Free operation single photon detector based on multistage refrigeration

Abstract

The invention discloses a free operation single photon detector based on multistage refrigeration, which comprises a shell, a radiator module, a PCB and a secondary refrigeration module, the secondary refrigeration module comprises an NFAD and a multilayer TEC which are arranged up and down, the radiator module comprises a radiator and a fan installed on the radiator, the PCB is fixed above the radiator module, and the PCB is fixed above the radiator module. The secondary refrigeration module is placed at the middle opening of the PCB, and the bottom surface of the secondary refrigeration module is in contact with the upper radiating surface of the radiator; first-stage refrigeration of the NFAD is realized through an internal TEC of the NFAD; the secondary refrigeration effect is realized on the basis of primary refrigeration by controlling the current direction and magnitude of the multiple layers of TECs; and a fan is arranged on the radiator module for power supply operation to realize three-stage refrigeration. According to the single-photon detector based on multistage refrigeration provided by the invention, rapid heat exchange of a core device can be realized through a multistage refrigeration strategy of device self refrigeration, multilayer TEC secondary refrigeration and fan forced air cooling.

Description

Technical Field

[0001] This patent belongs to the field of optoelectronic detection devices, and specifically relates to a free-running single-photon detector based on multi-stage refrigeration. Background Art

[0002] Currently, the free-running single-photon detection technology generally uses a negative-feedback avalanche diode (NFAD) as the core detection device, which can achieve rapid quenching of the avalanche current and suppress the after-pulse effect, providing solutions for asynchronous weak-light detection applications such as quantum communication, lidar, and fluorescence lifetime detection.

[0003] During operation, the lower the ambient temperature of the NFAD, the better the detection efficiency. However, the traditional thermoelectric cooler (TEC) requires a large amount of power to reach the low-temperature refrigeration target, and the heat exchange efficiency between devices is low, resulting in limited detection efficiency.

[0004] The Chinese patent "Refrigeration Device and Equipment for Single-Photon Detector" with the application number CN202220549806.6 discloses a refrigeration device and equipment for a single-photon detector, including a heat sink, a multi-layer thermoelectric cooler TEC, a thermal conductive film, and a photodetector. Among them, a through-hole for placing the single-photon detector is provided inside the heat sink; the multi-layer thermoelectric cooler TEC includes N layers of thermoelectric coolers TEC; the inside of the thermal conductive film is hollow and fixedly arranged on the top of the multi-layer thermoelectric cooler TEC; one end of the photodetector is fixedly arranged inside the heat sink, effectively utilizing the cold surface of the first-layer thermoelectric cooler in the multi-layer thermoelectric cooler TEC to achieve effective refrigeration of the single-photon detector and ensure the stability of the performance of the single-photon detector. However, the refrigeration method of this refrigeration device is single, and the devices are separated from each other and connected individually, with poor fastening effect. In actual use, the devices may become loose or even separate from each other; during the rapid refrigeration process, the surface of the pin parts of the photodetector and the single-photon detector is lower than the ambient temperature, and when the humid ambient air encounters the surface below the dew point, water vapor will condense to form condensation, resulting in a decrease in the working efficiency of the device or even causing failure, reducing the service life of the equipment.

[0005] In the Chinese patent "A Refrigeration Structure and a Single Photon Detection Device" with the application number CN202010244596.5, a refrigeration box structure is disclosed, which includes a plurality of refrigeration boxes arranged side by side. Each refrigeration box is individually encapsulated and includes a radiator, a housing, a TEC cooler, a bias plate, an APD tube (avalanche photodiode), and an optical fiber connector. The TEC cooler, the bias plate, and the APD tube are fixed inside the housing, the radiator is fixed outside the housing, and the optical fiber connector extends into the interior of the refrigeration box through an optical fiber connection hole for connecting the optical fiber of the APD tube inside the refrigeration box and the transmission optical fiber outside the refrigeration box. By arranging a plurality of refrigeration boxes side by side to form a refrigeration structure, when a certain channel fails, only the corresponding refrigeration box needs to be removed and repaired, without affecting other channels, improving the stability of the product. However, the core device of this device uses a traditional APD tube, and the heat dissipation method is through heat transfer by contact between the tube wall and the tube clamp, and the heat exchange effect is not good. Summary of the Invention

[0006] The technical problem to be solved by the present invention is how to improve the refrigeration effect of a free-running single photon detector.

