Flexible pressure sensor and preparation method thereof

Abstract

The invention provides a flexible pressure sensor and a preparation method thereof, and the method comprises the steps: mixing a polymer elastomer and a cross-linking agent according to a first preset weight ratio, and mixing and stirring the mixture with a diluent according to a second preset weight ratio to obtain a microfluid dispersion liquid; the method comprises the following steps: extruding a microfluid dispersion liquid into a preset continuous liquid on the basis of a droplet microfluidic technology to form droplets, and pretreating the droplets to form elastic microspheres; arranging at least two elastic microspheres with different diameters on the first electrode layer, and coating conductive liquid to form a conductive layer covering the elastic microspheres; a second electrode layer is arranged on the elastic microspheres covered with the conductive layer, and the elastic microspheres are limited between the first electrode layer and the second electrode layer; and the outer sides of the first electrode layer and the second electrode layer are respectively provided with a substrate to form a flexible pressure sensor monomer. The detection range of the sensor can be expanded, the sensitivity performance is improved, and the application requirements of different scenes are met.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology, and more specifically, to a flexible pressure sensor and a preparation method thereof. Background Art

[0002] In recent years, flexible pressure sensors have attracted widespread attention due to their ability to sense mechanical stimuli. They are considered to be key technologies for cutting-edge applications such as wearable electronics, soft robotics, surgery, and human-machine interfaces. The pressure generated by normal touch, object manipulation, and human circulation usually spans the low-pressure range and the medium-pressure range. The low-pressure state includes pressure in the body, including intraocular pressure and intracranial pressure, as well as pressure associated with daily gentle manipulation of objects. The study of pressure sensors in the low-pressure state is of great significance for the development of healthcare devices, medical diagnostics, and soft robotics, especially for applications involving gentle touch or grasping of soft objects. The medium-pressure state is well known for detecting blood pressure and pulse pressure and manipulating rigid objects. It is worth noting that manipulating soft and hard objects involves different pressure detection ranges. In robotics and prosthetic applications, it is crucial to have a sensor with a wide and scalable pressure detection range and high sensitivity to ensure reliability and stability in manipulating different objects.

[0003] Among them, according to the sensing mechanism, flexible pressure sensors are generally divided into piezoelectric, capacitive, piezoresistive and triboelectric types. Among them, piezoresistive pressure sensors stand out among many pressure sensor designs because of their advantages such as simple readout circuit, low crosstalk and low electromagnetic interference. At present, strategies to improve the sensitivity of pressure sensors can be roughly divided into three categories: increasing surface microstructure, increasing body porosity and their combination strategies.

[0004] However, existing pressure sensors with surface microstructures are usually manufactured using methods such as mold casting, photolithography, and 3D printing. Among them, in the mold casting method, the use of high-precision molds has a high cost, which limits their applicability to large-area devices. Although natural molds can produce large-area cardboard, their microstructures are controlled by natural molds, which limits their spatial uniformity and reproducibility. In addition, although the photolithography method can produce highly uniform and precise surface microstructures, it is limited by the cost of masks and the need to adjust sensor performance. Although 3D printing can produce precise, uniform, and adjustable surface microstructures, its scalability is limited.

[0005] In summary, there is an urgent need for a flexible pressure sensor preparation process that can achieve a mold-free, scalable and cost-effective method to manufacture pressure sensing devices with surface microstructures. Summary of the invention

[0006] In view of the above problems, the present invention provides a flexible pressure sensor and a method for preparing the same to solve the problems of poor sensor applicability, high cost, limited uniformity, reproducibility and scalability caused by the existing pressure sensor preparation process.

[0007] The flexible pressure sensor provided by the present invention comprises: after mixing a polymer elastomer and a cross-linking agent according to a first preset weight ratio, mixing and stirring with a diluent according to a second preset weight ratio to obtain a microfluidic dispersion; based on droplet microfluidics technology, extruding the microfluidic dispersion into a preset continuous liquid to form droplets, and pre-treating the droplets to form elastic microspheres; arranging at least two elastic microspheres with different diameters on a first electrode layer, and coating a conductive liquid on the first electrode layer to form a conductive layer covering the elastic microspheres; arranging a second electrode layer on the elastic microspheres covered with the conductive layer, and the elastic microspheres are limited between the first electrode layer and the second electrode layer; and arranging substrates on the outer sides of the first electrode layer and the second electrode layer to form a flexible pressure sensor monomer.

[0008] In addition, an optional technical solution is that the polymer elastomer includes at least one of polydimethylsiloxane, thermoplastic polyurethane elastomer and thermoplastic elastomer; the continuous liquid contains a surfactant, and the surfactant includes at least one of SDBS, SDS, SLS and CTAB.

[0009] In addition, an optional technical solution is that the first preset weight ratio range is: 20:1 to 20:6; the second preset weight ratio range is: 0 to 10:4.

