High-performance bidirectional strain sensing flexible magneto-sensitive strain sensor and preparation method and application thereof

Abstract

The invention relates to the technical field of strain detection, and discloses a high-performance bidirectional strain sensing flexible magneto-sensitive strain sensor and a preparation method and application thereof. The flexible magneto-sensitive strain sensor is of a bridge type structure, a magneto-elastic body serves as a bridge floor, and a magnetic sensing unit serves as a bridge bottom. Wherein the magnetoelastomer has a negative Poisson's ratio structure and non-single magnetic field distribution, and is prepared by taking an elastic matrix, magnetic particles and a dispersing agent as raw materials, preparing by adopting a template method and then magnetizing. The sensor is a flexible and stretchable magneto-sensitive strain sensor, has very high sensing characteristics and high sensitivity, can realize detection of micro strain, and has a very large working range.

Description

Technical Field

[0001] The present invention relates to the field of strain detection technology, and in particular to a high-performance flexible magnetic-sensitive strain sensor for bidirectional strain sensing and a preparation method and application thereof, and in particular to a stretchable flexible magnetic-sensitive strain sensor for bidirectional strain sensing that can measure tiny strains and a wide range of strains. Background Art

[0002] Flexible strain sensors have shown advantages such as high biocompatibility and real-time monitoring. They are widely used in human health monitoring and human-computer interaction. Due to their simple structural design, strain motion can be converted into electrical signals. This sensor can detect human daily activities, including joint and muscle movement, breathing, pulse, etc. Therefore, the development of flexible strain sensors is the key to the digitalization of medical health and one of the important ways to help the human body obtain health information.

[0003] However, human tissues, such as muscles, skin, and blood vessels, often show multi-directional, nonlinear, and time-varying deformations when subjected to external forces or internal physiological changes. This complexity requires strain sensors to have high sensitivity and multi-directional sensing capabilities to accurately capture and reflect these tiny and complex deformations.

[0004] The inventors of the present application realized that due to the Poisson's ratio effect, lateral deformation will also cause the longitudinal size of the elastic substrate to expand and contract, thereby resulting in inaccurate principal strain measurement of the stretchable flexible sensor and loss of lateral strain signals. The two main current solutions (introducing a tensile expansion structure or designing an array distribution to achieve lateral strain measurement) both have limitations. The former is difficult to achieve both large strain and high resolution due to the intrinsic mechanical properties of the material, while the latter has a complex design, cumbersome process and high cost.

[0005] Therefore, achieving high sensitivity and a large working range (stretchability) remains a challenge. Summary of the invention

[0006] According to one embodiment of the present invention, the purpose is to provide a flexible magnetic-sensitive strain sensor with high-performance bidirectional strain sensing having a negative Poisson's ratio structure and a preparation method and application thereof. The flexible magnetic-sensitive strain sensor has excellent sensing performance, high sensitivity, can detect micro-strains, and has a large working range.

[0007] The above purpose can be achieved by implementing the following technical solutions:

[0008] According to one aspect of the present invention, a high-performance bidirectional strain sensing flexible magnetically sensitive strain sensor is provided, which is a bridge structure, with a magnetic elastomer as the bridge deck and a magnetic sensing unit as the bridge bottom; wherein the magnetic elastomer has a negative Poisson's ratio structure and a non-single magnetic field distribution, and is made of an elastic matrix, magnetic particles and a dispersant as raw materials, and is prepared by a template method and then magnetized.

[0009] Optionally, the mass ratio of the elastic matrix to the magnetic particles is (1-6):1.

[0010] Optionally, the mass ratio of the magnetic particles to the dispersant is (0.5-6):1.

[0011] Optionally, the dispersant is selected from one or more of polycaprolactone, n-hexane, sodium dodecylbenzene sulfonate, polyethylene glycol, carboxyethyl cellulose, and triethanolamine.

[0012] Optionally, the elastic matrix is ​​selected from one or more of aliphatic aromatic random copolyesters, polydimethylsiloxane, silicone, rubber, resin, hydrogel, polyurethane, styrene block copolymer, PVC, polyimide, polyterephthalate plastics, polyethylene octene co-elastomer, and thermoplastic elastomer.

[0013] Optionally, the magnetic particles are selected from NdFeB powder, SmCo powder, AlNiCo powder, FeCrCo powder, BaFe 12 O 19 Powder, SrFe 12 O 19 One or more of Fe3O4 powder and Fe3O4 powder.

[0014] Optionally, the negative Poisson's ratio structure is one or a combination of a concave-angle hexagon, a double V-shape, and a rectangular perforated shape. Preferably, the negative Poisson's ratio structure is a double V-shape.

[0015] Optionally, the magnetic elastomer has a non-single magnetic field distribution, which means that the magnetic field distribution in the magnetic elastomer is one of an alternating magnetic field, a diagonal magnetic field, a Halbach magnetic field, and a curled magnetic field.

[0016] Optionally, the magnetic elastomer having a non-single magnetic field distribution is obtained by changing the state of the elastomer before the magnetization treatment and performing magnetization in the changed state.

[0017] Preferably, the magnetic elastomer has a Halbach magnetic field distribution. Further, the magnetic elastomer with a Halbach magnetic field distribution is obtained by three-dimensionally folding an elastomer obtained by a template method and then magnetizing it.

