Inductive magnetometer

Abstract

The present invention discloses an inductive magnetometer, and relates to the field of magnetic field measuring equipment. The inductive magnetometer comprises: a calibration coil, an inductive coil and an amplifying circuit. A fixing frame is arranged inside the coil frame of the calibration coil, and the inductive coil is mounted on the fixing frame. The calibration coil is used to provide a reference magnetic field signal, so as to obtain the conversion relationship between the magnetic field strength and the voltage by measuring the voltage signal output by the inductive coil. The amplifying circuit is electrically connected to the inductive coil, and is used to amplify and denoise the voltage signal output by the inductive coil. The inductive magnetometer disclosed by the present invention has a simple structure, greatly reduces the volume of the magnetometer, is easy to install, does not need to be operated by professional personnel, can realize low-noise amplification of the measurement signal, reduces the measurement error, and meets the collection of weak biological electromagnetic field signals of patients in the emergency department.

Description

Technical Field

[0001] The invention belongs to the field of magnetic field measurement equipment, and in particular relates to an inductive magnetometer. Background Art

[0002] With the development of quantum precision measurement technology, magnetometers are playing an increasingly important role in the field of biological extremely weak magnetic detection. They are often used in hospital emergency departments to collect weak biological electromagnetic field signals from patients.

[0003] Spin-Exchange Relaxation-Free (SERF) atomic magnetometers have become one of the key development directions for the next generation of weak bio-electromagnetic field imaging devices due to their high signal-to-noise ratio and the advantage of wearable probe arrays. However, due to the large size of SERF atomic magnetometers, the installation is difficult, professional personnel are required to operate them, and they have high requirements for shielding environments and are easily affected by external environmental noise, which brings great inconvenience to the collection of weak bio-electromagnetic field signals from patients. Summary of the invention

[0004] The purpose of the present invention is to provide an inductive magnetometer to solve the above problems existing in the prior art.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, an embodiment of the present application provides an inductive magnetometer, comprising: a calibration coil, an inductance coil and an amplification circuit, wherein a fixing frame is provided inside the coil frame of the calibration coil, and the inductance coil is mounted on the fixing frame, and the calibration coil is used to provide a reference magnetic field signal so as to obtain a conversion relationship between magnetic field strength and voltage by measuring the voltage signal output by the inductance coil, and the amplification circuit is electrically connected to the inductance coil, and is used to amplify and denoise the voltage signal output by the inductance coil.

[0007] In one possible design, the amplifier circuit includes a first operational amplifier circuit and a second operational amplifier circuit connected to the first operational amplifier circuit, the first operational amplifier circuit is used to control the amplification factor of the voltage signal, and the second operational amplifier circuit is used to reduce the swing of the voltage signal.

[0008] In one possible design, the first operational amplifier circuit uses an INA128 operational amplifier, and the second operational amplifier circuit uses an OPA2277P operational amplifier.

[0009] In one possible design, the output terminal of the INA128 operational amplifier is connected to a feedback circuit.

[0010] In a possible design, the gain multiple of the first operational amplifier circuit is 1000 times.

[0011] In one possible design, the calibration coil includes an inner group coil and an outer group coil, the ratio of the distance of the inner group coil from the origin to the coil radius of the calibration coil is 0.2248, the ratio of the distance of the outer group coil from the origin to the coil radius of the calibration coil is 0.9448, and the coil turns ratio of the inner group coil to the outer group coil is 2.25.

[0012] In a possible design, the ratio of the inner diameter of the inductor coil to the outer diameter of the inductor coil is 0.425, and the ratio of the axial length of the inductor coil to the outer diameter of the inductor coil is 0.69.

[0013] In a possible design, the fixing frame is provided with an arc surface matching the shape of the inductor coil.

[0014] Beneficial effects:

[0015] The present invention creatively provides an inductive magnetometer, including a calibration coil, an inductive coil and an amplifying circuit, wherein a fixing frame is arranged inside the coil frame of the calibration coil, the inductive coil is mounted on the fixing frame, the calibration coil is used to provide a reference magnetic field signal, so as to obtain the conversion relationship between the magnetic field strength and the voltage by measuring the voltage signal output by the inductive coil, and the amplifying circuit is electrically connected to the inductive coil, and is used to amplify and denoise the voltage signal output by the inductive coil. In this way, the inductive magnetometer constructed is simple in structure, greatly reduces the volume of the magnetometer, is easy to install, and does not need to be operated by professional personnel. At the same time, by setting an amplifying circuit for amplifying and denoising the voltage signal output by the inductive coil, low-noise amplification of the measurement signal can be achieved, and measurement errors can be reduced, which can meet the collection of weak biological electromagnetic field signals of patients in the emergency department, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0017] Figure 1 A schematic diagram of the structure of an inductive magnetometer provided in an embodiment of the present application;

[0018] Figure 2 A circuit diagram of an amplifier circuit provided in an embodiment of the present application;

[0019] Figure 3 A circuit diagram of a first operational amplifier circuit provided in an embodiment of the present application.

