Metal-doped graphene dry electrode, preparation method thereof and electrophysiological signal acquisition amplifier

Abstract

The invention relates to a metal-doped graphene dry electrode, a preparation method thereof and an electrophysiological signal acquisition amplifier, and the preparation method of the metal-doped graphene dry electrode comprises the following steps: step 1, taking pure titanium as a substrate, polishing and wiping the substrate, then carrying out ultrasonic cleaning, then soaking in a saturated salt solution of metal to be doped, standing and drying to obtain a sample for later use; and 2, placing the sample prepared in the step 1 on a sample table in a chamber of a direct-current arc plasma jet chemical vapor deposition system, and introducing a carbon source gas until chemical vapor deposition is completed, so as to obtain the metal-doped graphene dry electrode. The high conductivity, mechanical strength and biocompatibility of graphene and the capability of improving the electroactivity and the ion / electron current conversion efficiency of the electrode through the metal doping technology are utilized, the metal-doped graphene dry electrode provides higher sensitivity and selectivity, eye electricity, myoelectricity and electroencephalogram can be effectively distinguished, and the electrochemical performance of the electrode is improved. And high-density and high-resolution dry acquisition of a local channel is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of electrophysiological signal sensors, and in particular to a metal-doped graphene dry electrode and a preparation method thereof, and an electrophysiological signal acquisition amplifier. Background Art

[0002] In the field of neuroscience and clinical diagnosis, there is an increasing demand for accurate monitoring technology of brain activity, especially in applications such as motor imagery, prosthetic control, and peripheral control, which puts higher demands on high-resolution electrophysiological signal acquisition technology in local areas of the epidermis. This technology can not only provide more detailed images of brain activity, but also its small size and flexible wearable method will hardly interfere with the individual's daily life and work, which is of great significance for in-depth understanding of brain function, diagnosis of neurological diseases, and development of neurorehabilitation technology. However, the development of traditional electrophysiological signal acquisition technology is restricted by the design of electrode materials and signal acquisition amplifiers, and it is difficult to meet the growing demand for accuracy and resolution. Therefore, the development of new EEG electrode materials and amplifier technologies to achieve high-density acquisition of local channels has become a key research direction in the fields of human-computer interface, brain science, and neuroscience.

[0003] As a revolutionary two-dimensional material, graphene has become an ideal material for electrophysiological signal acquisition electrodes due to its excellent conductivity, mechanical strength and biocompatibility. The high conductivity of graphene ensures the efficient transmission of electrophysiological signals, reduces the attenuation of signals during transmission, and thus improves the fidelity of the signal. The large specific surface area of ​​graphene increases the efficiency of electrical contact with skin tissue, improving the sensitivity and resolution of signal acquisition. The flexibility of graphene enables it to better fit the scalp, reduce mechanical stimulation, and improve the comfort and stability of long-term monitoring. By modulating the electronic structure of graphene through metal doping, the electrical activity, sweat absorption and skin compatibility of the electrode can be enhanced, thereby optimizing the acquisition ability of electrophysiological signals. This modified graphene electrode shows high sensitivity and selectivity when collecting electrical biosignals, and can effectively distinguish and amplify weak electrical signals, which is crucial for high-density acquisition of local channels.

[0004] The present invention realizes dry acquisition and high-resolution acquisition of electrophysiological signals by using graphene materials and metal doping technology of chemical vapor deposition. The innovative design of the electrophysiological signal acquisition amplifier not only improves the signal-to-noise ratio of signal acquisition, but also realizes real-time acquisition and wireless transmission of signals, providing a powerful tool for brain science research and clinical applications. Summary of the invention

[0005] The purpose of the present invention is to provide a metal-doped graphene dry electrode and a preparation method thereof in view of the technical defects existing in the prior art;

[0006] Another object of the present invention is to provide an electrophysiological signal acquisition amplifier based on the metal-doped graphene dry electrode.

[0007] The technical solution adopted to achieve the purpose of the present invention is:

[0008] A method for preparing a metal-doped graphene dry electrode comprises the following steps:

[0009] Step 1, using pure titanium as a substrate, grinding and wiping the substrate, then ultrasonically cleaning the substrate, then immersing the substrate in a saturated salt solution of a metal to be doped, standing for a fixed time, taking it out and drying it, to obtain a sample for use;

[0010] Step 2, placing the sample prepared in step 1 on the sample table in the chamber of the DC arc plasma jet chemical vapor deposition system, introducing carbon source gas for chemical vapor deposition, the flow rate of the carbon source gas is 180-220L / min, the chemical vapor deposition temperature is 1150-1250°C, the deposition time is 3.5-4.5min, and after the chemical vapor deposition is completed, a metal-doped graphene dry electrode is obtained.

[0011] In the above technical solution, the metal to be doped is one of sodium, potassium, copper and lithium.

[0012] In the above technical solution, the metal-doped graphene dry electrode is cylindrical, with a diameter of 3.006 to 3.039 mm and a height of 1.606 to 1.639 mm.

