CN216595584U - Fresnel lens, detector and security system - Google Patents

Abstract

The application provides a Fresnel lens, a detector and a security system, wherein the Fresnel lens comprises a main body part, and the main body part is provided with an incident surface and a Fresnel surface which are arranged oppositely; the incident surface is an irregular surface which is convexly arranged outwards; the Fresnel surface is a spherical surface which is concavely arranged towards the incident surface, the Fresnel surface is provided with a plurality of lens units, each lens unit is provided with a plurality of concentric Fresnel teeth, and the lens units are used for focusing the light rays incident from the incident surface to the focus inside the main body part. The detector comprises a shell, a sensing piece and the Fresnel lens. The security system comprises the detector. The Fresnel lens can reduce the splicing difficulty in the process of splicing a plurality of lens units, and further the production cost of the Fresnel lens is reduced.

Description

Fresnel lens, detector and security system

Technical Field

The application belongs to the field of optical detection, and particularly relates to a Fresnel lens, a detector and a security system.

Background

Fresnel lens is many by polyolefin material injection moulding, and on passive infrared intrusion detector, fresnel lens can play the effect of focus, simultaneously, will survey the region and divide into a plurality of bright district and dark space, makes the removal object that gets into and surveys the region produce the change on PIR (PasiveInfrared Ray, pyroelectric infrared sensor) with temperature variation's form and releases infrared signal, and then is responded to by the detector.

Currently, a fresnel lens includes an incident surface and a fresnel surface that are oppositely disposed, wherein the fresnel surface is provided with a plurality of lens units, and each lens unit is provided with a plurality of concentric fresnel teeth. In the production process of the Fresnel lens, a plurality of lens units are spliced in advance in a mold cavity and are subjected to injection molding after splicing. Most fresnel lenses on the market are planar or spherical, and some detectors set the fresnel lenses to be irregular in order to meet the modeling requirements. However, in the irregular fresnel lens, the difficulty of splicing the lens units is high, which results in increased production cost.

SUMMERY OF THE UTILITY MODEL

An object of the embodiment of the application is to provide a Fresnel lens, a detector and a security system, so as to solve the problem that the production cost of the irregular Fresnel lens is high in the related art.

In order to achieve the above purpose, the embodiment of the present application adopts the following technical solutions:

in one aspect, a fresnel lens is provided, which includes a main body portion having an incident surface and a fresnel surface that are oppositely disposed;

the incident surface is an irregular surface which is convexly arranged outwards;

the Fresnel surface is a spherical surface which is concavely arranged towards the direction of the incidence surface, the Fresnel surface comprises a plurality of lens units, each lens unit is provided with a plurality of concentric Fresnel teeth, and the lens units are used for focusing light rays entering from the incidence surface to a focus on the inner side of the main body part.

In one embodiment, the incident surface includes a central spherical surface and an arc surface disposed at an edge of the central spherical surface.

The structure can enable the thickness of the part of the main body part between the central spherical surface and the Fresnel surface to be basically consistent, and reduces the influence of the irregular surface on the optical performance of the Fresnel lens.

In one embodiment, the fresnel surface includes a far distance multi-view region, an intermediate multi-view region disposed on a side of the far distance multi-view region, and a near multi-view region located on a side of the intermediate multi-view region remote from the far distance multi-view region, and the near multi-view region is located within the intermediate multi-view region; the distance multi-vision region, the intermediate multi-vision region and the near multi-vision region each include a plurality of the lens units.

The structure can lead the detector to detect a moving object at a longer distance by arranging the long-distance multi-visual area; the middle-distance multi-view area can enable the detector to detect the moving object within the middle distance; and the short-distance multi-view area enables the detector to detect the moving object at a short distance.

In one embodiment, the plurality of lens units of the distance multi-vision region are symmetrically distributed along a vertical center line of the main body part; the lens units of the intermediate distance multi-vision area are symmetrically distributed along the vertical central line of the main body part; the lens units of the near multi-vision area are symmetrically distributed along the vertical center line of the main body part.

The structure can ensure that the detection areas are symmetrical on the left side and the right side of the detector, and is convenient for the detector to detect moving objects.

