KR20190059252A - Dielectric for pressure sensor, method of manufacturing the same and capacitive type pressure sensor - Google Patents

Abstract

The present invention relates to a manufacturing method of a dielectric for a pressure sensor. According to one embodiment of the present invention, the manufacturing method of the dielectric for the pressure sensor comprises: (a) a step of mixing two different types of first and second polymers to manufacture a polymer mixture; (b) a step of mixing the polymer mixture with an aqueous solution of a blowing agent and a surfactant in which the surfactant is dissolved to manufacture a second mixture; (c) a step of mixing an acidic compound and an aqueous acidic compound solution in which the surfactant is dissolved in the second mixture to manufacture a dielectric composition; and (d) a step of heating the dielectric composition to cure the first polymer and the second polymer.

Description

TECHNICAL FIELD [0001] The present invention relates to a dielectric material for a pressure sensor, a manufacturing method thereof, and a capacitance type pressure sensor. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

The present invention relates to a dielectric material for a pressure sensor, a method of manufacturing the same, and a capacitance type pressure sensor, and more particularly, to a dielectric material for a pressure sensor in which pores are formed by using a polymer having elasticity and a manufacturing method thereof and a capacitance type pressure sensor having the same will be.

Pressure sensors can be divided into mechanical methods that use mechanical elasticity against external pressure and electrical methods that detect changes in electrical signals according to external pressure.

Among them, a pressure sensor using an electric method includes a piezoelectric pressure sensor, a pressure resistance type pressure sensor, and a capacitance type pressure sensor. In particular, a capacitive pressure sensor forms a dielectric between the electrodes of a pressure sensor and detects a change in capacitance that changes when the dielectric is compressed by an external pressure. Sensitivity can vary depending on the type of dielectric, which has the advantage of being able to measure the pressure accurately compared to mechanical pressure sensors and other electrical pressure sensors.

The dielectric used in the capacitive pressure sensor uses an elastomer that is compressed by external pressure and then restored. The sensitivity and pressure range of the pressure sensor are determined according to the properties of the elastomer.

The dielectric used for the conventional capacitive pressure sensor was formed by forming pores in the elastomer. The elasticity of the dielectric, that is, the sensitivity of the pressure sensor, can be changed according to the size and density of the pores formed as the matrix of the dielectric and the pores to be formed. However, it is not easy to control the physical properties of the dielectric material so as to have the sensitivity required to be used as a specific pressure sensor, and there is an unnecessary process during the process, and the performance is poor.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a pressure sensor dielectric having pores formed by using two different kinds of polymers, a method for manufacturing the same and an electrostatic capacity type pressure sensor The purpose is to provide.

It is another object of the present invention to improve the sensitivity of a pressure sensor by controlling the size and density of pores formed in a dielectric for a pressure sensor.

However, these problems are exemplary and do not limit the scope of the present invention.

According to one aspect of the present invention, there is provided a method for producing a polymer mixture, comprising: (a) mixing two different first polymers and a second polymer to prepare a polymer mixture; (b) (C) mixing the second mixture with an acidic compound and an aqueous solution of an acidic compound in which the surfactant is dissolved to prepare a dielectric composition; and (d) And heating the dielectric composition to cure the first polymer and the second polymer.

In the method for producing a dielectric material for a pressure sensor, the first polymer and the second polymer may be at least any one selected from the group consisting of polybutyrate, polyurethane, and polydimethylsiloxane (PDMS) .

In the step (b) of the method the pressure produced in the sensor dielectric for the foaming agent is _{H 2 CO 3, LiHCO 3,} NaHCO 3, KHCO 3, Mg (HCO 3) 2 and Ca (HCO ₃₎ from the group consisting of ₂ Wherein the acidic compound comprises at least one selected from the group consisting of citric acid (C ₆ H ₈ O ₇ ) and acetic acid (CH ₃ COOH).

The weight ratio of the foaming agent to the acidic compound in the dielectric composition in the step (c) of the method for producing a pressure sensor dielectric is 25 wt% to 40 wt%, and in the step (d) Lt; 0 > C.

In at least one of the steps (c) to (d) of the method for producing a dielectric substance for a pressure sensor, the foaming agent and the acidic compound react to form a gas, and the gas is introduced onto the polymer mixture matrix Thereby forming pores.

In the method for producing a dielectric material for a pressure sensor, it is preferable that the content of the polymer having a relatively high viscosity is higher, the content of the foaming agent is higher, the content of the acidic compound is higher, And the sensitivity of the dielectric to the pressure is increased.

According to another aspect of the present invention for solving the above problems, there is provided a process for preparing a polymer mixture comprising a polymer mixture in which two kinds of first and second polymers are mixed, wherein a matrix is formed, And a dielectric for a pressure sensor.

In the pressure sensor dielectric, the first polymer and the second polymer may each be at least one selected from the group consisting of polybutyrate, polyurethane, and polydimethylsiloxane (PDMS).

In the pressure sensor dielectric, the pores may be formed in the polymer mixture matrix by a gas generated by a reaction between a foaming agent and an acidic compound.

Wherein the foaming agent comprises at least any one selected from the group consisting of H ₂ CO ₃ , LiHCO ₃ , NaHCO ₃ , KHCO ₃ , Mg (HCO ₃ ) ₂ and Ca (HCO ₃ ) ₂ , The acidic compound may comprise citric acid (C ₆ H ₈ O ₇ ) or acetic acid (CH ₃ COOH).

According to another aspect of the present invention, there is provided an upper electrode and a lower electrode spaced apart from each other; And a polymer mixture, which is interposed between the upper electrode and the lower electrode and in which two kinds of first and second polymers are mixed, is used as a matrix, and a pore is formed in the polymer mixture matrix. A dielectric pressure sensor comprising: a dielectric;

In the capacitive pressure sensor, the first polymer and the second polymer may each be at least one selected from the group consisting of polybutyrate, polyurethane, and polydimethylsiloxane (PDMS) .

In the capacitance type pressure sensor, the pores may be formed in the polymer mixture matrix by a gas generated by a reaction between a foaming agent and an acidic compound.

Wherein the foaming agent comprises at least one selected from the group consisting of H ₂ CO ₃ , LiHCO ₃ , NaHCO ₃ , KHCO ₃ , Mg (HCO ₃ ) ₂ and Ca (HCO ₃ ) ₂ , The acidic compound may include citric acid (C ₆ H ₈ O ₇ ) or acetic acid (CH ₃ COOH).

