A dual-mode flexible sensor for measuring temperature and strain and a method for preparing the same

Abstract

The present invention discloses a dual-mode flexible sensor for measuring temperature and strain, comprising two flexible substrates (1) arranged at the outermost sides, the outer surfaces of the two flexible substrates (1) are respectively attached with strain sensitive materials (4), the inner surfaces are respectively covered with electrodes (3), and a dielectric material layer (2) is sandwiched between the two electrodes (3); the flexible substrate (1) is a flexible film and is non-conductive. The dual-mode flexible sensor realizes dual-mode measurement of temperature and strain by utilizing that the resistance of the strain sensitive material changes with strain and the dielectric constant ε and thickness d of the dielectric material change with temperature. In addition, the dual-mode flexible sensor has a simple structure, a simple and efficient preparation and use method, a wide temperature measurement range, and can realize temperature measurement of 20 to 200°C and strain measurement of 0 to 2000με. It has high measurement accuracy, a temperature measurement error of about 4.44%, and a strain measurement error of about 6.5%. It can be applied to the detection of automobile tire pressure and temperature.

Description

Technical Field

[0001] The present invention relates to the technical field of temperature and strain detection, and in particular to a dual-mode flexible sensor for measuring temperature and strain and a preparation method thereof. Background Art

[0002] Temperature directly affects the physical and chemical properties of devices or materials. Flexible temperature sensors have good flexibility and stretchability, can be bent or even folded freely, and have flexible and diverse structures, which can easily detect the measured value. The sensing mechanism of flexible temperature sensors refers to the signal conversion mechanism by which the sensor converts the measured temperature signal into an electrical signal, that is, through the change of the electrical signal of the flexible temperature sensor, it can be detected in time whether the device is operating normally, solve the problem of excessive operating temperature, and increase the service life of the device.

[0003] Flexible strain sensors are widely used in electronic skin, medical care, sports equipment and other fields. The sensing mechanism of flexible strain sensors refers to the signal conversion mechanism of the sensor to convert the measured strain signal into an electrical signal, which is mainly divided into three parts: piezoresistive effect, capacitive effect and piezoelectric effect. Strain is one of the important performance parameters of the device, and detecting strain under high temperature is of great significance for bearing working condition monitoring.

[0004] In order to achieve high integration of sensor equipment, developing dual-modal flexible sensors that can realize temperature measurement and strain measurement is one of the difficulties of current technology.

[0005] A Chinese patent document with publication number CN106017718B discloses a flexible temperature sensor, which includes: upper and lower flexible substrates; electrodes placed on the substrates; temperature sensitive materials between the electrodes; the electrode materials are made of metal materials or carbon powder materials, and the electrode processing method is screen printing.

[0006] A Chinese patent document with publication number CN112857468A discloses a dual-mode sensor, comprising: an elastic substrate, a conductive material and a magnetically sensitive material; the elastic substrate is non-conductive; the conductive material is attached to the surface of the elastic substrate; the magnetically sensitive material is inserted into the elastic substrate. The dual-mode sensor can simultaneously measure strain and magnetic field strength without interfering with each other, and the preparation and use methods are simple and efficient. Summary of the invention

[0007] The present invention provides a dual-mode flexible sensor for measuring temperature and strain, which can realize simultaneous measurement of temperature and strain without mutual interference, simple structure, simple and efficient preparation and use methods, wide temperature measurement range, and can realize temperature measurement of 30 to 200°C and strain measurement of 0 to 2000με.

[0008] The specific technical solutions adopted are as follows:

[0009] A dual-mode flexible sensor for measuring temperature and strain comprises two flexible substrates arranged at the outermost sides, the outer surfaces of the two flexible substrates are respectively attached with strain sensitive materials, the inner surfaces are respectively covered with electrodes, and a dielectric material layer is sandwiched between the two electrodes; the flexible substrate is a flexible film and is non-conductive.

[0010] The flexible substrate has the characteristics of softness, low modulus, and easy deformation. Preferably, the flexible substrate is made of at least one of polymethyl methacrylate (PMMA), polyethylene (PE), polypropylene (PP), polyimide (PI), polyamide (PA), polyvinylidene fluoride (PVDF), polydimethylsiloxane (PDMS), and ethylene propylene diene monomer (EPDM).

[0011] Further preferably, the flexible substrate is a polyimide film.

[0012] The electrode is made of an electrode material. Preferably, the electrode material is a solid conductive metal, a conductive polymer, an inorganic carbon-based conductive material or a liquid metal.

[0013] The inorganic carbon-based conductive materials include but are not limited to graphite, carbon nanotubes, graphene, etc.

