Electrode cap design method based on mechanical adaptation

Abstract

The invention provides an electrode cap design method based on mechanical adaptation, which comprises the following steps: regarding an electrode cap body as a uniform film, and describing a quantitative relation between cap body tension and contact pressure by adopting a Young-Laplace equation; under the constraint of the relation and boundary conditions, a cap body main stress path (rod unit) is dispersed into an international 10-10 standard electrode cap body network, adjacent electrodes are connected through silica gel strips and are regarded as a truss structure, a unit stiffness matrix of the rod unit is introduced, a global stiffness matrix is obtained through coordinate transformation, and the overall stiffness matrix is obtained. By adjusting the width, the thickness and the rigidity coefficient of the strip, the matching design of the pressure distribution of the skull target is realized.

Description

Electrode Cap Design Method Based on Mechanical Adaptation Technical Field

[0001] This invention relates to the field of brain-computer interface technology, specifically an electrode cap design method based on mechanical adaptation. Background Technology

[0002] As brain science and technology continue to advance towards higher precision, higher density, and longer-term monitoring, and as brain-computer interface technology rapidly gains popularity in medical rehabilitation and consumer electronics, unprecedentedly high standards are being placed on the performance of the core signal acquisition device—the electrode cap. In many fields such as medical diagnosis, scientific research, and clinical treatment, including electroencephalography (EEG), brain-computer interfaces, non-invasive electrical stimulation, and other neural signal acquisition devices, the structural design of the electrode cap directly determines the quality of the EEG signal, thus affecting the accuracy of diagnosis and the reliability of interaction.

[0003] Currently, mainstream electrode caps still generally follow standardized and experience-based design paradigms. Their structures largely rely on the overall binding force of elastic fabrics, passively adapting to complex individual head shape differences through macroscopic deformation of the material. This design concept has fundamental limitations: First, it cannot accurately match the mechanical properties according to the continuous changes in the three-dimensional curvature of the head, resulting in extremely uneven pressure distribution at the electrode contacts. Localized pressure concentration causes compressive discomfort for the wearer and may even affect local blood circulation. Second, the imbalance in pressure distribution directly affects the testing of electrical signals, manifesting as fluctuations in electrode-scalp contact impedance, a decrease in the overall signal-to-noise ratio, an increase in motion artifacts, and a weakening of effective neural components, making it difficult to obtain high-fidelity and stable EEG data. Summary of the Invention

[0004] To address the problems of existing technologies, this invention provides an electrode cap design method based on mechanical adaptation. The designed electrode cap enables uniform pressure on the scalp during wear, especially the pressure distribution at the electrode points, thereby improving the stability of signal acquisition and wearing comfort.

[0005] This invention provides a method for designing electrode caps based on mechanical adaptation, comprising the following steps:

[0006] 1) Establish a solid film mechanical model of the contact area between the electrode cap and the head, and regard the elastic cap body of the electrode cap as a thin film;

[0007] 2) The Young–Laplace equation is used to describe the quantitative relationship between cap tension and contact pressure, yielding...

[0008]

[0009] in, The pressure on the head, along the outer normal of the scalp, is expressed in Pa. The comfortable pressure range that the scalp can withstand is 5–20 kPa. T is the elastic tension of the cap, expressed in N / m. R is the radius of curvature of the spherical surface of the area in contact with the head, expressed in N, obtained by consulting average head circumference data. E is the elastic modulus of the cap material, expressed in Pa. t is the thickness of the cap, expressed in m. ε is the tensile strain of the cap.

[0010] 3) Determine the target contact pressure Given the radius of curvature R of the head, calculate the corresponding tension T;

[0011] 4) Select the material of the electrode cap, obtain the elastic modulus E and tensile strain ε based on the electrode cap material, and derive the thickness t of the cap body as a design parameter;

[0012] 5) Discretize the main force path (rod element) of the cap body into an electrode network that conforms to the international 10-10 standard. Connect adjacent electrodes with silicone strips, as shown in Figure 1. Simplify the electrode cap strips into rod elements. Calculate the global stiffness matrix based on the unit stiffness matrix of the rod elements. Adjust the displacement of electrode nodes 1 and 2 and the tension T of the strips by changing the stiffness coefficients of the strips (rod elements) to achieve a matching design for the pressure distribution P of the head target.