[0013] An electrophysiological signal acquisition component comprises an electrode fixing component and a plurality of metal-doped graphene dry electrodes prepared by the preparation method and fixed on the electrode fixing component; preferably, the electrode fixing component is made of polydimethylsiloxane, eight sockets are formed on the electrode fixing component, and a positioning component is inserted into each socket, and more preferably, the positioning component is a nut, the metal-doped graphene dry electrodes are fixed on the positioning component, and the end faces of the metal-doped graphene dry electrodes are exposed outside the fixing component to contact with the human body, and each metal-doped graphene dry electrode is connected to an electrophysiological signal transmission line.

[0014] Another aspect of the present invention also includes the application of the electrophysiological signal acquisition component in the acquisition of electrooculographic, electromyographic and electroencephalographic signals.

[0015] An electrophysiological signal acquisition amplifier comprises an electrophysiological signal acquisition component, an analog signal acquisition module, a main control module and a power management module, wherein the electrophysiological signal transmission line of the electrophysiological signal acquisition component is connected to the input end of the main control module through the analog signal acquisition module, and the power management module supplies power to each electrical component.

[0016] In the above technical solution, the analog signal acquisition module includes an analog front-end input circuit and an ADS1299 chip. The model of the main control module is ESP32-S3. The power management module includes a TP4056 chip. The ADS1299 chip is connected to the main control module ESP32-S3 through a serial peripheral interface bus J1. The main control module ESP32-S3 is connected to the host computer through WiFi.

[0017] In the above technical solution, the analog front-end circuit includes a first-order RC passive low-pass filter and an anti-static protection circuit. The anti-static protection circuit includes six transient voltage suppression diodes of the model TPD4E1B06DCKR. Each TPD4E1B06DCKR transient voltage suppression diode is provided with four IO ports, which are respectively connected to the input ends of 4 first-order RC passive low-pass filters. The output end of the first-order RC passive low-pass filter is connected to the ADS1299 chip.

[0018] In the above technical solution, the ADS1299 chip and the main control module ESP32-S3 adopt a double-layer PCB design, and the two layers of the double-layer PCB are connected by pin headers.

[0019] In the above technical solution, the power management module implements a hierarchical design, including a USB power supply circuit and a lithium battery power supply circuit.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1. The present invention uses metal-doped graphene dry electrodes such as sodium, potassium, copper, and lithium. By utilizing the high conductivity, mechanical strength, and biocompatibility of graphene, as well as the ability of metal doping technology to improve the electroactivity of the electrode and the ion / electron current conversion efficiency, high-resolution and high-signal-to-noise ratio acquisition of electrophysiological signals in a local area of the scalp is realized; the metal-doped graphene dry electrodes provide higher sensitivity and selectivity, can effectively distinguish electrooculogram, electromyogram, and electroencephalogram, can amplify weak electroencephalogram signals with high signal-to-noise ratio, and realize high-density and high-resolution dry acquisition of local channels.

[0022] 2. The electrophysiological signal acquisition amplifier of the present invention is exquisitely designed and consists of four parts: electrophysiological signal acquisition parts, analog signal acquisition modules, main control modules ESP32-S3 and power management modules. It is optimized for high-density acquisition of local channels. The circuit layout is compact, the resolution is high, and the wireless transmission rate is fast, so that the amplifier can accurately capture the slight changes in the local brain area. Its compact design and portability make it more convenient to wear and suitable for long-term and multi-scenario electrophysiological signal monitoring. The wearable device uses OpenBCI-GUI acquisition software. Due to its mature open source acquisition software, it has high scalability, universality and popularity, supports WIFI connection and data export, connects to the host computer through the WIFI module, transmits data in real time, and analyzes the spectrum online in the acquisition software interface, which improves the efficiency of data acquisition and analysis, making the acquisition and analysis of electrophysiological signals more intuitive and efficient.

[0023] 3. The ADS1299 chip and the main control module ESP32-S3 of the present invention both adopt a double-layer PCB design to optimize space utilization and signal transmission paths, reduce signal interference, improve signal integrity, implement a power layered design, provide independent power layers for analog and digital circuits, and reduce noise and interference; the circuit board design takes into account the wearability of the final product, and the shape and edges are optimized to adapt to the human body's bone contour adaptability. The circuit board is small in size and easy to integrate with other sensors, processing units and power systems, and is suitable for embedded applications, especially in wearable devices such as headbands and hats.

[0024] 4. The electrophysiological signal acquisition amplifier of the present invention can be customized and expanded according to specific needs. Users can adjust parameters such as gain and filter frequency to adapt to different types of EEG signal acquisition and application requirements.

[0025] 5. The low power consumption characteristics of ESP32-S3 adopted in the present invention enable the system to be energy-efficient in different working modes, which can extend the use time of the device and is particularly suitable for portable devices or long-term monitoring occasions.

[0026] 6. The present invention selects small-sized, high-performance surface mount components (SMD) to reduce the occupied space and improve the assembly density. The compact electrophysiological signal amplifier and simple operation process allow users to quickly obtain signals for experiments and research. The simplified circuit and modular design improve the ease of use and maintainability of the system.

