Solid-liquid-gas three-phase composite soft pressure sensor and manufacturing method thereof

Abstract

The invention relates to a solid-liquid-gas three-phase composite soft pressure sensor and a manufacturing method thereof. The method comprises the following steps: manufacturing a planar spiral liquid metal antenna on a soft substrate, and packaging with a soft material to form a micron-sized thickness protection layer; manufacturing a low-modulus open thin-wall cavity, and packaging the liquid drop in the central area of the antenna by using the cavity to form a solid-liquid-gas three-phase composite closed cavity; the composite cavity and the liquid metal antenna form an inductance-capacitance (LC) sensor. When the sensor is pressed, the liquid drops deform and increase the contact area with the antenna protection layer, so that the parasitic capacitance of the antenna is increased, and the resonant frequency is reduced; after the pressure is relieved, the pneumatic resilience force and the surface tension enable the cavity and the liquid drops to restore to original shapes respectively, so that the parasitic capacitance of the antenna is reduced, and the resonant frequency is increased. According to the invention, the influence of the viscoelasticity of the soft material on the sensing performance is reduced through the pneumatic rebound mechanism of the sealing cavity and the low hysteresis characteristic of the liquid drop, and the pressure sensor with the similar tissue modulus and the high sensing performance is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible pressure sensors, in particular to a solid-liquid-gas three-phase composite soft pressure sensor and a manufacturing method thereof. BACKGROUND

[0002] Pressure sensors have broad application prospects in the field of medical health, and are widely used in the monitoring of important physiological signals such as heart rate, respiration, intracranial pressure, and intraocular pressure. In order to realize seamless fitting of the sensor with the human body, its mechanical properties need to match the human soft tissue. The Young's modulus of human soft tissue is usually in the order of kPa, such as 10-500 kPa for the skin, about 15 kPa for the heart, and about 5 kPa for the brain tissue. However, most existing pressure sensors are made of rigid materials, and their Young's modulus is generally in the range of MPa to GPa, which is much higher than that of soft tissue, making it difficult to achieve compliant fitting.

[0003] A pressure sensor is usually composed of electrodes, a sensitive element, and a packaging layer. Although there have been studies to optimize the mechanical properties of these components, such as using liquid metal as electrode material, using ion gel or ion liquid droplets as sensitive element, and applying flat brush type elastomer for packaging, these optimizations are mostly limited to a single component of the device, and have not yet achieved coordinated optimization at the overall system level. More seriously, low Young's modulus materials generally have viscoelasticity problems, which cause the device to exhibit significant hysteresis and reduced response speed during use, thereby seriously affecting the sensing performance. SUMMARY

[0004] In view of the problems in the prior art, the purpose of the present application is to provide a solid-liquid-gas three-phase composite soft pressure sensor and a manufacturing method thereof, which can reduce the overall Young's modulus of the sensor while weakening the influence of the viscoelasticity of low Young's modulus materials on the sensor performance.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] A manufacturing method of a solid-liquid-gas three-phase composite soft pressure sensor, comprising the following steps:

[0007] Manufacturing a liquid metal antenna in a planar spiral structure, and packaging a soft material to form a micron-level thickness protective layer;

[0008] Manufacturing a low-modulus open thin-walled cavity;

[0009] Encapsulating a liquid droplet in the center area of the antenna through the low-modulus open thin-walled cavity to form a solid-liquid-gas three-phase composite sealed cavity, and the composite cavity and the liquid metal antenna form an inductance-capacitance (LC) sensor;

[0010] When the sensor is pressed, the air in the cavity is compressed, the droplet deforms and increases the contact area with the antenna protection layer, causing the antenna parasitic capacitance to increase, and the resonant frequency to decrease.

[0011] After the pressure is released, the pneumatic rebound force and surface tension make the cavity and droplet return to their original state, respectively, thereby reducing the antenna parasitic capacitance and increasing the resonant frequency.

[0012] Further, the manufacturing process of the liquid metal antenna is as follows: the liquid metal is added to the surface of the soft substrate, then the glass sheet is placed on the soft substrate covering the liquid metal, and is pressed to ensure that the glass sheet, the liquid metal, and the soft substrate are tightly attached. Then the glass sheet is slowly and uniformly extracted, and the operation is repeated several times to finally obtain a uniformly distributed liquid metal conductive film; the liquid metal conductive film is precisely cut using laser etching technology, and a planar spiral structure of the liquid metal antenna is successfully constructed.