[0013] 6) The method described above is a method for solving the global stiffness matrix. The element stiffness equation of the rod element in the local coordinate system is: The unit stiffness matrix of the bar element is: , The actual displacements of nodes 1 and 2 in the local coordinate system; derived from geometric relations (projection of global displacement to local axial displacement, denoted as C = (where θ is the angle between the direction of the rod element and the global coordinate system). ,in, , , For the displacement in the global coordinate system, the coordinate transformation matrix is: The stiffness matrix in the global coordinate system is obtained from the transformation matrix: The global stiffness matrix of a multi-member structure can be coupled into In the form of.

[0014] Further improvements include using medical-grade silicone, thermoplastic elastomer (TPE), or polyurethane (PU) elastic film as the electrode cap material, with an elastic modulus of 0.3-1.5 MPa.

[0015] Further improvements, in step 2), the specific process of characterizing the quantitative relationship between cap tension and contact pressure using the Young-Laplace equation in the form of a solid film is as follows:

[0016] 2.1) The Young–Laplace solid thin film form satisfies:

[0017]

[0018] in, The pressure difference across the surface, unit: Pa, 1 Pa = 1 N / m²; Surface tension of liquid, unit: N / m; , Let be the two principal radii of curvature of the surface, in meters;

[0019] 2.2) Since the head is approximately a quasi-sphere, any two principal radii of curvature of the sphere are equal, therefore R1=R2=R. = , liquid surface tension Replace it with the elastic tension T generated by the stretching of the cap body, and obtain .

[0020] Further improvements, step 5) describes the international 10-10 standard electrode network, which contains 64 electrode points and is an international arrangement system for EEG electrodes. The electrodes are arranged at equal intervals of 10% along the arc length of the scalp, with the nasal root-occipital point and the anterior points of both ear tragus as references.

[0021] The beneficial effects of this invention are as follows:

[0022] 1. The electrode cap is simplified into a thin-film shell. The Young-Laplace equation is used to quantify the relationship between the electrode cap tension and the pressure on the skull. Reverse structural optimization for mechanical adaptation is performed, ultimately achieving a technological leap from "passive adaptation" to "active adaptation," providing a solid theoretical basis and advanced design tools for the development of next-generation high-performance electrode caps.

[0023] 2. The optimized electrode cap is compatible with various head sizes, and personalized adaptation can be achieved by replacing local modules or adjusting the parameters of the connecting strip. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 shows a simplified diagram of the stress analysis and structure.

[0026] Figure 2 is a schematic diagram of the local-global coordinates of the strip (rod element). Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] One specific embodiment of the present invention is as follows:

[0029] 1. Establish a solid film mechanical model of the contact area between the electrode cap and the head, and regard the electrode cap or external shell as a thin film / shell attached to the outside of the scalp, as shown in Figure 1.

[0030] 2. The Young–Laplace equation is used to describe the quantitative relationship between cap tension and contact pressure. The contact area between the cap and the head can be approximated as a sphere (the principal radii of curvature are both the radius of curvature R of the head in this area), and for any two principal radii of curvature on the sphere, they are equal. =R), replacing the liquid surface tension in the original Young-Laplace equation with the elastic tension T generated by the cap's stretching, and finally establishing The quantification relationships with E, ε, t, and R yield the Young-Laplace equation for solid thin films (spherical case):

[0031]

[0032]

[0033] Pressure on the head, along the outer normal of the scalp, unit: Pa

[0034] T: Elastic tension of the cap, unit: N / m

[0035] R: Radius of spherical curvature of the head contact area, unit: N

[0036] E: Elastic modulus of the cap material, unit: Pa (N / m²)

[0037] t: Thickness of the cap, unit: m

[0038] ε: Tensile strain of the cap (dimensionless)

[0039] Based on the comfortable pressure range that the scalp can withstand (5–20 kPa) and the head circumference data in the "Chinese Three-Dimensional Human Head Measurement Study", the target contact pressure and the head curvature radius R are determined, and the corresponding tension T is calculated.

[0040] By determining Given R, calculate the tension T when the electrode cap is worn, and then according to... The deformation of the electrode cap was determined, and the size of the electrode cap when it was not worn was obtained.

[0041] 3. Based on the international 10–10 electrode layout standard, establish a 64-point structural model or the international 10–20 and 10–5 electrode layout standards, establish 16, 32, and 128-point structural models, as shown in Figure 1. The connection between adjacent electrode points via silicone strips is simplified into a truss structure. Using the finite element analysis method, the electrode cap strip is simplified into a rod element L. Based on the unit stiffness matrix of the rod element, the global stiffness matrix is ​​obtained. By changing the stiffness coefficient of the strip (rod element), the displacement of the electrode node and the tension T of the strip are adjusted to achieve the matching design of the pressure distribution p of the head target.