[0014] The liquid metal is mercury, gallium, gallium-indium alloy or gallium-indium-tin alloy; preferably, the liquid metal is gallium, gallium-indium alloy or gallium-indium-tin alloy doped with one or more transition metals or solid non-metallic elements.

[0015] Further preferably, the electrode material is gallium-indium alloy liquid metal.

[0016] Preferably, the dielectric material layer comprises a dielectric material or a mixture of a dielectric material and a thermally expandable polymer, and the dielectric material is a composite oxide ceramic of titanium dioxide, mica or hexagonal boron nitride.

[0017] The heat-expandable polymer includes, but is not limited to, polydimethylsiloxane, polystyrene, polypropylene, and polymethyl methacrylate.

[0018] Dielectric materials are sensitive to temperature, and the dielectric constant decreases with increasing temperature. Due to the positive coefficient of linear expansion, its thickness also increases with increasing temperature, which can convert temperature signals into electrical signals. The presence of thermally expandable polymers can further increase the thickness change of the dielectric material layer and improve the sensitivity of the dual-mode flexible sensor.

[0019] Further preferably, the dielectric material layer comprises a mixture of barium titanate ceramic and polydimethylsiloxane.

[0020] The resistance of strain-sensitive materials changes with strain, and the strain signal can be converted into an electrical signal.

[0021] The strain sensitive material includes silicon carbide semiconductor, antimonide steel semiconductor, indium tin oxide, titanium nitride ceramic, tantalum nitride ceramic, tantalum boride ceramic, copper-nickel alloy, nickel-chromium alloy, iron-chromium alloy, platinum-tungsten alloy or palladium-chromium alloy.

[0022] The loop-shaped structure of the strain sensitive material is simple to manufacture and has stable performance. When the dual-mode flexible sensor is deformed by force, the strain sensitive material is deformed at the same time, and the resistance value changes. The deformation amount of the dual-mode flexible sensor can be calculated based on the change in the resistance value.

[0023] The strain-sensitive material can be changed into different structures according to different needs.

[0024] Preferably, the strain sensitive material is attached to the outer surfaces of the two flexible substrates in a loop shape with a spacing of 300-500 μm.

[0025] The present invention also provides a method for preparing the dual-mode flexible sensor, comprising the following steps:

[0026] (1) uniformly coating or depositing an electrode material on the inner surface of a flexible substrate to form an electrode;

[0027] (2) coating or depositing a dielectric material or a mixture of a dielectric material and a heat-expandable polymer onto the electrode of step (1), and heating and curing the mixture to form a dielectric material layer;

[0028] (3) coating or depositing the electrode material onto the dielectric material layer to form an electrode, which is then packaged with a flexible substrate;

[0029] (4) The strain-sensitive material is coated or deposited onto the outer surfaces of the two flexible substrates to prepare the dual-modal flexible sensor.

[0030] Preferably, the strain sensitive material is NiCr alloy, which is coated on the outer surfaces of the two flexible substrates by magnetron sputtering.

[0031] The present invention also provides a method for using the dual-mode flexible sensor, comprising the following steps:

[0032] (1) measuring the capacitance of the dual-mode flexible sensor at a fixed temperature, changing the external temperature, obtaining a series of reference capacitance values ​​at different temperatures, and fitting a curve of the relationship between temperature and capacitance change rate;

[0033] (2) applying a fixed strain to the dual-mode flexible sensor, testing the resistance of the dual-mode flexible sensor, changing the strain, obtaining a series of reference resistance values ​​under different strains, and fitting to obtain a curve of the relationship between strain and resistance change rate;

[0034] (3) Keeping the same test conditions as in steps (1) and (2), the actual capacitance change rate and resistance change rate of the dual-mode flexible sensor are tested, and they are substituted into the temperature-capacitance change rate relationship curve and the strain-resistance change rate relationship curve, respectively, to obtain the measured temperature value and strain value.

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

[0036] (1) The present invention utilizes the fact that the resistance of strain-sensitive materials changes with strain and the dielectric constant ε and thickness d of dielectric materials change with temperature to achieve dual-mode measurement of temperature and strain.

[0037] (2) The dual-mode flexible sensor has a simple structure, and its preparation and use methods are simple and efficient. It can realize temperature and strain measurement simultaneously without interfering with each other. There is no coupling problem between temperature and strain output signals. It has a wide temperature measurement range and can realize temperature measurement from 30°C to 200°C and strain measurement from 0 to 2000με. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of the structure of the dual-mode flexible sensor in Example 1 of the present invention, wherein the reference numerals are: flexible substrate 1, dielectric material layer 2; electrode 3, strain sensitive material 4.