According to an embodiment of the present invention, as described above, there is provided a pressure sensor dielectric having pores formed by using two different kinds of polymers, a foaming agent, and an acidic compound, a method of manufacturing the same, and a capacitance type pressure sensor having the same can do.

In addition, according to the present invention, there is an effect that the sensitivity of the pressure sensor is improved by controlling the ratio of the polymer, the foaming agent, and the acidic compound in the composition to adjust the size and density of pores formed in the dielectric for pressure sensor.

Of course, the scope of the present invention is not limited by these effects.

1 is a flowchart showing a method of manufacturing a dielectric for a pressure sensor according to an embodiment of the present invention.
2 is a schematic view showing a method of manufacturing a dielectric for a pressure sensor according to an embodiment of the present invention.
3 is a schematic view showing a method of manufacturing a pressure sensor according to an embodiment of the present invention.
4 and 5 are scanning electron microscopy (SEM) photographs showing pores formed on the surface according to comparative examples of the present invention.
6 shows the dielectric constant change experiment result of the dielectric for pressure sensor according to one comparative example of the present invention.
7 is a photograph showing sodium hydrogencarbonate and citric acid aqueous solution according to an embodiment of the present invention.
FIG. 8 shows the experimental result of the capacitance change rate (? C / C ₀ ) measurement of the dielectric for a pressure sensor according to an embodiment of the present invention.
9 is a graph of compressive stress-compression elongation of a dielectric for a pressure sensor according to embodiments of the present invention.
10 is a graph showing a result of measuring a capacitance change rate (? C / C ₀ ) of a dielectric substance for a pressure sensor according to embodiments of the present invention.
11 is a scanning electron microscopy (SEM) photograph of a section of a dielectric according to the curing temperature in the third experimental example of the present invention.
12 is a graph showing the relationship between the pressure of the pressure sensor dielectric and the capacitance change rate (? C / C ₀ ) according to the curing temperature in the third experimental example of the present invention.
13 is a graph showing the relationship between compressive stress and compressive strain of a dielectric for a pressure sensor according to the curing temperature in the third experimental example of the present invention.
14 to 16 are graphs obtained by dividing sensitivity according to the curing temperature of the pressure sensor dielectric according to the curing temperature according to the pressure range in the third experiment example of the present invention.
17 is a graph showing the result of micro CT analysis of a dielectric material for a pressure sensor according to the ratio of pore forming precursor in the third experiment example of the present invention.
18 is a graph showing the relationship between the pressure of the pressure sensor dielectric and the rate of change in capacitance (? C / C ₀ ) according to the ratio of pore-forming precursor in the third experimental example of the present invention.
19 to 21 are graphs obtained by dividing the sensitivity of the pressure sensor dielectric according to the pressure range according to the pore forming precursor ratio in the third experimental example of the present invention.
FIG. 22 is a diagram showing an experimental result in which the lowest pressure measurable by the pressure sensor is evaluated in the third experimental example of the present invention. FIG.
FIG. 23 is a graph showing the reaction time according to the pressure of the pressure sensor in the third experimental example of the present invention, and FIG. 24 is an enlarged graph of the area M1 of FIG.
25 is a graph showing the reaction time according to the pressure of the pressure sensor in the third experimental example of the present invention. Fig. 26 is an enlarged view of the area M2 in Fig. 25, Fig. 27 is a graph to be.
28 and 29 are graphs showing the reliability evaluation results of the pressure sensor in the third experimental example of the present invention.

The following detailed description of the invention refers to the accompanying drawings, which illustrate, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It should be understood that the various embodiments of the present invention are different, but need not be mutually exclusive. For example, certain features, structures, and characteristics described herein may be implemented in other embodiments without departing from the spirit and scope of the invention in connection with an embodiment. It is also to be understood that the position or arrangement of the individual components within each disclosed embodiment may be varied without departing from the spirit and scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is to be limited only by the appended claims, along with the full scope of equivalents to which such claims are entitled, if properly explained. In the drawings, like reference numerals refer to the same or similar functions throughout the several views, and length and area, thickness, and the like may be exaggerated for convenience.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, so that those skilled in the art can easily carry out the present invention.

Method for manufacturing dielectric material for pressure sensor

A method of manufacturing the pressure sensor dielectric 100 according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG.

FIG. 1 is a flowchart showing a method of manufacturing a pressure sensor dielectric 100 according to an embodiment of the present invention. FIG. 2 is a schematic view showing a method of manufacturing a dielectric 100 for a pressure sensor according to an embodiment of the present invention. to be.

Referring to FIG. 1, a method of manufacturing a pressure sensor dielectric 100 includes the steps of (a) mixing two different first polymers 210 and second polymers 220 to produce a polymer mixture 200 (B) mixing the polymer mixture 200 with the foaming agent solution 350 in which the foaming agent 310 and the surfactant 320 are dissolved to prepare a second mixture 300; (c) 300) by mixing an acidic compound (410) and an aqueous acidic compound solution (450) in which the surfactant (320) is dissolved to prepare a dielectric composition (400); and (d) heating the dielectric composition (210) and the second polymer (220).

First, in step (a), two different kinds of polymers may be elastomers having elasticity as a polymer. The polymer used for the pressure sensor dielectric 100 can be restored to its original state after being compressed by external pressure. When compressed by external pressure, the dielectric constant of the dielectric changes and acts as a sensor, restoring the initial state, and the polymer may have elasticity to achieve the same performance over repeated use. Thus, two different polymers according to one embodiment of the present invention may be elastomers with elasticity. According to an embodiment of the present invention, in step (a), the first polymer 210 and the second polymer 220 may be formed of polybutyrate, polyurathane, and polydimethylsiloxane (PDMS) And the like. The first polymer 210 and the second polymer 220 may include polydimethylsiloxane (PDMS) or polybutyrate, preferably comprising a siloxane group (-Si-O-) have.

A polymer mixture 200 in which two different first polymers 210 and second polymers 220 are mixed can be formed. In the case of a dielectric prepared using only one polymer, durability and dielectric constant changes due to elasticity are small. However, when two different polymers are used, the durability is improved and the rate of change of capacitance can be controlled by adjusting the mixing ratio have. This has the effect of controlling the sensitivity, which is one of the factors measuring the performance of the pressure sensor.

