Material young's modulus measuring device based on electromagnetic-capacitive coupling mechanism and application

Abstract

The application relates to the technical field of material mechanical property testing, in particular to a material Young's modulus measuring device based on an electromagnetic-capacitive coupling mechanism and application. A non-magnetic support structure comprises a top wall, a side wall and a bottom wall, the top wall is provided with a guide structure on the side facing the bottom wall, the bottom wall is provided with a bottom opening, an electromagnetic driving unit comprises a magnetic ring arranged on the inner wall of the side wall and a coil coaxially arranged in the magnetic ring, the coil is electrically connected with an external power supply and reciprocally moves along the axial direction under the driving of a square wave electric signal to generate a controllable Lorentz force; a capacitive sensing unit comprises a first capacitive electrode and a second capacitive electrode, the first capacitive electrode is fixed on the guide structure, and the second capacitive electrode is fixed on the inner side of the coil. By coaxially integrating the electromagnetic driving unit and the capacitive sensing unit in a compact physical structure, a complete "excitation-response-parameter inversion" closed-loop measurement link is realized, and the detection sensitivity, measurement precision and stability are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of material mechanical property testing technology, specifically to a material Young's modulus measurement device and its application based on an electromagnetic-capacitive coupling mechanism. Background Technology

[0002] With the widespread application of biomaterials and soft materials in medicine, flexible electronics, and sensor technology, accurately measuring the Young's modulus of these materials has become an important research topic. Young's modulus is a crucial parameter describing the mechanical properties of materials, especially significant in evaluating soft tissues, biomimetic materials, and other biomaterials. However, existing methods for measuring Young's modulus still have significant limitations in some key applications, failing to meet the demands for high-precision, micro-load, and non-invasive measurements.

[0003] Currently, methods for measuring Young's modulus of biological and soft materials mainly include ultrasonic elastography and magnetic resonance elastography, direct mechanical loading methods (such as tensile / compression tests), and vibration-based impact excitation (IET). Among these, ultrasonic elastography and magnetic resonance elastography rely on large, expensive equipment, are complex to operate, and require high-precision testing environments, making them difficult to port and cost-effective. Furthermore, their accuracy and resolution are limited in measuring soft materials and biological samples, failing to meet the requirements for precise quantitative Young's modulus testing. Direct mechanical loading requires significant contact force, which can easily damage soft materials or biological samples, especially in testing small samples or thin-layer materials, where traditional contact loading can easily lead to sample destruction or errors. Moreover, this method is difficult to achieve accurate measurements under non-invasive, micro-load conditions, limiting its application in biomedical research and other fields. Traditional IET systems often rely on mechanical impact excitation and acoustic sensor detection, resulting in poor controllability of the excitation signal, low system integration, and difficulty in achieving miniaturization and high repeatability of excitation. Furthermore, the vibration frequency is greatly affected by factors such as material shape and structure, making it difficult to control measurement errors. While existing research has utilized the Lorentz force principle to achieve controllable excitation, it has primarily been applied to precision drive applications and has not yet been fully integrated with Young's modulus measurement systems. Although capacitive sensors are highly sensitive to micro-displacements, they are often used as independent sensing units in mechanical parameter inversion, failing to be effectively integrated with controllable excitation sources, thus hindering the provision of highly sensitive and stable excitation and response detection. Therefore, there is an urgent need to provide a Young's modulus measurement device with controllable excitation, sensitive detection, and high system integration to address these issues. Summary of the Invention

[0004] The purpose of this invention is to provide a material Young's modulus measurement device based on an electromagnetic-capacitive coupling mechanism. Through the integrated coupling mechanism of electromagnetic drive and capacitance detection, a complete "excitation-response-parameter inversion" closed-loop measurement link is formed to solve the problems of poor excitation controllability, low detection accuracy and sensitivity in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a material Young's modulus measurement device based on an electromagnetic-capacitive coupling mechanism, comprising:

[0006] A non-magnetic support structure includes a cylindrical portion and a guide structure. The cylindrical portion includes a top wall, a side wall, and a bottom wall. The guide structure is provided on the side of the top wall facing the bottom wall and extends along the axial direction of the cylindrical portion. The bottom wall has a bottom opening for communicating with the material to be tested.

[0007] The electromagnetic drive unit includes a magnetic ring disposed on the inner wall of the sidewall and a coil coaxially disposed inside the magnetic ring. The coil is electrically connected to an external power source and is sleeved around the periphery of the guide structure. The coil reciprocates axially under the drive of a square wave electrical signal from the external power source to provide controllable excitation to the material under test.

[0008] The capacitance sensing unit includes a first and a second capacitor electrode, both of which are ring-shaped. The first capacitor electrode is fixed to the periphery of the guide structure, and the second capacitor electrode is fixed to the inner side of the coil. In the non-working state, the second capacitor electrode is located directly opposite the first capacitor electrode. In the working state, the second capacitor electrode reciprocates along the axial direction with the coil, causing the area directly opposite the first capacitor electrode to change, thereby causing a change in capacitance. The capacitance sensing unit is electrically connected to an external monitoring unit, which is used to monitor capacitance and invert the Young's modulus of the material under test.

[0009] Furthermore, the amplitude of the axial reciprocating motion of the coil does not exceed 5 mm.

[0010] Furthermore, the heights of both the first and second capacitor electrodes are not less than the amplitude of the coil reciprocating along the axial direction, so that the first and second capacitor electrodes always have facing areas when the coil reciprocates along the axial direction.

