High-power high-frequency electric heating system for laser optical pumping atomic magnetometer

Abstract

Disclosed in the present invention is a high-power high-frequency electric heating system for a laser optical pumping atomic magnetometer, for use in heating an alkali metal vapor cell of the laser optical pumping atomic magnetometer. The high-power high-frequency electric heating system comprises an oscillation generation module, a temperature measurement module, a control module, a power output module, and a coil heating module. The oscillation generation module is used for transmitting a 1 MHz oscillation signal; the temperature measurement module is used for measuring the temperature of the alkali metal vapor cell to obtain a differential voltage; the control module performs amplitude modulation on the 1 MHz oscillation signal on the basis of the differential voltage to obtain an amplitude-modulated 1 MHz oscillation signal; the power output module is used for amplifying the voltage of the amplitude-modulated 1 MHz oscillation signal and inputting the voltage to the coil heating module; and the coil heating module is used for completing heating of the alkali metal vapor cell on the basis of the received voltage. The present invention uses an oscillation signal generation circuit as an oscillation source, thereby ensuring the stability of an output frequency; in addition, a topological structure is used to increase the ranges of an output voltage and the range of an output current of the heating system.

Description

A high-power high-frequency electric heating system for laser-pumped atomic magnetometers Technical Field

[0001] The present invention relates to the field of high-frequency electric heating circuits, and in particular to a high-power high-frequency electric heating system for a laser optically pumped atomic magnetometer. Background Art

[0002] Laser optically pumped atomic magnetometers, a new type of atomic magnetometer, including optically pumped magnetometers and NMOR magnetometers, have broad application prospects in high-sensitivity, high-precision detection in geomagnetic environments. Their magnetic field measurement principle utilizes the magnetic moment of alkali metal atoms generated by the splitting of packed energy levels, which in turn generates Larmor precession. The Larmor precession frequency is proportional to the external magnetic field, and magnetic field measurement can be achieved by monitoring the precession of atoms.

[0003] When a laser optically pumped atomic magnetometer is operating, it is necessary not only to heat the alkali metal gas chamber to a certain temperature to ensure that the alkali metal vaporizes and reaches the atomic density required for Zeeman energy level splitting, but also to ensure that the gas chamber heating process does not introduce magnetic field interference of the Larmor precession frequency and modulation frequency within the measurement range of the optically pumped magnetometer, and to ensure the heating control accuracy and a certain heating power. In addition, in order to ensure the integration and miniaturization of the optically pumped magnetometer, the volume of the heating device needs to be limited.

[0004] Currently, there are five main heating methods for laser optically pumped atomic magnetometer gas cells: airflow heating, intermittent heating, bidirectional current heating, high-frequency electric heating, and laser heating. Among them, airflow heating has low temperature control accuracy and a large heating device, which is not conducive to the integration and miniaturization of optically pumped magnetometers, and there is also airflow interference. Although the temperature control accuracy of the intermittent heating method is slightly higher than that of the airflow heating method, it cannot perform continuous magnetic field measurements due to its discontinuous heating process. The laser heating method has high temperature control accuracy, but its heating power is low and it adds an optical path, which is not conducive to the integration and miniaturization of optically pumped magnetometers. The bidirectional current heating method adjusts the layout of the heating membrane circuit to make the magnetic fields generated by the current cancel each other out. However, the use of DC heating introduces white noise and low-frequency noise, which has a significant impact on the Larmor precession frequency of the gas cell.

[0005] Summary of the Invention

[0006] In order to solve the technical problems in the above background, the present invention desires to propose a heating device that can maintain the electric heating output power under high frequency conditions and at the same time has a strong high-frequency load capacity of the linear power amplifier device.

[0007] To achieve the above objectives, the present invention provides a high-power, high-frequency electric heating system for a laser optically pumped atomic magnetometer. The system is used to heat the alkali metal gas chamber of the laser optically pumped atomic magnetometer, and includes: an oscillation generation module, a temperature detection module, a control module, a power output module, and a coil heating module.

[0008] The oscillation generating module is used to transmit a 1MHz oscillation signal;

[0009] The temperature detection module is used to measure the temperature of the alkali metal gas chamber to obtain a differential voltage;

[0010] The control module performs amplitude modulation on the 1 MHz oscillation signal based on the differential voltage to obtain the amplitude modulated 1 MHz oscillation signal;

[0011] The power output module is used to amplify the voltage of the amplitude-modulated 1MHz oscillation signal and input it to the coil heating module;

[0012] The coil heating module is used to heat the alkali metal gas chamber based on the received voltage.