[0013] Further, the packaging of the liquid metal antenna includes: placing the liquid metal antenna in a plasma cleaning machine for cleaning treatment, then adding uncured silicone to the surface of the liquid metal antenna, and uniformly coating it using a spin coating process, thereby constructing an antenna with a sandwich structure. Finally, the antenna is placed in an oven for heating and curing packaging.

[0014] Further, the patterned hydrophobic treatment of the packaged liquid metal antenna includes: fixing the packaged liquid metal antenna, then spraying the super-hydrophobic coating on the surface of the liquid metal antenna using a spray gun, and leaving a glue ring on the outer edge of the liquid metal antenna, which is not treated with hydrophobicity.

[0015] Further, the material selection of the low-modulus open thin-walled cavity: silicone materials such as Dowsil, Ecoflex gel, Ecoflex00_30, Ecoflex00_50, etc.; shape selection: cylinder.

[0016] The cylinder shape (D = 7 mm, H = 1.5 mm) matches the droplet of 7.5 μL. When the upper edge of the cylinder is chamfered with a radius of 1 mm, the sealed cavity deforms greatly under the action of air pressure.

[0017] The thickness of the low-modulus open thin-walled cavity: 5 μm, 10 μm, 20 μm, 40 μm, 60 μm, 120 μm, 250 μm, 500 μm.

[0018] Different pressurization methods (contact pressure, air pressure / liquid pressure) affect the deformation of the sealed cavity, which is affected by the thickness of the low-modulus open thin-walled cavity.

[0019] Under the same contact pressure, the thinner the low-modulus open thin-walled cavity, the easier the sealing cavity is compressed, that is, the thinner the low-modulus open thin-walled cavity, the smaller the external force required under the same deformation degree.

[0020] Under the same gas pressure / hydraulic pressure, the thicker the low-modulus open thin-walled cavity, the greater the degree of compression of the lowest point of the deformation of the upper surface.

[0021] Under the same gas pressure / hydraulic pressure, the thinner the low-modulus open thin-walled cavity, the greater the curvature of the deformation of the upper surface, that is, the closer to the plane compression (this process will sacrifice the compression height of the lowest point).

[0022] The manufacturing process of the low-modulus open thin-walled cavity is as follows:

[0023] (1) Manufacturing the inner PVA sacrificial layer: paste double-sided tape on the substrate, fix the mold on it. Spray release agent on the surface of the mold, then place it on the spin coater. Drop PVA solution and spin evenly, then put it in the oven for heating and curing, and take out the sample after curing;

[0024] (2) Manufacturing the low-modulus film: place the sample obtained in the previous step in the plasma cleaning machine, then place it on the spin coater, drop uncured silicone on the sample and spin, then put it in the oven for heating and curing to obtain a low-modulus film;

[0025] (3) Manufacturing the outer PVA support: place the sample obtained in the previous step on the spin coater, drop PVA solution on the mold and spin, then put it in the oven for heating and curing, and take out the sample after curing;

[0026] (4) Low-modulus open thin-walled cavity demolding: after demolding the sample obtained in the previous step, clean the inner PVA sacrificial layer to completely dissolve the inner PVA sacrificial layer, and obtain a groove structure containing a low-modulus open thin-walled cavity and an outer PVA support.

[0027] Further, when manufacturing the low-modulus open thin-walled cavity, different thicknesses of the low-modulus open thin-walled cavity can be obtained by adjusting the spin speed and spin times.

[0028] Further, it also includes a patterned hydrophobic treatment of the low-modulus open thin-walled cavity: plasma clean the low-modulus open thin-walled cavity, then paste the mask plate on the top center area of the inner surface of the groove structure, drop the super-hydrophobic solution and soak, then put it in the oven for heating and curing after absorbing the excess solution, and remove the mask plate to obtain a super-hydrophobic outer ring groove structure.

[0029] Further, the top center area of the inner surface of the groove structure is subjected to a hydrophilic treatment.

[0030] Further, the process of encapsulating the droplet by the low-modulus open thin-walled cavity: drop the uncured silicone on the glue-coated ring of the liquid metal antenna, then drop the droplet on the top center area of the inner surface of the groove structure, and then invert the groove structure together with the droplet on the surface of the glue-coated ring. After it is cured at room temperature, the outer PVA support is dissolved, and finally a solid-liquid-gas three-phase composite soft pressure sensor is obtained.