[0011] Furthermore, the height of the coil is greater than the height of the magnetic ring, so that when the coil reciprocates along the axial direction, there is always an overlapping area between the coil and the magnetic ring in the radial direction.

[0012] Furthermore, the outer diameter of the coil is smaller than the inner diameter of the magnetic ring, so that a radial gap is formed between the coil and the magnetic ring, providing the necessary mechanical margin for the coil to move axially.

[0013] Furthermore, it also includes a support column, which is fixed below the guide structure and coaxially arranged with the guide structure to prevent the coil from shifting position when it reciprocates along the axial direction.

[0014] Furthermore, the support column is a columnar iron core used to enhance the Lorentz force.

[0015] Furthermore, the inversion calculation formula for measuring the Young's modulus E of the material under test by the material Young's modulus measuring device is as follows: ;

[0016] in, The contact area between the material to be tested and the coil. The nominal length of the material to be tested. The initial overlap length between the first capacitor electrode and the second capacitor electrode. The initial capacitance of the capacitance sensing unit, The change in capacitance The fixed height of the non-magnetic support structure, Total effective loading force;

[0017] The formula for calculating the total effective loading force is: ,in, The Lorentz force generated by the coil, The total weight of the coil and the second capacitor electrode is denoted as .

[0018] Furthermore, both the first capacitor electrode and the second capacitor electrode include a dielectric layer and a conductive paste layer coated on the dielectric layer, with the conductive paste layer being the opposite side of the first capacitor electrode and the second capacitor electrode.

[0019] This application also provides the application of the above-mentioned Young's modulus measuring device in the field of Young's modulus measurement of biomaterials and soft materials.

[0020] The beneficial effects of this invention are as follows: The material Young's modulus measurement device based on the electromagnetic-capacitive coupling mechanism provided by this invention coaxially integrates an electromagnetic drive unit and a capacitance sensing unit into a compact physical structure. A square wave electrical signal drives a coil to reciprocate along the axis, generating a small, transient, and amplitude-controllable axial excitation force, thereby applying precise excitation to the material under test. Simultaneously, the capacitance sensing unit monitors capacitance changes in real time and can derive micron-level compressive displacement, thus accurately inverting the Young's modulus of the material under test. This achieves a complete "excitation-response-parameter inversion" closed-loop measurement chain, significantly improving the measurement accuracy and stability of the material Young's modulus measurement device. This material Young's modulus measurement device overcomes the limitations of traditional measurement methods in high-precision, micro-load, and non-invasive measurements, and has broad application prospects in the micro-load, non-invasive, and quantitative testing of biological and soft materials.

[0021] By coaxially arranging the magnet, coil, and capacitor electrodes and introducing a support column, the consistency of the excitation force and compressive displacement directions can be ensured, effectively reducing measurement errors caused by radial offset and enabling precise detection of minute deformations in the material under test. This significantly improves the detection accuracy and reliability of the Young's modulus measuring device, enhancing the stability and accuracy of the measurement results.

[0022] By limiting the amplitude of the coil and rationally designing the relative position and height of the capacitor electrodes, it can be ensured that the two capacitor electrodes remain partially overlapped throughout the measurement process. This makes the capacitance change proportional to the deformation of the material under test, thereby effectively reducing systematic errors and instability factors, and further improving the repeatability and long-term reliability of the Young's modulus measurement device.

[0023] By using a columnar iron core as a support column, the magnetic field strength in the coil region can be enhanced, thereby increasing the Lorentz force and significantly improving the resolution of the Young's modulus measurement device for this material. This enables more accurate detection of minute deformations in the material, providing strong support for high-precision measurement.

[0024] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0025] Figure 1 This is an exploded structural diagram of a material Young's modulus measuring device according to an embodiment of the present invention;

[0026] Figure 2 This is a schematic cross-sectional view of a material Young's modulus measuring device according to an embodiment of the present invention;

[0027] Figure 3This is a cross-sectional structural diagram of the Young's modulus measuring device of a material in a non-working state and a working state, according to an embodiment of the present invention.

[0028] Figure 4 This is a three-dimensional structural diagram of the Young's modulus measuring device for materials in a non-working state and a working state, according to an embodiment of the present invention.

[0029] Figure 5 This is a schematic diagram showing the forces acting on the Young's modulus measuring device and the material to be measured in the working state, according to an embodiment of the present invention.

[0030] Figure 6 The magnetic field distribution and magnetic field gradient along the axial direction of the Young's modulus measuring device for materials shown in an embodiment of the present invention;

[0031] Figure 7 This is a block stress-strain curve diagram of seven Shore Hardness A standard blocks as shown in an embodiment of the present invention;

[0032] Figure 8 The original response curves of the capacitance change over time for seven standard blocks under periodic excitation conditions, as shown in an embodiment of the present invention;

[0033] Figure 9 This is a comparison chart of the detection results and calibration experimental data of the material Young's modulus measuring device according to an embodiment of the present invention with the detection data of device B;

[0034] Figure label:

[0035] 1. Electromagnetic drive unit; 11. Magnetic ring; 12. Coil; 2. Non-magnetic support structure; 21. Side wall; 22. Top wall; 23. Bottom wall; 24. Guide structure; 3. Capacitance sensing unit; 31. Second capacitor electrode; 32. First capacitor electrode; 4. Support column; 5. External power supply; 6. Monitoring unit; 7. Material under test. Detailed Implementation