According to one embodiment of the present invention, the polymer mixture 200 comprises 35 wt% to 55 wt% of the first polymer 210 and 100 wt% of the second polymer 220 relative to 100 wt% of the polymer mixture 200 45% to 65% by weight.

Since the first polymer 210 and the second polymer 220 are different kinds of polymers, physical properties such as molecular weight and viscosity may be different. Particularly, when a polymer having a higher viscosity is included in a large amount, the viscosity of the pressure sensor dielectric 100 can be increased and the elasticity can be improved. This has the effect of enhancing the durability of the same level of performance even when the pressure sensor is repeatedly used several times. Accordingly, the polymer mixture 200 can be prepared by controlling the mixing ratio of the first polymer 210 and the second polymer 220. [ Preferably, 45% by weight of the first polymer 210 having a low viscosity and 55% by weight of the second polymer 220 are contained.

Next, in step (b), an aqueous foaming agent solution 350 containing the foaming agent 310 and the surfactant 320 may be prepared. The foaming agent 310 may be included to generate gas when the dielectric composition 400 is cured to form the dielectric 100 for a pressure sensor. The blowing agent 310 may generate gas by a temperature change or a chemical reaction. Gas production by heating is simple in process but may change physical properties depending on temperature. However, gas production by chemical reaction can regulate the content of additives and form pores by gas production without changing physical properties.

Surfactant 320 may be included in aqueous foaming agent solution 350 to disperse foaming agent 310 in polymer mixture 200. The foaming agent aqueous solution 350 may be phase separated from the polymer mixture 200 when the foaming agent 310 is ionized in the foaming agent aqueous solution 350 to have polarity and the polymer has hydrophobicity, The gas generated by the foaming agent 310 does not uniformly form pores in the entire region of the polymer, and pores may be formed only in some regions. That is, it means that the pressure sensor dielectric 100 may have different physical properties in some areas. Therefore, the surfactant 320 may be mixed with the foaming agent aqueous solution 350 to disperse the foaming agent 310 into the polymer mixture 200. Surfactant 320 may preferably be sodium dedocylbenzenesulfonate (SDBS).

According to an embodiment of the present invention, in the step (b), the foaming agent 310 is a mixture of H ₂ CO ₃ , LiHCO ₃ , NaHCO ₃ , KHCO ₃ , Mg (HCO ₃ ) ₂ and Ca (HCO ₃ ) ₂ The concentration of the surfactant 320 may be in the range of 0.1 wt% to 0.3 wt%, and the concentration of the foaming agent 310 may be in the range of 2.7 wt% to 4.9 wt%. In the blowing agent aqueous solution 350, have.

The foaming agent 310 may be ionized in the foaming agent aqueous solution 350 and may generate hydrogen carbonate ions (HCO 3 ^- ) with anions. The hydrogen carbonate ion can generate a gas by increasing the temperature or by reacting with the hydrogen ion (H ⁺ ) of the acidic compound. The gas generated by the chemical reaction may be vaporized at the curing temperature of the dielectric composition 400 to form the pores of the dielectric 100 for the pressure sensor. Preferably, the foaming agent 310 may be Baked Soda, which is NaHCO ₃ . The surfactant 320 may be added in a small amount in the foaming agent aqueous solution 350 to disperse the foaming agent 310 in the polymer mixture 200 well. The second mixture 300 produced in the step (b) may form an emulsion in which a hydrophobic polymer and a polar foaming agent aqueous solution 350 are mixed by the surfactant 320.

On the other hand, the foaming agent 310 may affect the size and density of the pores of the pressure sensor dielectric, and the content may be adjusted in the foaming agent aqueous solution 350 to form an emulsion in the second mixture 300 . As the content of the blowing agent 310 increases, the density of the pores can be increased because a large amount of gas is generated. The concentration of the foaming agent 310 in the foaming agent aqueous solution 350 is 2.7% by weight to 4.9% by weight, and the concentration of the surfactant (for example, 320) may be from 0.1% by weight to 0.5% by weight. More preferably, the foaming agent 310 is 5 wt%, and the surfactant 320 is 0.3 wt%.

Next, in step (c), an aqueous acidic compound solution 450 containing the acidic compound 410 and the surfactant 320 may be prepared. The acidic compound (410) may be included to react with the foaming agent (310) to produce gas. Hydrogen carbonate ions contained in the foaming agent 310 react with hydrogen ions of the acidic compound 410 to form a gas. The surfactant 320 may be included in the acidic compound aqueous solution 450 to disperse the acidic compound 410 in the polymer mixture 200 in the same manner as the aqueous foaming agent solution 350.

According to an embodiment of the present invention, in step (c), the pH of the acidic compound 410 is 3 to 5, the concentration of the surfactant 320 in the acidic compound aqueous solution 450 is 0.1% 0.5% by weight, and the concentration of the acidic compound (410) may be 64.7% by weight to 74.9% by weight.

If the pH of the acidic compound 410 is a strong acid, it may affect the polymer of the pressure sensor dielectric 100. Therefore, it is necessary to adjust the pH of the acidic compound 410 to such a degree as to produce gas with the foaming agent 310 have. Preferably, the acidic compound 410 may have a pH of 3.5 and include citric acid (C ₆ H ₈ O ₇ ). The acidic compound 410 may also affect the size and density of the pores of the pressure sensor dielectric 100 and the content of the acidic compound 410 in the aqueous acidic solution 450 may be adjusted so as to form an emulsion in the dielectric composition 400 Lt; / RTI > As the content of the acidic compound (410) increases, the density of the pores can be increased because a large amount of gas is generated. Therefore, in order to manufacture the pressure sensor dielectric 100 having such a sensitivity that it can be used as a pressure sensor, the acidic compound 410 in the acidic compound aqueous solution 450 has a concentration of 64.7 wt% to 74.9 wt% The concentration of the active agent 320 may be 0.1% by weight to 0.5% by weight. More preferably, the concentration of the acidic compound (410) is 70% by weight and the concentration of the surfactant (320) is 0.3% by weight.

The dielectric composition 400 may be prepared by mixing the acidic compound aqueous solution 450 with the second mixture 300. According to one embodiment of the present invention, the pressure sensor dielectric composition 100 includes a polymer mixture 200 in which two different kinds of polymers are mixed, a foaming agent 310, an acidic compound 410 and a surfactant 320 And the aqueous solution may be dispersed in the polymer mixture 200.