[0031] The top center area of the inner surface of the low-modulus open thin-walled cavity treated by hydrophilic treatment and the periphery of the groove structure treated by super-hydrophobic treatment can effectively fix the droplet in the center hydrophilic area. Combined with the super-hydrophobic treated liquid metal antenna, the droplet can maintain a hemispherical shape under the action of surface tension and has shape recovery ability, so as to change the contact area of the droplet and the protective layer of the liquid metal antenna, and realize the regulation of the resonance frequency of the liquid metal antenna.

[0032] The droplet can be a water droplet or an ionic liquid material (the selection is based on the difference in dielectric constant with air. Different types of droplets can realize sensing function, but there will be differences in sensitivity. The greater the dielectric constant, the higher the sensitivity).

[0033] A solid-liquid-gas three-phase composite soft pressure sensor is manufactured by the above method.

[0034] In general, the present application has the following advantages:

[0035] The present application simultaneously reduces the Young's modulus of the sensor from three aspects: (1) adopting a liquid metal antenna and forming a micron-level protective layer by encapsulating soft material; (2) selecting soft material to manufacture an open thin-walled cavity, and together with the liquid metal antenna to form a sealed cavity structure; (3) using a droplet as a sensing element, and air as a support layer. This innovative design reduces the Young's modulus while effectively protecting the sensitive droplet, and replaces the traditional solid pressure-sensitive layer rebound with a pneumatic rebound mechanism, which weakens the influence of the viscoelasticity of the solid soft material. The present application uses the low hysteresis (hysteresis less than 1%) of the droplet to improve the stability and durability of the sensor; and uses the high sensitivity of the droplet to detect a weight of 2-5 mg with a response time of 2-3 ms. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 It is a manufacturing process diagram of the liquid metal antenna of the present application.

[0037] Figure 2 It is a manufacturing process diagram of the low-modulus open thin-walled cavity of the present application.

[0038] Figure 3 It is a 3D modeling diagram of the solid-liquid-gas three-phase composite soft pressure sensor.

[0039] Figure 4 Process flow chart for solid-liquid-gas three-phase composite soft pressure sensor manufacturing.

[0040] Figure 5 Response graph for solid-liquid-gas three-phase composite soft pressure sensor under load of 1 kPa, 5 kPa, 10 kPa, 50 kPa, 100 kPa.

[0041] Figure 6 Hysteresis characterization graph for solid-liquid-gas three-phase composite soft pressure sensor (hysteresis is 0.46%).

[0042] Figure 7 Linearity and sensitivity characterization graph for solid-liquid-gas three-phase composite soft pressure sensor under hydraulic action.

[0043] Figure 8 Detection limit characteristics of the sensor are shown: air pressure detection limit curve.

[0044] Figure 9 Detection limit characteristics of the sensor are shown: contact pressure detection limit curve.

[0045] Figure 10 Pressure response hysteresis characteristics of the sensor in a sealed state are shown.

[0046] Figure 11 Pressure response hysteresis characteristics of the sensor in a non-sealed state are shown.

[0047] Figure 12 The test results of the sensor applied to pulse signal detection are shown.

[0048] In the figures:

[0049] 1 - low modulus thin-walled cavity, 2 - droplet, 3 - liquid metal antenna, 4 - soft substrate. DETAILED DESCRIPTION

[0050] In the field of flexible sensors, traditional solid materials will cause sensor hysteresis due to viscoelastic properties, and the lower the Young's modulus of the material, the more significant the viscoelastic effect and the more serious the hysteresis. The solid-liquid-gas three-phase soft pressure composite sensor designed in the application uses pneumatic rebound instead of traditional solid pressure-sensitive layer rebound, effectively weakening the negative effects of solid soft material viscoelasticity. At the same time, liquid droplet 2 and air are used as sensitive elements and support layers to avoid the problem of increasing the Young's modulus due to the solid support layer. Low-modulus silicone material is used to manufacture low-modulus thin-walled cavity 1, which is sealed with liquid metal antenna 3 to protect sensitive liquid droplet 2 and further reduce the overall Young's modulus, so that the Young's modulus of the sensitive layer is close to 0. The low hysteresis characteristics of liquid droplet 2 make the hysteresis of the solid-liquid-gas three-phase composite soft pressure sensor less than 1%, and the high sensitivity of liquid droplet 2 enables the solid-liquid-gas three-phase composite soft sensor to detect objects of 2-5mg. By optimizing the design of each part, lower Young's modulus and higher sensitivity are finally achieved.

