KR102448894B1 - Holographic metasurface gas sensors and wearable device including same - Google Patents

Abstract

According to one aspect of the present invention, provided is a holographic metasurface gas sensor which comprises: a metasurface layer where a plurality of nanostructures are provided; and liquid crystal layer provided on one side of the metasurface layer, and including a plurality of cells, of which arrangement can be changed by a specific substance coming in contact with the cells. The liquid crystal layer can change a polarized state of transmitted light penetrating the liquid crystal layer by changing arrangement of the plurality of cells by contact of the specific substance.

Description

Holographic metasurface gas sensors and wearable devices including the same

The present invention relates to a holographic metasurface gas sensor and a wearable device including the same.

A hologram refers to an image implemented using interference of light. Specifically, a hologram is a technology that can reproduce a three-dimensional shape, and by using the characteristics of a laser, the information of each part of an object is converted into a three-dimensional shape by the interference phenomenon between the object wave reflected from the object and the reference wave going straight from another angle. technology that can be regenerated. Such a hologram can be divided into a transmissive hologram, in which an image is formed as a reference wave passes through a hologram device, and a reflective hologram, in which an image is formed as the reference wave is reflected by the hologram device. The hologram technology used or used for anti-counterfeiting, etc. is a reflective hologram.

This hologram technology can be implemented through a metasurface, which is a nanostructure that is much thinner than the thickness of a human hair. Conventional reflective metasurface-based holograms use a metal-insulator-metal (MIM) structure, Although it has been implemented using a structure, the hologram of the MIM structure has a disadvantage in that it cannot be used in the entire visible light region due to the loss characteristics of the metal in the short-wavelength visible light region.

In addition, in the case of a non-metal, a hologram having a structure using titanium dioxide (TiO ₂ ) has a problem in that a structure having a high aspect ratio has to be made due to a relatively lower refractive index than that of a metal. In addition, in order to realize a high aspect ratio, a problem in that the manufacturing cost of the hologram is greatly increased may occur.

In addition, gas accidents occur every year in factories, sewerage systems, and electric fields. Existing risk detection sensors are composed of complex mechanical and electronic devices. There are disadvantages such as structure/material change.

Embodiments of the present invention are proposed to solve the above problems, and include a holographic metasurface gas sensor capable of generating different holographic images in real time by an external stimulus (eg, volatile gas) and the same To provide a wearable device that

Another object of the present invention is to provide a holographic metasurface gas sensor capable of detecting toxic gas (eg, volatile gas) in real time and providing a visual alarm function through holographic image information, and a wearable device including the same.

According to an aspect of the present invention, a meta-surface layer provided with a plurality of nanostructures; It is provided on one side of the meta-surface layer and includes a liquid crystal layer comprising a plurality of cells whose arrangement can be changed by a specific material in contact, wherein the liquid crystal layer comprises a plurality of cells by contact of the specific material. A holographic metasurface gas sensor capable of changing the polarization state of transmitted light passing through the liquid crystal layer by changing the arrangement can be provided.

In addition, when air not containing the specific material is in contact with the liquid crystal layer, the cells of the liquid crystal layer adjacent to the meta surface layer are aligned in one direction, and the cells of the liquid crystal layer in contact with the air are in the one direction and A holographic metasurface gas sensor that aligns in a different direction may be provided.

In addition, a holographic metasurface gas sensor may be provided in which the cells aligned in one direction form an angle of 3° to 5° with the polyimide coating layer.

In addition, there may be provided a holographic metasurface gas sensor in which the cells aligned in different directions are disposed at an angle perpendicular to the polyimide coating layer.

In addition, as the cell of the liquid crystal layer in contact with the air approaches the cell of the liquid crystal layer adjacent to the meta surface layer, a holographic meta surface gas sensor in which the angle between the cell and the polyimide coating layer becomes smaller can be provided. .

In addition, when a specific material is diffused into the liquid crystal layer, the liquid crystal layer may include an isotropic layer in which 4-cyano-4'-pentylbiphenyl is changed into an isotropic phase; and an anisotropic layer having 4-cyano-4'-pentylbiphenyl not in contact with a specific material may be provided.

In addition, when a specific material is in contact with the liquid crystal layer, at least a portion of the liquid crystal layer including the cell in contact with the specific material is changed to an isotropic layer having an isotropic phase may be provided with a holographic metasurface gas sensor. .

In addition, the isotropic layer having the isotropic phase may be provided with a holographic metasurface gas sensor that extends toward the metasurface layer over time.