[0039] Figure 2 This is a curve diagram showing the relationship between the capacitance change rate of the dual-mode flexible sensor prepared in Example 1 of the present invention and the temperature change.

[0040] Figure 3 1 is a curve diagram showing the relationship between the resistance change rate of the dual-mode flexible sensor prepared in Example 1 of the present invention and the change of strain, and GF represents the strain sensitivity coefficient. DETAILED DESCRIPTION

[0041] The present invention will be further described below in conjunction with the accompanying drawings and embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0042] Example 1

[0043] In this embodiment, the structure of the dual-mode flexible sensor is as follows: Figure 1As shown, the outer surfaces of the two flexible substrates 1 are respectively attached with strain sensitive materials 4, and the inner surfaces are respectively covered with electrodes 3, and a dielectric material layer 2 is sandwiched between the two electrodes 3. The strain sensitive materials 4 are attached to the outer surfaces of the two flexible substrates 1 in a loop shape with a spacing of 350μm.

[0044] In this embodiment, the flexible substrate 1 is a polyimide film that is bendable and non-conductive, the electrode 3 is made of gallium-indium alloy liquid metal, the dielectric material layer 2 includes a mixture of barium titanate ceramic and polydimethylsiloxane, and the strain sensitive material 4 is a NiCr alloy.

[0045] The preparation method of the dual-mode flexible sensor comprises the following steps:

[0046] (1) uniformly coating gallium-indium alloy liquid metal on the inner surface of a polyimide film to form an electrode;

[0047] (2) mixing barium titanate ceramic and polydimethylsiloxane, spin coating them onto the electrode, and heating and curing them to form a dielectric material layer;

[0048] (3) coating gallium-indium alloy liquid metal onto the dielectric material layer to form an electrode, and then encapsulating it with a polyimide film;

[0049] (4) NiCr alloy is deposited on the outer surfaces of the two polyimide films by means of loop-shaped magnetron sputtering to prepare the dual-mode flexible sensor.

[0050] The dual-mode flexible sensor was tested as follows:

[0051] (1) The capacitance change rate of the dual-mode flexible sensor was measured at different temperatures (30-200°C), thereby obtaining a series of reference capacitance change rates at different temperatures, and the fitting curves are shown in Figure 2. Figure 2 As shown, the capacitance change rate decreases gradually with the increase of temperature, and has good linearity (0.9983);

[0052] (2) Different strains (0 to 2000 με) were applied to the dual-mode flexible sensor to test the resistance change rate of the conductive material of the sensor, thereby obtaining a series of reference resistance change rates under different strains. The fitting curves are shown in Figure 2. Figure 3 As shown, the resistance is positively correlated with the strain and has good linearity, and the strain sensitivity coefficient GF=1.635.

[0053] (3) In actual application, the actual capacitance and resistance change rates of the dual-modal flexible sensor are tested under the same test conditions as in steps (1) and (2), and are substituted into the temperature-capacitance change rate relationship curve and the strain-resistance change rate relationship curve, respectively, to obtain the actual temperature value and strain value.

[0054] The dual-mode flexible sensor of this embodiment is placed in an environment of 90°C, and its capacitance change rate is 9.5%. Figure 2 The calculated temperature is 86°C, which means the relative error is 4.44%.

[0055] When a micro strain of 1000 με is applied to the dual-mode flexible sensor of this embodiment, the resistance change rate is 1624 ppm. Figure 3 The calculated strain is 1065με, which means the relative error is 6.50%.

[0056] Example 2

[0057] In the dual-mode flexible sensor of this embodiment, strain sensitive materials are attached to the outer surfaces of the two flexible substrates respectively, and electrodes are covered on the inner surfaces respectively. A dielectric material layer is sandwiched between the two electrodes. The strain sensitive materials are attached to the outer surfaces of the two flexible substrates in a loop shape with a spacing of 300 μm.

[0058] Among them, the flexible substrate is a polypropylene (PP) film, which is bendable and non-conductive, the electrode is made of graphite, the dielectric material layer contains lead zirconate titanate ceramic, and the strain sensitive material is indium tin oxide ITO.

[0059] The preparation method of the dual-mode flexible sensor comprises the following steps:

[0060] (1) Graphite is uniformly coated on the inner surface of a PP film to form an electrode;

[0061] (2) depositing lead zirconate titanate ceramic onto the electrode to form a dielectric material layer;

[0062] (3) coating graphite onto the dielectric material layer to form an electrode, and then encapsulating it with a PP film;

[0063] (4) ITO is deposited in a loop shape on the outer surfaces of the two PP films to prepare the dual-mode flexible sensor.