[0051] The application will be further described in detail below.

[0052] The object of the application is to design a sensor structure and manufacturing method to reduce the overall Young's modulus of the sensor while weakening the influence of low Young's modulus material viscoelasticity on sensor hysteresis, ultimately obtaining a low hysteresis, high sensitivity wireless passive soft pressure sensor with high accuracy in physiological signal monitoring and other applications. The solid-liquid-gas three-phase composite soft pressure sensor mainly includes liquid metal antenna 3, liquid droplet 2 and low-modulus thin-walled cavity 1.

[0053] The size parameters of the liquid metal antenna 3 are as follows: an outer diameter of 7 mm, a line width of 190 μm, a line distance of 60 μm, 8 turns, and an antenna protection layer thickness of 10 μm. Under the above parameter configuration, the resonant frequency of the liquid metal antenna 3 is in the range of 780-850 MHz (the resonant frequency of the antenna can be adjusted by adjusting the outer diameter, line width, line distance, and antenna protection layer thickness of the liquid metal antenna 3). The antenna protection layer thickness not only affects the inherent resonant frequency of the liquid metal antenna 3, but also affects the sensitivity of the solid-liquid-gas three-phase composite soft pressure sensor (the thinner the antenna protection layer, the more sensitive the solid-liquid-gas three-phase composite soft pressure sensor). The outer diameter, line width, line distance, and number of turns of the liquid metal antenna 3 have a great influence on the resonant frequency of the antenna. When the outer diameter is fixed, that is, the antenna size is fixed, the smaller the line width, the smaller the line distance, and the more the number of turns, the greater the parasitic capacitance of the antenna, the smaller the resonant frequency of the antenna, and the farther the communication distance of the antenna. When the line width of the antenna is less than 150 μm, the resistance of the antenna itself will be very large (more than 30 Ω), and the absolute value of S11 corresponding to the resonant frequency f will tend to 0 (loss increases, which is not conducive to sensing). The parameter design of the liquid metal antenna 3 of the present application can obtain a resonant frequency of 780-850 MHz (lower than 1 GHz) while obtaining S11 between -13 and -19 (when the communication distance is 1 mm).

[0054] For the sensitive liquid drop 2, a 7.5 μL water drop is used in the present embodiment. The volume of the water drop is constrained by the size of the antenna. The 7.5 μL water drop can be flattened to cover the entire liquid metal antenna 3 while maintaining a height range of 500 μm. To obtain a 7.5 μL inverted hemispherical water drop, the central circular area with a diameter of 3 mm of the low-modulus thin-walled cavity 1 needs to be treated with hydrophilic treatment, while the other areas are treated with super-hydrophobic treatment, so that the water drop can be fixed. The surface of the antenna protection layer also needs to be treated with super-hydrophobic treatment, so that the 7.5 μL water drop cannot be pinned to the surface of the antenna protection layer. On the basis of the above surface treatment, the liquid drop can maintain a hemispherical shape under the action of surface tension and has shape recovery ability. By changing the contact area between the liquid drop and the liquid metal antenna protection layer, the resonant frequency of the liquid metal antenna can be adjusted.

[0055] The change in the diameter of the hydrophilic area will affect the shape of the water drop: when the diameter is 2 mm, the water drop tends to be spherical; when the diameter is 3 mm, the water drop is hemispherical; and when the diameter is 4 mm, the water drop forms a 1 / 3 circular arc spherical shape. The difference in the geometric shape of the water drop directly changes the ratio of the pressing height H to the change in the antenna-water drop contact area, thereby adjusting the sensitivity characteristics of the sensor.

[0056] The low modulus thin-walled cavity 1 and the liquid metal antenna 3 form a sealed cavity, the size of the cavity is diameter D = 7 mm, height H = 1.5 mm, the corner radius is 1 mm, and the thickness of the low modulus thin-walled cavity 1 is 60 μm (the thickness can be adjusted). The sealed cavity mainly relies on the pressure difference between the inside and outside of the cavity to provide resilience, and the force provided by the air pressure is more than twice the force provided by the solid, so that the air spring is dominant, which can weaken the influence of the solid viscoelasticity on the performance of the sensor.