In one embodiment, the area of the remote multi-vision region is greater than one half of the area of the fresnel surface.

With this structure, the detection distance of the detector can be increased.

In one embodiment, the distance between the focal point and the main body portion is less than the radius of curvature of the fresnel surface; and/or, the first and/or second components,

the thickness of the main body part is 0.5mm-1.2 mm.

By the structure, when the sensing part of the detector is arranged at the focus position, the thickness of the detector is favorably reduced; the thickness of the main body part is set to be 0.5mm-1.2mm, infrared rays can easily penetrate through the Fresnel lens, and meanwhile, the structural strength of the Fresnel lens is guaranteed.

In one embodiment, a straight cylinder section is arranged on the edge of the main body part, a flange is arranged at one end, away from the main body part, of the straight cylinder section, and a positioning part is arranged on the flange.

According to the structure, the flanging is arranged to facilitate the assembly between the Fresnel lens and the shell of the detector, and the straight cylinder section can enable the main body part of the Fresnel lens to extend out of the shell of the detector.

In one embodiment, the positioning part comprises a plurality of positioning grooves formed in the turned-up edge and a plurality of positioning holes formed in the turned-up edge.

This structure can improve fresnel lens's commonality, and when fresnel lens installed the detector of difference, the corresponding location structure of detector can be fixed a position with constant head tank or locating hole.

In another aspect, a probe is provided, which includes a casing, a sensing element and the fresnel lens provided in any of the above embodiments, wherein the fresnel lens is mounted at an end portion of the casing, a main body portion of the fresnel lens extends out of the casing, the sensing element is mounted in the casing and faces the fresnel lens, and a detection end of the sensing element is located at a focus of the fresnel lens.

This structure adopts above-mentioned fresnel lens's detector, and each lens unit is the sphere, and a plurality of lens units can reduce the degree of difficulty of concatenation at the in-process of concatenation, and fresnel lens's manufacturing cost is lower, and then has reduced the manufacturing cost of detector.

In another aspect, a security system is provided, which includes the above-mentioned detector.

This structure adopts the security protection system of above-mentioned detector, and the manufacturing cost of detector is lower to can reduce the overall cost of security protection system.

The application provides a fresnel lens, detector and security protection system's beneficial effect lies in: the main body part of the Fresnel lens is provided with an incidence surface and a Fresnel surface which are oppositely arranged, and the incidence surface is arranged to be an irregular surface which is outwards protruded, so that the Fresnel lens meets the modeling requirement of the detector. The fresnel surface includes a plurality of lens elements, and is a spherical surface that is concavely provided toward the incident surface, so that each lens element is also a spherical surface. In the process of splicing a plurality of lens units, the splicing difficulty can be reduced, and further the production cost of the Fresnel lens is reduced.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or exemplary technical descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.

Fig. 1 is a first schematic structural diagram of a fresnel lens provided in an embodiment of the present application;

fig. 2 is a second schematic structural diagram of a fresnel lens provided in the embodiment of the present application;

fig. 3 is a schematic structural diagram of a fresnel surface provided in an embodiment of the present application;

FIG. 4 is a schematic diagram of arrangement of a far-distance multi-view region, an intermediate-distance multi-view region and a near-distance multi-view region according to an embodiment of the present application;

FIG. 5 is a schematic view of an arrangement of a Fresnel lens and a sensing element provided in an embodiment of the present disclosure;

FIG. 6 is a side view of a detection zone of a detector provided in an embodiment of the present application;

FIG. 7 is a top view of a detection region of a detector provided in an embodiment of the present application;

fig. 8 is a schematic structural diagram of a detector provided in an embodiment of the present application.

Wherein, in the drawings, the reference numerals are mainly as follows:

1. a main body portion; 11. an incident surface; 111. a central spherical surface; 112. a cambered surface; 12. a Fresnel surface; 121. a lens unit; 1211. fresnel teeth; 122. a remote multi-view zone; 123. a middle distance multi-view zone; 124. a near multi-view region;

2. a straight cylinder section;

3. flanging; 31. a positioning part; 311. positioning a groove; 312. positioning holes;

4. a detector; 41. a housing; 42. a sensing element.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present application clearer, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

It will be understood that when an element is referred to as being "secured to" or "disposed on" another element, it can be directly on the other element or be indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or be indirectly connected to the other element.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present application, "a plurality" means two or more unless specifically limited otherwise. The meaning of "a number" is one or more unless specifically limited otherwise.

