阅读说明：本技术 一种挠曲电柔性纳米曲率传感器及其制备和测试方法 (Flexoelectric flexible nano-curvature sensor and preparation and test method thereof ) 是由 胡淑玲 刘帅成 梁旭 范航海 于亦文 兰梦蝶 于 2020-12-12 设计创作，主要内容包括：本发明公开了一种挠曲电柔性纳米曲率传感器及其制备和测试方法,该柔性曲率传感器利用固相烧结法制备纳米颗粒,经过表面改性处理后均匀分散在柔性基体内形成复合柔性纳米高弹体。通过颗粒表面改性、调节质量参杂配比等工艺参数,可获得颗粒分布均匀、10％-50％不同质量比颗粒掺杂的挠曲电柔性纳米曲率传感器,该柔性曲率传感器克服了传统传感器在曲率监测方面的不足,使得整体变形能力与输出响应得以同步提升。本发明柔性曲率传感器响应速率快、幅值高、弯曲能力强、工艺简单且成本低廉,其可推动该曲率传感器在人体运动监测、电子皮肤、智能机器人以及微纳机电系统等领域的应用。(The invention discloses a flexible nano-curvature sensor of flexoelectric and a preparation and test method thereof. Through the process parameters of particle surface modification, mass doping proportion adjustment and the like, the flexoelectric flexible nano curvature sensor with uniformly distributed particles and different mass ratios of 10-50% doped with particles can be obtained, and the flexible curvature sensor overcomes the defects of the traditional sensor in the aspect of curvature monitoring, so that the integral deformation capacity and the output response are synchronously improved. The flexible curvature sensor has the advantages of high response speed, high amplitude, strong bending capability, simple process and low cost, and can promote the application of the curvature sensor in the fields of human motion monitoring, electronic skin, intelligent robots, micro-nano electromechanical systems and the like.)

1. The flexible flexoelectric nano curvature sensor is characterized by comprising a flexible elastomer (4), flexible electrodes (3) attached to the upper surface and the lower surface of the flexible elastomer (4) and a lead connected with the flexible electrodes (3), wherein the flexible elastomer (4) is formed by uniformly doping surface modified nanoparticles (1) in a flexible substrate (2), and the surface modified nanoparticles (1) are formed by surface modification of nanoparticles prepared by a solid-phase sintering method; when the sensor is stressed to bend, the flexible elastomer (4) generates strain gradient due to deformation, so that the surface modified nanoparticles in the flexible substrate are subjected to spontaneous polarization, positive and negative charges are respectively generated on the upper surface and the lower surface of the flexible elastomer (4), and accordingly, the output of a deflection electric signal in the bending deformation process is realized, and the output sensitivity is high.

2. A flexoelectric flexible nanocurvature sensor according to claim 1, wherein the thickness of the flexible elastomer (4) is 180-240 μm and the thickness of the flexible electrode material (3) is 0.1-0.2 μm.

3. A flexoelectric flexible nanocurvature sensor according to claim 1, wherein the surface-modified nanoparticles (1) are a material with a perovskite unit cell structure.

4. A flexoelectric flexible nanocurvature sensor according to claim 1, wherein the flexible matrix (2) is polydimethylsiloxane, polyvinylidene fluoride or epoxy.

5. A flexoelectric flexible nanocurvature sensor according to claim 1, wherein the flexible electrode (3) is a metal foil of aluminum, silver or gold foil or a polymer film plated with a conductive electrode.

6. The method for manufacturing a flexoelectric flexible nano-curvature sensor according to any one of claims 1 to 5, wherein nanoparticles having a uniform particle diameter are prepared by a solid phase sintering method, and then the surface of the nanoparticles is modified, specifically: mixing the nano particles, hydrogen peroxide and ethanol in a mass ratio of 1:5:1, uniformly mixing and ultrasonically treating, refluxing for overnight, centrifuging, and drying to form functionalized particles; then mixing the functionalized particles with ethanol in a mass ratio of 1:5, carrying out uniform ultrasonic treatment to form mixed particles, adding a silane coupling agent accounting for 1-5% of the mixed particles by mass ratio, carrying out uniform magnetic stirring, and carrying out drying treatment to obtain surface modified nanoparticles (1); adding the surface modified nanoparticles (1) into a flexible substrate (2) according to the doping quality proportion requirement, carrying out ultrasonic treatment uniformly, carrying out high-speed defoaming stirring, adding a curing agent, carrying out ultrasonic uniform and defoaming stirring treatment, then carrying out spin coating on the flexible elastomer (4) in a spin coating machine, and finally attaching flexible electrodes (3) to the upper surface and the lower surface of the flexible elastomer (4) to form the flexible electric flexible nano curvature sensor.