[0057] The present application simultaneously reduces the Young's modulus of the sensor from three aspects: (1) adopting a liquid metal antenna and packaging a micron-level protective layer with a soft material; (2) selecting a soft material to manufacture an open thin-walled cavity, and forming a sealed cavity structure together with the liquid metal antenna; and (3) taking a liquid drop as a sensing element, and combining air as a supporting layer, which realizes effective protection of the sensitive liquid drop while reducing the Young's modulus, and replaces the traditional solid pressure-sensitive layer spring with the air spring mechanism to weaken the influence of the solid soft material viscoelasticity. The present application utilizes the low hysteresis (hysteresis is less than 1%) of the liquid drop to improve the stability and durability of the sensor, and utilizes the high sensitivity of the liquid drop to detect a weight of 2-5 mg with a response time of 2-3 ms.

[0058] The sensing principle of the solid-liquid-air three-phase composite soft pressure sensor: the resonance frequency of the liquid metal antenna 3 is determined by the parasitic capacitance C and the inductance L of the antenna. Since the size and the number of turns of the antenna are fixed, the inductance of the antenna is a fixed value, and the parasitic capacitance of the antenna is affected by the dielectric constant of the medium. When the external pressure P acts on the low modulus thin-walled cavity 1, the sealed cavity is deformed (at this time, the internal pressure of the sealed cavity is greater than the external air pressure), the air in the sealed cavity is compressed, and the water drop located at the top center of the inner surface of the low modulus thin-walled cavity 1 is compressed, at this time, the water drop expands, causing the contact area between the water drop and the antenna protective layer to increase, the dielectric constant of the water drop is 78, which is greater than the dielectric constant of the air, 1, causing the parasitic capacitance of the antenna to increase, thereby reducing the resonance frequency f of the antenna. When the pressure P is removed, the sealed cavity will return to the initial state under the action of the pressure difference, and the water drop will return to the original state under the action of the surface tension, at this time, the parasitic capacitance of the antenna decreases, causing the resonance frequency f of the antenna to rise. By monitoring the shift of the resonance frequency, a linear response relationship between the pressure P and the frequency f can be established, realizing the pressure sensing function.

[0059] The sensor realizes signal transmission through electromagnetic coupling between the antenna electrode and the reading antenna of the vector network analyzer. The vector network analyzer can detect the resonance frequency shift of the sensor antenna in real time, thereby establishing a linear relationship between the pressure input signal P and the frequency output signal f. Based on this principle, the sensor can realize pressure sensing in a wireless and passive working mode.

[0060] The manufacturing process of the solid-liquid-gas three-phase composite soft pressure sensor is as follows, as shown in Figure 4

[0061] The manufacturing process of the liquid metal antenna 3 (as shown in Figure 1

[0062] (1) Soft substrate 4 manufacturing: The water-soluble adhesive tape is pasted on the 30 mm x 60 mm acrylic substrate, and the plasma cleaning machine (180 W 180 s) is used; then the substrate is fixed on the spin coater, and the vacuum degassed (1200 r / min stirring 120 s, vacuum degassing 45 s) Ecoflex 00_30 (1:1) silicone is added dropwise, and then a uniform thin film is formed by spin coating (at a speed of 400 r / min and 250 r / s 2 accelerating spin coating 120 s); then the sample is placed in an 80°C oven for 10 min to obtain a solidified 250 μm thick Ecoflex 00_30 soft substrate, and finally it is cooled at room temperature for standby.

[0063] (2) Manufacturing of liquid metal conductive film: First, the Ecoflex 00_30 soft substrate is placed in the plasma cleaning machine (180 W 180 s); then the liquid metal is uniformly added dropwise on the surface of the soft substrate to cover the entire electrode area, and the glass sheet is pressed to make the liquid metal closely adhere to the soft substrate. By slowly pulling away the glass sheet and repeating several times, the liquid metal is uniformly spread; finally, a flat liquid metal conductive film is formed, and if the electrode has flowability, the excess liquid metal can be adjusted to a stable state by suction.

[0064] (3) Manufacturing of liquid metal antenna 3: The prepared liquid metal electrode is fixed on the workbench of the laser cutting machine, and the focus is set to 95 mm, the processing current is 3 A, the pulse frequency is 20 kHz, and the cutting speed is 250 mm / s. Precise machining is performed to form.

[0065] First step of laser etching: Import the DXF file containing the cutting path, set the processing area to be the area outside the 2x5 circular array with a diameter of 7 mm and a center distance of 4 mm. Path filling is performed on this area, the adjacent path spacing is set to 10 μm, and the processing number is set to 3-4 times. Finally, a 2x5 circular liquid metal conductive film array is obtained.

