A temperature control system for SERF inertial measurement optical path based on non-magnetic temperature chamber

Abstract

A temperature control system for the optical path of a SERF inertial measurement system based on a non-magnetic temperature chamber effectively suppresses the impact of external environmental temperature fluctuations on the characteristics of optical components through passive insulation and internal active control of the chamber, thereby reducing parameter fluctuations in pumping and detection lasers. The system consists of an optical path temperature control module, a high-precision temperature control circuit, and a power amplifier drive circuit. In the optical path temperature control module, the insulating shell slows heat conduction and passively suppresses environmental temperature fluctuations; a semiconductor cooling chip increases the heat dissipation power of the chamber; a platinum resistance thermometer inputs the temperature at different locations in the optical path system to the high-precision temperature control circuit, which uses an active interference rejection algorithm to calculate the active control quantity, and after power amplification, drives the heating film. A boron nitride insulating layer is designed on the outer surface of the heating film to improve the temperature uniformity of the chamber and suppress electromagnetic interference introduced by heating; ultimately, the optical path temperature fluctuation is stabilized within ±10mK, improving the long-term stability of the SERF inertial measurement prototype.

Description

Technical Field

[0001] This invention relates to a temperature control system for the optical path of a SERF inertial measurement instrument based on a non-magnetic temperature chamber, which can be used in the field of SERF inertial measurement instruments. Background Technology

[0002] The SERF inertial measurement system uses a beam of pumped laser polarization gas to obtain alkali metal atoms in the chamber. It calculates parameters such as the polarizability of the atoms by measuring the optical rotation angle of the detection light. The optical components used in the optical path include Glan Taylor prisms, polarizers, lenses, liquid crystals, half-wave plates, and quarter-wave plates, all made of fused silica. When the temperature of the optical path system changes, the thickness of the silica material will change due to thermal expansion and contraction, which will cause changes in the phase delay of the waveplate, the beam splitting of the polarization beam splitter, and the laser ellipsoid.

[0003] After being emitted from the laser, the laser sequentially enters the polarizer, liquid crystal, analyzer, waveplate, and GlanTylene prism before finally entering the gas cell. When the characteristics of these optical components change, parameters such as the polarization degree and ellipsoid of the laser incident on the gas cell cannot be guaranteed. Simultaneously, temperature-induced changes in the splitting ratio and phase delay of the GlanTylene prism also affect the closed-loop feedback control effect of the laser power. Therefore, controlling the temperature changes of the pump and detection optical path systems, and suppressing interference from external environmental temperature fluctuations are key factors in improving the long-term stability of the SERF inertial measurement prototype. Summary of the Invention

[0004] This invention designs a temperature control system for the SERF inertial measurement optical path based on a non-magnetic temperature chamber. Based on the long-term stability requirements of the SERF inertial measurement prototype, the system controls the characteristics of optical components in the pumping and detection optical path system of the prototype to be unaffected by external ambient temperature fluctuations. The designed temperature chamber system utilizes multi-point distributed temperature control to suppress electromagnetic interference, while ensuring the temperature stability of the pumping and detection optical paths. Combined with an active disturbance rejection control algorithm, it suppresses external ambient temperature interference and coupling interference between various control loops, ultimately achieving a temperature fluctuation of no more than ±10mK in the pumping and detection optical paths.

[0005] The technical solution of this invention is as follows:

[0006] A SERF inertial measurement optical path temperature control system based on a non-magnetic temperature chamber comprises three parts: an optical path temperature control module, a high-precision temperature control circuit, and a power amplifier drive circuit. The optical path temperature control module consists of an insulating shell, a semiconductor cooling chip, a pump optical path platinum resistance thermometer, a detection optical path platinum resistance thermometer, a center optical path platinum resistance thermometer, an open-loop monitoring platinum resistance thermometer, a bottom heating film, a first parallel heating film, a second parallel heating film, and a boron nitride insulating layer on the surface of the heating films. The high-precision temperature control circuit consists of a first dual-sampling and dual-control circuit board, a second dual-sampling and dual-control circuit board, a host computer system, and a 12V DC power supply. The power amplifier drive circuit consists of a first power amplifier circuit board, a second power amplifier circuit board, a third power amplifier circuit board, and a ±65V DC power supply.

