CN217283322U

CN217283322U - Bluetooth headset with anti-interference function

Info

Publication number: CN217283322U
Application number: CN202220644480.5U
Authority: CN
Inventors: 何越
Original assignee: Dongguan Yuanze Acoustics Technology Co ltd
Current assignee: Dongguan Yuanze Acoustics Technology Co ltd
Priority date: 2022-03-23
Filing date: 2022-03-23
Publication date: 2022-08-23
Anticipated expiration: 2032-03-23

Abstract

The utility model belongs to the technical field of Bluetooth earphones, in particular to a Bluetooth earphone with an anti-interference function, which comprises an earphone shell, a moving coil and a battery; the earphone shell is internally provided with a containing cavity, the front end and the rear end of the earphone shell are respectively provided with a sound outlet pipe and an air inlet hole which are communicated with the containing cavity, the moving coil and the battery are both arranged in the containing cavity, and the moving coil is close to the sound outlet pipe; the moving coil comprises a shell, a moving coil unit, a first shielding plate, a second shielding plate and a circuit board; the movable coil unit is arranged in the mounting cavity and close to the sound outlet; the first shielding plate, the circuit board and the second shielding plate are sequentially arranged in the installation cavity, the first shielding plate is close to the moving coil unit, through holes are formed in the middle parts of the first shielding plate, the circuit board and the second shielding plate in a penetrating mode, and filter cotton covers the through holes; the moving coil unit and the battery are electrically connected with the circuit board.

Description

Bluetooth headset with anti-interference function

Technical Field

The utility model belongs to the technical field of bluetooth headset, especially, relate to a bluetooth headset with anti-interference function.

Background

The Bluetooth earphone applies the Bluetooth technology to the hands-free earphone, so that users can avoid annoying wiring stumbling and can easily talk in various ways. Since the advent of bluetooth headsets, it has been a good tool for the mobile commerce family to improve efficiency.

The existing wireless Bluetooth headset has poor anti-interference capability and is easily interfered by noise and electromagnetic waves, so that the tone quality of the wireless Bluetooth headset is influenced.

SUMMERY OF THE UTILITY MODEL

An object of the utility model is to provide a bluetooth headset with anti-interference function, it is relatively poor to aim at solving among the prior art bluetooth headset interference killing feature, receives noise and electromagnetic wave's interference easily to influence the technical problem of wireless bluetooth headset's tone quality.

In order to achieve the above object, an embodiment of the present invention provides a bluetooth headset with an anti-interference function, which includes a headset housing, a moving coil and a battery; the earphone shell is internally provided with a containing cavity, the front end and the rear end of the earphone shell are respectively provided with a sound outlet pipe and an air inlet hole which are communicated with the containing cavity, the moving coil and the battery are both arranged in the containing cavity, and the moving coil is close to the sound outlet pipe;

the moving coil comprises a shell, a moving coil unit, a first shielding plate, a second shielding plate and a circuit board; the movable coil unit is arranged in the mounting cavity and close to the sound outlet; the first shielding plate, the circuit board and the second shielding plate are sequentially arranged in the installation cavity, the first shielding plate is close to the moving coil unit, through holes are formed in the middle parts of the first shielding plate, the circuit board and the second shielding plate in a penetrating mode, and filter cotton covers the through holes; the moving coil unit and the battery are electrically connected with the circuit board.

Optionally, an installation table is convexly arranged on the inner wall of the accommodating cavity, and a plurality of threaded holes are formed in the installation table; a fixing table extends outwards from the edge of the mounting port, a plurality of first connecting holes are formed in the fixing table in a penetrating mode, a plurality of second connecting holes are formed in the second shielding plate in a penetrating mode, and the plurality of second connecting holes are respectively in one-to-one correspondence with the plurality of first connecting holes; the screw passes in proper order the second connecting hole with first connecting hole with screw hole threaded connection, thereby will casing with second shield plate fixed mounting in hold the intracavity.

Optionally, a plurality of jacks are uniformly distributed in the annular shape of the fixed platform, a plurality of inserting columns are uniformly distributed in the annular shape of the second shielding plate, and the plurality of inserting columns are respectively and fixedly inserted into the plurality of jacks.