[0020] Icon: 100-calibration coil; 200-inductance coil; 300-fixed bracket. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be noted that although the description of these embodiments is used to help understand the present invention, it does not constitute a limitation of the present invention. The specific structures and functional details disclosed herein are only used to describe the exemplary embodiments of the present invention. However, the present invention can be embodied in many alternative forms, and it should not be understood that the present invention is limited to the embodiments set forth herein.

[0022] It should be understood that when an element is referred to herein as being "connected," "connected," or "coupled" to another element, it can be directly connected or coupled to the other element, or intermediate elements may exist. Conversely, when an element is referred to herein as being "directly connected" or "directly coupled" to another element, no intermediate elements are present. Additionally, other words used to describe the relationship between elements (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.) should be interpreted in a similar manner.

[0023] It should be understood that the terms used herein are only used to describe specific embodiments and are not intended to limit the exemplary embodiments of the present invention. As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that when the terms "include", "comprises", "includes", and / or "comprising" are used herein, they specify the existence of the claimed features, integers, steps, operations, units, and / or components, and do not exclude the existence or addition of one or more other features, quantities, steps, operations, units, components, and / or their combinations.

[0024] It should be understood that certain details are provided in the following description to facilitate a complete understanding of the example embodiments. However, it should be understood by those of ordinary skill in the art that the example embodiments may be implemented without these certain details. For example, the system may be shown in a block diagram to avoid obscuring the example with unnecessary details. In other examples, well-known processes, structures, and techniques may not be shown in unnecessary detail to avoid obscuring the example embodiments.

[0025] Example:

[0026] like Figure 1As shown, this embodiment provides an inductive magnetometer for collecting weak bio-electromagnetic field signals, especially collecting weak bio-electromagnetic field signals of patients in emergency departments. The inductive magnetometer includes a calibration coil 100, an inductive coil 200 and an amplifying circuit (not shown).

[0027] Among them, a fixing frame 300 is arranged inside the coil frame of the calibration coil 100, and the inductor coil 200 is installed on the fixing frame 300. The calibration coil 100 is used to provide a reference magnetic field signal so as to obtain the conversion relationship between the magnetic field strength and the voltage by measuring the voltage signal output by the inductor coil 200. The amplification circuit is electrically connected to the inductor coil 200 and is used to amplify and denoise the voltage signal output by the inductor coil 200.

[0028] In the embodiment of the present application, the inductor 200 can be a simple cylindrical structure, which can achieve a larger inductance with a minimum resistance. The inductor 200 can be composed of 4000 turns of coil. The fixing frame 300 is used to install the inductor 200. Figure 1 To facilitate the installation of the inductor 200 , a curved surface matching the shape of the inductor 200 may be provided on the fixing frame 300 .

[0029] The calibration coil 100 is used to provide a reference magnetic field signal. In the embodiment of the present application, the calibration coil 100 is improved on the basis of the Lee-Whiting coil. The commonly used Lee-Whiting coil design scheme is usually to first assume the shape of the coil, set the specific structural parameters as the variables to be solved, and use the Biot-Savart law to derive and solve the derivatives of the magnetic field at the center point, set the derivatives to 0, and then solve the shape parameters to be determined. For a circular coil, generally only the magnetic field on the axis is required, and the expression of the derivatives of the center point of the coil along the axis is obtained, set it to 0, and solve the equation group. Under this condition, the ratio of the inner and outer turns of the calibration coil 100 can be calculated to be 2.2604. In actual engineering, in order to facilitate design, the integer approximation method is usually adopted to adjust the ampere-turn ratio of the calibration coil 100 from the decimal 2.2604 to the integer 9:4, which simplifies the coil structure and makes it easier to process and test in engineering, but seriously affects the uniformity of the magnetic field.

[0030] In the embodiment of the present application, the calibration coil 100 is configured to include an inner coil group and an outer coil group based on the optimization of the traditional Lee-Whiting coil. Assume that the distance between the inner coil group and the origin is d1, the distance between the outer coil group and the origin is d2, and the ratio of the number of turns of the outer coil to the inner coil is n. In this way, there are three unknowns d1, d2 and n. These three parameters are used as the parameters to be determined, and the magnetic field at a point on the axis is solved, and its derivatives of various orders at the center point of the coil are solved. Let z = 0, and obtain the derivatives of various orders at the center point of the coil:

[0031]

[0032] Among them, B (2) (0) represents the second-order derivative of the magnetic field at the center of the coil, B (4) (0) shows the fourth-order derivative of the magnetic field at the center of the coil, B (6) (0) represents the sixth-order derivative of the magnetic field at the center of the coil, μ0 represents the vacuum magnetic permeability, and I represents the current passing through the coil. (2) (0) = 0, B (4) (0) = 0, B (6) (0)=0, we can obtain d1 / R=0.2432, d2 / R=0.9407, n=2.2604.