In addition, the cell is provided with 4-cyano-4'-pentylbiphenyl, and 4-cyano-4'-pentylbiphenyl included in the anisotropic layer is at an angle of 25˚ to 30˚ at the interface of the isotropic layer. A holographic metasurface gas sensor with

In addition, when air not containing the specific material is in contact with the liquid crystal layer, the first image I1 is generated by the transmitted light passing through the liquid crystal layer and the meta surface layer, and the specific material is in contact with the liquid crystal layer In this case, a holographic metasurface gas sensor in which the second image I2 is generated by the transmitted light passing through the liquid crystal layer and the metasurface layer may be provided.

In addition, a holographic metasurface gas sensor in which the first image I1 and the second image I2 are generated as different holograms may be provided.

In addition, a change from the first image I1 to the second image I2 may be provided with a holographic metasurface gas sensor that occurs within 1 second after exposure to a volatile gas.

In addition, a holographic metasurface gas sensor in which the specific material is provided as a volatile gas may be provided.

In addition, the specific material may be provided with a holographic metasurface gas sensor provided with isopropyl alcohol (IPA).

In addition, the meta surface layer, the substrate layer comprising a polyimide coating layer in contact with the liquid crystal layer; and a holographic metasurface gas sensor including a plurality of nanostructures disposed on the upper side of the substrate layer.

In addition, the plurality of nanostructures includes a nanostructure included in the first group of nanostructures and a nanostructure included in the second group of nanostructures, wherein the nanostructures and the second nanostructure included in the first group of nanostructures are included. The nanostructures included in the structure group may be provided with a holographic metasurface gas sensor arranged to be orthogonal to each other.

In addition, the substrate layer of the metasurface layer may be provided with a holographic metasurface gas sensor provided as a deformable flexible substrate.

In addition, the nanostructure may be provided with a holographic metasurface gas sensor made of hydrogenated amorphous silicon.

In addition, the meta surface layer may be provided with a holographic meta surface gas sensor including a polyimide coating layer for aligning cells in one direction on a surface facing the liquid crystal layer.

In addition, the nanostructure may be provided with a holographic metasurface gas sensor including titanium dioxide nanoparticles.

According to one aspect of the present invention, as a wearable device that can be worn on a user's body, a wearable device to which the holographic metasurface gas sensor described in claim 1 is attached may be provided to a part of the wearable device.

A holographic metasurface gas sensor and a wearable device including the same according to embodiments of the present invention may generate different holographic images in real time by an external stimulus (eg, volatile gas).

In addition, it is possible to provide a visual alarm function through holographic image information by detecting toxic gas (eg, volatile gas) in real time.

1 is a diagram schematically showing a holographic metasurface gas sensor 1 according to an embodiment of the present invention.
FIG. 2 is a view showing that when incident light L1 is transmitted through the holographic metasurface gas sensor 1 of FIG. 1, different images are generated depending on whether the volatile gas is in contact.
FIG. 3 is a diagram schematically showing a part of the metasurface layer 10 of the holographic metasurface gas sensor 1 of FIG. 1 .
FIG. 4 is a diagram conceptually illustrating a change in the arrangement of cells 202 according to whether a volatile gas is in contact with the liquid crystal layer 20 of FIG. 1 .
FIG. 5 is a view showing changes in the liquid crystal layer 20 according to the contact between the holographic metasurface gas sensor 1 of FIG. 1 and the volatile gas.
6 is a graph showing the thickness of the isotropic layer 20B and the phase delay τ of the cell 202 generated over time after the contact of the volatile gas with the holographic metasurface gas sensor 1 of FIG. 1 . .
FIG. 7 is a diagram illustrating phase coverage and wavefront modulation of light passing through the nanostructure 102 according to the size and arrangement of the nanostructure 102 of the metasurface layer 10 of FIG. 1 . .
8 is a diagram illustrating a simulation for designing an optimal size of the nanostructure 102 .
FIG. 10 is a photograph of actually manufacturing the holographic metasurface gas sensor 1 of FIG. 1 .
11 is a photograph of attaching the holographic metasurface gas sensor 1 of FIG. 10 to goggles, which are wearable devices having a curved surface.
12 shows the wavelength of incident light L1 of the nanostructure 102 including titanium dioxide nanoparticles (TIO ₂ NPs) and the nanostructure 102 made of hydrogenated amorphous silicon (a-Si;H). The image resolution according to

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. In addition, in describing the present invention, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

FIG. 1 is a view schematically showing a holographic metasurface gas sensor 1 according to an embodiment of the present invention, and FIG. 2 is a holographic metasurface gas sensor 1 of FIG. It is a diagram showing that different images are generated depending on whether the volatile gas is in contact with the FIG. 4 is a diagram conceptually illustrating a change in the arrangement of cells 202 according to whether a volatile gas is in contact with the liquid crystal layer 20 of FIG. 1 .

