Stable atomic radio frequency magnetometer for eddy current measurements

Abstract

The application discloses a stable atomic radio frequency magnetometer which can be used for eddy current measurement, and the magnetometer comprises an atomic gas chamber, the side of the atomic gas chamber is provided with an eddy current coil, the magnetometer further comprises an optical device group and a data acquisition module which is used for collecting electric conductivity information, the magnetometer further comprises a compensation coil which is arranged at the side of the atomic gas chamber, a PID controller is connected to the compensation coil, and a phase-locked amplifier is connected to the PID controller; the side of the atomic gas chamber is provided with a radio frequency coil; a sample is placed in a main magnetic field, detection light sequentially passes through the atomic gas chamber and the optical device group, a transition signal of nonlinear Zeeman splitting is generated after the detection light is optically pumped, the transition signal is connected to the phase-locked amplifier, and the data acquisition module extracts electric conductivity information from a transition resonance peak of a Zeeman sub-energy level. The application can improve the stability of a background magnetic field, reduce measurement errors and improve the accuracy of measurement.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of magnetic signal measurement, in particular to a stable atomic radio frequency magnetometer for eddy current measurement. BACKGROUND

[0002] Magnetometer is a general term for instruments that measure the strength and direction of a magnetic field. The main purposes of magnetometer include collecting magnetic anomaly data and measuring rock magnetic parameters, etc. Due to different purposes and principles, magnetometers include many types. For a radio frequency atomic magnetometer, the background magnetic field is generated by a coil. When in use, the sample is placed in the background magnetic field, and then the measurement of the electrical conductivity information is performed.

[0003] When the radio frequency atomic magnetometer is in use, the instability of the current in the coil will cause the change of the background magnetic field, thereby changing the size of the Larmor frequency. Especially in the measurement of low electrical conductivity objects, it is usually necessary to increase the number of measurements to improve the signal-to-noise ratio. The change of the Larmor frequency makes the results of multiple measurements all have certain errors. When the results of multiple measurements are subsequently statistically processed, the errors may be enlarged, and the accuracy of the obtained results is lower. Therefore, how to design a magnetometer capable of stabilizing the background magnetic field has become a topic to be solved. SUMMARY

[0004] The present application aims to provide a stable atomic radio frequency magnetometer for eddy current measurement. The present application can improve the stability of the background magnetic field, reduce the measurement error, and improve the accuracy of the measurement.

[0005] The technical solution of the present application is a stable atomic radio frequency magnetometer for eddy current measurement. The magnetometer comprises an atomic gas chamber, a vortex coil is arranged on the side of the atomic gas chamber, the magnetometer further comprises an optical device group and a data acquisition module for acquiring electrical conductivity information, the magnetometer further comprises a compensation coil arranged on the side of the atomic gas chamber, a PID controller is connected to the compensation coil, and a phase-locked amplifier is connected to the PID controller; a radio frequency coil is arranged on the side of the atomic gas chamber.

[0006] The sample is placed in the main magnetic field, the probe light passes through the atomic gas chamber and the optical device group in turn, and the transition signal of the nonlinear Zeeman splitting is generated after the optical pumping. The transition signal is connected to the phase-locked amplifier, and the data acquisition module extracts the electrical conductivity information from the transition resonance peak of the Zeeman sub-energy level.

[0007] When the main magnetic field changes, the frequency of the transition signal between the Zeeman sub-energy levels changes. The phase-locked amplifier demodulates the error signal according to the pre-input reference frequency and transmits the error signal to the PID controller. The PID controller outputs a compensation current to the compensation coil according to the error signal. The compensation current flows through the compensation coil and generates a compensation magnetic field, thereby offsetting the change of the main magnetic field and realizing the function of stabilizing the magnetic field.

[0008] The stable atomic radio frequency magnetometer for eddy current measurement has the probe light direction perpendicular to the main magnetic field direction.

[0009] The stable atomic radio frequency magnetometer for eddy current measurement has the optical device group comprising optical elements and a photodetector, wherein the optical elements comprise a wave plate and a prism.

[0010] The stable atomic radio frequency magnetometer for eddy current measurement has the atom cell arranged at the center of the circle where the compensation coil is arranged.

[0011] The stable atomic radio frequency magnetometer for eddy current measurement has the output end of the balance detector connected with a lock-in amplifier, the photodetector inputs the main magnetic field frequency after demodulation into the lock-in amplifier, and two-way orthogonal magnetic field outputs are obtained from the lock-in amplifier.