[0018] Optionally, the magnetic sensing unit comprises an elastic bottom layer, a strain suppression layer printed on the surface of the elastic bottom layer, and a magnetic sensing element embedded in the strain suppression layer. Further, the strain suppression layer in the magnetic sensing unit serving as the bridge bottom faces upward.

[0019] Optionally, the magnetic sensing element is one of a Hall sensor, a giant magnetoresistance sensor, and a giant magnetoimpedance sensor.

[0020] Optionally, the gel of the strain suppression layer is prepared by mixing sodium alginate, anhydrous calcium chloride and deionized water in a ratio of 10:(0.1-5):500.

[0021] Optionally, in the bridge structure, the bridge deck and the bridge bottom are separated by a supporting layer, and the distance between the bridge deck and the bridge bottom is 2 to 6 mm.

[0022] According to another aspect of the present invention, the present invention provides a method for preparing a flexible magnetically sensitive strain sensor with high-performance bidirectional strain sensing, comprising: mixing an elastic matrix, magnetic particles and a dispersant in proportion, preparing an elastomer with a negative Poisson's ratio structure by a template method, magnetizing the elastomer to obtain a magnetic elastomer with a negative Poisson's ratio structure and a non-single magnetic field distribution; using the magnetic elastomer as a bridge deck and a magnetic sensing unit as a bridge bottom to form a flexible magnetically sensitive strain sensor with a bridge structure.

[0023] Optionally, before the elastomer is magnetized, the method further includes: changing the state of the elastomer; and obtaining a magnetic elastomer with a non-single magnetic field distribution by magnetizing the elastomer in the changed state.

[0024] According to another aspect of the present invention, the present invention provides an application of a high-performance bidirectional strain sensing flexible magnetic-sensitive strain sensor, wherein, when applied, the flexible magnetic-sensitive strain sensor senses the change in magnetic flux of the magnetic elastomer under a stretched state through a magnetic sensing unit and outputs a corresponding electrical signal, thereby realizing the detection of 0.05% to 200% strain.

[0025] Beneficial effects: According to one embodiment of the present invention, an elastomer is prepared by using an elastic matrix, magnetic particles and a dispersant as raw materials and adopting a template method, and a magnetic elastomer having a negative Poisson's ratio structure and a non-single magnetic field distribution is obtained by magnetization. Among them, the template in the template method is a negative Poisson's ratio structure template prepared by 3D printing, and the elastomer is prepared based on the template. A negative Poisson's ratio structure is introduced into the elastomer, so that the tensile properties of the elastomer are improved, and the sensitivity of the elastomer is greatly improved after magnetization. The magnetic elastomer with a negative Poisson's ratio structure and a non-single magnetic field distribution is used as a bridge deck to construct a flexible magnetically sensitive strain sensor, so that the sensor has high sensing performance, can achieve detection with a minimum strain resolution of 0.5%, and extend the range to 200%.

[0026] Compared with the prior art, the embodiments of the present invention also have the following advantages:

[0027] 1) Magnetic elastomer is made of elastic matrix, magnetic particles and dispersant. By adjusting the type and proportion of the dispersant, the content of magnetic powder in the elastomer is successfully increased (for example, the content of magnetic powder can be increased to more than 0.5 times that of the elastic matrix), the dispersibility of magnetic powder is improved, and the repeatability of magnetic elastomer is improved.

[0028] 2) First, a negative Poisson's ratio structure template was 3D printed through structural design. Based on the template, an elastomer with a negative Poisson's ratio structure was prepared using a template method. The introduction of this structure improved the tensile properties of the elastomer to a certain extent, increased the elongation at break, and reduced the Young's modulus. Moreover, after magnetization, the sensitivity of the elastomer with this structure was greatly improved compared with the unstructured film.

[0029] 3) The magnet obtained by the present invention, i.e. the magnetic elastomer, has a non-single magnetic field distribution (the magnetic field in the magnet is arranged in an array), and the sensitivity of the magnetic elastomer is improved. The magnetic field used in the magnetization treatment of the present invention is a single magnetic field, such as a longitudinal single magnetic field, and the magnet obtained is a magnet with a non-single magnetic field distribution; most of the existing technologies currently use a magnet array to achieve this magnetic field distribution, and the present application innovatively applies this special magnetic field distribution feature to a "single magnet", thereby improving the sensor sensing performance. In particular, the sensitivity of the magnetic elastomer with a Halbach magnetic field distribution obtained by three-dimensionally folding the elastomer and then magnetizing it is greatly improved, and the sensing performance of the corresponding sensor is greatly improved.

[0030] 4) The magnetic elastomer of the present invention has a negative Poisson's ratio structure and a non-single magnetic field distribution. The content of magnetic powder in the magnetic elastomer is regulated by adding a specific dispersant, and the distribution and intensity of the magnetic flux are controlled by further controlling the ratio of the magnetic powder in the magnetic elastomer / elastic matrix, so that the sensor can achieve a minimum strain resolution of 0.5% and an extended range of 200%.