In the description of the present application, it is to be understood that the terms "center", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are used only for convenience in describing the present application and for simplicity in description, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present application.

In the description of the present application, it is to be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art as the case may be.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present application. Thus, the appearances of the phrases "in one embodiment" or "in some embodiments" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

Referring to fig. 1 to fig. 3, a fresnel lens provided in an embodiment of the present application will now be described. The fresnel lens includes a main body portion 1, wherein the main body portion 1 is approximately square in shape. The main body 1 has an incident surface 11 and a fresnel surface 12 which are disposed opposite to each other, and it is easily understood that infrared rays emitted from a moving object in the detection region can enter the main body 1 through the incident surface 11 and exit the fresnel surface 12 of the main body 1. The incident surface 11 is an irregular surface protruding outward, and specifically, when the fresnel lens is mounted on the detector 4, the incident surface 11 protrudes away from the sensing element 42. Fresnel surface 12 is a concave spherical surface, that is, fresnel surface 12 is a concave spherical surface in a direction toward incident surface 11, and fresnel surface 12 is concave in the same direction as incident surface 11. The fresnel surface 12 includes a plurality of lens units 121, wherein the lens units 121 are in a spherical sheet structure, and the plurality of lens units 121 are mutually spliced to form the fresnel surface 12. Each lens unit 121 is provided with a plurality of concentric fresnel teeth 1211, and the fresnel teeth 1211 are illustratively circular or arc-shaped, have a tooth height of 0.15mm to 0.25mm, and the fresnel teeth 1211 and the lens unit 121 may be formed in one piece through a one-time molding process. The plurality of lens units 121 are for focusing the light beam incident from the incident surface 11 on the focal point inside the main body 1.

The anti-collision device provided by the embodiment has the beneficial effects that the main body part 1 of the fresnel lens is provided with the incident surface 11 and the fresnel surface 12 which are oppositely arranged, and the incident surface 11 is arranged to be an irregular surface which is convexly arranged outwards, so that the fresnel lens meets the modeling requirement of the detector 4. The fresnel surface 12 includes a plurality of lens units 121, and the fresnel surface 12 is a spherical surface that is recessed inward, so that each lens unit 121 is also a spherical surface. Compared with the lens units 121 with irregular surfaces, the lens units 121 are arranged to be spherical surfaces, so that the splicing difficulty and precision can be reduced in the splicing process of the lens units 121, and the production cost of the Fresnel lens is reduced.

In an embodiment, referring to fig. 1, as a specific implementation of the fresnel lens provided in the embodiments of the present application, the incident surface 11 includes a central spherical surface 111 and an arc surface 112 disposed at an edge of the central spherical surface 111. Illustratively, the main body of the incident surface 11 is a central spherical surface 111, and the central spherical surface 111 is approximately square. It is worth mentioning that the curvature of the central spherical surface 111 is the same as the curvature of the fresnel surface 12. The cambered surface 112 is used for transition from the edge of the central spherical surface 111 to the edge of the incident surface 11, and the specific radian of the cambered surface 112 is not limited in this embodiment, and those skilled in the art can set the cambered surface according to actual needs. Illustratively, when the fresnel lens is molded in the mold cavity, the incident surface 11 forms a central spherical surface 111 and a cambered surface 112 at the edge of the central spherical surface 111.

In this embodiment, the incident surface 11 includes a central spherical surface 111 and an arc surface 112 located at an edge of the central spherical surface 111, so that the incident surface 11 is formed into a central symmetric structure, and the modeling requirement of the detector is met. The thickness of the main body portion 1 between the central spherical surface 111 and the fresnel surface 12 is substantially uniform, and the influence of the irregularity on the optical performance of the fresnel lens can be reduced.