[0007] The prototype was placed in an insulated shell measuring 530mm*530mm*400mm. The interior of the insulated shell uses aluminum alloy as a supporting frame. Except for the top surface which is used for heat dissipation, the outer surfaces of the other walls are covered with rigid polyurethane foam insulation material to suppress interference caused by ambient temperature fluctuations.

[0008] Two parallel semiconductor cooling chips are installed on the top surface of the insulated outer shell, controlling its heat dissipation power to reach 50W. The inner walls of the insulated outer shell, except for the heat dissipation surface, are covered with flexible constantan heating films. The side heating films measure 520mm*390mm with a resistance of 200Ω, and the bottom heating film measures 520mm*520mm with a resistance of 100Ω. During heating, the side heating films are connected in parallel in pairs, and the resistance of the heating load after parallel connection is also 100Ω. Furthermore, to prevent electromagnetic interference to the prototype after the heating films are energized, a boron nitride insulating layer is added to the surface of the heating films. The high thermal conductivity of boron nitride ceramic material also helps improve temperature uniformity within the chamber.

[0009] Further, based on the positional distribution of the prototype's pumping and detection optical paths, the placement of the platinum resistance thermometers (RTTs) was selected. The control loops in each zone adjusted the heating film's heating according to the difference between the target set temperature and the actual temperature value measured by the RTT. Specifically, the heating film on the side of the insulation shell controls the temperature of the pumping and detection optical paths, with the temperature-measuring RTTs placed at the center of these paths; the heating film on the bottom of the insulation shell controls the average temperature of the entire optical system, with the RTTs placed at the center between the two optical paths. In summary, three control loops were used for distributed temperature control of the prototype's optical system. Due to the large controlled area, an additional monitoring RTT was attached to the prototype's optical system to provide feedback on temperature fluctuations at other locations along the optical path besides the temperature control points, thus more accurately reflecting the system's temperature control effect.

[0010] The temperature control circuit includes two high-precision dual-sampling and dual-control circuit boards and three high-precision power amplifier circuit boards. The dual-sampling and dual-control circuit boards consist of five parts: a low-noise power supply module, a platinum resistance thermometer drive circuit based on a Howland current source, a differential sampling circuit, an STM32G431C8T6 minimum system, and a DDS high-frequency signal generation circuit. The low-noise power supply module uses an LDO linear regulator circuit to achieve analog voltage conversion and a BUCK step-down circuit to achieve digital voltage conversion, ultimately powering the analog-to-digital chip in the circuit. The Howland current source circuit converts the input voltage into a stable current output, ensuring a constant output current even when the resistance of the temperature sensing resistor changes. The differential sampling circuit consists of a differential operational amplifier THS4131 and an ADC chip AD7190. The differential operational amplifier converts the voltage across the platinum resistance... The voltage signal is converted into a dual-ended output to the ADC chip to eliminate the influence of common-mode noise. The STM32G431C8T6 minimum system converts the collected platinum resistance value into temperature data. To suppress external environmental temperature fluctuations and coupling interference between heating control loops, an active disturbance rejection control algorithm is designed. External environmental interference, coupling disturbances between loops, and internal system disturbances are considered as the total disturbance. The changes in state and disturbance quantities are tracked by an extended observer, and the control output is calculated by combining the feedback control law. Finally, the high-frequency sine wave signal generated by the DDS chip is used in the high-frequency signal generation circuit to modulate the control signal to a high-frequency band that is not sensitive to atoms. Finally, the control voltage signal is amplified by the PA96 chip in the power amplifier circuit, thereby increasing the heating power. The output voltage of the power amplifier circuit is directly applied to both ends of the heating film to achieve high-precision temperature control.

[0011] This invention ultimately utilizes an active disturbance rejection control algorithm to control the heating of five heating films inside the thermal insulation shell through three control loops. This enables real-time, high-precision temperature control of the SERF inertial measurement principle prototype's pumping and detection optical path, suppressing changes in optical component characteristics caused by external environmental temperature fluctuations, thereby improving the long-term stability of the prototype's output signal.

[0012] The advantages of this invention over existing technologies are:

[0013] 1. The present invention adopts a combined active and passive temperature control scheme. On the one hand, the SERF inertial measurement principle prototype is placed in an insulated shell for passive heat insulation. On the other hand, the temperature of the optical path system is precisely adjusted by controlling the heating film. Compared with placing the prototype directly in the room temperature environment, this design makes the optical components in the optical path less affected by temperature fluctuations, and their polarization, beam splitting characteristics, etc. can remain stable for a long time.