7. The method according to claim 6, wherein the surface-modified nanoparticles (1) are doped in a mass ratio of 10% to 50% with respect to the flexible substrate (2), and the spin coater is rotated at a speed of 0.5Kr/min to 2.5 Kr/min.

8. The method for testing the flexoelectric flexible nano-curvature sensor according to any one of claims 1 to 5, wherein the flexoelectric flexible nano-curvature sensor is placed in the center of a four-point beam structure (11), a signal generator (8) outputs excitation waves in advance, the excitation waves are output to an actuator (6) by a power amplifier (7) to be subjected to signal excitation, a laser vibration meter (5) detects the displacement of the center point of the four-point beam structure (11) through the excitation waves output in advance, the excitation wave signal of the signal generator (8) is locked again to be subjected to excitation by locking the displacement value of the center point of the four-point beam structure (11), and after the flexoelectric flexible nano-curvature sensor is excited, an output electric signal passes through a charge amplifier (9), and finally an electric signal waveform is collected on an oscilloscope (10).

9. The test method according to claim 8, wherein the flexoelectric flexible nano-curvature sensor uses sine wave as an excitation source, and realizes the change of the deflection range of 0.1mm-1.8mm, the output charge range of 9.8pC-432pC and the sensitivity range of 13pC/mm-216 pC/mm.

Technical Field

The invention relates to the technical field of sensing monitoring, in particular to a flexible nano-curvature sensor based on flexoelectric and a preparation and test method thereof.

Background

The natural living beings have a plurality of sensing and driving capabilities, and control and sense external changes through self movement. In recent years, materials based on such sensing and driving biological characteristics have been widely used in the fields of human health monitoring, electronic skin, intelligent robots, micro-nano electromechanical systems and the like. Most sensors are applied to motion monitoring and are only limited to tension and compression monitoring, and for bending curvature monitoring, common sensors are mostly limited to the application of traditional inorganic materials, and the sensors are large in brittleness, poor in flexibility and incapable of bending deformation, or organic materials good in flexibility and capable of extending are adopted, but output response is low, sensing driving performance is poor, and the like. Compared with the prior art, the organic and inorganic composite material has the advantages of two materials, is combined to prepare the flexible material with excellent performance, has good bending deformation and output response, and realizes the synchronous promotion of response rate and deformation amplitude on the aspect of facing the difficult problem of curvature monitoring.

The sensing principle of the flexible nano-curvature sensor for the flexoelectric is that when the sensor is stressed to bend, the flexible elastomer generates strain gradient due to deformation, so that the nanoparticles with perovskite unit cell structures in the matrix are spontaneously polarized, positive and negative charges are respectively generated on the upper surface and the lower surface of the flexible elastomer, and the output of a deflection electric signal in the bending deformation process is realized. Therefore, the response rate and the deformability of the curvature sensor depend on the doping amount ratio of the particles, the uniformity degree of the particle distribution and the bending deformation degree of the sensor, respectively. Recent research results show that the flexoelectric effect can show more excellent force-electric coupling characteristics on a micro-nano scale. Therefore, the output performance of the whole flexible curvature sensor can be improved by doping the flexible matrix with the nano particles, and higher sensitivity is shown. The surface modified nano particles are uniformly dispersed in the flexible matrix, and more connecting channels are provided for an electric field generated by spontaneous polarization of the deformed nano particles. Therefore, the output performance and the sensitivity of the sensor are improved by uniformly distributing the particles in the matrix.

Disclosure of Invention

The invention aims to provide a flexoelectric flexible nano-curvature sensor and a preparation and test method thereof, so as to solve the technical problem that the response signal output and the deformability cannot be simultaneously improved in the background technology.