[0031] 5) The flexible magnetically sensitive strain sensor prepared by the present invention is a bidirectional strain sensor. Due to the Poisson effect, ordinary structures shrink in the transverse direction when stretched, so in some application scenarios, the transverse strain signal cannot be detected. In the present application, the longitudinal tensile deformation and transverse expansion of the negative Poisson's ratio structure occur simultaneously, so that the transverse signal can also be detected during longitudinal stretching, that is, bidirectional strain sensing in the longitudinal and transverse directions. In addition, based on the bidirectional strain sensing characteristics of the sensor, the present application can also realize and facilitate the effective regulation of transverse and longitudinal force-magnetic coupling. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1Schematic diagram of the bridge structure of a flexible magnetically sensitive strain sensor in one embodiment of the present invention.

[0033] Figure 2 It is the cross-sectional iron element energy spectrum distribution diagram corresponding to the magnetic elastomer with and without the dispersant added in the embodiment of the present invention.

[0034] Figure 3 It is a curve diagram showing the relationship between tensile properties, i.e., tensile stress and strain under a tensile test of a structure with a negative Poisson's ratio and an unstructured elastomer without magnetization in an embodiment of the present invention.

[0035] Figure 4 It is a curve diagram showing the relationship between the change in sensor impedance with strain after magnetization of the negative Poisson's ratio structured elastomer and the unstructured elastomer in the embodiment of the present invention.

[0036] Figure 5 It is a curve diagram showing the relationship between sensor impedance and strain of a magnetic elastomer with a non-single magnetic field distribution obtained after the elastomer is magnetized under different states in an embodiment of the present invention.

[0037] Figure 6 It is a curve diagram showing the relationship between the sensor impedance and the strain of the magnetic elastomer (introducing the same negative Poisson's ratio structure and Halbach magnetic field) under different magnetic powder contents in the embodiment of the present invention.

[0038] Figure 7 This is a curve diagram showing the relationship between the impedance of the flexible magnetically sensitive strain sensor and the change in strain in Example 1 of the present invention.

[0039] Figure 8 is a schematic diagram of a single structure in a negative Poisson's ratio structure in one embodiment of the present invention;

[0040] Fig. 9 is a Halbach magnetic field distribution diagram in a magnetic elastomer in one embodiment of the present invention;

[0041] Fig.10 This is the impedance variation curve of the sensor in Example 1 of the present invention under a small strain increasing by 0.05%. DETAILED DESCRIPTION

[0042] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] The flexible magnetically sensitive strain sensor with high-performance bidirectional strain sensing provided in the present application is a magnetic elastomer with a negative Poisson's ratio structure and a non-single magnetic field distribution obtained by mixing an elastic matrix, magnetic particles and a dispersant, preparing an elastomer by a template method, and then magnetizing it. The introduced negative Poisson's ratio structure improves the tensile properties of the elastomer, and the sensitivity of the elastomer is greatly improved after magnetization; by using the magnetic elastomer as the bridge surface and the magnetic sensing unit as the bridge bottom, a stretchable magnetically sensitive strain sensor with a bridge structure is constructed, which has high sensing performance. In the working state, when stretched, the magnetic flux of the magnetic elastomer changes with the change of strain, and the change of the magnetic flux of the magnet sensed by the magnetic sensing unit changes its electrical output, thereby realizing the detection of 0.05% to 200% strain.

[0044] In the present invention, the magnetic elastomer is obtained by mixing an elastic matrix, magnetic particles and a dispersant, and then casting and magnetizing the mixture. The present application adds a dispersant to the raw materials of the magnetic elastomer, and the dispersant can evenly disperse fine magnetic powder, i.e., magnetic particles, in the elastic matrix, thereby achieving uniform distribution of the magnetic powder, increasing the content of the magnetic powder, and further increasing the magnetic field of the magnetic elastomer, which is beneficial to improving the range and sensitivity of the sensor.

[0045] The elastic matrix is ​​selected from one or more of aliphatic aromatic random copolyesters, polydimethylsiloxane, silicone, rubber, resin, hydrogel, polyurethane, styrene block copolymer, PVC, polyimide, polyterephthalate plastics, polyethylene octene co-elastomer, and thermoplastic elastomer. Preferably, Ecoflex, an aliphatic aromatic random copolyester with greater elasticity, is selected.

[0046] The magnetic particles are selected from NdFeB powder, SmCo powder, AlNiCo powder, FeCrCo powder, BaFe 12 O 19 Powder, SrFe 12 O 19 One or more of Fe3O4 powder and NdFeB powder.

[0047] The dispersant is selected from one or more of polycaprolactone, n-hexane, sodium dodecylbenzene sulfonate, polyethylene glycol, carboxyethyl cellulose, and triethanolamine. Preferably, n-hexane is selected. The inventor of the present application noticed that the elastic matrix such as ecoflex is a very viscous polymer, while the magnetic powder particles are very small and very easy to agglomerate. Pure physical stirring of the two can easily form a large amount of magnetic powder agglomerates in the elastomer. The present application can reduce the viscosity of the elastic matrix by adding the above dispersant, and the magnetic powder can also be dispersed in the dispersant, and then evenly dispersed in the elastic matrix ecoflex through the dispersant.