[0014] 2. This invention attaches two semiconductor cooling chips in parallel to the top surface of the designed thermal insulation shell, which adds an active heat dissipation process to the system and avoids the increase in thermal equilibrium temperature of the SERF inertial measurement optical path system caused by the use of the thermal insulation shell, thus avoiding the normal operation of the laser in the prototype.

[0015] 3. The present invention uses a boron nitride insulating layer on the outer layer of the heating film, which not only avoids electromagnetic interference to the prototype caused by the heating film being energized, but also makes the temperature field inside the chamber more uniform due to the good thermal conductivity of boron nitride.

[0016] 4. This invention achieves multi-point temperature control of the optical path by using five heating films on the bottom and side surfaces to control three heating circuits respectively. Compared with single-point temperature control, this invention has stronger anti-interference ability, ensures the temperature stability of the optical path system over a larger range, and enables the system to better suppress temperature drift caused by external temperature fluctuations.

[0017] 5. Based on the active disturbance rejection algorithm, this invention treats the disturbance caused by the fluctuation of the external ambient temperature and the coupling between the three heating circuits as the total disturbance, performs real-time tracking and compensation for the disturbance, realizes fine control of the temperature of the optical path system, improves the system's anti-disturbance capability, reduces the influence of mutual coupling between the circuits, and enhances the system's stability. Attached Figure Description

[0018] Figure 1 This diagram shows the overall components of a SERF inertial measurement optical path temperature control system based on a non-magnetic temperature chamber.

[0019] Figure 2 This is a schematic diagram of the overall installation structure of a SERF inertial measurement optical path temperature control system based on a non-magnetic temperature chamber.

[0020] Figure 3 This is a top sectional view of the temperature control chamber in a SERF inertial measurement optical path temperature control system based on a non-magnetic temperature chamber.

[0021] Figure 4 This diagram shows the components of a prototype SERF inertial measurement system based on a non-magnetic temperature chamber.

[0022] Figure 5 This diagram shows the system structure of a prototype SERF inertial measurement system based on a non-magnetic temperature chamber.

[0023] Figure 6 Structure and dimensions of the side heating film in a SERF inertial measurement optical path temperature control system based on a non-magnetic temperature chamber.

[0024] Figure 7Structure and dimensions of the heating film on the bottom surface of the temperature control system based on the SERF inertial measurement optical path of a non-magnetic temperature chamber.

[0025] The markings in the diagram are as follows:

[0026] 1-Optical path temperature control module; 2-High-precision temperature control circuit; 3-Power amplifier drive circuit; 11-Pump optical path platinum resistance thermometer; 12-Detection optical path platinum resistance thermometer; 13-Optical path system center platinum resistance thermometer; 14-Open-loop monitoring platinum resistance thermometer; 15-Insulation shell; 16-SERF inertial measurement prototype; 17-Semiconductor cooling chip; 18-Boron nitride insulating layer; 19-Bottom heating film; 110-First parallel heating film; 111-Second parallel heating film Film, L1-Pump optical path, L2-Detection optical path, L3-Magnetic shielding system, L4-Non-magnetic electric heating system; 151-Heat dissipation surface, 152-Insulation outer wall, L11-First reflecting mirror of pump optical path, L12-Liquid crystal of pump optical path, L13-Beam expander of pump optical path, L14-First 1 / 2 wave plate of pump optical path, L15-First polarizing beam splitter of pump optical path, L16-1 / 4 wave plate of pump optical path, L17-Second reflecting mirror of pump optical path, L18 - Second polarizing beam splitter of the pump optical path, L19 - Second half-wave plate of the pump optical path, L110 - Pump laser, L21 - First reflecting mirror of the detection optical path, L22 - First half-wave plate of the detection optical path, L23 - First polarizing beam splitter prism of the detection optical path, L24 - Second half-wave plate of the detection optical path, L25 - Second polarizing beam splitter prism of the detection optical path, L26 - Third polarizing beam splitter prism of the detection optical path, L27 - Third half-wave plate of the detection optical path, L28 - Second reflector in the detection optical path, L29 - Detection laser, L210 - Fourth half-wave plate in the detection optical path, L211 - Wollaston prism, L212 - Balanced differential amplifier; 21 - First dual-sampling and dual-control circuit board, 22 - Second dual-sampling and dual-control circuit board, 23 - Host computer system, 24 - 12V DC power supply; 31 - First power amplifier circuit board, 32 - Second power amplifier circuit board, 33 - Third power amplifier circuit board, 34 - ±65V power supply Detailed Implementation