[0007] The present invention solves the above technical problems through the following technical means: A free-running single photon detector based on multi-stage refrigeration includes a housing (1), a radiator module (2), a PCB board (3), and a secondary refrigeration module (5). The radiator module (2), the PCB board (3), and the secondary refrigeration module (5) are all enclosed in the housing (1). The secondary refrigeration module (5) includes an NFAD (5-A) and a multi-layer TEC (5-D) arranged vertically. The radiator module (2) includes a radiator (2-A) and a fan (2-B) installed on the radiator. The PCB board (3) is fixed above the radiator module (2). The secondary refrigeration module (5) is placed at the middle opening of the PCB board (3) and its bottom surface is in contact with the heat dissipation surface on the radiator (2-A);

[0008] Through the internal TEC (5-A-4) of the NFAD (5-A), the first-stage refrigeration of the NFAD (5-A) is realized; by controlling the current direction and magnitude of the multi-layer TEC (5-D), the second-stage refrigeration effect is realized on the basis of the first-stage refrigeration; the fan (2-B) on the radiator module (2) is powered to operate to realize the third-stage refrigeration.

[0009] As an optimized technical solution, when in a normal ventilation and room temperature environment, two-stage refrigeration is carried out using the internal TEC (5-A-4) of the device and the multi-layer TEC (5-D), and the fan is set to the sleep state; when in a harsh environment with poor wind speed and high ambient temperature, the fan (2-B) is controlled to operate for third-stage refrigeration.

[0010] As an optimized technical solution, the secondary refrigeration module (5) is provided with an NFAD (5-A), a copper block base (5-B), a plastic pressing block (5-C), and a multi-layer TEC (5-D) from top to bottom. The bottom surface of the multi-layer TEC (5-D) is in contact with the upper surface of the radiator (2-A), and the copper block base (5-B) is fixed on the plastic pressing block (5-C) and is in contact with the top surface of the multi-layer TEC (5-D).

[0011] As an optimized technical solution, the plastic pressing block (5-C) is a ring frame, nested around the multi-layer TEC (5-D), and at the same time has a groove structure at the bottom to press the bottom layer of the multi-layer TEC (5-D). The plastic pressing block (5-C) is fixed on the surface of the radiator (2-A), and the multi-layer TEC (5-D) is fixedly installed between the radiator (2-A) and the plastic pressing block (5-C). The NFAD (5-A) is fixedly installed in the groove opened on the upper surface of the copper block base (5-B).

[0012] As an optimized technical solution, the free-running single-photon detector based on multi-stage refrigeration further includes a shielding cover module (4), and the secondary refrigeration module (5) is wrapped in the enclosed space formed by the shielding cover module (4).

[0013] As an optimized technical solution, the material of the shielding cover module (4) is aluminum alloy, and at the same time, the internal space of the shielding cover module (4) is filled with foam.

[0014] As an optimized technical solution, the optical fiber end of the NFAD (5-A) passes through the optical fiber hole (406) provided at the bottom side of the shielding cover module (4), and after being fixed, the gap of the optical fiber hole (406) is filled with glue.

[0015] As an optimized technical solution, the shielding cover module (4) is located at a corner of the radiator module (2). The upper end of the radiator module (2) extends out an installation post (202), and the PCB board (3) is fixed on the installation post (202). There are 3 installation posts (202), and a corner of the PCB board (3) that is not fixed on the installation post (202) is supported and fixed by the shielding cover module (4).

[0016] As an optimized technical solution, the radiator module (2) further includes a protruding post structure (203) that protrudes, and the protruding post structure (203) is in contact with the high-heat chips on the PCB board (3).

[0017] As an optimized technical solution, a plurality of threaded holes (201) are provided on the side of the radiator (2-A), and the screws are fixed to the threaded holes (201) through the mounting holes of the fan (2-B) to realize the installation of the fan (2-B). A cavity is provided at the position of the radiator (2-A) corresponding to the installation of the fan (2-B), and the whole fan (2-B) is recessed into the radiator (2-A) and integrated into one body.

