Low-load flexible capacitive electroencephalogram cap

Abstract

The invention discloses a low-load flexible capacitance type electroencephalogram cap, and aims to solve the problems that an electrode of a traditional electroencephalogram cap is complex in wearing step, poor in comfort, not suitable for long-term wearing and the like. The core innovation point of the invention is that the flexible design of the capacitive electrode enables the electrode to be in full contact with the scalp compared with a rigid capacitive electrode, so that the contact area is maximum and the average inter-plate distance is minimum under the condition that the size of a single electrode is ensured to be smaller as far as possible; therefore, the coupling capacitance between the electrode and the scalp is increased, the signal coupling effect is better, the advantages of the capacitive electrode are brought into full play, and the problems that the signal coupling capacity of the capacitive electrode is poor and the signal-to-noise ratio is low are solved. The electroencephalogram cap designed by the invention is improved on the basis of the hair band, electroencephalogram signal acquisition of at most 15 channels can be realized, the whole electroencephalogram cap is simple in structure and easy to carry and wear, and materials in contact with scalp are all flexible and good in comfort.

Description

Technical Field

[0001] The present invention relates to the field of electroencephalogram (EEG) wearable devices, and in particular to a low-load flexible capacitive EEG cap. Background Art

[0002] As people pay more and more attention to health, the focus of medical care has gradually shifted from disease diagnosis and treatment to disease prevention and long-term health management. In order to achieve this goal, real-time and long-term recording of various life signals is particularly important. Electroencephalogram (EEG), as a method of monitoring and recording brain electrical activity, contains rich physiological and pathological information and has been widely used in clinical diagnosis, brain function research, sleep monitoring, and evaluation of neurological diseases such as epilepsy. However, existing EEG caps still have some significant defects, mainly including complicated wearing steps, poor comfort, poor portability, and unsuitable for long-term wearing.

[0003] The development focus of the EEG field is reflected in the transformation of electrodes. Currently, most EEG signal recording devices use Ag / AgCl wet electrodes, as described in the Chinese patent technology (publication number: CN218075019U). This wet electrode needs to apply conductive paste on the scalp during use to ensure good signal conduction. However, the conductive paste is usually irritating and will gradually dry over time, resulting in a decrease in the contact quality between the electrode and the skin, affecting the stability of the signal. Although the wet electrode has a high signal-to-noise ratio and reliability in signal acquisition, the inconvenience and discomfort it brings have largely limited its promotion and application in a wider range of scenarios. To solve the above problems, dry electrodes (such as Chinese patent technology, publication number: CN220158257U) have begun to be gradually applied to EEG signal acquisition. Dry electrodes mainly include microneedle electrodes and finger electrodes. Although they avoid the trouble of using conductive paste, they still need to be in direct contact with the scalp, which will cause slight irritation or discomfort to the skin, especially when used for a long time. In addition, dry electrodes are difficult to maintain, costly, and inferior to wet electrodes in terms of signal acquisition quality. In contrast, capacitive non-contact electrodes (such as Chinese patent technology, publication number: CN213722033U) show certain advantages in human body sensor applications. The use of such electrodes does not require complicated preparation, reduces interference to users, and is more suitable for long-term wearable biopotential recording systems. However, although the concept of non-contact biopotential sensors has a history of decades and some laboratory equipment has appeared, practical application equipment for the mass market has not yet been widely available.

[0004] In summary, the current EEG cap technology has problems with comfort, portability and long-term wearing performance. Therefore, developing a new EEG cap that is more comfortable, portable and suitable for long-term wear has important research significance and broad commercial application prospects. Summary of the invention

[0005] The present invention provides a low-load flexible capacitive EEG cap, the core of which is a new type of capacitive electrode based on flexible PCB packaging to solve the shortcomings of traditional EEG electrodes in terms of comfort, portability and wearability. By applying this electrode to the EEG cap designed by the present invention, up to 15 channels of EEG signal collection are achieved, with good comfort, portability and wearability.