[0064] Example 3

[0065] In the dual-mode flexible sensor of this embodiment, strain sensitive materials are attached to the outer surfaces of the two flexible substrates respectively, and electrodes are covered on the inner surfaces respectively. A dielectric material layer is sandwiched between the two electrodes. The strain sensitive materials are attached to the outer surfaces of the two flexible substrates in a loop shape with a spacing of 400 μm.

[0066] Among them, the flexible substrate is a polyamide film, which is bendable and non-conductive, the electrode is made of a conductive polymer polyacetylene, the dielectric material layer contains mica and polystyrene, and the strain-sensitive material is a silicon carbide semiconductor.

[0067] The preparation method of the dual-mode flexible sensor comprises the following steps:

[0068] (1) Polyacetylene is uniformly coated on the inner surface of a polyamide film to form an electrode;

[0069] (2) mixing mica and polystyrene, spin coating them onto the electrode, and heating and curing them to form a dielectric material layer;

[0070] (3) coating polyacetylene onto the dielectric material layer to form an electrode, which is then encapsulated with a polyamide film;

[0071] (4) Silicon carbide is deposited in a loop shape on the outer surfaces of two polyamide films to prepare the dual-modal flexible sensor.

[0072] Example 4

[0073] In the dual-mode flexible sensor of this embodiment, strain sensitive materials are attached to the outer surfaces of the two flexible substrates respectively, and electrodes are covered on the inner surfaces respectively. A dielectric material layer is sandwiched between the two electrodes. The strain sensitive materials are attached to the outer surfaces of the two flexible substrates in a loop shape with a spacing of 450 μm.

[0074] Among them, the flexible substrate is a polyimide film, which is bendable and non-conductive, the electrode is made of gallium-indium-tin alloy liquid metal, the dielectric material layer contains hexagonal boron nitride, and the strain sensitive material is PdCr alloy.

[0075] The preparation method of the dual-mode flexible sensor comprises the following steps:

[0076] (1) uniformly coating gallium-indium-tin alloy liquid metal on the inner surface of a polyimide film to form an electrode;

[0077] (2) depositing hexagonal boron nitride onto the electrode to form a dielectric material layer;

[0078] (3) coating the gallium-indium-tin alloy liquid metal onto the dielectric material layer to form an electrode, and then encapsulating it with a polyimide film;

[0079] (4) PdCr alloy is deposited in a loop shape on the outer surfaces of the two polyimide films to prepare the dual-mode flexible sensor.

[0080] The embodiments described above provide a detailed description of the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements or similar substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A dual-mode flexible sensor for measuring temperature and strain, characterized in that: It comprises two flexible substrates (1) arranged at the outermost sides, the outer surfaces of the two flexible substrates (1) are respectively attached with strain sensitive materials (4), the inner surfaces are respectively covered with electrodes (3), and a dielectric material layer (2) is sandwiched between the two electrodes (3); the flexible substrate (1) is a flexible film and is non-conductive; The dielectric material layer (2) comprises a mixture of a dielectric material and a thermal expansion polymer, wherein the dielectric material is barium titanate ceramic; and the thermal expansion polymer is polydimethylsiloxane; The strain sensitive material is NiCr alloy; The strain sensitive material (4) is attached to the outer surfaces of the two flexible substrates (1) in a loop shape with a spacing of 300 to 500 μm; The electrode material is gallium-indium alloy liquid metal.

2. The dual-mode flexible sensor according to claim 1, characterized in that: The flexible substrate (1) is made of at least one of polymethyl methacrylate, polyethylene, polypropylene, polyimide, polyamide, polyvinylidene fluoride, polydimethylsiloxane, and ethylene propylene diene monomer rubber.

3. The method for preparing the dual-mode flexible sensor according to claim 1, characterized in that: The following steps are involved: (1) uniformly coating or depositing an electrode material on the inner surface of a flexible substrate to form an electrode; (2) coating or depositing a dielectric material or a mixture of a dielectric material and a heat-expandable polymer onto the electrode of step (1), and heating and curing the mixture to form a dielectric material layer; (3) coating or depositing the electrode material onto the dielectric material layer to form an electrode, which is then packaged with a flexible substrate; (4) The strain-sensitive material is coated or deposited onto the outer surfaces of the two flexible substrates to prepare the dual-modal flexible sensor.

4. The method for preparing the dual-mode flexible sensor according to claim 3, characterized in that: The strain sensitive material is coated on the outer surfaces of the two flexible substrates by magnetron sputtering.

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