Flexible modulus sensor capable of detecting softness and hardness of subcutaneous tissue at different depths

Abstract

The application relates to a flexible modulus sensor capable of detecting the softness and hardness of subcutaneous tissues at different depths, which comprises a pressure sensor and a displacement sensor; the pressure sensor adopts resistance type sensing and comprises a pinion copper electrode and a force-sensitive composite material; the displacement sensor adopts off-electric type sensing and comprises a plane copper electrode and a sensing medium, wherein the sensing medium is arranged in a micro-protruding structure; in the flexible modulus sensor, the pressure sensor detects stress, the displacement sensor detects strain, the two do not affect each other, and the modulus detection of subcutaneous tissues at different depths is realized under the action of the micro-protruding structure of the displacement sensor.

Description

Technical Field

[0001] This invention belongs to the field of sensing technology, and specifically relates to a flexible modulus sensor that can detect the softness and hardness of subcutaneous tissue at different depths. Background Technology

[0002] With the development of wearable sensing, the measurement of the hardness and softness of objects is becoming increasingly important, which can elevate the application of wearable sensing in human-computer interaction and medical health to a new dimension. The measurement of hardness and softness is essentially the detection of the elastic modulus of a material, which is the manifestation of the material's ability to deform under external force, and is the result of the coupling of force and displacement. Therefore, existing wearable modulus sensors are divided into two categories: (1) fixed force, detecting displacement. Specifically, a vibrator is placed on the surface of the flexible strain sensor. When the vibrator works with a constant amplitude and frequency, the deformation displacement generated by the strain sensor on the surface of the measured object is detected. (2) fixed displacement, detecting the magnitude of force. Specifically, a limiter is placed at the rear end of the flexible pressure sensor. When the limiter moves by a specified amount, the reverse force generated by the pressure sensor on the measured object is detected. Since there are no dynamic moving parts, the second scheme has lower power consumption and longer lifespan than the first scheme, and is the mainstream scheme for wearable modulus sensors at present.

[0003] From the perspective of testing principles, wearable modulus sensors based on fixed displacement detection force measure the hardness of a material's surface. However, in some cases, the object being tested lies at a certain depth below the surface, such as skin cancer lesions, which are typically located 3 cm below the skin. Even with current mainstream wearable modulus sensors increasing the range of the limiter's movement, the test result is still the average hardness of the material within that range, not the elastic modulus at a specific depth. Recent experiments have shown that ionic composites of blended ionic liquids with micro-protrusions shaped like paraboloids of revolution can detect the modulus of an object at a certain depth. Utilizing this characteristic can solve the problem of wearable modulus sensors being unable to detect the elastic modulus at specific depths. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a wearable modulus sensor and its preparation method, so as to realize the detection of the elastic modulus of skin tissue at a specific depth.

[0005] This invention provides a flexible modulus sensor capable of detecting the softness and hardness of subcutaneous tissue at different depths, comprising a pressure sensor and a displacement sensor. The pressure sensor employs a resistive sensing method, and the displacement sensor employs an ionization sensing method.

[0006] Preferably, the pressure sensor comprises a toothed copper electrode and a force-sensitive composite material.

[0007] Preferably, the force-sensitive composite material is made by blending silicone rubber and carbon-based conductive filler.

[0008] Preferably, the silicone rubber includes at least one of PDMS (polydimethylsiloxane), Ecoflex, or silicone; the carbon-based conductive filler includes at least one of carbon black, graphene, or carbon nanotubes (CNTs).

[0009] Preferably, the displacement sensor includes a planar copper electrode and a sensing medium; wherein the sensing medium has a micro-protrusion structure.

[0010] More preferably, the micro-protrusion structure is a parabolic shape.

[0011] Preferably, the sensing medium is made by blending an ionic liquid and a polar organic polymer.

[0012] Preferably, the ionic liquid comprises [EMIM]. + [TFSI] - [BMIM] + [TFSI] - Or [EMIM] + [TCM] - At least one of the following; the polar organic polymer includes at least one of PVDF (polyvinylidene fluoride) or PU (polyurethane).

[0013] Preferably, the toothed copper electrode and force-sensitive composite material of the pressure sensor, and the planar copper electrode and sensing medium of the displacement sensor are stacked sequentially.

[0014] The present invention also provides a method for preparing the above-mentioned flexible modulus sensor capable of detecting the softness and hardness of subcutaneous tissue at different depths, comprising the following steps:

[0015] (1) A toothed copper electrode is fabricated on a pressure sensor base;

[0016] (2) Preparation of force-sensitive composite material for pressure sensors;

[0017] (3) Coat the pressure sensor’s toothed copper electrode with force-sensitive composite material.

