A high-tensile, high-response flexible dual-mode magnetic / strain sensor and its application

Abstract

This invention discloses a high-tensile, high-response flexible dual-mode magnetic / strain sensor and its applications. The sensor includes a magnetic strain-sensitive material comprising a rubber matrix and conductive and magnetic particles uniformly distributed within the rubber matrix. The sensor of this invention is a dual-mode sensor possessing both contact and non-contact capabilities, enabling it to respond to external mechanical stimuli through a strain-based contact mode and to be applied to smart products through a magnetic-response non-contact mode.

Description

Technical Field

[0001] This invention belongs to the field of sensor technology, and particularly relates to a high-tensile, high-response flexible dual-mode magnetic / strain sensor and its applications. Background Technology

[0002] With the development of flexible electronic devices, flexible sensors are attracting increasing attention in applications such as human-computer interaction, intelligent robots, biomedicine, and electronic skin. It has been reported that bimodal devices for both contact and non-contact sensing are of great significance for next-generation artificial intelligence applications. It is worth noting that although strain or magnetic field sensors with single operating modes have seen rapid development in flexible electronics, they still suffer from the problem of limited sourcing and cannot meet the growing demand for multifunctionality. Therefore, it is necessary to design bimodal sensors that can respond to external mechanical stimuli not only through a contact mode of strain but also through a non-contact mode of magnetic response for application in smart products.

[0003] Currently, most reported strain sensors are sensitive to tensile / bending stimuli, exhibiting a single mechanical stimulus response mode. However, flexible sensors with high tensile strength and high sensitivity multimodal sensing have attracted widespread attention, with relatively little research on the fabrication of bimodal flexible strain sensors using magnetic materials. Existing conductive fillers for contact sensing in flexible strain sensors include materials such as CB (carbon black), carbon nanotubes, and Mxene. Since the brittleness of magnetic materials severely interferes with the long-term use of sensors, how to combine non-magnetic material matrices with magnetic material particles to obtain magnetic composite materials with magnetic braking properties is of great significance for the development of current sensors. This would facilitate non-contact response of strain sensors and endow them with magnetic / stress coupling sensing characteristics.

[0004] While contact-based strain sensors can directly monitor human movements, they are frequently used in devices such as keyboards, remote controls, and elevators, where frequent direct contact is required. Traditional contact sensing and operation cannot avoid the drawbacks of mechanical wear and fatigue. Therefore, achieving accurate sensing through both contact and non-contact modes is sought after in a wide range of fields, including security checks and intelligent control. Furthermore, in the context of the global COVID-19 pandemic, direct contact with everyday objects in environments with limited medical equipment can lead to bacterial and viral infections. Therefore, ultra-stable non-contact magnetic / strain sensors that protect people from bacteria and viruses have attracted widespread research in next-generation artificial intelligence products. Thus, the development of flexible magnetic / strain sensors with dual-modal operating modes has become an urgent need for smart electronic products. Summary of the Invention

[0005] Based on the technical problems existing in the background technology, the present invention provides a high tensile and high-response flexible dual-mode magnetic / strain sensor and its application. The sensor is a dual-mode sensor that has both contact and non-contact functions. It can not only be subjected to external mechanical stimulation through the contact mode of strain, but also be applied to smart products through the non-contact mode of magnetic response.

[0006] The present invention proposes a high tensile and high-response flexible dual-mode magnetic / strain sensor, which includes a magnetic strain-sensitive material comprising a rubber matrix and conductive particles and magnetic particles uniformly distributed in the rubber matrix.

[0007] In this invention, the magnetic strain-sensitive material, in which conductive and magnetic particles are uniformly distributed in a rubber matrix, is a composite material that simultaneously possesses magnetic actuation and strain response characteristics. When applied to a sensor, it ensures that the sensor has strain sensing function and flexibility while also possessing magnetic sensitivity characteristics, thereby obtaining a sensor that combines good contact sensing and non-contact sensing functions.