In an embodiment, referring to fig. 2 to 4, as an embodiment of the fresnel lens provided by the embodiment of the present application, the fresnel surface 12 includes a far-distance multi-vision region 122, an intermediate multi-vision region 123 disposed on a side of the far-distance multi-vision region 122, and a near multi-vision region 124 disposed on a side of the intermediate multi-vision region 123 far from the far-distance multi-vision region 122, and the near multi-vision region 124 is disposed in the intermediate multi-vision region 123. For example, when the fresnel lens is mounted on the detector and the detector is hung on a wall, the intermediate multi-vision region 123 is located below the far multi-vision region 122, the near multi-vision region 124 is located below the intermediate multi-vision region 123, and the edge of the near multi-vision region 124 is covered by the intermediate multi-vision region 123. The distance multi-view region 122, the intermediate multi-view region 123 and the near multi-view region 124 each include a plurality of lens units 121. Fig. 3 shows that the area of the distance multi-vision region 122 located at the edge portion lens unit 121 is larger than the area of the distance multi-vision region 122 located at the middle portion lens unit 121, and the area of the intermediate multi-vision region 123 located at the edge portion lens unit 121 is also larger than the area of the intermediate multi-vision region 123 located at the middle portion lens unit 121. When the fresnel lens is mounted on the detector 4, the sensing element 42 of the detector 4 faces the area of the fresnel surface 12 near the center, and the above arrangement can make the intensity of the infrared rays irradiated to the sensing element 42 by each lens unit 121 in the long distance multi-view area 122 and the middle distance multi-view area 123 approximately equal, thereby ensuring the detection effect of the detector 4.

In this embodiment, the far distance multi-view area 122 may form a far detection area to detect a far distance moving object, the middle distance multi-view area 123 may form a middle detection area to detect a middle distance moving object, and the near distance multi-view area 124 may form a near detection area to detect a near distance moving object. When the fresnel lens is mounted on the detector 4, the detector 4 may form a detection area of a solid sector as shown in fig. 6 and 7.

In an embodiment, referring to fig. 2 to 4, as a specific implementation of the fresnel lens provided by the embodiments of the present application, the lens units 121 of the far distance multi-vision zone 122 are symmetrically distributed along the vertical center line of the main body portion 1; the plurality of lens units 121 of the intermediate multi-vision region 123 are symmetrically distributed along the vertical center line of the main body part 1; the plurality of lens units 121 of the near multi-vision region 124 are all symmetrically distributed along the vertical center line of the main body 1. It should be noted that the vertical center line is a vertical center line of the fresnel lens in a use state, that is, when the fresnel lens is mounted on the detector and the detector is hung on a wall, the vertical center line is located in a middle position of a width of the fresnel lens. Specifically, L2 in fig. 3 and 4 is a vertical center line of the main body 1. The plurality of lens units 121 of the near multi-vision region 124 are symmetrically distributed along the vertical center line L2, the plurality of lens units 121 of the intermediate multi-vision region 123 are symmetrically distributed along the vertical center line L2, and the plurality of lens units 121 of the far multi-vision region 122 are also symmetrically distributed along the vertical center line L2. It will be readily appreciated that when the fresnel lens is mounted on the probe 4, the center of the sensing member 42 is directly opposite the vertical centerline L2.

In the present embodiment, when the fresnel lens is attached to the detector 4, the detection area of the detector 4 may be formed into a fan shape as shown in fig. 7, and the fan shape is symmetrical left and right with respect to the detector 4. The central angle of the sector may be, for example, 90 deg., facilitating the detection of a moving object by the detector 4.

In one embodiment, referring to fig. 3, 4 and 6, as an embodiment of the fresnel lens provided in the present application, the area of the far distance multi-vision region 122 is greater than one-half of the area of the fresnel surface 12. Specifically, the top end of the distance multi-vision region 122 is located at the top end of the Fresnel surface 12, and the bottom end of the distance multi-vision region 122 is located beyond the horizontal center line L1 of the Fresnel surface 12. The specific area of the distance multi-vision region 122 is not limited in this embodiment, and can be set by those skilled in the art according to actual needs. According to the arrangement, after the Fresnel lens is arranged on the detector 4, the detection distance of the detector 4 can be increased, so that the farthest detection distance of the detector 4 can reach 12 meters, and the detection effect of the detector 4 is improved.