Optionally, a first filter screen covering the air inlet is arranged in the accommodating cavity.

Optionally, a second filter screen covering the sound outlet end of the sound outlet pipe is arranged in the accommodating cavity.

Optionally, the second shielding plate further penetrates through a threading hole, the threading hole is sleeved with an anti-interference magnetic ring, a cable penetrates through the anti-interference magnetic ring, and two ends of the cable are electrically connected with the circuit board and the battery respectively.

Optionally, the moving coil unit comprises a T-iron, a voice diaphragm, a voice coil and an external magnet; the sound film, the external magnet and the T iron are sequentially arranged in the mounting cavity, and the sound film is close to the sound outlet; the T iron comprises a bottom plate and a bulge arranged in the middle of the bottom plate; the bulge is close to the sound film, the outer magnet is sleeved outside the bulge, and an accommodating groove is formed between the outer magnet and the bulge; one end of the voice coil is connected with the sound film, and the other end of the voice coil is movably accommodated in the accommodating groove; the circuit board is electrically connected with the voice coil; a first through hole penetrates through the middle of the protrusion, at least one second through hole penetrates through the bottom plate, and the second through hole is communicated with the accommodating groove.

Optionally, a mounting groove is dug at the bottom of the protrusion, and the first through hole is communicated with the mounting groove; an inner magnet is arranged in the mounting groove, the inner magnet and the outer magnet are arranged in an inner-outer corresponding mode, and a first clearance hole for avoiding the first through hole penetrates through the middle of the inner magnet.

Optionally, a washer is arranged between the external magnet and the sound film, and a second clearance hole for clearance of the voice coil penetrates through the middle of the washer.

Optionally, the first shielding plate is disc-shaped, the top end of the surrounding wall of the first shielding plate supports the edge of the bottom plate, the through hole is formed in the bottom wall of the second shielding plate, and a cavity for flowing air flow is formed between the first shielding plate and the bottom plate.

Compared with the prior art, the embodiment of the utility model provides an above-mentioned one or more technical scheme in the bluetooth headset with anti-interference function have one of following technological effect at least:

during operation, the moving coil unit generates sound through moving coil vibration and is transmitted out from the sound outlet pipe, and outside air and noise pass in and out of the moving coil unit through the air inlet holes and the through holes to balance airflow generated by the moving coil unit due to vibration, so that the tone quality of the moving coil unit is better. Wherein, electronic signal or electromagnetic wave in the second shield plate can effectively shield external noise, electronic signal or electromagnetic wave that first shield plate produced when effectively shielding circuit board functions, prevent that electronic signal or electromagnetic wave that the circuit board produced from causing the interference to the moving coil unit, the interference killing feature is high, and simultaneously, the noise that the outside air transmitted into can be filtered to the filter pulp, the tone quality of effectual assurance moving coil unit, make the tone quality of moving coil unit good, thereby make bluetooth headset's tone quality good.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the embodiments or the prior art descriptions will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive labor.

Fig. 1 is the utility model discloses a bluetooth headset with anti-interference function's structural schematic.

Fig. 2 is the utility model discloses a bluetooth headset with anti-interference function's cross-sectional view.

Fig. 3 is a sectional view of the moving coil of the present invention.

Fig. 4 is an exploded view of the moving coil of the present invention.

Wherein, in the figures, the respective reference numerals:

100. an earphone housing; 101. an accommodating chamber; 102. an installation table; 103. a threaded hole; 110. a sound outlet pipe; 120. An air inlet; 130. a first filter screen; 140. a second filter screen;

200. moving coils; 210. a housing; 211. a mounting cavity; 212. a sound outlet; 213. an installation port; 214. a cylindrical enclosure wall; 215. an end wall; 216. a fixed table; 217. a first connection hole; 218. a jack; 220. a moving coil unit; 221. t iron; 221a, a bottom plate; 221b, a projection; 221c, a first through hole; 221d, a second through hole; 221e, mounting grooves; 222. a voice coil; 223. an external magnet; 224. a containing groove; 225. a sound membrane; 226. An inner magnet; 227. washer; 230. a first shield plate; 231. a cavity; 240. a second shielding plate; 241. A second connection hole; 242. a screw; 243. inserting a column; 244. threading holes; 245. an anti-interference magnetic ring; 246. A cable; 250. a circuit board; 260. perforating; 261. filtering cotton;

300. a battery.