[0006] A low-load flexible capacitive electroencephalogram cap, comprising:

[0007] Headband:

[0008] A Y-shaped headband fixed on the head ring and used to fit the scalp;

[0009] Flexible capacitive EEG electrodes arranged on the inner sides of the head ring and the Y-shaped headband;

[0010] The flexible capacitive EEG electrode comprises:

[0011] Polyimide flexible substrate;

[0012] A copper foil electronic circuit layer and a copper foil conductive layer are arranged on both sides of the polyimide flexible base layer;

[0013] a first insulating layer disposed on the copper foil electronic circuit layer;

[0014] A second insulating layer disposed on the copper foil conductive layer;

[0015] The copper foil electronic circuit layer is electrically connected to the copper foil conductive layer through a wire passing through the polyimide flexible base layer.

[0016] The low-load flexible capacitive EEG cap and the number of flexible capacitive EEG electrodes on the headband are 6 to 10 (most preferably 8).

[0017] The low-load flexible capacitive EEG cap has 7 to 10 flexible capacitive EEG electrodes on the Y-shaped headband (most preferably 7).

[0018] The circuit of the copper foil electronic circuit layer adopts a signal preprocessing circuit, which includes a double-T trap circuit, a preamplifier high-pass filter circuit and a secondary amplifier low-pass filter circuit connected in sequence.

[0019] The input end of the double-T trap circuit is connected with an input bias resistor, which provides a suitable DC path so that the weak EEG signal can be effectively transmitted from the capacitive coupling to the input end of the amplifier circuit, ensuring normal signal amplification.

[0020] The center frequency of the double-T trap circuit is 50±2Hz.

[0021] The preamplifier high-pass filter circuit is a circuit that allows signals with a frequency greater than or equal to a frequency threshold to pass through.

[0022] The two-stage amplification low-pass filtering circuit refers to a circuit that allows signals with a frequency less than or equal to a frequency threshold to pass through.

[0023] The EEG cap of the present invention adopts a new type of capacitive electrode packaged in a flexible PCB, aiming to solve the problems of the traditional EEG cap electrode in the complicated wearing steps, poor comfort and unsuitability for long-term wearing. The core innovation of the present invention lies in the flexible design of the capacitive electrode. Compared with the rigid capacitive electrode, the flexible design can make the electrode fully contact with the scalp, and maximize the contact area and minimize the average inter-plate distance while ensuring that the volume of the single electrode itself is as small as possible, so that the coupling capacitance between the electrode and the scalp is increased, the signal coupling effect is better, and the advantages of the capacitive electrode are fully utilized, solving the problem of low signal-to-noise ratio and coupling signal capability of the capacitive electrode. The EEG cap designed by the present invention is improved based on the headband, and can realize EEG signal acquisition of up to 15 channels. The entire EEG cap has a simple structure, is easy to carry and wear, and the materials in contact with the scalp are all flexible and comfortable. The present invention directly integrates a streamlined EEG signal preprocessing circuit on the back of the electrode plate, pre-amplifies the signal, and adopts a two-stage amplification structure, with a common mode rejection ratio of up to 120dB, and supports online filtering, A / D conversion and Bluetooth wireless transmission. This invention shows significant advantages in signal stability and comfort, and is particularly suitable for long-term EEG monitoring and research.

[0024] Further preferably, a low-load flexible capacitive EEG cap based on flexible PCB packaging comprises:

[0025] (1) A flexible capacitive electrode, which is composed of a circular flexible PCB board with a diameter of 3 cm. The front of the PCB board integrates a signal preprocessing circuit, and the back is paved with a copper layer and sprayed with insulating paint, forming a capacitor with the scalp to couple EEG signals. A 2 mm wide grounding copper ring is designed around the circular board to provide an electromagnetic shielding effect. The flexible circular board is connected to a serpentine flexible board to form the flexible capacitive electrode. The serpentine board is used for routing signal lines and power lines. There is a 1×4P horizontal female header at the tail of the serpentine board, which can be connected to the circuit board on the back side of the cap body through a DuPont line. The serpentine design enhances the stability of the contact between the electrode and the scalp and buffers the electrode pulling caused by head movement.