[0010] In addition, an optional technical solution is to pre-treat the droplets to form elastic microspheres, including: solidifying the droplets, and during the solidification process, stirring a continuous liquid containing the droplets until the droplets form basic microspheres; washing the basic microspheres with deionized water and ethanol, and then drying the washed basic microspheres to form the elastic microspheres.

[0011] In addition, an optional technical solution is that when the first electrode layer or the second electrode layer squeezes the elastic microspheres under external pressure, the radius of the contact area between the first electrode layer or the second electrode layer and the elastic microspheres is expressed as:

[0012]

[0013] Wherein, E represents the Young's modulus of the elastic microsphere, v represents the Poisson's ratio of the elastic microsphere, a represents the radius of the elastic microsphere in an uncompressed state, and F represents the pressure on the elastic microsphere;

[0014] The contact resistance between the elastic microspheres and the first electrode layer and the second electrode layer is:

[0015] Rc=ρc / [4(r+r0)]

[0016] Wherein, ρc represents the resistivity of the elastic microsphere in contact with the first electrode layer or the second electrode layer, r represents the radius of the contact area, and r0 represents the initial radius of the contact area between the elastic microsphere and the first electrode layer or the second electrode layer in an uncompressed state;

[0017] The relative current change of the flexible pressure sensor under the external pressure P is expressed as:

[0018]

[0019] Wherein, A represents the area of ​​the substrate, P represents the pressure uniformly applied to the substrate, F=AP, ΔI represents the current change, I0 represents the initial current, and α represents the fitting parameter.

[0020] In addition, an optional technical solution is that the sensitivity of the flexible pressure sensor is expressed as:

[0021]

[0022] Wherein, S represents sensitivity, ΔI represents current change, I0 represents initial current, α represents fitting parameter, A represents the area of ​​the substrate, P represents the pressure uniformly applied to the substrate, v represents the Poisson's ratio of the elastic microsphere, a represents the radius of the elastic microsphere in an uncompressed state, and E represents the Young's modulus of the elastic microsphere.

[0023] In addition, an optional technical solution is that the at least two elastic microspheres with different diameters are spaced apart from each other and regularly distributed between the first electrode layer and the second electrode layer.

[0024] In addition, an optional technical solution is that the conductive layer has a temperature detection function; wherein the thickness of the conductive layer is 80 to 120 nm.

[0025] In addition, an optional technical solution is that after forming the flexible pressure sensor monomer, it also includes: encapsulating at least two flexible pressure sensor monomers through a PET film to form a sensor array.

[0026] On the other hand, the present invention also provides a flexible pressure sensor prepared using the above-mentioned flexible pressure sensor preparation method; wherein the flexible pressure sensor includes: an upper substrate, a lower substrate, a first electrode layer located on the lower side of the upper substrate, a second electrode layer located on the upper side of the lower substrate, and at least two elastic microspheres with different diameters located between the first electrode layer and the second electrode layer.

[0027] By utilizing the above-mentioned flexible pressure sensor and its preparation method, elastic microspheres are set between the two electrode layers, so that the flexible pressure sensor exhibits a larger pressure detection range while maintaining high sensitivity. The elastic microspheres are formed by droplet microfluidics technology, and the preparation process is simple and low-cost, which can meet the application requirements of the sensor in a variety of detection scenarios.

[0028] In order to achieve the above and related purposes, one or more aspects of the present invention include the features that will be described in detail later. The following description and the accompanying drawings describe some exemplary aspects of the present invention in detail. However, these aspects indicate only some of the various ways in which the principles of the present invention can be used. In addition, the present invention is intended to include all these aspects and their equivalents. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] By referring to the following description in conjunction with the accompanying drawings, and with a more comprehensive understanding of the present invention, other objects and results of the present invention will become more apparent and easy to understand. In the accompanying drawings:

[0030] Figure 1 is a flow chart of a method for preparing a flexible pressure sensor according to an embodiment of the present invention;

[0031] Figure 2 The principle of the flexible pressure sensor of a single elastic microsphere according to an embodiment of the present invention;

[0032] Figure 3 A working principle diagram of a flexible pressure sensor using double-sized elastic microspheres according to an embodiment of the present invention;

[0033] Figure 4 is a response curve diagram of the current change of the flexible pressure sensor to the normal pressure according to an embodiment of the present invention;

[0034] Figure 5 A comparative analysis diagram of the sensitivity and working pressure range of the flexible pressure sensor according to an embodiment of the present invention and the existing pressure sensor;

[0035] Figure 6 is a current variation curve diagram of the flexible pressure sensor under different pressures according to an embodiment of the present invention;

[0036] Figure 7 is a current response curve diagram of a pressure sensor using dual-size elastic microspheres under various pressures according to an embodiment of the present invention;

