CN118604695A - An integrated atomic magnetometer based on dual-plane coils - Google Patents

Abstract

The present invention discloses a dual-plane coil designed based on the target field method, comprising: a vertical cavity surface emitting laser, a collimating unit, a linear polarizer, a circular polarizer, a first dual-plane coil, a transparent heating plate, an anode-bonded atomic gas chamber, a second dual-plane coil and a photodetector arranged in sequence; the first dual-plane coil, the transparent heating plate, the anode-bonded atomic gas chamber and the second dual-plane coil are glued together. In the present invention, this coil is only distributed on a pair of parallel end faces of the atomic gas chamber, and the three-dimensional magnetic field in the atomic gas chamber space can be compensated by three groups of planar coils, thereby realizing a zero-field environment. This design has significant convenience in the development of integrated detectors, and is particularly suitable for designing a miniature atomic magnetometer detector based on a micro-gas chamber.

Description

An integrated atomic magnetometer based on dual-plane coils

Technical Field

The invention relates to the technical field of quantum magnetic measurement, and in particular to an integrated atomic magnetometer based on a double-plane coil.

Background Art

Traditional magnetometers, such as fluxgate magnetometers, giant magnetoimpedance magnetometers, and induction magnetometers, can meet the needs of magnetic field measurement to a certain extent, but due to their accuracy limitations, they are difficult to play a role in biological weak magnetic measurements of the fT to pT order. Biological weak magnetic measurements require extremely high accuracy in magnetic field detection, which has prompted the development and exploration of new technologies. In the past few decades, superconducting quantum interference magnetometers (SQUIDs) have dominated this field. However, a significant disadvantage of SQUID is that it needs to work in a liquid helium cooling environment, which increases its cost and use cost. In terms of application, the measurement distance of SQUID is limited by the liquid helium storage space, and for smaller magnetic sources, their magnetic fields decay rapidly with increasing distance, which has an adverse effect on the measurement.

In recent years, with the rapid development of quantum precision measurement technology, a new type of magnetometer, the atomic magnetometer, especially the atomic magnetometer based on the electron spin measurement principle of alkali metal vapor, has shown its extremely high detection sensitivity, which has approached or even surpassed the SQUID magnetometer in some aspects. The atomic magnetometer can not only work at room temperature and does not require liquid helium cooling, which greatly reduces the manufacturing and use costs, but also the distance between its core detection element, the atomic gas chamber, and the detection end face can be compressed to less than 1 cm, which is more suitable for weak biological magnetic measurements.

In particular, SERF atomic magnetometers are extremely sensitive, can work stably at room temperature, are easy to integrate, and are very suitable for biomagnetic field measurements. However, SERF atomic magnetometers need to work under high temperature and near-zero magnetic field conditions, and their stable working magnetic field range is usually within ±5nT. In order to achieve this condition, an external three-dimensional magnetic field compensation coil is usually required to offset the residual magnetic field in the magnetic shield. Existing solutions usually use regular rectangular or circular three-dimensional coils for compensation, such as square three-dimensional Helmholtz coils. Although these coils can generate a relatively uniform magnetic field at their center, the need to design corresponding mechanical structures in three directions to construct the coils has caused difficulties in improving the research on integrated or miniaturized SERF atomic magnetometers, and will increase the distance between the detection center, that is, the gas chamber and the magnetic source.

Summary of the invention

In order to solve this problem, the present invention proposes a double-plane coil designed based on the target field method. This coil is only distributed on a pair of parallel end faces of the atomic gas chamber. The three-dimensional magnetic field in the atomic gas chamber space can be compensated by three sets of plane coils, thereby achieving a zero-field environment. This design has significant convenience in the development of integrated detectors, and is particularly suitable for designing a miniature atomic magnetometer detector based on a miniature gas chamber.