[0026] (2) Signal preprocessing circuit, including a two-stage amplifier, has a common mode rejection ratio of 120 dB and an amplification gain of more than 5000 times, which can realize online filtering. Users can adjust the range of online filtering according to their needs, such as choosing to effectively amplify signals in the range of 1 Hz to 40 Hz and 65 Hz to 100 Hz.

[0027] (3) Signal post-processing circuit: This part can be connected to the external circuit through the USB Type-C interface and has two main functions: 1. Complete voltage conversion, convert the input voltage into the voltage required by the chip in the signal pre-processing circuit, and also has a voltage stabilization function. 2. Realize signal A / D conversion and wired or Bluetooth wireless transmission of the signal.

[0028] (3) The structure of the EEG cap is an improved design based on the headband, with a "Y"-shaped structure added on the top, which increases the wearing stability and the number of electrode sites; the flexible electrodes described in (1) are fixed on the cap body according to a certain arrangement rule to ensure stable contact with the scalp.

[0029] The capacitive EEG cap has a fixing method for the flexible electrode to the scalp, and the flexible electrode is pressed against the scalp by a highly elastic material, ensuring that the electrode fits tightly to the scalp, thereby reducing wearing pressure and improving wearing comfort.

[0030] The capacitive EEG cap has a flexible design that allows the electrode to fully contact the scalp, maximizes the contact area and minimizes the average inter-plate distance while ensuring that the volume of a single electrode itself is as small as possible, thereby increasing the coupling capacitance between the electrode and the scalp, achieving better signal coupling effect, giving full play to the advantages of the capacitive electrode, solving the problems of poor coupling signal capacity and low signal-to-noise ratio of the capacitive electrode, and thus improving the stability of signal acquisition.

[0031] The capacitive EEG cap has a signal preprocessing circuit integrated on the back side of the circular electrode sheet. This preamplifier structure design can directly amplify and filter the EEG signal coupled to the capacitive electrode, without the need to transmit the signal through a long wire before amplification and filtering, which can effectively avoid signal loss or distortion during wire transmission. The signal post-processing circuit board is installed in a rectangular housing box on the back side of the cap body, which is used to accommodate and protect the power module, A / D conversion module and Bluetooth transmission module.

[0032] The capacitive EEG cap uses flexible materials to ensure that the electrodes can flexibly deform according to the curve of the head, reduce mechanical pressure, and improve comfort and signal acquisition stability when worn for a long time.

[0033] The capacitive EEG cap is integrated with an A / D conversion module to convert the collected analog EEG signals into digital signals to ensure the integrity and accuracy of the signals.

[0034] The capacitive EEG cap is used for users who monitor and study EEG signals for a long time, and is suitable for signal collection and real-time transmission under various motion states.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] The EEG cap of the present invention fits the flexible electrode to the scalp through a highly elastic material, and the electrode can be flexibly deformed with the curve of the head, thereby reducing mechanical pressure and providing a more comfortable wearing experience. Compared with rigid capacitive electrodes, the flexible design can make the electrode fully contact with the scalp, and maximize the contact area and minimize the average inter-plate distance while ensuring that the volume of a single electrode itself is small as much as possible, thereby increasing the coupling capacitance between the electrode and the scalp, and achieving better signal coupling effect, giving full play to the advantages of capacitive electrodes, and solving the problems of low signal-to-noise ratio and coupling signal capability of capacitive electrodes. In addition, the flexible design also improves the stability of EEG signals, effectively reduces electrode displacement and signal distortion caused by movement, and is particularly suitable for long-term EEG monitoring and research. The EEG cap can be powered by batteries and supports Bluetooth wireless transmission. It is lightweight, portable and easy to use. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic diagram of the structure of the EEG cap;