[0036] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0037] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. In the description of this invention, it should be noted that unless otherwise explicitly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0038] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0039] A preferred embodiment of this application provides a material Young's modulus measurement device based on an electromagnetic-capacitive coupling mechanism, such as... Figure 1 As shown, the Young's modulus measuring device for this material includes an electromagnetic drive unit 1, a non-magnetic support structure 2, and a capacitance sensing unit 3. Among them, as... Figure 2As shown, the non-magnetic support structure 2 is used to support and position the entire Young's modulus measuring device, including a cylindrical part and a guide structure. The cylindrical part includes a top wall 22, a side wall 21, and a bottom wall 23. The guide structure 24 is provided on the side of the top wall 22 facing the bottom wall 23, and the guide structure 24 extends along the axial direction of the cylindrical part to support the capacitance sensing unit 3 and guide the coil 12 to reciprocate along the axial direction. The bottom wall 23 has a bottom opening to ensure that the coil 12 can smoothly pass through the non-magnetic support structure 2 and directly act on the material to be measured 7 when reciprocating along the axial direction, so as to achieve effective transmission of excitation force. The electromagnetic drive unit 1 includes a magnetic ring 11 and a coil 12. The magnetic ring 11 is disposed on the inner wall of the side wall 21 and is coaxially disposed with the side wall 21. The coil 12 is disposed inside the magnetic ring 11 and is coaxially disposed with the magnetic ring 11. The coil 12 is electrically connected to the external power supply 5 and is sleeved around the periphery of the guide structure. Driven by a square wave electrical signal, it can reciprocate axially, generating an axial, transient, and amplitude-controllable Lorentz force. This force is used to controllably excite the material 7 under test, effectively avoiding interference and damage that may occur with traditional contact excitation and ensuring the accuracy of the measurement results. The capacitance sensing unit 3 includes two annular capacitor electrodes of the same height, namely a first capacitor electrode 32 and a second capacitor electrode 31. The first capacitor electrode 32 is fixed to the periphery of the guide structure, and the second capacitor electrode 31 is fixed to the inner side of the coil 12; and, as Figure 3 As shown, when the Young's modulus measuring device is in a non-working state, i.e., when the coil 12 is not driven by a driving signal and reciprocates along the axial direction, the second capacitor electrode 31 is exactly in the position directly opposite the first capacitor electrode 32, and the area of ​​their direct contact reaches the initial set value. When the device enters the working state, the coil 12 reciprocates along the axial direction under the drive of an external electrical signal, and the second capacitor electrode 31 moves synchronously. At this time, the area of ​​the second capacitor electrode 31 and the first capacitor electrode 32 facing each other changes, thereby causing a change in the capacitance value. The first capacitor electrode 32 and the second capacitor electrode 31 are electrically connected to the external monitoring unit 6, which is used to monitor the capacitance value to deduce the compression displacement and inversely determine the Young's modulus of the material 7 under test. The Young's modulus measuring device adopts an integrated electromagnetic excitation-capacitance detection design, using a controllable electromagnetic drive as the excitation source and a highly sensitive capacitance sensing unit 3 as the detection unit, integrating the two into a compact physical structure to construct an integrated electromagnetic excitation-capacitance detection coupling mechanism. Based on this mechanism, a complete "excitation-response-parameter inversion" closed-loop measurement link is formed, ultimately yielding the Young's modulus of the material under test 7. The Young's modulus measuring device employs a coaxial arrangement of coil 12, magnetic ring 11, and capacitor electrodes, ensuring that the direction (axial) of the excitation force is completely consistent with the direction of the detected displacement. This effectively reduces measurement errors caused by directional deviations, thereby improving measurement accuracy and stability, and enhancing the accuracy and reliability of the measurement results.

[0040] In this embodiment or other embodiments, the non-magnetic support structure 2 is preferably made of non-magnetic resin material using 3D printing technology to avoid magnetic interference and achieve lightweight and customized effects. The inner cavity size of the sidewall 21 matches the shape of the magnetic ring 11 to fix the magnetic ring 11 and ensure the coaxiality and positioning stability of the magnetic ring 11 and the non-magnetic support structure 2 during assembly, thereby ensuring the stability of each functional component in spatial position and axial orientation.

[0041] In one embodiment, when coil 12 reciprocates along the axial direction, its upper and lower amplitudes are both limited to no more than 5 mm. That is, the maximum height of coil 12 rising or falling during axial reciprocating motion does not exceed 5 mm. This is to avoid excessive amplitude of coil 12 movement, which could lead to drastic or irregular changes in magnetic field strength and gradient, thereby affecting the stability of the electromagnetic driving force and significantly reducing the inversion accuracy of Young's modulus. Appropriate amplitude helps ensure that coil 12 is always within the effective region of the magnetic field gradient, stably sensing changes in the magnetic field and generating a controllable driving force, ensuring stable operation of the device and reliability of measurement results. It also avoids excessive amplitude causing coil 12 to deviate from the ideal working area, leading to drastic or irregular changes in magnetic field strength and gradient, thereby affecting the stability of the electromagnetic driving force and the inversion accuracy of Young's modulus.

[0042] In one embodiment, the first capacitor electrode 32 and the second capacitor electrode 31 have the same height, and are limited to a height not less than the maximum height of the coil 12 during its axial reciprocating motion. This limitation ensures that the first capacitor electrode 32 and the second capacitor electrode 31 remain partially overlapped during the axial reciprocating motion of the coil 12, thereby ensuring the continuity and accuracy of capacitance measurement and providing reliable data for the accurate inversion of Young's modulus. It should be noted that the heights of the first capacitor electrode 32 and the second capacitor electrode 31 refer to their own dimensions.