Detailed Description

Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and intended to explain the embodiments of the present invention and are not to be construed as limiting the present invention.

In the description of the embodiments of the present invention, it should be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like are used in the orientation or positional relationship indicated in the drawings, which is only for convenience in describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element so indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore should not be construed as limiting the invention.

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 embodiments of the present invention, "a plurality" means two or more unless specifically limited otherwise.

In the embodiments of the present invention, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "fixed" are to be construed broadly, e.g., as fixed or detachable connections or as an integral part; can be mechanically or electrically connected; they may be directly connected or indirectly connected through intervening media, or may be connected through the use of two elements or the interaction of two elements. The specific meaning of the above terms in the embodiments of the present invention can be understood by those skilled in the art according to specific situations.

In an embodiment of the present invention, referring to fig. 1 to 4, a bluetooth headset with anti-interference function is provided, which includes a headset housing 100, a moving coil 200 and a battery 300.

Referring to fig. 1 to 4, an accommodating cavity 101 is provided in the earphone housing 100, a sound outlet tube 110 and an air inlet hole 120 which are communicated with the accommodating cavity 101 are respectively provided at the front end and the rear end of the earphone housing 100, the moving coil 200 and the battery 300 are both installed in the accommodating cavity 101, and the moving coil 200 is close to the sound outlet tube 110.

Referring to fig. 1 to 4, the moving coil 200 includes a case 210, a moving coil unit 220, a first shield plate 230, a second shield plate 240, and a circuit board 250. The casing 210 is provided with a mounting cavity 211 therein, the opposite ends of the casing 210 are respectively provided with a sound outlet 212 and a mounting port 213 which are communicated with the mounting cavity 211, and the moving coil unit 220 is mounted in the mounting cavity 211 and close to the sound outlet 212.

Referring to fig. 1 to 4, the housing 210 includes a cylindrical surrounding wall 214 and an end wall 215 covering an end opening of the cylindrical surrounding wall 214. A mounting cavity 211 is formed between the cylindrical surrounding wall 214 and the end wall 215, the sound outlet 212 is provided in the end wall 215, and the other end of the cylindrical surrounding wall 214 is a mounting opening 213.

Referring to fig. 1 to 4, the first shielding plate 230, the circuit board 250, and the second shielding plate 240 are sequentially mounted in the mounting cavity 211, the first shielding plate 230 is close to the moving coil unit 220, through holes 260 are formed in the middle portions of the first shielding plate 230, the circuit board 250, and the second shielding plate 240, and the through holes 260 are covered with filter cotton 261. Specifically, the filter cotton 261 is fixedly connected to the through hole 260 by means of glue bonding.

Referring to fig. 1 to 4, the first shielding plate 230 and the second shielding plate 240 are used to shield electronic signals, and function to shield external electromagnetic waves from the internal circuit and to shield electromagnetic waves generated inside from being radiated to the outside. The materials of the first shield plate 230 and the second shield plate 240 are generally stainless steel with a thickness of 0.2mm to 1mm and cupronickel, which is a metal shield material that is easily tinned.

Referring to fig. 1 to 4, the moving coil unit 220 and the battery 300 are electrically connected to the circuit board 250. The battery 300 is a rechargeable battery 300, and the battery 300 provides power for the circuit board 250 and the moving coil 200.

Specifically, referring to fig. 1 to 4, in operation, the moving coil unit 220 generates sound by the vibration of the moving coil 200 and transmits the sound from the sound outlet pipe 110, and the external air and noise pass through the air inlet holes 120 and the through holes 260 into and out of the moving coil unit 220 to balance the air flow generated by the vibration of the moving coil unit 220, so that the sound quality of the moving coil unit 220 is better. Wherein, electronic signal or electromagnetic wave in the external noise can effectively be shielded to second shield plate 240, electronic signal or electromagnetic wave that first shield plate 230 produced when effectively shielding circuit board 250 and operating, prevent that electronic signal or electromagnetic wave that circuit board 250 produced from causing the interference to moving coil unit 220, the interference killing feature is high, and simultaneously, filter pulp 261 can filter the noise that the outside air transmitted into, the tone quality of effectual assurance moving coil unit 220, make the tone quality of moving coil unit 220 good, thereby make bluetooth headset's tone quality good.