[0012] Compared with the prior art, the present application has the following beneficial effects:

[0013] 1、In the present application, the compensation coil is arranged at the side of the atom cell, the PID controller is connected to the compensation coil, and the lock-in amplifier is connected to the PID controller; the side of the atom cell is provided with a radio frequency coil. The radio frequency coil can excite the transition of Zeeman sub-levels, the transition signal is input to the lock-in amplifier, when the main magnetic field changes, the frequency of the transition signal between the Zeeman sub-levels changes, the lock-in amplifier demodulates the error signal according to the pre-input reference frequency and transmits the error signal to the PID controller, the PID controller outputs the compensation current to the compensation coil according to the error signal, the compensation current flows through the compensation coil and generates the compensation magnetic field, thereby offsetting the change of the main magnetic field and realizing the function of stabilizing the magnetic field. In the stable magnetic field environment, multiple measurements are performed again, which can greatly reduce the error of each measurement, so that the accuracy of the final result is higher when the multiple measurement results are statistically processed.

[0014] 2、The present application uses different Zeeman sub-level transitions when the magnetic field changes to adjust the strength of the magnetic field, which does not interfere with the measurement of the conductivity information, thereby improving the accuracy of the measurement. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a structure schematic view of the present application in the Y-Z plane;

[0016] Figure 2 is a structure schematic view of the present application in the X-Z plane;

[0017] Figure 3 is the X-direction magneto-optical resonance signal under the condition of complete optical pumping polarization of the present application;

[0018] Figure 4is the Y direction magneto-optical resonance signal under the complete optical pumping polarization condition of the application;

[0019] Figure 5 is the X direction magneto-optical resonance signal under the partial optical pumping polarization condition of the application;

[0020] Figure 6 is the Y direction magneto-optical resonance signal under the partial optical pumping polarization condition of the application.

[0021] The marks in the drawing are: 1-probe light; 2-compensation coil; 3-sample; 4-eddy current coil; 5-atomic cell; 6-radio frequency coil; 7-PID controller; 8-data acquisition module; 9-lock-in amplifier; 10-optical device group; 11-pump light. DETAILED DESCRIPTION

[0022] The application will be further described below in combination with the drawing and examples, but it is not taken as the basis for limiting the application.

[0023] Example: stable magnetic field radio frequency magnetometer, as shown in the drawing Figure 1 and the drawing Figure 2 As shown in the drawing, the magnetometer comprises an atomic cell 5, the surface of the atomic cell 5 is provided with an anti-relaxation film, which can reduce the signal line width, the side of the atomic cell 5 is provided with an eddy current coil 4, the magnetometer further comprises an optical device group 10 and a data acquisition module 8 for acquiring conductivity information, the optical device group 10 comprises optical elements and a balanced detector, wherein the optical elements comprise a wave plate and a prism. The magnetometer further comprises a compensation coil 2 arranged at the side of the atomic cell 5, the atomic cell 5 is arranged opposite to the center of the circle where the compensation coil 2 is arranged, the compensation coil 2 is connected with a PID controller 7, and the PID controller 7 is connected with a lock-in amplifier 9; the side of the atomic cell 5 is provided with a radio frequency coil 6, and the radio frequency coil 6 is used for exciting the transition signal of the Zeeman sub-energy level.

[0024] The sample 3 is placed in the main magnetic field, the probe light 1 passes through the atomic cell 5 and the optical device group 10 in sequence, the direction of the probe light 1 is perpendicular to the direction of the main magnetic field, the transition signal of the nonlinear Zeeman splitting is generated after the optical pumping, the transition signal is connected to the lock-in amplifier 9, and the data acquisition module 8 extracts the conductivity information from the transition resonance peak of the Zeeman sub-energy level. The output end of the balanced detector is connected with the lock-in amplifier 9, the balanced detector inputs the lock-in amplifier 9 after demodulating the main magnetic field frequency, and two-way orthogonal magnetic field outputs, i.e. x direction output and y direction output, are obtained from the lock-in amplifier 9.