[0027] 7. The electrophysiological signal acquisition amplifier of the present invention improves signal quality, simplifies the operation process, optimizes portability and flexibility, and provides an efficient and reliable solution for the testing and analysis of electrophysiological signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1Shown is an optical image of a small-sized graphene dry electrode prepared in Example 1 of the present invention.

[0029] Figure 2 Shown is a scanning electron microscope image of the surface of the small-sized graphene dry electrode prepared in Example 1 of the present invention.

[0030] Figure 3 Shown is the preliminary model and size of the fixing part drawn by 3dMAX software in Example 1 of the present invention.

[0031] Figure 4 Shown is a 3D model of the PDMS mold drawn using 3dMAX software in Example 1 of the present invention.

[0032] Figure 5 The figure shows the actual mold processed by a 3D printer in Example 1 of the present invention.

[0033] Figure 6 The figure shows the electrode fixing part initially obtained in Example 1 of the present invention.

[0034] Figure 7 The figure shows a complete electrode fixing member in Example 1 of the present invention.

[0035] Figure 8 The figure shows the analog front-end input circuit designed in Embodiment 2 of the present invention.

[0036] Fig. 9 The figure shows the ADS1299 peripheral circuit designed in Example 2 of the present invention.

[0037] Fig.10 The figure shows the MCU main control circuit architecture designed in Example 2 of the present invention.

[0038] Fig.11 The figure shows the power module circuit designed in Example 2 of the present invention.

[0039] Fig.12 Shown is the double-layer PCB layout designed in Example 2 of the present invention.

[0040] Fig.13 Shown is a physical picture of the electrophysiological signal acquisition amplifier designed in Example 2 of the present invention, the analog signal acquisition module PCB and its connecting circuit (left) and the main control module PCB and its connecting circuit (right).

[0041] Fig.14 The figure shows a physical picture of the signal receiving terminal X6521WR-2x11H-C66030 designed in the embodiment 2 of the present invention.

[0042] Fig.15 The figure shows the packaging shell design in embodiment 2 of the present invention.

[0043] Fig.16 , 17 The figure shows the overall scene of the test subject wearing the test in Test Example 1 of the present invention.

[0044] Fig.18 Shown is the page of the acquisition software OpenBCI-GUI-v5.0.4 in Test Example 1 of the present invention.

[0045] Fig.19 Shown are the electrooculogram and electroencephalogram spectra collected using OpenBCI-GUI-v5.0.4 software in Test Example 1 of the present invention. DETAILED DESCRIPTION

[0046] The present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0047] Example 1

[0048] Reference Figure 1 , the preparation method of sodium-doped graphene (Na-VG) dry electrode comprises the following steps:

[0049] Step 1: The electrode material uses a cylindrical pure titanium substrate with a skin contact area diameter of 3 mm. The oxide layer on the surface of the sample is polished. The polished sample is wiped off the powder polished on the surface with 95% anhydrous ethanol and a dust-free cloth. The wiped sample is placed in a beaker, and ultrapure water-anhydrous ethanol-ultrapure water is ultrasonicated 3 times, 5 minutes each time. After completion, the sample is taken out, and the sodium salt aqueous solution is prepared with a saturated sodium chloride solution. 10mL of ultrapure water is measured in a beaker, and 3.6g of sodium chloride powder is measured with a balance and put into the beaker and stirred with a glass rod until the sodium chloride is completely dissolved. The sample is soaked in a saturated sodium chloride solution, and the sample is taken out after standing for 4 hours, and dried under an infrared lamp (375W) for use.

[0050] Step 2, the main experimental equipment is a DC arc plasma jet chemical vapor deposition system (DC arcplasma jet CVD) (Hebei Laser Research Institute). The DC arc plasma jet chemical vapor deposition system is mainly composed of a power control cabinet system, a vacuum deposition chamber, a water circulation cooling system, a vacuum pump system, and a magnetic field generation system. Before conducting a formal experiment, the growth chamber of the equipment needs to be polished, and the equipment needs to be kept in a vacuum state when not in use to ensure that the airtightness of the equipment is good during the experiment. Before opening the equipment, since the air pressure in the chamber is much lower than the atmospheric pressure, the vent valve should be opened, and the pressure in the chamber should be balanced with the external atmospheric pressure before the chamber is opened. After opening, unscrew the screws on the cathode head on the chamber and take them out, take out the copper ring and the sample stage base in the chamber, and polish them with fine sand in turn. After polishing, use anhydrous ethanol and a dust-free cloth to wipe the parts in the polished chamber to ensure that the chamber is pure and there is no interference from impurities in the experiment. After wiping, install the items taken out back in turn. Then take out the prepared sample and place it on the sample stage. Place the sample stage on the sample stage base in the chamber, turn on the instrument cabinet switch, start the rotation, adjust the height of the sample stage so that its vertical height with the copper ring above is 15mm, turn off the rotation, close the vent valve, and seal the chamber.