[0043] In one embodiment, the height of the coil 12 is greater than the height of the magnetic ring 11, ensuring that the coil 12 and the magnetic ring 11 always overlap in the radial direction when the coil 12 reciprocates along the axial direction. This guarantees the stability and controllability of the excitation force, making the measurement results more repeatable and reliable. In some embodiments, to further improve the stability and controllability of the excitation force, the difference between the height of the coil 12 and the height of the magnetic ring 11 is preferably not less than the maximum height of the coil 12 when it descends or rises along the axial direction. This ensures that when the coil 12 descends or rises to its maximum height, it can still penetrate the effective magnetic field range of the magnetic ring 11. It should be noted that the height of the coil 12 and the height of the magnetic ring 11 refer to their own dimensions. In this embodiment or other embodiments, the outer diameter of the coil 12 is smaller than the inner diameter of the magnetic ring 11, creating a radial gap between the coil 12 and the magnetic ring 11. This provides the necessary mechanical margin for the axial movement of the coil 12, preventing the coil 12 from colliding or rubbing against the magnetic ring 11 during axial reciprocating motion, and ensuring the smooth movement of the coil 12. However, a larger radial gap between coil 12 and magnetic ring 11 is not always better. When the radial gap is large, coil 12 is prone to radial offset or wobbling during movement. This will cause a change in the distance between the first capacitor electrode 32 and the second capacitor electrode 31. Since the capacitance value monitored by the external monitoring unit 6 is related to the distance and facing area between the two capacitor electrodes, the change in distance will directly lead to inaccurate capacitance values, resulting in errors in the final Young's modulus obtained by inversion, thus affecting the reliability of the measurement results. In some embodiments, the radial gap between coil 12 and magnetic ring 11 is preferably limited to no more than 2 mm. This is to ensure the freedom of movement of coil 12 while avoiding radial offset or wobbling of coil 12 during movement due to excessive radial gap, further improving the stability of the Young's modulus measuring device for this material.

[0044] In one embodiment, the Young's modulus measuring device further includes a support column 4, which is located below and coaxially arranged with the guide structure 24. By introducing the support column 4, positional shifts during the axial reciprocating motion of the coil 12 can be effectively prevented, ensuring the straightness and stability of the coil 12's movement, thereby improving the accuracy and repeatability of the measurement. In this embodiment or other embodiments, the support column 4 is a columnar iron core. The iron core has high permeability, which can enhance the magnetic field strength and gradient in the coil 12 region, thereby strengthening the Lorentz force and significantly improving the resolution of the Young's modulus measuring device. This allows for more precise detection of minute deformations in the material, providing strong support for high-precision measurement.

[0045] In one embodiment, the inversion calculation formula used when measuring the Young's modulus of the material under test 7 using the Young's modulus measuring device is as follows: ;

[0046] in, The contact area between the material to be tested and coil 12 is... The nominal length of material 7 to be tested. The initial overlap length of the first capacitor electrode 32 and the second capacitor electrode 31. The initial capacitance of capacitance sensing unit 3, The change in capacitance For the fixed elevation of non-magnetic support structure 2, This represents the total effective loading force. Furthermore, the formula for calculating the total effective loading force is: ,in, This is the axial electromagnetic force, i.e., the Lorentz force; The total weight of coil 12 and the second capacitor electrode 31 is given. By accurately deriving the Lorentz force and measuring the known weight of the material to be tested 7, the total effective loading force can be accurately calculated, providing accurate basic data for the calculation of Young's modulus.

[0047] In one embodiment, both the first capacitor electrode 32 and the second capacitor electrode 31 include a dielectric layer and a conductive paste layer coated on the dielectric layer, with the conductive paste layer forming the opposite sides of the first capacitor electrode 32 and the second capacitor electrode 31. The dielectric layer also serves as a substrate to support the conductive paste layer. In this embodiment or other embodiments, to avoid interference with the magnetic field, the dielectric layer is preferably a non-magnetic polymer material, such as a polyimide film. The conductive paste layer is preferably conductive silver paste, such as conductive silver paste based on silver nanoparticles as the conductive layer material of the capacitor electrode. Silver paste has good rheological properties and process adaptability, and can be uniformly deposited on the surface of the polymer substrate through a brush coating process. After low-temperature curing, it can form a continuous and dense conductive network, thereby ensuring that the capacitor electrode has stable electrical properties and providing reliable assurance for accurate measurement.

[0048] This application also provides the application of the aforementioned Young's modulus measuring device in the field of Young's modulus measurement of biomaterials and soft materials. Biomaterials and soft materials possess unique mechanical properties, and their Young's modulus is often small and sensitive to measurement conditions. The Young's modulus measuring device provided in this application, based on an electromagnetic-capacitive coupling mechanism, offers advantages such as high precision and high sensitivity. It is suitable for measuring the Young's modulus of biomaterials and soft materials, which often have small Young's moduli and are sensitive to measurement conditions. This effectively avoids damage to biomaterials and soft materials while accurately measuring their Young's modulus, providing important measurement methods and technical support for biomedical research, materials science, and other fields.