[0038] Figure 2 The three-view and three-dimensional images of the EEG cap;

[0039] Figure 3 This is a schematic diagram of wearing an EEG cap;

[0040] Figure 4 Design a schematic diagram for the EEG acquisition system;

[0041] Figure 5 Simplified structural cross-section diagram for flexible electrodes;

[0042] Figure 6 Schematic diagram of the morphology comparison between the rigid capacitive electrode (left) and the flexible capacitive electrode (right) when in contact with the scalp;

[0043] Figure 7 Schematic diagram of EEG signal preprocessing circuit;

[0044] Figure 8 Schematic diagram of the power supply circuit of the pre-processing circuit;

[0045] Fig. 9 This is the PCB design diagram of the EEG signal preprocessing circuit (2D on the left and 3D on the right);

[0046] Fig.10 This is the simulation result diagram of the spectrum response curve of the EEG signal preprocessing circuit; DETAILED DESCRIPTION

[0047] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0048] A low-load, long-term wearable EEG cap based on flexible capacitive electrodes includes the following design solutions:

[0049] (1) The present invention designs a simplified EEG signal preprocessing circuit, which adopts a two-stage amplification structure, has a common mode rejection ratio of more than 120dB, and a circuit amplification gain of more than 5000 times. At the same time, the circuit can perform online filtering, and users can adjust the range of online filtering according to their needs, such as choosing to effectively amplify signals in the range of 1Hz to 40Hz and 65Hz to 100Hz. At the same time, a signal post-processing circuit is also designed to realize signal A / D conversion and Bluetooth wireless transmission.

[0050] (2) The present invention completes the PCB layout design based on the above circuit design. The preprocessing circuit is integrated on a circular flexible board with a diameter of 3 cm, and the board is made of PI material. The design also includes a serpentine plate for signal input and output and power input. The "snake" design can enhance the contact stability between the electrode and the scalp and buffer the impact of large-scale head movement on the electrode. The circular plate and the serpentine plate are connected to form a whole, which is the capacitive electrode of the present invention. The front side carries the circuit, and the back side is copper-plated and sprayed with insulating paint. The copper area is connected to the front circuit through a via and is surrounded by a 2mm wide grounding copper ring for electromagnetic shielding. In practical applications, the copper-plated area forms a capacitor with the scalp to couple EEG signals.

[0051] (3) The electrode of the present invention adopts a flexible capacitive design. Unlike wet electrodes, capacitive electrodes do not require the application of conductive paste on the scalp or the soaking of the electrode with saline, nor do they require the electrode material to be inserted into the scalp like dry electrodes. Through theoretical derivation and practical experience, for a single capacitive electrode, the larger the capacitance value of the capacitor formed by its coupling with the scalp, the better the signal coupling effect. According to the capacitance calculation formula:

[0052]

[0053] Without changing the intermediate medium (ε r), increasing the contact area (S) and reducing the distance between the plates (d) can increase the capacitance. Compared with rigid capacitive electrodes, flexible designs can make the electrodes fully contact with the scalp (e.g. Figure 5 As shown in the figure, while ensuring that the volume of a single electrode is as small as possible, the contact area is maximized and the average distance between the plates is minimized, thereby increasing the coupling capacitance between the electrode and the scalp and achieving a better signal coupling effect.

[0054] (4) The EEG cap of the present invention is improved based on the headband structure, and a "Y"-shaped structure is added to the top longitudinally to increase the stability when worn and the number of electrode sites. The designed flexible capacitive electrodes are fixed on the EEG cap according to specific arrangement rules (such as Figure 1 , 2 As shown). A rectangular container is designed on the back of the EEG cap to place the circuit board, which performs the following three main functions: 1. Powering the signal preprocessing circuit: The designed voltage transformer and regulated power supply can be powered by a battery or a USB Type-C interface, with an input of 3-7V DC power supply and an output of ±12V DC power supply. 2. A / D conversion of the signal: The EEG signals collected by each electrode are converted into digital signals. 3. Signal transmission: The preprocessed EEG signals are wirelessly transmitted to a computer or mobile phone via Bluetooth, or wired connection is achieved through the USB Type-C interface. Figure 4 It is a schematic diagram of the overall system design of the present invention.