[0013] Preferably, the oscillation generating module includes: a 1MHz oscillation signal source, a follower amplitude modulation circuit and a bandpass filter;

[0014] The 1 MHz oscillation signal source is used to transmit the 1 MHz oscillation signal;

[0015] The follower amplitude modulation circuit adjusts the amplitude of the 1MHz oscillation signal;

[0016] The bandpass filter is used to filter the 1 MHz oscillation signal.

[0017] Preferably, the temperature detection module includes: a constant current source transmitting device, a four-wire pt1000 temperature detector and an instrument amplifier resistance value detector; the four-wire pt1000 temperature detector is connected to the constant current source transmitting device and the instrument amplifier resistance value detector respectively.

[0018] Preferably, the working process of the temperature detection module includes: using the constant current source transmitting device to transmit a constant current source, and connecting it to the four-wire pt1000 temperature detector, eliminating the line resistance error through the four-wire system, and finally differentially amplifying the voltage at both ends of the four-wire pt1000 temperature detector through the instrument amplifier resistance value detector to obtain the differential voltage, thereby completing the measurement of the gas chamber temperature.

[0019] Preferably, the control module includes: an analog-to-digital converter, a controller, a digital-to-analog converter, and a voltage-controlled gain amplifier; the controller is connected to the analog-to-digital converter and the digital-to-analog converter respectively; the digital-to-analog converter is connected to the voltage-controlled gain amplifier and the analog-to-digital converter respectively.

[0020] Preferably, the working process of the control module includes: after the differential voltage is converted into digital by the analog-to-digital converter, it is input into the controller; after processing by the controller, the control quantity is converted into a temperature control signal by the digital-to-analog converter and input into the voltage-controlled gain amplifier to complete closed-loop control; the voltage-controlled gain amplifier modulates the 1MHz oscillation signal based on the temperature control signal.

[0021] Preferably, the power output module is composed of four identical high-frequency power amplifiers, which are used to amplify the voltage of the amplitude-modulated 1 MHz oscillation signal and ensure stable output power under load.

[0022] Preferably, the power output module further achieves a maximum voltage output and a maximum current output of twice the maximum voltage output and the maximum current output under the rated bandwidth of the high-frequency power amplifier through a topological circuit.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention ensures the stability of the output frequency by using the oscillation signal generating circuit as the oscillation source; at the same time, the topological structure is used to improve the range of the output voltage and current of the heating system, reducing the output power requirement for the high-frequency power amplifier. While ensuring the output power, the frequency of the high-frequency electric heating is increased, which can further improve the magnetic measurement range of the optically pumped magnetometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] FIG1 is a schematic diagram of a structural framework of an embodiment of the present invention;

[0027] FIG2 is a control block diagram of an embodiment of the present invention;

[0028] FIG3 is a schematic structural diagram of a 1 MHz oscillation signal source according to an embodiment of the present invention;

[0029] FIG4 is a schematic structural diagram of a power output module according to an embodiment of the present invention.

[0030] Explanation of the accompanying symbols: 1. 1MHz oscillation signal source; 2. Follower amplitude modulation circuit; 3. Bandpass filter; 4. Voltage-controlled gain amplifier; 5. Power output module; 6. Coil heating module; 7. Constant current source transmitting device; 8. Four-wire pt1000 temperature detector; 9. Instrument amplifier resistance value detector; 10. Analog-to-digital converter; 11. Digital-to-analog converter. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Before we begin, let's first introduce the currently mainstream gas cell heating method. High-frequency electric heating offers high heating power and precise temperature control. By increasing the operating frequency, it stays away from the frequency range of magnetic or optical modulation used in laser-pumped atomic magnetometers, avoiding magnetic field interference within the measurement range. This makes it suitable for the integration and miniaturization of laser-pumped atomic magnetometers.

[0034] The frequency of magnetic modulation or optical modulation is related to the Larmor precession frequency. The Larmor precession frequency formula is: ω L =γB0

[0035] Among them, ω L is the Larmor precession frequency; γ is the gyromagnetic ratio of the gas chamber atoms, which is a constant and is related to the type of gas chamber atoms. The value for potassium atoms is about 7 Hz / nT, and the value for helium atoms is about 28 Hz / nT; B0 is the external magnetic field to be measured. In the case of the geomagnetic field, B0 is on the order of 50,000 nT.