[0051] Step 3: officially start the experiment. Turn on the main power, instrument cabinet power, water circulation power, and vacuum pump power switches in sequence; turn on the vacuum pump control switch and chamber pressure display switch to evacuate the chamber and wait for the chamber pressure to drop below 500 Pa; turn on the water pump, Roots pump, flow control switch, and turn on argon (Ar), hydrogen (H 2 ), methane (CH 4 ) gas cylinder switch, then turn on the magnetic control key switch to preheat the magnetic control equipment; wait for the chamber pressure to drop below 50Pa, control the hydrogen flow rate to 2L / min, the argon flow rate to 1.7L / min, turn on the rotary table switch, control the chamber pressure valve and the pump pressure valve to keep the chamber pressure at around 3200Pa, and the pump pressure at around 13200Pa, and stabilize for 4min (stabilize the chamber environment); turn on the magnetic control voltage to 7.2V and preheat for 2min; turn on the arc power control button switch, press the ignition button, and after the ignition is successful, adjust the arc current to 120A and control the chamber pressure to remain at 3200Pa; after completing the above operations, introduce methane (CH 4 ) gas and control the flow rate to 200L / min. At this time, an infrared thermometer is used to measure the surface temperature of the sample at 1150-1250℃, and the timing is 4min. After the growth is completed, the control valve and power switch of the equipment are closed in sequence, and the chamber pressure is reduced to below 50Pa. After waiting for cooling for 2-3h, the prepared sodium-doped graphene dry electrode is taken out.

[0052] The preparation process of the electrode fixing part of the metal-doped graphene dry electrode is as follows:

[0053] Step 1, refer to Figure 3 , design the preliminary 3D model of the required fixings in 3dMAX software, and mark the size; refer to Figure 4 To ensure the accuracy of the experiment, the 3D model of the PDMS mold was drawn using 3dMAX software. Figure 5 , use 3D printer to carry out physical processing of the mold. The material of 3D printing is ABS (acrylonitrile butadiene styrene copolymer), which is a thermoplastic polymer material with high strength, good toughness and easy processing and molding.

[0054] Step 2. The materials required for the electrode fixture are the polymer material polydimethylsiloxane (PDMS) and the silicone elastomer curing agent, with a mass ratio of 3:1. Use a balance to weigh 3g of (PDMS) and 1g of curing agent, mix and stir the two, pour the stirred mixture into a beaker, put it into a vacuum drying oven, evacuate to below -0.08Mpa, leave it for 30 minutes, and then take out the beaker. This operation is to reduce the bubbles in the flexible support material after curing. Spray a layer of release agent on the surface of the printed 3D mold, pour the mixture in the beaker into the 3D mold, and then place it on the heating table, adjust the heating table temperature to 70°C, and heat it for 20 minutes. After heating, the mixture will solidify. Remove the solidified mixture from the 3D mold to obtain a preliminary electrode fixture, such as Figure 6 shown.

[0055] Step 3, refer to Figure 7 The preliminary electrode fixture is a flexible support base with 8 holes. The electrophysiological signal transmission line (SPO2 Monitor) is welded with a cylindrical copper nut. The copper nut serves as a positioning piece for the metal-doped graphene dry electrode. The metal-doped graphene dry electrode is fixed with a thread for fixing with the copper nut. The copper nut is inserted into each hole and glued with conductive glue to obtain a complete electrode fixture.

[0056] Example 2

[0057] An electrophysiological signal acquisition amplifier comprises an electrophysiological signal acquisition component, an analog signal acquisition module, a main control module and a power management module, wherein the electrophysiological signal transmission line of the electrophysiological signal acquisition component is connected to the input end of the main control module through the analog signal acquisition module, and the power management module supplies power to each electrical component.

[0058] The analog signal acquisition module includes an analog front-end input circuit and an ADS1299 chip, the ADS1299 chip has an integrated preamplifier and an analog-to-digital converter, the main control module is ESP32-S3, the power management module is TP4056, the ADS1299 chip is connected to the main control module ESP32-S3 via a serial peripheral interface bus J1, and the main control module ESP32-S3 is connected to a host computer via WiFi. The ADS1299 chip includes an analog front-end input circuit and a peripheral circuit, the analog front-end circuit includes a first-order RC passive low-pass filter and an anti-static protection circuit, and the anti-static protection circuit is composed of six transient voltage suppression diodes of model TPD4E1B06DCKR, each TPD4E1B06DCKR transient voltage suppression diode is provided with four IO ports, which are respectively connected to the input ends of four first-order RC passive low-pass filters.

[0059] The main design process of the electrophysiological signal acquisition amplifier is as follows:

[0060] (1) Design preparation: Clarify the functional requirements of the electrophysiological signal amplifier, including the number of acquisition channels, sampling rate, common mode rejection ratio, input noise and bandwidth, etc. Select the appropriate analog signal converter ADC (such as ADS1299 chip), MCU (such as ESP32), power management chip, etc. according to the requirements.