In order to achieve the purpose, the invention adopts the following technical scheme:

a flexible electric flexible nanometer curvature sensor is composed of flexible electrodes 3 and leads, wherein the flexible electrodes 3 are attached to the upper surface and the lower surface of a flexible elastomer 4, the leads are connected with the flexible electrodes 3, the flexible elastomer 4 is formed by uniformly doping surface modified nanoparticles 1 into a flexible substrate 2, and the surface modified nanoparticles 1 are formed by surface modification of nanoparticles prepared by a solid-phase sintering method; when the sensor is stressed to bend, the flexible elastomer 4 generates strain gradient due to deformation, so that the surface modified nanoparticles in the flexible substrate are subjected to spontaneous polarization, positive and negative charges are respectively generated on the upper surface and the lower surface of the flexible elastomer 4, the output of a deflection electric signal in the bending deformation process is realized, and the output sensitivity is high.

The thickness of the flexible elastomer 4 is 180-240 μm, and the thickness of the flexible electrode material 3 is 0.1-0.2 μm.

The surface-modified nanoparticles 1 are materials having a perovskite unit cell structure.

The flexible matrix 2 is polydimethylsiloxane, polyvinylidene fluoride or epoxy resin.

The flexible electrode 3 is a metal foil of aluminum foil, silver foil or gold foil or a polymer film plated with a conductive electrode.

The preparation method of the flexoelectric flexible nanometer curvature sensor comprises the following steps of preparing nanometer particles with uniform particle sizes by using a solid-phase sintering method, and then carrying out surface modification treatment on the nanometer particles, wherein the method specifically comprises the following steps: mixing the nano particles, hydrogen peroxide and ethanol in a mass ratio of 1:5:1, uniformly mixing and ultrasonically treating, refluxing for overnight, centrifuging, and drying to form functionalized particles; then mixing the functionalized particles with ethanol in a mass ratio of 1:5, carrying out uniform ultrasonic treatment to form mixed particles, adding a silane coupling agent accounting for 1-5% of the mixed particles by mass ratio, carrying out uniform magnetic stirring, and carrying out drying treatment to obtain surface modified nanoparticles 1; adding the surface modified nano particles 1 into a flexible substrate 2 according to the doping quality ratio requirement, carrying out uniform ultrasonic treatment, carrying out high-speed defoaming stirring, adding a curing agent, carrying out uniform ultrasonic treatment and defoaming stirring treatment, then carrying out spin coating on the flexible elastomer 4 by a spin coater, and finally attaching flexible electrodes 3 to the upper surface and the lower surface of the flexible elastomer 4 to form the flexoelectric flexible nano curvature sensor.

The surface modified nano-particles 1 are doped according to the mass ratio of 210-50% of the flexible matrix, and the rotating speed of the spin coating machine is 0.5-2.5 Kr/min.

The method for testing the flexoelectric flexible nano-curvature sensor comprises the steps that the flexoelectric flexible nano-curvature sensor is placed in the center of a four-point beam structure 11, a signal generator 8 outputs excitation waves in advance, the excitation waves are output to an actuator 6 through a power amplifier 7 to be subjected to signal excitation, a laser vibration meter 5 detects displacement of the center point of the four-point beam structure 11 through the excitation waves output in advance, the signal generator 8 is locked to perform excitation through locking of the displacement value of the center point of the four-point beam structure 11, the flexoelectric flexible nano-curvature sensor outputs electric signals after excitation, the electric signals pass through a charge amplifier 9, and finally electric signal waveforms are collected on an oscilloscope 10.

The flexoelectric flexible nanometer curvature sensor takes sine waves as an excitation source, the deflection range is changed to be 0.1-1.8 mm, the output charge range is 9.8pC-432pC, and the sensitivity range is 13pC/mm-216 pC/mm.

Compared with the prior art, the invention has the advantages that:

(1) the flexoelectric flexible nanometer curvature sensor realizes synchronous lifting of deformability and output response, and makes up for short plates with low sensitivity of output response and incapable of being monitored by the existing sensor in the aspect of curvature monitoring. The method has wide application prospect in the fields of human health monitoring, electronic skin, intelligent robots, micro-nano electromechanical systems and the like.

(2) The flexible flexoelectric nano curvature sensor has the advantages of simple preparation process, high product stability and durability and low cost.