[0048] In an optional embodiment, the mass ratio of the magnetic particles to the dispersant is in the range of (0.5-6):1, for example, 0.5:1; 1:1; 2:1; 3:1; 4:1; 5:1, etc. The inventors of the present application have found that if the dispersant is too little, the magnetic powder will agglomerate; if the dispersant is too much, the solution will become thinner, which will lead to sedimentation during the curing process. The magnetic particles and the dispersant are within the above mass ratio range, which has a certain dispersion effect and no sedimentation occurs during the curing process. In this embodiment, by regulating the type and proportion of the dispersant in the elastomer, the content of magnetic particles in the elastomer / elastic matrix is ​​successfully increased, the dispersibility of the magnetic powder is improved, and the repeatability of the magnetic elastomer is improved; and the increase in the content of magnetic powder increases the magnetic field of the magnetic elastomer, which is beneficial to the expansion of the range and sensitivity of the GMI sensor; the improvement of the dispersibility of magnetic powder is conducive to the uniform distribution of the magnetic field of the magnetic elastomer. When stretched, the magnetic field changes evenly, making the impedance value of the sensor change more linearly; the improvement of repeatability makes the magnetic field distribution of the magnetic film close each time, so that the performance of the sensor can be repeated.

[0049] Further preferably, the mass ratio of the magnetic particles to the dispersant is in the range of (0.5-2): 1. In this range, the uniform dispersion effect is optimal, and when there are too many magnetic particles, that is, too little dispersant, for example, when the mass ratio of the magnetic particles to the dispersant exceeds 2: 1, partial agglomeration will occur.

[0050] Figure 2 The schematic diagram shows the cross-sectional iron energy spectrum distribution diagram of the magnetic elastomer with and without dispersant in the embodiment of the present invention. In this embodiment, the elastic matrix is ​​Ecoflex, the magnetic particles are NdFeB, and the dispersant is n-hexane. The negative Poisson's ratio structure and magnetic field distribution are the same, and the difference is mainly the ratio of magnetic particles to dispersant. Specifically, Figure 2 The left picture shows that the mass ratio of Ecoflex: NdFeB: n-hexane is 1:1:0 (i.e., no dispersant n-hexane is added); the right picture shows that the mass ratio of Ecoflex: NdFeB: n-hexane is 1:1:1. Figure 2 It can be seen that after adding the dispersant, the iron element, i.e. the magnetic powder, is evenly dispersed in the elastic matrix.

[0051] Furthermore, the mass ratio of the elastic matrix to the magnetic particles is in the range of (1-6):1, for example, 1:1; 2:1; 3:1; 4:1; 5:1; 6:1, etc. Based on the regulation of the type and proportion of the dispersant, the content of the magnetic powder in the magnetic elastomer is further controlled within the above range, and the distribution and intensity of the magnetic flux are controlled, so that the sensitivity of the magnetic elastomer is further improved, and the sensing performance of the sensor is further improved. The present invention makes the magnetic particles more evenly dispersed by adding a dispersant, and increases the content of the magnetic particles; and when the content of the magnetic particles is increased, the magnetic field of the magnetic elastomer is increased, thereby expanding the range of the sensor and improving the sensitivity. In particular, the content of the magnetic particles can be increased to 0.5 times or more of the elastic matrix, that is, the mass ratio of the elastic matrix to the magnetic particles can be in the range of (1-2):1, and the magnetic field is greatly increased. For example, the mass ratio of Ecoflex to NdFeB powder is 1:1; 1.5:1; 2:1, etc.

[0052] Figure 6 The following diagram schematically shows the relationship between sensor impedance and strain for a magnetic elastomer having the same negative Poisson's ratio structure and a Halbach magnetic field distribution at different magnetic powder contents in an embodiment of the present invention. Figure 6 As shown, the mass ratio of the elastic matrix to the magnetic particles is 1:1; 2:1; 3:1; 4:1; 5:1; 6:1. Figure 6 It can be seen that different magnetic powder contents have different magnetic field strengths; for the GMI effect (giant magneto-impedance effect), the strength of the magnetic field has a great influence on the sensitivity and range. Figure 6 As shown, when the magnetic powder content in the elastomer / elastic matrix is ​​high, for example, when the mass ratio of the elastic matrix to the magnetic particles is 1:1, the sensitivity is greatly improved.

[0053] In the present invention, the magnetic elastomer is firstly made to have a negative Poisson's ratio structure by using a template method, and then the elastomer with the negative Poisson's ratio structure is magnetized to form a magnetic film with a negative Poisson's ratio structure and a non-single magnetic field distribution. The template in the template method is a negative Poisson's ratio structure template obtained by 3D printing of structural design, and the elastomer is prepared by inverting the template.

[0054] In the present invention, the negative Poisson's ratio structure mainly includes: concave hexagon, double V-shape, rectangular perforation shape, etc. The introduction of the negative Poisson's ratio structure of the above shape improves the tensile properties of the elastomer to a certain extent, and the sensitivity of the elastomer after magnetization is greatly improved compared with the structureless film. Furthermore, the magnetic elastomer as the bridge deck has the above negative Poisson's ratio structure in its specific area, such as in the area of ​​the magnetic elastomer that is not in contact with the supporting layer.