[0049] Example 1

[0050] A material Young's modulus measurement device based on electromagnetic-capacitive coupling mechanism, such as Figure 4As shown, the device includes an electromagnetic drive unit 1, a non-magnetic support structure 2, and a capacitive sensing unit 3. The non-magnetic support structure 2 includes a cylindrical portion and a guide structure 24. The cylindrical portion includes a top wall 22, a side wall 21, and a bottom wall 23. The guide structure 24 is provided on the side of the top wall 22 facing the bottom wall 23 and extends axially along the cylindrical portion. A bottom opening is provided at the bottom wall 23. The electromagnetic drive unit 1 includes a coaxially arranged annular neodymium iron boron permanent magnet (N38) and a copper wire coil 12. A ring-shaped neodymium iron boron (NdFeB) permanent magnet is disposed on the inner wall of sidewall 21. The inner cavity size of sidewall 21 matches the shape of the NdFeB permanent magnet, allowing it to fit over the outer side of the NdFeB permanent magnet. The axis of sidewall 21 coincides with that of the NdFeB permanent magnet, ensuring strict alignment of the entire axis (z-axis) of the Young's modulus measuring device. This results in an approximately axisymmetric magnetic field distribution within the inner cavity of the NdFeB permanent magnet, laying the foundation for subsequent electromagnetic drive and mechanical response analysis. Coil 12 is electrically connected to the external power supply 5 and is fitted around the guide structure 24. The geometric dimensions of the NdFeB permanent magnet are: outer diameter (…). The inner diameter is 16mm. The thickness is 12mm, and its height is ( The diameter is 6mm. Copper wire coil 12 is wound with enameled copper wire, and the diameter of the copper wire in this enameled copper wire is... A total of 78 turns are wound, with a total length of approximately 2.72m. The copper wire coil 12 is placed inside the magnetic ring 11, and its own height ( The axial height of the copper wire coil 12 is set to 9mm. This setting results in a difference between the axial height of the copper wire coil 12 and the height of the neodymium iron boron permanent magnet ( ). The inner diameter of the copper wire coil 12 is 3.0 mm, ensuring that it maintains a sufficient and stable overlap with the effective magnetic field region of the neodymium iron boron permanent magnet throughout the entire movement. This means that within the axial displacement range of the copper wire coil 12, it remains within the magnetic field gradient region, providing an ideal magnetic field environment for subsequent electromagnetic interactions. According to the Lorentz force law, a current-carrying conductor in a magnetic field experiences a force closely related to the direction of the current and the distribution of magnetic flux. This structural design lays the physical foundation for achieving stable and controllable electromagnetic drive in the axial direction, enabling the entire measurement or drive system to operate more accurately and reliably. The inner diameter of the copper wire coil 12 ( The outer diameter is 10mm. The radial gap between the copper wire coil 12 and the neodymium iron boron permanent magnet is 10.90 mm. The radial gap is 0.55 mm. This radial gap provides the necessary mechanical margin for the axial movement of the coil 12 while ensuring magnetic flux coupling. A columnar iron core is disposed below the guide structure 24 and is coaxially arranged with the guide structure 24. It is used to increase the magnetic flux density in the area where the copper wire coil 12 is located, thereby amplifying the Lorentz force generated by the coil 12 in the ring magnetic field. The capacitance sensing unit 3 includes a first capacitance electrode 32 and a second capacitance electrode 31 of the same height. The first capacitance electrode 32 is sleeved on the guide structure 24, and the second capacitance electrode 31 is fixed to the inner side of the coil 12. In the non-working state, the second capacitance electrode 31 is located in a position directly opposite to the first capacitance electrode 32. In the working state, the second capacitance electrode 31 moves back and forth along the axial direction with the coil 12, causing the area directly opposite to the first capacitance electrode 32 to change, thereby causing a change in capacitance. The first capacitance electrode 32 is electrically connected to the external monitoring unit 6 for real-time monitoring of capacitance and inversion of the Young's modulus of the material 7 under test.

[0051] according to Figure 5 The force diagram shown illustrates the electromagnetic excitation, axial force, and the derivation and calculation methods of the Young's modulus measuring device for this material, as well as the following:

[0052] 1. Calculation of axial magnetic density of permanent magnets

[0053] The axial magnetic flux density of a permanent magnet at any position along its axis can be calculated using the analytical formula for an axially magnetized disk. The formula is as follows:

[0054] (1);

[0055] In formula (1), (z) is the magnetic field strength at the axis z. t is the remanence of the permanent magnet (such as a N38 toroidal neodymium iron boron magnet), t is the axial thickness of the permanent magnet, R is the radius of the permanent magnet, and z is the axial distance from the observation point to the geometric center of the permanent magnet.

[0056] 2. Axial magnetic field strength of a toroidal magnet

[0057] For a toroidal permanent magnet, the magnetic field strength at its axis The difference between the outer and inner radii is expressed as the sum of the outer and inner radii. Based on the principle of magnetic field superposition, a toroidal permanent magnet can be equivalently represented as the difference between the outer and inner radii of a cylindrical magnet, calculated using the following formula:

[0058] (2);

[0059] in, The radius of the permanent magnet body, The outer radius of the permanent magnet is denoted as .

[0060] 3. Magnetic field distribution of finite-length coil 12

[0061] For a finite-length coil 12, the axial magnetic field distribution exhibits a significant spatial dependence. In the central region of coil 12, the magnetic field is relatively uniform and close to its maximum value; near the end face of coil 12, the magnetic field strength along the axis remains relatively high due to the increased contribution of the end current element to the axial magnetic field; however, when the measurement position extends beyond the end face into the outside of coil 12, the magnetic field contribution rapidly weakens, and the overall magnetic field strength decreases rapidly with distance. This phenomenon reflects the end-face effect of the finite-length coil 12, which can usually be described by the Biot-Savart law or the analytical formula for a finite-length solenoid. Based on the magnet's geometry and material remanence, combined with the analytical magnetic field model of an axially uniformly magnetized cylindrical toroidal permanent magnet, the spatial distribution of the axial magnetic induction intensity can be calculated, as shown in the figure. Figure 6 As shown in (a). By Figure 6 From (a), we can see that at the geometric center of the magnet, z=0, the axial magnetic induction intensity is: Although this value is significantly smaller than the remanence of the magnet, it is not zero, indicating that a finite internal magnetic field still exists in the axial region of the magnet. Due to the axial symmetry of the magnet, the magnetic field distribution satisfies B(z) = B(-z), therefore, the magnetic field gradient at the axial position is zero. At axial positions away from the center, the magnetic field strength decreases and is accompanied by a significant spatial gradient. For example, in... At that location, calculation yields: Its amplitude is approximately (The sign is determined solely by the choice of the positive coordinate direction). To obtain the spatial distribution characteristics of the axial magnetic field gradient, based on differentiating the analytical expression of the axial magnetic field with respect to z and substituting the same geometric and material parameters, we obtain:

[0062] (3);

[0063] in, (4);

[0064] Therefore, the closed-form solution for the axial magnetic field gradient is:

[0065] (5);

[0066] In space, the axial magnetic field gradient changes as the observation point moves along the axis. Near the two ends of the magnet, the gradient is dominated by the magnetic charges of the lower and upper end faces, respectively; while in the geometric center region of the magnet, the end face effects cancel each other out. Therefore, the axial magnetic field gradient exhibits a non-monotonic variation and a sign reversal. This change originates from the physical mechanism of the magnet end face effect, rather than from numerical errors or modeling anomalies.

[0067] Based on formulas (5) and (2), an axial magnetic field gradient function is constructed in MATLAB, and the axial magnetic field gradient is sampled point by point to obtain the distribution curve as a function of z, as shown in the figure. Figure 6 As shown in (b).

[0068] Depend on Figure 6 As shown in (b), the axial magnetic field gradient exhibits an antisymmetric distribution, with a zero-crossing point at the geometric center of the magnet and reaching an extreme value near the end face. This sign-reversal characteristic of the magnetic field gradient reflects the competitive effect between the upper and lower magnetized end faces of the magnet, and is an intrinsic physical characteristic of the axial magnetic field variation of a finite-length magnet. This derivation method is entirely based on analytical expressions, avoiding the discrete errors and numerical oscillations that may occur in finite element analysis, and can directly reflect the intrinsic analytical characteristics of the axial magnetic field gradient of the permanent magnet. Although the magnetic field strength at the center of the magnet is not zero, the axial gradient is zero due to axisymmetry, so a static axial electromagnetic driving force cannot be generated at this location. When coil 12 deviates from the center of symmetry and enters the non-zero gradient region, the magnetic field gradient increases significantly, providing the necessary conditions for coupling between coil 12 and the non-uniform magnetic field, thereby enabling the device to generate an effective axial driving force. Based on this, to ensure that coil 12 can stably and continuously feel a large driving force when reciprocating along the axis, it is preferable to limit the maximum upper and lower amplitudes of coil 12 in reciprocating motion to no more than 5 mm.

[0069] 4. Calculation of electromagnetic excitation and axial force

[0070] When coil 12 is energized, the axial magnetic dipole moment of coil 12 The calculation formula is:

[0071] , (6);

[0072] in The number of turns of coil 12, The current amplitude of coil 12, The average cross-sectional area of ​​coil 12 This is the area of ​​the average radius of coil 12. When the characteristic dimensions of coil 12... The characteristic length of spatial variation relative to the magnetic field ,satisfy At this time, the magnetic field can be approximated as having a uniform gradient over the entire effective area of ​​coil 12. Therefore, the electromagnetic force on coil 12 can be approximated as the force on the magnetic dipole in the axial magnetic field gradient, and its axial electromagnetic force The expression for (i.e., Lorentz force) is:

[0073] (7);

[0074] This formula assumes that the magnetic field has a uniform gradient along the axial direction. It should be noted that this approximation will produce significant deviations when the coil 12 is close in size to the magnet or is located in a region where the magnetic field strength is non-uniform.

[0075] In this embodiment, the electrical signal of the driving coil 12 is a symmetrical square wave signal. For a symmetrical square wave, the current of the driving coil 12... Amplitude and RMS current Equal, that is ,in, The effective value of the driving voltage is given. Therefore, when calculating the magnetic dipole moment and axial force under square wave drive, the peak magnetic dipole moment can be obtained by substituting the amplitude current of the square wave into formula (6). To accurately estimate the peak axial excitation force applied to the material 7 by the Young's modulus measuring device, this embodiment considers the limitation of the actual current on the resistance of coil 12 and signal generator. The resistance of coil 12 is given. The output impedance of the signal generator (SDG1050) used is... Under series connection conditions, the total impedance R of coil 12 is: In a given In this case, the peak current of drive coil 12 for:

[0076] (8);

[0077] The coil has 12 turns, N=78, and the average radius is... ,but:

[0078] ;

[0079] Substitute into formula (6) to calculate the magnetic moment Therefore, the peak axial electromagnetic force generated by this magnetic dipole moment under a non-uniform axial magnetic field gradient can be calculated. for By comparing the rated output current of the signal generator under a 50Ω load. To make a comparison, that is It was confirmed that the current in coil 12 did not exceed the rated output of the signal generator under the experimental conditions, thus ensuring the feasibility of the experiment and the reliability of the data.

[0080] Therefore, the total excitation applied to the material under test, and the total mass of coil 12 and the second capacitor electrode 31 can be calculated. Take the acceleration due to gravity Then the total weight G of coil 12 and second capacitor electrode 31 is:

[0081] (9);

[0082] Therefore, the total effective loading force F used for inversion is taken as:

[0083] (10).

