Flexible modulus sensor capable of detecting hardness of subcutaneous tissues with different depths

Abstract

The invention relates to a flexible modulus sensor capable of detecting hardness of subcutaneous tissues with different depths. The flexible modulus sensor comprises a pressure sensor and a displacement sensor, the pressure sensor adopts resistance type sensing and comprises a gear shaping copper electrode and a force sensitive composite material; the displacement sensor adopts ionization type sensing and comprises a planar copper electrode and a sensing medium, and the sensing medium is of a micro-convex structure; according to the flexible modulus sensor, the pressure sensor detects stress, the displacement sensor detects strain, the pressure sensor and the displacement sensor do not influence each other, and modulus detection of subcutaneous tissues with different depths is achieved under the action of the micro-convex structure of the displacement sensor.

Description

Technical Field

[0001] The invention belongs to the field of sensor technology, and in particular relates to a flexible modulus sensor capable of detecting the softness and hardness of subcutaneous tissue at different depths. Background Art

[0002] With the development of wearable sensing, the measurement of the softness and hardness 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 softness and hardness measurement is essentially the detection of the elastic modulus of the material, which is the embodiment of the material's ability to deform under the action of external force and the coupling result of force and displacement. Therefore, the existing wearable modulus sensors are divided into two categories: (1) fixed force, detection of displacement. The specific implementation is to place a vibrator on the surface of the flexible strain sensor, and when the vibrator works at a constant amplitude and frequency, the deformation displacement generated by the strain sensor on the surface of the object being measured is detected. (2) Fixed displacement, detection of force. The specific implementation is to place a limiter at the back end of the flexible pressure sensor, and when the limiter moves a specified amount, the reverse force generated by the pressure sensor on the object being measured is detected. Since there is no dynamic moving component, the second solution has lower power consumption and longer life than the first solution, and is the mainstream solution for wearable modulus sensors at present.

[0003] From the analysis of the test principle, the wearable modulus sensor based on fixed displacement detection force detects the hardness of the surface of the material. In some cases, the object to be detected is located at a certain depth below the surface of the material, such as skin cancer lesions, which are generally located 3 cm below the human epidermis. Even if the current mainstream wearable modulus sensor increases the movement range of the limiter, its test result is the average hardness of the material within this range, rather than the elastic modulus at a specific depth. Recent experiments have shown that the ionic complex of the blended ionic liquid with a micro-protrusion in the shape of a rotating parabola can detect the modulus of an object at a certain depth. Using this feature, the problem that the wearable modulus sensor cannot detect the elastic modulus at a specific depth can be solved. Summary of the invention

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

[0005] The present 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 adopts a resistance-type sensor, and the displacement sensor adopts an ionization-type sensor.

[0006] Preferably, the pressure sensor comprises a slotted 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 organic silicone rubber includes at least one of PDMS (polydimethylsiloxane), Ecoflex or silicone; and the carbon-based conductive filler includes at least one of carbon black, graphene or carbon nanotubes (CNTs).

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

[0010] More preferably, the micro-protrusion structure is in the shape of a rotational parabola.

[0011] Preferably, the sensing medium is made of a blend of ionic liquid and polar organic polymer.

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

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

[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) Preparing a toothed copper electrode on a pressure sensor base;

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

[0017] (3) coating the force-sensitive composite material on the toothed copper electrode of the pressure sensor;

[0018] (4) preparing a planar copper electrode on the displacement sensor base, and covering the planar copper electrode of the displacement sensor on the force-sensitive composite material of the pressure sensor;

[0019] (5) preparing a sensing medium for a displacement sensor;

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

[0021] Preferably, the preparation method of the toothed copper electrode in step (1) and the planar copper electrode in step (4) comprises 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 prepared by etching a single-sided copper foil of a PI substrate.

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

[0024] Beneficial Effects

[0025] Since the flexible modulus sensor of the present invention has both a pressure sensor and a displacement sensor, it can measure the pressing pressure and displacement simultaneously without affecting each other, thereby obtaining the modulus of the measured object.

[0026] In the flexible modulus sensor of the present invention, the micro-protrusion structure in the displacement sensor in the shape of a rotational parabola can detect the modulus of subcutaneous tissue at different depths. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0028] Figure numerals: 1-sensing medium, 2-displacement sensor base, 3-force-sensitive composite material, 4-pressure sensor base. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0030] The flexible modulus sensor of the present invention, which can detect the softness and hardness of subcutaneous tissue at different depths, includes a pressure sensor and a displacement sensor; the pressure sensor adopts a resistive type sensor, including a toothed copper electrode and a force-sensitive composite material, and the force-sensitive composite material is made by blending organic silicone rubber and carbon-based conductive filler; the displacement sensor adopts an ionization type sensor, including a planar copper electrode and a sensing medium, wherein the sensing medium is arranged as a micro-convex structure.

[0031] The measuring principle of the flexible modulus sensor of the present invention is: the force-sensitive composite material in the pressure sensor converts the external pressure stimulus into a detectable electrical signal, that is, the change of its resistance, and then the toothed copper electrode collects and transmits the electrical signal; the sensing medium in the displacement sensor converts the deformation stimulus of the detected object under external pressure into a detectable electrical signal, that is, the change of its capacitance, and the flat copper electrode collects and transmits the electrical signal converted by the sensing medium. Specifically: under the action of pressure, the gap of the carbon-based conductive filler in the force-sensitive composite material is reduced, so that its internal conductive channel is increased, so the resistance of the device decreases with the increase of pressure; with the increase of the displacement of the pressure, the micro-convex structure of the sensing medium increases the contact area with the skin, causing a significant double-layer effect, so the capacitance of the device increases with the increase of displacement.

