A low-frequency magnetic field detection system based on a hollow sphere cavity

Abstract

The application provides a low-frequency magnetic field detection system based on a hollow sphere cavity, and high-sensitivity low-frequency magnetic field information detection can be realized by measuring a to-be-detected low-frequency signal superimposed on a high-frequency modulation signal. The frequency of the high-frequency modulation signal is consistent with the mechanical mode of the cavity, the structure parameters of two hollow sphere cavities on the left and right sides of the three hollow sphere cavities are changed through an electrostrictive medium, the mechanical mode of the sensing unit is changed, and the sensing unit has stronger low-frequency magnetic field detection capability. The advantage of the system is that tuning the mechanical mode frequency does not change the optical quality factor of the hollow sphere cavity where the light field transmission is located, so that the sensitivity of the sensing system is not reduced due to the regulation of the mechanical mode frequency. The application provides a new technical means for optical resonant cavity low-frequency magnetic field detection.

Description

Technical Field

[0001] This invention relates to a low-frequency magnetic field detection system based on a hollow spherical cavity, specifically a magnetic field sensing system constructed from a magnetostrictive medium, an electrostrictive medium, and multiple hollow spherical cavities, belonging to the field of optics. Background Technology

[0002] A magnetic field detection system is a device that converts magnetic fields and their changes into electrical signals. Magnetic fields or magnetic field-related information exist in many places in nature and human society, such as mobile communications, broadcasting, and aerospace; therefore, magnetic field detection is crucial. Currently, various magnetic field sensors are widely used in scientific research, production, and social life. Low-frequency magnetic field detection has significant application value in military and medical fields. Existing high-precision low-frequency magnetic field detection systems are expensive, and the performance of other low-frequency magnetic field detection systems still has considerable room for improvement. Existing magnetic field detection systems based on mechanical mode enhancement require the design of optical resonant cavities with low-frequency mechanical modes to achieve low-frequency detection. However, existing systems still cannot directly achieve high-sensitivity detection of magnetic fields near 1Hz. Directly tuning the mechanical mode of the cavity coupling the optical field to cover the low-frequency detection range reduces its optical quality factor, thus affecting its sensing performance. This invention proposes a low-frequency magnetic field detection system based on a hollow spherical cavity that can tune the mechanical mode of the sensing unit without affecting its optical quality factor. It has the potential to achieve high-sensitivity low-frequency magnetic field detection. Summary of the Invention

[0003] To improve the performance of optical magnetic field sensing systems, this invention proposes a low-frequency magnetic field detection system based on a hollow spherical cavity, which can be used for low-frequency magnetic field detection.

[0004] A low-frequency magnetic field detection system based on a hollow spherical cavity includes a signal generator, a tunable laser, an attenuator, a polarization controller, an optical fiber taper, a magnetic field sensing unit, a photodetector, a lock-in amplifier, a high-frequency modulation coil, and a data processing and display system; the magnetic field sensing unit includes a magnetostrictive medium, a hollow spherical cavity, an electrostrictive medium, a support, and adhesive.

[0005] One triangular wave signal output from the signal generator is simultaneously fed into the voltage tuning port of the tunable laser and the data processing and display system. The other output of the signal generator is used to generate a sinusoidal high-frequency modulation signal, which is fed into a lock-in amplifier and amplified before being output to the high-frequency modulation coil. The light output from the tunable laser is fed into the fiber optic taper via an attenuator and a polarization controller. The light field in the fiber optic taper enters the hollow spherical cavity in the middle of the magnetic field sensing unit through evanescent wave coupling. After the light field is transmitted within the cavity, it is coupled out to the photodetector receiver via the fiber optic taper. The signal output from the photodetector is fed into the lock-in amplifier, which then outputs the signal to the data processing and display system. In the sensing system, the connections between the tunable laser, isolator, attenuator, polarization controller, fiber taper, and photodetector are all made of optical fiber. The signal generator and tunable laser, the signal generator and lock-in amplifier, the signal generator and data processing and display system, the photodetector and lock-in amplifier, and the high-frequency modulation coil and lock-in amplifier are connected by electrical cables. The high-frequency modulation coil causes deformation of the magnetostrictive medium. The frequency of the magnetic field signal generated by the high-frequency modulation coil is consistent with the mechanical mode frequency. The low-frequency magnetic field to be measured will be superimposed on the high-frequency signal. By acquiring the changes of the low-frequency signal superimposed on the high-frequency signal output by the optical system, the low-frequency magnetic field information can be obtained.