[0037] Figure 8 is a current-time response curve diagram of the flexible pressure sensor under different load pressures according to an embodiment of the present invention;

[0038] Fig. 9 This is a multi-cycle test diagram of a pressure sensor using dual-size elastic microspheres at 5 kPa according to an embodiment of the present invention;

[0039] Fig.10 The temperature sensing performance of the dual-size microsphere type sensor according to an embodiment of the present invention is shown;

[0040] Fig.11 is a resistance versus temperature curve of the dual-size microsphere sensor according to an embodiment of the present invention under no-load condition;

[0041] Fig.12 is a current response curve diagram of the sensor glove according to an embodiment of the present invention;

[0042] Fig.13 A diagram showing the sensor distribution and connection principle of a soft gripper according to an embodiment of the present invention is shown;

[0043] Fig.14 shows a distribution diagram of a sensor array according to an embodiment of the present invention;

[0044] Fig.15 FIG. 4 is a circuit schematic diagram of a sensor array according to an embodiment of the present invention. DETAILED DESCRIPTION

[0045] In the following description, for the purpose of illustration, in order to provide a comprehensive understanding of one or more embodiments, many specific details are set forth. However, it is apparent that these embodiments may also be implemented without these specific details. In other examples, for ease of describing one or more embodiments, known structures and devices are shown in the form of block diagrams.

[0046] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0047] It will be understood by those skilled in the art that, unless otherwise stated, the singular forms "a", "an", "said" and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of the features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof. It should be understood that the term "and / or" used herein includes any unit and all combinations of one or more associated listed items.

[0048] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0049] To describe the flexible pressure sensor and the method for manufacturing the same in detail, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0050] Figure 1 The figure shows a schematic flow of a method for preparing a flexible pressure sensor according to an embodiment of the present invention.

[0051] like Figure 1 As shown, the method for preparing the flexible pressure sensor of the embodiment of the present invention comprises:

[0052] S100: After mixing the polymer elastomer and the cross-linking agent according to a first preset weight ratio, the mixture is mixed with the diluent according to a second preset total weight ratio to obtain a microfluid dispersion.

[0053] Wherein, the polymer elastomer includes at least one of polydimethylsiloxane, thermoplastic polyurethane elastomer and thermoplastic elastomer; the diluent includes at least one of low-viscosity silicone oil, cyclohexane, n-hexane, etc.; the continuous liquid is a low-viscosity solution containing a surfactant, such as an aqueous solution containing a surfactant, wherein the surfactant includes at least one of SDBS, SDS, SLS, and CTAB. In addition, the above-mentioned first preset weight ratio range is: 20:1 to 20:6; the second preset weight ratio range is: 0 to 10:4.

[0054] As a specific example, the present invention uses polydimethylsiloxane (PDMS) as a polymer elastomer material to prepare polymer elastic microspheres. In this step, the PDMS elastomer and its cross-linking agent are first mixed at a weight ratio of 10:1, and then mixed with low-viscosity silicone oil at a ratio of 10:2. The resulting mixture is then stirred at a speed of 60 rpm for 1 hour, and then degassed at room temperature to form a dispersion in a microfluid, i.e., a microfluid dispersion.

[0055] Specifically, because silicone oil has lower surface tension and good lubricity, it can penetrate into the microstructure of the elastomer, making the elastomer softer and more elastic. In addition, silicone oil can also improve the wear resistance and aging resistance of the elastomer. The lubricating effect of silicone oil can reduce the wear of the elastomer during use, and its chemical stability can also effectively resist the erosion of the elastomer by the external environment, thereby extending the service life of the elastomer, and silicone oil can also play a role in regulating the viscosity of the elastomer. By adjusting the addition amount of silicone oil, accurate control of the viscosity of the elastomer can be achieved, thereby meeting the demand for elastomer performance in different fields. Therefore, in the present invention, silicone oil is used to form a microfluid dispersion, and it is known that other materials with equivalent functions can also be selected.

[0056] S200: Based on the droplet microfluidics technology, the microfluidic dispersion is squeezed into a preset continuous liquid to form droplets, and the droplets are pre-treated to form elastic microspheres.

[0057] Among them, the process of pre-treating the droplets to form elastic microspheres can include: solidifying the droplets, and during the solidification process, stirring the continuous liquid containing the droplets until the droplets form basic microspheres; washing the basic microspheres with deionized water and ethanol, and then drying the washed basic microspheres to form elastic microspheres.

[0058] Specifically, a 2wt% SDBS (sodium dodecylbenzene sulfonate) solution can be used as a continuous liquid in a microfluidic, and a droplet microfluidic technique is used to control the generation of PDMS droplets. Then, these droplets are collected and cured at 100°C for 12 hours to produce PDMS microspheres (i.e., elastic microspheres, the same below). During the curing process, stirring can be performed at a speed of 100rpm to prevent the PDMS droplets from aggregating, the resulting cured PDMS microspheres are collected, and washed with deionized water and ethanol, and then dried in an oven at a temperature of 60°C for 12 hours, and finally the appearance of the dried PDMS microspheres can be checked by a scanning electron microscope to see if they meet the requirements.