[0061] (2) Analog front-end input circuit: refer to Figure 8 , which is a front differential input circuit (i.e., analog front-end input circuit) connected to the ADS1299 chip, and is used for the access end of the metal-doped graphene dry electrode. The circuit mainly includes a first-order RC passive low-pass filter and an anti-static protection circuit. It mainly suppresses high-frequency noise. When the electrode is connected, the actual cutoff frequency of the pre-filter will be reduced due to the impedance of the electrode itself. This design takes into account that the effective EEG signal is mainly concentrated in the frequency range of 0.5Hz to 100Hz. The higher initial cutoff frequency reserves sufficient margin for the influence of electrode impedance, thereby avoiding interference with the EEG signal components. In addition, the integration of the anti-static protection circuit enhances the system's anti-electrostatic discharge (ESD) capability. The anti-static protection circuit contains six transient voltage suppression diodes TVS, namely Figure 8In the D2, D3, D4, D5, D6, and D7 modules, the specific model of the six transient voltage suppression diodes used in this embodiment is TPD4E1B06DCKR. Each TPD4E1B06DCKR transient voltage suppression diode is provided with four IO ports, which are respectively connected to the input ends of four first-order RC passive low-pass filters. These transient voltage suppression diodes can protect the preamplifier and analog-to-digital converter from ESD damage. The protection circuit can effectively absorb and disperse the energy from ESD interference, electromagnetic interference, and fast overvoltage pulses to ensure the stability and reliability of the circuit. Finally, in terms of connection and layout, refer to Fig.14 , using the X6521WR-2x11H-C66030 connector, the connector spacing is 2.54mm, the insulation resistance is 1000MΩ, the high insulation resistance indicates that the X6521WR-2x11H-C66030 connector has good insulation performance and can prevent current leakage. At the same time, the contact resistance of the X6521WR-2x11H-C66030 connector is 20mΩ, which is conducive to the smooth passage of current. The X6521WR-2x11H-C66030 connector is designed with double rows of pins 1P~8P, 1N~8N, connecting the metal-doped graphene dry electrode, SRB1 and SRB2 are connected to the reference electrode, and GND is grounded to ensure accurate signal acquisition.

[0062] (3) Peripheral circuit design of ADS1299 chip: refer to Fig. 9 In the U6 part, the EEG signal is sampled by the analog front-end input circuit and connected to the ADS1299 peripheral circuit through IN1P~IN8P or IN1N~IN8N of each first-order RC passive low-pass filter. After entering the ADS1299, the original signal is amplified by the internal programmable gain amplifier. The system uses SRB as the reference electrode input terminal. The BIAS pin is the right leg drive circuit inside the chip, which is used to reduce common-mode and power frequency interference. The BIAS pin is connected to the input electrode terminal (i.e., the first-order RC circuit) through a parallel 1MΩ resistor and 1nF capacitor. The ADS1299 is mainly connected to the AVDD and AVSS pins by an analog voltage of + / -2.5V as the analog power supply. The digital power supply is a +3.3V digital voltage connected to the DVDD pin. The reference voltage of the ADS1299 is + / -2.5V. For the ADS1299 with 24-bit resolution, the least significant bit (LSB) voltage is: The reference voltage in this system is + / -2.5V, and N=24 (ADC resolution bits) to obtain VLSB≈0.298μV. On this basis, since the ADS1299 has a built-in programmable gain amplifier (PGA), when its gain is set to 24 times, the system's measurement sensitivity to the minimum resolvable signal will be further improved. After 24 times gain amplification, its theoretical minimum measurable signal amplitude is about 0.298 / 24=0.0124μV. It can be seen that the ADS1299 can meet the needs of high-precision weak EEG signal measurement, and can achieve accurate measurement of extremely low-amplitude physiological electrical signals while maintaining high resolution.

[0063] The ADS1299 chip is connected to the MCU (ESP32-S3) through the Serial Peripheral Interface (SPI) bus J1 (hereinafter referred to as connector J1). The functions of the SPI bus J1 include power connection, signal transmission, etc. The SPI bus J1 has multiple pins, including ADS-SCK (serial clock), ADS-RST (reset), ADS-DIN (data input), ADS-DOUT (data output), ADS-STA (start signal), etc. These pins are used to communicate with external digital systems. In this embodiment, ADS1299 is connected to pins 3, 4, 5, 6, 7, and 9 of connector J1 respectively. The signal sampled by ADS1299 is stored in the buffer in MCU by serial peripheral interface bus J1, and the data in the buffer is shifted out by serial data output. Whenever the DRDY pin outputs a falling edge signal, it indicates that an analog-to-digital conversion is completed, and the subsequent falling edge of the SCLK clock is set to a high level, and then waits for the next analog-to-digital conversion, where the SCLK input pin is the SPI communication clock pin of ADS1299.