[0008] Preferably, the rubber matrix is ​​silicone rubber, the conductive particles are carbon black, and the magnetic particles are Fe3O4 microparticles;

[0009] In this invention, silicone rubber, as the base rubber, exhibits excellent flexibility after curing, ensuring the flexibility of the resulting magnetic strain-sensitive material. Carbon black, as a conductive particle, is easily dispersed in silicone rubber, endowing the resulting magnetic strain-sensitive material with good strain-sensitive characteristics and ensuring good sensing function. Fe3O4 particles, as magnetic particles, when dispersed in silicone rubber, not only endow the magnetic strain-sensitive material with good magnetosensitive characteristics but also promote the uniform dispersion of conductive particles in silicone rubber, further improving the strain elongation characteristics of the resulting magnetic strain-sensitive material, which is beneficial for manufacturing high-performance flexible magnetic / strain sensors.

[0010] Preferably, the Fe3O4 particles have a particle size of 1-10 μm, and the carbon black has a particle size of 8-500 nm.

[0011] In this invention, the particle size of Fe3O4 microparticles has a significant impact on the mechanical properties such as tensile strength of the obtained magnetic strain-sensitive material. Selecting Fe3O4 microparticles with a particle size of 1-10 μm can not only endow the obtained material with stronger mechanical properties, but also avoid agglomeration caused by excessively small particle size.

[0012] Preferably, the weight ratio of carbon black to Fe3O4 particles is 1:10, and the weight ratio of silicone rubber to Fe3O4 particles is 1:1.

[0013] In this invention, carbon black and Fe3O4 particles are used as filler particles. Since Fe3O4 particles have a larger aspect ratio than carbon black, when added to silicone rubber, they can form a "grape bunch" structure, obtaining a new conductive path and thus exerting a synergistic enhancement effect. Therefore, different proportions of carbon black and Fe3O4 particles or silicone rubber and Fe3O4 particles can construct different conductive paths, resulting in differences in sensor performance. The inventors have found that when the weight ratio of carbon black to Fe3O4 particles is 1:10 and the weight ratio of silicone rubber to Fe3O4 particles is 1:1, the sensor can obtain the best magnetic / strain sensing function.

[0014] Preferably, the magnetic strain-sensitive material is obtained by dispersing conductive particles and magnetic particles in a solvent to form a dispersion, then mixing it with a rubber matrix and drying it.

[0015] Preferably, the magnetic / strain sensor specifically includes: an upper substrate layer, a lower substrate layer, and a strain sensing layer located between the upper substrate layer and the lower substrate layer, and made of the magnetic strain-sensitive material.

[0016] In this invention, the upper substrate layer and the lower substrate layer are used to transmit force loads and at the same time seal and protect the strain sensing layer.

[0017] Preferably, both the upper and lower substrate layers are made of silicone rubber.

[0018] Preferably, the magnetic / strain sensor further includes a left electrode and a right electrode located between the strain sensing layer and the upper or lower substrate layer, and in contact with the surface of the strain sensing layer.

[0019] In this invention, the electrode pair contacts the surface of the strain sensing layer to generate a measurable resistance that changes accordingly under external pressure.

[0020] Preferably, both the left and right electrodes are connected to external wires.

[0021] This invention proposes a method for fabricating the aforementioned high-tensile, high-response flexible dual-mode magnetic / strain sensor, comprising:

[0022] S1. Spin-coat the solution of magnetic strain-sensitive material onto the mold, and after drying and curing, demold to obtain the strain-sensing layer.

[0023] S2. After depositing conductive silver paste solution on the two ends of the strain sensing layer to form the left and right electrodes, the upper and lower substrate layers are then bonded to the upper and lower surfaces of the strain sensing layer to obtain the magnetic / strain sensor.

[0024] The present invention also proposes an application of the above-mentioned sensor in a contact magnetic keyboard or a human motion monitoring device.

[0025] In this invention, the sensor is a fully flexible structure, which has a wider range of applications compared to traditional rigid force sensors, including but not limited to applications in fields such as contact magnetic keyboards or human motion monitoring equipment. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the overall structure of the sensor described in this invention;

[0027] Figure 2 This is a schematic diagram of the assembly components of the sensor described in this invention;

[0028] Figure 3 This is a schematic diagram of the sensor structure after disassembly and assembly according to the present invention;

[0029] Figure 4 This is a flowchart illustrating the fabrication process of the sensor described in this invention.