[0055] Preferably, the negative Poisson's ratio structure is a double V-shaped structure, which is more compact and can significantly improve the tensile properties of the elastomer. The double V-shaped negative Poisson's ratio structure can be regarded as two ends of two Vs in the same direction connected to each other. Furthermore, in the double V-shaped negative Poisson's ratio structure, the angle of the double V is selected within 30 degrees to 180 degrees. In addition, the middle of the double V-shaped negative Poisson's ratio structure is hollow. Figure 1 As shown, the magnetic elastomer has a double V-shaped negative Poisson's ratio hollow structure.

[0056] Figure 8 A schematic diagram of a single structure with a negative Poisson's ratio in one embodiment of the present invention is shown schematically. The single structure with a negative Poisson's ratio (line diagram) is Figure 1 A single structure in a negative Poisson's ratio structure (3D image), Figure 8 The space between the two V lines is Figure 1 A single entity. Figure 8 As shown, in this embodiment, a double V shape is selected, and the negative Poisson's ratio structure is formed by staggered splicing of double V-shaped triangular structure chains. Among them, each large V frame has a side length of 1 to 5 mm and an angle of 30 to 150 degrees; the small V has a side length of 0.5 to 5 mm and an angle of 60 to 180 degrees. Figure 8 In the single structure shown, the big V is 60° and the small V is 120°; the side length of the hollow in the middle is 1.75mm, and the width of 0.28mm is the solid width. The double V-shaped negative Poisson's ratio structure has a tighter structure arrangement and can accommodate more structures per unit area. The theoretical Poisson's ratio can be calculated based on the height and width of a single structure, and the theoretical Poisson's ratio of the structure is -1 / 3, and the actual tested Poisson's ratio is -0.17.

[0057] Figure 3 The following diagram schematically shows the relationship between tensile stress and strain obtained in a tensile test at break when a negative Poisson's ratio structure and an unstructured elastic body (film) are introduced without magnetization in one embodiment of the present invention. Figure 3 The vertical drop point of the middle curve is the breaking point. Figure 3 As shown, compared with the unstructured elastomer, the elastomer introduced into the present invention with a negative Poisson's ratio structure has an increased elongation at break, a reduced Young's modulus, and better tensile properties.

[0058] Figure 4 The following is a schematic diagram showing the relationship between the sensor impedance and strain after magnetization of a negative Poisson's ratio structured elastic body and a non-structured elastic body in one embodiment of the present invention. Figure 4 As shown in the figure, compared with the unstructured film, the magnetic sensor corresponding to the elastomer with negative Poisson's ratio structure has a significantly improved impedance change rate under the same strain conditions. In particular, after 50% strain, its impedance change rate increases rapidly.

[0059] In the present invention, the magnet, i.e., the magnetic elastomer, has a special non-single magnetic field distribution, wherein the magnetic field distribution mainly includes: alternating magnetic field distribution, diagonal magnetic field distribution, Halbach magnetic field distribution, curled magnetic field distribution, etc.

[0060] Furthermore, the magnetic field distribution characteristic of "non-single magnetic field distribution" in the magnetic elastomer is achieved by "changing the state of the elastomer" before magnetization, that is, changing the magnetization state of the elastomer. Among them, "changing the state of the elastomer" means that before magnetization, the state of the elastomer before magnetization is designed according to the corresponding magnetic field distribution characteristics, and the elastomer is operated into a corresponding shape according to the designed structural state. For example, before magnetization, the magnetization state of the elastomer is changed by folding the elastomer, such as folding it several times, folding it three-dimensionally, etc., and magnetizing it in the said state can obtain a magnet with a corresponding magnetic field distribution.

[0061] Exemplarily, for example, by three-dimensionally folding an elastomer and then magnetizing it, a magnet with a halbach magnetic field distribution is obtained. By folding it in half along the long side and then magnetizing it, a magnet with an alternating magnetic field distribution is obtained. By folding it in half along the long side and then folding it in half along the short side, and then magnetizing it, a magnet with a diagonal magnetic field distribution is obtained. By winding it evenly and tightly with the short side as the central axis to form a solid cylinder, and then magnetizing it, a magnet with a curled magnetic field distribution is obtained. The same vertical magnetization is used during magnetization.

[0062] Preferably, the present invention selects a magnetic elastomer with a Halbach magnetic field distribution. Furthermore, by three-dimensionally folding the elastomer during magnetization, the final magnetic elastomer has the Halbach magnetic field distribution. During the magnetization process of the elastomer, the state of the elastomer is changed by three-dimensional folding, and the magnetization is performed in the three-dimensional folded state, so that the magnetic elastomer has a Halbach magnetic field distribution. In this way, the magnetic lines of force can be gathered on one side of the magnet and weakened on the other side. The sensitivity of the magnetic elastomer with a Halbach non-single magnetic field distribution is greatly improved, thereby improving the sensing performance of the sensor.

[0063] Fig. 9 The Halbach magnetic field distribution diagram on the surface of the magnetic elastomer in the embodiment of the present invention is schematically shown, wherein the X axis represents the length, the Y axis represents the width, and the Z axis represents the magnetic induction intensity.