[0059] S300: placing at least two elastic microspheres with different diameters on a first electrode layer, and coating the first electrode layer with a conductive liquid to form a conductive layer covering the elastic microspheres.

[0060] S400: Arranging a second electrode layer on the elastic microspheres covered with the conductive layer, wherein the elastic microspheres are confined between the first electrode layer and the second electrode layer.

[0061] S500: Disposing substrates on the outer sides of the first electrode layer and the second electrode layer respectively to form a flexible pressure sensor unit.

[0062] When the first electrode layer or the second electrode layer is pressed by external pressure against the elastic microspheres, the radius of the contact area between the first electrode layer or the second electrode layer and the elastic microspheres is expressed as:

[0063]

[0064] Wherein, E represents the Young's modulus of the elastic microsphere, v represents the Poisson's ratio of the elastic microsphere, a represents the radius of the elastic microsphere in the uncompressed state, and F represents the pressure on the elastic microsphere;

[0065] The contact resistance between the elastic microsphere and the first electrode layer and the second electrode layer is:

[0066] Rc=ρc / [4(r+r0)]

[0067] Wherein, ρc represents the resistivity of the elastic microsphere in contact with the first electrode layer or the second electrode layer, r represents the radius of the contact area, and r0 represents the initial radius of the contact area between the elastic microsphere and the first electrode layer or the second electrode layer in an uncompressed state;

[0068] The relative current change of the flexible pressure sensor under external pressure P is expressed as:

[0069]

[0070] Wherein, A represents the area of ​​the substrate, P represents the pressure uniformly applied to the substrate, F=AP, ΔI represents the current change, I0 represents the initial current, and α represents the fitting parameter.

[0071] The sensitivity of the flexible pressure sensor is expressed as:

[0072]

[0073] Among them, S represents sensitivity, ΔI represents the current change, I0 represents the initial current, α represents the fitting parameter, A represents the area of ​​the substrate, P represents the pressure uniformly applied to the substrate, v represents the Poisson's ratio of the elastic microsphere, a represents the radius of the elastic microsphere in the uncompressed state, and E represents the Young's modulus of the elastic microsphere.

[0074] From the above, it can be seen that the sensitivity of the flexible pressure sensor can be adjusted by controlling the size a and elasticity E of the elastic microspheres, and smaller and softer elastic microspheres can also show higher sensitivity in microsphere sensors, thereby improving the flexibility of the preparation of flexible pressure sensors and meeting the detection needs of various scenarios.

[0075] As a specific example, in the method for preparing the flexible pressure sensor of the present invention, a copper film with a thickness of about 0.1 mm is cut into 5×5 mm 2 size as the first electrode layer and the second electrode layer, and then approximately 50 elastic microspheres with a diameter of 150 μm and 50 elastic microspheres with a diameter of 300 μm are spaced apart and distributed on the copper film electrode (first electrode layer); then, a 0.1 mL volume of a polystyrene aqueous solution of 3,4-ethylenedioxythiophene (PEDOT:PSS) (solid content of 1.1-1.3%) is applied to the first electrode layer distributed with the elastic microspheres, and dried at 60°C for 24 hours, and finally a conductive layer with a thickness of about 100 nm is formed around the PDMS microspheres, and the thickness of the conductive layer can be set to 80-120 nm, and then another copper film (second electrode layer) is placed on top to assemble a flexible pressure sensor monomer, that is, a microsphere-type sensor unit, and silver wires are bonded to each copper film using silver paste to facilitate the transmission of electronic signals, and the entire sensor array can be composed of 8×8 sensor units.

[0076] In addition, at least two flexible pressure sensor monomers may be printed or packaged on the PET film to form a sensor array, wherein a 10×10 mm 2 The gold film was used as the first electrode and the second electrode layer to fabricate a 3×3 flexible sensor array.

[0077] In the preparation process of the above-mentioned flexible pressure sensor, at least two elastic microspheres with different diameters can be arranged between the first electrode layer and the second electrode layer, and at least two elastic microspheres with different diameters are spaced and regularly distributed between the first electrode layer and the second electrode layer. Among them, sensors with elastic microspheres of smaller sizes show higher sensitivity; however, compared with sensors using larger elastic microspheres, their operating pressure range is also narrower. This limitation stems from the limited load-bearing capacity inherent in smaller-sized elastic microspheres. To this end, in the flexible pressure sensor of the present invention, by combining elastic microspheres of multiple sizes, the resulting sensor unit can show a larger operating pressure range; wherein, due to the sensing capability provided by the smaller elastic microspheres, the sensor unit can also maintain a higher sensitivity under higher pressures.