[0064] (4) MCU main control circuit architecture design: refer to Fig.10 , the main control module uses ESP32-S3, refer to Fig.10 In the M1 module, the RXD and TXD interfaces of ESP32-S3 are connected to the USB conversion chip for data transmission and reception. Fig.10 U23 module, USB conversion chip reference Fig.10The U23 module is a USB-to-serial port chip, model CH343G, which converts USB signals into serial port signals, allowing traditional serial port devices to connect to the host system through the USB interface. It can provide data burning and common MODEM contact signals, such as RTS, DTR, DCD, RI, DSR, and CTS, which are used to control data flow and indicate device status. Pin 14 (TLY_SCL), pin 17 (TLY_SDA), and pin 18 (TLY_INA1) of ESP32-S3 are respectively connected to the three-axis linear accelerometer U1. U1 is an ultra-low power high-performance three-axis linear accelerometer. V1: power input, providing operating voltage for IC. TLY_SCL (pin 4): I2C clock line (SCL), used for synchronous data transmission. TLY_SDA (pin 7): I2C data line (SDA), used to transmit data between IC and host. TLY_INT1 (pin 11): interrupt pin, used to notify the host IC that there is new data or events to be processed. The main function of this module is to communicate with external devices through the I2C interface, while providing analog signal acquisition and conversion. The USB is connected to the A6 and A7 pins of the Type-C female connector J5. J5 is a Type-C female connector with 16 contacts, which can support a rated current of 3A, an operating temperature range of -40℃~+85℃, and an SMD package. As a USB Type-C interface, J5 allows devices to connect to external devices through the Type-C connector to achieve data transmission and power supply.

[0065] ESP32-S3, with its rich peripheral interfaces and resource characteristics, fully meets the requirements of the present invention for efficient transmission and reliable wireless communication. ESP32-S3 is based on the Xtensa LX7 dual-core processor, with a main frequency of up to 240MHz, and has powerful computing power and multi-tasking capabilities. It integrates 2.4GHz WiFi and Bluetooth 5 modules, which meet the system's requirements for data transmission and interaction, and is easy to develop. In the design of the main control circuit, the ESP32-S3 module, as the core processing unit of the system, undertakes the tasks of data acquisition, preprocessing and wireless transmission.

[0066] ESP32-S3 uses the integrated WiFi function to create a wireless LAN in AP mode and receives HTTP requests from the host computer through TCP / UDPSocket. After the host computer sends the HTTP request, the ESP32-S3 module parses the request content, performs corresponding operations or processes data, and returns the processing results or data to the host computer through HTTP response. In addition, the low power consumption characteristics of ESP32-S3 enable the system to be energy-efficient in different working modes, extend the battery life of the device, and is suitable for long-term portable applications.

[0067] (5) Main control code design: The ESP32-S3 lower computer was developed and burned in the Arduino environment using the C++ language. The main purpose of the lower computer design was to collect EEG data through SPI communication with the ADS1299 chip and transmit the data to the upper computer through the WiFi module of the ESP32-S3. To achieve this goal, the code covers multiple functions such as WiFi configuration, SPI communication, scheduled tasks, data processing, etc., to ensure that the device can operate stably in different network environments and achieve efficient data exchange.

[0068] In terms of data collection, the lower computer first communicates with ADS1299 through the SPI protocol. ESP32-S3 establishes a connection with the ADS1299 chip by defining multiple pins, including SCK, MISO, MOSI, SS and other pins, which together support data transmission of the SPI protocol. Through control commands, ESP32-S3 can start and stop data collection to ensure real-time acquisition of EEG data.

[0069] After data collection is completed, the EEG data is sent to the host computer. In the slave computer, ESP32-S3 uses the WiFi.h library to implement wireless communication functions and support HTTP communication between the device and other devices. Specifically, ESP32-S3 is configured in AP mode and can act as an HTTP server to handle requests from clients or as an HTTP client to send data to a remote server. In the slave computer, the WebServer.h library is used to set up the HTTP server and allow the host computer to interact.

[0070] By setting server.on(" / data",HTTP_GET,handleData), a processing function can be defined for HTTP GET requests. When a request is made to access / data, the ESP32-S3 will return the EEG data. During this process, the EEG data will first be processed into JSON format for transmission over the network. The ArduinoJson.h library can be used to easily create and parse JSON objects to ensure data standardization and compatibility.

[0071] When the host computer sends an HTTP GET request to access the / data path, ESP32-S3 calls the handleData function and sends the collected EEG data back to the client in JSON format.

[0072] In general, the lower computer uses the powerful communication capabilities of ESP32-S3 and the simple development method of the Arduino environment to send and receive EEG data through HTTP requests. Through HTTP instructions, the device can respond to the requests of the upper computer in real time, sending collected data or receiving control commands.