[0042] 4. The method described above is a method for solving the global stiffness matrix. As shown in Figure 2, the element stiffness equation of the rod element in the local coordinate system is: The unit stiffness matrix of the bar element is: , The actual displacements of nodes 1 and 2 in the local coordinate system; derived from geometric relations (projection of global displacement to local axial displacement, denoted as C = (where θ is the angle between the direction of the rod element and the global coordinate system). ,in, , , For the displacement in the global coordinate system, the coordinate transformation matrix is: The stiffness matrix in the global coordinate system is obtained from the transformation matrix: The global stiffness matrix of a multi-member structure can be coupled into In the form of.

[0043] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on its differences from other embodiments. In particular, for the device embodiments, the above descriptions are merely preferred embodiments of the present invention. Since they are fundamentally similar to the method embodiments, the descriptions are relatively simple, and relevant parts can be referred to the descriptions of the method embodiments. The above descriptions are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention, without departing from the principle of the present invention, should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for designing an electrode cap based on mechanical adaptation, characterized in that... Includes the following steps: 1) Establish a solid film mechanical model of the contact area between the electrode cap and the head, treating the elastic cap body as a thin film; 2) Use the Young-Laplace equation to describe the quantitative relationship between the cap tension and the contact pressure, obtaining... ;in, 1) The pressure on the head, along the outer normal direction of the scalp, is expressed in Pa; T is the tension of the cap strip, in N / m; R is the radius of curvature of the spherical surface of the head contact area, in m; E is the elastic modulus of the cap material, in Pa; t is the thickness of the cap, in m; ε is the tensile strain of the cap; 3) Determine the target contact pressure p and the radius of curvature R of the head, and calculate the corresponding tension T; 4) Select the material of the electrode cap, obtain the elastic modulus E and tensile strain ε based on the electrode cap material, and derive the thickness t of the cap as a design parameter; 5) Discretize the main force path of the cap, i.e., the rod element, into an electrode network of the international 10–10 standard, with adjacent electrodes connected by silicone strips, considered as a truss structure; 6) Treat the strips as rod elements, introduce the unit stiffness matrix of the rod element, and obtain the global stiffness matrix through coordinate transformation. By adjusting the strip width, thickness, and stiffness coefficient, the pressure distribution of the head target can be matched and the pressure uniformity can be improved. Here, A is the cross-sectional area of ​​the rod element, in m²; L is the length of the rod element, in m.

2. The electrode cap design method based on mechanical adaptation according to claim 1, characterized in that: The electrode cap material is selected from medical-grade silicone, thermoplastic elastomer (TPE), or polyurethane (PU) elastic film, with an elastic modulus of 0.3-1.5 MPa.

3. The electrode cap design method based on mechanical adaptation according to claim 1, characterized in that: Step 2) The specific process of using the Young–Laplace equation to describe the quantitative relationship between cap tension and contact pressure is as follows: 2.1) The Young–Laplace equation satisfies: ;in, The pressure of the membrane, in Pa, 1 Pa = 1 N / m²; Thin film tension, unit: N / m; 、 Let R1 be the two principal radii of curvature of the surface, in meters (m). 2.2) Since the head is approximately a quasi-sphere, any two principal radii of curvature of the sphere are equal; therefore, R1 = R2 = R. = , liquid surface tension Replace it with the elastic tension T generated by the stretching of the cap body, and obtain 。 4. The electrode cap design method based on mechanical adaptation according to claim 1, characterized in that: Step 5) The international 10-10 standard electrode network contains 64 electrode points and is an international arrangement system for EEG electrodes. Based on the nasal root-occipital point and the anterior points of both ear tragus, the electrodes are arranged at equal intervals of 10% along the arc length of the scalp.

5. The electrode cap design method based on mechanical adaptation according to claim 1, characterized in that: Step 6) The specific method for solving the global stiffness matrix is ​​as follows: The element stiffness equation of the rod element in the local coordinate system is: The unit stiffness matrix of the bar element is: ； The actual displacements in the local coordinate system of nodes 1 and 2; based on geometric relationships, i.e., the projection of the global displacement onto the local axial displacement: Where, let C = θ is the angle between the direction of the rod element and the global coordinate system. ， ， For the displacement in the global coordinate system, the coordinate transformation matrix is: The stiffness matrix in the global coordinate system is obtained from the transformation matrix: The global stiffness matrix of multiple members is coupled into In the form of.

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