[0006] The sensing unit contains three hollow spherical cavities, connected by two 2-micrometer diameter stretched optical fibers. Two 125-micrometer diameter optical fibers are connected to the sides of the two outer hollow cavities. A magnetostrictive medium is glued to the underside of the 125-micrometer diameter fibers to respond to magnetic fields. To adjust the frequency of the overall structure's mechanical mode, electrostrictive media are glued to the underside of the two outer hollow cavities. Changing the structural parameters of the outer cavities through the electrostrictive media thus modulates the frequency of their mechanical modes. The fiber taper used for coupling the optical field is coupled only to the central hollow spherical cavity.

[0007] Preferably, the wall thickness of the three hollow spherical cavities is less than 2 micrometers at its thinnest point, and the outer diameter of the three hollow cavities ranges from 100 micrometers to 5 millimeters. The overall structural dimensions must ensure that the frequency of the mechanical mode of the sensing unit is less than 100 kHz.

[0008] Preferably, the lock-in amplifier operates with a frequency band covering 100kHz, and the low-pass filter has a bandwidth greater than 10Hz, ensuring that the system can detect low-frequency signals within 10Hz.

[0009] Preferably, the data processing and display system can obtain the DC and low-frequency signals output by the system and provide amplitude or frequency information of the signals.

[0010] Preferably, the tuning range of the tunable laser should cover the detection range required for the experiment, the band should be a communication band, and it should match the receiving band of the detector.

[0011] Preferably, the hollow spherical cavity is made of silicon dioxide or other materials that support optical mode transmission, as long as low-loss transmission of the optical field inside the cavity is ensured and evanescent waves exist on the outer surface of the cavity.

[0012] Preferably, the magnetostrictive medium is Terfenol-D or other media capable of stretching under the influence of a magnetic field. The shape and position of the magnetostrictive medium must ensure that it exerts an effect on the hollow spherical cavity under the influence of the magnetic field.

[0013] Preferably, the electrostrictive medium is PZT or other media that can expand and contract under voltage or electric field. The shape and position of the electrostrictive medium must be such that the mechanical mode frequency of the cavity can be changed to meet the operating bandwidth requirements of the lock-in amplifier, thereby improving the cavity's ability to detect low-frequency signals.

[0014] Preferably, the polarization state of the polarization controller should ensure the highest optical quality factor of the optical mode.

[0015] Preferably, the attenuator must ensure that the optical power reaching the detector is within the detector's acceptable power range.

[0016] The design of the sensing unit in this invention reduces the impact of mechanical mode tuning on the optical mode, ensuring that the system's sensing sensitivity is not affected by a decrease in the optical quality factor due to mechanical mode tuning. The low-frequency magnetic field detection system of this invention features a tunable mechanical mode, and the tuning process does not affect its optical quality factor. The low-frequency signal is modulated into the high-frequency band to enhance the low-frequency magnetic field detection capability. Attached Figure Description

[0017] Figure 1 A schematic diagram of a low-frequency magnetic field detection system based on a hollow spherical cavity for the invention; Detailed Implementation

[0018] The following specific embodiments further illustrate the essential features and significant advancements of the present invention, but the scope of the present invention is not limited to the following embodiments:

[0019] Specific implementation method one: as follows Figure 1As shown, the low-frequency magnetic field detection system based on a hollow spherical cavity described in this embodiment includes a tunable laser 1, an attenuator 2, a polarization controller 3, an optical fiber taper 4, a magnetic field sensing unit 5, a photodetector 6, a lock-in amplifier 7, a data processing and display system 8, a signal generator 9, and a high-frequency modulation coil 10. The signal generator 9 outputs two signals: a triangular wave and a sine wave. The triangular wave signal is fed into the voltage tuning port of the tunable laser 1 and then into the data processing and display system 8. The sine wave, as a high-frequency modulation signal, is fed into the lock-in amplifier 7, amplified by the lock-in amplifier 7, and then output to the high-frequency modulation coil 10. The light-emitting end of the tunable laser 1 is connected to the input end of the attenuator 2, the output end of the attenuator 2 is connected to the input end of the polarization controller 3, and the output end of the polarization controller 3 is connected to the input end of the optical fiber taper 4. The optical field transmitted in fiber optic taper 4 enters the hollow spherical cavity in the middle of magnetic field sensing unit 5 via evanescent wave coupling. The optical field can be transmitted within the hollow spherical cavity, then coupled out through fiber optic taper 4 and sent to the receiving end of photodetector 6. The signal output from photodetector 6 enters lock-in amplifier 7, and the signal output from lock-in amplifier 7 enters data processing and display system 8. The connections between tunable laser 1, attenuator 2, polarization controller 3, fiber optic taper 4, and photodetector 6 are all made of optical fiber. The photodetector 6 is connected to lock-in amplifier 7, and the high-frequency modulation coil 10, and the data processing and display system 8, signal generator 9, tunable laser 1, signal generator 9, lock-in amplifier 7, and data processing and display system 8 are connected by electrical cables. The high-frequency modulation coil 10 causes the magnetostrictive medium to deform. The frequency of the magnetic field signal generated by the high-frequency modulation coil is consistent with the frequency of the mechanical mode. The low-frequency magnetic field to be measured will be superimposed on the high-frequency signal. By collecting the changes of the low-frequency signal superimposed on the high-frequency signal output by the optical system, the low-frequency magnetic field information can be obtained.

[0020] like Figure 1 As shown, the magnetic field sensing unit 5 of the low-frequency magnetic field detection system based on hollow spherical cavities described in this embodiment includes a magnetostrictive medium 11, an electrostrictive medium 12, three hollow spherical cavities 13, adhesive 14, drawn optical fibers 15, optical fibers 16, and a support 17. The three hollow spherical cavities are connected by drawn optical fibers 15 with a diameter of 2 micrometers. The hollow spherical cavities on both sides are connected by optical fibers 16 with a diameter of 125 micrometers. The hollow spherical cavities 13 on the left and right sides are bonded to the electrostrictive medium 12 with adhesive 14, and the optical fibers 16 at both ends are bonded to the magnetostrictive medium 11 with adhesive 14. The magnetostrictive medium 11 is bonded to the support 17 with adhesive 14, allowing the sensing unit to move freely.

[0021] The signal generator 9 outputs a sinusoidal high-frequency modulated signal to the lock-in amplifier 7. The lock-in amplifier 7 amplifies the signal and outputs it to the high-frequency modulation coil 10. The high-frequency magnetic field generated by the high-frequency modulation coil 10 causes the magnetostrictive medium 11 to deform, which in turn causes a change in the cavity length of the hollow spherical cavity 12, thereby altering the transmitted light field information of the system. Based on the high-frequency modulated signal, the low-frequency magnetic field signal to be measured will change the high-frequency response of the magnetostrictive medium. Therefore, the low-frequency magnetic field signal can be detected by observing the difference in the high-frequency response. The low-frequency magnetic field information to be measured can then be obtained in the data processing and display system 8.

[0022] By applying voltage to the electrostrictive medium 12, the hollow spherical cavities on both sides can be deformed, thereby changing the frequency of the mechanical mode of the entire sensing structure. This system can tune the frequency position of the mechanical mode without affecting the optical quality factor of the hollow spherical cavity for light field transmission. Therefore, it can tune the frequency of the mechanical mode without reducing the sensing sensitivity of the system.

Claims

1. A low-frequency magnetic field detection system based on a hollow spherical cavity, comprising a tunable laser (1), an attenuator (2), a polarization controller (3), an optical fiber taper (4), a magnetic field sensing unit (5), a photodetector (6), a lock-in amplifier (7), a data processing and display system (8), a signal generator (9), and a high-frequency modulation coil (10); characterized in that: The magnetic field sensing unit (5) includes a magnetostrictive medium (11), an electrostrictive medium (12), three hollow spherical cavities (13), glue (14), drawn optical fiber (15), optical fiber (16), and a support (17); wherein the three hollow spherical cavities are connected by drawn optical fiber (15), and optical fiber (16) is connected to the hollow spherical cavities on both sides. The hollow spherical cavities (13) on the left and right sides are bonded to the electrostrictive medium (12) by glue (14), and the optical fibers (16) at both ends are bonded to the magnetostrictive medium (11) by glue (14); the magnetostrictive medium (11) is bonded to the support (17) by glue (14) for free movement of the sensing unit; one triangular wave signal output by the signal generator (9) is simultaneously sent to the voltage tuning port of the tunable laser (1) and the data processing and display system (8). The other output of the signal generator (9) is used to generate a sinusoidal high-frequency modulation signal, which is sent to the lock-in amplifier (7). After being amplified by the lock-in amplifier (7), it is output to the high-frequency modulation coil (10). The light output end of the tunable laser (1) is connected to the input end of the attenuator (2). The output end of the attenuator (2) is connected to the input end of the polarization controller (3). The output end of the polarization controller (3) is connected to the input end of the fiber taper (4). The light field transmitted in the fiber taper (4) enters the hollow spherical cavity (13) in the middle position through evanescent wave coupling. The light field is transmitted in the hollow spherical cavity and then coupled out through the fiber taper (4) and sent to the receiving end of the photodetector (6). The signal output by the photodetector (6) enters the lock-in amplifier (7). The signal output by the lock-in amplifier (7) enters the data processing and display system (8).