[0078] It can be seen that compared with the sensor unit containing only single-sized microspheres, incorporating multi-sized or dual-sized elastic microspheres into the microsphere pressure sensor enables it to combine the high sensitivity derived from small-sized microspheres, so that the combination of multi-sized microspheres in the microsphere pressure sensor produces excellent pressure sensing performance, thereby opening up a way to adjust the sensitivity and working range of the pressure sensor by simply modifying the size of the elastic microspheres and combining microspheres of different sizes.

[0079] Embodiment 1

[0080] In the preparation process of the flexible pressure sensor of the present invention, controlled polymer droplets are formed by droplet microfluidics technology, and the polymer droplets are solidified into elastic microspheres. During the droplet generation process, the size of the polymer microspheres can be well controlled, and then a specific number of elastic microspheres of different sizes are placed on the electrode and coated with a conductive PEDOT:PSS solution to form a conductive coating (i.e., a conductive layer) about 100nm thick. Then, driven by the solid-liquid-gas three-phase interface, the elastic microspheres are assembled into a uniform array by solution evaporation. And another electrode (using a copper film or a printed gold film) is placed on the elastic microspheres coated with the conductive layer. The entire structure is finally encapsulated between two polymer substrates, which can be EcoflexTM00-30 or polyethylene terephthalate (PET), etc., and integrated into the sensor array according to specific functional requirements, wherein the flexibility of the microsphere-type flexible pressure sensor mainly depends on the stiffness of the encapsulation material.

[0081] It can be seen that due to the presence of the conductive coating (PEDOT:PSS), the elastic microspheres can convert pressure changes into changes in resistance. When the elastic microspheres are located between two electrodes, such as Figure 2 As shown, the total resistance includes the conductive resistance contributed by the electrode (Re) and the conductive coating (Rs), as well as the contact resistance (Rc) generated by the contact interface between the electrode and the elastic microsphere. Given the relatively high conductivity of the electrode and the PEDOT:PSS layer, Re and Rs exhibit small values ​​compared to the Rc fluctuation caused by the deformation of the PDMS microsphere. Therefore, the change in the detection signal mainly depends on the change in Rc. According to the Hertz theory, when a pressure F is applied to the sensor unit, the radius of the contact area between the electrode and the elastic microsphere is r, which can determine the relative current change under the external pressure p. The sensitivity s of the sensor can then be derived, and the sensitivity of the flexible pressure sensor can be adjusted by controlling the size a and elasticity E of the elastic microspheres. Smaller and softer elastic microspheres can also show higher sensitivity in microsphere-type sensors.

[0082] It can be seen that when the pressure sensor contains microspheres of multiple sizes, the relative current change under external pressure includes the different contributions of microspheres of different sizes. Therefore, compared with the pressure sensor with microspheres of only one size, this integration improves the sensor in terms of test sensitivity and measurement range. Figure 3 The working principle of the pressure sensor using dual-sized microspheres is explained. Under low applied pressure conditions P1, only the large-sized microspheres respond to pressure changes and deform. The pressure sensitivity of the microsphere-based sensor matches that of the sensor containing only large-sized microspheres, such as Figure 4 As shown in the red data in area ① in the middle. Further increasing the pressure of P2, the resistance of the microsphere-type sensor decreases significantly, which is due to the additional contact sites generated by the interaction between the small-sized microspheres and the electrodes. Therefore, the detected current increases significantly, as shown in Figure 4 As shown in the red data in the middle area ②. When a higher pressure P3 is applied, both large and small microspheres show elasticity to pressure. The additional deformation of the small microspheres enhances the sensitivity of the microsphere-type sensor, approaching the sensitivity of the sensor composed only of small microspheres, as shown in Figure 4 As shown in the red data in area ③. When the pressure is further increased to P4, both the small and large microspheres reach their deformation limits, resulting in a decrease in the sensitivity of the pressure sensor, as shown in Figure 4 The red data in area ④.

[0083] It is noteworthy that sensor units with smaller microspheres exhibited higher sensitivity; however, they also operated over a narrower pressure range than devices with larger microspheres. This limitation stems from the inherent limited load-bearing capacity of smaller microspheres, such as Figure 4 The blue and green data are shown in the figure. In contrast, by combining microspheres of multiple sizes, the resulting sensor unit exhibits a wider operating pressure range; the sensor unit maintains higher sensitivity at higher pressures due to the sensing capability provided by the smaller microspheres. Therefore, compared to sensor units containing only single-sized microspheres (150 or 300 μm), incorporating dual-sized microspheres into the microsphere-type pressure sensor enables it to combine the high sensitivity derived from small-sized microspheres (11 kPa in region ①) with the high sensitivity derived from small-sized microspheres. -1 ), 20 kPa in area ③ -1 ), and a wide operating range (35 kPa) associated with multi-sized microspheres. The pressure detection limit of the dual-sized microsphere type sensor is 70 kPa. The combination of dual-sized microspheres in the microsphere pressure sensor produces excellent pressure sensing performance, such as Figure 5 More importantly, the present invention opens up a way to adjust the sensitivity and working range of the pressure sensor by simply modifying the size of the microspheres and combining microspheres of different sizes.