Each configuration of the meta surface layer 10 and the liquid crystal layer 20 (eg, the size of the nanostructure 102 and the cell 202 , etc.) shown in FIGS. 1 to 4 is exaggerated to help understanding. .

1 to 4, the holographic metasurface gas sensor 1 according to an embodiment of the present invention includes a metasurface layer 10 provided with a plurality of nanostructures 102; and a liquid crystal layer 20 provided on one side of the metasurface layer 10 and including a plurality of cells 202 whose arrangement can be changed by a specific material in contact.

Here, the specific material may be a volatile gas, and the volatile gas may include isopropyl alcohol (IPA).

The toxicity of isopropyl alcohol (IPA) is known to cause abdominal pain, confusion, dizziness and slow breathing, and is suspected as one of the leading causes of leukemia in the semiconductor industry.

The holographic metasurface gas sensor 1 of this embodiment can visually inform immediately whether such toxic isopropyl alcohol (IPA) has leaked through a hologram. risk can be eliminated.

However, the spirit of the present invention is not limited thereto, and specific substances may include toxic liquids and solids in addition to gases.

The holographic metasurface gas sensor 1 of this embodiment combines the liquid crystal layer 20 and the metasurface layer 10 provided as liquid crystal, so that even if a trace amount (for example, 0.82ppm or less) of gas is detected, the liquid crystal layer By changing the arrangement of the cells 202 in (20), the polarization state incident to the metasurface layer 10 can be adjusted to change the holographic image.

The holographic metasurface gas sensor 1 of this embodiment designs the metasurface layer 10 based on dual magnetic resonances and geometric and propagation phases in the visible region of silicon. Two types of metasurface structures were used so that two types of holographic images could be floated in space according to the polarization direction.

One type may display the second image I2 when the left circularly polarized light is illuminated, and the other type may display the first image I1 when the right circularly polarized light is illuminated.

The hydrogenated amorphous silicon-based transmission hologram can generate two different on-axis holographic images very clearly without afterimage in a specific focal region as the incident light L1 polarized in left and right circles is incident.

Specifically, when the incident light L1 is incident on the holographic metasurface gas sensor 1 , different images may be output depending on whether a specific material (eg, volatile gas) is in contact with the liquid crystal layer 20 . have.

For example, when air that does not contain a volatile gas comes into contact with the liquid crystal layer 20 , the first image I1 may be generated by transmitted light passing through the holographic metasurface gas sensor 1 , and liquid crystal When the volatile gas contacts the layer 20 , the second image I2 may be generated by the transmitted light passing through the holographic metasurface gas sensor 1 .

In this embodiment, the first image I1 and the second image I2 are different images, respectively, exemplifying a smile-shaped hologram and an exclamation mark-shaped hologram in an equilateral triangle, but the spirit of the present invention is not limited thereto .

The shape represented by the first image I1 and the second image I2 may vary depending on the shape and arrangement of the nanostructure 102 of the metasurface layer 10 .

In the present embodiment, the incident light L1 may be understood as light directed to the first image I1, and the transmitted light L2 transmits the holographic metasurface gas sensor 1 to the holographic metasurface gas sensor 1 . It can be understood as light directed in a direction away from

The incident light L1 is incident on the holographic metasurface gas sensor 1, and the transmitted light L2 whose polarization state is changed as the volatile gas contacts the liquid crystal layer 20 can be introduced into the metasurface layer 10, As the transmitted light L2 whose polarization state is changed passes through the meta surface layer 10 , different hologram images may be output according to the polarization state.

For example, when air that does not contain a volatile gas contacts the liquid crystal layer 20, the transmitted light L21 whose polarization state is not changed after the incident light L1 has passed through the liquid crystal layer 20 is converted to the meta surface layer ( 10), and the transmitted light L21 whose polarization state is not changed passes through the meta-surface layer 10 to generate the first image I1.

In addition, when the volatile gas comes into contact with the liquid crystal layer 20 , the transmitted light L22 whose polarization state is changed after the incident light L1 has passed through the liquid crystal layer 20 may be introduced into the metasurface layer 10 and polarized The transmitted light L22 whose state is changed passes through the meta surface layer 10 to generate the second image I2 . A detailed description of the liquid crystal layer 20 will be described later.

The meta surface layer 10 is a substrate layer 100 including a polyimide coating layer 110 in contact with the liquid crystal layer 20; and a plurality of nanostructures 102 disposed on the upper side of the substrate layer 100 .