2. The low-frequency magnetic field detection system based on a hollow spherical cavity according to claim 1, characterized in that: The three hollow spherical cavities in the sensing unit are connected by two sections of drawn optical fiber with a diameter of 2 micrometers. Two sections of optical fiber with a diameter of 125 micrometers are connected to the two outer hollow spherical cavities on both sides. Magnetostrictive medium is glued to the bottom of the 125-micrometer diameter optical fiber to generate a response to the magnetic field. In order to adjust the frequency of the mechanical mode of the overall structure, electrostrictive medium is glued to the bottom of the hollow spherical cavities on both sides. The structural parameters of the hollow spherical cavities on both sides are changed by the electrostrictive medium, thereby controlling the frequency of their mechanical mode. The fiber cone used for coupling the optical field is only coupled to the middle hollow spherical cavity.

3. The low-frequency magnetic field detection system based on a hollow spherical cavity according to claim 1, characterized in that: The wall thickness of the three hollow spherical cavities is less than 2 micrometers at its thinnest point, and the outer diameter of the three hollow spherical cavities is in the range of 100 micrometers to 5 millimeters; the overall structural dimensions must ensure that the frequency of the mechanical mode of the sensing unit is less than 100 kHz.

4. The low-frequency magnetic field detection system based on a hollow spherical cavity according to claim 1, characterized in that: The lock-in amplifier operates over a frequency band of 100kHz, and the low-pass filter has a bandwidth greater than 10Hz, ensuring that the system can detect low-frequency signals within 10Hz.

5. A low-frequency magnetic field detection system based on a hollow spherical cavity according to claim 1, characterized in that: The output signal frequency range of the high-frequency modulation coil is less than 100kHz, and the frequency of the high-frequency modulation signal is consistent with the mechanical mode frequency of the sensing unit.

6. The low-frequency magnetic field detection system based on a hollow spherical cavity according to claim 1, characterized in that: The hollow spherical cavity is made of silicon dioxide, which ensures low-loss transmission of the optical field inside the cavity, and evanescent waves exist on the outer surface of the cavity.

7. A low-frequency magnetic field detection system based on a hollow spherical cavity according to claim 1 or 2, characterized in that: The electrostrictive medium is PZT; The shape and position of the electrostrictive medium must be such that the mechanical mode frequency of the cavity can be changed to meet the operating bandwidth requirements of the lock-in amplifier, thereby improving the cavity's ability to detect low-frequency signals.

8. A low-frequency magnetic field detection system based on a hollow spherical cavity according to claim 1 or 2, characterized in that: The magnetostrictive medium is Terfenol-D; the shape and position of the magnetostrictive medium must ensure that it acts on the hollow spherical cavity under the influence of the magnetic field.

9. A low-frequency magnetic field detection system based on a hollow spherical cavity according to claim 1, characterized in that: The data processing and display system can obtain the DC and low-frequency signals output by the system and provide the amplitude or frequency information of the signals.

10. A low-frequency magnetic field detection system based on a hollow spherical cavity according to claim 1, characterized in that: The tunable laser (1), attenuator (2), polarization controller (3), fiber taper (4), and photodetector (6) are all connected by optical fiber; the photodetector (6) is connected to the lock-in amplifier (7), the lock-in amplifier (7) and the high-frequency modulation coil (10), the lock-in amplifier (7) and the data processing and display system (8), the signal generator (9) and the tunable laser (1), the signal generator (9) and the lock-in amplifier (7), the signal generator (9) and the data processing and display system (8) are connected by electrical cables.

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