[0084] Figure 6The current change of the dual-size flexible pressure sensor is shown under different pressures ranging from 0 to 8 kPa and a consistent holding time of 20 s during the gradual application of pressure. The increase in pressure causes the contact area between the microsphere and the electrode to increase and the contact resistance to decrease, resulting in an increase in the measured current. It is worth noting that there is no drift and hysteresis in the resistance during the entire holding period, highlighting the excellent stability of the dual-size microsphere sensor. The corresponding current-voltage curve is shown in Figure 7 As shown. The linear relationship between voltage and current indicates that the sensor obeys Ohm's law, confirming that the resistance change comes only from the pressure difference. In addition, it is observed that the slope of the current-voltage curve increases with the increase of applied pressure, indicating that the resistance of the sensor decreases simultaneously with the increase of applied pressure. All these results show that this dual-size microsphere sensor can achieve highly predictable and reliable pressure detection through electrical signals.

[0085] Further, Figure 8 The current-time response of the dual-size microsphere sensor at two different pressures (0.1 kPa and 1 kPa) was shown, showing a fast response time of about 0.2 seconds at both pressures. These signals are unique, low-noise, and remain stable throughout the cyclic pressure loading process, thus confirming the repeatable sensing ability of the microsphere sensor. Fig. 9 As shown, after a cyclic external load of 5 kPa, the relative current change of the dual-size microsphere sensor fluctuates negligibly. This stability persists clearly and consistently over 3100 loading cycles, after which the dual-size microsphere sensor unit suffers mechanical damage. The fatigue life and stability of the microsphere-based sensor depends on the robustness of the conductive PDMS microspheres coated with PEDOT:PSS and the encapsulation structure containing silicone rubber.

[0086] It should be noted that in the application scenarios of robots and electronic skin, sensors are required to be able to simultaneously sense and distinguish various spatiotemporal tactile stimuli, including static pressure and temperature. Due to the excellent thermoelectric properties of PEDOT, the dual-size microsphere sensor uses PEDOT:PSS coating as the conductive layer. It also has a temperature detection function, and the thickness of the conductive layer can be set to 80-120 nm. Therefore, in the presence of a temperature difference, PEDOT:PSS can generate a thermoelectric voltage, expressed as VT=ST×ΔT, where ST represents the Seebeck coefficient and ΔT represents the temperature difference experienced by the PEDOT:PSS coating. The temperature sensing performance depends on ST. Therefore, by measuring the functional relationship between the thermovoltage generated by the PEDOT:PSS coating on microspheres of different sizes and the temperature difference (ΔT), as shown in FIG. Fig.10 As shown, the VT-ΔT curves of the PEDOT:PSS coatings on microspheres of different sizes showed a good linear relationship with the Seebeck coefficient (ST) value of 20 μV / K.

[0087] Therefore, at a constant detection voltage (0.5 V), the temperature sensitivity is determined to be 4 × 10 -5 K -1 The size change of the microspheres has minimal effect on the thermoelectric voltage. The repeatable thermoelectric conversion and strong linearity ensure detailed and accurate temperature detection through the electrical signal. Therefore, this flexible pressure sensor can reliably and accurately detect temperature changes under various conditions and is suitable for applications that require strict temperature monitoring and control. Fig.11 It can be seen that the resistance change of the PEDOT:PSS coating remains negligible at different temperatures. This result further confirms that temperature fluctuations have little effect on the current-voltage response of external pressure and can be ignored, which is also a key aspect of decoupling pressure-temperature sensing and facilitating independent detection of pressure and temperature signals. Therefore, the microsphere sensor now has the excellent ability to simultaneously detect pressure and temperature signals at a constant voltage (0.5V). The current output serves as a readout signal for pressure detection, while the voltage output serves as another signal for detecting temperature changes, which facilitates independent and accurate measurement of the two parameters.

[0088] Embodiment 2

[0089] The present invention also provides a sensing glove equipped with four flexible pressure sensors, namely dual-size microsphere sensors, which are distributed on the wearer's knuckles for identifying gestures. The signals emitted by each sensor can accurately capture the muscle movements associated with finger gestures, showing great application potential in electronic skin and wearable devices. Subsequently, the dual-size microsphere sensors can also be integrated into soft grippers to enhance their ability to sense and respond to external stimuli (including pressure and temperature stimuli), such as Fig.12 and then Fig.13 As shown, the soft gripper is designed to imitate the human hand and is driven by air pressure. Six sensors (marked in red) are fixed on the fingers and palm of the soft gripper, and five sensors (marked in blue) are fixed at the base of the fingers.