[0027] To facilitate understanding of the present invention, the present invention will be described in more detail below with reference to specific embodiments and comparative examples:

[0028] A SERF inertial measurement optical path temperature control system based on a non-magnetic temperature chamber consists of three parts: an optical path temperature control module 1, a high-precision temperature control circuit 2, and a power drive amplifier circuit 3.

[0029] The structural diagram of optical path temperature control module 1 is as follows: Figure 2As shown, the temperature-controlled chamber designed consists of an insulated outer shell 15, a semiconductor cooling chip 17, a boron nitride insulation layer 18, a bottom heating film 19, a first parallel heating film 110, and a second parallel heating film 111. The insulated outer shell 15 has two parts: its top surface is a heat dissipation surface 151 made of aluminum alloy, and the other five surfaces are insulated outer walls 152 made of polyurethane foam. The semiconductor cooling chip 17 is installed on the heat dissipation surface 151, with a heat dissipation power of 50W during operation. The heating film is pasted on the inner surface of the aluminum alloy of the insulated outer shell. The dimensions of the side heating film and the bottom heating film of the insulated outer shell are as shown in the figures. Figure 6 and Figure 7 As shown, and as Figure 3 As shown, the heating film on the left inner surface and the heating film on the rear inner surface are connected in parallel to form the first parallel heating film 110, and the heating film on the right inner surface and the heating film on the front inner surface are connected in parallel to form the second parallel heating film 111. At the same time, a boron nitride insulating layer 18 is added to the surface of each heating film to reduce the electromagnetic interference introduced by the heating film being energized and to improve the uniformity of the temperature field inside the chamber. Finally, the SERF inertial measurement principle prototype 16 is placed in the center of the heat insulation shell 15 for temperature control.

[0030] SERF Inertial Measurement Principle Prototype 16 Figure 4 The system consists of a pump optical path L1, a detection optical path L2, a magnetic shielding system L3, and a non-magnetic electric heating system L4. The pump optical path L1 uses a 770nm circularly polarized laser to polarize alkali metal atoms. The polarized alkali metal atoms then hyperpolarize the inert gas atoms in the gas chamber, making the system sensitive to rotational signals. The detection optical path L2 uses linearly polarized light with a wavelength of 795nm passing through the gas chamber to detect the optical rotation angle information and calculates the spin precession signal of the atoms using the polarization difference method. The magnetic shielding system L3 relies on three layers of permalloy for passive magnetic shielding and utilizes a triaxial magnetic compensation coil for active magnetic compensation, thus jointly resisting interference from external magnetic fields and providing a zero-magnetic environment inside the system. The gas chamber is fixed at the center of the oven in the non-magnetic electric heating system L4, and the outside of the oven is wrapped with a flexible heating film. A 100kHz high-frequency driving current heats the gas chamber to 180°C.

[0031] Because changes in the characteristics of optical components in the pumping and testing optical path system within the prototype cause fluctuations in parameters such as laser power, polarization state, and ellipticity, these fluctuations will directly affect the long-term stability of SERF inertial measurements. Therefore, it is necessary to control the temperature of the optical path system to reduce the impact of temperature fluctuations on temperature-sensitive components in the optical path.

[0032] according to Figure 5As shown, the pump optical path L1 consists of various optical elements L11 to L110. Among them, the pump optical path liquid crystal L12, the first polarizing beam splitter L15, and the second polarizing beam splitter L18 are most susceptible to temperature fluctuations in their optical characteristics. The detection optical path L2 consists of various optical elements L21 to L212, among which the multiple polarizing beam splitters in the optical path are most susceptible to temperature fluctuations. Therefore, as needed, platinum resistance thermometers are attached near the temperature-sensitive elements in the pump and detection optical path systems, such as... Figure 5 As shown, the platinum resistance thermometer 11 in the pump optical path and the platinum resistance thermometer 12 in the detection optical path are used to measure the temperature of the temperature-sensitive elements in the pump and detection optical paths, respectively. The temperature of the pump optical path is controlled by the first parallel heating film 110, and the temperature of the detection optical path is controlled by the second parallel heating film 111. At the same time, in order to stabilize the average temperature of the optical path system, the bottom heating film 19 and the platinum resistance thermometer 13 at the center of the optical path are attached to serve as the actuator and the measurement unit, respectively, for closed-loop feedback control. Finally, since the SERF inertial measurement optical path system has a large area, the open-loop monitoring platinum resistance thermometer 14 is also attached to measure the temperature changes at other locations in the optical path except for the control point.