[0055] The following is further explained with specific examples:

[0056] (1) Electrode design and manufacturing. Based on the flexible PCB packaging technology, the present invention designs a flexible capacitive electrode. Figure 5 The simplified cross-sectional view of the electrode. The PCB layout and wiring design was completed using Altium Designer 23 software. Fig. 9 This is the PCB design diagram of the EEG signal preprocessing circuit (2D on the left and 3D on the right). The design integrates the signal preprocessing circuit on a circular flexible board with a diameter of 3 cm to achieve signal amplification and filtering functions. The front of the electrode is used to carry the signal acquisition circuit, and the back is paved with a copper layer and sprayed with insulating paint to form a capacitor coupled to the scalp, and the coupled signal is connected to the input end of the front circuit through the vias on the board. A 2mm wide grounding copper ring is designed around the electrode to provide electromagnetic shielding.

[0057] (2) Design of EEG cap structure. Figure 1 , 2As shown, the appearance design of the EEG cap is based on the improvement of the headband structure, and a "Y"-shaped structure is added to the top to enhance the stability when worn and increase the number of electrode sites. The headband 1 and the Y-shaped headband 2 are both made of double-layer elastic material, with wires embedded in the headband 1, and flexible electrode sheets 3 (i.e., flexible capacitive EEG electrodes) embedded in the Y-shaped headband 2. The flexible capacitive EEG electrodes are fixed on the EEG cap according to certain arrangement rules to ensure effective coverage of the main brain areas of the scalp. A rectangular container box 4 made of plastic is located on the back of the cap, with a built-in circuit board for power supply, A / D conversion and wireless signal transmission. Reference numeral 5 represents two Type-C interfaces, one for connecting a power source and the other for wired transmission of signals. The rectangular container box 4 has a battery storage space and can also be powered by a battery.

[0058] (3) Signal preprocessing circuit, such as Figure 7 As shown, the circuit of the copper foil electronic circuit layer adopts a signal preprocessing circuit, which includes a 50Hz double-T trap circuit, a preamplifier high-pass filter circuit and a secondary amplifier low-pass filter circuit connected in sequence.

[0059] The 50Hz double-T trap circuit specifically includes: a first capacitor C1, a second capacitor C2 connected in series with the first capacitor C1, and a third capacitor C3 connected in parallel with the first capacitor C1 and the second capacitor C2. The values ​​of the first capacitor C1 and the third capacitor C3 are 50nF, and the value of the second capacitor C2 is 100nF;

[0060] The first resistor R1 is connected in series with the first capacitor C1, the second resistor R2 is connected in series with the second capacitor C2, the third resistor R3 is connected in series with the third capacitor C3, and the fourth resistor is connected in series with the second resistor R2. The value of the first resistor R1 is greater than 1MΩ, the values ​​of the second resistor R2 and the fourth resistor R4 are 64KΩ, and the value of the third resistor R3 is 32KΩ; the first resistor R1 is the input bias resistor.