In the step (c), the dielectric composition 400 contains 40% by weight to 50% by weight of the total amount of the foaming agent aqueous solution 350 and the acidic compound aqueous solution 450 relative to 100% by weight of the dielectric composition 400, 200) may comprise from 50% to 60% by weight.

The pressure sensor dielectric 100 may be manufactured by curing the dielectric composition 400. The physical properties of the pressure sensor dielectric 100 may vary depending on the composition ratio of the dielectric composition 400. [ The mixing ratio of the polymer mixture 200, the foaming agent solution 350 and the acidic compound aqueous solution 450 contained in the dielectric composition 400 may be controlled to control the composition ratio of the dielectric composition 400 relative to 100% by weight of the dielectric composition 400. The lower the content of the lower viscosity polymer in the polymer mixture 200 and the higher the ratio of the foaming agent 310 to the acid compound 410 in the dielectric composition 400 becomes, The sensitivity of the pressure sensor is increased. Accordingly, the foaming agent 310 and the acidic compound 410 in the dielectric composition 400 may be used in an amount of 40 wt% to 50 wt% based on 100 wt% of the dielectric composition 400, 50 wt% to 60 wt% of the polymer mixture 200, , Preferably 45% by weight of the foaming agent aqueous solution (350) and the aqueous acidic compound solution (450), and 55% by weight of the polymer mixture.

Next, in step (d), the dielectric composition 400 may be heated to cure the first polymer 210 and the second polymer 220. The dielectric composition 400 in which the polymer mixture 200, the foaming agent aqueous solution 350 and the aqueous acidic compound solution 450 are mixed is a material having a liquid viscosity. It is heated and cured to manufacture the dielectric 100 for a pressure sensor.

In step (d), heating is performed at a temperature of 80 to 150 ° C, and the foaming agent 310 and the acidic compound 410 react to form a gas, and the gas forms pores on the matrix of the polymer mixture 200 can do.

When the polymer of the dielectric composition 400 is cured by heating, the foaming agent 310 and the acidic compound 410 can generate gas to form pores on the polymer mixture 200 matrix. When the dielectric composition 400 is heated, the foaming agent 310 and the acidic compound 410 accelerate the reaction to produce a gas, and the gas generated as the polymer cures forms pores on the matrix of the polymer mixture 200. The size and distribution of the formed pores may vary depending on the ratio of the polymer, the foaming agent 310 and the acidic compound 410, and the shape of the pores may vary depending on the curing temperature of the dielectric composition 400.

If the curing temperature of the dielectric composition 400 is high, gas may be generated at a rapid rate to form large pores on the matrix before the polymer is cured. On the other hand, when the curing temperature is low, since the polymer is allowed to cure for a sufficient time, the pore size can be small and can be formed with a uniform distribution. Thus, the curing temperature of the dielectric composition can be adjusted to have the sensitivity required for the pressure sensor dielectric 100. The dielectric composition 400 can be heated at 80 占 폚 to 150 占 폚, and preferably at 110 占 폚.

Pressure sensor manufacturing method

Next, a method of manufacturing the pressure sensor 500 including the dielectric 100 for a pressure sensor according to an embodiment of the present invention will be described with reference to FIG.

3 is a schematic view showing a method of manufacturing the pressure sensor 500 according to an embodiment of the present invention.

First, a completely hardened pressure sensor dielectric 100 is prepared in the form of a substrate, and then silver (Ag) nanowire 600 is spray-coated on the dielectric material 100. Thereafter, The dielectric material 100 is laminated in the form of a substrate. The structure in which the dielectric layer 100 for the pressure sensor is laminated in the form of the nanowire 600 and the dielectric layer 100 for the pressure sensor can form the dielectric electrode 510 in the pressure sensor 500. A pressure sensor dielectric 100 manufactured in the form of a foam is prepared on the dielectric electrode 510. Since the pressure-sensor dielectric material 100 maintained in viscosity maintains the adhesive force, it can be bonded to the foam-type pressure-sensor dielectric material 100. After bonding the dielectric 100 for a pressure sensor in the form of a foam, the pressure sensor dielectric 100 in the form of a partially cured substrate is heated until it is completely cured.

A unit cell of the pressure sensor 500 is formed by laminating the dielectric electrode 510 on the foamed dielectric electrode 510 and completely curing it. When the unit cells are patterned in an array form, the pressure sensor 500 can be manufactured.

Example 1

Hereinafter, a pressure sensor dielectric using polydimethylsiloxane (PDMS) and Ecoflex according to an embodiment of the present invention will be described with reference to FIGS. 4 to 10. FIG.

Analysis of porosity according to curing temperature

Referring to Figs. 4 to 6, the shape of the pores formed in the pressure sensor dielectric according to the curing temperature of the dielectric composition will be described.

First, a sample used for analysis of pore shape will be described. In this experiment, the polymer used was a PDMS polymer, 7 wt% NaHCO ₃ as a foaming agent, and 16 wt% citric acid as an acidic compound.

The PDMS polymer and the curing agent were mixed at a weight ratio of 10: 1 to prepare a mixture. An aqueous NaHCO ₃ solution of 7 wt% and an aqueous solution of 16 wt% of citric acid were sequentially mixed to prepare a mixture of NaHCO ₃ and citric acid aqueous solution Weight%. The dielectric composition is a mixture of PDMS polymer and NaHCO ₃ and citric acid to form an emulsion. The dielectric material for a pressure sensor prepared by heating the dielectric composition at a curing temperature of 80 ° C, 90 ° C, 100 ° C, 110 ° C, 120 ° C, 130 ° C and 150 ° C to cure the PDMS polymer was analyzed by a scanning electron microscope SEM). The pressure sensor dielectrics were referred to as Comparative Examples 1 to 7 respectively according to the curing temperature.

4 and 5 are scanning electron microscopy (SEM) photographs showing pores formed on the surface according to comparative examples of the present invention. Figs. 4 (a) to 4 (g) are SEM photographs showing cross sections of the pressure sensor dielectrics of Comparative Examples 1 to 7 at 100 times magnification, Figs. 5 (a) Sectional view of the dielectric of the pressure sensor of Fig.

4 and 5, pores having a micrometer-unit size of 100 μm or more are formed in the dielectric substance for pressure sensor of Comparative Examples 1 to 7, and small pores having a micrometer-unit size of 1 μm or more and 100 μm or less It can be seen that it is distributed in the whole area. It is also seen that as the curing temperature of the dielectric composition is lowered, the pore size becomes smaller and the distribution becomes uniform.