[0073] (6) Power management and voltage stabilization circuit design: refer to Fig.11 The front-end analog chip of the system needs to receive 3.3V digital power, 2.5V analog power and -2.5V negative power input at the same time, while the MCU and other modules need 3.3V power. The 3.7V voltage output by the battery is passed through the low dropout regulator (LDO) chip TPS7333QDR (see Fig.11 U11 module) and LP5907MFX-3.3 (see Fig.11 The negative power supply -2.5V is then converted to 2.5V by the TLV70025DDCR (see the U4 module in Figure 11) to meet the needs of the analog circuit. Fig.11 U3 module) converts 3.3V to -3.3V, and then passes through TPS72325DBVR (see Fig.11 The negative voltage regulator chip in the VR1 module is adjusted to -2.5V. To achieve multiplexing, this embodiment uses the TP4056 battery charging management chip (see Fig.11 U24mok) to charge the battery. The TP4056 battery charging management chip includes battery connection (BAT), charging current setting (ISET), temperature monitoring (TEMP), and charging status indication (CHRG#, STDBY#). Through two LED light-emitting diodes (D36, D37), when the charger is charging the battery, the CHRG# pin is pulled to a low level by the internal switch. At this time, the LED (D36) connected to CHRG# will light up, indicating that charging is in progress. After charging is completed, the CHRG# pin is in a high-impedance state and the LED (D36) goes out, indicating that the charging process has ended. The STDBY# pin is pulled to a low level by the internal switch when the battery is fully charged. At this time, the LED (D37) connected to STDBY# will light up, indicating that the battery is fully charged and the charger enters standby mode. In other cases, the STDBY# pin is in a high-impedance state and the LED (D37) goes out.

[0074] The power input includes VUSB (5V) and lithium battery VBAT, which are multiplexed through the charging management chip TP4056. When USB power is available, the system gives priority to VUSB power supply and charges the lithium battery; when USB is disconnected, it automatically switches to lithium battery power supply. The overall power management solution improves energy efficiency and ensures reliable power supply of the system under various power conditions.

[0075] (7) PCB design: When conducting the PCB layout of the circuit board, a refined design strategy was adopted to ensure the compactness and efficiency of the circuit board, thereby achieving the application goals of portability and wearability.

[0076] 1. Precision layout planning: refer to Fig.12 , a double-layer PCB design is adopted to optimize space utilization and signal transmission paths and reduce signal interference. A double-layer PCB refers to a circuit board with two conductive layers (usually copper foil), which are located on the top and bottom layers of the PCB respectively. This design allows electrical connections to be made on both sides, allowing for more complex circuit layouts. The double-layer PCB connects the circuits on the top and bottom layers through vias, so that lines such as signals, power, and ground can be transmitted between the two layers. The component layout is compact, and priority is given to minimizing critical signal paths to reduce delays and improve signal integrity while reducing PCB area. The ASD1299 chip and the main control module ESP32-S3 are isolated and laid out, refer to Fig.13 , by designing two PCB boards and connecting them with pin headers, mutual interference is avoided and the purity of the signal is ensured. The output connector uses a 2-row 11-section pin header connector. The names of the upper pin header interfaces from top to bottom are SRB1, 1P to 8P, BIAS, GND, and the names of the lower pin header interfaces from top to bottom are SRB2, 1N to 8N, BIAS, GND. This precise layout planning and PCB design effectively improves signal transmission efficiency, reduces interference, and ensures high signal purity and high performance of the equipment.

[0077] 2. Optimize the power supply and ground layout: Implement power layering design to provide independent power layers for analog and digital circuits to reduce noise and interference; set up sufficient ground holes near key components to ensure good ground connection and low-impedance loop to reduce ground bounce effect; use power management chips and linear / switching regulators to provide stable power supply for ADC and CPU to ensure the stability of signal processing.

[0078] 3. Wearability considerations: The circuit board design takes into account the wearability of the final product, and the shape and edges are optimized to fit the contours of the human skeleton.

[0079] (8) Package shell design: refer to Fig.15The designed PCB mainly consists of three parts: analog signal board, digital signal board and battery. According to the appearance of these three parts, a 3D shell is designed using 3dMAX software. The material used is the same ABS material as the electrode fixing mold. The switch, USB and DuPont cable sockets should be reserved on the package, and the shell is printed out using a 3D printer.

[0080] Test Example 1

[0081] The specific process of collecting signals by the wearable local channel high-resolution electrophysiological signal acquisition amplifier of the present invention is as follows:

[0082] (1)Reference Fig.16 , Fig.17 , install the circular graphene dry electrode on the electrode fixture, and then install it on wearable clothing such as pockets and headbands, let the subjects wear it, connect the 8 brain wires to the acquisition amplifiers 1P~8P, and then connect the two ear clip electrodes to the reference SRB2 and GND.

[0083] (2) Toggle the switch on the board. After about 3 seconds, the LED light will light up and the device will start up. The acquisition board will generate a WIFI hotspot named TJUTBCIWiFi-xxxx. This WIFI hotspot has no password. Turn on the computer and connect to the WIFI hotspot (Note: During the connection process, it may remain in the connecting state. At this time, click outside the connection interface and observe the connection status. You will find that the connection is successful).

[0084] (3) Open the OpenBCl-GUI-v5.0.4 acquisition software, its interface is as follows Fig.18 As shown:

[0085] 1. In the "System Control Panel" on the left, select "CYTON (live)" as the data source and use the Cyton EEG device for real-time data collection.