Drawings

FIG. 1 is a schematic diagram of a method for fabricating a flexoelectric flexible nano-curvature sensor;

FIG. 2 is a schematic diagram of a method for testing a flexoelectric flexible nano-curvature sensor;

FIG. 3 is a surface electron microscope image of a flexoelectric flexible nano-curvature sensor;

FIG. 4 is a schematic diagram of flexible stretching of a flexoelectric flexible nano-curvature sensor;

FIG. 5 is the electrical signal response of a 10% mass ratio nanoparticle doped flexoelectric flexible nanofcurvature sensor under 0.6mm deflection deformation;

FIG. 6 is the electrical signal response of a 20% mass ratio nanoparticle doped flexoelectric flexible nanofcurvature sensor under 1.5mm deflection deformation;

FIG. 7 is the electrical signal response of a 30% mass ratio nanoparticle doped flexoelectric flexible nanofcurvature sensor under 0.9mm deflection deformation;

FIG. 8 is an electrical signal response of a 40% mass ratio nanoparticle doped flexoelectric flexible nanofcurvature sensor under 1.5mm deflection deformation;

FIG. 9 is an electrical signal response of a 50% mass ratio nanoparticle doped flexoelectric flexible nanofcurvature sensor under 1.2mm deflection deformation;

Detailed Description

The present invention will now be described in detail with reference to the drawings and specific embodiments, wherein the exemplary embodiments and descriptions of the present invention are provided to explain the present invention without limiting the invention thereto.

As shown in fig. 1, the flexoelectric flexible nano-curvature sensor of the present invention comprises a flexible elastomer 4, flexible electrodes 3 attached to the upper and lower surfaces of the flexible elastomer 4, and a lead connected to the flexible electrodes 3, wherein the flexible elastomer 4 is formed by uniformly doping surface-modified nanoparticles 1 into a flexible substrate 2, and the surface-modified nanoparticles 1 are formed by surface modification of nanoparticles prepared by a solid-phase sintering method; when the sensor is stressed to bend, the flexible elastomer 4 generates strain gradient due to deformation, so that the surface modified nanoparticles in the flexible substrate are subjected to spontaneous polarization, positive and negative charges are respectively generated on the upper surface and the lower surface of the flexible elastomer 4, the output of a deflection electric signal in the bending deformation process is realized, and the output sensitivity is high.

As a preferred embodiment of the present invention, the thickness of the flexible elastomer 4 is 180 μm to 240 μm, and the thickness of the flexible electrode material 3 is 0.1 μm to 0.2. mu.m.

As a preferred embodiment of the present invention, the surface-modified nanoparticles 1 are a material having a perovskite unit cell structure.

As a preferred embodiment of the present invention, the flexible substrate 2 is polydimethylsiloxane, polyvinylidene fluoride, or epoxy resin.

As a preferred embodiment of the present invention, the flexible electrode 3 is a metal foil of aluminum foil, silver foil or gold foil or a polymer film plated with a conductive electrode.

The invention relates to a method for preparing a flexible nano curvature sensor by using a flexoelectric method, which comprises the following steps of preparing nano particles with uniform particle size by using a solid-phase sintering method, and then carrying out surface modification treatment on the nano particles: mixing the nano particles, hydrogen peroxide and ethanol in a mass ratio of 1:5:1, uniformly mixing and ultrasonically treating, refluxing for overnight, centrifuging, and drying to form functionalized particles; then mixing the functionalized particles with ethanol in a mass ratio of 1:5, carrying out uniform ultrasonic treatment to form mixed particles, adding a silane coupling agent accounting for 1-5% of the mixed particles by mass ratio, carrying out uniform magnetic stirring, and carrying out drying treatment to obtain surface modified nanoparticles 1; adding the surface modified nano particles 1 into a flexible substrate 2 according to the doping quality ratio requirement, carrying out uniform ultrasonic treatment, carrying out high-speed defoaming stirring, adding a curing agent, carrying out uniform ultrasonic treatment and defoaming stirring treatment, then carrying out spin coating on the flexible elastomer 4 by a spin coater, and finally attaching flexible electrodes 3 to the upper surface and the lower surface of the flexible elastomer 4 to form the flexoelectric flexible nano curvature sensor.

As a preferred embodiment of the present invention, the surface-modified nanoparticles 1 are doped in a mass ratio of 210% to 50% of the flexible substrate, and the spin coater is rotated at a speed of 0.5Kr/min to 2.5 Kr/min.