[0064] Figure 5 The relationship between the impedance change rate and strain of a magnetic elastomer with a special magnetic field distribution (magnetic induction line distribution) obtained by magnetization under different states in one embodiment of the present invention is schematically shown. Figure 5 Includes: alternating twice (ie, the magnetic field NS alternates twice), alternating four times (ie, the magnetic field NS alternates four times), diagonal magnetization (diagonal magnetic field distribution), solid cylinder (curled magnetization), Halbach. Figure 5It can be seen that the sensitivity of the magnetic elastomer with Halbach magnetic induction line distribution obtained by magnetizing the magnetic film after three-dimensional folding is much higher than that of the other four magnetic field distributions. The present invention preferably uses the magnetic elastomer with Halbach magnetic field distribution obtained by magnetizing in a three-dimensional folded state as a bridge surface to construct a flexible magnetic sensitive strain sensor.

[0065] Figure 1 The structure of a flexible magnetically sensitive strain sensor provided in one embodiment of the present invention is schematically shown. Figure 1 As shown, the flexible magnetically sensitive strain sensor is a bridge structure, including a bridge deck, a bridge bottom and a supporting layer 4 supported between the bridge deck and the bridge bottom; wherein a magnetic elastomer 1 with a double V-shaped negative Poisson's ratio structure and a non-single magnetic field distribution is used as the bridge deck, and a magnetic sensing unit is used as the bridge bottom.

[0066] In the flexible magnetic strain sensor of the bridge structure, the spacing between the magnetoelastic matrix as the bridge deck and the magnetic sensing unit as the bridge bottom is controlled within a range of 2 to 6 mm, for example, 4 mm. Within this suitable spacing range, the magnetic sensing unit can more sensitively sense the change of magnetic flux, thereby completing strain detection, and taking into account both high sensitivity and wide range of stretchability.

[0067] like Figure 1 As shown, in this embodiment, the magnetic sensing unit includes: an elastic bottom layer, a magnetic sensing element 2 and a strain suppression layer 3; wherein the strain suppression layer is printed on the surface of the elastic bottom layer; and the magnetic sensing element is embedded in the strain suppression layer. Furthermore, the strain suppression layer embedded with the magnetic sensing element is located in the middle of the upper surface of the elastic bottom layer and faces upward, so that the magnetic flux change of the magnetic elastomer under the stretching state can be more accurately sensed.

[0068] like Figure 1 As shown, this embodiment uses two spaced support bodies as support layer 4 to separate the bridge deck and the bridge bottom. Specifically, the bridge structure is formed by laminating the lower surfaces of the two ends of the magnetic elastic body 1 with the upper surface of the support layer 4, and laminating the upper surface of the elastic bottom layer in the magnetic sensor unit with the lower surface of the support layer 4. The material of the support body can be PDMS, and the length can be controlled to be 2 to 3 cm.

[0069] In the magnetic sensor unit, the elastic bottom layer (ie the bridge bottom layer) is made of the same material as the elastic matrix in the magnetic elastomer, for example, Ecoflex, etc. The elastic bottom layer does not need to have a negative Poisson's ratio structure.

[0070] The magnetic sensing element can be one of a Hall sensor, a giant magnetoresistance sensor, and a giant magnetoimpedance sensor. Preferably, a giant magnetoimpedance sensor is selected. The giant magnetoimpedance sensor is composed of an inductor coil and a magnetic core; wherein the inductor coil is wound with copper wire, with 50 to 200 turns and a length of 0.5 to 2 cm; the magnetic core is selected from one or more of Fe-based amorphous wire, Co-based amorphous wire, FeCo-based amorphous wire, FeNi-based amorphous wire and CoNi-based amorphous wire. Further preferably, a giant magnetoimpedance sensor consisting of an inductor coil wound with 100 turns of copper wire and a Co-based amorphous wire magnetic core is used as the magnetic sensing element.

[0071] The strain suppression layer is formed by printing a strain suppression gel on the surface of the elastic bottom layer. The gel is prepared by mixing sodium alginate, anhydrous calcium chloride and deionized water in a ratio of 10: (0.1-5): 500. Preferably, the ratio is 10: 0.1: 500. By printing the above gel on the elastic bottom layer to form a strain suppression layer, a slightly higher Young's modulus is obtained. By embedding the magnetic sensor element in the strain suppression layer, the influence of the strain of the elastic bottom layer on the magnetic sensor unit can be avoided, thereby ensuring that the sensor of the present invention still maintains a higher resolution and a lower detection limit during a large range of stretching, and has a higher sensitivity.

[0072] A method for preparing a flexible magnetic strain sensor with high performance bidirectional strain sensing provided in an embodiment of the present application may include the following steps:

[0073] Step S1, mixing an elastic matrix, magnetic particles and a dispersant in proportion, preparing an elastomer with a negative Poisson's ratio structure by a template method, and magnetizing the elastomer to obtain a magnetic elastomer with a negative Poisson's ratio structure and a non-single magnetic field distribution. The template in the template method is a negative Poisson's ratio structure template prepared by structural design 3D printing, and the magnetic elastomer is an elastomer with a negative Poisson's ratio structure prepared by the template method based on the negative Poisson's ratio structure template.