[0066] Second step of laser etching: Process the 2x5 circular liquid metal conductive film array obtained in the previous step, set the cutting number to 15-25 times, and prepare a 2x5 array of liquid metal antenna 3 with a diameter D=7 mm, a line width of 190 μm, a line spacing of 60 μm, and 10 turns.

[0067] ​​(4) Encapsulation of liquid metal antenna 3: 2x5 antenna array was cleaned in a plasma cleaner (180W 180s); uncured silicone (vacuum degassing machine: 1200r / min 120s, vacuum degassing 45s) mixed with Ecoflex 00_30 (A:B) and diluent at a ratio of 1:1:3 was dropped onto the array. The sample was placed on a spin coater for spin coating (500r / min speed, 250r / s 2 acceleration for 120s) to obtain a sandwich structure encapsulated antenna; finally, the encapsulation was completed by curing in an 80°C oven for 20-25min.

[0068] (5) Patterned hydrophobic treatment of encapsulated antenna: the encapsulated 2x5 antenna array was separated into 10 individual antennas by detaching from the substrate, and then treated in a plasma cleaner (180W 180s). After the treatment, the individual antennas were fixed on a test platform, and a mask was used to cover the non-target area to define the hydrophobic treatment range. The super-hydrophobic coating was sprayed vertically at a distance of 200-250mm for 4-6 times, and finally cured in an 80°C oven for 5min to complete the single antenna hydrophobic treatment.

[0069] Manufacturing process of low-modulus thin-walled cavity 1 (as shown in Figure 2

[0070] (1) Manufacturing inner layer PVA sacrificial layer: double-sided tape was laid on a 30mm x 60mm substrate, and a mold with a diameter D = 7mm, height H = 1.5mm, and rounded corner 1mm was arranged and fixed in a 2x5 array (rounded corner side outward). Then, 3-5 times of release agent was sprayed, and the mold array was placed on a spin coater, and 80°C PVA solution with a concentration of 50% was dropped, and then spin coated at a speed of 1000r / min, 250r / s 2 acceleration for 120s. After spin coating, the sample was cured in an 80°C oven for 10min, and the above spin coating step was repeated to ensure that the PVA layer had no porosity. After curing, a tape was pasted on the edge of the inner layer PVA as a separation layer to protect the outer layer PVA support during subsequent dissolution of the sacrificial layer.

[0071] (2) Manufacturing Ecoflex00_30 low-modulus film: after the sample was cleaned in a plasma cleaner (180W 180s), it was placed on a spin coater, and vacuum-degassed Ecoflex00_30 (A:B:diluent = 5:5:1, 1200r / min stirring for 120s, vacuum degassing for 45s) was dropped, and then spin coated at a speed of 250r / s 2 acceleration for 120s. The thickness of the Ecoflex00_30 low-modulus thin-walled cavity 1 can be accurately controlled by adjusting the spin coating speed and number of times. As shown in the following table:

[0072] Table 1 - spin coating 1 time, adjusting spin coating speed.​

[0073] Spin speed (r / min) 8000 3000 1500 Spin thickness (pm) 3-6 8-12 19-24

[0074] Table 2 - Fixed spin coating speed of 1500 r / min, adjusting the number of spin coatings.

[0075] Spin number 1 2 3 4 5 6 8 Spin thickness (pm) 19-24 35-43 58-63 70-84 110-125 150-165 220-240

[0076] (3) Fabrication of the outer PVA scaffold: Place the sample on a spin coater, add a 50% concentration PVA solution at 80℃, and spin at 1000 r / min and 250 r / s. 2 Spin-coating was performed at an accelerated speed for 120 seconds. The sample was then cured in an 80°C oven for 10 minutes, and then spin-coated again with the same parameters to ensure that the PVA layer was free of pores after curing.

[0077] (4) Demolding and patterned hydrophobic treatment of low-modulus thin-walled cavity 1: After demolding the sample, a three-dimensional groove array was obtained. The inner PVA layer was dissolved by rinsing with running water for 15-20 minutes, retaining the Ecoflex00_30 low-modulus thin-walled cavity 1 and the outer PVA support. Next, the sample was cleaned with 50% ethanol, followed by plasma cleaning (180W 180s). Then, a 3mm diameter mask was pasted onto the top center area of ​​the inner surface of the low-modulus thin-walled cavity 1. A superhydrophobic solution was dropped into the groove and soaked for 10-15 seconds, and then the excess solution was removed. The sample was placed in an 80℃ oven for 2-5 minutes until the coating was cured. Finally, the mask was removed to obtain a packaging structure (including the outer support) with hydrophobic properties except for the central 3mm diameter circular area.