[0090] Among them, Fig.13As shown, the red sensors are connected in series and the blue sensors are connected in parallel, allowing each finger to simulate human perception. After being worn and gently contacted with human fingers, the individual fingers of the soft gripper can autonomously recognize and interact with human fingers. The soft gripper is sensitive to temperature changes and skillfully approaches a hot object (60°C) when it is close to it. In addition, when a 2.7g ball is carefully placed in the palm of the soft gripper, the soft gripper responds with perception, prompting all fingers to coordinate to try to grasp the ball. The dual-sized microsphere-type bimodal sensors have excellent flexibility and compact size, which can achieve seamless integration with soft grippers without causing significant changes in the stiffness of the soft grippers. Therefore, the movement of these soft grippers is not affected by the installation of these sensors. This effect highlights the great prospects of the developed dual-sized microsphere-type dual-mode sensors as key sensing elements, promoting the development of the field of intelligent soft robots and enhancing human-computer interaction.

[0091] Embodiment 3

[0092] The present invention also provides a sensor array, that is, the above-mentioned flexible pressure sensor, that is, the dual-size microsphere dual-mode sensor is expanded into the sensor array, specifically, by integrating an area of ​​5×5 mm 2 The sensor array is 15×15 mm in size and is made of 8×8 sensor units and covered with PET film, demonstrating the ability to digitally detect pressure and temperature changes over a large area. 2 The sensor array circuit design is as follows: Fig.14 and 15 As shown, each sensor unit (Rij) is connected in parallel with a fixed resistor (RSij) (i=1-8, j=1-8) and connected in series with other sensor units. Among them, the sensor unit and the array can be further reduced by using fine micro / nano manufacturing technology. Therefore, the array can integrate more sensor units and achieve higher sensing resolution.

[0093] In addition, the monitoring process for the sensing capability of the sensor array is as follows: First, three vials filled with different weights of room temperature (20°C) water are placed on the sensor array, with each vial occupying four sensor cells. The vial positions and respective weights are accurately determined by the current signal and represented by a weight cloud graph. Since the vials are at room temperature, the voltage signal does not provide position information. Subsequently, three vials with the same water weight but different temperatures (20, 50, 90°C) are placed on the sensor array. The vial positions and weights are accurately identified again by the current signal and displayed in the weight cloud graph. In addition, the temperature difference between each vial and the surrounding environment is also detected and displayed in the temperature cloud graph. In the presence of a temperature difference, such as vials filled with 50°C and 90°C water, accurate vial position identification can still be maintained. In addition, a vial filled with less water at 20°C and another vial filled with more water at 90°C are placed on the sensor array at the same time, enabling the simultaneous detection of weight and temperature, both of which are depicted in the cloud graph. These results confirm the excellent pressure and temperature sensing capabilities of the sensor array.

[0094] Thanks to the high sensitivity, wide pressure range and fast response of the microsphere sensor unit, the sensor array can detect handwriting through pen pressure, and the pen trajectory is captured in real time and visualized on the LED screen connected to our sensor array. This shows the feasibility of dual-size microsphere sensor units in creating applications such as signature collectors, human-machine interfaces and electronic input.

[0095] Corresponding to the preparation method of the above-mentioned flexible pressure sensor, the present invention also provides a flexible pressure sensor, which is prepared using the above-mentioned preparation method of the flexible pressure sensor; wherein the flexible pressure sensor includes: an upper substrate, a lower substrate, a first electrode layer located on the lower side of the upper substrate, a second electrode layer located on the upper side of the lower substrate, and at least two elastic microspheres with different diameters located between the first electrode layer and the second electrode layer.

[0096] It should be noted that the embodiments of the above-mentioned flexible pressure sensor can refer to the description in the embodiment of the method for preparing the flexible pressure sensor, which will not be described in detail here.

[0097] According to the scheme of the flexible pressure sensor and its preparation method of the present invention, multi-sized elastic microspheres are formed by droplet microfluidics, and a layer of conductive and thermally responsive functional material, such as PEDOT:PSS, is coated on the elastic microspheres, which are then incorporated into the sensor unit, and can simultaneously decouple the detection of pressure and temperature changes. The sensor unit formed by the multi-sized microspheres exhibits a larger pressure detection range (0.1-70 kPa) compared with a sensor containing a single-sized microsphere, while maintaining a high sensitivity (20 kPa -1 , 4×10 -5 K-1 ), in addition, the sensor unit can exhibit fast pressure response (0.2s), low hysteresis and high reliability, with an extended service life of more than 3000 cycles, and can be used in various applications requiring pressure and temperature detection, including gesture detection, tactile perception in soft robots, and large-area applications integrated into arrays, such as handwriting recognition. The preparation process is simple and the sensitivity is high, which can meet the detection needs of various scenarios.