On the other hand, pores having a micrometer-unit size of 100 μm or more, when the curing temperature is high, can generate gases at a high rate during the reaction of NaHCO ₃ and citric acid. A large amount of gas is generated before the polymer PDMS is cured, . It can be seen that the dielectric bodies having the curing temperatures of 120 캜, 130 캜 and 150 캜 of Comparative Examples 5 to 7 have uneven distribution of pores.

On the other hand, in the case of pores having a micrometer-unit size of 1 μm or more and 100 μm or less, the size of the pores according to the curing temperature hardly changes, but as the curing temperature is lower, And the size of the light-emitting layer becomes uniform. This means that large size pores are not formed because the curing temperature is low and gas is generated at a slow rate and a sufficient time is secured for the PDMS polymer to cure.

6 shows the dielectric constant change experiment result of the dielectric for pressure sensor according to one comparative example of the present invention.

The dielectric constant change with respect to the external pressure was measured using the PDMS dielectric cured at 150 ° C. of Comparative Example 7.

Referring to (a) of Figure 6, according to the intensity of the pressure applied from the outside, to measure the dielectric constant of the initial ₍₀ C) amount of change in dielectric constant (ΔC) of the capacitance change rate (ΔC / C ₀₎ for. The external pressure was applied for 3 seconds, and then removed again.

It can be seen that the dielectric sample of Comparative Example 7 had the same level of capacitance change rate (? C / C ₀ ) even after repeating the experiment of applying and removing pressure. When the external pressure is increased, the capacitance change rate? C / C ₀ also increases. This means that when the pressure sensor is manufactured including the comparative example 7, it can have the same performance even after repeated use for several times.

Referring to FIG. 6 (b), the rate at which the dielectric constant changes when external pressure is applied to and removed from the dielectric sample of 7 for 3 seconds at an intensity of 15.85 kPa can be seen. The gajida the electrostatic capacity change rate of the value (ΔC / C ₀₎ is 0, the capacitance change rate (ΔC / C ₀₎ time of 300ms or less until the have a maximum value of the take when the external pressure is applied. This means that the response speed to the external pressure of the dielectric of Comparative Example 7 is very good.

Accordingly, the pressure sensor dielectric increases the size of the pores to be formed as the curing temperature of the polymer increases, and the durability and sensitivity of the dielectric with pores can be improved.

Example 2

Performance Analysis of Ecoplex / PDMS Pressure Sensor Dielectric

Hereinafter, performance analysis of a pressure sensor dielectric using Ecoplex and PDMS as a polymer will be described with reference to FIGS. 7 to 10. FIG.

First, PDMS and Ecoflex which are polymers forming the pressure sensor dielectric will be described.

PDMS is an elastomer containing siloxane and is polydimethylsiloxane. Ecoflex is a polymer with elasticity and is classified as polybutyrate (Polybutyrate Adipate Terephthalate, PBAT). Hereinafter, they are referred to as PDMS and Ecoflex, respectively.

In step (a), a polymer mixture is prepared by mixing PDMS and Ecoflex. Both polymers can be mixed well together. Stir using a stick to produce a homogeneous mixture. At this time, the mixing ratio can be adjusted. The mixing ratio is such that the amount of Ecoflex is 35% by weight, 45% by weight and 55% by weight based on 100% by weight of the polymer mixture. These are defined as 35 wt% Ecoflex / PDMS, 45 wt% Ecoflex / PDMS and 55 wt% Ecoflex / PDMS, respectively.

Next, foaming agents, acidic compounds and surfactants in steps (b) and (c) will be described.

Sodium bicarbonate (NaHCO ₃ ) was used as the foaming agent, Citric acid (C ₆ H ₈ O ₇ ) was used as the acidic compound and Sodium dedocylbenzenesulfonate (SDBS) was used as the surfactant. Prepare. Sodium bicarbonate reacts with citric acid to produce CO ₂ gas and H ₂ O. The CO ₂ gas can evaporate and form pores on the Ecoflex / PDMS polymer matrix.

Sodium hydrogencarbonate is dissolved in SDBS surfactant and water to prepare an aqueous foaming agent solution. An aqueous foaming agent solution (NaHCO ₃ / SDBS (aq)) is prepared so that the concentration of sodium hydrogencarbonate and SDBS is 3 wt%, 5 wt% and 7 wt% in total. Then, citric acid is dissolved in SDBS surfactant and water to prepare an acidic compound aqueous solution. An aqueous acidic compound solution (citric acid / SDBS (aq)) is prepared so that the concentration of citric acid and SDBS is 70% by weight. A small amount of SDBS surfactant is added compared to solute NaHCO ₃ and citric acid. For example, the mass ratio of the SDBS: solution may be 0.3: 100.

The prepared NaHCO ₃ / SDBS (aq) and citric acid / SDBS (aq) contain a surfactant to be well dispersed in the Ecoflex / PDMS polymer. When only the PDMS polymer is included, it is dispersed even if there is no surfactant, but when the more hydrophobic Ecoflex is included, the aqueous solution needs to be dispersed by the surfactant. In the case of citric acid, however, even when the aqueous solution has a concentration of 70% by weight, when the aqueous solution is mixed with the Ecoflex / PDMS polymer, the aqueous solution is well dispersed without causing phase separation, When the concentration is more than the concentration by weight, the polymer and the aqueous solution may cause phase separation.

7 is a photograph showing sodium hydrogencarbonate and citric acid aqueous solution according to an embodiment of the present invention.

Referring to FIG. 7, it can be seen that sodium hydrogencarbonate and citric acid, including SDBS surfactant, are well dissolved in water. When the concentration of sodium hydrogencarbonate is 7% by weight, the aqueous solution has a slightly cloudy color, and the other aqueous solution samples are all transparent.

Next, a dielectric substance for a pressure sensor manufactured by using the Ecoflex / PDMS polymer, NaHCO ₃ / SDBS (aq) and citric acid / SDBS (aq) according to an embodiment of the present invention will be described.