Referring to fig. 1 to 4, the filter cotton 261 may be polyester fiber cotton soundproof cotton, centrifugal glass cotton, rock wool, mineral wool, plant fiber spray, etc., soundproof cotton is a mature prior art, noise passes through soundproof cotton, noise sound wave energy is converted into heat energy through reflection, mutual superposition and collision of countless fibers in soundproof cotton, noise sound wave intensity is weakened, and noise disappears.

In another embodiment of the present invention, referring to fig. 1 to 4, an installation platform 102 is protruded from an inner wall of the accommodating cavity 101, and the installation platform 102 is opened with a plurality of threaded holes 103. The edge of the mounting port 213 extends outward to form a fixed platform 216, the fixed platform 216 is provided with a plurality of first connection holes 217 in a penetrating manner, the second shielding plate 240 is provided with a plurality of second connection holes 241 in a penetrating manner, and the plurality of second connection holes 241 are respectively arranged in one-to-one correspondence with the plurality of first connection holes 217. A screw 242 sequentially penetrates through the second connection hole 241 and the first connection hole 217 to be in threaded connection with the threaded hole 103, so that the housing 210 and the second shielding plate 240 are fixedly installed in the accommodating cavity 101, the assembly is convenient, and the installation is firm.

Further, referring to fig. 1 to 4, a plurality of insertion holes 218 are annularly and uniformly distributed on the fixing table 216, a plurality of insertion posts 243 are annularly and uniformly distributed on the second shielding plate 240, and the plurality of insertion posts 243 are respectively fixedly inserted into the plurality of insertion holes 218, so that the second shielding plate 240 is fixed to the housing 210, and then the housing 210 is fixedly installed in the accommodating cavity 101, which is beneficial for assembly by workers.

Further, referring to fig. 1 to 4, a first filter 130 covering the air inlet 120 is disposed in the accommodating chamber 101, and the first filter 130 can filter out dust passing through the air inlet 120, so as to prevent dust in the environment from entering the accommodating chamber 101 and protect the moving coil unit 220.

Further, referring to fig. 1 to 4, a second filter screen 140 covering the sound outlet end of the sound outlet pipe 110 is arranged in the accommodating cavity 101, and the second filter screen 140 can filter out dust passing through the sound outlet pipe 110, so that dust in the environment is prevented from entering the accommodating cavity 101, and the moving coil unit 220 is protected.

Referring to fig. 1 to 4, the first filter 130 and the second filter 140 may be nylon meshes, and have a good dust filtering effect.

Further, referring to fig. 1 to 4, a threading hole 244 is further formed through the second shielding plate 240, an anti-interference magnetic ring 245 is sleeved on the threading hole 244, a cable 246 is arranged through the anti-interference magnetic ring 245, and two ends of the cable 246 are electrically connected to the circuit board 250 and the battery 300 respectively. The anti-interference magnetic ring 245 is a mature prior art, and the anti-interference magnetic ring 245 is used for suppressing interference of electronic signals or electromagnetic waves on a power line and a signal line (the cable 246), and has an electrostatic pulse absorbing capability.

In another embodiment of the present invention, referring to fig. 1 to 4, the moving coil unit 220 includes a T-iron 221, a voice diaphragm 225, a voice coil 222, and an outer magnet 223. The sound diaphragm 225, the external magnet 223 and the T-iron 221 are sequentially mounted in the mounting cavity 211, and the sound diaphragm 225 is close to the sound outlet 212.