[0033] The platinum resistance thermometer 11 in the pumping optical path, the platinum resistance thermometer 12 in the detection optical path, and the platinum resistance thermometer 13 in the center of the optical path serve as measurement units for closed-loop control. They measure and feed back the temperature at different locations within the entire optical path system area to the first dual-sampling dual-control circuit board 21 and the second dual-sampling dual-control circuit board 22. These circuit boards are powered by a 12V DC power supply 24. To reduce coupling interference caused by heat conduction between the three control loops, an active disturbance rejection control algorithm is developed. This algorithm treats the ambient temperature disturbance and the coupling interference between loops during system operation as the total external disturbance. The system differential equation is written in the following form:

[0034]

[0035] Where a1 and a2 are system characteristic parameters, b is the control gain, ω is the total external disturbance to the system, and a1, a2, and b are unknowns. Errors will also be introduced during the system model establishment process. The error between the model parameters and the actual parameters is regarded as a disturbance caused by the uncertainty inside the system.

[0036] Let b = b0 + Δb, then the generalized total disturbance of the system is defined as the sum of the model error and the external disturbance, that is:

[0037]

[0038] b0 is the known part of the controller gain b, while Δb is the unknown modeling error.

[0039] Based on the aforementioned differential equations, the system's state equations can be written. At this point, the total disturbance f has become an extended state of the system:

[0040]

[0041] Further utilize extended observers to quickly track and estimate changes in various state variables of the system:

[0042]

[0043] in C=[1 0 0], L=[-β1,-β2,-β3] T z1, z2, z3 are parameters y, And the estimated term of the total system disturbance f, where L is the observer error feedback gain matrix to be solved; by placing the poles of the system characteristic equation at the observer bandwidth, the observer gain matrix can be calculated as:

[0044]

[0045] Design a feedback controller to calculate the control quantity, let u = (-z3 + u0) / b0, and the controller output u0 = -k. p (z1-y ref )-k d z2, y ref This is the set value. Ignore z3 pair. The estimation error, the expression for the second-order system becomes:

[0046]

[0047] The closed-loop transfer function of the system is that of a second-order system without zeros:

[0048]

[0049] Design the controller gain matrix K = [k d k p ] T The design includes:

[0050] k d =2ω c

[0051] Where ω c For controller bandwidth;

[0052] The designed system expansion observer and control rate codes are programmed into the dual-acquisition, dual-control circuit board. The observer bandwidth ω is adjusted by the host computer system 23. o and controller bandwidth ω c To adjust and control performance;

[0053] The calculated three control signals are amplified by the first power amplifier circuit board 31, the second power amplifier circuit board 32, and the third power amplifier circuit board 33, respectively driving the first parallel heating film 110, the second parallel heating film 111, and the bottom heating film 19 for heating. Ultimately, relying on the above scheme, a SERF inertial measurement optical path temperature control system based on a non-magnetic temperature chamber can reduce the temperature fluctuation of the prototype's optical path system from ±1K to ±10mK, thereby ensuring the temperature stability of the optical path system in the SERF inertial measurement principle prototype, reducing pumping and detection laser fluctuations, and improving the long-term stability of the prototype.

[0054] It should be noted that the specific embodiments described above enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the present invention in any way. Therefore, although the present invention has been described in detail with reference to the accompanying drawings and embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention. In short, all technical solutions and changes that do not depart from the spirit and scope of the present invention should be covered within the protection scope of this patent.