[0018] (4) A planar copper electrode is prepared on the displacement sensor base, and the planar copper electrode of the displacement sensor is covered on the force-sensitive composite material of the pressure sensor.

[0019] (5) Prepare the sensing medium for the displacement sensor;

[0020] (6) 3D print the sensing medium of the displacement sensor on the planar copper electrode to form a micro-protrusion structure.

[0021] Preferably, the preparation methods of the toothed copper electrode in step (1) and the planar copper electrode in step (4) include chemical etching, photolithography, magnetron sputtering, thermal evaporation, etc.

[0022] More preferably, the toothed copper electrode in step (1) and the planar copper electrode in step (4) are formed by etching a single-sided copper foil on a PI substrate.

[0023] Preferably, the pressure sensor base and the displacement sensor base are made of PI substrate.

[0024] Beneficial effects

[0025] The flexible modulus sensor of the present invention has both a pressure sensor and a displacement sensor, so it can simultaneously measure the pressure and displacement of the pressing, and the two do not affect each other, thereby obtaining the modulus of the object being measured.

[0026] In the flexible modulus sensor of the present invention, the micro-protrusion structure with the shape of a parabolic rotation in the displacement sensor can detect the modulus of subcutaneous tissue at different depths. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the flexible modulus sensor of the present invention.

[0028] Reference numerals: 1-sensing medium, 2-displacement sensor base, 3-force-sensitive composite material, 4-pressure sensor base. Detailed Implementation

[0029] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0030] The present invention relates to a flexible modulus sensor capable of detecting the softness and hardness of subcutaneous tissue at different depths, comprising a pressure sensor and a displacement sensor; the pressure sensor employs resistive sensing and includes a toothed copper electrode and a force-sensitive composite material, wherein the force-sensitive composite material is made of a blend of silicone rubber and carbon-based conductive filler; the displacement sensor employs ionization sensing and includes a planar copper electrode and a sensing medium, wherein the sensing medium is configured as a micro-protrusion structure.

[0031] The measurement principle of the flexible modulus sensor of this invention is as follows: In the pressure sensor, the force-sensitive composite material converts external pressure stimulation into a detectable electrical signal, i.e., a change in its resistance. Subsequently, the toothed copper electrode collects and transmits this electrical signal. In the displacement sensor, the sensing medium converts the deformation stimulation of the detected object under external pressure into a detectable electrical signal, i.e., a change in its capacitance. The planar copper electrode collects and transmits the electrical signal converted by the sensing medium. Specifically, under pressure, the gaps in the carbon-based conductive filler in the force-sensitive composite material decrease, increasing the internal conductive channels. Therefore, the resistance of the device decreases with increasing pressure. As the pressing displacement increases, the micro-protrusion structure of the sensing medium increases its contact area with the skin, causing a significant double-layer effect. Therefore, the capacitance of the device increases with increasing displacement.

[0032] The method for preparing a flexible modulus sensor capable of detecting the softness and hardness of subcutaneous tissue at different depths in this invention includes the following steps:

[0033] (1) A toothed copper electrode is fabricated on the pressure sensor base 4;

[0034] (2) Preparation of force-sensitive composite material 3 for pressure sensor;

[0035] (3) Coat the force-sensitive composite material 3 onto the toothed copper electrode of the pressure sensor;

[0036] (4) A planar copper electrode is prepared on the displacement sensor base 2, and the planar copper electrode of the displacement sensor is covered on the force-sensitive composite material 3 of the pressure sensor.

[0037] (5) Prepare the sensing medium 1 of the displacement sensor;

[0038] (6) 3D print the sensing medium 1 of the displacement sensor on the planar copper electrode to form a micro-protrusion structure.

[0039] Example

[0040] The flexible modulus sensor in this embodiment includes a pressure sensor and a displacement sensor. The pressure sensor is composed of a toothed copper electrode and a polydimethylsiloxane-carbon nanotube (PDMS-CNTs) force-sensitive composite material. The displacement sensor is composed of a planar copper electrode and [EMIM]. + [TFSI] - Composition of ionic liquid-polyvinylidene fluoride (PVDF) blend sensing media.

[0041] The flexible modulus sensor in this embodiment is as follows: Figure 1 As shown, its preparation method is as follows:

[0042] (1) Fabrication of a toothed copper electrode on the pressure sensor base 4: The toothed electrode pattern is inkjet printed onto transfer paper, and then heated from 180°C to 200°C or held at 200°C for 10 min. The toothed electrode pattern on the transfer paper is then pressed tightly onto the copper foil of the PI substrate by hot pressing. Then, the copper foil is first immersed in H2O2 solution for 20-40 s, and then placed in HCl solution for 20 min to completely etch the copper in the untransfer area and preserve the electrode pattern well. Finally, the ink on the copper foil is treated with acetone to obtain the toothed copper electrode.