[0061] Requirements for input bias resistor: For the design of the present invention, it should be >=1MΩ. The role of input bias resistor: 1. Impedance matching: The output impedance of capacitive sensors is usually very high, and if the input impedance of the amplifier circuit is low, the signal may not be effectively transmitted. Connecting a larger resistor in series can improve the driving ability of the sensor end, making the signal easier to be received by the amplifier circuit. 2. Reduce the influence of parasitic capacitance: The initial capacitance of the capacitive sensor is very small, but the parasitic capacitance such as the lead cable capacitance connecting the sensor and the electronic circuit, the stray capacitance of the electronic circuit, and the capacitance formed by the capacitor plate and the surrounding conductor is large. The existence of these parasitic capacitances not only reduces the measurement sensitivity, but also causes nonlinear output. Connecting a large resistor in series may help reduce the influence of parasitic capacitance on the signal. 3. Isolating DC components: The RC coupling amplifier circuit uses the AC-passing and DC-blocking characteristics of the capacitor to allow AC signals to pass through while the DC component is blocked. In some cases, if the amplifier circuit is sensitive to the DC component, then connecting a large resistor in series may help isolate the DC component and avoid affecting the amplifier circuit. 4. Reduce noise and interference: Large resistors can act as filters to reduce the impact of high-frequency noise and interference signals on the amplifier circuit, thereby improving the signal-to-noise ratio of the signal. 5. Miller effect: In the amplifier circuit, due to the existence of the Miller effect, the capacitor at the input end will be equivalent to a larger capacitor due to the amplification effect. Connecting a large resistor in series may help reduce the impact of the Miller effect on the circuit, so that the signal can be amplified more accurately. The above is an analysis of the role of the pre-resistance from a professional perspective. In the actual test process, if this resistor is not added, the output end of the entire circuit cannot detect the target signal. Adding this resistor can do it.

[0062] The OFFSETN1 and OFFSETN2 pins of the first operational amplifier U1 (model UA741CD) are used to adjust the bias, the VCC+ and VCC- pins are connected to the +12V and -12V power supplies respectively, and the IN+ and IN- pins are connected to R4 and the OUT pin respectively;

[0063] A fifth resistor R5 is connected in series with the OUT pin of U1, a sixth resistor R6 is connected in series with R5 and then grounded, a value of the fifth resistor R5 is 1KΩ, and a value of the sixth resistor R6 is 10KΩ;

[0064] The second operational amplifier U2 (model UA741CD) has a similar structure to U1. Its OFFSETN1 and OFFSETN2 pins are used to adjust the bias, the VCC+ and VCC- pins are connected to the +12V and -12V power supplies respectively, the IN+ and IN- pins are connected to R6 and R3 respectively, and the OUT pin outputs the signal.

[0065] The preamplifier high-pass filter circuit specifically includes: a fourth capacitor C4, an eighth resistor R8 connected in parallel with the fourth capacitor C4, and the other end of the fourth capacitor C4 is grounded. The values ​​of the fourth capacitor C4 and the fifth capacitor C5 are 100uF, and the value of the eighth resistor R8 is 80.6KΩ;

[0066] The - and + pins of the fourth operational amplifier U3 (model UA128U) are connected to C4 and R5 respectively, the V+ and V- pins are connected to +12V and -12V power supplies respectively, the two RG pins are connected to both ends of the seventh resistor R7 respectively, the REF pin is grounded, and the output pin 6 is connected to the eighth resistor R8. The value of the seventh resistor R7 is 1KΩ.

[0067] The secondary amplification low-pass filter circuit specifically includes: a fifth capacitor C5, an eighth resistor R10 connected in parallel with the fifth capacitor C5, and the other end of the eighth resistor R10 is grounded. The value of the fifth capacitor C5 is 100nF, and the value of the eighth resistor R10 is 100KΩ;

[0068] The OFFSETN1 and OFFSETN2 pins of the sixth operational amplifier U4 (model UA741CD) are used to adjust the bias, the IN+ and IN- pins are connected to the fifth capacitor C5 and the ninth resistor R9 respectively, the other end of the ninth resistor R9 is grounded, and the OUT pin outputs the signal. The value of the ninth resistor R9 is 330Ω;

[0069] The sixth capacitor C6 is connected to the eleventh resistor R11 in parallel and connected to the OUT pin of U4, and the other end is connected to the IN- pin of U4. The value of the sixth capacitor C6 is 44nF, and the value of the eleventh resistor R11 is 36KΩ.

