strain layer is obtained by spinning on a non-woven fabric substrate through an electrospinning process. Specifically, the magnetic nanoparticles are dispersed in a dielectric material solution, and the magnetic nanoparticles are uniformly dispersed by ultrasonic or mechanical stirring to avoid the formation of agglomerated structures, obtaining a spinning solution; then the spinning solution is spun on both sides of the non-woven fabric substrate through the electrospinning process to obtain the 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] After the appropriate addition of magnetic nanoparticles in the dielectric material, the shielding ability of the dielectric layer can be improved to prevent external electromagnetic interference. In addition, when an alternating current or direct current electric field is applied between the electrodes, local heating is achieved by controlling the conductive path, which helps to stabilize the dielectric properties or achieve thermal management.

[0058] The assembly method of the pressure-capacitive flexible pressure sensor is: the strain layer is in contact with the side of the two electrode sheets loaded with conductive nanoparticles, the strain layer is assembled between the two electrode sheets, and then packaged with adhesive to protect the device from the external environment. Then separately connect the wires (copper wire, silver wire or copper foil) on each electrode sheet, and fix them with conductive adhesive (conductive silver paste or conductive carbon paste) to assemble the 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-electricity conversion based on the piezoelectric effect, as shown in Figure 4As 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, detection of the external force can be achieved.

[0061] The strain layer of the piezoelectric flexible pressure sensor uses a fabric substrate and forms a piezoelectric material (PVDF can be used) on the surface thereof. The piezoelectric material requires a specific crystal phase (usually β phase) to be formed.

[0062] Specifically, the preparation method of the strain layer includes:

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

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

[0065] 3) Add magnetic nanoparticles to the PVDF precursor solution and stir to uniformly disperse the magnetic nanoparticles in the PVDF precursor solution. The content of the magnetic nanoparticles in the PVDF precursor solution is 5wt%. When introducing the magnetic nanoparticles, the surface of the particles needs to be modified or optimized to avoid interfering with the formation of piezoelectric crystal phase, while appropriately promoting the orientation of β phase.

[0066] 4) Form a piezoelectric fiber layer on both sides of the fabric substrate by electrospinning to obtain the 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 produce local heating when an electric current is applied to the sensor, which is convenient for temperature regulation and prevents the influence of low temperature environment on the sensing performance.

[0068] Embodiment 4

[0069] This embodiment provides a system for fetal movement monitoring, such as Figure 5 and Figure 6As shown, it includes a sensing device, a charge amplifier, an ESP32 microcontroller, a power management module, and a host computer subsystem. The fetal movement monitoring sensor is connected to the fetal movement signal acquisition instrument using a medical-grade ECG cable, which effectively shields it from external interference and noise. The fetal movement signal generated by the sensor is output as an analog signal by the charge amplifier. The STM32 microcontroller's internal ADC converts the analog signal into a digital signal, and the collected data is wirelessly transmitted in real-time to the host computer subsystem via the built-in Bluetooth module for monitoring, facilitating timely information access for family doctors.

[0070] The sensing device is sewn into a skin-friendly waistband and includes a multi-channel analog switch and several fabric-based flexible pressure sensors arranged in an n×n array. Any of the sensors proposed in Examples 1 to 3 can be used. The multi-channel analog switch can be a TMUX1308A. In this embodiment, a capacitive flexible pressure sensor is used, forming a 7×7 array, such as... Figure 7 As shown, in the array, each sensor has a first wire and a second wire connected to both ends (the first and second wires are respectively connected to the two electrode layers of the sensor). The first wire of each sensor in each column is connected to a first multi-channel analog switch, and the second wire of each sensor in each row is connected to a second multi-channel analog switch. The output of the first multi-channel analog switch is connected to the column electrode (i.e., the first flexible electrode), and the output of the second multi-channel analog switch is connected to the row electrode (i.e., the second flexible electrode). The first and second flexible electrodes are then connected to a charge amplifier. Both multi-channel analog switches are controlled by an ESP32 microcontroller, allowing for the selection of individual sensors.

[0071] For the sensing device, the signal readout of each sensor in its array is completed by sequential scanning. Specifically, the sensors with smaller row numbers in the array are scanned first, and then the sensors with smaller column numbers in the array are scanned. That is, the scanning is performed in the following order: 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 3 column 3, ... During the scanning process, the channel switches corresponding to the row and column numbers of the sensors being scanned are closed in sequence so that the electrical signals generated by the sensors being scanned can be read out through the first and second flexible electrodes.