[0098] As described above, the flexible pressure sensor and the method for preparing the same according to the present invention are described by way of example with reference to the accompanying drawings. However, those skilled in the art should understand that various improvements can be made to the flexible pressure sensor and the method for preparing the same according to the present invention without departing from the content of the present invention. Therefore, the protection scope of the present invention should be determined by the content of the attached claims.

Claims

1. A method for preparing a flexible pressure sensor, characterized in that: include: After mixing the polymer elastomer and the cross-linking agent according to a first preset weight ratio, the mixture is mixed and stirred with the diluent according to a second preset weight ratio to obtain a microfluid dispersion; Based on the droplet microfluidics technology, the microfluidic dispersion is squeezed into a preset continuous liquid to form droplets, and the droplets are pre-treated to form elastic microspheres; Disposing at least two elastic microspheres with different diameters on the first electrode layer, and coating the first electrode layer with a conductive liquid to form a conductive layer covering the elastic microspheres; A second electrode layer is provided on the elastic microsphere covered with the conductive layer, wherein the elastic microsphere is limited between the first electrode layer and the second electrode layer; Substrates are respectively arranged outside the first electrode layer and the second electrode layer to form a flexible pressure sensor unit.

2. The method for preparing the flexible pressure sensor according to claim 1, characterized in that: The polymer elastomer includes at least one of polydimethylsiloxane, thermoplastic polyurethane elastomer and thermoplastic elastomer; The continuous liquid contains a surfactant, and the surfactant includes at least one of SDBS, SDS, SLS, and CTAB.

3. The method for preparing the flexible pressure sensor according to claim 1, characterized in that: The first preset weight ratio range is: 20:1 to 20:6; The second preset weight ratio range is: 0 to 10:

4.

4. The method for preparing the flexible pressure sensor according to claim 1, characterized in that: The process of pre-treating the droplets to form elastic microspheres includes: The droplets are solidified, and during the solidification process, the continuous liquid containing the droplets is stirred until the droplets form basic microspheres; The basic microspheres are cleaned with deionized water and ethanol, and then the cleaned basic microspheres are dried to form the elastic microspheres.

5. The method for preparing the flexible pressure sensor according to claim 1, characterized in that: When the first electrode layer or the second electrode layer is pressed against the elastic microsphere by external pressure, the radius of the contact area between the first electrode layer or the second electrode layer and the elastic microsphere is expressed as: Wherein, E represents the Young's modulus of the elastic microsphere, v represents the Poisson's ratio of the elastic microsphere, a represents the radius of the elastic microsphere in an uncompressed state, and F represents the pressure on the elastic microsphere; The contact resistance between the elastic microspheres and the first electrode layer and the second electrode layer is: Rc=ρc / [4(r+r0)] Wherein, ρc represents the resistivity of the elastic microsphere in contact with the first electrode layer or the second electrode layer, r represents the radius of the contact area, and r0 represents the initial radius of the contact area between the elastic microsphere and the first electrode layer or the second electrode layer in an uncompressed state; The relative current change of the flexible pressure sensor under the external pressure P is expressed as: Wherein, A represents the area of ​​the substrate, P represents the pressure uniformly applied to the substrate, F=AP, ΔI represents the current change, I0 represents the initial current, and α represents the fitting parameter.

6. The method for preparing the flexible pressure sensor according to claim 5, characterized in that: The sensitivity of the flexible pressure sensor is expressed as: Wherein, S represents sensitivity, ΔI represents current change, I0 represents initial current, α represents fitting parameter, A represents the area of ​​the substrate, P represents the pressure uniformly applied to the substrate, v represents the Poisson's ratio of the elastic microsphere, a represents the radius of the elastic microsphere in an uncompressed state, and E represents the Young's modulus of the elastic microsphere.

7. The method for preparing a flexible pressure sensor according to claim 1, characterized in that: The at least two elastic microspheres with different diameters are spaced apart from each other and regularly distributed between the first electrode layer and the second electrode layer.

8. The method for preparing a flexible pressure sensor according to claim 1, characterized in that: The conductive layer has a temperature detection function; wherein, The thickness of the conductive layer is 80-120 nm.

9. The method for preparing a flexible pressure sensor according to claim 1, characterized in that: After forming the flexible pressure sensor monomer, the method further includes: At least two flexible pressure sensor units are encapsulated by a PET film to form a sensor array.

10. A flexible pressure sensor, characterized in that: The flexible pressure sensor is prepared by the method for preparing the flexible pressure sensor according to any one of claims 1 to 9; wherein: The flexible pressure sensor includes an upper substrate, a lower substrate, a first electrode layer located at the lower side of the upper substrate, a second electrode layer located at the upper side of the lower substrate, and at least two elastic microspheres with different diameters located between the first electrode layer and the second electrode layer.

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