[0078] The process of encapsulating droplets in a low-modulus, thin-walled cavity:

[0079] A 7.5 μL water droplet was added to the hydrophilic treatment area of ​​the low-modulus thin-walled cavity 1 with a diameter of 3 mm. Due to the hydrophobic properties of the surrounding area, the droplet was fixed in the hydrophilic area. Next, uncured Ecoflex00_30 (A:B = 1:1, stirred at 1200 r / min for 120 s and then vacuum degassed for 45 s) was coated on the outer ring area of ​​the antenna. Then, the low-modulus thin-walled cavity 1 with droplets was placed on the outer ring area of ​​the antenna. Pressure was applied to the outer ring area of ​​the antenna with a diameter of 7 mm using a ring mold to ensure complete encapsulation. After standing and curing for 1 hour, the outer PVA support was dissolved, and finally a solid-liquid-gas three-phase composite soft pressure sensor was obtained, which is currently the softest wireless passive pressure sensor.

[0080] Figure 3 It is a solid-liquid-gas three-phase composite soft pressure sensor structure.

[0081] Figure 4 This is a schematic diagram of the manufacturing process of a solid-liquid-gas three-phase composite soft pressure sensor.

[0082] Figure 5 The response characteristic curve of the sensor under 1kPa, 5kPa, 10kPa, 50kPa and 100kPa pressure is shown.

[0083] Figure 6 The hysteresis of the sensor in the load-unload cycle test is only 0.46%, which shows excellent low hysteresis performance.

[0084] Figure 7 The sensitivity characteristic curve of the sensor is shown, which quantifies the pressure-electrical signal conversion performance.

[0085] Figure 8 The detection limit characteristic of the sensor is shown: the air pressure detection limit curve.

[0086] Figure 9 The detection limit characteristic of the sensor is shown: the contact pressure detection limit curve.

[0087] Figure 10 The pressure response hysteresis characteristic of the sensor in a sealed state is shown.

[0088] Figure 11 The pressure response hysteresis characteristic of the sensor in a non-sealed state is shown.

[0089] Figure 12 The test results of the sensor applied to pulse signal detection are shown.

[0090] According to the experiment, the water droplet has low hysteresis, super sensitivity and ultra-low Young's modulus, and the structural design of the sensor fully utilizes these three advantages.

[0091] The present application has the following advantages:

[0092] The overall Young's modulus is less than 60kPa: the present application adopts liquid metal antenna 3, sensitive liquid droplet 2 and low modulus thin-walled cavity 1, and forms a solid-liquid-gas three-phase composite sealed cavity with the three parts, which significantly reduces the overall Young's modulus of the sensor, so that it can better adapt to the deformation of human tissues, and thus shows superior performance in application scenarios such as physiological signal monitoring that require high adhesion.

[0093] The object with a mass of 2-5mg can be detected: due to the use of liquid droplet 2 as a sensitive element, the pressure sensor of the present application has high sensitivity and can more accurately detect physiological signals.

[0094] The effect of viscoelasticity of solid soft material is weakened: the low-modulus thin-walled cavity 1 is constructed as a sealed cavity with the antenna, and air and the liquid drop 2 are used together as a supporting layer. This innovative design effectively protects the sensitive liquid drop 2 while maintaining a low Young's modulus, and uses the aerodynamic rebound to replace the traditional solid pressure-sensitive layer rebound, thereby weakening the effect of viscoelasticity of solid soft material.

[0095] Hysteresis is lower than 1%: the liquid drop 2 is used as a sensitive element, and the low hysteresis of the liquid drop 2 is fully utilized to improve the stability and durability of the sensor.

[0096] The above embodiments are preferred embodiments of the present application, but the embodiments of the present application are not limited by the above embodiments, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application should be equivalent replacement methods, and are included in the protection scope of the present application.