[0084] 5. Young's modulus inversion method

[0085] In this embodiment, a coaxial cylindrical capacitive sensing unit 3 is used. Under the ideal coaxial approximation, when the overlap length is L, the capacitance is:

[0086] (11);

[0087] in, These are the outer diameter of the first capacitor electrode 32 and the inner diameter of the second capacitor electrode 31, respectively. The dielectric constant of the dielectric layer, This formula is the expression for a classic cylindrical coaxial capacitor.

[0088] Let the initial overlap length be The initial capacitance is The reciprocating movement of coil 12 causes a change in capacitance. At that time, the total displacement It can be inversely calculated from the linear relationship as follows:

[0089] (12);

[0090] If the Young's modulus measuring device for this material includes a fixed shim... That is, the fixed height of the non-magnetic support structure 2, only the displacement portion exceeding the height compresses the test material 7, therefore the effective compression amount of the test material 7 is... for:

[0091] (13);

[0092] And require To ensure positive compression.

[0093] It should be noted that the linear relationship between edge effects and calibration mentioned above holds true only if edge electric fields, dielectric inhomogeneities, proximity of conductive components, and parasitic capacitances are ignored. In actual experiments, calibration should be used to verify the linear range and coefficients. Under the assumption of axial stress and uniform compression of the material under test, Young's modulus Defined as:

[0094] (14);

[0095] in The contact area between the material to be tested and coil 12 is... The nominal length of the material to be tested. This represents the axial compression of the material under test. This is given in conjunction with the capacitance. The inversion expression can be obtained as:

[0096] (15);

[0097] Where, parameters The constants are Young's modulus E and the relative change in capacitance output by the Young's modulus measuring device for this material. Related.

[0098] To verify the accuracy, applicability, and repeatability of the Young's modulus measuring device provided in Example 1 when detecting the Young's modulus of materials 7 with different hardnesses, the following experiments were conducted. Various commercially available Shore A hardness standard blocks were selected as the test materials, and the Young's modulus measuring device was mounted on these standard blocks. During the test, a frequency of 1Hz and an effective value of 10 were applied to coil 12. A square wave excitation signal was used to drive the system and acquire the corresponding electrical response. All standard blocks were tested under the same contact and loading conditions to ensure comparability between standard blocks of different hardness. To further ensure the accuracy of the test, the force-displacement response of each standard block during loading was measured using a millimeter-level force gauge, and its equivalent Young's modulus was calculated based on the geometric parameters of the standard blocks. Specifically, to calibrate the measurement reliability and applicability of the constructed experimental platform, seven commercially available Shore A type elastomer standard blocks with nominal hardness ranging from 10A to 70A were selected as reference test materials, and their stress-strain curves were obtained. The results are as follows: Figure 7 As shown. These standard blocks cover multiple hardness grades from soft to hard, ensuring broad applicability of the test. Based on Figure 7 The stress-strain curves were described in the table, and the Young's modulus of standard blocks with different Shore A hardness was extracted under the same testing method. The results are summarized in Table 1. It should be noted that the extraction of Young's modulus was based on the initial linear interval of the stress-strain curve. This interval was limited by a linear fitting quality criterion to ensure that the comparison between standard blocks with different Shore A hardness had consistent physical meaning.

[0099] As shown in Table 1, the tested Young's modulus exhibits a monotonically increasing trend with increasing Shore hardness. This result is consistent with the conventional mechanical behavior of elastomer materials, indicating that the Young's modulus measuring device possesses stable and repeatable testing capabilities across a wide stiffness range. Therefore, the Young's modulus measuring device provided in this embodiment demonstrates sensitivity and resolution capabilities for differences in stiffness between different materials.

[0100]

[0101] The Young's modulus measuring device was installed on seven commercially available Shore A hardness standard blocks. The electrical response of the standard blocks with different hardnesses was measured to evaluate the device's ability to perceive and distinguish differences in material stiffness. During the test, a frequency of 1Hz and an effective value of [missing value] were applied to coil 12. The square wave excitation signal was recorded, and the raw electrical response signal output by the RF analyzer was recorded simultaneously. Typical raw signals measured by standard blocks of different hardness under the same excitation conditions are shown below. Figure 8 As shown.

[0102] Depend on Figure 8 It can be seen that as the hardness of the standard block increases, the signal output by the Young's modulus measuring device exhibits a significant systematic change in amplitude and response characteristics. This indicates that the device can accurately distinguish materials of different hardness and reflect hardness changes in real time. Furthermore, in each test, the capacitance signal demonstrates high repeatability and stability throughout the entire motion cycle, and its trend is highly consistent with the mechanical motion process. This further illustrates the reliable detection capability of the device under periodic mechanical disturbances, ensuring the accuracy of the capacitance response. In summary, the Young's modulus measuring device provided in this application exhibits excellent effectiveness and stability in testing the Young's modulus of materials with different hardnesses, and has high application potential in measuring the Young's modulus of materials with varying hardnesses.

[0103] To improve the accuracy of the Young's modulus measuring device for this material, the system was calibrated. By testing standard blocks with Shore hardness ranging from 10A to 70A and comparing the experimental measurements with their corresponding standard reference values, a correction coefficient was derived. This correction factor is obtained through a linear fitting method and is used to compensate for the overall proportional error of the test system. Furthermore, this correction factor is obtained through experimental calibration and does not change the measurement mechanism of the device; it is only used to compensate for systematic proportional errors.