[0074] Furthermore, before the magnetization treatment, the elastomer is first folded, and the magnetization state of the elastomer is changed by folding, so as to obtain a magnetic elastomer with a corresponding magnetic field distribution. Specific operation: first use a supporting mold to fold the elastomer with a negative Poisson's ratio structure obtained above; then magnetize it under a uniform large magnetic field, so as to obtain a magnetic elastomer with a special magnetic field distribution, and the special magnetic field distribution of the magnetic elastomer is a non-single magnetic field distribution. Preferably, before the magnetization treatment, the elastomer is first three-dimensionally folded, and the magnetization state of the elastomer is changed by three-dimensional folding, so as to obtain a magnetic elastomer with a Halbach magnetic field distribution.

[0075] Step S2, using the magnetic elastomer with a negative Poisson's ratio structure and a non-single magnetic field distribution obtained in step S1 as the bridge deck, and the magnetic sensing unit as the bridge bottom, and constructing a flexible magnetically sensitive strain sensor with a bridge structure through a supporting layer.

[0076] Among them, the preparation of the magnetic sensor unit may include the following steps: 1) winding an inductor coil, placing a magnetic core, and preparing a magnetic sensor element; 2) embedding the magnetic sensor element into an elastic base layer; 3) performing plasma treatment on the surface of the elastic base layer embedded with the magnetic sensor element; 4) directly extruding and printing gel on the surface of the elastic base layer after plasma treatment to form a strain suppression layer, thereby obtaining a magnetic sensor unit that can be used as a bridge bottom.

[0077] Furthermore, when constructing a bridge structure sensor, based on the action of plasma, the lower surface of the magnetic elastomer is adhered to the upper surface of the supporting layer, the elastic bottom layer and the plasma-treated surface are adhered to the lower surface of the supporting layer, and the strain suppression layer is facing upward, thereby forming a flexible magnetically sensitive strain sensor of the bridge structure.

[0078] In one embodiment of the present invention, a flexible magnetic-sensitive strain sensor with high-performance bidirectional strain sensing is also provided. When applied, the flexible magnetic-sensitive strain sensor senses the change in magnetic flux of the magnetic elastomer under the stretching state through a magnetic sensing unit and outputs a corresponding electrical signal, thereby realizing strain detection. Furthermore, the flexible magnetic-sensitive strain sensor of the present invention has high sensitivity and a large working range (stretchability), and can achieve a minimum strain resolution of 0.5% and an extended range of 200%.

[0079] When the present invention performs relevant performance tests on the sensor, a fixed strain is applied to the flexible magnetic-sensitive strain sensor, the sensor electrical signal (resistance, voltage, impedance) is tested, and the magnitude of the strain is changed, thereby obtaining a series of reference resistance values, voltage values ​​or impedance values ​​under different strains, and constructing a relationship curve. Working principle: When stretched, the magnetic flux of the magnetic elastomer changes with the change of strain, and the change of the magnetic flux of the magnet sensed by the magnetic sensing unit changes its electrical output, thereby realizing the detection of 0.05% to 200% strain.

[0080] The present invention is further described below in conjunction with a specific embodiment:

[0081] Example 1

[0082] 1) Preparation of magnetic elastomer

[0083] Raw materials: Ecoflex, an aliphatic aromatic random copolyester with high elasticity, is used as the elastic matrix, a neodymium iron boron mixture (neodymium iron boron powder) is used as the magnetic particles, and n-hexane is used as the dispersant; and the mass ratio of Ecoflex, neodymium iron boron powder and n-hexane is 1:1:1.

[0084] Preparation: The negative Poisson's ratio structure is designed to be a double V-shape, and a negative Poisson's ratio structure template is prepared by 3D printing; the raw materials are mixed and then prepared by a template method to obtain an elastomer with a double V-shaped negative Poisson's ratio structure; the elastomer is first three-dimensionally folded using a supporting mold, and the three-dimensionally folded elastomer is placed in a large magnetic field for magnetization treatment to obtain a magnetic elastomer with a Halbach magnetic field distribution.

[0085] 2) Preparation of magnetic induction unit

[0086] Ecoflex is used as the elastic bottom layer; a giant magneto-impedance sensor composed of an inductor coil wound with 100 turns of copper wire and a Co-based amorphous wire core is used as the magnetic sensing element; a gel of the strain suppression layer is prepared by mixing a mixture of sodium alginate, anhydrous calcium chloride and deionized water in a ratio of 10:0.1:500.

[0087] The magnetic sensing element is embedded in an elastic bottom layer; the surface of the elastic bottom layer in which the magnetic sensing element is embedded is subjected to plasma treatment; a strain suppression layer gel is directly printed on the surface of the elastic bottom layer after the plasma treatment to form a strain suppression layer, thereby obtaining a magnetic sensing unit that can be used as a bridge bottom.

[0088] 3) Build a bridge structure sensor

[0089] The supporting layer is prepared by the template method, the magnetic elastomer is used as the bridge surface, and the magnetic sensor unit is used as the bridge bottom. Under the action of plasma, the plasma-treated surfaces of the magnetic elastomer and the magnetic sensor unit are respectively adhered to the upper and lower surfaces of the supporting layer, with the strain suppression layer facing upward, thereby obtaining a bridge-type stretchable flexible magneto-sensitive strain sensor.