[0033] In order to improve the magnetic field uniformity of the coil, when the ampere-turn ratio is fixed at 9:4, the only adjustable parameters are d1 and d2. In this case, there are only two unknown parameters, and only two equations can be constructed using the second-order derivative and the fourth-order derivative. Let n = 2.25, B (2) (0) = 0, B (4) (0) = 0, and we can solve for d1 / R = 0.2448, d2 / R = 0.9448. That is, in the embodiment of the present application, the ratio of the distance of the inner coil group from the origin to the coil radius of the calibration coil can be 0.2248, the ratio of the distance of the outer coil group from the origin to the coil radius of the calibration coil is 0.9448, and the coil turns ratio of the inner coil group to the outer coil group is 2.25, so that at least the second-order derivative and the fourth-order derivative of the magnetic field at the center point of the coil can be 0, which can reduce the problem of decreased magnetic field uniformity performance caused by the integerization of the ampere-turn ratio of the ideal Lee-Whiting coil to a certain extent, thereby improving the magnetic field uniformity of the coil.

[0034] The voltage output by the inductor 200 can be expressed as:

[0035]

[0036] Where N is the number of windings, A is the effective cross-sectional area of ​​the coil, B(t) is the time-varying magnetic field with amplitude B, and f is the oscillation frequency of the magnetic field. Given the thermal Johnson noise generated by the winding resistance, the minimum magnetic field S that can be detected can be expressed as:

[0037]

[0038] Where K B is the Boltzmann constant, T is the temperature, and Rw is the coil resistance, which is given by formula (4).

[0039]

[0040] Where a is the average radius of the coil, ρ is the resistivity of the coil, and r coil Represents the coil radius length. Equations (2) and (3) can be used to find the inductor coil structure with the lowest noise level under given design constraints.

[0041] If the coil parameters of the inductor 200 are length L, coil outer diameter D, and coil inner diameter Di, the lowest level of dimension ratio Di:D=0.4251 can be given. In addition, when L / D=0.69, the optimal coil structure for measuring the axial component of the magnetic field can be achieved. Therefore, in the embodiment of the present application, the ratio of the coil inner diameter to the coil outer diameter of the inductor 200 is 0.425, and the ratio of the coil axial length of the inductor 200 to the coil outer diameter of the inductor 200 is 0.69. In this way, the inductor 200 can have the lowest noise level and achieve the optimal coil structure for measuring the axial component of the magnetic field.

[0042] The amplifier circuit is electrically connected to the inductor 200 and is used to amplify and remove noise from the voltage signal output by the inductor 200. Figure 2 and Figure 3 The amplifier circuit includes a first operational amplifier circuit and a second operational amplifier circuit connected to the first operational amplifier circuit, the first operational amplifier circuit is used to control the amplification factor of the voltage signal, and the second operational amplifier circuit is used to reduce the swing of the voltage signal.

[0043] In the embodiment of the present application, the first operational amplifier circuit uses an INA128 operational amplifier, and the second operational amplifier circuit uses an OPA2277P operational amplifier.

[0044] The INA128 operational amplifier is a low-noise operational amplifier used to control the gain and achieve signal amplification at high gain. Figure 3In the figure, RG is the gain resistor of the operational amplifier, which is used to control the gain multiple of the first operational amplifier circuit. In the embodiment of the present application, the gain multiple of the first operational amplifier circuit is 1000 times, and 1000 times high gain signal amplification can be achieved in the circuit.

[0045] In one or more embodiments, the output end of the INA128 operational amplifier is also connected to a feedback circuit, through which the DC bias doped in the original signal can be filtered out to achieve the effect of optimal signal-to-noise ratio. The feedback circuit is an existing circuit and is not described in detail in the embodiments of this application.

[0046] The OPA2277P operational amplifier is a high-precision operational amplifier that has the functions of improving noise, reducing output voltage swing, and increasing response speed. At the same time, the OPA2277P operational amplifier chip has high common-mode signal rejection ratio and power supply rejection ratio, which can be used to solve the problem of DC signal feedback filtering in weak bio-electromagnetic field signals.