[0070] The present invention designs a simplified EEG signal preprocessing circuit, such as Figure 7 As shown, the entire circuit is divided into three modules: a 50Hz double-T notch module, a preamplifier high-pass filter module, and a two-stage amplifier low-pass filter module. The signal amplification part adopts a two-stage amplification design, and integrates the high-pass and low-pass filter circuits into the two-stage amplification respectively, which not only saves components and simplifies the circuit structure, but also improves the signal-to-noise ratio of the entire circuit. The circuit uses two amplifier chips, μ741 and INA128, with a common mode rejection ratio of 120dB and an amplification gain of up to 5000 times. Through online filtering, the circuit only effectively amplifies signals within a specific frequency range set in advance by the user, such as signals in the range of 1Hz to 40Hz and 65Hz to 100Hz. Fig.10 This is the simulation result of the frequency response analysis of the circuit using Multisium software.

[0071] (4) The power management module uses signal post-processing circuits, such as Figure 8As shown, the signal post-processing circuit includes a DC-DC boost circuit and a DC-DC negative voltage circuit.

[0072] The DC-DC boost circuit (5V to 12V) specifically includes: a first diode D1 (model SS14), a first capacitor C1 connected in parallel with D1, a first resistor R1 connected in parallel with D1, a first inductor L1 connected in series with D1, and a second resistor R2 connected in series with the first resistor R1. The value of the first capacitor C1 is 22nF, the value of the first resistor R1 is 191KΩ, the value of the second resistor R2 is 10KΩ, and the value of the first inductor L1 is 4.7μH; a third resistor R3, C2 connected in parallel with the second capacitor, the value of the third resistor R3 is 100KΩ, and the value of the second capacitor C2 is 22μF; the SW pin of the first DC-DC rectifier chip IC1 is connected to the first diode D1+ pin, the FB pin is connected to the second resistor R2, the GND pin is grounded, the NC pin is vacant, the VCC pin is connected to the +5V power supply, and the EN pin is connected to the third resistor R3.

[0073] The DC-DC negative voltage circuit (5V to -12V) specifically includes: a first diode D2 (model SS34), a first capacitor C3 connected in parallel with D2, a fourth capacitor C4 connected in parallel with D2, a second capacitor C5 connected in series with C4, and a second inductor L2 connected in series with D2. The value of the third capacitor C3 is 0.1μF, the value of the fourth capacitor C4 is 470μF, the value of the second inductor L2 is 100μH, and the value of the fifth capacitor C5 is 1500pF; a fourth resistor R4, and a fifth resistor R5 connected in series with R4. The value of the fourth resistor R4 is 1KΩ, and the value of the fifth resistor R5 is 8.6KΩ; a seventh capacitor C7, a sixth capacitor C6 connected in parallel with C7, and a sixth resistor R6 connected in parallel with C7. The value of the seventh capacitor C7 is 0.1μF, the value of the sixth capacitor C6 is 100μF, and the value of the sixth resistor R6 is 240mΩ; pin 1 of the second DC-DC rectifier chip U1 (model MC34063AD) is connected to R6, pin 2 is connected to the - pin of D2, pin 3 is connected to C5, pin 4 is connected to R4, pin 5 is connected to R5, pin 6 is connected to R6, and pins 7 and 8 are short-circuited with pin 1.

[0074] The signal preprocessing circuit of the present invention uses two chips, μ741 and INA128. These two chips need to be driven by positive and negative dual power supplies when performing signal amplification. The magnitude of the driving voltage determines the signal output range of the signal preprocessing circuit. The battery power supply (usually 3.7V) or the charging power supply through the USB interface (usually 5V) used in daily life cannot meet the demand. Therefore, the present invention designs a power management module for the signal preprocessing circuit, such as Figure 8 This module can realize the functions of voltage conversion and voltage stabilization. When the input is a DC power supply in the range of 3 to 7V, it can stably output a DC power supply of ±12V.