[0030] Figure 5 The image is a scanning electron microscope image of the strain sensing layer of the sensor described in Example 1.

[0031] Figure 6 This is a schematic diagram of the tensile stress distribution of the sensor described in Example 1;

[0032] Figure 7 This is a schematic diagram of the bending stress distribution of the sensor described in Example 1;

[0033] Figure 8 This is a graph showing the stretch-relative resistance response change of the sensor described in Example 1;

[0034] Figure 9 The response / recovery time test curve of the sensor described in Example 1;

[0035] Figure 10 This is a voltage-current test curve of the sensor described in Example 1;

[0036] Figure 11 This is a curve showing the strain detection lower limit of the sensor described in Example 1;

[0037] Figure 12 This is a test curve of the strain step change of the sensor described in Example 1;

[0038] Figure 13 This is a test curve of the sensor described in Example 1 under cyclic tensile strain;

[0039] Figure 14This is a cyclic test curve of the sensor described in Example 1 under tensile / release strain.

[0040] Figure 15 The test curves of the sensor described in Example 1 at different tensile rates are shown.

[0041] Figure 16 This is a graph showing the cyclic durability and stability test results of the sensor described in Example 1.

[0042] Figure 17 This is a real-time response graph of the sensor described in Example 1 to the speed of an oncoming screw and a bicycle;

[0043] Figure 18 The graphs show the tensile-relative resistance response changes of the sensors described in Examples 1, 2, and 3.

[0044] Figure 19 The image shows the tensile-strain relationship curves of the sensors described in Examples 1, 4, and 5.

[0045] In the figure: 1. Upper substrate layer, 21. Strain sensing layer, 22. Left electrode, 23. Right electrode, 3. Lower substrate layer, 4. External wire. Detailed Implementation

[0046] The present invention will now be described in detail through specific embodiments. However, these embodiments are clearly provided for illustrative purposes and are not intended to limit the scope of the present invention.

[0047] Figure 1 This is a schematic diagram of the overall structure of the sensor described in this invention. Figure 2 This is a schematic diagram of the assembly components of the sensor described in this invention. Figure 3 This is a schematic diagram of the sensor structure after disassembly and assembly according to the present invention;

[0048] Reference Figure 1-3 As can be seen, the present invention proposes a high tensile and high response flexible dual-mode magnetic / strain sensor, including: an upper substrate layer 1, a lower substrate layer 3 and a strain sensing layer 21 located between the upper substrate layer 1 and the lower substrate layer 3, and a left electrode 22 and a right electrode 23 located at the left and right ends of the upper surface of the strain sensing layer 21.

[0049] The upper substrate layer 1 and the lower substrate layer 3 are symmetrically distributed with the strain sensing layer 21 as the plane of symmetry, and the layers are tightly bonded together. The left electrode 22 and the right electrode 23 are symmetrically distributed with respect to the center line of the strain sensing layer 21, and the left electrode 22 and the right electrode 23 are also connected to external wires 4 for measurement.

[0050] In one embodiment, the strain sensing layer 21 is made of a magnetic strain-sensitive material, and both the upper substrate layer 1 and the lower substrate layer 2 are made of flexible rubber material.

[0051] The following are several examples of the fabrication method for the above-mentioned high-tensile, high-response flexible dual-mode magnetic / strain sensor:

[0052] Example 1

[0053] This embodiment proposes a high-tensile, high-response flexible dual-mode magnetic / strain sensor. Figure 4 This is a flowchart illustrating the fabrication process of the sensor described in this invention, with reference to... Figure 4 It can be seen that the fabrication method of the magnetic / strain sensor specifically includes the following steps:

[0054] (1) Add 0.1g CB and 1g Fe3O4 microparticles (i.e., CB:Fe3O4 = 1:10) to 12mL of N,N-dimethylformamide, stir for 45min to ensure that CB and Fe3O4 microparticles are evenly dispersed, then add 1g silicone rubber SR (i.e., SR:Fe3O4 = 1:1), stir for 1h to obtain Fe3O4 / CB / SR composite solution;

[0055] (2) Design a mold in Solidworks 2019 software, print PLA material into a reusable mold using a high-precision 3D printer, spin coat the Fe3O4 / CB / SR composite solution onto the mold at a speed of 1000 rpm for 30 seconds, dry it in a vacuum drying oven for 8 minutes to remove air bubbles, and then cure it at 50°C for 3 hours. After removing the mold, the strain sensing layer 21 is obtained.

[0056] (3) Apply conductive silver paste solution to the two ends of the obtained strain sensing layer 21, dry it, and obtain the left electrode 22 and the right electrode 23. Connect the external wire 4 at the left electrode 22 and the right electrode 23.

[0057] (4) The silicone rubber solution is coated into a film and dried to obtain an upper substrate layer 1 and a lower substrate layer 3. The obtained upper substrate layer 1 and lower substrate layer 3 are then bonded to the upper and lower surfaces of the strain sensing layer 21 by silicone rubber. After pressing, a high tensile and high response flexible dual-mode magnetic / strain sensor is obtained.

[0058] Figure 5 The image shown is a scanning electron microscope image of the strain sensing layer of the sensor described in Example 1, with reference to... Figure 5 It can be seen that the surface of the strain sensing layer is smooth, Fe3O4 and CB are uniformly distributed, and the cross-sectional height is about 200 μm.

[0059] Figure 6 , 7These are schematic diagrams of tensile stress distribution and bending stress distribution of the sensor described in Example 1, respectively, for reference. Figure 6 The stress simulations of the sensor under 10%, 30%, and 50% strain show that when transverse tensile stress is applied to the strain sensor, the larger stress area is mainly concentrated in the middle region of the strain sensor; (Refer to...) Figure 7 It can be seen that when longitudinal tensile stress is applied to the strain sensor, the larger stress areas are mainly concentrated in the middle and sides of the strain sensor.

[0060] Figure 8 The diagram shows the stretch-relative resistance response curve of the sensor described in Example 1, with reference to... Figure 8 It can be seen that the relative resistance curve of the sensor under different strains is good, and the strain can reach up to 180%; and the response curve is divided into three linear regions with strains of 0-20%, 20-80%, and 80-180%, corresponding to sensitivities of 3.07, 2.85, and 21.985, respectively; obviously, the sensitivity gradually increases with a linear slope in the first two stages, and the resistance increases rapidly when the strain increases to 180%.

[0061] Figure 9 The response / recovery time test curve of the sensor described in Example 1 is shown in the figure. Figure 9 It can be seen that when 30%, 60%, and 80% strain are applied to the magnetic / strain sensor, the response time and recovery time of the sensor are 73ms and 65ms, respectively, proving that the obtained sensor can detect various movements in a timely manner.

[0062] Figure 10 The voltage-current curve of the sensor described in Example 1 is shown in the figure. Figure 10 The current-voltage curves of the sensor under different strains (0% to 90%) show that the current-voltage characteristic of the sensor strictly conforms to Ohm's law. In addition, the current-voltage characteristic curve shows a decreasing slope as the tensile strain of the sensor increases. This is mainly because the resistance of the magnetic strain-sensitive material increases with the increase of strain, indicating the high stability of the sensor's resistance.

[0063] Figure 11 The graph shows the strain detection lower limit test curve of the sensor described in Example 1. Another important parameter of the sensor is the strain detection lower limit. Cyclic tests were performed on this sensor with small strains of 0.25%, 0.5%, 1%, and 2%, referring to… Figure 11It can be seen that the relative resistance of the sensor shows a decreasing trend, mainly due to the gradual relaxation of the sensor after pre-stretching. It is worth noting that the designed strain sensor achieves a stable response signal at a small strain of 0.25%, showing an ultra-low strain detection limit. Due to the ultra-low detection limit, it is indicated that the sensor can detect micro-deformation.