[0018] The advantages of the present invention are as follows:

[0019] 1. The present invention proposes a free-running single-photon detector based on multi-stage refrigeration. Through the multi-stage refrigeration strategy of "device self-refrigeration - multi-layer TEC secondary refrigeration - fan forced air cooling", rapid heat exchange of the core device can be achieved;

[0020] 2. At the same time, the secondary refrigeration module is wrapped in a closed space that isolates air, preventing the device from being exposed to the air. During the rapid refrigeration process, it prevents the temperature of the pin part of the free-running single-photon detector based on multi-stage refrigeration from being lower than the ambient temperature, effectively solving the condensation problem and enhancing the environmental adaptability;

[0021] 3. A secondary refrigeration module is designed, which uses a copper block base and a plastic pressing block in cooperation to improve the installation stability and heat dissipation effect of the refrigeration device;

[0022] 4. The installation method of the secondary refrigeration module increases the fastening property of the secondary refrigeration module. Using the integrated NFAD design, the APD chip is integrally welded inside the NFAD without welding the pins to the circuit board, so there is no need to reserve a certain space for operation, further realizing the miniaturized design. Description of the Drawings

[0023] Figure 1 is an exploded view of a free-running single-photon detector based on multi-stage refrigeration according to an embodiment of the present invention;

[0024] Figure 2 is an exploded view of the housing in an embodiment of the present invention;

[0025] Figure 3 is an internal structure diagram of a free-running single-photon detector based on multi-stage refrigeration according to an embodiment of the present invention;

[0026] Figure 4 is a structure diagram of the radiator module in an embodiment of the present invention;

[0027] Figure 5 is a relative position structure diagram of the shielding cover module, the PCB board and the secondary refrigeration module in an embodiment of the present invention;

[0028] Figure 6 is a structure diagram of the secondary refrigeration module in an embodiment of the present invention;

[0029] Figure 7 is the explosion diagram of the secondary refrigeration module in the embodiment of the present invention;

[0030] Figure 8 is the cross-sectional view of NFAD in the embodiment of the present invention. Detailed implementation manners

[0031] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] Please refer to Figure 1 As shown, the present invention provides a freely operating single-photon detector based on multi-stage refrigeration, including a housing 1, a radiator module 2, a PCB board 3, a shielding cover module 4, and a secondary refrigeration module 5. The radiator module 2, the PCB board 3, the shielding cover module 4, and the secondary refrigeration module 5 are all enclosed in the housing 1. The PCB board 3 is fixed above the radiator module 2. The PCB board 3 is clamped in the middle of the shielding cover module 4. The bottom of the shielding cover module 4 is empty and fixed on the upper surface of the radiator 2-A. An opening is provided in the clamped part of the PCB board 3. The secondary refrigeration module 5 is placed in the middle opening of the PCB board 3. The overall structure of the secondary refrigeration module 5 is sealed in the shielding cover module 4 and the bottom surface is in contact with the upper heat dissipation surface of the radiator module 2.

[0033] Figure 2 is the explosion diagram of the housing 1, where 1-A is the front panel, 1-B is the U-shaped ring frame, 1-C is the rear panel, and 1-D is the upper cover. The front panel 1-A, the rear panel 1-C, the ring frame 1-B, and the upper cover 1-D together form a square housing 1. The positions and numbers of the boss structures on the front panel 1-A and the rear panel 1-C are the same. Specifically, the boss structures 101 at both ends of the upper side on the front panel 1-A, the boss structures 103 at both ends of the lower side, the boss structures (not shown in the figure) at both ends of the upper side on the rear panel 1-C, and the boss structures (not shown in the figure) at both ends of the lower side are respectively fixed to the mounting holes 102 (4) on the upper side of the side plate and the mounting holes 104 (4) on the lower side of the side plate of the ring frame 1-B by screws. The boss structure 106 on the upper cover 1-D and the mounting holes 105 at both ends of the upper side of the rear panel 1-C are fixed by screws.