An integrated atomic magnetometer based on a double-plane coil comprises: a vertical cavity surface emitting laser, a collimating unit, a linear polarizer, a circular polarizer, a first double-plane coil, a transparent heating plate, an anode-bonded atomic gas chamber, a second double-plane coil and a photodetector arranged in sequence;

The first double-plane coil, transparent heating plate, anode-bonded atomic gas chamber and second double-plane coil are glued together. The first double-plane coil, transparent heating plate and second double-plane coil are all made of transparent materials to ensure that the laser can pass through the glued whole normally and enter the photodetector. The first double-plane coil and the second double-plane coil include pairs of X-direction double-plane coils, Y-direction double-plane coils and Z-direction double-plane coils, wherein each pair of coils generates a uniform magnetic field in the corresponding direction in the anode-bonded atomic gas chamber space, which is used for environmental magnetic field compensation and can also be used for RF modulation magnetic field output. The transparent heating plate is made of double-layer serpentine routing transparent conductive material. The serpentine routing method can offset the residual magnetic field generated by the heating current. The opposite direction of the double-layer routing current further offsets the residual magnetic field generated by the heating current, thereby not affecting the external magnetic field measurement, and can heat the anode-bonded atomic gas chamber to 150-200°C.

The outer dimensions of the anode-bonded atomic gas chamber are 8×8×3mm, and the inner part is a cylindrical gas chamber with a diameter of 3mm and a thickness of 2mm, which is filled with saturated rubidium vapor and 300 Torr _N2 as buffer gas. After stable heating, the atomic number density inside the atomic gas chamber can reach ¹⁰¹⁴ / ^cm3 . The atomic gas chamber is the core of magnetic measurement, and only the second double-plane coil and the photodetector are included between its center and the outer measurement end face. In actual development, the thickness of the two can be controlled to be less than 3mm, which is lower than the measurement distance of 6mm in the prior art. The DC amount of the first double-plane coil and the second double-plane coil is adjusted to realize the magnetic field compensation in the anode-bonded atomic gas chamber, and the RF amplitude is controlled to realize the atomic polarization modulation and finally realize the construction of the SERF atomic magnetometer.

The first dual-plane coil and the second dual-plane coil form a three-dimensional dual-plane coil group.

The first double-plane coil includes: an X-direction coil wiring portion, a first insulating layer, a Y-direction wire-fixed wiring portion, a second insulating layer and a Z-direction coil wiring portion which are glued in sequence.

The X-direction coil wiring part, the Y-direction wire wiring part and the Z-direction coil wiring part are all arranged with two leads;

The transparent heating plate is provided with two leads.

The two leads of the X-direction coil wiring part, the two leads of the Y-direction wire wiring part, the two leads of the Z-direction coil wiring part and the two leads of the transparent heating plate are led out from the four sides of the first double-plane coil, and one side corresponds to two leads.

The second double-plane coil includes: an X-direction coil wiring portion, a first insulating layer, a Y-direction wire-fixed wiring portion, a second insulating layer and a Z-direction coil wiring portion which are glued in sequence.

The X-direction coil wiring part, the Y-direction coil wiring part and the Z-direction coil wiring part are all arranged with two lead wires.

The two leads of the X-direction coil wiring part, the two leads of the Y-direction coil wiring part and the two leads of the Z-direction coil wiring part are led out from three sides of the second double-plane coil, and one side corresponds to two leads.

The first double-plane coil includes three layers of coils, each layer of coils is hundreds of nanometers thick, the quartz substrate is hundreds of microns thick, and the thickness of the first double-plane coil and the second double-plane coil can be controlled at 1mm. The first double-plane coil and the second double-plane coil include pairs of double-plane coils in the X direction, double-plane coils in the Y direction, and double-plane coils in the Z direction, and each team of coils generates a uniform magnetic field in the corresponding direction. The distance from the center of the atomic gas chamber in the core part of the magnetic field detection to the outer surface of the photodetector can be compressed to 3mm, which is lower than the currently reported 6mm, which is conducive to the measurement of weak magnetic signals.

Compared with the prior art, the present invention has the following advantages:

In the present invention, the distance from the atomic gas chamber to the external measurement end face is smaller than that in the prior art, and the magnetic field decays rapidly with distance. This advantage can improve the signal-to-noise ratio of weak magnetic signal measurement; the external size of the integrated detector is less than 10×10×10mm, which is smaller than that in the prior art. It can more flexibly complete weak magnetic measurements in small volumes such as nerve, cell, drug or tumor positioning, and can greatly enhance the sampling density in multi-channel measurements, thereby improving the magnetic positioning accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a double-plane coil replacing a regular coil structure;

Figure 2 is a schematic diagram of a three-dimensional dual-plane coil design;

Figure 3 is an example of X-direction shimming coils;

Figure 4 is a three-dimensional dual-plane coil design based on transparent ITO material;

FIG5 is a schematic diagram of the structure of a micro SERF magnetometer system.