[0025] When the main magnetic field changes, the frequency of the transition signal between Zeeman sublevels changes. The lock-in amplifier 9 demodulates the error signal according to the pre-input reference frequency and transmits the error signal to the PID controller 7. The PID controller 7 outputs a compensation current to the compensation coil 2 based on the error signal. The compensation current flows through the compensation coil 2 and generates a compensation magnetic field, thereby counteracting the change in the main magnetic field and achieving the function of stabilizing the magnetic field. Specifically, after receiving the error signal, the PID controller 7 compares the error signal with the signal reference value and adjusts the gain of the proportional unit P, integral unit I, and differential unit D, thereby outputting a compensation current. This compensation current is input to the compensation coil 2. The current generates a compensation magnetic field as it passes through the compensation coil 2. More specifically, when the main magnetic field weakens, the direction of the magnetic field generated by the compensation coil 2 is the same as the direction of the main magnetic field; when the main magnetic field strengthens, the direction of the magnetic field generated by the compensation coil 2 is opposite to the direction of the main magnetic field.

[0026] In practical applications, taking conductivity measurement using a cesium atom magnetometer as an example, eight transition signals of nonlinear Zeeman splitting can be observed after optical pumping. The conductivity information is obtained from the Zeeman sublevel m=3 by data acquisition module 8. The energy level was extracted from the resonance peak of the transition at 4, and the sub-level m=2. The resonance signal between points 3 is then connected to the PID controller as an error signal. Specifically, see attached... Figures 3-6 As shown, radio frequency coil 6 excites the Zeeman sublevel m=2. The transition between 3 and 4 is fed into lock-in amplifier 9, where, attached Figure 3 and attached Figure 4 These are the X-axis and Y-axis magneto-optical resonance signals under fully optically pumped polarization, respectively. Figure 5 and attached Figure 6 These are the X-axis and Y-axis magneto-optical resonance signals under partially optically pumped polarization, respectively. After receiving the transition signal, the lock-in amplifier 9 demodulates the error signal and inputs it to the PID controller 7. The PID controller 7 outputs a compensation current to the compensation coil 2, generating a compensation magnetic field. This adjusts the background magnetic field, which is composed of the main magnetic field and the compensation magnetic field, to achieve a stable magnetic field. In a stable magnetic field environment, multiple measurements can be performed to enhance the signal-to-noise ratio and reduce measurement errors.

Claims

1. A stable atomic radio frequency magnetometer for eddy current measurement, the magnetometer comprising an atomic gas chamber (5), an eddy current coil (4) disposed on the side of the atomic gas chamber (5), the magnetometer further comprising an optical device group (10) and a data acquisition module (8) for acquiring conductivity information, characterized in that: The magnetometer also includes a compensation coil (2) disposed on the side of the atomic gas chamber (5), a PID controller (7) connected to the compensation coil (2), and a lock-in amplifier (9) connected to the PID controller (7); a radio frequency coil (6) is disposed on the side of the atomic gas chamber (5); the atomic gas chamber (5) is positioned directly opposite the center of the circle where the compensation coil (2) is located; The sample (3) is placed in the main magnetic field. The probe light (1) passes through the atomic gas cell (5) and the optical device group (10) in sequence. After optical pumping, a nonlinear Zeeman splitting transition signal is generated. The transition signal is connected to the lock-in amplifier (9). The data acquisition module (8) extracts the conductivity information from the transition resonance peak of the Zeeman sublevel. The conductivity information is obtained by the data acquisition module (8) from the Zeeman sublevel m=3. Extracted from the resonance peak of the 4-transition; When the main magnetic field changes, the frequency of the transition signal between Zeeman sublevels changes. The lock-in amplifier (9) demodulates the error signal according to the pre-input reference frequency. The error signal is the Zeeman sublevel m=2 The resonance signal between 3 transmits the error signal to the PID controller (7). The PID controller (7) outputs a compensation current to the compensation coil (2) according to the error signal. The compensation current flows through the compensation coil (2) and generates a compensation magnetic field, thereby offsetting the change of the main magnetic field and realizing the function of stabilizing the magnetic field.

2. The stable atomic radio frequency magnetometer for eddy current measurement according to claim 1, characterized in that: The direction of the probe light (1) is perpendicular to the direction of the main magnetic field.

3. The stable atomic radio frequency magnetometer for eddy current measurement according to claim 1, characterized in that: The optical device group (10) includes optical elements and a balance detector.

4. The stable atomic radio frequency magnetometer for eddy current measurement according to claim 3, characterized in that: The output terminal of the balanced detector is connected to the lock-in amplifier (9). The balanced detector demodulates the frequency of the main magnetic field and inputs it into the lock-in amplifier (9), and obtains two orthogonal magnetic field outputs from the lock-in amplifier (9).

Images