Table 1 below is a table summarizing examples of the dielectric composition for a pressure sensor prepared by mixing the Ecoflex / PDMS polymer, NaHCO ₃ / SDBS (aq) and citric acid / SDBS (aq) at different ratios.

sample
Type of Ecoflex / PDMS polymer (weight fraction of Ecoflex,% by weight)
The dielectric composition NaHCO3 ₃  And weight fraction (% by weight) of citric acid aqueous solution Example 1 Ecoflex / PDMS 35 wt% 40 wt% Example 2 Ecoflex / PDMS 35 wt% 50 wt% Example 3 Ecoflex / PDMS 45 wt% 40 wt% Example 4 Ecoflex / PDMS 45 wt% 50 wt% Example 5 Ecoflex / PDMS 55 wt% 40 wt%

Referring to Table 1, NaHCO3 / SDBS (aq) and citric acid / SDBS (aq) were mixed with a sample of Ecoflex of 35 wt%, 45 wt% and 55 wt% in the polymer of Ecoflex / . In this case, NaHCO 3 / SDBS (aq) and citric acid / SDBS (aq) were prepared in a total amount of 40% by weight or 50% by weight based on 100% by weight of the dielectric composition for pressure sensor.

The capacitance change rate (? C / C ₀ ) was measured as in the 'analysis of the pore shape according to the curing temperature' to test the performance of the pressure sensor.

First, in order to compare the performance of the dielectric material for a pressure sensor according to the curing temperature of the dielectric composition, the dielectric material of Example 2 was cured at 100 ° C or 150 ° C to prepare a pressure sensor dielectric, and the capacitance change rate ₀ ) was measured.

FIG. 8 shows the experimental result of the capacitance change rate (? C / C ₀ ) measurement of the dielectric for a pressure sensor according to an embodiment of the present invention.

8 (a) and 8 (b), a dielectric material for a pressure sensor manufactured by heating the dielectric composition of Example 2 at a curing temperature of 100 캜 or 150 캜 showed a capacitance change rate (? C / C ₀ ) It can be seen that the value is maintained at the same level as the initial value. That is, it is durable to pressure change and hysteresis appears because it contains the elastomer Ecoflex / PDMS. If higher the curing temperature of the dielectric composition, pressure pores formed in the sensor dielectric for the size of the larger I, (a) and (b) the comparison if the electrostatic capacity change rate with respect to the pressure to be applied in Fig. 8 (ΔC / C ₀₎ The slope of the graph has a large value when the curing temperature is 150 ° C. This means that the higher the curing temperature, the larger the pore size and the greater the sensitivity to the pressure sensor.

If in order to verify this in detail, with reference to (c) and (d) of Figure 8, the curing temperature when the dielectric for a high pressure sensor 150 ℃, applied to a small external pressure even when the capacitance change rate (ΔC / C ₀ ) Is increased. In order to quantify this, the slope of the graph of the capacitance change rate (ΔC / C ₀ ) is calculated as follows. When the curing temperature of the dielectric composition is 100 ° C. and 150 ° C., the slopes of the graphs are 0.18 / kPa and 0.0099 kPa, respectively. Accordingly, it can be seen that as the curing temperature of the dielectric composition increases, the size of the pores formed in the dielectric for the pressure sensor increases, and the sensitivity increases as the pressure sensor has improved performance.

Next, referring to Figs. 9 and 10, performance analysis of a dielectric material for a pressure sensor according to the ratio of the Ecoflex polymer in the polymer of Ecoflex / PDMS and the ratio of NaHCO3 / SDBS (aq) and citric acid / SDBS (aq) Will be described.

Examples 1 to 5 the dielectric composition of the heating at the curing temperature of 110 ℃ to prepare a dielectric for the pressure sensor, the compressed elongation according to the applied compressive stress (Compressive stress) (Compressive strain) and the capacitance change rate (ΔC / C ₀ ).

9 is a graph of compressive stress-compression elongation of a dielectric for a pressure sensor according to embodiments of the present invention.

9 (a) to 9 (e), it can be seen that the compressive stress-compression elongation graphs of the dielectrics for the pressure sensors of Examples 1 to 5 have different curves according to the contents of Ecoflex, NaHCO ₃ and citric acid . A low value of the slope of the curve means that the strain rate of the dielectric against stress is large, which means that it has high sensitivity as a pressure sensor.

Referring to FIG. 9 (f), the influence of the content of Ecoflex, NaHCO ₃ and citric acid in the pressure sensor dielectric material on the performance of the pressure sensor will be described.

First, Examples 1 and 5 and Examples 2 and 4, in which the contents of NaHCO ₃ and citric acid are the same and the curing temperature is the same and the content of Ecoflex is different, are compared. In both cases, the graph slope of Example 1, Example 2, where the content of Ecoflex is lower, has a lower value. This is because PDMS has a higher viscosity than Ecoflex, so that when the content of Ecoflex is lowered when the polymer is cured by heating, the effect of increasing the size of pores due to gas evolution is obtained. Thus, the lower the content of Ecoflex in the Ecoflex / PDMS polymer, the greater the pore size of the dielectric for the pressure sensor and the higher the sensitivity to pressure.

Next, Examples 1 and 2 in which the content of Ecoflex and the curing temperature are the same and the contents of NaHCO ₃ and citric acid are different are compared. The graph slope of Example 2, where the content of NaHCO ₃ and citric acid is larger, has a smaller value. This is because as the ratio of NaHCO ₃ and citric acid increases, the pore size decreases but the density increases. When the density of the pores is increased, the pressure sensor dielectric has a large number of pores, so that it is possible to perform comparatively more compression, and the elongation rate is increased, so that the slope of the graph becomes smaller. That is, the higher the content of NaHCO ₃ and citric acid, the smaller the pore size of the pressure sensor dielectric, but the density of pores increases and the sensitivity to pressure increases.

According to the above embodiments, the lower the content of Ecoflex in the Ecoflex / PDMS polymer is, the higher the content of NaHCO ₃ and citric acid in the dielectric composition, the higher the curing temperature, ₀ ) and the sensitivity increase, the performance of the pressure sensor is improved.

10 is a graph showing a result of measuring a capacitance change rate (? C / C ₀ ) of a dielectric substance for a pressure sensor according to embodiments of the present invention.

According to Fig. 10, the pressure of 35 wt% Ecoflex / PDMS and NaHCO ₃ , which is Example 2 in which the content of Ecoflex in the Ecoflex / PDMS polymer is low and the content of NaHCO ₃ and citric acid in the dielectric composition is high, It can be seen that the sensor dielectric has the largest slope in the graph of the capacitance change rate (? C / C ₀ ).