[0034] Figure 3This is the internal structure diagram of the detector. The PCB board 3 is fixed above the radiator module 2. The shielding cover module 4 is located at a corner of the radiator module 2. The PCB board 3 passes through the shielding cover module 4 and divides the shielding cover module 4 into upper and lower parts. The part of the circuit module where the high-performance chips are located on the PCB board 3 is clamped in the middle of the shielding cover module 4. This design can perform electromagnetic shielding and at the same time assist in supporting and fixing the PCB board 3. The bottom of the shielding cover module 4 is fixed on the upper surface of the radiator module 2 by screws.

[0035] Figure 4 This is the structure diagram of the radiator module 2. The radiator module 2 includes a radiator 2-A and a fan 2-B. After milling, the upper end of the radiator 2-A extends out the mounting posts 202. Figure 3 In this, the PCB board 3 is fixed on the mounting posts 202. There are actually only 3 mounting posts 202. One corner of the PCB board 3 that is not fixed on the mounting posts 202 is supported and fixed by the shielding cover module 4. Other protruding post structures 203 on the radiator 2-A are in contact with the high-heat chips on the PCB board 3 to achieve rapid heat exchange. A plurality of threaded holes 201 are provided on the side of the radiator 2-A. Screws pass through the mounting holes of the fan 2-B and are fixed in the threaded holes 201 to achieve the installation of the fan 2-B, reducing the number of parts required for installing the fan 2-B. And a cavity is provided at the position of the radiator 2-A corresponding to the installation of the fan 2-B. The fan 2-B is integrally recessed into the radiator 2-A, and the air direction of the fan 2-B corresponds to the fin direction.

[0036] Figure 5 This is the relative position structure diagram of the shielding cover module 4, the PCB board 3, and the secondary refrigeration module 5. The shielding cover module 4 includes a shielding cover upper cover 4-A, a shielding cover 4-B, and a shielding cover ring frame 4-C. The bottom of the shielding cover module 4 is empty. The shielding cover upper cover 4-A covers the shielding cover 4-B. The PCB board 3 is clamped between the shielding cover 4-B and the shielding cover ring frame 4-C. An opening is provided in the clamped part of the PCB board 3, dividing the shielding cover module 4 into upper and lower parts, thus forming upper and lower cavities with an opening in the middle. The upper cavity, that is, the space contained in the shielding cover 4-B, accommodates the high-performance chips on the PCB board 3.

[0037] At the same time, refer to Figure 6, It is the structure diagram of the secondary refrigeration module 5. The secondary refrigeration module 5 is placed at the middle opening of the PCB board 3. The overall structure of the secondary refrigeration module 5 penetrates the upper and lower cavities. The secondary refrigeration module 5 includes an NFAD 5-A, a copper block base 5-B, a plastic pressing block 5-C, and multiple layers of TEC 5-D arranged in sequence from top to bottom. Specifically, the shape of the opening of the PCB board 3 matches the shape of the NFAD 5-A of the secondary refrigeration module 5. The two pins on both sides of the NFAD 5-A are soldered to the PCB board 3, so that the NFAD 5-A is located in the upper cavity, that is, the shielding cover 4-B. The copper block base 5-B, the plastic pressing block 5-C, and multiple layers of TEC 5-D are fixed together and located in the lower cavity, that is, the shielding cover ring frame 4-C. The NFAD 5-A is fixed through the copper block base 5-B located below the PCB board 3, and its optical fiber tail end is ejected through the optical fiber hole 406 at the bottom side of the shielding cover ring frame 4-C. After fixing, the gap of the optical fiber hole 406 is filled with glue to make the overall structure of the shielding cover module 4 form a sealed space. The shielding cover upper cover 4-A and the shielding cover 4-B are fixed with screws through the mounting holes 401 and 402 (four each). The PCB board 3 is fixed with screws through the mounting holes 407 on it and the mounting holes 403 (four each) on the upper shielding cover 4-B and the mounting holes 404 (four each) on the lower shielding cover ring frame 4-C. The shielding cover ring frame 4-C is fixed on the upper surface of the radiator 2-A through the bosses 405 around the bottom. The material of the shielding cover module 4 is aluminum alloy, and the structural design meets the electromagnetic shielding requirements of high-performance chips on the PCB board 3. At the same time, the internal space of the shielding cover module 4 is filled with foam, and the secondary refrigeration module 5 is wrapped in the sealed space formed by the shielding cover module 4 to prevent the device from being exposed to the air, effectively solving the condensation problem caused by rapid refrigeration.