[0055] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

Claims

1. A SERF inertial measurement optical path temperature control system based on a non-magnetic temperature chamber, comprising three parts: an optical path temperature control module, a high-precision temperature control circuit, and a power amplifier drive circuit, characterized in that: The optical path temperature control module consists of an insulating shell, a semiconductor cooling chip, a pump optical path platinum resistance thermometer, a detection optical path platinum resistance thermometer, a center optical path platinum resistance thermometer, an open-loop monitoring platinum resistance thermometer, a bottom heating film, a first parallel heating film, a second parallel heating film, and boron nitride insulating layers on the surfaces of each heating film; the high-precision temperature control circuit consists of a first dual-sampling dual-control circuit board, a second dual-sampling dual-control circuit board, a host computer system, and a 12V DC power supply; the power amplification drive circuit consists of a first power amplification circuit board, a second power amplification circuit board, a third power amplification circuit board, and a ±65V DC power supply; The SERF inertial measurement prototype is housed in an insulated enclosure, with internal aluminum alloy plates for support. Rigid polyurethane foam is adhered to the sides and bottom to mitigate the impact of external temperature fluctuations on the interior, thus passively suppressing environmental interference. The SERF inertial measurement prototype's optical system includes a pump optical path and a detection optical path. To improve the overall temperature stability of the optical system, a distributed temperature control scheme is implemented. Platinum resistance thermometers (RTTs) are installed at the pump optical path, the detection optical path, and the center of the prototype's optical system to measure temperature fluctuations at different locations for subsequent feedback control. Additionally, an extra open-loop monitoring platinum RTD is added at any point in the optical system to monitor open-loop temperature fluctuations, reflecting temperature fluctuations at locations other than the control points. This is to suppress... To mitigate ambient temperature fluctuations, the system employs a non-magnetic electric heating film for active temperature control. This heating film is adhered to the inner surfaces of the sides and bottom of the insulation shell. The active heating system comprises three control loops. Loop one uses parallel heating films on the left and rear inner surfaces of the insulation shell as the first parallel heating loop, controlling temperature fluctuations at the pump optical path by incorporating feedback from the platinum resistance thermometer. Loop two uses parallel heating films on the right and front inner surfaces of the insulation shell as the second parallel heating loop, controlling temperature fluctuations at the detection optical path by incorporating feedback from the platinum resistance thermometer. Finally, loop three controls the bottom heating film, using feedback from the platinum resistance thermometer at the center of the optical path to stabilize the average temperature of the entire optical system. Simultaneously, the heating film utilizes a twisted-pair design to reduce the impact of the magnetic field generated by electric heating on SERF inertial measurements. The system employs an active disturbance rejection control (ADRC) algorithm to control the optical path temperature distribution. It considers external ambient temperature fluctuations, thermal coupling between control loops, and changes in the controlled object's parameters as total disturbances. The total disturbance is estimated in real-time using an extended observer, and the control quantity is calculated using a feedback control law. Furthermore, the DDS module on the dual-acquisition, dual-control circuit board modulates the control signal to a high-frequency band in which alkali metal atoms in the SERF inertial measurement system are insensitive, reducing magnetic field interference from the heating film. The modulated control signal is input to a power amplifier drive circuit to drive the heating film. Ultimately, this temperature control scheme effectively suppresses the impact of ambient temperature fluctuations on the performance of optical components in the SERF inertial measurement optical path system, ensuring the stability of parameters such as the power and polarization degree of the pump and detection laser incident on the gas chamber, and significantly improving the long-term stability of the system.

2. The optical path temperature control system according to claim 1, characterized in that: Because the SERF inertial measurement principle prototype requires high-temperature heating of the alkali metal gas chamber during operation, heat conduction within the prototype causes the optical path system temperature to be higher than the ambient temperature. After adding the insulation shell, the heat convection at the optical path is reduced, further increasing its thermal equilibrium temperature and thus affecting the normal operation of the laser. Therefore, a semiconductor cooling chip is added to the insulation shell for active heat dissipation. Two cooling chips are connected in parallel at the top of the insulation shell, with a heat dissipation power set at 50W.

3. The optical path temperature control system according to claim 1, characterized in that: The SERF inertial measurement prototype's casing is made of aluminum alloy conductor material. The bottom heating film is in direct contact with the prototype's casing. To further suppress electromagnetic interference caused by the heating film being energized, a boron nitride insulating layer needs to be added to the heating film. Its thermal conductivity is 20-100 W / m·K, which has good thermal conductivity characteristics. While providing electromagnetic insulation, it also makes the temperature field distribution inside the chamber more uniform.

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