Therefore, according to one embodiment of the present invention, it is possible to produce a pressure sensor dielectric by mixing and heating two different kinds of polymers with a foaming agent, an acidic compound and a surfactant, and the mixing ratio of the polymer, the foaming agent, So that the performance of the pressure sensor including the dielectric can be improved.

Example 3

Hereinafter, a mixture of Ecoplex and PDMS as a polymer mixture, sodium bicarbonate (NaHCO ₃ ) as a foaming agent, acetic acid (CH ₃ COOH) as an acidic compound, sodium Sodium dedocylbenzenesulfonate (SDBS) is prepared to prepare the dielectric for a pressure sensor described with reference to Figs. 1 and 2. Fig.

In the second embodiment, citric acid (C ₆ H ₈ O ₇ ) was used as the acidic compound. In order to overcome the disadvantage that it takes several tens of seconds to recover the initial capacitance due to viscosity when citric acid is used, It was replaced with (CH ₃ COOH).

In this case, when sodium bicarbonate (NaHCO ₃ ) is used as a foaming agent and acetic acid (CH ₃ COOH), which is an acidic compound, is used, a chemical reaction as shown in Chemical Formula 1 occurs.

[Chemical Formula 1]

NaHCO ₃ + CH ₃ COOH - > CO ₂ + H ₂ O + NaCH ₃ COO

1 mole of NaHCO ₃ reacts with 1 mole of CH ₃ COOH to produce 1 mole of CO ₂ as shown in Formula 1, so that NaHCO ₃ solution and CH ₃ COOH solution are uniformly mixed in the elastomer so that the mole number of NaHCO ₃ 3 and CH ₃ COOH is the same After mixing, the pore formation was induced by thermosetting.

Table 2 below is a table summarizing the weight ratio of Ecoflex in the polymer mixture and the weight ratio of the foaming agent and the acidic compound in the dielectric composition together with the curing temperature in the third experimental example.

Ecoflex / (PDMS + Ecoflex)
(Weight of NaHCO ₃ + CH ₃ COOH) / (weight of PDMS + weight of Ecoflex + weight of NaHCO ₃ + weight of CH ₃ COOH)
Curing temperature 70wt% 33wt% 80 ℃ 70wt% 33wt% 100 ℃ 70wt% 33wt% 120 DEG C

11 is a scanning electron microscopy (SEM) photograph of a section of a dielectric according to the curing temperature in the third experimental example of the present invention. The photographs at the top are relatively low magnification, and the photographs at the bottom are relatively high magnification.

Referring to FIG. 11, it can be seen that as the curing temperature of the third experimental example increases to 80 ° C., 100 ° C. and 120 ° C., the pore size increases and the interval between the pores decreases. It can be confirmed that the pore size increases with the increase in the curing temperature and the interval between the pores decreases with the curing temperature in the range of 80 to 120 ° C. These results show that the curing temperature of 120 ℃ is the best in terms of the sensitivity of the pressure sensor. The curing temperature of the elastomer mixture of Ecoplex and PDMS is sufficient within 150 캜, and the curing temperature of 120 캜 can be set as an optimum embodiment.

12 is a graph showing the relationship between the pressure of the pressure sensor dielectric and the capacitance change rate (? C / C ₀ ) according to the curing temperature in the third experimental example of the present invention. Referring to FIG. 12, the pressure sensor device was manufactured according to the curing temperature, and the measurement was performed. When the curing temperature was 120 ° C at 80 ° C, 100 ° C, or 120 ° C, .

13 is a graph showing the relationship between compressive stress and compressive strain of a dielectric for a pressure sensor according to the curing temperature in the third experimental example of the present invention. Referring to FIG. 13, as the curing temperature increases to 80 ° C, 100 ° C, and 120 ° C, it can be seen that the compressive stress applied when the compressive strain is the same decreases. This is because the Young's modulus due to pore decreases It is because.

14 to 16 are graphs obtained by dividing sensitivity according to the curing temperature of the pressure sensor dielectric according to the curing temperature according to the pressure range in the third experiment example of the present invention. Referring to FIGS. 14 to 16, it can be confirmed that the sensitivity is the best in all the pressure ranges at the curing temperatures of 80 ° C, 100 ° C and 120 ° C and 120 ° C.

Table 3 below is a table summarizing the conditions for varying the ratio of the pore-forming precursor under the condition that the weight ratio of the Ecoflex in the polymer mixture and the curing temperature are fixed in the third experiment example. The ratio of the pore-forming precursor corresponds to the weight ratio of NaHCO ₃ , which is a blowing agent, and CH ₃ COOH, which is an acidic compound, relative to the total weight of the dielectric composition.

Ecoflex / (PDMS + Ecoflex)
(Weight of NaHCO ₃ + CH ₃ COOH) / (weight of PDMS + weight of Ecoflex + weight of NaHCO ₃ + weight of CH ₃ COOH)
Curing temperature 70wt% 0wt% 120 DEG C 70wt% 28wt% 120 DEG C 70wt% 33wt% 120 DEG C 70wt% 38wt% 120 DEG C

17 is a graph showing the result of micro CT analysis of a dielectric material for a pressure sensor according to the ratio of pore forming precursor in the third experiment example of the present invention.

Referring to FIG. 17, porosity decreases gradually to 73.614%, 72.533%, and 67.897% as the ratio of pore-forming precursors increases to 28 wt%, 33 wt%, and 38 wt%, respectively. As can be seen, the pore size gradually decreases.

18 is a graph showing the relationship between the pressure of the pressure sensor dielectric and the rate of change in capacitance (? C / C ₀ ) according to the ratio of pore-forming precursor in the third experimental example of the present invention. 19 to 21 are graphs obtained by dividing the sensitivity of the pressure sensor dielectric according to the pressure range according to the pore forming precursor ratio in the third experimental example of the present invention.

18 to 21, since the pores are formed due to the reaction of NaHCO ₃ , which is a foaming agent, and CH ₃ COOH, which is an acidic compound, the sensitivity is greatly improved in the whole region, but the sensitivity of 2kPa It can be seen that the sensitivity decreases below. Considering this point, it can be confirmed that the sensitivity and uniformity are optimum in the case where the pore-forming precursor ratio is 33 wt%.

FIG. 22 is a diagram showing an experimental result in which the lowest pressure measurable by the pressure sensor is evaluated in the third experimental example of the present invention. FIG.