[0064] Figure 12 The strain gradient test curve of the sensor described in Example 1 is shown in the figure. Figure 12 It can be seen that when the strain applied to the sensor gradually increases from 0% to 18%, the change in relative resistance gradually increases with the stretching of the sensor, showing a regular step change on the relative resistance response curve, which demonstrates the high stability and excellent mechanical elasticity of the sensor.

[0065] Figure 13 The test curve of the sensor described in Example 1 under cyclic tensile strain is shown in the figure. Figure 13 It can be seen that the periodic strain sensing characteristics of the sensor under various strains show repeatability and accurate signal for various strains within the range of relative resistance change; the amplitude of the signal increases proportionally with tensile strain from 5% to 50%, and due to the strain sensitivity of the strain sensor throughout the entire range, it exhibits good recoverability and repeatability.

[0066] Figure 14 The cyclic curves (3%, 13%, 23%, 33%, 43%, and 53%) of the tensile / release strain of the sensor described in Example 1 are shown below. Figure 14 The cyclic strain response behavior of the sensor under six different strains was observed. The resistance of the sensor increases during the stretching process and decreases during the recovery process. The results were repeated seven times for each strain, demonstrating the excellent repeatability and stability of the sensor under various strains.

[0067] Figure 15 The graphs shown are those of the sensor described in Example 1 at different tensile rates (4, 20, 100, and 500 mm / min), with reference to... Figure 15 It can be seen that when repeated stretching / releasing at speeds of 4, 20, 100 and 500 mm / min, the relative resistance change of the sensor remains constant at different speeds, demonstrating stable sensing performance and proving the sensor's good independence at different test speeds.

[0068] Figure 16 The graph shows the cyclic durability and stability test curves of the sensor described in Example 1. Durability and stability are fundamental considerations for magnetic strain sensors in practical applications. The long-term tensile / release cycle of the sensor is evaluated using a 10% strain. (Refer to...) Figure 16It can be seen that the magnetic strain sensor maintains a stable signal output after 9000 cycles; Figure 16 The illustrations show that the relative resistance change signal is almost identical in three different cycles, confirming the excellent durability and good stability of the magnetic strain sensor.

[0069] Figure 17 This is a real-time response graph of the sensor described in Example 1 to an oncoming screw and the speed of a bicycle. Compared to traditional strain sensors that rely on contact, the sensor described in this example can also be used in a non-contact mode; such as... Figure 17 As shown in diagram a, to evaluate contact and non-contact modes, a magnet is mounted on the head of a screw, which is gradually brought closer and passes through the magnetic / strain sensor at a fixed height. In non-contact mode, the resistance increases sharply as the screw passes through, then decreases and tends to plateau. In contact mode, the magnetic response and strain sensing mechanisms are activated, and a peak in the relative resistance is observed. Therefore, this specific behavior of the relative resistance helps in identifying contact and oncoming objects, which is crucial for intelligent control and the automotive industry. Furthermore, Figure 17 Figure b shows a magnetic / strain sensor fixed to the bicycle frame, with the magnet positioned on the rear wheel. As the rotating sensor is attracted to the vicinity of the magnet, the relative resistance of the sensor gradually increases; as the sensor moves away from the magnet, the relative resistance decreases. This figure illustrates the change in relative resistance during riding, and by calculating the peak and total values, the speed and distance traveled by the bicycle can be easily tracked.

[0070] Example 2

[0071] This embodiment proposes a high tensile and high-response flexible dual-mode magnetic / strain sensor. Its preparation process is the same as that in Example 1, except that in step (1), 0.05g of CB and 1g of Fe3O4 microparticles are added (i.e., CB:Fe3O4 = 1:20).

[0072] Example 3

[0073] This embodiment proposes a high-tensile, high-response flexible dual-mode magnetic / strain sensor. Its preparation process is the same as in Example 1, except that in step (1), 0.2g of CB and 1g of Fe3O4 microparticles are added (i.e., CB:Fe3O4 = 1:5).