Referring to fig. 1 to 4, the T-bar 221 includes a bottom plate 221a and a protrusion 221b disposed in the middle of the bottom plate 221 a; the protrusion 221b is close to the sound film 225, the outer magnet 223 is sleeved outside the protrusion 221b, and a receiving groove 224 is formed between the outer magnet 223 and the protrusion 221 b. One end of the voice coil 222 is connected to the voice diaphragm 225, and the other end of the voice coil 222 is movably accommodated in the accommodating groove 224. The circuit board 250 is electrically connected to the voice coil 222. A first through hole 221c is formed through the middle of the protrusion 221b, at least one second through hole 221d is formed through the bottom plate 221a, and the second through hole 221d is communicated with the accommodating groove 224.

Specifically, referring to fig. 1 to 4, a varying current is passed through the voice coil 222 via the circuit board 250, and a varying magnetic field generated by the voice coil 222 interacts with a magnetic field of the external magnet 223, so that the voice coil 222 reciprocates in the accommodating groove 224, and the voice diaphragm 225 is driven to vibrate to generate sound. The vibration of sound membrane 225 is when the vibration, and the air vibration that promotes the cavity between sound membrane 225 and the T iron 221 produces the air current, and the air current can flow into or flow above-mentioned cavity (promptly above-mentioned cavity interior air current pass through first through-hole 221c, second through- hole 221d perforation 260 with the inlet port 120 flows outside the bluetooth headset, and the bluetooth headset outer air can pass through the inlet port 120 perforation 260 and first through-hole 221c and second through-hole 221d flow into above-mentioned cavity), make the interior air current of cavity flow even, thereby reach the air current that produces because of the vibration of sound membrane 225 in the balanced cavity, make sound membrane 225 vibrate more smoothly, promote bluetooth headset's low frequency, intermediate frequency and high frequency performance, further promote bluetooth headset tone quality, thereby promote bluetooth headset's tone quality.

Further, referring to fig. 1 to 4, an installation groove 221e is dug at the bottom of the protrusion 221b, and the first through hole 221c is communicated with the installation groove 221 e; an inner magnet 226 is arranged in the mounting groove 221e, the inner magnet 226 and the outer magnet 223 are arranged correspondingly inside and outside, and a first clearance hole for avoiding the first through hole 221c penetrates through the middle of the inner magnet 226. The air flow can flow into or out of the chamber through the air inlet holes 120, the through holes 260, the first through holes 221c and the first clearance holes. The outer magnet 223 and the inner magnet 226 interact together to form a stable magnetic field, and the voice coil 222 does not shift up and down along the accommodating groove 224 in a reciprocating manner, so that the vibration stability of the voice coil 222 and the voice diaphragm 225 is improved, and the tone quality of the Bluetooth headset is improved.

Further, referring to fig. 1 to 4, a washer 227 is disposed between the outer magnet 223 and the sound film 225, and a second clearance hole for avoiding the voice coil 222 is disposed through the middle of the washer 227. Specifically, the washer 227 has a magnetic conduction effect, and the magnetic field lines generated by the outer magnet 223 form a stable magnetic field around the washer 227 so as to provide stable motion for the voice coil 222 and ensure the sound quality of sound generated by the vibration of the sound film 225.

Further, referring to fig. 1 to 4, the first shielding plate 230 is disc-shaped, the top end of the surrounding wall of the first shielding plate 230 holds the edge of the bottom plate 221a, the through hole 260 is formed in the bottom wall of the second shielding plate, and a cavity 231 for flowing air is formed between the first shielding plate 230 and the bottom plate 221 a. Specifically, the first shielding plate 230 with a disc-shaped structure enables the first shielding plate 230 to support the T-bar 221 without blocking the second through hole 221d, so that the air flow in the cavity can flow out of the bluetooth headset through the second through hole 221d, the cavity 231, the through hole 260 and the air inlet hole 120 in sequence, and the air flow outside the bluetooth headset can flow into the cavity through the air inlet hole 120, the through hole 260, the cavity 231 and the second through hole 221d in sequence, thereby ensuring smooth flow of the air flow.

Referring to fig. 1 to 4, the circuit board 250 supports the first shielding plate 230, and the second shielding plate 240 supports the circuit board 250, so that the first shielding plate 230, the second shielding plate 240 and the circuit board 250 are stably mounted at the mounting cavity 211.

The rest of this embodiment is the same as the first embodiment, and the unexplained features in this embodiment are explained by the first embodiment, which is not described herein again.