Claims

1. A method for manufacturing a solid-liquid-gas three-phase composite soft pressure sensor, characterized in that: Includes the following steps: A liquid metal antenna with a planar spiral structure was fabricated and encapsulated with a soft material to form a protective layer with a thickness of micrometers. Manufacturing low-modulus open thin-walled cavities; A droplet is encapsulated in the central region of the antenna through a low-modulus open thin-walled cavity, forming a solid-liquid-gas three-phase composite sealed cavity. This composite sealed cavity and the liquid metal antenna form an inductive-capacitive sensor. When the sensor is compressed, the air inside the cavity is compressed, the droplet deforms and increases the contact area with the antenna protective layer, which causes the antenna parasitic capacitance to increase and the resonant frequency to decrease. After the pressure is released, the pneumatic rebound force and surface tension restore the cavity and droplet to their original shapes, thereby reducing the antenna's parasitic capacitance and increasing the resonant frequency.

2. The manufacturing method according to claim 1, characterized in that: The manufacturing process of the liquid metal antenna is as follows: Liquid metal is dropped onto the surface of a soft substrate, and then a glass plate is placed on the soft substrate covered with liquid metal and pressed to ensure that the glass plate, liquid metal and soft substrate are in close contact. Then the glass plate is slowly and uniformly removed. This operation is repeated several times to finally obtain a uniformly distributed liquid metal conductive film. Laser etching technology is used to precisely cut the liquid metal conductive film to successfully construct a planar spiral structure liquid metal antenna.

3. The manufacturing method according to claim 2, characterized in that: The encapsulation of liquid metal antennas includes: cleaning the liquid metal antenna in a plasma cleaner, then applying uncured silicone to its surface and uniformly coating it using a spin coating process to create an antenna with a sandwich structure. Finally, the antenna is placed in an oven for heat curing and encapsulation.

4. The manufacturing method according to claim 3, characterized in that: The process includes patterned hydrophobic treatment of the encapsulated liquid metal antenna: the encapsulated liquid metal antenna is fixed in place, and then a superhydrophobic coating is sprayed onto the surface of the liquid metal antenna using a spray gun. A coating ring is reserved on the outer edge of the liquid metal antenna, and the coating ring is not treated with hydrophobicity.

5. The manufacturing method according to claim 1, characterized in that: The manufacturing process of the low-modulus open thin-walled cavity is as follows: (1) Manufacturing the inner PVA sacrificial layer: Double-sided tape is attached to the substrate, the mold is fixed on it, the mold surface is sprayed with release agent, and then placed on a spin coater, PVA solution is added and spin coated evenly. After completion, it is placed in an oven for heating and curing. After curing, the sample is taken out. (2) Manufacturing soft material film: The sample obtained in the previous step is cleaned in a plasma cleaner, and then placed on a spin coater. Uncured silicone is dropped onto the sample for spin coating. After completion, it is placed in an oven for heating and curing to obtain a soft material film. (3) Manufacturing the outer PVA support: Place the sample obtained in the previous step on a spin coater, drop the PVA solution onto the mold for spin coating, and after completion, put it in an oven for heating and curing. After curing, take out the sample. (4) Demolding of low-modulus thin-walled cavity: After demolding the sample obtained in the previous step, clean the inner PVA sacrificial layer to dissolve the inner PVA sacrificial layer completely, and obtain a groove structure containing a low-modulus open thin-walled cavity and an outer PVA support.

6. The manufacturing method according to claim 5, characterized in that: When manufacturing low-modulus open thin-walled cavities, different thicknesses of low-modulus open thin-walled cavities can be obtained by adjusting two parameters: spin coating speed and spin coating number.

7. The manufacturing method according to claim 5, characterized in that: The process includes patterned hydrophobic treatment of a low-modulus open thin-walled cavity: the low-modulus open thin-walled cavity is plasma cleaned, then a mask is pasted on the top center area of ​​the inner surface of the groove structure, a superhydrophobic solution is added for soaking, excess solution is absorbed, and then it is placed in an oven for heating and curing. The mask is then removed to obtain a superhydrophobic outer ring groove structure.

8. The manufacturing method according to claim 7, characterized in that: The top center area of ​​the inner surface of the groove structure is hydrophilic.

9. The manufacturing method according to claim 8, characterized in that: The process of encapsulating a droplet in a low-modulus open thin-walled cavity: Uncured silicone is dropped onto the coated ring of a liquid metal antenna, and then the droplet is dropped onto the top center area of ​​the inner surface of the groove structure. The groove structure and the droplet are then inverted onto the surface of the coated ring. After curing at room temperature, the outer PVA support is dissolved, and finally a solid-liquid-gas three-phase composite soft pressure sensor is obtained.

10. A solid-liquid-gas three-phase composite soft pressure sensor, characterized in that: It is prepared by the manufacturing method described in any one of claims 1-9.

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