[0074] Example 4

[0075] This embodiment proposes a high tensile and high-response flexible dual-mode magnetic / strain sensor. Its preparation process is the same as that in Example 1, except that in step (1), 2g of silicone rubber SR (i.e., SR:Fe3O4 = 2:1) is added.

[0076] Example 5

[0077] This embodiment proposes a high tensile and high-response flexible dual-mode magnetic / strain sensor. Its preparation process is the same as that in Example 1, except that in step (1), 0.5g of silicone rubber SR (i.e., SR:Fe3O4 = 1:2) is added.

[0078] Figure 18 These are the stretch-relative resistance response curves of the sensors described in Examples 1, 2, and 3, for reference. Figure 18 It can be seen that the sensor performance and sensing characteristics obtained by different proportions of Fe3O4 and CB dispersed in SR are different. As shown in the figure, the sensor has the best sensing performance when the mass ratio of CB to Fe3O4 is 1:10.

[0079] Figure 19 These are the tensile-strain relationship curves of the sensors described in Examples 1, 4, and 5, for reference. Figure 19 It can be seen that when the mass ratio of SR to Fe3O4 is 1:1, the Fe3O4 content in the strain sensing layer is relatively high, and the sensor can withstand a maximum tensile force of 7.42N. At this time, the maximum strain of the sensor can reach 180%.

[0080] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high-tensile, high-response flexible dual-mode magnetic / strain sensor, characterized in that, The sensor includes a magnetic strain-sensitive material, which comprises a rubber matrix and conductive and magnetic particles uniformly distributed in the rubber matrix. The magnetic strain-sensitive material is obtained by dispersing conductive particles and magnetic particles in a solvent to form a dispersion, then mixing it with a rubber matrix and drying it. The rubber matrix is ​​silicone rubber, the conductive particles are carbon black, and the magnetic particles are Fe3O4 microparticles; The Fe3O4 particles have a particle size of 1-10 μm, and the carbon black has a particle size of 8-500 nm. The weight ratio of carbon black to Fe3O4 particles is 1:10, and the weight ratio of silicone rubber to Fe3O4 particles is 1:

1. Carbon black and Fe3O4 particles are used as filler particles. Fe3O4 particles have a larger aspect ratio than carbon black. When added to silicone rubber, the two form a "grape bunch"-like structure, creating a new conductive path.

2. The high-tensile, high-response flexible dual-mode magnetic / strain sensor according to claim 1, characterized in that, The magnetic / strain sensor specifically includes: an upper substrate layer (1), a lower substrate layer (3), and a strain sensing layer (21) located between the upper substrate layer (1) and the lower substrate layer (3) and made of the magnetic strain-sensitive material.

3. The high-tensile, high-response flexible dual-mode magnetic / strain sensor according to claim 2, characterized in that, Both the upper substrate layer (1) and the lower substrate layer (3) are made of silicone rubber.

4. The high-tensile, high-response flexible dual-mode magnetic / strain sensor according to claim 2 or 3, characterized in that, The magnetic / strain sensor further includes a left electrode (22) and a right electrode (23) located between the strain sensing layer (21) and the upper substrate layer (1) or the lower substrate layer (3) and in contact with the surface of the strain sensing layer (21).

5. The high-tensile, high-response flexible dual-mode magnetic / strain sensor according to claim 4, characterized in that, Both the left electrode (22) and the right electrode (23) are connected to external wires (4).

6. A method for fabricating a high-tensile, high-response flexible dual-mode magnetic / strain sensor according to any one of claims 1-5, characterized in that, include: S1. Spin coat the solution of magnetic strain-sensitive material onto the mold, dry and solidify it, and then demold to obtain the strain-sensing layer (21). S2. After depositing conductive silver paste solution on the two ends of the strain sensing layer (21) to form the left electrode (22) and the right electrode (23), the upper substrate layer (1) and the lower substrate layer (3) are then bonded to the upper and lower surfaces of the strain sensing layer (21) to obtain the magnetic / strain sensor.

7. The application of the sensor according to any one of claims 1-5 in a contact magnetic keyboard or a human motion monitoring device.

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