The substrate layer 100 may have a flat plate shape, and may be formed by continuously arranging a plurality of unit elements 111 . Here, the plane may be understood as a plane extending in the X-axis and Y-axis directions, and the Z-axis may be understood as a direction in which the incident light L1 travels in a direction perpendicular to the plane.

One unit element 111 may have a square shape with a side length P when viewed from the front in the XY plane.

The substrate layer 100 may be made of silicon dioxide (SIO2), and the thickness of the substrate layer 100 may be 10 nm to 100 nm.

A plurality of nanostructures 102 may be provided on the upper side of the substrate layer 100 . Here, the nanostructure 102 may be made of hydrogenated amorphous silicon (a-Si;H).

One nanostructure 102 may be disposed on one unit element 111 , and nanostructures 102 disposed on consecutively disposed unit elements 111 are arranged to form the metasurface layer 10 . can do.

In this embodiment, the nanostructure 102 may have a rectangular parallelepiped shape having a length (L), a width (W), and a height (H).

The substrate layer 100 may be provided as a deformable flexible substrate, wherein the nanostructure 102 may include titanium dioxide nanoparticles (TIO ₂ NPs). A detailed description thereof will be given later.

The plurality of nanostructures 102 may be provided in a size and arrangement in which different hologram images are output according to the polarization state of the transmitted light L2 passing through the metasurface layer 10 .

For example, when the transmitted light L21 having the same polarization state as the incident light L1 passes through the meta surface layer 10, the first image I1 is generated, and the transmitted light L22 having a different polarization state from the incident light L1. ) passes through the meta surface layer 10 , the second image I2 may be generated.

Here, the change in the polarization state may vary depending on the presence or absence of a volatile gas in contact with the liquid crystal layer 20 , and the wavelength of the incident light L1 may be 633 nm.

A more detailed description of the generation of different images according to the arrangement of the plurality of nanostructures 102 will be described later.

The liquid crystal layer 20 may include a plurality of cells 202 .

Here, the cell 202 may be provided as a nematic liquid crystal cell. For example, the nematic liquid crystal may be provided as 4-Cyano-4'-pentylbiphenyl (5CB).

Figure 4 (a) is a diagram conceptually showing the arrangement of the cells 202 of the liquid crystal layer 20 in contact with air that does not contain a volatile gas, Figure 4 (b) is a volatile liquid crystal layer (20) It is a diagram conceptually showing the change of the cell 202 when the gas is contacted.

When the liquid crystal layer 20 is in contact with air containing no volatile gas (refer to (a) of FIG. 4), the cells 202 of the liquid crystal layer 20 adjacent to the meta surface layer 10 are aligned in one direction and , the cells 202 of the liquid crystal layer 20 in contact with air may be aligned in one direction and the other direction.

Here, the cells 202 aligned in one direction may be disposed at an angle of 3° to 5° with the polyimide coating layer 110 , and preferably may be disposed at an angle of 3.8°. Such an angle may be formed by the rubbed polyimide coating layer 110 coated on the substrate layer 100 .

In addition, the cells 202 aligned in different directions may be disposed at a perpendicular angle to the polyimide coating layer 110 . Here, the angle may be an angle between the long axis of the cell 202 and the polyimide coating layer 110 or the substrate layer 100 .

In addition, when the liquid crystal layer 20 is in contact with air that does not contain a volatile gas, the liquid crystal layer 20 adjacent to the polyimide coating layer 110 from the cell 202 of the liquid crystal layer 20 in contact with air. As the cell 202 approaches, the angle formed between the cell 202 and the polyimide coating layer 110 may become smaller. The arrangement of the cells 202 may be referred to as a hybrid anchoring configuration.

When the liquid crystal layer 20 is in contact with air that does not contain a volatile gas, the cells 202 may have the above-described arrangement (FIG. 4(a)), and thus transmitted light whose polarization state is not changed. (L21) may appear.

When a volatile gas (eg, isopropyl alcohol (IPA)) comes into contact with the liquid crystal layer 20 (see FIG. 4 (b)), the volatile gas molecules diffuse into the liquid crystal layer 20, and the cell 202 ) may be lowered (lowering the LC ordering). That is, the cell 202 provided as a nematic liquid crystal cell may be transferred to an isotropic phase, and this layer is referred to as an isotropic layer 20B.

The transition from the nematic liquid crystal to the isotropic phase starts at the side in contact with the volatile gas, and over time, the isotropic phase expands toward the metasurface layer 10 . can be

These results indicate the ability of the cell 202, which serves as a nematic liquid crystal, to instantly sense a volatile gas (or toxic gas) and convert the polarization of the transmitted light.