[0036] Taking the potassium atom optical pumping magnetometer and potassium atom NMOR magnetometer as examples, the potassium atom optical pumping magnetometer measures Larmor precession by detecting the change in the intensity of the transmitted light passing through the gas chamber. To this end, a modulated magnetic field is required for magnetic resonance, and its frequency requirement is: ω rf =ω L According to the Larmor precession frequency calculation formula, the modulation frequency in the geomagnetic environment is about 350kHz. The potassium atom NMOR magnetometer measures the Larmor precession frequency by the change in the optical rotation angle. It is necessary to use the intensity of the linearly polarized light entering the gas chamber to modulate to produce a strong resonance curve. The frequency requirement is: ω m =2ωL According to the Larmor precession frequency calculation formula, the modulation frequency in the geomagnetic environment is about 700kHz.

[0037] Therefore, high-power high-frequency electric heating equipment above 1 MHz is currently needed to heat the gas chamber of the laser-pumped atomic magnetometer.

[0038] However, due to the difficulty in achieving these functions, especially maintaining electric heating output power at high frequencies between 500kHz and 1MHz, high requirements are placed on the gain-bandwidth product and slew rate of the output device. These devices often have voltage output limitations. Furthermore, linear power amplifiers have poor high-frequency load capabilities, resulting in maximum output voltage and current values ​​failing to meet design requirements at high frequencies. Currently, no commercially available device can achieve a 4W high-power output at 1MHz.

[0039] Based on the defects of the above-mentioned mainstream heating methods, this embodiment designs a high-power high-frequency electric heating system for a laser optically pumped atomic magnetometer, as shown in Figure 1, including: an oscillation generating module, a temperature detection module, a control module, a power output module and a coil heating module; the oscillation generating module is used to transmit a 1MHz oscillation signal; the temperature detection module is used to measure the temperature of the alkali metal gas chamber to obtain a differential voltage; the control module modulates the 1MHz oscillation signal based on the differential voltage to obtain an amplitude-modulated 1MHz oscillation signal; the power output module is used to amplify the voltage of the amplitude-modulated 1MHz oscillation signal and input it to the coil heating module; the coil heating module is used to complete the heating of the alkali metal gas chamber based on the received voltage; the control block diagram of the system is shown in Figure 2.

[0040] The specific structural components of each part of the present invention will be described in detail below in conjunction with this embodiment.

[0041] The oscillation generation module includes: a 1MHz oscillation signal source 1, a follower amplitude modulation circuit 2, and a bandpass filter 3. The specific structure of the 1MHz oscillation signal source 1 is shown in Figure 3. L1, C1, and C2 form an LC resonant tank circuit. When the circuit is operating, C1 and C2 charge, and after the capacitor is fully charged, they discharge through L1 to achieve the purpose of oscillation signal oscillation. The high-precision, low-noise operational amplifier OP uses a voltage follower structure to ensure a constant voltage across R1. R1 is a high-precision resistor, so the current through R1 is:

[0042] Among them, I1 is the current passing through R1, V1 and V2 are the input voltages, and I E is the emitter current of the P-channel transistor, and U E =V2

[0043] Among them, U E is the emitter voltage of the transistor.

[0044] Therefore, by changing the input voltages V1 and V2, the emitter current and emitter voltage passing through the transistor can be changed, and the amplification bias point of the transistor and the amplitude voltage when the oscillation is stable can be changed.

[0045] L1, C1, C2 and the transistor form a feedback amplification loop, and the feedback amount is amplified through the common-emitter amplification of the transistor to ensure the stability of the oscillation amplitude, ultimately forming an unbiased stable sine wave with a frequency of 1MHz; L2 is used to isolate the ground and the oscillation circuit to prevent the oscillation signal from being transmitted into the ground, and provides a discharge circuit for C1 and C2, which is conducive to the oscillation of the LC resonant tank circuit; because the oscillation signal source has no load capacity, it is necessary to add a follower amplitude modulation circuit 2 to ensure its load capacity and subsequent output distortion; at the same time, the oscillation signal is proportionally amplified by an operational amplifier so that the amplitude of the oscillation signal meets subsequent requirements; finally, to eliminate the influence of noise in the oscillation signal, the oscillation signal is filtered using a bandpass filter 3.

[0046] The temperature detection module includes a constant current source transmitter 7, a four-wire PT1000 temperature detector 8, and an instrumentation amplifier resistance detector 9. The constant current source transmitter 7 provides a constant current source with an output accuracy of 1uA and is connected to the four-wire PT1000 temperature detector 8. The four-wire system eliminates line resistance errors. The instrumentation amplifier resistance detector 9 differentially amplifies the voltage across the four-wire PT1000 temperature detector 8 to obtain an output voltage (differential voltage) that is linearly related to the temperature, completing the measurement of the gas chamber temperature.