[0038] Figure 7 It is the explosion diagram of the secondary refrigeration module 5. Also refer to Figure 1 and Figure 4 , The installation method of the secondary refrigeration module 5 can improve the installation stability of the secondary refrigeration module 5. The specific installation method is as follows:

[0039] STEP1: The bottom surface of the multiple layers of TEC 5-D contacts the upper surface of the radiator 2-A, which can conduct the heat of the bottom hot surface to the radiator 2-A to achieve a rapid heat exchange effect;

[0040] STEP2: The plastic pressing block 5-C can be designed as a ring frame and nested around the multiple layers of TEC 5-D. At the same time, a groove structure is provided at the bottom, which can press the bottom layer of the multiple layers of TEC 5-D. Through holes 504 are opened at the four corners of the plastic pressing block 5-C. After the screws pass through the through holes 504, they are fixed on the surface mounting holes of the radiator 2-A to fix the multiple layers of TEC 5-D between the radiator 2-A and the plastic pressing block 5-C;

[0041] STEP 3: The copper block base 5-B is located above the plastic pressing block 5-C and is in contact with the top surface of the multi-layer TEC 5-D. The copper block base 5-B and the plastic pressing block 5-C share the same set of mounting through holes 503 and 504 (four each). The copper block base 5-B is fixed to the plastic pressing block 5-C by screws and presses the top surface of the multi-layer TEC 5-D.

[0042] STEP 4: The NFAD 5-A is located above the copper block base 5-B. A groove is provided on the upper surface of the copper block base 5-B, and threaded holes 502 for fixing the NFAD 5-A are provided at the four corners of the groove. The NFAD 5-A is placed in the groove of the copper block base 5-B, and the NFAD 5-A is fixedly installed on the copper block base 5-B by screws passing through the mounting holes 501 of the NFAD 5-A. Copper has high heat exchange efficiency, and at the same time, the contact area of the hot surface of the NFAD 5-A is increased.

[0043] See Figure 8 , which is a cross-sectional view of the NFAD 5-A. The NFAD 5-A includes an optical fiber 5-A-1, a chip 5-A-2, a temperature sensor 5-A-3, an internal TEC 5-A-4, and a housing 5-A-5. The optical fiber 5-A-1 and the internal TEC 5-A-4 are fixed on the housing 5-A-5. The chip 5-A-2 is arranged on the cold surface of the internal TEC 5-A-4. The temperature sensor 5-A-3 is located on the chip 5-A-2 and is connected to the chip 5-A-2. The temperature sensor 5-A-3 is used to monitor the internal temperature condition of the NFAD 5-A and transmit signals to the chip 5-A-2 for temperature control.

[0044] The multi-stage refrigeration strategy of the free-running single-photon detector based on multi-stage refrigeration designed by the present invention is as follows: The internal TEC 5-A-4 of the NFAD 5-A can achieve the first-stage refrigeration of the NFAD 5-A, avoiding low-efficiency heat exchange in a contact manner; by controlling the direction and magnitude of the current of the multi-layer TEC 5-D, a second-stage refrigeration effect can be achieved on the basis of the first-stage refrigeration inside the NFAD 5-A itself; the fan 2-B on the radiator module 2 is powered to operate, and the heat of each chip of the detector can be blown away by forced air cooling, realizing the third-stage refrigeration.

[0045] The present invention can adapt to different environments: When in a normal ventilation and room temperature environment (such as a laboratory), two-stage refrigeration is carried out using the internal TEC 5-A-4 and the multi-layer TEC 5-D of the device, and the fan is set to the sleep state, which can not only meet the heat dissipation requirements but also avoid problems such as the short service life of the fan itself and the noise generated during operation; when in a harsh environment with poor air velocity and high ambient temperature (such as an equipment machine room), the fan 2-B is controlled to operate for third-stage refrigeration, and rapid heat exchange is achieved through forced air cooling.