This can be evidenced by the phase delay τ of the cell 202 that progressively decreases over time of exposure to the volatile gas. Also, the thickness of the isotropic layer 20B may be extracted from the phase delay τ of the cell 202 .

In addition, 4-cyano-4'-pentylbiphenyl (5CB) provided to the cell 202 included in the anisotropic layer 20A is at the interface of the isotropic layer 20B. It may have an angle of 25° to 30°, preferably an angle of 26.5°.

The cell 202 for polarization modulation may be coupled to a glass plate in which the liquid crystal layer 20 includes a polyimide coating layer 110 . The polyimide coating layer 110 may be prepared by spin coating at 1000 rpm for 10 seconds and then spin coating at 2500 rpm for 30 seconds.

Thereafter, the polyimide coating layer 110 is baked at 230° C. for 50 minutes, and the cells 202 can be aligned in one direction by rubbing the polyimide coating layer 110 . The spacing between the cells 202 may be provided in a range of 10 μm to 30 μm, preferably 20 μm.

FIG. 5 is a view showing changes in the liquid crystal layer 20 according to the contact between the holographic metasurface gas sensor 1 of FIG. 1 and the volatile gas.

6 is a graph showing the thickness of the isotropic layer 20B and the phase delay τ of the cell 202 generated over time after the contact of the volatile gas with the holographic metasurface gas sensor 1 of FIG. 1 . .

FIG. 5 is a view of the liquid crystal layer 20 viewed from the upper side, and a small square in the lower left corner of FIG. 5 shows a side view.

5 (a) is a view when the liquid crystal layer 20 is not exposed to the volatile gas, and FIG. 5 (b) is a few seconds after the liquid crystal layer 20 is exposed to the volatile gas (for example, 1 second), and (c) of FIG. 5 is a view after 140 seconds have elapsed after the volatile gas is exposed to the liquid crystal layer 20 .

Referring to FIG. 5 , it can be seen that the isotropic layer 20B having an isotropic phase in the anisotropic layer 20A including the cell 202 is expanded as the volatile gas is exposed to the liquid crystal layer 20 . have.

(a), (b), and (c) of FIG. 6 may correspond to a blue dot, a green dot, and a red dot, respectively.

Referring to FIG. 6 , it can be seen that the phase delay τ of the cell 202 decreases and the thickness of the isotropic layer 20B increases as the exposure time of the volatile gas increases.

Hereinafter, the meta surface layer 10 including a plurality of nanostructures 102 will be described in more detail.

It may be understood that the plurality of nanostructures 102 are arranged to take advantage of an asymmetric-spin orbit interaction (A-SOI) helicity.

FIG. 7 is a view showing phase coverage and wavefront modulation of light passing through the nanostructure 102 according to the size and arrangement of the nanostructure 102 of the metasurface layer 10 of FIG. 1 . , FIG. 8 is a diagram illustrating a simulation for designing an optimal size of the nanostructure 102 .

7 and 8 , the plurality of nanostructures 102 may include a plurality of nanostructures arranged in a vertical direction to each other.

For example, the plurality of nanostructures 102 may include a first nanostructure 1021 , a second nanostructure 1022 , a third nanostructure 1023 , and a fourth nanostructure provided as a first group of nanostructures 102A. A structure 1024 and a fifth nanostructure 1025, a sixth nanostructure 1026, a seventh nanostructure 1027, and an eighth nanostructure 1028 serving as the second nanostructure group 102B, and , The nanostructures 1021 , 1022 , 1023 , 1024 of the first group of nanostructures 102A may be arranged to be orthogonal to the nanostructures 1025 , 1026 , 1027 , and 1028 of the second group of nanostructures 102B.

In addition, the nanostructures 1021 , 1022 , 1023 , and 1024 included in the first nanostructure group 102A may have different sizes and may be arranged to have the same angle. In addition, the nanostructures 1025 , 1026 , 1027 , and 1028 included in the second nanostructure group 102B also have different sizes, but may be arranged to have the same angle.

As such, two groups including nanostructures orthogonal to each other can cover the 2π phase range in 8 steps. In addition, in FIG. 7 , the phase difference of light passing through the adjacent nanostructures 102 is 45 degrees.

The nanostructures 1021, 1022, 1023, 1024 included in the first group of nanostructures 102A provide the necessary phase delay τ, and the nanostructures 1025 and 1026 included in the second group of nanostructures 102B. , 1027 and 1028 may have the same size as the nanostructures 1021 , 1022 , 1023 , 1024 included in the first nanostructure group 102A, but may be disposed to have an angle of 90 degrees to each other.