[0075] (5) Wearing and operation of the EEG cap. Figure 3 This is a diagram of how to wear an EEG cap. The user wears the EEG cap on the head and adjusts the cap strap and the "Y" design position to ensure that the electrodes fit tightly against the scalp. The flexible material can deform according to the curve of the head to reduce wearing pressure. After starting the device, the electrodes automatically collect EEG signals and transmit them to the receiving device in real time via wireless or wired means. The user can monitor and analyze the data through the supporting software.

[0076] Figure 6 The cross-sectional schematic diagram of the rigid electrode and the flexible electrode in contact with the scalp respectively is simulated. The black line simulates the scalp contour, the green line represents the rigid capacitive electrode, and the yellow line represents the flexible capacitive electrode. Compared with the rigid capacitive electrode, the flexible design can make the electrode fully contact with the scalp, and maximize the contact area and minimize the average inter-plate distance while ensuring that the volume of a single electrode itself is as small as possible, thereby increasing the coupling capacitance between the electrode and the scalp and achieving better signal coupling effect, giving full play to the advantages of capacitive electrodes and solving the problems of poor coupling signal capability and low signal-to-noise ratio of capacitive electrodes.

[0077] The following is a case of measuring EEG using a low-load flexible capacitive EEG cap.

[0078] Step 1: Clean the skin around your forehead and right ear.

[0079] Step 2: Press Figure 3 As shown in the wearing diagram, the EEG cap is worn on the head, ensuring that all flexible electrodes are in close contact with the scalp, and the rectangular receiving box on the cap body is located near the back of the head.

[0080] Step 3: Turn on the power switch, turn on the computer or other mobile device, and maintain data communication.

[0081] Step 4: Carry out the required tasks or tests. The EEG signals will be transmitted to the host device in wireless or wired form, and displayed in real time in a graphical form. After the experiment, you can choose to save the EEG signal data.

[0082] Step 5: Turn off the power, disconnect, and take off the EEG cap.

[0083] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0084] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0085] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0086] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0087] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A low-load flexible capacitive EEG cap, characterized in that: include: Headband; A Y-shaped headband, the Y-shaped headband is fixed on the head ring and is used to fit the scalp; Flexible capacitive EEG electrodes arranged on the inner sides of the head ring and the Y-shaped headband; The flexible capacitive EEG electrode comprises: Polyimide flexible substrate; A copper foil electronic circuit layer and a copper foil conductive layer are arranged on both sides of the polyimide flexible base layer; a first insulating layer disposed on the copper foil electronic circuit layer; A second insulating layer disposed on the copper foil conductive layer; The copper foil electronic circuit layer is electrically connected to the copper foil conductive layer through a wire passing through the polyimide flexible base layer.

2. The low-load flexible capacitive EEG cap according to claim 1, characterized in that: The number of the flexible capacitive EEG electrodes on the headband is 6 to 10.

3. The low-load flexible capacitive EEG cap according to claim 1, characterized in that: The number of the flexible capacitive EEG electrodes on the Y-shaped headband is 7 to 10.

4. The low-load flexible capacitive EEG cap according to claim 1, characterized in that: The circuit of the copper foil electronic circuit layer adopts a signal preprocessing circuit, which includes a double-T trap circuit, a preamplifier high-pass filter circuit and a secondary amplifier low-pass filter circuit connected in sequence.

5. The low-load flexible capacitive EEG cap according to claim 4, characterized in that: The input end of the double-T trap circuit is connected with an input bias resistor.

6. The low-load flexible capacitive EEG cap according to claim 4, characterized in that: The center frequency of the double-T trap circuit is 50±2Hz.

7. The low-load flexible capacitive EEG cap according to claim 4, characterized in that: The preamplifier high-pass filter circuit is a circuit that allows signals with a frequency greater than or equal to a frequency threshold to pass through.

8. The low-load flexible capacitive EEG cap according to claim 4, characterized in that: The two-stage amplification low-pass filtering circuit refers to a circuit that allows signals with a frequency less than or equal to a frequency threshold to pass through.

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