[0047] The control module includes an analog-to-digital converter 10, a controller, a digital-to-analog converter 11, and a voltage-controlled gain amplifier 4. The differential voltage obtained by the temperature measurement module is converted to a digital by the analog-to-digital converter 10 and then input into the controller. The voltage is compared with the set value in the controller to obtain the error between the current temperature measurement voltage and the target temperature voltage. When this error is zero, the measured temperature reaches the design temperature, the heating power does not need to be changed, and the temperature control signal remains unchanged. When the error is positive, the measured temperature is higher than the design temperature, the heating power needs to be reduced, and the temperature control signal decreases. When the error is negative, the measured temperature is lower than the design temperature, the heating power needs to be increased, and the temperature control signal increases. After processing by the controller, the control variable is converted into a temperature control signal (a voltage signal) by the digital-to-analog converter 11 and input into the voltage-controlled gain amplifier 4, completing closed-loop control. The voltage-controlled gain amplifier 4 amplitude-modulates the 1MHz oscillation signal based on the temperature control signal. After amplitude modulation by the voltage-controlled gain amplifier 4, the magnitude of the output 1MHz oscillation signal is related to the difference between the set temperature value and the gas chamber temperature value.

[0048] Power output module 5 amplifies the voltage of the amplitude-modulated 1MHz oscillating signal and ensures stable output power under load. The power output module consists of four identical high-frequency power amplifiers. Through this topological circuit, it can achieve a maximum voltage output and maximum current output of twice the maximum voltage and current output at the rated bandwidth of the high-frequency power amplifier.

[0049] The topology circuit of the power output module 5 provided in this embodiment is as follows: OP1, OP2, OP3, and OP4 in FIG4 are all the same high-frequency power amplifiers. OP1 and OP3 form a voltage-carrying topology loop, and its working principle is as follows:

[0050] The OP1 input voltage is an oscillating signal after amplitude modulation by a voltage-controlled gain amplifier. After reverse amplification, its output voltage U1 is:

[0051] Among them U i is the sinusoidal signal after amplitude modulation by the voltage-controlled gain amplifier, and its expression is:

[0052] Among them, A i is the amplitude of the oscillation signal; ω i is the oscillation signal frequency, which is 1MHz; is the phase error of the oscillation signal. Therefore, the output voltage U1 of OP1 is:

[0053] in, The amplitude of the oscillation signal output by OP1 is limited by the maximum output voltage of OP1, and its maximum value is U MAX , that is: U 1MAX =U MAX

[0054] The input voltage of OP3 is the output voltage of OP1. After reverse amplification, its output voltage U2 is:

[0055] R3 and R4 are high-precision resistors with the same resistance value, so the output voltage U2 is:

[0056] in, The amplitude of the oscillation signal output by OP3 is limited by the maximum output voltage of OP3. OP3 and OP1 belong to the same high-frequency power amplifier, so its maximum value is also U MAX That is: U 3MAX =U MAX

[0057] Since OP1 and OP3 are connected to the two ends of the load resistor, the voltage Uout for:

[0058] U out The maximum amplitude of the output oscillation signal is: U outMAX =U 3MAX -(-U 1MAX )=2U MAX

[0059] Since the voltage signals at both ends of the load are differential, the voltage U out The maximum output voltage limit of the current feedback amplifier is twice the maximum output voltage limit, completing the output voltage topology.

[0060] The topology circuit provided in this embodiment, wherein OP1 and OP2, OP3 and OP4 respectively form the same current topology loop, taking OP1 and OP2 as an example, the OP1 input voltage is the oscillation signal U after amplitude modulation by the voltage-controlled gain amplifier. i , after reverse amplification, its output voltage U1 is:

[0061] According to the virtual short and virtual break principle of the current feedback amplifier, the current I1 passing through R1 is:

[0062] The current I passing through the load load for:

[0063] Among them, R load It is the load resistor, and its resistance is much smaller than R1, and the ratio of the resistance of R2 to the resistance of R1 is the amplification factor of the OP1 circuit.