By arranging the nanostructures of the first nanostructure group 102A and the nanostructures of the second nanostructure group 102B perpendicular to each other and optimizing the size of the nanostructures, an additional phase independent of the direction in which the nanostructures are arranged A phase shift can be achieved. Thereby, it is possible to output different holographic images according to the polarization state.

In addition, FIG. 8 shows the transmission of left circularly polarized light after right circularly polarized (RCP) incident light L1 has passed through the nanostructure 102 as a function of the length (L) and width (W) of the nanostructure 102 . It is a diagram showing the efficiency (TLR).

White dots indicate four selected nanostructures 102 having high diffraction efficiency while considering resolution.

The nanostructure 102 may have a length (L) of 180 nm to 250 nm, and a width (W) of 60 nm to 120 nm. In addition, the height (H) of the nanostructure 102 may be 300 nm to 500 nm, preferably 400 nm.

Also, the length P of one side of the unit element 111 may be 300 nm.

와

는 각각 LCP 및 RCP에서 두 개의 고유한 홀로그램 패턴을 생성하는 데 필요한 두 개의 별개 대상 이미지의 위상 분포를 나타내며 다음과 같이 표현될 수 있습니다.

Wow

represents the phase distribution of two distinct target images required to generate two distinct holographic patterns in LCP and RCP, respectively, and can be expressed as

및

의 값을 결정하는 데 사용할 수 있는 두 방정식의 조합이다.the above formula

and

It is a combination of two equations that can be used to determine the value of .

및 방향각도(orientation angle)

로 암호화된다.All optimized nanostructures 102 have a retardation phase corresponding to their position in the metasurface layer 10 .

and orientation angle

is encrypted with

및

를 결정할 수 있다. 이와 같은 나노 구조체(102)들을 배치함으로써 편광상태에 따라 제1 이미지 또는 제2 이미지가 출력될 수 있다. We use a two-dimensional image representing the first image, the smile shape, and the second image, the alarm state shape, to distribute the phases, respectively.

and

can be decided By disposing the nanostructures 102 as described above, the first image or the second image may be output according to the polarization state.

Hereinafter, the design of the cell 202 of the liquid crystal layer 20 will be examined in more detail.

The placement of the cells 202 in an anisotropic medium with long-rage molecular ordering may be controlled by an external stimulus (eg, a volatile gas).

)에 의해 설명되고, 회전의 정도(degree of orientation)는 순서 매개 변수(s)에 의해 다음과 같이 표현된다.The direction of the cell 202 is the director (director,

), and the degree of orientation is expressed by the order parameter (s) as

는 디렉터(

)와 셀(202)의 축(molecular axis) 사이의 각도이다.here,

is the director (

) and the angle between the molecular axis of the cell 202 .

S varies with temperature, and decreases with increasing temperature, so that a randomly ordered state can be induced.

S=1 when cell 202 is parallel to director n, and S=0 when cell 202 is in an isotropic phase.

The phase delay τ of the light passing through the liquid crystal layer 20 may be adjusted by the order or arrangement of the cells 202 .

Repositioning of the cell 202 according to the contact of the volatile gas may change the effective refractive index of the cell 202 , and the change in the effective refractive index may be expressed by the following equation.

는 접선 원점(tangential orientation)을 나타낼 수 있다. Here, _{ne may represent an extraordinary reflective index, n o may} represent an ordinary reflective index,

may represent a tangential orientation.

Accordingly, the polarization state of the transmitted light L2 passing through the liquid crystal layer 20 can be controlled by realizing the phase retardation of the cell 202 .

Here, the phase retardation of the cell 202 can be expressed as follows.

Here, d may be understood as the thickness of the liquid crystal layer 20, λ may be understood as the wavelength of the incident light L1 incident on the liquid crystal layer 20, and the wavelengths of the incident light L1 and the transmitted light L2 may be the same. .

Hereinafter, a method for manufacturing the flexible metasurface layer 10 by utilizing a one-step nanocasting process for extending the holographic metasurface gas sensor 1 to a wearable device is presented.

9 shows a method for manufacturing a flexible metasurface layer 10 using a one-step nanocasting process for extending the holographic metasurface gas sensor 1 of FIG. 1 to a wearable device.

Referring to FIG. 9 , the meta surface layer 10 is prepared by using a master stamp having the shape and arrangement of the nanostructure 102 to prepare a polymer mold; Spin coating a UV curable resin containing titanium dioxide nanoparticles (TIO ₂ NPs) on a polymer mold; curing the UV curing resin by applying UV and pressure; and separating the polymer mold to form a nanostructure 102 including titanium dioxide nanoparticles (TIO ₂ NPs).

When the meta surface layer 10 is manufactured by this process, the nanostructure 102 may include titanium dioxide nanoparticles (TIO ₂ NPs).