[0047] In an embodiment of the present application, the amplifier circuit can be integrated into a printed circuit board (PCB). The circuit board can adopt a circular double-layer design and can reserve interfaces for inspection signals and test amplified signals through reserved pins, which is convenient for subsequent troubleshooting and debugging.

[0048] In summary, the inductive magnetometer provided in the embodiment of the present application includes a calibration coil, an inductive coil and an amplifying circuit. A fixing frame is provided in the coil frame of the calibration coil, and the inductive coil is installed on the fixing frame. The calibration coil is used to provide a reference magnetic field signal, so as to obtain the conversion relationship between the magnetic field strength and the voltage by measuring the voltage signal output by the inductive coil. The amplifying circuit is electrically connected to the inductive coil and is used to amplify and denoise the voltage signal output by the inductive coil. In this way, the inductive magnetometer constructed has a simple structure, greatly reduces the volume of the magnetometer, is easy to install, and does not need to be operated by professional personnel. At the same time, by setting an amplifying circuit for amplifying and denoising the voltage signal output by the inductive coil, it is possible to achieve low-noise amplification of the measurement signal, reduce measurement errors, and meet the collection of weak biological electromagnetic field signals of patients in the emergency department, and has good application prospects. At the same time, the ratio of the distance of the inner group coil of the calibration coil from the origin to the coil radius of the calibration coil is 0.2248, the ratio of the distance of the outer group coil from the origin to the coil radius of the calibration coil is 0.9448, and the coil turns ratio of the inner group coil to the outer group coil is 2.25, so that at least the second-order derivative and the fourth-order derivative of the magnetic field at the center point of the coil are 0, which can reduce the problem of the degradation of the magnetic field uniformity performance caused by the integerization of the ampere-turn ratio of the ideal Lee-Whiting coil to a certain extent, thereby improving the magnetic field uniformity of the coil. Secondly, the ratio of the inner diameter of the inductor coil to the outer diameter of the coil is 0.425, and the ratio of the axial length of the inductor coil to the outer diameter of the inductor coil is 0.69, which can make the inductor coil have the lowest noise level and achieve the best coil structure for measuring the axial component of the magnetic field. In addition, the first operational amplifier circuit uses the INA128 operational amplifier, which can achieve signal amplification under high gain. The second operational amplifier circuit uses the OPA2277P operational amplifier, which has the functions of improving noise, reducing output voltage swing and increasing response speed. The OPA2277P operational amplifier chip has high common-mode signal rejection ratio and power supply rejection ratio, which can be used to solve the problem of DC signal feedback filtering in weak bio-electromagnetic field signals. Finally, the output end of the INA128 operational amplifier is also connected to a feedback circuit, through which the DC bias doped in the original signal can be filtered out to achieve the effect of optimal signal-to-noise ratio.

[0049] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An inductive magnetometer, characterized in that: include: A calibration coil, an inductor coil and an amplifier circuit, wherein a fixing frame is arranged inside the coil frame of the calibration coil, the inductor coil is mounted on the fixing frame, the calibration coil is used to provide a reference magnetic field signal, so as to obtain a conversion relationship between magnetic field strength and voltage by measuring the voltage signal output by the inductor coil, and the amplifier circuit is electrically connected to the inductor coil and is used to amplify and denoise the voltage signal output by the inductor coil; The calibration coil includes an inner group coil and an outer group coil. The ratio of the distance of the inner group coil from the origin to the coil radius of the calibration coil is 0.2248, the ratio of the distance of the outer group coil from the origin to the coil radius of the calibration coil is 0.9448, and the coil turns ratio of the inner group coil to the outer group coil is 2.

25.

2. The inductive magnetometer according to claim 1, characterized in that: The amplifier circuit includes a first operational amplifier circuit and a second operational amplifier circuit connected to the first operational amplifier circuit, the first operational amplifier circuit is used to control the amplification factor of the voltage signal, and the second operational amplifier circuit is used to reduce the swing of the voltage signal.

3. The inductive magnetometer according to claim 2, characterized in that: The first operational amplifier circuit uses an INA128 operational amplifier, and the second operational amplifier circuit uses an OPA2277P operational amplifier.

4. The inductive magnetometer according to claim 3, characterized in that: The output end of the INA128 operational amplifier is connected to a feedback circuit.

5. The inductive magnetometer according to claim 2, characterized in that: The gain multiple of the first operational amplifier circuit is 1000 times.

6. The inductive magnetometer according to claim 1, characterized in that: The ratio of the inner diameter of the inductor coil to the outer diameter of the inductor coil is 0.425, and the ratio of the axial length of the inductor coil to the outer diameter of the inductor coil is 0.

69.

7. The inductive magnetometer according to claim 1, characterized in that: The fixing frame is provided with an arc surface matching the shape of the inductor coil.

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