[0072] The charge amplifier is used to amplify the signal output by the sensing device. The amplifier can use TI's OPA2206 chip. OPA2206 has excellent performance, is the ideal choice for high-precision and low-power systems, its single power supply feature simplifies the design of power supply circuit, reduces the size of the instrument, uses vertical double operational amplifier instrument amplifier circuit to realize high input impedance, high common mode rejection ratio (CMRR), low distortion and low noise, etc. to reduce the interference to the fetal movement signal.

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

[0074] Considering the portability and safety of the fetal movement signal acquisition device, the fetal movement monitoring system uses a lithium battery power supply. The power management module mainly includes three parts: voltage stabilizing circuit, charging circuit and switch control circuit.

[0075] The voltage stabilizing circuit uses T1's TLV70033 voltage stabilizing chip to achieve voltage stabilization, with a static current as low as 31μA and a maximum output current of 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. MCP73831 uses a constant voltage charging method to charge the lithium battery, and can automatically limit the charging current to reduce the chip temperature at high ambient temperature. This thermal regulation optimizes the charging time while ensuring device reliability. The switch control circuit uses ON Semiconductor's dual MOS tube NTJD1155L, which is particularly suitable for portable electronic devices that require signal control, low battery voltage and high load current.

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

[0077] The host computer subsystem also has Bluetooth connection management functions, can automatically search and connect sensing devices, and reconnect when interrupted; has real-time data visualization functions, making fetal movement data visually displayed in curve form, supporting data scaling and dragging; has historical data analysis and trend display functions, helping to analyze long-term fetal movement patterns; has personalized setting functions, allowing adjustment of monitoring parameters; has data security and privacy protection functions, supporting data encryption and backup, ensuring data security and user privacy.

[0078] In addition, in the waist fixing belt, magnetic nanoparticles are added to each sensor that makes up the sensing device. The magnetic response and certain electrical conductivity of the magnetic nanoparticles help to 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 signals of the sensor from external interference. Figure 9 As shown in the electromagnetic shielding effectiveness curve of the sensor with magnetic nanoparticles under high-frequency electromagnetic interference, from Figure 9 It can be seen that the shielding effectiveness (SE) changes with the change of electromagnetic frequency, where the EMI value is less than -18 dB within 8-13 GHz. The shielding performance of the magnetic nanoparticles is stable and improved within a wide frequency band (≥5 GHz), solving the limitations of traditional materials with insufficient high-frequency attenuation. In addition, from Figure 9It can be seen that the average electromagnetic shielding effectiveness of the sensor in the range of 8-18 GHz reaches-22 dB, indicating that the sensor has excellent high-frequency adaptability in the X-band (8-12 GHz) to Ku-band (12-18 GHz) and is suitable for high-frequency electromagnetic interference (EMI) suppression scenarios. Through verification by a vector network analyzer (VNA) in a standard test environment, the sensor meets the electromagnetic shielding effectiveness test specifications of IEEE 299, and the above data show that the sensor has SE≤-20 dB in the range of 8-9 GHz and 10-13 GHz, meeting the industrial high-frequency shielding requirements (SE≤-20 dB).

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

[0080] Embodiment 5

[0081] The embodiment provides a preparation method of a piezoresistive flexible pressure sensor, and the method comprises the following steps:

[0082] 1. Preparing a strain layer: configuring a PDMS solution, adding Fe3O4 particles into the PDMS solution, uniformly dispersing the Fe3O4 particles by using ultrasonic waves or high-shear dispersion technology, and preparing a spinning solution. The content of the Fe3O4 particles in the spinning solution is 15 wt%. The spinning solution is used to prepare a film on both sides of a fabric substrate by using an electrospinning process, and the strain layer is obtained. The thickness of the film is controlled to be between 50-200 μm. The fabric can be a non-woven fabric.

[0083] 2. Preparing a polyurethane nanofiber precursor solution: weighing a certain amount of TPU particles, cleaning the attached oil stains and pollutants with a detergent, then soaking in ethanol for 5 min; then washing with deionized water for multiple times, after removing the ethanol, placing the TPU particles in an oven at 50°C for drying for 5 min; then adding into a mixed solution of DMF: acetone = 1:1 (V / V), and magnetically stirring at room temperature for 8 h to completely dissolve the TPU particles, so as to configure a spinning solution with a mass fraction of 5%, which is the precursor solution before the electrospinning process.

[0084] 3. Preparing polyurethane nanofiber: setting the parameters for preparing the TPU nanofiber film by electrospinning, including: the voltage is 10 kV; the distance between the spinning head tip and the collector is 10 cm; the spinning head speed is 0.3 mL / h; the spinning needle diameter is 0.21 mm; the relative humidity is 50%; the indoor temperature is 25°C; and the receiving drum is wrapped with aluminum foil.