In an embodiment, referring to fig. 5, as a specific implementation of the fresnel lens provided in the embodiment of the present application, a distance between the focal point and the main body portion 1 is smaller than a radius of curvature of the fresnel surface 12. It will be readily appreciated that when the fresnel lens is mounted on the detector 4, the sensing end of the sensing element 42 is located at the focal point of the fresnel lens. That is, the distance between the sensor 42 and the main body 1 is smaller than the radius of curvature of the fresnel surface 12. This arrangement reduces the distance between the sensing element 42 and the fresnel lens, which facilitates a reduction in the thickness of the detector 4.

In a possible implementation, the thickness of the body portion 1 is 0.5mm-1.2 mm. When the thickness of the body 1 is less than 0.5mm, the body 1 is weak in strength and is easily deformed. When the thickness of the main body 1 is greater than 1.2mm, the infrared ray is lost more when passing through the main body 1, which affects the detection effect of the detector 4. That is to say, the thickness of the main body part 1 is set to be 0.5mm-1.2mm, so that the infrared rays have better penetrating power on the basis of ensuring the strength of the main body part 1, and the detection effect of the detector 4 is ensured. However, when the strength of the main body 1 allows, the thinner the thickness of the main body 1, the better the detection effect of the probe 4.

In an embodiment, referring to fig. 1, fig. 2 and fig. 5, as a specific implementation of the fresnel lens provided in the embodiments of the present application, a straight-tube section 2 is disposed at an edge of the main body portion 1, and when the fresnel lens is mounted on the probe 4, the straight-tube section 2 extends toward the inside of the probe 4. One end of the straight cylinder section 2, which is far away from the main body part 1, is provided with a flanging 3, wherein the flanging 3 extends towards the outer side of the straight cylinder section 2. The skilled person can set the specific width of the flange 3 according to actual needs, and the embodiment is not limited herein. In the process of assembling the fresnel lens, the flange 3 can be clamped between the housing 41 of the probe 4 and the support, so that the assembly between the fresnel lens and the housing 41 is realized. The positioning portion 31 is arranged on the flange 3, illustratively, the shell 41 of the detector 4 is provided with a limiting portion matched with the positioning portion 31, and after the positioning portion 31 is connected with the limiting portion, the Fresnel lens can be prevented from moving relative to the shell 41, and the alignment precision and efficiency between the Fresnel lens and the shell 41 are improved.

In this embodiment, the flange 3 is provided to facilitate the assembly between the fresnel lens and the casing 41 of the detector 4, the straight cylinder section 2 can enable the main body portion 1 of the fresnel lens to extend out of the casing 41 of the detector 4, and the flange 3 is provided with the positioning portion 31 to facilitate the accurate positioning between the fresnel lens and the casing 41.

In an embodiment, referring to fig. 1 and fig. 2, as a specific implementation of the fresnel lens provided in the embodiment of the present application, the positioning portion 31 includes a plurality of positioning slots 311 formed on the flange 3 and a plurality of positioning holes 312 formed on the flange 3. Illustratively, the number of the positioning slots 311 may be three, wherein one positioning slot 311 is opened at the middle position of the bottom of the flange 3, the other two positioning slots 311 are opened at the top of the flange 3, and the two positioning slots 311 are arranged at intervals. The number of the positioning holes 312 may be three, and the three positioning holes 312 are respectively formed on the left and right sides and the top of the flange 3. Of course, the embodiment is only exemplary, and those skilled in the art can set specific positions and numbers of the positioning slots 311 and the positioning holes 312 according to actual needs, which is not limited herein.

In this embodiment, the positioning portion 31 includes a plurality of positioning grooves 311 and a plurality of positioning holes 312, which can improve the versatility of the fresnel lens. Specifically, when the housing 41 of the detector 4 is provided with a positioning post, the positioning post may be matched with the positioning hole 312 of the fresnel lens; when the housing 41 of the probe 4 is provided with the positioning projection, the positioning projection may be engaged with the positioning groove 311 of the fresnel lens. That is, the fresnel lens provided in this embodiment can be applied to different types of detectors 4.