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

[0033] (1) Preparing a toothed copper electrode on the pressure sensor base 4;

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

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

[0036] (4) preparing a planar copper electrode on the displacement sensor base 2, and covering the planar copper electrode of the displacement sensor on the force-sensitive composite material 3 of the pressure sensor;

[0037] (5) preparing a sensing medium 1 of a displacement sensor;

[0038] (6) The sensing medium 1 of the displacement sensor is 3D printed 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, and the displacement sensor is composed of a planar copper electrode and [EMIM] + [TFSI] - The blended sensing medium composition of ionic liquid and polyvinylidene fluoride (PVDF).

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

[0042] (1) Preparing a toothed copper electrode on the pressure sensor base 4: inkjet printing the toothed electrode pattern on the transfer paper, then heating from 180°C to 200°C or keeping at 200°C for 10 minutes, and making the toothed electrode pattern on the transfer paper closely attached to the copper foil of the PI substrate by hot pressing; then soaking the copper foil in H2O2 solution for 20 to 40 seconds, and then standing in HCl solution for 20 minutes, completely etching the copper in the untransferred part and preserving the electrode pattern relatively intact; finally, treating the ink on the copper foil with acetone to obtain a toothed copper electrode;

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

[0044] (3) Scrape the force-sensitive composite material 3 on the toothed copper electrode of the pressure sensor; use laser to engrave the PET film, leaving a suitable gap in the middle, the film size is 7.6cm×2.5cm, the gap size is 1.8cm×1.8cm, the PET film is adhered to the PI substrate, the gap corresponds to the toothed copper electrode and two lead electrodes are left, and then a layer of PDMS-CNTs force-sensitive composite material 3 is scraped on the gap; finally, tear off the PET film and retain the force-sensitive composite material 3;

[0045] (4) Prepare a planar copper electrode on the displacement sensor base 2, and cover the planar copper electrode of the displacement sensor on the force-sensitive composite material 3 of the pressure sensor: prepare the planar copper electrode in the same way as step (1), inkjet print the planar electrode pattern on the transfer paper, and then make the planar electrode pattern on the transfer paper close to the copper foil on the PI substrate, and transfer the pattern to the copper foil by hot pressing, under the conditions of heating from 180°C to 200°C or keeping at 200°C for 10 minutes; then use a chemical solution to etch away the remaining copper, etching steps: first soak the copper foil in H2O2 solution for 20 to 40 seconds, and then stand in HCl solution for 20 minutes, completely etch the untransferred copper and keep the electrode pattern intact; finally, use acetone to treat the ink on the copper foil to obtain a 1.8 cm × 1.8 cm square planar copper electrode; then make the PI substrate of the planar copper electrode directly contact and bond with the force-sensitive composite material 3 of the pressure sensor;

[0046] (5) Preparation of displacement sensor sensing medium 1: mixed [EMIM] + [TFSI] - Ionic liquid and PVDF are used to prepare the sensing medium of the displacement sensor 1;

[0047] (6) On the planar copper electrode of the displacement sensor, the sensing medium 1 of the displacement sensor is 3D printed on the planar copper electrode to form a micro-convex structure in the shape of a rotating parabola; and then 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: It comprises a pressure sensor and a displacement sensor. The pressure sensor adopts a resistance type sensor, and the displacement sensor adopts an ionization type sensor.

2. The flexible modulus sensor according to claim 1, characterized in that: The pressure sensor includes a slotted copper electrode and a force-sensitive composite material.

3. The flexible modulus sensor according to claim 2, characterized in that: The force-sensitive composite material is prepared by blending organic silicone rubber and carbon-based conductive filler.

4. The flexible modulus sensor according to claim 3, characterized in that: The organic 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.

5. The flexible modulus sensor according to claim 1, characterized in that: The displacement sensor comprises a planar copper electrode and a sensing medium; wherein the sensing medium is a micro-protrusion structure.

6. The flexible modulus sensor according to claim 5, characterized in that: The micro-protrusion structure is in the shape of a rotation parabola.

7. The flexible modulus sensor according to claim 5, characterized in that: The sensing medium is prepared by blending ionic liquid and polar organic polymer.

8. The flexible modulus sensor according to claim 7, characterized in that: The ionic liquid comprises [EMIM] + [TFSI] - , [BMIM] + [TFSI] - or [EMIM] + [TCM] - At least one of; the polar organic polymer includes at least one of PVDF or PU.

9. According to the flexible modulus sensor of claim 1, the toothed copper electrode and the force-sensitive composite material of the pressure sensor and the planar copper electrode and the sensing medium of the displacement sensor are stacked in sequence.

10. A method for preparing a flexible modulus sensor capable of detecting the softness and hardness of subcutaneous tissue at different depths as claimed in any one of claims 1 to 9, comprising the following steps: (1) Preparing a toothed copper electrode on a pressure sensor base; (2) Preparation of force-sensitive composite materials for pressure sensors; (3) coating the force-sensitive composite material on the toothed copper electrode of the pressure sensor; (4) preparing a planar copper electrode on the displacement sensor base, and covering the planar copper electrode of the displacement sensor on the force-sensitive composite material of the pressure sensor; (5) preparing a sensing medium for a displacement sensor; (6) The sensing medium of the displacement sensor is 3D printed on the planar copper electrode to form a micro-protrusion structure.

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