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

[0086] 4. Preparing the electrode layer: the TPU nanofiber membrane is pre-stretched along the directions of the four top corners by using the X-shaped stretching load method, the same stress is applied in the four directions, and the area of the stretched fiber membrane is expanded by 25%; the fiber membrane is fixed on the experimental table by using adhesive tape, 1 mL of a syringe is used to suck the conductive nanoparticle solution and spray it on the TPU nanofiber membrane; the clamp is removed, the loaded fiber membrane is laid on the paperboard, and a layer of paperboard is covered; the paperboard is clamped by the clamp and placed in a 60°C oven for drying for 1 h.

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

[0088] 5. Assembling the flexible pressure sensor: the strain layer is sandwiched between two electrode sheets for assembly, specifically, the strain layer is in contact with the side of the two electrode sheets loaded with conductive nanoparticles; an adhesive is used for packaging to protect the device from the external environment.

[0089] 6. A lead resistance type flexible pressure sensor is prepared by separately connecting a lead wire (copper wire, silver wire or copper foil) on each electrode sheet of the sensor and fixing it using conductive adhesive (conductive silver paste or conductive carbon paste). The adhesive is one of polyimide insulating tape, polydimethylsiloxane and polyurethane medical tape.

[0090] Based on the prepared lead resistance type flexible pressure sensor, the embodiment also provides an assembly method of a skin-friendly type waist fixing belt as shown in Figure 8 . Specifically, the flexible pressure sensor is arranged in a 7x7 array and sewn on the side of the fabric close to the skin. The sensing device is connected to the external circuit through the lead wire, specifically, one electrode layer of each sensor is connected with a first lead wire, and the other electrode layer is connected with a second lead wire, in the array, the first lead wire of each sensor in each column is connected with a first multi-channel analog switch, the second lead wire of each sensor in each row is connected with a second multi-channel analog switch, the output end of the first multi-channel analog switch is connected with a first flexible electrode, the output end of the second multi-channel analog switch is connected with a second flexible electrode, and the first and second flexible electrodes are connected to a charge amplifier. This wiring method not only reduces the number of lead wire connections, but also makes the overall circuit clearer and reduces the cost.

[0091] The fabric base and the skin-friendly type ring waist fixing belt are knitted by fly shuttle weaving and knitting technology, so that the softness and comfort between the fixing belt and the abdomen are ensured; one male magic tape and one female magic tape are arranged at two ends of the fixing belt away from the abdomen, and a user can adjust the tightness degree of the fixing belt and perform adhesion.

[0092] Embodiment 6

[0093] The embodiment provides a preparation method of a pressure capacity type flexible pressure sensor, and only the preparation mode of a strain layer is different compared with the preparation method of the piezoresistive flexible pressure sensor in Embodiment 5.

[0094] Specifically, in the embodiment, the preparation mode of the strain layer is as follows:

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

[0096] The solution containing the magnetic nanoparticles is spun to form on both sides of the non-woven fabric by using an electrospinning process. In the process, the electrospinning parameters are set as follows: the voltage is 10kV; the distance between the spinneret tip and the collector is 10cm; the spinneret speed is 3500r / min; the spinneret diameter is 0.21mm; the relative humidity is 50%; the indoor temperature is 25℃; and the receiving roller is wrapped with aluminum foil.

[0097] Embodiment 7

[0098] The embodiment provides a preparation method of a piezoelectric flexible pressure sensor, and only the preparation mode of a strain layer is different compared with the preparation method of the piezoresistive flexible pressure sensor in Embodiment 5.

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

[0100] 1) Configure a PVDF (polyvinylidene fluoride) precursor solution, and according to the required solution concentration, weigh a proper amount of PVDF with a mass ratio of 20%. Add the PVDF powder into a solvent (such as DMF or NMP), for example, 10 grams of PVDF powder is added into 90 milliliters of DMF.

[0101] 2) Stir the solution by using a magnetic stirrer, and heat to 70℃, to ensure that the PVDF is completely dissolved. The dissolution process generally needs 4-6 hours, until the solution is transparent and free of particulate matter.

[0102] 3) adding magnetic nanoparticles into the 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%. The surface of the magnetic nanoparticles is modified or optimized to avoid interfering with the formation of piezoelectric crystal phase and to appropriately promote the orientation of the β phase when the magnetic nanoparticles are introduced.

[0103] 4) spinning to form a piezoelectric fiber layer on both sides of the fabric substrate by an electrospinning process to obtain a strain layer.

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

[0105] Finally, it should be pointed out that the above examples are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should be covered by the scope of the claims of the present application.