The method for testing the flexoelectric flexible nano-curvature sensor comprises the steps that the flexoelectric flexible nano-curvature sensor is placed in the center of a four-point beam structure 11, a signal generator 8 outputs excitation waves in advance, the excitation waves are output to an actuator 6 through a power amplifier 7 to be subjected to signal excitation, a laser vibration meter 5 locks displacement of the center point of the four-point beam structure 11 through the excitation waves output in advance, then the excitation wave signal of the signal generator 8 is locked to be excited, after the flexoelectric flexible nano-curvature sensor is excited, an electric signal is output to pass through a charge amplifier 9, and finally, the waveform of the electric signal is collected on an oscilloscope 10.

The flexoelectric flexible nanometer curvature sensor takes sine waves as an excitation source, the deflection range is changed to be 0.1-1.8 mm, the output charge range is 9.8pC-432pC, and the sensitivity range is 13pC/mm-216 pC/mm.

Example 1:

50% mass ratio surface modified nanoparticle doped flexoelectric flexible nano-curvature sensor. The surface and cross-sectional scanning electron micrographs are shown in FIG. 3, from which it can be seen that: the surface modified nanoparticles are uniformly dispersed in the flexible matrix. Figure 4 shows that the flexible elastomer has excellent tensile properties and can achieve excellent bending deformability. The preparation method is as shown in figure 1, the traditional solid phase sintering method is adopted to prepare nano particles with uniform particle size, the surface of the nano particles is modified, the surface modified nano particles 1 are doped into a flexible substrate 2, ultrasonic and mechanical dispersion is carried out, then spin coating and curing treatment are carried out, the spin coating rotating speed is maintained at 2.5Kr/min, spin coating is carried out for 3 times after curing, finally, the flexible elastomer 4 with the thickness of 180-240 mu m is obtained, and the flexible electrode 3 with the thickness of 0.1-0.2 mu m is attached to the upper surface and the lower surface of the flexible elastomer 4 to lead out wires to form the flexible electric flexible nano curvature sensor. As shown in fig. 2, the flexoelectric flexible nano-curvature sensor is placed in the center of a four-point beam structure 11, a signal generator 8 takes a sine wave with a frequency of 1HZ as excitation, a laser vibration meter 5 collects displacement change deflection 1.2mm of the center of the four-point beam structure 11 to realize sine excitation with the change deflection of 1.2mm, the sine excitation is output to an actuator 6 through a power amplifier 7, after the flexoelectric flexible nano-curvature sensor is excited, the maximum charge of an output signal output to an oscilloscope 10 through a charge amplifier 9 is 257pC, and the sensitivity can reach 216pC/mm, as shown in fig. 9.

Example 2:

a 40% mass specific surface modified nanoparticle doped flexoelectric flexible nanofcurvature sensor. The preparation method is as shown in figure 1, the traditional solid phase sintering method is adopted to prepare nano particles with uniform particle size, the surface of the nano particles is modified, the surface modified nano particles 1 are doped into a flexible substrate 2, ultrasonic and mechanical dispersion is carried out, then spin coating and curing treatment are carried out, the spin coating rotating speed is maintained at 1.8Kr/min, spin coating is carried out for 3 times after curing, finally, the flexible elastomer 4 with the thickness of 180-240 mu m is obtained, and the flexible electrode 3 with the thickness of 0.1-0.2 mu m is attached to the upper surface and the lower surface of the flexible elastomer 4 to lead out wires to form the flexible electric flexible nano curvature sensor. As shown in fig. 2, the flexoelectric flexible nano-curvature sensor is placed in the center of a four-point beam structure 11, a signal generator 8 takes a sine wave with a frequency of 1HZ as excitation, a laser vibration meter 5 collects displacement change deflection 1.5mm of the center of the four-point beam structure 11 to realize sine excitation with the change deflection of 1.5mm, the sine excitation is output to an actuator 6 through a power amplifier 7, after the flexoelectric flexible nano-curvature sensor is excited, an output signal is output to maximum charge 216pC on an oscilloscope 10 through a charge amplifier 9, and the sensitivity can reach 159.63pC/mm, as shown in fig. 8.