DETAILED DESCRIPTION

The design idea of the present invention is shown in Figure 1. Indium tin oxide (ITO) material (but not limited to ITO material) transparent to the atomic working wavelength is used as the conductive coil material to construct three sets of dual-plane coils to replace the magnetic field compensation coils of conventional SERF magnetometers, such as FPC or copper wires. The three sets of dual-plane coils can compensate for the residual magnetic field in the three directions of X, Y, and Z of the atomic gas chamber in a Cartesian coordinate system. This magnetic compensation method does not have a complex coil structure, does not affect the optical path of the SERF magnetometer, and can greatly improve the integration scale of the atomic magnetometer. It can also greatly reduce the distance between the atomic gas chamber and the detection end face, reducing the attenuation of the amplitude of the magnetic field signal to be detected due to the distance.

The integrated atomic magnetometer involved in the present invention mainly includes an optical path part, an atomic gas chamber part, a planar three-dimensional magnetic compensation/radio frequency coil part and a signal detection part. The light source of the optical path part is a linearly polarized laser of the ⁸⁷ Rb atom D1 line (using the working atom selection laser, this patent takes the Rb ⁸⁷ atom as an example), which is adjusted to circularly polarized light by a circular polarizer, then enters the atomic gas chamber to interact with atoms, and finally is received by a photoelectric detector.

The atomic gas chamber is filled with alkali metals, which may be one or more of K, Rb, and Cs. The present invention takes Rb atoms as an example. The atomic gas chamber is filled with nitrogen as a buffer or quenching gas.

The planar three-dimensional magnetic compensation/RF coil part is composed of three groups of dual-plane coils, and the spatial structure is shown in Figure 2. The planar coil adopts the target field method, and its basic idea is to use Fourier transform theory to associate the current density distribution on two parallel planes with the field gradient of the target magnetic field or the target area, and invert the current density distribution by minimizing a certain cost function (CostFunction). The cost function is usually expressed in the form of a weighted sum of the fitting error of the target magnetic field and the total energy or inductance of the coil. Use a continuous stream function to construct a discrete coil, define the stream function as the vector potential of the current density function, then its contour line is the conductor position, and the three-dimensional magnetic field coil can be designed by the above method. Figure 3 is a schematic diagram of the design of the X-direction shim coil. The present invention designs the magnetic field for the atomic gas chamber space, so the target field space is the space inside the atomic gas chamber, the target magnetic field is a three-directional uniform magnetic field, and the size of the heating and insulation layer outside the atomic gas chamber is used as the plane of the planar coil, and the X-direction shim coil, the Y-direction shim coil and the Z-direction shim coil are designed in sequence. The magnetic field compensation is controlled by the DC part of the current source, and the polarized radio frequency magnetic field is controlled by the AC part of the current source, so as to achieve three-axis magnetic field compensation and complete the application of radio frequency modulation magnetic field. The signal detection part mainly includes a photodetector and a phase-locked amplifier. After the interaction between light and atoms, the magnetic field information is included in the light intensity signal, which is amplified by the amplifier circuit and demodulated by the phase-locked amplifier to obtain the real-time magnetic field signal detected by the atom.

Example

The micro SERF magnetometer system of the present invention mainly includes four parts: an optical path part, an atomic gas chamber part, a planar three-dimensional magnetic compensation/radio frequency coil part and a signal detection part. The atomic magnetometer specifically includes a vertical cavity surface emitting laser 1, a collimating unit 2, a linear polarizer 3, a circular polarizer 4, a three-dimensional double-plane coil group 5, a heating plate 6, an anode-bonded miniaturized atomic gas chamber 7 and a photodetector 8.

1. Optical path: A vertical cavity surface emitting laser generates a beam of laser light, which is converted into a collimated light spot by an optical collimation unit. According to the laser polarization suppression ratio parameter, it is selected whether to use a linear polarizer for polarization purification. The linear polarizer purifies to obtain a collimated linear polarized light, which is converted into collimated uniform circular polarized light by a quarter wave plate. The circular polarized light is collimated into the atomic gas chamber for pumping the polarized atomic gas chamber, and the final output light is received by the photodetector. The overall design diagram is shown in Figure 5.