The foregoing is a more detailed description of the present invention, taken in conjunction with the specific preferred embodiments thereof, and it is not intended that the invention be limited to the specific embodiments shown and described. To the utility model belongs to the technical field of the ordinary technical personnel, do not deviate from the utility model discloses under the prerequisite of design, its framework form can be nimble changeable, can derive series of products. But merely as a matter of simple deductions or substitutions, should be considered as belonging to the scope of patent protection of the present invention as determined by the claims submitted.

Claims

1. A Bluetooth headset with an anti-interference function is characterized by comprising a headset shell, a moving coil and a battery; the earphone shell is internally provided with a containing cavity, the front end and the rear end of the earphone shell are respectively provided with a sound outlet pipe and an air inlet hole which are communicated with the containing cavity, the moving coil and the battery are both arranged in the containing cavity, and the moving coil is close to the sound outlet pipe;

2. The bluetooth headset with anti-jamming capability according to claim 1, wherein: the inner wall of the accommodating cavity is convexly provided with an installation platform, and the installation platform is provided with a plurality of threaded holes; a fixing table extends outwards from the edge of the mounting port, a plurality of first connecting holes are formed in the fixing table in a penetrating mode, a plurality of second connecting holes are formed in the second shielding plate in a penetrating mode, and the second connecting holes are respectively in one-to-one correspondence with the first connecting holes; the screw passes in proper order the second connecting hole with first connecting hole with screw hole threaded connection, thereby will casing with second shield plate fixed mounting in hold the intracavity.

3. The bluetooth headset with anti-interference function according to claim 2, wherein: the fixed station is annularly and uniformly distributed with a plurality of jacks, the second shielding plate is annularly and uniformly distributed with a plurality of inserting columns, and the inserting columns are respectively and fixedly inserted into the jacks.

4. The bluetooth headset having an anti-jamming function according to claim 1, characterized in that: the containing cavity is internally provided with a first filter screen which covers the air inlet.

5. The bluetooth headset with anti-jamming capability according to claim 1, wherein: and a second filter screen covering the sound outlet end of the sound outlet pipe is arranged in the accommodating cavity.

6. The bluetooth headset having an anti-jamming function according to claim 1, characterized in that: the second shielding plate is further provided with a threading hole in a penetrating mode, an anti-interference magnetic ring is sleeved on the threading hole, a cable penetrates through the anti-interference magnetic ring, and two ends of the cable are respectively electrically connected with the circuit board and the battery.

7. The bluetooth headset with anti-jamming function according to any of claims 1-6, characterized in that: the moving coil unit comprises a T iron, a voice film, a voice coil and an outer magnet; the sound film, the external magnet and the T iron are sequentially arranged in the mounting cavity, and the sound film is close to the sound outlet; the T iron comprises a bottom plate and a bulge arranged in the middle of the bottom plate; the bulge is close to the sound film, the outer magnet is sleeved outside the bulge, and an accommodating groove is formed between the outer magnet and the bulge; one end of the voice coil is connected with the sound film, and the other end of the voice coil is movably accommodated in the accommodating groove; the circuit board is electrically connected with the voice coil; a first through hole penetrates through the middle of the protrusion, at least one second through hole penetrates through the bottom plate, and the second through hole is communicated with the accommodating groove.

8. The bluetooth headset with anti-interference function according to claim 7, wherein: an installation groove is dug at the bottom of the bulge, and the first through hole is communicated with the installation groove; an inner magnet is arranged in the mounting groove, the inner magnet and the outer magnet are arranged in an inner-outer corresponding mode, and a first clearance hole for avoiding the first through hole penetrates through the middle of the inner magnet.

9. The bluetooth headset having an anti-interference function according to claim 7, wherein: and a washer is arranged between the outer magnet and the voice film, and a second clearance hole for avoiding the voice coil penetrates through the middle part of the washer.

10. The bluetooth headset with anti-interference function according to claim 7, wherein: the first shielding plate is disc-shaped, the top end of a surrounding wall of the first shielding plate supports the edge of the bottom plate, the through hole is formed in the bottom wall of the second shielding plate, and a cavity for air flow flowing is formed between the first shielding plate and the bottom plate.