[0090] 4) Conduct the test:

[0091] A fixed external strain is applied to the flexible magnetic strain sensor, and a 250kHz AC current is passed through the sensor to test the sensor impedance. The strain is changed to obtain a series of reference impedance values ​​under different strains.

[0092] Figure 7 4 is a curve diagram showing the relationship between the impedance of the flexible magnetically sensitive strain sensor of this embodiment and the change in strain. Fig.10 The impedance change curve of the sensor under a small strain of 0.05% is schematically shown. It can be seen that the magnetic elastomer with a negative Poisson's ratio structure and Halbach magnetic field distribution is assembled into a sensor for strain testing, which can achieve a large range response of 200% and greatly improve the sensitivity (impedance change rate).

[0093] The description of the present invention is given for the purpose of illustration and description, and is not intended to be exhaustive or to limit the invention to the disclosed form. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments are selected and described in order to better illustrate the principles and practical applications of the present invention and to enable those of ordinary skill in the art to understand the present invention and thereby design various embodiments with various modifications suitable for particular uses.

Claims

1. A flexible magnetic strain sensor with high performance bidirectional strain sensing, characterized in that: It is a bridge structure, with a magnetic elastic body as the bridge deck and a magnetic sensor unit as the bridge bottom; The magnetic elastomer has a negative Poisson's ratio structure and a non-single magnetic field distribution. It is prepared by a template method and then magnetized using an elastic matrix, magnetic particles and a dispersant as raw materials; the mass ratio of the magnetic particles to the dispersant is (0.5-6):1; the mass ratio of the elastic matrix to the magnetic particles is (1-6):

1.

2. The flexible magnetic strain sensor with high performance bidirectional strain sensing according to claim 1 is characterized in that: The dispersant is selected from one or more of polycaprolactone, n-hexane, sodium dodecylbenzene sulfonate, polyethylene glycol, carboxyethyl cellulose and triethanolamine.

3. The flexible magnetic strain sensor with high performance bidirectional strain sensing according to claim 2 is characterized in that: The elastic matrix is ​​selected from one or more of aliphatic aromatic random copolyesters, polydimethylsiloxane, silicone, rubber, resin, hydrogel, polyurethane, styrene block copolymer, PVC, polyimide, polyterephthalate plastics, polyethylene octene co-elastomer, and thermoplastic elastomer; The magnetic particles are selected from NdFeB powder, SmCo powder, AlNiCo powder, FeCrCo powder, BaFe 12 O 19 Powder, SrFe 12 O 19 One or more of Fe3O4 powder and Fe3O4 powder.

4. The flexible magnetic strain sensor with high performance bidirectional strain sensing according to claim 1 is characterized in that: The negative Poisson's ratio structure is one or a combination of concave-angle hexagon, double V-shape, and rectangular perforated shape.

5. The flexible magnetic strain sensor with high performance bidirectional strain sensing according to claim 4 is characterized in that: The negative Poisson's ratio structure is a double V-shape.

6. The flexible magnetic strain sensor with high performance bidirectional strain sensing according to claim 1 is characterized in that: The magnetic elastomer has a non-single magnetic field distribution, which means that the magnetic field distribution in the magnetic elastomer is one of an alternating magnetic field, a diagonal magnetic field, a Halbach magnetic field, and a curled magnetic field.

7. The flexible magnetic strain sensor with high performance bidirectional strain sensing according to claim 6 is characterized in that: The magnetic elastomer has a Halbach magnetic field distribution and is obtained by three-dimensionally folding the elastomer obtained by the template method and then magnetizing it.

8. The flexible magnetic strain sensor with high performance bidirectional strain sensing according to claim 1 is characterized in that: The magnetic sensing unit includes an elastic base layer, a strain suppression layer printed on the surface of the elastic base layer, and a magnetic sensing element embedded in the strain suppression layer; In the bridge structure, the bridge deck and the bridge bottom are separated by a supporting layer, the distance between the bridge deck and the bridge bottom is 2 to 6 mm, and the strain suppression layer in the magnetic sensing unit of the bridge bottom faces upward; The magnetic sensing element is one of a Hall sensor, a giant magnetoresistance sensor and a giant magnetoimpedance sensor; the gel of the strain suppression layer is prepared by mixing sodium alginate, anhydrous calcium chloride and deionized water in a ratio of 10: (0.1-5):

500.

9. A method for preparing a flexible magnetic strain sensor with high performance bidirectional strain sensing according to any one of claims 1 to 8, characterized in that: include: An elastic matrix, magnetic particles and a dispersant are mixed in proportion, an elastomer having a negative Poisson's ratio structure is prepared by a template method, and the elastomer is magnetized to obtain a magnetic elastomer having a negative Poisson's ratio structure and a non-single magnetic field distribution; The magnetic elastic body is used as the bridge surface, and the magnetic sensing unit is used as the bridge bottom to form a flexible magnetic sensitive strain sensor with a bridge structure.

10. An application of a flexible magnetic strain sensor for high-performance bidirectional strain sensing according to any one of claims 1 to 8, characterized in that: When used, the flexible magnetosensitive strain sensor senses the change in magnetic flux of the magnetoelastic body under the stretching state through the magnetic sensing unit and outputs a corresponding electrical signal, thereby realizing the detection of 0.05% to 200% strain.

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