[0086] 2. In the "PICK TRANSFER PROTOCOL" section, select "Wifi (from Wifi Shield)" as the data transfer method. Data will be transferred from the device to the host computer via WiFi.

[0087] 3. In the "WIFI SHIELDS" section, select "STATIC IP" and enter a static IP address (for example: 192.168.4.1) for the IP address of the WiFi shield or device to be used for data transmission.

[0088] 4. In the "SAMPLE RATE" section, select a sampling rate (for example: 1000Hz). The sampling rate determines the number of times data is collected per second. 1000Hz means 1000 data points are collected per second.

[0089] 5. Click the "START SESSION" button to start a data acquisition session, which will initiate the process of transmitting data from the Cyton device to the host computer via WiFi.

[0090] (4) After clicking START SESSION, enter the acquisition page. Click Hardware Settings to set the channels, select the grounding method (Bias include select no, SRB1 select On, SRB2 select Off), click Send, and "Hardware Settings sent to board!" will appear at the bottom of the page, indicating that the channel settings are successful. Click Time Series to return to the acquisition page. Click Start Data Stream, and EEG signals will appear in the time domain graph on the acquisition page to start the acquisition. Refer to Fig.19 , make a blinking motion, and obvious high-amplitude EOG signals with blinking fluctuations and EEG beta rhythm signals when opening the eyes can be seen on the time domain graph.

[0091] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a metal-doped graphene dry electrode, characterized in that: The following steps are involved: Step 1, using pure titanium as a substrate, grinding and wiping the substrate, then ultrasonically cleaning the substrate, then immersing the substrate in a saturated salt solution of a metal to be doped, standing for a fixed time, taking it out and drying it, to obtain a sample for use; Step 2, placing the sample prepared in step 1 on the sample table in the chamber of the DC arc plasma jet chemical vapor deposition system, introducing carbon source gas for chemical vapor deposition, the flow rate of the carbon source gas is 180-220L / min, the chemical vapor deposition temperature is 1150-1250°C, the deposition time is 3.5-4.5min, and after the chemical vapor deposition is completed, a metal-doped graphene dry electrode is obtained.

2. The metal-doped graphene dry electrode prepared by the preparation method according to claim 1, characterized in that: The metal to be doped is one of sodium, potassium, copper and lithium.

3. The metal-doped graphene dry electrode prepared by the preparation method according to claim 2, characterized in that: The metal-doped graphene dry electrode is cylindrical, with a diameter of 3.006-3.039 mm and a height of 1.606-1.639 mm.

4. An electrophysiological signal acquisition device, characterized in that: It comprises an electrode fixing part and a plurality of metal-doped graphene dry electrodes prepared by the preparation method of claim 1 and fixed on the electrode fixing part; preferably, the material of the electrode fixing part is polydimethylsiloxane, eight sockets are formed on the electrode fixing part, and a positioning part is inserted in each socket, and more preferably, the positioning part is a nut, the metal-doped graphene dry electrode is fixed on the positioning part, the end face of the metal-doped graphene dry electrode is exposed outside the fixing part to contact with the human body, and each metal-doped graphene dry electrode is connected to an electrophysiological signal transmission line.

5. Application of the electrophysiological signal acquisition component as claimed in claim 4 in the acquisition of electrooculographic, electromyographic and electroencephalographic signals.

6. An electrophysiological signal acquisition amplifier, characterized in that: It comprises the electrophysiological signal acquisition component, analog signal acquisition module, main control module and power management module as described in claim 4, wherein the electrophysiological signal transmission line of the electrophysiological signal acquisition component is connected to the input end of the main control module through the analog signal acquisition module, and the power management module supplies power to each electrical component.

7. The electrophysiological signal acquisition amplifier according to claim 6, characterized in that: The analog signal acquisition module includes an analog front-end input circuit and an ADS1299 chip. The model of the main control module is ESP32-S3. The power management module includes a TP4056 chip. The ADS1299 chip is connected to the main control module ESP32-S3 via a serial peripheral interface bus J1. The main control module ESP32-S3 is connected to a host computer via WiFi.

8. The electrophysiological signal acquisition amplifier according to claim 7, characterized in that: The analog front-end circuit includes a first-order RC passive low-pass filter and an anti-static protection circuit. The anti-static protection circuit includes six transient voltage suppression diodes of model TPD4E1B06DCKR. Each TPD4E1B06DCKR transient voltage suppression diode is provided with four IO ports, which are respectively connected to the input ends of four first-order RC passive low-pass filters. The output end of the first-order RC passive low-pass filter is connected to the ADS1299 chip.

9. The electrophysiological signal acquisition amplifier according to claim 7, characterized in that: The ADS1299 chip and the main control module ESP32-S3 adopt a double-layer PCB design, and the two layers of the double-layer PCB are connected by pin headers.

10. The electrophysiological signal acquisition amplifier according to claim 6, characterized in that: The power management module implements a hierarchical design, including a USB power supply circuit and a lithium battery power supply circuit.

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