Claims

1. A system for fetal movement monitoring, characterized by, The device comprises a waist fixing belt, a sensing device, a control circuit and a host computer subsystem; the sensing device is sewn on the side close to the skin of the waist fixing belt, and the sensing device is fixed on the abdominal position through the waist fixing belt; the sensing 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; the host computer subsystem filters, denoises and extracts features of the fetal movement monitoring data, and displays the fetal movement information in a graphical manner; 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, and the two ends of each multifunctional fabric-based flexible pressure sensor are respectively connected with a first lead wire and a second lead wire. The first lead wire of each multifunctional fabric-based flexible pressure sensor is connected with a first flexible electrode through the first multi-channel analog switch, and the second lead wire of each multifunctional fabric-based flexible pressure sensor is connected with a second flexible electrode through the second multi-channel analog switch; the first flexible electrode and the second flexible electrode are respectively connected with the control circuit, and the control circuit sequentially selects each multifunctional fabric-based flexible pressure sensor through the multi-channel analog switch to read the electrical signal generated by each multifunctional fabric-based flexible pressure sensor.

2. The system of claim 1, wherein, The multifunctional fabric-based flexible pressure sensor comprises a strain layer, electrode layers attached to the two sides of the strain layer, and protective layers for protecting the two electrode layers respectively; 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 with the first lead wire and the second lead wire through conductive glue.

3. The system of claim 1, wherein, The control circuit comprises a charge amplifier, a microcontroller and a power management module; the charge amplifier is connected with the first flexible electrode and the second flexible electrode respectively, amplifies the electrical signal collected by the sensing device and outputs the signal to the microcontroller, the microcontroller stores the analog-to-digital converted electrical signal and transmits the collected data to the host computer subsystem through Bluetooth communication; and the power management module is connected with the charge amplifier and the microcontroller respectively.

4. The system of claim 1, wherein, The multifunctional fabric-based flexible pressure sensor is one of a piezoresistive flexible pressure sensor, a piezocapacitive flexible pressure sensor and a piezoelectric flexible pressure sensor.

5. The system of claim 2 or 4, wherein, In the piezoresistive flexible pressure sensor, the strain layer comprises a fabric substrate and a film formed on the surface of the fabric substrate and mixed with a polymer material and magnetic nanoparticles, and the electrode layer is a nanofiber film loaded with conductive nanoparticles.

6. The system of claim 2 or 4, wherein, In the piezocapacitive flexible pressure sensor, the strain layer comprises a fabric substrate and a film formed on the surface of the fabric substrate and mixed with a dielectric material and magnetic nanoparticles, and the electrode layer is a nanofiber film loaded with conductive nanoparticles.

7. The system of claim 2 or 4, wherein, In the piezoelectric flexible pressure sensor, the strain layer comprises a fabric substrate and a piezoelectric fiber film formed on the surface of the fabric substrate and mixed with a piezoelectric material and magnetic nanoparticles, and the electrode layer is a nanofiber film loaded with conductive nanoparticles.

8. A method for the preparation of a multifunctional fabric-based flexible pressure sensor for fetal movement monitoring, characterized by, The method comprises: uniformly dispersing magnetic nanoparticles into a strain material solution to obtain a spinning solution; A film is made on both sides of a fabric substrate by electrospinning process to obtain a strain layer; A certain mass of polymer material particles is weighed, cleaned of attached oil stains and contaminants, and then soaked in ethanol for rinsing; after removing the ethanol with deionized water, the particles are dried; the dried polymer material particles are added to a mixed solution of DMF and acetone, stirred to completely dissolve the polymer material particles, and then prepared into an electrospinning precursor solution; and the precursor solution is made into a nanofiber membrane by electrospinning process; The nanofiber membrane is clamped and pre-stretched in the direction of the four corners by X-shaped tensile load method, and the stress applied in the four directions is the same; the stretched nanofiber membrane is fixed horizontally, and a solution of conductive nanoparticles is sucked by a syringe and sprayed on the nanofiber membrane; the clamp is removed, the nanofiber membrane is laid on a paperboard, and a layer of paperboard is covered; the paperboard is clamped with a clamp and placed in an oven for drying to obtain an electrode layer; The strain layer is clamped between the two electrode layers, and the side of the electrode layer loaded with conductive nanoparticles is in contact with the strain layer; an adhesive is used for packaging to protect the sensor from the external environment; Then, a lead wire is connected to each electrode layer, and the lead wire is fixed using conductive adhesive to obtain a piezoresistive flexible pressure sensor.

9. The method of claim 8, wherein, The parameters of the electrospinning process include: a voltage of 10kV; a distance between the spinneret tip and the collector of 10cm; a spinneret speed of 3500r / min; a spinning needle diameter of 0.21mm; a relative humidity of 50%; an indoor temperature of 25℃; and an aluminum foil is used to cover the receiving roller.

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

1. In the mixed solution of DMF and acetone, the volume ratio of DMF to acetone is 1:1.

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