After that, the substrate layer 100 including the nanostructure 102 and the polyimide coating layer 110 are combined to form the meta surface layer 10, and the meta surface layer 10 and the liquid crystal layer 20 are combined to form a single A graphic metasurface gas sensor 1 can be fabricated.

Here, the nanoparticle-resin composite (NPC) contained in the titanium dioxide nanoparticles (TIO ₂ NPs) has an extinction coefficient of 0 in the entire visible spectrum, and the refractive index (n) is 1.5 to 2.5. Therefore, it can be used as a dielectric metasurface.

Therefore, the metasurface layer 10 provided as a nanostructure 102 on the substrate layer 100 shown in FIG. can be implemented By this process, the metasurface layer 10 and the holographic metasurface gas sensor 1 can be mass-produced.

As shown in A of FIG. 9, the master stamp is coated with SAM (self-assembled monolayer) to produce a meta surface layer 10 including a nanoparticle-resin composite (NPC) to reduce the adhesive force, thereby forming a polymer mold. It can be easily separated.

In addition, hard polydimethylsiloxane (h-PDMS) can be spin-coated on a master stamp and heat-cured to replicate the meta-surface structure implemented by the nanostructure 102 . Additional PDMS can be coated on the h-PDMS layer because the single h-PDMS layer is in strong contact and cannot be separated from the master stamp without breaking.

After separating the polymer mold from the master stamp, a nanoparticle-resin composite (NPC) is spin-coated on the polymer mold to uniformly fill the pattern of the polymer mold and remove the residual solvent. After that, place the polymer mold face down containing the nanoparticle-resin composite (NPC) on a flexible polyethylene terephthalate (PET) substrate. The mechanical stability and high UV transparency of the polymer mold enable the casting of titanium dioxide nanoparticles (TIO ₂ NPs) using UV exposure with appropriate pressure. UV exposure during the curing process can polymerize the monomers of titanium dioxide nanoparticles (TIO ₂ NPs). The residual solvent of NPC diffuses into the polymer mold due to its high permeability, and the NPC adheres more strongly to the PET substrate than the polymer mold with low surface energy, so it can be easily separated. After the polymer mold is released, the nanostructure 102 including titanium dioxide nanoparticles (TIO ₂ NPs) may remain on the substrate layer 100 .

The meta-surface layer 10 including the thus prepared titanium dioxide nanoparticles (TIO ₂ NPs) is shown in C and D of FIG. 9 .

10 is a photograph of the actual production of the holographic metasurface gas sensor 1 of FIG. 1 , and FIG. 11 is a photograph of the holographic metasurface gas sensor 1 of FIG. 10 attached to goggles, which are wearable devices having a curved surface. .

When an operator wears a wearable device with such a holographic metasurface gas sensor 1 attached to it and works, a danger mark is immediately displayed on the wearable device through the holographic metasurface gas sensor 1 when exposed to harmful gases. can Accordingly, it is possible to prevent damage that may occur due to exposure to harmful gases to workers who work in an environment having a risk of exposure to harmful gases.

12 shows a nanostructure 102 including titanium dioxide nanoparticles (TIO2NPs) and a nanostructure 102 made of hydrogenated amorphous silicon (a-Si;H) according to the wavelength of incident light L1 Indicates the image resolution.

12 , the nanostructure 102 including titanium dioxide nanoparticles (TIO ₂ NPs) shows a clear image when the wavelength of incident light is 532 nm or less, and is made of hydrogenated amorphous silicon (a-Si;H). The manufactured nanostructure 102 shows a clear image when the wavelength of the incident light L1 is 600 nm or more.

Therefore, in this embodiment, the holographic metasurface gas sensor 1 having a nanostructure 102 including titanium dioxide nanoparticles (TIO ₂ NPs) may be irradiated with incident light L1 having a wavelength of 532 nm or less,

The holographic metasurface gas sensor 1 having the nanostructure 102 made of hydrogenated amorphous silicon (a-Si;H) may be irradiated with incident light L1 having a wavelength of 600 nm or more.

Above, the holographic metasurface gas sensor 1 and the wearable device including the same according to the embodiment of the present invention have been described as specific embodiments, but this is merely an example and the present invention is not limited thereto, and the basic idea disclosed in the present specification should be construed as having the widest range according to A person skilled in the art may practice unspecified embodiments by combining and substituting the disclosed embodiments, but this also does not depart from the scope of the present invention. In addition, those skilled in the art can easily change or modify the disclosed embodiments based on the present specification, and it is clear that such changes or modifications also fall within the scope of the present invention.