Example 3:

the surface modified nanoparticle doped flexoelectric flexible nano curvature sensor with the mass ratio of 30 percent. The preparation method is as shown in figure 1, the traditional solid phase sintering method is adopted to prepare nano particles with uniform particle size, the surface of the nano particles is modified, the surface modified nano particles 1 are doped into a flexible substrate 2, ultrasonic and mechanical dispersion is carried out, then spin coating and curing treatment are carried out, the spin coating rotating speed is maintained at 1.3Kr/min, spin coating is carried out for 3 times after curing, finally, the flexible elastomer 4 with the thickness of 180-240 mu m is obtained, and the flexible electrode 3 with the thickness of 0.1-0.2 mu m is attached to the upper surface and the lower surface of the flexible elastomer 4 to lead out wires to form the flexible electric flexible nano curvature sensor. As shown in fig. 2, the flexoelectric flexible nano-curvature sensor is placed in the center of a four-point beam structure 11, a signal generator 8 takes a sine wave with a frequency of 1HZ as excitation, a laser vibration meter 5 collects displacement change deflection of 0.9mm from the center of the four-point beam structure 11 to realize sine excitation with the change deflection of 0.9mm, the sine excitation is output to an actuator 6 through a power amplifier 7, after the flexoelectric flexible nano-curvature sensor is excited, an output signal is output to a maximum charge of 67.5pC on an oscilloscope 10 through a charge amplifier 9, and the sensitivity can reach 75.2pC/mm as shown in fig. 7.

Example 4:

20% mass ratio surface modified nanoparticle doped flexoelectric flexible nano-curvature sensor. The preparation method is as shown in figure 1, the traditional solid phase sintering method is adopted to prepare nano particles with uniform particle size, the surface of the nano particles is modified, the surface modified nano particles 1 are doped into a flexible substrate 2, ultrasonic and mechanical dispersion is carried out, then spin coating and curing treatment are carried out, the spin coating rotating speed is maintained at 1.0Kr/min, spin coating is carried out for 3 times after curing, finally, the flexible elastomer 4 with the thickness of 180-240 mu m is obtained, and the flexible electrodes 3 with the thickness of 0.1-0.2 mu m are attached to the upper surface and the lower surface of the flexible elastomer 4 to lead out wires to form the flexible electric flexible nano curvature sensor. As shown in fig. 2, the flexoelectric flexible nano-curvature sensor is placed in the center of a four-point beam structure 11, a signal generator 8 takes a sine wave with a frequency of 1HZ as excitation, a laser vibration meter 5 collects displacement change deflection 1.5mm of the center of the four-point beam structure 11 to realize sine excitation with the change deflection of 1.5mm, the sine excitation is output to an actuator 6 through a power amplifier 7, after the flexoelectric flexible nano-curvature sensor is excited, an output signal is output to a maximum charge 62pC on an oscilloscope 10 through a charge amplifier 9, and the sensitivity can reach 46.37pC/mm, as shown in fig. 6.

Example 5:

10% mass ratio surface modified nanoparticle doped flexoelectric flexible nano-curvature sensor. The preparation method is as shown in figure 1, the traditional solid phase sintering method is adopted to prepare nano particles with uniform particle size, the surface of the nano particles is modified, the surface modified nano particles 1 are doped into a flexible substrate 2, ultrasonic and mechanical dispersion is carried out, then spin coating and curing treatment are carried out, the spin coating rotation speed is maintained at 0.5Kr/min, spin coating is carried out for 3 times after curing, finally, the flexible elastomer 4 with the thickness of 180-240 mu m is obtained, and the flexible electrodes 3 with the thickness of 0.1-0.2 mu m are attached to the upper surface and the lower surface of the flexible elastomer 4 to lead out wires to form the flexible electric flexible nano curvature sensor. As shown in fig. 2, the flexoelectric flexible nano-curvature sensor is placed in the center of a four-point beam structure 11, a signal generator 8 takes a sine wave with a frequency of 1HZ as excitation, a laser vibration meter 5 collects displacement change deflection of 0.6mm from the center of the four-point beam structure 11 to realize sine excitation with the change deflection of 0.6mm, the sine excitation is output to an actuator 6 through a power amplifier 7, after the flexoelectric flexible nano-curvature sensor is excited, an output signal is output to a maximum charge of 8.8pC on an oscilloscope 10 through a charge amplifier 9, and the sensitivity can reach 13.42pC/mm as shown in fig. 5.

The above-described embodiments are merely preferred embodiments of the present invention, and do not limit the scope of the claims. Any changes or substitutions that may be easily made by those skilled in the art within the technical scope of the present disclosure are intended to be included within the scope of the present disclosure. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.