[0104] Specifically, the Young's modulus measuring device provided in Example 1 was used to test standard blocks with a Shore hardness of 10A to 70A, and the monitoring unit collected data at the initial overlap length. Initial capacitance below And in the measurement process And calculate its relative change. The result is as follows Figure 9 As shown. Based on the theoretical model established above, under the small strain approximation condition, the inverse relationship between the capacitance change of the coaxial capacitive sensing unit and the axial loading force can ultimately be confirmed as follows:

[0105] ;

[0106] in The equivalent Young's modulus of the sample under test is given by , and F is the total effective loading force. These are correction parameters related to the geometry and electromechanical coupling characteristics of the Young's modulus measuring device. The Young's modulus measuring device provided in this embodiment, after inversion and correction, is derived as follows: =4.

[0107] Depend on Figure 9 It can be seen that within the Shore hardness range of 10A to 60A, the Young's modulus inversion results from the standard block maintain a consistent trend with the calibration platform, with reasonable data point distribution, comparable physical ranges, and concentration in similar structural response regions. However, under the Shore hardness condition of 70A, the experimental data show a significant deviation; the relative change in capacitance no longer follows the existing linear trend, resulting in a large mismatch between the inverted Young's modulus and the calibration value, a significant increase in relative error, and distortion of the overall fitting curve. This indicates that within the Shore hardness range of 10A to 60A, the Young's modulus measurement device for this material is in a stable linear strain response range, enabling reliable qualitative assessment of the mechanical modulus of soft polymer materials.

[0108] In summary, the effective testing range of the Young's modulus measuring device provided in this application is further preferably Shore hardness 10A to 60A. This provides a reliable basis for the subsequent inversion of the Young's modulus of unknown samples, and also points the way for further optimization of the device's performance. For example, the measurement accuracy and applicability of the device can be improved by optimizing the electrode structure, reducing the assembly gap, and constructing a large strain correction inversion model suitable for materials with different hardnesses.

[0109] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0110] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A device for measuring the Young's modulus of materials based on an electromagnetic-capacitive coupling mechanism, characterized in that, include: A non-magnetic support structure includes a cylindrical portion and a guide structure. The cylindrical portion includes a top wall, a side wall, and a bottom wall. The guide structure is provided on the side of the top wall facing the bottom wall. The guide structure extends along the axial direction of the cylindrical portion. The bottom wall has a bottom opening for communicating with the material to be tested. The electromagnetic drive unit includes a magnetic ring disposed on the inner wall of the side wall and a coil coaxially disposed inside the magnetic ring. The coil is electrically connected to an external power source and is sleeved on the periphery of the guide structure. The coil reciprocates along the axial direction under the drive of the square wave electrical signal of the external power source to provide controllable excitation to the material under test. The capacitance sensing unit includes a first and a second capacitor electrode, both of which are annular. The first capacitor electrode is fixed to the periphery of the guide structure, and the second capacitor electrode is fixed to the inner side of the coil. In the non-working state, the second capacitor electrode is located directly opposite the first capacitor electrode. In the working state, the second capacitor electrode reciprocates along the axial direction with the coil, causing the area directly opposite the first capacitor electrode to change, thereby causing a change in capacitance. The capacitance sensing unit is electrically connected to an external monitoring unit, which is used to monitor capacitance and invert the Young's modulus of the material under test. The inversion calculation formula for measuring the Young's modulus E of the material under test by the material Young's modulus measuring device is as follows: ; in, The contact area between the material to be tested and the coil is [missing information]. The nominal length of the material to be tested. The initial overlap length between the first capacitor electrode and the second capacitor electrode is denoted as . The initial capacitance of the capacitance sensing unit is [value]. This represents the change in capacitance. The fixed height of the non-magnetic support structure, The total effective loading force; The formula for calculating the total effective loading force is: ,in, The Lorentz force generated by the coil, The total weight of the coil and the second capacitor electrode is denoted as .

2. The material Young's modulus measuring device as described in claim 1, characterized in that, The amplitude of the axial reciprocating motion of the coil does not exceed 5 mm.

3. The material Young's modulus measuring device as described in claim 2, characterized in that, The heights of the first capacitor electrode and the second capacitor electrode are both not less than the amplitude of the coil reciprocating along the axial direction, so that the first capacitor electrode and the second capacitor electrode always have a facing area when the coil reciprocates along the axial direction.

4. The material Young's modulus measuring device as described in claim 2, characterized in that, The height of the coil is greater than the height of the magnetic ring, so that when the coil reciprocates along the axial direction, there is always an overlapping area between the coil and the magnetic ring in the radial direction.

5. The material Young's modulus measuring device as described in claim 2, characterized in that, The outer diameter of the coil is smaller than the inner diameter of the magnetic ring, so that a radial gap is formed between the coil and the magnetic ring, providing the necessary mechanical margin for the coil to move axially.

6. The material Young's modulus measuring device as described in claim 1, characterized in that, It also includes a support column, which is fixed below the guide structure and coaxially arranged with the guide structure to prevent the coil from shifting position when it reciprocates along the axial direction.

7. The material Young's modulus measuring device as described in claim 6, characterized in that, The support column is a columnar iron core used to enhance the Lorentz force.

8. The material Young's modulus measuring device as described in claim 1, characterized in that, Both the first capacitor electrode and the second capacitor electrode include a dielectric layer and a conductive paste layer coated on the dielectric layer, with the conductive paste layer on the opposite side of the first capacitor electrode and the second capacitor electrode.

9. The application of the Young's modulus measuring device according to any one of claims 1-8 in the field of Young's modulus measurement of biomaterials and soft materials.

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