[0064] OP2 is a voltage follower, the input voltage is the output voltage of OP1, and since Rs is a resistor with the same resistance value, the current I flowing through Rs is s The same as:

[0065] Since the resistance of R1 is much larger than R load , and I1 is very small, at the 1uA level, and I load can be ignored, so we can get:

[0066] Therefore, I s The maximum output current of the current feedback amplifier is limited to I s This parameter is determined by the current feedback amplifier performance and circuit structure. Its maximum output current value I sMAX For: I sMAX =I MAX

[0067] The current I passing through the load load The maximum output current value I loadMAX For: I loadMAX ≈2I sMAX =2I MAX

[0068] At this time, the current flowing through the load is I load The maximum output current limit of the current feedback amplifier is twice the maximum output current limit, completing the output current topology.

[0069] The coil heating module 6 is a double-layer coil structure with two voltage input ports connected to the output values ​​U1 and U2 of the power output module respectively. The current in the coil causes the resistor to heat the target gas chamber. The heating power formula is:

[0070] Where W is the coil heating power, I is the amplitude of the sinusoidal current signal, and R is the resistance of the heating coil. If the resistance of the heating coil remains constant, as the amplitude of the sinusoidal voltage through the coil increases, the amplitude of the current flowing through it increases proportionally, and the coil heating power also increases proportionally. Therefore, the coil heating power can be controlled by the coil input voltage.

[0071] At the same time, in order to ensure that no current magnetic noise is introduced during the coil heating process, a double-layer symmetrical electric heating film is used as the heating coil.

[0072] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A high-power high-frequency electric heating system for a laser optically pumped atomic magnetometer, the system being used to heat an alkali metal gas chamber of a laser optically pumped atomic magnetometer, characterized in that: include: Oscillation generation module, temperature detection module, control module, power output module and coil heating module; The oscillation generating module is used to transmit a 1 MHz oscillation signal; The temperature detection module is used to measure the temperature of the alkali metal gas chamber to obtain a differential voltage; The control module modulates the 1 MHz oscillation signal based on the differential voltage to obtain an amplitude modulated 1 MHz oscillation signal; The power output module is used to amplify the voltage of the 1MHz oscillation signal after amplitude modulation and input it to the coil heating module; wherein the power output module is composed of four identical high-frequency power amplifiers, which are used to amplify the voltage of the 1MHz oscillation signal after amplitude modulation; at the same time, the power output module also completes the maximum voltage output and the maximum current output of twice the maximum voltage output and the maximum current output under the rated bandwidth of the high-frequency power amplifier through the topological circuit; The coil heating module is used to heat the alkali metal gas chamber based on the received voltage.

2. The high-power high-frequency electric heating system for a laser optically pumped atomic magnetometer according to claim 1, characterized in that: The oscillation generation module includes: a 1MHz oscillation signal source, a follower amplitude modulation circuit and a bandpass filter; The 1 MHz oscillation signal source is used to transmit the 1 MHz oscillation signal; The follower amplitude modulation circuit adjusts the amplitude of the 1MHz oscillation signal; The bandpass filter is used to filter the 1 MHz oscillation signal.

3. The high-power high-frequency electric heating system for a laser optically pumped atomic magnetometer according to claim 1, characterized in that: The temperature detection module comprises: a constant current source transmitting device, a four-wire pt1000 temperature detector and an instrument amplifier resistance value detector; the four-wire pt1000 temperature detector is connected to the constant current source transmitting device and the instrument amplifier resistance value detector respectively.

4. The high-power high-frequency electric heating system for a laser optically pumped atomic magnetometer according to claim 3 is characterized in that: The working process of the temperature detection module includes: using the constant current source transmitting device to transmit the constant current source and connecting it to the four-wire pt1000 temperature detector, eliminating the line resistance error through the four-wire system, and finally differentially amplifying the voltage at both ends of the four-wire pt1000 temperature detector through the instrument amplifier resistance value detector to obtain the differential voltage and complete the measurement of the gas chamber temperature.

5. The high-power high-frequency electric heating system for a laser optically pumped atomic magnetometer according to claim 3, characterized in that: The control module includes: an analog-to-digital converter, a controller, a digital-to-analog converter, and a voltage-controlled gain amplifier; the controller is connected to the analog-to-digital converter and the digital-to-analog converter respectively; the digital-to-analog converter is connected to the voltage-controlled gain amplifier and the analog-to-digital converter respectively.

6. The high-power high-frequency electric heating system for a laser optically pumped atomic magnetometer according to claim 5, characterized in that: The working process of the control module includes: after the differential voltage is converted into a digital form by the analog-to-digital converter, it is input into the controller; after being processed by the controller, the control quantity is converted into a temperature control signal by the digital-to-analog converter and input into the voltage-controlled gain amplifier to complete closed-loop control; the voltage-controlled gain amplifier modulates the 1MHz oscillation signal based on the temperature control signal.

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