1: Holographic metasurface gas sensor
10: meta surface layer
100: substrate layer
102: nano structure
102A: first group of nanostructures
102B: second nanostructure group
110: polyimide coating layer
20: liquid crystal layer
202 : cell
20A: anisotropic layer
20B: isotropic layer

Claims (21)

A meta surface layer provided with a plurality of nano structures;
It is provided on one side of the meta surface layer and includes a liquid crystal layer including a plurality of cells whose arrangement can be changed by a specific material in contact,
The liquid crystal layer is
By changing the arrangement of the plurality of cells by contact of the specific material, it is possible to change the polarization state of transmitted light passing through the liquid crystal layer.
Holographic metasurface gas sensor. The method of claim 1,
When air not containing the specific material is in contact with the liquid crystal layer, the cells of the liquid crystal layer adjacent to the meta surface layer are aligned in one direction, and the cells of the liquid crystal layer in contact with the air are in a direction different from the one direction sorted by
Holographic metasurface gas sensor. 3. The method of claim 2,
The cells aligned in one direction are arranged at an angle of 3° to 5° with the polyimide coating layer.
Holographic metasurface gas sensor. 3. The method of claim 2,
The cells aligned in the other direction are arranged at an angle perpendicular to the polyimide coating layer.
Holographic metasurface gas sensor. 3. The method of claim 2,
As the cell of the liquid crystal layer in contact with the air approaches the cell of the liquid crystal layer adjacent to the meta surface layer, the angle between the cell and the polyimide coating layer becomes smaller.
Holographic metasurface gas sensor. The method of claim 1,
When a specific substance is diffused in the liquid crystal layer,
The liquid crystal layer is
an isotropic layer in which 4-cyano-4'-pentylbiphenyl is changed into an isotropic phase; and
Comprising an anisotropic layer having 4-cyano-4'-pentylbiphenyl not in contact with a specific material
Holographic metasurface gas sensor. The method of claim 1,
When a specific material is in contact with the liquid crystal layer, at least a portion of the liquid crystal layer including the cell in contact with the specific material is changed to an isotropic layer having an isotropic phase
Holographic metasurface gas sensor. 8. The method of claim 7,
The isotropic layer having the isotropic phase expands toward the metasurface layer over time.
Holographic metasurface gas sensor. 9. The method of claim 8,
The cell is provided as 4-cyano-4'-pentylbiphenyl,
4-cyano-4'-pentylbiphenyl included in the anisotropic layer has an angle of 25° to 30° at the interface of the isotropic layer
Holographic metasurface gas sensor. The method of claim 1,
When air that does not contain the specific material comes into contact with the liquid crystal layer, a first image I1 is generated by transmitted light passing through the liquid crystal layer and the meta surface layer,
When a specific material is in contact with the liquid crystal layer, the second image I2 is generated by the transmitted light passing through the liquid crystal layer and the meta surface layer.
Holographic metasurface gas sensor. 11. The method of claim 10,
The first image I1 and the second image I2 are generated as different holograms.
Holographic metasurface gas sensor. 12. The method of claim 11,
The change from the first image I1 to the second image I2 occurs within 1 second after exposure to a volatile gas.
Holographic metasurface gas sensor. The method of claim 1,
The specific substance is provided as a volatile gas
Holographic metasurface gas sensor. The method of claim 1,
This particular substance is provided as isopropyl alcohol (IPA).
Holographic metasurface gas sensor. The method of claim 1,
The meta surface layer,
a substrate layer including a polyimide coating layer in contact with the liquid crystal layer; and
comprising a plurality of nanostructures disposed on the upper side of the substrate layer
Holographic metasurface gas sensor. The method of claim 1,
A plurality of nanostructures,
Nanostructures included in the first group of nanostructures, and
and a nanostructure included in the second group of nanostructures,
The nanostructures included in the first group of nanostructures and the nanostructures included in the second group of nanostructures are arranged to be orthogonal to each other.
Holographic metasurface gas sensor. The method of claim 1,
The substrate layer of the meta surface layer is provided as a deformable flexible substrate
Holographic metasurface gas sensor. The method of claim 1,
The nanostructure is provided with hydrogenated amorphous silicon
Holographic metasurface gas sensor. The method of claim 1,
The meta surface layer,
A polyimide coating layer for aligning cells in one direction on a surface facing the liquid crystal layer
Holographic metasurface gas sensor. The method of claim 1,
The nanostructure includes titanium dioxide nanoparticles
Holographic metasurface gas sensor. A wearable device that can be worn on a user's body, wherein the holographic metasurface gas sensor according to claim 1 is attached to a part of the wearable device.
wearable devices.

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