22, the capacitance was measured by increasing the number of 10-mg objects in order to determine the lowest measurable pressure of a pressure sensor element manufactured with a 33 wt% sensor body in which the pore-forming precursor ratio was an optimum embodiment. According to this, it can be confirmed that the minimum pressure measurable by the pressure sensor is 0.915 Pa.

FIG. 23 is a graph showing the reaction time according to the pressure of the pressure sensor in the third experimental example of the present invention, and FIG. 24 is an enlarged graph of the area M1 of FIG. That is, the graphs were measured to confirm whether the pore formation precursor ratio closely follows the reaction time and the pressure change of the pressure sensor element manufactured with the 33 wt% sensor body as the optimum embodiment.

Referring to FIG. 23, when the reaction time is confirmed with 0.4 kPa pressure applied, the minimum time of 75 ms is required in the limit of the measuring equipment. Therefore, it is considered that the reaction time is suitable for use as a pressure sensor.

25 is a graph showing the reaction time according to the pressure of the pressure sensor in the third experimental example of the present invention. FIG. 26 is an enlarged view of the area M2 in FIG. 25, FIG. 27 is a graph to be. 25 to 27 correspond to the capacitance change rate (? C / C ₀ ) and the hollow (?,?,?) Items correspond to the pressure (kPa) Value.

Referring to FIGS. 25-27, it is possible to confirm that the change in capacitance due to the change in pressure is greater for larger pressures. According to this, it can be seen that the capacitance of the device and the change of the pressure closely follow both the increase and decrease of the pressure.

28 and 29 are graphs showing the reliability evaluation results of the pressure sensor in the third experimental example of the present invention. Here, a pressure sensor element made of a 33 wt% sensor body in which the pore forming precursor ratio is the optimum embodiment was used.

Referring to FIG. 28, it can be seen that the device responds well to the real-time pressure change. Referring to FIG. 29, when the pressure is repeatedly applied to the two pressures (25 kPa, 50 kPa) It can be confirmed that the performance is maintained well.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken in conjunction with the present invention. Variations and changes are possible. Such variations and modifications are to be considered as falling within the scope of the invention and the appended claims.

100: Dielectric for pressure sensor
200: polymer mixture
210: First polymer
220: Second polymer
300: second mixture
310: foaming agent
320: Surfactant
350: aqueous solution of foaming agent
400: dielectric mixture
410: acidic compound
450: aqueous solution of an acidic compound
500: Pressure sensor
510: dielectric electrode
600: nanowire

Claims (14)

(a) mixing two different types of first and second polymers to produce a polymer mixture;
(b) mixing the polymer mixture with an aqueous foaming agent solution in which the foaming agent and the surfactant are dissolved to prepare a second mixture;
(c) mixing the second mixture with an acidic compound and an aqueous solution of an acidic compound in which the surfactant is dissolved to prepare a dielectric composition; And
(d) curing the first polymer and the second polymer by heating the dielectric composition;
And forming a dielectric layer on the dielectric layer. The method according to claim 1,
In the step (a), each of the first polymer and the second polymer may be at least one selected from the group consisting of polybutyrate, polyurethane, and polydimethylsiloxane (PDMS) / RTI > The method according to claim 1,
In the step (b), wherein the blowing agent comprises _{H 2 CO 3, LiHCO 3,} NaHCO 3, KHCO 3, Mg (HCO 3) 2 and Ca (HCO ₃₎ at least one selected from the group consisting of _2,
In the step (c), the acidic compound includes citric acid (C ₆ H ₈ O ₇ ) or acetic acid (CH ₃ COOH)
A method for manufacturing a dielectric for a pressure sensor. The method according to claim 1,
In the step (c), the weight ratio of the foaming agent to the acidic compound in the dielectric composition is 25 wt% to 40 wt%
Wherein, in the step (d), the heating is carried out at a temperature of 80 ° C to 150 ° C.
A method for manufacturing a dielectric for a pressure sensor. The method according to claim 1,
In at least one of the steps (c) to (d)
Wherein the foaming agent reacts with the acidic compound to form a gas, and the gas forms pores on the polymeric mixture matrix. The method according to claim 1,
The higher the content of the polymer having a higher viscosity is higher, the content of the foaming agent is higher, the content of the acidic compound is higher, the size of the pores becomes larger, and the pressure of the dielectric Is increased,
A method for manufacturing a dielectric for a pressure sensor. A polymer mixture in which two different first and second polymers are mixed is used as a matrix,
Characterized in that pores are formed in the polymeric mixture matrix.
Dielectric for pressure sensors. 8. The method of claim 7,
Wherein the first polymer and the second polymer are at least any one selected from the group consisting of polybutyrate, polyurethane and polydimethylsiloxane (PDMS)
Dielectric for pressure sensors. 8. The method of claim 7,
Wherein the pores are formed in the polymer mixture matrix by a gas produced by a reaction of a foaming agent and an acidic compound.
Dielectric for pressure sensors. 10. The method of claim 9,
Wherein the foaming agent comprises at least one selected from the group consisting of H ₂ CO ₃ , LiHCO ₃ , NaHCO ₃ , KHCO ₃ , Mg (HCO ₃ ) ₂ and Ca (HCO ₃ ) ₂ ,
Wherein the acidic compound comprises citric acid (C ₆ H ₈ O ₇ ) or acetic acid (CH ₃ COOH)
Dielectric for pressure sensors. An upper electrode and a lower electrode spaced apart from each other; And
A dielectric layer for pressure sensor having pores formed in the matrix of the polymer mixture, the polymer mixture being sandwiched between the upper electrode and the lower electrode and having two kinds of different first polymer and second polymer mixed, ≪ / RTI >
Capacitive pressure sensor. 12. The method of claim 11,
Wherein the first polymer and the second polymer are at least any one selected from the group consisting of polybutyrate, polyurethane and polydimethylsiloxane (PDMS)
Capacitive pressure sensor. 12. The method of claim 11,
Wherein the pores are formed in the polymer mixture matrix by a gas produced by a reaction of a foaming agent and an acidic compound.
Capacitive pressure sensor. 14. The method of claim 13,
Wherein the foaming agent comprises at least one selected from the group consisting of H ₂ CO ₃ , LiHCO ₃ , NaHCO ₃ , KHCO ₃ , Mg (HCO ₃ ) ₂ and Ca (HCO ₃ ) ₂ ,
Wherein the acidic compound comprises citric acid (C ₆ H ₈ O ₇ ) or acetic acid (CH ₃ COOH)
Capacitive pressure sensor.

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