[0043] (2) Preparation of force-sensitive composite material for pressure sensor 3: 10g of PDMS basic component and curing agent were completely mixed at a weight ratio of 10:1, and 0.5g of CNT (5wt%) was added. S After stirring for 5 minutes, vacuum was applied to remove air bubbles. Hexane was added during stirring to reduce viscosity and accelerate stirring, resulting in PDMS-CNT. S 3. Blended force-sensitive composite material;

[0044] (3) Coat the force-sensitive composite material 3 on the toothed copper electrode of the pressure sensor; use laser to engrave a PET film, leaving a suitable gap in the middle. The film size is 7.6cm×2.5cm and the gap size is 1.8cm×1.8cm. Adhere the PET film to the PI substrate, with the gap corresponding to the toothed copper electrode and leaving two lead-out electrodes. Then coat a layer of PDMS-CNTs force-sensitive composite material 3 in the gap; finally peel off the PET film and keep the force-sensitive composite material 3.

[0045] (4) Prepare a planar copper electrode on the displacement sensor base 2 and cover the pressure sensor force-sensitive composite material 3 with the planar copper electrode of the displacement sensor: Prepare the planar copper electrode in the same way as in step (1), inkjet print the planar electrode pattern on the transfer paper, and then make the planar electrode pattern on the transfer paper adhere tightly to the copper foil on the PI substrate. Transfer the pattern onto the copper foil by hot pressing under the following conditions: heat from 180°C to 200°C or hold at 200°C for 10 min. Then use a chemical solution to etch away the remaining copper. The etching steps are: first immerse the copper foil in H2O2 solution for 20-40s, then stand in HCl solution for 20min to completely etch away the copper in the untransferred part and preserve the electrode pattern well. Finally, use acetone to treat the ink on the copper foil to obtain a square planar copper electrode of 1.8cm×1.8cm. Then make the PI substrate of the planar copper electrode directly contact and bond it to the force-sensitive composite material 3 of the pressure sensor.

[0046] (5) Preparation of the sensing medium 1 for the displacement sensor: a mixture of [EMIM] + [TFSI] - Sensing medium for displacement sensors prepared from ionic liquids and PVDF;

[0047] (6) On the planar copper electrode of the displacement sensor, the sensing medium 1 of the displacement sensor is 3D printed to form a micro-protrusion structure with the shape of a paraboloid of revolution; then it is baked in an oven at 70°C for 10 min.

Claims

1. A flexible modulus sensor capable of detecting the softness and hardness of subcutaneous tissue at different depths, characterized in that, The flexible modulus sensor includes a pressure sensor and a displacement sensor. The pressure sensor employs resistive sensing, and the displacement sensor employs ionization sensing. The pressure sensor includes a toothed copper electrode and a force-sensitive composite material. The displacement sensor includes a planar copper electrode and a sensing medium. The toothed copper electrode, the force-sensitive composite material, the planar copper electrode, and the sensing medium are stacked sequentially. The sensing medium is made of a blend of ionic liquid and polar organic polymer, and a micro-protrusion structure is formed by 3D printing. The micro-protrusion structure is a parabolic rotational surface. The force-sensitive composite material is made of a blend of silicone rubber and carbon-based conductive filler.

2. The flexible modulus sensor according to claim 1, characterized in that, The silicone rubber includes at least one of PDMS, Ecoflex, or silicone; the carbon-based conductive filler includes at least one of carbon black, graphene, or carbon nanotubes.

3. The flexible modulus sensor according to claim 1, characterized in that, The ionic liquid includes [EMIM]. + [TFSI] - [BMIM] + [TFSI] - Or [EMIM] + [TCM] - At least one of the following; the polar organic polymer includes at least one of PVDF or PU.

4. A method for preparing a flexible modulus sensor capable of detecting the softness and hardness of subcutaneous tissue at different depths, as described in any one of claims 1 to 3, comprising the following steps: (1) Fabricate a toothed copper electrode on the pressure sensor base; (2) Preparation of force-sensitive composite material for pressure sensors; (3) Coat the pressure sensor’s toothed copper electrode with a force-sensitive composite material. (4) A planar copper electrode is fabricated on the displacement sensor base, and the planar copper electrode of the displacement sensor is covered on the force-sensitive composite material of the pressure sensor. (5) Preparation of the sensing medium for the displacement sensor; (6) 3D print the sensing medium of the displacement sensor on the planar copper electrode to form a micro-protrusion structure.

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