Referring to fig. 8, a probe 4 is further provided in the present embodiment, which includes a housing 41, a sensing element 42, and a fresnel lens provided in any of the above embodiments. For example, the detector 4 may be hung on a wall 2.2 meters high, so that the detector 4 forms a stereo fan-shaped detection area. Here, PIR (pyroelectric infrared sensor) may be used as the sensing element 42. The fresnel lens is mounted on the end of the casing 41 and the fresnel lens body 1 extends from the casing 41, the sensor 42 is mounted in the casing 41 and faces the fresnel lens, and the detection end of the sensor 42 is located at the focus of the fresnel lens.

In this embodiment, the detector 4 using the above fresnel lens has the spherical surface of each lens unit 121, the difficulty of splicing can be reduced in the splicing process of the lens units 121, the production cost of the fresnel lens is low, and the production cost of the detector 4 is reduced.

The embodiment of the application also provides a security system which comprises the detector 4 provided by the embodiment. For example, the security system provided by the embodiment may further include an alarm, and the alarm is electrically connected to the detector 4. When the detector 4 detects a moving object in the detection area, the detector 4 sends an electric signal to the alarm, and the alarm sends an alarm after receiving the electric signal. This structure adopts above-mentioned detector 4's security protection system, because detector 4's manufacturing cost is lower to security protection system's overall cost has been reduced.

The present invention is not intended to be limited to the particular embodiments shown and described, but is to be accorded the widest scope consistent with the principles and novel features herein disclosed.

Claims (10)

1. A Fresnel lens including a main body portion having an incident surface and a Fresnel surface which are arranged to face each other;

the incident surface is an irregular surface which is convexly arranged outwards;

the Fresnel surface is a spherical surface which is concavely arranged towards the direction of the incidence surface, the Fresnel surface comprises a plurality of lens units, each lens unit is provided with a plurality of concentric Fresnel teeth, and the lens units are used for focusing light rays entering from the incidence surface to a focus on the inner side of the main body part.

2. The fresnel lens according to claim 1, wherein the incident surface comprises a central spherical surface and a curved surface provided at an edge of the central spherical surface.

3. The fresnel lens according to claim 1, wherein the fresnel surface includes a far-distance multi-vision region, an intermediate multi-vision region provided on a side of the far-distance multi-vision region, and a near-distance multi-vision region located on a side of the intermediate multi-vision region remote from the far-distance multi-vision region, and the near-distance multi-vision region is located within the intermediate multi-vision region; the distance multi-vision region, the intermediate multi-vision region and the near multi-vision region each include a plurality of the lens units.

4. The fresnel lens according to claim 3, wherein the plurality of lens units of the distance multi-vision region are symmetrically distributed along a vertical center line of the main body portion; the lens units of the intermediate distance multi-vision area are symmetrically distributed along the vertical central line of the main body part; the lens units of the near multi-vision area are symmetrically distributed along the vertical center line of the main body part.

5. A fresnel lens according to claim 3, wherein the area of the distance multi-vision region is greater than one-half of the area of the fresnel surface.

6. A fresnel lens according to claim 1, wherein the distance between the focal point and the main body portion is smaller than the radius of curvature of the fresnel surface; and/or the presence of a gas in the gas,

the thickness of the main body part is 0.5mm-1.2 mm.

7. The Fresnel lens according to any one of claims 1 to 6, wherein a straight cylinder section is provided at an edge of the main body, a flange is provided at an end of the straight cylinder section away from the main body, and a positioning portion is provided on the flange.

8. The fresnel lens according to claim 7, wherein the positioning portion includes a plurality of positioning grooves provided on the flange and a plurality of positioning holes provided on the flange.

9. A probe, comprising a housing, a sensing element, and a Fresnel lens according to any one of claims 1 to 8, wherein the Fresnel lens is mounted on an end portion of the housing with a main body portion of the Fresnel lens extending from the housing, the sensing element is mounted in the housing so as to face the Fresnel lens, and a detection end of the sensing element is located at a focal point of the Fresnel lens.

10. A security system comprising a detector as claimed in claim 9.

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