2. Atomic gas chamber part 7: The atomic gas chamber is preferably a micro gas chamber based on anode bonding, and the gas chamber is filled with saturated alkali metal gas and quenching gas. The quenching gas is mainly nitrogen, and an appropriate amount of helium can also be filled to increase the buffering effect, extend the transverse relaxation time of the atoms, and improve the sensitivity of the magnetometer. The non-magnetic heating plate is attached to one side or both sides of the gas chamber to heat the atomic gas chamber. The non-magnetic heating plate adopts alternating current heating. It is preferred to use a transparent conductive material, such as indium tin oxide, as the heating coil material to achieve the effect of light transmission.

3. Planar 3D magnetic compensation/RF coil part: The atomic gas chamber and the heating plate are placed in the planar 3D magnetic compensation coil. The magnetic field uniformity at the atomic gas chamber is ensured by coil design. The residual magnetic field in the measurement area is compensated to the SERF magnetic force optimal working range along the x, y and z axes, and an AC RF modulated magnetic field can be output to modulate the atomic polarization vector. The coil is divided into two symmetrical parts (the first double-plane coil and the second double-plane coil). Figure 4 shows the design structure of the first double-plane coil.

4. Coil preparation method: Quartz glass or other materials with low absorption coefficient for working wavelength are used as substrates. Glass is preferred for Rb ⁸⁷ atoms. The coil material uses a conductive material with low absorption coefficient for working wavelength, preferably indium tin oxide, and the coil routing is designed by the above method. The dotted box of the substrate in Figure 4 is the coil pattern area, and the port of the coil is led out from the black part. Starting from the substrate, the first coil layer is prepared in sequence, and the electrode port is reserved at the edge; an insulating layer is prepared between the two coil layers, for example, an aluminum oxide insulating film is deposited using atomic layer deposition technology, and the insulating layer covers the coil routing part (ie, inside the dotted box), exposing the electrode part; then the coil layers in the other two directions and the insulating layer between the coil layers are prepared in sequence.

5. The signal detection part converts the light intensity change signal into an electrical signal through a photoelectric detector. After being collected by the amplifying circuit, it is input into the phase-locked amplifier for demodulation to obtain the magnetic field signal detected by the atomic gas chamber, thereby realizing the measurement of the magnetic field information.

Claims (8)

1. An integrated atomic magnetometer based on a dual-plane coil, characterized in that it comprises: a vertical cavity surface emitting laser, a collimating unit, a linear polarizer, a circular polarizer, a first dual-plane coil, a transparent heating plate, an anode-bonded atomic gas chamber, a second dual-plane coil and a photodetector arranged in sequence; The first double-plane coil, the transparent heating plate, the anode-bonded atomic gas chamber and the second double-plane coil are glued together. 2. The integrated atomic magnetometer based on dual-plane coils according to claim 1, characterized in that the first dual-plane coil and the second dual-plane coil form a three-dimensional dual-plane coil group. 3. The integrated atomic magnetometer based on dual-plane coils according to claim 1 is characterized in that the first dual-plane coil comprises: an X-direction coil wiring portion, a first insulating layer, a Y-direction wire-fixed wiring portion, a second insulating layer and a Z-direction coil wiring portion which are glued in sequence. 4. The integrated atomic magnetometer based on dual-plane coils according to claim 3 is characterized in that the X-direction coil wiring part, the Y-direction wire-solid wiring part and the Z-direction coil wiring part are all arranged with two leads; The transparent heating plate is provided with two leads. 5. The integrated atomic magnetometer based on dual-plane coils according to claim 4 is characterized in that the two leads of the X-direction coil routing portion, the two leads of the Y-direction wire-solid routing portion, the two leads of the Z-direction coil routing portion, and the two leads of the transparent heating plate are led out from four sides of the first dual-plane coil, and one side corresponds to two leads. 6. The integrated atomic magnetometer based on dual-plane coils according to claim 1 is characterized in that the second dual-plane coil comprises: an X-direction coil wiring portion, a first insulating layer, a Y-direction wire-fixed wiring portion, a second insulating layer and a Z-direction coil wiring portion which are glued in sequence. 7. The integrated atomic magnetometer based on dual-plane coils according to claim 6 is characterized in that the X-direction coil wiring part, the Y-direction wire-solid wiring part and the Z-direction coil wiring part are all arranged with two lead wires. 8. The integrated atomic magnetometer based on dual-plane coils according to claim 7 is characterized in that the two leads of the X-direction coil routing portion, the two leads of the Y-direction wire-solid routing portion and the two leads of the Z-direction coil routing portion are led out from three sides of the second dual-plane coil, and one side corresponds to two leads.