[0046] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A free-running single-photon detector based on multi-stage refrigeration, characterized in that: It includes a housing (1), a radiator module (2), a PCB board (3), and a secondary refrigeration module (5). The radiator module (2), the PCB board (3), and the secondary refrigeration module (5) are all enclosed within the housing (1). The secondary refrigeration module (5) includes an NFAD (5-A) and multiple layers of TECs (5-D) arranged vertically. The radiator module (2) includes a radiator (2-A) and a fan (2-B) installed on the radiator. The PCB board (3) is fixed above the radiator module (2). The secondary refrigeration module (5) is placed at the middle opening of the PCB board (3) and its bottom surface contacts the heat dissipation surface on the radiator (2-A). Through the internal TEC (5-A-4) of the NFAD (5-A), primary refrigeration of the NFAD (5-A) is achieved. By controlling the current direction and magnitude of the multiple layers of TECs (5-D), a secondary refrigeration effect is achieved on the basis of primary refrigeration. The fan (2-B) on the radiator module (2) is powered to operate to achieve tertiary refrigeration.

2. The free-running single-photon detector based on multi-stage refrigeration according to claim 1, characterized in that: When in a normal ventilation and room temperature environment, two-stage refrigeration is carried out using the internal TEC (5-A-4) of the device and the multiple layers of TECs (5-D), and the fan is set to the sleep state. When in a harsh environment with poor wind speed and high ambient temperature, the fan (2-B) is controlled to operate for tertiary refrigeration.

3. The free-running single-photon detector based on multi-stage refrigeration according to claim 1, wherein: The secondary refrigeration module (5) is sequentially provided with an NFAD (5-A), a copper block base (5-B), a plastic pressing block (5-C), and multiple layers of TECs (5-D) from top to bottom. The bottom surface of the multiple layers of TECs (5-D) contacts the upper surface of the radiator (2-A). The copper block base (5-B) is fixed on the plastic pressing block (5-C) and contacts the top surface of the multiple layers of TECs (5-D).

4. The free-running single-photon detector based on multi-stage refrigeration according to claim 3, wherein: The plastic pressing block (5-C) is a ring frame, nested around the multiple layers of TECs (5-D), and at the same time has a groove structure at the bottom to press the bottom layer of the multiple layers of TECs (5-D). The plastic pressing block (5-C) is fixed on the surface of the radiator (2-A), and the multiple layers of TECs (5-D) are fixedly installed between the radiator (2-A) and the plastic pressing block (5-C). The NFAD (5-A) is fixedly installed in the groove opened on the upper surface of the copper block base (5-B).

5. The free-running single-photon detector based on multi-stage refrigeration according to claim 1, wherein: It further includes a shielding cover module (4). The secondary refrigeration module (5) is enclosed within the enclosed space formed by the shielding cover module (4).

6. The free-running single-photon detector based on multi-stage refrigeration according to claim 5, characterized in that: The material of the shielding cover module (4) is aluminum alloy, and at the same time, the internal space of the shielding cover module (4) is filled with foam.

7. The free-running single-photon detector based on multi-stage refrigeration according to claim 5, wherein: The optical fiber end of the NFAD (5-A) passes through the optical fiber hole (406) provided at the bottom side of the shielding cover module (4). After being fixed, the gap of the optical fiber hole (406) is filled with glue.

8. A free-running single-photon detector based on multi-stage refrigeration according to claim 5, characterized in that: The shielding cover module (4) is located at a corner of the radiator module (2). The upper end of the radiator module (2) extends out the mounting posts (202). The PCB board (3) is fixed on the mounting posts (202). There are 3 mounting posts (202), and a corner of the PCB board (3) not fixed on the mounting posts (202) is supported and fixed by the shielding cover module (4).

9. The free-running single-photon detector based on multi-stage refrigeration according to claim 8, characterized in that: The radiator module (2) further includes a protruding stud structure (203), and the stud structure (203) is in contact with the high-heat chips on the PCB board (3).

10. A free-running single-photon detector based on multi-stage refrigeration according to claim 1, characterized in that: A plurality of threaded holes (201) are provided on the side of the radiator (2-A). Screws pass through the mounting holes of the fan (2-B) and are fixed in the threaded holes (201) to realize the installation of the fan (2-B). A cavity is provided at the position of the radiator (2-A) corresponding to the installation of the fan (2-B), and the whole fan (2-B) is recessed into the radiator (2-A) and integrated into one body.

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